Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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41663 Publications

Transferability of DFT surrogate models: Temperature and system size

Fiedler, L.; Cangi, A.

Abstract

While Density Functional Theory (DFT) is the most common tool for the investigation of materials under extreme conditions, its scaling behavior with respect to both system size and temperature makes large scale simulations challenging. Yet, progress in this regard would enable accurate modeling of planetary interiors or radiation damage in fusion reactor walls.
One possible route to alleviate these scaling problems is through the use of surrogate models, i.e., machine-learning models. These are trained on DFT data and are able to reproduce DFT observables at comparable accuracy, but negligible computational cost.
In order to actually be useful for such investigations, existing models need to be able to work across length scales and be transferable within desired temperature ranges. Here we show how models based on local mappings of electronic structure information [1], implemented in the Materials Learning Algorithms (MALA) package [2] can be trained on small number of atoms and select temperatures, yet perform accurately when used to make predictions for extended systems within a range of temperatures.

Keywords: Density Functional Theory; Machine Learning

  • Poster
    Strongly Coupled Coulomb Systems 2022, 24.-29.07.2022, Görlitz, Deutschland
  • Lecture (Conference)
    Multiscale Modeling of Matter under Extreme Conditions, 11.-16.09.2022, Görlitz, Deutschland
  • Poster
    Big data analytical methods for complex systems, 06.10.2022, Wrocław, Polen

Permalink: https://www.hzdr.de/publications/Publ-34827


Data publication: Curvilinear spin-wave dynamics beyond the thin-shell approximation: Magnetic nanotubes as a case study

Körber, L.; Verba, R.; Otálora, J. A.; Kravchuk, V.; Lindner, J.; Faßbender, J.; Kakay, A.

Abstract

This dataset contains the numerical data for our publication "Curvilinear spin-wave dynamics beyond the thin-shell approximation: Magnetic nanotubes as a case study" published in Physical Review B. The data consists of dispersion, magnetization ground states and mode profiles of spin waves in vortex-state magnetic nanotubes of different thicknesses, and has been calculated with the TetraX micromagnetic modeling package. All calculations are described within each subfolder by a jupyter notebook.

Keywords: spin waves; nanotubes; curvilinear magnetism; curvature effects; micromagnetic modeling; tetrax; nonreciprocity

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Permalink: https://www.hzdr.de/publications/Publ-34826


The M4,5 edges HERFD XANES: approaches to calculations

Amidani, L.; Kvashnina, K.

Abstract

X-ray Absorption Near-Edge Structure (XANES) in the High-Energy-Resolution Fluorescence Detected Mode (HERFD) is a very powerful technique for actinide systems. The M4,5 edges are of particular interest because they probe directly 5f states. However, before the advent of HERFD they were scarcely used because the large core-hole lifetime broadening results in broad and featureless spectra. With the improved resolution of the HERFD mode, the characterristic edge shift of different oxidation states is well resolved and several spectral features are observed in M4,5 HERFD XANES of actinides. The richness of physicochemical information coded in the spectra are hard to extract due to the complexity of XANES interpretaion and drawing conclusions on the system under study is not trivial.

In this regards, spectral calculations are fundamental for a correct interpretation. Calculating HERFD XANES on actinide systems is however particularly challenging. Relativistic effects, spin-orbit and interelectronic interactions and the influence of the atomic environment are all relevant and need to be considered in calculations. In last years, despite several approaches has been used with promising results, we still miss a theoretical framework that can address the complexity of M4,5 HERFD XANES on actinide systems.

In this presentation we will report the results we obtained with a DFT-based approach on the M4 edge of U6+ systems. Our results will be compared with works done with other approaches in order to give an overview of the level of agreement with experimental data that can be reached today. Special emphasis will be given to the investigation of covalency of 5f states.

Involved research facilities

Related publications

  • Lecture (Conference)
    Actinide revisited 2022, 21.-23.09.2022, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-34825


Magnetic-field-assisted electrodeposition at conically structured metal layers

Huang, M.

Abstract

Micro- and nano-sized conical structures possess specific magnetic, superhydrophobic and electrocatalytic properties and are therefore attractive for numerous applications. Among the various methods of manufacturing such structured layers, electrodeposition appears a simple and inexpensive method. Beside the use of capping agents, the application of magnetic fields could support the local growth of cones on a non-templated planar electrode.
This dissertation investigates electrodeposition at conically structured metal layers in external magnetic fields. Depending on the direction and the intensity of the magnetic field, the Lorentz force and the magnetic gradient force can generate electrolyte flow and bring electrolyte enriched with metal ions towards the cone tips. As a result, the local deposition rate is increased and conical growth is promoted. In order to obtain a basic understanding of the magnetic field effects, systematic numerical and theoretical investigations are performed for electrodeposition at mm-sized cones of different materials, shapes and arrangements under different electrochemical and magnetic conditions. If a uniform external magnetic field is oriented parallel to the cone axis, the magnetic gradient force enabled by the magnetization of ferromagnetic cones provides a strong support for conical growth, thereby often dominating over the Lorentz force and the buoyancy force arising from electrode reactions. This supporting effect is only slightly mitigated when neighboring cones are getting closer. The numerical results shown are validated by experimental data for different configurations and deposition parameters.
In order to explore the prospects of magnetic fields to enhance the growth of smaller, micro- and nanometer sized conical structures, scaling laws of the local flows driven by the magnetic forces are derived numerically and confirmed analytically for shrinking cone sizes. Although the magnetic gradient force can generate a beneficial flow at ferromagnetic cones, the small flow region and the nearly constant thickness of the concentration boundary layer limit the support of the magnetic field. Enhancements of the structuring effect are observed for pulsed deposition and, despite only moderately, at higher magnetic field intensities. Furthermore, a simplified modeling approach is developed to simulate the growth mechanism of nano-cones with respect to the influence of capping agents.
Experimental results of the electrodeposition of Ni cones in magnetic fields obtained by partners in Krakow are analyzed by performing simulations of both the global cell flow and the local flows generated by magnetic fields of different orientations. This two-step approach provides an interpretation of the experimental results, and gives a deeper insight on how the capping agent influences the local growth.
Finally, the impact of the hydrogen side reaction on the electrodeposition in magnetic fields is considered. The numerical results indicate that hydrogen bubbles sitting at the cone tips may damp conical growth, while the magnetic-field-driven flow imposes a weak stabilizing force on the bubble.

Keywords: Metal electrodeposition; Nano-structured catalyst; Lorentz force; Magnetic gradient force; Numerical simulation; Magnetic field

  • Doctoral thesis
    TU Dresden, 2022
    Mentor: Dr. Gerd Mutschke, Prof. Kerstin Eckert

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Permalink: https://www.hzdr.de/publications/Publ-34824


Nonlinear THz spectroscopy of two-dimensional systems

Helm, M.

Abstract

Nonlinear THz spectroscopy of two-dimensional systems (pump-probe in graphene, with and without magnetic field, dressed microcavity polaritons).

Keywords: THz; free-electron laser; graphene; Landau levels; polariton

Involved research facilities

  • F-ELBE
  • Invited lecture (Conferences)
    Workshop on "Semiconductors,nanostructures, 2D systems, and Dirac matter", 20.-22.06.2022, Grenoble, France

Permalink: https://www.hzdr.de/publications/Publ-34823


Learning local dominant force balances in active particle systems

Sturm, D.; Maddu, S.; Sbalzarini, I. F.

Abstract

Systems of self-propelled particles exhibit self-organized collective behavior that leads to the formation of complex spatio-temporal patterns that can be observed all over nature — from the active self-assembly of microtubules in cells through the action of kinesin motor proteins, to flocking birds. Because of their abundance, the question of how these rich macroscopic structures emerge from the microscopic interactions of their constituents remains of central interest. While there exist several hydrodynamic theories that help better understand the physical mechanisms, it is often difficult to determine which local microscopic interactions shape and regulate self-organized structures in active particle systems. Using a combination of unsupervised clustering algorithms and sparsity-promoting inference, we learn from data dominant force balance laws that locally drive the emergence of macroscopic patterns in active particle systems. We consider a classic hydrodynamic model of self-propelled particle systems that hosts solutions composed of spatiotemporal patterns like asters and propagating stripes. We show that 1) propagating stripes are formed by local alignment interactions and driven by gradients in polarization density and 2) steady-state asters are shaped by a mechanism of splay-induced negative compressibility arising from strong particle interactions. These data-driven discoveries are in excellent agreement with analytical predictions. We therefore believe that the presented data-driven strategy, in combination with physical modeling, can help our mechanistic understanding of active material systems as well as the design of biomimetic materials.

Keywords: active particle systems; active hydrodynamics; data-driven modeling; dominant balance models

Related publications

  • Open Access Logo Lecture (Conference)
    9th GACM Colloquium on Computational Mechanics, 21.-23.09.2022, Essen, Germany
  • Open Access Logo Poster
    HZDR Doctoral Seminar 2022, 19.-21.10.2022, Wroclaw, Poland

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Permalink: https://www.hzdr.de/publications/Publ-34822


Convection triggers MRI amplitude and phase signal changes during proton beam irradiation of liquid water phantoms

Peter, J.; Gantz, S.; Karsch, L.; Pawelke, J.; Hoffmann, A. L.

Abstract

In-beam MRI has recently proven capable of visualising proton beams in liquid-filled
phantoms based on beam-induced local MR signal amplitude loss. This holds promise for on-
line beam range verification and dosimetric as well as geometric quality assurance for hybrid
MRI-proton therapy systems currently under development. The purpose of this study was
firstly to determine whether, in addition to MR signal amplitude loss, the MRI phase signal is
affected by the proton beam and secondly, to test whether these changes in MRI signals are
triggered by beam-induced convection.

Involved research facilities

  • OncoRay
  • Contribution to proceedings
    13th interventional MRI symposium 2022, 14.-15.10.2022, Leipzig, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-34821


Combined proton radiography and irradiation for high-precision preclinical studies in small animals

Schneider, M.; Elisabeth, B.; Suckert, T.; Beyreuther, E.; Bock, J.; Dietrich, A.; Gantz, S.; Heuchel, L.; Krause, M.; Neubeck, C. V.; Nexhipi, S.; Tillner, F.; Schürer, M.; Lühr, A.; Müller, J.

Abstract

Background and purpose: Proton therapy has become a popular treatment modality in the field of radiooncology due to higher spatial dose conformity compared to conventional radiotherapy, which holds the potential to spare normal tissue. Nevertheless, unresolved research questions, such as the much debated relative biological effectiveness (RBE) of protons, call for preclinical research, especially regarding in vivo studies. To mimic clinical workflows, high-precision small animal irradiation setups with image-guidance are needed.

Material and methods: A preclinical experimental setup for small animal brain irradiation using proton radiographies was established to perform planning, repositioning, and irradiation of mice. The image quality of proton radiographies was optimized regarding the resolution, contrast-to-noise ratio (CNR), and minimal dose deposition in the animal. Subsequently, proof-of-concept histological analysis was conducted by staining for DNA double-strand breaks that were then correlated to the delivered dose.

Results: The developed setup and workflow allow precise brain irradiation with a lateral target positioning accuracy of <0.26mm for in vivo experiments at minimal imaging dose of <23mGy per mouse. The custom-made software for image registration enables the fast and precise animal positioning at the beam with low observer-variability. DNA damage staining validated the successful positioning and irradiation of the mouse hippocampus.

Conclusion: Proton radiography enables fast and effective high-precision lateral alignment of proton beam and target volume in mouse irradiation experiments with limited dose exposure. In the future, this will enable irradiation of larger animal cohorts as well as fractionated proton irradiation.

Keywords: Proton therapy; Proton radiography; Mouse brain irradiation; preclinical (in vivo) studies; DNA damage; Relative biological effectiveness (RBE)

Involved research facilities

  • OncoRay

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Permalink: https://www.hzdr.de/publications/Publ-34820


Flow Morphology of TEG Desiccant in a Structured Packing Air Dehumidifier Exposed to Floating Conditions

Mamedov, T.; Schleicher, E.; Schubert, M.; Ehlert, T.; Kenig, E. Y.; Hampel, U.

Abstract

In this work, an approach is proposed to study the influence of floating conditions on the fluid flow behavior of separation columns. A structured packing (Mellapak 250Y) air dehumidifier was embarked on a hexapod ship motion emulator with six-degree-of-freedom motions to mimic swell. A novel flow imaging sensor has been developed to visualize the flow morphology dynamics of triethylene glycol evolving on the corrugated sheets of packings. Furthermore, a numerical model was developed based on the hydrodynamic analogy concept to evaluate the separation performance using experimentally observed flow patterns. In our contribution, we describe the flow imaging sensor design as well as the impact of tilt on efficiency losses in comparison with the conventional upright stationary column.

Keywords: Moving columns; Hydrodynamics; FPSO; Flow imaging sensor; HA approach

  • Contribution to proceedings
    The 12th international conference Distillation & Absorption 2022, 18.-21.09.2022, Toulouse, France

Permalink: https://www.hzdr.de/publications/Publ-34819


Liquid flow morphology investigation in structured packings for offshore applications using a novel flow imaging sensor

Mamedov, T.; Schleicher, E.; Schubert, M.; Ehlert, T.; Kenig, E. Y.; Hampel, U.

Abstract

Environmental and economic constraints for oil and gas production necessitate the development of cost-effective operating facilities in the modern offshore industry. For this reason, floating production systems are increasingly used to operate oil and gas fields in deepwater locations, whereby high submarine pipeline expenditures of fixed offshore platforms are eliminated. Apart from economic advantages, floating production systems maintain a safe operation and continuous production under severe ocean conditions, i.e. cyclones, huge waves and floating icebergs. Whilst traditional fossil energy sources are continuously losing their dominance, liquefied natural gas (LNG) is gaining popularity in the energy market owing to the comparatively lower greenhouse gas emissions. For LNG production, Floating Production Storage and Offloading (FPSO) units combine the feature of onshore LNG plants and that of storage tankers in a single large marine vessel. Thus, the number of FPSOs for LNG production has been growing in the offshore industry. The design principles for land-based process units cannot be directly applied to FPSO topside equipment because of wind-generated wave effects. Separation columns are more susceptible to the motion impact than most of the onboard process equipment, and consequent product quality losses represent the main concern.
Separation columns with structured packings are mostly used on floating platforms due to their low pressure drop, high capacity and performance. To study the dynamics of the flow morphology in the packing and the corresponding mass transfer performance, a structured packing column is embarked on a hexapod motion simulator, which mimics the six-degree-of-freedom ship motion (cf. Fig. 1). The process of air dehumidification by triethylene glycol (TEG) solutions is used as an example. A novel flow imaging sensor was developed to visualize the flow morphology dynamics evolving on the corrugated sheets of the structured packing (Fig. 2). The sensor detects most relevant morphologies, i.e. unwetted, partially and fully wetted channels and their corresponding film thicknesses on the packing sheets for the tilted and moving column allowing a comparison with the vertically oriented configuration.
At a later step, along with the fluid dynamics, the separation performance of air dehumidification and the liquid desiccant regeneration processes will be evaluated. The experimental data will be used to develop a new modelling approach for floating structured packing columns based on hydrodynamic analogies between complex flow patterns in real columns and simplified fluid-dynamic elements.

  • Contribution to proceedings
    Jahrestreffen der ProcessNet-Fachgruppen Fluidverfahrenstechnik und Hochdruckverfahrenstechnik, 02.-03.05.2022, Frankfurt am Main, Deutschland
    Proceedings des Jahrestreffens der ProcessNet-Fachgruppen Fluidverfahrenstechnik und Hochdruckverfahrenstechnik
  • Poster
    Jahrestreffen der ProcessNet-Fachgruppen Fluidverfahrenstechnik und Hochdruckverfahrenstechnik, 02.-03.05.2022, Frankfurt am Main, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-34818


Optimization and preliminary design of a high-temperature, low pressure-ratio sCO2-compressor for a wide operating range

Rath, S.; Unger, S.; Hampel, U.; Gampe, U.

Abstract

Power cycles based on supercritical carbon dioxide (sCO2) promise higher thermal efficiencies and more compact components than conventional technologies. Within the CARBOSOLA project, funded by the German Federal Ministry for Economic Affairs and Energy, a large-scale experimental facility is being set up by a consortium of scientific and industrial partners to actively contribute to the development of sCO2 technology. The first expansion stage provides a circulation of the sCO2 flow without expansion devices in the test loop. Thereby the compressor is intended to compensate for pressure losses and consequently for low pressure differences. In addition to that, a preferably wide operating range, regarding temperature and pressure, shall provide a high degree of flexibility of the test rig.
This work presents the design optimization of the impeller aiming at a wide operating range in compliance with the boundary conditions set for the test rig and the use of sCO2. For this purpose, a hybrid approach is used, combining parametric three-dimensional modeling with a one-dimensional performance criterion for operating range estimation. A large number of impeller designs have been simulated numerically within an optimization procedure using a genetic algorithm. On this basis, several designs have been selected and compared against each other. The evaluation includes sets of performance lines and the validation of the one-dimensional criterion used for optimization.

Involved research facilities

  • TOPFLOW Facility
  • Open Access Logo Contribution to proceedings
    7th International sCO2 Power Cycles Symposium, 21.-24.02.2022, San Antonio, Texas, USA
    Optimization and preliminary design of a high-temperature, low pressure-ratio sCO2-compressor for a wide operating range
  • Open Access Logo Poster
    Optimization and preliminary design of a high-temperature, low pressure-ratio sCO2-compressor for a wide operating range, 21.-24.02.2022, San Antonio, Texas, USA

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Permalink: https://www.hzdr.de/publications/Publ-34817


Comparative analysis of uranium(VI) reduction by a sulfate- and an iron-reducing bacterium

Hilpmann, S.; Jeschke, I.; Steudtner, R.; Hübner, R.; Stumpf, T.; Cherkouk, A.

Abstract

The safe disposal of high-level radioactive waste represents a significant scientific and societal challenge. According to geological, geochemical, and geophysical properties, clay formations represent a suitable host rock for the long-term storage of this waste. However, for a comprehensive safety assessment, the influence of naturally occurring microorganisms in clay rock and in the backfill material bentonite must be taken into account.
Desulfosporosinus species play a crucial role in the community of sulfate-reducing bacteria present in clay rock and bentonite.[1,2] Desulfosporosinus hippei DSM 8344T is a close relative of the isolated species and was originally found in permafrost soils.[3] Desulfitobacterium sp. G1-2 has been isolated from bentonite samples and is an important representative of iron-reducing bacteria. As members of the microbial community from deep geological layers, these strains were selected to get a more profound knowledge about their interactions with U(VI).
During time-dependent experiments in bicarbonate buffer (30 mM, 100 µM U(VI)), Desulfitobacterium sp. G1-2 showed a removal of up to 80% within 5 days. UV/Vis studies of the dissolved cell pellets verified the formation of U(IV) during the process.
In contrast to these findings, Desulfosporosinus hippei DSM 8344T was not able to reduce U(VI) in the presence of bicarbonate. Therefore, experiments in artificial Opalinus Clay pore water [4] (100 µM U(VI), pH 5.5) were conducted. Determinations of the U concentrations showed a removal of up to 80% of the radionuclide from the supernatants within only 48 h. UV/Vis studies of the dissolved cell pellets provided clear proof of a partially reduction of U(VI) to U(IV), although bands of U(VI) were also still observable. These findings propose a combined association-reduction process as a possible interaction mechanism for this microorganism.
TEM images combined with EDX analysis revealed the presence of two different U-containing aggregates inside cells of Desulfitobacterium sp. G1-2. Furthermore, cells of Desulfosporosinus hippei DSM 8344T released membrane vesicles as a possible defense mechanism against encrustation by U precipitates on the cell surface. However, cells showed almost no uptake of U.
In this study, different analytical methods were used to better understand the U(VI) reduction by sulfate- and iron-reducing bacteria. Significant differences in the occurring mechanisms were evident between both microorganisms, highlighting the importance of studies on the U(VI) interactions of different microorganisms present in clay rock. Moreover, these results contribute to a safety concept for a nuclear repository in clay formations and for final disposal sites using bentonite as backfill material.

