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  - 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  - 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  - 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  - Dorsch, Matti
A1  - Jeffery, C. Simon
A1  - Irrgang, Andreas
A1  - Woolf, Vincent
A1  - Heber, Ulrich
T1  - EC 22536-5304
BT  - a lead-rich and metal-poor long-period binary
JF  - Astronomy and astrophysics : an international weekly journal
N2  - Helium-burning hot subdwarf stars of spectral types O and B (sdO/B) are thought to be produced through various types of binary interactions. The helium-rich hot subdwarf star EC 22536-5304 was recently found to be extremely enriched in lead. Here, we show that EC 22536-5304 is a binary star with a metal-poor subdwarf F-type (sdF) companion. We performed a detailed analysis of high-resolution SALT/HRS and VLT/UVES spectra, deriving metal abundances for the hot subdwarf, as well as atmospheric parameters for both components. Because we consider the contribution of the sdF star, the derived lead abundance for the sdOB, + 6.3 +/- 0.3 dex relative to solar, is even higher than previously thought. We derive T-eff = 6210 +/- 70 K, log g = 4.64 +/- 0.10, [FE/H] = - 1.95 +/- 0.04, and [alpha/Fe] = + 0.40 +/- 0.04 for the sdF component. Radial velocity variations, although poorly sampled at present, indicate that the binary system has a long orbital period of about 457 days. This suggests that the system was likely formed through stable Roche lobe overflow (RLOF). A kinematic analysis shows that EC 22536-5304 is on an eccentric orbit around the Galactic centre. This, as well as the low metallicity and strong alpha enhancement of the sdF-type companion, indicate that EC 22536-5304 is part of the Galactic halo or metal-weak thick disc. As the first long-period hot subdwarf binary at [FE/H] less than or similar to- 1, EC 22536-5304 may help to constrain the RLOF mechanism for mass transfer from low-mass, low-metallicity red giant branch (RGB) stars to main-sequence companions.
KW  - stars: abundances
KW  - stars: chemically peculiar
KW  - subdwarfs
KW  - stars: individual: EC 22536-5304
KW  - binaries: spectroscopic
Y1  - 2021
U6  - https://doi.org/10.1051/0004-6361/202141381
SN  - 1432-0746
VL  - 653
PB  - EDP Sciences
CY  - Les Ulis
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  - 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  - 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  - Wiebeler, Christian
A1  - Vollbrecht, Joachim
A1  - Neuba, Adam
A1  - Kitzerow, Heinz
A1  - Schumacher, Stefan
T1  - Unraveling the electrochemical and spectroscopic properties of neutral and negatively charged perylene tetraethylesters
JF  - Scientific reports
N2  - A detailed investigation of the energy levels of perylene-3,4,9,10-tetracarboxylic tetraethylester as a representative compound for the whole family of perylene esters was performed. It was revealed via electrochemical measurements that one oxidation and two reductions take place. The bandgaps determined via the electrochemical approach are in good agreement with the optical bandgap obtained from the absorption spectra via a Tauc plot. In addition, absorption spectra in dependence of the electrochemical potential were the basis for extensive quantum-chemical calculations of the neutral, monoanionic, and dianionic molecules. For this purpose, calculations based on density functional theory were compared with post-Hartree-Fock methods and the CAM-B3LYP functional proved to be the most reliable choice for the calculation of absorption spectra. Furthermore, spectral features found experimentally could be reproduced with vibronic calculations and allowed to understand their origins. In particular, the two lowest energy absorption bands of the anion are not caused by absorption of two distinct electronic states, which might have been expected from vertical excitation calculations, but both states exhibit a strong vibronic progression resulting in contributions to both bands.
Y1  - 2021
U6  - https://doi.org/10.1038/s41598-021-95551-0
SN  - 2045-2322
VL  - 11
IS  - 1
PB  - Macmillan Publishers Limited, part of Springer Nature
CY  - London
ER  - 
TY  - JOUR
A1  - Wolff, Nora
A1  - Klimm, Detlef
A1  - Habicht, Klaus
A1  - Fritsch, Katharina
T1  - Crystal growth and thermodynamic investigation of Bi2M2+O4 (M = Pd, Cu)
JF  - CrystEngComm / The Royal Society of Chemistry
N2  - Phase equilibria that are relevant for the growth of Bi2MO4 have been studied experimentally, and the ternary phase diagrams of Bi2O3-PdO2-Pd and Bi2O3-Cu2O-CuO and its isopleth section Bi2O3-CuO were redetermined. It is shown that every melting and crystallization process is always accompanied by a redox process at the phase boundary and that for both title compounds, the valence of the transition metal is lowered during melting. Vice versa, during crystal growth, O-2 must be transported through the melt to the phase boundary. Based on these new insights provided by our thermodynamic studies, Bi2CuO4 single crystals with a length of up to 7 cm and a diameter of 6 mm were grown by the OFZ technique to be used for investigations of magnetic, electronic and thermal transport properties. The grown crystals were characterized by powder X-ray diffraction, Laue, magnetization and specific heat measurements.
Y1  - 2021
U6  - https://doi.org/10.1039/d1ce00220a
SN  - 1466-8033
VL  - 23
IS  - 17
SP  - 3230
EP  - 3238
PB  - Royal Society of Chemistry
CY  - Cambridge
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  - Bozzo, Enrico
A1  - Ferrigno, Carlo
A1  - Oskinova, Lida
A1  - Ducci, Lorenzo
T1  - Accretion of a clumped wind from a red supergiant donor on to a magnetar is suggested by the analysis of the XMM-Newton and NuSTAR observations of the X-ray binary 3A 1954+319
JF  - Monthly notices of the Royal Astronomical Society
N2  - 3A 1954+319 has been classified for a long time as a symbiotic X-ray binary, hosting a slowly rotating neutron star and an aged M red giant. Recently, this classification has been revised thanks to the discovery that the donor star is an M supergiant. This makes 3A 1954+319 a rare type of high-mass X-ray binary consisting of a neutron star and a red supergiant donor. In this paper, we analyse two archival and still unpublished XMM-Newton and NuSTAR observations of the source. We perform a detailed hardness ratio-resolved spectral analysis to search for spectral variability that could help investigating the structures of the inhomogeneous M supergiant wind from which the neutron star is accreting. We discuss our results in the context of wind-fed supergiant X-ray binaries and show that the newest findings on 3A 1954+319 reinforce the hypothesis that the neutron star in this system is endowed with a magnetar-like magnetic field strength (greater than or similar to 10(14) G).
KW  - accretion
KW  - stars: massive
KW  - stars: neutron
KW  - X-rays: binaries
KW  - X-rays: individual: 3A 1954+319
KW  - X-rays: stars
KW  - accretion discs
Y1  - 2021
U6  - https://doi.org/10.1093/mnras/stab3688
SN  - 0035-8711
SN  - 1365-2966
VL  - 510
IS  - 3
SP  - 4645
EP  - 4653
PB  - Oxford Univ. Press
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Mösenlechner, Gerald
A1  - Paunzen, Ernst
A1  - Pelisoli, Ingrid D.
A1  - Seelig, Joseph
A1  - Stidl, Sarah
A1  - Maitzen, Hans Michael
T1  - A Kepler K2 view of subdwarf A-type stars
JF  - Astronomy and astrophysics : an international weekly journal
N2  - Context.  The spectroscopic class of subdwarf A-type (sdA) stars has come into focus in recent years because of their possible link to extremely low-mass white dwarfs, a rare class of objects resulting from binary evolution. Although most sdA stars are consistent with metal-poor halo main-sequence stars, the formation and evolution of a fraction of these stars are still matters of debate. Aims. The identification of photometric variability can help to put further constraints on the evolutionary status of sdA stars, in particular through the analysis of pulsations. Moreover, the binary ratio, which can be deduced from eclipsing binaries and ellipsoidal variables, is important as input for stellar models. In order to search for variability due to either binarity or pulsations in objects of the spectroscopic sdA class, we have extracted all available high precision light curves from the Kepler K2 mission. 
Methods.  We have performed a thorough time series analysis on all available light curves, employing three different methods. Frequencies with a signal-to-noise ratio higher than four have been used for further analysis. 
Results.  From the 25 targets, 13 turned out to be variables of different kinds (i.e., classical pulsating stars, ellipsoidal and cataclysmic variables, eclipsing binaries, and rotationally induced variables). For the remaining 12 objects, a variability threshold was determined.
KW  - subdwarfs
KW  - white dwarfs
KW  - binaries: general
KW  - stars: evolution
KW  - stars: variables: general
Y1  - 2022
U6  - https://doi.org/10.1051/0004-6361/202037789
SN  - 0004-6361
SN  - 1432-0746
VL  - 657
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Sprengel, Maximilian
A1  - Mohr, Gunther
A1  - Altenburg, Simon J.
A1  - Evans, Alexander
A1  - Serrano-Munoz, Itziar
A1  - Kromm, Arne
A1  - Pirling, Thilo
A1  - Bruno, Giovanni
A1  - Kannengießer, Thomas
T1  - Triaxial residual stress in Laser Powder Bed Fused 316L
BT  - effects of interlayer time and scanning velocity
JF  - Advanced engineering materials
N2  - The control of residual stress (RS) remains a challenge in the manufacturing of metallic parts using the laser powder bed fusion process (LPBF). This layer-by-layer manufacturing approach gives rise to complex triaxial RS distributions, which require extensive characterization effort for a broader acceptance of LPBF in industry. This study focuses on the distribution of bulk triaxial RS and surface RS in LPBF austenitic steel 316L. The RS are determined by X-ray and neutron diffraction to characterize the RS distribution. Variations in the LPBF parameters interlayer time (ILT) and scanning velocity and their influence on the temperature distribution and resulting RS is investigated using thermographic data from in situ process monitoring. The RS in the LPBF 316L is tensile at the surface and compressive in the bulk. The RS is directly related to the thermal history of the part as shown by the in situ thermography data. Shorter ILT leads to higher temperatures of the part during the manufacturing, which decrease the RS and RS formation mechanisms. Interestingly, the surface RS does not agree with this observation. This study highlights the benefit of using multiple RS determination methods and in situ thermography monitoring to characterize the RS in LPBF processed parts.
KW  - in situ thermography
KW  - interlayer time
KW  - laser powder bed fusions
KW  - triaxial residual stresses
KW  - X-ray and neutron diffractions
Y1  - 2021
U6  - https://doi.org/10.1002/adem.202101330
SN  - 1438-1656
SN  - 1527-2648
VL  - 24
IS  - 6
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Kuhla, Kilian
A1  - Willner, Sven N.
A1  - Otto, Christian
A1  - Geiger, Tobias
A1  - Levermann, Anders
T1  - Ripple resonance amplifies economic welfare loss from weather extremes
JF  - Environmental research letters : ERL / Institute of Physics
N2  - The most complex but potentially most severe impacts of climate change are caused by extreme weather events. In a globally connected economy, damages can cause remote perturbations and cascading consequences-a ripple effect along supply chains. Here we show an economic ripple resonance that amplifies losses when consecutive or overlapping weather extremes and their repercussions interact. This amounts to an average amplification of 21% for climate-induced heat stress, river floods, and tropical cyclones. Modeling the temporal evolution of 1.8 million trade relations between >7000 regional economic sectors, we find that the regional responses to future extremes are strongly heterogeneous also in their resonance behavior. The induced effect on welfare varies between gains due to increased demand in some regions and losses due to demand or supply shortages in others. Within the current global supply network, the ripple resonance effect of extreme weather is strongest in high-income economies-an important effect to consider when evaluating past and future economic climate impacts.
KW  - consecutive disasters
KW  - economic ripple resonance
KW  - repercussion resonance
KW  - weather extremes
KW  - supply network
KW  - climate impacts
KW  - climate change
Y1  - 2021
U6  - https://doi.org/10.1088/1748-9326/ac2932
SN  - 1748-9326
VL  - 16
IS  - 11
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Sorgenfrei, Nomi
A1  - Giangrisostomi, Erika
A1  - Jay, Raphael Martin
A1  - Kühn, Danilo
A1  - Neppl, Stefan
A1  - Ovsyannikov, Ruslan
A1  - Sezen, Hikmet
A1  - Svensson, Svante
A1  - Föhlisch, Alexander
T1  - Photodriven transient picosecond top-layer semiconductor to metal phase-transition in p-doped molybdenum disulfide
JF  - Advanced materials
N2  - Visible light is shown to create a transient metallic S-Mo-S surface layer on bulk semiconducting p-doped indirect-bandgap 2H-MoS2. Optically created electron-hole pairs separate in the surface band bending region of the p-doped semiconducting crystal causing a transient accumulation of electrons in the surface region. This triggers a reversible 2H-semiconductor to 1T-metal phase-transition of the surface layer. Electron-phonon coupling of the indirect-bandgap p-doped 2H-MoS2 enables this efficient pathway even at a low density of excited electrons with a distinct optical excitation threshold and saturation behavior. This mechanism needs to be taken into consideration when describing the surface properties of illuminated p-doped 2H-MoS2. In particular, light-induced increased charge mobility and surface activation can cause and enhance the photocatalytic and photoassisted electrochemical hydrogen evolution reaction of water on 2H-MoS2. Generally, it opens up for a way to control not only the surface of p-doped 2H-MoS2 but also related dichalcogenides and layered systems. The findings are based on the sensitivity of time-resolved electron spectroscopy for chemical analysis with photon-energy-tuneable synchrotron radiation.
