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41396 Publications

Designing chiral magnetic responses by tailoring geometry of thin films: curvilinear ferro- and antiferromagnets

Makarov, D.

Conventionally, tailoring of the Dzyaloshinskii-Moriya interaction (DMI) is done by optimizing materials, either doping a bulk single crystal or adjusting interface properties of thin films and multilayers. A viable alternative to the conventional material screening approach can be the exploration of the interplay between the sample geometry and topology of the order parameter. The research field in magnetism, which is dealing with the study of the impact of geometrical curvature on magnetic responses of curved 1D wires and 2D shells is known as curvilinear magnetism [1-3]. The lack of the inversion symmetry and the emergence of a curvature induced effective anisotropy and DMI stemming from the exchange interaction [4,5] are characteristic of curved surfaces, leading to curvature-driven magnetochiral effects. Volkov et al. has proven that the exchange-driven chiral effects in curvilinear ferromagnets are experimental observables [6] and can be used to realize nanostructures with tunable magnetochiral properties from standard magnetic materials.
A counterpart of the intrinsic DMI for the case of curvilinear magnets is the mesoscale Dzyaloshinskii-Moriya interaction, which is a result of the interplay between the intrinsic (spin-orbit-driven) and extrinsic (curvature-driven) DMI terms [7]. The mesoscale DMI governs the magnetochiral properties of any curvilinear ferromagnetic nanosystem and depends both on the material and geometrical parameters. Its strength and orientation can be tailored by properly choosing the geometry, which allows stabilizing distinct magnetic chiral textures including skyrmion and skyrmionium states as well as skyrmion lattices [8-10]. Interestingly, skyrmion states can be formed in a material even without an intrinsic DMI [8,10]. Very recently, Sheka et al. discovered a novel non-local chiral symmetry breaking effect, which does not exist in planar thin film magnets: it is essentially non-local and manifests itself even in static spin textures living in curvilinear magnetic nanoshells [5].
The field of curvilinear magnetism was recently extended towards curvilinear antiferromagnets. Pylypovskyi et al. demonstrated that intrinsically achiral one-dimensional curvilinear antiferromagnet behaves as a chiral helimagnet with geometrically tunable DMI, orientation of the Neel vector and the helimagnetic phase transition [11,12]. This positions curvilinear antiferromagnets as a novel platform for the realization of geometrically tunable chiral antiferromagnets for antiferromagnetic spinorbitronics.

[1] R. Streubel et al., J. Phys. D: Appl. Phys. 49 (2016), 363001.
[2] D. Sander et al., J. Phys. D: Appl. Phys. 50 (2017), 363001.
[3] E. Vedmedenko et al., J. Phys. D: Appl. Phys. 53 (2020), 453001.
[4] Y. Gaididei et al., Phys. Rev. Lett. 112 (2014), 257203.
[5] D. Sheka et al., Communications Physics 3 (2020), 128.
[6] O. Volkov et al., Phys. Rev. Lett. 123 (2019), 077201.
[7] O. Volkov et al., Scientific Reports 8 (2018), 866.
[8] V. Kravchuk et al., Phys. Rev. B 94 (2016), 144402.
[9] V. Kravchuk et al., Phys. Rev. Lett. 120 (2018), 067201.
[10] O. Pylypovskyi et al., Phys. Rev. Appl. 10 (2018), 064057.
[11] O. Pylypovskyi et al., Nano Letters 20 (2020), 8157.
[12] O. Pylypovskyi et al., Appl. Phys. Lett. 118 (2021), 182405.

Keywords: flexible magnetic field sensors; curvilinear magnetism

Related publications

  • Invited lecture (Conferences) (Online presentation)
    IEEE Trends in Magnetism, 06.-10.09.2021, Palermo, Italy

Permalink: https://www.hzdr.de/publications/Publ-32968
Publ.-Id: 32968


Nanomagnetism and spintronics of Cr2O3 magnetoelectric antiferromagnets

Makarov, D.

Thin film antiferromagnets (AF) have potential to revolutionize spintronics due to their inherently magnetic-field stable magnetic order and high-frequency operation. To explore their application potential, it is necessary to understand modifications of the magnetic properties and magnetoelectric responses of AF thin films with respect to their bulk counterparts. Considering grainy morphology of thin films, questions regarding the change of the intergranular exchange, criticality behavior and switching of the order parameter need to be addressed.
Our approach is based on the electron transport characterization of magnetic responses of thin film antiferromagnets [1-4]. This task is difficult as minute uncompensated surface magnetization of antiferromagnets needs to be detected, which imposes strict requirements to the sensitivity of the method. We will outline our developments of zero-offset anomalous Hall magnetometry [1] applied to study the physics of conventional metallic IrMn and insulating magnetoelectric Cr2O3 antiferromagnets. To build a reliable description of the material properties, the analysis of the transport data is backed up by structural characterization and real space imaging of AF domain patterns using NV microscopy [2,5]. Based on this unique and novel combination, we for the first time observe the formation of nanoscale antiferromagnetic domains in thin films of Chromia (Cr2O3) across its ordering temperature at ~300 K. Our quantitative results yield a detailed understanding of the domain formation process in Cr2O3 and allow us to determine the efficiency of inter-granular magnetic exchange coupling [5]. This coupling strength has proven decisive in the decades long development of ferromagnetic memory media and will be of equal importance for future antiferromagnetic spintronics technologies, for which we here present a powerful new development tool.
The fundamental understanding of the magnetic microstructure of magnetoelectric α-Cr2O3 thin films and the possibility to read-out its antiferromagnetic order parameter all-electrically enabled the entirely new recording concept where a magnetoelectric memory cell can be addressed without using a ferromagnet. With this approach, we opened an appealing topic of purely antiferromagnetic magnetoelectric random access memory (AF-MERAM) [2].
By exploring the interaction of antiferrmagnetic domain walls with morphological structures prepared on the surface of Cr2O3 single crystals, we access the nanoscale mechanics of AF domain walls. We propose to employ nanoscale patterns as engineered pinning centers for AF domain walls,
where binary information is encoded by the direction of the Neel vector. Our results bear significant potential for technological exploitation be it in the form of the proposed antiferromagnetic memory devices, or ultimately for the realisation of DW logic using antiferromagnets.
These recent developments on the fabrication and characterization of Cr2O3-based functional elements will be discussed in this presentation.
REFERENCES
[1] T. Kosub, M. Kopte, F. Radu, O. G. Schmidt, D. Makarov, “All-Electric access to the Magnetic-Field-Invariant Magnetization of Antiferromagnets”, Phys. Rev. Lett. 115, 097201 (2015).
[2] T. Kosub, M. Kopte, R. Hühne, P. Appel, B. Shields, P. Maletinsky, R. Hübner, M. O. Liedke, J. Fassbender, O. G. Schmidt, and D. Makarov, “Purely antiferromagnetic magnetoelectric random access memory”, Nature Communications 8, 13985 (2017).
[3] R. Schlitz, T. Kosub, A. Thomas, S. Fabretti, K. Nielsch, D. Makarov, and S. T. B. Goennenwein, “Evolution of the spin hall magnetoresistance in Cr2O3/Pt bilayers close to the Neel temperature”, Appl. Phys. Lett. 112, 132401 (2018).
[4] P. Muduli, R. Schlitz, T. Kosub, R. Hübner, A. Erbe, D. Makarov, and S. T. B. Goennenwein, “Local and nonlocal spin Seebeck effect in lateral Pt-Cr2O3-Pt devices at low temperatures”, Appl. Phys. Lett. Materials 9, 021122 (2021).
[5] P. Appel, B. J. Shields, T. Kosub, R. Hübner, J. Fassbender, D. Makarov, and P. Maletinsky, “Nanomagnetism of magnetoelectric granular thin film antiferromagnets”, Nano Letters 19, 1682 (2019).
[6] O. V. Pylypovskyi, A. V. Tomilo, D. D. Sheka, J. Fassbender, and D. Makarov, “Boundary conditions for the Neel order parameter in a chiral antiferromagnetic slab”, Phys. Rev. B 103, 134413 (2021).
[7] N. Hedrich, K. Wagner, O. V. Pylypovskyi, B. J. Shields, T. Kosub, D. D. Sheka, D. Makarov, and P. Maletinsky, “Nanoscale mechanics of antiferromagnetic domain walls”, Nature Physics (2021). https://doi.org/10.1038/s41567-020-01157-0.

Keywords: antiferromagnetic spintronics

Related publications

  • Invited lecture (Conferences) (Online presentation)
    2021 IEEE 11th International Conference on "Nanomaterials: Applications & Properties", 05.-11.09.2021, Odesa, Ukraine

Permalink: https://www.hzdr.de/publications/Publ-32967
Publ.-Id: 32967


Ecological consequences of large herbivore exclusion in an African savanna: 12 years of data from the UHURU experiment

Alston, J.; Reed, C. G.; Khasoha, L. M.; Brown, B. R. P.; Busienei, G.; Carlson, N.; Coverdale, T. C.; Dudenhoeffer, M.; Dyck, M. A.; Ekeno, J.; Hassan, A. A.; Hohbein, R.; Jakopak, R. P.; Kimiti, B.; Kurukura, S.; Lokeny, P.; Louthan, A. M.; Musila, S.; Musili, P. M.; Tindall, T.; Weiner, S.; Kartzinel, T. R.; Palmer, T. M.; Pringle, R. M.; Goheen, J. R.

Diverse communities of large mammalian herbivores (LMH), once widespread, are now rare. LMH exert strong direct and indirect effects on community structure and ecosystem functions, and measuring these effects is important for testing ecological theory and for understanding past, current, and future environmental change. This in turn requires long-term experimental manipulations, owing to the slow and often nonlinear responses of populations and assemblages to LMH removal. Moreover, the effects of particular species or body-size classes within diverse LMH guilds are difficult to pinpoint, and the magnitude and even direction of these effects often depends on environmental context. Since 2008, we have maintained the Ungulate Herbivory Under Rainfall Uncertainty (UHURU) experiment, a series of size-selective LMH exclosures replicated across a rainfall/productivity gradient in a semi-arid Kenyan savanna. The goals of the UHURU experiment are to measure the effects of removing successively smaller size classes of LMH (mimicking the process of size-biased extirpation) and to establish how these effects are shaped by spatial and temporal variation in rainfall. The UHURU experiment comprises three LMH-exclusion treatments and an unfenced control, applied to 9 randomized blocks of contiguous 1 ha plots (n = 36). The fenced treatments are: “MEGA” (exclusion of megaherbivores, elephant and giraffe); “MESO” (exclusion of herbivores ≥40 kg); and “TOTAL” (exclusion of herbivores ≥5 kg). Each block is replicated three times at three sites across the 20 km rainfall gradient, which has fluctuated over the course of the experiment. The first five years of data were published previously (Ecological Archives E095-064) and have been used in numerous studies. Since publication of this original data paper, we have (a) continued to collect data according to the original protocols, (b) improved the taxonomic resolution and accuracy of plant and small-mammal identifications, and (c) begun collecting several new data sets. Here, we present updated and extended raw data from the first 12 years of the UHURU experiment (2008–2019). Data include daily rainfall data throughout the experiment; annual surveys of understory plant communities; annual censuses of woody-plant communities; annual measurements of individually tagged woody plants; monthly monitoring of flowering and fruiting phenology; every-other-month small-mammal mark-recapture data; and quarterly large-mammal dung surveys.

Keywords: climate change; dik-dik (Madoqua); East African savannas; elephant (Loxodonta africana); extinction; food webs; grazing and browsing herbivores; impala (Aepyceros melampus); long-term ecological field experiments; rangeland ecology

Permalink: https://www.hzdr.de/publications/Publ-32965
Publ.-Id: 32965


Complexation of Np(V) with the dicarboxylates malonate and succinate: complex stoichiometry, thermodynamic data and structural information

Maiwald, M. M.; Müller, K.; Heim, K.; Rothe, J.; Dardenne, K.; Roßberg, A.; Koke, C.; Trumm, M.; Skerencak-Frech, A.; Panak, P. J.

The complexation of Np(V) with malonate and succinate is studied by different spectroscopic techniques, namely attenuated total reflection FT-IR (ATR FT-IR) and extended X-ray absorption fine structure (EXAFS) spectroscopy, as well as by quantum chemistry to determine the speciation, thermodynamic data and structural information of the formed complexes. For complex stoichiometries and thermodynamic functions (log beta0n(T), Delta rH0n, Delta rS0n) near infrared absorption spectroscopy (Vis/NIR) is applied. The complexation reactions are investigated as a function of the total ligand concentration ([Mal2-]total, [Succ2-]total), ionic strength (Im = 0.5 – 4.0 mol kg-1 Na+(Cl-/ClO4-)) and temperature (T = 20 – 85 °C). Besides the solvated NpO2+ ion, the formation of two Np(V) species with the stoichiometry NpO2(L)n1-2n (n = 1, 2, L = Mal2-, Succ2-) is observed. With increasing temperature the molar fractions of both complex species increase and the application of the law of mass action yields the temperature dependent conditional stability constants log beta`n(T) at given ionic strengths. The log beta`n(T) are extrapolated to IUPAC reference state conditions (Im = 0) according to the specific ion interaction theory (SIT) revealing thermodynamic log 0n(T) values. For all formed complexes (NpO2(Mal)-: log 01(25 °C) = 3.36 ± 0.11, NpO2(Mal)23-: log 02(25 °C) = 3.95 ± 0.19, NpO2(Succ)-: log 01(25 °C) = 2.05 ± 0.45, NpO2(Succ)23-: log 02(25 °C) = 0.75 ± 1.22) the stability constants increase with increasing temperature confirming an endothermic complexation reaction. The temperature dependence of the thermodynamic stability constants is described by the integrated Van’t Hoff equation yielding the standard reaction enthalpies and entropies for the complexation reactions. In addition, the sum of the specific binary ion-ion interaction coefficients 0n(T) for the complexation reactions are obtained from SIT modelling as a function of the temperature.
The structure of the complexes and the coordination mode of malonate and succinate are investigated using EXAFS spectroscopy, ATR-FT-IR spectroscopy and quantum chemical calculations. The results show, that in case of malonate 6-membered chelate complexes are formed, whereas the formation of 7-membered rings with succinate is energetically unfavourable in the equatorial plane of the Np(V) ion (as NpO2+ cation).

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Permalink: https://www.hzdr.de/publications/Publ-32963
Publ.-Id: 32963


A contribution to wettability and wetting characterisation of ultrafine particles with varying shape and degree of hydrophobization

Sygusch, J.; Rudolph, M.

Many particle separation processes are based on differences in wettabilities. Therefore, one needs to understand the interfacial properties and micro processes taking place on the material surface. The main quantity to account for wettability is the Young contact angle. However, this method requiring homogeneous flat and smooth sub-strates has drawbacks when analysing particles and is rather system specific as particles are not planar and exhibit rough surfaces. Here, we demonstrate the challenges of proper wettability analysis of particulate material as available methods are influenced strongly by multiple particle properties such as shape and size. Three fractions of glass particles with different shapes are investigated, fibres, fragments, spheres, and their wettability is modified by esterification with alcohols. These particle systems are characterised via analytic particle solvent extraction, static and dynamic contact angle measurements, and inverse gas chromatography. Alcohols with longer alkyl chains result in more hydrophobic particles with more homogeneous wettability characteristics in terms of surface energy. Comparing the characterisation methods reveals the influence of particle morphology on the interfacial wetting behaviour. Applying inverse gas chromatography for wettability characterisation in combination with the other methods underlines its potentials as well as limitations in understanding particulate surface properties.

Keywords: Wettability; Hydrophobicity; Surface heterogeneity; Surface free energy; Inverse gas chromatography; Contact angle

Permalink: https://www.hzdr.de/publications/Publ-32962
Publ.-Id: 32962


Development of machine learning framework for interface force closures based on bubble tracking data

Tai, C.-K.; Bolotnov, I.; Evdokimov, I.; Schlegel, F.; Lucas, D.

Understanding the liquid-water interaction serves as the basis to credibility of two-phase flow models and
safety of light water reactors. The topic is of researchers’ long interest due to the complexity of underlying
physics. Recently, with growing availability to high performance computing resources, interface tracking
direct numerical simulation becomes an advantage measure to probe the two-phase flow. Resulting
accumulation of high-fidelity numerical data also makes data-driven modeling with machine learning
methods an attractive option to gain insight to the phenomena.

This work presents an interfacial force data-driven modeling framework aims to develop a bubble tracking
direct numerical simulation data-based machine learning drag model for application in Euler-Euler
simulations of bubbly flows. Besides technical demonstration, this work also provides a guidance for DNS
data generation for relevant applications.

The data-driven modeling framework is firstly verified by a benchmark problem, where artificial data is
utilized to make feedforward neural network assimilate drag correlation by Tomiyama et al. (1998). The
obtained model is utilized in a Euler-Euler solver for on-the-fly drag coefficient query. In the test case,
resulting velocity and void fraction distribution by machine learning model is consistent with the reference
model.

Secondly, this work utilized direct numerical simulation bubble tracking data set to form machine learning
drag model for bubbly flow based on Reynolds and Eötvös number. Pseudo-steady state filtering in Frenet
frame is carried out to obtain bubble drag coefficient. The machine learning drag model is examined in a
test case by Wang et al. (1987). Results and suggestions for future works are discussed.

Keywords: direct numerical simulation; interfacial force modeling; machine learning

  • Contribution to proceedings
    19th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-19), 06.-11.03.2022, Brüssel, Belgien
    Proceedings of NURETH-19
  • Open Access Logo Nuclear Engineering and Design 399(2022), 112032
    DOI: 10.1016/j.nucengdes.2022.112032
    Cited 2 times in Scopus

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Permalink: https://www.hzdr.de/publications/Publ-32961
Publ.-Id: 32961


Organische Synthese einer potenten Leitverbindung zur Entwicklung neuer Radioliganden für die molekulare Bildgebung der mutierten Form der Isocitrat-Dehydrogenase 1 im Gehirn mittels Positronen-Emissions-Tomographie

Linke, J.

Organische Synthese einer potenten Leitverbindung zur Entwicklung neuer Radioliganden für die molekulare Bildgebung der mutierten Form der Isocitrat-Dehydrogenase 1 im Gehirn mittels Positronen-Emissions-Tomographie

Keywords: Isocitrat-Dehydrogenase 1; mIDH1; Ligand; PET; molekulare Bildgebung

  • Master thesis
    Universität Leipzig, 2021
    Mentor: Dr. Rodrigo Teodoro, Dr. Matthias Scheunemann
    80 Seiten

Permalink: https://www.hzdr.de/publications/Publ-32960
Publ.-Id: 32960


Large-scale test facility for modeling bubble behavior and liquid metal two-phase flows in a steel ladle

Wondrak, T.; Timmel, K.; Bruch, C.; Gardin, P.; Hackl, G.; Lachmund, H.; Bodo Lüngen, H.; Odenthal, H.-J.; Eckert, S.

A new experimental facility has been designed and constructed which represents a 1:5.25 model of an industrial 185 t steel ladle. This setup is intended for systematic investigations of complex liquid metal multiphase flows created by gas blowing from the bottom. Two tons of a Sn40wt.%Bi alloy are employed as working fluid, its thermophysical properties are very similar to those of liquid steel. The relatively low operating temperatures (T~200°C) compared to the real industrial process allow the use of powerful measuring techniques for characterizing the behavior of the gas phase and resulting flow regimes. Argon gas is injected through diverse plug systems into a cylindrical fluid vessel which is equipped with a pressure tight lid to achieve low-pressure conditions for vacuum processing. This paper presents first measurements of the gas distribution close to the free liquid metal surface for various gas flow rates, plug positions and types. Moreover, the pressure in the vessel has been varied between 1 mbar and ambient pressure. The experiments provide a copious data base about the flow regimes, void fraction, liquid and bubble velocities, and bubble properties, which can be used to provide so far unknown boundary conditions for numerical simulations of various metallurgical reactors such as steelmaking converters or steelmaking ladles.

