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41421 Publications

Cell voltage model for Li-Bi liquid metal batteries

Weber, N.; Duczek, C.; Horstmann, G. M.; Landgraf, S.; Nimtz, M.; Personnettaz, P.; Weier, T.; Sadoway, D. R.

The dataset contains the raw data and python codes for the publication: https://doi.org/10.1016/j.apenergy.2021.118331

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Permalink: https://www.hzdr.de/publications/Publ-33890
Publ.-Id: 33890


Introducing natural adversarial observations to a Deep Reinforcement Learning agent for Atari Games

Hanfeld, P.

Deep Learning methods are known to be vulnerable to adversarial attacks. Since Deep Reinforcement Learning agents are based on these methods, they are prone to tiny input data changes. Three methods for adversarial example generation will be introduced and applied to agents trained to play Atari games. The attacks target either single inputs or can be applied universally to all possible inputs of the agents. They were able to successfully shift the predictions towards a single action or to lower the agent’s confidence in certain actions, respectively. All proposed methods had a severe impact on the agent’s performance while producing invisible adversarial perturbations. Since natural-looking adversarial observations should be completely hidden from a human evaluator, the negative impact on the performance of the agents should additionally be undetectable. Several variants of the proposed methods were tested to fulfil all posed criteria. Overall, seven generated observations for two of three Atari games are classified as natural-looking adversarial observations.

Keywords: Reinforcement Learning; Adversarial Attacks; Deep Learning

  • Master thesis
    Hochschule Mittweida, 2021
    Mentor: Chorowski, Jan; Villmann, Thomas
    75 Seiten

Permalink: https://www.hzdr.de/publications/Publ-33889
Publ.-Id: 33889


Emergence of pion parton distributions

Cui, Z.-F.; Ding, M.; Morgado, J. M.; Raya, K.; Binosi, D.; Chang, L.; de Soto, F.; Roberts, C. D.; Rodriguez-Quintero, J.; Schmidt, S. M.

Supposing only that there is an effective charge which defines an evolution scheme for parton distribution functions (DFs) that is all-orders exact, strict lower and upper bounds on all Mellin moments of the valence-quark DFs of pion-like systems are derived. Exploiting contemporary results from numerical simulations of lattice-regularised quantum chromodynamics (QCD) that are consistent with these bounds, parameter-free predictions for pion valence, glue, and sea DFs are obtained. The form of the valence-quark DF at large values of the light-front momentum fraction is consistent with predictions derived using the QCD-prescribed behaviour of the pion wave function.

Permalink: https://www.hzdr.de/publications/Publ-33888
Publ.-Id: 33888


Concerning pion parton distributions

Cui, Z.-F.; Ding, M.; Morgado, J. M.; Raya, K.; Binosi, D.; Chang, L.; Papavassiliou, J.; Roberts, C. D.; Rodriguez-Quintero, J.; Schmidt, S. M.

Analyses of the pion valence-quark distribution function (DF), ${\mathpzc u}^\pi(x;\zeta)$, which explicitly incorporate the behaviour of the pion wave function prescribed by quantum chromodynamics (QCD), predict ${\mathpzc u}^\pi(x\simeq 1;\zeta) \sim (1-x)^{\beta(\zeta)}$, $\beta(\zeta \gtrsim m_p)>2$, where $m_p$ is the proton mass. Nevertheless, more than forty years after the first experiment to collect data suitable for extracting the $x\simeq 1$ behaviour of ${\mathpzc u}^\pi$, the empirical status remains uncertain because some methods used to fit existing data return a result for ${\mathpzc u}^\pi$ that violates this constraint. Such disagreement entails one of the following conclusions: the analysis concerned is incomplete; not all data being considered are a true expression of qualities intrinsic to the pion; or QCD, as it is currently understood, is not the theory of strong interactions. New, precise data are necessary before a final conclusion is possible. In developing these positions, we exploit a single proposition, \emph{viz}.\ there is an effective charge which defines an evolution scheme for parton DFs that is all-orders exact. This proposition has numerous corollaries, which can be used to test the character of any DF, whether fitted or calculated.

Permalink: https://www.hzdr.de/publications/Publ-33887
Publ.-Id: 33887


Optical absorption and carrier multiplication at graphene edges in a magnetic field

Queisser, F.; Lang, S.; Schützhold, R.

We study optical absorption at graphene edges in a transversal magnetic field. The magnetic field bends the trajectories of particle- and hole excitations into antipodal direction which generates a directed current. We find a rather strong amplification of the edge current by impact ionization processes. More concretely, the primary absorption and the subsequent carrier multiplication is analyzed for a graphene fold and a zigzag edge. We identify exact and approximate selection rules and discuss the dependence of the decay rates on the initial state.

Keywords: Graphene; Auger processes; optical absorption

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Permalink: https://www.hzdr.de/publications/Publ-33886
Publ.-Id: 33886


Optical absorption and carrier multiplication at graphene edges in a magnetic field

Queisser, F.; Lang, S.; Schützhold, R.

We study optical absorption at graphene edges in a transversal magnetic field. The magnetic field bends the trajectories of particle- and hole excitations into antipodal direction which generates a directed current. We find a rather strong amplification of the edge current by impact ionization processes. More concretely, the primary absorption and the subsequent carrier multiplication is analyzed for a graphene fold and a zigzag edge. We identify exact and approximate selection rules and discuss the dependence of the decay rates on the initial state.

Keywords: Graphene; Auger processes; optical absorption

Permalink: https://www.hzdr.de/publications/Publ-33885
Publ.-Id: 33885


Density Functional Theory Perspective on the Non-Linear Response of Correlated Electrons Across Temperature Regimes

Moldabekov, Z.; Vorberger, J.; Dornheim, T.

We explore a new formalism to study the nonlinear electronic density response based on
Kohn-Sham density functional theory (KS-DFT) at partially and strongly quantum degenerate regimes.
It is demonstrated that the KS-DFT calculations are able to accurately reproduce the available path integral Monte Carlo simulation results at temperatures relevant for warm dense matter research.
The existing analytical results for the quadratic and cubic response functions are rigorously tested. It is demonstrated that the analytical results for the quadratic response function closely agree with the KS-DFT data. Furthermore, the performed analysis reveals that currently available analytical formulas for the cubic response function are not able to describe simulation results, neither qualitatively nor quantitatively, at small wave-numbers $q<2q_F$, with $q_F$ being the Fermi wave-number.
The results show that KS-DFT can be used to describe warm dense matter that is strongly perturbed by an external field with remarkable accuracy. Furthermore, it is demonstrated that KS-DFT constitutes a valuable tool to guide the development of the non-linear response theory of correlated quantum electrons from ambient to extreme conditions. This opens up new avenues to study nonlinear effects in a gamut of different contexts at conditions that cannot be accessed with previously used path integral Monte Carlo methods [T. Dornheim \emph{et al.}, \textit{Phys.~Rev.~Lett.}~\textbf{125}, 085001 (2020)].

Keywords: warm dense matter

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Permalink: https://www.hzdr.de/publications/Publ-33884
Publ.-Id: 33884


On the measurement of local concentrations in bubbly flows for the reaction of FeII(edta) with NO using fiber optical probe

Kipping, R.; Kryk, H.; Hampel, U.

Topics of current research activities within the DFG priority program SPP 1740 “Reactive Bubbly Flows” are studies on local mass transfer and reaction processes in order to gain a deeper understanding about the coupling of hydrodynamics, mass transfer and reaction kinetics in reactive bubbly flows.
This contribution presents the results of an experimental study on reaction of FeII(EDTA) and NO. The reaction forms a very stable complex of [Fe(EDTA)NO)2-]. The aim of the experiments is the measurement of the local species concentration of the product complex in the bubble wake. For this purpose, a fiber optical probe, especially designed for this application was used. The sensor is equipped with two LED’s and optical filters of different wavelengths (λ_1 = 435 nm, λ_2 = 780 nm), respectively. The selection of the wavelengths is based on the absorption spectra of [Fe(EDTA)NO)2-], in order to provide a product specific wavelength (λ_1 = 435 nm) and reference wavelength (λ_2 = 780 nm). In that way, the concentration of the product species and information about the prevailing phase (liquid or gas) were recorded simultaneously. Experiments were carried out in a bubble column with 74mm inner diameter and single needle gas injection (see Figure 1a). Figure 1b shows an example of the time signal of the concentration of the product species, where disturbed signals due to bubble-probe interactions are removed based on the signals of the reference wavelength. In this contribution, characteristic parameters of the species concentration in the bubble wake obtained from measurements with the fiber optical probe are presented for different initial concentrations of the solution and different hydrodynamic conditions.

The authors gratefully acknowledge the financial support provided by the German Research Foundation (DFG) within Priority Program “Reactive Bubbly Flows” SPP 1740.

  • Lecture (Conference) (Online presentation)
    Jahrestreffen der ProcessNet Fachgruppen Mehrphasenströmung (MPH) und Computational Fluid Dynamics (CFD), 09.-10.03.2021, Paderborn, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-33883
Publ.-Id: 33883


Tetra‐substituted p‐tert‐butylcalix[4]arene with phosphoryl and salicylamide functional groups: synthesis, complexation and selective extraction of f‐element cations

Glasneck, F.; Roode-Gutzmer, Q.; Stumpf, T.; Kersting, B.

A new series of lanthanide (1-5) and uranyl (6) complexes with a tetra-substituted bifunctional calixarene ligand H₂L is described.The coordination environment for the Ln³+ and UO₂²+ ions is provided by phosphoryl and salicylamidefunctional groups appended to the lower rim of the p-tert-butylcalix[4]arenescaffold. Ligand interactions with lanthanide cations (light: La³+, Pr³+; intermediate: Eu³+and Gd³+; and heavy: Yb³+), as well as the uranyl cation (UO₂²+) is examined in the solution and solid state, respectively with spectrophotometric titration and single crystal X-ray diffractometry. The ligand is fully deprotonated in the complexation of trivalent lanthanide ions forming di-cationic complexes 2:2 M:L, [Ln2(L)2(H2O)]2+(1-5), in solution, whereas uranyl formed a 1:1 M:L complex [UO2(L)(MeOH)]∞(6) that demonstrated very limited solubility in 12 organic solvents. Solvent extraction behaviour is examined for cation selectivity and extraction efficiency. H₂L was found to be an effective extracting agent for UO₂²+ over La³+ and Yb³+ cations. The separation factors at pH 6.0 are: ß UO₂²+/La³+ = 121.0 and ß UO₂²+/Yb³+ = 70.0.

Keywords: tetra-substituted calixarene; f-elements; uranyl; lanthanides; solvent extraction

Permalink: https://www.hzdr.de/publications/Publ-33882
Publ.-Id: 33882


Antigen-specific redirection of off-the-shelf NK-92 cells using the universal CAR platform ‘‘UniCAR’’

Mitwasi, N.; Feldmann, A.; Arndt, C.; Koristka, S.; Loureiro, L. R.; Berndt, N.; Tonn, T.; Bergmann, R.; Rössig, C.; Wels, W. S.; Bachmann, M.

Modifying of immune effector cells with chimeric antigen receptors (CARs) has revealed a promising therapeutic potential for targeting cancer, especially with CAR-modified T cells. However, the use of other immune cells like primary NK cells or NK cell lines appeared as another advantageous approach that can be combined with CAR technology. Unlike T cells, established NK cell lines can be used allogenically as an off-the-shelf product with reduced risk of toxicities. We have established previously a modular Universal CAR platform (UniCAR) which can be switched on/off and allows the flexible targeting of various tumor antigens. This system consists of two parts, the UniCAR-expressing immune effector cells and a target module (TM). The UniCAR-immune cells cannot recognize surface antigens but are only redirected with the TM which contains an antigen-binding moiety on one hand and an epitope recognized by the UniCAR molecules on the other hand. Here, we provide a proof of concept for using the UniCAR system in combination with the NK-92 cell line to target disialoganglioside GD2-expressing tumors. The UniCAR NK-92 cells induced increase in lysis of neuroblastoma and melanoma cell lines in the presence of scFv- or human IgG4-based TMs, associated with specific release of pro-inflammatory cytokines. Moreover, UniCAR NK-92 cells were shown to be functional in eradicating GD2-expressing tumors in experimental mice. In order to investigate the in vivo half-life of the scFv- and IgG4-based TMs, they were radiolabeled with 64Cu and detected using PET imaging. Dynamic PET scanning has shown that the IgG4 format increased the half-life of the TM to around 24 folds in comparison to the scFv-based TMs. In summary, UniCAR NK-92 provides an off-the-shelf universal platform that can be combined with various antibody formats, and can be easily expanded for therapeutic use.

  • Poster
    International Conference on Lymphocyte Engineering, 31.03.-02.04.2022, Munich, Germany

Permalink: https://www.hzdr.de/publications/Publ-33879
Publ.-Id: 33879


Magnetic field assisted electrodeposition of metal on conically structured electrodes

Huang, M.; Eckert, K.; Mutschke, G.

The electrodeposition of metal on conically shaped diamagnetic and ferromagnetic electrodes is studied under the influence of a vertical magnetic field. Analytical and numerical results show a beneficial influence of the magnetic field to enhance the cone growth, which can be attributed to the electrolyte flow forced by the Lorentz force and the magnetic gradient force. The influences of cone shape, cone size and distance between neighbouring cones are investigated in detail. The results deliver insights into the feasibility of magnetic field assisted electrodeposition towards nano-structured conical electrodes.

  • Lecture (Conference) (Online presentation)
    International Congress of Theoretical and Applied Mechanics (ICTAM 2020+1), 26.08.2021, Milano, Italien

Permalink: https://www.hzdr.de/publications/Publ-33878
Publ.-Id: 33878


As small as it can be: short peptide-derived target molecules for redirection of UniCAR T-cells and imaging of SSTR2-expressing cancers

Loureiro, L. R.; Bergmann, R.; Wodtke, R.; Brandt, F.; Arndt, C.; González Soto, K. E.; Mitwasi, N.; Kegler, A.; Bartsch, T.; Drewitz, L.; Máthé, D.; Feldmann, A.; Bachmann, M.

Chimeric antigen receptor (CAR) T-cells are undoubtedly a promising approach in cancer immunotherapy. Nevertheless, mild to severe toxicities are associated with this approach including on-target/off-tumor effects and cytokine release syndrome. Aiming for increased clinical safety, adaptor CAR technologies were developed which include the modular universal CAR (UniCAR) platform developed by our group. UniCAR T-cells are exclusively activated in the presence of a target module (TM), which establishes the cross-link between cancer cells and UniCAR T-cells. These TMs are highly versatile molecules that can be constructed not only by using antibody fragments but also e.g. peptides specifically targeting a receptor or molecule on the cell´s surface. Somatostatin receptor (SSTR) subtype 2 is highly expressed in a variety of malignancies and has therefore been studied as a marker and target for cancer diagnosis and treatment. Currently, SSTR2 agonists and antagonists, such as Tyr3-octreotate (TATE) and BASS or JR11, respectively, are particularly well established and clinically implemented mostly used for diagnostic nuclear medicine. Given this and the proven flexibility and efficacy of the UniCAR system, we hereby aimed to develop small peptide-derived TMs targeting SSTR2 that can be used for both immunotherapeutic and diagnostic approaches. For that, the abovementioned SSTR2 agonist and antagonists were chemically linked to the E5B9 peptide and equipped with the radiometal chelator NODAGA. These TMs were tested in vitro and in vivo, in which they have proven to specifically redirect UniCAR T-cells to human neuroendocrine and breast SSTR2-expressing cancer cells. Furthermore, the enrichment of these anti-SSTR2 peptide TMs at the tumor site was confirmed by positron emission tomography (PET) studies. We hereby designed novel small peptide-derived TMs that can be used for redirection of UniCAR T-cells to SSTR2-expressing cancer cells as well as for PET imaging, proving to be promising and innovative immunotheranostics tools to foster cancer treatment.

  • Open Access Logo Lecture (Conference)
    International Conference on Lymphocyte Engineering: ICLE 2022, 31.03.2022, Munich, Germany

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Permalink: https://www.hzdr.de/publications/Publ-33876
Publ.-Id: 33876


Selective binding of UO22+ by different peptide families

Tsushima, S.; Takao, K.

Actinide interaction with proteins and peptides is little explored field in actinide chemistry, though there are biophysical studies where relative high affinity was found for U interaction with proteins. However, in vivo studies showed minor increases of U in serum, attributed to rapid urinary excretion. U–protein interaction is apparently not the major pathway associated with U genotoxicity. Nevertheless there are other scenarios where U interaction with amino acids can become potentially important such as extraction of uranium from sea water using protein (e.g. Wang et al. Angew. Chem. Int. Ed. 2019, 131, 11911). Here, we studied selective binding of UO22+ with several different peptide families including (a) cyclic peptides consisting of 6 –10 amino acids, (b) non–cyclic peptides of similar size, (c) 33–amino acid peptide corresponding to EF hand of the calcium–binding site I of calmodulin. For small peptides (a and b), we used standard DFT approaches to study their interaction with UO22+. For a larger peptide family (c), classical molecular dynamics (MD) simulations were used to study binding of peptide with UO22+, followed by fragment molecular orbital (FMO) calculations (e.g. Rossberg et al. Chem. Comm. 2019, 55, 2015) to study their interactions at a quantum chemical level. At the meeting, we will present the strategy to design peptides which have high affinity and selectivity towards UO22+. This work was partially funded by Grant-in-Aid for Scientific Research of the Japan Society for the Promotion of Science.

  • Invited lecture (Conferences) (Online presentation)
    The International Chemical Congress of Pacific Basin Societies 2021 (PACIFICHEM 2021), 16.-21.12.2021, Honolulu, Hawaii, U.S.A.

Permalink: https://www.hzdr.de/publications/Publ-33875
Publ.-Id: 33875


Mathematical model of the inertia-controlled microlayer profile in nucleate boiling

Zhang, J.; Ding, W.; Hampel, U.

Accurate simulation of the boiling heat transfer in a nuclear system requires extensive investigations of the microlayer dynamics during the nucleate boiling. In particular, the inertia-controlled microlayer profile, which plays a significant role in the microlayer evaporation and bubble dynamics, is the key parameter for the nucleate boiling simulation. In this work, the microlayer model in the inertia-controlled bubble growth stage was established through the disjoining pressure method and the lubrication theory. Two regions are distinguished: the contact line region, where the disjoining pressure is dominated; the microlayer region, where the effect of disjoining pressure fails, and the profile is determined by the balance of the surface tension and hydrodynamic forces. We found that in the contact line region, the profile is bent to approach the wall surface due to the disjoining pressure, while in the microlayer, the thickness increases almost linearly with respect to the microlayer length. The predicted profile was compared with experimental data and a very good agreement was obtained. Unlike the overestimated microlayer profiles from previous models, our results clearly demonstrate that the presence of the disjoining pressure is the key factor to supress microlayer thickness. Our model accurately captures the surface molecular force in the contact line region and provides the apparent contact angle for the microlayer. This offers a proper way to set up boundary conditions in the nucleate boiling simulations.

