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41397 Publications

Quantification of micromagnetic parameters in ultrathin asymmetrically sandwiched magnetic thin films

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

Ultrathin asymmetrically sandwiched ferromagnetic films support fast moving chiral magnetic domain walls and skyrmions [1,2]. This paves the way to the realization of prospective racetrack memory concept, the performance of which is determined by the static and dynamic micromagnetic parameters [3]. The necessity of having strong Dzyaloshinskii-Moriya interactions (DMI) and perpendicular magnetic anisotropy requires the utilization of ultrathin magnetic (~1 nm) layers, which compromized structural quality, that substantially enhances the magnetic damping for non-collinear magnetic textures.

Here, we present the experimental and theoretical analysis of ultrathin Co films with asymmetric interfaces //CrO x /Co/Pt and estimation of their micromagnetic parameters based on the analysis of the temperature dependence of magnetization as well as imaging of the morphology of magnetic domain walls (DWs) in stripes. Namely, we show that the best fit to the magnetometry data up to room temperature is obtained within a quasi-2D model, accounting for the lowest transversal magnons [4]. The fit provides access to the exchange constant in asymmetric stackes which is found to be about 1 order of magnitude smaller compared to the bulk Co. The experimentally observed tilt of magnetic domain walls in stripes in statics can be explained based on two models: (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 [5]. (II) A static DW tilt could appear due to the spatial variation of magnetic parameters, which introduce pinning centers for moving tilted DWs driven by magnetic field and can fix them at remanence [6]. We found that the second model is in line with the experimental observations and allows to determine self-consistently the DW damping parameter and DMI constant for the particular layer stack. The DW damping is found to be about 0.1 and explained by the enhanced longitudinal relaxation mechanism. The latter is shown to much stronger tan the standard transversal relaxation and can be even stronger than the spin pumping contribution for the case of ultrathin ferromagnetic films [7].

References:

[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] I. A. Yastremsky, O. M. Volkov, M. Kopte, T. Kosub, S. Stienen, K. Lenz, J. Lindner, J. Fassbender, B. A. Ivanov and D. Makarov, “Thermodynamics and Exchange Sti ff ness of Asymmetrically Sandwiched Ultrathin Ferromagnetic Films with Perpendicular Anisotropy”, Phys. Rev. Appl. 12, 064038 (2019).
[5] 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).
[6] 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).
[7] I. A. Yastremsky, J. Fassbender, B. A. Ivanov, and D. Makarov, “Enhanced Longitudinal Relaxation of Magnetic Solitons in Ultrathin Films”, Phys. Rev. Appl. 17, L061002 (2022).

  • Lecture (Conference)
    The 67th Annual Conference on Magnetism and Magnetic Materials (MMM 2022), 31.10.-04.11.2022, Minneapolis, USA

Permalink: https://www.hzdr.de/publications/Publ-35247
Publ.-Id: 35247


Local and Nonlocal Curvature-induced Chiral Effects in Nanomagnetism

Volkov, O.; Pylypovskyi, O.; Kakay, A.; Kravchuk, V. P.; Sheka, D. D.; Faßbender, J.; Makarov, D.

The interplay between geometry and topology of the order parameter is crucial properties in soft and condensed matter physics, including cell membranes [1], nematic crystals [2,3], superfluids [4], semiconductors [5], ferromagnets [6] and superconductors [7]. Until recently, in the case of magentism, the influence of the geometry on the magnetization vector fields was addressed primarily by the design of the sample boundaries, aiming to tailor anisotropy of the samples. With the development of novel fabrication techniques allowing to realize complex 3D architectures, not only boundary effects, but also local curvatures can be addressed rigorously for the case of ferromagnets and antiferromagnets. It is shown that curvature governs the appearance of geometry-induced chiral and anisotropic responses [6-8].

Here we provide experimental confirmations of the existence of local and non-local curvature-induced chiral interactions of the exchange and magnetostatic origin in conventional soft ferromagnetic materials. Namely, we will present the experimental validation of the appearance of exchange-driven Dzyaloshinskii-Moriya interaction interaction (DMI, local effect) for the case of conventional achiral yet geometrically curved magnetic materials [9,10]. This curvature induced DMI is predicted to stabilize skyrmions [11] and skyrmionium states [12]. Furthermore, we will address the impact of nonlocal magnetostatic interaction on the properties of curvilinear ferromagnets, which enables the stabilization of topological magnetic textures [13,14], realization of high-speed magnetic racetracks [15] and curvature-induced asymmetric spin-wave dispersions in nanotubes [16]. Furthermore, symmetry analysis demonstrates the possibility to generate a fundamentally new chiral symmetry breaking effect, which is essentially nonlocal [13]. Thus, geometric curvature of thin films and nanowires is envisioned as a toolbox to create artificial chiral nanostructures from achiral magnetic materials.

References:

[1] H. T. McMahon and J. L. Gallop “Membrane curvature and mechanisms of dynamic cell membrane remodelling”, Nature 438, 590 (2005).
[2] T. Lopez-Leon, V. Koning, K. B. S. Devaiah, V. Vitelli and A. Fernandez-Nieves, “Frustrated nematic order in spherical geometries”, Nature Physics 7, 391 (2011).
[3] G. Napoli, O. V. Pylypovskyi, D. D. Sheka and L. Vergori, “Nematic shells: new insights in topology- and curvature-induced e ff ects”, Soft Matter 17, 10322-10333 (2021).
[4] H. Kuratsuji, “Stochastic theory of quantum vortex on a sphere”, Phys. Rev. E 85, 031150 (2012).
[5] C. Ortix, Phys, “Quantum mechanics of a spin-orbit coupled electron constrained to a space curve”, Phys. Rev. B 91, 245412 (2015).
[6] D. D. Sheka, O. V. Pylypovskyi, O. M. Volkov, K. V. Yershov, V. P. Kravchuk and D. Makarov, “Fundamentals of Curvilinear Ferromagnetism: Statics and Dynamics of Geometrically Curved Wires and Narrow Ribbons”, Small 18, 2105219 (2022).
[7] D. Makarov, O. M. Volkov, A. Kakay, O. V. Pylypovskyi, B. Budinská and O. V. Dobrovolskiy, “New Dimension in Magnetism and Superconductivity: 3D and Curvilinear Nanoarchitectures”, Adv. Mater. 34, 2101758 (2022).
[8] Y. Gaididei, V. P. Kravchuk and D. D. Sheka, “Curvature Effects in Thin Magnetic Shells”, Phys. Rev. Lett. 112, 257203 (2014).
[9] O. M. Volkov, D. D. Sheka, Y. Gaididei, V. P. Kravchuk, U. K. Rößler, J. Fassbender and D. Makarov, ”Mesoscale Dzyaloshinskii-Moriya interaction: geometrical tailoring of the magnetochirality”, Sci. Rep. 8, 866 (2018).
[10] O. M. Volkov, A. Kákay, F. Kronast, I. Mönch, M.-A. Mawass, J. Fassbender and D. Makarov, “Experimental observation of exchange-driven chiral effects in curvilinear magnetism”, Phys. Rev. Lett. 123, 077201 (2019).
[11] V. P. Kravchuk, D. D. Sheka, A. Kákay, O. M. Volkov, U. K. Rößler, J. van den Brink, D. Makarov and Y. Gaididei, “Multiplet of Skyrmion States on a Curvilinear Defect: Reconfigurable Skyrmion Lattices”, Phys. Rev. Lett. 120, 067201 (2018).
[12] O. V. Pylypovskyi, D. Makarov, V. P. Kravchuk, Y. Gaididei, A. Saxena and D. D. Sheka, “Chiral Skyrmion and Skyrmionium States Engineered by the Gradient of Curvature”, Phys. Rev. Appl. 10, 064057 (2018).
[13] D. D. Sheka, O. V. Pylypovskyi, P. Landeros, Y. Gaididei, A. Kákay and D. Makarov, “Nonlocal chiral symmetry breaking in curvilinear magnetic shells”, Commun. Phys. 3, 128 (2020).
[14] C. Donnelly, A. Hierro-Rodrı́guez, C. Abert, K. Witte, L. Skoric, D. Sanz-Hernández, S. Finizio, F. Meng, S. McVitie, J. Raabe, D. Suess, R. Cowburn and A. Fernández-Pacheco, “Complex free-space magnetic field textures induced by three-dimensional magnetic nanostructures”, Nat. Nanotech. 17, 136–142 (2022).
[15] M. Yan, A. Kákay, S. Gliga and R. Hertel, “Beating the Walker limit with massless domain walls in cylindrical nanowires”, Phys. Rev. Lett. 104, 057201 (2010).
[16] J. A. Otálora, M. Yan, H. Schultheiss, R. Hertel and A. Kákay, “Curvature-induced asymmetric spin-wave dispersion”, Phys. Rev. Lett. 117, 227203 (2016).

Keywords: Curvature-induced effects; Chiral effects; Nanomagnetism

  • Lecture (Conference)
    The 67th Annual Conference on Magnetism and Magnetic Materials (MMM 2022), 31.10.-04.11.2022, Minneapolis, USA

Permalink: https://www.hzdr.de/publications/Publ-35246
Publ.-Id: 35246


3D quantitative mineral characterization of particles using X-ray computed tomography

Da Assuncao Godinho, J. R.; Hassanzadehmahaleh, A.; Heinig, T.

A new method to measure and quantify the 3D mineralogical composition of particulate
materials using X-ray computed micro-tomography (CT) is presented. The new method is
part of a workflow designed to standardize the analysis of particles based on their
microstructures without the need to segment the individual classes or grains. Classification
follows a decision tree with criteria derived from particle histogram parameters that are
specific to each microstructure, which in turn can be identified by 2D-based automated
quantitative mineralogy. The quantification of mineral abundances is implemented at the
particle level according to the complexity of the particle by taking into consideration the
partial volume effect at interphases. The new method was tested on two samples with
different particle size distributions from a carbonate rock containing various microstructures
and phases. The method allowed differentiation and quantification of more mineral classes
than traditional 3D image segmentation that uses only the grey-scale for mineral classification.
Nevertheless, due to lower spatial resolution and lack of chemical information, not all
phases identified in 2D could be distinguished. However, quantification of the mineral
classes that could be distinguished was more representative than their 2D quantification,
especially for coarser particle sizes and for minor phases. Therefore, the new 3D method
shows great potential as a complement to 2D-based methods and as an alternative to traditional
phase segmentation analysis of 3D images. Particle-based quantification of mineralogical
and 3D geometrical properties of particles opens new applications in the raw
materials and particle processing industries.

Keywords: X-ray computed tomography; mineralogy; MSPaCMAn; Quantification; Classification; 3d image

Related publications

Permalink: https://www.hzdr.de/publications/Publ-35245
Publ.-Id: 35245


Modeling fish species diversity in river networks

Tripathi, R.; Mertel, A.; Su, G.; Kelling, J.; Calabrese, J.

River basins across the world are shaped by local land topography and generally have a dendritic structure formed by convergence of river streams originating in a watershed until they end up in the main river. These river basins are also home to a plethora of aquatic lifeforms. Movement patterns of riverine biodiversity, especially fishes, are shaped by dendritic structure of river networks (see Figure 1) and habitat capacity of river basins. The ongoing river networks project at CASUS is specifically aimed at developing models to study the effects of dendritic network topology on fish biodiversity and thereby be able to predict biodiversity patterns across various river basins. Starting with an initial distribution of fish species on the river network, we explore how the biodiversity patterns, such as local species richness (LSR), in dendritic river networks evolve with time, under the assumption of species being equivalent on a per capita basis. Such neutral biodiversity models have been able to successfully explain a suite of biodiversity indices of plant and animal species across various ecological systems. In summary, the river project aims to bring together the neutral biodiversity theory and the framework of dispersal over networks to make predictions on biodiversity in riverine systems across the world. This would enable understanding the factors shaping present biodiversity and allow us to explore how climate change might affect future riverine biodiversity.

  • Open Access Logo Poster
    Big data analytical methods for complex systems, 06.-07.10.2022, Wroclaw, Poland

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Permalink: https://www.hzdr.de/publications/Publ-35243
Publ.-Id: 35243


Interdisciplinary biophysical studies of membrane proteins bacteriorhodopsin and rhodopsin

Fahmy, K.; Sakmar, T.

The centenary of the birth of H. Gobind Khorana provides an auspicious opportunity to review the origins and evolution of parallel advances in biophysical methodology and molecular genetics technology used to study membrane proteins. Interdisciplinary work in the Khorana laboratory in the late 1970s and for the next three decades led to productive collaborations and fostered three subsequent scientific generations whose biophysical work on membrane proteins has led to detailed elucidation of the molecular mechanisms of energy transduction by the light-driven proton pump bacteriorhodopsin (bR) and signal transduction by the G protein–coupled receptor (GPCR) rhodopsin. This review will highlight the origins and advances of biophysical studies of membrane proteins made possible by the application of molecular genetics approaches to engineer site-specific alterations of membrane protein structures.

Keywords: Har Gobind Khorana; Fourier transform infrared spectrosopy; amber codon suppression; Raman specroscopy

Permalink: https://www.hzdr.de/publications/Publ-35242
Publ.-Id: 35242


Dynamics of chiral domain walls under applied current in cylindrical magnetic nanowires

Fernandez Roldan, J. A.; Chubykalo-Fesenko, O.

Dynamics of two types of chiral magnetic domain walls in magnetic cylindrical nanowires under spin-polarised current are investigated by means of micromagnetic simulations. We show that Bloch point domain wall with chirality identical to that of the Oersted field can propagate without dynamical instabilities with velocities ca. 300 m/s. Domain wall width is shown to widen for a larger current density which limits the velocity increase. For domain walls with opposite chirality, we observed a new pinning mechanism created by the action of the Oersted field and limiting their propagation distance even after chirality switching. Vortex-antivortex domain walls transform into Bloch point domain wall, after which they can unexpectedly propagate either along or against the current direction. Our results demonstrate that domain wall dynamics under current in cylindrical magnetic nanowires can result in a plethora of different behaviors which will have important implications for future 3D spintronic devices.

Keywords: domain wall dynamics; cylindrical nanowire; spin-polarized current; micromagnetics; Bloch Point; Vortex-Antivortex; Oersted field; chirality; domain wall

Permalink: https://www.hzdr.de/publications/Publ-35241
Publ.-Id: 35241


Elastic response of U3Cu4Ge4 to spontaneous and field-induced phase transitions

Gorbunov, D.; Hibino, R.; Scurschii, I.; Yanagisawa, T.; Andreev, A. V.; Zherlitsyn, S.; Wosnitza, J.

U3Cu4Ge4 is a uniaxial ferromagnet that displays a first-order magnetization process (FOMP) at 25 T for field applied along the hard b axis. Here, we report on ultrasound and magnetostriction measurements of U3Cu4Ge4 in static and pulsed magnetic fields up to 40 T. The FOMP causes stepwise anomalies in the magnetoelastic properties. U3Cu4Ge4 elongates along the a and c axes and shrinks along the b axis, leading to an almost zero volume effect. The sound velocities of the longitudinal and transverse acoustic waves decrease sharply at the FOMP, whereas the sound attenuation shows pronounced peaks. An analysis of the ultrasound data using a mean-field theory suggests the existence of quadrupolar interactions and crystal-electric-field effects. The 5 f electronic states are between itinerant and localized, typical of uranium-based intermetallic compounds.

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Permalink: https://www.hzdr.de/publications/Publ-35240
Publ.-Id: 35240


D7.8 aMUSE Data Management Plan

Burzachechi, G.; Casarsa, M.; Collamati, F.; Diociaiuti, E.; Ferrari, A.; Fertl, M.; Gallinaro, M.; Giovannella, S.; Happacher, F.; Incagli, M.; Lucchesi, D.; Müller, S.; Papa, A.; Renga, F.; Silarski, M.; Stoeckinger, D.; Zola, L.

This document is the first version of the Data Management Plan (DMP) of the project ”advanced Muon Campus in US and Europe contribution” (aMUSE), funded by the European Union under the call ”H2020-MSCA-RISE-2020” (Research and Innovation Staff Exchange) with Grant Agreement number 101006726.

The aMUSE project coordinates the activities of about 80 researchers from twelve European research institutes and industries participating to the search for New Physics in the muon sector and to the design of new generation muon accelerators in high-profile US laboratories (Fermilab, BNL, SLAC). The project involves the two Fermilab Muon Campus Experiments:

  • Muon (g-2), aiming to shed light on the discrepancy on the anomalous magnetic momentum of the muon;
  • Mu2e, whose goal is to improve by four order of magnitudes the discover sensitivity for the not yet observed conversion of a muon to an electron.

aMUSE proposes also an ambitious extension of the activities already foreseen for the Muon Campus: an RD program for innovative detectors for the Mu2e upgrade (Mu2e-II, with 10 times larger beam intensity) and the design of a new beamline for CLFV searches based on muon decays as an alternative to Mu2e-II. aMUSE also constitutes a launch pad for a European-USA network for the development of muon beams for low (CLFV) and high (muon collider) energy frontiers.

During the duration of the aMUSE project (from 1.1.2022 to 31.12.2025), this first version of the Data Management Plan will be regularly evaluated and eventually adjusted to suit the needs of the aMUSE project.

This document was submitted as deliverable D7.8 in Work Package 7.

Keywords: aMUSE; HORIZON2020

Related publications

Permalink: https://www.hzdr.de/publications/Publ-35239
Publ.-Id: 35239


Frontiers of Computational Quantum Many-body Theory

Dornheim, T.

The fundamental laws necessary for the mathematical treatment of a large part of physics and the whole of chemistry are thus completely known, and the difficulty lies only in the fact that application of these laws leads to equations that are too complex to be solved." Nearly a century has passed, yet the famous quote by Paul Dirac still gets to the heart of many research fields within theoretical physics, quantum chemistry, material science, etc. In this talk, I will show how we can use cutting-edge numerical methods on modern high-performance computing systems to effectively overcome these limitations in many cases. In this way, we get unprecedented insights into quantum many-body systems on the nanoscale going all the way from ultracold atoms like superfluid helium to warm dense matter that occurs within planetary interiors and thermonuclear fusion applications.

  • Lecture (Conference)
    Big data analytical methods for complex systems, 06.10.2022, Wroclaw, Poland

Permalink: https://www.hzdr.de/publications/Publ-35238
Publ.-Id: 35238


Field-resolved THz-pump laser-probe measurements with CEP-unstable THz light sources

Ilyakov, I.; Ponomaryov, O.; Klopf, J. M.; Pashkin, O.; Deinert, J.-C.; de Oliveira, T.; Evtushenko, P.; Helm, M.; Winnerl, S.; Kovalev, S.

Radiation sources with a stable carrier-envelope phase (CEP) are highly demanded tools for field-resolved studies of light-matter interaction, providing access both to the amplitude and phase information of dynamical processes. At the same time, many coherent light sources, including those with outstanding power and spectral characteristics lack CEP stability, and so far could not be used for this type of research. In this work, we present a method enabling linear and non-linear phase-resolved terahertz (THz) -pump laser-probe experiments with CEP-unstable THz sources. THz CEP information for each pulse is extracted using a specially designed electro-optical detection scheme. The method correlates the extracted CEP value for each pulse with the THz-induced response in the parallel pump-probe experiment to obtain an absolute phase-resolved response after proper sorting and averaging. As a proof-of-concept, we demonstrate experimentally field-resolved THz time-domain spectroscopy with sub-cycle temporal resolution using the pulsed radiation of a CEP-unstable infrared free-electron laser (IR-FEL) operating at 13 MHz repetition rate. In spite of the long history of IR-FELs and their unique operational characteristics, no successful realization of CEP-stable operation has been demonstrated yet. Being CEP-unstable, IR-FEL radiation has so far only been used in non-coherent measurements without phase resolution. The technique demonstrated here is robust, operates easily at high-repetition rates and for short THz pulses, and enables common sequential field-resolved time-domain experiments. The implementation of such a technique at IR-FEL user end-stations will facilitate a new class of linear and non-linear experiments for studying coherent light-driven phenomena with increased signal-to-noise ratio.