Keywords: liquid metal; two-phase flow; bubble measurement; ladle treatment

Permalink: https://www.hzdr.de/publications/Publ-32959
Publ.-Id: 32959


A particle-center-averaged Euler-Euler model for monodisperse bubbly flows

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

The standard Euler-Euler model is based on the phase-averaging method. Each bubble force is a function of the local gas volume fraction. As a result, the coherent motion of each bubble as a whole is not enforced when the bubble diameter is larger than the mesh size. However, the bubble force models are typically developed by tracking the bubbles' centers of mass and assuming that the forces act on these locations. In simulations, this inconsistency can lead to a nonphysical gas concentration in the center or near the wall of a pipe when the bubble diameter is larger than the mesh size. Besides, a mesh independent solution may not exist in such cases.

In the present contribution, a particle-center-averaging method is used to average the solution variables for the disperse phase, which allows to represent the bubble forces as forces that act on the bubbles' centers of mass. An approach to simulate bubbly flows is formed by combining the Euler-Euler model framework using the particle-center-averaging method and a diffusion-based method that relates phase-averaged and particle-center-averaged quantities. The remediation of the inconsistency with the standard Euler-Euler model based on phase-averaging method is demonstrated using a simplified two-dimensional test case. The test results illustrate that the particle-center-averaging method can alleviate the over-prediction of the gas volume fraction peak in the channel center and provide mesh independent solutions. Furthermore, a comparison of both approaches is shown for several bubbly pipe flow cases where experimental data are available. The results show that the particle-center-averaging method can alleviate the over-prediction of the gas volume fraction peaks in the wall peaking cases as well.

Keywords: particle-center-averaging; phase-averaging; bubble number density; diffusion equation; wall-contact force model; multiphase flow; Euler-Euler model

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Permalink: https://www.hzdr.de/publications/Publ-32958
Publ.-Id: 32958


Stretchable Thin Film Mechanical Strain Gated Switches and Logic Gate Functions Based on a Soft Tunneling Barrier

Chae, S.; Jin Choi, W.; Fotev, I.; Bittrich, E.; Uhlmann, P.; Schubert, M.; Makarov, D.; Wagner, J.; Pashkin, O.; Fery, A.

Mechanical strain gated switches are cornerstone components of material embedded circuits that perform logic operations without using conventional electronics. This technology requires a single material system to exhibit three distinct functionalities: strain-invariant conductivity and an increase or decrease of conductivity upon mechanical deformation. Herein, we demonstrate mechanical strain-gated electric switches based on a thin-film architecture that features an insulator-to-conductor transition when mechanically stretched. The conductivity changes by nine orders of magnitude over a wide range of tunable working strains (as high as 130%). Our approach relies on a nanometer-scale sandwiched bi-layer Au thin film with an ultrathin polydimethylsiloxane elastomeric barrier layer applied strain alters the electron tunneling currents through the barrier. Mechanical-force-controlled electric logic circuits are achieved by realizing strain-controlled basic (AND and OR) and universal (NAND and NOR) logic gates in a single system. The proposed material system can be used to fabricate material-embedded logics of arbitrary complexity for wide range of applications including soft robotics, wearable/implantable electronics, human machine interface and internet of things.

Keywords: Strain gated electric switch; logic gates; tunneling; stretchable circuit; thin film

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Permalink: https://www.hzdr.de/publications/Publ-32957
Publ.-Id: 32957


Inverted fine structure of a 6H-SiC qubit enabling robust spin-photon interface

Breev, I. D.; Shang, Z.; Poshakinskiy, A. V.; Singh, H.; Berencen, Y.; Hollenbach, M.; Nagalyuk, S. S.; Mokhov, E. N.; Babunts, R. A.; Baranov, P. G.; Suter, D.; Tarasenko, S. A.; Astakhov, G.; Anisimov, A. N.

Optically controllable solid-state spin qubits are one of the basic building blocks for applied quantum technology. Efficient extraction of emitted photons and a robust spin-photon interface are crucial for the realization of quantum sensing protocols and essential for the implementation of quantum repeaters. Though silicon carbide (SiC) is a very promising material platform hosting highly-coherent silicon vacancy spin qubits, a drawback for their practical application is the unfavorable ordering of the electronic levels in the optically excited state. Here, we demonstrate that due to polytypism of SiC, a particular type of silicon vacancy qubits in 6H-SiC possesses an unusual inverted fine structure. This results in the directional emission of light along the hexagonal crystallographic axis, making photon extraction more efficient and integration into photonic structures technologically straightforward. From the angular polarization dependencies of the emission, we reconstruct the spatial symmetry and determine the optical selection rules depending on the local deformation and spin-orbit interaction, enabling direct implementation of robust spin-photon entanglement schemes. Furthermore, the inverted fine structure leads to unexpected behavior of the spin readout contrast. It vanishes and recovers with lattice cooling due to two competing optical spin pumping mechanisms. Our experimental and theoretical approaches provide a deep insight into the optical and spin properties of atomic-scale qubits in SiC required for quantum communication and distributed quantum information processing.

Keywords: Solid-state spin qubits; Silicon vacancy; 6H-SiC; Quantum communication

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Permalink: https://www.hzdr.de/publications/Publ-32955
Publ.-Id: 32955


Numerical Investigation of Degasification in an Electrocoagulation Reactor

Höhne, T.; Farhikhteh Asl, V.; Ople Villacorte, L.; Herskind, M.; Momeni, M.; Al-Fayyad, D.; Taș-Koehler, S.; Lerch, A.

In order to enhance retention of particulate and colloidal (organic) matter, chemical coagulation (CC) is often used prior to pressure driven membrane filtration. Electrocoagulation (EC) is an alternative to CC usually carried out in an electrochemical reactor consisting of an electrolytic cell containing at least one anode (sacrificial) and one cathode. The EC combined with a membrane filtration to a hybrid membrane system may be a potential possibility for environmental problems dealing with drinking water treatment, water reuse and rational waste management. In this study, an EC reactor with spiral electrodes was investigated numerically, focusing on modelling with a given design/geometry, configuration and boundary conditions. Two-phase flow interactions between water (liquid) and hydrogen (gas) were modelled via computational fluid dynamics (CFD). Different flow rates (Q=1-1000 l/h) through two batches of the watering stage (Case 1-3) and the degassing stage (Case 4-6) were simulated. Degassing the feed of the membrane system is of high importance in order to achieve stable operation. The results provided information about flow characteristics such as sufficient retention time, water circulation by velocity vectors, undesirable gas penetration into the water inlet channel, gas holdup during watering and degassing, and finally the optimal period for the degasification. The results showed that as the water velocity increases, retention time decreases. The results also showed that thirty seconds seemed the optimal time with the gas holdup of 0.020%, 0.028%, and 0.027% respectively for Case 4, Case 5, and Case 6. Another finding is that the consideration for the most abundant gas holdup for the typical BC was the smallest ratio of water flow to gas flow.

Keywords: hybrid membrane process; electrocoagulation; CFD; hydrogen bubble; degassing optimization

Permalink: https://www.hzdr.de/publications/Publ-32954
Publ.-Id: 32954


An updated strategic research agenda for the integration of radioecology in the european radiation protection research

Gilbin, R.; Arnold, T.; Beresford, N. A.; Berthomieu, C.; Brown, J. E.; de With, G.; Horemans, N.; Madruga, M. J.; Masson, O.; Merroun, M.; Michalik, B.; Muikku, M.; O’Toole, S.; Mrdakovic Popic, J.; Nogueira, P.; Real, A.; Sachs, S.; Salbu, B.; Stark, K.; Steiner, M.; Sweek, L.; Vandenhove, H.; Vidal, M.; Vives I. Batlle, J.

The ALLIANCE Strategic Research Agenda (SRA) for radioecology is a living document that defines a long-term vision (20 years) of the needs for, and implementation of, research in radioecology in Europe. The initial SRA, published in 2012, included consultation with a wide range of stakeholders (Hinton et al., 2013). This revised version is an update of the research strategy for identified research challenges, and includes a strategy to maintain and develop the associated required capacities for workforce (education and training) and research infrastructures and capabilities. Beyond radioecology, this SRA update constitutes a contribution to the implementation of a Joint Roadmap for radiation protection research in Europe (CONCERT, 2019a). This roadmap, established under the H2020 European Joint Programme CONCERT, provides a common and shared vision for radiation protection research, priority areas and strategic objectives for collaboration within a European radiation protection research programme to 2030 and beyond. Considering the advances made since the first SRA, this updated version presents research challenges and priorities including identified scientific issues that, when successfully resolved, have the potential to impact substantially and strengthen the system and/or practice of the overall radiation protection (game changers) in radioecology with regard to their integration into the global vision of European research in radiation protection. An additional aim of this paper is to encourage contribution from research communities, end users, decision makers and other stakeholders in the evaluation, further advancement and accomplishment of the identified priorities.

Keywords: Strategic Research Agenda for radioecology; Environmental exposure to radionuclides; Radiation protection of the environment; Integration of radiation protection research; Education and training; Infrastructures

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Permalink: https://www.hzdr.de/publications/Publ-32953
Publ.-Id: 32953


Large magnetic entropy change in Nd2In near the boiling temperature of natural gas

Liu, W.; Scheibel, F.; Gottschall, T.; Bykov, E.; Dirba, I.; Skokov, K.; Gutfleisch, O.

Natural gas is useful for the transition from traditional fossil fuels to renewable energies. The consumption of liquid natural gas has been rising, and the demand is predicted to double by 2040. In this context, magnetocaloric gas liquefaction, as an emerging and energy-saving technology, could be an alternative to the traditional gas-compression refrigeration. In this work, we report a large magnetic entropy change of 7.42 J/kg K under a magnetic field change of 2 T in Nd2In at 109 K, which is near the boiling temperature of natural gas of 112 K. The maximum adiabatic temperature change reaches 1.13K under a magnetic field change of 1.95 T and is fully reversible. The magnetic phase transition is confirmed to be of the first-order type with the negligible thermal hysteresis. Further investigations on the thermal expansion and the magnetostriction reveal that the magnetic transition undergoes two stages with a negligible volume change. The longitudinal strain increases with magnetic fields and then decreases. These interesting properties are useful for the practical design of a magnetocaloric natural gas liquefaction system and for the fundamental understanding of the phase transitions in other RE2In intermetallics.

Permalink: https://www.hzdr.de/publications/Publ-32952
Publ.-Id: 32952


Influence of microstructure on the application of Ni-Mn-In Heusler compounds for multicaloric cooling using magnetic field and uniaxial stress

Pfeuffer, L.; Gracia-Condal, A.; Gottschall, T.; Koch, D.; Faske, T.; Bruder, E.; Lemke, J.; Taubel, A.; Ener, S.; Scheibel, F.; Durst, K.; Skokov, K. P.; Manosa, L.; Planes, A.; Gutfleisch, O.

Novel multicaloric cooling utilizing the giant caloric response of Ni-Mn-based metamagnetic shape- memory alloys to different external stimuli such as magnetic field, uniaxial stress and hydrostatic pressure is a promising candidate for energy-efficient and environmentally-friendly refrigeration. However, the role of microstructure when several external fields are applied simultaneously or sequentially has been scarcely discussed in literature. Here, we synthesized ternary Ni-Mn-In alloys by suction casting and arc melting and analyzed the microstructural influence on the response to magnetic fields and uniaxial stress. By combining SEM-EBSD and stress-strain data, a significant effect of texture on the stress- induced martensitic transformation is revealed. It is shown that a <001> texture can strongly reduce the critical transformation stresses. The effect of grain size on the material failure is demonstrated and its influence on the magnetic-field-induced transformation dynamics is investigated. Temperature-stress and temperature-magnetic field phase diagrams are established and single caloric performances are characterized in terms of ΔsT and ΔTad. The cyclic ΔTad values are compared to the ones achieved in the multicaloric exploiting-hysteresis cycle. It turns out that a suction-cast microstructure and the combination of both stimuli enables outstanding caloric effects in moderate external fields which can significantly exceed the single caloric performances. In particular for Ni-Mn-In, the maximum cyclic effect in magnetic fields of 1.9 T is increased by more than 200 % to -4.1 K when a moderate sequential stress of 55 MPa is applied. Our results illustrate the crucial role of microstructure for multicaloric cooling using Ni-Mn- based metamagnetic shape-memory alloys.

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Permalink: https://www.hzdr.de/publications/Publ-32951
Publ.-Id: 32951


Evaluation of the effective temperature change in Gd-based composite wires assessed by static and pulsed-field magnetic measurements

Beyer, L.; Weise, B.; Freudenberger, J.; Hufenbach, J. K.; Gottschall, T.; Krautz, M.

Gd cladded in a seamless 316L austenitic steel tube has been swaged into wires by the powder-in-tube (PIT) technology, resulting in an outer diameter of 1 mm, a wall thickness of approx. 100 μm and a filling factor of around 62 vol%. Such wires provide an advantageous geometry for heat exchangers and have the benefit to protect the Gadolinium, i.e. from corrosion when being in contact with a heat transfer fluid. The magnetocaloric composite has been studied by static and pulsed magnetic-field measurements in order to evaluate the performance of Gd as a core material. By the analysis of magnetization and heat capacity data, the influences of deformation-induced defects on Gadolinium are presented. The subsequent heat treatment at 773 K for 1 h in Ar atmosphere allowed restoring the magnetic properties of the wire after deformation. Data of the pulsed magnetic-field measurements on the Gd-filled PIT-wires and a Gd–core separated from the jacket are presented, with an achievable temperature change of 1.2 K for the wire and 5.2 K for the Gd in 2 T, respectively. A comparison to previously studied La(Fe, Co, Si)13-filled composite wires is included. It indicates that performance losses due to the passive matrix material cannot be overcome only by an increased adiabatic temperature change of the core material, but instead the wire components need to be chosen regarding an optimized heat capacity ratio, as well.

Permalink: https://www.hzdr.de/publications/Publ-32950
Publ.-Id: 32950


THEREDA – Thermodynamic Reference Database for the nuclear waste disposal in Germany

Bok, F.; Moog, H. C.; Gaona, X.; Freyer, D.; Wissmeier, L.

The disposal of nuclear waste including the assessment of long-term safety is still an open question in Germany. In addition to the pending decision about the repository host rock (salt, granite, or clay) and the associated site selection, the basic necessity of a consistent and obligatory thermodynamic reference database persists. Such a database is essential to assess potential radionuclide migration scenarios accurately and to make well-founded predictions about the long-term safety up to one million years. Specific challenges are comprehensive datasets covering also elevated temperatures and high salinities. Concerning the required elements (actinides, fission products as well as matrix and building materials), no other thermodynamic database is available that is compatible with the expected conditions. Due to these deficiencies THEREDA (Altmaier et al., 2008&&>&&>&&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt>nbsp&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt>lt>&&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt>nbsp&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt>nbsp&>&&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt>nbsp&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt>lt>&&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt>nbsp&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt>lt>&&>&&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt>nbsp&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt>lt>&&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt>nbsp&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt>nbsp&>&&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt>nbsp&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt>lt>&&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt>nbsp&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt>nbsp&>&&>&&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt>nbsp&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt>lt>&&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt>nbsp&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt>nbsp&>&&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt>nbsp&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt>lt>&&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt>nbsp&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt>lt>&&>&&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt>nbsp&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt>lt>&&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt>nbsp&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt>nbsp&>&&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt>nbsp&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt>lt>&&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt>nbsp&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt> Moog et al., 2015) a joint project of institutions leading in the field of safety research for nuclear waste disposal in Germany and Switzerland, was started in the year 2006.

Database features
THEREDA offers evaluated thermodynamic data for many compounds (solid phases, aqueous species, or constituents of the gaseous phase) of elements relevant according to the present state of research. In particular, all oxidation states expected for disposal site conditions are considered. In the present release, THEREDA includes data for actinides and their chemical analogues (Th, U, Np, Pu, Am, Cm & Nd), fission products (Se, Sr, Tc & Cs) and matrix elements (Na, K, Mg, Ca, Al, Si | Cl, SO4, CO3). For the calculation of cementitious phases the current version of CEMDATA (18.1) was integrated (Lothenbach et al, 2019).
THEREDA is based on a relational databank whose structure intrinsically ensures the internal consistency of thermodynamic data. Data considered respond to the needs of both Gibbs Energy Minimizers (ChemApp, GEMS) and Law-of-Mass-Action codes (Geochemist’s Workbench, PHREEQC, ToughReact). The database is designed generically so that it can store interaction parameters for various models. Namely, the PITZER ion interaction approach to describe activity coefficients of hydrated ions and molecules in saline solutions (Pitzer, 1991) as well as ideal and non-ideal solid solution approaches are considered in the actual dataset.
THEREDA is accessible via internet through www.thereda.de. This is not only a portal to view the data, uncertainties and the primary references of the data&&>&&>&&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt>nbsp&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt>lt>&&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt>nbsp&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt>nbsp&>&&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt>nbsp&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt>lt>&&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt>nbsp&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt>lt>&&>&&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt>nbsp&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt>lt>&&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt>nbsp&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt>nbsp&>&&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt>nbsp&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt>lt>&&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt>nbsp&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt>nbsp&>&&>&&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt>nbsp&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt>lt>&&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt>nbsp&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt>nbsp&>&&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt>nbsp&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt>lt>&&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt>nbsp&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt>lt>&&>&&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt>nbsp&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt>lt>&&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt>nbsp&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt>nbsp&>&&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt>nbsp&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt>lt>&&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt>nbsp&>&&>lt>nbsp&>lt>lt>&&>lt>nbsp&>lt> it provides also additional information on issues concerning the database. Ready-to-use parameter files are available for download in a variety of formats (geochemical code specific formats and generic ASCII type). They are also used for internal test calculations – an essential element of the quality assurance scheme. The capabilities of THEREDA are demonstrated using approx. 400 application case calculations, whose results were compared with experimental values published in literature.

Keywords: THEREDA; Thermodynamic Reference Database; Pitzer; Solubility; thermodynamic data

  • Poster
    3rd Conference on Key Topics in Deep Geological Disposal, 04.-06.07.2022, Köln, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-32949
Publ.-Id: 32949


Plasmonic terahertz nonlinearity in graphene disks

Han, J.; Chin, M. L.; Matschy, S.; Poojali, J.; Seidl, A.; Winnerl, S.; Hafez, H. A.; Turchinovich, D.; Kumar, G.; Myers-Ward, R. L.; Dejarld, M. T.; Daniels, K. M.; Drew, H. D.; Murphy, T. E.; Mittendorff, M.

The discovery of graphene and its unique optical and electronic properties triggered intense developments in a vast number of optoelectronic applications, especially in spectral regions that are not easily accessible with conventional semiconductors. Particularly in the THz regime, where the free-carrier interaction with low energetic photons usually dominates, detectors and modulators based on graphene often feature an improved response time. Nevertheless, the light-matter interaction suffers from the small interaction volume. One way to enhance the efficiency of such devices at elevated frequencies, is patterning graphene into plasmonic structures like disks. In addition to the increased linear absorption, the plasmon resonance also creates a strong, surface-localized field that enhances the nonlinear optical response. While experimental studies so far have focused on hot carrier effects, theoretical studies also suggest an increase of the nonlinearity beyond thermal effects. Here we present polarization dependent pump-probe measurements on graphene disks that enable disentangling the contributions of thermal and plasmonic nonlinearity. An increase of the pump-induced transmission is observed when pump and probe radiation are co-polarized. To further elucidate the interplay of thermal and plasmonic effects, we develop a model that supports the origin of the polarization dependent enhancement of the observed THz nonlinearities.

Keywords: graphene; plasmon; nonlinearity; polarization dependence

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Permalink: https://www.hzdr.de/publications/Publ-32948
Publ.-Id: 32948


Correlated effects of fluorine and hydrogen in fluorinated tin oxide (FTO) transparent electrodes deposited by sputtering at room temperature

Morán-Pedroso, M.; Gago, R.; Julin, J. A.; Salas-Colera, E.; Jimenez, I.; de Andrés, A.; Prieto, C.

