Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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Approved and published publications
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41338 Publications

Fully Linear Graph Convolutional Networks for Semi-Supervised and Unsupervised Classification

Cai, Y.; Zhang, Z.; Ghamisi, P.; Cai, Z.; Liu, X.; Ding, Y.

This article presents FLGC, a simple yet effective fully linear graph convolutional network for semi-supervised and unsupervised learning. Instead of using gradient descent, we train FLGC based on computing a global optimal closed-form solution with a decoupled procedure, resulting in a generalized linear framework and making it easier to implement, train, and apply. We show that (1) FLGC is powerful to deal with both graph-structured data and regular data, (2) training graph convolutional models with closed-form solutions improve computational efficiency without degrading performance, and (3) FLGC acts as a natural generalization of classic linear models in the non-Euclidean domain (e.g., ridge regression and subspace clustering). Furthermore, we implement a semi-supervised FLGC and an unsupervised FLGC by introducing an initial residual strategy, enabling FLGC to aggregate long-range neighborhoods and alleviate over-smoothing. We compare our semi-supervised and unsupervised FLGCs against many state-of-the-art methods on a variety of classification and clustering benchmarks, demonstrating that the proposed FLGC models consistently outperform previous methods in terms of accuracy, robustness, and learning efficiency. The core code of our FLGC is released at https://github.com/AngryCai/FLGC.

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  • Secondary publication expected

Permalink: https://www.hzdr.de/publications/Publ-37887
Publ.-Id: 37887


Local Window Attention Transformer for Polarimetric SAR Image Classification

Jamali, A.; Roy, S. K.; Bhattacharya, A.; Ghamisi, P.

Convolutional neural networks (CNNs) have recently found great attention in image classification since deep CNNs have exhibited excellent performance in computer vision. Owing to their immense success, of late, scientists are exploring the functionality of transformers in Earth observation applications. Nevertheless, the primary issue with transformers is that they demand significantly more training data than CNN classifiers. Thus, the use of these transformers in remote sensing is considered challenging, notably in utilizing polarimetric synthetic aperture radar (PolSAR) data, due to the insufficient number of existing labeled data. In this letter, we develop and propose a vision transformer (ViT)-based framework that utilizes 3-D and 2-D CNNs as feature extractors and, in addition, local window attention (LWA) for the effective classification of PolSAR data. Extensive experimental results demonstrated that the developed model PolSARFormer obtained better classification accuracy than the state-of-the-art vision Swin Transformer and FNet algorithms. The PolSARFormer outperformed the Swin Transformer and FNet by the margin of 5.86% and 17.63%, in terms of average accuracy (AA) in the San Francisco data benchmark. Moreover, the results over the Flevoland dataset illustrated that the PolSARFormer exceeds several other algorithms, including the ResNet (97.49%), Swin Transformer (96.54%), FNet (95.28%), 2-D CNN (94.57%), and AlexNet (91.83%), with a kappa index (KI) of 99.30%. The code will be made available publicly at https://github.com/aj1365/PolSARFormer .

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Permalink: https://www.hzdr.de/publications/Publ-37886
Publ.-Id: 37886


Scalable machine learning for predicting the electronic structure in many-particle systems

Cangi, A.

In this presentation, I will present our recent progress in integrating machine learning to significantly boost the computational efficiency of electronic structure calculations [1]. I will specifically address our efforts to speed up density functional theory calculations, for which we have developed the Materials Learning Algorithms framework [2]. Our findings illustrate significant improvements in calculation speed for metals at their melting point. Additionally, our use of automated machine learning has yielded significant reductions in computational resources required to identify optimal neural network architectures, laying the groundwork for extensive investigations [3]. Furthermore, I will show the transferability of our ML model across temperatures [4]. Most importantly, I will present our latest breakthrough, which enables fast neural-network driven electronic structure calculations for systems unattainable by conventional density functional theory calculations [5].

References
[1] L. Fiedler, K. Shah, M. Bussmann, A. Cangi, Phys. Rev. Materials, 6, 040301 (2022).
[2] J. Ellis, L. Fiedler, G. Popoola, N. Modine, J. Stephens, A. Thompson, A. Cangi, S. Rajamanickam, Phys. Rev. B, 104, 035120 (2021).
[3] L. Fiedler, N. Hoffmann, P. Mohammed, G. Popoola, T. Yovell, V. Oles, J. Austin Ellis, S. Rajamanickam, A. Cangi, Mach. Learn.: Sci. Technol., 3, 045008 (2022).
[4] L. Fiedler, N. A. Modine, K. D. Miller, and A. Cangi Phys. Rev. B 108, 125146 (2023).
[5] L. Fiedler, N. Modine, S. Schmerler, D. Vogel, G. Popoola, A. Thompson, S. Rajamanickam, A. Cangi, npj. Comput. Mater., 9, 115 (2023).

Keywords: Machine learning; Electronic structure theory; Density functional theory; Neural networks

  • Invited lecture (Conferences)
    Many-Particle Systems under Extreme Conditions, WE-Heraeus Seminar and Max Born Symposium, 03.-06.12.2023, Görlitz, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-37883
Publ.-Id: 37883


Liquid Metal Batteries: transport phenomena and cycling behavior

Weier, T.

There is a close and multifaceted relation between fluid dynamics and
the charge/discharge behavior of liquid metal batteries. The talk will
give an overview of numerical and experimental work on transport
phenomena in liquid metal batteries and discuss how they influence
the cycling behavior of the cells.

Keywords: liquid metal batteries; transport phenomena; heat transfer; mass transfer; solutal convection; internally heated convection

  • Invited lecture (Conferences) (Online presentation)
    Annual Meeting of the Mexican Physical Society - Division of Fluid Dynamics (DDF-SMF), 04.-06.12.2023, Mexico City, Mexico

Permalink: https://www.hzdr.de/publications/Publ-37882
Publ.-Id: 37882


Report on research data management interviews conducted for HMC Hub Energy in 2022

Ballani, F.; Schaller, T.; Steinmeier, L.; Koubaa, M. A.; Schweikert, J.; Stucky, K.-U.; Süß, W.

The Energy Hub of the Helmholtz Metadata Collaboration (HMC) conducted interviews with various stakeholders from the Helmholtz Research Field Energy on the topic of research data management (RDM) in 2022. The intentions were to build and serve a metadata community in the energy research field and to extend the Helmholtz-wide survey conducted by HMC in 2021 Arndt et al., 2022). Besides the deeper insight into the current state of RDM and metadata handling at the Helmholtz sites relevant to the Energy Hub the interviews focused on the related needs and difficulties of researchers and their satisfaction with the current state. Furthermore, we tried to discover already existing workflows and software solutions, to establish contacts and to make HMC better known.

Keywords: Helmholtz Metadata Collaboration; Research data management

Permalink: https://www.hzdr.de/publications/Publ-37881
Publ.-Id: 37881


Data publication: Ion emission from warm dense matter produced by irradiation with a soft x-ray free-electron laser

Krása, J.; Burian, T.; Hájková, V.; Chalupský, J.; Jelínek, Š.; Frantálová, K.; Krupka, M.; Kuglerová, Z.; Kumar Singh, S.; Vozda, V.; Vyšín, L.; Smid, M.; Perez-Martin, P.; Kühlman, M.; Pintor, J.; Cikhardt, J.; Dreimann, M.; Eckermann, D.; Rosenthal, F.; Vinko, S. M.; Forte, A.; Gawne, T. D.; Campbell, T.; Ren, S.; Shi, Y.; Hutchinson, T.; Humphries, O. S.; Preston, T.; Makita, M.; Nakatsutsumi, M.; Pan, X.; Köhler, A.; Harmand, M.; Toleikis, S.; Falk, K.; Juha, L.

Data set on the ion emission of different materials. Each dataset is separate and titled with the chemical symbol or abbreviation of the specific material.

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Permalink: https://www.hzdr.de/publications/Publ-37880
Publ.-Id: 37880


Effect of Chain Length on Swelling Transitions of Brodie Graphite Oxide in Liquid 1-Alcohols

Iakunkov, A.; Nordenström, A.; Boulanger, N.; Li, G.; Hennig, C.; Jørgensen, M. R. V.; Kantor, I.; Talyzin, . A. V.

Swelling is the most fundamental property of graphite oxides (GO). Here, a structural study of Brodie graphite oxide (BGO) swelling in a set of long chain 1-alcohols (named C11 to C22 according to the number of carbons) performed using synchrotron radiation X-ray diffraction at elevated temperatures is reported. Even the longest of tested alcohols (C22) is found to intercalate BGO with enormous expansion of the interlayer distance from ≈6Å up to ≈63Å, the highest expansion of GO lattice ever reported. Swelling transitions from low temperature alpha-phase to high temperature beta-phase are found for BGO in all alcohols in the C11–C22 set. The transitions correspond to decrease of inter-layer distance correlating with the length of alcohol molecules, and change in their orientation from perpendicular to GO planes to layered parallel to GO (Type II transitions). These transitions are very different compared to BGO swelling transitions (Type I) found in smaller alcohols and related to insertion/de-insertion of additional layer of alcohol parallel to GO. Analysis of general trends in the whole set of 1-alcohols (C1 to C22) shows that the 1-alcohol chain length defines the type of swelling transition with Type I found for alcohols with C<10 and Type II for C>10.

Related publications

Permalink: https://www.hzdr.de/publications/Publ-37879
Publ.-Id: 37879


Geometry Optimization in 2D Materials

Friedrich, R.

Tutorial on geometry optimization in 2D materials.

Related publications

  • Invited lecture (Conferences)
    DFG SPP 2244 Summer School 2023, 29.08.2023, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-37878
Publ.-Id: 37878


AFLOW: Integrated infrastructure for computational materials discovery

Friedrich, R.; Eckert, H.; Divilov, S.; Curtarolo, S.

Hands-on introduction to the AFLOW software for materials design.

Related publications

  • Invited lecture (Conferences)
    International Summer School Materials 4.0, 23.08.2023, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-37877
Publ.-Id: 37877


Predictive Design of Novel Two-Dimensional Materials

Friedrich, R.

The predictive power of physical theories has led to remarkable findings such as the discovery of planets,
new elementary particles, and gravitational waves. The Dresden-concept group “Autonomous Materials
Thermodynamics – AutoMaT” leverages ab initio density functional theory as a predictive tool for
materials design. We specifically focus on the data-driven discovery of novel two-dimensional (2D)
materials for future electronics and energy applications with strong partners from HZDR,
Forschungszentrum Jülich, the DFG collaborative research center “Synthetic Two-dimensional
Materials” hosted at TU Dresden, and Duke University (United States).
Two-dimensional (2D) materials are traditionally derived from bulk layered compounds. The recent
surprising experimental realization of some 2D sheets obtained from non-layered crystals [1,2]
foreshadows a new direction for this diverse class of nanostructures. Generalizing these findings, we
recently predicted by data-driven methods and autonomous ab initio calculations a large set of novel
representatives [3,4] (see Figure 1). They exhibit diverse magnetic properties such as complex surface
spin polarizations enabling spintronics. These systems are thus an attractive platform for fundamental and
applied nanoscience.
[1] A. Puthirath Balan et al., Nat. Nanotechnol. 13, 602 (2018).
[2] A. Puthirath Balan et al., Chem. Mater. 30, 5923 (2018).
[3] R. Friedrich et al., Nano Lett. 22, 989 (2022).
[4] T. Barnowsky et al., Adv. Electron. Mater. 2201112 (2023).

Related publications

  • Lecture (Conference)
    HZDR Science Conference, 16.11.2023, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-37876
Publ.-Id: 37876


Data-driven Design of Novel Materials and Interfaces Enabling Future Technologies

Friedrich, R.

Every technology is intimately connected to a certain materials platform. Information technology is based
on silicon, modern batteries are made from lithium compounds, and magnetic materials are important for
the energy sector. Moreover, interfaces between materials are often the enabler of dedicated
functionalities calling for not only the design of individual materials but also of their interfaces.
The Dresden-concept group “Autonomous Materials Thermodynamics – AutoMaT” leverages state of the
art predictive computational methods for materials and interface design. We specifically focus on the
data-driven discovery of novel two-dimensional (2D) materials for future electronics and energy
applications with strong partners from the DFG collaborative research center 1415 “Synthetic Two-dimensional
Materials” hosted at TU Dresden, HZDR, Forschungszentrum Jülich, and Duke University
(United States).
Two-dimensional materials are traditionally derived from bulk layered compounds. The recent surprising
experimental realization of some 2D sheets obtained from non-layered crystals foreshadows a new
direction for this diverse class of nanostructures. Generalizing these findings, we recently predicted by
data-driven methods and autonomous ab initio calculations a large set of novel representatives. They
exhibit appealing magnetic properties enabling spintronics. These systems and their interfaces are thus an
attractive platform for fundamental and applied nanoscience.

Related publications

  • Invited lecture (Conferences) (Online presentation)
    DRESDEN-concept lunch retreat, 21.11.2023, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-37875
Publ.-Id: 37875


Data-Driven Materials Science

Friedrich, R.

Invited talk at the HZDR data management day.

Related publications

  • Invited lecture (Conferences)
    HZDR Data Management Day, 21.11.2023, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-37874
Publ.-Id: 37874


The Multi-Dimensional Problem of Discovering Novel (Two-Dimensional) Materials

Friedrich, R.

Invited talk at the AFLOW seminar series.

Related publications

  • Invited lecture (Conferences) (Online presentation)
    AFLOW seminar, 09.11.2023, online, online

Permalink: https://www.hzdr.de/publications/Publ-37873
Publ.-Id: 37873


Ion Irradiation-Induced Sinking of Ag Nanocubes into Substrates

Choupanian, S.; Möller, W.; Seyring, M.; Pacholski, C.; Wendler, E.; Undisz, A.; Ronning, C.

Ion irradiation can cause burrowing of nanoparticles in substrates, strongly depending on the material properties and irradiation parameters. In this study, it is demonstrated that the sinking process can be accomplished with ion irradiation of cube-shaped Ag nanoparticles on top of silicon; how ion channeling affects the sinking rate; and underline the importance of the amorphous state of the substrate upon ion irradiation. Based on these experimental findings, the sinking process is described as being driven by capillary forces enabled by ion-induced plastic flow of the substrate.

Permalink: https://www.hzdr.de/publications/Publ-37872
Publ.-Id: 37872


Experimentelle und rechnerische Bestimmung der Aktivierung für die Rückbauplanung von Kernkraftwerken

Barkleit, A.; Rachamin, R.; Pönitz, E.; Konheiser, J.

Vorstellung der FORKA-Projekte EMPRADO und WERREBA

  • Lecture (Conference)
    55. Kraftwerkstechni­sches Kolloquium, 10.-11.10.2023, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-37871
Publ.-Id: 37871


Comparative structural and (radio-)chemical investigations of activated cement and concrete samples

Zilbermann, M. E.

To help with the decommissioning of the unit 2 of the Greifswald NPP, this study aims at determining the activities of 3H, 14C, 60Co, 152Eu and 154Eu in the concrete to estimate the maximal activity in the entire bioshield.
The study will focus on the activity as a function of depth in the concrete layer, as well as composition of the mineral phases. As the flux of neutrons generated during fission reaction encounters the mineral phases of concrete, the natural elements present in these phases absorb neutrons, which leads to the formation of their radioactive isotopes. Therefore, the elemental composition of each mineral phase in the concrete is important in the activation process, and the concrete being a heterogeneous material, different phases will present different activities.
A precise knowledge of the activities and of the elemental composition of the concrete and its mineral phases helps refining the models to calculate and predict the activities in a long-term scale. The calculations and the experimental results support the sorting of the materials for disposal.
This study will analyze the concrete with three main objectives:

  • Activation;
  • Chemical composition;
  • Structure of the concrete and mineral phases.
  • Master thesis
    TU Dresden, 2023
    Mentor: Prof. Dr. Thorsten Stumpf, Dr. Astrid Barkleit

Permalink: https://www.hzdr.de/publications/Publ-37870
Publ.-Id: 37870


Multi-scale and multi-source hyperspectral imaging for mapping lithium-bearing minerals

Booysen, R.; Kirsch, M.; Thiele, S. T.; Lorenz, S.; Madriz Diaz, Y. C.; Nex, P.; Kinnaird, J.; Gloaguen, R.

The transition towards a net-zero economy has led to an increased need for several critical raw materials required for green technologies. Lithium (Li) is one of these materials. Significant mineral exploration using sustainable, efficient and innovative methods is required to not only improve mineral detection and mapping, but also to foster social acceptability for the mining and exploration industry. Hyperspectral imaging (HSI) allows for fast and systematic identification of key minerals. In this contribution, we propose an innovative approach for exploration by using hyperspectral data from multiple sensors at various scales to non-invasively map ore and pathfinder minerals. We showcase this approach in an open-pit and under-ground sites in South Africa, Namibia and Germany by acquiring data in the short-wave infrared (SWIR) with both a tripod and a drone. Hand-samples and drill-cores were used to identify the relevant minerals as well as for training/validation purposes. Using computer vision techniques, we were able to create a three-dimensional (3D) point cloud of the sites with HSI attributes to allow for the subsequent spectral mapping of relevant Li-bearing minerals. Results were validated using drill-core data, LIBS measurements and geochemical analyses of hand samples.

Keywords: Lithium-bearing minerals; Hyperspectral imaging; Multi-scale

  • Contribution to proceedings
    17th SGA Biennial Meeting, 28.08.-01.09.2023, Zurich, Switzerland

Permalink: https://www.hzdr.de/publications/Publ-37869
Publ.-Id: 37869


Hyperspectral Imaging for Mapping Outcropping Li-bearing Pegmatites

Booysen, R.; Lorenz, S.; Madriz Diaz, Y. C.; Fuchsloch, W.; Nex, P.; Marais, T.; Gloaguen, R.

The transition towards a net-zero economy has led to an increased need for several critical raw materials required for green technologies. Lithium (Li) is one of these materials, which is experiencing a sharp increase in demand that recycling alone is not capable of meeting. Significant mineral exploration using sustainable, efficient and innovative methods is required to not only improve mineral detection and mapping, but also foster social acceptability for the mining and exploration industry. Hyperspectral imaging (HSI) is a rapidly developing technology that allows for fast and systematic identification of key minerals and provides information about mineral abundances and associations. In this contribution, we propose an innovative approach for exploration by using hyperspectral data from multiple sensors at various scales to non-invasively map ore and pathfinder minerals. We showcase this approach at the Uis pegmatite complex located in Namibia. Hand-samples taken at the Uis pit were used to identify the relevant minerals as well as for training/validation purposes, and we acquired HSI data of the pit using a short-wave infrared (SWIR) camera mounted on a tripod. Using machine learning and computer vision techniques, we upscaled this information to the outcrop scale and created a three-dimensional (3D) point cloud of the pit with HSI attributes to map relevant Li-bearing minerals, such as cookeite and montebrasite. Results were validated using drill-core data, LIBS measurements and XRF analyses. We recently acquired uncrewed-aerial vehicle (UAV)-based SWIR data, to allow flexible data acquisition and mitigate access limitations. With in-house tools, the data is being processed (e.g., geometric and radiometric corrections) and we expect to map Li-bearing minerals in a similar manner. This approach enables rapid and efficient mapping of complex terrains in a sustainable exploration scheme, and can be used for monitoring and optimisation of ore extraction.

