Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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Without submitted and only approved publications
Only approved publications

32346 Publications
Automated SEM Mineral Liberation Analysis (MLA) with Generically Labelled EDX Spectra in the Mineral Processing of Rare Earth Element Ores
Schulz, B.; Merker, G.; Gutzmer, J.ORC
Many rare earth element (REE) deposits have experienced multistage geological enrichment processes resulting in REE bearing mineral assemblages of considerable complexity and variability. Automated scanning electron microscopy (SEM) mineral liberation analysis of such REE ores is confronted by the difficult assignment of energy-dispersive X-ray (EDX) spectra to REE mineral names. To overcome and bypass this problem, a generic and reliable labelling of EDX reference spectra obtained from REE-bearing minerals based on their contents of Si, Ca, F and P in a bulk normalised analysis is proposed. The labelled spectra are then combined into groups of REE-P (similar to monazite), REE-Ca-Si-P (similar to britholite), REE-Ca-F (similar to synchysite) and REE-F (similar to bastnaesite, parisite, fluocerite). Mixed spectra with low counts for REE from minute REE mineral grains are combined into a separate group. This classification scheme is applied to automated SEM mineral liberation analysis (MLA) data from beneficiation products by comminution and multistage flotation of REE carbonatite ores. Mineral modes, mineral grain size distribution, mineral liberation, mineral locking and mineral grade versus recovery curves based on the analysis of >200,000 particles in a sample can be recognised and interpreted in virtual grain size fractions. The approach as proposed here will allow future process mineralogical studies of REE deposits to be robust and comparable.

Publ.-Id: 29796 - Permalink

Independent Geometrical Control of Spin and Charge Resistances in Curved Spintronics
Das, K. S.; Makarov, D.ORC; Gentile, P.; Cuoco, M.; van Wees, B. J.; Ortix, C.; Vera-Marun, I. J.
Spintronic devices operating with pure spin currents represent a new paradigm in nanoelectronics, with a higher energy efficiency and lower dissipation as compared to charge currents. This technology, however, will be viable only if the amount of spin current diffusing in a nanochannel can be tuned on demand while guaranteeing electrical compatibility with other device elements, to which it should be integrated in high-density three-dimensional architectures. Here, we address these two crucial milestones and demonstrate that pure spin currents can effectively propagate in metallic nanochannels with a three-dimensional curved geometry. Remarkably, the geometric design of the nanochannels can be used to reach an independent tuning of spin transport and charge transport characteristics. These results laid the foundation for the design of efficient pure spin current-based electronics, which can be integrated in complex three-dimensional architectures.
Keywords: curved nanoarchitectures, electrical and spin resistance, geometrical control, nonlocal spin valves, Spintronics

Publ.-Id: 29794 - Permalink

Engineering Self-Supported Noble Metal Foams Toward Electrocatalysis and Beyond
Du, R.; Jin, X.; Hübner, R.; Fan, X.; Hu, Y.; Eychmüller, A.;
Noble metals, despite their expensiveness, display irreplaceable roles in widespread fields. To acquire novel physicochemical properties and boost the performance-to-price ratio for practical applications, one core direction is to engineer noble metals into nanostructured porous networks. Noble metal foams (NMFs), featuring self-supported, 3D interconnected networks structured from noble-metal-based building blocks, have drawn tremendous attention in the last two decades. Inheriting structural traits of foams and physicochemical properties of noble metals, NMFs showcase a variety of interesting properties and impressive prospect in diverse fields, including electrocatalysis, heterogeneous catalysis, surface-enhanced Raman scattering, sensing and actuation, etc. A number of NMFs have been created and versatile synthetic approaches have been developed. However, because of the innate limitation of specific methods and the insufficient understanding of formation mechanisms, flexible manipulation of compositions, structures, and corresponding properties of NMFs are still challenging. Thus, the correlations between composition/structure and properties are seldom established, retarding material design/optimization for specific applications. This review is devoted to a comprehensive introduction of NMFs ranging from synthesis to applications, with an emphasis on electrocatalysis. Challenges and opportunities are also included to guide possible research directions in this field and promote the interest of interdisciplinary scientists.

Publ.-Id: 29789 - Permalink

Updates on the FLUKA geometry for the MU2E experiment
Müller, S.ORC; Ferrari, A.ORC; Rachamin, R.ORC
Presentation at Mu2e Collaboration Meeting 16.10.2019
Keywords: Mu2e, FLUKA, Monte Carlo, CLFV
  • Lecture (Conference)
    Mu2e Collaboration Meeting, 16.-19.10.2019, Fermilab, Batavia, USA

Publ.-Id: 29784 - Permalink

Synthesis and cyclooxygenase inhibition of sulfonamide-substituted (dihydro)pyrrolo[3,2,1-hi]indoles and their potential prodrugs
Laube, M.ORC; Gassner, C.; Knieß, T.ORC; Pietzsch, J.ORC
Non-invasive imaging of cyclooxygenase-2 (COX-2) by radiolabeled ligands is attractive for the diagnosis of cancer and novel highly affine leads with optimized pharmacokinetic profile are of high interest for future developments. Recent findings have shown that methylsulfonyl-substituted (dihydro)pyrrolo[3,2,1-hi]indoles represent highly potent and selective COX-2 inhibitors but possess unsuitable pharmacokinetic properties for radiotracer applications. Based on these results, we herein present the development and evaluation of a second series of sulfonamide-substituted (dihydro)pyrrolo[3,2,1-hi]indoles and their conversion into the respective more hydrophilic N-propionamide-substituted analogs. In comparison to the methylsulfonyl-substituted leads, COX inhibition potency and selectivity was retained in the sulfonamide-substituted compounds; however, the high lipophilicity might hinder their future use. The N-propionamide-substituted analogs showed a significantly decreased lipophilicity and, as expected, lower or no COX-inhibition potency. Hence, the N-(sulfonyl)propionamides can be regarded as potential prodrugs, which represents a potential approach for more sophisticated radiotracer developments.
Keywords: Cancer; Imaging; Inflammation; Lipophilicity; McMurry cyclization; Structure-Activity-Relationship

Publ.-Id: 29783 - Permalink

Hyperspectral outcrop models for palaeoseismic studies
Kirsch, M.ORC; Lorenz, S.; Zimmermann, R.ORC; Andreani, L.ORC; Tusa, L.; Pospiech, S.; Jackisch, R.ORC; Unger, G.; Khodadadzadeh, M.; Ghamisi, P.; Middleton, M.; Ojala, A.; Mattila, J.; Nordbäck, N.; Palmu, J.-P.; Ruskeeniemi, T.; Sutinen, R.; Tiljander, M.; Heikkilä, P.; Gloaguen, R.ORC
The traditional study of palaeoseismic trenches, involving logging, stratigraphic and structural interpretation, can be time consuming and affected by biases and inaccuracies. To overcome these limitations, a new workflow is presented that integrates infrared hyperspectral and photogrammetric data to support field-based palaeoseismic observations. As a case study, this method is applied on two palaeoseismic trenches excavated across a post-glacial fault scarp in northern Finnish Lapland. The hyperspectral imagery (HSI) is geometrically and radiometrically corrected, processed using established image processing algorithms and machine learning approaches, and co-registered to a structure-from-motion point cloud. HSI-enhanced virtual outcrop models are a useful complement to palaeoseismic field studies as they not only provide an intuitive visualisation of the outcrop and a versatile data archive, but also enable an unbiased assessment of the mineralogical composition of lithologic units and a semi-automatic delineation of contacts and deformational structures in a 3D virtual environment.
Keywords: palaeoseismology, SfM photogrammetry, hyperspectral imaging, geology, remote sensing, outcrop models

Publ.-Id: 29768 - Permalink

Amphiphilic Siderophores – A group of complexing surfactant bioreagents for the application in froth flotation separation
Schrader, S.; Kutschke, S.; Hartmann, S.; Pollmann, K.; Rudolph, M.ORC
The consumption of metallic raw materials is constantly increasing. The coverage of demand is getting more difficult, because both primary and secondary raw materials become more and more complex. To find a solution, new approaches will have to be developed, like the combination of biotechnology with classic processing methods.
The idea of this work is the biotechnological production of siderophores for the application as a reagent in conventional froth flotation processes. Siderophores are small organic molecules with a high affinity for binding Fe(III) and to selectively form strong complexes also with other metals. They are produced by microorganisms (aerobic bacteria and fungi) and some plants. Especially the group of amphiphilic siderophores are very interesting. The hydrophilic part, carrying hydroxamate functional groups, is responsible for the selective binding of the metals. Flotation agents produced by the chemical industry with the same functional groups have already been applied successfully in this processing method. It can be suggested siderophores carrying the same and even more selective functional groups are highly potential as ecofriendly collector molecules for flotation and should generally be interesting for the surfactant industry. The molecule’s tail, that is representing the hydrophobic part, gets in contact with the bubble and spares additional chemicals and further working steps for making the target mineral particles hydrophobic.
Besides the biotechnological production of these amphiphilic siderophores, this work includes also interaction studies and flotation experiments of different scales, including bubble pick-up tests, Halimond tube microflotation and batch lab flotation experiments of iron and copper bearing ores.
The application of amphiphilic siderophores as biochemicals in the froth flotation process can change the classic processing method in a more sustainable process – the Bioflotation process. This will reduce the usage of other chemical agents. Moreover, the specific metal binding of siderophores changes flotation in a more purposeful and efficient process and is an important enrichment for the field of Biohydrometallurgy.
Keywords: Marinobactin, Marinobacter, amphiphilic, Siderophores froth flotation
  • Poster
    Jahrestreffen der ProcessNet-Fachgruppen Zerkleinern und Klassieren, Kristallisation und Grenzflächenbestimmte Systeme und Prozesse, 12.-13.03.2019, Bamberg, Deutschland

Publ.-Id: 29764 - Permalink

Integriertes Management und Publikation von wissenschaftlichen Artikeln, Software und Forschungsdaten am Helmholtz-Zentrum Dresden-Rossendorf (HZDR)
Reschke, E.ORC; Konrad, U.ORC
Mit dem Ziel, das Publizieren von Artikeln, Forschungsdaten und wissenschaftlicher Software gemäß den FAIR-Prinzipien ( zu unterstützen, wurde am HZDR ein integriertes Publikationsmanagement aufgebaut. Insbesondere Daten- und Softwarepublikationen erfordern die Entwicklung bedarfsgerechter organisatorischer und technischer Strukturen ergänzend zu bereits sehr gut funktionierenden Services im Publikationsmanagement. In der Zusammenarbeit mit Wissenschaftlern des HZDR und internationalen Partnern in ausgewählten Projekten wurde der Bedarf an Unterstützung im Forschungsdatenmanagement analysiert. Darauf aufbauend wurde schrittweise ein integriertes System von Infrastrukturen und Services entwickelt und bereitgestellt. In einer seit Mai 2018 gültigen Data Policy wurden die Rahmenbedingungen und Regelungen sowohl für wissenschaftliche Mitarbeiter als auch für externe Messgäste definiert. Im Vortrag wird auf die Erfahrungen im integrierten Publikationsmanagement für Artikel, Forschungsdaten und Forschungssoftware eingegangen und daraus resultierend werden die nächsten Aufgaben und Ziele entwickelt.
Keywords: Open Access, Research Data, Rodare, Robis, Research Infrastructure
  • Open Access LogoInvited lecture (Conferences)
    „Forschungsdaten in Sachsen: Planen – Organisieren – Nachnutzen“ – 1. sächsische FDM-Tagung, 19.09.2019, Dresden, Deutschland
    Published in the HZDR-Repository RODARE (Test)
    DOI 10.14278/rodare.353


Publ.-Id: 29763 - Permalink

Production of the amphiphilic siderophore marinobactin and the application as froth flotation reagent
Schrader, S.; Kutschke, S.; Rudolph, M.ORC; Pollmann, K.
The consumption of metallic raw materials increased in the last years. The coverage of demand is getting more difficult, because both primary and secondary raw materials become more and more complex. To find a solution, some new ways have to be gone, like the combination of biotechnology with classic processing methods.
The idea of this work is the biotechnological production of siderophores for the application as a reagent in the classic froth flotation process. Siderophores are small organic molecules with a high affinity for binding Fe(III) and to form strong complexes also with other metals. They are produced by microorganisms (aerobic bacteria and fungi) and some plants. Especially the group of amphiphilic siderophores are very interesting. The hydrophilic part, carrying hydroxamate groups, is responsible for the binding of the metals. Flotation agents produced by the chemical industry with the same functional groups have already been applied successfully in this processing method. It can be suggested siderophores carrying the same functional groups, also work well as collectors. The fatty acid tail, that is representing the hydrophobic part, gets in contact with the bubble and spares additional chemicals and further working steps for making the target mineral particles hydrophobic.
Besides the biotechnological production of these amphiphilic siderophores, this work presents interaction studies and flotation experiments of different scales, including “Bubble pick up test”, Halimond tube tests and one-liter flotation experiments of iron, copper and PGM containing ores.
The application of amphiphilic siderophores as biochemicals in the froth flotation process can change the classic processing method in a more sustainable process – the Bioflotation process. This will reduce the usage of other chemical agents. Moreover, the specific metal binding of siderophores changes flotation in a more purposeful and efficient process and is an important enrichment for the field of Biohydrometallurgy.
Keywords: Marinobactin, Marinobacter, amphiphilic, Siderophores froth flotation
  • Poster
    4th Green & Sustainable Chemistry Conference, 05.-08.05.2019, Dresden, Deutschland

Publ.-Id: 29762 - Permalink

Design and Evaluation of a STM-FPGA-DAQ-HLS-Template for the Mu2e Experiment
Knodel, O.ORC
Overview and status of the STM-FPGA-DAQ-HLS-Template for the Mu2e Experiment located Fermilab.
Keywords: Data Management; DAQ; FPGA; Mu2e
  • Invited lecture (Conferences)
    STM-Working Group Meeting, 09.10.2019, Batavia, United States

Publ.-Id: 29759 - Permalink

HZDR Data Management Strategy — An Overview
Knodel, O.ORC; Müller, S.ORC
Overview of the HZDR data management strategy, hosted services for collaborative work and a (planned) technical realization.
Keywords: Data Management
  • Invited lecture (Conferences)
    Meeting with the Scientific Computing Division at Fermilab, 08.10.2019, Batavia, United States

Publ.-Id: 29758 - Permalink

Recent progress in application of computational chemistry to actinide interaction with biomolecules
Tsushima, S.ORC
Thanks to rapid advancement in computing technology, computer chemistry is becoming increasingly important in the field of biology. This approach is nowadays a common tool for drug discovery or for studying diseases such as HIV. In this talk, I will present several examples in which computer chemistry was applied for studying potential health risk of accidental ingestion of actinides and lanthanides. The new approach called “fragment molecular orbital method” has been implemented to drastically reduce computing time, which made it possible to calculate interactions of actinide/lanthanide with large biological molecules such as DNA and protein using full quantum mechanical description. In one example, how uranium ingestion could damage DNA in a molecular scale will be presented.
  • Invited lecture (Conferences)
    Engineering Physics Seminar Series at the Department of Engineering Physics of the McMaster University, 04.10.2019, Hamilton, Canada

Publ.-Id: 29757 - Permalink

Re-mining of mine wastes in Germany: Challenges and opportunities
Büttner, P.; Nühlen, J.; Meima, J.; Gutzmer, J.ORC
The Fraunhofer Institute for Environmental, Safety, and Energy Technology and the Helmholtz Institute Freiberg for Resource Technology (HIF) have together compiled a mine waste cadaster for Germany on behalf of the Federal Institute for Geosciences and Natural Resources (BGR). For this purpose, a wide variety of data sources was evaluated with the aim to create a national database able to provide an overview about the content of critical raw materials (CRM) in mine waste repositories in Germany. Yet, even though mine wastes containing economically significant amounts of CRM, re-mining these anthropogenic “ore bodies” faces considerable technical and non-technical challenges.

Mine wastes often create environmental problems, such as acid rock drainage with associated high sulfate and heavy metal concentrations. This creates societal pressure for remediation. Remediation, however, is usually achieved by covering the surface with a water impermeable layer, an approach that is not sustainable, because of the required follow-up care and the inaccessibility of the resources that remain contained in the mine wastes. Besides that, legislative barriers are in conflict with recovering CRM and other metals and minerals from historic mine wastes. Many sites have essentially been abandoned since mining ceased in the 20th century. High metal contents and acidity released during sulfide oxidation has facilitated the establishment of a very specific flora and fauna. Species on these sites are often rare and strictly protected by environmental legislation. Metal recovery is all but impossible from such sites, despite the fact that acid rock drainage from these sites leads to environmental degradation downstream from the mine waste site.

Another important aspect is the general lack of suitable beneficiation and metallurgical infrastructure in Germany. Large capital investment would thus be necessary to enable the recovery of strategic metals from historic mine waste. Even if high metal concentrations are present in some mine wastes, small volumes will render the set-up of large, stationary plants unfeasible. Instead, flexible and semi-mobile small-scale technologies need to be developed. Such technologies are, at present, not available on the market.

