Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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34121 Publications

Time efficient scatter correction for time-of-flight PET: the immediate scatter approximation

Nikulin, P.; Maus, J.; Hofheinz, F.; Lougovski, A.; van den Hoff, J.

Utilization of Time-Of-Flight (TOF) information allows to improve image quality and convergence rate in iterative PET image reconstruction. In order to obtain quantitatively correct images accurate scatter correction (SC) is required that accounts for the non-uniform distribution of scatter events over the TOF bins. However, existing simplified TOF-SC algorithms frequently exhibit limited accuracy while the currently accepted gold standard — the TOF extension of the single scatter simulation approach (TOF-SSS) — is computationally demanding and can substantially slow down the reconstruction. In this paper we propose and evaluate a new accelerated TOF-SC algorithm in order to improve this situation. The key idea of the algorithm is the use of an immediate scatter approximation (ISA) for scatter time distribution calculation which speeds up estimation of the required TOF scatter by a factor of up to five in comparison to TOF-SSS. The proposed approach was evaluated in dedicated phantom measurements providing challenging high activity contrast conditions as well as in representative clinical patient data sets. Our results show that ISA is a viable alternative to TOF-SSS. The reconstructed images are in excellent quantitative agreement with those obtained with TOF-SSS while overall reconstruction time can be reduced by a factor of two in whole-body studies, even when using a listmode reconstruction not optimized for speed.

Keywords: PET; Scatter Correction; Immediate Scatter Approximation; Image Reconstruction; TOF; SSS; TOF-SSS; TOF-SC; ISA


Publ.-Id: 28997

Towards best practice guidelines for Euler-Euler simulations of poly-disperse bubbly flows

Lucas, D.; Liao, Y.; Rzehak, R.; Krepper, E.

Poly-disperse bubbly flows are involved in normal operation as well as in accident scenarios of Light Water Reactors. There are many activities to qualify CFD-methods for the simulation of safety-relevant processes. However, due to the complexity of such flows many details have to be carefully considered to define a proper setup for such simulations. The present paper aims at the establishment of a guideline how to prepare and conduct such a simulation as well as to evaluate the simulation results according to the best practice. The procedure has to start with an analysis of the expected flow situation, flow parameters and observed phenomena. Accordingly a classification should be done. Beside boundary conditions, the numerical grid, the time stepping and other issues a careful selection of the modelling framework (e.g. inclusion of a population balance, two- or multi-field approach) and the closure models has to be done based on the previous analysis. A set of well suited closure models is defined by the so-called baseline model for poly-disperse flows. Numerical convergence has to be checked throughout the simulation. For the comparison with experimental data possible uncertainties of the input data used and the experimental data used for comparison have to be considered. Besides the presentation of the state of the art best practice guidelines also their limitation and requirements for future research are discussed.

Keywords: CFD; bubbly flow; Euler-Euler; best practice guidelines

  • Contribution to proceedings
    The 18th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-18), 18.-22.08.2019, Portland, OR, USA
  • Lecture (Conference)
    The 18th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-18), 18.-22.08.2019, Portland, OR, USA

Publ.-Id: 28996

Influence of the bubble size distribution on the bubble column flow regime

Lucas, D.; Ziegenhein, T.

The role of the bubble size dependent lateral lift force on the flow regime is experimentally investigated in a tall bubble column. In the experiments, only the initial bubble size distribution was modified by using a gas sparger with different injection needles and varying the flow through specific injection needles. The gas flow rate was kept unchanged in all experiments. Depending on the bubble size distribution homogeneous, transitional or heterogeneous flow regimes were observed. The flow regime is in good agreement with the predictions from the stability criterion obtained by a previously done linear stability analysis for poly-dispersed flow. It was found that as a rule of thumb the following criterion can be used.
If most of the gas volume is transported by bubbles smaller than the critical diameter at which the lift force changes its sign, the flow is stabilized leading to a homogeneous flow regime. If most of the gas volume is transported by bubbles larger than that diameter the flow is de-stabilized leading a heterogeneous flow regime. If the fraction of gas transported by small and large bubbles is about the same, the initial conditions remain dominant throughout the column height.

Keywords: bubble size; lift force; stability; bubble column; flow regime; regime transition


  • Secondary publication expected

Publ.-Id: 28995

Quantum Critical Dynamics of a Heisenberg-Ising Chain in a Longitudinal Field: Many-Body Strings versus Fractional Excitations

Wang, Z.; Schmidt, M.; Loidl, A.; Wu, J.; Zou, H.; Yang, W.; Dong, C.; Kohama, Y.; Kindo, K.; Gorbunov, D. I.; Niesen, S.; Breunig, O.; Engelmayer, J.; Lorenz, T.

We report a high-resolution terahertz spectroscopic study of quantum spin dynamics in the antiferromagnetic Heisenberg-Ising spin-chain compound BaCo2V2O8 as a function of temperature and longitudinal magnetic field. Confined spinon excitations are observed in an antiferromagnetic phase below TN ≃ 5.5 K. In a field-induced gapless phase above Bc = 3.8 T, we identify many-body string excitations as well as low-energy fractional psinon/antipsinon excitations by comparing to Bethe-Ansatz calculations. In the vicinity of Bc, the high-energy string excitations are found to be dynamically dominant over the fractional excitations.

Publ.-Id: 28993

Protecting Pulsed High-Power Lasers with Real-Time Object Detection

Kelling, J.; Gebhardt, R.; Helbig, U.; Bock, S.; Schramm, U.; Juckeland, G.

In Petawatt laser systems, firing at 10Hz, suddenly appearing scatterers can damage components. Damage(-spreading) can be avoided by suspending operation immediately on occurrence of such an event. This poster presents our approach for the automatic detection of critical failure states in real-time, employing state-of-the-art object localization on intensity profiles of the laser beam.

Learn, how we fitted the You Look Only Once (YOLO) approach, which is suited to low-latency object detection, to our problem and how we adapted the required multi-step training protocol to the available experimental data.
In this application accuracy trumps high recall, as false positives would severely impede productivity or even render our system useless. This had us refrain from general anomaly detection and thus we also present different ways in which we tune the object-detection for minimal false-positive rates.

