Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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41709 Publications

Dual role of ER stress in response to metabolic co-targeting and radiosensitivity in head and neck cancer cells

Chen, O.; Manig, F.; Lehmann, L.; Sorour, N.; Löck, S.; Yu, Z.; Dubrovska, A.; Baumann, M.; M. Kessler, B.; Stasyk, O.; A. Kunz-Schughart, L.

Abstract

Arginine deprivation therapy (ADT) is a new metabolic targeting approach with high therapeutic potential for various solid cancers. Combination of ADT with low doses of the natural arginine analog canavanine effectively sensitizes malignant cells to irradiation. However, the molecular mechanisms determining the sensitivity of intrinsically non-auxotrophic cancers to arginine deficiency are still poorly understood. We here show for the first time that arginine deficiency is accompanied by global metabolic changes and protein/membrane breakdown, and results in the induction of specific, more or less pronounced (severe vs. mild) ER stress responses in head and neck squamous cell carcinoma (HNSCC) cells that differ in their intrinsic ADT sensitivity. Combination of ADT with canavanine triggered catastrophic ER stress via the eIF2α-ATF4(GADD34)-CHOP pathway, thereby inducing apoptosis; the same signaling arm was irrelevant in ADT-related radiosensitization. The particular strong supra-additive effect of ADT, canavanine and irradiation in both intrinsically more and less sensitive cancer cells supports the rational of ER stress pathways as novel target for improving multi-modal metabolic anti-cancer therapy.

Keywords: 3-D culture; Arginine-deprivation therapy; Canavanine; ER stress; Head and neck squamous carcinoma; Metabolic targeting; Radiosensitization

Permalink: https://www.hzdr.de/publications/Publ-33956


Data publication: Describing chain-like assembly of ethoxygroup-functionalized organic molecules on Au(111) using high-throughput simulations

Lokamani, M.; Kelling, J.; Ohmann, R.; Meyer, J.; Kühne, T.; Cuniberti, G.; Wolf, J.; Juckeland, G.; Huhn, T.; Zahn, P.; Moresco, F.; Gemming, S.

Abstract

Bei diesem Datensatz handelt es sich um die Grundzustandsstruktur von PEEB auf Au(111) und die Inputdatei für DFTB+.

Keywords: DFTB; 1,4-bis(phenylethynyl)-2,5-bis(ethoxy)benzene (PEEB); STM; High-Throughput; Meta-Structures

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Permalink: https://www.hzdr.de/publications/Publ-33955


Conceptual design report for the LUXE experiment

Abramowicz, H.; Hernandez Acosta, U.; Altarelli, M.; Assmann, R.; Bai, Z.; Behnke, T.; Benhammou, Y.; Blackburn, T.; Boogert, S.; Borysov, O.; Borysova, M.; Brinkmann, R.; Bruschi, M.; Burkart, F.; Büßer, K.; Cavanagh, N.; Davidi, O.; Decking, W.; Dosselli, U.; Elkina, N.; Fedotov, A.; Firlej, M.; Fiutowski, T.; Fleck, K.; Gostkin, M.; Grojean, C.; Andrew Hallford, J.; Harsh, H.; Hartin, A.; Heinemann, B.; Heinzl, T.; Helary, L.; Hoffmann, M.; Huang, S.; Huang, X.; Idzik, M.; Ilderton, A.; Magdalena Jacobs, R.; Kämpfer, B.; King, B.; Lakhno, H.; Levanon, A.; Levy, A.; Levy, I.; List, J.; Lohmann, W.; Ma, T.; John Macleod, A.; Malka, V.; Meloni, F.; Mironov, A.; Morandin, M.; Moron, J.; Negodin, E.; Perez, G.; Pomerantz, I.; Poeschl, R.; Prasad, R.; Quere, F.; Ringwald, A.; Roedel, C.; Rykovanov, S.; Salgado, F.; Santra, A.; Sarri, G.; Saevert, A.; Sbrizzi, A.; Schmitt, S.; Schramm, U.; Schuwalow, S.; Seipt, D.; Shaimerdenova, L.; Shchedrolosiev, M.; Skakunov, M.; Soreq, Y.; Streeter, M.; Swientek, K.; Tal Hod, N.; Tang, S.; Teter, T.; Thoden, D.; Titov, A.; Tolbanov, O.; Torgrimsson, G.; Tyazhev, A.; Wing, M.; Zanetti, M.; Zarubin, A.; Zeil, K.; Zepf, M.; Zhemchukov, A.

Abstract

This Conceptual Design Report describes LUXE (Laser Und XFEL Experiment), an experimental campaign that aims to combine the high-quality and high-energy electron beam of the European XFEL with a powerful laser to explore the uncharted terrain of quantum electrodynamics characterised by both high energy and high intensity. We will reach this hitherto inaccessible regime of quantum physics by analysing high-energy electron-photon and photon-photon interactions in the extreme environment provided by an intense laser focus. The physics background and its relevance are presented in the science case which in turn leads to, and justifies, the ensuing plan for all aspects of the experiment: Our choice of experimental parameters allows (i) field strengths to be probed where the coupling to charges becomes non-perturbative and (ii) a precision to be achieved that permits a detailed comparison of the measured data with calculations. In addition, the high photon flux predicted will enable a sensitive search for new physics beyond the Standard Model. The initial phase of the experiment will employ an existing 40 TW laser, whereas the second phase will utilise an upgraded laser power of 350 TW. All expectations regarding the performance of the experimental set-up as well as the expected physics results are based on detailed numerical simulations throughout.

Keywords: energy: high; photon photon: interaction; new physics: search for; electron: beam; photon: flux; laser; quantum electrodynamics; numerical calculations: Monte Carlo; proposed experiment

Permalink: https://www.hzdr.de/publications/Publ-33954


From conventional to unconventional superconductivity

Wosnitza, J.

Involved research facilities

  • High Magnetic Field Laboratory (HLD)
  • Invited lecture (Conferences)
    Quantum Matter Bordeaux School 2021, 15.-19.11.2021, Bordeaux, Frankreich

Permalink: https://www.hzdr.de/publications/Publ-33953


Verflüssigung von Wasserstoff durch magnetische Kühlung

Gottschall, T.

Abstract

Magnetische Materialien ändern ihre Temperatur, wenn sie einem Magnetfeld ausgesetzt werden. Dieser sogenannte magnetokalorische Effekt lässt sich nutzen, um alternative Kühlkonzepte zu entwickeln. Während in den letzten Jahren der wissenschaftliche Fokus auf der Kühlung nahe Raumtemperatur lag, ist kürzlich die magnetische Verflüssigung von Wasserstoff als Anwendungsgebiet stärker ins Blickfeld gerückt. Die konventionelle Herstellung von Flüssigwasserstoff ist ein äußerst energieintensiver Prozess. Effizienzsteigerungen sind durch den Einsatz maßgeschneiderter magnetischer Materialien und hoher Magnetfelder möglich. In diesem Beitrag werden die physikalischen Grundlagen der magnetischen Kühlung diskutiert und ausgewählte magnetokalorische Materialklassen vorgestellt. Des Weiteren werden die technologischen Herausforderungen und Vorteile thematisiert.

Involved research facilities

  • High Magnetic Field Laboratory (HLD)
  • Invited lecture (Conferences)
    Deutsche Kälte-und Klimatagung 2021 Dresden, 19.11.2021, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-33952


Magnetic cooling: from materials to application

Gottschall, T.

Abstract

With the world's increasingly affluent population demanding more comfortable living and working conditions, it is vital that we address the development of much more efficient cooling technologies as an urgent priority. An alternative approach is based on solid-state refrigeration by one of the caloric effects – electrocaloric, magnetocaloric, barocaloric or elastocaloric - where the material's temperature is forced to change under the application of an electrical, magnetic, or mechanical field. However, there is also the possibility to combine these different effects in a beneficial way, in the so-called multicaloric cooling cycle. Magnetic Ni-Mn-based Heusler alloys are ideally suited for multicaloric applications due to their coupled magnetostructural transformation between martensite and austenite. In this work, we discuss the current progress in the characterization of these materials for novel cooling technologies.

Involved research facilities

  • High Magnetic Field Laboratory (HLD)
  • Invited lecture (Conferences) (Online presentation)
    Phd-Retreat CRC 270, 02.12.2021, Darmstadt, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-33950


Magnetic properties and microstructure of Sm5Fe17-based composite magnets

Dirba, I.; Sepehri-Amin, H.; Skokov, K.; Scurschii, I.; Hono, K.; Gutfleisch, O.

Abstract

We have investigated synthesis, magnetic properties and microstructure of Sm5Fe17-based hard magnetic phase with a Sm20Fe70Ti10 composition. Ultrahigh coercivities, μ0Hc = 7.18 T at room temperature and μ0Hc = 8.86 T at 10 K, have been achieved. The room-temperature coercivity, determined from high-field pulse measurements, reaches 35 % of the anisotropy field μ0Ha = 20.7±0.8 T. Further, it is demonstrated that a coercivity of 2.18 T is maintained even at 500 K. The Curie temperature Tc of Sm20Fe70Ti10 is 577 K and the calculated exchange stiffness parameter A is 7.72 pJ/m. Detailed transmission electron microscopy investigations show a two-phase microstructure consisting of the Sm6Fe17-based hard magnetic matrix phase with grain size below 200 nm and finer, below 100 nm, Fe2Ti grains. Majority of the Fe2Ti phase is located at the grain boundaries with some finer inclusions found also inside the 5:17 grains. Despite the high fraction of the Fe2Ti grains, nearly single-phase demagnetization loops are observed. In order to enhance Ms, the effect of Ti content on phase constitution, magnetic properties and microstructure was studied in detail. Ms increases and Hc decreases for the Ti-lean compositions.

Involved research facilities

  • High Magnetic Field Laboratory (HLD)

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Permalink: https://www.hzdr.de/publications/Publ-33949


Anisotropic magnetization, critical temperature, and paramagnetic Curie temperature in the highly anisotropic magnetic Heusler compound Rh2CoSb

He, Y.; Sibille, R.; Chen, D.; Kroder, J.; Helm, T.; Schnelle, W.; Felser, C.; Fecher, G. H.

Abstract

The paramagnetic Curie temperature θp is a concept that describes the magnetic ordering temperature in the well-established Curie-Weiss law. Despite the successful explanations of the magnetic behavior, the anisotropy is not usually considered. Although anisotropic θp has been reported for several layered antiferromagnetic or ferrimagnetic materials owing to the orientation-dependent exchange, in ferromagnetic systems, θp was thought to be almost isotropic for decades, and the occasionally reported small difference has remained unexplained. In this paper, we experimentally report the anisotropic magnetization, critical temperature, and paramagnetic Curie temperature in highly anisotropic magnetic Rh2CoSb caused by a large magnetocrystalline anisotropy. The saturation magnetization along the c axis is 25% larger than that along the a axis. The critical temperature and paramagnetic Curie temperature along the c axis are 6 and 15 K higher than those along the a axis, respectively, as deduced from the Arrott plots and inverse susceptibility. A simple modification of the Curie-Weiss law was made to calculate the anisotropic θp, which well explains not only Rh2CoSb, but also many other previously reported ferromagnetic materials.

Involved research facilities

  • High Magnetic Field Laboratory (HLD)

Permalink: https://www.hzdr.de/publications/Publ-33948


Experimental Investigation of Na-Zn Molten Salt Batteries

Weber, N.; Lee, J.; Monrrabal Marquez, G.; Sarma, M.; Weier, T.; Gebarowski, W.; Kjos, O.; Sommerseth, C.; Heinz, M.; Salvo, M.; Smeacetto, F.; Ding, W.

Abstract

High-temperature batteries with molten metal electrodes have been explored for more than 50 years. Today, three such devices are commercially available: the sodium-sulphur battery, the ZEBRA (or Na-NiCl2) battery and the Ca-Sb liquid metal battery. In view of the need to integrate large amounts of renewable energy into the electric grid, several alternative stationary energy storage technologies are currently being explored. The main objective of this research is to reduce the storage price and improve the lifetime, sustainability and recyclability of these devices. Within the Horizon 2020 project SOLSTICE1, two different Na-Zn molten salt batteries are currently being developed. While the first cell operates with a solid ceramic electrolyte at 300°C, the second employs a fully liquid electrolyte working at 600°C.
The talk will give an overview of the working principle, challenges and opportunities of the Na-Zn battery concept also highlighting the fluid dynamic aspects of battery operation. Some first experimental results, which have been obtained during the last year, will be presented.

  • Lecture (Conference)
    PAMIR International Conference on Fundamental and Applied MHD, 04.07.2022, Krakau, Polen

Permalink: https://www.hzdr.de/publications/Publ-33947


New Method to Correct Energy Losses of Wire-Mesh Sensor Data

de Assis Dias, F.; Wiedemann, P.; Schleicher, E.; Da Silva, M. J.; Hampel, U.