To work at the intersection of society, legislation, remediation and re-mining is the aim of the new rECOmine partnership. This partnership is funded by the Federal Ministry of Education and Research (BMBF) for the next five years within the WIR! Program. It will be coordinated by HIF and build up three test sites in Saxony to develop combined remediation and re-mining technologies under real conditions with local partners.
Keywords: Re-Mining, Mine Waste, Resource, Tailing, Feasilbility, MLA
  • Lecture (Conference)
    GeoMünster 2019, 22.-25.09.2019, Münster, Germany

Publ.-Id: 29755 - Permalink

Delayed arrival of arterial blood in cortex is associated with decreased CSF levels of amyloid beta in predementia Alzheimer's disease
Palhaugen, L.; Selnes, P.; Tecelao, S.; Lysvik, E. K.; Ingala, S.; Petr, J.ORC; Bjornerud, A.; Mutsaerts, H. J.; Fladby, T.
Delayed arrival of arterial blood in cortex is associated with decreased CSF levels of amyloid beta in predementia Alzheimer's disease
  • Open Access LogoContribution to proceedings
    Congress of the European Academy of Neurology, 29.06.2019, Oslo, Norway
  • Open Access LogoPoster
    Congress of the European Academy of Neurology, 29.06.2019, Oslo, Norway

Publ.-Id: 29751 - Permalink

Scalable particle-in-cell simulations on many-core hardware with the free and open source code PIConGPU
Steiniger, K.ORC; Bastrakov, S.ORC; Cowan, T.ORC; Debus, A.ORC; Garten, M.ORC; Göthel, I.; Hübl, A.ORC; Juckeland, G.ORC; Kelling, J.; Kluge, T.ORC; Koßagk, S.; Matthes, A.ORC; Pausch, R.ORC; Schramm, U.ORC; Starke, S.; Widera, R.ORC; Worpitz, B.; Bussmann, M.ORC
Exploring new regimes, optimizing experimental setups, or quantifying sensitivity of final beam parameters on experimental parameters, represent current challenges for simulations of laser plasma accelerators. Time-to-solution and scalability are key parameters for codes to minimize turnaround times in order to scan e.g. tens of parameters such as the laser leading edge, resolve solid density target physics and run full-scale start-to-end simulations. PIConGPU reaches unprecedented performance by accelerating 100% of its computations on many-core architectures and leveraging next-generation scalable I/O. High-resolution, full-geometry studies on top-ten listed supercomputers decisively enhance predictive capabilities. PIConGPU's design allows for utilizing various compute architectures, including modern X86 and ARM CPUs and GPUs with a single, adaptable code base. Users can now run PIConGPU on almost any machine, either by easy recompiling or using predefined Docker images, and everybody can download, use and contribute to the code without extensive knowledge in compute architectures. We highlight latest additions to PIConGPU such as scalable file I/O via a new openPMD-API including ADIOS2 support for on the fly loosely coupled data analysis, live visualization with particle and field rendering, non-standard Gaussian laser pulses via Laguerre modes, in-situ X-ray scattering image generation, and an pythonic simulation setup interface.
Keywords: PIConGPU, Manycore, Scalable I/O, Alpaka, openPMD
  • Open Access LogoLecture (Conference)
    4th European Advanced Accelerator Concepts Workshop (EAAC2019), 15.-20.09.2019, La Biodola Bay - 57037 Portoferraio Isola d’Elba, Repubblica Italiana

Publ.-Id: 29750 - Permalink

Origin of the butterfly magnetoresistance in a Dirac nodal-line system
Chiu, Y.-C.; Chen, K.-W.; Schönemann, R.; Quito, V. L.; Sur, S.; Zhou, Q.; Graf, D.; Kampert, W. A. G.; Förster, T.; Yang, K.; Mccandless, G. T.; Chan, J. Y.; Baumbach, R. E.; Johannes, M. D.; Balicas, L.;
We report a study on the magnetotransport properties and on the Fermi surfaces (FS) of ZrSi(Se,Te) semimetals. Density-functional theory (DFT) calculations, in absence of spin orbit coupling (SOC), reveal that both the Se and the Te compounds display Dirac nodal lines (DNL) close to the Fermi level εF at symmorphic and nonsymmorphic positions, respectively. We find that the geometry of their FSs agrees well with DFT predictions. ZrSiSe displays low residual resistivities, pronounced magnetoresistivity, high carrier mobilities, and a butterflylike angle-dependent magnetoresistivity (AMR), although its DNL is not protected against gap opening. As in Cd3As2, its transport lifetime is found to be 102 to 103 times larger than its quantum one. ZrSiTe, which possesses a protected DNL, displays conventional transport properties. Our evaluation indicates that both compounds most likely are topologically trivial. Nearly angle-independent effective masses with strong angle-dependent quantum lifetimes lead to the butterfly AMR in ZrSiSe.

Publ.-Id: 29749 - Permalink

The tremendous influence of hydrogenation on magnetism of NdMnGe
Ovchenkova, I. A.; Tereshina, I. S.; Bogdanov, A. E.; Tereshina-Chitrova, E. A.; Paukov, M. A.; Gorbunov, D.; Nikitin, S. A.;
The hydride NdMnGeH with the tetragonal ZrSiCuAs-type of structure (P4/nmm, N129, tP8) was obtained by hydrogen absorption at 523 K and 1 MPa from the NdMnGe intermetallic compound with a the tetragonal CeFeSi crystal structure (P4/nmm, N129, tP6). Measurements of magnetization in high magnetic fields up to 60 T and heat capacity measurements reveal pronounced changes in the magnetic properties of NdMnGe after hydrogenation. The Nd sublattice changes its ordering type from ferromagnetic to the antiferromagnetic one with a more than twofold decrease of and its magnetic ordering temperature (from 199 to 84 K). We explain the observed effects by the altered exchange interactions within the Nd sublattice resulting from the changed Nd–Nd interplane distances by interstitial atoms. The results are compared with data obtained previously for the NdMn1- xTixGe compounds, where the Ti substitution also changes significantly the magnetic properties.

Publ.-Id: 29748 - Permalink

THz relaxation dynamics and nonlinear optics in graphene
Helm, M.;
Graphene, because of its peculiar linear band structure, shows some fascinating effects in the relaxation processes of excited electrons. Due to the zero band gap, many of those processes are best investigated at low energies, in the THz region. By linearly polarized pump-probe measurements we show that fast thermalization occurs only with respect to energy, but not to momentum, i.e. the electron distribution remains anisotropic for more than 5 ps (Phys. Rev. Lett. 117, 087401 (2016)). Applying a magnetic field splits the bands into non-equidistant Landau levels. This gives rise to a situation, where strong pumping of a Landau level actually leads to its depletion, due to strong Auger type electron-electron scattering (Nat. Phys. 11, 75 (2015)). In the same system, a large, resonant third-order optical nonlinearity is demonstrated via degenerate four-wave mixing (Nano Lett. 17, 2184 (2017)). All experiments were performed with a THz free-electron laser at frequencies around 20 THz, in collaboration with M. Mittendorff, J. König-Otto, S. Winnerl, A. Pashkin H. Schneider, with theory support by F. Wendler, T. Winzer, F. Kadi, E. Malic, A. Knorr, Y. Wang, A. Belyanin, and samples from W. de Heer and C. Berger.
Keywords: free electron laser, graphene, terahertz, relaxation, nonlinear optics
  • Invited lecture (Conferences)
    2D Materials 2019, 30.09.-04.10.2019, Sochi, Russia

Publ.-Id: 29745 - Permalink

Helium interactions with (Y, Ti, O) nanoclusters in bcc Fe
Vallinayagam, M.; Posselt, M.ORC; Faßbender, J.ORC
Nanometer size (Y, Ti, O) clusters in nanostructured ferritic/martensitic Fe-Cr alloys can act as sinks for the transmutation product helium. In this manner irradiation swelling can be retarded significantly. Many details of He storage in or near the clusters are still not understood. In this work interactions of He with (Y, Ti, O) clusters in bcc Fe are investigated by density functional theory (DFT) calculations. Four different cluster structures studied in our previous work [1] are considered: Cage-type clusters with (i) 6 O atoms, 9 vacancies (v) and 6 Y atoms, and (ii) with 7 O, 9 v, 3 Y, and 3 Ti, as well as clusters with O in the center containing (iii) 6 O, 9 v, 6 Y, and (iv) 7 O, 9 v, 3 Y, 3 Ti. It is found that the most stable position of He is in the center of the cluster, followed by the interfacial substitutional site and other interstitial positions between metal or oxygen atoms, and sites away from the cluster. This shows the He trapping may be nearly irrespective of cluster morphology and mainly depend on cluster composition. Adding a second He atom to the cluster structure is investigated for selected cases. Furthermore, barriers for possible jumps between different sites at the rim of the cluster and the center are determined. First results show that these barriers are higher if the cluster contains Ti and that there is a strong dependence on the particular position at the rim. For the discussion of the results also the DFT data obtained from studies on the interaction of He with single O, Y, and Ti atoms as well as with a single vacancy are used.

[1] Vallinayagam Investigation of structural models for O-Y and O-Y-Ti clusters in bcc Fe: A DFT study J. Phys.: Condens. Matter (2018)
Keywords: DFT ODS He storage
  • Lecture (Conference)
    EUROMAT-2019 Conference, 01.09.-04.10.2019, Stockholm, Sweden

Publ.-Id: 29736 - Permalink

Lift Forces on Solid Spherical Particles in Wall-bounded Flows
Shi, P.ORC; Rzehak, R.
The present work is concerned with the lift forces acting on particles immersed in a wall-bounded fluid. Conditions where the particle translates in a fluid at rest and in a linear shear flow are considered. Likewise, non-rotating particles and particles in free rotation driven solely by the flow are considered. Furthermore, situations where the wall lies in the inner region and in the outer region of the flow disturbance produced by the particle are distinguished. The focus is on solid spherical particles at Reynolds numbers up to O(〖10〗^2 ) which are relevant for particulate flows in chemical and minerals engineering. A comprehensive review of existing results from analytical, experimental, and direct numerical simulation studies is given. The available correlations are critically assessed by comparison to data from these studies. Based on the comparison recommendations are given which correlations to use, including some new proposals, and gaps in the data are identified.
Keywords: lift force, particles, wall-bounded flow, particle rotation, inner / outer region, correlation

Publ.-Id: 29729 - Permalink

Au incorporation into various ZnO crystallographic cuts realised by ion implantation – ZnO damage characterization
Mackova, A.; Malinsky, P.; Jagerova, A.; Miksova, R.; Nekvindova, P.; Cajzl, J.; Böttger, R.; Akhmadaliev, S.;
Non-polar surfaces, such as a-plane (11–20) and m-plane (10-10), for ZnO have become more attractive as numerous efforts have recently been made to grow non-polar ZnO facets for applications in nanoscale photonic devices. Noble-metal incorporation into transparent semiconductors such as ZnO has been investigated because of the non-linear optical response of such structures. This paper presents a study of defect evolution in various ZnO crystallographic cuts caused by Au implantation. The investigation has focused on ZnO structure characterisation, Au distribution and the interior morphology of the a-, m- and c-planes ZnO single crystals implanted with 400 keV Au+ ions at the ion fluences of 5 × 1014 and 1 × 1015 cm−2 and subsequently annealed at 600 °C in O2. The structure modification was studied using Rutherford backscattering spectrometry (RBS) in the channelling mode (RBS/C) and Raman spectroscopy. After the ion-implantation process, low surface damage was observed in all ZnO orientations unlike deep structural damage. Deep structural damage grew with increased Au-ion fluence and Au did not exhibit strong out-diffusion from the depth to the surface during the post-implantation annealing. Small but noticeable differences were observed between different ZnO orientations. RBS measurements during ion implantation revealed more progressive deep-damage formation in the c- and m-planes than in the a-plane ZnO. Simultaneously, the smallest Zn sub-lattice disorder deduced from RBS/C measurements was observed in the a-plane ZnO. During post-implantation annealing, a slight structure recovery (about 4%) was observed in all orientations. Raman spectroscopy confirmed the increasing structure disorder with the enhanced ion fluence for all as-implanted ZnO orientations and a partial reconstruction of the ZnO structure during annealing, when the intensity of E2 phonons was increased and that of longitudinal optical (LO) phonons was suppressed because of the disorder recovery. E2 (high) and E1(LO) Raman phonon modes connected with oxygen sub-lattice ordering/disordering have been investigated in detail – they show a significant modification mainly in the m-plane. The cause of the different behaviour of ZnO planes as well as the differences in the incorporation and movement of Au and Er atoms in the ZnO structure are discussed in the work.

Publ.-Id: 29728 - Permalink

Entwicklung des Gesamtsystems - Stand der Modellierungs- und Simulationsarbeiten
Fogel, S.ORC
Entwicklung eines tubularen Dampf-Elektrolyseurs mit integrierter Kohlenwasserstoffsynthese (DELTA)
  • Lecture (others)
    5. Projekttreffen DELTA, 25.04.2019, Dresden, Deutschland

Publ.-Id: 29727 - Permalink

3. Zwischenbericht DELTA
Fogel, S.ORC
Entwicklung eines tubularen Dampf-Elektrolyseurs mit integrierter Kohlenwasserstoffsynthese (DELTA)
  • Other report
    Dresden: HZDR, 2019
    27 Seiten

Publ.-Id: 29726 - Permalink

Single Cell and System Modeling of Tubular Proton Conducting Solid Oxide Steam Electrolyzers for Intermittent Operation
Fogel, S.ORC; Kryk, H.; Hampel, U.ORC
Due to the constantly growing utilization of wind and solar energy, the demand for technologies for temporal and spatial decoupling of energy provision and consumption is steadily increasing. The application of proton-conducting solid oxide electrolysis cells (H-SOEC) has been a main concern in recent research activities since they offer an environmentally friendly and efficient technique for the conversion of excess energy into hydrogen. As renewables occur intermittently, SOEC designs and all employed materials have to be capable of withstanding large electrical transients and therefore harsh operating conditions. Tubular cell designs of SOEC received increased attention in recent years due to their inherent advantages. They offer rapid startup capabilities as well as high resistance to heat, thermal cycling, thermal stresses and high-pressure application capabilities. Since the knowledge of the dynamic behavior of SOECs is key to their future application, this work aims to study the transient behavior of a single, proton conducting SOEC during rapid load variations and of multi-tubular stacks on a system scale under high-pressure operation. The use of different load variation speeds is discussed with respect to cell control.
Keywords: SOEC, load variation, transient operation, tubular cell, proton conduction
  • Lecture (Conference)
    12th European Congress of Chemical Engineering ECCE, 15.-19.09.2019, Florence, Italy

Publ.-Id: 29725 - Permalink

Transient behavior of tubular solid oxide electrolyzer cells under fast load variations
Fogel, S.ORC; Kryk, H.; Hampel, U.ORC
Solid oxide electrolyzer cells (SOEC) pose a promising technology for the production of hydrogen gained from renewables, such as wind and PV. Due to the fluctuating nature of these sources, the transient behavior of SOEC under various load cases plays a crucial role in terms of their long-time stability, degradation behavior, conver-sion efficiency and application. As a consequence of the intermittent occurrence of renewables, SOEC designs and all employed materials have to be capable of with-standing harsh operating conditions, leading to strict demands regarding process control and the overall cell design. Tubular cell designs of SOECs received in-creased attention in recent years due to their inherent advantages. They offer rapid startup capabilities as well as high resistance to heat and thermal stresses. Further-more, tubular cells are characterized by significantly smaller sealing lengths in com-parison to planar cells, enabling a high-pressure application. Operating SOECs at elevated pressures poses beneficial opportunities for their future system application, since the produced hydrogen does not need to be compressed using a separate compressor stage or the electrolyzer can be combined with promising downstream synthesis units (e.g. methanol synthesis). Dynamic simulations can be used to de-termine the transient behavior of SOECs during operation with harsh load-transients. This simulation work aimed to study the transient behavior of a single, proton conducting SOEC during rapid load variations under high-pressure opera-tion. For this purpose, a two-dimensional model of a tubular SOEC was developed and different load steps and their influence on crucial operational parameters, such as temperature profiles, cell potential and species concentrations were investigated. The feasibility of the cell design regarding harsh transient load variations was stud-ied. Various load-pulse shapes and durations, different flow configurations and steam mass flow rates have been investigated and their influence on the short-term transient behavior of the cell were examined. With the aid of the aforementioned simulations, limiting operational states of the cell (e.g. steam starvation and tempera-ture hot-spots) as well as beneficial process parameter combinations for an im-proved cell operational behavior were ought to be identified with respect to advanc-es in cell control strategies.
Keywords: SOEC, dynamic operation, proton conduction
  • Poster
    Jahrestreffen der ProcessNet-Fachgruppe Energieverfahrenstechnik, 06.-07.03.2019, Frankfurt am Main, Deutschland

Publ.-Id: 29723 - Permalink

Effect of nozzle geometry on pressure drop in submerged gas injection
Xiao, J.; Yan, H.-J.; Schubert, M.; Unger, S.; Liu, L.; Schleicher, E.; Hampel, U.ORC
Submerged gas injection into liquid leads to complex multiphase flow, in which nozzle geometries are crucial important for the operational expenditure in terms of pressure drop. The influence of the nozzle geometry on pressure drop between nozzle inlet and outlet has been experimentally studied for different gas flow rates and bath depths.
Nozzles with circular, gear-like and four-leaf cross-sectional shape have been studied. The results indicate that, besides the hydraulic diameter of the outlet, the orifice area and the perimeter of the nozzle tip also play significant roles. For the same superficial gas velocity, the average pressure drop from the four-leaf-shaped geometry is the least. The influence of bath depth was found negligible. A correlation for the modified Euler number considering the pressure drop is proposed depending on nozzle geometric parameter AoL o −2 and on the modified Froude number gd o 5 Q−2 with the hydraulic diameter of the nozzle do as characteristic length.
Keywords: submerged gas injection; nozzle geometry; hydraulic diameter; pressure drop; modified Euler number

Publ.-Id: 29718 - Permalink

Effect of Bath Depth and Nozzle Geometry on Spout Height in Submerged Gas Injection at Bottom
Xiao, J.; Yan, H.; Liu, L.; Möller, F.; Hu, Z.; Unger, S.;
Spout height is a widely used parameter to quantitatively analyze the performance of the submerged gas injection in industrial applications. However, the effect of bath depth and nozzle geometry on spout height in submerged gas injection is still unclear. In this work, the effect of bath depth and nozzle geometry on spout height in submerged gas injection at bottom was experimentally investigated. Circular-shaped, three-leaf-shaped, four-leaf-shaped, and four-flower-shaped nozzles were used for this study. Spout height was extracted from the images captured by high-speed camera and analyzed by digital image processing. The results indicate that the effect of nozzle geometry on spout height is as important as gas flow rate and bath depth. Through dimensional analysis, predictive correlations of spout height from circular shape and four-leaf shape were developed with dimensionless bath depth and a modified Froude number using orifice perimeter and opening area as characteristic parameters. Experimental data were compared with the correlations from literature and good agreement was found.

