TY  - JOUR
A1  - Totz, Sonja Juliana
A1  - Löber, Jakob
A1  - Totz, Jan Frederik
A1  - Engel, Harald
T1  - Control of transversal instabilities in reaction-diffusion systems
JF  - New journal of physics : the open-access journal for physics
N2  - In two-dimensional reaction-diffusion systems, local curvature perturbations on traveling waves are typically damped out and vanish. However, if the inhibitor diffuses much faster than the activator, transversal instabilities can arise, leading from flat to folded, spatio-temporally modulated waves and to spreading spiral turbulence. Here, we propose a scheme to induce or inhibit these instabilities via a spatio-temporal feedback loop. In a piecewise-linear version of the FitzHugh-Nagumo model, transversal instabilities and spiral turbulence in the uncontrolled system are shown to be suppressed in the presence of control, thereby stabilizing plane wave propagation. Conversely, in numerical simulations with the modified Oregonator model for the photosensitive Belousov-Zhabotinsky reaction, which does not exhibit transversal instabilities on its own, we demonstrate the feasibility of inducing transversal instabilities and study the emerging wave patterns in a well-controlled manner.
KW  - traveling waves
KW  - control
KW  - transversal instabilities
Y1  - 2018
U6  - https://doi.org/10.1088/1367-2630/aabce5
SN  - 1367-2630
VL  - 20
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Nunez Valdez, Maribel
A1  - Efthimiopoulos, Ilias
A1  - Taran, Michail
A1  - Mueller, Jan
A1  - Bykova, Elena
A1  - McCammon, Catherine
A1  - Koch-Müller, Monika
A1  - Wilke, Max
T1  - Evidence for a pressure-induced spin transition in olivine-type LiFePO4 triphylite
JF  - Physical review : B, Condensed matter and materials physics
N2  - We present a combination of first-principles and experimental results regarding the structural and magnetic properties of olivine-type LiFePO4 under pressure. Our investigations indicate that the starting Pbnm phase of LiFePO4 persists up to 70 GPa. Further compression leads to an isostructural transition in the pressure range of 70-75 GPa, inconsistent with a former theoretical study. Considering our first-principles prediction for a high-spin to low-spin transition of Fe2+ close to 72 GPa, we attribute the experimentally observed isostructural transition to a change in the spin state of Fe2+ in LiFePO4. Compared to relevant Fe-bearing minerals, LiFePO4 exhibits the largest onset pressure for a pressure-induced spin state transition.
Y1  - 2018
U6  - https://doi.org/10.1103/PhysRevB.97.184405
SN  - 2469-9950
SN  - 2469-9969
VL  - 97
IS  - 18
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Vafin, Sergei
A1  - Lazar, M.
A1  - Fichtner, H.
A1  - Schlickeiser, R.
A1  - Drillisch, M.
T1  - Solar wind temperature anisotropy constraints from streaming instabilities
JF  - Astronomy and astrophysics : an international weekly journal
N2  - Due to the relatively low rate of particle-particle collisions in the solar wind, kinetic instabilities (e.g., the mirror and firehose) play an important role in regulating large deviations from temperature isotropy. These instabilities operate in the high beta(parallel to) > 1 plasmas, and cannot explain the other limits of the temperature anisotropy reported by observations in the low beta beta(parallel to) < 1 regimes. However, the instability conditions are drastically modified in the presence of streaming (or counterstreaming) components, which are ubiquitous in space plasmas. These effects have been analyzed for the solar wind conditions in a large interval of heliospheric distances, 0.3-2.5 AU. It was found that proton counter-streams are much more crucial for plasma stability than electron ones. Moreover, new instability thresholds can potentially explain all observed bounds on the temperature anisotropy, and also the level of differential streaming in the solar wind.