The optical and electrical properties of fluorinated tin oxide (FTO) films deposited at room temperature by sputtering have been investigated varying the fluorine content and the hydrogen atmosphere. The complex behavior of the obtained films is disclosed using a wide set of characterization techniques that reveals the combined effects of these two parameters on the generated defects. These defects control the electrical transport (carrier density, mobility and conductivity), the optical properties (band gap and defects-related absorption and photoluminescence) and finally promote the amorphization of the samples. H₂ in the sputtering gas does not modify the H content in the films but induces the partial reduction of tin (from Sn4+ to Sn2+) and the consequent generation of oxygen vacancies with shallow energy levels close to the valence band. A variation of up to four orders of magnitude in electrical conductivity is reported in samples with the appropriate fluorine doping and hydrogen fraction in the sputtering gas, maintaining excellent optical transparency. Optimized room temperature grown electrodes reach sheet resistance ~20 Ω/□ and transparency >90%. This room temperature deposition process enables film preparation on flexible organic substrates, such as polyethylene terephthalate (PET), with identical performance of doubtless interest in flexible and large scale electronics.

Keywords: Transparent conductive materials; Fluorinated tin oxide; Room temperature film preparation

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Permalink: https://www.hzdr.de/publications/Publ-32947
Publ.-Id: 32947


Impact of Si on the high-temperature oxidation of AlCr(Si)N coatings

Jager, N.; Meindlhumer, M.; Zitek, M.; Spor, S.; Hruby, H.; Nahif, F.; Julin, J.; Keckes, J.; Mitterer, C.; Daniel, R.

The resistance of wear protective coatings against oxidation is crucial for their use at high temperatures. Here, three nanocomposite AlCr(Si)N coatings with a fixed Al/Cr atomic ratio of 70/30 and a varying Si-content of 0 at.%, 2.5 at.% and 5 at.% were analyzed by differential scanning calorimetry, thermogravimetric analysis and X-ray in order to understand the oxidation behavior depending on their Si-content. Additionally, a partially oxidized AlCrSiN coating with 5 at.% Si on a sapphire substrate was studied across the coating thickness by depth-resolved cross-sectional X-ray nanodiffraction and scanning trans-mission electron microscopy to investigate the elemental composition, morphology, phases and residual stress evolution of the oxide scale and the non-oxidized coating underneath. The results reveal enhanced oxidation properties of the AlCr(Si)N coatings with increasing Si-content, as demonstrated by a retarded onset of oxidation to higher temperatures from 1100 °C for AlCrN to 1260 °C for the Si containing coatings and a simultaneous deceleration of the oxidation process. After annealing of the AlCrSiN sample with 5 at.% Si at an extraordinary high temperature of 1400 °C for 60 min in ambient air, three zones developed throughout the coating strongly differing in their composition and structure: (i) a dense oxide layer comprising an Al-rich and a Cr-rich zone formed at the very top, followed by (ii) a fine-grained transition zone with incomplete oxidation and (iii) a non-oxidized zone with a porous structure. The varying elemental composition of these zones is furthermore accompanied by micro-structural variations and a complex residual stress development revealed by cross-sectional X-ray nanodiffraction. The results provide a deeper understanding of the oxidation behavior of AlCr(Si)N coatings depending on their Sicontent and the associated elemental, microstructural and residual stress evolution during high-temperature oxidation.

Keywords: AlCrSiN; Nanocomposite; Cathodic arc; Oxidation behaviour; Cross-sectional X-ray nanodiffraction

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Permalink: https://www.hzdr.de/publications/Publ-32946
Publ.-Id: 32946


The application of deep learning on slit-scan images processing and emittance prediction

Ma, S.; Arnold, A.; Ryzhov, A.; Schaber, J.; Petr, M.; Paul, Z.; Teichert, J.; Xiang, R.

The radiation source ELBE (Electron Linac for beams with high Brilliance and low Emittance) delivers multiple secondary beams, both electromagnetic radiation, and particles. To measure beam emittance effectively before user time, a fast and accurate method, the continue moving slit-scan system for high bunch charge has been developed. To accelerate the process of the images, the parallel algorithm, images classification Convolutional Neural Network (CNN), and autoencoder network are used.

Keywords: emittance; slit-scan; deep learning

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  • Open Access Logo Lecture (Conference) (Online presentation)
    DPG-Frühjahrstagung (Dortmund), 15.-19.03.2021, Dortmund, Germany

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Permalink: https://www.hzdr.de/publications/Publ-32945
Publ.-Id: 32945


UDV methods for characterizing flows in liquid metal batteries

Cheng, J.; Wang, B.; Mohammad, I.; Horstmann, G. M.; Kelley, D.

We present ultrasound measurements from a laboratory model of a liquid metal battery (LMB). Two major flow
drivers interact within LMBs: thermal gradients due to the presence of internal heating, and electrovortex flow
(EVF) driven by diverging current densities. The product of these interactions remains poorly characterized. We
approach this problem with ultrasonic Doppler velocimetry (UDV) combined with a laboratory model of an LMB
fluid layer. Using ultrasound probes placed around a liquid gallium vessel, we elucidate typical velocities, flow
structures, and flow statistics in a representative volume of the flow field. UDV measurements reveal that pure
convection takes the form of the recently-discovered ‘jump rope vortex,’ with a characteristic frequency visible in
velocity statistics. They also indicate that EVF goes through stable, unstable, and oscillatory flow regimes. In
progress is an approach for training physics-informed neural networks (PINNs) on UDV data, allowing us to
reconstruct flow in regions where no probe measurements have taken place by leveraging the equations of motion.

  • Contribution to proceedings
    13th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering (ISUD 2021), 13.-15.06.2021, Zürich, Schweiz

Permalink: https://www.hzdr.de/publications/Publ-32944
Publ.-Id: 32944


Highlight selection of radiochemistry and radiopharmacy developments by editorial board

Alves, F.; Antunes, I.; Cazzola, E.; Cleeren, F.; Cornelissen, B.; Denkova, A.; Engle, J.; Faivre-Chauvet, A.; Gillings, N.; Hendrikx, J.; Jalilian, A.; van der Meulen, N.; Mikolajczak, R.; Neels, O.; Pillai, M.; Reilly, R.; Rubow, S.; Seimbille, Y.; Spreckelmeyer, S.; Szymanski, W.; Taddei, C.

Background: The Editorial Board of EJNMMI Radiopharmacy and Chemistry releases a biyearly highlight commentary to update the readership on trends in the field of radiopharmaceutical development.
Results: This commentary of highlights has resulted in 21 different topics selected by each member of the Editorial Board addressing a variety of aspects ranging from novel radiochemistry to first in man application of novel radiopharmaceuticals. Also the first contribution in relation to MRI-agents is included.
Conclusion: Trends in (radio)chemistry and radiopharmacy are highlighted demonstrating the progress in the research field being the scope of EJNMMI Radiopharmacy and Chemistry.

Permalink: https://www.hzdr.de/publications/Publ-32943
Publ.-Id: 32943


Hydrodynamic and efficiency data pertaining to an air-water column mockup (of 0.8 m internal diameter) equipped with sieve trays

Vishwakarma, V.; Marchini, S.; Schleicher, E.; Schubert, M.; Hampel, U.
DataCollector: Vishwakarma, Vineet; DataCollector: Marchini, Sara; RelatedPerson: Schleicher, Eckhard; ContactPerson: Schubert, Markus; Supervisor: Hampel, Uwe

The hydrodynamic data including effective froth height, liquid holdup and tracer flow and patterns related to an operational sieve tray inside a 0.8 m diameter air-water column simulator are provided here. These data were obtained via an advanced multiplex flow profiler at several gas and liquid loadings. The generated data were examined for predicting the tray efficiency using mathematical models. For model validation, the stripping of isobutyl acetate from the aqueous solution over the tray was employed, and the liquid samples at several tray locations were analyzed via UV spectroscopy. The resulting efficiencies and related information are provided here, too. All raw data files, data processing scripts and supporting information with proper indexing and sequencing are uploaded. All these data are intended for non-commercial use only.

Keywords: Column tray; two-phase crossflow; 3D liquid holdup; effective froth height; tracer-response analysis; tray efficiency calculations

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Permalink: https://www.hzdr.de/publications/Publ-32942
Publ.-Id: 32942


Curium(III) speciation in the presence of microbial cell wall components

Moll, H.; Barkleit, A.; Frost, L.; Raff, J.

Trivalent actinides such as Cm(III) are able to strongly interact with microbes and especially with bacterial cell walls. However, detailed knowledge of the influence of different cell wall components is somewhat lacking. For this investigation, we studied the formation of aqueous Cm(III) complexes with cell wall components (e.g., lipopolysaccharide, peptidoglycan, and plasma membranes) using time-resolved laser-induced fluorescence spectroscopy (TRLFS). For all systems, two specific Cm(III) complexes with the biomacromolecules were observed as a function of pH. Specifically, Cm(III) was found to bind to phosphate and carboxyl groups present in the structure of the biomacromolecules. Stability constants and luminescence parameters of the specific Cm(III) complexes were determined and are presented. The pH of the surrounding aqueous solution, the plasma membrane concentration, and proteins included in the crude plasma membrane fraction were found to significantly impact the complexation of Cm(III). The Cm(III) luminescence spectra with plasma membranes, cell wall polymers, as well as Gram-negative (Sporomusa sp. MT-2.99 and Pseudomonas fluorescens) and Gram-positive (Paenibacillus sp. MT-2.2) bacteria will be explained by linear combination fitting using the investigated components.

Keywords: curium; lipopolysaccharide; peptidoglycan; plasma membrane; bacterial cell walls; luminescence spectroscopy

Permalink: https://www.hzdr.de/publications/Publ-32941
Publ.-Id: 32941


Spin pumping at interfaces with ferro- and paramagnetic Fe60Al40 films acting as spin source and spin sink

Strusch, T.; Lenz, K.; Meckenstock, R.; Bali, R.; Ehrler, J.; Lindner, J.; Faßbender, J.; Farle, M.; Potzger, K.; Semisalova, A.

We present a study of spin pumping efficiency and determine the spin mixing conductance and spin diffusion length in thin bilayer films based on 3d transition metal alloy Fe60Al40. Due to its magnetostructural phase transition, Fe60Al40 can be utilized as a ferromagnetic (FM) or paramagnetic (PM) material at the same temperature depending on its structural order, thus thin Fe60Al40 film can act as a spin source or a spin sink when interfaced with a paramagnet or a ferromagnet, correspondingly. Ferromagnetic resonance (FMR) measurements were performed in a frequency range of 5 - 35 GHz on bilayer films composed of FM-Fe60Al40 / Pd and PM-Fe60Al40 / permalloy Ni80Fe20. The increase of damping parameter with the thickness of paramagnetic layer was interpreted as a result of spin pumping into a paramagnet. In the first case, the FM-Fe60Al40 acts as a spin source and in the second case PM-Fe60Al40 serves as a spin sink. We determine the spin mixing conductance 𝑔𝑃𝑑↑↓=(3.8±0.5)×1018 m-2 at the FM-Fe60Al40/Pd interface and the spin diffusion length 𝜆𝑃𝑑=9.1 ±2.0 nm in Pd. For the PM-Fe60Al40/permalloy interface we find a spin mixing conductance 𝑔𝐹𝑒𝐴𝑙↑↓=(2.1±0.2)×1018 m-2 and a spin diffusion length 𝜆𝐹𝑒𝐴𝑙=11.9 ±0.2 nm for PM-Fe60Al40. Demonstrated bi-functionality of Fe60Al40 alloy in spin pumping structures may be promising for spintronic applications

Keywords: Ferromagnetic resonance; spin pumping; ferromagnetic films; ferromagnetism; FeAl alloys; spin diffusion; damping; linewidth

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Permalink: https://www.hzdr.de/publications/Publ-32940
Publ.-Id: 32940


Direct tomographic observation of brine percolation into MgO-shotcrete drill cores

Kulenkampff, J.

Heterogeneity and tightness of the barrier demand particular sensitive and lasting measuring methods, as well as resolution of small details. For this reason we developed a guard-ring surface-packer for process tomography of brine migration into barrier material with positron-emission-tomography (PET). Based on radiolabeling, this method is extremely sensitive, non-destructive and without retroaction.
As example for transport in the engineered barrier, we investigated injection of [²²Na]NaCl-sat – solution from a fluid reservoir with a diameter of 20 mm into the contact zone of adjacent MgO-shotcrete layers. The driving pressure was 2 bar, which caused intrusion of 1 mL of solution over a period of 260 d.
Overlay of the sequence of PET images and the structural CT image shows that deeper penetration (> 10 mm) occurred predominantly along one single pathway that was predetermined by the porous structure. Also, we observed a slowly propagating diffuse front that encompassed only a small portion of the injected fluid.
Although the permeability of the material is very low (1e-20 m²), the major portion of the brine propagates through a very confined channel and thus may reach a significant penetration depth, beyond the predictions based on assumed homogeneous material.

Keywords: radioactive waste disposal; engineered barrier; transport experiments; positron emission tomography; CT; MgO

  • Open Access Logo Lecture (Conference)
    Saltmech X, 05.-08.07.2022, Utrecht, Nederland
    DOI: 10.1201/9781003295808
  • Open Access Logo Contribution to proceedings
    10th Conference on the Mechanical Behavior of Salt (SaltMech X), 05.-08.07.2022, Utrecht, Nederland
    The Mechanical Behavior of Salt X Proceedings of the 10th Conference on the Mechanical Behavior of Salt (SaltMech X), Utrecht, The Netherlands, 06-08 July 2022, London: CRC Press, 9781003295808, 98-106
    DOI: 10.1201/9781003295808

Permalink: https://www.hzdr.de/publications/Publ-32939
Publ.-Id: 32939


Superconducting solenoid field measurement and optimization

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

The solenoid is a significant part of an electron injector to provide a proper focusing, and preserve the beam projected emittance. A superconducting solenoid is applied for the SRF photoinjector at HZDR. The solenoid itself can degrade electron beam quality due to magnetic field imperfections like multipole components. In order to determine the field aberrations in the solenoid, we measured the superconducting solenoid magnetic field in the cryomodule. A simple and effective method is used to analyze the multipole field components, which will be presented in this paper.

Keywords: solenoid; magnetic field

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  • Open Access Logo Contribution to proceedings
    12th International Particle Accelerator Conference (IPAC’21), 24.-28.05.2021, Brasília, Brazil
    Proceedings of IPAC’21: JACoW

Permalink: https://www.hzdr.de/publications/Publ-32938
Publ.-Id: 32938


Generalized Landau-Khalatnikov-Fradkin transformations for arbitrary N-point fermion correlators

Ahmadiniaz, N.; Edwards, J. P.; Nicasio, J.; Schubert, C.

We examine the nonperturbative gauge dependence of arbitrary configuration space fermion correlators in quantum electrodynamics (QED). First, we study the dressed electron propagator (allowing for emission or absorption of any number of photons along a fermion line) using the first quantized approach to quantum field theory and analyze its gauge transformation properties induced by virtual photon exchange. This is then extended to the N-point functions where we derive an exact, generalized version of the fully nonperturbative Landau-Khalatnikov-Fradkin (LKF) transformation for these correlators. We discuss some general aspects of the application in perturbation theory and investigate the structure of the LKF factor aboutD¼2dimensions

Keywords: LKFT; Worldline formalism; Non-perturbative QED

Permalink: https://www.hzdr.de/publications/Publ-32937
Publ.-Id: 32937


Transport properties of systematically disordered Cr2AlC films

Salgado Cabaco, J.; Kentsch, U.; Lindner, J.; Faßbender, J.; Leyens, C.; Bali, R.; Boucher, R.

Nano-lamellar composite materials, known as MAX-phases, can possess a combination of ceramic and metallic properties. A prototype compound is Cr2AlC, formed from a unit cell of Cr2C sandwiched be-tween atomic planes of Al. Here we observe the modifications to the structural, transport and magnetic behavior of 500 nm thick Cr2AlC after irradiation with Co+ions, and Ar+noble gas ions as control.X-ray shows that ion-irradiation induces a suppression of the 0002 reflection, indicating a deterioration of the crystal structure. Increasing the ion fluence leads to an increase of the saturation magnetization at 1.5 K, whereby both Ar+ and Co+ cause an increased magnetization, respectively to 150 kA.m−1and 190 kA.m−1, for the highest fluences used. At Co+ fluences of 5E13 ions.cm−2 the magnetoresistance (MR) shows a 2 orders of magnitude increase, up to 3%(10 T) at 100K. A similar effect also occurs for 5E12 ions.cm−2 Ar+ irradiated films, however, with a smaller MR-increase. The disordering of MAX phase films may reveal interesting spin-related transport phenomena.

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  • Poster
    84. Jahrestagung der DPG, 27.09.2021, Online, Germany

Permalink: https://www.hzdr.de/publications/Publ-32936
Publ.-Id: 32936


High-entropy carbons: From high-entropy aromatic species to single-atom catalysts for electrocatalysis

Ding, J.; Wu, D.; Zhu, J.; Rodríguez-Hernández, F.; Chen, Y.; Lu, C.; Zhou, S.; Zhang, J.; Tranca, D.; Zhuang, X.

Single-atom catalysts (SACs) have rapidly entered the field of nanomaterials and demonstrated great potential for energy devices in recent years. Of all types of SACs, porous carbon-based SACs are the most popular species because of their excellent conductivity, large specific surface area, and easily tunable heteroatom and metal components. However, most of the reported cases focus on the metal centers and their coordination environments, while they do not pay much attention to carbon precursors and carbon transformation during high-temperature treatment. In this work, we use a high-entropy aromatic molecule, azulene, for rational synthesis of azulene-enriched, sandwich-like polymer nanosheets and corresponding single-Fe-dispersed porous carbon nanosheets. The azulene-based metal-free polymer nanosheets exhibit a narrow band gap and temperature-dependent magnetism. As proof-of-concept electrocatalysts for CO2 reduction, the prepared carbon nanosheets exhibit high activity and stability. Operando X-ray absorption spectroscopy and density functional theory studies reveal the high activity of Fe-N coordination sites in the presence of 5/7-membered carbon ring-based topological defects in the carbon skeleton. Taken together, this work provides a new method of synthesizing high-entropy carbons using azulene-based high-entropy molecule as precursor and paves the way toward high-efficiency SACs with rich topological defects for energy conversion.

Keywords: High-entropy aromatic molecule; Topological defect; Single-atom catalyst; Porous carbon nanosheet; Carbon dioxide conversion

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Permalink: https://www.hzdr.de/publications/Publ-32934
Publ.-Id: 32934


QE and life time of Cs2Te photocathodes on copper for SRF gun-II at HZDR

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

The SRF gun-II at HZDR has been stably applied as the electron
source for high power THz radiation since 2018, generating CW beams
with bunch charges up to 300 pC at 100 kHz. It is an excellent demonstration
that SRF guns can work reliably in a high power user facility.
In order to generate higher current beam with MHz repetition rate,
Cs2Te photocathodes are required. However, in last two experiments
with Cs2Te, the Mo substrate plugs were overheated in superconducting
rf cavity. The reason is that different thermal expansion coefficient
of Mo and Cu led to a bad thermal contact between the Mo plug and
Cu holder. Thus we decided to use Cu as new substratum of Cs2Te
cathodes. In last year we prepared several Cs2Te photocathodes on Cu
plugs and improved the vacuum of cathode transfer system in order
to achieve satisfied lifetime. In this contribution, we will present the
study result of QE and life time of Cs2Te photocathodes with different
thickness.

Keywords: SRF gun; photocathode; Cs2Te

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Permalink: https://www.hzdr.de/publications/Publ-32933
Publ.-Id: 32933


Observability of Coulomb-assisted quantum vacuum birefringence

Ahmadiniaz, N.; Bussmann, M.; Cowan, T.; Debus, A.; Kluge, T.; Schützhold, R.