Keywords: Nucleate boiling; microlayer; disjoining pressure

  • Contribution to proceedings
    19th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, 06.-11.03.2022, Brussels, Belgium, ISBN 9789076971261

Permalink: https://www.hzdr.de/publications/Publ-33874
Publ.-Id: 33874


Laser induced crystallization of Co–Fe–B films

Almeida, M.; Sharma, A.; Matthes, P.; Köhler, N.; Busse, S.; Müller, M.; Hellwig, O.; Horn, A.; Zahn, D. R. T.; Salvan, G.; Schulz, S. E.

Local crystallization of ferromagnetic layers is crucial in the successful realization of miniaturized
tunneling magnetoresistance (TMR) devices. In the case of Co–Fe–B TMR devices, used most
successfully so far in applications and devices, Co–Fe–B layers are initially deposited in an amorphous
state and annealed post-deposition to induce crystallization in Co–Fe, thereby increasing the device
performance. In this work, first direct proof of locally triggered crystallization of 10 nm thick Co–Fe–B
films by laser irradiation is provided by means of X-ray diffraction (XRD) using synchrotron radiation.
A comparison with furnace annealing is performed for benchmarking purposes, covering different
annealing parameters, including temperature and duration in the case of furnace annealing, as
well as laser intensity and scanning speed for the laser annealing. Films of Co–Fe–B with different
stoichiometry sandwiched between a Ru and a Ta or MgO layer were systematically assessed by XRD
and SQUID magnetometry in order to elucidate the crystallization mechanisms. The transformation
of Co–Fe–B films from amorphous to crystalline is revealed by the presence of pronounced CoFe(110)
and/or CoFe(200) reflexes in the XRD θ-2θ scans, depending on the capping layer. For a certain window
of parameters, comparable crystallization yields are obtained with furnace and laser annealing.
Samples with an MgO capping layer required a slightly lower laser intensity to achieve equivalent Co–
Fe crystallization yields, highlighting the potential of laser annealing to locally enhance the TMR ratio.

Permalink: https://www.hzdr.de/publications/Publ-33873
Publ.-Id: 33873


Noncollinear Remanent Textures Induced by Surface Spin Flop in Synthetic Antiferromagnets with Perpendicular Anisotropy

Böhm, B.; Fallarino, L.; Pohl, D.; Rellinghaus, B.; Hellwig, O.

The surface spin flop, observed in synthetic antiferromagnets (SAFs) with uniaxial anisotropy and
strong antiferromagnetic (AF) interlayer exchange coupling, can be considered as a laterally homoge-
neous, vertical AF domain wall pushed into the SAF from either the top or the bottom in the presence
of a strong external vertical magnetic field. As a result, the AF domain wall can be described as a one-
dimensional entity. In this work, we present a concept to stabilize laterally homogeneous vertical AF
domain walls by local variation of the perpendicular magnetic anisotropy in Co/Pt-based SAFs. Our
approach not only allows the stabilization of the vertical AF domain wall in the absence of any exter-
nal magnetic field, but furthermore enables a deterministic selection among four different remanent states,
each one stable within a broad external magnetic field range of almost one tesla. We also demonstrate an
extension to our concept by stabilizing two coexisting vertical AF domain walls, thus yielding a system
with a total of six different selectable (and reprogrammable) remanent states. The controlled stabiliza-
tion of noncollinear AF textures in the form of vertical AF domain walls at remanence could be used as
an infrastructure for propagating spin waves within the AF domain wall itself, as well as for tuning the
dynamic behavior of perpendicular standing spin wave modes existing vertically across the SAF.

Permalink: https://www.hzdr.de/publications/Publ-33872
Publ.-Id: 33872


CoCrFeNi High-Entropy Alloy Thin Films Synthesised by Magnetron Sputter Deposition from Spark Plasma Sintered Targets

Schwarz, H.; Uhlig, T.; Rösch, N.; Lindner, T.; Ganss, F.; Hellwig, O.; Lampke, T.; Wagner, G.; Seyller, T.

Two magnetron sputter targets of CoCrFeNi High-Entropy Alloy (HEA), both in equal atomic ratio, were prepared by spark plasma sintering. One of the targets was fabricated from a homogeneous HEA powder produced via gas atomisation; for the second target, a mixture of pure element powders was used. Economic benefits can be achieved by mixing pure powders in the intended ratio in comparison to the gas atomisation of the specific alloy composition. In this work, thin films deposited via magnetron sputtering from both targets are analysed. The surface elemental composition is investigated by X-ray photoelectron spectroscopy, whereas the bulk stoichiometry is measured by X-ray fluorescence spectroscopy. Phase information and surface microstructure are investigated using X-ray diffraction and scanning electron microscopy, respectively. It is demonstrated that the stoichiometry, phase composition and microscopic structure of the as-deposited HEA thin films are almost identical if the same deposition parameters are used.

Keywords: high-entropy alloy; magnetron sputtering; spark plasma sintering; X-ray photoelectron spectroscopy; X-ray diffraction; scanning electron microscopy

Permalink: https://www.hzdr.de/publications/Publ-33871
Publ.-Id: 33871


Worldline instantons for nonlinear Breit-Wheeler pair production and Compton scattering

Degli Esposti, G.; Torgrimsson, G.

Worldline instantons have previously been used to study the probability of Schwinger pair production (both the exponential and pre-exponential parts) and photon-stimulated pair production (the exponential part). Previous studies obtained the pair-production probability on the probability level by using unitarity, i.e. the imaginary part of the effective action for Schwinger pair production or the imaginary part of the polarization tensor for photon-stimulated pair production. The corresponding instantons are closed loops in the complex plane. Here we show how to use instantons on the amplitude level, which means open instanton lines with start and end points representing fermions at asymptotic times. The amplitude is amputated with LSZ using, in general, field-dependent asymptotic states. We show how to use this formalism for photon-stimulated/Breit-Wheeler pair production and nonlinear Compton scattering.

Permalink: https://www.hzdr.de/publications/Publ-33869
Publ.-Id: 33869


Edge and Point-Defect Induced Electronic and Magnetic Properties in Monolayer PtSe₂

Li, J.; Joseph, T.; Ghorbani Asl, M.; Kolekar, S.; Krasheninnikov, A.; Batzill, M.

Edges and point defects in layered dichalcogenides are important for tuning their electronic and magnetic properties. By combining scanning tunneling microscopy (STM) with density functional theory (DFT), the electronic structure of edges and point defects in 2D-PtSe2 are investigated where the 1.8 eV- band gap of monolayer PtSe2 facilitates the detailed characterization of defect-induced gap states by STM. The stoichiometric zigzag edge terminations are found to be energetically favored. STM and DFT show that these edges exhibit metallic one-dimensional states with spin-polarized bands. Various native point defects in PtSe2 are also characterized by STM. A comparison of the experiment with simulated images enables the identification of Se-vacancies, Pt-vacancies, and Se-antisites as the dominant defects in PtSe2. In contrast to Se- or Pt- vacancies, the Se-antisites are almost devoid of gap states. Pt-vacancies exhibit defect-induced states that are spin-polarized, emphasizing their importance for inducing magnetism in PtSe2. The atomic-scale insights into defect-induced electronic states in monolayer PtSe2 provide the fundamental underpinning for defect engineering of PtSe2-monolayers and the newly identified spin-polarized edge states offer prospects for engineering magnetic properties in PtSe2 nanoribbons.

Keywords: 2D materials; defect engineering; edge states; spin polarized defects; electronic defect states; scanning probe microscopy

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Permalink: https://www.hzdr.de/publications/Publ-33868
Publ.-Id: 33868


A machine learning approach to determine bubble sizes in foam at a transparent wall

Knüpfer, L.; Heitkam, S.

This article describes the use of a machine learning based technique to measure the bubble sizes of foam with polyhedral bubble shape in contact with a transparent wall. For two different experimental cases images are obtained of foam in a cylindrical column and labeled with a classical image processing algorithm. An available neural network based model, initially designed for cell image applications, is trained and validated to segment the images. When comparing the bubble size distribution in images found using the trained model with manually segmented images a good agreement over a large range of diameters can be found. The error of the mean diameter in both cases lies below $10\%$, mostly attributed to the failed recognition of tiny round bubbles in dry foam. The trained model is provided for further usage.

Keywords: bubble; foam; image segmentation

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Permalink: https://www.hzdr.de/publications/Publ-33867
Publ.-Id: 33867


Dressed Dirac Propagator from a Locally Supersymmetric N=1 Spinning Particle

Degli Esposti, G.; Corradini, O.

We study the Dirac propagator dressed by an arbitrary number N of photons by means of a worldline approach, which makes use of a supersymmetric N=1 spinning particle model on the line, coupled to an external Abelian vector field. We obtain a compact off-shell master formula for the tree level scattering amplitudes associated to the dressed Dirac propagator. In particular, unlike in other approaches, we express the particle fermionic degrees of freedom using a coherent state basis, and consider the gauging of the supersymmetry, which ultimately amounts to integrating over a worldline gravitino modulus, other than the usual worldline einbein modulus which corresponds to the Schwinger time integral. The path integral over the gravitino reproduces the numerator of the dressed Dirac propagator.

Permalink: https://www.hzdr.de/publications/Publ-33866
Publ.-Id: 33866


Data, code, and metadata for: Daily torpor reduces the energetic consequences of microhabitat selection for a widespread bat

Alston, J.; Dillon, M. E.; Keinath, D. A.; Abernethy, I. M.; Goheen, J. R.

This repository contains all data, code, and metadata required to reproduce the results detailed in "Daily torpor reduces the energetic consequences of microhabitat selection for a widespread bat" by Alston et al.

Keywords: Bayesian hierarchical models; climate change; daily torpor; fringed myotis (Myotis thysanodes); temporal heterothermy; thermal ecology; VHF telemetry

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Permalink: https://www.hzdr.de/publications/Publ-33865
Publ.-Id: 33865


The Potential of Machine Learning for a More Responsible Sourcing of Critical Raw Materials

Ghamisi, P.; Rafiezadeh Shahi, K.; Duan, P.; Rasti, B.; Lorenz, S.; Booysen, R.; Thiele, S. T.; Contreras Acosta, I. C.; Kirsch, M.; Gloaguen, R.

The digitization and automation of the raw material sector is required to attain the targets set by the Paris Agreements and support the sustainable development goals defined by the United Nations. While many aspects of the industry will be affected, most of the technological innovations will require smart imaging sensors. In this review, we assess the relevant recent developments of machine learning for the processing of imaging sensor data. We first describe the main imagers and the acquired data types as well as the platforms on which they can be installed. We briefly describe radiometric and geometric corrections as these procedures have been already described extensively in previous works. We focus on the description of innovative processing workflows and illustrate the most prominent approaches with examples. We also provide a list of available resources, codes, and libraries for researchers at different levels, from students to senior researchers, willing to explore novel methodologies on the challenging topics of raw material extraction, classification, and process automatization.

Keywords: Deep learning (DL); Earth observation; machine learning; Mining; Raw materials.

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Permalink: https://www.hzdr.de/publications/Publ-33864
Publ.-Id: 33864


Unsupervised Data Fusion with Deeper Perspective: A Novel Multi-Sensor Deep Clustering Algorithm

Rafiezadeh Shahi, K.; Ghamisi, P.; Rasti, B.; Scheunders, P.; Gloaguen, R.

The ever-growing developments in technology to capture different types of image data (e.g., hyperspectral imaging and Light Detection and Ranging (LiDAR)-derived digital surface model (DSM)), along with new processing techniques, have led to a rising interest in imaging applications for Earth observation. However, analyzing such datasets in parallel remains a challenging task. In this paper, we propose a multi-sensor deep clustering (MDC) algorithm for the joint processing of multi-source imaging data. The architecture of MDC is inspired by autoencoder (AE)-based networks. The MDC paradigm includes three parallel networks, a spectral network using an autoencoder structure, a spatial network using a convolutional autoencoder structure, and lastly, a fusion network that reconstructs the concatenated image information from the concatenated latent features from the spatial and spectral network. The proposed algorithm combines the reconstruction losses obtained by the aforementioned networks to optimize the parameters (i.e., weights and bias) of all three networks simultaneously. To validate the performance of the proposed algorithm, we use two multi-sensor datasets from different applications (i.e., geological and rural sites) as benchmarks. The experimental results confirm the superiority of our proposed deep clustering algorithm compared to a number of state-of-the-art clustering algorithms. The code will be available at: https://github.com/Kasra2020/MDC.

Keywords: Multi-sensor Data Fusion; Deep Learning; Autoencoder; Convolutional Autoencoder; Remote Sensing

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Permalink: https://www.hzdr.de/publications/Publ-33863
Publ.-Id: 33863


Quantum magnetism of ferromagnetic spin dimers in α-KVOPO4

Mukharjee, P. K.; Somesh, K.; Ranjith, K. M.; Baenitz, M.; Scurschii, I.; Adroja, D. T.; Khalyavin, D.; Tsirlin, A. A.; Nath, R.

Magnetism of the spin- 1/2 α-KVOPO4 is studied by thermodynamic measurements, 31P nuclear magnetic resonance, neutron diffraction, and density-functional band-structure calculations. Ferromagnetic Curie-Weiss temperature of θCW ≃ 15.9 K and the saturation field of μ0Hs ≃ 11.3 T suggest the predominant ferromagnetic coupling augmented by a weaker antiferromagnetic exchange that leads to a short-range order below 5 K and the long-range antiferromagnetic order below TN ≃ 2.7 K in zero field. Magnetic structure with the propagation vector k = (0, 1/2, 0) and the ordered magnetic moment of 0.58 μB at 1.5 K exposes a nontrivial spin lattice where strong ferromagnetic dimers are coupled antiferromagnetically. The reduction in the ordered magnetic moment with respect to the classical value (1 μB) indicates sizable quantum fluctuations in this setting, despite the predominance of ferromagnetic exchange. We interpret this tendency toward ferromagnetism as arising from the effective orbital order in the folded chains of the VO6 octahedra.

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Permalink: https://www.hzdr.de/publications/Publ-33862
Publ.-Id: 33862


A contribution to the principle particle-bubble interactions in froth flotation - hydrophobic adhesion of heterogeneous surfaces, the change of signs in van der Waals interactions and measures of flotability/wettability

Rudolph, M.; Buchmann, M.; van den Boogaart, K. G.; Wu, H.; Sandbrink, J.; Babel, B. M.

Even though froth flotation is by far the most important fine particle separation process in mineral processing and recycling for a variety materials, there are still fundamental questions on its working principles.
Lately, we found that detachment forces of hydrophobic AFM colloidal probes from hydrophobized surfaces observed in aqueous conditions and supported by contact angle measures, visualization of adsorption layers and microflotation studies, is not reflected in existing detachment models. The additional observation that collectors of oily type in sulfide flotation and surfactant type in oxide mineral flotation adsorb in a heterogeneous patchy manor let us to extent existing detachment models We present a modelling approach for adhesion forces caused by gas-capillary interactions on surfaces with a macroscopic contact angle below 90°. In addition we show how both collector layers as well as surface gas can turn van der Waals interactions attractive with no need of an additional hydrophobic interaction.

  • Lecture (Conference) (Online presentation)
    Flotation'21, 08.-12.11.2021, Cape Town, South Africa

Permalink: https://www.hzdr.de/publications/Publ-33861
Publ.-Id: 33861


Aktuelle Erkenntnisse bei der flotativen Aufbereitung von Schwarzmasse und Entwicklungen bei der Schwarzmassecharakterisierung mit den Methoden der Prozessmineralogie und Aufschlussanalytik

Rudolph, M.; Vanderbruggen, A.; Bachmann, K.

Lithium-Ionen-Batterien (LIBs) gehören zu den derzeit wichtigsten elektrochemischen Energiespeichersystemen für elektronische Mobilgeräte und Elektrofahrzeuge. Die wachsende weltweite Nachfrage nach LIBs geht mit einer Erhöhung des Bedarfs an Co, Mn, Ni, Li und Graphit einher. Diese Erhöhung der Nachfrage dieser Rohstoffe stellt eine besondere Herausforderung für den schon jetzt angespannten weltweiten Rohstoffmarkt dar, verbunden mit Versorgungsrisiken, Preisschwankungen und Marktmonopolen. Tatsächlich sind Co und natürlicher Graphit in Europa seit 2010 als kritische Rohstoffe (CRM) geführt, Li sowie Mn befinden sich an der Grenze der Kritikalität. Um potenziell die Kluft zwischen Angebot und Nachfrage zu verringern sowie die europäischen Nachhaltigkeitsziele zu erreichen, hat das Recycling von Lithium-Ionen-Batterien (LIB) in den letzten Jahren viel Aufmerksamkeit auf sich gezogen. Hierbei wird sich hauptsächlich auf die wertvollen Metalle wie Kobalt, Nickel und Lithium konzentriert. Allerdings gehen während des Recyclingprozesses erhebliche Mengen anderer Komponenten wie Elektrolyt, Separator oder Graphit verloren. So kann Graphit zum Beispiel während der pyrometallurgischen Behandlung entweder abgeschlackt oder als Reduktionsmittel verbraucht werden. Darüber hinaus gehen einige andere wertvolle Metalle wie Co in den Grobfraktionen durch einen zu geringen Aufschlussgrad an die Berge verloren. Aus diesem Grund müssen neue und umfassende LIB-Recyclingverfahren gefunden werden.
In dieser Studie werden wir auf die aktuellen Ergebnisse der Schwarzmasseaufbereitung und der Charakterisierung der Lithium-Ionen Batterie Recyclatströmen.

  • Lecture (Conference)
    Aufbereitung und Recycling 2021, 11.-12.11.2021, Freiberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-33860
Publ.-Id: 33860


It’s all in an ever changing cycle | (mineral) fine particle processing in times of circular economy and energy transition

Rudolph, M.

Humanity has always felt itself to be in the area of conflict between innovative technological developments aimed at positively influencing the quality of life, the limited available resources and the sometimes destructive effects on our environment. In 2011, motivated by the demonstrably severe impact on the Earth‘s climate of greenhouse gases, such as CO2 produced by the burning of fossil fuels, as well as the nuclear reactor disaster in Fukushima, political leaders called for a transition to renewable energies.

This necessitates the large-scale employment of new technologies, such as electric cars, efficient wind turbines with magnets containing rare earths and hydrogen technologies. This development is strongly influencing the material mix and thus the raw material requirements. The complexity of the composite materials, with their extremely complex, polymetallic character and fine distribution of raw materials, is characteristic of many new technological developments, as famously exemplified by the material mix in smartphones, which contains numerous elements of the periodic table.

The availability of metals and mineral resources is a critical factor in a healthy economy, especially one that is also striving to be a circular economy. For thermodynamic reasons, such an economy cannot be closed, i.e. in addition to secondary resources; primary resources always have to play a role.

