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34877 Publications

Observation of strong magneto plasmonic nonlinearity in bilayer graphene discs

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

Graphene patterned into plasmonic structures like ribbons or discs strongly increases the linear and nonlinear optical interaction at resonance. The nonlinear optical response is governed by hot carriers, leading to a red-shift of the plasmon frequency. In magnetic fields, the plasmon hybridizes with the cyclotron resonance, resulting in a splitting of the plasmonic absorption into two branches. Here we present how this splitting can be exploited to tune the nonlinear optical response of graphene discs. In the absence of a magnetic field, a strong pump-induced increase in on-resonant transmission can be observed, but fields in the range of 3 T can change the characteristics completely, leading to an inverted nonlinearity. A two temperature model is provided that describes the observed behavior well.

Keywords: magnetoplasmonics; graphene; nonlinear optics

Related publications

Permalink: https://www.hzdr.de/publications/Publ-31743
Publ.-Id: 31743


Microbial interaction with and tolerance of radionuclides: underlying mechanisms and biotechnological applications

Lopez Fernandez, M.; Jroundi, F.; Ruiz. Fresneda, M. A.; Merroun, M. L.

Radionuclides (RN) generated by nuclear and civil industries are released in natural ecosystems and may have a hazardous impact on human health and the environment. RN polluted environments harbor different microbial species that become highly tolerant of these elements through mechanisms including biosorption, biotransformation, biomineralization and intracellular accumulation. Such microbial-RN interaction processes hold biotechnological potential for the design of bioremediation strategies to deal with several contamination problems. This paper, with its multidisciplinary approach, provides a state-of-the-art review of most research endeavors aimed to elucidate how microbes deal with radionuclides and how they tolerate ionizing radiations. In addition, the most recent findings related to new biotechnological applications of microbes in the bioremediation of radionuclides and in the long-term disposal of nuclear wastes are described and discussed.

Permalink: https://www.hzdr.de/publications/Publ-31741
Publ.-Id: 31741


Multisystem combined uranium resistance mechanisms and bioremediation potential of Stenotrophomonas bentonitica BII-R7: Transcriptomics and microscopic study

Pinel-Cabello, M.; Jroundi, F.; Lopez Fernandez, M.; Geffers, R.; Jarek, M.; Jauregui, R.; Link, A.; Vílchez-Vargas, R.; Merroun, M. L.

The potential use of microorganisms in the bioremediation of U pollution has been extensively described.
However, a lack of knowledge on molecular resistance mechanisms has become a challenge for the use of these technologies. We reported on the transcriptomic and microscopic response of Stenotrophomonas bentonitica BII-R7 exposed to 100 and 250 μM of U. Results showed that exposure to 100 μM displayed up-regulation of 185 and 148 genes during the lag and exponential phases, respectively, whereas 143 and 194 were down-regulated, out of 3786 genes (>1.5-fold change). Exposure to 250 μM of U showed up-regulation of 68 genes and down-regulation of 290 during the lag phase. Genes involved in cell wall and membrane protein synthesis, efflux systems and phosphatases were up-regulated under all conditions tested. Microscopic observations evidenced the formation of U-phosphate minerals at membrane and extracellular levels. Thus, a biphasic process is likely to occur: the increased cell wall would promote the biosorption of U to the cell surface and its precipitation as U-phosphate minerals enhanced by phosphatases. Transport systems would prevent U accumulation in the cytoplasm. These findings contribute to an understanding of how microbes cope with U toxicity, thus allowing for the development of efficient bioremediation strategies.

Permalink: https://www.hzdr.de/publications/Publ-31740
Publ.-Id: 31740


Oxidation of amorphous HfNbTaTiZr high entropy alloy thin films prepared by DC magnetron sputtering

Hruška, P.; Lukáč, F.; Cichoň, S.; Vondráček, M.; Čížek, J.; Fekete, L.; Lančok, J.; Veselý, J.; Minárik, P.; Cieslar, M.; Melikhova, O.; Kmječ, T.; Liedke, M. O.; Butterling, M.; Wagner, A.

High entropy alloys represent a new type of materials with a unique combination of physical properties originating from the occurrence of single-phase solid solutions of numerous elements. The preparation of nanostructured or amorphous structure in a form of thin films promises increased effective surface and high intergranular diffusion of elements as well as a high affinity to oxidation. In this work, we studied HfNbTaTiZr thin films were deposited at room temperature by DC magnetron sputtering from a single bcc phase target. Films exhibit cellular structure (~100 nm) with fine substructure (~10 nm) made of round-shape amorphous clusters. Films composition is close to equimolar with slight Ti enrichment and without any mutual segregation of elements. Oxidation at the ambient atmosphere leads to the formation of Ti, Zr, Nb, Hf, and Ta oxide clusters in the film up to the depth of 200 – 350 nm out of the total film thickness of 1650 nm. Oxygen absorption takes place preferentially in the large vacancy clusters located in between the amorphous cluster aggregates. The dominant type of defect is small open volumes with a size comparable with vacancy. The distribution of these defects is uniform with depth and is not influenced by the presence of oxygen in the film.

Keywords: positron annihilation spectroscopy; high entropy alloys; defects; monovacancy; HfNbTaTiZr; sputtering

Permalink: https://www.hzdr.de/publications/Publ-31738
Publ.-Id: 31738


Methodology for DNS Data-driven Machine Learning Bubble Drag Model and Its Integration to OpenFOAM

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

This work aims to develop a two-phase DNS data-driven bubble drag model and to implement it into a multiphase flow CFD simulation. To accomplish the goal, a Tensorflow (TF)-OpenFOAM(OF) integration interface has been established. Such an interface is capable of calling and making machine learning model to predict a quantity of interest on the fly. A benchmark case for the bubble drag coefficient is proposed to validate the interface. A Feed forward neural network (FNN) approach was utilized to approximate the drag correlation (Tomiyama et al., 1998) using artificially generated data. Results of the integration showed good consistency in radial void fraction and velocity profiles. As the next step actual DNS bubble tracking datasets are used as a data source (Fang et al., 2017, Cambareri et al., 2019). The data segments where bubble have quasi-stable main-stream velocity were filtered out for drag coefficient calculation. The DNS-informed model predicts bubble drag coefficient by taking bubble Reynolds number (Re) and Eötvös number (Eo) as input to consider the effects from local fluid and bubble shape. The model is applied in a Euler-Euler two-phase flow simulation of a bubbly pipe flow in OF. The required closure terms, except the drag model, utilize the baseline model of Liao et al. (2020) The results of radial void fraction and velocity profiles are discussed and compared to a reference solution with the baseline model.

Keywords: DNS; bubbly flow; drag; machine learning

  • Lecture (Conference) (Online presentation)
    APS DFD Annual Meeting, 22.-24.11.2020, Chicago - online, USA
  • Contribution to proceedings
    APS DFD Annual Meeting, 22.-24.11.2020, Chicago - online, USA

Permalink: https://www.hzdr.de/publications/Publ-31737
Publ.-Id: 31737


Short-duration dynamic FDG PET imaging: Optimization and clinical application

Samimi, R.; Kamali-Asl, A.; Geramifar, P.; van den Hoff, J.; Rahmim, A.

We aimed to investigate whether short dynamic PET imaging started at injection, complemented with routine clinical acquisition at 60-min post-injection (static), can achieve reliable kinetic analysis.
Methods
Dynamic and static 18F-2-fluoro-2-deoxy-D-glucose (FDG) PET data were generated using realistic simulations to assess uncertainties due to statistical noise as well as bias. Following image reconstructions, kinetic parameters obtained from a 2-tissue-compartmental model (2TCM) were estimated, making use of the static image, and the time duration of dynamic PET data were incrementally shortened. We also investigated, in the first 2-min, different frame sampling rates, towards optimized dynamic PET imaging. Kinetic parameters from shortened dynamic datasets were additionally estimated for 9 patients (15 scans) with liver metastases of colorectal cancer, and were compared with those derived from full dynamic imaging using correlation and Passing–Bablok regression analyses.
Results
The results showed that by reduction of dynamic scan times from 60-min to as short as 5-min, while using static data at 60-min post-injection, bias and variability stayed comparable in estimated kinetic parameters. Early frame samplings of 5, 24 and 30 s yielded highest biases compared to other schemes. An early frame sampling of 10 s generally kept both bias and variability to a minimum. In clinical studies, strong correlation (r ≥ 0.97, P < 0.0001) existed between all kinetic parameters in full vs. shortened scan protocols.
Conclusions
Shortened 5-min dynamic scan, sampled as 12 × 10 + 6 × 30 s, followed by 3-min static image at 60-min post-injection, enables accurate and robust estimation of 2TCM parameters, while enabling generation of SUV estimates.

Keywords: Dynamic PET; Kinetic modelling; GATE; STIR; FDG PET

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Permalink: https://www.hzdr.de/publications/Publ-31736
Publ.-Id: 31736


Message from the Guest Editor of the 17th Multiphase Flow Conference Special Issue

Lucas, D.

Selected contributions of the 17th Multiphase Flow Conference at HZDR were published in a special issue of the Open Access Journal Experimental and Computational Multiphase Flow. In this contribution an overview on the conference and a short introduction to the single papers is given.

Keywords: multiphase flow; conference

  • Open Access Logo Abstract in refereed journal
    Experimental and Computational Multiphase Flow 3(2021)3, 137-138
    DOI: 10.1007/s42757-020-0087-x

Permalink: https://www.hzdr.de/publications/Publ-31735
Publ.-Id: 31735


Data for: Bonding Trends in Tetravalent Th–Pu Monosalen Complexes

Radoske, T.; März, J.; Patzschke, M.; Kaden, P.; Walter, O.; Schmidt, M.; Stumpf, T.

[AnCl2(salen)(Pyx)2] (H2salen=N,N′‐bis(salicylidene)ethylenediamine; Pyx=pyridine, 4‐methylpyridine, 3,5‐dimethylpyridine) + An(IV) with An=Th, U, Np, and Pu.

EA data, QC calculation results, NMR spectra and data analysis.

Related publications

  • Reseach data in the HZDR data repository RODARE
    Publication date: 2020-12-15
    DOI: 10.14278/rodare.585

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-31730
Publ.-Id: 31730


Measurement of Ehrlich-Schwoebel barrier contribution to the self-organized formation of ordered surface patterns on Ge(001)

Myint, P.; Erb, D.; Zhang, X.; Wiegart, L.; Zhang, Y.; Fluerasu, A.; Headrick, R.; Facsko, S.; Ludwig, K.

Normal-incidence 1-keV Ar+ ion bombardment leads to amorphization and ultrasmoothing of Ge at room temperature, but at elevated temperatures the Ge surface remains crystalline and is unstable to the formation of self-organized nanoscale patterns of ordered pyramid-shaped pits. The physical phenomenon distinguishing the high-temperature patterning from room-temperature ultrasmoothing is believed to be a surface instability due to the Ehrlich-Schwoebel barrier for diffusing vacancies and adatoms, which is not present on the amorphous material. This real-time grazing-incidence small-angle x-ray scattering study compares smoothing of a prepatterned Ge sample at room temperature with patterning of an initially flat Ge sample at an elevated temperature. In both experiments, when the nanoscale structures are relatively small in height, the average kinetics can be explained by a linear theory. The linear theory coefficients, indicating surface stability or instability, were extracted for both experiments. A comparison between the two measurements allows estimation of the contribution of the Ehrlich-Schwoebel barrier to the self-organized formation of ordered nanoscale patterns on crystalline Ge surfaces.

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Permalink: https://www.hzdr.de/publications/Publ-31729
Publ.-Id: 31729


The role of computational methods for automating and improving clinical target volume definition

Unkelbach, J.; Bortfeld, T.; Cardenas, C. E.; Gregoire, V.; Hager, W.; Heijmen, B.; Jeraj, R.; Korreman, S. S.; Ludwig, R.; Pouymayou, B.; Shusharina, N.; Söderberg, J.; Toma-Dasu, I.; Troost, E. G. C.; Osorio, E. V.

Treatment planning in radiotherapy distinguishes three target volume concepts: the gross tumor volume (GTV), the clinical target volume (CTV), and the planning target volume (PTV). Over time, GTV definition and PTV margins have improved through the development of novel imaging techniques and better image guidance, respectively. CTV definition is sometimes considered the weakest element in the planning process. CTV definition is particularly complex since the extension of microscopic disease cannot be seen using currently available in-vivo imaging techniques. Instead, CTV definition has to incorporate knowledge of the patterns of tumor progression. While CTV delineation has largely been considered the domain of radiation oncologists, this paper, arising from a 2019 ESTRO Physics research workshop, discusses the contributions that medical physics and computer science can make by developing computational methods to support CTV definition. First, we overview the role of image segmentation algorithms, which may in part automate CTV delineation through segmentation of lymph node stations or normal tissues representing anatomical boundaries of microscopic tumor progression. The recent success of deep convolutional neural networks has also enabled learning entire CTV delineations from examples. Second, we discuss the use of mathematical models of tumor progression for CTV definition, using as example the application of glioma growth models to facilitate GTV-to-CTV expansion for glioblastoma that is consistent with neuroanatomy. We further consider statistical machine learning models to quantify lymphatic metastatic progression of tumors, which may eventually improve elective CTV definition. Lastly, we discuss approaches to incorporate uncertainty in CTV definition into treatment plan optimization as well as general limitations of the CTV concept in the case of infiltrating tumors without natural boundaries.

Keywords: Automatic image segmentation; Clinical target volume; Computational tumor growth models

Permalink: https://www.hzdr.de/publications/Publ-31728
Publ.-Id: 31728


Numerical modeling and simulation of reactive flow and transport processes in subsurface formations

Yuan, T.

Subsurface water-rock interactions involve the coupled phenomena of chemical reactions and fluid transport, in which the chemical reactions between minerals and water can cause mineral dissolution/precipitation and aqueous species adsorption/desorption. The subsurface reactive transport processes play an important role in the enhanced prediction of oil and gas migration in the petroleum reservoirs as well as radionuclides migration in the host rocks. Consequently, an efficient numerical model that can rigorously capture such coupled phenomena is thus essential to the optimized design of implementations for those addressed problems.
In this talk, we first present a 3D mathematical model that couples the Stokes-Brinkman equation and reactive transport model for modeling the coupled processes of reactive flow and transport in fractured porous media. The numerical experiments show that the proposed model can efficiently simulate the coupled processes of fluid flow, reactive transport, and alterations of rock properties in fractured porous media under both linear and radial flow. Secondly, we focus on radionuclides transport and retention in claystone formations using GeoPET analysis and reactive transport modeling. We propose an integrated upscaling workflow to predict effective diffusivity of radionuclides diffusion in the shaly facies of Opalinus clay based on the reconstructed multi-scale digital rocks. The GeoPET measurements provide analytical insights into spatial and temporal tracer distribution, which can be utilized to validate the numerical model. The combination of pore-scale reactivity and core scale transport modeling provides critical insight into the radionuclide migration heterogeneity. We discuss these results with a focus on upscaling strategies to the field scale of host rocks.

  • Invited lecture (Conferences) (Online presentation)
    Numerical simulation of subsurface flow, 25.09.2020, Beijing, China

Permalink: https://www.hzdr.de/publications/Publ-31727
Publ.-Id: 31727


Quantification of the Inconvenient Truths about the Circular Economy (CE) Digital Twinning of Very Large Systems

Bartie, N. J.; Reuter, M.

We discuss the limitations to material flows from recycling in the circular economy, using as a case the simulation-based analysis of the CdTe Photovoltaic cells. It is important to use a simulation basis for the analysis, since this permits the quantification of all material losses both in terms of exergy and energy simultaneously i.e. 1st and 2nd law of thermodynamics. Harmonizing this with the power supply flowing into the system and minimizing energy usage as well as exergy losses will maximize the resource efficiency.

  • Open Access Logo Contribution to external collection
    Dagmar Boedicker, Sebastian Jekutsch, Dietrich Meyer-Ebrecht: FIfF-Kommunikation 3/2020 Technologie und Ökologie, Bremen: FIfF e.V., 2020, 0938-3476, 43-48

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Permalink: https://www.hzdr.de/publications/Publ-31726
Publ.-Id: 31726


Radionuclide transport and retention at the core scale identified by GeoPET analysis and reactive transport modeling

Yuan, T.; Kulenkampff, J.; Bollermann, T.; Fischer, C.

Low-permeability Opalinus clay formations are considered as a potential host rock for the storage of high-level nuclear waste (Nagra 2002). The diffusion of dissolved species is the dominating transport process in this rock type (Van Loon et al. 2003). Stratification and spatial variability of composition cause anisotropic and heterogeneous diffusion patterns, which could significantly speed up diffusive transport compared to commonly assumed homogeneous conditions. Anisotropy of diffusive transport has been studied on oriented samples in diffusion cells and with positron emission tomography (Kulenkampff et al. 2016). The heterogeneity of the diffusive spreading is increased still further due to sandy layers and diagenetic carbonates, affecting the radionuclide migration behavior at the core scale.
Here, we parameterize a reactive transport model by using experimental and analytical data on Eu(III) sorption efficiency at the pore scale. The effective retention coefficients calculated at the pore scale serve as input values for the reactive transport simulation at the core scale. Diffusive transport model parametrization utilizes GeoPET/μCT results on the migration behavior of 22Na+ at the core scale. Numerical simulation is performed using an existing code (Yuan et al. 2019), which contains the reactive transport model for simulating reactive diffusion process at the core scale. The combination of pore-scale reactivity and core scale transport modeling provides critical insight into the radionuclide migration heterogeneity. We discuss these results with a focus on upscaling strategies to the field scale of host rocks.

  • Lecture (Conference) (Online presentation)
    InterPore 2020, 31.08.-04.09.2020, Qing Dao, China

Permalink: https://www.hzdr.de/publications/Publ-31725
Publ.-Id: 31725


Convection in Liquid Metal Batteries

Weier, T.; Horstmann, G. M.; Landgraf, S.; Nimtz, M.; Personnettaz, P.; Weber, N.