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 bacteria; Iron-reducing bacteria

  • Lecture (Conference)
    14th International Symposium on Nuclear and Environmental Radiochemical Analysis: ERA14, 12.-15.09.2022, York, Großbritannien

Permalink: https://www.hzdr.de/publications/Publ-34816


Simulation of particle resuspension by wind in an urban system

Banari, A.; Hertel, D.; Schlink, U.; Hampel, U.; Lecrivain, G.

Abstract

Air pollution caused by particle resuspension is a growing public health problem in many cities. Pollen and anthropogenic pollutants, such as heavy metal particles and micro-plastics debris, settle onto urban ground surfaces. Prolonged urban heat waves are propitious for heavy and continuous deposition. Particles in the submillimeter size range eventually resuspend by urban winds within seconds, may be inhaled, cause allergic reactions and escape the city's boundaries. Here, the resuspension and subsequent dispersion of generic particles ranging from 10 to 100 μm in size are simulated. The city area “Bayerischer Bahnhof” in Leipzig, Germany, has been chosen as a practical example. To track the resuspended particles, a Lagrangian model is used. Taking advantage of graphics processing unit, turbulent flow simulations at different wind speeds are performed in almost real time. The results show that particle resuspension starts, when the inlet wind speed beyond the canopy, that is at a height of 40 m, exceeds 7 m/s. At wind speed beyond 14 m/s, resuspension occurs in almost all city parts. At moderate wind speed, high-risk areas are identified. The effect of green infrastructures on both the flow field and particle resuspension is also investigated.

Keywords: particle resuspension; Bayerischer Bahnhof; public health

Permalink: https://www.hzdr.de/publications/Publ-34815


Untersuchung der Innenströmung einer Taylorblase mit einem neuartigen PIV-System mit deformierbarem Spiegel

Bürkle, F.; Lecrivain, G.; Maestri, R.; Hampel, U.; Czarske, J.; Büttner, L.

Abstract

Aerosolpartikel liegen in nahezu allen Gasen vor. Die Abscheidung dieser Partikel ist unter anderem bei der Reinigung von Luft von Feinstaub und Viren relevant. Auch in der Verfahrenstechnik reagieren beispielsweise Gase mit Feststoffen, wie bei der Gasphasenpolymerisation. Für Partikel im Größenbereich von 0,1 – 10 µm sind bisher aufgrund zu weniger empirischer Daten keine zuverlässigen Vorhersagen der Prozesse möglich.
In diesem Beitrag werden Messungen der Innenströmung einer Blase in verschiedenen, mit Wasser durchströmten Rohren gezeigt. In einem Rohr mit konstantem Durchmesser ist ein langgezogener Wirbel sichtbar. Zur Beeinflussung der Blaseninnenströmung ist in einem Rohr eine Verjüngung eingebracht. Die Verjüngung erzeugt in der Blase einen zweiten Wirbel, welcher die gleiche Rotationsrichtung aufweist. Im Berührungsbereich zwischen beiden Wirbeln treffen entgegengesetzte Strömungen aufeinander.

  • Lecture (Conference)
    29. Fachtagung "Experimentelle Strömungsmechanik", 06.-08.09.2022, Ilmenau, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-34814


XANES calculations of actinide-based materials

Amidani, L.; Kvashnina, K.

Abstract

XANES, with its high sensitivity to the oxidation state and the local structure, is a very powerful tool to investigate actinide-based materials. The use of the High-Energy-Resolution Fluores-cence-Detected (HERFD) mode opened new perspective in this field. By reducing the core-hole lifetime broadening, HERFD allows a relevant gain in resolution at the L3 edge and a major im-provement for M4,5 edges.
The information contained in a XANES spectrum are often hard to extract and therefore need the support of theory. However, calculations of actinide materials made complex by the compa-rable strength of intra-electronic interactions, spin-orbit and influence of the local environment. Efforts are ongoing to take all the relevant physics into account, however today none of the the-oretical framework used in XANES calculations can account for all relevant interactions over a large cluster of atoms.
If we do not yet have a unique theoretical framework that can be applied to all actinide systems, we can still select the theory that is more adapted to specific cases. In this contribution we will present progresses in the interpretation of XANES of actinide systems obtained by using the DFT–based code FDMNES [1]. Results at the L3 and M4,5 edges on Th4+ and U6+ systems will be presented [2-4]. These systems, where the intra-electronic interactions are less relevant due to the absence of 5f valence electrons, are particularly suited to investigate the importance of the local environment on the spectral shape.
Our results endorse the use of HERFD XANES coupled with DFT-based calculations to investi-gate complex actinide-containing systems.

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  • Lecture (Conference)
    ATAS-AnXAS 2022 - joint workshop, 17.-21.10.2022, Grenoble, France

Permalink: https://www.hzdr.de/publications/Publ-34813


Application of laser-induced nanostructured metal surfaces

Lorenz, P.; Zajadacz, J.; Bez, E. A.; Marquardt, F.; Franz, R.; Lecrivain, G.; Peter, S.; Hommes, G.; Ehrhardt, M.; Himmerlich, M.; Zimmer, K.

Abstract

Nature teaches that nanostructured surfaces show a variety of beneficial macroscopic effects. The laser texturing of metal surfaces allows the fast, defined, and adjustable large-area nano- and micro surface structuring using ultrashort laser pulses. Such hierarchical structures comprising of determined micro patterns and self-organized nanostructures allow the customization of metal surface properties for applications in accelerators, optics, and fluidics. Here, the laser exposure of superhydrophobic SSt can cause a localized modification of the surface tension which enables the guiding and pining of water droplets which was studied using high-speed optical imaging.
The laser-induced micro- and nano structuring and the chemical modification of the metal surfaces allows the fast and defined adjustment of the macroscopic properties of metals with manifold applications.

  • Lecture (Conference)
    16th International Conference on Laser Ablation, 24.-29.04.2022, Matsue, Japan

Permalink: https://www.hzdr.de/publications/Publ-34812


Modulating properties by light ion irradiation: From novel functional materials to semiconductor power devices

Yuan, Y.; Zhou, S.; Wang, X.

Abstract

In this review, the application of light ion irradiation is discussed for tailoring novel functional materials and for improving the performance in SiC or Si based electrical power devices. The deep traps and electronic disorder produced by light ion irradiation can modify the electrical, magnetic, and optical properties of films (e.g., dilute ferromagnetic semiconductors and topological materials). Additionally, benefiting from the high reproducibility, precise manipulation of functional depth and density of defects, as well as the flexible patternability, the helium or proton ion irradiation has been successfully employed in improving the dynamic performance of SiC and Si based PiN diode power devices by reducing their majority carrier lifetime, although the static performance is sacrificed due to deep level traps. Such a trade-off has been regarded as the key point to compromise the static and dynamic performances of power devices. As a result, herein the light ion irradiation is highlighted in both exploring new physics and optimizing the performance in functional materials and electrical devices.

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Permalink: https://www.hzdr.de/publications/Publ-34811


A high-k Cu-doped ZnO film formed via Ga-ion implantation: The acceptor-donor co-doping approach

Shi, Y.-L.; Huang, D.; Kentsch, U.; Zhou, S.; Ling, F. C.-C.

Abstract

Dielectric thin films having high permittivity (high-k) and low dielectric loss is essential for developing high performance capacitive devices like metal oxide field effect transistor or thin film transistor. Ga ion implantation performed on Cu-doped ZnO film fabricated by pulsed laser deposition with optimized doping concentrations and post-implantation annealing yielded film having high permittivity and low dielectric loss (ε = 87 and tan δ = 0.17 at the frequency of 1 kHz). Moreover, the permittivity exhibits good stability over a wide range of frequency from 20 Hz to 10 MHz. The high-k film was characterized by detailed dielectric studies, including frequency dependence of permittivity and dielectric loss, complex electrical modulus analysis, impedance spectroscopy and ac conductivity. The enhancement of the permittivity was attributed to the correlated potential barrier hopping of electrons between the neighboring acceptor-donor defect complex states in the band gap created by the co-doping, thus acting as electric dipoles polarizing the film. This work opens up future possibility for ‘dielectric engineering’. The three-dimensional dielectric spatial profile can be controlled via the selective area ion implantation with the depth controlled by the ion implantation energy.

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  • Secondary publication expected

Permalink: https://www.hzdr.de/publications/Publ-34810


Tunable structural colors in all-dielectric photonic crystals using energetic ion beams

Li, J.; Zhang, K.; Pang, C.; Zhao, Y.; Zhou, H.; Chen, H.; Lu, G.; Liu, F.; Wu, A.; Du, G.; Akhmadaliev, S.; Zhou, S.; Chen, F.

Abstract

The modulation of structural color through various methods has attracted considerable attention. Herein, a new modulation method for the structural colors in all-dielectric photonic crystals (PCs) using energetic ion beams is proposed. One type of periodic PC and two different defective PCs were experimentally investigated. Under carbon-ion irradiation, the color variation primarily originated from the blue shift of the optical spectra. The varying degrees of both the reflection and transmission structural colors mainly depended on the carbon-ion fluences. Such nanostructures are promising for tunable color filters and double-sided chromatic displays based on PCs.

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Permalink: https://www.hzdr.de/publications/Publ-34809


In-Plane Oriented Two-Dimensional Conjugated Metal–Organic Framework Films for High-Performance Humidity Sensing

Park, S.; Zhang, Z.; Qi, H.; Liang, B.; Mahmood, J.; Noh, H.-J.; Hambsch, M.; Wang, M.; Wang, M.; Hoang Ly, K.; Wang, Z.; Weidinger, I. M.; Zhou, S.; Baek, J.-B.; Kaiser, U.; Mannsfeld, S. C. B.; Feng, X.; Dong, R.

Abstract

Two-dimensional conjugated metal–organic frameworks (2D c-MOFs) have emerged as a new generation of conducting MOFs for electronics. However, controlled synthesis of thin-film samples with high crystallinity and defined layer orientation, which is beneficial for achieving high-performance devices and reliable structure–property relationship, has remained a challenge. Here, we develop a surfactant-directed two-step synthesis of layered 2D c-MOF films based on benzene and triphenylene ligands linked by copper-bis(diimino) complexes (HIB-Cu and HITP-Cu, respectively). The achieved layered 2D c-MOF films are featured as free-standing, in-plane oriented, and polycrystalline films with domain size up to ∼8000 nm2 and a tunable thickness in the range of 8–340 nm. Benefiting from the intrinsic electrical conductivity and quasi-one-dimensional pore channels, a HIB-Cu film based chemiresistive sensor is constructed, displaying effective humidity sensing with a response as fast as ∼21 s, superior to the reported MOF-powder-based chemiresistive sensors (in the orders of minutes).

Permalink: https://www.hzdr.de/publications/Publ-34808


Second harmonic generation from precise diamond blade diced ridge waveguides

Xu, H.; Li, Z.; Pang, C.; Li, R.; Li, G.; Akhmadaliev, S.; Zhou, S.; Lu, Q.; Jia, Y.; Chen, F.

Abstract

In this work, carbon ion irradiation and precise diamond blade dicing are applied for Nd:GdCOB ridge waveguide fabrication. The propagation properties of the fabricated Nd:GdCOB waveguides are investigated through experiments and theoretical analysis. The micro-Raman analysis reveals that the lattice of Nd:GdCOB crystal expands during the irradiation process. The micro-second harmonic spectroscopic analysis suggests that the original nonlinear properties of the Nd:GdCOB crystal are greatly enhanced within the waveguide volume. Under a pulsed 1064-nm laser pumping, second harmonic generation (SHG) at 532 nm have been achieved in the fabricated waveguides. The maximum SHG conversion efficiencies are determined to be ~8.32%W^-1 and ~22.36%W^-1 for planar and ridge waveguides, respectively.

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Permalink: https://www.hzdr.de/publications/Publ-34807


Single-crystal epitaxial europium iron garnet films with strain-induced perpendicular magnetic anisotropy: Structural, strain, magnetic, and spin transport properties

Guo, M. X.; Cheng, C. K.; Liu, Y. C.; Wu, C. N.; Chen, W. N.; Chen, Y. T.; Wu, C. T.; Hsu, C. H.; Zhou, S.; Chang, C. F.; Tjeng, L. H.; Lee, S. F.; Pai, C. F.; Hong, M.; Kwo, J.

Abstract

Single-crystal europium iron garnet (EuIG) thin films were epitaxially grown on gadolinium gallium garnet (GGG)(001) substrates using off-axis sputtering and showed strain-induced perpendicular magnetic anisotropy (PMA). By varying the sputtering conditions, we have tuned the europium/iron (Eu/Fe) composition ratios in the films to tailor the film strains. The films exhibited an extremely smooth, particle-free surface with a root-mean-square roughness as low as 0.1 nm, as observed by atomic force microscopy. High-resolution x-ray diffraction analysis and reciprocal space maps showed pseudomorphic film growth, a very smooth film/substrate interface, excellent film crystallinity with a rocking curve of 0.012° (ω scans), and an in-plane compressive strain without relaxation. In addition, spherical aberration-corrected scanning transmission electron microscopy showed an atomically abrupt interface between the EuIG film and GGG. The saturation magnetization (Ms) and coercive field (Hc) were measured using a vibrating sample magnetometer. The square-shaped out-of-plane M-H loops in conjunction with angle-dependent x-ray magnetic dichroism demonstrated the PMA in the films. The spin Hall magnetoresistance on Pt/EuIG samples was measured to obtain the PMA field strength (H⊥), which increases from 4.21 to 18.87 kOe with the increasing Eu/Fe ratio and in-plane compressive strain. We also measured spin transport in the Pt/EuIG bilayer structure and directly obtained the real part of spin mixing conductance to be 3.48×10^14Ω–1m–2. We demonstrated current-induced magnetization switching with a low critical switching current density of 3.5×10^6A/cm2, showing excellent potential for low-dissipation spintronic devices.

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Permalink: https://www.hzdr.de/publications/Publ-34806


Atomically Thin Delta-Doping of Self-Assembled Molecular Monolayers by Flash Lamp Annealing for Si-Based Deep UV Photodiodes

Chang, S.; He, J.; Prucnal, S.; Zhang, J.; Zhang, J.; Zhou, S.; Helm, M.; Dan, Y.

Abstract

Delta doping (δ-doping) can find a wide range of applications in advanced metal oxide semiconductor field effect transistors, deep UV photodetectors, quantum devices, and others. In this work, we formed a δ-doping layer in silicon by employing flash lamp annealing to treat the PCl3 monolayers grafted on silicon surfaces. The δ-doping layer is atomically thin (<1 nm). Low-temperature Hall measurements show that the δ-doping layer is in a metallic state and exhibits a weak localization phenomenon, implying that a two-dimensional electron gas is formed. When we form such an n-type δ-doping layer on a highly doped p-type Si substrate, a highly sensitive solar-blind UV photodetector is created, which traditionally was only possible by using wide band gap semiconductors such as gallium nitride (GaN) or silicon carbide (SiC).

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Permalink: https://www.hzdr.de/publications/Publ-34805


A mechanistic view on curium(III) sorption on natural K-feldspar surfaces

Demnitz, M.; Schymura, S.; Neumann, J.; Schmidt, M.; Schäfer, T.; Stumpf, T.; Müller, K.

Abstract

For a reliable safety assessment for future deep underground repositories for highly active nu-clear waste a comprehensive understanding of the radionuclide retention by the surrounding host rock is required. Several parameters such as mineral heterogeneity and surface roughness, as well as pore water chemistry, influence radionuclide retention. Although many studies have been performed to investigate individual parameters, their interplay with each other is not yet well understood.

In our study, we focus on the sorption of trivalent curium on K-feldspar, a representative for the large alkali feldspar fractions contained in most crystalline rocks. We use cleaved macroscopic K-feldspar crystals and perform experiments at different pH values (5.5 and 6.9) to determine its impact on surface sorption with varying surface roughness. Furthermore, we investigate a K-feldspar mineral grain, which is part of a complex heterogeneous crystalline rock, obtained from the Grimsel Test Site.

To assess the sorption dependencies, we apply a correlative spectromicroscopy approach. In de-tail, the topography and surface roughness of the K-feldspar crystals as well as the mineral thin section is determined by vertical scanning interferometry. In addition, Raman microscopy deliv-ers information about the thin section’s surface mineralogy. The quantitative amount of sorbed Cm(III) is obtained by calibrated autoradiography and partially µTRLFS (micro-focus time-resolved laser-induced fluorescence spectroscopy), which is also the only method capable of measuring Cm(III) surface speciation on the molecular level via analysis of luminescence spec-tra and lifetimes.

Our results indicate that rougher K-feldspar surfaces exhibit increased Cm(III) uptake and stronger surface complexation. Similarly, the increase in pH leads to higher surface loading and stronger Cm(III) binding to the surface. Results obtained on the thin section reveal, that within a heterogeneous mineralogical system, sorption is affected by dissolution of neighboring minerals and competitive sorption between different mineral phases, such as mica and feldspar. The ob-tained findings express a need for investigating relevant processes on multiple scales of dimen-sion and complexity to better understand radionuclide retention by potential repository host rocks.

The authors acknowledge funding provided by the German Federal Ministry of Education and Research (iCross project 02NUK053B), the Helmholtz Association (iCross project SO-093 and CROSSING project PIE-0007), as well as by the German Federal Ministry of Economics and Technology (SMILE project 02E11668B). We thank F. Bok R. Moeckel, S. Beutner and S. Schöne.

Keywords: µTRLFS; correlative spectroscopy; microscopy; Cm(III); feldspar; orthoclase

  • Contribution to proceedings
    ATAS-AnXAS 2022 - Joint Workshop, 17.-21.10.2022, Grenoble, France
  • Poster
    ATAS-AnXAS 2022 - Joint Workshop, 17.-21.10.2022, Grenoble, France

Permalink: https://www.hzdr.de/publications/Publ-34804


Two decades of CW SRF operation at ELBE

Arnold, A.

Abstract

ELBE is a compact, accelerator-driven photon and particle source. The variety of secondary radiation being offered extends from high-energy gamma rays to infrared and THz radiation as well as from neutrons to positrons and electrons. Since 2001 ELBE is operated as a user facility, providing more than 5500 hours of beamtime with an efficiency of more than 90% each year. The electron accelerator is based on four superconducting 9-cell TESLA cavities that are driven in CW operation to accelerate an average current of 1 mA up to beam energies of 40 MeV.

The the talk will summarize our experiences of operating TESLA cavities over two decades in CW. In detail, this includes the cavity performance and attempts to improve it, as well as investigations on their limitations. Additionally, we will discuss several issues that are related to the high average RF as well as beam power and we will present appropriate measures to protect the machine. In this regard we will also report on long-term experiences with our 10kW 1.3 GHz solid state power amplifiers and introduce a resonant ring for RF component tests at CW power levels up to 100 kW.

Keywords: ELBE; CW SRF; TESLA cavity

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  • Open Access Logo Invited lecture (Conferences) (Online presentation)
    e-LINAC Reliability Workshop (ERW), 09.-10.05.2022, Vancouver, Canada

Permalink: https://www.hzdr.de/publications/Publ-34802


Overview of SRF gun developments in Germany and perspectives of high charge (1 nC) operation

Arnold, A.

