TY - JOUR
A1 - Alexoudi, Xanthippi
T1 - On the parameter refinement of inflated exoplanets with large radius uncertainty based on TESS observations
JF - Astronomische Nachrichten = Astronomical notes
N2 - We revisited 10 known exoplanetary systems using publicly available data provided by the transiting exoplanet survey satellite (TESS). The sample presented in this work consists of short period transiting exoplanets, with inflated radii and large reported uncertainty on their planetary radii. The precise determination of these values is crucial in order to develop accurate evolutionary models and understand the inflation mechanisms of these systems. Aiming to evaluate the planetary radius measurement, we made use of the planet-to-star radii ratio, a quantity that can be measured during a transit event. We fit the obtained transit light curves of each target with a detrending model and a transit model. Furthermore, we used emcee, which is based on a Markov chain Monte Carlo approach, to assess the best fit posterior distributions of each system parameter of interest. We refined the planetary radius of WASP-140 b by approximately 12%, and we derived a better precision on its reported asymmetric radius uncertainty by approximately 86 and 67%. We also refined the orbital parameters of WASP-120 b by 2 sigma. Moreover, using the high-cadence TESS datasets, we were able to solve a discrepancy in the literature, regarding the planetary radius of the exoplanet WASP-93 b. For all the other exoplanets in our sample, even though there is a tentative trend that planetary radii of (near-) grazing systems have been slightly overestimated in the literature, the planetary radius estimation and the orbital parameters were confirmed with independent observations from space, showing that TESS and ground-based observations are overall in good agreement.
KW - planetary systems
KW - techniques
KW - photometric
KW - stars
KW - WASP-140
KW - HAT-P-16
KW - WASP-108
KW - WASP-113
KW - WASP-120
KW - WASP-123
KW - WASP-136
KW - WASP-20
KW - WASP-76
KW - WASP-93
Y1 - 2022
U6 - https://doi.org/10.1002/asna.20224012
SN - 0004-6337
SN - 1521-3994
VL - 343
IS - 3
PB - Wiley-VCH
CY - Weinheim
ER -
TY - JOUR
A1 - Loebner, Sarah
A1 - Yadav, Bharti
A1 - Lomadze, Nino
A1 - Tverdokhleb, Nina
A1 - Donner, Hendrik
A1 - Saphiannikova, Marina
A1 - Santer, Svetlana
T1 - Local direction of optomechanical stress in azobenzene containing polymers during surface relief grating formation
JF - Macromolecular materials and engineering
N2 - In this work, it is revealed how the photoinduced deformation of azobenzene containing polymers relates to the local direction of optomechanical stresses generated during irradiation with interference patterns (IPs). It can be substantiated by the modeling approach proposed by Saphiannikova et al., which describes the directional photodeformations in glassy side-chain azobenzene polymers, and proves that these deformations arise from the reorientation of rigid backbone segments along the light polarization direction. In experiments and modeling, surface relief gratings in pre-elongated photosensitive colloids of few micrometers length are inscribed using different IPs such as SS, PP, +/- 45, SP, RL, and LR. The deformation of colloidal particles is studied in situ, whereby the local variation of polymer topography is assigned to the local distribution of the electrical field vector for all IPs. Experimentally observed shapes are reproduced exactly with modeling azopolymer samples as visco-plastic bodies in the finite element software ANSYS. Orientation approach correctly predicts local variations of the main axis of light-induced stress in each interference pattern for both initially isotropic and highly oriented materials. With this work, it is suggested that the orientation approach implements a self-sufficient and convincing mechanism to describe photoinduced deformation in azopolymer films that in principle does not require auxiliary assumptions.
KW - azobenzene containing polymers
KW - colloidal particles
KW - direction of optomechanical stress
KW - orientation approaches
Y1 - 2022
U6 - https://doi.org/10.1002/mame.202100990
SN - 1438-7492
SN - 1439-2054
VL - 307
IS - 8
PB - Wiley-VCH
CY - Weinheim
ER -
TY - JOUR
A1 - Heinsohn, Natascha Katharina
A1 - Niedl, Robert Raimund
A1 - Anielski, Alexander
A1 - Lisdat, Fred
A1 - Beta, Carsten
T1 - Electrophoretic mu PAD for purification and analysis of DNA samples
JF - Biosensors : open access journal
N2 - In this work, the fabrication and characterization of a simple, inexpensive, and effective microfluidic paper analytic device (mu PAD) for monitoring DNA samples is reported. The glass microfiber-based chip has been fabricated by a new wax-based transfer-printing technique and an electrode printing process. It is capable of moving DNA effectively in a time-dependent fashion. The nucleic acid sample is not damaged by this process and is accumulated in front of the anode, but not directly on the electrode. Thus, further DNA processing is feasible. The system allows the DNA to be purified by separating it from other components in sample mixtures such as proteins. Furthermore, it is demonstrated that DNA can be moved through several layers of the glass fiber material. This proof of concept will provide the basis for the development of rapid test systems, e.g., for the detection of pathogens in water samples.
KW - microfluidic paper analytic device (mu PAD)
KW - patterning glass microfiber
KW - fiber-electrophoresis chip
KW - DNA
KW - imprinted electrodes
KW - cross layer chip
KW - polymerase chain reaction (PCR)
KW - purification
Y1 - 2022
U6 - https://doi.org/10.3390/bios12020062
SN - 2079-6374
VL - 12
IS - 2
PB - MDPI
CY - Basel
ER -
TY - JOUR
A1 - Vollbrecht, Joachim
A1 - Tokmoldin, Nurlan
A1 - Sun, Bowen
A1 - Brus, Viktor V.
A1 - Shoaee, Safa
A1 - Neher, Dieter
T1 - Determination of the charge carrier density in organic solar cells
BT - a tutorial
JF - Journal of applied physics
N2 - The increase in the performance of organic solar cells observed over the past few years has reinvigorated the search for a deeper understanding of the loss and extraction processes in this class of device. A detailed knowledge of the density of free charge carriers under different operating conditions and illumination intensities is a prerequisite to quantify the recombination and extraction dynamics. Differential charging techniques are a promising approach to experimentally obtain the charge carrier density under the aforementioned conditions. In particular, the combination of transient photovoltage and photocurrent as well as impedance and capacitance spectroscopy have been successfully used in past studies to determine the charge carrier density of organic solar cells. In this Tutorial, these experimental techniques will be discussed in detail, highlighting fundamental principles, practical considerations, necessary corrections, advantages, drawbacks, and ultimately their limitations. Relevant references introducing more advanced concepts will be provided as well. Therefore, the present Tutorial might act as an introduction and guideline aimed at new prospective users of these techniques as well as a point of reference for more experienced researchers. Published under an exclusive license by AIP Publishing.
KW - Electrical properties and parameters
KW - Organic semiconductors
KW - Solar cells
KW - Photoconductivity
KW - Capacitance spectroscopy
Y1 - 2022
U6 - https://doi.org/10.1063/5.0094955
SN - 0021-8979
SN - 1089-7550
SN - 1520-8850
VL - 131
IS - 22
PB - American Institute of Physics
CY - Melville, NY
ER -
TY - JOUR
A1 - Mascarenhas, Eric Johnn
A1 - Fondell, Mattis
A1 - Büchner, Robby
A1 - Eckert, Sebastian
A1 - Vaz da Cruz, Vinícius
A1 - Föhlisch, Alexander
T1 - Photo-induced ligand substitution of Cr(CO)(6) in 1-pentanol probed by time resolved X-ray absorption spectroscopy
JF - Physical chemistry, chemical physics : a journal of European Chemical Societies
N2 - Cr(CO)(6) was investigated by X-ray absorption spectroscopy. The spectral signature at the metal edge provides information about the back-bonding of the metal in this class of complexes. Among the processes it participates in is ligand substitution in which a carbonyl ligand is ejected through excitation to a metal to ligand charge transfer (MLCT) band. The unsaturated carbonyl Cr(CO)(5) is stabilized by solution media in square pyramidal geometry and further reacts with the solvent. Multi-site-specific probing after photoexcitation was used to investigate the ligand substitution photoreaction process which is a common first step in catalytic processes involving metal carbonyls. The data were analysed with the aid of TD-DFT computations for different models of photoproducts and signatures for ligand rearrangement after substitution were found. The rearrangement was found to occur in about 790 ps in agreement with former studies of the photoreaction.
Y1 - 2022
U6 - https://doi.org/10.1039/d1cp05834g
SN - 1463-9076
SN - 1463-9084
VL - 24
IS - 30
SP - 17979
EP - 17985
PB - Royal Society of Chemistry
CY - Cambridge
ER -
TY - JOUR
A1 - Wang, Wei
A1 - Metzler, Ralf
A1 - Cherstvy, Andrey G.
T1 - Anomalous diffusion, aging, and nonergodicity of scaled Brownian motion with fractional Gaussian noise: overview of related experimental observations and models
JF - Physical chemistry, chemical physics : PCCP ; a journal of European chemical societies
N2 - How does a systematic time-dependence of the diffusion coefficient D(t) affect the ergodic and statistical characteristics of fractional Brownian motion (FBM)? Here, we answer this question via studying the characteristics of a set of standard statistical quantifiers relevant to single-particle-tracking (SPT) experiments. We examine, for instance, how the behavior of the ensemble- and time-averaged mean-squared displacements-denoted as the standard MSD < x(2)(Delta)> and TAMSD <<(delta(2)(Delta))over bar>> quantifiers-of FBM featuring < x(2) (Delta >> = <<(delta(2)(Delta >)over bar>> proportional to Delta(2H) (where H is the Hurst exponent and Delta is the [lag] time) changes in the presence of a power-law deterministically varying diffusivity D-proportional to(t) proportional to t(alpha-1) -germane to the process of scaled Brownian motion (SBM)-determining the strength of fractional Gaussian noise. The resulting compound "scaled-fractional" Brownian motion or FBM-SBM is found to be nonergodic, with < x(2)(Delta >> proportional to Delta(alpha+)(2H)(-1) and <(delta 2(Delta >) over bar > proportional to Delta(2H). We also detect a stalling behavior of the MSDs for very subdiffusive SBM and FBM, when alpha + 2H - 1 < 0. The distribution of particle displacements for FBM-SBM remains Gaussian, as that for the parent processes of FBM and SBM, in the entire region of scaling exponents (0 < alpha < 2 and 0 < H < 1). The FBM-SBM process is aging in a manner similar to SBM. The velocity autocorrelation function (ACF) of particle increments of FBM-SBM exhibits a dip when the parent FBM process is subdiffusive. Both for sub- and superdiffusive FBM contributions to the FBM-SBM process, the SBM exponent affects the long-time decay exponent of the ACF. Applications of the FBM-SBM-amalgamated process to the analysis of SPT data are discussed. A comparative tabulated overview of recent experimental (mainly SPT) and computational datasets amenable for interpretation in terms of FBM-, SBM-, and FBM-SBM-like models of diffusion culminates the presentation. The statistical aspects of the dynamics of a wide range of biological systems is compared in the table, from nanosized beads in living cells, to chromosomal loci, to water diffusion in the brain, and, finally, to patterns of animal movements.
