@article{GuliakovaGorokhovatskyGalikhanovetal.2019, author = {Guliakova, A. A. and Gorokhovatsky, Yu. A. and Galikhanov, M. F. and Fr{\"u}bing, Peter}, title = {Thermoactivational spectroscopy of the high impact polystyrene based composite films}, series = {St. Petersburg Polytechnic University Journal : Physics and Mathematics}, volume = {12}, journal = {St. Petersburg Polytechnic University Journal : Physics and Mathematics}, number = {4}, publisher = {Elsevier}, address = {Amsterdam}, issn = {2405-7223}, doi = {10.18721/JPM.12401}, pages = {9 -- 16}, year = {2019}, abstract = {The relaxation processes in the high impact polystyrene (HIPS) films filled with 2, 4, 6 vol.\% of titanium dioxide (TiO2) of the rutile modification have been studied using the thermally stimulated depolarization current (TSDC) technique. Three relaxation processes were observed in the composite HIPS films. The first one (a-relaxation peak) appeared at about 93 degrees C and represented the glass transition. The second peak p was a high-temperature part of the first one and overlapped it. The p peak was caused by the release and subsequent motion of excess charges deposited during the electret preparation or the polarization process. The third peak appeared at about 150 degrees C and occurred only in the spectra of the composite films. The overlapping peaks were separated by the thermal cleaning technique. The subsequent application of the numerical methods (the Tikhonov regularization technique) allowed to determine the activation energy of the second process and to compare the obtained value with the corresponding data on the dielectric relaxation.}, language = {ru} } @article{KrapfLukatMarinarietal.2019, author = {Krapf, Diego and Lukat, Nils and Marinari, Enzo and Metzler, Ralf and Oshanin, Gleb and Selhuber-Unkel, Christine and Squarcini, Alessio and Stadler, Lorenz and Weiss, Matthias and Xu, Xinran}, title = {Spectral Content of a Single Non-Brownian Trajectory}, series = {Physical review : X, Expanding access}, volume = {9}, journal = {Physical review : X, Expanding access}, number = {1}, publisher = {American Physical Society}, address = {College Park}, issn = {2160-3308}, doi = {10.1103/PhysRevX.9.011019}, pages = {13}, year = {2019}, abstract = {Time-dependent processes are often analyzed using the power spectral density (PSD) calculated by taking an appropriate Fourier transform of individual trajectories and finding the associated ensemble average. Frequently, the available experimental datasets are too small for such ensemble averages, and hence, it is of a great conceptual and practical importance to understand to which extent relevant information can be gained from S(f, T), the PSD of a single trajectory. Here we focus on the behavior of this random, realization-dependent variable parametrized by frequency f and observation time T, for a broad family of anomalous diffusions-fractional Brownian motion with Hurst index H-and derive exactly its probability density function. We show that S(f, T) is proportional-up to a random numerical factor whose universal distribution we determine-to the ensemble-averaged PSD. For subdiffusion (H < 1/2), we find that S(f, T) similar to A/f(2H+1) with random amplitude A. In sharp contrast, for superdiffusion (H > 1/2) S(f, T) similar to BT2H-1/f(2) with random amplitude B. Remarkably, for H > 1/2 the PSD exhibits the same frequency dependence as Brownian motion, a deceptive property that may lead to false conclusions when interpreting experimental data. Notably, for H > 1/2 the PSD is ageing and is dependent on T. Our predictions for both sub-and superdiffusion are confirmed by experiments in live cells and in agarose hydrogels and by extensive simulations.}, language = {en} } @article{SemenyshynHentschelStanglmairetal.2018, author = {Semenyshyn, Rostyslav and Hentschel, Mario and Stanglmair, Christoph and Teutsch, Tanja and Tarin, Cristina and Pacholski, Claudia and Giessen, Harald and Neubrech, Frank}, title = {In vitro monitoring conformational changes of polypeptide monolayers using infrared plasmonic nanoantennas}, series = {Nano letters : a journal dedicated to nanoscience and nanotechnology}, volume = {19}, journal = {Nano letters : a journal dedicated to nanoscience and nanotechnology}, number = {1}, publisher = {American Chemical Society}, address = {Washington}, issn = {1530-6984}, doi = {10.1021/acs.nanolett.8b02372}, pages = {1 -- 7}, year = {2018}, abstract = {Proteins and peptides play a predominant role in biochemical reactions of living cells. In these complex environments, not only the constitution of the molecules but also their three-dimensional configuration defines their functionality. This so-called secondary structure of proteins is crucial for understanding their function in living matter. Misfolding, for example, is suspected as the cause of neurodegenerative diseases such as Alzheimer's and Parkinson's disease. Ultimately, it is necessary to study a single protein and its folding dynamics. Here, we report a first step in this direction, namely ultrasensitive detection and discrimination of in vitro polypeptide folding and unfolding processes using resonant plasmonic nanoantennas for surface-enhanced vibrational spectroscopy. We utilize poly-l-lysine as a model system which has been functionalized on the gold surface. By in vitro infrared spectroscopy of a single molecular monolayer at the amide I vibrations we directly monitor the reversible conformational changes between α-helix and β-sheet states induced by controlled external chemical stimuli. Our scheme in combination with advanced positioning of the peptides and proteins and more brilliant light sources is highly promising for ultrasensitive in vitro studies down to the single protein level.}, language = {en} } @article{HintonOngTorres2019, author = {Hinton, James Anthony and Ong, R. A. and Torres, D.}, title = {Introduction to CTA Science}, series = {Science with the Cherenkov Telescope Array}, journal = {Science with the Cherenkov Telescope Array}, publisher = {World Scientific}, address = {New Jersey}, isbn = {978-981-327-008-4}, doi = {10.1142/9789813270091_0001}, pages = {1 -- 25}, year = {2019}, abstract = {Ground-based gamma-ray astronomy is a young field with enormous scientific potential. The possibility of astrophysical measurements at teraelectronvolt (TeV) energies was demonstrated in 1989 with the detection of a clear signal from the Crab nebula above 1 TeV with the Whipple 10 m imaging atmospheric Cherenkov telescope (IACT). Since then, the instrumentation for, and techniques of, astronomy with IACTs have evolved to the extent that a flourishing new scientific discipline has been established, with the detection of more than 150 sources and a major impact in astrophysics and more widely in physics. The current major arrays of IACTs, H.E.S.S., MAGIC, and VERITAS, have demonstrated the huge physics potential at these energies as well as the maturity of the detection technique. Many astrophysical source classes have been established, some with many well-studied individual objects, but there are indications that the known sources represent the tip of the iceberg in terms of both individual objects and source classes. The Cherenkov Telescope Array (CTA) will transform our understanding of the high-energy universe and will explore questions in physics of fundamental importance. As a key member of the suite of new and upcoming major astroparticle physics experiments and observatories, CTA will exploit synergies with gravitational wave and neutrino observatories as well as with classical photon observatories. CTA will address a wide range of major questions in and beyond astrophysics, which can be grouped into three broad themes…}, language = {en} } @article{SteppaHolch2019, author = {Steppa, Constantin Beverly and Holch, Tim Lukas}, title = {HexagDLy-Processing hexagonally sampled data with CNNs in PyTorch}, series = {SoftwareX}, volume = {9}, journal = {SoftwareX}, publisher = {Elsevier}, address = {Amsterdam}, issn = {2352-7110}, doi = {10.1016/j.softx.2019.02.010}, pages = {193 -- 198}, year = {2019}, abstract = {HexagDLy is a Python-library extending the PyTorch deep learning framework with convolution and pooling operations on hexagonal grids. It aims to ease the access to convolutional neural networks for applications that rely on hexagonally sampled data as, for example, commonly found in ground-based astroparticle physics experiments.}, language = {en} } @article{FeudelTuckermanZaksetal.2017, author = {Feudel, Fred and Tuckerman, Laurette S. and Zaks, Michael and Hollerbach, Rainer}, title = {Hysteresis of dynamos in rotating spherical shell convection}, series = {Physical review fluids / American Physical Society}, volume = {2}, journal = {Physical review fluids / American Physical Society}, publisher = {American Physical Society}, address = {College Park}, issn = {2469-990X}, doi = {10.1103/PhysRevFluids.2.053902}, pages = {11}, year = {2017}, abstract = {Bifurcations of dynamos in rotating and buoyancy-driven spherical Rayleigh-Benard convection in an electrically conducting fluid are investigated numerically. Both nonmagnetic and magnetic solution branches comprised of rotating waves are traced by path-following techniques, and their bifurcations and interconnections for different Ekman numbers are determined. In particular, the question of whether the dynamo branches bifurcate super- or sub-critically and whether a direct link to the primary pure convective states exists is answered.}, language = {en} } @article{SelsingMalesaniGoldonietal.2019, author = {Selsing, Jonatan and Malesani, D. and Goldoni, P. and Fynbo, Johan and Kr{\"u}hler, T. and Antonelli, L. A. and Arabsalmani, M. and Bolmer, J. and Cano, Z. and Christensen, L. and Covino, S. and De Cia, A. and de Ugarte Postigo, A. and Flores, H. and Fliis, M. and Gomboc, A. and Greiner, J. and Groot, P. and Hammer, F. and Hartoog, O. E. and Heintz, K. E. and Hjorth, J. and Jakobsson, P. and Japelj, J. and Kann, D. A. and Kaper, L. and Ledoux, C. and Leloudas, G. and Levan, A. J. and Maiorano, E. and Melandri, A. and Milvang-Jensen, B. and Palazzi, E. and Palmerio, J. T. and Perley, D. A. and Pian, E. and Piranomonte, S. and Pugliese, G. and Sanchez-Ramirez, R. and Savaglio, S. and Schady, P. and Schulze, S. and Sollerman, J. and Sparre, Martin and Tagliaferri, G. and Tanvir, N. R. and Thone, C. C. and Vergani, S. D. and Vreeswijk, P. and Watson, D. and Wiersema, K. and Wijers, R. and Xu, D. and Zafar, T.}, title = {The X-shooter GRB afterglow legacy sample (XS-GRB)}, series = {Astronomy and astrophysics : an international weekly journal}, volume = {623}, journal = {Astronomy and astrophysics : an international weekly journal}, publisher = {EDP Sciences}, address = {Les Ulis}, issn = {1432-0746}, doi = {10.1051/0004-6361/201832835}, pages = {42}, year = {2019}, abstract = {In this work we present spectra of all gamma-ray burst (GRB) afterglows that have been promptly observed with the X-shooter spectrograph until 31/03/2017. In total, we have obtained spectroscopic observations of 103 individual GRBs observed within 48 hours of the GRB trigger. Redshifts have been measured for 97 per cent of these, covering a redshift range from 0.059 to 7.84. Based on a set of observational selection criteria that minimise biases with regards to intrinsic properties of the GRBs, the follow-up effort has been focused on producing a homogeneously selected sample of 93 afterglow spectra for GRBs discovered by the Swift satellite. We here provide a public release of all the reduced spectra, including continuum estimates and telluric absorption corrections. For completeness, we also provide reductions for the 18 late-time observations of the underlying host galaxies. We provide an assessment of the degree of completeness with respect to the parent GRB population, in terms of the X-ray properties of the bursts in the sample and find that the sample presented here is representative of the full Swift sample. We have constrained the fraction of dark bursts to be <28 per cent and confirm previous results that higher optical darkness is correlated with increased X-ray absorption. For the 42 bursts for which it is possible, we have provided a measurement of the neutral hydrogen column density, increasing the total number of published HI column density measurements by similar to 33 per cent. This dataset provides a unique resource to study the ISM across cosmic time, from the local progenitor surroundings to the intervening Universe.}, language = {en} } @article{LiuWangXueetal.2019, author = {Liu, Ruo-Yu and Wang, Kai and Xue, Rui and Taylor, Andrew M. and Wang, Xiang-Yu and Li, Zhuo and Yan, Huirong}, title = {Hadronuclear interpretation of a high-energy neutrino event coincident with a blazar flare}, series = {Physical review : D, Particles, fields, gravitation, and cosmology}, volume = {99}, journal = {Physical review : D, Particles, fields, gravitation, and cosmology}, number = {6}, publisher = {American Physical Society}, address = {Melville}, issn = {2470-0010}, doi = {10.1103/PhysRevD.99.063008}, pages = {11}, year = {2019}, abstract = {Although many high-energy neutrinos detected by the IceCube telescope are believed to have an extraterrestrial origin, their astrophysical sources remain a mystery. Recently, an unprecedented discovery of a high-energy muon neutrino event coincident with a multiwavelength flare from a blazar, TXS 0506 + 056, shed some light on the origin of the neutrinos. It is usually believed that a blazar is produced by a relativistic jet launched from an accreting supermassive black hole (SMBH). Here, we show that the high-energy neutrino event can be interpreted by the inelastic hadronuclear interactions between the accelerated cosmic-ray protons in the relativistic jet and the dense gas clouds in the vicinity of the SMBH. Such a scenario only requires a moderate proton power in the jet, which could be much smaller than that required in the conventional hadronic model which instead calls upon the photomeson process. Meanwhile, the flux of the multiwavelength flare from the optical to gamma-ray band can be well explained by invoking a second radiation zone in the jet at a larger distance to the SMBH. In our model, the neutrino emission lasts a shorter time than the multiwavelength flare, so the neutrino event is not necessarily correlated with the flare, but it is probably accompanied by a spectrum hardening above a few giga-electron-volt (GeV).}, language = {en} } @article{Goychuk2019, author = {Goychuk, Igor}, title = {Perfect anomalous transport of subdiffusive cargos by molecular motors in viscoelastic cytosol}, series = {Biosystems : journal of biological and information processing sciences}, volume = {177}, journal = {Biosystems : journal of biological and information processing sciences}, publisher = {Elsevier}, address = {Oxford}, issn = {0303-2647}, doi = {10.1016/j.biosystems.2018.11.004}, pages = {56 -- 65}, year = {2019}, abstract = {Multiple experiments show that various submicron particles such as magnetosomes, RNA messengers, viruses, and even much smaller nanoparticles such as globular proteins diffuse anomalously slow in viscoelastic cytosol of living cells. Hence, their sufficiently fast directional transport by molecular motors such as kinesins is crucial for the cell operation. It has been shown recently that the traditional flashing Brownian ratchet models of molecular motors are capable to describe both normal and anomalous transport of such subdiffusing cargos by molecular motors with a very high efficiency. This work elucidates further an important role of mechanochemical coupling in such an anomalous transport. It shows a natural emergence of a perfect subdiffusive ratchet regime due to allosteric effects, where the random rotations of a "catalytic wheel" at the heart of the motor operation become perfectly synchronized with the random stepping of a heavily loaded motor, so that only one ATP molecule is consumed on average at each motor step along microtubule. However, the number of rotations made by the catalytic engine and the traveling distance both scale sublinearly in time. Nevertheless, this anomalous transport can be very fast in absolute terms.}, language = {en} } @article{ThapaLukatSelhuberUnkeletal.2019, author = {Thapa, Samudrajit and Lukat, Nils and Selhuber-Unkel, Christine and Cherstvy, Andrey G. and Metzler, Ralf}, title = {Transient superdiffusion of polydisperse vacuoles in highly motile amoeboid cells}, series = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr}, volume = {150}, journal = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr}, number = {14}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0021-9606}, doi = {10.1063/1.5086269}, pages = {18}, year = {2019}, abstract = {We perform a detailed statistical analysis of diffusive trajectories of membrane-enclosed vesicles (vacuoles) in the supercrowded cytoplasm of living Acanthamoeba castellanii cells. From the vacuole traces recorded in the center-of-area frame of moving amoebae, we examine the statistics of the time-averaged mean-squared displacements of vacuoles, their generalized diffusion coefficients and anomalous scaling exponents, the ergodicity breaking parameter, the non-Gaussian features of displacement distributions of vacuoles, the displacement autocorrelation function, as well as the distributions of speeds and positions of vacuoles inside the amoeba cells. Our findings deliver novel insights into the internal dynamics of cellular structures in these infectious pathogens. Published under license by AIP Publishing.}, language = {en} } @article{MenzelHeuerMilonni2019, author = {Menzel, Ralf and Heuer, Axel and Milonni, Peter W.}, title = {Entanglement, Complementarity, and Vacuum Fields in Spontaneous Parametric Down-Conversion}, series = {Atoms}, volume = {7}, journal = {Atoms}, number = {1}, publisher = {MDPI}, address = {Basel}, issn = {2218-2004}, doi = {10.3390/atoms7010027}, pages = {14}, year = {2019}, abstract = {Using two crystals for spontaneous parametric down-conversion in a parallel setup, we observe two-photon interference with high visibility. The high visibility is consistent with complementarity and the absence of which-path information. The observations are explained as the effects of entanglement or equivalently in terms of interfering probability amplitudes and also by the calculation of a second-order field correlation function in the Heisenberg picture. The latter approach brings out explicitly the role of the vacuum fields in the down-conversion at the crystals and in the photon coincidence counting. For comparison, we show that the Hong-Ou-Mandel dip can be explained by the same approach in which the role of the vacuum signal and idler fields, as opposed to entanglement involving vacuum states, is emphasized. We discuss the fundamental limitations of a theory in which these vacuum fields are treated as classical, stochastic fields.}, language = {en} } @article{MorgnerBennemannCywińskietal.2017, author = {Morgner, Frank and Bennemann, Mark and Cywiński, Piotr J. and Kollosche, Matthias and G{\´o}rski, Krzysztof and Pietraszkiewicz, Marek and Geßner, Andr{\´e} and L{\"o}hmannsr{\"o}ben, Hans-Gerd}, title = {Elastic FRET sensors for contactless pressure measurement}, series = {RSC Advances : an international journal to further the chemical sciences}, volume = {7}, journal = {RSC Advances : an international journal to further the chemical sciences}, publisher = {RSC Publishing}, address = {Cambridge}, issn = {2046-2069}, doi = {10.1039/c7ra06379b}, pages = {50578 -- 50583}, year = {2017}, abstract = {Contactless pressure monitoring based on Forster resonance energy transfer between donor/acceptor pairs immobilized within elastomers is demonstrated. The donor/acceptor energy transfer is employed by dispersing terbium(III) tris[(2-hydroxybenzoyl)-2-aminoethyl] amine complex (LLC, donor) and CdSe/ZnS quantum dots (QD655, acceptor) in styrene-ethylene/buthylene-styrene (SEBS) and poly(dimethylsiloxane) (PDMS). The continuous monitoring of QD luminescence showed a reversible intensity change as the pressure signal is alternated between two stable states indicating a pressure sensitivity of 6350 cps kPa(-1). Time-resolved measurements show the pressure impact on the FRET signal due to an increase of decay time (270 ms up to 420 ms) for the donor signal and parallel drop of decay time (170 mu s to 155 mu s) for the acceptor signal as the net pressure applied. The LLC/QD655 sensors enable a contactless readout as well as space resolved monitoring to enable miniaturization towards smaller integrated stretchable opto-electronics. Elastic FRET sensors can potentially lead to developing profitable analysis systems capable to outdo conventional wired electronic systems (inductive, capacitive, ultrasonic and photoelectric sensors) especially for point-of-care diagnostics, biological monitoring required for wearable electronics.