KW  - solar wind
KW  - instabilities
KW  - waves
KW  - turbulence
Y1  - 2018
U6  - https://doi.org/10.1051/0004-6361/201731852
SN  - 1432-0746
VL  - 613
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Vitali, Silvia
A1  - Sposini, Vittoria
A1  - Sliusarenko, Oleksii
A1  - Paradisi, Paolo
A1  - Castellani, Gastone
A1  - Pagnini, Gianni
T1  - Langevin equation in complex media and anomalous diffusion
JF  - Interface : journal of the Royal Society
N2  - The problem of biological motion is a very intriguing and topical issue. Many efforts are being focused on the development of novel modelling approaches for the description of anomalous diffusion in biological systems, such as the very complex and heterogeneous cell environment. Nevertheless, many questions are still open, such as the joint manifestation of statistical features in agreement with different models that can also be somewhat alternative to each other, e.g. continuous time random walk and fractional Brownian motion. To overcome these limitations, we propose a stochastic diffusion model with additive noise and linear friction force (linear Langevin equation), thus involving the explicit modelling of velocity dynamics. The complexity of the medium is parametrized via a population of intensity parameters (relaxation time and diffusivity of velocity), thus introducing an additional randomness, in addition to white noise, in the particle's dynamics. We prove that, for proper distributions of these parameters, we can get both Gaussian anomalous diffusion, fractional diffusion and its generalizations.
KW  - anomalous diffusion
KW  - heterogeneous media
KW  - biological transport
KW  - Gaussian processes
KW  - space-time fractional diffusion equation
KW  - fractional Brownian motion
Y1  - 2018
U6  - https://doi.org/10.1098/rsif.2018.0282
SN  - 1742-5689
SN  - 1742-5662
VL  - 15
IS  - 145
PB  - Royal Society
CY  - London
ER  - 
TY  - JOUR
A1  - Szalay, J. R.
A1  - Poppe, A. R.
A1  - Agarwal, J.
A1  - Britt, D.
A1  - Belskaya, I.
A1  - Horanyi, M.
A1  - Nakamura, T.
A1  - Sachse, M.
A1  - Spahn, Frank
T1  - Dust Phenomena Relating to Airless Bodies
JF  - Space science reviews
N2  - Airless bodies are directly exposed to ambient plasma and meteoroid fluxes, making them characteristically different from bodies whose dense atmospheres protect their surfaces from such fluxes. Direct exposure to plasma and meteoroids has important consequences for the formation and evolution of planetary surfaces, including altering chemical makeup and optical properties, generating neutral gas and/or dust exospheres, and leading to the generation of circumplanetary and interplanetary dust grain populations. In the past two decades, there have been many advancements in our understanding of airless bodies and their interaction with various dust populations. In this paper, we describe relevant dust phenomena on the surface and in the vicinity of airless bodies over a broad range of scale sizes from to , with a focus on recent developments in this field.
KW  - Dust
KW  - Airless bodies
KW  - Interplanetary dust
Y1  - 2018
U6  - https://doi.org/10.1007/s11214-018-0527-0
SN  - 0038-6308
SN  - 1572-9672
VL  - 214
IS  - 5
PB  - Springer
CY  - Dordrecht
ER  - 
TY  - JOUR
A1  - Cestnik, Rok
A1  - Rosenblum, Michael
T1  - Inferring the phase response curve from observation of a continuously perturbed oscillator
JF  - Scientific reports
N2  - Phase response curves are important for analysis and modeling of oscillatory dynamics in various applications, particularly in neuroscience. Standard experimental technique for determining them requires isolation of the system and application of a specifically designed input. However, isolation is not always feasible and we are compelled to observe the system in its natural environment under free-running conditions. To that end we propose an approach relying only on passive observations of the system and its input. We illustrate it with simulation results of an oscillator driven by a stochastic force.
Y1  - 2018
U6  - https://doi.org/10.1038/s41598-018-32069-y
SN  - 2045-2322
VL  - 8
PB  - Nature Publ. Group
CY  - London
ER  - 
TY  - JOUR
A1  - Akimoto, Takuma
A1  - Cherstvy, Andrey G.
A1  - Metzler, Ralf
T1  - Ergodicity, rejuvenation, enhancement, and slow relaxation of diffusion in biased continuous-time random walks
JF  - Physical review : E, Statistical, nonlinear and soft matter physics
N2  - Bias plays an important role in the enhancement of diffusion in periodic potentials. Using the continuous-time random walk in the presence of a bias, we report on an interesting phenomenon for the enhancement of diffusion by the start of the measurement in a random energy landscape. When the variance of the waiting time diverges, in contrast to the bias-free case, the dynamics with bias becomes superdiffusive. In the superdiffusive regime, we find a distinct initial ensemble dependence of the diffusivity. Moreover, the diffusivity can be increased by the aging time when the initial ensemble is not in equilibrium. We show that the time-averaged variance converges to the corresponding ensemble-averaged variance; i.e., ergodicity is preserved. However, trajectory-to-trajectory fluctuations of the time-averaged variance decay unexpectedly slowly. Our findings provide a rejuvenation phenomenon in the superdiffusive regime, that is, the diffusivity for a nonequilibrium initial ensemble gradually increases to that for an equilibrium ensemble when the start of the measurement is delayed.