Publ.-Id: 29717 - Permalink

Control and stimulation of three-magnon scattering in a magnetic vortex
Körber, L.ORC; Schultheiß, K.ORC; Hula, T.; Verba, R.ORC; Hache, T.ORC; Schultheiß, H.ORC
When applying a large enough RF field amplitude, spin waves in a magnetic vortex disk can decay into two other spin waves via three-magnon scattering. In order to reach the threshold of this process, the energy flux from the decay of the directly excited mode must overcome the internal losses of the secondary modes. The resulting scattering processes obey certain selection rules which result in the two output frequencies to be distinct from one another. Moreover, three-magnon scattering of the directly excited mode into multiple pairs of secondary modes is possible. However, typically one of these scattering channels has a lower threshold than the others which leads to this channel being activated first and limiting the energy flux in the other possible “silent” channels. Here, we show that three-magnon scattering in such a system can be stimulated below the usual instability threshold by additionaly pumping one of the secondary modes. This is achieved by coupling the magnetic vortex to an adjacent magnonic wave guide. The response to the stimulation is instantaneous and can be used to activate the silent three-magnon channels, as well.
Keywords: nonlinear, magnon, vortex, magnetism, magnonics
  • Lecture (Conference)
    Magnonics 2019, 28.07.-01.08.2019, Carovigno, Italien

Publ.-Id: 29716 - Permalink

Liquid metal battery research activities at HZDR
Weier, T.; Horstmann, G. M.ORC; Landgraf, S.; Nimtz, M.; Personnettaz, P.; Stefani, F.; Weber, N.
Liquid metal batteries are promising candidates for low-cost, large-scale stationary electricity storage. Different systems investigated at HZDR are discussed with a focus on fluid dynamic phenomena like interfacial wave interactions, mass transfer, and electro-vortex flows.
Keywords: liquid metal batteries, mass transfer, electro-vortex flows
  • Invited lecture (Conferences)
    Institutskolloquium Institut für Thermo- und Fluiddynamik TU Ilmenau, 12.09.2019, Ilmenau, Deutschland

Publ.-Id: 29715 - Permalink

Anisotropic temperature-field phase diagram of single crystalline β-Li2IrO3: Magnetization, specific heat, and 7Li NMR study
Majumder, M.; Freund, F.; Dey, T.; Prinz-Zwick, M.; Büttgen, N.; Scurschii, I.; Jesche, A.; Tsirlin, A. A.; Gegenwart, P.;
Detailed magnetization, specific heat, and 7Li nuclear magnetic resonance (NMR) measurements on single crystals of the hyperhoneycomb Kitaev magnet β-Li2IrO3 are reported. At high temperatures, anisotropy of the magnetization is reflected by the different Curie-Weiss temperatures for different field directions, in agreement with the combination of a ferromagnetic Kitaev interaction (K) and a negative off-diagonal anisotropy (Γ) as two leading terms in the spin Hamiltonian. At low temperatures, magnetic fields applied along a or c have only a weak effect on the system and reduce the Néel temperature from 38 K at 0 T to about 35.5 K at 14 T, with no field-induced transitions observed up to 58 T on a powder sample. In contrast, the field applied along b causes a drastic reduction in the TN that vanishes around Hc = 2.8 T, giving way to a crossover toward a quantum paramagnetic state. Li NMR measurements in this field-induced state reveal a gradual line broadening and a continuous evolution of the line shift with temperature, suggesting the development of local magnetic fields. The spin-lattice relaxation rate shows a peak around the crossover temperature 40 K and follows power-law behavior below this temperature.

Publ.-Id: 29713 - Permalink

Microstructural Characterization of a VVER-440 type Reactor Pressure Vessel Steel by Electron Microscopy
Chekhonin, P.; Röder, F.; Müller, G.; Roßner, M.; Heintze, C.; Bergner, F.;
A microstructural investigation of a VVER400-type reactor pressure vessel (RPV) steel in the initial state (unirradiated) is presented. Key points include a detailed characterization by electron backscatter diffraction and an analysis of precipitates and inclusions performed by transmission as well as scanning electron microscopy.
Keywords: Microstructure, Reactor Pressure Vessel Steels, Electron Microscopy
  • Lecture (Conference)
    IGRDM-21 - 21st meeting of International Group on Radiation Damage Mechanism, 19.-24.05.2019, Gifu, Japan

Publ.-Id: 29711 - Permalink

Electronic properties of GaAs/InₓGa₁₋ₓAs and GaAs/InₓAl₁₋ₓAs core/shell nanowires studied by pump – probe THz spectroscopy
Fotev, I.ORC; Balaghi, L.ORC; Shan, S.; Hübner, R.; Schmidt, J.; Schneider, H.ORC; Helm, M.; Dimakis, E.ORC; Pashkin, A.ORC
We report terahertz response of photoexcited core/shell nanowires. The obtained parameters of the localized surface plasmon mode allow us to estimate electron mobilities, concentrations and recombination lifetimes. The extracted mobilities reach 4000 cm²/V·s at room temperature, while the carrier lifetimes range from 80 to 300 ps, depending on the shell composition and the photoexcitation level.
  • Lecture (Conference)
    French-German THz Conference 2019, 02.-05.04.2019, Kaiserslautern, Germany

Publ.-Id: 29709 - Permalink

Thz User Operation With 200 pC CW Beam Generated by the ELBE SRF Gun II
Arnold, A.; Awari, N.; Chen, M.; Deinert, J.-C.ORC; Evtushenko, P.; Green, B. W.ORC; Klopf, J. M.; Kovalev, S.; Lehnert, U.; Ma, S.; Murcek, P.; Michel, P.; Schaber, J.; Teichert, J.; Xiang, R.; Zwartek, P.
As a new electron source with higher brilliance, the second superconducting RF photoinjector (SRF Gun II) has been built at the ELBE radiation center for high power radiation sources. One of the main goals of SRF gun II is to achieve a higher bunch charge (>200 pC) and lower emittance (3 mm mrad) than the present ELBE thermionic DC gun. SRF Gun II features a 3.5-cell niobium cavity as well as a superconducting solenoid in the same cryomodule. With Mg photocathodes the gun is able to provide medium current beam with bunch charge of more than 200 pC and sub-ps bunch length at 100 kHz repetition rate. With this contribution we present convincing results from long-term user operation of SRF gun II in combination with the bunching concept of the ELBE accelerator in order to produce THz radiation with much higher stability and power than available using the existing thermionic gun.
Keywords: SRF Gun, THz, ELBE, electron source, photoinjector
  • Open Access LogoPoster
    63rd ICFA Advanced Beam Dynamics Workshop on Energy Recovery Linacs, 15.-20.09.2019, Berlin, Deutschland

Publ.-Id: 29708 - Permalink

Developing multi-sensor drones for geological mapping and mineral exploration: setup and first results from the MULSEDRO project
Heincke, B.; Jackisch, R.ORC; Saartenoja, A.; Salmirinne, H.; Rapp, S.; Zimmermann, R.ORC; Pirttijärvi, M.; Vest Sörensen, E.; Gloaguen, R.ORC; Ek, L.; Bergström, J.; Karinen, A.; Salehi, S.; Madriz Diaz, Y. C.; Middleton, M.
The use of Unmanned Aerial Systems (UAS), also known as drones, is becoming increasingly important for geological applications. Thanks to lower operational costs and ease of use, UAS offer an alternative approach to aircraft-based and ground-based geoscientific measurements (Colomina & Molina 2014). Magnetic and hyperspectral UAS surveys hold particular promise for mineral exploration, and several groups have recently published studies of magnetic data collected by UAS for such applications (Malehmir et al. 2017; Cunningham et al. 2018), although equivalent studies using hyperspectral data are still rare (Kirsch et al. 2018). Combining both techniques is particularly useful. Magnetic measurements play an important role in mineral exploration, since magnetisation in rocks is mainly associated with magnetite and other iron minerals, which can be used in mapping and targeting of mineral deposits (Dentith & Mudge 2014). Hyperspectral imaging (HSI) is a powerful exploration and mapping technique in areas where the rock surface is well-exposed, and where geological units and mineral compositions can be estimated from spectral features of the electromagnetic spectrum in the visual and infrared range.
Keywords: Drones, Geological Mapping, Unmanned Aerial System, Hyperspectral imaging, Magnetic survey

Publ.-Id: 29707 - Permalink

Pump – Probe THz Spectroscopy Study of Electronic Properties of Semiconductor Nanowires
Fotev, I.ORC; Balaghi, L.ORC; Shan, S.; Hübner, R.; Schmidt, J.; Schneider, H.ORC; Helm, M.; Dimakis, E.ORC; Pashkin, O.ORC
THz radiation is a perfect tool for probing electrical properties of semiconductor nanostructures in a contactless way. When applied to semiconductor nanowires, THz probe pulses can drive the oscillations of photoexcited electrons and holes in the form of localized surface plasmon. We used optical pump – THz probe spectroscopy to study plasmonic response of charge carriers in GaAs/InₓGa₁₋ₓAs core/shell nanowires. The carrier lifetimes are about 80-100 ps, depending on the shell composition and the photoexcitation level, while the extracted mobilities reach 3700 cm²/V·s at room temperature.
Keywords: GaAs nanowires, terahertz spectroscopy, ultrafast dynamics, electron mobility, plasmon, carrier lifetime
  • Lecture (Conference)
    44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), 01.-06.09.2019, Paris, France

Publ.-Id: 29706 - Permalink

Current management of pheochromocytoma/paraganglioma: A guide for the practicing clinician in the era of precision medicine
Nölting, S.; Ullrich, M.ORC; Pietzsch, J.ORC; Ziegler, C. G.; Eisenhofer, G.; Grossman, A.; Pacak, K.
Pheochromocytomas and paragangliomas (PCC/PGLs) are rare, mostly catecholamine-producing neuroendocrine tumors of the adrenal gland (PCCs) or the extra-adrenal paraganglia (PGL). They can be separated into three different molecular clusters depending on their underlying gene mutations in any of the at least 20 known susceptibility genes: the pseudohypoxia-associated cluster 1, the kinase signaling-associated cluster 2, and the Wnt signaling-associated cluster 3. Besides tumor size, location (adrenal vs. extra-adrenal), age of first diagnosis, and presence of metastatic disease (including tumor burden), other decisive factors for best clinical management of PCC/PGL include the underlying germline mutation. The above factors can impact the choice of different biomarkers and imaging modalities for diagnosis, as well as screening for other neoplasms, staging, follow-up, and therapy options. This review provides a guide for practicing clinicians summarizing current management of PCC/PGL according to tumor size, location, age of first diagnosis, presence of metastases and especially underlying mutations in the era of precision medicine.
Keywords: pheochromocytoma, paraganglioma, guideline, genetics, diagnosis, imaging, follow-up, therapy, precision medicine

Publ.-Id: 29705 - Permalink

Enhanced ion acceleration from a non-ideal laser pulse contrast
Garten, M.ORC; Huebl, A.; Widera, R.ORC; Göthel, I.; Obst-Huebl, L.; Ziegler, T.ORC; Zeil, K.; Cowan, T.ORC; Schramm, U.ORC; Bussmann, M.ORC; Kluge, T.ORC
The major challenges of compact proton sources driven by an ultrashort high-intensity laser are currently to establish precise control over proton beam parameters and shot-to-shot stability. Shooting ultrathin targets has shown to yield higher proton energies, which became recently accessible due to temporal laser pulse shape control using plasma-mirror techniques. We find that the intensity ramp, transmitted to the target by the plasma mirror during the last picosecond before the pulse peak, becomes significantly decisive for the subsequent acceleration performance. Reliable characterization of this ramp with modern laser diagnostics remains challenging and immense computational needs required to fully resolve the plasma kinetics leave it mostly unexplored in today's simulations of laser-solid interaction. We present the results of 3D large-scale simulations with PIConGPU, taking into account realistic contrast conditions, bridging the scales from picosecond pre-plasma formation over transient, non-equilibrium dynamics of the tens of femtosecond laser duration down to attosecond plasma oscillations. Adding to beneficial acceleration conditions presented by hybrid acceleration mechanisms and the onset of relativistic transparency, we show that the maximum proton energy can be optimized by a specific leading pulse edge via a combination of pre-thermal and thermal TNSA, surpassing the performance of the ideal diffraction-limited Gaussian pulse.
Keywords: laser-ion acceleration, TNSA, simulation, PIConGPU, CSCS, Piz Daint, PRACE, HPC
  • Lecture (Conference)
    4th European Advanced Accelerator Concepts Workshop, 15.-21.09.2019, Isola d'Elba, Italia

Publ.-Id: 29695 - Permalink

Nanoscale Ferromagnetism in Alloy Thin Film via Lattice Disordering
Bali, R.; Schmeink, A. H.ORC; Eggert, B.; Ehrler, J.; Liersch, V.; Semisalova, A.; Hlawacek, G.ORC; Potzger, K.; Faßbender, J.ORC; Thomson, T.; Wende, H.; Lindner, J.
Structural disorder in certain alloys leads to the onset of strong ferromagnetism. Disorder can be induced in desired locations, at the nanoscale, making such materials useful for magnetic nano-patterning. Examples of these alloys include Fe60Al40,[1] Fe50Rh50,[2] and Fe60V40. Disorder can be generated locally using focussed ion- as well as laser- beams,[1 - 3] inducing nanoscale ferromagnetism. Furthermore, the effect can be reversed via thermal re-ordering of the alloy, achieving re-writeable magnetic structures.
Insights into the mechanisms of the ferromagnetic onset in prototype systems, helps achieve a broader understanding of magneto-structural correlations in general. For instance, in paramagnetic B2-ordered Fe60Al40 as well as D8b-type Fe60V40, the ferromagnetic onset is caused by antisite defects i.e. site swapping of the Fe and Al (V) atoms, resulting in a transition to the bcc (A2) structure. An increase of antisite defects can cause the Ms of Fe60Al40 as well as Fe60V40 to increase from nearly-zero in the ordered structures to 780 and 660 kAm-1, in their respective disordered structures. In contrast, in B2 Fe50Rh50 the well-ordered film is antiferromagnetic, and static disordering may be sufficient to fully transform the alloy to the ferromagnetic phase, possessing an Ms of ~ 1250 kAm-1 at 300 K. Thus, whereas the Ms in the above alloys increases drastically with lattice disorder, the microscopic nature of the disordering varies.
Here we deploy ion-irradiation to sensitively induce lattice disorder in the above binary alloy systems, while tracing the manifested ferromagnetic onsets, thereby obtaining insights into the correlation between magnetic behaviour and the structure. Properties of magnetic arrays and magneto-transport devices produced using lattice disorder will be discussed.
[1] “Printing Nearly-Discrete Magnetic Patterns Using Chemical Disorder Induced Ferromagnetism”, R. Bali et al., Nano Letters 14, 435 (2014).
[2] “Tuning the antiferromagnetic to ferromagnetic phase transition in FeRh thin films by means of low-energy/low fluence ion irradiation”, A. Heidarian et al., Nucl. Instrum. Methods Phys. Res. B 358, 251 (2015).
[3] “Laser-Rewriteable Ferromagnetism at Thin-Film Surfaces”, J. Ehrler et al., ACS Appl. Mater. Interfaces 10, 15232 (2018).
  • Invited lecture (Conferences)
    6th International Conference from Nanoparticles and Nanomaterials to Nanodevices and Nanosystems (6th IC4N), 30.06.-03.07.2019, Corfu, Greece
  • Invited lecture (Conferences)
    Symposium „Spins, Waves and Interactions“, 03.-05.09.2019, Greifswald, Deutschland

Publ.-Id: 29691 - Permalink

Filling the 5-10 THz gap using Ge-based photoconductive emitter
Singh, A.; Pashkin, O.ORC; Winnerl, S.; Helm, M.; Schneider, H.
We present here a Ge photoconductive emitter generating THz pulses with a spectrum up to 13 THz free from any absorption lines if detected with a proper detector. Ge is a centrosymmetric non-polar crystal and hence its phonons are not IR-active. Therefore, Ge shows high and almost uniform transmission of THz radiation up to frequencies more than 20 THz besides a weak two-phonon absorption band near 10 THz [1]. Ge also has high carrier mobility required for efficient THz emission. Bowtie-like electrode structures with 10 µm electrode gap are deposited on a pure Ge substrate to fabricate the photoconductive THz emitter. The carrier lifetime in pure Ge is of the order of µs, thus it requires a pump laser with pulse repetition rate less than a MHz. A Ti:sapphire amplified laser system operating at 800 nm wavelength, 250 kHz repetition rate and ~ 65 fs pulse width is used to pump the Ge emitter and probe the radiated THz pulse using the electro optic sampling technique.
[1] A. Singh, A. Pashkin, S. Winnerl, M. Helm and H. Schneider, “Gapless broadband terahertz emission from a germanium photoconductive emitter”, ACS Photonics 5, 2718−2723 (2018).
Keywords: terahertz emitter, germanium
  • Lecture (Conference)
    Conference on Lasers and Electro-Optics (CLEO), 06.-10.05.2019, San José, USA
  • Contribution to proceedings
    Conference on Lasers and Electro-Optics (CLEO), 05.-10.05.2019, San José, USA
    Conference on Lasers and Electro-Optics OSA Technical Digest (Optical Society of America, 2019), 345 E 47TH ST, NEW YORK, NY 10017 USA: IEEE, 978-1-943580-57-6
    DOI: 10.1364/CLEO_SI.2019.STu3F.3

Publ.-Id: 29688 - Permalink

Scalable Large-Area Terahertz Emitters with Improved Electrode Design
Singh, A.; Welsch, M.; Winnerl, S.; Helm, M.; Schneider, H.;
We have systematically investigated the influence of electrode parameters on the emission efficiency of scalable large-area photoconductive THz emitters. We identify two contributions to THz emission, originating from the photoexcited carriers in the semiconductor and from the interdigitated metal electrodes acting as dipole antennae, respectively. Both contributions are optimized for maximum THz emission efficiency by varying the gap and stripe widths of the interdigitated metal electrodes. Using this approach we achieve a 50% improvement of the radiated THz electric field as compared to electrodes with equal stripe and gap widths.
Keywords: terahertz emitter, large-area emitter
  • Lecture (Conference)
    The 44th International Conference on Infrared, Millimeter and Terahertz Waves (IRMMW-THz'2019), 01.-06.09.2019, Paris, France

Publ.-Id: 29687 - Permalink

Linear and nonlinear THz spectroscopy at HZDR
Schneider, H.;
In this talk I have presented some experiments on linear and nonlinear THz spectroscopy at HZDR
Keywords: terahertz spectroscopy, free-electron laser
  • Lecture (others)
    Seminarvortrag, Harbin Institute of Technology, 22.07.2019, Harbin, China

Publ.-Id: 29686 - Permalink

Nonlinear dressing of excitons, polaritons, and intersubband transitions using a terahertz free-electron laser
Schneider, H.;
This talk reports some recent experiments making use of intense, spectrally narrow terahertz(THz) pulses from a free-electron laser (FEL) as a unique tool for nonlinear dressing of elementary transitions in the THz range.
Keywords: terahertz, free-electron laser, exciton, dressed state
  • Lecture (Conference)
    VII International Conference “Frontiers of Nonlinear Physics”, 28.06.-04.07.2019, Nizhny Novgorod, Russian Federation

