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38150 Publications

Actinide Chemistry - From Small Molecules To Real Rock

Schmidt, M.

Actinide chemistry is of utmost importance for chemical engineering and environmental science related to the nuclear industry or nuclear waste repositories. Yet, their chemistry remains underexplored relative to other elements in the periodic table. This is equally true for fundamental studies regarding complexation chemistry or redox properties and applied investigations of geochemical behavior and environmental transport.
In this presentation, I will give an overview of recent (and not so recent) studies attempting to link the actinides’ fundamental properties with their environmental transport. Systematic studies of their coordination chemistry offer a promising route to obtain fundamental knowledge about chemical bonding in actinide compounds. Here, a suitable approach is to study series of isostructural actinide compounds, in which the metal is present in the same oxidation state. Changes in structures, bond distances, or spectroscopic properties can then be related to changes in f-orbital occupation. One important issue in this context is the degree of covalency in these compounds and how it depends on the donor atoms of a ligand, or the electronic structure and oxidation state of the actinide.
It is this chemical behavior, which then affects how mobile actinides can be if they are released into the environment as a consequence of nuclear accidents, other accidental releases or in the context of nuclear waste disposal. In these scenarios, special attention must be paid to processes occurring at the water/mineral interface. Here, we will discuss how a combination of spectroscopy, microscopy, and surface X-ray diffraction can be used to both, obtain molecular level information from the interfacial region and also relate this molecular processes to retention behavior in macroscopic, close-to-realistic systems, such as natural crystalline rock.

Keywords: Actinides; Coordination Chemistry; Sorption; Geochemistry; TRLFS; Spectroscopy; XRD

  • Invited lecture (Conferences)
    GDCh Fachtagung Nuklearchemie 2022, 04.-06.10.2022, Bergisch Gladbach, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-35648
Publ.-Id: 35648


Local Neumann semitransparent layers: Resummation, pair production, and duality

Ahmadiniaz, N.; Franchino-Vinas, S.; Manzo, L.; Mazzitelli, F. D.

We consider local semitransparent Neumann boundary conditions for a quantum scalar field as imposed by a quadratic coupling to a source localized on a flat codimension-one surface. Upon a proper regularization to give meaning to the interaction, we interpret the effective action as a theory in a first-quantized phase space. We compute the relevant heat-kernel to all order in a homogeneous background and quadratic order in perturbations, giving a closed expression for the corresponding effective action in $D=4$. In the dynamical case, we analyze the pair production caused by a harmonic perturbation and a Sauter pulse. Notably, we prove the existence of a strong/weak duality that links this Neumann field theory to the analogue Dirichlet one.

Keywords: Neumann boundary conditions; Dynamical Casimir effect; Quantum field theory in background fields; Effective action; Pair creation; Duality; Dirichlet semitransparent boundary conditions

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Permalink: https://www.hzdr.de/publications/Publ-35643
Publ.-Id: 35643


In Search of Covalency in Tetravalent Actinide (Th - Pu) Monosalen Complex Series

Blei, M. K.; Patzschke, M.; Kvashnina, K.; Waurick, L.; Schmidt, M.; Stumpf, T.; März, J.

Actinides play an important role in chemical engineering and environmental science related to the nuclear industry or nuclear waste repositories.[1] One of the major tools to obtain a profound basic knowledge about actinide (An) binding is the coordination chemistry of An using model ligands. However, fundamental An chemistry is still relatively little explored. Characteristic of the actinides is their huge variety of possible oxidation states, typically ranging from +II to +VII for early An, making their chemistry complex but interesting. A suitable approach to explore fundamental physico-chemical properties of the actinides is to study series of isostructural An compounds in which the An is in the same oxidation state.[2] Observed changes in e.g. the binding situation or magnetic effects among the An series may deliver insight into their unique electronic properties mainly originating from the f-electrons. A question still remaining in the field of An chemistry is the degree of “covalency” in compounds across the An series,[3] which may be addressed by systematic studies on series of An compounds, including transuranium (TRU) elements.
In this study we investigate the coordination chemistry of tetravalent actinides (An(IV)), which are dominant particularly under anoxic environmental conditions, using the organic salen ligand (salen = N,N’-bis(salicylidene)ethylenediamine) as a small N,O donor.[4] In addition, we change halogen (F, Cl, Br, I) and solvent (MeOH, THF, MeCN, pyridine) donors (see Figure 1) in order to analyse the ligand’s effect on covalency trends as well as their mutual influence, mainly using single crystal X-ray diffraction (SC-XRD), high-energy-resolution fluorescence detection X-ray absorption near edge spectroscopy (HERFD-XANES), and quantum chemical calculations (QCC).

Keywords: actinides; complexes; SC-XRD; quantum chemical calculations; thorium; uranium; neptunium; plutonium; N-donor ligands

Related publications

  • Invited lecture (Conferences)
    Plutonium Futures, 27.09.2022, Avignon, Frankreich

Permalink: https://www.hzdr.de/publications/Publ-35642
Publ.-Id: 35642


Early An(IV) complexes with N-donor ligands

März, J.; Fichter, S.; Patzschke, M.; Kaden, P.; Köhler, L.; Schmidt, M.; Stumpf, T.

The 5f electrons of particularly the early actinides are found to participate in bonding, e.g. to organic ligands, in contrast to the strongly shielded 4f electrons of the lanthanides. Reactivity and complexation strength of such bonds are affected by donor properties of the ligand and the electronic situation of the actinide metal center. Furthermore, coinciding properties of ligand and actinide ion regarding Pearson’s principle of hard and soft acids and bases (HSAB) can even drive the development of selective ligands, e.g. for extraction processes. Here, soft N-donor ligands were found to interact stronger with trivalent actinides in comparison to their harder lanthanide analogues.1
To evaluate how these electronic properties can be extended to a series of tetravalent actinides and their interactions with N-donor ligands, we have studied the complexation of tetravalent Th, Pa, U, Np, and Pu with the amidinate (S,S)-N,N’-bis-(1-phenylethyl)-benzamidine (PEBA), and the Schiff base N,N’-ethylene-bis((pyrrole-2-yl)methan¬imine (pyren).2-4
Complex syntheses using one equivalent of AnCl4(dme)x (An = Th, U, Np, Pu; x = 0 for U, x = 2 for Th, Np, Pu) and three equivalents of PEBA, or two equivalents of pyren led to isostructural heteroleptic 3:1 complexes [AnCl(PEBA)3] or homoleptic 2:1 complexes [An(pyren)2]. Both series were analyzed in the solid state by SC-XRD and IR, as well as in solution by NMR spectroscopy. SC-XRD results and quantum chemical calculations (QCC) revealed differences in AnIV–ligand bond length and strength between the different nitrogen donors (Namidinate, Nimine, Npyrrolide). In addition, with the help of QCC, trends regarding the covalency of the metal-ligand bonds could be derived and assigned to the involved orbitals. Delocalization indices for N–PaIV showed a strong preference of the highly polarizable 5f 1 configuration of PaIV to pyren in its homoleptic complex. This effect disappears in the heteroleptic amidinate complex. Calculated quadrupole moments give a first explanation, showing an isotropically distributed charge arround PaIV in [Pa(pyren)2] but a polarization in [PaCl(PEBA)3].
Halogen exchange reactions of Cl in [AnCl(PEBA)3] was successful for F, Br, and N3 (see Fig. 1). NMR spectra revealed a strong effect of the halogen on the paramagnetic shift, potentially again indicating the impact of the halogen on the polarizabiliy of charge arround the tetravalent actinide.

Keywords: actinides; complex; SC-XRD; quantum chemical calculations; thorium; uranium; neptunium; plutonium; N-donor ligands

  • Lecture (Conference)
    Actinides Revisited, 21.09.2022, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-35641
Publ.-Id: 35641


Bonding trends in full early actinide (Th-Pu) pyren complex series

Köhler, L.; Patzschke, M.; Kaden, P.; Kvashnina, K.; Schmidt, M.; Stumpf, T.; März, J.

In contrast to the strongly shielded 4f electrons of the lanthanides, 5f electrons of particularly the early actinides are found to participate in bonding, e.g. to organic ligands. Reactivity and complexation strength of such bonds are the most influenced by donor properties of the ligand and the electronic situation of the actinide metal center. Furthermore, coinciding properties of ligand and actinide ion regarding Pearson’s principle of hard and soft acids and bases (HSAB) can even drive the development of selective ligands, e.g. for extraction processes. Here, soft N-donor ligands were found to interact stronger with trivalent actinides in comparison to their harder lanthanide analogues.1
To evaluate how these HSAB properties can be extended to a series of tetravalent actinides and their interactions with N-donor ligands, we have studied the complexation of tetravalent Th, Pa, U, Np, and Pu with N,N’-ethylene-bis((pyrrole-2-yl)methanimine (pyren) in comparison to its structural N,O-analogue, the salen ligand.2
Complex syntheses using one equivalent of AnCl4(dme)x (An = Th, U, Np, Pu; x = 0 for U, x = 2 for Th, Np, Pu) and two equivalents of pyren led to isostructural 2:1 complexes, which were analyzed in the solid state by SC-XRD and IR, as well as in solution via NMR spectroscopy. SC-XRD results and quantum chemical calculations revealed differences in AnIV–ligand bond length and strength within pyren (Nimine vs. Npyrrolide donors) or salen (Nimine vs. Ophenolate). Interestingly, the overall bond strength of the N-donor vs. N,O-donor to An(IV), however, is almost equal for both, [An(pyren)2] and [An(salen)2] (An = Th-Pu). Delocalization indices even confirmed slightly more covalent interactions between the N,O-donor salen and Th, U, Np, and Pu in comparison with pyren. For Pa, on the other hand, this trend is reversed. QTAIM analysis could prove particularly strong interactions with the pure N-donor ligand pyren. This extraordinarily good electron sharing between pyren and Pa can be explained by the 5f1 configuration of Pa(IV), being particularly well polarizable and thus well suited for an effective backbonding to the soft N-donors of the pyren ligand.

Keywords: actinides; complex; SC-XRD; quantum chemical calculations; thorium; uranium; neptunium; plutonium; N-donor ligands

Related publications

  • Invited lecture (Conferences)
    19th Radiochemical Conference, 16.-20.05.2022, Mariánské Lázně, Tschechien

Permalink: https://www.hzdr.de/publications/Publ-35640
Publ.-Id: 35640


Insights into Uranium binding properties by magnetotactic bacteria

Krawczyk-Bärsch, E.; Ramtke, J.; Drobot, B.; Müller, K.; Steudtner, R.; Hübner, R.; Raff, J.

Magnetotactic bacteria are characterized by intracellular magnetic mineral crystals of magnetite (Fe3O4) or greigite (Fe3S4), which helps them to orientate themselves along the Earth's magnetic field for reaching regions of optimal oxygen concentrations. They are facultative anaerobe and usually found in a large abundance in oxic-anoxic transition zones of aquatic environments, in sediments of freshwater, brackish, marine, and hypersaline habitats [1]. Assuming that magnetotactic bacteria can also be found in the far-field of a nuclear waste repository, studies on the interaction of a natural bacterial strain of Magnetospirillum magneticum AMB-1 cells with U were carried out for the first time using a multidisciplinary approach combining microscopy and different spectroscopic techniques to achieve a better molecular understanding. Results of batch sorption experiments show that Magnetospirillum magneticum AMB-1 can survive both in a wide pH range and with relatively high U concentrations of up to 0.1 mM, while effectively and almost completely immobilizing U in the first hours of incubation. (S)TEM/EDXS studies on ultrathin sections of cells loaded with 0.1 mM U clearly indicate that U is predominantly located in the cell wall. Since it is known from previous studies [2] that U often binds to the cell wall of bacteria by interacting with cell wall compounds, important ligands were used, such as peptidoglycan, lipopolysaccharide, L-rhamnose, D-(+) galactose and D-(+) mannose as possible complexants for U and measured by cryo-TRLFS combined with PARAFAC. The results show five U species and highlight the dominant role of peptidoglycan as main sorbent of U on the cell wall of Magnetospirillum magneticum AMB-1 cells, showing three characteristic peptidoglycan species. In-situ ATR FT-IR studies confirm the predominant binding to carboxylic functionalities and reveal that polynuclear species seem to play an important role at higher pH.

Keywords: magnetotactic bacteria; uranium; sorption; peptidoglycan

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

Permalink: https://www.hzdr.de/publications/Publ-35636
Publ.-Id: 35636


A local model to study precessing turbulence

Pizzi, F.; Mamatsashvili, G.; Giesecke, A.; Stefani, F.

Precession driven flows are ubiquitous natural phenomena. Similarly to other
forcing mechanism, precession motion causes complex behavior in the fluid flow
consisting of interplay between rotating and inertial wave turbulence. Turbulent
precessing flows can drive dynamo action

Keywords: Rotating turbulence; Precession

  • Poster
    17TH SEDI (Study Earth's Deep Interior) symposium, 11.07.2022, Zurich, Switzerland

Permalink: https://www.hzdr.de/publications/Publ-35635
Publ.-Id: 35635


Data publication: Numerical and theoretical framework for the DRESDYN precession dynamo experiment

Pizzi, F.; Giesecke, A.; Simkanin, J.; Kumar, V.; Gundrum, T.; Stefani, F.

This dataset is the base of the publication. It has been computed through a fully nonlinear DNS code (SEMTEX) and a code for the computation of magnetic field written by Dr. Andre' Giesecke.

Keywords: Direct Numerical Simulations (DNS); Dynamo; MHD

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Permalink: https://www.hzdr.de/publications/Publ-35633
Publ.-Id: 35633


Suppression of Interband Heating for Random Driving

Zhao, H.; Knolle, J.; Moessner, R.; Mintert, F.

Heating to high-lying states strongly limits the experimental observation of driving induced nonequilibrium phenomena, particularly when the drive has a broad spectrum. Here we show that, for entire
families of structured random drives known as random multipolar drives, particle excitation to higher bands
can be well controlled even away from a high-frequency driving regime. This opens a window for
observing drive-induced phenomena in a long-lived prethermal regime in the lowest band.

Permalink: https://www.hzdr.de/publications/Publ-35631
Publ.-Id: 35631


Biostimulation of uranium reducing bacteria in contaminated mine water for bioremediation purposes: multidisciplinary approach study

Newman Portela, A.; Krawczyk-Bärsch, E.; Lopez-Fernandez, M.; Bok, F.; Kassahun, A.; Merroun, M. L.; Raff, J.

Uranium (U) and its mining have historically been strongly related to East Germany. From the second half of the 20th century onwards, the Federal States of Saxony and Thuringia have been the scene of intense mining activity. The cessation of mining activities in 1990, has led to the generation of U contaminated areas. Nowadays, conventional remediation methodologies are not able to remove soluble U entirely. Microorganisms offer an environmental friendly water remediation strategy for U through bioreduction or biomineralization. The present study describes a strategy for in situ bioremediation of U(VI) from a U mine water by biostimulation of the native U reducing microbial community.
The geochemical profile of the mine water was characterized by Inductively Coupled Plasma-Mass spectrometry (ICP-MS) and Ionic Chromatography (IC), showing a substantial concentration of U (1.01mg/L), SO4 2- (335mg/L), Fe (0.99mg/L) and Mn (1.44mg/L). Cryo-Time-Resolved Laser Fluorescence spectroscopy (cryo-TRLFS) and Parallel Factor Analysis (PARAFAC) determined the aqueous species Ca2UO2(CO3)3 4- as the main U species in mine water. In addition, 16S and ITS1 rRNA gene analyses were used to characterize the microbial community, indicating a relative abundance of natural microbial groups with U(VI)-reduction ability (e.g., Desulfovibrio, GallionellaSideroxydans). For the design of an in situ bioremediation technology for U contaminated waters, a set of anoxic microcosms supplemented with glycerol (10mM) as electron donor was previously designed. A thermodynamic Eh-pH dominance diagram calculated using Geochemist's Workbench predicted the reduction of U(VI) and the formation of the solid U-mineral (uraninite). After 3 months, ICP-MS and Ion-Chromatography analysis from the microcosms revealed a decrease of U (≈98%), SO42- (≈88%) and Fe (≈91%). Furthermore, the black precipitate formed at the bottom of the microcosm was analyzed by UV-Vis spectroscopy, identifying mainly U(IV).
The results obtained revealed the U enzymatic reduction of U(VI) to U(IV) by the addition of an electron donor in low concentrated U contaminated mine waters. Thus, this strategy might be an efficient bioremediation approach for U contaminated mine waters, by biostimulating their indigenous microbial community.

Keywords: microorganismens; uranium; mine water; reduction

  • Lecture (Conference)
    Goldschnmidt Conference 2022, 10.-15.07.2022, Honolulu, Hawaii, US

Permalink: https://www.hzdr.de/publications/Publ-35630
Publ.-Id: 35630


A glimpse into pion gravitational form factor

Xing, Z.; Ding, M.; Chang, L.

We provide a novel approach to calculate the gravitational form factor of pion under the ladder approximation of the Bethe-Salpeter equation, with contact interactions. Central to this approach is a symmetry-preserving treatment of the dressed ππ amplitude, which shows explicitly the contributions from intrinsic quarks and bound states, the latter being necessary to produce the D-term of pion in the soft-pion limit. The approach we provide in this work can be applied to many processes of physical significance.

Permalink: https://www.hzdr.de/publications/Publ-35627
Publ.-Id: 35627


High dimensional tori and chaotic and intermittent transients in magnetohydrodynamic Couette flows

Garcia Gonzalez, F.; Ogbonna, J. E.; Giesecke, A.; Stefani, F.

The magnetised spherical Couette (MSC) problem, a three dimensional magnetohydrodynamic paradigmatic model in geo- and astrophysics, is considered to investigate bifurcations to high-dimensional invariant tori and chaotic flows in large scale dissipative dynamical systems with symmetry. The main goal of the present study is to elucidate the origin of chaotic transients and intermittent behaviour from two different sequences of Hopf bifurcations involving invariant tori with four fundamental frequencies, which may be resonant. Numerical evidence of the existence of a crisis event destroying chaotic attractors and giving rise to the chaotic transients is provided. It is also shown that unstable invariant tori take part in the time evolution of these chaotic transients. For one sequence of bifurcations, the study demonstrates that chaotic transients display on-off intermittent behaviour. A possible explanatory mechanism is discussed.

Permalink: https://www.hzdr.de/publications/Publ-35626
Publ.-Id: 35626


Experimental investigation of the nutation angle's effect on the flow inside a precessing cylinder

Kumar, V.; Giesecke, A.; Gundrum, T.; Pizzi, F.; Ratajczak, M.; Anders, S.; Stefani, F.