This lecture shall outline the recent developments and research topics in the field of mineral processing in times of the circular economy and energy transition where a mineral is understand as more than just a naturally occurring crystalline material but will more and more be artificial. I would like to (self critically) highlight where the art of the modern mineral processing expertise is needed and how batteries, hydrogen electrolyzers and engineered artificial minerals in industrial slags can be seen as examples of the raw materials of the future of an efficient circular economy with as little as possible primary production.

  • Open Access Logo Invited lecture (Conferences) (Online presentation)
    CoE Minerals Signature Series, 29.09.2021, Melbourne, Australia

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Permalink: https://www.hzdr.de/publications/Publ-33859
Publ.-Id: 33859


Why do particles float at contact angles below 90° and what is our recent understanding in hydrophobic bubble-particle attachment?

Rudolph, M.; Buchmann, M.; van den Boogaart, K. G.; Babel, B. M.

Even though froth flotation is by far the most important unit operation to separate fine particles in mineral processing as well as in recycling for a variety of raw materials, there are still manifold fundamental questions on the working principle. Ever since the flotation process has been developed and successfully applied in industry it was for example reported that for particles to float efficiently the macroscopic contact angle with water is well below 90°, even though every undergraduate student is taught, that hydrophobicity requires contact angles to exceed 90°.
In the last few years, we have developed a colloidal probe atomic force microscopy approach to allow for flotability mapping with direct force measurements. We found that the detachment forces of the hydrophobic colloidal probes from hydrophobized surfaces observed in aqueous conditions and supported by conventional contact angle measures, visualization of adsorption layers and laboratory microflotation studies on particle fractions is not reflected in existing detachment models. The additional observation that collectors of oily type in sulfide flotation and surfactant type in oxide mineral flotation adsorb in a heterogeneous patchy manor let us to extent existing detachment models which are based on numerically solving the Young-Laplace equation. Hence, we present a modelling approach for adhesion forces caused by gas-capillary interactions on surfaces with a macroscopic contact angle below 90°, which is not possible with previous models.
With our findings we can contribute to the question why flotability is indeed given for macroscopic contact angles below 90°.
Furthermore we will discuss these findings in the framework of the recent understanding of the crucial hydrophobic interactions leading to bubble-particle attachment including the theory of capillary waves. This is especially of interest for the recovery of very fine particles in highly turbulent processing environments.

  • Lecture (Conference) (Online presentation)
    Jahrestreffen der ProcessNet-Fachgruppen Lebensmittelverfahrenstechnik, Mischvorgänge, Grenzflächenbestimmte Systeme und Prozesse, 11.-12.03.2021, On-Line, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-33858
Publ.-Id: 33858


A comparison between approaches for the calculation of van der Waals interactions in flotation systems

Weber, C.; Knüpfer, P.; Buchmann, M.; Rudolph, M.; Peuker, U. A.

Among the multitude of surface/interfacial forces, van der Waals forces have an impact on the performance of industrial processes in which dispersed substances such as drops, bubbles or particles are treated. The material dependent expression of the resulting forces is represented by the Hamaker function. This paper contains a selection of various methods for calculating the Hamaker function from the Lifshitz approach with a focus on heterocoagulation processes such as froth flotation. As an example, differences between the results of the full Lifshitz theory and approximate treatments are presented for selected Material - Water - Air systems. Such systems resemble the interaction between solids and air bubbles across water in flotation. In addition we present calculations of the Hamaker function in layered systems, which aim at modeling the adsorption of chemicals in flotation. Furthermore it is possible to treat so-called interfacial gas enrichment within this approach. Both, interfacial gas enrichment and adsorbed layers have a significant effect on the short-distance van der Waals interactions and increase the range of the interaction. The manuscript details the numerical solution of the Lifshitz equations and provides a list of the material properties required to calculate the Hamaker function for minerals.

Keywords: Froth Flotation; Hamaker Constant; Particle Interactions

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  • Secondary publication expected

Permalink: https://www.hzdr.de/publications/Publ-33857
Publ.-Id: 33857


Electrochemical Characterization of Sulphide Minerals–Halophilic Bacteria Surface Interaction for Bioflotation Applications

González-Poggini, S.; Luque Consuegra, G.; Kracht, W.; Rudolph, M.; Colet-Lagrille, M.

The effects of halophilic bacteria (Halobacillus sp. and Marinobacter sp.) on pyrite and chalcopyrite surface oxidation in artificial seawater are studied by electrochemical impedance spectroscopy (EIS) in conjunction with X-ray diffraction (XRD) and cyclic voltammetry analysis (CV), in order to explain the influence of these microorganisms on the minerals floatability. EIS analyses on pyrite electrodes suggest that biomaterial from both bacteria adheres to the mineral surface, which is reinforced by CV experiments as capacitive currents are promoted by both bacteria. Additionally, XRD analyses of pyrite samples after immersion in artificial seawater with and without bacteria indicate the formation of hematite on the mineral surface in the presence of Halobacillus sp., which together with the adherence of biomaterial could promote the depression of pyrite during flotation. On the other hand, EIS and CV analyses on chalcopyrite electrodes suggest that the adherence of Halobacillus sp. and Marinobacter sp. to the surface of the mineral have no significant effects on the kinetics of the chalcopyrite oxidation processes. These results together with XRD analyses of the chalcopyrite samples after immersion in artificial seawater with and without bacteria suggest that superficial sulphur might have a stronger influence on chalcopyrite flotability than the presence of bacteria.

Keywords: Froth Flotation; Mineral Surfaces; Sulfide Minerals; Biotechnology

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Permalink: https://www.hzdr.de/publications/Publ-33856
Publ.-Id: 33856


A contribution to exploring the importance of surface air nucleation in froth flotation – The effects of dissolved air on graphite flotation

Xu, M.; Li, C.; Zhang, H.; Kupka, N.; Peuker, U. A.; Rudolph, M.

The formation of surface microbubbles induced by air nucleation on graphite surfaces and the air diffusion process in oversaturated water play important roles in increasing the recovery of graphite and other valuable minerals in flotation. A microscope equipped with a cuvette, a laser diffraction particle size analyzer, and single bubble pick-up experiments were combined with micro-flotation experiments to clarify these effects. The diffusion-controlled growth process of surface microbubbles was observed with a microscope. It can be shown that higher degrees of dissolved air can improve the probability of surface microbubbles forming on graphite surfaces. Micro-flotation and microscopic experiments confirmed that surface microbubbles occurred selectively on graphite surface but not quartz. Besides, bubble-particle aggregates formed during the conditioning process were observed under the microscope while bubble pick-up experiments indicated that the bubble load increased with the increasing degree of dissolved air. Size distribution analysis also showed that the nucleation microbubbles on graphite surfaces improved the recovery of fine graphite particles due to the formation of microbubble-particle aggregates. Coarser microbubble-particle aggregates induced by surface nucleation bubbles can improve the collision and attachment probability to external carrying bubbles compared to single graphite particles, which is especially relevant for fine particles. This study indicates that nucleation microbubbles on graphite surfaces can significantly promote flotation efficiency, and shows the importance of air nucleation on mineral surfaces in flotation process.

Keywords: surface microbubbles; air nucleation; diffusion; flotation; bubble-particle aggregates

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Permalink: https://www.hzdr.de/publications/Publ-33855
Publ.-Id: 33855


ASL-BIDS, the brain imaging data structure extension for arterial spin labeling

Clement, P.; Castellaro, M.; Okell, T. W.; Thomas, D. L.; Vandemaele, P.; Elgayar, S.; Oliver-Taylor, A.; Kirk, T.; Woods, J. G.; Vos, S.; Kuijer, J. P. A.; Achten, E.; van Osch, M. J. P.; Gau, R.; Detre, J.; Lu, H.; Alsop, D. C.; Chappell, M. A.; Hernandez-Garcia, L.; Petr, J.; Mutsaerts, H. J. M. M.

Arterial spin labeling (ASL) is a non-invasive MRI technique, allowing quantitative measurement of cerebral perfusion. Incomplete or inaccurate reporting of acquisition parameters complicates quantification, analysis, and sharing of ASL data, particularly for studies across multiple sites, platforms, and ASL methods. Therefore, there is a strong need for standardization of ASL data storage, including acquisition metadata. Recently ASL-BIDS, the BIDS extension for ASL, was developed and released in BIDS 1.5.0. This manuscript provides an overview of the development and design choices of this first ASL-BIDS extension, which is mainly aimed at clinical ASL applications. The structure of the ASL data, focusing on storage order of the ASL time series and implementation of calibration approaches, unit scaling, ASL-related BIDS fields, and storage of the labeling plane information, are discussed. Additionally, an overview of ASL-BIDS compatible conversion and ASL analysis software and ASL example datasets in BIDS format is provided. It is anticipated that large-scale adoption of ASL-BIDS will improve the reproducibility of ASL research.

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Permalink: https://www.hzdr.de/publications/Publ-33854
Publ.-Id: 33854


An experimental study on the multiscale properties of turbulence in bubble-laden flows

Ma, T.; Hessenkemper, H.; Lucas, D.; Bragg, A. D.

The properties of bubble-laden turbulent flows at different scales are investigated experimentally, focusing on the flow kinetic energy, energy transfer, and extreme events. The experiments employed particle shadow velocimetry measurements to measure the flow in a column generated by a homogeneous bubble swarm rising in water, for two different bubble diameters ($2.7$ mm $\&$ $3.9$ mm) and moderate gas volume fractions ($0.26\%\sim1.31\%$). The two velocity components were measured at high-resolution, and used to construct structure functions up to twelfth order for separations spanning the small to large scales in the flow. Concerning the flow anisotropy, the velocity structure functions are found to differ for separations in the vertical and horizontal directions of the flow, and the cases with smaller bubbles are the most anisotropic, with a dependence on void fraction. The degree of anisotropy is shown to increase as the order of the structure functions is increased, showing that extreme events in the flow are the most anisotropic. Our results show that the average energy transfer with the horizontal velocity component is downscale, just as for the three-dimensional single-phase turbulence. However, the energy transfer associated with the vertical component of the fluid velocity is upscale. The probability density functions of the velocity increments reveal that extreme values become more probable with decreasing Reynolds number, the opposite of the behaviour in single-phase turbulence. We visualize those extreme events and find that regions of intense small scale velocity increments occur near the turbulent/non-turbulent interface at the boundary of the bubble wake.

Keywords: turbulence; bubbly flows

Permalink: https://www.hzdr.de/publications/Publ-33852
Publ.-Id: 33852


Weak branch and multimodal convection in rapidly rotating spheres at low Prandtl number

Garcia Gonzalez, F.; Stefani, F.; Dormy, E.

The focus of this study is to investigate primary and secondary bifurcations to weakly nonlinear flows (weak branch) in convective rotating spheres in a regime where only strongly nonlinear oscillatory sub- and supercritical flows (strong branch) were previously found [E. J. Kaplan, N. Schaeffer, J. Vidal, and P. Cardin, Phys. Rev. Lett. 119, 094501 (2017)]. The relevant regime corresponds to low Prandtl and Ekman numbers, indicating a predominance of Coriolis forces and thermal diffusion in the system. We provide the bifurcation diagrams for rotating waves (RWs) computed by means of continuation methods and the corresponding stability analysis of
these periodic flows to detect secondary bifurcations giving rise to quasiperiodic modulated rotating waves (MRWs). Additional direct numerical simulations (DNS) are performed for the analysis of these quasiperiodic flows for which Poincaré sections and kinetic energy spectra are presented. The diffusion timescales are investigated as well. Our study reveals very large initial transients (more than 30 diffusion time units) for the nonlinear saturation of solutions on the weak branch, either RWs or MRWs, when DNS are employed. In addition, we demonstrate that MRWs have multimodal nature involving resonant triads. The modes can be located in the bulk of the fluid or attached to the outer sphere and exhibit multicellular structures. The different resonant modes forming the nonlinear quasiperiodic flows can be predicted with the stability analysis of RWs, close to the Hopf bifurcation point, by analyzing the leading unstable Floquet eigenmode.

Keywords: Hopf bifurcation

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Permalink: https://www.hzdr.de/publications/Publ-33851
Publ.-Id: 33851


Arterial Spin-Labeling Parameters and Their Associations with Risk Factors, Cerebral Small-Vessel Disease, and Etiologic Subtypes of Cognitive Impairment and Dementia

Gyanwali, B.; Seng Tan, C.; Petr, J.; Tirado Escobosa, L. L.; Vrooman, H.; Chen, C.; Mutsaerts, H. J. M. M.; Hilal, S.

Background and purpose: Cerebral small vessel disease (SVD) may alter cerebral blood flow (CBF) leading to brain changes and hence cognitive impairment and dementia. CBF and spatial coefficient of variation (sCoV) can be measured quantitatively by Arterial Spin Labeling (ASL). We aim to investigate the associations of demographic, vascular risk factors, location and severity of SVD as well as etiologic subtypes of cognitive impairment and dementia with ASL parameters.
Methods: 390 patients; no cognitive impairment, cognitive impairment no dementia (CIND), vascular CIND (VCIND), Alzheimer’s disease (AD), and Vascular Dementia (VaD) were recruited from memory-clinic. Cerebral microbleeds (CMBs) and lacunes were categorized into strictly lobar, strictly deep, and mixed-location; enlarged perivascular spaces (ePVS) into centrum semiovale and basal ganglia. Total and region-specific white matter hyperintensity (WMH) volumes were segmented using FreeSurfer. CBF (n= 333) and sCoV (n=390) were analyzed with ExploreASL from 2D-EPI pseudo-continuous ASL-images.
Results: Increasing age, male sex, hypertension, hyperlipidemia, history of heart disease and smoking were associated with lower CBF and higher sCoV. Higher numbers of lacunes and CMBs were associated with lower CBF and higher sCoV. Location-specific analysis showed mixed-location lacunes and CMBs were associated with lower CBF. Higher total, anterior and posterior WMH volumes were associated with higher sCoV. No association was observed between ePVS and ASL parameters. Higher sCoV was associated with the diagnosis of VCIND, AD and VaD.
Conclusion: Reduced CBF and increased sCoV were associated with SVD, cognitive impairment, and dementia, suggesting that hypoperfusion might be the key underlying mechanism for vascular brain damage.

Permalink: https://www.hzdr.de/publications/Publ-33850
Publ.-Id: 33850


Numerical simulation of solid-density plasma dynamics driven by optical short pulse relativistic lasers and XFELs

Huang, L. G.

The state-of-the-art optical short pulse relativistic lasers and X-ray free electron lasers (XFELs) with unprecedented light pressures enable to create the high-energy solid-density plasmas relevant to the interior of stars and planets, astrophysical jets and fusion devices. Yet, it is hardly accessible to fully probe the complex ultrafast plasma dynamics limited by the diagnostic spatial and temporal resolutions in experiments. Thus, the numerical simulations based on the particle-in-cell (PIC), magneto-hydrodynamics (MHD), molecular dynamics (MD), Vlasov-Fokker–Planck (VFP) and density-functional theory (DFT) provide the essential complementary capabilities to predict, explore and understand the fundamental plasma physics, with the aid of modern high performance computing clusters. In this talk, we will briefly introduce the algorithms of PIC code and implemented physics modules including binary collisions, non-equilibrium ionizations, and radiation transport in addition to the standard PIC cycle. Then we will give an overview of the PIC simulations of solid-density plasma dynamics driven by the optical short pulse relativistic lasers, with regard to the electron transport and secondary radiation, target heating and ionization, instabilities, and extreme electromagnetic fields generation. Lastly, we will present the numerical results to retrieve the temporal processes of XFEL-matter interactions with the newly implemented radiation transport model, for understanding the damaging mechanisms of the samples irradiated by an XFEL with intensity on the order of 1020 W/cm2 performed by our recent large-scale experiments.

  • Lecture (others) (Online presentation)
    HZDR scientific seminar series ‚Hardware & Numerics‘, 09.11.2021, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-33849
Publ.-Id: 33849


Using XFELs to Probe Extreme Magnetic Fields in Relativistic High Power Laser Matter Interactions

Huang, L. G.; Schlenvoigt, H.-P.; Toncian, T.; Kluge, T.; Cowan, T. E.

The relativistic laser matter interaction is a complex interplay of ionization, extreme current densities, rapidly
evolving strong fields and acceleration processes. Understanding the interaction physics is a challenging but
highly rewarding endeavor. The recently commissioned X-Ray free electron lasers (XFELs) with unprecedented
brightness and polarization purity open a new window for discovering the interior of solid-density plasmas
created by relativistic laser interactions with matter, resolving the relevant femtosecond and nanometer scales
experimentally. Here, we focus on discussing the feasibility of probing the Kilotesla to Megatesla-level magnetic
fields by X-Ray polarimetry via Faraday rotation using XFELs. The synthetic simulations show that XFELs are
capable to detect the extreme magnetic fields from relativistic laser interactions with solid and near-critical
density targets[1, 2].

[1] L. G. Huang, H. P. Schlenvoigt, H. Takabe, and T. E. Cowan,
Physics of Plasmas 24, 103115 (2017).
[2] T. Wang, T. Toncian, M. S. Wei, and A. V. Arefiev, Physics of
Plasmas 26, 013105 (2019).

  • Poster (Online presentation)
    MML-Workshop 2021, 22.-24.11.2021, online, Germany

Permalink: https://www.hzdr.de/publications/Publ-33848
Publ.-Id: 33848


Association of arterial spin labeling parameters with cognitive decline, vascular events and mortality in a memory-clinic sample

Gyanwali, B.; Mutsaerts, H. J. M. M.; Seng Tan, C.; Rajab Kaweilh, O.; Petr, J.; Chen, C.; Hilal, S.

Background: Cognitive decline in older adults has been attributed to reduced cerebral blood flow (CBF). Recently, the spatial coefficient of variation (sCoV) of ASL has been proposed as a proxy marker of cerebrovascular insufficiency. We investigated the association between baseline ASL parameters with cognitive decline, incident cerebrovascular disease and risk of vascular events and mortality.
Design, Setting and Participants: 368 memory-clinic patients underwent three-annual neuropsychological assessments and brain MRI scans at baseline and follow-up. MRIs were graded for white matter hyperintensities (WMH), lacunes, cerebral microbleeds (CMBs), cortical infarcts and intracranial stenosis. Baseline gray (GM) and white matter (WM) CBF and GM-sCoV were obtained with ExploreASL from 2D-EPI pseudo-continuous ASL images. Cognitive assessment was done using a validated neuropsychological battery. Data on incident vascular events (heart disease, stroke, transient ischemic attack) and mortality were obtained.
Results: Higher baseline GM-sCoV was associated with decline in the memory domain over three years of follow-up. Furthermore, higher GM-sCoV was associated with a decline in the memory domain only in participants without dementia. Higher baseline GM-sCoV was associated with progression of WMH and incident CMBs. During a mean follow-up of 3 years, 29 (7.8%) participants developed vascular events and 18 (4.8%) died. Participants with higher baseline mean GM-sCoV were at increased risk of vascular events.
Conclusions: Higher baseline GM-sCoV of ASL was associated with a decline in memory and risk of incident cerebrovascular disease and vascular events, suggesting that cerebrovascular insufficiency may contribute to accelerated cognitive decline and worse clinical outcomes in memory clinic participants.

