Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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35174 Publications

Synthesis, Receptor Affinity, and Antiallodynic Activity of Spirocyclic σ Receptor Ligands with Exocyclic Amino Moiety

Bergkemper, M.; Kronenberg, E.; Thum, S.; Börgel, F.; Daniliuc, C.; Schepmann, D.; Nieto, F. R.; Brust, P.; Reinoso, R. F.; Alvarez, I.; Wünsch, B.

In order to detect novel σ receptor ligands, the rigit spiro [[2]benzopyran-1,1'-cyclohexan]-4'-one was connected with amino moieties derived from σ2 receptor preferring lead compounds resulting in mixtures of trans- and cis-configured amines 6, 18, and 27. In a four step synthesis the methyl acetals 6 were converted into fluoroethyl derivatives 13 and 30. The most promising σ2 receptor ligand is the methyl acetal 6a bearing a 2,4-dimethylbenzylamino moiety. The fluoroethyl derivatives 13c and 13d reveal high σ1 affinity but moderate selectivity over the σ2 subtype. In mice 13c and 13d showed antiallodynic activity that is stronger than that of the reference σ1 antagonist BD-1063 (34). Since the antiallodynic activity of 13c could only be partially reversed by the σ1 agonist PRE-084 (35), it is postulated that a second mechanism contributes to its overall antiallodynic effect. In contrast, the antiallodynic effect of its diastereomer 13d can be totally explained by a σ1 antagonism.


Publ.-Id: 28319

The Serial Interface Package -- v2.0

Seilmayer, M.

The 'serial' package as an extension to the programming language R enables reading and writing binary and ASCII data to RS232/RS422/RS485 or any other virtual serial interfaces of the computer.

Keywords: serial interface; RS232; RS422; RS485; R

  • Software in external data repository
    Publication year 2018
    Programming language: R
    System requirements: Windows, Mac, Unix
    License: GPL-2
    Hosted on Link to location

Publ.-Id: 28318

Characterization and beneficiation of pyrolyzed black mass from spent lithium ion batteries

Vanderbruggen, A.

The lithium-ion battery (LiB) market is growing rapidly which leads to a considerable increase of LiB wastes. Despite the enhancement in graphite consumptions, there is no graphite recycling process from LiBs so far. Thus, graphite usually remains in slags from the metallurgical treatments.
The LiB components contain cobalt (Co), lithium (Li) and graphite, counted as critical materials. The aim of the present thesis is to increase the recycling recovery of the LiBs by developing a new innovative process, which minimizes metal losses and is able to recover graphite. By using flotation two valuable products, one of graphite and one with the valuable metals, are recovered in the light of their integration to the value chain of LiB production.
Mineral liberation analysis (MLA), x-ray fluorescence (XRF) and x-ray diffraction (XRD) were used for characterization of the black mass to understand the liberation behavior of the crushed LiB particles. Flotation tests were carried out in an Outotec GTK Labcell, the main studied parameters are the pre-treatment with attritioning, the flotation pH and the reagents dosages. Kerosene was used as a promoter for graphite and MIBC as a frother.
It was found that graphite particles were fully liberated from the copper foils, and the organic layer on the active particles was removed which increases the separation efficiency. However, only 62 wt. % of the cathode active particles are liberated from the aluminum foil. Based on this characterization results, particularly the liberation degree, a new flowsheet is designed to concentrate all the active material (graphite, Co, Ni, Mn and Li) in the < 50 μm fraction without current foil particles. Flotation studies show that pretreatment, such as attritioning, improved the process efficiency while preserving the spherical shape of graphite. Graphite recovery is +98 % with a grade of 72 wt. % and the tailings recover more than 90% of the precious metals Co, Ni and Li from the spent LiBS, with the respective grades 27 wt. % Co, 7 wt. % and 2.5 wt. % Li. Most of the concentrate impurities are fine particles from cathode active materials, which could be removed with a desliming process and flotation cleaner stages. This research is at its beginning and is expected to bring about an innovative and useful process for the recycling industry, despite the challenges involved. This process can recover the graphite and the lithium, which are usually ending the slags. At present, there might be legitimate questions regarding the expense and benefits of graphite recycling. However, the treatment of LiBs will become necessary in the near future due to environmental issues as well as the scarcity and criticality of LiB components. Consequently, graphite will become a valuable and needed by-product from the metals recycling. The dependence on imports of graphite from China would be reduced, providing a solution to meet the significant predicted demand of battery grade graphite. Moreover, LiB as a key driver of the transition away from a carbon-based economy, it is necessary to ensure a truly positive impact over the lifecycle of LiB, and consequently to reach a closed-loop system.

Keywords: Attritionning; black mass; characterization; flotation; graphite; mineral liberation analysis (MLA); pre-treatment; recycling; spent lithium-ion battery; surface analysis

  • Master thesis
    TU Freiberg, 2018
    Mentor: Dr. Martin Rudolph

Publ.-Id: 28317

Characterization and beneficiation of pyrolyzed black mass from lithium ion batteries

Vanderbruggen, A.; Gilbricht, S.; Möckel, R.; Rudolph, M.

The lithium-ion battery (LiB) market is growing rapidly. Consequently, LiB wastes will increase in the future and LiB components such as Co, Li, but also graphite, are forecast to be critical materials. These critical materials are contained in the black mass produced by LiBs recycling. This original research focuses on graphite beneficiation from cathode lithium metal oxides by flotation. Detailed characterization of the pyrolyzed black mass (inculding MLA, XRF and XRD) shows that the graphite particles are fully liberated from the copper foils, and the organic layer PVDF is removed. Batch flotation shows that pretreatment, such as attritioning, improves process efficiency while preserving the shape of spheriodized graphite. Concentrate impurities mainly comprise fine particles from cathode active materials, which can be removed with desliming and flotation cleaner stages. As an outlook, this reasearch is expected to bring about an innovative and useful process for the recycling industry.

Keywords: Attritionning; black mass; characterization; flotation; graphite; mineral liberation analysis (MLA); pre-treatment; recycling; spent lithium ion battery; surface analysis

  • Poster
    Minerals Engineering International (MEI) conference: Process Mineralogy '18, 19.-21.11.2018, Cape Town, South Africa

Publ.-Id: 28316

Serpent solution of the X2 VVER-1000 benchmark fresh core experiments

Bilodid, Y.; Fridman, E.

The X2 VVER-1000 benchmark describes first 4 fuel cycles of the Khmelnitsky NPP 2nd unit with VVER-1000 reactor as well as some operational transients. The benchmark specifications contain description of the reactor core material, geometry and operational history supplemented by measured operational data and startup experiments. In this work, the hot zero power experiments conducted during the fresh core startup are modelled with the Serpent-2 Monte Carlo code. The numerical results are validated against the available measured core data. The calculated and measured values of a critical boron concentration, temperature reactivity effect, and control rod worth are in a very good agreement while the deviations lay within the measurement uncertainties. Since the power distribution was not measured at the hot zero power state, the obtained Serpent solution could be used as a reference for a deterministic codes verification.

Keywords: X2 benchmark; VVER-1000; Serpent

  • Contribution to proceedings
    PHYSOR 2018: Reactor Physics Paving The Way Towards More Efficient Systems, 22.-26.04.2018, Cancun, Mexico, 1982-1989

Publ.-Id: 28315

Doping issues in silicon nanowires by ion implantation and flash lamp annealing

Berencen, Y.; Prucnal, S.; Wang, M.; Rebohle, L.; Helm, M.; Zhou, S.; Skorupa, W.

Semiconducting nanowires (NWs) hold promises for functional nanoscale devices. Although several applications have been demonstrated in the areas of electronics, photonics and sensing, the doping of NWs remains challenging. Ion implantation is a standard doping method in top-down semiconductor industry, which offers precise control over the areal dose and depth profile as well as allows for the doping of all elements of the periodic table even beyond their equilibrium solid solubility. Yet its major disadvantage is the concurrent material damage. A subsequent annealing process is commonly used for the healing of implant damage and the electrical activation of dopants. This step, however, might lead to the out-diffusion of dopants and eventually the degradation of NWs because of the low thermal stability caused by the large surface–area-to-volume ratio.

In this work, we report on non-equilibrium processing (flash lamps) for controlled doping of drop-casted Si/SiO2 core/shell NWs with shallow- and deep-level dopants below and above their equilibrium solid solubility. The approach lies on the implantation of either shallow-level dopants, such as B and P, or deep-level dopants like Se followed by millisecond flash lamp annealing. In case of amorphization upon high-fluence implantation, recrystallization takes place via a bottom-up template-assisted solid phase epitaxy. Non-equilibrium Se concentrations lead to intermediate-band Si/SiO2 core/shell NWs that have room-temperature sub-band gap photoresponse when configured as a photoconductor device [1]. Alternatively, the formation of a cross-sectional p-n junction is demonstrated by co-implanting P and B in individual NWs at different depth along the NW core.
[1] Y. Berencén, et al. Adv. Mater. Interfaces 2018, 1800101

Keywords: doping; nanowires; semiconductor; silicon; ion implantation; flash lamp annealing

  • Lecture (Conference)
    22nd International Conference on Ion Implantation Technology, 16.-21.09.2018, Würzburg, Deutschland

Publ.-Id: 28313

Hydrodynamics, mixing and mass transfer in a pilot-scale bubble column with dense internals

Möller, F.; Lavetty, C.; Schleicher, E.; Löschau, M.; Hampel, U.; Schubert, M.

Bubble column reactors with exothermic reactions are often equipped with dense tube bundle heat exchangers. While there is some knowledge about the impact of such internals on hydrodynamics and mass transfer for narrow columns, its role in pilot-scale columns is less clear. In this paper we report on a study of hydrodynamics and mass transfer in a BCR of 4.2 m height and 0.392 m diameter. We investigated different tube arrangements with triangular and square pitch and tube diameters of 32×10-3 m and 45×10-3 m at the same cross-sectional coverage (~25%). The column was operated at homogeneous and heterogeneous flow conditions. A customized three-layer wire-mesh sensor was utilized to visualize gas phase dynamics and liquid mixing characteristics in the column’s cross-section. We found that sub-channel size is the most crucial geometric design parameter. Tracer mixing experiments reveal that internals enhance the liquid dispersion due to induction of large-scale liquid circulation. Mass transfer was studied with the oxygen stripping method. Here we found, that the effect of the internals on the gas-liquid mass transfer is almost negligible. Eventually, correlations for gas holdup, axial liquid dispersion and the volumetric gas-liquid mass transfer coefficient are given, which take the internals’ geometry into account.

Keywords: Pilot-scale bubble column; Heat exchanger internals; Hydrodynamics; Liquid mixing; Mass transfer; Wire-mesh sensor


Publ.-Id: 28312

Advanced doping issues using nonequilibrium processing

Skorupa, W.; Rebohle, L.; Prucnal, S.; Berencen, Y.; Zhou, S.; Helm, M.

In this talk I will introduce with a short view on the background of the transistor invention as a key element driving the topic of semiconductor doping. After that I will discuss examples of advanced doping including ion beam based and other methods: doping and alloying of germanium, hyperdoping of silicon, doping from deposited layers, doping of silicon nanowires, doping from deposited layers. In all cases the experiments were performed in correlation to nonequilibrium thermal processing using flash lamps in the millisecond time range.

Keywords: semiconductor doping; ion beam based methods; flash lamp annealing

  • Lecture (others)
    Eingeladener Seminarvortrag an der Marie-Curie-Universität Lublin/Polen, 11.10.2018, Lublin, Polen

Publ.-Id: 28311

Dataset on characterization, ion irradiation and nanoindentation of ODS Fe14Cr-based alloys

Bergner, F.

The dataset comprises raw data of the nanoindentation tests and processed data on the ion irradiations and irradiation-induced hardness changes. File formats are excel, word, origin and ascii.

Related publications

  • Reseach data in the HZDR data repository RODARE
    Publication date: 2018-12-04
    DOI: 10.14278/rodare.72


Publ.-Id: 28310

Bonding and stability analysis of tetravalent f-element complexes with mixed N-, O-donor ligands

Kloditz, R.; Radoske, T.; Patzschke, M.; Stumpf, T.

The contribution of the f-orbitals leads to a very rich chemistry of the f-elements[1] where it is known that this contribution is less important for lanthanides. Of special interest is the influence of these orbitals on the bonding character of actinides and lanthanides with organic ligands re- flecting natural bonding motifs.
This study shows the different bonding behaviour of tetravalent f-elements with Schiff bases, like salen (see Fig. 1) and derivatives, by means of real-space bonding analysis. This includes the popular quantum theory of atoms in molecules (QTAIM), plots of the non-covalent inter- actions (NCI)[2] and density differences complemented by natural population analysis (NPA). Thermodynamic calculations on the stability of these complexes are presented. The obtained results are a direct consequence of the different interaction strengths of the f-elements.
First studies reveal a strong interaction of the actinides, i.e. Th to Pu, with the oxygen of salen characterized by a high electron density concentration between the atoms. In contrast, the inter- action between the actinides and the nitrogen of salen is much weaker.
By acquiring knowledge about the different behaviours of bonding and complexation it is possi- ble to understand the chemical properties of the f-elements and predict yet unknown complexes.

Keywords: Bonding analysis; Theoretical Chemistry; DFT; QTAIM; Actinides

  • Poster
    Symposium on Theoretical Chemistry, 17.-20.09.2018, Halle, Deutschland

Publ.-Id: 28309

Nanoindentation of single- (Fe) and dual-beam (Fe and He) ion-irradiated ODS Fe-14Cr-based alloys: Effect of the initial microstructure on irradiation-induced hardening

Heintze, C.; Hilger, I.; Bergner, F.; Weissgärber, T.; Kieback, B.

Although the view that nm-sized oxide particles modify and essentially improve the irradiation resistance of Fe-Cr-based alloys is widely accepted, the correctness of this view has only been demonstrated in singular cases. An extension of the field of considered microstructures, irradiation conditions, and measures of irradiation resistance is required. The present study is focused on nanostructured ferritic Fe-14%Cr-based alloys, with and without the addition of 0.6 wt% Y2O3, produced via mechanical alloying and consolidation by spark plasma sintering. The materials were exposed to single-beam (Fe) and dual-beam (Fe+He) ion irradiations at room temperature. The initial microstructures were characterized, bimodal grain size distributions were observed and nanoindentation was applied to measure irradiation hardening for fine-grained and coarse-grained areas separately. We have found that grain size governs irradiation hardening for single-beam irradiation, while oxide nanoparticles play a dominant role for dual-beam irradiations. This sheds a light on the role of particle-matrix interfaces on helium management.

Keywords: Nanostructured ferritic alloys; oxide dispersion strengthening; ion irradiation; dual-beam irradiation; helium; nanoindentation; irradiation hardening

Related publications


Publ.-Id: 28308

Bonding and stability analysis of tetravalent actinide and lanthanide complexes with N,O-donor ligands

Kloditz, R.; Radoske, T.; Patzschke, M.; Stumpf, T.

The contribution of the f-orbitals leads to a very rich chemistry of the f-elements[1] where it is known that this contribution is less important for lanthanides. Of special interest is the influence of these orbitals on the bonding character of actinides and lanthanides with organic ligands reflecting natural binding motifs.
This study shows the different bonding behaviour of tetravalent actinide and lanthanide complexes with Schiff bases, like salen (see Fig. 1) and derivatives, by means of real-space bonding analysis. This includes the popular quantum theory of atoms in molecules (QTAIM), plots of the non-covalent interactions (NCI)[2] and density differences complemented by natural population analysis (NPA). Thermodynamic calculations on the stability of these complexes are done being a direct consequence of the different interaction strengths of the f-elements.
First studies reveal a strong interaction of the actinides, i.e. Th to Pu, with the oxygen of salen characterized by a high electron density concentration between the atoms. In contrast, the interaction between the actinides and the nitrogen of salen is much weaker.
By acquiring knowledge about the different behaviours of bonding and complexation it is possible to understand the chemical properties of the f-elements and predict yet unknown complexes.

Keywords: Bonding; Salen; Actinides; theoretical chemistry; DFT; QTAIM

  • Lecture (Conference)
    International Symposium on Nano and Supramolecular Chemistry, 09.-12.07.2018, Dresden, Deutschland

Publ.-Id: 28307

The Study and Development of Pulsed High-field Magnets for Application in Laser-plasma Physics

Kroll, F.

The thesis at hand addresses design, characterization and experimental testing of pulsed high-field magnets for utilization in the field of laser-plasma physics. The central task was to establish a technology platform that allows to manipulate laser-driven ion sources in a way that the accelerated ions can be used in complex application studies, e.g. radiobiological cell or tumor irradiation.

Laser-driven ion acceleration in the regime of target normal sheath acceleration (TNSA) offers the unique opportunity to accelerate particles to kinetic energies of few 10MeV on the micrometer scale. The generated bunches are short, intense, show broad exponentially decaying energy spectra and high divergence. In order to efficiently use the generated particles, it is crucial to gain control over their divergence directly after their production. For most applications it additionally is favorable to reduce the energy spread of the beam. This work shows that the developed pulsed high-field magnets, so-called solenoids (cylindrical magnets), can efficiently capture, transport and focus laser-accelerated protons. The chromaticity of the magnetic lens thereby provides for energy selection.

Three prototype solenoids, adapted to fit different application scenarios, and associated current pulse drivers have been developed. The magnets generate fields of several 10 T. Pulse durations are of the order of one millisecond and thus the fields can be considered as quasi-static for laser-plasma interaction processes taking place on the ps- to ns-scale. Their high field strength in combination with abandoning magnetic cores make the solenoids compact and light-weight.

The presented experiments focus on a solenoid magnet designed for the capture of divergent laser-driven ion beams. They have been carried out at the 6MV tandetron accelerator and the laser acceleration source Draco of Helmholtz-Zentrum Dresden – Rossendorf as well as at the PHELIX laser of GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt. The results show that the developed technology platform breaks ground for a variety of practical applications of laser ion acceleration. It is shown that laser-driven ion beams can be efficiently injected into conventional accelerator structures to allow for phase space modulation. Furthermore, first practical studies on medical beam guidance systems are presented. Hence, the developed magnets allow to investigate feasibility and potential of the frequently proposed laser-based ion beam therapy of tumor diseases. The pulsed high-field magnets bring us one step closer to the realization of this ambitious endeavor, as they pave the way for compact and efficient beam guidance toward the patient but also, in the phase of translational research, allow to study the radiobiological properties of the novel particle source. In this context, worldwide first irradiation studies with laser-accelerated protons on volumetric tumors in the mouse model have been prepared and their feasibility studied, identifying already met radiobiological criteria and hurdles yet to overcome.

Keywords: Pulsed magnets; high-field magnets; beam transport; laser-acceleration; laser acceleration; TNSA; laser particle acceleration; laser-radiooncology

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-094 2018
    ISSN: 2191-8708, eISSN: 2191-8716


Publ.-Id: 28306

Photo-induced THz response of VO2 under high pressures

Braun, J. M.; Schneider, H.; Helm, M.; Mirek, R.; Boatner, L. A.; Marvel, R. E.; Haglund, R. F.; Pashkin, A.

We apply ultrafast optical pump – THz probe spectroscopy in order to investigate the nature of the high pressure metallic state of VO2 single crystal. The pump excitation was performed using near-infrared pulses at the wavelength of 800 nm. The probe pulses with a frequency of 30 THz were generated by difference frequency mixing and focused on the sample mounted inside a diamond anvil pressure cell. Using the probe photon energy far below the bandgap of VO2 we were able to explore the response of free charge carriers near the Fermi level.

  • Lecture (Conference)
    Non-equilibrium Dynamics of Condensed Matter in the Time Domain, 03.-06.09.2018, Kerkrade, Netherlands

Publ.-Id: 28305

Photoinduced non-thermal insulator-to-metal transition in NbO2 epitaxial thin films

Rana, R.; Klopf, M. J.; Grenzer, J.; Schneider, H.; Helm, M.; Pashkin, A.