Abstract

Capacitance wire-mesh sensor is a multielectrode instrument for the measurement of multiphase flows. Since it was originally designed to measure fluids with no or very small conductivities, the sensor may suffer from energy losses when used to measure mixtures with conductivity greater than 100 µS/cm. Consequently, when derived flow parameters are estimated from WMS raw data, unphysical results may be obtained, i.e. negative phase fraction. Threshold methods are commonly employed to cut-off such negative values. However, such approaches work well only for flow regimes where the phases are almost binary, e.g. stratified flows. For this reason, we present a new arrangement and a new method to correct energy losses of a capacitance WMS, which generates reliable data also for complex phase fraction distributions. In the new arrangement, an additional transmitter wire is placed outside the flow domain forming external flow-independent crossing-points. Thus, the change in readings of the external crossing points are used to estimate the loss factor of each receiver wire, which in turn are employed to compensate the energy loss of each local measurement. Experimental and numerical results suggest that the new method is fundamental to expand the conductivity range of capacitance WMS and to measure complex flow structures, i.e. emulsions, foam, ionic tracers, etc. In the examples presented in this paper, deviations of some local measurements were reduced from the range of 20% to less than 3.3%.

Keywords: wire-mesh sensor; multiphase flow; energy loss correction

Related publications

  • Open Access Logo Contribution to proceedings
    10th World Congress on Industrial Process Tomography (WCIPT), 13.-16.09.2021, Virtual meeting, Virtual meeting
    Proceedings of the 10th World Congress on Industrial Process Tomography

Permalink: https://www.hzdr.de/publications/Publ-33945


New limits on double-beta decay of 190Pt and 198Pt

Danevich, F. A.; Hult, M.; Junghans, A.; Kasperovych, D. V.; Kropivyansky, B. N.; Lutter, G.; Marissens, G.; Polischuk, O. G.; Romaniuk, M. V.; Stroh, H.; Tessalina, S.; Tretyak, V. I.; Ware, B.

Abstract

A search for double-beta decay of 190Pt and 198Pt
with emission of γ -ray quanta was realized at the HADES
underground laboratory with a 148 g platinum sample measured
by two ultralow-background HPGe detectors over 8946
h. The isotopic composition of the platinum sample has
been measured with high precision using inductively coupled
plasma mass spectrometry. New lower limits for the
half-lives of 190Pt relative to different channels and modes
of the decays were set on the level of lim T1/2 ∼ 10^14–10^16
year. A possible exact resonant 0νKN transition to the 1,2
1326.9 keV level of 190Os is limited for the first time as
T1/2 ≥ 2.5 × 10^16 year. A new lower limit on the double beta
decay of 198Pt to the first excited level of 198Hg was set
as T1/2 ≥ 3.2 × 10^19 year, one order of magnitude higher
than the limit obtained in the previous experiment.

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Permalink: https://www.hzdr.de/publications/Publ-33943


Pre-treatment visualization of predicted radiation-induced acute alopecia in brain tumour patients

In’T Ven, L.; Compter, I.; van Eijsden, K.; Zindler, J.; Swinnen, A.; de Ruysscher, D.; Rozema, T.; Troost, E. G. C.; Eekers, D.

Abstract

Background and purpose: Temporary alopecia is a common side-effect in brain tumour patients receiving cranial radiotherapy with a significant psychological burden for the affected patient. The purpose of this study was to generate a method in our treatment planning system (TPS) to visualize the expected radiation-induced alopecia 4 weeks after treatment, in order to inform the patients thereupon before the start of radiotherapy.
Material and methods: A pilot study was conducted in ten patients receiving hypo- (HF) or conventionally fractionated (CF) photon beam Volumetric Modulated Arc Therapy (VMAT) for an intracranial lesion. Dose calculations were correlated to visible alopecia four weeks after the end of treatment to create a structure predictive of alopecia in our TPS. These alopecia structures for both fractionation schedules were validated in two cohorts of 69 HF and 78 CF patients undergoing radiotherapy between 2016 and 2019.
Results: In the pilot cohort, a total physical dose of 4 Gy for HF and 12.6 Gy for CF radiotherapy were found to be predictive of alopecia 4 weeks after treatment. Applying these doses to our validation cohort, we found an accurate prediction of alopecia in 59/69 (86%) HF and 73/78 (96%) CF patients. For the total patient group of 147 patients, the predicted amount of alopecia was accurate in 90% of the cases. All inaccurate predictions overestimated the expected extent of alopecia.
Conclusion: The presented straightforward method to visualize predicted alopecia 4 weeks after treatment has proven to predict the extent alopecia highly accurate in the vast majority of patients. Sharing these results with the patients pre-treatment may result in stress reduction before cranial irradiation.

Keywords: Radiotherapy; neuro-oncology; brain tumour; alopecia; hair loss; prediction

Permalink: https://www.hzdr.de/publications/Publ-33942


Generierung von FPGA Kernen auf Basis einer HLS-basierten Continuous Integration Pipeline für Experimente mit MePS am Zentrum für Hochleistungs-Strahlenquellen "ELBE"

Ufer, R.

Abstract

Hochgeschwindigkeits-Digitizer sind in vielen Forschungsanlagen vertreten. Darunter auch an der derzeitig größten Forschungsanlage des Helmholtz-Zentrums Dresden-Rossendorfs (HZDRs), dem Elektronen Linearbeschleuniger mit hoher Brillanz und geringer Emittanz (ELBE). Dessen Primärstrahl ist die Grundlage für viele Experimente. Dazu gehört die am Monoenergetische Positronen-Spektroskopie (MePS) System durchgeführten Positronen-Annihilations-Lebensdauer-Spektroskopie (PALS), zur zerstörungsfreien Materialuntersuchung. Dabei ist eine Digitalisierung, Vorverarbeitung und Reduktion von großen Mengen an Messdaten, noch während der Durchführung des Experimentes notwendig. Die digitale Verarbeitung der Daten wird innerhalb des Digitizers von einem Field Programmable Gate Array (FPGA) vorgenommen. Um dessen Firmware zu modifizieren bedarf es spezielle Kenntnisse im Bereich des Hardwareentwurfs und hohen zeitlichen Aufwand.

In dieser Belegarbeit wurde die Implementierung eines Algorithmus zur Datenauswertung, unter Nutzung eines High-Level Synthese (HLS) Compilers und C/C++, sowie dessen Einbindung in eine herstellerspezifische Firmware untersucht. Zusammen mit der komplexen Firmwaregenerierung wurde ein Konzept zur Automatisierung der Erstellung des Bitstreams und Memory Configuration Files vorgestellt und für den produktiven Einsatz vereinfacht.

Die Evaluierung zeigt das die Adaptierung eines benutzerdefinierten Algorithmus, unter Einhaltung des Ressourcenbedarfs und der Taktfrequenz in die Firmware theoretisch realisierbar ist. Aufgrund von auftretenden Probleme konnte dies aber nicht auf dem FPGA des Digitizers im realen Versuchsaufbau abschließend getestet werden.

Keywords: FPGA; ELBE; MePS; PALS; Digitizer; HLS; C/C++; Datenauswertung

  • Study thesis
    TU Dresden, 2021
    Mentor: Seniorprofessor Dr.-Ing. habil. Rainer G. Spallek, Dr.-Ing. Oliver Knodel
    31 Seiten

Permalink: https://www.hzdr.de/publications/Publ-33940


Erweiterung einer Plattform um die Verwaltung von Metadaten nach den FAIR Prinzipien

Voigt, M.

Abstract

Die HELmholtz ScIentific Project WORkflow PlaTform (HELIPORT) ist eine Kollaboration von Helmholtz-Zentren Dresden-Rossendorf (HZDR), Forschungszentrum Jülich (FZJ) und Helmholtz-Institut Jena (HIJ) und wird durch die Helmholtz Metadata Collaboration (HMC) finanziert. HELIPORT verknüpft über den gesamten Lebenszyklus eines wissenschaftlichen Projekts verwendete Systeme zu einer Projektbeschreibung im Sinne der FAIR Prinzipien. Dafür müssen in HELIPORT Metadaten zu Artefakten der beteiligten Systeme verwaltet werden. Dies ist nach den FAIR Prinzipien eng mit der Vergabe von persistenten und eindeutigen Identifiern (PIDs) verbunden. Daraus ergibt sich das Ziel für diese Arbeit, entsprechende Ansätze in HELIPORT zu untersuchen und anhand des HELIPORT Prototypen eine geeignete Möglichkeit dafür zu implementieren.

Diese Arbeit bietet zunächst einen Überblick über die FAIR Prinzipien mit Vertiefung der für das Thema relevanten Konzepte Metadaten und Identifier. Im Anschluss daran werden, unter Beachtung der bestehenden HELIPORT Infrastruktur, verschiedene Designentscheidungen diskutiert und eine daraus resultierende Umsetzung vorgenommen. Diese wird anhand der FAIR Prinzipien und konkreter Experimente evaluiert.

In dieser Arbeit wird ein gesteigertes Gewicht auf Programmarchitektur gelegt. Um die Verwaltung von PIDs und Metadaten zu implementieren, wurde mittels DigitalObjects eine Abstraktion für verschiedene Artefakte geschaffen, die auch bei zukünftigen Features in HELIPORT einen Mehrwert bietet.

Keywords: HELIPORT; FAIR; Metadata; Handles; FAIR Digital Objects; Django; Python

Related publications

  • Study thesis
    TU Dresden, 2022
    Mentor: Prof. Dr. Wolfgang E. Nagel, Dr. Ralph Müller-Pfefferkorn, Dr. Oliver Knodel
    38 Seiten

Permalink: https://www.hzdr.de/publications/Publ-33939


Data-Driven Quest for Two-Dimensional Non-van der Waals Materials

Friedrich, R.; Ghorbani-Asl, M.; Curtarolo, S.; Krasheninnikov, A. V.

Abstract

Two-dimensional (2D) materials are frequently associated with the sheets forming bulk layered compounds bonded by van der Waals (vdW) forces. The anisotropy and weak interaction between the sheets have also been the main criteria in the computational search for new 2D systems, predicting ∼2000 exfoliable compounds. However, some representatives of a new type of non-vdW 2D systems, without layered 3D analogues, were recently manufactured. For this novel materials class, data-driven design principles are still missing. Here, we outline a set of 8 binary and 20 ternary candidates by filtering the AFLOW-ICSD database according to structural prototypes. The oxidation state of the surface cations regulates the exfoliation energy with low oxidation numbers leading to weak bonding - a useful descriptor to obtain novel 2D materials also providing clear guidelines for experiments. A vast range of appealing electronic, optical, and magnetic properties make the candidates attractive for various applications and particularly spintronics.

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

Involved research facilities

Related publications

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Permalink: https://www.hzdr.de/publications/Publ-33938


Beitrag zur Abschätzung der Recyclingfähigkeit von Multi-Material-Strukturen: Numerische Modellierung der Aufschlusszerkleinerung

Heibeck, M.; Richter, J.; Mütze, T.; Rudolph, M.; Hornig, A.; Modler, N.; Reuter, M.; Filippatos, A.

Abstract

Hintergrund: Eine zunehmende Anzahl von Produkten von Fahrzeugen bis Haushaltsgeräten besteht aus Multi-Material Strukturen, die Verbindungen zwischen unterschiedlichen Werkstof-fen enthalten. Diese Verbindungen müssen im Recycling meist wieder aufgeschlossen wer-den, um hohe Recyclingraten für alle eingesetzten Werkstoffe zu erzielen. Typischerweise erfolgt der Aufschluss von Materialien durch mechanische Zerkleinerungsprozesse, bei denen die Recycler konstruktive und prozesstechnische Parameter auf vorliegende Strukturen und Materialverbindungen anpassen und optimieren. Für nachhaltige Recycling-Lösungen sind neben der Recyclingindustrie aber auch Produkthersteller bereits in der Konstruktionsphase mit einzubeziehen, da ihre Designentscheidungen die Recyclingfähigkeit stark beeinflusst. Derzeit fehlen jedoch meist Methoden, um die Auswirkungen von Designentscheidungen auf das Aufschlussverhalten abzuschätzen. Die Finite Elemente Analyse könnte eine vielverspre-chende Lösung sein.
Fragestellung: Welche Möglichkeiten und Grenzen gibt es derzeit bei der Anwendung der Finiten Elemente Methode zur Untersuchung der Aufschlusszerkleinerung von Multi-Material-Strukturen?
Methodik & Durchführung: Mithilfe der Finiten Elemente (FE) Methode wurde ein physika-lisch basiertes, numerisches Modell der Aufschlusszerkleinerung entwickelt. Das Modell wur-de für die Zerkleinerung von Prüfkörpern aus der Automobilbranche (Metall-Kunststoff-Verbünde) in einem Rotorreißer eingesetzt. Für die FE-Modellierung wurde die Software LS-DYNA verwendet und Materialmodelle, welche die Plastizität und das Versagen der beteilig-ten Werkstoffe sowie deren Kontaktstellen berücksichtigen. Die Simulation wurde für ver-schiedene Lastfälle durchgeführt, die aus unterschiedlichen Orientierungen des Prüfkörpers im Rotorreißers resultieren. Numerische Ergebnisse wurden mit experimentellen Ergebnissen grundlegender Zerkleinerungsversuche verglichen.
Ergebnisse: Erste Ergebnisse zeigen eine hohe Übereinstimmung zwischen experimentellen und numerischen Ergebnissen im Bereich des plastischen Verformungsverhaltens duktiler Werkstoffe sowie beim Versagensverhalten.
Wissenschaftlicher Beitrag: Die Finite Elemente Methode ist ein gängiges Tool in der Kon-struktionsphase von Produkten, um z. B. das Strukturverhalten in verschiedenen Belastungssi-tuationen abschätzen zu können. Neuwertig ist die Anwendung der FE Methode zur Modellie-rung des Zerkleinerungsprozesses beim Recycling von Multi-Material-Strukturen. Die Methode leistet einen Beitrag dazu, dass Konstrukteure zukünftig schon im Designstadium das Auf-schlussverhalten und die Recyclingfähigkeit von Produkten abschätzen können.