We consider the scattering of an x-ray free-electron laser (XFEL) beam on the superposition of
a strong magnetic field $\bf{B}_{\rm ext}$ with the Coulomb field $\bf{E}_{\rm ext}$
of a nucleus with charge number $Z$. In contrast to Delbr\"uck scattering
(Coulomb field only), the magnetic field $\bf{B}_{\rm ext}$
introduces an asymmetry (i.e., polarization dependence) and renders the effective interaction volume quite
large, while the nuclear Coulomb field facilitates a significant momentum transfer $\Delta\bf k$.
For a field strength of $B_{\rm ext}=10^6 T$ (corresponding to an intensity of order $10^{22}~\rm W/cm^2$)
and an XFEL frequency of 24~keV, we find a differential cross section
$d\sigma/d\Omega\sim10^{-25}~Z^2/(\Delta{\bf k})^2$ in forward direction for one nucleus.
Thus, this effect might be observable in the near future at facilities such as the
Helmholtz International Beamline for Extreme Fields (HIBEF) at the European XFEL.

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Permalink: https://www.hzdr.de/publications/Publ-32932
Publ.-Id: 32932


Caesium-deposition on GaN as a potential Photocathode

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

SRF injectors need materials which can promise high quantum efficiency, long lifetime and good vacuum stability, fast response time and low thermal emittance.
It is assumed that GaN, like GaAs, as a novel electron source for particle accelerators shows an enormous potential.
P-type GaN on different substrate material is activated by a thin layer of caesium and illuminated at the same time by ultra-violet (UV) light. As a consequence of a NEA surface and photoeffect, the generated photoelectrons enter into vacuum and are collected by an anode. The resulting photocurrent is detected during the whole activation process and stopped when a maximum photocurrent is reached. Quantum efficiency (QE) can be calculated from the photocurrent. Its decay is tracked in the following days after activation. It is also studied to re-activate the sample again by using thermal heat treatment and caesium Deposition once more.
High 11.5% QE can be provided from GaN:Cs on sapphire substrate at the moment. After 600 h of lifetime this photocathode shows still 1.4% QE.
Besides the outstanding experimental results so far further investigations are still required.

Keywords: gallium nitride; photocathode; SRF Gun; ceasium deposition; III-V semiconductor

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    International Conference on RF Superconductivity (SRF 2021), 27.06.-02.07.2021, Michigan, USA

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Permalink: https://www.hzdr.de/publications/Publ-32931
Publ.-Id: 32931


GaN:Cs Photocathode for SRF Guns

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

Magnesium bulk cathodes and caesium telluride cathodes work routinely in SRF Gun II at ELBE. However, the particle accelerator community is always looking for new materials which can promise higher quantum efficiency, longer lifetime and good vacuum stability, fast response time and low thermal emittance.
P-type GaN on different substrate material is activated by a thin layer of caesium and illuminated at the same time by ultra-violet light. As a consequence of a negative electron affinity and photoeffect, the generated photoelectrons enter into vacuum and are collected by a copper ring anode. The resulting photocurrent is detected during the activation process and stopped when a maximum photocurrent is reached. Quantum efficiency can be calculated from the photocurrent and its decay is tracked in the following days after activation.
By a comparison of differences in substrate material, chemical pre-cleaning, thermal heat treatment and activation parameters (e.g. caesium-flux), the photocurrent, quantum efficiency and its decay is studied.

Keywords: gallium nitride; photocathode; SRF Gun; caesium deposition

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    12th International Particle Accelerator Conference (IPAC 2021), 24.-28.05.2021, Campinas, Brasilien

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Permalink: https://www.hzdr.de/publications/Publ-32930
Publ.-Id: 32930


Caesium deposition on GaN to obtain a photocathode for particle accelerator

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

Negative electron affinity (NEA) GaAs- and GaN-based photocathodes are used in modern night vison detectors and light emitting diodes1. GaAs semiconductors are already used as electron sources in particle accelerators and well- studied2. Like GaAs, GaN belongs to the
III-V semiconductor group with similar properties. It is assumed that GaN, like GaAs, shows enormous potential as a novel electron source for particle accelerators.

P-type GaN on different substrate material (sapphire, silicon, copper or SiC) is activated by a thin layer of caesium and illuminated by ultra-violet (UV) light at the same time. As a consequence of negative electron affinity (NEA) and photoeffect, the generated photoelectrons enter into vacuum and are collected by a copper ring anode. The resulting photocurrent is detected during the whole activation process and stopped when a maximum photocurrent is reached.
The GaN is chemical cleaned and transferred into a UHV chamber where it undergoes a thermal heat treatment at 250°C for 20 min using a halogen lamp. The aim of the thermal treatment is to remove residual adsorbed gas molecules from the sample surface.
Afterwards when the sample is back at room temperature, the thermal-cleaned GaN is activated with a thin layer of caesium. The photocurrent and the QE is observed in the following days until the QE vanishes. Then it is tested to re-activate the cathode again, meaning to thermal clean it again and to activate it with caesium once more.

By a comparison of differences in substrate material, chemical pre-cleaning, thermal heat treatment and activation parameters (e.g. caesium-flux), the photocurrent, quantum efficiency and the re-activation of the photocathode is studied. Additionally the GaN samples are examined by AFM, SEM and EDX.
From the experimental results obtained so far, it appears that GaN:Cs could be used as a photocathode in particle accelerators, but further investigations are still required and needed.

Keywords: gallium nitride; photocathode; caesium deposition; SRF Gun

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    DPG-Frühjahrstagung des Fachverbandes Oberflächenphysik, 01.-04.03.2021, Hannover, Deutschland

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Permalink: https://www.hzdr.de/publications/Publ-32929
Publ.-Id: 32929


Status Report of GaN photocathode

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

The photocathodes determine the beam quality in linear accelerators and represent a key component for many accelerator projects. Free-electron lasers (FEL), synchrotron- and THz radiation sources require injector systems with high brightness electron beams.

High quantum efficiency, a long lifetime and good vacuum stability, fast response time and low thermal emittance are desirable parameters for a perfect photocathode used in accelerators. Semiconductors such as GaN and GaAs as novel materials for photocathodes are showing an enormous potential.
GaAs is a well-known material for photocathodes. After activation with caesium and oxygen, it has a high QE for visible light (red or green). An advantage of GaAs is the opportunity of the layers to emit spin-polarized electrons.
GaN is a semi-conductive material and well known for its high QE when lighted with UV light. For improving the QE only caesium for activation is required.
At the moment GaN is used for photocathode-based detectors such as photomultipliers or phototubes and for LEDs. They have characteristics of low dark current, high-speed response and high sensitivity. It is very new for application in SRF Guns. It seems to be more robust and achieves higher QE than other photocathodes [1].
Crystallinity and surface parameters define the photoemission properties. Modern analytical methods are used for identification of impurities, dislocations and characterization of the crystallinity of the semiconductors and the right cleaning treatment as well as the right caesium rating.
[1] Uchiyama, Shoichi et al. 2011. “GaN-Based Photocathodes with Extremely High Quantum Efficiency” 103511(2005):1–4.

Keywords: gallium nitride; photocathode; SRF Gun

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    High Brightness Electron beams generated from novel THermal resistant photocathodes (BETH) 3rd Collaboration Meeting, 01.03.2021, Siegen, Deutschland

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Permalink: https://www.hzdr.de/publications/Publ-32928
Publ.-Id: 32928


DNA Based Formation of Nanodisc-Stacks

Subramanian, M.; Kielar, C.; Tsushima, S.; Fahmy, K.; Oertel, J.

We describe here the formation of multimers of membrane-scaffolding protein MSP1D1-bounded nanodiscs using the thiol reactivity of engineered cysteines. The mutated positions N42 and K163 in MSP1D1 were chosen to support chemical modification as evidenced by fluorescent labeling with pyrene. The direct disulphide bond formation of nanodiscs formed by the MSP1D1_N42C variant led to dimers and trimers with low yield. In contrast, transmission electron microscopy revealed that the attachment of oligonucleotides to the engineered cysteines of MSP1D1 allowed the growth of submicron-sized tracts of stacked nanodiscs through the hybridization of nanodisc populations carrying complementary strands and a flexible spacer.

Keywords: membrane-scaffolding protein; nanodisc; membrane protein; lipid bilayer; lipid protein interaction; multimerization; self-assembly; bionanotechnology

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Permalink: https://www.hzdr.de/publications/Publ-32927
Publ.-Id: 32927


And yet it moves: Oxidation of the Nuclear Autoantigen La/SS-B is the Driving Force for Nucleo-Cytoplasmic Shuttling

Berndt, N.; Bippes, C. C.; Michalk, I.; Bartsch, T.; Arndt, C.; Puentes-Cala, E.; Soto, J. A.; Loureiro, L. R.; Kegler, A.; Bachmann, D.; Gross, J. K.; Gross, T.; Kurien, B.; Scofield, T. R. H.; Farris, A. D.; James, J. A.; Bergmann, R.; Schmitz, M.; Feldmann, A.; Bachmann, M.

Already decades ago, we and many other groups showed a nucleo-cytoplasmic translocation of La protein in cultured cells. This shuttling of La protein was seen after e.g. UV irradiation, virus infections, hydrogen peroxide exposure, and Fenton reaction based on iron or copper ions. In common, all these conditions are somehow related to oxidative stress. Unfortunately, all these harsh conditions could also cause an artificial release of La protein. Even until today, the shut-tling and a cytoplasmic function of La/SS-B are controversially discussed. Moreover, the driving mechanism for the shuttling of La protein remains unclear. Recently we showed that La protein undergoes redox dependent conformational changes. Moreover, we developed anti-La mono-clonal antibodies (anti-La mAbs) which are specific for either the reduced form of La protein or the oxidized form. Using these tools, here we show that redox dependent conformational changes are the driving force for the shuttling of La protein. Moreover, we show that transloca-tion of La protein to the cytoplasm can be triggered in a ligand/receptor dependent manner un-der physiological conditions. We show that ligands of toll-like receptors lead to a redox de-pendent shuttling of La protein. The shuttling of La protein depends on the redox status of the respective cell type. Endothelial cells are usually resistant to the shuttling of La protein while dendritic cells are highly sensitive. However, deprivation of intracellular reducing agents in endothelial cells turns endothelial cells sensitive to a redox dependent shuttling of La protein.

Keywords: anti-La/SS-B antibodies; primary Sjögren’s Syndrome; autoimmunity; La/SS-B autoantigen; Systemic Lupus Erythematosus; Redox sensor; Shuttling of La protein

Permalink: https://www.hzdr.de/publications/Publ-32925
Publ.-Id: 32925


Mounted Single Particle Characterization for 3D Mineralogical Analysis - MSPaCMAn

Da Assuncao Godinho, J. R.; Danelon Grilo, B. L.; Hellmuth, F.; Siddique, A.

This paper demonstrates a new method to classify mineral phases in 3D images of particulate materials obtained by x-ray computed tomography. The method consists of 1) sample preparation and scanning of a particle dispersion; 2) image processing optimized towards the labelling of individual particles in the sample; 3) phase identification is done at the particle level using an interpretation of the grey-values of all voxels in a particle rather than of all voxels in the sample. The method allows minimizing the impact of typical image artefacts in the classification of voxels, i.e. beam hardening, partial volume effect, spot blurriness and cone beam. Additionally, the particle’s geometry and microstructure can be used as classification criteria besides the grey-values. The result is an increased accuracy of phase classification, reduced detection limit of phases, lower grain size to voxel size ratio that can be detected, individual particle statistics can be measured instead of only bulk statistics. Consequently, the method broadens the applicability of 3D imaging techniques for particle analysis at low particle size to voxel size ratio, which is typically limited by unreliable phase classification that leads to inaccurate quantification. This opens the possibility for 3D semi-automated mineralogy.

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Permalink: https://www.hzdr.de/publications/Publ-32924
Publ.-Id: 32924


Two Examples for AI Communities

Juckeland, G.; Steinbach, P.

This short talk presents two approaches for building AI communities in the Dresden area. First the top down approach of Helmholtz AI, where HZDR is one of six hubs of consultants to assist and train scientists. Second with the Machine Learning Community (MLC) Dresden a bottom up approach of practitioners just sharing experience and information in regular seminars and other asynchronous communication channels.

Keywords: Helmholtz AI

  • Open Access Logo Invited lecture (Conferences) (Online presentation)
    Kick-Off of Scientific Area Network “Dimensions of Artificial Intelligence”, 16.07.2021, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-32923
Publ.-Id: 32923


Operational experience of photocathodes for HZDR SRF gun

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

The SRF gun-II at HZDR has been stably applied as the electron source for high power THz radiation since 2018, generating CW beams with bunch charges up to 300 pC at 100 kHz. It is an excellent demonstration that SRF guns can work reliably in a high power user facility.
As well known, that the quality of the photocathodes is critical for the stability and reliability of the gun operation. In last years, thank to the successful ps UV laser cleaning, Mg photocathodes were successfully used for gun operation at kHz repitition rate.
In order to satisfy user request of MHz operation, Cs2Te is still in demand. However, the Mo plugs were overheated in superconducting rf cavity due to thermal contact problem, and SRF Gun-II faced twice serious contamination in 2017. The Cs2Te could not be used in gun untill Cu is adopted in stead of Mo as new substratum. Up to now three Cs2Te cathodes on Cu plugs have been applied in the Gun-II.
In this contribution, we will present the operational aspect of the photocathodes for SRF gun, and discuss the possible improvement in the future application.

Keywords: SRF gun; photocathode

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    2021 International Conference RF Superconductivity, 28.06.-02.07.2021, East Lansing, USA

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Permalink: https://www.hzdr.de/publications/Publ-32922
Publ.-Id: 32922


Review of superconducting radiofrequency gun

Xiang, R.

The success of proposed high power free-electron lasers (FELs) and energy recovery linac (ERL) largely depends on the development of the electron source, which requires the best beam quality and CW operation. An elegant way to realize both high brilliance and high current is to com-bine the high beam quality of the normal conducting radio frequency photoinjector with the quick developing superconducting radio frequency technology, to build superconducting rf photoinjectors (SRF guns).
In last decade, several SRF gun programs based on dif-ferent approaches have achieved promising progress, even succeeded in routine operation at BNL and HZDR. In the near future SRF guns are expected to play an im-portant role for hard X-ray FEL facilities. In this contribu-tion, we will review the design concepts, parameters, and status of the major SRF gun projects.

Keywords: SRF gun

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    12th International Particle Accelerator Conference - IPAC’21, 24.-28.05.2021, virtual format, Brazil
    Proceedings of IPAC’21: JACoW
    DOI: 10.18429/JACoW-IPAC2021-WEXC03

Permalink: https://www.hzdr.de/publications/Publ-32921
Publ.-Id: 32921


Solving overheating of Cs2Te cathodes in the ELBE SRF gun

Arnold, A.

In 2014, the second-generation of the ELBE SRF gun replaced its predecessor, which had been in operation since 2007. In the first two years, copper and magnesium cathodes were initially used without any discernible problems. However, after switching to Cs2Te in 2017, it was found that the layers of two cathodes evaporated within a few days during RF operation in the Gun. Since this was never observed in Gun I, an extensive root cause search was conducted using a dedicated cathode test setup. The findings pointed to loose thermal contact between the cathode plug and the cathode body and ultimately resulted in a change
of the used cathode substrate from molybdenum to copper. Although this was accompanied by a lower quantum efficiency of about 5% after preparation, it stabilized to 1-2% during beam operation in the SRF gun. As of May 2020, three of these cathodes have now been successfully used for THz user beam time and a total charge of 26 C has been extracted. Together with the electrons still produced by Mg cathodes in 2019/2020, a total of 217 user shifts could be served and 2600h hours of beam time were delivered. This demonstrates the reliability of CW SRF in combination with normal conducting cathode and is so far unique in the world. During the talk, the reason for overheating, the preparation on Cu substrate as well as experiences from the past two years of user beam operation will be presented in detail.

Keywords: SRF gun; SRF; superconducting; radio frequency; ELBE

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    7th MT meeting (virtuell), 01.-03.02.2021, Online, Deutschland

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Permalink: https://www.hzdr.de/publications/Publ-32920
Publ.-Id: 32920


RF Experience from 6 Years of ELBE SRF-Gun II Operation

Arnold, A.; Lu, P.; Ma, S.; Murcek, P.; Ryzhov, A.; Schaber, J.; Teichert, J.; Xiang, R.; Ciovati, G.; Kneisel, P.; Vennekate, H.

At the electron accelerator for beams with high bril-liance and low emittance (ELBE), the second version of a superconducting radio-frequency (SRF) pho-toinjector was brought into operation in 2014. After a period of commissioning, a gradual transfer to routine operation took place in 2017 and 2018, so that now more than 3400h of user beam have already been gen-erated since 2019. During this time, a total of 20 cath-odes (2 Cu, 12 Mg, 6 Cs2Te) were used, but no serious cavity degradation was observed. In this paper, we summarize the operational experience of the last 6 years of SRF gun operation, with special emphasis on main RF properties of the gun cavity.

Keywords: SRF gun; SRF; superconducting; radio frequency; ELBE

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    2021 International Conference on RF Superconductivity (SRF'21), 28.06.-02.07.2021, East Lansing, Michican, USA
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    2021 International Conference on RF Superconductivity (SRF'21), 28.06.-02.07.2021, East Lansing, Michican, USA
    Proceedings of the 2021 International Conference on RF Superconductivity (SRF'21)
    DOI: 10.18429/JACoW-SRF2021-TUPTEV001

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Permalink: https://www.hzdr.de/publications/Publ-32919
Publ.-Id: 32919


Upgrade of the ELBE Timing System

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

At the ELBE accelerator center a superconducting linac is operated to drive manifold secondary radiation sources like two infrared FELs, a positron source and a THz facility. The machine uses two injectors as electron sources that are accelerated in the main linac. The user experiments demand a large variety of bunch patterns from single shot to macro pulsed and cw beam at up to 26 MHz repetition rate. At ELBE a new timing system is being developed based on the MRF hardware platform and the MRF Timing System IOC. It uses two masters and a scalable number of connected receivers to generate the desired pulse patterns for operating the machine and to control user experiments. The contribution will show the architecture of the timing system, the control interfacing and performance measurements acquired on the test bench.

Keywords: ELBE; Timing; MicroTCA

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  • Poster (Online presentation)
    International Particle Accelerator Conference 2021, 24.-28.05.2021, Campina, Brazil

Permalink: https://www.hzdr.de/publications/Publ-32917
Publ.-Id: 32917


Unusual field-induced spin reorientation in FeCr2S4: Field tuning of the Jahn-Teller state

Prodan, L.; Yasin, S.; Jesche, A.; Deisenhofer, J.; Krug Von Nidda, H.-A.; Mayr, F.; Zherlitsyn, S.; Wosnitza, J.; Loidl, A.; Tsurkan, V.

The multiferroic spinel FeCr2S4 is a benchmark material for exploring the competition of spin-orbit (SO) and Jahn-Teller (JT) coupling. Our magnetic and thermodynamic studies of stoichiometric single-crystalline samples evidence a magnetic-field-induced spin-reorientation transition in the cooperative JT state below 10 K. At 2 K, at a critical magnetic field of 4.5 T, the magnetization measured along the hard magnetization axis [111] manifests a jump to the fully saturated state accompanied by a steplike decrease of the sound velocity and an abrupt increase of the magnetostriction. All these quantities reveal a hysteretic behavior pointing towards a first-order magnetostructural transformation. Below the JT transition, the specific heat shows a complex behavior upon the application of magnetic fields depending on the crystallographic directions. The observed reduction by 20% of the magnetic anisotropy below the JT transition is attributed to the competition of the SO and JT interactions tuned by external magnetic fields. The concomitant change of the structural symmetry results in a change of the splitting of the lowest levels of the 5E doublet of the tetrahedrally coordinated Fe2+ ions.