The quest for renewable energy sources entails an increasingly intermittent electricity supply.
Transmission grid updates can only partially account for balancing the resulting variations and large-scale stationary storage will gain importance in future energy landscapes dominated by volatile sources.
Today’s battery technologies were, with the notable exception of redox-flow batteries, mainly designed for and driven by mobile applications. Those prioritize properties (energy density, power rating) that are less important for stationary storage. Thus, battery technologies developed from the ground up to meet the needs of stationary storage have the potential to much better address the specifics of huge capacity installations.
Liquid metal batteries (LMBs) are a new technology for grid-scale energy storage. They consist of all liquid cells that operate with liquid metals as electrodes and molten salts as electrolytes. The liquids separate into three stably stratified layers by virtue of density and mutual immiscibility. This conceptually very simple and self-assembling structure has the unique advantage to allow for an easy scale-up at the cell level: single-cell cross sections can potentially reach several square-meters. Such cell sizes enable highly favourable and otherwise unattainable ratios of active to construction material because of the cubic scaling (volume) of the former and the quadratic scaling (surface) of the latter. The total costs should therefore largely be determined by those of the active materials.
The talk will start with a general introduction to LMBs and then focus on the fluid mechanics in these devices. Electric currents, magnetic fields, and heat and mass transfer are tightly coupled with the cells’ electrochemistry. First a number of fluid dynamic instabilities will be discussed in relation to operational safety. The remainder of the talk will deal with transport phenomena in the positive electrode. While transport in most modern battery systems is typically dominated by diffusion and migration in micrometer-scale liquid layers and solids, convection - with exception of the aforementioned redox-flow batteries - rarely plays a role. This is in stark contrast to LMBs were mediated by the fully liquid interior fluid flow can be driven by various mechanisms. The influence of solutal convection on the cycling behavior of a cell will be demonstrated. Electromagnetically induced convection can be used to improve mixing thereby mitigating diffusion overpotentials.

  • Invited lecture (Conferences) (Online presentation)
    Liquid Metal Technologies, 20.11.2020, Morelia, Mexiko

Permalink: https://www.hzdr.de/publications/Publ-31723
Publ.-Id: 31723


Accurate determination of quasi-particle electronic and optical spectra of anatase titanium dioxide

Sruthil Lal, S. B.; Devaraj, M.; Posselt, M.; Sharan, A.

The electronic structure and quasi-particle absorption spectra of anatase titanium dioxide has been calculated by employing state of the art density functional theory(DFT) and Many-Body Perturbation Theory methods(MBPT) within the framework of Hybrid Density Functional(HSE). GW methods are used in combination with Bethe-Salpeter Equation (BSE) to determine the Quasi Particle energy levels and the role of excitons in optical absorption spectra. Accurate optical and electronic band gap are determined from these methods. In addition to it an analysis of charge redistribution within the anatase unit cell is also presented within the PBE - DFT to analyze the orbital hybridization patterns and the character of chemical bonds.

Keywords: Anatase Titanium Oxide; Density Functional Theory; Electronic structure; Optical Spectra

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Permalink: https://www.hzdr.de/publications/Publ-31722
Publ.-Id: 31722


Tailoring Particle-enzyme Nanoconjugates for Biocatalysis at the Organic-organic Interface

Sun, Z.; Cai, M.; Hübner, R.; Ansorge-Schumacher, M. B.; Wu, C.

Nonaqueous Pickering emulsions (PEs) are a powerful platform for catalysis design, offering both a large interface contact and a preferable environment for water-sensitive synthesis. However, up to now, little progress has been made to incorporate insoluble enzymes into the nonaqueous system for biotransformation. Herein, we present biocatalytically active nonaqueous PEs, stabilized by particle-enzyme nanoconjugates, for the fast transesterification and esterification, and eventually for biodiesel synthesis. Our nanoconjugates are the hybrid biocatalysts tailor-made by loading hydrophilic Candida antarctica lipase B onto hydrophobic silica nanoparticles, resulting in not only catalytically active but highly amphiphilic particles for stabilization of a methanol-decane emulsion. The enzyme activity in these PEs is significantly enhanced, ca. 375-time higher than in the nonaqueous biphasic control. Moreover, the PEs can be multiply reused without significant loss of enzyme performance. With this proof‐of‐concept, we reasonably expect that our system can be expanded for many advanced syntheses using different enzymes in the future.

Keywords: biphasic biocatalysis; nonaqueous Pickering emulsions; solvent-free reactions; enzyme catalysis; nanoconjugates

Permalink: https://www.hzdr.de/publications/Publ-31721
Publ.-Id: 31721


Mechanosynthesis of polymer-stabilized lead bromide perovskites: insight into the formation and phase conversion of nanoparticles

Jiang, G.; Erdem, O.; Hübner, R.; Georgi, M.; Wei, W.; Fan, X.; Wang, J.; Demir, H. V.; Gaponik, N.

The application of polymers to replace oleylamine (OLA) and oleic acid (OA) as ligands for perovskite nanocrystals is an effective strategy to improve their stability and durability especially for the solution-based processing. Herein, we report a mechanosynthesis of lead bromide perovskite nanoparticles (NPs) stabilized by partially hydrolyzed poly(methyl methacrylate) (h-PMMA) and high-molecular-weight highly-branched poly(ethylenimine) (PEI-25K). The as-synthesized NP solutions exhibited green emission centered at 516 nm, possessing a narrow full-width at half-maximum of 17 nm and as high photoluminescence quantum yield (PL QY) as 85%, while showing excellent durability and resistance to polar solvents, e.g., methanol. The colloids of polymer-stabilized NPs were directly processable to form stable and strongly-emitting thin films and solids, making them attractive as gain media. Furthermore, the roles of h-PMMA and PEI-25K in the grinding process were studied in depth. The h-PMMA can form micelles in the grinding solvent of dichloromethane to act as size-regulating templates for the growth of NPs. The PEI-25K with large amounts of amino groups induced significant enrichment of PbBr2 in the reaction mixture, which in turn caused the formation of CsPb2Br5-mPbBr23-Cs4PbBr6-nCsBr NPs. The presence of CsPbBr3-Cs4PbBr6-nCsBr NPs was responsible for the high PL QY, as the Cs4PbBr6 phase with a wide energy bandgap can passivate the surface defects of the CsPbBr3 phase. This work describes a direct and facile mechanosynthesis of polymer-coordinated perovskite NPs and promotes in-depth understanding of the formation and phase conversion for perovskite NPs in the grinding process.

Keywords: lead bromide perovskites; mechanosynthesis; polymer ligands; polymer micelles; poly(ethyleneimine)-i

Permalink: https://www.hzdr.de/publications/Publ-31720
Publ.-Id: 31720


Nonlinear IR and THz Spectroscopy of Semiconductor Nanowires

Helm, M.; Fotev, I.; Balaghi, L.; Lang, D.; Rana, R.; Winnerl, S.; Schneider, H.; Dimakis, E.; Pashkin, A.

We report nonlinear charge-carrier response in GaAs/InGaAs core/shell nanowires that are driven by intense THz pulses. In the first experiment, half-cycle THz pulses emitted from an organic DSTMS crystal lead to a red-shift of the plasmon Peak indicating intervalley transfer of the electrons. In the second experiment, a single, highly electron doped nanowire is investigated by scattering near-field infrared microscopy using intense free-electron laser (FEL) pulses. Here the observed red shift of the mid-infrared plasma resonance depends on the pulse energy and can be explained by heating the electron system in the nonparabolic conduction band.

Keywords: nanowire; THz; infrared; free-electron laser; near-field microscopy; nonlinear

  • Invited lecture (Conferences) (Online presentation)
    45th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz 2020), 08.-13.11.2020, Buffalo, USA

Permalink: https://www.hzdr.de/publications/Publ-31719
Publ.-Id: 31719


Data for: Nonlinear losses in magnon transport due to four-magnon scattering

Hula, T.; Schultheiß, K.; Buzdakov, A.; Körber, L.; Bejarano, M.; Flacke, L.; Liensberger, L.; Weiler, M.; Shaw, J. M.; Nembach, H. T.; Faßbender, J.; Schultheiß, H.

We utilized the following methods in order to obtain the presented data: micro focused Brilluoin light scattering (BLS), micromagnetic simulations in MuMax3 and micro focused magneto-optical Kerr effect (MOKE). The experimental data were obtained on the sample which is labeled with: 'CoFe_WMI_6'. On that sample, we investigated the structures 'E1' and 'F1' which are essentially rectangular stripes (5 micrometer x 65 micrometer, thickness: 30 nm) out of Co25Fe75 alloy. The metadata for all measurements (including ALL parameters) are included in the uploaded primary data subdirectories. The references to the directory of the measured data within our local IT infrastructure are given along with the files themselves. All scripts that were used for data analysis (in Python) are included as well with a short description.

Related publications

  • Reseach data in the HZDR data repository RODARE
    Publication date: 2020-11-26
    DOI: 10.14278/rodare.604

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-31718
Publ.-Id: 31718


Bonding Trends in Tetravalent Th–Pu Monosalen Complexes

Radoske, T.; März, J.; Patzschke, M.; Kaden, P.; Walter, O.; Schmidt, M.; Stumpf, T.

We report the synthesis of three complex series of the form [AnCl₂(salen)(pyx)₂] (H₂salen = N,N’-bis(salicyl¬idene)ethylene-diamine; Pyx = pyridine, 4-methylpyridine, 3,5-dimethylpyridine) with tetravalent early actinides (An = Th, U, Np, Pu) with the goal to elucidate the affinity of these heavy elements for small neutral N-donor molecules. Structure determination via single-crystal XRD and characterization of bulk powders with infrared spectroscopy reveal isostructurality within each respective series and the same complex conformation in all reported structures. While the trend of interatomic distances for An–Cl and An–N (imine nitrogen of salen or pyridyl nitrogen of Pyx) were found to reflect an ionic behaviour, the trend of the An–O distances can only be described with additional covalent interactions for all elements heavier than thorium. All experimental results are supported by quantum chemical calculations, which confirm the mostly ionic character in the An–N and An–Cl bonds, as well as the highest degree of covalency of the An–O bonds. Structurally, the calculations indicate just minor electronic or steric effects of the additional Pyx substituents on the complex properties.

Keywords: tetravalent actinide; salen; covalency; pyridine; bonding analysis; thorium; uranium; neptunium; plutonium

Related publications

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  • Secondary publication expected from 15.12.2021

Permalink: https://www.hzdr.de/publications/Publ-31714
Publ.-Id: 31714


"CFD-grade" Experimental data for Solid-liquid Flow in a Stirred Tank

Sommer, A.-E.; Rox, H.; Eckert, K.; Shi, P.; Rzehak, R.

A solid-liquid flow in stirred tanks occurs frequently in different branches of process engineering where particles need to be suspended in a liquid. Computational Fluid Dynamics (CFD) simulations of such flow on industrial scales are feasible if the closure models implemented therein are appropriate. A large number of closure models exist, but due to a lack of data sources for validation, no systematic assessment of these different models has appeared so far. The present dataset aims to accumulate a comprehensive ''CFD-grade'' database based on experiments of the single-phase and two-phase flows in a standardized stirred tank with a diameter of 90 mm. The velocity fields of the liquid (deionized water) and, in the two-phase case, the solid phase were measured with Particle Image Velocimetry (PIV) and Particle Shadow Velocimetry (PSV), respectively. The experiments cover a range of parameters to achieve an extensive database. A narrow particle distribution of nearly neutrally buoyant particles (polyethylene spheres), as well as heavy particles (glass spheres) in the suspension, are considered over a wide range of particle diameter (63µm-500µm), solid volume fraction (0.025 vol% - 0.1vol%), as well as impeller rotation speed (650rpm - 1500rpm). The transient flow field on the plane midway between two baffles was recorded over 50 impeller rotations to achieve statistical significance. The time-averaged (resp. angle-resolved) mean and fluctuation velocities were then obtained by averaging the transient data in the laboratory frame of reference (resp. the frame of reference rotating with the impeller). The data is organized and analyzed as described in the corresponding journal publication "Solid-liquid Flow in Stirred Tanks: ”CFD-grade” Experimental Investigation".

Keywords: stirred tanks; solid-liquid flow; Particle Image Velocimetry (PIV); Particle Shadow Velocimetry (PSV); "Computational Fluid Dynamics (CFD)-grade" database

  • Reseach data in the HZDR data repository RODARE
    Publication date: 2020-11-15
    DOI: 10.14278/rodare.263

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Permalink: https://www.hzdr.de/publications/Publ-31713
Publ.-Id: 31713


Terahertz magneto-optical investigation of quadrupolar spin-lattice effects in magnetically frustrated Tb2Ti2O7

Amelin, K.; Alexanian, Y.; Nagel, U.; Rõõm, T.; Robert, J.; Debray, J.; Simonet, V.; Decorse, C.; Wang, Z.; Ballou, R.; Constable, E.; de Brion, S.

Condensed matter magneto-optical investigations can be a powerful probe of a material's microscopic magnetoelectric properties. This is because subtle interactions between electric and magnetic multipoles on a crystal lattice show up in predictable and testable ways in a material's optical response tensor, which dictates the polarization state and absorption spectrum of propagating electromagnetic waves. Magneto-optical techniques are therefore strong complements to probes such as neutron scattering, particularly when spin-lattice coupling effects are present. Here we perform a magneto-optical investigation of vibronic spin-lattice coupling in the magnetically frustrated pyrochlore Tb2Ti2O7. Coupling of this nature involving quadrupolar mixing between the Tb3+ electronic levels and phonons in Tb2Ti2O7 has been a topic of debate for some time. This is particularly due to its implication for describing the exotic spin-liquid phase diagram of this highly debated system. A manifestation of this vibronic effect is observed as splitting of the ground and first excited crystal field doublets of the Tb3+ electronic levels, providing a fine structure to the absorption spectra in the terahertz (THz) frequency range. In this investigation, we apply a static magnetic field along the cubic [111] direction while probing with linearly polarized THz radiation. Through the Zeeman effect, the magnetic field enhances the splitting within the low-energy crystal field transitions revealing new details in our THz spectra. Complementary magneto-optical quantum calculations including quadrupolar terms show that indeed vibronic effects are required to describe our observations at 3 K. A further prediction of our theoretical model is the presence of a novel magneto-optical birefringence as a result of this vibronic process. Essentially, spin-lattice coupling within Tb2Ti2O7 may break the optical isotropy of the cubic system, supporting two different electromagnetic wave propagations within the crystal. Together our results reveal the significance of considering quadrupolar spin-lattice effects when describing the spin-liquid ground state of Tb2Ti2O7. They also highlight the potential for future magneto-optical investigations to probe complex materials where spin-lattice coupling is present and reveal new magneto-optical activity in the THz range.

Permalink: https://www.hzdr.de/publications/Publ-31712
Publ.-Id: 31712


Broad Beam-Induced Fragmentation and Joining of Tungsten Oxide Nanorods: Implications for Nanodevice Fabrication and the Development of Fusion Reactors

Rajbhar, M. K.; Möller, W.; Satpati, B.; Manju, U.; Chaudhary, Y. S.; Chatterjee, S.

In this work, for the first time, fragmentation and joining of tungsten oxide (WO3) nanorods induced by a broad ion beam are reported. Although at low energy (5 keV) and moderate ion fluence, nanorods fragment into smaller pieces along the length, at higher ion energies (50-100 keV), a contrary process occurs, which leads to the joining of the nanorods. A state-of-the-art ion-solid interaction simulation, namely, TRI3DYN, has been invoked to explore the possible mechanisms that reveal subtle contributions of surface defects, ion-beam mixing, and sputtering. High-resolution electron microscopy, photoluminescence study, and X-ray photoelectron spectroscopy support the observed results and proposed mechanisms. Such modifications have interesting effects on the electrical conductivity of the nanorod assembly. The change in sample color upon ion irradiation from initial white to yellow, light blue, deep blue, light green, and cyan shows an excellent and reversible chromatic response of tungsten oxide nanorods to irradiation. Such a property can be exploited to fabricate radiation sensors. The fragmentation and joining at different energy scales have essential implications in nanodevice fabrication through the bottom-up approach as well as for the development of fusion reactors.

Keywords: electrical conductivity; fusion reactor material; ion irradiation; nanofragmentation; nanojoining; radiation sensor; tungsten oxide nanorods; wettability

Permalink: https://www.hzdr.de/publications/Publ-31710
Publ.-Id: 31710


Hypofractionated Versus Standard Fractionated Radiotherapy in Patients With Early Breast Cancer or Ductal Carcinoma In Situ in a Randomized Phase III Trial: The DBCG HYPO Trial

Offersen, B. V.; Alsner, J.; Nielsen, H. M.; Jakobsen, E. H.; Nielsen, M. H.; Krause, M.; Stenbygaard, L.; Mjaaland, I.; Schreiber, A.; Kasti, U.-M.; Overgaard, J.

PURPOSE Given the poor results using hypofractionated radiotherapy for early breast cancer, a dose of 50 Gy in 25 fractions (fr) has been the standard regimen used by the Danish Breast Cancer Group (DBCG) since 1982. Results from more recent trials have stimulated a renewed interest in hypofractionation, and the noninferiority DBCG HYPO trial (ClincalTrials.gov identifier: NCT00909818) was designed to determine whether a dose of
40 Gy in 15 fr does not increase the occurrence of breast induration at 3 years compared with a dose of 50 Gy in 25 fr.

PATIENTS AND METHODS One thousand eight hundred eighty-two patients .40 years of age who underwent breast-conserving surgery for node-negative breast cancer or ductal carcinoma in situ (DCIS) were randomly assigned to radiotherapy at a dose of either 50 Gy in 25 fr or 40 Gy in 15 fr. The primary end point was 3-year grade 2-3 breast induration assuming noninferiority regarding locoregional recurrence.

