TY  - JOUR
A1  - Gottwald, Georg A.
A1  - Reich, Sebastian
T1  - Supervised learning from noisy observations
BT  - Combining machine-learning techniques with data assimilation
JF  - Physica : D, Nonlinear phenomena
N2  - Data-driven prediction and physics-agnostic machine-learning methods have attracted increased interest in recent years achieving forecast horizons going well beyond those to be expected for chaotic dynamical systems. In a separate strand of research data-assimilation has been successfully used to optimally combine forecast models and their inherent uncertainty with incoming noisy observations. The key idea in our work here is to achieve increased forecast capabilities by judiciously combining machine-learning algorithms and data assimilation. We combine the physics-agnostic data -driven approach of random feature maps as a forecast model within an ensemble Kalman filter data assimilation procedure. The machine-learning model is learned sequentially by incorporating incoming noisy observations. We show that the obtained forecast model has remarkably good forecast skill while being computationally cheap once trained. Going beyond the task of forecasting, we show that our method can be used to generate reliable ensembles for probabilistic forecasting as well as to learn effective model closure in multi-scale systems. (C) 2021 Elsevier B.V. All rights reserved.
KW  - Data-driven modelling
KW  - Random feature maps
KW  - Data assimilation
Y1  - 2021
U6  - https://doi.org/10.1016/j.physd.2021.132911
SN  - 0167-2789
SN  - 1872-8022
VL  - 423
PB  - Elsevier
CY  - Amsterdam
ER  - 
TY  - JOUR
A1  - Guggenberger, Tobias
A1  - Chechkin, Aleksei V.
A1  - Metzler, Ralf
T1  - Fractional Brownian motion in superharmonic potentials and non-Boltzmann stationary distributions
JF  - Journal of physics : A, Mathematical and theoretical
N2  - We study the stochastic motion of particles driven by long-range correlated fractional Gaussian noise (FGN) in a superharmonic external potential of the form U(x) proportional to x(2n) (n is an element of N). When the noise is considered to be external, the resulting overdamped motion is described by the non-Markovian Langevin equation for fractional Brownian motion. For this case we show the existence of long time, stationary probability density functions (PDFs) the shape of which strongly deviates from the naively expected Boltzmann PDF in the confining potential U(x). We analyse in detail the temporal approach to stationarity as well as the shape of the non-Boltzmann stationary PDF. A typical characteristic is that subdiffusive, antipersistent (with negative autocorrelation) motion tends to effect an accumulation of probability close to the origin as compared to the corresponding Boltzmann distribution while the opposite trend occurs for superdiffusive (persistent) motion. For this latter case this leads to distinct bimodal shapes of the PDF. This property is compared to a similar phenomenon observed for Markovian Levy flights in superharmonic potentials. We also demonstrate that the motion encoded in the fractional Langevin equation driven by FGN always relaxes to the Boltzmann distribution, as in this case the fluctuation-dissipation theorem is fulfilled.
KW  - anomalous diffusion
KW  - Boltzmann distribution
KW  - non-Gaussian distribution
Y1  - 2021
U6  - https://doi.org/10.1088/1751-8121/ac019b
SN  - 1751-8113
SN  - 1751-8121
VL  - 54
IS  - 29
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Beckus, Siegfried
A1  - Eliaz, Latif
T1  - Eigenfunctions growth of R-limits on graphs
JF  - Journal of spectral theory / European Mathematical Society
N2  - A characterization of the essential spectrum of Schrodinger operators on infinite graphs is derived involving the concept of R-limits. This concept, which was introduced previously for operators on N and Z(d) as "right-limits," captures the behaviour of the operator at infinity. For graphs with sub-exponential growth rate, we show that each point in sigma(ss)(H) corresponds to a bounded generalized eigenfunction of a corresponding R-limit of H. If, additionally, the graph is of uniform sub-exponential growth, also the converse inclusion holds.
KW  - Essential spectrum
KW  - Schrodinger operators
KW  - graphs
KW  - right limits
KW  - generalized eigenfunctions
Y1  - 2021
U6  - https://doi.org/10.4171/JST/389
SN  - 1664-039X
SN  - 1664-0403
VL  - 11
IS  - 4
SP  - 1895
EP  - 1933
PB  - EMS Press, an imprint of the European Mathematical Society - EMS - Publishing House GmbH, Institut für Mathematik, Technische Universität
CY  - Berlin
ER  - 
TY  - JOUR
A1  - Kumar, Mohit
A1  - Rosenblum, Michael
T1  - Two mechanisms of remote synchronization in a chain of Stuart-Landau oscillators
JF  - Physical review : E, Statistical, nonlinear and soft matter physics
N2  - Remote synchronization implies that oscillators interacting not directly but via an additional unit (hub) adjust their frequencies and exhibit frequency locking while the hub remains asynchronous. In this paper, we analyze the mechanisms of remote synchrony in a small network of three coupled Stuart-Landau oscillators using recent results on higher-order phase reduction. We analytically demonstrate the role of two factors promoting remote synchrony. These factors are the nonisochronicity of oscillators and the coupling terms appearing in the secondorder phase approximation. We show a good correspondence between our theory and numerical results for small and moderate coupling strengths.
Y1  - 2021
U6  - https://doi.org/10.1103/PhysRevE.104.054202
SN  - 2470-0045
SN  - 2470-0053
VL  - 104
IS  - 5
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Hannemann, Mandy
A1  - Wegner, Gino
A1  - Henkel, Carsten
T1  - No-slip boundary conditions for electron hydrodynamics and the thermal Casimir pressure
JF  - Universe : open access journal
N2  - We derive modified reflection coefficients for electromagnetic waves in the THz and far infrared range. The idea is based on hydrodynamic boundary conditions for metallic conduction electrons. The temperature-dependent part of the Casimir pressure between metal plates is evaluated. The results should shed light on the "thermal anomaly," where measurements deviate from the standard fluctuation electrodynamics for conducting metals.
KW  - dispersion force
KW  - metal optics
KW  - Drude model
KW  - hydrodynamic model
KW  - spatial
KW  - dispersion
KW  - viscosity
KW  - non-contact heat transfer
Y1  - 2021
U6  - https://doi.org/10.3390/universe7040108
SN  - 2218-1997
VL  - 7
IS  - 4
PB  - MDPI
CY  - Basel
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  - Henkel, Carsten
T1  - Heat transfer and entanglement
BT  - non-equilibrium correlation spectra of two quantum oscillators
JF  - Annalen der Physik
N2  - The non-equilibrium state of two oscillators with a mutual interaction and coupled to separate heat baths is discussed. Bosonic baths are considered, and an exact spectral representation for the elements of the covariance matrix is provided analytically. A wide class of spectral densities for the relevant bath modes is allowed for. The validity of the fluctuation-dissipation relation is established for global equilibrium (both baths at the same temperature) in the stationary state. Spectral measures of entanglement are suggested by comparing to the equilibrium spectrum of zero-point fluctuations. No rotating-wave approximation is applied, and anomalous heat transport from cold to hot bath, as reported in earlier work, is demonstrated not to occur.
KW  - entanglement
KW  - heat transfer
KW  - non-equilibrium steady state
KW  - master
KW  - equation
KW  - quantum thermodynamics
Y1  - 2021
U6  - https://doi.org/10.1002/andp.202100089
SN  - 0003-3804
SN  - 1521-3889
VL  - 533
IS  - 10
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Horovitz, Baruch
A1  - Henkel, Carsten
T1  - Spin entanglement via scanning tunneling microscope current
JF  - Physical review : B, Condensed matter and materials physics
N2  - We consider a system of two spins under a scanning tunneling microscope bias and derive its master equation. We find that the tunneling elements to the electronic contacts (tip and substrate) generate an exchange interaction between the spins as well as a Dzyaloshinskii-Moriya interaction in the presence of spin-orbit coupling. The tunnel current spectrum then shows additional lines compared to conventional spin-resonance experiments. When the spins have degenerate Larmor frequencies and equal tunneling amplitudes (without spin orbit), there is a dark state with a vanishing decay rate. The coupling to the electronic environment generates significant spin-spin entanglement via the dark state, even if the initial state is nonentangled.
Y1  - 2021
U6  - https://doi.org/10.1103/PhysRevB.104.L081405
SN  - 2469-9950
SN  - 2469-9969
VL  - 104
IS  - 8
PB  - American Physical Society
CY  - Ridge, NY
ER  - 
TY  - JOUR
A1  - Feudel, Fred
A1  - Feudel, Ulrike
T1  - Bifurcations in rotating spherical shell convection under the influence of differential rotation
JF  - Chaos : an interdisciplinary journal of nonlinear science
N2  - The bifurcations of thermal convection in a rotating spherical shell heated from the inner sphere and driven by the buoyancy of a central gravity field are studied numerically. This model of spherical Rayleigh-Benard convection describes large-scale convection in planets and in the outer zones of celestial bodies. In this work, the influence of an additionally imposed differential rotation of the inner sphere with respect to the outer one on the heat transfer and, more generally, on the whole bifurcation structure is investigated. In addition to numerical simulations, path-following techniques are applied in order to compute both stable and unstable solution branches. The dynamics and the heat transfer are essentially determined by a global bifurcation, which we have identified as a homoclinic bifurcation that consists of a collision of a stable modulated rotating with an unstable rotating wave.
Y1  - 2021
U6  - https://doi.org/10.1063/5.0063113
SN  - 1054-1500
SN  - 1089-7682
VL  - 31
IS  - 11
PB  - AIP
CY  - Melville
ER  - 
TY  - JOUR
A1  - Pikovskij, Arkadij
T1  - Transition to synchrony in chiral active particles
JF  - Journal of physics. Complexity
N2  - I study deterministic dynamics of chiral active particles in two dimensions. Particles are considered as discs interacting with elastic repulsive forces. An ensemble of particles, started from random initial conditions, demonstrates chaotic collisions resulting in their normal diffusion. This chaos is transient, as rather abruptly a synchronous collisionless state establishes. The life time of chaos grows exponentially with the number of particles. External forcing (periodic or chaotic) is shown to facilitate the synchronization transition.
KW  - active particles
KW  - chirality
KW  - synchronization
KW  - chaos
KW  - transient chaos
Y1  - 2021
U6  - https://doi.org/10.1088/2632-072X/abdadb
SN  - 2632-072X
VL  - 2
IS  - 2
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Frieß, Fabian
A1  - Lendlein, Andreas
A1  - Wischke, Christian
T1  - Switching microobjects from low to high aspect ratios using a shape-memory effect
JF  - Soft matter
N2  - Spherical particles from shape-memory polymers (SMP) can be stretched to ellipsoids with high aspect ratio (AR) and temporarily stabilized. They can switch back to low AR upon thermal stimulation. Here, the creation of an alternative shape-switching capability of particles from low to high AR is introduced, where a SMP matrix from polyvinyl alcohol (PVA) is used to create crosslinked high AR particles and to program the embedded micrometer-sized particles from a second SMP (oligo(epsilon-caprolactone) micronetworks, MN) with a low switching temperature T-sw. This programming proceeds through shape-recovery of the PVA matrix, from which the MN are harvested by PVA matrix dissolution. The use of a dissolvable SMP matrix may be a general strategy to efficiently create systems with complex moving capabilities.
Y1  - 2021
U6  - https://doi.org/10.1039/d1sm00947h
SN  - 1744-6848
VL  - 17
IS  - 41
SP  - 9326
EP  - 9331
PB  - Royal Society of Chemistry
CY  - London
ER  - 
TY  - JOUR
A1  - Scali, Stefano
A1  - Anders, Janet
A1  - Correa, Luis A.
T1  - Local master equations bypass the secular approximation
JF  - Quantum : the open journal for quantum science
N2  - Master equations are a vital tool to model heat flow through nanoscale thermodynamic systems. Most practical devices are made up of interacting subsystems and are often modelled using either local master equations (LMEs) or global master equations (GMEs). While the limiting cases in which either the LME or the GME breaks down are well understood, there exists a 'grey area' in which both equations capture steady-state heat currents reliably but predict very different transient heat flows. In such cases, which one should we trust? Here we show that, when it comes to dynamics, the local approach can be more reliable than the global one for weakly interacting open quantum systems. This is due to the fact that the secular approximation, which underpins the GME, can destroy key dynamical features. To illustrate this, we consider a minimal transport setup and show that its LME displays exceptional points (EPs). These singularities have been observed in a superconducting-circuit realisation of the model [1]. However, in stark contrast to experimental evidence, no EPs appear within the global approach. We then show that the EPs are a feature built into the Redfield equation, which is more accurate than the LME and the GME. Finally, we show that the local approach emerges as the weak-interaction limit of the Redfield equation, and that it entirely avoids the secular approximation.
Y1  - 2021
U6  - https://doi.org/10.22331/q-2021-05-01-451
SN  - 2521-327X
VL  - 5
PB  - Verein zur Förderung des Open Access Publizierens in den Quantenwissenschaften
CY  - Wien
ER  - 
TY  - JOUR
A1  - Eerqing, Narima
A1  - Subramanian, Sivaraman
A1  - Rubio Jimenez, Jesus
A1  - Lutz, Tobias
A1  - Wu, Hsin-Yu
A1  - Anders, Janet
A1  - Soeller, Christian
A1  - Vollmer, Frank
T1  - Comparing transient oligonucleotide hybridization kinetics using DNA-PAINT and optoplasmonic single-molecule sensing on gold nanorods
JF  - ACS photonics / American Chemical Society
N2  - We report a comparison of two photonic techniques for single-molecule sensing: fluorescence nanoscopy and optoplasmonic sensing. As the test system, oligonucleotides with and without fluorescent labels are transiently hybridized to complementary "docking" strands attached to gold nanorods. Comparing the measured single-molecule kinetics helps to examine the influence of the fluorescent labels as well as factors arising from different sensing geometries. Our results demonstrate that DNA dissociation is not significantly altered by the fluorescent labels and that DNA association is affected by geometric factors in the two techniques. These findings open the door to exploiting plasmonic sensing and fluorescence nanoscopy in a complementary fashion, which will aid in building more powerful sensors and uncovering the intricate effects that influence the behavior of single molecules.
KW  - single-molecule
KW  - plasmonics
KW  - whispering gallery modes
KW  - optoplasmonic
KW  - DNA-PAINT
KW  - fluorescence
KW  - localization microscopy
Y1  - 2021
U6  - https://doi.org/10.1021/acsphotonics.1c01179
SN  - 2330-4022
VL  - 8
IS  - 10
SP  - 2882
EP  - 2888
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Ritschel, Stefan
A1  - Cherstvy, Andrey G.
A1  - Metzler, Ralf
T1  - Universality of delay-time averages for financial time series
BT  - analytical results, computer simulations, and analysis of historical stock-market prices
JF  - Journal of physics. Complexity
N2  - We analyze historical data of stock-market prices for multiple financial indices using the concept of delay-time averaging for the financial time series (FTS). The region of validity of our recent theoretical predictions [Cherstvy A G et al 2017 New J. Phys. 19 063045] for the standard and delayed time-averaged mean-squared 'displacements' (TAMSDs) of the historical FTS is extended to all lag times. As the first novel element, we perform extensive computer simulations of the stochastic differential equation describing geometric Brownian motion (GBM) which demonstrate a quantitative agreement with the analytical long-term price-evolution predictions in terms of the delayed TAMSD (for all stock-market indices in crisis-free times). Secondly, we present a robust procedure of determination of the model parameters of GBM via fitting the features of the price-evolution dynamics in the FTS for stocks and cryptocurrencies. The employed concept of single-trajectory-based time averaging can serve as a predictive tool (proxy) for a mathematically based assessment and rationalization of probabilistic trends in the evolution of stock-market prices.
KW  - econophysics
KW  - geometric Brownian motion
KW  - time-series analysis
Y1  - 2021
U6  - https://doi.org/10.1088/2632-072X/ac2220
SN  - 2632-072X
VL  - 2
IS  - 4
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  - 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  - Decker, Regis
A1  - Born, Artur
A1  - Ruotsalainen, Kari
A1  - Bauer, Karl
A1  - Haverkamp, Robert
A1  - Büchner, Robby
A1  - Pietzsch, Annette
A1  - Föhlisch, Alexander
T1  - Spin-lattice angular momentum transfer of localized and valence electrons in the demagnetization transient state of gadolinium
JF  - Applied physics letters
N2  - The electron-phonon scattering is one of the main microscopic mechanisms responsible for the spin-flip in the transient state of ultrafast demagnetization. Here, we present an experimental determination of the temperature-dependent electron-phonon scattering rate in Gd. Using a static x-ray emission spectroscopy method, where the reduction of the decay peak intensities when increasing the temperature is quantified, we measure independently the electron-phonon scattering rate for the 5d and the 4f electrons. We deduce the temperature dependence of scattering for the 5d electrons, while no effect on the phonon population is observed for the 4f electrons. Our results suggest that the ultrafast magnetization dynamics in Gd is triggered by the spin-flip in the 5d electrons. We also evidence the existence of a temperature threshold, above which spin-flip scattering of the 5d electrons takes place. We deduce that during the transient state of ultrafast demagnetization, the exchange energy between 5d electrons has to be overcome before the microscopic electron-phonon scattering process can occur.