KW  - catalysis
KW  - dichalcogenides
KW  - hydrogen evolution reaction
KW  - phase transitions
KW  - photoelectron spectroscopy
Y1  - 2021
U6  - https://doi.org/10.1002/adma.202006957
SN  - 0935-9648
SN  - 1521-4095
VL  - 33
IS  - 14
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Tait, Claudia E.
A1  - Reckwitz, Anna
A1  - Arvind, Malavika
A1  - Neher, Dieter
A1  - Bittl, Robert
A1  - Behrends, Jan
T1  - Spin-spin interactions and spin delocalisation in a doped organic semiconductor probed by EPR spectroscopy
JF  - Physical chemistry, chemical physics : PCCP ; a journal of European chemical societies
N2  - The enhancement and control of the electrical conductivity of organic semiconductors is fundamental for their use in optoelectronic applications and can be achieved by molecular doping, which introduces additional charge carriers through electron transfer between a dopant molecule and the organic semiconductor. Here, we use Electron Paramagnetic Resonance (EPR) spectroscopy to characterise the unpaired spins associated with the charges generated by molecular doping of the prototypical organic semiconductor poly(3-hexylthiophene) (P3HT) with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F(4)TCNQ) and tris(pentafluorophenyl)borane (BCF). The EPR results reveal the P3HT radical cation as the only paramagnetic species in BCF-doped P3HT films and show evidence for increased mobility of the detected spins at high doping concentrations as well as formation of antiferromagnetically coupled spin pairs leading to decreased spin concentrations at low temperatures. The EPR signature for F(4)TCNQ-doped P3HT is found to be determined by spin exchange between P3HT radical cations and F(4)TCNQ radical anions. Results from continuous-wave and pulse EPR measurements suggest the presence of the unpaired spin on P3HT in a multitude of environments, ranging from free P3HT radical cations with similar properties to those observed in BCF-doped P3HT, to pairs of dipolar and exchange-coupled spins on P3HT and the dopant anion. Characterisation of the proton hyperfine interactions by ENDOR allowed quantification of the extent of spin delocalisation and revealed reduced delocalisation in the F(4)TCNQ-doped P3HT films.
Y1  - 2021
U6  - https://doi.org/10.1039/d1cp02133h
SN  - 1463-9076
SN  - 1463-9084
VL  - 23
IS  - 25
SP  - 13827
EP  - 13841
PB  - Royal Society of Chemistry
CY  - Cambridge
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  - 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  - Nakoudi, Konstantina
A1  - Ritter, Christoph
A1  - Stachlewska, Iwona Sylwia
T1  - Properties of cirrus clouds over the European Arctic (Ny-Alesund, Svalbard)
JF  - Remote sensing / Molecular Diversity Preservation International (MDPI)
N2  - Cirrus is the only cloud type capable of inducing daytime cooling or heating at the top of the atmosphere (TOA) and the sign of its radiative effect highly depends on its optical depth. However, the investigation of its geometrical and optical properties over the Arctic is limited. In this work the long-term properties of cirrus clouds are explored for the first time over an Arctic site (Ny-Alesund, Svalbard) using lidar and radiosonde measurements from 2011 to 2020. The optical properties were quality assured, taking into account the effects of specular reflections and multiple-scattering. Cirrus clouds were generally associated with colder and calmer wind conditions compared to the 2011-2020 climatology. However, the dependence of cirrus properties on temperature and wind speed was not strong. Even though the seasonal cycle was not pronounced, the winter-time cirrus appeared under lower temperatures and stronger wind conditions. Moreover, in winter, geometrically- and optically-thicker cirrus were found and their ice particles tended to be more spherical. The majority of cirrus was associated with westerly flow and westerly cirrus tended to be geometrically-thicker. Overall, optically-thinner layers tended to comprise smaller and less spherical ice crystals, most likely due to reduced water vapor deposition on the particle surface. Compared to lower latitudes, the cirrus layers over Ny-Alesund were more absorbing in the visible spectral region and they consisted of more spherical ice particles.
KW  - Arctic clouds
KW  - cirrus clouds
KW  - ice clouds
KW  - lidar
Y1  - 2021
U6  - https://doi.org/10.3390/rs13224555
SN  - 2072-4292
VL  - 13
IS  - 22
PB  - MDPI
CY  - Basel
ER  - 
TY  - JOUR
A1  - Tönjes, Ralf
A1  - Fiore, Carlos E.
A1  - Pereira da Silva, Tiago
T1  - Coherence resonance in influencer networks
JF  - Nature Communications
N2  - Complex networks are abundant in nature and many share an important structural property: they contain a few nodes that are abnormally highly connected (hubs). Some of these hubs are called influencers because they couple strongly to the network and play fundamental dynamical and structural roles. Strikingly, despite the abundance of networks with influencers, little is known about their response to stochastic forcing. Here, for oscillatory dynamics on influencer networks, we show that subjecting influencers to an optimal intensity of noise can result in enhanced network synchronization. This new network dynamical effect, which we call coherence resonance in influencer networks, emerges from a synergy between network structure and stochasticity and is highly nonlinear, vanishing when the noise is too weak or too strong. Our results reveal that the influencer backbone can sharply increase the dynamical response in complex systems of coupled oscillators. Influencer networks include a small set of highly-connected nodes and can reach synchrony only via strong node interaction. Tonjes et al. show that introducing an optimal amount of noise enhances synchronization of such networks, which may be relevant for neuroscience or opinion dynamics applications.
Y1  - 2021
U6  - https://doi.org/10.1038/s41467-020-20441-4
SN  - 2041-1723
VL  - 12
IS  - 1
PB  - Nature Publishing Group UK
CY  - London
ER  - 
TY  - JOUR
A1  - Becker, George D.
A1  - D'Aloisio, Anson
A1  - Christenson, Holly M.
A1  - Zhu, Yongda
A1  - Worseck, Gábor
A1  - Bolton, James S.
T1  - The mean free path of ionizing photons at 5 < z < 6
BT  - evidence for rapid evolution near reionization
JF  - Monthly notices of the Royal Astronomical Society
N2  - The mean free path of ionizing photons, lambda(mfp), is a key factor in the photoionization of the intergalactic medium (IGM). At z greater than or similar to 5, however, lambda(mfp) may be short enough that measurements towards QSOs are biased by the QSO proximity effect. We present new direct measurements of lambda(mfp) that address this bias and extend up to z similar to 6 for the first time. Our measurements at z similar to 5 are based on data from the Giant Gemini GMOS survey and new Keck LRIS observations of low-luminosity QSOs. At z similar to 6 we use QSO spectra from Keck ESI and VLT X-Shooter. We measure lambda(mfp) = 9.09(-1.28)(+1.62) proper Mpc and 0.75(-0.45)(+0.65) proper Mpc (68 percent confidence) at z = 5.1 and 6.0, respectively. The results at z = 5.1 are consistent with existing measurements, suggesting that bias from the proximity effect is minor at this redshift. At z = 6.0, however, we find that neglecting the proximity effect biases the result high by a factor of two or more. Our measurement at z = 6.0 falls well below extrapolations from lower redshifts, indicating rapid evolution in lambda(mfp) over 5 < z < 6. This evolution disfavours models in which reionization ended early enough that the IGM had time to fully relax hydrodynamically by z = 6, but is qualitatively consistent with models wherein reionization completed at z = 6 or even significantly later. Our mean free path results are most consistent with late reionization models wherein the IGM is still 20 percent neutral at z = 6, although our measurement at z = 6.0 is even lower than these models prefer.
KW  - intergalactic medium
KW  - quasars: absorption lines
KW  - cosmology: observations
KW  - dark ages
KW  - large-scale structure of Universe
KW  - reionization
KW  - first stars
Y1  - 2021
U6  - https://doi.org/10.1093/mnras/stab2696
SN  - 0035-8711
SN  - 1365-2966
VL  - 508
IS  - 2
SP  - 1853
EP  - 1869
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  - Zeitz, Maria
A1  - Reese, Ronja
A1  - Beckmann, Johanna
A1  - Krebs-Kanzow, Uta
A1  - Winkelmann, Ricarda
T1  - Impact of the melt-albedo feedback on the future evolution of the Greenland Ice Sheet with PISM-dEBM-simple
JF  - The Cryosphere : TC ; an interactive open access journal of the European Geosciences Union
N2  - Surface melting of the Greenland Ice Sheet contributes a large amount to current and future sea level rise. Increased surface melt may lower the reflectivity of the ice sheet surface and thereby increase melt rates: the so-called melt-albedo feedback describes this self-sustaining increase in surface melting. In order to test the effect of the melt-albedo feedback in a prognostic ice sheet model, we implement dEBM-simple, a simplified version of the diurnal Energy Balance Model dEBM, in the Parallel Ice Sheet Model (PISM). The implementation includes a simple representation of the melt-albedo feedback and can thereby replace the positive-degree-day melt scheme. Using PISM-dEBM-simple, we find that this feedback increases ice loss through surface warming by 60 % until 2300 for the high-emission scenario RCP8.5 when compared to a scenario in which the albedo remains constant at its present-day values. With an increase of 90 % compared to a fixed-albedo scenario, the effect is more pronounced for lower surface warming under RCP2.6. Furthermore, assuming an immediate darkening of the ice surface over all summer months, we estimate an upper bound for this effect to be 70 % in the RCP8.5 scenario and a more than 4-fold increase under RCP2.6. With dEBM-simple implemented in PISM, we find that the melt-albedo feedback is an essential contributor to mass loss in dynamic simulations of the Greenland Ice Sheet under future warming.
Y1  - 2021
U6  - https://doi.org/10.5194/tc-15-5739-2021
SN  - 1994-0416
SN  - 1994-0424
VL  - 15
IS  - 12
SP  - 5739
EP  - 5764
PB  - Copernicus
CY  - Katlenburg-Lindau
ER  - 
TY  - JOUR
A1  - Perdigón-Toro, Lorena
A1  - Le Quang Phuong, 
A1  - Zeiske, Stefan
A1  - Vandewal, Koen
A1  - Armin, Ardalan
A1  - Shoaee, Safa
A1  - Neher, Dieter
T1  - Excitons dominate the emission from PM6
BT  - Y6 solar cells, but this does not help the open-circuit voltage of the device
JF  - ACS energy letters / American Chemical Society
N2  - Non-fullerene acceptors (NFAs) are far more emissive than their fullerene-based counterparts. Here, we study the spectral properties of photocurrent generation and recombination of the blend of the donor polymer PM6 with the NFA Y6. We find that the radiative recombination of free charges is almost entirely due to the re-occupation and decay of Y6 singlet excitons, but that this pathway contributes less than 1% to the total recombination. As such, the open-circuit voltage of the PM6:Y6 blend is determined by the energetics and kinetics of the charge-transfer (CT) state. Moreover, we find that no information on the energetics of the CT state manifold can be gained from the low-energy tail of the photovoltaic external quantum efficiency spectrum, which is dominated by the excitation spectrum of the Y6 exciton. We, finally, estimate the charge-separated state to lie only 120 meV below the Y6 singlet exciton energy, meaning that this blend indeed represents a high-efficiency system with a low energetic offset.
Y1  - 2021
U6  - https://doi.org/10.1021/acsenergylett.0c02572
SN  - 2380-8195
VL  - 6
IS  - 2
SP  - 557
EP  - 564
PB  - American Chemical Society
CY  - Washington
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  - Pauzon, Camille
A1  - Mishurova, Tatiana
A1  - Evsevleev, Sergei
A1  - Dubiez-Le Goff, Sophie
A1  - Murugesan, Saravanakumar
A1  - Bruno, Giovanni
A1  - Hryha, Eduard
T1  - Residual stresses and porosity in Ti-6Al-4V produced by laser powder bed fusion as a function of process atmosphere and component design
JF  - Additive manufacturing
N2  - The influence of the process gas, laser scan speed, and sample thickness on the build-up of residual stresses and porosity in Ti-6Al-4V produced by laser powder bed fusion was studied. Pure argon and helium, as well as a mixture of those (30% helium), were employed to establish process atmospheres with a low residual oxygen content of 100 ppm O-2. The results highlight that the subsurface residual stresses measured by X-ray diffraction were significantly lower in the thin samples (220 MPa) than in the cuboid samples (645 MPa). This difference was attributed to the shorter laser vector length, resulting in heat accumulation and thus in-situ stress relief. The addition of helium to the process gas did not introduce additional subsurface residual stresses in the simple geometries, even for the increased scanning speed. Finally, larger deflection was found in the cantilever built under helium (after removal from the baseplate), than in those produced under argon and an argon-helium mixture. This result demonstrates that complex designs involving large scanned areas could be subjected to higher residual stress when manufactured under helium due to the gas's high thermal conductivity, heat capacity, and thermal diffusivity.
KW  - Residual stresses
KW  - Laser powder bed fusion
KW  - Process atmosphere
KW  - Helium
KW  - Ti-6Al-4V
Y1  - 2021
U6  - https://doi.org/10.1016/j.addma.2021.102340
SN  - 2214-8604
VL  - 47
PB  - Elsevier
CY  - Amsterdam
ER  - 
TY  - JOUR
A1  - Pranav, Manasi
A1  - Benduhn, Johannes
A1  - Nyman, Mathias
A1  - Hosseini, Seyed Mehrdad
A1  - Kublitski, Jonas
A1  - Shoaee, Safa
A1  - Neher, Dieter
A1  - Leo, Karl