  • Lecture (Conference)
    11. DGAW-Wissenschaftskongress "Abfall- und Ressourcenwirtschaft", 17.-18.03.2022, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-33937


Aufschlusszerkleinerung beim Recycling von Multi-Material-Strukturen: Experimentelle und numerische Untersuchungen

Heibeck, M.; Richter, J.; Mütze, T.; Rudolph, M.; Hornig, A.; Modler, N.; Reuter, M.; Filippatos, A.

Abstract

Eine zunehmende Anzahl von Gebrauchsgütern, von Fahrzeugen bis Haushaltsgerä-ten, besteht aus Multi-Material Strukturen. Sie enthalten Verbindungen zwischen un-terschiedlichen Materialien, die für Herstellung und Nutzungsphase eines Produktes wichtige Funktionen erfüllen, aber im Recycling meist wieder aufgeschlossen werden müssen, um hohe Recyclingraten für alle verbauten Materialien zu erzielen. Typi-scherweise erfolgt der Aufschluss von Materialien durch mechanische Zerkleine-rungsprozesse, bei denen die Recycler konstruktive und prozesstechnische Parame-ter auf vorliegende Strukturen und Materialverbindungen anpassen und optimieren. Für nachhaltige Recycling-Lösungen sind neben der Recyclingindustrie aber auch Produkthersteller bereits in der Konstruktionsphase mit einzubeziehen, da ihre Desig-nentscheidungen die Recyclingfähigkeit stark beeinflusst. Derzeit fehlen jedoch meist Methoden, um die Auswirkungen von Designentscheidungen auf das Aufschlussver-halten abzuschätzen.
Vor diesem Hintergrund wird im Rahmen des BMBF-Projekts Circular by Design un-tersucht, welche Parameter bereits während der Bauteilentwicklung beeinflussbar sind, um den Materialaufschluss bei der mechanischen Aufbereitung zu optimieren, ohne Funktion und Lebensdauer der Struktur in der Nutzungsphase zu beeinträchti-gen. Dazu wurden in einem Rotorreißer grundlegende Versuche an Prüfkörpern aus der Automobilbranche zum Einfluss verschiedener Verbindungscharakteristika auf das Aufschlussverhalten durchgeführt. Wegen der aufwändigen experimentellen Datener-hebung aufgrund hoher Parametervariabilität im Produktdesign und Zerkleinerungs-prozess wurde zudem mithilfe der Finiten Elemente Methode (FEM) ein physikalisch basiertes, numerisches Modell der Aufschlusszerkleinerung entwickelt.
Für die FEM-Modellierung wurde die Software LS-DYNA verwendet und Materialmo-delle, welche die Plastizität und das Versagen der beteiligten Werkstoffe sowie deren Kontaktstellen berücksichtigen. Die Simulation wurde für verschiedene Lastfälle durchgeführt, welche beispielsweise unterschiedliche Orientierungen des Prüfkörpers im Rotorreißer abbilden. Im vorliegenden Beitrag werden experimentelle und erste numerische Ergebnisse am Beispiel einer Metall-Kunststoff-Hybridstruktur vorgestellt.

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

Permalink: https://www.hzdr.de/publications/Publ-33936


The influence of thermoelectric magnetohydrodynamics in microstructure evolution

Kao, A.; Attwood, R.; Clark, S.; Eckert, S.; Fan, X.; Gan, T.; Lee, P. D.; Pericleous, K.; Shevchenko, N.; Soar, P.; Tonry, C.

Abstract

The application of a static magnetic field to alloy solidification has been shown to significantly influence microstructure evolution, through convective transport generated by the so-called thermoelectric magnetohydrodynamic (TEMHD) effect. Strong effects have been observed across a wide range of solidification length and time scales, from the slow growth of directional solidification to the rapid growth of undercooled solidification and additive manufacturing (AM). Observed changes to the microstructure reported include the generation of an ‘Archimedes’ screw during rotation, the control of channels responsible for ‘freckle’ defects, melt pool morphology in AM and influence of tip growth velocity. These changes have been observed experimentally and predicted numerically using our code TESA (ThermoElectric Solidification Algorithm), a bespoke parallelised microstructure solidification code that intimately couples the effect of the magnetic field and fluid flow through Cellular Automata and Lattice Boltzmann methods. TESA captures the interaction of key transport phenomena, competition of MHD flow with buoyancy and Marangoni driven convection and ultimately the effect on evolving microstructure across a wide range of processes.
This talk focuses on the effect of a magnetic field on channel formation in DS, and melt pool dynamics and solute redistribution in AM. A particularly interesting aspect of such phenomena is the inter-dependency of the thermo-solutal, hydrodynamic and electromagnetic problems. Thermoelectric (TE) currents are dependent on the temperature and solute distribution, which in turn through the convective transport influencing solidification alters the TE currents. This leads to an interesting consequence where both the temperature field (controlled externally as in DS or as a localised heat source in AM) and magnetic field have strong influences on the formation of TE currents and ultimately TEMHD. This coupling of temperature and magnetic field potentially opens many avenues for novel control techniques in solidification.

Keywords: Thermoelectric magnetohydrodynamics; Microstructure solidification; Magnetic field; Convective transport

  • Invited lecture (Conferences)
    The 6th International Conference on Advances in Solidification Processes, ICASP-6, 20.-24.06.2022, Bischoffsheim, France

Permalink: https://www.hzdr.de/publications/Publ-33935


Modelling concurrent structural mechanical mechanisms in microstructure solidification

Soar, P.; Kao, A.; Djambazov, G.; Shevchenko, N.; Eckert, S.; Pericleous, K.

Abstract

Experimental observations point to structural mechanics as a factor that can significantly alter the development of a cast metal alloy’s microstructure. Forces such as gravity or drag due to solute flow can induce dendrites to deform and/or change orientation. Such changes in microstructural development can lead to defects including stray grains and slivers that degrade macroscopic material properties. However, the interaction of microstructure evolution with structural mechanics is often neglected as a factor in numerical models, potentially rendering them incapable of capturing key defect formation mechanisms. A numerical method coupling a Finite Volume Structural Mechanics solver to a Cellular Automata microstructure solidification solver has been developed, where the growth behaviour of solidifying dendrites is altered by changes to the crystallographic orientation obtained from the calculated displacements. Scenarios where small deformations lead to large orientation changes to accumulate were examined, finding the behaviour to be analogous to that observed in experiments.

Keywords: Microstructure; numerical model; structural mechanics; dendrites; deformation

  • Lecture (Conference)
    TMS Annual Meeting & Exhibition 2022, 27.02.-03.03.2022, Anaheim, California, USA

Permalink: https://www.hzdr.de/publications/Publ-33934


Controlling Freckle Defect Formation using Magnetic Fields

Kao, A.; Shevchenko, N.; Fan, X.; Tonry, C.; Lee, P.; Eckert, S.; Pericleous, K.

Abstract

The application of a static magnetic field has been shown to have a significant effect on channel formation in the GaIn freckle defect forming alloy. The underlying mechanisms are via Thermoelectric Magnetoydrodynamics (TEMHD) driving inter-dendritic fluid flow. Thermoelectric currents form due to the inherent thermal gradient and spatial variation in composition due to solute partitioning. In the presence of a magnetic field these currents interact generating the flow driving Lorentz force. Convective solute transport then alters solidification behaviour. This causes spatial repositioning of the channel, preferential growth, secondary effects such as plume migration and complex grain boundary interactions.
TESA (ThermoElectric Solidification Algorithm) is a parallel Cellular Automata Lattice Boltzmann based numerical model that has been validated against Xray synchrotron experiments. Using TESA the dependency of the magnetic field orientation and magnitude has been explored, providing further predictions for controlling the channel.

Keywords: freckle defects; Ga-In alloy; numerical model; Cellular Automata Lattice Boltzmann model; magnetic fields

  • Lecture (Conference)
    TMS Annual Meeting & Exhibition 2022, 27.02.-03.03.2022, Anaheim, California, USA

Permalink: https://www.hzdr.de/publications/Publ-33933


The effect of magnetic fields on freckle evolution during solidification

Shevchenko, N.; Kao, A.; Fan, X.; Tonry, C.; Clark, S.; Atwood, R.; Lee, P.; Pericleous, K.; Eckert, S.

Abstract

The formation of freckle defects in the presence of a static magnetic field is studied by combining in-situ synchrotron imaging with numerical simulations. The formation, growth and motion of freckle channels during directional solidification are investigated in a Hele-Shaw cell for a low melting point Ga-In alloy. The solidification setup is developed at HZDR and is described in detail elsewhere. The solidification cell is placed in a permanent magnet system providing a flux density of about 120 mT within the cell. The turn of the magnet system about a vertical cell axis allow to get both the Bx (perpendicular to a X-ray beam) and the Bz (parallel to a X-ray beam) component of the magnetic field.
Numerical simulations, using a microscopic parallelized Cellular Automata lattice Boltzmann method, are validated by these in situ experiments. An excellent match between the numerical model and experiments conducted on thin rectangle sample alloy is achieved. Evaluation of the in situ X-ray data and numerical analysis shows the role of thermoelectric magnetohydrodynamics (TEMHD) and electromagnetic damping (EMD) in the formation of channels and ultimately freckle defects. For instance, Figures 1c and 1d show clear evidence of the effect of the magnetic field on the microstructure. Figure 1d displays the formation of a solute channel at the left side of the sample in the presence of a magnetic field. This channel development can be attributed to the thermoelectric Lorentz force acting on the inter-dendritic liquid flow by causing the solute to accumulate at one side of the cell.
In situ synchrotron experiments allow us to resolve the complex channel dynamics and simultaneously show how large-scale flow fields may alter them. Both temperature gradient and grain orientation can affect the dynamics of the segregation channels formation in the presence of the magnetic field. The effect of electromagnetic damping force to convective transport needs future investigations. The in situ synchrotron data and numerical modelling will provide further understanding of the underlying mechanisms and identifying further interesting phenomena.

Keywords: solidification; magnetic fields; freckle defects; in-situ synchrotron imaging; numerical modelling

  • Lecture (Conference) (Online presentation)
    Electromagnetic Processing of Materials, EPM 2021, 14.-16.06.2021, Riga, Latvia

Permalink: https://www.hzdr.de/publications/Publ-33932


Orthotopic glioblastoma models for evaluation of the CTV concept

Bütof, R.; Hönscheid, P.; Aktar, R.; Sperling, C.; Tillner, F.; Rassamegevanon, T.; Dietrich, A.; Meinhardt, M.; Aust, D.; Krause, M.; Troost, E. G. C.

Abstract

Background and purpose: In times of high-precision radiotherapy, the accurate and precise
definition of the primary tumour localisation and its microscopic spread is of enormous
importance. In glioblastoma, the microscopic tumour extension is uncertain and therefore
population-based margins for clinical target volume (CTV) definition are clinically used, which
could either be too small leading to increased risk of loco-regional recurrences or too large thus
enhancing the probability of normal tissue toxicity. Therefore, the aim of this project is to
investigate an individualized definition of the CTV in preclinical glioblastoma models, based
on specific biological tumour characteristics.
Material and methods: The microscopic tumour extensions of two different orthotopic brain
tumour models (U87MG_mCherry; G7_mCherry) were evaluated before and during
fractionated radiotherapy and correlated with corresponding histological data. Representative
tumour slices were analysed using Matrix-assisted Laser Desorption/Ionization (MALDI) and
stained for putative cancer stem cell markers as well as invasion markers (Nestin, MMP14,
Musashi 1, CD44).
Results: The edges of the tumour are clearly shown by the MALDI segmentation via
unsupervised clustering of mass spectra and are consistent with the histologically defined
border in H&E staining in both models. MALDI component analysis supposed specific peaks
as potential markers for normal brain tissue (e.g. 1339 m/z), whereas other peaks demarcated
the tumours very well (e.g. 1562 m/z for U87MG_mCherry) irrespective of treatment. MMP14
staining revealed only a few positive cells mainly in the tumour border, which could reflect the
invasive front in both models.
Conclusion: The results of this study indicate that a step towards an individualized CTV
definition based on biological tumour characteristics, especially using MALDI information, in
glioblastoma models seems possible. Visualization of tumour volume and protein heterogeneity
can be potentially used to define radiotherapy-sensitive and resistant areas. In-depth image
analyses will be performed in order to further improve the model for CTV definition.

Keywords: Glioblastoma; CTV; orthotopic model; MALDI; invasion

Permalink: https://www.hzdr.de/publications/Publ-33931


Techno-ökonomische Bewertung eines dezentralen und lastflexiblen Power-to-Methanol Prozesses

Schnatz, O.

