Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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39008 Publications

Accelerating Equilibration in First-Principles Molecular Dynamics with Orbital-Free Density Functional Theory

Fiedler, L.; Moldabekov, Z.; Shao, X.; Jiang, K.; Dornheim, T.; Pavanello, M.; Cangi, A.

We introduce a practical hybrid approach that combines orbital-free density functional theory (DFT) with Kohn-Sham DFT for speeding up first-principles molecular dynamics simulations. Equilibrated ionic configurations are generated using orbital-free DFT for subsequent Kohn-Sham DFT molecular dynamics. This leads to a massive reduction of the simulation time without any sacrifice in accuracy. We assess this finding across systems of different sizes and temperature, up to the warm dense matter regime. To that end, we use the cosine distance between the time series of radial distribution functions representing the ionic configurations. Likewise, we show that the equilibrated ionic configurations from this hybrid approach significantly enhance the accuracy of machine-learning models that replace Kohn-Sham DFT. Our hybrid scheme enables systematic first-principles simulations of warm dense matter that are otherwise hampered by the large numbers of atoms and the prevalent high temperatures. Moreover, our finding provides an additional motivation for developing kinetic and noninteracting free energy functionals for orbital-free DFT.

Keywords: Density Functional Theory; Machine Learning

Permalink: https://www.hzdr.de/publications/Publ-34778
Publ.-Id: 34778


Stable Multi-Day Performance and Diagnosis of the DRACO Laser Wakefield Accelerator for Secondary Applications

Couperus Cabadağ, J. P.; Bock, S.; Chang, Y.-Y.; Debus, A.; Gebhardt, R.; Helbig, U.; Irman, A.; Koehler, A.; Kurz, T.; Guntram Pausch, R.; Püschel, T.; Schoebel, S.; Ufer, P.; Zarini, O.; Zeil, K.; Lumpkin, A.; Schramm, U.; Ghaith, A.; Downer, M.; Laberge, M.

We report on the operation of the DRACO Laser Driven electron source for stable multi-day operation of secondary applications with demanding beam requirements. The nC-class accelerator delivers charge densities around 10 pC/MeV*, 1 mrad rms divergence at energies up to 0.5 GeV and peak currents of over 10kA**. Precise characterisation is paramount for controlled operation of demanding applications, this includes: spectrally resolved charge diagnostic, source size diagnostics based both on betatron radiation*** as well as on coherent optical transition radiation (TR) to resolve microbunch beam structures**** and TR-based multioctave high-dynamic range spectrometry for sub-fs resolved characterisation of the 10 fs rms electron bunches**. Achieved stability allows systematic exploration of applications, resulting in the recent demonstration of the first LWFA based Beam-driven Plasma Wakefield Accelerator*****. In an effort toward LWFA based Free Electron Lasing, the COXINEL manipulation line developed at Synchrotron SOLEIL was recently installed at our facility. At initial commissioning, successful beam transport was achieved with over 13000 delivered shots within 9 experimental days.

* J.P. Couperus et al., Nat. Comm. 8 (2017)
** O. Zarini et al., PRAB (2022)
*** A. Köhler et al., PRAB (2021)
**** A. Lumpkin et al., PRL 125 (2020)
***** T. Kurz et al., Nat. Comm. 12 (2021)

  • Poster
    13th International Particle Accelerator Conference (IPAC’22), 12.-17.06.2022, Bangkok, Thailand

Permalink: https://www.hzdr.de/publications/Publ-34777
Publ.-Id: 34777


Untersuchung der Wechselwirkung von Uran(VI) mit den Biofluiden des menschlichen Verdauungssystems sowie mit Nierenzellen

Butscher, D.; Senwitz, C.; Steudtner, R.; Heller, A.; Stumpf, T.; Barkleit, A.

Wenn Radionuklide (RN) in die Nahrungskette gelangen und vom Menschen aufgenommen werden, stellen sie aufgrund ihrer Radio- und Chemotoxizität ein mögliches Gesundheitsrisiko dar. Dabei kommen die RN nach der oralen Aufnahme zuerst mit den Biofluiden des Verdauungssystems in Kontakt und interagieren mit diesen. Die Ausscheidung der Schwermetalle erfolgt größtenteils renal. Für die Entwicklung einer schnellen sowie effizienten Methode zur Dekorporation der RN ist es notwendig, die biokinetischen Prozesse sowie die Speziation im Verdauungs- und Ausscheidungssystem zu kennen. Ziel dieser Arbeit ist es daher, die Wechselwirkungen von Uran(VI) mit den Biofluiden des menschlichen Verdauungssystems, mit den gastrointestinalen Verdauungssegmenten Magen und Dünndarm sowie des gesamten Verdauungssystems auf molekularer Ebene zu untersuchen. Für die Simulierung der Biofluide wurden Speichel, Magen-, Pankreassaft und Gallenflüssigkeit sowie die Verdauungssegmente basierend auf der menschlichen Physiologie synthetisch hergestellt.[1] Die chemische Speziation wurde mittels zeitaufgelöster laserinduzierter Fluoreszenz-Spektroskopie unter kryogenen Bedingungen (Kryo-TRLFS) bei 153 K untersucht sowie die Ergebnisse mit thermodynamischen Modellierungen verglichen.
Anhand der TRLFS-Experimente kann gezeigt werden, dass die Speziation von Uran überwiegend von den anorganischen Bestandteilen, hauptsächlich Carbonat und zu einem geringeren Anteil Phosphat, dominiert wird. Bei den organischen Komponenten ist lediglich das Protein Mucin bei sauren pH-Werten, wie z. B. im Magen, an der Speziation beteiligt, weshalb die Komplexierung von Mucin mit Uran(VI) genauer betrachtet wurde. Des Weiteren wurden Zellexperimente mit Nierenzellen von Menschen (HEK-293) und Ratten (NRK-52E) in vitro durchgeführt, um den Effekt von Uran auf die Zellen mittels XTT-Assays zu untersuchen. Um den biochemischen Mechanismus auf molekularer Ebene zu verstehen, wurde die Speziation von Uran im Zellkulturmedium ebenfalls mittels Kryo-TRLFS analysiert. Bei der Hauptspezies, welche auf die Zellen einwirkt, handelt es sich um eine Uranylcarbonatverbindung.
Diese Arbeit wird vom Bundesministerium für Bildung und Forschung (BMBF) unter dem Förderkennzeichen 02NUK057A gefördert und ist Teil des Verbundprojekts RADEKOR.
Referenzen:
[1] C. Wilke et al., J. Inorg. Biochem. 2017, 175, 248-258.

  • Poster
    Jahrestagung der Fachgruppe Nuklearchemie 2022, 04.-06.10.2022, Bergisch Gladbach, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-34776
Publ.-Id: 34776


Cans production of technetium-99m and technetium-101

Mayordomo, N.; Mausolf, E. J.; Johnstone, E.; Williams, D. L.; Guan, E. Y. Z.; Gary, C. K.; Davis, J.

Technetium-99m (99mTc, t1/2 = 6.007 h) has been widely used for radiodiagnostic purposes for decades, and it is still one of the most used radioisotopes worldwide with an estimated 40 million doses consumed annually. Tc-99m can be produced through various nuclear transmutation methods, but commercially speaking, it is generally derived from molybdenum-99 (99Mo, t1/2 = 65.925 h), where the origin of it is dependent upon chemistry and isotopic composition of the target material, e.g., natural or enriched Mo, or enriched 235U targets. However, the production and distribution of 99mTc relies on a complex supply-chain that has proven itself prone to disruptions in years past and was most recently observed during the SARS-CoV-2 pandemic.[1] Ultimately, this leads to delays on diagnoses of patients due to postponed imaging procedures as well as the loss of material and capital.
As a solution to this problem, the deployment of a decentralised network of compact accelerator neutron sources (CANS) for producing 99mTc and 101Tc (t1/2 = 14.22 min) using the (n,𝛾) reaction on Mo-based targetry has been proposed.[2] For example, the use of fusion-driven deuterium-deuterium (D-D) neutron generators for producing both 99mTc and 101Tc has been demonstrated along with their subsequent isolation using a separation tailored for low-specific activity 99Mo targets.[2]
Another under-utilised source of neutrons already being generated in this fashion is during the production of many positron emission tomography (PET) radionuclides in cyclotrons, where parasitic neutrons are liberated from the cyclotron target, e.g., 18O(p,n)18F. The implementation of larger production batches, high yield targetry, and more production runs are all complementary to generating neutrons. From this, the hybridised production of 99mTc and 101Tc concurrently during [18F]FDG has been demonstrated and its feasibility explored.[3]
The aim of the work presented herein is to compare various CANS production modes for 99mTc and 101Tc production in regards to their subsequent applications. Further, it provides potential alternatives for the future production of radiopharmaceuticals, meanwhile meeting the objectives of several Unesco and sustainable development goals.

REFERENCES
[1] K. SADRI, V.R. DABBAGH, M.N. FORGHANI, M. ASADI, R. SADEGUI, Lymphoscintigraphy in the Time of COVID-19: Effect of Molybdenum-99 Shortage on Feasibility of Sentinel Node Mapping, Lymphat. Res. Biol. 19 (2021) 134–140.
[2] E.J. MAUSOLF, E.V. JOHNSTONE, N. MAYORDOMO, D.L. WILLIAMS, E.Y.Z. GUAN, C.K. GARY, Fusion-Based Neutron Generator Production of Tc-99m and Tc-101 : A Prospective Avenue to Technetium Theranostics, Pharmaceuticals. 14 (2021) 1–19.
[3] E.V. JOHNSTONE, E.J. MAUSOLF. Hybridized Production of 18F and 99mTc on a Low-Energy Cyclotron. Internal Document, IFS, LLC (2021).

Keywords: Technetium; Neutron generator; Compact accelerator neutron sources; Radiopharmaceuticals

  • Lecture (Conference) (Online presentation)
    International Conference on Accelerators for Research and Sustainable Development: From Good Practices Towards Socioeconomic Impact, 23.-27.05.2022, Viena, Austria

Permalink: https://www.hzdr.de/publications/Publ-34775
Publ.-Id: 34775


Correlation Between Quantitative PSMA PET Parameters and Clinical Risk Factors in Non-Metastatic Primary Prostate Cancer Patients

Zschaeck, S.; Andela, S. B.; Amthauer, H.; Furth, C.; Rogasch, J. M.; Beck, M.; Hofheinz, F.; Huang, K.

Background

PSMA PET is frequently used for staging of prostate cancer patients. Furthermore, there is increasing interest to use PET information for personalized local treatment approaches in surgery and radiotherapy, especially for focal treatment strategies. However, it is not well established which quantitative imaging parameters show highest correlation with clinical and histological tumor aggressiveness.

Methods

This is a retrospective analysis of 135 consecutive patients with non-metastatic prostate cancer and PSMA PET before any treatment. Clinical risk parameters (PSA values, Gleason score and D’Amico risk group) were correlated with quantitative PET parameters maximum standardized uptake value (SUVmax), mean SUV (SUVmean), tumor asphericity (ASP) and PSMA tumor volume (PSMA-TV).

Results

Most of the investigated imaging parameters were highly correlated with each other (correlation coefficients between 0.20 and 0.95). A low to moderate, however significant, correlation of imaging parameters with PSA values (0.19 to 0.45) and with Gleason scores (0.17 to 0.31) was observed for all parameters except ASP which did not show a significant correlation with Gleason score. Receiver operating characteristics for the detection of D’Amico high-risk patients showed poor to fair sensitivity and specificity for all investigated quantitative PSMA PET parameters (Areas under the curve (AUC) between 0.63 and 0.73). Comparison of AUC between quantitative PET parameters by DeLong test showed significant superiority of SUVmax compared to SUVmean for the detection of high-risk patients. None of the investigated imaging parameters significantly outperformed SUVmax.

Conclusion

Our data confirm prior publications with lower number of patients that reported moderate correlations of PSMA PET parameters with clinical risk factors. With the important limitation that Gleason scores were only biopsy-derived in this study, there is no indication that the investigated additional parameters deliver superior information compared to SUVmax.

Keywords: PSMA; prostate specific membrane antigen; positron emission tomography; primary prostate cancer; quantitative PET parameters

Permalink: https://www.hzdr.de/publications/Publ-34774
Publ.-Id: 34774


Insights into the Enigmatic TcO₂·xH₂O Structure via Atomistic Simulations

Faria Oliveira, A.; Kuc, A. B.; Heine, T.; Scheinost, A.

Technetium is the lightest element without a stable isotope. The β‑emitting ⁹⁹Tc is especially relevant for nuclear waste management due to its long half-life (ca. 2.1×10⁵ years) and relatively high formation yield (≥6%) in ²³⁵U and ²³⁹Pu nuclear reactors. In this context, redox reactions at mineral/water interfaces are crucial for the safety of nuclear waste repositories.

In the absence of complexing agents, Tc exists in water as Tc(VII) and Tc(IV). The former predominates in non-reducing conditions as TcO₄⁻(aq), which is highly mobile in the environment due to its solubility and weak interaction with adsorbents. Studies show that Fe(II) minerals can reduce Tc(VII) to Tc(IV), which is then immobilized by adsorption onto or incorporation into the oxidized Fe mineral and by precipitation as TcO₂·xH₂O. However, even in the simpler case (precipitation) the structure of TcO₂·xH₂O remains controversial.

Lukens et al. [1] demonstrated that, despite being amorphous, TcO₂·xH₂O has a well-defined local structure. Based on EXAFS measurements, they proposed that TcO₂·xH₂O forms linear chains of equally spaced edge-sharing TcO₄(H₂O)₂ octahedra, with terminal H₂O ligands at the apical positions. Vichot et al. [2] obtained similar results but, despite having extracted only one Tc‑Tc distance from the EXAFS, proposed that Tc atoms would be separated by shorter and longer alternating distances as in the monoclinic TcO₂ crystal. More recently, Yalçintaş et al. [3] showed that both models can be fitted equally well to the EXAFS and, thus, the TcO₂·xH₂O structure remained unsolved.

In this work, we use density functional theory (DFT) to investigate the polymeric TcO₂·xH₂O structure. Our calculations reveal that, in contrast to previous models, a zigzag configuration with the terminal H₂O groups at neighboring positions of the octahedra is more likely. The zigzag configuration is energetically more favored and results in a better agreement with the EXAFS measurement.

[1] Lukens et al. (2002), Environ. Sci. Technol. 36, 1124-1129.
[2] Vichot et al. (2002), Radiochim. Acta 90, 575-579.
[3] Yalçintaş et al. (2016), Dalton Trans. 45, 17874-17885.

Keywords: DFT; EXAFS; Technetium

Related publications

  • Lecture (Conference) (Online presentation)
    Goldschmidt2022, 10.-15.07.2022, Honolulu, Hawaii, USA

Permalink: https://www.hzdr.de/publications/Publ-34773
Publ.-Id: 34773


Porous Dithiine-Linked Covalent Organic Framework as a Dynamic Platform for Covalent Polysulfide Anchoring in Lithium–Sulfur Battery Cathodes

Haldar, S.; Wang, M.; Bhauriyal, P.; Hazra, A.; Khan, A. H.; Bon, V.; Isaacs, M. A.; de Ankita, L. S.; Boenke, T.; Grothe, J.; Heine, T.; Brunner, E.; Feng, X.; Dong, R.; Schneemann, A.; Kaskel, S.

Dithiine linkage formation via a dynamic and self-correcting nucleophilic aromatic substitution reaction enables the de novo synthesis of a porous thianthrene-based two-dimensional covalent organic framework (COF). For the first time, this organo-sulfur moiety is integrated as a structural building block into a crystalline layered COF. The structure of the new material deviates from the typical planar interlayer stacking of the COF to form undulated layers caused by bending along the C-S-C bridge, without loss of aromaticity and crystallinity of the overall COF structure. Comprehensive experimental and theoretical investigations of the COF and a model compound, featuring the thianthrene moiety, suggest partial delocalization of sulfur lone pair electrons over the aromatic backbone of the COF decreasing the band gap and promoting redox activity.
Postsynthetic sulfurization allows for direct covalent attachment of polysulfides to the carbon backbone of the framework to afford a molecular-designed cathode material for lithium-sulfur (Li-S) batteries with a minimized polysulfide shuttle. The fabricated coin cell delivers nearly 77% of the initial capacity even after 500 charge-discharge cycles at 500 mA/g current density. This novel sulfur linkage in COF chemistry is an ideal structural motif for designing model materials for studying advanced electrode materials for Li-S batteries on a molecular level.

Keywords: Aromatic compounds; Covalent organic frameworks; Layers; Lithium; Sulfur

Permalink: https://www.hzdr.de/publications/Publ-34771
Publ.-Id: 34771


Dataset for Inversion of GISAXS data (3 layers)

Zhdanov, M.; Ganeva, M.; Randolph, L.; Kluge, T.; Hoffmann, N.

The dataset consists of 50000 X-ray diffraction patterns simulated by BornAgain [1] software. For each simulation, a multilayer sample model of the following structure was used: air, tantalum oxide, tantalum, copper nitride, silicon dioxide, and substrate. Parameters of air, silicon dioxide, and substrate were kept fixed. Hence, each diffraction pattern is set to depend on the parameters of tantalum oxide, tantalum, and copper nitride layers. For each layer, those are real and complex parts of refractive index, thickness, roughness, Hurst parameter, and correlation length. Each simulation output is stored in an h5py file consisting of 1) diffraction image as a NumPy array of shape [1200, 120]; 2) parameters of a sample as a NumPy array with 18 elements. For further details regarding simulation see https://github.com/maxxxzdn/gisaxs-reconstruction/simulation/simulation.

[1] Pospelov, G., Van Herck, W., Burle, J., Carmona Loaiza, J.M., Durniak, C., Fisher, J., Ganeva, M., Yurov, D., & Wuttke, J. (2020). BornAgain: software for simulating and fitting grazing-incidence small-angle scattering. Journal of Applied Crystallography, 53, 262 - 276.

Keywords: GISAXS; Inverse problems

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Permalink: https://www.hzdr.de/publications/Publ-34770
Publ.-Id: 34770


Dataset for Inversion of GISAXS data (1 layer)

Zhdanov, M.; Ganeva, M.; Randolph, L.; Kluge, T.; Hoffmann, N.

The dataset consists of 50000 X-ray diffraction patterns simulated by BornAgain [1] software. For each simulation, a multilayer sample model of the following structure was used: air, tantalum oxide, silicon dioxide, and substrate. Parameters of each layer but tantalum oxide were kept fixed. Hence, each diffraction pattern depends on the parameters of the tantalum oxide layer: real and complex part of refractive index, thickness, roughness, Hurst parameter, and correlation length. Each simulation output is stored in an h5py file consisting of 1) diffraction image as a NumPy array of shape [1024, 512]; 2) sample parameters as a NumPy array with 6 elements. For further details regarding simulation, see https://github.com/maxxxzdn/gisaxs-reconstruction/simulation/simulation.

[1] Pospelov, G., Van Herck, W., Burle, J., Carmona Loaiza, J.M., Durniak, C., Fisher, J., Ganeva, M., Yurov, D., & Wuttke, J. (2020). BornAgain: software for simulating and fitting grazing-incidence small-angle scattering. Journal of Applied Crystallography, 53, 262 - 276.

Keywords: GISAXS; Inverse problems

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Permalink: https://www.hzdr.de/publications/Publ-34769
Publ.-Id: 34769


Data and Scripts for "Accelerating Equilibration in First-Principles Molecular Dynamics with Orbital-Free Density Functional Theory"

Fiedler, L.; Moldabekov, Z.; Shao, X.; Jiang, K.; Dornheim, T.; Pavanello, M.; Cangi, A.

# Data and Scripts for "Accelerating Equilibration in First-Principles Molecular Dynamics with Orbital-Free Density Functional Theory"

This dataset contains data and calculation scripts for the publication "Boosting first-principles molecular dynamics with orbital-free density functional theory".
Its goal is to enable interested parties to reproduce the experiments we have carried out. 

## Prerequesites

The following software versions are needed for the python scripts:

- `python`: 3.8.x
- `mala`: 1.1.0 (with `dftpy` installed)

Further, make sure you have a working `Quantum ESPRESSO` and `VASP` installation and have downloaded additional 
data such as local pseudopotentials and ML models (for references, see publication).

## Contents

- `scripts/`: Example scripts for the three principal python tasks associated with out work: ML inference, trajectory
analysis and OF-DFT-MD runs (via DFTPy). The scripts are general blueprints for these experiments and can be adjusted
to perform all of the calculations given in the publication.
- `data/`: Contains raw calculation data for the three investigated systems (hydrogen, beryllium and aluminium).
Since the main goal of this work is to compare OF-DFT-MD initialized and ideal crystal structure initialized 
trajectories and inferences, each of the three system-folders contains a `MD_ideal_crystal_structure` and 
`MD_ofdft_init` folder, with ideal crystal structure and OF-DFT-MD initialized data, respectively. Therein, contents
may differ; e.g. aluminium contains DFT calculation data, for beryllium data is divided by system size and Nosé mass,
while for hydrogen data for different temperatures is given. 