Precession-driven flows are considered as potential sources of dynamo action on Earth, ancient moon, and some asteroids. At the Helmholtz-Zentrum Dresden-Rossendorf (HZDR), a precession-driven dynamo experiment is now being constructed as part of the DRESDYN project. It is a cylinder filled with liquid sodium with a radius of 1 m and a height of 2 m. The cylinder rotates at a frequency of up to 10 Hz and precesses around the second axis at a rate of up to 1 Hz.
To gain a better understanding of the hydrodynamics of a precessing cylinder, a downscaled 1:6 water mockup with the same aspect ratio, rotation, and precession frequency was built. The typical non-axisymmetric Kelvin mode, which initially increases as the precession ratio increases, is alone not suitable for dynamo action in the experiment. However, a secondary axisymmetric mode that appears in a narrow region of the precession ratio was demonstrated to be particularly promising for dynamo action in the sodium experiment.
To predict dynamo behavior for different precession ratios and precession angles, a thorough understanding of the flow structure in the precessing cylindrical vessel is required. For that purpose, we performed a series of precession measurements on the downscaled water experiment with Ultrasonic Doppler velocimetry (UDV) at various precession angles of 60o, 75o, and 90o. We present the effect of precession angle and rotation direction (i.e. prograde or retrograde) on the dominant flow modes, and quantify this behaviour in dependence on the rotation rate, which is parameterized by the Reynolds number Re = ΩcR2/ν, and the precession ratio Po = Ωp/Ωc, where ν is the viscosity and Ωp = 2πfp is the angular frequency of the precession. The experimental results are compared with numerical simulations.

  • Poster
    9th International Symposium on Bifurcations and Instabilities in Fluid Dynamics, 16.-19.08.2022, Groningen, the Netherlands

Permalink: https://www.hzdr.de/publications/Publ-35619
Publ.-Id: 35619


The Effect of the Nutation Angle on the Flow in a Precessing Cylinder: Experimental Results

Kumar, V.; Giesecke, A.; Gundrum, T.; Pizzi, F.; Ratajczak, M.; Stefani, F.

Precession-driven flows are discussed as possible sources for dynamo action in the Earth [1], the ancient moon, and in some asteroids. A precession-driven dynamo experiment is currently under construction at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) as part of the DRESDYN project. It consists of a liquid sodium filled cylinder with a radius of 1 m and a height of 2 m. The cylinder rotates at a frequency of up to 10 Hz and precesses at a frequency of up to 1 Hz around the second axis [2].
A downscaled 1:6 water mockup with the same aspect ratio and rotation and precession frequencies was developed to better understand the hydrodynamics in a precessing cylinder. The typical non-axisymmetric Kelvin mode, which initially increases as the precession ratio increases, is alone not suitable for dynamo action in the experiment. However, a secondary axisymmetric mode that appears in a narrow region of the precession ratio was demonstrated to be particularly promising for dynamo action in the sodium experiment [3].
To be able to anticipate dynamo behaviour for various precession ratios and precession angles, a complete understanding of the flow structure in the precessing cylindrical vessel is required. For that purpose, we conducted a series of precession measurements using Ultrasonic Doppler velocimetry (UDV) on the downscaled water experiment at various precession angles of 60o, 75o, and 90o. We present the effect of precession angle and rotation direction (i.e. prograde or retrograde) on the dominant flow modes, and quantify this behaviour in dependence on the rotation rate, which is parameterized by the Reynolds number Re = ΩcR2/ν, and the precession ratio Po = Ωp/Ωc, where ν is the viscosity and Ωp = 2πfp is the angular frequency of the precession. The experimental results are compared with numerical simulations [4].

  • Contribution to proceedings
    12th International PAMIR Conference - Fundamental and Applied MHD, 04.-08.07.2022, Krakow, Poland

Permalink: https://www.hzdr.de/publications/Publ-35618
Publ.-Id: 35618


NMR spectroscopy of selected aqueous systems investigated at HZDR–IRE

Kretzschmar, J.; Stumpf, T.

Nuclear magnetic resonance (NMR) spectroscopy is a powerful method for both structure elucidation of molecules and their metal complexes, and also for studying their behavior in terms of thermodynamics and kinetics, as well as reactions occurring in situ in dependence on a variety of physico-chemical parameters. In this context, NMR spectroscopy of aqueous (D₂O) solutions features some peculiarities. That is, first and foremost, the pH (pD) of the solution affects the speciation of both the molecule (ligand) and the metal ion (actinide or lanthanide) under study. Furthermore, the ligand can be subject to deuteration, and either component can undergo redox reactions.

The intracellularly occurring tripeptide glutathione (GSH) constitutes a redox equilibrium with its oxidized (dimeric) form glutathione disulfide (GSSG). Hexavalent uranium, U(VI), forms complexes with the latter over a wide pH range, while GSH reduces U(VI) to U(IV). However, the redox reaction occurs only between pH 6 and 10, i.e. close to the thiol group’s pKa, presumably due to homolytic cleavage of the S–H group in GSH’s cysteine residue. The redox reaction appears to take place intermolecularly without the need for U(VI) complexation by the reductant [1, 2].
Uranyl(VI) citrate dimeric and trimeric complexes exhibit interesting structural and (¹⁷O) NMR spectroscopic features such as superstructure formation upon varying pH or concentration, and polarization of uranyl units acting as Lewis base in metal ion coordination (O=U=O⟶Mn+) [3, 4]. Irradation of uranyl(VI) citrate by visible light yields complexes of lower valent uranium. The reaction again occurs intermolecularly, whereby in situ oxidation of excessive ligand through several intermediates can be comprehended by NMR spectroscopy.
In studies investigating the interaction of radionuclides (RNs) with a solid phase in equilibrium with an aqueous phase, the influence of organics on RN retention can be complemented by qualitative and quantitative solution NMR methods by determining their speciation (free, metal ion-bound, oxidized) and concentration in the supernatant.
NMR spectroscopy can also be utilized as a robust and elegant method for determining ligand’s pKa along with the originating site of the abstracted proton as shown for GSH/GSSG, 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC), as well as nitrilotriacetate (NTA) and ethylene glycol-bis(aminoethyl ether)-N,N,N’,N’-tetraacetic acid (EGTA) [5]. The latter two, being representatives of the so-called complexones, show Lewis acid-catalyzed in situ deuteration of the N acetyl methylene groups in NaOD media, which is applied for speciation analyses in artificial body fluids by means of ²H NMR spectroscopy as the only deuterated component.

Acknowledgement
This research received funding by the German Federal Ministry for Economic Affairs and Energy (BMWi) with-in the GRaZ II projects, nos. 02E11860B and 02E11860G, the German Federal Ministry of Education and Research (BMBF) within the RADEKOR project, no. 02NUK057A, as well as by the European Union’s Horizon 2020 research and innovation programme’s CORI project, no. 847593.

References
[1] Kretzschmar, J.; Haubitz, T.; et al. Chem. Commun., 2018, 54, 8697.
[2] Kretzschmar, J.; Strobel, A.; et al. Inorg. Chem., 2020, 59, 4244.
[3] Kretzschmar, J.; Tsushima, S.; et al. Chem. Commun., 2020, 56, 13133.
[4] Kretzschmar, J.; Tsushima, S.; et al. Inorg. Chem., 2021, 60, 7998.
[5] Kretzschmar, J.; Wollenberg, A.; et al. Molecules, 2022, 27, 4067.

Keywords: NMR spectroscopy; Uranium; Radioecology; Aqueous system; Thermodynamics; Kinetics; Redox reaction; Speciation

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

Permalink: https://www.hzdr.de/publications/Publ-35617
Publ.-Id: 35617


Influence of the precession angle on the flow inside a precessing cylinder

Kumar, V.; Giesecke, A.; Gundrum, T.; Pizzi, F.; Ratajczak, M.; Stefani, F.

Precession driven flows are potential drivers for dynamo action in the Earth [1], the ancient moon, and some asteroids. As part of the DRESDYN project at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) a precession-driven dynamo experiment is presently under construction, which consists of a liquid sodium filled cylinder with a radius of 1 m and a height of 2 m respectively. The cylinder rotates with a frequency of up to 10 Hz and precess around the second axis with a frequency of up to 1 Hz [2].
To understand the hydrodynamics in a precessing cylinder a downscaled 1:6 water mockup was built with the same aspect ratio and rotation frequencies. The typical non-axisymmetric Kelvin mode that grows as the precession ratio rises is alone not suitable for dynamo action in the experiment. However, a secondary axisymmetric mode that emerges in a small region of the precession ratio was shown to be very promising for dynamo action in the sodium experiment [3].
The ability to predict dynamo behaviour for different precession ratios and precession angles requires a thorough understanding of the flow structure in the precessing cylindrical vessel. Consequently, we have performed series of precession measurements with Ultrasonic flow velocimetry (UDV) on the downscaled water experiment with various precession angles α at 60o, 75o, 90o [4]. In this paper, we present the effect of precession angle and rotation direction (i.e. prograde or retrograde) on the dominant flow modes, and quantify this behaviour in dependence of the rotation rate parameterized by the Reynolds number Re = ΩcR2/ν and the precession ratio Po = Ωp/Ωc, with ν the viscosity and Ωp = 2πfp the angular frequency of the precession. We have not taken into account the effect of the precession angle, which changes the definition of Reynolds number. The experimental results are supported by numerical simulations.

  • Lecture (Conference) (Online presentation)
    The Fourth Russian Conference on Magnetohydrodynamics, 20.-22.09.2021, Perm, Russia

Permalink: https://www.hzdr.de/publications/Publ-35615
Publ.-Id: 35615


Element separation chemistry and cosmogenic 10Be dating of a ferromanganese crust

Koll, D.; Wallner, A.; Battisson, S.; Fichter, S.; Fifield, L. K.; Froehlich, M. B.; Lachner, J.; Merchel, S.; Pavetich, S.; Rugel, G.; Slavkovská, Z.; Tims, S. G.; Ziegenrücker, R.

Oceanic archives are contemporary witnesses of Earth's recent astrophysical history by incorporating extraterrestrial
radionuclides. VA13/2 - 237KD is one of the most studied ferromanganese crusts and it has been shown that the crust
contains live interstellar 60Fe. Here, we have characterized a large piece of this crust with a 3D optical scan, a micro-CT
scan and 3D modeling, followed by the chemical extraction of highly purified, element-specific fractions for accelerator mass
spectrometry. High-accuracy cosmogenic 10Be dating of two independent drill-holes showed a time-dependent variability in
growth rate across the surface of the crust. This well-characterized crust is used to search for interstellar radionuclides, such
as supernova-produced 60Fe and the r-process nuclide 244Pu. Other extraterrestrial radionuclides including 26Al, 53Mn,
129I, 182Hf or 247Cm could be investigated in the future.

Keywords: 10Be; 244Pu; 60Fe; AMS; Ferromanganese crust; Nuclear astrophysics; Separation chemistry

Related publications

Downloads

  • Secondary publication expected from 26.09.2023

Permalink: https://www.hzdr.de/publications/Publ-35614
Publ.-Id: 35614


Some news from the synchronization front

Stefani, F.

The lecture summarizes our recent activities to establish a self-consistent planetary synchronization model for short-, medium- and long-term cycles of the solar dynamo.

  • Lecture (Conference)
    5th Dynamo Thinkshop, 27.-28.06.2022, Freiburg im Breisgau, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-35612
Publ.-Id: 35612


Batteries, dynamos, and all that

Stefani, F.

The lecture gives an overview about the various flow phenomena which can occur in liquid metal batteries, including the Tayler instability, thermal and solutal convection, electrovortex flows, metal pad roll instabilities, and various surface waves. For some of those cases, surprising links to corresponding effects with relevance to the solar dynamo are also discussed.

  • Invited lecture (Conferences)
    Open for Business event: Liquid Metal Batteries, 15.-16.11.2022, Cambridge, UK

Permalink: https://www.hzdr.de/publications/Publ-35610
Publ.-Id: 35610


Shaken and stirred: precessionally driven and tidally synchronized dynamos

Stefani, F.

The first part of the lecture gives an overview about our recent efforts to set-up a self-consistent planetary synchronization model for short-, medium- and long-term cycles of the solar dynamo. In the second part, we discuss the scientific background and the present status of the preparations of the precession-driven dynamo experiment in frame of the DRESDYN project.

  • Invited lecture (Conferences)
    Leeds satellite workshop: Fluid flow and magnetic field generation in fluids and plasmas, 17.-21.10.2022, Leeds, UK

Permalink: https://www.hzdr.de/publications/Publ-35609
Publ.-Id: 35609


Dynamo experiments: A grateful tribute to Karl-Heinz Rädler

Stefani, F.

The talk commemorates the various contributions of Karl-Heinz Rädler to the preparation and interpretation of liquid-metal dynamo experiments.

  • Invited lecture (Conferences)
    Special colloquium in honour of Karl-Heinz Rädler's life achievements: “Tracing the origin of magnetic fields throughout the cosmos”, 23.06.2022, Potsdam, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-35605
Publ.-Id: 35605


Liquid metal experiments on the generation and action of cosmic magnetic fields

Stefani, F.

The lecture starts with an introduction about the various interactions between the flows of electrically conducting fluids with magnetic fields, including the homogeneous dynamo effect and the celebrated magnetorotational instability in accretion disks. It continuous with an overview about previous liquid metal experiments dedicated to the laboratory demonstration of both effects, and concludes with an outlook on the large-sale liquid sodium experiments that are planned in the framework of the DRESDYN project.

  • Invited lecture (Conferences)
    Institutsseminar am Lehrstuhl Aerodynamik und Strömungslehre an der Brandenburgischen Technischen Universität Cottbus-Senftenberg, 17.03.2022, Cottbus, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-35603
Publ.-Id: 35603


DPA calculation with FLUKA2021, PHITS and MCNP6

Ferrari, A.; Müller, S.; Rachamin, R.

Input-files for Monte Carlo-Codes FLUKA2021, PHITS, MCNP62 to calculate the DPA results presented at SATIF15

Keywords: Monte Carlo; FLUKA; PHITS; MCNP; DPA

Downloads

Permalink: https://www.hzdr.de/publications/Publ-35601
Publ.-Id: 35601


Data publication: Synchronizing the helicity of Rayleigh-Bénard convection by a tide-like electromagnetic forcing

Jüstel, P.; Röhrborn, S.; Eckert, S.; Galindo, V.; Gundrum, T.; Stepanov, R.; Stefani, F.

Package of raw and refined data underlying the figures of the connected paper. Included is also the software used to generate the figures.

Keywords: Electromagnetic forcing; Magnetohydrodynamics; Helicity synchronization

Related publications

Downloads

Permalink: https://www.hzdr.de/publications/Publ-35600
Publ.-Id: 35600


Future air quality predictions using a machine learning-based model over the contiguous United States

Fan, K.; Lee, Y. H.

Air quality regulations have reduced emissions of pollutants in the U.S., but many prognostic studies suggest that future air quality might be degraded by global climate change. The simulated climate by various climate models shows a large variation in the future decades, and it is important to account for such variations to study future air quality. We have developed a machine learning (ML) based air quality model to study, in an efficient way, how future air quality might be influenced by climate change. Our ML model uses two-phase random forest to predict the O3 and PM2.5 concentrations with training datasets of key meteorological information and air quality pollutant emissions. To evaluate the model performance, we used the input datasets for the U.S. Environmental Protection Agent (EPA) the Community Multiscale Air Quality Modeling System (CMAQ) simulations and compared our model predictions against the CMAQ output as a benchmark. The ML model is well performed for hourly O3 predictions over the whole domain in four selected months (January, February, July, and August), and the R2 values are in 0.5 – 0.7, the normalized mean bias (NMB) values are within ±3%, the overall normalized mean error (NME) values are below 20%. Predicting PM2.5 is more challenging than predicting O3, but our ML model performance is still acceptable. The overall R2 values of PM2.5 predictions are in 0.4 – 0.6, and the NMB values are within ±6%, but the NME can be up to 60%. Our ML model with GPU acceleration runs less than one hour using a single GPU processor to predict 11-year one-month (total 11 months) simulations. It uses significantly less computing resources compared to the 3D models, like CMAQ, while it results in comparable predictability to CMAQ. It shows that our ML model a reliable and efficient tool to assess the air quality under various climate change scenarios.

Keywords: Machine learning; Air quality prediction; GPU acceleration

  • Open Access Logo Lecture (Conference) (Online presentation)
    Sustainability Research & Innovation Congress 2022 (SRI2022) / Early-career pathways and resources: communication, cross-disciplinary collaboration, and FE's mission, 20.-24.06.2022, Pretoria, South Africa

Permalink: https://www.hzdr.de/publications/Publ-35599
Publ.-Id: 35599


Data-driven approach to early estimate the inflection points of infected cases in Saxony, Germany

Fan, K.

We develop a data-driven forecasting model of COVID-19 for Saxony using autoregressive integrated moving average (ARIMA) and Holt’s models in the presence and absence of seasonal parameters. Owing to a daily-updated data curation facility, we employ a version control of daily-updated data for Saxony which serve as training data of seasonal parameter to forecast up to 4 horizons. We find that this method is capable of immediately estimating inflection points after a turning point is present. The results are also compatible with the counties of Saxony. We also tried to use multiple datasets (including infection, death, recovery, vaccination data) to train a random forest machine learning model. The preliminary result looks promising and further exploration will be done.

Keywords: COVID-19; Database server; Forecast

  • Open Access Logo Lecture (Conference)
    1st Symposium for Machine Learning for Infection and Disease in Görlitz, 15.-16.09.2022, Görlitz, Germany

Permalink: https://www.hzdr.de/publications/Publ-35594
Publ.-Id: 35594


Precise tuning of interlayer electronic coupling in layered conductive metal-organic frameworks

Lu, Y.; Zhang, Y.; Yang, C.-Y.; Revuelta, S.; Qi, H.; Huang, C.; Jin, W.; Li, Z.; Vega-Mayoral, V.; Liu, Y.; Huang, X.; Pohl, D.; Položij, M.; Zhou, S.; Cánovas, E.; Heine, T.; Fabiano, S.; Feng, X.; Dong, R.

