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41346 Publications

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.

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.

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

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.

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


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

Unger, S.

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.

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

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

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.

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


CFD applications in nuclear engineeering

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

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
Publ.-Id: 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.

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

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


Simulation-based Inference of Beamline Characteristics at BESSY

Steinbach, P.; Hartmann, G.

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
Publ.-Id: 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.

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
Publ.-Id: 33921


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

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

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
Publ.-Id: 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.

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
Publ.-Id: 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.

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
Publ.-Id: 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.

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
Publ.-Id: 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.

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
Publ.-Id: 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.

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
Publ.-Id: 33914


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

Günther, U.

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.

Related publications

  • 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
Publ.-Id: 33912


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

Günther, U.; Harrington, K.

This is the video recording of the talk.

Keywords: visualisation; rendering; kotlin; java; jvm

Related publications

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


Realtime 3D graphics and VR with Kotlin and Vulkan

Günther, U.; Harrington, K.

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

Related publications

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

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


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

Büttner, P.; Engelhardt, J.

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
Publ.-Id: 33909


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

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

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
Publ.-Id: 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.

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
Publ.-Id: 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.

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
Publ.-Id: 33906


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

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

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
Publ.-Id: 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.

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
Publ.-Id: 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.

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
Publ.-Id: 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.

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
Publ.-Id: 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.

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
Publ.-Id: 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.

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
Publ.-Id: 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.

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
Publ.-Id: 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.

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
Publ.-Id: 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.

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
Publ.-Id: 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.

Data from: Estimating encounter location distributions from animal tracking data

Related publications

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

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.

Related publications

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

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
Publ.-Id: 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.

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

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


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

Hanfeld, P.

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

Keywords: Reinforcement Learning; Adversarial Attacks; Deep Learning

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

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


Emergence of pion parton distributions

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

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

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


Concerning pion parton distributions

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

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

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


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

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

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

Keywords: Graphene; Auger processes; optical absorption

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


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

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

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

Keywords: Graphene; Auger processes; optical absorption

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


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

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

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

Keywords: warm dense matter

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


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

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

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

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

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

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


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

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

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

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

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


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

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

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

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

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


Magnetic field assisted electrodeposition of metal on conically structured electrodes

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

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

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

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


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

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

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

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

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


Selective binding of UO22+ by different peptide families

Tsushima, S.; Takao, K.

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

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

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


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

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

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

Keywords: Nucleate boiling; microlayer; disjoining pressure

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

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


Laser induced crystallization of Co–Fe–B films

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

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

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


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

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

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

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


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

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

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

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

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


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

Degli Esposti, G.; Torgrimsson, G.

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

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


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

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

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

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

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


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

Knüpfer, L.; Heitkam, S.

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

Keywords: bubble; foam; image segmentation

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


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

Degli Esposti, G.; Corradini, O.

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

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


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

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

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

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

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


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

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

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

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

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


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

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

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

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

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


Quantum magnetism of ferromagnetic spin dimers in α-KVOPO4

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

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

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


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

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

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

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

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


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

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

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

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

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


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

Rudolph, M.

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

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

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

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

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

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


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

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

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

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

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


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

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

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

Keywords: Froth Flotation; Hamaker Constant; Particle Interactions

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  • Secondary publication expected

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


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

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

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

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

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


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

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

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

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

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


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

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

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

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


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

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

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

Keywords: turbulence; bubbly flows

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


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

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

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

Keywords: Hopf bifurcation

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


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

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

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

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


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

Huang, L. G.

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

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

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


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

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

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

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

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

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


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

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

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

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


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

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

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

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


High electron mobility in strained GaAs nanowires

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

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

Related publications

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

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


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

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

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

Related publications

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

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


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

Dimakis, E.

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

Related publications

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

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


Anomalous quantum oscillations of CeCoIn5 in high magnetic fields

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

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

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


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

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

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

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

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


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

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

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

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


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

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

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

Related publications

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


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

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

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

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

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

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


Superparamagnetism and ferrimagnetism in the Sr2FeMoO6–δ nanoscale powder

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

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

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

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


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

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

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

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

Related publications

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

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


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

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

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

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

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

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


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

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

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

Keywords: thermal conductivity; atomistic simulations

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


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

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

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

Keywords: 2D materials; AlCl3; CuCl2

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


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

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

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

Keywords: Cr2Ge2Te6; Magnetic properties; Strain engineering

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


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

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

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

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

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


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

Debus, A.; La Berge, M.

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

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

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


PIConGPU at NERSC

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

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

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

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

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


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

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

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

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

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


Relativistic laser plasma physics in a nutshell

Debus, A.; Kluge, T.

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

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

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


Digital twins of Laser-plasma interactions

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

Digital twin challenges:

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

Joining forces in meeting these challenges:

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

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

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


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

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

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

Lessons learnt:

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

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

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

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


Exascale Plasma-Accelerator Simulations with PIConGPU

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

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

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

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

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

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


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

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

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

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

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

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


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

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

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

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

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

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

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

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

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


MALA (Materials Learning Algorithms)

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

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

Keywords: Density Functional Theory; Machine Learning

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


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

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

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

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

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


Simulation of highly divergent Optical Beams

Kotik, D.; Götte, J. B.

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

References

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

Keywords: FDTD; Meep; Cython; Gaussian beam

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

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


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