Y1  - 2021
U6  - https://doi.org/10.1063/5.0063404
SN  - 0003-6951
SN  - 1077-3118
VL  - 119
IS  - 15
PB  - AIP Publishing
CY  - Melville
ER  - 
TY  - JOUR
A1  - Born, Artur
A1  - Decker, Regis
A1  - Haverkamp, Robert
A1  - Ruotsalainen, Kari
A1  - Bauer, Karl
A1  - Pietzsch, Annette
A1  - Föhlisch, Alexander
A1  - Büchner, Robby
T1  - Thresholding of the Elliott-Yafet spin-flip scattering in multi-sublattice magnets by the respective exchange energies
JF  - Scientific reports
N2  - How different microscopic mechanisms of ultrafast spin dynamics coexist and interplay is not only relevant for the development of spintronics but also for the thorough description of physical systems out-of-equilibrium. In pure crystalline ferromagnets, one of the main microscopic mechanism of spin relaxation is the electron-phonon (el-ph) driven spin-flip, or Elliott-Yafet, scattering. Unexpectedly, recent experiments with ferro- and ferrimagnetic alloys have shown different dynamics for the different sublattices. These distinct sublattice dynamics are contradictory to the Elliott-Yafet scenario. In order to rationalize this discrepancy, it has been proposed that the intra- and intersublattice exchange interaction energies must be considered in the microscopic demagnetization mechanism, too. Here, using a temperature-dependent x-ray emission spectroscopy (XES) method, we address experimentally the element specific el-ph angular momentum transfer rates, responsible for the spin-flips in the respective (sub)lattices of Fe20Ni80, Fe50Ni50 and pure nickel single crystals. We establish how the deduced rate evolution with the temperature is linked to the exchange coupling constants reported for different alloy stoichiometries and how sublattice exchange energies threshold the related el-ph spin-flip channels. Thus, these results evidence that the Elliott-Yafet spin-flip scattering, thresholded by sublattice exchange energies, is the relevant microscopic process to describe sublattice dynamics in alloys and elemental magnetic systems.
Y1  - 2021
U6  - https://doi.org/10.1038/s41598-021-81177-9
SN  - 2045-2322
VL  - 11
IS  - 1
PB  - Springer Nature
CY  - Berlin
ER  - 
TY  - JOUR
A1  - Büchner, Robby
A1  - Fondell, Mattis
A1  - Mascarenhas, Eric Johnn
A1  - Pietzsch, Annette
A1  - Vaz da Cruz, Vinícius
A1  - Föhlisch, Alexander
T1  - How hydrogen bonding amplifies isomeric differences in pyridones toward strong changes in acidity and tautomerism
JF  - The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces & biophysical chemistry
N2  - Steric hindrance of hydration and hydrogen bond enhancement by localized charges have been identified as key factors for the massive chemical differences between the hydroxypyridine/pyridone isomers in aqueous solution. While all isomers occur mainly in the hydroxypyridine form in the gas phase, they differ by more than 3 orders of magnitude both in their acidity and tautomeric equilibrium constants upon hydration. By monitoring the electronic and solvation structures as a function of the protonation state and the O- substitution position on the pyridine ring, the amplification of the isomeric differences in aqueous solution has been investigated. Near-edge X-ray absorption fine structure (NEXAFS) measurements at the N K-edge served as the probe of the chemical state. The combination of molecular dynamics simulations, complete active space self-consistent field (CASSCF), and time-dependent density functional theory (TD-DFT) spectral calculations contributes to unraveling the principles of tautomerism and acidity in multiple biochemical systems based on tautomerism.
Y1  - 2021
U6  - https://doi.org/10.1021/acs.jpcb.0c10873
SN  - 1520-6106
SN  - 1520-5207
VL  - 125
IS  - 9
SP  - 2372
EP  - 2379
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Nadammal, Naresh
A1  - Mishurova, Tatiana
A1  - Fritsch, Tobias
A1  - Serrano-Munoz, Itziar
A1  - Kromm, Arne
A1  - Haberland, Christoph
A1  - Portella, Pedro Dolabella
A1  - Bruno, Giovanni
T1  - Critical role of scan strategies on the development of microstructure, texture, and residual stresses during laser powder bed fusion additive manufacturing
JF  - Additive manufacturing
N2  - Laser based powder bed fusion additive manufacturing offers the flexibility to incorporate standard and user-defined scan strategies in a layer or in between the layers for the customized fabrication of metallic components. In the present study, four different scan strategies and their impact on the development of microstructure, texture, and residual stresses in laser powder bed fusion additive manufacturing of a nickel-based superalloy Inconel 718 was investigated. Light microscopy, scanning electron microscopy combined with electron back-scatter diffraction, and neutron diffraction were used as the characterization tools. Strong textures with epitaxially grown columnar grains were observed along the build direction for the two individual scan strategies. Patterns depicting the respective scan strategies were visible in the build plane, which dictated the microstructure development in the other planes. An alternating strategy combining the individual strategies in the successive layers and a 67 degrees rotational strategy weakened the texture by forming finer micro-structural features. Von Mises equivalent stress plots revealed lower stress values and gradients, which translates as lower distortions for the alternating and rotational strategies. Overall results confirmed the scope for manipulating the microstructure, texture, and residual stresses during laser powder bed fusion additive manufacturing by effectively controlling the scan strategies.
KW  - Additive manufacturing
KW  - Laser powder bed fusion
KW  - Nickel-based
KW  - superalloys
KW  - Scan strategies
KW  - Residual stresses
KW  - Microstructure and
KW  - texture
Y1  - 2021
U6  - https://doi.org/10.1016/j.addma.2020.101792
SN  - 2214-8604
VL  - 38
PB  - Elsevier
CY  - Amsterdam
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  - Ihlenburg, Ramona
A1  - Mai, Tobias
A1  - Thünemann, Andreas F.
A1  - Baerenwald, Ruth
A1  - Saalwächter, Kay
A1  - Koetz, Joachim
A1  - Taubert, Andreas
T1  - Sulfobetaine hydrogels with a complex multilength-scale hierarchical structure
JF  - The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces & biophysical chemistry
N2  - Hydrogels with a hierarchical structure were prepared from a new highly water-soluble crosslinker N,N,N',N'-tetramethyl-N,N'-bis(2-ethylmethacrylate)-propyl-1,3-diammonium dibromide and from the sulfobetaine monomer 2-(N-3-sulfopropyl-N,N-dimethyl ammonium)ethyl methacrylate. The free radical polymerization of the two compounds is rapid and yields near-transparent hydrogels with sizes up to 5 cm in diameter. Rheology shows a clear correlation between the monomer-to-crosslinker ratio and the storage and loss moduli of the hydrogels. Cryo-scanning electron microscopy, low-field nuclear magnetic resonance (NMR) spectroscopy, and small-angle X-ray scattering show that the gels have a hierarchical structure with features spanning the nanometer to the sub-millimeter scale. The NMR study is challenged by the marked inhomogeneity of the gels and the complex chemical structure of the sulfobetaine monomer. NMR spectroscopy shows how these complications can be addressed via a novel fitting approach that considers the mobility gradient along the side chain of methacrylate-based monomers.
KW  - Defects
KW  - Hydrogels
KW  - Nuclear magnetic resonance spectroscopy
KW  - Scattering
KW  - X-ray scattering
Y1  - 2021
U6  - https://doi.org/10.1021/acs.jpcb.0c10601
SN  - 1520-6106
SN  - 1520-5207
VL  - 125
IS  - 13
SP  - 3398
EP  - 3408
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Franović, Igor
A1  - Omel'chenko, Oleh
A1  - Wolfrum, Matthias
T1  - Bumps, chimera states, and Turing patterns in systems of coupled active rotators
JF  - Physical review : E, Statistical, nonlinear and soft matter physics
N2  - Self-organized coherence-incoherence patterns, called chimera states, have first been reported in systems of Kuramoto oscillators. For coupled excitable units, similar patterns where coherent units are at rest are called bump states. Here, we study bumps in an array of active rotators coupled by nonlocal attraction and global repulsion. We demonstrate how they can emerge in a supercritical scenario from completely coherent Turing patterns: a single incoherent unit appears in a homoclinic bifurcation, undergoing subsequent transitions to quasiperiodic and chaotic behavior, which eventually transforms into extensive chaos with many incoherent units. We present different types of transitions and explain the formation of coherence-incoherence patterns according to the classical paradigm of short-range activation and long-range inhibition.
Y1  - 2021
U6  - https://doi.org/10.1103/PhysRevE.104.L052201
SN  - 2470-0045
SN  - 2470-0053
VL  - 104
IS  - 5
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Cherstvy, Andrey G.
A1  - Vinod, Deepak
A1  - Aghion, Erez
A1  - Sokolov, Igor M.
A1  - Metzler, Ralf
T1  - Scaled geometric Brownian motion features sub- or superexponential ensemble-averaged, but linear time-averaged mean-squared displacements
JF  - Physical review : E, Statistical, nonlinear and soft matter physics
N2  - Various mathematical Black-Scholes-Merton-like models of option pricing employ the paradigmatic stochastic process of geometric Brownian motion (GBM). The innate property of such models and of real stock-market prices is the roughly exponential growth of prices with time [on average, in crisis-free times]. We here explore the ensemble- and time averages of a multiplicative-noise stochastic process with power-law-like time-dependent volatility, sigma(t) similar to t(alpha), named scaled GBM (SGBM). For SGBM, the mean-squared displacement (MSD) computed for an ensemble of statistically equivalent trajectories can grow faster than exponentially in time, while the time-averaged MSD (TAMSD)-based on a sliding-window averaging along a single trajectory-is always linear at short lag times Delta. The proportionality factor between these the two averages of the time series is Delta/T at short lag times, where T is the trajectory length, similarly to GBM. This discrepancy of the scaling relations and pronounced nonequivalence of the MSD and TAMSD at Delta/T << 1 is a manifestation of weak ergodicity breaking for standard GBM and for SGBM with s (t)-modulation, the main focus of our analysis. The analytical predictions for the MSD and mean TAMSD for SGBM are in quantitative agreement with the results of stochastic computer simulations.
Y1  - 2021
U6  - https://doi.org/10.1103/PhysRevE.103.062127
SN  - 2470-0045
SN  - 2470-0053
VL  - 103
IS  - 6
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Ocampo-Espindola, Jorge Luis
A1  - Omel'chenko, Oleh
A1  - Kiss, Istvan Z.
T1  - Non-monotonic transients to synchrony in Kuramoto networks and electrochemical oscillators
JF  - Journal of physics. Complexity
N2  - We performed numerical simulations with the Kuramoto model and experiments with oscillatory nickel electrodissolution to explore the dynamical features of the transients from random initial conditions to a fully synchronized (one-cluster) state. The numerical simulations revealed that certain networks (e.g., globally coupled or dense Erdos-Renyi random networks) showed relatively simple behavior with monotonic increase of the Kuramoto order parameter from the random initial condition to the fully synchronized state and that the transient times exhibited a unimodal distribution. However, some modular networks with bridge elements were identified which exhibited non-monotonic variation of the order parameter with local maximum and/or minimum. In these networks, the histogram of the transients times became bimodal and the mean transient time scaled well with inverse of the magnitude of the second largest eigenvalue of the network Laplacian matrix. The non-monotonic transients increase the relative standard deviations from about 0.3 to 0.5, i.e., the transient times became more diverse. The non-monotonic transients are related to generation of phase patterns where the modules are synchronized but approximately anti-phase to each other. The predictions of the numerical simulations were demonstrated in a population of coupled oscillatory electrochemical reactions in global, modular, and irregular tree networks. The findings clarify the role of network structure in generation of complex transients that can, for example, play a role in intermittent desynchronization of the circadian clock due to external cues or in deep brain stimulations where long transients are required after a desynchronization stimulus.
KW  - synchronization
KW  - networks
KW  - Kuramoto model
KW  - electrochemistry
KW  - chemical
KW  - oscillations
Y1  - 2021
U6  - https://doi.org/10.1088/2632-072X/abe109
SN  - 2632-072X
VL  - 2
IS  - 1
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Bataille-Gonzalez, Martin
A1  - Clerc, Marcel G.
A1  - Omel'chenko, Oleh
T1  - Moving spiral wave chimeras
JF  - Physical review : E, Statistical, nonlinear and soft matter physics
N2  - We consider a two-dimensional array of heterogeneous nonlocally coupled phase oscillators on a flat torus and study the bound states of two counter-rotating spiral chimeras, shortly two-core spiral chimeras, observed in this system. In contrast to other known spiral chimeras with motionless incoherent cores, the two-core spiral chimeras typically show a drift motion. Due to this drift, their incoherent cores become spatially modulated and develop specific fingerprint patterns of varying synchrony levels. In the continuum limit of infinitely many oscillators, the two-core spiral chimeras can be studied using the Ott-Antonsen equation. Numerical analysis of this equation allows us to reveal the stability region of different spiral chimeras, which we group into three main classes-symmetric, asymmetric, and meandering spiral chimeras.
Y1  - 2021
U6  - https://doi.org/10.1103/PhysRevE.104.L022203
SN  - 2470-0045
SN  - 2470-0053
VL  - 104
IS  - 2
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Chechkin, Aleksei V.
A1  - Sokolov, Igor M.
T1  - Relation between generalized diffusion equations and subordination schemes
JF  - Physical review : E, Statistical, nonlinear and soft matter physics
N2  - Generalized (non-Markovian) diffusion equations with different memory kernels and subordination schemes based on random time change in the Brownian diffusion process are popular mathematical tools for description of a variety of non-Fickian diffusion processes in physics, biology, and earth sciences. Some of such processes (notably, the fluid limits of continuous time random walks) allow for either kind of description, but other ones do not. In the present work we discuss the conditions under which a generalized diffusion equation does correspond to a subordination scheme, and the conditions under which a subordination scheme does possess the corresponding generalized diffusion equation. Moreover, we discuss examples of random processes for which only one, or both kinds of description are applicable.
Y1  - 2021
U6  - https://doi.org/10.1103/PhysRevE.103.032133
SN  - 2470-0045
SN  - 2470-0053
VL  - 103
IS  - 3
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Wendt, Martin
A1  - Bouche, Nicolas F.
A1  - Zabl, Johannes
A1  - Schroetter, Ilane
A1  - Muzahid, Sowgat
T1  - MusE GAs FLOw and Wind V. The dust/metallicity-anisotropy of the circum-galactic medium
JF  - Monthly notices of the Royal Astronomical Society
N2  - We investigate whether the dust content of the circum-galactic medium (CGM) depends on the location of the quasar sightline with respect to the galaxy major-axis using 13 galaxy-Mg II absorber pairs (9-81 kpc distance) from the MusE GAs FLOw and Wind (MEGAFLOW) survey at 0.4 < z < 1.4. The dust content of the CGM is obtained from [Zn/Fe] using ultraviolet and visual echelle spectrograph data. When a direct measurement of [Zn/Fe] is unavailable, we estimate the dust depletion from a method that consists in solving for the depletion from multiple singly ionized ions (e.g. Mn II, Cr II, and Zn II) since each ion depletes on dust grains at different rates. We find a positive correlation between the azimuthal angle and [Zn/Fe] with a Pearson's gamma = 0.70 +/- 0.14. The sightlines along the major axis show [Zn/Fe] < 0.5, whereas the [Zn/Fe] is > 0.8 along the minor axis. These results suggest that the CGM along the minor axis is on average more metal enriched (by approximate to 1 dex) than the gas located along the major axis of galaxies provided that dust depletion is a proxy for metallicity. This anisotropic distribution is consistent with recent results on outflow and accretion in hydro-dynamical simulations.