Y1 - 2022
U6 - https://doi.org/10.1039/d2cp01741e
SN - 1463-9076
SN - 1463-9084
VL - 24
IS - 31
SP - 18482
EP - 18504
PB - RSC Publ.
CY - Cambridge
ER -
TY - JOUR
A1 - Scott, Shane
A1 - Weiss, Matthias
A1 - Selhuber-Unkel, Christine
A1 - Barooji, Younes F.
A1 - Sabri, Adal
A1 - Erler, Janine T.
A1 - Metzler, Ralf
A1 - Oddershede, Lene B.
T1 - Extracting, quantifying, and comparing dynamical and biomechanical properties of living matter through single particle tracking
JF - Physical chemistry, chemical physics : a journal of European Chemical Societies
N2 - A panoply of new tools for tracking single particles and molecules has led to an explosion of experimental data, leading to novel insights into physical properties of living matter governing cellular development and function, health and disease. In this Perspective, we present tools to investigate the dynamics and mechanics of living systems from the molecular to cellular scale via single-particle techniques. In particular, we focus on methods to measure, interpret, and analyse complex data sets that are associated with forces, materials properties, transport, and emergent organisation phenomena within biological and soft-matter systems. Current approaches, challenges, and existing solutions in the associated fields are outlined in order to support the growing community of researchers at the interface of physics and the life sciences. Each section focuses not only on the general physical principles and the potential for understanding living matter, but also on details of practical data extraction and analysis, discussing limitations, interpretation, and comparison across different experimental realisations and theoretical frameworks. Particularly relevant results are introduced as examples. While this Perspective describes living matter from a physical perspective, highlighting experimental and theoretical physics techniques relevant for such systems, it is also meant to serve as a solid starting point for researchers in the life sciences interested in the implementation of biophysical methods.
Y1 - 2022
U6 - https://doi.org/10.1039/d2cp01384c
SN - 1463-9076
SN - 1463-9084
VL - 25
IS - 3
SP - 1513
EP - 1537
PB - RSC Publ.
CY - Cambridge
ER -
TY - JOUR
A1 - Raman Venkatesan, Thulasinath
A1 - Smykalla, David
A1 - Ploss, Bernd
A1 - Wübbenhorst, Michael
A1 - Gerhard, Reimund
T1 - Tuning the relaxor-ferroelectric properties of Poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) Terpolymer films by means of thermally induced micro- and nanostructures
JF - Macromolecules : a publication of the American Chemical Society
N2 - The effects of thermal processing on the micro- and nanostructural features and thus also on the relaxor-ferroelectric properties of a P(VDF-TrFE-CFE) terpolymer were investigated in detail by means of dielectric experiments, such as dielectric relaxation spectroscopy (DRS), dielectric hysteresis loops, and thermally stimulated depolarization currents (TSDCs). The results were correlated with those obtained from differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), and Fourier-transform infrared spectroscopy (FTIR). The results from DRS and DSC show that annealing reduces the Curie transition temperature of the terpolymer, whereas the results from WAXD scans and FTIR spectra help to understand the shift in the Curie transition temperatures as a result of reducing the ferroelectric phase fraction, which by default exists even in terpolymers with relatively high CFE contents. In addition, the TSDC traces reveal that annealing has a similar effect on the midtemperature transition by altering the fraction of constrained amorphous phase at the interphase between the crystalline and the amorphous regions. Changes in the transition temperatures are in turn related to the behavior of the hysteresis curves on differently heat-treated samples. During heating, evolution of the hysteresis curves from ferroelectric to relaxor-ferroelectric, first exhibiting single hysteresis loops and then double hysteresis loops near the Curie transition of the sample, is observed. When comparing the dielectric-hysteresis loops obtained at various temperatures, we find that annealed terpolymer films show higher electric-displacement values and lower coercive fields than the nonannealed sample, irrespective of the measurement temperature, and also exhibit ideal relaxor- ferroelectric behavior at ambient temperatures, which makes them excellent candidates for applications at or near room temperature. By tailoring the annealing conditions, it has been shown that the application temperature could be increased by fine tuning the induced micro- and nanostructures.
KW - Annealing (metallurgy)
KW - Hysteresis
KW - Insulators
KW - Phase transitions
KW - Polarization
Y1 - 2022
U6 - https://doi.org/10.1021/acs.macromol.2c00302
SN - 0024-9297
SN - 1520-5835
VL - 55
IS - 13
SP - 5621
EP - 5635
PB - American Chemical Society
CY - Washington
ER -
TY - JOUR
A1 - Dahlke, Sandro
A1 - Solbès, Amélie
A1 - Maturilli, Marion
T1 - Cold air outbreaks in fram strait: climatology, trends, and observations during an extreme season in 2020
JF - Journal of geophysical research : atmospheres
N2 - Fram Strait in the northern North Atlantic is a key region for marine cold air outbreaks (MCAOs), southward discharges of polar air under northerly air flow, which have a strong impact on air-sea heat fluxes, boundary layer processes and severe weather. This study investigates climatologies and decadal trends of Fram Strait MCAOs of different intensity classes based on the ERA5 reanalysis product for 1979-2020. Among striking interannual variability, it is shown that the main MCAO season is December through March, when MCAOs occur around 2/3 of the time. We report on significant decadal MCAO decreases in December and January, and a significant increase in March. While the mid-winter decrease is mainly related to the different paces of warming between the surface and the lower atmosphere, the increase in March can be related to changes in synoptic circulation patterns. As an explanation for the latter, a possible feedback between retreating Barents Sea sea ice, enhanced cyclonic activity and Fram Strait MCAOs is postulated. Exemplifying the trend toward stronger MCAOs during March, the study details the recordbreaking MCAO season in early 2020, and an observational case study of an extreme MCAO event in March 2020 is conducted. Thereby, radiosonde observations are combined with kinematic air back-trajectories to provide rare observational evidence for the diabatic cooling and drying during the MCAO preconditioning phase.
KW - cold air outbreak
KW - North Atlantic variability
KW - air mass transformation;
KW - ocean-atmosphere energy exchange
Y1 - 2022
U6 - https://doi.org/10.1029/2021JD035741
SN - 2169-897X
SN - 2169-8996
VL - 127
IS - 3
PB - American Geophysical Union
CY - Washington
ER -
TY - JOUR
A1 - Emma, Mattia
A1 - Schianchi, Federico
A1 - Pannarale, Francesco
A1 - Sagun, Violetta
A1 - Dietrich, Tim
T1 - Numerical simulations of dark matter admixed neutron star binaries
JF - Particles
N2 - Multi-messenger observations of compact binary mergers provide a new way to constrain the nature of dark matter that may accumulate in and around neutron stars. In this article, we extend the infrastructure of our numerical-relativity code BAM to enable the simulation of neutron stars that contain an additional mirror dark matter component. We perform single star tests to verify our code and the first binary neutron star simulations of this kind. We find that the presence of dark matter reduces the lifetime of the merger remnant and favors a prompt collapse to a black hole. Furthermore, we find differences in the merger time for systems with the same total mass and mass ratio, but different amounts of dark matter. Finally, we find that electromagnetic signals produced by the merger of binary neutron stars admixed with dark matter are very unlikely to be as bright as their dark matter-free counterparts. Given the increased sensitivity of multi-messenger facilities, our analysis gives a new perspective on how to probe the presence of dark matter.
KW - numerical relativity
KW - dark matter
KW - neutron stars
KW - equation of state;
KW - gravitational-wave astronomy
KW - multi-messenger astrophysics
Y1 - 2022
U6 - https://doi.org/10.3390/particles5030024
SN - 2571-712X
VL - 5
IS - 3
SP - 273
EP - 286
PB - MDPI
CY - Basel
ER -
TY - JOUR
A1 - Cestnik, Rok
A1 - Pikovskij, Arkadij
T1 - Exact finite-dimensional reduction for a population of noisy oscillators and its link to Ott-Antonsen and Watanabe-Strogatz theories
JF - Chaos : an interdisciplinary journal of nonlinear science
N2 - Populations of globally coupled phase oscillators are described in the thermodynamic limit by kinetic equations for the distribution densities or, equivalently, by infinite hierarchies of equations for the order parameters. Ott and Antonsen [Chaos 18, 037113 (2008)] have found an invariant finite-dimensional subspace on which the dynamics is described by one complex variable per population. For oscillators with Cauchy distributed frequencies or for those driven by Cauchy white noise, this subspace is weakly stable and, thus, describes the asymptotic dynamics. Here, we report on an exact finite-dimensional reduction of the dynamics outside of the Ott-Antonsen subspace. We show that the evolution from generic initial states can be reduced to that of three complex variables, plus a constant function. For identical noise-free oscillators, this reduction corresponds to the Watanabe-Strogatz system of equations [Watanabe and Strogatz, Phys. Rev. Lett. 70, 2391 (1993)]. We discuss how the reduced system can be used to explore the transient dynamics of perturbed ensembles. Published under an exclusive license by AIP Publishing.
Y1 - 2022
U6 - https://doi.org/10.1063/5.0106171
SN - 1054-1500
SN - 1089-7682
VL - 32
IS - 11
PB - AIP
CY - Melville
ER -
TY - JOUR
A1 - Zeiske, Stefan
A1 - Sandberg, Oskar J.
A1 - Kurpiers, Jona
A1 - Shoaee, Safa
A1 - Meredith, Paul
A1 - Armin, Ardalan
T1 - Probing charge generation efficiency in thin-film solar cells by integral-mode transient charge extraction
JF - ACS photonics
N2 - The photogeneration of free charges in light-harvesting devices is a multistep process, which can be challenging to probe due to the complexity of contributing energetic states and the competitive character of different driving mechanisms. In this contribution, we advance a technique, integral-mode transient charge extraction (ITCE), to probe these processes in thin-film solar cells. ITCE combines capacitance measurements with the integral-mode time-of-flight method in the low intensity regime of sandwich-type thin-film devices and allows for the sensitive determination of photogenerated charge-carrier densities. We verify the theoretical framework of our method by drift-diffusion simulations and demonstrate the applicability of ITCE to organic and perovskite semiconductor-based thin-film solar cells. Furthermore, we examine the field dependence of charge generation efficiency and find our ITCE results to be in excellent agreement with those obtained via time-delayed collection field measurements conducted on the same devices.