RESULTS A total of 1,854 consenting patients (50 Gy, n 5937; 40 Gy, n 5917) were enrolled from 2009-2014 from eight centers. There were 1,608 patients with adenocarcinoma and 246 patients with DCIS. The 3-year rates of induration were 11.8% (95% CI, 9.7% to 14.1%) in the 50-Gy group and 9.0% (95% CI, 7.2% to 11.1%) in the 40-Gy group (risk difference, 22.7%; 95% CI, 25.6% to 0.2%; P 5 .07). Systemic therapies and radiotherapy boost did not increase the risk of induration. Telangiectasia, dyspigmentation, scar appearance, edema, and pain were detected at low rates, and cosmetic outcome and patient satisfaction with breast appearance were high with either no difference or better outcome in the 40-Gy cohort compared with the 50-Gy cohort. The 9-year risk of locoregional recurrence was 3.3% (95% CI, 2.0% to 5.0%) in the 50-Gy group and 3.0% (95% CI, 1.9% to 4.5%) in the 40-Gy group (risk difference, 20.3%; 95% CI, 22.3% to 1.7%). The 9-year overall survival was 93.4% (95% CI, 91.1% to 95.1%) in the 50-Gy group and 93.4% (95% CI, 91.0% to 95.2%)
in the 40-Gy group. The occurrence of radiation-associated cardiac and lung disease was rare and not influenced by the fractionation regimen.

CONCLUSION Moderately hypofractionated breast irradiation of node-negative breast cancer or DCIS did not result in more breast induration compared with standard fractionated therapy. Other normal tissue effects were minimal, with similar or less frequent rates in the 40-Gy group. The 9-year locoregional recurrence risk was low.

Permalink: https://www.hzdr.de/publications/Publ-31708
Publ.-Id: 31708


Underground experimental study finds no evidence of low-energy resonance in the 6Li(p,γ)7Be reaction

Piatti, D.; Chillery, T.; Depalo, R.; Aliotta, M.; Bemmerer, D.; Best, A.; Boeltzig, A.; Broggini, C.; Bruno, C. G.; Caciolli, A.; Cavanna, F.; Ciani, G. F.; Corvisiero, P.; Csedreki, L.; Davinson, T.; Di Leva, A.; Elekes, Z.; Ferraro, F.; Fiore, E. M.; Formicola, A.; Fülöp, Z.; Gervino, G.; Gnech, A.; Guglielmetti, A.; Gustavino, C.; Gyürky, G.; Imbriani, G.; Junker, M.; Kochanek, I.; Lugaro, M.; Marcucci, L. E.; Marigo, P.; Masha, E.; Menegazzo, R.; Mossa, V.; Pantaleo, F. R.; Paticchio, V.; Perrino, R.; Prati, P.; Schiavulli, L.; Stöckel, K.; Straniero, O.; Szücs, T.; Takács, M. P.; Zavatarelli, S.

The astrophysical 6Li(p,γ)7Be reaction occurs during Big Bang nucleosynthesis and the pre-main sequence and main sequence phases of stellar evolution. The low-energy trend of its cross section remains uncertain, since different measurements have provided conflicting results. A recent experiment reported a resonancelike structure at center-of-mass energy 195 keV, associated to a positive-parity state of 7Be. The existence of such resonance is still a matter of debate. We report a new measurement of the 6Li(p,γ)7Be cross section performed at the Laboratory for Underground Nuclear Astrophysics, covering the center-of-mass energy range E=60–350 keV. Our results rule out the existence of low-energy resonances. The astrophysical S-factor varies smoothly with energy, in agreement with theoretical models.

Permalink: https://www.hzdr.de/publications/Publ-31707
Publ.-Id: 31707


Optimization of multi-group energy structures for diffusion analyses of sodium-cooled fast reactors assisted by simulated annealing – Part I: methodology demonstration

Di Nora, V. A.; Fridman, E.; Nikitin, E.; Bilodid, Y.; Mikityuk, K.

This study presents an approach to the selection of optimal energy group structures for multi-group nodal diffusion analyses of Sodium-cooled Fast Reactor cores. The goal is to speed up calculations, particularly in transient calculations, while maintaining an acceptable accuracy of the results.
In Part I of the paper, possible time-savings due to collapsing of energy groups are evaluated using 24-group energy structure as a reference. Afterwards, focusing on energy structures with a number of groups leading to significant calculation speedups, optimal grid configurations are identified. Depending on a number of possible energy grid configurations to explore, the optimization is conducted by either a direct search or applying the simulated annealing method. Speedup and optimization studies are performed on a selected case of the Superphénix static neutronic benchmark by using the nodal diffusion DYN3D code. The results demonstrate noticeable improvements in DYN3D performance with a marginal deterioration of the accuracy.

Keywords: Serpent; XS condensation; energy structure optimization; simulated annealing

  • Reseach data in the HZDR data repository RODARE
    Publication date: 2020-11-26
    DOI: 10.14278/rodare.583

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Permalink: https://www.hzdr.de/publications/Publ-31706
Publ.-Id: 31706


A Molecular Octafluoridoneptunate(IV) anion in (NH₄)₄[NpF₈] and Theoretical Investigations of the [MF₈]₄-System (M = Th - Bk)

Scheibe, B.; Patzschke, M.; März, J.; Conrad, M.; Kraus, F.

Olive-green single crystals of ammonium octafluoridoneptunate(IV), (NH₄)₄[NpF₈], were obtained by converting NpO₂ to a green neptunium tetrafluoride hydrate with hydrofluoric acid and subsequent treatment of the fluoride with an aqueous NH₄F solution. The crystal structure of the compound was determined by single-crystal X ray diffraction and observed to be isotypic to the uranium analogue. In (NH₄)₄[NpF₈], molecular [NpF₈]⁴‾ anions, which can either be described as a distorted square-antiprism or a bicapped trigonal prism, are present which are bound to the NH₄⁺ ions via N−H∙∙∙F hydrogen bonds. Quantum-chemical calculations of [MF₈]⁴‾ anions show that the M−F bonds are highly ionic and the energy differences between different ligand arrangements likely can be overcome by lattice energies of different crystal structures in the solid state.

Keywords: actinide; density functional calculations; neptunium; fluorine; single-crystal X-ray diffraction

Permalink: https://www.hzdr.de/publications/Publ-31705
Publ.-Id: 31705


HIM FIBID dataset for Superconducting properties of in-plane W-C nanowires grown by He+ Focused Ion Beam Induced Deposition

Hlawacek, G.

HIM images and NPVE dataset created during the preparation of the W(CO)6 nanowires.

Keywords: helium ion microscopy; focused ion beam induced deposition

Related publications

  • Reseach data in the HZDR data repository RODARE
    Publication date: 2020-11-11
    DOI: 10.14278/rodare.581
    License: CC-BY-4.0

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Permalink: https://www.hzdr.de/publications/Publ-31704
Publ.-Id: 31704


Superconducting properties of in-plane W-C nanowires grown by He+ Focused Ion Beam Induced Deposition

Orús, P.; Córdoba, R.; Hlawacek, G.; de Teresa, J. M.

Focused Ion Beam Induced Deposition (FIBID) is a nanopatterning technique that makes use of a focused beam of charged ions to decompose a gaseous precursor. So far, the flexible patterning capabilities of FIBID have been widely exploited in the fabrication of superconducting nanostructures, using the W(CO) 6 precursor mostly in combination with a focused beam of Ga+ ions. Here, the fabrication and characterization of superconducting in-plane tungsten-carbon (W-C) nanostructures by He+ FIBID of the W(CO)6 precursor is reported. A virtually unattainable for Ga+ FIBID patterning resolution of 10 nm has been achieved. When the nanowires are patterned with widths of 20 nm and above, the deposited material is superconducting below 3.5 – 4 K. In addition, 60 and 90 nm-wide nanostructures have been found to sustain long-range controlled non-local superconducting vortex transfer along 3 μm. Overall, these findings strengthen the capabilities of He+ FIBID of W-C in the growth and patterning of in-plane superconducting nanodevices.

Keywords: superconductivity; Helium Ion Microscopy; FIBID; nanowires; vortexdynamics; electrical transport properties

Related publications

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Permalink: https://www.hzdr.de/publications/Publ-31703
Publ.-Id: 31703


Evolution of cast iron- and copper- corrosion in "400 day-bentonite-microcosms"

Sushko, V.; Dressler, M.; Neubert, T.; Kühn, L.; Cherkouk, A.; Schierz, A.; Matschiavelli, N.

Copper and cast iron are potential materials for the storage canisters of high-level radioactive waste. We designed slurry-experiments for analyzing the microbial influence on the corrosion process of these metals. These slurry experiments contain the Bavarian B25 bentonite, synthetic Opalinus Clay pore water or diluted cap rock solution as well as copper- or cast iron plates in various combinations. During an incubation time of 400 days under anaerobic conditions at 37 °C cast iron plates corrode very fast. The respective metal surfaces show the formation of iron oxides and –carbonates which could form a passivating film that protects the cast iron from further corrosion.

  • Open Access Logo Lecture (Conference) (Online presentation)
    iCross annual meeting 2020, 25.-26.11.2020, Dresden-Webinar, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-31702
Publ.-Id: 31702


Cd2+ incorporation in small pores LEV/ERI intergrown zeolites: a multi-methodological study

Cametti, G.; Scheinost, A.; Churakov, S. V.

Small pores zeolites are successfully employed as catalysts, sorbents and molecular sieves. Their physiochemical properties can be improved by modifying their extraframework (EF) cation content via ion exchange. In this study, we investigate the crystal structure of a Cd-exchanged levyne (LEV) intergrown with erionite (ERI) by combining Single Crystal X-ray Diffraction (SCXRD), Molecular Dynamic simulations (MD) and Extended X-ray Absorption Fine- Structure analysis spectroscopy (EXAFS). Data obtained from the different techniques, consistently indicated that Cd2+ distribute in an almost ordered fashion in LEV. In contrast, strong disorder of the EF species (Cd2+ and H2O) is observed in the ERI cavities. In the latter, Cd2+ form aqueous complexes that are more mobile in comparison towith respect Cd2+ in LEV, where it bonds to H2O and framework-oxygen atoms. The formation of Cd-clusters is excluded based on EXAFS analysis. Finally, to discriminate between thermal and static disorder, we proposed a new approach based on a combined MD and geometry optimization analysis.

Keywords: zeolite; levyne; MD simulations; DFT; XRD; EXAFS; ROBL

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  • Secondary publication expected from 17.12.2021

Permalink: https://www.hzdr.de/publications/Publ-31700
Publ.-Id: 31700


Ideen zur Untersuchung der MIC Beständigkeit von vorgealterten Materialien

Raff, J.; Cherkouk, A.; Matschiavelli, N.; Sushko, V.; Dressler, M.

Neben abiotischen Faktoren können auch mikrobielle Prozesse einen Einfluss auf die Langzeitsicherheit eines nuklearen Endlagers haben. Darum wird aktuell im Rahmen des Projekts iCROSS die mikrobiellen Diversität in dem Verfüllmaterial Bentonit untersucht und die mikrobielle Aktivität mittels Mikrokosmosexperimenten bestimmt. Weitere Experimente befassen sich außerdem mit der mikrobiell beeinflussten Korrosion von Behältermaterialien. Letzteres ist auch von hoher Relevanz für andere technische Anlagen und Prozesse. Aus diesem Grund werden in dem Vortrag außerdem Möglichkeiten für weitere Projektideen aufgezeigt und diskutiert.

Keywords: Mikrobielle Diversität; nukleares Endlager; Bentonit; MIC

  • Lecture (Conference) (Online presentation)
    DECHEMA/GfKORR Fachgruppensitzung „Mikrobielle Materialzerstörung und Materialschutz“ 27.10.2020, 27.10.2020, Online, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-31699
Publ.-Id: 31699


PIConGPU setup: PWFA simulations

Pausch, R.; Debus, A.; Steiniger, K.; Widera, R.

This is the PIConGPU source code and setup files for generating PWFA simulations. This setup was used to study wake elongation.

Keywords: PIConGPU, PWFA

  • Software in the HZDR data repository RODARE
    Publication date: 2020-11-10
    DOI: 10.14278/rodare.579
    License: GPL-3.0

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Permalink: https://www.hzdr.de/publications/Publ-31697
Publ.-Id: 31697


Operating system (OS) independent job configuration for image reconstruction at HEMERA

Bieberle, A.; Wagner, M.; Windisch, D.; Hampel, U.

The Institute of Fluid Dynamics at the HZDR operates ultrafast electron beam X-ray CT scanners, a.k.a. ROFEX-CT scanners, that are used to visualize rapidly moving two-phase gas-liquid scenarios in technical devices with an imaging rate of up to 8,000 images per second. This means, radiographic projections are acquired from different angular positions of the two-phase flow and reconstruction algorithms, e.g. filtered back projection or algebraic reconstruction technique, are applied to obtain a stack of cross-sectional images as a sequence of time. The scanners can be operated in single or dual-plane mode. The presentation highlights the construct that is developed to start OS-independent data reconstruction jobs at HEMERA.

Keywords: X-ray CT scanner; HPC

  • Lecture (others) (Online presentation)
    Seminar Series - Hardware and Numerics, 08.12.2020, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-31696
Publ.-Id: 31696


mallocMC - Memory Allocator for Many Core Architectures

Widera, R.; Eckert, C.; Hübl, A.; Gruber, B. M.; Bastrakov, S.; Worpitz, B.; Grund, A.

This project provides a framework for fast memory managers on many core accelerators. It is based on alpaka to run on many different accelerators and implements the ScatterAlloc algorithm.

Keywords: CUDA; HIP; AMD; NVIDIA; memory allocation; many core; scatter alloc; C++

  • Software in external data repository
    Publication year 2020
    Programming language: C++
    System requirements: - OS: Linux/Windows/OSX - C++ 11 compiler - CUDA
    License: MIT
    Hosted on GitHub: Link to location
    DOI: 10.5281/zenodo.3862375

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Permalink: https://www.hzdr.de/publications/Publ-31694
Publ.-Id: 31694


Influence of precursor thin-film quality on the structural properties of large-area MoS2 films grown by sulfurization of MoO3 on c-sapphire

Spanková, M.; Sojková, M.; Dobrocka, E.; Hutár, P.; Bodík, M.; Munnik, F.; Hulman, M.; Chromik, S.

In recent years, molybdenum disulfide (MoS2) has been investigated due to its unique electronic, optical, and mechanical properties with a variety of applications. Sulfurization of pre-deposited MoO3 layers is one of the methods of the preparation of large-area MoS2 thin films. The MoO3 layers have been grown on c-sapphire substrates, using two different techniques (rf sputtering, pulsed laser deposition). The films were subsequently annealed in vapors of sulfur at high temperatures what converted them to MoS2 films. The quality of MoS2 is strongly influenced by the properties of the precursor MoO3 layers. The pre-deposited MoO3, as well as the sulfurized MoS2, have been characterized by several techniques including Raman, Rutherford backscattering spectroscopy, atomic force microscopy, scanning electron microscopy, and X-ray diffraction. Here we compare two types of MoS2 films prepared from different MoO3 layers to determine the most suitable MoO3 layer properties providing good quality MoS2 films for future applications.

Keywords: Molybdenum disulfide; Sulfurization; Sputtering; Pulsed laser deposition; Structural properties

Permalink: https://www.hzdr.de/publications/Publ-31693
Publ.-Id: 31693


Diffraction techniques in nuclear materials

Bergner, F.

The presentation is aimed at introducing diffraction techniques and their applications in the field of structural nuclear materials. After a brief introduction, three selected experimental techniques are presented in more detail. These are X-ray line profile analysis (XLPA), electron backscatter diffraction (EBSD) and small-angle neutron scattering (SANS). XLPA is applied to derive microstructure parameters such as crystallite size, dislocation density and twin probability of a nanostructured high-entropy alloy processed by means of high pressure torsion. EBSD is shown to be useful for the characterization of the bainitic microstructure in terms of subunits of the prior austenite grains and their orientation relationship with the parent phase. As an example for the application of SANS, the effects of neutron flux and neutron fluence on the volume fraction and mean size of irradiation-induced solue atom clusters are characterized.

Keywords: Diffraction; Scattering; Nuclear materials; Irradiation effects

  • Invited lecture (Conferences) (Online presentation)
    European School on Nuclear Material Science, 09.-13.11.2020, Online, Online

Permalink: https://www.hzdr.de/publications/Publ-31692
Publ.-Id: 31692


Frequency- and magnetic-field-dependent properties of ordered magnetic nanoparticle arrangements

Neugebauer, N.; Hache, T.; Elm, M.; Hofmann, D. M.; Heiliger, C.; Schultheiß, H.; Klar, P. J.

We present a frequency and magnetic field dependent investigation of ordered arrangements of 20 nm magnetic
nanoparticles (MNPs) consisting of magnetite (Fe3O4) by employing micro Brillouin light scattering
microscopy. We utilized electron beam lithography to prepare hexagonally arranged, circularly shaped MNPassemblies
consisting of a single layer of MNPs using a variant of the Langmuir-Blodgett technique. By
comparing the results with non-structured, layered superlattices of MNPs, further insight into the influence
of size and geometry of the arrangement on the collective properties is obtained. We show that at low static
external field strengths, two signals occur in frequency dependent measurements for both non-structured and
structured assemblies. Enlarging the static external field strength leads to a sharpening of the main signal,
while the satellite signal decreases in its intensity and increases in its linewidth. The occurrence of multiple
signals at low external field strengths is also confirmed by sweeping the static external field and keeping the
excitation frequency constant. Micromagnetic simulations unravel the origin of the different signals and their
dependence on the static external field strength, enabling an interpretation of the observed characteristics in
terms of different local environments of an MNPs forming the MNP assembly.

  • Reseach data in the HZDR data repository RODARE
    Publication date: 2020-11-09
    DOI: 10.14278/rodare.577
    License: CC-BY-4.0

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Permalink: https://www.hzdr.de/publications/Publ-31690
Publ.-Id: 31690


ISAAC - In Situ Animation of Accelerated Computations

Meyer, F.; Widera, R.; Pausch, R.; Matthes, A.; Hübl, A.; Gerber, V.; Zenker, E.; Kosukhin, S.