KW  - galaxies: evolution
KW  - galaxies: formation
KW  - intergalactic medium
KW  - quasars:
KW  - absorption lines
Y1  - 2021
U6  - https://doi.org/10.1093/mnras/stab049
SN  - 0035-8711
SN  - 1365-2966
VL  - 502
IS  - 3
SP  - 3733
EP  - 3745
PB  - Oxford Univ. Press
CY  - Oxford
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  - Krivenkov, Maxim
A1  - Marchenko, Dimitry
A1  - Sánchez-Barriga, Jaime
A1  - Golias, Evangelos
A1  - Rader, Oliver
A1  - Varykhalov, Andrei
T1  - Origin of the band gap in Bi-intercalated graphene on Ir(111)
JF  - 2D Materials
N2  - Proximity to heavy sp-elements is considered promising for reaching a band gap in graphene that could host quantum spin Hall states. The recent report of an induced spin-orbit gap of 0.2 eV in Pb-intercalated graphene detectable by spin-resolved photoemission has spurred renewed interest in such systems (Klimovskikh et al 2017 ACS Nano 11, 368). In the case of Bi intercalation an even larger band gap of 0.4 eV has been observed but was assigned to the influence of a dislocation network (Warmuth et al 2016 Phys. Rev. B 93, 165 437). Here, we study Bi intercalation under graphene on Ir(111) and report a nearly ideal graphene dispersion without band replicas and no indication of hybridization with the substrate. The band gap is small (0.19 eV) and can be tuned by +/- 25 meV through the Bi coverage. The Bi atomic density is higher than in the recent report. By spin-resolved photoemission we exclude induced spin-orbit interaction as origin of the gap. Quantitative agreement of a photoemission intensity analysis with the measured band gap suggests sublattice symmetry breaking as one of the possible band gap opening mechanisms. We test several Bi structures by density functional theory. Our results indicate the possibility that Bi intercalates in the phase of bismuthene forming a graphene-bismuthene van der Waals heterostructure.
KW  - graphene
KW  - bismuth
KW  - Ir(111)
KW  - spin-orbit interaction
KW  - ARPES
KW  - STM
KW  - bismuthene
Y1  - 2021
U6  - https://doi.org/10.1088/2053-1583/abd1e4
SN  - 2053-1583
VL  - 8
IS  - 3
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Yarman, Aysu
A1  - Kurbanoğlu, Sevinç
A1  - Zebger, Ingo
A1  - Scheller, Frieder W.
T1  - Simple and robust
BT  - the claims of protein sensing by molecularly imprinted polymers
JF  - Sensors and actuators : B, Chemical : an international journal devoted to research and development of chemical transducers
N2  - A spectrum of 7562 publications on Molecularly Imprinted Polymers (MIPs) has been presented in literature within the last ten years (Scopus, September 7, 2020). Around 10 % of the papers published on MIPs describe the recognition of proteins. The straightforward synthesis of MIPs is a significant advantage as compared with the preparation of enzymes or antibodies. MIPs have been synthesized from only one up to six functional monomers while proteins are made up of 20 natural amino acids. Furthermore, they can be synthesized against structures of low immunogenicity and allow multi-analyte measurements via multi-target synthesis. Electrochemical methods allow simple polymer synthesis, removal of the template and readout. Among the different sensor configurations electrochemical MIP-sensors provide the broadest spectrum of protein analytes. The sensitivity of MIP-sensors is sufficiently high for biomarkers in the sub-nanomolar region, nevertheless the cross-reactivity of highly abundant proteins in human serum is still a challenge. MIPs for proteins offer innovative tools not only for clinical and environmental analysis, but also for bioimaging, therapy and protein engineering.
KW  - Molecularly imprinted polymer
KW  - Plastibodies
KW  - Functional scaffolds
KW  - Biomimetic sensors
KW  - Proteins
Y1  - 2021
U6  - https://doi.org/10.1016/j.snb.2020.129369
SN  - 0925-4005
SN  - 1873-3077
VL  - 330
PB  - Elsevier Science
CY  - Amsterdam [u.a.]
ER  - 
TY  - JOUR
A1  - Heidenreich, Anna
A1  - Buchner, Martin
A1  - Walz, Ariane
A1  - Thieken, Annegret
T1  - How to deal with heat stress at an open-air event?
BT  - Exploring visitors’ vulnerability, risk perception, and adaptive behavior with a multimethod approach
JF  - Weather, climate & society / American Meteorological Society
N2  - Heat waves are increasingly common in many countries across the globe, and also in Germany, where this study is set. Heat poses severe health risks, especially for vulnerable groups such as the elderly and children. This case study explores visitors' behavior and perceptions during six weekends in the summer of 2018 at a 6-month open-air horticultural show. Data from a face-to-face survey (n = 306) and behavioral observations ( n = 2750) were examined by using correlation analyses, ANOVA, and multiple regression analyses. Differences in weather perception, risk awareness, adaptive behavior, and activity level were observed between rainy days (maximum daily temperature, 25 degrees C), warmsummer days (25 degrees-30 degrees C), and hot days (>30 degrees C). Respondents reported a high level of heat risk awareness, butmost (90%) were unaware of actual heat warnings. During hot days, more adaptive measures were reported and observed. Older respondents reported taking the highest number of adaptive measures. We observed the highest level of adaptation in children, but they also showed the highest activity level. From our results we discuss how to facilitate individual adaptation to heat stress at open-air events by taking the heterogeneity of visitors into account. To mitigate negative health outcomes for citizens in the future, we argue for tailored risk communication aimed at vulnerable groups. <br /> SIGNIFICANCE STATEMENT: People around the world are facing higher average temperatures. While higher temperatures make open-air events a popular leisure time activity in summer, heat waves are a threat to health and life. Since there is not much research on how visitors of such events perceive different weather conditions-especially hot temperatures-we explored this in our case study in southern Germany at an open-air horticultural show in the summer of 2018. We discovered deficits both in people's awareness of current heat risk and the heat adaptation they carry out themselves. Future research should further investigate risk perception and adaptation behavior of private individuals, whereas event organizers and authorities need to continually focus on risk communication and facilitate individual adaptation of their visitors.
KW  - Extreme events
KW  - Adaptation
KW  - Communications/decision making
KW  - Emergency
KW  - preparedness
KW  - Emergency response
KW  - Field experiments
KW  - Societal impacts
Y1  - 2021
U6  - https://doi.org/10.1175/WCAS-D-21-0027.1
SN  - 1948-8327
SN  - 1948-8335
VL  - 13
IS  - 4
SP  - 989
EP  - 1002
PB  - American Meteorological Soc.
CY  - Boston
ER  - 
TY  - JOUR
A1  - Fischer, Eric W.
A1  - Saalfrank, Peter
T1  - Ground state properties and infrared spectra of anharmonic vibrational polaritons of small molecules in cavities
JF  - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr
N2  - Recent experiments and theory suggest that ground state properties and reactivity of molecules can be modified when placed inside a nanoscale cavity, giving rise to strong coupling between vibrational modes and the quantized cavity field. This is commonly thought to be caused either by a cavity-distorted Born-Oppenheimer ground state potential or by the formation of light-matter hybrid states, vibrational polaritons. Here, we systematically study the effect of a cavity on ground state properties and infrared spectra of single molecules, considering vibration-cavity coupling strengths from zero up to the vibrational ultrastrong coupling regime. Using single-mode models for Li-H and O-H stretch modes and for the NH3 inversion mode, respectively, a single cavity mode in resonance with vibrational transitions is coupled to position-dependent molecular dipole functions. We address the influence of the cavity mode on polariton ground state energies, equilibrium bond lengths, dissociation energies, activation energies for isomerization, and on vibro-polaritonic infrared spectra. In agreement with earlier work, we observe all mentioned properties being strongly affected by the cavity, but only if the dipole self-energy contribution in the interaction Hamiltonian is neglected. When this term is included, these properties do not depend significantly on the coupling anymore. Vibro-polaritonic infrared spectra, in contrast, are always affected by the cavity mode due to the formation of excited vibrational polaritons. It is argued that the quantized nature of vibrational polaritons is key to not only interpreting molecular spectra in cavities but also understanding the experimentally observed modification of molecular reactivity in cavities.
Y1  - 2021
U6  - https://doi.org/10.1063/5.0040853
SN  - 0021-9606
SN  - 1089-7690
VL  - 154
IS  - 10
PB  - American Institute of Physics
CY  - Melville
ER  - 
TY  - JOUR
A1  - Varghese, Alan J.
A1  - Chechkin, Aleksei
A1  - Metzler, Ralf
A1  - Sujith, Raman I.
T1  - Capturing multifractality of pressure fluctuations in thermoacoustic systems using fractional-order derivatives
JF  - Chaos : an interdisciplinary journal of nonlinear science
N2  - The stable operation of a turbulent combustor is not completely silent; instead, there is a background of small amplitude aperiodic acoustic fluctuations known as combustion noise. Pressure fluctuations during this state of combustion noise are multifractal due to the presence of multiple temporal scales that contribute to its dynamics. However, existing models are unable to capture the multifractality in the pressure fluctuations. We conjecture an underlying fractional dynamics for the thermoacoustic system and obtain a fractional-order model for pressure fluctuations. The data from this model has remarkable visual similarity to the experimental data and also has a wide multifractal spectrum during the state of combustion noise. Quantitative similarity with the experimental data in terms of the Hurst exponent and the multifractal spectrum is observed during the state of combustion noise. This model is also able to produce pressure fluctuations that are qualitatively similar to the experimental data acquired during intermittency and thermoacoustic instability. Furthermore, we argue that the fractional dynamics vanish as we approach the state of thermoacoustic instability.
Y1  - 2021
U6  - https://doi.org/10.1063/5.0032585
SN  - 1054-1500
SN  - 1089-7682
VL  - 31
IS  - 3
PB  - American Institute of Physics, AIP
CY  - Melville
ER  - 
TY  - JOUR
A1  - Schöniger, Franziska
A1  - Thonig, Richard
A1  - Resch, Gustav
A1  - Lilliestam, Johan
T1  - Making the sun shine at night
BT  - comparing the cost of dispatchable concentrating solar power and photovoltaics with storage
JF  - Energy sources. B, Economics, planning and policy
N2  - Sustainable electricity systems need renewable and dispatchable energy sources. Solar energy is an abundant source of renewable energy globally which is, though, by nature only available during the day, and especially in clear weather conditions. We compare three technology configurations able to provide dispatchable solar power at times without sunshine: Photovoltaics (PV) combined with battery (BESS) or thermal energy storage (TES) and concentrating solar power (CSP) with TES. Modeling different periods without sunshine, we find that PV+BESS is competitive for shorter storage durations while CSP+TES gains economic advantages for longer storage periods (also over PV+TES). The corresponding tipping points lie at 2-3 hours (current cost), and 4-10 hours if expectations on future cost developments are taken into consideration. PV+TES becomes only more competitive than CSP+TES with immense additional cost reductions of PV. Hence, there remain distinct niches for two technologies: PV+BESS for short storage durations and CSP+TES for longer ones.
KW  - Concentrating solar power (CSP)
KW  - dispatchable renewable electricity
KW  - thermal energy storage
KW  - photovoltaics
KW  - utility-scale batteries
KW  - flexibility
KW  - energy system modeling
Y1  - 2021
U6  - https://doi.org/10.1080/15567249.2020.1843565
SN  - 1556-7249
SN  - 1556-7257
VL  - 16
IS  - 1
SP  - 55
EP  - 74
PB  - Taylor & Francis Group
CY  - Philadelphia
ER  - 
TY  - JOUR
A1  - Raman Venkatesan, Thulasinath
A1  - Smykalla, David
A1  - Ploss, Bernd
A1  - Wübbenhorst, Michael
A1  - Gerhard, Reimund
T1  - Non-linear dielectric spectroscopy for detecting and evaluating structure-property relations in a P(VDF-TrFE-CFE) relaxor-ferroelectric terpolymer
JF  - Applied physics : A, Materials science & processing
N2  - Non-linear dielectric spectroscopy (NLDS) is employed as an effective tool to study relaxation processes and phase transitions of a poly(vinylidenefluoride-trifluoroethylene-chlorofluoroethylene) (P(VDF-TrFE-CFE)) relaxor-ferroelectric (R-F) terpolymer in detail. Measurements of the non-linear dielectric permittivity epsilon 2 ' reveal peaks at 30 and 80 degrees C that cannot be identified in conventional dielectric spectroscopy. By combining the results from NLDS experiments with those from other techniques such as thermally stimulated depolarization and dielectric-hysteresis studies, it is possible to explain the processes behind the additional peaks. The former peak, which is associated with the mid-temperature transition, is found in all other vinylidene fluoride-based polymers and may help to understand the non-zero epsilon 2 ' values that are detected on the paraelectric phase of the terpolymer. The latter peak can also be observed during cooling of P(VDF-TrFE) copolymer samples at 100 degrees C and is due to conduction and space-charge polarization as a result of the accumulation of real charges at the electrode-sample interface.
KW  - Non-linear dielectric spectroscopy
KW  - P(VDF-TrFE-CFE)
KW  - Relaxor-ferroelectric polymer
KW  - Dielectric hysteresis
KW  - Curie-transition
KW  - Mid-temperature transition
Y1  - 2021
U6  - https://doi.org/10.1007/s00339-021-04876-0
SN  - 0947-8396
SN  - 1432-0630
VL  - 127
IS  - 10
PB  - Springer
CY  - Berlin ; Heidelberg ; New York
ER  - 
TY  - JOUR
A1  - Wang, Jingwen
A1  - Rychkov, Dmitry
A1  - Gerhard, Reimund
T1  - Space-charge electret properties of polypropylene films with transcrystalline or spherulitic structures
BT  - a comparison of functionalities at interfaces
JF  - Journal of applied physics : AIP's archival journal for significant new results in applied physics / publ. by the American Institute of Physics
N2  - Spherulite-related space-charge electret properties of polypropylene (PP) have been widely discussed in the past decades. In the present paper, a less-common crystalline structure in PP-transcrystalline PP-is studied regarding its electret behavior in comparison with the typical spherulitic morphology. Polarized light microscopy and differential scanning calorimetry were employed to characterize the crystallite types and crystallinities of transcrystalline and spherulitic PP. Their electret functionality is investigated by means of thermally stimulated discharge experiments, where the cross-over phenomenon is observed on transcrystalline PP films, whereas surface-potential saturation and undercharging on the surface occur on the spherulitic samples. Besides, an asymmetrical behavior of positive and negative surface-charge stabilities is found on PP with spherulites, the negatively charged spherulitic surfaces show a better charge stability. It is shown that PP electrets are very sensitive to changes in the microscopic crystalline structures and their interfaces as well as in the molecular conformations controlled through adjustments of the respective processing steps. In addition, surface and bulk nanocomposites of PP or low-density polyethylene with inorganic particles are included in the comparison. In view of recent developments in the areas of PP-based electret-fiber filters and cellular-foam ferroelectrets, the observed changes in the charge-storage properties may have particular relevance, as the required film, fiber, or foam processing might significantly modify crystalline morphologies and nano-scale interfaces in PP electrets. Limitations in the charge-storage capabilities of interface structures may also be of interest in the context of high-voltage electrical-insulation materials where reduced space-charge accumulation and slightly increased charge transport can be advantageous.
Y1  - 2021
U6  - https://doi.org/10.1063/5.0039867
SN  - 0021-8979
SN  - 1089-7550
VL  - 129
IS  - 6
PB  - American Institute of Physics
CY  - Melville
ER  - 
TY  - JOUR
A1  - Rüdiger, Günther
A1  - Schultz, Manfred
A1  - Hollerbach, Rainer
T1  - Destabilization of super-rotating Taylor-Couette flows by current-free helical magnetic fields
JF  - Journal of plasma physics
N2  - In an earlier paper we showed that the combination of azimuthal magnetic fields and super-rotation in Taylor-Couette flows of conducting fluids can be unstable against non-axisymmetric perturbations if the magnetic Prandtl number of the fluid is Pm not equal 1. Here we demonstrate that the addition of a weak axial field component allows axisymmetric perturbation patterns for Pm of order unity depending on the boundary conditions. The axisymmetric modes only occur for magnetic Mach numbers (of the azimuthal field) of order unity, while higher values are necessary for the non-axisymmetric modes. The typical growth time of the instability and the characteristic time scale of the axial migration of the axisymmetric mode are long compared with the rotation period, but short compared with the magnetic diffusion time. The modes travel in the positive or negative z direction along the rotation axis depending on the sign of B phi Bz. We also demonstrate that the azimuthal components of flow and field perturbations travel in phase if vertical bar B phi vertical bar >> vertical bar B-z vertical bar, independent of the form of the rotation law. Within a short-wave approximation for thin gaps it is also shown (in an appendix) that for ideal fluids the considered helical magnetorotational instability only exists for rotation laws with negative shear.