Publ.-Id: 29685 - Permalink

Nonlinear terahertz spectroscopy of III-V semiconductor quantum wires and quantum wells using a free-electron laser
Schneider, H.;
This talk reviews some recent experiments using intense narrow-band terahertz (THz) fields from a free-electron laser for exploring electronic properties in semiconductor nanostructures. In n-type III-V semiconductor nanowires (NW), intense THz excitation causes a nonlinear plasmonic response, which manifests itself by a strong red shift of the plasma resonance. This nonlinearity is investigated by scattering-type scanning near-field infrared microscopy. For the NWs under study, a spectrally sharp plasma resonance, located at a photon energy of 125 meV for weak excitation, undergoes a power-dependent redshift to about 95 meV. We attribute this nonlinearity to an increase of the effective mass caused by transient carrier heating. In another experiment, we use strong narrowband THz excitation to dress the 2-3 intersubband transition in a 40 nm wide GaAs quantum well (QW). The resulting nonlinearities are explored by THz time-domain spectroscopy using synchronous broadband THz probe pulses and electro-optic sampling. Tuning the THz pump beam into resonance with the 2-3 intersubband transition, we have investigated the induced coherent signatures in the vicinity of the 1-2 intersubband transition and found evidence for mixed light-matter states in the QW giving rise to a THz Autler-Townes effect.
The presented work was conducted in collaboration with D. Lang and J. Schmidt (HZDR) who did most experiments, L. Balaghi, E. Dimakis, M. Helm, R. Hübner, D. Lang, A. Pashkin, S. Winnerl (HZDR), and S.C. Kehr, L.M. Eng (TU Dresden, Germany).
Keywords: terahertz, free-electron laser, nonlinear spectroscopy, quantum wire, quantum well
  • Invited lecture (Conferences)
    Light Conference 2019, 16.-18.07.2019, Changchun, China

Publ.-Id: 29684 - Permalink

Gamma, neutron and muon background in the new Felsenkeller underground accelerator laboratory
Szücs, T.ORC; Bemmerer, D.ORC; Grieger, M.; Hensel, T.; Ludwig, F.; Zuber, K.
Astrophysically relevant nuclear reactions between charged particles usually occurring in stars at deep sub-Coulomb energies. A direct experimental study of such reactions in the laboratory requires high luminosity coupled with low background in the detectors to compensate for the tiny reaction yield to be measured. The new Felsenkeller underground accelerator laboratory is equipped with a high current particle accelerator and has very low background.
This contribution will report about the experimental study of the muon flux and angular distribution of the muons in the new laboratory, which is required to optimize the veto detector arrangements. In addition, the measured neutron flux and energy spectrum at Felsenkeller will be reported. Finally, the actual γ background in muon vetoed HPGe detectors will be presented. The measured background and known ion beam current will allow the study many astrophysically relevant reactions direct in their stellar energy range.
Keywords: Nuclear astrophysiscs; Underground; Felsenkeller; Laboratory background
  • Poster
    Nuclear Physics in Astrophysics IX, 15.-20.09.2019, Castle Waldthausen; Frankfurt, Germany

Publ.-Id: 29683 - Permalink

Background studies with actively vetoed germanium gamma-ray detector in Felsenkeller tunnels VIII and IX
Szücs, T.ORC; Bemmerer, D.ORC; Zuber, K.
A new underground accelerator facility is being built in tunnels VIII and IX of the Dresden Felsenkeller. Previous gamma-ray background measurements in another part of the tunnelsystem showed suitable conditions for in-beam nuclear astrophysics experiments [1, 2] using germanium detectors with active veto against the cosmic-ray muons. These stableion beam experiments are of high importance to understand the reactions of the stellar burning phases, and in particular the solar fusion reactions.
The new laboratory is now ready to host measurements mapping the background conditions. This work reports on the measured background in actively vetoed gamma-ray detectorat the place of the target station in the laboratory used for the upcoming experiments.
[1] T.Szücs et al., Eur. Phys. Jour. A 48 (2012) 8. [2] T.Szücs et al., Eur. Phys. Jour. A 51 (2015) 33.
Keywords: Nuclear astrophysics; underground; Felsenkeller; Gamma-background
  • Poster
    XV International Symposium on Nuclei in the Cosmos (NIC XV), 24.-29.06.2018, Assergi, Italy
  • Poster
    5th International Solar Neutrino Conference, 11.-14.06.2018, TU Dresden, Germany

Publ.-Id: 29682 - Permalink

Resonance strengths in the 14N(p,γ)15O astrophysical key reaction measured with activation
Gyürky, G.; Halász, Z.; Kiss, G. G.; Szücs, T.ORC; Csík, A.; Török, Z.; Huszánk, R.; Kohan, M. G.; Wagner, L.; Fülöp, Z.
Background: The 14N(p ,γ )15O reaction plays a vital role in various astrophysical scenarios. Its reaction rate must be accurately known in the present era of high precision astrophysics. The cross section of the reaction is often measured relative to a low energy resonance, the strength of which must therefore be determined precisely. Purpose: The activation method, based on the measurement of 15O decay, has not been used in modern measurements of the 14N(p ,γ )15O reaction. The aim of the present work is to provide strength data for two resonances in the 14N(p ,γ )15O reaction using the activation method. The obtained values are largely independent from previous data measured by in-beam γ spectroscopy and are free from some of their systematic uncertainties. Method: Solid state TiN targets were irradiated with a proton beam provided by the Tandetron accelerator of Atomki using a cyclic activation. The decay of the produced 15O isotopes was measured by detecting the 511 keV positron annihilation γ rays. Results: The strength of the Ep=278 keV resonance was measured to be ω γ278=(13.4 ±0.8 ) meV while for the Ep=1058 keV resonance ω γ1058=(442 ±27 ) meV . Conclusions: The obtained Ep=278 keV resonance strength is in fair agreement with the values recommended by two recent works. However, the Ep=1058 keV resonance strength is about 20% higher than the previous value. The discrepancy may be caused in part by a previously neglected finite target thickness correction. As only the low energy resonance is used as a normalization point for cross section measurements, the calculated astrophysical reaction rate of the 14N(p ,γ )15O reaction and therefore the astrophysical consequences are not changed by the present results.
Keywords: Nuclear Astrophysics


Publ.-Id: 29681 - Permalink

Magnetic Nanoparticle Chains in Gelatin Ferrogels: Bioinspiration from Magnetotactic Bacteria
Sturm, S.; Siglreitmeier, M.; Wolf, D.; Vogel, K.; Gratz, M.; Faivre, D.; Lubk, A.; Büchner, B.; Sturm, E.; Cölfen, H.;
Inspired by chains of ferrimagnetic nanocrystals (NCs) in magnetotactic bacteria (MTB), the synthesis and detailed characterization of ferrimagnetic magnetite NC chain-like assemblies is reported. An easy green synthesis route in a thermoreversible gelatin hydrogel matrix is used. The structure of these magnetite chains prepared with and without gelatin is characterized by means of transmission electron microscopy, including electron tomography (ET). These structures indeed bear resemblance to the magnetite assemblies found in MTB, known for their mechanical flexibility and outstanding magnetic properties and known to crystallographically align their magnetite NCs along the strongest <111> magnetization easy axis. Using electron holography (EH) and angular dependent magnetic measurements, the magnetic interaction between the NCs and the generation of a magnetically anisotropic material can be shown. The electro- and magnetostatic modeling demonstrates that in order to precisely determine the magnetization (by means of EH) inside chain-like NCs assemblies, their exact shape, arrangement and stray-fields have to be considered (ideally obtained using ET).
Keywords: bioinspiration; electron holography; electron tomography; gelatin; magnetite

Publ.-Id: 29680 - Permalink

Layer Rotation-Angle-Dependent Excitonic Absorption in van der Waals Heterostructures Revealed by Electron Energy Loss Spectroscopy
Gogoi, P. K.; Lin, Y.-C.; Senga, R.; Komsa, H.-P.; Liang, S.; Chi, W. D.; Krasheninnikov, A. V.ORC; Li, L.-J.; Breese, M. B. H.; Pennycook, S. J.; Wee, A. T. S.; Suenaga, K.
Heterostructures comprising van der Waals (vdW) stacked transition metal dichalcogenide (TMDC) monolayers are a fascinating class of two-dimensional (2D) materials. The presence of interlayer excitons, where the electron and the hole remain spatially separated in the two layers due to ultrafast charge transfer, is an intriguing feature of these heterostructures. The optoelectronic functionality of 2D heterostructure devices is critically dependent on the relative rotation angle of the layers. However, the role of the relative rotation angle of the constituent layers on intralayer absorption is not clear yet. Here, we investigate MoS2/WSe2 vdW heterostructures using monochromated low-loss electron energy loss (EEL) spectroscopy combined with aberration-corrected scanning transmission electron microscopy and report that momentum conservation is a critical factor in the intralayer absorption of TMDC vdW heterostructures. The evolution of the intralayer excitonic low-loss EEL spectroscopy peak broadenings as a function of the rotation angle reveals that the interlayer charge transfer rate can be about an order of magnitude faster in the aligned (or anti-aligned) case than in the misaligned cases. These results provide a deeper insight into the role of momentum conservation, one of the fundamental principles governing charge transfer dynamics in 2D vdW heterostructures.
Keywords: 2D materials, EELS, TEM, electronic structure calculations


  • Secondary publication expected from 25.07.2020

Publ.-Id: 29678 - Permalink

Enhanced sensitivity of MoSe2 monolayer for gas adsorption induced by electric field
Ai, W.; Kou, L.; Hu, X.; Wang, Y.; Krasheninnikov, A.; Sun, L.; Shen, X.;
According to recent studies, gas sensors based on MoSe2 have better detection performance than graphene-based sensors, especially for N-based gas molecules, but the reason for that is not fully understood at the microscopic level. Here, we investigate the adsorption of CO, CO2, NH3, NO and NO2 gas molecules on MoSe2 monolayer by the density functional theory calculations. Our results reveal that indeed MoSe2 monolayer is more sensitive to adsorption of N-containing gas molecules than C-containing, which can be attributed to the distinct charge transfer between the gas molecules and MoSe2. The conductance was further calculated using the nonequilibrium Green's function (NEGF) formalism. The reduced conductance was found for NH3 and NO2 adsorbed MoSe2, consistent with the high sensitivity of MoSe2 for NH3 and NO2 molecules in the recent experiments. In addition, the adsorption sensitivity can significantly be improved by an external electric field, which implies the controllable gas detection by MoSe2. The magnetic moments of adsorbed NO and NO2 molecules can also be effectively modulated by the field-sensitive charge transfer. Our results not only give microscopic explanations to the recent experiments, but also suggest using MoSe2 as a promising material for controlled gas sensing.
Keywords: 2D materials , first-principles calculations


  • Secondary publication expected from 02.08.2020

Publ.-Id: 29677 - Permalink

Fluctuation electron microscopy on silicon amorphized at varying self ion-implantation conditions
Radic, D.; Hilke, S.; Peterlechner, M.; Posselt, M.ORC; Bracht, H.
The medium range order of self-ion-implanted amorphous silicon was studied by variable resolution fluctuation electron microscopy and characterized by the normalized variance V(k, R). The ion-implantation was conducted at sequentially increasing ion energies ranging from 50 keV to 300 keV. Two silicon-on-insulator wafers were amorphized at different implantation conditions. From each material, one as-prepared and one ex situ annealed specimen were chosen for analysis. Fluctuation electron microscopy on cross-sectional prepared samples confirms the presence of medium range order due to the amorphization process. We propose three explanations on how the observed medium range order is created by silicon ion-implantation. Two of these suggestions involve paracrystals formed by thermal spikes while a third explanation assumes a medium range order due to nanoscale regions unaffected by the amorphization. Although the two amorphized silicon samples reveal different local structures due to the ion-implantation process, no difference in the self-diffusion behavior is evident, which demonstrates that self-diffusion mainly proceeds within the amorphous phase.
Keywords: fluctuation electron microscopy; amorphous silicon, ion implantation

Publ.-Id: 29676 - Permalink

Ultrafast neutralization dynamics of highly charged ions upon impact on 2D materials
Wilhelm, R. A.ORC
Heavy ions in high charge states carry a large amount of potential energy in addition to their kinetic energy. The potential energy can amount to several 10keV and is released upon neutralization [1]. We recently showed that neu- tralization of slow highly charged Ar and Xe ions proceeds on a sub-10fs time scale, i.e. during transmission through the very first monolayers of a solid [2]. This feat makes highly charged ions an intriguing tool for efficient modification of 2D materials preventing significant damage to a substrate at the same time. Here we present data on the neutralization dynamics of slow highly charged ions in freestanding single layer graphene and freestanding single layer MoS2. Special emphasise is put on charge exchange of the ions, their kinetic energy loss, and the emission of secondary electrons/photons from the interaction pro- cess.
  • Invited lecture (Conferences)
    Towards Reality in Nanoscale Materials X, 12.-14.02.2019, Levi, Finnland

Publ.-Id: 29672 - Permalink

Interaction of highly charged ions with 2D materials
Wilhelm, R. A.ORC
Slow highly charged ions (HCI) provide an efficient toolkit for surface modifications at the nanoscale [1]. Due to the potential energy of HCIs, nanoscale surface melting or atom sputtering can be ob- served in susceptible materials with an efficiency of about 100% (one surface feature per ion). The neutralization of the HCIs driving the potential energy deposition is typically considered to be finished in ’a shallow region’ in the surface, i.e. ’on the first nanometers’. To further quantify the HCI neutral- ization dynamics we recently took a new approach and used freestanding 2D materials as the target. Due to the atomic thickness of the materials, ions are not stopped in the materials and are available for spectroscopic analysis. At the same time the 2D materials are available for post-irradiation microscopic analysis, which finally al- lows us to determine (1) the kinetic and potential energy lost by the ion, (2) the energy dissipated by emission of secondary particles (electrons and photons), and (3) the en- ergy spend in the nanostructure formation process.
By applying our ion beam spectroscopy, we performed charge state and kinetic energy analysis of ions transmit- ted through freestanding single layer graphene (SLG) [2], amorphous 1nm thick Carbon Nanomembranes (CNM) [3], freestanding single layer MoS2, SLG/MoS2 het- erostructures and others. As a first result we found an ultrafast (sub-10 fs ∼ 1 monolayer) neutralization taking place, much faster than established models would have an- ticipated [4]. Furthermore, kinetic energy loss is signifi- cantly enhanced compared to the value of singly charged ions under the same conditions.
To facilitate a comprehensive understanding of the plethora of observed phenomena and their interplay, we use an en- ergy, angle, and charge state resolved spectroscopy in co- incidence with yield and energy resolved measurement of emitted secondary particles [5]. We further developed an exchange and electronic decay taking the time-dependent atomistic model for ion stopping, charge ion charge state explicitly into account [6].
In this contribution I will give an overview about our recent progress in the field of ion scattering from 2D materials and put the results in perspective to nanostructure formation.
  • Invited lecture (Conferences)
    Nanopatterning Workshop, 07.-10.07.2019, Guildford, United Kingdom

Publ.-Id: 29671 - Permalink

Collisions of highly charged ions with 2D materials
- What we learn from ion transmission spectroscopy -
Wilhelm, R. A.ORC
Slow ions in high charge states impacting a solid surface represent a far-from-equilibrium system. Upon impact, the ions capture dozens of electrons and these electrons decay into the atomic ground state already during the collision driven by non-radiative de-excitation processes such as Interatomic Coulombic Decay [1]. The neutralization and electronic decay of the ion leads to the release of its potential energy, which amounts up to several 10 keV facilitating nanostructure formation in suscep- tible materials (mainly insulators with strong electron-phonon coupling).
When a freestanding 2D material is used as a solid target, the ions are still available for spectroscopic measurements after the ion-surface interaction. We performed charge state and kinetic energy analy- sis of ions transmitted through freestanding single layer graphene (SLG) [2], amorphous 1 nm thick Carbon Nanomembranes (CNM) [3], freestanding single layer MoS2, SLG/MoS2 heterostructures and others. As a first result we found an ultrafast (sub-10 fs) neutralization taking place, much faster than established models would have anticipated. Further, kinetic energy loss is significantly en- hanced over the expected value from singly charged ions under the same conditions. We are able to find charge exchange patterns, utilizing angle-resolved charge exchange spectroscopy [4]. To facilitate a comprehensive understanding of the plethora of observed phenomena and their interplay, we developed an atomistic model for ion stopping, charge exchange and electronic decay taking the time-dependent ion charge state explicitly into account [5].
In this contribution I will show that charge exchange pattern together with an atomistic and local model for charge exchange can be used to determine the structure of 2D materials on a sub-nm level, especially important for amorphous materials where atomically-resolved microscopy is hard to perform.
  • Invited lecture (Conferences)
    XXXI International Conference on Photonic, Electronic and Atomic Collisions (ICPEAC), 23.-30.07.2019, Deauville, Frankreich

Publ.-Id: 29669 - Permalink

Roadmap on photonic, electronic and atomic collision physics: III. Heavy particles: with zero to relativistic speeds
Aumayr, F.; Ueda, K.; Sokell, E.; Schippers, S.; Sadeghpour, H.; Merkt, F.; Gallagher, T. F.; Dunning, F. B.; Scheier, P.; Echt, O.; Kirchner, T.; Fritzsche, S.; Surzhykov, A.; Ma, X.; Rivarola, R.; Fojon, O.; Tribedi, L.; Lamour, E.; Crespo López-Urrutia, J. R.; Litvinov, Y. A.; Shabaev, V.; Cederquist, H.; Zettergren, H.; Schleberger, M.; Wilhelm, R. A.ORC; Azuma, T.; Boduch, P.; Schmidt, H. T.; Stöhlker, T.
We publish three Roadmaps on photonic, electronic and atomic collision physics in order to celebrate the 60th anniversary of the ICPEAC conference. Roadmap III focusses on heavy particles: with zero to relativistic speeds. Modern theoretical and experimental approaches provide detailed insight into the wide range of many-body interactions involving projectiles and targets of varying complexity ranging from simple atoms, through molecules and clusters, complex biomolecules and nanoparticles to surfaces and crystals. These developments have been driven by technological progress and future developments will expand the horizon of the systems that can be studied. This Roadmap aims at looking back along the road, explaining the evolution of the field, and looking forward, collecting nineteen contributions from leading scientists in the field.
Keywords: heavy particles, many-body interactions, clusters, complex biomolecules

Publ.-Id: 29667 - Permalink

Charge-Exchange-Driven Low-Energy Electron Splash Induced by Heavy Ion Impact on Condensed Matter
Schwestka, J.ORC; Niggas, A.; Creutzburg, S.; Kozubek, R.ORC; Heller, R.; Schleberger, M.ORC; Wilhelm, R. A.ORC; Aumayr, F.
Low-energy electrons (LEEs) are of great relevance for ion-induced radiation damage in cells and genes. We show that charge exchange of ions leads to LEE emission upon impact on condensed matter. By using a graphene monolayer as a simple model system for condensed organic matter and utilizing slow highly charged ions (HCIs) as projectiles, we highlight the importance of charge exchange alone for LEE emission. We find a large number of ejected electrons resulting from individual ion impacts (up to 80 electrons/ion for Xe40+). More than 90% of emitted electrons have energies well below 15 eV. This “splash” of low-energy electrons is interpreted as the consequence of ion deexcitation via an interatomic Coulombic decay (ICD) process.