KW - charge generation
KW - thin-film solar cells
KW - organic semiconductors;
KW - perovskite semiconductors
KW - external generation efficiency
Y1 - 2022
U6 - https://doi.org/10.1021/acsphotonics.1c01532
SN - 2330-4022
VL - 9
IS - 4
SP - 1188
EP - 1195
PB - American Chemical Society
CY - Washington
ER -
TY - JOUR
A1 - Ilić Petković, Nikoleta
A1 - Poppenhäger, Katja
A1 - Hosseini, Seyede Marzieh
T1 - Tidal star-planet interaction and its observed impact on stellar activity in planet-hosting wide binary systems
JF - Monthly notices of the Royal Astronomical Society
N2 - Tidal interaction between an exoplanet and its host star is a possible pathway to transfer angular momentum between the planetary orbit and the stellar spin. In cases where the planetary orbital period is shorter than the stellar rotation period, this may lead to angular momentum being transferred into the star's rotation, possibly counteracting the intrinsic stellar spin-down induced by magnetic braking. Observationally, detecting altered rotational states of single, cool field stars is challenging, as precise ages for such stars are rarely available. Here we present an empirical investigation of the rotation and magnetic activity of a sample of planet-hosting stars that are accompanied by wide stellar companions. Without needing knowledge about the absolute ages of the stars, we test for relative differences in activity and rotation of the planet hosts and their co-eval companions, using X-ray observations to measure the stellar activity levels. Employing three different tidal interaction models, we find that host stars with planets that are expected to tidally interact display elevated activity levels compared to their companion stars. We also find that those activity levels agree with the observed rotational periods for the host stars along the usual rotation-activity relationships, implying that the effect is indeed caused by a tidal interaction and not a purely magnetic interaction that would be expected to affect the stellar activity, but not necessarily the rotation. We conclude that massive, close-in planets have an impact on the stellar rotational evolution, while the smaller, more distant planets do not have a significant influence.
KW - planet-star interactions
KW - stars: activity
KW - binaries: general
KW - stars:
KW - evolution
KW - planets and satellites: general
KW - X-rays: stars
Y1 - 2022
U6 - https://doi.org/10.1093/mnras/stac861
SN - 0035-8711
SN - 1365-2966
VL - 513
IS - 3
SP - 4380
EP - 4404
PB - Oxford Univ. Press
CY - Oxford
ER -
TY - JOUR
A1 - Oster, Simon
A1 - Fritsch, Tobias
A1 - Ulbricht, Alexander
A1 - Mohr, Gunther
A1 - Bruno, Giovanni
A1 - Maierhofer, Christiane
A1 - Altenburg, Simon
T1 - On the registration of thermographic in situ monitoring data and computed tomography reference data in the scope of defect prediction in laser powder bed fusion
JF - Metals : open access journal
N2 - The detection of internal irregularities is crucial for quality assessment in metal-based additive manufacturing (AM) technologies such as laser powder bed fusion (L-PBF). The utilization of in-process thermography as an in situ monitoring tool in combination with post-process X-ray micro computed tomography (XCT) as a reference technique has shown great potential for this aim. Due to the small irregularity dimensions, a precise registration of the datasets is necessary as a requirement for correlation. In this study, the registration of thermography and XCT reference datasets of a cylindric specimen containing keyhole pores is carried out for the development of a porosity prediction model. The considered datasets show variations in shape, data type and dimensionality, especially due to shrinkage and material elevation effects present in the manufactured part. Since the resulting deformations are challenging for registration, a novel preprocessing methodology is introduced that involves an adaptive volume adjustment algorithm which is based on the porosity distribution in the specimen. Thus, the implementation of a simple three-dimensional image-to-image registration is enabled. The results demonstrate the influence of the part deformation on the resulting porosity location and the importance of registration in terms of irregularity prediction.
KW - selective laser melting (SLM)
KW - laser powder bed fusion (L-PBF)
KW - additive
KW - manufacturing (AM)
KW - process monitoring
KW - infrared thermography
KW - X-ray
KW - micro computed tomography (XCT)
KW - defect detection
KW - image registration
Y1 - 2022
U6 - https://doi.org/10.3390/met12060947
SN - 2075-4701
VL - 12
IS - 6
PB - MDPI
CY - Basel
ER -
TY - JOUR
A1 - Sun, Bowen
A1 - Sandberg, Oskar
A1 - Neher, Dieter
A1 - Armin, Ardalan
A1 - Shoaee, Safa
T1 - Wave optics of differential absorption spectroscopy in thick-junction organic solar cells
BT - optical artifacts and correction strategies
JF - Physical review applied / The American Physical Society
N2 - Differential absorption spectroscopy techniques serve as powerful techniques to study the excited species in organic solar cells. However, it has always been challenging to employ these techniques for characterizing thick-junction organic solar cells, especially when a reflective top contact is involved. In this work, we present a detailed and systematic study on how a combination of the presence of the interference effect and a nonuniform charge-distribution profile, severely manipulates experimental spectra and the decay dynamics. Furthermore, we provide a practical methodology to correct these optical artifacts in differential absorption spectroscopies. The results and the proposed correction method generally apply to all kinds of differential absorption spectroscopy techniques and various thin-film systems, such as organics, perovskites, kesterites, and two-dimensional materials. Notably, it is found that the shape of differential absorption spectra can be strongly distorted, starting from 150-nm active-layer thickness; this matches the thickness range of thick-junction organic solar cells and most perovskite solar cells and needs to be carefully considered in experiments. In addition, the decay dynamics of differential absorption spectra is found to be disturbed by optical artifacts under certain conditions. With the help of the proposed correction formalism, differential spectra and the decay dynamics can be characterized on the full device of thin-film solar cells in transmission mode and yield accurate and reliable results to provide design rules for further progress.
Y1 - 2022
U6 - https://doi.org/10.1103/PhysRevApplied.17.054016
SN - 2331-7019
VL - 17
IS - 5
PB - American Physical Society
CY - College Park
ER -
TY - JOUR
A1 - Doerries, Timo J.
A1 - Chechkin, Aleksei V.
A1 - Metzler, Ralf
T1 - Apparent anomalous diffusion and non-Gaussian distributions in a simple mobile-immobile transport model with Poissonian switching
JF - Interface : journal of the Royal Society
N2 - We analyse mobile-immobile transport of particles that switch between the mobile and immobile phases with finite rates. Despite this seemingly simple assumption of Poissonian switching, we unveil a rich transport dynamics including significant transient anomalous diffusion and non-Gaussian displacement distributions. Our discussion is based on experimental parameters for tau proteins in neuronal cells, but the results obtained here are expected to be of relevance for a broad class of processes in complex systems. Specifically, we obtain that, when the mean binding time is significantly longer than the mean mobile time, transient anomalous diffusion is observed at short and intermediate time scales, with a strong dependence on the fraction of initially mobile and immobile particles. We unveil a Laplace distribution of particle displacements at relevant intermediate time scales. For any initial fraction of mobile particles, the respective mean squared displacement (MSD) displays a plateau. Moreover, we demonstrate a short-time cubic time dependence of the MSD for immobile tracers when initially all particles are immobile.
KW - diffusion
KW - mobile-immobile model
KW - tau proteins
Y1 - 2022
U6 - https://doi.org/10.1098/rsif.2022.0233
SN - 1742-5689
SN - 1742-5662
VL - 19
IS - 192
PB - Royal Society
CY - London
ER -
TY - JOUR
A1 - Nemati, Somayyeh
A1 - Henkel, Carsten
A1 - Anders, Janet
T1 - Coupling function from bath density of states
JF - epl : a letters journal exploring the frontiers of physics
N2 - Modelling of an open quantum system requires knowledge of parameters that specify how it couples to its environment. However, beyond relaxation rates, realistic parameters for specific environments and materials are rarely known. Here we present a method of inferring the coupling between a generic system and its bosonic (e.g., phononic) environment from the experimentally measurable density of states (DOS). With it we confirm that the DOS of the well-known Debye model for three-dimensional solids is physically equivalent to choosing an Ohmic bath. We further match a real phonon DOS to a series of Lorentzian coupling functions, allowing us to determine coupling parameters for gold, yttrium iron garnet (YIG) and iron as examples. The results illustrate how to obtain material-specific dynamical properties, such as memory kernels. The proposed method opens the door to more accurate modelling of relaxation dynamics, for example for phonon-dominated spin damping in magnetic materials.
Y1 - 2022
U6 - https://doi.org/10.1209/0295-5075/ac7b42
SN - 0295-5075
SN - 1286-4854
VL - 139
IS - 3
PB - IOP Publ. Ltd.
CY - Bristol
ER -
TY - JOUR
A1 - Poppenhäger, Katja
T1 - Helium absorption in exoplanet atmospheres is connected to stellar coronal abundances
JF - Monthly notices of the Royal Astronomical Society
N2 - Transit observations in the helium triplet around 10 830 Angstrom are a successful tool to study exoplanetary atmospheres and their mass loss. Forming those lines requires ionization and recombination of helium in the exoplanetary atmosphere. This ionization is caused by stellar photons at extreme ultraviolet (EUV) wavelengths; however, no currently active telescopes can observe this part of the stellar spectrum. The relevant part of the stellar EUV spectrum consists of individual emission lines, many of them being formed by iron at coronal temperatures. The stellar iron abundance in the corona is often observed to be depleted for high-activity low-mass stars due to the first ionization potential (FIP) effect. I show that stars with high versus low coronal iron abundances follow different scaling laws that tie together their X-ray emission and the narrow-band EUV flux that causes helium ionization. I also show that the stellar iron to oxygen abundance ratio in the corona can be measured reasonably well from X-ray CCD spectra, yielding similar results to high-resolution X-ray observations. Taking coronal iron abundance into account, the currently observed large scatter in the relationship of EUV irradiation with exoplanetary helium transit depths can be reduced, improving the target selection criteria for exoplanet transmission spectroscopy. In particular, previously puzzling non-detections of helium for Neptunic exoplanets are now in line with expectations from the revised scaling laws.