KW  - plasma instabilities
KW  - astrophysical plasmas
Y1  - 2021
U6  - https://doi.org/10.1017/S0022377821000295
SN  - 1469-7807
VL  - 87
IS  - 2
PB  - Cambridge University Press
CY  - London
ER  - 
TY  - JOUR
A1  - Eckert, Sebastian
A1  - Vaz da Cruz, Vinícius
A1  - Ochmann, Miguel
A1  - Ahnen, Inga von
A1  - Föhlisch, Alexander
A1  - Huse, Nils
T1  - Breaking the symmetry of pyrimidine
BT  - solvent effects and core-excited state dynamics
JF  - The journal of physical chemistry letters
N2  - Symmetry and its breaking crucially define the chemical properties of molecules and their functionality. Resonant inelastic X-ray scattering is a local electronic structure probe reporting on molecular symmetry and its dynamical breaking within the femtosecond scattering duration. Here, we study pyrimidine, a system from the C-2v point group, in an aqueous solution environment, using scattering though its 2a(2) resonance. Despite the absence of clean parity selection rules for decay transitions from in-plane orbitals, scattering channels including decay from the 7b(2) and 11a(1) orbitals with nitrogen lone pair character are a direct probe for molecular symmetry. Computed spectra of explicitly solvated molecules sampled from a molecular dynamics simulation are combined with the results of a quantum dynamical description of the X-ray scattering process. We observe dominant signatures of core-excited Jahn-Teller induced symmetry breaking for resonant excitation. Solvent contributions are separable by shortening of the effective scattering duration through excitation energy detuning.
Y1  - 2021
U6  - https://doi.org/10.1021/acs.jpclett.1c01865
SN  - 1948-7185
VL  - 12
IS  - 35
SP  - 8637
EP  - 8643
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Silanteva, Irina A.
A1  - Komolkin, Andrei
A1  - Mamontova, Veronika V.
A1  - Gabrusenok, Pavel
A1  - Vorontsov-Velyaminov, Pavel N.
A1  - Santer, Svetlana
A1  - Kasyanenko, Nina A.
T1  - Cis-isomers of photosensitive cationic azobenzene surfactants in DNA solutions at different NaCl concentrations
BT  - Experiment and modeling
JF  - The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces & biophysical chemistry
N2  - The DNA interaction with cis-isomers of photosensitive azobenzene-containing surfactants was studied by both experimental methods and computer simulation. It was shown that before the organization of micelles, such surfactants in the cis-conformation form associates of only a single type with a disordered orientation of molecules. In contrast, for trans-isomers, there exist two types of associates with head-to-head or head-to-tail orientations of molecules in dependence on salt concentration in a solution. The comparison of cis- and trans-isomer binding to DNA and the influence of salt concentration on the formation of their complexes with DNA were studied. It was shown that cis-isomers interact with phosphate groups of DNA and that their molecules were also located along the minor groove of DNA.
Y1  - 2021
U6  - https://doi.org/10.1021/acs.jpcb.1c07864
SN  - 1520-6106
SN  - 1520-5207
VL  - 125
IS  - 40
SP  - 11197
EP  - 11207
PB  - American Chemical Society
CY  - Washington
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  - Pasemann, Gregor
A1  - Flemming, Sven
A1  - Alonso, Sergio
A1  - Beta, Carsten
A1  - Stannat, Wilhelm
T1  - Diffusivity estimation for activator-inhibitor models
BT  - theory and application to intracellular dynamics of the actin cytoskeleton
JF  - Journal of nonlinear science
N2  - A theory for diffusivity estimation for spatially extended activator-inhibitor dynamics modeling the evolution of intracellular signaling networks is developed in the mathematical framework of stochastic reaction-diffusion systems. In order to account for model uncertainties, we extend the results for parameter estimation for semilinear stochastic partial differential equations, as developed in Pasemann and Stannat (Electron J Stat 14(1):547-579, 2020), to the problem of joint estimation of diffusivity and parametrized reaction terms. Our theoretical findings are applied to the estimation of effective diffusivity of signaling components contributing to intracellular dynamics of the actin cytoskeleton in the model organism Dictyostelium discoideum.
KW  - Parametric drift estimation
KW  - Stochastic reaction– diffusion
KW  - systems
KW  - Maximum likelihood estimation
KW  - Actin cytoskeleton dynamics
Y1  - 2021
U6  - https://doi.org/10.1007/s00332-021-09714-4
SN  - 0938-8974
SN  - 1432-1467
VL  - 31
IS  - 3
PB  - Springer
CY  - New York
ER  - 
TY  - JOUR
A1  - Pikovskij, Arkadij
T1  - Synchronization of oscillators with hyperbolic chaotic phases
JF  - Izvestija vysšich učebnych zavedenij : naučno-techničeskij žurnal = Izvestiya VUZ. Prikladnaja nelinejnaja dinamika = Applied nonlinear dynamics
N2  - Topic and aim. Synchronization in populations of coupled oscillators can be characterized with order parameters that describe collective order in ensembles. A dependence of the order parameter on the coupling constants is well-known for coupled periodic oscillators. The goal of the study is to extend this analysis to ensembles of oscillators with chaotic phases, moreover with phases possessing hyperbolic chaos. Models and methods. Two models are studied in the paper. One is an abstract discrete-time map, composed with a hyperbolic Bernoulli transformation and with Kuramoto dynamics. Another model is a system of coupled continuous-time chaotic oscillators, where each individual oscillator has a hyperbolic attractor of Smale-Williams type. Results. The discrete-time model is studied with the Ott-Antonsen ansatz, which is shown to be invariant under the application of the Bernoulli map. The analysis of the resulting map for the order parameter shows, that the asynchronouis state is always stable, but the synchronous one becomes stable above a certain coupling strength. Numerical analysis of the continuous-time model reveals a complex sequence of transitions from an asynchronous state to a completely synchronous hyperbolic chaos, with intermediate stages that include regimes with periodic in time mean field, as well as with weakly and strongly irregular mean field variations. Discussion. Results demonstrate that synchronization of systems with hyperbolic chaos of phases is possible, although a rather strong coupling is required. The approach can be applied to other systems of interacting units with hyperbolic chaotic dynamics.
N2  - Тема и цель. Синхронизация в популяциях связанных осцилляторов может быть охарактеризована параметрами порядка, описывающими коллективный порядок в ансамблях. Зависимость параметра порядка от коэффициентов связи хорошо известна для связанных периодических осцилляторов. Целью данного исследования является обобщение этого анализа на ансамбли осцилляторов с хаотическими фазами, а именно, с фазами, распределёнными на гиперболическом аттракторе. Модели и методы. В работе исследуются две модели. Первая – абстрактное отображение в дискретном времени, составленное из гиперболического преобразования Бернулли и динамики Курамото. Вторая – это система связанных хаотических осцилляторов в непрерывном времени, где каждый отдельный осциллятор имеет гиперболический аттрактор типа Смейла–Вильямса. Результаты. Модель в дискретном времени изучается с помощью подхода Отта–Антонсена, который, как показано, инвариантен при применении отображения Бернулли. Анализ полученного отображения по параметрам порядка показывает, что асинхронное состояние всегда устойчиво, а синхронное состояние становится устойчивым выше определенной силы связи. Численный анализ модели в непрерывном времени показывает сложную последовательность переходов из асинхронного состояния в полностью синхронный гиперболический хаос с промежуточными стадиями, которые включают режимы с периодическим во времени средним полем, а также со слабо и сильно нерегулярными вариациями среднего поля.
Обсуждение. Результаты показывают, что синхронизация систем с гиперболическим фазовым хаосом возможна, хотя требуется довольно сильная связь. Данный подход может быть применен и к другим системам взаимодействующих звеньев с гиперболической хаотической динамикой.
T2  - Синхронизация осцилляторов с гиперболическими хаотическими фазами
KW  - hyperbolic attractor
KW  - synchronization
KW  - collective dynamics
KW  - иперболический аттрактор
KW  - синхронизация
KW  - оллективная динамика
Y1  - 2021
U6  - https://doi.org/10.18500/0869-6632-2021-29-1-78-87
SN  - 0869-6632
SN  - 2542-1905
VL  - 29
IS  - 1
SP  - 78
EP  - 87
PB  - Saratov State University
CY  - Saratov
ER  - 
TY  - JOUR
A1  - Cano Crespo, Ana
A1  - Traxl, Dominik
A1  - Thonicke, Kirsten
T1  - Spatio-temporal patterns of extreme fires in Amazonian forests
JF  - European physical journal special topics
N2  - Fires are a fundamental part of the Earth System. In the last decades, they have been altering ecosystem structure, biogeochemical cycles and atmospheric composition with unprecedented rapidity. In this study, we implement a complex networks-based methodology to track individual fires over space and time. We focus on extreme fires-the 5% most intense fires-in the tropical forests of the Brazilian Legal Amazon over the period 2002-2019. We analyse the interannual variability in the number and spatial patterns of extreme forest fires in years with diverse climatic conditions and anthropogenic pressure to examine potential synergies between climate and anthropogenic drivers. We observe that major droughts, that increase forest flammability, co-occur with high extreme fire years but also that it is fundamental to consider anthropogenic activities to understand the distribution of extreme fires. Deforestation fires, fires escaping from managed lands, and other types of forest degradation and fragmentation provide the ignition sources for fires to ignite in the forests. We find that all extreme forest fires identified are located within a 0.5-km distance from forest edges, and up to 56% of them are within a 1-km distance from roads (which increases to 73% within 5 km), showing a strong correlation that defines spatial patterns of extreme fires.
Y1  - 2021
U6  - https://doi.org/10.1140/epjs/s11734-021-00164-3
SN  - 1951-6355
SN  - 1951-6401
VL  - 230
IS  - 14-15
SP  - 3033
EP  - 3044
PB  - Springer
CY  - Berlin ; Heidelberg
ER  - 
TY  - JOUR
A1  - Bekir, Marek
A1  - Jelken, Joachim
A1  - Jung, Se-Hyeong
A1  - Pich, Andrij
A1  - Pacholski, Claudia
A1  - Kopyshev, Alexey
A1  - Santer, Svetlana
T1  - Dual responsiveness of microgels induced by single light stimulus
JF  - Applied physics letters
N2  - We report on the multiple response of microgels triggered by a single optical stimulus. Under irradiation, the volume of the microgels is reversibly switched by more than 20 times. The irradiation initiates two different processes: photo-isomerization of the photo-sensitive surfactant, which forms a complex with the anionic microgel, rendering it photo-responsive; and local heating due to a thermo-plasmonic effect within the structured gold layer on which the microgel is deposited. The photo-responsivity is related to the reversible accommodation/release of the photo-sensitive surfactant depending on its photo-isomerization state, while the thermo-sensitivity is intrinsically built in. We show that under exposure to green light, the thermo-plasmonic effect generates a local hot spot in the gold layer, resulting in the shrinkage of the microgel. This process competes with the simultaneous photo-induced swelling. Depending on the position of the laser spot, the spatiotemporal control of reversible particle shrinking/swelling with a predefined extent on a per-second base can be implemented.
Y1  - 2021
U6  - https://doi.org/10.1063/5.0036376
SN  - 0003-6951
SN  - 1077-3118
VL  - 118
IS  - 9
PB  - American Institute of Physics
CY  - Melville
ER  - 
TY  - JOUR
A1  - Rosenau, Philip
A1  - Pikovskij, Arkadij
T1  - Waves in strongly nonlinear Gardner-like equations on a lattice
JF  - Nonlinearity / the Institute of Physics and the London Mathematical Society
N2  - We introduce and study a family of lattice equations which may be viewed either as a strongly nonlinear discrete extension of the Gardner equation, or a non-convex variant of the Lotka-Volterra chain. Their deceptively simple form supports a very rich family of complex solitary patterns. Some of these patterns are also found in the quasi-continuum rendition, but the more intriguing ones, like interlaced pairs of solitary waves, or waves which may reverse their direction either spontaneously or due a collision, are an intrinsic feature of the discrete realm.
KW  - nonlinear lattice
KW  - solitary wave
KW  - Gardner equation
KW  - compacton
Y1  - 2021
U6  - https://doi.org/10.1088/1361-6544/ac0f51
SN  - 0951-7715
SN  - 1361-6544
VL  - 34
IS  - 8
SP  - 5872
EP  - 5896
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Cherstvy, Andrey G.
A1  - Safdari, Hadiseh
A1  - Metzler, Ralf
T1  - Anomalous diffusion, nonergodicity, and ageing for exponentially and logarithmically time-dependent diffusivity
BT  - striking differences for massive versus massless particles
JF  - Journal of physics. D, Applied physics
N2  - We investigate a diffusion process with a time-dependent diffusion coefficient, both exponentially increasing and decreasing in time, D(t)=D-0(e +/- 2 alpha t). For this (hypothetical) nonstationary diffusion process we compute-both analytically and from extensive stochastic simulations-the behavior of the ensemble- and time-averaged mean-squared displacements (MSDs) of the particles, both in the over- and underdamped limits. Simple asymptotic relations derived for the short- and long-time behaviors are shown to be in excellent agreement with the results of simulations. The diffusive characteristics in the presence of ageing are also considered, with dramatic differences of the over- versus underdamped regime. Our results for D(t)=D-0(e +/- 2 alpha t) extend and generalize the class of diffusive systems obeying scaled Brownian motion featuring a power-law-like variation of the diffusivity with time, D(t) similar to t(alpha-1). We also examine the logarithmically increasing diffusivity, D(t)=D(0)log[t/tau(0)], as another fundamental functional dependence (in addition to the power-law and exponential) and as an example of diffusivity slowly varying in time. One of the main conclusions is that the behavior of the massive particles is predominantly ergodic, while weak ergodicity breaking is repeatedly found for the time-dependent diffusion of the massless particles at short times. The latter manifests itself in the nonequivalence of the (both nonaged and aged) MSD and the mean time-averaged MSD. The current findings are potentially applicable to a class of physical systems out of thermal equilibrium where a rapid increase or decrease of the particles' diffusivity is inherently realized. One biological system potentially featuring all three types of time-dependent diffusion (power-law-like, exponential, and logarithmic) is water diffusion in the brain tissues, as we thoroughly discuss in the end.
KW  - anomalous diffusion
KW  - scaled Brownian motion
KW  - stochastic processes
KW  - nonstationary diffusivity
KW  - water diffusion in the brain
KW  - nonergodicity
Y1  - 2021
U6  - https://doi.org/10.1088/1361-6463/abdff0
SN  - 0022-3727
SN  - 1361-6463
VL  - 54
IS  - 19
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Letellier, Christophe
A1  - Abraham, Ralph
A1  - Shepelyansky, Dima L.
A1  - Rossler, Otto E.
A1  - Holmes, Philip
A1  - Lozi, Rene
A1  - Glass, Leon
A1  - Pikovsky, Arkady
A1  - Olsen, Lars F.
A1  - Tsuda, Ichiro
A1  - Grebogi, Celso
A1  - Parlitz, Ulrich
A1  - Gilmore, Robert
A1  - Pecora, Louis M.
A1  - Carroll, Thomas L.
T1  - Some elements for a history of the dynamical systems theory
JF  - Chaos : an interdisciplinary journal of nonlinear science
N2  - Writing a history of a scientific theory is always difficult because it requires to focus on some key contributors and to "reconstruct" some supposed influences. In the 1970s, a new way of performing science under the name "chaos" emerged, combining the mathematics from the nonlinear dynamical systems theory and numerical simulations. To provide a direct testimony of how contributors can be influenced by other scientists or works, we here collected some writings about the early times of a few contributors to chaos theory. The purpose is to exhibit the diversity in the paths and to bring some elements-which were never published-illustrating the atmosphere of this period. Some peculiarities of chaos theory are also discussed.
Y1  - 2021
U6  - https://doi.org/10.1063/5.0047851
SN  - 1054-1500
SN  - 1089-7682
VL  - 31
IS  - 5
PB  - AIP Publishing
CY  - Melville
ER  - 
TY  - JOUR
A1  - Höhle, Barbara
A1  - Fritzsche, Tom
A1  - Boll-Avetisyan, Natalie
A1  - Hullebus, Marc
A1  - Gafos, Adamantios I.
T1  - Respect the surroundings
BT  - effects of phonetic context variability on infants' learning of minimal pairs
JF  - JASA Express Letters
N2  - Fourteen-month-olds' ability to distinguish a just learned word, /bu?k/, from its minimally different word, /du?k/, was assessed under two pre-exposure conditions: one where /b, d/-initial forms occurred in a varying vowel context and another where the vowel was fixed but the final consonant varied. Infants in the experiments benefited from the variable vowel but not from the variable final consonant context, suggesting that vowel variability but not all kinds of variability are beneficial. These results are discussed in the context of time-honored observations on the vowel-dependent nature of place of articulation cues for consonants.