Keywords: Terahertz; Free electron laser; Electro-optic sampling; Terahertz time-domain spectroscopy

Permalink: https://www.hzdr.de/publications/Publ-35236
Publ.-Id: 35236


Durch den Service-Dschungel zum Tempel des Wissens - Forschungsdatenmanagement am HZDR

Fiedler, M.; Grzondziel, J.; Knodel, O.

Schon früh wurde am Helmholtz-Zentrum Dresden – Rossendorf (HZDR) die Relevanz eines nachhaltigen Umgangs mit Forschungsdaten und -Software gemäß FAIR-Prinzipen erkannt. Vor diesem Hintergrund wurden seit 2017 schrittweise neue (Forschungs-)Infrastrukturen wie das Invenio-basierte Forschungsdatenrepositorium RODARE geschaffen, Tools wie der Research Data Management Organizer (RDMO) adaptiert und am Zentrum implementiert sowie Data und Software-Policies vereinbart.

Seither stellen sich die Interessengruppen und Akteure den generellen Herausforderungen des Forschungsdatenmanagements (FDM) wie den multidisziplinären Anforderungen, den mehrstufigen Prozessen oder der nachgelagerten Betrachtung in Projektverläufen vor allem der spezifischen Situation am HZDR. Eigenständigkeit und Kooperation unter den einzelnen Instituten gehen am Zentrum Hand in Hand. Die daraus entstehende umfangreiche Bandbreite an wissenschaftlichen Themen hat zur Folge, das immer wieder sehr spezifische Anforderungen an das FDM herangetragen werden, welche großen Einfluss auf die konkrete Ausgestaltung der Lösungsansätze haben.

Das HZDR hat die überragende Bedeutung des Wissenstransfers im FDM erkannt und zur agilen Begegnung der genannten Herausforderungen konzeptionell wichtige Weichenstellungen vorgenommen. Das FDM-Team der Bibliothek und der Abteilung „Computational Science“ bündelt die Aktivitäten aller weiteren wichtigen Akteure (u. a. „Programmplanung und Internationale Projekte“, IT-Infrastruktur, Technologie-Transfer und Rechtsabteilung) rund um das Thema. Durch gemeinsame Entwicklungen entstehen Maßnahmen, welche den Anforderungen (Metadaten, Transfer, Dokumentation, Guidelines etc.) durch das aufeinander abgestimmte Zusammenspiel von technischen Werkzeugen (Weiterentwicklung RODARE, Integration FIS und RODARE, HZDR-Cloud, Projekt Dashboard HELIPORT, Automatisierte Software Publikation über HERMES, GitLab, Dokumentation im HZDR-internen MediaWiki etc.) und Serviceleistungen (Schulungen, Workshops, Beratungen) gerecht werden sollen.

Um die offerierten Tools und Services noch besser bekannt zu machen und an den einzelnen Punkten des Forschungs-/Publikationszyklus zu implementieren, werden das HZDR-Intranet als wichtige Plattform des Wissenstransfers für die einzelnen Wertschöpfungsprozesse entlang des Datenlebenszyklus neu konzipiert und übersichtliche sowie leicht handhabbare Möglichkeiten für den Direktkontakt zwischen Wissenschaft und Dienstleister geschaffen. Der dabei gewählte ganzheitliche Ansatz soll dabei helfen, alle Facetten von Open Science nachhaltig gestalten und zukünftigen Anforderungen aktiv begegnen zu können.

Das Poster will das Konzept vorstellen, zum konstruktiven Austausch einladen sowie als Inspirationsquelle für konsequente Weiterentwicklungen im FDM dienen.

Keywords: Data Life Cycle; Information; Services; Research Data Management; Forschungsdaten

  • Open Access Logo Poster
    3. Sächsische FDM-Tagung - Forschungsdatenmanagement im Spannungsfeld zwischen Idealen, Anforderungen und Praxis, 22.09.2022, Leipzig, Deutschland
    DOI: 10.5281/zenodo.7143070

Permalink: https://www.hzdr.de/publications/Publ-35235
Publ.-Id: 35235


Curvilinear nanomagnetism

Volkov, O.

Broken magnetic symmetry is a key aspect in condensed matter physics and in particular in magnetism. It results in the appearance of chiral effects, e.g. topological Hall effect [1] and non-collinear magnetic textures including chiral domain walls and skyrmions [2,3]. These magnetochiral effects originate from an antisymmetric exchange interaction, the intrinsic Dzaloshinskii-Moriya interaction (DMI). At present, tailoring of DMI is done rather conventionally by optimizing materials, either doping a bulk single crystal or adjusting interface properties of thin films and multilayers.
A viable alternative to the conventional material screening approach can be the exploration of the interplay between geometry and topology. In the emergent field of curvilinear magnetism chiral effects are associated to the geometrically broken inversion symmetries [4]. Those appear in curvilinear architectures of even conventional materials. There are numerous exciting theoretical predictions of exchange- and magnetostatically-driven curvature effects, which do not rely on any specific modification of the intrinsic magnetic properties, but allow to create non-collinear magnetic textures in a controlled manner by tailoring local curvatures and shapes [5,6]. Until now the predicted chiral effects due to curvatures remained a neat theoretical abstraction.
Here, I present the very first experimental confirmation of the existence of the curvature-induced chiral interaction with exchange origin in a conventional soft ferromagnetic material [7,8]. It is experimentally explored the theoretical predictions, that the magnetisation reversal of flat parabolic stripes shows a two step process. By measuring the domain wall depinning field, we established that it is linked to the exchange-induced DMI and scales with curvature, that is in line with the theoretical prediction. Furthermore, the exchange-induced DMI strength can be tuned by changing the local curvature at the apex of parabola.

[1] N. Nagaosa, et al., Nature Nanotech. 8, 899 (2013).
[2] U. K. Rößler, et al., Nature 442, 797 (2006).
[3] A. Fert, et al., Nature Rev. Mat. 2, 17031 (2017).
[4] Y. Gaididei, et al., Phys. Rev. Lett. 112, 257203 (2014).
[5] J. A. Otálora, et al., Phys. Rev. Lett. 117, 227203 (2016).
[6] V. P. Kravchuk, et al., Phys. Rev. Lett. 120, 067201 (2018).
[7] O. M. Volkov et al., Phys. Rev. Lett. 123, 077201 (2019).
[8] O. M. Volkov et al., Physica Status Solidi – Rapid Research Lett. 13, 1800309 (2019).

Keywords: Dzaloshinskii-Moriya interaction; Cuvilinear magnetism; Chiral effects

  • Invited lecture (Conferences)
    3-day International Conference on Materials Science, 26.-28.10.2022, Verona, Italy

Permalink: https://www.hzdr.de/publications/Publ-35234
Publ.-Id: 35234


Simulation of mass transfer in Bubble columns

Khan, H.; Rzehak, R.

Bubble column reactors are extensively used in a variety of industrial processes involving gas-liquid mass transfer along with chemical reactions. Despite intensive research, knowledge on the mass transfer is still limited in comparison with that on the fluid dynamics, which provides an open field of research.

In this study, mass transfer of CO2 between air bubbles and water in a bubble column is investigated using Euler-Euler simulations in OpenFOAM. Previously validated fluid dynamics models are applied and focus is put on the description of the mass transfer. Experimental data to validate the results are taken from the study of Deckwer providing axial profiles of gas fraction, and carbon dioxide concentration in both phases. Previous work considering only cases with co-current absorption is extended to also include the cases with counter-current flow and desorption. Some simplifications are made in accordance with the previous work, i.e. taking the bubble diameter to be constant and using the experimentally determined values for the mass transfer coefficient. Despite these simplifications, the simulation results show a quite good agreement with the experimental data.

As a second step, the change in bubble size due to the mass transfer is included in the simulations by means of a population balance equation discretized using the class method. The well-known model of Brauer is implemented as an example of a bubble size dependent mass transfer coefficient. Since experimental data including the development of bubble size are not available for comparison, an initial validation is provided by comparison of the polydisperse calculation with two monodisperse calculations corresponding to initial and final size in the former.

Keywords: Euler-Euler simulation; Mass-transfer; Dispersed gas-liquid multiphase flow; Closure relations

  • Lecture (Conference)
    14th European Fluid Mechanics Conference (EMFC), 13.-16.09.2022, Athens, Greece

Permalink: https://www.hzdr.de/publications/Publ-35233
Publ.-Id: 35233


Effect of surfactant-related lift force modifications in bubble columns

Heßenkemper, H.; Lucas, D.

Bubble columns and bubble column reactors are well established in the field of chemical and biochemical engineering. As the flow in such apparatus influence the performance of mixing or heat and mass transfer processes, numerous studies focus on the hydrodynamic description of the flow as well as the spatial distribution of bubbles inside the vessel. For the latter, the shear-induced lift force plays a key role as it acts lateral to the bubble rise direction and correspondingly affects the lateral distribution of bubbles. However, studies regarding the lift force usually focus on rather clean or uncontaminated systems, although even small amounts of surfactants are known to significantly change bubble characteristics like drag, coalescence and breakup behavior as well as the bubble shape in the case of ellipsoidal bubbles.
In previous studies we investigated the influence of surfactants on the lift force of ellipsoidal single bubbles and could reveal strong changes of the lift coefficient 𝐶 𝐿 in comparison to clean bubbles 1 . To elaborate the effect of the lift force in buoyancy driven bubbly flows, we present measurements conducted in a 2.0 m tall column with a polydisperse bubble size. This allows to study the development of bubble size-dependent gas fraction profiles along a distance that is sufficient for the effect of the lift force to unfold sufficiently. In these experiments, we added different dozes of 1-Pentanol to the flow in order to investigate a surfactant-related modification of the lift force in dependence on the contamination degree. We use shadowgraphic high-speed imaging to determine liquid velocity and gas phase properties. For the former we use a PIV-like technique called Particle Shadow Velocimetry, while for the latter we use a novel deep learning based procedure that uses Convolutional Neural Networks to
determine bubbles and reconstruct occluded bubble parts in the images. Although the addition of surfactants affects bubbles in multiple aspects, we link some of the findings to our previous studies on the shear-induced lift force and demonstrate the influence of surfactants on several flow characteristics in bubble columns.

  • Poster
    4th International Symposium on Multiscale Multiphase Process Engineering (MMPE), 26.-27.09.2022, Berlin, Germany

Permalink: https://www.hzdr.de/publications/Publ-35232
Publ.-Id: 35232


Processing and application of arterial spin labeling magnetic resonance imaging

Petr, J.

This thesis focuses on the image processing methods for brain perfusion measurement using a magnetic resonance imaging (MRI) sequence called arterial spin labeling (ASL). We show the importance of dealing with brain volume changes as a measurement confounder, we propose a framework for integrating all processing steps in a robust processing pipeline, and lastly, we show an application of the ASL acquisition and processing to adverse effect measurements in healthy brain tissue of patients undergoing brain radio-chemotherapy demonstrating the usefulness of the method in uncovering structural and physiological changes in the brain.

  • Other
    Czech Technical University in Prague, 2022
    PURL: http://hdl.handle.net/10467/104314

Permalink: https://www.hzdr.de/publications/Publ-35231
Publ.-Id: 35231


Data publication: Stabilization of nanoscale iron films by self-terminated electrodeposition in sulfate electrolyte

Nichterwitz, M.; Duschek, K.; Zehner, J.; Oswald, S.; Heller, R.; Leistner, K.

All RBS Data from measurements with both standard RBS as well as liquid cell RBS, including Simulation files in SIMNRA data format

Keywords: Electrodeposition; sulfate electrolyte; electro chemistry; Rutherford backscattering; iron oxide; nano structures; magnetic properties

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Permalink: https://www.hzdr.de/publications/Publ-35230
Publ.-Id: 35230


Accurate Temperature Diagnostics for Matter under Extreme Conditions

Dornheim, T.

The experimental investigation of matter under extreme densities and temperatures as they occur for example in astrophysical objects and nuclear fusion applications constitutes one of the most active frontiers at the interface of material science, plasma physics, and engineering. The central obstacle is given by the rigorous interpretation of the experimental results, as even the diagnosis of basic parameters like the temperature T is rendered highly difficult by the extreme conditions. In this work, we present a simple, approximation-free method to extract the temperature of arbitrarily complex materials from scattering experiments, without the need for any simulations or an explicit deconvolution. This new paradigm can be readily implemented at modern facilities and corresponding experiments will have a profound impact on our understanding of warm dense matter and beyond, and open up a gamut of appealing possibilities in the context of thermonuclear fusion, laboratory astrophysics, and related disciplines.

  • Lecture (Conference)
    10th Workshop on High Pressure, Planetary and Plasma Physics (10HP4), 28.09.2022, Brussels, Belgium

Permalink: https://www.hzdr.de/publications/Publ-35229
Publ.-Id: 35229


Stabilization of nanoscale iron films by self-terminated electrodeposition in sulfate electrolyte

Nichterwitz, M.; Duschek, K.; Zehner, J.; Oswald, S.; Heller, R.; Leistner, K.

Iron and iron oxide nanostructures are of broad interest for numerous applications, such as in the fields of magnetic data
storage, spintronics, biosensing and catalysis. In all of these cases, defined deposition on nanometer scale is essential for
functionality. For conventional electrodeposition of transition metals, precise thickness control and layer stability at the
nanoscale are difficult due to dissolution tendencies in acidic electrolytes after the voltage is switched off. In contrast to
previous studies that focused on self-termination of Ni and Ni-based alloys, we investigate the thickness control of nanoscale
iron oxide/iron layers using self-terminated electrodeposition from sulfate electrolytes. Electrochemical quartz crystal
microbalance measurements show that self-terminated thickness can be controlled by both deposition potential and iron ion
concentration. Comparison of experimental results with model calculations based on diffusion theory reveal two different
growth modes for self-termination. At low iron ion concentration, self-termination of iron proceeds via the formation of an
ultrathin iron hydroxide layer. At larger iron ion concentration, precipitation of bulk Fe(OH)2 dominates the film growth and
self-termination is shifted to more negative potentials. All self-terminated layers exhibit enhanced stability in the electrolyte
after the voltage is switched off compared to those deposited in the conventional deposition regime. With in situ Rutherford
backscattering spectrometry measurements, we can follow the self-terminating deposition and the stability after voltage
switch-off for longer times online. Surface analytical and morphological analyses show that the self-terminated layers exhibit
a higher iron oxide/iron ratio and are smoother than layers obtained by conventional electrodeposition.

Keywords: Electrodeposition; sulfate electrolyte; electro chemistry; Rutherford backscattering; iron oxide; nano structures; magnetic properties

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Permalink: https://www.hzdr.de/publications/Publ-35228
Publ.-Id: 35228


Data publication: Training-free hyperparameter optimization of neural networks for electronic structures in matter

Fiedler, L.; Hoffmann, N.; Mohammed, P.; Popoola, G. A.; Yovell, T.; Oles, V.; Ellis, J. A.; Rajamanickam, S.; Cangi, A.

This repository contains scripts to reproduce the results of the publication
"Electronic Structure Machine Learning Surrogates without Training". Training data has to be downloaded separately.

Keywords: Density Functional Theory; Machine Learning; Surrogate Model

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Permalink: https://www.hzdr.de/publications/Publ-35227
Publ.-Id: 35227


Ion-Induced Surface Charge Dynamics in Freestanding Monolayers of Graphene and MoS2 Probed by the Emission of Electrons

Niggas, A.; Schwestka, J.; Balzer, K.; Weichselbaum, D.; Schlünzen, N.; Heller, R.; Sascha, C.; Inani, H.; Tripathi, M.; Speckmann, C.; McEvoy, N.; Susi, T.; Kotakoski, J.; Gan, Z.; George, A.; Turchanin, A.; Bonitz, M.; Aumayr, F.; Wilhelm, R. A.

We compare the ion-induced electron emission from freestanding monolayers of graphene and MoS2 to find a sixfold higher number of emitted electrons for graphene even though both materials have similar work functions. An effective single-band Hubbard model explains this finding by a charge-up in MoS2 that prevents low energy electrons from escaping the surface within a period of a few femtoseconds after ion impact. We support these results by measuring the electron energy distribution for correlated pairs of electrons and transmitted ions. The majority of emitted primary electrons have an energy below 10 eVand are therefore subject to the dynamic charge-up effects at surfaces.

Keywords: Highly charged ions; 2D materials; Graphene; MoS2; Electron Emission; Surface Charge; Ion induced surface modifications

Permalink: https://www.hzdr.de/publications/Publ-35226
Publ.-Id: 35226


Training-free hyperparameter optimization of neural networks for electronic structures in matter

Fiedler, L.; Hoffmann, N.; Mohammed, P.; Popoola, G. A.; Yovell, T.; Oles, V.; Ellis, J. A.; Rajamanickam, S.; Cangi, A.

A myriad of phenomena in materials science and chemistry rely on quantum-level simulations of the electronic structure in matter. While moving to larger length and time scales has been a pressing issue for decades, such large-scale electronic structure calculations are still challenging despite modern software approaches and advances in high-performance computing.
The silver lining in this regard is the use of machine learning to accelerate electronic structure calculations -- this line of research has recently gained growing attention.
The grand challenge therein is finding a suitable machine-learning model during a process called hyperparameter optimization. This, however, causes a massive computational overhead in addition to that of data generation.
We accelerate the construction of neural network models by roughly two orders of magnitude by circumventing excessive training during the hyperparameter optimization phase. We demonstrate our workflow for Kohn-Sham density functional theory, the most popular computational method in materials science and chemistry.

Keywords: Density Functional Theory; Machine Learning; Surrogate Model

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Permalink: https://www.hzdr.de/publications/Publ-35225
Publ.-Id: 35225


Extension of the multi-regime two-fluid model towards wall-bounded multi-scale liquid films

Porombka, P.; Schlottke, J.

Multiregime closure models for the two-fluid model often focus on continuous-dispersed and large-scale interface flow morphologies (Cerne, Petelin and Tiselj, 2021), (Hänsch et al., 2012), (Mathur et al., 2019).
Thin liquid films at solid walls, e.g. in annular flow or film condensation, so far have not been considered in a multi-regime two-fluid (MTF) model.
Rather, thin liquid films are currently treated as large-scale interfaces.
The film interface thus has to be resolved, which is conflicting with the two-fluid model approach and increases computational cost.
For the interface resolving volume-of-fluid method, coupling to a liquid film (LF) model was previously proposed to treat subgrid size liquid films (Kakimpa, Morvan and Hibberd, 2016).
Here, we adapt this approach to the framework of the MTF model.
A film thickness transport equation and film momentum equation are solved in a shell region of the two-fluid model volume domain.
Mass- and momentum transfer between both models is included depending on a critical film volume fraction in the first cell at the wall.
Thus a hybrid representation of liquid films depending on the local film thickness is obtained in the proposed LF-MTF model.
The implementation in the CFD solver STAR-CCM+ is outlined and a basic verification case is presented.
Validation results of LF-MTF model simulations against X-ray microtomographic data of horizontal annular flow (Porombka et al., 2021) show qualitative agreement and outline paths for further model improvement.
Finally, simulation results of droplet separators demonstrate the applicability of the LF-MTF model to industrial CFD.