Related publications

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Permalink: https://www.hzdr.de/publications/Publ-34767
Publ.-Id: 34767


Multiscale modelling in nuclear ferritic steels: from nano-sized defects to embrittlement

Castin, N.; Bonny, G.; Konstantinović, M. J.; Bakaev, A.; Bergner, F.; Courilleau, C.; Domain, C.; Gómez-Ferrer, B.; Hyde, J. M.; Messina, L.; Monnet, G.; Pascuet, M. I.; Radiguet, B.; Serrano, M.; Malerba, L.

Radiation-induced embrittlement of nuclear steels is one of the main limiting factors for safe long-term operation of nuclear power plants. In support of accurate and safe reactor pressure vessel (RPV) lifetime assessments, we developed a physics-based model that predicts RPV steel hardening and subsequent embrittlement as a consequence of the formation of nano-sized clusters of minor alloying elements. This model is shown to provide reliable assessments of embrittlement for a very wide range of materials, with higher accuracy than industrial correlations. The core of our model is a multiscale modelling tool that predicts the kinetics of solute clustering, given the steel chemical composition and its irradiation conditions. It is based on the observation that the formation of solute clusters ensues from atomic transport driven by radiation-induced mechanisms, differently from classical nucleation-and-growth theories. We then show that the predicted information about solute clustering can be translated into a reliable estimate for radiation-induced embrittlement, via standard hardening laws based on the dispersed barrier model. We demonstrate the validity of our approach by applying it to hundreds of nuclear reactors vessels from all over the world.

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Permalink: https://www.hzdr.de/publications/Publ-34766
Publ.-Id: 34766


Highly accessible and dense surface single metal FeN4 active sites for promoting the oxygen reduction reaction

Chen, G.; An, Y.; Liu, S.; Sun, F.; Qi, H.; Wu, H.; He, Y.; Liu, P.; Shi, R.; Zhang, J.; Kuc, A. B.; Kaiser, U.; Zhang, T.; Heine, T.; Wu, G.; Feng, X.

Single iron atom and nitrogen-codoped carbon (Fe–N–C) electrocatalysts, which have great potential to catalyze the kinetically sluggish oxygen reduction reaction (ORR), have been recognized as the most promising alternatives to the precious metal platinum. Unfortunately, the ORR properties of the existing Fe–N–C catalysts are significantly hampered by the inferior accessibility and intrinsic activity of FeN4 moieties. Here, we constructed densely exposed surface FeN4 moieties on a hierarchically porous carbon (sur-FeN4-HPC) by Fe ion anchoring and a subsequent pyrolysis strategy using the nitrogen- doped hierarchically porous carbon (NHPC) as the scaffold. The high surface area of the NHPC with abundant surface Fe anchoring sites enabled the successful fabrication of densely accessible FeN4 active moieties (34.7 􏰁x 10^19 sites g^-􏰂1) on sur-FeN4-HPC. First-principles calculations further suggested that the edge effect could regulate the electronic structure of the single Fe site, hence promoting the intrinsic ORR activity of the FeN4 moiety. As a result, the sur-FeN4-HPC electrocatalyst exhibited excellent ORR activity in acidic media with a high half-wave potential of 0.83 V (vs. the reversible hydrogen electrode). We further examined sur-FeN4-HPC as a cathode catalyst in proton exchange membrane fuel cells (PEMFCs). The membrane electrode assembly delivered a high current density of 24.2 mA cm􏰂2 at 0.9 ViR-free (internal resistance-compensated voltage) under 1.0 bar O2 and a maximum peak power den- sity of 0.412 W cm􏰂2 under 1.0 bar air. Importantly, the catalyst demonstrated promising durability during 30000 voltage cycles under harsh H2 and air conditions. The PEMFC performance of sur-FeN4-HPC outperforms those of the previously reported Fe–N–C electrocatalysts. The engineering of highly acces- sible and dense surface FeN4 sites on sur-FeN4-HPC offers a fruitful pathway for designing high- performance electrocatalysts for different electrochemical processes.

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  • Secondary publication expected from 04.05.2023

Permalink: https://www.hzdr.de/publications/Publ-34764
Publ.-Id: 34764


Lanmodulin peptides – unravelling the binding of the EF-Hand loop sequences stripped from the structural corset

Gutenthaler, S. M.; Tsushima, S.; Steudtner, R.; Gailer, M.; Hoffmann-Röder, A.; Drobot, B.; Daumann, L. J.

Lanmodulin (LanM), a naturally lanthanide (Ln)-binding protein with a remarkable selectivity for Lns over Ca(II ) and affinities in the picomolar range, is an attractive target to address challenges in Ln separation. Why LanM has such a high selectivity is currently not entirely understood; both specific amino acid
sequences of the EF-Hand loops and cooperativity effects have been suggested. Here, we removed the effect of cooperativity and synthesised all four 12-amino acid EF-Hand loop peptides, and investigated their affinity for two Lns (Eu( III) and Tb(III)), the actinide Cm(III) and Ca(II). Using isothermal titration calorimetry and time-resolved laser fluorescence spectroscopy (TRLFS) combined with parallel factor analysis, we show that the four short peptides behave very similarly, having affinities in the micromolar range for Eu(III) and Tb(III). Ca(II) was shown not to bind to the peptides, which was verified with circular dichroism spectroscopy. This technique also revealed an increase in structural organisation upon Eu(III) addition, which was supported by molecular dynamics simulations. Lastly, we put Eu(III) and Cm(III) in direct competition using TRLFS. Remarkably, a slightly higher affinity for Cm(III) was found. Our results demonstrate that the picomolar affinities in LanM are largely an effect of pre-structuring and therefore a reduction of flexibility in combination with cooperative effects, and that all EF-Hand loops possess similar affinities when detached from the protein backbone, albeit still retaining the high selectivity for lanthanides and actinides over calcium.

Permalink: https://www.hzdr.de/publications/Publ-34763
Publ.-Id: 34763


Structure-imposed electronic topology in cove-edged graphene nanoribbons

Arnold, F. M.; Liu, T.-J.; Kuc, A. B.; Heine, T.

In cove-edged zigzag graphene nanoribbons (ZGNR-C), one terminal CH group per length unit is removed on each zigzag edge, forming a regular pattern of coves which controls their electronic structure. Based on three structural parameters that unambiguously characterize the atomistic structure of ZGNR-C, we present a scheme that classifies their electronic state, i.e., if they are metallic, topological insulators or trivial semiconductors, for all possible widths N, unit lengths a and cove position offsets at both edges b, thus showing the direct structure-electronic structure relation. We further present an empirical formula to estimate the band gap of the semiconducting ribbons from N,a, and b. Finally, we identify all geometrically possible ribbon terminations and provide rules to construct ZGNR-C with well-defined electronic structure.

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Permalink: https://www.hzdr.de/publications/Publ-34762
Publ.-Id: 34762


Correlating oxidation states and electrocatalytic activity in bifunctional two-dimensional conjugated di-copper metal-organic frameworks

Maria Dominic, A.; Wang, Z.; Kuc, A. B.; Petkov, P.; Khoa Ly, H.; Lam Huong Pham, T.; Kutzschbach, M.; Cao, Y.; Bachmann, J.; Feng, X.; Dong, R.; Weidinger, I. M.

Interfacial synthetic Cu-phthalocyanine-based two-dimensional conjugated metal-organic framework (CuPc-CuO4 2D c-MOF) films were transferred to graphite electrodes and analyzed via electrochemical resonance Raman spectroscopy. Comparison of CuPc-CuO4 with the corresponding monomer, combined with Density Functional Theory (DFT) calculations allowed a detailed assignment of the vibrational bands. CuPc-CuO4 films attached to graphite electrodes via an Nickel-Nitrilo Triaacetic Acid (Ni-NTA) linker exhibited excellent bifunctional catalytic activity towards oxygen reduction (ORR) and oxygen evolution (OER) reaction. Potential dependent Raman spectroscopy yielded three different species in the respective potential window that could be assigned to an ORR active CuI/CuI state, an inactive CuII/CuI state and an CuII/CuII state that could be activated for OER. From the spectroelectrochemical data, the redox potentials of Cu in the CuPc moieties and the Cu-catecholate nodes could be determined to be ECuPc = -0.04 V and ECuO4 = 0.33 V vs. Ag|AgCl, respectively. Furthermore, DFT calculations of bandagps and density of states showed the smalest bandgap and highest -conjugation for the CuI/CuI state and the largest bandgap and lower conjugation for the mixed CuII/CuI state state, agreeing very well with the experimental activity of the species. Our results suggest that the coupling between metal oxidation changes and long range electron transfer of the 2D c-MOF is a key parameter to achieve the high electrocatalytic activity.

  • Poster
    MOF2022, 04.-07.09.2022, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-34761
Publ.-Id: 34761


Terahertz-slicing — an all-optical synchronization for 4th generation light sources

Chen, M.; de Oliveira, T.; Ilyakov, I.; Nörenberg, T.; Kuschewski, F.; Deinert, J.-C.; Awari, N.; Ponomaryov, O.; Kuntzsch, M.; Kehr, S. C.; Eng, L. M.; Gensch, M.; Kovalev, S.

A conceptually new approach to synchronizing accelerator-based light sources and external laser systems is presented. The concept is based on utilizing a sufficiently intense accelerator-based single-cycle terahertz pulse to slice a thereby intrinsically synchronized femtosecond-level part of a longer picosecond laser pulse in an electro-optic crystal. A precise synchronization of the order of 10 fs is demonstrated, allowing for real-time lock-in amplifier signal demodulation. We demonstrate successful operation of the concept with three benchmark experiments using a 4th generation accelerator-based terahertz light source, i.e. (i) far-field terahertz time-domain spectroscopy, (ii) terahertz high harmonic generation spectroscopy, and (iii) terahertz scattering-type scanning near-field optical microscopy.

Keywords: s-SNOM; Synchronization; Ultrafast Science; van der Waals; High Harmonic Generation

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Permalink: https://www.hzdr.de/publications/Publ-34759
Publ.-Id: 34759


Blacklight sintering of ceramics

Porz, L.; Scherer, M.; Huhn, D.; Heine, L.-M.; Britten, S.; Rebohle, L.; Neubert, M.; Brown, M.; Lascelles, P.; Kitson, R.; Rettenwander, D.; Fulanovic, L.; Bruder, E.; Breckner, P.; Isaia, D.; Frömling, T.; Rödel, J.; Rheinheimer, W.

For millennia, ceramics have been densified via sintering in a
furnace, a time-consuming and energy-intensive process. The need
to minimize environmental impact calls for new physical concepts
beyond large kilns relying on thermal radiation and insulation. Here,
we realize ultrarapid heating with intense blue and UV-light.
Thermal management is quantified in experiment and finite element
modelling and features a balance between absorbed and radiated
energy. With photon energy above the band gap to optimize
absorption, bulk ceramics are sintered within seconds and with
outstanding efficiency (~2 kWh/kg) independent of batch size.
Sintering on-the-spot with blacklight as a versatile and widely
applicable power source is demonstrated on ceramics needed for
energy storage and conversion and in electronic and structural
applications foreshadowing economic scalability.

Keywords: flash lamp annealing; laser annealing; ceramics

Permalink: https://www.hzdr.de/publications/Publ-34758
Publ.-Id: 34758


Crystallization of semiconductor thin films by flash lamp annealing

Rebohle, L.

Flash lamp annealing is a non-equilibrium annealing method on the sub-second time scale which excellently meets the requirements of thin film processing. It has already been used in microelectronics to activate dopants, to recrystallize amorphous semiconductor layers and to anneal out defects. However, in the last 20 years, flash lamp annealing has opened up new areas of application like thin films on glass, sensors, printed electronics, flexible electronics, batteries etc. Since two years, the Helmholtz Innovation blitzlab aims to transfer this technology to industry and application-related research.
In this presentation, we give a short introduction to flash lamp annealing and discuss the pros and cons of this technology for thin film and semiconductor processing. In the main part we report about our activities in the field of Ge-based materials for electronic applications. This includes the n-type doping of Ge above the solubility level by ion implantation and flash lamp annealing, the doping of GeSn alloys, and the fabrication of NiGe for contact formation.

Keywords: semiconductor thin film; flash lamp annealing; Crystallization

Related publications

  • Lecture (others) (Online presentation)
    Innovation Talk Infineon, 01.06.2022, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-34757
Publ.-Id: 34757


Flash lamp annealing of GaN

Rebohle, L.; Prucnal, S.; Akhmadaliev, S.; Kentsch, U.

The presentation gives a short overview of our recent activities to dope GaN with Mg by ion implantation and flash lamp annealing.

Keywords: gallium nitride; Mg doping; ion implantation; flash lamp annealing

Related publications

  • Lecture (Conference)
    Nutzertreffen "Heißprozesse und RTP" und "Ionenimplantation", 18.05.2022, Erlangen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-34756
Publ.-Id: 34756


Contactless inductive flow tomography in fundamental and applied fluid dynamics

Sieger, M.; Mitra, R.; Glavinic, I.; Sonntag, S.; Gundrum, T.; Stefani, F.; Wondrak, T.; Eckert, S.

Contactless inductive flow tomography (CIFT) is a flow measurement technique developed at Helmholtz-Zentrum Dresden-Rossendorf that can reconstruct the global 3D flow field in electrically conducting fluids such as liquid metals. The velocity field of the moving fluid can be reconstructed by solving the underlying inverse problem using appropriate regularization methods. This publication introduces the key concept and mathematical foundation of the method and illustrates the measurement capability of CIFT on two examples: continuous casting of steel in applied fluid dynamics and Rayleigh-Bénard convection as a paradigmatic system in fundamental fluid dynamics.

Keywords: Flow measurement techniques; liquid metal; tomography; inverse problem; Rayleigh-Bénard

  • Contribution to proceedings
    29. Fachtagung "Experimentelle Strömungsmechanik", 06.-08.09.2022, Ilmenau, Deutschland
  • Lecture (Conference)
    29. Fachtagung "Experimentelle Strömungsmechanik", 06.-08.09.2022, Ilmenau, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-34755
Publ.-Id: 34755


Metadatamanagement - How to make your data FAIR

Steinmeier, L.; Schaller, T.; Rau, F.; Schweikert, J.

The necessity of exhaustive documentation of research data arises from an increasing depth of scientific understanding and investigations of unknown phenomena with research teams of different areas and fields. Different methods and definitions and insufficient documentation of field work, experimental and numerical examinations lead to information loss, especially over time. To counteract this problem the scientific community aims to make research data Findable, Accessible, Interoperable and Reusable (FAIR). Unfortunately infrastructure, tools, personnel and acceptability for these additional steps are often missing and result in the mentioned paucity of information and data. Within the Helmholtz Association the Helmholtz Metadata Collaboration (HMC) has taken on the task of building this infrastructure to support high quality data documentation and publication throughout the entire lifecycle of research data and to raise the awareness for necessary structural changes in the wider scientific community.
One goal of HMC is the mapping of existing data management structures and demands in the different research fields of the Helmholtz Community. These fields are especially addressed with Hubs, being the connection between HMC and the specific needs of the research fields. Based on the collected information HMC will implement tools to assist scientists, data managers and IT administrators in making their research data FAIR. Furthermore members of HMC will connect with other (meta-)data initiatives to work towards necessary structural changes in the world of scientific research by e.g. defining standards.
In this poster we will discuss the FAIR principles and introduce the Helmholtz Metadata Collaboration and their tasks. Also, we will show concrete examples from the geoscientific part of Hub Energy. The Hub in which we are active.

Keywords: FAIR; Metadata; Helmholtz Metadata Collaboration; Deutsche Geophysikalische Gesellschaft

  • Open Access Logo Poster
    Helmholtz Energy Young Scientists Workshop 2022, 30.-31.05.2022, Maintal (Hessen), Germany

Permalink: https://www.hzdr.de/publications/Publ-34754
Publ.-Id: 34754


Data publication: Switching on Cytotoxicity of Water-Soluble Diiron Organometallics by UV Irradiation

Biancalana, L.; Kubeil, M.; Schoch, S.; Zacchini, S.; Marchetti, F.

decarbonylation studies By IR, NMR, UV/vis myoglobin assay cell proliferation assay

cristallographic data available by collaboration partner

Keywords: PhotoCORM; Carbon Monoxide; Bioorganometallic Chemistry; Diiron complexes; Photoactivation; Cytotoxicity; Aminocarbyne Ligand; Vinyliminium Ligand; PTA; water solubility

Related publications

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Permalink: https://www.hzdr.de/publications/Publ-34752
Publ.-Id: 34752


Switching on Cytotoxicity of Water-Soluble Diiron Organometallics by UV Irradiation

Biancalana, L.; Kubeil, M.; Schoch, S.; Zacchini, S.; Marchetti, F.

The diiron compounds [Fe2Cp2(CO)2(μ-CO)(μ-CSEt)]CF3SO3, [1]CF3SO3, K[Fe2Cp2(CO)3(CNCH2CO2)], K[2], [Fe2Cp2(CO)2(μ-CO)(μ-CNMe2)]NO3, [3]NO3, [Fe2Cp2(CO)2(PTA){μ-CNMe(Xyl)}]CF3SO3, [4]CF3SO3, and [Fe2Cp2(CO)(μ-CO){μ−η:1η3-C(4-C6H4CO2H)CHCNMe2}]CF3SO3, [5]CF3SO3, containing a bridging carbyne, isocyanoacetate, or vinyliminium ligand, were investigated for their photoinduced cytotoxicity. Specifically, the novel water-soluble compounds K[2], [3]NO3, and [4]CF3SO3 were synthesized and characterized by elemental analysis and IR and multinuclear NMR spectroscopy. Stereochemical aspects concerning [4]CF3SO3 were elucidated by 1H NOESY NMR and single-crystal X-ray diffraction. Cell proliferation studies on human skin cancer (A431) and nontumoral embryonic kidney (HEK293) cells, with and without a 10-min exposure to low-power UV light (350 nm), highlighted the performance of the aminocarbyne [3]NO3, nicknamed NIRAC (Nitrate-Iron-Aminocarbyne), which is substantially nontoxic in the dark but shows a marked photoinduced cytotoxicity. Spectroscopic (IR, UV−vis, NMR) measurements and the myoglobin assay indicated that the release of one carbon monoxide ligand represents the first step of the photoactivation process of NIRAC, followed by an extensive disassembly of the organometallic scaffold.

Keywords: PhotoCORM; Carbon Monoxide; Bioorganometallic Chemistry; Diiron complexes; Photoactivation; Cytotoxicity; Aminocarbyne Ligand; Vinyliminium Ligand; PTA; water solubility

Permalink: https://www.hzdr.de/publications/Publ-34751
Publ.-Id: 34751


Numerical simulation of metal electrodeposition under the influence of a magnetic field towards nano-sized conically structured deposits

Huang, M.; Skibinska, K.; Zabinski, P.; Eckert, K.; Mutschke, G.

Nano-structured cones have gained much attention due to their superior super-hydrophobic and electrocatalytic properties recently. This work aims to explore if magnetic fields could support the electrodeposition of nano-cone arrays on electrodes that are not externally templated. The magnetic forces, including the Lorentz force and the magnetic gradient force, can generate a flow that brings electrolyte enriched with electroactive ions towards the cone tips, and thus may enhance the local mass transfer and support the conical growth.
Numerical studies on single diamagnetic (Cu) and ferromagnetic (Fe) cathodes of conical shape at mm length scale provide a basic understanding of the flow and the mass transfer at conical structures during electrodeposition in a uniform external magnetic field. It is found that beside the Lorentz force, the magnetic gradient force caused by the magnetization of the Fe cones can efficiently enhance conical growth. Working towards nano-sized cone arrays, upon shrinking the cone size we find that conical growth becomes less supported. Damping effects from neighboring cones and weaker electrolyte flow in general are weakening the mass transfer enhancements near the cone tip. However, the flow caused by the magnetic gradient force (Fe case) is clearly less affected than that caused by the Lorentz force (Cu case).
Despite the weaker flow effects when the cone size shrinks, a beneficial influence of the magnetic field on conical growth, especially for ferromagnetic deposits, can be stated also at small scales.

  • Lecture (Conference)
    14th International Workshop on Electrodeposited Nanostructures, 09.-10.06.2022, Krakow, Poland

Permalink: https://www.hzdr.de/publications/Publ-34750
Publ.-Id: 34750


Modelling and A-Posteriori Assessment of Closure Models for Sub-Grid Surface Tension Considering a Rising Gas Bubble

Meller, R.; Schlegel, F.; Klein, M.