A1  - Spoltore, Donato
T1  - Enhanced charge selectivity via anodic-C60 layer reduces nonradiative losses in organic solar cells
JF  - ACS applied materials & interfaces
N2  - Interfacial layers in conjunction with suitable charge-transport layers can significantly improve the performance of optoelectronic devices by facilitating efficient charge carrier injection and extraction. 
This work uses a neat C-60 interlayer on the anode to experimentally reveal that surface recombination is a significant contributor to nonradiative recombination losses in organic solar cells. 
These losses are shown to proportionally increase with the extent of contact between donor molecules in the photoactive layer and a molybdenum oxide (MoO3) hole extraction layer, proven by calculating voltage losses in low- and high-donor-content bulk heterojunction device architectures. 
Using a novel in-device determination of the built-in voltage, the suppression of surface recombination, due to the insertion of a thin anodic-C-60 interlayer on MoO3, is attributed to an enhanced built-in potential. 
The increased built-in voltage reduces the presence of minority charge carriers at the electrodes-a new perspective on the principle of selective charge extraction layers. 
The benefit to device efficiency is limited by a critical interlayer thickness, which depends on the donor material in bilayer devices. 
Given the high popularity of MoO3 as an efficient hole extraction and injection layer and the increasingly popular discussion on interfacial phenomena in organic optoelectronic devices, these findings are relevant to and address different branches of organic electronics, providing insights for future device design.
KW  - nonradiative losses
KW  - molybdenum oxide
KW  - organic solar cells
KW  - interfacial layers
KW  - charge selectivity
Y1  - 2021
U6  - https://doi.org/10.1021/acsami.1c00049
SN  - 1944-8244
SN  - 1944-8252
VL  - 13
IS  - 10
SP  - 12603
EP  - 12609
PB  - American Chemical Society
CY  - Washington
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  - 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  - Tokmoldin, Nurlan
A1  - Vollbrecht, Joachim
A1  - Hosseini, Seyed Mehrdad
A1  - Sun, Bowen
A1  - Perdigón-Toro, Lorena
A1  - Woo, Han Young
A1  - Zou, Yingping
A1  - Neher, Dieter
A1  - Shoaee, Safa
T1  - Explaining the fill-factor and photocurrent losses of nonfullerene acceptor-based solar cells by probing the long-range charge carrier diffusion and drift lengths
JF  - Advanced energy materials
N2  - Organic solar cells (OSC) nowadays match their inorganic competitors in terms of current production but lag behind with regards to their open-circuit voltage loss and fill-factor, with state-of-the-art OSCs rarely displaying fill-factor of 80% and above. The fill-factor of transport-limited solar cells, including organic photovoltaic devices, is affected by material and device-specific parameters, whose combination is represented in terms of the established figures of merit, such as theta and alpha. Herein, it is demonstrated that these figures of merit are closely related to the long-range carrier drift and diffusion lengths. Further, a simple approach is presented to devise these characteristic lengths using steady-state photoconductance measurements. This yields a straightforward way of determining theta and alpha in complete cells and under operating conditions. This approach is applied to a variety of photovoltaic devices-including the high efficiency nonfullerene acceptor blends-and show that the diffusion length of the free carriers provides a good correlation with the fill-factor. It is, finally, concluded that most state-of-the-art organic solar cells exhibit a sufficiently large drift length to guarantee efficient charge extraction at short circuit, but that they still suffer from too small diffusion lengths of photogenerated carriers limiting their fill factor.
KW  - diffusion length
KW  - drift length
KW  - figure of merit
KW  - lifetime‐ mobility product
KW  - steady‐ state photoconductance
Y1  - 2021
U6  - https://doi.org/10.1002/aenm.202100804
SN  - 1614-6840
VL  - 11
IS  - 22
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Schlemm, Tanja
A1  - Levermann, Anders
T1  - A simple parametrization of mélange buttressing for calving glaciers
JF  - The Cryosphere : TC ; an interactive open access journal of the European Geosciences Union
N2  - Both ice sheets in Greenland and Antarctica are discharging ice into the ocean. In many regions along the coast of the ice sheets, the icebergs calve into a bay. If the addition of icebergs through calving is faster than their transport out of the embayment, the icebergs will be frozen into a melange with surrounding sea ice in winter. In this case, the buttressing effect of the ice melange can be considerably stronger than any buttressing by mere sea ice would be. This in turn stabilizes the glacier terminus and leads to a reduction in calving rates. Here we propose a simple parametrization of ice melange buttressing which leads to an upper bound on calving rates and can be used in numerical and analytical modelling.
Y1  - 2021
U6  - https://doi.org/10.5194/tc-15-531-2021
SN  - 1994-0416
SN  - 1994-0424
VL  - 15
IS  - 2
SP  - 531
EP  - 545
PB  - Copernicus
CY  - Göttingen
ER  - 
TY  - JOUR
A1  - 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  - Nedora, Vsevolod
A1  - Radice, David
A1  - Bernuzzi, Sebastiano
A1  - Perego, Albino
A1  - Daszuta, Boris
A1  - Endrizzi, Andrea
A1  - Prakash, Aviral
A1  - Schianchi, Federico
T1  - Dynamical ejecta synchrotron emission as a possible contributor to the changing behaviour of GRB170817A afterglow
JF  - Monthly notices of the Royal Astronomical Society
N2  - Over the past 3 yr, the fading non-thermal emission from the GW170817 remained generally consistent with the afterglow powered by synchrotron radiation produced by the interaction of the structured jet with the ambient medium. Recent observations by Hajela et al. indicate the change in temporal and spectral behaviour in the X-ray band. We show that the new observations are compatible with the emergence of a new component due to non-thermal emission from the fast tail of the dynamical ejecta of ab-initio binary neutron star merger simulations. This provides a new avenue to constrain binary parameters. Specifically, we find that equal mass models with soft equations of state (EOSs) and high-mass ratio models with stiff EOSs are disfavoured as they typically predict afterglows that peak too early to explain the recent observations. Moderate stiffness and mass ratio models, instead, tend to be in good overall agreement with the data.
KW  - equation of state
KW  - gravitational waves
KW  - neutron star mergers
Y1  - 2021
U6  - https://doi.org/10.1093/mnras/stab2004
SN  - 0035-8711
SN  - 1365-2966
VL  - 506
IS  - 4
SP  - 5908
EP  - 5915
PB  - Oxford Univ. Press
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Thomas, Timon
A1  - Pfrommer, Christoph
A1  - Pakmor, Rüdiger
T1  - A finite volume method for two-moment cosmic ray hydrodynamics on a moving mesh
JF  - Monthly notices of the Royal Astronomical Society
N2  - We present a new numerical algorithm to solve the recently derived equations of two-moment cosmic ray hydrodynamics (CRHD). The algorithm is implemented as a module in the moving mesh AREPO code. Therein, the anisotropic transport of cosmic rays (CRs) along magnetic field lines is discretized using a path-conservative finite volume method on the unstructured time-dependent Voronoi mesh of AREPO. The interaction of CRs and gyroresonant Alfven waves is described by short time-scale source terms in the CRHD equations. We employ a custom-made semi-implicit adaptive time stepping source term integrator to accurately integrate this interaction on the small light-crossing time of the anisotropic transport step. Both the transport and the source term integration step are separated from the evolution of the magnetohydrodynamical equations using an operator split approach. The new algorithm is tested with a variety of test problems, including shock tubes, a perpendicular magnetized discontinuity, the hydrodynamic response to a CR overpressure, CR acceleration of a warm cloud, and a CR blast wave, which demonstrate that the coupling between CR and magnetohydrodynamics is robust and accurate. We demonstrate the numerical convergence of the presented scheme using new linear and non-linear analytic solutions.
KW  - hydrodynamics
KW  - MHD
KW  - methods: numerical
KW  - cosmic rays
Y1  - 2021
U6  - https://doi.org/10.1093/mnras/stab397
SN  - 0035-8711
SN  - 1365-2966
VL  - 503
IS  - 2
SP  - 2242
EP  - 2264
PB  - Oxford University Press
CY  - Oxford
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  - 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  - 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  - Willner, Sven N.
A1  - Glanemann, Nicole
A1  - Levermann, Anders
T1  - Investment incentive reduced by climate damages can be restored by optimal policy
JF  - Nature Communications
N2  - Increasing greenhouse gas emissions are likely to impact not only natural systems but economies worldwide. If these impacts alter future economic development, the financial losses will be significantly higher than the mere direct damages. So far, potentially aggravating investment responses were considered negligible. Here we consistently incorporate an empirically derived temperature-growth relation into the simple integrated assessment model DICE. In this framework we show that, if in the next eight decades varying temperatures impact economic growth as has been observed in the past three decades, income is reduced by similar to 20% compared to an economy unaffected by climate change. Hereof similar to 40% are losses due to growth effects of which similar to 50% result from reduced incentive to invest. This additional income loss arises from a reduced incentive for future investment in anticipation of a reduced return and not from an explicit climate protection policy. Under economically optimal climate-change mitigation, however, optimal investment would only be reduced marginally as mitigation efforts keep returns high.
Y1  - 2021
U6  - https://doi.org/10.1038/s41467-021-23547-5
SN  - 2041-1723
VL  - 12
IS  - 1
PB  - Nature Publishing Group UK
CY  - London
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  - 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  - 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  - 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  - Worseck, Gábor
A1  - Khrykin, Ilya Sergeevich
A1  - Hennawi, Joseph F.
A1  - Prochaska, J. Xavier
A1  - Farina, Emanuele Paolo
T1  - Dating individual quasars with the He II proximity effect
JF  - Monthly notices of the Royal Astronomical Society
N2  - Constraints on the time-scales of quasar activity are key to understanding the formation and growth of supermassive black holes (SMBHs), quasar triggering mechanisms, and possible feedback effects on their host galaxies. However, observational estimates of this so-called quasar lifetime are highly uncertain (t(Q) similar to 10(4)-10(9) yr), because most methods are indirect and involve many model-dependent assumptions. Direct evidence of earlier activity is gained from the higher ionization state of the intergalactic medium (IGM) in the quasar environs, observable as enhanced Ly alpha transmission in the so-called proximity zone. Due to the similar to 30 Myr equilibration time-scale of He II in the z similar to 3 IGM, the size of the He II proximity zone depends on the time the quasar had been active before our observation t(on) <= t(Q), enabling up to +/- 0.2 dex precise measurements of individual quasar on-times that are comparable to the e-folding time-scale t(S) <= 44 Myr of SMBH growth. Here we present the first statistical sample of 13 quasars whose accurate and precise systemic redshifts allow for measurements of sufficiently precise He II quasar proximity zone sizes between similar or equal to 2 and similar or equal to 15 proper Mpc from science-grade Hubble Space Telescope (HST) spectra. Comparing these sizes to predictions from cosmological hydrodynamical simulations post-processed with 1D radiative transfer, we infer a broad range of quasar on-times from t(on) less than or similar to 1Myr to t(on) > 30 Myr that does not depend on quasar luminosity, black hole mass, or Eddington ratio. These results point to episodic quasar activity over a long duty cycle, but do not rule out substantial SMBH growth during phases of radiative inefficiency or obscuration.
KW  - intergalactic medium
KW  - quasars: absorption lines
KW  - quasars: general
KW  - quasars: supermassive black holes
KW  - dark ages, reionization, first stars
Y1  - 2021
U6  - https://doi.org/10.1093/mnras/stab1685
SN  - 0035-8711
SN  - 1365-2966
VL  - 505
IS  - 4
SP  - 5084
EP  - 5103
PB  - Oxford Univ. Press
CY  - Oxford
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  - 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  - 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  - 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  - Reindl, Nicole
A1  - Schaffenroth, Veronika
A1  - Filiz, Semih
A1  - Geier, Stephan
A1  - Pelisoli, Ingrid
A1  - Kepler, Souza Oliveira
T1  - Mysterious, variable, and extremely hot
BT  - White dwarfs showing ultra-high excitation lines: I. Photometric variability
JF  - Astronomy and astrophysics : an international weekly journal / European Southern Observatory (ESO)
N2  - Context. 
About 10% of all stars exhibit absorption lines of ultra-highly excited (UHE) metals (e.g., O VIII) in their optical spectra when entering the white dwarf cooling sequence. This is something that has never been observed in any other astrophysical object, and poses a decades-long mystery in our understanding of the late stages of stellar evolution. The recent discovery of a UHE white dwarf that is both spectroscopically and photometrically variable led to the speculation that the UHE lines might be created in a shock-heated circumstellar magnetosphere. 