}, language = {en} } @article{TeichmannLewandowskiAlemani2022, author = {Teichmann, Erik and Lewandowski, Heather J. and Alemani, Micol}, title = {Investigating students' views of experimental physics in German laboratory classes}, series = {Physical Review Physics Education Research}, volume = {18}, journal = {Physical Review Physics Education Research}, edition = {1}, publisher = {APS}, address = {College Park, Maryland, United States}, issn = {1554-9178}, doi = {10.1103/PhysRevPhysEducRes.18.010135}, pages = {010135-1 -- 010135-17}, year = {2022}, abstract = {There is a large variety of goals instructors have for laboratory courses, with different courses focusing on different subsets of goals. An often implicit, but crucial, goal is to develop students' attitudes, views, and expectations about experimental physics to align with practicing experimental physicists. The assessment of laboratory courses upon this one dimension of learning has been intensively studied in U.S. institutions using the Colorado Learning Attitudes about Science Survey for Experimental Physics (E-CLASS). However, there is no such an instrument available to use in Germany, and the influence of laboratory courses on students views about the nature of experimental physics is still unexplored at German-speaking institutions. Motivated by the lack of an assessment tool to investigate this goal in laboratory courses at German-speaking institutions, we present a translated version of the E-CLASS adapted to the context at German-speaking institutions. We call the German version of the E-CLASS, the GE-CLASS. We describe the translation process and the creation of an automated web-based system for instructors to assess their laboratory courses. We also present first results using GE-CLASS obtained at the University of Potsdam. A first comparison between E-CLASS and GE-CLASS results shows clear differences between University of Potsdam and U.S. students' views and beliefs about experimental physics.}, language = {en} } @article{GrossmannAransonPeruani2020, author = {Großmann, Robert and Aranson, Igor S. and Peruani, Fernando}, title = {A particle-field approach bridges phase separation and collective motion in active matter}, series = {Nature Communications}, volume = {11}, journal = {Nature Communications}, number = {1}, publisher = {Nature Publishing Group}, address = {London}, issn = {2041-1723}, doi = {10.1038/s41467-020-18978-5}, pages = {12}, year = {2020}, abstract = {Whereas self-propelled hard discs undergo motility-induced phase separation, self-propelled rods exhibit a variety of nonequilibrium phenomena, including clustering, collective motion, and spatio-temporal chaos. In this work, we present a theoretical framework representing active particles by continuum fields. This concept combines the simplicity of alignment-based models, enabling analytical studies, and realistic models that incorporate the shape of self-propelled objects explicitly. By varying particle shape from circular to ellipsoidal, we show how nonequilibrium stresses acting among self-propelled rods destabilize motility-induced phase separation and facilitate orientational ordering, thereby connecting the realms of scalar and vectorial active matter. Though the interaction potential is strictly apolar, both, polar and nematic order may emerge and even coexist. Accordingly, the symmetry of ordered states is a dynamical property in active matter. The presented framework may represent various systems including bacterial colonies, cytoskeletal extracts, or shaken granular media. Interacting self-propelled particles exhibit phase separation or collective motion depending on particle shape. A unified theory connecting these paradigms represents a major challenge in active matter, which the authors address here by modeling active particles as continuum fields.}, language = {en} } @article{FernandezCharcharCherstvyetal.2020, author = {Fernandez, Amanda Diez and Charchar, Patrick and Cherstvy, Andrey G. and Metzler, Ralf and Finnis, Michael W.}, title = {The diffusion of doxorubicin drug molecules in silica nanoslits is non-Gaussian, intermittent and anticorrelated}, series = {Physical chemistry, chemical physics}, volume = {22}, journal = {Physical chemistry, chemical physics}, number = {48}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1463-9076}, doi = {10.1039/d0cp03849k}, pages = {27955 -- 27965}, year = {2020}, abstract = {In this study we investigate, using all-atom molecular-dynamics computer simulations, the in-plane diffusion of a doxorubicin drug molecule in a thin film of water confined between two silica surfaces. We find that the molecule diffuses along the channel in the manner of a Gaussian diffusion process, but with parameters that vary according to its varying transversal position. Our analysis identifies that four Gaussians, each describing particle motion in a given transversal region, are needed to adequately describe the data. Each of these processes by itself evolves with time at a rate slower than that associated with classical Brownian motion due to a predominance of anticorrelated displacements. Long adsorption events lead to ageing, a property observed when the diffusion is intermittently hindered for periods of time with an average duration which is theoretically infinite. This study presents a simple system in which many interesting features of anomalous diffusion can be explored. It exposes the complexity of diffusion in nanoconfinement and highlights the need to develop new understanding.}, language = {en} } @article{DahlkeMaturilli2017, author = {Dahlke, Sandro and Maturilli, Marion}, title = {Contribution of atmospheric advection to the amplified winter warming in the arctic north atlantic region}, series = {Advances in meteorology}, journal = {Advances in meteorology}, publisher = {Hindawi Publ. Corp.}, address = {New York}, issn = {1687-9309}, doi = {10.1155/2017/4928620}, pages = {8}, year = {2017}, abstract = {Arctic Amplification of climate warming is caused by various feedback processes in the atmosphere-ocean-ice system and yields the strongest temperature increase during winter in the Arctic North Atlantic region. In our study, we attempt to quantify the advective contribution to the observed atmospheric warming in the Svalbard area. Based on radiosonde measurements from Ny-{\AA}lesund, a strong dependence of the tropospheric temperature on the synoptic flow direction is revealed. Using FLEXTRA backward trajectories, an increase of advection from the lower latitude Atlantic region towards Ny-{\AA}lesund is found that is attributed to a change in atmospheric circulation patterns. We find that about one-quarter (0.45 K per decade) of the observed atmospheric winter near surface warming trend in the North Atlantic region of the Arctic (2 K per decade) is due to increased advection of warm and moist air from the lower latitude Atlantic region, affecting the entire troposphere.}, language = {en} } @article{CestnikPikovsky2022, author = {Cestnik, Rok and Pikovsky, Arkady}, title = {Hierarchy of exact low-dimensional reductions for populations of coupled oscillators}, series = {Physical review letters}, volume = {128}, journal = {Physical review letters}, number = {5}, publisher = {American Physical Society}, address = {College Park}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.128.054101}, pages = {6}, year = {2022}, abstract = {We consider an ensemble of phase oscillators in the thermodynamic limit, where it is described by a kinetic equation for the phase distribution density. We propose an Ansatz for the circular moments of the distribution (Kuramoto-Daido order parameters) that allows for an exact truncation at an arbitrary number of modes. In the simplest case of one mode, the Ansatz coincides with that of Ott and Antonsen [Chaos 18, 037113 (2008)]. Dynamics on the extended manifolds facilitate higher-dimensional behavior such as chaos, which we demonstrate with a simulation of a Josephson junction array. The findings are generalized for oscillators with a Cauchy-Lorentzian distribution of natural frequencies.}, language = {en} } @article{Omelʹchenko2020, author = {Omelʹchenko, Oleh E.}, title = {Nonstationary coherence-incoherence patterns in nonlocally coupled heterogeneous phase oscillators}, series = {Chaos : an interdisciplinary journal of nonlinear science}, volume = {30}, journal = {Chaos : an interdisciplinary journal of nonlinear science}, number = {4}, publisher = {American Institute of Physics}, address = {Melville}, issn = {1054-1500}, doi = {10.1063/1.5145259}, pages = {8}, year = {2020}, abstract = {We consider a large ring of nonlocally coupled phase oscillators and show that apart from stationary chimera states, this system also supports nonstationary coherence-incoherence patterns (CIPs). For identical oscillators, these CIPs behave as breathing chimera states and are found in a relatively small parameter region only. It turns out that the stability region of these states enlarges dramatically if a certain amount of spatially uniform heterogeneity (e.g., Lorentzian distribution of natural frequencies) is introduced in the system. In this case, nonstationary CIPs can be studied as stable quasiperiodic solutions of a corresponding mean-field equation, formally describing the infinite system limit. Carrying out direct numerical simulations of the mean-field equation, we find different types of nonstationary CIPs with pulsing and/or alternating chimera-like behavior. Moreover, we reveal a complex bifurcation scenario underlying the transformation of these CIPs into each other. These theoretical predictions are confirmed by numerical simulations of the original coupled oscillator system.}, language = {en} } @article{WangCherstvyChechkinetal.2020, author = {Wang, Wei and Cherstvy, Andrey G. and Chechkin, Aleksei V. and Thapa, Samudrajit and Seno, Flavio and Liu, Xianbin and Metzler, Ralf}, title = {Fractional Brownian motion with random diffusivity}, series = {Journal of physics : A, Mathematical and theoretical}, volume = {53}, journal = {Journal of physics : A, Mathematical and theoretical}, number = {47}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {1751-8113}, doi = {10.1088/1751-8121/aba467}, pages = {34}, year = {2020}, abstract = {Numerous examples for a priori unexpected non-Gaussian behaviour for normal and anomalous diffusion have recently been reported in single-particle tracking experiments. Here, we address the case of non-Gaussian anomalous diffusion in terms of a random-diffusivity mechanism in the presence of power-law correlated fractional Gaussian noise. We study the ergodic properties of this model via examining the ensemble- and time-averaged mean-squared displacements as well as the ergodicity breaking parameter EB quantifying the trajectory-to-trajectory fluctuations of the latter. For long measurement times, interesting crossover behaviour is found as function of the correlation time tau characterising the diffusivity dynamics. We unveil that at short lag times the EB parameter reaches a universal plateau. The corresponding residual value of EB is shown to depend only on tau and the trajectory length. The EB parameter at long lag times, however, follows the same power-law scaling as for fractional Brownian motion. We also determine a corresponding plateau at short lag times for the discrete representation of fractional Brownian motion, absent in the continuous-time formulation. These analytical predictions are in excellent agreement with results of computer simulations of the underlying stochastic processes. Our findings can help distinguishing and categorising certain nonergodic and non-Gaussian features of particle displacements, as observed in recent single-particle tracking experiments.}, language = {en} } @article{KurilovichMantsevichStevensonetal.2020, author = {Kurilovich, Aleksandr A. and Mantsevich, Vladimir and Stevenson, Keith J. and Chechkin, Aleksei V. and Palyulin, V. V.}, title = {Complex diffusion-based kinetics of photoluminescence in semiconductor nanoplatelets}, series = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, volume = {22}, journal = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, number = {42}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1463-9076}, doi = {10.1039/d0cp03744c}, pages = {24686 -- 24696}, year = {2020}, abstract = {We present a diffusion-based simulation and theoretical models for explanation of the photoluminescence (PL) emission intensity in semiconductor nanoplatelets. It is shown that the shape of the PL intensity curves can be reproduced by the interplay of recombination, diffusion and trapping of excitons. The emission intensity at short times is purely exponential and is defined by recombination. At long times, it is governed by the release of excitons from surface traps and is characterized by a power-law tail. We show that the crossover from one limit to another is controlled by diffusion properties. This intermediate region exhibits a rich behaviour depending on the value of diffusivity. The proposed approach reproduces all the features of experimental curves measured for different nanoplatelet systems.}, language = {en} } @article{KleinRosenberger2021, author = {Klein, Markus and Rosenberger, Elke}, title = {The tunneling effect for Schr{\"o}dinger operators on a vector bundle}, series = {Analysis and mathematical physics}, volume = {11}, journal = {Analysis and mathematical physics}, number = {2}, publisher = {Springer International Publishing AG}, address = {Cham (ZG)}, issn = {1664-2368}, doi = {10.1007/s13324-021-00485-5}, pages = {35}, year = {2021}, abstract = {In the semiclassical limit (h) over bar -> 0, we analyze a class of self-adjoint Schrodinger operators H-(h) over bar = (h) over bar L-2 + (h) over barW + V center dot id(E) acting on sections of a vector bundle E over an oriented Riemannian manifold M where L is a Laplace type operator, W is an endomorphism field and the potential energy V has non-degenerate minima at a finite number of points m(1),... m(r) is an element of M, called potential wells. Using quasimodes of WKB-type near m(j) for eigenfunctions associated with the low lying eigenvalues of H-(h) over bar, we analyze the tunneling effect, i.e. the splitting between low lying eigenvalues, which e.g. arises in certain symmetric configurations. Technically, we treat the coupling between different potential wells by an interaction matrix and we consider the case of a single minimal geodesic (with respect to the associated Agmon metric) connecting two potential wells and the case of a submanifold of minimal geodesics of dimension l + 1. This dimension l determines the polynomial prefactor for exponentially small eigenvalue splitting.}, language = {en} } @article{SteppaEgberts2020, author = {Steppa, Constantin and Egberts, Kathrin}, title = {Modelling the Galactic very-high-energy gamma-ray source population}, series = {Astronomy and astrophysics : an international weekly journal}, volume = {643}, journal = {Astronomy and astrophysics : an international weekly journal}, publisher = {EDP Sciences}, address = {Les Ulis}, issn = {0004-6361}, doi = {10.1051/0004-6361/202038172}, pages = {11}, year = {2020}, abstract = {Context. The High Energy Stereoscopic System Galactic plane survey (HGPS) is to date the most comprehensive census of Galactic gamma -ray sources at very high energies (VHE; 100 GeV <= E <= 100 TeV). As a consequence of the limited sensitivity of this survey, the 78 detected gamma -ray sources comprise only a small and biased subsample of the overall population. The larger part consists of currently unresolved sources, which contribute to large-scale diffuse emission to a still uncertain amount.Aims. We study the VHE gamma -ray source population in the Milky Way. For this purpose population-synthesis models are derived based on the distributions of source positions, extents, and luminosities.Methods. Several azimuth-symmetric and spiral-arm models are compared for spatial source distribution. The luminosity and radius function of the population are derived from the source properties of the HGPS data set and are corrected for the sensitivity bias of the HGPS. Based on these models, VHE source populations are simulated and the subsets of sources detectable according to the HGPS are compared with HGPS sources.Results. The power-law indices of luminosity and radius functions are determined to range between -1.6 and -1.9 for luminosity and -1.1 and -1.6 for radius. A two-arm spiral structure with central bar is discarded as spatial distribution of VHE sources, while azimuth-symmetric distributions and a distribution following a four-arm spiral structure without bar describe the HGPS data reasonably well. The total number of Galactic VHE sources is predicted to be in the range from 800 to 7000 with a total luminosity and flux of (1.6-6.3) x 10(36) ph s(-1) and (3-15) x 10(-10) ph cm(-2) s(-1), respectively.Conclusions. Depending on the model, the HGPS sample accounts for (68-87)\% of the emission of the population in the scanned region. This suggests that unresolved sources represent a critical component of the diffuse emission measurable in the HGPS. With the foreseen jump in sensitivity of the Cherenkov Telescope Array, the number of detectable sources is predicted to increase by a factor between 5 and 9.}, language = {en} } @article{SarabadaniMetzlerAlaNissila2022, author = {Sarabadani, Jalal and Metzler, Ralf and Ala-Nissila, Tapio}, title = {Driven polymer translocation into a channel: Isoflux tension propagation theory and Langevin dynamics simulations}, series = {Physical Review Research}, volume = {4}, journal = {Physical Review Research}, edition = {3}, publisher = {American Physical Society}, address = {College Park, Maryland, USA}, issn = {2643-1564}, doi = {10.1103/PhysRevResearch.4.033003}, pages = {033003-1 -- 033003-14}, year = {2022}, abstract = {Isoflux tension propagation (IFTP) theory and Langevin dynamics (LD) simulations are employed to study the dynamics of channel-driven polymer translocation in which a polymer translocates into a narrow channel and the monomers in the channel experience a driving force fc. In the high driving force limit, regardless of the channel width, IFTP theory predicts τ ∝ f βc for the translocation time, where β = -1 is the force scaling exponent. Moreover, LD data show that for a very narrow channel fitting only a single file of monomers, the entropic force due to the subchain inside the channel does not play a significant role in the translocation dynamics and the force exponent β = -1 regardless of the force magnitude. As the channel width increases the number of possible spatial configurations of the subchain inside the channel becomes significant and the resulting entropic force causes the force exponent to drop below unity.