Correctly predicting the behaviour gas-liquid multiphase flows with numerical simulation tools is a highly complex task, especially when considering industrial scales. The most challenging task in that regard might be the large range of length scales of turbulent as well as of interfacial structures. Based on the two-fluid model, a hybrid methodology is developed with the goal to adaptively combine Euler-Euler and Volume-of-Fluid (VOF) simulation methods for statistical and scale-resolving representation of gas-liquid interfaces, respectively (Meller et al., 2021). With that approach, inevitably situations arise, where interfacial dynamics need to be predicted with VOF in combination with a particularly coarse grid resolution.
Low-pass filtering of the underlying two-fluid equations in this context reveals an unclosed sub-grid surface tension term, besides the convective and other unclosed terms (Meller et al., 2022). This contribution expresses the interfacial forces due to surface tension, which are not captured on a comparatively coarse computational grid. Different functional and structural closure models for that unclosed term are assessed in an a-posteriori fashion in case of a gas bubble rising in stagnant liquid. This contributes to an improved predictive power of the numerical model regarding large-scale interface and turbulent dynamics, even with low spatial resolution.

  • Lecture (Conference)
    Colloquium 625, Advances in LES of Turbulent Multiphase Flows, 22.-24.06.2022, Udine, Italia

Permalink: https://www.hzdr.de/publications/Publ-34749
Publ.-Id: 34749


Pulse reverse plating of copper micro-structures in magnetic gradient fields

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

Micro-structured copper layers are obtained from pulse-reverse electrodeposition on a planar gold electrode that is magnetically patterned by magnetized iron wires underneath. 3D numerical simulations of the electrodeposition based on an adapted reaction kinetics are able to nicely reproduce the micro-structure of the deposit layer, despite the height values still remain underestimated. It is shown that the structuring is enabled by the magnetic gradient force, which generates a local flow that supports deposition and hinders dissolution in the regions of high magnetic gradients. The Lorentz force originating from radial magnetic field components near the rim of the electrode causes a circumferential cell flow. The resulting secondary flow, however, is superseded by the local flow driven by the magnetic gradient force in the vicinity of the wires. Finally, the role of solutal buoyancy effects is discussed to better understand the limitations of structured growth in different modes of deposition and cell geometries.

Keywords: Magnetoelectrodeposition; Surface structuring; Magnetic gradient force; Lorentz force; Pulse reverse plating

Permalink: https://www.hzdr.de/publications/Publ-34748
Publ.-Id: 34748


Benchmark results for real-time UFXCT data processing

Windisch, D.

This dataset holds the subset of benchmark results relevant for the publication "Real-time data processing for Ultrafast X-Ray Computed Tomography using Modular CUDA based Pipelines". Alongside the data, Matlab scripts are provided for parsing and plotting the data.

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Permalink: https://www.hzdr.de/publications/Publ-34747
Publ.-Id: 34747


Size‑ and position‑controlled Ge nanocrystals separated by high‑k dielectrics

Lehninger, D.; Honeit, F.; Rafaja, D.; Klemm, V.; Röder, C.; Khomenkova, L.; Schneider, F.; Borany, J.; Heitmann, J.

Germanium nanocrystals embedded in high-k dielectric matrices are of main interest for infrared sensing application, as a role model for Ge-based nano-electronics passivation or for nonvolatile memory devices. The capability of the size control of those nanocrystals via rapid thermal processing of superlattice structures is shown for the [Ge–TaZrOx/TaZrOx]n, [Ge–TaZrOx/SiO2/TaZrOx]6, and [TaZrOx/Ge–SiO2]n superlattice systems. All superlattices were deposited by radiofrequency magnetron sputtering. Transmission electron microscopy (TEM) imaging confirms the formation of spherically shaped nanocrystals. Raman scattering proved the crystallization of Ge above 700°C. The TaZrOx crystallizes above 770°C, associated with a phase separation of Ta2O5 and ZrO2 as confirmed by x-ray diffraction. For the composite layers having 3 nm and 6 nm thickness, the size of the Ge nanocrystals correlates
with the deposited layer thickness. Thicker composite layers (above 9 nm) form two fractions of nanocrystals with different sizes. An additional SiO2
layer in the [Ge–TaZrOx/SiO2/TaZrOx]6 superlattice stacks facilitates the formation of larger and better separated Ge nanocrystals. The deposition of Ge-SiO2 composite layers separated by pure TaZrOx illustrates the barrier effect of TaZrOx against Ge diffusion. All three material systems allow the controlled formation of Ge nanocrystals in amorphous matrices at temperatures above 700 and below 770°C.

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Permalink: https://www.hzdr.de/publications/Publ-34746
Publ.-Id: 34746


Aerosolüberwachung beim Umgang mit radiopharmazeutischen Alphastrahlern

Wendler, M.; Kowe, S.; Walter, M.; Schöne, F.

Im Institut für Radiopharmazeutische Krebsforschung des Helmholtz-Zentrums Dresden-Rossendorf e. V. wird zukünftig verstärkt mit kurzlebigen Alphaemittern umgegangen. dabei handelt es sich vor allem um die Radionuklide Ra-224, Ac-225 und Th-227. Die Überwachung der Mitarbeiter beim Umgang mit diesen Radionukliden bringt Herausforderungen im Hinblick auf die Inkorporationsüberwachung mit sich. Ein Inkorporationsnachweis kann bei den genannten Radionukliden nur mittels kostenintensiver und aufwendiger Ausscheidungsanalyse erfolgen. Um den Mitarbeitern diese routinemäßige Maßnahme zu ersparen, wird auf die Aerosolmessung in der Raumluft gesetzt. Die Aerosolüberwachung wird parallel durch Aerosolmonitoring und Aerosolsammlung umgesetzt und liefert ein Ergebnis, welches zur weiteren Anweisung von Maßnahmen führen kann. Bedingt durch die räumlichen Anforderungen, die Anforderungen an den Arbeitsschutz hinsichtlich der Geräuschemission und die Herausforderung natürlicher Radionuklide in der Luft mussten spezielle Verfahrensweisen umgesetzt werden.

Keywords: Strahlenschutz; Radiation Protection; Alphaemitter; Aerosol; Inkorporation; Radiopharmazie

  • Poster
    53. Jahrestagung des Fachverbands für Strahlenschutz e. V., 26.-30.09.2022, Konstanz, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-34744
Publ.-Id: 34744


Euler-Euler model of bubbly flow using particle-center-averaging method

Lyu, H.; Schlegel, F.; Rzehak, R.; Lucas, D.

The Euler-Euler model is widely used in bubbly flow simulations up to industrial dimensions. The standard Euler-Euler model is based on the phase-averaging method. After averaging, the bubble forces in the field equations are functions of the local gas volume fraction. In simulations, when the bubble diameter is larger than the computational cell spacing, the forces can transport the gas belonging to the same bubble in different directions. By contrast, a closure model for the bubble force is typically developed based on the assumption that the force is a resultant force that acts on the bubble's center-of-mass. This inconsistency can lead to a nonphysical gas concentration in the center of a channel or near the channel wall if the bubble diameter is larger than the cell spacing.

The purpose of the present contribution is to developed an Euler-Euler model where the bubble force consistency is recovered for two-phase flow simulations where the diameter of the disperse phase can be larger than the cell spacing. Such an Euler-Euler model is developed by combining an existing particle-center-averaged Euler-Euler framework with a Gaussian convolution method. To validate this Euler-Euler approach, a comparison is made with experimental data for the bubbly flows in two different vertical pipes. The results show that the proposed Euler-Euler model recovers the bubble force consistency and alleviates the over-prediction of the gas volume fraction peak near the wall, while its simulation results in the axial gas and liquid velocity and the liquid turbulence kinetic energy are similar to the results of the standard Euler-Euler model.

Keywords: bubbly flow simulation; Euler-Euler model; particle-center-averaging method; Gaussian convolution method; bubble's number density

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  • Secondary publication expected from 16.12.2023

Permalink: https://www.hzdr.de/publications/Publ-34742
Publ.-Id: 34742


Laser-proton acceleration developments at DRACO-PW enabling “in-vivo” radiobiology

Ziegler, T.; Bernert, C.; Beyreuther, E.; Brack, F.-E.; Cowan, T.; Garten, M.; Gaus, L.; Kluge, T.; Kraft, S.; Kroll, F.; Metzkes-Ng, J.; Pawelke, J.; Reimold, M.; Rehwald, M.; Schlenvoigt, H.-P.; Umlandt, M. E. P.; Schramm, U.; Zeil, K.

We report technological developments at DRACO-PW to monitor and improve laser-plasma conditions resulting in a stable particle-source >60MeV, which in combination with our transport-beamline and high-quality dosimetry enabled first dose-controlled “in-vivo” studies with laser-driven protons.

  • Lecture (Conference)
    High-Brightness Sources and Light-Driven Interactions Congress, 22.-25.03.2022, Budapest, Ungarn

Permalink: https://www.hzdr.de/publications/Publ-34741
Publ.-Id: 34741


Electronic properties of van der Waals crystals under hydrostatic pressure

Wozniak, T.; Faria Junior, P. E.; Oliva, R.; Tołłoczko, A.; Kopaczek, J.; Zelewski, S.; Dybała, F.; Fabian, J.; Scharoch, P.; Kudrawiec, R.

Electronic properties of layered van der Waals crystals can be effectively tuned by means of external and configurational factors. It allows for the investigation of the fundamental material properties that are valuable for technological applications. Here we show, how Density Functional Theory (DFT) calculations allow to interpret the experimental results on quantitative level.
We present experimental and DFT studies of the electronic band structure of MoTe2 at high hydrostatic pressures. Modulated photoreflectance measurements allowed determination of the pressure coefficients of six direct transitions, with positive and negative values, which can be attributed to a strong splitting of the conduction bands with increasing pressure and the presence of hidden spin-polarized electronic states. These results prove that the spin-valley locking effect takes place in centrosymmetric transition metal dichalcogenides [1].
We also report experimental and theoretical study of the electronic band structure of orthorhombic GeS crystals under hydrostatic pressure. Polarization-resolved photoreflectance measurements allowed to extract the energies, optical dichroic ratios, and pressure coefficients of the direct optical transitions. These findings are discussed in view of DFT calculations, which predict that nondegenerate states in different valleys can be individually selected through linearly polarized light. Based on this, an assignation of the direct optical transitions to the electronic band structure is provided. These results provide evidence that GeS is a strong candidate for valleytronic applications in nondegenerate systems [2, 3].
Finally, we combined calculations within DFT and the effective Bethe-Salpeter equation, with high-pressure optical measurements in order to thoroughly describe the effect of strain and dielectric environment onto the electronic band structure and optical properties of a few-layered WS2. Our results show that WS2 remains fully adhered to the substrate at least up to a 0.6% in-plane compressive strain for a wide range of substrate materials. We provide a useful model to describe effect of strain on the optical properties on general strain conditions. Within this model, exceptionally large compressive uniaxial and biaxial in-plane gauge factors were obtained, which confirm transition metal dichalcogenides as very promising candidates for flexible functionalities [4].

[1] R. Oliva, T. Woźniak, F. Dybała, J. Kopaczek, P. Scharoch, R. Kudrawiec, Mater. Res. Lett. 8, 75 (2020).
[2] A. Tołłoczko, R. Oliva, T. Woźniak, J. Kopaczek, P. Scharoch, R. Kudrawiec, Mater. Advances 6, 1886 (2020).
[3] R. Oliva, T. Woźniak, F. Dybała, A. Tołłoczko, J. Kopaczek, P. Scharoch, R. Kudrawiec, Phys. Rev. B 101, 235205 (2020).
[4] R. Oliva, T. Woźniak, P. E. Faria Junior, F. Dybała, J. Kopaczek, J. Fabian, P. Scharoch, R. Kudrawiec, arXiv:2202.08551 (2022).

  • Poster
    50th International School & Conference on the Physics of Semiconductors "Jaszowiec 2022", 04.-10.06.2022, Szczyrk, Poland

Permalink: https://www.hzdr.de/publications/Publ-34740
Publ.-Id: 34740


Heterogeneity of ASL perfusion MRI in low-grade paediatric glioma as imaging biomarker to assess treatment effect

Alic, L.; Willekens, S. C.; Mutsaerts, H.-J. M. M.; Petr, J.; Schouten-Van Meeteren, N. A. Y. N.; Lequin, M. M. H.; Wiegers, E. E. C.

ASL-MRI is reported as an option to assess potentially heterogeneous physiological processes important for tumour treatment. Therefore, we explored the heterogeneity in normalised CBF as an imaging biomarker for assessment of treatment effect in pLGG. There is a noticeable effect of chemotherapy observed as a change in texture of healthy appearing brain tissue. A high difference in texture between treated and non-treated patients for non-enhancing tumour part is observed, suggesting that texture, based on co-occurrence matrices, is suitable as an imaging biomarker for assessment of treatment effect in pLGG.

  • Contribution to proceedings
    ISMRM '22: Proceedings of the ISMRM 30th Annual Meeting & Exhibition, 07.-12.05.2022, London, United Kingdom
  • Poster
    ISMRM '22: Proceedings of the ISMRM 30th Annual Meeting & Exhibition, 07.-12.05.2022, London, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-34739
Publ.-Id: 34739


Multimodal MRI-derived phenotypes in preclinical Alzheimer’s Disease: results from the EPAD cohort

Lorenzini, L.; Ingala, S.; Wink, A. M.; Kuijer, J. P. A.; Wottschel, V.; Sudre, C. H.; Haller, S.; Molinuevo, J. L.; Gispert, J. D.; Cash, D. M.; Thomas, D. L.; Vos, S. B.; Ferran, P.; Petr, J.; Wolz, R.; Palombit, A.; Schwarz, A. J.; Chételat, G.; Payoux, P.; Di Perri, C.; Pernet, C.; Frisoni, G.; Fox, N. C.; Ritchie, C.; Wardlaw, J.; Waldman, A.; Barkhof, F.; Mutsaerts, H. J. M. M.

Image-derived phenotypes (IDPs) from multimodal MRI sequences constitute an important resource that allows the characterization of brain alterations in the early stages of Alzheimer diseases and other neurodegenerative conditions. Here, we showed the computation of multimodal IDPs from the European Prevention of Alzheimer Dementia (EPAD) cohort and assessed their relationship with non-imaging markers of neurodegeneration. We demonstrated the clinical relevance of IDPs to uncover early brain alteration in AD by showing expected association with non-imaging data.

  • Contribution to proceedings
    ISMRM '22: ISMRM 30th Annual Meeting & Exhibition, 07.-12.05.2022, London, United Kingdom
    Proceedings of the ISMRM 30th Annual Meeting & Exhibition
  • Lecture (Conference)
    ISMRM '22: ISMRM 30th Annual Meeting & Exhibition, 07.-12.05.2022, London, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-34738
Publ.-Id: 34738


Novel arterial spin labelling (ASL) brain injury symmetry assessment in retired professional athletes: a preliminary study

Danielli, E.; Padrela, B.; Doughty, M.; Petr, J.; Mutsaerts, H.; Noseworthy, M. D.

3D PCASL scans were acquired for seventeen aging, retired professional football players with a history of head traumas. Left, right and bilateral CBF and ASL spatial coefficient of variation (sCoV) values were examined for twelve concussion-related ROIs. A Z-scoring approach was applied, with outliers defined as mild, moderate, or severe injury burden (IB). An IB symmetry index was also calculated. Outliers were detected in all 12 ROIs, and the anterior parahippocampal gyrus and inferior frontal gyrus pars opercularis had the highest CBF and ASL sCoV IB, respectively. IB was not biased towards the left or right hemisphere.

  • Contribution to proceedings
    ISMRM '22: Proceedings of the ISMRM 30th Annual Meeting & Exhibition, 07.-12.05.2022, London, United Kingdom
  • Poster
    ISMRM '22: ISMRM 30th Annual Meeting & Exhibition, 07.-12.05.2022, London, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-34737
Publ.-Id: 34737


The Open Science Initiative for Perfusion Imaging (OSIPI): Results from the ASL MRI Challenge

Anazodo, U.; Pinto, J.; Kennedy McConnell, F.; Gould Van Praag, C.; Mutsaerts, H.; Oliver-Taylor, A.; Petr, J.; Pineda-Ordóñez, D.; Dounavi, M.-E.; Brumer, I.; Chan, W. S. M.; Toner, J.; Hu, J.; Zhang, L. X.; Bell, L.; Woods, J. G.; Zhao, M. Y.; Croal, P.; Paschoal, A. M.

The OSIPI ASL MRI Challenge is an initiative of the ASL community aiming to characterize the variability of CBF quantification arising from different pipelines. The goal of this challenge is to establish best practice in ASL data processing, understand the sources of variability, make ASL analysis more reproducible, and enable fair comparison between studies. Here, we analyzed 3 submitted entries from 7 teams registered in the challenge. The preliminary results showed pipelines based in different programming languages and analysis tools, leading to important variability in the quantitative CBF maps compared to the ground-truth.

  • Contribution to proceedings
    ISMRM '22: ISMRM 30th Annual Meeting & Exhibition, 07.-12.05.2022, London, United Kingdom
    Proceedings of the ISMRM 30th Annual Meeting & Exhibition
  • Poster
    ISMRM '22: ISMRM 30th Annual Meeting & Exhibition, 07.-12.05.2022, London, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-34736
Publ.-Id: 34736


Amyloid burden and vascular risk factors correlate with regional cerebral blood flow in a cognitively unimpaired population

Padrela, B. E.; Lorenzini, L.; Collij, L. E.; Ten Kate, M.; Den Braber, A.; Tomassen, J.; van Berckel, B.; Visser, P. J.; Barkhof, F.; Petr, J.; Mutsaerts, H. J. M. M.

Recent findings suggest additive effects of cerebrovascular disease and Alzheimer's disease (AD) on cognitive decline. MR imaging of cerebral blood flow holds great promise as an early dementia biomarker. Supply and demand of blood flow in the brain can be affected by, respectively, the loss of vascular health and the decrease of neuronal activity, as a consequence of AD. This study investigates to what extent vascular and AD components affect CBF and how they interact with each other.

  • Lecture (Conference)
    ISMRM '22 Workshop on Perfusion MRI: From Head to Toe, 04.-07.03.2022, Los Angeles, USA
  • Contribution to proceedings
    ISMRM '22: Proceedings of the ISMRM 30th Annual Meeting & Exhibition, 07.-12.05.2022, London, United Kingdom
  • Lecture (Conference)
    ISMRM '22: ISMRM 30th Annual Meeting & Exhibition, 07.-12.05.2022, London, United Kingdom
  • Poster
    Alzheimer's Association International Conference, 31.07.2022, San Diego, USA
  • Contribution to proceedings
    Alzheimer's Association International Conference, 31.07.2022, San Diego, USA
  • Contribution to proceedings
    International Conference on Alzheimer’s and Parkinson’s Diseases and related neurological disorders (ADPD), 15.03.2022, Barcelona, Spain
  • Lecture (Conference)
    International Conference on Alzheimer’s and Parkinson’s Diseases and related neurological disorders, 15.03.2022, Barcelona, Spain

Permalink: https://www.hzdr.de/publications/Publ-34735
Publ.-Id: 34735


OSIPI Inventory of ASL Pipelines

Petr, J.

Cerebral blood flow (CBF) is an important physiological parameter for assessing cerebrovascular health and blood flow demand both in healthy and diseased conditions [refs]. Arterial spin labeling (ASL) perfusion MRI provides a non-contrast acquisition method for quantification of regional CBF. Its non-invasive nature and ability to quantify absolute CBF make it ideal in research and clinical settings requiring repeated acquisitions. ASL-MRI has been extensively validated with other methods that use exogenous contrast agents, such as 15O-H2O-PET and dynamic susceptibility contrast MRI (DSC) (1–6), and has already shown extensive impact on the neurological, neuropsychological, and neuropsychiatric research fields [refs].

ASL involves i) magnetic labeling of the arterial blood water while it flows through internal carotid and vertebral arteries that supply blood to the brain, ii) acquiring a “labeled” brain image after waiting for a brief period to allow the blood to reach the capillaries, and iii) computing a perfusion-weighted image by subtracting the labeled image from a “control” image obtained without labeling. Depending on the methods of spin labeling and image acquisition, ASL can vary significantly and has undergone significant improvement since its inception (7). For example, the labeling can be performed at the neck using pseudo-continuous ASL (PCASL) (8) or pulsed ASL (PASL) (9) or close to the site of imaging using velocity selective imaging (10). Image readout can be performed using 2D echo-planar imaging (EPI) (11), 3D gradient and spin-echo (GRASE) (12), or 3D spiral imaging (13). Each type of image acquisition can be associated with background suppression of static tissue to increase the signal-to-noise ratio (14). Additionally, the post-labeling delay (PLD) can be fixed or variable (single-PLD or multi-PLD) or obtained using a time-encoding technique (15).