Aims. 
We aim to gain a better understanding of these mysterious objects by studying the photometric variability of the whole population of UHE white dwarfs, and white dwarfs showing only the He II line problem, as both phenomena are believed to be connected. 

Methods.
We investigate (multi-band) light curves from several ground- and space-based surveys of all 16 currently known UHE white dwarfs (including one newly discovered) and eight white dwarfs that show only the He II line problem.


Results. 
We find that 75(-13)(+8) % of the UHE white dwarfs, and 75(-19)(+9)% of the He II line problem white dwarfs are significantly photometrically variable, with periods ranging from 0.22 d to 2.93 d and amplitudes from a few tenths to a few hundredths of a magnitude. The high variability rate is in stark contrast to the variability rate amongst normal hot white dwarfs (we find 9(2)(+4)%), marking UHE and He II line problem white dwarfs as a new class of variable stars. The period distribution of our sample agrees with both the orbital period distribution of post-common-envelope binaries and the rotational period distribution of magnetic white dwarfs if we assume that the objects in our sample will spin-up as a consequence of further contraction.


Conclusions. 
We find further evidence that UHE and He II line problem white dwarfs are indeed related, as concluded from their overlap in the Gaia HRD, similar photometric variability rates, light-curve shapes and amplitudes, and period distributions. The lack of increasing photometric amplitudes towards longer wavelengths, as well as the nondetection of optical emission lines arising from the highly irradiated face of a hypothetical secondary in the optical spectra of our stars, makes it seem unlikely that an irradiated late-type companion is the origin of the photometric variability. Instead, we believe that spots on the surfaces of these stars and/or geometrical effects of circumstellar material might be responsible.
KW  - white dwarfs
KW  - stars: variables: general
KW  - starspots
KW  - binaries: close
Y1  - 2021
U6  - https://doi.org/10.1051/0004-6361/202140289
SN  - 1432-0746
VL  - 647
PB  - EDP Sciences
CY  - Les Ulis
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  - Caesar, Levke
A1  - Rahmstorf, Stefan
A1  - Feulner, Georg
T1  - Reply to comment on 'On the relationship between Atlantic meridional overturning circulation slowdown and global surface warming'
JF  - Environmental research letters
N2  - In their comment on our paper (Caesar et al 2020 Environ. Res. Lett. 15 024003), Chen and Tung (hereafter C&T) argue that our analysis, showing that over the last decades Atlantic meridional overturning circulation (AMOC) strength and global mean surface temperature (GMST) were positively correlated, is incorrect. Their claim is mainly based on two arguments, neither of which is justified: first, C&T claim that our analysis is based on 'established evidence' that was only true for preindustrial conditions-this is not the case. Using data from the modern period (1947-2012), we show that the established understanding (i.e. deep-water formation in the North Atlantic cools the deep ocean and warms the surface) is correct, but our analysis is not based on this fact. Secondly, C&T claim that our results are based on a statistical analysis of only one cycle of data which was furthermore incorrectly detrended. This, too, is not true. Our conclusion that a weaker AMOC delays the current surface warming rather than enhances it, is based on several independent lines of evidence. The data we show to support this covers more than one cycle and the detrending (which was performed to avoid spurious correlations due to a common trend) does not affect our conclusion: the correlation between AMOC strength and GMST is positive. We do not claim that this is strong evidence that the two time series are in phase, but rather that this means that the two time series are not anti-correlated.
KW  - Atlantic meridional overturning circulation
KW  - global surface warming
KW  - ocean heat uptake
Y1  - 2021
U6  - https://doi.org/10.1088/1748-9326/abc776
SN  - 1748-9326
VL  - 16
IS  - 3
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Middelanis, Robin
A1  - Willner, Sven N.
A1  - Otto, Christian
A1  - Kuhla, Kilian
A1  - Quante, Lennart
A1  - Levermann, Anders
T1  - Wave-like global economic ripple response to Hurricane Sandy
JF  - Environmental research letters : ERL / Institute of Physics
N2  - Tropical cyclones range among the costliest disasters on Earth. Their economic repercussions along the supply and trade network also affect remote economies that are not directly affected. We here simulate possible global repercussions on consumption for the example case of Hurricane Sandy in the US (2012) using the shock-propagation model Acclimate. The modeled shock yields a global three-phase ripple: an initial production demand reduction and associated consumption price decrease, followed by a supply shortage with increasing prices, and finally a recovery phase. Regions with strong trade relations to the US experience strong magnitudes of the ripple. A dominating demand reduction or supply shortage leads to overall consumption gains or losses of a region, respectively. While finding these repercussions in historic data is challenging due to strong volatility of economic interactions, numerical models like ours can help to identify them by approaching the problem from an exploratory angle, isolating the effect of interest. For this, our model simulates the economic interactions of over 7000 regional economic sectors, interlinked through about 1.8 million trade relations. Under global warming, the wave-like structures of the economic response to major hurricanes like the one simulated here are likely to intensify and potentially overlap with other weather extremes.
KW  - supply chains
KW  - Hurricane Sandy
KW  - economic ripples
KW  - extreme weather
KW  - impacts
KW  - loss propagation
KW  - natural disasters
Y1  - 2021
U6  - https://doi.org/10.1088/1748-9326/ac39c0
SN  - 1748-9326
VL  - 16
IS  - 12
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Quante, Lennart
A1  - Willner, Sven N.
A1  - Middelanis, Robin
A1  - Levermann, Anders
T1  - Regions of intensification of extreme snowfall under future warming
JF  - Scientific reports
N2  - Due to climate change the frequency and character of precipitation are changing as the hydrological cycle intensifies. With regards to snowfall, global warming has two opposing influences; increasing humidity enables intense snowfall, whereas higher temperatures decrease the likelihood of snowfall. Here we show an intensification of extreme snowfall across large areas of the Northern Hemisphere under future warming. This is robust across an ensemble of global climate models when they are bias-corrected with observational data. While mean daily snowfall decreases, both the 99th and the 99.9th percentiles of daily snowfall increase in many regions in the next decades, especially for Northern America and Asia. Additionally, the average intensity of snowfall events exceeding these percentiles as experienced historically increases in many regions. This is likely to pose a challenge to municipalities in mid to high latitudes. Overall, extreme snowfall events are likely to become an increasingly important impact of climate change in the next decades, even if they will become rarer, but not necessarily less intense, in the second half of the century.
Y1  - 2021
U6  - https://doi.org/10.1038/s41598-021-95979-4
SN  - 2045-2322
VL  - 11
IS  - 1
PB  - Macmillan Publishers Limited, part of Springer Nature
CY  - Berlin
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  - 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  - 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  - 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  - Wang, Ningzhen
A1  - Daniels, Robert
A1  - Connelly, Liam
A1  - Sotzing, Michael
A1  - Wu, Chao
A1  - Gerhard, Reimund
A1  - Sotzing, Gregory A.
A1  - Cao, Yang
T1  - All-organic flexible ferroelectret nanogenerator with fabric-based electrodes for self-powered body area networks
JF  - Small : nano micro
N2  - Due to their electrically polarized air-filled internal pores, optimized ferroelectrets exhibit a remarkable piezoelectric response, making them suitable for energy harvesting. Expanded polytetrafluoroethylene (ePTFE) ferroelectret films are laminated with two fluorinated-ethylene-propylene (FEP) copolymer films and internally polarized by corona discharge. Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS)-coated spandex fabric is employed for the electrodes to assemble an all-organic ferroelectret nanogenerator (FENG). The outer electret-plus-electrode double layers form active device layers with deformable electric dipoles that strongly contribute to the overall piezoelectric response in the proposed concept of wearable nanogenerators. Thus, the FENG with spandex electrodes generates a short-circuit current which is twice as high as that with aluminum electrodes. The stacking sequence spandex/FEP/ePTFE/FEP/ePTFE/FEP/spandex with an average pore size of 3 mu m in the ePTFE films yields the best overall performance, which is also demonstrated by the displacement-versus-electric-field loop results. The all-organic FENGs are stable up to 90 degrees C and still perform well 9 months after being polarized. An optimized FENG makes three light emitting diodes (LEDs) blink twice with the energy generated during a single footstep. The new all-organic FENG can thus continuously power wearable electronic devices and is easily integrated, for example, with clothing, other textiles, or shoe insoles.
KW  - all-organic ferroelectret nanogenerator (FENG)
KW  - all-organic
KW  - piezoelectric nanogenerator (PENG)
KW  - expanded polytetrafluoroethylene
KW  - ferroelectret
KW  - micro-energy harvesting
KW  - (PEDOT
KW  - PSS)-coated porous
KW  - fabric electrodes
KW  - wearable electronics
Y1  - 2021
U6  - https://doi.org/10.1002/smll.202103161
SN  - 1613-6810
SN  - 1613-6829
VL  - 17
IS  - 33
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Stubning, Tobias
A1  - Denes, Istvan
A1  - Gerhard, Reimund
T1  - Tuning electro-mechanical properties of EAP-based haptic actuators by adjusting layer thickness and number of stacked layers
BT  - a comparison
JF  - Engineering research express
N2  - In our fast-changing world, human-machine interfaces (HMIs) are of ever-increasing importance. Among the most ubiquitous examples are touchscreens that most people are familiar with from their smartphones. The quality of such an HMI can be improved by adding haptic feedback-an imitation of using mechanical buttons-to the touchscreen. Thin-film actuators on the basis of electro-mechanically active polymers (EAPs), with the electroactive material sandwiched between two compliant electrodes, offer a promising technology for haptic surfaces. In thin-film technology, the thickness and the number of stacked layers of the electroactive dielectric are key parameters for tuning a system. Therefore, we have experimentally investigated the influence of the thickness of a single EAP layer on the electrical and the electro-mechanical performance of the transducer. In order to achieve high electro-mechanical actuator outputs, we have employed relaxor-ferroelectric ter-fluoropolymers that can be screen-printed. By means of a model-based approach, we have also directly compared single- and multi-layer actuators, thus providing guidelines for optimized transducer configurations with respect to the system requirements of haptic applications for which the operation frequency is of particular importance.