Publ.-Id: 29666 - Permalink

Ultrasonic Determination of the Jahn–Teller Effect Parameters in Impurity-Containing Crystals
Averkiev, N. S.; Bersuker, I. B.; Gudkov, V. V.; Zhevstovskikh, I. V.; Sarychev, M. N.; Zherlitsyn, S.; Yasin, S.; Korostellin, Y. V.; Surikov, V. T.;
A method is developed to determine the symmetry properties of strains and the type of Jahn–Teller effect in crystals with impurity ions in a triply degenerate electronic T state. This method is based on a calculation of the isothermal contribution of the impurity subsystem to the elastic moduli of a crystal and the absorption and velocity of normal modes for all three possible problems, namely, T ⊗ e, T ⊗ t2, and T ⊗ (e + t2). The calculation results are compared with experimental data. The efficiency of the method is demonstrated for a CdSe:Cr2+ crystal. The CrSe4 center is found to be described in terms of the problem T ⊗ e. The parameters of the ground-state adiabatic potential are determined.

Publ.-Id: 29665 - Permalink

Pronounced 2/3 magnetization plateau in a frustrated S = 1 isolated spin-triangle compound: Interplay between Heisenberg and biquadratic exchange interactions
Chattopadhyay, S.; Lenz, B.; Kanungo, S.; Sushila, S.; Panda, S. K.; Biermann, S.; Schnelle, W.; Manna, K.; Kataria, R.; Uhlarz, M.; Skourski, Y.; Zvyagin, S. A.; Ponomaryov, A.; Herrmannsdörfer, T.; Patra, R.; Wosnitza, J.;
We report the synthesis and characterization of a new quantum magnet [2-[Bis(2-hydroxybenzyl) aminomethyl]pyridine]Ni(II)-trimer (BHAP-Ni3) in single-crystalline form. Our combined experimental and theoretical investigations reveal an exotic spin state that stabilizes a robust 2/3 magnetization plateau between 7 and 20 T in an external magnetic field. AC-susceptibility measurements show the absence of any magnetic order/glassy state down to 60 mK. The magnetic ground state is disordered and specific-heat measurements reveal the gapped nature of the spin excitations. Most interestingly, our theoretical modeling suggests that the 2/3 magnetization plateau emerges due to the interplay between antiferromagnetic Heisenberg and biquadratic exchange interactions within nearly isolated spin S = 1 triangles.


Publ.-Id: 29664 - Permalink

Chemical Shift and Exchange Interaction Energy of the 1s States of Magnesium Donors in Silicon. The Possibility of Stimulated Emission
Shastin, V. N.; Zhukavin, R. K.; Kovalevsky, K. A.; Tsyplenkov, V. V.; Rumyantsev, V. V.; Shengurov, D. V.; Pavlov, S. G.; Shuman, V. B.; Portsel, L. M.; Lodygin, A. N.; Astrov, Y. A.; Abrosimov, N. V.; Klopf, J. M.ORC; Hübers, H.-W.
The results of experiments aimed at the observation of split 1s states in Mg-doped Si are reported. From the results, it is possible to determine the chemical shift and exchange interaction energy of a neutral Mg donor in Si. The position of the 1s(E), 1s(T2), and 2s(A1) parastates determines the possibility for attaining population inversion and the specific mechanism of stimulated Raman scattering. The energy of the 1s(T2) parastate is determined from the position of the Fano resonances in the photoconductivity spectrum of Si:Mg at T = 4 K, and the energies of the 1s(T2) and 1s(E) orthostates from the transmittance spectra at elevated temperatures. On the basis of the experimental data, the relaxation rates are estimated, and the possible mechanisms of stimulated emission are analyzed.
Keywords: neutral double donor magnesium spectroscopy Fano resonance photoconductivity population inversion stimulated Raman scattering
  • Contribution to proceedings
    XXIII International Symposium "Nanophysics and Nanoelectronics", 11.-14.03.2019, Nizhny Novgorod, Russia
    Semiconductors 53(9), 1234-1237
    DOI: 10.1134/S1063782619090197

Publ.-Id: 29662 - Permalink

Characterization of suprathermal electrons inside a laser accelerated plasma via highly-resolved K⍺-emission
Smid, M.ORC; Renner, O.ORC; Colaitis, A.ORC; Tikhonchuk, V. T.ORC; Schlegel, T.; Rosmej, F. B.
Suprathermal electrons are routinely generated in high-intensity laser produced plasmas via instabilities driven by non-linear laser-plasma interaction. Their accurate characterization is crucial for the performance of inertial confinement fusion as well as for performing experiments in laboratory astrophysics and in general high-energy-density physics. Here, we present studies of non-thermal atomic states excited by suprathermal electrons in kJ-ns-laser produced plasmas. Highly spatially and spectrally resolved X-ray emission from the laser-deflected part of the warm dense Cu foil visualized the hot electrons. A multi-scale two-dimensional hydrodynamic simulation including non-linear laser-plasma interactions and hot electron propagation has provided an input for ab initio non-thermal atomic simulations. The analysis revealed a significant delay between the maximum of laser pulse and presence of suprathermal electrons. Agreement between spectroscopic signatures and simulations demonstrates that combination of advanced high-resolution X-ray spectroscopy and non-thermal atomic physics offers a promising method to characterize suprathermal electrons inside the solid density matter.


Publ.-Id: 29661 - Permalink

Experimental study on the air-side thermal-flow performance of additively manufactured heat exchangers with novel fin designs
Unger, S.; Beyer, M.; Gruber, S.; Willner, R.; Hampel, U.;
We introduce novel fin designs for finned tube heat exchangers which enhance the conduction heat transfer within the fin and the convective heat transfer along the fin surface simultaneously. Oval tubes with circular plain fins (CPF), circular integrated pin fins (CIPF) and a serrated integrated pin fins (SIPF) were additively manufactured via Selective Laser Melting (SLM) and their heat transfer and flow characteristics studied in a flow channel for different Reynolds number between 1800 and 7800 as well as fin spacing values between 6 mm and 16 mm. From the experiments an improvement of Nusselt number and a reduction of friction factor was found for all fin designs when fin spacing increases. CIPF showed a higher Nusselt number compared to CPF at all Reynolds numbers and fin spacing values. The highest Nusselt number as well as moderate friction factor values were found for the SIPF design. However, for SIPF the fin efficiency of 30:3 % is lowest due to the high heat dissipation along the fin surface. In order to evaluate the thermal and flow performance three parameters were studied: the performance evaluation criterion, the volumetric heat flux density and the global performance. CIPF gives a higher performance evaluation criterion compared to CPF and SIPF performs best compared to the other fin designs. Highest volumetric heat flux density of 2:72 mkW3K was achieved with CIPF at lowest fin spacing. Small differences in the global performance criterion between the fin designs and for various fin spacing were observed.
The SIPF design is of advantage, if the required surface area, the material cost and the weight of the finned tube heat exchanger are relevant. From the experimental results a heat transfer correlation that includes Nusselt number, Reynolds number, Prandtl number, fin spacing and fin design has been derived.
Keywords: Finned tube heat exchanger, Novel fin designs, Heat transfer, Friction factor, Thermal-flow performance, Additive manufacturing, Selective laser melting

Publ.-Id: 29658 - Permalink

Two types of magnetic shape-memory effects from twinned microstructure and magneto-structural coupling in Fe1+yTe
Rößler, S.; Koz, C.; Wang, Z.; Skourski, Y.; Doerr, M.; Kasinathan, D.; Rosner, H.; Schmidt, M.; Schwarz, U.; Rößler, U. K.; Wirth, S.;
A detailed experimental investigation of Fe1+yTe (y = 0.11, 0.12) using pulsed magnetic fields up to 60 T confirms remarkable magnetic shape-memory (MSM) effects. These effects result from magnetoelastic transformation processes in the low-temperature antiferromagnetic state of these materials. The observation of modulated and finely twinned microstructure at the nanoscale through scanning tunneling microscopy establishes a behavior similar to that of thermoelastic martensite. We identified the observed, elegant hierarchical twinning pattern of monoclinic crystallographic domains as an ideal realization of crossing twin bands. The antiferromagnetism of the monoclinic ground state allows for a magnetic-field–induced reorientation of these twin variants by the motion of one type of twin boundaries. At sufficiently high magnetic fields, we observed a second isothermal transformation process with large hysteresis for different directions of applied field. This gives rise to a second MSM effect caused by a phase transition back to the field-polarized tetragonal
lattice state.
  • Proceedings of the National Academy of Sciences of the United States of America 116(2019)34, 16697-16702
    DOI: 10.1073/pnas.1905271116

Publ.-Id: 29657 - Permalink

Cross section of the reaction 18O(p,γ)19F at astrophysical energies: The 90 keV resonance and the direct capture component
Best, A.; Pantaleo, F. R.; Boeltzig, A.; Imbriani, G.; Aliotta, M.; Balibrea-Correa, J.; Bemmerer, D.; Broggini, C.; Bruno, C. G.; Buompane, R.; Caciolli, A.; Cavanna, F.; Chillery, T.; Ciani, G. F.; Corvisiero, P.; Csedreki, L.; Davinson, T.; Deboer, R. J.; Depalo, R.; Di Leva, A.; Elekes, Z.; Ferraro, F.; Fiore, E. M.; Formicola, A.; Fülöp, Z.; Gervino, G.; Guglielmetti, A.; Gustavino, C.; Gyürky, G.; Junker, M.; Kochanek, I.; Lugaro, M.; Marigo, P.; Menegazzo, R.; Mossa, V.; Paticchio, V.; Perrino, R.; Piatti, D.; Prati, P.; Schiavulli, L.; Stöckel, K.; Straniero, O.; Strieder, F.; Szücs, T.; Takács, M. P.; Trezzi, D.; Wiescher, M.; Zavatarelli, S.;
The observation of oxygen isotopes in giant stars sheds light on mixing processes operating in their interiors. Due to the very strong correlation between nuclear burning and mixing processes it is very important to reduce the uncertainty on the cross sections of the nuclear reactions that are involved. In this paper we focus our attention on the reaction . While the channel is thought to be dominant, the (p,γ) channel can still be an important component in stellar burning in giants, depending on the low energy cross section. So far only extrapolations from higher-energy measurements exist and recent estimates vary by orders of magnitude. These large uncertainties call for an experimental reinvestigation of this reaction. We present a direct measurement of the cross section using a high-efficiency 4π BGO summing detector at the Laboratory for Underground Nuclear Astrophysics (LUNA). The reaction cross section has been directly determined for the first time from 140 keV down to 85 keV and the different cross section components have been obtained individually. The previously highly uncertain strength of the 90 keV resonance was found to be 0.53 ± 0.07 neV, three orders of magnitude lower than an indirect estimate based on nuclear properties of the resonant state and a factor of 20 lower than a recently established upper limit, excluding the possibility that the 90 keV resonance can contribute significantly to the stellar reaction rate.
Keywords: Experimental nuclear astrophysics Underground nuclear physics Hydrogen burning Stellar evolution

Publ.-Id: 29655 - Permalink

Dataset on Relationships between primary radiation damage, irradiation-induced microstructure and hardening of ion-irradiated Fe-Cr and ODS Fe-Cr alloys
Vogel, K.; Heintze, C.; Chekhonin, P.; Akhmadaliev, S.; Altstadt, E.ORC; Bergner, F.ORC

Dataset on Relationships between primary radiation damage, irradiation-induced microstructure and hardening of ion-irradiated Fe-Cr and ODS Fe-Cr alloys including SRIM calculations, nanoindentation, TEM and modelling.

  • Reseach data in the HZDR data repository RODARE
    Publication date: 2019-09-11
    DOI: 10.14278/rodare.183


Publ.-Id: 29653 - Permalink

Binding, uptake and transport of radionuclides and their analogues by the fungus Schizophyllum commune under natural conditions
Wollenberg, A.; Hübner, R.; Günther, A.; Freitag, L.; Raff, J.ORC; Stumpf, T.
Radionuclides occur naturally and can be released into nature through anthropogenic effects. Through leaching and migration, also the anthropogenically released radionuclides can enter the groundwater and endanger the environment, animals and humans. However, the microbial community living in the soil may influence the mobility and thus the migration behaviour of radionuclides.
Since the Chernobyl accident at the latest, it became clear that various fungi are able to accumulate considerable amounts of heavy metals and radionuclides in their fruiting bodies [1-3]. However, it has not yet been determined, which processes lead to this significant accumulation in the fungal fruiting body.
For this reason, the interaction of a model fungus, namely Schizophyllum commune, with various radionuclides was studied in detail in the steps of binding and uptake by the fungal cells and transport within the mycelium.
For the visualization of the radionuclide and heavy metal transport through the hyphae, TEM and STEM imaging in combination with Energy-dispersive X-ray spectroscopy analysis were used to locate accumulation sites within the cells and to identify the formed species. The first results with uranium show that it is accumulated in form of phosphate minerals mainly on the cell membrane. Furthermore, microcosm experiments were conducted in which the bidirectional growth of the fungus was exploited: parts of the mycelium were growing upwards, while the other parts were growing into the contaminated soil. In order to check the transport of soil contaminants through the hyphae, the part of the mycelium that has no direct contact with the soil was sampled and analysed by ICP-MS. First results show that uranium could be detected in the samples, suggesting transport through the hyphae.
In addition to the transport of uranium, the experiments also investigate the transport of europium as an analogue for trivalent actinides, as well as the transport of inactive caesium and strontium within the mycelium.
Keywords: Fungi, Uranium, Transport, Uptake
  • Poster
    17th International Conference on the Chemistry and Migration Behavior of Actinides and Fission Products in the Geosphere, 15.-20.09.2019, Kyoto, Japan

Publ.-Id: 29652 - Permalink

Investigation of the potential of fungi for precautionary radiation protection in soil
Wollenberg, A.; Freitag, L.; Hübner, R.; Günther, A.; Raff, J.ORC; Stumpf, T.
Due to the multifaceted use of radionuclides in research, medicine and industry, there is an increased risk of a release into the environment during the extraction and use of radioactive materials, but also during the storage of the resulting radioactive waste. If radionuclides are released into the soil, they can migrate through soil layers to the groundwater or can be absorbed by crops. In any case, it endangers the environment, animals and humans. For this reason, an effective precautionary radiation protection method must be found which can limit the mobility of possible released radionuclides in the environment.
Since the Chernobyl accident at the latest, it became clear, that fungi influence the migration behavior of radionuclides in the soil by accumulating them in large quantities. Due to other positive properties of fungi, such as the spread of one organism over several square kilometers and their high life expectancy, they provide a good basis for a bio-based precautionary radiation protection. Nevertheless, previous studies have also shown, that the effectiveness of radionuclide accumulation depends on the respective fungal strain [1-3].
For this reason, the molecular interactions of four different fungi with uranium were investigated and compared.
First TEM and STEM images of the fungus Schizophyllum commune, which is widely used as a model organism, show mineralization of uranium in form of needles at the cell membrane. Energy-dispersive X-ray spectroscopy analysis and time-resolved laser-induced fluorescence spectroscopy (TRLFS) have shown, that uranium is mineralized with phosphate. A second fungus, called Leucoagaricus naucinus, shows a different form of mineralization and localization of uranium in the cell. However, first TRLFS experiments suggest that it is a phosphate mineral as well. Together with two other fungi, Pleurotus ostreatus and Macrolepiota procera, a better understanding of the interactions of different fungi with radionuclides will be generated in order to evaluate the potential of fungi for the precautionary radiation protection of soils and to lay the basis for the development of a practicable process.
Keywords: Fungi, Radionuclide, TRLFS, precautionary radiation protection
  • Lecture (Conference)
    Jahrestagung der Fachgruppe Nuklearchemie 2019, 25.-27.09.2019, Dresden, Deutschland

Publ.-Id: 29651 - Permalink

Research and Implementation of Efficient Parallel Processing of Big Data at TELBE User Facility
Bawatna, M.ORC; Green, B.ORC; Kovalev, S.ORC; Deinert, J.-C.ORC; Knodel, O.ORC; Spallek, R. G.
In recent years, improvements in high-speed Analog-to-Digital Converters (ADC) and sensor technology has encouraged researchers to improve the performance of Data Acquisition (DAQ) systems for scientific experiments which require high speed and continuous data measurements — in particular, measuring the electronic and magnetic properties of materials using pump-probe experiments at high repetition rates. Experiments at TELBE are capable of acquiring almost 100 Gigabytes of raw data every ten minutes. The DAQ system used at TELBE partitions the raw data into various subdirectories for further parallel processing utilizing the multicore structure of modern CPUs.
Furthermore, several other types of processors that accelerate data processing like the GPU and FPGA have emerged to solve the challenges of processing the massive amount of raw data. However, the memory and network bottlenecks become a significant challenge in big data processing, and new scalable programming techniques are needed to solve these challenges. In this contribution, we will outline the design and implementation of our practical software approach for efficient parallel processing of our large data sets at the TELBE user facility.
Keywords: Big Data, Data Processing Pipeline, Data Acquisition Systems, Signal Processing, Data analytics
  • Contribution to proceedings
    2019 International Symposium on Performance Evaluation of Computer and Telecommunication Systems (SPECTS), 22.07.2019, Berlin, Deutschland
    2019 International Symposium on Performance Evaluation of Computer and Telecommunication Systems (SPECTS): IEEE, 978-1-5108-8479-3
    DOI: 10.23919/SPECTS.2019.8823486