These differences lead to greater heterogeneity of data types in ASL MRI than typically seen in other MRI modalities and a consensus recommendation on acquisition has been formed (16) to facilitate its use in different settings. Nonetheless, different flavors of ASL are still in use based on the availability of specific protocols or scanners, and the expertise of the clinicians and investigators at the clinical or research sites. Most scanners, however, output only the raw ASL data, and the end-users need to derive the quantitative CBF maps from that. Therefore, many potential users such as radiologists and neuroscientists, who may not have the technical expertise, have to struggle their way through implementing these processing steps and finding a suitable software. And a recent European survey noted that technical difficulty and lack of tools are indeed one of the main hurdles to the more widespread use of ASL and quantitative MRI in general (17).

While more than twenty ASL toolboxes have been released (18–30), there is even a higher variety of different ASL sequences, data formats (31), and processing methods (19). As there is no standard defined for ASL image processing, it can be a daunting process to identify a pipeline that is suitable and optimal for users’ needs. Both new and experienced ASL users looking for different functionalities, and the ASL research field in general, may benefit from a comprehensive and detailed list of ASL image processing software to guide this search.

The Open Science Initiative for Perfusion Imaging (OSIPI) is an initiative of the International Society for Magnetic Resonance in Medicine (ISMRM) perfusion study group. Established in May 2020, its mission is to create open access resources for perfusion imaging research to improve the reproducibility of perfusion imaging research, speed up the translation into tools for discovery science, drug development, and clinical practice, and eliminate the practice of duplicate development [ref]. The activities of OSIPI were divided among task forces; Task Force 1.1 (TF1.1) aims to create an inventory of the available ASL pipelines, summarizing their features and requirements, thus making the pipelines more accessible to ASL users. This study provides a comprehensive list of pipelines available, listing their features. Additionally, it delivers an independent assessment of the user-friendliness of the pipelines and the technical level needed for operating the pipeline.

  • Invited lecture (Conferences)
    ISMRM '22 Workshop on Perfusion MRI: From Head to Toe, 04.-07.03.2022, Los Angeles, USA

Permalink: https://www.hzdr.de/publications/Publ-34734
Publ.-Id: 34734


Open Science Initiative for Perfusion Imaging (OSIPI): Arterial Spin Labeling Imaging and Analysis Lexicon and Reporting Recommendations

Suzuki, Y.; Clement, P.; Dai, W.; Dolui, S.; Fernández-Seara, M.; Lindner, T.; Mutsaerts, H. J.; Petr, J.; Shao, X.; Taso, M.; Thomas, D. L.

The 2015 consensus statement1 published by the ISMRM Perfusion Study Group and the EU COST Action ‘ASL in Dementia’ aimed to encourage the
implementation of robust Arterial Spin Labeling (ASL) perfusion MRI for clinical applications and promote consistency across scanner types, sites, and studies.
Subsequently, the recommended 3D pseudo-continuous ASL (PCASL) sequence has been implemented by most major MRI manufacturers. However, ASL remains a
rapidly and widely developing field, both in terms of improving the accuracy of cerebral blood flow (CBF) quantification and providing other output derivatives in
addition to CBF. These advances have greatly expanded the scope of ASL, but also bring further divergence of the technique, particularly in the terminology used,
which can lead to confusion and hamper research reproducibility. As part of the Open Science Initiative for Perfusion Imaging (OSIPI), the ASL Lexicon Task Force
has been working on the development of an ‘ASL Perfusion Imaging and Analysis Lexicon and Reporting Recommendations’, aiming: 1) to develop standardized
nomenclature and terminology for the broad range of ASL imaging techniques and parameters, as well as the physiological constants required for quantitative
analysis, and 2) to provide a community-endorsed recommendation on a minimal list of parameters that should be reported in publications.

  • Poster
    ISMRM '22 Workshop on Perfusion MRI: From Head to Toe, 04.-07.03.2022, Los Angeles, USA
  • Contribution to proceedings
    ISMRM '22: Proceedings of the ISMRM 30th Annual Meeting & Exhibition, 07.-12.05.2022, London, United Kingdom
  • Poster
    ISMRM '22: ISMRM 30th Annual Meeting & Exhibition, 07.-12.05.2022, London, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-34733
Publ.-Id: 34733


Cerebrovascular Brain-age

Dijsselhof, M. B. J.; Barboure, M.; Stritt, M.; Nordhøy, W.; Wink, A. M.; Westlye, L. T.; Cole, J. H.; Barkhof, F.; Petr, J.; Mutsaerts, H. J. M. M.

Brain-age estimates the biological brain age from structural MRI images based on changes in brain-tissue integrity and irreversible
structural changes [1]. The brain-age offset to the chronological age — the age gap — is associated with cognitive pathology [2]. Adding
vascular or functional MRI biomarkers may add sensitivity to physiological and metabolic changes, complementing and improving structural
brain-age, and possibly improving its sensitivity to earlier disease changes. Arterial spin labeling (ASL) MRI is a potential early biomarker of
cerebrovascular health and correlates with the initial stages of cognitive pathology [3]. Here, we propose the ‘Cerebrovascular Brain-age’ as a
combination of T1w, FLAIR, and ASL image features composed of the spatial Coefficient of Variation (CoV) and vascular-territory derived
(VT) cerebral blood flow (CBF).

  • Poster
    ISMRM '22 Workshop on Perfusion MRI: From Head to Toe, 04.-07.03.2022, Los Angeles, USA
  • Contribution to proceedings
    ISMRM '22: 30th Annual Meeting & Exhibition, 07.-12.05.2022, London, United Kingdom
    Proceedings of the ISMRM 30th Annual Meeting & Exhibition
  • Poster
    ISMRM '22: 30th Annual Meeting & Exhibition, 07.-12.05.2022, London, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-34732
Publ.-Id: 34732


Recycling of technical structures: The recyclability of refrigerators

Mütze, T.; Heibeck, M.

Consumer goods often consist of multi-material structures whose connections be-tween different materials fulfil important functions for production and use. In recycling, these structures must be disconnected in order to achieve high recycling rates for the individual materials. In this context, the BMBF project Circular by Design uses refrigerators/freezers to investigate which parameters can already be influenced during the design stage in order to optimise liberation during recycling without impairing the function and durability of the object in the use phase.

Keywords: recycling; design for recycling; design for repair; design for dismantling; liberation; multi-material structures

  • Contribution to proceedings
    Dresden Nexus Conference 2022, 23.-25.05.2022, Dresden, Deutschland
    Biodiversity - stewardship for vital resources

Permalink: https://www.hzdr.de/publications/Publ-34730
Publ.-Id: 34730


Photo-neutron cross-section of nat-Gd in the bremsstrahlung end-point energies of 12 - 16 MeV and 60 - 70 MeV

Naik, H.; Kim, G. N.; Schwengner, R.; Jang, W.; Nguyen, T. H.; Shin, S. G.; Kye, Y.; Massarczyk, R.; John, R.; Junghans, A.; Wagner, A.; Cho, M.-H.

The spectrum-averaged cross-sections of nat Gd(gamma,xn)159,153 Gd reactions induced by the bremsstrahlung end-point energies of 12, 14, 16. 60, 65, and 70 MeV were measured by activation and off-line gamma-ray spectrometric technique using the 20 MeV electron linac (ELBE) at HZDR, Dresden, Germany, and 100 MeV electron linac at Pohang Accelerator Laboratory, Korea. The TALYS 1.9 code was also used to calculate the theoretical nat Gd(gamma, xn)159,153 Gd reaction cross-sections as a function of photon energy. The spectrum-averaged values at various end-point energies were calculated from the literature data as well as theoretical values based on the TALYS 1.9 code, which is for mono-energetic photons. They were found to be in good agreement with
the flux-weighted values of the current experimental data. It was also observed that the experimental and theoretical cross-sections increase from the threshold values to a certain energy, at which point another reaction channel opens, indicating the role of excitation energy. Individual reaction cross-
sections decrease after a certain value as bremsstrahlung energy increases due to the opening of other reactions, indicating energy shearing among the different reaction channels.

Keywords: Photoactivation; bremsstrahlung; photoabsorption cross section; statistical reaction model

Permalink: https://www.hzdr.de/publications/Publ-34729
Publ.-Id: 34729


Data publication: Mode splitting of spin waves in magnetic nanotubes with discrete symmetries

Körber, L.; Kézsmárki, I.; Kakay, A.

This data set contains the numerical raw data for "Mode splitting of spin waves in magnetic nanotubes with discrete symmetries" published in Physical Review B. The data has been obtained using our in-house developed finite-element dynamic-matrix approach for propagating spin waves [see AIP Advances 11, 095006 (2021) for details]. 

  • The folder high-res-only-k0/ contains the lateral mode profiles and frequencies of polygonal nanotubes with different number of corners at k = 0. It also contains a python script used to calculate the microwave absorption from the mode profiles.
  • The folders poly_*/ contain only the dispersion without lateral mode profiles for the different polygonal tubes as well as a round nanotube
  • All folders contain the geometry and mesh files as well as sparam and eparam yaml files containg the material parameters and experimental parameters, respectively. The equilibrium states are saved as m_eq.h5 hdf5 files.

Keywords: Spin wave; magnon; micromagnetic modeling; symmetry; nanotubes; group theory; micromagnetism; tetrax

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Permalink: https://www.hzdr.de/publications/Publ-34728
Publ.-Id: 34728


Particle tracking velocimetry in liquid gallium flow around a cylindrical obstacle

Birjukov, M.; Zvejnieks, P.; Lappan, T.; Sarma, M.; Heitkam, S.; Trtik, P.; Mannes, D.; Eckert, S.; Jakovics, A.

This paper demonstrates particle tracking velocimetry performed for a model system wherein particle-laden liquid metal flow around a cylindrical
obstacle was studied. We present the image processing methodology developed for particle detection in images with disparate and often low
signal- and contrast-to-noise ratios, and the application of our MHT-X tracing algorithm for particle trajectory reconstruction for the wake
flow around the obstacle. Preliminary results indicate that the utilized methods enable consistent particle detection and recovery of long, representative
particle trajectories with high confidence. However, we also underline the necessity of implementing a more advanced particle position
extrapolation approach for increased tracking accuracy. Satisfactory tracking accuracy can be inferred from the fact that the fluctuations
in the measured particle velocity are dominated by frequencies that agree sufficiently well with the expected frequencies of the cylinder wake.

Keywords: liquid metal; particle flow; wake flow; neutron radiography; particle tracking; image processing

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Permalink: https://www.hzdr.de/publications/Publ-34727
Publ.-Id: 34727


Kombinierte optische und Röntgen-Messungen einer überlaufenden Schaumströmung

Lappan, T.; Herting, D.; Zamaraeva, E.; Stenzel, J.; Ziauddin, M.; Skrypnik, A.; Shevchenko, N.; Eckert, S.; Eckert, K.; Heitkam, S.

Schaum und dessen Strömungsverhalten sind von zentraler Bedeutung bei der Schaumflotation zur Mineralaufbereitung. Die zu gewinnenden Mineralpartikel lagern sich an aufsteigenden Gasblasen an und werden mit dem Schaum aus der Flotationszelle heraustransportiert. In industriellen Flotationsanlagen wird die Rückgewinnung von Feststoff- und Flüssigphase aus der überlaufenden Schaumströmung mittels optischer Messtechnik überwacht und ist daher auf die freie Oberfläche des partikelbeladenen Schaums beschränkt. Die vorliegende Arbeit untersucht das Strömungsverhalten eines wässrigen Schaums an einem Überlauf vergleichend mittels optischer und Röntgen-Messungen. Der Schaum wurde kontinuierlich erzeugt, strömte in vertikaler Richtung durch einen Kanal mit quadratischem Querschnitt und floss durch einen einseitigen horizontalen Überlauf in die freie Umgebung. Die bildgebenden Strömungsmessungen fokussierten sich auf den Schaum im Bereich des Überlaufs. Gleichzeitig wurde hier der Flüssigkeitsanteil des Schaums mittels Messung der elektrischen Leitfähigkeit zwischen jeweils zwei Elektroden bestimmt. Die optischen Messungen erfolgten einerseits durch die transparente Kanalwand und andererseits an der freien Oberfläche des überlaufenden Schaums. Die dortigen Strömungsgeschwindigkeiten wurden mittels angepasster PIV-Algorithmen ausgewertet, welche Lichtreflexionen auf den Schaumblasen als Messinformation nutzten. Aufgrund der Undurchsichtigkeit des Schaums erfassen diese optischen Messungen nur die oberflächennahen Schaumblasen. Unsere Variante der Röntgen-Radiographie mit maßgeschneiderten Tracer-Partikeln (X-PTV) gibt Aufschluss über die drei-dimensionale Schaumströmung. Die in dieser Arbeit verwendeten Tracer bestanden aus einer 3D-gedruckten polymeren Trägerstruktur in Form eines Tetraeders mit insgesamt vier kleinen Metallkügelchen an dessen Ecken. Dank der Tetraeder-Form und des geringen Gewichts des Materialverbunds hafteten die Tracer in der Schaumstruktur und wurden in der Strömung mitgetragen. Die Röntgenbildsequenzen zeigen die Bewegungsbahnen der zu jedem Tracer gehörenden Metallkügelchen und bilden lokal die Stromlinien der Schaumströmung ab. Weiterhin visualisieren die Röntgenbilder des Schaums dessen Flüssigkeitsanteil im gesamten Bildfeld. Sie bestätigen und erweitern die lokalen Messungen des Flüssigkeitsanteils mittels der Elektrodenpaare, sind aber mit einer höheren Messunsicherheit behaftet. Die tracer-basierten Röntgenmessungen belegen die vergleichsweise hohen Strömungsgeschwindigkeiten im Inneren des Kanals und unmittelbar am Überlauf, während die optischen Strömungsmessungen Wand- bzw. Oberflächeneffekten unterliegen, welche in tendenziell geringeren Geschwindigkeiten resultieren. Allerdings zeigen die Messergebnisse auch die Grenzen der Röntgenmessungen mit den Schaum-Tracern auf: ihr Folgevermögen ist in instabilem Schaum mit hohem Flüssigkeitsanteil und bei hoher Strömungsgeschwindigkeit stark vermindert.

  • Lecture (Conference)
    29. Fachtagung "Experimentelle Strömungsmechanik", 06.-08.09.2022, Ilmenau, Deutschland
  • Open Access Logo Contribution to proceedings
    29. Fachtagung "Experimentelle Strömungsmechanik", 06.-08.09.2022, Ilmenau, Deutschland, 978-3-9816764-8-8, 16.1-16.12

Permalink: https://www.hzdr.de/publications/Publ-34726
Publ.-Id: 34726


Low-energy Se ion implantation in MoS₂ monolayers

Bui, M. N.; Rost, S.; Auge, M.; Tu, J.-S.; Zhou, L.; Aguilera, I.; Aguilera Stefan Blügel, I.; Ghorbani Asl, M.; Krasheninnikov, A.; Hashemi, A.; Komsa, H.-P.; Jin, L.; Kibkalo, L.; O’Connell, E. N.; Ramasse, Q. M.; Bangert, U.; Hofsäss, H. C.; Grützmacher, D.; Kardynal, B. E.

In this work, we study ultra-low energy implantation into MoS₂ monolayers to evaluate the potential of the technique in two-dimensional materials technology. We use 80 Se⁺ ions at the energy of 20 eV and with fluences up to 5.0 · 10¹⁴ cm⁻².
Raman spectra of the implanted films show that the implanted ions are predominantly incorporated at the sulfur sites and MoS₂₋₂ₓ Se₂ₓ alloys are formed, indicating high ion retention rates, in agreement with the predictions of molecular dynamics simulations of Se ion irradiation on MoS₂ monolayers. We found that the ion retention rate is improved when implantation is
performed at an elevated temperature of the target monolayers. Photoluminescence spectra reveal the presence of defects, which are mostly removed by post-implantation annealing at 200 ˚C, suggesting that, in addition to the Se atoms in the substitutional positions, weakly bound Se adatoms are the most common defects introduced by implantation at this ion energy.

Keywords: transition metal dichalcogenide monolayer; dry viscoelasic transfer; ultralow energy ion implantation; MoS₂; defect healing; photoluminescence; Raman spectroscopy

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Permalink: https://www.hzdr.de/publications/Publ-34725
Publ.-Id: 34725


Combining optical and X-ray measurements of an overflowing liquid foam

Lappan, T.; Herting, D.; Zamaraeva, E.; Stenzel, J.; Ziauddin, M.; Skrypnik, A.; Shevchenko, N.; Eckert, S.; Eckert, K.; Heitkam, S.

Froth flow is of central importance for mineral processing by froth flotation. In flotation plants, the recovery of solid mineral particles and liquid from the overflowing froth is monitored by optical observation and, therefore, limited to the froth’s free surface. The laboratory-scale experiment in this work investigates the flow behaviour of an aqueous foam at a horizontal overflow (Fig. 1) in combined optical and X-ray radiographic measurements. Simultaneously, the foam’s liquid fraction was determined by measuring the electrical conductivity between electrode pairs. The optical measurements, performed both through a transparent wall and at the free surface of the overflowing foam, captured light reflexions on the foam bubbles, which were analysed by adapting particle image velocimetry algorithms. While the opacity of the foam limits optical measurements to the surface-near bubbles, our approach of X-ray particle tracking velocimetry (X-PTV) sheds light on the three-dimensional foam flow. The customised tracer particles used in this work consisted of a 3D-printed tetrahedral polymer structure with a total of four small metal beads at its corners (Fig. 1). Owing to their shape and the light-weight material composite, the tracers adhered to the bubble-scale foam structure and were carried by the foam. X-ray radiography visualises the motion paths of each tracer’s metal beads, representing the local streamlines of the foam flow. Further, the X-ray radiographs map the foam’s liquid fraction distribution, thus extending the local measurement of the liquid fraction by means of the electrode pairs. X-PTV reveals comparatively high flow velocities of the three-dimensional foam flow, in particular near the overflow, whereas the optical measurements are sub-jected to wall or surface effects, yielding lower flow velocities. However, X-PTV with customised foam flow tracers comes to its limit in unstable foams at high liquid fraction and high flow velocity.

  • Lecture (Conference)
    EUFoam 2022, 03.-06.07.2022, Kraków, Polska

Permalink: https://www.hzdr.de/publications/Publ-34724
Publ.-Id: 34724


Neutron radiography of liquid drops ascending in a liquid metal

Lappan, T.; Sarma, M.; Trtik, P.; Heitkam, S.; Eckert, K.; Eckert, S.

Multiphase flows of dispersed gas bubbles and solid particles in liquid metals are hardly to investigate in situ in industrial-scale metallurgical reactors. Laboratory-scale model experiments with low-melting metal alloys have proven very beneficial for radiographic flow investigations. To extend previous experimental studies that were focussed on either bubble or particle flows in liquid gallium and its alloys, we used neutron radiography for visualising liq-uid-liquid two-phase flows of silicone oil drops in the eutectic gallium-tin alloy. We determined the average size of the ascending drops, measured the velocity of each drop along its motion path, and estimated dimensionless numbers to compare drop and bubble characteristics. Here, we exemplarily present the results for drops of 4 mm in diameter, which may serve as a valuable basis for future experiments and simulations with drops and particles in the liquid metal.

Keywords: drops; gallium; neutron radiography; single-particle tracking; two-phase flow

  • Lecture (Conference) (Online presentation)
    12th pamir International Conference on Fundamental and Applied MHD, 04.-08.07.2022, Kraków, Polska

Permalink: https://www.hzdr.de/publications/Publ-34723
Publ.-Id: 34723


Adversarial attacks for machine learning denoisers and how to resist them

Hecht, M.; Shao, Z.; Jain, S. B.

Adversarial attacks rely on the instability phenomenon appearing in general for all inverse problems, e.g., image classification and reconstruction, independently of the computational scheme or method used to solve the prob- lem. We mathematically prove and empirically show that machine learning denoisers (MLD) are not excluded. That is to prove the existence of adversarial attacks given by noise patterns making the MLD run into instability, i.e., the MLD increases the noise instead of decreasing it. We further demonstrate that adversarial retraining or classic filtering do not provide an exit strategy for this dilemma. Instead, we show that adversarial attacks can be inferred by polynomial regression. Removing the underlying inferred polynomial distribution from the total noise distribution delivers an efficient technique yielding robust MLDs that make consistent computer vision tasks such as image segmentation or classification more reliable.