Keywords: UAV; Drones; Hyperspectral imaging; Pegmatites; Lithium

  • Contribution to proceedings
    Society of Economic Geologists 2022 Conference: Minerals For Our Future, 27.-30.08.2022, Denver, USA

Permalink: https://www.hzdr.de/publications/Publ-37868
Publ.-Id: 37868


Innovative hyperspectral imaging for Lithium exploration

Booysen, R.; Thiele, S. T.; Lorenz, S.; Madriz Diaz, Y. C.; Nex, P.; Gloaguen, R.

The current transition towards a sustainable future is rooted in the use of green technologies. These technologies have led to a large rise in demand for previously obscure minerals and metals. One such sought-after element is lithium (Li), due to its use in Li-ion batteries for electric vehicles. Recycling alone cannot meet the present demand for this material, thus exploration of new resources and the improvement of existing mining activities are required. Conventional exploration methods are typically performed by a team of geoscientists and involve geological fieldwork, geophysical surveys and extensive drilling. These methods are time-consuming, expensive, vulnerable to weather conditions or in-accessible terrains and often carry a considerable environmental impact. In the case of Li exploration, the typical geochemical analyses and assaying methods fall short in accurately identifying and quantifying the presence of Li. Therefore, we suggest a non-invasive, hyperspectral imaging (HSI) approach for the detection of mineralized outcrops. HSI is a fast developing technology that allows for rapid mineral mapping, facilitating mineral exploration at various scales. In this contribution, we demonstrate our approach at the Uis Li-bearing pegmatite mine in Namibia by utilizing a variety of platforms and sensors in order to map key minerals associated with Li-mineralization. We collected hand samples from the main pit to identify relevant minerals. In addition, we captured hyperspectral data covering the main pit in the visible and near infrared (VNIR) and short-wave infrared (SWIR) range of the electromagnetic spectrum with a tripod mounted hyperspectral sensor. We acquired RGB photos of the main pit for Structure-from-Motion (SfM) multi-view stereo (MVS) photogrammetry to create a three-dimensional (3D) model. By using computer vision and machine learning techniques, we combined the hyperspectral data with the 3D information to produce a 3D point cloud with hyperspectral attributes. This workflow was performed using the open-source python based toolbox hylite and allowed us to produce a geometrically correct and spatially continuous 3D map of Li-bearing minerals. We validated our result with drill-core data as well as laser induced breakdown spectroscopy (LIBS) measurements and X-ray fluorescence (XRF) analyses of the hand samples. Additionally, we recently acquired drone-borne SWIR data over the same mine, allowing for more flexible data acquisition in order to mitigate access limitation. Taking a HSI approach enables us to rapidly and efficiently map complex terrains in a non-invasive and sustainable exploration scheme.

Keywords: Lithium; Hyperspectral imaging; Pegmatite

  • Open Access Logo Contribution to proceedings
    12th IEEE Whispers Conference - Hyperspectral Image and Signal Processing, 13.-16.09.2022, Rome, Italy

Permalink: https://www.hzdr.de/publications/Publ-37867
Publ.-Id: 37867


On the missing single collision peak in low energy heavy ion scattering

Wilhelm, R. A.; Deuzeman, M. J.; Rai, S.; Husinsky, W.; Szabo, P. S.; Biber, H.; Stadlmayr, R.; Cupak, C.; Hundsbichler, J.; Lemell, C.; Möller, W.; Mutzke, A.; Hobler, G.; Versolato, O. O.; Aumayr, F.; Hoekstra, R.

We present experimental and simulation data on the oblique angle scattering of heavy Sn ions at 14 keV energy from a Mo surface. The simulations are performed with the binary collision approximation codes TRIM, TRIDYN, TRI3DYN, SDTrimSP, and IMSIL. Additional simulations were performed in the molecular dynamics framework with LAMMPS. Our key finding is the absence of an expected peak in the experimental energy spectrum of backscattered Sn ions associated with the pure single collision regime. In sharp contrast to this, however, all simulation codes we applied do show a prominent single collision signature both in the energy spectrum and in the angular scatter pattern. We discuss the possible origin of this important discrepancy and show in the process, that widely used binary collision approximation codes may contain hidden parameters important to know and to understand.

Keywords: Binary collision approximation; Heavy ions; Ion scattering; Molecular dynamics

Permalink: https://www.hzdr.de/publications/Publ-37866
Publ.-Id: 37866


Der Einbrennvorgang des Bethe-Weizsäcker-Zyklus

Bemmerer, D.; Rümmler, S.; Herrera, Y.

Das Wasserstoffbrennen in der Sonne wird von der sogenannten Proton-Proton-Kette bestimmt. Ein zweiter, parallel ablaufender Prozess ist der Bethe-Weizsäcker- oder CNO-Zyklus. Bei der Sonne trägt er nur etwa 0,8 % zur Energieerzeugung bei, kann aber zur Bestimmung der Kohlenstoffhäufigkeit im Sonneninnern genutzt werden. Neue Labordaten zur ersten Reaktion im Zyklus zeigen für massereiche Sterne eine 25 % geringere Rate als bislang angenommen, während sich für unsere Sonne wenig ändert.

Permalink: https://www.hzdr.de/publications/Publ-37865
Publ.-Id: 37865


Post growth thermal treatments of Si1-x-yGexSny alloys

Steuer, O.; Schwarz, D.; Oehme, M.; Hübner, R.; Ganss, F.; Khan, M. M.; Cheng, Y.; Rebohle, L.; Zhou, S.; Helm, M.; Cuniberti, G.; Georgiev, Y.; Prucnal, S.

Si1-x-yGexSny alloys are promising materials for future applications in opto- and nanoelectronics. These alloys enable effective band gap engineering, a broad adjustability of the lattice parameter, exhibit much higher carrier mobility than pure Si and are compatible with CMOS technology. Unfortunately, the equilibrium solid solubility of Sn in Si1-xGex is less than 1% and pseudomorphic growth of Si1-xyGexSny on Ge or Si causes in-plane compressive strain in the grown layer, which degrades the superior properties of the alloys. Therefore, the post-growth strain engineering using ultrafast non-equilibrium thermal treatments like flash lamp annealing (FLA) or pulsed laser annealing (PLA) to improve the layer quality is needed. In this contribution, we discuss the influence of millisecond FLA and nanosecond PLA on Si1-x-yGexSny alloys and present an efficient way to improve the layer quality of thin film Si1-x-yGexSny on insulator by PLA. Different Si1-xyGexSny alloys are directly grown on commercial silicon-on-insulator (SOI) wafers and treated by FLA or PLA. The material is analysed by micro-Raman spectroscopy, Rutherford backscattering spectrometry (RBS) and X-ray diffraction (XRD) before and after the thermal treatments. It is shown that after annealing, the material is single-crystalline with much better crystallinity than the as-grown layer.

Related publications

  • Poster
    E-MRS 2023 Spring Meeting, 29.05.-02.06.2023, Strasbourg, Frankreich

Permalink: https://www.hzdr.de/publications/Publ-37864
Publ.-Id: 37864


Post growth thermal treatments of Silicon-Germanium-Tin-on-insulator alloys

Steuer, O.; Schwarz, D.; Oehme, M.; Hübner, R.; Ganss, F.; Khan, M. M.; Cheng, Y.; Rebohle, L.; Zhou, S.; Helm, M.; Cuniberti, G.; Georgiev, Y.; Prucnal, S.

Si1-x-yGexSny alloys are promising materials for future applications in opto- and nanoelectronics. These alloys enable effective band gap engineering, a broad adjustability of the lattice parameter, exhibit much higher carrier mobility than pure Si and are compatible with CMOS technology. Unfortunately, the equilibrium solid solubility of Sn in Si1-xGex is less than 1% and pseudomorphic growth of Si1-xyGexSny on Ge or Si causes in-plane compressive strain in the grown layer, which degrades the superior properties of the alloys. Therefore, the post-growth strain engineering using ultrafast non-equilibrium thermal treatments like flash lamp annealing (FLA) or pulsed laser annealing (PLA) to improve the layer quality is needed. In this contribution, we discuss the influence of millisecond FLA and nanosecond PLA on Si1-x-yGexSny alloys and present an efficient way to improve the layer quality of thin film Si1-x-yGexSny on insulator by PLA. Different Si1-xyGexSny alloys are directly grown on commercial silicon-on-insulator (SOI) wafers and treated by FLA or PLA. The material is analysed by micro-Raman spectroscopy, Rutherford backscattering spectrometry (RBS) and X-ray diffraction (XRD) before and after the thermal treatments. It is shown that after annealing, the material is single-crystalline with much better crystallinity than the as-grown layer.

Related publications

  • Poster
    3rd Joint International Conference on Silicon Epitaxy and Heterostructures & International SiGe Technology and Device Meeting, 22.-25.05.2023, Como, Italy

Permalink: https://www.hzdr.de/publications/Publ-37863
Publ.-Id: 37863


Evolution of point defects in pulsed-laser-melted Ge1-xSnx probed by positron annihilation lifetime spectroscopy

Steuer, O.; Liedke, M. O.; Butterling, M.; Schwarz, D.; Schulze, J.; Li, Z.; Wagner, A.; Fischer, I. A.; Hübner, R.; Zhou, S.; Helm, M.; Cuniberti, G.; Georgiev, Y.; Prucnal, S.

Rohdaten und analysedaten der Publikation

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Permalink: https://www.hzdr.de/publications/Publ-37862
Publ.-Id: 37862


Data publication: Aluminium substituted yttrium iron garnet thin films with reduced Curie temperature

Scheffler, D.; Steuer, O.; Zhou, S.; Siegl, L.; Goennenwein, S. T. B.; Lammel, M.

RBS Messungen der Aluminium substituted yttrium iron garnet thin films

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Permalink: https://www.hzdr.de/publications/Publ-37861
Publ.-Id: 37861


Aluminium substituted yttrium iron garnet thin films with reduced Curie temperature

Scheffler, D.; Steuer, O.; Zhou, S.; Siegl, L.; Goennenwein, S. T. B.; Lammel, M.

Magnetic garnets such as yttrium iron garnet (Y3 Fe 5 O12 , YIG) are widely used in spintronic and magnonic
devices. Their magnetic and magneto-optical properties can be modified over a wide range by tailoring their
chemical composition. Here, we report the successful growth of Al-substituted yttrium iron garnet (YAlIG) thin
films via radio frequency sputtering in combination with an ex situ annealing step. Upon selecting appropriate
process parameters, we obtain highly crystalline YAlIG films with different Al 3+ substitution levels on both
single crystalline Y 3 Al 5 O12 (YAG) and Gd 3 Ga 5 O12 (GGG) substrates. With increasing Al 3+ substitution levels,
we observe a reduction of the saturation magnetization as well as a systematic decrease of the magnetic ordering
temperature to values well below room temperature. YAlIG thin films thus provide an interesting material
platform for spintronic and magnonic experiments in different magnetic phases.

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Permalink: https://www.hzdr.de/publications/Publ-37860
Publ.-Id: 37860


Comparando las estimaciones de selección de hábitat mediante modelos de distribución de especies y step selection functions

Saraiva De Menezes, J. F.

Recently, two methods of habitat selection have gained more relevance in the scientific literature: step selection functions (SSF) and MaxEnt. Despite their similarity these models are hardly ever used in the same context. The former is usually associated with studies based in movement ecology, and the latter is connected to species distribution modeling. Motivated by the difficulty in estimating habitat preferences using SSF, I compared the accuracy of predictions from both models based on movement data. As a case study, I utilized jaguar movement data from 5 countries in Latin American and created SSF and MaxEnt models based on climatic data and land use available from WorldClim and satellite imagery. I compared the accuracy of both types of models using the “Area Under Curve” (AUC) metric, on a separate subset of data. SSF models presented an average AUC of 0.5510 ± 0.0147 in comparison with 0.7544 ± 0.0185 of their MaxEnt equivalents. I believe those differences are partially caused by the convergence difficulties of SSF and conditional logistic regression. Consequently, I recommend the use of MaxEnt in predictive modelling, such as the ones needed in reserve and corridor design.

Keywords: Latin America; Jaguars; niche modelling; resource selection function; trajectory

Permalink: https://www.hzdr.de/publications/Publ-37859
Publ.-Id: 37859


Data publication: SAPPHIRE - Establishment of small animal proton and photon image-guided radiation experiments

Schneider, M.; Schilz, J.; Schürer, M.; Gantz, S.; Dreyer, A.; Rothe, G.; Tillner, F.; Bodenstein, E.; Horst, F. E.; Beyreuther, E.

This repository contains the data shown in the results part of the paper entitled: SAPPHIRE - Establishment of small animal proton and photon image-guided radiation experiments.

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Permalink: https://www.hzdr.de/publications/Publ-37852
Publ.-Id: 37852


Data publication: Preparation of 18F-Labeled Tracers Targeting Fibroblast Activation Protein via Sulfur [18F]Fluoride Exchange Reaction

Craig, A.; Kogler, J.; Laube, M.; Ullrich, M.; Donat, C.; Wodtke, R.; Kopka, K.; Stadlbauer, S.

The data concerns the preparation of two new 18F-labeled radiotracers using a ultra-fast radiolabeling method for tumor detection using positron emission tomography (PET) imaging.

Keywords: Automation; cancer-associated fibroblast; FAPI; 18F-fluorination; positron emission tomography (PET); [18F]SuFEx

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Permalink: https://www.hzdr.de/publications/Publ-37850
Publ.-Id: 37850


Nontrivial Aharonov-Bohm effect and alternating dispersion of magnons in cone-state ferromagnetic rings

Uzunova, V.; Körber, L.; Kavvadia, A.; Quasebarth, G.; Schultheiß, H.; Kakay, A.; Ivanov, B.

Soft magnetic dots in the form of thin rings have unique topological properties. They can be in a vortex state with no vortex core. Here, we study the magnon modes of such systems both analytically and numerically. In an external magnetic field, magnetic rings are characterized by easy-cone magnetization and shows a giant splitting of doublets for modes with the opposite value of the azimuthal mode quantum number. The effect of the splitting can be refereed as a magnon analog of the topology-induced Aharonov-Bohm effect. For this we develop an analytical theory to describe the non-monotonic dependence of the mode frequencies on the azimuthal mode number, influenced by the balance between the local exchange and non-local dipole interactions.

Keywords: Spin waves; Topology; Vortex; Magnetism; Aharonov-Bohm effect; Micromagnetism

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Permalink: https://www.hzdr.de/publications/Publ-37849
Publ.-Id: 37849


Using Julia to Accelerate Monte Carlo Event Generation with Neural Importance Sampling

Jungnickel, T.; Steiniger, K.; Bussmann, M.; Hernandez Acosta, U.

Monte Carlo event generation is essential for analysis in high energy physics and fast implementations are required to keep up with the large amounts of data measured by experiments. Therefore, these methods need to reflect the theoretical predictions accurately to enable efficient data generation, e.g. by rejection sampling. However, traditional importance sampling algorithms, such as the commonly used VEGAS algorithm, often struggle with adapting targets with multiple or non-coordinate aligned features, as is common in high energy physics. Especially in strong-field QED, processes dynamically depend on field parameters, which means the use of established codes for these problems needs to be questioned. An importance sampling approach using neural networks applied to strong-field processes is presented within the framework QED.jl. The quality of the generated proposals, e.g. the unweighting efficiency, is compared to VEGAS, providing insights beneficial to applications beyond strong-field QED.

Keywords: strong field QED; machine learning; Julia; QED.jl; neural importance sampling

  • Lecture (Conference)
    JuliaHEP 2023, 06.-09.11.2023, Erlangen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-37848
Publ.-Id: 37848


Investigation of Mixing using Microfocus X-ray Computed Tomography (µCT)

Baecke, A. M.

Fine-grained solid particles from various industrial sources, which would otherwise be discarded, should ideally be processed to valuable products or inert residues. Among others, a) shredder fines from electronics and end-of-life vehicles, and b) flue dusts from non-ferrous metallurgical processes are of timely interest. They contain valuable residuals, such as metals, that can be returned to the industrial cycle instead of being landfilled. This is one aim of the Helmholtz project FINEST in which this work is embedded. In this work, mixing and agglomeration of such particles with a size below 1 mm are investigated for further use in the metallurgical industry. Different particle sizes and densities are considered. The process is observed experimentally using camera imaging technique and µCT. From the µCT images a mixing index is acquired. We present an experimental setup and methods for the aforementioned investigations.

Keywords: Microfocus X-Ray Computed Tomography; Particle Flow; Mixing and Segregation

  • Lecture (Conference)
    Bałdyga Technical Seminars - Mixing meets reality, 14.-15.09.2023, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-37846
Publ.-Id: 37846


Accelerating Event Generation in Strong-Field QED with Neural Importance Sampling

Jungnickel, T.; Steiniger, K.; Hernandez Acosta, U.; Bussmann, M.

Efficient Monte Carlo integreation is crucial for modeling processes at the European XFEL. However, traditional approaches to importance sampling like VEGAS do not perform well when integrands display multiple features or non-coordinate aligned features. In this work, we present an implementation of neural importance sampling (NIS) in the Julia programming language to address this challenge. We demonstrate the effectiveness of NIS by applying it to processes in strong-field QED at high energies, showing superior adaption of the integrand and thus enabling efficient event generation.

Keywords: strong field QED; machine learning; Julia; QED.jl; neural importance sampling

  • Poster
    Helmholtz AI Conference 2023, 12.-14.06.2023, Hamburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-37845
Publ.-Id: 37845


Probing Iron in Earth's Core With Molecular-Spin Dynamics

Nikolov, S.; Ramakrishna, K.; Rohskopf, A.; Lokamani, M.; Tranchida, J.; Carpenter, J.; Cangi, A.; Wood, M. A.

Dynamic compression of iron to Earth-core conditions is one of the few ways to gather important elastic and transport properties needed to uncover key mechanisms surrounding the geodynamo effect. Herein a new machine-learned ab-initio derived molecular-spin dynamics (MSD) methodology with explicit treatment for longitudinal spin-fluctuations is utilized to probe the dynamic phase-diagram of iron. This framework uniquely enables an accurate resolution of the phase-transition kinetics and Earth-core elastic properties, as highlighted by compressional wave velocity and adiabatic bulk moduli measurements. In addition, a unique coupling of MSD with time-dependent density functional theory enables gauging electronic transport properties, critically important for resolving geodynamo dynamics.

Keywords: Molecular dynamics; Density functional theory; Machine Learning; Phase transitions; Geodynamo

Permalink: https://www.hzdr.de/publications/Publ-37844
Publ.-Id: 37844


Critical review on production, characterization and applications of microalgal hydrochar: Insights on circular bioeconomy through hydrothermal carbonization

Supraja, K. V.; Doddapaneni, T. R. K. C.; Ramasamy, P. K.; Kaushal, P.; Ahammad, S. Z.; Pollmann, K.; Jain, R.

Exploitation of microalgal biomass as a valuable resource is hindered by the challenges associated with high downstream
processing costs, including biomass harvesting, drying, and product extraction. Direct utilization of microalgae as a solid fuel
source, soil conditioner, capacitor or adsorbent material raises environmental concerns. Hydrothermal carbonization (HTC)
is a highly efficient and promising technology for microalgal biomass conversion. This comprehensive review provides an indepth
understanding of the HTC reaction mechanisms involved in microalgal hydrochar production, shedding light on the
underlying processes and factors affecting the quality of hydrochar. HTC has the potential to improve fixed carbon content,
thermal stability and nutrient availability in the resulting hydrochar. Furthermore, this review explores the integration of HTC
with anaerobic digestion (AD) to establish a circular bioeconomy, thereby promoting sustainability in energy generation. The
synergistic combination offers a promising approach for the efficient utilization of microalgal biomass, where hydrochar can
serve as a renewable energy source while the aqueous fraction can be utilized as a nutrient-rich feedstock for biogas
production. By highlighting the potential benefits and futuristic directives associated with microalgal biomass valorisation
through HTC, this review aims to contribute to the development of sustainable waste management strategies for recovery of
value-added compounds from microalgae. Ultimately, this review strives to foster the transition towards a more
environmentally friendly and resource-efficient bioeconomy.