Y1  - 2021
U6  - https://doi.org/10.1121/10.0003574
SN  - 2691-1191
VL  - 1
IS  - 2
PB  - AIP Publ.
CY  - Melville
ER  - 
TY  - JOUR
A1  - Haubitz, Toni
A1  - Drobot, Björn
A1  - Tsushima, Satoru
A1  - Steudtner, Robin
A1  - Stumpf, Thorsten
A1  - Kumke, Michael Uwe
T1  - Quenching mechanism of uranyl(VI) by chloride and bromide in aqueous and non-aqueous solutions
JF  - The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment & general theory
N2  - A major hindrance in utilizing uranyl(VI) luminescence as a standard analytical tool, for example, in environmental monitoring or nuclear industries, is quenching by other ions such as halide ions, which are present in many relevant matrices of uranyl(VI) speciation. Here, we demonstrate through a combination of time-resolved laser-induced fluorescence spectroscopy, transient absorption spectroscopy, and quantum chemistry that coordinating solvent molecules play a crucial role in U(VI) halide luminescence quenching. We show that our previously suggested quenching mechanism based on an internal redox reaction of the 1:2-uranyl-halide-complex holds also true for bromide-induced quenching of uranyl(VI). By adopting specific organic solvents, we were able to suppress the separation of the oxidized halide ligand X-2(center dot-) and the formed uranyl(V) into fully solvated ions, thereby "reigniting" U(VI) luminescence. Time-dependent density functional theory calculations show that quenching occurs through the outer-sphere complex of U(VI) and halide in water, while the ligand-to-metal charge transfer is strongly reduced in acetonitrile.
Y1  - 2021
U6  - https://doi.org/10.1021/acs.jpca.1c02487
SN  - 1089-5639
SN  - 1520-5215
VL  - 125
IS  - 20
SP  - 4380
EP  - 4389
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Wang, Wei
A1  - Cherstvy, Andrey G.
A1  - Kantz, Holger
A1  - Metzler, Ralf
A1  - Sokolov, Igor M.
T1  - Time averaging and emerging nonergodicity upon resetting of fractional Brownian motion and heterogeneous diffusion processes
JF  - Physical review : E, Statistical, nonlinear and soft matter physics
N2  - How different are the results of constant-rate resetting of anomalous-diffusion processes in terms of their ensemble-averaged versus time-averaged mean-squared displacements (MSDs versus TAMSDs) and how does stochastic resetting impact nonergodicity? We examine, both analytically and by simulations, the implications of resetting on the MSD- and TAMSD-based spreading dynamics of particles executing fractional Brownian motion (FBM) with a long-time memory, heterogeneous diffusion processes (HDPs) with a power-law space-dependent diffusivity D(x) = D0|x|gamma and their "combined" process of HDP-FBM. We find, inter alia, that the resetting dynamics of originally ergodic FBM for superdiffusive Hurst exponents develops disparities in scaling and magnitudes of the MSDs and mean TAMSDs indicating weak ergodicity breaking. For subdiffusive HDPs we also quantify the nonequivalence of the MSD and TAMSD and observe a new trimodal form of the probability density function. For reset FBM, HDPs and HDP-FBM we compute analytically and verify by simulations the short-time MSD and TAMSD asymptotes and long-time plateaus reminiscent of those for processes under confinement. We show that certain characteristics of these reset processes are functionally similar despite a different stochastic nature of their nonreset variants. Importantly, we discover nonmonotonicity of the ergodicitybreaking parameter EB as a function of the resetting rate r. For all reset processes studied we unveil a pronounced resetting-induced nonergodicity with a maximum of EB at intermediate r and EB similar to(1/r )-decay at large r. Alongside the emerging MSD-versus-TAMSD disparity, this r-dependence of EB can be an experimentally testable prediction. We conclude by discussing some implications to experimental systems featuring resetting dynamics.
Y1  - 2021
U6  - https://doi.org/10.1103/PhysRevE.104.024105
SN  - 2470-0045
SN  - 2470-0053
VL  - 104
IS  - 2
PB  - American Institute of Physics
CY  - Woodbury, NY
ER  - 
TY  - JOUR
A1  - Chaurasia, Swami Vivekanandji
A1  - Dietrich, Tim
A1  - Rosswog, Stephan
T1  - Black hole-neutron star simulations with the BAM code
BT  - first tests and simulations
JF  - Physical review : D, Particles, fields, gravitation, and cosmology
N2  - The first detections of black hole-neutron star mergers (GW200105 and GW200115) by the LIGO-Virgo-Kagra Collaboration mark a significant scientific breakthrough. The physical interpretation of pre- and postmerger signals requires careful cross-examination between observational and theoretical modelling results. Here we present the first set of black hole-neutron star simulations that were obtained with the numerical-relativity code BAM. Our initial data are constructed using the public LORENE spectral library, which employs an excision of the black hole interior. BAM, in contrast, uses the moving-puncture gauge for the evolution. Therefore, we need to "stuff" the black hole interior with smooth initial data to evolve the binary system in time. This procedure introduces constraint violations such that the constraint damping properties of the evolution system are essential to increase the accuracy of the simulation and in particular to reduce spurious center-of-mass drifts. Within BAM we evolve the Z4c equations and we compare our gravitational-wave results with those of the SXS collaboration and results obtained with the SACRA code. While we find generally good agreement with the reference solutions and phase differences less than or similar to 0.5 rad at the moment of merger, the absence of a clean convergence order in our simulations does not allow for a proper error quantification. We finally present a set of different initial conditions to explore how the merger of black hole neutron star systems depends on the involved masses, spins, and equations of state.
Y1  - 2021
U6  - https://doi.org/10.1103/PhysRevD.104.084010
SN  - 2470-0010
SN  - 2470-0029
VL  - 104
IS  - 8
PB  - American Physical Society
CY  - Ridge, NY
ER  - 
TY  - JOUR
A1  - Mendez, Vicenc
A1  - Maso-Puigdellosas, Axel
A1  - Sandev, Trifce
A1  - Campos, Daniel
T1  - Continuous time random walks under Markovian resetting
JF  - Physical review : E, Statistical, nonlinear and soft matter physics
N2  - We investigate the effects of Markovian resetting events on continuous time random walks where the waiting times and the jump lengths are random variables distributed according to power-law probability density functions. 
We prove the existence of a nonequilibrium stationary state and finite mean first arrival time. 
However, the existence of an optimum reset rate is conditioned to a specific relationship between the exponents of both power-law tails. 
We also investigate the search efficiency by finding the optimal random walk which minimizes the mean first arrival time in terms of the reset rate, the distance of the initial position to the target, and the characteristic transport exponents.
Y1  - 2021
U6  - https://doi.org/10.1103/PhysRevE.103.022103
SN  - 2470-0045
SN  - 2470-0053
VL  - 103
IS  - 2
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Zuo, Guangzheng
A1  - Shoaee, Safa
A1  - Kemerink, Martijn
A1  - Neher, Dieter
T1  - General rules for the impact of energetic disorder and mobility on nongeminate recombination in phase-separated organic solar cells
JF  - Physical review applied
N2  - State-of-the-art organic solar cells exhibit power conversion efficiencies of 18% and above. These devices benefit from the suppression of free charge recombination with regard to the Langevin limit of charge encounter in a homogeneous medium. It is recognized that the main cause of suppressed free charge recombination is the reformation and resplitting of charge-transfer (CT) states at the interface between donor and acceptor domains. Here, we use kinetic Monte Carlo simulations to understand the interplay between free charge motion and recombination in an energetically disordered phase-separated donor-acceptor blend. We identify conditions for encounter-dominated and resplitting-dominated recombination. In the former regime, recombination is proportional to mobility for all parameters tested and only slightly reduced with respect to the Langevin limit. In contrast, mobility is not the decisive parameter that determines the nongeminate recombination coefficient, k(2), in the latter case, where k2 is a sole function of the morphology, CT and charge-separated (CS) energetics, and CT-state decay properties. Our simulations also show that free charge encounter in the phase-separated disordered blend is determined by the average mobility of all carriers, while CT reformation and resplitting involves mostly states near the transport energy. Therefore, charge encounter is more affected by increased disorder than the resplitting of the CT state. As a consequence, for a given mobility, larger energetic disorder, in combination with a higher hopping rate, is preferred. These findings have implications for the understanding of suppressed recombination in solar cells with nonfullerene acceptors, which are known to exhibit lower energetic disorder than that of fullerenes.
Y1  - 2021
U6  - https://doi.org/10.1103/PhysRevApplied.16.034027
SN  - 2331-7019
VL  - 16
IS  - 3
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Bolotov, Maxim I.
A1  - Smirnov, Lev A.
A1  - Bubnova, E. S.
A1  - Osipov, Grigory V.
A1  - Pikovskij, Arkadij
T1  - Spatiotemporal regimes in the Kuramoto-Battogtokh system of nonidentical oscillators
JF  - Journal of experimental and theoretical physics
N2  - We consider the spatiotemporal states of an ensemble of nonlocally coupled nonidentical phase oscillators, which correspond to different regimes of the long-term evolution of such a system. We have obtained homogeneous, twisted, and nonhomogeneous stationary solutions to the Ott-Antonsen equations corresponding to key variants of the realized collective rotational motion of elements of the medium in question with nonzero mesoscopic characteristics determining the degree of coherence of the dynamics of neighboring particles. We have described the procedures of the search for the class of nonhomogeneous solutions as stationary points of the auxiliary point map and of determining the stability based on analysis of the eigenvalue spectrum of the composite operator. Static and breather cluster regimes have been demonstrated and described, as well as the regimes with an irregular behavior of averaged complex fields including, in particular, the local order parameter.
Y1  - 2021
U6  - https://doi.org/10.1134/S1063776121010106
SN  - 1063-7761
SN  - 1090-6509
VL  - 132
IS  - 1
SP  - 127
EP  - 147
PB  - Springer
CY  - Heidelberg [u.a.]
ER  - 
TY  - JOUR
A1  - Klett, Kolja
A1  - Cherstvy, Andrey G.
A1  - Shin, Jaeoh
A1  - Sokolov, Igor M.
A1  - Metzler, Ralf
T1  - Non-Gaussian, transiently anomalous, and ergodic self-diffusion of flexible dumbbells in crowded two-dimensional environments
BT  - coupled translational and rotational motions
JF  - Physical review : E, Statistical, nonlinear and soft matter physics
N2  - We employ Langevin-dynamics simulations to unveil non-Brownian and non-Gaussian center-of-mass self-diffusion of massive flexible dumbbell-shaped particles in crowded two-dimensional solutions. We study the intradumbbell dynamics of the relative motion of the two constituent elastically coupled disks. Our main focus is on effects of the crowding fraction phi and of the particle structure on the diffusion characteristics. We evaluate the time-averaged mean-squared displacement (TAMSD), the displacement probability-density function (PDF), and the displacement autocorrelation function (ACF) of the dimers. For the TAMSD at highly crowded conditions of dumbbells, e.g., we observe a transition from the short-time ballistic behavior, via an intermediate subdiffusive regime, to long-time Brownian-like spreading dynamics. The crowded system of dimers exhibits two distinct diffusion regimes distinguished by the scaling exponent of the TAMSD, the dependence of the diffusivity on phi, and the features of the displacement-ACF. We attribute these regimes to a crowding-induced transition from viscous to viscoelastic diffusion upon growing phi. We also analyze the relative motion in the dimers, finding that larger phi suppress their vibrations and yield strongly non-Gaussian PDFs of rotational displacements. For the diffusion coefficients D(phi) of translational and rotational motion of the dumbbells an exponential decay with phi for weak and a power-law variation D(phi) proportional to (phi - phi(star))(2.4) for strong crowding is found. A comparison of simulation results with theoretical predictions for D(phi) is discussed and some relevant experimental systems are overviewed.
Y1  - 2021
U6  - https://doi.org/10.1103/PhysRevE.104.064603
SN  - 2470-0045
SN  - 2470-0053
VL  - 104
IS  - 6
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Dörries, Timo
A1  - Loos, Sarah Anna Marie
A1  - Klapp, Sabine H. L.
T1  - Correlation functions of non-Markovian systems out of equilibrium
BT  - analytical expressions beyond single-exponential memory
JF  - Journal of statistical mechanics: theory and experiment : JSTAT
N2  - This paper is concerned with correlation functions of stochastic systems with memory, a prominent example being a molecule or colloid moving through a complex (e.g. viscoelastic) fluid environment. Analytical investigations of such systems based on non-Markovian stochastic equations are notoriously difficult. A common approximation is that of a single-exponential memory, corresponding to the introduction of one auxiliary variable coupled to the Markovian dynamics of the main variable. As a generalization, we here investigate a class of 'toy' models with altogether three degrees of freedom, giving rise to more complex forms of memory. Specifically, we consider, mainly on an analytical basis, the under- and overdamped motion of a colloidal particle coupled linearly to two auxiliary variables, where the coupling between variables can be either reciprocal or non-reciprocal. Projecting out the auxiliary variables, we obtain non-Markovian Langevin equations with friction kernels and colored noise, whose structure is similar to that of a generalized Langevin equation. For the present systems, however, the non-Markovian equations may violate the fluctuation-dissipation relation as well as detailed balance, indicating that the systems are out of equilibrium. We then study systematically the connection between the coupling topology of the underlying Markovian system and various autocorrelation functions. We demonstrate that already two auxiliary variables can generate surprisingly complex (e.g. non-monotonic or oscillatory) memory and correlation functions. Finally, we show that a minimal overdamped model with two auxiliary variables and suitable non-reciprocal coupling yields correlation functions resembling those describing hydrodynamic backflow in an optical trap.
KW  - correlation functions
KW  - memory effects
KW  - friction
Y1  - 2021
U6  - https://doi.org/10.1088/1742-5468/abdead
SN  - 1742-5468
IS  - 3
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Cherstvy, Andrey G.
A1  - Wang, Wei
A1  - Metzler, Ralf
A1  - Sokolov, Igor M.
T1  - Inertia triggers nonergodicity of fractional Brownian motion
JF  - Physical review : E, Statistical, nonlinear and soft matter physics
N2  - How related are the ergodic properties of the over- and underdamped Langevin equations driven by fractional Gaussian noise? We here find that for massive particles performing fractional Brownian motion (FBM) inertial effects not only destroy the stylized fact of the equivalence of the ensemble-averaged mean-squared displacement (MSD) to the time-averaged MSD (TAMSD) of overdamped or massless FBM, but also dramatically alter the values of the ergodicity-breaking parameter (EB). Our theoretical results for the behavior of EB for underdamped or massive FBM for varying particle mass m, Hurst exponent H, and trace length T are in excellent agreement with the findings of stochastic computer simulations. The current results can be of interest for the experimental community employing various single-particle-tracking techniques and aiming at assessing the degree of nonergodicity for the recorded time series (studying, e.g., the behavior of EB versus lag time). To infer FBM as a realizable model of anomalous diffusion for a set single-particle-tracking data when massive particles are being tracked, the EBs from the data should be compared to EBs of massive (rather than massless) FBM.
Y1  - 2021
U6  - https://doi.org/10.1103/PhysRevE.104.024115
SN  - 2470-0045
SN  - 2470-0053
VL  - 104
IS  - 2
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Andersson, Edvin K. W.
A1  - Sångeland, Christofer
A1  - Berggren, Elin
A1  - Johansson, Fredrik O. L.
A1  - Kühn, Danilo
A1  - Lindblad, Andreas
A1  - Mindemark, Jonas
A1  - Hahlin, Maria
T1  - Early-stage decomposition of solid polymer electrolytes in Li-metal batteries
JF  - Journal of materials chemistry : A, Materials for energy and sustainability
N2  - Development of functional and stable solid polymer electrolytes (SPEs) for battery applications is an important step towards both safer batteries and for the realization of lithium-based or anode-less batteries. The interface between the lithium and the solid polymer electrolyte is one of the bottlenecks, where severe degradation is expected. Here, the stability of three different SPEs - poly(ethylene oxide) (PEO), poly(epsilon-caprolactone) (PCL) and poly(trimethylene carbonate) (PTMC) - together with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt, is investigated after they have been exposed to lithium metal under UHV conditions. Degradation compounds, e.g. Li-O-R, LiF and LixSyOz, are identified for all SPEs using soft X-ray photoelectron spectroscopy. A competing degradation between polymer and salt is identified in the outermost surface region (<7 nm), and is dependent on the polymer host. PTMC:LiTFSI shows the most severe decomposition of both polymer and salt followed by PCL:LiTFSI and PEO:LiTFSI. In addition, the movement of lithium species through the decomposed interface shows large variation depending on the polymer electrolyte system.