Abstract

The contribution highlights the developments of superconducting radio frequency photo electron source (SRF gun) in Germany. The success at HZDR, as well as the progress at HZB and DESY are discussed. The presentation completes with detailed beam dynamics simulations for the typical bunch charges and an gives perspectives of high charge (1 nC) operation.

Keywords: SRF gun; superconducting radio frequency photo electron source

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  • Invited lecture (Conferences)
    FELs of Europe - Topical Workshop on selected problems in FEL physics: from soft X‐rays to THz, 25.-27.04.2022, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-34801


A scalable pipeline for COVID-19: the case study of Germany, Czechia and Poland

Abdussalam, W.; Mertel, A.; Fan, K.; Schüler, L.; Schlechte-Welnicz, W.; Calabrese, J.

Abstract

Throughout the coronavirus disease 2019 (COVID-19) pandemic, decision makers have relied on forecasting models to determine and implement non-pharmaceutical interventions (NPI). In building the forecasting models, continuously updated datasets from various stakeholders including developers, analysts, and testers are required to provide precise predictions. Here we report the design of a scalable pipeline which serves as a data synchronization to support inter-country top-down spatiotemporal observations and forecasting models of COVID-19, named the \textit{where2test}, for Germany, Czechia and Poland. We have built an operational data store (ODS) using PostgreSQL to continuously consolidate datasets from multiple data sources, perform collaborative work, facilitate high performance data analysis, and trace changes. The ODS has been built not only to store the COVID-19 data from Germany, Czechia, and Poland but also other areas. Employing the dimensional fact model, a schema of metadata is capable of synchronizing the various structures of data from those regions, and is scalable to the entire world. Next, the ODS is populated using batch Extract, Transfer, and Load (ETL) jobs. The SQL queries are subsequently created to reduce the need for pre-processing data for users. The data can then support not only forecasting using a version-controlled Arima-Holt model and other analyses to support decision making, but also risk calculator and optimisation apps. The data synchronization runs at a daily interval, which is displayed at https://www.where2test.de.

Keywords: COVID-19; Database Server; Data warehouse; Data pipeline; Database model; Forecast

  • Open Access Logo Contribution to proceedings
    DEco - First International Workshop on Data Ecosystems in conjunction with very large databases, 05.-09.09.2022, Sydney Hybrid, Australia
    Proceedings of DEco
    DOI: 10.48550/arXiv.2208.12928
    URN: https://ceur-ws.org/Vol-3306/

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Permalink: https://www.hzdr.de/publications/Publ-34800


Numerische Simulation der Zweiphasenströmung an einem Festventil eines Kolonnenbodens

Wiedemann, P.; Schubert, M.; Hampel, U.

Abstract

Die zunehmende Energieversorgung aus regenerativen Quellen erfordert ein höheres Maß an Flexibilität beim Betrieb thermischer Trennkolonnen. Vor diesem Hintergrund werden Bodenkolonnen vermehrt mit Festventilen ausgestattet, da diese im Vergleich zu anderen Bodentypen auch bei Teil- oder Überlastfahrweisen eine hohe Trenneffizienz aufweisen. Die Auslegung solcher Böden stellt in der Praxis jedoch eine Herausforderung dar, da es bislang an verlässlichen Daten und Methoden mangelt, um den Einfluss der Ventilanordnung auf die komplexe Zweiphasenströmung abzuschätzen. Im Rahmen eines aktuellen Forschungsprojektes soll daher ein grobskaliger CFD-Ansatz entwickelt werden, mit dessen Hilfe Strömungsszenarien auf Festventilböden mit vertretbarem Aufwand vorausberechnet werden können.
Im vorliegenden Beitrag werden erste Ergebnisse der Verwendung eines hybriden Modellierungsansatzes vorgestellt, mit dem sowohl disperse Strukturen als auch aufgelöste Phasengrenzflächen innerhalb einer Simulationsumgebung abgebildet werden können. Beispielhaft wird dieses Morphologie-adaptive Mehrfeld-Zweifluid-Modell hier zur Simulation der Strömung an einem einzelnen Festventil eingesetzt. Die Abbildung des Ventils erfolgt dabei nicht durch die Auflösung seiner Geometrie im Rechengitter, sondern durch die Implementierung lokaler Massen- und Impulsquellen in der Gasphase. Zur Verifikation der Simulationsergebnisse werden experimentelle Daten der Phasenverteilung um ein Ventil herangezogen, die an einem mit Luft und Wasser betriebenen Laborversuchstand mit einem Leitfähigkeitssensorarray erfasst wurden. Der Vergleich zeigt, dass die im zeitlichen Mittel auftretenden Phasengrenzflächen bei Verwendung statischer Quellterme bereits zufriedenstellend abgebildet werden können. Zur angemessenen Vorhersage des transienten Verhaltens ist jedoch eine Einbeziehung dynamischer Parameter erforderlich. Hierfür können beispielsweise experimentell ermittelte Ablösefrequenzen der Gasblasen vom Ventil verwendet werden. In weiterführenden Arbeiten soll der vielversprechende Ansatz zunächst auf Ventilgruppen und schließlich auf Böden im industriellen Maßstab übertragen werden.

Keywords: Numerische Simulation; Hybrides CFD Model; Festventil; Destillationskolonne

  • Poster
    Jahrestreffen der ProcessNet-Fachgruppen Fluidverfahrenstechnik und Hochdruckverfahrenstechnik, 02.-03.05.2022, Frankfurt a.M., Deutschland

Permalink: https://www.hzdr.de/publications/Publ-34799


Recent technical developments in ASL: A Review of the State of the Art

Hernandez-Garcia, L.; Aramendia, V.; Dai, W.; Bolar, D.; Fernández-Seara, M. A.; Guo, J.; Madhuranthakam, A. J.; Mutsaerts, H.; Petr, J.; Qin, Q.; Schollenberger, J.; Suzuki, Y.; Taso, M.; Thomas, D. L.; van Osch, M. J. P.; Woods, J.; Zhao, M. Y.; Yan, L.; Wang, Z.; Zhao, L.; Okell, T. W.

Abstract

This review article provides an overview of a range of recent technical developments in
advanced arterial spin labeling (ASL) methods that have been developed or adopted by
the community since the publication of a previous ASL consensus paper by Alsop et al.
1 . It is part of a series of review/recommendation papers from the International Society
for Magnetic Resonance in Medicine (ISMRM) Perfusion Study Group. Here, we focus
on advancements in readouts and trajectories, image reconstruction, noise reduction,
partial volume correction, quantification of non-perfusion parameters, fMRI,
fingerprinting, vessel selective ASL, angiography, deep learning, and ultra-high field
ASL. We aim to provide a high level understanding of these new approaches and some
guidance for their implementation, with the goal of facilitating the adoption of such
advances by research groups and by MRI vendors. Topics that are outside the scope of
this article, and are reviewed at length in separate articles, include velocity selective
ASL, multiple-timepoint ASL, body ASL, and clinical ASL recommendations.

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  • PET-Center

Permalink: https://www.hzdr.de/publications/Publ-34798


A new tomography-based approach for the fluid dynamic description of conventional structured packings and sandwich packings

Flechsig, S.; Sohr, J.; Schubert, M.; Hampel, U.; Kenig, E. Y.

Abstract

Pressure drop, holdup and flooding points are essential factors for the hydraulic design of columns equipped with structured packings. This is also true for sandwich packings representing a combination of two alternating layers of conventional structured packings with different geometric surface areas. Such a combination results in a heterogeneous flow pattern evolving within certain operating ranges. In order to describe accurately the fluid dynamics over the entire operating range of both common structured packings and sandwich packings, a modelling approach is proposed based on conventional measurements and tomographic investigations. The approach distinguishes film-like flow patterns and froth regimes. For film-like flow patterns, packing-typical descriptions are used, whereas the froth in packings is described using an analogy to trays. Correlations were derived to determine the liquid holdup for film and froth flow, the dry and irrigated pressure drop as well as the gas velocities at the loading limits. The fluid dynamic model was verified with 1595 measurements for pressure drop and 510 measurements for holdup for the test system water/air.

Keywords: fluid dynamics; modelling; sandwich packings; structured packings; tomography

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  • TOPFLOW Facility

Permalink: https://www.hzdr.de/publications/Publ-34797


Investigation of the interaction of uranium(VI) with the biofluids of the human digestive system

Butscher, D.; Steudtner, R.; Stumpf, T.; Barkleit, A.

Abstract

When radionuclides (RNs) enter the food chain and are ingested by humans, they pose a potential health risk due to their radio- and chemotoxicity. After oral ingestion, RNs first come into contact and interact with the biofluids of the digestive system. For the development of a rapid as well as ef-ficient method for the decorporation of RNs, it is necessary to know the biokinetic processes as well as the speciation in the digestive system. Therefore, the aim of this work was to investigate the in-teractions of uranium(VI) with the biofluids of the human digestive system, with the gastrointesti-nal digestive segments stomach and small intestine as well as the whole digestive system at the mo-lecular level. To simulate the biofluids, saliva, gastric juice, pancreatic juice and bile, and the diges-tive segments were synthesized based on human physiology.[1] For the determination of chemical speciation, luminescence spectra were measured using time-resolved laser-induced fluorescence spectroscopy under cryogenic conditions (cryo-TRLFS) at 153 K. Species distribution was then de-termined by parallel factor analysis (parafac), where the resulting species were assigned using the spectra of the individual complexes. These results were compared with thermodynamic modeling.
Based on the TRLFS experiments, it can be shown that the speciation of uranium is predominantly dominated by the inorganic components, mainly carbonate and to a smaller extent phosphate. Among the organic components, only the protein mucin is involved in speciation at acidic pH val-ues, such as in the stomach. Therefore, the complexation of mucin with uranium(VI) was investi-gated in more detail.

This work is funded by the German Federal Ministry of Education and Research (BMBF) under grant number 02NUK057A and is part of the joint project RADEKOR.

[1] Wilke, C. et al. (2017) J. Inorg. Biochem. 175, 248-258.

  • Lecture (Conference)
    ATAS-AnXAS workshop 2022, 17.-21.10.2022, Grenoble, Frankreich

Permalink: https://www.hzdr.de/publications/Publ-34796


Assessing the impact of forest structure disturbances on the arboreal movement of orangutans - an agent-based modelling approach

Widyastuti, K.; Reuillon, R.; Chapron, P.; Abdussalam, W.; Nasir, D.; Harrison, M. E.; Morrogh-Bernard, H.; Imron, M. A.; Berger, U.

Abstract

Orangutans encounter habitat quality deterioration due to land-use changes and associated forest fires. This creates a complex stress scenario for the individual animals and threatens populations. The disturbance of forest canopies or loss of trees induce changes in primates' movement behavior: the preferred arboreal movement needs to be complemented by movements on the ground requiring more energy, and prolonging the search for fruiting and nesting trees. This all together leads to a change in the daily activity patterns (time spent to travel, feeding and resting) and subsequently to shift in the available energy budget decreasing the fitness of the animals. While agent-based models have been developed and widely employed to check the impact of disturbances or conservation management on the habitat use, population development and viability, there has been less emphasis on studying the direct impact of canopy disturbances on the arboreal movement of individual primates, which can be the origin of cascading effects on animals health, vitality and subsequent life processes. We developed the agent-based simulation model BORNEO (arBOReal aNimal movEment mOdel), which explicitly describes both orangutans' arboreal and terrestrial movement between trees in a forest depending on distances among trees and canopy structure. Orangutans in the model perform activities with a motivation to balance energy intake and expenditure involving mechanical work of locomotion. The model was tested with forest inventory data obtained in Sebangau National Park, Central Kalimantan, Indonesia. Information on tree constellations, sizes etc. were used to reconstruct a virtual forest with similar characteristics (e.g., trees network in terms of connections between overlapping canopies) as in the real world. In order to parameterise the energy related processes of the orangutans described in the model, we applied a computationally intensive evolutionary algorithm on high computing clusters and evaluated the simulation results against behavioural patterns of the orangutans observed in Sebangau. Both the simulated variability and proportion of activity budgets including feeding, resting, and travelling time for female and male orangutans respectively, confirmed the suitability of the model for its purpose. We used the calibrated model to compare the activity patterns and energy budgets of orangutans in both natural and disturbed forests. The results confirm field observations that orangutans in the disturbed forest are prone to experiencing deficit energy balance by spending more time travelling and less time feeding. The finding of a threshold of forest disturbances which affects a significant change in the activity pattern points out that forest deterioration may even threaten the survival of orangutans to some extent.

Our study (a) introduces the first agent-based model describing the arboreal movement of primates and can serve as a tool to investigate the direct impact of forest changes and disturbances on the behaviour of orangutans; and (b) demonstrates the suitability of high-performance computing to optimise the calibration of complex agent-based models describing animal behaviour at a fine spatiotemporal scale (1-meter and 1-second granularity).

Keywords: orangutan; forest structure; peatland; primates; energy budget; agent-based model; 39 calibration; optimisation; distributed computing

Permalink: https://www.hzdr.de/publications/Publ-34795


Data publication: Numerical simulation of tidal synchronization of the Large-Scale Circulation in Rayleigh-Bénard Convection with aspect ratio 1

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

Abstract

wichtige Simulationsdaten + Bilder

Keywords: Magnetohydrodynamics; Rayleigh-Bénard convection; liquid metal flow; electromagnetic forcing; CFD

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Permalink: https://www.hzdr.de/publications/Publ-34794


Data publication: Analyzing a modulated electromagnetic m=2 forcing and its capability to synchronize the Large Scale Circulation in a Rayleigh-Bénard cell of aspect ratio Г = 1

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

Abstract

Relevante Simulationsdaten + Bilder

Keywords: Magnetohydrodynamics; Rayleigh-Bénard convection; liquid metal flow; electromagnetic forcing; CFD

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Permalink: https://www.hzdr.de/publications/Publ-34793


Data publication: Lanmodulin Peptides – Unravelling the Binding of the EF-Hand Loop Sequences Stripped from the Structural Corset

Gutenthaler, S. M.; Tsushima, S.; Steudtner, R.; Gailer, M.; Hoffmann-Röder, A.; Drobot, B.; Daumann, L. J.

Abstract

Daten für die Publikation

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Permalink: https://www.hzdr.de/publications/Publ-34792


Recovery of fine gold loss to tailings using advanced reactor pneumatic flotation ImhoflotTM

Hoang, D. H.; Imhof, R.; Sambrook, T.; Bakulin, E. A.; Murzabekov, M. K.; Abubakirov, A. B.; Baygunakova, K. R.; Rudolph, M.

Abstract

Gold concentration usually consists of gravity separation and froth flotation. However, flotation faces difficulties due to gold-bearing ores often being refractory and finely disseminated in nature. Poor recovery and low flotation kinetics of fine particles are mainly due to the low frequencies of particle-bubble collisions and an increase in entrainment of fine gangue particles decreases the grade. In this study, applications of two pilot ImhoflotTM G-14 (tangential feed to the separator vessel with 1.4 m diameter) cells in an open circuit demonstrated its ability to recover fines with high gold grade and achieved a high recovery of 65–68 % for the particle size fraction of −20 µm. The gold content in the −20 µm fraction of tailings is only about 0.36 g/t, which is lower than in the existing flotation circuit (0.47 g/t), including rougher and scavenger banks. Furthermore, bubble size measurements indicate that pneumatic ImhoflotTM generated very fine bubbles in a high shear environment, improving particle-bubble collision frequencies.

Keywords: pneumatic flotation; G-cell; gold tailings; reactor-separator; fine bubbles; high shear

Permalink: https://www.hzdr.de/publications/Publ-34791


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

Knüpfer, L.; Heitkam, S.

Abstract

Images which has been used to train the model as well as the trained model weights.

Keywords: bubble; foam; image segmentation

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Permalink: https://www.hzdr.de/publications/Publ-34790


A minimal-invasive method for the evaluation of liquid fractions in foams with a point level sensor

Staud, R.; Heller, D.; Knüpfer, L.; Heitkam, S.; Einfalt, D.; Jasch, K.; Scholl, S.

Abstract

Liquid foams occur whether intentionally or unintentionally across different industrial sectors. The detection of foam and characterization of its liquid content currently requires complex measurement methods such as electrical conductivity measurements. This paper presents a novel method for foam detection and characterization of its liquid fraction based on a capacitive level sensor. A correlation between the sensor output signal and defined liquid fractions of dry to wet foam indicated a high accuracy of this sensor technique. Regarding the sensor operation in different liquid solutions, a minimum screw-in depth is presented. The sensor allows minimal invasive inline measurements in equipment regardless of the wall material and extreme process conditions e.g. explosion hazard areas.

Keywords: foam; liquid fraction; sensor

Permalink: https://www.hzdr.de/publications/Publ-34789


PET imaging of cannabinoid receptors type 2 (CB2R) in an animal model of local CB2R overexpression

Rareş-Petru, M.

Abstract

The development PET radioligands for imaging of the cannabinoid type 2 receptors (CB2R) has been intensively explored due to their upregulation in various pathological conditions [1]. Recently, we reported the development of [18F]JHU94620 [2], however, this radioligand suffered from low metabolic stability in vivo. Here, we describe the development of the deuterated analogues [18F]JHU94620-d4 and -d8 as well as their biological evaluation (Figure 1). The precursors for radiofluorination were obtained by coupling 4,5-dimethylthiazol-ylidene-2,2,3,3-tetramethylcyclopropane-1-carboxamide with either d4 or d8 1,4-butanediol-bistosylate and radiofluorinated in the presence of Kryptand K2.2.2. and K2CO3. [18F]JHU94620-d4 and -d8 were obtained in 10% radiochemical yield and >99% radiochemical purity. The fraction of radiometabolites was quantified in mice plasma, brain and spleen of CD1 mice at 30 min p.i. Both [18F]JHU94620-d4 and -d8 demonstrated an improved metabolic stability with 80% intact radioligand detected in the brain vs. 36% for [18F]JHU94620. The CB2 affinity and specificity of [18F]JHU94620-d8 was determined by in vitro binding experiments and a KD(rCB2) of 0.36 nM was determined. Additionally, we evaluated the [18F]JHU94620-d8 uptake by PET-studies into the spleen of healthy rats and in a rat model carrying an adeno-associated viral (AAV2/7) vector expressing hCB2R(D80N) at high densities in the right striatum (hCB2-rs) [3, 4]. Our PET study with [18F]JHU94620-d8 revealed a rCB2 specific uptake into the spleen (AUC0-30min = 33 vs. 17 SUV min after blocking with GW405833). In the hCB2-rs model we could show a target specific uptake of [18F]JHU94620-d8 with a constant SUV of 6.7±0.3 from 6 to 60 min p.i. and an SUVr (right striatum-to-cerebellum) of 43±7at 60 min p.i., as well as a reversible binding in displacement studies. Thus, [18F]JHU94620-d8 is a new PET tracer with improved metabolic stability and excellent ability to image the CB2 receptors in-vivo. Its further evaluation is underway.

  • Invited lecture (Conferences)
    Advancing cancer nanomedicine to the clinics: hypes, hopes and hurdles, 16.-17.06.2022, Magdeburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-34787


Comparative Analysis of Mononuclear 1:1 and 2:1 Tetravalent Actinide (U, Th, Np) Complexes: Crystal Structure, Spectroscopy, and Electrochemistry

Bansal, D.; Kaden, P.; Patzschke, M.; März, J.; Schmidt, M.