KW - planets and satellites: atmospheres
KW - stars: abundances
KW - stars: coronae
KW - stars: late-type
KW - ultraviolet: stars
KW - X-rays: stars
Y1 - 2022
U6 - https://doi.org/10.1093/mnras/stac507
SN - 0035-8711
SN - 1365-2966
VL - 512
IS - 2
SP - 1751
EP - 1764
PB - Oxford Univ. Press
CY - Oxford
ER -
TY - JOUR
A1 - Mallonn, Matthias
A1 - Poppenhäger, Katja
A1 - Granzer, Thomas
A1 - Weber, Michael
A1 - Strassmeier, Klaus G.
T1 - Detection capability of ground-based meter-sized telescopes for shallow exoplanet transits
JF - Astronomy and astrophysics : an international weekly journal
N2 - Meter-sized ground-based telescopes are frequently used today for the follow-up of extrasolar planet candidates. While the transit signal of a Jupiter-sized object can typically be detected to a high level of confidence with small telescope apertures as well, the shallow transit dips of planets with the size of Neptune and smaller are more challenging to reveal. We employ new observational data to illustrate the photometric follow-up capabilities of meter-sized telescopes for shallow exoplanet transits. We describe in detail the capability of distinguishing the photometric signal of an exoplanet transit from an underlying trend in the light curve. The transit depths of the six targets we observed, Kepler-94b, Kepler-63b, K2-100b, K2-138b, K2-138c, and K2-138e, range from 3.9 ppt down to 0.3 ppt. For five targets of this sample, we provide the first ground-based photometric follow-up. The timing of three targets is precisely known from previous observations, and the timing of the other three targets is uncertain and we aim to constrain it. We detect or rule out the transit features significantly in single observations for the targets that show transits of 1.3 ppt or deeper. The shallower transit depths of two targets of 0.6 and 0.8 ppt were detected tentatively in single light curves, and were detected significantly by repeated observations. Only for the target of the shallowest transit depth of 0.3 ppt were we unable to draw a significant conclusion despite combining five individual light curves. An injection-recovery test on our real data shows that we detect transits of 1.3 ppt depth significantly in single light curves if the transit is fully covered, including out-of-transit data toward both sides, in some cases down to 0.7 ppt depth. For Kepler-94b, Kepler-63b, and K2-100b, we were able to verify the ephemeris. In the case of K2-138c with a 0.6 ppt deep transit, we were able to refine it, and in the case of K2-138e, we ruled out the transit in the time interval of more than ±1.5 σ of its current literature ephemeris.
KW - methods: observational
KW - techniques: photometric
KW - planets and satellites: fundamental parameters
Y1 - 2022
U6 - https://doi.org/10.1051/0004-6361/202140599
SN - 0004-6361
SN - 1432-0746
VL - 657
PB - EDP Sciences
CY - Les Ulis
ER -
TY - JOUR
A1 - Fischer, Eric Wolfgang
A1 - Anders, Janet
A1 - Saalfrank, Peter
T1 - Cavity-altered thermal isomerization rates and dynamical resonant localization in vibro-polaritonic chemistry
JF - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr
N2 - It has been experimentally demonstrated that reaction rates for molecules embedded in microfluidic optical cavities are altered when compared to rates observed under "ordinary" reaction conditions. However, precise mechanisms of how strong coupling of an optical cavity mode to molecular vibrations affects the reactivity and how resonance behavior emerges are still under dispute. In the present work, we approach these mechanistic issues from the perspective of a thermal model reaction, the inversion of ammonia along the umbrella mode, in the presence of a single-cavity mode of varying frequency and coupling strength. A topological analysis of the related cavity Born-Oppenheimer potential energy surface in combination with quantum mechanical and transition state theory rate calculations reveals two quantum effects, leading to decelerated reaction rates in qualitative agreement with experiments: the stiffening of quantized modes perpendicular to the reaction path at the transition state, which reduces the number of thermally accessible reaction channels, and the broadening of the barrier region, which attenuates tunneling. We find these two effects to be very robust in a fluctuating environment, causing statistical variations of potential parameters, such as the barrier height. Furthermore, by solving the time-dependent Schrodinger equation in the vibrational strong coupling regime, we identify a resonance behavior, in qualitative agreement with experimental and earlier theoretical work. The latter manifests as reduced reaction probability when the cavity frequency omega(c) is tuned resonant to a molecular reactant frequency. We find this effect to be based on the dynamical localization of the vibro-polaritonic wavepacket in the reactant well.
Y1 - 2022
U6 - https://doi.org/10.1063/5.0076434
SN - 0021-9606
SN - 1089-7690
VL - 156
IS - 15
PB - American Institute of Physics
CY - Melville, NY
ER -
TY - JOUR
A1 - Wang, Feipeng
A1 - Zhang, Zheng
A1 - Yan, Yuyang
A1 - Shen, Zijia
A1 - Wang, Qiang
A1 - Gerhard, Reimund
T1 - Surface reconstruction on electro-spun PVA/PVP nanofibers by water evaporation
JF - Nanomaterials
N2 - Tailoring the secondary surface morphology of electro-spun nanofibers has been highly desired, as such delicate structures equip nanofibers with distinct functions. Here, we report a simple strategy to directly reconstruct the surface of polyvinyl alcohol/polyvinylpyrrolidone (PVA/PVP) nanofibers by water evaporation. The roughness and diameter of the nanofibers depend on the temperature during vacuum drying. Surface changes of the nanofibers from smooth to rough were observed at 55 degrees C, with a significant drop in nanofiber diameter. We attribute the formation of the secondary surface morphology to the intermolecular forces in the water vapor, including capillary and the compression forces, on the basis of the results from the Fourier-transform infrared (FTIR) and X-ray photoelectron (XPS) spectroscopy. The strategy is universally effective for various electro-spun polymer nanofibers, thus opening up avenues toward more detailed and sophisticated structure design and implementation for nanofibers.
KW - surface reconstruction
KW - intermolecular force
KW - surface-roughened
KW - nanofiber
Y1 - 2022
U6 - https://doi.org/10.3390/nano12050797
SN - 2079-4991
VL - 12
IS - 5
PB - MDPI
CY - Basel
ER -
TY - JOUR
A1 - Tönjes, Ralf
A1 - Kori, Hiroshi
T1 - Phase and frequency linear response theory for hyperbolic chaotic oscillators
JF - Chaos : an interdisciplinary journal of nonlinear science
N2 - We formulate a linear phase and frequency response theory for hyperbolic flows, which generalizes phase response theory for autonomous limit cycle oscillators to hyperbolic chaotic dynamics. The theory is based on a shadowing conjecture, stating the existence of a perturbed trajectory shadowing every unperturbed trajectory on the system attractor for any small enough perturbation of arbitrary duration and a corresponding unique time isomorphism, which we identify as phase such that phase shifts between the unperturbed trajectory and its perturbed shadow are well defined. The phase sensitivity function is the solution of an adjoint linear equation and can be used to estimate the average change of phase velocity to small time dependent or independent perturbations. These changes in frequency are experimentally accessible, giving a convenient way to define and measure phase response curves for chaotic oscillators. The shadowing trajectory and the phase can be constructed explicitly in the tangent space of an unperturbed trajectory using co-variant Lyapunov vectors. It can also be used to identify the limits of the regime of linear response.
Y1 - 2022
U6 - https://doi.org/10.1063/5.0064519
SN - 1054-1500
SN - 1089-7682
VL - 32
IS - 4
PB - AIP Publishing
CY - Melville
ER -
TY - JOUR
A1 - Wulff, Peter
A1 - Mientus, Lukas
A1 - Nowak, Anna
A1 - Borowski, Andreas
T1 - Utilizing a pretrained language model (BERT) to classify preservice physics teachers' written reflections
JF - International journal of artificial intelligence in education
N2 - Computer-based analysis of preservice teachers' written reflections could enable educational scholars to design personalized and scalable intervention measures to support reflective writing. Algorithms and technologies in the domain of research related to artificial intelligence have been found to be useful in many tasks related to reflective writing analytics such as classification of text segments. However, mostly shallow learning algorithms have been employed so far. This study explores to what extent deep learning approaches can improve classification performance for segments of written reflections. To do so, a pretrained language model (BERT) was utilized to classify segments of preservice physics teachers' written reflections according to elements in a reflection-supporting model. Since BERT has been found to advance performance in many tasks, it was hypothesized to enhance classification performance for written reflections as well. We also compared the performance of BERT with other deep learning architectures and examined conditions for best performance. We found that BERT outperformed the other deep learning architectures and previously reported performances with shallow learning algorithms for classification of segments of reflective writing. BERT starts to outperform the other models when trained on about 20 to 30% of the training data. Furthermore, attribution analyses for inputs yielded insights into important features for BERT's classification decisions. Our study indicates that pretrained language models such as BERT can boost performance for language-related tasks in educational contexts such as classification.
KW - Reflective writing
KW - NLP
KW - Deep learning
KW - Science education
Y1 - 2022
U6 - https://doi.org/10.1007/s40593-022-00290-6
SN - 1560-4292
SN - 1560-4306
IS - 33
SP - 439
EP - 466
PB - Springer
CY - New York
ER -
TY - JOUR
A1 - Zhao, Siqi Q.
A1 - Yan, Huirong
A1 - Liu, Terry Z.
A1 - Liu, Mingzhe
A1 - Wang, Huizi
T1 - Multispacecraft analysis of the properties of magnetohydrodynamic fluctuations in Sub-Alfvenic solar wind turbulence at 1 au
JF - The astrophysical journal : an international review of spectroscopy and astronomical physics
N2 - We present observations of three-dimensional magnetic power spectra in wavevector space to investigate the anisotropy and scalings of sub-Alfvenic solar wind turbulence at magnetohydrodynamic (MHD) scale using the Magnetospheric Multiscale spacecraft. The magnetic power distributions are organized in a new coordinate determined by wavevectors ((kappa) over cap) and background magnetic field ((b) over cap (0)) in Fourier space. This study utilizes two approaches to determine wavevectors: the singular value decomposition method and multispacecraft timing analysis. The combination of the two methods allows an examination of the properties of magnetic field fluctuations in terms of mode compositions without any spatiotemporal hypothesis. Observations show that fluctuations (delta B-perpendicular to 1) in the direction perpendicular to (kappa) over cap and (b) over cap (0) prominently cascade perpendicular to (b) over cap (0), and such anisotropy increases with wavenumbers. The reduced power spectra of 6.8 11 follow Goldreich-Sridhar scalings: (P) over cap (k(perpendicular to)) proportional to k(perpendicular to)(-5/3) and (P) over cap (k(parallel to)) proportional to k(parallel to)(-2). In contrast, fluctuations within the (k) over cap(b) over cap (0) plane show isotropic behaviors: perpendicular power distributions are approximately the same as parallel distributions. The reduced power spectra of fluctuations within the (k) over cap(b) over cap (0) plane follow the scalings (P) over cap (k(perpendicular to)) proportional to k(perpendicular to)(-3/2) and (P) over cap (k(parallel to)) proportional to k(parallel to)(-3/2). Comparing frequency-wavevector spectra with theoretical dispersion relations of MHD modes, we find that delta B-perpendicular to 1 are probably associated with Alfven modes. On the other hand, magnetic field fluctuations within the (k) over cap(b) over cap (0) plane more likely originate from fast modes based on their isotropic behaviors. The observations of anisotropy and scalings of different magnetic field components are consistent with the predictions of current compressible MHD theory. Moreover, for the Alfvenic component, the ratio of cascading time to the wave period is found to be a factor of a few, consistent with critical balance in the strong turbulence regime. These results are valuable for further studies of energy compositions of plasma turbulence and their effects on energetic particle transport.