# extended abstract
High-power lasers are operated at our research center for investigations of exotic states of matter and medical applications, among others. This project to improve the automatic shutdown/interlock system of two lasers (one in operation, one currently under construction) has the goal of reducing the probability of, potentially expensive, damage-spreading scenarios, while at the same time avoiding false alarms. In order to achieve high precision, we train for high recall only for known indicators, instead of using anomaly detection.

After we presented a proof-of-concept for this type of failure-state-detection at GTC 2018, where the main challenge was in dealing with a far too small dataset, we are now working on a pure deep-learning approach driven by systematic experimental data. In the new design, intended for production use, the classification takes place on differences between a running average of non-signaling images and the current shot. This is required, because no images can be obtained which can be classified as "good" without context. In order to achieve fast object-detection, to highlight potential problems for the operator, the you look only once (YOLO) approach[1], which we modify by removing the final layers for bounding-box prediction and train the network to directly produce an expressive feature map (lazy YOLO).

From this talk, the audience can learn how we adapted the well-known YOLO approach to our real-world application, from the employed network to the multi-step training protocol. Another topic is the design for short response times, to which end we employ Caffe, OpenCV on GPU and use C++ as main programming language instead of python.

[1] Redmon, J., Farhadi, A.: YOLO9000: Better, Faster, Stronger, ArXiv e-prints, 2016

Keywords: Image Classification; Caffe; automatic Laser-safety shutdown; Object Detection

Publ.-Id: 28992

Dimeric Uranium(VI)–Citrate Complexes: Structures and Dynamics

Kretzschmar, J.; Tsushima, S.; Jäckel, E.; Meyer, R.; Steudtner, R.; Müller, K.; Schmeide, K.; Brendler, V.; Stumpf, T.

The aqueous chemistry of the uranium(VI)–citrate system is challenging, as evidenced by still controversial discussions on complex stoichiometries and structures [1–4]. For a sound understanding of the chemical behavior in general and the environmental fate in particular, knowledge of both aqueous speciation and molecular structures in solution is crucial. Here, complexes formed by the uranyl ion, U(VI), and citrate (Cit) were examined in the pH range 2–8 by combining one- and two-dimensional NMR with UV-Vis, ATR FT-IR, and EXAFS spectroscopies as well as DFT-based quantum chemical calculations.
Upon complexation, a chiral center is induced in Cit’s central carbon, resulting in the formation of two diastereomeric pairs of enantiomers, whereupon the dimeric complexes exhibit syn and anti configured isomers. In fact, the combination of 17O NMR (note: at natural abundance) and DFT calculations allowed an unambiguous decision on complex geometry and overall configurations. It is evidenced for the first time that the syn isomer is favored in aqueous solution in contrast to the preferably crystallizing anti isomer. Both isomers coexist and interconvert among one another, with a rate estimated to be in the order of 10² s¹ at 25 °C in acidic media, and a corresponding activation energy of approximately 60 kJ mol¹.
Upon increasing pH, the ternary dimeric U(VI)–Cit mono- and bis-hydroxo (2:2:1 and 2:2:2) complexes form as evidenced by both UV-Vis and ATR FT-IR spectroscopy. The latter methods provided stability constants (log β): 19.5 (2:2:0), 14.0 (2:2:1), and 6.5 (2:2:2). Accordingly, the process can be referred to as U(VI) hydrolysis within the U(VI)–Cit complex as the two coordinating water molecules in the respective fifth coordination site each abstract H+. Thus, any U(VI)-coordinating water in ever so stable complexes is susceptible to hydrolysis even in strong acidic media as consequence of the interplay between metal ion Lewis acidity and solution pH.
Virtually all single-crystal X-ray structures containing the dimeric U(VI)–Cit complex in any manner, reveal anti configuration, e.g. [4]. The predominance of the syn isomer in solution was hitherto unnoticed, demonstrating that, particularly upon different physico-chemical properties of the isomers, the (crystalline) solid phase does not necessarily reflect speciation and structures found in (aqueous) solution, underlining the importance of rigorous solution studies.

[1] I. Feldman et al., J. Am. Chem. Soc., 1954, 76, 4726.
[2] M. T. Nunes and V. M. S. Gil, Inorg. Chim. Acta, 1987, 129, 283.
[3] S. P. Pasilis and J. E. Pemberton, Inorg. Chem., 2003, 42, 6793.
[4] M. Basile et al., Chem. Commun. 2015, 51, 5306.

Keywords: uranium; uranyl; U(VI); citric acid; molecular structure; NMR; ATR FT-IR; UV-Vis; spectroscopy; ternary complex; uranium hydrolysis; stability constant; isomerization

  • Lecture (Conference)
    Jahrestagung der Fachgruppe Nuklearchemie 2019, 25.-27.09.2019, Dresden, Deutschland

Publ.-Id: 28991

Simultaneous 8.2 keV phase-contrastimaging and 24.6 keV X-ray diffraction fromshock-compressed matter at the LCLS

Seiboth, F.; Fletcher, L. B.; Mcgonegle, D.; Anzellini, S.; Dresselhaus-Cooper, L. E.; Frost, M.; Galtier, E.; Goede, S.; Harmand, M.; Lee, H. J.; Levitan, A. L.; Miyanishi, K.; Nagler, B.; Nam, I.; Ozaki, N.; Rödel, M.; Schropp, A.; Spindloe, C.; Sun, P.; Wark, J. S.; Hastings, J.; Glenzer, S. H.; Mcbride, E. E.