Abstract

Eine Schlüsseltechnologie zur Erzeugung von Methanol aus erneuerbaren Energien (grünes Methanol) und gleichzeitiger Defossilisierung des Chemiesektors ist die Power-to-X-Technologie, speziell für die Methanolproduktion der Power-to-Methanol Prozess (PtM). Um eine zukünftige Substitution von fossilen Rohstoffen in der Methanolproduktion realisieren zu können, muss zunächst die Wirtschaftlichkeit der PtM-Prozesse untersucht werden. Infolgedessen war das Ziel der vorliegenden Arbeit die Recherche sowie Auswahl einer geeigneten Methodik zur Durchführung einer techno-ökonomischen Bewertung. Mit Hilfe der Simulationssoftware MATLAB wurde ein Berechnungsmodell zur techno-ökonomischen Bewertung des PtM-Prozesses entwickelt, wobei ein bereits entwickeltes transientes Modell zur Erfassung entsprechender prozesstechnischer Daten genutzt wurde. Unter Verwendung der bereitgestellten technischen Daten sowie weiteren ökonomischen Annahmen erfolgte die Ermittlung unterschiedlicher Kostenpositionen für einen Referenzfall im Jahr 2020/21. Daran anschließend wurde eine Wirtschaftlichkeitsanalyse für die gesamte Anlage durchgeführt. Es konnte nachgewiesen werden, dass sich die Investition in die PtM-Anlage nach aktuellem Kenntnisstand als nicht rentabel erweist. Grund hierfür sind die hohen Investitionskosten, die durch die Ausrüstungskosten des Elektrolyseurs dominiert werden. Anhand der erzielten Ergebnisse des Referenzfalls wurden Sensitivitätsanalysen durchgeführt, um die Einflussfaktoren zur Senkung der Herstellungskosten zu ermitteln. Dabei wurde gezeigt, dass die Ausrüstungskosten der SOEC sowie die Stromkosten einer der signifikantesten Kostenfaktoren darstellen. Um das zukünftige ökonomische Potential der PtM-Technologie zu beleuchten, wurden für Jahrzehnte 2030, 2040 und 2050 jeweils Wirtschaftlichkeitsanalysen durchgeführt. Dabei zeigten die Projektionen, dass sich der Betrieb einer PtM-Anlage unter den angenommenen Prognosen, bereits im Zeitraum zwischen 2030 und 2040 als wirtschaftlich profitabel erweist. Ebenso konnte gezeigt werden, dass sich die Herstellungskosten über den betrachteten Zeitraum bis 2050 relativ konstant bleiben. Grund hierfür ist die Verschiebung der Kostenverteilung von Investitionskosten und Betriebskosten. Während die Strompreise laut Prognosen in den nächsten Jahren weiter ansteigen werden, ist ein Sinken der Ausrüstungskosten für die SOEC anzunehmen. Die abschließende Untersuchung des dynamischen Betriebs ergab, dass eine dynamische Konfiguration der Anlage in Abhängigkeit von Strompreisgrenzen erst im Jahr 2050 wirtschaftlich rentabel sein wird. Ursächlich hierfür ist die Prognose des Anstieges des Strompreises, trotz voraussichtlicher Senkung der Ausrüstungskosten des Elektrolyseurs in den nächsten Jahren. Resümierend wurde in der vorliegenden Arbeit das aktuelle und zukünftige wirtschaftliche Potential der PtM-Technologie mittels einer techno-ökomischen Bewertung erfasst.

Keywords: Elektrolyse; SOEC; Power-to-X; TEA

Involved research facilities

  • TOPFLOW Facility
  • Diploma thesis
    Technische Universität Dresden, 2021
    Mentor: Fogel, Stefan
    83 Seiten

Permalink: https://www.hzdr.de/publications/Publ-33930


Hysteretic effects and magnetotransport of electrically switched CuMnAs

Zubác, J.; Kaspar, Z.; Krizek, F.; Förster, T.; Campion, R. P.; Novak, V.; Jungwirth, T.; Olejnik, K.

Abstract

Antiferromagnetic spintronics allows us to explore storing and processing information in magnetic crystals with vanishing magnetization. In this paper, we investigate magnetoresistance effects in antiferromagnetic CuMnAs upon switching into high-resistive states using electrical pulses. By employing magnetic field sweeps up to 14 T and magnetic field pulses up to ∼60 T, we reveal hysteretic phenomena and changes in the magnetoresistance, as well as the resilience of the switching signal in CuMnAs to the high magnetic field. These properties of the switched state are discussed in the context of recent studies of antiferromagnetic textures in CuMnAs.

Involved research facilities

  • High Magnetic Field Laboratory (HLD)

Downloads

Permalink: https://www.hzdr.de/publications/Publ-33929


Quantum Oscillations in Ferromagnetic (Sb,V)2Te3 Topological Insulator Thin Films

Zhang, L.; Helm, T.; Lin, H.; Fan, F.; Le, C.; Sun, Y.; Markou, A.; Felser, C.

Abstract

An effective way of manipulating 2D surface states in magnetic topological insulators may open a new route for quantum technologies based on the quantum anomalous Hall effect. The doping-dependent evolution of the electronic band structure in the topological insulator Sb2− V Te3 (0 ≤ x ≤ 0.102) thin films is studied by means of electrical transport. Sb2− V Te3 thin films were prepared by molecular beam epitaxy, and Shubnikov–de Hass (SdH) oscillations are observed in both the longitudinal and transverse transport channels. Doping with the 3d element, vanadium, induces long-range ferromagnetic order with enhanced SdH oscillation amplitudes. The doping effect is systematically studied in various films depending on thickness and bottom gate voltage. The angle-dependence of the SdH oscillations reveals their 2D nature, linking them to topological surface states as their origin. Furthermore, it is shown that vanadium doping can efficiently modify the band structure. The tunability by doping and the coexistence of the surface states with ferromagnetism render Sb2− V Te3 thin films a promising platform for energy band engineering. In this way, topological quantum states may be manipulated to crossover from quantum Hall effect to quantum anomalous Hall effect, which opens an alternative route for the design of quantum electronics and spintronics.

Involved research facilities

  • High Magnetic Field Laboratory (HLD)

Permalink: https://www.hzdr.de/publications/Publ-33928


Experimentelle und numerische Untersuchung der Wärmeübertragungs- und Strömungscharakteristik von berippten Einzelrohren und Rohrbündeln mit neuartigem Rippendesign

Unger, S.

Abstract

Die Übertragung thermischer Energie durch Wärmeübertrager ist ein essentieller Vorgang in unterschiedlichen, technischen Prozessen. Die am häufigsten vorkommende Wärmeübertragerbauform bei der Wärmeabgabe an ein Gas ist der Rippenrohrwärmeübertrager. Bis zu 85 % des thermischen Widerstandes treten nach Wang et al. (2002) dabei gasseitig auf, weshalb eine Verbesserung des Wärmeüberganges wesentlich zur Erhöhung der Gesamtleistung beiträgt. Eine typische Anwendung von geneigten Rippenrohren sind luftgekühlte Kondensatoren.
Der Einfluss der Rohrneigung auf die Wärmeübertragungs- und Strömungscharakteristik von Rippenrohren wurde in der Literatur bislang kaum untersucht. Luftgekühlte Kondensatoren werden allerdings in geneigter Orientierung installiert, um einen Kondensatablauf auf der Rohrinnenseite zu ermöglichen. Daher würde der Auslegungsprozess von luftgekühlten Kondensatoren wesentlich von einer experimentellen Charakterisierung des Einflusses der Rohrneigung auf die Wärmeübertragungs- und Strömungscharakteristik profitieren. Es existiert eine Vielzahl von Rippendesigns zur Erhöhung der luftseitigen Turbulenz entlang der Rippenoberfläche. In der Literatur konnten keine Rippendesigns gefunden werden, welche neben der Turbulenzerzeugung auch die Wärmeleitung von der Rippenbasis zur Rippenspitze verbessern und somit eine homogenere Temperaturverteilung erreichen. Wissenschaftliche Arbeiten zur Naturkonvektion beschränken sich auf numerische und experimentelle Analysen von berippten Einzelrohren. Rippenrohrbündel unter Naturkonvektion sowie der Einfluss der relevanten Rippen- und Rohrparameter auf die Wärmeübertragung der Rohrbündel wurde bislang kaum untersucht.
Für die experimentellen Untersuchungen wurde ein 6,5 𝑚 langer vertikaler Strömungskanal errichtet, in welchem unterschiedliche Gleichrichter zur Homogenisierung der Strömung installiert waren. Mittels einer Kombination aus analytischen Näherungsverfahren und Vermessung der lokal aufgelösten Rippenoberflächentemperatur wurde der Rippenwirkungsgrad bestimmt. Die Neigung der Rohrachse gegenüber der Horizontalen erhöht die Nusselt-Zahl bei erzwungener Konvektion und erniedrigt diese bei natürlicher Konvektion. Bei erzwungener Konvektion ist das Leistungsverhalten der Wärmeübertrager unter geneigter Orientierung aufgrund des höheren Druckverlustes reduziert. Für beide Konvektionsarten sinkt der Einfluss des Neigungswinkels auf die Nusselt-Zahl mit abnehmendem Rippenabstand. Basierend auf den experimentellen Untersuchungen wurden Korrelationen entwickelt, um den Wärmeübergang in Abhängigkeit von der Reynolds-Zahl oder Rayleigh-Zahl, dem Neigungswinkel und dem Rippenabstand zu beschreiben.
Die existierenden Rippendesigns zielen darauf ab, den gasseitigen konvektiven Wärmeübergang zu verbessern. Die Steigerung der Wärmeleitung durch das Rippendesign wird dabei weitestgehend vernachlässigt. Die Beeinflussung der Wärmeleitung, beispielsweise durch Veränderung des wärmeleitenden Querschnittes entlang des Rippenumfanges, ist durch konventionelle Fertigungstechnologien nur schwierig oder gar nicht realisierbar. Mit neuartigen Herstellungsverfahren, wie der additiven Fertigung, können diese komplexen Geometrien erzeugt und somit auch die Wärmeleitung lokal erhöht werden. Bei der additiven Fertigung wird ein Pulverbett selektiv mit einem Laser oder Elektronenstrahl aufgeschmolzen und das Bauteil schrittweise generiert. In der vorliegenden Arbeit wurde diese Technologie genutzt, um Rippen mit verstärkenden, in der Rippenoberfläche integrierten, Stiften zu fertigen. Dadurch werden die Wärmeleitung und die Konvektion entlang der Rippenoberfläche verbessert. Zwei neuartige Designs wurden additiv gefertigt, experimentell in einem vertikalen Strömungskanal charakterisiert und patentiert. Bei den Untersuchungen wurde festgestellt, dass das Leistungsbewertungskriterium der geschlitzten integrierten Stiftrippe (SIPF) um 78,5 % höher und die Kompaktheit der runden integrierten Stiftrippe (CIPF) um 24,3 % höher ist als bei der konventionellen glatten Rohrrippe. Die Rohre mit neuartigem Rippendesign wurden auch unter verschiedenen Neigungswinkeln untersucht. Die Zunahme des Druckverlustes mit dem Rohrneigungswinkel ist niedriger als bei der konventionellen Rippe. Die SIPF erreicht bei einer Neigung von 𝛼=20 ° das höchste Leistungsverhalten und die CIPF erreicht bei 𝛼=40 ° Neigung die höchste volumetrische Wärmestromdichte. Die entwickelten Korrelationen beschreiben die Abhängigkeit dieser Designs von der Reynolds-Zahl für verschiedene Rippenabstände sowie von der Reynolds-Zahl für verschiedenen Neigungswinkel.
Eine typische Anwendung von geneigten Rippenrohren sind luftgekühlte Kondensatoren, bei denen die Erfassung der thermischen Wärmeübertragungsleistung auf der Rohrinnenseite aufgrund des Phasenwechsels unter Umständen schwierig ist. Eine neue Messtechnik, der Temperatur-Anemometrie-Gittersensor (TAGS), wurde genutzt, um die luftseitige Temperatur und Strömungsgeschwindigkeit zeitgleich und ortsaufgelöst zur ermitteln. Die gemessene Temperaturverteilung ist für geneigte Rippenrohre stark ungleich verteilt. Fünf verschiedene Varianten zur Berechnung der thermischen Wärmeübertragungsleistung werden miteinander verglichen. Die Bestimmung mittels gewichteter Wärmestromdichten zeigt dabei die geringsten Abweichungen.
Der numerische Strömungsberechnungscode ANSYS CFX 19.0 wurde verwendet, um den Einfluss der Rippen- und Rohrparameter auf die Naturkonvektion von Rippenrohrbündeln qualitativ zu analysieren. Basierend auf der numerischen Studie wurden die zu optimierenden Rippen- und Rohrparameter ausgewählt. Zu diesen Parametern zählen die Rippendicke, der Rippenabstand, die Rippenhöhe, das Rohrachsenverhältnis, die Rohranordnung, die transversalen und longitudinalen Rohrabstände sowie die Rohrreihenanzahl. Diese Optimierung wurde mit Erkenntnissen bezüglich der erzwungenen Konvektion aus der Literatur kombiniert, wobei das ovale Rippenrohrbündel ein Achsenverhältnis von 1:2, eine Rippendicke von 1 𝑚𝑚, einen Rippenabstand von 5 𝑚𝑚 und eine Rippenhöhe von 17 𝑚𝑚 hat. Die versetzte Anordnung hat einen longitudinalen Rohrabstand von 63 𝑚𝑚 sowie einen transversalen Rohrabstand von 53 𝑚𝑚 und wurde in zwei- und dreireihiger Rohrreihenanzahl ausgeführt. Numerische Simulationen dieses optimierten Wärmeübertragers wurden für Naturkonvektion und für erzwungene Konvektion durchgeführt und qualitativ verglichen. Die Simulationsergebnisse zeigen für beide Konvektionsarten ähnliche Strömungsphänomene, wie beispielsweise Staupunkte am Rohr, Nachlaufgebiete stromabwärts des Rohres und Beschleunigungsbereich zwischen den Rohrrippen.
Die optimierten Rohrbündelwärmeübertrager wurden mit konventionellen Rippen und den neuartigen Rohrrippen in zweireihiger und dreireihiger Ausführung realisiert. In einer dafür angepassten Testsektion wurden die experimentellen Untersuchungen durchgeführt. Im Vergleich zur konventionellen Rippe zeigt die SIPF ein höheres Leistungsbewertungskriterium und eine um 52 % höhere Nusselt-Zahl für beide Ausführungen. Die CIPF erreicht eine um 22,4 % und 27,8 % höhere volumetrische Wärmestromdichte für die zweireihige und dreireihige Ausführung verglichen mit der konventionellen Rippe. Die Ergebnisse der experimentellen Untersuchungen der Rohrbündelwärmeübertrager unter Naturkonvektion in einem Kamin zeigen durchschnittlich 19,7 % und 10,9 % höhere Nusselt-Zahlen sowie 11,2 % und 4,0 % höhere volumetrische Wärmestromdichten der SIPF für die dreireihigen und zweireihigen Wärmeübertrager im Vergleich zum konventionellen Design. Ein verbessertes thermisches Leistungsverhalten für CIPF bei Naturkonvektion ist nicht zu erkennen.
Diese Arbeit zeigt, wie durch moderne Fertigungsverfahren und neue Designs auch Komponenten mit einem hohen technologischen Reifegrad weiter optimiert werden können. Durch verbesserte Wärmeübertragungsleistung bei gleichzeitig niedrigerem Materialverbrauch können Wärmeübertrager effizienter und ressourcenschonender hergestellt und betrieben werden.