Publ.-Id: 29650 - Permalink

Novel High Affinity Histone Deacetylase Inhibitors as Potential Radiotracers for PET
Clauß, O.; Schäker-Hübner, L.; Scheunemann, M.; Hansen, F. K.ORC; Brust, P.ORC
Epigenetics investigates heritable phenotype changes that do not involve alterations in the DNA sequence. The related phenomena play a key role in gene expression by enzyme-mediated post-translational modifications (PTMs) of proteins. One of the most relevant modifications is the process of deacetylation of the lysine side chains on histones, which are regulated by histone deacetylases (HDACs). The catalyzed deacetylation of lysine residues on histones modulates the chromatin and thus influences the gene expression and transcription. The class I histone deacetylases 1, 2 and 3 are overexpressed in several types of cancer, neurodegenerative diseases and inflammation. Inhibition of those zinc-dependent HDACs relaxes the chromatin structure and can result in transcriptional activation and anticancer effects, e.g. cell cycle arrest and induced differentiation. Consequently, radiolabeled HDAC inhibitors have emerged as a potential tool for the diagnostic imaging of tumors by positron emission tomography (PET). [1]
The aim of this work is the development of novel highly affine and selective fluorine-containing derivatives of a class I selective HDAC inhibitor to obtain the corresponding 18F-labeled PET radiotracers with an ortho-aminoanilide as zinc-binding motif for targeting class I HDACs in tumors. Recently, we discovered a new highly affine HDAC 1 ligand LSH-A30 with an IC50 for HDAC 1 inhibition of 4.4 ± 0.1 nM. In this connection, the structure of LSH-A30 serves as lead for the development of a series of fluorinated reference compounds, which are currently synthesized. The binding affinities and selectivities towards the class I HDAC isoforms will be determined. Our strategy is mainly focused on the medicinal chemistry of fluorine-containing derivatives, which are suitable for direct and indirect nucleophilic radiofluorination. For the most promising compounds, precursors for radiolabeling will be synthesized, the evaluation of physicochemical properties, e.g. stability and lipophilicity of the radiolabeled compounds will be assessed and further in vitro and in vivo investigations will be performed.
Keywords: HDAC inhibitors, PET tracer development, ortho-aminoanilides
  • Open Access LogoPoster
    GDCh Wissenschaftsforum Chemie 2019, 15.-18.09.2019, Aachen, Deutschland


Publ.-Id: 29649 - Permalink

Dendritic structure formation of magnesium alloys for the manipulation of corrosion properties: Part 2-corrosion
Lakoma, P.; Ditze, A.; Scharf, C.;
In pure magnesium and aluminum-containing magnesium alloys, the microstructure also plays a role in the corrosion properties. In Part 1, the grain sizes, secondary dendrite arm spacings (SDAS) and precipitates of b phase were determined by casting samples with 0, 3, 6, 9 and 12% aluminum (all compositions in mass percentage) at different cooling rates. These samples were tested for corrosion properties by immersion and salt spray tests. The modeling of the corrosion process enables establishing a mathematical link between the microstructure and corrosion properties of an alloy. The results show an increase in the corrosion rate with increasing aluminum contents and the cooling rate.

The precipitations at the grain boundaries have a relevant impact on corrosion properties of the magnesium-aluminum alloys. A random comparison using the salt spray test tends to confirm the results.

Publ.-Id: 29641 - Permalink

Terahertz excitations in α-RuCl3: Majorana fermions and rigid-plane shear and compression modes
Reschke, S.; Tsurkan, V.; Do, S.-H.; Choi, K.-Y.; Lunkenheimer, P.; Wang, Z.; Loidl, A.;
Spin liquids may host emergent quasiparticles, collective excitations of the spin degrees of freedom with characteristic features of Majorana fermions, which experimentally are detectable by broad excitation continua due to spin fractionalization. The latter is predicted for the Kitaev spin liquid, an exactly solvable model with bond-dependent interactions on a two-dimensional honeycomb lattice. Here we report on detailed terahertz experiments in α-RuCl3, identifying these characteristic fingerprints of Majorana fermions. The continuum intensity decreases and finally vanishes on increasing temperature. It partly overlaps with phonon modes, representing characteristic sliding and compression modes of the van der Waals bonded molecular layers.

Publ.-Id: 29639 - Permalink

A comparative evaluation of calix[4]arene-1,3-crown-6 as a ligand for selected divalent cations of radiopharmaceutical interest
Bauer, D.; Blumberg, M.; Köckerling, M.; Mamat, C.ORC
Radionuclides of divalent metals like lead-203, lead-212 and the radionuclides of alkaline earth metals barium-131 and strontium 89 are promising candidates for a radiopharmaceutical application. In addition, the heavy homologues radium-223 and radium-224 – with similar properties to barium - are suitable alpha-emitters for the targeted alpha-particle therapy. However, there is a lack of suitable chelation agents, especially for heavy group 2 metals. The macrocycle calix[4]arene-1,3-crown-6 seems to strongly interact with these metals. Therefore, this ligand and its coordination to the divalent cations of barium, strontium, and lead have been investigated. The complex formation was analyzed by NMR and UV/Vis titration experiments in acetonitrile, and stability constants were determine with both methods. It was found that the stability of these complexes increase in the order of strontium, barium, and lead. Additional to these investigations, X-ray crystallography, solvent-dependent 1H-NMR, and 207Pb NMR measurements were performed to deliver a deeper insight into the coordination chemistry of this ligand.
Keywords: Calix[4]arene, Radium, Barium, X-ray


Publ.-Id: 29638 - Permalink

Electroforming-free resistive switching in yttrium manganite thin films by cationic substitution
Rayapati, V. R.; Bürger, D.; Du, N.; Patra, R.; Skorupa, I.; Blaschke, D.; Stöcker, H.; Matthes, P.; Schulz, S. E.; Schmidt, H.;
We report unipolar resistive switching in polycrystalline, hexagonal yttrium manganite thin films grown on unpatterned Pt metal coated SiO2/Si substrates with circular Al top electrodes. Electroforming-free or electroforming-based resistive switching is observed, depending on the chemical composition (Y1Mn1O3, Y0.95Mn1.05O3, Y1Mn0.99Ti0.01O3, and Y0.94Mn1.05Ti0.01O3). The number of loading cycles measured at room temperature for samples with Y1Mn1O3 and Y0.95Mn1.05O3 composition is larger than 103. The dominant conduction mechanism of the metal-insulator-metal structures between 295 K and 373 K in the high resistance state is space charge limited conduction and in the low resistance state is ohmic conduction. Activation energies in Ohm's law region in the high resistance state are calculated from the Arrhenius equation and are evaluated to be 0.39 ± 0.01 eV (Y1Mn1O3), 0.43 ± 0.01 eV (Y0.95Mn1.05O3), 0.34 ± 0.01 eV (Y1Mn0.99Ti0.01O3), and 0.38 ± 0.02 eV (Y0.94Mn1.05Ti0.01O3).

Publ.-Id: 29637 - Permalink

Droplet retention time and pressure drop in SiSiC open-cell foams used as droplet separation devices – A numerical approach
Hernandez, J. N. C.ORC; Lecrivain, G.ORC; Schubert, M.; Hampel, U.ORC
Open-cell foams are a promising alternative for the separation of liquid droplets suspended in gas flows at comparably low pressure drop. The separation in such ceramic foams is investigated using the residence time distribution of droplets derived from pore-scale CFD-simulations. 20 and 45 pores per inch (ppi) silicon-infiltrated silicon carbide (SiSiC) open-cell foams samples are considered. The foam structure was reconstructed from micro-computed tomography (µCT) images. To track the droplets, a Lagrangian discrete-phase model was used. The effect of pore size and pore density on the droplet retention time was studied. The flow pressure drop showed a remarkable agreement with the in-house experimental measurements. The droplet separation efficiency within the foam structure was found to generally increase with the inlet gas velocity and the droplet inertia.
Keywords: Ceramic foams, liquid droplet entrainment, gas-droplet flow, resolved pore-scale CFD simulations, droplet residence time, droplet separator device


Publ.-Id: 29635 - Permalink

Alkyne-based cysteine cathepsin inhibitors as basis for PET tracer development
Behring, L.; Trapp, C.; Morales, M.; Wodtke, R.; Kuhne, K.; Belter, B.; Pietzsch, J.ORC; Löser, R.
Among the intertwined processes leading to cancer progression, protease activity plays an important role. Various attempts to develop molecular imaging probes have been made, as such probes can allow functional imaging and thus improve the understanding of tumour progression mechanisms and enable personalised cancer treatment. PET and SPECT tracers are particularly suitable for such applications. However, novel tracers have to overcome challenges such as stability, target efficiency and off-target effects.
Multiple members of the cathepsin family have been demonstrated to be involved in tumour invasion, metastasis, and angiogenesis. Especially high expression levels of the cysteine cathepsins B, K, L, S, and X are correlated with an increased metastatic potential and poor prognosis [1]. Due to their high expression in a multitude of tumours, those enzymes represent promising targets for the therapy and imaging of tumours.
Despite being virtually chemically inert, alkynes were shown to be able to irreversibly inhibit cysteine proteases: Both EKKEBUS et al. and SOMMER et al. independently described the unexpected inactivation of de-ubiquitinating enzymes by ubiquitin or ubiquitin-like modifiers bearing propargylamine in place of C-terminal glycine [2, 3]. We aimed to take advantage of those findings for designing alkyne-based cysteine cathepsin inhibitors suitable for radiolabelling with PET nuclides. The probes thus obtained would irreversibly bind to the target molecule without showing indiscriminate thiol reactivity.
Based on a potent, highly selective dipeptidyl nitrile-based cathepsin B inhibitor reported by GREENSPAN et al. (left structure) [4], we designed dipeptide alkynes by isoelectronic replacement of the nitrile nitrogen atom by a methine group. To avoid partial enantiomerisation during the formation of the C-C triple bond as observed for the open-chain serine-derived alkyne, the synthesis was performed via Garner’s aldehyde. This ensured high stereochemical purity of the final compounds. The inhibitory potential was investigated against cathepsin B, S, L and K. To optimise the inhibitory potential and selectivity, we consecutively varied all moieties attached to the dipeptidic scaffold.
We identified potent alkyne-based inhibitors for all tested cathepsins, with inactivation constants (kinact/KI) up to 10133 M-1s-1 and distinct selectivity profiles. We demonstrated irreversibility in a “jump-dilution” experiment and inhibitor reactivity in cell lysates and on living cells was exemplarily verified for cathepsin B. During our research, MONS et al. successfully demonstrated irreversible cathepsin K inhibition by alkyne-based small molecule inhibitors with no indiscriminate thiol reactivity [5], which indicates the viability of our concept.
Among the tested inhibitors we identified two promising radiotracer candidates which are selective for cathepsin S and L. We successfully radiolabelled the cathepsin S-selective inhibitor with N-succinimidyl 4-[18F]fluorobenzoate ([18F]SFB). Radiopharmacological characterisation of the activity-based probe obtained by that approach is in progress.

[1] Löser, R; Pietzsch, J.: Front. Chem., 2015, 3: 37.
[2] Ekkebus et al.: J. Am. Chem. Soc., 2013, 135(8): 2867-2870.
[3] Sommer et al.: Bioorg. Med. Chem., 2013, 21(9): 2511-2517.
[4] Greenspan et al.: J. Med. Chem., 2001, 44(26): 4524-4534.
[5] Mons et al.: J. Am. Soc. 2019, 141(8): 3507-3514.
  • Poster
    Annual Meeting of the German Pharmaceutical Society - DPhG, 01.-04.09.2019, Heidelberg, Deutschland

Publ.-Id: 29632 - Permalink

Radiotherapy Beamline Design for Laser-driven Proton Beams
Masood, U.ORC
Motivation: Radiotherapy is an important modality in cancer treatment commonly using photon beams from compact electron linear accelerators. However, due to the inverse depth dose profile (Bragg peak) with maximum dose deposition at the end of their path, proton beams allow a dose escalation within the target volume and reduction in surrounding normal tissue. Up to 20% of all radiotherapy patients could benefit from proton therapy (PT). Conventional accelerators are utilized to obtain proton beams with therapeutic energies of 70 – 250 MeV. These beams are then transported to the patient via magnetic transferlines and a rotatable beamline, called gantry, which are large and bulky. PT requires huge capex, limiting it to only a few big centres worldwide treating much less than 1% of radiotherapy patients. The new particle acceleration by ultra-intense laser pulses occurs on micrometer scales, potentially enabling more compact PT facilities and increasing their widespread. These laser-accelerated proton (LAP) bunches have been observed recently with energies of up to 90 MeV and scaling models predict LAP with therapeutic energies with the next generation petawatt laser systems.
  • Open Access LogoWissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-104 2019


Publ.-Id: 29631 - Permalink

Implantable highly compliant devices for heating of internal organs: towards cancer treatment
Cañón Bermudez, G. S.; Kruv, A.; Voitsekhivska, T.; Hochnadel, I.; Lebanov, A.; Potthoff, A.; Fassbender, J.; Yevsa, T.; Makarov, D.;
Flexible electronics have a strong potential to revolutionize the health care sector. Numerous flexible diagnostic or therapeutic devices have been successfully demonstrated. However, tumor treatment remains rather unexplored in the field of flexible electronics. Here, we demonstrate that the electrical and mechanical properties of highly compliant electronics are advantageous for targeting tumor sites at internal organs. This kind of electronics could be implanted to heat and thereby render the treated tissue susceptible to chemotherapy, radiation or other available treatments. Our method relies on the implantation directly at the tumor site of an ultra-thin flexible device comprising a resistive heater and temperature sensor. The device consists of a 6 µm thick polymeric foil hosting the heater and sensor, capped with a 5 µm thick encapsulation layer. Due to its ultrathin nature, it seamlessly conforms to the very soft liver tissue and allows for precisely controlled thermal treatment. Its high mechanical compliance provides stable readings even upon severe mechanical deformations, enabling a temperature accuracy of 0.1°C at bending radii of 2.5 mm, characteristic for mouse liver tissues. We demonstrate a proof-of-concept prototype and evaluate its electrical and mechanical performance when applied to murine cancer models. The presented highly compliant device paves the way for handling of exophytic (located at the organ surface) tumor nodules via thermal destruction of tissue, targeted drug release, or enhancement of anti-tumor immune responses. In addition, it raises the possibility to further study the effects of thermal treatment in enhancing the development of the new cancer therapies, especially for severe malignancies as liver cancer.
Keywords: flexible electronics, cancer

Publ.-Id: 29629 - Permalink

A bimodal soft electronic skin for tactile and touchless interaction in real time
Ge, J.; Wang, X.; Drack, M.; Volkov, O.; Liang, M.; Cañón Bermúdez, G. S.; Illing, R.; Wang, C.; Zhou, S.; Fassbender, J.; Kaltenbrunner, M.; Makarov, D.;
The emergence of smart electronics, human friendly robotics and supplemented or virtual reality demands electronic skins with both tactile and touchless perceptions for the manipulation of real and virtual objects. Here, we realize bifunctional electronic skins equipped with a compliant magnetic microelectromechanical system able to transduce both tactile - via mechanical pressure - and touchless - via magnetic fields - stimulations simultaneously. The magnetic microelectromechanical system separates electric signals from tactile and touchless interactions into two different regions, allowing the electronic skins to unambiguously distinguish the two modes in real time. Besides, its inherent magnetic specificity overcomes the interference from non-relevant objects and enables signal-programmable interactions. Ultimately, the magnetic microelectromechanical system enables complex interplay with physical objects enhanced with virtual content data in augmented reality, robotics, and medical applications.
Keywords: flexible electronics, magnetic field sensors

Publ.-Id: 29628 - Permalink

Interplay Between Relaxation and Resonance in Ultrasound Attenuation by the Cubic Crystal ZnSe:Cr
Baryshnikov, K.; Averkiev, N.; Bersuker, I.; Gudkov, V.; Zhevstovskikh, I.; Sarychev, M.; Zherlitsyn, S.; Yasin, S.; Korostelin, Y.;
Resonance ultrasound attenuation, albeit broadened, is observed in doped cubic crystal ZnSe with a part of the Zn ions substituted by magnetic anisotropic Cr2+ ions. In the tetrahedral selenium environment the latter form a T term Jahn–Teller (JT) center with a T⊗e JT problem and three equivalent distortions along the three tetragonal axes. In sufficiently strong magnetic fields (B > 4 T) applied along the [001] direction the degeneracy of the ground state is removed, and the ultrasound wave propagating along [110] and polarized along [110] (at T = 1.3 K) does not interact with the center, its impurity attenuation being reduced to zero. By comparison, this allows to estimate the contribution of the Cr centers to the attenuation of ultrasound in the ZnSe:Cr crystal in zero magnetic field. The experimental data revealed a strong dependence of the attenuation on the ultrasound frequency, evidencing for the resonance nature of the attenuation: there is no frequency dependence in relaxational attenuation with the relaxation time much larger than the period of the ultrasonic wave. The resonance attenuation is attributed to transitions between the ground state energy levels, split by spin-orbital interaction. The high sensitivity of the resonance absorption on the ultrasound power is also discussed.

Publ.-Id: 29627 - Permalink

Diffusion of Phosphorus and Boron from Atomic Layer Deposition Oxides into Silicon
Beljakowa, S.; Pichler, P.; Kalkofen, B.; Hübner, R.;
Oxides containing group III or group V elements (B2O3/Sb2O5 and P2O5/Sb2O5) are grown by plasma-assisted atomic layer deposition (ALD) on single-crystalline silicon and serve as dopant sources for conformal and shallow doping. Transport phenomena in ALD-oxide–Si structures during rapid thermal annealing (RTA) are investigated subsequently by X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and secondary ion mass spectrometry (SIMS). The XPS and TEM analyses of the annealed ALD oxide–Si structures demonstrate that the ALD oxide converts to a silicon oxide and partially evaporates during annealing. In addition, dopant-containing, spherical, and partially crystalline particles form in the oxide, and Si-P precipitates at the oxide–Si interface. After diffusion annealing at 1000 °C, the SIMS analyses reveal phosphorus and boron concentration profiles in the silicon substrate with maximum concentrations exceeding their solid solubility limits by roughly one order of magnitude. Experimental doping profiles of phosphorus and boron in silicon are compared with simulation results, considering a slight injection of self-interstitials and dynamical defect clustering.