}, language = {en} } @article{KietheHeuerJechow2017, author = {Kiethe, Jan and Heuer, Axel and Jechow, Andreas}, title = {Second-order coherence properties of amplified spontaneous emission from a high-power tapered superluminescent diode}, series = {Laser physics letters}, volume = {14}, journal = {Laser physics letters}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {1612-2011}, doi = {10.1088/1612-202X/aa772c}, pages = {4}, year = {2017}, abstract = {We study the degree of second-order coherence of the emission of a high-power multi-quantum well superluminescent diode with a lateral tapered amplifier section with and without optical feedback. When operated in an external cavity, the degree of second-order coherence changed from the almost thermal case of g((2))(0)approximate to 1.9 towards the mostly coherent case of g((2)) (0) approximate to 1.2 when the injection current at the tapered section was increased. We found good agreement with semi-classical laser theory near and below threshold while above laser threshold a slightly higher g((2))(0) was observed. As a free running device, the superluminescent diode yielded more than 400 mW of optical output power with good spatial beam quality of M-slow(2) < 1.6. In this case, the degree of second-order coherence dropped only slightly from 1.9 at low powers to 1.6 at the maximum output power. To our knowledge, this is the first investigation of a high-power tapered superluminescent diode concerning the degree of second-order coherence. Such a device might be useful for real-world applications probing the second order coherence function, such as ghost imaging.}, language = {en} } @article{ParkLuehrKervalishvilietal.2017, author = {Park, Jaeheung and L{\"u}hr, Hermann and Kervalishvili, Guram and Rauberg, Jan and Stolle, Claudia and Kwak, Young-Sil and Lee, Woo Kyoung}, title = {Morphology of high-latitude plasma density perturbations as deduced from the total electron content measurements onboard the Swarm constellation}, series = {Journal of geophysical research : A, Space physics}, volume = {122}, journal = {Journal of geophysical research : A, Space physics}, number = {1}, publisher = {American Geophysical Union}, address = {Washington}, issn = {2169-9380}, doi = {10.1002/2016JA023086}, pages = {1338 -- 1359}, year = {2017}, abstract = {In this study, we investigate the climatology of high-latitude total electron content (TEC) variations as observed by the dual-frequency Global Navigation Satellite Systems (GNSS) receivers onboard the Swarm satellite constellation. The distribution of TEC perturbations as a function of geographic/magnetic coordinates and seasons reasonably agrees with that of the Challenging Minisatellite Payload observations published earlier. Categorizing the high-latitude TEC perturbations according to line-of-sight directions between Swarm and GNSS satellites, we can deduce their morphology with respect to the geomagnetic field lines. In the Northern Hemisphere, the perturbation shapes are mostly aligned with the L shell surface, and this anisotropy is strongest in the nightside auroral (substorm) and subauroral regions and weakest in the central polar cap. The results are consistent with the well-known two-cell plasma convection pattern of the high-latitude ionosphere, which is approximately aligned with L shells at auroral regions and crossing different L shells for a significant part of the polar cap. In the Southern Hemisphere, the perturbation structures exhibit noticeable misalignment to the local L shells. Here the direction toward the Sun has an additional influence on the plasma structure, which we attribute to photoionization effects. The larger offset between geographic and geomagnetic poles in the south than in the north is responsible for the hemispheric difference.}, language = {en} } @article{SposiniKrapfMarinarietal.2022, author = {Sposini, Vittoria and Krapf, Diego and Marinari, Enzo and Sunyer, Raimon and Ritort, Felix and Taheri, Fereydoon and Selhuber-Unkel, Christine and Benelli, Rebecca and Weiss, Matthias and Metzler, Ralf and Oshanin, Gleb}, title = {Towards a robust criterion of anomalous diffusion}, series = {Communications Physics}, volume = {5}, journal = {Communications Physics}, publisher = {Springer Nature}, address = {London}, issn = {2399-3650}, doi = {10.1038/s42005-022-01079-8}, pages = {10}, year = {2022}, abstract = {Anomalous-diffusion, the departure of the spreading dynamics of diffusing particles from the traditional law of Brownian-motion, is a signature feature of a large number of complex soft-matter and biological systems. Anomalous-diffusion emerges due to a variety of physical mechanisms, e.g., trapping interactions or the viscoelasticity of the environment. However, sometimes systems dynamics are erroneously claimed to be anomalous, despite the fact that the true motion is Brownian—or vice versa. This ambiguity in establishing whether the dynamics as normal or anomalous can have far-reaching consequences, e.g., in predictions for reaction- or relaxation-laws. Demonstrating that a system exhibits normal- or anomalous-diffusion is highly desirable for a vast host of applications. Here, we present a criterion for anomalous-diffusion based on the method of power-spectral analysis of single trajectories. The robustness of this criterion is studied for trajectories of fractional-Brownian-motion, a ubiquitous stochastic process for the description of anomalous-diffusion, in the presence of two types of measurement errors. In particular, we find that our criterion is very robust for subdiffusion. Various tests on surrogate data in absence or presence of additional positional noise demonstrate the efficacy of this method in practical contexts. Finally, we provide a proof-of-concept based on diverse experiments exhibiting both normal and anomalous-diffusion.}, language = {en} } @article{KontroBuschhueter2020, author = {Kontro, Inkeri and Buschh{\"u}ter, David}, title = {Validity of Colorado Learning Attitudes about Science Survey for a high-achieving, Finnish population}, series = {Physical review. Physics education research}, volume = {16}, journal = {Physical review. Physics education research}, number = {2}, publisher = {American Physical Society}, address = {College Park, MD}, issn = {2469-9896}, doi = {10.1103/PhysRevPhysEducRes.16.020104}, pages = {11}, year = {2020}, abstract = {The Colorado Learning Attitudes about Science Survey (CLASS) is an instrument which is widely used in physics education to characterize students' attitudes toward physics and learning physics and compare them with those of experts. While CLASS has been extensively validated for use in the context of higher education institutions in the United States, there has been less information about its use with European students. We have studied the structural, content, and substantive aspects of validity of CLASS by first doing a confirmatory factor analysis of N = 642 sets of student answers from the University of Helsinki, Finland. The students represented a culturally and demographically different subset of university physics students than in previous studies. The confirmatory factor analysis used a 3-factor, 15-item factor structure as a starting point and the resulting factor structure was similar to the original. Just minor modifications were needed for fit parameters to be in the acceptable range. We explored the differences by student interviews and consultation of experts. With the exception of one item, they supported the new 14-item, 3-factor structure. The results show that the interpretations made from CLASS results are mostly transferable, and CLASS remains a useful instrument for a wide variety of populations.}, language = {en} } @article{BeckusPinchover2020, author = {Beckus, Siegfried and Pinchover, Yehuda}, title = {Shnol-type theorem for the Agmon ground state}, series = {Journal of spectral theory}, volume = {10}, journal = {Journal of spectral theory}, number = {2}, publisher = {EMS Publishing House}, address = {Z{\"u}rich}, issn = {1664-039X}, doi = {10.4171/JST/296}, pages = {355 -- 377}, year = {2020}, abstract = {LetH be a Schrodinger operator defined on a noncompact Riemannianmanifold Omega, and let W is an element of L-infinity (Omega; R). Suppose that the operator H + W is critical in Omega, and let phi be the corresponding Agmon ground state. We prove that if u is a generalized eigenfunction ofH satisfying vertical bar u vertical bar <= C-phi in Omega for some constant C > 0, then the corresponding eigenvalue is in the spectrum of H. The conclusion also holds true if for some K is an element of Omega the operator H admits a positive solution in (Omega) over bar = Omega \ K, and vertical bar u vertical bar <= C psi in (Omega) over bar for some constant C > 0, where psi is a positive solution of minimal growth in a neighborhood of infinity in Omega. Under natural assumptions, this result holds also in the context of infinite graphs, and Dirichlet forms.}, language = {en} } @article{GhaffarvandMokariSardhaei2020, author = {Ghaffarvand Mokari, Payam and Sardhaei, Nasim Mahdinezhad}, title = {Predictive power of cepstral coefficients and spectral moments in the classification of Azerbaijani fricatives}, series = {The journal of the Acoustical Society of America}, volume = {147}, journal = {The journal of the Acoustical Society of America}, number = {3}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0001-4966}, doi = {10.1121/10.0000830}, pages = {EL228 -- EL234}, year = {2020}, abstract = {This study compares the classification of Azerbaijani fricatives based on two sets of features: (a) spectral moments, spectral peak, amplitude, duration, and (b) cepstral coefficients employing Hidden Markov Models to divide each fricative into three regions such that the variances of the measures within each region are minimized. The cepstral coefficients were found to be more reliable predictors in the classification of all nine Azerbaijani fricatives and the cepstral measures yielded highly successful classification rates (91.21\% across both genders) in the identification of the full set of fricatives of Azerbaijani.}, language = {en} } @article{KrylovDylovRosenblum2020, author = {Krylov, Dmitrii and Dylov, Dmitry V. and Rosenblum, Michael}, title = {Reinforcement learning for suppression of collective activity in oscillatory ensembles}, series = {Chaos : an interdisciplinary journal of nonlinear science}, volume = {30}, journal = {Chaos : an interdisciplinary journal of nonlinear science}, number = {3}, publisher = {American Institute of Physics}, address = {Melville}, issn = {1054-1500}, doi = {10.1063/1.5128909}, pages = {10}, year = {2020}, abstract = {We present the use of modern machine learning approaches to suppress self-sustained collective oscillations typically signaled by ensembles of degenerative neurons in the brain. The proposed hybrid model relies on two major components: an environment of oscillators and a policy-based reinforcement learning block. We report a model-agnostic synchrony control based on proximal policy optimization and two artificial neural networks in an Actor-Critic configuration. A class of physically meaningful reward functions enabling the suppression of collective oscillatory mode is proposed. The synchrony suppression is demonstrated for two models of neuronal populations-for the ensembles of globally coupled limit-cycle Bonhoeffer-van der Pol oscillators and for the bursting Hindmarsh-Rose neurons using rectangular and charge-balanced stimuli.}, language = {en} } @article{SecklerMetzler2022, author = {Seckler, Henrik and Metzler, Ralf}, title = {Bayesian deep learning for error estimation in the analysis of anomalous diffusion}, series = {Nature Communnications}, volume = {13}, journal = {Nature Communnications}, publisher = {Nature Publishing Group UK}, address = {London}, issn = {2041-1723}, doi = {10.1038/s41467-022-34305-6}, pages = {13}, year = {2022}, abstract = {Modern single-particle-tracking techniques produce extensive time-series of diffusive motion in a wide variety of systems, from single-molecule motion in living-cells to movement ecology. The quest is to decipher the physical mechanisms encoded in the data and thus to better understand the probed systems. We here augment recently proposed machine-learning techniques for decoding anomalous-diffusion data to include an uncertainty estimate in addition to the predicted output. To avoid the Black-Box-Problem a Bayesian-Deep-Learning technique named Stochastic-Weight-Averaging-Gaussian is used to train models for both the classification of the diffusionmodel and the regression of the anomalous diffusion exponent of single-particle-trajectories. Evaluating their performance, we find that these models can achieve a wellcalibrated error estimate while maintaining high prediction accuracies. In the analysis of the output uncertainty predictions we relate these to properties of the underlying diffusion models, thus providing insights into the learning process of the machine and the relevance of the output.}, language = {en} } @article{RyllSchmitzdeBooretal.2018, author = {Ryll, Britta and Schmitz, Andreas and de Boor, Johannes and Franz, Alexandra and Whitfield, Pamela S. and Reehuis, Manfred and Hoser, Andreas and M{\"u}ller, Eckhard and Habicht, Klaus and Fritscht, Katharina}, title = {Structure, phase composition, and thermoelectric properties of YbxCo4Sb12 and their dependence on synthesis method}, series = {ACS applied energy materials}, volume = {1}, journal = {ACS applied energy materials}, number = {1}, publisher = {American Chemical Society}, address = {Washington}, issn = {2574-0962}, doi = {10.1021/acsaem.7b00015}, pages = {113 -- 122}, year = {2018}, abstract = {We present a combined microscopic and macroscopic study of YbxCo4Sb12 skutterudites for a range of nominal filling fractions, 0.15 < x < 0.75. The samples were synthesized using two different methods — a melt-quench-annealing route in evacuated quartz ampoules and a non-equilibrium ball-mill route — for which we directly compare the crystal structure and phase composition as well as the thermoelectric properties. Rietveld refinements of high-quality neutron powder diffraction data reveal about a 30-40\% smaller Yb occupancy on the crystallographic 2a site than nominally expected for both synthesis routes. We observe a maximum filling fraction of at least 0.439(7) for a sample synthesized by the ball-mill routine, exceeding theoretical predictions of the filling fraction limit of 0.2-0.3. A single secondary phase of CoSb2 is observed in ball-mill-synthesized samples, while two secondary phases, CoSb2 and YbSb2, are detected for samples prepared by the ampoule route. A detrimental influence of the secondary phases on the thermoelectric properties is observed for secondary-phase fractions larger than 8 wt \% regardless of the kind of secondary phase. The largest figure of merit of all samples with a ZT ∼ 1.0 at 723 K is observed for the sample with a refined Yb content of x2a = 0.159(3), synthesized by the ampoule route.}, language = {en} } @article{AwadMetzler2020, author = {Awad, Emad and Metzler, Ralf}, title = {Crossover dynamics from superdiffusion to subdiffusion}, series = {Fractional calculus and applied analysis : an international journal for theory and applications}, volume = {23}, journal = {Fractional calculus and applied analysis : an international journal for theory and applications}, number = {1}, publisher = {De Gruyter}, address = {Berlin ; Boston}, issn = {1311-0454}, doi = {10.1515/fca-2020-0003}, pages = {55 -- 102}, year = {2020}, abstract = {The Cattaneo or telegrapher's equation describes the crossover from initial ballistic to normal diffusion. Here we study and survey time-fractional generalisations of this equation that are shown to produce the crossover of the mean squared displacement from superdiffusion to subdiffusion. Conditional solutions are derived in terms of Fox H-functions and the dth-order moments as well as the diffusive flux of the different models are derived. Moreover, the concept of the distribution-like is proposed as an alternative to the probability density function.}, language = {en} } @article{GomezNavaGrossmannHintscheetal.2020, author = {G{\´o}mez-Nava, Luis and Grossmann, Robert and Hintsche, Marius and Beta, Carsten and Peruani, Fernando}, title = {A novel approach to chemotaxis}, series = {epl : a letters journal exploring the frontiers of physics}, volume = {130}, journal = {epl : a letters journal exploring the frontiers of physics}, number = {6}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {0295-5075}, doi = {10.1209/0295-5075/130/68002}, pages = {7}, year = {2020}, abstract = {Motivated by the observation of non-exponential run-time distributions of bacterial swimmers, we propose a minimal phenomenological model for taxis of active particles whose motion is controlled by an internal clock. The ticking of the clock depends on an external concentration field, e.g., a chemical substance. We demonstrate that these particles can detect concentration gradients and respond to them by moving up- or down-gradient depending on the clock design, albeit measurements of these fields are purely local in space and instantaneous in time. Altogether, our results open a new route in the study of directional navigation: we show that the use of a clock to control motility actions represents a generic and versatile toolbox to engineer behavioral responses to external cues, such as light, chemical, or temperature gradients.}, language = {en} } @article{GroitlKellerHabicht2018, author = {Groitl, Felix and Keller, Thomas and Habicht, Klaus}, title = {Generalized resolution matrix for neutron spin-echo three-axis spectrometers}, series = {Journal of applied crystallography}, volume = {51}, journal = {Journal of applied crystallography}, publisher = {International Union of Crystallography}, address = {Chester}, issn = {1600-5767}, doi = {10.1107/S1600576718005307}, pages = {818 -- 830}, year = {2018}, abstract = {This article describes the energy resolution of spin-echo three-axis spectrometers (SE-TASs) by a compact matrix formalism. SE-TASs allow one to measure the line widths of elementary excitations in crystals, such as phonons and magnons, with an energy resolution in the mu eV range. The resolution matrices derived here generalize prior work: (i) the formalism works for all crystal structures; (ii) spectrometer detuning effects are included; these arise typically from inaccurate knowledge of the excitation energy and group velocity; (iii) components of the gradient vector of the dispersion surface d omega/dq perpendicular to the scattering plane are properly treated; (iv) the curvature of the dispersion surface is easily calculated in reciprocal units; (v) the formalism permits analysis of spin-echo signals resulting from multiple excitation modes within the three-axis spectrometer resolution ellipsoid.}, language = {en} } @article{MayerMatthaeiHeueretal.2019, author = {Mayer, Dennis and Matthaei, Christian T. and Heuer, Axel and G{\"u}hr, Markus}, title = {Kagome-fiber prism compressor combination for Yb}, series = {Journal of optics}, volume = {21}, journal = {Journal of optics}, number = {2}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {2040-8978}, doi = {10.1088/2040-8986/aafdf6}, pages = {6}, year = {2019}, abstract = {Spectral broadening in hollow-core fibers is an important tool for pulse compression of low-peak power laser pulses, especially for Yb-based lasers. Here, we present a pulse compression scheme to reduce the pulse duration of a commercial Yb:KGW laser operating at 100 kHz repetition rate and 40 mu J pulse energy from 390 to 38 fs. The spectral broadening is accomplished using a krypton-filled Kagome-type fiber. We report broadened spectra for variable Kr-pressures and input powers. At optimal settings of 8 bar Kr-pressure and 3.3 W input power, the bandwidth of the pulse at the -10 dB level increased from 9.5 to 85 nm corresponding to a Fourier limit of 26 fs. A simple SF10 prism compressor is used to reduce the accumulated chirp and shortens the fiber output from about 500 to 38 fs. In addition to the spectral broadening, a pressure dependent change of the polarization is observed.