Keywords: thin film model; two-fluid model; CFD

  • Lecture (Conference)
    International Conference on Numerical Methods in Multiphase Flows - 4, 28.-30.09.2022, Venedig, Italien

Permalink: https://www.hzdr.de/publications/Publ-35224
Publ.-Id: 35224


aMUSE Report June 2022

Burzachechi, G.; Casarsa, M.; Collamati, F.; Diociaiuti, E.; Ferrari, A.; Fertl, M.; Gallinaro, M.; Giovannella, S.; Happacher, F.; Incagli, M.; Lucchesi, D.; Martini, M.; Müller, S.; Papa, A.; Renga, F.; Silarski, M.; Stöckinger, D.; Zola, L.

This document summarizes the aMUSE activities carried on in the first six months of the
project (January-June 2022). For each Work Package, an overview of the progresses done
so far is reported. Outreach, dissemination and training activities are also listed.

Keywords: aMUSE; HORIZON2020

  • Other report
    Brüssel: EU Commission, 2022

Permalink: https://www.hzdr.de/publications/Publ-35223
Publ.-Id: 35223


Electrical Conductivity of High-Pressure Iron from Microscopic Ohm’s Law

Ramakrishna, K.; Lokamani, M.; Vorberger, J.; Baczewksi, A.; Cangi, A.

Understanding the electronic transport properties of iron under high temperatures and pressures is essential for constraining geophysical processes. The difficulty of reliably measuring these properties calls for sophisticated theoretical methods that can support diagnostics. We present electrical conductivity results from simulating microscopic Ohm’s law using the real-time formalism of time-dependent density functional theory for conditions ranging from high-pressure solid at ambient temperature to earth-core conditions.

Keywords: Matter under Extreme Conditions; Planetary Physics; High-Performance computing; Ab-initio Methods

  • Lecture (Conference)
    10th Joint Workshop on High Pressure Planetary and Plasma Physics (HP4), 28.09.2022, Brussels, Belgium

Permalink: https://www.hzdr.de/publications/Publ-35222
Publ.-Id: 35222


Gutachten zu Elektro-/Elektronikschrott für das Technikfolgen-Abschätzungs-Büro des Deutschen Bundestages

Dirlich, S.

Die Präsentation im Rahmen eines Projekttreffens von "Circular by Design" stellt die wesentlichen Ergebnisse des Gutachtens vor.. Neben den gesetzlichen Grundlagen wird der aktuelle Stand in der Sammlung und Verwertung ebenso vorgestellt, wie gute Beispiele, die als Grundlage für die erarbeiteten Lösungsansätze und Handlungsempfehlungen dienen. ,

Keywords: Elektroschrott; Recycling; Rezyklate; Kreislaufwirtschaft; Gutachten

  • Lecture (others) (Online presentation)
    Projekttreffen "Circular by Design", 07.09.2022, Freiberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-35221
Publ.-Id: 35221


Hydrogen Electrolyzer Recycling - Characterization of the layers and particle components of membrane electrode assemblies to assess the ultrafine particle separation ability

Ahn, S.; Rudolph, M.; Mütze, T.

In water electrolyzer cells, active materials contain various fine-grained critical raw materials such as platinum group metals or rare earth elements. Although the readiness level of water electrolysis technology is high and large scale of hydrogen production is targeted worldwide, there has been no significant research on recycling of end of life (EOL) water electrolyzer cells. For a functioning circular economy, recycling processes for these valuable materials have to be developed especially on the fine particle scale below 100 μm.
The in-depth characterization of water electrolyzer cells and their components allows to assess their liberation behavior and subsequent separability based on different particle properties, e.g. size, density, wettability, etc. Thus, this paper aims at identifying the material composition and properties of proton exchange membrane electrolyzer cell (PEMEL) and high temperature electrolyzer cell (HTEL) before processing. In PEMEL, critical raw materials such as iridium, ruthenium, and platinum are used, while nickel, lanthanum, and yttrium are used in HTEL. Techniques such as automated mineralogical analysis (MLA), X-ray fluorescence spectroscopy and microscopy (XRF) and laser diffraction are used to identify the possibility of liberation. To ensure a high recovery rate of critical raw materials, the surface properties of individual component have been studied. Additional contact angle studies by means of pressed bubble and the particle attachment on single air bubbles revealed the wettability of membrane electrode assemblies and significant differences between the components. Furthermore, pH and salinity show to influence the wetting behaviour of the components. These findings provide the design of the separation study for EOL electrolyzer cells.

Keywords: Characterization; Recycling; Particle separation; proton exchange membrane electrolyzer; high temperature electrolyzer

  • Lecture (Conference)
    World Congress on Particle Technology (WCPT 9), 18.-22.09.2022, Madrid, Spain

Permalink: https://www.hzdr.de/publications/Publ-35220
Publ.-Id: 35220


A New Group of Two-Dimensional Non-van der Waals Materials with Ultra Low Exfoliation Energies

Barnowsky, T.; Krasheninnikov, A.; Friedrich, R.

The exfoliation energy — quantifying the energy required to extract a two-dimensional (2D) sheet from the surface of a bulk
material — is a key parameter determining the synthesizability of 2D compounds. Here, using ab initio calculations, we present
a new group of non-van der Waals 2D materials derived from non-layered crystals which exhibit ultra low exfoliation energies.
In particular for sulfides, surface relaxations are essential to correctly describe the associated energy gain needed to obtain
reliable results. Taking into account long-range dispersive interactions has only a minor effect on the energetics and ultimately
proves that the exfoliation energies are close to the ones of traditional van der Waals bound 2D compounds. The candidates
with the lowest energies, 2D SbTlO3 and MnNaCl3, exhibit appealing electronic, potential topological, and magnetic
features as evident from the calculated band structures making these systems an attractive platform for fundamental and applied
nanoscience.

Keywords: 2D materials; exfoliation; computational materials science

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Permalink: https://www.hzdr.de/publications/Publ-35218
Publ.-Id: 35218


Defect engineering in two-dimensional materials

Ghorbani Asl, M.

It is well known that structural defects have a remarkable influence on the optical, electrical, and catalytic properties of 2D materials. In addition to imaging utilization, irradiation with electron and ion beams allows precise control of defect generation by altering beam conditions and exposure dose4. We have studied the effects of ion irradiation on 2D materials by using first-principles calculations combined with analytical potential molecular dynamics. In particular, the defect production mechanisms for various free-standing and supported 2D targets were studied. The amount of damage in single-layer transition-metal dichalcogenides was explored under the impacts of noble gases with a wide range of energies and incident angles. We showed that ion irradiation can produce uniform pores in 2D transition metal dichalcogenides for applications such as gas separation. The possibility of changing defect concentrations opens a path for tuning electronic, and magnetic properties of 2D materials via a combination of thermal treatment and a reactive vapor. Moreover, defect engineering can be used to generate luminescent centers to enable quantum emitter applications.

Keywords: 2D materials; defects; electronics; optics

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  • Invited lecture (Conferences) (Online presentation)
    Webinar talks from leading international experts from various fields of STEM, 12.09.2022, Bengaluru, India

Permalink: https://www.hzdr.de/publications/Publ-35217
Publ.-Id: 35217


Wafer-scale nanofabrication of single telecom quantum emitters in silicon

Hollenbach, M.; Klingner, N.; Jagtap, N.; Bischoff, L.; Fowley, C.; Kentsch, U.; Hlawacek, G.; Erbe, A.; Abrosimov, N.; Helm, M.; Berencen, Y.; Astakhov, G.

Single-photon sources are one of the elementary building blocks for photonic quantum information and optical quantum computing [1]. One of the upcoming challenges is the monolithic photonic integration and coupling of single-photon emission, reconfigurable photonic elements and single-photon detection on a silicon chip in a controllable manner. Particularly, fully integrated single-photon emitters on-demand are required for enabling a smart integration of advanced functionalities in on-chip quantum photonic circuits [2].

This work presents a mask-free nanofabrication method involving a quasi-deterministic creation of scalable extrinsic color centers in silicon emitting in the optical telecom O-band [3] on a commercial silicon-on-insulator platform using focused ion beam writing. We also show the local writing of an intrinsic color center in silicon, which is linked to a tri-interstitial complex and reveals quantum emission close to the telecom band [4]. The successful integration of these telecom quantum emitters into photonic structures such as micro-resonators, nanopillars [5] and photonic crystals with sub-micrometer precision paves the way toward a monolithic, all-silicon-based semiconductor-superconductor quantum circuit.

[1]D. D. Awschalom et al.,Nature Photonics 12,516 (2018)
[2]J. C. Adcock et al.,IEEE, 27, 2, (2021)
[3]M. Hollenbach et al.,Optics Express 28,26111 (2020)
[4]Y. Baron et al.,arXiv:2108.04283 (2021)
[5]M. Hollenbach et al.,arXiv:2112.02680 (2021)

Related publications

  • Lecture (Conference) (Online presentation)
    LEAPS meets Quantum Technology, 15.-20.05.2022, Elba Island, Italy

Permalink: https://www.hzdr.de/publications/Publ-35216
Publ.-Id: 35216


Impact of nitrilotriacetic acid on Eu(III) retention by repository relevant solid phases

Sieber, C.; Kretzschmar, J.; Drobot, B.; Schmeide, K.; Stumpf, T.

Radionuclide speciation inside long-term radioactive waste repositories needs to be
understood in order to ensure effective containment of the waste. Organic ligands
originating from the degradation of organic components inside such a repository can
possibly affect the mobility of radionuclides in solution. The present study focuses on
nitrilotriacetic acid, NTA, as a model molecule and europium, Eu(III), as a
nonradioactive analog with outstanding luminescence and magnetic properties.
The complexation of NTA with Eu(III) as a function of pH was studied using nuclear
magnetic resonance (NMR) spectroscopy. Samples were prepared with Eu(III) to NTA
ratios of 1:1 and 1:2 in D₂O with 1 M NaCl as background electrolyte to simulate high
ionic strength. The ¹H and ¹³C NMR spectra of the NTA solutions with Eu(III) show
clearly distinguishable signals for the free NTA and two Eu-NTA complexes, which is
indicative of a 1:1 and a 1:2 Eu-NTA complex. The interaction of Eu(III) with NTA is
relatively strong and favors the 1:2 Eu-NTA complex even in solution containing 1:1
Eu-NTA ratio, except in very acidic solutions. Time-resolved laser-induced
fluorescence spectroscopy (TRLFS) measurements yield quantitative information on
the complexation behavior.
As repository relevant cationic groundwater components, the influence of Ca(II) and
Al(III) on Eu(III) complexation with NTA is studied in detail with NMR spectroscopy.
This combination of NMR spectroscopy and TRLFS yields qualitative and quantitative
information on the coordination environment from the ligand’s and the metal ion’s
perspective, respectively. In subsequent studies focusing on ternary systems
comprising repository relevant solid phases (e.g. calcium aluminum silicate hydrate
(C-A-S-H) phases), radionuclides and organic ligands, this will allow the identification
of radionuclide speciation in solution and on solid phases.

Keywords: nitrilotriacetic acid; europium

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

Permalink: https://www.hzdr.de/publications/Publ-35215
Publ.-Id: 35215


Zebrafish Embryo Model of the FLASH Effect - In Regard to Böhlen et al.

Horst, F. E.; Brand, M.; Hans, S.; Karsch, L.; Leßmann, E.; Löck, S.; Schürer, M.; Pawelke, J.; Beyreuther, E.

Böhlen et al. [1] recently proposed a model that describes the magnitude of the normal tissue sparing Flash effect as a function of dose based on available in vivo data. The newly introduced flash modifying factor FMF translates doses applied at ultra-high dose rate to equivalent doses at conventional dose rate similar to the concept of relative biological effectiveness [1]. Primarily founded on rodent data, the model [1] includes only one study that demonstrated a dose-dependent Flash effect by length differences measured at 5 days-old zebrafish embryo (ZFE) after irradiation with electron doses of 5 – 12 Gy [2]. We studied this systematic overview about the available Flash data with great interest and acknowledged it as a very useful guidance for future Flash research. Coincidentally, we have just recently measured ZFE data in the high dose range (15 – 50 Gy) that appear to match very well with the existing rodent data.
Comparable to our previous studies at the ELBE accelerator [3, 4], one day-old ZFE were irradiated using electron beams of reference (mean dose rate 0.11 Gy/s) and ultra-high dose rate (UHDR; mean dose rate 0.9×105 Gy/s) (Fig. 1a). Normal tissue toxicity was quantified by analyzing the length deficit of the 5 days-old embryos compared to unirradiated controls. Since the controls grew on average 30% from irradiation to analysis this is the maximum length deficit that can be caused by irradiation. The derived FMF values extend the available ZFE data [2] and cover in a single experiment almost the entire dose range applied in the rodent studies for different tissues. Comparable to the rodent data (Fig. 1b) the ZFE FMF increases with dose.
The good agreement of our ZFE data with the rodent data [1] demonstrates the feasibility of the ZFE model for basic Flash effect studies, e.g., on the influence of physical beam parameters [3–6]. Hence, the ZFE model could be deployed as a high-throughput alternative to rodent studies at this translational level [5] promising the exploration of a large dose and dose rate range of clinically relevant beams.

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Permalink: https://www.hzdr.de/publications/Publ-35212
Publ.-Id: 35212


Ultrabroadband terahertz emission from a Ge:Au photoconductive antenna excited by a mode-locked fiber laser

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

We demonstrate a broadband photoconductive THz emitter compatible with femtosecond fiber lasers operating at wavelengths of 1.1 and 1.55 m. The emitted 1.5-cycle transient covers the spectral range up to 70 THz.

Related publications

  • Lecture (Conference)
    The 25th Congress of the International Commission for Optics (ICO), 05.-09.09.2022, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-35211
Publ.-Id: 35211


Electron mobility in strained nanowires probed by THz spectroscopy

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

We utilize optical pump – THz probe spectroscopy to estimate electron mobility in strained GaAs/(In,Al)As core/shell nanowires. Our results demonstrate that strain-induced reduction of the effective electron mass leads to a remarkable increase of the mobility. The data analysis indicates an important role of the inhomogeneous plasmon broadening that may affect THz spectra of dense ensembles of nanowires.

  • Lecture (Conference)
    47th International Conference on Infrared, Millimeter and Terahertz Waves (IRMMW-THz), 28.08.-02.09.2022, Delft, Netherlands
  • Contribution to proceedings
    47th International Conference on Infrared, Millimeter and Terahertz Waves (IRMMW-THz), 28.08.-02.09.2022, Delft, Netherlands
    2022 47th International Conference on Infrared, Millimeter and Terahertz Waves (IRMMW-THz): IEEE
    DOI: 10.1109/IRMMW-THz50927.2022.9895645

Permalink: https://www.hzdr.de/publications/Publ-35210
Publ.-Id: 35210


Intergrated Data Workflow using HELIPORT at TELBE

Lokamani, M.; Pape, D.; Deinert, J.-C.; Gruber, T.; Juckeland, G.; Kelling, J.; Knodel, O.; Müller, S.; Voigt, M.

At the High-Field High-Repetition-Rate Terahertz facility @ ELBE (TELBE)[1],
ultrafast terahertz-induced dynamics can be probed in various states of matter with highest precision. The TELBE sources offer both, stable and tunable narrowband THz radiation with pulse energies of several microjoules at high repetition rates and a synchronized coherent diffraction radiator,that provides broadband single-cycle pulses. The measurements at TELBE are data intensive, which can be as high as 20GB per experiment, that can lasts up to several minutes. As a result, the current data aquisition and data analysis stages are decoupled, where in the first step the primary data is processed and stored at HZDR and in a later step, restricted data access is made available to the user for post-processing.

In this poster contribution, we present an integrated workflow for post-processing of the experimental data at TELBE with in-built exchange of metadata between the experiment control software LabView and the workflow execution engine UNICORE[2]. We also present the guidance system HELIPORT[3] which manages the metadata of the associated project proposal and job information from UNICORE, and integrates with the electronic lab notebook (MediaWiki[4]), providing a user-friendly interface for monitoring the actively running experiments at TELBE.

[1] https://doi.org/10.1063/1.4978042
[2] https://doi.org/10.1109/HPCSim.2016.7568392
[3] https://doi.org/10.1145/3456287.3465477
[4] https://www.mediawiki.org/wiki/Project:About

Keywords: metadata; heliport; unicore; workflow; telbe; integration

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  • Open Access Logo Poster (Online presentation)
    Helmholtz Metadata Collaboration | Conference 2022, 05.-06.10.2022, online, Germany
    DOI: 10.5281/zenodo.7054583

Permalink: https://www.hzdr.de/publications/Publ-35209
Publ.-Id: 35209


Tailoring crosstalk between localized 1D spin-wave nanochannels using focused ion beams

Iurchuk, V.; Pablo-Navarro, J.; Hula, T.; Narkovic, R.; Hlawacek, G.; Körber, L.; Kakay, A.; Schultheiß, H.; Faßbender, J.; Lenz, K.; Lindner, J.

1D spin-wave conduits are envisioned as nanoscale components of magnonics-based logic and computing schemes for future generation electronics. A-la-carte methods of versatile control of the local magnetization dynamics in such nanochannels are highly desired for efficient steering of the spin waves in magnonic devices. Here, we present a study of localized dynamical modes in 1-$\mu$m-wide Permalloy conduits probed by microresonator ferromagnetic resonance technique. We clearly observe the lowest-energy edge mode in the microstrip after its edges were finely trimmed by means of focused Ne+ ion irradiation. Furthermore, after milling the microstrip along its long axis by focused ion beams, creating consecutively ~50 and ~100 nm gaps, additional resonances emerge and are attributed to modes localized at the inner edges of the separated strips. To visualize the mode distribution, spatially resolved Brillouin light scattering microscopy was used showing an excellent agreement with the ferromagnetic resonance data and confirming the mode localization at the outer/inner edges of the strips depending on the magnitude of the applied magnetic field. Micromagnetic simulations confirm that the lowest-energy modes are localized within $\sim$15-nm-wide regions at the edges of the strips and their frequencies can be tuned in a wide range (up to 5 GHz) by changing the magnetostatic coupling (i.e. spatial separation) between the microstrips.