Y1 - 2022
U6 - https://doi.org/10.3847/1538-4357/ac822e
SN - 0004-637X
SN - 1538-4357
VL - 937
IS - 2
PB - IOP Publ. Ltd.
CY - Bristol
ER -
TY - JOUR
A1 - Kliem, Bernhard
A1 - Seehafer, Norbert
T1 - Helicity shedding by flux rope ejection
JF - Astronomy and astrophysics : an international weekly journal
N2 - We quantitatively address the conjecture that magnetic helicity must be shed from the Sun by eruptions launching coronal mass ejections in order to limit its accumulation in each hemisphere. By varying the ratio of guide and strapping field and the flux rope twist in a parametric simulation study of flux rope ejection from approximately marginally stable force-free equilibria, different ratios of self- and mutual helicity are set and the onset of the torus or helical kink instability is obtained. The helicity shed is found to vary over a broad range from a minor to a major part of the initial helicity, with self helicity being largely or completely shed and mutual helicity, which makes up the larger part of the initial helicity, being shed only partly. Torus-unstable configurations with subcritical twist and without a guide field shed up to about two-thirds of the initial helicity, while a highly twisted, kink-unstable configuration sheds only about one-quarter. The parametric study also yields stable force-free flux rope equilibria up to a total flux-normalized helicity of 0.25, with a ratio of self- to total helicity of 0.32 and a ratio of flux rope to external poloidal flux of 0.94. These results numerically demonstrate the conjecture of helicity shedding by coronal mass ejections and provide a first account of its parametric dependence. Both self- and mutual helicity are shed significantly; this reduces the total initial helicity by a fraction of ∼0.4--0.65 for typical source region parameters.
KW - instabilities
KW - magnetic fields
KW - magnetohydrodynamics (MHD)
KW - Sun
KW - corona
KW - coronal mass ejections (CMEs)
KW - flares
Y1 - 2022
U6 - https://doi.org/10.1051/0004-6361/202142422
SN - 0004-6361
SN - 1432-0746
VL - 659
PB - EDP Sciences
CY - Les Ulis
ER -
TY - JOUR
A1 - Foster, Mary Grace
A1 - Poppenhäger, Katja
A1 - Ilić Petković, Nikoleta
A1 - Schwope, Axel
T1 - Exoplanet X-ray irradiation and evaporation rates with eROSITA
JF - Astronomy and astrophysics : an international weekly journal
N2 - High-energy irradiation is a driver for atmospheric evaporation and mass loss in exoplanets. This work is based on data from eROSITA, the soft X-ray instrument on board the Spectrum Roentgen Gamma mission, as well as on archival data from other missions. We aim to characterise the high-energy environment of known exoplanets and estimate their mass-loss rates. We use X-ray source catalogues from eROSITA, XMM-Newton, Chandra, and ROSAT to derive X-ray luminosities of exoplanet host stars in the 0.2–2 keV energy band with an underlying coronal, that is, optically thin thermal spectrum. We present a catalogue of stellar X-ray and EUV luminosities, exoplanetary X-ray and EUV irradiation fluxes, and estimated mass-loss rates for a total of 287 exoplanets, 96 of which are characterised for the first time based on new eROSITA detections. We identify 14 first-time X-ray detections of transiting exoplanets that are subject to irradiation levels known to cause observable evaporation signatures in other exoplanets. This makes them suitable targets for follow-up observations.
KW - stars: coronae
KW - stars: activity
KW - planet-star interactions
KW - planets and
KW - satellites: atmospheres
KW - X-rays: stars
Y1 - 2022
U6 - https://doi.org/10.1051/0004-6361/202141097
SN - 0004-6361
SN - 1432-0746
VL - 661
PB - EDP Sciences
CY - Les Ulis
ER -
TY - JOUR
A1 - Tockhorn, Philipp
A1 - Sutter, Johannes
A1 - Cruz Bournazou, Alexandros
A1 - Wagner, Philipp
A1 - Jäger, Klaus
A1 - Yoo, Danbi
A1 - Lang, Felix
A1 - Grischek, Max
A1 - Li, Bor
A1 - Li, Jinzhao
A1 - Shargaieva, Oleksandra
A1 - Unger, Eva
A1 - Al-Ashouri, Amran
A1 - Köhnen, Eike
A1 - Stolterfoht, Martin
A1 - Neher, Dieter
A1 - Schlatmann, Rutger
A1 - Rech, Bernd
A1 - Stannowski, Bernd
A1 - Albrecht, Steve
A1 - Becker, Christiane
T1 - Nano-optical designs for high-efficiency monolithic perovskite-silicon tandem solar cells
JF - Nature nanotechnology
N2 - Designing gentle sinusoidal nanotextures enables the realization of high-efficiency perovskite-silicon solar cells
Perovskite-silicon tandem solar cells offer the possibility of overcoming the power conversion efficiency limit of conventional silicon solar cells. Various textured tandem devices have been presented aiming at improved optical performance, but optimizing film growth on surface-textured wafers remains challenging. Here we present perovskite-silicon tandem solar cells with periodic nanotextures that offer various advantages without compromising the material quality of solution-processed perovskite layers. We show a reduction in reflection losses in comparison to planar tandems, with the new devices being less sensitive to deviations from optimum layer thicknesses. The nanotextures also enable a greatly increased fabrication yield from 50% to 95%. Moreover, the open-circuit voltage is improved by 15 mV due to the enhanced optoelectronic properties of the perovskite top cell. Our optically advanced rear reflector with a dielectric buffer layer results in reduced parasitic absorption at near-infrared wavelengths. As a result, we demonstrate a certified power conversion efficiency of 29.80%.
Y1 - 2022
U6 - https://doi.org/10.1038/s41565-022-01228-8
SN - 1748-3387
SN - 1748-3395
VL - 17
IS - 11
SP - 1214
EP - 1221
PB - Nature Publishing Group
CY - London [u.a.]
ER -
TY - JOUR
A1 - Walker, Simon N.
A1 - Boynton, Richard J.
A1 - Shprits, Yuri
A1 - Balikhin, Michael A.
A1 - Drozdov, Alexander
T1 - Forecast of the energetic electron environment of the radiation belts
JF - Space Weather: The International Journal of Research and Applications
N2 - Different modeling methodologies possess different strengths and weakness. For instance, data based models may provide superior accuracy but have a limited spatial coverage while physics based models may provide lower accuracy but provide greater spatial coverage. This study investigates the coupling of a data based model of the electron fluxes at geostationary orbit (GEO) with a numerical model of the radiation belt region to improve the resulting forecasts/pastcasts of electron fluxes over the whole radiation belt region. In particular, two coupling methods are investigated. The first assumes an average value for L* for GEO, namely LGEO* L-GEO* = 6.2. The second uses a value of L* that varies with geomagnetic activity, quantified using the Kp index. As the terrestrial magnetic field responds to variations in geomagnetic activity, the value of L* will vary for a specific location. In this coupling method, the value of L* is calculated using the Kp driven Tsyganenko 89c magnetic field model for field line tracing. It is shown that this addition can result in changes in the initialization of the parameters at the Versatile Electron Radiation Belt model outer boundary. Model outputs are compared to Van Allen Probes MagEIS measurements of the electron fluxes in the inner magnetosphere for the March 2015 geomagnetic storm. It is found that the fixed LGEO* L-GEO* coupling method produces a more realistic forecast.
KW - radiation belt forecasts
KW - data based NARMAX modeling
KW - verb simulations;
KW - geostationary orbit
KW - electron flux forecasts
Y1 - 2022
U6 - https://doi.org/10.1029/2022SW003124
SN - 1542-7390
VL - 20
IS - 12
PB - American Geophysical Union
CY - Washington
ER -
TY - JOUR
A1 - Lewenstein, Maciej
A1 - Cirauqui, David
A1 - Angel Garcia-March, Miguel
A1 - Corominas, Guillem Guigo
A1 - Grzybowski, Przemyslaw
A1 - Saavedra, Jose R. M.
A1 - Wilkens, Martin
A1 - Wehr, Jan
T1 - Haake-Lewenstein-Wilkens approach to spin-glasses revisited
JF - Journal of physics : A, Mathematical and theoretical
N2 - 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
KW - Edwards-Anderson order parameter
KW - Haake-Lewenstein-Wilkens approach
KW - spin glass
KW - Saddle Point
KW - Steppest Descend method
Y1 - 2022
U6 - https://doi.org/10.1088/1751-8121/ac9d10
SN - 1751-8113
SN - 1751-8121
VL - 55
IS - 45
PB - IOP Publ. Ltd.