Many computations like physics or biologists simulations these days run on accelerated hardware like CUDA GPUs or Intel Xeon Phi, which are itself distributed in a big compute cluster communicating over MPI. The goal of ISAAC is to visualize this data without the need to download it to the host while using the high computation speed of the accelerator.

  • Software in the HZDR data repository RODARE
    Publication date: 2020-11-06
    DOI: 10.14278/rodare.573
    License: LGPL-3.0

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Permalink: https://www.hzdr.de/publications/Publ-31686
Publ.-Id: 31686


A New Highly Anisotropic Rh-Based Heusler Compound for Magnetic Recording

He, Y.; Fecher, G. H.; Fu, C.; Pan, Y.; Manna, K.; Kroder, J.; Jha, A.; Wang, X.; Hu, Z.; Agrestini, S.; Herrero-Martin, J.; Valvidares, M.; Scurschii, I.; Schnelle, W.; Stamenov, P.; Borrmann, H.; Tjeng, L. H.; Schaefer, R.; Parkin, S. S. P.; Coey, J. M. D.; Felser, C.

The development of high-density magnetic recording media is limited by superparamagnetism in very small ferromagnetic crystals. Hard magnetic materials with strong perpendicular anisotropy offer stability and high recording density. To overcome the difficulty of writing media with a large coercivity, heat-assisted magnetic recording was developed, rapidly heating the media to the Curie temperature Tc before writing, followed by rapid cooling. Requirements are a suitable Tc, coupled with anisotropic thermal conductivity and hard magnetic properties. Here, Rh2CoSb is introduced as a new hard magnet with potential for thin-film magnetic recording. A magnetocrystalline anisotropy of 3.6 MJ m−3 is combined with a saturation magnetization of μ0Ms = 0.52 T at 2 K (2.2 MJ m−3 and 0.44 T at room temperature). The magnetic hardness parameter of 3.7 at room temperature is the highest observed for any rare-earth-free hard magnet. The anisotropy is related to an unquenched orbital moment of 0.42 μB on Co, which is hybridized with neighboring Rh atoms with a large spin–orbit interaction. Moreover, the pronounced temperature dependence of the anisotropy that follows from its Tc of 450 K, together with a thermal conductivity of 20 W m−1 K−1, make Rh2CoSb a candidate for the development of heat-assisted writing with a recording density in excess of 10 Tb in.−2.

Permalink: https://www.hzdr.de/publications/Publ-31685
Publ.-Id: 31685


Superconducting Accelerators as Sources for Intense Secondary Radiations

Wagner, A.

The Helmholtz-Center Dresden-Rossendorf operates a superconducting electron linear accelerator (named ELBE radiation source) as a driver for secondary beams of electromagnetic radiation, neutrons, and positrons. The combination of high-intensity secondary beams, superior timing resolution, and adjustable beam repetition rates allows performing experiments, which are hardly possible using alternative technologies. The facility runs as a dedicated user facility thus serving an international community. Applications range from tunable coherent infra-red radiation from an Free-Electron Laser, coherent super-radiant THz radiation with sub-ps timing, high-energy gamma-rays and neutrons for nuclear physics to secondary positron beams for materials research.
Several recent scientific results will be presented and plans for a successor, the Dresden Advanced Light Infrastructure (DALI), will be shown.

Keywords: ELBE; DALI; positrons; THz; FELBE; TELBE; neutrons; gammas; Felsenkeller; nuclear astrophysics

  • Lecture (others) (Online presentation)
    Physikalisches Kolloquium der Martin-Luther Universität Halle-Wittenberg, 05.11.2020, Halle/Saale, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-31684
Publ.-Id: 31684


Rare earth minerals and rare-earth mining

Lorenz, T.; Bertau, M.; Möckel, R.

The book chapter is about the geology of rare earth elements, their mineral carrier as well as secondary raw materials.

  • Book chapter
    Prof. Dr. Rainer Pöttgen, Prof. Dr. Christian Strassert, Prof. Dr. Thomas Jüstel: Rare Earth Chemistry, Berlin/Boston: Walter de Gruyter, 2020, 978-3110653601, 15-36
    DOI: 10.1515/9783110654929-002

Permalink: https://www.hzdr.de/publications/Publ-31683
Publ.-Id: 31683


Nanoparticle emission by electronic sputtering of CaF2 single crystals

Alencar, I.; Hatori, M.; Marmitt, G. G.; Trombini, H.; Grande, P. L.; Dias, J. F.; Papaléo, R. M.; Mücklich, A.; Assmann, W.; Toulemonde, M.; Trautmann, C.

Material sputtered from CaF2 single crystals by 180 MeV Au ions impinging at different incidence angles were collected on high-purity amorphous C-coated Cu grids and Si100 wafer catcher surfaces over a broad angular range. These catcher surfaces were characterized complementary by transmission electron microscopy, atomic force microscopy and medium energy ion scattering, revealing the presence of a distribution of partially buried CaF2 nanoparticles in conjunction to a thin layer of deposited CaF2 material. Particle size distributions do not follow simple power laws and depend on the angles of ion incidence and particle detection. It is shown that the particle ejection is directly related to the jet-like component of sputtering, previously observed in ionic crystals, contributing significantly to the total yield. This contribution enhances as the impinging ions approach grazing incidence. Possible scenarios for the emission of particles are discussed in light of these observations.

Keywords: Atomic force microscopyCatcher technique; Nanoparticle; Medium energy ion scattering; Electronic sputtering; Swift heavy ions; Transmission electron microscopy

Permalink: https://www.hzdr.de/publications/Publ-31682
Publ.-Id: 31682


Pictures worth more than a thousand words: prediction of survival in medulloblastoma patients

Rabasco Meneghetti, A.; Zwanenburg, A.; Löck, S.

In this invited comment we discuss the results of the manuscript of Yan et al. EbioMedicine, with title "Incremental prognostic value and underlying biological pathways of radiomics patterns in medulloblastoma"

Permalink: https://www.hzdr.de/publications/Publ-31680
Publ.-Id: 31680


Voltage‐driven motion of nitrogen ions: a new paradigm for magneto‐ionics

de Rojas, J.; Quintana, A.; Lopeandia, A.; Salguero, J.; Muñiz, B.; Ibrahim, F.; Chshiev, M.; Nicolenco, A.; Liedke, M. O.; Butterling, M.; Wagner, A.; Sireus, V.; Abad, L.; Jensen, C.; Liu, K.; Nogues, J.; Costa-Krämer, J.; Sort, J.; Menéndez, E.

Magneto‐ionics, understood as voltage‐driven ion transport in magnetic materials, has largely relied on controlled migration of oxygen ions. Here, we demonstrate room‐temperature voltagedriven nitrogen transport (i.e., nitrogen magneto‐ionics) by electrolyte‐gating of a CoN film.
Nitrogen magneto‐ionics in CoN is compared to oxygen magneto‐ionics in Co3O4. Both materials are nanocrystalline (face‐centered‐cubic structure) and show reversible voltage‐driven ON‐OFF ferromagnetism. In contrast to oxygen, nitrogen transport occurs uniformly creating a plane‐wavelike migration front, without assistance of diffusion channels. Remarkably, nitrogen magnetoionics requires lower threshold voltages and exhibits enhanced rates and cyclability. This is due to the lower activation energy for ion diffusion and the lower electronegativity of nitrogen compared to oxygen. These results may open new avenues in applications such as brain‐inspired computing or iontronics in general.

Keywords: positron annihilation spectroscopy; magneto-ionics; positron annihilation lifetime spectroscopy; defetcs; nitrogen; Co

Permalink: https://www.hzdr.de/publications/Publ-31678
Publ.-Id: 31678


Lithium-assisted Exfoliation and Photoelectrocatalytic Water Splitting of 2D Palladium Thiophosphate

Wu, B.; Kempt, R.; Kovalska, E.; Luxa, J.; Kuc, A. B.; Heine, T.; Sofer, Z.

Efficient photoelectrocatalytic (PEC) water splitting could be the solution for environmental and energy problems on planet Earth. Here, we explore 2D palladium thiophosphate Pd3(PS4)2, which is a promising photocatalyst absorbing light in the visible range. We obtain a few-layer Pd3(PS4)2 through lithium-assisted exfoliation from the bulk phase and characterize it employing Raman spectroscopy, XPS, AFM, and STM combined with DFT calculations. The measured band gap for as-obtained few-layer Pd3(PS4)2 is 2.57 eV (indirect) and its band edges span the electrochemical potentials of the hydrogen and oxygen evolution reactions. The performance in the water-splitting reaction is studied under acidic, neutral, and alkaline conditions under violet irradiation at 420 nm. 2D palladium phosphochalcogenides semiconductor with bifunctional electrocatalytic and photoelectrocatalytic properties. Our results show competitive performance compared with industrial Pt/C catalysts for solar-driven water splitting under acidic and alkaline conditions.

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  • Secondary publication expected from 11.01.2022

Permalink: https://www.hzdr.de/publications/Publ-31677
Publ.-Id: 31677


The dithiol-dithione tautomerism of 2,3-pyrazinedithiol in the synthesis of copper and silver coordination compounds

Henfling, S.; Kempt, R.; Klose, J.; Kuc, A. B.; Kersting, B.; Krautscheid, H.

A promising strategy for new electrically conductive coordination polymers is the combination of d10 metal ions, which tolerate short metal···metal distances, with dithiolene linkers, known for their “non-innocent” redox behavior. This study explores the coordination chemistry of 2,3-pyrazinedithiol (H2pdt) towards Cu+ and Ag+ ions, highlighting similarities and differences. The synthetic approach, starting with the fully protonated ligand, allowed the isolation of a homoleptic bis(dithiolene) complex with formal CuI atoms, [Cu(H2pdt)2]Cl (1). This complex was further transformed to a one-dimensional coordination polymer with short metal···metal distances, 1D[Cu(Hpdt)] (2Cu). The larger Ag+ ion directly built up a very similar coordination polymer 1D[Ag(Hpdt)] (2Ag), without any appearance of an intermediate metal complex. The coordination polymer 1D[Cu(H2pdt)I] (4), like complex 1, bears fully protonated H2pdt ligands in their dithione form. Upon heating, both compounds underwent auto-oxidation coupled with a dehydrogenation of the ligand to form the open shell neutral copper(II) complex [Cu(Hpdt)2] (3) and the coordination polymer 1D[Cu2I2(Hpdt)(H2pdt)] (5), respectively. For all presented compounds, crystal structures are discussed in-depth. Furthermore, properties of 1, 3, as well as of the three one-dimensional coordination polymers 2Ag, 2Cu and 4, were investigated by UV-Vis-NIR spectroscopy, cyclic voltammetry, and variable temperature magnetic susceptibility, and DC-conductivity measurements. The experimental results are compared and discussed with the aid of DFT simulations.

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  • Secondary publication expected from 22.10.2021

Permalink: https://www.hzdr.de/publications/Publ-31674
Publ.-Id: 31674


Asphericity of tumor FDG uptake in non-small cell lung cancer: Reproducibility and implications for harmonization in multicenter studies

Rogasch, J.; Furth, C.; Bluemel, S.; Radojewski, P.; Amthauer, H.; Hofheinz, F.

Background

Asphericity (ASP) of the primary tumor’s metabolic tumor volume (MTV) in FDG-PET/CT is independently predictive for survival in patients with non-small cell lung cancer (NSCLC). However, comparability between PET systems may be limited. Therefore, reproducibility of ASP was evaluated at varying image reconstruction and acquisition times to assess feasibility of ASP assessment in multicenter studies.

Methods

This is a retrospective study of 50 patients with NSCLC (female 20; median age 69 years) undergoing pretherapeutic FDG-PET/CT (median 3.7 MBq/kg; 180 s/bed position). Reconstruction used OSEM with TOF4/16 (iterations 4; subsets 16; in-plane filter 2.0, 6.4 or 9.5 mm), TOF4/8 (4 it; 8 ss; filter 2.0/6.0/9.5 mm), PSF + TOF2/17 (2 it; 17 ss; filter 2.0/7.0/10.0 mm) or Bayesian-penalized likelihood (Q.Clear; beta, 600/1750/4000). Resulting reconstructed spatial resolution (FWHM) was determined from hot sphere inserts of a NEMA IEC phantom. Data with approx. 5-mm FWHM were retrospectively smoothed to achieve 7-mm FWHM. List mode data were rebinned for acquisition times of 120/90/60 s. Threshold-based delineation of primary tumor MTV was followed by evaluation of relative ASP/SUVmax/MTV differences between datasets and resulting proportions of discordantly classified cases.

Results

Reconstructed resolution for narrow/medium/wide in-plane filter (or low/medium/high beta) was approx. 5/7/9 mm FWHM. Comparing different pairs of reconstructed resolution between TOF4/8, PSF + TOF2/17, Q.Clear and the reference algorithm TOF4/16, ASP differences was lowest at FWHM of 7 versus 7 mm. Proportions of discordant cases (ASP > 19.5% vs. ≤ 19.5%) were also lowest at 7 mm (TOF4/8, 2%; PSF + TOF2/17, 4%; Q.Clear, 10%). Smoothing of 5-mm data to 7-mm FWHM significantly reduced discordant cases (TOF4/8, 38% reduced to 2%; PSF + TOF2/17, 12% to 4%; Q.Clear, 10% to 6%), resulting in proportions comparable to original 7-mm data. Shorter acquisition time only increased proportions of discordant cases at < 90 s.

Conclusions

ASP differences were mainly determined by reconstructed spatial resolution, and multicenter studies should aim at comparable FWHM (e.g., 7 mm; determined by in-plane filter width). This reduces discordant cases (high vs. low ASP) to an acceptable proportion for TOF and PSF + TOF of < 5% (Q.Clear: 10%). Data with better resolution (i.e., lower FWHM) could be retrospectively smoothed to the desired FWHM, resulting in a comparable number of discordant cases.

Permalink: https://www.hzdr.de/publications/Publ-31672
Publ.-Id: 31672


"Full-Core" VVER-1000 calculation benchmark

Sprinzl, D.; Krysl, V.; Mikolas, P.; Zavorka, J.; Timr, J.; Bilodid, Y.; Temesvari, E.; Pos, I.; Kalinin, Y.; Shcherenko, A.; Aleshin, S.; Bahadir, T.

This work deals with the \Full-Core" VVER-1000 calculation benchmark which was proposed on the 26th Symposium of AER [1]. Recently, the calculation benchmarks \Full-Core" VVER-440 [2] and its extension [3] have been introduced in the AER community with positive response [4, 5]. Therefore we have decided to prepare a similar benchmark for VVER-1000. This benchmark is also a 2D calculation benchmark based on the VVER-1000 reactor core cold state geometry, explicitly taking into account the geometry of the radial reflector. The loading pattern for this core is very similar to the fresh fuel loading of cycle 9 at Unit 1 of the Temelin NPP (Czech Republic). This core is filled with six types of fuel assemblies with enrichment from 1.3%w 235U to 4.0%w 235U with up to 9 fuel pins with Gd burnable absorber per FA. The main task of this benchmark is to test the pin-by-pin power distribution in fuel assemblies predicted by macro-codes that are used for neutron-physics calculations especially for VVER reactors. In this contribution we present the overview of available macro-codes results.

Permalink: https://www.hzdr.de/publications/Publ-31671
Publ.-Id: 31671


Tailoring magnetocaloric effect in all- d -metal Ni-Co-Mn-Ti Heusler alloys: a combined experimental and theoretical study

Taubel, A.; Beckmann, B.; Pfeuffer, L.; Fortunato, N.; Scheibel, F.; Ener, S.; Gottschall, T.; Skokov, K. P.; Zhang, H.; Gutfleisch, O.

Novel Ni-Co-Mn-Ti all- d -metal Heusler alloys are exciting due to large multicaloric effects combined with enhanced mechanical properties. An optimized heat treatment for a series of these compounds leads to very sharp phase transitions in bulk alloys with isothermal entropy changes of up to 38 J kg−1 K−1 for a magnetic field change of 2 T. The differences of as-cast and annealed samples are analyzed by investigating microstructure and phase transitions in detail by optical microscopy. We identify different grain structures as well as stoichiometric (in)homogenieties as reasons for differently sharp martensitic transitions after ideal and non-ideal annealing. We develop alloy design rules for tuning the magnetostructural phase transition and evaluate specifically the sensitivity of the transition temperature towards the externally applied magnetic fields (dTt0dH) by analyzing the different stoichiometries. We then set up a phase diagram including martensitic transition temperatures and austenite Curie temperatures depending on the e/a ratio for varying Co and Ti content. The evolution of the Curie temperature with changing stoi- chiometry is compared to other Heusler systems. Density Functional Theory calculations reveal a correlation of TC with the stoichiometry as well as with the order state of the austenite. This combined approach of experiment and theory allows for an efficient development of new systems towards promising magnetocaloric properties. Direct adiabatic temperature change measurements show here the largest value of -4 K in a magnetic field change of 1.93 T for Ni35Co15Mn37Ti13.

Permalink: https://www.hzdr.de/publications/Publ-31670
Publ.-Id: 31670


Photo-neutron cross-section of natDy in the bremsstrahlung end-point energies of 12, 14, 16, 65, and 75 MeV

Naik, H.; Kim, G. N.; Schwengner, R.; Wooyoung, J.; Hien, N. T.; Kim, K.; Shin, S. G.; Kye, Y.; Junghans, A.; Wagner, A.; Cho, M.-H.