Keywords: Algae; Anaerobic digestion; Bioconversion; Biomass; Carbonization; Microorganisms; Nutrients; Soils

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  • Secondary publication expected from 01.10.2024

Permalink: https://www.hzdr.de/publications/Publ-37842
Publ.-Id: 37842


Rohstoffe und Ressourcen

Möckel, R.

Im Vortrag geht es um Resourcen und Rohstoffe, Einteilung, Kritikalität, circular economy, Recycling und Alternativen, sowie als Beispiel um Seltene Erden

  • Lecture (others)
    Schulische Veranstaltung, 27.10.2023, Chemnitz, Montessori-Gymnasium, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-37839
Publ.-Id: 37839


Mineralogy, Geochemistry, and Genesis of Agates from Chihuahua, Northern Mexico

Mrozik, M.; Götze, J.; Pan, Y.; Möckel, R.

The present study aimed to investigate the genesis and characteristics of some of the world-famous agate deposits in the state of Chihuahua, Mexico (Rancho Coyamito, Ojo Laguna, Moctezuma, Huevos del Diablo, Agua Nueva). Geochemical and textural studies of host rocks showed that all the studied deposits are related to the same rock type within the geological unit of Rancho el Agate andesite, a quartz-free latite that shows clear indications of magma mixing. As a result of their large-scale distribution and various differentiation processes, as well as transport separation, different textures and local chemical differences between rocks of different localities can be observed. These differences have also influenced the properties of SiO2 mineralization in the rocks. The mixing of near-surface fluids from rock alterations with magmatic hydrothermal solutions led to the accumulation of various elements in the SiO2 matrix of the agates, which were, on the one hand, mobilized during secondary rock alteration (Fe, U, Ca, K, Al, Si) and, on the other hand, transported with magmatic fluids (Zn, Sb, Si, Zr, Cr). Different generations of chalcedony indicate a multi-stage formation as well as multiple cycles of filling the cavities with fluids. The hydrothermal fluids are presumably related to the residual solutions of a rhyolitic volcanism, which followed the latitic extrusions in the area and probably caused the formation of polymetallic ore deposits in the Chihuahua area. The enrichment of highly immobile elements indicates the involvement of volatile fluids in the agate formation. The vivid colors of the agates are almost exclusively due to various mineral inclusions, which consist mainly of iron compounds.

Keywords: agate; chalcedony; trace elements; EPR spectroscopy; silica minerals; agate colors; cathodoluminescence; geology; Rancho Coyamito; Ojo laguna; Moctezuma; Agua Nueva

Permalink: https://www.hzdr.de/publications/Publ-37838
Publ.-Id: 37838


A new approach to model the fluid dynamics in sandwich packings

Franke, P.; Shabanilemraski, I.; Schubert, M.; Hampel, U.; Kenig, E. Y.

Sandwich packings represent new separation column internals, with a potential to intensify mass
transfer. They comprise two conventional structured packings with different specific geometrical surface areas.
In this work, the complex fluid dynamics in sandwich packings is modeled using a novel approach based on a onedimensional,
steady momentum balance of the liquid and gas phases. The interactions between the three present
phases (gas, liquid, and solid) are considered by closures incorporated into the momentum balance. The
formulation of these closures is derived from two fluid-dynamic analogies for the film and froth flow patterns.
The adjustable parameters in the closures are regressed for the film flow using dry pressure drop measurements
and liquid hold-up data in trickle flow conditions. For the froth flow, the tuning parameters are fitted to overall
pressure drop measurements and local liquid hold-up data acquired from ultra-fast X-ray tomography (UFXCT).
The model predicts liquid hold-up and pressure drop data with an average relative deviation of 16.4 % and 19 %,
respectively. Compared to previous fluid dynamic models for sandwich packings, the number of adjustable
parameters could be reduced while maintaining comparable accuracy.

Keywords: sandwich packings; modeling; tomography; fluid dynamics

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Permalink: https://www.hzdr.de/publications/Publ-37836
Publ.-Id: 37836


Data publication: Fluid Transport in Ordinary Portland Cement and Slag Cement from in-situ Positron Emission Tomography

Reiss, A.; Kulenkampff, J.; Fischer, C.
RelatedPerson: Gruhne, Stefan; RelatedPerson: Lösel, Dagmar; RelatedPerson: Schößler, Claudia

Supplemental Primary PET Data to Fluid Transport in Ordinary Portland Cement and Slag Cement from in-situ Positron Emission Tomography Reiss, A.; Kulenkampff, J.; Bar-Nes, G.; Fischer, C.; Emmanuel, S. Submitted to Cement and Concrete Research 02.11.24 Material and procedure are characterized in the paper. PET data are supplied in Interfile format (Original: Cradduck T.D., Bailey D.L., Hutton BF, Deconinck F., Busemann Sokole E., Bergmann H., Noelpp U.: “A standard protocol for the exchange of nuclear medicine image files. Nucl Med Commun; 10:703-713 (1989), used version: https://stir.sourceforge.net/links/petinterfile03.pdf). The interfile format includes an ASCII header file (.hv) and a binary file containing the volume data (.v). Import filters exist for many visualization frameworks (e.g. Matlab, Avizo); otherwise the binary data files can be imported as raw data, taking into account the format given in the header file. The header tags were extended for relevant experimental parameters of non-medical PET experiments and in this way serve as experimental protocol. List of data files: cem1_F-18.7z: 17 PET frames from the 18F intrusion experiment cem1_Cu-64.7z: 31 PET frames from the 64Cu intrusion experiment cem1_I-124.7z: 34 PET frames from the 124I intrusion experiment The PET data sets (LMFs) were acquired with a tilted ClearPET-scanner (Elysia-Raytest) with a vertical axis of the cylindrical FOV at HZDR. The “trues”-projections were corrected for attenuation and scatter with a procedure based on the STIR-library (https://stir.sourceforge.net, version 3.0, Kris Thielemans, Charalampos Tsoumpas, Sanida Mustafovic, Tobias Beisel, Pablo Aguiar, Nikolaos Dikaios, and Matthew W Jacobson, STIR: Software for Tomographic Image Reconstruction Release 2, Physics in Medicine and Biology, 57 (4), 2012 pp.867-883).

Keywords: Positron Emission Tomography (PET); Imbibition; Cement paste; Fluid transport

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Permalink: https://www.hzdr.de/publications/Publ-37835
Publ.-Id: 37835


Large-Scale Formation of DNA Origami Lattices on Silicon

Tapio, K.; Kielar, C.; Parikka, J. M.; Keller, A.; Järvinen, H.; Fahmy, K.; Jussi Toppari, J.

In recent years, hierarchical nanostructures have found applications in fields like diagnostics, medicine, nano-optics, and nanoelectronics, especially in challenging applications like the creation of metasurfaces with unique optical properties. One of the promising materials to fabricate such nanostructures has been DNA due to its robust self-assembly properties and plethora of different functionalization schemes. Here, we demonstrate the assembly of a two-dimensional fishnet-type lattice on a silicon substrate using cross-shaped DNA origami as the building block, i.e., tile. The effects of different environmental and structural factors are investigated under liquid atomic force microscopy (AFM) to optimize the lattice assembly. Furthermore, the arm-to-arm binding affinity of the tiles is analyzed, revealing preferential orientations. From the liquid AFM results, we develop a methodology to produce closely-spaced DNA origami lattices on silicon substrate, which allows further nanofabrication process steps, such as metallization. This formed polycrystalline lattice has high surface coverage and is extendable to the wafer scale with an average domain size of about a micrometer. Further studies are needed to increase the domain size toward a single-crystalline large-scale lattice.

Permalink: https://www.hzdr.de/publications/Publ-37834
Publ.-Id: 37834


Pulsed interactions unify reaction-diffusion and spatial nonlocal models for biological pattern formation

Colombo, E. H.; Martinez Garcia, R.; Calabrese, J.; López, C.; Hernández-García, E.

The emergence of a spatially-organized population distribution depends on the dynamics of the population and mediators of interaction (activators and inhibitors). Two broad classes of models have been used to investigate when and how self-organization is triggered, namely, reaction-diffusion and spatially nonlocal models. Nevertheless, these models implicitly assume smooth propagation scenarios, neglecting that individuals many times interact by exchanging short and abrupt pulses of the mediating substance. A recently proposed framework advances in the direction of properly accounting for these short-scale fluctuations by applying a coarse-graining procedure on the pulse dynamics. In this paper, we generalize the coarse-graining procedure and apply the extended formalism to new scenarios in which mediators influence individuals' reproductive success or their motility. We show that, in the slow- and fast-mediator limits, pulsed interactions recover, respectively, the reaction-diffusion and nonlocal models, providing a mechanistic connection between them. Furthermore, at each limit, the spatial stability condition is qualitatively different, leading to a timescale-induced transition where spatial patterns emerge as mediator dynamics becomes sufficiently fast.

Keywords: self-organization; population dynamics; pattern formation; animal communication

Permalink: https://www.hzdr.de/publications/Publ-37832
Publ.-Id: 37832


Test Center Location Problem: A bi-objective Model and Algorithms

Davoodi Monfared, M.; Calabrese, J.

The optimal placement of healthcare facilities, including the placement of diagnostic test centers, plays a pivotal role in ensuring efficient and equitable access to healthcare services. However, the emergence of unique complexities in the context of a pandemic, exemplified by the COVID-19 crisis, has necessitated the development of customized solutions. This paper introduces a bi-objective integer linear programming model designed to achieve two key objectives: minimizing average travel time for individuals visiting testing centers and maximizing an equitable workload distribution among testing centers. To address this problem, we propose a customized local search algorithm based on the Voronoi diagram. Additionally, we employ an $\epsilon$-constraint approach, which leverages the Gurobi solver. We rigorously examine the effectiveness of the model and the algorithms through numerical experiments and demonstrate their capability to identify Pareto-optimal solutions. We show that while the Gurobi performs efficiently in small-size instances, our proposed algorithm outperforms it in large-size instances of the problem.

Keywords: Testing center; Facility location; k-balance; k-median; Bi-objective optimization

Permalink: https://www.hzdr.de/publications/Publ-37831
Publ.-Id: 37831


Preparation of Volborthite by a Facile Synthetic Chemical Solvent Extraction Method

Sánchez-Loredo, M. G.; Palomares-Sánchez, S. A.; Labrada-Delgado, G. J.; Helbig, T.; Chekhonin, P.; Ebert, D.; Möckel, R.; Owusu Afriyie, J.; Kelly, N.

In this work, the extraction of vanadium (V) ions from an alkaline solution using a commercial quaternary ammonium salt and the production of metal vanadates through precipitation stripping were carried out. The crystallization of copper vanadates from the extracts was performed using a solution containing a copper(II) source in concentrated chloride media as a stripping agent. In an attempt to control growth, a stabilizing polymer (polyvinylpyrrolidone, PVP) was added to the stripping solution. The structural characteristics of the crystallized products, mainly copper pyrovanadate (volborthite, Cu3V2O7(OH)2·(H2O)2) nanoflakes and nanoflowers and the experimental parameter influencing the efficiency of the stripping process were studied. From the results, the synthesis of nanostructured vanadates is a simple and versatile method for the fabrication of valuable three-dimensional structures providing abundant active zones for energy and catalytic applications.

Keywords: vanadium(V) extraction; anion exchange; quaternary ammonium salt; precipitation stripping; nanostructured vanadates; volborthite; polyvinylpyrrolidone

Permalink: https://www.hzdr.de/publications/Publ-37830
Publ.-Id: 37830


Geochemistry and formation of agate-bearing lithophysae in Lower Permian volcanics of the NW-Saxonian Basin (Germany)

Götze, J.; Möckel, R.; Pan, Y.; Müller, A.

Geochemical and mineralogical investigations of the Lower Permian Kemmlitz rhyolite within the NW-Saxonian Basin
(Germany) and associated lithophysae (high-temperature crystallization domains) as well as agates were carried out to
constrain the genesis and characteristics of these volcanic rocks and the origin of the agate-bearing lithophysae. The
volcanic rocks of rhyolitic composition are dominated by quartz, sanidine, and orthoclase and most likely derive from lava
flows. Agate-bearing lithophysae were exclusively formed in a glassy facies (pitchstone) of the rhyolites, which was
afterwards altered to illite-smectite mixed-layer clays. The results of this study show that agate formation can be related to
the alteration of the volcanic rocks accompanied by the infill of mobilized silica into cavities of lithophysae. Fluid inclusion
studies point to temperatures of agate formation above 150 °C, indicating that the mobilization and accumulation of silica
started already during a late phase of or soon after the volcanic activities. Remarkable high concentrations of B (29 ppm),
Ge (> 18 ppm), and U (> 19 ppm) as well as chondrite-normalized rare earth element (REE) distribution patterns of the
agates with pronounced negative Eu-anomalies, slightly positive Ce-anomalies and enriched heavy rare earth elements
(HREE) indicate interactions of the host rocks and transport of SiO2 with magmatic volatiles (F/Cl, CO2) and heated
meteoric water. Characteristic yellow cathodoluminescence (CL), heterogeneous internal textures as well as high defect
density of micro- and macrocrystalline quartz detected by electron paramagnetic resonance (EPR) spectroscopy point to
crystallization processes via an amorphous silica precursor under non-equilibrium conditions.

Keywords: Agate; Geochemistry; Lithophysae; Permian rhyolites; Quartz

Permalink: https://www.hzdr.de/publications/Publ-37829
Publ.-Id: 37829


Neutron radiography of liquid foam structure near a vertical wall

Skrypnik, A.; Knüpfer, L.; Trtik, P.; Tholan, V.; Parkes, S.; Heitkam, S.

At a solid boundary, the structural formation of bubbles is different from that in the bulk of a liquid foam. The presence of a solid boundary imposes additional constraints, resulting in a crystalline arrangement of the bubbles. For dry and monodisperse foam, the Kelvin and Fejes-T ́ oth structure is expected in the vicinity of the wall, while a random ordering should occur in the bulk. In this study, we investigate the transition from a crystalline to a random structure near a vertical wall located in the middle of a flat foam cell. The corresponding layering of the liquid was quantified by measuring the distribution of liquid fraction within the cell using neutron radiography. The amplitude of the liquid fraction distribution and its decay with distance from the solid boundary were correlated with the foam bubble size and polydispersity. Furthermore, by applying forced drainage, we measured the corresponding permeability and wetting front velocity near the vertical wall. We found that the crystalline sorting reduces the permeability and wetting front velocity compared to a randomly packed foam.

Keywords: Neutron Radiography; Foam

Permalink: https://www.hzdr.de/publications/Publ-37827
Publ.-Id: 37827


A comparative study on the measurement of surface bubble size distributions in dry aqueous foams using optical methods

Knüpfer, L.; Eckert, K.; Heitkam, S.

The measurement of bubble sizes in aqueous foams based on images of the surface is a typical method used in laboratory and industrial scales. In this article the relationship between the size distribution of the facet areas and the bubble size of wall-touching bubbles is investigated. To achieve this an invasive sampling approach is used for in-situ collection of wall-touching bubbles in dry foams, while the surface is imaged in parallel. Bubble and facet
size distributions are obtained using automated image processing. It is shown that sharp peaks in the bubble size distribution will appear smoother in the facet size distribution. This results in an overestimation of polydispersity by the surface measurements. Furthermore, it is observed that the mean equivalent diameter of the facets is on average 6% smaller than the bubble diameter obtained using the sampling method. An approach proposed by
Wang and Neethling (Colloids Surf. A: Physicochem. Eng. Asp. 33, 73-81 (2009)) gives a good approximation of the relation between facet and bubble size and can be used to reduce potential uncertainties in surface based bubble size measurements.

Keywords: Foam; Bubble Size; Optical Measurement

Permalink: https://www.hzdr.de/publications/Publ-37825
Publ.-Id: 37825


Investigating the effect of multiple particle properties on the separation of ultrafine particles via froth flotation by means of MLA and multivariate Tromp maps

Sygusch, J.; Rudolph, M.

Although, the wettability is the most prominent separation feature in froth flotation, other particle properties, such as size or morphology also affect the separation process since it includes a number of complex micro processes with specific particle-bubble interactions that occur in the pulp and in the froth phase. A novel separation apparatus is used that combines the advantages of a mechanical flotation cell (high particle-bubble collision rate) with those from a flotation column (fractionating effect of the deep froth). A well-characterised model system of ultrafine particles (< 10 µm), consisting of glass spheres and glass fragments as the floatable fraction and magnetite as the non-floatable fraction is used for the separation tests. Based on image analysis bivariate tromp maps are computed which reveal the combined effect of the particle properties of size and shape on the separation behaviour of ultrafine particles.

Keywords: Ultrafine particles; Multidimensional separation; Flotation; Multivariate Tromp maps

  • Poster
    Flotation '23, 06.-09.11.2023, Cape Town, South Africa

Permalink: https://www.hzdr.de/publications/Publ-37824
Publ.-Id: 37824


Unit and Integration testing in modularized Julia package eco-systems

Ehrig, S.

In high-energy physics, we want to simulate complex physical processes that require computational resources of the fastest HPC systems in the world. In order to fully use the computational resources, software that is maintainable, performant and extensible is required. To achieve these goals, automated testing is essential.
Modern Julia HEP software is modularized into sub-packages to improve maintainability and extensibility. This creates new challenges for automated testing. Unit tests and integration tests are required. If the code of one package is changed, unit tests ensure that the package is still working, whereas integration tests ensure that in dependent packages no functionality break is caused by the change.
Using the QED.jl [1] project as an example, I will demonstrate how we implemented unit and integration tests for the main QED.jl package and its sub-packages.

[1] https://github.com/QEDjl-project/QED.jl

Keywords: Julia; Integration Tests; QED.jl; Automatic Testing

  • Open Access Logo Lecture (Conference)
    JuliaHEP 2023 Workshop, 06.-09.11.2023, Erlangen Centre for Astroparticle Physics, Deutschland

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Permalink: https://www.hzdr.de/publications/Publ-37823
Publ.-Id: 37823


Ion emission from warm dense matter produced by irradiation with a soft x-ray free-electron laser

Krása, J.; Burian, T.; Hájková, V.; Chalupský, J.; Jelínek, Š.; Frantálová, K.; Krupka, M.; Kuglerová, Z.; Kumar Singh, S.; Vozda, V.; Vyšín, L.; Smid, M.; Perez-Martin, P.; Kühlman, M.; Pintor, J.; Cikhardt, J.; Dreimann, M.; Eckermann, D.; Rosenthal, F.; Vinko, S. M.; Forte, A.; Gawne, T. D.; Campbell, T.; Ren, S.; Shi, Y.; Hutchinson, T.; Humphries, O. S.; Preston, T.; Makita, M.; Nakatsutsumi, M.; Pan, X.; Köhler, A.; Harmand, M.; Toleikis, S.; Falk, K.; Juha, L.