Abstract

Six mononuclear tetravalent actinide complexes (1-6) have been synthesized using a new Schiff base ligand 2-methoxy-6-(((2-methyl-1-(pyridin-2-yl)propyl)imino)methyl)phenol (HLpr). The HLpr is treated with tetravalent actinide elements in varied stoichiometry to afford mononuclear 1:1 complexes [MCl3-Lpr∙nTHF] (1-3) and 2:1 complexes [MCl2-Lpr2] (4-6) (M = Th4+ (1 and 4), U4+ (2 and 5) and Np4+ (3 and 6)). All complexes are characterized using different analytical techniques such as IR, NMR, and absorption spectroscopy as well as crystallography. UV-vis spectroscopy revealed more red-shifted absorption spectra for 2:1 complexes as compared to 1:1 complexes. 1H NMR of Th(IV) complexes exhibit diamagnetic spectra whereas U(IV) and Np(IV) complexes revealed paramagnetically shifted 1H NMR. Interestingly, NMR signals are paramagnetically shifted between -70 to 40 ppm in 2 and 3, but are confined within -35 to 25 ppm in 2:1 complexes 5 and 6. Single crystal structures for 1:1 complexes revealed an eight-coordinated Th(IV) complex (1) and seven-coordinated U(IV) (2) and Np(IV) (3) complexes. Whereas, all 2:1 complexes 4-6 were isolated as eight-coordinated isostructural molecules. The geometry around the Th4+ center in 1 is found to be trigonal dodecahedral and, capped trigonal prismatic around U(IV) and Np(IV) centers in 2 and 3, respectively. Whereas, An4+ centers in 2:1 complexes are present in dodecahedral geometry. Importantly, 2:1 complexes exhibit increased bond distances in comparison to their 1:1 counterparts as well as interesting bond modulation w.r.t. ionic radii of An(IV) centers. Cyclic voltammetry displays an increased oxidation potential of the ligand by 300 to 500 mV, after coordination with An4+. CV studies indicates Th(IV)/Th(II) reduction beyond −2.3 V whereas attempts were made to identify redox potentials for U(IV) and Np(IV) centers. Spectroscopic binding studies reveal that complex stability in 1:1 stoichiometry follows the order Th4+≈ U4+ > Np4+.

Keywords: Actinides; Coordination; Electrochemistry; Crystal structure

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Data publication: Spin-resolved density response of the warm dense electron gas

Dornheim, T.

Abstract

This repository contains the PIMC results from the article "Spin-resolved density response of the warm dense electron gas"; parameters are given in the file names; all results are unpolarized (Xi=0) unless otherwise stated; same units as in the original publication.

Keywords: Path integral Monte Carlo; Uniform electron gas; Linear response theory; spin effects

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Permalink: https://www.hzdr.de/publications/Publ-34785


Bomb-pulse radiocarbon record for a well-dated Caribbean coral core

Winkler, S.; Steier, P.; Carilli, J.

Abstract

The radiocarbon bomb-pulse created by nuclear weapons testing in the 1950s and 1960s has created a massive spike of atmospheric ¹⁴C, which has been used in the study of the global carbon cycle in many subsystems including the marine environment. Coral records of bomb-pulse era ¹⁴C have been studied over the past decades to gain insight into the uptake and mixing of atmospheric CO₂ in the ocean. The ¹⁴C level seen in surface waters is specific to the origin of the water masses and ocean-atmosphere exchange of CO₂.
We present results for radiocarbon levels in coral aragonite with yearly resolution for a coral core from Belize. The core has a well-established stratigraphy, stretching from the onset of atmospheric testing of thermonuclear devices to 2007. The core has previously been analyzed for and trace metal content in relation to environmental impacts and the bomb-pulse of ²³⁶U. We compare the results with existing results and model expectations for the Caribbean Sea. We further discuss the close agreement for the prior results in terms of feasibility and the achievable accuracy of cross-dating of cores using the rise of radiocarbon by the atmospheric bomb-pulse.

  • Poster
    Radiocarbon International Conference, 11.-16.09.2022, Zürich, Schweiz

Permalink: https://www.hzdr.de/publications/Publ-34784


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

Dornheim, T.

Abstract

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

  • Lecture (Conference)
    The 13th International Conference on High Energy Density Laboratory Astrophysics (HEDLA) 2022, 25.05.2022, Lisbon, Portugal

Permalink: https://www.hzdr.de/publications/Publ-34783


Data publication: Effective electronic forces and potentials from ab initio path integral Monte Carlo simulations

Dornheim, T.

Abstract

This repository contains all path integral Monte Carlo (PIMC) results for the article "Effective electronic forces and potentials from ab initio path integral Monte Carlo simulations" in the same units as they are plotted in Figs. 4, 5 and 8.

Keywords: Path integral Monte Carlo; Uniform electron gas; effective force

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I-V-T Characteristics and Temperature Sensor Performance of a Fully-2D WSe2/MoS2 Heterojunction Diode at Cryogenic Temperatures

Matthus, C. D.; Chava, P.; Watanabe, K.; Taniguchi, T.; Mikolajick, T.; Helm, M.; Erbe, A.

Abstract

In this work, we demonstrate the usability of a fully-2D-material based device consisting of MoS2/WSe2 heterojunction encapsu-lated by hBN and contacted by graphene as temperature sensor for linear temperature measurement at cryogenic temperatures. More precisely, temperatures in the range of 10 K up to 300 K were applied to the device while recording the I-V characteris-tics. From this, we had a deeper look on the current transport mechanism by obtaining the activation energy of the saturation current in the Arrhenius diagram. It is 1.3 eV, which can be related to the bandgap of MoS2 or WSe2 (both nominal 1.3 eV) as for traditional pn-junction diodes in bulk materials. Further-more, we applied a constant forward current to the device while measuring the voltage drop at different temperatures to investi-gate the temperature-sensor performance. In the range of 40 K up to 300 K, the sensitivity of the sensor is ~2 mV/K, which is comparable to Si devices, while the linearity is still lower (R2 ~ 0.94). On the other hand, the demonstrated device consists only of 2D materials and is, thus, substrate independent, ultra-thin, and can be fabricated on a fully flexible substrate in a low-cost process.

Keywords: Temperature sensing; 2D-material diode; hetero-junction; flexible sensor

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Permalink: https://www.hzdr.de/publications/Publ-34781


Data publication: Distinguishing local demagnetization contribution to the magnetization process in multisegmented nanowires

Marqués Marchán, J.; Fernandez Roldan, J. A.; Bran, C.; Puttock, R.; Barton, C.; Moreno, J. A.; Kösel, J.; Vazquez, M.; Kazakova, O.; Chubykalo-Fesenko, O.; Asenjo, A.

Abstract

Article and Suplementary information available on the Open Access Journal:https://www.mdpi.com/2079-4991/12/12/1968/htm

Figure S1: Nonstandard 2D MFM images of a single NW for an applied magnetic field of (a) ±47 mT and (b) ±28 mT;
Figure S2: (a) Sketch of two simulated CoNi/Cu NWs with different segments and Cu layer lengths. (b) Hysteresis loops of NWs with different anisotropies (68° and 65° with respect to NW axis) and geometries as shown in (a). (c) Zoom of hysteresis loops of NWs with anisotropy at 65° and different geometries.

Keywords: magnetic nanowires; magnetization reversal processes; magnetoresistance; Magnetic Force Microscopy (MFM); CoNi; Cu; nanomagnetism; spintronics

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Permalink: https://www.hzdr.de/publications/Publ-34779


Accelerating Equilibration in First-Principles Molecular Dynamics with Orbital-Free Density Functional Theory

Fiedler, L.; Moldabekov, Z.; Shao, X.; Jiang, K.; Dornheim, T.; Pavanello, M.; Cangi, A.

Abstract

We introduce a practical hybrid approach that combines orbital-free density functional theory (DFT) with Kohn-Sham DFT for speeding up first-principles molecular dynamics simulations. Equilibrated ionic configurations are generated using orbital-free DFT for subsequent Kohn-Sham DFT molecular dynamics. This leads to a massive reduction of the simulation time without any sacrifice in accuracy. We assess this finding across systems of different sizes and temperature, up to the warm dense matter regime. To that end, we use the cosine distance between the time series of radial distribution functions representing the ionic configurations. Likewise, we show that the equilibrated ionic configurations from this hybrid approach significantly enhance the accuracy of machine-learning models that replace Kohn-Sham DFT. Our hybrid scheme enables systematic first-principles simulations of warm dense matter that are otherwise hampered by the large numbers of atoms and the prevalent high temperatures. Moreover, our finding provides an additional motivation for developing kinetic and noninteracting free energy functionals for orbital-free DFT.

Keywords: Density Functional Theory; Machine Learning

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Permalink: https://www.hzdr.de/publications/Publ-34778


Stable Multi-Day Performance and Diagnosis of the DRACO Laser Wakefield Accelerator for Secondary Applications

Couperus Cabadağ, J. P.; Bock, S.; Chang, Y.-Y.; Debus, A.; Gebhardt, R.; Helbig, U.; Irman, A.; Koehler, A.; Kurz, T.; Guntram Pausch, R.; Püschel, T.; Schoebel, S.; Ufer, P.; Zarini, O.; Zeil, K.; Lumpkin, A.; Schramm, U.; Ghaith, A.; Downer, M.; Laberge, M.

Abstract

We report on the operation of the DRACO Laser Driven electron source for stable multi-day operation of secondary applications with demanding beam requirements. The nC-class accelerator delivers charge densities around 10 pC/MeV*, 1 mrad rms divergence at energies up to 0.5 GeV and peak currents of over 10kA**. Precise characterisation is paramount for controlled operation of demanding applications, this includes: spectrally resolved charge diagnostic, source size diagnostics based both on betatron radiation*** as well as on coherent optical transition radiation (TR) to resolve microbunch beam structures**** and TR-based multioctave high-dynamic range spectrometry for sub-fs resolved characterisation of the 10 fs rms electron bunches**. Achieved stability allows systematic exploration of applications, resulting in the recent demonstration of the first LWFA based Beam-driven Plasma Wakefield Accelerator*****. In an effort toward LWFA based Free Electron Lasing, the COXINEL manipulation line developed at Synchrotron SOLEIL was recently installed at our facility. At initial commissioning, successful beam transport was achieved with over 13000 delivered shots within 9 experimental days.

* J.P. Couperus et al., Nat. Comm. 8 (2017)
** O. Zarini et al., PRAB (2022)
*** A. Köhler et al., PRAB (2021)
**** A. Lumpkin et al., PRL 125 (2020)
***** T. Kurz et al., Nat. Comm. 12 (2021)

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  • Draco
  • Poster
    13th International Particle Accelerator Conference (IPAC’22), 12.-17.06.2022, Bangkok, Thailand

Permalink: https://www.hzdr.de/publications/Publ-34777


Untersuchung der Wechselwirkung von Uran(VI) mit den Biofluiden des menschlichen Verdauungssystems sowie mit Nierenzellen

Butscher, D.; Senwitz, C.; Steudtner, R.; Heller, A.; Stumpf, T.; Barkleit, A.

Abstract

Wenn Radionuklide (RN) in die Nahrungskette gelangen und vom Menschen aufgenommen werden, stellen sie aufgrund ihrer Radio- und Chemotoxizität ein mögliches Gesundheitsrisiko dar. Dabei kommen die RN nach der oralen Aufnahme zuerst mit den Biofluiden des Verdauungssystems in Kontakt und interagieren mit diesen. Die Ausscheidung der Schwermetalle erfolgt größtenteils renal. Für die Entwicklung einer schnellen sowie effizienten Methode zur Dekorporation der RN ist es notwendig, die biokinetischen Prozesse sowie die Speziation im Verdauungs- und Ausscheidungssystem zu kennen. Ziel dieser Arbeit ist es daher, die Wechselwirkungen von Uran(VI) mit den Biofluiden des menschlichen Verdauungssystems, mit den gastrointestinalen Verdauungssegmenten Magen und Dünndarm sowie des gesamten Verdauungssystems auf molekularer Ebene zu untersuchen. Für die Simulierung der Biofluide wurden Speichel, Magen-, Pankreassaft und Gallenflüssigkeit sowie die Verdauungssegmente basierend auf der menschlichen Physiologie synthetisch hergestellt.[1] Die chemische Speziation wurde mittels zeitaufgelöster laserinduzierter Fluoreszenz-Spektroskopie unter kryogenen Bedingungen (Kryo-TRLFS) bei 153 K untersucht sowie die Ergebnisse mit thermodynamischen Modellierungen verglichen.
Anhand der TRLFS-Experimente kann gezeigt werden, dass die Speziation von Uran überwiegend von den anorganischen Bestandteilen, hauptsächlich Carbonat und zu einem geringeren Anteil Phosphat, dominiert wird. Bei den organischen Komponenten ist lediglich das Protein Mucin bei sauren pH-Werten, wie z. B. im Magen, an der Speziation beteiligt, weshalb die Komplexierung von Mucin mit Uran(VI) genauer betrachtet wurde. Des Weiteren wurden Zellexperimente mit Nierenzellen von Menschen (HEK-293) und Ratten (NRK-52E) in vitro durchgeführt, um den Effekt von Uran auf die Zellen mittels XTT-Assays zu untersuchen. Um den biochemischen Mechanismus auf molekularer Ebene zu verstehen, wurde die Speziation von Uran im Zellkulturmedium ebenfalls mittels Kryo-TRLFS analysiert. Bei der Hauptspezies, welche auf die Zellen einwirkt, handelt es sich um eine Uranylcarbonatverbindung.
Diese Arbeit wird vom Bundesministerium für Bildung und Forschung (BMBF) unter dem Förderkennzeichen 02NUK057A gefördert und ist Teil des Verbundprojekts RADEKOR.
Referenzen:
[1] C. Wilke et al., J. Inorg. Biochem. 2017, 175, 248-258.

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

Permalink: https://www.hzdr.de/publications/Publ-34776


Cans production of technetium-99m and technetium-101

Mayordomo, N.; Mausolf, E. J.; Johnstone, E.; Williams, D. L.; Guan, E. Y. Z.; Gary, C. K.; Davis, J.

Abstract

Technetium-99m (99mTc, t1/2 = 6.007 h) has been widely used for radiodiagnostic purposes for decades, and it is still one of the most used radioisotopes worldwide with an estimated 40 million doses consumed annually. Tc-99m can be produced through various nuclear transmutation methods, but commercially speaking, it is generally derived from molybdenum-99 (99Mo, t1/2 = 65.925 h), where the origin of it is dependent upon chemistry and isotopic composition of the target material, e.g., natural or enriched Mo, or enriched 235U targets. However, the production and distribution of 99mTc relies on a complex supply-chain that has proven itself prone to disruptions in years past and was most recently observed during the SARS-CoV-2 pandemic.[1] Ultimately, this leads to delays on diagnoses of patients due to postponed imaging procedures as well as the loss of material and capital.
As a solution to this problem, the deployment of a decentralised network of compact accelerator neutron sources (CANS) for producing 99mTc and 101Tc (t1/2 = 14.22 min) using the (n,𝛾) reaction on Mo-based targetry has been proposed.[2] For example, the use of fusion-driven deuterium-deuterium (D-D) neutron generators for producing both 99mTc and 101Tc has been demonstrated along with their subsequent isolation using a separation tailored for low-specific activity 99Mo targets.[2]
Another under-utilised source of neutrons already being generated in this fashion is during the production of many positron emission tomography (PET) radionuclides in cyclotrons, where parasitic neutrons are liberated from the cyclotron target, e.g., 18O(p,n)18F. The implementation of larger production batches, high yield targetry, and more production runs are all complementary to generating neutrons. From this, the hybridised production of 99mTc and 101Tc concurrently during [18F]FDG has been demonstrated and its feasibility explored.[3]
The aim of the work presented herein is to compare various CANS production modes for 99mTc and 101Tc production in regards to their subsequent applications. Further, it provides potential alternatives for the future production of radiopharmaceuticals, meanwhile meeting the objectives of several Unesco and sustainable development goals.

REFERENCES
[1] K. SADRI, V.R. DABBAGH, M.N. FORGHANI, M. ASADI, R. SADEGUI, Lymphoscintigraphy in the Time of COVID-19: Effect of Molybdenum-99 Shortage on Feasibility of Sentinel Node Mapping, Lymphat. Res. Biol. 19 (2021) 134–140.
[2] E.J. MAUSOLF, E.V. JOHNSTONE, N. MAYORDOMO, D.L. WILLIAMS, E.Y.Z. GUAN, C.K. GARY, Fusion-Based Neutron Generator Production of Tc-99m and Tc-101 : A Prospective Avenue to Technetium Theranostics, Pharmaceuticals. 14 (2021) 1–19.
[3] E.V. JOHNSTONE, E.J. MAUSOLF. Hybridized Production of 18F and 99mTc on a Low-Energy Cyclotron. Internal Document, IFS, LLC (2021).

Keywords: Technetium; Neutron generator; Compact accelerator neutron sources; Radiopharmaceuticals

  • Lecture (Conference) (Online presentation)
    International Conference on Accelerators for Research and Sustainable Development: From Good Practices Towards Socioeconomic Impact, 23.-27.05.2022, Viena, Austria

Permalink: https://www.hzdr.de/publications/Publ-34775


Correlation Between Quantitative PSMA PET Parameters and Clinical Risk Factors in Non-Metastatic Primary Prostate Cancer Patients

Zschaeck, S.; Andela, S. B.; Amthauer, H.; Furth, C.; Rogasch, J. M.; Beck, M.; Hofheinz, F.; Huang, K.

Abstract

Background

PSMA PET is frequently used for staging of prostate cancer patients. Furthermore, there is increasing interest to use PET information for personalized local treatment approaches in surgery and radiotherapy, especially for focal treatment strategies. However, it is not well established which quantitative imaging parameters show highest correlation with clinical and histological tumor aggressiveness.

Methods

This is a retrospective analysis of 135 consecutive patients with non-metastatic prostate cancer and PSMA PET before any treatment. Clinical risk parameters (PSA values, Gleason score and D’Amico risk group) were correlated with quantitative PET parameters maximum standardized uptake value (SUVmax), mean SUV (SUVmean), tumor asphericity (ASP) and PSMA tumor volume (PSMA-TV).

Results

Most of the investigated imaging parameters were highly correlated with each other (correlation coefficients between 0.20 and 0.95). A low to moderate, however significant, correlation of imaging parameters with PSA values (0.19 to 0.45) and with Gleason scores (0.17 to 0.31) was observed for all parameters except ASP which did not show a significant correlation with Gleason score. Receiver operating characteristics for the detection of D’Amico high-risk patients showed poor to fair sensitivity and specificity for all investigated quantitative PSMA PET parameters (Areas under the curve (AUC) between 0.63 and 0.73). Comparison of AUC between quantitative PET parameters by DeLong test showed significant superiority of SUVmax compared to SUVmean for the detection of high-risk patients. None of the investigated imaging parameters significantly outperformed SUVmax.

Conclusion

Our data confirm prior publications with lower number of patients that reported moderate correlations of PSMA PET parameters with clinical risk factors. With the important limitation that Gleason scores were only biopsy-derived in this study, there is no indication that the investigated additional parameters deliver superior information compared to SUVmax.

Keywords: PSMA; prostate specific membrane antigen; positron emission tomography; primary prostate cancer; quantitative PET parameters

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  • PET-Center

Permalink: https://www.hzdr.de/publications/Publ-34774


Insights into the Enigmatic TcO₂·xH₂O Structure via Atomistic Simulations

Faria Oliveira, A.; Kuc, A. B.; Heine, T.; Scheinost, A.