The flux-weighted average cross-sections of natDy(γ, xn)159,157,155Dy reactions were measured at the bremsstrahlung end-point energies of 12, 14, 16, 65 and 75 MeV with the activation and off-line γ-ray spectrometric technique using the 20 MeV Electron Linac for beams with high Brilliance and low Emittance (ELBE) at Helmholtz-Zentrum Dresden-Rossendorf, Dresden, Germany and the 100 MeV electron linac at the Pohang Accelerator Laboratory, Korea. The natDy(γ, xn)157,155Dy reaction cross sections as a function of photon energy were also calculated theoretically using TALYS 1.9 code. Then the flux-weighted average values at different end-point energies were obtained based on the theoretical values of mono-energetic photons. These values were compared with the flux-weighted values of present work and are found to be in general agreement. It was also found that the experimental and theoretical formation cross sections of 159Dy, 157Dy and 155Dy from the natDy(γ, xn) reactions increased from their respective threshold values to a certain energy where other reaction channels opened. After reaching a maximum value, the individual reaction cross-sections slowly decreased with the increase of the bremsstrahlung energy due to the initiation of other competing reactions at higher energy, which indicates the impact of the excitation energy. However, the production cross sections of 157Dy and 155Dy from the natDy(γ, xn) reactions slightly increase in between and then decreased slowly with bremsstrahlung energy, which is due to the contributing reactions of higher mass isotopes.

Keywords: Photonuclear reactions; photoabsorption cross section; photodissociation

Permalink: https://www.hzdr.de/publications/Publ-31669
Publ.-Id: 31669


Screening of a test charge in a free-electron gas at warm dense matter and dense non-ideal plasma conditions

Moldabekov, Z.; Dornheim, T.; Bonitz, M.

The screening of a test charge by partially degenerate non-ideal free electrons at conditions related to warm dense matter and dense plasmas is investigated using linear response theory and the local field correction based on ab inito Quantum Monte-Carlo simulations data. The analysis of the obtained results is performed by comparing to the random phase approximation and the Singwi-Tosi-Land-Sjölander approximation. The applicability of the long-wavelength approximation for the description of screening is investigated. The impact of electronic exchange-correlations effects on structural properties and the applicability of the screened potential from linear response theory for the simulation of the dynamics of ions are discussed.

Permalink: https://www.hzdr.de/publications/Publ-31668
Publ.-Id: 31668


Dynamic properties of the warm dense electron gas based on ab initio path integral Monte Carlo simulations

Hamann, P.; Dornheim, T.; Vorberger, J.; Moldabekov, Z.; Bonitz, M.

There is growing interest in warm dense matter (WDM), an exotic state on the border between condensed matter and plasmas. Due to the simultaneous importance of quantum and correlation effects, WDM is complicated to treat theoretically. A key role has been played by ab initio path integral Monte Carlo (PIMC) simulations, and recently extensive results for thermodynamic quantities have been obtained. The first extension of PIMC simulations to the dynamic structure factor of the uniform electron gas was reported by Dornheim et al. [Phys. Rev. Lett. 121, 255001 (2018)]. This was based on an accurate reconstruction of the dynamic local field correction. Here we extend this concept to other dynamical quantities of the warm dense electron gas including the dynamic susceptibility, the dielectric function, and the conductivity.

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Permalink: https://www.hzdr.de/publications/Publ-31667
Publ.-Id: 31667


Ion energy-loss characteristics and friction in a free-electron gas at warm dense matter and nonideal dense plasma conditions

Moldabekov, Z.; Dornheim, T.; Bonitz, M.; Ramazanov, T.

We investigate the energy-loss characteristics of an ion in warm dense matter (WDM) and dense plasmas concentrating on the influence of electronic correlations. The basis for our analysis is a recently developed ab initio quantum Monte Carlo– (QMC) based machine learning representation of the static local field correction (LFC) [Dornheim et al., J. Chem. Phys. 151, 194104 (2019)], which provides an accurate description of the dynamical density response function of the electron gas at the considered parameters. We focus on the polarization-induced stopping power due to free electrons, the friction function, and the straggling rate. In addition, we compute the friction coefficient which constitutes a key quantity for the adequate Langevin dynamics simulation of ions. Considering typical experimental WDM parameters with partially degenerate electrons, we find that the friction coefficient is of the order of γ/ωpi=0.01, where ωpi is the ionic plasma frequency. This analysis is performed by comparing QMC-based data to results from the random-phase approximation (RPA), the Mermin dielectric function, and the Singwi-Tosi-Land-Sjölander (STLS) approximation. It is revealed that the widely used relaxation time approximation (Mermin dielectric function) has severe limitations regarding the description of the energy loss of ions in a correlated partially degenerate electrons gas. Moreover, by comparing QMC-based data with the results obtained using STLS, we find that the ion energy-loss properties are not sensitive to the inaccuracy of the static local field correction (LFC) at large wave numbers, k/kF>2 (with kF being the Fermi wave number), but that a correct description of the static LFC at k/kF≲1.5 is important.

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Permalink: https://www.hzdr.de/publications/Publ-31665
Publ.-Id: 31665


Path-integral Monte Carlo simulations of quantum dipole systems in traps: Superfluidity, quantum statistics, and structural properties

Dornheim, T.

We present extensive ab initio path-integral Monte Carlo (PIMC) simulations of two-dimensional quantum dipole few-body systems (2≤N≤7) in a harmonic confinement, taking into account both Bose- and Fermi-statistics. This allows us to study the nonclassical rotational inertia, which can lead to a negative superfluid fraction in the case of fermions [Phys. Rev. Lett. 112, 235301 (2014)]. Moreover, we study in detail the structural characteristics of such systems and are able to clearly resolve the impact of quantum statistics on density profiles and the respective shell structure. Further, we present results for a more advanced center-two-particle correlation function [Phys. Rev. E 91, 043104 (2015)], which allows detection of differences between Fermi and Bose systems even when they are almost absent in other observables like the density. Overall, we find that bosonic systems sensitively react to even small values of the dipole-dipole coupling strength, whereas such a weak interaction is effectively masked for fermions by the Pauli exclusion principle. In addition, the abnormal superfluid fraction for fermions is not reflected by the structural properties of the system, which are equal to the bosonic case even though the moments of inertia diverge from each other. Lastly, we have explored the possibility of fermionic PIMC simulations of quantum dipole systems despite the notorious fermion sign problem, which can be further extended in future investigations in this field.

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Permalink: https://www.hzdr.de/publications/Publ-31664
Publ.-Id: 31664


Restricted configuration path integral Monte Carlo

Yilmaz, A.; Hunger, K.; Dornheim, T.; Groth, S.; Bonitz, M.

Quantum Monte Carlo (QMC) belongs to the most accurate simulation techniques for quantum many-particle systems. However, for fermions, these simulations are hampered by the sign problem that prohibits simulations in the regime of strong degeneracy. The situation changed with the development of configuration path integral Monte Carlo (CPIMC) by Schoof et al. [Contrib. Plasma Phys. 51, 687 (2011)] that allowed for the first ab initio simulations for dense quantum plasmas [Schoof et al., Phys. Rev. Lett. 115, 130402 (2015)]. CPIMC also has a sign problem that occurs when the density is lowered, i.e., in a parameter range that is complementary to traditional QMC formulated in coordinate space. Thus, CPIMC simulations for the warm dense electron gas are limited to small values of the Brueckner parameter—the ratio of the interparticle distance to the Bohr radius—rs=r⎯⎯⎯/aB≲1
. In order to reach the regime of stronger coupling (lower density) with CPIMC, here we investigate additional restrictions on the Monte Carlo procedure. In particular, we introduce two different versions of “restricted CPIMC”—called RCPIMC and RCPIMC+—where certain sign changing Monte Carlo updates are being omitted. Interestingly, one of the methods (RCPIMC) has no sign problem at all, but it introduces a systematic error and is less accurate than RCPIMC+, which neglects only a smaller class of the Monte Carlo steps. Here, we report extensive simulations for the ferromagnetic uniform electron gas with which we investigate the properties and accuracy of RCPIMC and RCPIMC+. Furthermore, we establish the parameter range in the density–temperature plane where these simulations are both feasible and accurate. The conclusion is that RCPIMC and RCPIMC+ work best at temperatures in the range of Θ = kBT/EF ∼ 0.1…0.5, where EF is the Fermi energy, allowing to reach density parameters up to rs ∼ 3…5, thereby partially filling a gap left open by existing ab initio QMC methods.

Permalink: https://www.hzdr.de/publications/Publ-31663
Publ.-Id: 31663


Reconstruction of austenite grain boundaries in bainitic reactor pressure vessel steels by EBSD

Chekhonin, P.; Bergner, F.

The reconstruction of austenite grain boundaries in bainitic reactor pressure vessel (RPV) steels by means of electron backscatter diffraction (EBSD) was done on two examples. In the case of VVER-440 RPV steel the reconstruction works very well, while in JFL RPV steel the reconstruction is faulty due to the accented presence of low angle boundaries.

  • Lecture (Conference) (Online presentation)
    AK-Treffen Mikrostrukturcharakterisierung im REM, 22.10.2020, Freiberg, Germany

Permalink: https://www.hzdr.de/publications/Publ-31662
Publ.-Id: 31662


Enhanced spin correlations in the Bose-Einstein condensate compound Sr3Cr2O8

Nomura, T.; Scurschii, I.; Quintero-Castro, D. L.; Zvyagin, A. A.; Suslov, A. V.; Gorbunov, D.; Yasin, S.; Wosnitza, J.; Kindo, K.; Islam, A. T. M. N.; Lake, B.; Kohama, Y.

Combined experimental and modeling studies of the magnetocaloric effect, ultrasound, and magnetostriction were performed on single-crystal samples of the spin-dimer system Sr3Cr2O8 in large magnetic fields to probe the spin-correlated regime in the proximity of the field-induced XY-type antiferromagnetic order also referred to as a Bose-Einstein condensate of magnons. The magnetocaloric effect, measured under adiabatic conditions, reveals details of the field-temperature (H, T ) phase diagram, a dome characterized by critical magnetic-fields Hc1 = 30.4, Hc2 = 62 T, and a single maximum ordering temperature Tmax(45 T) = 8 K. The sample temperature was observed to drop significantly as the magnetic field is increased, even for initial temperatures above Tmax, indicating a significantmagnetic entropy associated with the field-induced closure of the spin gap. The ultrasound and magnetostriction experiments probe the coupling between the lattice degrees of freedom and the magnetism in Sr3Cr2O. Our experimental results are qualitatively reproduced by a minimalistic phenomenological model of the exchange striction by which sound waves renormalize the effective exchange couplings.

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Permalink: https://www.hzdr.de/publications/Publ-31661
Publ.-Id: 31661


Strong anisotropy of the electron-phonon interaction in NbP probed by magnetoacoustic quantum oscillations

Schindler, C.; Gorbunov, D.; Zherlitsyn, S.; Galeski, S.; Schmidt, M.; Wosnitza, J.; Gooth, J.

In this study, we report on the observation of de Haas–van Alphen–type quantum oscillations (QOs) in the ultrasound velocity of NbP as well as “giant QOs” in the ultrasound attenuation in pulsed magnetic fields. The difference in the QO amplitude for different acoustic modes reveals a strong anisotropy of the effective deformation potential, which we estimate to be as high as 9 eV for certain parts of the Fermi surface. Furthermore, the natural filtering of QO frequencies and the tracing of the individual Landau levels to the quantum limit allows for a more detailed investigation of the Fermi surface of NbP, as was previously achieved by means of analyzing QOs observed in magnetization or electrical resistivity.

Permalink: https://www.hzdr.de/publications/Publ-31660
Publ.-Id: 31660


Detection of manufactured nanomaterials in complex environmental compartments – An expert review

Schymura, S.; Hildebrand, H.; Völker, D.; Schwirn, K.; Franke, K.; Fischer, C.

Manufactured nanomaterials (NMs) are materials in which 50% or more of the particles have one or more dimensions between 1 nm and 100 nm. These NMs show interesting properties. However, the same properties that motivate their use in applications are also reason for concern, as NMs can cause toxic reactions and have mobilities in the environment different from bulk materials of the same elements. Despite considerable scientific efforts, the selective detection of manufactured NMs in environmental compartments is still a very complex and challenging task. An expert review of the literature has been conducted to identify relevant methods for nanomaterial detection in complex media in the context of environmental monitoring and a need for action was concluded from the existing body of work.
A literature review was performed using predominantly “Web of Science”. More than 150 scientific publications which themselves refer to more than 10000 sources were evaluated concerning nanoparticle detection methods. The techniques identified through the literature review were evaluated for their capability to detect the relevant NM-related properties such as size, concentration, com- position, shape, etc. of arbitrary NMs in environmental samples.
Evaluating the relevant literature quickly led to the conclusion that while some detection methods will lend themselves more easily towards detection of NMs in a specific environmental compartment, there is no strictly compartment specific method. NMs can be detected with any of the different methods after application of suitable sample preparation techniques. Consequently, a generalized method for NM detection in environmental samples would consist of standardized sampling procedures followed by an extraction step that serves to largely remove the complex matrix followed by a size fractionation step which would then lead into a multi-method analysis depending on the desired information depth.
The need for action for the establishment of routine environmental monitoring of manufactured NMs is thus the development, validation and coupling of suitable extraction, pre-sorting and if necessary pre- concentration procedures, as well, as analysis techniques. One promising combined approach would consist of: CPE, AF4, MALS and sp-ICP-TOF-MS.

Keywords: nanoparticles; detection; environmental compartments

  • Poster (Online presentation)
    Nanosafe 2020, 16.-20.11.2020, Grenoble, France

Permalink: https://www.hzdr.de/publications/Publ-31659
Publ.-Id: 31659


Assessing nanoparticle release from waste water treatment using radiolabeled nanoparticles

Schymura, S.; Hildebrand, H.; Neugebauer, M.; Lange, T.; Schneider, P.; Franke, K.

Waste water treatment plants (WWTPs) represent an important step in the life cycle of manufactured nanomaterials. A considerable amount of nanoparticles (NPs) that are released from consumer products will end up in WWTPs, so that WWTPs can both serve as a potential end of life point for these nanoparticles, as well as a point of reentry into the environment via the WWTP effluents. It is thus of utmost importance to accurately quantify the fate of manufactured nanomaterials in waste water treatment in order to assess the risk
We used the radiolabeling of nanoparticles to accurately quantify the distribution of nanoparticles between the effluents of a model waste water treatment plant. In order to achieve this TiO2 NP were radiolabeled with V-48 using proton irradiation at our cyclotron. Multi-wall carbon nanotubes (MWCNT) were radiolabeled with Be-7 via recoil at our cyclotron. CdSe/ZnS Quantum dots were radiolabeled with Zn-65 and Se-75 via radiosynthesis. The radiolabeled NPs were used in batch experiments and model waste water treatment plant experiments.
The radiolabeling allowed us to quantify NP distribution between sludge and water phase in the WWTP and in the WWTP effluents. A distribution of about 10000 : 1 between sludge-associated NPs and free NPs in water is reached in the WWTP already shortly after injection of the NPs. Thus the elimination of the NPs from the WWTP is mainly controlled by the removal of surplus sludge taking place every day of operation. The NPs are eliminated from the WWTP with a half-life of about 6 days reflecting the pre-set sludge age. After about 22 days of operation 10 % of the initial NPs remain in the WWTP. Approximately 1 % of the NPs leave the WWTP via the cleared waste water, mainly associated with non-sedimented sludge particles, such that only about 1 ‰ of the NPs leave the WWTP as free particles via the cleared water. An impact of the NPs on the clearing process, as monitored by chemical oxygen demand of the inflow vs. the outflow, was not observed.

Keywords: nanoparticles; waste water treatment; radiolabeling

  • Lecture (Conference) (Online presentation)
    Nanosafe 2020, 16.-20.11.2020, Grenoble, France

Permalink: https://www.hzdr.de/publications/Publ-31658
Publ.-Id: 31658


Radiolabeling as a versatile tool in nanosafety research – accurate quantification in complex media

Schymura, S.; Hildebrand, H.; Rybkin, I.; Fricke, T.; Neugebauer, M.; Freyer, A.; Rijavec, T.; Lapanje, A.; Strok, M.; Lange, T.; Holzwarth, U.; Gibson, N.; Franke, K.

Accurate quantification of nanoparticles (NPs) in complex media remains a considerable challenge when assessing the risk that manufactured nanoparticles pose for humans and environment. The radiolabeling of nanoparticles is a valuable tool for conducting lab-studies with realistic systems and realistically low NP concentrations.
We have developed various methods of introducing radiotracers into some of the most common nanoparticles, such as Ag, carbon, SiO2, CeO2 and TiO2 nanoparticles. The labeling techniques are the synthesis of the nanoparticles using radioactive starting materials, the binding of the radiotracer to the nanoparticles, the activation of the nanoparticles using proton irradiation, the recoil labeling utilizing the recoil of a nuclear reaction to implant a radiotracer into the nanoparticle, and the in-diffusion of radiotracers into the nanoparticles at elevated temperatures. Using these methods we have produced [105/110mAg]Ag, [124/125/131I]CNTs, [48V]TiO2, [13/1419Ce]CeO2, [7Be]MWCNT, [64Cu]SiO2, [44/45Ti]TiO2, etc. for accurate quantification in complex media at environmentally relevant low concentrations.
The nanoparticles labeled by our methods can be detected at minimal concentrations well in the ng/L range even with a background of the same element and without complicated sample preparations necessary. The methods are adaptable for a wide range of other nanoparticles. The labeled particles have been successfully used in release studies, environmental mobility studies, fate studies in waste water treatment and plant uptake studies.

Keywords: Radiolabeling; Nanoparticles

  • Poster
    Nanosafe 2020, 16.-20.11.2020, Grenoble, France

Permalink: https://www.hzdr.de/publications/Publ-31657
Publ.-Id: 31657


Scalable Workflows for OpenFOAM Evaluation

Evdokimov, I.; Hänsch, S.; Schlegel, F.

The proposed research paper has a strong application bias and aims to address the practical problem of managing dozens, potentially hundreds of OpenFOAM cases. The workflow management includes routine tasks such as migrations on new solver versions, testing sub-models and solvers, as well as developing entirely new OpenFOAM applications validated against established setups. The proposed methodology was successfully tested on a set of 55 OpenFOAM cases specifically designed for the validation of new sub-models for Euler-Euler simulations of multiphase flows.