Ultrafast insulator-to-metal transition in the correlated oxides such as vanadium dioxide (VO2) has been extensively explored for rich physics and potential applications. In this regard, its isovalent counterpart niobium dioxide (NbO2) with considerably higher transition temperature (Tc = 1080 K) can be envisaged as a potential candidate. We have performed time-resolved optical pump – terahertz (THz) probe measurements on NbO2 epitaxial thin at room temperature.
The onset of the THz conductivity is followed by an exponential decay on a timescale of 400 fs. The photoinduced change in THz transmission at later delay times exhibits excitation threshold of 17.5 mJ/cm2. Notably, in contrast to VO2, the pump energy required for the switching into a metastable metallic state is smaller than the energy necessary for heating NbO2 up to Tc providing a strong evidence for the non-thermal character of the photoinduced insulator-to-metal transition in this system. The transient optical conductivity in the metastable state can be modelled using the Drude model confirming its metallic character.

  • Lecture (Conference)
    DPG-Frühjahrstagung 2018, 11.-16.03.2018, Berlin, Germany

Publ.-Id: 28304

Development of a new 18F-labeled radioligand for imaging of sigma2 receptors by positron emission tomography

Ludwig, F.-A.; Fischer, S.; Moldovan, R.-P.; Deuther-Conrad, W.; Kranz, M.; Schepmann, D.; Jia, H.; Wünsch, B.; Brust, P.

Objectives: Sigma2 receptors (S2R) have been found in CNS, liver, kidney, as well as endocrine glands and are suggested to play important roles in the regulation of cell differentiation. Besides their overexpression in various tumor cell lines, derived from e.g. breast, brain, colon, lung, pancreas, and prostate, they show a 10-fold higher expression in the proliferating vs quiescent status and thus are possible markers of solid tumor’s proliferative status. To quantify the S2R availability in living subjects, we aim for the development of a new class of S2R ligands that could be labeled by fluorine-18.
Methods: Starting from structural motifs known for S2R ligands [1, 2], we modified the indole ring system in A and synthesized a novel series of fluorine containing indole and aza-indole derivatives (1a-d and 2-6 in Fig. 1). Their binding affinities towards sigma2 and sigma1 receptors were determined by radioligand-binding assays, and 2 was selected for synthesis of a boronic acid pinacol ester precursor for radiolabeling. Synthesis of [18F]2 was optimized starting from 100-500 MBq of 18F-fluoride, using Kryptofix (K2.2.2.)/ K2CO3 (0.18-1.8 µmol/ 0.04-0.35 µmol) as well as TBAHCO3 (2.3 and 7.5 µmol) and 2-4 mg of precursor 7, in the presence of Cu(OTf)2py4 (0.4-6.8 eq.) in various solvent systems at 80-135 °C, monitored for 5-20 min. For monitoring, several analytical methods (radio-UHPLC, -HPLC, and -TLC) have been established, e.g. on the basis of RP18 und RP8 stationary phases for LC systems. Besides, different techniques for purification and isolation were investigated, including a substitution of semi-preparative HPLC by time-saving cartridge systems.
Results: By altering the heterocyclic system of A, a small series of fluorinated aza-indoles was synthesized (Fig. 1), of which 2 showed most promising binding affinity and selectivity (Ki(S2R) = 1.6 nM; Ki(S1R) = 691 nM). Radiosynthesis of [18F]2 was achieved with RCYs in a range of 20-45% (n = 2, all non-isolated, radio-UHPLC) by use of 2.0 mg of precursor 7 (4.1 µmol) and 3.6 eq. of Cu(OTf)2py4 at 115 °C within 10 min. The reaction was accompanied by the formation of a by-product (bp) which increased over time. Using the K2.2.2./ K2CO3 system resulted in RCYs of 21.5% (bp 5.5%) and 27.7 % (bp 4.6%), in DMF and DMA/ n-BuOH, respectively. Application of TBAHCO3 showed further increased conversions, represented by a RCY of 44.8% (bp 9.1%) in DMA/ n-BuOH. For subsequent semi-preparative HPLC, separation conditions were optimized, but still lack from low recoveries. As an alternative, SPE procedures using cartridge systems (SiO2, RP18) are being established and could be used as a time saving technique for the isolation of [18F]2.
Conclusions: A novel S2R-affine aza-indole derivative 2 was synthesized and radiofluorination of the appropriate boronic acid pinacol ester precursor afforded [18F]2 in RCYs of up to 45% (non-isolated). The optimal parameters for the radiosynthesis, conducted in a synthesis automat or module, have to be determined to setup a procedure for the production of [18F]2, which enables detailed preclinical in vitro and in vivo studies of this promising radioligand.
Acknowledgement: The authors would like to thank the Deutsche Forschungsgemeinschaft (DFG) for financial support (BR 1360/13-1).
[1] Georgiadis, M.-O. et al. Molecules 2017, 22, 1408;
[2] Wang, L. et al. Bioorg Med. Chem. 2017, 25, 3792-3802

Keywords: Positron emission tomography; PET; fluorine-18; sigma2; indole; aza-indole

  • Poster
    23. International Symposium on Radiopharmaceutical Sciences (ISRS 2019), 26.-31.05.2019, Peking, China
  • Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 62(2019), 181

Publ.-Id: 28303

Electron dynamics in InxGa1-xAs shells around GaAs nanowires probed by terahertz spectroscopy

Fotev, I.; Balaghi, L.; Schmidt, J.; Schneider, H.; Helm, M.; Dimakis, E.; Pashkin, A.

We present the electrical properties of GaAs/InxGa1-xAs core/shell nanowires measured by ultrafast optical pump - terahertz probe spectroscopy.
This contactless technique was used to measure the photoconductivity of nanowires with shell compositions of x = 0.20, 0.30 and 0.44. The results were fitted with the model of localized surface plasmon in a cylinder in order to obtain electron mobilities, concentrations and lifetimes in the InxGa1-xAs NW shells.
The estimated lifetimes are about 80 - 100 ps and the electron mobility reaches 3700 cm2/Vs at room temperature. This makes GaAs/InGaAs nanowires good candidates for the near-future realization of InGaAs based high-electronmobility transistor.

Keywords: GaAs nanowires; terahertz spectroscopy; ultrafast dynamics; electron mobility; plasmon; carrier lifetime

Publ.-Id: 28302

Nonthermal nature of photo-induced insulator-to-metal transition in NbO2

Rana, R.; Klopf, J. M.; Grenzer, J.; Schneider, H.; Helm, M.; Pashkin, A.

We study the photo-induced metallization process in niobium dioxide NbO2. This compound undergoes the thermal insulator-to-metal transition at the remarkably high temperature of 1080 K. Our optical pump ¬– terahertz probe measurements reveal the ultrafast switching of the film on a sub-picosecond timescale and the formation of a metastable metallic phase when the incident pump fluence exceeds the threshold of ~10 mJ/cm2. Remarkably, this threshold value corresponds to the deposited energy which is capable of heating NbO2 only up to 790 K, thus, evidencing the non-thermal character of the photo-induced insulator-to-metal transition. We also observe an enhanced formation of the metallic phase above the second threshold of ~17.5 mJ/cm2 which corresponds to the onset of the thermal switching. The transient optical conductivity in the metastable phase can be modeled using the Drude-Smith model confirming its metallic character. The present observation of non-thermal transition in NbO2 can serve as an important test bed for understanding photo-induced phenomena in strongly correlated oxides.

Keywords: metal-insulator transition; pump-probe spectroscopy; transition metal oxides


Publ.-Id: 28301

Optical Pump – THz Probe Response of VO2 under High Pressure

Braun, J. M.; Schneider, H.; Helm, M.; Mirek, R.; Boatner, L. A.; Marvel, R. E.; Haglund, R. F.; Pashkin, A.

We present the ultrafast THz response of VO2 under high pressures. A clear anomaly is observed around 8 GPa indicating a pressure-induced phase transition. Our observations can be interpreted in terms of a bandwidth-controlled Mott-Hubbard transition.

Keywords: metal-insulator transition; high pressure; VO2; pump-probe spectroscopy

  • Open Access Logo Contribution to proceedings
    XXI International Conference on Ultrafast Phenomena, 15.-20.07.2018, Hamburg, Deutschland
    Proceedings of Ultrafast Phenomena XXI, 91944 Les Ulis cedex A - France: EDP Sciences Web of Conferences
    DOI: 10.1051/epjconf/201920504003

Publ.-Id: 28300

Optical Pump – THz Probe Response of VO2 under High Pressure

Braun, J. M.; Schneider, H.; Helm, M.; Mirek, R.; Boatner, L. A.; Marvel, R. E.; Haglund, R. F.; Pashkin, A.

We present the ultrafast THz response of VO2 under high pressures. Pump-probe signals and a photoexcitation threshold are detected even in a metallic state. Our observations can be described as a pressure-driven Mott-Hubbard transition.

Keywords: vanadium dioxide; high pressure; pump-probe spectroscopy

  • Lecture (Conference)
    XXI. International Conference on Ultrafast Phenomena, 15.-20.07.2018, Hamburg, Deutschland

Publ.-Id: 28299

Freie Software in der Wissenschaft: Prototypen, Reproduzierbarkeit, Infrastruktur

Huebl, A.

Beitrag zur Ringvorlesung der FSFW im Wintersemester 2018 an der HTW, TU Dresden und Bürgeruniversität.

Keywords: open science; open source; open infrastructure; open data

  • Lecture (others)
    Ringvorlesung WS2018: Freie Software und Freies Wissen als Beruf, 27.11.2018, Dresden, Germany
    DOI: 10.5281/zenodo.1884442

Publ.-Id: 28298

Measurement of torsional and sloshing modes in Rayleigh-Bénard convection using contactless inductive flow tomography

Wondrak, T.; Stefani, F.; Galindo, V.; Eckert, S.

Flows driven by temperature differences play an important role in geo- and astrophysics as well as in many metallurgical applications. The dynamics of the large scale circulation (LSC) of Rayleigh-Bénard (RB) convection include azimuthal reorientations, cessations, torsional and sloshing modes. In this presentation we will show that the contactless inductive flow tomography (CIFT) is able to visualise these features. This will be shown using numerical simulations as well as measurements at a small model filled with GaInSn.

Keywords: contactless inductive flow tomography; liquid metal; flow measurement; Rayleigh-Bénard convection

  • Lecture (Conference)
    MHD Days and GDRI Dynamo Meeting, 26.-28.11.2018, Dresden, Deutschland

Publ.-Id: 28297

Contactless inductive flow tomography for a Rayleigh-Bénard setup with aspect ratio 0.5

Wondrak, T.; Galindo, V.; Stefani, F.; Schindler, F.; Vogt, T.; Eckert, S.

The contactless inductive flow tomography (CIFT) allows the reconstruction of the three-dimensional flow field in liquid metals by applying one or more primary magnetic fields to the melt and measuring the flow induced perturbation of those fields outside the melt. From these measurements, the flow is then reconstructed by solving a linear inverse problem using Tikhonov regularisation technique [1].
In recent experiments, CIFT was able to reconstruct the dynamics of the large scale circulation (LSC) in a small modified Rayleigh-Bénard convection cell which was filled with the eutectic alloy GaInSn and consists of a cylindrical vessel with a diameter and a height of 87 mm [2]. Typical time dependent features of the LSC like azimuthal rotations, cessations as well as torsional modes could be visualised by CIFT. Numerical simulations suggest that a sensor arrangement of 8 sensors in azimuthal direction in 3 planes equally spaced over the height of the vessel is a good choice [3]. The developed CIFT configuration allows for measurement times longer than 12 hours with an accuracy of about 20 nT.
Encouraged by these promising results, the measurement system will be adapted to a larger cylindrical Rayleigh-Bénard cell with diameter of 320 mm and height of 640 mm. It is planned to use simultaneously CIFT and UDV in order to reconstruct the global flow while selected flow components are measured in high temporal and spatial resolution with UDV.
In this paper we will present the first design of the arrangement of the excitation coils and the magnetic field sensors. Based on this new setup first reconstructions will be shown. Figure 1 shows a preliminary simulation of the flow in the cylindrical vessel as well as the flow induced magnetic field outside the vessel for a constant primary field in vertical direction with the strength of 1mT.

Keywords: contactless inductive flow tomography; liquid metal; Rayleigh-Bénard convection; flow measurement

  • Lecture (Conference)
    11th PAMIR international conference fundamental and applied MHD, 01.-05.07.2019, Reims, France
  • Contribution to proceedings
    11th Pamir International Conference Fundamental and Applied MHD, 01.-5.7.2019, Reims, France
  • Magnetohydrodynamics 56(2020), 195-202
    DOI: 10.22364/mhd.56.2-3.11

Publ.-Id: 28296

AER Working Group Meeting on VVER safety analysis - report of the 2018 meeting

Kliem, S.

The AER Working Group D on VVER reactor safety analysis held its 27th meeting in Rossendorf, Germany, during the period 12-13 June, 2018. The meeting was hosted by Helmholtz-Zentrum Dresden-Rossendorf. Altogether 19 participants from nine AER member organizations attended the meeting of the working group D. The co-ordinator of the working group, Mr. S. Kliem, served as the chairperson of the meeting.
The meeting started with a general information exchange about the recent activities in the participating organizations.
The given 13 presentations and the discussions can be attributed to the following topics:

  • Safety analyses methods and results
  • Code development and benchmarking
  • Severe accident analyses
  • Future activities
The Working Group decided to include also in future the severe accident analyses into the scope of the activities.
A list of the participants and a list of the handouts distributed at the meeting are attached to the report. The corresponding PDF-files of the handouts can be obtained from the chairperson.
  • Contribution to proceedings
    28. Symposium of AER, 08.-12.10.2018, Olomouc, Czech Republic
    Proceedings of the 28. Symposium of AER, Budapest: MTA EK Budapest, 9789637351303, 665-671
  • Lecture (Conference)
    28. Symposium of AER, 08.-12.10.2018, Olomouc, Czech Republic

Publ.-Id: 28295

Aerosol particle deposition and resuspension in turbulent air channel flows

Lecrivain, G.; Hampel, U.

The deposition of aerosol graphite particles in a turbulent channel flow obstructed with periodic steps is here investigated et experimentally at Reynolds number Re = 8,000. Particles in the size range d = 1...100µm deposit non-uniformly on the various wall surfaces and eventually form a fairly thick layer of dust. The build-up of the dust layer affects the air flow which in turn affects the deposition rate of the conveyed particles. To numerically reproduce the growth of the dust layer an interdisciplinary study involving the dynamic coupling of fluid simulation, Lagrangian particles, mesh deformation and granular bed is carried out. The numerical results compare well with the experimental data.

  • Invited lecture (Conferences)
    Workshop on particle resuspension, 04.09.2018, Nice, France

Publ.-Id: 28294

Numerical Models for the DRESDYN Precession Dynamo Experiment

Giesecke, A.; Vogt, T.; Gundrum, T.; Stefani, F.

More than 100 years ago, Henri Poincare in his pioneering study showed that the inviscid base flow in a precessing spheroid is described by a constant vorticity solution, the spin-over mode. Since then there have been repeated discussions whether the geodynamo is driven (or at least influenced) by precession. More recently, precession has also been considered as an important mechanism for the explanation of the ancient lunar dynamo.

Experiments with precessing fluids in cylindrical and in spherical geometry showed that precession indeed is an efficient mechanism to drive substantial flows even on the laboratory scale without making use of propellers or pumps. A precession dynamo experiment is currently under construction within the project DRESDYN (DREsden Sodium facility for DYNamo and thermohydraulic studies) at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) in which a precession driven flow of liquid sodium will be used to drive dynamo action.

In the present study we address related numerical and experimental examinations in order to identify parameter regions where the onset of magnetic field excitation will be possible. Preliminary kinematic dynamo models using a prescribed flow field from hydrodynamic simulations, exhibit magnetic field excitation at critical magnetic Reynolds numbers around Rm_c ≈ 430, which is well within the range of the planned liquid sodium experiment. Our results show that large scale inertial modes excited by precission are able to excite dynamo action when their structure is sufficient complex, i.e. the forcing is sufficient strong.

More advanced models that take into account the container's finite conductivity show that boundary conditions may play an important role, but the critical magnetic Reynolds number will still be achievable in the planned experiment. Finally, we discuss the role of turbulent flow fluctuations for the occurrence of dynamo action.

Keywords: Dynamo; DRESDYN

  • Poster
    AGU Fall Meeting 2018, 09.-14.12.2018, Washington DC, USA
  • Open Access Logo Contribution to proceedings
    AGU Fall Meeting 2018, 09.-14.12.2018, Washington DC, USA

Publ.-Id: 28293

Numerical simulations for the DRESDYN precession dynamo

Giesecke, A.; Vogt, T.; Gundrum, T.; Stefani, F.

More than 100 years ago, Henri Poincar{\'e} in his pioneering study showed that the inviscid base flow in a precessing spheroid is described by a constant vorticity solution, the spin-over mode. Since then there have been repeated discussions whether the geodynamo is driven (or at least influenced) by precession. More recently, precession has also been considered as an important mechanism for the explanation of the ancient lunar dynamo.

Experiments with precessing fluids in cylindrical and in spherical geometry showed that precession indeed is an efficient mechanism to drive substantial flows even on the laboratory scale without making use of propellers or pumps. A precession dynamo experiment is currently under construction within the project DRESDYN (DREsden Sodium facility for DYNamo and thermohydraulic studies) at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) in which a precession driven flow of liquid sodium will be used to drive dynamo action.

Here we address related numerical and experimental examinations in order to identify parameter regions where the onset of magnetic field excitation will be possible. Preliminary kinematic dynamo models using a prescribed flow field from hydrodynamic simulations, exhibit magnetic field excitation at critical magnetic Reynolds numbers around ${\rm{Rm}}_{\rm{c}} \approx 430$, which is well within the range of the planned liquid sodium experiment. Our results show that large scale inertial modes excited by precession are able to excite dynamo action when their structure is sufficiently complex, i.e. the forcing is sufficiently strong.
More advanced models that take into account the container's finite conductivity show that boundary conditions may play an important role, but the critical magnetic Reynolds number will still be achievable in the planned experiment.

Keywords: Dynamo; DRESDYN

  • Lecture (Conference)
    MHD Days 2018, 26.-29.11.2018, Dresden, Germany

Publ.-Id: 28292

Kopplung von CFD, Elektrochemie und Elektrodynamik am Beispiel Flüssigmetallbatterie

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

Flüssigmetallbatterien (FMB) werden seit etwa 10 Jahren als preisgünstige stationäre Speicher für die Energiewende diskutiert. Der Aufbau aus zwei flüssigen Metallen, welche nur durch eine dünne Salzschmelze getrennt sind, erlaubt extreme Stromdichten und eine potentiell sehr hohe Lebensdauer. Für einen optimalen Wirkungsgrad muss die Salzschicht möglichst dünn sein – ohne jedoch einen Kurzschluss zuzulassen. Weiterhin ist effektiver Massetransport durch Konvektion von zentraler Bedeutung.

Im ersten Teil des Vortrags soll Aufbau und Funktionsweise einer FMB kurz erklärt werden. Anschließend werden verschiedene physikalische Phänomene an Hand von OpenFOAM-Simulationen diskutiert (thermische und solutale Konvektion, magnetohydrodynamische Instabilitäten, Elektrochemie, Stromverteilung in der Zelle). Im letzten Teil des Vortrags wird auf die Kopplung von CFD mit Elektrodynamik sowie von Massetransport mit der Potential- und Stromverteilung detailiert eingegangen.

  • Lecture (Conference)
    Jahrestreffen der ProcessNet-Fachgruppe Computational Fluid Dynamics mit OpenFOAM Workshop, 19.03.2019, Frankfurt, Deutschland

Publ.-Id: 28291

Liquid Metal Batteries: coupling electrochemistry, heat and mass transfer with magnetohydrodynamics

Weber, N.; Herreman, W.; Horstmann, G. M.; Nore, C.; Personnettaz, P.; Weier, T.