KW  - haptic feedback
KW  - vinylidenefluoride(VDF)-based polymers
KW  - screen-printed
KW  - systems
KW  - thin-film actuators
KW  - multi-layer systems
KW  - equivalent-circuit
KW  - modelling
KW  - electro-mechanically active polymers
Y1  - 2021
U6  - https://doi.org/10.1088/2631-8695/abd286
SN  - 2631-8695
VL  - 3
IS  - 1
PB  - Institute of Physics
CY  - London
ER  - 
TY  - JOUR
A1  - Werhahn, Maria
A1  - Pfrommer, Christoph
A1  - Girichidis, Philipp
T1  - Cosmic rays and non-thermal emission in simulated galaxies - III. Probing cosmic-ray calorimetry with radio spectra and the FIR-radio correlation
JF  - Monthly notices of the Royal Astronomical Society
N2  - An extinction-free estimator of the star formation rate (SFR) of galaxies is critical for understanding the high-redshift universe. To this end, the nearly linear, tight correlation of far-infrared (FIR), and radio luminosity of star-forming galaxies is widely used. While the FIR is linked to massive star formation, which also generates shock-accelerated cosmic-ray (CR) electrons and radio synchrotron emission, a detailed understanding of the underlying physics is still lacking. Hence, we perform three-dimensional magnetohydrodynamical (MHD) simulations of isolated galaxies over a broad range of halo masses and SFRs using the moving-mesh code AREPO, and evolve the CR proton energy density self-consistently. In post-processing, we calculate the steady-state spectra of primary, shock-accelerated and secondary CR electrons, which result from hadronic CR proton interactions with the interstellar medium. The resulting total radio luminosities correlate with the FIR luminosities as observed and are dominated by primary CR electrons if we account for anisotropic CR diffusion. The increasing contribution of secondary emission up to 30 per cent in starbursts is compensated by the larger bremsstrahlung and Coulomb losses. CR electrons are in the calorimetric limit and lose most of their energy through inverse Compton interactions with star light and cosmic microwave background (CMB) photons while less energy is converted into synchrotron emission. This implies steep steady-state synchrotron spectra in starbursts. Interestingly, we find that thermal free-free emission flattens the total radio spectra at high radio frequencies and reconciles calorimetric theory with observations while free-free absorption explains the observed low-frequency flattening towards the central regions of starbursts.
KW  - MHD
KW  - methods: numerical
KW  - cosmic rays
KW  - galaxies: magnetic fields
KW  - galaxies: starburst
KW  - radio continuum: galaxies
Y1  - 2021
U6  - https://doi.org/10.1093/mnras/stab2535
SN  - 0035-8711
SN  - 1365-2966
VL  - 508
IS  - 3
SP  - 4072
EP  - 4095
PB  - Oxford Univ. Press
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Vaz da Cruz, Vinícius
A1  - Eckert, Sebastian
A1  - Föhlisch, Alexander
T1  - TD-DFT simulations of K-edge resonant inelastic X-ray scattering within the restricted subspace approximation
JF  - Physical chemistry, chemical physics : PCCP ; a journal of European Chemical Societies
N2  - A scheme for simulations of resonant inelastic X-ray scattering (RIXS) cross-sections within time-dependent density functional theory (TD-DFT) applying the restricted subspace approximation (RSA) is presented. Therein both occupied core and valence Kohn-Sham orbitals are included in the donor-space, while the accepting virtual orbital space in the linear response TD-DFT equations is restricted to efficiently compute both the valence- and core-excited states of the many electron system. This yields a consistent description of all states contributing to the RIXS scattering process within a single calculation. The introduced orbital truncation allows to automatize the method and facilitates RIXS simulations for systems considerably larger than ones accessible with wave-function based methods. Using the nitrogen K-edge RIXS spectra of 2-thiopyridone and its deprotonated anion as a showcase, the method is benchmarked for different exchange-correlation functionals, the impact of the RSA is evaluated, and the effects of explicit solvation are discussed. Improvements compared to simulations in the frozen orbital approximation are also assessed. The general applicability of the framework is further tested by comparison to experimental data from the literature. The use of TD-DFT core-excited states to the calculation of vibrationally resolved RIXS spectra is also investigated by combining potential energy scans along relevant coordinates with wave packet simulations.
Y1  - 2020
U6  - https://doi.org/10.1039/d0cp04726k
SN  - 1463-9076
SN  - 1463-9084
VL  - 23
IS  - 3
SP  - 1835
EP  - 1848
PB  - Royal Society of Chemistry
CY  - Cambridge
ER  - 
TY  - JOUR
A1  - Pohl, Martin
T1  - Time-dependent treatment of cosmic-ray spectral steepening due to turbulence driving
JF  - The astrophysical journal : an international review of spectroscopy and astronomical physics
N2  - Cosmic-ray acceleration at non-relativistic shocks relies on scattering by turbulence that the cosmic rays drive upstream of the shock. We explore the rate of energy transfer from cosmic rays to non-resonant Bell modes and the spectral softening it implies. Accounting for the finite time available for turbulence driving at supernova-remnant shocks yields a smaller spectral impact than found earlier with steady-state considerations. Generally, for diffusion scaling with the Bohm rate by a factor eta, the change in spectral index is at most eta divided by the Alfvenic Mach number of the thermal sub-shock. For M (A) less than or similar to 50 it is well below this limit. Only for very fast shocks and very efficient cosmic-ray acceleration can the change in spectral index reach 0.1. For standard SNR parameters, it is negligible. Independent confirmation is derived by considering the synchrotron energy losses of electrons: if intense nonthermal multi-keV emission is produced, the energy loss, and hence the spectral steepening, is very small for hadronic cosmic rays that produce TeV-band gamma-ray emission.
Y1  - 2021
U6  - https://doi.org/10.3847/1538-4357/ac21cf
SN  - 1538-4357
VL  - 921
IS  - 2
PB  - IOP Publ. Ltd.
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  - 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  - Werhahn, Maria
A1  - Pfrommer, Christoph
A1  - Girichidis, Philipp
A1  - Puchwein, Ewald
A1  - Pakmor, Rüdiger
T1  - Cosmic rays and non-thermal emission in simulated galaxies
BT  - I. Electron and proton spectra compared to Voyager-1 data
JF  - Monthly notices of the Royal Astronomical Society
N2  - Current-day cosmic ray (CR) propagation studies use static Milky Way models and fit parametrized source distributions to data. Instead, we use three-dimensional magnetohydrodynamic (MHD) simulations of isolated galaxies with the moving-mesh code arepo that self-consistently accounts for hydrodynamic effects of CR protons. In post-processing, we calculate their steady-state spectra, taking into account all relevant loss processes. We show that this steady-state assumption is well justified in the disc and generally for regions that emit non-thermal radio and gamma rays. Additionally, we model the spectra of primary electrons, accelerated by supernova remnants, and secondary electrons and positrons produced in hadronic CR proton interactions with the gas. We find that proton spectra above 10 GeV only weakly depend on galactic radius, while they acquire a radial dependence at lower energies due to Coulomb interactions. Radiative losses steepen the spectra of primary CR electrons in the central galactic regions, while diffusive losses dominate in the outskirts. Secondary electrons exhibit a steeper spectrum than primaries because they originate from the transported steeper CR proton spectra. Consistent with Voyager-1 and AMS-02 data, our models (i) show a turnover of proton spectra below GeV energies due to Coulomb interactions so that electrons start to dominate the total particle spectra and (ii) match the shape of the positron fraction up to 10 GeV. We conclude that our steady-state CR modelling in MHD CR galaxy simulations is sufficiently realistic to capture the dominant transport effects shaping their spectra, arguing for a full MHD treatment to accurately model CR transport in the future.
KW  - astroparticle physics
KW  - MHD
KW  - methods: numerical
KW  - cosmic rays
KW  - local
KW  - interstellar matter
Y1  - 2021
U6  - https://doi.org/10.1093/mnras/stab1324
SN  - 0035-8711
SN  - 1365-2966
VL  - 505
IS  - 3
SP  - 3273
EP  - 3294
PB  - Oxford University Press
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Vanaraj, Viswajith
A1  - Niederhofer, Florian
A1  - Goudfrooij, Paul
T1  - Role of host galaxy in the formation of multiple stellar populations
BT  - analysis of NGC 1786 and NGC 1898
JF  - Monthly notices of the Royal Astronomical Society
N2  - Even after decades of research, the origin of multiple stellar populations in globular clusters (GCs) remains enigmatic. The question as to whether the galaxy environment plays a role in their formation remains unanswered. To that extent, we analysed two classical (>10 Gyr old) Large Magellanic Cloud GCs, NGC 1786 and NGC 1898, using imaging data from Hubble Space Telescope to compare and contrast them with ancient Galactic GCs to assess systematic differences that might exist between their abundance variations. We calculated their red giant branch width, subtracted the effect of metallicity, and compared it with the available data on Galactic GCs by plotting them against initial and current cluster mass. We see that the two clusters follow the same general trend as that of the Galactic GCs, and Galactic GCs from different progenitors follow the same general trend as one another, indicating that the galaxy environment may only play a minor role in the formation of multiple stellar populations within GCs.
KW  - Hertzsprung-Russell and colour-magnitude diagrams
KW  - globular clusters: general
KW  - galaxies: individual: LMC
KW  - galaxies: star clusters: individual
KW  - NGC 1786
KW  - NGC 1898
Y1  - 2021
U6  - https://doi.org/10.1093/mnras/stab2094
SN  - 0035-8711
SN  - 1365-2966
VL  - 507
IS  - 1
SP  - 282
EP  - 299
PB  - Oxford University Press
CY  - Oxford
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  - 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  - 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  - Krtička, Jiří
A1  - Feldmeier, Achim
T1  - Stochastic light variations in hot stars from wind instability
BT  - finding photometric signatures and testing against the TESS data
JF  - Astronomy and astrophysics : an international weekly journal / European Southern Observatory (ESO)
N2  - Context
Line-driven wind instability is expected to cause small-scale wind inhomogeneities, X-ray emission, and wind line profile variability. The instability can already develop around the sonic point if it is initiated close to the photosphere due to stochastic turbulent motions. In such cases, it may leave its imprint on the light curve as a result of wind blanketing.