Y1  - 2018
U6  - https://doi.org/10.1103/PhysRevE.98.022105
SN  - 2470-0045
SN  - 2470-0053
VL  - 98
IS  - 2
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Cecchini, Gloria
A1  - Schelter, Björn
T1  - Analytical approach to network inference
BT  - Investigating degree distribution
JF  - Physical review : E, Statistical, nonlinear and soft matter physics
N2  - When the network is reconstructed, two types of errors can occur: false positive and false negative errors about the presence or absence of links. In this paper, the influence of these two errors on the vertex degree distribution is analytically analyzed. Moreover, an analytic formula of the density of the biased vertex degree distribution is found. In the inverse problem, we find a reliable procedure to reconstruct analytically the density of the vertex degree distribution of any network based on the inferred network and estimates for the false positive and false negative errors based on, e.g., simulation studies.
Y1  - 2018
U6  - https://doi.org/10.1103/PhysRevE.98.022311
SN  - 2470-0045
SN  - 2470-0053
VL  - 98
IS  - 2
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Mardoukhi, Yousof
A1  - Jeon, Jae-Hyung
A1  - Chechkin, Aleksei V.
A1  - Metzler, Ralf
T1  - Fluctuations of random walks in critical random environments
JF  - Physical chemistry, chemical physics : a journal of European Chemical Societies
N2  - Percolation networks have been widely used in the description of porous media but are now found to be relevant to understand the motion of particles in cellular membranes or the nucleus of biological cells. Random walks on the infinite cluster at criticality of a percolation network are asymptotically ergodic. On any finite size cluster of the network stationarity is reached at finite times, depending on the cluster's size. Despite of this we here demonstrate by combination of analytical calculations and simulations that at criticality the disorder and cluster size average of the ensemble of clusters leads to a non-vanishing variance of the time averaged mean squared displacement, regardless of the measurement time. Fluctuations of this relevant experimental quantity due to the disorder average of such ensembles are thus persistent and non-negligible. The relevance of our results for single particle tracking analysis in complex and biological systems is discussed.
Y1  - 2018
U6  - https://doi.org/10.1039/c8cp03212b
SN  - 1463-9076
SN  - 1463-9084
VL  - 20
IS  - 31
SP  - 20427
EP  - 20438
PB  - Royal Society of Chemistry
CY  - Cambridge
ER  - 
TY  - JOUR
A1  - Koopman, Wouter-Willem Adriaan
A1  - Natali, Marco
A1  - Bettini, Cristian
A1  - Melucci, Manuela
A1  - Muccini, Michele
A1  - Toffanin, Stefano
T1  - Contact Resistance in Ambipolar Organic Field-Effect Transistors Measured by Confocal Photoluminescence Electro-Modulation Microscopy
JF  - ACS applied materials & interfaces
N2  - Although it is theoretically expected that all organic semiconductors support ambipolar charge transport, most organic transistors either transport holes or electrons effectively. Single-layer ambipolar organic field-effect transistors enable the investigation of different mechanisms in hole and electron transport in a single device since the device architecture provides a controllable planar pn-junction within the transistor channel. However, a direct comparison of the injection barriers and of the channel conductivities between electrons and holes within the same device cannot be measured by standard electrical characterization. This article introduces a novel approach for determining threshold gate voltages for the onset of the ambipolar regime from the position of the pn-junction observed by photoluminescence electromodulation (PLEM) microscopy. Indeed, the threshold gate voltage in the ambipolar bias regime considers a vanishing channel length, thus correlating the contact resistance. PLEM microscopy is a valuable tool to directly compare the contact and channel resistances for both carrier types in the same device. The reported results demonstrate that designing the metal/organic semiconductor interfaces by aligning the bulk metal Fermi levels to the highest occupied molecular orbital or lowest unoccupied molecular orbital levels of the organic semiconductors is a too simplistic approach for optimizing the charge injection process in organic field-effect devices.
KW  - electro-modulation microscopy
KW  - organic field-effect transistors
KW  - threshold voltages
KW  - contact resistance
KW  - photoluminescence
Y1  - 2018
U6  - https://doi.org/10.1021/acsami.8b05518
SN  - 1944-8244
VL  - 10
IS  - 41
SP  - 35411
EP  - 35419
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Paalvast, M.