In this work, we demonstrate simultaneous phase-contrast imaging (PCI) and X-ray diffractionfrom shock compressed matter at the Matter in Extreme Conditions endstation, at the LinacCoherent Light Source (LCLS). We utilize the chromaticity from compound refractive X-ray lensesto focus the 24.6 keV 3rd order undulator harmonic of the LCLS to a spot size of 5lm on target toperform X-ray diffraction. Simultaneous PCI from the 8.2 keV fundamental X-ray beam is used tovisualize and measure the transient properties of the shock wave over a 500lm field of view.Furthermore, we demonstrate the ability to extend the reciprocal space measurements by 5 Angstroem, rel-ative to the fundamental X-ray energy, by utilizing X-ray diffraction from the 3rd harmonic of theLCLS.

Keywords: Phase Contrast Imaging; PCI; Matter in Extreme Conditions; MEC; LCLS; shock compression; x-ray diffraction; XFEL; germanium; shock; release


Publ.-Id: 28990

A Polka-Dot Pattern Emerges in Superfluid Helium

Wosnitza, J.

A surprising two-dimensional pattern appears in superfluid helium-3 when the liquid is confined to a micrometer-thick cell and exposed to a magnetic field.

Publ.-Id: 28989

Low anisotropic upper critical fields in SmO1−xFxFeAs thin films with a layered hybrid structure

Haindl, S.; Kampert, E.; Sasase, M.; Hiramatsu, H.; Hosono, H.

We report on the upper critical fields in SmO1−xFxFeAs thin films prepared by pulsed laser deposition. With an F-content gradient along their thickness, the films could be described approximately as layered two-phase hybrid structures comprised of one superconducting layer and one antiferromagnetic layer. An analytical characterization of different thin film samples by Auger electron spectroscopy and energy-dispersive x-ray spectroscopy in scanning transmission electron microscopy is provided and structural defects, such as antiphase boundaries, were confirmed for films grown at lower deposition temperatures. Electrical transport measurements in pulsed magnetic fields yielded upper critical fields higher than 80 T with an anisotropy γHc2 ≤ 2.25.

Publ.-Id: 28988

Microscopic and spectroscopic investigations of the interactions of a Halobacterium-isolate with uranium

Hilpmann, S.; Bader, M.; Bachran, M.; Steudtner, R.; Schmidt, M.; Stumpf, T.; Cherkouk, A.

Rock salt formations are potential host rocks for the long-term storage of high-level radioactive waste in a deep geological repository, besides clay and crystalline rock. There are multiple studies about the geological, geochemical and geophysical properties of these host rocks. However, there exists still a lack of knowledge about indigenous microorganisms and their influence on the chemical speciation. For a long-term risk assessment, it is of high interest to study how these microorganisms interact with radionuclides. Therefore, the interactions of an extremely halophilic archaeon, Halobacterium sp. GP5 1-1 with uranium, one of the major radionuclides of concern, were investigated in detail. This extremely halophilic archaeon was isolated from a German rock salt sample. Different microscopic and spectroscopic methods were combined to decipher the occurring processes on a molecular level.
To investigate the interaction kinetics of uranium(VI) onto the cells of Halobacterium sp. GP5 1-1, time-dependent association experiments with two different uranium(VI) concentrations were performed. At both concentrations the amount of bioassociated uranium(VI) increased with the incubation time. It was determined that the association process at the higher concentration (30 µM) was much slower than the kinetic at the lower uranium(VI) concentration (10 µM).
Various microscopic and spectroscopic methods were used to understand the interaction mechanisms on a molecular level. Overall, the association process is not exclusively a biosorption, which is a passive process and in general completed after a short time of incubation (0 – 2 h) [1]. The microscopic images of the live/dead staining show the formation of cell agglomerates after a certain exposition time at both concentrations. During the process, organic matter is excreted from the cells. Therefore, more functional groups are available for further uranium(VI) binding.
Electron microscopic images of the cells allowed drawing conclusions about different microbe-radionuclide interactions at different uranium(VI) concentrations. A biomineralization takes place at lower concentrations (10 µM) and uranium(VI) is bound to biofilm-like structures at higher concentrations (60 µM).
Using time-resolved laser-induced luminescence spectroscopy, different aqueous species could be extracted from the supernatant. These species differ slightly in dependence on the uranium(VI) concentration. In both cases, a uranyl-carbonate-complex is formed during the association process due to microbial released CO2. Additionally the formation of a phosphate species in the cell pellets at low uranium(VI) concentrations was observed in a uranium(VI) concentration-dependent experiment (10-60 µM). In contrast, at higher uranium(VI) concentrations a carboxylic species was formed. This is in agreement with the already mentioned excretion of organic matter from the cells during the uranium(VI) incubation.
These findings offer new insights into the microbe-actinide interactions at highly saline conditions relevant to high-level radioactive waste disposal in rock salt.[1]

[1] J. R. Lloyd, L. E. Macaskie (2002) in “Interactions of Microorganisms with Radionuclides” (Eds.: M.J. Keith-Roach, F. R. Livens), Elsevier, pp. 313-381

  • Lecture (Conference)
    Migration 2019, 15.-20.09.2019, Kyoto, Japan

Publ.-Id: 28987

Complex formation between UO22+ and α-isosaccharinic acid: insights on a molecular level

Brinkmann, H.; Patzschke, M.; Kaden, P.; Raiwa, M.; Rossberg, A.; Kloditz, R.; Heim, K.; Moll, H.; Stumpf, T.

Cellulosic materials present as tissue, paper, wood, or filter materials in low and intermediate level waste will degrade under alkaline conditions if water ingresses in a cementitious backfilled repository. The main degradation product is isosaccharinic acid. Complex formation with isosaccharinic acid may adversely affect the retention of radionuclides by sorption or formation of solid phases. Hence, this compound is of particular concern in the context of nuclear waste disposal. Structural information of complexes are limited to spherical metal centers and little is known about the interaction of uranyl (UVIO22+) with isosaccharinic acid. Therefore, the interaction of UO22+ with α-isosaccharinate (ISA) was studied under acidic conditions focusing particularly on the structural characterization of the formed complexes. Attenuated total reflection Fourier-transform infrared (ATR-FTIR), nuclear magnetic resonance (NMR), UV-Vis, extended X-ray absorption fine structure (EXAFS) spectroscopy and electrospray-ionization mass spectrometry (ESI-MS) were combined with theoretical calculations to obtain a process understanding on the molecular level. The dominant binding motifs in the formed complexes are 5- and 6-membered rings involving the carboxylic group as well as the α- or β-hydroxy group of ISA. Two concentration dependent complex formation mechanisms were identified involving either mono- ([UO2(ISA)(H2O)3]+) or binuclear ([(UO2)2(ISA)(H2O)6]3+) species. Furthermore, this study unveils the interaction of UO22+ with the protonated α-isosaccharinic acid (HISA) promoting its transformation to the corresponding α-isosaccharinate-1,4-lactone (ISL) and inhibiting the formation of polynuclear UO22+-ISA species. Future studies on related systems will benefit from the comprehensive knowledge concerning the behavior of ISA as complexing agent gained in the present study.