Liquid metal batteries (LMBs) are discussed as cheap stationary energy storage. Built as a stable density stratification of two liquid metals separated by a molten salt, such cells offer extreme current densities at a potentially unlimited life time. Beyond that, it is especially the low price which makes LMBs an ideal candidate for balancing highly fluctuating renewable energy sources. The efficiency of LMBs is mainly determined by two aspects. Most importantly, the electrolyte layer must be as thin as possible as it has a high ohmic resistance. Still, it needs to be thick enough to prevent a short-circuit. Secondly, efficient mass transfer needs to be ensured. Optimising an LMB means therefore understanding the interplay of thermal and solutal convection, mass transfer, electrochemistry and electrodynamically driven flow with the current distribution in the cell. The talk will start with an introduction to built-up and operation of LMBs. The different physical effects will be discussed using simulations performed in OpenFOAM. Numerical details will be provided on coupling hydro- and electrodynamics, magnetic field calculation as well as the coupling of electrochemistry with current and potential distributions.

  • Lecture (Conference)
    Congress on Numerical Methods in Engineering, 01.07.2019, Guimarães, Portugal

Publ.-Id: 28290

Antihypertensive drug classes, not blood pressure, are associated with cerebral perfusion. Results from the PREvention of Dementia by Intensive VAscular care (PREDIVA) study

van Dalen, J.; Mutsaerts, H.; Petr, J.; van Charante, M. E.; van Gool, W.; Nederveen, A.; Richard, E.

Background: Constant cerebral blood flow (CBF) is fundamental to cerebral function. With aging and chronic hypertension, arteriolar damage may disrupt the CBF autoregulatory capacity. This might cause CBF to fluctuate with blood pressure (BP) levels, low BP and antihypertensive medication (AHM), potentially evoking hypoperfusion. We investigated the cross-sectional and longitudinal relations of BP and AHM with cerebral perfusion using arterial spin labeling (ASL).
Methods: In 186 community-dwelling individuals with hypertension (77±3 years, 53% female), 125 (67%) with 3-year follow-up (Figure 1), we assessed grey matter (GM) and white matter (WM) CBF (ml/100g/min) and the spatial coefficient of variation (CoV; SD CBF/mean CBF). Cross-sectional associations were assessed combining baseline and follow-up data using mixed models, longitudinal associations using linear regression assessing change, adjusted for baseline. We additionally adjusted for age, sex, AHM, stroke and parenchymal fraction.
Results: Cross-sectionally, higher diastolic BP was associated with lower GM and WM CBF (Table 1). AHM were associated with lower GM CBF and higher spatial CoV. Since calcium channel blockers (CCB) and angiotensin receptor blockers (ARB) in our main study were specifically associated with lower dementia risk compared to other AHM, we assessed these separately. Other AHM were associated with lower GM and WM CBF, while CCBs and ARBs were not. There were no correlations between BP change and perfusion changes (Table 2). We observed no J-shaped relationships.
Discussion: We found no evidence for any direct relation between BP and cerebral perfusion. Possibly, higher diastolic BP was associated with lower CBF by being a marker of more severe long-standing hypertension evoking vascular damage. Our finding that ARBs and CCBs are relatively protective of CBF compared to other AHM is consistent with findings of a protective effect of these AHM classes on dementia incidence, and could influence future treatment.

  • Contribution to proceedings
    VasCog 2018 - The 9th International Conference of The International Society of Vascular Behavioural and Congnitive Disorders, 14.11.2018, Hong-Kong, China
  • Poster
    VasCog 2018 - The 9th International Conference of The International Society of Vascular Behavioural and Congnitive Disorders, 14.11.2018, Hong-Kong, China

Publ.-Id: 28289

Cognitive complaints associated with spatial coefficient of cerebral blood flow in community-dwelling older people in the PREvention of Dementia by Intensive VAscular care (PREDIVA) study

van Dalen, J.; Mutsaerts, H.; Petr, J.; van Charante, M. E.; van Gool, W.; Nederveen, A.; Richard, E.

Background: Low cerebral perfusion is cross-sectionally associated with dementia and predicts accelerated dementia progression. Hypothetically, impaired cerebral autoregulation, associated with aging and hypertension, and consequent cerebral hypoperfusion may contribute to the development of old-age cognitive decline. We investigated the cross-sectional and longitudinal relation between cognition and cerebral perfusion in older people without dementia using arterial spin labeling (ASL).
Methods: We included 186 community-dwelling individuals with hypertension (77 ±3 years, 53% female), 125 (67%) with 3-year follow-up neuroimaging (Figure 1). Cognitive measures included the mini-mental state examination (MMSE), visual association test (VAT) and subjective memory complaints (SMC) assessed using one question. Perfusion measures included grey matter (GM) cerebral blood flow (CBF, ml/100g/min), white matter (WM) CBF and spatial coefficient of variation (CoV; SD CBF/mean CBF, a potential proxy of vascular insufficiency). Cross-sectional analyses combined baseline and follow-up data using mixed models. Longitudinal analyses comprised linear regression of follow-up values adjusted for baseline. We additionally adjusted for age, sex, antihypertensives, WM hyperintensity volume and brain parenchymal fraction.
Results: Participants with memory complaints had a significantly higher CoV (Table 1). Furthermore, participants with better VAT scores had lower CoV, although this was attenuated after adjustment. Cerebral perfusion did not predict change in cognition (Table 2) but increasing CoV was associated with declining MMSE and, to a lesser extent, VAT scores. There were no significant relations between CBF and cognition.
Discussion: Our results suggest that higher CoV is associated with worse cognitive function and CoV changes concordantly with cognitive function. Spatial CoV may be a more sensitive cerebral hemodynamic parameter related to cerebral function compared to CBF. None of the cerebral perfusion parameters predicted future cognitive decline, suggesting that low perfusion does not precede cognitive decline in non-demented older people or that the perfusion measures employed were insufficiently sensitive.

  • Contribution to proceedings
    VasCog 2018 - The 9th International Conference of The International Society of Vascular Behavioural and Congnitive Disorders, 14.11.2018, Hong-Kong, China
  • Poster
    VasCog 2018 - The 9th International Conference of The International Society of Vascular Behavioural and Congnitive Disorders, 14.11.2018, Hong-Kong, China

Publ.-Id: 28288

ASL-vascular insufficiency parameters can differentiate healthy controls from Alzheimer’s and Parkinson’s diseases

Ingala, S.; Petr, J.; Pålhaugen, L.; Gajdos, M.; Fladby, T.; Selnes, P.; Barkhof, F.; Bjørnerud, A.; Rektorova, I.; Mutsaerts, H.

Decreased/Poor vascular health - e.g. increased vascular resistance, tortuosity - may lead to a delayed arrival of labelled blood to brain tissue causing vascular artefacts on arterial spin labeling (ASL) images [Figure 1]. Although these artefacts are traditionally treated as a nuisance, their presence can be quantified by the spatial coefficient of variance (CoV) parameter and used as an indication of vascular insufficiency. . Here, the goal was to investigate the ability of spatial CoV to assess the vascular health by comparing it between healthy controls and subjects with Alzheimer’s (AD) and Parkinson’s (PD) diseases.

Methods: We analyzed the MRI scans of 143 APGeM study participants, including healthy controls (HC, n=56) and subjects with AD- (n=41) or PD-related (n=46) mild cognitive impairment or dementia [Table]. We calculated CBF, spatial CoV, and WMH volume using ExploreASL [ref]. Pearson’s correlations of spatial CoV with age and WMH volume were investigated, as well as a t-test for the relation between spatial CoV and sex. A linear regression model was used to evaluate whether spatial CoV was able to discriminate HC vs. AD, HC vs. PD, and AD vs. PD after correction for age and sex.

Results: Spatial CoV measures showed a positive correlation with age (cor=0.35, p <0.001 and with WMH volume (cor=0.38, p <0.001 [Figure 2A], and differed between sexes (p <0.001). Differences in spatial CoV values were detected between HC and AD and between HC and PD subjects (p<0.05 in both cases) [Figure 2B]. With our model, spatial CoV was not able to discriminate between AD and PD.

Conclusions: These findings suggest that spatial CoV can provide insight in the vascular component of AD and PD pathologies. Validation of these results in larger cohorts and across a wider range of disorders might provide further insight in the relation between cerebrovascular health and neurodegeneration.

  • Contribution to proceedings
    VasCog 2018 - The 9th International Conference of The International Society of Vascular Behavioural and Congnitive Disorders, 14.11.2018, Hong-Kong, China
  • Poster
    VasCog 2018 - The 9th International Conference of The International Society of Vascular Behavioural and Congnitive Disorders, 14.11.2018, Hong-Kong, China

Publ.-Id: 28287

Effects of intracranial stenosis on brain perfusion and cognitive performance in a memory clinic population

Hilal, S.; Mutsaerts, H.; Ferro, D.; Petr, J.; Kuijf, H.; Biessels, G.; Chen, C.

Background: Intracranial stenosis (ICS) contributes to cognitive dysfunction possibly via decreased cerebral blood flow (CBF). However, CBF measurements by Arterial Spin Labelling (ASL) are affected by vascular artefacts making it difficult to apply in elderly with large vessel disease. Recently, spatial coefficient of variance (CoV) is proposed as a robust estimate to quantify vascular artifacts and may be used as a proxy marker of large vessel insufficiency. We investigate the association of ICS with ASL measurements and its eventual effects on cognition in a memory clinic population.
Methods: We included 403 participants (mean age=72.3±7.9years, women=53.7%). ICS was graded as ≥50% stenosis in any intracranial vessel on 3D Time of Flight Magnetic Resonance Angiography. Gray matter spatial CoV and gray matter CBF were analyzed with ExploreASL from 2D EPI pseudo-continuous ASL images. Global cognition was assessed by a detailed neuropsychological test.
Results: ICS was present in 70 (17.4%) individuals. Persons with ICS had higher GM spatial CoV (mean difference (β)= 0.17, 95%CI: 0.07; 0.28, p=0.001) and lower CBF (β= -0.21, 95%CI: -0.33; -0.09), p=<0.001). This association persisted after partial volume correction of spatial CoV and CBF. The lateralization of spatial CoV and CBF (asymmetry index) (β for CoV: 0.23, 95%CI: 0.05; 0.40, p=0.013 and β for CBF: -0.22, 95%CI: -0.33; -0.11, p=<0.001) were correlated with ipsilateral stenosis. Spatial CoV was associated with worse cognition independent of CBF (β= -0.76, 95%CI: -1.09; -0.43, p=<0.001). Moreover, ICS was associated with global cognition, independent of gray matter CoV and CBF, although this effect attenuated in the presence of cortical microinfarcts (β= -0.23, 95%CI: -0.49; 0.02, p=0.072).
Conclusion: These findings suggest an association of ASL perfusion with ICS and cognition, which has a predominant component of large vessel insufficiency. Moreover, cortical microinfarcts mediate the link between ICS and cognition independent of large vessel insufficiency.

  • Contribution to proceedings
    VasCog 2018 - The 9th International Conference of The International Society of Vascular Behavioural and Congnitive Disorders, 14.11.2018, Hong-Kong, China
  • Poster
    VasCog 2018 - The 9th International Conference of The International Society of Vascular Behavioural and Congnitive Disorders, 14.11.2018, Hong-Kong, China

Publ.-Id: 28286

Tissue inhibitor of proteinase-1 and cerebral blood flow in predementia

Pålhaugen, L.; Selnes, P.; Kirkeby, E.; Tecelao, S.; Ingala, S.; Petr, J.; Bjørnerud, A.; Mutsaerts, H.; Fladby, T.

Cerebrovascular disease (CVD) can increase the risk of dementia and is frequently seen in Alzheimer’s disease. Tissue inhibitor of proteinase-1 (TIMP-1) measured in cerebrospinal fluid (CBF) is considered a promising biomarker of subcortical small vessel disease (SSVD). In addition to inhibition of matrix metalloproteases, it occurs in several biological processes, such as protection of the blood brain barrier. This study explores how TIMP-1 is associated with CBF in amyloid and non-amyloid pre-dementia cases as well as in controls.

Cases and controls, aged 40-80, were included from the Norwegian multi-site study “DDI” (n=69, age=63.2 +/- SD, m/f=26/43). Participants underwent cognitive assessment, MRI and lumbar puncture. Cases were staged as Subjective Cognitive Decline (SCD) or Mild Cognitive Impairment (MCI). We stratified by A1-42 pathology (A+/-) using an amyloid-PET verified CSF cutoff. Cerebral blood flow (CBF) was measured with arterial spin labeling and analyzed using ExploreASL. Linear regression analysis was performed with TIMP-1 and CBF in total gray matter (GM), total white matter (WM) and several GM regions (frontal, temporal, insula, parietal, occipital, thalamus, putamen and caudate nucleus), adjusting for age and sex. CBF was log-transformed.

In the A- group (n=50, age=61.6, m/f=17/33, Controls/SCD/MCI=21/22/7) there was a significant positive relationship between TIMP-1 and CBF in total GM (=-0.46, p=0.001), total WM (=-0.44, p=0.002), frontal (=-0.41, p=0.004), temporal (=-0.45, p=0.001), insula (=-0.39, p=0.006), parietal (=-0.48, p<0.001), occipital (=-0.45, p=0.001), thalamus (=-0.53, p<0.001), putamen (=-0.41, p=0.004) and caudate nucleus (=-0.48, p=0.001) GM regions. There were no significant associations in the A+ group (n=19, age=67.4, m/f=9/10, Controls/SCD/MCI=2/7/10) or in the whole sample.

We found that TIMP-1 correlates positively with CBF in the A- group, whereas there were no significant association in the A+ group. Putatively, this may reflect different mechanisms for vascular pathology in the two groups.

  • Contribution to proceedings
    VasCog 2018 - The 9th International Conference of The International Society of Vascular Behavioural and Congnitive Disorders, 14.11.2018, Hong-Kong, China
  • Poster
    VasCog 2018 - The 9th International Conference of The International Society of Vascular Behavioural and Congnitive Disorders, 14.11.2018, Hong-Kong, China

Publ.-Id: 28285

Cortical microinfarcts in memory clinic patients are associated with reduced cerebral perfusion

Ferro, D.; Mutsaerts, H.; Hilal, S.; Kuijf, H.; Petersen, E.; Petr, J.; van Veluw, S.; Venketasubramanian, N.; Biessels, G.; Chen, C.

Background: Cerebral cortical microinfarcts (CMIs) are small ischemic lesions visible on autopsy and structural MRI. As CMIs occur/are observed more frequently in the cortical watershed areas, we hypothesize that hypoperfusion plays a role in their development. We investigated whether CMI presence is associated with decreased cerebral perfusion using arterial spin labeling (ASL).
Methods: We have analyzed 180 memory clinic patients (mean age 72 ± 9y, 51% male, 72% CMIs present ) with pCASL acquired at 3T MRI (PLD=xx ms, labeling duration=xx ms). Cerebral blood flow (CBF) was quantified (in ml/100g/min) and mean CBF and spatial coefficient of variation (CoV, quantitative proxy of transit time, expressed as SD of the CBF/mean CBF) was calculated in gray matter in each vascular territory. Vascular artefacts were observed in 33 patients due to prolonged transit time, and these were excluded from the CBF but not CoV analysis. CMIs were rated according to previously established criteria.
Results: In this cohort, CMIs presence was associated with a higher burden of cerebrovascular disease (Table 1). Patients with CMIs had lower CBF and a higher spatial CoV in the anterior circulatory territory, indicating a decreased perfusion and a delayed transit time (Table 1, Figure 1). The total number of CMIs was correlated to a lower CBF and a higher spatial CoV (p<.02). A sub-analysis in patients with unilateral CMI presence revealed no significant inter-hemisphere differences in CBF (n=27, .56 ±.7 ml/100g/min) or in CoV (n=36, .05 ±.25).
Conclusion: This is the first study to demonstrate that CMIs presence is associated with reduced global cerebral perfusion. Further research should identify at which level of the vascular tree the cause of hypoperfusion originates.

  • Contribution to proceedings
    VasCog 2018 - The 9th International Conference of The International Society of Vascular Behavioural and Congnitive Disorders, 14.11.2018, Hong-Kong, China
  • Lecture (Conference)
    VasCog 2018 - The 9th International Conference of The International Society of Vascular Behavioural and Congnitive Disorders, 14.11.2018, Hong-Kong, China

Publ.-Id: 28284

µTRLFS: Spatially-resolved sorption studies of Eu(III) on Eibenstock granite with time-resolved laser fluorescence spectroscopy

Molodtsov, K.; Schymura, S.; Rothe, J.; Dardenne, K.; Krause, J.; Schmidt, M.

Finding a safe long-term repository for high-level nuclear waste is a highly relevant global issue. To that end, the interaction of radionuclides with mineral phases contained in possible host rocks and construction materials must be understood. On a time scale of up to one million years, especially the scenario of a water intrusion into the repository and thus dissolution of radionuclides has to be considered.

To investigate the sorption behaviour of actinides (e.g. Cm(III) and U(VI)O22+) and lanthanides (e.g. Eu(III)), time-resolved laser fluorescence spectroscopy (TRLFS) is a widely used method, because of its trace concentration sensitivity and capability to distinguish multiple species in complex systems. On the one hand this method gives the spectral information of the emitted fluorescence light, which allows determining the symmetry and the grade of complexation of the sorbed Ln/An. On the other hand the lifetimes of the excited electronic states provide information about the surrounding quenchers, mainly water. Typically, TRLFS investigations will focus on the interaction of an actinide with one relevant mineral phase. For a real rock formation, e.g. granite, sorption will however be a competitive process involving multiple mineral phases at the same time.

In this study a new method called µTRLFS is introduced, which will add a spatial dimension to TRLFS. By doing so, it is possible to separate the multi-phase system into discrete single-phase systems and therefore to make a step beyond model systems by investigating, for example whole natural granite rock with TRLFS. Because of its advantageous fluorescence properties, we use Eu(III) as an analogue for the trivalent actinides Am and Cm. Spatially resolved sorption experiments with Eu(III) on granite samples from Eibenstock, Germany are presented. These samples are excited by a focused laser beam at a wavelength of 394 nm, and scanned through the laser’s focal point by an XYZ-stage with a resolution of approximately 20 µm. Through this approach it becomes possible to characterize Eu(III) sorption on single grains of the complex material by mapping fluorescence intensity, F2/F1-band ratios, as well as fluorescence lifetimes.

A combination of spatially-resolved X-ray fluorescence spectroscopy (µXRF) and electron probe microanalysis (EPMA) is used to reveal the mineral phase composition in each point of measurement which can then be correlated to the µTRLFS maps. In addition, these methods provide impurity distributions of e.g. Fe or Mn as additional quenchers. By doing so, µTRLFS mapping of sorption capacity, complexation strength and surrounding quenchers can be correlated to phase distribution mappings and thus provide information about the sorption behaviour of each phase within the complete multi-phase system. The µTRLFS data can be directly compared to single phase TRLFS data of the main granite components quartz, feldspar, and mica. For verification, the Eu(III) distribution obtained from µTRLFS data will be compared to autoradiography images.

Keywords: µTRLFS; europium; sorption; granite

  • Poster
    10th International Conference on f-elements, 03.-06.09.2018, Lausanne, Schweiz
  • Lecture (Conference)
    Advanced Techniques in Actinide Spectroscopy, 06.-09.11.2018, Nice, France

Publ.-Id: 28283

µTRLFS: Spatially- and time-resolved laser fluorescence spectroscopy with Eu(III) as a fluorophore on Eibenstock granite

Molodtsov, K.; Schmidt, M.

Time-resolved laser fluorescence spectroscopy (TRLFS) is a widely used method to obtain information about the surrounding chemical environment of fluorophores with trace concentration sensitivity. This method allows determining the symmetry and grade of complexation of the fluorophore and provides information about the surrounding quenchers, mainly water as well. For highly heterogeneous systems however distinguishing and separating multiple binding species becomes an unsolvable problem. In this study a new method called µTRLFS is introduced, which will add a spatial dimension to TRLFS, giving the possibility to separate a multi-phase system into discrete single-phase systems. Because of its advantageous fluorescence properties we use europium as an analogue for Am(III) and Cm(III) to study the sorption behaviour of granite as a possible host rock for high-level nuclear waste repositories. Spatially resolved sorption experiments with Eu(III) on granite samples from Eibenstock, Germany are presented. These samples are excited by a focused and pulsed UV laser beam, and scanned with a resolution of 20 µm. Through this approach it becomes possible to characterize Eu(III) sorption on single grains of the complex material by mapping fluorescence intensity, band ratios, as well as lifetimes.