CY - Bristol
ER -
TY - JOUR
A1 - Raman Venkatesan, Thulasinath
A1 - Wübbenhorst, Michael
A1 - Gerhard, Reimund
T1 - Structure-property relationships in three-phase relaxor-ferroelectric terpolymers
JF - Ferroelectrics
N2 - Poly(vinylidenefluoride-trifluoroethylene)-based (P(VDF-TrFE)-based) terpolymers represent a new class of electroactive polymer materials that are relaxor-ferroelectric (RF) polymers and that offer unique and attractive property combinations in comparison with conventional ferroelectric polymers. The RF state is achieved by introducing a fluorine-containing termonomer as a "defect" into the ferroelectric P(VDF-TrFE) copolymer, which reduces the interaction between the VDF/TrFE dipoles. The resulting terpolymer exhibits a low Curie transition temperature and small remanent and coercive fields yielding a slim hysteresis loop that is typical for RF materials. Though the macroscopic behavior is similar to RF ceramics, the mechanisms of relaxor ferroelectricity in semi-crystalline polymers are different and not fully understood yet. Structure-property relationships play an important role in RF terpolymers, as they govern the final RF properties. Hence, a review of important characteristics, previous studies and relevant developments of P(VDF-TrFE)-based terfluoropolymers with either chlorofluoroethylene (CFE) or chlorotrifluoroethylene (CTFE) as the termonomer is deemed useful. The role of the termonomer and of its composition, as well as the effects of the processing conditions on the semi-crystalline structure which in turn affects the final RF properties are discussed in detail. In addition, the presence of noteworthy transition(s) in the mid-temperature range and the influence of preparation conditions on those transitions are reviewed. A better understanding of the fundamental aspects affecting the semi-crystalline structures will help to elucidate the nature of RF activity in VDF-based terpolymers and also help to further improve their applications-relevant electroactive properties.
KW - Relaxor-ferroelectric (RF) fluoropolymers
KW - structure-property
KW - relationships
KW - Curie transition
KW - dielectric hysteresis
KW - thermal
KW - processing
KW - mid-temperature transition(s)
Y1 - 2022
U6 - https://doi.org/10.1080/00150193.2021.2014260
SN - 0015-0193
SN - 1563-5112
VL - 586
IS - 1
SP - 60
EP - 81
PB - Routledge, Taylor & Francis Group
CY - Abingdon
ER -
TY - JOUR
A1 - Smirnov, Artem
A1 - Shprits, Yuri
A1 - Allison, Hayley
A1 - Aseev, Nikita
A1 - Drozdov, Alexander
A1 - Kollmann, Peter
A1 - Wang, Dedong
A1 - Saikin, Anthony
T1 - An empirical model of the equatorial electron pitch angle distributions in earth's outer radiation belt
JF - Space Weather: the International Journal of Research and Applications
N2 - In this study, we present an empirical model of the equatorial electron pitch angle distributions (PADs) in the outer radiation belt based on the full data set collected by the Magnetic Electron Ion Spectrometer (MagEIS) instrument onboard the Van Allen Probes in 2012-2019. The PADs are fitted with a combination of the first, third and fifth sine harmonics. The resulting equation resolves all PAD types found in the outer radiation belt (pancake, flat-top, butterfly and cap PADs) and can be analytically integrated to derive omnidirectional flux. We introduce a two-step modeling procedure that for the first time ensures a continuous dependence on L, magnetic local time and activity, parametrized by the solar wind dynamic pressure. We propose two methods to reconstruct equatorial electron flux using the model. The first approach requires two uni-directional flux observations and is applicable to low-PA data. The second method can be used to reconstruct the full equatorial PADs from a single uni- or omnidirectional measurement at off-equatorial latitudes. The model can be used for converting the long-term data sets of electron fluxes to phase space density in terms of adiabatic invariants, for physics-based modeling in the form of boundary conditions, and for data assimilation purposes.
KW - pitch angle
KW - radiation belt
KW - model
KW - magnetosphere
KW - van allen probes;
KW - electrons
Y1 - 2022
U6 - https://doi.org/10.1029/2022SW003053
SN - 1542-7390
VL - 20
IS - 9
PB - American Geophysical Union
CY - Washington, DC
ER -
TY - JOUR
A1 - Deb, Marwan
A1 - Popova, Elena
A1 - Jaffrès, Henri-Yves
A1 - Keller, Niels
A1 - Bargheer, Matias
T1 - Polarization-dependent subpicosecond demagnetization in iron garnets
JF - Physical review : B, covering condensed matter and materials physics
N2 - Controlling the magnetization dynamics at the fastest speed is a major issue of fundamental condensed matter physics and its applications for data storage and processing technologies. It requires a deep understanding of the interactions between the degrees of freedom in solids, such as spin, electron, and lattice as well as their responses to external stimuli. In this paper, we systematically investigate the fluence dependence of ultrafast magnetization dynamics induced by below-bandgap ultrashort laser pulses in the ferrimagnetic insulators BixY3-xFe5O12 with 1 xBi 3. We demonstrate subpicosecond demagnetization dynamics in this material followed by a very slow remagnetization process. We prove that this demagnetization results from an ultrafast heating of iron garnets by two-photon absorption (TPA), suggesting a phonon-magnon thermalization time of 0.6 ps. We explain the slow remagnetization timescale by the low phonon heat conductivity in garnets. Additionally, we show that the amplitudes of the demagnetization, optical change, and lattice strain can be manipulated by changing the ellipticity of the pump pulses. We explain this phenomenon considering the TPA circular dichroism. These findings open exciting prospects for ultrafast manipulation of spin, charge, and lattice dynamics in magnetic insulators by ultrafast nonlinear optics.
Y1 - 2022
U6 - https://doi.org/10.1103/PhysRevB.106.184416
SN - 2469-9950
SN - 2469-9969
VL - 106
IS - 18
PB - American Institute of Physics, American Physical Society
CY - Woodbury, NY
ER -
TY - JOUR
A1 - Pietzsch, Annette
A1 - Niskanen, Johannes
A1 - Vaz da Cruz, Vinicius
A1 - Büchner, Robby
A1 - Eckert, Sebastian
A1 - Fondell, Mattis
A1 - Jay, Raphael Martin
A1 - Lu, Xingye
A1 - McNally, Daniel
A1 - Schmitt, Thorsten
A1 - Föhlisch, Alexander
T1 - Cuts through the manifold of molecular H2O potential energy surfaces in liquid water at ambient conditions
JF - Proceedings of the National Academy of Sciences of the United States of America
N2 - The fluctuating hydrogen bridge bonded network of liquid water at ambient conditions entails a varied ensemble of the underlying constituting H2O molecular moieties. This is mirrored in a manifold of the H2O molecular potentials. Subnatural line width resonant inelastic X-ray scattering allowed us to quantify the manifold of molecular potential energy surfaces along the H2O symmetric normal mode and the local asymmetric O-H bond coordinate up to 1 and 1.5 angstrom, respectively. The comparison of the single H2O molecular potentials and spectroscopic signatures with the ambient conditions liquid phase H2O molecular potentials is done on various levels. In the gas phase, first principles, Morse potentials, and stepwise harmonic potential reconstruction have been employed and benchmarked. In the liquid phase the determination of the potential energy manifold along the local asymmetric O-H bond coordinate from resonant inelastic X-ray scattering via the bound state oxygen ls to 4a(1) resonance is treated within these frameworks. The potential energy surface manifold along the symmetric stretch from resonant inelastic X-ray scattering via the oxygen 1 s to 2b(2) resonance is based on stepwise harmonic reconstruction. We find in liquid water at ambient conditions H2O molecular potentials ranging from the weak interaction limit to strongly distorted potentials which are put into perspective to established parameters, i.e., intermolecular O-H, H-H, and O-O correlation lengths from neutron scattering.
KW - water
KW - potential ene rgy surface
KW - RIXS
Y1 - 2022
U6 - https://doi.org/10.1073/pnas.2118101119
SN - 1091-6490
VL - 119
IS - 28
PB - National Acad. of Sciences
CY - Washington, DC
ER -
TY - JOUR
A1 - Deb, Marwan
A1 - Popova, Elena
A1 - Jaffrès, Henri-Yves
A1 - Keller, Niels
A1 - Bargheer, Matias
T1 - Controlling high-frequency spin-wave dynamics using double-pulse laser excitation
JF - Physical review applied
N2 - Manipulating spin waves is highly required for the development of innovative data transport and processing technologies. Recently, the possibility of triggering high-frequency standing spin waves in magnetic insulators using femtosecond laser pulses was discovered, raising the question about how one can manipulate their dynamics. Here we explore this question by investigating the ultrafast magnetiza-tion and spin-wave dynamics induced by double-pulse laser excitation. We demonstrate a suppression or enhancement of the amplitudes of the standing spin waves by precisely tuning the time delay between the two pulses. The results can be understood as the constructive or destructive interference of the spin waves induced by the first and second laser pulses. Our findings open exciting perspectives towards generating single-mode standing spin waves that combine high frequency with large amplitude and low magnetic damping.
Y1 - 2022
U6 - https://doi.org/10.1103/PhysRevApplied.18.044001
SN - 2331-7019
VL - 18
IS - 4
PB - American Physical Society
CY - College Park
ER -
TY - JOUR
A1 - Poelking, Carl
A1 - Benduhn, Johannes
A1 - Spoltore, Donato
A1 - Schwarze, Martin
A1 - Roland, Steffen
A1 - Piersimoni, Fortunato
A1 - Neher, Dieter
A1 - Leo, Karl
A1 - Vandewal, Koen
A1 - Andrienko, Denis
T1 - Open-circuit voltage of organic solar cells
BT - interfacial roughness makes the difference
JF - Communications physics
N2 - Organic photovoltaics (PV) is an energy-harvesting technology that offers many advantages, such as flexibility, low weight and cost, as well as environmentally benign materials and manufacturing techniques. Despite growth of power conversion efficiencies to around 19 % in the last years, organic PVs still lag behind inorganic PV technologies, mainly due to high losses in open-circuit voltage. Understanding and improving open circuit voltage in organic solar cells is challenging, as it is controlled by the properties of a donor-acceptor interface where the optical excitations are separated into charge carriers. Here, we provide an electrostatic model of a rough donor-acceptor interface and test it experimentally on small molecule PV materials systems. The model provides concise relationships between the open-circuit voltage, photovoltaic gap, charge-transfer state energy, and interfacial morphology. In particular, we show that the electrostatic bias generated across the interface reduces the photovoltaic gap. This negative influence on open-circuit voltage can, however, be circumvented by adjusting the morphology of the donor-acceptor interface.
Organic solar cells, despite their high power conversion efficiencies, suffer from open circuit voltage losses making them less appealing in terms of applications. Here, the authors, supported with experimental data on small molecule photovoltaic cells, relate open circuit voltage to photovoltaic gap, charge-transfer state energy, and donor-acceptor interfacial morphology.