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Permalink: https://www.hzdr.de/publications/Publ-33847
Publ.-Id: 33847


Cerebral perfusion and the risk for cognitive decline and dementia in community dwelling older people

Abdulrahman, H.; Hafdi, M.; Mutsaerts, H. J. M. M.; Nederveen, A. J.; Petr, J.; Gool, W. A. V.; Richard, E.; Dalen, J. V.

Background. The arterial spin labeling-spatial coefficient of variation (sCoV) is a new vascular magnetic resonance imaging (MRI) parameter that could be a more sensitive marker for dementia-associated cerebral microvascular disease than the commonly used MRI markers cerebral blood flow (CBF) and white matter hyperintensity volume (WMHV).
Methods. 195 community-dwelling older people with hypertension underwent MRI twice with a three-year interval. Cognition was evaluated every two years for 6-8 years using the mini-mental state examination (MMSE). Dementia diagnoses were registered up to 9 years after the first scan. We assessed relations of sCoV, CBF and WMHV with cognitive decline during follow-up, and compared MRI parameters between participants that did and did not develop dementia.
Results. sCoV and CBF were not associated with MMSE changes during 6-8 years of follow-up and did not differ between participants who did (n=15) and did not (n=180) develop dementia. Higher WMHV was associated with declining MMSE scores (-0.15 points/year/ml, 95%CI=-0.30; -0.01), and with participants who developed dementia after the first MRI (13.3 vs 6.1mL, p<0.001). There were no associations between longitudinal change in any of the MRI parameters and cognitive decline or subsequent dementia.
Conclusion. Global sCoV and CBF were less sensitive longitudinal markers of cognitive decline and dementia compared to WMHV in community-dwelling older people with hypertension. Larger longitudinal MRI perfusion studies are needed to identify possible (regional) patterns of cerebral perfusion preceding cognitive decline and dementia diagnosis.

Permalink: https://www.hzdr.de/publications/Publ-33846
Publ.-Id: 33846


High electron mobility in strained GaAs nanowires

Balaghi, L.; Shan, S.; Fotev, I.; Moebus, F.; Rana, R.; Venanzi, T.; Hübner, R.; Mikolajick, T.; Schneider, H.; Helm, M.; Pashkin, O.; Dimakis, E.

Novel transistor concepts based on semiconductor nanowires promise high performance, lower energy consumption and better integrability in various platforms in nanoscale dimensions. Concerning the intrinsic transport properties of electrons in nanowires, relatively high mobility values that approach those in bulk crystals have been obtained only in core/shell heterostructures, where electrons are confined inside the core and, thus, their scattering on the nanowire surface is suppressed.
Here, we demonstrate that the strain in core/shell nanowires with large lattice-mismatch between the core and the shell can affect the effective mass and the scattering of electrons in a way that boosts their mobility to higher levels compared to results obtained by any other means. Specifically, we use GaAs/InAlAs core/shell nanowires grown self-catalyzed on Si substrates by molecular beam epitaxy. Overgrown with an 80-nm-thick shell, the 22-nm-thick core is hydrostatically tensile-strained as found by both Raman scattering and photoluminescence measurements. The transport properties and dynamics of electrons were probed at room temperature by optical-pump THz-probe spectroscopy, which is an established contactless method that circumvents challenges in the fabrication of electrical contacts on nanowires. We found that the mobility of electrons inside the strained GaAs core undergoes a remarkable enhancement, becoming twice as high as in unstrained GaAs/AlGaAs nanowires and 65% higher than in bulk GaAs (despite the small core thickness). This is understood as the result of both the reduced electron effective mass and the reduced electron-phonon scattering rate in the tensile-strained GaAs core.
Such mobility enhancement is of major importance for the realization of transistors with high speed and low power consumption, having the potential to trigger major advancements in high-performance nanowire electronic devices.

Related publications

  • Lecture (Conference) (Online presentation)
    European Congress and Exhibition on Advanced Materials and Processes - EUROMAT 2021, 13.-17.09.2021, Vienna, Austria

Permalink: https://www.hzdr.de/publications/Publ-33845
Publ.-Id: 33845


Bandgap tuning and electron mobility enhancement in strained III-V nanowires

Balaghi, L.; Tauchnitz, T.; Hilliard, D.; Moebus, F.; Shan, S.; Fotev, I.; Pashkin, O.; Hübner, R.; Grenzer, J.; Ghorbani Asl, M.; Krasheninnikov, A.; Schneider, H.; Helm, M.; Dimakis, E.

Nanowire geometry allows for realising defect-free heterostructures with large lattice mismatch, in addition to the possibility for their monolithic integration on foreign substrates. Engineering of the built-in strain can be employed to tailor the electronic properties and fit them to the needs of photonic or electronic devices. This talk focuses on the epitaxial growth, the built-in strain and the modified electronic properties of free-standing GaAs/InxGa1-xAs and GaAs/InxAl1-xAs core/shell nanowires on Si substrates. The thin GaAs core can be hydrostatically tensile strained to a level that depends on the chemical composition and the thickness of the shell. As a result, the bandgap of the GaAs core can be tuned to be anywhere between 1.4 and 0.8 eV, with potential applications in telecom photonics. The same mechanism is employed to shift also the emission of GaAs/AlxGa1-xAs quantum dots that can be grown inside the core, in a scheme that could be employed for photon sources in quantum technology. Furthermore, the reduced effective mass of electrons inside the strained GaAs core results in increased mobility values (higher than those in unstrained GaAs nanowires or in bulk GaAs), which is promising for the advancement of gate-all-around transistors.

Related publications

  • Invited lecture (Conferences) (Online presentation)
    Compound Semiconductor Week 2021, 09.-13.05.2021, Stockholm, Sweden

Permalink: https://www.hzdr.de/publications/Publ-33844
Publ.-Id: 33844


Heterostructures in self-catalyzed III-As nanowires: benefits and challenges

Dimakis, E.

Heterostructures in self-catalyzed III-As nanowires: benefits and challenges

Related publications

  • Invited lecture (Conferences) (Online presentation)
    Nanostructures for Photonics, 15.-17.11.2021, St. Petersburg, Russia

Permalink: https://www.hzdr.de/publications/Publ-33843
Publ.-Id: 33843


Anomalous quantum oscillations of CeCoIn5 in high magnetic fields

Hornung, J.; Mishra, S.; Stirnat, J.; Raba, M.; Schwarze, B. V.; Klotz, J.; Aoki, D.; Wosnitza, J.; Helm, T.; Sheikin, I.

We report on magnetic-torque and resistivity measurements of the heavy-fermion compound CeCoIn5 in static magnetic fields up to 36 T and temperatures down to 50 mK. While quantum oscillations of the de Haas–van Alphen (dHvA) as well as the Shubnikov–de Haas (SdH) effect confirm the previously reported Fermi surfaces, an analysis of the field dependence reveals two anomalous features. The first is seen at about 22 T as a sharp anomaly in the resistivity for current applied along the a direction. The second appears as nonmonotonic fielddependent oscillation frequencies and amplitudes in both dHvA and SdH signals. This second feature emerges at about 28 T. This field is close to that of the nematic transition reported for CeRhIn5 and the proposed Lifshitz transition in CeIrIn5. We discuss possible common grounds of these latter features that might originate from the very similar band structures of these materials.

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Permalink: https://www.hzdr.de/publications/Publ-33841
Publ.-Id: 33841


Diffuse glioma perfusion quantification with ASL and DSC: head-to-head comparison with 15O-H2O PET

Petr, J.; Verburg, N.; Kuijer, J. P. A.; Koopman, T.; Keil, V. C.; Warnert, E. A. H.; Barkhof, F.; van den Hoff, J.; Boellaard, R.; de Witt Hamer, P. C.; J. M. M. Mutsaerts, H.

Background: Arterial spin-labeling (ASL) is a viable non-invasive alternative to dynamic susceptibility contrast (DSC) for measuring cerebral blood flow (CBF). While quantitative accuracy of ASL and DSC was compared in healthy volunteers and patients, a comparison to a reference standard in patients diagnosed with glioma is still missing.
Purpose: To probe the quantitative agreement between perfusion measurements based on ASL and DSC in comparison to the gold standard of PET in patients with glioma.
Materials and Methods: This secondary analysis included pre-surgical ASL and DSC perfusion measurements in participants diagnosed with grade 2-4 gliomas drawn from the prospective FRONTIER study (Dutch National Trial Register - NTR5354) and compared the two techniques with the gold-standard perfusion measurement 15O-H2O-PET. The quantitative comparison was performed both in normal-appearing tissue as well as in the tumor region. The mean, maximum, and voxel-wise perfusion values were with and without normalization to normal-appearing tissue. And finally, a qualitative analysis was performed on individual cases to help interpret the quantitative results.
Results: Eight patients (age 40.5 ± 17.0 years, 3 women) were analyzed. ASL showed better voxel-wise agreement with PET in the normal-appearing tissue than DSC (mean relative error of 26.8% vs. 33.8%). Within the tumor, cerebral blood flow (CBF) normalized contralateral gray matter showed similar tumor maximum values in both techniques - mean relative error of 23.2% for ASL and 22.0% for DSC. However, the mean relative error on a voxel-wise basis was better for ASL (27.2%) than for DSC (35.0%). Qualitatively, ASL tended to overestimate CBF in macrovessels, and DSC tended to overestimate CBF in non-enhancing tumors with small vessel diameters.
Conclusion: While neither ASL nor DSC can readily replace 15O-H2O-PET in tumor quantitative perfusion measurement, ASL CBF presents a viable non-invasive semi-quantitative alternative to DSC for glioma imaging.

  • Contribution to proceedings
    Deutsche Gesellschaft für Nuklearmedizin, 27.04.2022, Leipzig, Germany
  • Lecture (Conference)
    Deutsche Gesellschaft für Nuklearmedizin, 27.04.2022, Leipzig, Germany

Permalink: https://www.hzdr.de/publications/Publ-33840
Publ.-Id: 33840


HERMES: A concept for automated workflows for software publication with rich metadata

Druskat, S.; Bertuch, O.; Juckeland, G.; Knodel, O.; Schlauch, T.

To satisfy the principles of FAIR software, software sustainability and software citation, research software must be formally published. Publication repositories make this possible and provide published software versions with unique and persistent identifiers. However, software publication is still a tedious, mostly manual process.
To streamline software publication, HERMES, a project funded by the Helmholtz Metadata Collaboration, develops automated workflows to publish research software with rich metadata.
The tooling developed by the project utilizes continuous integration solutions to retrieve, collate, and process existing metadata in source repositories, and publish them on publication repositories, including checks against existing metadata requirements. To accompany the tooling and enable researchers to easily reuse it, the project also provides comprehensive documentation and templates for widely used CI solutions. In this paper, we outline the concept for these workflows, and describe how our solution advance the state of the art in research software publication.

Permalink: https://www.hzdr.de/publications/Publ-33839
Publ.-Id: 33839


A convenient route to new (radio)fluorinated and (radio)iodinated cyclic tyrosine analogues.

Noelia Chao, M.; Chezal, J.-M.; Debiton, E.; Canitrot, D.; Witkowski, T.; Levesque, S.; Degoul, F.; Tarrit, S.; Wenzel, B.; Miot-Noirault, E.; Serre, A.; Maisonial-Besset, A.

The use of radiolabelled non-natural amino acids can provide high contrast SPECT/PET meta-bolic imaging of solid tumours. Among them, radiohalogenated tyrosine analogues (i.e. [123I]IMT, [18F]FET, [18F]FDOPA, [123I]8-iodo-L-TIC(OH), etc.) are of particular interest. While ra-dioiodinated derivatives, like [123I]IMT, are easily available via electrophilic aromatic substitu-tions, the production of radiofluorinated aryl tyrosine analogues was a long standing challenge for radiochemists before the development of innovative radiofluorination processes using ar-ylboronate, arylstannane or iodoniums salts as precursors. Surprisingly, despite these method-ological advances, no radiofluorinated analogues have been reported for [123I]8-iodo-L-TIC(OH), a very promising radiotracer for SPECT imaging of prostatic tumours. This work describes a convergent synthetic pathway to obtain new radioiodinated and radiofluorinated derivatives of TIC(OH), as well as their non-radiolabelled counterparts. Using organotin compounds as key intermediates, [125I]5-iodo-L-TIC(OH), [125I]6-iodo-L-TIC(OH) and [125I]8-iodo-L-TIC(OH) were efficiently prepared with good radiochemical yield (RCY, 51-78%), high radiochemical purity (RCP, > 98%), molar activity (Am, > 1.5-2.9 GBq/µmol) and enantiomeric excess (e.e. > 99%). The corresponding [18F]fluoro-L-TIC(OH) derivatives were also successfully obtained by radiofluor-ination of the organotin precursors in the presence of tetrakis(pyridine)copper(II) triflate and nucleophilic [18F]F- with 19-28 % RCY d.c., high RCP (> 98.9%), Am (20-107 GBq/µmol) and e.e. (> 99%)

Related publications

Permalink: https://www.hzdr.de/publications/Publ-33838
Publ.-Id: 33838


Synthetic probing of ionization dynamics in the solid density plasmas driven by relativistic laser pulses using resonant SAXS

Huang, L. G.; Kluge, T.; Gaus, L.; Schlenvoigt, H.-P.; Cowan, T. E.

Understanding the ionization dynamics is fundamentally important in the interaction of a relativistic laser pulse with a solid density target. In this talk, firstly we present the particle-in-cell (PIC) simulations with various collisional ionization and potential models, showing the target heating, magnetic instabiltiy and plasma resistivity are highly model-dependent \cite{Huang2016,Huang2017}. Secondly, we propose to probe the evolution of ionic density at specific bound-bound resonances by scanning the XFEL photon energy via established SAXS method, which is cable to access the spatial–temporal resolution down to few nanometers and femtoseconds simultaneously. The plasma opacity plays a key role of the XFEL absorption, which in turn affects the resonant SAXS pattern contributed by the imaginary part of ionic scattering form factor\cite{Kluge2016}. We present the calculation of plasma opacity using the atomic collisional-radiative code SCFLY and further simulate the synthetic resonant SAXS imaging pattern which shows strong asymmetric feature. Our recently performed experiment reveals the connection of the temporal evolution of the asymmetry signal and ionization dynamics \cite{Gaus2020}.

[1] L. G. Huang, T. Kluge, and T. E. Cowan, Physics of Plasmas23, 063112 (2016).[2] L. G. Huang, H. P. Schlenvoigt, H. Takabe, and T. E. Cowan, Physics of Plasmas24, 103115 (2017).
[3] T. Kluge, M. Bussmann, H.-K. Chung, C. Gutt, L. G. Huang, M. Zacharias, U. Schramm, and T. E.Cowan, Physics of Plasmas23, 033103 (2016).
[4] L. Gaus, L. Bischoff, M. Bussmann, E. Cunningham, C. B. Curry, E. Galtier, M. Gauthier, A. L.Garc ́ıa, M. Garten, S. Glenzer, J. Grenzer, C. Gutt, N. J. Hartley, L. Huang, U. H ̈ubner, D. Kraus,H. J. Lee, E. E. McBride, J. Metzkes-Ng, B. Nagler, M. Nakatsutsumi, J. Nikl, M. Ota, A. Pelka,I. Prencipe, L. Randolph, M. R ̈odel, Y. Sakawa, H.-P. Schlenvoigt, M.ˇSm ́ıd, F. Treffert, K. Voigt,K. Zeil, T. E. Cowan, U. Schramm, and T. Kluge, “Probing ultrafast laser plasma processes insidesolids with resonant small-angle x-ray scattering,” (2020), arXiv:2012.07922 [physics.plasm-ph].

  • Lecture (Conference)
    SAXS Workshop@XFELs, HI and HE lasers driven matters, 04.-05.11.2021, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-33837
Publ.-Id: 33837


Superparamagnetism and ferrimagnetism in the Sr2FeMoO6–δ nanoscale powder

Kalanda, N.; Yarmolich, M.; Burko, A.; Temirov, A.; Kislyuk, A.; Demyanov, S.; Lenz, K.; Lindner, J.; Kim, D.-H.

As a result of using combined synthesis modes and optimized conditions for ultrasonic dispersion, a single-phase nanosized Sr2FeMoO6–δ powder with a high degree of superstructural ordering of Fe/Mo cations (88%) with an average grain size of 70.8 nm was obtained. Based on the results of Mössbauer spectroscopy and magnetic measurements, it was established that the obtained nanosized strontium ferromolybdate powder is in a magnetically inhomogeneous state, consisting of superparamagnetic and ferrimagnetic phases. The ferrimagnetic component of magnetization is characterized by higher values of magnetization in comparison with the superparamagnetic component, and a smooth increase is noted for this component, which reaches saturation with decreasing temperature. It is shown that there is no exchange magnetic interaction between superparamagnetic grains in the superparamagnetic phase, which made it possible, based on the Neel-Brown model, to estimate the critical sizes of nanoparticles, dSPM, in the single-domain state. The obtained dSPM values are smaller than the sizes of single-domain particles, which confirms the absence of a frozen state in some of the superparamagnetic particles. The results of this work are important for understanding the effect of nanosized grains on the magnetic properties and features of magnetization of the Sr2FeMoO6–δ polydisperse powder that is very promising for spintronic device application.

Keywords: Perovskites; sol-gel processes; electron microscopy; magnetic properties

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Permalink: https://www.hzdr.de/publications/Publ-33836
Publ.-Id: 33836


Oxygen Depletion in Ultra-High Dose Rates for Protons And Electrons: Experimental Approach In Water And Biological Samples

Jansen, J.; Beyreuther, E.; Pawelke, J.; Karsch, L.; Schürer, M.; Kroll, F.; Brack, F.-E.; Reimold, M.; Metzkes-Ng, J.; Schramm, U.; Seco, J.

Background and aims
In FLASH radiotherapy (RT), a protective effect of healthy tissue was observed, while tumor control remains comparable to conventional RT[1]. One possible explanation is the oxygen depletion hypothesis, in which radiolysis of water/cytoplasma causes the production of radicals that then react with O2 dissolved in water.
This would cause a reduction in O2, which results in a hypoxic target and thus a radio-protective effect.
In a previous study[2], we measured O2 depletion in sealed water phantoms during irradiation at high dose rates (<300 Gy/s) for protons, carbon ions and photons.
Methods
In the study presented here, this experiment was conducted further to ultra-high dose rates (10^9 Gy/s) with protons at DRACO and electrons at ELBE, where also the impact of different pulse structures on O2 depletion was tested. In addition, various settings were tested in order to irradiate zebrafish embryos with FLASH while simultaneously measuring O2.
Results and Conclusion
We were able to confirm the results of the previous study even at ultra-high dose rates and with electrons and came to two conclusions:
1. not enough O2 was depleted at clinical doses to explain a FLASH effect based on radiation-induced hypoxia
2. the amount of O2 depleted per dose depends on dose rate, and higher dose rates deplete slightly less O2.
Furthermore, it was possible to measure O2 depletion during zebrafish embryo irradiation making a simultaneous study of biological response and O2 depletion possible.