Keywords: Image Denoising; Inverse Problems; Instability Phenomenon; Adversarial Attacks; Active Learning

  • Invited lecture (Conferences) (Online presentation)
    Emerging Topics in Artificial Intelligence (ETAI), 21.-25.08.2022, San Diego, USA
    DOI: 10.1117/12.2632954
  • Contribution to proceedings
    Emerging Topics in Artificial Intelligence (ETAI) 2022, 03.10.2022, San Diego, USA

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Permalink: https://www.hzdr.de/publications/Publ-34722
Publ.-Id: 34722


Microscopic and spectroscopic insights into uranium(VI) association-reduction processes by a sulfate-reducing microorganism

Hilpmann, S.; Steudtner, R.; Roßberg, A.; Hübner, R.; Prieur, D.; Bauters, S.; Kvashnina, K.; Stumpf, T.; Cherkouk, A.

Clay rock represents a suitable host rock for the long-term storage of high-level radioactive waste with bentonite as backfill material. In the event of a worst-case scenario, water can enter the repository. It is possible that naturally occurring microorganisms can interact with the radionuclides and thereby change the chemical speciation or induce redox reactions.
Among different sulfate-reducing bacteria, Desulfosporosinus species represent important members of the microbial communities in both clay rock and bentonite.[1,2] Desulfosporosinus hippei DSM 8344T is a close phylogenetic relative to an isolated bacterium from bentonite.[3] Therefore, this strain was selected to get a more profound insight into the uranium(VI) interactions with naturally occurring microorganisms from deep geological layers.
Time-dependent experiments in artificial Opalinus Clay pore water[4] (100 µM uranium(VI), pH 5,5) showed a high removal of uranium from the supernatants within a short time range. UV/Vis studies of the dissolved cell pellets provided clear proof of a partial reduction of uranium(VI) to uranium(IV) in the samples, although bands of uranium(VI) were still observable. These findings propose a combined association-reduction process as an explanation for the ongoing interaction mechanism.
Uranium aggregates formed on the cell surface were visible in TEM images. Furthermore, cells released membrane vesicles as a possible defense mechanism against cell encrustation.
In addition, HERFD-XANES measurements confirmed the reduction of uranium(VI). But with these measurements also the presence of uranium(V) in the cell pellets could be demonstrated. This provides first evidence of the involvement of uranium(V) in uranium(VI) reduction by sulfate-reducing microorganisms. With the help of EXAFS measurements, different cell-related uranium species were detected.
This study helps to better understand the complexity of redox processes in the environment and contribute to a safety concept for a nuclear repository in clay rock. Moreover, new insights into the uranium(VI) reduction mechanisms of sulfate-reducing bacteria were presented.

References:

[1] Bagnoud et al. (2016) Nat. Commun 7, 1–10.
[2] Matschiavelli et al. (2019) Environ. Sci. Technol. 53, 10514–10524.
[3] Vatsurina et al. (2008) Int. J. Syst. Evol. Microbiol. 58, 1228–1232.
[4] Wersin et al. (2011) Appl. Geochemistry 26, 931–953.

Keywords: Uranium(VI) reduction; Sulfate-reducing bacteria; Clay rock

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  • Lecture (Conference) (Online presentation)
    Goldschmidt 2022, 10.-15.07.2022, Hawaii, USA

Permalink: https://www.hzdr.de/publications/Publ-34721
Publ.-Id: 34721


Curvilinear spin-wave dynamics beyond the thin-shell approximation: Magnetic nanotubes as a case study

Körber, L.; Verba, R.; Otálora, J. A.; Kravchuk, V.; Lindner, J.; Faßbender, J.; Kakay, A.

Surface curvature of magnetic systems can lead to many static and dynamic effects which are not present in flat systems of the same material. These emergent magnetochiral effects can lead to frequency nonreciprocity of spin waves, which has been shown to be a bulk effect of dipolar origin and is related to a curvature-induced symmetry breaking in the magnetic volume charges. So far, such effects have been investigated theoretically mostly for thin shells, where the spatial profiles of the spin waves can be assumed to be homogeneous along the thickness. Here, using a finite-element dynamic-matrix approach, we investigate the transition of the spin-wave spectrum from thin to thick curvilinear shells, at the example of magnetic nanotubes in the vortex state. With increasing thickness, we observe the appearance of higher-order radial modes which are strongly hybridized and resemble the perpendicular-standing-waves (PSSWs) in flat films. Along with an increasing dispersion asymmetry, we uncover the curvature-induced non-reciprocity of the mode profiles. This is explained in a very simple picture general for thick curvilinear shells, considering the inhomogeneity of the emergent geometric volume charges along the thickness of the shell. Such curvature-induced mode-profile asymmetry also leads to non-reciprocal hybridization which can facilitate unidirectional spin-wave propagation. With that, we also show how curvature allows for nonlinear three-wave splitting of a higher-order radial mode into secondary modes which can also propagate unidirectionally. We believe that our study provides a significant contribution to the understanding of the spin-wave dynamics in curvilinear magnetic systems, but also advertises these for novel magnonic applications.

Keywords: spin waves; nanotubes; curvilinear magnetism; curvature effects; micromagnetic modeling; tetrax; nonreciprocity

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Permalink: https://www.hzdr.de/publications/Publ-34720
Publ.-Id: 34720


Mode splitting of spin waves in magnetic nanotubes with discrete symmetries

Körber, L.; Kézsmárki, I.; Kakay, A.

We investigate how geometry influences spin dynamics in polygonal magnetic nanotubes. We find that lowering the rotational symmetry of nanotubes, by decreasing the number of planar facets, splits an increasing number spin-wave modes, which are doubly degenerate in cylindrical tubes. This symmetry-governed splitting is distinct form the topological split recently observed in cylindrical nanotubes. Doublet modes, where the azimuthal period is half-integer or integer multiple of the number of facets, split to singlet pairs with lateral standing-wave profiles of opposing mirror-plane symmetries. Moreover, the polygonal geometry facilitates the hybridization of modes with different azimuthal periods but the same symmetry, manifested in avoided level crossings. These phenomena, unimaginable in cylindrical geometry, provide new tools to control spin dynamics on the nanoscale. Our concepts can be generalized to nano-objects of versatile geometries and order parameters, offering new routes to understand and engineer dynamic responses in mesoscale physics.

Keywords: Spin wave; magnon; micromagnetic modeling; symmetry; nanotubes; group theory; micromagnetism; tetrax

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Permalink: https://www.hzdr.de/publications/Publ-34719
Publ.-Id: 34719


Data publication: Influence of fabrication parameters on the magnetic and structural properties of Mn5Ge3

Xie, Y.; Li, Z.; Begeza, V.; Funk, H. S.; Fischer, I. A.; Zeng, Y.-J.; Helm, M.; Zhou, S.; Prucnal, S.

XRD, RBS, el. transport and VSM measurements of fabricated Mn5Ge3 layers on Ge <111> substrates.

Keywords: solid phase epitaxy; flash lamp annealing; ferromagnetic film; spintronic; fabrication parameter; structural property

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Permalink: https://www.hzdr.de/publications/Publ-34718
Publ.-Id: 34718


Impacts of environmental variables on biogeochemical results - orientation survey in the Peräpohja Belt, northern Finland

Middleton, M.; Pospiech, S.; Kinnunen, J.; Tolosana Delgado, R.

The potential of biogeochemistry, i.e. plant ionome, for mineral exploration has been previously demonstrated in case studies in Fennoscandia, where soils are formed on glacially transported sediments. Because plant element uptake is controlled by a variety of processes, anomalies can be weak and not necessarily caused by the underlying bedrock geochemistry. The goals of this study were: 1) to understand the effect of selected environmental variables on plant ionome and 2) to propose a compositional data analysis approach for selecting the most effective element log-ratios, plant species and their tissue types, and elementsfor a routine exploration survey in an orientation survey set-up.

The test site is located on Au-Co prospects at Rajapalot, northern Finland, stretching over highly variable metasedimentary bedrock in an undisturbed boreal forest. Sampling microsites included well-drained soils and edges of the peatlands over a variety of overburden thicknesses, which resulted in a broad spectrum of rootzone conditions. Based on existing geophysical data sets (magnetic, resistivity), used as proxies for lithological contrast, and nature type mapping, we set up a stratified random sampling design (n=98) to collect a multi-species dataset of conifer tree species and common juniper.

The compositional data analysis results show that soil moisture had a weak effect on the plant ionome. However, element log-ratios involving the target element Co in common juniper and Norway spruce were highly affected by the root zone bulk electrical conductivity. These findings highlight the importance of including the soil conditions in the sampling design and using soil electrical conductivity and dielectric permittivity measurements in the data interpretation. The response of plant ionome to bedrock was compared to the geophysical data as a coarse proxy for lithological contrasts between geological domains and to drill core lithogeochemical data as evidence for mineralization. The highly variable bedrock complicated interpretation of results in terms of relating plant ionome to geological domains. However, when compared to bedrock resistivity data, which roughly delineates the mineralized prospects, the plant ionome allowed prediction of sites with high probability for the concealed mineralized bodies at depths of several tens of meters.

Keywords: plant geochemistry; mineral exploration; anomaly; spatial pattern; environmentally friendly

  • Lecture (Conference)
    29th International Applied Geochemistry Symposium IAGS2022 - Facing the challenges of today using applied geochemistry, 23.-28.10.2022, Viña del Mar, Chile

Permalink: https://www.hzdr.de/publications/Publ-34717
Publ.-Id: 34717


Dataset for Inversion of 1D SAXS grating signal

Thiessenhusen, E.; Hoffmann, N.; Kluge, T.

This simulated dataset consists of 48k train, 6k validation and 6k test data in the h5py file format. A small example on how to access the data is located in the python script "load_data_example.py". "all_params.h5" are the three parameters of each grating in the order sigma, g, b. "all_dist.h5" are the gratings and "all_endproduct.h5" are the 2048D lineouts of the SAXS diffraction pattern. Besides the |FFT|^2 SAXS propagator a number of pertubations were implemented in order to close the domain gap between simulation and experiment.

Keywords: SAXS; lineout; grating; inversion

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Permalink: https://www.hzdr.de/publications/Publ-34715
Publ.-Id: 34715


Ultrasound Localization Microscopy in Liquid Metal Flows

Weik, D.; Grüter, L.; Räbiger, D.; Singh, S.; Vogt, T.; Eckert, S.; Czarske, J.; Büttner, L.

Liquid metal convection plays an important role in natural and technical processes. In experimental studies, an
instrumentation with a sub-millimeter spatial resolution is required in an opaque fluid to resolve the flow field near the
boundary layer. Using ultrasound methods, the trade-off between the frequency and imaging depth of typical laboratory
experiments limits the spatial resolution. Therefore, the method of ultrasound localization microscopy (ULM) was introduced
in liquid metal experiments for the first time in this study. To isolate the intrinsic scattering particles, an adaptive nonlinear
beamformer was applied. As a result, an average spatial resolution of 188 μm could be achieved, which corresponded to a
fraction of the ultrasound wavelength of 0.28. A convection experiment was measured using ULM. Due to the increased
spatial resolution, the high-velocity gradients and the recirculation areas of a liquid metal convection experiment could be
observed for the first time. The presented technique paves the way for in-depth flow studies of convective turbulent liquid
metal flows that are close to the boundary layer.

Keywords: adaptive beamforming; magnetohydrodynamic convection; sub-diffraction imaging; ultra-fast imaging; ultrasound imaging; ultrasound localization microscopy

Permalink: https://www.hzdr.de/publications/Publ-34714
Publ.-Id: 34714


Upgrade of Timing System at HZDR ELBE Facility

Zenker, K.; Kuntzsch, M.; Justus, M.; Schwarz, A.; Krmpotić, L.; Oven, Z.; Legat, U.; Rojec, U.

The ELBE center for high power radiation sources is operating an electron linear accelerator to generate various secondary radiation like neutrons, positrons, intense THz and IR pulses and Bremsstrahlung. Timing system, that is currently in operation, has been modified and extended in the last two decades to enable new experiments. At the moment parts of this timing system are using obsolete components which makes maintenance a very challenging endeavour. To make ELBE timing system again a more homogenous system, that will allow for easier adaption to new and more complex trigger patterns, an upgrade based on Micro Research Finland (MRF) hardware platform is currently in progress. This upgrade will enable parallel operation of two electron sources and subsequent kickers to serve multiple end stations at the same time. Selected hardware enables low jitter emission of timing patterns and a long-term delay compensation of the distribution network. We are currently in the final phase of development and with plans for commissioning to be completed in 2022.

Keywords: Timing; MTCA

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  • Open Access Logo Contribution to proceedings
    18th Int. Conf. on Acc. and Large Exp. Physics Control Systems, 14.-22.10.2021, Shanghai, China
    Upgrade of Timing System at HZDR ELBE Facility: JACoW Publishing, 978-3-95450-221-9, 931-934
    DOI: 10.18429/JACoW-ICALEPCS2021-THPV031

Permalink: https://www.hzdr.de/publications/Publ-34713
Publ.-Id: 34713


Nanoindentation applied to ion-irradiated and neutron-irradiated Fe-9Cr and Fe-9Cr-NiSiP model alloys

Bergner, F.; Kaden, C.; Das, A.; Merino, S.; Diego, G.; Hähner, P.

Nanoindentation of ion-irradiated materials has attracted much interest as a tool envisaged to derive the dose dependence of bulk-equivalent hardness from small samples. A major challenge arises from the steep damage gradient in the thin ion-irradiated layer and its unavoidable interplay with the indentation size effect. The present study relies on a number of choices aimed at simplifying the interpretation of the results and strengthening the conclusions. The studied alloys are two ferritic Fe-9Cr model alloys differing in controlled amounts of Ni, Si and P known to enhance irradiation hardening. Both ion-irradiated (5 MeV Fe2+ ions) and neutron-irradiated samples along with the unirradiated references were investigated using Berkovich tips. According to the collaborative nature of the study, tests were conducted in two different laboratories using different equipment. A generalized Nix–Gao approach was applied to derive the bulk-equivalent hardness and characteristic length scale parameters for the homogeneous unirradiated and neutron-irradiated samples. Comparison with Vickers hardness indicates a 6% overestimation of the bulk-equivalent hardness as compared to the ideal correlation. For the case of ion irradiation, a first model assumes a homogeneous irradiated layer on a homogeneous substrate, while a second model explicitly takes into account the damage gradient. The first model was combined with both the original and the generalized Nix–Gao relation. We have found that the results revealed for Fe-9Cr versus Fe-9Cr-NiSiP are compatible with expectations based upon known irradiation-induced microstructures. The bulk-equivalent hardness derived for ion-irradiated samples reasonably agrees with the observation for neutron-irradiated samples.

Keywords: Fe-Cr alloys; Radiation effects; Neutron irradiation; Ion irradiation; Nanoindentation; Hardness; Indentation size effect; Modelling

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  • Open Access Logo Journal of Applied Physics 132(2022), 045101
    Online First (2022) DOI: 10.1063/5.0098807

Permalink: https://www.hzdr.de/publications/Publ-34712
Publ.-Id: 34712


Three-dimensional, km-scale hyperspectral data of a well-exposed Zn-Pb mineral exploration target at Black Angel Mountain, Greenland

Lorenz, S.; Thiele, S. T.; Kirsch, M.; Unger, G.; Zimmermann, R.; Guarnieri, P.; Baker, N.; Vest Sørensen, E.; Rosa, D.; Gloaguen, R.

Hyperspectral imaging is a most promising innovative technology for non-invasive material mapping and is starting to be adapted in a wide range of applications, including geosciences, ag-riculture, and food quality control. Novel processing workflows have revolutionized the way we can correct, interpret, and integrate hyperspectral data in the past decade. The reprojection of planar hyperspectral scans to real 3D point cloud representations (“hyperclouds”) has opened up new possibilities for the mapping of large and topographically complex targets. So far, only a few tools have been developed to process and visualize this kind of data. In this contribution we pre-sent an open-source hypercloud dataset capturing complex but spectacularly well exposed geolo-gy from the Black Angel Mountain in Maarmorilik, West Greenland, alongside a detailed and interactive tutorial documenting the workflow that was used to create it.

Keywords: open-source dataset; hyperspectral data; spectral imaging; 3D hyperclouds; photogrammetry; mineral mapping; Black Angel Maarmorilik; minimum wavelength mapping; interactive workflow

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Permalink: https://www.hzdr.de/publications/Publ-34711
Publ.-Id: 34711


Data publication: Contactless Inductive Flow Tomography for real-time control of electromagnetic actuators in metal casting

Glavinic, I.; Galindo, V.; Stefani, F.; Eckert, S.; Wondrak, T.

Dataset containing the raw and post-processed data used for in the associated publication. Dataset contains the measurements of the flow-induced magnetic field for identification of the compensation parameters and the test data used to validate the model. It also contains the down-sampled velocity profile generated from the numerical simulations, and the reconstructions of the same velocity profile.

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Permalink: https://www.hzdr.de/publications/Publ-34710
Publ.-Id: 34710


Influence of fabrication parameters on the magnetic and structural properties of Mn5Ge3

Xie, Y.; Li, Z.; Begeza, V.; Funk, H. S.; Fischer, I. A.; Zeng, Y.-J.; Helm, M.; Zhou, S.; Prucnal, S.

Mn5Ge3 is a ferromagnetic material with the high potential for spintronic applications. Usually, it is grown by conventional solid state reaction of manganese with germanium using molecular beam epitaxy. Here, we report the structural and magnetic properties of Mn5Ge3 layers grown on Ge substrates using ultrafast-solid phase epitaxy (SPE) method. We investigate the influence of the substrate orientation, Mn layer thickness and annealing parameters on the crystallographic orientation and magnetization of Mn5Ge3. It is shown that after millisecond range SPE, Mn5Ge3 films always have a preferred (100) orientation whether grown on Ge (001) or (111) substrates, which determines the orientation of the magnetization easy axis lying in the film plane along c axis independent of the layer thickness. The Curie temperature of Mn5Ge3 weakly depends on fabrication parameters.

Keywords: solid phase epitaxy; flash lamp annealing; ferromagnetic film; spintronic; fabrication parameter; structural property

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Permalink: https://www.hzdr.de/publications/Publ-34709
Publ.-Id: 34709


Germanium ultrabroadband THz photoconductive antennas

Helm, M.; Singh, A.; Pashkin, O.; Winnerl, S.; Beckh, C.; Sulzer, P.; Leitenstorfer, A.; Schneider, H.

Photoconductive antennas fabricated from III-V semiconductors exhibit a spectral gap around their Reststrahlen region. This can be avoided in nonpolar semiconductors such as Si and Ge, the latter with a relatively small bandgap and high carrier mobility. Using Ge we have demonstrated the generation of a gapless THz spectrum extending up to 13 THz, limited only by the duration of the 65 fs excitation laser pulses. A severe drawback, however, is the long recombination time in the microsecond range owed to the indirect nature of the band gap. Although not essential for broadband THz emission, shorter lifetimes are necessary to ensure complete carrier recombination between subsequent laser pulses and to make these emitters compatible with standard mode-locked laser systems operating at pulse repetition rates up to hundreds of MHz.

To overcome this restriction, we have introduced deep traps into Ge via gold ion implantation. This leads to a reduction of the carrier lifetime to sub-nanosecond values. We demonstrate a photoconductive THz antenna fabricated on this Au-implanted Ge material that can be excited with mode-locked fiber lasers operating at wavelengths of 1.1 and 1.55 um and with pulse repetition rates of tens of MHz. Using extremely short excitation pulses of 11 fs, we observe a THz emission spectrum reaching up to 70 THz bandwidth, which is almost one order of magnitude higher than that of existing state-of–the-art photoconductive THz emitters fabricated on GaAs or InGaAs. We also succeeded to excite the implanted Ge antenna with pulses centered at the telecom wavelength of 1550 nm. The corresponding spectrum turned out to be somewhat weaker and less broadband, which can be related to the fact that the long-wavelength part does not overlap with the direct absorption of Ge, i.e. it is too weakly absorbed through the indirect transition.

We have shown that the group-IV elemental semiconductor Ge can be used as a broadband THz emitter without spectral gap up to 13 THz. Using Au implanted Ge and short enough excitation laser pulses, the spectrum even extends up to 70 THz and excitation can be done with fiber lasers in the telecom range. This points towards the possibility of compact, high-bandwidth THz photonic devices compatible with Si CMOS technology.

Keywords: terahertz; germanium; antenna; emitter

  • Invited lecture (Conferences)
    International School on Terahertz Photonics and Electronics, 08.-14.05.2022, Pisa, Italy

Permalink: https://www.hzdr.de/publications/Publ-34708
Publ.-Id: 34708


Contactless Inductive Flow Tomography for real-time control of electromagnetic actuators in metal casting

Glavinic, I.; Galindo, V.; Stefani, F.; Eckert, S.; Wondrak, T.