Involved research facilities

  • TOPFLOW Facility
  • Doctoral thesis
    Sächsische Landesbibliothek - Staats- und Universitätsbibliothek Dresden, 2021
    Mentor: Prof. Uwe Hampel
    188 Seiten

Permalink: https://www.hzdr.de/publications/Publ-33927


High-Field Magnetization Study of Laves Phase (Gd,Y,Sm)Fe2-H

Tereshina, I. S.; Gorbunov, D.; Karpenkov, A. Y.; Doerr, M.; Drulis, H.; Granovski, S. A.; Tereshina-Chitrova, E. A.

Abstract

The crystal structure and magnetic properties of the multicomponent Laves phase compounds (Gd1-xYx)0.8Sm0.2Fe2Hz (x = 0, 0.2, 0.4, 0.6, 0.8, 1; z = 0 and 3.4) are investigated. These compounds crystallize into an MgCu2 type of structure. Hydrogenation does not change the crystal structure type but boosts the unit cell volume of (Gd,Y,Sm)Fe2 by ∼25%. Both parent and the hydrogen-charged ferrimagnetic compounds demonstrate magnetic compensation (mutual cancellation of magnetic moments of the individual magnetic sublattices). The exact compositions with zero magnetization state (compensated compositions) predicted using a three-sublattice model are in good agreement with the experiment. In the hydrides, the magnetic compensation takes place at a lower Y content as compared to the parent alloys. Pulsed magnetic fields reveal a distinctly different behavior of magnetization in the hydrides. With the increase of magnetic field, magnetization increases much faster in the hydrides as compared to the parent compounds.

Involved research facilities

  • High Magnetic Field Laboratory (HLD)

Permalink: https://www.hzdr.de/publications/Publ-33926


CFD applications in nuclear engineeering

Tian, W.; Petrov, V.; Erkan, N.; Liao, Y.; Wang, M.

Abstract

Computational fluid dynamics (CFD) and computational multiphase fluid dynamics (CMFD) methods have attracted great attentions in predicting single-phase and multiphase flows under steady-state or transient conditions in the field of nuclear reactor engineering. The CFD research circle is rapidly expanding, and the CFD topic has been covered in many international conferences on nuclear engineering, such as ICONE, NURETH, NUTHOS, and CFD4NRS, which greatly extends the forum to exchange information in the application of CFD codes to nuclear reactor safety issues.
Currently, more and more scholars are devoting their efforts to CFD study in the nuclear engineering community, and a series of valuable research results have emerged in recent years. Therefore, this research topic was proposed, and the issue was organized by Tian from Xi’an Jiaotong University, Petrov from University of Michigan, Erkan from the University of Tokyo, Liao from Helmholtz-Zentrum Dresden-Rossendorf, and Wang from Xi’an Jiaotong University, aiming to share the most advanced progress and innovations related to CFD study in nuclear engineering around the world.
In this topic, the CFD simulation in rod bundles is carried out, and the simulation results are validated based on the LDA measurement in a 5 × 5 rod bundle installed with two split-mixing-vane grids (Xiong et al.). The models of internal heating and natural convention buoyancy, as well as the models of WMLES turbulence and phase changing, were applied in the open-source CFD software OpenFOAM to perform numerical simulations of the COPRA single-layer molten pool experiment (Xi et al.). Three-dimensional computational fluid dynamic (CFD) simulations were performed to study the long-term heat removal mechanisms in the General Atomics’ Modular High Temperature Gas-cooled Reactor (MHTGR) design during a P-LOFC accident (Wang et al.). The transient hydraulic characteristics of multistage centrifugal pump during start-up process were also studied using the CFD method (Long et al.).
In terms of two-phase flow simulation using the CFD method, the capabilities and advantages provided by a model that includes an elliptic-blending Reynolds stress turbulence closure (EB-RSM), allowing fine resolution of the velocity field in the near-wall region, are tested over a large database
(Colombo and Fairweather). Ling et al. (2020) present a numerical simulation of subcooled flow boiling at a high-pressure condition. An interface tracking method, VOSET, was used to handle the moving interface, and conjugate heat transfer between the wall and the fluid was included in the
numerical model. A comparison of the CFD simulation results with the high-resolution experimental data from a helical coil experimental setup operated with a mixture of water and air is discussed, with special emphasis on two-phase pressure drops and void fraction distributions (Che et al.). Zeng et al.
studied the detailed helium bubble rising behavior in the crosstype channel using CFD software ANSYS Fluent.
With the rapid development of the GEN-IV reactors, the application of CFD in liquid metal flow and heat transfer is also widely accepted. Chai et al. performed the wall-resolved large-eddy simulation (LES) to study the flow and heat transfer properties in a turbulent channel at low Prandtl number. The numerical study on the 19-pin wire-wrapped assembly cooled by lead–bismuth eutectic in liquid metal cooled reactor was also carried out using the CFD method (Li et al.).
Park et al. summarizes the recent activities in the development of SOPHIA code using smoothed particle hydrodynamics (SPH), which is effective to solve the nuclear safety issues encountered in natural disasters and severe accidents accompanied by highly nonlinear deformations. Numerical simulation and validation of aerosol particle removal by water spray droplets with OpenFOAM during the Fukushima daiichi fuel debris retrieval was performed by considering the collection mechanisms of inertial impaction, interception, and Brownian diffusion (Liang et al.).
Finally, 12 articles in total from the United States, Europe, Japan, Korea, and China were collected, to show the recent progress of CFD study in nuclear engineering around the world. This research topic covers across both light water reactors and liquid metal cooled reactors and is definitely a
pioneer in this field. It provides valuable references, guidelines, and is leading a fast-forwarding progress for the application of CFD in the nuclear reactor thermal hydraulic analysis. Anyway, we have to confess that the CFD is still developing, and more efforts are required to make it play a more significant role in the nuclear reactor design and safety analysis. We are planning to initiate a new special issue on the “CFD in Numerical Nuclear
Reactor” in future. Please feel free to contact us if you have any questions or suggestions.

Permalink: https://www.hzdr.de/publications/Publ-33924


Vacancy-Dynamics in Niobium and its Native Oxides and their implications for Quantum Computing and Superconducting Accelerators

Wenskat, M.; Cizek, J.; Liedke, M. O.; Butterling, M.; Stiehl, M.; Dalla Lana Semione, G.; Backes, C.; Bate, C.; Melikhova, O.; Hirschmann, E.; Wagner, A.; Weise, H.; Stierle, A.; Aeschlimann, M.; Hillert, W.

Abstract

In recent years, superconducting radio-frequency (SRF) cavities have been considered as candidates for qubits in quantum computing, showing a significantly longer decoherence time compared to many other realizations. Originally, SRF cavities are the workhorse of modern particle accelerators and ongoing R&D pursuits to improve their properties, to increase the accelerating field and reduce the surface resistance in order to increase the energy reach and duty cycle of accelerators. Although few experimental milestones have been realized, the underlying mechanisms of the still observed losses have not been fully understood. In this contribution we are going to show that a recently reported temperature treatment of Nb SRF cavities in the temperature range of 573-673 K, which reduces the residual surface resistance to unprecedented values, is linked to a reorganization of the niobium oxide and near-surface vacancy structure and that this reorganization can explain the observed improved performance in both applications, quantum computing and SRF cavities.

Keywords: positron annihilation spectroscopy; positron annihilation lifetime spectroscopy; Doppler broadening; Nb; superconductors; quantum computing

Involved research facilities

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Permalink: https://www.hzdr.de/publications/Publ-33923


Simulation-based Inference of Beamline Characteristics at BESSY

Steinbach, P.; Hartmann, G.

Abstract

Poster presented at Helmholtz AI Conference 2021

Keywords: machine learning; simulation based inference; accelerator control

  • Open Access Logo Poster (Online presentation)
    Helmholtz AI annual conference, 14.-16.04.2021, virtual, Germany

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Permalink: https://www.hzdr.de/publications/Publ-33922


Chemical deposition of Cu2O films with ultra-low resistivity: correlation with the defect landscape.

Sekkat, A.; Liedke, M. O.; Huong Nguyen, V.; Butterling, M.; Baiutti, F.; Dios Sirvent Verdu, J. D.; Weber, M.; Rapenne, L.; Bellet, D.; Chichignoud, G.; Kaminski-Cachopo, A.; Hirschmann, E.; Wagner, A.; Muñoz-Rojas, D.

Abstract

Cuprous oxide (Cu2O) is a promising p-type semiconductor material for many applications. So far, the lowest resistivity values are obtained for films deposited by physical methods and/or at high temperatures (~1000 °C), limiting their mass integration. Here, Cu2O thin films with ultra-low resistivity values of 0.4 Ω.cm were deposited at only 260 °C by atmospheric pressure spatial atomic layer deposition, a scalable chemical approach. The carrier concentration (7.1014−2.1018 cm−3), mobility (1–86 cm2/V.s), and optical bandgap (2.2–2.48 eV) are easily tuned by adjusting the fraction of oxygen used during deposition. The properties of the films are correlated to the defect landscape, as revealed by a combination of techniques (positron annihilation spectroscopy (PAS), Raman spectroscopy and photoluminescence). Our results reveal the existence of large complex defects and the decrease of the overall defect concentration in the films with increasing oxygen fraction used during deposition.

Keywords: positron annihilation spectroscopy; positron annihilation lifetime spectroscopy; defects; Cu2O; p-type semiconductor; resistivity; atmospheric pressure spatial atomic layer deposition

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Permalink: https://www.hzdr.de/publications/Publ-33921


Data publication: The fate of fluvially-deposited organic carbon during transient floodplain storage

S. Scheingross, J.; N. Repasch, M.; Hovius, N.; Fuchs, M.

Abstract

The data set contains all relevant luminescence measurement data used in the corresponding article: Scheingross et al. 2021. The fate of fluvially-deposited organic carbon during transient floodplain storage. EPSL 561, 116822, doi: 10.1016/j.epsl.2021.116822.

Keywords: optically stimulated luminescence data

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Permalink: https://www.hzdr.de/publications/Publ-33920


The fate of fluvially-deposited organic carbon during transient floodplain storage

S. Scheingross, J.; N. Repasch, M.; Hovius, N.; Sachse, D.; Lupker, M.; Fuchs, M.; Halevy, I.; R. Gröcke, D.; Y. Golombek, N.; Haghipour, N.; I. Eglinton, T.; Orfeo, O.; Maria Schleicher, A.