Y1  - 2021
U6  - https://doi.org/10.1039/d1ta05015j
SN  - 2050-7488
SN  - 2050-7496
VL  - 9
IS  - 39
SP  - 22462
EP  - 22471
PB  - Royal Society of Chemistry
CY  - Cambridge
ER  - 
TY  - JOUR
A1  - Smirnov, Lev A.
A1  - Bolotov, Maxim I.
A1  - Osipov, Grigorij V.
A1  - Pikovskij, Arkadij
T1  - Disorder fosters chimera in an array of motile particles
JF  - Physical review : E, Statistical, nonlinear and soft matter physics
N2  - We consider an array of nonlocally coupled oscillators on a ring, which for equally spaced units possesses a Kuramoto-Battogtokh chimera regime and a synchronous state. We demonstrate that disorder in oscillators positions leads to a transition from the synchronous to the chimera state. For a static (quenched) disorder we find that the probability of synchrony survival depends on the number of particles, from nearly zero at small populations to one in the thermodynamic limit. Furthermore, we demonstrate how the synchrony gets destroyed for randomly (ballistically or diffusively) moving oscillators. We show that, depending on the number of oscillators, there are different scalings of the transition time with this number and the velocity of the units.
Y1  - 2021
U6  - https://doi.org/10.1103/PhysRevE.104.034205
SN  - 2470-0045
SN  - 2470-0053
VL  - 104
IS  - 3
PB  - American Physical Society
CY  - Melville, NY
ER  - 
TY  - JOUR
A1  - Breternitz, Joachim
A1  - Schorr, Susan
T1  - Symmetry relations in wurtzite nitrides and oxide nitrides and the curious case of Pmc2(1)
JF  - Acta crystallographica / International Union of Crystallography. Section A, Foundations and advances
N2  - Binary III-V nitrides such as AlN, GaN and InN in the wurtzite-type structure have long been considered as potent semiconducting materials because of their optoelectronic properties, amongst others. With rising concerns over the utilization of scarce elements, a replacement of the trivalent cations by others in ternary and multinary nitrides has led to the development of different variants of nitrides and oxide nitrides crystallizing in lower-symmetry variants of wurtzite. This work presents the symmetry relationships between these structural types specific to nitrides and oxide nitrides and updates some prior work on this matter. The non-existence of compounds crystallizing in Pmc2(1), formally the highest subgroup of the wurtzite type fulfilling Pauling's rules for 1:1:2 stoichiometries, has been puzzling scientists for a while; a rationalization is given, from a crystallographic basis, of why this space group is unlikely to be adopted.
KW  - group-subgroup relationships
KW  - nitride materials
KW  - wurtzite type
Y1  - 2021
U6  - https://doi.org/10.1107/S2053273320015971
SN  - 2053-2733
VL  - 77
IS  - 3
SP  - 208
EP  - 216
PB  - Blackwell
CY  - Oxford [u.a.]
ER  - 
TY  - JOUR
A1  - Deb, Marwan
A1  - Molho, Pierre
A1  - Barbara, Bernard
T1  - Tunable exchange-bias-like effect in bi-substituted Gadolinium iron garnet film
JF  - Physical review applied
N2  - Using magneto-optical Faraday and Kerr measurements, we investigate the magnetic and magnetooptical properties of a thick Bi-substituted gadolinium iron garnet film over a broad range of wavelengths (250-850 nm) and temperatures (150-300 K), including the magnetization compensation point, TM. We observe an exchange-bias-like effect in the vicinity of TM. By slightly changing the sample temperature, we can precisely tune the bias field, which reaches a magnitude 6 times higher than the coercive field. We explain this phenomenon by considering the short-range superexchange interaction and a change in the magnetic behavior when moving from the surface to the bulk of the film. This finding may lead to the development of single-film magneto-optical devices based on the exchange-bias effect.
Y1  - 2021
U6  - https://doi.org/10.1103/PhysRevApplied.15.054064
SN  - 2331-7019
VL  - 15
IS  - 5
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Rodríguez Zuluaga, Juan
A1  - Stolle, Claudia
A1  - Yamazaki, Yosuke
A1  - Xiong, Chao
A1  - England, Scott L.
T1  - A synoptic-scale wavelike structure in the nighttime equatorial ionization anomaly
JF  - Earth and Space Science : ESS
N2  - Both ground- and satellite-based airglow imaging have significantly contributed to understanding the low-latitude ionosphere, especially the morphology and dynamics of the equatorial ionization anomaly (EIA). The NASA Global-scale Observations of the Limb and Disk (GOLD) mission focuses on far-ultraviolet airglow images from a geostationary orbit at 47.5 degrees W. This region is of particular interest at low magnetic latitudes because of the high magnetic declination (i.e., about -20 degrees) and proximity of the South Atlantic magnetic anomaly. In this study, we characterize an exciting feature of the nighttime EIA using GOLD observations from October 5, 2018 to June 30, 2020. It consists of a wavelike structure of a few thousand kilometers seen as poleward and equatorward displacements of the EIA-crests. Initial analyses show that the synoptic-scale structure is symmetric about the dip equator and appears nearly stationary with time over the night. In quasi-dipole coordinates, maxima poleward displacements of the EIA-crests are seen at about +/- 12 degrees latitude and around 20 and 60 degrees longitude (i.e., in geographic longitude at the dip equator, about 53 degrees W and 14 degrees W). The wavelike structure presents typical zonal wavelengths of about 6.7 x 10(3) km and 3.3 x 10(3) km. The structure's occurrence and wavelength are highly variable on a day-to-day basis with no apparent dependence on geomagnetic activity. In addition, a cluster or quasi-periodic wave train of equatorial plasma depletions (EPDs) is often detected within the synoptic-scale structure. We further outline the difference in observing these EPDs from FUV images and in situ measurements during a GOLD and Swarm mission conjunction.
KW  - equatorial ionization anomaly
KW  - equatorial ionosphere
KW  - equatorial plasma bubbles
KW  - wave structure
KW  - forcing from below
Y1  - 2021
U6  - https://doi.org/10.1029/2020EA001529
SN  - 2333-5084
VL  - 8
IS  - 2
PB  - American Geophysical Union
CY  - Malden, Mass.
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  - Bernardi, Rafael L.
A1  - Berdja, Amokrane
A1  - Dani Guzman, Christian
A1  - Torres-Torriti, Miguel
A1  - Roth, Martin M.
T1  - Restoration of images with a spatially varying PSF of the T80-S telescope optical model using neural networks
JF  - Monthly notices of the Royal Astronomical Society
N2  - Most image restoration methods in astronomy rely upon probabilistic tools that infer the best solution for a deconvolution problem. They achieve good performances when the point spread function (PSF) is spatially invariant in the image plane. 

However, this condition is not always satisfied in real optical systems. We propose a new method for the restoration of images affected by static and anisotropic aberrations using Deep Neural Networks that can be directly applied to sky images. 
The network is trained using simulated sky images corresponding to the T80-S Telescope optical model, a 80-cm survey imager at Cerro Tololo (Chile), which are synthesized using a Zernike polynomial representation of the optical system. 

Once trained, the network can be used directly on sky images, outputting a corrected version of the image that has a constant and known PSF across its field of view. The method is to be tested on the T80-S Telescope. 
We present the method and results on synthetic data.
KW  - methods: statistical
KW  - techniques: image processing
Y1  - 2021
U6  - https://doi.org/10.1093/mnras/stab3400
SN  - 0035-8711
SN  - 1365-2966
VL  - 510
IS  - 3
SP  - 4284
EP  - 4294
PB  - Oxford Univ. Press
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Zu, Fengshuo
A1  - Warby, Jonathan
A1  - Stolterfoht, Martin
A1  - Li, Jinzhao
A1  - Shin, Dongguen
A1  - Unger, Eva
A1  - Koch, Norbert
T1  - Photoinduced energy-level realignment at interfaces between organic semiconductors and metal-halide perovskites
JF  - Physical review letters
N2  - In contrast to the common conception that the interfacial energy-level alignment is affixed once the interface is formed, we demonstrate that heterojunctions between organic semiconductors and metal-halide perovskites exhibit huge energy-level realignment during photoexcitation. Importantly, the photoinduced level shifts occur in the organic component, including the first molecular layer in direct contact with the perovskite. This is caused by charge-carrier accumulation within the organic semiconductor under illumination and the weak electronic coupling between the junction components.
Y1  - 2021
U6  - https://doi.org/10.1103/PhysRevLett.127.246401
SN  - 0031-9007
SN  - 1079-7114
VL  - 127
IS  - 24
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Zeuschner, Steffen Peer
A1  - Mattern, Maximilian
A1  - Pudell, Jan-Etienne
A1  - Reppert, Alexander von
A1  - Rössle, Matthias
A1  - Leitenberger, Wolfram
A1  - Schwarzkopf, Jutta
A1  - Boschker, Jos
A1  - Herzog, Marc
A1  - Bargheer, Matias
T1  - Reciprocal space slicing
BT  - a time-efficient approach to femtosecond x-ray diffraction
JF  - Structural dynamics
N2  - An experimental technique that allows faster assessment of out-of-plane strain dynamics of thin film heterostructures via x-ray diffraction is presented. In contrast to conventional high-speed reciprocal space-mapping setups, our approach reduces the measurement time drastically due to a fixed measurement geometry with a position-sensitive detector. This means that neither the incident (ω) nor the exit (2θ) diffraction angle is scanned during the strain assessment via x-ray diffraction. Shifts of diffraction peaks on the fixed x-ray area detector originate from an out-of-plane strain within the sample. Quantitative strain assessment requires the determination of a factor relating the observed shift to the change in the reciprocal lattice vector. The factor depends only on the widths of the peak along certain directions in reciprocal space, the diffraction angle of the studied reflection, and the resolution of the instrumental setup. We provide a full theoretical explanation and exemplify the concept with picosecond strain dynamics of a thin layer of NbO2.
Y1  - 2020
U6  - https://doi.org/10.1063/4.0000040
SN  - 2329-7778
VL  - 8
IS  - 1
PB  - AIP Publishing LLC
CY  - Melville, NY
ER  - 
TY  - JOUR
A1  - Klose, Ann Kristin
A1  - Wunderling, Nico
A1  - Winkelmann, Ricarda
A1  - Donges, Jonathan
T1  - What do we mean, 'tipping cascade'?
JF  - Environmental research letters : ERL
N2  - Based on suggested interactions of potential tipping elements in the Earth's climate and in ecological systems, tipping cascades as possible dynamics are increasingly discussed and studied. The activation of such tipping cascades would impose a considerable risk for human societies and biosphere integrity. However, there are ambiguities in the description of tipping cascades within the literature so far. Here we illustrate how different patterns of multiple tipping dynamics emerge from a very simple coupling of two previously studied idealized tipping elements. In particular, we distinguish between a two phase cascade, a domino cascade and a joint cascade. A mitigation of an unfolding two phase cascade may be possible and common early warning indicators are sensitive to upcoming critical transitions to a certain degree. In contrast, a domino cascade may hardly be stopped once initiated and critical slowing down-based indicators fail to indicate tipping of the following element. These different potentials for intervention and anticipation across the distinct patterns of multiple tipping dynamics should be seen as a call to be more precise in future analyses of cascading dynamics arising from tipping element interactions in the Earth system.
KW  - tipping cascade
KW  - domino effect
KW  - tipping interactions
KW  - cascading regime
KW  - shifts
KW  - early warning indicators
Y1  - 2021
U6  - https://doi.org/10.1088/1748-9326/ac3955
SN  - 1748-9326
VL  - 16
IS  - 12
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Zheng, Chunming
A1  - Tönjes, Ralf
A1  - Pikovskij, Arkadij
T1  - Transition to synchrony in a three-dimensional swarming model with helical trajectories
JF  - Physical review : E, Statistical, nonlinear and soft matter physics
N2  - We investigate the transition from incoherence to global collective motion in a three-dimensional swarming model of agents with helical trajectories, subject to noise and global coupling. Without noise this model was recently proposed as a generalization of the Kuramoto model and it was found that alignment of the velocities occurs discontinuously for arbitrarily small attractive coupling. Adding noise to the system resolves this singular limit and leads to a continuous transition, either to a directed collective motion or to center-of-mass rotations.
Y1  - 2021
U6  - https://doi.org/10.1103/PhysRevE.104.014216
SN  - 2470-0045
SN  - 2470-0053
VL  - 104
IS  - 1
PB  - American Physical Society
CY  - College Park
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  - Kleinpeter, Erich
A1  - Koch, Andreas
T1  - Quantification of sigma-acceptor and pi-donor stabilization in O, S and Hal analogues of N-heterocyclic carbenes (NHCs) on the magnetic criterion
JF  - The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment & general theory
N2  - The spatial magnetic properties, through-space NMR shieldings (TSNMRSs), of stable O, S and Hal analogues of N-heterocyclic carbenes (NHCs) have been calculated using the GIAO perturbation method employing the nucleus-independent chemical shift (NICS) concept and the results visualized as iso-chemical-shielding surfaces (ICSSs) of various sizes and directions. The TSNMRS values (actually the anisotropy effects measurable in H-1 NMR spectroscopy) are employed to qualify and quantify the position of the present mesomeric equilibria (carbenes <-> ylides). The results are confirmed by geometry (bond angles and bond lengths), IR spectra, UV spectra, and C-13 chemical shifts of the electron-deficient carbon centers.
Y1  - 2021
U6  - https://doi.org/10.1021/acs.jpca.1c05257
SN  - 1089-5639
SN  - 1520-5215
VL  - 125
IS  - 33
SP  - 7235
EP  - 7245
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Petreska, Irina
A1  - Sandev, Trifce
A1  - Lenzi, Ervin Kaminski
T1  - Comb-like geometric constraints leading to emergence of the time-fractional Schrödinger equation
JF  - Modern physics letters : A, Particles and fields, gravitation, cosmology, nuclear physics
N2  - This paper presents an overview over several examples, where the comb-like geometric constraints lead to emergence of the time-fractional Schrodinger equation. Motion of a quantum object on a comb structure is modeled by a suitable modification of the kinetic energy operator, obtained by insertion of the Dirac delta function in the Laplacian. First, we consider motion of a free particle on two- and three-dimensional comb structures, and then we extend the study to the interacting cases. A general form of a nonlocal term, which describes the interactions of the particle with the medium, is included in the Hamiltonian, and later on, the cases of constant and Dirac delta potentials are analyzed. At the end, we discuss the case of non-integer dimensions, considering separately the case of fractal dimension between one and two, and the case of fractal dimension between two and three. All these examples show that even though we are starting with the standard time-dependent Schrodinger equation on a comb, the time-fractional equation for the Green's functions appears, due to these specific geometric constraints.
KW  - Comb model
KW  - time-fractional Schrödinger equation
KW  - Green’ s functions
Y1  - 2021
U6  - https://doi.org/10.1142/S0217732321300056
SN  - 0217-7323
SN  - 1793-6632
VL  - 36
IS  - 14
PB  - World Scientific
CY  - Singapore
ER  - 
TY  - JOUR
A1  - Bouakline, Foudhil
A1  - Saalfrank, Peter
T1  - Seemingly asymmetric atom-localized electronic densities following laser-dissociation of homonuclear diatomics
JF  - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistry
N2  - Recent experiments on laser-dissociation of aligned homonuclear diatomic molecules show an asymmetric forward-backward (spatial) electron-localization along the laser polarization axis. Most theoretical models attribute this asymmetry to interference effects between gerade and ungerade vibronic states. Presumably due to alignment, these models neglect molecular rotations and hence infer an asymmetric (post-dissociation) charge distribution over the two identical nuclei. In this paper, we question the equivalence that is made between spatial electron-localization, observed in experiments, and atomic electron-localization, alluded by these theoretical models. We show that (seeming) agreement between these models and experiments is due to an unfortunate omission of nuclear permutation symmetry, i.e., quantum statistics. Enforcement of the latter requires mandatory inclusion of the molecular rotational degree of freedom, even for perfectly aligned molecules. Unlike previous interpretations, we ascribe spatial electron-localization to the laser creation of a rovibronic wavepacket that involves field-free molecular eigenstates with opposite space-inversion symmetry i.e., even and odd parity. Space-inversion symmetry breaking would then lead to an asymmetric distribution of the (space-fixed) electronic density over the forward and backward hemisphere. However, owing to the simultaneous coexistence of two indistinguishable molecular orientational isomers, our analytical and computational results show that the post-dissociation electronic density along a specified space-fixed axis is equally shared between the two identical nuclei-a result that is in perfect accordance with the principle of the indistinguishability of identical particles. Published under an exclusive license by AIP Publishing.