Publ.-Id: 29626 - Permalink

PIConGPU simulation settings for TWEAC
Debus, A.ORC; Steiniger, K.ORC; Pausch, R.ORC; Huebl, A.ORC; Widera, R.ORC

The input sets of the simulations as used in the publication "Circumventing the Dephasing and Depletion Limits of Laser-Wakefield Acceleration" by A. Debus et al. .

The input sets include TWEAC scenarios, the LWFA scenario and the laser-propagation scenario of Appendix D. The src-directories include custom additions to the PIConGPU source code.

The simulations were run using the beta-rc6, 0.3.1, and 0.4.0 releases of PIConGPU (see DOI: 10.5281/zenodo.591746). The input sets are shown according to the respective PIConGPU version used in the original simulation. However, for running the simulations we recommend adapting the input sets to the 0.4.0 release.

Keywords: Optics; Photonics; Plasma Physics
Related publications
Circumventing the dephasing and depletion limits of … (Id 25244) is documented by this publication
  • Reseach data in the HZDR data repository RODARE
    Publication date: 2019-09-04
    DOI: 10.14278/rodare.150
    License: CC-BY-4.0


Publ.-Id: 29625 - Permalink

Efficiency estimation of tray columns based on flow profiles and vapor-liquid equilibrium characteristics of binary mixtures
Vishwakarma, V.ORC; Rigos, N.; Schubert, M.ORC; Hampel, U.

A systematic approach for estimating the column efficiency based on tray flow profiles and vapor-liquid equilibrium (VLE) characteristics of binary mixtures exclusively for each tray is proposed. A novel iterative technique for approximating the slope of the VLE curve and the tray efficiency is also developed. For demonstrating the predictive capabilities of the new approach, two case studies are formulated in this work - one with a theoretical column processing selected binary mixtures at total reflux, and the other involving an industrial column whose performance data is acquired from the literature. An in-depth analysis of these studies reveals the superiority of the new approach over the most applied method. Such an approach would allow a priori calculation of the column efficiency in the tray’s design phase.

Keywords: Column efficiency; Murphree tray efficiency; flow maldistribution; vapor-liquid equilibrium; residence time distribution.
  • Reseach data in the HZDR data repository RODARE
    Publication date: 2019-09-02
    DOI: 10.14278/rodare.148
    License: CC-BY-4.0


Publ.-Id: 29624 - Permalink

Modulated Rotating Waves in the Magnetised Spherical Couette System
Garcia Gonzalez, F.; Seilmayer, M.ORC; Giesecke, A.; Stefani, F.
We present a study devoted to a detailed description of modulated rotating waves (MRW) in the magnetised spherical Couette system. The set-up consists of a liquid metal confined between two differentially rotating spheres and subjected to an axially applied magnetic field. When the magnetic field strength is varied, several branches of MRW are obtained by means of three-dimensional direct numerical simulations. The MRW originate from parent branches of rotating waves and are classified according to Rand’s (Arch Ration Mech Anal 79:1–37, 1982) and Coughling and Marcus (J Fluid Mech 234:1–18, 1992) theoretical description. We have found relatively large intervals of multistability of MRW at low magnetic field, corresponding to the radial jet instability known from previous studies. However, at larger magnetic field, corresponding to the return flow regime, the stability intervals of MRW are very narrow and thus they are unlikely to be found without detailed knowledge of their bifurcation point. A careful analysis of the spatio-temporal symmetries of the most energetic modes involved in the different classes of MRW will allow in the future a comparison with the HEDGEHOG experiment, a magnetised spherical Couette device hosted at the Helmholtz-Zentrum Dresden-Rossendorf.
Keywords: Magnetohydrodynamics, Nonlinear waves, Bifurcation theory, Symmetry breaking, Experiments, Astrophysics

Publ.-Id: 29619 - Permalink

Melting behaviour of uranium-americium mixed oxides under different atmospheres
Epifano, E.; Prieur, D.ORC; Martin, P. M.; Guéneau, C.; Dardenne, K.; Rothe, J.; Vitova, T.; Wiss, T.; Dieste, O.; Konings, R. J. M.; Manara, D.
In the context of a comprehensive campaign for the characterisation of transmutation fuels for next generation nuclear reactors, the melting behaviour of mixed uranium-americium dioxides has been experimentally studied for the first time by laser heating, for Am concentrations up to 70 mol. % under different types of atmospheres. Extensive post-melting material characterisations were then performed by X-ray absorption spectroscopy and electron microscopy. The melting temperatures observed for the various compositions follow a markedly different trend depending on the experimental atmosphere. Uranium-rich samples melt at temperatures significantly lower (around 2700 K) when they are laser-heated in a strongly oxidizing atmosphere compressed air at (0.300 ± 0.005) MPa, compared to the melting points (beyond 3000 K) registered for the same compositions in an inert environment (pressurised Ar). This behaviour has been interpreted on the basis of the strong oxidation of such samples in air, leading to lower-melting temperatures. Thus, the melting temperature trend observed in air is characterized, in the purely pseudo-binary dioxide plane, by an apparent maximum melting temperature around 2850 K for 0.3 < x(AmO2) < 0.5. The melting points measured under inert atmosphere uniformly decrease with increasing americium content, displaying an approximately ideal solution behaviour if a melting point around 2386 K is assumed for pure AmO2. In reality, it will be shown that the (U, Am)-oxide system can only be rigorously described in the ternary U-Am-O phase diagram, rather than the UO2-AmO2 pseudo-binary, due to the aforementioned over-oxidation effect in air. Indeed, general departures from the oxygen stoichiometry (Oxygen/Metal ratios ≠ 2.0) have been highlighted by the X-ray Absorption Spectroscopy (XAS). Finally, to help interpret the experimental results, thermodynamic computations based on the CALPHAD method will be presented.
Keywords: Uranium americium dioxide, Melting, Transmutation targets, CALPHAD


  • Secondary publication expected from 01.01.2021

Publ.-Id: 29617 - Permalink

A novel meta-stable pentavalent plutonium solid phase on the pathway from aqueous Pu(VI) to PuO2 nanoparticles
Kvashnina, K.; Romanchuk, A.; Pidchenko, I.; Amidani, L.ORC; Gerber, E.; Trigub, A.; Roßberg, A.; Weiß, S.; Popa, K.; Walter, O.; Caciuffo, R.; Scheinost, A.; Butorin, S.; Kalmykov, S.
We report here experimental evidence that the formation of PuO2 nanoparticles from oxidized Pu(VI) under environmentally relevant conditions proceeds through the formation of an intermediate Pu(V) solid phase, similar to NH4PuO2CO3, which is stable over a period of several months. State-of-the-art experiments at Pu M4 and L3 absorption edges combined with theoretical calculations unambiguously allowed us to determine the oxidation state and the local structure of this intermediate phase

Publ.-Id: 29614 - Permalink

Direct measurements of low-energy resonance strengths of the 23Na(p,γ)24Mg reaction for astrophysics
Boeltzig, A.; Best, A.; Pantaleo, F. R.; Imbriani, G.; Junker, M.; Aliotta, M.; Balibrea-Correa, J.; Bemmerer, D.ORC; Broggini, C.; Bruno, C. G.; Buompane, R.; Caciolli, A.; Cavanna, F.; Chillery, T.; Ciani, G. F.; Corvisiero, P.; Csedreki, L.; Davinson, T.; Deboer, R. J.; Depalo, R.; Di Leva, A.; Elekes, Z.; Ferraro, F.; Fiore, E. M.; Formicola, A.; Fülöp, Z.; Gervino, G.; Guglielmetti, A.; Gustavino, C.; Gyürky, G.; Kochanek, I.; Lugaro, M.; Marigo, P.; Menegazzo, R.; Mossa, V.; Munnik, F.; Paticchio, V.; Perrino, R.; Piatti, D.; Prati, P.; Schiavulli, L.; Stöckel, K.; Straniero, O.; Strieder, F.; Szücs, T.ORC; Takács, M. P.; Trezzi, D.; Wiescher, M.; Zavatarelli, S.
The NeNa and the MgAl cycles play a fundamental role in the nucleosynthesis of asymptotic giant branch stars undergoing hot bottom burning. The 23Na (p , γ)24Mg reaction links these two cycles and a precise determination of its rate is required to correctly estimate the contribution of these stars to the chemical evolution of various isotopes of Na, Mg and Al. At temperatures of 50 ≲ T ≲ 110MK, narrow resonances at Ep = 140 and 251keV are the main contributors to the reaction rate, in addition to the direct capture that dominates in the lower part of the temperature range. We present new measurements of the strengths of these resonances at the Laboratory for Underground Nuclear Astrophysics (LUNA). We have used two complementary detection approaches: high efficiency with a 4π BGO detector for the 140 keV resonance, and high resolution with a HPGe detector for the 251 keV resonance. Thanks to the reduced cosmic ray background of LUNA, we were able to determine the resonance strength of the 251 keV resonance as ωγ = 482 (82) μeV and observed new gamma ray transitions for the decay of the corresponding state in 24Mg at Ex = 11931keV. With the highly efficient BGO detector, we observed a signal for the 140 keV resonance for the first time in a direct measurement, resulting in a strength of ωγ140 = 1.46-0.53+0.58 neV (68% CL). Our measurement reduces the uncertainty of the 23Na (p , γ)24Mg reaction rate in the temperature range from 0.05 to 0.1 GK to at most -35%+50% at 0.07 GK. Accordingly, our results imply a significant reduction of the uncertainties in the nucleosynthesis calculations.
Keywords: LUNA; Nuclear Astrophysiscs; Underground nuclear physics; Hydrogen burning; Stellar evolution

Publ.-Id: 29612 - Permalink

Untersuchung disperser Zweiphasenströmungen in komplexen Geometrien – Methodenentwicklung und Experimente
Neumann, M.ORC; Hampel, U.ORC
Das Gesamtziel des Vorhabens war die Verbesserung der methodischen experimentellen Basis für die Weiterentwicklung von CFD-Codes zur Berechnung dreidimensionaler zweiphasiger Strömungsvorgänge, wie sie im Kühlkreislauf von Kernkraftwerken auftreten. Es ordnet sich damit in das strategische Ziel der Reaktorsicherheitsforschung ein, wobei die nachhaltige Verbesserung der experimentellen Basis zur Validierung von CFD-Modellen für die Berechnung sicherheitsrelevanter Strömungsvorgänge in Kernkraftwerken im Fokus stand. Die erzielten Ergebnisse der experimentellen Studien liefern zudem wertvolle Grundlagenkenntnisse zu Zweiphasenströmungen sowie Validierungsdaten für zukünftige Weiterentwicklungen von CFD-Codes.
Wesentliche Bestandteile aktueller CFD-Code-Weiterentwicklung, speziell für den Reaktorkreislauf, sind die Turbulenzmodellierung und Zweiphasenströmungen. Hierfür werden räumlich und zeitlich hochaufgelöste experimentelle Validierungsdaten benötigt. In diesem Vorhaben wurden dafür zwei moderne Messverfahren für die Charakterisierung von zweiphasigen Strömungen eingesetzt. Mit diesen wurden die Phasenverteilung und Gasphasendynamik, sowie Flüssigphasengeschwindigkeit und Turbulenz in ausgewählten generischen Experimenten untersucht.
Weiterhin wurden in diesem Vorhaben ausgewählte experimentelle Ergebnisse mit CFD-Vorausrechnungen verglichen. Die zweiphasige Strömungssimulation wurde mit dem verfügbaren Simulationswerkzeug ANSYS-CFX durchgeführt, um für diesen Anwendungsfall bereits verfügbare Standardmodelle auf ihre Anwendbarkeit zu prüfen.
Keywords: ultrafast x-ray CT, hot-wire anemometry, two-phase flow, bubbly pipe flow, three-dimensional flow, obstacle, CFD
  • Other report
    Dresden: Eigenverlag, 2019
    147 Seiten

Publ.-Id: 29604 - Permalink

Investigation of three-dimensional two-phase flow using combined ultrafast X-ray tomography and hot-film anemometry
Neumann, M.ORC; Hampel, U.ORC
Gas-liquid two-phase flow modelling is of highest relevance in nuclear safety analyses. This concerns e.g. the modelling of steam-water two-phase flow and heat transfer in the reactor core, the steam generators, the containment and the spent fuel pool under accident conditions. Prediction of flow conditions by Computational Fluid Dynamics (CFD) tools is of particular interest for supporting safety assessments. However, achieving physically correct simulations is quite challenging due to the complexity of the flow, which includes turbulence, highly deformable gas-liquid interfaces and heat, mass and momentum transfer across the interfaces. Today, two-phase flow models contain a large number of empirical correlations and closure models, which are derived from experimental data. The role of thermal hydraulics experiments nowadays still lies in the creation of such data but moreover they are also needed for model validation.
This contribution describes an experimental study of a generic three-dimensional two phase flow, which should serve as a future benchmark experiment for CFD code validation. The experiments were conducted at the Transient Two-Phase Flow (TOPFLOW) facility at Helmholtz-Zentrum Dresden – Rossendorf (HZDR) and are a continuation of earlier studies, which were performed using a moveable flow obstacle and the wire-mesh sensor technique. Although these investigations already provided very good data for a generic two-phase flow, the intrusiveness of both sensor and obstacle motion unit lead to some non-idealities with respect to the fully undisturbed flow. With a new imaging technique, ultrafast electron beam X-ray tomography, we are now able to perform investigations fully non-intrusively and to study the gas phase dynamics with high temporal and spatial resolution in two planes simultaneously. Furthermore, the previous studies did not provide measurement data of liquid velocities, which are required for CFD code validation. Thus, for this study ultrafast X-ray tomography and hot-film anemometry was used in combination to extend the available experimental database. This paper presents selected results of this experimental study.
Keywords: ultrafast x-ray CT, hot-wire anemometry, two-phase flow, bubbly pipe flow, three-dimensional flow, obstacle, CFD
  • Lecture (Conference)
    50th Annual Meeting on Nuclear Technology, 07.-08.05.2019, Berlin, Deutschland
  • Contribution to proceedings
    50th Annual Meeting on Nuclear Technology, 07.-08.05.2019, Berlin, Dresden
    Proceedings of the 50th Annual Meeting on Nuclear Technology

Publ.-Id: 29603 - Permalink

Investigation of three-dimensional two-phase flow using combined ultrafast X-ray tomography and hot-film anemometry
Neumann, M.ORC; Hampel, U.ORC
In vielen industriellen Prozessen und Apparaten treten Mehrphasenströmungen auf. Dies sind häufig Flüssigkeits-Gas-Strömungen, beispielsweise in der Kraftwerkstechnik, in Wärmetauschern, chemischen Reaktoren und Trennapparaten oder in Ölfördersystemen. Ein großes Ziel ist die Berechnung solcher Strömungen mittels computergestützter Simulationswerkzeuge (CFD Codes) zur Unterstützung der Auslegung, zur Optimierung, aber auch zur Sicherheitsbewertung. Die komplexe Physik von Zweiphasenströmungen erschwert dieses Vorhaben im Vergleich zu einphasigen Strömungen erheblich. Grund dafür ist die Komplexität der Transportprozesse über stark verformbare und sich verändernde Phasengrenzflächen in mehreren Zeit- und Längenskalen. Zudem werden durch anlagentechnische Komponenten, wie beispielsweise Krümmer, Ventile, T-Stücke oder querschnittsverändernde Einbauten, ausgeprägte dreidimensionale Strömungsfelder erzeugt, welche von aktuellen CFD-Codes nur sehr stark eingeschränkt berechnet werden können.
Der Beitrag beschäftigt sich mit der experimentellen Untersuchung von generischen dreidimensionalen Zweiphasenströmungen. Mit Hilfe neuartiger experimenteller Methoden wurde eine Datenbasis für die nachhaltige Validierung und Weiterentwicklung von CFD-Codes, speziell für dreidimensionale Strömungseffekte, generiert.
Keywords: ultrafast x-ray CT, hot-wire anemometry, two-phase flow, bubbly pipe flow, three-dimensional flow, obstacle, CFD
  • Lecture (Conference)
    Jahrestreffen Reaktionstechnik 2019 gemeinsam mit der Fachgruppe Mehrphasenströmungen, 27.-29.05.2019, Würzburg, Deutschland

Publ.-Id: 29602 - Permalink

Experimental investigation of three-dimensional bubbly two-phase pipe flows
Neumann, M.ORC; Hampel, U.ORC
Modelling gas-liquid two-phase flow is a topic of constant relevance in nuclear thermal hydraulics. Gas-disperse two-phase flows occur in e.g. fuel elements in the reactor core, in pipes and components during pressure loss, sudden reflooding or other events. Due to the deformable gas-liquid interface and the complexity of heat, mass and momentum transfer across the interface, gas-liquid two-phase flow is very difficult to model and simulate. On the device scale it is common to use Euler/Euler multi-fluid approaches for CFD simulations, which require a good number of empirical correlations as closure models. Such models are commonly derived from experiments. Validation of the correctness of predictive simulations then also requires experiments, which must be simplified to a degree to allow provision of CFD-grade experimental data but complex enough to resemble real flow situations. The latter calls especially for investigations on flow fields in more complex three-dimensional domains, which are prototypical for e.g. bends, valves, T-junctions and rod bundles.
Keywords: ultrafast x-ray CT, two-phas flow, three-dimensional flow, obstacle
  • Lecture (Conference)
    East German Centre of Competence in Nuclear Technology Workshop of Doctoral Candidates, 13.12.2018, Zittau, Deutschland

Publ.-Id: 29601 - Permalink

Mitigating Meniscus Instabilities in Solution-Sheared Polymer Films for Organic Field-Effect Transistors
Da Rocha, C. T.; Qu, G.; Yang, X.ORC; Shivhare, R.; Hambsch, M.; Diao, Y.; Mannsfeld, S. C. B.
Semiconducting donor−acceptor copolymers are considered to be a promising material class for solution-coated, large-scale organic electronic applications. A large number of works have shown that the best-performing organic field-effect transistors (OFETs) are obtained on low-surface-energy substrates. The meniscus instabilities that occur when coating on such surfaces considerably limit the effective deposition speeds. This represents a limiting factor for the upscaling of device fabrication for mass production, an issue that needs to be addressed if organic electronic devices are ever to become commercially relevant. In this work, we present a method to increase the accessible window of coating speeds for the solution shearing of donor−acceptor semiconductor polymers for the fabrication of OFETs. By incorporating a piezo crystal that is capable of producing high-frequency vibrations into the coating head, we are able to mitigate contact line instabilities due to the depinning of the contact line, thereby suppressing the commonly encountered “stick-and-slip” phenomenon.
Keywords: organic field-effect transistors, solution shearing, meniscus instabilities, vibration, large-area fabrication


  • Secondary publication expected from 12.08.2020

Publ.-Id: 29600 - Permalink

p-type codoping effect in (Ga,Mn)As: Mn lattice location versus magnetic properties
Xu, C.ORC; Zhang, C.; Wang, M.; Xie, Y.; Hübner, R.; Heller, R.; Yuan, Y.; Helm, M.; Zhang, X.; Zhou, S.
In the present work, we perform a systematic investigation on p-type codoping in (Ga,Mn)As. Through gradually increasing Zn doping concentration, the hole concentration increases, which should theoretically lead to an increase of the Curie temperature (TC) according to the p-d Zener model. Unexpectedly, although the film keeps its epitaxial structure, both TC and the magnetization decrease. The samples present a phase transition from ferromagnetism to paramagnetism upon increasing hole concentration. In the intermediate regime, we observe a signature of antiferromagnetism. By using channeling Rutherford backscattering spectrometry and particle-induced x-ray emission, the substitutional Mn atoms are observed to shift to interstitial sites, while more Zn atoms occupy Ga sites, which explains the observed behavior. This is also consistent with first-principles calculations, showing that the complex of substitutional Zn and interstitial Mn has the lowest formation energy.