[1]Favaudon, et al. (2014) https://doi.org/10.1126/scitranslmed.3008973
[2]Jansen, et al. (2021) https://doi.org/10.1002/mp.14917

Related publications

  • Lecture (Conference) (Online presentation)
    Flash Radiotherapy and Particle Therapy Conference, 01.-03.12.2021, Wien, Österreich

Permalink: https://www.hzdr.de/publications/Publ-33835
Publ.-Id: 33835


Bewertung verschiedener Messverfahren zur Ermittlung des axialen Dispersionskoeffizienten der Gasphase in Blasensäulen mittels Volumenstrommodulation

Marchini, S.; Bieberle, A.; Schleicher, E.; Schubert, M.; Hampel, U.

Dispersionsphänomene bestimmen die Verweilzeit fluider Phasen in Gas-Flüssigkeits-Kontaktapparaten und damit das Prozessverhalten erheblich. Mit dem axialen Dispersionsmodell (ADM) kann die Auswirkung der Dispersion auf Prozesse bereits bei der Auslegung berücksichtigt werden. Dies setzt allerdings eine zuverlässige Quantifizierung des axialen Dispersionskoeffizienten voraus.
Die herkömmlichen Ansätze zur Messung axialer Dispersionskoeffizienten basieren auf dem Einsatz von Tracer-Substanzen, die mit dem Gas- oder Flüssigkeitsstrom injiziert werden. Aufgrund ihres invasiven Charakters sind diese Verfahren kaum universell anwendbar, können schädliche Verunreinigungen und Prozessstillstände verursachen und die physikalischen Eigenschaften der Flüssigkeit verändern.
Von Hampel [1] wurde kürzlich ein neuartiger, nicht-intrusiver Ansatz zur Bestimmung des axialen Gasdispersionskoeffizienten D_G in Blasensäulen entwickelt. Im Gegensatz zum Einsatz von Tracer-Substanzen basiert dieser Ansatz auf einer aufgeprägten sinusförmigen Modulation um einen konstanten Gaseintrittsvolumenstrom. Dies führt zu einer Modulation des Gasholdups ϵ(t,x) in der Blasensäule. Die Amplitude der aufsteigenden Holdupwelle wird durch die Gasdispersion gedämpft und in der Phase verschoben. Amplitudendämpfung V und Phasenverschiebung Δϕ können experimentell gemessen und mit dem Wert des axialen Dispersionskoeffizienten unter Verwendung des eindimensionalen ADM in Beziehung gesetzt werden. Im Rahmen einer Machbarkeitsstudie von Döß et al. [2] wurde gezeigt, dass mittels sinusförmig aufgelöster Gammastrahlen-Densitometrie die Bestimmung der Amplitudendämpfung und der Phasenverschiebung zwischen zwei axialen Säulenpositionen – und damit die Berechnung des axialen Dispersionskoeffizienten – möglich ist. Abbildung 1 zeigt das Prinzip und den Versuchsaufbau.
Der Betrieb von Gammastrahlenquellen im industriellen Umfeld erfordert einige Aufwendungen für den Strahlenschutz. Daher wurde in dieser Studie die Verwendung alternativer, nicht-strahlungsbasierter Techniken zur Messung der Gasholdupwelle untersucht. Eingesetzt wurden dabei insbesondere Differenzdrucksensoren, Leitfähigkeitssensoren und optische Nadelsonden. Da keine der genannten Techniken den Holdup direkt misst, wurden jeweils Strategien zur Berechnung der Amplitudendämpfung und der Phasenverschiebung ausgearbeitet.
Um nachweisbare Amplituden- und Phasenänderungen an ausgewählten axialen Positionen zu gewährleisten und gleichzeitig das hydrodynamische Verhalten nicht zu verändern, wurden verschiedene Gasmodulationsschemata in Bezug auf die initiale Modulationsamplitude und -frequenz untersucht. Die mit den Techniken verbundenen experimentellen Unsicherheiten wurden ebenfalls quantifiziert.

Dispersion phenomena significantly determine the residence time of fluid phases in gas-liquid contact apparatus and thus the process behaviour. With the axial dispersion model (ADM), the effect of dispersion on processes can already be taken into account during design. However, this requires a reliable quantification of the axial dispersion coefficient.
The conventional approaches to measuring axial dispersion coefficients are based on the use of tracer substances injected with the gas or liquid flow. Due to their invasive nature, these methods are hardly universally applicable, can cause harmful contamination and process downtime, and alter the physical properties of the liquid.
A novel, non-intrusive approach to determine the axial gas dispersion coefficient D_G in bubble columns was recently developed by Hampel [1]. In contrast to the use of tracer substances, this approach is based on an imposed sinusoidal modulation around a constant gas inlet volume flow. This leads to a modulation of the gas holdup ϵ(t,x) in the bubble column. The amplitude of the rising holdup wave is damped by the gas dispersion and shifted in phase. Amplitude damping V and phase shift Δϕ can be measured experimentally and related to the value of the axial dispersion coefficient using the one-dimensional ADM. Within the framework of a feasibility study by Döß et al [2], it was shown that by means of sinusoidally resolved gamma-ray densitometry the determination of the amplitude attenuation and the phase shift between two axial column positions - and thus the calculation of the axial dispersion coefficient - is possible. Figure 1 shows the principle and the experimental setup.
The operation of gamma radiation sources in an industrial environment requires some expenditure for radiation protection. Therefore, this study investigated the use of alternative, non-radiation-based techniques for measuring the gasoldup wave. In particular, differential pressure sensors, conductivity sensors and optical needle probes were used. Since none of the techniques mentioned directly measures the holdup, strategies for calculating the amplitude attenuation and the phase shift were worked out in each case.
To ensure detectable amplitude and phase changes at selected axial positions while not altering the hydrodynamic behaviour, different gas modulation schemes were investigated in terms of initial modulation amplitude and frequency. The experimental uncertainties associated with the techniques were also quantified.

  • Lecture (Conference) (Online presentation)
    Jahrestreffen der ProcessNet-Fachgruppen Mehrphasenströmungen, Mechanische Flüssigkeitsabtrennung sowie Zerkleinern und Klassieren, 21.-22.02.2022, online, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-33833
Publ.-Id: 33833


Effcient Calculation of the Lattice Thermal Conductivity by Atomistic Simulations with Ab Initio Accuracy

Brorsson, J.; Hashemi, A.; Fan, Z.; Fransson, E.; Eriksson, F.; Ala-Nissila, T.; Krasheninnikov, A.; Komsa, H.-P.; Erhart, P.

High-order force constant expansions can provide accurate representations of the potential energy surface relevant to vibrational mo- tion. They can be efficiently parametrized using quantum mechanical calculations and subsequently sampled at a fraction of the cost of the underlying reference calculations. Here, we combine force constant expansions via the hiphive package with GPU-accelerated molecular dynamics simulations via the GPUMD package to obtain an accurate, transferable and efficient approach for sampling the dynamical properties of materials. We demonstrate the performance of this methodology by applying it both to materials with very low thermal conductivity (Ba8Ga16Ge30, SnSe) and a material with a relatively high lattice thermal conductivity (monolayer-MoS2). These cases cover both situations with weak (monolayer-MoS2, SnSe) and strong (Ba8Ga16Ge30) phonon renormalization. The sim- ulations also enable us to access complementary information such as the spectral thermal conductivity, which allows us to discrimi- nate the contribution by different phonon modes while accounting for scattering to all orders. The software packages described here are made available to the scientific community as free and open-source software in order to encourage the more widespread use of these techniques as well as their evolution through continuous and collaborative development.

Keywords: thermal conductivity; atomistic simulations

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Permalink: https://www.hzdr.de/publications/Publ-33832
Publ.-Id: 33832


Polymorphic Phases of Metal Chlorides in the Confined 2D Space of Bilayer Graphene

Lin, Y.-C.; Motoyama, A.; Kretschmer, S.; Ghaderzadeh, S.; Ghorbani Asl, M.; Araki, Y.; Krasheninnikov, A.; Ago, H.; Suenaga, K.

Unprecedented two-dimensional (2D) metal chloride structures were grown between sheets of bilayer graphene through intercalation of metal and chlorine atoms. Numerous spatially confined 2D phases of AlCl3 and CuCl2 distinct from their typical bulk forms were found, and the transformations between these new phases under the electron beam were directly observed by in situ scanning transmission electron microscopy (STEM). Our density functional theory calculations confirmed the metastability of the atomic structures derived from the STEM experiments and provided insights into the electronic properties of the phases, which range from insulators to semimetals. Additionally, the co-intercalation of different metal chlorides was found to create completely new hybrid systems; in-plane quasi-1D AlCl3/CuCl2 heterostructures were obtained. The existence of polymorphic phases hints at the unique possibilities for fabricating new types of 2D materials with diverse electronic properties confined between graphene sheets.

Keywords: 2D materials; AlCl3; CuCl2

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Permalink: https://www.hzdr.de/publications/Publ-33831
Publ.-Id: 33831


Tunable electronic properties and enhanced ferromagnetism in Cr2Ge2Te6 monolayer by strain engineering

Liu, L.; Hu, X.; Wang, Y.; Krasheninnikov, A.; Chen, Z.; Sun, L.

Recently, as a new representative of Heisenberg's two-dimensional (2D) ferromagnetic materials, 2D Cr2Ge2Te6 (CGT) has attracted much attention due to its intrinsic ferromagnetism. Unfortunately, the Curie temperature (TC) of CGT monolayer is only 22K, which greatly hampers the development of the applications based on the CGT materials. Herein, the electronic and magnetic properties of Cr2Ge2Te6 monolayer under the applied strain was explored by density functional theory calculation. It is demonstrated that the band gap of CGT monolayer can be remarkably modulated by applying the tensile strain, which first increases and then decreases with the increase of tensile strain. In addition, it is found that the strain can increase the Curie temperature and magnetic moment, so that largely enhance the ferromagnetism of CGT monolayer. Notably, the obvious enhancement of TC by 191% is achieved at 10% strain. The results demonstrate that strain engineering can not only tune the electronic properties, but also provide a promising avenue to improve the ferromagnetism of CGT monolayer. The remarkable electronic and magnetic response to biaxial strain can also facilitate the development of CGT-based spin devices.

Keywords: Cr2Ge2Te6; Magnetic properties; Strain engineering

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Permalink: https://www.hzdr.de/publications/Publ-33830
Publ.-Id: 33830


Data publication: Impact of intervention on the spread of COVID-19 in India: A model based study

Senapati, A.; Rana, S.; Das, T.; Chattopadhyay, J.

This contains a set of MATLAB scripts and data that were used to generate the figures and results in the manuscripts.

Keywords: COVID-19; Mathematical modelling; Basic reproduction number; Intervention; Outbreak; India

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Permalink: https://www.hzdr.de/publications/Publ-33828
Publ.-Id: 33828


Combine single-shot coherent transition radiation spectroscopy and imaging to determine the µm/fs-scale electron phase-space of laser-plasma accelerators

Debus, A.; La Berge, M.

Goal: Determine the three dimensional, µm-scale structure of relativistic electron beams in single-shot acquisition.
Measurements: Single-shot CTR spectroscopy (200nm – 12µm) + electron spectra and profiles + far-field and near-field imaging (~10 CCDs, 400-1000nm)
Data extraction challenge: Solve inverse problem to determine the initial 3D electron distribution.

  • Lecture (others) (Online presentation)
    Laserlab-Europe: Network on Data Analysis in Imaging and Spectroscopy -- Kick-off meeting, 30.3.2021, Virtuell, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-33827
Publ.-Id: 33827


PIConGPU at NERSC

Debus, A.; Lebedev, A.; Pausch, R.; Steiniger, K.; Bastrakov, S.; Widera, R.; Stephan, J.; Leinhauser, M.; Hübl, A.; Chatterjee, A.

After briefly introducing PIConGPU and its typical science cases we detail the team plan for the NERSC hackathon 2021 at Perlmutter.

Keywords: PIC simulation; plasma radiation; Liénard-Wiechert potentials; HPC

  • Lecture (others) (Online presentation)
    NERSC hackathon 2021 at Perlmutter, 19.-28.7.2021, Virtuell, USA

Permalink: https://www.hzdr.de/publications/Publ-33826
Publ.-Id: 33826


Development of common input/output standards of Particle In Cell (PIC) codes and associated in-situ and post-processing tools

Debus, A.; Bertini, D.; Hornung, J.; Vincenti, H.; Quere, F.; Maslarova, D.; Krus, M.; Vieira, J.

JRA PRISES, Task 2.5: Development of common input/output standards of Particle-In-Cell (PIC) codes and associated in-situ and post-processing tools, Status reports and collaboration meetings

  • Lecture (others) (Online presentation)
    Laserlab-Europe JRA PRISES Task 2.5 -- Status report, 30.4.2021, Virtuell, Deutschland
  • Lecture (others) (Online presentation)
    Collaboration meeting for Laserlab Europe JRA PRISES 2.5, 3.6.2021, Virtuell, Deutschland
  • Lecture (others)
    Joint JRA Meeting, 13.-14.6.2022, GSI, Darmstadt, Deutschland
  • Lecture (others) (Online presentation)
    Laserlab-Europe JRA PRISES Task 2.5 -- Task meeting, 29.11.2022, HZDR, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-33825
Publ.-Id: 33825


Relativistic laser plasma physics in a nutshell

Debus, A.; Kluge, T.

Lecture for the HZDR summer students on the fundamentals of relativistic laser plasma physics.

  • Lecture (others)
    Lecture series for the HZDR summer students 2021, 27.07.-23.8.2021, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-33824
Publ.-Id: 33824


Digital twins of Laser-plasma interactions

Debus, A.; Pausch, R.; Kluge, T.; Vorberger, J.; Hoffmann, N.

Digital twin challenges:

* Hybrid LWFA+PWFA accelerator -- a compact plasma wakefield accelerator
* Scaling plasma ion accelerators to therapeutical energies -- high precision control of the plasma dynamics using ultra-intense ultra-short laser pulses
* Producing, probing, and simulating warm dense matter -- X-ray scattering and first principle simulations

Joining forces in meeting these challenges:

* Road to Exascale for particle-in-cell code PIConGPU
* From particle-in-cell simulation to surrogate models -- surrogate modelling and reconstruction of LWFA by invertible neural networks
* DFT and Monte Carlo as first principle input for PIC and MHD simulations.

  • Lecture (Conference) (Online presentation)
    DMA-ST3 Meeting, 18.5.2021, Virtuell, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-33823
Publ.-Id: 33823


Knowledge extraction in Laser-plasma simulations -- A case study on why start-to-end simulations are just the beginning

Debus, A.; Pausch, R.; Köhler, A.; Schöbel, S.; Couperus Cabadağ, J. P.; Irman, A.; Schramm, U.; Bussmann, M.

Based on a recent laser-wakefield acceleratror experiment studying the electron beam dynamics during acceleration using betatron radiation diagnostics, we present the knowledge-extraction challenges in modeling recent experiments with particle-in-cell simulations such as PIConGPU.

Lessons learnt:

* Matching experiment and simulation results via start-to-end simulations is essential, but not the end. It is the beginning for knowledge extraction to gain physics understanding.
* In-situ diagnostics toolkit needs to be flexible enough to minimize post-processing.
* Reduced models help distinguishing, understanding and excluding different physics processes.
* Particularly intermediate simulation states, such as particle distributions after ionization injection, need to be filterable and interfacable to other codes (--> openPMD).
* Outlook: Next generation of simulations requires more than one order more data. In-situ diagnostics and machine-learning methods need to be further extended.

Keywords: PIC simulations; LWFA; betatron radiation; knowledge extraction; openPMD

  • Lecture (Conference) (Online presentation)
    DMA-ST3 Meeting 2021, 18.5.2021, Virtuell, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-33822
Publ.-Id: 33822


Exascale Plasma-Accelerator Simulations with PIConGPU

Debus, A.; Kluge, T.; Widera, R.; Bastrakov, S.; Steiniger, K.; Garten, M.; Lebedev, A.; Pausch, R.; Meyer, F.; Pöschel, F.; Kelling, J.; Juckeland, G.; Stephan, J.; Herten, A.; Chandrasekaran, S.; Leinhauser, M.; Young, J.; Davis, J. H.; Diaz, J. M.; Huebl, A.; Hernandez, B.; Chatterjee, R.; Rogers, D.; Bussmann, M.

* Next-generation Laser-plasma Accelerators (protons and electrons) require fast and predictive 3D particle-in-cell simulations at the exascale.
* PIConGPU is performance portable & available as a single source through Alpaka.
* PIConGPU scales to the largest supercomputers of the world, leveraging Alpaka for running on the latest GPUs from NVIDIA (A100) and AMD (MI100)
* HIP & OpenMP 5+ backends now available on Alpaka and PIConGPU.
* PIConGPU performance scales on Juwels Booster and Summit machines.

Starting from typical simulation applications and requirements in laser-plasma accelerators, we present the PIConGPU software stack and current scaling results on large-scale compute clusters. We show results from the Frontier CAAR project and the JUWELS Booster early-access project.

Keywords: PIC simulation; PIConGPU; exascale computing; HPC; laser-plasma physics; Alpaka; performance portability

  • Lecture (Conference) (Online presentation)
    7th MT Meeting, 01.-3.2.2021, Virtuell, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-33821
Publ.-Id: 33821


Scaling EUV and X-ray Thomson Scattering Sources to Optical Free-Electron Laser Operation using Traveling-Wave Thomson-Scattering

Debus, A.; Steiniger, K.; Albach, D.; Bussmann, M.; Löser, M.; Pausch, R.; Röser, F.; Siebold, M.; Schramm, U.

Traveling-Wave Thomson-Scattering (TWTS) is a novel Thomson scattering geometry which allows for orders of magnitude higher photon yields than classic head-on Thomson sources. TWTS thereby remains compact and provides narrowband and ultra-short ultraviolet to γ-ray radiation pulses just as classic Thomson sources.
Even the realization of optical free-electron lasers (OFELs) is possible with the TWTS geometry since it provides both optical undulators with thousands of periods needed to microbunch the electron beam and a reduction of electron beam quality requirements compared to classic Thomson scattering to a level technically feasible today. TWTS employs a side-scattering geometry in which laser and electron propagation direction of motion enclose the interaction angle φ. Tilting the laser pulse front with respect to the wave front by half the interaction angle ensures
continuous overlap of electrons and laser pulse over the whole laser pulse width while the laser pulse crosses the electron beam trajectory. In this way the interaction length becomes controllable by the laser pulse width and independent of the laser pulse duration. Utilizing wide, petawatt class laser pulses for TWTS allows to realize thousands of optical undulator periods. The variability of TWTS with respect to the interaction angle can be used to control the radiation wavelength even for electron sources with fixed energy. For a fixed target wavelength on the other hand, the free choice of interaction angle enables control over electron beam quality requirements. Small interaction angle scenarios (φ ∼10°) typically yield the best trade-off between requirements on electron beam quality, laser power and laser intensity stability. We will show that TWTS OFELs emitting extreme ultraviolet
radiation are realizable today with existing technology for electron accelerators and laser systems. We detail an experimental setup to generate the tilted TWTS laser pulses which aims at compactness and provides focusing of these highpower pulses and compensation of dispersion accompanying pulse-front tilts. The method presented for dispersion compensation is especially relevant when building high yield X- and γ-ray sources in large interaction angle setups of TWTS.