Two-dimensional conjugated metal-organic frameworks (2D c-MOFs) have attracted increasing interests for (opto)-electronics and spintronics. They generally consist of van der Waals stacked layers and exhibit layer-depended electronic properties. While considerable efforts have been made to regulate the charge transport within a layer, precise control of electronic coupling between layers has not yet been achieved. Herein, we report a strategy to precisely tune interlayer charge transport in 2D c-MOFs via side-chain induced control of the layer spacing. We design hexaiminotriindole ligands allowing programmed functionalization with tailored alkyl chains (HATI_CX, X = 1,3,4; X refers to the carbon numbers of the alkyl chains) for the synthesis of semiconducting Ni3(HATI_CX)2. The layer spacing of these MOFs can be precisely varied from 3.40 to 3.70 Å, leading to widened band gap, suppressed carrier mobilities, and significant improvement of the Seebeck coefficient. With this demonstration, we further achieve a record-high thermoelectric power factor of 68 ± 3 nW m−1 K−2 in Ni3(HATI_C3)2, superior to the reported holes-dominated MOFs.

Permalink: https://www.hzdr.de/publications/Publ-35591
Publ.-Id: 35591


Nonlinear Evolution of Magnetorotational Instability in a Magnetized Taylor-Couette Flow: Scaling Properties and Relation to Upcoming DRESDYN-MRI Experimen

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

Magnetorotational instability (MRI) is considered as the most likely mechanism driving angular
momentum transport in astrophysical disks. However, despite many efforts, a direct and conclusive
experimental evidence of MRI in laboratory is still missing. Recently, performing 1D linear analysis
of the standard version of MRI (SMRI) between two rotating coaxial cylinders with an imposed axial
magnetic field, we showed that SMRI can be detected in the upcoming DRESDYN-MRI experiment
based on cylindrical magnetized Taylor-Couette (TC) flow with liquid sodium. In this follow-up
study, being also related to the DRESDYN-MRI experiments, we focus on the nonlinear evolution
and saturation properties of SMRI and analyze its scaling behavior with respect to various param-
eters of the basic TC flow using a pseudo-spectral code. We conduct a detailed analysis over the
extensive ranges of magnetic Reynolds number Rm ∈ [8.5, 37.1], Lundquist number Lu ∈ [1.5, 15.5]
and Reynolds number, Re ∈ [103, 105]. For fixed Rm, we investigate the nonlinear dynamics of
SMRI for small magnetic Prandtl numbers down to P m ∼ O(10−4), aiming ultimately for those
values typical of liquid sodium used in the experiments. In the saturated state, the magnetic en-
ergy of SMRI and associated torque exerted on the cylinders, characterising angular momentum
transport, both increase with Rm for fixed (Lu, Re), while for fixed (Lu, Rm), the magnetic energy
decreases and torque increases with increasing Re. We also study the scaling of the magnetic en-
ergy and torque in the saturated state as a function of Re and find a power law dependence of the
form Re−0.6...−0.5 for the magnetic energy and Re0.4...0.5 for the torque at all sets of (Lu, Rm) and
sufficiently high Re ≥ 4000. We also explore the dependence on Lundquist number and angular
velocity. The scaling laws derived here will be instrumental in the subsequent analysis and com-
parison of numerical results with those obtained from the DRESDYN-MRI experiments in order to
conclusively and unambiguously identify SMRI in laboratory.Magnetorotational instability (MRI) is considered as the most likely mechanism driving angular
momentum transport in astrophysical disks. However, despite many efforts, a direct and conclusive
experimental evidence of MRI in laboratory is still missing. Recently, performing 1D linear analysis
of the standard version of MRI (SMRI) between two rotating coaxial cylinders with an imposed axial
magnetic field, we showed that SMRI can be detected in the upcoming DRESDYN-MRI experiment
based on cylindrical magnetized Taylor-Couette (TC) flow with liquid sodium. In this follow-up
study, being also related to the DRESDYN-MRI experiments, we focus on the nonlinear evolution
and saturation properties of SMRI and analyze its scaling behavior with respect to various param-
eters of the basic TC flow using a pseudo-spectral code. We conduct a detailed analysis over the
extensive ranges of magnetic Reynolds number Rm ∈ [8.5, 37.1], Lundquist number Lu ∈ [1.5, 15.5]
and Reynolds number, Re ∈ [103, 105]. For fixed Rm, we investigate the nonlinear dynamics of
SMRI for small magnetic Prandtl numbers down to P m ∼ O(10−4), aiming ultimately for those
values typical of liquid sodium used in the experiments. In the saturated state, the magnetic en-
ergy of SMRI and associated torque exerted on the cylinders, characterising angular momentum
transport, both increase with Rm for fixed (Lu, Re), while for fixed (Lu, Rm), the magnetic energy
decreases and torque increases with increasing Re. We also study the scaling of the magnetic en-
ergy and torque in the saturated state as a function of Re and find a power law dependence of the
form Re^(−0.6...−0.5) for the magnetic energy and Re^(0.4...0.5) for the torque at all sets of (Lu, Rm) and
sufficiently high Re ≥ 4000. We also explore the dependence on Lundquist number and angular
velocity. The scaling laws derived here will be instrumental in the subsequent analysis and com-
parison of numerical results with those obtained from the DRESDYN-MRI experiments in order to
conclusively and unambiguously identify SMRI in laboratory.

  • Lecture (Conference)
    The 12th pamir International Conference on Fundamental and Applied MHD, 04.07.2022, Krakow, Poland
  • Lecture (Conference)
    9th International Symposium on Bifurcations and Instabilities in Fluid Dynamics, 16.-19.08.2022, Groningen, Netherlands
  • Contribution to WWW
    arXiv:2211.10811 [physics.flu-dyn]: https://arxiv.org/abs/2211.10811

Permalink: https://www.hzdr.de/publications/Publ-35588
Publ.-Id: 35588


Dynamic transitions of the magnetized spherical Couette flow between its base state and the return flow instability

Ogbonna, J. E.; Garcia Gonzalez, F.; Gundrum, T.; Seilmayer, M.; Stefani, F.

The transition between the stable base state of the magnetized spherical Couette (MSC) flow and the return flow instability is experimentally investigated. The experiments are conducted using an MSC setup consisting of insulating spheres with the ratio of the inner to the outer radii ri/ro = 0.5, Reynolds number Re = 1000 and Hartmann number Ha ∈ [25, 29]. The transition is characterized by changes in the power spectra of the azimuthal modes in the flow as Ha is dynamically changed. The transition occurs in the interval Ha ∈ [26.5, 27.5]. The evolution of the power spectra of the azimuthal modes exhibits hysteretic effect depending on whether Ha is increased or decreased within the experimental interval. The power spectra in the azimuthal modes m ∈ {3, 4} increases and remains dominant as Ha is increased, while the power spectra in m ∈ {2, 4} are dominant while the flow is time dependent due to return flow instability as Ha is decreased.

Keywords: Magnetohydrodynamics; Experimental fluid mechanics; Fluid instability

Permalink: https://www.hzdr.de/publications/Publ-35587
Publ.-Id: 35587


Sorption and Modeling of Actinides on Ca-Feldspars

Lessing, J.; Neumann, J.; Bezzina, J. P.; Bok, F.; Lützenkirchen, J.; Brendler, V.; Stumpf, T.; Schmidt, M.

This poster gives a small overview of the investigations on sorption on plagioclases (Ca-feldspars). The topic is of main importance to find an suitable final radioactive waste repository.
The surface of the minerals was characterzied with zeta potenzial. Batch sorption experiments were conducted to gain information about the sorption of the lanthanide Eu3+ and actinide Am3+. Time resolved laser induced spectroscopy was applied to understand the sorption on a molecular level. All these data were then used for a surface complexation model, that will be used for simulation of the sorption of actinides at different geochemical conditions.

Keywords: Sorption; actinides; Ca-feldspar; plagioclase; TRLFS; batch sorption; SCM

  • Open Access Logo Poster
    ChemTUgether, 13.-14.05.2022, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-35585
Publ.-Id: 35585


Natural and synthetic plagioclases: Surface charge characterization and sorption of trivalent Ln and An

Lessing, J.; Neumann, J.; Bezzina, J. P.; Bok, F.; Lützenkirchen, J.; Brendler, V.; Stumpf, T.; Schmidt, M.

Das Wissen über den Transport von Radionukliden in der Umwelt ist essenziell zur Beur-teilung der Sicherheit eines radioaktiven Endlagers. Einen globalen Konsens bildet zurzeit die tiefengeologische Lagerung, da diese verspricht den Abfall über geologische Zeiträume von der Biosphäre zu isolieren. In einigen Ländern, u. a. Deutschland wird Kristallingestein, welches sich neben Quarz und Glimmern vorwiegend aus Feldspäten zusammensetzt, als mögliches Wirtsgestein für ein tiefengeologisches Endlager betrachtet. Deshalb ist es von enormer Bedeutung, die Rückhaltung der dreiwertigen minoren Actinide (Cm, Am), welche über Jahrtausende die Radiotoxizität im Endlager dominieren an Feldspäte zu verstehen. In dieser Studie wurden speziell Ca-Feldspäte betrachtet, da deren Retentionsverhalten noch nicht ausreichend untersucht wurde, aber Unterschiede in Kristallstruktur und Gitterladung im Vergleich zum besser untersuchten K-Feldspat auftreten.
Zunächst wurden Zetapotenzial-Messungen von Ca-Feldspäten mit verschiedenen Ca-Anteilen durchgeführt. Sie zeigen einen ungewöhnlichen Anstieg der Oberflächenladung bei pH 4 – 7, wobei der Anstieg des Zetapotenzials mit steigender Ca-Konzentration im Kris-tallgitter des Feldspats zunimmt. Dies wird durch die Sorption von Ca2+ und AlDas Wissen über den Transport von Radionukliden in der Umwelt ist essenziell zur Beur-teilung der Sicherheit eines radioaktiven Endlagers. Einen globalen Konsens bildet zurzeit die tiefengeologische Lagerung, da diese verspricht den Abfall über geologische Zeiträume von der Biosphäre zu isolieren. In einigen Ländern, u. a. Deutschland wird Kristallingestein, welches sich neben Quarz und Glimmern vorwiegend aus Feldspäten zusammensetzt, als mögliches Wirtsgestein für ein tiefengeologisches Endlager betrachtet. Deshalb ist es von enormer Bedeutung, die Rückhaltung der dreiwertigen minoren Actinide (Cm, Am), welche über Jahrtausende die Radiotoxizität im Endlager dominieren an Feldspäte zu verstehen. In dieser Studie wurden speziell Ca-Feldspäte betrachtet, da deren Retentionsverhalten noch nicht ausreichend untersucht wurde, aber Unterschiede in Kristallstruktur und Gitterladung im Vergleich zum besser untersuchten K-Feldspat auftreten.
Zunächst wurden Zetapotenzial-Messungen von Ca-Feldspäten mit verschiedenen Ca-Anteilen durchgeführt. Sie zeigen einen ungewöhnlichen Anstieg der Oberflächenladung bei pH 4 – 7, wobei der Anstieg des Zetapotenzials mit steigender Ca-Konzentration im Kris-tallgitter des Feldspats zunimmt. Dies wird durch die Sorption von Ca2+ und Al3+ und/oder Ausfällung einer Al-Phase verursacht.[1]
Im Vergleich zum K-Feldspat treten nur geringe Unterschiede im Rückhaltevermögen und in der Oberflächenspeziation auf. Ca-Feldspäte zeigen ein leicht höheres Rückhaltevermö-gen gegenüber dreiwertigen Metallionen. Ein innersphärischer (IS) Oberflächenkomplex so-wie dessen zwei Hydrolyseformen wurden an beiden Mineralen identifiziert, allerdings tritt die Hydrolyse des IS-Komplexes an Ca-Feldspäten bereits bei niedrigeren pH-Werten auf.[1,2]
Batchsorptionsdaten und spektroskopische Informationen wurden schließlich kombiniert, um ein Oberflächenkomplexierungsmodell zu entwickeln und die Bildungskonstanten der drei Oberflächenkomplexe zu bestimmen (log K0 = -8,37; -10,81 bzw. -16,35). Diese Werte un-terscheiden sich nur unwesentlich von den Werten für K-Feldspat. [1,2]
Die gewonnenen Daten stehen für Transportsimulationen für die Sicherheitsbeurteilung eines potenziellen Endlagers für radioaktiven Abfall zur Verfügung.
und/oder Ausfällung einer Al-Phase verursacht.[1]
Im Vergleich zum K-Feldspat treten nur geringe Unterschiede im Rückhaltevermögen und in der Oberflächenspeziation auf. Ca-Feldspäte zeigen ein leicht höheres Rückhaltevermö-gen gegenüber dreiwertigen Metallionen. Ein innersphärischer (IS) Oberflächenkomplex so-wie dessen zwei Hydrolyseformen wurden an beiden Mineralen identifiziert, allerdings tritt die Hydrolyse des IS-Komplexes an Ca-Feldspäten bereits bei niedrigeren pH-Werten auf.[1,2]
Batchsorptionsdaten und spektroskopische Informationen wurden schließlich kombiniert, um ein Oberflächenkomplexierungsmodell zu entwickeln und die Bildungskonstanten der drei Oberflächenkomplexe zu bestimmen (log K0 = -8,37; -10,81 bzw. -16,35). Diese Werte un-terscheiden sich nur unwesentlich von den Werten für K-Feldspat. [1,2]
Die gewonnenen Daten stehen für Transportsimulationen für die Sicherheitsbeurteilung eines potenziellen Endlagers für radioaktiven Abfall zur Verfügung.
Referenzen:
[1] Neumann and Lessing et al., in preparation. [2] J. Neumann et al., J. Colloid Interface Sci., 2021, 591, 490–499.

Keywords: Plagioclases; surface chemistry; actinides; lanthanides

  • Open Access Logo Poster
    Jahrestagung der FG Nuklearchemie 2022, 04.-06.10.2022, Bergisch Gladbach, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-35584
Publ.-Id: 35584


Mineral revolution for the Wellbeing Economy

Gloaguen, R.; Ajjabou, L.; Ali, S.; Herrington, R.; Downey, E.; Stewart, I. S.

Non-technical summary. As we consider a transition to a low-carbon future, there is a need to examine the mineral needs for
this transformation at a scale reminiscent of the Green Revolution. The efficiency gains of the agrarian transition came at
ecological and social costs that should provide important lessons about future metal sourcing. We present three options for a
Mineral Revolution: status quo, incremental adaption and revolutionary change. We argue that a sustainable Mineral
Revolution requires a paradigm shift that considers wellbeing as a purpose and focuses on preserving natural capital.
Technical summary. As we consider a transition to a low-carbon future, there is a need to examine the mineral needs for this
transformation at a scale reminiscent of the Green Revolution. The efficiency gains of the agrarian transition came at
ecological and social costs that can also provide important lessons about the Mineral Revolution. We lay out some of the key
ways in which such a mineral revolution can be delineated over temporal scales in a paradigm shift that considers wellbeing
as a purpose and focuses on preserving natural capital. These prospects are conceptually presented as three pathways that
consider the status quo, incremental adaption and revolutionary change as a means of planning more effectively for a lowcarbon
transition. Social media summary. Sourcing metals sustainably will require to consider wellbeing as a purpose and to
preserve natural capital.

Keywords: industrial activities; social value; planning and design; natural resources (biological and non-biological)

Permalink: https://www.hzdr.de/publications/Publ-35583
Publ.-Id: 35583


Spectroscopic and modeling study of Ln³⁺ (Eu³⁺, Y³⁺) and An³⁺ (Cm³⁺, Am³⁺) on feldspars

Lessing, J.; Neumann, J.; Bezzina, J. P.; Brendler, V.; Lützenkirchen, J.; Stumpf, T.; Schmidt, M.

Influence of the competition of Al on the retention of trivalent actinides and their homologues in orthoclase
J. Lessing,1 M. Schmidt,1 T. Stumpf1
1 Helmholtz-Zentrum Dresden-Rossendorf e.V., Institute of Resource Ecology, Bautzner Landstraße 400,
01328 Dresden, Germany, email: j.lessing@hzdr.de

Most countries worldwide consider disposal in a deep geological formation as the safest concept for nuclear waste disposal. For a realistic safety assessment of such a repository, understanding the mechanisms of the prevalent retention processes is of utmost importance. Sorption of radio-active elements on many minerals is well described in literature, but there is a lack of data re-garding the influence of other natural cations especially Al3+ [1]. These cations will be present in all scenarios as Al3+ is the third most common element (following O and Si) in the earth crust, and will occur locally e.g. due to the dissolution of minerals (especially alumino-silicates). Its concentration can be expected to exceed that of the actinides manifold. In addition to competi-tion for sorption site, Al3+ can then also re-precipitate on a primary mineral’s surface and form a secondary phase, which will impact the interaction of the radionuclides with these minerals.
Alumino-silicates, such as feldspars (orthoclase) and mica, together with quartz are the main components of crystalline rock, which is considered as possible host rock for radioactive waste repositories. The other common option are clay formations, which also consist of alumino-silicate minerals. The retention of trivalent actinides by feldspars was already investigated thor-oughly [2,3]. The minor actinides (Np, Am, and Cm) as well as plutonium dominate the radio-toxicity of spent nuclear fuel over geological time scales. Am and Cm are predominantly triva-lent in aqueous solution and Pu is also expected to occur at least partly in its trivalent state, due to the expected reducing conditions in deep geological formations. The less radiotoxic lantha-nide Eu3+ is often used as homologue for the trivalent actinides with excellent luminescence properties.
Here, we study the effect of dissolved Al3+ on the retention of trivalent actinides (Cm3+) and lan-thanides (Eu3+) on orthoclase. The quantitative effect of different [Al3+] on actinide retention was first evaluated in batch sorption experiments using Eu3+ as an analogue. For further analysis on a molecular level, time resolved laser spectroscopy (TRLFS) was applied, from which infor-mation about the formed surfaces complexes can be gained. We will discuss the results with re-spect to the impact of Al3+ on quantity and speciation of An3+ sorption on feldspars.
The derived speciation and quantitative retention data is foreseen to be implemented into a sur-face complexation model, with parameters available in thermodynamic databases. Ultimately this will provide a better understanding of the fundamental mechanisms of sorption process of the minor actinides Am and Cm on naturally occurring mineral phases under close to natural conditions.

Keywords: sorption; actinides; Cm3+; Eu3+; spectroscopy

  • Open Access Logo Poster
    ATAS/AnXAS joint workshop, 17.-21.10.2022, Grenoble, France

Permalink: https://www.hzdr.de/publications/Publ-35582
Publ.-Id: 35582


Flotation Process and Computational Modeling

Buchmann, M.; Draw, M.; Rzehak, R.; van den Boogaart, K. G.; Rudolph, M.