Keywords: Uranium; Isosaccharinic acid; Complexation; Lactonization; Spectroscopy

Publ.-Id: 28986

From Exploration towards Predictive Geometallurgy - The Role of SEM-based Automated Mineralogy and Statistical Assessment

Birtel, S.; Bachmann, K.; Büttner, P.; Tolosana Degado, R.; van den Boogaart, K. G.; Gutzmer, J.

Geometallurgical models are constructed to quantitatively predict how ores will behave during extraction and beneficiation. Depending on data availability, complexity of data and operational stage different classes of geometallurgical models can be distinguished: 1) resource potential, 2) recoverable resources, 3) first order predictive models, 4) predictive models, and 5) real-time mining models. Here, two case studies are presented where modal mineralogy and microstructural data obtained from SEM-based image analysis are combined with complementary analytical data and statistically assessed in order to predict raw material behaviour during mineral processing. For both case studies, the necessary steps to develop existing models into truly predictive geometallurgical models are outlined. The first case study concerns the recovery of Sn from a historic flotation tailings storage facility. The second case study centres on the recovery of PGE as by-products from a chromite ore deposit as a first order predictive geometallurgical model.

Keywords: SEM based automated mineraloy; statistcal assement; case studies; process optimization

  • Contribution to proceedings
    15th Biennial Meeting of the Society for Geology Applied to Mineral Deposits, 27.-30.08.2019, Glasgow, UK
    Proceedings to 15th Biennial Meeting of the Society for Geology Applied to Mineral Deposits, 1474-1477
  • Lecture (Conference)
    15th Biennial Meeting of the Society for Geology Applied to Mineral Deposits, 27.-30.08.2019, Glasgow, UK

Publ.-Id: 28985

Photogeneration of Manganese(III) from Luminescent Manganese(II) Complexes with Thiacalixarene Ligands: Synthesis, Structures and Photophysical Properties

O'Toole, N.; Lecourt, C.; Suffren, Y.; Hauser, A.; Khrouz, L.; Jeanneau, E.; Brioude, A.; Luneau, D.; Desroches, C.

The photophysical properties of the compound [(ThiaSO₂)(MnII)₂(DMF)₄(H₂O)₂] (2), ThiaSO₂ = p-tert-butylsulfonylcalix[4]arene, are presented and compared to the ones of [(ThiaSO₂)₂(MnII)₄F]K (1). The orange luminescence of 2 is attributed, as for 1, to the MnII centred ⁴T₁→⁶A₁ transition and shows, for this type of complex, the weak influence of the Mn²⁺ coordination and ThiaSO₂ conformation on this luminescence, the temperature and pressure dependence and quenching bymolecular dioxygen of which are reported for 2. The latter is attributed to energy transfer from the ⁴T₁ state exciting dioxygen to its ⁱΣ⁺ᵍ state and is responsible for the photosynthesis of the [(ThiaSO₂)(MnIII)(DMF)₂]Na (3) complex in DMF solution from 1 or 2. This reaction was studied by UV/Visible and EPR spectroscopy. The molecular structure and EPR spectroscopy of 3 are also presented.

Keywords: Thiacalixarene; Luminescence; Photooxidation; Manganese

Publ.-Id: 28984

Strong and Selective Ni(II) Extractants Based on Synergistic Mixtures of Sulfonic Acids and Bidentate N-Heterocycles

Roebuck, J. W.; Bailey, P. J.; Doidge, E. D.; Fischmann, A. J.; Healy, M. R.; Nichol, G. S.; O'Toole, N.; Pelser, M.; Sassi, T.; Sole, K. C.; Tasker, P. A.

Bidentate 5,5ʹ-alkyl-3,3ʹ-bi-1H-pyrazole and 2-(5-alkyl-1H-pyrazol-3-yl)pyridine ligands, L⁵ and L⁶ , have been shown to be stronger synergists for the solvent extraction of Ni(II) from sulfate solutions by dinonylnaphthalene sulfonic acid (DNNSAH) than the structurally related tridentate ligand 2,6-bis-[5-n-nonylpyrazol-3-yl]pyridine, L¹ , previously reported by Zhou and Pesic. The bidentate ligands are highly selective, providing the option of sequential recovery of Ni(II) and Co(II) and rejection of other metals commonly found in the liquors resulting from the acidic sulfate leaching of laterite ores. They were the strongest synergists identified in a screening carried out on 18 types of bidentate and tridentate N-heterocyclic ligands, including the recently reported 2-(2ʹ-pyridyl)imidazoles, L⁹⁻¹¹ . X-ray crystal structures of Ni(II) complexes of model ligands for L⁵ and L⁶ , having t-butyl rather than long-chain alkyl groups and with 2-naphthalene sulfonate rather than DNNSA⁻ as counteranions, show that the [Ni(L)₃ ]²⁺ complexes form strong H-bonds from the pyrazolyl NH groups to the oxygen atoms of the sulfonate groups, an arrangement that will stabilize [Ni(L)₃ ·(DNNSA)₂ ] assemblies and shield their polar functionalities from diluent molecules of the water-immiscible phase. UV–visible spectra and mass spectrometry provide evidence for the strong synergists displacing all water molecules from the inner coordination sphere of the Ni(II) ions.