Keywords: Ferromagnetic resonance; Helium-ion microscope; Brillouin light scattering; Micromagnetic modelling; Magnetostatic coupling; Edge modes

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Permalink: https://www.hzdr.de/publications/Publ-35208
Publ.-Id: 35208


High electron mobility in strained core/shell nanowires revealed by optical pump – THz probe spectroscopy

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

Optical pump – THz probe spectroscopy has been established as a tool for contactless probing of electronic transport in semiconductor nanowires (NWs) [1]. Particularly in III-V NWs, scattering rates of charge carriers, as well as their plasmonic resonances for typical doping levels, are located in the THz range. The analysis of the optical conductivity spectra using the localized surface plasmon model provides an estimation of the carrier density and the mobility.
Here, we employ THz spectroscopy to study electron mobility in the strained GaAs core of GaAs/InAlAs core/shell nanowires. Owing to the lattice mismatch between the core and the shell in these NWs, the bandgap energy in the strained GaAs core exhibits a reduction by up to 40% [2]. Our results demonstrate that this effect is accompanied by a notable increase in the electron mobility by 30-50% with respect to a bulk GaAs [3]. We discuss the role of various scattering mechanisms and their dependence on strain and temperature. In addition to the homogeneous plasmon broadening caused by the carrier scattering, we also observe an inhomogeneous broadening in dense ensembles of NWs as illustrated in Fig. 1(a). Our modelling demonstrates that such broadening stems from the plasmonic interaction between neighboring NWs leading to the shift of the plasmon frequency as shown in Fig. 1(b). This effect has to be considered in the analysis of THz response of NWs since it may result in a significant underestimation of the mobility values.

  • Lecture (Conference)
    9th International Conference on Optical Terahertz Science and Technology (OTST 2022), 19.-24.06.2022, Budapest, Hungary

Permalink: https://www.hzdr.de/publications/Publ-35207
Publ.-Id: 35207


Terahertz Plasmonics of Semiconductor Core-Shell Nanowires

Pashkin, O.

Core-shell nanowires (NWs) made of III-V semiconductors are promising nanostructures for optoelectronic and photovoltaic applications. One of the advantages is the possibility to epitaxially grow the NWs on Si substrates despite the large lattice mismatch, since the Si-GaAs interface area is very small. Moreover, the large surface-to-volume ratio for the NWs’ core allows to impose a very large strain when the core is overgrown with a lattice-mismatched shell, without creating any misfit dislocations. In this way, the bandgap of the core semiconductor can be tuned in a broad range via strain engineering [1].
Pump-probe terahertz spectroscopy has been proven as a perfect tool for contactless probing of electrical properties of semiconductor NWs [2]. The analysis of the optical conductivity spectra using the localized surface plasmon model allows to estimate the carrier lifetime and the carrier mobility. Recently, using THz spectroscopy we have demonstrated that the mobility in highly strained GaAs NW cores can exceed the mobility in bulk GaAs by 30-50% [3]. We found out the particular importance of the geometrical factor that defines the rescaling of the localized surface plasmon frequency in NWs. Its dependence on the aspect ratio can be derived analytically in the approximation of the cylindrical NW shape [4]. However, for a dense ensemble of NWs, where some can form bundles or touch each other, the geometric factor may vary, leading to an inhomogeneous broadening of the plasmon resonances. We discuss the role of this effect and its impact on the estimation of carrier mobility.
Finally, we demonstrate a THz nonlinearity of photodoped GaAs/In0.2Ga0.8As core-shell NWs using single-cycle intense THz pulses with peak electric fields up to 0.6 MV/cm. We found that with increasing the peak THz field, the plasmon frequency demonstrates a redshift accompanied by a suppression of the spectral weight. Remarkably, the spectral weight does not remain proportional to the square of the plasmon frequency, indicating an onset of a spatially inhomogeneous carrier distribution across the NW. The observed behavior can be ascribed to nonlinear effects caused by the intervalley scattering occurring in the high electric field regime. However, in contrast to bulk semiconductors, this effect initially sets in at hot spots of the NW where the local electric field is enhanced by the plasmonic resonance [5].

[1] L. Balaghi et al., Nat. Commun. 10, 2793 (2019).
[2] H. J. Joyce et al., Semicond. Sci. Technol. 31, 103003 (2016)
[3] L. Balaghi et al., Nat. Commun. 12, 6642 (2021).
[4] I. Fotev et al., Nanotechnology 30, 244004 (2019).
[5] R. Rana et al., Nano Lett. 20, 3225 (2020).

  • Lecture (Conference)
    10th International Workshop on Terahertz Technology and Applications, 31.05.-01.06.2022, Kaiserslautern, Germany

Permalink: https://www.hzdr.de/publications/Publ-35206
Publ.-Id: 35206


Ultrabroadband terahertz pulses from a Ge:Au photoconductive emitter

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

Using gold-implantated germanium, where the carrier lifetime is shortened by more than three orders of magnitude, we have demonstrated a broadband photoconductive THz emitter compatible with modelocked fiber lasers operating at wavelengths of 1.1 and 1.55 um and pulse repetition rates up to 20 MHz. The emitted THz spectrum spans up to 70 THz. This approach opens up a prospect for manufacturing of compact, high-bandwidth THz photonic devices compatible with Si CMOS technology.

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  • Invited lecture (Conferences) (Online presentation)
    8th International Conference on Antennas and Electromagnetic Systems (AES2022), 24.-27.05.2022, Marrakesh, Morocco

Permalink: https://www.hzdr.de/publications/Publ-35205
Publ.-Id: 35205


In situ measurements of non-equilibrium positron state defects during He irradiation in Si

Auguste, R.; Liedke, M. O.; Butterling, M.; Uberuaga, B. P.; Selim, F. A.; Wagner, A.; Hosemann, P.

Radiation-induced property changes in materials originate with the energy transfer from an incoming particle to a lattice and the displacement of the atoms from their original location. The displaced atoms can, depending on conditions, lead to the formation of extended defects such as dislocation loops, voids, or precipitates. The non-equilibrium defects created during damage events and that determine the extent of these larger defects are a function of dose rate, material, and temperature. However, these defects are transient and can only be probed indirectly. This work presents direct experimental measurements and evidence of non-equilibrium vacancy formation during irradiation, where in-situ positron annihilation spectroscopy was used to prove the generation of non-equilibrium defects in silicon.

Keywords: defects; positron annihilation spectroscopy; irradiation; Si; He; non-equilibrium defects

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  • Secondary publication expected from 08.05.2024

Permalink: https://www.hzdr.de/publications/Publ-35201
Publ.-Id: 35201


Trajectory dependence of electronic energy-loss straggling at keV ion energies

Lohmann, S.; Holeňák, R.; Grande, P. L.; Primetzhofer, D.

We measured the electronic energy-loss straggling of protons, helium, boron and silicon ions in silicon using a time-of-flight approach. Ions with velocities 0.25 - 1.6 times the Bohr velocity were transmitted through single-crystalline Si(100) nanomembranes in either channelling or random geometry to study the trajectory dependence of energy-loss straggling. Nuclear and path length contributions were determined with the help of Monte Carlo simulations. Our results exhibit an increase in straggling with increasing ion velocity for channelled trajectories for all projectiles as well as for protons and helium in random geometry. For heavier ions, electronic straggling at low velocities does not decrease further but plateaus and even seems to increase again. A satisfying agreement between experiment and transport cross section calculations for helium shows that energy deposition of light ions is dominated by electron-hole pair excitations. No agreement is found for boron and silicon indicating that local electron-promotion and charge-exchange events significantly contribute to energy loss at low velocities.

Permalink: https://www.hzdr.de/publications/Publ-35200
Publ.-Id: 35200


Case report: Incidentally discovered case of pheochromocytoma as a cause of long COVID-19 syndrome

Ziegler, C. G.; Riediger, C.; Gruber, M.; Kunath, C.; Ullrich, M.; Pietzsch, J.; Nölting, S.; Siepmann, T.; Bornstein, S. R.; Remde, H.; Constantinescu, G.

Pheochromocytomas (PCCs) are rare but potentially lethal tumors that arise from the adrenal medulla. The clinical suspicion and diagnosis of PCC can be challenging due to the non-specific nature of signs and symptoms. In many patients, infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) could lead to long-term symptoms including fatigue, headaches, and cognitive dysfunction. Here, we present the case of a patient incidentally diagnosed with an adrenal mass that proved to be a PCC after imaging was performed due to persisting complaints after coronavirus disease 2019 (COVID-19) infection. A 37-year-old male patient was referred to our center because of a right-sided inhomogeneous adrenal mass, incidentally found during a computed tomographic scan of the thorax performed due to cough and dyspnea that persisted after COVID-19 infection. Other complaints that were present prior to COVID-19 infection included profuse sweating, dizziness, exhaustion with chronic fatigue, and concentration difficulties. The patient had no history of hypertension, his blood pressure was normal, and the 24-h ambulatory blood pressure monitoring confirmed normotension but with the absence of nocturnal dipping. Plasma normetanephrine was 5.7-fold above the upper limit (UL) of reference intervals (738 pg/ml, UL = 129 pg/ml), whereas plasma metanephrine and methoxytyramine were normal at 30 pg/ml (UL = 84 pg/ml) and <4 pg/ml (UL = 16 pg/ml), respectively. Preoperative preparation with phenoxybenzamine was initiated, and a 4-cm tumor was surgically resected. Profuse sweating as well as dizziness was resolved after adrenalectomy pointing toward PCC and not COVID-19-associated patient concerns. Altogether, this case illustrates the difficulties in recognizing the possibility of PCC due to the non-specific nature of signs and symptoms of the tumor, which in this case did not include hypertension and coincided with some of the symptoms of long COVID-19.

Permalink: https://www.hzdr.de/publications/Publ-35199
Publ.-Id: 35199


Structural 130 K phase transition and emergence of a two-ion Kondo state in Ce2Rh2Ga explored by 69,71Ga nuclear quadrupole resonance

Yamamoto, S.; Fujii, T.; Luther, S.; Yasuoka, H.; Sakai, H.; Bärtl, F.; Ranjith, K. M.; Rosner, H.; Wosnitza, J.; Strydom, A. M.; Kühne, H.; Baenitz, M.

We have studied the microscopic magnetic properties, the nature of the 130 K phase transition, and the ground state in the recently synthesized compound CeRh2Ga by use of 69,71Ga nuclear quadrupole resonance (NQR). The NQR spectra clearly show an unusual phase transition at Tt ∼ 130 K, yielding a splitting of the hightemperature single NQR line into two well-resolved NQR lines, providing evidence for two crystallographically inequivalent Ga sites. The NQR frequencies are in good agreement with fully relativistic calculations of the band structure. Our NQR results indicate the absence of magnetic or charge order down to 0.3 K. The temperature dependence of the spin-lattice relaxation rate 1/T1 shows three distinct regimes, with onset temperatures at Tt and 2 K. The temperature-independent 1/T1, observed between Tt and 2 K, crosses over to a Korringa process, 1/T1 ∝ T , below ∼2 K, which evidences a rare two-ion Kondo scenario: The system evolves into a dense Kondo coherent state below 2.0 and 0.8 K probed by the two different Ga sites.

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Permalink: https://www.hzdr.de/publications/Publ-35198
Publ.-Id: 35198


Milliwatt terahertz harmonic generation from topological insulator metamaterials

Tielrooij, K. J.; Principi, A.; Saleta Reig, D.; Block, A.; Varghese, S.; Schreyeck, S.; Brunner, K.; Karczewski, G.; Ilyakov, I.; Ponomaryov, O.; de Oliveira, T.; Chen, M.; Deinert, J.-C.; Gomez Carbonell, C.; Valenzuela, S. O.; Molenkamp, L. W.; Kiessling, T.; Astakhov, G.; Kovalev, S.

Achieving efficient, high-power harmonic generation in the terahertz (THz) spectral domain has technological applications, for example in sixth generation (6G) communication networks [1, 2]. Massless Dirac fermions possess extremely large THz nonlinear susceptibilities and harmonic conversion efficiencies [3–7]. However, the observed maximum generated harmonic power is limited, because of saturation effects at increasing incident powers, as shown recently for graphene [8]. Here, we demonstrate room-temperature THz harmonic generation in a Bi2Se3 topological insulator (TI) and TI-grating metamaterial structures with surface-selective THz field enhancement. We obtain a third-harmonic power approaching the milliwatt range for an incident power of 75 mW – an improvement by two orders of magnitude compared to a benchmarked graphene sample. We establish a framework in which this exceptional performance is the result of thermodynamic harmonic generation by the massless topological surface states, benefiting from ultrafast dissipation of electronic heat via surface-bulk Coulomb interactions. These results are an important step towards on-chip THz (opto)electronic applications.

Permalink: https://www.hzdr.de/publications/Publ-35197
Publ.-Id: 35197


Project HELIPORT: The Integrated Research Data Lifecycle of the HELIPORT Project

Knodel, O.

The HELIPORT project aims to make the components or steps of the entire life cycle of a research project at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) and the Helmholtz-Institute Jena (HIJ) discoverable, accessible, interoperable and reusable according to the FAIR principles. In particular, this data management solution deals with the entire lifecycle of research experiments, starting with the generation of the first digital objects, the workflows carried out and the actual publication of research results. For this purpose, a concept was developed that identifies the different systems involved and their connections. By integrating computational workflows (CWL and others), HELIPORT can automate calculations that work with metadata from different internal systems (application management, Labbook, GitLab, and further). This presentation will cover the first year of the project, the current status and the path taken so far in the life cycle of the project.

Keywords: Data Management; Metadata; FAIR; Data provenance; Digital Objects; Workflows

  • Open Access Logo Invited lecture (Conferences) (Online presentation)
    Helmholtz Metadata Collaboration | Conference 2022, 05.-06.10.2022, online, online
    DOI: 10.5281/zenodo.7180647

Permalink: https://www.hzdr.de/publications/Publ-35196
Publ.-Id: 35196


Data publication: A New Group of Two-Dimensional Non-van der Waals Materials with Ultra Low Exfoliation Energies

Barnowsky, T.; Krasheninnikov, A.; Friedrich, R.

This dataset includes the primary research data for the publication "A New Group of Two-Dimensional Non-van der Waals Materials with Ultra Low Exfoliation Energies".

Keywords: 2D materials; exfoliation; data-driven research; computational materials science; high-throughput computing

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Permalink: https://www.hzdr.de/publications/Publ-35195
Publ.-Id: 35195


The Chemotype of Chromanones as a Privileged Scaffold for Multineurotarget Anti-Alzheimer Agents

Keuler, T.; Lemke, C.; Elsinghorst, P. W.; Iriepa, I.; Chioua, M.; Martínez-Grau, M. A.; Beadle, C. D.; Vetman, T.; López-Muñoz, F.; Wille, T.; Bartz, U.; Deuther-Conrad, W.; Marco-Contelles, J.; Gütschow, M.

The multifactorial nature of Alzheimer’s disease necessitates the development of agents able to interfere with different relevant targets. A series of 22 tailored chromanones was conceptualized, synthesized and subjected to biological evaluation. We identified one representative bearing a linker-connected azepane moiety (compound 19) with balanced pharmacological properties. Compound 19 exhibited inhibitory activities against human acetyl-, butyrylcholinesterase and monoamine oxidase-B, as well as high affinity to both the 1 and 2 receptor. Our study provides a framework for the development of further chromanone-based multineurotarget agents.

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Permalink: https://www.hzdr.de/publications/Publ-35194
Publ.-Id: 35194


PSMA-Macropa-Conjugates for Radiolabeling with Actinium-225 and Iodine-123

Mamat, C.

Small actinium-225-labeled prostate-specific membrane antigen (PSMA)-targeted radioconjugates have been described for targeted alpha therapy of metastatic castration-resistant prostate cancer. Transient binding to serum albumin as a highly abundant, inherent transport protein represents a commonly applied strategy to modulate the tissue distribution profile of such low-molecular-weight radiotherapeutics and to enhance radioactivity uptake into tumor lesions with the ultimate objective of improved therapeutic outcome. Two ligands mcp-M-alb-PSMA and mcp-D-alb-PSMA were synthesized by combining a macropa-derived chelator with either one or two lysine-ureido-glutamate-based PSMA- and 4-(p-iodophenyl)butyrate albumin-binding entities using multistep peptide-coupling chemistry. Both compounds were labeled with [225Ac]Ac3+ under mild conditions and their reversible binding to serum albumin was analyzed by an ultrafiltration assay as well as microscale thermophoresis measurements. Saturation binding studies and clonogenic survival assays using PSMA-expressing LNCaP cells were performed to evaluate PSMA-mediated cell binding and to assess the cytotoxic potency of the novel radioconjugates [225Ac]Ac-mcp-M-alb-PSMA and [225Ac]Ac-mcp-D-alb-PSMA, respectively. Biodistributions of both 225Ac-radioconjugates were investigated using LNCaP tumor-bearing SCID mice.

Keywords: actinium-225; theranostic concept; iodine-123; PSMA

  • Lecture (Conference)
    Actinides Revisited 2022, 21.-23.09.2022, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-35193
Publ.-Id: 35193


Euler-Euler two-fluid simulation of turbulent bubbly jet flows

Kamble, V. V.; Rzehak, R.; Fröhlich, J.

A set of closure models for the Euler-Euler two-fluid framework that was previously established for bubbly flows, in a variety of different geometries comprising pipes, bubble columns and stirred tanks by Rzehak et al. 2017 and Shi et al. 2018, is applied here to a turbulent bubbly jet. The closure models for momentum exchange comprise drag-, lift-, wall force-, virtual mass force-, and turbulent dispersion -force. The turbulence in the liquid phase is calculated using the SST k-ω model with an additional source terms to consider the effects of bubble induced turbulence. The open-source Computational Fluid Dynamics (CFD) tool OpenFOAM is used to perform these simulations.
Experimental data for validation are obtained from the previous work performed by Sun et al. 1986. In the experiment, a bubbly jet was injected from a round nozzle of diameter (D=5.08mm) oriented in vertical upward direction into a still water tank. These data featured a comprehensive set of observables including mean phasic velocities, liquid turbulent kinetic energy, and gas fraction along profiles in axial and radial directions. Primarily, the value of the bubble sizes is reported from the experiment, and this was used as an input parameter to the closure relations in the CFD simulation. Sample results of the present simulations are reported in the following wok. Closer to the nozzle they, are in good agreement with the measurement data along the axial and radial directions. At larger distances from the nozzle region, however, deviations are observed in the gas fraction. In an attempt to improve the prediction ability of the model, most likely the dispersion effects due to bubble-induced turbulence should be considered at an increasing gas injection from the nozzle.

Keywords: submerged turbulent-jets; dispersed multiphase flows; Euler-Euler two fluid model; bubbly jet flows; interfacial closure models

  • Lecture (Conference)
    14th European Fluid Mechanics Conference (EMFC), 13.-16.09.2022, Athens, Greece

Permalink: https://www.hzdr.de/publications/Publ-35192
Publ.-Id: 35192


Simulation studies of a pion production target for the Mu2e-II experiment

Müller, S.; Ferrari, A.; Mackenzie, M.; Pronskikh, V. S.; Rachamin, R.

The Mu2e experiment, which is currently under construction at the Fermi National Accelerator Laboratory near Chicago, will search for the neutrinoless conversion of muons to electrons in the field of an aluminum nucleus with a sensitivity four orders of magnitude better than previous experiments. This process, which violates charged lepton flavor, is highly suppressed in the Standard Model and therefore undetectable. However, scenarios for physics beyond the Standard Model predict small but observable rates.

An extension of the Mu2e experiment making use of the PIP-II
accelerator upgrade at FNAL is currently studied. The Mu2e-II experiment aims
to improve the sensitivity by at least a factor of 10 compared to Mu2e.
To achieve this, it will utilize an 800 MeV proton beam with a beam power of 100 kW hitting a production target to produce the required amount of
pions and muons. This high beam intensity requires a substantially more
advanced target design with respect to Mu2e.