Aims
We study the photometric signatures of the line-driven wind instability.

Methods
We used line-driven wind instability simulations to determine the wind variability close to the star. We applied two types of boundary perturbations: a sinusoidal one that enables us to study in detail the development of the instability and a stochastic one given by a Langevin process that provides a more realistic boundary perturbation. We estimated the photometric variability from the resulting mass-flux variations. The variability was simulated assuming that the wind consists of a large number of independent conical wind sectors. We compared the simulated light curves with TESS light curves of OB stars that show stochastic variability.

Results
We find two typical signatures of line-driven wind instability in photometric data: a knee in the power spectrum of magnitude fluctuations, which appears due to engulfment of small-scale structure by larger structures, and a negative skewness of the distribution of fluctuations, which is the result of spatial dominance of rarefied regions. These features endure even when combining the light curves from independent wind sectors.

Conclusions
The stochastic photometric variability of OB stars bears certain signatures of the line-driven wind instability. The distribution function of observed photometric data shows negative skewness and the power spectra of a fraction of light curves exhibit a knee. This can be explained as a result of the line-driven wind instability triggered by stochastic base perturbations.
KW  - stars: winds
KW  - outflows
KW  - stars: mass-loss
KW  - stars: early-type
KW  - hydrodynamics
KW  - instabilities
KW  - stars: variables: general
Y1  - 2021
U6  - https://doi.org/10.1051/0004-6361/202040148
SN  - 1432-0746
VL  - 648
PB  - EDP Sciences
CY  - Les Ulis
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  - 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  - 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  - Whittingham, Joseph
A1  - Sparre, Martin
A1  - Pfrommer, Christoph
A1  - Pakmor, Rüdiger
T1  - The impact of magnetic fields on cosmological galaxy mergers
BT  - I. Reshaping gas and stellar discs
JF  - Monthly notices of the Royal Astronomical Society
N2  - Mergers play an important role in galaxy evolution. In particular, major mergers are able to have a transformative effect on galaxy morphology. In this paper, we investigate the role of magnetic fields in gas-rich major mergers. To this end, we run a series of high-resolution magnetohydrodynamic (MHD) zoom-in simulations with the moving-mesh code arepo and compare the outcome with hydrodynamic simulations run from the same initial conditions. This is the first time that the effect of magnetic fields in major mergers has been investigated in a cosmologically consistent manner. In contrast to previous non-cosmological simulations, we find that the inclusion of magnetic fields has a substantial impact on the production of the merger remnant. Whilst magnetic fields do not strongly affect global properties, such as the star formation history, they are able to significantly influence structural properties. Indeed, MHD simulations consistently form remnants with extended discs and well-developed spiral structure, whilst hydrodynamic simulations form more compact remnants that display distinctive ring morphology. We support this work with a resolution study and show that whilst global properties are broadly converged across resolution and physics models, morphological differences only develop given sufficient resolution. We argue that this is due to the more efficient excitement of a small-scale dynamo in higher resolution simulations, resulting in a more strongly amplified field that is better able to influence gas dynamics.
KW  - MHD
KW  - methods: numerical
KW  - galaxies: interactions
KW  - galaxies: magnetic
KW  - fields
Y1  - 2021
U6  - https://doi.org/10.1093/mnras/stab1425
SN  - 0035-8711
SN  - 1365-2966
VL  - 506
IS  - 1
SP  - 229
EP  - 255
PB  - Oxford Univ. Press
CY  - Oxford
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  - 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  - 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  - Büchner, Robby
A1  - Fondell, Mattis
A1  - Haverkamp, Robert
A1  - Pietzsch, Annette
A1  - Vaz da Cruz, Vinícius
A1  - Föhlisch, Alexander
T1  - The porphyrin center as a regulator for metal-ligand covalency and pi hybridization in the entire molecule
JF  - Physical chemistry, chemical physics : PCCP ; a journal of European Chemical Societies
N2  - The central moiety of porphyrins is shown to control the charge state of the inner complex and links it by covalent interaction to the peripheral substituents. This link, which enables the versatile functions of porphyrins, is not picked up in the established, reduced four orbital picture [Gouterman, J. Mol. Spectrosc., 1961, 6, 138]. X-ray absorption spectroscopy at the N K-edge with density functional theory approaches gives access to the full electronic structure, in particular the pi* manifold beyond the Gouterman orbitals. Systematic variation of the central moiety highlights two linked, governing trends: The ionicity of the porphyrin center increases from the aminic N-H to N-Cu to N-Zn to N-Mg to the iminic N:. At the same time covalency with peripheral substituents increases and compensates the buildup of high charge density at the coordinated nitrogen sites.
Y1  - 2021
U6  - https://doi.org/10.1039/d1cp03944j
SN  - 1463-9076
SN  - 1463-9084
VL  - 23
IS  - 43
SP  - 24765
EP  - 24772
PB  - Royal Society of Chemistry
CY  - Cambridge
ER  - 
TY  - JOUR
A1  - Kreuzer, Moritz
A1  - Reese, Ronja
A1  - Huiskamp, Willem Nicholas
A1  - Petri, Stefan
A1  - Albrecht, Torsten
A1  - Feulner, Georg
A1  - Winkelmann, Ricarda
T1  - Coupling framework (1.0) for the PISM (1.1.4) ice sheet model and the MOMS (5.1.0) ocean model via the PICO ice shelf cavity model in an Antarctic domain
JF  - Geoscientific model development : an interactive open access journal of the European Geosciences Union
N2  - The past and future evolution of the Antarctic Ice Sheet is largely controlled by interactions between the ocean and floating ice shelves. To investigate these interactions, coupled ocean and ice sheet model configurations are required. Previous modelling studies have mostly relied on high-resolution configurations, limiting these studies to individual glaciers or regions over short timescales of decades to a few centuries. We present a framework to couple the dynamic ice sheet model PISM (Parallel Ice Sheet Model) with the global ocean general circulation model MOM5 (Modular Ocean Model) via the ice shelf cavity model PICO (Pots-dam Ice-shelf Cavity mOdel). As ice shelf cavities are not resolved by MOM5 but are parameterized with the PICO box model, the framework allows the ice sheet and ocean components to be run at resolutions of 16 km and 3 degrees respectively. This approach makes the coupled configuration a useful tool for the analysis of interactions between the Antarctic Ice Sheet and the global ocean over time spans of the order of centuries to millennia. In this study, we describe the technical implementation of this coupling framework: sub-shelf melting in the ice sheet component is calculated by PICO from modelled ocean temperatures and salinities at the depth of the continental shelf, and, vice versa, the resulting mass and energy fluxes from melting at the ice-ocean interface are transferred to the ocean component. Mass and energy fluxes are shown to be conserved to machine precision across the considered component domains. The implementation is computationally efficient as it introduces only minimal overhead. Furthermore, the coupled model is evaluated in a 4000 year simulation under constant present-day climate forcing and is found to be stable with respect to the ocean and ice sheet spin-up states. The framework deals with heterogeneous spatial grid geometries, varying grid resolutions, and timescales between the ice and ocean component in a generic way; thus, it can be adopted to a wide range of model set-ups.
Y1  - 2021
U6  - https://doi.org/10.5194/gmd-14-3697-2021
SN  - 1991-959X
SN  - 1991-9603
VL  - 14
IS  - 6
SP  - 3697
EP  - 3714
PB  - Copernicus
CY  - Göttingen
ER  - 
TY  - JOUR
A1  - Robinson, Matthew Scott
A1  - Niebuhr, Mario
A1  - Lever, Fabiano
A1  - Mayer, Dennis
A1  - Metje, Jan
A1  - Gühr, Markus
T1  - Ultrafast photo-ion probing of the ring-opening process in trans-stilbene oxide
JF  - Chemistry - a European journal
N2  - The ultrafast photo-induced ring opening of the oxirane derivative trans-stilbene oxide has been studied through the use of ultrafast UV/UV pump-probe spectroscopy by using photo-ion detection. Single- and multiphoton probe paths and final states were identified through comparisons between UV power studies and synchrotron-based vacuum ultraviolet (VUV) single-photon ionization studies. Three major time-dependent features of the parent ion (sub-450 fs decay, (1.5 +/- 0.2) ps, and >100 ps) were observed. These decays are discussed in conjunction with the primary ring-opening mechanism of stilbene oxide, which occurs through C-C dissociation in the oxirane ring. The appearance of fragments relating to the masses of dehydrogenated diphenylmethane (167 amu) and dehydrogenated methylbenzene (90 amu) were also investigated. The appearance of the 167 amu fragment could suggest an alternative ultrafast ring-opening pathway via the dissociation of one of the C-O bonds within the oxirane ring.
KW  - femtochemistry
KW  - mass spectrometry
KW  - photochemistry
KW  - small ring systems
KW  - stilbene oxide
Y1  - 2021
U6  - https://doi.org/10.1002/chem.202101343
SN  - 1521-3765
VL  - 27
IS  - 44
SP  - 11418
EP  - 11427
PB  - Wiley-VCH
CY  - Weinheim
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  - 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  - Frenkel, Mark
A1  - Arya, Pooja
A1  - Bormashenḳo, Edṿard
A1  - Santer, Svetlana
T1  - Quantification of ordering in active light driven colloids
JF  - Journal of colloid and interface science
N2  - Hypothesis:
Light driven diffusioosmosis allows for the controlled self-assembly of colloidal particles. Illuminating of colloidal suspensions built of nanoporous silica microspheres dispersed in aqueous solution containing photosensitive azobenzene cationic surfactant enables manufacturing self-assembled well-ordered 2D colloidal patterns. We conjectured that ordering in this patterns may be quantified with the Voronoi entropy.