Flow control of liquid metals based on the actual flow condition is important in many metallurgical applications. For instance, the liquid steel flow in the mould of a continuous caster strongly influences the product quality. The flow can be modified by an electromagnetic brake (EMBr). However, due to the lack of appropriate flow measurement techniques, the control of those
actuators is usually not based on the actual flow condition. This paper describes the recent developments of the Contactless Inductive Flow Tomography (CIFT) towards a real-time monitoring system, which can be used as an input to the control loop for an EMBr. CIFT relies on measuring the flow-induced perturbation of an applied magnetic field and the solution of an underlying linear inverse problem. In order to implement the CIFT reconstructions in combination with EMBr, two issues have to be solved: (i) compensation of the effects of the change in EMBr strength on the CIFT measurement system and (ii) real-time solution of the inverse problem. We present solutions of both problems for a model of a continuous caster with a ruler-type EMBr. The EMBr introduces offsets of the measured magnetic field that are several orders of magnitude larger than the very flow-induced perturbations. The offset stems from the ferromagnetic hysteresis exhibited by the ferrous parts of the EMBr in the proximity of the measurement coils. Compensation of the offset was successfully achieved by implementing a numerical model of hysteresis to predict the offset. Real-time reconstruction was achieved by precalculating the computationaly-heavy matrix inverses for a predefined set of regularization parameters and choosing the optimal every measurement frame. Finally, we show that this approach does not hinder the reconstruction quality.

Keywords: Contactless inductive flow tomography; Continuous casting; Flow monitoring; EMBr; Inductive measurements; mini-LIMMCAST

Permalink: https://www.hzdr.de/publications/Publ-34707
Publ.-Id: 34707


Real-Time Monitoring of Blood Parameters in the Intensive Care Unit: State-of-the-Art and Perspectives

Bockholt, R.; Paschke, S.; Heubner, L.; Ibarlucea, B.; Laupp, A.; Janićijević, Ž.; Klinghammer, S.; Balakin, S.; Maitz, M. F.; Werner, C.; Cuniberti, G.; Baraban, L.; Spieth, P. M.

The number of patients in intensive care units has increased over the past years. Critically
ill patients are treated with a real time support of the instruments that offer monitoring of relevant
blood parameters. These parameters include blood gases, lactate, and glucose, as well as pH and temperature.
Considering the COVID-19 pandemic, continuous management of dynamic deteriorating
parameters in patients is more relevant than ever before. This narrative review aims to summarize the
currently available literature regarding real-time monitoring of blood parameters in intensive care.
Both, invasive and non-invasive methods are described in detail and discussed in terms of general
advantages and disadvantages particularly in context of their use in different medical fields but
especially in critical care. The objective is to explicate both, well-known and frequently used as well as
relatively unknown devices. Furtehrmore, potential future direction in research and development of
realtime sensor systems are discussed. Therefore, the discussion section provides a brief description
of current developments in biosensing with special emphasis on their technical implementation. In
connection with these developments, the authors focus on different electrochemical approaches to
invasive and non-invasive measurements in vivo.

Keywords: monitoring; intensive care; critical care; blood parameters; electrochemistry

Permalink: https://www.hzdr.de/publications/Publ-34706
Publ.-Id: 34706


Novel radioiodinated and radiofluorinated analogues of FT-2102 for SPECT or PET imaging of mIDH1 mutant tumours

Weber, V.; Arnaud, L.; Dukic-Stefanovic, S.; Wenzel, B.; Roux, V.; Chezal, J.-M.; Hang Lai, T.; Teodoro, R.; Kopka, K.; Miot-Noirault, E.; Deuther-Conrad, W.; Maisonial-Besset, A.

Isocitrate dehydrogenases (IDH) are metabolic enzymes commonly mutated in human cancers (glioma, acute myeloid leukemia, chondrosarcoma, and intrahepatic cholangiocarcinoma). These mutated variants of IDH (mIDH) acquire a neomorphic activity namely conversion of α-ketoglutarate to the oncometabolite D-2-hydroxyglutarate involved in tumourigenesis. Thus, mIDH have emerged as highly promising therapeutic targets and several mIDH specific inhibitors have been developed. However, the evaluation of the mIDH status, currently assessed by biopsy, is essential for patient stratification and thus treatment and follow-up. We report herein the development of new radioiodinated and radiofluorinated analogues of olutasidenib (FT-2102) as tools for non-invasive single photon emission computed tomography (SPECT) or positron emission tomography (PET) imaging of mIDH1 up- and dysregulation in tumours. Non-radiolabelled derivatives 2 and 3 halogenated at position 6 of the quinolinone scaffold were synthesised and tested in vitro for their inhibitory potencies and selectivities in comparison with the lead compound FT-2102. Using a common organotin precursor, (S)-[125I]2 and (S)-[18F]3 were efficiently synthesised by either radioiododemetallation or copper-mediated radiofluorination. Both radiotracers were stable at room temperature in saline or DPBS solution and at 37 °C in mouse serum, allowing future planning of their in vitro and in vivo evaluations in glioma and chondrosarcoma models.

Keywords: SPECT/PET imaging; mIDH1; FT-2102; radioiodination; radiofluorination

Permalink: https://www.hzdr.de/publications/Publ-34705
Publ.-Id: 34705


Optimization of 10Be measurements at the 6MV AMS facility DREAMS

Lachner, J.; Rugel, G.; Vivo Vilches, C.; Koll, D.; Stübner, K.; Winkler, S.; Wallner, A.

We investigated benefits from raising the ion beam energy during measurements of 10Be with Accelerator Mass Spectrometry (AMS) at the 6MV DREAMS (DREsden AMS) facility. Increasing the terminal voltage to ≥ 5MV hardly reduces the yield of the Be2+ charge state after the accelerator if one applies only a thin Ar gas stripper and makes use of an overpopulation of the 2+ charge state with respect to the expected equilibrium charge state yield. As a further stripping to the 4+ charge state is conducted in a 1 μm silicon nitride degrader foil after the analysing magnet, it is desirable to hit this foil with the highest available velocity in order to have optimal stripping of 10Be2+ to the naked ion. The efficiency of 10Be measurements can be improved by ca. 36% if increasing the terminal voltage from 4.5MV to 5.8MV and already by 7.5% if going to 5.0MV.

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  • Secondary publication expected from 01.02.2024

Permalink: https://www.hzdr.de/publications/Publ-34703
Publ.-Id: 34703


Master Curve Testing of RPV Steels using Mini-C(T) Specimens – Irradiation Effects and Censoring Statistics

Das, A.; Chekhonin, P.; Houska, M.; Obermeier, F.; Altstadt, E.

Includes master curve data for the materials used in this work as well as the SEM images of the fracture surfaces.

Keywords: Fracture mechanics testing; sub-sized specimen; transition temperature; reactor pressure vessel steels; Master Curve; neutron-irradiation

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Permalink: https://www.hzdr.de/publications/Publ-34701
Publ.-Id: 34701


The Ecological Potential of Manure Utilisation in Small-Scale Biogas Plants

Eggemann, L.; Rau, F.; Stolten, D.

The main sources of greenhouse gas emissions, accelerating global climate change, are heat and electricity generation. To lower these emissions, an expansion of renewable energy usage is required. Biogas plants, a flexible renewable power source, are one possibility, and are already widely established in the European energy system. This study focuses on the utilisation of raw manure in closed systems to reduce direct CO2 eq. emissions. It is the first to compare manure treatment in different types of small-scale biogas applications and under the impact of increasing temperatures resulting from climate change. The environmental impact in terms of four impact categories is evaluated by means of a life cycle assessment. Two cases are investigated: a biogas plant with either subsequent combustion in a combined heat and power plant or the direct usage of biogas as a simplified and less expensive application. The analysis shows that the first case yields ‑173 kg CO2 eq. per m³ of manure, whereas the simplified one causes 20.9 kg CO2 eq. per m³ of manure. If the first case is scaled with the currently existing number of small-manure plants in Germany, emissions of 464 mil. t CO2 eq. are mitigated per year. With increasing average annual temperatures, higher manure credits are generated and so the emissions of both plant options are reduced to ‑264 and ‑69.5 kg CO2 eq. per m³ of manure, respectively, ascribing the direct biogas usage reductions of GHG emissions. Consequently, both systems have the potential for reducing emissions due to improved manure management and can contribute to mitigating climate change.

Keywords: Life cycle assessment; improved manure management; manure credit; Environmental impact; co-product credit; negative emissions

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  • Secondary publication expected from 02.12.2023

Permalink: https://www.hzdr.de/publications/Publ-34700
Publ.-Id: 34700


Effective electronic forces and potentials from ab initio path integral Monte Carlo simulations

Dornheim, T.; Tolias, P.; Moldabekov, Z.; Cangi, A.; Vorberger, J.

The rigorous description of correlated quantum many-body systems constitutes one of the most challenging tasks in contemporary physics and related disciplines. In this context, a particularly useful tool is the concept of effective pair potentials that take into account the effects of the complex many-body medium consistently. In this work, we present extensive, highly accurate \emph{ab initio} path integral Monte Carlo (PIMC) results for the effective interaction and the effective force between two electrons in the presence of the uniform electron gas (UEG). This gives us a direct insight into finite-size effects, thereby opening up the possibility for novel domain decompositions and methodological advances. In addition, we present unassailable numerical proof for an effective attraction between two electrons under moderate coupling conditions, without the mediation of an underlying ionic structure. Finally, we compare our exact PIMC results to effective potentials from linear-response theory, and we demonstrate their usefulness for the description of the dynamic structure factor. All PIMC results are made freely available online and can be used as a thorough benchmark for new developments and approximations.

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Permalink: https://www.hzdr.de/publications/Publ-34699
Publ.-Id: 34699


Spin-resolved density response of the warm dense electron gas

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

We present extensive new \emph{ab initio} path integral Monte Carlo (PIMC) results for the spin-resolved density response of the uniform electron gas (UEG) at warm dense matter conditions. This allows us to unambiguously assess the accuracy of previous theoretical approximations, thereby providing valuable new insights for the future development of dielectric schemes. From a physical perspective, we observe a nontrivial manifestation of an effective electron--electron attraction that emerges in the spin-offdiagonal static density response function at strong coupling, r_s>5. All PIMC results are freely available online and can be used to benchmark new approximations and simulation schemes.

Permalink: https://www.hzdr.de/publications/Publ-34698
Publ.-Id: 34698


Low-lying dipole strength distribution in 204Pb

Shizuma, T.; Endo, S.; Kimura, A.; Massarczyk, R.; Schwengner, R.; Beyer, R.; Hensel, T.; Hoffmann, H.; Junghans, A.; Römer, K.; Turkat, S.; Wagner, A.; Tsoneva, N.

Dipole and quadrupole strength distribution of 204 Pb was investigated via a nuclear resonance fluorescence experiment using bremsstrahlung produced using an electron beam at a kinetic energy of 10.5 MeV at the linear accelerator ELBE. We identified 136 states resonantly excited at energies from 3.6 to 8.4 MeV. The present experimental results were used to investigate the E1 transition probabilities by comparison with predictions from the quasiparticle-phonon model (QPM) with the self-consistent energy-density functional (EDF).

Keywords: Nuclear structure; photon scattering; nuclear resonance fluorescence; electromagnetic transition strengths; quasiparticle-phonon model.

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  • Secondary publication expected from 26.10.2023

Permalink: https://www.hzdr.de/publications/Publ-34697
Publ.-Id: 34697


A Beginner’s Guide to Arterial Spin Labeling (ASL) Image Processing

Clement, P.; Petr, J.; Dijsselhof, M. B.; Padrela, B.; Pasternak, M.; Dolui, S.; Jarutyte, L.; Pinter, N.; Hernandez Garcia, L.; Jahn, A.; Kuijer, J. P.; Barkhof, F.; Mutsaerts, H. J.; Keil, V. C.

Arterial spin labeling (ASL) is a non-invasive and cost-effective MRI technique for brain perfusion measurements. While it has
developed into a robust technique for scientific and clinical use, its image processing can still be daunting.
The 2019 Ann Arbor ISMRM ASL working group established that education is one of the main areas that can accelerate the use of
ASL in research and clinical practice. Specifically, the post-acquisition processing of ASL images and their preparation for region-
of-interest or voxel-wise statistical analyses is a topic that has not yet received much educational attention.
This educational review is aimed at medical and technical researchers with an interest in ASL image processing and analysis. We
provide summaries of all typical ASL processing steps on both single-subject and group levels. The readers are assumed to have a
basic understanding of cerebral perfusion (patho)physiology; a basic level of programming or image analysis is not required.
Starting with an introduction of the physiology and MRI technique behind ASL, and how they interact with the image processing,
we present an overview of processing pipelines and explain the specific ASL processing steps. Example video and image
illustrations of ASL studies of different cases, as well as model calculations, help the reader develop an understanding of which
processing steps to check for their own studies. Some of the educational content can be extrapolated to the processing of other
MRI data. We anticipate that this educational review will help accelerate the application of ASL MRI for clinical brain research.

Permalink: https://www.hzdr.de/publications/Publ-34696
Publ.-Id: 34696


Extrinsic localized excitons in patterned 2D semiconductors

Yagodkin, D.; Greben, K.; Eljarrat Ascunce, A.; Kovalchuk, S.; Ghorbani Asl, M.; Jain, M.; Kretschmer, S.; Severin, N.; Rabe, J. P.; Krasheninnikov, A.; Koch, C. T.; Bolotin, K. I.

We demonstrate a new localized excitonic state in patterned monolayer 2D semiconductors. The signature of an exciton associated with that state is observed in the photoluminescence spectrum after electron beam exposure of several 2D semiconductors. The localized state, which is distinguished by non-linear power dependence, survives up to room temperature and is patternable down to 20 nm resolution. We probe the response of the new exciton to the changes of electron beam energy, nanomechanical cleaning, and encapsulation via multiple microscopic, spectroscopic, and computational techniques. All these approaches suggest that the state does not originate from irradiation-induced structural defects or spatially non-uniform strain, as commonly assumed. Instead, we show that it is extrinsic, likely a charge transfer exciton associated with the organic substance deposited onto the 2D semiconductor. By demonstrating that structural defects are not required for the formation of localized excitons. Our work opens new possibilities for further understanding of localized excitons as well as their use in the applications that are sensitive to the presence of defects, e.g. chemical sensing and quantum technologies.

Keywords: Two-dimensional materials; Excitons; MoS2; Electron beam; Defects; Patterning

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Permalink: https://www.hzdr.de/publications/Publ-34695
Publ.-Id: 34695


Numerical Study of Species Distribution and Overpotentials in Liquid Metal Batteries

Duczek, C.; Weber, N.; Weier, T.

The liquid metal battery (LMB) technology is highly promising for grid scale stationary energy storage. Those batteries consist of two liquid electrodes and a liquid or solid state electrolyte. Due to the possible usage of earth-abundant and inexpensive materials, LMBs are sustainable and eco-friendly. The LMBs in the present study contain a molten salt liquid electrolyte. Since the batteries are fully liquid, fluid flow needs to be considered additionally to electrochemistry and electromagnetic fields. For numerical investigations, coupling of the corresponding fundamental equations as well as the different regions in the battery is needed, which is highly challenging. Besides multiple fluid flow phenomena that are affecting the battery performance positively as well as negatively, species transport in the electrolyte and the cathode has an influence on the cell potential as well.
In the presented talk, a quasi-one-dimensional method to calculate the ionic species distribution and the corresponding overpotentials in a LMB is presented. Since these phenomena are – to the best knowledge of the authors – rarely investigated, fluid flow is neglected for simplicity. The method is based on a simulation that solves current density and potential distribution in the whole battery. This requires modeling of the electrochemical double layer as well as multi-field coupling. Hereby, the finite volume method (FVM) is used and the simulations are performed using the open source tool OpenFOAM. Application cases are Li||Bi and Na||Zn cells (see Figure 1), having slightly differing working concepts. Li||Bi batteries are already investigated to a large extend and most material properties are readily available. Therefore, a validation study of the numerical solver is performed with these LMBs. On the other hand, Na||Zn batteries are even more sustainable and eco-friendly. The authors contribute, among others, to the development of the latter within the European Union’s Horizon 2020 project SOLSTICE.

Keywords: Liquid metal technologies; Energy conversion and propulsion

  • Lecture (Conference)
    12th pamir International Conference on Fundamental and Applied MHD, 04.-08.07.2022, Krakow, Polska
  • Contribution to proceedings
    12th pamir International Conference on Fundamental and Applied MHD, 04.-08.07.2022, Krakow, Polska

Permalink: https://www.hzdr.de/publications/Publ-34694
Publ.-Id: 34694


Modeling Potential and Species Distribution in a Li||Bi Liquid Metal Battery Using the Finite Volume Method

Duczek, C.; Weber, N.; Landgraf, S.; Weier, T.

The abstract submitted to the 241st ECS meeting deals with the principle of liquid metal batteries (LMB), their pros and cons and the occuring flow phenomena in general. A special focus is set on Li||Bi cells as well as on occuring overpotentials when operating the battery. A numerical approach that is used to investigate the cell using the tool OpenFOAM is presented. Further, a validation study is performed and an application case is studied.
Attached, the full abstract can be found.

Keywords: liquid metal battery; grid storage; Finite-Volume-Methode; internal jump

  • Lecture (Conference)
    241st ECS Meeting, 29.05.-02.06.2022, Vancouver, BC, Canada

Permalink: https://www.hzdr.de/publications/Publ-34693
Publ.-Id: 34693


Composition dependent polymorphism and superconductivity in Y3+x{Rh,Ir}4Ge13-x

Feig, M.; Carrillo-Cabrera, W.; Bobnar, M.; Simon, P.; Curfs, C.; Levytskyi, V.; Tsirlin, A. A.; Leithe-Jasper, A.; Gumeniuk, R.

Polymorphism is observed in the Y3+xRh4Ge13−x series. The decrease of Y-content leads to the transformation of the primitive cubic Y3.6Rh4Ge12.4 [x = 0.6, space group Pm3¯n, a = 8.96095(9) Å], revealing a strongly disordered structure of the Yb3Rh4Sn13 Remeika prototype, into a body-centred cubic structure [La3Rh4Sn13 structure type, space group I4132, a = 17.90876(6) Å] for x = 0.4 and further into a tetragonal arrangement (Lu3Ir4Ge13 structure type, space group I41/amd, a = 17.86453(4) Å, a = 17.91076(6) Å) for the stoichiometric (i.e. x =0)Y3Rh4Ge13. Analogous symmetry lowering is found within the Y3+xIr4Ge13−x series, where the compound with Y-content x = 0.6 is crystallizing with La3Rh4Sn13 structure type [a = 17.90833(8) Å] and the stoichiometric Y3Ir4Ge13 is isostructural with the Rh-analogue [a = 17.89411(9) Å, a = 17.9353(1) Å]. The structural relationships of these derivatives of the Remeika prototype are discussed. Compounds from the Y3+xRh4Ge13−x series are found to be weakly-coupled BCS-like superconductors with Tc = 1.25, 0.43 and 0.6, for x = 0.6, 0.4 and 0, respectively. They also reveal low thermal conductivity (<1.5 W K−1 m−1 in the temperature range 1.8–350 K) and small Seebeck coefficients. The latter are common for metallic systems. Y3Rh4Ge13 undergoes a first-order phase transition at Tf = 177 K, with signatures compatible to a charge density wave scenario. The electronic structure calculations confirm the instability of the idealized Yb3Rh4Sn13-like structural arrangements for Y3Rh4Ge13 and Y3Ir4Ge13.

Keywords: Superconductivity; ROBL

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  • Secondary publication expected from 04.05.2023

Permalink: https://www.hzdr.de/publications/Publ-34692
Publ.-Id: 34692


Software publication: Influence of surface cleaning on quantum efficiency, lifetime and surface morphology of p-GaN:Cs photocathodes

Schaber, J.; Xiang, R.; Teichert, J.; Arnold, A.; Murcek, P.; Zwartek, P.; Ryzhov, A.; Ma, S.; Gatzmaga, S.; Michel, P.; Gaponik, N.

Origin-files zur Darstellung von thermischen Reinigung, Aktivierung und Quanteneffizienz-Überwachung von GaN Fotokathoden SEM Bilder als .tif Dateien EDX Spektren als Exel-files zur Darstellung von EDX Analysen AFM Orginal Bilder die mit dem Programm Gwiddion geöffnet werden können

Keywords: p-GaN; UV-photocathode; quantum efficiency; surface cleaning; surface morphology

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Permalink: https://www.hzdr.de/publications/Publ-34690
Publ.-Id: 34690


Advanced CFD and measurement technology for the study of multiphase flow in a media with complex structures.

Ding, W.; Schubert, M.

In this presentation, an overview of the development of the Computational Multiphase Fluid Dynamics (CMFD) and measurement technology for the multiphase fluid flow in a complex geometry will be presented. With the application of the Euerlian Eulerian method, population balance model, closure models for interfacial force, Algebraic interfacial area density model (AIAD), a Generalized TwO-Phase flow concept (GENTOP) was developed which is able to simulate a multiscale multiphase flow which contains large free surface structure between liquid and vapor, small dispersed bubbles and droplets simultaneously. Simulation and modeling requires also verification and validation from experiment data. Here, an invasive measurement technology (Wire-Mesh Sensors) and two non-invasive technologies (Gamma ray CT, ultra fast X_ray CT) which are able to capture cross-sectional phase distribution will be introduced.