}, language = {en} } @article{MayerLeverGuehr2022, author = {Mayer, Dennis and Lever, Fabiano and G{\"u}hr, Markus}, title = {Data analysis procedures for time-resolved x-ray photoelectron spectroscopy at a SASE free-electron-laser}, series = {Journal of physics : B, Atomic, molecular and optical physics}, volume = {55}, journal = {Journal of physics : B, Atomic, molecular and optical physics}, number = {5}, publisher = {IOP Publ.}, address = {Bristol}, issn = {0953-4075}, doi = {10.1088/1361-6455/ac3c91}, pages = {9}, year = {2022}, abstract = {The random nature of self-amplified spontaneous emission (SASE) is a well-known challenge for x-ray core level spectroscopy at SASE free-electron lasers (FELs). Especially in time-resolved experiments that require a combination of good temporal and spectral resolution the jitter and drifts in the spectral characteristics, relative arrival time as well as power fluctuations can smear out spectral-temporal features. We present a combination of methods for the analysis of time-resolved photoelectron spectra based on power and time corrections as well as self-referencing of a strong photoelectron line. Based on sulfur 2p photoelectron spectra of 2-thiouracil taken at the SASE FEL FLASH2, we show that it is possible to correct for some of the photon energy drift and jitter even when reliable shot-to-shot photon energy data is not available. The quality of pump-probe difference spectra improves as random jumps in energy between delay points reduce significantly. The data analysis allows to identify coherent oscillations of 1 eV shift on the mean photoelectron line of 4 eV width with an error of less than 0.1 eV.}, language = {en} } @article{NiebuhrHeuer2017, author = {Niebuhr, Mario and Heuer, Axel}, title = {Phase measurement and far-field reconstruction on externally coupled laser diode arrays}, series = {Optics express}, volume = {25}, journal = {Optics express}, number = {13}, publisher = {Optical Society of America}, address = {Washington, DC}, issn = {1094-4087}, doi = {10.1364/OE.25.014317}, pages = {14317 -- 14322}, year = {2017}, abstract = {Passive coherent combination of several discrete low power laser diodes is a promising way to overcome the issue of degrading beam quality when scaling single emitters to > 10W output power. Such systems would be an efficient alternative to current high power sources, yet they suffer from fatal coherence loss when operated well above threshold. We present a new way to obtain detailed coherence information for laser diode arrays using a spatial light modulator to help identify the underlying decoherence processes. Reconstruction tests of the emitted far-field distribution are conducted to evaluate the performance of our setup.}, language = {en} } @article{BaerMazzeo2021, author = {B{\"a}r, Christian and Mazzeo, Rafe}, title = {Manifolds with many Rarita-Schwinger fields}, series = {Communications in mathematical physics}, volume = {384}, journal = {Communications in mathematical physics}, number = {1}, publisher = {Springer}, address = {Berlin}, issn = {0010-3616}, doi = {10.1007/s00220-021-04030-0}, pages = {533 -- 548}, year = {2021}, abstract = {The Rarita-Schwinger operator is the twisted Dirac operator restricted to 3/2-spinors. Rarita-Schwinger fields are solutions of this operator which are in addition divergence-free. This is an overdetermined problem and solutions are rare; it is even more unexpected for there to be large dimensional spaces of solutions. In this paper we prove the existence of a sequence of compact manifolds in any given dimension greater than or equal to 4 for which the dimension of the space of Rarita-Schwinger fields tends to infinity. These manifolds are either simply connected Kahler-Einstein spin with negative Einstein constant, or products of such spaces with flat tori. Moreover, we construct Calabi-Yau manifolds of even complex dimension with more linearly independent Rarita-Schwinger fields than flat tori of the same dimension.}, language = {en} } @article{ThapaLomholtKrogetal.2018, author = {Thapa, Samudrajit and Lomholt, Michael Andersen and Krog, Jens and Cherstvy, Andrey G. and Metzler, Ralf}, title = {Bayesian analysis of single-particle tracking data using the nested-sampling algorithm: maximum-likelihood model selection applied to stochastic-diffusivity data}, series = {Physical chemistry, chemical physics : PCCP ; a journal of European Chemical Societies}, volume = {20}, journal = {Physical chemistry, chemical physics : PCCP ; a journal of European Chemical Societies}, number = {46}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1463-9076}, doi = {10.1039/c8cp04043e}, pages = {29018 -- 29037}, year = {2018}, abstract = {We employ Bayesian statistics using the nested-sampling algorithm to compare and rank multiple models of ergodic diffusion (including anomalous diffusion) as well as to assess their optimal parameters for in silico-generated and real time-series. We focus on the recently-introduced model of Brownian motion with "diffusing diffusivity'-giving rise to widely-observed non-Gaussian displacement statistics-and its comparison to Brownian and fractional Brownian motion, also for the time-series with some measurement noise. We conduct this model-assessment analysis using Bayesian statistics and the nested-sampling algorithm on the level of individual particle trajectories. We evaluate relative model probabilities and compute best-parameter sets for each diffusion model, comparing the estimated parameters to the true ones. We test the performance of the nested-sampling algorithm and its predictive power both for computer-generated (idealised) trajectories as well as for real single-particle-tracking trajectories. Our approach delivers new important insight into the objective selection of the most suitable stochastic model for a given time-series. We also present first model-ranking results in application to experimental data of tracer diffusion in polymer-based hydrogels.}, language = {en} } @article{RuedigerSchultz2020, author = {R{\"u}diger, G{\"u}nther and Schultz, Manfred}, title = {Large-scale dynamo action of magnetized Taylor-Couette flows}, series = {Monthly notices of the Royal Astronomical Society}, volume = {493}, journal = {Monthly notices of the Royal Astronomical Society}, number = {1}, publisher = {Oxford Univ. Press}, address = {Oxford}, issn = {0035-8711}, doi = {10.1093/mnras/staa293}, pages = {1249 -- 1260}, year = {2020}, abstract = {A conducting Taylor-Couette flow with quasi-Keplerian rotation law containing a toroidal magnetic field serves as a mean-field dynamo model of the Tayler-Spruit type. The flows are unstable against non-axisymmetric perturbations which form electromotive forces defining a effect and eddy diffusivity. If both degenerated modes with m = +/- 1 are excited with the same power then the global a effect vanishes and a dynamo cannot work. It is shown, however, that the Tayler instability produces finite alpha effects if only an isolated mode is considered but this intrinsic helicity of the single-mode is too low for an alpha(2) dynamo. Moreover, an alpha Omega dynamo model with quasi-Keplerian rotation requires a minimum magnetic Reynolds number of rotation of Rm similar or equal to 2000 to work. Whether it really works depends on assumptions about the turbulence energy. For a steeper-than-quadratic dependence of the turbulence intensity on the magnetic field, however, dynamos are only excited if the resulting magnetic eddy diffusivity approximates its microscopic value, eta(T) similar or equal to eta. By basically lower or larger eddy diffusivities the dynamo instability is suppressed.}, language = {en} } @article{AndersSaitHorsley2022, author = {Anders, Janet and Sait, Connor R. J. and Horsley, Simon A. R.}, title = {Quantum Brownian motion for magnets}, series = {New journal of physics : the open-access journal for physics}, volume = {24}, journal = {New journal of physics : the open-access journal for physics}, number = {3}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {1367-2630}, doi = {10.1088/1367-2630/ac4ef2}, pages = {21}, year = {2022}, abstract = {Spin precession in magnetic materials is commonly modelled with the classical phenomenological Landau-Lifshitz-Gilbert (LLG) equation. Based on a quantized three-dimensional spin + environment Hamiltonian, we here derive a spin operator equation of motion that describes precession and includes a general form of damping that consistently accounts for memory, coloured noise and quantum statistics. The LLG equation is recovered as its classical, Ohmic approximation. We further introduce resonant Lorentzian system-reservoir couplings that allow a systematic comparison of dynamics between Ohmic and non-Ohmic regimes. Finally, we simulate the full non-Markovian dynamics of a spin in the semi-classical limit. At low temperatures, our numerical results demonstrate a characteristic reduction and flattening of the steady state spin alignment with an external field, caused by the quantum statistics of the environment. The results provide a powerful framework to explore general three-dimensional dissipation in quantum thermodynamics.}, language = {en} } @article{KlugeSchewe2021, author = {Kluge, Lucas and Schewe, Jacob}, title = {Evaluation and extension of the radiation model for internal migration}, series = {Physical review : E, Statistical, nonlinear and soft matter physics}, volume = {104}, journal = {Physical review : E, Statistical, nonlinear and soft matter physics}, number = {5}, publisher = {American Physical Society}, address = {College Park}, issn = {2470-0045}, doi = {10.1103/PhysRevE.104.054311}, pages = {9}, year = {2021}, abstract = {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.}, language = {en} } @article{CaetanoCarvalhoMetzleretal.2020, author = {Caetano, Daniel L. Z. and Carvalho, Sidney Jurado de and Metzler, Ralf and Cherstvy, Andrey G.}, title = {Critical adsorption of multiple polyelectrolytes onto a nanosphere}, series = {Interface : journal of the Royal Society}, volume = {17}, journal = {Interface : journal of the Royal Society}, number = {167}, publisher = {Royal Society}, address = {London}, issn = {1742-5689}, doi = {10.1098/rsif.2020.0199}, pages = {10}, year = {2020}, abstract = {Employing extensive Monte Carlo computer simulations, we investigate in detail the properties of multichain adsorption of charged flexible polyelectrolytes (PEs) onto oppositely charged spherical nanoparticles (SNPs). We quantify the conditions of critical adsorption-the phase-separation curve between the adsorbed and desorbed states of the PEs-as a function of the SNP surface-charge density and the concentration of added salt. We study the degree of fluctuations of the PE-SNP electrostatic binding energy, which we use to quantify the emergence of the phase subtransitions, including a series of partially adsorbed PE configurations. We demonstrate how the phase-separation adsorption-desorption boundary shifts and splits into multiple subtransitions at low-salt conditions, thereby generalizing and extending the results for critical adsorption of a single PE onto the SNP. The current findings are relevant for finite concentrations of PEs around the attracting SNP, such as the conditions for PE adsorption onto globular proteins carrying opposite electric charges.}, language = {en} } @article{StojkoskiSandevBasnarkovetal.2020, author = {Stojkoski, Viktor and Sandev, Trifce and Basnarkov, Lasko and Kocarev, Ljupco and Metzler, Ralf}, title = {Generalised geometric Brownian motion}, series = {Entropy}, volume = {22}, journal = {Entropy}, number = {12}, publisher = {MDPI}, address = {Basel}, issn = {1099-4300}, doi = {10.3390/e22121432}, pages = {34}, year = {2020}, abstract = {Classical option pricing schemes assume that the value of a financial asset follows a geometric Brownian motion (GBM). However, a growing body of studies suggest that a simple GBM trajectory is not an adequate representation for asset dynamics, due to irregularities found when comparing its properties with empirical distributions. As a solution, we investigate a generalisation of GBM where the introduction of a memory kernel critically determines the behaviour of the stochastic process. We find the general expressions for the moments, log-moments, and the expectation of the periodic log returns, and then obtain the corresponding probability density functions using the subordination approach. Particularly, we consider subdiffusive GBM (sGBM), tempered sGBM, a mix of GBM and sGBM, and a mix of sGBMs. We utilise the resulting generalised GBM (gGBM) in order to examine the empirical performance of a selected group of kernels in the pricing of European call options. Our results indicate that the performance of a kernel ultimately depends on the maturity of the option and its moneyness.}, language = {en} } @article{GottwaldReich2021, author = {Gottwald, Georg A. and Reich, Sebastian}, title = {Combining machine learning and data assimilation to forecast dynamical systems from noisy partial observations}, series = {Chaos : an interdisciplinary journal of nonlinear science}, volume = {31}, journal = {Chaos : an interdisciplinary journal of nonlinear science}, number = {10}, publisher = {AIP}, address = {Melville}, issn = {1054-1500}, doi = {10.1063/5.0066080}, pages = {8}, year = {2021}, abstract = {We present a supervised learning method to learn the propagator map of a dynamical system from partial and noisy observations. In our computationally cheap and easy-to-implement framework, a neural network consisting of random feature maps is trained sequentially by incoming observations within a data assimilation procedure. By employing Takens's embedding theorem, the network is trained on delay coordinates. We show that the combination of random feature maps and data assimilation, called RAFDA, outperforms standard random feature maps for which the dynamics is learned using batch data.}, language = {en} } @article{GaebelBeinMathaueretal.2021, author = {Gaebel, Tina and Bein, Daniel and Mathauer, Daniel and Utecht, Manuel and Palmer, Richard E. and Klamroth, Tillmann}, title = {Nonlocal STM manipulation of chlorobenzene on Si(111)-7 x 7}, series = {The journal of physical chemistry : C, Nanomaterials and interfaces}, volume = {125}, journal = {The journal of physical chemistry : C, Nanomaterials and interfaces}, number = {22}, publisher = {American Chemical Society}, address = {Washington}, issn = {1932-7447}, doi = {10.1021/acs.jpcc.1c02612}, pages = {12175 -- 12184}, year = {2021}, abstract = {We use quantum chemical cluster models together with constrained density STM Ph CI functional theory (DFT) and ab initio molecular dynamics (AIMD) for open system to simulate tip and rationalize nonlocal scanning tunneling microscope (STM) manipulation experiments for Philh ci chlorobenzene (PhCl) on a Si(111)-7 X 7 surface. We consider three different processes, namely, the electron-induced dissociation of the carbon-chlorine bond for physisorbed PhCl molecules at low temperatures and the electron- or hole-induced desorption of chemisorbed PhCl at 300 K. All processes can be induced nonlocally, i.e., up to several nanometers (nm) away from the injection site, in STM experiments. We rationalize and explain the experimental findings regarding the STM-induced dissociation using constrained DFT. The coupling of STM-induced ion resonances to nuclear degrees of freedom is simulated with AIMD using the Gadzuk averaging approach for open systems. From this data, we predict a 4 fs lifetime for the cationic resonance. For the anion model, desorption could not be observed. In addition, the same cluster models are used for transition-state theory calculations, which are compared to and validated against time-lapse STM experiments.}, language = {en} } @article{KuentzerJuracyMoreiraetal.2020, author = {Kuentzer, Felipe A. and Juracy, Leonardo R. and Moreira, Matheus T. and Amory, Alexandre M.}, title = {Testing the blade resilient asynchronous template}, series = {Analog integrated circuits and signal processing : an international journal}, volume = {106}, journal = {Analog integrated circuits and signal processing : an international journal}, number = {1}, publisher = {Springer}, address = {Dordrecht}, issn = {0925-1030}, doi = {10.1007/s10470-020-01651-8}, pages = {219 -- 234}, year = {2020}, abstract = {As VLSI design moves into ultra-deep-submicron technologies, timing margins added to the clock period are mandatory, to ensure correct circuit behavior under worst-case conditions. Timing resilient architectures emerged as a promising solution to alleviate these worst-case timing margins. These architectures allow improving system performance and reducing energy consumption. Asynchronous systems, on the other hand, have the potential to improve energy efficiency and performance. Blade is an asynchronous timing resilient template that leverages the advantages of both asynchronous and timing resilient techniques. However, Blade still presents challenges regarding its testability, which hinders its commercial or large-scale application. This paper demonstrates that scan chains can be prohibitive for Blade due to their high silicon costs., which can reach more than 100\%. Then, it proposes an alternative test approach that allows concurrent testing, stuck-at, and delay testing. The test approach is based on the reuse the Blade features to provide testability, with silicon area overheads between 4 and 7\%.}, language = {en} } @article{WiesnerLadyman2021, author = {Wiesner, Karoline and Ladyman, James}, title = {Complex systems are always correlated but rarely information processing}, series = {Journal of physics. Complexity}, volume = {2}, journal = {Journal of physics. Complexity}, number = {4}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {2632-072X}, doi = {10.1088/2632-072X/ac371c}, pages = {4}, year = {2021}, abstract = {'Complex systems are information processors' is a statement that is frequently made. Here we argue for the distinction between information processing-in the sense of encoding and transmitting a symbolic representation-and the formation of correlations (pattern formation/self-organisation). The study of both uses tools from information theory, but the purpose is very different in each case: explaining the mechanisms and understanding the purpose or function in the first case, versus data analysis and correlation extraction in the latter. We give examples of both and discuss some open questions. The distinction helps focus research efforts on the relevant questions in each case.}, language = {en} } @article{SecklerMetzler2022, author = {Seckler, Henrik and Metzler, Ralf}, title = {Bayesian deep learning for error estimation in the analysis of anomalous diffusion}, series = {Nature Communications}, volume = {13}, journal = {Nature Communications}, number = {1}, publisher = {Nature portfolio}, address = {Berlin}, issn = {2041-1723}, doi = {10.1038/s41467-022-34305-6}, pages = {13}, year = {2022}, abstract = {Modern single-particle-tracking techniques produce extensive time-series of diffusive motion in a wide variety of systems, from single-molecule motion in living-cells to movement ecology. The quest is to decipher the physical mechanisms encoded in the data and thus to better understand the probed systems. We here augment recently proposed machine-learning techniques for decoding anomalous-diffusion data to include an uncertainty estimate in addition to the predicted output. To avoid the Black-Box-Problem a Bayesian-Deep-Learning technique named Stochastic-Weight-Averaging-Gaussian is used to train models for both the classification of the diffusion model and the regression of the anomalous diffusion exponent of single-particle-trajectories. Evaluating their performance, we find that these models can achieve a well-calibrated error estimate while maintaining high prediction accuracies. In the analysis of the output uncertainty predictions we relate these to properties of the underlying diffusion models, thus providing insights into the learning process of the machine and the relevance of the output.