A1  - Verhamme, A.
A1  - Straka, L. A.
A1  - Brinchmann, J.
A1  - Herenz, Edmund Christian
A1  - Carton, D.
A1  - Gunawardhana, M. L. P.
A1  - Boogaard, L. A.
A1  - Cantalupo, S.
A1  - Contini, T.
A1  - Epinat, Benoit
A1  - Inami, H.
A1  - Marino, R. A.
A1  - Maseda, M. V.
A1  - Michel-Dansac, L.
A1  - Muzahid, S.
A1  - Nanayakkara, T.
A1  - Pezzulli, Gabriele
A1  - Richard, J.
A1  - Schaye, Joop
A1  - Segers, M. C.
A1  - Urrutia, Tanya
A1  - Wendt, Martin
A1  - Wisotzki, Lutz
T1  - Properties and redshift evolution of star-forming galaxies with high [0 III]/[O II] ratios with MUSE at 0.28 < z < 0.85
JF  - Astronomy and astrophysics : an international weekly journal
N2  - We present a study of the [O III]/[O II] ratios of star-forming galaxies drawn from Multi-Unit Spectroscopic Explorer (MUSE) data spanning a redshift range 0.28 < z < 0.85. Recently discovered Lyman continuum (LyC) emitters have extremely high oxygen line ratios: [O III]lambda 5007/[O II]lambda lambda 3726, 3729 > 4. Here we aim to understand the properties and the occurrences of galaxies with such high line ratios. Combining data from several MUSE Guaranteed Time Observing (GTO) programmes, we select a population of star-forming galaxies with bright emission lines, from which we draw 406 galaxies for our analysis based on their position in the z-dependent star formation rate (SFR) stellar mass (M*) plane. Out of this sample 15 are identified as extreme oxygen emitters based on their [O III]/[O II] ratios (3.7%) and 104 galaxies have [O III]/[O II] > 1 (26%). Our analysis shows no significant correlation between M*, SFR, and the distance from the SFR M, relation with [O III]/[O II]. We find a decrease in the fraction of galaxies with [O III]/[O II] > 1 with increasing M*, however, this is most likely a result of the relationship between [O III]/[O II] and metallicity, rather than between [O III]/[O II] and M. We draw a comparison sample of local analogues with < z > 0.03 from the Sloan Digital Sky Survey, and find similar incidence rates for this sample. In order to investigate the evolution in the fraction of high [O III]/[O II] emitters with redshift, we bin the sample into three redshift subsamples of equal number, but find no evidence for a dependence on redshift. Furthermore, we compare the observed line ratios with those predicted by nebular models with no LyC escape and find that most of the extreme oxygen emitters can be reproduced by low metallicity models. The remaining galaxies are likely LyC emitter candidates.
KW  - galaxies: evolution
KW  - galaxies: ISM
KW  - galaxies: abundances
KW  - ISM: structure
KW  - ISM: kinematics and dynamics
KW  - dark ages, reionization, first stars
Y1  - 2018
U6  - https://doi.org/10.1051/0004-6361/201832866
SN  - 0004-6361
SN  - 1432-0746
VL  - 618
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Münch, Thomas
A1  - Laepple, Thomas
T1  - What climate signal is contained in decadal- to centennial-scale isotope variations from Antarctic ice cores?
JF  - Climate of the past : CP
N2  - Ice-core-based records of isotopic composition are a proxy for past temperatures and can thus provide information on polar climate variability over a large range of timescales. However, individual isotope records are affected by a multitude of processes that may mask the true temperature variability. The relative magnitude of climate and non-climate contributions is expected to vary as a function of timescale, and thus it is crucial to determine those temporal scales on which the actual signal dominates the noise. At present, there are no reliable estimates of this timescale dependence of the signal-to-noise ratio (SNR). Here, we present a simple method that applies spectral analyses to stable-isotope data from multiple cores to estimate the SNR, and the signal and noise variability, as a function of timescale. The method builds on separating the contributions from a common signal and from local variations and includes a correction for the effects of diffusion and time uncertainty. We apply our approach to firn-core arrays from Dronning Maud Land (DML) in East Antarctica and from the West Antarctic Ice Sheet (WAIS). For DML and decadal to multi-centennial timescales, we find an increase in the SNR by nearly 1 order of magnitude (similar to 0.2 at decadal and similar to 1.0 at multi-centennial scales). The estimated spectrum of climate variability also shows increasing variability towards longer timescales, contrary to what is traditionally inferred from single records in this region. In contrast, the inferred variability spectrum for WAIS stays close to constant over decadal to centennial timescales, and the results even suggest a decrease in SNR over this range of timescales. We speculate that these differences between DML and WAIS are related to differences in the spatial and temporal scales of the isotope signal, highlighting the potentially more homogeneous atmospheric conditions on the Antarctic Plateau in contrast to the marine-influenced conditions on WAIS. In general, our approach provides a methodological basis for separating local proxy variability from coherent climate variations, which is applicable to a large set of palaeoclimate records.