We report on an experiment performed at the FLASH2 free-electron laser (FEL) aimed at producing warm dense matter via soft x-ray isochoric heating. In the experiment, we focus on study of the ions emitted during the soft x-ray ablation process using time-of-flight electron multipliers and a shifted Maxwell–Boltzmann velocity distribution model. We find that most emitted ions are thermal, but that some impurities chemisorbed on the target surface, such as protons, are accelerated by the electrostatic field created in the plasma by escaped electrons. The morphology of the complex crater structure indicates the presence of several ion groups with varying temperatures. We find that the ion sound velocity is controlled by the ion temperature and show how the ion yield depends on the FEL radiation attenuation length in different materials.

Related publications

  • Open Access Logo Matter and Radiation at Extremes 9(2024)1, 016602
    Online First (2023) DOI: 10.1063/5.0157781

Permalink: https://www.hzdr.de/publications/Publ-37822
Publ.-Id: 37822


Synthese und Charakterisierung von Lanthanoid- und Actinoid-Zirkonaten

Richter, S.

Since 1954, over 390,000 metric tons of nuclear waste have been produced by
commercial nuclear power stations worldwide. Spent nuclear fuel does not only contain
uranium, but also various fission and neutron activation products such as plutonium, americium,
and curium. If they were released into the biosphere, they could present a health hazard for
humans and animals. Therefore, the isolation of nuclear waste from the environment over
long periods of time becomes necessary. Many countries favor deep geological repositories
with a multi-barrier system. The immobilized radioactive material will be stored in dry, corrosion
resistant metal or concrete containers which are surrounded by various buffer and back-fill
materials as well as the host rock itself. Hereby, the waste matrix presents the first barrier
preventing the release of radionuclides into the environment.

Related publications

  • Lecture (others) (Online presentation)
    Women in Nuclear Germany Preis 2023, 29.09.2023, Grafenrheinfeld, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-37821
Publ.-Id: 37821


Synthesis and characterization of lanthanide and actinide doped zirconates

Richter, S.; Gilson, S.; Braga Ferreira Dos Santos, L.; Stumpf, T.; Huittinen, N. M.

Zirconium dioxide is a corrosion product of the Zircaloy cladding, which houses the nuclear fuel pellets. It can form solid solutions with uranium as well as fission and activation products. Moreover, ZrO2 and other zirconium bearing crystalline solid phases, such as pyrochlores, are being investigated as potential host matrices for the immobilization of radionuclides present in high-level waste streams. Zirconate pyrochlores are characterized by high chemical durability and radiation resistance. However, upon irradiation, some zirconate pyrochlores undergo a phase transition to the defect fluorite crystal structure, or become amorphous, which could hamper a continued immobilization of radionuclides in the solid matrix. In the current study, the influence of different synthesis methods on the phase purity of Ce/Nd-co-doped zirconates was investigated. Furthermore, phase transformations occurring in zirconate phases as a result of different U/Y-dopant concentrations were studied.
Ce/Nd-co-doped zirconates and U/Y-co-doped zirconates were obtained via coprecipitation. In addition, identical zirconate compositions were synthesized using three different solid-state methods involving manual mixing with a mortar and pestle, mechanical mixing with a ball mill or magnetic mixing in a slurry. PXRD measurements of all solids were done for crystal structure analysis.
For the Ce/Nd-co-doped zirconates synthesized via coprecipitation, rather phase-pure monoclinic, cubic defect fluorite and cubic pyrochlore structures could be obtained. The samples synthesized via solid-state methods were found to contain multiple phases due to insufficient mixing of the educts. Manual mixing led to the most phase-pure ceramics and was therefore chosen for further investigation. It was shown that re-sintering the ceramics as well as longer grinding time resulted in enhanced phase purity. Furthermore, an increase of the Nd-content also correlates with an improved phase purity.
PXRD data of the U-doped zirconates showed a peak-shift towards lower two theta values with increasing U-concentration. At the same dopant concentrations, U/Y-co-doped zirconates showed higher symmetry crystal structures than Ce/Nd-co-doped zirconates. This is caused by the larger ionic radius of U4+ compared to Ce4+ allowing for the stabilization of higher symmetry crystal structures at equal dopant concentrations.

Related publications

  • Poster
    NEA Global Forum Rising Stars Workshop in Nuclear Education, Science, Technology and Policy, 21.-22.09.2023, Boston, USA

Permalink: https://www.hzdr.de/publications/Publ-37820
Publ.-Id: 37820


Microbial immobilization of technetium-99

Cardaio, I.; Mayordomo, N.; Cherkouk, A.; Stumpf, T.; Müller, K.

Iron-reducing bacteria perform anaerobic respiration by coupling the oxidation of organic molecules to the reduction of Fe(III)-species via dissimilatory iron reduction. This leads to the formation of ferrous minerals, such as vivianite [Fe(II)₃(PO₄)₂], pyrite (Fe(II)S₂), siderite (Fe(II)CO₃) and jahnsite [(CaMn(II))Fe(II)₂Fe(III)₂(PO₄)₄(OH)₂·(H₂O)₈], which, depending on oxygen exposure and the cultivation nutrients, may oxidize and generate magnetite (Fe(II)Fe(III)₂O₄) and/or hematite (Fe(III)₂O₃). The aforementioned secondary Fe(II)-minerals may promote the reduction of radionuclides such as the β-emitter technetium-99 (⁹⁹Tc).
⁹⁹Tc is a long lived fission product (t(1/2) = 2.13 × 10⁵ years) of ²³⁵U and ²³⁹Pu. It can also originate from the decay chain of ⁹⁹₄₂Mo, (Mo-99 → ₄₃Tc-99m + e⁻, 66 h; ₄₃Tc-99m → ₄₃Tc-99 + γ, 6.02 h). In the environment, Tc is prevalent as Tc(VII) or Tc(IV). Due to the common use of Tc-99m in radiodiagnostics, water contamination through the highly hydrosoluble pertechnetate Tc(VII)O₄⁻ must be considered. Nevertheless, Tc can be immobilized by reducing it to the low-soluble oxide Tc(IV)O₂.
This work aims at unravelling the interactions between pivotal anaerobic bacteria (e.g. the iron reducer Desulfitobacterium sp. G1-2) that can be found in bentonite (a clay potentially used as a barrier material for deep geological repositories) and Tc(VII), to achieve its reduction to Tc(IV) and preserve the environmental safeguard.
The authors acknowledge the German Federal Ministry of Education and Research (BMBF) for the financial support of NukSiFutur TecRad young investigator group (02NUK072).

Keywords: microorganisms; technetium; iron minerals; deep geological repositories

  • Lecture (Conference)
    HZDR Science Conference 2023, 15.-16.11.2023, Helmholtz-Zentrum Dresden-Rossendorf e. V., Deutschland

Permalink: https://www.hzdr.de/publications/Publ-37819
Publ.-Id: 37819


Molecular Adhesion of a Pilus-derived Peptide Involved in Pseudomonas aeruginosa Biofilm Formation on non-polar ZnO Surfaces

Prüßner, T.; Meinderink, D.; Zhu, S.; Orive, A. G.; Kielar, C.; Huck, M.; Steinrück, H.-G.; Keller, A.; Grundmeier, G.

Bacterial colonization and biofilm formation on abiotic surfaces are initiated by the adhesion of peptides and proteins. Understanding the adhesion of such peptides and proteins at a molecular level thus represents an important step toward controlling and suppressing biofilm formation on technological and medical materials. This study investigates the molecular adhesion of a pilus-derived peptide that facilitates biofilm formation of Pseudomonas aeruginosa, a multidrug-resistant opportunistic pathogen frequently encountered in healthcare settings. Single-molecule force spectroscopy (SMFS) was performed on chemically etched ZnO(112̅0)surfaces to gather insights about peptide adsorption force and its kinetics. Metal-free click chemistry for the fabrication of peptide-terminated SMFS cantilevers was performed on amine-terminated gold cantilevers and verified by X-ray photoelectron spectroscopy (XPS) and polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS). Atomic force microscopy (AFM) and XPS analyses reveal stable topographies and surface chemistries of the substrates that are not affected by SMFS. Rupture events described by the worm-like chain model (WLC) up to 600 pN were detected for the non-polar ZnOsurfaces. The dissociation barrier energy at zero force ΔG(0), the transition state distance xband bound-unbound dissociation rate at zero force koff(0) for the single crystalline substrate indicate that coordination and hydrogen bonds dominate thepeptide/surfaceinteraction.

Keywords: Adsorption; Bell-Evans theory; peptides; Single-molecule studies; ZnO

Permalink: https://www.hzdr.de/publications/Publ-37817
Publ.-Id: 37817


Wechselwirkung von Tc mit Eisen(II)phosphaten

Börner, C.

Technetium (Tc, Ordnungszahl 43) ist das leichteste Element, welches keine stabilen Isotope besitzt. Das Hauptvorkommen von Tc stammt aus anthropogen Quellen, wie abgebrannten Brennstoffen aus Kernkraftwerken, Atomwaffentests, sowie nuklearen Unfällen. Das Radionuklid Tc-99 entsteht hierbei als ein Spaltprodukt mit rund 6% Ausbeute und ist somit im nuklearen Abfall vorhanden, welcher im geologischen Tiefenendlager für 1Mio Jahre gelagert werden soll. Zusätzlich wird Tc-99m als Kontrastmittel in der Medizindiagnostik angewendet, welches zu Tc-99 zerfällt und in das Abwasser gelangt. Aus diesen Gründen besteht die Notwendigkeit, die Interaktion von Tc mit Mineralen zu untersuchen, um Möglichkeiten zur immobilisierung zu finden. Das in Wasser mobile Pertechnetat (Tc(VII)O₄⁻) kann durch Sorption und Reduktion zu schwerlöslichem TcO₂ an Fe(II)-haltigen Mineralen zurückgehalten werden.
In dieser Arbeit wurde die Retention an Vivianit (Fe₃(PO₄)₂·8 H₂O) untersucht. Das türkisfarbene Mineral wurde erfolgreich über eine Präzipitation unter Inertgas synthetisch hergestellt. Mittels XRD und Raman konnte die Übereinstimmung mit Referenzspektren für Vivianit bei dem Gleichwichts-pH-Wert pH 6,7 festgestellt werden. Bei einer Verringerung des pH-Wertes auf pH 5 ist Vivianit weiterhin stabil, während bei einem pH-Wert von pH 12 eine Phasenänderung zu Amakinit (Fe(II)(OH)₂) stattfindet. TcO₄− kann durch suspendiertes Vivianit aus der Lösung bei pH 8 im Verlauf von 20 d entfernt werden, während bei pH 6,5 die Immobilisierung nicht stattfindet. Mit steigender Konzentration an Vivianit in der Lösung steigt auch die Entfernung von TcO₄− bei pH 6,5. Bei pH 8 hingegen sinkt die Entfernung mit größerer Mineralkonzentration bei 3 d Sorptionszeit, wobei nach 10 d Tc in der Lösung nicht mehr detektierbar ist. Vermutet wird die Bildung löslicher Tc-phosphate. Mit steigendem pH-Wert steigt die Immobilisierung von Tc aus der Lösung. Bei niedrigen pH-Werten ist die geringe Sorption auf die hohe Löslichkeit des Minerals und damit auf die kinetisch gehinderte Homoreduktion von Tc(VII) durch gelöstes Fe(II) zurückzuführen. Die Untersuchung der Oberfläche mit XPS deutet auf eine vollständige Reduktion von Tc(VII) zu Tc(IV) hin. Die weiterhin hohe Löslichkeit des Tc untermauert die Theorie der Tc-phosphatverbindungen.
Ein Anstieg an oxidischen Verbindungen, welche auf TcO₂ hindeuten, wurden einzig bei pH 12 detektiert. Die Reoxidationsexperimente in dieser Arbeit haben eine geringe Remobilisierung von Technetium unter oxidierenden Bedingungen nach 30 d gezeigt. Im Gegenteil konnte sogar eine Steigerung der Immobilisierung bei niedrigen pH-Werten festgestellt werden.

Keywords: Technetium; Vivianite; Immobilization; Re-oxidation; Reduction

  • Master thesis
    Technische Universität Dresden, 2023
    Mentor: Prof. Thorsten Stumpf and Dr. Natalia Mayordomo

Permalink: https://www.hzdr.de/publications/Publ-37815
Publ.-Id: 37815


Application of dissimilatory iron reduction by a novel Desulfitobacterium sp. isolate for Tc-99 immobilization

Cardaio, I.; Mayordomo, N.; Stumpf, T.; Cherkouk, A.; Müller, K.

Dissimilatory iron reduction is an anaerobic respiratory pathway, wherein ferric (Fe³) reducers couple the oxidation of organic acids, sugars and aromatic hydrocarbons to the reduction of Fe³-species [1]. This may lead to the formation of minerals such as magnetite (Fe²Fe³₂O₄) and siderite (Fe²CO₃) [2], which, in turn, can mediate the reduction of soluble pollutants as pertechnetate (Tc⁷O₄⁻) to insoluble oxides (Tc⁴O₂) [3].
The genus Desulfitobacterium contains obligate anaerobic bacteria that are capable of utilizing a wide range of electron acceptors, including nitrite, sulfite, metals, humic acids and halogenated organic compounds [4].
In this work, the Fe³ reduction of a Desulfitobacterium species was examined. The microorganism has been isolated from bentonite, which is potentially used as geotechnical barrier in deep geological repositories for radioactive waste [5].
The cultivation conditions included DSMZ 579 medium with Na-acetate as electron donor to reduce Fe³ citrate [6]. During cultivation, the formation of white precipitates was observed. The phases were collected both under aerobic and anaerobic conditions and repeatedly investigated by using Raman microscopy and powder X-ray diffraction (pXRD). It was noticed that the phases turned immediately to blue-greenish overnight under oxic conditions. Both Raman spectra and pXRD diffractograms can be attributed to vivianite (Fe²₃(PO₄)₂). Moreover, Raman spectra revealed the possible presence of pyrite (Fe²S₂), siderite, magnetite and hematite (Fe³₂O₃). These results suggest the ability of the bacterium of forming different Fe²-minerals. Notwithstanding, both methods indicate the change of the chemistry of the precipitates according to environmental factors. The Fe²-minerals formation by this microorganism depending on Fe³-compounds and background electrolytes is currently ongoing. The biogenic ferrous minerals will be studied regarding the reduction of Tc⁷O₄⁻.
The authors acknowledge the German Federal Ministry of Education and Research (BMBF) for the financial support of NukSiFutur TecRad young investigator group (02NUK072).

Keywords: microorganisms; iron minerals; technetium; deep geological repositories

  • Lecture (Conference)
    ChemTUgether 2023 & Alumni Meeting 2023, 29.09.2023, TU Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-37814
Publ.-Id: 37814


Tc(VII) reductive immobilization by S(-II) pre-sorbed on alumina

Garcia-Gomez, S.; Börner, C.; Gimenez, J.; Casas, I.; Llorca, J.; de Pablo, J.; Müller, K.; Mayordomo, N.

Tc-99 is a fission product of U-235 and Pu-239 with a long half-live (2.14∙10⁵ years). Under oxidizing conditions, Tc main species (Tc(VII)O₄⁻) exhibits a high solubility and hardly interacts with minerals. In contrast, under reducing conditions, Tc(IV) presents a more limited mobility, either because Tc(IV) interacts with minerals or Tc(IV)O₂ is formed [1]. However, the formation of Tc(IV)O₂ is not sufficient to ensure the immobilization of Tc, since when it is in contact with O₂, the reoxidation of Tc(IV) to Tc(VII) would be thermodynamically favorable. In contrast, the formation of Tc(IV) polysulfide species (such as TcSx or Tc₂S7) could inhibit Tc oxidation under oxidizing conditions [2]. Therefore, S(-II) seems a promising candidate to immobilize Tc. Sulfide would be present in the nuclear waste repository due to the addition of fly ash in the concrete, as well as the presence of minerals such as pyrite (FeS₂). It has been proven for Fe(II) that Tc(VII) reduction is more favorable when Fe(II) takes part in the mineral structure or it is sorbed on a surface than when Tc(VII) reduction is carried by dissolved Fe(II) homoreduction) [3]. We have recently showed that Tc(VII) heteroreduction (reduction occurring at the mineral-water interface) by Fe(II) pre-sorbed on alumina nanoparticles is highly efficient [4].
Thus, in this work, we have studied kinetically as a function of pH: i) S(-II) sorption on alumina, and ii) subsequent Tc uptake promoted by S(-II) pre-sorbed on alumina. We have also focused on the effect of different sulfide sources on Tc(VII) reduction. All the experiments were performed in a N₂ glove box free of CO₂ and O₂ (< 2 ppm). The alumina
nanoparticles used in the experiments has been previously characterized with 127 m² /g N₂ BET and pH 9 as isoelectric point pH [5]. For the batch sorption experiments, suspensions of alumina (0.5 g/L) containing 50 μM of NaHS at pH 5.3, 6.7 and 7.7 were prepared and shaken for two days. Then, KTcO₄ was added to the suspensions to obtain 5 μM of KTcO₄. Subsequently, the suspensions were placed in a horizontal shaker. The suspension pH was monitored frequently and readjusted when needed. Samples were taken periodically and centrifuged at 14,000 rpm for 45 min. The Tc concentration in the supernatant solution was measured by liquid scintillation counter to determine the percentage of Tc removed.
Figure 1 shows the uptake of Tc in % as a function of time and pH. Tc removal increases with decreasing pH. This is in agreement with the highest anion sorption on alumina nanoparticles at lower pH, when alumina surface is positive charged [5]. The maximum Tc retention is 70% at pH 5.3, being complete after one day of contact. Whereas at higher pH values, Tc removal is significantly lower, i.e., 10% at pH 6.7 and 5% at pH 7.7. It is noteworthy to mention that the NaHS reactant used for the experiments in Figure 1. was partially oxidized. Despite of its oxidation, reduction of Tc(VII) yield at pH 5.3 was above 70% after one day of contact.

Further contact experiments have been performed to isolate the contribution of S(-II) in Tc(VII) heteroreduction, and the effect of the sulfide source on Tc removal. Raman microscopy and X-ray absorption spectroscopy have been used to determine the changes occurring at a molecular level when Tc(VII) is heteroreduced by S(-II).

Acknowledgements: The authors acknowledge the Spanish Ministry of Research and Universities for the abroad internship fellowship (PRE2018-085618) and the project (ENE2017-83048-R). Part of this work was financially supported by the German Federal Ministry of Education and Research (BMBF) NukSiFutur TecRad young investigator group (02NUK072).

Keywords: Technetium; Sulfide; Reduction; Removal; Scavenging

  • Poster
    18th International Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere (Migration), 25.-29.09.2023, Nantes, France

Permalink: https://www.hzdr.de/publications/Publ-37813
Publ.-Id: 37813


Fundamental investigations of actinide immobilization by incorporation into solid phases relevant for final disposal

Huittinen, N. M.; Braga Ferreira Dos Santos, L.; Gilson, S.; Hennig, C.; Lender, T.; Marquardt, J.; Murphy, G.; Nießen, J.; Peters, L.; Richter, S.