Results on modeling and simulation of flotation processes obtained by groups of Helmholtz-Zentrum Dresden-Rossendorf and Helmholtz Institute Freiberg for Resource Technologygroups are shown. These comprise a flotation kinetic model based on the multilayer structure and van der Waals interactions, and a hydrodynamic model using the Eularian multiphase framework. Unfortunately, a full validation of the combined model for data from a real flotation system was not possible yet due to numerical stability issues.

Keywords: Froth Flotation; hydrodynamic model; flotation kinetic model; Eulerian multiphase framework; van der Waals interactions

  • Poster
    FineFuture Final Conference, 14.-15.11.2022, Brussels, Belgium

Permalink: https://www.hzdr.de/publications/Publ-35581
Publ.-Id: 35581


openPMD – F.A.I.R Scientific I/O at the Exascale

Pöschel, F.; Hübl, A.

This talk presents openPMD, an open and F.A.I.R. standard for particle-mesh data, and its impact in heterogeneous scientific workflows.
Particle accelerator codes need to span various time and length scales, leading to data processing pipelines consisting of multiple heterogeneous codes.
Standardization of physical data helps bridging the different models with a commonly-understood markup, creating interoperable and flexible workflows.

The openPMD standard is made accessible to scientific software via the openPMD-api, a library for the description of scientific data.
The backend implementations of the openPMD-api are based on established I/O framworks such as HDF5 and ADIOS2, and also include a scalable streaming backend for HPC workflows, provided by ADIOS2.
The talk gives an insight into the existing ecosystem of openPMD and describes the basic concepts of the data markup.

It shortly illuminates recent trends in large-scale I/O and their impact on scientific compute workflows. While traditional attempts at counteracting such trends, e.g. through compression, remain available in the openPMD-api, we propose loose coupling and online analysis via streaming workflows as a sustainable solution that avoids parallel filesystem bottlenecks.

Keywords: high performance computing; F.A.I.R; particle-mesh data; openPMD; streaming; big data

  • Open Access Logo Invited lecture (Conferences)
    EuroNNAc Special Topics Workshop, 18.-24.09.2022, La Biodola Bay, Isola d'Elba, Italien
  • Open Access Logo Poster
    EuroNNAc Special Topics Workshop, 18.-24.09.2022, La Biodola Bay, Isola d'Elba, Italien
  • Open Access Logo Poster
    8. Annual MT Meeting, 26.-27.09.2022, Hamburg, Deutschland

Downloads

Permalink: https://www.hzdr.de/publications/Publ-35580
Publ.-Id: 35580


Hydrodynamic model validation of gas-solid-liquid flow in a slurry bubble column

Draw, M.; Rzehak, R.

The understanding of gas-solid-liquid three-phase flow is very importnant for the development of Reflux Flotation Cell. CFD simulations of such flows are feasible even on industrial scales within the Eulerian framework of interpenetrating continua. The performance of the framework, however, relies on the suitability of the closure models to account for phenomena on the scale of individual particles or bubbles, which are not resolved in this approach. To this end, the present work attempts to combine closure relations that were previously established for two-phase gas-liquid and solid-liquid flows. Due to the complexity of the RFC system, CFD-grade data to evaluate the overall closure model for three-phase gas-solid-liquid flows are not available yet. Therefore, comparison is made with a dataset from Rampure et al. [Can. J. Chem. Eng. 81 (2003), 692-706] for a slurry bubble column. Agreement of the combined model with the data is not entirely satisfactory yet. Possible reasons concerning both modeling and experiment are discussed and directions for further research identified.

Keywords: gas-solid-liquid three-phase flow; hydrodynamic validation; Reflux Flotation Cell; CFD simulation; closure model

  • Lecture (Conference)
    International RFC Upscaling Symposium, 04.-07.10.2022, Newcastle, Australia

Permalink: https://www.hzdr.de/publications/Publ-35579
Publ.-Id: 35579


openPMD – Open and F.A.I.R I/O for Particle-Mesh Data at the Exascale

Pöschel, F.; E, J.; Godoy, W. F.; Podhorszki, N.; Klasky, S.; Eisenhauer, G.; Davis, P. E.; Wan, L.; Gainaru, A.; Gu, J.; Koller, F.; Widera, R.; Bussmann, M.; Huebl, A.

This talk presents openPMD, an open and F.A.I.R. standard for particle-mesh data, and its impact in Exascale scientific workflows. The openPMD standard is made accessible to scientific software via the openPMD-api, a library for the description of scientific data. It approaches recent challenges posed by hardware heterogeneity by decoupling the data description in domain sciences, such as plasma physics simulations, from concrete implementations in hardware and IO. This concept helps us build a transition path from file-based IO to streaming-based workflows of scientific applications in an HPC environment. The streaming backend is provided by the ADIOS2 framework, developed at Oak Ridge National Laboratory.
This talk discusses two openPMD-based loosely coupled setups to demonstrate flexible applicability and to evaluate performance. In loose coupling, as opposed to tight coupling, two (or more) applications are executed separately, e.g. in individual MPI contexts, yet cooperate by exchanging data. This way, a streaming-based workflow allows for standalone codes instead of tightly-coupled plugins, using a unified streaming-aware API and leveraging high-speed communication infrastructure available in modern compute clusters for massive data exchange.
The presented setups show the potential for a more flexible use of compute resources brought by streaming IO as well as the ability to increase throughput by avoiding filesystem bottlenecks.

Keywords: high performance computing; big data; streaming; RDMA; openPMD; ADIOS

  • Open Access Logo Invited lecture (Conferences) (Online presentation)
    SIAM Conference on Parallel Processing for Scientific Computing (PP22), 23.-26.02.2022, Seattle, USA

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Permalink: https://www.hzdr.de/publications/Publ-35578
Publ.-Id: 35578


Euler-Euler Simulation of Absorption and Desorption in Co- and Counter-current Bubble Column Flows

Khan, H.; Lehnigk, R.; Rzehak, R.

Mass transfer in bubbly flows is important in many engineering applications. Simulation of such processes on technical scales is feasible by the Euler-Euler two-fluid model, which relies on suitable closure relations describing interfacial exchange processes. In comparison with the pure fluid dynamics of bubbly flows however, modeling and simulation of bubbly flows including mass transfer is significantly less developed. In particular, previous studies have focused entirely on absorption in upward vertical flows, whereas the present study considers a larger variety of conditions including desorption and counter-current (downward) flow. Suitable experimental data for comparison are available from the classic work of Deckwer et al. [Canadian Journal of Chemical Engineering 56 (1978) 43-55]. In line with previous studies on the co-current absorption cases from that work, a monodisperse approximation is made. In addition, a class method to treat bubble shrinkage and growth is implemented in the OpenFOAM code and tested by showing the crossover between two monodisperse cases.

Keywords: mass-transfer; dispersed gas-liquid multiphase flow; Euler-Euler two-fluid model; closure relations; CFD simulation; model validation

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  • Secondary publication expected from 17.11.2023

Permalink: https://www.hzdr.de/publications/Publ-35574
Publ.-Id: 35574


Complexation of Eu(III) and Cm(III) by EGTA related aminopolycarboxylic acids

Friedrich, S.; Kretzschmar, J.; Drobot, B.; Stumpf, T.; Barkleit, A.

For radiation protection and chelation therapy, aminopolycarboxylic acids like ethylenedia-minetetraacetic acid (EDTA) or diethylenetriaminepentaacetic acid (DTPA) are clinical approved decorporation agents. They show promising results in complexation of Ln(III)/An(III). For EDTA and DTPA related compound ethylene glycol-bis(β-aminoethyl ether)-N,N,N’,N’-tetraacetic acid (EGTA), complexes with trivalent europium (Eu) have been characterized by NMR spectroscopy and x-ray diffraction. In these complexes, EGTA acts as an octadentate lig-and.[1,2] In addition to this, the knowledge on the Eu-EGTA-system is extended by time-resolved laser-induced fluorescence spectroscopy (TRLFS), ²H-NMR spectroscopy and isother-mal titration calorimetry (ITC). These speciation studies on Eu(III) show promising results for EGTA as a complexing agent (Fig. 1).
To expand this group of ligands, EGTA related compounds were synthesized (Fig. 2). With these compounds, the complexation behavior with Eu(III) and curium(III) were determined and com-prehensively characterized with TRLFS from both sides: the ligands and metals perspective. The overall goal is a better understanding of the influence of the ligand design on the affinity to complex trivalent Ln and An. Hence, in the future these ligands may contribute to an advanced chelation therapy.
This work is funded by the German Federal Ministry of Education and Research (BMBF) under grant number 02NUK057A and part of the joint project RADEKOR.

  • Open Access Logo Lecture (Conference)
    ATAS-AnXAS 2022 - Joint Workshop, 17.-21.10.2022, Grenoble, France

Permalink: https://www.hzdr.de/publications/Publ-35573
Publ.-Id: 35573


Incorporation of lanthanides into zirconia: a study of solid phase transformations

Braga Ferreira Dos Santos, L.; Marquardt, J.; Nießen, J.; Tonnesen, T.; Svitlyk, V.; Hennig, C.; Stumpf, T.; Huittinen, N. M.

Zirconia (ZrO2) is the primary corrosion product of the Zircaloy cladding material surrounding nuclear fuel rods [1]. It has also been envisioned as a ceramic host phase for specific high- level waste streams, immobilizing radionuclides and being able to become a protective barrier. In the case of doped ZrO2 matrices, a very high radiation tolerance has been reported, however, discrepancies exist regarding the role of the different structural polymorphs in the high radiation resistance. Ce has been used as a surrogate for Pu due to comparable chemical properties in the oxidation states +III and +IV, similar ionic radius, and its easier handling [2]. In the current study, phase transformations occurring in the ZrO2 material when doped with Ce(IV) and Gd(III), have been explored.

Related publications

  • Poster
    Plutonium Futures, 26.-29.09.2022, Avignon, France
    PURL: http://pufutures2022.org/img/PuFutures2022_Poster_Abstracts.pdf

Permalink: https://www.hzdr.de/publications/Publ-35571
Publ.-Id: 35571


MRI-turbulence and large-scale dynamo in astrophysical disks: specific nonlinear anisotropy – transverse cascade – and sustenance scheme

Mamatsashvili, G.

We investigate the sustenance and dynamical balances of MRI-turbulence in accretion disks with a zero net magnetic flux. Zero net flux MRI has attracted a great interest in the last decade, because of its importance in MRI-dynamo in disks. It is unique, in the sense that there is no characteristic length-scale for MRI to grow purely exponentially and hence the instability is instead of a subcritical type, being energetically powered by linear nonmodal, or transient growth of perturbations. This transient growth of MRI is not, however, able to ensure a long-term sustenance of the turbulence and necessitates nonlinear feedback replenishing such transiently growing modes. To examine the existence of such a nonlinear feedback and ultimately understand the whole self-sustenance process of MRI-turbulence, we first performed simulations and then a detailed analysis of the turbulence dynamics in Fourier space. We showed that the disk flow shear gives rise to anisotropy of nonlinear processes in Fourier space. As a result, the key nonlinear process for the sustenance appears to be a topologically new type of angular (i.e., over wavevector orientations) redistribution of modes in Fourier space – the nonlinear transverse cascade – in contrast to the well-known direct/inverse cascades in the absence of shear in classical theories of isotropic turbulence. Moreover, the transverse cascade is a generic nonlinear process in different kinds of shear flows. The sustenance of zero net flux MRI-turbulence relies on the interplay between the two basic processes -- linear transient growth of MRI and the nonlinear transverse cascade. They mostly operate at length scales comparable to the box size (disk scale height), which we call the vital area of the turbulence in Fourier space. Base on this self-sustenance scheme we give a physical interpretation of the dependence (sensitivity) of the zero net flux MRI-turbulence with respect to magnetic Prandtl number in terms of competition between transverse and direct cascades.

Keywords: accretion; accretion discs; turbulence; MHD; instabilities

  • Lecture (Conference)
    Leeds Dynamo Workshop: Fluid Flow and Magnetic Field Generation in Fluids and Plasmas, 16.-21.10.2022, Leeds, United Kingdom
  • Lecture (others) (Online presentation)
    Seminar at the Georgian National Astrophysical Observtaory, 21.11.2022, Tbilisi, Georgia

Permalink: https://www.hzdr.de/publications/Publ-35569
Publ.-Id: 35569


Specific anisotropy of nonlinear processes and self-sustenance of MRI-turbulence in accretion discs

Mamatsashvili, G.

We investigate the sustenance and dynamical balances of MRI-turbulence in accretion disks with a zero net magnetic flux. Zero net flux MRI has attracted a great interest in the last decade, because of its importance in MRI-dynamo in disks. It is unique, in the sense that there is no characteristic length-scale for MRI to grow purely exponentially and hence the instability is instead of a subcritical type, being energetically powered by linear nonmodal, or transient growth of perturbations. This transient growth of MRI is not, however, able to ensure a long-term sustenance of the turbulence and necessitates nonlinear feedback replenishing such transiently growing modes. To examine the existence of such a nonlinear feedback and ultimately understand the whole self-sustenance process of MRI-turbulence, we first performed simulations and then a detailed analysis of the turbulence dynamics in Fourier space. We showed that the disk flow shear gives rise to anisotropy of nonlinear processes in Fourier space. As a result, the key nonlinear process for the sustenance appears to be a topologically new type of angular (i.e., over wavevector orientations) redistribution of modes in Fourier space – the nonlinear transverse cascade – in contrast to the well-known direct/inverse cascades in the absence of shear in classical theories of isotropic turbulence. Moreover, the transverse cascade is a generic nonlinear process in different kinds of shear flows. The sustenance of zero net flux MRI-turbulence relies on the interplay between the two basic processes -- linear transient growth of MRI and the nonlinear transverse cascade. They mostly operate at length scales comparable to the box size (disk scale height), which we call the vital area of the turbulence in Fourier space. Base on this self-sustenance scheme we give a physical interpretation of the dependence (sensitivity) of the zero net flux MRI-turbulence with respect to magnetic Prandtl number in terms of competition between transverse and direct cascades.

Keywords: accretion; accretion discs; instabilities; MHD; turbulence

  • Lecture (others) (Online presentation)
    Seminar at Max Planck Institute for Gravitational Physics, 28.06.2022, Potsdam, Germany

Permalink: https://www.hzdr.de/publications/Publ-35568
Publ.-Id: 35568


From helical to standard magnetorotational instability: Predictions for upcoming sodium experiments

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

We conduct a linear analysis of axisymmetric magnetorotational instability (MRI) in a magnetized cylindrical Taylor-Couette (TC) flow for its standard version (SMRI) with a purely axial background magnetic field and two additional types—helically modified SMRI (H-SMRI) and helical MRI (HMRI)—in the presence of combined axial and azimuthal magnetic fields. This study is intended as preparatory for upcoming new cutting-edge large-scale liquid sodium MRI experiments planned within the DRESDYN project at Helmholtz-Zentrum Dresden-Rossendorf, so we explore these instability types for typical values of the main parameters: the magnetic Reynolds number, the Lundquist number, and the ratio of the angular velocities of the cylinders, which are attainable in these experiments. In contrast to previous attempts at detecting MRI in the laboratory, our results demonstrate that SMRI and its helically modified version can in principle be detected in the DRESDYN-TC device for the range of the above parameters, including the astrophysically most important Keplerian rotation, despite the extremely small magnetic Prandtl number of liquid sodium. Since in the experiments we plan to approach (H-)SMRI from the previously studied HMRI regime, we characterize the continuous and monotonous transition between these two regimes. We show that H-SMRI, like HMRI, represents an overstability (traveling wave) with nonzero frequency linearly increasing with azimuthal field. Because of its relevance to finite-size flow systems in experiments, we also analyze the absolute form of H-SMRI and compare its growth rate and onset criterion with the convective one.

Keywords: instabilities; MHD; Taylor-Couette flow

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

Permalink: https://www.hzdr.de/publications/Publ-35567
Publ.-Id: 35567


MRI turbulence in accretion discs at large magnetic Prandtl numbers

Held, L.; Mamatsashvili, G.

The effect of large magnetic Prandtl number Pm (the ratio of viscosity to resistivity) on the turbulent transport and energetics of the magnetorotational instability (MRI) is poorly understood, despite the realization of this regime in astrophysical environments as disparate as discs from binary neutron star (BNS) mergers, the inner regions of low-mass X-ray binaries and active galactic nuclei, and the interiors of protoneutron stars. We investigate the MRI dynamo and associated turbulence in the regime Pm > 1 by carrying out fully compressible, 3D MHD-shearing box simulations using the finite-volume code PLUTO, focusing mostly on the case of Keplerian shear relevant to accretion discs. We find that when the magnetic Reynolds number is kept fixed, the turbulent transport (as parameterized by α, the ratio of stress to thermal pressure) scales with the magnetic Prandtl number as $α ~ Pm^δ$, with $δ ~ 0.5-0.7$ up to $Pm ~ 128$. However, this scaling weakens as the magnetic Reynolds number is increased. Importantly, compared to previous studies, we find a new effect at very large Pm - the turbulent energy and stress begin to plateau, no longer depending on Pm. To understand these results we have carried out a detailed analysis of the turbulent dynamics in Fourier space, focusing on the effect of increasing Pm on the transverse cascade - a key non-linear process induced by the disc shear flow that is responsible for the sustenance of MRI turbulence. Finally, we find that α-Pm scaling is sensitive to the box vertical-to-radial aspect ratio, as well as to the background shear.

Keywords: accretion; accretion discs; instabilities; MHD; turbulence

  • Open Access Logo Monthly Notices of the Royal Astronomical Society 517(2022)2, 2309-2330
    Online First (2022) DOI: 10.1093/mnras/stac2656
    arXiv: 2206.00497

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Permalink: https://www.hzdr.de/publications/Publ-35565
Publ.-Id: 35565


Status of the SLAC/MSU SRF Gun Development Project

Lewellen, J. W.; Adolphsen, C.; Coy, R.; Ge, L.; Ji, F.; Murphy, M.; Xiao, L.; Kelly, M.; Peterson, T.; Choi, Y.; Compton, C.; Du, X.; Greene, D.; Hartung, W.; Kim, S.-H.; Konomi, T.; Miller, S. J.; Morris, D.; Patil, M. S.; Popielarski, J. T.; Popielarski, L.; Saito, K.; Xu, T.; Arnold, A.; Gatzmaga, S.; Murcek, P.; Xiang, R.