Abstract

Technetium is the lightest element without a stable isotope. The β‑emitting ⁹⁹Tc is especially relevant for nuclear waste management due to its long half-life (ca. 2.1×10⁵ years) and relatively high formation yield (≥6%) in ²³⁵U and ²³⁹Pu nuclear reactors. In this context, redox reactions at mineral/water interfaces are crucial for the safety of nuclear waste repositories.

In the absence of complexing agents, Tc exists in water as Tc(VII) and Tc(IV). The former predominates in non-reducing conditions as TcO₄⁻(aq), which is highly mobile in the environment due to its solubility and weak interaction with adsorbents. Studies show that Fe(II) minerals can reduce Tc(VII) to Tc(IV), which is then immobilized by adsorption onto or incorporation into the oxidized Fe mineral and by precipitation as TcO₂·xH₂O. However, even in the simpler case (precipitation) the structure of TcO₂·xH₂O remains controversial.

Lukens et al. [1] demonstrated that, despite being amorphous, TcO₂·xH₂O has a well-defined local structure. Based on EXAFS measurements, they proposed that TcO₂·xH₂O forms linear chains of equally spaced edge-sharing TcO₄(H₂O)₂ octahedra, with terminal H₂O ligands at the apical positions. Vichot et al. [2] obtained similar results but, despite having extracted only one Tc‑Tc distance from the EXAFS, proposed that Tc atoms would be separated by shorter and longer alternating distances as in the monoclinic TcO₂ crystal. More recently, Yalçintaş et al. [3] showed that both models can be fitted equally well to the EXAFS and, thus, the TcO₂·xH₂O structure remained unsolved.

In this work, we use density functional theory (DFT) to investigate the polymeric TcO₂·xH₂O structure. Our calculations reveal that, in contrast to previous models, a zigzag configuration with the terminal H₂O groups at neighboring positions of the octahedra is more likely. The zigzag configuration is energetically more favored and results in a better agreement with the EXAFS measurement.

[1] Lukens et al. (2002), Environ. Sci. Technol. 36, 1124-1129.
[2] Vichot et al. (2002), Radiochim. Acta 90, 575-579.
[3] Yalçintaş et al. (2016), Dalton Trans. 45, 17874-17885.

Keywords: DFT; EXAFS; Technetium

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  • Lecture (Conference) (Online presentation)
    Goldschmidt2022, 10.-15.07.2022, Honolulu, Hawaii, USA

Permalink: https://www.hzdr.de/publications/Publ-34773


Research data: Fano interference between collective modes in cuprate high-Tc superconductors

Chu, H.; Kovalev, S.; Xiao Wang, Z.; Schwarz, L.; Dong, T.; Feng, L.; Haenel, R.; Kim, M.-J.; Phuong Hoang, L.; Honasoge, K.; David Dawson, R.; Putzky, D.; Kim, G.; Puviani, M.; Chen, M.; Awari, N.; Ponomaryov, O.; Ilyakov, I.; Bluschke, M.; Boschini, F.; Zonno, M.; Zhdanovich, S.; Na, M.; Christiani, G.; Logvenov, G.; Jones, D. J.; Damascelli, A.; Minola, M.; Keimer, B.; Manske, D.; Wang, N.; Deinert, J.-C.; Kaiser, S.

Abstract

Research data and metadata that was used in the corresponding publication "Fano interference between collective modes
in cuprate high-Tc superconductors" ( https://doi.org/10.1038/s41467-023-36787-4 ).

Keywords: Terahertz; Higgs spectroscopy; ultrafast; phase-resolved; Superconductivity; cuprates; magnetic fields; doping

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Permalink: https://www.hzdr.de/publications/Publ-34772


Porous Dithiine-Linked Covalent Organic Framework as a Dynamic Platform for Covalent Polysulfide Anchoring in Lithium–Sulfur Battery Cathodes

Haldar, S.; Wang, M.; Bhauriyal, P.; Hazra, A.; Khan, A. H.; Bon, V.; Isaacs, M. A.; de Ankita, L. S.; Boenke, T.; Grothe, J.; Heine, T.; Brunner, E.; Feng, X.; Dong, R.; Schneemann, A.; Kaskel, S.

Abstract

Dithiine linkage formation via a dynamic and self-correcting nucleophilic aromatic substitution reaction enables the de novo synthesis of a porous thianthrene-based two-dimensional covalent organic framework (COF). For the first time, this organo-sulfur moiety is integrated as a structural building block into a crystalline layered COF. The structure of the new material deviates from the typical planar interlayer stacking of the COF to form undulated layers caused by bending along the C-S-C bridge, without loss of aromaticity and crystallinity of the overall COF structure. Comprehensive experimental and theoretical investigations of the COF and a model compound, featuring the thianthrene moiety, suggest partial delocalization of sulfur lone pair electrons over the aromatic backbone of the COF decreasing the band gap and promoting redox activity.
Postsynthetic sulfurization allows for direct covalent attachment of polysulfides to the carbon backbone of the framework to afford a molecular-designed cathode material for lithium-sulfur (Li-S) batteries with a minimized polysulfide shuttle. The fabricated coin cell delivers nearly 77% of the initial capacity even after 500 charge-discharge cycles at 500 mA/g current density. This novel sulfur linkage in COF chemistry is an ideal structural motif for designing model materials for studying advanced electrode materials for Li-S batteries on a molecular level.

Keywords: Aromatic compounds; Covalent organic frameworks; Layers; Lithium; Sulfur

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Dataset for Inversion of GISAXS data (3 layers)

Zhdanov, M.; Ganeva, M.; Randolph, L.; Kluge, T.; Hoffmann, N.

Abstract

The dataset consists of 50000 X-ray diffraction patterns simulated by BornAgain [1] software. For each simulation, a multilayer sample model of the following structure was used: air, tantalum oxide, tantalum, copper nitride, silicon dioxide, and substrate. Parameters of air, silicon dioxide, and substrate were kept fixed. Hence, each diffraction pattern is set to depend on the parameters of tantalum oxide, tantalum, and copper nitride layers. For each layer, those are real and complex parts of refractive index, thickness, roughness, Hurst parameter, and correlation length. Each simulation output is stored in an h5py file consisting of 1) diffraction image as a NumPy array of shape [1200, 120]; 2) parameters of a sample as a NumPy array with 18 elements. For further details regarding simulation see https://github.com/maxxxzdn/gisaxs-reconstruction/simulation/simulation.

[1] Pospelov, G., Van Herck, W., Burle, J., Carmona Loaiza, J.M., Durniak, C., Fisher, J., Ganeva, M., Yurov, D., & Wuttke, J. (2020). BornAgain: software for simulating and fitting grazing-incidence small-angle scattering. Journal of Applied Crystallography, 53, 262 - 276.

Keywords: GISAXS; Inverse problems

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Permalink: https://www.hzdr.de/publications/Publ-34770


Dataset for Inversion of GISAXS data (1 layer)

Zhdanov, M.; Ganeva, M.; Randolph, L.; Kluge, T.; Hoffmann, N.

Abstract

The dataset consists of 50000 X-ray diffraction patterns simulated by BornAgain [1] software. For each simulation, a multilayer sample model of the following structure was used: air, tantalum oxide, silicon dioxide, and substrate. Parameters of each layer but tantalum oxide were kept fixed. Hence, each diffraction pattern depends on the parameters of the tantalum oxide layer: real and complex part of refractive index, thickness, roughness, Hurst parameter, and correlation length. Each simulation output is stored in an h5py file consisting of 1) diffraction image as a NumPy array of shape [1024, 512]; 2) sample parameters as a NumPy array with 6 elements. For further details regarding simulation, see https://github.com/maxxxzdn/gisaxs-reconstruction/simulation/simulation.

[1] Pospelov, G., Van Herck, W., Burle, J., Carmona Loaiza, J.M., Durniak, C., Fisher, J., Ganeva, M., Yurov, D., & Wuttke, J. (2020). BornAgain: software for simulating and fitting grazing-incidence small-angle scattering. Journal of Applied Crystallography, 53, 262 - 276.

Keywords: GISAXS; Inverse problems

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Permalink: https://www.hzdr.de/publications/Publ-34769


Palbociclib impairs the proliferative capacity of activated T cells while retaining their cytotoxic efficacy

Arndt, C.; Tunger, A.; Wehner, R.; Rothe, R.; Kourtellari, E.; Luttosch, S.; Hannemann, K.; Koristka, S.; Loureiro, L. R.; Feldmann, A.; Tonn, T.; Link, T.; Kuhlmann, J. D.; Wimberger, P.; Bachmann, M.; Schmitz, M.

Abstract

The cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitor palbociclib is an emerging cancer therapeutic that just recently gained Food and Drug Administration approval for treatment of estrogen receptor (ER)-positive, human epidermal growth factor receptor (Her)2-negative breast cancer in combination with the ER degrader fulvestrant. However, CDK4/6 inhibitors are not cancer-specific and may affect also other proliferating cells. Given the importance of T cells in antitumor defense, we studied the influence of palbociclib/fulvestrant on human CD3+ T cells and novel emerging T cell-based cancer immunotherapies. Palbociclib considerably inhibited the proliferation of activated T cells by mediating G0/G1 cell cycle arrest. However, after stopping the drug supply this suppression was fully reversible. In light of combination approaches, we further investigated the effect of palbociclib/fulvestrant on T cell-based immunotherapies by using a CD3-PSCA bispecific antibody or universal chimeric antigen receptor (UniCAR) T cells. Thereby, we observed that palbociclib clearly impaired T cell expansion. This effect resulted in a lower total concentration of interferon-g and tumor necrosis factor, while palbociclib did not inhibit the average cytokine release per cell. In addition, the cytotoxic potential of the redirected T cells was unaffected by palbociclib and fulvestrant. Overall, these novel findings may have implications for the design of treatment modalities combining CDK4/6 inhibition and T cell-based cancer immunotherapeutic strategies.

Keywords: cancer immunotherapy; CDK4/6; palbociclib; fulvestrant; bispecific antibody; CAR T cell; adoptive T therapy

Permalink: https://www.hzdr.de/publications/Publ-34768


Data and Scripts for "Accelerating Equilibration in First-Principles Molecular Dynamics with Orbital-Free Density Functional Theory"

Fiedler, L.; Moldabekov, Z.; Shao, X.; Jiang, K.; Dornheim, T.; Pavanello, M.; Cangi, A.

Abstract
# Data and Scripts for "Accelerating Equilibration in First-Principles Molecular Dynamics with Orbital-Free Density Functional Theory"

This dataset contains data and calculation scripts for the publication "Boosting first-principles molecular dynamics with orbital-free density functional theory".
Its goal is to enable interested parties to reproduce the experiments we have carried out. 

## Prerequesites

The following software versions are needed for the python scripts:

- `python`: 3.8.x
- `mala`: 1.1.0 (with `dftpy` installed)

Further, make sure you have a working `Quantum ESPRESSO` and `VASP` installation and have downloaded additional 
data such as local pseudopotentials and ML models (for references, see publication).

## Contents

- `scripts/`: Example scripts for the three principal python tasks associated with out work: ML inference, trajectory
analysis and OF-DFT-MD runs (via DFTPy). The scripts are general blueprints for these experiments and can be adjusted
to perform all of the calculations given in the publication.
- `data/`: Contains raw calculation data for the three investigated systems (hydrogen, beryllium and aluminium).
Since the main goal of this work is to compare OF-DFT-MD initialized and ideal crystal structure initialized 
trajectories and inferences, each of the three system-folders contains a `MD_ideal_crystal_structure` and 
`MD_ofdft_init` folder, with ideal crystal structure and OF-DFT-MD initialized data, respectively. Therein, contents
may differ; e.g. aluminium contains DFT calculation data, for beryllium data is divided by system size and Nosé mass,
while for hydrogen data for different temperatures is given. 

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Permalink: https://www.hzdr.de/publications/Publ-34767


Multiscale modelling in nuclear ferritic steels: from nano-sized defects to embrittlement

Castin, N.; Bonny, G.; Konstantinović, M. J.; Bakaev, A.; Bergner, F.; Courilleau, C.; Domain, C.; Gómez-Ferrer, B.; Hyde, J. M.; Messina, L.; Monnet, G.; Pascuet, M. I.; Radiguet, B.; Serrano, M.; Malerba, L.

Abstract

Radiation-induced embrittlement of nuclear steels is one of the main limiting factors for safe long-term operation of nuclear power plants. In support of accurate and safe reactor pressure vessel (RPV) lifetime assessments, we developed a physics-based model that predicts RPV steel hardening and subsequent embrittlement as a consequence of the formation of nano-sized clusters of minor alloying elements. This model is shown to provide reliable assessments of embrittlement for a very wide range of materials, with higher accuracy than industrial correlations. The core of our model is a multiscale modelling tool that predicts the kinetics of solute clustering, given the steel chemical composition and its irradiation conditions. It is based on the observation that the formation of solute clusters ensues from atomic transport driven by radiation-induced mechanisms, differently from classical nucleation-and-growth theories. We then show that the predicted information about solute clustering can be translated into a reliable estimate for radiation-induced embrittlement, via standard hardening laws based on the dispersed barrier model. We demonstrate the validity of our approach by applying it to hundreds of nuclear reactors vessels from all over the world.

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Permalink: https://www.hzdr.de/publications/Publ-34766


Fano interference between collective modes in cuprate high-Tc superconductors

Chu, H.; Kovalev, S.; Xiao Wang, Z.; Schwarz, L.; Dong, T.; Feng, L.; Haenel, R.; Kim, M.-J.; Shabestari, P.; Phuong Hoang, L.; Honasoge, K.; David Dawson, R.; Putzky, D.; Kim, G.; Puviani, M.; Chen, M.; Awari, N.; Ponomaryov, O.; Ilyakov, I.; Bluschke, M.; Boschini, F.; Zonno, M.; Zhdanovich, S.; Na, M.; Christiani, G.; Logvenov, G.; Jones, D. J.; Damascelli, A.; Minola, M.; Keimer, B.; Manske, D.; Wang, N.; Deinert, J.-C.; Kaiser, S.

Abstract

In spectroscopy studies of solids, interaction between a discrete mode and a continuum of excitations sometimes leads to an interference effect known as the Fano resonance, characterized by the asymmetric scattering amplitude of the discrete mode as a function of electromagnetic driving frequency. Cuprate high-Tc superconductors are known for its intertwined interactions and the coexistence of competing orders. In this study, we report a new type of Fano resonance manifested by the collective amplitude oscillations of the superconducting order, i.e. the Higgs mode, in cuprate high-Tc superconductors, where we resolve both the amplitude and phase signatures of the Fano resonance. Our observation suggests that the heavily damped Higgs mode is coupled to another collective mode in the system. Based on the results of an extensive hole-doping and magnetic field dependent investigation, we speculate charge density wave fluctuations as the coupled mode. Our study highlights the possibility of a dynamical interaction between superconductivity and charge density wave in cuprate high-Tc superconductors, which demonstrates the scientific prospect of Higgs spectroscopy as a new type of spectroscopy method.

Keywords: Terahertz; Higgs spectroscopy; ultrafast; phase-resolved; Superconductivity; cuprates; magnetic fields; doping

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Permalink: https://www.hzdr.de/publications/Publ-34765


Highly accessible and dense surface single metal FeN4 active sites for promoting the oxygen reduction reaction

Chen, G.; An, Y.; Liu, S.; Sun, F.; Qi, H.; Wu, H.; He, Y.; Liu, P.; Shi, R.; Zhang, J.; Kuc, A. B.; Kaiser, U.; Zhang, T.; Heine, T.; Wu, G.; Feng, X.

Abstract

Single iron atom and nitrogen-codoped carbon (Fe–N–C) electrocatalysts, which have great potential to catalyze the kinetically sluggish oxygen reduction reaction (ORR), have been recognized as the most promising alternatives to the precious metal platinum. Unfortunately, the ORR properties of the existing Fe–N–C catalysts are significantly hampered by the inferior accessibility and intrinsic activity of FeN4 moieties. Here, we constructed densely exposed surface FeN4 moieties on a hierarchically porous carbon (sur-FeN4-HPC) by Fe ion anchoring and a subsequent pyrolysis strategy using the nitrogen- doped hierarchically porous carbon (NHPC) as the scaffold. The high surface area of the NHPC with abundant surface Fe anchoring sites enabled the successful fabrication of densely accessible FeN4 active moieties (34.7 􏰁x 10^19 sites g^-􏰂1) on sur-FeN4-HPC. First-principles calculations further suggested that the edge effect could regulate the electronic structure of the single Fe site, hence promoting the intrinsic ORR activity of the FeN4 moiety. As a result, the sur-FeN4-HPC electrocatalyst exhibited excellent ORR activity in acidic media with a high half-wave potential of 0.83 V (vs. the reversible hydrogen electrode). We further examined sur-FeN4-HPC as a cathode catalyst in proton exchange membrane fuel cells (PEMFCs). The membrane electrode assembly delivered a high current density of 24.2 mA cm􏰂2 at 0.9 ViR-free (internal resistance-compensated voltage) under 1.0 bar O2 and a maximum peak power den- sity of 0.412 W cm􏰂2 under 1.0 bar air. Importantly, the catalyst demonstrated promising durability during 30000 voltage cycles under harsh H2 and air conditions. The PEMFC performance of sur-FeN4-HPC outperforms those of the previously reported Fe–N–C electrocatalysts. The engineering of highly acces- sible and dense surface FeN4 sites on sur-FeN4-HPC offers a fruitful pathway for designing high- performance electrocatalysts for different electrochemical processes.

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Permalink: https://www.hzdr.de/publications/Publ-34764


Lanmodulin peptides – unravelling the binding of the EF-Hand loop sequences stripped from the structural corset

Gutenthaler, S. M.; Tsushima, S.; Steudtner, R.; Gailer, M.; Hoffmann-Röder, A.; Drobot, B.; Daumann, L. J.

Abstract

Lanmodulin (LanM), a naturally lanthanide (Ln)-binding protein with a remarkable selectivity for Lns over Ca(II ) and affinities in the picomolar range, is an attractive target to address challenges in Ln separation. Why LanM has such a high selectivity is currently not entirely understood; both specific amino acid
sequences of the EF-Hand loops and cooperativity effects have been suggested. Here, we removed the effect of cooperativity and synthesised all four 12-amino acid EF-Hand loop peptides, and investigated their affinity for two Lns (Eu( III) and Tb(III)), the actinide Cm(III) and Ca(II). Using isothermal titration calorimetry and time-resolved laser fluorescence spectroscopy (TRLFS) combined with parallel factor analysis, we show that the four short peptides behave very similarly, having affinities in the micromolar range for Eu(III) and Tb(III). Ca(II) was shown not to bind to the peptides, which was verified with circular dichroism spectroscopy. This technique also revealed an increase in structural organisation upon Eu(III) addition, which was supported by molecular dynamics simulations. Lastly, we put Eu(III) and Cm(III) in direct competition using TRLFS. Remarkably, a slightly higher affinity for Cm(III) was found. Our results demonstrate that the picomolar affinities in LanM are largely an effect of pre-structuring and therefore a reduction of flexibility in combination with cooperative effects, and that all EF-Hand loops possess similar affinities when detached from the protein backbone, albeit still retaining the high selectivity for lanthanides and actinides over calcium.

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Permalink: https://www.hzdr.de/publications/Publ-34763


Structure-imposed electronic topology in cove-edged graphene nanoribbons

Arnold, F. M.; Liu, T.-J.; Kuc, A. B.; Heine, T.