Keywords: workflow; OpenFOAM; validation

  • Lecture (Conference) (Online presentation)
    The Open Conference of the ISPRAS, 11.12.2020, Moscow, Russia

Permalink: https://www.hzdr.de/publications/Publ-31655
Publ.-Id: 31655


Series of Tetravalent Actinide Amidinates: Structure Determination and Bonding Analysis.

Kloditz, R.; Fichter, S.; Kaufmann, S.; Brunner, T. S.; Kaden, P.; Patzschke, M.; Stumpf, T.; Roesky, P. W.; Schmidt, M.; März, J.

NMR spectra for the complex series in the publication together with the xyz coordinates of the optimized complexes. An example input-file for ORCA v4.1.2 for the calculation of the wavefunction used for QTAIM is presented as well.

Keywords: actinides; NMR; DFT; QTAIM; NPA; coordination chemistry; transuranium

Related publications

  • Reseach data in the HZDR data repository RODARE
    Publication date: 2020-09-17
    DOI: 10.14278/rodare.517

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Permalink: https://www.hzdr.de/publications/Publ-31654
Publ.-Id: 31654


Data for: Spectral X-ray Computed Micro Tomography: 3-dimensional chemical imaging

Sittner, J.; Da Assuncao Godinho, J. R.; Renno, A.; Cnudde, V.; Boone, M.; de Schryver, T.; van Loo, D.; Merkulova, M.; Roine, A.; Liipo, J.

The files show the data we used for the publication.

Keywords: X-ray computed tomography; Spectral X-ray tomography; Photon counting detector; 3D imaging

Related publications

  • Reseach data in the HZDR data repository RODARE
    Publication date: 2020-09-22
    DOI: 10.14278/rodare.525
    License: CC-BY-4.0

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Permalink: https://www.hzdr.de/publications/Publ-31653
Publ.-Id: 31653


Are two-dimensional materials radiation tolerant?

Krasheninnikov, A.

Two-dimensional (2D) materials have many unique properties, which can be exploited in various applications. In particular, electronic devices based on 2D materials should ideally be suited for the operation in outer cosmic space due to their low weight, small size and low power consump- tion. This brings about the issue of their radiation hardness, or tolerance, which has recently been addressed in a number of studies. The results of these investigations are somewhat counterintu- itive: although one can naively expect that atomically thin structures should easily be destroyed by the beams of energetic particles, the devices made from 2D materials were reported to exhibit extraordinary radiation hardness. In this Focus article, an overview of the recent studies on the subject is given, followed by the discussion of the origin of the reported high tolerance, which is inherently related to the response of 2D materials, the systems with the reduced dimensionality, to irradiation. The analysis of the experimental and theoretical data on the behavior of 2D systems under irradiation indicates that although free-standing 2D materials can indeed be referred to as radiation resilient systems under irradiation conditions corresponding to the outer space, this is generally not the case, as the environment, e.g., the substrate, can strongly influence the radiation tolerance of 2D materials and devices based on these systems.

Keywords: 2D materials; irradiation; radiation tolerance

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  • Secondary publication expected from 18.09.2021

Permalink: https://www.hzdr.de/publications/Publ-31650
Publ.-Id: 31650


Influence of chemical zoning on sandstone calcite cement dissolution: The case of manganese and iron

Trindade Pedrosa, E.; Fischer, C.; Morales, L. F.; Rohlfs, R. D.; Luttge, A.

Chemical zoning of crystals is often found in nature. Crystal zoning can play a role in a mineral's thermodynamic stability and in its kinetic response in the presence of fluids. Dissolution experiments at far-from-equilibrium conditions were performed using a sandstone sample containing calcite cement crystal patches. The surface normal retreat of the calcite crystals was obtained by vertical scanning interferometry (VSI) in their natural position in the rock. Dissolution rate maps showed contrasting surface dissolution areas within the crystals, in the same locations where electron microprobe (EMP) maps showed the presence of manganese (Mn) and iron (Fe) substitutions for calcium in the calcite structure. Iron zoning was only identified in combination with manganese. Maximum registered manganese contents were 1.9(9) wt% and iron were 2(1) wt%. Manganese zoning of only 0.9(5) wt% resulted in around 40% lower dissolution rates than the adjacent pure calcite zones. The combination of both Mn and Fe cation substitutions resulted in one order of magnitude lower dissolution rates compared to pure calcite in the same sample. These results show that mineral zoning can significantly affect reaction rates, a parameter that needs better understanding for the improvement of kinetic geochemical models at the pore scale.

Keywords: Sandstone; Calcite; Dissolution; Zoning; Manganese; Iron

Permalink: https://www.hzdr.de/publications/Publ-31649
Publ.-Id: 31649


Dyke apertures record stress accumulation during sustained volcanism

Thiele, S. T.; Cruden, A. R.; Micklethwaite, S.; Köpping, J.; Bunger, A. P.

The feedback between dyke and sill intrusions and the evolution of stresses within volcanic systems is poorly understood, despite its importance for magma transport and volcano instability. Long-lived ocean island volcanoes are crosscut by thousands of dykes, which must be accommodated through a combination of flank slip and visco-elastic deformation. Flank slip is dominant in some volcanoes (e.g., Kilauea), but how intrusions are accommodated in other volcanic systems remains unknown. Here we apply digital mapping techniques to collect > 400,000 orientation and aperture measurements from 519 sheet intrusions within Volcán Taburiente (La Palma, Canary Islands, Spain) and investigate their emplacement and accommodation. We show that vertically ascending dykes were deflected to propagate laterally as they approached the surface of the volcano, forming a radial dyke swarm, and propose a visco-elastic model for their accommodation. Our model reproduces the measured dyke-aperture distribution and predicts that stress accumulates within densely intruded regions of the volcano, blocking subsequent dykes and causing eruptive activity to migrate. These results have significant implications for the organisation of magma transport within volcanic edifices, and the evolution and stability of long-lived volcanic systems.

Permalink: https://www.hzdr.de/publications/Publ-31648
Publ.-Id: 31648


High Performance Computing: ISC High Performance 2020 International Workshops

Jagode, H.; Anzt, H.; Juckeland, G.; Ltaief, H.

This book constitutes the refereed post-conference proceedings of 10 workshops held at the 35th International ISC High Performance 2020 Conference, in Frankfurt, Germany, in June 2020:
First Workshop on Compiler-assisted Correctness Checking and Performance Optimization for HPC (C3PO); First International Workshop on the Application of Machine Learning Techniques to Computational Fluid Dynamics Simulations and Analysis (CFDML); HPC I/O in the Data Center Workshop (HPC-IODC); First Workshop \Machine Learning on HPC Systems" (MLHPCS); First International Workshop on Monitoring and Data Analytics (MODA); 15th Workshop on Virtualization in High-Performance Cloud Computing (VHPC).

The 25 full papers included in this volume were carefully reviewed and selected. They cover all aspects of research, development, and application of large-scale, high performance experimental and commercial systems. Topics include high-performance computing (HPC), computer architecture and hardware, programming models, system software, performance analysis and modeling, compiler analysis and optimization techniques, software sustainability, scientific applications, deep learning.

Keywords: artificial intelligence; computer hardware; computer networks; computer science; computer systems; distributed computer systems; distributed systems; education; HPC; parallel architectures

Permalink: https://www.hzdr.de/publications/Publ-31647
Publ.-Id: 31647


The resource potential of mine waste – More than metal concentrations

Büttner, P.; Nühlen, J.; Engelhardt, J.

In the last decade, several national and European funding programs addressed the resource potential of mine wastes (including tailings and metallurgical slag dumps), with a clear focus on the development of new sources for critical raw materials (CRM). The European Commission defined CRMs as highly important for the European high tech industry. European and national resource strategies refer to this definition and include the development of new CRM sources as one of their main objectives. The German Federal Ministry for Research and Education (BMBF) funded the program “r3 –strategic metals and minerals – innovative technologies for resource efficiency” that started in 2012. The aim of the program was to ensure the domestic supply of strategically significant metals and minerals. Suitable projects had to act in the fields of recycling and substitution of raw materials as well as in the field of reduced material consumption. Urban mining and the evaluation of resource efficiency were further topics that suited the program. The Helmholtz Institute Freiberg for Resource Technology (HIF) and the Fraunhofer Institute for Environmental, Safety, and Energy Technology (UMSICHT) worked already together in different projects about mine waste characterization and resource extraction in r3.
The Helmholtz Institute Freiberg for Resource Technology pursues the objective of developing innovative technologies for the economy so that mineral and metalliferous raw materials become more available, undergo highly efficient processes and recycle in an environmentally
friendly manner. As a part of the national strategy for raw materials in 2011, the German government initiated the HIF. It is a constituent part of the Helmholtz-Zentrum Dresden-Rossendorf and works in close collaboration with TU Bergakademie Freiberg. The HIF is a core member of the European EIT RawMaterials network, having played a decisive role in its establishment. Fraunhofer UMSICHT is a pioneer for sustainable energy and raw materials management by supplying and transferring scientific results into companies, society and politics. The dedicated UMSICHT team researches and develops, together with partners, sustainable products, processes and services. Together with industry and public partners, such as the Geological Survey of Germany (BGR), UMSICHT and HIF founded the r³-mine-waste-cluster in order to determine a realistic mine waste
potential for Germany and give a reliable resource estimation for secondary raw materials. Nowadays, however, there is a political and public interest beyond the potential of valuable metals from mine wastes. After the catastrophic tailings accident in Vales Corrego do Feijão mine, Brazil, the social pressure to lower these risks raised on the mining industry, on the mine waste owners (e.g. states) and on the politics. With the new Global Industry Standard on Tailings Management a new set of guidelines was developed in order to avoid these accidents in the future. “The International Council
on Mining and Metals (ICMM), the United Nations Environment Programme (UNEP) and the Principles for Responsible Investment (PRI) share a commitment to the adoption of global best practices on tailings storage facilities. They have co-convened this global tailings review to establish an international standard.” Their environmental risks and at the same time their high potential as a source for (critical) raw materials make mine waste projects a complex exercise. There is a need for solutions that respect environmental, technical, civil and economic issues and provide holistic and sustainable approaches. In order to validating and adjusting different approaches, the HIF coordinates the recomine-alliance. Local stakeholders representing environmental, technical, scientific, governmental and civil institutions assemble in recomine for a development of holistic mine waste solutions for a worldwide application.

Keywords: re-mining; resources; HIF; tailings; mine waste; mining; CRM; slag dump; mine water; WIR!; r3; recomine; Freiberg; Network; Alliance; BMBF; holistic; remediation; sustainable

  • World of Mining - Surface & Underground 72(2020)5, 264-269

Permalink: https://www.hzdr.de/publications/Publ-31646
Publ.-Id: 31646


A FDG-PET radiomics signature detects esophageal squamous cell carcinoma patients who do not benefit from chemoradiation

Li, Y.; Beck, M.; Päßler, T.; Lili, C.; Wu, H.; Ha, D.; Amthauer, H.; Biebl, M.; Thuss-Patience, P.; Berger, J.; Stromberger, C.; Tinhofer, I.; Kruppa, J.; Budach, V.; Hofheinz, F.; Lin, Q.; Zschaeck, S.

Detection of patients with esophageal squamous cell carcinoma (ESCC) who do not benefit from standard chemoradiation (CRT) is an important medical need. Radiomics using 18-fluorodeoxyglucose (FDG) positron emission tomography (PET) is a promising approach. In this retrospective study of 184 patients with locally advanced ESCC. 152 patients from one center were grouped into a training cohort (n = 100) and an internal validation cohort (n = 52). External validation was performed with 32 patients treated at a second center. Primary endpoint was disease-free survival (DFS), secondary endpoints were overall survival (OS) and local control (LC). FDG-PET radiomics features were selected by Lasso-Cox regression analyses and a separate radiomics signature was calculated for each endpoint. In the training cohort radiomics signatures containing up to four PET derived features were able to identify non-responders in regard of all endpoints (DFS p < 0.001, LC p = 0.003, OS p = 0.001). After successful internal validation of the cutoff values generated by the training cohort for DFS (p = 0.025) and OS (p = 0.002), external validation using these cutoffs was successful for DFS (p = 0.002) but not for the other investigated endpoints. These results suggest that pre-treatment FDG-PET features may be useful to detect patients who do not respond to CRT and could benefit from alternative treatment.

Permalink: https://www.hzdr.de/publications/Publ-31643
Publ.-Id: 31643


Dissolution of donor-vacancy clusters in heavily doped n-type germanium

Prucnal, S.; Liedke, M. O.; Wang, X.; Butterling, M.; Posselt, M.; Knoch, J.; Windgassen, H.; Hirschmann, E.; Berencen, Y.; Rebohle, L.; Wang, M.; Napoltani, E.; Frigerio, J.; Ballabio, A.; Isella, G.; Hübner, R.; Wagner, A.; Bracht, H.; Helm, M.; Zhou, S.

The n-type doping of Ge is a self-limiting process due to the formation of vacancy-donor complexes (DnV with n ≤ 4) that deactivate the donors. This work unambiguously demonstrates that the dissolution of the dominating P4V clusters in heavily phosphorus-doped Ge epilayers can be achieved by millisecond-flash lamp annealing at about 1050 K. The P4V cluster dissolution increases the carrier concentration by more than three-fold together with a suppression of phosphorus diffusion. Electrochemical capacitance-voltage measurements in conjunction with secondary ion mass spectrometry, positron annihilation lifetime spectroscopy and theoretical calculations enabled us to address and understand a fundamental problem that has hindered so far the full integration of Ge with complementary-metal-oxide-semiconductor technology.

Keywords: Ge; vacancies; doping; positron annihilation lifetime spectroscopy; flash lamp annealing

Permalink: https://www.hzdr.de/publications/Publ-31641
Publ.-Id: 31641


The GeDI project-a German DIBH database

Duma, M. N.; Krause, M.; Hoinkis, C.; Gurtner, K.; Richter, C.; Corradini, S.; Pazos, M. E.; Schoencker, S.; Walke, M.; Gabriel, C.; Brunner, T.; Krug, D.; Hoerner-Rieber, J.; Grosu, A. L.; Nicolay, N. H.; Wittig, A.

Background: Studies indicate that all left-sided breast cancer patients benefit from the deep inspiration breath hold technique (DIBH), however, not all patients experience the same benefit. A meta-analysis performed by Latty et al. reviewed 18 studies evaluating DIBH, which demonstrated a relative reduction of mean dose (Dmean) to the heart ranging from 26.2% to 75% as compared to irradiation in free breathing. However, as most papers report averages rather than patient-by-patient analyses, outliers remain unidentified. Thus, a lack of data and knowledge exists in determining selection criteria to predict individual patient benefit from DIBH.

Methods: We are planning to establish a large retrospective database of breast cancer patients treated with deep inspiration breath hold (DIBH) radiotherapy techniques. Data will be collected anonymized from all participating centres. A detailed analysis of:

1. Differences in OAR sparing by anatomical conditions
2. Differences in OAR sparing by used DIBH techniques (free breathing, RPM, surface scanning with camera or laser systems etc)
3. Differences in OAR sparing by fractionation schedules (normalized to EQD2)
4. Differences in OAR sparing by PTV volumes and CTV definitions

but not limited to, will be performed.

Discussion: Patient data will be stratified according to different anatomical conditions (such as large breasts vs. small breasts), radiation techniques, fractionation schedules and PTV volumes (for e.g. chest wall after mastectomy vs. breast only vs. breast and lymphatics etc). This multicentre database will allow for the first time an in depth analysis of the impact of DIBH. It will enhance our knowledge on outliers and will provide selection criteria to predict individual patient benefit from DIBH.

  • Lecture (Conference) (Online presentation)
    DEGRO, 24.-28.06.2020, Wiesbaden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-31639
Publ.-Id: 31639


Magnetic-field-assisted electrodeposition of metal to obtain conically structured ferromagnetic layers

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

Micro- or nano-structured ferromagnetic layers often possess superior electrocatalytic properties but are difficult to manufacture in general. The present work investigates how a magnetic field can possibly support local cone growth on a planar electrode during electrodeposition, thus simplifying fabrication. Analytical and numerical studies were performed on conical structures of mm size to elaborate the influence of the magnetic forces caused by an electrode-normal external field. It is shown that, beside the Lorentz force studied earlier in the case of single cones [1], the magnetic gradient force enabled by the field alteration near the ferromagnetic cathode significantly supports cone growth. Detailed studies performed for sharp and flat single cones allow conclusions to be drawn on the support at different stages in the evolution of conical deformations. Furthermore, the influence from neighboring cones is studied with arrays of cones at varying distances apart. Nearby neighbors generally tend to mitigate the flow driven by the magnetic forces. Here, the support for cone growth originating from the magnetic gradient force is less heavily affected than that from the Lorentz force. Our results clearly show that the magnetic field has a beneficial effect on the growth of ferromagnetic conical structures, which could also be useful on the micro- and nanometer scales.

Keywords: metal electrodeposition; magnetic field; surface-structured electrode; Lorentz force; magnetic gradient force; numerical simulation

Related publications

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  • Secondary publication expected from 30.10.2021

Permalink: https://www.hzdr.de/publications/Publ-31638
Publ.-Id: 31638


Vortrag der Gleichstellungsbeauftragten des HZDR vor dem AGBR

Fiedler, F.

Vortrag der GSB vor dem AGBR

  • Lecture (others) (Online presentation)
    Treffen des AGBR, 27.10.2020, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-31635
Publ.-Id: 31635


Experience with the Sperradiant THz user Facility Driven by a Quasi-CW SRF Accelerator at ELBE

Bawatna, M.; Green, B. W.