Abstract

CO2 release from particulate organic carbon (POC) oxidation during fluvial transit can influence climate over a range of timescales. Identifying the mechanistic controls on such carbon fluxes requires determining where POC oxidation occurs in river systems. While field data show POC oxidation and replacement moving downstream in lowland rivers, flume studies show that oxidation during active fluvial transport is limited. This suggests that most fluvial POC oxidation occurs during transient floodplain storage, but this idea has yet to be tested. Here, we isolate the influence of floodplain storage time on POC oxidation by exploiting a chronosequence of floodplain deposits above the modern groundwater table in the Rio Bermejo, Argentina. Measurements from 15 floodplain cores with depositional ages from 1 y to 20 ky show a progressive POC concentration decrease and 13C-enrichment with increasing time spent in floodplain storage. These results from the Rio Bermejo indicate that over 80% of fluvially-deposited POC can be oxidized over millennial timescales in aerated floodplains. Furthermore, POC in the oldest floodplain cores is more 14C-enriched than expected based on the independently-dated floodplain ages, indicating that a portion of this oxidized POC is replaced by autochthonous POC produced primarily by floodplain vegetation. We suggest floodplain storage timescales control the extent of oxidation of fluvially-deposited POC, and may play a prominent role in determining if rivers are significant atmospheric CO2 sources.

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Permalink: https://www.hzdr.de/publications/Publ-33919


Laboratory evidence for an asymmetric accretion structure upon slanted matter impact in young stars

Burdonov, K.; Revet, G.; Bonito, R.; Argiroffi, C.; Béard, J.; Bolanõs, S.; Cerchez, M.; Chen, S. N.; Ciardi, A.; Espinosa, G.; Filippov, E.; Pikuz, S.; Rodriguez, R.; Smid, M.; Starodubtsev, M.; Willi, O.; Orlando, S.; Fuchs, J.

Abstract

Aims. Investigating the process of matter accretion onto forming stars through scaled experiments in the laboratory is important in
order to better understand star and planetary system formation and evolution. Such experiments can indeed complement observations
by providing access to the processes with spatial and temporal resolution. A previous investigation revealed the existence of a two-
component stream: a hot shell surrounding a cooler inner stream. The shell was formed by matter laterally ejected upon impact and
refocused by the local magnetic field. That laboratory investigation was limited to normal incidence impacts. However, in young
stellar objects, the complex structure of magnetic fields causes variability of the incident angles of the accretion columns. This led us
to undertake an investigation, using laboratory plasmas, of the consequence of having a slanted accretion impacting a young star.
Methods. Here, we used high power laser interactions and strong magnetic field generation in the laboratory, complemented by
numerical simulations, to study the asymmetry induced upon accretion structures when columns of matter impact the surface of
young stars with an oblique angle.
Results. Compared to the scenario where matter accretes perpendicularly to the star surface, we observe a strongly asymmetric plasma
structure, strong lateral ejecta of matter, poor confinement of the accreted material, and reduced heating compared to the normal
incidence case. Thus, slanted accretion is a configuration that seems to be capable of inducing perturbations of the chromosphere and
hence possibly influencing the level of activity of the corona.

Permalink: https://www.hzdr.de/publications/Publ-33918


Parametric study of high-energy ring-shaped electron beams from a laser wakefield accelerator

Maitrallain, A.; Brunetti, E.; Streeter, M.; Kettle, B.; Spesyvtsev, R.; Vieux, G.; Shazhad, M.; Ersfeld, B.; Yoffe, S.; Kornaszewski, A.; Finlay, O.; Ma, Y.; Albert, F.; Bourgeois, N.; Jd Dann, S.; Lemos, N.; Cipiccia, S.; M. Cole, J.; Gallardo González, I.; Higginbotham, A.; Hussein, A.; Smid, M.; Falk, K.; Krushelnick, K.; C. Lopes, N.; Gerstmayr, E.; Lumsdon, C.; Lundh, O.; Mangles, S.; Najmudin, Z.; P. Rajeev, P.; Symes, D.; G. R. Thomas, A.; A. Jaroszynski, D.

Abstract

Laser wakefield accelerators commonly produce on-axis, low-divergence, high-energy electron beams. However, a high charge, annular shaped beam can be trapped outside the bubble and accelerated to high energies. Here we present a parametric study on the production of low-energy-spread, ultra-relativistic electron ring beams in a two-stage gas cell. Ring-shaped beams with energies higher than 750 MeV are observed simultaneously with on axis, continuously injected electrons. Often multiple ring shaped beams with different energies are produced and parametric studies to control the generation and properties of these structures were conducted. Particle tracking and particle-in-cell simulations are used to determine properties of these beams and investigate how they are formed and trapped outside the bubble by the wake produced by on-axis injected electrons. These unusual femtosecond duration, high-charge, high-energy, ring electron beams may find use in beam driven plasma wakefield accelerators and radiation sources.

Permalink: https://www.hzdr.de/publications/Publ-33917


Microstructured layered targets for improved laser-induced x-ray backlighters

Sander, S.; Ebert, T.; Hartnagel, D.; Hesse, M.; Pan, X.; Schaumann, G.; Smid, M.; Falk, K.; Roth, M.

Abstract

We present the usage of two-layer targets with laser-illuminated front-side microstructures for x-ray backlighter applications. The targets consisted of a silicon front layer and copper back side layer. The structured layer was irradiated by the 500-fs PHELIX laser with an intensity above 1020Wcm−2. The total emission and one-dimensional extent of the copper Kα x-ray emission as well as a wide spectral range between 7.9 and 9.0 keV were recorded with an array of crystal spectrometers. The measurements show that the front-side modifications of the silicon in the form of conical microstructures maintain the same peak brightness of the Kα emission as flat copper foils while suppressing the thermal emission background significantly. The observed Kα source sizes can be influenced by tilting the conical microstructures with respect to the laser axis. Overall, the recorded copper Kα photon yields were in the range of 1011sr−1, demonstrating the suitability of these targets for probing applications without subjecting the probed material to additional heating from thermal line emission.

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Permalink: https://www.hzdr.de/publications/Publ-33915


Observation and modelling of stimulated Raman scattering driven by an optically smoothed laser beam in experimental conditions relevant for shock ignition

Cristoforetti, G.; Hüller, S.; Koester, P.; Antonelli, L.; Atzeni, S.; Baffigi, F.; Batani, D.; Baird, C.; Booth, N.; Galimberti, M.; Glize, K.; Héron, A.; Khan, M.; Loiseau, P.; Mancelli, D.; Notley, M.; Oliveira, P.; Renner, O.; Smid, M.; Schiavi, A.; Tran, G.; Woolsey, N. C.; Gizzi, L. A.

Abstract

We report results and modelling of an experiment performed at the Target Area West Vulcan laser facility, aimed at investigating laser–plasma interaction in conditions that are of interest for the shock ignition scheme in inertial confinement fusion (ICF), that is, laser intensity higher than 1016 W/cm2 impinging on a hot (T > 1 keV), inhomogeneous and long scalelength pre-formed plasma. Measurements show a significant stimulated Raman scattering (SRS) backscattering (∼ 4%−20% of laser energy) driven at low plasma densities and no signatures of two-plasmon decay (TPD)/SRS driven at the quarter critical density region. Results are satisfactorily reproduced by an analytical model accounting for the convective SRS growth in independent laser speckles, in conditions where the reflectivity is dominated by the contribution from the most intense speckles, where SRS becomes saturated. Analytical and kinetic
simulations well reproduce the onset of SRS at low plasma densities in a regime strongly affected by non-linear Landau damping and by filamentation of the most intense laser speckles. The absence of TPD/SRS at higher densities is explained by pump depletion and plasma smoothing driven by filamentation. The prevalence of laser coupling in the low-density profile justifies the low temperature measured for hot electrons (7−12 keV), which is well reproduced by
numerical simulations.

Permalink: https://www.hzdr.de/publications/Publ-33914


Bionic Tracking - Making tracking tasks faster and more ergonomic with Eye Tracking in VR

Günther, U.

Abstract

We present Bionic Tracking, a novel method for solving biological cell tracking problems with eye tracking in virtual reality using commodity hardware. Using gaze data, and especially smooth pursuit eye movements, we are able to track cells in time series of 3D volumetric datasets. The problem of tracking cells is ubiquitous in developmental biology, where large volumetric microscopy datasets are acquired on a daily basis, often comprising hundreds or thousands of time points that span hours or days. The image data, however, is only a means to an end, and scientists are often interested in the reconstruction of cell trajectories and cell lineage trees. Reliably tracking cells in crowded three-dimensional space over many timepoints remains an open problem, and many current approaches rely on tedious manual annotation and curation. In our Bionic Tracking approach, we substitute the usual 2D point-and-click annotation to track cells with eye tracking in a virtual reality headset, where users simply have to follow a cell with their eyes in 3D space in order to track it. We detail the interaction design of our approach and explain the graph-based algorithm used to connect different time points, also taking occlusion and user distraction into account. We demonstrate our cell tracking method using the example of two different biological datasets. Finally, we report on a user study with seven cell tracking experts, demonstrating the benefits of our approach over manual point-and-click tracking.

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  • Open Access Logo Invited lecture (Conferences) (Online presentation)
    Euro Bioimaging Virtual Pub, 09.07.2021, Turku, Finland

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Permalink: https://www.hzdr.de/publications/Publ-33912


Data publication: Realtime 3D graphics and VR with Kotlin and Vulkan

Günther, U.; Harrington, K.

Abstract

This is the video recording of the talk.

Keywords: visualisation; rendering; kotlin; java; jvm

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Permalink: https://www.hzdr.de/publications/Publ-33911


Realtime 3D graphics and VR with Kotlin and Vulkan

Günther, U.; Harrington, K.

Abstract

This talk is gonna be about the scenery framework, a framework we have developed for visualising geometry and large volumetric data (TB+) using Kotlin and Vulkan or OpenGL. Coroutines, Kotlin's conciseness and syntactic sugar enabled the efficient codebase of scenery to integrate with popular image processing tools, and support Virtual Reality rendering, both on headsets and on distributed multi-projector systems like CAVEs. We'll show code, demos, lessons learned, and demonstrate how we use the framework in a visualisation software for end users, sciview, that we have also developed.

Keywords: visualisation; rendering; kotlin; java; jvm

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  • Open Access Logo Lecture (Conference) (Online presentation)
    FOSDEM 2021, 06.-07.02.2021, Brussels/online, Belgium

Permalink: https://www.hzdr.de/publications/Publ-33910


“recomine” – Sustainable Recycling of Contaminated Mine Waste with a Combination of Environmental Technology, Resource Technology and Digitalization

Büttner, P.; Engelhardt, J.

Abstract

Abandoned contaminated mining sites such as heaps or slag usually cause major environmental problems, which are or have been rehabilitated in Germany by the government with large amount of taxes. However, they usually also contain significant amounts of urgently needed strategic raw materials and consist mainly of mineral components that can be used in the ceramics or construction materials industry. These components are not won as part of traditional coverage rehabilitation. “recomine” is a WIR! association of over 70 partnering institutions, funded by the German Federal Ministry of Education and Research (BMBF), that deals with the global challenges of contaminated soils and works on innovative, comprehensive concepts regarding their handling. For this matter, the association merges a vast know-how in the Erzgebirge region. The partnering institutions in the fields of environmental, and resource technology, digitalization, construction materials, and community are working together with the aim of marketing the developed, holistic concepts worldwide. First international success was achieved at the BHP Tailings Challenge where the recomine team was chosen by the raw materials conglomerate BHP as one of ten teams out of 153 international contenders for the ongoing proof-of-concept phase.

Keywords: re-mining; remining; recomine; HIF; circular economy; tailings; mine waste; mining; sustainable mining; recycling

Permalink: https://www.hzdr.de/publications/Publ-33909


Biotechnological production of the amphiphilic siderophore marinobactin for the usage as reagent in froth flotation process

Schrader, S.; Kutschke, S.; Pollmann, K.

Abstract

The consumption of metallic raw materials increased in the last years. The coverage of demand is getting more difficult, because both primary and secondary raw materials become more and more complex. To find a solution, some new ways have to be gone, like the combination of biotechnology with classic processing methods.
The idea of this work is the biotechnological production of amphiphilic siderophores for the application as a reagent in the classic froth flotation process. Siderophores are small organic molecules with a high affinity for binding Fe(III) and to form strong complexes also with other metals. They are produced by microorganisms (aerobic bacteria and fungi) and some plants. Especially the group of amphiphilic siderophores is very interesting. The hydrophilic part, carrying hydroxamate groups, is responsible for the binding of the metals. Flotation agents produced by the chemical industry with the same functional groups have already been applied successfully in this processing method. The fatty acid tail, that is representing the hydrophobic part, gets in contact with the bubble and spares additional chemicals and further working steps for making the target mineral particles hydrophobic.
The adapted biotechnological production for these amphiphilic siderophores, challenges the improvement of production rate under high stress conditions. Furthermore, this work presents interaction studies and flotation experiments of different scales of iron, copper and PGM containing ores.
The application of amphiphilic siderophores as biochemicals in the froth flotation process can change the classic processing method in a more sustainable process – the Bioflotation process. This will reduce the usage of other chemical agents. Moreover, the specific metal binding of siderophores changes flotation in a more purposeful and efficient process and is an important enrichment for the field of Biohydrometallurgy.