Keywords: Ni recovery; laterite processing; synergistic solvent extraction; outer-sphere bonding; supramolecular chemistry


Publ.-Id: 28983

Stationary beam full-field transmission helium ion microscopy using sub-50 keV He+: Projected images and intensity patterns

Mousley, M.; Eswara, S.; de Castro, O.; Bouton, O.; Klingner, N.; Koch, C. T.; Hlawacek, G.; Wirtz, T.

A dedicated Transmission Helium Ion Microscope (THIM) for sub-50 keV helium was developed to investigate ion scattering processes and contrast mechanisms to develop new imaging and analysis modalities. Unlike a commercial Helium Ion Microscope (HIM), the in-house built instrument allows full flexibility in experimental configuration. Here, we report transmission imaging and scattering patterns obtained from powder and bulk crystalline samples using a stationary broad-beam as well as convergent-beam illumination conditions in THIM. The scattered He+ ions formed unexpected spot patterns in the far-field for MgO, BN and NaCl powder samples, but not for Si bulk sample. The mechanistic origins of the spot patterns in these samples were investigated. Surface diffraction of ions was excluded as a possible cause because the recorded scattering angles do not correspond to the predicted Bragg angles. Complementary Secondary Electron (SE) imaging in a HIM revealed that these samples charge significantly under He+ ion irradiation. It is suggested that the spot patterns obtained in THIM experiments are artefacts related to sample charging. The results presented here indicate that factors other than channelling, blocking and surface diffraction of ions have an impact on the final scattered intensity distribution in the far-field. Hence, the different processes contributing to the final scattered intensities should be understood in more detail to decouple and study the relevant ion beam scattering phenomena.

Keywords: Helium Ion Microscopy; ion scattering; Transmission Ion Microscopy

Publ.-Id: 28982

Uranium(VI) Complexes of Glutathione Disulfide Forming in Aqueous Solution

Kretzschmar, J.; Strobel, A.; Haubitz, T.; Drobot, B.; Steudtner, R.; Barkleit, A.; Brendler, V.; Stumpf, T.

The interactions between glutathione disulfide, GSSG, the redox partner and dimer of the intracellular detoxification agent glutathione, GSH, and hexavalent uranium, U(VI), were extensively studied by solution NMR, complemented by time-resolved laser-induced fluorescence and IR spectroscopies. As expected for the hard Lewis acid U(VI), coordination facilitates by the ligands’ O-donor carboxyl groups. However, owing to the adjacent cationic α-amino group, the glutamyl-COO reveal monodentate binding, while the COO of the glycyl residues show bidentate coordination. The log K value for the reaction UO₂2+ + H₃GSSG = [UO₂H₃GSSG]+ (pH 3, 0.1 M NaClO₄) was determined for the first time, being 4.81 ± 0.08; extrapolation to infinite dilution gave log K° = 5.24 ± 0.08. U(VI) and GSSG form precipitates in the whole pD range studied (2 – 8), showing least solubility for 4 < pD < 6.5. Thus, particularly GSSG, hereby representing also other peptides and small proteins, affects the mobility of U(VI), strongly depending on the speciation of either component.

Keywords: uranium; uranyl; U(VI); glutathione; GSH; glutathione disulfide; GSSG; oxidized glutathione; complex; NMR; TRLFS; FT-IR; spectroscopy; stability constant


  • Secondary publication expected from 06.04.2021

Publ.-Id: 28981

Efficient calculation methods for the diffusion coefficient of interstitial solutes in dilute alloys

Wang, X.; Faßbender, J.; Posselt, M.

In the example of oxygen diffusion in dilute ferritic iron alloys it is shown that the calculation of the diffusion coefficient can be separated into a contribution related to the migration in the interaction region between oxygen and the substitutional solute and a part related to diffusion in pure bcc Fe. The corresponding diffusion times are determined by analytical expressions using Density-Functional-Theory (DFT) data for the respective binding energies. The diffusion coefficient in the interaction region must be determined by atomistic kinetic Monte Carlo (AKMC) simulations with DFT values for the migration barriers as inputs data. However, in contrast to previous calculations, AKMC simulation must be performed only for one concentration of the substitutional solute, and the obtained results can be employed to obtain data for other concentrations in a very efficient manner. This leads to a tremendous decrease of computational efforts. Under certain conditions it is even possible to use only analytical expression where merely DFT data for the binding energies are needed. The limits of applicability of the presented calculation procedures are discussed in detail. The methods presented in this work can be generalized to interstitial diffusion in other host materials with small concentrations of substitutional solutes.

Keywords: Diffusion coefficient; Interstitial solute; dilute alloy; Efficient calculation; First-principle calculations; Atomistic kinetic Monte Carlo simulations

  • Open Access Logo Materials 12(2019)9, 1491
    DOI: 10.3390/ma12091491
  • Lecture (Conference)
    EUROMAT 2019, 01.-05.09.2019, stockholm, sweden

Publ.-Id: 28979

Defects and mechanical properties in weakly damaged Si ion implanted GaAs

Creutzburg, S.; Schmidt, E.; Kutza, P.; Loetzsch, R.; Uschmann, I.; Undisz, A.; Rettenmayr, M.; Gala, F.; Zollo, G.; Boulle, A.; Debelle, A.; Wendler, E.

Damage formation is investigated in GaAs implanted with 1 MeV Si ions to ion fluences from 3 × 10¹² to 5 × 10¹⁵ cm⁻² at room temperature. Under the conditions applied, amorphization of the implanted layers does not occur. The weakly damaged layers are studied by applying different experimental techniques including Rutherford backscattering spectrometry in channeling configuration, x-ray diffraction, in situ curvature measurement, optical subgap spectroscopy, and transmission electron microscopy. The results are evaluated and quantitatively connected with each other. Damage formation is described as a function of the ion fluence using a common defect evolution model. Point defects and defect clusters have to be taken into account in the ion fluence range of main interest up to 2 × 10¹⁵ cm⁻². Point defects contribute by a factor of about 8 more to both perpendicular strain and in-plane stress than defect clusters. When the concentration of point defects or the induced strain reaches a critical value, defect clusters form, which ensures that no further increase of perpendicular strain occurs. This reveals a clear driving force for cluster formation. The microstructure of the defect clusters cannot be determined from the results. As₃Ga₂ interstitial clusters are supposed. A remarkable decrease of the shear modulus of the implanted layers below the value of pristine GaAs by ≈ −35% is observed. Surprisingly, the change of shear modulus already sets in at a very low damage level of a few percent

Publ.-Id: 28978

Performance enhancement and characterization of liquid displacement battery having faradaic membrane

Mushtaq, K.; Zhao, J.; Weber, N.; Sadoway, D.