Y1  - 2018
U6  - https://doi.org/10.5194/cp-14-2053-2018
SN  - 1814-9324
SN  - 1814-9332
VL  - 14
IS  - 12
SP  - 2053
EP  - 2070
PB  - Copernicus Gesellschaft mbH
CY  - Göttingen
ER  - 
TY  - GEN
A1  - Lewandowsky, Stephan
A1  - Cowtan, Kevin
A1  - Risbey, James S.
A1  - Mann, Michael E.
A1  - Steinman, Byron A.
A1  - Oreskes, Naomi
A1  - Rahmstorf, Stefan
T1  - Erratum: The 'pause' in global warming in historical context: II. Comparing models to observations (Environmental research letters. - Vol 13, (2018) 123007)
T2  - Environmental research letters
N2  - We review the evidence for a putative early 21st-century divergence between global mean surface temperature (GMST) and Coupled Model Intercomparison Project Phase 5 (CMIP5) projections. We provide a systematic comparison between temperatures and projections using historical versions of GMST products and historical versions of model projections that existed at the times when claims about a divergence were made. The comparisons are conducted with a variety of statistical techniques that correct for problems in previous work, including using continuous trends and a Monte Carlo approach to simulate internal variability. The results show that there is no robust statistical evidence for a divergence between models and observations. The impression of a divergence early in the 21st century was caused by various biases in model interpretation and in the observations, and was unsupported by robust statistics.
Y1  - 2019
U6  - https://doi.org/10.1088/1748-9326/aafbb7
SN  - 1748-9326
VL  - 14
IS  - 4
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Bouma, Sietske Jeltje Deirdre
A1  - Richter, Philipp
A1  - Fechner, Cora
T1  - A population of high-velocity absorption-line systems residing in the Local Group
JF  - Astronomy and astrophysics : an international weekly journal
N2  - Aims. We investigated the ionisation conditions and distances of Galactic high-velocity clouds (HVCs) in the Galactic halo and beyond in the direction of the Local Group (LG) barycentre and anti-barycentre, by studying spectral data of 29 extragalactic background sources obtained with the Cosmic Origins Spectropgraph (COS) installed on the Hubble Space Telescope (HST). Methods. We model column-densities of low, intermediate, and high ions such as Si ii, C ii, Si iii, Si vi, and C iv, and use these data to construct a set of Cloudy ionisation models. Results. In total, we found 69 high-velocity absorption components along the 29 lines of sight. The components in the direction of the LG barycentre span the entire range of studied velocities, 100 less than or similar to vertical bar nu(LSR)vertical bar less than or similar to 400 km s(-1), while those in the anti-barycentre sample have velocities up to about 300 km s(-1). For 49 components, we infer the gas densities. In the direction of the LG barycentre, the gas densities exhibit a wide range from log nH = -3.96 to -2.55, while in the anti-barycentre direction the densities are systematically higher, log nH > -3.25. The barycentre absorbers can be split into two groups based on their density: a high-density group with log nH > -3.54, which can be affected by the Milky Way radiation field, and a low-density group (log nH <= -3.54). The latter has very low thermal pressures of P/k < 7.3 Kcm(-3). Conclusions. Our study shows that part of the absorbers in the LG barycentre direction trace gas at very low gas densities and thermal pressures. These properties indicate that the absorbers are located beyond the virial radius of the Milky Way. Our study also confirms results from earlier, single-sightline studies, suggesting the presence of a metal-enriched intragroup medium filling the LG near its barycentre.