We will present simulation studies for several target designs. In particular,
we will compare results for energy deposition, radiation damage and particle
yields for both the targets and the surrounding materials using the MARS15,
FLUKA2021 and GEANT4 particle transport and reaction code packages.

Keywords: Mu2e-II; FLUKA; MARS15; GEANT4; MCNP6; PHITS; Monte Carlo; Radiation Transport

Related publications

  • Lecture (Conference)
    15th workshop on Shielding aspects of Accelerators, Targets, and Irradiation Facilities (SATIF-15), 20.-23.09.2022, East Lansing, USA

Permalink: https://www.hzdr.de/publications/Publ-35191
Publ.-Id: 35191


Application of a morphology adaptive multifield model towards a plunging jet considering entrainment

Meller, R.; Krull, B.; Schlegel, F.; Tekavcic, M.

The numerical simulation of gas-liquid flows is a challenging task, when dynamics of systems at industrial scales are considered. A significant contribution to this complexity arises due to the coexistence and interaction of different flow morphologies, such as bubbly and stratified flows. One of the phenomena is the entrainment of small gas bubbles into the liquid bulk at a large-scale gas-liquid interface in regions of high shear rates. In order to capture such phenomena and make reliable predictions, hybrid modelling approaches are used. One of those is the morphology adaptive multifield model developed by Meller et al. (2021), which combines an Euler-Euler method with an algebraic Volume-of-Fluid method for disperse and continuous gas structures, respectively. The interfacial drag coupling is adapted to the local grid resolution at the interface location (Meller et al., 2022). In such a modelling framework, morphology changes are realised by transfers between numerical phases, which are treated differently according to the basic simulation methodologies mentioned above.
In that sense, entrainment processes are characterised by multiple numerical aspects: 1) entrapping of large-scale gas structures, which subsequently disintegrate into smaller ones and 2) direct conversion of continuous towards disperse portions of gas due to processes taking place at sub-grid scales, which are described by dedicated entrainment models, such as the one of Ma et al. (2011). In this work, the individual effects as well as the interplay of the aforementioned processes are assessed and validated in comparison to experimental data of a liquid plunging jet (Chanson et al., 2004). This also considers the balance between the two numerical aspects mentioned above. The goal is to improve the reliability of predictions of gas entrainment with high as well as with low spatial resolution.

  • Lecture (Conference)
    International Conference on Numerical Methods in Multiphase Flows - 4, 28.-30.09.2022, Venedig, Italien

Permalink: https://www.hzdr.de/publications/Publ-35190
Publ.-Id: 35190


A modelling approach for the numerical simulation of disperse and resolved multiphase structures including morphology transfer

Meller, R.; Krull, B.; Schlegel, F.; Tekavcic, M.

In the past decades, numerical simulation tools have developed much, becoming a reliable instrument for design and failure analysis of components in the field of aero- and hydrodynamics. The focus of research continuously shifts towards challenges that are more complex, such as multiphase flow problems. These flows typically involve strong dynamics, a number of complex physical phenomena as well as a large range of length and time scales, which are mainly connected to interfacial and turbulence structures. Such problems are particularly prevalent in the chemical and process industries. Typically, the development of tools for the numerical simulation focuses on a single morphology: a) disperse interfacial structures, which are not captured by the computational grid (Euler-Euler or Euler-Lagrange) or b) approaches resolving the interface between two different phases (volume-of-fluid or level-set). In many practical applications, the occurring flow morphology is unknown in advance and therefore, the most appropriate numerical model cannot be easily identified a-priori. Corresponding industrial facilities are flotation cells, refrigeration systems, biological and chemical reactors, distillation columns, swirl separators or centrifugal pumps, to name a few examples. In the past years, special hybrid simulation approaches have been developed to describe the aforementioned problems: 2-field methods considering blending between different morphologies, 4-field methods, where two phases represent the same physical phase, but with different morphology, drift-flux models based on the volume-of-fluid approach or methods blending between Euler-Euler and level-set models.
We present a 4-field approach, which is developed and validated at Helmholtz-Zentrum Dresden – Rossendorf as an add-on to the public domain library OpenFOAM. Central development criteria and goals are:
- Robust applicability to engineering problems at the industrial scale
- A unified set of conservation equations uniting different simulation methods without blending between them
- If the spatial resolution of the computational grid is high enough, the hybrid model should behave like a algebraic volume-of-fluid model
- In the case of coarse computational grids, disperse interfacial structures are modelled using the Euler-Euler method
- Phases forming large scale (resolved) interfaces and such that are dispersed within another phase, are treated as individual numerical phases

  • Special mass transfer model formulations allow a phase to change morphology via transfer between different numerical phases
  • Disperse phases can interact with large-scale interfaces by, e.g. bursting of bubbles or formation of foam
The current state of this development considers modelling of resolved interfaces in the two-fluid model including successful validation against well accepted volume-of-fluid simulations and description of disperse gas structures by means of a phase averaged treatment (Euler-Euler model). Furthermore, modelling of resolved interfaces on coarse computational grids is realised via appropriate closure models, the Euler-Euler “mode” is stabilised in the limit of high grid resolutions. Additionally, morphology transfer models allow for transition between different flow regimes. The latter is demonstrated for the case of a distillation column and a swirl separator for gas bubbles.
The main intention of this contribution is to present the simulation software described above to industry representatives in order to establish cooperations and find more real-world applications for further development regarding robustness and functionality. Cooperations between industry and research centres should help to overcome shortcomings in currently available simulation methods, in order to allow for more reliability and safety in the future design and operation of facilities.
  • Lecture (Conference)
    CHISA 2022, 21.-25.08.2022, Prag, Tschechische Republik

Permalink: https://www.hzdr.de/publications/Publ-35189
Publ.-Id: 35189


Probing Defects and Spin-Phonon Coupling in CrSBr via Resonant Raman Scattering

Torres, K.; Kuc, A. B.; Maschio, L.; Pham, T.; Reidy, K.; Dekanovsky, L.; Sofer, Z.; Ross, F. M.; Klein, J.

Understanding the stability limitations and defect formation mechanisms in 2D magnets is essen- tial for their utilization in spintronic and memory technologies. Here, we correlate defects in mono- to multilayer CrSBr with their structural and vibrational properties. We use resonant Raman scattering to reveal distinct vibrational defect signatures. In pristine CrSBr, we show that bromine atoms mediate vibrational interlayer coupling, allowing for distinguishing between surface and bulk defect modes. We show that environmental exposure causes drastic degradation in monolayers, with intralayer defects forming more readily in monolayers. Through deliberate ion irradiation, we tune the formation of defect modes, which we show are strongly polarized and resonantly enhanced, reflecting the quasi-1D electronic character of CrSBr. Overall, we present a structural and vibrational study of defective CrSBr, demonstrate the air stability above the monolayer threshold, and provide further insight into the quasi-1D physics present, creating crucial understanding for defect engineering of magnetic textures.

Permalink: https://www.hzdr.de/publications/Publ-35188
Publ.-Id: 35188


CFD Simulation of Gas-Solid-Liquid Bubble Column

Draw, M.; Rzehak, R.

The dependence of froth flotation performance on various inter-related chemical, operational and instrumental components, makes optimizing a flotation system a very complex task. Computational Fluid Dynamics tools provide the means to study the flow inside a flotation cell by employing mathematical models that describe the interaction between the different phases of the system. The purpose of this work is to use Euler-Euler-Euler CFD simulations in OpenFOAM to validate a set of interfacial models to determine the hydrodynamics of a gas-solid-liquid flow. The combination of previously well validated baseline models for gas-liquid flows and solid-liquid flows is used for this purpose. The baseline combination includes drag, lift, wall, turbulent dispersion and virtual mass forces as well as bubble induced turbulence for gas-liquid interaction, and drag, lift, turbulent dispersion and virtual mass forces for solid-liquid interaction. Based on an extensive literature review of gas-solid-liquid experiments, the bubble column data of Rampure et al. are chosen for the numerical validation. Preliminary results show that the bubble diameter, which was not measured precisely, plays a significant role for the gas volume fraction distribution. Bubble diameter of 7 mm yields gas volume fraction profiles in agreement with the experimental data. The baseline combination yields higher particle suspension than indicated by the experimental data. This leads to a systematic study of the closure models. Choosing a model set similar to that of Rampure et al. improves the agreement of the solid distribution but deteriorates that of the gas distribution. It must be noted that, the high gas flow rate and high solid concentration likely require consideration of further aspects that are expected to have a significant effect on the flow. These may include a PIT model, a swarm corrector for the bubble and particle drag force, modifying the bubble drag force due to the existence of particles and vice versa, a solid pressure due to particle collisions and modifying the liquid viscosity due to the presence of particles. The study of the effect of these aspects is still on-going.

Keywords: Euler-Euler Simulation; Gas-Solid-Liquid; Bubble Column; Multiphase

  • Lecture (Conference)
    14th European Fluid Mechanics Conference, 13.-16.09.2022, Athen, Griechenland

Permalink: https://www.hzdr.de/publications/Publ-35187
Publ.-Id: 35187


Bubbly flow simulation with particle-center-averaged Euler-Euler model: Fixed polydispersity and bubble deformation

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

Bubble size and deformation are important factors for the closure models required in Euler-Euler simulations of bubbly flows. To properly simulate polydisperse bubbly flows where the bubble size spectrum may cover a range of several millimeters, several velocity groups with different sizes have to be considered. To this end, the theory for the particlecenter-averaged Euler-Euler model is generalized for the simulation with multiple bubble velocity groups. Furthermore, bubble deformation effects have been included in appropriate bubble force models. The particle-center-averaged Euler-Euler model provides additional freedom to consider the bubble shape during the conversion between the bubble number density and the gas volume fraction. Therefore, the theory is also generalized to consider an oblate ellipsoidal bubble shape in simulations. A bubbly pipe flow is used to validate the theory and to demonstrate the improvements of the proposed generalizations.

Keywords: fixed polydispersity; bubble deformation; particle-center-averaging method; Euler-Euler model

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Permalink: https://www.hzdr.de/publications/Publ-35186
Publ.-Id: 35186


Spin wave non-reciprocity at the spin-flop transition region in synthetic antiferromagnets

Gladii, O.; Salikhov, R.; Hellwig, O.; Schultheiß, H.; Lindner, J.; Gallardo, R.

We investigate the frequency non-reciprocity in CoFeB/Ru/CoFeB synthetic antiferromagnets near the spin-flop transition region, where the magnetic moments in the two ferromagnetic layers are non-collinear. Using conventional Brillouin light scattering, we perform systematic measurements of the frequency non-reciprocity as a function of an external magnetic field. For the antiparallel alignment of the magnetic moments in the two layers, we observe a significant frequency non-reciprocity of up to a few GHz, which vanishes when the relative magnetization orientation switches into the parallel configuration at saturation. A non-monotonous dependence of the frequency non-reciprocity is found in the region where the system transitions from the antiparallel to the parallel orientation, with a maximum frequency shift around the spin-flop critical point. This non-trivial dependence of the non-reciprocity is attributed to the non-monotonous dependence of the dynamic dipolar interaction, which is the main factor that causes asymmetry in the dispersion relation. Furthermore, we found that the sign of the frequency shift changes even without switching the polarity of the bias field. These results show that one can precisely control the non-reciprocal propagation of spin waves via field-driven magnetization reorientation.

Keywords: Spin waves; Magnetization switching; Magnetization dynamics; Dipolar interaction; Magnetic multilayers; Synthetic antiferromagnets

Permalink: https://www.hzdr.de/publications/Publ-35185
Publ.-Id: 35185


A fluorescence anisotropy assay with guanine nucleotides provides access to functional analysis of Gαi1 proteins

Penanian, A.; Sommerfeld, P.; Kasprzyk, R.; Kühl, T.; Binbay, A.; Hauser, C.; Löser, R.; Wodtke, R.; Bednarczyk, M.; Chrominski, M.; Kowalska, J.; Jemielity, J.; Imhof, D.; Pietsch, M.

Gα proteins as part of heterotrimeric G proteins are molecular switches essential for GPCR mediated intracellular signaling. The role of the Gα subunits has been examined for decades with various guanine nucleotides to elucidate the activation mechanism and Gα protein-dependent signal transduction. Several approaches describe fluorescent ligands mimicking the GTP
function, yet lacking the efficient estimation of the proteins’ GTP binding activity and fraction of active protein. Herein, we report the development of a reliable fluorescence anisotropy-based method to determine the affinity of ligands at the GTP-binding site and to quantify the fraction of active Gαi1 protein. An advanced bacterial expression protocol was applied to produce active human Gαi1 protein, whose GTP binding capability was determined with novel fluorescently labeled guanine nucleotides acting as highaffinity Gαi1 binders compared to the commonly used BODIPY FL GTPγS. This study thus contributes a new method for future investigations of the characterization of Gαi and other Gα protein subunits, exploring their corresponding signal transduction systems and potential for biomedical applications.

Permalink: https://www.hzdr.de/publications/Publ-35184
Publ.-Id: 35184


Clinical use and future requirements of relative biological effectiveness: Survey among all European proton therapy centres

Heuchel, L.; Hahn, C.; Pawelke, J.; Singers Sørensen, B.; Dosanjh, M.; Lühr, A.

Background and purpose: The relative biological effectiveness (RBE) varies along the treatment field.
However, in clinical practice, a constant RBE of 1.1 is assumed, which can result in undesirable side
effects. This study provides an accurate overview of current clinical practice for considering proton
RBE in Europe.
Materials and methods: A survey was devised and sent to all proton therapy centres in Europe that treat
patients. The online questionnaire consisted of 39 questions addressing various aspects of RBE consider-
ation in clinical practice, including treatment planning, patient follow-up and future demands.
Results: All 25 proton therapy centres responded. All centres prescribed a constant RBE of 1.1, but also
applied measures (except for one eye treatment centre) to counteract variable RBE effects such as avoid-
ing beams stopping inside or in front of an organ at risk and putting restrictions on the minimum number
and opening angle of incident beams for certain treatment sites. For the future, most centres (16) asked
for more retrospective or prospective outcome studies investigating the potential effect of the effect of a
variable RBE. To perform such studies, 18 centres asked for LET and RBE calculation and visualisation
tools developed by treatment planning system vendors.
Conclusion: All European proton centres are aware of RBE variability but comply with current guidelines
of prescribing a constant RBE. However, they actively mitigate uncertainty and risk of side effects result-
ing from increased RBE by applying measures and restrictions during treatment planning. To change RBE-
related clinical guidelines in the future more clinical data on RBE are explicitly demanded.

Keywords: Relative biological effectiveness (RBE); Linear energy transfer (LET); Proton Beam Therapy; Treatment planning; Current clinical practice; Survey; Europe

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Permalink: https://www.hzdr.de/publications/Publ-35183
Publ.-Id: 35183


Data publication: Integrated radiogenomics analyses allow for subtype classification and improved outcome prognosis of patients with locally advanced HNSCC

Rabasco Meneghetti, A.; Zwanenburg, A.; Linge, A.; Lohaus, F.; Grosser, M.; Baretton, G.; Kalinauskaite, G.; Tinhofer, I.; Guberina, N.; Stuschke, M.; Balermpas, P.; von der Grün, J.; Ganswindt, U.; Belka, C.; Peeken, J. C.; Combs, S. E.; Böke, S.; Zips, D.; Troost, E. G. C.; Krause, M.; Baumann, M.; Löck, S.

RDS data of models developed and reported for the article entitled "Integrated radiogenomics analyses allow for subtype classification and improved outcome prognosis of patients with locally advanced HNSCC". Software package version is also available in repository

Keywords: HNSCC; Radiomics; Radiogenomics; Transcriptomics; Machine Learning; Prognostic markers

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Permalink: https://www.hzdr.de/publications/Publ-35182
Publ.-Id: 35182


Integrated radiogenomics analyses allow for subtype classification and improved outcome prognosis of patients with locally advanced HNSCC

Rabasco Meneghetti, A.; Zwanenburg, A.; Linge, A.; Lohaus, F.; Grosser, M.; Baretton, G.; Kalinauskaite, G.; Tinhofer, I.; Guberina, N.; Stuschke, M.; Balermpas, P.; von der Grün, J.; Ganswindt, U.; Belka, C.; Peeken, J. C.; Combs, S. E.; Böke, S.; Zips, D.; Troost, E. G. C.; Krause, M.; Baumann, M.; Löck, S.

Patients with locally advanced head and neck squamous cell carcinoma (HNSCC) may benefit from personalised treatment, requiring biomarkers that characterize the tumour and predict treatment response. We integrate pre-treatment CT radiomics and whole-transcriptome data from a multicentre retrospective cohort of 206 patients with locally advanced HNSCC treated with primary radiochemotherapy to classify tumour molecular subtypes based on radiomics, develop surrogate radiomics signatures for gene-based signatures related to different biological tumour characteristics and evaluate the potential of combining radiomics features with full-transcriptome data for the prediction of loco-regional control (LRC). Using end-to-end machine-learning, we developed and validated a model to classify tumours of the atypical subtype (AUC [95% confidence interval]: 0.69 [0.53-0.83]) based on CT imaging, observed that CT-based radiomics models have limited value as surrogates for six selected gene signatures (AUC<0.60), and showed that combining a radiomics signature with a transcriptomics signature consisting of two metagenes representing the hedgehog pathway and E2F transcriptional targets improves the prognostic value for LRC compared to both individual sources (validation C-index [95% confidence interval], combined: 0.63 [0.55-0.73] vs radiomics: 0.60 [0.50-0.71] and transcriptomics: 0.59 [0.49-0.69]). These results underline the potential of multi-omics analyses to generate reliable biomarkers for future application in personalized oncology.

Keywords: HNSCC; Radiomics; Radiogenomics; Transcriptomics; Machine Learning; Prognostic markers

Related publications

Permalink: https://www.hzdr.de/publications/Publ-35181
Publ.-Id: 35181


Recent progress of laboratory astrophysics with intense lasers

Takabe, H.; Kuramitsu, Y.

Thanks to a rapid progress of high-power lasers since the birth of laser by T. H. Maiman in 1960, intense lasers have been developed mainly for studying the scientific feasibility of laser fusion. Inertial confinement fusion with an intense laser has attracted attention as a new future energy source after two oil crises in the 1970s and 1980s. From the beginning, the most challenging physics is known to be the hydrodynamic instability to realize the spherical implosion to achieve more than 1000 times the solid density. Many studies have been performed theoretically and experimentally on the hydrodynamic instability and resultant turbulent mixing of compressible fluids. During such activities in the laboratory, the explosion of supernova SN1987A was observed in the sky on 23 February 1987. The X-ray satellites have revealed that the hydrodynamic instability is a key issue to understand the physics of supernova explosion. After collaboration between laser plasma researchers and astrophysicists, the laboratory astrophysics with intense lasers was proposed and promoted around the end of the 1990s. The original subject was mainly related to hydrodynamic instabilities. However, after two decades of laboratory astrophysics research, we can now find a diversity of research topics. It has been demonstrated theoretically and experimentally that a variety of nonlinear physics of collisionless plasmas can be studied in laser ablation plasmas in the last decade. In the present paper, we shed light on the recent 10 topics studied intensively in laboratory experiments. A brief review is given by citing recent papers. Then, modeling cosmic-ray acceleration with lasers is reviewed in a following session as a special topic to be the future main topic in laboratory astrophysics research.