Keywords: µTRLFS; europium; sorption; granite

  • Lecture (Conference)
    Deutsche Physikalische Gesellschaft Frühjahrstagung, 04.-09.03.2018, Erlangen, Deutschland

Publ.-Id: 28282

The muon flux in the Felsenkeller shallow underground laboratory

Ludwig, F.; Wagner, L.; Al-Abdullah, T.; Barnaföldi, G. G.; Bemmerer, D.; Degering, D.; Surányi, G.; Zuber, K.

The muon intensity and angular distribution in the shallow-underground laboratory Felsenkeller in Dresden, Germany
have been studied using a portable muon detector based on the closed cathode chamber design. Data has been taken at
four positions in Felsenkeller tunnels VIII and IX, where a new 5 MV underground ion accelerator is being installed, and
in addition at four positions in Felsenkeller tunnel IV, which hosts a low-radioactivity counting facility. At each of the
eight positions studied, seven different orientations of the detector were used to compile a map of the upper hemisphere
with 0.85 ◦ angular resolution. The muon intensity is found to be suppressed by a factor of 40 due to the 45 m thick rock
overburden, corresponding to 140 meters water equivalent.
The angular data are matched by two different simulations taking into account the known geodetic features of the
terrain: First, simply by determining the cutoff energy using the projected slant depth in rock and the known muon
energy spectrum, and second, in a GEANT4 simulation propagating the muons through a column of rock equal to the
known slant depth. The present data are instrumental for studying muon-induced effects at these depths and also in the
planning of an active veto for accelerator-based underground nuclear astrophysics experiments.

Keywords: Muon intensity; Underground laboratories; GEANT4; nuclear astrophysics; wire chambers; muon tomography; muon radiography

Publ.-Id: 28281

Trivalent Actinide Incorporation into Zirconium(IV) oxide – Eu3+ and Cm3+ luminescence spectroscopic studies

Eibl, M.; Shaw, S.; Morris, K.; Hennig, C.; Stumpf, T.; Huittinen, N.

In a final repository for spent nuclear fuel (SNF), the mobilization of actinides from the UO2 matrix is a great concern for safety considerations. The SNF rods are surrounded by zircalloy cladding material, which, similarly to the UO2 waste matrix, has a very low solubility in aqueous solution. Despite the very good corrosion resistance of the cladding material, corrosion and dissolution are expected to occur together with the leaching of radionuclides from the SNF over geological timescales. Therefore, the dissolution of zircalloy and the formation of a corrosion layer mainly composed of zirconia (ZrO2) on the cladding surface may be accompanied by reactions with dissolved, long-lived radionuclides from the SNF matrix.
At ambient conditions zirconium oxide has a monoclinic (m) crystal structure. However, the incorporation of metal cations can stabilize the high-temperature zirconia phases, i.e. the tetragonal (t) and the cubic (c) phases, leading to the formation of stable structures at ambient conditions.[1] Such phase transformation may be expected when actinides from the SNF become incorporated and thus, immobilized within the zirconia corrosion layer.
In the present study the incorporation of aliovalent actinides in zirconia, and their stabilizing influence on the crystal structure, have been investigated. The crystallinity and structural properties of the resultant actinide-doped zirconia solids were investigated with powder x-ray diffraction (PXRD), while the local structure around the incorporated dopant was studied with laser-induced luminescence spectroscopy (TRLFS). Cm3+ and Eu3+ were taken as representatives for the trivalent actinides.
The PXRD results of calcined Eu3+ doped zirconia samples show that a systematic transformation of the monoclinic to the cubic phase via the tetragonal structure occurs as a function of increasing Eu3+ doping (Fig. 1, left) whilst the Eu3+ TRLFS results show a 7F1, 7F2 emission band splitting corresponding to a low symmetry environment despite the cubic bulk symmetry (Fig. 1, middle).

The Cm3+ co-doped luminescence spectra show strong red-shifts of the emission spectra in the cubic bulk system with a peak maximum of 643.9 nm (Fig. 1, right) which have been observed before.[2] Both spectroscopic methods point towards a strongly distorted local structure, caused by the effect of oxygen vacancies and lattice stress induced by the largely oversized dopant ions.

  • Lecture (Conference)
    4th International Workshop on Advanced Actinide Spectroscopy, 06.-09.11.2018, Nice, France

Publ.-Id: 28280

Pressure-tuning of the magnetic properties of the Heusler compound Mn2PtGa

Salazar Mejia, C.; Najak, A. K.; Felser, C.; Nicklas, M.

We report on the pressure-tuning of the magnetic properties of the Heusler alloy Mn2PtGa. At ambient pressure, Mn2PtGa orders ferrimagnetically below TC ≈ 222 K, followed by a first-order ferrimagnetic to antiferromagnetic transition around TFI-AF ≈ 102 K upon cooling. Magnetization measurements up to 1.2 GPa evidence a stabilization of the ferrimagnetic phase, i.e., TC increases while TFI-AF decreases upon application of pressure. The magnetic properties in the ferromagnetic phase are not altered upon increasing pressure. However, the fraction of the ferrimagnetic phase present in the inhomogeneous antiferromagnetic low-temperature phase increases with pressure.

Publ.-Id: 28279

Entwicklung einer alternativen Methode zur selektiven Laugung von Seltenen Erden aus Zirkonsilikaten

Balinski, A.; Scharf, C.

Zirkonsilikate spielen als Quelle für Seltene Erden trotz der geringen Belastung mit Uran und Thorium, des günstigeren Verhältnisses von schweren zu leichten Seltenen Erden und der Anwesenheit von wertvollen Begleitelementen immer noch eine untergeordnete Rolle. Eine industriell rentable Gewinnung von Seltenen Erden aus dieser Rohstoffgruppe hat sich trotz vieler initiierter Projekte bis auf eine Lagerstätte in Russland bisher nicht durchgesetzt. Der Grund dafür liegt in den geringen Konzentrationen der Zielelemente, der Kieselgelbildung während der Laugung und der Entstehung von komplexen Multielement-Laugungslösungen begründet. Die Arbeit beschäftigt sich mit der Entwicklung einer alternativen Methode zur Gewinnung von Seltenen Erden und der relevanten Begleitelemente unter Anwendung des unterschiedlichen Verhaltens der Sulfate der beiden Metallgruppen. Als Zwischenprodukte werden wässrige Phasen angereichert mit jeweils wertvollen Metallen beziehungsweise Seltenen Erden zur weiteren Raffination erzeugt.

  • Poster
    Jahrestreffen der Processnet-Fachgruppen Extraktion und Rohstoffe, 12.-13.03.2018, Frankfurt am Main, Deutschland

Publ.-Id: 28278

SE-FLECX-Projekt: alternative Ansätze zur Gewinnung von Seltenen Erden

Balinski, A.; Scharf, C.

Seltene Erden (Lanthanoide), eine Gruppe von 17 Elementen mit ähnlichen Eigenschaften, sind aus einer Vielzahl heutiger Produkte nicht mehr wegzudenken. Dazu gehören sowohl Gegenstände des täglichen Bedarfs wie z.B. LCD-Bildschirme oder Akkus für Laptops als auch hochspezifische Anwendungen wie z.B. Dauermagneten in Windkraftanlagen.
Um eine sichere Versorgung mit Seltenen Erden zu gewährleisten, müssen neue und innovative Methoden sowohl zur Aufbereitung von Erzen und Konzentraten als auch zur Verbesserung der weiteren Prozesskette durch Entwicklung von neuartigen Extraktionsmitteln gefunden werden. Das Forscherteam von „SE-FLECX“ nimmt die beiden Herausforderungen an, wobei drei Hauptziele im Fokus stehen: die Aufbereitung von unkonventionellen Rohstoffen, die Abtrennung der Actinoide und die selektive Auftrennung einzelner Seltenen Erden. Aufgrund der ähnlichen Eigenschaften der Elemente und der steigenden Komplexität der Erze ist die Bewältigung dieser Aufgaben entscheidend für die Erarbeitung von zukünftig durchsetzbaren Prozessen.

Keywords: Seltene Erden; Calixarene; unkonventionelle Rohstoffe; Flüssig-Flüssig-Extraktion

  • Lecture (Conference)
    r4-Clusterworkshop 2018, 10.-11.10.2018, Hannover, Deutschland

Publ.-Id: 28277

A Parallel Cellular Automata Lattice Boltzmann Method for Convection-Driven Solidification

Kao, A.; Krastins, I.; Alexandrakis, M.; Shevchenko, N.; Eckert, S.; Pericleous, K.

This paper presents a novel coupling of numerical techniques that enable 3D convection-driven microstructure simulations to be conducted on practical time scales appropriate for small size components or experiments. On the microstructure side, the cellular automata method is efficient for relatively large-scale simulations, while the lattice Boltzmann method provides one of the fastest transient hydrodynamic CFD solvers. Both of these methods have been parallelized and coupled in a single code, allowing resolution of large-scale convection-driven solidification problems. The numerical model is validated against benchmark cases, extended to capture solute plumes in directional solidification and finally used to model alloy solidification of an entire differentially heated cavity capturing both microstructural and meso/macro-scale phenomena.

Keywords: Lattice Boltzmann method; large-scale simulations; convection-driven solidification; fluid flow

Publ.-Id: 28276

SE-FLECX: Selektive Flüssig-Flüssig-Extraktion von Lanthanoiden und Actinoiden durch präorganisierte Calixarene

Balinski, A.; Scharf, C.

Zur Gewährleistung der sicheren Versorgung mit Seltenen Erden (Sc, Y und Lanthanoide) müssen innovative Methoden sowohl zur Aufbereitung von Rohstoffen als auch zur Verbesserung der weiteren Prozesskette durch Entwicklung von neuartigen Extraktionsmitteln gefunden werden. Im SE-FLECX-Projekt sollen diese Ziele durch die Anwendung der besonderen Eigenschaften von Calix[4]arenen und eine gezielte Aufbereitung der unkonventionellen Rohstoffquellen erreicht werden.
Die Entwicklung neuartiger Extraktionsmittel erfolgte durch die gezielte Substitution an makrocyclischen Calix[4]arenen. Zwei Typen von Liganden wurden für die effiziente Trennung der Actinoide (Typ A) und der Seltenen Erden (Typ B) synthetisiert, charakterisiert und erprobt.
Im Laufe des Projektes wurden zwei Vertreter gefunden, die aus einfach zusammengesetzten Systemen (Modelllösungen) sowohl Seltene Erden quantitativ in einer Stufe extrahieren (FG20) als auch U(VI) sehr effizient abtrennen können (AJ46).
Bei AJ46 wurde neben der Fähigkeit zur Uranabtrennung ebenso eine starke Affinität zu Schweren Seltenen Erden festgestellt. Sein industrieller Einsatz wurde jedoch aufgrund der hohen Synthesekosten als unwirtschaftlich bewertet. Diese konnten durch die Entwicklung einer alternativen Syntheseroute signifikant reduziert werden.

Keywords: Seltene Erden; Calixarene; Flüssig-Flüssig-Extraktion

  • Lecture (Conference)
    r4-Statuskonferenz, 31.01.-01.02.2018, Berlin, Deutschland
  • Poster
    r4-Statuskonferenz 2018, 31.01.-01.02.2018, Berlin, Deutschland
  • Poster
    24 Stunden für Ressourceneffizienz", Ressourceneffizienz-Kongress für Nachwuchsforscherinnen und Nachwuchsforscher, 14.-15.02.2017, Pforzheim, Deutschland

Publ.-Id: 28275

X-ray visualisation of melt flow effects on dendritic solidification

Shevchenko, N.; Keplinger, O.; Grenzer, J.; Rack, A.; Eckert, S.

X-ray radiography is an effective tool for investigating flow phenomena and solidification processes in opaque metallic alloys. This work is devoted to complex interaction between dendritic growth and melt flow during solidification of Ga-In alloys under natural and forced convection. Natural convection is caused by density variations within the solidifying alloys. Forced convection was produced by electromagnetic stirring. The conventional X-ray radioscopic experiments with sufficient spatial resolution (5-10 µm) deliver simultaneous information of both the dendrite structure and the flow patterns ahead of the solidification front and especially near the mushy zone. Melt convection alters the solutal field near the solidification front leading to different microstructures or even to the formation of freckle defects. The coarsening stage of dendritic structure is characterized by transformation of the sidearm morphology present after growth. The direct investigation of dendritic sidearm evolution during coarsening appears to be rather complex and impose high requirements with respect to the spatial and temporal resolution and sensitivity of the detector. The synchrotron imaging experiments with solidifying Ga-In alloys were performed at the BM20 and ID19 beamlines (ESRF, France) at a spatial resolution of < 1 µm. The present measurements provide real-time in-situ data on three phenomena that are of major importance in coarsening of dendrites: sidearm retraction, pinch-off and coalescence of neighboring sidearms. Using an advanced image analysis of high temporal and spatial resolution experimental data allows us to verify existing microstructural models.

Keywords: X-ray radiography; dendritic growth; melt flow; sidearm evolution

  • Lecture (Conference)
    32nd International Congress on High Speed Imaging and Photonics, 09.-12.10.2018, Twente, The Netherlands

Publ.-Id: 28274

In-situ observation of dendritic growth under the influence of electromagnetically driven flow

Shevchenko, N.; Keplinger, O.; Eckert, S.

Many studies have demonstrated that the application of electromagnetic stirring enhances the area of equiaxed grains and reduces the mean grain size (see e.g. [1-2]). It is widely accepted that flow-induced grain refinement and the CET (columnar to equiaxed transition) in metallic alloys is triggered by the appearance of additional dendrite fragments originating from the columnar front. The mechanism for grain multiplication by melt convection is supposed to be complex and is not fully understood until now.
The X-ray radiography was used for an in-situ study of the effect of electromagnetic stirring during the solidification of a Ga-25wt%In alloy in a Hele-Shaw cell [3]. The experimental setup was extended by a magnetic wheel, which allowed for controlled excitation of a melt flow in the liquid phase. The forced flow induces different effects on dendrite morphology, such as the uneven growth of primary trunks or lateral branches, remelting of single dendrites and also of lager dendrite ensembles, freckle formation, changes the inclination angle of the dendrites and leads to an increasing arm spacing. These effects are primarily governed by the convective redistribution of solute. Figure 1 demonstrates an interesting effect of "repairing" of a segregation channel (see the right-hand side part of Fig. 1a) after switching off the magnetic wheel (Fig 1b). It can be seen that an area with equiaxed or fine dendrites was formed instead of a segregation channel. The appearance of small equiaxed grains in the undercooled melt in the segregation pools is triggered by quick redistribution of solute after stopping the magnetic pump.
1. B. Willers et al, Materials Science and Engineering A 402 (2005) 55-65
2. T. Campanella et al, Metallurgical and Materials Transactions A 35 (2004) 3201-3210
3. N. Shevchenko et al, Journal of Crystal Growth 417 (2015) 1-8

Keywords: Electromagnetic stirring; solidification; X-ray radiography; freckle formation; Ga-In alloy

  • Lecture (Conference)
    9th International Symposium on Electromagnetic Processing of Materials (EPM2018), 14.-18.10.2018, Awaji, Hyogo, Japan

Publ.-Id: 28273

Pd catalyzed cross-coupling of [11C]MeLi and its application in the synthesis and evaluation of a potential PET tracer for the vesicular acetylcholine transporter (VAChT)

Helbert, H.; Wenzel, B.; Deuther-Conrad, W.; Luurtsema, G.; Szymanskic, W.; Brust, P.; Feringa, B. L.; Dierckx, R. A. J. O.; Elsinga, P. H.

The short half-life of 11C (t1/2 = 20.33 min) requires ultra-fast reactivity in order to perform efficient labelling of PET tracers. A recently discovered cross-coupling methodology1 enables the coupling between aryl bromides and organolithium reagents within seconds and therefore can be an attractive strategy to access 11C-labelled compounds. In this work several clinically relevant structures were labelled via this method. The scope of the reaction was further explored and expanded, allowing radiolabelling of highly reactive compounds, such as aldehydes. Then we focused our attention on the development of a new potential tracer for vesicular acetylcholine transporter (VAChT) which was enabled by this novel cross-coupling of [ 11C]MeLi.

[11C]MeLi was prepared via lithium-halogen exchange by trapping [11C]MeI in a solution of n-BuLi. The prepared [11C]MeLi was further reacted in a Pd catalyzed cross-coupling reaction with aryl bromides at r.t. for 4 minutes. After quench and evaporation of the solvent, the mixture was directly purified by HPLC. A series of synthesized vesamicol derivatives were subjected to affinity studies.

Scheme 1: Relevant structures for PET labelled via cross-coupling of [11C]MeLi

Several clinically relevant structures with application in breast cancer imaging and early diagnosis of Alzheimer’s disease had been successfully labelled using this procedure (scheme 1). Employing this same methylation strategy, novel potential tracers for VAChT were synthesized and evaluated in vitro, identifying a compound with good selectivity for VAChT versus σ1 and σ2 and compared to established (-)FEOBV.

Table 1: In vitro affinities measured on rat VAChT (VAChT-PC12), n = 3; human σ1 (hS1-HEK293), n = 3; rat σ2 (rat liver), n = 2
Affinity (nM) (±)1-Me (±)2-Me (±)3-Me (-)3-Me (-)FEOBV
Ki(VAChT) 8.7 ± 0.1 7.2 ± 1.2 27 ± 18 28 ± 16 7 ± 2
Ki(σ1) 2.1 ± 0.5 5.3 ± 1.7 362 ± 36 382 ± 166 2275 ± 390
Ki(σ2) 373 ± 147 618 ± 257 1650 ± 650 >5000 2118 ± 1058
σ1/VAChT : σ2/VAChT 0.2 : 43 0.7 : 86 13 : 50 14 : >150 >300 : >300

A new labelling methodology was successfully applied to the synthesis of clinically interesting radiotracers, providing the purified target molecules in R.C.Y. ranging from 34% to 56% within 30 to 40 minutes (EOB). This procedure offers new opportunities in the development of novel tracers, illustrated by the synthesis of a novel VAChT tracer.

1Heijnen D, Tosi F, Vila C, Stuart M, Elsinga P, Szymanski W, Feringa B. Angew. Chem. Int. Ed. 2017, 56 (12), 3354-3359

  • Lecture (Conference)
    ISRS 2019, 26.05.-01.06.2019, Beijing, China
  • Lecture (Conference)
    Annual EANM congress 2019, 12.10.2019, Barcelona, Spanien

Publ.-Id: 28272

Characterization of Isostructural An(IV) Complexes with Hetero-donor Imine Ligands

Radoske, T.; Schöne, S.; Kaden, P.; Ikeda-Ohno, A.; Stumpf, T.

The coordination chemistry of actinides (An) serves as fundamental knowledge for chemical engineering and environmental science related to the nuclear industry.[1] However, as compared with other transition metals, the basic chemistry of An is far less explored. The chemistry of An is complicated by, e.g., various possible oxidation states ranging from II to VII for the early An. One possible approach to understand the chemical nature of the An series is the comparison of isostructural compounds containing different actinides with the same oxidation state.[2,3,4] With this approach, the relative changes observed among the An series could allow us to gain insight into their unique chemical nature, such as electronic properties originating from their f-electron orbitals. One major question remaining in the field of An chemistry is the degree of “covalency” across the An series.[5] In order to study the “covalency” across the An series, one would require to perform a systematic study on a wide series of An, including transuranium (TRU) elements. Nonetheless, precedent studies covering TRU elements are rather scarce. This background motivates us to perform the current study focusing on a systematic comparison of the isostructural An complexes (Th, U and Np).
In this study we investigate the coordination chemistry of tetravalent actinides (An(IV)), which is dominant particularly under anoxic environmental conditions.[1] Synthesis of their compounds and the experiments should be conducted under inert and water-free atmosphere. The ligands used in this study are a hetero-donor imine ligand of salen and its derivatives (Fig. 1). These ligands have a capability to coordinate to metal ions tetradentately and exhibit both the hard- (oxygen) and medium-donor (nitrogen) characters, which could be a simple analog of natural occurring organic molecules. The eightfold coordination, which is often preferred for An complexes, can be readily achieved with these ligands by coordination of two ligand molecules. Salen and its derivatives have also been employed as a framework for catalytic and extraction agents.[6,7]

  • Lecture (Conference)
    Plutonium Futures 2018, 11.09.2018, San Diego, Vereinigte Staaten von Amerika

Publ.-Id: 28271

Actinide Bonding – Comparative Study of Isostructural An(IV) Imine Complexes

Radoske, T.; Kaden, P.; Schöne, S.; Ikeda-Ohno, A.; Stumpf, T.