Permalink: https://www.hzdr.de/publications/Publ-32915
Publ.-Id: 32915


Endocytosis is a significant contributor to uranium(VI) uptake in tobacco (Nicotiana tabacum) BY-2 cells in phosphate-deficient culture

John, W.; Lückel, B.; Matschiavelli, N.; Hübner, R.; Matschi, S.; Hoehenwarter, W.; Sachs, S.

Endocytosis of metals in plants is a growing field of study involving metal uptake from the rhizosphere. Uranium, which is naturally and artificially released into the rhizosphere, is known to be taken up by certain species of plant, such as Nicotiana tabacum, and we hypothesize that endocytosis contributes to the uptake of uranium in tobacco. The endocytic uptake of uranium was investigated in tobacco BY 2 cells using an optimized setup of culture in phosphate-deficient medium. A combination of methods in biochemistry, microscopy and spectroscopy, supplemented by proteomics, were used to study the interaction of uranium and the plant cell. We found that under environmentally relevant uranium concentrations, endocytosis remained active and contributed to 14% of the total uranium bioassociation. Proteomics analyses revealed that uranium induced a change in expression of the clathrin heavy chain variant, signifying a shift in the type of endocytosis taking place. However, the rate of endocytosis remained largely unaltered. Electron microscopy and energy dispersive X-ray spectroscopy showed an adsorption of uranium to cell surfaces and deposition in vacuoles. Our results demonstrate that endocytosis constitutes a considerable proportion of uranium uptake in BY 2 cells, and that endocytosed uranium is likely targeted to the vacuole for sequestration, providing a physiologically safer route for the plant than uranium transported through the cytosol.

Keywords: plant cell; proteomics; radionuclide transport; heavy metal interaction; vesicle uptake

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Permalink: https://www.hzdr.de/publications/Publ-32914
Publ.-Id: 32914


Experimental Data: Endocytosis is a means of uranium(VI) uptake in tobacco (Nicotiana tabacum) BY-2 cells

John, W.; Lückel, B.; Matschiavelli, N.; Hübner, R.; Matschi, S.; Hoehenwarter, W.; Sachs, S.

The interaction of tobacco (Nicotiana tabacum) BY-2 cells with uranyl(VI) nitrate in phosphate-deficient medium was investigated. The hypothesis was that endocytosis is a means of uranium uptake in these cells. Analysis was in the form of physiological studies (growth and viability), electron microscopy, proteomics and biochemical studies.

Keywords: uranium; tobacco BY-2; endocytosis; radionuclide interaction; TEM-EDX; proteomics

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Permalink: https://www.hzdr.de/publications/Publ-32913
Publ.-Id: 32913


Intra-unitcell cluster-cluster magnetic compensation and large exchange bias in cubic alloys

Giri, B.; Sahni, B.; Salazar Mejia, C.; Chattopadhyay, S.; Zeitler, U.; Alam, A.; Nayak, A. K.

Composite quantum materials are the ideal examples of multifunctional systems, which simultaneously host more than one novel quantum phenomenon in physics. Here, we present a combined theoretical and experimental study to demonstrate the presence of an extremely large exchange bias in the range 0.8–2.7 T and a fully compensated magnetic state (FCF) in a special type of Pt and Ni-doped Mn3In cubic alloy. Here, oppositely aligned uncompensated moments in two different atomic clusters sum up to zero, which are responsible for the FCF state. Our density functional theory (DFT) calculations show the existence of several possible ferromagnetic configurations with the FCF as the energetically most stable one. The microscopic origin of the large exchange bias can be interpreted in terms of the exchange interaction between the FCF background and the uncompensated ferrimagnetic clusters stabilized due to its negligible energy difference with respect to the FCF phase. We utilize pulsed magnetic field up to 60 T and 30 T static-field magnetization measurements to confirm the intrinsic nature of exchange bias in our system. Finally, our Hall effect measurements demonstrate the importance of uncompensated noncoplanar interfacial moments for the realization of large EB. The present finding of gigantic exchange bias in a unique compensated ferrimagnetic system opens up a direction for the design of novel quantum phenomena for the technological applications.

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Permalink: https://www.hzdr.de/publications/Publ-32912
Publ.-Id: 32912


Reconfigurable Spin-Wave Interferometer at the Nanoscale

Chen, J.; Wang, H.; Hula, T.; Liu, C.; Liu, S.; Liu, T.; Jia, H.; Song, Q.; Guo, C.; Zhang, Y.; Zhang, J.; Han, X.; Yu, D.; Wu, M.; Schultheiß, H.; Yu, H.

Spin waves with nanoscale wavelengths can transfer information free of electron transport and hence are promising for wave-based computing technologies with low-power consumption as a solution to the severe energy losses in modern electronics. Logic circuits based on the interference of spin waves have been proposed for more than a decade. However, spin-wave interference at the nanoscale has yet been realized. Here, we demonstrate experimentally the interference of spin waves with wavelengths down to 50 nm in a low-damping magnetic insulator. The constructive and destructive interference of spin waves is detected in the frequency domain using propagating spin-wave spectroscopy, which is further confirmed by the Brillouin light scattering. The interference pattern is found to be highly sensitive to the distance between two magnetic nanowires acting as spin-wave emitters. By controlling the magnetic configuration of the double-wire system, one can switch the spin-wave interferometer on and off. The observed phenomena are theoretically accounted for by the interlayer magnon-magnon coupling. Our demonstrations are thus key to the realization of spin-wave computing system based on non-volatile nanomagnets at the GHz frequencies.

Keywords: spin waves; magnetism; Brillouin spectroscopy; interferometer; interference; nanotechnologie

Permalink: https://www.hzdr.de/publications/Publ-32911
Publ.-Id: 32911


Nonstationary spin waves in a single rectangular permalloy microstrip under uniform magnetic excitation

Pile, S.; Stienen, S.; Lenz, K.; Narkovic, R.; Wintz, S.; Förster, J.; Mayr, S.; Buchner, M.; Weigand, M.; Ney, V.; Lindner, J.; Ney, A.

The ferromagnetic resonance modes in a single rectangular Py microstrip were directly imaged using timeresolved STXM-FMR measurements and the findings were corroborated by micromagnetic simulations. The spin wave resonance modes showed a nonstanding character, when the wave-vector is parallel to the external static magnetic field due to the highly inhomogeneous effective field inside the strip. The propagating character is observed for all the observed spin waves. The influence of the edge quality was analyzed using micromagnetic simulations.

Keywords: ferromagnetic resonance; scanning x-ray transmission microscopy; spin waves; nanostructures; micromagnetism

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Permalink: https://www.hzdr.de/publications/Publ-32909
Publ.-Id: 32909


A contribution to understanding the flotation behavior of lithium metal oxides and spheroidized graphite for lithium-ion battery recycling

Vanderbruggen, A.; Sygusch, J.; Rudolph, M.; Serna-Guerrero, R.

The treatment of end-of-life lithium-ion batteries (LIBs) using froth flotation has recently gained interest as a method to separate valuable lithium transition-metal oxides (LMOs) and graphite particles from the so-called “black mass” mixture. However, the flotation mechanisms of the cathode active particles have not been properly discussed so far, likely since they are generally accepted to be hydrophilic and are thus expected to remain suspended in the bulk phase and recovered in the underflow. Nevertheless, the froth phase products reported in the literature often contain more than 10% LMOs. This results in losses of cathode materials, while hampering the quality of the recovered anode components. As graphite is one of the main materials used for anode manufacturing, being categorized as a critical raw material, its recovery plays an essential role in the electric vehicle revolution.

This work provides the first fundamental study on the flotation mechanisms of the fine particulate black mass components, with the aim of properly identifying the challenges to overcome in order to drive selectivity in froth flotation separation. A series of analysis using model black mass were carried out to circumvent the influence of residual hydrophobic binder found in LIB waste. Studies of wettability with captive bubble and Washburn capillary rise methods show contact angles for LMOs varying from 14° to 52.6° depending on the technique used. Using a bubble-particle attachment set-up it was found that LMO particles can attach to air bubbles spontaneously and in measurable quantities, contrary to the commonly assumed hydrophilic character of cathode active particles. It was also observed that the typically used oil-based collectors (e.g., Escaid 110) interact with both spheroidized graphite and lithium metal oxides, increasing their hydrophobicity and promoting agglomeration. Finally, the particle agglomeration of black mass components provides another flotation mechanism for LMOs through entrapment.

Keywords: Black mass; Lithium ion batteries; Lithium transition metal oxides; Spheroidized graphite; Recycling; Froth flotation

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Permalink: https://www.hzdr.de/publications/Publ-32908
Publ.-Id: 32908


Microstructure and texture development during hot-compression of Ti5321

Gu, B.; Chekhonin, P.; Xin, S. W.; Liu, G. Q.; Ma, C. L.; Zhou, L.; Skrotzki, W.

The microstructure and texture development of the metastable β‑titanium alloy Ti5321 during hot-compression were investigated by electron backscatter diffraction. Above the β-transus temperature, deformation is accompanied by continuous dynamic recrystallization leading to immediate steady state flow. The deformation below the β-transus temperature is significantly affected by α-precipitation. Dynamic globularization of the α-lamellae leads to flow softening. During hot-compression, parallel to the compression axis a 〈100〉〈111〉double fiber texture develops. With increasing temperature the intensity of 〈100〉increases, while that of <111> decreases. At all temperatures <100> is dominant.

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Permalink: https://www.hzdr.de/publications/Publ-32907
Publ.-Id: 32907


Proton beam visualisation for in-beam MR imaging

Peter, J.; Schellhammer, S.; Gantz, S.; Uber, S.; van der Kraaij, E.; Smeets, J.; Karsch, L.; Pawelke, J.; Hoffmann, A. L.

Introduction
In-beam MRI is expected to improve the targeting accuracy of proton therapy for moving target volumes providing real-time anatomical images and allowing the simultaneous visualisation of the therapeutic proton beam in liquid-filled phantoms [1,2]. The aim of this contribution is to provide an overview of our previous work on MRI-based proton beam visualisation.

Materials & Methods
A 0.22 T open MR scanner was positioned at a fixed horizontal proton research beamline in a clinical proton therapy facility. Water, ethanol, petroleum and mayonnaise phantoms were irradiated with nominal proton beam energies between 190 - 225 MeV at beam currents of 1 - 64 nA. A range of pulse sequences was used for the acquisition of a horizontal slice within the beam volume. Material, sequence, beam current and energy dependence of the beam signal were evaluated.

Results
The proton beam induces a beam current and energy dependent MRI signal in liquids of low viscosity. For fixed beam current setting, the beam range in water extracted from the MR images matches the expected residual range within a few millimetres. Gradient echo-based pulse sequences appear more sensitive to the beam-induced effect than spin echo-based sequences.

Summary
The method holds potential for on-line quality assurance for MR-integrated proton therapy. The underlying image contrast mechanism requires elucidation to enable the development of specifically tailored sequences with increased sensitivity for the beam-induced effect.

Appendix 1

Figure 1: Beam current dependence of the 207 MeV beam signal in water acquired using a Time-of-Flight-Angiography sequence.


Figure 2: Inversion Recovery-Gradient Echo images of water under irradiation at a beam current of 9 nA. The dotted lines indicate the expected proton ranges.

References
[1] Schellhammer SM. Technical feasibility of MR-integrated proton therapy: Beam deflection
and image quality. Doctoral thesis, Technische Universität Dresden, 2019.
[2] Gantz S. Investigation of the physical and technical feasibility of MRI integrated proton
therapy using a horizontally scanning beam. Doctoral thesis, Technische Universität Dresden,
2021.

  • Invited lecture (Conferences) (Online presentation)
    Joint Conference of the ÖGMP, DGMP and SGSMP, 19.-21.09.2021, Online, Online
  • Contribution to proceedings
    Joint Conference of the ÖGMP, DGMP & SGSMP, 21.09.2021, online, online, 978-3-948023-16-4, 212-213

Permalink: https://www.hzdr.de/publications/Publ-32906
Publ.-Id: 32906


Introduction to machine learning operations for HelmholtzAI

Sultova, N.

Introduction to machine learning operations for potential usage within HelmholtzAI

This presentation gives an overview of the machine learning operations landscape and our specific use case.

It further presents a detailed comparison between three potential candidates, Metaflow, MLflow and DVC and an outlook based on the gained information.

Keywords: machine learning; mlops; infrastructure; version control

  • Open Access Logo Lecture (others) (Online presentation)
    Voucher presentation at DESY, 13.07.2021, Dresden, Germany

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Permalink: https://www.hzdr.de/publications/Publ-32904
Publ.-Id: 32904


Amphiphilic ionic oligomers as functionalizable stabilizers for gene therapy nanoparticles

Schmid, M.; Mitrach, F.; Wenzel, B.; Schulz-Siegmund, M.; Hacker, M.-C.

Inorganic nano drug delivery vehicles require the use of an appropriate organic stabilizer. Examples are uncharged thiol containing macromolecules or polymers for gold NPs [1] , positively charged polyethylenimines for metals [2], or carboxylate bearing polymers for cationic calcium phosphates [3].To match a variety of demands, including ion interaction, solubility, good synthetic availability, cellular uptake and endosomal escape, we present the synthesis of amphiphilic functionalizable terpolymers. Our work is based on a broad experience in the synthesis and application of free radical synthesis of maleic anhydride-containing cooligomers. [4],[5],[6] The shown terpolymers [Fig. 1] consist of tetradecylacrylate (14), methoxy-poly(ethylenglycol) methacrylate (PEG, Mn 950) and maleic anhydride (MA). The addition of filler monomers such as 4-acryloylmorpholine (AMO) or N-vinylpyrrolidone (NVP) has also been realized. Reactive anhydride moieties allowed for accessible functionalization by amide formation e.g. with Cy5 amine as fluorescent label or with the azide linker (11-azido-3,6,9-trioxaundecan-1-amine) which renders the oligomers accessible for any kind of Cu (I) catalysed azide alkyne click reaction.

Figure 1: A Anhydride-containing terpolymer synthesis and B illustration of stabilization of in situ generated siRNA-loaded calcium phosphate nanoparticles.
Anhydride content and intactness were determined by conductometric titration. 1H-NMR was used to quantify comonomer integration and size exclusion chromatography for molecular weight analysis. Terpolymer synthesis yields ranged between 24.1 and 51.1%, and molecular weights between 4500 and 6500 Da. MA incorporation was controlled by the reaction feed and anhydride intactness in the oligomers was higher than 60% (o14PEGMA (4/4/10)). Effects of comonomer feed on integration in the resulting purified oligomers are presented. Pristine oligomers were transferred to the respective polyanionic ammonia salt. The here presented oligomers are able to stabilize siRNA bearing calciumphosphate nanoparticles, show typical amphiphilic behaviour and can be functionalized by alkyne-azide cycloaddition.
Acknowledgements: European Development Found Saxony (EFRE) and the SAB (Sächsische Aufbaubank, Saxony, Germany) for funding
References:
1. Masse, Florence, et al.: Molecules 2019. 24 (16):
2. Norouzi, Mohammad, et al.: Nanomaterials 2020. 10 (3):
3. Zhang, Shuiquan, et al.: J. Mater. Chem. B 2020. 8 (41): 9589–9600.
4. Nawaz, Hafiz Awais, et al.: J. Mater. Chem. B 2021 (9): 2295–2307.
5. Wölk, Christian, et al.: Adv. Mater. Interfaces 2020. 7 (22): 2001168.
6. Loth, Tina, et al.: React. Funct. Polym. 2013. 73 (11): 1480–1492.

  • Poster (Online presentation)
    DPhG-Jahrestagung, 28.09.-01.10.2021, Leipzig, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-32903
Publ.-Id: 32903


CFD-Modelling of Boiling in a Heated Pipe Including Flow Pattern Transition

Setoodeh, H.; Moonesi Shabestary, A.; Ding, W.; Lucas, D.; Hampel, U.

Flow boiling occurs when a subcooled liquid enters a heating pipe and its temperature near the heating wall exceeds the boiling onset temperature. Bubbles are generated on the heating wall and the more downstream the larger the average bubble size due to progressing evaporation and coalescence. Further downstream, the two-phase flow morphologies may change from bubbly to slug, plug, and annular flow. Since these flow patterns have a great impact on the heat and mass transfer rates, an accurate prediction of them becomes critical.
In this work, the recently developed GEneralized-TwO Phase concept (GENTOP) was used for flow patterns transition modelling and their effects on the wall heat transfer during the upward subcooled flow boiling inside a vertical heating pipe. Furthermore, a previously developed mechanistic bubble dynamics model was implemented in the GENTOP framework as a sub-model. This model is based on the force balance on a single growing bubble considering evaporation of the microlayer underneath the bubble, thermal diffusion and condensation around the bubble as well as the dynamic inclination and contact angles. It does not require a recalibration of parameters to predict the bubble dynamics. For implementing this model in the Euler-Euler (E-E) framework an extension of the current nucleation site density and heat partitioning model was required. Eventually, for a generic test case, flow boiling regimes of water in a vertical heating pipe were simulated using ANSYS CFX 18.2.

Keywords: bubble dynamics; flow boiling regimes; GENTOP; Computational Fluid Dynamics (CFD)

Permalink: https://www.hzdr.de/publications/Publ-32902
Publ.-Id: 32902


Sorption and reduction of uranium(VI) by a sulfate-reducing microorganism in synthetic Opalinus Clay pore water

Hilpmann, S.; Drobot, B.; Steudtner, R.; Bok, F.; Stumpf, T.; Cherkouk, A.

For a fully comprehensive safety concept of a nuclear repository, it is necessary to investigate not only the geological, geochemical and geophysical properties but also the influence of naturally occurring microorganisms in the deep geological layers. Clay rocks are a possible host rock formation for the long-term storage of the highly radioactive waste, with bentonite to be used as backfill material.
Various studies show that, among other sulfate-reducing microorganisms, Desulfosporosinus species are present in both clay rock and bentonite.[1,2] A phylogenetically close relative to the isolated species is Desulfosporosinus hippei DSM 8344, an anaerobic, spore-forming microorganism originally found in permafrost soils.[3] Therefore, this strain was selected to get a deeper insight into the uranium(VI) interactions with naturally occurring microorganisms from deep geological layers.
A time-dependent experiment in artificial Opalinus Clay pore water[4] (100 µM uranium(VI), pH 5.5) showed the removal of about 80 % of the uranium(VI) from the supernatants within 48 h. Corresponding live/dead images of the cells taken by fluorescence microscopy exhibit the formation of cell agglomerates and an increasing number of dead cells within the incubation time.
Further examination of the supernatants using time-resolved laser-induced fluorescence spectroscopic techniques revealed the presence of two uranium(VI) species, a lactate and a carbonate complex. The proportion of the carbonate species remained constant over the incubation period, whereas the lactate species decreased.
The comparison of UV/Vis band positions of the dissolved cell pellets with reference spectra provides clear proof of a partially reduction of uranium(VI) to uranium(IV), although bands of uranium(VI) were also still observable. Therefore, it could be that the ongoing interaction mechanism is a combined sorption-reduction process.
These findings are an important contribution to a safety concept for a nuclear repository in clay rock and provide new insights into the interactions of sulfate-reducing microorganisms with uranium(VI).

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

Keywords: uranium(VI) reduction; sulfate-reducing microorganisms; clay rock

  • Lecture (Conference) (Online presentation)
    Goldschmidt 2021 Virtual, 04.-09.07.2021, Lyon, Frankreich

Permalink: https://www.hzdr.de/publications/Publ-32901
Publ.-Id: 32901


Superconductivity of highly spin-polarized electrons in FeSe probed by 77Se NMR

Molatta, S.; Opherden, D.; Wosnitza, J.; Opherden, L.; Zhang, Z. T.; Wolf, T.; von Löhneysen, H.; Sarkar, R.; Biswas, P. K.; Grafe, H.-J.; Kühne, H.