KW  - Galaxy: halo
KW  - Galaxy: structure
KW  - Galaxy: evolution
KW  - ISM: kinematics and dynamics
KW  - techniques: spectroscopic
KW  - ultraviolet: ISM
Y1  - 2019
U6  - https://doi.org/10.1051/0004-6361/201935078
SN  - 1432-0746
VL  - 627
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Cestnik, Rok
A1  - Abel, Markus
T1  - Inferring the dynamics of oscillatory systems using recurrent neural networks
JF  - Chaos : an interdisciplinary journal of nonlinear science
N2  - We investigate the predictive power of recurrent neural networks for oscillatory systems not only on the attractor but in its vicinity as well. For this, we consider systems perturbed by an external force. This allows us to not merely predict the time evolution of the system but also study its dynamical properties, such as bifurcations, dynamical response curves, characteristic exponents, etc. It is shown that they can be effectively estimated even in some regions of the state space where no input data were given. We consider several different oscillatory examples, including self-sustained, excitatory, time-delay, and chaotic systems. Furthermore, with a statistical analysis, we assess the amount of training data required for effective inference for two common recurrent neural network cells, the long short-term memory and the gated recurrent unit. Published under license by AIP Publishing.
Y1  - 2019
U6  - https://doi.org/10.1063/1.5096918
SN  - 1054-1500
SN  - 1089-7682
VL  - 29
IS  - 6
PB  - American Institute of Physics
CY  - Melville
ER  - 
TY  - JOUR
A1  - Teomy, Eial
A1  - Roichman, Yael
A1  - Shokef, Yair
T1  - Multiple peaks in the displacement distribution of active random walkers
JF  - Journal of statistical mechanics: theory and experiment
N2  - We consider a simple model for active random walk with general temporal correlations, and investigate the shape of the probability distribution function of the displacement during a short time interval. We find that under certain conditions the distribution exhibits multiple peaks and we show analytically and numerically that the existence of these peaks is governed by the walker?s tendency to move forward, while the correlations between the timing of its active motion control the magnitude and shape of the peaks. In particular, we find that in a homogeneous system such peaks can occur only if the persistence is strong enough.
KW  - 16
KW  - 4
Y1  - 2019
U6  - https://doi.org/10.1088/1742-5468/ab4fde
SN  - 1742-5468
VL  - 2019
IS  - 11
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Diercke, Andrea
A1  - Denker, Carsten
T1  - Chromospheric Synoptic Maps of Polar Crown Filaments
JF  - Solar physics : a journal for solar and solar-stellar research and the study of solar terrestrial physics
N2  - Polar crown filaments form above the polarity inversion line between the old magnetic flux of the previous cycle and the new magnetic flux of the current cycle. Studying their appearance and their properties can lead to a better understanding of the solar cycle. We use full-disk data of the Chromospheric Telescope (ChroTel) at the Observatorio del Teide, Tenerife, Spain, which were taken in three different chromospheric absorption lines (H alpha lambda 6563 angstrom, Ca II K lambda 3933 angstrom, and He I lambda 10830 angstrom), and we create synoptic maps. In addition, the spectroscopic He I data allow us to compute Doppler velocities and to create synoptic Doppler maps. ChroTel data cover the rising and decaying phase of Solar Cycle 24 on about 1000 days between 2012 and 2018. Based on these data, we automatically extract polar crown filaments with image-processing tools and study their properties. We compare contrast maps of polar crown filaments with those of quiet-Sun filaments. Furthermore, we present a super-synoptic map summarizing the entire ChroTel database. In summary, we provide statistical properties, i.e. number and location of filaments, area, and tilt angle for both the maximum and the declining phase of Solar Cycle 24. This demonstrates that ChroTel provides a promising data set to study the solar cycle.
KW  - Chromosphere, quiet
KW  - Prominences, quiescent
KW  - Prominences, magnetic field
KW  - Solar Cycle, observations
KW  - Instrumentation and data management
Y1  - 0201
U6  - https://doi.org/10.1007/s11207-019-1538-z
SN  - 0038-0938
SN  - 1573-093X
VL  - 294
IS  - 11
PB  - Springer
CY  - Dordrecht
ER  - 
TY  - JOUR
A1  - Göttgens, Fabian
A1  - Husser, Tim-Oliver
A1  - Kamann, Sebastian
A1  - Dreizler, Stefan
A1  - Giesers, Benjamin
A1  - Kollatschny, Wolfram
A1  - Weilbacher, Peter Michael
A1  - Roth, Martin M.