Permalink: https://www.hzdr.de/publications/Publ-35180
Publ.-Id: 35180


Flow‐dependent zinc corrosion in boric acid‐containing electrolytes

Harm, U.; Kryk, H.; Hampel, U.

In recent research concerning zinc dissolution studies in boric acid
electrolytes, it was shown that moderate variations of the fluid temperatures
or the boric acid concentration only cause small changes (<10%) in resulting
initial zinc corrosion rates. A stronger dependency was found, however, on the
fluid flow. Thus, a series of electrochemical measurements were carried out
using a rotating disc electrode (zinc) in boric acid electrolytes for a better
understanding of influencing parameters on the zinc corrosion rates. The main
results of these electrochemical polarization experiments (e.g., Tafel plots)
showed similar dependencies of the zinc corrosion rates as described in the
aforementioned zinc dissolution experiments. The zinc corrosion process
strongly depends on the mass transfer limitation of the dissolved oxygen to the
zinc surface (cathodic process). Increased rotation speeds (higher flow rates)
lead to extensively enhanced current densities (corrosion rates) and the
extrapolation to infinite high rotation speeds (Levich extrapolation) was used
to describe the corresponding corrosion process without transfer limitations.

Keywords: boric acid; corrosion; cyclic polarization; zinc; electrochemistry

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  • Secondary publication expected

Permalink: https://www.hzdr.de/publications/Publ-35179
Publ.-Id: 35179


Unraveling the spatial distribution of Eu(III) in tobacco BY-2 cells by chemical microscopy

Klotzsche, M.; Drobot, B.; Steudtner, R.; Vogel, M.; Raff, J.; Stumpf, T.

Rare earth elements (REE) have become critical components in science and industry. Their anthropogenic release into the environment and entry into the food chain poses a risk for the health of living beings. Therefore, a comprehensive understanding of the transfer and migration behaviour, the resulting localization and molecular characterization of REE in biological systems is crucial for a reasonable risk assessment and remediation strategies.

Keywords: Chemical microscopy; Europium; Luminescence; Tobacco BY-2; Plant cells; Raman microspectroscopy

  • Poster
    18th Confocal Raman Imaging Symposium, 26.-28.09.2022, Ulm, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-35178
Publ.-Id: 35178


Quantum accurate interaction potentials for warm dense aluminum

Kumar, S.; Tahmasbi, H.; Ramakrishna, K.; Lokamani, M.; Cangi, A.

Modeling warm dense matter is relevant for various applications including the interior of gas giants and exoplanets, inertial confinement fusion, and ablation of metals. Ongoing and upcoming experimental campaigns in photon sources around the globe rely on numerical simulations which are accurate on the level of electronic structures. In that regard, density functional theory molecular dynamics (DFT-MD) simulations have been widely used to compute dynamical and thermodynamical properties of warm dense matter. However, two challenges impede further progress: (1) DFT-MD becomes computational infeasible with increasing temperature (2) finite-size effects render many computational observables inaccurate, because DFT-MD is limited to a few hundred atoms on current HPC platforms. Recently, molecular dynamics simulations using machine learning-based interatomic potentials (ML-IAP) could overcome these computational limitations. Here, we propose a method to construct ML-IAPs from DFT data based on SNAP descriptors [1]. We demonstrate our workflow for aluminum. In particular, we investigate the transferability of ML-IAPs over a large range of temperatures and pressures, which currently is a topic of active research.

References:

[1] A. P. Thompson, L. P. Swiler, C. R. Trott, S. M. Foiles, and G. J. Tucker, Journal of
Computational Physics, 285, 316-330, 2015.

Keywords: Computational Physics; Warm Dense Matter; Machine Learning; Molecular Dynamics

  • Poster
    DFT Methods for Matter under Extreme Conditions, 21.-22.02.2022, Görlitz, Germany

Permalink: https://www.hzdr.de/publications/Publ-35177
Publ.-Id: 35177


Quantum-accurate interatomic potentials for aluminum at high temperatures

Kumar, S.; Tahmasbi, H.; Ramakrishna, K.; Lokamani, M.; Cangi, A.

Modeling warm dense matter is relevant for various applications including the interior of gas giants and exoplanets, inertial confinement fusion, and ablation of metals. Ongoing and upcoming experimental campaigns in photon sources around the globe rely on numerical simulations which are accurate on the level of electronic structures. In that regard, density functional theory molecular dynamics (DFT-MD) simulations [1] have been widely used to compute dynamical and thermodynamical properties of warm dense matter. However, two challenges impede further progress: (1) DFT-MD becomes computational infeasible with increasing temperature (2) finite-size effects render many computational observables
inaccurate, because DFT-MD is limited to a few hundred atoms on current HPC platforms. Recently, molecular dynamics simulations using machine learning-based interatomic potentials (ML-IAP) could overcome these computational limitations. Here, we propose a method to construct ML-IAPs from DFT data based on SNAP descriptors [2]. We present our results for aluminum. In particular, we investigate the transferability of ML-IAPs over a large range of temperatures and pressures, which currently is a topic of active research.

References:

[1] G. Kresse and J. Hafner, Phys. Rev. B 47, 558 (1993).
[2] A. P. Thompson, L. P. Swiler, C. R. Trott, S. M. Foiles, and G. J. Tucker, Journal of Computational Physics, 285, 316-330, 2015.

Keywords: Computational Physics; Warm Dense Matter; Machine Learning; Transport Coefficients; Molecular Dynamics

  • Poster
    Strongly Coupled Coulomb Systems, 24.-29.07.2022, Görlitz, Germany

Permalink: https://www.hzdr.de/publications/Publ-35176
Publ.-Id: 35176


A snapshot review on flash lamp annealing of semiconductor materials

Rebohle, L.; Prucnal, S.; Berencen, Y.; Begeza, V.; Zhou, S.

Flash lamp annealing (FLA) is a non-equilibrium annealing method on the sub-second time scale which excellently meets the requirements of thin film processing. FLA has already been used in microelectronics, mostly after ion implantation, to activate dopants, to recrystallize amorphous semiconductor layers, and to anneal out defects. Another field of application is the formation of silicide and germanide materials for contact fabrication. However, in the last twenty years, FLA has opened up new areas of application like thin films on glass, sensors, printed electronics, flexible electronics, energy materials etc. For two years, the Helmholtz Innovation Blitzlab aims to transfer this technology to industry and application-related research.
After a short introduction, a brief overview of FLA is given, discussing the advantages and challenges of this technology. The main part displays various examples from literature and from our own research, in which FLA has been applied to semiconductors, namely to Si, Ge and GaN. In detail, the doping close or even above the solubility limit of dopants, the crystallization of Ge during FLA, the formation of NiGe for contacts, and p-type doping in GaN are addressed.

Keywords: Flash lamp annealing; Pulsed light sintering; Semiconductors; Ion implantation; Crystallization

Related publications

  • Invited lecture (Conferences)
    International Conference on Ion Implantation Technology 2022, 25.-29.09.2022, San Diego, USA
  • Open Access Logo MRS Advances 7(2022), 1301-1309
    Online First (2022) DOI: 10.1557/s43580-022-00425-w
    Cited 2 times in Scopus
  • Lecture (Conference)
    47. Nutzertreffen „Heißprozesse und RTP“, 07.-08.12.2022, München, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-35175
Publ.-Id: 35175


Effect of laser annealing on the magnetic properties of Co/Pt based multilayers

Rasabathina, L.; Sharma, A.; Busse, S.; Böhm, B.; Samad, F.; Salvan, G.; Horn, A.; Hellwig, O.

Two modes of laser annealing, namely, Continuous Wave (CW) and Pulsed Wave (PW) mode, are used for modifying the magnetic properties of perpendicular magnetic anisotropy (PMA) multilayers in a controlled manner. For this we compare two types of samples - a PMA (Co/Pt)10 multilayer and an antiferromagnetically interlayer exchange coupled PMA (Co/Pt)4/Co/Ir/(Co/Pt)5 multilayer. Room temperature hysteresis loops using polar MOKE magnetometry are measured for the different laser annealing modes. Thus, a relationship between the applied laser parameters and the magnetic properties is extracted, which provides an opportunity to alter magnetic properties of PMA multilayer systems locally with high spatial resolution on demand.

  • Poster
    DPG conference Regensburg 2022, 08.09.2022, Regensburg, Germany

Permalink: https://www.hzdr.de/publications/Publ-35174
Publ.-Id: 35174


Influence of adhesion layer and sputter gas pressure on structural and magnetic properties of Co/Pt multilayers

Ehrler, R.; Uhlig, T.; Hellwig, O.

Co/Pt multilayers (MLs) are standard systems for perpendicular anisotropy layered thin films. The use of a specific underlayer, sometimes in combination with additional, very thin adhesion layers, is a common practice to define a crystalline texture for the ML on amorphous substrates. In addition, the sputter gas pressure during deposition can be used to tune the lateral heterogeneity and laminate order, which strongly affect the magnetic behavior of the system. However, the precise interplay between adhesion and sputter gas pressure, especially for the seed layer, is often neglected.

In this context, we will discuss the impact of the underlayers on the structural and magnetic properties of the Co/Pt ML system. We will emphasize the influence of an adhesion layer on the whole system and combine this with a systematic and separate variation of the sputter deposition pressure of Pt seed and Co/Pt ML. Carefully tuning these parameters enables us to exert a high degree of control on the structure of these systems, with characteristics ranging from continuous thin films to isolated grain structures.

Keywords: cobalt platin multilayer; structural properties

  • Lecture (Conference)
    DPG conference Regensburg 2022, 07.09.2022, Regensburg, Germany

Permalink: https://www.hzdr.de/publications/Publ-35173
Publ.-Id: 35173


Evidence for perpendicular anisotropy gradients in Co thin films on Pt seeds

Patel, G. I.; Stienen, S.; Salikhov, R.; Gallardo, R.; Fallarino, L.; Lenz, K.; Lindner, J.; Hellwig, O.

Tailoring the magnetization dynamics and anisotropy in ferromagnetic thin films by different seed layers is of great fundamental and practical importance, e.g., different seed layer materials lead to different microstructure and magnetocrystalline anisotropy energy. We have used Ta and Pt as seed layers for thin Co films and studied their broadband ferromagnetic resonance (FMR) in out-of-plane saturation as a function of Co thickness and determined the respective perpendicular magnetic anisotropy. For Ta seeds, the magnetic anisotropy decreases and shows an inverse thickness dependence. In contrast for Pt seeds the magnetic anisotropy is no longer monotonous with thickness, but shows an initial thickness dependent decrease with a distinct minimum and subsequently a steady increase again. XRD measurements show that for Pt seeds, the Co develops a well-defined hcp texture with a thickness dependent strain relaxation. As a result of this structural evolution for Co on Pt seeds our FMR measurements reveal a strong anisotropy gradient in growth direction for this system.

Keywords: cobalt; magnetic anisotropy; FMR

  • Lecture (Conference)
    DPG conference Regensburg 2022, 07.09.2022, Regensburg, Germany

Permalink: https://www.hzdr.de/publications/Publ-35172
Publ.-Id: 35172


Magnetostructural phase transition in Fe60V40 alloy thin films

Anwar, M. S.; Cansever, H.; Böhm, B.; Gallardo, R.; Hübner, R.; Zhou, S.; Kentsch, U.; Eggert, B.; Rauls, S.; Wende, H.; Potzger, K.; Faßbender, J.; Lenz, K.; Lindner, J.; Hellwig, O.; Bali, R.

Ferromagnetism can be induced in non-ferromagnetic alloys such as B2 Fe60Al40[1] and B2 Fe50Rh50[2] through lattice disordering. Here we study a magnetostructural transition in Fe60V40 thin films using ion-irradiation. We show that the as-grown films possess an MS of 17 kA/m and irradiation with 25 keV Ne+-ions at a fluence of 5 x 1015ions/cm2 leads to an increase of MS to ∼ 750 kA/m. A structural short-range order is observed in the as-grown films that transforms to A2 phase via ion-irradiation. Mössbauer spectroscopy and Ferromagnetic Resonance have been applied to track the variation of local magnetic ordering and dynamic behaviour respectively.

Financial support by DFG grants BA 5656/1-2 and WE 2623/14-2 is acknowledged.

[1]Ehrler, J.et al., New J. Phys.,22,073004(2020)

[2]Eggert, B.et al., RSC Adv.,10,14386(2020)

Keywords: iron vanadium; ion irradiation

Related publications

  • Lecture (Conference)
    DPG conference Regensburg 2022, 05.09.2022, Regensburg, Germany

Permalink: https://www.hzdr.de/publications/Publ-35171
Publ.-Id: 35171


Spin-orbit torque mediated coupling of terahertz light with magnon modes in heavy-metal/ferromagnet heterostructures

Salikhov, R.; Ilyakov, I.; Körber, L.; Kakay, A.; Lenz, K.; Faßbender, J.; Bonetti, S.; Hellwig, O.; Lindner, J.; Kovalev, S.

Nonvolatile and energy-efficient spin-based technologies call for new prospects to realize computation and communication devices that are able to operate at terahertz (THz) frequencies. In particular, the coupling of electro-magnetic radiation to a spin system is a general requirement for future communication units and sensors. Here we propose a layered metallic system, based on a ferromagnetic film sandwiched in between two heavy metals that allows a highly effective coupling of millimeter wavelength THz light to nanometer-wavelength magnon modes. Using single-cycle broadband THz radiation we are able to excite spin-wave modes with a frequency of up to 0.6 THz and a wavelength as short as 6 nm. Our experimental and theoretical studies demonstrate that the coupling originates solely from interfacial spin-orbit torques. These results are of general applicability to magnetic multilayered structures, and offer the perspective of coherent THz excitation of exchange-dominated nanoscopic magnon modes.

Keywords: terahertz; magnon

  • Lecture (Conference)
    DPG conference Regensburg 2022, 07.09.2022, Regensburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-35169
Publ.-Id: 35169


Magnetization reversal of Co/Pt multilayer systems with weak perpendicular magnetic anisotropy

Heinig, P.; Salikhov, R.; Samad, F.; Fallarino, L.; Kakay, A.; Hellwig, O.

Perpendicular anisotropy thin film systems are well known for their highly periodic magnetic stripe domains. Here we study [Co(3.0 nm)/Pt(0.6 nm)]X multilayers in the regime of transitional in-plane to out-of-plane anisotropy. For this we vary the number of repeats X in order to tune the remanent state from purely in-plane (IP) via tilted stripe domains (tilted), i.e. with significant out-of plane as well as in-plane magnetization component, to fully out-of-plane stripe domains (OOP). Vibrating Sample Magnetometry and Magnetic Force Microscopy are used to investigate three characteristic samples with X = 6,11 and 22, which represent the three above mentioned remanent states, respectively. In contrast to fully in-plane or fully out-of-plane systems experimental data and corresponding micromagnetic simulation of the tilted magnetization regime (X=11) reveals fully reversible field regions as well as distinct points of irreversibility during an external field sweep. This collective reversal behavior seems at first sight somewhat counter intuitive for a macroscopic system and has qualitative similarities with microscopic systems, such as the Stoner Wohlfarth particle and the vortex reversal in an in-plane magnetized disk, which both show as well distinct points of irreversibility.

Keywords: tilted magnetization; weak anisotropy; Co/Pt multilayer

  • Lecture (Conference)
    DPG conference Regensburg 2022, 07.09.2022, Regensburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-35168
Publ.-Id: 35168


Herausforderungen bei der TEM-Probenpräparation von neuartigen Elektroden-Materialen für Li-Ionen-Batterien

Engelmann, H.-J.; Heinig, K.-H.; Aniol, R.

Herausforderungen bei der TEM-Probenpräparation von neuartigen Elektroden-Materialen für Li-Ionen-Batterien

Keywords: TEM-Probenpräparation; FIB; TEM; Li-Ionen-Batterien

Related publications

  • Lecture (others)
    Sächsisches TEM-Präparatorentreffen, 22.09.2022, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-35167
Publ.-Id: 35167


Tuning up catalytical properties of electrochemically prepared nanoconical Co-Ni deposit for HER and OER

Skibinska, K.; Wojtaszek, K.; Krause, L.; Yang, X.; Marzec, M. M.; Wojnicki, M.; Żabiński, P.

Catalysts can be successfully prepared by a simple electrochemical process. Their surface composition distinguishes catalytic activity toward hydrogen and oxygen evolution reactions. In this work, uniform Co-Ni cones were synthesized using the onestep method from an electrolyte containing a crystal modifier. Electrodeposited layers were oxidized and/or reduced in the furnace at 100°C. Freshly electrodeposited coating was stored in air atmosphere for seven days. This results in an oxide layer forming on the surface of the catalyst. Changes in the surface composition, confirmed by the XPS method, strongly influenced the wettability, catalytic performance, and size of evolved hydrogen bubbles. The conical Co-Ni surface oxidized in a controlled way possesses the best catalytic activity towards hydrogen and oxygen evolution. Conversely, the spontaneously formed oxide layer decreases the catalytic performance in mentioned reactions compared with the fresh sample. The proper storage of synthesized samples is essential due to their desired catalytic applications. Proposed controlled oxidation can be an accessible way to increase nanomaterials catalytic performance.

Keywords: conical structures; wettability; catalytical properties; Hydrogen evolution reaction; Oxygen evolution reaction

Permalink: https://www.hzdr.de/publications/Publ-35166
Publ.-Id: 35166


Spatial magnetic imaging of non-axially symmetric vortex domains in cylindrical nanowire by transmission X-ray microscopy

Fernandez Roldan, J. A.; Bran, C.; Asenjo, A.; Vázquez, M.; Sorrentino, A.; Ferrer, S.; Chubykalo-Fesenko, O.; Del Real, R. P.

The spatial magnetization texture of a cylindrical nanowire has been determined by Transmission X-ray Microscopy (TXM) and X-ray magnetic circular dichroism (XMCD). For this purpose, nanowires with designed geometry, consisting of CoNi/Ni periodic segments, have been grown by designed electrodeposition into alumina templates. Experimental data allows one to conclude the presence of mono- and trivortex magnetic domains in CoNi segments but, unusually, these states are characterized by an asymmetric XMCD contrast across the nanowire’s section. Micromagnetic modelling shows non-trivial three-dimensional structures with ellipsoidal vortex cores and non-axially symmetric magnetization along the nanowire direction. The modelled TXM contrast of micromagnetic structures allows to correlate the experimental asymmetric XMCD contrast to the easy axis direction of the uniaxial magnetocrystalline anisotropy.

Keywords: magnetic nanowires; vortex magnetic domains; magnetic domain wall; Transmission X-ray Microscopy (TXM); X-ray magnetic circular dichroism (XMCD); CoNi; nanomagnetism; three-dimensional; cylindrical nanowire; spin texture

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Permalink: https://www.hzdr.de/publications/Publ-35165
Publ.-Id: 35165


Photo-induced macro/mesoscopic scale ion displacement in mixed-halide perovskites: ring structures and ionic plasma oscillations

Sun, X.; Zhang, Y.; Ge, W.