Because of their unique electronic properties originating from 5f-orbitals, the coordination chemistry of actinides (An) is still an attractive research field in terms not only of nuclear engineering but also of basic chemistry. In particular, the early An show profound complex chemistry due to a wide variety of possible oxidation states ranging from +II to +VII, which is in contrast to the dominant trivalent state for their chemical analog of lanthanides. The aim of our research activities is to gain knowledge about the interaction of An with a variety of hard- and soft-donor ligands, eventually providing a comprehensive understanding of the electronic nature of actinide compounds. The ligands used in this study possess both O- (i.e. hard) and N-donor (soft) containing functionalities (Fig.1) and could also be considered as a simplified model of naturally relevant organic O/N-donor ligands.
A series of single crystals of [AnIV(Lp)2] complexes were synthesized from the tetrachloride compounds of An = Th, U and Np. SC-XRD measurements on the obtained crystals reveal their crystal structures, all showing the eight-fold coordination of the metal centre with the ligands on their primary coordination sphere, forming a trigonal dodecahedral geometry around the metal centre.
1H-NMR spectra of the dissolved complexes [ThIV(Le)2], [UIV(Le)2], [CeIV(Le)2] and the pure ligand in solution were recorded. The observed shifts show unique features when comparing isostructural diamagnetic compounds of lanthanides and actinides, which can not be explained by charge density differences.

  • Lecture (Conference)
    ISNSC - 10th International Symposium on Nano and Supramolecular Chemistry 2018, 10.07.2018, Dresden, Deutschland

Publ.-Id: 28270

Atomic-level thermodynamics and kinetics in solids: Examples for Si, Ge, and SiC

Posselt, M.

In this talk examples of atomistic simulations on thermodynamics and kinetics in Si, Ge, and SiC are presented.

Keywords: Atomic-level simulations; thermodynamics; Si; Ge; SiC

  • Lecture (others)
    Seminar "Topical Problems in Theoretical Physics", 28.11.2018, Chemnitz, Deutschland

Publ.-Id: 28269

Age and genesis of polymetallic veins in the Freiberg district, Erzgebirge, Germany: constraints from radiogenic isotopes

Ostendorf, J.; Henjes-Kunst, F.; Seifert, T.; Gutzmer, J.

The Freiberg mining district in the Erzgebirge hosts three principal types of polymetallic veins. These are (1) the quartz-bearing polymetallic sulfide type, (2) the carbonate-bearing polymetallic sulfide type, and (3) the barite-fluorite-sulfide type. We investigated the genesis of each vein-type using Rb-Sr sphalerite geochronology, Sm-Nd fluorite geochronology, and Pb, Sr, and Nd isotope systematics of ore and gangue minerals. Field relationships and the Rb-Sr and Pb isotope systematics of sulfides from quartz-bearing polymetallic sulfide veins and carbonate-bearing polymetallic sulfide veins confirm their close genetic affiliation and yield a combined Rb-Sr errorchron age of 276 ± 16 Ma. The high mean squared weighted deviation (MSWD) value of 42 on the regression is considered to reflect initial isotopic heterogeneity, which is probably related to fluid-rock interaction during the hydrothermal mineralization process. Although some sphalerites from barite-fluorite-sulfide veins have strongly disturbed Rb-Sr isotope systematics, six sphalerites and one co-genetic fahlore yield a robust isochron age of 121.3 ± 4.2 Ma with an MSWD of 2.9. This age is supported by a fluorite Sm-Nd isochron age of 101 ± 18 Ma (MSWD = 1.3). The new ages and radiogenic isotope data place robust constraints on the long-held hypothesis that veins in the Freiberg district formed during two hydrothermal events. The Lower Permian age of first stage quartz-bearing polymetallic sulfide veins and carbonate-bearing polymetallic sulfide veins coincides with post-Variscan crustal reorganization and Rotliegend volcanism. The Mid-Cretaceous age of second stage barite-fluorite-sulfide veins coincides with opening of the North Atlantic Ocean during the break-up of Pangea.

Keywords: Erzgebirge; Freiberg district; Pb isotopesRb-Sr sphalerite dating; Sm-Nd fluorite dating; Vein-type deposit

Publ.-Id: 28268

Cerebral perfusion changes in presymptomatic genetic frontotemporal dementia: a GENFI study

Mutsaerts, H. J. M. M.; Mirza, S. S.; Petr, J.; Thomas, D. L.; Cash, D. M.; Bocchetta, M.; de Vita, E.; Metcalfe, A. W.; Shirzadi, Z.; Robertson, A. D.; Carmela Tartaglia, M.; Mitchell, S. B.; Black, S. E.; Freedman, M.; Tang-Wai, D.; Keren, R.; Rogaeva, E.; van Swieten, J.; Laforce, R. J.; Tagliavini, F.; Borroni, B.; Galimberti, D.; Rowe, J. B.; Graff, C.; Frisoni, G. B.; Finger, E.; Sorbi, S.; de Mendonça, A.; Rohrer, J. D.; Macintosh, B. J.; Masellis, M.

Genetic forms of frontotemporal dementia are most commonly due to mutations in three genes, C9orf72, GRN or MAPT, with presymptomatic carriers from families representing those at risk. While cerebral blood flow shows differences between frontotemporal dementia and other forms of dementia, there is limited evidence of its utility in presymptomatic stages of frontotemporal dementia. This study aimed to delineate the cerebral blood flow signature of presymptomatic, genetic frontotemporal dementia using a voxel-based approach. In the multi-centre GENetic Frontotemporal dementia Initiative (GENFI) study, we investigated cross-sectional differences in arterial spin labeling MRI-based cerebral blood flow between presymptomatic C9orf72, GRN or MAPT mutation carriers (n=107) and non-carriers (n=113), using general linear mixed-effects models and voxel-based analyses. Cerebral blood flow within regions of interest derived from this model was then explored to identify differences between individual gene carrier groups and to estimate a timeframe for the expression of these differences. The voxel-based analysis revealed a significant inverse association between cerebral blood flow and the expected age of symptom onset in carriers, but not non-carriers. Regions included the bilateral insulae/orbitofrontal cortices, anterior cingulate/paracingulate gyri, and inferior parietal cortices, as well as the left middle temporal gyrus. For all bilateral regions, associations were greater on the right side. After correction for partial volume effects in a region of interest analysis, the results were found to be largely driven by the C9orf72 genetic subgroup. These cerebral blood flow differences first appeared approximately 15 years before the expected symptom onset determined on an individual basis. Cerebral blood flow was lower in presymptomatic mutation carriers closer to and beyond their expected age of symptom onset in key frontotemporal dementia signature regions. These results suggest that arterial spin labeling MRI may be a promising non-invasive imaging biomarker for the presymptomatic stages of genetic frontotemporal dementia.

Keywords: genetic frontotemporal dementia; arterial spin labeling; cerebral blood flow; presymptomatic biomarker

Publ.-Id: 28267

Sub-gap optical response in the Kitaev spin-liquid candidate α-RuCl3

Reschke, S.; Mayr, F.; Widmann, S.; Krug Von Nidda, H.-A.; Tsurkan, V.; Eremin, M. V.; Do, S.-H.; Choi, K.-Y.; Wang, Z.; Loidl, A.

We report detailed optical experiments on the layered compound α-RuCl3 focusing on the THz and sub-gap optical response across the structural phase transition from the monoclinic high-temperature to the rhombohedral low-temperature structure, where the stacking sequence of the molecular layers is changed. This type of phase transition is characteristic for a variety of tri-halides crystallizing in a layered honeycomb-type structure and so far is unique, as the low-temperature phase exhibits the higher symmetry. One motivation is to unravel the microscopic nature of THz and spin-orbital excitations via a study of temperature and symmetry-induced changes. The optical studies are complemented by thermal expansion experiments. We document a number of highly unusual findings: A characteristic two-step hysteresis of the structural phase transition, accompanied by a dramatic change of the reflectivity. A complex dielectric loss spectrum in the THz regime, which could indicate remnants of Kitaev physics. Orbital excitations, which cannot be explained based on recent models, and an electronic excitation, which appears in a narrow temperature range just across the structural phase transition. Despite significant symmetry changes across the monoclinic to rhombohedral phase transition and a change of the stacking sequence, phonon eigenfrequencies and the majority of spin-orbital excitations are not strongly influenced. Obviously, the symmetry of a single molecular layer determines the eigenfrequencies of most of these excitations. Only one mode at THz frequencies, which becomes suppressed in the high-temperature monoclinic phase and one phonon mode experience changes in symmetry and stacking. Finally, from this combined terahertz, far- and mid-infrared study we try to shed some light on the so far unsolved low energy (<1 eV) electronic structure of the ruthenium 4d5 electrons in α-RuCl3.


Publ.-Id: 28266

From curvilinear magnetism to shapeable magnetoelectronics

Makarov, D.

In this talk I will Review our activities on curvilinear magnetism and shapeable magnetoelectronics.

Keywords: curvilinear magnetism; shapeable magnetoelectronics

  • Invited lecture (Conferences)
    Seminar at the Department of Physics, University of Konstanz, 22.01.2019, Konstanz, Germany

Publ.-Id: 28265

Highly compliant planar Hall effect sensor with sub 50 nT sensitivity

Granell, P. N.; Wang, G.; Cañon Bermudez, G. S.; Kosub, T.; Golmar, F.; Steren, L.; Fassbender, J.; Makarov, D.

Next generation of flexible appliances such as soft robots aim to become fully autonomous and will require ultra-thin and flexible navigation modules, body tracking and relative position monitoring systems, which typically include magnetic field sensors as key building blocks. Although there is a great progress in the field of shapeable magnetoelectronics [1], there is no technology available which can enable sensitivities to magnetic fields lower than 1 μT (below the geomagnetic field) in a mechanically compliant form factor. To address this challenging task we introduced a new fundamental effect towards magnetic field sensing --the planar Hall effect (PHE) [2-5]-- in the field of shapeable magnetoelectronics. We demonstrate that even when prepared on mechanically imperceptible 6-μm-thick polymeric foils, magnetic field sensors based on the planar Hall effect have a remarkable sensitivity of 0.86 V/T and are capable of detecting magnetic fields in the range of sub 50 nT. Furthermore, these sensors can be bent to a radius of 1 mm without any degradation of their electrical resistance and shows excellent cyclic bending performance with only 0.3% resistance variation after more than 150 bending cycles. The application potential of the device is showcased in two examples of an angle and proximity sensors. For the latter, we demonstrate that the compliant PHE sensor is able to detect small magnetic stray fields of magnetically functionalized objects as needed for conventional metrology as well as point of care diagnostics. High sensitivity of the prepared sensing devices combined with a remarkable simplicity of fabrication, is a step forward in the realization of cost efficient flexible magnetoelectronic devices, with possible application in soft robotics, interactive devices for virtual- and augmented reality [6,7] and point of care platforms for the detection of magnetic objects [8].
References: [1] D. Makarov, Applied Physics Reviews, Vol. 3, p.011101 (2016)
[2] F. G. West, Journal of Applied Physics, Vol. 34, p.1171 (1963)
[3] C. Goldberg, Physical Review, Vol. 94, p.1121 (1954)
[5] A. Schuhl, Applied Physics Letters, Vol. 66, p.2751 (1995)
[5] V. Mor, Journal of Applied Physics, Vol. 111 (2012)
[6] G. S. Cañón Bermúdez, Science Advances, Vol. 4 (2018)
[7] M. Melzer, Nature Communications, Vol. 6 (2015)
[8] G. Lin, Lab Chip, Vol. 14, p.4050 (2014)

Keywords: magnetic field sensors; flexible electronics

  • Lecture (Conference)
    The 2019 Joint MMM-Intermag Conference, 14.-18.01.2019, Washington DC, USA

Publ.-Id: 28264

Droplet-based magnetofluidic platforms for detection and analytics

Makarov, D.

The development of next-generation biosensing technologies has picked up momentum in the past decade. Particularly, among a variety of biosensing principles, magnetic biosensing technologies based on magnetic particles and magnetic field sensors have attracted growing attention due to the unprecedented advantages brought by this unique sensing format.
Our contribution to this exciting field of research and technology includes the development of a compact droplet-based magnetofluidic platform encompassing integrated novel functionalities, e.g. analytics in a flow cytometry format [1-3], magnetic barcoding [4] and sorting of magnetically encoded emulsion droplets [5,6]. We put forth a novel high-capacity indexing scheme based on multiphase microfluidic networks for large-scale screening applications [5,6] and realized flexible microfluidic platform with integrated magnetoresistive sensorics [4]. The technology on how to integrate high-performance magnetic field sensors into multi-functional self-assembled tubular architectures [7-9] for lab-in-a-tube concept [10] will be discussed. These features are crucial to address the needs of modern medical research, e.g. drug discovery [11].
These developments will be outlined in my talk.

[1] G. Lin, D. Makarov et al., “Magnetoresistive emulsion analyzer”. Sci. Rep. 3, 2548 (2013).
[2] G. Lin, D. Makarov et al., “Magnetofluidic platform for multidimensional magnetic and optical barcoding of droplets”. Lab Chip 15, 216 (2015).
[3] D. Karnaushenko, D. Makarov et al., “Monitoring microbial metabolites using an inductively coupled resonance circuit”. Sci. Rep. 5, 12878 (2015).
[4] G. Lin, D. Makarov et al., “A highly flexible and compact magnetoresistive analytic device”. Lab Chip 14, 4050 (2014).
[5] G. Lin, D. Makarov et al., “Magnetic suspension array technology: Controlled synthesis and screening in microfluidic networks”. Small 12, 4553 (2016).
[6] W. Song, D. Makarov et al., “Encoding micro-reactors with droplet chains in microfluidics”. ACS Sensors 2, 1839 (2017).
[7] I. Mönch, D. Makarov et al., “Rolled-up magnetic sensor: Nanomembrane architecture for in-flow detection of magnetic objects”. ACS Nano 5, 7436 (2011).
[8] D. Karnaushenko, D. Makarov et al., “Self-assembled on-chip integrated giant magneto-impedance sensorics”. Adv. Mater. 27, 6582 (2015).
[9] T. Ueltzhöffer, D. Makarov et al., “Magnetically patterned rolled-up exchange bias tubes: A paternoster for superparamagnetic beads”. ACS Nano 10, 8491 (2016).
[10] E. J. Smith, D. Makarov et al., “Lab-in-a-tube: ultracompact components for on-chip capture and detection of individual micro-/nanoorganisms”. Lab Chip (Tutorial Review) 12, 1917 (2012).
[11] G. Lin, D. Makarov et al., “Magnetic sensing platform technologies for biomedical applications”. Lab Chip (Critical Review) 17, 1884 (2017).

Keywords: droplet Fluidics; millifluidics; magnetic field sensors

  • Invited lecture (Conferences)
    The 2019 Joint MMM-Intermag Conference, 14.-18.01.2019, Washington DC, USA

Publ.-Id: 28263

Exchange-driven chiral effects in curvilinear magnetism: theoretical abstraction or experimental observable

Makarov, D.

In this talk I will Review our recent exterimental and theoretical activities on curvilinear nanomagnets.

Keywords: curved magnetic thin films; curvilinear magnetism

  • Invited lecture (Conferences)
    Workshop „Topological Phenomena in Quantum Materials“, 04.-05.12.2018, Dresden, Germany

Publ.-Id: 28262

Shapeable magnetoelectronics with sensitivities to geomagnetic fields and below

Makarov, D.

The recent rapid advance and eagerness of portable consumer electronics stimulate the development of functional elements towards being lightweight, flexible, and wearable. Next generation flexible appliances aim to become fully autonomous and will require ultra-thin and flexible navigation modules, body tracking and relative position monitoring systems. Key building blocks of navigation and position tracking devices are magnetic field sensors.
Although there is a remarkable progress in the field of shapeable magnetoelectronics [1], there is no technology available which can enable sensitivities to geomagnetic fields of 50 µT and, ultimately, magnetic fields of smaller than 1 µT in a mechanically compliant form factor. If available, these devices would contribute greatly to the realization of high-performance on-skin interactive electronics [2,3] and point of care applications [4].
Here, I will review two technological platforms allowing to realize not only mechanically imperceptible electronic skins, which enable perception of the geomagnetic field (e-skin compasses) [4], but also enable sensitivities down to ultra-small fields of sub-50 nT [6]. We demonstrate that e-skin compasses allow humans to orient with respect to earth’s magnetic field ubiquitously. Furthermore, biomagnetic orientation enables novel interactive devices for virtual and augmented reality applications. We showcase this by realizing touchless control of virtual units in a game engine using omnidirectional magnetosensitive skins.

[1] D. Makarov et al., Applied Physics Reviews 3, 011101 (2016).
[2] G.S. Canon Bermudez, D. Makarov et al., Science Advances 4, eaao2623 (2018).
[3] M. Melzer, D. Makarov et al., Nature Communications 6, 6080 (2015).
[4] G. Lin, D. Makarov et al., Lab Chip 14, 4050 (2014).
[5] G.S. Canon Bermudez, D. Makarov et al., Nature Electronics, in press.
[6] P.N. Granell, D. Makarov et al., npj Flexible Electronics, in press.

Keywords: flexible electronics; magnetic field sensors

  • Invited lecture (Conferences)
    2018 International Workshop on Nanomembrane Origami Technology, 10.-11.11.2018, Shanghai, China

Publ.-Id: 28261

Observation of charge density waves in free-standing 1T-TaSe2 monolayers by transmission electron microscopy

Börner, P. C.; Kinyanjui, M. K.; Björkman, T.; Lehnert, T.; Krasheninnikov, A. V.; Kaiser, U.

While bulk 1T-TaSe2 is characterized by a commensurate charge density wave (CCDW) state below 473K, the stability of the CCDW state in a 1T-TaSe2 monolayer, although theoretically predicted, has not been experimentally confirmed so far. As charge density waves and periodic lattice distortions (PLDs) always come together, we evaluate the PLD in a 1T-TaSe2 monolayer from low-voltage aberration-corrected high-resolution transmission electron microscopy experiments. To prevent fast degradation of 1T-TaSe2 during exposure to the electron-beam, a 1T-TaSe2/graphene heterostructure was prepared. We also perform the image simulations based on atom coordinates obtained using density functional theory calculations. From the agreement between the experimental and simulated images, we confirm the stability of the CCDW/PLD in a monolayer 1T-TaSe2/graphene heterostructure at room temperature in the form of a 13 13 superstructure. At the same time, we find that in comparison to multi-layer structures, the superstructure is less pronounced.

Keywords: 1T-TaSe2; graphene; TEM; first-principles calculations


Publ.-Id: 28260

Reversible superdense ordering of lithium between two graphene sheets

Kühne, M.; Börrnert, F.; Fecher, S.; Ghorbani-Asl, M.; Biskupek, J.; Samuelis, D.; Krasheninnikov, A. V.; Kaiser, U.; Smet, J. H.

Many carbon allotropes can act as host materials for reversible lithium uptake1,2, thereby laying the foundations for existing and future electrochemical energy storage. However, insight into how lithium is arranged within these hosts is difficult to obtain from a working system. For example, the use of in situ transmission electron microscopy3–5 to probe light elements (especially lithium)6,7 is severely hampered by their low scattering cross-section for impinging electrons and their susceptibility to knock-on damage8. Here we study the reversible intercalation of lithium into bilayer graphene by in situ low-voltage transmission electron microscopy, using both spherical and chromatic aberration correction9 to enhance contrast and resolution to the required levels. The microscopy is supported by electron energy-loss spectroscopy and density functional theory calculations. On their remote insertion from an electrochemical cell covering one end of the long but narrow bilayer, we observe lithium atoms to assume multi-layered close-packed order between the two carbon sheets. The lithium storage capacity associated with this superdense phase far exceeds that expected from formation of LiC6, which is the densest configuration known under normal conditions for lithium intercalation within bulk graphitic carbon10. Our findings thus point to the possible existence of distinct storage arrangements of ions in two-dimensional layered materials as compared to their bulk parent compounds.