A1  - Wendt, Martin
T1  - A stellar census in globular clusters with MUSE: A spectral catalogue of emission-line sources
JF  - Astronomy and astrophysics : an international weekly journal
N2  - Aims. Globular clusters produce many exotic stars due to a much higher frequency of dynamical interactions in their dense stellar environments. Some of these objects were observed together with several hundred thousand other stars in our MUSE survey of 26 Galactic globular clusters. Assuming that at least a few exotic stars have exotic spectra (i.e. spectra that contain emission lines), we can use this large spectroscopic data set of over a million stellar spectra as a blind survey to detect stellar exotica in globular clusters. Methods. To detect emission lines in each spectrum, we modelled the expected shape of an emission line as a Gaussian curve. This template was used for matched filtering on the di fferences between each observed 1D spectrum and its fitted spectral model. The spectra with the most significant detections of H alpha emission are checked visually and cross-matched with published catalogues. Results. We find 156 stars with H alpha emission, including several known cataclysmic variables (CV) and two new CVs, pulsating variable stars, eclipsing binary stars, the optical counterpart of a known black hole, several probable sub-subgiants and red stragglers, and 21 background emission-line galaxies. We find possible optical counterparts to 39 X-ray sources, as we detected H alpha emission in several spectra of stars that are close to known positions of Chandra X-ray sources. This spectral catalogue can be used to supplement existing or future X-ray or radio observations with spectra of potential optical counterparts to classify the sources.
KW  - globular clusters: general
KW  - stars: emission-line, Be
KW  - novae
KW  - cataclysmic variables
KW  - catalogs
KW  - techniques: imaging spectroscopy
Y1  - 2019
U6  - https://doi.org/10.1051/0004-6361/201936485
SN  - 0004-6361
SN  - 1432-0746
VL  - 631
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Hsu, H. F.
A1  - Krekhov, Andrey
A1  - Tarantola, Marco
A1  - Beta, Carsten
A1  - Bodenschatz, Eberhardt
T1  - Interplay between myosin II and actin dynamics in chemotactic amoeba
JF  - New journal of physics : the open-access journal for physics
N2  - The actin cytoskeleton and its response to external chemical stimuli is fundamental to the mechano-biology of eukaryotic cells and their functions. One of the key players that governs the dynamics of the actin network is the motor protein myosin II. Based on a phase space embedding we have identified from experiments three phases in the cytoskeletal dynamics of starved Dictyostelium discoideum in response to a precisely controlled chemotactic stimulation. In the first two phases the dynamics of actin and myosin II in the cortex is uncoupled, while in the third phase the time scale for the recovery of cortical actin is determined by the myosin II dynamics. We report a theoretical model that captures the experimental observations quantitatively. The model predicts an increase in the optimal response time of actin with decreasing myosin II-actin coupling strength highlighting the role of myosin II in the robust control of cell contraction.
KW  - actin
KW  - myosin II
KW  - chemotaxis
KW  - oscillations
KW  - coupling
KW  - delay differential equation
KW  - contraction
Y1  - 2019
U6  - https://doi.org/10.1088/1367-2630/ab5822
SN  - 1367-2630
VL  - 21
IS  - 11
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Kar, M.
A1  - Körzdörfer, Thomas
T1  - Computational screening of methylammonium based halide perovskites with bandgaps suitable for perovskite-perovskite tandem solar cells
JF  - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr
N2  - We aim to find homovalent alternatives for lead and iodine in CH3NH3PbI3 perovskites that show bandgaps suitable for building novel perovskite-perovskite tandem solar cells. To this end, we employ a computational screening for materials with a bandgap between 1.0 eV and 1.9 eV, using density functional theory calculations at the Perdew-Burke-Ernzerhof and Heyd-Scuseria-Ernzerhof levels of theory. The room-temperature stability of the materials and their phases that satisfy the bandgap criteria is evaluated based on the empirical Goldschmidt tolerance factor. In total, our screening procedure covers 30 different perovskite structures in three phases (orthorhombic, cubic, tetragonal) each. We find 9 materials that are predicted to be stable at room temperature and to have bandgaps in an energy range suitable for application in tandem solar cells. Published by AIP Publishing.
Y1  - 2018
U6  - https://doi.org/10.1063/1.5037535
SN  - 0021-9606
SN  - 1089-7690
VL  - 149
IS  - 21
PB  - American Institute of Physics
CY  - Melville
ER  -