Y1 - 2022
U6 - https://doi.org/10.1038/s42005-022-01084-x
SN - 2399-3650
VL - 5
IS - 1
PB - Nature portfolio
CY - Berlin
ER -
TY - JOUR
A1 - Kölsch, Maximilian
A1 - Dietrich, Tim
A1 - Ujevic, Maximiliano
A1 - Brügmann, Bernd
T1 - Investigating the mass-ratio dependence of the prompt-collapse threshold with numerical-relativity simulations
JF - Physical review : D, Particles, fields, gravitation, and cosmology
N2 - The next observing runs of advanced gravitational-wave detectors will lead to a variety of binary neutron star detections and numerous possibilities for multimessenger observations of binary neutron star systems. In this context a clear understanding of the merger process and the possibility of prompt black hole formation after merger is important, as the amount of ejected material strongly depends on the merger dynamics. These dynamics are primarily affected by the total mass of the binary, however, the mass ratio also influences the postmerger evolution. To determine the effect of the mass ratio, we investigate the parameter space around the prompt-collapse threshold with a new set of fully relativistic simulations. The simulations cover three equations of state and seven mass ratios in the range of 1.0 <= q <= 1.75, with five to seven simulations of binary systems of different total mass in each case. The threshold mass is determined through an empirical relation based on the collapse time, which allows us to investigate effects of the mass ratio on the threshold mass and also on the properties of the remnant system. Furthermore, we model effects of mass ratio and equation of state on tidal parameters of threshold configurations.
Y1 - 2022
U6 - https://doi.org/10.1103/PhysRevD.106.044026
SN - 2470-0010
SN - 2470-0029
VL - 106
IS - 4
PB - American Physical Society
CY - College Park
ER -
TY - JOUR
A1 - Schaffenroth, Veronika
A1 - Pelisoli, Ingrid
A1 - Barlow, Brad N.
A1 - Geier, Stephan
A1 - Kupfer, Thomas
T1 - Hot subdwarfs in close binaries observed from space I.
BT - orbital, atmospheric, and absolute parameters and the nature of
their companions
JF - Astronomy and astrophysics : an international weekly journal
N2 - Context:
About a third of the hot subdwarfs of spectral type B (sdBs), which are mostly core-helium-burning objects on the extreme horizontal branch, are found in close binaries with cool, low-mass stellar, substellar, or white dwarf companions. They can show light variations due to di fferent phenomena.
Aims:
Many hot subdwarfs now have space-based light curves with a high signal-to-noise ratio available. We used light curves from the Transiting Exoplanet Survey Satellite and the K2 space mission to look for more sdB binaries. Their light curves can be used to study the hot subdwarf primaries and their companions, and obtained orbital, atmospheric, and absolute parameters for those systems, when combined with other analysis methods.
Methods:
By classifying the light variations and combining these with the fit of the spectral energy distribution, the distance derived by the parallaxes obtained by Gaia, and the atmospheric parameters, mainly from the literature, we could derive the nature of the primaries and secondaries in 122 (75%) of the known sdB binaries and 82 newly found reflection e ffect systems. We derived absolute masses, radii, and luminosities for a total of 39 hot subdwarfs with cool, low-mass companions, as well 29 known and newly found sdBs with white dwarf companions.
Results:
The mass distribution of hot subdwarfs with cool, low-mass stellar and substellar companions, di ffers from those with white dwarf companions, implying they come from di fferent populations. By comparing the period and minimum companion mass distributions, we find that the reflection e ffect systems all have M dwarf or brown dwarf companions, and that there seem to be several di fferent populations of hot subdwarfs with white dwarf binaries - one with white dwarf minimum masses around 0.4 M-circle dot, one with longer periods and minimum companion masses up to 0.6 M-circle dot, and at the shortest period, another with white dwarf minimum masses around 0.8 M-circle dot. We also derive the first orbital period distribution for hot subdwarfs with cool, low-mass stellar or substellar systems selected from light variations instead of radial velocity variations. It shows a narrower period distribution, from 1.5 h to 35 h, compared to the distribution of hot subdwarfs with white dwarfs, which ranges from 1 h to 30 days. These period distributions can be used to constrain the previous common-envelope phase.
KW - binaries: close
KW - subdwarfs
KW - white dwarfs
KW - stars: late-type
KW - stars:
KW - horizontal-branch
KW - stars: fundamental parameters
Y1 - 2022
U6 - https://doi.org/10.1051/0004-6361/202244214
SN - 0004-6361
SN - 1432-0746
VL - 666
PB - EDP Sciences
CY - Les Ulis
ER -
TY - JOUR
A1 - Adolfs, Marjolijn
A1 - Hoque, Mohammed Mainul
A1 - Shprits, Yuri
T1 - Storm-time relative total electron content modelling using machine learning techniques
JF - Remote sensing
N2 - Accurately predicting total electron content (TEC) during geomagnetic storms is still a challenging task for ionospheric models. In this work, a neural-network (NN)-based model is proposed which predicts relative TEC with respect to the preceding 27-day median TEC, during storm time for the European region (with longitudes 30 degrees W-50 degrees E and latitudes 32.5 degrees N-70 degrees N). The 27-day median TEC (referred to as median TEC), latitude, longitude, universal time, storm time, solar radio flux index F10.7, global storm index SYM-H and geomagnetic activity index Hp30 are used as inputs and the output of the network is the relative TEC. The relative TEC can be converted to the actual TEC knowing the median TEC. The median TEC is calculated at each grid point over the European region considering data from the last 27 days before the storm using global ionosphere maps (GIMs) from international GNSS service (IGS) sources. A storm event is defined when the storm time disturbance index Dst drops below 50 nanotesla. The model was trained with storm-time relative TEC data from the time period of 1998 until 2019 (2015 is excluded) and contains 365 storms. Unseen storm data from 33 storm events during 2015 and 2020 were used to test the model. The UQRG GIMs were used because of their high temporal resolution (15 min) compared to other products from different analysis centers. The NN-based model predictions show the seasonal behavior of the storms including positive and negative storm phases during winter and summer, respectively, and show a mixture of both phases during equinoxes. The model's performance was also compared with the Neustrelitz TEC model (NTCM) and the NN-based quiet-time TEC model, both developed at the German Aerospace Agency (DLR). The storm model has a root mean squared error (RMSE) of 3.38 TEC units (TECU), which is an improvement by 1.87 TECU compared to the NTCM, where an RMSE of 5.25 TECU was found. This improvement corresponds to a performance increase by 35.6%. The storm-time model outperforms the quiet-time model by 1.34 TECU, which corresponds to a performance increase by 28.4% from 4.72 to 3.38 TECU. The quiet-time model was trained with Carrington averaged TEC and, therefore, is ideal to be used as an input instead of the GIM derived 27-day median. We found an improvement by 0.8 TECU which corresponds to a performance increase by 17% from 4.72 to 3.92 TECU for the storm-time model using the quiet-time-model predicted TEC as an input compared to solely using the quiet-time model.
KW - ionosphere
KW - relative total electron content
KW - geomagnetic storms
KW - neural
KW - networks
KW - NTCM
KW - European storm-time model
Y1 - 2022
U6 - https://doi.org/10.3390/rs14236155
SN - 2072-4292
VL - 14
IS - 23
PB - MDPI
CY - Basel
ER -
TY - JOUR
A1 - Moldenhawer, Ted
A1 - Moreno, Eduardo
A1 - Schindler, Daniel
A1 - Flemming, Sven
A1 - Holschneider, Matthias
A1 - Huisinga, Wilhelm
A1 - Alonso, Sergio
A1 - Beta, Carsten
T1 - Spontaneous transitions between amoeboid and keratocyte-like modes of migration
JF - Frontiers in Cell and Developmental Biology
N2 - The motility of adherent eukaryotic cells is driven by the dynamics of the actin cytoskeleton. Despite the common force-generating actin machinery, different cell types often show diverse modes of locomotion that differ in their shape dynamics, speed, and persistence of motion. Recently, experiments in Dictyostelium discoideum have revealed that different motility modes can be induced in this model organism, depending on genetic modifications, developmental conditions, and synthetic changes of intracellular signaling. Here, we report experimental evidence that in a mutated D. discoideum cell line with increased Ras activity, switches between two distinct migratory modes, the amoeboid and fan-shaped type of locomotion, can even spontaneously occur within the same cell. We observed and characterized repeated and reversible switchings between the two modes of locomotion, suggesting that they are distinct behavioral traits that coexist within the same cell. We adapted an established phenomenological motility model that combines a reaction-diffusion system for the intracellular dynamics with a dynamic phase field to account for our experimental findings.
KW - cell migration
KW - amoeboid motility
KW - keratocytle-like motility
KW - modes of
KW - migration
KW - D. discoideum
KW - actin dynamics
Y1 - 2022
U6 - https://doi.org/10.3389/fcell.2022.898351
SN - 2296-634X
VL - 10
PB - Frontiers Media
CY - Lausanne
ER -
TY - JOUR
A1 - Moreno, Eduardo
A1 - Großmann, Robert
A1 - Beta, Carsten
A1 - Alonso, Sergio
T1 - From single to collective motion of social amoebae
BT - a computational study of interacting cells
JF - Frontiers in physics
N2 - 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.
KW - cell motility
KW - cell polarity
KW - reaction-diffusion models
KW - cell-cell
KW - interactions
KW - phase field model
KW - collective motion
KW - active matter
Y1 - 2022
U6 - https://doi.org/10.3389/fphy.2021.750187
SN - 2296-424X
VL - 9
PB - Frontiers Media
CY - Lausanne
ER -
TY - JOUR
A1 - Kranjc Horvat, Anja
A1 - Wiener, Jeff
A1 - Schmeling, Sascha
A1 - Borowski, Andreas
T1 - Learning goals of professional development programs at science research institutions
BT - a Delphi study with different stakeholder groups
JF - Journal of science teacher education : the official journal of the Association for the Education of Teachers in Science
N2 - Effective professional development programs (PDPs) rely on well-defined goals. However, recent studies on PDPs have not explored the goals from a multi-stakeholder perspective. This study identifies the most important learning goals of PDPs at science research institutions as perceived by four groups of stakeholders, namely teachers, education researchers, government representatives, and research scientists. Altogether, over 100 stakeholders from 42 countries involved in PDPs at science research institutions in Europe and North America participated in a three-round Delphi study. In the first round, the stakeholders provided their opinions on what they thought the learning goals of PDPs should be through an open-ended questionnaire. In the second and third rounds, the stakeholders assessed the importance of the learning goals that emerged from the first round by rating and ranking them, respectively. The outcome of the study is a hierarchical list of the ten most important learning goals of PDPs at particle physics laboratories. The stakeholders identified enhancing teachers' knowledge of scientific concepts and models and enhancing their knowledge of the curricula as the most important learning goals. Furthermore, the results show strong agreement between all the stakeholder groups regarding the defined learning goals. Indeed, all groups ranked the learning goals by their perceived importance almost identically. These outcomes could help policymakers establish more specific policies for PDPs. Additionally, they provide PDP practitioners at science research institutions with a solid base for future research and planning endeavors.