Übersicht über die Forschungsarbeiten zu "Liquid Displacement Batteries" am MIT, USA.

  • Poster
    14th Workshop on Reactive Metal Processing, 15.03.2019, Boston, USA

Publ.-Id: 28977

Compliance-current-modulated resistive switching with multi-level resistance states in single-crystalline LiNbO3 thin film

Pan, X.; Shuai, Y.; Wu, C.; Luo, W.; Sun, X.; Zeng, H.; Guo, H.; Yuan, Y.; Zhou, S.; Böttger, R.; Cheng, H.; Zhang, J.; Zhang, W.; Schmidt, H.

Resistive switching behavior of a ca. 600 nm thick single-crystalline LiNbO3 (LNO) film has been investigated after vacuum-annealing. Oxygen vacancies (OVs) were generated in the LNO thin film during the annealing process. After electro-forming, filamentary resistive switching has been observed, and the performance of switching can be tuned by the compliance current level. Multi-level resistance states including four different low resistance states, were realized by setting different compliance currents, revealing that both concentration of OVs within the conductive filament and the geometry of the conductive filament influence the switching behavior. The conduction mechanisms of the charge transport during switching is discussed based on the current-voltage curves.

Publ.-Id: 28976

Proton irradiation induced defects in β-Ga2O3: A combined EPR and theory study

Bardeleben, H.; Zhou, S.; Gerstmann, U.; Skachkov, D.; Lambrecht, W.; Ho, Q.; Deák, P.

Proton irradiation of both n-type and semi-insulating bulk samples of β-Ga2O3 leads to the formation of two paramagnetic defects with spin S = 1/2 and monoclinic point symmetry. Their high introduction rates indicate them to be primary irradiation induced defects. The first electron spin resonance (EPR1) has a g-tensor with principal values of gb = 2.0313, gc = 2.0079, and ga* = 2.0025 and quasi-isotropic superhyperfine interaction of 13G with two equivalent Ga neighbors. Under low temperature photoexcitation, this defect is quenched and replaced by a different metastable spin S = 1/2 center of comparable intensity. This second defect (EPR2) has similar principal g-values of gb = 2.0064, gc = 2.0464, and ga* = 2.0024 and shows equally superhyperfine interaction with two equivalent Ga atoms. This EPR2 defect is stable up to T = 100 K, whereas for T > 100 K the initial defect is recovered. Density functional theory calculations of the spin Hamiltonian parameters of various intrinsic defects are carried out using the gauge including projector augmented wave method in order to determine the microscopic structure of these defects. The intuitive models of undistorted gallium monovacancies or self-trapped hole centers are not compatible with neither of these two defects.

Publ.-Id: 28975

Double-peak specific heat and spin freezing in the spin-2 triangular lattice antiferromagnet FeAl2Se4

Li, K.; Jin, S.; Guo, J.; Xu, Y.; Su, Y.; Feng, E.; Liu, Y.; Zhou, S.; Ying, T.; Li, S.; Wang, Z.; Chen, G.; Chen, X.

We report the properties of a triangular lattice iron-chalcogenide antiferromagnet FeAl2Se4.The spin susceptibility reveals a significant antiferromagnetic interaction with a Curie-Weiss temperature Θ_CW≃−200K and a spin-2 local moment. Despite a large spin and a large ∣Θ_CW∣, the low-temperature behaviors are incompatible with conventional classical magnets. No long-range order is detected down to 0.4 K. Similar to the well-known spin-1 magnet NiGa2S4, the specific heat of FeAl2Se4 exhibits a double-peak structure and a T2 power law at low temperatures, which are attributed to the underlying quadrupolar spin correlations and the Halperin-Saslow modes, respectively. The spin freezing occurs at ∼14 K, below which the relaxation dynamics is probed by the ac susceptibility. Our results are consistent with the early theory for the spin-1 system with Heisenberg and biquadratic spin interactions. We argue that the early proposal of the quadrupolar correlation and gauge glass dynamics may be well extended to FeAl2Se4. Our results provide useful insights about the magnetic properties of frustrated quantum magnets with high spins.


Publ.-Id: 28974

Oxyhydride Nature of Rare-Earth-Based Photochromic Thin Films

Cornelius, S.; Colombi, G.; Nafezarefi, F.; Schreuders, H.; Heller, R.; Munnik, F.; Dam, B.

Thin films of rare-earth (RE)−oxygen−hydrogen compounds prepared by reactive magnetron sputtering show a unique color-neutral photochromic effect at ambient conditions. While their optical properties have been studied extensively, the understanding of the relationship between photochromism, chemical composition, and structure is limited. Here we establish a ternary RE−O−H composition-phase diagram based on chemical composition analysis by a combination of Rutherford backscattering and elastic recoil detection. The photochromic films are identified as oxyhydrides with a wide composition range described by the formula REOxH3−2x where 0.5 ≤ x ≤ 1.5. We propose an anion-disordered structure model based on the face-centered cubic unit cell where the O2− and H− anions occupy tetrahedral and octahedral interstices. The optical band gap varies continuously with the anion ratio, demonstrating the potential of band gap tuning for reversible optical switching applications.

Publ.-Id: 28973

Extension of the nodal code DYN3D to SFR applications

Nikitin, E.