Instabilities in beam and bunch parameters, such as bunch charge, beam energy, or changes in the phase or amplitude of the accelerating field in the RF cavities can be the source of noise in the various secondary sources driven by the electron beam. Bunch charge fluctuations lead to in-tensity instabilities in the superradiant THz sources. The primary electron beam driving the light sources has a maximum energy of 40 MeV and a maximum current of 1.6 mA. Depending on the mode of operation required, there are two available injectors in use at ELBE. The first is the thermionic injector, which is used for regular operating modes and supports repetition rates up to 13 MHz and bunch charges up to 100 pC. The second is the SRF photo-cathode injector, which is used for experiments that may require lower emittance or higher bunch charges of up to 1 nC. It has a maximum repetition rate of 13 MHz, which can be adjusted to lower rates if desired, also including different macro pulse modes of operation. In this contribution, we will present our work in the pulse-resolved intensity measurement that allows for the correction of intensity instabilities.

  • Open Access Logo Contribution to proceedings
    FEL2019 - 39th International Free-Electron Laser Conference, 26.-30.08.2019, Hamburg, Germany
    Proceedings of the 39th International Free-Electron Laser Conference: JACoW, 978-3-95450-210-3
    DOI: 10.18429/JACoW-FEL2019-TUP007

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Permalink: https://www.hzdr.de/publications/Publ-31632
Publ.-Id: 31632


Data for: Scanning transmission imaging in the helium ion microscope using a microchannel plate with a delay line detector

Serralta Hurtado De Menezes, E.; Klingner, N.; de Castro, O.; Mousley, M.; Eswara, S.; Duarte Pinto, S.; Wirtz, T.; Hlawacek, G.

  A detection system based on a microchannel plate with a delay line readout structure has been developed to perform scanning transmission ion microscopy (STIM) in the helium ion microscope (HIM). This system is an improvement over other existing approaches since it combines the information of the scanning beam position on the sample with the position (scattering angle) and time of the transmission events. Various imaging modes such as bright and dark field or the direct image of the transmitted signal can be created by post-processing the collected STIM data. Furthermore, the detector has high spatial and time resolution, is sensitive to both ions and neutral particles over a wide energy range, and shows robustness against ion beam-induced damage. A special in-vacuum movable support gives the possibility of moving the detector vertically, placing the detector closer to the sample for the detection of high-angle scattering events, or moving it down to increase the angular resolution and distance for time-of-flight measurements. With this new system, we show composition-dependent contrast for amorphous materials and the contrast difference between small and high angle scattering signals. We also detect channeling related contrast on polycrystalline silicon, thallium chloride nanocrystals, and single crystalline silicon by comparing the signal transmitted at different directions for the same data set.

Keywords: helium ion microscopy; scanning transmission ion microscopy; delay line detector; channeling; bright field; dark field

Related publications

  • Reseach data in the HZDR data repository RODARE
    Publication date: 2020-09-09
    DOI: 10.14278/rodare.515
    License: CC-BY-1.0

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-31631
Publ.-Id: 31631


Negative resistance for colloids driven over two barriers in a microchannel

Zimmermann, U.; Löwen, H.; Kreuter, C.; Erbe, A.; Leiderer, P.; Smallenburg, F.

When considering the flow of currents through obstacles, one core expectation is that the total resis- tance of sequential single resistors is additive. While this rule is most commonly applied to electronic circuits, it also applies to other transport phenomena such as the flow of colloids or nanoparti- cles through channels containing multiple obstacles, as long as these obstacles are sufficiently far apart. Here we explore the breakdown of this additivity for fluids of repulsive colloids driven over two energetic barriers in a microchannel, using real-space microscopy experiments, particle-resolved simulations, and dynamical density functional theory. If the barrier separation is comparable to the particle correlation length, the resistance is highly non-additive, such that the resistance added by the second barrier can be significantly higher or lower than that of the first. Surprisingly, in some cases the second barrier can even add a negative resistance, such that two identical barriers are easier to cross than a single one. We explain this counterintuitive observation in terms of the structuring of particles trapped between the barriers.

Keywords: colloidal model systems; soft matter; transport phenomena

Permalink: https://www.hzdr.de/publications/Publ-31629
Publ.-Id: 31629


Metal Pad Roll Instability at Room Temperature Using Pairs of Liquid Metals

Herreman, W.; Nore, C.; Cappanera, L.; Guermond, J.-L.; Weier, T.

Metal pad roll instability is a well known phenomenon that occurs in aluminium reduction cells [1] Since long, scientists and engineers have been searching for an experimental model that recreates the metal pad roll instability in a well controlled laboratory environment. [2] partly succeeded in this task by using GaInSn eutectic alloy in replacement of aluminium and a steel wire array, in replacement of the badly conducting cryolite layer. A rolling wave motion was observed but comparison to fluid based theoretical models remains difficult.
In this talk, we demonstrate that it is possible to observe metal pad roll instability in a centimeter scale cylindrical set-up at room temperature and using different liquid metal pairs as working fluids: gallium liquid metal over mercury (immiscible case) or gallium over GaInSn eutectic alloy (miscible case). Despite the small difference in electrical conductivity, the stability theory of [3] suggests that metal pad roll instability occurs for reasonable values of the imposed magnetic field and electrical current. We confirm this theoretical prediction with some very challenging direct numerical simulations of the multiphase magnetohydrodynamical flow in this set-up, done with our massively parallel solver SFEMaNS [4].

Keywords: liquid metal battery; aluminum reduction cell; metal pad roll instability

  • Lecture (Conference) (Online presentation)
    14th World Congress on Computational Mechanics, 11.-15.01.2021, Paris, Frankreich

Permalink: https://www.hzdr.de/publications/Publ-31628
Publ.-Id: 31628


Propagation of spin waves through a Néel domain wall

Wojewoda, O.; Hula, T.; Flajšman, L.; Vaňatka, M.; Gloss, J.; Holobrádek, J.; Staňo, M.; Stienen, S.; Körber, L.; Schultheiß, K.; Schmid, M.; Schultheiß, H.; Urbánek, M.

Spin waves have the potential to be used as a next-generation platform for data transfer and processing as they can reach wavelengths in the nanometer range and frequencies in the terahertz range. To realize a spin-wave device, it is essential to be able to manipulate the amplitude as well as the phase of spin waves. Several theoretical and recent experimental works have also shown that the spin-wave phase can be manipulated by the transmission through a domain wall (DW). Here, we study propagation of spin waves through a DW by means of micro-focused Brillouin light scattering microscopy (μBLS). The 2D spin-wave intensity maps reveal that spin-wave transmission through a Néel DW is influenced by a topologically enforced circular Bloch line in the DW center and that the propagation regime depends on the spin-wave frequency. In the first regime, two spin-wave beams propagating around the circular Bloch line are formed, whereas in the second regime, spin waves propagate in a single central beam through the circular Bloch line. Phase-resolved μBLS measurements reveal a phase shift upon transmission through the domain wall for both regimes. Micromagnetic modeling of the transmitted spin waves unveils a distortion of their phase fronts, which needs to be taken into account when interpreting the measurements and designing potential devices. Moreover, we show that, by means of micromagnetic simulations, an external magnetic field can be used to move the circular Bloch line within the DW and to manipulate spin-wave propagation.
The authors thank R. Schäfer and O. Fruchart for the discussions on the DW classification.
This research was supported by the CEITEC Nano+ project (No. CZ.02.1.01/0.0/0.0/16013/0001728) and Austrian Science Fund (FWF) project I1937. M. Staňo acknowledges support by the ESF under the project CZ.02.2.69/0.0/0.0/19_074/0016239. CzechNanoLab project LM2018110 funded by MEYS CR is gratefully acknowledged for the financial support of the measurement and sample fabrication at the CEITEC Nano Research Infrastructure.

Keywords: Magnetic ordering; Spectrum analyzer; Light scattering; Magnetic force microscopy

Permalink: https://www.hzdr.de/publications/Publ-31627
Publ.-Id: 31627


Zero-field propagation of spin waves in waveguides prepared by focused ion beam direct writing

Flajšman, L.; Wagner, K.; Vaňatka, M.; Gloss, J.; Křižáková, V.; Schmid, M.; Schultheiß, H.; Urbánek, M.

Metastable face-centered-cubic Fe78Ni22 thin films are excellent candidates for focused ion beam direct writing of magnonic structures due to their favorable magnetic properties after ion-beam-induced transformation. The focused ion beam transforms the originally nonmagnetic fcc phase into the ferromagnetic bcc phase with additional control over the direction of uniaxial magnetic in-plane anisotropy and saturation magnetization. Local magnetic anisotropy direction control eliminates the need for external magnetic fields, paving the way towards complex magnonic circuits with waveguides pointing in different directions. In the present study, we show that the magnetocrystalline anisotropy in transformed areas is strong enough to stabilize the magnetization in the direction perpendicular to the long axis of narrow waveguides. Therefore, it is possible to propagate spin waves in these waveguides in the favorable Damon-Eshbach geometry without the presence of any external magnetic field. Phase-resolved microfocused Brillouin light scattering yields the dispersion relation of these waveguides in zero as well as in nonzero external magnetic fields.

Keywords: Ferromagnetism; Magnetic Anisotropy; Magnetic phase transition; Magnetization Dynamics; Spin Dynamics; Spin Waves; Structural Phase transition; Focused ion beam

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Permalink: https://www.hzdr.de/publications/Publ-31626
Publ.-Id: 31626


Performance investigation of bulk photoconductive semiconductor switch based on reversely biased p+in+ structure

Hu, L.; Xu, M.; Li, X.; Wang, Y.; Wang, Y.; Dong, H.; Schneider, H.

We present an investigation of a low-energy-triggered bulk gallium arsenide (GaAs) photoconductive semiconductor switch (PCSS) that is characterized by powerful avalanche domains. The performance of the switch is investigated using a reversely biased p⁺-i-n⁺ structure with 0.625-mm thickness, and the 8.0-kV, 170-ps bulk PCSS that is triggered by a 905-nm laser at the energy of 5.7 nJ is achieved. In the low-energy-triggered mode, it is found experimentally that the reduction of required energy for switching operation is not always kept by the continuous increase of the bias field in the bulk PCSS due to Franz–Keldysh effect. We also analyze the triggering efficiency depending on the laser wavelength numerically, and results indicate that the earlier formation of the powerful avalanche domains is realized by the increased wavelength, which causes lower laser energy for switching operation. Moreover, the prestudy of high-power microwave (HPM) applications is also introduced utilizing bulk PCSS, and we constructed the basic units for ultrawide-band (UWB) pulse and HPM-driven pulse.

Keywords: photoconductive semiconductor switch; avalanche domain; GaAs

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Permalink: https://www.hzdr.de/publications/Publ-31625
Publ.-Id: 31625


Mode-locked short pulses from an 8 μm wavelength semiconductor laser

Hillbrand, J.; Opačcak, N.; Piccardo, M.; Schneider, H.; Strasser, G.; Capasso, F.; Schwarz, B.

Quantum cascade lasers (QCL) have revolutionized the generation of mid-infrared light. Yet, the ultrafast carrier transport in mid-infrared QCLs have so far constituted a seemingly insurmountable obstacle for the formation of ultrashort light pulses. Here, we demonstrate that careful quantum design of the gain medium and control over the intermode beat synchronization enable transform-limited picosecond pulses from QCL frequency combs. Both an interferometric radio-frequency technique and second-order autocorrelation shed light on the pulse dynamics and confirm that mode-locked operation is achieved from threshold to rollover current. Furthermore, we show that both antiphase and in-phase synchronized states exist in QCLs. Being electrically pumped and compact, mode-locked QCLs pave the way towards monolithically integrated non-linear photonics in the molecular fingerprint region beyond 6 μm wavelength.

Keywords: quantum cascade laser; two-photon QWIP; mid-infrared, frequency comb

Permalink: https://www.hzdr.de/publications/Publ-31624
Publ.-Id: 31624


Wire-mesh sensor measurements of single-phase liquid flows at different temperatures

Wiedemann, P.; de Assis Dias, F.; Schleicher, E.; Hampel, U.

The dataset contains raw data that is related to the investigation "Temperature Compensation for Conductivity-Based Phase Fraction Measurements with Wire-Mesh Sensors in Gas-Liquid Flows of Dilute Aqueous Solutions".

A 16x16 conductivity-based wire-mesh sensor was placed in a single-phase liquid loop with adjustable fluid temperature. The dataset includes the wire-mesh sensor measurements with water at several temperature levels from 12.5°C to 80°C and the corresponding electrical conductivites. Two water samples, namely deionized water and a mixed water sample, were investigated. The latter one is composed of 95% deionized water and 5% local tap water.

Keywords: wire-mesh sensor; temperature compensation; electrical conductivity

Related publications

  • Reseach data in the HZDR data repository RODARE
    Publication date: 2020-10-21
    DOI: 10.14278/rodare.555

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-31623
Publ.-Id: 31623


High-Intensity Laser-Driven Oxygen Source from CW Laser-Heated Titanium Tape Targets

Kondo, K.; Nishiuchi, M.; Sakaki, H.; Dover, N. P.; Lowe, H. F.; Miyahara, T.; Watanabe, Y.; Ziegler, T.; Zeil, K.; Schramm, U.; Ditter, E. J.; Hicks, G. S.; Ettlinger, O. C.; Najmudin, Z.; Kiriyama, H.; Kando, M.; Kondo, K.

The interaction of high-intensity laser pulses with solid targets can be used as a highly charged, energetic heavy ion source. Normally, intrinsic contaminants on the target surface suppress the performance of heavy ion acceleration from a high-intensity laser–target interaction, resulting in preferential proton acceleration. Here, we demonstrate that CW laser heating of 5 µm titanium tape targets can remove contaminant hydrocarbons in order to expose a thin oxide layer on the metal surface, ideal for the generation of energetic oxygen beams. This is demonstrated by irradiating the heated targets with a PW class high-power laser at an intensity of 5 x 10^21 W/cm^2, showing enhanced acceleration of oxygen ions with a non-thermal-like distribution. Our new scheme using a CW laser-heated Ti tape target is promising for use as a moderate repetition energetic oxygen ion source for future applications.

Keywords: Ti Sapphire laser; high-power laser; laser-driven heavy ion acceleration; surface treatment; CW laser heating; oxygen ion source

Permalink: https://www.hzdr.de/publications/Publ-31622
Publ.-Id: 31622


Frequency control of auto-oscillations of the magnetization in spin Hall nano-oscillators

Hache, T.

This thesis experimentally demonstrates four approaches of frequency control of magnetic autooscillations in spin Hall nano-oscillators (SHNOs).
The frequency can be changed in the GHZ-range by external magnetic fields as shown in this work. This approach uses large electromagnets, which is inconvenient for future applications.The nonlinear coupling between oscillator power and frequency can be used to control the latter one by changing the applied direct current to the SHNO. The frequency can be controlled over a range of several 100 MHz as demonstrated in this thesis.
The first part of the experimental chapter demonstrates the synchronization (injection-locking) between magnetic auto-oscillations and an external microwave excitation. The additionally applied microwave current generates a modulation of the effective magnetic field, which causes the interaction with the auto-oscillation. Both synchronize over a range of several 100 MHz. In this range, the auto-oscillation frequency can be controlled by the external stimulus. An increase of power and a decrease of line width is achieved in the synchronization range. This is explained by the increased coherence of the auto-oscillations. A second approach is the synchronization of auto-oscillations to an alternating magnetic field. This field is generated by a freestanding antenna, which is positioned above the SHNO.
The second part of the experimental chapter introduces a bipolar concept of SHNOs and its experimental demonstration. In contrast to conventional SHNOs, bipolar SHNOs generate autooscillations for both direct current polarities and both directions of the external magnetic field. This is achieved by combining two ferromagnetic layers in an SHNO. The combination of two different ferromagnetic materials is used to switch between two frequency ranges in dependence of the direct current polarity since it defines the layer showing auto-oscillations. This approach can be used to change the frequency in the GHz-range by switching the direct current polarity.

  • Reseach data in the HZDR data repository RODARE
    Publication date: 2020-10-21
    DOI: 10.14278/rodare.553
    License: CC-BY-4.0

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Permalink: https://www.hzdr.de/publications/Publ-31619
Publ.-Id: 31619


Magnetic texture based magnonics

Yu, H.; Xiao, J.; Schultheiß, H.

The spontaneous magnetic orders arising in ferro-, ferri- and antiferromagnets stem from various magnetic interactions. Depending on the interplay and competition among the Heisenberg exchange interaction, Dzyaloshinskii-Moriya exchange interaction, magnetic dipolar interaction and crystal anisotropies, a great variety of magnetic textures may be stabilized, such as magnetic domain walls, vortices, Skyrmions and spiral helical structures. While each of these spin textures responds to external forces in a specific manner with characteristic resonance frequencies, they also interact with magnons, the fundamental collective excitation of the magnetic order, which can propagate in magnetic materials free of charge transport and therefore with low energy dissipation. Recent theories and experiments found that the interplay between spin waves and magnetic textures is particularly interesting and rich in physics. In this review, we introduce and discuss the theoretical framework of magnons living on a magnetic texture background, as well as recent experimental progress in the manipulation of magnons via magnetic textures. The flexibility and reconfigurability of magnetic textures are discussed regarding the potential for applications in information processing schemes based on magnons.

Keywords: magnetic textures; spin waves; magnetization dynamics; Skyrmions; antiferromagnets; Dzyaloshinskii Moria; chiral magnetism; domain walls; vortices

Permalink: https://www.hzdr.de/publications/Publ-31616
Publ.-Id: 31616


Potential microbial influence on the performance of subsurface, salt-based nuclear waste repositories

Swanson, J. S.; Bader, M.; Cherkouk, A.

Microrganisms can influence the performance of nuclear waste repositories through activities or processes that affect radionuclide migration. In the case of subterranean salt-based repositories, the influence of microorganisms may be limited by the unique constraints of such sutes (e.g. high ionic strength, low water activity, nutient supply) coupled with conditions of the repositories themselves (e.g. anoxia,radioactivity, high temperatures). Indigenous extremely halophilic archaea can survive long-term at high ionic strength and may remain viable throughout a repository´s lifetime. However, their ability to affect repository performance through waste and radionuclide transformation is uncertain, as they are mostly arobic and repositories are projected to be anoxic. Microorganisms introduced with waste may contribute to transformations within drums but may not survive high salt concentrations once drums have been breached and inundated with brine. However, both indigenous and introduced organisms may associate with radionuclides and enhance or mitigate radionuclide migration in this capacity.