This contribution provides an overview of a current research network funded by the German Federal Ministry of Education and Research (BMBF), entitled “Fundamental investigations of actinide immobilization by incorporation into solid phases relevant for final disposal” – AcE. The AcE project aims at understanding the incorporation and immobilization of actinides (An) in crystalline, repository-relevant solid phases, such as zirconia (ZrO2) and UO2, but also in zircon (ZrSiO4), pyrochlores (Ln2Zr2O7) and orthophosphates of the monazite type (LnPO4), which may find use as host matrices for the immobilization and safe disposal of high-level waste streams.
Recent studies by the AcE-project consortium, addressing the structure, properties, and the radiation tolerance of monazites and Zr(IV)-based solid phases containing actinides or their surrogates from the lanthanide series will be presented. Material synthesis strategies in the AcE project have aimed at generating single-phase solid solutions in the form of polycrystalline powders, dense ceramics, and single crystals. Structural studies using powder X-ray diffraction at ambient conditions, but also at high temperatures and pressures have been complemented with a wide range of microscopic and spectroscopic techniques to address differences between the host- and dopant environments in the solid matrices at ambient and extreme conditions. The radiation tolerance of the synthetic solid phases have been investigated by combining external heavy-ion irradiation of inactive Ln-doped materials and in situ self-irradiation of 241Am-doped Zr(IV)-phases with monoclinic, cubic defect fluorite and pyrochlore structures. The latter experiments have been conducted in joint efforts with the Joint Research Center in Karlsruhe within the ActUsLab programme.

Related publications

  • Poster
    Actinides 2023, 04.-08.06.2023, Golden Colorado, United States

Permalink: https://www.hzdr.de/publications/Publ-37809
Publ.-Id: 37809


Interaction of Marangoni and buoyancy effects during mass transfer at liquid interfaces

Schwarzenberger, K.; Köllner, T.; Boeck, T.; Eckert, K.

Complex flow patterns frequently emerge when a surface active substance undergoes mass transfer between an organic and an aqueous phase. At the same time, density effects can play a major role, e.g. during the partial dissolution of floating organic droplets \cite{cejkova2019dancing}. The resulting droplet ensemble dynamics can be understood by highly resolved measurements of the transient velocity field via particle image velocimetry (PIV). At bubbles in a shear flow, the interaction of the Marangoni effect with the surrounding bulk flow leads to the formation of a circulating flow at the bubble surface \cite{eftekhari2021interfacial}. Bubbles or droplets which are placed in a vertical concentration gradient of a surface-active solute show an intriguing interaction of solutal Rayleigh and Marangoni convection in the form of relaxation oscillations \cite{mokbel2018information}. Depending on the distance between multiple droplets, convective interaction can lead to collective relaxation oscillations over the whole ensemble.

A repeated coupling of Rayleigh and Marangoni effects likewise can occur during mass transfer of a solute at a planar interface between two liquid layers. Solutal Rayleigh instability is able to provoke intense Marangoni-driven spreading motions at the interface, even if the mass transfer system is primarily stable towards stationary Marangoni convection \cite{koellner2016eruptive}. A more detailed study \cite{koellner2023eruptive} unravels the underlying mechanisms by a defined variation of key parameters: the layer height and the initial concentration of the solute. The flow structures are analyzed in detail by experiments and elaborate three-dimensional simulations of the two liquid layers. The flow in the interfacial region decouples from the bulk volume flow since for deep layers, the interfacial velocity gets invariant under a change of the nondimensional layer height. Due to the additional convection, mass transfer is strongly enhanced in comparison to the purely diffusive process. This can significantly increase the efficiency of liquid-liquid extraction processes.

\bibitem{cejkova2019dancing} J.~{\v{C}}ejkov{\'a}, K.~Schwarzenberger, K.~Eckert, S.~Tanaka, Colloids and Surfaces A, 566, 141 (2019)
\bibitem{mokbel2018information} M.~Mokbel, K.~Schwarzenberger, S.~Aland, K.~Eckert, Soft Matter, 14, 9250 (2018)
\bibitem{eftekhari2021interfacial} M.~Eftekhari, K.~Schwarzenberger, S.~Heitkam, K.~Eckert, Journal of Colloid and Interface Science, 599, 837 (2021)
\bibitem{koellner2016eruptive} T.~K{\"o}llner, K.~Schwarzenberger, K.~Eckert, T.~Boeck, Journal of Fluid Mechanics, 791, R4 (2016)
\bibitem{koellner2023eruptive} T.~K{\"o}llner, K.~Schwarzenberger, K.~Eckert, T.~Boeck, in progress (2023)

  • Lecture (Conference)
    Dynamic Days Europe 2023 Conference, 03.-08.09.2023, Neapel, Italien

Permalink: https://www.hzdr.de/publications/Publ-37807
Publ.-Id: 37807


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

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

The shear stress of an axisymmetric flow field triggers a nonuniform distribution of adsorbed
surfactants at the surface of a rising bubble. This creates a surface tension gradient that
counteracts the viscous shear stress of the flow and thus reduces the mobility of the interface.
However, in technological processes the flow field often is asymmetric, e.g. due to the
vorticity in the flow. Under such conditions, the interface experiences an unbalanced shear
stress that is not free of curl, i.e. it cannot be compensated by the redistribution of the surfactants
at the interface (Vlahovska et al., 2009). Here, we conduct model experiments with
a bubble at the tip of a capillary placed in a defined asymmetric flow field, in the presence of
surfactants and nanoparticles. Unlike classical surfactants, nanoparticles adsorb irreversibly
at the bubble surface. Thus, a different interaction between the bulk flow and the interface
is expected. In this study, we show a direct experimental observation of the circulating flow
at the interface under asymmetric shear stress (Eftekhari et al., 2021a,b). The results indicate
that the interface remains mobile regardless of the surfactant concentration. Additionally, we
show that the nanoparticle-laden interface adopts a solid-like state and resists the interfacial
flow upon surface compression. Our results imply that the immobilization of the interface
can be described by the ratio of the interfacial elasticity to the bulk viscous forces.
Vlahovska, P. M., Bławzdziewicz, J., & Loewenberg, M. (2009). Small-deformation theory for a
surfactant-covered drop in linear flows. J.Fluid Mech., 624, 293.
Eftekhari, M., Schwarzenberger, K., Heitkam, S., & Eckert, K. (2021). Interfacial flow of a surfactant-
laden interface under asymmetric shear flow. J. Colloid Interface Sci., 599, 837.
Eftekhari, M., Schwarzenberger, K., Heitkam, S., Javadi, A., Bashkatov, A., Ata, S., & Eckert, K.
(2021). Interfacial behavior of particle-laden bubbles under asymmetric shear flow. Langmuir,
37, 13244.

  • Lecture (Conference)
    93rd Annual Meeting of the International Association of Applied Mathematics and Mechanics, 30.05.-02.06.2023, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-37805
Publ.-Id: 37805


Grenzflächenkonvektion an Tropfen und Blasen

Schwarzenberger, K.; Eftekhari, M.; Mokbel, M.; Weber, N.; Aland, S.; Eckert, K.

Die Grenzflächenkonvektion (Marangoni-Effekt) ist eine kleinskalige Strömung, die
durch Gradienten der Grenzflächenspannung verursacht wird. Sie beeinflusst den
Stofftransport und die Strömungsbedingungen in einer Vielzahl von natürlichen und
technologischen Prozessen. Grenzflächenkonvektion kann an Tropfen oder Blasen
beobachtet werden, die in einem vertikalen Konzentrationsgradienten einer gelösten
grenzflächenaktiven Substanz platziert werden [1,2]. Die Frequenz der
Strömungswirbel wird direkt vom anliegenden Konzentrationsgradienten des
gelösten Stoffs bestimmt. Mehrere benachbarte Tropfen oder Blasen (Abb. 1, links)
synchronisieren sich durch konvektive Interaktion zu Oszillationen über das gesamte
Ensemble. Die genannten Erkenntnisse werden durch numerische Simulationen
bestätigt.
Abbildung 1: Wechselwirkung von Grenzflächenkonvektion an benachbarten Tropfen (links [2]),
Geschwindigkeitsfeld um zwei schwimmende Decanoltropfen (mittig [4]), asymmetrische
Bulkströmung um partikelbeladene Blasenoberfläche (rechts)
Grenzflächenkonvektion beeinflusst zudem die Dynamik von schwimmenden
Dichlormethan- und Decanoltropfen [3,4]. Durch zeitlich und örtlich hochaufgelöste
Particle Image Velocimetry (PIV)-Messungen kann der Einfluss der
Grenzflächenkonvektion auf die Deformation und Interaktion der schwimmenden
Tropfen verstanden werden (Abb. 1, mittig).
1 mm
Mit dieser Technik konnte auch zum ersten Mal eine kontinuierliche
Grenzflächenkonvektion auf der Blasenoberfläche aufgrund einer asymmetrischen
Scherkraft durch die anliegende Bulkströmung visualisiert werden [5]. In diesem
Prozess bleibt die Grenzfläche unabhängig von der Konzentration eines klassischen
Tensids mobil. Bei Adsorption von Partikeln auf der Blasenoberfläche nimmt die
Mobilität der Grenzfläche jedoch ab (Abb. 1, rechts). Durch eine Kompression der
Oberfläche bildet sich weiterhin ein zusammenhängendes Netzwerk aus Partikeln,
das die Grenzflächenkonvektion schließlich zum Erliegen bringt [6].
Dies zeigt, dass in Abhängigkeit von der Art des adsorbierten Stoffs deutlich
unterschiedliche Randbedingungen für die Strömung an der Grenzfläche von Tropfen
und Blasen vorherrschen können [7]. Die kleine Längenskala der
Grenzflächenkonvektion eröffnet zudem die Möglichkeit, diesen Effekt zur passiven
Durchmischung [8] oder zur Informationsübertragung in mikrofluidischen Prozessen
zu nutzen [2].
Publikationen:
[1] Schwarzenberger, K., Aland, S., Domnick, H., Odenbach, S., & Eckert, K. (2015). Relaxation
oscillations of solutal Marangoni convection at curved interfaces. Colloids and Surfaces A, 481, 633.
[2] Mokbel, M., Schwarzenberger, K., Aland, S., & Eckert, K. (2018). Information transmission by
Marangoni-driven relaxation oscillations at droplets. Soft Matter, 14(45), 9250.
[3] Antoine, C., Irvoas, J., Schwarzenberger, K., Eckert, K., Wodlei, F., & Pimienta, V. (2016). Selfpinning
on a liquid surface. The Journal of Physical Chemistry Letters, 7(3), 520.
[4] Čejková, J., Schwarzenberger, K., Eckert, K., & Tanaka, S. (2019). Dancing performance of
organic droplets in aqueous surfactant solutions. Colloids and Surfaces A, 566, 141.
[5] Eftekhari, M., Schwarzenberger, K., Heitkam, S., & Eckert, K. (2021). Interfacial flow of a
surfactant-laden interface under asymmetric shear flow. Journal of Colloid and Interface Science, 599,
837.
[6] Eftekhari, M., Schwarzenberger, K., Heitkam, S., Javadi, A., Bashkatov, A., Ata, S., & Eckert, K.
(2021). Interfacial Behavior of Particle-Laden Bubbles under Asymmetric Shear Flow. Langmuir,
37(45), 13244.
[7] Keshavarzi, B., Krause, T., Sikandar, S., Schwarzenberger, K., Eckert, K., Ansorge-Schumacher,
M. B., & Heitkam, S. (2022). Protein enrichment by foam Fractionation: Experiment and modeling.
Chemical Engineering Science, 256, 117715.
[8] Bratsun, D., Kostarev, K., Mizev, A., Aland, S., Mokbel, M., Schwarzenberger, K., & Eckert, K.
(2018). Adaptive micromixer based on the solutocapillary Marangoni effect in a continuous-flow
microreactor. Micromachines, 9(11), 600.

  • Lecture (Conference)
    Jahrestreffen der DECHEMA-Fachgruppen Kristallisation, Grenzflächenbestimmte Systeme und Prozesse sowie Mechanische Flüssigkeitsabtrennung, 09.-10.03.2023, Frankfurt, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-37804
Publ.-Id: 37804


Jupyter notebooks to calculate the electric field and properties of focusing (Gaussian) laser pulses

Steiniger, K.

These are the Jupyter notebooks which are used to compute the figures in K. Steiniger et al., "Distortions in focusing laser pulses due to spatio-temporal couplings - An analytic description".

They can be used to:

(1) Numerically calculate the electric field of laser pulses in time-space domain which are defined in frequency-space domain,

(2) Analytically calculate the properties and dispersion parameters of Gaussian laser pulses in time-space domain in the course of propagation through their focus,

(3) Compute the values of laser dispersion parameters in the focus of an off-axis parabolic mirror from the dispersion parameters before focusing at the mirror.

Keywords: laser pulse propagation; pulse-front tilt; laser dispersion; high-power laser; ultrafast optics

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Permalink: https://www.hzdr.de/publications/Publ-37803
Publ.-Id: 37803


Machine Learning-Driven Structure Prediction for Iron Hydrides

Tahmasbi, H.; Ramakrishna, K.; Lokamani, M.; Cangi, A.

We created a computational workflow to analyze the potential energy surface (PES) of materials using machine-learned interatomic potentials in conjunction with the minima hopping algorithm. We demonstrate this method by producing a versatile machine-learned interatomic potential for iron hydride via a neural network using an iterative training process to explore its energy landscape under different pressures. To evaluate the accuracy and comprehend the intricacies of the PES, we conducted comprehensive crystal structure predictions using our neural network-based potential paired with the minima hopping approach. The predictions spanned pressures ranging from ambient to 100 GPa. Our results reproduce the experimentally verified global minimum structures such as \textit{dhcp}, \textit{hcp}, and \textit{fcc}, corroborating previous findings. Furthermore, our in-depth exploration of the iron hydride PES at different pressures has revealed complex alterations and stacking faults in these phases, leading to the identification of several new low-enthalpy structures. This investigation has not only confirmed the presence of regions of established FeH configurations but has also highlighted the efficacy of using data-driven, extensive structure prediction methods to uncover the multifaceted PES of materials.

Permalink: https://www.hzdr.de/publications/Publ-37800
Publ.-Id: 37800


Measurement of the flux-weighted cross-sections for the natYb(γ,xn)175,169,167Yb reactions in the Bremsstrahlung end-point energies of 12 - 16 MeV and 60 - 70 MeV

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

The flux-weighted cross-sections of the natYb(γ,xn)175,169,167Yb reactions were measured at the bremsstrahlung end-point energies of 12, 14, 16, 60, 65, and 70 MeV by the activation and off-line γ-ray spectrometric technique using the 20 MeV electron linac (ELBE) at Helmholtz-Zentrum Dresden-Rossendorf (HZDR), Dresden, Germany, and 100 MeV electron linac at the Pohang Accelerator Laboratory (PAL), Korea. The
natYb(γ,xn)175,169,167Yb reaction cross-sections as a function of photon energy were also calculated theoretically using the TALYS 1.9 code. The flux-weighted average values at different end-point energies were obtained from the literature as well as from the theoretical values reported in
the TALYS library based on mono-energetic photons. They were compared with the flux-weighted values based on the present experimental data and were found to be in general agreement. It was also found that the experimental and theoretical cross-section data increased from the threshold values to a certain energy, where other reaction channels opened, which highlights the role of excitation energy. After a certain value, the individual reaction cross-sections
decrease with an increase in bremsstrahlung energy owing to the opening of other reaction channels, which indicates the partitioning of energy in different reaction channels.

Keywords: Nuclear structure; nuclear reactions; photoactivation; bremsstrahlung; gamma-ray spectroscopy; statistical reaction model

Related publications

Permalink: https://www.hzdr.de/publications/Publ-37799
Publ.-Id: 37799


Role of Protein Solvation in Liquid-Liquid Phase Separation

Adams, E.

Solvation water is integral in influencing in the structure, dynamics, and function of proteins. Coupling of water molecules to the protein surface results in an interfacial region in which water molecules within this region have distinctly different properties than bulk water. Using Terahertz (THz) spectroscopy, we are able to gain insight into protein hydration water by monitoring changes in the water hydrogen-bonding network.

Liquid-liquid phase separation (LLPS) of intrinsically disordered proteins results in the formation of biomolecular condensates, which are membrane-less liquid-like protein enriched droplets. Here we investigate how protein solvation water contributes to condensate formation. Characterization of the hydrogen bonding network reveals that water solvating hydrophobic groups is stripped away in the membrane-less biomolecular condensates. Additionally, water left inside of the biomolecular condensates is highly constrained, indicative of a population of bound hydration water. These results uncover the vital role of hydration water in LLPS: the entropically favorable release of unfavorable hydration water serves as a driving force for LLPS.

  • Invited lecture (Conferences) (Online presentation)
    CMWS Seminar, 02.11.2023, DESY, Germany

Permalink: https://www.hzdr.de/publications/Publ-37795
Publ.-Id: 37795


Selecting active matter according to motility in an acoustofluidic setup: Self-propelled particles and sperm cells

Misko, V. R.; Baraban, L.; Makarov, D.; Huang, T.; Gelin, P.; Mateizel, I.; Wouters, K.; de Munck, N.; Nori, F.; de Malsche, W.

Active systems – including sperm cells, living organisms like bacteria, fish, birds, or active soft matter systems like synthetic “microswimmers” – are characterized by motility, i.e., the ability to propel using their own “engine”. Motility is the key feature that distinguishes active systems from passive or externally driven systems. In a large ensemble, motility of individual species can vary in a wide range. Selecting active species according to their motility represents an exciting and challenging problem. We propose a new method for selecting active species based on their motility using an acoustofluidic setup where highly motile species escape from the acoustic trap. This is demonstrated in simulations and in experiments with self-propelled Janus particles and human sperm. The immediate application of this method is selecting highly motile sperm for medically assisted reproduction (MAR). Due to the tunable acoustic trap, the proposed method is more flexible than the existing passive microfluidic methods. The proposed selection method based on motility can also be applied to other active systems that require selecting highly motile species or removing immotile species.

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  • Secondary publication expected from 30.10.2024

Permalink: https://www.hzdr.de/publications/Publ-37787
Publ.-Id: 37787


Spark Plasma Sintering for synthesis of transition metal oxides

Veremchuk, I.; Grin, Y.; Makarov, D.

The solid-state synthesis of transition metal oxides (TMO’s) is a challenging task. Slow diffusion and mass transfer of reagents are characteristic of such solid-state reactions (SSR’s). In this context, spark plasma sintering (SPS) seems to emerge a promising and technologically applicable synthetic route to obtain TMO’s. We successfully conducted SSR of Ti2O3 synthesis using SPS with dc-current acting as an accelerator of the diffusion-controlled processes between TiO2 and Ti [1]. Further, this approach was applied to directly synthesize different TMO’s (titanium oxides [2], molybdenum oxides [3], tungsten oxides [4], and chromium oxides [5]). Among the advantages of such synthetic routes, we would like to stress: i) simple pre-experiment preparation (i.e., mixing of the initial powders); ii) simultaneous compaction and shaping of products; iii) short synthesis time (i.e., from minutes to about the few hours), iv) enormous accuracy (i.e., ≅ 0.1 at % of oxygen) as well as v) high degree of reproducibility.
New types of electrochemical using SPS SSR was recently performed in our laboratories using SPS. By sintering TiO2 (insulator) with WO2 (metal) mixed in different proportions, we obtained solid solution based on rutile (i.e., TiO2) structure. However, an appearance of elemental tungsten cannot be avoided while performing the synthesis with graphite foils as separators between the reacting mixture and the punches. To shed light on the mechanism of such an electrochemical process we performed two reactions, applying the opposite polarity of dc-current pulses, to the placed in graphite die layers of unmixed TiO2 and WO2. The further combined metallographic-EDX investigation of the polished cuts of the reacted specimens revealed that in the case when WO2 was under positive pole (i.e., being an anode) free W is forming at “+”-electrode, whereas the switch of the polarity results in the formation of tungsten inclusion on the phases border between reactants. Thus, elemental tungsten seems to be the product of electrochemical reduction of WO2. Avoiding this reaction, a single phase Ti1-xWxO2 is obtained replacing the graphite foils by tungsten ones.