Contrary to the common belief that the light-induced halide ion segregation in a mixed halide alloy occurs within the illuminated area, we find that the Br ions released by light are expelled from the illuminated area, which generates a macro/mesoscopic size anion ring surrounding the illuminated area, exhibiting a photoluminescence ring. This intriguing phenomenon can be explained as resulting from two counter-balancing effects: the outward diffusion of the light-induced free Br ions and the Coulombic force between the anion deficit and surplus region. Right after removing the illumination, the macro/mesoscopic scale ion displacement results in a built-in voltage of about 0.4 V between the ring and the center. Then, the displaced anions return to the illuminated area, and the restoring force leads to a damped ultra-low-frequency oscillatory ion motion, with a period of about 20–30 h and lasting over 100 h. This finding may be the first observation of an ionic plasma oscillation in solids. Our understanding and controlling the “ion segregation” demonstrate that it is possible to turn this commonly viewed “adverse phenomenon” into novel electronic applications, such as ionic patterning, self-destructive memory, and energy storage.

Permalink: https://www.hzdr.de/publications/Publ-35164
Publ.-Id: 35164


Kombinierte Bewertung von Dichte- und Größeneffekten beim Windsichten mittels Mineral Liberation Analyses (MLA)

Buchmann, M.; Heinicke, F.; Mütze, T.

Windsichten ist in der Zementindustrie ein seit Jahrzehnten bekanntes Verfahren zum Klassieren im Bereich 0,01-1,0 mm. Zusätzlich kann in entsprechenden Trockenmahlkreisläufen in Kombination mit Maschinen wie Hochdruckmahlwalzen (HPGR) der Energieverbrauch im Vergleich zu Nassanwendungen deutlich reduziert werden. Diese trocken arbeitenden Systeme sind in der Mineralaufbereitung noch nicht Stand der Technik, aber erste Prototypen wurden installiert und eine zunehmende Anzahl von Projekten beginnt, diese Alternative näher zu untersuchen.
Eine Herausforderung in diesem Bereich ist die mineralische Zusammensetzung von Erzen, die in Bezug auf Dichte und Größe eine weitaus größere Vielfalt aufweisen als Zement. Partikel mit hoher Dichte, wie z. B. eisenhaltige Partikel, haben bei gleicher Größe höhere Sinkgeschwindigkeiten als Silikatpartikel mit niedrigerer Dichte. Der vorliegende Beitrag untersucht, wie dieser Effekt bewertet werden kann. Dazu wurde eine quantitative Methode auf Basis der Mineral Liberation Analysis (MLA) entwickelt, um zweidimensionale Trennfunktionen zu berechnen. Zusätzliche statistische Analysen ermöglichen es, die Wechselwirkung von Dichte und Größe isoliert voneinander zu betrachten und so, entsprechende Effekte bei der Dimensionierung von Prozessanlagen zu berücksichtigen. In dem Beitrag werden die Methode und ausgewählte Ergebnisse für ein Eisenerz vorgestellt.

Keywords: MLA; Windsichten; Eisenerz; trockene Aufbereitung

  • Aufbereitungstechnik 63(2022)9, 52-64
    ISSN: 1434-9302

Permalink: https://www.hzdr.de/publications/Publ-35163
Publ.-Id: 35163


Machine learning-based quantum accurate interatomic potentials for warm dense aluminum

Kumar, S.; Tahmasbi, H.; Ramakrishna, K.; Lokamani, M.; Cangi, A.

Modeling warm dense matter is relevant for various applications including the interior of gas giants and exoplanets, inertial confinement fusion, and ablation of metals. Ongoing and upcoming experimental campaigns in photon sources around the globe rely on numerical simulations which are accurate on the level of electronic structures. In that regard, density functional theory molecular dynamics (DFT-MD) simulations [1] have been widely used to compute the dynamical and thermodynamical properties of warm dense matter. However, two challenges impede further progress: (1) DFT-MD becomes computationally infeasible with increasing temperature (2) finite-size effects render many computational observables inaccurate, because DFT-MD is limited to a few hundred atoms on current HPC platforms. Recently, molecular dynamics simulations using machine learning-based interatomic potentials (ML-IAP) could overcome these computational limitations. Here, we propose a method to construct ML-IAPs from DFT data based on SNAP descriptors [2]. We present our results for aluminum. In particular, we investigate the transferability of ML-IAPs over a large range of temperatures (1000 to 100000 K) and pressures (ambient to 800 GPa), which currently is a topic of active research. To test the transferability of the SNAP potential, we calculate thermal conductivity, viscosity, diffusion coefficient, and sound velocity in and out of the data training range.

References:

[1]. G. Kresse and J. Hafner, Phys. Rev. B 47, 558 (1993).
[2]. A. P. Thompson, L. P. Swiler, C. R. Trott, S. M. Foiles, and G. J. Tucker, J. Comput. Phys., 285, 316-330, 2015.

Keywords: Computational Physics; Warm Dense Matter; Machine Learning; Transport Coefficients

  • Lecture (Conference)
    Multiscale Modeling of Matter under Extreme Conditions, 11.-16.09.2022, Görlitz, Germany

Permalink: https://www.hzdr.de/publications/Publ-35162
Publ.-Id: 35162


A single bubble rising in the vicinity of a vertical wall: A numerical study based on volume of fluid method

Yan, H.; Zhang, H.; Liao, Y.; Zhang, H.; Zhou, P.; Liu, L.

Single bubble rising in the close vicinity of a vertical wall is one of the focuses in the field of gas-liquid two-phase flow. In this work, three-dimensional direct numerical simulation based on volume of fluid (VOF) and adaptive mesh refinement method is performed to investigate the bubble rising and wake structures near a vertical wall. The bubble migration trajectory, deformation, velocity and wake structures were analyzed under various Galileo numbers and initial wall distances. Bubbles with a Galileo number of 8.8 significantly migrate away from the wall, which is driven by the repulsive force as a result of the suppression of the vortex diffusion on the bubble surface. As the Galileo number increases, the asymmetry of the shedding vortex tends to play a vital role on the repulsive force, which is exacerbated by the presence of the vertical wall. A periodic shedding of the vortex appears behind the bubble when the Galileo number reaches at 95. Meanwhile, the bubble trajectory changes from rectilinear to spiral along with a periodic oscillation. Due to the interaction between the vertical wall and the bubble wake, a transition from a rectilinear rising path to a spiral rising path is more likely to occur compared to that without a vertical wall. The presence of a vertical wall contributes to bubble-rising oscillations. A decrease of the bubble terminal velocity due to viscous effect near the vertical wall is observed for bubbles at low Galileo numbers. However, the viscous effect is less pronounced as the Galileo number increases.

Keywords: Single bubble; Migration trajectory; Wall effect; Wake structure; VOF; OpenFOAM

Permalink: https://www.hzdr.de/publications/Publ-35161
Publ.-Id: 35161


Data publication: FPGA Testbench for Beam-Based Feedback

Maalberg, A.; Kuntzsch, M.; Petlenkov, E.

The testbench data to compare the time response of a 4th-order regulator implemented in fixed-point with the same regulator simulated in a floating-point MATLAB model.

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Permalink: https://www.hzdr.de/publications/Publ-35160
Publ.-Id: 35160


Electrical Conductivity of Iron in Earth’s Core from Microscopic Ohm’s Law

Ramakrishna, K.; Vorberger, J.; Cangi, A.; Baczewski, A.; Lokamani, M.

Understanding the electronic transport properties of iron under high temperatures and pressures is essential for constraining geophysical processes. The difficulty of reliably measuring these properties calls for sophisticated theoretical methods that can support diagnostics. We present results of the electrical conductivity within the pressure and temperature ranges found in Earth's core by simulating microscopic Ohm's law using time-dependent density functional theory.

Keywords: Computational Physics; Warm dense matter; TDDFT

  • Lecture (Conference)
    Multiscale Modeling of Matter under Extreme Conditions, 13.09.2022, Görlitz, Germany

Permalink: https://www.hzdr.de/publications/Publ-35156
Publ.-Id: 35156


wrap up & discussion: consensus and controversial aspects of CT innovation in RT

Richter, C.

consensus and controversial aspects of CT innovation in RT

  • Invited lecture (Conferences)
    ESTRO 2022 Congress, 06.-10.05.2022, Copenhagen, Denmark

Permalink: https://www.hzdr.de/publications/Publ-35155
Publ.-Id: 35155


Treating Knock-On Displacements in Fluctuation Electron Microscopy Experiments

Radic, D.; Peterlechner, M.; Posselt, M.; Bracht, H.

This work investigates how knock-on displacements influence fluctuation electron microscopy (FEM) experiments. FEM experiments were conducted on amorphous silicon, formed by self-ion implantation, in a transmission electron microscope at 300 kV and 60 kV at various electron doses, two different binnings and with two different cameras, a CCD and a CMOS one. Furthermore, energy filtering has been utilized in one case. Energy filtering greatly enhances the FEM data by removing the inelastic background intensity, leading to an improved speckle contrast. The CMOS camera yields a slightly larger normalized variance than the CCD at an identical electron dose and appears more prone to noise at low electron counts. Beam-induced atomic displacements affect the 300 kV FEM data, leading to a continuous suppression of the normalized variance with increasing electron dose. Such displacements are considerably reduced for 60 kV experiments since the primary electron’s maximum energy transfer to an atom is less than the displacement threshold energy of amorphous silicon. The results show that the variance suppression due to knock-on displacements can be controlled in two ways: Either by minimizing the electron dose to the sample or by conducting the experiment at a lower acceleration voltage.

Keywords: amorphous silicon; beam damage; diffraction mapping; fluctuation electron microscopy; medium-range order

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Permalink: https://www.hzdr.de/publications/Publ-35154
Publ.-Id: 35154


Y(III) sorption at the orthoclase (001) surface measured by X-ray reflectivity

Neumann, J.; Lessing, J.; Lee, S. S.; Stubbs, J. E.; Eng, P. J.; Demnitz, M.; Fenter, P.; Schmidt, M.

Interactions of heavy metals with charged mineral surfaces control their mobility in the environment. Here, we investigate the adsorption of Y(III) onto the orthoclase (001) basal plane, the former as a representative of rare earth elements and an analogue of trivalent actinides and the latter as a representative of naturally abundant K-feldspar minerals. We apply in-situ high-resolution X-ray reflectivity to determine the sorption capacity and molecular distribution of adsorbed Y species as a function of Y3+ concentration and pH. We observe an inner-sphere (IS) sorption complex at a distance of ~1.5 Å from the surface and an outer-sphere (OS) complex at 3–4 Å. Based on the adsorption height of the IS complex a bidentate, binuclear binding mode, in which Y3+ binds to two terminal oxygens seems most plausible. The total Y coverages of IS and OS species are max. ~1.3 Y3+/AUC for all Y concentrations (AUC: area of the unit cell = 111.4 Ų), which is in the expected range based on the estimated surface charge of orthoclase (001).

Keywords: solid liquid interface; rare earth elements; trivalent actinides; crystal truncation rod; resonant anomalous X-ray reflectivity; feldspars

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Permalink: https://www.hzdr.de/publications/Publ-35153
Publ.-Id: 35153


Effect of He+ implantation on nanomechanical resonators in 3C-SiC

Jagtap, N.; Klaß, Y.; David, F.; Bredol, P.; Weig, E.; Helm, M.; Astakhov, G.; Erbe, A.

Silicon carbide (SiC) is a suitable candidate for Micro- and Nanoelectromechanical systems due to its superior mechanical properties. We would like to use it as a quantum sensor to sense small magnetic fields. It can be achieved by coupling a spin associated silicon vacancy (V_Si) in 4H-SiC with a mechanical mode of a resonator. Spin-mechanical resonance is observed when resonance frequency from V_Si matches resonance frequency of a mechanical mode.
In the initial experiments, we focus on the material modification by helium (He+) ion broad beam implantation on a strained resonator based on 3C-SiC implanted with high fluence of (1*10^14 /cm^2) and low fluence (1*10^12 /cm^2) at 14 keV. The change in resonance frequency and quality factors as a function of fluence is studied. We also show the effect on stress and higher modes of the nanomechanical resonators.

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  • Open Access Logo Lecture (others)
    NanoNet^+ Workshop 2022 - Görlitz, 04.-06.10.2022, Görlitz, Saxony, Germany

Permalink: https://www.hzdr.de/publications/Publ-35152
Publ.-Id: 35152


MRI-based computational model generation for cerebral perfusion simulations in health and ischaemic stroke

Józsa, T. I.; Petr, J.; Barkhof, F.; Payne, S. J.; Mutsaerts, H. J. M. M.

Cerebral perfusion models were found to be promising research tools to predict the impact of acute ischaemic stroke and related treatments on cerebral blood flow (CBF) linked to patients’ functional outcome. To provide insights relevant to clinical trials, perfusion simulations need to become suitable for group-level investigations, but computational studies to date have been limited to a few patient-specific cases. This study set out to overcome issues related to automated parameter inference, that restrict the sample size of perfusion simulations, by integrating neuroimaging data. Seventy-five brain models were generated using measurements from a cohort of 75 healthy elderly individuals to model resting-state CBF distributions. Computational perfusion model geometries were adjusted using healthy reference subjects’ T1-weighted MRI. Haemodynamic model parameters were determined from CBF measurements corresponding to arterial spin labelling perfusion MRI. Thereafter, perfusion simulations were conducted for 150 acute ischaemic stroke cases by simulating an occlusion and cessation of blood flow in the left and right middle cerebral arteries. The anatomical (geometrical) fitness of the brain models was evaluated by comparing the simulated grey and white matter (GM and WM) volumes to measurements in healthy reference subjects. Statistically significant, strong positive correlations were found in both cases (GM: Pearson’s r 0.74, P-value< 0.001; WM: Pearson’s r 0.84, P-value< 0.001). Haemodynamic parameter tuning was verified by comparing total volumetric blood flow rate to the brain in reference subjects and simulations resulting in Pearson’s r 0.89, and P-value< 0.001. In acute ischaemic stroke cases, the simulated infarct volume using a perfusion-based proxy was 197±25 ml. Computational results showed excellent agreement with anatomical and haemodynamic literature data corresponding to T1-weighted, T2-weighted, and phase-contrast MRI measurements both in healthy scenarios and in acute ischaemic stroke cases. Simulation results represented solely worst-case stroke scenarios with large infarcts because compensatory mechanisms, e.g. collaterals, were neglected. The established computational brain model generation framework provides a foundation for population-level cerebral perfusion simulations and for in silico clinical stroke trials which could assist in medical device and drug development.

Permalink: https://www.hzdr.de/publications/Publ-35151
Publ.-Id: 35151


Regulatory Requirements for the Translation of Radiopharmaceuticals

Kiß, O.

Regulatory Requirements for the Translation of Radiopharmaceuticals

  • Invited lecture (Conferences)
    5th GyMIC Molecular Imaging Symposium, 15.-16.09.2022, Leipzig, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-35150
Publ.-Id: 35150


ELBE High Power RF System

Kuntzsch, M.

The ELBE accelerator at Helmholtz-Zentrum Dresden-Rossendorf has been commissioned in 2001 using klystron power amplifiers. In the course of a major machine upgrade in 2012, solid state power amplifiers have been installed to drive the superconducting cavities and to increase the maximum beam current to 1.6 mA. The talk will introduce the high power radio frequency system of the continuous wave (CW) accelerator ELBE, wrap-up the operational experience and will give an outlook to the potential successor of machine called DALI.

Keywords: ELBE; high power RF

Related publications

  • Invited lecture (Conferences)
    Power Amplifier for Particle Accelerator - PA² conference, 15.-16.11.2022, Freiburg im Breisgau, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-35149
Publ.-Id: 35149


Frontiers of Computational Quantum Many-Body Theory

Dornheim, T.

The fundamental laws necessary for the mathematical treatment of a large part of physics and the whole of chemistry are thus completely known, and the difficulty lies only in the fact that application of these laws leads to equations that are too complex to be solved." Nearly a century has passed, yet the famous quote by Paul Dirac still gets to the heart of many research fields within theoretical physics, quantum chemistry, material science, etc. In this talk, I will show how we can use cutting-edge numerical methods on modern high-performance computing systems to effectively overcome these limitations in many cases. In this way, we get unprecedented insights into quantum many-body systems on the nanoscale going all the way from ultracold atoms like superfluid helium to warm dense matter that occurs within planetary interiors and thermonuclear fusion applications.

  • Lecture (Conference)
    International Conference of Advanced Systems Research, 14.07.2022, Wroclaw, Poland

Permalink: https://www.hzdr.de/publications/Publ-35148
Publ.-Id: 35148


Electronic pair alignment and roton feature in the warm dense electron gas

Dornheim, T.

The study of matter under extreme densities and temperatures as they occur e.g. in astrophysical objects and nuclear fusion applications has emerged as one of the most active frontiers in physics, material science, and related disciplines. In this context, a key quantity is given by the dynamic structure factor S(q,ω), which is probed in scattering experiments -- the most widely used method of diagnostics at these extreme conditions. In addition to its crucial importance for the study of warm dense matter, the modeling of such dynamic properties of correlated quantum many-body systems constitutes one of the most fundamental theoretical challenges of our time. Here we report a hitherto unexplained roton feature in S(q,ω) of the warm dense electron gas [1], and introduce a microscopic explanation in terms of a new electronic pair alignment model [2]. This new paradigm will be highly important for the understanding of warm dense matter, and has a direct impact on the interpretation of scattering experiments. Moreover, we expect our results to give unprecedented insights into the dynamics of a number of correlated quantum many-body systems such as ultracold helium, dipolar supersolids, and bilayer heterostructures.

[1] T. Dornheim, S. Groth, J. Vorberger, and M. Bonitz, Phys. Rev. Lett. 121, 255001 (2018)
[2] T. Dornheim, Zh. Moldabekov, J. Vorberger, H. Kählert, and M. Bonitz, arXiv:2203.12288

  • Lecture (Conference)
    Strongly Coupled Coulomb Systems (SCCS), 26.07.2022, Görlitz, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-35147
Publ.-Id: 35147


Relation between Ga vacancies, photoluminescence and growth conditions of MOVPE prepared GaN layers

Hospodková, A.; Čížek, J.; Hájek, F.; Hubáček, T.; Pangrác, J.; Dominec, F.; Kuldová, K.; Batysta, J.; Liedke, M. O.; Hirschmann, E.; Butterling, M.; Wagner, A.

A set of GaN layers prepared by metalorganic vapor phase epitaxy under different technological conditions (growth temperature carrier gas type and Ga precursor) were investigated by varia-ble energy positron annihilation spectroscopy (VEPAS) to find a link between technological conditions, GaN layer properties and the concentration of galium vacancies (VGa). Different cor-relations between technological parameters and VGa concentration were observed for layers grown from triethyl gallium (TEGa) and trimethyl gallium (TMGa) precursors. In case of TEGa formation of VGa was significantly influenced by type of reactor atmosphere (N2 or H2), while no similar behaviour was observed for growth from TMGa. Formation of VGa was suppressed with increasing temperature for the growth from TEGa. On the contrary, enhancement of VGa concen-tration was observed for growth from TMGa with cluster formation for the highest temperature of 1100°C. From the correlation of photoluminescence results with VGa concentration determined by VEPAS it can be concluded, that yellow band in GaN is likely not connected with VGa and ad-ditionally, increased VGa concentration enhances excitonic luminescence. Probable explanation is that VGa prevents formation of some other highly efficient nonradiative defects. Possible types of such defects are suggested.

Keywords: GaN; Ga vacancy; metalorganic vapor phase epitaxy; positron annihilation spectroscopy; photoluminescence; MOVPE

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Permalink: https://www.hzdr.de/publications/Publ-35146
Publ.-Id: 35146


New Perspectives for Warm-dense Matter Theory: From Quantum Monte Carlo to Temperature Diagnostics

Dornheim, T.