Abstract

In cove-edged zigzag graphene nanoribbons (ZGNR-C), one terminal CH group per length unit is removed on each zigzag edge, forming a regular pattern of coves which controls their electronic structure. Based on three structural parameters that unambiguously characterize the atomistic structure of ZGNR-C, we present a scheme that classifies their electronic state, i.e., if they are metallic, topological insulators or trivial semiconductors, for all possible widths N, unit lengths a and cove position offsets at both edges b, thus showing the direct structure-electronic structure relation. We further present an empirical formula to estimate the band gap of the semiconducting ribbons from N,a, and b. Finally, we identify all geometrically possible ribbon terminations and provide rules to construct ZGNR-C with well-defined electronic structure.

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Permalink: https://www.hzdr.de/publications/Publ-34762


Oxidation State Dependent Conjugation Controls Electrocatalytic Activity in a Two-Dimensional Di-Copper Metal–Organic Framework

Maria Dominic, A.; Wang, Z.; Kuc, A. B.; Petkov, P.; Khoa Ly, H.; Lam Huong Pham, T.; Kutzschbach, M.; Cao, Y.; Bachmann, J.; Feng, X.; Dong, R.; Weidinger, I. M.

Abstract

Interfacial synthetic Cu-phthalocyanine-based two-dimensional conjugated metal-organic framework (CuPc-CuO4 2D c-MOF) films were transferred to graphite electrodes and analyzed via electrochemical resonance Raman spectroscopy. Comparison of CuPc-CuO4 with the corresponding monomer, combined with Density Functional Theory (DFT) calculations allowed a detailed assignment of the vibrational bands. CuPc-CuO4 films attached to graphite electrodes via an Nickel-Nitrilo Triaacetic Acid (Ni-NTA) linker exhibited excellent bifunctional catalytic activity towards oxygen reduction (ORR) and oxygen evolution (OER) reaction. Potential dependent Raman spectroscopy yielded three different species in the respective potential window that could be assigned to an ORR active CuI/CuI state, an inactive CuII/CuI state and an CuII/CuII state that could be activated for OER. From the spectroelectrochemical data, the redox potentials of Cu in the CuPc moieties and the Cu-catecholate nodes could be determined to be ECuPc = -0.04 V and ECuO4 = 0.33 V vs. Ag|AgCl, respectively. Furthermore, DFT calculations of bandagps and density of states showed the smalest bandgap and highest -conjugation for the CuI/CuI state and the largest bandgap and lower conjugation for the mixed CuII/CuI state state, agreeing very well with the experimental activity of the species. Our results suggest that the coupling between metal oxidation changes and long range electron transfer of the 2D c-MOF is a key parameter to achieve the high electrocatalytic activity.

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Permalink: https://www.hzdr.de/publications/Publ-34761


Terahertz-slicing — an all-optical synchronization for 4th generation light sources

Chen, M.; de Oliveira, T.; Ilyakov, I.; Nörenberg, T.; Kuschewski, F.; Deinert, J.-C.; Awari, N.; Ponomaryov, O.; Kuntzsch, M.; Kehr, S. C.; Eng, L. M.; Gensch, M.; Kovalev, S.

Abstract

A conceptually new approach to synchronizing accelerator-based light sources and external laser systems is presented. The concept is based on utilizing a sufficiently intense accelerator-based single-cycle terahertz pulse to slice a thereby intrinsically synchronized femtosecond-level part of a longer picosecond laser pulse in an electro-optic crystal. A precise synchronization of the order of 10 fs is demonstrated, allowing for real-time lock-in amplifier signal demodulation. We demonstrate successful operation of the concept with three benchmark experiments using a 4th generation accelerator-based terahertz light source, i.e. (i) far-field terahertz time-domain spectroscopy, (ii) terahertz high harmonic generation spectroscopy, and (iii) terahertz scattering-type scanning near-field optical microscopy.

Keywords: s-SNOM; Synchronization; Ultrafast Science; van der Waals; High Harmonic Generation

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Permalink: https://www.hzdr.de/publications/Publ-34759


Blacklight sintering of ceramics

Porz, L.; Scherer, M.; Huhn, D.; Heine, L.-M.; Britten, S.; Rebohle, L.; Neubert, M.; Brown, M.; Lascelles, P.; Kitson, R.; Rettenwander, D.; Fulanovic, L.; Bruder, E.; Breckner, P.; Isaia, D.; Frömling, T.; Rödel, J.; Rheinheimer, W.

Abstract

For millennia, ceramics have been densified via sintering in a
furnace, a time-consuming and energy-intensive process. The need
to minimize environmental impact calls for new physical concepts
beyond large kilns relying on thermal radiation and insulation. Here,
we realize ultrarapid heating with intense blue and UV-light.
Thermal management is quantified in experiment and finite element
modelling and features a balance between absorbed and radiated
energy. With photon energy above the band gap to optimize
absorption, bulk ceramics are sintered within seconds and with
outstanding efficiency (~2 kWh/kg) independent of batch size.
Sintering on-the-spot with blacklight as a versatile and widely
applicable power source is demonstrated on ceramics needed for
energy storage and conversion and in electronic and structural
applications foreshadowing economic scalability.

Keywords: flash lamp annealing; laser annealing; ceramics

Permalink: https://www.hzdr.de/publications/Publ-34758


Crystallization of semiconductor thin films by flash lamp annealing

Rebohle, L.

Abstract

Flash lamp annealing is a non-equilibrium annealing method on the sub-second time scale which excellently meets the requirements of thin film processing. It has already been used in microelectronics to activate dopants, to recrystallize amorphous semiconductor layers and to anneal out defects. However, in the last 20 years, flash lamp annealing has opened up new areas of application like thin films on glass, sensors, printed electronics, flexible electronics, batteries etc. Since two years, the Helmholtz Innovation blitzlab aims to transfer this technology to industry and application-related research.
In this presentation, we give a short introduction to flash lamp annealing and discuss the pros and cons of this technology for thin film and semiconductor processing. In the main part we report about our activities in the field of Ge-based materials for electronic applications. This includes the n-type doping of Ge above the solubility level by ion implantation and flash lamp annealing, the doping of GeSn alloys, and the fabrication of NiGe for contact formation.

Keywords: semiconductor thin film; flash lamp annealing; Crystallization

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  • Lecture (others) (Online presentation)
    Innovation Talk Infineon, 01.06.2022, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-34757


Flash lamp annealing of GaN

Rebohle, L.; Prucnal, S.; Akhmadaliev, S.; Kentsch, U.

Abstract

The presentation gives a short overview of our recent activities to dope GaN with Mg by ion implantation and flash lamp annealing.

Keywords: gallium nitride; Mg doping; ion implantation; flash lamp annealing

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  • Lecture (Conference)
    Nutzertreffen "Heißprozesse und RTP" und "Ionenimplantation", 18.05.2022, Erlangen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-34756


Contactless inductive flow tomography in fundamental and applied fluid dynamics

Sieger, M.; Mitra, R.; Glavinic, I.; Sonntag, S.; Gundrum, T.; Stefani, F.; Wondrak, T.; Eckert, S.

Abstract

Contactless inductive flow tomography (CIFT) is a flow measurement technique developed at Helmholtz-Zentrum Dresden-Rossendorf that can reconstruct the global 3D flow field in electrically conducting fluids such as liquid metals. The velocity field of the moving fluid can be reconstructed by solving the underlying inverse problem using appropriate regularization methods. This publication introduces the key concept and mathematical foundation of the method and illustrates the measurement capability of CIFT on two examples: continuous casting of steel in applied fluid dynamics and Rayleigh-Bénard convection as a paradigmatic system in fundamental fluid dynamics.

Keywords: Flow measurement techniques; liquid metal; tomography; inverse problem; Rayleigh-Bénard

  • Contribution to proceedings
    29. Fachtagung "Experimentelle Strömungsmechanik", 06.-08.09.2022, Ilmenau, Deutschland
  • Lecture (Conference)
    29. Fachtagung "Experimentelle Strömungsmechanik", 06.-08.09.2022, Ilmenau, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-34755


Metadatamanagement - How to make your data FAIR

Steinmeier, L.; Schaller, T.; Rau, F.; Schweikert, J.

Abstract

The necessity of exhaustive documentation of research data arises from an increasing depth of scientific understanding and investigations of unknown phenomena with research teams of different areas and fields. Different methods and definitions and insufficient documentation of field work, experimental and numerical examinations lead to information loss, especially over time. To counteract this problem the scientific community aims to make research data Findable, Accessible, Interoperable and Reusable (FAIR). Unfortunately infrastructure, tools, personnel and acceptability for these additional steps are often missing and result in the mentioned paucity of information and data. Within the Helmholtz Association the Helmholtz Metadata Collaboration (HMC) has taken on the task of building this infrastructure to support high quality data documentation and publication throughout the entire lifecycle of research data and to raise the awareness for necessary structural changes in the wider scientific community.
One goal of HMC is the mapping of existing data management structures and demands in the different research fields of the Helmholtz Community. These fields are especially addressed with Hubs, being the connection between HMC and the specific needs of the research fields. Based on the collected information HMC will implement tools to assist scientists, data managers and IT administrators in making their research data FAIR. Furthermore members of HMC will connect with other (meta-)data initiatives to work towards necessary structural changes in the world of scientific research by e.g. defining standards.
In this poster we will discuss the FAIR principles and introduce the Helmholtz Metadata Collaboration and their tasks. Also, we will show concrete examples from the geoscientific part of Hub Energy. The Hub in which we are active.

Keywords: FAIR; Metadata; Helmholtz Metadata Collaboration; Deutsche Geophysikalische Gesellschaft

  • Open Access Logo Poster
    Helmholtz Energy Young Scientists Workshop 2022, 30.-31.05.2022, Maintal (Hessen), Germany

Permalink: https://www.hzdr.de/publications/Publ-34754


Data publication: Switching on Cytotoxicity of Water-Soluble Diiron Organometallics by UV Irradiation

Biancalana, L.; Kubeil, M.; Schoch, S.; Zacchini, S.; Marchetti, F.

Abstract

decarbonylation studies By IR, NMR, UV/vis myoglobin assay cell proliferation assay

cristallographic data available by collaboration partner

Keywords: PhotoCORM; Carbon Monoxide; Bioorganometallic Chemistry; Diiron complexes; Photoactivation; Cytotoxicity; Aminocarbyne Ligand; Vinyliminium Ligand; PTA; water solubility

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Permalink: https://www.hzdr.de/publications/Publ-34752


Switching on Cytotoxicity of Water-Soluble Diiron Organometallics by UV Irradiation

Biancalana, L.; Kubeil, M.; Schoch, S.; Zacchini, S.; Marchetti, F.

Abstract

The diiron compounds [Fe2Cp2(CO)2(μ-CO)(μ-CSEt)]CF3SO3, [1]CF3SO3, K[Fe2Cp2(CO)3(CNCH2CO2)], K[2], [Fe2Cp2(CO)2(μ-CO)(μ-CNMe2)]NO3, [3]NO3, [Fe2Cp2(CO)2(PTA){μ-CNMe(Xyl)}]CF3SO3, [4]CF3SO3, and [Fe2Cp2(CO)(μ-CO){μ−η:1η3-C(4-C6H4CO2H)CHCNMe2}]CF3SO3, [5]CF3SO3, containing a bridging carbyne, isocyanoacetate, or vinyliminium ligand, were investigated for their photoinduced cytotoxicity. Specifically, the novel water-soluble compounds K[2], [3]NO3, and [4]CF3SO3 were synthesized and characterized by elemental analysis and IR and multinuclear NMR spectroscopy. Stereochemical aspects concerning [4]CF3SO3 were elucidated by 1H NOESY NMR and single-crystal X-ray diffraction. Cell proliferation studies on human skin cancer (A431) and nontumoral embryonic kidney (HEK293) cells, with and without a 10-min exposure to low-power UV light (350 nm), highlighted the performance of the aminocarbyne [3]NO3, nicknamed NIRAC (Nitrate-Iron-Aminocarbyne), which is substantially nontoxic in the dark but shows a marked photoinduced cytotoxicity. Spectroscopic (IR, UV−vis, NMR) measurements and the myoglobin assay indicated that the release of one carbon monoxide ligand represents the first step of the photoactivation process of NIRAC, followed by an extensive disassembly of the organometallic scaffold.

Keywords: PhotoCORM; Carbon Monoxide; Bioorganometallic Chemistry; Diiron complexes; Photoactivation; Cytotoxicity; Aminocarbyne Ligand; Vinyliminium Ligand; PTA; water solubility

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Permalink: https://www.hzdr.de/publications/Publ-34751


Numerical simulation of metal electrodeposition under the influence of a magnetic field towards nano-sized conically structured deposits

Huang, M.; Skibinska, K.; Zabinski, P.; Eckert, K.; Mutschke, G.

Abstract

Nano-structured cones have gained much attention due to their superior super-hydrophobic and electrocatalytic properties recently. This work aims to explore if magnetic fields could support the electrodeposition of nano-cone arrays on electrodes that are not externally templated. The magnetic forces, including the Lorentz force and the magnetic gradient force, can generate a flow that brings electrolyte enriched with electroactive ions towards the cone tips, and thus may enhance the local mass transfer and support the conical growth.
Numerical studies on single diamagnetic (Cu) and ferromagnetic (Fe) cathodes of conical shape at mm length scale provide a basic understanding of the flow and the mass transfer at conical structures during electrodeposition in a uniform external magnetic field. It is found that beside the Lorentz force, the magnetic gradient force caused by the magnetization of the Fe cones can efficiently enhance conical growth. Working towards nano-sized cone arrays, upon shrinking the cone size we find that conical growth becomes less supported. Damping effects from neighboring cones and weaker electrolyte flow in general are weakening the mass transfer enhancements near the cone tip. However, the flow caused by the magnetic gradient force (Fe case) is clearly less affected than that caused by the Lorentz force (Cu case).
Despite the weaker flow effects when the cone size shrinks, a beneficial influence of the magnetic field on conical growth, especially for ferromagnetic deposits, can be stated also at small scales.

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  • Lecture (Conference)
    14th International Workshop on Electrodeposited Nanostructures, 09.-10.06.2022, Krakow, Poland

Permalink: https://www.hzdr.de/publications/Publ-34750


Modelling and A-Posteriori Assessment of Closure Models for Sub-Grid Surface Tension Considering a Rising Gas Bubble

Meller, R.; Schlegel, F.; Klein, M.

Abstract

Correctly predicting the behaviour gas-liquid multiphase flows with numerical simulation tools is a highly complex task, especially when considering industrial scales. The most challenging task in that regard might be the large range of length scales of turbulent as well as of interfacial structures. Based on the two-fluid model, a hybrid methodology is developed with the goal to adaptively combine Euler-Euler and Volume-of-Fluid (VOF) simulation methods for statistical and scale-resolving representation of gas-liquid interfaces, respectively (Meller et al., 2021). With that approach, inevitably situations arise, where interfacial dynamics need to be predicted with VOF in combination with a particularly coarse grid resolution.
Low-pass filtering of the underlying two-fluid equations in this context reveals an unclosed sub-grid surface tension term, besides the convective and other unclosed terms (Meller et al., 2022). This contribution expresses the interfacial forces due to surface tension, which are not captured on a comparatively coarse computational grid. Different functional and structural closure models for that unclosed term are assessed in an a-posteriori fashion in case of a gas bubble rising in stagnant liquid. This contributes to an improved predictive power of the numerical model regarding large-scale interface and turbulent dynamics, even with low spatial resolution.

  • Lecture (Conference)
    Colloquium 625, Advances in LES of Turbulent Multiphase Flows, 22.-24.06.2022, Udine, Italia

Permalink: https://www.hzdr.de/publications/Publ-34749


Pulse reverse plating of copper micro-structures in magnetic gradient fields

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

Abstract

Micro-structured copper layers are obtained from pulse-reverse electrodeposition on a planar gold electrode that is magnetically patterned by magnetized iron wires underneath. 3D numerical simulations of the electrodeposition based on an adapted reaction kinetics are able to nicely reproduce the micro-structure of the deposit layer, despite the height values still remain underestimated. It is shown that the structuring is enabled by the magnetic gradient force, which generates a local flow that supports deposition and hinders dissolution in the regions of high magnetic gradients. The Lorentz force originating from radial magnetic field components near the rim of the electrode causes a circumferential cell flow. The resulting secondary flow, however, is superseded by the local flow driven by the magnetic gradient force in the vicinity of the wires. Finally, the role of solutal buoyancy effects is discussed to better understand the limitations of structured growth in different modes of deposition and cell geometries.

Keywords: Magnetoelectrodeposition; Surface structuring; Magnetic gradient force; Lorentz force; Pulse reverse plating

Permalink: https://www.hzdr.de/publications/Publ-34748


Benchmark results for real-time UFXCT data processing

Windisch, D.

Abstract

This dataset holds the subset of benchmark results relevant for the publication "Real-time data processing for Ultrafast X-Ray Computed Tomography using Modular CUDA based Pipelines". Alongside the data, Matlab scripts are provided for parsing and plotting the data.

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Permalink: https://www.hzdr.de/publications/Publ-34747


Size‑ and position‑controlled Ge nanocrystals separated by high‑k dielectrics

Lehninger, D.; Honeit, F.; Rafaja, D.; Klemm, V.; Röder, C.; Khomenkova, L.; Schneider, F.; von Borany, J.; Heitmann, J.

Abstract

Germanium nanocrystals embedded in high-k dielectric matrices are of main interest for infrared sensing application, as a role model for Ge-based nano-electronics passivation or for nonvolatile memory devices. The capability of the size control of those nanocrystals via rapid thermal processing of superlattice structures is shown for the [Ge–TaZrOx/TaZrOx]n, [Ge–TaZrOx/SiO2/TaZrOx]6, and [TaZrOx/Ge–SiO2]n superlattice systems. All superlattices were deposited by radiofrequency magnetron sputtering. Transmission electron microscopy (TEM) imaging confirms the formation of spherically shaped nanocrystals. Raman scattering proved the crystallization of Ge above 700°C. The TaZrOx crystallizes above 770°C, associated with a phase separation of Ta2O5 and ZrO2 as confirmed by x-ray diffraction. For the composite layers having 3 nm and 6 nm thickness, the size of the Ge nanocrystals correlates
with the deposited layer thickness. Thicker composite layers (above 9 nm) form two fractions of nanocrystals with different sizes. An additional SiO2
layer in the [Ge–TaZrOx/SiO2/TaZrOx]6 superlattice stacks facilitates the formation of larger and better separated Ge nanocrystals. The deposition of Ge-SiO2 composite layers separated by pure TaZrOx illustrates the barrier effect of TaZrOx against Ge diffusion. All three material systems allow the controlled formation of Ge nanocrystals in amorphous matrices at temperatures above 700 and below 770°C.

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Permalink: https://www.hzdr.de/publications/Publ-34746


Aerosolüberwachung beim Umgang mit radiopharmazeutischen Alphastrahlern

Wendler, M.; Kowe, S.; Walter, M.; Schöne, F.

Abstract

Im Institut für Radiopharmazeutische Krebsforschung des Helmholtz-Zentrums Dresden-Rossendorf e. V. wird zukünftig verstärkt mit kurzlebigen Alphaemittern umgegangen. dabei handelt es sich vor allem um die Radionuklide Ra-224, Ac-225 und Th-227. Die Überwachung der Mitarbeiter beim Umgang mit diesen Radionukliden bringt Herausforderungen im Hinblick auf die Inkorporationsüberwachung mit sich. Ein Inkorporationsnachweis kann bei den genannten Radionukliden nur mittels kostenintensiver und aufwendiger Ausscheidungsanalyse erfolgen. Um den Mitarbeitern diese routinemäßige Maßnahme zu ersparen, wird auf die Aerosolmessung in der Raumluft gesetzt. Die Aerosolüberwachung wird parallel durch Aerosolmonitoring und Aerosolsammlung umgesetzt und liefert ein Ergebnis, welches zur weiteren Anweisung von Maßnahmen führen kann. Bedingt durch die räumlichen Anforderungen, die Anforderungen an den Arbeitsschutz hinsichtlich der Geräuschemission und die Herausforderung natürlicher Radionuklide in der Luft mussten spezielle Verfahrensweisen umgesetzt werden.