A number of recent experiments indicate that the iron-chalcogenide FeSe provides the long-sought possibility to study bulk superconductivity in the cross-over regime between the weakly coupled Bardeen-Cooper-Schrieffer (BCS) pairing and the strongly coupled Bose-Einstein condensation (BEC). We report on 77Se nuclear magnetic resonance experiments of FeSe, focused on the superconducting phase for strong magnetic fields applied along the c axis, where a distinct state with large spin polarization was reported. We determine this high-field state as bulk superconducting with high spatial homogeneity of the low-energy spin fluctuations. Further, we find that the static spin susceptibility becomes unusually small at temperatures approaching the superconducting state, despite the presence of pronounced spin fluctuations. Taken together, our results clearly indicate that FeSe indeed features an unusual field-induced superconducting state of a highly spin-polarized Fermi liquid in the BCS-BEC crossover regime.

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Permalink: https://www.hzdr.de/publications/Publ-32900
Publ.-Id: 32900


Simultaneous compression and opacity data from time-series radiography with a Lagrangian marker

Swift, D. C.; Kritcher, A. L.; Hawreliak, J. A.; Gaffney, J.; Lazicki, A.; Macphee, A.; Bachmann, B.; Döppner, T.; Nilsen, J.; Whitley, H. D.; Collins, G. W.; Glenzer, S.; Rothman, S. D.; Kraus, D.; Falcone, R. W.

Time-resolved radiography can be used to obtain absolute shock Hugoniot states by simultaneously measuring at least two mechanical parameters of the shock, and this technique is particularly suitable for one-dimensional converging shocks where a single experiment probes a range of pressures as the converging shock strengthens. However, at sufficiently high pressures, the shocked material becomes hot enough that the x-ray opacity falls significantly. If the system includes a Lagrangian marker such that the mass within the marker is known, this additional information can be used to constrain the opacity as well as the Hugoniot state. In the limit that the opacity changes only on shock heating, and not significantly on subsequent isentropic compression, the opacity of the shocked material can be determined uniquely. More generally, it is necessary to assume the form of the variation of opacity with isentropic compression or to introduce multiple marker layers. Alternatively, assuming either the equation of state or the opacity, the presence of a marker layer in such experiments enables the non-assumed property to be deduced more accurately than from the radiographic density reconstruction alone. An example analysis is shown for measurements of a converging shock wave in polystyrene at the National Ignition Facility.

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Publ.-Id: 32899


Demonstration of an X-ray Raman Spectroscopy setup to study warm dense carbon at the High Energy Density Instrument of European XFEL

Voigt, K.; Zhang, M.; Ramakrishna, K.; Amouretti, A.; Appel, K.; Brambrink, E.; Cerantola, V.; Chekrygina, D.; Döppner, T.; Falcone, R. W.; Falk, K.; Fletcher, L. B.; Gericke, D. O.; Göde, S.; Harmand, M.; Hartley, N.; Hau-Riege, S. P.; Huang, L.; Humphries, O. S.; Lokamani, M.; Makita, M.; Pelka, A.; Prescher, C.; Schuster, A.; Smid, M.; Toncian, T.; Vorberger, J.; Zastrau, U.; Preston, T. R.; Kraus, D.

We present a proof-of-principle study demonstrating X-ray Raman Spectroscopy (XRS) from carbon samples at ambient conditions in conjunction with other common diagnostics to study warm dense matter, performed at the High Energy Density scientific instrument of the European X-ray Free Electron Laser (European XFEL). We obtain sufficient spectral resolution to identify the local structure and chemical bonding of diamond and graphite samples, using highly annealed pyrolytic graphite spectrometers. Due to the high crystal reflectivity and XFEL brightness, we obtain signal strengths that will enable accurate XRS measurements in upcoming pump-probe experiments with high repetition-rate, where the samples will be pumped with high-power lasers. Molecular dynamics simulations based on density functional theory together with XRS simulations demonstrate the potential of this technique and show predictions for high-energy-density conditions. Our setup allows simultaneous implementation of several di erent diagnostic methods to reduce ambiguities in the analysis of the experimental results, which, for warm dense matter, often relies on simplifying model assumptions. The promising capabilities demonstrated here provide unprecedented insights into chemical and structural dynamics in warm dense matter states of light elements, including conditions similar to the
interiors of planets, low-mass stars and other celestial bodies.

Permalink: https://www.hzdr.de/publications/Publ-32898
Publ.-Id: 32898


Enhanced Photoluminescence of Gold Nanoparticle-Quantum Dot Hybrids Confined in Hairy Polymer Nanofibers

Singh, S.; Raulo, A.; Singh, A.; Mittal, M.; Horechyy, A.; Hübner, R.; Formanek, P.; Srivastava, R. K.; Sapra, S.; Fery, A.; Nandan, B.

In the present work, we have studied the influence of gold nanoparticles (AuNPs) on the photoluminescence (PL) behavior of cadmium selenide (CdSe) quantum dots (QDs) confined in spatially separated soft nanoscale cylindrical domains. These cylindrical domains, in the form of hairy core-shell nanofibers, were fabricated via cooperative self-assembly of polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) block copolymer (BCP) mixed with pre-synthesized CdSe QDs and AuNPs. The CdSe QDs and AuNPs were simultaneously incorporated in the P4VP cylindrical domains of the self-assembled BCP structure. It was found that the confinement imposed by the nanometer-sized cylindrical core resulted in the localization of the CdSe QDs and AuNPs in close proximity. Notably, it was observed that the PL intensity of the CdSe QDs could be manipulated by varying the amount of AuNPs present in the cylinder core. Interestingly, in the presence of a very low fraction of AuNPs, the PL intensity of the CdSe QDs increased compared to the AuNPs-free system. However, further increase in the fraction of AuNPs led to gradual quenching of the photoluminescence intensity. The PL enhancement and quenching plausibly was due to the interplay between the energy transfer due to surface plasmon coupling and FRET/electron transfer from QDs to the AuNPs. The resulting functional nanofibers could have potential applications in sensing, bioimaging, and optoelectronic devices.

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Permalink: https://www.hzdr.de/publications/Publ-32897
Publ.-Id: 32897


Simulation of Flow Boiling Transition Patterns by Using GENTOP Concept and a Mechanistic Bubble Dynamics Model

Hamed Setoodeh; Wei Ding; Dirk Lucas; Uwe Hampel

Flow boiling occurs when a subcooled liquid enters a vertical heating pipe and its temperature near the heating wall exceeds the boiling onset temperature. Bubbles are generated on the heating wall. Further, along the pipe the bulk fluid temperature increases and coalescence and evaporation create large bubbles which results in two-phase flow patterns formation including bubbly, slug and annular flows.

Flow patterns transition in flow boiling is simulated by using the recently developed concept of GEneralized-TwO Phase (GENTOP) and a developed bubble dynamics model. The GENTOP concept is an extension of the inhomogeneous MUltiple SIze Group (iMUSIG) by adding a continuous gas phase in the multi-field Euler-Euler (E-E) approach. Transitions between the fields result from coalescence and breakup of the gas bubbles.

A recently developed mechanistic bubble dynamics model, which is based on the balance of forces applied on a single bubble, is implemented in the GENTOP framework as a sub-model. This model also considers the evaporation of the microlayer underneath the bubble, thermal diffusion and condensation around the bubble as well as the dynamic inclination and contact angles. In addition, it does not require a recalibration of parameters to predict the bubble dynamics and its implementation in the E-E framework needs an extension of the current nucleation site density and heat partitioning models. Finally, for a generic demonstration case, flow boiling morphological patterns in a vertical heated pipe is simulated by ANSYS CFX.

Keywords: bubble dynamics; flow boiling regimes; GENTOP; Computational Fluid Dynamics (CFD)

  • Contribution to proceedings
    19th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-19), 06.03.2022, Brussels, Belgium

Permalink: https://www.hzdr.de/publications/Publ-32895
Publ.-Id: 32895


Data publication: Optical Kerr nonlinearity and multi-photon absorption of DSTMS measured by Z-scan method

Li, J.; Rana, R.; Zhu, L.; Liu, C.; Schneider, H.; Pashkin, O.

Z-scan data (polarization dependent)

Matlab scripts for the fitting and simulations

FTIR transmission data

------------------------------------------

Center wavelength of OPA: 1430 nm

FWHM duration of OPA pulses: 75 fs

Pulse energy: 20 nJ

thickness of DSTMS: 0.4 mm

'OA' means open aperture 'CA' meams close aperture

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Permalink: https://www.hzdr.de/publications/Publ-32894
Publ.-Id: 32894


Optical Kerr nonlinearity and multi-photon absorption of DSTMS measured by Z-scan method

Li, J.; Rana, R.; Zhu, L.; Liu, C.; Schneider, H.; Pashkin, O.

We investigate the optical Kerr nonlinearity and multi-photon absorption (MPA) properties of 4-N, N-dimethylamino-4’-N’-methyl-stilbazolium 2, 4, 6- trimethylbenzene-sulfonate (DSTMS) excited by femtosecond pulses at a wavelength of 1.43 μm, which is optimal for terahertz generation via difference frequency mixing. The MPA and the optical Kerr coefficients of DSTMS at 1.43 μm are strongly anisotropic indicating a dominating contribution from cascaded 2nd-order nonlinearity.

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Permalink: https://www.hzdr.de/publications/Publ-32893
Publ.-Id: 32893


Investigations on axial gas dispersion coefficients in bubble columns using gas flow modulation

Marchini, S.; Döß, A.; Bieberle, A.; Schubert, M.; Hampel, U.

Gas-liquid contactors, such as bubble columns, are subject to dispersion phenomena in both gas and liquid phase. The Axial Dispersion Model (ADM) is the most widely used theoretical approach to account for the effects of dispersion [1].
A reliable quantification of the axial dispersion coefficients is crucial for process performance assessment as well as design and optimization of such contactors. Conventional approaches for determining axial dispersion coefficients rely on tracer substances. However, such methods are hardly universally applicable, may cause detrimental impurities or process downtimes and can even alter the physical properties of the system.
To overcome these issues, Döß et al. [2] introduced a novel non-invasive approach for determining the axial gas dispersion coefficient in bubble columns. Instead of a tracer substance, a marginal sinusoidal modulation is superimposed to the gas inlet flow rate and used as a virtual tracer. This modulation introduces a sinusoidal variation of the gas holdup in time, called gas density wave. Along the column, the gas density wave is damped in amplitude and is shifted in phase, due to gas dispersion. Amplitude damping and phase shift can be measured and related to the value of the axial dispersion coefficient via a dispersion model. A schematic sketch of the working principle is provided in Figure 1.
Döß et al. [2] successfully used sinusoidal-resolved gamma-ray densitometry to investigate the amplitude damping and phase shift. The deviation caused by the statistical behaviour of the gamma-ray photons was reduced by increasing the measurement time.As the operation of gamma-ray sources may be challenging for industrial applicability, this study assesses the possibility of using alternative non-radiative techniques to measure the gas density wave. Several measurement techniques and different gas modulation schemes in terms of initial modulation amplitude and frequency have been studied to ensure detectable amplitude and phase changes at chosen axial positions, while not altering the hydrodynamic behaviour. Uncertainties associated with the axial dispersion coefficient have been evaluated in comparison to gamma-ray densitometry.

  • Lecture (Conference) (Online presentation)
    European Chemical Engineering Conference, 20.-24.09.2021, Berlin, Germany

Permalink: https://www.hzdr.de/publications/Publ-32892
Publ.-Id: 32892


Analysis of the effect of uncertainties in hydrodynamic parameters on the accuracy of the gas flow modulation technique for bubble columns

Marchini, S.; Schubert, M.; Hampel, U.

The gas flow modulation technique has recently been proposed as a novel method for determining the axial gas dispersion coefficient in bubble columns. The approach is based on a marginal sinusoidal modulation of the gas inlet flow rate that acts as a virtual tracer. Axial gas dispersion is then inversely calculated from amplitude damping and phase shift via an analytical solution of the axial dispersion model. The proposed study provides an analysis of the inherent uncertainties related to the assumptions of constant axial gas dispersion coefficient and bubble rise velocity, which are crucial for implementing the method. Besides, the sensitivity of the approach is assessed as function of the modulation parameters, the bubble rise velocity and the axial gas dispersion coefficient. Eventually, the possibility of tailoring the modulation parameters depending on the expected value of the axial gas dispersion coefficient to increase the sensitivity and to reduce the uncertainty is also assessed.

Keywords: bubble columns; bubble column reactors; axial dispersion coefficient; axial dispersion model; uncertainty analysis; sensitivity analysis

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Permalink: https://www.hzdr.de/publications/Publ-32891
Publ.-Id: 32891


Convective, absolute and global azimuthal magnetorotational instabilities

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

We study the convective and absolute forms of azimuthal magnetorotational instability (AMRI) in a cylindrical Taylor–Couette (TC) flow with an imposed azimuthal magnetic field. We show that the domain of the convective AMRI is wider than that of the absolute AMRI. Actually, it is the absolute instability which is the most relevant and important for magnetic TC flow experiments. The absolute AMRI, unlike the convective one, stays in the device, displaying a sustained growth that can be experimentally detected. We also study the global AMRI in a TC flow of finite height using direct numerical simulation and find that its emerging butterfly-type structure – a spatio-temporal variation in the form of axially upward and downward travelling waves – is in a very good agreement with the linear analysis, which indicates the presence of two dominant absolute AMRI modes in the flow giving rise to this global butterfly pattern.

Keywords: absolute/convective instability; Taylor-Couette flow

  • Open Access Logo Journal of Fluid Mechanics 922(2021), R4
    DOI: 10.1017/jfm.2021.548
    Cited 3 times in Scopus
  • Lecture (Conference) (Online presentation)
    International Couette-Taylor Workshop 2021, 05.-09.07.2021, Enschede, Netherlands

Permalink: https://www.hzdr.de/publications/Publ-32890
Publ.-Id: 32890


Transport properties of systematically disordered Cr2AlC films

Salgado Cabaco, J.; Kentsch, U.; Lindner, J.; Faßbender, J.; Leyens, C.; Bali, R.; Boucher, R.

Nano-lamellar composite materials, known as MAX-phases, can possess a combination of ceramic and metallic properties. A prototype compound is Cr2AlC, formed from a unit cell of Cr2C sandwiched between atomic planes of Al, thereby imparting a goodelectrical conductivity, as well as mechanical stability, radiationand oxidationresistance [1, 2]. Theseproperties rely on the lamellar structure of the compound, and systematic introduction of defects, such as displacing or doping atoms within the layers, has the potential to tune electron transport and modify magnetic properties. An ideal tool for defect implantation is ion-irradiation, available both in the form of a broad-beam for wafer-scale processing as well as focused ion-beams for device prototyping.Here we observe the modifications to the structural, transport and magnetic behavior of 500 nm thickCr2AlC afterirradiation with Co+ions, and Ar+noble gas ions as control. The films were irradiated with 450keV of Co+ions at fluences varying from 5E12 to 5E15 ions.cm-2, and the control samples with 400 keV Ar+ions keeping the sample fluences.Structural analysis using XRD shows that ion-irradiation induces asuppression of the 0002 reflection, indicating a gradual decay of the nano-lamellar structure, see Fig.1a. Increasing ion-fluence also leads toan increase of the saturation magnetizationat 1.5K, whereby both Ar+and Co+cause an increased magnetization, respectively to 150and 190 kA.m-1, for the highest fluences used.Large variations of the transport properties are observed(Fig. 1 b).Magnetoresistance (MR) in the non-irradiated sample shows a classical B2dependency, even up to high temperatures.At Co+fluences of 5E13ions.cm-2the MR at 10 T shows a 2 orders of magnitude increase, upto 3%(10 T)at 100 K, see Fig. 1b. A similar effect also occurs for 5E12ions.cm-2Ar+irradiated films, however with a smaller MR-increase.It appears that resistivity increases and the residual resistance ratio reduces with increasing fluence due to the introduction of disorder.Theseresults show that ion irradiation induces significant changes in the transport properties of MAX phase materials, that will be further investigated.The systematic disordering of nano-laminated MAX phase films may therefore reveal interesting disorder and spin-related transport phenomena.

[1]A. S. Ingason, M. Dahlqvist, J. Rosen, Magnetic MAX phases from theory and experiments; a review; J. Phys.: Condens. Matter 28 (2016), 433003.[2]M. W. Barsoum, MAX Phases: Properties of Machinable Ternary Carbides and Nitrides; Weinheim: Willey-VCH (2013).[3] C. Wang, T. Yang, C. L. Tracy, C. Lu, H. Zhang, Y.-J. Hu, L. Wang, L. Qi, L. Gu, Q. Huang, J.Zhang, J. Wang, J. Xue, R. C. Ewing, Y. Wang, Disorder in Mn+1AXnphases at the atomic scale, Nature Communications 10, 622 (2019).

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  • Poster
    EuFN workshop, 27.-30.09.2021, WROCLAW, Poland

Permalink: https://www.hzdr.de/publications/Publ-32889
Publ.-Id: 32889


Transient behaviour of electrovortex flow in a cylindrical container

Liu, K.; Stefani, F.; Weber, N.; Weier, T.; Li, B.-W.

This study is a continuation of a combined experimental and numerical investigation of the flow of the eutectic alloy GaInSn inside a cylindrical vessel exposed to a constant electrical current. The emerging electro-vortex flow (EVF), caused by the interaction of the current, which is applied through a tapered electrode, with its own magnetic field, might have both detrimental and advantageous effects in liquid metal batteries (LMBs). While the former work was mainly concerned with time-averaged results, this paper focuses on the transient behaviour of the EVF which becomes most relevant under the influence of an external axial field. The additional Lorentz force, generated by the interaction of the imposed current with the vertical component of the geomagnetic field (bz), drives the ordinary EVF jet flow into a swirling motion. The velocity distributions and motion characteristics, such as spiral streamlines, and shortened and irregularly swinging jet regions, are investigated. The mechanism is analysed in detail for bz = −25.5 µT. The maximum angular velocity of the rotating jet region is basically linearly dependent on bz , at least for the values studied here. A good agreement between the transient simulation and experimental result is shown.

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Permalink: https://www.hzdr.de/publications/Publ-32886
Publ.-Id: 32886


Flow Reconstruction in a Rayleigh-Bénard Convection Cell with an Aspect Ratio 0.5 by Contactless Inductive Flow Tomography

Mitra, R.; Sieger, M.; Galindo, V.; Schindler, F.; Stefani, F.; Wondrak, T.

The time dependent behaviour of the large-scale circulation in a Rayleigh-Bénard convection cell exhibits a rich set of different three-dimensional flow features like rotations or torsional modes. In this paper, the applicability of the contactless inductive flow tomography (CIFT) to visualise these flow features in a cylindrical cell filled with GaInSn is investigated numerically. The simulated flow in the cylinder with a diameter of 320 mm and a height of 640 mm serves as a basis to investigate the quality of the reconstructed velocity field by CIFT.

Keywords: Rayleigh-Bénard convection; Large-scale circulation; Liquid metal flow; Contactless inductive flow tomography

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  • Open Access Logo Contribution to proceedings
    Electromagnetic Processing of Materials, 14.-16.06.2021, Riga, Latvia
    Proceedings of the 10th international conference in Electromagnetic Processing of Materials, Riga: The University of Latvia Press, 978-9934-18-686-8, 182-187
  • Lecture (Conference) (Online presentation)
    Electromagnetic Processing of Materials, 14.-16.06.2021, Riga, Latvia
  • Magnetohydrodynamics 58(2022)1-2, 81-88
    DOI: 10.22364/mhd.58.1-2.8
    Cited 3 times in Scopus

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Permalink: https://www.hzdr.de/publications/Publ-32885
Publ.-Id: 32885


Radiative characterization of supersonic jets and shocks in a laser-plasma experiment

Bohlin, H.; Brack, F.-E.; Cervenak, M.; Chodukowski, T.; Cikhardt, J.; Dostál, J.; Dudžák, R.; Hubner, J.; Huo, W.; Jelinek, S.; Klír, D.; Kroll, F.; Krupka, M.; Krůs, M.; Pisarczyk, T.; Rusiniak, Z.; Schramm, U.; T.-H, N.-B.; Weber, S.; Zaraś-Szydłowska, A.; Zeil, K.; Kumar, D.; Schlegel, T.; Tikhonchuk, V.