Diffusive motions in complex environments such as living biological cells or soft matter systems can be analyzed with single-particle-tracking approaches, where accuracy of output may vary. The authors involve a machine-learning technique for decoding anomalous-diffusion data and provide an uncertainty estimate together with predicted output.}, language = {en} } @article{Clavier2021, author = {Clavier, Pierre J.}, title = {Borel-{\´E}calle resummation of a two-point function}, series = {Annales Henri Poincar{\´e} : a journal of theoretical and mathematical physics / ed. jointly by the Institut Henri Poincar{\´e} and by the Swiss Physical Society}, volume = {22}, journal = {Annales Henri Poincar{\´e} : a journal of theoretical and mathematical physics / ed. jointly by the Institut Henri Poincar{\´e} and by the Swiss Physical Society}, number = {6}, publisher = {Springer}, address = {Cham}, issn = {1424-0637}, doi = {10.1007/s00023-021-01057-w}, pages = {2103 -- 2136}, year = {2021}, abstract = {We provide an overview of the tools and techniques of resurgence theory used in the Borel-ecalle resummation method, which we then apply to the massless Wess-Zumino model. Starting from already known results on the anomalous dimension of the Wess-Zumino model, we solve its renormalisation group equation for the two-point function in a space of formal series. We show that this solution is 1-Gevrey and that its Borel transform is resurgent. The Schwinger-Dyson equation of the model is then used to prove an asymptotic exponential bound for the Borel transformed two-point function on a star-shaped domain of a suitable ramified complex plane. This proves that the two-point function of the Wess-Zumino model is Borel-ecalle summable.}, language = {en} } @article{DierckeKuckeinVermaetal.2021, author = {Diercke, Andrea and Kuckein, Christoph and Verma, Meetu and Denker, Carsten}, title = {Filigree in the surroundings of polar crown and high-latitude filaments}, series = {Solar physics : a journal for solar and solar-stellar research and the study of solar terrestrial physics}, volume = {296}, journal = {Solar physics : a journal for solar and solar-stellar research and the study of solar terrestrial physics}, number = {2}, publisher = {Springer}, address = {Dordrecht}, issn = {0038-0938}, doi = {10.1007/s11207-021-01776-7}, pages = {25}, year = {2021}, abstract = {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.}, language = {en} } @article{Regenstein2022, author = {Regenstein, Wolfgang}, title = {Statistische Beschreibung des Resonanzenergietransfers in L{\"o}sungen}, doi = {10.25932/publishup-56500}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-565009}, pages = {23}, year = {2022}, abstract = {In resonance energy transfer, photons are transferred from an excited donor to an acceptor over an interaction distance. According to F{\"o}rster's quantum mechanical theory, this distance can be calculated using the overlap integral of the fluorescence spectrum of the donor and the absorption spectrum of the acceptor. Another possibility of determination is obtained with the help of statistical models, which are compiled in an overview. The distance can be determined by evaluating the extinction curve. In this work, a further statistical variant of the determination of the interaction radius is added and demonstrated in detail using an example.}, language = {de} } @article{TroendleLilliestamMarellietal.2020, author = {Tr{\"o}ndle, Tim and Lilliestam, Johan and Marelli, Stefano and Pfenninger, Stefan}, title = {Trade-offs between geographic scale, cost, and infrastructure requirements for fully renewable electricity in Europe}, series = {Joule}, volume = {4}, journal = {Joule}, number = {9}, publisher = {Cell Press}, address = {Cambridge , Mass.}, issn = {2542-4351}, doi = {10.1016/j.joule.2020.07.018}, pages = {1929 -- 1948}, year = {2020}, abstract = {The European potential for renewable electricity is sufficient to enable fully renewable supply on different scales, from self-sufficient, subnational regions to an interconnected continent. We not only show that a continental-scale system is the cheapest, but also that systems on the national scale and below are possible at cost penalties of 20\% or less. Transmission is key to low cost, but it is not necessary to vastly expand the transmission system. When electricity is transmitted only to balance fluctuations, the transmission grid size is comparable to today's, albeit with expanded cross-border capacities. The largest differences across scales concern land use and thus social acceptance: in the continental system, generation capacity is concentrated on the European periphery, where the best resources are. Regional systems, in contrast, have more dispersed generation. The key trade-off is therefore not between geographic scale and cost, but between scale and the spatial distribution of required generation and transmission infrastructure.}, language = {en} } @article{MauRosenblum2022, author = {Mau, Erik Thomas Klaus and Rosenblum, Michael}, title = {Optimizing charge-balanced pulse stimulation for desynchronization}, series = {Chaos : an interdisciplinary journal of nonlinear science}, volume = {32}, journal = {Chaos : an interdisciplinary journal of nonlinear science}, number = {1}, publisher = {AIP}, address = {Melville}, issn = {1054-1500}, doi = {10.1063/5.0070036}, pages = {15}, year = {2022}, abstract = {Collective synchronization in a large population of self-sustained units appears both in natural and engineered systems. Sometimes this effect is in demand, while in some cases, it is undesirable, which calls for control techniques. In this paper, we focus on pulsatile control, with the goal to either increase or decrease the level of synchrony. We quantify this level by the entropy of the phase distribution. Motivated by possible applications in neuroscience, we consider pulses of a realistic shape. Exploiting the noisy Kuramoto-Winfree model, we search for the optimal pulse profile and the optimal stimulation phase. For this purpose, we derive an expression for the change of the phase distribution entropy due to the stimulus. We relate this change to the properties of individual units characterized by generally different natural frequencies and phase response curves and the population's state. We verify the general result by analyzing a two-frequency population model and demonstrating a good agreement of the theory and numerical simulations.}, language = {en} } @article{MorenoGrossmannBetaetal.2022, author = {Moreno, Eduardo and Großmann, Robert and Beta, Carsten and Alonso, Sergio}, title = {From single to collective motion of social amoebae}, series = {Frontiers in physics}, volume = {9}, journal = {Frontiers in physics}, publisher = {Frontiers Media}, address = {Lausanne}, issn = {2296-424X}, doi = {10.3389/fphy.2021.750187}, pages = {17}, year = {2022}, abstract = {The coupling of the internal mechanisms of cell polarization to cell shape deformations and subsequent cell crawling poses many interdisciplinary scientific challenges. Several mathematical approaches have been proposed to model the coupling of both processes, where one of the most successful methods relies on a phase field that encodes the morphology of the cell, together with the integration of partial differential equations that account for the polarization mechanism inside the cell domain as defined by the phase field. This approach has been previously employed to model the motion of single cells of the social amoeba Dictyostelium discoideum, a widely used model organism to study actin-driven motility and chemotaxis of eukaryotic cells. Besides single cell motility, Dictyostelium discoideum is also well-known for its collective behavior. Here, we extend the previously introduced model for single cell motility to describe the collective motion of large populations of interacting amoebae by including repulsive interactions between the cells. We performed numerical simulations of this model, first characterizing the motion of single cells in terms of their polarity and velocity vectors. We then systematically studied the collisions between two cells that provided the basic interaction scenarios also observed in larger ensembles of interacting amoebae. Finally, the relevance of the cell density was analyzed, revealing a systematic decrease of the motility with density, associated with the formation of transient cell clusters that emerge in this system even though our model does not include any attractive interactions between cells. This model is a prototypical active matter system for the investigation of the emergent collective dynamics of deformable, self-driven cells with a highly complex, nonlinear coupling of cell shape deformations, self-propulsion and repulsive cell-cell interactions. Understanding these self-organization processes of cells like their autonomous aggregation is of high relevance as collective amoeboid motility is part of wound healing, embryonic morphogenesis or pathological processes like the spreading of metastatic cancer cells.}, language = {en} } @article{VollbrechtBrus2020, author = {Vollbrecht, Joachim and Brus, Viktor V.}, title = {On charge carrier density in organic solar cells obtained via capacitance spectroscopy}, series = {Advanced electronic materials}, volume = {6}, journal = {Advanced electronic materials}, number = {10}, publisher = {Wiley}, address = {Hoboken}, issn = {2199-160X}, doi = {10.1002/aelm.202000517}, pages = {9}, year = {2020}, abstract = {The determination of the voltage-dependent density of free charge carriers via capacitance spectroscopy is considered an important step in the analysis of emerging photovoltaic technologies, such as organic and perovskite solar cells. In particular, an intimate knowledge of the density of free charge carriers is required for the determination of crucial parameters such as the effective mobility, charge carrier lifetime, nongeminate recombination coefficients, average extraction times, and competition factors. Hence, it is paramount to verify the validity of the commonly employed approaches to obtain the density of free charge carriers. The advantages, drawbacks, and limitations of the most common approaches are investigated in detail and strategies to mitigate misleading values are explored. To this end, two types of nonfullerene organic solar cells based on a PTB7-Th:ITIC-2F blend and a PM6:Y6 blend, respectively, are used as a case study to assess how subsequent analyses of the nongeminate recombination dynamics depend on the chosen approach to calculate the density of free charge carriers via capacitance spectroscopy.}, language = {en} } @article{VollbrechtBrus2020, author = {Vollbrecht, Joachim and Brus, Viktor V.}, title = {On the recombination order of surface recombination under open circuit conditions}, series = {Organic electronics : physics, materials and applications}, volume = {86}, journal = {Organic electronics : physics, materials and applications}, publisher = {Elsevier Science}, address = {Amsterdam [u.a.]}, issn = {1566-1199}, doi = {10.1016/j.orgel.2020.105905}, pages = {7}, year = {2020}, abstract = {Understanding the recombination dynamics of organic and perovskite solar cells has been a crucial prerequisite in the steadily increasing performance of these promising new types of photovoltaics. Surface recombination in particular has turned out to be one of the last remaining roadblocks, which specifically reduces the open circuit voltage. In this study, the relationship between the rate of surface recombination and the density of charge carriers is analyzed, revealing a cubic dependence between these two parameters. This hypothesis is then tested and verified with the recombination dynamics of an organic solar cell known to exhibit significant surface recombination and a high energy proton irradiated CH3NH3PbI3 pemvskite solar cell during white light illumination. Incidentally, these results can also explain recombination orders exceeding the commonly known threshold for bimolecular recombination that have been observed in some studies without the need for a charge carrier dependent bimolecular recombination coefficient.}, language = {en} } @article{JainWheelerEssetal.2019, author = {Jain, Varun and Wheeler, Joshua J. and Ess, Daniel H. and Noack, Sebastian and Vacogne, Charlotte D. and Schlaad, Helmut and Bahr, Stephan and Dietrich, Paul and Meyer, Michael and Thissen, Andreas and Linford, Matthew R.}, title = {Poly(gamma-benzyl l-glutamate), by near-ambient pressure XPS}, series = {Surface science spectra : SSS : an international journal \& database devoted to archiving spectra from surfaces \& interfaces}, volume = {26}, journal = {Surface science spectra : SSS : an international journal \& database devoted to archiving spectra from surfaces \& interfaces}, number = {2}, publisher = {American Institute of Physics}, address = {Melville}, issn = {1055-5269}, doi = {10.1116/1.5109121}, pages = {10}, year = {2019}, abstract = {Near-ambient pressure x-ray photoelectron spectroscopy (NAP-XPS) is a less traditional form of XPS that allows samples to be analyzed at relatively high pressures, i. e., at greater than 2500 Pa. In this study, poly(.- benzyl L- glutamate) (PBLG) with a molar mass of 11.3 kg/mol was analyzed by NAP-XPS; here, we show the survey, C 1s, N 1s, and O 1s narrow scans of PBLG. The C 1s peak envelope was fitted in three different ways, to five, six, or seven synthetic peaks. In each fit, there was also a shake-up signal. The O 1s narrow scan was well fit with three peaks: CZO and CvO in a 1:2 ratio from the polymer, and a higher energy signal from water vapor. Hartree-Fock orbital energies of a model monomer served as a guide to an additional fit of the C 1s envelope.}, language = {en} } @article{AbdoulCarimeBaldIllenbergeretal.2018, author = {Abdoul-Carime, Hassan and Bald, Ilko and Illenberger, Eugen and Kopyra, Janina}, title = {Selective Synthesis of Ethylene and Acetylene from Dimethyl Sulfide Cold Films Controlled by Slow Electrons}, series = {The journal of physical chemistry : C, Nanomaterials and interfaces}, volume = {122}, journal = {The journal of physical chemistry : C, Nanomaterials and interfaces}, number = {42}, publisher = {American Chemical Society}, address = {Washington}, issn = {1932-7447}, doi = {10.1021/acs.jpcc.8b07377}, pages = {24137 -- 24142}, year = {2018}, abstract = {One of the major challenges in chemical synthesis is to trigger and control a specific reaction route leading to a specific final product, while side products are avoided. Methodologies based on resonant processes at the molecular level, for example, photochemistry, offer the possibility of inducing selective reactions. Electrons at energies below the molecular ionization potential (<10 eV) are known to dissociate molecules via resonant processes with higher cross sections and specificity than photons. Here we show that even subexcitation electrons with energies as low as 1 eV produce ethylene and acetylene from dimethyl sulfide in competing reactions. However, the production of ethylene can specifically be targeted by controlling the energy of electrons (similar to 3 to 4 eV). Finally, pure ethylene is selectively desorbed by heating the substrate from 90 to 105 K. Beyond the synthesis of these versatile hydrocarbons for various industrial applications from a biogenic sulfur compound, our findings demonstrate the feasibility of electron induced selective chemistry applicable on the nanoscale.}, language = {en} } @article{KelesMallomvonEssenetal.2021, author = {Keles, Engin and Mallom, Matthias and von Essen, Carolina and Caroll, Thorsten A. and Alexoudi, Xanthippi and Pino, Lorenzo and Ilyin, Ilya and Poppenh{\"a}ger, Katja and Kitzmann, Daniel and Nascimbeni, Valerino and Turner, Jake D. and Strassmeier, Klaus G.}, title = {The potassium absorption on HD189733b and HD209458b}, series = {Monthly Notices of the Royal Astronomical Society: Letters}, volume = {489}, journal = {Monthly Notices of the Royal Astronomical Society: Letters}, number = {1}, publisher = {Oxford Univ. Press}, address = {Oxford}, doi = {10.1093/mnrasl/slz123}, pages = {L37 -- L41}, year = {2021}, abstract = {In this work, we investigate the potassium excess absorption around 7699 {\AA} of the exoplanets HD189733b and HD209458b. For this purpose, we used high-spectral resolution transit observations acquired with the 2 × 8.4 m Large Binocular Telescope (LBT) and the Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI). For a bandwidth of 0.8 {\AA}, we present a detection >7σ with an absorption level of 0.18 per cent for HD189733b. Applying the same analysis to HD209458b, we can set 3σ upper limit of 0.09 per cent, even though we do not detect a K-excess absorption. The investigation suggests that the K feature is less present in the atmosphere of HD209458b than in the one of HD189733b. This comparison confirms previous claims that the atmospheres of these two planets must have fundamentally different properties.}, language = {en} } @article{HolmesAndersMintert2020, author = {Holmes, Zoe and Anders, Janet and Mintert, Florian}, title = {Enhanced energy transfer to an optomechanical piston from indistinguishable photons}, series = {Physical review letters}, volume = {124}, journal = {Physical review letters}, number = {21}, publisher = {American Physical Society}, address = {College Park, Md.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.124.210601}, pages = {6}, year = {2020}, abstract = {Thought experiments involving gases and pistons, such as Maxwell's demon and Gibbs' mixing, are central to our understanding of thermodynamics. Here, we present a quantum thermodynamic thought experiment in which the energy transfer from two photonic gases to a piston membrane grows quadratically with the number of photons for indistinguishable gases, while it grows linearly for distinguishable gases. This signature of bosonic bunching may be observed in optomechanical experiments, highlighting the potential of these systems for the realization of thermodynamic thought experiments in the quantum realm.}, language = {en} } @article{EberhardSchaikSchibalskietal.2020, author = {Eberhard, Julius and Schaik, N. Loes M. B. and Schibalski, Anett and Gr{\"a}ff, Thomas}, title = {Simulating future salinity dynamics in a coastal marshland under different climate scenarios}, series = {Vadose zone journal}, volume = {19}, journal = {Vadose zone journal}, number = {1}, publisher = {Wiley}, address = {Hoboken}, issn = {1539-1663}, doi = {10.1002/vzj2.20008}, pages = {15}, year = {2020}, abstract = {Salinization is a well-known problem in agricultural areas worldwide. In the last 20-30 yr, rising salinity in the upper, unconfined aquifer has been observed in the Freepsumer Meer, a grassland near the German North Sea coast. For investigating long-term development of salinity and water balance during 1961-2099, the one-dimensional Soil-Water-Atmosphere-Plant (SWAP) model was set up and calibrated for a soil column in the area. The model setup involves a deep aquifer as the source of salt through upward seepage. In the vertical salt transport equation, dispersion and advection are included. Six different regional outputs of statistical downscaling methods were used as climate scenarios. These comprise different rates of increasing surface temperature and different trends in seasonal rainfall. The simulation results exhibit opposing salinity trends for topsoil and deeper layers. Although projections of some scenarios entail decreasing salinities near the surface, most of them project a rise in subsoil salinity, with the strongest trends of up to +0.9 mg cm(-3) 100 yr(-1) at -65 cm. The results suggest that topsoil salinity trends in the study area are affected by the magnitude of winter rainfall trends, whereas high subsoil salinities correspond to low winter rainfall and high summer temperature. How these projected trends affect the vegetation and thereby future land use will depend on the future management of groundwater levels in the area.