[1] Veremchuk I., Antonyshyn I., Candolfi C., et al. Inorg. Chem. (2013) 52, 4458.
[2] Feng B., Martin H.‐P., Börner F.‐D., Veremchuk I., et al. Adv. Eng. Mat. (2014) 16, 1252.
[3] Kaiser F., Schmidt M., Grin Yu., Veremchuk I., Chem. of Mater. (2020) 32, 2025.
[4] Kaiser F., Simon P., Burkhardt U., Kieback B., Grin Yu., Veremchuk I. Crystals (2017)7, 271.
[5] Veremchuk I., et al. ACS Appl. Electron. Mater. (2022) 4, 2943.

  • Lecture (Conference)
    2nd Conference on FAST/SPS from Research to Industry, 16.-18.10.2023, Warsaw, Poland

Permalink: https://www.hzdr.de/publications/Publ-37786
Publ.-Id: 37786


Magnetism and magnetoelectricity of textured thin films and polycrystalline bulk α-Cr2O3

Veremchuk, I.; Makushko, P.; Hedrich, N.; Zabila, Y.; Kosub, T.; Liedke, M. O.; Butterling, M.; Elsherif, A. G. A.; Wagner, A.; Ganss, F.; Burkhardt, U.; Pylypovskyi, O.; Hübner, R.; Faßbender, J.; Maletinsky, P.; Makarov, D.

Magnetoelectric antiferromagnets like α-Cr2O3 are attractive for the realization of energy-efficient and high-speed spin−orbitronic-based memory devices controlled by electric fields [1-3]. In contrast to single crystals, the quality of Cr2O3 thin films and bulk polycrystalline samples is usually compromised by the presence of point defects and their agglomerations at grain boundaries, putting into question their application potential. Here, we experimentally investigated the defect nanostructure of magneton-sputtered 250-nm-thick Cr2O3 thin films prepared under different conditions on single crystals of Al2O3 (0001) and correlate it with the integral and local magnetic properties of the samples [4]. Also, we fabricated of polycrystalline bulk α-Cr2O3 sample in conditions far out of equilibrium relying on spark plasma sintering (SPS) allows high quality material with a density close to that of a single crystal [5]. The sintered sample possesses a preferential [0001] texture at the surface, which can be attributed to uniaxial strain applied to the sample during the sintering process [5]. We evaluated the type and relative concentration of defects. For this purpose, positron annihilation spectroscopy (PAS) was used as a unique probe for open-volume defects in the samples. Our analysis reveals that the Cr2O3 samples are characterized by the presence of complex defects at grain boundaries, formed by groups of single monovacancies, coexisting with complex defects and dislocations. The concentration of complex defects for the thin films can be controlled by the sample fabrication conditions including the deposition temperature as well as the post-annealing in vacuum or in air [4]. The antiferromagnetic state of the sample and linear magnetoelectric effect are accessed all electrically relying on the spin Hall magnetoresistance effect in the Pt electrode interfaced with Cr2O3 [6]. In line with the integral magnetometry measurements, the magnetotransport characterization reveals that the samples possesses the magnetic phase transition temperature of about 308 K, which is hardly affected by the formed defects. The antiferromagnetic domain patterns consist of small domains with size equals the grain size, which is formed due to the granular structure of the samples. Furthermore, the presence of larger defects like grain boundaries has a strong influence on the pinning of magnetic domain walls in studied samples. The possibility to access the magnetoelectric properties of the samples relying on magnetotransport measurements indicates the potential of the thin films and polycrystalline bulk Cr2O3 samples for prospective research in antiferromagnetic spintronics.
[1] X. He, Y. Wang, N. Wu, A. N. Caruso, E. Vescovo, K. D. Belashchenko, P. A. Dowben, C. Binek, Nature Mater., 9, 579 (2010).
[2] T. Kosub, M. Kopte, R. Hühne, P. Appel, B. Shields, P. Maletinsky, R. Hübner, M. O. Liedke, J. Fassbender, O. G. Schmidt, D. Makarov, Nature Commun., 8, 13985 (2017).
[3] N. Hedrich, K. Wagner, O. V. Pylypovskyi, B. J. Shields, T. Kosub, D. D. Sheka, D. Makarov, P. Maletinsky, Nature Phys., 17, 574 (2021).
[4] I. Veremchuk, M. O. Liedke, P. Makushko, T. Kosub, N. Hedrich, O. V. Pylypovskyi, F. Ganss, M. Butterling, R. Hübner, E. Hirschmann, A. G. Attallah, A. Wagner, K. Wagner, B. Shields, P. Maletinsky, J. Fassbender, D. Makarov, Small, 18, 2201228 (2022).
[5] I. Veremchuk, P. Makushko, N. Hedrich, Y. Zabila, T. Kosub, M. O. Liedke, M. Butterling, A. G. Attallah, A. Wagner, U. Burkhardt, O. V. Pylypovskyi, R. Hübner, J. Fassbender, P. Maletinsky, and D. Makarov, ACS Appl. Electron. Mater., 4, 2943 (2022).
[6] R. Schlitz, T. Kosub, A. Thomas, S. Fabretti, K. Nielsch, D. Makarov, S. T. B. Goennenwein, Appl. Phys. Lett., 112, 132401 (2018).

  • Lecture (Conference)
    CMD30 FisMat, 04.-08.09.2023, Milan, Italy

Permalink: https://www.hzdr.de/publications/Publ-37785
Publ.-Id: 37785


Defect nanostructure and its impact on magnetism of α-Cr2O3 thin films.

Veremchuk, I.; Liedke, M. O.; Makushko, P.; Kosub, T.; Hedrich, N.; Pylypovskyi, O.; Ganss, F.; Butterling, M.; Hübner, R.; Hirschmann, E.; Wagner, A.; Elsherif, A. G. A.; Wagner, K.; Shields, B.; Maletinsky, P.; Faßbender, J.; Makarov, D.

Thin films of the magnetoelectric insulator Cr$_{2}$O$_{3}$ are technologically relevant for energy-efficient magnetic memory devices controlled by electric fields. We experimentally investigated the defect nanostructure of 250-nm-thick Cr$_{2}$O$_{3}$ thin films prepared under different conditions on single crystals of Al$_{2}$O$_{3}$ (0001) and correlate it with the integral and local magnetic properties of the samples. Positron annihilation spectroscopy (PAS) was used as a unique probe for open-volume defects in thin films. Analysis reveals that the Cr$_{2}$O$_{3}$ thin films are characterized by the presence of complex defects at grain boundaries, formed by groups of monovacancies, coexisting with monovacancies and dislocations. The concentration of complex defects can be controlled by the sample fabrication conditions. The defect nanostructure strongly affects the magnitude of the electrical readout, which is measured of the Cr$_{2}$O$_{3}$ samples capped with a thin layer of Pt relying on spin Hall effect. Furthermore, the presence of larger defects like grain boundaries has a strong influence on the pinning of magnetic domain walls in thin films. Independent of these findings, we showed that the N\'{e}el temperature, which is one of the important technological metrics, is hardly affected by the formed defects in a broad range of deposition parameters.

  • Lecture (Conference)
    DPG spring meeting 2023, 26.-31.03.2023, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-37784
Publ.-Id: 37784


Low temperature diffusion in thin film Pt-(Au-)-Co heterostructures: structural and magnetic characterization

Pedan, R.; Makushko, P.; Yavorskyi, Y.; Dubikovskyi, O.; Bodnaruk, A.; Burmak, A.; Golub, V.; Voloshko, S.; Hübner, R.; Makarov, D.; Igor, V.

Formation of functional thin films for nanoelectronics and magnetic data storage via thermally induced diffusion-driven structural phase transformations in multilayer stacks is a promising technology-relevant approach. Ferromagnetic thin films based on Co Pt alloys are considered as a material science platform for the development of various applications such as spin valves, spin orbit torque devices, and high-density data storage media. Here, we study diffusion processes in Pt-Co-based stacks with the focus on the effect of layers inversion (Pt/Co/substrate vs. Co/Pt/substrate) and insertion of an intermediate Au layer on the structural transitions and magnetic properties. We demonstrate that layer stacking has a pronounced effect on the diffusion rate at temperatures, where the diffusion is dominated by grain boundaries. We quantify effective diffusion coefficients, which characterize the diffusion rate of Co and Pt through the interface and grain boundaries, providing the possibility to control the homogenization rate of Pt-Co-based heterostructures. The obtained values are in the range of 10-16 – 10-13 cm2/s for temperatures of 150 °C – 350 °C. Heat treatment of thin-film samples results in the coercivity enhancement, which is attributed to short-range chemical ordering effects. We show that introducing an additional Au intermediate layer leads to an increase of the coercive field of the annealed samples due to a modification of exchange coupling between the magnetic grains at the grain boundaries.

Keywords: diffusion coefficient; grain boundary diffusion; magnetic thin films; short-range chemical order; Co-Pt alloy

Permalink: https://www.hzdr.de/publications/Publ-37783
Publ.-Id: 37783


Tunable room temperature nonlinear Hall effect from the surfaces of elementary bismuth thin films

Makushko, P.; Kovalev, S.; Zabila, Y.; Ilyakov, I.; Ponomaryov, O.; Arshad, A.; Prajapati, G. L.; de Oliveira, T.; Deinert, J.-C.; Chekhonin, P.; Veremchuk, I.; Kosub, T.; Scurschii, I.; Ganss, F.; Makarov, D.; Carmine, O.

The nonlinear Hall effect (NLHE) with time-reversal symmetry constitutes the appearance of a transverse voltage quadratic in the applied electric field. It is a secondorder electronic transport phenomenon that induces frequency doubling and occurs in non-centrosymmetric crystals with large Berry curvature – an emergent magnetic field encoding the geometric properties of electronic wavefunctions. The design of (opto)electronic devices based on the NLHE is however hindered by the fact that this nonlinear effect typically appears at low temperatures and in complex compounds characterized by Dirac or Weyl electrons Here, we show a strong room temperature NLHE in the centrosymmetric elemental material bismuth synthesized in the form of technologically relevant polycrystalline thin films. The (111) surface electrons of this material are equipped with a Berry curvature triple that activates side jumps and skew scatterings generating nonlinear transverse currents. We also report a boost of the zero field nonlinear transverse voltage in arc-shaped bismuth stripes due to a extrinsic geometric classical counterpart of the NLHE This electrical frequency doubling in curved geometries is then extended to optical second harmonic generation in the terahertz (THz) spectral range. The strong nonlinear electrodynamical responses of the surface states are further demonstrated by a concomitant highly efficient THz third harmonic generation which we achieve in a broad range of frequencies in Bi and Bi-based heterostructures. Combined with the possibility of growth on CMOS-compatible and mechanically flexible substrates, these results highlight the potential of Bi thin films for THz (opto)electronic applications.

Permalink: https://www.hzdr.de/publications/Publ-37781
Publ.-Id: 37781


Flexomagnetic Effects in Antiferromagnetic Epitaxial Cr2O3 Thin Films

Makushko, P.; Kosub, T.; Pylypovskyi, O.; Hedrich, N.; Li, J.; Pashkin, O.; Avdoshenko, S.; Hübner, R.; Ganss, F.; Wolf, D.; Lubk, A.; Liedke, M. O.; Butterling, M.; Wagner, A.; Wagner, K.; Shields, B.; Lehmann, P.; Veremchuk, I.; Faßbender, J.; Maletinsky, P.; Makarov, D.

Thin films of antiferromagnetic insulators (Cr2O3, Fe2O3, NiO etc.) are a prospective material platform for magnonics, spin superfluidity, THz spintronics, and non-volatile data storage. A standard micromagnetic approach for the description of thin film system commonly relies on the effective parameters, assumed to be homogeneously distributed within a material. The family of magnetomechanical effects includes piezo- and flexomagnetic responses, which determine the modification of the magnetic order parameters due to homogeneous or inhomogeneous strain, respectively. Accounting for the strain-gradient-driven magnetomechanical coupling promises technological advantages: the cross-coupling between elastic, magnetic and electric subsystems opens additional degrees of freedom in the control of the respective order parameters [1]-[3].
In this work, we discover the presence of flexomagnetic effects in epitaxial antiferromagnetic Cr2O3 thin films [4]. We demonstrate that a gradient of mechanical strain affect the order-disorder magnetic phase transition resulting in the distribution of the Néel temperature along the thickness of Cr2O3 thin film. The inhomogeneous reduction of the antiferromagnetic order parameter induces a flexomagnetic coefficient of about 15 µB nm-2. The antiferromagnetic ordering in the strained films can persist up to 100 °C, rendering Cr2O3 as a prospective material for industrial spintronic applications. Strain gradient in Cr2O3 thin films enables fundamental research on magnetomechanics and thermodynamics of antiferromagnetic solitons, spin waves and artificial spin ice systems in magnetic materials with continuously graded parameters.

  • Lecture (Conference)
    8th International conference on superconductivity and magnetism, 04.-11.05.2023, Fethiye, Turkey

Permalink: https://www.hzdr.de/publications/Publ-37779
Publ.-Id: 37779


Flexomagnetism and vertically graded Néel temperature in the epitaxial Cr2O3 thin films

Makushko, P.; Kosub, T.; Pylypovskyi, O.; Hedrich, N.; Li, J.; Pashkin, O.; Avdoshenko, S.; Hübner, R.; Ganss, F.; Wolf, D.; Lubk, A.; Liedke, M. O.; Butterling, M.; Wagner, A.; Wagner, K.; Shields, B.; Lehmann, P.; Veremchuk, I.; Faßbender, J.; Maletinsky, P.; Makarov, D.

Thin films of magnetoelectric antiferromagnetic insulators (Cr2O3, BiFeO3 etc.) have emerged as a prospective material platform for magnonics, spin superfluidity, THz spintronics, and energy efficient spin-orbitronics. Understanding the magnetomechanical coupling in antiferromagnets offers vast advantages in the control of the primary order parameters. A standard micromagnetic approach for the description of a material relies on the effective parameters being homogeneously distributed throughout the system. Such an approach is commonly sufficient, but does not provide full characterization of the system. The family of magnetomechanical effects includes piezo- and flexomagnetic responses, which determine the modification of the magnetic order parameters due to homogeneous or inhomogeneous strain, respectively. Accounting for the flexomagnetic effects promises technological advantages for multiferroic and antiferromagnetic materials, where cross-coupling between elastic, magnetic and electric subsystems open additional degrees of freedom in the control of the respective order parameters [1, 2].
In this work, we discover the effect of strain gradient onto the magnetic behaviour of epitaxial Cr2O3 thin films [3, 4]. We demonstrate that by tuning the parameters of Cr2O3 epitaxial growth a fine control of the crystallographic and defect structure can be realized. A persistent strain gradient was obtained in Cr2O3 affecting its magnetic order parameters rendering a distribution of the Néel temperature along the thickness of the thin film. The antiferromagnetic ordering in the strained films can persist up to 100°C, rendering Cr2O3 as a prospective material for industrial electronics applications. The inhomogeneous enhancement of the antiferromagnetic order parameter induced by the strain gradient renders a flexomagnetic response of about 15 µB nm-2.
Strain gradient in Cr2O3 thin films enables fundamental research on magnetomechanics and thermodynamics of antiferromagnetic solitons, spin waves and artificial spin ice systems in magnetic materials with graded parameters. Distribution of the Neel temperature along the thin film thickness introduces temperature as a took for realization of reconfigurable spintronic and magnonic devices.

  • Lecture (Conference)
    CMD30 FisMat 2023, 04.-08.09.2023, Milano, Italy

Permalink: https://www.hzdr.de/publications/Publ-37778
Publ.-Id: 37778


Flexomagnetism and vertically graded Néel temperature of antiferromagnetic Cr2O3 thin films

Makushko, P.; Kosub, T.; Pylypovskyi, O.; Hedrich, N.; Li, J.; Pashkin, O.; Avdoshenko, S.; Hübner, R.; Ganss, F.; Wolf, D.; Lubk, A.; Liedke, M. O.; Butterling, M.; Wagner, A.; Wagner, K.; Shields, B.; Lehmann, P.; Veremchuk, I.; Faßbender, J.; Maletinsky, P.; Makarov, D.

Thin films of antiferromagnetic insulators are a prospective material platform for magnonics, spin superfluidity, THz spintronics, and nonvolatile data storage. Here, we explore the presence of flexomagnetic effects in epitaxial Cr2O3 [1]. We demonstrate that a gradient of mechanical strain effect the order-disorder magnetic phase transition, resulting in the distribution of the Néel temperature along the thickness of a Cr2O3 film. The inhomogeneous reduction of the antiferromagnetic order parameter induces a flexomagnetic coefficient of about 15µB nm−2. The
antiferromagnetic ordering in the strained films can persist up to 100∘C, rendering Cr2O3 as a prospective material for industrial electronics applications.

  • Lecture (Conference)
    DPG Spring Meeting 2023, 26.-31.03.2023, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-37777
Publ.-Id: 37777


Rollenscan Data Science und KI

Ernst, M.; Hartmann, M.; Marx, S.; Schindler, T.; Steinbach, P.; Wilde, A.

Im Zeitalter der datengestützten Entscheidungsfindung hat sich der Bereich Datenwissenschaft (Data Science) zu einem wichtigen Katalysator für Innovation und Fortschritt sowohl in der Industrie als auch in der Wissenschaft entwickelt. Die Rollen und Aufgaben von Data Scientists haben sich jedoch erheblich weiterentwickelt und umfassen ein breites Spektrum an Fähigkeiten, Fachwissen und Anwendungen. Um die Vielschichtigkeit dieser Rollen zu erfassen und unser kollektives Verständnis zu vermitteln, traf sich eine Gruppe von sechs Fachleuten bei Silicon Saxony und nutzte "Personas" als Methode, um unsere derzeitigen Ansichten über die Rolle von Datenwissenschaftler:innen zu formulieren. Dieses Papier fasst die Erkenntnisse dieser Aktivität zusammen.

Keywords: Data Science; Skill Set; Beruf; Industrie

Permalink: https://www.hzdr.de/publications/Publ-37776
Publ.-Id: 37776


Laser-Induced Positional and Chemical Lattice Reordering Generating Ferromagnetism

Pflug, T.; Pablo-Navarro, J.; Anwar, M. S.; Olbrich, M.; Magén, C.; Ibarra, M. R.; Potzger, K.; Faßbender, J.; Lindner, J.; Horn, A.; Bali, R.

Atomic scale reordering of lattices can induce local modulations of functional material properties, such as reflectance and ferromagnetism. Pulsed femtosecond laser irradiation enables lattice reordering in the picosecond range. However, the dependence of the phase transitions on the initial lattice order as well as the temporal dynamics of these transitions remain to be understood. This study investigates the laser-induced atomic reordering and the concomitant onset of ferromagnetism in thin Fe-based alloy films with vastly differing initial atomic orders. The optical response to single fs laser pulses on selected prototype systems, one that initially possesses positional disorder, Fe60V40, and a second system initially in a chemically ordered state, Fe60Al40, has been tracked with time. Despite the vastly different initial atomic orders the structure in both systems converges to a positionally ordered but chemically disordered state, accompanied by the onset of ferromagnetism. Time-resolved measurements of the transient reflectance combined with simulations of the electron and phonon temperature reveal that the reordering processes occur via the formation of a transient molten state with an approximate lifetime of 200 ps. These findings provide insights into fundamental processes involved in laser-induced atomic reordering, paving the way for controlling material properties in the picosecond range.