The interaction of supersonic laser-generated plasma jets with a secondary gas target was studied experimentally. The plasma parameters of the jet, and the resulting shock, were characterized using a combination of multi-frame interferometry/shadowgraphy, and x-ray diagnostics, allowing for a detailed study of their structure and evolution. The velocity was obtained with an x-ray streak camera, and filtered x-ray pinhole imaging was used to infer the electron temperature of the jet and shock. The topology of the ambient plasma density was found to have a significant effect on the jet and shock formation, as well as on their radiation characteristics. The experimental results were compared with radiation hydrodynamic simulations, thereby providing further insights into the underlying physical processes of the jet and shock formation and evolution.

Keywords: Supersonic jets; Shocks; Laser Plasma; X-ray imaging; Hydrodynamic

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Permalink: https://www.hzdr.de/publications/Publ-32883
Publ.-Id: 32883


On the study of hydrodynamic instabilities in the presence of background magnetic fields in high-energy-density plasmas

Manuel, M. J.-E.; Khiar, B.; Rigon, G.; Albertazzi, B.; Klein, S. R.; Kroll, F.; Brack, F.-E.; Michel, T.; Mabey, P.; Pikuz, S.; Williams, J. C.; Koenig, M.; Casner, A.; Kuranz, C. C.

Blast-wave-driven hydrodynamic instabilities are studied in the presence of a background B-field through experiments and simulations in the high-energy-density (HED) physics regime. In experiments conducted at the Laboratoire pour l’utilisation des lasers intenses (LULI), a laser-driven shock-tube platform was used to generate a hydrodynamically unstable interface with a prescribed sinusoidal surface perturbation, and short-pulse x-ray radiography was used to characterize the instability growth with and without a 10-T B-field. The LULI experiments were modeled in FLASH using resistive and ideal magnetohydrodynamics (MHD), and comparing the experiments and simulations suggests that the Spitzer model implemented in FLASH is necessary and sufficient for modeling these planar systems. These results suggest insufficient amplification of the seed B-field, due to resistive diffusion, to alter the hydrodynamic behavior. Although the ideal-MHD simulations did not represent the experiments accurately, they suggest that similar HED systems with dynamic plasma-β (=2*μ_0*ρ*v^2/B^2) values of less than ∼100 can reduce the growth of blast-wave-driven Rayleigh–Taylor instabilities. These findings validate the resistive-MHD FLASH modeling that is being used to design future experiments for studying B-field effects in HED plasmas.

Keywords: Shock waves; Nebulae; Supernovae; Radiography; Magnetohydrodynamics; High pressure instruments; Magnetic fields; Fluid instabilities; Electromagnetic coils

Permalink: https://www.hzdr.de/publications/Publ-32882
Publ.-Id: 32882


robust training, adversarial examples and what it tells us about modern medical ML classifiers

Steinbach, P.

Undoubtedly, the advent of deep learning for image classification or pattern recognition has created a ecosystem stir in the
medical domain of unprecedented extension. In this talk, I'd like to discuss the question how adversarial examples can help us
quantify the quality of a Deep Learning trained classifyer. With this approach, I'd like to underline how observations and
methods from commercial applications can or cannot be transferred to medical applications. The slidedeck is meant to motivate a discussion on what we expect machine learning to leverage and how this relates to clinical applications with robustness of solutions in mind.

Keywords: robust AI; robust ML; adversarial examples; adversarial attacks; medical imaging; radiology

  • Open Access Logo Invited lecture (Conferences) (Online presentation)
    EMPAIA Committee “Validation of AI solutions”, 24.06.2021, virtuell, Germany
    DOI: 10.6084/m9.figshare.14838330.v1

Permalink: https://www.hzdr.de/publications/Publ-32881
Publ.-Id: 32881


Update of the EPTN atlas for CT- and MR-based (3T and 7T) contouring in Neuro-Oncology

Eekers, D. B. P.; Di, P. D.; Roelofs, E.; Postma, A.; Dijkstra, J.; Ajithkumar, T.; Alapetite, C.; Blomstrand, M.; Burnet, N. G.; Calugaru, V.; Compter, I.; Coremans, I. E. M.; Harrabi, S.; Iannalfi, A.; Klaver, Y. L. B.; Lambrecht, M.; Méndez Romero, A.; Paulsen, F.; Timmermann, B.; Vitek, P.; van der Weide, H. L.; Whitfield, G. A.; Nyström, P.; Zindler, J.; De, R. D.; Langendijk, J.; Weber, D. C.; Troost, E. G. C.

Background and purpose:To update the digital online atlas for organs at risk (OARs) delineation in neuro-oncology based on high-quality computed tomography (CT) and magnetic resonance (MR) imaging withnew OARs.Materials and methods:In this planned update of the neurological contouring atlas published in 2018, tennew clinically relevant OARs were included, after thorough discussion between experienced neuro-radiation oncologists (RTOs) representing 30 European radiotherapy-oncology institutes. Inclusion wasbased on daily practice and research requirements. Consensus was reached for the delineation after crit-ical review. Contouring was performed on registered CT with intravenous (IV) contrast (soft tissue & bonewindow setting) and 3 Tesla (T) MRI (T1 with gadolinium & T2 FLAIR) images of one patient (1 mm slices).For illustration purposes, delineation on a 7 T MRI without IV contrast from a healthy volunteer wasadded. OARs were delineated by three experienced RTOs and a neuroradiologist based on the relevant lit-erature.Results:The presented update of the neurological contouring atlas was reviewed and approved by 28experts in the field. The atlas is available online and includes in total 25 OARs relevant to neurooncology, contoured on CT and MRI T1 and FLAIR (3 T & 7 T). Three-dimensional (3D) rendered films arealso available online.Conclusion:In order to further decrease inter- and intra-observer OAR delineation variability in the fieldof neuro-oncology, we propose the use of this contouring atlas in photon and particle therapy, in clinicalpractice and in the research setting. The updated atlas is freely available onwww.cancerdata.org.

Keywords: Atlas for neuro-oncology; Brain; Organs at risk; Particle therapy; Radiotherapy; European Particle Therapy Net

Permalink: https://www.hzdr.de/publications/Publ-32880
Publ.-Id: 32880


Simultaneous localisation and mapping for laparoscopic liver navigation: a comparative evaluation study

Docea, R.; Pfeiffer, M.; Bodenstedt, S.; Kolbinger, F.; Höller, L.; Wittig, I.; Hoffmann, R.; Troost, E. G. C.; Riediger, C.; Weitz, J.; Speidel, S.

Computer-Assisted Surgery (CAS) aids the surgeon by enriching the surgical scene with additional information
in order to improve patient outcome. One such aid may be the superimposition of important structures (such as
blood vessels and tumors) over a laparoscopic image stream. In liver surgery, this may be achieved by creating
a dense map of the abdominal environment surrounding the liver, registering a preoperative model (CT scan)
to the liver within this map, and tracking the relative pose of the camera. Thereby, known structures may be
rendered into images from the camera perspective. This intraoperative map of the scene may be constructed, and
the relative pose of the laparoscope camera estimated, using Simultaneous Localisation and Mapping (SLAM).
The intraoperative scene poses unique challenges, such as: homogeneous surface textures, sparse visual features,
specular reflections and camera motions specific to laparoscopy. This work compares the efficacies of two state-of-
the-art SLAM systems in the context of laparoscopic surgery, on a newly collected phantom dataset with ground
truth trajectory and surface data. The SLAM systems chosen contrast strongly in implementation: one sparse and
feature-based, ORB-SLAM3,1–3 and one dense and featureless, ElasticFusion.4 We find that ORB-SLAM3 greatly
outperforms ElasticFusion in trajectory estimation and is more stable on sequences from laparoscopic surgeries.
However, when extended to give a dense output, ORB-SLAM3 performs surface reconstruction comparably to
ElasticFusion. Our evaluation of these systems serves as a basis for expanding the use of SLAM algorithms in
the context of laparoscopic liver surgery and Minimally Invasive Surgery (MIS) more generally.

Permalink: https://www.hzdr.de/publications/Publ-32879
Publ.-Id: 32879


Value of PET imaging for radiation therapy

Lapa, C.; Nestle, U.; Albert, N.; Baues, C.; Beer, A.; Buck, A.; Budach, V.; Bütof, R.; Combs, S.; Derlin, T.; Eiber, M.; Fendler, W.; Furth, C.; Gani, C.; Gkika, E.; Grosu, A.; Henkenberens, C.; Ilhan, H.; Löck, S.; Marnitz-Schulze, S.; Miederer, M.; Mix, M.; Nicolay, N.; Niyazi, M.; Pöttgen, C.; Rödel, C.; Schatka, I.; Schwarzenboeck, S.; Todica, A.; Weber, W.; Wegen, S.; Wiegel, T.; Zamboglou, C.; Zips, D.; Zöphel, K.; Zschaeck, S.; Thorwarth, D.; Troost, E. G. C.

This comprehensive review written by experts in their field gives an overview on the current status of incorporating positron emission tomography (PET) into radiation treatment planning. Moreover, it highlights ongoing studies for treatment individualisation and per-treatment tumour response monitoring for various primary tumours. Novel tracers and image analysis methods are discussed. The authors believe this contribution to be of crucial value for experts in the field as well as for policy makers deciding on the reimbursement of this powerful imaging modality.

Keywords: PET; radiation oncology; functional imaging; radiomics

Permalink: https://www.hzdr.de/publications/Publ-32878
Publ.-Id: 32878


ROCOCO Performance Score translates dosimetric differences into clinically relevant endpoints: comparing IMPT to VMAT in pilocytic astrocytoma

In, ’. V. L.; Roelofs, E.; Cubillos, M. M.; Compter, I.; Klaver, Y.; Smeenk, R.; Janssens, G. O.; Kaanders, J. H. A. M.; Fajardo, R. D.; Oldenburger, F.; De, R. D.; Troost, E. G. C.; Eekers, D.

Background and purpose: Proton therapy is expected to outperform photon-based treatment regarding organs at risk (OAR) sparing but to date there is no method to practically measure clinical benefit. Here, we introduce the novel ROCOCO Performance Scoring System (RPSS) translating dose differences
into clinically relevant endpoints and apply this to a treatment plan comparison of volumetric modulated arc therapy (VMAT) and intensity modulated proton therapy (IMPT) in 20 pilocytic astrocytoma patients.
Material and methods: The RPSS was developed on the basis of expert-based weighting factors and toxicity scores per OAR. The imaging datasets of 20 pilocytic astrocytoma patients having undergone radiotherapy were included in this in silico dosimetric comparison trial as proof of principle. For each of these patients, treatment plans to a total dose of 54 Gy (RBE) were generated for VMAT and IMPT and these were compared regarding radiation dose to the clinical target volume (CTV) and OARs. The RPSS was calculated for each treatment plan comparing VMAT and IMPT.
Results: In 40 analysed treatment plans, the average and low dose volumes to various OARs were significantly reduced when using IMPT compared to VMAT (p < 0.05). Using the RPSS, a significant difference between both treatment modalities was found, with 85% of the patients having a lower RPSS in favour of the IMPT plan.
Conclusion: There are dosimetric differences between IMPT and VMAT in pilocytic astrocytoma patients. In absence of clinically validated NTCP models we introduce the RPSS model in order to objectively compare treatment modalities by translating dosimetric differences in potential clinical differences.

Keywords: Low grade glioma; Pilocytic astrocytoma; Organ at risk; Proton therapy; Cognition; Scoring system

Permalink: https://www.hzdr.de/publications/Publ-32877
Publ.-Id: 32877


Formation of plutonium (IV) silicate species in very alkaline reactive media

Estevenon, P.; Dumas, T.; Lorenzo Solari, P.; Welcomme, E.; Szenknect, S.; Mesbah, A.; Kvashnina, K. O.; Moisy, P.; Poinssot, C.; Dacheux, N.

The formation of stable plutonium (IV) silicate colloidal suspension has been identified in very alkaline reactive media (pH ≥ 13). XAS measurements allowed to observe that these species exhibit a structure similar to those reported at (IV) oxidation state, like for thorium, uranium and neptunium silicates counterparts. These colloids can be stabilized in aqueous solution at concentrations around 10 2 mol·L 1 and successive filtration process allowed to evaluate that most of these silicates had a size ranging between 3 and 6 nm. This result may bring new outlooks on the behavior of plutonium in silicate ions rich reactive media

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Permalink: https://www.hzdr.de/publications/Publ-32876
Publ.-Id: 32876


An open-access future for Journal of Synchrotron Radiation

Kvashnina, K.; Amemiya, Y.; Bhattacharyya, D.; Lindau, I.; Allen, A.

The entire Journal of Synchrotron Radiation (JSR) editorial team would like to take this opportunity to inform all our readers, authors and supporters about the coming transition to open access. All papers submitted to JSR after 1 October 2021, will be for open-access publication. By taking this step, JSR is supporting a journey towards open science in general.

Permalink: https://www.hzdr.de/publications/Publ-32875
Publ.-Id: 32875


Generation of Reverse Meniscus Flow by Applying An Electromagnetic Brake

Vakhrushev, A.; Kharicha, A.; Karimi-Sibaki, E.; Wu, M.; Ludwig, A.; Nitzl, G.; Tang, Y.; Hackl, G.; Watzinger, J.; Eckert, S.

A numerical study is presented that deals with the flow in the mold of a continuous slab caster under the influence of a DC magnetic field (electromagnetic brakes (EMBrs)). The arrangement and geometry investigated here is based on a series of previous experimental studies carried out at the mini-LIMMCAST facility at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR). The magnetic field models a ruler-type EMBr and is installed in the region of the ports of the
submerged entry nozzle (SEN). The current article considers magnet field strengths up to 441 mT, corresponding to a Hartmann number of about 600, and takes the electrical conductivity of the solidified shell into account. The numerical model of the turbulent flow under the applied magnetic field is implemented using the open-source CFD package OpenFOAM. Our numerical results reveal that a growing magnitude of the applied magnetic field may cause a reversal of the flow direction at the meniscus surface, which is related the formation of a ‘‘multiroll’’ flow pattern in the mold. This phenomenon can be
explained as a classical magnetohydrodynamics (MHD) effect: (1) the closure of the induced electric current results not primarily in a braking Lorentz force inside the jet but in an acceleration in regions of previously weak velocities, which initiates the formation of an opposite vortex (OV) close to the mean jet; (2) this vortex develops in size at the expense of the main vortex until it reaches the meniscus surface, where it becomes clearly visible. We also show
that an acceleration of the meniscus flow must be expected when the applied magnetic field is smaller than a critical value. This acceleration is due to the transfer of kinetic energy from smaller turbulent structures into the mean flow. A further increase in the EMBr intensity leads to the expected damping of the mean flow and, consequently, to a reduction in the size of the upper roll. These investigations show that the Lorentz force cannot be reduced to a simple
damping effect; depending on the field strength, its action is found to be topologically complex.

Keywords: continuous casting; mold flow; electromagnetic brake; numerical simulation

Permalink: https://www.hzdr.de/publications/Publ-32874
Publ.-Id: 32874


Resolution Enhancement for Drill-Core Hyperspectral Mineral Mapping

Contreras Acosta, I. C.; Khodadadzadeh, M.; Gloaguen, R.

Drill-core samples are a key component in mineral exploration campaigns, and their rapid and objective analysis is becoming increasingly important. Hyperspectral imaging of drill-cores is a non-destructive technique that allows for non-invasive and fast mapping of mineral phases and alteration patterns. The use of adapted machine learning techniques such as supervised learning algorithms allows for a robust and accurate analysis of drill-core hyperspectral data. One of the remaining challenge is the spatial sampling of hyperspectral sensors in operational conditions, which does not allow us to render the textural and mineral diversity that is required to map minerals with low abundances and fine structures such as veins and faults. In this work, we propose a methodology in which we implement a resolution enhancement technique, a coupled non-negative matrix factorization, using hyperspectral, RGB images and high-resolution mineralogical data to produce mineral maps at higher spatial resolutions and to improve the mapping of minerals. The results demonstrate that the enhanced maps not only provide better details in the alteration patterns such as veins but also allow for mapping minerals that were previously hidden in the hyperspectral data due to its low spatial sampling.

Keywords: resolution enhancement; sampling enhancement; hyperspectral; high-spatial resolution multi-spectral; drill-cores; mineral mapping; machine learning

Permalink: https://www.hzdr.de/publications/Publ-32872
Publ.-Id: 32872


Comparative High-Field Magnetization Study of (Sm,Er)2Fe17 and Er2Fe17 Compounds and their Nitrides

Ivanov, L.; Paukov, M.; Tereshina, I.; Veselova, S.; Akimova, O.; Verbetsky, V.; Gorbunov, D.

Magnetic properties of the R2Fe17 compounds are sensitive to the atomic substitutions and interstitial absorption of nitrogen. In our work, both were combined and their effect on the magnetization behavior of Er2Fe17 compound in magnetic fields up to 58 T was studied. Er2Fe17N2, Sm1.2Er0.8Fe17N2 and Sm1.8Er0.2Fe17N2.1 nitrides were prepared. Magnetization measurements were carried out, mainly on powder samples (excluding Er2Fe17 single crystal). Nanopowders of Sm1.2Er0.8Fe17N2 were obtained by mechanical grinding. The grinding time was varied from 0 to 60 minutes. The strength of the inter-sublattice coupling in samples is estimated by analyzing high-field magnetization data.

Permalink: https://www.hzdr.de/publications/Publ-32871
Publ.-Id: 32871


Magnetocaloric properties and specifics of the hysteresis at the first-order metamagnetic transition in Ni-doped FeRh

Chirkova, A. M.; Skokov, K. P.; Scurschii, I.; Scheibel, F.; Karpenkov, A. Y.; Volegov, A. S.; Baranov, N. V.; Nielsch, K.; Schultz, L.; Müller, K.-H.; Woodcock, T. G.; Gutfleisch, O.

Measurements of the magnetization in quasistatic and pulsed magnetic fields with different sweep rates, measurements of the specific heat in various magnetic fields, and direct measurements of the adiabatic temperature change have been employed to study the metamagnetic phase transition from an antiferromagnetic (AF) to the ferromagnetic (FM) state in an (Fe0.98Ni0.02)49Rh51 alloy with a critical AF-FM transition temperature, Ttr, reduced to 266 K. Based on the obtained results, a magnetic phase diagram for this alloy has been constructed. The AF-FM transition induced by the magnetic field below 10 K is found to occur in a steplike fashion in contrast to smooth behavior at 10K < T < Ttr. The adiabatic temperature change ΔTad in the magnetic field of 2 T exceeds 6.5 K in pulsed fields (∼100 T/s) and in the Halbach setup (∼0.5 T/s), which is in agreement with the estimation from the S-T diagram constructed based on the specific heat measurements. The reversible ΔTad reaches −4.6 K under cyclic conditions in the Halbach setup (2 T). A complete transformation to the FM state in the whole temperature range requires a magnetic field of 14 T. Direct measurements of ΔTad in pulsed fields of 14 T revealed an irreversible part of the magnetocaloric effect associated with the presence of magnetic hysteresis and respective losses during the magnetization process.

Permalink: https://www.hzdr.de/publications/Publ-32870
Publ.-Id: 32870


Development of a high-speed ultrasonic tomography system for measurements of rising bubbles in a horizontal cross-section

Murakawa, H.; Tomoyuki, S.; Eckert, S.