Experiments: 
Depending on the isomerization state the surfactant either tends to absorb (trans-state) into negatively charged pores or diffuse out (cis-isomer) of the particles generating an excess concentration near the colloids outer surface and thus resulting in the initiation of diffusioosmotic flow. The direction of the flow can be controlled by the wavelength and intensity of irradiation. Under irradiations with blue light the colloids separate within a few seconds forming equidistant particle ensemble where long range diffusioosmotic repulsion acts over distances exceeding several times the particle diameter. Hierarchy of ordering in the studied colloidal systems is distinguished, namely: i) ordering of individual separated colloidal particles; ii) ordering of clusters built of colloidal particles; iii) ordering within clusters of individual colloidal particles. 

Findings: 
The study of the temporal change in the Voronoi entropy for the light illuminated colloidal dispersions allowed quantification of ordering evolution on different lateral scales and under different irradiation conditions. Fourier analysis of the time evolution of the Voronoi entropy is presented. Fourier spectrum of the "small-area" (100 x 100 mu m) reveals the pronounced peak at f = 1.125 Hz reflecting the oscillations of individual particles at this frequency. Ordering in hierarchical colloidal system emerging on different lateral scales is addressed. The minimal Voronoi entropy is intrinsic for the close packed 2D clusters. (C) 2020 Published by Elsevier Inc.
KW  - Azobenzene containing cationic surfactants
KW  - Light induced diffusioosmotic flow
KW  - 2D colloid ordering
KW  - Voronoi entropy
Y1  - 2021
U6  - https://doi.org/10.1016/j.jcis.2020.10.053
SN  - 0021-9797
SN  - 1095-7103
VL  - 586
SP  - 866
EP  - 875
PB  - Elsevier
CY  - San Diego
ER  - 
TY  - JOUR
A1  - Rikani, Albano
A1  - Schewe, Jacob
T1  - Global bilateral migration projections accounting for diasporas, transit and return flows, and poverty constraints
JF  - Demographic research
N2  - BACKGROUND
Anticipating changes in international migration patterns is useful for demographic studies and for designing policies that support the well-being of those involved. Existing forecasting methods do not account for a number of stylized facts that emerge from large-scale migration observations and theories: existing migrant communities - diasporas - act to lower migration costs and thereby provide a mechanism of self-amplification; return migration and transit migration are important components of global migration flows; and poverty constrains emigration.

OBJECTIVE
Here we present hindcasts and future projections of international migration that explicitly account for these nonlinear features.

METHODS
We develop a dynamic model that simulates migration flows by origin, destination, and place of birth. We calibrate the model using recently constructed global datasets of bilateral migration. 

RESULTS
We show that the model reproduces past patterns and trends well based only on initial migrant stocks and changes in national incomes. We then project migration flows under future scenarios of global socioeconomic development.

CONCLUSIONS
Different assumptions about income levels and between-country inequality lead to markedly different migration trajectories, with migration flows either converging towards net zero if incomes in presently poor countries catch up with the rest of the world; or remaining high or even rising throughout the 21st century if economic development is slower and more unequal. Importantly, diasporas induce significant inertia and sizable return migration flows.
KW  - diaspora
KW  - international migration
KW  - migration transition
KW  - return migration
KW  - simulation model
KW  - transit migration
Y1  - 2021
U6  - https://doi.org/10.4054/DemRes.2021.45.4
SN  - 2363-7064
VL  - 45
SP  - 87
EP  - 140
PB  - Max Planck Inst. for Demographic Research
CY  - Rostock
ER  - 
TY  - JOUR
A1  - Diercke, Andrea
A1  - Kuckein, Christoph
A1  - Verma, Meetu
A1  - Denker, Carsten
T1  - Filigree in the surroundings of polar crown and high-latitude filaments
JF  - Solar physics : a journal for solar and solar-stellar research and the study of solar terrestrial physics
N2  - High-resolution observations of polar crown and high-latitude filaments are scarce. We present a unique sample of such filaments observed in high-resolution H alpha narrow-band filtergrams and broad-band images, which were obtained with a new fast camera system at the Vacuum Tower Telescope (VTT), Tenerife, Spain. The Chromospheric Telescope (ChroTel) provided full-disk context observations in H alpha, CaiiK, and Hei 10830 angstrom. The Helioseismic and Magnetic Imager (HMI) and the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO) provided line-of-sight magnetograms and ultraviolet (UV) 1700 angstrom filtergrams, respectively. We study filigree in the vicinity of polar crown and high-latitude filaments and relate their locations to magnetic concentrations at the filaments' footpoints. Bright points are a well studied phenomenon in the photosphere at low latitudes, but they were not yet studied in the quiet network close to the poles. We examine size, area, and eccentricity of bright points and find that their morphology is very similar to their counterparts at lower latitudes, but their sizes and areas are larger. Bright points at the footpoints of polar crown filaments are preferentially located at stronger magnetic flux concentrations, which are related to bright regions at the border of supergranules as observed in UV filtergrams. Examining the evolution of bright points on three consecutive days reveals that their amount increases while the filament decays, which indicates they impact the equilibrium of the cool plasma contained in filaments.
KW  - Chromosphere
KW  - Quiet
KW  - Granulation
KW  - Magnetic fields
KW  - Photosphere
KW  - Prominences
KW  - Quiescent
Y1  - 2021
U6  - https://doi.org/10.1007/s11207-021-01776-7
SN  - 0038-0938
SN  - 1573-093X
VL  - 296
IS  - 2
PB  - Springer
CY  - Dordrecht
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  - Wiesner, Karoline
A1  - Ladyman, James
T1  - Complex systems are always correlated but rarely information processing
JF  - Journal of physics. Complexity
N2  - 'Complex systems are information processors' is a statement that is frequently made. Here we argue for the distinction between information processing-in the sense of encoding and transmitting a symbolic representation-and the formation of correlations (pattern formation/self-organisation). The study of both uses tools from information theory, but the purpose is very different in each case: explaining the mechanisms and understanding the purpose or function in the first case, versus data analysis and correlation extraction in the latter. We give examples of both and discuss some open questions. The distinction helps focus research efforts on the relevant questions in each case.
KW  - correlations
KW  - information theory
KW  - complex systems
KW  - information
KW  - processing
KW  - self-organisation
Y1  - 2021
U6  - https://doi.org/10.1088/2632-072X/ac371c
SN  - 2632-072X
VL  - 2
IS  - 4
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Culpan, Rick
A1  - Pelisoli, Ingrid
A1  - Geier, Stephan
T1  - Clean catalogues of blue horizontal-branch stars using Gaia EDR3
JF  - Astronomy and astrophysics : an international weekly journal / European Southern Observatory (ESO)
N2  - Context.
Blue horizontal-branch stars evolve from low-mass stars that have completed their main-sequence lifetimes and undergone a helium flash at the end of their red-giant phase. As such, blue horizontal-branch stars are very old objects that can be used as markers in studies of the Galactic structure and formation history. To create a clean sky catalogue of blue horizontal-branch stars, we cross-matched the Gaia data release 2 (DR2) dataset with existing reference catalogues to define selection criteria based on Gaia DR2 parameters. Following the publication of Gaia early data release 3 (EDR3), these methods were verified and subsequently applied to this latest release. 