Keywords: positional order; chemical order; atomic reordering; ferrmagnetism; pump-probe reflectometry

Permalink: https://www.hzdr.de/publications/Publ-37775
Publ.-Id: 37775


Data publication: Fermionic physics from ab initio path integral Monte Carlo simulations of fictitious identical particles

Dornheim, T.

This repository contains the PIMC/CPIMC results shown in J. Chem. Phys. 159, 164113 (2023).

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Permalink: https://www.hzdr.de/publications/Publ-37774
Publ.-Id: 37774


Virial coefficients of the Uniform Electron Gas from Path Integral Monte Carlo Simulations

Röpke, G.; Dornheim, T.; Vorberger, J.; Blaschke, D.; Mahato, B.

The properties of plasmas in the low-density limit are described by virial expansions. Analytical expressions are known from Green's function approaches only for the first three virial coefficients. Accurate path integral Monte Carlo (PIMC) simulations have recently been performed for the uniform electron gas, allowing the virial expansions to be analyzed and interpolation formulas to be derived. The exact expression for the second virial coefficient is used to test the accuracy of the PIMC simulations and the range of validity of the interpolation formula of Groth {\it et al.}~[Phys.~Rev.~Lett.~\textbf{119}, 135001 (2017)]. We discuss the fourth virial coefficient, which is of interest, e.g., for properties of solar plasmas, but has not yet been precisely known. Combining PIMC simulations with benchmarks from exact results of the virial expansion would allow us to obtain precise results for the equation of state (EoS) in a wide range of parameters.

Permalink: https://www.hzdr.de/publications/Publ-37773
Publ.-Id: 37773


Calorimetry as a tool to improve the dosimetric accuracy in novel radiotherapy modalities

Horst, F. E.

The main quantity of interest in radiotherapy dosimetry is absorbed dose to water, i.e. the energy that is deposited by the radiotherapy beam in water per unit mass. The most common method to measure dose in radiotherapy is by using air-filled ionization chambers via the charge released in their active volume by ionizations. These ionization chambers are typically absolute calibrated in 60Co beams in terms of absorbed dose to water. If a measurement is carried out in another radiation quality (e.g. proton beams), the different response of the chamber in that radiation quality compared to 60Co photons due to a different water-to-air stopping power ratio and chamber-specific geometry effects is taken into account by applying a beam quality correction factor kQ. Because kQ might be sensitive to several factors, it is recommended that absolute absorbed dose to water measurements should be performed within defined reference conditions (e.g. field size and water depth), and therefore such measurements are referred to as reference dosimetry [1]. In addition to kQ, also several other corrections may be necessary (e.g., recombination or air density correction).
Compared to ionization chamber dosimetry, a more direct way to measure dose is calorimetry where the deposited energy in the detector is measured via its temperature increase. Calorimetry is considered as the most accurate method of dose determination but requires a large logistic effort, stable thermal conditions in the room plus a good isolation and those devices are usually very sensitive and complicated to operate. Therefore calorimetry is at present mostly applied as primary standard for absorbed dose in permanently installed setups at national metrology institutes [2], to which the calibration of ionization chambers used in radiotherapy clinics can be traced back to.
The natural choice of the calorimeter medium is water because absorbed dose to water is the quantity of interest in radiotherapy dosimetry. Due to some practical limitations of water calorimeters, there are also calorimeter designs based on solid materials, typically graphite. Graphite calorimeters can be a lot more compact than water calorimeters and due to the smaller specific heat capacity of graphite, the temperature increase (i.e., the measurement signal) is about a factor 5 higher than for water at the same dose. However, the higher thermal conductivity of graphite requires additional insulation of the calorimeter core. Another characteristic of graphite calorimetry is that it requires a conversion from absorbed dose to graphite to absorbed dose to water and therefore the stopping power ratio in the radiation field of interest must be calculated.
Besides applications as primary standard for absorbed dose to water, calorimetric measurements can also be helpful to guarantee the dosimetric accuracy when novel radiotherapy modalities, for which standard dosimetry protocols are not suitable, are introduced. Recent examples are magnetic resonance guided radiotherapy [3], where the response of ionization chambers is modified by the magnetic field, or FLASH radiotherapy at ultra-high dose rate (UHDR) [4,5] where recombination effects in ionization chambers become more pronounced than in conventional radiotherapy. For calorimetric measurements, the UHDR delivery can even be considered an advantage because the quasi-instantaneous dose application makes the heat drift become less relevant. For instance at the Physikalisch-Technische Bundesanstalt (PTB) in Germany, efforts were made to establish a water calorimeter as primary standard in the UHDR beam of their 20 MeV electron accelerator [4]. Another example is the first proton FLASH patient trial at the Cincinnati Children’s Hospital Medical Center in the USA where a group from the National Physical Laboratory (NPL) of the United Kingdom supported the dosimetric characterization of UHDR beams with their graphite calorimeter [5]. Recently, water calorimeters have been used to determine ionization chamber specific beam quality correction factors in clinical proton (6) and carbon ion beams [7,8].
Generally, for protons and heavy ions no actual primary standards have been established up to now [9], because the national metrology institutes do not have suitable accelerators and beam qualities on-site but would have to travel to clinical facilities with their calorimetry equipment. For this purpose, since several years many metrology groups work on the development of portable calorimeters (see for example ref. [10] for an early work).
At NPL a portable graphite calorimeter was developed [11]. This device is now intended to be applied for secondary standard measurements in UHDR proton beams in order to improve the dosimetric accuracy for this novel radiotherapy modality. Like ionization chamber dosimetry, also calorimetry requires a number of correction factors to be applied to the measured signal. Cotterill and colleagues present in their paper [12], published in this ESTRO 2023 Physics Highlights special issue of phiRO, detailed Monte Carlo simulations on their so-called Small-body Portable Graphite Calorimeter. They derived correction factors for 250 MeV protons correcting for the graphite impurity and the air gap between the graphite core and its jacket. They show that the dominating perturbation (almost 0.5%) is due to missing scatter contributions from the styrofoam insulation around the device, for which they introduce a new correction factor. By applying the obtained correction factors, the dosimetric accuracy of the calorimeter can be improved considerably. The in- and out-scattering of protons from the different components of the device was studied in detail and the dose conversion factor from absorbed dose in the graphite core to absorbed dose to water at the reference point was calculated.
Even though portable calorimeters like the one presented by Cotterill et al. are still more complicated to operate than ionization chambers, they are much more convenient to transport and set up than classic calorimetry setups.
It will be very interesting to see if these developments will contribute to a wider spread of calorimetric measurements in radiotherapy, or even a routine use in radiotherapy clinics as envisioned by Cotterill et al., and if the establishment of a primary standard for absorbed dose to water in proton (and heavy ion) beams will finally succeed.

Permalink: https://www.hzdr.de/publications/Publ-37772
Publ.-Id: 37772


Magnetic membrane polymers with onboard electronic skins for supervised actuation

Oliveros Mata, E. S.; Ha, M.; Canon Bermudez, G. S.; Liu, J. A.-C.; Evans, B. A.; Tracy, J. B.; Makarov, D.

Soft actuators have been developed to mimic the biomechanics of living organisms, enabling complex movements such as crawling, flapping, and twisting upon the application of physical and chemical stimuli [1]. Magnetic membrane soft polymers have been used for controlled, programmable, and fast actuation in uniform and gradient magnetic fields [2,3]. This allows for multipurpose biomimetic systems that can move untethered using permanent magnets and electromagnets for use in remote surgery, cargo transport, and artificial muscles [4]. To achieve the full potential of these types of soft actuators, it is needed a suitable system that mimics the sensory and proprioception capabilities of living beings.
Here, we show the integration of highly flexible electronic skins that are laminated to the body of magnetic flexible membranes to supervise their actuation mechanisms [5]. The electronic skins contain flexible magnetic field sensors based on thin films fabricated on ultrathin (2.5-µm-thick) polymeric foils. This highly compliant e-skin acts as an onboard sensory system of magnetic cues, such as the own magnetization state of the soft actuator and the magnetic fields employed for deforming the membranes. This allows the system to orient itself with respect to a reference magnetic source and be aware of its folding state. We demonstrate the signal readout and supervision of magnetic soft membrane actuators during their assembly into box and boat-like layouts [5].
[1] D. Rus, et al. Nature. 521, 467 (2015).
[2] X. Wang, et al. Commun. Mater. 67, 1 (2020)
[3] H. Chung, et al. Adv. Intell. Syst. 3, 2000186 (2021).
[4] S. Wu, et al. Multifunct. Mater. 3, 042003. (2020).
[5] M. Ha, E.S. Oliveros Mata, et al. Adv. Mater. 33, 2008751 (2021)

Keywords: magnetic; soft robot; actuator; polymer; composite

  • Lecture (Conference)
    European-MRS 2023 Spring Meeting, 29.05.-02.06.2023, Strasbourg, France

Permalink: https://www.hzdr.de/publications/Publ-37769
Publ.-Id: 37769


Printed human machine interfaces using touchless interaction via magnetic fields

Oliveros Mata, E. S.; Voigt, C.; Xu, R.; Ha, M.; Canon Bermudez, G. S.; Zabila, Y.; Fritsch, M.; Mosch, S.; Kusnezoff, M.; Vinnichenko, M.; Makarov, D.

Printed and flexible electronics have gained significant attention in recent years for their potential in various applications including medical, wearable, and Internet of Things (IoT) devices [1]. In this work, we focus on the development and characterization of printed magnetic field sensors for use in human-machine interfaces enabling the control and monitoring of various systems and devices. We developed a set of printable magnetically sensitive pastes based on microflakes and microparticles showing anisotropic [2,3], giant [4], and large magnetoresistance [5] effects. Our sensors are fabricated using cost-effective, scalable, and large-area automatized printing techniques, making them prospectively suitable for large-scale
production.
The design and production of the printed sensors are based on the properties of the paste fillers, binder, substrate, and techniques used in the fabrication process. By adjusting the mechanical properties of the binder, we were able to give the printed sensors the capability to conform to various shapes and surfaces. The use of polymeric binders in the printing process on flexible foils allowed us to laminate the sensors onto objects with complex geometries, including human skin. For example, we were able to create stretchable magnetic field sensors that can undergo 100% strain by using a styrene-butadiene-styrene block copolymer as a binder. We have also demonstrated that these sensors remain functional even when folded to a
radius of 16 µm. [4]
We have also shown that it is possible to produce large quantities of magnetic field sensors using automatized dispenser printing and laser sintering Bi pastes [5]. This method allows large-area, cost-effective, and customizable fabrication of flexible, fully printed magnetic field sensors using minimal materials. This manufacturing capability has the potential to pave the way for more extensive interactive smart surfaces and touchless control boards. Our research represents a significant advancement in the integration of printed and flexible electronics into human machine interfaces, and it opens the door for further research for creating customized solutions to user-specific needs.
[1] Y. Khan, et al. Adv. Mater. 32, 1905279 (2020)
[2] E.S. Oliveros Mata, et al. Appl. Phys. A 127, 280 (2021)
[3] R. Xu, et al. Nat. Commun. 13, 6587 (2022)
[4] M. Ha, et al. Adv. Mater. 33, 2005521 (2021)
[5] E.S. Oliveros‐Mata, E. S., C. Voigt, et al. Adv. Mater. Technol. 2200227 (2022)

Keywords: printed electronics; magnetic; human machine interfaces; flexible electronics

  • Lecture (Conference)
    European-MRS 2023 Spring Meeting, 29.05.-02.06.2023, Strasbourg, France

Permalink: https://www.hzdr.de/publications/Publ-37768
Publ.-Id: 37768


Yamdb - Yet Another Materials DataBase

Weier, T.; Nash, W.; Personnettaz, P.; Weber, N.

Yamdb (Yet Another Materials Database/YAMl materials DataBase) is a
Python library providing thermophysical properties of liquid metals
and molten salts in an easily accessible manner. Mathematical
relations describing material properties - usually determined by
experiment - are taken from the literature and implemented in
Python. The coefficients of these equations are stored separately in
YAML files.

Keywords: material properties; liquid metals; molten salts; YAML; Python

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Permalink: https://www.hzdr.de/publications/Publ-37766
Publ.-Id: 37766


Goma - using Yamdb material databases from the commandline

Weier, T.; Nash, W.; Personnettaz, P.; Weber, N.

Goma (GO MAterials database) is a program enabling command line access to the  YAML files distributed with Yamdb. It implements the equations necessary to calculate the thermophysical properties from the coefficients stored in the YAML database. Yamdb (Yet another materials data base) and Goma address the need to provide thermophysical properties of liquid metals and molten salts in an easily accessible manner. Mathematical relations describing material properties - usually determined by experiment - are taken from the literature. Equations and their coefficients are stored separately. The former can be implemented in any programming language (Go in this case) and the latter are kept in YAML files together with additional information (source, temperature range, composition, accuracy if available, etc).

Keywords: material properties; liquid metal; molten salts; YAML; Go

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Permalink: https://www.hzdr.de/publications/Publ-37765
Publ.-Id: 37765


First measurement of the low-energy direct capture in ²⁰Ne(p,γ)²¹Na and improved energy and strength of the E(c.m.) = 368 keV resonance

Masha, E.; Barbieri, L.; Skowronski, J.; Aliotta, M.; Ananna, C.; Barile, F.; Bemmerer, D.; Best, A.; Boeltzig, A.; Broggini, C.; Bruno, C. G.; Caciolli, A.; Campostrini, M.; Casaburo, F.; Cavanna, F.; Ciani, G. F.; Ciapponi, A.; Colombetti, P.; Compagnucci, A.; Corvisiero, P.; Csedreki, L.; Davinson, T.; Depalo, R.; Di Leva, A.; Elekes, Z.; Ferraro, F.; Fiore, E. M.; Formicola, A.; Fülöp, Z.; Gervino, G.; Guglielmetti, A.; Gustavino, C.; Gyürky, G.; Imbriani, G.; José, J.; Junker, M.; Lugaro, M.; Manoj, P.; Marigo, P.; Menegazzo, R.; Paticchio, V.; Piatti, D.; Prati, P.; Rapagnani, D.; Rigato, V.; Robb, D.; Schiavulli, L.; Sidhu, R. S.; Straniero, O.; Szücs, T.; Zavatarelli, S.

The ²⁰Ne(p,γ)²¹Na reaction is the slowest in the NeNa cycle and directly affects the abundances of the Ne and Na isotopes in a variety of astrophysical sites. Here we report the measurement of its direct capture contribution, for the first time below E(c.m.) = 352 keV, and of the contribution from the E(c.m.) = 368 keV resonance, which dominates the reaction rate at T = 0.03–1.00 GK. The experiment was performed deep underground at the Laboratory for Underground Nuclear Astrophysics, using a high-intensity proton beam and a windowless neon gas target. Prompt γ rays from the reaction were detected with two high-purity germanium detectors. We obtain a resonance strength ωγ = (0.112 ± 0.002(stat) ± 0.005(sys)) meV, with an uncertainty a factor of 3 smaller than previous values. Our revised reaction rate is 20% lower than previously adopted at T < 0.1 GK and agrees with previous estimates at temperatures T ≤ 0.1 GK. Initial astrophysical implications are presented.

Keywords: Nuclear Astrophysics; Underground Laboratory; Cross Section Measurement; Neon-Sodium-Cycle; LUNA

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Permalink: https://www.hzdr.de/publications/Publ-37764
Publ.-Id: 37764


Observing the onset of pressure-driven K-shell delocalization

Döppner, T.; Bethkenhagen, M.; Gericke, D.; Kraus, D.; Bachmann, B.; Chapman, D.; Böhme, M.; Divol, L.; Dornheim, T.; Falcone, R.; Fletcher, L.; Kruse, M.; Landen, O.; Macdonald, M.; Glenzer, S.; Redmer, R.; Schörner, M.; Sterne, P.; Vorberger, J.

We have developed an experimental platform for x-ray Thomson scattering (XRTS) at NIF to characterize plasma conditions in ICF indirectly-driven capsule implosions near stagnation [1,2]. This enabled us to investigate up to 30 times compressed ablator materials reaching pressures above 3 Gigabars, at conditions where the distance between the nuclei becomes comparable to the extent of the core shell bound states, which will eventually lead to their pressure ionization. In this talk we will present results from experiments with beryllium shells. We observe reduced elastic scattering for the most extreme conditions [2]. We interpret this reduction as the precursor of pressure ionization of the remaining K-shell electrons, that is, a strongly modified bound state. The beryllium charge state inferred from the data is considerable higher than standard models predict but agrees well with results from DFT simulations [2,3]. Accurate modelling of the K-shell occupation of light elements is imperative for creating predictive capabilities for ICF implosions. Our experiments yield valuable benchmarks for this process and demonstrating a complex pathway of pressure ionization.

  • Lecture (Conference)
    APS DPP, 30.10.-03.11.2023, Denver, USA

Permalink: https://www.hzdr.de/publications/Publ-37763
Publ.-Id: 37763


Towards a model-free interpretation of X-ray Thomson scattering signals

Dornheim, T.

Matter under extreme densities and temperatures is ubiquitous throughout our universe and naturally occurs in a plethora of astrophysical objects such as giant planet interiors and brown dwarfs. In addition, such warm dense matter (WDM) is of key importance for a number of technological applications, most notably inertial confinement fusion. Yet, the accurate diagnostics of experiments with WDM is rendered challenging by the extreme conditions. Indeed, even basic parameters such as the temperature often cannot be measured directly and have to be inferred from other observations. In this context, X-ray Thomson scattering (XRTS) [1] has emerged as a key diagnostic, but the interpretation of an XRTS signal is often based on de-facto uncontrolled approximations such as the decomposition into bound and free electrons within the popular Chihara model.

In this contribution, I outline how one can get direct access to the physical properties of interest by analyzing the measured signal in the imaginary-time domain [2]. No simulations/models and, therefore, no approximations are required. First and foremost, this allows us to infer the temperature of a given system with high accuracy [3]. Moreover, we can use XRTS to probe electron—electron correlations by utilizing the f-sum rule in the imaginary-time domain [4]. Finally, we show how the idea of imaginary-time correlation functions can be generalized to characterize the degree of nonequilibrium in the probed system [5], with important implications for equation-of-state measurements and the understanding of relaxation times.

[1] S. Glenzer and R. Redmer, Reviews of Modern Physics 81, 1625 (2009)

[2] T. Dornheim et al, arXiv:2209.02254 (submitted)

[3] T. Dornheim et al, Nature Communications 13, 7911 (2022)

[4] T. Dornheim et al, arXiv:2305.15305 (submitted)

[5] J. Vorberger et al, arXiv:2302.11309 (submitted)

  • Lecture (Conference)
    APS DPP, 30.10.-03.11.2023, Denver, USA

Permalink: https://www.hzdr.de/publications/Publ-37762
Publ.-Id: 37762


Fate of Oxidation States at Actinide Centers in Redox-Active Ligand Systems Governed by Energy Levels of 5f Orbitals

Takeyama, T.; Tsushima, S.; Gericke, R.; Kaden, P.; März, J.; Takao, K.