Keywords: Traveling-wave Thomson scattering; TWTS; optical free-electron laser; FEL; laser pulse-front tilt; Thomson source; Compton source

  • Poster
    17th International Conference on the Physics of Non-Ideal Plasmas, 20.-24.9.2021, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-33820
Publ.-Id: 33820


Machine-learning to better understand radiation emitted by laser-plasma interactions

Debus, A.; Pausch, R.; Leinhauser, M.; Chandrasekaran, S.; Bussmann, M.; Bethke, F.; Willmann, A.; Dieckmann, J.; Hoffmann, N.

Radiation signatures emitted by Laser-plasma interactions are ubiquitous and are straightforward to experimentally acquire via imaging and spectroscopy. The data encodes phase-space dynamics on the smallest temporal and spatial scales. Yet such data is hard to interpret and thus is frequently discarded as being too complex. For theory and data analysis this raises several central questions: What are experimentally promising radiation signatures? What do they mean physically and are these robust and unambigous indicators?

Calculating classical radiation emitted by relativistic plasmas from all charged particles across the entire spectrum from the IR to the x-ray range and emitted into the full solid angle, while retaining coherence and polarization properties, is a prime HPC data challenge, currently requiring exascale compute capabilities. These calculations, are successfully perfomed in-situ by the particle-in-cell code PIConGPU at the cost of increasing computational requirements by several orders of magnitudes.

By exploiting machine learning techniques we aim for two goals: Speeding up calculations of these radiation signatures, as well as for improving knowledge extraction, i.e. connecting simulated and experimentally relevant radiation signatures, ideally unambigously, to the initial radiation sources and physics processes.

We introduce the data challenge and motivate how a large-scale distributed analysis of a huge set of unstructed point cloud data via an autoencoder approach, can be used to map a compressed representation to radiation diagnostics via invertible neural network. Initial results on a smaller scale of a specialized application have been encouraging: invertible neural networks based on variational autoencoders successfully have been trained on flashes of radiation in Laser-wakefield accelerators to identify and spatially localize the instances of electron injection.

Keywords: plasma radiation; machine learning; PIC simulations; autoencoder; INN; relativistic plasma physics; LWFA; PWFA

  • Lecture (Conference) (Online presentation)
    ML@HZDR Symposium 2021, 6.12.2021, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-33819
Publ.-Id: 33819


MALA (Materials Learning Algorithms)

Cangi, A.; Ellis, J. A.; Fiedler, L.; Kotik, D.; Modine, N. A.; Oles, V.; Popoola, G. A.; Rajamanickam, S.; Schmerler, S.; Stephens, J. A.; Thompson, A. P.

MALA (Materials Learning Algorithms) is a data-driven framework to generate surrogate models of density functional theory calculations based on machine learning. Its purpose is to enable multiscale modeling by bypassing computationally expensive steps in state-of-the-art density functional simulations.

Keywords: Density Functional Theory; Machine Learning

Permalink: https://www.hzdr.de/publications/Publ-33818
Publ.-Id: 33818


ReLaX: the Helmholtz International Beamline for Extreme Fields high-intensity short-pulse laser driver for relativistic laser–matter interaction and strong-field science using the high energy density instrument at the European X-ray free electron laser facility

Laso García, A.; Höppner, H.; Pelka, A.; Bähtz, C.; Brambrink, E.; Di Dio Cafiso, S. D.; Dreyer, J.; Göde, S.; Hassan, M. K. Y.; Kluge, T.; Liu, J.; Makita, M.; Möller, D.; Nakatsutsumi, M.; Preston, T. R.; Priebe, G.; Schlenvoigt, H.-P.; Schwinkendorf, J.-P.; Smid, M.; Talposi, A.-M.; Toncian, M.; Zastrau, U.; Schramm, U.; Cowan, T.; Toncian, T.

High-energy and high-intensity lasers are essential for pushing the boundaries of science. Their development has allowed leaps forward in basic research areas, including laser–plasma interaction, high-energy density science, metrology, biology and medical technology. The Helmholtz International Beamline for Extreme Fields user consortium contributes and operates two high-peak-power optical lasers using the high energy density instrument at the European X-ray free electron laser (EuXFEL) facility. These lasers will be used to generate transient extreme states of density and temperature to be probed by the X-ray beam. This paper introduces the ReLaX laser, a short-pulse high-intensity Ti:Sa laser system, and discusses its characteristics as available for user experiments. It will also present the first experimental commissioning results validating its successful integration into the EuXFEL infrastructure and viability as a relativistic-intensity laser driver.

Keywords: X-ray Free Electron Laser; High-intensity laser; relativistic intensity laser; Ti:Sa laser

Permalink: https://www.hzdr.de/publications/Publ-33817
Publ.-Id: 33817


Simulation of highly divergent Optical Beams

Kotik, D.; Götte, J. B.

Optical-beams-MEEP [1] provides a Cython module and several Python/Scheme scripts for spatio-temporal simulation of various optical beams in two and three dimensions. The provided scripts are designed to serve as configurations files for the powerful Meep [2] tool, an established open-source FDTD simulation software package for electromagnetic fields. The objective of these scripts is the simulation of reflection and refraction of highly divergent polarised optical beams at plane and curved dielectric interfaces. Currently supported are Gaussian beams (2d), Laguerre-Gaussian beams (3d) and Airy beams (2d).
Utilizing Meep to simulate the propagation of a Gaussian beam in a homogeneous medium is fairly easy: specifying its real valued current distribution at waist is sufficient. However, for highly divergent beams with the waist being placed at or close to an intersection of regions of different optical properties, this requires specifying the exact complex-valued current distribution at a certain distance to the beam's waist. This is typically done by calculating the beam profile via a plane wave decomposition which involves integration of the real and imaginary parts of a highly oscillating integrand. Meep's deprecated Guile/Scheme interface could handle this with a fast numeric integration routine. With Python however, due to its expensive function call overhead, multiple integration becomes such a computationally intense task by itself that it would put Meep's Python interface almost useless for the considered simulation tasks.
In order to overcome this problem, we developed a Python extension module based on Cython, employing highly optimized C code that can be called from within Python. Since SciPy's adaptive quadrature routine allows for low-level compiled functions, we manage to completely circumvent Python's tremendous overhead when calling the integrand functions many times.
In conclusion, our module allows for using Meep's more modern, easier to use Python interface while keeping the computational overhead low.

References

[1] Daniel Kotik, & Jörg Götte. https://github.com/DanielKotik/Optical-beams-MEEP/. Zenodo. http://doi.org/10.5281/zenodo.369179
[2] https://github.com/NanoComp/meep

Keywords: FDTD; Meep; Cython; Gaussian beam

  • Poster (Online presentation)
    720. WE-Heraeus-Seminar / Structures in Confined Light - from Topology to Microscopy, 16.-17.08.2021, online, Germany

Permalink: https://www.hzdr.de/publications/Publ-33816
Publ.-Id: 33816


Role of the metal supply pathway on silicon patterning by oblique ion beam sputtering

Redondo-Cubero, A.; Palomares, F. J.; Lorenz, K.; Rubio-Zuazo, J.; Hübner, R.; Mompéan, F. J.; García-Hernández, M.; Castro, G. R.; Vázquez, L.

The dynamics of the pattern induced on a silicon surface by oblique incidence of a 40 keV Fe ion beam is studied. The results are compared with those obtained for two reference systems, namely a noble gas ion beam either without or with Fe co-deposition. The techniques employed include Atomic Force Microscopy, Rutherford Backscattering Spectrometry, Transmission Electron Microscopy, X-ray Photoelectron and hard X-ray photoelectron spectroscopies, as well as Superconducting Quantum Interference Device measurements. The Fe-induced pattern differs from those of both reference systems since a pattern displaying short hexagonal ordering develops, although it shares some features with them. In both Fe systems a chemical pattern, with iron silicide-rich and -poor regions, is formed upon prolonged irradiation. The metal pathway has a marked influence on the patterns’ morphological properties and on the spatial correlation between the chemical and morphological patterns. It also determines the iron silicide stoichiometry and the surface pattern magnetic properties that are better for the Feimplanted system. These results show that in ion-beam-induced silicon surface patterning with reactive metals, the metal supply pathway is critical to determine not only the morphological pattern properties, but also the chemical and magnetic ones.

Keywords: Surface nanopatterning; Ion beam sputtering; Silicon; Magnetic properties; Silicides; Iron

Related publications

Permalink: https://www.hzdr.de/publications/Publ-33811
Publ.-Id: 33811


Current driven kink instabilities in relativistic jets: dissipation properties

Bodo, G.; Mamatsashvili, G.; Rossi, P.; Mignone, A.

We analyze the evolution of current driven kink instabilities of a highly magnetized relativistic plasma column, focusing in particular on its dissipation properties. The instability evolution leads to the formation of thin current sheets where the magnetic energy is dissipated. We find that the total amount of dissipated magnetic energy is independent of the dissipation properties. Dissipation occurs in two stages: a peak when the instability saturates, which is characterized by the formation of a helicoidal current sheet at the boundary of the deformed plasma column, followed by a weaker almost flat phase, in which turbulence develops. The detailed properties of these two phases depend on the equilibrium configuration and other parameters, in particular on the steepness of the pitch radial profile, on the presence of an external axial magnetic field and on the amount of magnetization. These results are relevant for high energy astrophysical sources, since current sheets can be the sites of magnetic reconnection where particles can be accelerated to relativistic energies and give rise to the observed radiation.

Keywords: galaxies:jets; methods:numerical; MHD instabilities; magnetic reconnection; turbulence

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Permalink: https://www.hzdr.de/publications/Publ-33810
Publ.-Id: 33810


Towards new cutting edge MRI experiments

Mamatsashvili, G.; Mishra, A.; Stefani, F.

We present recent progress on the development of standard MRI and its variants -- helical and azimuthal MRI -- in a liquid sodium cylindrical Taylor-Couette (TC) flow in connection with a new large-scale experimental campaign planned at Helmholtz-Zentrum Dresden-Rossendorf (HZDR), which is devoted to the detection of this instability in the lab. Currently, a new TC experimental device is under construction and will be put in operation in 2022. In preparation for these experiments, we performed targeted linear and nonlinear study of MRI for those values of key parameters (Lundquist, Reynolds, magnetic Prandtl numbers, etc) relevant for the upcoming experiments and show its feasibility under new experimental conditions. After that we will present the current status and preparatory work for these experiments at HZDR. Due to very small magnetic Prandtl numbers of liquid metals used, the Reynolds numbers needed to excite MRI in experiments are extremely high, of the order of million. For this reason the instability has always remained evasive in the previous TC experiments. The large size of the experimental device and a wide range of rotation rates are among the main advantages of our new TC device, which offer a unique possibility to reach such high Reynolds numbers and hence to capture MRI in the lab. However, a careful further analysis is required in this case to correctly disentangle MRI modes from other possible instabilities at high Reynolds numbers arising in a finite-length TC flow under the effect of the top and bottom endcaps.

Keywords: Taylor-Couette flow; Magnetohydrodynamics; Magnetorotational instability

  • Invited lecture (Conferences)
    Spinning Fluids 2021: Laboratory Fluid Dynamics for Disks and Planets, 05.-10.09.2021, Ringberg Castle, Kreuth, Bavaria, Germany

Permalink: https://www.hzdr.de/publications/Publ-33809
Publ.-Id: 33809


Flexible and printable magnetic field sensors

Makarov, D.

The talk will summarize our application-oriented activities on flexible and printable magnetic field sensors.

Keywords: flexible magnetic field sensors; printable magnetic field sensors

Related publications

  • Lecture (Conference) (Online presentation)
    Flexible Electronics and Sensors for Health Workshop (Healthtronics EU – Japan Bridge), 31.01.2022, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-33808
Publ.-Id: 33808


Skin conformal and printable magnetoelectronics for human-machine interfaces and soft robotics

Makarov, D.

Motion sensing is the primary task in numerous disciplines including industrial robotics, prosthetics, virtual and augmented reality appliances. In rigid electronics, rotations, displacements and vibrations are typically monitored using magnetic field sensors. Here, we will discuss the fabrication of flexible [1-3], stretchable [4,5] and printable [5] magnetoelectronic devices. The technology platform relies on high-performance magnetoresistive and Hall effect sensors deposited or printed on ultrathin polymeric foils. These skin conformal flexible and printable magnetosensitive elements enable touchless interactivity with our surroundings based on the interaction with magnetic fields [6], which is relevant for electronics skins [3,5], smart wearables [1,4,5], soft robotics [2] and human-machine interfaces [1,3-5,7].

[1] P. Makushko et al., “Flexible Magnetoreceptor with Tunable Intrinsic Logic for On-Skin Touchless Human-Machine Interfaces”, Adv. Funct. Mater. 31, 2101089 (2021).

[2] M. Ha et al., “Reconfigurable Magnetic Origami Actuators with On-Board Sensing for Guided Assembly”, Adv. Mater. 33, 2008751 (2021).

[3] G. S. Canon Bermudez et al., “Electronic-skin compasses for geomagnetic field driven artificial magnetoreception and interactive electronics”, Nature Electronics 1, 589 (2018).

[4] G. S. Canon Bermudez et al., “Magnetosensitive e-skins with directional perception for augmented reality”, Science Advances 4, eaao2623 (2018).

[5] M. Ha et al., “Printable and Stretchable Giant Magnetoresistive Sensors for Highly Compliant and Skin-Conformal Electronics”, Adv. Mater. 33, 2005521 (2021).

[6] G. S. Canon Bermudez et al., “Magnetosensitive E-Skins for Interactive Devices”, Adv. Funct. Mater. 31, 2007788 (2021).

[7] J. Ge et al., “A bimodal soft electronic skin for tactile and touchless interaction in real time”, Nature Communications 10, 4405 (2019).

Keywords: flexible magnetic field sensors; printable magnetic field sensors; magnetic soft robots

Related publications

  • Invited lecture (Conferences)
    International Intelligent Materials-IIM 2022, 29.06.-01.07.2022, Kiel, Germany

Permalink: https://www.hzdr.de/publications/Publ-33807
Publ.-Id: 33807


From curvilinear magnetism to shapeable magnetoelectronics

Makarov, D.

I had a pleasure and honor to work with Yuri Gaididei on the topic of curvature effects in magnetism, which is now emerged in a new research field known as curvilinear magnetism. Our cooperation started back in 2013 with a visit of Prof. Gaididei and his team to the Leibniz Institute for Solid State and Materials Research Dresden. The outcome of numerous discussions, which we had during that visit, was the foundational work on the description of curvature effects in magnetic thin films [1]. This work pushed the understanding of the experimental data to the qualitatively new level and predicted numerous effects stemming from the geometry induced anisotropic and chiral interactions. In my talk, I will discuss the experimental realisations of geometrically curved low-dimensional architectures and their characterization, which among others resulted in the experimental confirmation of the geometrically induced chiral effects [2] predicted by Yuri Gaididei. Geometrically curved magnetic thin films are interesting not only fundamentally. They are the key component of mechanically flexible magnetic field sensors. I will briefly outline our activities on the so-called shapeable magnetoelectronics, which includes flexible, stretchable and printable magnetic field sensors for the realisation of human-machine interfaces [3,4], interactive electronics for virtual [5] and augmented [6] reality applications and soft robotics [7] to mention just a few. The presence of the geometrical curvature in a magnetic thin film influences pinning of magnetic domain walls and in this respect it affects the sensitivity of mechanically flexible magnetic field sensors. This is an intimate link between the fundamental topic of curvilinear magnetism and application-oriented activities on shapeable magnetoelectornics. This link will be discussed in the presentation as well.

[1] Y. Gaididei et al., “Curvature Effects in Thin Magnetic Shells”, Physical Review Letters 112, 257203 (2014).
[2] O. Volkov et al., “Experimental observation of exchange-driven chiral effects in curvilinear magnetism”, Physical Review Letters 123, 077201 (2019).
[3] P. Makushko et al., “Flexible Magnetoreceptor with Tunable Intrinsic Logic for On-Skin Skin Touchless Human-Machine Interfaces”, Advanced Functional Materials 31, 2101089 (2021).
[4] J. Ge et al., “A bimodal soft electronic skin for tactile and touchless interaction in real time”, Nature Communications 10, 4405 (2019).
[5] G. S. Canon Bermudez et al., “Electronic-skin compasses for geomagnetic field driven artificial magnetoception and interactive electronics”, Nature Electronics 1, 589 (2018).
[6] G. S. Canon Bermudez et al., “Magnetosensitive e-skins with directional perception for augmented reality”, Science Advances 4, eaao2623 (2018).
[7] M. Ha et al., “Reconfigurable Magnetic Origami Actuators with On-Board Sensing for Guided Assembly”, Advanced Materials 33, 2008751 (2021).

Keywords: curvature effects in magnetism; curvilinear magnetism; flexible magnetoelectronics; printable magnetic field sensors

Related publications

  • Invited lecture (Conferences) (Online presentation)
    Yuri Gaididei memorial workshop, 02.-03.02.2022, Kyiv, Ukraine

Permalink: https://www.hzdr.de/publications/Publ-33806
Publ.-Id: 33806


Curvilinear magnetism: fundamentals and applications

Makarov, D.

In this presentation, I reviewed our activities on flexible and printable magnetic field sensors for the realization of human-machine interfaces, interactive virtual and augmented reality applications and soft robotics.

Keywords: flexible magnetic field sensors; printable magnetic field sensors; magnetic soft robots

Related publications

  • Lecture (others) (Online presentation)
    Lu Jiaxi International Team Annual Meeting, 10.12.2021, Ningbo, China

Permalink: https://www.hzdr.de/publications/Publ-33805
Publ.-Id: 33805


Impact of intervention on the spread of COVID-19 in India: A model based study

Senapati, A.; Rana, S.; Das, T.; Chattopadhyay, J.