Publ.-Id: 29599 - Permalink

Background in γ-ray detectors and carbon beam tests in the Felsenkeller shallow-underground accelerator laboratory
Szücs, T.ORC; Bemmerer, D.ORC; Degering, D.; Domula, A.; Grieger, M.; Ludwig, F.; Schmidt, K.; Steckling, J.; Turkat, S.; Zuber, K.
The relevant interaction energies for astrophysical radiative capture reactions are very low, much below the repulsive Coulomb barrier. This leads to low cross sections, low counting rates in γ-ray detectors, and therefore the need to perform such experiments at ion accelerators placed in underground settings, shielded from cosmic rays. Here, the feasibility of such experiments in the new shallow-underground accelerator laboratory in tunnels VIII and IX of the Felsenkeller site in Dresden, Germany, is evaluated. To this end, the no-beam background in three diff erent types of germanium detectors, i.e. a Euroball/Miniball triple cluster and two large monolithic detectors, is measured over periods of 26-66 days. The cosmic-ray induced background is found to be reduced by a factor of 500-2400, by the combined eff ects of, first, the 140 meters water equivalent overburden attenuating the cosmic muon flux by a factor of 40, and second, scintillation veto detectors gating out most of the remaining muon-induced eff ects. The new background data are compared to spectra taken with the same detectors at the Earth’s surface and at other underground sites. Subsequently, the beam intensity from the cesium sputter ion source installed in Felsenkeller has been studied over periods of several hours. Based on the background and beam intensity data reported here, for the example of the 12 C(α,γ) 16 O reaction it is shown that highly sensitive experiments will be possible.
Keywords: Nuclear Astrophysiscs; Underground experiment, sputter source, Felsenkeller

Publ.-Id: 29598 - Permalink

Photodecarbonylation and in vitro studies of dicarbonyl ruthenium complexes
Kubeil, M.ORC; Geri, S.; Stephan, H.
Carbon monoxide has been demonstrated to exhibit several beneficial effects on biological targets (anti-inflammatory, anti-proliferative, anti-apoptotic effects, causes vasodilation, etc.).[1] Consequently, the development of CO releasing molecules (CORMs) that allows a controlled release of CO under physiological conditions has therefore become a major field of scientific and medical interest.[2] Considerable research interest has been drawn on light-activated CORMs (photoCORMs) which only release CO upon radiation with certain wavelengths. However, despite a large number of photoCORMs reported, relatively little information is available on the precise mechanism of CO release from most photoCORMs and even less compounds have been tested as anti-cancer agents in cells so far. Herein, we report the synthesis of ruthenium(II) carbonyl complexes functionalized with (fluorescent) bidentate pyridyl (1) and tridentate diquinolyl ligands (2) and investigate the mechanism of CO release in aqueous media (before and after light-activation). The photo-induced CO release kinetics of the Ru(II) photoCORMs, as well as in vitro studies in cancerous and healthy cell lines will be presented [3].

[1] R. Motterlini, L. E. Otterbein, Nat. Rev. Drug Discov. 9 (2010) 728-743.
[2] U. Schatzschneider, Br. J. Pharmacol. 172 (2015) 1638-1650.
[3] M. Kubeil, R. R. Vernooij, C. Kubeil, B. R. Wood, B. Graham, H. Stephan, L. Spiccia, Inorg. Chem.
56 (2017) 5941-5952.
[4] M. Kubeil, T. Joshi, B. R. Wood, H. Stephan, ChemistryOpen (2019) accepted.
  • Lecture (Conference)
    19th International Conference on Biological Inorganic Chemistry, 11.-16.08.2019, Interlaken, Schweiz

Publ.-Id: 29597 - Permalink

Carbon nanotubes for mechanical sensor applications
Wagner, C.ORC; Meszmer, P.ORC; Blaudeck, T.ORC; Böttger, S.ORC; Fuchs, F.ORC; Hermann, S.; Schuster, J.ORC; Wunderle, B.; Schulz, S. E.
This article features the evolution of carbon nanotubes as functional material in nano and microelectromechanical systems. Introducing materials morphologies for the CNTs in a homologue series (single CNTs - bundles, fibers, yarns - networks and thin films), different concepts for mechanical sensors based on the intrinsic and extrinsic properties of the CNT material are introduced (piezoresistive effect, strain-induced band bending, charge tunneling).
In a rigorous theoretical treatment, the limits of the achievable sensor performance (i.e., gauge factor) are derived and discussed in the context of applications. A careful literature survey shows that highest sensitivity is reached for devices exploiting the intrinsic transport properties of single CNTs. For reliability tests of such sensor systems made from nanomaterials and classical MEMS, a specimen-centered approach is introduced to give viable insights into the structure-property relationships and failure modes.
Keywords: carbon nanotubes (CNTs), sensors, micro- and nano electromechanical systems (MEMS, NEMS), strain, reliability


  • Secondary publication expected from 09.09.2020

Publ.-Id: 29595 - Permalink

Interlayer excitons in van-der-Waals heterostructures: MoS2 on GaSe
Wagner, C.ORC; Rahaman, M.; Zahn, D. R. T.; Gemming, S.
Hybrid van-der-Waals heterostructures of two-dimensional nanomaterials are a vibrant field of study: The (weak) electronic interaction between two layers is often reasonably described by a perturbation of the physical effects of the isolated layers, such as electrostatic doping and increased screening of intralayer excitons. However, it turns out that this picture of the weak interaction is not exhaustive in terms of all optical properties: the formation of bound excitons from electrons of one layer and holes from the other layer yields the formation of interlayer excitons. These mixed states are measured experimentally by photoluminescence and photocurrents and predicted by theory. Examples are of MoS2 or MoSe2 on WSe2, MoS2 or GaSe due to type-II band alignment [1-3].
The conditions for the formation of interlayer excitons are elucidated from a first-principles point of view. For this, first-principles studies of a minimal test system of MoS2 on GaSe is conducted [1].
This work envisions to predict the interlayer states as a function of the heterostack in order to specifically tailor efficient photon absorption.
Keywords: 2D materials, DFT, Bethe-Salpeter, Density-functional perturbation theory, MoS2, GaSe, bilayer, van-der-Waals heterostructure, interlayer exciton
  • Lecture (Conference)
    Chem2DMat, 03.-06.09.2019, Dresden, Deutschland

Publ.-Id: 29594 - Permalink

Order/disorder processes and electromechanical properties of monoclinic GdCa4O(BO3)3
Münchhalfen, M.; Schreuer, J.; Reuther, C.; Möckel, R.; Götze, J.; Mehner, E.; Stöcker, H.; Meyer, D.;
Large single crystals of GdCa₄O(BO₃)₃ (space group Cm) were grown by the Czochralski method. Dielectric, piezoelectric and elastic coefficients at room temperature as well as specific heat capacity, thermal expansion and cation disorder were studied employing a variety of methods including resonant ultrasound spectroscopy, differential scanning calorimetry, dilatometry and X-ray diffraction techniques. The electromechanical parameters (4 dielectric, 10 piezoelectric and 13 elastic stiffness coefficients) obtained on different samples are in excellent agreement indicating high internal consistency of our approach, whereas the values reported in literature differ significantly. The elastic behaviour of GdCa₄O(BO₃)₃ resembles the one of structurally related fluorapatite, i.e. the elastic anisotropy is relatively small and the longitudinal effect of the deviations from Cauchy-relations exhibit a pronounced minimum along the direction of the dominating chains of cation polyhedra. GdCa₄O(BO₃)₃ exhibits a maximum longitudinal piezoelectric effect of 7.67 × 10−12 CN−10, a value in the order of that of langasite-type materials. Significant changes of the calcium/gadolinium distribution on the 3 independent cation sites accompanied by characteristic anomalies of heat capacity and thermal expansion suggest processes of nonconvergent cation ordering above about 900 K in GdCa₄O(BO₃)₃.
Keywords: elasticity; GdCa₄O(BO₃)₃; heat capacity; nonconvergent cation ordering; piezoelectricity; thermal expansion

Publ.-Id: 29591 - Permalink

Sample preparation for AMS astrophysics projects – Size does (not) matter
Merchel, S.ORC; Child, D.; Faestermann, T.; Fröhlich, M.; Golser, R.; Hotchkis, M.; Koll, D.; Korschinek, G.; Pavetich, S.; Wallner, A.; a lot of more AMS colleagues
The determination of long-lived radionuclides by means of accelerator mass spectrometry (AMS) is usually outstandingly successful when an interdisciplinary team comes together. The “heart” of AMS research is of course an accelerator equipped with sophisticated ion sources, analytical tools and detectors run by experienced and ambitious physicists [e.g. 1-3]. Setting-up and further developing AMS systems is one of the most interesting and challenging topics. The reputation to be reached here is the greatest uniqueness of analysis possible, lowest detection levels, and/or most reliable data world-wide.
For sure, another primary pillar of AMS research is based on the questions addressed within fundamental and applied research. “How have supernovae explosions influenced Earth, our solar system and beyond?” [e.g. 4] or “How does the Earth’s surface and environment respond to earthquakes, climate change and anthropogenic influences?” [e.g. 5] are just two examples of high-quality studies.
However, somehow in-between there are groups of hidden figures like people developing software for data analysis or performing the required chemical sample preparation for AMS. These often unacknowledged individuals do crucial work for the overall outcome of the studies.
Chemists can spend weeks and months trying (and failing) on sample preparation before they find a “safe way” and start the actual work on the most valuable sample material, repeat all over again the same “recipe” for hundreds of samples, or train non-chemists the secrets of their successful recipes. Nevertheless, interdisciplinary AMS work can also be very exciting for a chemist: touching (and destroying) samples from outer space, the deep ocean or (currently) frozen places like Antarctica is quite thrilling. But at the end of the day, the whole AMS chemist’s work can be described as “reducing the sample matrix, other impurities and especially isobars to a level the AMS machine can handle while enriching the radionuclide of interest”.
Starting materials for applications such as astrophysical research can be “orders of magnitude” different: a neutron-irradiated sample of 1 g tungsten powder [6], over 40 g of clay-rich material from the Cretaceous–Tertiary (K-T) boundary, 100 g of ultra-pure sodium iodide, or 500 kg of snow from Antarctica [4] can cause totally different and sometimes unexpected problems in the chemistry lab. In general, smaller samples are not always easier to handle for example if they are chemically rather resistant or reactive. The cream of the crop of failure and success in a few AMS chemistry labs will be presented.

[1] P. Steier et al., Int. J. Mass Spectr. 444, 116175 (2019).
[2] G. Rugel et al., Nucl. Instr. Meth. B 370, 94 (2016).
[3] D. Koll et al., Nucl. Instr. Meth. B 438, 180 (2019).
[4] D. Koll et al., Phys. Rev. Lett. 123, 072701 (2019) and this meeting.
[5] W. Schwanghart et al., Science 351, 147 (2016).
[6] M. Martschini et al., this meeting.
Keywords: AMS, long-lived radionuclides
  • Lecture (Conference)
    Heavy Ion Accelerator Symposium on Fundamental and Applied Science (HIAS), 09.-13.09.2019, Canberra, Australia

Publ.-Id: 29588 - Permalink

Lanthanide–induced conformational change of methanol dehydrogenase involving coordination change of cofactor pyrroloquinoline quinone
Tsushima, S.ORC
There is emerging interests to the role of lanthanides as cofactor in XoxF-type methanol dehydrogenase (MHD). Here, classical molecular dynamics simulations combined with fragment molecular orbital calculations were employed to rationalize enzymatic activities of MHD (both XoxF- and MxaF- types) carrying different lanthanides. In XoxF–type MDH, lanthanide binding to cofactor pyrroloquinoline quinone was found to switch from tridentate to unidentate fashion as it switches from lighter to heavier lanthanide. This fact possibly plays crucial role to the enzymatic activity exclusive to XoxF–type MDH incorporating lighter lanthanides.
  • Physical Chemistry Chemical Physics 21(2019), 21979-21983
    DOI: 10.1039/C9CP03953H
  • Poster
    17th International Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere (Migration 2019), 15.-20.09.2019, Kyoto, Japan

Publ.-Id: 29587 - Permalink

A theranostic PSMA ligand for PET imaging and retargeting of T cells expressing the universal chimeric antigen receptor UniCAR
Arndt, C.; Feldmann, A.ORC; Koristka, S.; Schäfer, M.; Bergmann, R.ORC; Metwasi, N.; Berndt, N.; Bachmann, D.; Kegler, A.; Schmitz, M.; Puentes-Cala, E.; Soto, J. A.; Ehninger, G.; Pietzsch, J.; Liolios, C.; Wunderlich, G.; Kotzerke, J.; Kopka, K.ORC; Bachmann, M.ORC
Chimeric antigen receptor (CAR) T cells have shown impressive therapeutic potential. Due to the lack of direct control mechanisms, therapy-related adverse reactions including cytokine release- and tumor lysis syndrome can even become life-threatening. In case of target antigen expression on non-malignant cells, CAR T cells can also attack healthy tissues. To overcome such side effects, we have established a modular CAR platform termed UniCAR: UniCAR T cells per se are inert as they recognize a peptide epitope (UniCAR epitope) that is not accessible on the surface of living cells. Bifunctional adapter molecules termed target modules (TM) can cross-link UniCAR T cells with target cells. In the absence of TMs, UniCAR T cells automatically turn off. Until now, all UniCAR TMs were constructed by fusion of the UniCAR epitope to an antibody domain. To open up the wide field of low-molecular weight compounds for retargeting of UniCAR T cells to tumor cells, and to follow in parallel the progress of UniCAR T cell therapy by PET imaging we challenged the idea to convert a PET tracer into a UniCAR-TM. For proof of concept, we selected the clinically used PET tracer PSMA-11, which binds to the prostate-specific membrane antigen overexpressed in prostate carcinoma. Here we show that fusion of the UniCAR epitope to PSMA-11 results in a low-molecular weight theranostic compound that can be used for both retargeting of UniCAR T cells to tumor cells, and for non-invasive PET imaging and thus represents a member of a novel class of theranostics.
Keywords: PSMA ligand, UniCAR, prostate cancer, immunotherapy, PET imaging

Publ.-Id: 29586 - Permalink

1,4,7-Triazacyclononane ligands as bifunctional radiocoppper chelating agents
Stephan, H.; Joshi, T.;
design of tailor-made bifunctional chelating agents (BFCAs) for radioactive transition metals in view of nuclear medical applications as well as acquisition of reliable information about the biodistribution of different materials represents an intensive and rapidly developing field of research [1]. In this context, the tridentate macrocycle 1,4,7-triazacyclononane (TACN) is of special interest since it forms stable complexes with transition metal ions particularly with Cu(II) [2]. Further, the introduction of donor groups, such as pyridyl units, on the TACN scaffold, significantly enhances the thermodynamic stability as well as the kinetic inertness of the Cu(II) complexes formed. Furthermore, the ligand structure offers various possibilities to introduce biological vectors and suitable linkers for tuning the lipophilicity, overall charge and aqueous solubility of the final bioconjugates. For example, TACN ligands with two pyridylmethyl side-arms (DMPTACN derivatives) rapidly chelate copper(II) radionuclides under ambient conditions and the resulting complexes show high in vivo stability. One such derivative, 2-[4,7-bis(2-pyridylmethyl)-1,4,7-triazacyclononan-1-yl]acetic acid (DMPTACN-COOH), containing two coordinating picoline groups, not only exhibits excellent in vivo stability after 64Cu radiolabeling, but also allows for direct attachment of vector molecules as well as easy introduction of bioconjugatable functionalities (e.g., maleimide, isothiocyanate) via the carboxylate pendant. This makes DMPTACN-COOH and its derivatives promising BFCAs for radiocopper (DMPTACN-based BFCAs), facilitating the preparation of radiolabeled targeting molecules and bio(nano)materials.
Examples of target-specific peptides and bio(nano)materials equipped with DMPTACN ligands for labeling with 64Cu as an ideal positron emitter are discussed. This enables tumor imaging and the biodistribution of the materials to be studied over a period of days via positron emission tomography (PET).

[1] E. Boros, A. B. Packard, Chem. Rev. 119 (2019) 870-901.
[2] T. Joshi, M. Kubeil, A. Nsubuga, G. Singh, G. Gasser, H. Stephan, ChemPlusChem 83 (2018) 554-564.
  • Lecture (Conference)
    19th International Conference on Biological Inorganic Chemistry, 11.-16.08.2019, Interlaken, Schweiz

Publ.-Id: 29584 - Permalink

PIConGPU simulation setup for L|PWFA simulation
Pausch, R.ORC; Steiniger, K.ORC; Debus, A.ORC

The input set of the L|PWFA simulation as used in the publication "Demonstration of a compact plasma wakefield accelerator powered by laser-accelerated electron beams" by T.Kurz et al. .
To run the simulation use PIConGPU 0.4.2 (see DOI: 10.5281/zenodo.1491926).           

  • Software in the HZDR data repository RODARE
    Publication date: 2019-08-19
    DOI: 10.14278/rodare.146
    License: CC-BY-4.0


Publ.-Id: 29581 - Permalink

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