The LCLS-II-HE Project at SLAC seeks to increase the photon energy reach of the LCLS-II FEL to at least 20 keV. In addition to upgrading the undulator system, and increasing the electron beam energy to 8 GeV, the project will also construct a low-emittance injector (LEI) in a new tunnel. To achieve the LEI emittance goals, a low-MTE photocathode will be required, as will on-cathode electric fields up to 50% higher than those achievable in the current LCLSII photoinjector.
The beam source for the LEI will be based around a superconducting quarter-wave cavity resonant at 185.7 MHz. A prototype gun is currently being designed and fabricated at the Facility for Rare Isotope Beams (FRIB) at Michigan State University (MSU). This paper presents performance goals for the new gun design, an overview of the prototype development effort, status, and future plans including fabrication of a “production” gun for the LEI.

  • Open Access Logo Poster
    North American Particle Accelerator Conference 2022 (NAPAC'22), 07.-12.08.2022, Albuquerque, New Mexico, USA
  • Open Access Logo Contribution to proceedings
    North American Particle Accelerator Conference 2022 (NAPAC'22), 07.-12.08.2022, Albuquerque, New Mexico, USA
    Proceedings of North American Particle Accelerator Conference 2022: JACoW, 978-3-95450-232-5
    DOI: 10.18429/JACoW-NAPAC2022-WEPA03
    ISSN: 2226-0366

Permalink: https://www.hzdr.de/publications/Publ-35564
Publ.-Id: 35564


Design of the Cathode Stalk for the LCLS-II-HE Low Emittance Injector

Konomi, T.; Hartung, W.; Kim, S.-H.; Miller, S.; Morris, D.; Popielarski, J.; Saito, K.; Taylor, A.; Xu, T.; Adolphsen, C.; Lewellen, J.; Gatzmaga, S.; Murcek, P.; Xiang, R.; Kelly, M.; Petersen, T.

Superconducting radio-frequency (SRF) electron guns are attractive for delivery of beams at a high bunch repetition rate with a high accelerating field. An SRF gun is the most suitable injector for the high-energy upgrade of the Linac Coherent Light Source (LCLS-II-HE), which will produce high-energy Xrays at high repetition rate. An SRF gun is being developed for LCLS-II-HE as a collaborative effort by FRIB, HZDR, ANL, and SLAC. The cavity operating frequency is 185.7 MHz, and the target accelerating field at the photocathode is 30 MV/m. The photocathode is replaceable. The cathode is held by a fixture ('cathode stalk') that is designed for thermal isolation and particle-free cathode exchange. The stalk must allow for precise alignment of the cathode position, cryogenic or room-temperature cathode operating temperature, and DC bias to inhibit multipacting. We are planning a test of the stalk to confirm that the design meets the requirements for RF power dissipation and biasing. In this presentation, we will describe the cathode stalk design and RF/DC stalk test plan.

  • Open Access Logo Poster
    North American Particle Accelerator Conference 2022 (NAPAC'22), 07.-12.08.2022, Albuquerque, New Mexico, USA
    DOI: 10.18429/JACoW-NAPAC2022-MOPA87
    ISSN: 2226-0366
  • Open Access Logo Contribution to proceedings
    North American Particle Accelerator Conference 2022 (NAPAC'22), 07.-12.08.2022, Albuquerque, New Mexico, USA
    Proceedings of North American Particle Accelerator Conference 2022: JACoW, 978-3-95450-232-5
    DOI: 10.18429/JACoW-NAPAC2022-MOPA87
    ISSN: 2226-0366

Permalink: https://www.hzdr.de/publications/Publ-35563
Publ.-Id: 35563


Robust spin injection via thermal magnon pumping in antiferromagnet/ferromagnet hybrid systems

Rodriguez, R.; Regmi, S.; Zhang, H.; Yuan, W.; Makushko, P.; Montoya, E. A.; Veremchuk, I.; Hübner, R.; Makarov, D.; Shi, J.; Cheng, R.; Barsukov, I.

Robust spin injection and detection in antiferromagnetic thin films is a prerequisite for the exploration
of antiferromagnetic spin dynamics and the development of nanoscale antiferromagnet-based spintronic applications.
Previous studies have shown spin injection and detection in antiferromagnet/nonmagnetic metal
bilayers; however, spin injection in these systems has been found effective at cryogenic temperatures only.
Here, we experimentally demonstrate sizable interfacial spin transport in a hybrid antiferromagnet/ferromagnet
system, consisting of Cr2O3 and permalloy, which remains robust up to the room temperature. We examine our
experimental data within a spin diffusion model and find evidence for the important role of interfacial magnon
pumping in the signal generation. The results bridge spin-orbitronic phenomena of ferromagnetic metals with
antiferromagnetic spintronics and demonstrate an advancement toward antiferromagnetic spin-torque devices.

Keywords: antiferromagnetic spintronics; Cr2O3 thin films; spin injection

Related publications

Permalink: https://www.hzdr.de/publications/Publ-35561
Publ.-Id: 35561


Data publication: Longitudinal and multimodal radiomics models for head-and-neck cancer outcome prediction

Starke, S.; Zwanenburg, A.; Leger, K.; Zöphel, K.; Kotzerke, J.; Krause, M.; Baumann, M.; Troost, E. G. C.; Löck, S.

We include the input data, analysis scripts, analysis results and scripts to create the visualizations and plots used in the manuscript and supplement to our article "Longitudinal and multimodal radiomics models for head-and-neck cancer outcome prediction".

Keywords: radiomics; head-and-neck cancer; loco-regional control; survival analysis; computed tomography; positron emission tomography; cox proportional hazards; longitudinal imaging

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Permalink: https://www.hzdr.de/publications/Publ-35560
Publ.-Id: 35560


Data for: The influence of sedimentary heterogeneity on the diffusion of radionuclides in the sandy facies of Opalinus Clay at the field scale

Chen, C.; Yuan, T.; Lu, R.; Fischer, C.; Kolditz, O.; Shao, H.

Radionuclide migration in clay-rich formations is typically dominated by diffusion considering the low permeability of these formations. An accurate estimation of radionuclide migration in host rocks using numerical tools plays a key role in the safety assessment of disposal concepts for nuclear waste. In the sandy facies of the Opalinus Clay (SF-OPA), the spatial variability of the pore space network and compositional heterogeneity at the pore scale (nm to µm) cause heterogeneous diffusion at the core scale (cm to dm). Such heterogeneous diffusion patterns affect the migration of radionuclides in various sedimentary layers even above the core scale (m). In this work, we study the heterogeneous diffusion of cations based on a two-dimensional (2D) structural model at the m-scale. As key parameters for the diffusive transport calculation, the effective diffusion coefficients in different sedimentary layers are quantified based on our previous developed up-scaling workflow from pore- to core-scale simulation combined with the multi-scale digital rock models. The heterogeneous effective diffusivities are then implemented into the large-scale structural model for diffusive transport simulation using the FEM-based OpenGeoSys-6 simulator. The sensitivity analysis focuses on the effects of the SF-OPA bedding angle and the effect of different layer-succession layout with different canister emplacement on the spatio-temporal evolution of radionuclide diffusion front line. Results show that the moving distance of the diffusion front is farther away from the canister center, along the direction with the neighboring layer having lower diffusion coefficient within the total simulation time of 2000 years. When the bedding angle increases, the diffusion front moves farther in in vertical upward direction direction, which has less retardation effect for the radionuclide from the ground surface point. For different layer-succession layout with different canister emplacement, the smallest migration distance of the diffusion front line is 1.65 m. Within 2000 years, for the conceptual model 2B that the canister is emplaced in the layer with the highest diffusivity coefficient, the diffusion front can migrate 0.19 m farther along vertical downward direction due to the influence of the neighboring layer. The numerical results provide insight into the effects of rocks heterogeneity on diffusion of radionuclides, contributing to enhanced long-term predictability of radionuclide migration in SF-OPA as potential host rock for a deep geological repository.

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Permalink: https://www.hzdr.de/publications/Publ-35558
Publ.-Id: 35558


The influence of sedimentary heterogeneity on the diffusion of radionuclides in the sandy facies of Opalinus Clay at the field scale

Chen, C.; Yuan, T.; Lu, R.; Fischer, C.; Kolditz, O.; Shao, H.

Radionuclide migration in clay-rich formations is typically dominated by diffusion considering the low permeability of these formations. An accurate estimation of radionuclide migration in host rocks using numerical tools plays a key role in the safety assessment of disposal concepts for nuclear waste. In the sandy facies of the Opalinus Clay (SF-OPA), the spatial variability of the pore space network and compositional heterogeneity at the pore scale (nm to µm) cause heterogeneous diffusion at the core scale (cm to dm). Such heterogeneous diffusion patterns affect the migration of radionuclides in various sedimentary layers even above the core scale (m). In this work, we study the heterogeneous diffusion of cations based on a two-dimensional (2D) structural model at the m-scale. As key parameters for the diffusive transport calculation, the effective diffusion coefficients in different sedimentary layers are quantified based on our previous developed up-scaling workflow from pore- to core-scale simulation combined with the multi-scale digital rock models. The heterogeneous effective diffusivities are then implemented into the large-scale structural model for diffusive transport simulation using the FEM-based OpenGeoSys-6 simulator. The sensitivity analysis focuses on the effects of the SF-OPA bedding angle and the effect of different layer-succession layout with different canister emplacement on the spatio-temporal evolution of radionuclide diffusion front line. Results show that the moving distance of the diffusion front is farther away from the canister center, along the direction with the neighboring layer having lower diffusion coefficient within the total simulation time of 2000 years. When the bedding angle increases, the diffusion front moves farther in in vertical upward direction direction, which has less retardation effect for the radionuclide from the ground surface point. For different layer-succession layout with different canister emplacement, the smallest migration distance of the diffusion front line is 1.65 m. Within 2000 years, for the conceptual model 2B that the canister is emplaced in the layer with the highest diffusivity coefficient, the diffusion front can migrate 0.19 m farther along vertical downward direction due to the influence of the neighboring layer. The numerical results provide insight into the effects of rocks heterogeneity on diffusion of radionuclides, contributing to enhanced long-term predictability of radionuclide migration in SF-OPA as potential host rock for a deep geological repository.

Permalink: https://www.hzdr.de/publications/Publ-35556
Publ.-Id: 35556


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

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

Froth flow is of central importance for mineral processing by froth flotation. In industrial-scale
flotation plants, the recovery of solid mineral particles [Neethling, 2002] and liquid from the overflowing froth [Stevenson, 2003] is monitored by optical observation and, therefore, limited to the
froth’s free surface. This lab-scale experimental work investigates the flow behaviour of an aqueous foam at a horizontal overflow in combined optical and X-ray radiographic measurements.
Simultaneously, the foam’s liquid fraction was determined by measuring the electrical conductivity between electrode pairs. The optical measurements, performed both through a transparent wall
and at the free surface of the overflowing foam, captured light reflexions on the foam bubbles,
which were analysed by adapting particle image velocimetry algorithms. While the opacity of the
foam limits optical measurements to the surface-near bubbles, our approach of X-ray particle
tracking velocimetry (X-PTV) [Lappan, 2020] sheds light on the three-dimensional foam flow.
The customised tracer particles used in this work consisted of a 3D-printed tetrahedral polymer
structure with a total of four small metal beads at its corners. Owing to their shape and the lightweight material composite, the tracers adhered to the bubble-scale foam structure and were carried
by the foam. X-ray radiography visualises the motion paths of each tracer’s metal beads, representing the local streamlines of the foam flow. Further, the X-ray radiographs map the foam’s
liquid fraction distribution, thus extending the local measurement of the liquid fraction by means
of the electrode pairs. X-PTV reveals comparatively high flow velocities of the three-dimensional
foam flow, in particular near the overflow, whereas the optical measurements are subjected to wall
or surface effects, yielding lower flow velocities. However, X-PTV with customised foam flow
tracers comes to its limit in unstable foams at high liquid fraction and high flow velocity.

  • Lecture (Conference)
    EUFOAM, 03.-06.07.2022, Krakow, Poland

Permalink: https://www.hzdr.de/publications/Publ-35551
Publ.-Id: 35551


Neutron radiography of foam and froth.

Heitkam, S.; Skrypnik, A.; Lappan, T.; Trtik, P.; Eckert, K.

Neutron radiography is a useful tool for researching opaque multi phase flow such as foam and froth.

  • Lecture (Conference)
    RFC Upscaling Symposium, 04.-07.10.2022, Newcastle, Australia

Permalink: https://www.hzdr.de/publications/Publ-35548
Publ.-Id: 35548


Characterizing foam and froth with ultrasound reflectometry.

Knüpfer, L.; Emmerich, H.; Büttner, L.; Czarske, J.; Heitkam, S.

Der Einsatz moderner Meßtechnik kann einen wesentlichen Beitrag für den ressourceneffizienten Betrieb von Anlagen für die Schaumflotation leisten. Insbesondere die Kenntnis der
Stoffzusammensetzung des überströmenden Schaums kann hilfreich für die optimierte Echtzeit-Steuerung des Flotationsprozesses sein. Aufgrund der komplexen und lichtundurchlässigen Struktur der Schaumphase existieren zum heutigen Zeitpunkt allerdings nur wenige Möglichkeiten die Schaumzusammensetzung in Echtzeit und im Volumen zu bestimmen. Zusätzliche Anforderungen an die Robustheit des Maßsystems entstehen aus den rauhen Umgebungsbedingungen in industriellen Anwendungen.

  • Lecture (Conference)
    Tagung Aufbereitung und Recycling, 10.-11.11.2022, Freiberg, Germany

Permalink: https://www.hzdr.de/publications/Publ-35547
Publ.-Id: 35547


Optical Measurement of the stress and flow profile of foams in an idealized deglutition

Heitkam, S.; Gerstenberg, C.; Skrypnik, A.; Morelle, E.; McHardy, C.; Rauh, C.

Various physicochemical properties play a decisive role in the evaluation of foods, influencing
taste, odor, texture and mouthfeel when the food is distorted. Therefore, rheological investiga-
tions of foods are used in product development to specifically improve the texture or mouthfeel
of a product. Since mouthfeel describes the physical interaction between the food and various
haptic sensors in the mouth during the chewing and swallowing process, it is advantageous to
perform rheological measurements in geometries and under conditions that reflect the flow
conditions present in the mouth. Up to now, such investigations have been limited primarily to
viscous or lumpy foodstuffs. Here, foam, as a multiphase system consisting of a (highly) vis-
cous liquid and dispersed gas, exhibits complex rheological behavior due to its compressibility.
In addition, the foam undergoes partial destruction of its structure during the swallowing pro-
cess, which can change its rheological properties over time.
For the imaging of the swallowing process, an experimental setup was developed consisting
of a two-dimensional replica of the palate and a movable tongue based on dental impressions.
Foam with different properties such as the mean bubble size and the liquid content or the
degree of polydispersity can be generated. Furthermore, two tongue geometries with different
roughness are available. The flow as well as the deformation of the foam is evaluated by optical
methods such as PIV and particle tracking. The resulting velocity, shear rate and (wall) shear
stress distributions can provide information about the haptic perception in the mouth during the
swallowing process.

  • Contribution to proceedings
    Fachtagung “Experimentelle Strömungsmechanik", 06.-08.09.2022, Ilmenau, Germany
    ISSN: 978-3-9816764-8-8

Permalink: https://www.hzdr.de/publications/Publ-35546
Publ.-Id: 35546


Rsn‐2‐mediated directed foam enrichment of β‐lactamase

Krause, T.; Keshavarzi, B.; Dressel, J.; Heitkam, S.; Mb, A.

Today, the availability of methods for the activity-preserving and cost-efficient downstream processing of enzymes forms a major bottleneck to the use of these valuable tools in technical processes. A promising technology appears to be foam fractionation, which utilizes the adsorption of proteins at a gas–liquid interface. However, the employment of surfactants and the dependency of the applicability on individual properties of the target molecules are considerable drawbacks. Here, we demonstrate that a reversible fusion of the large, surface-active protein Ranaspumin-2 (Rsn-2) to a β-lactamase (Bla) enabled both surfactant-free formation of a stable foam and directed enrichment of the enzyme by the foaming. At the same time, Bla maintained 70% of its catalytic activity, which was in stark contrast to the enzyme without fusion to Rsn-2. Rsn-2 predominantly mediated adsorption. Comparable results were obtained after fusion to the structurally more complex penicillin G acylase (PGA) as the target enzyme. The results indicate that using a surface-active protein as a fusion tag might be the clue to the establishment of foam fractionation as a general method for enzyme downstream processing.

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Permalink: https://www.hzdr.de/publications/Publ-35544
Publ.-Id: 35544


Investigating Pore‐Opening of Hydrogel Foams at the Scale of Freestanding Thin Films

Sébastien, A.; Mayur, P.; Leandro, J.; Aurélie, H.-F.; Heitkam, S.; Wiebke, D.

Controlling the pore connectivity of polymer foams is key for most of their applications, ranging from liquid uptake, mechanics, and acoustic/thermal insulation to tissue engineering. Despite their importance, the scientific phenomena governing the pore-opening processes remain poorly understood, requiring tedious trial-and-error procedures for property optimization. This lack of understanding is partly explained by the high complexity of the different interrelated, multiscale processes which take place as the foam transforms from an initially fluid foam into a solid foam. To progress in this field, this work takes inspiration from long-standing research on liquid foams and thin films to develop model experiments in a microfluidic “Thin Film Pressure Balance.” These experiments allow the investigation of isolated thin films under well-controlled environmental conditions reproducing those arising within a foam undergoing cross-linking and drying. Using the example of alginate hydrogel films, the evolution of isolated thin films undergoing gelation and drying is correlated with the evolution of the rheological properties of the same alginate solution in bulk. The overall approach is introduced and a first set of results is presented to propose a starting point for the phenomenological description of the different types of pore-opening processes and the classification of the resulting pore-opening types.

Permalink: https://www.hzdr.de/publications/Publ-35543
Publ.-Id: 35543


Activation calculations of selected RPV internal components for optimal decommissioning of nuclear power plants

Rachamin, R.; Konheiser, J.; Seidl, M.

In this study, the specific activities of selected RPV components’ segments (such as the RPV, core barrel, etc.) of a German PWR were calculated with a novel method based on the combined use of two Monte-Carlo codes, MCNP6.2 and FLUKA2021. In the first step, the MCNP6.2 code was used to calculate the neutron fluence rate characteristics (spectrum, distribution, and current entering the segment surfaces) in the studied segment using a 3D detailed reactor model. The neutron fluence rate prediction capability of the MCNP6.2 model has been validated via metal foil-activation measurements carried out in two German PWRs. The validation studies showed that the MCNP6.2 model is reliable and suitable for evaluating the neutron radiation field in the reactor for the ensuing activation calculations. In the second step, the FLUKA2021 code was used to calculate the specific activity distribution in the studied segment using a 3D exact model of the segment and complex source terms built based on the neutron fluence rate parameters calculated using the MCNP6.2 code. The results of the calculations were obtained with great accuracy and evidenced that the used method can serve as a powerful and non-destructive tool for the radiological characterization of the RPV and its internals.