Aims. 
Previous catalogues of blue horizontal-branch stars were developed using spectral analyses or were restricted to individual globular clusters. The purpose of this catalogue is to identify a set of blue horizontal-branch star candidates that have been selected using photometric and astrometric observations and exhibits a low contamination rate. This has been deemed important as the success of the Gaia mission has changed the way that targets are selected for large-scale spectroscopic surveys, meaning that far fewer spectra will be acquired for blue horizontal-branch stars in the future unless they are specifically targeted. <br /> Methods. We cross-matched reference blue horizontal-branch datasets with the Gaia DR2 database and defined two sets of selection criteria. Firstly, in Gaia DR2 - colour and absolute G magnitude space, and secondly, in Gaia DR2 - colour and reduced proper motion space. The main-sequence contamination in both subsets of the catalogue was reduced, at the expense of completeness, by concentrating on the Milky Way's Galactic halo, where relatively young main-sequence stars were not expected. The entire catalogue is limited to those stars with no apparent neighbours within 5 arcsec. These methods were verified and subsequently applied to the Gaia EDR3.

Results.
We present a catalogue, based on Gaia EDR3, of 57 377 blue horizontal-branch stars. The Gaia EDR3 parallax was used in selecting 16 794 candidates and the proper motions were used to identify a further 40 583 candidates.
KW  - Hertzsprung-Russell and C-M diagrams
KW  - stars: horizontal-branch
KW  - catalogs
KW  - Galaxy: stellar content
Y1  - 2021
U6  - https://doi.org/10.1051/0004-6361/202040074
SN  - 1432-0746
VL  - 654
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Rüdiger, Günther
A1  - Küker, Manfred
T1  - Angular momentum transport by magnetoconvection and the magnetic modulation of the solar differential rotation
JF  - Astronomy and astrophysics : an international weekly journal / European Southern Observatory (ESO)
N2  - In order to explain the variance of the solar rotation law during the activity minima and maxima, the angular momentum transport by rotating magnetoconvection is simulated in a convective box penetrated by an inclined azimuthal magnetic field. Turbulence-induced kinetic and magnetic stresses and the Lorentz force of the large-scale magnetic background field are the basic transporters of angular momentum. Without rotation, the sign of the magnetic stresses naturally depends on the signs of the field components as positive (negative) B theta B phi transport the angular momentum poleward (equatorward). For fast enough rotation, however, the turbulence-originated Reynolds stresses start to dominate the transport of the angular momentum flux. The simulations show that positive ratios of the two meridional magnetic field components to the azimuthal field reduce the inward radial as well as the equatorward latitudinal transport, which result from hydrodynamic calculations. Only for B theta B phi>0 (generated by solar-type rotation laws with an accelerated equator) does the magnetic-influenced rotation at the solar surface prove to be flatter than the nonmagnetic profile together with the observed slight spin-down of the equator. The latter phenomenon does not appear for antisolar rotation with polar vortex as well as for rotation laws with prevailing radial shear.
KW  - magnetic fields
KW  - Sun
KW  - rotation
KW  - convection
Y1  - 2021
U6  - https://doi.org/10.1051/0004-6361/202039912
SN  - 1432-0746
VL  - 649
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Shoaee, Safa
A1  - Sanna, Anna Laura
A1  - Sforazzini, Giuseppe
T1  - Elucidating charge generation in green-solvent processed organic solar cells
JF  - Molecules : a journal of synthetic chemistry and natural product chemistry / Molecular Diversity Preservation International
N2  - Organic solar cells have the potential to become the cheapest form of electricity. Rapid increase in the power conversion efficiency of organic solar cells (OSCs) has been achieved with the development of non-fullerene small-molecule acceptors. Next generation photovoltaics based upon environmentally benign "green solvent" processing of organic semiconductors promise a step-change in the adaptability and versatility of solar technologies and promote sustainable development. However, high-performing OSCs are still processed by halogenated (non-environmentally friendly) solvents, so hindering their large-scale manufacture. In this perspective, we discuss the recent progress in developing highly efficient OSCs processed from eco-compatible solvents, and highlight research challenges that should be addressed for the future development of high power conversion efficiencies devices.
KW  - organic solar cells
KW  - green solvents
KW  - non-halogenated solvents
KW  - exaction
KW  - diffusion
KW  - photoluminescence quenching
Y1  - 2021
U6  - https://doi.org/10.3390/molecules26247439
SN  - 1420-3049
VL  - 26
IS  - 24
PB  - MDPI
CY  - Basel
ER  - 
TY  - JOUR
A1  - 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  - Chimeras on a social-type network
JF  - Mathematical modelling of natural phenomena : MMNP
N2  - We consider a social-type network of coupled phase oscillators. Such a network consists of an active core of mutually interacting elements, and of a flock of passive units, which follow the driving from the active elements, but otherwise are not interacting. We consider a ring geometry with a long-range coupling, where active oscillators form a fluctuating chimera pattern. We show that the passive elements are strongly correlated. This is explained by negative transversal Lyapunov exponents.
KW  - Network
KW  - Chimera
KW  - correlations
KW  - Lyapunov exponent
Y1  - 2021
U6  - https://doi.org/10.1051/mmnp/2021012
SN  - 0973-5348
SN  - 1760-6101
VL  - 16
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Schindler, Daniel
A1  - Moldenhawer, Ted
A1  - Stange, Maike
A1  - Lepro, Valentino
A1  - Beta, Carsten
A1  - Holschneider, Matthias
A1  - Huisinga, Wilhelm
T1  - Analysis of protrusion dynamics in amoeboid cell motility by means of regularized contour flows
JF  - PLoS Computational Biology : a new community journal
N2  - Amoeboid cell motility is essential for a wide range of biological processes including wound healing, embryonic morphogenesis, and cancer metastasis. It relies on complex dynamical patterns of cell shape changes that pose long-standing challenges to mathematical modeling and raise a need for automated and reproducible approaches to extract quantitative morphological features from image sequences. Here, we introduce a theoretical framework and a computational method for obtaining smooth representations of the spatiotemporal contour dynamics from stacks of segmented microscopy images. Based on a Gaussian process regression we propose a one-parameter family of regularized contour flows that allows us to continuously track reference points (virtual markers) between successive cell contours. We use this approach to define a coordinate system on the moving cell boundary and to represent different local geometric quantities in this frame of reference. In particular, we introduce the local marker dispersion as a measure to identify localized membrane expansions and provide a fully automated way to extract the properties of such expansions, including their area and growth time. The methods are available as an open-source software package called AmoePy, a Python-based toolbox for analyzing amoeboid cell motility (based on time-lapse microscopy data), including a graphical user interface and detailed documentation. Due to the mathematical rigor of our framework, we envision it to be of use for the development of novel cell motility models. We mainly use experimental data of the social amoeba Dictyostelium discoideum to illustrate and validate our approach. <br /> Author summary Amoeboid motion is a crawling-like cell migration that plays an important key role in multiple biological processes such as wound healing and cancer metastasis. This type of cell motility results from expanding and simultaneously contracting parts of the cell membrane. From fluorescence images, we obtain a sequence of points, representing the cell membrane, for each time step. By using regression analysis on these sequences, we derive smooth representations, so-called contours, of the membrane. Since the number of measurements is discrete and often limited, the question is raised of how to link consecutive contours with each other. In this work, we present a novel mathematical framework in which these links are described by regularized flows allowing a certain degree of concentration or stretching of neighboring reference points on the same contour. This stretching rate, the so-called local dispersion, is used to identify expansions and contractions of the cell membrane providing a fully automated way of extracting properties of these cell shape changes. We applied our methods to time-lapse microscopy data of the social amoeba Dictyostelium discoideum.
Y1  - 2021
U6  - https://doi.org/10.1371/journal.pcbi.1009268
SN  - 1553-734X
SN  - 1553-7358
VL  - 17
IS  - 8
PB  - PLoS
CY  - San Fransisco
ER  - 
TY  - JOUR
A1  - 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  - Vollbrecht, Joachim
A1  - Brus, Viktor V.
T1  - Effects of recombination order on open-circuit voltage decay measurements of organic and perovskite solar cells
JF  - Energies : open-access journal of related scientific research, technology development and studies in policy and management / Molecular Diversity Preservation International (MDPI)
N2  - Non-geminate recombination, as one of the most relevant loss mechanisms in organic and perovskite solar cells, deserves special attention in research efforts to further increase device performance. It can be subdivided into first, second, and third order processes, which can be elucidated by the effects that they have on the time-dependent open-circuit voltage decay. In this study, analytical expressions for the open-circuit voltage decay exhibiting one of the aforementioned recombination mechanisms were derived. It was possible to support the analytical models with experimental examples of three different solar cells, each of them dominated either by first (PBDBT:CETIC-4F), second (PM6:Y6), or third (irradiated CH3NH3PbI3) order recombination. Furthermore, a simple approach to estimate the dominant recombination process was also introduced and tested on these examples. Moreover, limitations of the analytical models and the measurement technique itself were discussed.
KW  - organic solar cells
KW  - perovskite solar cells
KW  - non-geminate recombination
KW  - recombination order
KW  - open-circuit voltage decay
Y1  - 2021
U6  - https://doi.org/10.3390/en14164800
SN  - 1996-1073
VL  - 14
IS  - 16
PB  - MDPI
CY  - Basel
ER  - 
TY  - JOUR
A1  - 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  - Kluge, Lucas
A1  - Schewe, Jacob
T1  - Evaluation and extension of the radiation model for internal migration
JF  - Physical review : E, Statistical, nonlinear and soft matter physics
N2  - Human migration is often studied using gravity models. These models, however, have known limitations, including analytic inconsistencies and a dependence on empirical data to calibrate multiple parameters for the region of interest. Overcoming these limitations, the radiation model has been proposed as an alternative, universal approach to predicting different forms of human mobility, but has not been adopted for studying migration. Here we show, using data on within-country migration from the USA and Mexico, that the radiation model systematically underpredicts long-range moves, while the traditional gravity model performs well for large distances. The universal opportunity model, an extension of the radiation model, shows an improved fit of long-range moves compared to the original radiation model, but at the cost of introducing two additional parameters. We propose a more parsimonious extension of the radiation model that introduces a single parameter. We demonstrate that it fits the data over the full distance spectrum and also-unlike the universal opportunity model-preserves the analytical property of the original radiation model of being equivalent to a gravity model in the limit of a uniform population distribution.
Y1  - 2021
U6  - https://doi.org/10.1103/PhysRevE.104.054311
SN  - 2470-0045
SN  - 2470-0053
SN  - 2470-0061
VL  - 104
IS  - 5
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Magkos, Sotirios
A1  - Kupsch, Andreas
A1  - Bruno, Giovanni
T1  - Suppression of cone-beam artefacts with Direct Iterative Reconstruction Computed Tomography Trajectories (DIRECTT)
JF  - Journal of imaging : open access journal
N2  - The reconstruction of cone-beam computed tomography data using filtered back-projection algorithms unavoidably results in severe artefacts. We describe how the Direct Iterative Reconstruction of Computed Tomography Trajectories (DIRECTT) algorithm can be combined with a model of the artefacts for the reconstruction of such data. The implementation of DIRECTT results in reconstructed volumes of superior quality compared to the conventional algorithms.
KW  - iteration method
KW  - signal processing
KW  - X-ray imaging
KW  - computed tomography
Y1  - 2021
U6  - https://doi.org/10.3390/jimaging7080147
SN  - 2313-433X
VL  - 7
IS  - 8
PB  - MDPI
CY  - Basel
ER  -