We report the formation of a Np(IV) complex from the complexation of Np(VI)O22+ with the redox-active ligand tBu-pdiop2-=2,6-bis[N-(3,5-di-tert-butyl-2-hydroxyphenyl)iminomethyl]pyridine. To the best of our knowledge, this is the first example of the direct complexation-induced chemical reduction of Np(VI)O22+ to Np(IV). In contrast, the complexation of U(VI)O22+ with tBu-pdiop2- did not induce the reduction of U(VI)O22+, not even after the two-electron electrochemical reduction of [U(VI)O2(tBu-pdiop)]. This contrast between the Np and U systems may be ascribed to the decrease of the energy of the 5f orbitals in Np compared to those in U. The present findings indicate that the redox chemistry between U(VI)O22+ and Np(VI)O22+ should be clearly differentiated in redox-active ligand systems.

Permalink: https://www.hzdr.de/publications/Publ-37759
Publ.-Id: 37759


Extended-gate field-effect transistor chemo- and biosensors: State of the art and perspectives

Janićijević, Ž.; Nguyen Le, T. A.; Baraban, L.

Extended-gate field-effect transistor (EG-FET) chemo- and biosensors are emerging tools for a wide range of biomedical applications. Significant efforts have been made to make them ultrasensitive to biomolecules via the development of miniaturized sensing transistors, design and optimization of extended gate sensing layer, exploration of the multiplexing ability of EG-FET configuration, and advanced data analysis. Here, we specifically focus on several important aspects related to the construction and current applications of EG-FET sensors. Namely, we review the materials, fabrication, properties of the transducer, specificities of the conditioning electronics, and signal analysis. At the same time, we discuss the current drawbacks of these sensors preventing their straightforward commercialization, such as output signal variation and non-linearities of the response. We also review the recent key applications of EG-FET sensors in the areas of early medical diagnostics, ecology, food and chemical industries, and others. Finally, we briefly discuss the future perspectives in the development of this class of sensors.

Keywords: Extended gate; Field-effect transistors; Bioelectronics; Biosensors; Potentiometric measurement; Nanosensors

Permalink: https://www.hzdr.de/publications/Publ-37758
Publ.-Id: 37758


Possible Eliashberg-Type Superconductivity Enhancement Effects in a Two-Band Superconductor MgB2 Driven by Narrow-Band THz Pulses

Sobolev, S.; Lanz, A. P.; Dong, T.; Pokharel, A.; Kabanov, V.; Xu, T.-Q.; Wang, Y.; Gan, Z.-Z.; Shi, L.-Y.; Wang, N.-L.; Pashkin, O.; Uykur, E.; Winnerl, S.; Helm, M.; Demsar, J.

We study THz-driven condensate dynamics in epitaxial thin films of MgB2, a prototype two-band superconductor (SC) with weak interband coupling. The temperature and excitation density dependent dynamics follow the behavior predicted by the phenomenological bottleneck model for the single-gap SC, implying adiabatic coupling between the two condensates on the ps timescale. The amplitude of the THz-driven suppression of condensate density reveals an unexpected decrease in pair-breaking efficiency with increasing temperature—unlike in the case of optical excitation. The reduced pair-breaking efficiency of narrow-band THz pulses, displaying minimum near ≈0.7  Tc, is attributed to THz-driven, long-lived, nonthermal quasiparticle distribution, resulting in Eliashberg-type enhancement of superconductivity, competing with pair breaking.

Related publications

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Permalink: https://www.hzdr.de/publications/Publ-37757
Publ.-Id: 37757


Investigation of microalgae and bubble interaction in electroflotation via image processing

Marquardt, T.; Schwarzenberger, K.; Krujatz, F.; Eckert, K.

Microalgae are becoming increasingly important for numerous applications such as food or pharmaceutical products. Flotation is an effective and comparatively inexpensive process for dewatering of the algal biomass after cultivation. In electroflotation, the hydrophobic algal cells attach to the surface of rising gas bubbles generated by water electrolysis and can be removed as a concentrated froth. For enhanced floatability, the size of microalgae can be increased by flocculation, e.g., with chitosan. Chitosan is a non-toxic, non-contaminating biopolymer that has proven to be a practical flocculant for microalgae. The effectiveness of the flotation process is influenced by numerous variables. At the same time, the mechanisms of the attachment of the algae to the bubbles are not fully understood. Hence, the aim of the presented work is to gain a deeper insight into the processes involved in the electroflotation of microalgae, like the algae-bubble-interaction, using optical measurement methods and machine learning (ML) based image processing.
A main focus is on the number and size of bubbles generated by electrolysis, as well as the size of Chlorella vulgaris agglomerates created by flocculation with chitosan. The properties of the bubbles were influenced by changing the electrolysis voltage and evaluated by image processing methods on microscopic images. Using laser diffraction spectroscopy, the influence of different chitosan dosages and flocculation times on the agglomerate size were analyzed. The size distribution is found to depend strongly on the varying biological properties of the microalgal suspension. Nevertheless, some general recommendations for an optimal chitosan concentration range could be deduced. In order to identify conditions promoting a successful attachment of algae to bubbles, an ML based method using series of microscopic images for visualization of the rising bubble and agglomerate paths during bubble-algal interaction was developed. The results show that a similar size of bubble and microalgal agglomerate is beneficial for enhanced bubble-algae interaction. For the analyzed voltage range, the mean bubble size was approximately 20 μm. The flocculation experiments showed that agglomerate sizes of 20 μm or higher are also achievable and thus, the microalgae flocs can be tuned to a well-floatable size range. Summing up, it was possible to derive first conclusions on how to promote effective electroflotation of microalgae. The developed visualization method contributes to a better understanding of flotation mechanisms and can be used as a basis for further research.

Keywords: Electroflotation; Microalgae; Image Processing; Flocculation; Rising Bubbles

  • Lecture (Conference)
    93rd Annual Meeting of the International Association of Applied Mathematics and Mechanics, 30.05.-02.06.2023, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-37756
Publ.-Id: 37756


Evaluating Iron Ore Characteristics through Machine Learning and 2D LiDAR Technology

Matos, S.; Pinto, T.; Domingues, J.; Ranieri, C.; Albuquerque, K.; Moreira, V.; Souza, E.; Ueyama, J.; Melo Euzebio, T. A.; Pessin, G.

Conveyor belts are the most effective way to transport ore in a mining complex. The ore that comes from the mining areas can be heterogeneous in size and type. As the ore needs to pass through several processing steps, online information about the ore’s type and degree of fragmentation can help improve mineral processing for both safety and efficiency. Current instrumentation systems are expensive and require frequent calibration and maintenance. This paper presents a novel intelligent instrument for online recognition of type and degree of fragmentation. A 2D LiDAR sensor and machine learning techniques were used to estimate the characteristics of iron ore particles on conveyor belts. An experiment was conducted using several types of ore and granulometry. Five machine learning models were compared using statistical methods, including analysis of average accuracy and normality and hypotheses tests. Among them, the Random Forest models achieved the highest average accuracy, 93.81% for ore type and 85.52% for the degree of fragmentation. These models were improved by a voting mechanism, resulting in a reduction of classification errors of 93.3% for ore type and 99.2% for the degree of fragmentation. These findings demonstrate potential for improving mineral processing controls and elevating operational safety within the mining sector.

Keywords: Light Detection and Ranging; Conveyor Belt; Machine Learning; Mining Industry

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  • Secondary publication expected from 13.12.2024

Permalink: https://www.hzdr.de/publications/Publ-37754
Publ.-Id: 37754


Data publication: Unraveling dispersion and buoyancy dynamics around radial A + B → C reaction fronts: microgravity experiments and numerical simulations.

Stergiou, Y.; Escala Vodopivec, D.; Papp, P.; Horváth, D.; Hauser, M.; Brau, F.; de Wit, A.; Tóth, Á.; Eckert, K.; Schwarzenberger, K.

This dataset includes the image data obtained from the Sounding Rocket experiment (TEXUS 57) and numerical simulation data.

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Permalink: https://www.hzdr.de/publications/Publ-37753
Publ.-Id: 37753


µCT data of two drill cores of fractured crystalline rock (Grimsel)

Kulenkampff, J.
DataCollector: Loesel, Dagmar; DataCollector: Schoessler, Claudia; Researcher: Jankovsky, Filip; Researcher: Zuna, Milan

Two crystalline rock drill cores from the Grimsel site were scanned with a Nikon XT H 225 - scanner. The samples were prepared (formatted and cast in epoxy) by UJV Rez, Czech Republic. The CT-data were acquired and processed at HZDR-FWOT.

Sample 1 (GAM_UJV_1C_1) contains a complex system of interconnected fractures.
Sample 2 (GAM_UJV_1C_2) contains one single end-to-end fracture with larger aperture.

Size of both samples: Diameter 80 mm, length 165 mm.

Two tomograms were acquired for both samples:
1) Complete drill core as one scan, voxel size ca. 75 µm.
2) HR-tomogram merged from three sections with maximum resolution, voxel size ca. 40 µm.

The tomograms were stored as 3D-raw files. Data format, acquisition parameters, and processing workflow, are documented in the tomogram header files (nrrd-format (text):  see https://teem.sourceforge.net/nrrd/format.html).
This data format is importable into open-source visualization programs as 3D slicer (https://www.slicer.org) or Paraview (https://www.paraview.org). The data processing has been conducted with Avizo (https://www.thermofisher.com/de/de/home/electron-microscopy/products/software-em-3d-vis/avizo-software.html).

Files:
Sample 1
GAM_UJV_1C_1_complet-2_01_NLM: Graylevel image of complete sample, ring artifact removal, non-local-means filter
GAM_UJV_1C_1_complet-2_01_thresholded: Tentative label image of complete sample, threshold segmentation with manual edit
Merged-GAM_UJV_1C_1_HR.Frac_section: Graylevel image of merged fracture section, unfiltered
Merged-GAM_UJV_1C_1_HR.Frac_section.Threshold: Tentative label image of merged fracture section, adaptive threshold segmentation with manual edit
GAM_UJV_1C_1_complet_2.png: Figure of complete sample 
GAM_UJV_1C_1_HR_Frac_Y2.png: Figure of merged high-resolution tomogram

Sample 2
GAM_UJV_1C_2_complet_01.filtered: Graylevel image of complete sample, ring artifact removal, non-local-means filter
GAM_UJV_1C_2_complet_01.filtered.thresholded: Tentative label image of complete sample,  threshold segmentation with manual edit
Merged-GAM_UJV_1C_2_A_01.Frac_section.filtered: Graylevel image of merged fracture section, ring artifact removal, non-local-means filter
Merged-GAM_UJV_1C_2_A_01.Frac_section.filtered.segm: Tentative label image of merged fracture section, threshold segmentation with manual edit
GAM_UJV_1C_2_complett_2.png: Figure of complete sample
GAM_UJV_1C_2_HR_Frac_Y2.png: Figure of merged high-resolution tomogram

Original acquistion data are stored on the HZDR bulk data storage system and available for reprocessing on request.


Financial support was granted from the European Union’s Horizon 2020 research and innovation program under grant agreement No. 847593 (EURAD, WP FUTURE, task 2.2).
 

Keywords: X-ray computed tomography; crystalline rock; granite; drill core; fracture

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Permalink: https://www.hzdr.de/publications/Publ-37750
Publ.-Id: 37750


A Monte Carlo photonic model to simulate the UV inactivation of airborne microorganisms

Cavagnola, M. A.; Hampel, U.; Lecrivain, G.

The goal is to develop a model based on a photonic approach that allows us to track each of the flowing airborne microorganisms and predict, by using a kinetic Monte Carlo algorithm, whether it is active or not

  • Poster
    DLR GANDALF - Graduate School, 26.10.2023, Köln, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-37748
Publ.-Id: 37748


Magneto-structural phase transitions for direct magnetic patterning

Bali, R.; Potzger, K.; Lindner, J.; Faßbender, J.

The use of focused ion beams for sensitively controlling the intrinsic magnetic as well as transport properties at the nanoscale requires materials, wherein small atomic displacements results in large property changes. Typical examples are binary alloys consisting of a 3d metal such as Fe and elements such as Al [1], Rh [2] and most recently, V [3]. These materials act as non-ferromagnetic templates onto which atomic reordering within confined regions can be used to realize the direct writing of ferromagnetism. These alloys are deployed as prototypes for exploring nanoscale ion-induced property modulation.

The type of phase transition may vary, for instance, a transition in the chemical order of Fe60Al40 in contrast with the emergence of a crystalline lattice from a short-range ordered structure in Fe60V40. Due to chemical disordering, the localized ferromagnetic in the former alloy imparts spin scattering that can be observed in the anomalous Hall effect, whereas in the latter, the lattice reordering propagates in a layer like fashion providing homogenous ferromagnetic layers. The phase transition characteristics influence their potential applications, such as in ferromagnetic resonance and transport.

Observations of the evolving nearest-neighbour environment of atoms as a function of the atomic displacements helps unravel some of the microscopic processes leading to the large intrinsic property changes. This current research is being performed with the help of large-scale facilities, such as the Ion-Beam-Centre as well as the ELBE at HZDR.

References:

1. S. Sorokin et al., New J. Phys. (2023).
2. W. Griggs et al., APL Materials (2020) 8, 121103.
3. Md. S. Anwar et al., ACS Appl. Elec. Mater. (2022) 4, 8, 3860.

Keywords: ion irradiation; magnetism; magnetic patterning; structural phase transition

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  • Invited lecture (Conferences)
    7th International Conference on Nanostructuring by Ion Beams (ICNIB 2023), 02.-04.11.2023, Dehradun, Indien

Permalink: https://www.hzdr.de/publications/Publ-37747
Publ.-Id: 37747


Systematic investigation of the Pygmy Dipole Resonance near the magic N = 82 shell closure

Kluwig, F.; Müscher, M.; Savran, D.; Schwengner, R.; Schüttler, T.; Zilges, A.

The Pygmy Dipole Resonance is part of the electric dipole response of an atomic nucleus. There are still several open questions concerning, e.g., its structure. Systematic studies are crucial to improve the knowledge of this excitation mode. Such systematic studies have already been performed along the magic N = 82
isotonic chain using the Nuclear Resonance Fluorescence (NRF) technique, hinting to a trend of increasing strength with increasing N/Z ratio. Comparing these results to those from further NRF experiments on neighbouring non-magic isotopes and on 142Ce, a more fragmented strength distribution seems to occur.

Keywords: Nuclear structure; Dipole excitations; Nuclear resonance fluorescence; Photon scattering; Gamma-ray spectroscopy

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Permalink: https://www.hzdr.de/publications/Publ-37745
Publ.-Id: 37745


Dipole excitations in open shell nuclides near the neutron threshold energy from (g,g') experiments: The case of Ge isotopes

Benouaret, N.; Schwengner, R.; Massarczyk, R.; Shizuma, T.; Bemmerer, D.; Beyer, R.; Junghans, A.; Wagner, A.

The dipole response of the open-shell nuclide 70Ge has been investigated in high-resolution (g,g') experiments using bremsstrahlung produced with electron beams of energies of 8.5 and 14.7 MeV at the linear accelerator ELBE. A resonance-like structure of levels mostly with spin J = 1 has been identified, distributed between 5 MeV up to neutron separation energy Sn as in the case of 76Ge and in contast to 74Ge where the level density is lower and ceases abruptly at about 1 MeV below Sn . The distibution strength was complemented by the unresolved levels using simulations of statistical gamma-ray cascades, corrected by estimations of branching transitions. The summed strength in 70 Ge, completed by the data from 74,76Ge do not fit with a linear trend as function
of the neutron excess. Such unexpected behaviour might be related to the nuclear deformation which seems to play the major role in the moderately deformed germanium isotopic chain.

Keywords: Nuclear structure; Dipole excitations; Photon scattering; Nuclear resonance fluorescence; Gamma-ray cascades

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Permalink: https://www.hzdr.de/publications/Publ-37744
Publ.-Id: 37744


UQTestFuns: A Python3 Library of Uncertainty Quantification (UQ) Test Functions

Wicaksono, D. C.; Hecht, M.

UQTestFuns is an open-source Python3 library of test functions commonly used within the applied uncertainty quantification (UQ) community. Specifically, the package provides:

  • an implementation with minimal dependencies (i.e., NumPy and SciPy) and a common interface of many test functions
  • single entry point collecting test functions and their probabilistic input specifications in a single Python package
  • an opportunity for an open-source contribution, supporting the implementation of new test functions or posting reference results.

In short, UQTestFuns is an homage to the Virtual Library of Simulation Experiments (VLSE).

v0.4.1 includes one additional test function used in the context of metamodeling. The package documentation has been updated following the review process during the submission to the Journal of Open Source Software (JOSS). This release is part of the acceptance of the package to JOSS.

This archive is part of the archival process to ROBIS.

Keywords: python; uncertainty-quantification; benchmark; sensitivity-analysis; metamodeling; reliability-analysis

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Permalink: https://www.hzdr.de/publications/Publ-37736
Publ.-Id: 37736


UQTestFuns: A Python3 library of uncertainty quantification (UQ) test functions

Wicaksono, D. C.; Hecht, M.

Researchers are continuously developing novel methods and algorithms in the field of applied uncertainty quantification (UQ).
During the development phase of a novel method or algorithm, researchers and developers often rely on test functions taken from the literature for validation purposes.
Afterward, they employ these test functions as a fair means to compare the performance of the novel method against that of the state-of-the-art methods in terms of accuracy and efficiency measures.

UQTestFuns is an open-source Python3 library of test functions commonly used within the applied UQ community.
Specifically, the package provides:

  • an implementation with minimal dependencies (i.e., NumPy and SciPy) and a common interface of many test functions available in the UQ literature
  • a single entry point collecting test functions and their probabilistic input specifications in a single Python package
  • an opportunity for an open-source contribution, supporting the implementation of new test functions and posting reference results.

UQTestFuns aims to save the researchers' and developers' time from having to reimplement many of the commonly used test functions themselves.

Keywords: test functions; benchmark; uncertainty quantification; metamodeling; surrogate modeling; sensitivity analysis; reliability analysis; rare event estimation

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Permalink: https://www.hzdr.de/publications/Publ-37735
Publ.-Id: 37735


DAG Optimizations for Feynman Diagrams of High-Multiplicity Scattering Processes in Julia

Reinhard, A.; Ehrig, S.; Hernandez Acosta, U.; Widera, R.

The description of scattering processes in high-energy physics is usually done with Feynman Diagrams. The number of Feynman Diagrams that can be generated for a given process explodes factorially with the number of particles. We discuss a possible approach enabling the calculation of higher-multiplicity scattering processes. We propose representing the calculation for a process as a directed acyclic graph (DAG) of small computation tasks. Using Julia, we can optimize this graph using subgraph replacement strategies together with an optimization algorithm. Finally, efficient code targeting arbitrary heterogeneous HPC systems can be generated from the optimized DAG.

Keywords: Julia; Scattering Processes; Compton; High-Energy Physics; DAG; Optimization; HPC

  • Open Access Logo Lecture (Conference)
    JuliaHEP 2023 Workshop, 06.-09.11.2023, Erlangen Centre for Astroparticle Physics, Deutschland

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Permalink: https://www.hzdr.de/publications/Publ-37734
Publ.-Id: 37734


Tunable room-temperature non-linear Hall effect from the surfaces of elementary bismuth thin films

Makarov, D.

In this presentation I will describe our recent experiments with polycrystalline Bi thin films, where we observed non-linear Hall effect.

Keywords: Bi thin films; non-linear Hall effect; geometric non-linear Hall effect

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  • Invited lecture (Conferences) (Online presentation)
    Annual meeting of the Lu Jiaxi international team, 25.-26.11.2023, Ningbo, China

Permalink: https://www.hzdr.de/publications/Publ-37733
Publ.-Id: 37733


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