Keywords: Siderophores; Marinobactin; Marinobacter spp.

  • Lecture (Conference) (Online presentation)
    13th European Congress of Chemical Engineering and 6th European Congress of Applied Biotechnology, 20.-23.09.2021, Virtuell, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-33908


A self-assembled matrix system for cell-bioengineering applications in different dimensions, scales, and geometries

Xu, Y.; Patino Gaillez, M.; Zheng, K.; Voigt, D.; Cui, M.; Kurth, T.; Xiao, L.; Rothe, R.; Hauser, S.; Lee, P. W.; Wieduwild, R.; Lin, W.; Bornhäuser, M.; Pietzsch, J.; Boccaccini, A. R.; Zhang, Y.

Abstract

Stem cell bioengineering and therapy require different model systems and materials in different stages of development. If a chemically defined biomatrix system can fulfill most tasks, it can minimize the discrepancy among various setups. By screening biomaterials synthesized through a coacervation-mediated self-assembling mechanism, a biomatrix system optimal for human mesenchymal stromal cell (hMSC) two dimensional (2D) culture and osteogenesis is identified. Its utility for hMSC bioengineering has been further demonstrated in coating porous bioactive glass scaffolds and nano-particle synthesis for esiRNA delivery to knock down the SOX-9 gene with high delivery efficiency. The self-assembled injectable system was further utilized for three dimensional (3D) cell culture, segregated co-culture of hMSC with Human umbilical vein endothelial cells (HUVEC) as angiogenesis model, and 3D bioprinting. Most interestingly, the coating of bioactive glass with the self-assembled biomatrix not only supports the proliferation and osteogenesis of hMSC in the 3D scaffold but also induces the amorphous bioglass scaffold surface to form new apatite crystals resembling the bone-like plate structures. Thus, the self-assembled biomatrix system can be utilized in various dimensions, scales, and geometries for many different bioengineering applications.

Keywords: Extracellular matrix; Self-assembled matrix; Cell-bioengineering; Bioglass scaffold; Injectable hydrogel; 3D printing

Permalink: https://www.hzdr.de/publications/Publ-33907


Immunotargeting of CD98hc for Elimination of Radioresistant Head and Nek Squamous Cell Carcinoma

Köseer, A. S.; Arndt, C.; Feldmann, A.; Linge, A.; Bachmann, M.; Krause, M.; Dubrovska, A.

Abstract

Majority of patients with head and neck squamous cell carcinomas (HNSCC) are diagnosed during the locally advanced (LA) stage and are given standard treatments such as primary radiochemotherapy (RCTx) or postoperative radiochemotherapy (PORT-C). Due to heterogenous tumor response, patients show various treatment outcomes. Our previous retrospective biomarker analyses showed that SLC3A2 is a promising biomarker for locoregional control (LRC) in LA HNSCC patients with HPV-negative tumors treated with primary RCTx or PORT-C, with increased LRC rates in patients with low SLC3A2 mRNA and its protein product CD98hc levels (1,2). The siRNA- and CRISPR-Cas9 mediated inhibition of CD98hc expression increased radiosensitivity of HNSCC cells. Hence, CD98hc is a promising target for radiosensitization of the HNSCC. One of the strategies for radiosensitization is targeted immunotherapy. However, Chimeric Antigen Receptor (CAR)-equipped T-cell therapy cannot be fully controlled. Therefore, the switchable Universal CAR (UniCAR) system was developed (3, 4) that is currently in phase I clinical trial (NCT04230265) (5). UniCAR T cell activity and specificity is controlled by the presence of target modules (TM) with short half-lives (3). We aim to define the clinical value of new treatment approaches by combining radio(chemo)therapy with CD98hc-targeted immunotherapy. We have used previously described radioresistant Cal33 HNSCC cells (2, 6). These tumor cells were co-cultured with UniCAR T cells in the presence or absence of a novel CD98 TM. Our data shows that CD98-redirected UniCAR T cells have the capability to induce cell lysis of radioresistant HNSCC cells in in vitro 3D culture. The most promising combination of therapeutic approach will be further tested in xenograft tumor models to evaluate the best performing combination of immunotherapy and radio(chemo)therapy. This system can be potentially used to approach the combination of the UniCAR system with radio(chemo)therapy for synergistic improvement of treatment efficacy of patients with metastatic radioresistant tumors.

  • Open Access Logo Lecture (Conference) (Online presentation)
    2nd International Conference “Cancer Metastasis”, 13.-17.12.2021, VIRTUAL, VIRTUAL

Permalink: https://www.hzdr.de/publications/Publ-33906


Movement ecology of vulnerable lowland tapirs across a gradient of human disturbance

Medici, E.; Mezzini, S.; Fleming, C.; Calabrese, J.; Noonan, M.

Abstract

Animal movement is a key ecological process that is tightly coupled to local environmental conditions. While agriculture, urbanisation, and transportation infrastructure are critical to human socio-economic improvement, these have spurred substantial changes in animal movement across the globe with potential impacts on fitness and survival. Notably, however, human disturbance can have differential effects across species, and responses to human activities are thus largely taxa and context specific. As human disturbance is only expected to worsen over the next decade it is critical to better understand how species respond to human disturbance in order to develop effective, case-specific conservation strategies. Here, we use an extensive telemetry dataset collected over 22 years to fill a critical knowledge gap in the movement ecology of lowland tapirs (Tapirus terrestris) across a gradient of human disturbance within three biomes in southern Brazil: the Pantanal, Cerrado, and Atlantic Forest.

Permalink: https://www.hzdr.de/publications/Publ-33905


Population-level inference for home-range areas

Fleming, C.; Deznabi, I.; Alavi, S.; Crofoot, M.; Hirsch, B.; Medici, E.; Noonan, M.; Kays, R.; Fagan, W.; Sheldon, D.; Calabrese, J.

Abstract

Home-range estimates are a common product of animal tracking data, as each range informs on the area needed by a given individual. Population-level inference on home-range areas—where multiple individual home-ranges are considered to be sampled from a population—is also important to evaluate changes over time, space, or covariates, such as habitat quality or fragmentation, and for comparative analyses of species averages. Population-level home-range parameters have traditionally been estimated by first assuming that the input tracking data were sampled independently when calculating home ranges via conventional kernel density estimation (KDE) or minimal convex polygon (MCP) methods, and then assuming that those individual home ranges were measured exactly when calculating the population-level estimates. This conventional approach does not account for the temporal autocorrelation that is inherent in modern tracking data, nor for the uncertainties of each individual home-range estimate, which are often large and heterogeneous. Here, we introduce a statistically and computationally efficient framework for the population-level analysis of home-range areas, based on autocorrelated kernel density estimation (AKDE), that can account for variable temporal autocorrelation and estimation uncertainty. We apply our method to empirical examples on lowland tapir (Tapirus terrestris), kinkajou (Potos flavus), white-nosed coati (Nasua narica), white-faced capuchin monkey (Cebus capucinus), and spider monkey (Ateles geoffroyi), and quantify differences between species, environments, and sexes. Our approach allows researchers to more accurately compare different populations with different movement behaviors or sampling schedules, while retaining statistical precision and power when individual home-range uncertainties vary. Finally, we emphasize the estimation of effect sizes when comparing populations, rather than mere significance tests.

Permalink: https://www.hzdr.de/publications/Publ-33903


Integrating theory and experiments to link local mechanisms and ecosystem-level consequences of vegetation patterns in drylands

Martinez-Garcia, R.; Cabal, C.; Calabrese, J.; Hernandez-Garcia, E.; Tarnita, C.; Lopez, C.; Bonachela, J.

Abstract

Self-organized spatial patterns of vegetation are frequent in water-limited regions and have been suggested as important indicators of ecosystem health. However, the mechanisms underlying their emergence remain unclear. Some theories hypothesize that patterns could result from a scale-dependent feedback (SDF), whereby interactions favoring plant growth dominate at short distances and growth-inhibitory interactions dominate in the long range. However, we know little about how net plant-to-plant interactions may change sign with inter-individual distance, and in the absence of strong empirical support, the relevance of this SDF for vegetation pattern formation remains disputed. These theories predict a sequential change in pattern shape from gapped to labyrinthine to spotted spatial patterns as precipitation declines. Nonetheless, alternative theories show that the same sequence of patterns could emerge even if net interactions between plants were always inhibitory (purely competitive feedbacks, PCF). Although these alternative hypotheses lead to visually indistinguishable patterns they predict very different desertification dynamics following the spotted pattern. Moreover, vegetation interaction with other ecosystem components can introduce additional spatio-temporal scales that reshape both the patterns and the desertification dynamics. Therefore, to make reliable ecological predictions for a focal ecosystem, it is crucial that models accurately capture the mechanisms at play in the system of interest. Here, we review existing theories for vegetation self-organization and their conflicting predictions about desertification dynamics. We further discuss possible ways for reconciling these predictions and potential empirical tests via manipulative experiments to improve our understanding of how vegetation self-organizes and better predict the fate of the ecosystems where they form.

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Permalink: https://www.hzdr.de/publications/Publ-33902


TiAl-based semi-finished material produced by reaction annealing of Ti/Al layered composite sheets

Pukenas, A.; Chekhonin, P.; Scharnweber, J.; Chulist, R.; Oertel, C.-G.; Freudenberger, J.; Skrotzki, W.

Abstract

In this study multi-layered Ti/Al sheets prepared by accumulative roll bonding (ARB) underwent a two-step heat
treatment (HT) to form intermetallic compounds. The microstructure and crystal structure of the samples were
examined by scanning and transmission electron microscopy as well as energy-dispersive X-ray spectroscopy and synchrotron diffraction. In the first solid-state reaction annealing step, Ti-rich ARB samples containing 60 at% Ti and 40 at% Al were held at 600°C for 12 h under a uniaxial pressure between 0 MPa and 50 MPa applied along
the normal direction of the sheets. At this stage, Al is completely consumed by forming mainly Al-rich intermetallic
phases and to a lower extent other titanium aluminides such as Ti3Al and TiAl. In the second step, hightemperature annealing produces TiAl and Ti3Al as major phases during both pressureless annealing at 1100°C, 1200°C and 1300°C and annealing under an uniaxial pressure of about 100 MPa at 1200°C. Pore formation during the reaction annealing can be significantly reduced by the applied pressure. As a result, a TiAl-based semifinished material was fabricated.

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Permalink: https://www.hzdr.de/publications/Publ-33901


Resource selection of a nomadic ungulate in a dynamic landscape

Stratmann, T.; Dejid, N.; Calabrese, J.; Fagan, W.; Fleming, C.; Olson, K.; Mueller, T.

Abstract

Nomadic movements are often a consequence of unpredictable resource dynamics. However, how nomadic ungulates select dynamic resources is still understudied. Here we examined resource selection of nomadic Mongolian gazelles (Procapra gutturosa) in the Eastern Steppe of Mongolia. We used daily GPS locations of 33 gazelles tracked up to 3.5 years. We examined selection for forage during the growing season using the Normalized Difference Vegetation Index (NDVI). In winter we examined selection for snow cover which mediates access to forage and drinking water. We studied selection at the population level using resource selection functions (RSFs) as well as on the individual level using step-selection functions (SSFs) at varying spatio-temporal scales from 1 to 10 days. Results from the population and the individual level analyses differed. At the population level we found selection for higher than average NDVI during the growing season. This may indicate selection for areas with more forage cover within the arid steppe landscape. In winter, gazelles selected for intermediate snow cover, which may indicate preference for areas which offer some snow for hydration but not so much as to hinder movement. At the individual level, in both seasons and across scales, we were not able to detect selection in the majority of individuals, but selection was similar to that seen in the RSFs for those individuals showing selection. Difficulty in finding selection with SSFs may indicate that Mongolian gazelles are using a random search strategy to find forage in a landscape with large, homogeneous areas of vegetation. The combination of random searches and landscape characteristics could therefore obscure results at the fine scale of SSFs. The significant results on the broader scale used for the population level RSF highlight that, although individuals show uncoordinated movement trajectories, they ultimately select for similar vegetation and snow cover.

Permalink: https://www.hzdr.de/publications/Publ-33899


Laser-proton acceleration with cryogenic hydrogen jets

Zeil, K.; Rehwald, M.; Bernert, C.; Assenbaum, S.; Brack, F.; Bussmann, M.; Cowan, T.; Curry, C.; Fiuza, F.; Garten, M.; Gaus, L.; Gauthier, M.; Göde, S.; Goethel, I.; Glenzer, S.; Huebl, A.; Kim, J.; Kluge, T.; Kraft, S.; Kroll, F.; Metzkes-Ng, J.; Loeser, M.; Obst-Huebl, L.; Reimold, M.; Schlenvoigt, H.-P.; Schoenwaelder, C.; Schramm, U.; Siebold, M.; Treffert, F.; Ziegler, T.