Keywords: Strahlenschutz; Radiation Protection; Alphaemitter; Aerosol; Inkorporation; Radiopharmazie

  • Poster
    53. Jahrestagung des Fachverbands für Strahlenschutz e. V., 26.-30.09.2022, Konstanz, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-34744


Real-time Data Processing for Ultrafast X-Ray Computed Tomography using Modular CUDA based Pipelines

Windisch, D.; Kelling, J.; Juckeland, G.; Bieberle, A.

Abstract

In this article, a new version of the Real-time Image Stream Algorithms (RISA) data processing suite is introduced. It now features
online detector data acquisition, high-throughput data dumping and enhanced real-time data processing capabilities. The achieved
low-latency real-time data processing extends the application of ultrafast electron beam X-ray computed tomography (UFXCT)
scanners to real-time scanner control and process control. We implemented high performance data packet reception based on data
plane development kit (DPDK) and high-throughput data storing using both hierarchical data format version 5 (HDF5) as well
as the adaptable input/output system version 2 (ADIOS2). Furthermore, we extended RISA’s underlying pipelining framework to
support the fork-join paradigm. This allows for more complex workflows as it is necessary, e.g. for online data processing. Also,
the pipeline configuration is moved from compile-time to runtime, i.e. processing stages and their interconnections can now be
configured using a configuration file. In several benchmarks, RISA is profiled regarding data acquisition performance, data storage
throughput and overall processing latency. We found that using direct IO mode significantly improves data writing performance
on the local data storage. We could further prove that RISA is now capable of processing data from up to 768 detector channels
(3072MB/s) at 8000 fps on a single-GPU computer in real-time.

Keywords: real-time; data processing; parallel processing

Involved research facilities

  • ROFEX

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Permalink: https://www.hzdr.de/publications/Publ-34743


Euler-Euler model of bubbly flow using particle-center-averaging method

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

Abstract

The Euler-Euler model is widely used in bubbly flow simulations up to industrial dimensions. The standard Euler-Euler model is based on the phase-averaging method. After averaging, the bubble forces in the field equations are functions of the local gas volume fraction. In simulations, when the bubble diameter is larger than the computational cell spacing, the forces can transport the gas belonging to the same bubble in different directions. By contrast, a closure model for the bubble force is typically developed based on the assumption that the force is a resultant force that acts on the bubble's center-of-mass. This inconsistency can lead to a nonphysical gas concentration in the center of a channel or near the channel wall if the bubble diameter is larger than the cell spacing.

The purpose of the present contribution is to developed an Euler-Euler model where the bubble force consistency is recovered for two-phase flow simulations where the diameter of the disperse phase can be larger than the cell spacing. Such an Euler-Euler model is developed by combining an existing particle-center-averaged Euler-Euler framework with a Gaussian convolution method. To validate this Euler-Euler approach, a comparison is made with experimental data for the bubbly flows in two different vertical pipes. The results show that the proposed Euler-Euler model recovers the bubble force consistency and alleviates the over-prediction of the gas volume fraction peak near the wall, while its simulation results in the axial gas and liquid velocity and the liquid turbulence kinetic energy are similar to the results of the standard Euler-Euler model.

Keywords: bubbly flow simulation; Euler-Euler model; particle-center-averaging method; Gaussian convolution method; bubble's number density

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Permalink: https://www.hzdr.de/publications/Publ-34742


Laser-proton acceleration developments at DRACO-PW enabling “in-vivo” radiobiology

Ziegler, T.; Bernert, C.; Beyreuther, E.; Brack, F.-E.; Cowan, T.; Garten, M.; Gaus, L.; Kluge, T.; Kraft, S.; Kroll, F.; Metzkes-Ng, J.; Pawelke, J.; Reimold, M.; Rehwald, M.; Schlenvoigt, H.-P.; Umlandt, M. E. P.; Schramm, U.; Zeil, K.

Abstract

We report technological developments at DRACO-PW to monitor and improve laser-plasma conditions resulting in a stable particle-source >60MeV, which in combination with our transport-beamline and high-quality dosimetry enabled first dose-controlled “in-vivo” studies with laser-driven protons.

Involved research facilities

  • Draco
  • Lecture (Conference)
    High-Brightness Sources and Light-Driven Interactions Congress, 22.-25.03.2022, Budapest, Ungarn

Permalink: https://www.hzdr.de/publications/Publ-34741


Electronic properties of van der Waals crystals under hydrostatic pressure

Wozniak, T.; Faria Junior, P. E.; Oliva, R.; Tołłoczko, A.; Kopaczek, J.; Zelewski, S.; Dybała, F.; Fabian, J.; Scharoch, P.; Kudrawiec, R.

Abstract

Electronic properties of layered van der Waals crystals can be effectively tuned by means of external and configurational factors. It allows for the investigation of the fundamental material properties that are valuable for technological applications. Here we show, how Density Functional Theory (DFT) calculations allow to interpret the experimental results on quantitative level.
We present experimental and DFT studies of the electronic band structure of MoTe2 at high hydrostatic pressures. Modulated photoreflectance measurements allowed determination of the pressure coefficients of six direct transitions, with positive and negative values, which can be attributed to a strong splitting of the conduction bands with increasing pressure and the presence of hidden spin-polarized electronic states. These results prove that the spin-valley locking effect takes place in centrosymmetric transition metal dichalcogenides [1].
We also report experimental and theoretical study of the electronic band structure of orthorhombic GeS crystals under hydrostatic pressure. Polarization-resolved photoreflectance measurements allowed to extract the energies, optical dichroic ratios, and pressure coefficients of the direct optical transitions. These findings are discussed in view of DFT calculations, which predict that nondegenerate states in different valleys can be individually selected through linearly polarized light. Based on this, an assignation of the direct optical transitions to the electronic band structure is provided. These results provide evidence that GeS is a strong candidate for valleytronic applications in nondegenerate systems [2, 3].
Finally, we combined calculations within DFT and the effective Bethe-Salpeter equation, with high-pressure optical measurements in order to thoroughly describe the effect of strain and dielectric environment onto the electronic band structure and optical properties of a few-layered WS2. Our results show that WS2 remains fully adhered to the substrate at least up to a 0.6% in-plane compressive strain for a wide range of substrate materials. We provide a useful model to describe effect of strain on the optical properties on general strain conditions. Within this model, exceptionally large compressive uniaxial and biaxial in-plane gauge factors were obtained, which confirm transition metal dichalcogenides as very promising candidates for flexible functionalities [4].

[1] R. Oliva, T. Woźniak, F. Dybała, J. Kopaczek, P. Scharoch, R. Kudrawiec, Mater. Res. Lett. 8, 75 (2020).
[2] A. Tołłoczko, R. Oliva, T. Woźniak, J. Kopaczek, P. Scharoch, R. Kudrawiec, Mater. Advances 6, 1886 (2020).
[3] R. Oliva, T. Woźniak, F. Dybała, A. Tołłoczko, J. Kopaczek, P. Scharoch, R. Kudrawiec, Phys. Rev. B 101, 235205 (2020).
[4] R. Oliva, T. Woźniak, P. E. Faria Junior, F. Dybała, J. Kopaczek, J. Fabian, P. Scharoch, R. Kudrawiec, arXiv:2202.08551 (2022).

  • Poster
    50th International School & Conference on the Physics of Semiconductors "Jaszowiec 2022", 04.-10.06.2022, Szczyrk, Poland

Permalink: https://www.hzdr.de/publications/Publ-34740


Heterogeneity of ASL perfusion MRI in low-grade paediatric glioma as imaging biomarker to assess treatment effect

Alic, L.; Willekens, S. C.; Mutsaerts, H.-J. M. M.; Petr, J.; Schouten-Van Meeteren, N. A. Y. N.; Lequin, M. M. H.; Wiegers, E. E. C.

Abstract

ASL-MRI is reported as an option to assess potentially heterogeneous physiological processes important for tumour treatment. Therefore, we explored the heterogeneity in normalised CBF as an imaging biomarker for assessment of treatment effect in pLGG. There is a noticeable effect of chemotherapy observed as a change in texture of healthy appearing brain tissue. A high difference in texture between treated and non-treated patients for non-enhancing tumour part is observed, suggesting that texture, based on co-occurrence matrices, is suitable as an imaging biomarker for assessment of treatment effect in pLGG.

Involved research facilities

  • PET-Center
  • Contribution to proceedings
    ISMRM '22: Proceedings of the ISMRM 30th Annual Meeting & Exhibition, 07.-12.05.2022, London, United Kingdom
  • Poster
    ISMRM '22: Proceedings of the ISMRM 30th Annual Meeting & Exhibition, 07.-12.05.2022, London, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-34739


Multimodal MRI-derived phenotypes in preclinical Alzheimer’s Disease: results from the EPAD cohort

Lorenzini, L.; Ingala, S.; Wink, A. M.; Kuijer, J. P. A.; Wottschel, V.; Sudre, C. H.; Haller, S.; Molinuevo, J. L.; Gispert, J. D.; Cash, D. M.; Thomas, D. L.; Vos, S. B.; Ferran, P.; Petr, J.; Wolz, R.; Palombit, A.; Schwarz, A. J.; Chételat, G.; Payoux, P.; Di Perri, C.; Pernet, C.; Frisoni, G.; Fox, N. C.; Ritchie, C.; Wardlaw, J.; Waldman, A.; Barkhof, F.; Mutsaerts, H. J. M. M.

Abstract

Image-derived phenotypes (IDPs) from multimodal MRI sequences constitute an important resource that allows the characterization of brain alterations in the early stages of Alzheimer diseases and other neurodegenerative conditions. Here, we showed the computation of multimodal IDPs from the European Prevention of Alzheimer Dementia (EPAD) cohort and assessed their relationship with non-imaging markers of neurodegeneration. We demonstrated the clinical relevance of IDPs to uncover early brain alteration in AD by showing expected association with non-imaging data.

Involved research facilities

  • PET-Center
  • Contribution to proceedings
    ISMRM '22: ISMRM 30th Annual Meeting & Exhibition, 07.-12.05.2022, London, United Kingdom
    Proceedings of the ISMRM 30th Annual Meeting & Exhibition
  • Lecture (Conference)
    ISMRM '22: ISMRM 30th Annual Meeting & Exhibition, 07.-12.05.2022, London, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-34738


Novel arterial spin labelling (ASL) brain injury symmetry assessment in retired professional athletes: a preliminary study

Danielli, E.; Padrela, B.; Doughty, M.; Petr, J.; Mutsaerts, H.; Noseworthy, M. D.

Abstract

3D PCASL scans were acquired for seventeen aging, retired professional football players with a history of head traumas. Left, right and bilateral CBF and ASL spatial coefficient of variation (sCoV) values were examined for twelve concussion-related ROIs. A Z-scoring approach was applied, with outliers defined as mild, moderate, or severe injury burden (IB). An IB symmetry index was also calculated. Outliers were detected in all 12 ROIs, and the anterior parahippocampal gyrus and inferior frontal gyrus pars opercularis had the highest CBF and ASL sCoV IB, respectively. IB was not biased towards the left or right hemisphere.

Involved research facilities

  • PET-Center
  • Contribution to proceedings
    ISMRM '22: Proceedings of the ISMRM 30th Annual Meeting & Exhibition, 07.-12.05.2022, London, United Kingdom
  • Poster
    ISMRM '22: ISMRM 30th Annual Meeting & Exhibition, 07.-12.05.2022, London, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-34737


The Open Science Initiative for Perfusion Imaging (OSIPI): Results from the ASL MRI Challenge

Anazodo, U.; Pinto, J.; Kennedy McConnell, F.; Gould Van Praag, C.; Mutsaerts, H.; Oliver-Taylor, A.; Petr, J.; Pineda-Ordóñez, D.; Dounavi, M.-E.; Brumer, I.; Chan, W. S. M.; Toner, J.; Hu, J.; Zhang, L. X.; Bell, L.; Woods, J. G.; Zhao, M. Y.; Croal, P.; Paschoal, A. M.

Abstract

The OSIPI ASL MRI Challenge is an initiative of the ASL community aiming to characterize the variability of CBF quantification arising from different pipelines. The goal of this challenge is to establish best practice in ASL data processing, understand the sources of variability, make ASL analysis more reproducible, and enable fair comparison between studies. Here, we analyzed 3 submitted entries from 7 teams registered in the challenge. The preliminary results showed pipelines based in different programming languages and analysis tools, leading to important variability in the quantitative CBF maps compared to the ground-truth.

Involved research facilities

  • PET-Center
  • Contribution to proceedings
    ISMRM '22: ISMRM 30th Annual Meeting & Exhibition, 07.-12.05.2022, London, United Kingdom
    Proceedings of the ISMRM 30th Annual Meeting & Exhibition
  • Poster
    ISMRM '22: ISMRM 30th Annual Meeting & Exhibition, 07.-12.05.2022, London, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-34736


Amyloid burden and vascular risk factors correlate with regional cerebral blood flow in a cognitively unimpaired population

Padrela, B. E.; Lorenzini, L.; Collij, L. E.; Ten Kate, M.; Den Braber, A.; Tomassen, J.; van Berckel, B.; Visser, P. J.; Barkhof, F.; Petr, J.; Mutsaerts, H. J. M. M.

Abstract

Recent findings suggest additive effects of cerebrovascular disease and Alzheimer's disease (AD) on cognitive decline. MR imaging of cerebral blood flow holds great promise as an early dementia biomarker. Supply and demand of blood flow in the brain can be affected by, respectively, the loss of vascular health and the decrease of neuronal activity, as a consequence of AD. This study investigates to what extent vascular and AD components affect CBF and how they interact with each other.

Involved research facilities

  • PET-Center
  • Lecture (Conference)
    ISMRM '22 Workshop on Perfusion MRI: From Head to Toe, 04.-07.03.2022, Los Angeles, USA
  • Contribution to proceedings
    ISMRM '22: Proceedings of the ISMRM 30th Annual Meeting & Exhibition, 07.-12.05.2022, London, United Kingdom
  • Lecture (Conference)
    ISMRM '22: ISMRM 30th Annual Meeting & Exhibition, 07.-12.05.2022, London, United Kingdom
  • Poster
    Alzheimer's Association International Conference, 31.07.2022, San Diego, USA
  • Contribution to proceedings
    Alzheimer's Association International Conference, 31.07.2022, San Diego, USA
  • Contribution to proceedings
    International Conference on Alzheimer’s and Parkinson’s Diseases and related neurological disorders (ADPD), 15.03.2022, Barcelona, Spain
  • Lecture (Conference)
    International Conference on Alzheimer’s and Parkinson’s Diseases and related neurological disorders, 15.03.2022, Barcelona, Spain

Permalink: https://www.hzdr.de/publications/Publ-34735


OSIPI Inventory of ASL Pipelines

Petr, J.

Abstract

Cerebral blood flow (CBF) is an important physiological parameter for assessing cerebrovascular health and blood flow demand both in healthy and diseased conditions [refs]. Arterial spin labeling (ASL) perfusion MRI provides a non-contrast acquisition method for quantification of regional CBF. Its non-invasive nature and ability to quantify absolute CBF make it ideal in research and clinical settings requiring repeated acquisitions. ASL-MRI has been extensively validated with other methods that use exogenous contrast agents, such as 15O-H2O-PET and dynamic susceptibility contrast MRI (DSC) (1–6), and has already shown extensive impact on the neurological, neuropsychological, and neuropsychiatric research fields [refs].

ASL involves i) magnetic labeling of the arterial blood water while it flows through internal carotid and vertebral arteries that supply blood to the brain, ii) acquiring a “labeled” brain image after waiting for a brief period to allow the blood to reach the capillaries, and iii) computing a perfusion-weighted image by subtracting the labeled image from a “control” image obtained without labeling. Depending on the methods of spin labeling and image acquisition, ASL can vary significantly and has undergone significant improvement since its inception (7). For example, the labeling can be performed at the neck using pseudo-continuous ASL (PCASL) (8) or pulsed ASL (PASL) (9) or close to the site of imaging using velocity selective imaging (10). Image readout can be performed using 2D echo-planar imaging (EPI) (11), 3D gradient and spin-echo (GRASE) (12), or 3D spiral imaging (13). Each type of image acquisition can be associated with background suppression of static tissue to increase the signal-to-noise ratio (14). Additionally, the post-labeling delay (PLD) can be fixed or variable (single-PLD or multi-PLD) or obtained using a time-encoding technique (15).

These differences lead to greater heterogeneity of data types in ASL MRI than typically seen in other MRI modalities and a consensus recommendation on acquisition has been formed (16) to facilitate its use in different settings. Nonetheless, different flavors of ASL are still in use based on the availability of specific protocols or scanners, and the expertise of the clinicians and investigators at the clinical or research sites. Most scanners, however, output only the raw ASL data, and the end-users need to derive the quantitative CBF maps from that. Therefore, many potential users such as radiologists and neuroscientists, who may not have the technical expertise, have to struggle their way through implementing these processing steps and finding a suitable software. And a recent European survey noted that technical difficulty and lack of tools are indeed one of the main hurdles to the more widespread use of ASL and quantitative MRI in general (17).

While more than twenty ASL toolboxes have been released (18–30), there is even a higher variety of different ASL sequences, data formats (31), and processing methods (19). As there is no standard defined for ASL image processing, it can be a daunting process to identify a pipeline that is suitable and optimal for users’ needs. Both new and experienced ASL users looking for different functionalities, and the ASL research field in general, may benefit from a comprehensive and detailed list of ASL image processing software to guide this search.

The Open Science Initiative for Perfusion Imaging (OSIPI) is an initiative of the International Society for Magnetic Resonance in Medicine (ISMRM) perfusion study group. Established in May 2020, its mission is to create open access resources for perfusion imaging research to improve the reproducibility of perfusion imaging research, speed up the translation into tools for discovery science, drug development, and clinical practice, and eliminate the practice of duplicate development [ref]. The activities of OSIPI were divided among task forces; Task Force 1.1 (TF1.1) aims to create an inventory of the available ASL pipelines, summarizing their features and requirements, thus making the pipelines more accessible to ASL users. This study provides a comprehensive list of pipelines available, listing their features. Additionally, it delivers an independent assessment of the user-friendliness of the pipelines and the technical level needed for operating the pipeline.

Involved research facilities

  • PET-Center
  • Invited lecture (Conferences)
    ISMRM '22 Workshop on Perfusion MRI: From Head to Toe, 04.-07.03.2022, Los Angeles, USA

Permalink: https://www.hzdr.de/publications/Publ-34734


Open Science Initiative for Perfusion Imaging (OSIPI): Arterial Spin Labeling Imaging and Analysis Lexicon and Reporting Recommendations

Suzuki, Y.; Clement, P.; Dai, W.; Dolui, S.; Fernández-Seara, M.; Lindner, T.; Mutsaerts, H. J.; Petr, J.; Shao, X.; Taso, M.; Thomas, D. L.