KW - Teacher professional development
KW - Delphi study
KW - multi-stakeholder
KW - analysis
KW - pedagogical content knowledge
Y1 - 2021
U6 - https://doi.org/10.1080/1046560X.2021.1905330
SN - 1046-560X
SN - 1573-1847
VL - 33
IS - 1
SP - 32
EP - 54
PB - Routledge, Taylor & Francis Group
CY - Abingdon
ER -
TY - JOUR
A1 - Vinod, Deepak
A1 - Cherstvy, Andrey G.
A1 - Metzler, Ralf
A1 - Sokolov, Igor M.
T1 - Time-averaging and nonergodicity of reset geometric Brownian motion with drift
JF - Physical review : E, Statistical, nonlinear and soft matter physics
N2 - How do near-bankruptcy events in the past affect the dynamics of stock-market prices in the future? Specifically, what are the long-time properties of a time-local exponential growth of stock-market prices under the influence of stochastically occurring economic crashes? Here, we derive the ensemble- and time-averaged properties of the respective "economic" or geometric Brownian motion (GBM) with a nonzero drift exposed to a Poissonian constant-rate price-restarting process of "resetting." We examine-based both on thorough analytical calculations and on findings from systematic stochastic computer simulations-the general situation of reset GBM with a nonzero [positive] drift and for all special cases emerging for varying parameters of drift, volatility, and reset rate in the model. We derive and summarize all short- and long-time dependencies for the mean-squared displacement (MSD), the variance, and the mean time-averaged MSD (TAMSD) of the process of Poisson-reset GBM under the conditions of both rare and frequent resetting. We consider three main regions of model parameters and categorize the crossovers between different functional behaviors of the statistical quantifiers of this process. The analytical relations are fully supported by the results of computer simulations. In particular, we obtain that Poisson-reset GBM is a nonergodic stochastic process, with generally MSD(Delta) not equal TAMSD(Delta) and Variance(Delta) not equal TAMSD(Delta) at short lag times Delta and for long trajectory lengths T. We investigate the behavior of the ergodicity-breaking parameter in each of the three regions of parameters and examine its dependence on the rate of reset at Delta/T << 1. Applications of these theoretical results to the analysis of prices of reset-containing options are pertinent.
Y1 - 2022
U6 - https://doi.org/10.1103/PhysRevE.106.034137
SN - 2470-0045
SN - 2470-0053
VL - 106
IS - 3
PB - American Physical Society
CY - College Park
ER -
TY - JOUR
A1 - Seckler, Henrik
A1 - Metzler, Ralf
T1 - Bayesian deep learning for error estimation in the analysis of anomalous diffusion
JF - Nature Communications
N2 - 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.
Y1 - 2022
U6 - https://doi.org/10.1038/s41467-022-34305-6
SN - 2041-1723
VL - 13
IS - 1
PB - Nature portfolio
CY - Berlin
ER -
TY - THES
A1 - Kotz, Maximilian
T1 - The economic costs of climate change
BT - accounting for the changing variability and extremes of temperature and precipitation
Y1 - 2022
ER -
TY - JOUR
A1 - Anders, Janet
A1 - Sait, Connor R. J.
A1 - Horsley, Simon A. R.
T1 - Quantum Brownian motion for magnets
JF - New journal of physics : the open-access journal for physics
N2 - 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.
KW - open quantum systems
KW - coloured and quantum noise
KW - memory effects
KW - spin
KW - dynamics
KW - LLG equation
KW - magnetisation
KW - quantum thermodynamics
Y1 - 2022
U6 - https://doi.org/10.1088/1367-2630/ac4ef2
SN - 1367-2630
VL - 24
IS - 3
PB - IOP Publ. Ltd.
CY - Bristol
ER -
TY - THES
A1 - Schlemm, Tanja
T1 - The marine ice cliff instability of the Antarctic ice sheet
T1 - Die marine Eisklippeninstabilität des antarktischen Eisschildes
BT - a theory of mélange-buttressed cliff calving and its application in the Parallel Ice Sheet Model
BT - eine Theorie des Mélange-gebremsten Klippenkalbens und ihre Anwendung im Parallel Ice Sheet Model
N2 - The Antarctic ice sheet is the largest freshwater reservoir worldwide. If it were to melt completely, global sea levels would rise by about 58 m. Calculation of projections of the Antarctic contribution to sea level rise under global warming conditions is an ongoing effort which
yields large ranges in predictions. Among the reasons for this are uncertainties related to the physics of ice sheet modeling. These
uncertainties include two processes that could lead to runaway ice retreat: the Marine Ice Sheet Instability (MISI), which causes rapid grounding line retreat on retrograde bedrock, and the Marine Ice Cliff Instability (MICI), in which tall ice cliffs become unstable and calve off, exposing even taller ice cliffs.
In my thesis, I investigated both marine instabilities (MISI and MICI) using the Parallel Ice Sheet Model (PISM), with a focus on MICI.
N2 - Der antarktische Eisschild ist das größte Süßwasserreservoir der Welt. Würde er vollständig schmelzen, würde der globale Meeresspiegel um etwa 58 m ansteigen. Die Ermittlung von Prognosen über den Beitrag der Antarktis zum Anstieg des Meeresspiegels infolge der globalen Erwärmung ist ein fortlaufender Prozess, der große Unterschiede in den Vorhersagen zur Folge hat. Einer der Gründe dafür sind Ungewissheiten im Zusammenhang mit der Physik der Eisschildmodellierung. Zu diesen Unsicherheiten gehören zwei Prozesse, die zu einem unkontrollierten Eisrückzug führen könnten:
die Marine Ice Sheet Instability (MISI), die zu einem schnellen Rückzug der Grundlinie auf rückläufigem Grundgestein führt, und die Marine Ice Cliff Instability (MICI), bei der hohe Eisklippen instabil werden und abkalben, wodurch noch höhere Eisklippen freigelegt werden.
In meiner Dissertation untersuchte ich beide marinen Instabilitäten (MISI und MICI) mit Hilfe des Parallel Ice Sheet Model (PISM), wobei der Schwerpunkt auf MICI lag.
KW - Antarctica
KW - ice sheet modelling
KW - iceberg calving
KW - Antarktis
KW - Eisschildmodellierung
KW - Eisbergkalbung
Y1 - 2022
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-586333
ER -
TY - JOUR
A1 - Mau, Erik Thomas Klaus
A1 - Rosenblum, Michael
T1 - Optimizing charge-balanced pulse stimulation for desynchronization
JF - Chaos : an interdisciplinary journal of nonlinear science
N2 - 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.
Y1 - 2022
U6 - https://doi.org/10.1063/5.0070036
SN - 1054-1500
SN - 1089-7682
VL - 32
IS - 1
PB - AIP
CY - Melville
ER -
TY - JOUR
A1 - Foster, Grace
A1 - Poppenhäger, Katja
T1 - Identifying interesting planetary systems for future X-ray observations
JF - Astronomische Nachrichten = Astronomical notes
N2 - X-ray observations of star-planet systems are important to grow our understanding of exoplanets; these observations allow for studies of photoevaporation of the exoplanetary atmosphere, and in some cases even estimations of the size of the outer planetary atmosphere. The German-Russian eROSITA instrument onboard the SRG (Spectrum Roentgen Gamma) mission is performing the first all-sky X-ray survey since the 1990s, and provides X-ray fluxes and spectra of exoplanet host stars over a much larger volume than was accessible before. Using new eROSITA data as well as archival data from XMM-Newton, Chandra, and ROSAT, we estimate mass-loss rates of exoplanets under an energy-limited escape scenario and identify several exoplanets with strong X-ray irradiation and expected mass loss that are amenable to follow-up observations at other wavelengths. We model sample spectra using a toy model of an exoplanetary atmosphere to predict what exoplanet transit observations with future X-ray missions such as Athena will look like and estimate the observable X-ray transmission spectrum for a typical hot Jupiter-type exoplanet.
KW - planets and satellites
KW - general
KW - stars
KW - activity
KW - coronae
KW - planetary systems
KW - X-rays
Y1 - 2022
U6 - https://doi.org/10.1002/asna.20220007
SN - 1521-3994
VL - 343
IS - 4
PB - Wiley-VCH
CY - Berlin
ER -
TY - JOUR
A1 - Ilin, Ekaterina
A1 - Poppenhäger, Katja
A1 - Alvarado-Gómez, Julián David
T1 - Localizing flares to understand stellar magnetic fields and space weather in exo-systems
JF - Astronomische Nachrichten = Astronomical notes
N2 - Stars are uniform spheres, but only to first order. The way in which stellar rotation and magnetism break this symmetry places important observational constraints on stellar magnetic fields, and factors in the assessment of the impact of stellar activity on exoplanet atmospheres. The spatial distribution of flares on the solar surface is well known to be nonuniform, but elusive on other stars. We briefly review the techniques available to recover the loci of stellar flares, and highlight a new method that enables systematic flare localization directly from optical light curves. We provide an estimate of the number of flares we may be able to localize with the Transiting Exoplanet Survey Satellite, and show that it is consistent with the results obtained from the first full sky scan of the mission. We suggest that nonuniform flare latitude distributions need to be taken into account in accurate assessments of exoplanet habitability.
KW - stars
KW - activity - stars
KW - flare - stars
KW - magnetic fields - methods
KW - data
KW - analysis
Y1 - 2022
U6 - https://doi.org/10.1002/asna.20210111
SN - 1521-3994
VL - 343
IS - 4
PB - Berlin
CY - Wiley-VCH
ER -
TY - JOUR
A1 - Omel'chenko, Oleh
A1 - Laing, Carlo R.
T1 - Collective states in a ring network of theta neurons
JF - Proceedings of the Royal Society of London. Series A, Mathematical, physical and engineering sciences
N2 - We consider a ring network of theta neurons with non-local homogeneous coupling. We analyse the corresponding continuum evolution equation, analytically describing all possible steady states and their stability. By considering a number of different parameter sets, we determine the typical bifurcation scenarios of the network, and put on a rigorous footing some previously observed numerical results.
KW - theta neurons
KW - neural networks
KW - bumps
Y1 - 2022
U6 - https://doi.org/10.1098/rspa.2021.0817
SN - 1364-5021
SN - 1471-2946
VL - 478
IS - 2259
PB - Royal Society
CY - London
ER -