Keywords: Multiphase phase flow; invasive/non-invasive measurement

  • Invited lecture (Conferences) (Online presentation)
    The 9th International Conference on Energy, Resources, Environment and Sustainable Development, 26.-27.05.2022, Online & Xuzhou, China

Permalink: https://www.hzdr.de/publications/Publ-34689
Publ.-Id: 34689


A CFD approach for the flow regime transition in a gas-liquid vane-type separator

Yin, J.; Zhang, T.; Krull, B.; Meller, R.; Schlegel, F.; Lucas, D.; Dezhong, W.; Liao, Y.

Two-phase flows generally occur with various flow regimes, even in fixed geometries. The transition from one regime to another requires careful numerical modeling. In vane-type gas-liquid separators, the transition from bubbly flow to stratified flow is the dominating phenomena. This paper describes the application of a morphology adaptive hybrid multi-field model (OpenFOAM-Hybrid) to predict the complex flow in such vane-type separator, covering different regimes and the corresponding transitions. By means of OpenFOAM-Hybrid, the coexistence of dispersed bubbles and continuous gas core is modelled simultaneously with the same set of equations. The key issue here is the definition of a morphology transition criterion describing the formation of continuous gas out of dispersed gas. Such a transition criterion, based on the local volume fractions of the dispersed and the continuous gas phase, is proposed. It combines coalescence and absorption transfer processes. This model is added to OpenFOAM-Hybrid and validated by predicting both gas bubbles and a continuous gas core as well as transitional regimes in the vane-type separator. The gas core morphology evolution is investigated in detail. OpenFOAM-Hybrid is capable of capturing the gas core dynamics in the vane-type separator and thus proves to be a reliable predictive tool.

Keywords: gas core stability; multi-scale interface; multi-field simulation; swirling flow; OpenFOAM

Permalink: https://www.hzdr.de/publications/Publ-34688
Publ.-Id: 34688


Investigation of Tumor Cells and Receptor-Ligand Simulation Models for the Development of PET Imaging Probes Targeting PSMA and GRPR and a Possible Crosstalk between the Two Receptors

Liolios, C.; Patsis, C.; Lambrinidis, G.; Tzortzini, E.; Roscher, M.; Bauder-Wüst, U.; Kolocouris, A.; Kopka, K.

Prostate-specific membrane antigen (PSMA) and gastrin-releasing peptide receptor (GRPR) have both been used in nuclear medicine as targets for molecular imaging and therapy of prostate (PCa) and breast cancer (BCa). Three bioconjugate probes, the PSMA specific: [68Ga]Ga-1, ((HBED-CC)-Ahx-Lys-NH-CO-NH Glu or PSMA-11), the GRPR specific: [68Ga]Ga-2, ((HBED-CC)-4-amino-1-carboxymethyl piperidine-[D-Phe6, Sta13]BN(6-14), a bombesin (BN) analogue), and 3 (the BN analogue: 4-amino-1-carboxymethyl piperidine-[(R)-Phe6, Sta13]BN(6-14) connected with the fluorescent dye, BDP-FL), were synthesized and tested in vitro with PCa and BCa cell lines, more specifically, with PCa cells, PC-3 and LNCaP, with BCa cells, T47D, MDA-MB-231, and with the in-house created PSMA-overexpressing PC-3(PSMA), T47D(PSMA), and MDA-MB-231(PSMA). In addition, biomolecular simulations were conducted on the association of 1 and 2 with PSMA and GRPR. The PSMA overexpression resulted in an increase of cell-bound radioligand [68Ga]Ga-1 (PSMA) for PCa and BCa cells and also of [68Ga]Ga-2 (GRPR), especially in those cell lines already expressing GRPR. The results were confirmed by fluorescence-activated cell sorting with a PE-labeled PSMA-specific antibody and the fluorescence tracer 3. The docking calculations and molecular dynamics simulations showed how 1 enters the PSMA funnel region and how pharmacophore Glu-urea-Lys interacts with the arginine patch, the S1', and S1 subpockets by forming hydrogen and van der Waals bonds. The chelating moiety of 1, that is, HBED-CC, forms additional stabilizing hydrogen bonding and van der Waals interactions in the arene-binding site. Ligand 2 is diving into the GRPR transmembrane (TM) helical cavity, thereby forming hydrogen bonds through its amidated end, water-mediated hydrogen bonds, and π-π interactions. Our results provide valuable information regarding the molecular mechanisms involved in the interactions of 1 and 2 with PSMA and GRPR, which might be useful for the diagnostic imaging and therapy of PCa and BCa.

Keywords: GRPR; LNCaP; MD simulations; MD-MB231; PC-3; PET imaging; PSMA; T47D; breast cancer; prostate cancer

Permalink: https://www.hzdr.de/publications/Publ-34687
Publ.-Id: 34687


Investigation of Eu3+ uptake and spatial distribution in tobacco BY-2 cells

Klotzsche, M.

Lanthanides have become essential for modern life due to their unique chemical, optical and magnetic properties.[1] On the contrary, their versatility causes an accumulation in soils and plants, thus posing a risk for the health of animals and humans. Therefore, a comprehensive understanding of the transfer and migration behavior of lanthanides into plants is crucial for a reasonable risk assessment.
In this work, suspension cultured cells of Nicotiana tabacum Bright-Yellow 2 (BY-2)[2] have been utilized to investigate the uptake of Eu(III) on a molecular level. The bioassociation of the metal was studied quantitatively by ICP MS upon the exposure to the lanthanide, and qualitatively by time-resolved laser-induced fluorescence spectroscopy (TRLFS) and chemical microscopy with particular focus on the spatial distribution and intracellular speciation of Eu(III).

[1] J.-C. Bünzli, in Encyclopedia of Chemical Technology, Wiley Blackwell, 2013, pp. 1-43.
[2] T. Nagata, Y. Nemoto, S. Hasezawa, International review of cytology 1992, 132, 1-30.

Keywords: Plant cell culture; Tobacco BY-2; Europium; Bioassociation; Speciation; Chemical microscopy; Laser spectroscopy

  • Lecture (Conference)
    ChemTUgether 2022 - Graduate Exchange To Enhance Excellent Research, 13.-14.05.2022, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-34686
Publ.-Id: 34686


Stability of doped zirconia under extreme conditions: towards long-term and secure storage of radioactive waste

Svitlyk, V.; Weiß, S.; Hennig, C.

Extreme temperatures and pressures were applied to systems based on stabilized zirconia, ZrO2, doped with Ce4+ ions as surrogate for tetravalent Actinides in order to conclude on their long term stability in deep geological underground. Both tetragonal and cubic Yttrium-stabilized ZrO2 (YSZ) exhibit excellent phase and structural stabilities up to 1150 K. In addition, incorporated guest Ce4+ did not show any increase in their mobility at elevated temperatures. Application of external pressure did not induce any structural or phase changes in cubic YSZ doped with 5 at.% Ce as well. However, a corresponding tetragonal analogue with lower Yttrium content exhibits a 2nd order phase transition towards higher cubic symmetry around 9 GPa. Remarkably, no discharge of the guest Ce4+ ions was observed throughout the transition and further upon increase in pressure. This together with T-dependent data indicates excellent affinity of guest Ce atoms with the host YSZ matrices. The parent YSZ phases are, therefore, promising candidates as host materials for long term underground immobilization for radiotoxic tetravalent elements like U, Th or Pu.

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Permalink: https://www.hzdr.de/publications/Publ-34685
Publ.-Id: 34685


Estimation of Dzyaloshinskii-Moriya interaction and domain wall damping in ultrathin nanostripes

Volkov, O.; Pylypovskyi, O.; Kronast, F.; Abert, C.; Oliveros Mata, E. S.; Makushko, P.; Mawass, M.-A.; Kravchuk, V. P.; Sheka, D.; Faßbender, J.; Makarov, D.

Asymmetric ultrathin magnetic thin films represent intriguing materil platforms, which support emerging fundamentals effects, such as skyrmion and topological [1] Hall effects and fast motion of chiral magnetic non-collinear textures [2], that underlie prospective memory and logic devices based on spin-orbit torques. Such asymmetric stacks can provide strong perpendicular magnetic anisotropy and Dzyaloshinskii-Moriya interactions (DMI), which is necessary for the sabilization of chiral non-collinear magnetic textures. As the performance of spin-orbitronic devices is determined by the static and dynamic micromagnetic parameters [3], it is crucial to determine all internal micromagnetic parameters for the particular layer combination and sample geometry. In particular, the speed of a domain wall (DW) based racetrack is determined by the DMI constant, $D$, and the DW damping parameter, $\alpha$. The necessity of having strong DMI requires the utilization of ultrathin magnetic (~1 nm) layers, which implies polycrystalinity and compromized structural quality, that substantially enhances the magnetic damping compared to bulk. Accessing this parameters typically requires dynamic experiments, whose interpretations are cumbersome due to the creep regime.
Here, we present the experimental and theoretical investigation of tilted DWs in perpendicularly magnetized asymmetric //CrOx/Co/Pt layer stacks with the surface-induced DMI. We will discuss two possible theoretical mechanism for the appearance of titled DWs: (I) A unidirectional tilt could appear in equilibrium as a result of the competition between the DMI and additional in-plane easy-axis anisotropy, which breaks the symmetry of the magnetic texture and introduce tilts [4]. (II) A static DW tilt could appear due to the spatial variation of magnetic parameters, which introduce pinning centers for DWs [5]. A moving DW can be trapped in a tilted state after the external driving field is off. Based on these theoretical approaches, we perform a statistical analysis of the DW tilt angles obtained in staticts after the external magnetic field used for the sample demagnetization was off. We found that the second approach confirms the experimental observations and allows to determine self-consistently the range of DW damping parameters and DMI constants for the particular layer stack. Using two reference fields, which provide two characteristic tilt angles, allow us to retrieve the range of DMI strength $D \geq 0.8$ mJ/m2 and DW damping parameters $\alpha \geq 0.1$. The upper limit for the DMI constant agrees with an independent transport-based measurement giving $D=0.90 \pm 0.13$ mJ/m2, which further refines our estimate of the damping parameter $\alpha=0.13 \pm 0.02$. Thus, the combination of the proposed method with standard metrological techniques opens up opportunities for the quantification of both static and dynamic micromagnetic parameters based on static measurements of the DW morphology.
[1] N. Nagaosa and Y. Tokura, “Topological properties and dynamics of magnetic skyrmions”, Nat. Nanotechnol. 8, 899 (2013).
[2] A. Fert, N. Reyren, and V. Cros, “Magnetic skyrmions: advances in physics and potential applications”, Nat. Rev. Mater. 2, 17031 (2017).
[3] C. Garg, S.-H. Yang, T. Phung, A. Pushp and S. S. P. Parkin, “Dramatic influence of curvature of nanowire on chiral domain wall velocity”, Sci. Adv. 3, e1602804 (2017).
[4] O. V. Pylypovskyi, V. P. Kravchuk, O. M. Volkov, J. Fassbender, D. D. Sheka and D. Makarov, “Unidirectional tilt of domain walls in equilibrium in biaxial stripes with Dzyaloshinskii–Moriya interaction”, J. Phys. D: Appl. Phys. 53, 395003 (2020).
[5] O. M. Volkov, F. Kronast, C. Abert, E. Se. Oliveros Mata, T. Kosub, P. Makushko, D. Erb, O. V. Pylypovskyi, M.-A. Mawass, D. Sheka, S. Zhou, J. Fassbender and D. Makarov, “Domain-Wall Damping in Ultrathin Nanostripes with Dzyaloshinskii-Moriya Interaction”, Phys. Rev. Appl. 15, 034038 (2021).

Keywords: Dzyaloshinskii-Moriya interaction; Ultrathin asymmetric magnetic layers; Domain wall

Related publications

  • Contribution to proceedings
    IEEE NAP 2022 Conference, 11.-16.09.2022, Kraków, Poland
    Proceedings of the IEEE NAP 2022 Conference

Permalink: https://www.hzdr.de/publications/Publ-34684
Publ.-Id: 34684


Printed Magnetic Field Sensors: From Wearable Devices To Interactive Surfaces

Oliveros Mata, E. S.; Voigt, C.; Ha, M.; Canon Bermudez, G. S.; Kosub, T.; Mönch, J. I.; Zabila, Y.; Illing, R.; Wang, Y.; Valdez-Garduño, N. M.; Fritsch, M.; Mosch, S.; Kusnezof, M.; Faßbender, J.; Vinnichenko, M.; Makarov, D.

Printing electronics is developing as an on-site fabrication approach to obtaining customized functional devices. [1] In particular, printed devices can be designed to suit
the specifications of each user, e.g. size, location, and functionality. Our research focuses on developing touchless devices that interact via printed magnetic field sensors. Here we will show our approach to fabricating magnetoresistive printable pastes containing magnetosensitive particles embedded in a polymeric binder. The engineering of the printed sensors relies on the properties of the paste fillers, binder, substrate, and processing techniques. The properties of the fillers change the output response of the printed sensors. For example, flake particles showing anisotropic magnetoresistance [2] and giant magnetoresistance [3] have excellent sensitivity below 1 mT making them attractive for wearable and on-skin applications. On the other hand, we studied the capabilities of bismuth-based printed sensors [4] showing non-saturating large magnetoresistance; the output characteristics of these devices made them attractive for wide-range magnetic field sensors. Tuning the mechanical properties of the binder gives special deforming capabilities to
the printed sensors. Polymeric binders used to print our sensors on flexible foils allowed us to laminate our printed systems on objects with complex geometries and even on the
human skin. For instance, we achieved stretchable (100% strain) magnetic field sensors by using a styrene-butadiene-styrene block copolymer as a binder. We demonstrated
that these printed sensors are functional after bending to 16 µm bending radius. [3] We demonstrated the scalability of printing magnetic field sensors using automatized
dispenser printing and laser sintering. This technique offers large-area, affordable, customized fabrication of flexible fully printed magnetic field sensors with minimal material requirements. [4] Such fabrication capabilities open the path for extended interactive smart surfaces and touchless terminal boards. We foresee further developing flexible printed touchless devices in 2D and even 3D printed [5] fully embedded systems for navigation, gaming, personal dosimeters, and health monitoring.
[1] Y. Khan, et al. Adv. Mater. 32, 1905279 (2020)
[2] E.S. Oliveros Mata, et al. Appl. Phys. A 127, 280 (2021)
[3] M. Ha, et al. Adv. Mater. 33, 2005521 (2021)
[4] E.S. Oliveros‐Mata, E. S., C. Voigt, et al. Adv. Mater. Technol. 2200227 (2022)
[5] E.M. Palmero, et al. IEEE Trans. Magn. 55, 1 (2018)

  • Lecture (Conference)
    2022 IEEE 12th International Conference Nanomaterials: Applications & Properties, 11.-16.09.2022, Kraków, Polska

Permalink: https://www.hzdr.de/publications/Publ-34683
Publ.-Id: 34683


Magnetic Electronic Skins For Self-Supervised Origami Soft Actuators

Oliveros Mata, E. S.; Ha, M.; Canon Bermudez, G. S.; Liu, J. A.-C.; Evans, B.; Tracy, J.; Makarov, D.

Soft actuators are coming closer to the capabilities of biological mechanical systems.[1] Biomechanics rely on soft, reconfigurable, and efficient structures that allow the
movement, displacement, and interaction of biological systems with their environment. Among others, magnetic soft actuators excel due to the untethered actuation via
electromagnetic fields.[2] Such electromagnetic actuation can be controlled via permanent magnets or coils. Alternating magnetic fields combined with the smart design
of soft actuators have achieved 100 Hz actuation speeds which are attractive to quickly react and adapt to environmental conditions.[3] Additionally, magnetic origami-like
actuators can be specifically magnetized to achieve more complex shape morphing.[4] To close the loop between the actuation of soft systems and the control of their
movements is needed a suitable sensing unit. Robotic systems are normally integrated with sensing awareness to interact with their surroundings. Flexible sensors
mechanically conformal with soft actuators are still under research development. Here, we show the first adaptation of magnetosensitive skins laminated on magnetically
actuated soft actuators.[5] Ultrathin conformal magnetic field GMR and Hall effect sensors were used to detect the magnetization state, the orientation, and the folding
state of origami-like actuators. The magnetic origami foils were made of NdFeB microparticles in PDMS. We found the best thickness and concentration parameters to
achieve untethered magnetic folds defined on the fly. We demonstrate the synergistic combination of magnetic soft actuators and e-skins allowed self-guided assembly into a
box and boat-like layouts. The assembly process was followed and controlled by the signal recovered from the laminated sensing e-skins. We expect further alike integrations for autonomous remote soft mechatronic systems, where untethered actuation is needed.
[1] A. Miriyev, et al. Nat. Commun. 8, 596 (2017)
[2] S. Wu, et al. Multifunct. Mater. 3, 042003 (2020)
2022 IEEE NAP / Abstract 2
[3] X. Wang, et al. Commun. Matter. 1, 67 (2020)
[4] Y. Kim, et al. Nature. 558, 274 (2018)
[5] M. Ha, et al. Adv. Mater. 33, 2008751 (2021)

  • Lecture (Conference)
    2022 IEEE 12th International Conference Nanomaterials: Applications & Properties, 11.-16.09.2022, Kraków, Poland

Permalink: https://www.hzdr.de/publications/Publ-34682
Publ.-Id: 34682


Geometry-induced magnetic effects in planar curvilinear nanosystems

Yershov, K.; Volkov, O.

Historically, investigation of curvature-induced effects in micromagnetism has started from planar curved ferromagnetic systems, e.g. rings, spirals, curved wires and narrow ribbons. In general, these systems could be considered as quasi one-dimensional magnetic objects, whose parameters change only along the wire while remaining constant in cross section. Thus, in the scope of this chapter much attention is dedicated to the general theoretical toolbox for the description of magnetic effects in flat curved systems without torsion. Here, the theoretical activities on the topic of curvilinear wires are summarized providing a systematic description of various static and dynamic curvature-induced effects in such systems. Also, it is discussed the available methods for the fabrication, characterization, and utilization of flat curved systems for the formation of new artificial chiral nanostructures with defined properties from standard magnetic materials.

Keywords: Curvilinear magnetism; Dzyaloshinskii- Moriya interaction; Nanostructures

  • Book chapter
    Makarov, D., Sheka, D.D: Curvilinear Micromagnetism. Topics in Applied Physics, Cham: Springer, 2022, 978-3-031-09086-8, 1-35
    DOI: 10.1007/978-3-031-09086-8_1

Permalink: https://www.hzdr.de/publications/Publ-34681
Publ.-Id: 34681


Magnetic soft actuators: magnetic soft robots from macro- to nanoscale

Canon Bermudez, G. S.; Lopez, M. N.; Evans, B. A.; Yershov, K.; Makarov, D.; Pylypovskyi, O.

In this chapter, we make the very first attempt to apply concepts of curvilinear magnetism to the active research field of magnetic soft actuators and, in particular, magnetic soft robots. Specifically, we describe the interplay between the mechanical and magnetic degrees of freedom in mechanically flexible materials. The discussion starts with the common approach based on the analysis of the balance of magnetic and mechanical forces and torques to describe the actuation behavior and performance of mechanically soft magnetic thin films, wires and ribbons. The framework of curvilinear magnetism is then applied to provide an intuitive physical picture of a complex behavior of actuators possessing a complex magnetic texture.

Keywords: soft robotics; actuation; flexible magnet

  • Book chapter
    Denys Makarov and Denis Sheka: Curvilinear Micromagnetism: from fundamentals to applications, Europe: Springer, 2022
    DOI: 10.1007/978-3-031-09086-8_8

Permalink: https://www.hzdr.de/publications/Publ-34680
Publ.-Id: 34680


Complex-shaped 3D nano-architectures for magnetism and superconductivity

Dobrovolskiy, O. V.; Pylypovskyi, O.; Skoric, L.; Fernandez-Pacheco, A.; van den Berg, A.; Ladak, S.; Huth, M.

This chapter gives an overview of the current state of 3D nanofabrication techniques and perspectives of geometry effects in complex-shaped systems. Various nano-architectures are considered, including nanostructured junctions and magnetic nanowire lattices with frustration, wireframe and mesh-like 3D objects, and 3D systems with non-trivial topology and chirality. In addition to the theoretical background, a large section is devoted to novel fabrication techniques relying upon 3D optical lithography and 3D nanoprinting by focused electron and ion beam-induced deposition. Emphasis is on 3D nano-architectures made from materials exhibiting cooperative ground states such as ferromagnetism and superconductivity.