Keywords: Li storage; graphene; TEM; first-principles caclulations


Publ.-Id: 28259

Epitaxial Mn5Ge3 (100) layer on Ge (100) substrates obtained by flash lamp annealing

Xie, Y.; Yuan, Y.; Wang, M.; Xu, C.; Hübner, R.; Grenzer, J.; Zeng, Y.; Helm, M.; Zhou, S.; Prucnal, S.

Mn5Ge3 thin films have been demonstrated as promising spin-injector materials for germanium-based spintronic devices. So far, Mn5Ge3 has been grown epitaxially only on Ge (111) substrates. In this letter, we present the growth of epitaxial Mn5Ge3 films on Ge (100) substrates. The Mn5Ge3 film is synthetized via sub-second solid-state reaction between Mn and Ge upon flash lamp annealing for 20 ms at the ambient pressure. The single crystalline Mn5Ge3 is ferromagnetic with a Curie temperature of 283 K. Both the c-axis of hexagonal Mn5Ge3 and the magnetic easy axis are parallel to the Ge (100) surface. The millisecond-range flash epitaxy provides a new avenue for the fabrication of Ge-based spin-injectors fully compatible with CMOS technology.

Keywords: Mn5Ge3; epitaxial thin film; ferromagnetism; spintronic devices

Publ.-Id: 28258

First Series of Tetravalent Thorium-, Uranium- and Neptunium-Amidinate Complexes

Schöne, S.; Kaden, P.; Patzschke, M.; Roesky, P. W.; Stumpf, T.; März, J.

Actinides (An) can possess a variety of different oxidation states, which typically range from +III to +VI for the early actinides Th-Cm. They have unique electronic properties originating from the 5f-orbitals, what makes their coordination chemistry a fascinating area of research for both, the nuclear engineering but also for fundamental chemistry. Thorium (Th), uranium (U), neptunium (Np) and plutonium (Pu) can form highly charged cations with the oxidation state of four (An4+), which is the dominant one under reductive conditions. Furthermore, An(IV) are of particular interest for the coordination chemistry because of their strong interaction with ligands.
Hence, the overall aim of our investigations is a deep understanding of the interaction mechanisms between tetravalent An (An(IV)) and ligands bearing soft donor atoms, such as nitrogen (N). Thus, we focused on the synthesis and characterization of a series of An(IV) complexes with the N-donor ligand N,N’-Diisopropylbenzamidine (iPr2BA) both in solution and in solid state.
The structures of the synthesised complex series were determined by single-crystal X-ray diffraction (SC-XRD), showing the An(IV) coordinated by three iPr2BA molecules and one chloro ligand in a monocapped octahedral coordination geometry. This is the very first example of an An(IV) complex series including Np(IV) as a transuranium element with an amidinate ligand. The isostructural complexes allow a direct comparison of the binding situation of the An(IV) across the series. Quantum chemical calculation strongly supported the experimental results to to further study the electronic structure of the complexes.
NMR-spectroscopic investigations of the dissolved complexes in toluene-d8 showed significant chemical shifts due to considerable effects of the paramagnetic metal centres U(IV) and Np(IV) compared to the diamagnetic reference [Th(iPr2BA)3Cl].

Keywords: actinide; amidinate; coordination chemistry; thorium; uranium; neptunium; NMR; SC-XRD

  • Invited lecture (Conferences)
    10th International Conference on f-Elements (ICFE-10), 03.-07.09.2018, Lausanne, Schweiz

Publ.-Id: 28257

Coordination Chemistry of Tetravalent Actinides: Series & Trends

Schöne, S.; Radoske, T.; Kloditz, R.; Köhler, L.; Kaden, P.; Patzschke, M.; Roesky, P. W.; Stumpf, T.; März, J.

The coordination chemistry of actinides (An) using model ligands helps to deeply understand their bonding situation on a molecular level. However, the basic An chemistry is still little explored. Characteristic of An is a huge variety of possible oxidation states, typically ranging from II to VII for early An. A suitable approach to explore the fundamental phico-chemical properties of An is to study a series of isostructural An compounds in the same oxidation state. Observed changes in e.g. the binding situation or magnetic effects among the An series could deliver insight into their unique electronic properties mainly origination from the f-electrons. A question still remaining in An chemistry is the degree of "covalency". However, studies covering TRU elements are rather scarce. Against this background, we are strongly motivated to perform a systematic comparison of isostructural An complexes (Th, U and Np).
In this study we investigate the coordination chemistry of tetravalent actinides (An(IV)) for two major reasons: a) the series of An(IV) is the largest accessible one within the early actinides, and b) the tetravalent state is the dominant one particularly under anoxic conditions. The ligands used in this study range from hard- (oxygen) and medium- (nitrogen) to pure soft-donor (carbon) character, according to Pearsons's HSAB concept. Due to the expected changes in orbital overlap between the metal and ligand, the formed complexes could further provide us a deep insight into the electronic situation of the actinides.
The An(IV) complexes are characterised in solution by NMR-, IR- and UV-vis spectroscopy as well as in the solid-state by SC_XRD. The acquired experimental results are further supported by quantum chemical calculations with a focus on the electronic structure of the complexes.

Keywords: actinide; coordination chemistry; thorium; uranium; neptunium

  • Invited lecture (Conferences)
    ISNSC - 10th International Symposium on Nano and Supramolecular Chemistry 2018, 08.-13.07.2018, Dresden, Deutschland

Publ.-Id: 28256

Synthesis and Characterization of U(IV) Imidazol-2-ylidene Complexes

Köhler, L.; März, J.; Patzschke, M.; Kaden, P.; Monkowius, U.

In the field of actinide coordination chemistry, it is assumed that ligands bearing soft donor atoms, according to Pearson’s hard-soft-acid-base concept, such as sulphur, phosphorous or carbon lead to stable complexes. Furthermore, due to the expected strong orbital overlap between the metal and ligand, the formed complexes would provide us a deep insight into the electronic situation of the actinides. However, the majority of published actinide compounds still focusses on complexes with hard donor atoms such as oxygen.
A few examples of actinide-carbene complexes reported in the literature emphasise the remarkable strong σ donor properties of the carbon donor ligands, making the complexes e.g. excellent catalysts in organic synthesis1. Of particular interest are N-heterocyclic carbenes (NHCs) based on an imidazole-2-ylidene backbone, also known as “Arduengo carbenes”. For instance, the stability and electronic properties of these ligands can be easily tuned by synthetic introduction of suitable substituents at the nitrogen atoms.
The aim of this study is the synthesis of tetravalent actinide (An(IV)) complexes with soft-donor carbene ligands according to Figure 1 and the characterisation of the formed complexes in solution by NMR-, IR- and UV-vis spectroscopy as well as the solid-state characterisation with the help of single crystal X-ray diffraction. The acquired experimental results are further supported by quantum chemical calculations to further study the electronic structure of the complexes.

Keywords: actinide; coordination chemistry; carbene; uranium

  • Poster
    ISNSC - 10th International Symposium on Nano and Supramolecular Chemistry 2018, 08.-12.07.2018, Dresden, Deutschland

Publ.-Id: 28255

Coordination Chemistry of Uranium (U(IV) and -(VI)) with Bidentate N-donor Ligands

März, J.; Schöne, S.; Radoske, T.; Patzschke, M.; Stumpf, T.; Ikeda-Ohno, A.

The bidentate N-donor ligands 2,2’-bipyridine (bipy) and 1,10-phenanthroline (phen) have attracted considerable attention in the field of coordination chemistry over the last decades because of their remarkable stability towards a wide variety of transition metals1. The coordination chemistry of uranium (U) has been explored with these N-donor ligands as well with a primary focus on its hexavalent state (U(VI) as UO₂2+). To the contrary, much less attention has been paid for the lower oxidation states, such as a tetravalent state (U(IV)). Here we present a systematic study on the coordination chemistry of U(IV) and -(VI) with bipy and phen under different chemical conditions, such as different solvents and changing the metal / ligand ratio.

In this study we succeeded to obtain a series of U(IV) complexes with U:ligand ratios of 1:1 and 1:2, all of which show an eight-fold coordinated uranium centre. In addition to the ligand, chloro and methanolato ligands are coordinating to the metal centre for charge compensation. Interestingly, the complexation between U(IV) and the ligand does occur even in protic solvents, in which the ligand is expected to be protonated. We also obtained another series of U(VI) complexes with both bipy and phen, underlining the versatile coordination chemistry of uranyl (UO22+). That is, the coordination between uranyl and the ligand depends strongly on the pH of the solvent used. For instance, in media with lower pH mononuclear complexes are formed, showing the uranyl unit in an unusually bent geometry.3 On the other hand, dinuclear uranyl arrangements with hydroxo-brinding are dominated in the media with higher pH, as shown in the right of Fig. 1. As illustrated in Fig. 1, bipy and phen are forming isostructural complexes both with U(IV) and- (VI).

Keywords: uranium; coordination chemistry; N-donor ligand; bipyridine; phenanthroline

  • Lecture (Conference)
    RadChem 2018, 13.-18.05.2018, Mariánské Lázně, Tschechien

Publ.-Id: 28254

Recovery of gallium from wafer fabrication industry wastewaters by Desferrioxamine B and E using reversed-phase chromatography approach

Jain, R.; Fan, S.; Kaden, P.; Tsushima, S.; Foerstendorf, H.; Barthen, R.; Lehmann, F.; Pollmann, K.

Gallium (Ga) is a critical element in developing renewable energy generation and energy efficient systems. The supply of Ga is at risk and needed recycling technologies for its availability in future. This study demonstrated the recovery of Ga3+ from low gallium concentrated wafer fabrication industry wastewaters using the siderophores desferrioxamine B (DFOB) and desferrioxamine E (DFOE). The complexation of Ga3+ by DFOB and DFOE was through hydroxamate group as demonstrated by infrared spectroscopy, nuclear magnetic resonance and density functional theory calculations. The high selectivity of DFOB/E towards Ga3+ was observed due to the formation of highly stable complex. Indeed, due to the formation of such high stability complex, the DFOB and DFOE were able to successfully complex 100% Ga in the two different wastewater from wafer fabrication industry. For the recovery of the siderophores, a high rate of decomplexation of Ga (>90%) was achieved upon addition of 6 times excess of ethylenediaminetetraacetic acid (EDTA) at pH of 3.5. More than 95% of Ga-DFOB and Ga-DFOE complex were recovered with purity (% of Ga moles in comparison to total moles of metals) of 70.4 and 94.9%, respectively by application of a C18 reversed-phase chromatography column. A preliminary cost-calculation demonstrated that acetonitrile consumption and desferrioxamines are major cost input for the technology. This study, for the first time, demonstrated a technical solution to the recovery of Ga3+ from the low concentrated wastewater based on siderophores and reversed-phase chromatography. A German patent application had been filed for this technology.

Keywords: Metal recovery; recycling; resource efficiency; cost-benefit; wastewater

Publ.-Id: 28253

Pulsating dissolution of crystalline matter

Fischer, C.; Lüttge, A.

Fluid-solid reactions result in dissolution or precipitation reactions. The prediction of the related material flux
from or to the reacting surface, its variations and changes with time are of interest to a wide array of disciplines.
Reaction rate maps that are derived from sequences of topography maps illustrate the spatial distribution of
reaction rates across the crystal surface [1]. Here we present dissolution rate maps that reveal the existence
of rhythmic pulses of the material flux from the crystal surface. This observation leads to a change in our
understanding of the way crystalline matter dissolves. Rhythmic fluctuations of the reactive surface site density
and potentially concomitant oscillations in the fluid saturation imply spatial and temporal variability in surface
reaction rates. Knowledge of such variability could aid attempts to upscale microscopic rates and predict reactive
transport through changing porous media.
[1] Fischer, C., Luttge, A., 2017. Beyond the conventional understanding of water–rock reactivity. Earth and
Planetary Science Letters 457, 100-105.

  • Lecture (Conference)
    EGU 2018 - European Geosciences Union General Assembly 2018, 08.-13.04.2018, Wien, Österreich

Publ.-Id: 28252

Dissolution rate variability of sandstone calcite cement

Pedrosa, E. T.; Fischer, C.; Lüttge, A.

For a holistic understanding of the long-term usage and safety analysis of reservoir rocks it is crucial to understand the fundamental mineral reactions and its control mechanisms. Kinetic quantification of the processes involved with fluid-rock interactions are especially important for predicting the evolution of pore space in rocks subjected to fluid injection, such as in CO2-sequestration and hydrocarbon exploration techniques.
The calcite cement selected for this study belongs to a fluvial-aeolian Rotliegend succession exposed near Bebertal (Flechtinge High, Germany) that was deposited in the same conditions as those that form the prolific gas reservoirs of the Southern Permian Basin1,2. Optical microscopy, SEM-BSE images and Cathodoluminescence analysis of the unreacted samples showed that two types of cement were present, although the calcite cement patches were composed of single crystals. We hypothesized that these different types of cement would react differently to fluid input. We used polished thick-sections of plug samples for dissolution experiments in a flow-through cell using a 2 mmol Na2CO3 solution (pH = 8.6, T≈ 21°C), for 7 reaction intervals (3 to 32 hours). Before and after each experiment the sample’s topography changes were mapped using a vertical scanning interferometer (VSI). High-resolution surface maps are subsequently used to calculate surface dissolution rates3.
After experiments, VSI images revealed an increase of the surface roughness in the cement patches. Detailed analysis of the rate dissolution variability in between the calcite cement patches and the intravariability of each cement patch related to chemical composition variability in the samples will be presented.
1Fischer, C., Gaupp, R., Dimke, M., Sill, O., 2007. A 3D high resolution model of bounding surfaces in aelian-fluvial deposits: An outcrop analogue study from the Permian Rotliegend, Northern Germany. Journal of Petroleum Geology, 30(3), 257–273.
2Fischer, C.; Dunkl, I.; von Eynatten, H.; Wijbrans, J. R.; Gaupp, R., 2012. Products and timing of diagenetic processes in Upper Rotliegend sandstones from Bebertal (North German Basin, Parchim Formation, Flechtingen High, Germany). Geological Magazine, 149 (5), 827-840.
3Luttge, A., and Bolton, E., 1999. An interferometric study of the dissolution kinetics of anorthite : The role of reactive surface area. American Journal of Science, 299, 652–678.

  • Lecture (Conference)
    GeoBonn 2018, 02.-06.09.2018, Bonn, Deutschland

Publ.-Id: 28251

Precipitation and dissolution of cement minerals in sandstone: Opportunities and limitations of pore and plug scale flow analysis for reactive transport modelling approaches

Kulenkampff, J.; Karimzadeh, L.; Fischer, C.

Reservoir properties of sandstones are controlled by precipitation and dissolution reactions at the pore walls. Both, the formation and dissolution of cement minerals are responsible for the complex pattern formation of porosity and permeability in reservoir rocks.
At the scale of drilled core sections (plugs), experimental and analytical approaches utilize positron emission tomography (PET) with radiotracers (Kulenkampff et al. 2016). Resulting spatiotemporal concentration distributions provide quantitative insight into fluid flow and diffusion parameters. The sensitivity is in the picomolar range of the utilized radiotracers and the spatial resolution is about 1 mm. Thus, mechanistically-important surface features such as etch pits or growth hillocks and their evolution during reaction are not yet part of the direct analysis of the flow field.
Here, we present an approach based on existing information about the complex crystal surface morphology and rate evolution (Fischer& Luttge 2017). We utilize artificial materials that are produced by 3D printing capabilities. Such an approach using PET analysis of sequences of machined surfaces in flow-through experiments provides quantitative insight into the local stability vs. temporal heterogeneity of fluid flow close to reacting surfaces. The measured flow velocity data from PET are implemented into reactive transport models and compared to existing small-scale calculations. We discuss the resulting size and complexity of surface rate patterns.

Fischer, C. and A. Luttge (2017). Beyond the conventional understanding of water–rock reactivity. Earth and Planetary Science Letters, 457: 100-105
J. Kulenkampff, M. Gründig, A. Zakhnini and J. Lippmann-Pipke (2016): Geoscientific process monitoring with positron emission tomography (GeoPET). Solid Earth, 7: 1217-1231

  • Lecture (Conference)
    Interpore 2018, 14.-17.05.2018, New Orleans, USA

Publ.-Id: 28250

Surface-Functionalized Mesoporous Nanoparticles as Heterogeneous Supports To Transfer Bifunctional Catalysts into Organic Solvents for Tandem Catalysis

Zhang, N.; Hübner, R.; Wang, Y.; Zhang, E.; Zhou, Y.; Dong, S.; Wu, C.

The combination of chemo- and biocatalysts offers a powerful platform to address synthetic challenges in chemistry, particularly in synthetic cascades. However, transferring both catalysts into organic solvents remains technically difficult because of the enzyme inactivation and catalyst precipitation. Herein, we designed a facile approach using functionalized mesoporous silica nanoparticles (MSN) to transfer chemo- and biocatalysts into a variety of organic solvents. As a proof-of-concept, two distinct catalysts, palladium nanoparticles (Pd NPs) and Candida antarctica lipase B (CalB), were stepwise loaded into separate locations of the mesoporous structure, which not only provided catalysts with heterogeneous supports for the recycling but also avoided their mutual inactivation. Moreover, mesoporous particles were hydrophobized by surface alkylation, resulting in a tailor-made particle hydrophobicity, which allowed bifunctional catalysts to be dispersed in eight organic solvents. Eventually, these attractive material properties provided the MSN-based bifunctional catalysts with remarkable catalytic performance for cascade reaction synthesizing benzyl hexanoate in toluene. With a broader perspective, the success of this study opens new avenues in the field of multifunctional catalysts where a plethora of other chemo- and biocatalysts can be incorporated into surface-functionalized materials ranging from soft matters to porous networks for synthetic purposes in organic solvents.

Keywords: multifunctional biocatalyst; mesoporous silica nanoparticles (MSN); palladium nanoparticles; lipase CalB; cascade reaction

Publ.-Id: 28249

Strong Variation Of Electronic Properties Of MoS2 And WS2 Nanotubes In Presence Of External Electric Fields

Zibouche, N.; Philipsen, P.; Kuc, A.

Transition-metal dichalcogenides attracted a huge international research focus from the point of two-dimensional materials. These materials exist also as nanotubes, how- ever, they have been mostly studied for their lubricant properties. Despite their inter- esting electronic properties, quite similar to their 2D counterparts, nanotubes remain much less explored. Like in 2D materials, electronic properties of nanotubes can be strongly modulated by external means, such as strain or electric field. Here, we report on the effect of external electric fields on the electronic properties of MoS2 and WS2 nanotubes, using density functional theory. We show that the electric field induces a strong polarization in these nanotubes, what results in a nearly linear decrease of the band gaps with the field strength and eventually in a semiconductor-metal transi- tion. In particular for large tube diameters, this transition can occur for field strengths between 1 - 2 V nm−1. This is an order of magnitude weaker than fields required to close the band gaps in the corresponding 2D mono- and bilayers of transition-metal dichalcogenides. We also observe splittings of the degenerate valence and conduction band states due to the Stark effect. Accordingly, such nanotubes could be used in na- noelectronics as logical switches, even at moderate field strengths that can be achieved experimentally, for example, by applying a gate voltage.


Publ.-Id: 28248

Trace element geochemistry of sphalerite in contrasting hydrothermal fluid systems of the Freiberg district, Germany: insights from LA-ICP-MS analysis, near-infrared light microthermometry of sphalerite-hosted fluid inclusions, and sulfur isotope geochemistry

Bauer, M. E.; Burisch, M.; Ostendorf, J.; Krause, J.; Frenzel, M.; Seifert, T.; Gutzmer, J.