Keywords: German PWR; Decommissioning; Neutron fluence; Activation; MCNP; FLUKA

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

Permalink: https://www.hzdr.de/publications/Publ-35542
Publ.-Id: 35542


Dosimetry for Decommissioning of Nuclear Power Plants

Rachamin, R.; Konheiser, J.; Barkleit, A.; Seidl, M.

In this study, a 3D detailed Monte-Carlo (MC) model of a German PWR was developed to calculate the neutron fluence characteristics within the ex-vessel components of the reactor. The neutron fluence prediction capability of the developed model was validated based on metal foil-activation measurements. Metal foil-activation measurement has been successfully used in reactor dosimetry for many years. It is an ideal method for collecting information on neutron fluence in an active reactor. This paper gives an overview of the MC model of the reactor and presents the foils activation measurement procedure. Then, the results of the MC simulations and the experimental measurements are presented and discussed.

Keywords: German PWR; Decommissioning; Neutron fluence; Activation; MCNP; Validation

  • Open Access Logo Contribution to proceedings
    14th International Conference on Radiation Shielding and 21st Topical Meeting of the Radiation Protection and Shielding Division (ICRS 14/RPSD 2022), 25.-29.09.2022, Seattle, USA
  • Open Access Logo Lecture (Conference)
    14th International Conference on Radiation Shielding and 21st Topical Meeting of the Radiation Protection and Shielding Division (ICRS 14/RPSD 2022), 25.-29.09.2022, Seattle, USA

Permalink: https://www.hzdr.de/publications/Publ-35541
Publ.-Id: 35541


Population Kinetics for Particle in Cell Simulations

Marre, B. E.; Hübl, A.; Bastrakov, S.; Bussmann, M.; Widera, R.; Schramm, U.; Cowan, T.; Kluge, T.

Population Kinetics for PIC

Standard atomic physics models in PIC simulation either neglect excited states, predict
atomic state population in post processing only, or assume quasi-thermal plasma conditions.

This is no longer sufficient for high-intensity short-pulse laser generated plasmas, due
to their non-equilibrium, transient and non-thermal plasma conditions, which are now becoming
accessible in XFEL experiments at HIBEF (EuropeanXFEL), SACLA (Japan) or at MEC (LCLS/SLAC).
To remedy this, we have developed a new extension for our ParticleInCell simulation
framework PIConGPU to allow us to model atomic population kinetics in situ in PIC-Simulations,
in transient plasmas and without assuming temperatures.
This extension is based on a reduced atomic state model, which is directly coupled to the
existing PIC-simulation and for which the atomic rate equation is solved explicitly in
time, depending on local interaction spectra and with feedback to the host simulation.
This allows us to model de-/excitation and ionization and of ions in transient plasma
conditions, as typically encountered in laser generated plasmas.
This new approach to atomic physics modeling will be very useful in plasma
emission prediction, plasma condition probing with XFELs and better understanding
of isochoric heating processes, since all of these rely on an accurate prediction of
atomic state populations inside transient plasmas.

Keywords: Atomic Population Kinetics; FLYonPIC; PIConGPU; PIC; Particle in Cell; Simulation; Atomic Physics

  • Lecture (Conference)
    Radiation Properties of Hot Dense Matter, 14.-18.11.2022, Santa Fe, New Mexico, United States of America

Permalink: https://www.hzdr.de/publications/Publ-35539
Publ.-Id: 35539


Response of a surfactant- and particle-laden bubble surface to asymmetric shear flow

Eftekhari, M.; Schwarzenberger, K.; Heitkam, S.; Javadi, A.; Eckert, K.

The shear stress of an axisymmetric flow field triggers a nonuniform distribution of adsorbed surfactants at the surface of a rising bubble. This creates a surface tension gradient that counteracts the viscous shear stress of the flow and thus reduces the mobility of the interface. However, in technological processes the flow field often is asymmetric, e.g. due to the vorticity in the flow. Under such conditions, the interface experiences an unbalanced shear stress that is not free of curl, i.e. it cannot be compensated by the redistribution of the surfactants at the interface (Vlahovska et al., 2009).
Here, we conduct model experiments with a bubble at the tip of a capillary placed in a defined asymmetric flow field, in the presence of surfactants and nanoparticles. Unlike classical surfactants, nanoparticles adsorb irreversibly at the bubble surface. Thus, a different interaction between the bulk flow and the interface is expected.
In this study, we show a direct experimental observation of the circulating flow at the interface under asymmetric shear stress (Eftekhari et al., 2021a,b). The results indicate that the interface remains mobile regardless of the surfactant concentration. Additionally, we show that the nanoparticle-laden interface adopts a solid-like state and resists the interfacial flow upon surface compression. Our results imply that the immobilization of the interface can be described by the ratio of the interfacial elasticity to the bulk viscous forces.

  • Lecture (Conference)
    AERC, 26.-28.04.2022, Seville, Spain

Permalink: https://www.hzdr.de/publications/Publ-35538
Publ.-Id: 35538


Induction of pulmonary HLA-G expression by SARS-CoV-2 infection

Seliger, B.; Jasinski-Bergner, S.; Masssa, C.; Müller, A.; Biehl, K.; Yang, B.; Bachmann, M.; Jonigk, D.; Eichhorn, P.; Hartmann, A.; Wickenhauser, C.; Bauer, M.

The non-classical human leukocyte antigen (HLA)-G exerts immune-suppressive properties modulating both NK and T cell responses. While it is physiologically expressed at the maternal–fetal interface and in immune-privileged organs, HLA-G expression is found in tumors and in virus-infected cells. So far, there exists little information about the role of HLA-G and its interplay with immune cells in biopsies, surgical specimen or autopsy tissues of lung, kidney and/or heart muscle from SARS-CoV-2-infected patients compared to control tissues. Heterogeneous, but higher HLA-G protein expression levels were detected in lung alveolar epithelial cells of SARS-CoV-2-infected patients compared to lung epithelial cells from influenza-infected patients, but not in other organs or lung epithelia from non-viral-infected patients, which was not accompanied by high levels of SARS-CoV-2 nucleocapsid antigen and spike protein, but inversely correlated to the HLA-G-specific miRNA expression. High HLA-G expression levels not only in SARS-CoV-2-, but also in influenza-infected lung tissues were associated with a high frequency of tissue-infiltrating immune cells, but low numbers of CD8+ cells and an altered expression of hyperactivation and exhaustion markers in the lung epithelia combined with changes in the spatial distribution of macrophages and T cells. Thus, our data provide evidence for an involvement of HLA-G and HLA-G-specific miRNAs in immune escape and as suitable therapeutic targets for the treatment of SARS-CoV-2 infections.

Keywords: HLA-G; Immune cell infiltration; Immune response; microRNA; SARS-CoV-2

Permalink: https://www.hzdr.de/publications/Publ-35535
Publ.-Id: 35535


Advanced thermal-hydraulic experiments and instrumentation for heavy liquid metal reactors

Pacio, J.; van Tichelen, K.; Eckert, S.; Wondrak, T.; Di Piazza, I.; Lorusso, P.; Tarantino, M.; Daubner, M.; Litfin, K.; Ariyoshi, G.; Obayashi, H.; Sasa, T.

Heavy-liquid metals (HLMs), such as lead and lead–bismuth eutectic (LBE), are proposed as primary coolants in accelerator driven systems and next-generation fast reactors. In Europe, the reference systems using HLMs are MYRRHA (LBE) and ALFRED (lead). Extensive R&D programs have been established for supporting their detailed design and safety assessment, including thermal–hydraulic experiments at representative operating conditions in an HLM environment. These experiments aim both at a design verification and at the validation of numerical models, which allow an extrapolation of the results. Advanced instrumentation, capable of sustaining high temperatures and corrosion, is necessary for accurate measurements, often in compact geometries. This article presents an overview of recent experiences and ongoing activities on pool-type and loop-type HLM experiments. Pool tests include the measurement of forced- and natural-circulation flow patterns in several scenarios representative of nominal and decay heat removal conditions. Loop tests are focused on the evaluation of specific components, like mockups of the fuel assembly, control rod and heat exchangers. They involve the measurement of global variables, such as flow rate and pressure difference, and local quantities like temperature, velocity and vibrations. In addition to traditional techniques, other instrumentation based on optical fibers, ultrasonic and electromagnetic methods are discussed.

Keywords: liquid metal; experiment; instrumentation

Permalink: https://www.hzdr.de/publications/Publ-35532
Publ.-Id: 35532


Nano- and Flexomagnetism in Magnetoelectric Cr2O3 Thin-Film Antiferromagnets

Makarov, D.

In this presentation, we will review our recent activities on thin films and bulk of Cr2O3 for energy efficient memory devices and antiferromagnetic spintronic applications. The newly discovered flexomagnetic effect in thin films of Cr2O3 will be presented as well.
[1] Nature Physics 17, 574 (2021).
[2] Nature Comm. 13, 6745 (2022).
[3] Small 18, 2201228 (2022).
[4] ACS Appl. Electron. Mater. 4, 2943 (2022).

Keywords: antiferromagnetic spintronics; magnetic thin films; Cr2O3

Related publications

  • Lecture (others) (Online presentation)
    Lu Jiaxi International Team Annual Meeting, 02.12.2022, Ningbo, China

Permalink: https://www.hzdr.de/publications/Publ-35530
Publ.-Id: 35530


Curvilinear micromagnetism: from fundamentals to applications

Makarov, D.

Extending 2D structures into 3D space has become a general trend in multiple disciplines, including electronics, photonics, plasmonics, superconductivity and magnetism [1,2]. This approach provides means to modify conventional or to launch novel functionalities by tailoring curvature and 3D shape of magnetic thin films [3] and nanowires [4]. In this talk, we will address fundamentals of curvature-induced effects and discuss experimental realisations of geometrically curved low-dimensional architectures and their characterization, which among others resulted in the experimental confirmation of the exchange-driven chiral effects [5]. Geometrically curved magnetic thin films are interesting not only fundamentally. They are the key component of mechanically flexible magnetic field sensors. We will briefly outline activities on shapeable magnetoelectronics [6,7], which includes flexible, stretchable and printable magnetic field sensors for the realisation of human-machine interfaces [8,9], interactive electronics for virtual [10] and augmented [11] reality applications and soft robotics [12] to mention just a few. Very recently, self-healable magnetic field sensors for interactive printed electronics were reported [13]. The presence of the geometrical curvature in a magnetic thin film influences pinning of magnetic domain walls and in this respect it affects the sensitivity of mechanically flexible magnetic field sensors. This is an intimate link between the fundamental topic of curvilinear magnetism and application-oriented activities on shapeable magnetoelectronics. This link will be discussed in the presentation as well.

[1] P. Gentile et al., Electronic materials with nanoscale curved geometries. Nature Electronics (Review) 5, 551 (2022).
[2] D. Makarov et al., Curvilinear micromagnetism: from fundamentals to applications. Springer Nature Switzerland (2022). https://link.springer.com/book/10.1007/978-3-031-09086-8
[3] D. Makarov et al., New Dimension in Magnetism and Superconductivity: 3D and Curvilinear Nanoarchitectures. Advanced Materials (Review) 34, 2101758 (2022).
[4] D. Sheka et al., Fundamentals of Curvilinear Ferromagnetism: Statics and Dynamics of Geometrically Curved Wires and Narrow Ribbons. Small (Review) 18, 2105219 (2022).
[5] O. Volkov et al., Experimental observation of exchange-driven chiral effects in curvilinear magnetism. Physical Review Letters 123, 077201 (2019).
[6] D. Makarov et al., Shapeable Magnetoelectronics. Appl. Phys. Rev. (Review) 3, 011101 (2016).
[7] G. S. Canon Bermudez et al., Magnetosensitive e-skins for interactive devices. Advanced Functional Materials (Review) 31, 2007788 (2021).
[8] P. Makushko et al., Flexible Magnetoreceptor with Tunable Intrinsic Logic for On-Skin Skin Touchless Human-Machine Interfaces. Advanced Functional Materials 31, 2101089 (2021).
[9] J. Ge et al., A bimodal soft electronic skin for tactile and touchless interaction in real time. Nature Communications 10, 4405 (2019).
[10] G. S. Canon Bermudez et al., Electronic-skin compasses for geomagnetic field driven artificial magnetoception and interactive electronics. Nature Electronics 1, 589 (2018).
[11] G. S. Canon Bermudez et al., Magnetosensitive e-skins with directional perception for augmented reality. Science Advances 4, eaao2623 (2018).
[12] M. Ha et al., Reconfigurable Magnetic Origami Actuators with On-Board Sensing for Guided Assembly. Advanced Materials 33, 2008751 (2021).
[13] R. Xu et al., Self-healable printed magnetic field sensors using alternating magnetic fields. Nature Communications 13, 6587 (2022).

Keywords: flexible magnetic field sensors; printable magnetic field sensors; curved magnetic thin films

Related publications

  • Lecture (others)
    Seminar at the Northeastern University, Electrical and Computer Engineering, 28.11.2022, Boston, USA

Permalink: https://www.hzdr.de/publications/Publ-35528
Publ.-Id: 35528


Neutron scattering methods

Bergner, F.

This lecture is about neutron scattering methods and their applications in the field of nuclear material science.

Keywords: Small-angle neutron scattering; Diffuse neutron scattering; Nuclear materials

  • Lecture (others)
    European School on Nuclear Materials Science, 07.-11.11.2022, Institut d'Etudes Scientifiques (IESC) Cargèse, France

Permalink: https://www.hzdr.de/publications/Publ-35523
Publ.-Id: 35523


X-ray and electron diffraction methods

Bergner, F.

This lecture is about X-ray and electron diffraction methods and their application in the field of nuclear material science

Keywords: X-ray diffraction; Electron diffraction; Nuclear materials

  • Lecture (others)
    European School on Nuclear Materials Science, 07.-11.11.2022, Institut d'Etudes Scientifiques (IESC) Cargèse, France

Permalink: https://www.hzdr.de/publications/Publ-35522
Publ.-Id: 35522


Study on kinetics and mechanism of Re(VII) ion adsorption and desorption using commercially available activated carbon and solutions containing Se(VI) as an impurity

Kołczyk-Siedlecka, K.; Socha, R. P.; Yang, X.; Eckert, K.; Wojnicki, M.

This paper presents the potential use of carbon sorbents in recovering rhenium(VII) from highly diluted electrolytes. Tests were performed using synthetic solutions containing selenium(VI) as an impurity. Adsorption of Re(VII) is selective with respect to selenium(VI). Activated carbon is a suitable sorbent for rhenium recovery because unlike ion-exchange resins, it has high chemical resistance and osmotic-shock resistance. The results show that the sorption mechanism is complex. Two follow-up processes occurred—physical adsorption and the reduction of Re(VII) to Re(VI). The processes were strongly influenced by the temperature. The lower the temperature, the higher the process efficiency. The observed sorption capacity was as high as 7.6 mg/g at 298 K and decreased as the temperature increased. The adsorption was a mixed-control process. Increasing the temperature altered the rate-limiting process. The activation parameters were determined using rate constant (k) and Arrhenius equation. In the first step, the activation energy was approximately 0 kJ mol-1. In the second step, the activation energy for k2,obs and k3,obs was determined as 57.3 kJ mol-1. The pre-exponential factors were calculated; their value was 2.98 × 107 min-1. For k1,obs, the activation energy was nearly 0 kJ mol-1.

Keywords: Rhenium(VII) adsorption; selenium(VI) adsorption; chemical reduction; activated carbon; kinetic studies; selenium ions

Permalink: https://www.hzdr.de/publications/Publ-35514
Publ.-Id: 35514


Molecular Dynamics Simulation on Bubble Related Issues

Ding, W.

Activities introduction of Molecular Dynamics simulation on bubble related issues in FWDF, HZDR.

Keywords: Molecular Dynamics; Bubble

  • Lecture (others)
    ECCM Kick off meeting, 27.-28.10.2022, TU Twent, Niederland

Permalink: https://www.hzdr.de/publications/Publ-35512
Publ.-Id: 35512


Nanobending of the microscopic liquid-gas interface on the solid surface and its potential impact on nanobubbles

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

Young contact angle is widely applied to evaluate liquid wetting phenomena on solid surfaces. For example, it gives a truncated-spherical shape prediction of a droplet/bubble profile through the Young-Laplace equation. However, recent measurements have shown the deviation of a microscopic droplet profile from the spherical shape, indicating that the conventional Young contact angle as the boundary condition is insufficient to describe the microscopic liquid wetting phenomena which play a critical role when nanobubbles on the wall. Here, we reveal a liquid-gas interface nano-bending, which is caused by the nonlinear coupling between the effects of the microscopic interface geometry and solid-liquid interactions and is responsible for this deviation. Based on molecular dynamics simulations and mathematical modeling, we describe the structure of the nano-bending and explain the mechanism of the nonlinear-coupled effect. We further apply our findings to illustrate the saddle-shaped profile in the vicinity near the contact region. The interface nano-bending, rather than the Young contact angle, acts as the boundary at the contact line and dictates the liquid wetting system. In this way, we succeed in accurately predicting the microlayer profile (µm thickness liquid film beneath a nucleation bubble) captured by different experiments. These findings not only provide insight into recent nano-scale droplet- and bubble-related wetting phenomena, but are also helpful for surface engineering concerning nano-scale wetting control.

Keywords: Nano Bending; Nano Bubble; nonlinear coupled effect

  • Poster
    Nanobubble, 19.-21.09.2022, Magdeburg, Germany

Permalink: https://www.hzdr.de/publications/Publ-35511
Publ.-Id: 35511


The effect of the microscopic liquid film interface on the heat transfer in multiphase dynamics

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

Microlayer plays a critical role in the bubble dynamics and heat transfer in nucleate boiling. Yet, an accurate description of the microlayer has been a challenge for decades. In this work, we investigate the microlayer profile in the inertia-controlled bubble growth stage by using molecular simulations and mathematical modeling. A multiscale microlayer model was established through the disjoining pressure method and lubrication theory. Our model succeeds in accurately describing the microlayer profile captured by different experiments for the first time in decades. We reveal that the nonlinear coupling between microscopic liquid/vapor interface geometry and surface energy near the surface has a dominant effect on the overall microlayer profile. An interface nano-bending caused by the coupling acts as a three-dimensional boundary for the liquid wetting system and governs the wetting behavior. These findings provide insight into the understanding of heat transfer in nucleate boiling.