Abstract

The 2015 consensus statement1 published by the ISMRM Perfusion Study Group and the EU COST Action ‘ASL in Dementia’ aimed to encourage the
implementation of robust Arterial Spin Labeling (ASL) perfusion MRI for clinical applications and promote consistency across scanner types, sites, and studies.
Subsequently, the recommended 3D pseudo-continuous ASL (PCASL) sequence has been implemented by most major MRI manufacturers. However, ASL remains a
rapidly and widely developing field, both in terms of improving the accuracy of cerebral blood flow (CBF) quantification and providing other output derivatives in
addition to CBF. These advances have greatly expanded the scope of ASL, but also bring further divergence of the technique, particularly in the terminology used,
which can lead to confusion and hamper research reproducibility. As part of the Open Science Initiative for Perfusion Imaging (OSIPI), the ASL Lexicon Task Force
has been working on the development of an ‘ASL Perfusion Imaging and Analysis Lexicon and Reporting Recommendations’, aiming: 1) to develop standardized
nomenclature and terminology for the broad range of ASL imaging techniques and parameters, as well as the physiological constants required for quantitative
analysis, and 2) to provide a community-endorsed recommendation on a minimal list of parameters that should be reported in publications.

Involved research facilities

  • PET-Center
  • Poster
    ISMRM '22 Workshop on Perfusion MRI: From Head to Toe, 04.-07.03.2022, Los Angeles, USA
  • Contribution to proceedings
    ISMRM '22: Proceedings of the ISMRM 30th Annual Meeting & Exhibition, 07.-12.05.2022, London, United Kingdom
  • Poster
    ISMRM '22: ISMRM 30th Annual Meeting & Exhibition, 07.-12.05.2022, London, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-34733


Cerebrovascular Brain-age

Dijsselhof, M. B. J.; Barboure, M.; Stritt, M.; Nordhøy, W.; Wink, A. M.; Westlye, L. T.; Cole, J. H.; Barkhof, F.; Petr, J.; Mutsaerts, H. J. M. M.

Abstract

Brain-age estimates the biological brain age from structural MRI images based on changes in brain-tissue integrity and irreversible
structural changes [1]. The brain-age offset to the chronological age — the age gap — is associated with cognitive pathology [2]. Adding
vascular or functional MRI biomarkers may add sensitivity to physiological and metabolic changes, complementing and improving structural
brain-age, and possibly improving its sensitivity to earlier disease changes. Arterial spin labeling (ASL) MRI is a potential early biomarker of
cerebrovascular health and correlates with the initial stages of cognitive pathology [3]. Here, we propose the ‘Cerebrovascular Brain-age’ as a
combination of T1w, FLAIR, and ASL image features composed of the spatial Coefficient of Variation (CoV) and vascular-territory derived
(VT) cerebral blood flow (CBF).

Involved research facilities

  • PET-Center
  • Poster
    ISMRM '22 Workshop on Perfusion MRI: From Head to Toe, 04.-07.03.2022, Los Angeles, USA
  • Contribution to proceedings
    ISMRM '22: 30th Annual Meeting & Exhibition, 07.-12.05.2022, London, United Kingdom
    Proceedings of the ISMRM 30th Annual Meeting & Exhibition
  • Poster
    ISMRM '22: 30th Annual Meeting & Exhibition, 07.-12.05.2022, London, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-34732


Recycling of technical structures: The recyclability of refrigerators

Mütze, T.; Heibeck, M.

Abstract

Consumer goods often consist of multi-material structures whose connections be-tween different materials fulfil important functions for production and use. In recycling, these structures must be disconnected in order to achieve high recycling rates for the individual materials. In this context, the BMBF project Circular by Design uses refrigerators/freezers to investigate which parameters can already be influenced during the design stage in order to optimise liberation during recycling without impairing the function and durability of the object in the use phase.

Keywords: recycling; design for recycling; design for repair; design for dismantling; liberation; multi-material structures

  • Contribution to proceedings
    Dresden Nexus Conference 2022, 23.-25.05.2022, Dresden, Deutschland
    Biodiversity - stewardship for vital resources

Permalink: https://www.hzdr.de/publications/Publ-34730


Photo-neutron cross-section of nat-Gd in the bremsstrahlung end-point energies of 12 - 16 MeV and 60 - 70 MeV

Naik, H.; Kim, G. N.; Schwengner, R.; Jang, W.; Nguyen, T. H.; Shin, S. G.; Kye, Y.; Massarczyk, R.; John, R.; Junghans, A.; Wagner, A.; Cho, M.-H.

Abstract

The spectrum-averaged cross-sections of nat Gd(gamma,xn)159,153 Gd reactions induced by the bremsstrahlung end-point energies of 12, 14, 16. 60, 65, and 70 MeV were measured by activation and off-line gamma-ray spectrometric technique using the 20 MeV electron linac (ELBE) at HZDR, Dresden, Germany, and 100 MeV electron linac at Pohang Accelerator Laboratory, Korea. The TALYS 1.9 code was also used to calculate the theoretical nat Gd(gamma, xn)159,153 Gd reaction cross-sections as a function of photon energy. The spectrum-averaged values at various end-point energies were calculated from the literature data as well as theoretical values based on the TALYS 1.9 code, which is for mono-energetic photons. They were found to be in good agreement with
the flux-weighted values of the current experimental data. It was also observed that the experimental and theoretical cross-sections increase from the threshold values to a certain energy, at which point another reaction channel opens, indicating the role of excitation energy. Individual reaction cross-
sections decrease after a certain value as bremsstrahlung energy increases due to the opening of other reactions, indicating energy shearing among the different reaction channels.

Keywords: Photoactivation; bremsstrahlung; photoabsorption cross section; statistical reaction model

Involved research facilities

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Permalink: https://www.hzdr.de/publications/Publ-34729


Data publication: Mode splitting of spin waves in magnetic nanotubes with discrete symmetries

Körber, L.; Kézsmárki, I.; Kakay, A.

Abstract

This data set contains the numerical raw data for "Mode splitting of spin waves in magnetic nanotubes with discrete symmetries" published in Physical Review B. The data has been obtained using our in-house developed finite-element dynamic-matrix approach for propagating spin waves [see AIP Advances 11, 095006 (2021) for details]. 

  • The folder high-res-only-k0/ contains the lateral mode profiles and frequencies of polygonal nanotubes with different number of corners at k = 0. It also contains a python script used to calculate the microwave absorption from the mode profiles.
  • The folders poly_*/ contain only the dispersion without lateral mode profiles for the different polygonal tubes as well as a round nanotube
  • All folders contain the geometry and mesh files as well as sparam and eparam yaml files containg the material parameters and experimental parameters, respectively. The equilibrium states are saved as m_eq.h5 hdf5 files.

Keywords: Spin wave; magnon; micromagnetic modeling; symmetry; nanotubes; group theory; micromagnetism; tetrax

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Permalink: https://www.hzdr.de/publications/Publ-34728


Particle tracking velocimetry in liquid gallium flow around a cylindrical obstacle

Birjukov, M.; Zvejnieks, P.; Lappan, T.; Sarma, M.; Heitkam, S.; Trtik, P.; Mannes, D.; Eckert, S.; Jakovics, A.

Abstract

This paper demonstrates particle tracking velocimetry performed for a model system wherein particle-laden liquid metal flow around a cylindrical
obstacle was studied. We present the image processing methodology developed for particle detection in images with disparate and often low
signal- and contrast-to-noise ratios, and the application of our MHT-X tracing algorithm for particle trajectory reconstruction for the wake
flow around the obstacle. Preliminary results indicate that the utilized methods enable consistent particle detection and recovery of long, representative
particle trajectories with high confidence. However, we also underline the necessity of implementing a more advanced particle position
extrapolation approach for increased tracking accuracy. Satisfactory tracking accuracy can be inferred from the fact that the fluctuations
in the measured particle velocity are dominated by frequencies that agree sufficiently well with the expected frequencies of the cylinder wake.

Keywords: liquid metal; particle flow; wake flow; neutron radiography; particle tracking; image processing

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Permalink: https://www.hzdr.de/publications/Publ-34727


Kombinierte optische und Röntgen-Messungen einer überlaufenden Schaumströmung

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

Abstract

Schaum und dessen Strömungsverhalten sind von zentraler Bedeutung bei der Schaumflotation zur Mineralaufbereitung. Die zu gewinnenden Mineralpartikel lagern sich an aufsteigenden Gasblasen an und werden mit dem Schaum aus der Flotationszelle heraustransportiert. In industriellen Flotationsanlagen wird die Rückgewinnung von Feststoff- und Flüssigphase aus der überlaufenden Schaumströmung mittels optischer Messtechnik überwacht und ist daher auf die freie Oberfläche des partikelbeladenen Schaums beschränkt. Die vorliegende Arbeit untersucht das Strömungsverhalten eines wässrigen Schaums an einem Überlauf vergleichend mittels optischer und Röntgen-Messungen. Der Schaum wurde kontinuierlich erzeugt, strömte in vertikaler Richtung durch einen Kanal mit quadratischem Querschnitt und floss durch einen einseitigen horizontalen Überlauf in die freie Umgebung. Die bildgebenden Strömungsmessungen fokussierten sich auf den Schaum im Bereich des Überlaufs. Gleichzeitig wurde hier der Flüssigkeitsanteil des Schaums mittels Messung der elektrischen Leitfähigkeit zwischen jeweils zwei Elektroden bestimmt. Die optischen Messungen erfolgten einerseits durch die transparente Kanalwand und andererseits an der freien Oberfläche des überlaufenden Schaums. Die dortigen Strömungsgeschwindigkeiten wurden mittels angepasster PIV-Algorithmen ausgewertet, welche Lichtreflexionen auf den Schaumblasen als Messinformation nutzten. Aufgrund der Undurchsichtigkeit des Schaums erfassen diese optischen Messungen nur die oberflächennahen Schaumblasen. Unsere Variante der Röntgen-Radiographie mit maßgeschneiderten Tracer-Partikeln (X-PTV) gibt Aufschluss über die drei-dimensionale Schaumströmung. Die in dieser Arbeit verwendeten Tracer bestanden aus einer 3D-gedruckten polymeren Trägerstruktur in Form eines Tetraeders mit insgesamt vier kleinen Metallkügelchen an dessen Ecken. Dank der Tetraeder-Form und des geringen Gewichts des Materialverbunds hafteten die Tracer in der Schaumstruktur und wurden in der Strömung mitgetragen. Die Röntgenbildsequenzen zeigen die Bewegungsbahnen der zu jedem Tracer gehörenden Metallkügelchen und bilden lokal die Stromlinien der Schaumströmung ab. Weiterhin visualisieren die Röntgenbilder des Schaums dessen Flüssigkeitsanteil im gesamten Bildfeld. Sie bestätigen und erweitern die lokalen Messungen des Flüssigkeitsanteils mittels der Elektrodenpaare, sind aber mit einer höheren Messunsicherheit behaftet. Die tracer-basierten Röntgenmessungen belegen die vergleichsweise hohen Strömungsgeschwindigkeiten im Inneren des Kanals und unmittelbar am Überlauf, während die optischen Strömungsmessungen Wand- bzw. Oberflächeneffekten unterliegen, welche in tendenziell geringeren Geschwindigkeiten resultieren. Allerdings zeigen die Messergebnisse auch die Grenzen der Röntgenmessungen mit den Schaum-Tracern auf: ihr Folgevermögen ist in instabilem Schaum mit hohem Flüssigkeitsanteil und bei hoher Strömungsgeschwindigkeit stark vermindert.

  • Lecture (Conference)
    29. Fachtagung "Experimentelle Strömungsmechanik", 06.-08.09.2022, Ilmenau, Deutschland
  • Open Access Logo Contribution to proceedings
    29. Fachtagung "Experimentelle Strömungsmechanik", 06.-08.09.2022, Ilmenau, Deutschland, 978-3-9816764-8-8, 16.1-16.12

Permalink: https://www.hzdr.de/publications/Publ-34726


Low-energy Se ion implantation in MoS₂ monolayers

Bui, M. N.; Rost, S.; Auge, M.; Tu, J.-S.; Zhou, L.; Aguilera, I.; Blügel, S.; Ghorbani Asl, M.; Krasheninnikov, A.; Hashemi, A.; Komsa, H.-P.; Jin, L.; Kibkalo, L.; O’Connell, E. N.; Ramasse, Q. M.; Bangert, U.; Hofsäss, H. C.; Grützmacher, D.; Kardynal, B. E.

Abstract

In this work, we study ultra-low energy implantation into MoS₂ monolayers to evaluate the potential of the technique in two-dimensional materials technology. We use 80 Se⁺ ions at the energy of 20 eV and with fluences up to 5.0 · 10¹⁴ cm⁻².
Raman spectra of the implanted films show that the implanted ions are predominantly incorporated at the sulfur sites and MoS₂₋₂ₓ Se₂ₓ alloys are formed, indicating high ion retention rates, in agreement with the predictions of molecular dynamics simulations of Se ion irradiation on MoS₂ monolayers. We found that the ion retention rate is improved when implantation is performed at an elevated temperature of the target monolayers. Photoluminescence spectra reveal the presence of defects, which are mostly removed by post-implantation annealing at 200 ˚C, suggesting that, in addition to the Se atoms in the substitutional positions, weakly bound Se adatoms are the most common defects introduced by implantation at this ion energy.

Keywords: transition metal dichalcogenide monolayer; dry viscoelasic transfer; ultralow energy ion implantation; MoS₂; defect healing; photoluminescence; Raman spectroscopy

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Permalink: https://www.hzdr.de/publications/Publ-34725


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

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

Abstract

Froth flow is of central importance for mineral processing by froth flotation. In flotation plants, the recovery of solid mineral particles and liquid from the overflowing froth is monitored by optical observation and, therefore, limited to the froth’s free surface. The laboratory-scale experiment in this work investigates the flow behaviour of an aqueous foam at a horizontal overflow (Fig. 1) in combined optical and X-ray radiographic measurements. Simultaneously, the foam’s liquid fraction was determined by measuring the electrical conductivity between electrode pairs. The optical measurements, performed both through a transparent wall and at the free surface of the overflowing foam, captured light reflexions on the foam bubbles, which were analysed by adapting particle image velocimetry algorithms. While the opacity of the foam limits optical measurements to the surface-near bubbles, our approach of X-ray particle tracking velocimetry (X-PTV) sheds light on the three-dimensional foam flow. The customised tracer particles used in this work consisted of a 3D-printed tetrahedral polymer structure with a total of four small metal beads at its corners (Fig. 1). Owing to their shape and the light-weight material composite, the tracers adhered to the bubble-scale foam structure and were carried by the foam. X-ray radiography visualises the motion paths of each tracer’s metal beads, representing the local streamlines of the foam flow. Further, the X-ray radiographs map the foam’s liquid fraction distribution, thus extending the local measurement of the liquid fraction by means of the electrode pairs. X-PTV reveals comparatively high flow velocities of the three-dimensional foam flow, in particular near the overflow, whereas the optical measurements are sub-jected to wall or surface effects, yielding lower flow velocities. However, X-PTV with customised foam flow tracers comes to its limit in unstable foams at high liquid fraction and high flow velocity.

  • Lecture (Conference)
    EUFoam 2022, 03.-06.07.2022, Kraków, Polska

Permalink: https://www.hzdr.de/publications/Publ-34724


Neutron radiography of liquid drops ascending in a liquid metal

Lappan, T.; Sarma, M.; Trtik, P.; Heitkam, S.; Eckert, K.; Eckert, S.

Abstract

Multiphase flows of dispersed gas bubbles and solid particles in liquid metals are hardly to investigate in situ in industrial-scale metallurgical reactors. Laboratory-scale model experiments with low-melting metal alloys have proven very beneficial for radiographic flow investigations. To extend previous experimental studies that were focussed on either bubble or particle flows in liquid gallium and its alloys, we used neutron radiography for visualising liq-uid-liquid two-phase flows of silicone oil drops in the eutectic gallium-tin alloy. We determined the average size of the ascending drops, measured the velocity of each drop along its motion path, and estimated dimensionless numbers to compare drop and bubble characteristics. Here, we exemplarily present the results for drops of 4 mm in diameter, which may serve as a valuable basis for future experiments and simulations with drops and particles in the liquid metal.

Keywords: drops; gallium; neutron radiography; single-particle tracking; two-phase flow

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

Permalink: https://www.hzdr.de/publications/Publ-34723


Adversarial attacks for machine learning denoisers and how to resist them

Hecht, M.; Shao, Z.; Jain, S. B.

Abstract

Adversarial attacks rely on the instability phenomenon appearing in general for all inverse problems, e.g., image classification and reconstruction, independently of the computational scheme or method used to solve the prob- lem. We mathematically prove and empirically show that machine learning denoisers (MLD) are not excluded. That is to prove the existence of adversarial attacks given by noise patterns making the MLD run into instability, i.e., the MLD increases the noise instead of decreasing it. We further demonstrate that adversarial retraining or classic filtering do not provide an exit strategy for this dilemma. Instead, we show that adversarial attacks can be inferred by polynomial regression. Removing the underlying inferred polynomial distribution from the total noise distribution delivers an efficient technique yielding robust MLDs that make consistent computer vision tasks such as image segmentation or classification more reliable.

Keywords: Image Denoising; Inverse Problems; Instability Phenomenon; Adversarial Attacks; Active Learning

  • Invited lecture (Conferences) (Online presentation)
    Emerging Topics in Artificial Intelligence (ETAI), 21.-25.08.2022, San Diego, USA
    DOI: 10.1117/12.2632954
  • Contribution to proceedings
    Emerging Topics in Artificial Intelligence (ETAI) 2022, 03.10.2022, San Diego, USA

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Permalink: https://www.hzdr.de/publications/Publ-34722


Microscopic and spectroscopic insights into uranium(VI) association-reduction processes by a sulfate-reducing microorganism

Hilpmann, S.; Steudtner, R.; Roßberg, A.; Hübner, R.; Prieur, D.; Bauters, S.; Kvashnina, K.; Stumpf, T.; Cherkouk, A.

Abstract

Clay rock represents a suitable host rock for the long-term storage of high-level radioactive waste with bentonite as backfill material. In the event of a worst-case scenario, water can enter the repository. It is possible that naturally occurring microorganisms can interact with the radionuclides and thereby change the chemical speciation or induce redox reactions.
Among different sulfate-reducing bacteria, Desulfosporosinus species represent important members of the microbial communities in both clay rock and bentonite.[1,2] Desulfosporosinus hippei DSM 8344T is a close phylogenetic relative to an isolated bacterium from bentonite.[3] Therefore, this strain was selected to get a more profound insight into the uranium(VI) interactions with naturally occurring microorganisms from deep geological layers.
Time-dependent experiments in artificial Opalinus Clay pore water[4] (100 µM uranium(VI), pH 5,5) showed a high removal of uranium from the supernatants within a short time range. UV/Vis studies of the dissolved cell pellets provided clear proof of a partial reduction of uranium(VI) to uranium(IV) in the samples, although bands of uranium(VI) were still observable. These findings propose a combined association-reduction process as an explanation for the ongoing interaction mechanism.
Uranium aggregates formed on the cell surface were visible in TEM images. Furthermore, cells released membrane vesicles as a possible defense mechanism against cell encrustation.
In addition, HERFD-XANES measurements confirmed the reduction of uranium(VI). But with these measurements also the presence of uranium(V) in the cell pellets could be demonstrated. This provides first evidence of the involvement of uranium(V) in uranium(VI) reduction by sulfate-reducing microorganisms. With the help of EXAFS measurements, different cell-related uranium species were detected.
This study helps to better understand the complexity of redox processes in the environment and contribute to a safety concept for a nuclear repository in clay rock. Moreover, new insights into the uranium(VI) reduction mechanisms of sulfate-reducing bacteria were presented.

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 bacteria; Clay rock

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  • Lecture (Conference) (Online presentation)
    Goldschmidt 2022, 10.-15.07.2022, Hawaii, USA

Permalink: https://www.hzdr.de/publications/Publ-34721


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