The historic silver mining district of Freiberg (Germany) comprises hydrothermal vein-style mineralization of Permian and Cretaceous age. We compare sphalerite compositions with associated ore-forming fluids and constrain the behavior of critical metals such as In, Ge, and Ga in contrasting hydrothermal environments. Fluid inclusion studies reveal that the Permian veins formed due to boiling and cooling of a low-salinity (0 to 6% eq. w[NaCl]) magmatic-hydrothermal fluid at 350 to 230 °C. In contrast, Cretaceous veins formed by mixing of highly saline (17 to 24% eq. w[NaCl + CaCl2] and variable Na/(Na + Ca) ratios) brines at low temperatures (~ 120 °C). Sulfides of the Permian ore stage have a narrow range of δ34SVCDT from − 2.3 to + 0.9‰, while the sulfides of the Cretaceous stage have a large scatter and significantly more negative δ34SVCDT values (− 30.9 to − 5.5‰), supporting the different nature of the hydrothermal systems. Contrasting fluid systems and ore-forming mechanisms correspond to markedly different trace element systematics in sphalerite. Permian sphalerite is significantly enriched in In (up to 2500 μg/g In) relative to two sphalerite generations of Cretaceous veins. The latter have higher Ge (up to 2700 μg/g Ge) and Ga (up to 1000 μg/g Ga) concentrations. The observed trace element systematics of different sphalerite generations imply that In is enriched in high-temperature, low- to intermediate-salinity fluids with a significant magmatic-hydrothermal fluid component, while Ge and Ga are more concentrated in low-temperature, high-salinity crustal fluids with no obvious magmatic-hydrothermal affiliation.

Keywords: Sphalerite; Indium; Germanium; Gallium; Critical metals; EPMA; LA-ICP-MS; Fluid inclusions; Near-infrared light microthermometry; Sulfur isotopes; Geothermometer; Erzgebirge

Publ.-Id: 28247

Indium and selenium distribution in the Neves-Corvo deposit, Iberian Pyrite Belt, Portugal

Carvalho, J. R. S.; Relvas, J. M. R. S.; Pinto, A. M. M.; Frenzel, M.; Krause, J.; Gutzmer, J.; Pacheco, N.; Fonseca, R.; Santos, S.; Caetano, P.; Reis, T.; Goncalves, M.

High concentrations of indium (In) and selenium (Se) have been reported in the Neves-Corvo volcanic-hosted massive sulfide deposit, Portugal. The distribution of these ore metals in the deposit is complex as a result of the combined effects of early ore-forming processes and late tectonometamorphic remobilization. The In and Se contents are higher in Cu-rich ore types, and lower in Zn-rich ore types. At the deposit scale, both In and Se correlate positively with Cu, whereas their correlations with Zn are close to zero. This argues for a genetic connection between Cu, In and Se in terms of metal sourcing and precipitation. However, re-distribution and re-concentration of In and Se associated with tectonometamorphic deformation are also processes of major importance for the actual distribution of these metals throughout the whole deposit. Although minor roquesite and other In-bearing phases were recognized, it is clear that most In within the deposit is found incorporated within sphalerite and chalcopyrite. When chalcopyrite and sphalerite coexist, the In content in sphalerite (avg. 1400 ppm) is, on average, 2–3 times higher than in chalcopyrite (avg. 660 ppm). The In content in stannite (avg. 1.3 wt.%) is even higher than in sphalerite, but the overall abundance of stannite is subordinate to either sphalerite or chalcopyrite. Selenium is dispersed widely between many different ore minerals, but galena is the main Se-carrier. On average, the Se content in galena is ~50 times greater than in either chalcopyrite (avg. 610 ppm) or sphalerite (avg. 590 ppm). The copper concentrate produced at Neves-Corvo contains very significant In (+Se) content, well above economic values if the copper smelters recovered it. Moreover, the high In content of sphalerite from some Cu-Zn ores, or associated with shear structures, could possibly justify, in the future, a selective exploitation strategy for the production of an In-rich zinc concentrate.

Keywords: Neves-Corvo; indium; selenium


Publ.-Id: 28246

A spectroscopic study of trivalent cation (Cm3+ and Eu3+) sorption on monoclinic zirconia (ZrO2)

Eibl, M.; Virtanen, S.; Pischel, F.; Bok, F.; Lönnrot, S.; Shaw, S.; Huittinen, N.

Zirconia (ZrO2) formed by corrosion of zircalloy, can immobilize radioactive contaminants (e.g. actinides) in repositories for spent nuclear fuel (SNF). The presence of organic and inorganic carbon at the highly reactive ZrO2 surface impacts the adsorption of these metal ions and their surface speciation.
Sorption of Eu3+ and Cm3+ on zirconia was studied in batch-sorption experiments, and via laser spectroscopy (TRLFS). Two zirconia solids with varying carbon content were utilized. The influence of carbon impurities on the ZrO2 surface charge was investigated via zeta-potential measurements. Batch data was collected for various Eu3+ concentrations, while the pH-dependent Cm3+ surface speciation was studied with TRLFS. The spectroscopic sorption data was modeled using the Diffuse Double Layer (DDL) model.
The ZrO2 surface charge measurements yielded a pHIEP of 6 which was influenced by the presence of inorganic and organic carbon species. The pH-dependent sorption of Eu3+ showed a maximum sorption above pH 5.5, with no impact of the carbon concentration. The speciation of the trivalent metal, however, was different in the presence of intrinsic organic carbon in the sample, resulting in the formation of an organic Cm3+-complex on the surface. The sorption data was well described by our DDL model.

Keywords: Cm3+; Eu3+; zirconia (ZrO2); organic impurity; laser spectroscopy (TRLFS); sorption; surface complexation modeling


  • Secondary publication expected

Publ.-Id: 28245

Bestimmung der Input Funktion für das kinetische Modelling von (+)-[18F]Flubatine

Patt, M.; Tiepolt, S.; Sattler, B.; Hoepping, A.; Smits, R.; Deuther-Conrad, W.; Becker, G. A.; Steinbach, J.; Brust, P.; Sabri, O.

Der Abstract wird nachgereicht.

  • Lecture (Conference)
    56. Jahrestagung der DGN, 18.-21.04.2018, Bremen, Deutschland
  • Abstract in refereed journal
    Nuklearmedizin 56(2018), V10

Publ.-Id: 28244

C-11 Markierung von zwei neuen Liganden für den Alpha7-Subtyp des nikotinischen Acetylcholinrezeptor (nAChR)

Patt, J. T.; Deuther-Conrad, W.; Peters, D.; Barthel, H.; Brust, P.; Sabri, O.; Patt, M.

Abstract wird nachgereicht.

  • Lecture (Conference)
    56. Jahrestagung der DGN, 18.-21.04.2018, Bremen, Deutschland
  • Abstract in refereed journal
    Nuklearmedizin 56(2018), V24

Publ.-Id: 28243

On Development and Validation of subcooled nucleate models for OpenFOAM Foundation Release

Peltola, J.; Bainbridge, W.; Lehnigk, R.; Schlegel, F.; Pättikangas, T. J. H.

Subcooled nucleate boiling capability based on [1] was introduced to OpenFOAM 4.0 [2] within multiphase framework called reactingEulerFoam that supports two- and multiphase simulations. Since then the capability has been further refined and extended in subsequent releases 5.0 and 6. The present implementation - available in OpenFOAM Foundation development release [3] - includes the RPI wall boiling model [4] with run time selectable nucleation site density and bubble departure diameter and frequency models. Runtime selectable wall heat transfer models for distribution of wall heat flux between gas and liquid phases are also included for non-equilibrium phase change simulations. Interfacial heat transfer and phase change are calculated with two-resistance approach and interface temperature using user selectable heat transfer models and saturation temperature model. For turbulence modelling, single-phase models available in the release can be selected and there are also specialized k-ε and k-ω two-phase models available. For bubble diameter modelling algebraic [5], IATE [6] and inhomogeneous class method models are available [7, 8].

The present paper compares simulation results obtained with different model combinations to publicly available experimental data from DEBORA and other experiments. The implications of the choices of the models and model parameters on accuracy and performance are discussed and practical recommendations are given for those that intend to use this publicly available resource for further research.

[1] Peltola, J., & Pättikangas, T.J.H. (2012). CFD4NRS-4, paper 59.
[2] OpenFOAM Foundation, OpenFOAM 4.0, (2016)
[3] OpenFOAM Foundation, OpenFOAM-dev, (2014-2018)
[4] N. Kurul and M.Z. Podowski, 27th National Heat Transfer Conference, Minneapolis, USA, July 28–31, 1991.
[5] Anglart, H., Nylund, O., Kurul, N., & Podowski, M. Z. (1997). Nuc. Engineering and Design, 177(1-3), 215-228.
[6] Ishii, M., Kim, S., & Kelly, J. (2005). Nuclear Engineering and Technology, 37(6), 525-536.
[7] Kumar, S., & Ramkrishna, D. (1996). Chemical Engineering Science, 51(8), 1311-1332.
[8] Liao, Y., Oertel, R., Kriebitzsch, S., Schlegel, F., & Lucas, D. (2018). Int. J. Num. Meth. Fluids, 87(4), 202-215

  • Lecture (Conference)
    18th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-18), 18.-23.08.2019, Portland, USA
  • Contribution to proceedings
    18th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-18), 18.-23.08.2019, Portland, USA
    Proceedings of NURETH-18

Publ.-Id: 28242

Compact high-brightness X-ray sources for ultrafast probing of explosively driven solid-density materials by Travelling-Wave Thomson-Scattering

Steiniger, K.; Bussmann, M.; Loeser, M.; Albach, D.; Debus, A.; Pausch, R.; Roeser, F.; Schramm, U.; Siebold, M.; Debus, A.

The Traveling-Wave Thomson-Scattering geometry is introduced and the possibility to realize optical free-electron lasers with it explained. An example setup for a TWTS OFEL providing 1 Angström radiation is shown and its application to the probing of the ion dynamics in a laser driven cryogenic hydrogen slab presented.

  • Lecture (Conference)
    EUCALL Joint Foresight Topical Workshop: Theory and Simulation of Photon-Matter Interaction, 02.-05.07.2018, Szeged, Hungary

Publ.-Id: 28241

Two-bubble class approach based on measured bubble size distribution for bubble columns with and without internals

Möller, F.; Kipping, R.; Lavetty, C.; Hampel, U.; Schubert, M.

The complex flow patterns in bubble columns can be phenomenologically described by the two-bubble class approach. For the first time, this approach is applied to bubble columns with dense internals. Internals of square and triangular pitch tube patterns of two tube sizes (8×10-3 and 13×10-3 m) with flat and U-tube bottom design and cross-sectional occupation of ~25% were inserted in a bubble column of 0.1 m diameter and 2 m height. Contrary to the well-known gas disengagement technique, dual-plane ultrafast X-ray computed tomography data have been used for the bubble class allocation. Experiments were performed at superficial gas velocities ranging from 0.02 m s-1 to 0.20 m s-1 to cover homogeneous and heterogeneous flow conditions. The contributions of small and large bubble classes on total holdup, flow structure and bubble rise velocities were determined. Furthermore, the regime transition onset was determined based on the two-bubble class approach. Eventually, new correlations for regime transition, small and large bubble rise velocity, large bubble holdup as well as total holdup are proposed based on sub-channel area, sub-channel hydraulic diameter and occlusion area.

Keywords: Bubble column; heat exchanger internals; two-bubble class approach; bubble size distribution; gas holdup; bubble rise velocity; ultrafast X-ray tomography


Publ.-Id: 28240

Compact, high-yield incoherent and coherent X-ray sources by Traveling-Wave Thomson-Scattering

Steiniger, K.; Loeser, M.; Albach, D.; Pausch, R.; Roeser, F.; Schramm, U.; Siebold, M.; Bussmann, M.; Debus, A.

In Traveling-Wave Thomson-Scattering pulse-front tilted, petawatt class laser pulses are scattered off relativistic electrons to realize compact optical free-electron lasers or brilliant incoherent X-ray sources with state-of-the-art electron accelerators and high-power laser systems. Example setups of TWTS OFELs providing ultraviolet radiation are presented together with an optical setup to compensate laser dispersion.

  • Invited lecture (Conferences)
    Visions on Future Laser-based X-ray Science and Technology, 19.-20.11.2018, Castelldefels, Spain

Publ.-Id: 28239

Irradiation tests at HZDR

Müller, S. E.; Ferrari, A.

Irradiation tests at HZDR in the framework of the MUSE project are presented

  • Lecture (Conference)
    MUSE meeting, 22.10.2018, Fermilab, USA

Publ.-Id: 28238

FLUKA simulations for the Mu2e experiment

Müller, S. E.; Ferrari, A.

FLUKA simulations for the Mu2e experiment are presented

  • Lecture (Conference)
    MU2E collaboration meeting, 18.10.2018, 18.10.2018, Fermilab, USA

Publ.-Id: 28237

Laser-driven plasma pinching in e−e+ cascade

Efimenko, E. S.; Bashinov, A. V.; Gonoskov, A. A.; Bastrakov, S. I.; Muraviev, A. A.; Meyerov, I. B.; Kim, A. V.; Sergeev, A. M.

The cascaded production and dynamics of electron-positron plasma in ultimately focused laser fields of extreme intensity are studied by 3D particle-in-cell simulations with the account for the relevant processes of quantum electrodynamics (QED). We show that, if the laser facility provides a total power above 20 PW, it is possible to trigger not only a QED cascade but also pinching in the produced electron-positron plasma. The plasma self-compression in this case leads to an abrupt rise of the peak density and magnetic (electric) field up to at least 10^28 cm^−3 and 1/20 (1/40) of the Schwinger field, respectively. Determining the actual limits and physics of this process might require quantum treatment beyond the used standard semiclassical approach. The proposed setup can thus provide extreme conditions for probing and exploring fundamental physics of the matter and vacuum.

Publ.-Id: 28236

Unconventional trace elements in sphalerite – Clues to fluid origin?

Frenzel, M.; Slattery, A.; Wade, B.; Gilbert, S.; Ciobanu, C. C.; Cook, N. J.; Voudouris, P.

It is well known that the trace element content of sphalerite correlates with the conditions of ore formation (T, fS2). However, the suite of trace elements analysed in geological studies is generally restricted to the chalcophile and siderophile elements (Ag, As, Cd, Co, Fe, Ga, Ge, In, Mn, Sb, Se etc.). This may limit the inferences that can be made about the chemistry of the ore-forming fluids.

We used an integrated analytical approach consisting of electron probe micro-analysis, laser-ablationinductively coupled plasma-mass spectrometry, scanning electron microscopy and transmission electron microscopy to investigate the incorporation of the halogens Cl and Br, as well as the alkali metals Na and K into natural sphalerite from a range of deposits. This allowed us to study element distribution at length scales from >1 mm down to ~1 nm.

We found that Cl, Br, Na and K occur in measurable concentrations (100s to 1000s of ppm) in samples from several deposits. Chlorine occurs as either atomic substitutions in the sphalerite lattice or as a mixture of substitution and nano-inclusions. Unfortunately, analytical limitations mean that an investigation of the nanoscale distribution of Br, Na and K was not possible. However, concentrations of these elements (determined by LA-ICP-MS) correlate with Cl concentrations suggesting that they may be present together
with Cl in the sphalerite lattice.

The levels of trace elements present as atomic substitutions are generally related to the chemistry of the oreforming fluids. Therefore, our findings raise the possibility to measure Cl concentrations as well as Cl/Br ratios in natural sphalerite, and use these measurements to constrain fluid salinity and origin. However, more work will be required to constrain the relevant thermodynamic relationships and improve the detection limits of Cl and Br before such measurements can become a standard tool in economic geology.

  • Lecture (Conference)
    SEG 2018 conference, Keystone, 24.09.2018, Keystone, Colorado, United States of America

Publ.-Id: 28235

Criticality - What makes a raw material critical?

Frenzel, M.; Kullik, J.; Reuter, M. A.; Gutzmer, J.

A key to the current debate on the supply security of mineral raw materials is the concept of 'criticality'. This presentation provides a brief review of the criticality concept, as well as the methodologies used in its assessment, including a critical evaluation of their validity. Furthermore, it discusses several risks present in global raw materials markets that are not captured by most criticality assessments. The key result is that current assessments of raw material criticality are fundamentally flawed in several ways. This is mostly due to a lack of adherence to risk theory, and highly limits their applicability. Many of the raw materials generally identified as critical may not be critical, meaning that new assessments are urgently required.

While these are important results for policy makers, it is not necessarily clear what their implications are for geoscientific research on critical element deposits, the topic of this session. Therefore, this question will briefly be explored in the second part of the presentation.

  • Invited lecture (Conferences)
    GeoBonn, 05.09.2018, Bonn, Deutschland

Publ.-Id: 28233

Investigation of 18F-labelled pyrazolo[2,3-d]pyrimidines for molecular imaging of the adenosine A2A receptor with positron emission tomography (PET)

Lai, T. H.; Moldovan, R.-P.; Brust, P.

Objectives: The adenosine A2A receptor (A2AR) is a promising target for the development of PET radiotracers for molecular imaging of neurodegenerative diseases and cancer. Based on binding-affinities the 4 and 2-fluorobenzyl derivatives 1 (Ki(hA2A) = 5.3 nM) and 2 (Ki(hA2A) = 2.1 nM) were chosen for radiofluorination. Methods: Three different strategies for the synthesis of [18F]1 have been investigated. The first two are using [18F]fluorobenzaldehyde, which was applied either in a reductive amination or in a reduction followed by an Appel and benzylation reaction. The third strategy is based on a one-step radiolabelling starting from a boronic acid pinacol ester precursor employing [18F]TBAF and Cu(OTf)2(py)4 in n-BuOH/DMA. The specific binding of [18F]1 and [18F]2 on mice brain slices was evaluated by in vitro autoradiography. Results: The two- and four-step labelling strategies resulted in a radiochemical yield (RCY) of only 1.4% or 10% [18F]1 (non-isolated). Thus, [18F]1 and [18F]2 were prepared by a one-step procedure with a RCY of 52+7 or 9+1% (EOB), a molar activity of 135+64 or 132 GBq/µmol (EOS) and a radiochemical purity of >98%. In vitro autoradiography performed with [18F]2 demonstrated high binding to the striatum, a brain region with high density of A2AR, which could be blocked by selective A2A ligands. Conclusions: An efficient copper-mediated one-step radiolabelling procedure was established for two new highly affine A2A radiotracers. The first in vitro study with [18F]2 demonstrated excellent potential for the imaging of adenosine A2AR. Current work focuses on further in vitro and in vivo investigations.

Keywords: adenosine A2A; PET; radiotracer; 18F

  • Poster
    15th Research Festival Leipzig 2019, 18.01.2019, Leipzig, Deutschland

Publ.-Id: 28232

The geometallurgical assessment of by-products - Geochemical proxies for the complex mineralogical deportment of indium at Neves-Corvo, Portugal

Frenzel, M.; Bachmann, K.; Carvalho, J. R. S.; Relvas, J. M. R. S.; Pacheco, N.; Gutzmer, J.

Many by-productmetals are classified as critical.However, they are only ofmarginal interest tomanymining companies and are rarely part of detailed resource statements or geometallurgical assessments. As a result, there is a general lack of reliable quantitative data on the mineralogy and spatial distribution of these metals in ore deposits—hampering assessments of future availability.We propose here an innovative approach to integrate by-product metals into geometallurgical assessments. As an example, we use the distribution and deportment of indium at Neves-Corvo, a major European base-metal mine (Cu + Zn), and one of the largest and richest volcanichosted massive sulfide (VHMS) deposits in the world. Based on a combination of bulk-ore geochemistry and mineralogical and microanalytical data, this study is the first to develop a quantitativemodel of indium deportment inmassive sulfide ores, demonstrating how regularities in indium partitioning between different minerals can be used to predict its mineralogical deportment in individual drill-core samples. Bulk-ore assays of As, Cu, Fe, Pb, S, Sb, Sn, Zn, and In are found to be sufficient for reasonably accurate predictions. The movement of indium through the ore processing plants is fully explained by its mineralogical deportment, allowing for specific mine and process planning. The novel methodologies implemented in this contribution for (1) the assessment of analytical uncertainties, (2) the prediction of complex mineralogical deportments from bulk geochemical data, and (3) the modeling of byproduct recoveries from individual mining blocks, are of general applicability to the geometallurgical assessment of many other byproduct metals in polymetallic sulfide ores, including Ga, Ge, Mo, Re, Se, Te, as well as the noble metals.