Abstract

Demanding applications like radiation therapy of cancer have pushed the development of laser proton accelerators and defined necessary proton beam properties as well as levels of control and stability. The presentation will give an overview of the recent experiments for laser driven proton acceleration employing µm-sized cylindrical and sheet-like cryogenic jet targets to produce high energy proton beams without causing any debris. The low plasma density (30 nc) hydrogen jet was irradiated with the Petawatt laser source DRACO at the HZDR. Substantial improvements of the target system stability led to a proton acceleration performance comparable with that obtained with foil targets in optimized TNSA conditions. Furthermore, correlations between laser temporal profile and proton beam performance was investigated by using a synchronized off-harmonic optical probe beam for measuring the temporal evolution of the target expansion prior to the main pulse. Additional tailoring of the jet’s density profile by using artificial pre-pulses allowed for triggering the regime of relativistically induced transparency, yielding proton energies of up to about 80 MeV. Moreover, structured proton beam profiles were used to study the influence of the millimetres scale vacuum environment surrounding the target, where residual gas molecules are ionized by the remnant laser light that is not absorbed into the plasma but reflected or transmitted. This effect leads to the counter-intuitive observation of laser near-field feature imprints in the detected proton beam profiles.

  • Invited lecture (Conferences) (Online presentation)
    47th EPS Plasma Physics conference, 22.06.2021, Barcelona, Spain
  • Invited lecture (Conferences) (Online presentation)
    SPIE Optics + Optoelectronics, 19.04.2021, Prag, Tschechien

Permalink: https://www.hzdr.de/publications/Publ-33897


Laser ion acceleration for radio-biological application – Pushing proton energy frontiers with pre-expanded, actively controlled, near critical density targets

Zeil, K.; Rehwald, M.; Bernert, C.; Assenbaum, S.; Brack, F.; Bussmann, M.; Cowan, T.; Curry, C.; Fiuza, F.; Garten, M.; Gaus, L.; Gauthier, M.; Göde, S.; Goethel, I.; Glenzer, S.; Huang, L.; Huebl, A.; Kim, J.; Kluge, T.; Kraft, S.; Kroll, F.; Metzkes-Ng, J.; Loeser, M.; Obst-Huebl, L.; Reimold, M.; Schlenvoigt, H.-P.; Schoenwaelder, C.; Schramm, U.; Siebold, M.; Treffert, F.; Yang, L.; Ziegler, T.; Pawelke, J.; Beyreuther, E.

Abstract

Demanding applications like radiation therapy of cancer are pushing the frontier of laser
driven proton accelerators with controlled and well-defined proton beam properties.
This talk will give an overview of recent achievements at the high-contrast high power
laser source DRACO at HZDR providing high contrast pulses of >500 TW on target for
the reliable generation of proton beams with energies of around 60 MeV. For efficient
capturing and shaping of the divergent TNSA proton pulses, a setup of two pulsed highfield solenoid magnets has been developed and proven to reliably generate
homogeneous depth dose distributions precisely adapted to the three-dimensional
sample geometry for ultra-high pulse dose rate irradiation scenarios. Using this method,
worldwide first dose controlled volumetric irradiation of in vivo samples with laseraccelerated protons were conducted.
The performance of laser based ion acceleration and the scaling of the laser energy to
achieve increased ion energies strongly depend on the laser temporal contrast and its
effect on the target plasma scale length. Plasma mirror setups have proven to be a
valuable tool to significantly improve the temporal contrast by reducing pre-pulse
intensity and steepening the rising edge of the main laser pulse. With such contrast
enhancement techniques including novel diagnostic schemes, laser proton acceleration
using ultra-thin foil targets as well as renewable debris-free hydrogen jets were
investigated in a series of experiments within the near-critical density regime. An
important implication of this is the demonstration of a credible path toward high
repetition rate laser-based ion acceleration applications.

  • Lecture (others)
    Seminar at Bella Labs, Berkeley National Lab, 07.12.2021, Berkely, Vereinigte Staaten von Amerika
  • Lecture (others) (Online presentation)
    Imperial College Plasma Group Seminar, 17.03.2021, Oxford, United Kingdom
  • Lecture (others) (Online presentation)
    Seminar Physik und Technik von Beschleunigern, TU Darmstadt, 26.04.2021, Darmstadt, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-33896


Pushing proton energy frontiers with pre-expanded, actively controlled, near critical density targets

Zeil, K.; Rehwald, M.; Bernert, C.; Assenbaum, S.; Brack, F.; Bussmann, M.; Cowan, T.; Curry, C.; Fiuza, F.; Garten, M.; Gaus, L.; Gauthier, M.; Göde, S.; Goethel, I.; Glenzer, S.; Huang, L.; Huebl, A.; Kim, J.; Kluge, T.; Kraft, S.; Kroll, F.; Metzkes-Ng, J.; Loeser, M.; Obst-Huebl, L.; Reimold, M.; Schlenvoigt, H.-P.; Schoenwaelder, C.; Schramm, U.; Siebold, M.; Treffert, F.; Yang, L.; Ziegler, T.

Abstract

The performance of laser based ion acceleration and the scaling of the laser energy to
achieve increased ion energies strongly depend on the laser temporal contrast and its
effect on the target plasma scale length. Plasma mirror setups have proven to be a
valuable tool to significantly improve the temporal contrast by reducing pre-pulse
intensity and steepening the rising edge of the main laser pulse. With such contrast
enhancement techniques including novel diagnostic schemes, laser proton acceleration
using ultra-thin foil targets as well as renewable debris-free hydrogen jets were
investigated in a series of experiments within the near-critical density regime. An
important implication of this is the demonstration of a credible path toward high
repetition rate laser-based ion acceleration applications.

  • Invited lecture (Conferences)
    TARG5 Targetry for High Repetition Rate Laser-Driven Sources Workshop, 25.10.2021, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-33895


Data publication of (radio)fluorinated and (radio)iodinated cyclic tyrosine analogues.

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

Abstract

The document contains i) organic synthesis protocols, ii) NMR data, iii) radio-TLC data and iv) radio-HPLC chromatograms.

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Permalink: https://www.hzdr.de/publications/Publ-33894


Data publication: Estimating encounter location distributions from animal tracking data

Noonan, M.; Martinez-Garcia, R.; Davis, G.; Crofoot, M.; Kays, R.; Hirsch, B.; Caillaud, D.; Payne, E.; Sih, A.; Sinn, D.; Spiegel, O.; Fagan, W.; Fleming, C.; Calabrese, J.

Abstract

Data from: Estimating encounter location distributions from animal tracking data

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Permalink: https://www.hzdr.de/publications/Publ-33893


Estimating encounter location distributions from animal tracking data

Noonan, M.; Martinez-Garcia, R.; Davis, G.; Crofoot, M.; Kays, R.; Hirsch, B.; Caillaud, D.; Payne, E.; Sih, A.; Sinn, D.; Spiegel, O.; Fagan, W.; Fleming, C.; Calabrese, J.

Abstract

Ecologists have long been interested in linking individual behaviour with higher level processes. For motile species, this ‘upscaling’ is governed by how well any given movement strategy maximizes encounters with positive factors and minimizes encounters with negative factors. Despite the importance of encounter events for a broad range of ecological processes, encounter theory has not kept pace with developments in animal tracking or movement modelling. Furthermore, existing work has focused primarily on the relationship between animal movement and encounter rates while the relationship between individual movement and the spatial locations of encounter events in the environment has remained conspicuously understudied. Here, we bridge this gap by introducing a method for describing the long-term encounter location probabilities for movement within home ranges, termed the conditional distribution of encounters (CDE). We then derive this distribution, as well as confidence intervals, implement its statistical estimator into open-source software and demonstrate the broad ecological relevance of this distribution. We first use simulated data to show how our estimator provides asymptotically consistent estimates. We then demonstrate the general utility of this method for three simulation-based scenarios that occur routinely in biological systems: (a) a population of individuals with home ranges that overlap with neighbours; (b) a pair of individuals with a hard territorial border between their home ranges; and (c) a predator with a large home range that encompassed the home ranges of multiple prey individuals. Using GPS data from white-faced capuchins Cebus capucinus, tracked on Barro Colorado Island, Panama, and sleepy lizards Tiliqua rugosa, tracked in Bundey, South Australia, we then show how the CDE can be used to estimate the locations of territorial borders, identify key resources, quantify the potential for competitive or predatory interactions and/or identify any changes in behaviour that directly result from location-specific encounter probability. The CDE enables researchers to better understand the dynamics of populations of interacting individuals. Notably, the general estimation framework developed in this work builds straightforwardly off of home range estimation and requires no specialized data collection protocols. This method is now openly available via the ctmm R package.

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Permalink: https://www.hzdr.de/publications/Publ-33892


Magnetic separation of rare-earth ions: property database and Kelvin force distribution

Lei, Z.; Fritzsche, B.; Salikhov, R.; Schwarzenberger, K.; Hellwig, O.; Eckert, K.

Abstract

This work bridges two gaps in the magnetic separation of rare-earth ions. 1) A material property database is provided for the solutal expansion coefficient and the magnetic susceptibility of eleven out of seventeen trivalent rare-earths. 2) A novel protocol is developed to enhance and resolve the magnetic term of the Kelvin force. For that purpose, an assembly of partition magnets is created where the individual magnets function in the first quadrant of their magnetic hysteresis loop. The mutual reinforcement is quantified in a particle magnetic levitation system. Thus, compared to exisiting magnetic assemblies, an enhancement in $\frac{\partial B^2}{2 \mu_0 \partial z}$ as high as 2 orders of magnitudes is realized that covers 90\% of the normalized spatial scale and requires 1 order of magnitude less magnet mass. Modeling the energy density field makes it possible to quantify the equilibrium position of the particle cloud at rest, which is attained via magnetophoresis of the particles regardless of their initial position. This enables the magnetic trapping and manipulation of particles with small hydrodynamic diameters. Optically tracking the transient magnetophoresis enables a high-fidelity, sub-mm resolution of $\frac{\partial \bm{B}^2}{2 \mu_0 \partial z}$ which is further used to quantify the magnetic susceptibility of Ho(III), Tb(III), Er(III) and Gd(III).

Keywords: rare-earth; molar magnetic susceptibility; diamagnetic; Kelvin force; magnetic levitation

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  • Secondary publication expected

Permalink: https://www.hzdr.de/publications/Publ-33891


Cell voltage model for Li-Bi liquid metal batteries

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

Abstract

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

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


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

Hanfeld, P.

Abstract

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

Keywords: Reinforcement Learning; Adversarial Attacks; Deep Learning

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

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


Emergence of pion parton distributions

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

Abstract

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

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


Concerning pion parton distributions

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

Abstract

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

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


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

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

Abstract

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

Keywords: Graphene; Auger processes; optical absorption

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


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

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

Abstract

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

Keywords: Graphene; Auger processes; optical absorption

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


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

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

Abstract

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

Keywords: warm dense matter

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


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

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

Abstract

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

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

Involved research facilities

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

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


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

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

Abstract

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

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

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


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

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

Abstract

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

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

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


Magnetic field assisted electrodeposition of metal on conically structured electrodes

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

Abstract

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

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

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


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

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

Abstract

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

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

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


Selective binding of UO22+ by different peptide families

Tsushima, S.; Takao, K.

Abstract

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

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

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


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

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

Abstract

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

Keywords: Nucleate boiling; microlayer; disjoining pressure

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

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


Laser induced crystallization of Co–Fe–B films

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

Abstract

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

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


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

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

Abstract

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

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


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

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

Abstract

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

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

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


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

Degli Esposti, G.; Torgrimsson, G.

Abstract

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

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


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

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

Abstract

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

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

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


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

Knüpfer, L.; Heitkam, S.

Abstract

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

Keywords: bubble; foam; image segmentation

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


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

Degli Esposti, G.; Corradini, O.

Abstract

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

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


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

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

Abstract

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

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

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


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

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

Abstract

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

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

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


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

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

Abstract

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

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

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


Quantum magnetism of ferromagnetic spin dimers in α-KVOPO4

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

Abstract

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

Involved research facilities

  • High Magnetic Field Laboratory (HLD)

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


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

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

Abstract

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

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

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


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

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

Abstract

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

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

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


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

Rudolph, M.

Abstract

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

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

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

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

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

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


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

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

Abstract

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

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

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


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

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

Abstract

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

Keywords: Froth Flotation; Hamaker Constant; Particle Interactions

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  • Secondary publication expected

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


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

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

Abstract

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

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

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


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

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

Abstract

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

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

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


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

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

Abstract

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

Involved research facilities

  • PET-Center

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


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

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

Abstract

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

Keywords: turbulence; bubbly flows

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


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

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

Abstract

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

Keywords: Hopf bifurcation

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


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

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

Abstract

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

Involved research facilities

  • PET-Center

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


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

Huang, L. G.

Abstract

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

Involved research facilities

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

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


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

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

Abstract

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

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

Involved research facilities

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

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


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

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

Abstract

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

Involved research facilities

  • PET-Center

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


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

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

Abstract

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

Involved research facilities

  • PET-Center

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


High electron mobility in strained GaAs nanowires

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

Abstract

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

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Related publications

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

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


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

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

Abstract

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

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Related publications

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

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


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

Dimakis, E.

Abstract

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

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Related publications

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

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


Anomalous quantum oscillations of CeCoIn5 in high magnetic fields

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

Abstract

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

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  • High Magnetic Field Laboratory (HLD)

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


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