}, language = {en} } @article{GalkaMoontahaSiniatchkin2020, author = {Galka, Andreas and Moontaha, Sidratul and Siniatchkin, Michael}, title = {Constrained expectation maximisation algorithm for estimating ARMA models in state space representation}, series = {EURASIP journal on advances in signal processing}, volume = {2020}, journal = {EURASIP journal on advances in signal processing}, number = {1}, publisher = {Springer}, address = {Heidelberg}, issn = {1687-6180}, doi = {10.1186/s13634-020-00678-3}, pages = {37}, year = {2020}, abstract = {This paper discusses the fitting of linear state space models to given multivariate time series in the presence of constraints imposed on the four main parameter matrices of these models. Constraints arise partly from the assumption that the models have a block-diagonal structure, with each block corresponding to an ARMA process, that allows the reconstruction of independent source components from linear mixtures, and partly from the need to keep models identifiable. The first stage of parameter fitting is performed by the expectation maximisation (EM) algorithm. Due to the identifiability constraint, a subset of the diagonal elements of the dynamical noise covariance matrix needs to be constrained to fixed values (usually unity). For this kind of constraints, so far, no closed-form update rules were available. We present new update rules for this situation, both for updating the dynamical noise covariance matrix directly and for updating a matrix square-root of this matrix. The practical applicability of the proposed algorithm is demonstrated by a low-dimensional simulation example. The behaviour of the EM algorithm, as observed in this example, illustrates the well-known fact that in practical applications, the EM algorithm should be combined with a different algorithm for numerical optimisation, such as a quasi-Newton algorithm.}, language = {en} } @article{CaruccioDeufemiaNaumannetal.2021, author = {Caruccio, Loredana and Deufemia, Vincenzo and Naumann, Felix and Polese, Giuseppe}, title = {Discovering relaxed functional dependencies based on multi-attribute dominance}, series = {IEEE transactions on knowledge and data engineering}, volume = {33}, journal = {IEEE transactions on knowledge and data engineering}, number = {9}, publisher = {Institute of Electrical and Electronics Engineers}, address = {New York, NY}, issn = {1041-4347}, doi = {10.1109/TKDE.2020.2967722}, pages = {3212 -- 3228}, year = {2021}, abstract = {With the advent of big data and data lakes, data are often integrated from multiple sources. Such integrated data are often of poor quality, due to inconsistencies, errors, and so forth. One way to check the quality of data is to infer functional dependencies (fds). However, in many modern applications it might be necessary to extract properties and relationships that are not captured through fds, due to the necessity to admit exceptions, or to consider similarity rather than equality of data values. Relaxed fds (rfds) have been introduced to meet these needs, but their discovery from data adds further complexity to an already complex problem, also due to the necessity of specifying similarity and validity thresholds. We propose Domino, a new discovery algorithm for rfds that exploits the concept of dominance in order to derive similarity thresholds of attribute values while inferring rfds. An experimental evaluation on real datasets demonstrates the discovery performance and the effectiveness of the proposed algorithm.}, language = {en} } @article{XuDengSandev2020, author = {Xu, Pengbo and Deng, Weihua and Sandev, Trifce}, title = {Levy walk with parameter dependent velocity}, series = {Journal of physics : A, Mathematical and theoretical}, volume = {53}, journal = {Journal of physics : A, Mathematical and theoretical}, number = {11}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {1751-8113}, doi = {10.1088/1751-8121/ab7420}, pages = {26}, year = {2020}, abstract = {To analyze stochastic processes, one often uses integral transform (Fourier and Laplace) methods. However, for the time-space coupled cases, e.g. the Levy walk, sometimes the integral transform method may fail. Here we provide a Hermite polynomial expansion approach, being complementary to the integral transform method, to the Levy walk. Two approaches are compared for some already known results. We also consider the generalized Levy walk with parameter dependent velocity. Namely, we consider the Levy walk with velocity which depends on the walking length or on the duration of each step. Some interesting features of the generalized Levy walk are observed, including the special shapes of the probability density function, the first passage time distributions, and various diffusive behaviors of the mean squared displacement.}, language = {en} } @article{GottwaldReich2021, author = {Gottwald, Georg A. and Reich, Sebastian}, title = {Supervised learning from noisy observations}, series = {Physica : D, Nonlinear phenomena}, volume = {423}, journal = {Physica : D, Nonlinear phenomena}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0167-2789}, doi = {10.1016/j.physd.2021.132911}, pages = {15}, year = {2021}, abstract = {Data-driven prediction and physics-agnostic machine-learning methods have attracted increased interest in recent years achieving forecast horizons going well beyond those to be expected for chaotic dynamical systems. In a separate strand of research data-assimilation has been successfully used to optimally combine forecast models and their inherent uncertainty with incoming noisy observations. The key idea in our work here is to achieve increased forecast capabilities by judiciously combining machine-learning algorithms and data assimilation. We combine the physics-agnostic data -driven approach of random feature maps as a forecast model within an ensemble Kalman filter data assimilation procedure. The machine-learning model is learned sequentially by incorporating incoming noisy observations. We show that the obtained forecast model has remarkably good forecast skill while being computationally cheap once trained. Going beyond the task of forecasting, we show that our method can be used to generate reliable ensembles for probabilistic forecasting as well as to learn effective model closure in multi-scale systems. (C) 2021 Elsevier B.V. All rights reserved.}, language = {en} } @article{SchneiderHoffmannVogel2020, author = {Schneider, Sebastian and Hoffmann-Vogel, Regina}, title = {Electrostatic forces above graphene nanoribbons and edges interpreted as partly hydrogen-free}, series = {Nanoscale}, volume = {12}, journal = {Nanoscale}, number = {34}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {2040-3364}, doi = {10.1039/d0nr03348k}, pages = {17895 -- 17901}, year = {2020}, abstract = {Graphene nanoribbons' electronic transport properties strongly depend on the type of edge, armchair, zigzag or other, and on edge functionalization that can be used for band-gap engineering. For only partly hydrogenated edges interesting magnetic properties are predicted. Electric charge accumulates at edges and corners. Scanning force microscopy has so far shown the centre of graphene nanoribbons with atomic resolution using a quartz crystal tuning fork sensor of high stiffness. Weak long-range electrostatic forces related to the charge accumulation on the edges of graphene nanoribbons could not be imaged so far. Here, we show the electrostatic forces at the corners and edges of graphene nanoribbons are amenable to measurement. We use soft cantilevers and a bimodal imaging technique to combine enhanced sensitivity to weak long-range electrostatic forces with the high resolution of the second-frequency shift. Additionally, in our work the edges of the nanoribbons are mainly hydrogen-free, opening to the route to investigations of partly hydrogenated magnetic nanoribbons.}, language = {en} } @article{NoechelReddyWangetal.2015, author = {N{\"o}chel, Ulrich and Reddy, Chaganti Srinivasa and Wang, Ke and Cui, Jing and Zizak, Ivo and Behl, Marc and Kratz, Karl and Lendlein, Andreas}, title = {Nanostructural changes in crystallizable controlling units determine the temperature-memory of polymers}, series = {Journal of Materials Chemistry A, Materials for energy and sustainability}, volume = {16}, journal = {Journal of Materials Chemistry A, Materials for energy and sustainability}, number = {3}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {2050-7488}, doi = {10.1039/c4ta06586g}, pages = {8284 -- 8293}, year = {2015}, abstract = {Temperature-memory polymers remember the temperature, where they were deformed recently, enabled by broad thermal transitions. In this study, we explored a series of crosslinked poly[ethylene-co-(vinyl acetate)] networks (cPEVAs) comprising crystallizable polyethylene (PE) controlling units exhibiting a pronounced temperature-memory effect (TME) between 16 and 99 °C related to a broad melting transition (∼100 °C). The nanostructural changes in such cPEVAs during programming and activation of the TME were analyzed via in situ X-ray scattering and specific annealing experiments. Different contributions to the mechanism of memorizing high or low deformation temperatures (Tdeform) were observed in cPEVA, which can be associated to the average PE crystal sizes. At high deformation temperatures (>50 °C), newly formed PE crystals, which are established during cooling when fixing the temporary shape, dominated the TME mechanism. In contrast, at low Tdeform (<50 °C), corresponding to a cold drawing scenario, the deformation led preferably to a disruption of existing large crystals into smaller ones, which then fix the temporary shape upon cooling. The observed mechanism of memorizing a deformation temperature might enable the prediction of the TME behavior and the knowledge based design of other TMPs with crystallizable controlling units.}, language = {en} } @article{DebPopovaKeller2019, author = {Deb, Marwan and Popova, Elena and Keller, Niels}, title = {Different magneto-optical response of magnetic sublattices as a function of temperature in ferrimagnetic bismuth iron garnet films}, series = {Physical review : B, Condensed matter and materials physics}, volume = {100}, journal = {Physical review : B, Condensed matter and materials physics}, number = {22}, publisher = {American Physical Society}, address = {College Park}, issn = {2469-9950}, doi = {10.1103/PhysRevB.100.224410}, pages = {7}, year = {2019}, abstract = {In this paper we investigate the magneto-optical (MO) and magnetic properties of bismuth iron garnet Bi3Fe5O12 thin films over a wide range of photon energies (1.6-3.5 eV) and temperatures (5-740 K). Depending on the photon energy range, the Faraday rotation (Theta(F)) and ellipticity (epsilon(F)) vary nonmonotonously with temperature. This behavior cannot be explained by a magnetization variation that can only decrease with increasing temperature. Theta(F) and epsilon(F) spectra have therefore been analyzed using a model based on two optical transitions of a diamagnetic nature, representing the tetrahedral and octahedral iron sites. Thus, the contribution of each magnetic sublattice has been extracted from the global macroscopic MO response and investigated as a function of temperature. The magnetic properties of octahedral and tetrahedral sublattices depend differently on temperature, suggesting a different anisotropy due to oxygen coordination. We have demonstrated that this relatively simple macroscopic measurement with a subsequent analysis can grant access to the information on the properties at a microscopic level. These results can advance the fundamental understanding of MO properties in multisublattice magnetic materials.}, language = {en} } @article{RuedigerKuekerKapylaetal.2019, author = {R{\"u}diger, G{\"u}nther and K{\"u}ker, Manfred and Kapyla, P. J. and Strassmeier, Klaus G.}, title = {Antisolar differential rotation of slowly rotating cool stars}, series = {Astronomy and astrophysics : an international weekly journal}, volume = {630}, journal = {Astronomy and astrophysics : an international weekly journal}, publisher = {EDP Sciences}, address = {Les Ulis}, issn = {1432-0746}, doi = {10.1051/0004-6361/201935280}, pages = {9}, year = {2019}, abstract = {Rotating stellar convection transports angular momentum towards the equator, generating the characteristic equatorial acceleration of the solar rotation while the radial flux of angular momentum is always inwards. New numerical box simulations for the meridional cross-correlation < u(theta)u(phi)>, however, reveal the angular momentum transport towards the poles for slow rotation and towards the equator for fast rotation. The explanation is that for slow rotation a negative radial gradient of the angular velocity always appears, which in combination with a so-far neglected rotation-induced off-diagonal eddy viscosity term nu(perpendicular to) provides "antisolar rotation" laws with a decelerated equator Similarly, the simulations provided positive values for the rotation-induced correlation < u(r)u(theta)>, which is relevant for the resulting latitudinal temperature profiles (cool or warm poles) for slow rotation and negative values for fast rotation. Observations of the differential rotation of slowly rotating stars will therefore lead to a better understanding of the actual stress-strain relation, the heat transport, and the underlying model of the rotating convection.}, language = {en} } @article{SchulzLieutenantXiaoetal.2020, author = {Schulz, Christian and Lieutenant, Klaus and Xiao, Jie and Hofmann, Tommy and Wong, Deniz and Habicht, Klaus}, title = {Characterization of the soft X-ray spectrometer PEAXIS at BESSY II}, series = {Journal of synchrotron radiation}, volume = {27}, journal = {Journal of synchrotron radiation}, publisher = {International Union of Crystallography}, address = {Chester}, issn = {1600-5775}, doi = {10.1107/S1600577519014887}, pages = {238 -- 249}, year = {2020}, abstract = {The performance of the recently commissioned spectrometer PEAXIS for resonant inelastic soft X-ray scattering (RIXS) and X-ray photoelectron spectroscopy and its hosting beamline U41-PEAXIS at the BESSY II synchrotron are characterized. The beamline provides linearly polarized light from 180 eV to 1600 eV allowing for RIXS measurements in the range 200-1200 eV. The monochromator optics can be operated in different configurations to provide either high flux with up to 10(12) photons s(-1) within the focal spot at the sample or high energy resolution with a full width at half maximum of <40 meV at an incident photon energy of similar to 400 eV. The measured total energy resolution of the RIXS spectrometer is in very good agreement with theoretically predicted values obtained by ray-tracing simulations. PEAXIS features a 5 m-long RIXS spectrometer arm that can be continuously rotated about the sample position by 106 degrees within the horizontal photon scattering plane, thus enabling the study of momentum-transfer-dependent excitations. Selected scientific examples are presented to demonstrate the instrument capabilities, including measurements of excitations in single-crystalline NiO and in liquid acetone employing a fluid cell sample manipulator. Planned upgrades of the beamline and the RIXS spectrometer to further increase the energy resolution to similar to 100 meV at 1000 eV incident photon energy are discussed.}, language = {en} } @article{GuggenbergerChechkinMetzler2021, author = {Guggenberger, Tobias and Chechkin, Aleksei V. and Metzler, Ralf}, title = {Fractional Brownian motion in superharmonic potentials and non-Boltzmann stationary distributions}, series = {Journal of physics : A, Mathematical and theoretical}, volume = {54}, journal = {Journal of physics : A, Mathematical and theoretical}, number = {29}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {1751-8113}, doi = {10.1088/1751-8121/ac019b}, pages = {17}, year = {2021}, abstract = {We study the stochastic motion of particles driven by long-range correlated fractional Gaussian noise (FGN) in a superharmonic external potential of the form U(x) proportional to x(2n) (n is an element of N). When the noise is considered to be external, the resulting overdamped motion is described by the non-Markovian Langevin equation for fractional Brownian motion. For this case we show the existence of long time, stationary probability density functions (PDFs) the shape of which strongly deviates from the naively expected Boltzmann PDF in the confining potential U(x). We analyse in detail the temporal approach to stationarity as well as the shape of the non-Boltzmann stationary PDF. A typical characteristic is that subdiffusive, antipersistent (with negative autocorrelation) motion tends to effect an accumulation of probability close to the origin as compared to the corresponding Boltzmann distribution while the opposite trend occurs for superdiffusive (persistent) motion. For this latter case this leads to distinct bimodal shapes of the PDF. This property is compared to a similar phenomenon observed for Markovian Levy flights in superharmonic potentials. We also demonstrate that the motion encoded in the fractional Langevin equation driven by FGN always relaxes to the Boltzmann distribution, as in this case the fluctuation-dissipation theorem is fulfilled.}, language = {en} } @article{YestePrimusAlcantaraetal.2020, author = {Yeste, Maria Pilar and Primus, Philipp-Alexander and Alcantara, Rodrigo and Cauqui, Miguel Angel and Calvino, Juan Jose and Pintado, Jos{\´e} Mar{\´i}a and Blanco, Ginesa}, title = {Surface characterization of two Ce0.62Zr0.38O2 mixed oxides with different reducibility}, series = {Applied surface science : a journal devoted to applied physics and chemistry of surfaces and interfaces}, volume = {503}, journal = {Applied surface science : a journal devoted to applied physics and chemistry of surfaces and interfaces}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0169-4332}, doi = {10.1016/j.apsusc.2019.144255}, pages = {9}, year = {2020}, abstract = {This paper presents a study of the surface properties of two Ce/Zr mixed oxides with different reducibility, obtained by applying distinct thermal ageing treatments to an oxide with the composition Ce0.62Zr0.38O2. The surface composition was investigated by XPS. Chemical reactivity of the surface was studied by adsorption of the probe molecules CO2, D-2 and methanol. Nanostructural characterization was carried out by XRD, Raman and high-resolution Eu3+ spectroscopy (FLNS). The characterization showed only slight variations in surface composition and bulk Ce-Zr distribution, but hardy differences concerning the type and strength of acidic surface centres, as well as strong differences in the ability to dissociate hydrogen. Structural variations between both samples were identified by comparing the optical spectra of Eu3+ in surface doped samples.}, language = {en} } @article{BeckusEliaz2021, author = {Beckus, Siegfried and Eliaz, Latif}, title = {Eigenfunctions growth of R-limits on graphs}, series = {Journal of spectral theory / European Mathematical Society}, volume = {11}, journal = {Journal of spectral theory / European Mathematical Society}, number = {4}, publisher = {EMS Press, an imprint of the European Mathematical Society - EMS - Publishing House GmbH, Institut f{\"u}r Mathematik, Technische Universit{\"a}t}, address = {Berlin}, issn = {1664-039X}, doi = {10.4171/JST/389}, pages = {1895 -- 1933}, year = {2021}, abstract = {A characterization of the essential spectrum of Schrodinger operators on infinite graphs is derived involving the concept of R-limits. This concept, which was introduced previously for operators on N and Z(d) as "right-limits," captures the behaviour of the operator at infinity. For graphs with sub-exponential growth rate, we show that each point in sigma(ss)(H) corresponds to a bounded generalized eigenfunction of a corresponding R-limit of H. If, additionally, the graph is of uniform sub-exponential growth, also the converse inclusion holds.