The present study deals with high-speed ultrasonic tomography (UT) as a powerful tool to characterize the behavior of multiphase flows. A major goal of the work is to improve the temporal resolution for the detection of transit flow structures and time-dependent phenomena such as the incidence of rising gas bubbles. A special transducer with a wide divergence angle of 110° and a vertical height of the measurement volume of approx. 4 mm was developed and tested. The system thus enables the acquisition of cross-sectional images at a frame rate of up to 1,000 frames/s. Scatter noise was eliminated using a time series filtering method. This UT system was applied to a chain of gas bubbles rising in a cylindrical container with an internal diameter of 50 mm. The measurement system provides qualitative observations of the turbulent dynamics of bubbly flows including bubble-bubble interactions, such as the coalescence of individual bubbles.

Keywords: full-matrix capture; reflection mode; time-series filtering; pseudo three-dimensional image; bubble column

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Permalink: https://www.hzdr.de/publications/Publ-32869
Publ.-Id: 32869


Solidification and fluid convection - the story of an inseparable couple

Eckert, S.; Anders, S.; Shevchenko, N.; Keplinger, O.; Kao, A.

In numerous processes in nature and technology, convection is caused by density differences resulting from temperature and concentration gradients. If the rates of diffusion of the two variables differ, this is called double-diffusive convection. Solidification processes under the influence of gravitational forces almost always occur in combination with convective flows. In nature, double-diffusive convection is responsible for magma flow in the mantle of planets or occurs during freezing of seawater. Thermo-solutal convection in industrial castings may result in a composition variation over distances comparable to the size of the solidification domain due to transport of rejected solute by fluid flow, the phenomenon being known as macrosegregation. This paper is dedicated to the interplay between solidification and convection, which are usually closely coupled, interacting in many different ways and thus can lead to very complex phenomena. Results from various experiments conducted both in metals and transparent analogues are presented and discussed.

Keywords: solidification; double-diffusive convection; macrosegregation

  • Invited lecture (Conferences) (Online presentation)
    TMS 2021, annual Meeting & Exhibition, 15.-18.03.2021, virtual, online, USA

Permalink: https://www.hzdr.de/publications/Publ-32868
Publ.-Id: 32868


Investigate utilization of machine-learning methods to derive drag models for Euler-Euler simulations from DNS data

Patel, H.

Multiphase flow plays a vital role in many industrial applications. DNS simulations provide an insight
into the complexity of multiphase flows but are limited due to very high computational costs. Instead,
Euler-Euler (E-E) simulations provide a reliable prediction for a wide range of engineering applications.
E-E simulations are highly dependent on the choice of closure models for the interaction terms. Modeling
of interfacial drag force is one of the main aspect of E-E simulations. In this thesis an attempt has been
made to develop a drag model for E-E simulations by analyzing the DNS data using machine learning
techniques. The entire work was carried out at HZDR (Helmholtz Zentrum Dresden Rossendorf).

  • Master thesis
    TU Dresden, 2021
    Mentor: Dr. Fabian Schlegel
    73 Seiten

Permalink: https://www.hzdr.de/publications/Publ-32867
Publ.-Id: 32867


Experimental validation of 4D log file-based proton dose reconstruction for interplay assessment considering amplitude-sorted 4DCTs

Spautz, S.; Jakobi, A.; Meijers, A.; Peters, N.; Löck, S.; Knopf, A. C.; Troost, E. G. C.; Richter, C.; Stützer, K.

Purpose: The unpredictable interplay between dynamic proton therapy delivery and target motion (in the thorax) can lead to severe dose distortions. A fraction-wise four-dimensional (4D) dose reconstruction workflow allows to assess the applied dose after patient treatment considering the actual beam delivery sequence extracted from machine log files, the recorded breathing pattern and the geometric information from a 4D computed tomography scan (4DCT). Such an algorithm capable of accounting for amplitude sorted 4DCTs was implemented and its accuracy as well as its sensitivity to input parameter variations was experimentally evaluated.
Methods: An anthropomorphic thorax phantom with a movable insert containing a target surrogate and a radiochromic film was irradiated with a monoenergetic field for various 1D target motion forms (sin, sin4) and peak-to-peak amplitudes (5/10/15/20/30 mm). The measured characteristic film dose distributions were compared to the respective sections in the 4D reconstructed doses using a 2D γ-analysis; γ-pass rates were derived for different dose grid resolutions (1mm/3mm) and deformable image registrations (DIR, automatic/manual) applied during the 4D dose reconstruction process. In an additional analysis, the sensitivity of reconstructed dose distributions against potential asynchronous timing of the motion and machine log files was investigated for both a monoenergetic field and more realistic 4D robustly optimized fields by artificially introduced offsets of ± 1/5/25/50/250 ms. The resulting dose distributions with asynchronized log files were compared to the those with synchronized log files by means of a 3D γ-analysis and the evaluation of absolute dose differences.
Results: The induced characteristic interplay patterns on the films were well reproduced by the 4D dose reconstruction with 2D γ-pass rates ≥95% for almost all cases with motion magnitudes ≤15 mm. In general, the γ-pass rates showed a significant decrease for larger motion amplitudes and increase when using a finer dose grid resolution but were not affected by the choice of motion form (sin, sin4). There was also a statistical trend towards the manually defined DIR for better quality of the reconstructed dose distributions in the area imaged by the film. The 4D dose reconstruction results for the monoenergetic as well as the 4D robustly optimized fields were robust against small asynchronies between motion and machine log files of up to 5 ms, which is in the order of potential network latencies.
Conclusions: We have implemented a 4D log file-based proton dose reconstruction that accounts for amplitude sorted 4DCTs. Its accuracy was proven to be clinically acceptable for target motion magnitudes of up to 15 mm. Particular attention should be paid to the synchronization of the log file generating systems as the reconstructed dose distribution may vary with log file asynchronies larger than those caused by realistic network delays.

Keywords: proton therapy; log file-based dose reconstruction; pencil beam scanning; 4D dose; interplay effect

Permalink: https://www.hzdr.de/publications/Publ-32866
Publ.-Id: 32866


5f states in UGa2 probed by x-ray spectroscopies

Kolomiets, A. V.; Paukov, M.; Valenta, J.; Chatterjee, B.; Andreev, A. V.; Kvashnina, K. O.; Wilhelm, F.; Rogalev, A.; Drozdenko, D.; Minarik, P.; Kolorenc, J.; Richter, M.; Prchal, J.; Havela, L.

The 5f -based ferromagnet UGa2 with the Curie temperature TC = 125K was investigated by x-ray absorption
spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) experiments at the U–M4,5 and Ga–K
edges. The position of the U–M4 white line, determined in the high-energy resolution fluorescence detection
XAS, suggests that UGa2 is neither a localized 5f 2 nor an itinerant system with 5f occupancy close to n5f = 3.
The analysis of the acquired M4,5XANES and XMCD spectra indicates the 5f occupancy close to 2.5 and a
large orbital magnetic moment of the uranium 5f states (3.18 μB) that is partly compensated by the antiparallel
spin moment (1.31 μB). Thus, the total 5f magnetic moment of 1.87 μB is obtained, which is smaller than
the known bulk magnetization of 3.0 μB per formula unit, while the magnetic moments of the Ga atoms are
negligible. Several methods based on density-functional theory were applied and the obtained results were
compared with XAS spectral features, the Sommerfeld coefficient of the electronic specific heat, and the size of
the U moments and 5f occupancies. A clear correlation is revealed between the U–M4 white-line position of three
metallic uranium compounds and the calculated uranium ionicity. It is demonstrated that only electronic structure
methods taking appropriate care of orbital magnetism and related atomic multiplet effects can successfully
describe all considered properties

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Permalink: https://www.hzdr.de/publications/Publ-32865
Publ.-Id: 32865


Research data: Neutralization dynamics and kinetic energy loss of highly charged ions transmitted through graphene

Creutzburg, S.

This depository contains research data (measured ESA spectra and evaluated data) for highly charged ion transmission though graphene. 

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Permalink: https://www.hzdr.de/publications/Publ-32864
Publ.-Id: 32864


Peeling graphite layer by layer reveals the charge exchange dynamics of ions inside a solid

Niggas, A.; Creutzburg, S.; Schwestka, J.; Wöckinger, B.; Gupta, T.; Grande, P. L.; Eder, D.; Marques, J. P.; Bayer, B. C.; Aumayr, F.; Bennett, R.; Wilhelm, R. A.

Over seventy years ago, Niels Bohr described how the charge state of an atomic ion moving through a solid changes dynamically as a result of electron capture and loss processes, eventually resulting in an equilibrium charge state. Although obvious, this process has so far eluded direct experimental observation. By peeling a solid, such as graphite, layer by layer, and studying the transmission of highly charged ions through single-, bi- and trilayer graphene, we can now observe dynamical changes in ion charge states with monolayer precision. In addition we present a new first-principles approach based on the virtual photon model for interparticle energy transfer to corroborate our findings. Our model that uses a Gaussian shaped dynamic polarisability rather than a spatial delta function is a major step in providing a self-consistent description for interparticle de-excitation processes at the limit of small separations.

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Permalink: https://www.hzdr.de/publications/Publ-32862
Publ.-Id: 32862


Autocorrelation-informed home range estimation: a review and practical guide

Simoes Silva, I. M.; Fleming, C. H.; Noonan, M. J.; Alston, J.; Folta, C.; Fagan, W. F.; Calabrese, J.

1. Modern tracking devices allow for the collection of high-volume animal tracking data at improved sampling rates over VHF radiotelemetry. Home range estimation is a key output from these tracking datasets, but the inherent properties of animal movement can lead traditional statistical methods to under- or overestimate home range areas.
2. The Autocorrelated Kernel Density Estimation (AKDE) family of estimators were designed to be statistically efficient while explicitly dealing with the complexities of modern movement data: autocorrelation, small sample sizes, and missing or irregularly sampled data. Although each of these estimators has been described in separate technical papers, here we review how these estimators work and provide a user-friendly guide on how they may be combined to reduce multiple biases simultaneously.
3. We describe the magnitude of the improvements offered by these estimators and their impact on home range area estimates, using both empirical case studies and simulations, contrasting their computational costs.
4. Finally, we provide guidelines for researchers to choose among alternative estimators and an R script to facilitate the application and interpretation of AKDE home range estimates.

Keywords: home range; tracking data; telemetry; kernel density estimation; movement process; ecology; ctmm; AKDE; autocorrelation

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Permalink: https://www.hzdr.de/publications/Publ-32861
Publ.-Id: 32861


Behavior of implanted Xe and Kr in nanodiamond and thin graphene stacks: experiment and modeling

Shiryaev, A. A.; Trigub, A. L.; Voronina, E. N.; Kvashnina, K. O.; Bukhovets, V. L.

Implantation and subsequent behaviour of heavy noble gases (Ar, Kr, Xe) in few-layer graphene sheets and in nanodiamonds
is studied both using computational methods and experimentally using X-ray absorption spectroscopy. For the first time the
Xe-vacancy (Xe-V) defect is experimentally confirmed as a main site for Xe in the diamond. It is shown that noble gases in
thin graphene stacks distort the layers, forming bulges. The energy of an ion placed in between flat graphene sheets is
notably lower than in domains with high curvature. However, if the ion is trapped in the curved domain, considerable
additional energy is required to displace it.

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Permalink: https://www.hzdr.de/publications/Publ-32860
Publ.-Id: 32860


Prompt Gamma-Ray Range Verification in Particle Therapy

Kögler, T.

Particle therapy (PT) has become a widely accepted and promising option for tumor treatment. It supplements conventional radiation therapy with MV X-rays and electrons and is becoming increasingly important for more and more applications. More than 100 clinical PT facilities are already in operation worldwide, around 40 are currently under construction and just as many are planned.
The accuracy of the prediction of the particle range in the tissue is, however, influenced by uncertainties in patient positioning, by patient movements during irradiation, by anatomical changes during one or between several fractions and by other factors that are difficult to quantify in daily clinical routine. These uncertainties are considered by conservative safety margins in the treatment planning, but these margins reduce the advantage of particle beams compared to conventional therapies in many cases. Real-time range verification is therefore a necessity in order to exploit the full potential of particle therapy.
Range verification of therapeutic ions has been investigated for over 50 years now. Many systems have been developed in this time, some devices have been tested under clinical conditions and only a few make it to clinical trials. However, so far there is no system that is used in daily clinical routine. While the first devices still made use of the annihilation radiation of the positron emitters generated in the therapy, the international community mainly concentrates on the use of prompt gamma rays today.
This talk gives an overview of the current status of prompt gamma-ray based range verification. The focus is on the three currently most promising options (Prompt Gamma Ray Imaging, Spectroscopy and Timing). The metrological fundamentals of the individual systems are presented and discussed with regard to their use in everyday clinical practice.

Keywords: Prompt Gamma Treatment Verification; Range Verification in Particle Therapy; Prompt Gamma Ray Timing; Prompt Gamma Ray Imaging; Prompt Gamma Ray Spectroscopy

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  • Lecture (others) (Online presentation)
    Heidelberg Particle Therapy Seminar, 07.07.2021, Heidelberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-32859
Publ.-Id: 32859


Radiolabeled PSMA inhibitors

Neels, O.; Kopka, K.; Liolios, C.; Afshar-Oromieh, A.

Prostate-specific membrane antigen (PSMA) has shown to be a promising target for diagnosis and therapy (theranostics) of prostate cancer. An introducing overview on the regulatory status of PSMA-targeting radiopharmaceuticals in the US and Europe is given. We review developments in the field of radio- and fluorescence-guided surgery and targeted photodynamic therapy as well as multitargeting PSMA inhibitors also addressing albumin and GRPr. Technical and quality aspects of PSMA-targeting radiopharmaceuticals are described and new radiolabeling strategies are presented. Finally, insights are given into production, application and potential of alternatives beyond the commonly used radionuclides for radiolabeling PSMA inhibitors. An additional re-finement of radiopharmaceuticals is required in order to further improve dose-limiting factors like nephrotoxicity and salivary gland uptake during endoradiotherapy. The combination of ra-dionuclide therapy with therapy options of other disciplines shows a way to improve the treat-ment of patients.

Keywords: PSMA; Prostate-specific membrane antigen; PSMA inhibitor; Radiolabeling; PET; SPECT; fluorescence; endoradiotherapy; theranostics; radioguided surgery; fluorescence-guided surgery; targeted photodynamic therapy; radionuclides

Permalink: https://www.hzdr.de/publications/Publ-32858
Publ.-Id: 32858


Data and code for: Experimental evidence that effects of megaherbivores on mesoherbivore space use are influenced by species' traits

Wells, H. B. M.; Crego, R. D.; Opedal, Ø. H.; Khasoha, L. M.; Alston, J. M.; Reed, C. G.; Weiner, S.; Kurukura, S.; Hassan, A. A.; Namoni, M.; Ekadeli, J.; Kimuyu, D.; Young, T. P.; Kartzinel, T. R.; Palmer, T. M.; Pringle, R. M.; Goheen, J. R.

Data and code that can be used to reproduce the analyses underlying "Experimental evidence that effects of megaherbivores on mesoherbivore space use are influenced by species’ traits" by Wells et al. (2021) https://doi.org/10.1111/1365-2656.13565

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Permalink: https://www.hzdr.de/publications/Publ-32857
Publ.-Id: 32857


Rational Design of Two-dimensional Binary Polymers from Heterotriangulenes for Photocatalytic Water Splitting

Zhou, Z.; Springer, M.; Geng, W.; Zhu, X.; Li, T.; Li, M.; Jing, Y.; Heine, T.

Based on first principles calculations, we report the design of three two-dimensional (2D) binary honeycomb-kagome polymers composed of B- and N-centered heterotriangulenes in the same plane with a periodically alternate arrangement as in hexagonal boron nitride. The 2D binary polymers with donor-acceptor characteristics, are semiconductors with a direct band gap of 1.98-2.28 eV. The enhanced in-plane electron conjugation contributes to high charge carrier mobilities for both electrons and holes, about 6.70 and 0.24 × 103 cm2 V-1 s-1, respectively, for the 2D binary polymer with carbonyl bridges (2D CTPAB). With appropriate band edge alignments to match the water redox potentials and pronounced light adsorption for the ultraviolet and visible range of spectra, 2D CTPAB is predicted to be an effective individual photocatalyst to promote overall water splitting.

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Permalink: https://www.hzdr.de/publications/Publ-32856
Publ.-Id: 32856


Garnet major-element composition as an indicator of host-rock type: a machine learning approach using the random forest classifier

Schönig, J.; von Eynatten, H.; Tolosana Delgado, R.; Meinhold, G.

The major-element chemical composition of garnet provides valuable petrogenetic information about its primary host lithologies, particularly in metamorphic rocks. When facing detrital garnet, information about the bulk composition and mineral paragenesis of the initial garnet-bearing host rock is absent. This prevents the application of chemical thermobarometric techniques and calls for quantitative empirical approaches. Here we present a new garnet host-rock discrimination scheme that is based on a random forest machine-learning algorithm trained on a large dataset of 13,615 garnet analyses that covers a wide variety of garnet-bearing lithologies. Considering the out-of-bag error, the scheme correctly predicts the original garnet host-rock in (i) >95 % concerning the setting, that is mantle versus metamorphic versus igneous versus metasomatic; (ii) >84 % concerning the metamorphic facies, that is blueschist/greenschist versus amphibolite versus granulite versus eclogite/ultrahigh-pressure; and (iii) >93 % concerning the host-rock composition, that is intermediate–felsic/metasedimentary versus mafic versus ultramafic versus alkaline versus calcsilicate. The wide coverage of potential host rocks, the detailed prediction classes, the high discrimination rates, and the successfully tested real-case applications demonstrate that the introduced scheme overcomes many issues related to previous schemes. This highlights the potential of transferring the applied discrimination strategy to the broad range of detrital minerals beyond garnet, as well as many other quantitative empirical challenges in Earth sciences. For easy and quick usage, a freely accessible web app is provided that guides the user in five steps from garnet composition to prediction results including data visualization.

Permalink: https://www.hzdr.de/publications/Publ-32854
Publ.-Id: 32854


Challenges in Contactless Inductive Flow Tomography for Rayleigh-Bénard Convection Cells

Sieger, M.; Mitra, R.; Schindler, F.; Vogt, T.; Stefani, F.; Eckert, S.; Wondrak, T.

Contactless inductive flow tomography (CIFT) can reconstruct the complex 3-dimensional flow structure of the large scale circulation in liquid metal filled Rayleigh-Bénard (RB) convection cells. The method relies on the precise measurement of weak magnetic fields induced by currents in the conducting liquid arising from the fluid motion in combination with primary excitation fields. The velocity distribution is reconstructed from the magnetic field measurements by solving a linear inverse problem using the Tikhonov regularization and L-curve method. A number of technical challenges have to be overcome to reach the desired accuracy of the measurement signals. In this paper we will describe our design of a new CIFT set-up for a large RB vessel with a diameter of 320 mm and a height of 640 mm. We outline the major factors perturbing the measurement signal of several tens of nanoteslas and describe solutions to decrease mechanical drifts by thermal expansion to a sub-critical level to enable CIFT measurements for high-Rayleigh number flows.

Keywords: contactless inductive flow tomography; large scale circulation; liquid metal flow; Rayleigh-Bénard convection

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  • Contribution to proceedings
    Electromagnetic processing of materials 2021, 14.-16.06.2021, Riga / virtual, Latvia
    Proceedings of the 10th international conference Electromagnetic Processing of Materials, Riga: The University of Latvia Press, 978-9934-18-686-8, 1-280
  • Lecture (Conference) (Online presentation)
    Electromagnetic processing of materials 2021, 16.06.2021, Riga / virtual, Latvia
  • Magnetohydrodynamics 58(2022)1/2, 25-32
    DOI: 10.22364/mhd.58.1-2.3
    Cited 4 times in Scopus

Permalink: https://www.hzdr.de/publications/Publ-32853
Publ.-Id: 32853


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