The outbreak of coronavirus disease 2019 (COVID-19), caused by the virus severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has already created emergency situations in almost every country of the world. The disease spreads all over the world within a very short period of time after its first identification in Wuhan, China in December, 2019. In India, the outbreak, starts on 2nd March, 2020 and after that the cases are increasing exponentially. Very high population density, the unavailability of specific medicines or vaccines, insufficient evidences regarding the transmission mechanism of the disease also make it more difficult to fight against the disease properly in India. Mathematical models have been used to predict the disease dynamics and also to assess the efficiency of the intervention strategies in reducing the disease burden. In this work, we propose a mathematical model to describe the disease transmission mechanism between the individuals. Our proposed model is fitted to the daily new reported cases in India during the period 2nd March, 2020 to 12th November, 2020. We estimate the basic reproduction number, effective reproduction number and epidemic doubling time from the incidence data for the above-mentioned period. We further assess the effect of implementing preventive measures in reducing the new cases. Our model projects the daily new COVID-19 cases in India during 13th November, 2020 to 25th February, 2021 for a range of intervention strength. We also investigate that higher intervention effort is required to control the disease outbreak within a shorter period of time in India. Moreover, our analysis reveals that the strength of the intervention should be increased over the time to eradicate the disease effectively.

Keywords: COVID-19; Mathematical modelling; Basic reproduction number; Intervention; Outbreak; India

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Permalink: https://www.hzdr.de/publications/Publ-33803
Publ.-Id: 33803


Data publication: Mineral quantification at deposit scale using drill-core hyperspectral data: A case study in the Iberian Pyrite Belt

de La Rosa Ferna; Khodadadzadeh, M.; Tusa, L.; Kirsch, M.; Gisbert, G.; Tornos, F.; Tolosana Delgado, R.; Gloaguen, R.

We present a semi-automated workflow for large scale interpretation of Hyperspectral data, founded on a novel approach of mineral mapping based on a supervised dictionary learning technique. This approach exploits the complementary information from scanning electron microscopy based automated mineralogy and hyperspectral imaging techniques for estimating mineral quantities along all boreholes. We propose that it is effectively possible to propagate the mineral quantification to the entire borehole from small samples with high resolution mineralogical information strategically selected throughout the deposit. In order to apply this type of research techniques aiming at a 3D model of the alteration areas of the entire deposit based on the hyperspectral data, it is essential to have the availability of drill cores along the whole extension of the mineral deposit. Consequently, the research was focused in a study area in the Southern Spain, the Elvira deposit of the MATSA–VALORIZA mining company, where 7 km of drill core were scanned with the hyperspectral sensors. This data repository contains 24 SEM-MLA mineral maps used as training data for the Multi-scale multi-sensor data co-registration and dictionary learning algorithm.

Keywords: Hyperspectral data; Drill-cores; Mineral quantification; Dictionary learning; Machine learning; 3D modelling

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Permalink: https://www.hzdr.de/publications/Publ-33801
Publ.-Id: 33801


Mineral quantification at deposit scale using drill-core hyperspectral data: A case study in the Iberian Pyrite Belt

de La Rosa Ferna; Khodadadzadeh, M.; Tusa, L.; Kirsch, M.; Gisbert, G.; Tornos, F.; Tolosana Delgado, R.; Gloaguen, R.

Drill-core analysis is paramount for the characterization of deposits in mineral exploration. Over the past years, the use of hyperspectral (HS) sensors has rapidly increased to improve the reliability and efficiency of core logging. However, scanning drill-core samples of an entire mineral deposit entails several complex challenges, from transport logistics to large scale data management and analysis. Hence, academic studies on new applications of drill-core HS data at a mineral deposit scale remain rare.
We present a semi-automated workflow for large scale interpretation of HS data, founded on a novel approach of mineral mapping based on a supervised dictionary learning technique. This approach exploits the complementary information from scanning electron microscopy based automated mineralogy and hyperspectral imaging techniques for estimating mineral quantities along all boreholes. We propose that it is effectively possible to propagate the mineral quantification to the entire borehole from small samples with high resolution miner- alogical information strategically selected throughout the deposit.
We showcase this approach on data acquired in the Elvira shale-hosted volcanogenic massive sulphide (VMS) deposit located at the Iberian Pyrite Belt (IPB), where 7000 m of drill-core were acquired along 80 boreholes. Resulting maps provide insights on the controls on the mineral assemblages and chemical composition of specific minerals across the whole volume at several spatial scales, from large scale variations within apparently ho- mogeneous black shales to small scale mineral composition variations, of potential use as vectors towards mineralization. This approach adds value to the core data, allowing for a better understanding of the geological setting of the Elvira deposit and providing valuable insights for future exploration targeting in the region.
This approach based on machine learning can easily be transposed to different ore deposits with a limited input from a geologist.

Keywords: Hyperspectral data; Drill-cores; Mineral quantification; Dictionary learning; Machine learning; 3D modelling

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Permalink: https://www.hzdr.de/publications/Publ-33800
Publ.-Id: 33800


Surrogate Modeling of Ion Acceleration with Invertible Neural Networks

Miethlinger, T.; Garten, M.; Göthel, I.; Hoffmann, N.; Schramm, U.; Kluge, T.

The interaction of overdense plasma with ultra-intense laser pulses presents a promising approach to enable the development of very compact ion sources. Prospective applications of high-energetic protons and ions include, but are not limited to, medical applications (in particular ion beam radiotherapy), laboratory astrophysics and nuclear fusion. However, current records for maximum proton energies (94 MeV, 2018) are still below the required values for the aforementioned applications (typically in the range of 150-250 MeV), and especially challenges such as stability and spectral control remain unsolved to this day. In particular, significant effort per experiment and a high-dimensional design space renders naive sampling approaches ineffective. Furthermore, due to the strong nonlinearities of the underlying laser-plasma physics, synthetic observations by means of particle-in-cell (PIC) simulations are computationally very costly, and the maximum distance between two sampling points is strongly limited as well. Consequently, in order to build useful surrogate models for future data generation and experimental understanding and control, a combination of highly optimized simulation codes (where we employ PIConGPU), powerful data-based methods, such as artificial neural networks (ANNs), and modern sampling approaches are essential.
Specifically, we employ invertible neural networks for bidirectional learning of input (parameter) and output (observables) and convolutional autoencoder to reduce intermediate field data to a lower-dimensional latent representation.

Keywords: Laser-Plasma; Ion Acceleration; Target Normal Sheath Acceleration; Machine Learning; Surrogate Modeling; Invertible Neural Networks

Related publications

  • Poster
    17th International Conference on the Physics of Non-Ideal Plasmas, 20.-24.09.2021, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-33799
Publ.-Id: 33799


Surrogate Modelling of Ion Acceleration and Overdense Laser-Plasma Interactions

Miethlinger, T.; Garten, M.; Göthel, I.; Hoffmann, N.; Schramm, U.; Kluge, T.

Interaction of an overdense plasma with ultra-intense laser pulses represents a promising route to enable the development of compact ion sources. Prospective applications of high-energetic protons and ions include, but are not limited to, medical applications, materials science and nuclear fusion. However, current records for maximum proton energies (94 MeV, Higginson Nat Commun 9, 724 2018) are still well below the required values for many applications (typically 150-250 MeV) and many challenges remain unsolved to this day. In particular, a high-dimensional parameter space, as well as considerable effort per observation, make it impossible to uniformly sample the parameter space by means of simulations, let alone experimentally, while simultaneously strong nonlinearities limit the coarseness of the grid. Consequently, a combination of modern sampling approaches, optimized simulation codes and powerful data-based methods are essential for building realistic surrogate models. More specifically, we want to employ invertible neural networks (Ardizzone arXiv:1808.04730, 2018) for bidirectional learning of input and output, and convolutional autoencoder (Vincent J. Mach. Learn. Res. 11, 12 2010) to reduce intermediate field data to a lower-dimensional latent representation.

Keywords: Laser-Plasma; Ion Acceleration; Particle-in-cell; Machine Learning; Surrogate Modeling

Related publications

  • Poster (Online presentation)
    Helmholtz AI Virtual Conference 2021, 14.-15.04.2021, Online, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-33798
Publ.-Id: 33798


Control of site occupancy by variation of the Zn and Al content in NiZnAl ferrite epitaxial films with low magnetic damping

Lumetzberger, J.; Ney, V.; Zhakarova, A.; Primetzhofer, D.; Lenz, K.; Ney, A.

The structural and magnetic properties of Zn/Al doped nickel ferrite thin films can be adjusted by changing the Zn and Al content. The films are epitaxially grown by reactive magnetron sputtering using a triple cluster system to sputter simultaneously from three different targets. Upon the variation of the Zn content the films remain fully strained with similar structural properties, while the magnetic properties are strongly affected. The saturation magnetization and coercivity as well as resonance position and linewidth from ferromagnetic resonance (FMR) measurements are altered depending on the Zn content in the material. The reason for these changes can be elucidated by investigation of the x-ray magnetic circular dichroism spectra to gain site and valence specific information with elemental specificity. Additionally, from a detailed investigation by broadband FMR a minimum in g-factor and linewidth could be found as a function of film thickness. Furthermore, the results from a variation of the Al content using the same set of measurement techniques is given. Other than for Zn, the variation of Al affects the strain and even more pronounced changes to the magnetic properties are apparent.

Keywords: Spinel; Ferromagnetic resonance; damping; epitaxial films; XMCD; Ferrites

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Permalink: https://www.hzdr.de/publications/Publ-33797
Publ.-Id: 33797


The Influence of the internal domain wall structure on spin wave band structure in periodic magnetic stripe domain

Gruszecki, P.; Banerjee, C.; Mruczkiewicz, M.; Hellwig, O.; Barman, A.; Krawczyk, M.

The magnetization dynamics in periodic magnetic stripe domain patterns in thin ferromagnetic films is summarized. First, a brief theoretical background of magnetization dynamics and spin wave dynamics in the presence of a single domain wall for various configuration of magnetic domains (in-plane and out-of-plane) and domain walls (Bloch- and Néel-type domain walls) is introduced. Then, spin wave dynamics in periodic stripe magnetic domain pattern is studied on an example of a multilayer system composed of Co/Pd. The considered magnetization configuration is non-collinear across both the domain walls and the film thickness. It has the form of a “corkscrew”-like structure that consists of a Bloch wall in the film's center with two Néel caps at the film's surfaces. All domain walls have the same polarity. The Brillouin light scattering measurements were performed to study magnetization dynamics experimentally, and the results were interpreted with the use of micromagnetic simulations. The periodic arrangement of the magnetization increases the number of spin wave bands similarly like a one-dimensional magnonic crystal. The properties of the dynamical excitation related to translational motion of the domain wall (zero-frequency Goldstone modes) are shown. Further, the dynamics of the magnetization configurations with the same and alternating polarities of the neighboring walls are compared. The magnetization dynamics for the propagation along the domain walls direction is analyzed, as well. Here, the interaction between the walls and nonreciprocal properties result in the formation of unidirectional channels, where waves travel in every second wall in the opposite direction.

Keywords: Spin Waves; Domain wall; Magnonics; Magnonic crystal; Magnetization dynamics

Permalink: https://www.hzdr.de/publications/Publ-33796
Publ.-Id: 33796


Effective Static Approximation: A Fast and Reliable Tool for Warm-Dense Matter Theory

Dornheim, T.

Warm dense matter is of high current interest for many applications, including astrophysics, material science, and fusion research. Yet, the accurate description of electronic correlation effects at these conditions is most difficult, and often computationally intensive ab-initio methods have to be used. Here we present the effective static approximation (ESA) [1] to the local field correction (LFC) of the electron gas, which enables highly accurate calculations of electronic properties like the dynamic structure factor S(q,ω), the static structure factor S(q), and the interaction energy v with no computational extra cost compared to the random phase approximation (RPA).
More specifically, the ESA combines the recent neural-net representation of ab-initio path integral Monte Carlo results [2] of the temperature-dependent LFC in the exact static limit with a consistent large wave-number limit. It is suited for a straightforward integration into existing codes. We demonstrate the importance of the LFC for practical applications by re-evaluating the recent x-ray Thomson scattering experiment on aluminum by Sperling et al. [3]. We find that an accurate incorporation of electronic correlations within the ESA leads to a different prediction of the inelastic scattering spectrum than obtained from state-of-the-art models like linear-response time-dependent density functional theory. Furthermore, the ESA scheme is particularly relevant for the development of advanced exchange-correlation functionals in density functional theory, or for the computation of material properties like the thermal/electrical conductivity, stopping power, etc.
Finally, the ESA is now readily available as an analytical representation [4] and can be easily incorporated into existing codes.

[1] T. Dornheim et al., Phys. Rev. Lett. 125, 235001 (2020)
[2] T. Dornheim et al., J. Chem. Phys. 151, 194104 (2019)
[3] P. Sperling et al., Phys. Rev. Lett. 115, 115001 (2015)
[4] T. Dornheim et al., Phys. Rev. B 103, 165102 (2021)

  • Lecture (others)
    17th International Conference on the Physics of Non-Ideal Plasmas, 20.-24.09.2021, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-33795
Publ.-Id: 33795


Effective Static Approximation: A Fast and Reliable Tool for Warm-Dense Matter Theory

Dornheim, T.

Warm dense matter is of high current interest for many applications, including astrophysics, material science, and fusion research. Yet, the accurate description of electronic correlation effects at these conditions is most difficult, and often computationally intensive ab-initio methods have to be used. Here we present the effective static approximation (ESA) [1] to the local field correction (LFC) of the electron gas, which enables highly accurate calculations of electronic properties like the dynamic structure factor S(q,ω), the static structure factor S(q), and the interaction energy v with no computational extra cost compared to the random phase approximation (RPA).
More specifically, the ESA combines the recent neural-net representation of ab-initio path integral Monte Carlo results [2] of the temperature-dependent LFC in the exact static limit with a consistent large wave-number limit. It is suited for a straightforward integration into existing codes. We demonstrate the importance of the LFC for practical applications by re-evaluating the recent x-ray Thomson scattering experiment on aluminum by Sperling et al. [3]. We find that an accurate incorporation of electronic correlations within the ESA leads to a different prediction of the inelastic scattering spectrum than obtained from state-of-the-art models like linear-response time-dependent density functional theory. Furthermore, the ESA scheme is particularly relevant for the development of advanced exchange-correlation functionals in density functional theory, or for the computation of material properties like the thermal/electrical conductivity, stopping power, etc.

[1] T. Dornheim et al., Phys. Rev. Lett. 125, 235001 (2020)
[2] T. Dornheim et al., J. Chem. Phys. 151, 194104 (2019)
[3] P. Sperling et al., Phys. Rev. Lett. 115, 115001 (2015)

  • Lecture (others) (Online presentation)
    41st International Workshop on High Energy Density Physics with Intense Ion and Laser Beams, 02.02.2021, Hirsschegg, Austria

Permalink: https://www.hzdr.de/publications/Publ-33794
Publ.-Id: 33794


Ab-initio description of Warm Dense Matter: Goals, challenges, and opportunities

Dornheim, T.

Warm dense matter (WDM)---an extreme state that is characterized by extreme densities and temperatures---has emerged as one of the most active frontiers in plasma physics and material science. In nature, WDM occurs in astrophysical objects such as giant planet interiors and brown dwarfs. In addition, WDM is highly important for cutting-edge technological applications such as inertial confinement fusion and the discovery of novel materials.
In the laboratory, WDM is studied experimentally in large facilities around the globe, and new techniques have facilitated unprecedented insights into exciting phenomena like the formation of nano diamonds at planetary interior conditions [1]. Yet, the interpretation of these experiments requires a reliable diagnostics based on accurate theoretical modeling, which is a notoriously difficult task [2].
In this talk, I give an overview of recent ground-breaking developments in WDM theory, including its static [3], dynamic [4], and nonlinear [5] properties. Finally, I will present a road map towards a true ab-initio description of WDM.

[1] D. Kraus et al., Nature Astronomy 1, 606-611 (2017)
[2] M. Bonitz et al., Physics of Plasmas 27, 042710 (2020)
[3] T. Dornheim et al., Physics Reports 744, 1-86 (2018)
[4] T. Dornheim et al., Physical Review Letters 121, 255001 (2018)
[5] T. Dornheim et al., Physical Review Letters 125, 085001 (2020)

  • Lecture (others) (Online presentation)
    Physikalisches Kolloquium der Universität zu Kiel, 07.12.2021, Kiel, Germany

Permalink: https://www.hzdr.de/publications/Publ-33793
Publ.-Id: 33793


Ab initio path integral Monte Carlo results for the dynamic and static density response of correlated electrons

Dornheim, T.

Over the last decades, there has emerged a growing interest in warm dense matter (WDM), an exotic state with extreme densities and temperatures. These conditions are relevant for, e.g., the description of astrophysical objects and laser-excited solids, but a theoretical description is notoriously difficult.

In this work, we focus on the uniform electron gas (UEG), one of the most fundamental model systems in physics and quantum chemistry. Although most ground state properties of the UEG have been known for decades, a full thermodynamic description at WDM conditions has only been achieved recently [1,2]. In this contribution, we extend these considerations to the response of the UEG to an external perturbation, which is of key relevance both for theory and the interpretation of experiments.

More specifically, we have carried out extensive path integral Monte Carlo simulations of the UEG going from WDM conditions to the strongly correlated electron liquid regime to compute an imaginary-time density—density correlation function. The latter is subsequently used as input for a new reconstruction procedure, which allows to obtain ab initio results for the dynamic structure factor including all exchange-correlation effects [3,4]. Interestingly, we find nontrivial shapes around intermediate wave vectors, which manifest in a negative dispersion relation at strong coupling.

Moreover, we present extensive new results and a subsequent machine-learning representation of the static local field correction [5], which is of high importance for many applications, and new results for the electron liquid regime [6].

[1] S. Groth et al., Phys. Rev. Lett. 119, 135001 (2017)
[2] T. Dornheim et al., Phys. Reports 744, 1-86 (2018)
[3] T. Dornheim et al., Phys. Rev. Lett. 121, 255001 (2018)
[4] S. Groth et al., Phys. Rev. B 99, 235122 (2019)
[5] T. Dornheim et al., J. Chem. Phys. 151, 194104 (2019)
[6] T. Dornheim et al., Phys. Rev. B 101, 045129 (2020)

  • Invited lecture (Conferences) (Online presentation)
    PACIFICHEM, 16.-22.12.2021, Hawaii (virtual), USA

Permalink: https://www.hzdr.de/publications/Publ-33792
Publ.-Id: 33792


Assessment of inclined rotating fixed-bed reactors – Modeling and characterization

Timaeus, R.; Hampel, U.; Schubert, M.

In this contribution, the process intensification potential of the advanced reactor concept is demonstrated and a hybrid modeling approach is proposed, which allows assessing the STY and identifying optimal operating conditions. The model consists of a 3D Eulerian-Eulerian model and a 1D heterogeneous continuum model to predict hydrodynamics (i.e. gas-liquid interface position and pressure drop), mass transfer and reaction.

Keywords: inclined rotating fixed-bed reactor; hybrid modeling approach; hydrodynamics and reactor performance

  • Lecture (Conference) (Online presentation)
    26th International Symposium on Chemical Reaction Engineering, 05.-08.12.2021, Delhi, Indien

Permalink: https://www.hzdr.de/publications/Publ-33791
Publ.-Id: 33791


Data for "Dissociating the phononic, magnetic and electronic contributions to thermal conductivity: a computational study in α-iron"

Cangi, A.; Ramakrishna, K.; Lokamani, M.