Y1  - 2021
U6  - https://doi.org/10.1063/5.0049710
SN  - 0021-9606
SN  - 1089-7690
VL  - 154
IS  - 23
PB  - American Institute of Physics
CY  - Melville
ER  - 
TY  - JOUR
A1  - Omel'chenko, Oleh
A1  - Ocampo-Espindola, Jorge Luis
A1  - Kiss, István Z.
T1  - Asymmetry-induced isolated fully synchronized state in coupled oscillator populations
JF  - Physical review : E, Statistical, nonlinear and soft matter physics
N2  - A symmetry-breaking mechanism is investigated that creates bistability between fully and partially synchronized states in oscillator networks. Two populations of oscillators with unimodal frequency distribution and different amplitudes, in the presence of weak global coupling, are shown to simplify to a modular network with asymmetrical coupling. With increasing the coupling strength, a synchronization transition is observed with an isolated fully synchronized state. The results are interpreted theoretically in the thermodynamic limit and confirmed in experiments with chemical oscillators.
Y1  - 2021
U6  - https://doi.org/10.1103/PhysRevE.104.L022202
SN  - 2470-0045
SN  - 2470-0053
VL  - 104
IS  - 2
PB  - American Physical Society
CY  - Melville, NY
ER  - 
TY  - JOUR
A1  - Fischer, Eric Wolfgang
A1  - Saalfrank, Peter
T1  - A thermofield-based multilayer multiconfigurational time-dependent Hartree approach to non-adiabatic quantum dynamics at finite temperature
JF  - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistry
N2  - We introduce a thermofield-based formulation of the multilayer multiconfigurational time-dependent Hartree (MCTDH) method to study finite temperature effects on non-adiabatic quantum dynamics from a non-stochastic, wave function perspective. Our approach is based on the formal equivalence of bosonic many-body theory at zero temperature with a doubled number of degrees of freedom and the thermal quasi-particle representation of bosonic thermofield dynamics (TFD). This equivalence allows for a transfer of bosonic many-body MCTDH as introduced by Wang and Thoss to the finite temperature framework of thermal quasi-particle TFD. As an application, we study temperature effects on the ultrafast internal conversion dynamics in pyrazine. We show that finite temperature effects can be efficiently accounted for in the construction of multilayer expansions of thermofield states in the framework presented herein. Furthermore, we find our results to agree well with existing studies on the pyrazine model based on the pMCTDH method.
Y1  - 2021
U6  - https://doi.org/10.1063/5.0064013
SN  - 0021-9606
SN  - 1089-7690
VL  - 155
IS  - 13
PB  - American Institute of Physics
CY  - Melville
ER  - 
TY  - JOUR
A1  - Dahlenburg, Marcus
A1  - Chechkin, Aleksei
A1  - Schumer, Rina
A1  - Metzler, Ralf
T1  - Stochastic resetting by a random amplitude
JF  - Physical review : E, Statistical, nonlinear and soft matter physics
N2  - Stochastic resetting, a diffusive process whose amplitude is reset to the origin at random times, is a vividly studied strategy to optimize encounter dynamics, e.g., in chemical reactions. Here we generalize the resetting step by introducing a random resetting amplitude such that the diffusing particle may be only partially reset towards the trajectory origin or even overshoot the origin in a resetting step. We introduce different scenarios for the random-amplitude stochastic resetting process and discuss the resulting dynamics. Direct applications are geophysical layering (stratigraphy) and population dynamics or financial markets, as well as generic search processes.
Y1  - 2021
U6  - https://doi.org/10.1103/PhysRevE.103.052123
SN  - 2470-0045
SN  - 2470-0053
VL  - 103
IS  - 5
PB  - American Physical Society
CY  - Woodbury, NY
ER  - 
TY  - JOUR
A1  - Milde, Peter
A1  - Langenhorst, Malte
A1  - Hölscher, Hendrik
A1  - Rottmann-Matthes, Jens
A1  - Hundertmark, Dirk
A1  - Eng, Lukas
A1  - Hoffmann-Vogel, Regina
T1  - Out-of-equilibrium optomechanical resonance self-excitation
JF  - Journal of applied physics
N2  - The fundamental sensitivity limit of atomic force microscopy is strongly correlated to the thermal noise of cantilever oscillation. A method to suppress this unwanted noise is to reduce the bandwidth of the measurement, but this approach is limited by the speed of the measurement and the width of the cantilever resonance, commonly defined through the quality factor Q. However, it has been shown that optomechanical resonances in interferometers might affect cantilever oscillations resulting in an effective quality factor Q(eff). When the laser power is sufficiently increased cantilever oscillations might even reach the regime of self-oscillation. In this self-oscillation state, the noise of the system is partially determined by the interaction with laser light far from equilibrium. Here, we show and discuss how tuning of laser power leads to nonlinear optomechanical effects that can dramatically increase the effective quality factor of the cantilever leading to out-of-equilibrium noise. We model the effects using a fourth order nonlinearity of the damping coefficient. Published under an exclusive license by AIP Publishing.
KW  - Electrical properties and parameters
KW  - Ultra-high vacuum
KW  - Electronic noise
KW  - Signal processing
KW  - Noise floor
KW  - Atomic force microscopy
KW  - Hooke's law
KW  - Interferometry
KW  - Optical resonators
KW  - Thermo optic effects
Y1  - 2021
U6  - https://doi.org/10.1063/5.0054509
SN  - 0021-8979
SN  - 1089-7550
VL  - 130
IS  - 3
PB  - American Institute of Physics
CY  - Melville
ER  - 
TY  - JOUR
A1  - Chigarev, Vladimir
A1  - Kazakov, Alexey
A1  - Pikovskij, Arkadij
T1  - Mutual singularities of overlapping attractor and repeller
JF  - Chaos : an interdisciplinary journal of nonlinear science
N2  - We apply the concepts of relative dimensions and mutual singularities to characterize the fractal properties of overlapping attractor and repeller in chaotic dynamical systems. We consider one analytically solvable example (a generalized baker's map); two other examples, the Anosov-Mobius and the Chirikov-Mobius maps, which possess fractal attractor and repeller on a two-dimensional torus, are explored numerically. We demonstrate that although for these maps the stable and unstable directions are not orthogonal to each other, the relative Renyi and Kullback-Leibler dimensions as well as the mutual singularity spectra for the attractor and repeller can be well approximated under orthogonality assumption of two fractals.
Y1  - 2021
U6  - https://doi.org/10.1063/5.0056891
SN  - 1054-1500
SN  - 1089-7682
VL  - 31
IS  - 8
PB  - American Institute of Physics
CY  - Melville
ER  - 
TY  - JOUR
A1  - Kluge, Lucas
A1  - Socolar, Joshua E. S.
A1  - Schöll, Eckehard
T1  - Random logic networks
BT  - from classical Boolean to quantum dynamics
JF  - Physical review : E, Statistical, nonlinear and soft matter physics
N2  - We investigate dynamical properties of a quantum generalization of classical reversible Boolean networks. The state of each node is encoded as a single qubit, and classical Boolean logic operations are supplemented by controlled bit-flip and Hadamard operations. We consider synchronous updating schemes in which each qubit is updated at each step based on stored values of the qubits from the previous step. We investigate the periodic or quasiperiodic behavior of quantum networks, and we analyze the propagation of single site perturbations through the quantum networks with input degree one. A nonclassical mechanism for perturbation propagation leads to substantially different evolution of the Hamming distance between the original and perturbed states.
Y1  - 2021
U6  - https://doi.org/10.1103/PhysRevE.104.064308
SN  - 2470-0045
SN  - 2470-0053
VL  - 104
IS  - 6
PB  - American Physical Society
CY  - Woodbury, NY
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. <br /> 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  - 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  - Mardoukhi, Yousof
A1  - Chechkin, Aleksei V.
A1  - Metzler, Ralf
T1  - Spurious ergodicity breaking in normal and fractional Ornstein–Uhlenbeck process
JF  - New Journal of Physics
N2  - The Ornstein–Uhlenbeck process is a stationary and ergodic Gaussian process, that is fully determined by its covariance function and mean. We show here that the generic definitions of the ensemble- and time-averaged mean squared displacements fail to capture these properties consistently, leading to a spurious ergodicity breaking. We propose to remedy this failure by redefining the mean squared displacements such that they reflect unambiguously the statistical properties of any stochastic process. In particular we study the effect of the initial condition in the Ornstein–Uhlenbeck process and its fractional extension. For the fractional Ornstein–Uhlenbeck process representing typical experimental situations in crowded environments such as living biological cells, we show that the stationarity of the process delicately depends on the initial condition.
KW  - Ornstein–Uhlenbeck process
KW  - stationary stochastic process
KW  - ensemble and time averaged mean squared displacement
Y1  - 2020
U6  - https://doi.org/10.1088/1367-2630/ab950b
SN  - 1367-2630
VL  - 22
PB  - IOP
CY  - London
ER  - 
TY  - JOUR
A1  - Marschall, Raphael
A1  - Skorov, Yuri
A1  - Zakharov, Vladimir
A1  - Rezac, Ladislav
A1  - Gerig, Selina-Barbara
A1  - Christou, Chariton
A1  - Dadzie, S. Kokou
A1  - Migliorini, Alessandra
A1  - Rinaldi, Giovanna
A1  - Agarwal, Jessica
A1  - Vincent, Jean-Baptiste
A1  - Kappel, David
T1  - Cometary comae-surface links the physics of gas and dust from the surface to a spacecraft
JF  - Space science reviews
N2  - A comet is a highly dynamic object, undergoing a permanent state of change. These changes have to be carefully classified and considered according to their intrinsic temporal and spatial scales. The Rosetta mission has, through its contiguous in-situ and remote sensing coverage of comet 67P/Churyumov-Gerasimenko (hereafter 67P) over the time span of August 2014 to September 2016, monitored the emergence, culmination, and winding down of the gas and dust comae. This provided an unprecedented data set and has spurred a large effort to connect in-situ and remote sensing measurements to the surface. In this review, we address our current understanding of cometary activity and the challenges involved when linking comae data to the surface. We give the current state of research by describing what we know about the physical processes involved from the surface to a few tens of kilometres above it with respect to the gas and dust emission from cometary nuclei. Further, we describe how complex multidimensional cometary gas and dust models have developed from the Halley encounter of 1986 to today. This includes the study of inhomogeneous outgassing and determination of the gas and dust production rates. Additionally, the different approaches used and results obtained to link coma data to the surface will be discussed. We discuss forward and inversion models and we describe the limitations of the respective approaches. The current literature suggests that there does not seem to be a single uniform process behind cometary activity. Rather, activity seems to be the consequence of a variety of erosion processes, including the sublimation of both water ice and more volatile material, but possibly also more exotic processes such as fracture and cliff erosion under thermal and mechanical stress, sub-surface heat storage, and a complex interplay of these processes. Seasons and the nucleus shape are key factors for the distribution and temporal evolution of activity and imply that the heliocentric evolution of activity can be highly individual for every comet, and generalisations can be misleading.
KW  - comets
KW  - coma
KW  - gas
KW  - dust
KW  - dynamics
KW  - modelling
KW  - inversion
Y1  - 2020
U6  - https://doi.org/10.1007/s11214-020-00744-0
SN  - 0038-6308
SN  - 1572-9672
VL  - 216
IS  - 8
PB  - Springer
CY  - Dordrecht
ER  - 
TY  - JOUR
A1  - Haubitz, Toni
A1  - Fudickar, Werner
A1  - Linker, Torsten
A1  - Kumke, Michael Uwe
T1  - pH-sensitive fluorescence switching of pyridylanthracenes
BT  - the effect of the isomeric pattern
JF  - The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment & general theory
N2  - 9,10-substituted anthracenes are known for their useful optical properties like fluorescence, which makes them frequently used probes in sensing applications. In this article, we investigate the fundamental photophysical properties of three pyridyl-substituted variants. The nitrogen atoms in the pyridinium six-membered rings are located in the ortho-, meta-, and para-positions in relation to the anthracene core. Absorption, fluorescence, and transient absorption measurements were carried out and were complemented by theoretical calculations. We monitored the photophysics of the anthracene derivatives in chloroform and water investigating the protonated as well as their nonprotonated forms. We found that the optical properties of the nonprotonated forms are strongly determined by the anthracene chromophore, with only small differences to other 9,10-substituted anthracenes, for example diphenyl anthracene. In contrast, protonation leads to a strong decrease in fluorescence intensity and lifetime. Transient absorption measurements and theoretical calculations revealed the formation of a charge-transfer state in the protonated chromophores, where electron density is shifted from the anthracene moiety toward the protonated pyridyl substituents. While the para- and ortho-derivatives' charge transfer is still moderately fluorescent, the meta-derivative is affected much stronger and shows nearly no fluorescence. This nitrogen-atom-position-dependent sensitivity to hydronium activity makes a combination of these fluorophores very attractive for pH-sensing applications covering a broadened pH range.
KW  - Absorption
KW  - Aromatic compounds
KW  - Fluorescence
KW  - Hydrocarbons
KW  - Reaction mechanisms
Y1  - 2020
U6  - https://doi.org/10.1021/acs.jpca.0c09911
SN  - 1089-5639
SN  - 1520-5215
VL  - 124
IS  - 52
SP  - 11017
EP  - 11024
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Malass, Ihsane
A1  - Tarkhanov, Nikolaj Nikolaevič
T1  - A perturbation of the de Rham complex
T1  - Возмущение комплекса де Рама
JF  - Journal of Siberian Federal University : Mathematics & Physics
JF  - Žurnal Sibirskogo Federalʹnogo Universiteta : Matematika i fizika
N2  - We consider a perturbation of the de Rham complex on a compact manifold with boundary. This perturbation goes beyond the framework of complexes, and so cohomology does not apply to it. On the other hand, its curvature is "small", hence there is a natural way to introduce an Euler characteristic and develop a Lefschetz theory for the perturbation. This work is intended as an attempt to develop a cohomology theory for arbitrary sequences of linear mappings.
N2  - Рассмотрим возмущение комплекса де Рама на компактном многообразии с краем. Это возмущение выходит за рамки комплексов, и поэтому когомологии к нему не относятся. С другой стороны, его кривизна "мала", поэтому существует естественный способ ввести характеристику Эйлера и разработать теорию Лефшеца для возмущения. Данная работа предназначена для попытки разработать теорию когомологий для произвольных последовательностей линейных отображений.
KW  - de Rham complex
KW  - cohomology
KW  - Hodge theory
KW  - Neumann problem
KW  - комплекс де Рама
KW  - когомологии
KW  - теория Ходжа
KW  - проблема Неймана
Y1  - 2020
U6  - https://doi.org/10.17516/1997-1397-2020-13-5-519-532
SN  - 1997-1397
SN  - 2313-6022
VL  - 13
IS  - 5
SP  - 519
EP  - 532
PB  - Siberian Federal University
CY  - Krasnojarsk
ER  - 
TY  - JOUR
A1  - Abdalla, Hassan E.
A1  - Adam, Remi
A1  - Aharonian, Felix A.
A1  - Benkhali, Faical Ait
A1  - Angüner, Ekrem Oǧuzhan
A1  - Arakawa, Masanori
A1  - Arcaro, C
A1  - Armand, Catherine
A1  - Armstrong, T.
A1  - Egberts, Kathrin
T1  - Very high energy γ-ray emission from two blazars of unknown redshift and upper limits on their distance
JF  - Monthly Notices of the Royal Astronomical Society
N2  - We report on the detection of very high energy (VHE; E > 100 GeV) gamma-ray emission from the BL Lac objects KUV 00311-1938 and PKS 1440-389 with the High Energy Stereoscopic System (H.E.S.S.). H.E.S.S. observations were accompanied or preceded by multiwavelength observations with Fermi/LAT, XRT and UVOT onboard the Swift satellite, and ATOM. Based on an extrapolation of the Fermi/LAT spectrum towards the VHE gamma-ray regime, we deduce a 95 per cent confidence level upper limit on the unknown redshift of KUV 00311-1938 of z < 0.98 and of PKS 1440-389 of z < 0.53. When combined with previous spectroscopy results, the redshift of KUV 00311-1938 is constrained to 0.51 <= z < 0.98 and of PKS 1440-389 to 0.14 (sic) z < 0.53.