}, language = {en} } @article{SandevIominKocarev2020, author = {Sandev, Trifce and Iomin, Alexander and Kocarev, Ljupco}, title = {Hitting times in turbulent diffusion due to multiplicative noise}, series = {Physical review : E, Statistical, nonlinear and soft matter physics}, volume = {102}, journal = {Physical review : E, Statistical, nonlinear and soft matter physics}, number = {4}, publisher = {American Institute of Physics}, address = {Woodbury, NY}, issn = {2470-0045}, doi = {10.1103/PhysRevE.102.042109}, pages = {10}, year = {2020}, abstract = {We study a distribution of times of the first arrivals to absorbing targets in turbulent diffusion, which is due to a multiplicative noise. Two examples of dynamical systems with a multiplicative noise are studied. The first one is a random process according to inhomogeneous diffusion, which is also known as a geometric Brownian motion in the Black-Scholes model. The second model is due to a random processes on a two-dimensional comb, where inhomogeneous advection is possible only along the backbone, while Brownian diffusion takes place inside the branches. It is shown that in both cases turbulent diffusion takes place as the one-dimensional random process with the log-normal distribution in the presence of absorbing targets, which are characterized by the Levy-Smirnov distribution for the first hitting times.}, language = {en} } @article{MassoltBorowski2020, author = {Massolt, Joost Willem and Borowski, Andreas}, title = {Perceived relevance of university physics problems by pre-service physics teachers}, series = {International journal of science education}, volume = {42}, journal = {International journal of science education}, number = {2}, publisher = {Routledge, Taylor \& Francis Group}, address = {Abingdon}, issn = {0950-0693}, doi = {10.1080/09500693.2019.1705424}, pages = {167 -- 189}, year = {2020}, abstract = {Pre-service physics teachers often do not recognise the relevance for their future career in their university content knowledge courses. A lower perceived relevance can, however, have a negative effect on their motivation and on their academic success. Several intervention studies have been undertaken with the goal to increase this perceived relevance. A previous study shows that conceptual physics problems used in university physics courses are perceived by pre-service physics teachers as more relevant for their future career than regular, quantitative problems. It is however not clear, what the students' meaning of the construct 'relevance' is: what makes a problem more relevant to them than another problem? To answer this question, N = 7 pre-service teachers were interviewed using the repertory grid technique, based on the personal construct theory. Nine physics problems were discussed with regards to their perceived relevance and with regards to problem properties that distinguish these problems from each other. We are able to identify six problem properties that have a positive influence on the perceived relevance. Physics problems that are based on these properties should therefore potentially have a higher perceived relevance, which can have a positive effect on the motivation of the pre-service teachers who solve these problems.}, language = {en} } @article{LewensteinCirauquiAngelGarciaMarchetal.2022, author = {Lewenstein, Maciej and Cirauqui, David and Angel Garcia-March, Miguel and Corominas, Guillem Guigo and Grzybowski, Przemyslaw and Saavedra, Jose R. M. and Wilkens, Martin and Wehr, Jan}, title = {Haake-Lewenstein-Wilkens approach to spin-glasses revisited}, series = {Journal of physics : A, Mathematical and theoretical}, volume = {55}, journal = {Journal of physics : A, Mathematical and theoretical}, number = {45}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {1751-8113}, doi = {10.1088/1751-8121/ac9d10}, pages = {20}, year = {2022}, abstract = {We revisit the Haake-Lewenstein-Wilkens approach to Edwards-Anderson (EA) model of Ising spin glass (SG) (Haake et al 1985 Phys. Rev. Lett. 55 2606). This approach consists in evaluation and analysis of the probability distribution of configurations of two replicas of the system, averaged over quenched disorder. This probability distribution generates squares of thermal copies of spin variables from the two copies of the systems, averaged over disorder, that is the terms that enter the standard definition of the original EA order parameter, qEA 0 0}, language = {en} } @article{EvsevleevMishurovaCabezaetal.2018, author = {Evsevleev, Sergei and Mishurova, Tatiana and Cabeza, Sandra and Koos, R. and Sevostianov, Igor and Garc{\´e}s, Gonzales and Requena, Guillermo and Fernandez, R. and Bruno, Giovanni}, title = {The role of intermetallics in stress partitioning and damage evolution of AlSil2CuMgNi alloy}, series = {Materials Science and Engineering: A-Structural materials: properties, microstructure and processing}, volume = {736}, journal = {Materials Science and Engineering: A-Structural materials: properties, microstructure and processing}, publisher = {Elsevier}, address = {Lausanne}, issn = {0921-5093}, doi = {10.1016/j.msea.2018.08.070}, pages = {453 -- 464}, year = {2018}, abstract = {Load partitioning between phases in a cast AlSi12CuMgNi alloy was investigated by in-situ compression test during neutron diffraction experiments. Computed tomography (CT) was used to determine volume fractions of eutectic Si and intermetallic (IM) phases, and to assess internal damage after ex-situ compression tests. The CT reconstructed volumes showed the interconnectivity of IM phases, which build a 3D network together with eutectic Si. Large stresses were found in IMs, revealing their significant role as a reinforcement for the alloy. An existing micromechanical model based on Maxwell scheme was extended to the present case, assuming the alloy as a three-phase composite (Al matrix, eutectic Si, IM phases). The model agrees well with the experimental data. Moreover, it allows predicting the principal stresses in each phase, while experiments can only determine stress differences between the axial and radial sample directions. Finally, we showed that the addition of alloying elements not only allowed developing a 3D interconnected network, but also improved the strength of the Al matrix, and the ability of the alloy constituents to bear mechanical load.}, language = {en} } @article{EvsevleevPaciornikBruno2020, author = {Evsevleev, Sergei and Paciornik, Sidnei and Bruno, Giovanni}, title = {Advanced deep learning-based 3D microstructural characterization of multiphase metal matrix composites}, series = {Advanced engineering materials}, volume = {22}, journal = {Advanced engineering materials}, number = {4}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1438-1656}, doi = {10.1002/adem.201901197}, pages = {6}, year = {2020}, abstract = {The quantitative analysis of microstructural features is a key to understanding the micromechanical behavior of metal matrix composites (MMCs), which is a premise for their use in practice. Herein, a 3D microstructural characterization of a five-phase MMC is performed by synchrotron X-ray computed tomography (SXCT). A workflow for advanced deep learning-based segmentation of all individual phases in SXCT data is shown using a fully convolutional neural network with U-net architecture. High segmentation accuracy is achieved with a small amount of training data. This enables extracting unprecedently precise microstructural parameters (e.g., volume fractions and particle shapes) to be input, e.g., in micromechanical models.}, language = {en} } @article{KumarRosenblum2021, author = {Kumar, Mohit and Rosenblum, Michael}, title = {Two mechanisms of remote synchronization in a chain of Stuart-Landau oscillators}, series = {Physical review : E, Statistical, nonlinear and soft matter physics}, volume = {104}, journal = {Physical review : E, Statistical, nonlinear and soft matter physics}, number = {5}, publisher = {American Physical Society}, address = {College Park}, issn = {2470-0045}, doi = {10.1103/PhysRevE.104.054202}, pages = {6}, year = {2021}, abstract = {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.}, language = {en} } @article{BuschhueterSpodenBorowski2017, author = {Buschh{\"u}ter, David and Spoden, Christian and Borowski, Andreas}, title = {Physics knowledge of first semester physics students in Germany}, series = {International journal of science education}, volume = {39}, journal = {International journal of science education}, number = {9}, publisher = {Routledge, Taylor \& Francis Group}, address = {Abingdon}, issn = {0950-0693}, doi = {10.1080/09500693.2017.1318457}, pages = {1109 -- 1132}, year = {2017}, abstract = {Over the last decades, the percentage of the age group choosing to pursue university studies has increased significantly across the world. At the same time, there are university teachers who believe that the standards have fallen. There is little research on whether students nowadays demonstrate knowledge or abilities similar to that of the preceding cohorts. However, in times of educational expansion, empirical evidence on student test performance is extremely helpful in evaluating how well educational systems cope with the increasing numbers of students. In this study, we compared a sample of 2322 physics freshmen from 2013 with another sample of 2718 physics freshmen from 1978 at universities in Germany with regard to their physics knowledge based on their results in the same entrance test. Previous results on mathematics knowledge and abilities in the same sample of students indicated that there was no severe decline in their average achievement. This paper compares the physics knowledge of the same two samples of students. Contrary to their mathematics results, their physics results showed a substantial decrease in physics knowledge as measured by the test.}, language = {en} } @article{MishurovaBrunoEvsevleevetal.2020, author = {Mishurova, Tatiana and Bruno, Giovanni and Evsevleev, Sergei and Sevostianov, Igor}, title = {Determination of macroscopic stress from diffraction experiments}, series = {Journal of applied physics}, volume = {128}, journal = {Journal of applied physics}, number = {2}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0021-8979}, doi = {10.1063/5.0009101}, pages = {14}, year = {2020}, abstract = {The paper is motivated by some inconsistencies and contradictions present in the literature on the calculation of the so-called diffraction elastic constants. In an attempt at unifying the views that the two communities of Materials Science and Mechanics of Materials have on the subject, we revisit and define the terminology used in the field. We also clarify the limitations of the commonly used approaches and show that a unified methodology is also applicable to textured materials with a nearly arbitrary grain shape. We finally compare the predictions based on this methodology with experimental data obtained by in situ synchrotron radiation diffraction on additively manufactured Ti-6Al-4V alloy. We show that (a) the transverse isotropy of the material yields good agreement between the best-fit isotropy approximation (equivalent to the classic Kroner's model) and the experimental data and (b) the use of a general framework allows the calculation of all components of the tensor of diffraction elastic constants, which are not easily measurable by diffraction methods. This allows us to extend the current state-of-the-art with a predictive tool.}, language = {en} } @article{Regenstein2022, author = {Regenstein, Wolfgang}, title = {Statistische Beschreibung des Resonanzenergietransfers in L{\"o}sungen}, edition = {2. Version}, doi = {10.25932/publishup-56597}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-565977}, pages = {23}, year = {2022}, abstract = {Beim Resonanzenergietransfer werden Fotonen von einem angeregten Donator {\"u}ber einen Wechselwirkungsabstand auf einen Akzeptor {\"u}bertragen. Nach der quantenmechanischen Theorie von F{\"O}RSTER kann dieser Abstand mit Hilfe des {\"U}berlappungsintegrals von Fluoreszenzspektrum des Donators und Absorp-tionsspektrum des Akzeptors berechnet werden. Eine andere M{\"o}glichkeit der Bestimmung erh{\"a}lt man mit Hilfe von statistischen Modellen, die in einem {\"U}berblick zusammengestellt sind. Dabei kann der Abstand durch Auswertung der L{\"o}schkurve bestimmt werden. In dieser Arbeit wird dazu eine weitere statistische Variante der Bestimmung des Wechselwirkungsradius hinzugef{\"u}gt und an einem Beispiel ausf{\"u}hrlich demonstriert.}, language = {de} } @article{DonnerSeehaferSanjuanetal.2006, author = {Donner, Reik Volker and Seehafer, Norbert and Sanjuan, Miguel Angel Fernandez and Feudel, Fred}, title = {Low-dimensional dynamo modelling and symmetry-breaking bifurcations}, series = {Physica. D, Nonlinear phenomena}, volume = {223}, journal = {Physica. D, Nonlinear phenomena}, number = {2}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0167-2789}, doi = {10.1016/j.physd.2006.08.022}, pages = {151 -- 162}, year = {2006}, abstract = {Motivated by the successful Karlsruhe dynamo experiment, a relatively low-dimensional dynamo model is proposed. It is based on a strong truncation of the magnetohydrodynamic (MHD) equations with an external forcing of the Roberts type and the requirement that the model system satisfies the symmetries of the full MHD system, so that the first symmetry-breaking bifurcations can be captured. The backbone of the Roberts dynamo is formed by the Roberts flow, a helical mean magnetic field and another part of the magnetic field coupled to these two by triadic mode interactions. A minimum truncation model (MTM) containing only these energetically dominating primary mode triads is fully equivalent to the widely used first-order smoothing approximation. However, it is shown that this approach works only in the limit of small wave numbers of the excited magnetic field or small magnetic Reynolds numbers (\$Rm ll 1\$). To obtain dynamo action under more general conditions, secondary mode}, language = {en} } @article{MakwanaYan2020, author = {Makwana, Kirit D. and Yan, Huirong}, title = {Properties of magnetohydrodynamic modes in compressively driven plasma turbulence}, series = {Physical Review X}, volume = {10}, journal = {Physical Review X}, number = {3}, publisher = {American Physical Society (APS)}, address = {College Park}, issn = {2160-3308}, doi = {10.1103/PhysRevX.10.031021}, pages = {15}, year = {2020}, abstract = {We study properties of magnetohydrodynamic (MHD) eigenmodes by decomposing the data of MHD simulations into linear MHD modes-namely, the Alfven, slow magnetosonic, and fast magnetosonic modes. We drive turbulence with a mixture of solenoidal and compressive driving while varying the Alfven Mach number (M-A), plasma beta, and the sonic Mach number from subsonic to transsonic. We find that the proportion of fast and slow modes in the mode mixture increases with increasing compressive forcing. This proportion of the magnetosonic modes can also become the dominant fraction in the mode mixture. The anisotropy of the modes is analyzed by means of their structure functions. The Alfven-mode anisotropy is consistent with the Goldreich-Sridhar theory. We find a transition from weak to strong Alfvenic turbulence as we go from low to high M-A. The slow-mode properties are similar to the Alfven mode. On the other hand, the isotropic nature of fast modes is verified in the cases where the fast mode is a significant fraction of the mode mixture. The fast-mode behavior does not show any transition in going from low to high M-A. We find indications that there is some interaction between the different modes, and the properties of the dominant mode can affect the properties of the weaker modes. This work identifies the conditions under which magnetosonic modes can be a major fraction of turbulent astrophysical plasmas, including the regime of weak turbulence. Important astrophysical implications for cosmic-ray transport and magnetic reconnection are discussed.}, language = {en} } @article{ChenMuellerPrinzetal.2020, author = {Chen, Cong and M{\"u}ller, Bernd R. and Prinz, Carsten and Stroh, Julia and Feldmann, Ines and Bruno, Giovanni}, title = {The correlation between porosity characteristics and the crystallographic texture in extruded stabilized aluminium titanate for diesel particulate filter applications}, series = {Journal of the European Ceramic Society}, volume = {40}, journal = {Journal of the European Ceramic Society}, number = {4}, publisher = {Elsevier}, address = {Oxford}, issn = {0955-2219}, doi = {10.1016/j.jeurceramsoc.2019.11.076}, pages = {1592 -- 1601}, year = {2020}, abstract = {Porous ceramic diesel particulate filters (DPFs) are extruded products that possess macroscopic anisotropic mechanical and thermal properties. This anisotropy is caused by both morphological features (mostly the orientation of porosity) and crystallographic texture. We systematically studied those two aspects in two aluminum titanate ceramic materials of different porosity using mercury porosimetry, gas adsorption, electron microscopy, X-ray diffraction, and X-ray refraction radiography. We found that a lower porosity content implies a larger isotropy of both the crystal texture and the porosity orientation. We also found that, analogous to cordierite, crystallites do align with their axis of negative thermal expansion along the extrusion direction. However, unlike what found for cordierite, the aluminium titanate crystallite form is such that a more pronounced (0 0 2) texture along the extrusion direction implies porosity aligned perpendicular to it.}, language = {en} } @article{BlasiusRudolfWeithoffetal.2019, author = {Blasius, Bernd and Rudolf, Lars and Weithoff, Guntram and Gaedke, Ursula and Fussmann, Gregor F.}, title = {Long-term cyclic persistence in an experimental predator-prey system}, series = {Nature : the international weekly journal of science}, volume = {577}, journal = {Nature : the international weekly journal of science}, number = {7789}, publisher = {Nature Publ. Group}, address = {London}, issn = {0028-0836}, doi = {10.1038/s41586-019-1857-0}, pages = {226 -- 230}, year = {2019}, abstract = {Predator-prey cycles rank among the most fundamental concepts in ecology, are predicted by the simplest ecological models and enable, theoretically, the indefinite persistence of predator and prey(1-4). However, it remains an open question for how long cyclic dynamics can be self-sustained in real communities. Field observations have been restricted to a few cycle periods(5-8) and experimental studies indicate that oscillations may be short-lived without external stabilizing factors(9-19). Here we performed microcosm experiments with a planktonic predator-prey system and repeatedly observed oscillatory time series of unprecedented length that persisted for up to around 50 cycles or approximately 300 predator generations. The dominant type of dynamics was characterized by regular, coherent oscillations with a nearly constant predator-prey phase difference. Despite constant experimental conditions, we also observed shorter episodes of irregular, non-coherent oscillations without any significant phase relationship. However, the predator-prey system showed a strong tendency to return to the dominant dynamical regime with a defined phase relationship. A mathematical model suggests that stochasticity is probably responsible for the reversible shift from coherent to non-coherent oscillations, a notion that was supported by experiments with external forcing by pulsed nutrient supply. Our findings empirically demonstrate the potential for infinite persistence of predator and prey populations in a cyclic dynamic regime that shows resilience in the presence of stochastic events.