  • Book chapter
    Jonathan Lloyd, Andrea Cherkouk: The Microbiology of Nuclear Waste Disposal 1st Edition, Amsterdam: Elsevier, 2020

Permalink: https://www.hzdr.de/publications/Publ-31615
Publ.-Id: 31615


Molecular techniques for understanding microbial abundance and activity in clay barriers used for geodisposal

Mijnendonckx, K.; Monsieurs, P.; Cerna, K.; Hlavackova, V.; Steinova, J.; Burzan, N.; Bernier-Latmani, R.; Boothman, C.; Miettinen, H.; Kluge, S.; Matschiavelli, N.; Cherkouk, A.; Jroundi, F.; Larbi Merroun, M.; Engel, K.; Neufeld, J. D.; Leys, N.

Clays are commonly used in design concepts for geological disposal of nuclear waste. It is thus essential to identify and quantify microbial communities in clay-rich samples to study microbial processes during geological disposal. Although advances in culture-independent techiques have enablesd detailed studies of microbial communities in diverse ecosystems, the efficiency and sensitivity of these molecular techniques depend on chartacteristics of the environment studied. Moreover, the outcome of nucleic acid-based approaches depends on the extraction method, prmer specificity, PCR amplification, sequencing artefacts and downstream bioinformatic analyses. Clays are recalcitrant to DNA extraction and are challenging for analysis by standard techniques using viability stains and measurement of metabolic activity. This chapter explores the impact of various sequencing and bioinformatic pipelines used for 16S rRNA gene profiling of microbial communities and compares the efficiency of different DNA extraction methods from clay. Moreover, non-DNA based techniques used to assess microbial activity and viability in clay samples will be also discussed.

  • Book chapter
    Jonathan Lloyd Andrea Cherkouk: The Microbiology of Nuclear Waste Disposal 1st Edition, Amsterdam: Elsevier, 2020

Permalink: https://www.hzdr.de/publications/Publ-31614
Publ.-Id: 31614


The Microbiology of Nuclear Waste Disposal

Lloyd, J.; Cherkouk, A.

The Microbiology of Nuclear Waste Disposal is a state-of-the-art reference featuring contributions focusing on the impact of microbes on the safe long-term disposal of nuclear waste. This book is the first to cover this important emerging topic, and is written for a wide audience encompassing regulators, implementers, academics, and other stakeholders. The book is also of interest to those working on the wider exploitation of the subsurface, such as bioremediation, carbon capture and storage, geothermal energy, and water quality.

Planning for suitable facilities in the U.S., Europe, and Asia has been based mainly on knowledge from the geological and physical sciences. However, recent studies have shown that microbial life can proliferate in the inhospitable environments associated with radioactive waste disposal, and can control the long-term fate of nuclear materials. This can have beneficial and damaging impacts, which need to be quantified.

  • Book (Editorship)
    Amsterdam: Elsevier, 2020
    ISBN: 9780128186954

Permalink: https://www.hzdr.de/publications/Publ-31613
Publ.-Id: 31613


Raw data: CoFeB beamtime overview

Awari, N.; Deinert, J.-C.

Collection of raw data and evaluated data for the CoFeB experiments carried out in collaboration with Stefano Bonetti et al.

Keywords: Spin dynamics; nutation; CoFeB; Terahertz

Related publications

  • Reseach data in the HZDR data repository RODARE
    Publication date: 2020-10-19
    DOI: 10.14278/rodare.551

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Permalink: https://www.hzdr.de/publications/Publ-31612
Publ.-Id: 31612


Parametric optimization in rougher flotation performance of a sulfidized mixed copper ore

Hassanzadehmahaleh, A.; Azizi, A. A.; Masdarian, M. A.; Bahri, Z. C.; Niedoba, T. D.; Surowiak, A. D.

The dominant challenge of current copper beneficiation plants is the low recoverability of oxide copper-bearing minerals associated with sulfide type ones. Furthermore, applying commonly used conventional methodologies does not allow the interactional effects of critical parameters in the flotation processes to be investigated, which is mostly overlooked in the literature. To tackle this issue, the present paper aimed at characterizing the behavior of five key effective factors and their interactions in a sulfidized copper ore. In this context, dosage of collector (sodium di-ethydithiophosphate, 60–100 g/t), depressant (sodium silicate, 80–120 g/t) and frother (methyl isobutyl carbinol (MIBC), 6–10 g/t), pulp pH (7–11) and agitation rate (900–1300 rpm) were examined and statistically analyzed using response surface methodology. Flotation experiments were conducted in a Denver type agitated flotation cell at the rougher stage. The experimental results showed that increasing the pH (from 8 to 10) at low agitation rate (1000 rpm) enhanced the recovery from 80.36% to 85.22%, while at high agitation rate (1200 rpm), a slight declination occurred in the recovery. Meanwhile, increasing the collector dosage at a lower frother value (7 g/t), caused a reduction of about 4.44% in copper recovery owing to the interactions between factors, whereas at a higher frother level (9 g/t), the recovery was almost unchanged. The optimization process was also performed using the goal function approach, and maximum copper recovery of 92.75% was obtained using ~70 g/t collector, 110 g/t depressant, 7 g/t frother, pulp pH of 10 and 1000 rpm agitation rate.

Keywords: sulfidized copper ore; flotation; interaction effects; recovery; optimization

Permalink: https://www.hzdr.de/publications/Publ-31611
Publ.-Id: 31611


Point and extended defects in heteroepitaxial β-Ga2O3 films

Saadatkia, P.; Agarwal, S.; Hernandez, A.; Reed, E.; Brackenbury, I. D.; Codding, C. L.; Liedke, M. O.; Butterling, M.; Wagner, A.; Selim, F. A.

Ga2O3 is emerging as an excellent potential semiconductor for high power and optoelectronic devices.
However, the successful development of Ga2O3 in a wide range of applications requires a full understanding of the role and nature of its point and extended defects. In this work, high quality epitaxial Ga2O3 films were grown on sapphire substrates by metal-organic chemical vapor deposition and fully characterized in terms of structural, optical, and electrical properties. Then defects in the films were investigated by a combination of depth-resolved Doppler broadening and lifetime of positron annihilation spectroscopies and thermally stimulated emission (TSE). Positron annihilation techniques can provide information about the nature and concentration of defects in the films, while TSE reveals the energy level of defects in the bandgap. Despite very good structural properties, the films exhibit short positron diffusion length, which is an indication of high defect density and long positron lifetime, a sign for the formation of Ga vacancy related defects and large vacancy clusters. These defects act as deep and shallow traps for charge carriers as revealed from TSE, which explains the reason behind the difficulty of developing conductive Ga2O3 films on non-native substrates. Positron lifetime measurements also show nonuniform distribution of vacancy clusters throughout the film depth. Further, the work investigates the modification of defect nature and properties through thermal treatment in various environments. It demonstrates the sensitivity of Ga2O3 microstructures to the growth and thermal treatment environments and the significant effect of modifying defect structure on the bandgap and optical and electrical properties of Ga2O3

Keywords: positron annihilation spectroscopy; positron annihilation lifetime spectroscopy; Doppler broadening; defetcs; Ga2O3

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Permalink: https://www.hzdr.de/publications/Publ-31609
Publ.-Id: 31609


Non-plasmonic improvement in photoconductive THz emitters using nano- and micro-structured electrodes

Singh, A.; Welsch, M.; Winnerl, S.; Helm, M.; Schneider, H.

We investigate here terahertz enhancement effects arising from micrometer and nanometer structured electrode features of photoconductive terahertz emitters. Nanostructured electrode based emitters utilizing the palsmonic effect are currently one of the hottest topics in the research field. We demonstrate here that even in the absence of any plasmonic resonance with the pump pulse, such structures can improve the antenna effect by enhancing the local d.c. electric field near the structure edges. Utilizing this effect in Hilbert-fractal and grating-like designs, enhancement of the THz field of up to a factor of ~ 2 is observed. We conclude that the cause of this THz emission enhancement in our emitters is different from the earlier reported plasmonic-electrode effect in a similar grating-like structure. In our structure, the proximity of photoexcited carriers to the electrodes and local bias field enhancement close to the metallization cause the enhanced efficiency. Due to the nature of this effect, the THz emission efficiency is almost independent of the pump laser polarization. Compared to the plasmonic effect, these effects work under relaxed device fabrication and operating conditions.

Keywords: Terahertz sources; Teraherhertz emitter; Photoconductive THz emitter; Photoconductive antenna

Permalink: https://www.hzdr.de/publications/Publ-31607
Publ.-Id: 31607


Temperature Compensation for Conductivity-Based Phase Fraction Measurements with Wire-Mesh Sensors in Gas-Liquid Flows of Dilute Aqueous Solutions

Wiedemann, P.; de Assis Dias, F.; Schleicher, E.; Hampel, U.

Wire-mesh sensors are well-established scientific instruments for measuring the spatio-temporal phase distribution of two-phase flows based on different electrical conductivities of the phases. Presently, these instruments are also applied in industrial processes and need to cope with dynamic operating conditions increasingly. However, since the quantification of phase fractions is achieved by normalizing signals with respect to a separately recorded reference measurement, the results are sensitive to temperature differences in any application. Therefore, the present study aims at proposing a method to compensate temperature effects in the data processing procedure. Firstly, a general approach is theoretically derived from the underlying measurement principle and compensation procedures for the electrical conductivity from literature models. Additionally, a novel semi-empirical model is developed on the basis of electrochemical fundamentals. Experimental investigations are performed using a single-phase water loop with adjustable fluid temperature in order to verify the theoretical approach for wire-mesh sensor applications and to compare the different compensation models by means of real data. Finally, the preferred model is used to demonstrate the effect of temperature compensation with selected sets of experimental two-phase data from a previous study. The results are discussed in detail and show that temperature effects need to be handled carefully --- not merely in industrial applications, but particularly in laboratory experiments.

Keywords: wire-mesh sensor; temperature compensation; multicomponent electrolyte solution; ionic conductivity; two-phase thermohydraulics

Related publications

Permalink: https://www.hzdr.de/publications/Publ-31605
Publ.-Id: 31605


Code, data and supplementary material for: An improved contact method for quantifying the mixing of a binary granular mixture

Papapetrou, T. N.; Lecrivain, G.; Bieberle, M.; Boudouvis, A.; Hampel, U.

This material is related to the publication "An improved contact method for quantifying the mixing of a binary granular mixture", submitted on 13.05.2020 to Granular Matter. The original camera video, an intermediate masked video and the final preprocessed video used in the calculations, made from frames 4-1004 of the masked one, are included. The code used for all calculations in the paper and supplementary material, including the implementation of the mixing index evaluation methods, as well as the static artificial images and the generated data, are also included. All images used in the calculations are stored in the required data form. The figures of the paper are also included, as well as two supplementary materials: a version of Figure 12 with the points of the original contact method, and a discussion on the calculation of the minimum modified contact length.

Keywords: binary particle mixing; rotating drum; image analysis; mixing index; contact method; variance method

  • Reseach data in the HZDR data repository RODARE
    Publication date: 2020-10-13
    DOI: 10.14278/rodare.548

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Permalink: https://www.hzdr.de/publications/Publ-31602
Publ.-Id: 31602


UO2 nanoparticles: from peculiarities to similarities with PuO2

Gerber, E.; Romanchuk, A. Y.; Weiss, S.; Bauters, S.; Schacherl, B.; Vitova, T.; Hübner, R.; Shams Aldin Azzam, S.; Detollenaere, D.; Banerjee, D.; Butorin, S. M.; Kalmykov, S. N.; Kvashnina, K.

Fast chemical deposition of uranium(IV) under reducing conditions at pH 8-11 results in the formation of highly crystalline UO2 nanoparticles (NPs) with sizes of 2-3 nm, which is similar to the formation mechanism of PuO2 NPs. UO2 NPs are characterized by various microscopic and spectroscopic techniques including high energy transmission electron microscopy (HRTEM), high energy resolution fluorescence detection (HERFD) X-ray absorption spectroscopy and extended X-ray absorption fine structure (EXAFS) spectroscopy. Despite U(IV) being the dominant oxidation state of the freshly prepared UO2 NPs, they readily oxidize to U4O9 with time and under the X-ray beam. This oxidation of NPs is accompanied by their growth in size to 6 nm. The high tendency of UO2 NPs towards oxidation differs from PuO2 NPs’ behaviour due to the extremely high stability of Pu(IV) and much lower stability of oxidized Pu(V/VI) as compared to U(V/VI).

Permalink: https://www.hzdr.de/publications/Publ-31601
Publ.-Id: 31601


The effect of Pd(II) chloride complexes anchoring on the formation and properties of Pd/MgAlOx catalysts

Belskaya, O. B.; Zaikovskii, V. I.; Gulyaeva, T. I.; Talsi, V. P.; Trubina, S. V.; Kvashnina, K.; Nizovskii, A. I.; Kalinkin, A. V.; Bukhtiyarov, V. I.; A. Likholobov, V.

Pd(II) chloride complexes were anchored using magnesium-aluminum layered double
hydroxides (LDHs) with interlayer anions 3 2 and ), which possess different exchange properties, and MgAl mixed oxide during its rehydration. It was shown that the catalysts of the same chemical composition with different size, morphology and electronic state of supported palladium particles can be synthesized by varying the localization of Pd precursor. The properties of Pd/MgAlOx catalysts were studied in aqueous-phase hydrogenation of furfural.
Anchoring of the Pd precursor in the interlayer space of LDHs is accompanied by the formation of non-isometric agglomerated palladium particles which contain less oxidized metal and show a higher activity toward hydrogenation of furfural. Magnesium-aluminum oxides in Pd/MgAlOx catalysts are rehydrated in the aqueous-phase reaction to yield the activated MgAl-LDH species as a support, which promotes the furfural conversion via hydrogenation of the furan cycle.

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  • Secondary publication expected from 08.10.2021

Permalink: https://www.hzdr.de/publications/Publ-31600
Publ.-Id: 31600


Development of New 14 Cr ODS Steels by Using New Oxides Formers and B as an Inhibitor of the Grain Growth

Meza, A.; Macía, E.; García-Junceda, A.; Antonio Díaz, L.; Chekhonin, P.; Altstadt, E.; Serrano, M.; Eugenia Rabanal, M.; Campos, M.

In this work, new oxide dispersion strengthened (ODS) ferritic steels have been produced by powder metallurgy using an alternative processing route and characterized afterwards by comparing them with a base ODS steel with Y2O3 and Ti additions. Different alloying elements like boron (B), which is known as an inhibitor of grain growth obtained by pinning grain boundaries, and complex oxide compounds (Y-Ti-Zr-O) have been introduced to the 14Cr prealloyed powder by using mechanical alloying (MA) and were further consolidated by spark employing plasma sintering (SPS). Techniques such as x-ray diffraction (XRD), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM) were used to study the obtained microstructures.
Micro-tensile tests and microhardness measurements were carried out at room temperature to analyze the mechanical properties of the differently developed microstructures, which was considered to result in a better strength in the ODS steels containing the complex oxide Y-Ti-Zr-O. In addition, small punch (SP) tests were performed to evaluate the response of the material under high temperatures conditions, under which promising mechanical properties were attained by the materials containing Y-Ti-Zr-O (14Al-X-ODS and 14Al-X-ODS-B) in comparison with the other commercial steel, GETMAT. The differences in mechanical strength can be attributed to the precipitate’s density, nature, size, and to the density of dislocations in each ODS steel.

Permalink: https://www.hzdr.de/publications/Publ-31597
Publ.-Id: 31597


Feature extraction for hyperspectral mineral domain mapping: A test of conventional and innovative methods

Lorenz, S.; Ghamisi, P.; Kirsch, M.; Jackisch, R.; Rasti, B.; Gloaguen, R.

Hyperspectral (HS) imaging holds great potential for the mapping of geological targets. Innovative acquisition modes such as drone-borne or terrestrial remote sensing open up new scales and angles of observation, which allow to analyze small-scale, vertical, or difficult-to-access outcrops. A variety of available sensors operating in different spectral ranges can provide information about the abundance and spatial location of various geologic materials. However geological outcrops are inherently uneven and spectrally heterogeneous, may be covered by dust, lichen or weathering crusts, or contain spectrally indistinct objects, which is why classifications or domain mapping approaches are often used in geoscientific and mineral exploration applications as a means to discriminate mineral associations (e.g. ore or alteration zones) based on overall variations in HS data. Feature extraction (FE) algorithms are prominently used as a preparatory step to identify the first order variations within the data and, simultaneously, reduce noise and data dimensionality. The most established FE algorithms in geosciences are, by far, Principal Component Analysis (PCA) and Minimum Noise Fraction (MNF). Major progress has been conducted in the image processing community within the last decades, yielding innovative FE methods that incorporate spatial information for smoother and more accurate classification results. In this paper, we test the applicability of conventional (PCA, MNF) and innovative FE techniques (OTVCA: Orthogonal total variation component analysis and WSRRR: Wavelet-based sparse reduced-rank regression) on three case studies from geological HS mapping campaigns, including drone-borne mineral exploration, terrestrial paleoseismic outcrop scanning and thermal HS lithological mapping. This allows us to explore the performance of different FE approaches on complex geological data with sparse or partly inaccurate validation data. For all case studies, we demonstrate advantages of innovative FE algorithms in terms of classification accuracy and geological interpretability. We promote the use of advanced image processing methods for applications in geoscience and mineral exploration as a tool to support geological mapping activities.

Keywords: feature extraction; domain mapping; mineral exploration; image processing; hyperspectral imaging; classification

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  • Secondary publication expected from 22.10.2021

Permalink: https://www.hzdr.de/publications/Publ-31596
Publ.-Id: 31596


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