Keywords: Microlayer; Bubble; Molecular force; mutual effect; nano bending

  • Poster
    Annual Meeting on Reaction Engineering and ProcessNet Subject Division Heat and Mass Transfer 2022, 18.-20.07.2022, Würzburg, Germany

Permalink: https://www.hzdr.de/publications/Publ-35510
Publ.-Id: 35510


Introduction to Density Functional Theory

Cangi, A.

A formal introduction to density functional theory.

Keywords: Density Functional Theory

  • Invited lecture (Conferences) (Online presentation)
    Forschungsseminar "Vielteilchentheorie", Christian-Albrechts-Universität zu Kiel, 25.10.2022-14.02.2023, Kiel, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-35509
Publ.-Id: 35509


Recovery of valuable elements from tailings dumps accompanied by environmental remediation – the pilot plant project “ReMiningPlus”

Pinka, J.; Haubrich, F.; Werner, A.; Büttner, P.; Meißner, S.; Puschmann, R.; Pretzsch, E.

Flotation tailings from a former lead-zinc mine near Freiberg (Germany) consist of fine-grained quartz, feldspar, mica and the sulfide minerals pyrite, galena and sphalerite, which are not recovered by flotation. Sphalerite contains significant amounts of indium (up to 0.38 % (w/w)) in addition to iron, copper and cadmium, resulting in assumed average indium content of 30 mg/kg in the tailings. The presentation shows the development of biohydrometallurgical recovery of indium from laboratory to pilot scale. In a 2 m³ bioreactor, maximum zinc and indium leaching rates of 80 % were obtained at a pulp density of 25%. For the recovery of indium from the PLS (pregnant leaching solution), a stepwise precipitation process is being developed consisting of a combined iron/indium precipitation and a subsequent treatment of the indium precipitate product. A new project has been started in which a modular plant for the utilization of valuable materials from these sulfide tailings and their environmentally friendly remediation is being set up directly at the tailings site. Combining resource technology to utilize valuable elements (indium and zinc) from tailings and environmental technology to eliminate harmful substances (arsenic and cadmium) with the use of inert components (e.g. as building material) represents a win-win situation. After its completion, the modular plant consists of three parts: the leaching, the recyclables and the environmental modules. Results and findings of the project will be processed for environmental education in schools and used for the development of a web application (app) that can be used to content for integration into existing tourism concepts. Through the implementation of the aforementioned goals, the project provides a decisive contribution to the structural change in the region, as it a concept for linking rehabilitation and secondary raw material extraction and a possible economic and touristic reuse.

Keywords: Bioleaching; Circular Economy; Indium; Tailings; Zinc

  • Contribution to proceedings
    The 24th International Biohydrometallurgy Symposium, 20.-23.11.2022, Perth, Australia
    Biotechnology for resource sustainability and circular economy. Book of Abstracts., Australia: CSIRO, 101-101

Permalink: https://www.hzdr.de/publications/Publ-35508
Publ.-Id: 35508


Editorial: Experimental and simulation research on nuclear reactor thermal-hydraulics

Zhang, L.; Pan, L.-M.; Wang, J.; Ding, W.

The researches on nuclear reactor thermal-hydraulics have achieved outstanding progresses in the past decades. In recent years, basic research on multiphase flow dynamics and corresponding measurement technology, as well as preliminary research on Gen IV reactors based on experiments and simulations are attracting more and more attention. However, the inside complicated physics and outside extreme conditions will also bring risks and challenges to the development of nuclear industry.

Keywords: nuclear reactor; thermal; hydraulics; experiments; simulation

Permalink: https://www.hzdr.de/publications/Publ-35507
Publ.-Id: 35507


Preparatory simulations and experiments for the DRESDYN precession dynamo

Giesecke, A.; Pizzi, F.; Wilbert, M.; Grauer, R.; Kumar, V.; Anders, S.; Ratajczak, M.; Gundrum, T.; Vogt, T.; Stefani, F.

Precession represents a possibility to power the early geodynamo or the ancient lunar dynamo.
Precession driven dynamo action was found in simulations in various geometries (sph/cyl/cube).
related experiments by R. Gans yield an amplification of an external field by a factor of three.

Keywords: Dynamo; DRESDYN

  • Poster
    Fluid flow and magnetic field generation in fluids and plasmas - theory and laboratory experiments, 16.-21.10.2022, Leeds, Great Britain

Permalink: https://www.hzdr.de/publications/Publ-35505
Publ.-Id: 35505


Boundary conditions in MRI and Dynamo Experiments

Ji, H.; Giesecke, A.

There is no abtract.

Keywords: Dynamo; DRESDYN; MRI; Boundary Conditions

  • Invited lecture (Conferences)
    Frontiers in dynamo theory: from the Earth to the stars, 27.10.2022, Cambridge, Great Britain

Permalink: https://www.hzdr.de/publications/Publ-35504
Publ.-Id: 35504


The Fluid Flow in a Precessing Cylinder

Giesecke, A.; Pizzi, F.; Anders, S.; Vogt, T.; Kumar, V.; Ratajczak, M.; Gundrum, T.; Stefani, F.

The planned liquid sodium facility DRESDYN (DREsden Sodium facility for DYNamo and thermohydraulic studies) is a new platform for a variety of liquid sodium experiments devoted to problems of geo- and astrophysical magnetohydrodynamics. Most ambitious experiment will be a large-scale precession driven dynamo experiment. The experiment is motivated by the idea of a precession-driven flow as a complementary energy source for the geodynamo (Malkus, Science 1968, 160, 3825) or the ancient lunar dynamo (Noir and Cebron 2013, JFM, 737, 412; Dwyer et al. 2011, Nature, 479, 7372; Weiss et al. 2014, Science 346, 1246753). Precessional forcing is of great interest from the experimental point of view, because it represents a natural mechanism which allows an efficient driving of conducting fluid flows on the laboratory scale without making use of propellers or pumps. Currently, we conduct preparative studies that involve numerical simulations and flow measurements at a downscaled model experiment filled with water. These studies aim at the design of the planned large scale experiment and provide parameter island where dynamo action is most likely.

Keywords: Dynamo; DRESDYN

  • Invited lecture (Conferences)
    Frontiers in dynamo theory: from the Earth to the stars, 12.10.2022, Cambridge, Great Britain

Permalink: https://www.hzdr.de/publications/Publ-35503
Publ.-Id: 35503


On the Growth Regimes of Hydrogen Bubbles at Microelectrodes

Bashkatov, A.; Hossain, S. S.; Mutschke, G.; Yang, X.; Rox, H.; Weidinger, I. M.; Eckert, K.

The growth of single hydrogen bubbles at micro-electrodes is studied in an acidic electrolyte over a wide range of concentrations and cathodic potentials. New bubble growth regimes have been identified which differ in terms of whether the bubble evolution proceeds in the presence of a monotonic or oscillatory variation in the electric current and a carpet of microbubbles underneath the bubble. Key features such as the growth law of the bubble radius, the dynamics of the microbubble carpet, the onset time of the oscillations and the oscillation frequencies have been characterized as a function of the concentration and electric potential. Furthermore, the system's response to jumps in the cathodic potential has been studied. Based on the analysis of the forces involved and their scaling with the concentration, potential and electric current, a sound hypothesis is formulated regarding the mechanisms underlying the micro-bubble carpet and oscillations.

Keywords: hydrogen; bubble dynamics; water electrolysis; force balance; electric force; marangoni convection; bubble oscillations

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  • Secondary publication expected from 12.10.2023

Permalink: https://www.hzdr.de/publications/Publ-35502
Publ.-Id: 35502


Formation of In-Plane Semiconductor-Metal Contacts in 2D Platinum Telluride by Converting PtTe₂ to Pt₂Te₂

Lasek, K.; Li, J.; Ghorbani Asl, M.; Khatun, S.; Alanwoko, O.; Pathirage, V.; Krasheninnikov, A.; Batzill, M.

Monolayers of platinum tellurides are particularly interesting 2D materials because they exhibit phases with different stoichiometries and electronic properties. Specifically, PtTe₂ is a narrow gap semiconductor while Pt₂Te₂ is a metal. Here we show that the former can be transformed into the latter by reaction with vapor-deposited Pt atoms. Owing to low surface diffusion barriers of Pt ad-atoms, the transformation occurs by nucleating the Pt₂Te₂ phase within the PtTe₂ islands, so that a metal-semiconductor lateral junction is formed. Using scanning tunneling microscopy/spectroscopy, the electronic structure of this lateral junction is studied. A flat band structure is found with the Fermi-level of the metal aligning with the Fermi-level of the intrinsically p-doped PtTe₂ suggesting low contact resistance. This flat band is achieved by an interface dipole that accommodates the ~0.2 eV shift in the work functions of the two materials. First-principles calculations indicate that the origin of the interface dipole is the atomic scale charge redistributions at the heterojunction. The demonstrated compositional phase transformation of a 2D semiconductor into a 2D metal is a promising approach for making in-plane metal contacts that are required for efficient charge injection and is of particular interest for semiconductors with large spin-orbit coupling, like PtTe₂.

Keywords: lateral heterojunctions; two-dimensional materials; platinum Telluride; electronics

Related publications

Permalink: https://www.hzdr.de/publications/Publ-35498
Publ.-Id: 35498


Liquid Metal Batteries: Numerical Investigations on Fluid Flow and Mass Transfer

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

Charge transfer and mass transport are directly linked with operating batteries. In liquid metal batteries (LMBs) additional flow phenomena heavily influence the cell performance. Those have widely been investigate numerically as well as experimentally. But, concentration gradients due to mass transport were mostly neglected in previous research – especially in the electrolyte. Implementing the prevalent equations into the finite volume solver OpenFOAM and investigating mass transfer overpotentials in the electrolyte independently revealed that they can have a significant influence on the cell performance. So, the interplay between flow phenomena and electrochemical transport should be subject of future investigations.
Na||Zn batteries differ from the previously investigated “classical” LMBs, hence it is important to asses the possible flow phenomena and their area of occurrence.

  • Poster
    Liquid Metal Batteries, 15.-16.11.2022, Cambridge, Great Britain

Permalink: https://www.hzdr.de/publications/Publ-35495
Publ.-Id: 35495


Shell engineering in soft alginate-based capsules for culturing liver spheroids

Peng, X.; Janićijević, Ž.; Lemm, S.; Laube, M.; Pietzsch, J.; Bachmann, M.; Baraban, L.

We demonstrate the fluidics-based low-cost methodology to reproducibly generate the alginate and alginate-chitosan microcapsules and apply it to grow human hepatoma (HepG2) spheroids of different dimensions and geometries. Focusing specifically on the composition and thickness of the hydrogel shell, permeability of the microcapsules was selectively tuned. The diffusion of the selected benchmark molecules through the shell has been systematically investigated using both, experiments and simulations, which is essential to ensure efficient mass transfer and/or filtering of the biochemical species. Depending on available space, phenotypically different 3D cell assemblies have been observed inside the capsules, varying in the tightness of cell aggregations and their shapes. Metabolic activity of spheroids in microcapsules was confirmed by tracking the turnover of testosterone to androstenedione with chromatography studies in a metabolic assay. Because of the facile tuning of the shell thickness and permeability, we believe that our system is suitable for studying the formation of cancer spheroids and their functional interaction with the surrounding microenvironment.

Permalink: https://www.hzdr.de/publications/Publ-35494
Publ.-Id: 35494


Using ultrasound for characterizing overflowing froth

Knüpfer, L.; Emmerich, H.; Büttner, L.; Czarske, J.; Eckert, K.; Heitkam, S.

Flotation is a separation process in which hydrophobic particles inside a liquid bath
attach to uprising bubbles, which subsequently form a froth layer on the liquid
surface. This froth phase, which consist of foam with particles, has a large impact on
the transport of separated materials and therefore the overall process efficiency.
Despite the importance for process control, a notable lack of suitable techniques for
on-line characterization of the froth’s properties such as the liquid fraction or particle
content can be found. An potential approach to gain information on the different
phase fractions in froth is the application of low-frequency ultrasound measurement
techniques. In this contribution an overflowing froth containing varying mass fractions
of Quartz particles and liquid is analyzed using combined optical and ultrasonic
measurements. The measured intensity of the ultrasonic reflections sent from above
the froth’s surface correlate to the fraction of solids inside the froth (Figure 1).
Therefore it is shown, that current optical froth characterization techniques can be
improved by incorporating ultrasonic measurements, which can be seen as a first
step towards advanced process control in industrial flotation processes.

Keywords: froth; flotation; ultrasound

  • Poster
    4th International Symposium on Multiscale Multiphase Process Engineering (MMPE), 25.-28.09.2022, Berlin, Deutschland
  • Poster
    Tagung Aufbereitung und Recycling, 10.-11.11.2022, Freiberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-35489
Publ.-Id: 35489


A particle-center-averaged Euler-Euler model for bubbly flow simulations

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

An inconsistency exists in bubble force models used in the standard Euler-Euler simulations. The bubble force models are typically developed by assuming that the forces act on the bubbles' centers of mass. However, in the standard Euler-Euler model, each bubble force is a function of the local gas volume fraction because the phase-averaging method is used. This inconsistency can lead to gas over-concentration in the center or near the wall of a channel when the bubble diameter is larger than the computational cell size. Besides, a mesh-independent solution may not exist in such cases. In addition, the bubble dimension is not fully considered in the standard Euler-Euler model.
In the present study, a particle-center-averaging method is used to represent the bubble forces as forces that act on the bubbles' centers of mass. A particle-center-averaged Euler-Euler approach for bubbly flow simulations is developed by combining the particle-center-averaged Euler-Euler framework with a Gaussian convolution method. The convolution method is used to convert the phase-averaged and the particle-center-averaged quantities. The test results illustrate that the particle-center-averaging method alleviates the over-prediction of the gas volume fraction peak in the channel center and provides a mesh-independent solution. In the particle-center-averaged Euler-Euler model, the bubble dimension is fully considered and bubble deformation can be considered by using anisotropic diffusion in quantities conversion.

Keywords: CFD; bubbly flow; Euler-Euler

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

Permalink: https://www.hzdr.de/publications/Publ-35488
Publ.-Id: 35488


Future Liquid Metal Battery Projects at HZDR

Horstmann, G. M.; Weber, N.; Duczek, C.; Sarma, M.; Weier, T.

Since 2011, fluid dynamics research in liquid metal batteries has been pursued at HZDR, with multiple flow instabilities identified as critical for safe and efficient operation. This is still an ongoing process from which new research topics are constantly emerging. In the poster presentation, I will introduce two future research projects closely connected to liquid metal batteries: firstly, a new model experiment to study the metal pad roll instability, which is currently under preparation in the framework of a recently approved DFG project. Secondly, we are planning another project on the investigation of different solutal- and electrocapillary flow phenomena, hitherto widely disregarded in the context of liquid metal batteries.

  • Poster
    Liquid Metal Batteries, 15.-16.11.2022, Cambridge, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-35487
Publ.-Id: 35487


Theory on Tidally Forced Planetary Waves in the Tachocline of Solar-like Stars

Horstmann, G. M.; Mamatsashvili, G.; Giesecke, A.; Stefani, F.

We present a new shallow-water formulation of forced magnetohydrodynamic Ross-
by waves originating in the tachocline of solar-like stars. As a novelty to former descriptions,
we add an external tidal potential to the equations and further include a linear damping law,
allowing us to study wave motions driven by arbitrary tidal forces. The model is applied to the
specific case of our sun, where we consider the action of the tidally dominant planet Jupiter.
We present an explicit analytic solution to this problem, which we finally use to estimate
characteristic responding wave amplitudes.

  • Lecture (Conference)
    5th Dynamo Thinkshop, 26.-28.06.2022, Freiburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-35485
Publ.-Id: 35485


Magnetic properties of red diamonds produced by high-temperature electron irradiation

Barzola-Quiquia, J.; Osmic, E.; Lühmann, T.; Böhlmann, W.; Meijer, J.; Knolle, W.; Abel, B.

The magnetization of crystalline red diamond bulk samples were investigated in the temperature range between 2 K and 125 K and with the applied maximal magnetic field of ±7 T. The investigated diamond samples are of Type Ib with a nitrogen content less than 200 ppm. Diamonds without any treatment display a yellow color and were transformed to red color after irradiation with 10 MeV electrons at T = 900 °C, in vacuum, owing to the formation of nitrogen-vacancy centers. Field dependent magnetization m(H) measurements for temperatures T ≲ 10 K show unusual hysteresis loops, which we interpret as consequence of the superposition of coexisting superconducting and paramagnetic regions present in the sample. Temperature dependence of the magnetization m(T) measured in the zero field and field cooled modus shows a paramagnetic behavior accompanied with an irreversibility for T ≲ 13 K, while at higher temperatures shows a diamagnetic behavior which is similar to undoped diamond. Coexistence of superconductivity and paramagnetism is established because both phenomena exist in the same temperature range and fits done to the m(H) using an equation based upon Bean model, support our conclusion. Room temperature confocal photoluminescence measurements were done on both yellow and red diamond, showing that in the red diamond the amount of neutral NV° and negative charged nitrogen-vacancy centers NV° have been significantly created. The transformation process from yellow to red diamond has mainly caused the alteration of the superparamagnetic regions into paramagnetic, while the superconducting contribution of the sample was less affected, according to the parameters obtained after we fitted the field dependent magnetization results.

Permalink: https://www.hzdr.de/publications/Publ-35482
Publ.-Id: 35482


High-Pressure and High-Temperature Chemistry of Phosphorus and Nitrogen: Synthesis and Characterization of α- and γ‑P3N5

Ceppatelli, M.; Scelta, D.; Serrano-Ruiz, M.; Dziubek, K.; Izquierdo-Ruiz, F.; Manuel Recio, J.; Garbarino, G.; Svitlyk, V.; Mezouar, M.; Peruzzini, M.; Bini, R.

The direct chemical reactivity between phosphorus and nitrogen was induced under high-pressure and high-temperature conditions (9.1 GPa and 2000−2500 K), generated by a laser heated diamond anvil cell and studied by synchrotron X-ray diffraction, Raman spectroscopy, and DFT calculations. α-P3N5 and γ-P3N5 were identified as reaction products. The structural parameters and vibrational frequencies of γ-P3N5 were characterized as a function of pressure during room-temperature compression and decompression to ambient conditions, determining the equation of state of the material up to 32.6 GPa and providing insight about the lattice dynamics of the unit cell during compression, which essentially proceeds through the rotation of the PN5 square pyramids and the distortion of the PN4 tetrahedra. Although the identification of α-P3N5 demonstrates for the first time the direct synthesis of this compound from the elements, its detection in the outer regions of the laser-heated area suggests α-P3N5 as an intermediate step in the progressive nitridation of phosphorus toward the formation of γ-P3N5 with increasing coordination number of P by N from 4 to 5. No evidence of a higher pressure phase transition was observed, excluding the existence of predicted structures containing octahedrally hexacoordinated P atoms in the investigated pressure range.