KW  - BL Lacertae objects: individual
KW  - galaxies: high-redshift
KW  - gamma-rays: general
KW  - Resolved and unresolved sources as a function of wavelength
Y1  - 2020
VL  - 494
IS  - 4
PB  - Wiley-Blackwell
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Schirdewahn, Daniel
T1  - Stability of a parametric harmonic oscillator with dichotomic noise
JF  - Chaos : an interdisciplinary journal of nonlinear science
N2  - The harmonic oscillator is a powerful model that can appear as a limit case when examining a nonlinear system. A well known fact is that, without driving, the inclusion of a friction term makes the origin of the phase space-which is a fixed point of the system-linearly stable. In this work, we include a telegraph process as perturbation of the oscillator's frequency, for example, to describe the motion of a particle with fluctuating charge gyrating in an external magnetic field. Increasing intensity of this colored noise is capable of changing the quality of the fixed point. To characterize the stability of the system, we use a stability measure that describes the growth of the displacement of the system's phase space position and express it in a closed form. We expand the respective exponent for light friction and low noise intensity and compare both the exact analytic solution and the expansion to numerical values. Our findings allow stability predictions for several physical systems.
Y1  - 2020
U6  - https://doi.org/10.1063/5.0012946
SN  - 1054-1500
SN  - 1089-7682
VL  - 30
IS  - 9
PB  - American Institute of Physics
CY  - Melville
ER  - 
TY  - JOUR
A1  - Rosenblum, Michael
T1  - Controlling collective synchrony in oscillatory ensembles by precisely timed pulses
JF  - Chaos : an interdisciplinary journal of nonlinear science
N2  - We present an efficient technique for control of synchrony in a globally coupled ensemble by pulsatile action. We assume that we can observe the collective oscillation and can stimulate all elements of the ensemble simultaneously. We pay special attention to the minimization of intervention into the system. The key idea is to stimulate only at the most sensitive phase. To find this phase, we implement an adaptive feedback control. Estimating the instantaneous phase of the collective mode on the fly, we achieve efficient suppression using a few pulses per oscillatory cycle. We discuss the possible relevance of the results for neuroscience, namely, for the development of advanced algorithms for deep brain stimulation, a medical technique used to treat Parkinson's disease.
Y1  - 2020
U6  - https://doi.org/10.1063/5.0019823
SN  - 1054-1500
SN  - 1089-7682
VL  - 30
IS  - 9
PB  - American Institute of Physics
CY  - Melville
ER  - 
TY  - JOUR
A1  - Xu, Pengbo
A1  - Zhou, Tian
A1  - Metzler, Ralf
A1  - Deng, Weihua
T1  - Lévy walk dynamics in an external harmonic potential
JF  - Physical review : E, Statistical, nonlinear, and soft matter physics
N2  - Levy walks (LWs) are spatiotemporally coupled random-walk processes describing superdiffusive heat conduction in solids, propagation of light in disordered optical materials, motion of molecular motors in living cells, or motion of animals, humans, robots, and viruses. We here investigate a key feature of LWs-their response to an external harmonic potential. In this generic setting for confined motion we demonstrate that LWs equilibrate exponentially and may assume a bimodal stationary distribution. We also show that the stationary distribution has a horizontal slope next to a reflecting boundary placed at the origin, in contrast to correlated superdiffusive processes. Our results generalize LWs to confining forces and settle some longstanding puzzles around LWs.
Y1  - 2020
U6  - https://doi.org/10.1103/PhysRevE.101.062127
SN  - 2470-0045
SN  - 2470-0053
SN  - 1550-2376
SN  - 1063-651X
SN  - 1539-3755
VL  - 101
IS  - 6
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Quade, Markus
A1  - Isele, Thomas
A1  - Abel, Markus
T1  - Machine learning control
BT  - explainable and analyzable methods
JF  - Physica : D, Nonlinear phenomena
N2  - Recently, the term explainable AI came into discussion as an approach to produce models from artificial intelligence which allow interpretation. For a long time, symbolic regression has been used to produce explainable and mathematically tractable models. In this contribution, we extend previous work on symbolic regression methods to infer the optimal control of a dynamical system given one or several optimization criteria, or cost functions. In earlier publications, network control was achieved by automated machine learning control using genetic programming. Here, we focus on the subsequent path continuation analysis of the mathematical expressions which result from the machine learning model. In particular, we use AUTO to analyze the solution properties of the controlled oscillator system which served as our model. As a result, we show that there is a considerable advantage of explainable symbolic regression models over less accessible neural networks. In particular, the roadmap of future works may be to integrate such analyses into the optimization loop itself to filter out robust solutions by construction.
KW  - Explainable AI
KW  - Machine learning control
KW  - Dynamical systems
KW  - Synchronization control
KW  - Genetic programming
Y1  - 2020
U6  - https://doi.org/10.1016/j.physd.2020.132582
SN  - 0167-2789
SN  - 1872-8022
VL  - 412
PB  - Elsevier
CY  - Amsterdam
ER  - 
TY  - JOUR
A1  - Sangian, Danial
T1  - Improving the performance of dielectric-elastomer actuators at elevated operating temperatures by means of thermal softening
JF  - Smart materials and structures
N2  - Dielectric elastomer devices operate on the principle of Maxwell stress and their operating performance significantly rely on the elastomer and compliant electrode's electrical and mechanical properties. This paper reports that performing actuation tests at elevated temperatures resulted in an enhanced performance due to the reduction of Young's modulus and the increase of dielectric permittivity. As a result, considerably higher isometric forces and isotonic strains were achieved above the ambient operating temperature. For actuators made of silicone, polyurethane and acrylic elastomers, 166%, 70% and 266% higher isometric forces and 450%, 250% and 54% higher isotonic strains were observed, respectively, when tested at the temperature of 100 degrees C in comparison to ambient temperature values using the same operating voltages. Values of up to 0.4 J kg(-1) and 3.1 W kg(-1) were achieved for the work and power outputs per mass, respectively, on a silicone elastomer driven with a voltage of 1.5 kV at a temperature of 100 degrees C.
KW  - elevated-temperature effects on the operation of dielectric-elastomer
KW  - actuators
KW  - thermally enhanced actuators
KW  - thermal stimulation of
KW  - electro-electrets
Y1  - 2020
U6  - https://doi.org/10.1088/1361-665X/ab6079
SN  - 0964-1726
SN  - 1361-665X
VL  - 29
IS  - 2
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Perovic, Milena
A1  - Qin, Qing
A1  - Oschatz, Martin
T1  - From molecular precursors to nanoparticles
BT  - tailoring the adsorption properties of porous carbon materials by controlled chemical functionalization
JF  - Advanced functional materials
N2  - Nanoporous carbon materials (NCMs) provide the "function" of high specific surface area and thus have large interface area for interactions with surrounding species, which is of particular importance in applications related to adsorption processes. The strength and mechanism of adsorption depend on the pore architecture of the NCMs. In addition, chemical functionalization can be used to induce changes of electron density and/or electron density distribution in the pore walls, thus further modifying the interactions between carbons and guest species. Typical approaches for functionalization of nanoporous materials with regular atomic construction like porous silica, metal-organic frameworks, or zeolites, cannot be applied to NCMs due to their less defined local atomic construction and abundant defects. Therefore, synthetic strategies that offer a higher degree of control over the process of functionalization are needed. Synthetic approaches for covalent functionalization of NCMs, that is, for the incorporation of heteroatoms into the carbon backbone, are critically reviewed with a special focus on strategies following the concept "from molecules to materials." Approaches for coordinative functionalization with metallic species, and the functionalization by nanocomposite formation between pristine carbon materials and heteroatom-containing carbons, are introduced as well. Particular focus is given to the influences of these functionalizations in adsorption-related applications.
KW  - composites
KW  - heteroatoms
KW  - metal species
KW  - porous carbon materials
KW  - surface
KW  - functionalization
Y1  - 2020
U6  - https://doi.org/10.1002/adfm.201908371
SN  - 1616-301X
SN  - 1616-3028
VL  - 30
IS  - 41
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Fumani, F. Khastehdel
A1  - Nemati, Somayyeh
A1  - Mahdavifar, Saeed
T1  - Quantum critical lines in the ground state phase diagram of spin-1/2 frustrated transverse-field ising chains
JF  - Annalen der Physik
N2  - This paper focuses on the ground state phase diagram of a 1D spin-1/2 quantum Ising model with competing first and second nearest neighbour interactions known as the axial next nearest neighbour Ising model in the presence of a transverse magnetic field. Here, using quantum correlations, both numerically and analytically, some evidence is provided to clarify the identification of the ground state phase diagram. Local quantum correlations play a crucial role in detecting the critical lines either revealed or hidden by symmetry-breaking. A non-symmetry-breaking disorder transition line can be identified by the first derivative of both entanglement of formation and quantum discord between nearest neighbour spins. In addition, the quantum correlations between the second neighbour spins can also be used to reveal Kosterlitz-Thouless phase transition when their interaction strength grows and becomes closer to the first nearest neighbour one. The results obtained using the Jordan-Wigner transformation confirm the accuracy of the numerical case.
KW  - axial next nearest neighbour Ising chains
KW  - quantum correlations
KW  - quantum
KW  - phase transitions
Y1  - 2020
U6  - https://doi.org/10.1002/andp.202000384
SN  - 0003-3804
SN  - 1521-3889
VL  - 533
IS  - 2
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Siddiqi, Muhammad Ali
A1  - Dörr, Christian
A1  - Strydis, Christos
T1  - IMDfence
BT  - architecting a secure protocol for implantable medical devices
JF  - IEEE access
N2  - Over the past decade, focus on the security and privacy aspects of implantable medical devices (IMDs) has intensified, driven by the multitude of cybersecurity vulnerabilities found in various existing devices. However, due to their strict computational, energy and physical constraints, conventional security protocols are not directly applicable to IMDs. Custom-tailored schemes have been proposed instead which, however, fail to cover the full spectrum of security features that modern IMDs and their ecosystems so critically require. In this paper we propose IMDfence, a security protocol for IMD ecosystems that provides a comprehensive yet practical security portfolio, which includes availability, non-repudiation, access control, entity authentication, remote monitoring and system scalability. The protocol also allows emergency access that results in the graceful degradation of offered services without compromising security and patient safety. The performance of the security protocol as well as its feasibility and impact on modern IMDs are extensively analyzed and evaluated. We find that IMDfence achieves the above security requirements at a mere less than 7% increase in total IMD energy consumption, and less than 14 ms and 9 kB increase in system delay and memory footprint, respectively.
KW  - protocols
KW  - implants
KW  - authentication
KW  - ecosystems
KW  - remote monitoring
KW  - scalability
KW  - authentication protocol
KW  - battery-depletion attack
KW  - battery
KW  - DoS
KW  - denial-of-service attack
KW  - IMD
KW  - implantable medical device
KW  - non-repudiation
KW  - smart card
KW  - zero-power defense
Y1  - 2020
U6  - https://doi.org/10.1109/ACCESS.2020.3015686
SN  - 2169-3536
VL  - 8
SP  - 147948
EP  - 147964
PB  - Institute of Electrical and Electronics Engineers
CY  - Piscataway
ER  - 
TY  - JOUR
A1  - Laing, Carlo R.
A1  - Omel'chenko, Oleh
T1  - Moving bumps in theta neuron networks
JF  - Chaos : an interdisciplinary journal of nonlinear science
N2  - We consider large networks of theta neurons on a ring, synaptically coupled with an asymmetric kernel. Such networks support stable "bumps" of activity, which move along the ring if the coupling kernel is asymmetric. We investigate the effects of the kernel asymmetry on the existence, stability, and speed of these moving bumps using continuum equations formally describing infinite networks. Depending on the level of heterogeneity within the network, we find complex sequences of bifurcations as the amount of asymmetry is varied, in strong contrast to the behavior of a classical neural field model.
Y1  - 2020
U6  - https://doi.org/10.1063/1.5143261
SN  - 1054-1500
SN  - 1089-7682
VL  - 30
IS  - 4
PB  - American Institute of Physics
CY  - Melville
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  - 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  - Fernandez, Amanda Diez
A1  - Charchar, Patrick
A1  - Cherstvy, Andrey G.
A1  - Metzler, Ralf
A1  - Finnis, Michael W.
T1  - The diffusion of doxorubicin drug molecules in silica nanoslits is non-Gaussian, intermittent and anticorrelated
JF  - Physical chemistry, chemical physics
N2  - In this study we investigate, using all-atom molecular-dynamics computer simulations, the in-plane diffusion of a doxorubicin drug molecule in a thin film of water confined between two silica surfaces. We find that the molecule diffuses along the channel in the manner of a Gaussian diffusion process, but with parameters that vary according to its varying transversal position. Our analysis identifies that four Gaussians, each describing particle motion in a given transversal region, are needed to adequately describe the data. Each of these processes by itself evolves with time at a rate slower than that associated with classical Brownian motion due to a predominance of anticorrelated displacements. Long adsorption events lead to ageing, a property observed when the diffusion is intermittently hindered for periods of time with an average duration which is theoretically infinite. This study presents a simple system in which many interesting features of anomalous diffusion can be explored. It exposes the complexity of diffusion in nanoconfinement and highlights the need to develop new understanding.
Y1  - 2020
U6  - https://doi.org/10.1039/d0cp03849k
SN  - 1463-9076
SN  - 1463-9084
VL  - 22
IS  - 48
SP  - 27955
EP  - 27965
PB  - Royal Society of Chemistry
CY  - Cambridge
ER  - 
TY  - JOUR
A1  - Omelʹchenko, Oleh E.
T1  - Nonstationary coherence-incoherence patterns in nonlocally coupled heterogeneous phase oscillators
JF  - Chaos : an interdisciplinary journal of nonlinear science
N2  - We consider a large ring of nonlocally coupled phase oscillators and show that apart from stationary chimera states, this system also supports nonstationary coherence-incoherence patterns (CIPs). For identical oscillators, these CIPs behave as breathing chimera states and are found in a relatively small parameter region only. It turns out that the stability region of these states enlarges dramatically if a certain amount of spatially uniform heterogeneity (e.g., Lorentzian distribution of natural frequencies) is introduced in the system. In this case, nonstationary CIPs can be studied as stable quasiperiodic solutions of a corresponding mean-field equation, formally describing the infinite system limit. Carrying out direct numerical simulations of the mean-field equation, we find different types of nonstationary CIPs with pulsing and/or alternating chimera-like behavior. Moreover, we reveal a complex bifurcation scenario underlying the transformation of these CIPs into each other. These theoretical predictions are confirmed by numerical simulations of the original coupled oscillator system.
KW  - chimera states
KW  - synchronization
KW  - networks
KW  - Kuramoto
KW  - populations
KW  - dynamics
KW  - bumps
KW  - model
Y1  - 2020
U6  - https://doi.org/10.1063/1.5145259
SN  - 1054-1500
SN  - 1089-7682
VL  - 30
IS  - 4
PB  - American Institute of Physics
CY  - Melville
ER  - 
TY  - JOUR
A1  - Wang, Wei
A1  - Cherstvy, Andrey G.
A1  - Chechkin, Aleksei V.
A1  - Thapa, Samudrajit
A1  - Seno, Flavio
A1  - Liu, Xianbin
A1  - Metzler, Ralf
T1  - Fractional Brownian motion with random diffusivity
BT  - emerging residual nonergodicity below the correlation time
JF  - Journal of physics : A, Mathematical and theoretical
N2  - Numerous examples for a priori unexpected non-Gaussian behaviour for normal and anomalous diffusion have recently been reported in single-particle tracking experiments. Here, we address the case of non-Gaussian anomalous diffusion in terms of a random-diffusivity mechanism in the presence of power-law correlated fractional Gaussian noise. We study the ergodic properties of this model via examining the ensemble- and time-averaged mean-squared displacements as well as the ergodicity breaking parameter EB quantifying the trajectory-to-trajectory fluctuations of the latter. For long measurement times, interesting crossover behaviour is found as function of the correlation time tau characterising the diffusivity dynamics. We unveil that at short lag times the EB parameter reaches a universal plateau. The corresponding residual value of EB is shown to depend only on tau and the trajectory length. The EB parameter at long lag times, however, follows the same power-law scaling as for fractional Brownian motion. We also determine a corresponding plateau at short lag times for the discrete representation of fractional Brownian motion, absent in the continuous-time formulation. These analytical predictions are in excellent agreement with results of computer simulations of the underlying stochastic processes. Our findings can help distinguishing and categorising certain nonergodic and non-Gaussian features of particle displacements, as observed in recent single-particle tracking experiments.
KW  - stochastic processes
KW  - anomalous diffusion
KW  - fractional Brownian motion
KW  - diffusing diffusivity
KW  - weak ergodicity breaking
Y1  - 2020
U6  - https://doi.org/10.1088/1751-8121/aba467
SN  - 1751-8113
SN  - 1751-8121
VL  - 53
IS  - 47
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  -