DYN3D is a well-established Light Water Reactor (LWR) simulation tool and is being extended for safety analyses of Sodium cooled Fast Reactors (SFRs) at the Helmholtz-Zentrum Dresden-Rossendorf. This thesis focuses on the first stage of the development process, that is, the extension and application of DYN3D for steady-state and transient SFR calculations on reactor core level. In contrast to LWRs, the SFR behavior is especially sensitive to thermal expansions of the reactor components. Therefore, a new thermal-mechanical module accounting for thermal expansions is implemented into DYN3D. At first step, this module is capable of treating two important thermal expansion effects occurring within the core, namely axial expansion of fuel rods and radial expansion of diagrid. In order to perform nodal calculations with DYN3D, pre-generated homogenized few-group cross sections (XS) are necessarily needed. Therefore, prior to the development of thermal expansion models, a general methodology for XS generation is established for SFR nodal calculations based on the use of the Monte Carlo code Serpent. The new methodological developments presented in this thesis are verified against the Monte Carlo solutions of Serpent. Two SFR cores are used for testing: the large oxide core of the OECD/NEA benchmark and a smaller core from the Phenix end-of-life tests. Finally, the extended DYN3D is validated against selected IAEA benchmark tests on the Phenix end-of-life experiments that contain both steady-state and transient calculations. The contribution to the SFR-related developments at the HZDR, as presented in this thesis, makes it possible of performing steady-state and transient calculations for SFRs on reactor core level by using DYN3D. With this study, the basis of the next stage of DYN3D developments is established, that is, the up-scale of SFR analysis to system level can continue by coupling with a sodium capable thermal-hydraulic system code.

Keywords: SFR; thermal expansion; group constant generation; nodal methods; spatial kinetics; Monte Carlo; Serpent; DYN3D


Publ.-Id: 28972

Source term calculation and validation for F-18 production with a cyclotron for medical applications at HZDR

Konheiser, J.; Müller, S. E.; Magin, A.; Naumann, B.; Ferrari, A.

In this document we present the calculation and experimental validation of a source term for F-18 production with a cyclotron for medical applications operating at 18 MeV proton energy and 30 microA proton current. The Monte Carlo codes MCNP6 and FLUKA were used for the calculation of the source term. In addition, the radiation field around the O-18 enriched water target was simulated with the two codes. To validate the radiation field obtained in the simulation, an experimental program has been started using activation samples which are placed close to the water target during an F-18 production run of the cyclotron. After the irradiation, the samples are analyzed and the resulting activation is compared to Monte Carlo calculations of the expected sample activation. We and good agreement between simulations and experimental results, with most calculation to experiment (C/E) ratios well between 0.6 and 1.4.

Keywords: F-18; MCNP; FLUKA; Source Term; Cyclotron

Related publications

Publ.-Id: 28971

Fast-neutron-induced fission cross section of Pu(242) measured at the neutron time-of-flight facility nELBE

Kögler, T.

This dataset includes the processed data of the fast neutron-induced fission of Pu(242) experiement performed in November 2014 at the neutron time-of-flight facility nELBE which was published in T. Kögler et al., Phys. Rev. C 99, 024604

It contains the absolute (Pu242_nfis_Koegler_2019.csv) and relative (Pu242_U235_nfis_Koegler_2019.csv) cross section data ranging from 0.5 MeV to 10 MeV. The cross section data is given in comma separated ASCII files, as well as in a MS Excel-Sheet.

The columns of the tables are defined as follows:

  1. EN...neutron kinetic energy from the measured time of flight (ToF)
  2. EN-ERR...uncertainty of neutron kinetic energy = 0.5*(ToF bin width) = 1 ns
  3. DATA...cross section data
  4. ERR-S...statistical uncertainty of the cross section data
  5. ERR-SY...systematic uncertainty of the cross section data
  6. ERR-T...combined standard uncertainty of the cross section data
  7. ERR-0...relative uncertainty counting
  8. ERR-1...relative uncertainty normalization
  9. ERR-2...relative uncertainty reference cross section
  10. ERR-3...relative uncertainty FF detection inefficiency
  11. ERR-4...relative stat. uncertainty scattering correction H19
  12. ERR-5...relative sys. uncertainty scattering correction H19
  13. ERR-6...relative stat. uncertainty scattering correction PuFC
  14. ERR-7...relative sys. uncertainty scattering correction PuFC

Additionally, a root (see file is supplied, including the determined cross sections and all nessessary data to reconstruct the experiment. This includes the measured quantities, reference data, correction factors, evaluated cross sections etc.

To have the whole functionality of the root file, additional libary files ( and libGo4UserAnalysis_rdict.pcm) are also given here.

Keywords: neutron-induced fission; plutonium-242; cross section measurements; nuclear reactions; nucleon induced nuclear reactions; nELBE

Related publications

  • Reseach data in the HZDR data repository RODARE
    Publication date: 2019-03-06
    DOI: 10.14278/rodare.117
    License: CC-BY-4.0


Publ.-Id: 28970

Supplementary Data: Spectral Control via Multi-Species Effects in PW-Class Laser-Ion Acceleration

Huebl, A.; Rehwald, M.; Obst-Huebl, L.; Ziegler, T.; Garten, M.; Widera, R.; Zeil, K.; Cowan, T. E.; Bussmann, M.; Schramm, U.; Kluge, T.

Supplementary materials for our paper "Spectral Control via Multi-Species Effects in PW-Class Laser-Ion Acceleration".

Additional high-resolution, raw HDF5 files using the openPMD standard (DOI:10.5281/zenodo.1167843) increase simulation output data to 4.7 TByte and are available from the corresponding author upon reasonable request. 

Keywords: LPA; laser-ion acceleration; TNSA; multi-species; cryogenic target; particle-in-cell

Related publications

  • Reseach data in the HZDR data repository RODARE
    Publication date: 2019-03-06
    DOI: 10.14278/rodare.115
    License: CC-BY-SA-4.0


Publ.-Id: 28969

Understanding the size effects on the electronic structure of ThO2 nanoparticles

Amidani, L.; Plakhova, T. V.; Romanchuk, A. Y.; Gerber, E.; Weiss, S.; Efimenko, A.; Sahle, C. J.; Butorin, S. M.; Kalmykovc, S. N.; Kvashnina, K. O.