Keywords: curvilinear magnetism; theory; fabrication; characterization

  • Book chapter
    Denys Makarov and Denis Sheka: Curvilinear Micromagnetism: from fundamentals to applications, Europe: Springer, 2023
    DOI: 10.1007/978-3-031-09086-8_5

Permalink: https://www.hzdr.de/publications/Publ-34679
Publ.-Id: 34679


Effects of curvature and torsion on magnetic nanowires

Pylypovskyi, O.; Phatak, C.; Volkov, O.

Here, we consider theoretical description and fabrication of thin wires, which are arranged along space curves. Geometry of these nanoarchitectures is characterized by two functions: curvature and torsion, which determine the modification of magnetic responses. The torsion being the key distinguishing parameter from flat curvilinear wires (discussed in Chapter 1) is in the focus of this chapter. The presented analytical approach to address thin wires of circular cross-section (wires) and rectangular cross-section (thin ribbons) deals with the geometry-induced effects stemming from the symmetric and antisymmetric exchange, as well as symmetries of spin-orbit and spin-transfer torques. Using helix- and helicoid-based samples as a case study, we discuss fundamental features in magnetic textures of geometries with twists in three-dimensional space and compare properties of ferromagnetic samples with antiferromagnetic spin chains. The experimental techniques to develop and characterize ferromagnetic nanowires of arbitrary shape at the nanoscale are described.

Keywords: magnetic nanowire; curvature; torsion; theory; fabrication; characterization

  • Book chapter
    Denys Makarov and Denis Sheka: Curvilinear Micromagnetism: from fundamentals to applications, Europe: Springer, 2022
    DOI: 10.1007/978-3-031-09086-8_2

Permalink: https://www.hzdr.de/publications/Publ-34677
Publ.-Id: 34677


Electronic materials with nanoscale curved geometries

Gentile, P.; Cuoco, M.; Volkov, O.; Ying, Z.-J.; Vera-Marun, I. J.; Makarov, D.; Ortix, C.

As the dimensions of a material shrink from an extended bulk solid to a nanoscale structure, size and quantum confinement effects become dominant, altering the properties of the material. Materials with nanoscale curved geometries, such as rolled-up nanomembranes and zigzag-shaped nanowires, have recently been found to exhibit a number of intriguing electronic and magnetic properties due to shape-driven modifications of charge motion or confinement effects. Local strain generated by curvature can also lead to changes in material properties due to electromechanical coupling. Here we review the development of electronic materials with nanoscale curved geometries. We examine the origin of shape-, confinement- and strain-induced effects and explore how to exploit these in electronic, spintronic and superconducting devices. We also consider the methods required to synthesize and characterize curvilinear nanostructures, and highlight key areas for the future development of curved electronics.

Keywords: Curvilinear magnetism; Curved electronics; Spintronics; Geometry-induced effects

Permalink: https://www.hzdr.de/publications/Publ-34676
Publ.-Id: 34676


Flexomagnetism and vertically graded Néel temperature of antiferromagnetic Cr2O3 thin films

Makushko, P.; Kosub, T.; Pylypovskyi, O.; Hedrich, N.; Li, J.; Pashkin, O.; Avdoshenko, S.; Hübner, R.; Ganss, F.; Liedke, M. O.; Butterling, M.; Wagner, A.; Wagner, K.; Shields, B. J.; Lehmann, P.; Veremchuk, I.; Faßbender, J.; Maletinsky, P.; Makarov, D.

Antiferromagnetic insulators are a prospective material science platform for magnonics, spin superfluidity, THz spintronics, and non-volatile data storage. A magnetomechanical coupling in antiferromagnets offers vast advantages in the control and manipulation of the primary order parameter yet remains largely unexplored both fundamentally and technologically. Here, we discover a new member in the family of flexoeffects in thin films of technologically relevant antiferromagnetic Cr2O3. We demonstrate that a gradient of mechanical strain can impact the magnetic phase transition resulting in the distribution of the N ́eel temperature along the thickness of a 50-nm-thick film and induces a sizable flexomagnetic coefficient of about 15 μb/nm2 originating from the inhomogeneous reduction of the antiferromagnetic order parameter. The antiferromagnetic ordering in inhomogeneously strained thin films of Cr2O3 can persist up to 100◦ C, rendering Cr2O3 relevant for industrial electronics applications. The presence of a strain gradient in thin films of Cr2O3 may therefore allow for the realization of reconfigurable antiferromagnetic racetracks, magnonic waveguides and magnon crystals. The presence of a strain gradient in ultrathin films of Cr2O3 enables new fundamental research directions on magnetomechanics and thermodynamics of antiferromagnetic solitons, spin waves and artificial spin ice systems in magnetic materials with continuously graded parameters.

Keywords: antiferromagnetism; flexomagnetism; Cr2O3; Neel temperature; NV magnetometry; magnetotransport

Related publications

Permalink: https://www.hzdr.de/publications/Publ-34673
Publ.-Id: 34673


Current- and field- induced magnetization dynamics and magnetic configurations in cylindrical nanowires

Fernandez Roldan, J. A.

In the last years the take-off of three-dimensional nanomagnetism has brought into scene diverse novel non-trivial magnetic textures that could be of interest for spintronic and nanoelectronics applications [1,2]. Particularly, cylindrical nanowires are fascinating building blocks of nanoarchitectures due to its surface curvature that promotes domain walls that are likely to reach the high velocities required for fast recording technologies like the Bloch Point (BP) domain wall [3-6], and non-trivial magnetic configurations like Skyrmion tubes [7-9]. The challenge in several technologies based on these objects is to achieve the fast controlled propagation of domain walls and tailoring magnetic domain structure. In this talk I will review recent developments in spin-polarized current- and field- magnetization processes in cylindrical nanowires [4,5], and present three-dimensional magnetic configurations that are appealing for the development of advanced technologies.

[1] A. Fernandez-Pacheco et al., Three-dimensional nanomagnetism. Nat. Commun. 8, 15756 (2017)
[2] B. Dieny et al., Opportunities and challenges for spintronics in the microelectronics industry. Nat. Electron. 3, 446–459 (2020).
[3] S. Da Col et al., Observation of Bloch-point domain walls in cylindrical magnetic nanowires, Phys. Rev. B, 89, 180405 (2014).
[4] X.-P. Ma et al., Cherenkov-type three-dimensional breakdown behavior of the Bloch-point domain wall motion in the cylindrical nanowire, Appl. Phys. Lett. 117, 062402 (2020).
[4] J.A. Fernandez-Roldan et al., Electric current and field control of vortex structures in cylindrical magnetic nanowires, Phys. Rev. B 102, 024421 (2020).
[5] M. Schöbitz et al., Fast Domain Wall Motion Governed by Topology and Oersted Fields in Cylindrical Magnetic Nanowires. Phys. Rev. Lett. 123, 217201 (2019).
[6] J. A. Fernandez-Roldan, C. Bran, R. P. del Real, M. Vazquez and O. Chubykalo-Fesenko. Bloch Point propagation in cylindrical nanowires under spin-polarized currents. (Submitted) (2021)
[7] J. A. Fernandez-Roldan et al, Magnetization pinning in modulated nanowires: from topological protection to the “corkscrew” mechanism, Nanoscale 10, 5923 (2018)
[8] J. Garcia et al, Narrow Segment Driven Multistep Magnetization Reversal Process in Sharp Diameter Modulated Fe67Co33 Nanowires, Nanomaterials 2021, 11(11), 3077 (2021).
[9] E. Berganza et al., Evidence of Skyrmion-Tube Mediated Magnetization Reversal in Modulated Nanowires. Materials 14, 5671 (2021).

Keywords: Cylindrical Magnetic Nanowire; magnetic domain wall; magnetic domain; spin-polarized current; Oersted field; skyrmion tube; three-dimensional nanomagnetism

  • Open Access Logo Invited lecture (Conferences) (Online presentation)
    Magnetic Resonance Laboratory Seminars (Argentina), 17.05.2022, Bariloche, Rio Negro, Argentina

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Permalink: https://www.hzdr.de/publications/Publ-34672
Publ.-Id: 34672


Treatment planning comparison in the PROTECT-trial randomising proton versus photon beam therapy in oesophageal cancer: results from eight European centres

Hoffmann, L.; Mortensen, H.; Shamshad, M.; Berbee, M.; Bizzocchi, N.; Bütof, R.; Canters, R.; Defraene, G.; Ehmsen, M.; Fiorini, F.; Haustermans, K.; Hulley, R.; Korevaar, E.; Clarke, M.; Makocki, S.; Muijs, C.; Murray, L.; Nicholas, O.; Nordsmark, M.; Radhakrishna, G.; Thomas, M.; Troost, E. G. C.; Vilches-Freixas, G.; Visser, S.; Weber, D.; Møller, D.

Purpose: To compare dose distributions and robustness in treatment plans from eight European centres
in preparation for the European randomized phase-III PROTECT-trial investigating the effect of proton
therapy (PT) versus photon therapy (XT) for oesophageal cancer.
Materials and methods: All centres optimized one PT and one XT nominal plan using delineated 4DCT
scans for four patients receiving 50.4 Gy (RBE) in 28 fractions. Target volume receiving 95% of prescribed
dose (V95%iCTVtotal) should be >99%. Robustness towards setup, range, and respiration was evaluated. The
plans were recalculated on a surveillance 4DCT (sCT) acquired at fraction ten and robustness evaluation
was performed to evaluate the effect of respiration and inter-fractional anatomical changes.
Results: All PT and XT plans complied with V95%iCTVtotal >99% for the nominal plan and V95%iCTVtotal >97%
for all respiratory and robustness scenarios. Lung and heart dose varied considerably between centres for
both modalities. The difference in mean lung dose and mean heart dose between each pair of XT and PT
plans was in median [range] 4.8 Gy [1.1;7.6] and 8.4 Gy [1.9;24.5], respectively. Patients B and C showed
large inter-fractional anatomical changes on sCT. For patient B, the minimum V95%iCTVtotal in the worst-
case robustness scenario was 45% and 94% for XT and PT, respectively. For patient C, the minimum
V95%iCTVtotal was 57% and 72% for XT and PT, respectively. Patient A and D showed minor inter-
fractional changes and the minimum V95%iCTVtotal was >85%.
Conclusion: Large variability in dose to the lungs and heart was observed for both modalities. Inter-
fractional anatomical changes led to larger target dose deterioration for XT than PT plans.

Keywords: Oesophageal cancer; Proton therapy; Intensity modulated radiotherapy; Treatment planning; Respiratory motion; Anatomical changes; Quality assurance; Phase III trial

Permalink: https://www.hzdr.de/publications/Publ-34670
Publ.-Id: 34670


Distinguishing local demagnetization contribution to the magnetization process in multisegmented nanowires

Marqués Marchán, J.; Fernandez Roldan, J. A.; Bran, C.; Puttock, R.; Barton, C.; Moreno, J. A.; Kösel, J.; Vazquez, M.; Kazakova, O.; Chubykalo-Fesenko, O.; Asenjo, A.

Cylindrical magnetic nanowires are promising materials with prospects to be used in a wide range of applications. The versatility of these nanostructures is based on the tunability of their magnetic properties by the appropriate selection of the composition and morphology. In addition, stochastic behaviour has attracted attention for the development of neuromorphic devices relying on probabilistic magnetization switching. Here, we present a study of the magnetization reversal process in multisegmented CoNi/Cu nanowires. Non-standard 2D magnetic maps, recorded under in-plane magnetic field produces datasets which are correlated with the magnetoresistance measurements and micromagnetic simulations. From this, the contribution of the individual segments to the demagnetization process can be distinguished. The results show that the magnetization reversal in these nanowires does not occur through a single Barkhausen jump but rather by multi-step switching, as individual CoNi segments in the NW undergo magnetization reversal. The existence of vortex states is confirmed by their footprint in the magnetoresistance and 2D MFM maps. In addition, the stochasticity of the magnetization reversal is analysed. On the one hand, we observe different switching fields among the segments due to a slight variation in geometrical parameters or magnetic anisotropy. On the other hand, the stochasticity is observed in a series of repetitions of the magnetization reversal processes for the same NW under the same conditions.

Keywords: magnetic nanowires; magnetization reversal processes; magnetoresistance; Magnetic Force Microscopy (MFM); CoNi

Permalink: https://www.hzdr.de/publications/Publ-34669
Publ.-Id: 34669


Three-dimensional antiferromagnetic architectures

Pylypovskyi, O.

Emergent geometry-driven responses in curvilinear antiferromagnets offer new possibilities to tailor chiral and anisotropic properties of the ground state and non-collinear textures. This includes a possibility to tailor weak ferromagnetism and Dzyaloshinskii-Moriya interaction by means of selection of sample’s shape.

Keywords: antiferromagnet; curvilinear nanostructure

  • Invited lecture (Conferences)
    META 2022, the 12th International Conference on Metamaterials, Photonic Crystals and Plasmonics, 19.-22.07.2022, Torremolinos, Spain

Permalink: https://www.hzdr.de/publications/Publ-34668
Publ.-Id: 34668


Curvilinear antiferromagnets for spintronics applications

Pylypovskyi, O.

Geometry-driven effects in curvilinear magnets provide an effective way to tailor functionality of magnetic nanoarchitectures. Antiferromagnets are perspective materials for novel spintronic devices. In scope of the field of curvilinear magnetism, there is a possibility to tune their chiral, anisotropic and weakly ferromagnetic responses.

Keywords: antiferromagnet; curvilinear nanostructure

  • Invited lecture (Conferences)
    IEEE nano, 04.-08.07.2022, Palma de Mallorka, Spain

Permalink: https://www.hzdr.de/publications/Publ-34667
Publ.-Id: 34667


Curvature-induced Local and Nonlocal Chiral Effects in Curvilinear Ferromagnetic Shells and Wires

Pylypovskyi, O.; Volkov, O.; Sheka, D.; Kakay, A.; Kravchuk, V.; Landeros, P.; Kronast, F.; Mönch, J. I.; Mawass, M.-A.; Saxena, A.; Faßbender, J.; Makarov, D.

Conventional magnetic nanoscale devices are based on planar thin films and straight racetracks hosting magnetic topological solitons. Recent progress in fabrication and characterization methods allows to realise and study of complex-shaped planar and three-dimensional (3D) architectures. In the planar case, boundaries of nanodots lead to the formation of inhomogeneous textures, such as vortices and antivortices. In 3D, the magnetostatic interaction favours a spatially inhomogeneous shape anisotropy, which acts as easy-axis anisotropy along wires or hard axis of anisotropy perpendicular to the film surface. These interactions track the sample geometry and enable curvature-induced symmetry-breaking effects, such as topology-induced magnetization patterning and emergent anisotropic and chiral responses of the Dzyaloshinskii-Moriya interaction (DMI) type [1,2].

Curvature-induced magnetic responses can be classified as being local or nonlocal. In ferromagnets, local effects stem from the exchange interaction and DMI. The curvature-induced DMI originates from exchange: it is linear in curvatures and has the symmetry of the interfacial DMI. Its strength can be comparable with typical values of the intrinsic DMI. This is experimentally confirmed by the stabilization of chiral domain walls (CDW) on the apex of a Permalloy parabola-shaped stripe [3]. The strength of the CDW depinning field gives an estimation for the curvature-induced DMI constant and can be tuned by the geometry. In contrast to curvature itself, also curvature gradients offer a possibility to pin CDW, which was studied with an example of a circular indentation with a conic cross-section profile. This geometry supports circular CDWs described by the forced skyrmion equation, where the effective force acts as the stabilizing factor for large-radius skyrmion and skyrmionium states [4].

The magnetostatic interaction is a source of novel curvature-induced chiral effects, which are essentially nonlocal, in contrast to the conventional DMI [5]. The effect emerges in shells with non-zero mean curvature due to the non-equivalence between the top and bottom surfaces of a geometrically curved shell. It is possible to show that the analysis of nonlocal effects in curvilinear shells can be more intuitive with a split of a conventional volume magnetostatic charge into two terms: (i) tangential charge, governed by the tangent to the sample's surface, and (ii) geometrical charge, given by the normal component of magnetization and the mean curvature. In addition to the shape anisotropy (local effect), four additional nonlocal terms appear, determined by the surface curvature. Three of them are zero for any magnetic texture in shells with the geometry of minimal surfaces. The fourth term becomes zero only for the special symmetries of magnetic textures.

The impact of local and nonlocal chiral effects on magnetic textures in curvilinear architectures will be discussed in this presentation.

Keywords: ferromagnetism; curvilinear shell

  • Lecture (Conference)
    IEEE NAP 2022, 12th International Conference Nanomaterials: Applications & Properties, 11.-16.09.2022, Krakov, Poland

Permalink: https://www.hzdr.de/publications/Publ-34666
Publ.-Id: 34666


Chiral Effects in Curvilinear 1D Antiferromagnets

Pylypovskyi, O.; Kononenko, D.; Borysenko, Y.; Tomilo, A.; Yershov, K.; Roessler, U. K.; Faßbender, J.; van den Brink, J.; Sheka, D.; Makarov, D.

Spin-orbit phenomena enable new ways to manipulate magnetic ordering in low dimensional magnetism. In this respect, materials with antiferromagnetic (AFM) coupling attract significant attention providing higher eigenfrequencies, a rich diversity of material properties and perspectives of spatial scaling due to the absence of significant stray fields. Tailoring the geometry of AFM thin films and nanowires in planar or 3D architectures provides a possibility for changing magnetic responses by means of shape of the magnet [1,2].

In this presentation, we will discuss the recently discovered chiral and anisotropic effects peculiar for curvilinear 1D antiferromagnetic spin chains.

A spin chain arranged along a space curve is a prototypical example of a curvilinear AFM whose shape is characterized by the curvature and torsion. In the absence of intrinsic anisotropy, the dipolar interaction renders the tangential direction as the hard axis of the anisotropy [3]. The competition of this geometry-tracking interaction with the nearest-neighbor exchange leads to the emergence of additional anisotropic and chiral energy terms, whose coefficients are determined by the curvature and torsion. The geometry-induced anisotropy is of easy-axis type and determines the direction of the AFM order parameter within the easy-plane enabled by the dipolar interaction. The geometry-induced inhomogeneous Dzyaloshinskii-Moriya interaction (DMI) renders the curvilinear spin chain acting as a chiral helimagnet. The latter leads to the geometrically-driven helimagnetic phase transition in helix-shaped AFM spin chains [3].

A local variation of the anisotropy axis can result in the non-collinearity of the neighboring spins in curvilinear spin chains. 1D AFMs exhibit the parity-breaking effect, which forbids exchanging sublattices once they are selected. This leads to the emergent magnetization at non-collinear AFM textures Therefore, in any spin chain arranged along a space curve, there is a weak ferromagnetism proportional to the curvature and torsion of the curve [4].

Spin chains arranged on a planar surface have the only ground state along the binormal direction [3]. In presence of an external magnetic field, their spin-flop state is dependent on geometrical parameters. The spin-reorientation transition is followed by the canted state for small enough rings due to the exchange-driven DMI. Furthermore, we will show that the curvature-induced DMI results in the hybridization of spin wave modes and enables a geometrically-driven local minimum of the low frequency branch, which opens exciting perspectives to study long-lived collective magnon states in AFMs [3]. This positions curvilinear 1D antiferromagnets as a novel platform for the realization of geometrically tunable chiral antiferromagnets for antiferromagnetic spinorbitronics and fundamental discoveries in the formation of coherent magnon condensates in the momentum space.

Keywords: spin chain; curvature; torsion; antiferromagnetism

  • Lecture (Conference)
    IEEE NAP 2022, 12th International Conference Nanomaterials: Applications & Properties, 11.-16.09.2022, Krakov, Poland

Permalink: https://www.hzdr.de/publications/Publ-34665
Publ.-Id: 34665


Magnetic composites: from printed magnetoelectronics to smart magnetic soft robots

Makarov, D.

In this presentation, we will review our activities on the realization of printed magnetic field sensors and magnetic soft robots, which are controlled by highly flexible magnetic field sensors.

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

Related publications

  • Invited lecture (Conferences)
    MRS Fall meeting, 27.11.-02.12.2022, Boston, USA

Permalink: https://www.hzdr.de/publications/Publ-34664
Publ.-Id: 34664


Curvature effects in curvilinear and 3D low dimensional magnetic architectures

Makarov, D.

In this talk, we will review current activities in the realization of geometrically curved and 3D magnetic thin film and nanowires.

Keywords: curvature effects in magnetism; curvilinear magnetism

Related publications

  • Invited lecture (Conferences)
    8th Spanish Workshop in Nanolithography, Nanolito 2022, 26.-28.10.2022, Valencia, Spain

Permalink: https://www.hzdr.de/publications/Publ-34663
Publ.-Id: 34663


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