Warm dense matter (WDM)---an extreme state that is characterized by extreme densities and temperatures---has emerged as one of the most active frontiers in plasma physics and material science. In nature, WDM occurs in astrophysical objects such as giant planet interiors and brown dwarfs. In addition, WDM is highly important for cutting-edge technological applications such as inertial confinement fusion and the discovery of novel materials.
In the laboratory, WDM is studied experimentally in large facilities around the globe, and new techniques have facilitated unprecedented insights into exciting phenomena like the formation of nano diamonds at planetary interior conditions [1]. Yet, the interpretation of these experiments requires a reliable diagnostics based on accurate theoretical modeling, which is a notoriously difficult task [2].
In this talk, I give an overview of recent ground-breaking developments in this field [3,4], which will allow for the first time to rigorously treat the intricate interplay of Coulomb coupling with thermal excitations and quantum degeneracy effects. Moreover, I show how cutting-edge quantum Monte Carlo simulation techniques will help to decisively improve density functional theory (DFT) simulations of WDM, thereby opening up unprecedented perspectives and new paradigms such as the experimental and theoretical study of nonlinear effects [5,6]. Finally, I will present a new idea to extract the exact temperature from an X-ray Thomson scattering experiment without any models or simulations [7].

[1] D. Kraus et al., Nature Astronomy 1, 606-611 (2017)
[2] M. Bonitz et al., Physics of Plasmas 27, 042710 (2020)
[3] T. Dornheim et al., Physics Reports 744, 1-86 (2018)
[4] T. Dornheim et al., Physical Review Letters 121, 255001 (2018)
[5] T. Dornheim et al., Physical Review Letters 125, 085001 (2020)
[6] Zh. Moldabekov et al., Journal of Chemical Theory and Computation 18, 2900-2912 (2022)
[7] T. Dornheim et al., arXiv:2206.12805

  • Invited lecture (Conferences)
    Multiscale Modeling of Matter under Extreme Conditions, 12.09.2022, Görlitz, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-35145
Publ.-Id: 35145


Data publication: Bubble size distribution and electrode coverage at porous nickel electrodes in a novel 3-electrode flow-through cell

Rox, H.; Bashkatov, A.; Yang, X.; Loos, S.; Mutschke, G.; Gerbeth, G.; Eckert, K.

Porous materials are frequently used as e.g. electrodes or porous transport layers in various types of electrolyzers. A better understanding of the bubble dynamics on porous electrodes is especially important to optimize new electrolyzer designs like membraneless electrolyzers. The developed 3-electrode cell was optimized with regard to the analysis of the bubble nucleation, growth and detachment on the applied working electrode. Noteworthy in this regard is the 2-dimensional optical measurement system to characterize the bubble dynamics from the side and top. The cell provides a platform to run parametric studies in alkaline electrolytes. The present data set compares three different expanded nickel metals at applied current densities of |j|= 10, 20, 50, 100 or 200 mA/cm² and flow rates of ̇ = 0 or 5 ml/min. As electrolyte 1 M KOH is used. An overview of all performed experiments and the main parameters (current density j and flow rate ) is given in the file Overview of all performed experiments.pdf. The data is analyzed as described in the corresponding journal publication Bubble size distribution and electrode coverage at porous nickel electrodes in a novel 3-electrode flow-through cell. For each parameter set 3 data sets are given to ensure statistical confidence. Each data set, stored as .hdf5-file, is structured in groups as follows:

  • Electrochemical Measurement Data
  • Sideview Raw Images
  • Topview Raw Images
  • Results
    • Detected Bubbles
    • Electrode Coverage

In the attributes assigned to the groups in the .hdf5-file all relevant metadata is given, including the experimental parameters, used devices and characteristics of the mounted WE. In addition to exemplary data sets for all three electrodes, the CAD files of the experimental setup used and sample videos of the raw images are also provided within this data publication. The remaining data sets of all measurements performed can be made available upon request.

Keywords: bubble dynamics; alkaline electrolysis; porous electrodes; membraneless electrolyzer; machine learning; additive manufacturing

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Permalink: https://www.hzdr.de/publications/Publ-35144
Publ.-Id: 35144


Automatic detection and classification of treatment deviations in proton therapy from realistically simulated prompt gamma imaging data

Pietsch, J.; Khamfongkhruea, C.; Berthold, J.; Janssens, G.; Stützer, K.; Löck, S.; Richter, C.

Background:

A clinical study regarding the potential of range verification in proton therapy by prompt gamma imaging (PGI) is carried out at our institution. Manual interpretation of the detected spot-wise range shift information is time-consuming, highly complex, and therefore not feasible in a broad routine application.

Purpose:

Here, we present an approach to automatically detect and classify treatment deviations in realistically simulated PGI data for head and neck cancer (HNC) treatments using convolutional neural networks (CNNs) and conventional machine learning (ML) approaches.

Methods:

For 12 HNC patients and one anthropomorphic head phantom (n=13), pencil beam scanning (PBS) treatment plans were generated and one field per plan was assumed to be monitored with the IBA slit camera. In total, 386 scenarios resembling different relevant or non-relevant treatment deviations were simulated on planning and control CTs and manually classified into 7 classes: non-relevant changes (NR) and relevant changes (RE) triggering treatment intervention due to range prediction errors (±RP), setup errors in beam direction (±SE), anatomical changes (AC), or a combination of such errors (CB). PBS spots with reliable PGI information were considered with their nominal Bragg peak position for the generation of two 3D spatial maps of 16⨯16⨯16 voxels containing PGI-determined range shift and proton number information. Three complexity levels of simulated PGI data were investigated: (I) optimal PGI data, (II) realistic PGI data with simulated Poisson noise based on the locally delivered proton number, and (III) realistic PGI data with an additional positioning uncertainty of the slit camera following an experimentally determined distribution.
For each complexity level, 3D-CNNs were trained on a data subset (n=9) using patient-wise leave-one-out cross-validation and tested on an independent test cohort (n=4). Both the binary task of detecting RE and the multi-class task of classifying the underlying error source were investigated. Similarly, four different conventional ML classifiers (logistic regression, multi-layer perceptron, random forest, support vector machine) were trained using five previously established handcrafted features extracted from the PGI data and used for performance comparison.

Results:

On the test data, the CNN ensemble achieved a binary accuracy of 0.95, 0.96, and 0.93 and a multi-class accuracy of 0.83, 0.81, and 0.76 for the complexity levels (I), (II), and (III), respectively. In the case of binary classification, the CNN ensemble detected treatment deviations in the most realistic scenario with a sensitivity of 0.95 and a specificity of 0.88. The best performing ML classifiers showed a similar test performance.

Conclusions:

This study demonstrates that CNNs can reliably detect relevant changes in realistically simulated PGI data and classify most of the underlying sources of treatment deviations. The CNNs extracted meaningful features from the PGI data with a performance comparable to ML classifiers trained on previously established handcrafted features. These results highlight the potential of a reliable, automatic interpretation of PGI data for treatment verification, which is highly desired for broad clinical application and a prerequisite for the inclusion of PGI in an automated feedback loop for online adaptive proton therapy.

Keywords: range verification; prompt gamma imaging; proton therapy; artificial intelligence; machine learning

Permalink: https://www.hzdr.de/publications/Publ-35143
Publ.-Id: 35143


A High-Order-Integration Scheme for Global Polynomial Representations of Closed Surfaces

Zavalani, G.; Hecht, M.

We provide a novel high-order integration scheme crossing the limitations of established curved triangle techniques, that can be applied to a broad class of surfaces, providing a high-order approximation of the integrand and the geometry of the surface. This approach relies on recent results of multivariate interpolation which enable a global polynomial level set to be used to implicitly represent a broad class of closed surfaces.

Keywords: high-order integration; global polynomial level set; multivariate interpolation; curved triangles; closed surfaces

  • Poster
    11th Conference on Applied Mathematics and Scientific Computing, 05.-09.09.2022, Brijuni, Croatia

Permalink: https://www.hzdr.de/publications/Publ-35140
Publ.-Id: 35140


Recommendations on compiling test datasets for evaluating artificial intelligence solutions in pathology

Homeyer, A.; Geißler, C.; Ole Schwen, L.; Zakrzewski, F.; Evans, T.; Strohmenger, K.; Westphal, M.; David Bülow, R.; Kargl, M.; Karjauv, A.; Munné-Bertran, I.; Orge Retzlaff, C.; Romero-López, A.; Sołtysiński, T.; Plass, M.; Carvalho, R.; Steinbach, P.; Lan, Y.-C.; Bouteldja, N.; Haber, D.; Rojas-Carulla, M.; Vafaei Sadr, A.; Kraft, M.; Krüger, D.; Fick, R.; Lang, T.; Boor, P.; Müller, H.; Hufnagl, P.; Zerbe, N.

Artificial intelligence (AI) solutions that automatically extract information from digital histology images have shown great promise for improving pathological diagnosis. Prior to routine use, it is important to evaluate their predictive performance and obtain regulatory approval. This assessment requires appropriate test datasets. However, compiling such datasets is challenging and specific recommendations are missing. A committee of various stakeholders, including commercial AI developers, pathologists, and researchers, discussed key aspects and conducted extensive literature reviews on test datasets in pathology. Here, we summarize the results and derive general recommendations on compiling test datasets. We address several questions: Which and how many images are needed? How to deal with low-prevalence subsets? How can potential bias be detected? How should datasets be reported? What are the regulatory requirements in different countries? The recommendations are intended to help AI developers demonstrate the utility of their products and to help pathologists and regulatory agencies verify reported performance measures. Further research is needed to formulate criteria for sufficiently representative test datasets so that AI solutions can operate with less user intervention and better support diagnostic workflows in the future.

Keywords: machine learning; pathology; test datasets

Permalink: https://www.hzdr.de/publications/Publ-35139
Publ.-Id: 35139


Accurate temperature diagnostics for matter under extreme conditions

Dornheim, T.; Böhme, M.; Kraus, D.; Döppner, T.; Preston, T.; Moldabekov, Z.; Vorberger, J.

The experimental investigation of matter under extreme densities and temperatures as they occur for example in astrophysical objects and nuclear fusion applications constitutes one of the most active frontiers at the interface of material science, plasma physics, and engineering. The central obstacle is given by the rigorous interpretation of the experimental results, as even the diagnosis of basic parameters like the temperature T is rendered highly difficult by the extreme conditions. In this work, we present a simple, approximation-free method to extract the temperature of arbitrarily complex materials from scattering experiments, without the need for any simulations or an explicit deconvolution. This new paradigm can be readily implemented at modern facilities and corresponding experiments will have a profound impact on our understanding of warm dense matter and beyond, and open up a gamut of appealing possibilities in the context of thermonuclear fusion, laboratory astrophysics, and related disciplines.

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Permalink: https://www.hzdr.de/publications/Publ-35138
Publ.-Id: 35138


Physical insights from imaginary-time density--density correlation functions

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

The accurate theoretical description of the dynamic properties of correlated quantum many-body systems such as the dynamic structure factor S(q,ω) constitutes an important task in many fields. Unfortunately, highly accurate quantum Monte Carlo methods are usually restricted to the imaginary time domain, and the analytic continuation of the imaginary time density--density correlation function F(q,τ) to real frequencies is a notoriously hard problem. In this work, we argue that no such analytic continuation is required as F(q,τ) contains, by definition, the same physical information as S(q,ω), only in an unfamiliar representation. Specifically, we show how we can directly extract key information such as the temperature or quasi-particle excitation energies from the τ-domain, which is highly relevant for equation-of-state measurements of matter under extreme conditions. As a practical example, we consider \emph{ab initio} path integral Monte Carlo results for the uniform electron gas (UEG), and demonstrate that even nontrivial processes such as the \emph{roton feature} of the UEG at low density straightforwardly manifest in F(q,τ). In fact, directly working in the τ-domain is advantageous for many reasons and holds the enticing promise for unprecedented agreement between theory and experiment.

Permalink: https://www.hzdr.de/publications/Publ-35137
Publ.-Id: 35137


Ab Initio Static Exchange-Correlation Kernel across Jacob’s Ladder without Functional Derivatives

Moldabekov, Z.; Böhme, M.; Vorberger, J.; Blaschke, D.; Dornheim, T.

The electronic exchange-correlation (XC) kernel constitutes a fundamental input for the estimation of a gamut of material properties such as the dielectric characteristics, the thermal and electrical conductivity, the construction of effective potentials, or the response to an external perturbation. In practice, no reliable method has been known that allows to compute the kernel of real materials. In this work, we overcome this long-standing limitation by introducing a new, formally exact methodology for the computation of the static XC kernel of arbitrary materials exclusively within the framework of density functional theory (DFT) -- no external input apart from the usual XC-functional is required. As a first practical demonstration of the utility and flexibility of our methodology, we compare our new results with exact quantum Monte Carlo (QMC) data for the archetypical uniform electron gas model at both ambient and warm dense matter conditions. This gives us unprecedented insights into the performance of different XC-functionals, and has important implications for the development of new functionals that are designed for the application at extreme temperatures. In addition, we obtain new DFT results for the XC kernel of warm dense hydrogen as it occurs in fusion applications and astrophysical objects such as planetary interiors. The observed excellent agreement to the recent QMC results by Böhme \emph{et al.}~[Phys.~Rev.~Lett.~\textbf{129}, 066402 (2022)] clearly demonstrates that our framework is capable to even capture nontrivial effects such as XC-induced isotropy breaking in the density response of hydrogen at large wave numbers. Our method can easily be applied using standard DFT codes and will open up new avenues for the computation of the properties of real materials.

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Permalink: https://www.hzdr.de/publications/Publ-35136
Publ.-Id: 35136


Numerical design optimization of recuperator designs for sCO2 power cycle by CFD

Guille-Bourdas, A. F.

As a part of my graduation internship in engineering and master’s degree, I work in the Helmholtz Zentrum Dresden-Rosseendorf institute for an internship of 6-months. I am a part of a team consisting of my supervisor, Dr. Sebastian Unger and a PhD student, Mrs. Malini Bangalore. The latter studies a thermal energy storage (TES). The storage would store electricity as heat from renewable energy sources when the supply in electricity is higher than the demand. In case of residual load demand, the stored thermal energy would be released to a power cycle and supply the electrical grid. Therefore, a heat exchanger , connecting the thermal storage system to the power cycle, needs to ben designed and here is where I intervene.
Before I came, it was already decided, that the power cycle uses supercritical fluid as working fluid and working fluid in the thermal energy storage circuit, more specifically the hot fluid, is CO2 at atmospheric pressure. It was also decided that the heat exchanger type is a printed circuit heat exchanger (PCHE), that the heat transfer rate is set to 10 MW and the hot fluid inlet temperature is 600 °C. However, to completely determine the geometry of the PCHE, the boundary conditions, i.e. temperature, pressure and mass flow rates in hot and cold channels, need to be determined.
To that end, a review of cycles and their modelling is made. It helps to calculate the boundary conditions for the cold side. Then, a cost-optimization analysis of the PCHE leads to determine the boundary conditions of the hot fluid. Indeed, as the hot fluid is CO2 at atmospheric pressure, even the smaller pressure drop has a significant impact on the operation cost of the PCHE. Therefore, a reference case may be determined.
Finally, CFD simulations were conducted on the reference case geometry. Furthermore, the behaviour of the PCHE is examined, when the mass flow rate is changed, e.g. because of different system operation. Finally, the CFD simulation results are compared to existing correlations.

  • Master thesis
    Universite de Poitiers, 2022
    Mentor: Sebastian Unger
    91 Seiten

Permalink: https://www.hzdr.de/publications/Publ-35135
Publ.-Id: 35135


Online-adaptive particle therapy: Current status and vision for the future

Richter, C.

Online-adaptive particle therapy: Current status and vision for the future
Richter, Christian

  • Lecture (Conference)
    DGMP Konferenz, 21.-24.09.2022, Aachen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-35134
Publ.-Id: 35134


Pages: [1.] [2.] [3.] [4.] [5.] [6.] [7.] [8.] [9.] [10.] [11.] [12.] [13.] [14.] [15.] [16.] [17.] [18.] [19.] [20.] [21.] [22.] [23.] [24.] [25.] [26.] [27.] [28.] [29.] [30.] [31.] [32.] [33.] [34.] [35.] [36.] [37.] [38.] [39.] [40.] [41.] [42.] [43.] [44.] [45.] [46.] [47.] [48.] [49.] [50.] [51.] [52.] [53.] [54.] [55.] [56.] [57.] [58.] [59.] [60.] [61.] [62.] [63.] [64.] [65.] [66.] [67.] [68.] [69.] [70.] [71.] [72.] [73.] [74.] [75.] [76.] [77.] [78.] [79.] [80.] [81.] [82.] [83.] [84.] [85.] [86.] [87.] [88.] [89.] [90.] [91.] [92.] [93.] [94.] [95.] [96.] [97.] [98.] [99.] [100.] [101.] [102.] [103.] [104.] [105.] [106.] [107.] [108.] [109.] [110.] [111.] [112.] [113.] [114.] [115.] [116.] [117.] [118.] [119.] [120.] [121.] [122.] [123.] [124.] [125.] [126.] [127.] [128.] [129.] [130.] [131.] [132.] [133.] [134.] [135.] [136.] [137.] [138.] [139.] [140.] [141.] [142.] [143.] [144.] [145.] [146.] [147.] [148.] [149.] [150.] [151.] [152.] [153.] [154.] [155.] [156.] [157.] [158.] [159.] [160.] [161.] [162.] [163.] [164.] [165.] [166.] [167.] [168.] [169.] [170.] [171.] [172.] [173.] [174.] [175.] [176.] [177.] [178.] [179.] [180.] [181.] [182.] [183.] [184.] [185.] [186.] [187.] [188.] [189.] [190.] [191.] [192.] [193.] [194.] [195.] [196.] [197.] [198.] [199.] [200.] [201.] [202.] [203.] [204.] [205.] [206.] [207.] [208.] [209.] [210.] [211.] [212.] [213.] [214.] [215.] [216.] [217.] [218.] [219.] [220.] [221.] [222.] [223.] [224.] [225.] [226.] [227.] [228.] [229.] [230.] [231.] [232.] [233.] [234.] [235.] [236.] [237.] [238.] [239.] [240.] [241.] [242.] [243.] [244.] [245.] [246.] [247.] [248.] [249.] [250.] [251.] [252.] [253.] [254.] [255.] [256.] [257.] [258.] [259.] [260.] [261.] [262.] [263.] [264.] [265.] [266.] [267.] [268.] [269.] [270.] [271.] [272.] [273.] [274.] [275.] [276.] [277.] [278.] [279.] [280.] [281.] [282.] [283.] [284.] [285.] [286.] [287.] [288.] [289.] [290.] [291.] [292.] [293.] [294.] [295.] [296.] [297.] [298.] [299.] [300.] [301.] [302.] [303.] [304.] [305.] [306.] [307.] [308.] [309.] [310.] [311.] [312.] [313.] [314.] [315.] [316.] [317.] [318.] [319.] [320.] [321.] [322.] [323.] [324.] [325.] [326.] [327.] [328.] [329.] [330.] [331.] [332.] [333.] [334.] [335.] [336.] [337.] [338.] [339.] [340.] [341.] [342.] [343.] [344.] [345.] [346.] [347.] [348.] [349.]