}, language = {en} } @article{BastianYudeGuerenuKurganovaetal.2020, author = {Bastian, Philipp U. and Yu, Leixiao and de Guere{\~n}u Kurganova, Anna Lopez and Haag, Rainer and Kumke, Michael Uwe}, title = {Bioinspired confinement of upconversion nanoparticles for improved performance in aqueous solution}, series = {The journal of physical chemistry : C, Nanomaterials and interfaces}, volume = {124}, journal = {The journal of physical chemistry : C, Nanomaterials and interfaces}, number = {52}, publisher = {American Chemical Society}, address = {Washington, DC}, issn = {1932-7447}, doi = {10.1021/acs.jpcc.0c09798}, pages = {28623 -- 28635}, year = {2020}, abstract = {The resonance energy transfer (RET) from NaYF4:Yb,Er upconverting nanoparticles (UNCPs) to a dye (5-carboxytetramethylrhodamine (TAMRA)) was investigated by photoluminescence experiments and microscale thermophoresis (MST). The dye was excited via RET from the UCNPs which was excited in the near-infrared (NIR). The change of the dye diffusion speed (free vs coupled) was investigated by MST. RET shows significant changes in the decay times of the dye as well as of the UCNPs. MST reveals significant changes in the diffusion speed. A unique amphiphilic coating polymer (customized mussel protein (CMP) polymer) for UCNP surface coating was used, which mimics blood protein adsorption and mussel food protein adhesion to transfer the UCNP into the aqueous phase and to allow surface functionalization. The CMP provides very good water dispersibility to the UCNPs and minimizes ligand exchange and subsequent UCNP aging reactions because of the interlinkage of the CMP on the UCNP surface. Moreover, CMP provides N-3-functional groups for dick chemistry-based functionalization demonstrated with the dye 5-carboxytetramethylrhodamine (TAMRA). This establishes the principle coupling scheme for suitable biomarkers such as antibodies. The CMP provides very stable aqueous UCNP dispersions that are storable up to 3 years in a fridge at 5 degrees C without dissolution or coagulation. The outstanding properties of CMP in shielding the UCNP from unwanted solvent effects is reflected in the distinct increase of the photoluminescence decay times after UCNP functionalization. The UCNP-to-TAMRA energy transfer is also spectroscopically investigated at low temperatures (4-200 K), revealing that one of the two green Er(III) emission bands contributes the major part to the energy transfer. The TAMRA fluorescence decay time increases by a factor of 9500 from 2.28 ns up to 22 mu s due to radiationless energy transfer from the UCNP after NIR excitation of the latter. This underlines the unique properties of CMP as a versatile capping ligand for distinctly improving the UCNPs' performance in aqueous solutions, for coupling of biomolecules, and for applications for in vitro and in vivo experiments using UCNPs as optical probes in life science applications.}, language = {en} } @article{ThiedeCabezaMishurovaetal.2018, author = {Thiede, Tobias and Cabeza, Sandra and Mishurova, Tatiana and Nadammal, Naresh and Kromm, Arne and Bode, Johannes and Haberland, Christoph and Bruno, Giovanni}, title = {Residual Stress in Selective Laser Melted Inconel 718}, series = {Materials performance and characterization}, volume = {7}, journal = {Materials performance and characterization}, number = {4}, publisher = {American Society for Testing and Materials}, address = {West Conshohocken}, issn = {2379-1365}, doi = {10.1520/MPC20170119}, pages = {717 -- 735}, year = {2018}, abstract = {The residual stress distribution in IN718 elongated prisms produced by selective laser melting was studied by means of neutron (bulk) and laboratory X-ray (surface) diffraction. Two deposition hatch lengths were considered. A horizontal plane near the top surface (perpendicular to the building direction) and a vertical plane near the lateral surface (parallel to the building direction) were investigated. Samples both in as-built (AB) condition and removed from the base plate (RE) were characterized. While surface stress fields seem constant for the AB condition, X-ray diffraction shows stress gradients along the hatch direction in the RE condition. The stress profiles correlate with the distortion maps obtained by tactile probe measurements. Neutron diffraction shows bulk stress gradients for all principal components along the main sample directions. We correlate the observed stress patterns with the hatch length, i.e., with its effect on temperature gradients and heat flow. The bulk stress gradients partially disappear after removal from the base plate.}, language = {en} } @article{ErdmannKupschMuelleretal.2019, author = {Erdmann, Maren and Kupsch, Andreas and M{\"u}ller, Bernd Randolf and Hentschel, Manfred P. and Niebergall, Ute and B{\"o}hning, Martin and Bruno, Giovanni}, title = {Diesel-induced transparency of plastically deformed high-density polyethylene}, series = {Journal of materials science}, volume = {54}, journal = {Journal of materials science}, number = {17}, publisher = {Springer}, address = {New York}, issn = {0022-2461}, doi = {10.1007/s10853-019-03700-8}, pages = {11739 -- 11755}, year = {2019}, abstract = {High-density polyethylene becomes optically transparent during tensile drawing when previously saturated with diesel fuel. This unusual phenomenon is investigated as it might allow conclusions with respect to the material behavior. Microscopy, differential scanning calorimetry, density measurements are applied together with two scanning X-ray scattering techniques: wide angle X-ray scattering (WAXS) and X-ray refraction, able to extract the spatially resolved crystal orientation and internal surface, respectively. The sorbed diesel softens the material and significantly alters the yielding characteristics. Although the crystallinity among stretched regions is similar, a virgin reference sample exhibits strain whitening during stretching, while the diesel-saturated sample becomes transparent. The WAXS results reveal a pronounced fiber texture in the tensile direction in the stretched region and an isotropic orientation in the unstretched region. This texture implies the formation of fibrils in the stretched region, while spherulites remain intact in the unstretched parts of the specimens. X-ray refraction reveals a preferred orientation of internal surfaces along the tensile direction in the stretched region of virgin samples, while the sample stretched in the diesel-saturated state shows no internal surfaces at all. Besides from stretching saturated samples, optical transparency is also obtained from sorbing samples in diesel after stretching.}, language = {en} } @article{MackLaquaiMuelleretal.2019, author = {Mack, Daniel Emil and Laquai, Rene and Mueller, Bernd and Helle, Oliver and Sebold, Doris and Vassen, Robert and Bruno, Giovanni}, title = {Evolution of porosity, crack density, and CMAS penetration in thermal barrier coatings subjected to burner rig testing}, series = {Journal of the American Ceramic Society}, volume = {102}, journal = {Journal of the American Ceramic Society}, number = {10}, publisher = {Wiley}, address = {Hoboken}, issn = {0002-7820}, doi = {10.1111/jace.16465}, pages = {6163 -- 6175}, year = {2019}, abstract = {Degradation of thermal barrier coatings (TBCs) in gas-turbine engines due to calcium-magnesium-aluminosilicate (CMAS) glassy deposits from various sources has been a persistent issue since many years. In this study, state of the art electron microscopy was correlated with X-ray refraction techniques to elucidate the intrusion of CMAS into the porous structure of atmospheric plasma sprayed (APS) TBCs and the formation and growth of cracks under thermal cycling in a burner rig. Results indicate that the sparse nature of the infiltration as well as kinetics in the burner rig are majorly influenced by the wetting behavior of the CMAS. Despite the obvious attack of CMAS on grain boundaries, the interaction of yttria-stabilized zirconia (YSZ) with intruded CMAS has no immediate impact on structure and density of internal surfaces. At a later stage the formation of horizontal cracks is observed in a wider zone of the TBC layer.}, language = {en} } @article{MishurovaArtztHaubrichetal.2018, author = {Mishurova, Tatiana and Artzt, Katia and Haubrich, Jan and Requena, Guillermo and Bruno, Giovanni}, title = {New aspects about the search for the most relevant parameters optimizing SLM materials}, series = {Additive manufacturing}, volume = {25}, journal = {Additive manufacturing}, publisher = {Elsevier}, address = {Amsterdam}, issn = {2214-8604}, doi = {10.1016/j.addma.2018.11.023}, pages = {325 -- 334}, year = {2018}, abstract = {While the volumetric energy density is commonly used to qualify a process parameter set, and to quantify its influence on the microstructure and performance of additively manufactured (AM) materials and components, it has been already shown that this description is by no means exhaustive. In this work, new aspects of the optimization of the selective laser melting process are investigated for AM Ti-6Al-4V. We focus on the amount of near-surface residual stress (RS), often blamed for the failure of components, and on the porosity characteristics (amount and spatial distribution). First, using synchrotron x-ray diffraction we show that higher RS in the subsurface region is generated if a lower energy density is used. Second, we show that laser de-focusing and sample positioning inside the build chamber also play an eminent role, and we quantify this influence. In parallel, using X-ray Computed Tomography, we observe that porosity is mainly concentrated in the contour region, except in the case where the laser speed is small. The low values of porosity (less than 1\%) do not influence RS.}, language = {en} } @article{StegemannCabezaPelkneretal.2018, author = {Stegemann, Robert and Cabeza, Sandra and Pelkner, Matthias and Lyamkin, Viktor and Pittner, Andreas and Werner, Daniel and Wimpory, Robert and Boin, Mirko and Kreutzbruck, Marc and Bruno, Giovanni}, title = {Influence of the microstructure on magnetic stray fields of low-carbon steel welds}, series = {Journal of Nondestructive Evaluation}, volume = {37}, journal = {Journal of Nondestructive Evaluation}, number = {3}, publisher = {Springer}, address = {New York}, issn = {0195-9298}, doi = {10.1007/s10921-018-0522-0}, pages = {18}, year = {2018}, abstract = {This study examines the relationship between the magnetic mesostructure with the microstructure of low carbon steel tungsten inert gas welds. Optical microscopy revealed variation in the microstructure of the parent material, in the heat affected and fusion zones, correlating with distinctive changes in the local magnetic stray fields measured with high spatial resolution giant magneto resistance sensors. In the vicinity of the heat affected zone high residual stresses were found using neutron diffraction. Notably, the gradients of von Mises stress and triaxial magnetic stray field modulus follow the same tendency transverse to the weld. In contrast, micro-X-ray fluorescence characterization indicated that local changes in element composition had no independent effect on magnetic stray fields.}, language = {en} } @article{FernandezCabezaMishurovaetal.2018, author = {Fernandez, R. and Cabeza, Sandra and Mishurova, Tatiana and Fernandez-Castrillo, P. and Gonzalez-Doncel, Gaspar and Bruno, Giovanni}, title = {Residual stress and yield strength evolution with annealing treatments in an age-hardenable aluminum alloy matrix composite}, series = {Materials Science and Engineering: A}, volume = {731}, journal = {Materials Science and Engineering: A}, publisher = {Elsevier}, address = {Lausanne}, issn = {0921-5093}, doi = {10.1016/j.msea.2018.06.031}, pages = {344 -- 350}, year = {2018}, abstract = {We investigated the possibility of minimizing tensile matrix residual stresses in age hardenable aluminum alloy metal matrix composites without detrimentally affect their mechanical properties (such as yield strength). Specifically, we performed thermal treatments at different temperatures and times in an age-hardenable aluminum matrix composite 2014Al-15vol\%Al2O3. Using X-ray synchrotron radiation diffraction and mechanical tests, we show that below a certain treatment temperature (250 degrees C) it is possible to identify an appropriate thermal treatment capable of relaxing residual stress in this composite while even increasing its yield strength, with respect to the as processed conditions.}, language = {en} } @article{BuljakBruno2018, author = {Buljak, Vladimir and Bruno, Giovanni}, title = {Numerical modeling of thermally induced microcracking in porous ceramics}, series = {Journal of the European Ceramic Society}, volume = {38}, journal = {Journal of the European Ceramic Society}, number = {11}, publisher = {Elsevier}, address = {Oxford}, issn = {0955-2219}, doi = {10.1016/j.jeurceramsoc.2018.03.041}, pages = {4099 -- 4108}, year = {2018}, abstract = {A numerical framework is developed to study the hysteresis of elastic properties of porous ceramics as a function of temperature. The developed numerical model is capable of employing experimentally measured crystallographic orientation distribution and coefficient of thermal expansion values. For realistic modeling of the microstructure, Voronoi polygons are used to generate polycrystalline grains. Some grains are considered as voids, to simulate the material porosity. To model intercrystalline cracking, cohesive elements are inserted along grain boundaries. Crack healing (recovery of the initial properties) upon closure is taken into account with special cohesive elements implemented in the commercial code ABAQUS. The numerical model can be used to estimate fracture properties governing the cohesive behavior through inverse analysis procedure. The model is applied to a porous cordierite ceramic. The obtained fracture properties are further used to successfully simulate general non-linear macroscopic stress-strain curves of cordierite, thereby validating the model.}, language = {en} } @article{SevostianovBruno2018, author = {Sevostianov, Igor and Bruno, Giovanni}, title = {Maxwell scheme for internal stresses in multiphase composites}, series = {Mechanics of Materials}, volume = {129}, journal = {Mechanics of Materials}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0167-6636}, doi = {10.1016/j.mechmat.2018.12.005}, pages = {320 -- 331}, year = {2018}, abstract = {The paper focuses on the reformulation of classic Maxwell's (1873) homogenization method for calculation of the residual stresses in matrix composites. For this goal, we equate the far fields produced by a set of inhomogeneities subjected to known eigenstrains and by a fictitious domain with unknown eigenstrain. The effect of interaction between the inhomogeneities is reduced to the calculation of the additional field acting on an inhomogeneity due to the eigenstrains in its neighbors. An explicit formula for residual stresses is derived for the general case of a multiphase composite. The method is illustrated by several examples. The results are compared with available experimental data as well as with predictions provided by the non-interaction approximation (Eshelby solution). It is shown that accounting for interaction can explain many experimentally observed phenomena and is required for adequate quantitative analytical modeling of the residual stresses in matrix composites.}, language = {en} } @article{FernandezBrunoGarcesetal.2020, author = {Fernandez, Ricardo and Bruno, Giovanni and Garces, Gerardo and Nieto-Luis, H. and Gonzalez-Doncel, Gaspar}, title = {Fractional brownian motion of dislocations during creep deformation of metals}, series = {Materials science \& engineering. A, Structural materials}, volume = {796}, journal = {Materials science \& engineering. A, Structural materials}, publisher = {Elsevier}, address = {Lausanne}, issn = {0921-5093}, doi = {10.1016/j.msea.2020.140013}, pages = {8}, year = {2020}, abstract = {The present work offers an explanation on how the long-range interaction of dislocations influences their movement, and therefore the strain, during creep of metals. It is proposed that collective motion of dislocations can be described as a fractional Brownian motion. This explains the noisy appearance of the creep strain signal as a function of time. Such signal is split into a deterministic and a stochastic part. These terms can be related to two kinds of dislocation motions: individual and collective, respectively. The description is consistent with the fractal nature of strain-induced dislocation structures predicated in previous works. Moreover, it encompasses the evolution of the strain rate during all stages of creep, including the tertiary one. Creep data from Al99.8\% and Al3.85\%Mg tested at different temperatures and stresses are used to validate the proposed ideas: it is found that different creep stages present different diffusion characters, and therefore different dislocation motion character.}, language = {en} } @article{LaquaiMuellerSchneideretal.2020, author = {Laquai, Rene and M{\"u}ller, Bernd R. and Schneider, Judith Ann and Kupsch, Andreas and Bruno, Giovanni}, title = {Using SXRR to probe the nature of discontinuities in SLM additive manufactured inconel 718 specimens}, series = {Metallurgical and Materials Transactions A}, volume = {51}, journal = {Metallurgical and Materials Transactions A}, number = {8}, publisher = {Springer}, address = {New York}, issn = {1073-5623}, doi = {10.1007/s11661-020-05847-5}, pages = {4146 -- 4157}, year = {2020}, abstract = {The utilization of additive manufacturing (AM) to fabricate robust structural components relies on understanding the nature of internal anomalies or discontinuities, which can compromise the structural integrity. While some discontinuities in AM microstructures stem from similar mechanisms as observed in more traditional processes such as casting, others are unique to the AM process. Discontinuities in AM are challenging to detect, due to their submicron size and orientation dependency. Toward the goal of improving structural integrity, minimizing discontinuities in an AM build requires an understanding of the mechanisms of formation to mitigate their occurrence. This study utilizes various techniques to evaluate the shape, size, nature and distribution of discontinuities in AM Inconel 718, in a non-hot isostatic pressed (HIPed) as-built, non-HIPed and direct age, and HIPed with two step age samples. Non-destructive synchrotron radiation refraction and transmission radiography (SXRR) provides additional information beyond that obtained with destructive optical microscopy. SXRR was able to distinguish between voids, cracks and lack of melt in, due to its sensitivity to the orientation of the discontinuity.}, language = {en} } @article{FernandezGonzalezDoncelGarcesetal.2020, author = {Fernandez, Ricardo and Gonzalez-Doncel, Gaspar and Garces, Gerardo and Bruno, Giovanni}, title = {Towards a comprehensive understanding of creep}, series = {Materials science \& engineering. A, Structural materials: properties, microstructure and processing}, volume = {776}, journal = {Materials science \& engineering. A, Structural materials: properties, microstructure and processing}, publisher = {Elsevier}, address = {Lausanne}, issn = {0921-5093}, doi = {10.1016/j.msea.2020.139036}, pages = {7}, year = {2020}, abstract = {We show that the equation proposed by Takeuchi and Argon to explain the creep behavior of Al-Mg solid solution can be used to describe also the creep behavior of pure aluminum. In this frame, it is possible to avoid the use of the classic pre-exponential fitting parameter in the power law equation to predict the minimum creep strain rate. The effect of the fractal arrangement of dislocations, developed at the mesoscale, must be considered to fully explain the experimental data. These ideas allow improving the recently introduced SSTC model, fully describing the primary and secondary creep regimes of aluminum alloys without the need for fitting. Creep data from commercially pure A199.8\% and Al-Mg alloys tested at different temperatures and stresses are used to validate the proposed ideas.}, language = {en} }