Permalink: https://www.hzdr.de/publications/Publ-35481
Publ.-Id: 35481


Effect of Magnetic Impurities on Superconductivity in LaH10

Semenok, D. V.; Troyan, I. A.; Sadakov, A. V.; Zhou, D.; Galasso, M.; Kvashnin, A. G.; Ivanova, A. G.; Kruglov, I. A.; Bykov, A. A.; Terent'Ev, K. Y.; Cherepakhin, A. V.; Sobolevskiy, O. A.; Pervakov, K. S.; Seregin, A. Y.; Helm, T.; Förster, T.; Grockowiak, A. D.; Tozer, S. W.; Nakamoto, Y.; Shimizu, K.; Pudalov, V. M.; Lyubutin, I. S.; Oganov, A. R.

Polyhydrides are a novel class of superconducting materials with extremely high critical parameters, which is very promising for sensor applications.
On the other hand, a complete experimental study of the best so far known superconductor, lanthanum superhydride LaH10, encounters a serious complication because of the large upper critical magnetic field Hc2(0), exceeding 120–160 T. It is found that partial replacement of La atoms by magnetic Nd atoms results in significant suppression of superconductivity in LaH10: each at% of Nd causes a decrease in Tc by 10–11 K, helping to control the critical parameters of this compound. Strong pulsed magnetic fields up to 68 T are used to study the Hall effect, magnetoresistance, and the magnetic phase diagram of ternary metal polyhydrides for the first time. Surprisingly, (La,Nd)H10 demonstrates completely linear Hc2(T) ∝ |T – Tc|, which calls into question the applicability of the Werthamer–Helfand–Hohenberg model for polyhydrides. The suppression of superconductivity in LaH10 by magnetic Nd atoms and the robustness of Tc with respect to nonmagnetic impurities (e.g., Y, Al, C) under Anderson’s theorem gives new experimental evidence of the isotropic (s-wave) character of conventional electron–phonon pairing in lanthanum decahydride.

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Permalink: https://www.hzdr.de/publications/Publ-35480
Publ.-Id: 35480


Micrometer thick Sm-Co films for applications on flexible systems

Tzanis, A.; Koutsokostas, N.; Helm, T.; Kollia, C.; Speliotis, T.

In the industry 4.0 eco-system, flexible electronic devices bear a huge potential for a broad range of applications due to their diverse properties, such as high stretchability, biocompatibility, portability, light weight, and low costs. In this work, Cobalt-samarium permanent magnetic thin films on flexible polyimide substrate are studied. The influence of the sputter deposition pressure on the structural, morphological, and magnetic properties is analyzed. A method for growing flexible magnetic films is proposed by achieving a maximum coercivity of 13.86 kOe and an energy product of 16.9 MGOe. These results lay the foundations for the design and fabrication of flexible magnetic devices.

Permalink: https://www.hzdr.de/publications/Publ-35479
Publ.-Id: 35479


Static magnetic and ESR spectroscopic properties of the dimer-chain antiferromagnet BiCoPO5

Iakovleva, M.; Petersen, T.; Alfonsov, A.; Skourski, Y.; Grafe, H.-J.; Vavilova, E.; Nath, R.; Hozoi, L.; Kataev, V.

We report a comprehensive study of the static susceptibility, high-field magnetization and highfrequency/high-magnetic field electron spin resonance (HF-ESR) spectroscopy of polycrystalline samples of the bismuth cobalt oxyphosphate BiCoPO5. This compound features a peculiar spin system that can be considered as antiferromagnetic (AFM) chains built of pairs of ferromagnetically coupled Co spins and interconnected in all three spatial directions. It was previously shown that BiCoPO5 orders antiferromagnetically at TN ≈ 10 K and this order can be continuously suppressed by magnetic field towards the critical value μ0Hc ≈ 15 T. In our experiments we find strongly enhanced magnetic moments and spectroscopic g factors as compared to the expected spin-only values, suggesting a strong contribution of orbital magnetism for the Co2+ ions. This is quantitatively confirmed by ab initio quantum chemical calculations.Within the AFM ordered phase, we observe a distinct field-induced magnetic phase transition. Its critical field rises to ∼6 T at T << TN. The HF-ESR spectra recorded at T << TN are very rich comprising up to six resonance modes possibly of the multimagnonic nature that soften towards the critical region around 6 T. Interestingly, we find that the Co moments are not yet fully polarized at Hc which supports a theoretical proposal identifying Hc as the quantum critical point for the transition of the spin system in BiCoPO5 to the quantum disordered state at stronger fields.

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Permalink: https://www.hzdr.de/publications/Publ-35478
Publ.-Id: 35478


Nanoscale magnetic bubbles in Nd2Fe14B at room temperature

He, Y.; Helm, T.; Soldatov, I.; Schneider, S.; Pohl, D.; Srivastava, A. K.; Sharma, A. K.; Kroder, J.; Schnelle, W.; Schaefer, R.; Rellinghaus, B.; Fecher, G. H.; Parkin, S. S. P.; Felser, C.

The increasing demand for computer data storage with a higher recording density can be addressed by using smaller magnetic objects, such as bubble domains. Small bubbles predominantly require a strong saturation magnetization combined with a large magnetocrystalline anisotropy to resist self-demagnetization. These conditions are well satisfied for highly anisotropic materials. Here, we study the domain structure of thin Nd2Fe14B lamellae. Magnetic bubbles with a minimum diameter of 74 nm were observed at room temperature, approaching even the range of magnetic skyrmions. The stripe domain width and the bubble size are both thickness dependent. Furthermore, a kind of bubble was observed below the spin-reorientation transition temperature that combine bubbles with opposite helicity. In this paper, we reveal Nd2Fe14B to be a good candidate for a high-density magnetic bubble-based memory.

Permalink: https://www.hzdr.de/publications/Publ-35477
Publ.-Id: 35477


Deformed spin-1/2 square lattice in antiferromagnetic NaZnVOPO4(HPO4)

Guchhait, S.; Ambika, D. V.; Ging, Q.-P.; Uhlarz, M.; Furukawa, Y.; Tsirlin, A. A.; Nath, R.

We report the structural and magnetic properties of a new spin-1/2 antiferromagnet NaZnVOPO4(HPO4) studied via x-ray diffraction, magnetic susceptibility, high-field magnetization, specific heat, and 31P nuclear magnetic resonance (NMR) measurements, as well as density-functional band-structure calculations. While thermodynamic properties of this compound are well described by the J1-J2 square-lattice model, ab initio calculations suggest a significant deformation of the spin lattice. From fits to the magnetic susceptibility we determine the averaged nearest-neighbor and second-neighbor exchange couplings of J1 ≃ −1.3 K and J2 ≃ 5.6 K, respectively, resulting in the effective frustration ratio α = J2/J1 ≃ −4.3 that implies columnar antiferromagnetic order as the ground state. Experimental saturation field of 15.3 T is consistent with these estimates if 20 % spatial anisotropy in J1 is taken into account. Specific heat data signal the onset of a magnetic long-range order at TN ≃ 2.1 K, which is further supported by a sharp peak in the NMR spin-lattice relaxation rate. The NMR spectra mark the superposition of two P lines due to two nonequivalent P sites where the broad line with the strong hyperfine coupling and short T1 is identified as the P(1) site located within the magnetic planes, while the narrow line with the weak hyperfine coupling and long T1 is designated as the P(2) site located between the planes.

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Permalink: https://www.hzdr.de/publications/Publ-35476
Publ.-Id: 35476


Ce and Dy substitutions in Nd2Fe14B: Site-specific magnetic anisotropy from first principles

Boust, J.; Aubert, A.; Fayyazi, B.; Skokov, K. P.; Skourski, Y.; Gutfleisch, O.; Pourovskii, L. V.

A first-principles approach combining density-functional and dynamical mean-field theories in conjunction with a quasiatomic approximation for the strongly localized 4 f shell is applied to Nd2Fe14B-based hard magnets to evaluate crystal-field and exchange-field parameters at rare-earth sites and their corresponding single-ion contribution to the magnetic anisotropy. In pure Nd2Fe14B, our calculations reproduce the easy-cone to easy-axis transition; theoretical magnetization curves agree quantitatively with experiment. Our study reveals that the rare-earth single-ion anisotropy in the 2-14-1 structure is strongly site dependent, with the g rare-earth site exhibiting a larger value. In particular, we predict that increased f- and g-site occupancy of R = Ce and Dy, respectively, leads to an increase of the magnetic anisotropy of the corresponding (Nd, R)2Fe14B-substituted
compounds.

Permalink: https://www.hzdr.de/publications/Publ-35475
Publ.-Id: 35475


Martensitic fcc-hcp transformation pathway in solid krypton and xenon and its effect on their equations of state

Rosa, A. D.; Dewaele, A.; Garbarino, G.; Svitlyk, V.; Morard, G.; de Angelis, F.; Krstulovic, M.; Briggs, R.; Irifune, T.; Mathon, O.; Bouhifd, M. A.

The martensitic transformation is a fundamental physical phenomenon at the origin of important industrial applications. However, the underlying microscopic mechanism, which is of critical importance to explain the outstanding mechanical properties of martensitic materials, is still not fully understood. This is because for most martensitic materials the transformation is a fast process that makes in situ studies extremely challenging. Noble solids krypton and xenon undergo a progressive pressure-induced face-centered cubic (fcc) to hexagonal close-packed (hcp) martensitic transition with a very wide coexistence domain. Here, we took advantage of this unique feature to study the detailed transformation progress at the atomic level by employing in situ x-ray diffraction and absorption spectroscopy.We evidenced a four-stage pathway and suggest that the lattice mismatch between the fcc and hcp forms plays a key role in the generation of strain.We also determined precisely the effect of the transformation on the compression behavior of these materials.

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Permalink: https://www.hzdr.de/publications/Publ-35474
Publ.-Id: 35474


Data publication: Variability of radionuclide sorption efficiency on muscovite cleavage planes

Schabernack, J.; Faria Oliveira, A.; Heine, T.; Fischer, C.

Dataset of outputs produced by DFT and KMC simulation described in the associated paper.

KMC data:

  • Adsorption distribution (Ad_mov_01.pdb to Ad_mov_10.pdb)
  • Surface nanotopography (surface_1.pdb)
  • Statistic files for dissolution and adsorption (Ad_num.txt, Ad_Sites_Stat.txt, sites_stat_1.txt, diss_num.txt)
  • Input files (testmusc9_KMC_Mica_1_6.inp, EuAdsorption_2_0.inp)
  • Excel files for adsorption evaluation (Adsorption_Results_File), input energy calculation (EnergyParameterCalc) and site sorting (Site-INDL-Sorting)

DFT data:

  • Excel file adsorption energy barriers (Adsorption_Energy_Barrier)
  • Site adsorption energies (.cvs files)
  • Site adsorption trajectories (.xyz files)

Excel file for the estimation of the desorption factor

Keywords: Radionuclide Sorption; Kinetic Monte Carlo; Density Functional Theory; Muscovite; Europium

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Permalink: https://www.hzdr.de/publications/Publ-35469
Publ.-Id: 35469


Resolving surface chemical states of p-GaN:Cs photocathodes by XPS analysis

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

An x-ray photoelectron spectrometer (XPS) is used in the HZDR photocathode lab to understand the surface states of GaN photocathodes during its cleaning, cesium activation and degradation. The XPS probes the electronic structure of the p-doped GaN photocathode after each step of the preparation process. Using energies between 1200-0 eV the core levels and auger photoemission peaks of Ga, N, O, C and Cs are monitored.

Keywords: GaN photocathode; quantum efficiency; cesium activation; photocathode degradation; organic - cesium

Related publications

  • Open Access Logo Invited lecture (Conferences)
    EWPAA 2022: European workshop on photocathodes for particle accelerator applications, 20.-22.09.2022, Mailand, Italien

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Permalink: https://www.hzdr.de/publications/Publ-35467
Publ.-Id: 35467


Resolving surface chemical states of p-GaN:Cs photocathodes by XPS analysis

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

An x-ray photoelectron spectrometer (XPS) is used in the HZDR photocathode lab to understand the surface states of GaN photocathodes during its cleaning, cesium activation and degradation. The XPS probes the electronic structure of the p-doped GaN photocathode after each step of the preparation process. Using energies between 1200-0 eV the core levels and auger photoemission peaks of Ga, N, O, C and Cs are monitored.
In our experiments, p-GaN on sapphire samples were cleaned with 99 % ethanol in an ultrasonic bath, followed by a thermal cleaning in a vacuum with the intention to remove carbon and oxygen contaminations on the p-GaN surface. Although still some carbon remained on the surface, the p-GaN was successfully activated by the deposition of a thin layer of cesium. Quantum efficiencies (QE) of
3 - 9 % were achieved. XPS photoemission spectra show a shift towards higher binding energies for the photoemission peaks, which is caused by a new component, so-called organic – cesium.
During the storage under ultra – high vacuum, the GaN:Cs photocathodes were measured from time to time in the photocurrent and by XPS. We found a shift of 0.35 eV towards lower binding energies, which is related to the formation of the organic – cesium islands. This island growth is assumed to be in close correlation to the photocathode degradation.
The p-GaN:Cs photocathodes showed a big QE loss after XPS analysis and therefore we investigated the potential damage from x-ray irradiation. The long-time irradiation experiments show that the x-ray damage has a high influence on the cesium component and the degradation of the p-GaN:Cs photocathode.

Keywords: GaN photocathode; photocathode degradation; cesium deposition

Related publications

  • Open Access Logo Poster
    International Workshop on Nitride Semiconductors (IWN), 09.-14.10.2022, Berlin, Deutschland

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Permalink: https://www.hzdr.de/publications/Publ-35465
Publ.-Id: 35465


Cleaning influence on p-GaN surfaces for photocathodes with negative electron affinity

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

Achieving an atomically clean surface is an important step to improving the quality of semiconductor photocathodes, but it is a challenging requirement for surface treatment [1]. In order to understand the surface during the cleaning, the cesium deposition, and the storage of the photocathode, the use of an x-ray photoelectron spectrometer (XPS) is needed. The XPS probes the electronic structure of the p-doped gallium nitride (GaN) photocathode after each step of the preparation process. Using energies between 1200-0 eV the core levels of Ga, N, O, C and Cs are monitored.

Keywords: GaN photocathode; cesium deposition; quantum efficiency; photocathode degradation

Related publications

  • Open Access Logo Poster
    ECASIA 2022-European Conference on Applications of Surface and Interface Analysis, 30.05.-03.06.2022, Limerick, Irland

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Permalink: https://www.hzdr.de/publications/Publ-35463
Publ.-Id: 35463


New Perspectives for Warm Dense Matter Theory: from Quantum Monte Carlo to Temperature Diagnostics

Dornheim, T.

Warm dense matter (WDM) an extreme state that is characterized by extreme densities and temperatures has emerged as
one of the most active frontiers in plasma physics and material science. In nature, WDM occurs in astrophysical objects
such as giant planet interiors and brown dwarfs. In addition, WDM is highly important for cutting-edge technological
applications such as inertial confinement fusion and the discovery of novel materials.
In the laboratory, WDM is studied experimentally in large facilities around the globe, and new techniques have facilitated
unprecedented insights into exciting phenomena like the formation of nanodiamonds at planetary interior conditions [1].
Yet, the interpretation of these experiments requires a reliable diagnostics based on accurate theoretical modeling, which is
a notoriously difficult task [2].
In this talk, I give an overview of recent developments in this field [3,4,5], which will allow for a rigorous treatment of the
intricate interplay of Coulomb coupling with thermal excitations and quantum degeneracy effects based on approximation-
free quantum Monte Carlo (QMC) simulations. Finally, I will present a new idea to extract the exact temperature [6] and
other material properties [7] from an X-ray Thomson scattering experiment without any models or simulations.
[1] D. Kraus et al., Nature Astronomy 1, 606-611 (2017)
[2] M. Bonitz et al., Physics of Plasmas 27, 042710 (2020)
[3] T. Dornheim et al., Physics Reports 744, 1-86 (2018)
[4] T. Dornheim et al., Physical Review Letters 121, 255001 (2018)
[5] M. Böhme et al., Physical Review Letters 129, 066402 (2022)
[6] T. Dornheim et al., arXiv:2206.12805
[7] T. Dornheim et al., arXiv:2209.02254

  • Lecture (others)
    Physikseminar der Universität Rostock, 15.11.2022, Rostock, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-35462
Publ.-Id: 35462


Effects of static magnetic fields in antiferromagnetic ring-shaped spin chains

Borysenko, Y.; Sheka, D.; Faßbender, J.; van den Brink, J.; Makarov, D.; Pylypovskyi, O.

While antiferromagnets with the easy axis of anisotropy are considered to be robust against external magnetic fields of a moderate strength, strong-field-driven spin reorientations provide an insight into subtle properties of the material usually hidden by the high symmetry of the ground state. Here, we address theoretically the effects of curvature in the curvilinear antiferromagnetic achiral anisotropic ring-shaped spin chains in strong magnetic fields. We identify the geometry-driven helimagnetic phase transition above the spin-flop field between the vortex and onion states. The spin-flop transition is of the first- or second-order depending on the ring curvature, which is influenced by the geometry-induced Dzyaloshinskii–Moriya interaction. Inhomogeneity of the Néel vector distribution in spin-flop phase generates weakly ferromagnetic response, which lies in the plane perpendicular to the applied magnetic field. Our findings provide an understanding of complex responses of curvilinear antiferromagnets on magnetic fields and allow further experimental study of geometrical effects relying on spin-chain-based nanomagnets.

Keywords: antiferromagnetism; spin chains; ring

  • Lecture (Conference)
    DPG Meeting of the Condensed Matter Section: Magnetism Division, 04.-09.09.2022, Regensburg, Germany

Permalink: https://www.hzdr.de/publications/Publ-35457
Publ.-Id: 35457


Uncertainty quantification for neural network models

Schmerler, S.

Uncertainty quantification for neural network models

Keywords: machine learning; uncertainty

  • Open Access Logo Lecture (others) (Online presentation)
    ML at HZDR symposium, 06.12.2021, Dresden, Germany

Downloads

Permalink: https://www.hzdr.de/publications/Publ-35456
Publ.-Id: 35456


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