Keywords: Geometallurgy; By-products; Trace elements; Automated mineralogy; Mineral balances; VMS deposits; VHMS deposits


Publ.-Id: 28231

Simulation-based exergy, thermo-economic and environmental footprint analysis of primary copper production

Abadías Llamas, A.; Reuter, M. A.; Valero Capilla, A.; Torres Cuadra, C.; Peltomäki, M.; Stelter, M.; Valero Delgado, A.; Roine, A.; Hultgren, M.

The transition from a Linear to Circular Economy has become a societal challenge to be tackled. However, the increasing complexity of materials and products increases also the sophistication of the circular economy systems required to deal with them. These systems are very resource consuming, therefore, a rigorous evaluation of the impact of every “actor” in circular economy must be done at design and operation stages to ensure the sustainability of the metal-production value chain.

A circular economy system implies, among others, low consumption of energy and material resources and low production of wastes or pollutant emissions. Its sustainability cannot therefore be evaluated just with one indicator. In this paper, we integrate indicators such as recovery rates, environmental impact indicators, as well as the quantities and qualities of the flows, losses and emissions, quantified through exergy. These must all be considered and evaluated simultaneously to perform a rigorous sustainability analysis.

The challenges of achieving a circular processing system and society are illustrated using a unique copper flowsheet that covers the complete processing chain from ore to refined metal including among others minor elements refining, scrap recycling, residue processing, steam utilization, sulphur capture and power generation in 129 unit operations linked by 289 streams and all the compositional and thermochemical detail. Using a simulation-based approach, two scenarios have been studied and compared: (i) a representative primary copper flowsheet and (ii) excluding all waste treatment processes. This unique simulated flowsheet permits a complete evaluation of various scenarios of all copper related processing options (while any additional unit operations can also be added) and also rigorously permits an allocation of impacts of all flows, products, residues etc. as a function of the complete mineral composition.

This approach to evaluating systems shows how to estimate the true losses from a system and will be a key approach to evaluate the true circularity of the circular economy system.

Keywords: Circular economy; Metallurgical process simulation; Thermoeconomics; Exergy; Copper production; Life Cycle Assessment (LCA); System design

Publ.-Id: 28230

Application of Layered Double Hydroxides for 99Tc remediation

Daniels, N.; Franzen, C.; Kvashnina, K.; Petrov, V.; Torapava, N.; Bukaemskiy, A.; Kowalski, P.; Hölzer, A.; Walther, C.

The present study investigates possible use of Layered Double Hydroxides (LDH) for Tc(VII) remediation. Mg/Al- and Mg/Fe-LDH were obtained by a hydrothermal route and thermally activated at 450°C, which was shown to significantly improve the Tc(VII) removal efficiency. Based on XRD investigation of Tc-LDH phases, the Tc(VII) uptake follows the restoring of an LDH structure. X-ray absorption spectroscopy demonstrates that Tc ions interact solely via the Tc-O bond, leaving no evidences of farther atomic interactions with, e.g., layers of LDH. The presence of competing anions, like NO3-, or CO32- in the solution decreases Tc(VII) uptake by LDH. Presently investigated thermally activated Mg0.67/Al0.33-LDH revealed a maximum uptake capacity of up to 1.27 mol/kg (or 20 wt.%), which is higher than that of the Mg0.75/Fe0.25-LDH (0.9 mol/kg). In agreement with these findings, theoretical simulations predicted incorporation energies for Mg0.67/Al0.33-LDH and Mg0.75/Fe0.25-LDH of -128 kJ/mol and -110 kJ/mol, respectively. Investigation of Tc-LDH in different leaching media demonstrated a rather high Tc(VII) stability in LDH in contact with diluted solutions containing Cl- and OH-, however, in a high saline solution, like Q-brine a rather fast release of TcO4- occurs due to anionic exchange with Cl-.

Keywords: Technetium; Layered Double Hydroxides; uptake; disposal


Publ.-Id: 28229

Developments in the estimation of tensile strength by small punch testing

Holmström, S.; Simonovski, I.; Baraldi, D.; Bruchhausen, M.; Altstadt, E.; Delville, R.

The Small Punch (SP) test is a relatively simple test well suited for material ranking and material property estimation in situations where standard testing is not possible or considered too material consuming. The material tensile properties, e.g. the ultimate tensile strength (Rm) and proof strength (Rp02) are usually linearly correlated to the force-deflection behaviour of a SP test. However, if the test samples and test set-up dimensions are not according to standardized dimensions or the material ductility does not allow the SP sample to deform to the pre-defined displacements used in these correlations, the standard formulations can naturally not be used. Also, in cases where no supporting Rm data is available the applied correlation factors cannot be verified. In this paper a formulation is proposed that enables the estimation of Rm without supporting uniaxial tensile strength data for a range of materials, both for the soon to be standardized flat samples as well as for curved (tube section) samples. The proposed equations are based on the classical and recent SP and Small Punch Creep (SPC) formulations. It is claimed that the both equivalent stress in small punch creep and tensile strength can be robustly estimated with the same type of equations at least for ductile and semi-ductile ferritic/martensitic and austenitic steels. It is also shown that the same equations can be applied on non-standard test samples and test set-ups. The tensile strength of semi-ductile materials such as 46% cold worked 15-15Ti cladding steel tubes are successfully estimated by correcting the correlations for the curvature of the samples. The usability of the SP testing and assessment method for estimating tensile strength of engineering steels in general and for nuclear claddings in specific has been verified.

Keywords: small punch testing; tensile strength; models; fuel claddings

Publ.-Id: 28228

Dancing performance of organic droplets in aqueous surfactant solutions

Cejkova, J.; Schwarzenberger, K.; Eckert, K.; Tanaka, S.

Droplet systems remain the subject of a constant fascination in science and technology. Here we focus on organic droplets floating on the surface of aqueous surfactant solutions. These droplets can exhibit intriguing interactions. Recently we have found independently in two laboratories that we can observe almost the same complex collective behaviour in two different droplet systems. The aim of this paper is to compare both droplets systems, present their differences and show their similar oscillatory behaviour. The first system consists of decanol droplets floating on sodium decanoate solution. In the second one, the droplets consist of a mixture of ethyl salicylate and liquid paraffin and they are placed on the surface of aqueous sodium dodecyl sulphate solution. Although the mechanism of these spatio-temporal interactions of droplets is not fully understood yet, we believe that this behaviour is based on the same phenomena.

Publ.-Id: 28227

Materials research in high magnetic fields

Wosnitza, J.

  • Invited lecture (Conferences)
    12th Annual Matsurf Seminar, 05.11.2018, Turku, Finnland

Publ.-Id: 28226

FFLO states in organic superconductors − Modulated order parameter

Wosnitza, J.

  • Invited lecture (Conferences)
    Workshop on “Emergent Phenomena in Strongly Correlated Quantum Matter”, 26.-31.08.2018, Natal, Brasilien

Publ.-Id: 28225

"Superconductivity under Extreme Conditions” (Discussion Leader of this Session)

Wosnitza, J.

  • Invited lecture (Conferences)
    Gordon Research Conference on Conductivity and Magnetism in Molecular Materials, 12.-17.08.2018, Smithfield, USA

Publ.-Id: 28224

Spin-imbalanced superconductivity in layered organic superconductors

Wosnitza, J.

  • Invited lecture (Conferences)
    International Conference on Science and Technology of Synthetic Metals 2018 (ICSM 2018), 01.-06.07.2018, Busan, Korea

Publ.-Id: 28223

Frustrated and low-dimensional magnets in high magnetic fields

Wosnitza, J.

  • Invited lecture (Conferences)
    12th International Conference on Research in High Magnetic Fields (RHMF 2018), 24.-28.06.2018, Santa Fe, USA

Publ.-Id: 28222

Kinetic concepts for quantitative prediction of fluid-solid interactions

Lüttge, A.; Arvidson, R. S.; Fischer, C.; Kurganskaya, I.

In a unique “perspectives” format that examines both past and future, we appraise the field of crystal dissolution kinetics, showing how the last century’s strong progress in experimental discovery has both driven, and been driven by, the tandem evolution of basic theory. To provide context for examining the current state-of-the-art in this critical field, we highlight the key milestones that have punctuated our progress in understanding the dynamics of crystalline surfaces. For crystal growth, these are the energy relations between kinks on stepped surfaces, and the phenomena of screw dislocations sustaining steady state growth at low thermodynamic overstep. For crystal dissolution, the corresponding recognition is the tie between defects, hollow cores, and macroscopic etch pits. These latter relationships have been more recently formalized in the stepwave model, incorporating etch pit nucleation, step generation, and global retreat of the crystal surface: the total dissolution rate. All these conceptual advances contain an assertion of a link, fundamental but often implicit, between mass action and kinetics, where chemical potential is the primary driver of rates of physical process. This link is inherent in many “classical” rate equations, whose parameterization is often the endgame of laboratory observations.
Today, this extant framework serves as the conceptual basis for organizing the data available from a sophisticated suite of analytical and experimental instrumentation. These resources permit ever-increasing resolution of reacting surfaces in breathtaking detail, often under in situ conditions. These direct observations are now further enhanced by powerful computer-driven simulation and numerical modeling, allowing the virtual exploration of complex reaction systems, ranging from isolated single crystals to porous, multiphase networks. Despite the exhilarating breadth and detail of these accomplishments, it is also becoming increasingly apparent that we are moving further, not closer, from the goal of predictive understanding, a goal that is an increasingly vital social responsibility of our science. A major source of this divergence reflects the fact that at key intersecting points of study, our prowess in technical observation has effectively outpaced our theoretical understanding. In confronting the daunting complexity of these systems, we must be careful to first identify major vacancies in theory. Until we resolve these deficits, more observations may be of only limited utility.
In assessing this problem, a major uncertainty is how to properly reconcile thermodynamics, by its very nature a macroscopic formalism, with our current focus on atomic scales of reaction. This may be a problem unique to crystalline materials and their interactions with phases whose components are otherwise mobile. Detailed balancing and related microscopic reversibility, the implicit link referred to above, is often used to form a mechanistic bridge between the macroscopic distribution of energy and microscopic heterogeneity of events in crystal surfaces, but its employment creates two problems: spatial and temporal. First, reaction mechanism is truly atomic in dimension, involving actual, nondegenerate collisions at crystal surface sites, whereas 〖∆G〗_r or ∆μ is macroscopic. Second, the rate at which a crystal surface dissolves reflects both the chemical composition of the ambient fluid and the distribution of surface energy. Reaction towards “equilibrium”, involving the typically slow redistribution of surface energy, may thus inherit topography inconsistent with the computed “driving force”. This reactivity mismatch yields surfaces that evolve over time, producing a heterogeneous distribution of rates. This distribution can be efficiently characterized by rate spectra: the span of non-steady-state rates reflecting diversity of reactive sites established under previous 〖∆G〗_r regimes. We use these spectra as a basic compact variable: a signal that encodes the complex link between site-specific surficial energy distributions, solution and surface chemistry, and the cumulative rate that results. Because this encoding is efficiently captured by numerous surface analytical microscopies (VSI, AFM), this approach permits the testing of hypotheses regarding the probabilistic nature of rate distributions, a process we hope the community will embrace, serving ultimately as a key step forward in establishing useful predictive approaches. We illustrate this potential with a series of case studies that target a range of composition, space, and time scales.

Publ.-Id: 28221

Compact millijoule Yb³⁺:CaF₂ with 162fs pulses

Löser, M.; Bernet, C.; Albach, D.; Zeil, K.; Schramm, U.; Siebold, M.

We report on a compact diode-pumped, chirped pulse regenerative amplifier system with a pulse duration of 162 fs and an output pulse energy of 1 mJ before as well as 910 µJ after compression optimized for the probing of ultrafast relativistic laser-plasma processes. A chirped volume Bragg grating (CVBG) acts as a combined pulse stretcher/compressor representing a robust solution for a CPA laser system in the millijoule range. Yb3+:CaF2 is used as gain medium to support a large bandwidth of 16 nm (FWHM) when spectral gain shaping is applied. Chirped mirrors compensate for any additional dispersion introduced to the system.

Keywords: ytterbium laser; laser amplifier; CVBG; CPA laser

Publ.-Id: 28220

Neutronic analyses of the FREYA experiments in support of the ALFRED LFR core design and licensing

Sarotto, M.; Firpo, G.; Kochetkov, A.; Krása, A.; Fridman, E.; Cetnar, J.; Domanska, G.

During the EURATOM FP7 project FREYA, a number of experiments was performed in a critical core assembled in the VENUS-F zero-power reactor able to reproduce the ALFRED lead-cooled fast reactor spectrum in a dedicated island. The experiments dealt with the measurements of integral and local neutronic parameters, such as: the core criticality, the control rod and the lead void reactivity worth, the axial distributions of fission rates for the nuclides of major interest in a fast spectrum, the spectral indices of important actinides (U238, Pu239, Np237) respect to U235. With the main aim to validate the neutronic codes adopted for the ALFRED core design, the VENUS-F core and its characterisation measurements were simulated with both deterministic (ERANOS) and stochastic (MCNP, SERPENT) codes, by adopting different nuclear data libraries (JEFF, ENDF/B, JENDL, TENDL). This paper summarises the main results obtained and points out a general agreement between measurements and simulations, with few discrepancies for some parameters that are here discussed. Additionally, a sensitivity and uncertainty analysis was performed with deterministic methods for the core reactivity: it clearly indicates that the calculation accuracy of the different codes/libraries resulted to be lower than the uncertainties due to nuclear data.

Keywords: FREYA EU FP7 project; ALFRED LFR, VENUS-F reactor; Measurements of neutronic parameters; ERANOS deterministic code; MNCP and SERPENT stochastic codes

  • Journal of Nuclear Engineering and Radiation Science 6(2020)1, 011402
    DOI: 10.1115/1.4044000


  • Secondary publication expected

Publ.-Id: 28219

Wasserstoffbrennen in der Sonne: Die 12C(p,γ)13N-Reaktion und die Radiofrequenz-Ionenquelle für den Felsenkeller-Beschleuniger

Reinicke, S.

Die Reaktion 12C(p,γ)13N bestimmt die Rate des Bethe-Weizsäcker-Zyklus in der anfänglichen Entwicklungsphase von Sternen und am äußeren Rand der Sonne. Eine genaue Kenntnis der Reaktionsrate ist somit für die Entwicklung von stellaren Modellen erforderlich. Über das Verhältnis der Raten von den Protoneneinfangreaktionen von 12C und 13C kann außerdem das entsprechende Isotopenverhältnis in Sternen bestimmt werden. Eine Revision der Rate von 12C(p,γ)13N könnte damit einen unerwartet hohen Isotopenanteil von 13C erklären, der in verschiedenen Meteoriteneinschlüssen gemessen wurde und mit den existierenden stellaren Modellen nicht hinreichend in Konsistenz gebracht werden kann.
Für den S-Faktor der Reaktion existieren im Energiebereich unterhalb von 190 keV nur Messdaten aus den 1950er Jahren. Bei der Untersuchung von ähnlichen Reaktionen des Wasserstoffbrennens wurden die mit der verwendeten Messtechnik erlangten Messdaten durch moderne Experimente teilweise um einen Faktor zwei oder höher revidiert.
Ziel der gegenwärtigen Arbeit war das Messen von S-Faktor-Werten in einem weiten Energiebereich von 130 keV bis 450 keV zur Überprüfung der alten Messdaten und um eine zukünftige präzisere Extrapolation zu astrophysikalisch relevanten Energien hin zu ermöglichen. Dabei wurde eine Messung in inverser Kinematik, eine Methode, für die bisher keine publizierten Daten zu der Reaktion existieren, am HZDR 3 MV Tandetron Beschleuniger durchgeführt mit TiH2-Proben, die mit 12C2+-Ionen bestrahlt wurden. Die Reaktion wurde mittels Gammaspektrometrie ausgewertet und die Proben durch die Methode der Nuklearen Resonanz-Reaktionsanalyse charakterisiert.
Die neuen Messdaten sind im Energiebereich von 130 keV bis 170 keV im Mittel etwa 20 % höher als die Werte eines existierenden Fits an die bestehenden Messdaten, im Rahmen der Messunsicherheiten aber mit diesen konsistent. Im Energiebereich der Resonanz oberhalb von 420 keV wurde eine Diskrepanz zu den alten Messwerten festgestellt. Die neuen Werte liegen in diesem Bereich systematisch bis zu 50 % unterhalb der alten Messwerte.
Als weiteres Ziel dieser Arbeit wurde mithilfe von ionenoptischen Simulationen mit SIMION 8.1 ein elektrostatischer Deflektor und eine Einzellinse für eine RadiofrequenzIonenquelle entwickelt, die im Inneren des Hochspannungsterminals des Felsenkeller Beschleunigers eingesetzt werden soll. Durch die Erkenntnisse der Simulationen konnte ein Deflektor gebaut und getestet werden, der unter den Bedingungen auf dem Beschleuniger-Terminal funktionsfähig ist und zusammen mit der Ionenquelle einen intensiven Strahl von Wasserstoff oder Helium in die Beschleunigungsstrecke umlenken kann. Die Simulationen sagen Strahlverluste von maximal 10 % für Wasserstoff und 1.5 % für Helium voraus, womit, basierend auf den Messungen an einem Vakuumteststand und den Angaben des Herstellers der Ionenquelle, Strahlströme von 80 µA für 4He+ und über 100 µA für Protonen nach Verlassen des Beschleunigers zu erwarten sind. Der Untertage-Beschleuniger am Felsenkeller und die Radiofrequenz-Ionenquelle können zu einer weiteren Messung der Reaktion 12C(p,γ)13N mit besserer Statistik und einem zu niedrigeren Energien erweiterten Messbereich verwendet werden.

The reaction 12C(p,γ)13N determines the rate of the Bethe-Weizsäcker cycle in the initial development phase of stars and near the surface of the Sun. An exact knowledge of the reaction rate is thus required for the development of precise stellar models. In addition, the ratio of the rates of the proton capture reactions of 12C and 13C is used to determine the corresponding isotopic ratio in stars. A revision of the rate of 12C(p,γ)13N might help to explain an unexpectedly high isotopic abundance of 13C, which was measured in presolar grains and cannot be sufficiently explained with the existing stellar models.
For the S-factor of 12C(p,γ)13N in an energy range below 190 keV, the only existing data were measured in the 1950s. For similar reactions of hydrogen burning, data obtained with these measuring techniques were revised by a factor of two or higher by modern experiments.
The aim of the present thesis was to measure S-factor data in a wide energy range from 130 keV to 450 keV in order to verify the old data and to allow a more precise extrapolation towards astrophysically relevant energies in the future. A measurement in inverse kinematics, a method for which no published data on the reaction exist, was performed at the HZDR 3 MV Tandetron accelerator with a 12C2+ ion beam and the use of TiH2 targets. Gamma spectroscopy was used to measure the yield and the targets were characterized with nuclear resonant reaction analysis (NRRA).
In the energy range from 130 keV to 170 keV, the new values are on average about 20 % higher than the values of a recent fit to the old data, but they are consistent within uncertainties. In the energy range of the resonance above 420 keV, a discrepancy to the old data was found. The new values in this region are up to 50 % lower than the values from previous measurements.
Another goal of this work was the development of an electrostatic deflector and an einzel lens for a radio frequency ion source inside the high voltage terminal of the Felsenkeller accelerator. For this purpose, ion-optics simulations with SIMION 8.1 were performed, which lead to a design choice for the deflector allowing the transmission of intensive beams through the accelerator. The simulation predicts beam losses of less than 10 % for hydrogen and less than 1.5 % for helium, which based on easurements with a vacuum test chamber leads to expected beam currents of 80 µA for 4He+ at the exit of the acceleration tube. According to the data sheet of the radio frequency ion source, proton beams of more than 100 µA are to be expected.
The Felsenkeller underground accelerator and its radio frequency ion source can be used to perform further measurements of the reaction 12C(p,γ)13N with improved statistical uncertainties and an extension of the energy region towards lower energies.

  • Doctoral thesis
    TU Dresden, 2018
    Mentor: Prof. Dr. Kai Zuber, PD Dr. Daniel Bemmerer
    171 Seiten
  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-095 2019
    ISSN: 2191-8708, eISSN: 2191-8716


Publ.-Id: 28218

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