This repository contains the data and script to generate the electronic component of the thermal conductivity in iron (alpha phase) relevant for the linked publication.

Keywords: Density functional theory; Electron transport properties; Thermal conductivity; Electrical conductivity

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Permalink: https://www.hzdr.de/publications/Publ-33790
Publ.-Id: 33790


Improving I/O Performance for Exascale Applications Through Online Data Layout Reorganization

Wan, L.; Hübl, A.; Gu, J.; Pöschel, F.; Gainaru, A.; Wang, R.; Chen, J.; Liang, X.; Ganyushin, D.; Munson, T.; Foster, I.; Vay, J.-L.; Podhorszki, N.; John Wu, K.; Klasky, S.

The applications being developed within the U.S. Exascale Computing Project (ECP) to run on imminent Exascale computers will generate scientific results with unprecedented fidelity and record turn-around time. Many of these codes are based on particle-mesh methods and use advanced algorithms, especially dynamic load-balancing and mesh-refinement, to achieve high performance on Exascale machines. Yet, as such algorithms improve parallel application efficiency, they raise new challenges for I/O logic due to their irregular and dynamic data distributions. Thus, while the enormous data rates of Exascale simulations already challenge existing file system write strategies, the need for efficient read and processing of generated data introduces additional constraints on the data layout strategies that can be used when writing data to secondary storage. We review these I/O challenges and introduce two online data layout reorganization approaches for achieving good tradeoffs between read and write performance. We demonstrate the benefits of using these two approaches for the ECP particle-in-cell simulation WarpX, which serves as a motif for a large class of important Exascale applications. We show that by understanding application I/O patterns and carefully designing data layouts we can increase read performance by more than 80 percent.

Keywords: parallel IO; data layout IO; IO performance; WarpX; data access optimization

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Permalink: https://www.hzdr.de/publications/Publ-33789
Publ.-Id: 33789


Understanding and leveraging the I/O patterns of emerging machine learning analytics

Gainaru, A.; Ganyushin, D.; Xie, B.; Kurc, T.; Saltz, J.; Oral, S.; Podhorszki, N.; Pöschel, F.; Hübl, A.; Klasky, S.

The scientific community is currently experiencing unprecedented amounts of data generated by cutting-edge science facilities. Soon facilities will be producing up to 1 PB/s which will force scientist to use more autonomous techniques to learn from the data. The adoption of machine learning methods, like deep learning techniques, in large-scale workflows comes with a shift in the workflow’s computational and I/O patterns. These changes often include iterative processes and model architecture searches, in which datasets are analyzed multiple times in different formats with different model configurations in order to find accurate, reliable and efficient learning models. This shift in behavior brings changes in I/O patterns at the application level as well at the system level. These changes also bring new challenges for the HPC I/O teams, since these patterns contain more complex I/O workloads. In this paper we discuss the I/O patterns experienced by emerging analytical codes that rely on machine learning algorithms and highlight the challenges in designing efficient I/O transfers for such workflows. We comment on how to leverage the data access patterns in order to fetch in a more efficient way the required input data in the format and order given by the needs of the application and how to optimize the data path between collaborative processes. We will motivate our work and show performance gains with a study case of medical applications.

Keywords: emerging HPC applications; deep learning methods; I/O patterns; I/O optimization; data management

  • Contribution to proceedings
    Smoky Mountains Computational Sciences & Engineering Conference (SMC2021), 18.-20.10.2021, Oak Ridge, USA

Permalink: https://www.hzdr.de/publications/Publ-33788
Publ.-Id: 33788


openPMD – API and Hands-on Session

Pöschel, F.; Hübl, A.

The openPMD-api is a library for the description of scientific data according to the Open Standard for Particle-Mesh Data (openPMD). Its approach towards recent challenges posed by hardware and workflow heterogeneity lies in the decoupling of data description in domain sciences from concrete implementations in hardware and IO. This is reflected in the openPMD standard which defines the logical structure, but not the physical implementation of scientific data. This seminar talk gives an introduction on the openPMD standard as well as the openPMD-api. Two live demonstrations show how to write and read openPMD data in Python, and how to visualize openPMD data in the openPMD-viewer.

Keywords: openPMD; high-performance computing; IO; ADIOS; HDF5; streaming

  • Invited lecture (Conferences)
    Workshop on SAXS@XFELs and HI & HE laser driven matter, 04.-05.11.2021, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-33787
Publ.-Id: 33787


X-ray radiation transport in GPU accelerated Particle In Cell simulations

Ordyna, P.; Kluge, T.; Schramm, U.; Cowan, T.

Ultra-high-intensity laser pulse interactions with solid density targets are of central importance for modern accelerator physics, Inertial Confinement Fusion(ICF) and astrophysics.

In order to meet the requirements of real-world applications, a deeper understanding of the underlying plasma dynamics, including plasma instabilities and acceleration mechanisms, is needed.

Due to high electron density, the over-dense target bulk is impenetrable to probes in the optical range.
Hence, several X-ray diagnostics, such as small-angle X-ray scattering (SAXS) and X-ray polarimetry, were proposed by the community.

Therefore, we bring a Monte Carlo based X-ray radiation transport module into our Particle In Cell simulation framework PIConGPU. Among others, this allows for Thompson scattering, e.g. for SAXS, and Faraday effect calculation for polarimetry - as online, in-situ diagnostics.

  • Lecture (Conference) (Online presentation)
    Workshop on SAXS@XFELs and HI & HE laser driven matter, 05.11.2021, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-33786
Publ.-Id: 33786


Anisotropic microwave propagation in a reconfigurable chiral spin soliton lattice

Shimamoto, Y.; Trindade Goncalves, F. J.; Sogo, T.; Kousaka, Y.; Togawa, Y.

We investigated microwave propagation in the chiral spin soliton lattice (CSL) phase of micrometer-sized crystals of the monoaxial chiral helimagnet
CrNb₃S₆. An advantage of the CSL is that its periodicity can be reconfigured over a macroscopic length scale by means of an external magnetic field. Using a two-antenna microwave spectroscopy technique, we measured the anisotropic response of the transmitted microwaves via the spin dynamics of the CSL. When propagating along the direction parallel to the helical axis, the microwave amplitude increased up to a factor of twenty with decreasing the number of chiral soliton kinks. When the propagation direction was rotated by 90 degrees with regards to the helical axis, the microwave amplitude increased by one order of magnitude upon formation of the chiral helimagnetic order in the vicinity of zero magnetic field, exceeding that of the ferromagnetic phase above the critical field. Our findings open a novel route for controlling the characteristics of microwave propagation using noncollinear spin textures.

Keywords: Spin waves; Chiral magnets; Ferromagnetic resonance

Permalink: https://www.hzdr.de/publications/Publ-33785
Publ.-Id: 33785


Analysis of scheelite ore with scanning electron microscopy (2D) and X-ray computer tomography (3D), and correlation of data with Deep Learning methods

Hellmuth, F.

This thesis demonstrates a combination of three consecutive methods to achieve reliable phase classification in a 3D-image of particulate material obtained by X-ray computed tomography (CT). The method consists of 1.) sample preparation to minimise the effect of image artefacts on the CT-scan and enable the subsequent analysis with Scanning Electron Microscopy (SEM) techniques, 2.) Alignment of 2D SEM-based phase classification to a specific location in the 3D-image and 3.) implementation of the 2D-mineral classification as training data for a Convolutional Neural Network (CNN). The trained neural network enables phase segmentation of the particles in the 3D-image based on the 2D-phase classification.

Keywords: X-Ray Computed Tomography; Scheelite; Deep learning; Mineralogy; Scanning Electron Microscopy

  • Master thesis
    TU Bergakademie Freiberg, 2021
    Mentor: Prof. Bernhard Schulz; Dr. Axel Renno
    71 Seiten

Permalink: https://www.hzdr.de/publications/Publ-33782
Publ.-Id: 33782


Testing the robustness of particle-based separation models for the magnetic separation of a complex skarn ore

Pereira, L.; Frenzel, M.; Buchmann, M.; Kern, M.; Tolosana Delgado, R.; van den Boogaart, K. G.; Gutzmer, J.

Physical separation processes are best understood in terms of the behaviour of individual ore particles. Yet, while different empirical particle-based separation modelling approaches have been developed, their predictive performance has never been tested under variable process conditions. Here, we investigated the predictive performance of a state-of-the-art particle-based separation model under variable feed composition for a laboratory-scale magnetic separation of a skarn ore. Two scenarios were investigated: one in which the mass flow of the different processing streams could be measured and one in which it had to be estimated from data. In both scenarios, the predictive models were sufficiently general to predict the process outcomes of new samples of variable composition. Nevertheless, the scenario in which mass flow could be measured was ≈ 4% more precise in predicting mass balances. The process behaviour of minerals present at concentrations above 0.1 wt% could be accurately predicted. Our findings indicate the potential use of this method to minimize the costs of metallurgical testwork while providing in-depth understanding of the recovery behaviour of individual ore particles. Moreover, the method may be used to establish powerful tools to forecast mineral recoveries for partly new ore types at a running mining operation.

Keywords: Metallurgical tests; particle-based separation modelling; magnetic separation; cassiterite recovery

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Permalink: https://www.hzdr.de/publications/Publ-33781
Publ.-Id: 33781


Self-powered Stretchable Strain Sensors for Motion Monitoring and Wireless Control

Li, S.; Cao, P.; Li, F.; Asghar, W.; Wu, Y.; Xiao, H.; Liu, Y.; Zhou, Y.; Yang, H.; Zhang, Y.; Shang, J.; Makarov, D.; Li, R.-W.

Smart skins and smart textiles equipped with strain sensors for motion detection are of prime significance for personalized health monitoring, lifestyle and fitness applications. Yet, the dependence of these devices on wired power supplies and rigid batteries limits their use in everyday settings. Here, we report self-powered and highly elastic strain sensors withstanding stretching to 200% for monitoring the human motion. The sensor is based on a torsional-spring-shaped coil of liquid metal wound around an elastomeric tubing and equipped with a tiny piece of a magnetic ring. The energy is harvested from the body motion relying on the Faraday’s law of electromagnetic induction when the coil is exposed to a time-varying magnetic field of the magnetic ring upon the mechanical deformation of the strain sensor. The max short-circuit current is 2mA, which is much higher than previous work, and the peak power of our device is 20 µW, sufficiently high to drive conventional low-power electronics. We demonstrate the application potential of our sensor for wearable electronics for monitoring the motion of arms and legs during fitness workout and riding bicycle. The sensor can measure motion of fingers and wrist for health applications and establish wireless control of robotic hands.

Keywords: Stretchable strain sensor; Liquid metal; Self-powered; Electromagnetic induction; Human health monitoring

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Permalink: https://www.hzdr.de/publications/Publ-33780
Publ.-Id: 33780


Structural Templating of an Organic Solar Cell Absorber by Ellagic Acid To Tune Its Aggregation, Molecular Orientation, and Optical Properties

Bittrich, E.; Domke, J.; Levichkova, M.; Jehnichen, D.; Bittrich, L.; Janke, A.; Formanek, P.; Hübner, R.; Uhlmann, P.; Eichhorn, K.-J.; Forker, R.; Gruenewald, M.; Al-Hussein, M.; Fritz, T.; Walzer, K.

Structural templating with homogeneous template layers is one of the strategies for controlling the orientation of small molecular absorbers in the photoactive layer of an organic solar cell to increase its power conversion efficiency. A main challenge thereby is the energetic alignment of the template molecules to the photoactive and charge-transporting materials. In the present study, the effects of a cluster-like template layer of ellagic acid (EA) on the morphology and optical properties of side-chain-substituted dicyanovinyl quaterthiophene (DCV4T-Et2) thin films are discussed. In the monolayer regime, J-aggregation of DCV4T-Et2 is confirmed. Insertion of the EA template layer leads to an improved aggregation behavior and formation of J-aggregates in DCV4T-Et2 films near the EA interface. The orientation of DCV4T-Et2 molecules in 30 nm thick films changes from “edge-on” to “face-on” due to a π−π interaction between the flat-lying EA molecules and the DCV4T-Et2 molecules. The face-on orientation by templating is preserved in blend layers with C60, and a considerable increase in the crystallinity of the DCV4T-Et2 phase in the blend is induced. Organic solar cells based on templated DCV4T-Et2:C60 active layers exhibit more than a 50% increase in the efficiency compared to nontemplated active layers. The short-circuit current density and the fill factor are significantly improved. Although the energetic alignment of EA is not ideal, no additional open-circuit voltage losses were observed with templating, due to the cluster-like morphology of the EA layer. Our results demonstrate a cluster-like templating approach with the novel template molecule EA to tailor the molecular orientation, crystallinity, and consequently optical properties of organic semiconducting molecules without significant energetic losses favorable for use in organic electronics.

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Permalink: https://www.hzdr.de/publications/Publ-33779
Publ.-Id: 33779


Research data: Electrical tunability of terahertz nonlinearity in graphene

Kovalev, S.; Hafez, H. A.; Tielrooij, K.-J.; Deinert, J.-C.; Ilyakov, I.; Awari, N.; Alcaraz, D.; Soundarapandian, K.; Saleta, D.; Germanskiy, S.; Chen, M.; Bawatna, M.; Green, B. W.; Koppens, F. H. L.; Mittendorff, M.; Bonn, M.; Gensch, M.; Turchinovich, D.

This research data publications contains the sorted pulse-resolved data and metadata corresponding to the linked publication: Electrical tunability of terahertz nonlinearity in graphene.

The final data evaluation and preparation of figures was done externally by Dr. Hassan Hafez, who should be contacted in terms of assigning raw data to data shown in publication.

Keywords: Graphene; THz-driven dynamics; Terahertz; Dirac material; Electrical gating; High harmonic generation; Optoelectronics; Ultrafast

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Permalink: https://www.hzdr.de/publications/Publ-33778
Publ.-Id: 33778


Physical properties of liquid oxygen under ultrahigh magnetic fields

Nomura, T.; Ikeda, A.; Gen, M.; Matsuo, A.; Kindo, K.; Kohama, Y.; Matsuda, Y. H.; Zherlitsyn, S.; Wosnitza, J.; Tsuda, H.

We studied the acoustic properties of liquid oxygen up to 90 T by means of ultrasound measurements. We observed a monotonic decrease of the sound velocity and an asymptotic increase of the sound attenuation when applying magnetic fields. The unusual attenuation, twenty times as large as the zero-field value, suggests strong fluctuations of the local molecular arrangement.We assume that the observed fluctuations are related to a liquid-liquid transition or crossover, from a small-magnetization to a large-magnetization liquid, which is characterized by a local-structure rearrangement. To investigate higher-field properties of liquid oxygen, we performed single-turn-coil experiments up to 180 T by means of the acoustic, dilatometric, magnetic, and optical techniques. We observed only monotonic changes of these properties, reflecting the absence of the proposed liquid-liquid transition in our experimental conditions.

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Permalink: https://www.hzdr.de/publications/Publ-33777
Publ.-Id: 33777


ComputationalRadiationPhysics/picongpu: C++14, New Solvers, I/O via openPMD API, HIP Support

Bastrakov, S.; Bastrakova, K.; Marre, B. E.; Debus, A.; Garten, M.; Gruber, B. M.; Hübl, A.; Trojok, J.; Kelling, J.; Lebedev, A.; Meyer, F.; Ordyna, P.; Pöschel, F.; Sprenger, L.; Steiniger, K.; Wang, M.; Starke, S.; Thévenet, M.; Pausch, R.; Widera, R.

This release switches to C++14 as minimum required version. Transition to C++17 is planned for upcoming releases.

We extended PIConGPU with a few new solvers. Binary collisions are now available. We added arbitrary-order FDTD Maxwell's solver. All field solvers are now compatible with perfectly matched layer absorber, which became default. Yee solver now supports incident field generation using total field/scattered field technique. We added Higuera-Cary particle pusher and improved compatibility of pushers with probe species. Implementation of particle boundaries was extended to support custom positions, reflecting and thermal boundary kinds were added.

With this release, PIConGPU fully switches to openPMD API library for performing I/O. The native HDF5 and ADIOS output plugins were replaced with a new openPMD plugin. All other plugins were updated to use openPMD API. Plugins generally support HDF5 and ADIOS2 backends of openPMD API, a user can choose file format based on their installation of openPMD API. We also added new plugins for SAXS and particle merging.

We added support for HIP as a computational backend. In particular, it allows running on AMD GPUs. Several performance optimizations were added. Some functors and plugins now have performance-influencing parameters exposed to a user.

The code was largely modernized and refactored, documentation was extended.

Thanks to Sergei Bastrakov, Kseniia Bastrakova, Brian Edward Marre, Alexander Debus, Marco Garten, Bernhard Manfred Gruber, Axel Huebl, Jakob Trojok, Jeffrey Kelling, Anton Lebedev, Felix Meyer, Paweł Ordyna, Franz Poeschel, Lennert Sprenger, Klaus Steiniger, Manhui Wang, Sebastian Starke, Maxence Thévenet, Richard Pausch, René Widera for contributions to this release!

Keywords: C++; HPC; CUDA; HIP; Particle-in-Cell; PIConGPU; Laser; Plasma

  • Software in external data repository
    Publication year 2021
    Programming language: C++, Python, Shell, CMake, Dockerfile, Awk
    System requirements: Computer
    License: GPLv3+, LGPLv3+, CC-BY 4.0 (Link to license text)
    Hosted on https://github.com/ComputationalRadiationPhysics/picongpu: Link to location
    DOI: 10.5281/zenodo.5795557

Permalink: https://www.hzdr.de/publications/Publ-33776
Publ.-Id: 33776


Efficient optical-to-terahertz conversion in large-area InGaAs photo-Dember emitters with increased indium content

Ilyakov, I.; Shishkin, B. V.; Malevich, V. L.; Ponomarev, D. S.; Galiev, R. R.; Pavlov, A. Y.; Yachmenev, A. E.; Kovalev, S.; Chen, M.; Akhmedzhanov, R. A.; Khabibullin, R. A.

In this Letter, optical-to-terahertz (THz) conversion of 800 nm femtosecond laser pulses in large-area bias-free InGaAs emitters based on photo-Dember (PD) and lateral photo-Dember (LPD) effects is experimentally investigated. We use metamorphic buffers to grow sub-micrometer thick In𝑥Ga1−𝑥As layers with indium mole fractions 𝑥=0.37, 0.53, and 0.70 on a GaAs substrate. A strong enhancement of THz output energy with an increase of indium content is observed. On the surface of the sample providing the strongest emission (𝑥=0.7), we have fabricated a 1.5cm² area of asymmetrically shaped metallic grating for LPD emission. This LPD emitter allows achieving high conversion efficiency of 0.24⋅10−3 and a broad generation bandwidth of up to 6 THz. We also demonstrate that there is no significant difference in the conversion efficiency when operating at 1 and 200 kHz repetition rates. Our results show that large-area LPD emitters give a convenient, competitive way to generate intense high-repetition-rate THz pulses.

Keywords: Terahertz; Terahertz emitter; Photo Dember

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