Developing characterization techniques and analysis methods adapted to the investigation of nanoparticles (NPs) is of fundamental importance considering the role of these materials in many fields of research. The study of actinide based NPs, despite their environmental relevance, is still underdeveloped compared to that of NPs based on stable and lighter elements. We present here an investigation of ThO2 NPs performed with High-Energy Resolution Fluorescence Detected (HERFD) X-ray Absorption Near-Edge Structure (XANES) and with ab initio XANES simulations. Structural models of ThO2 NPs with sharp edges and corners reproduce the size effect observed in experimental data. Inspection of the simulations from Th atoms in the core and on the surface of the NP indeed demonstrates that the origin of the effect is the lowering of the number of coordinating atoms for Th at the surface of the NP. The sensitivity of HERFD XANES to the less coordinated atoms at the surface may be exploited to investigate surface interactions.


Publ.-Id: 28968

Ion irradiation driven changes of magnetic anisotropy in ultrathin Co films sandwiched between Au or Pt covers

Mazalski, P.; Kurant, Z.; Sveklo, I.; Dobrogowski, W.; Fassbender, J.; Wawro, A.; Maziewski, A.

Modifications of magnetic anisotropy of 30 keV Ga + ion irradiated ultrathin Co films sandwiched between Au or Pt buffer and capping layers are investigated as a function of magnetic layer thickness, d Co , and the ion fluence, F. Maps (d Co , F) of saturation fields have been derived from local magnetooptical polar Kerr effect (PMOKE) measurements. The areas with increased remanent magnetization and/or saturation fields, which are directly related to the uniaxial anisotropy, adopt linear shapes for the two branches in the maps. They are very distinct, especially for the Pt/Co/Pt system irradiated at lower and higher fluence. Replacement of Pt with Au in the buffer layer results in minor influence on the magnetization properties of the irradiated trilayers. Au as a capping layer significantly decreases the anisotropy in the branch appearing at lower fluence. In the Au/Pt/Au sandwich, a severe reduction of induced anisotropy is observed in both branches. The proposed phenomenological model describing experimentally investigated magnetic anisotropies enables separation of surface and volume contributions to both branches of enhanced anisotropy.

Keywords: Chemical driving force demixing; Ion beam irradiation; Magnetooptics; Perpendicular magnetic anisotropy


Publ.-Id: 28967

Digital LLRF Operation using MicroTCA at ELBE

Gümüş, Ç.; Hierholzer, M.; Kuntzsch, M.; Pfeiffer, S.; Schmidt, C.; Steinbrück, R.; Zenker, K.

The upgrade of the Low Level RF (LLRF) system of the Electron Linac for beams with high Brilliance and low Emittance (ELBE) at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) was accomplished in 2018 . Now a digital system based on MTCA.4 can be used instead of the analogue system, which is operated since almost 20 years.The digital LLRF controller is implemented on a FPGA. The parametrisation and monitoring of the controller is performed by a ChimeraTK server application. ChimeraTK is a control system and hardware interface tool kit, which among others can provide an OPC-Unified Architecture (OPC-UA) interface. On the one hand, this interface is used to integrate the digital LLRF into the existing ELBE control and machine protection system, that is based on a Siemens PLC (S7) infrastructure. On the other hand, it is used to implement different additional clients of the ChimeraTK server application, such as the ELBE human machine interface used by the operators (WinCC, SCADA) or expert panels (e.g. LabView or Python). An overview of the new system including hardware as well as software components is given. In addition, an amplitude and phase noise measurement of a superconducting RF module are presented.

  • Invited lecture (Conferences)
    5. Annual Matter and Technology Meeting, 05.-07.03.2019, Jena, Germany

Publ.-Id: 28966

SPECT-Untersuchungen mit dem 123 I-markierten Dopamintransporter-Liganden FP-CIT (DaTSCAN):DGN-Handlungsempfehlung (S1-Leitlinie)

Tatsch, K.; Buchert, R.; Bartenstein, P.; Barthel, H.; Boecker, H.; Brust, P.; Drzezga, A.; La Fougère, C.; Gründer, G.; Grünwald, F.; Krause, B.-J.; Kuwert, T.; Langen, K.-J.; Rominger, A.; Sabri, O.; Schreckenberger, M.; Meyer, P. T.

Die S1-Leitlinie soll bei der Indikationsstellung, Durchführung, Interpretation und Befundung von SPECT-Untersuchungen des Dopamintransporters (DAT) mit DaTSCANTM unterstützen.
Gegenüber der Vorgängerversion von 2007 berücksichtigt die vorliegende Aktualisierung und Überarbeitung die neuere wissenschaftliche Literatur, zwischenzeitlich veröffentlichte Guidelines der europäischen (EANM) und amerikanischen Fachgesellschaften (SNM), sowie die aktuelle Fassung der S3-Leitlinie „Idiopathisches Parkinson-Syndrom“ der Deutschen Gesellschaft für Neurologie. Zudem finden neue technische Möglichkeiten Berücksichtigung.

  • Nuklearmedizin 58(2019)1, 5-16

Publ.-Id: 28965

Source term calculation and validation for F-18 production with a cyclotron for medical applications at HZDR

Konheiser, J.; Mueller, S. E.; Magin, A.; Naumann, B.; Ferrari, A.

Data contained in Fig. 2 of the

Keywords: Cyclotron; Source term; MCNP6; FLUKA

Related publications

  • Reseach data in the HZDR data repository RODARE
    Publication date: 2019-03-04
    DOI: 10.14278/rodare.113
    License: CC-BY-4.0


Publ.-Id: 28964

CFD-based optimization of heat exchanger tube bundle arrangement for passive spent fuel pool cooling to ambient air

Unger, S.; Beyer, M.; Krepper, E.; Hampel, U.

The storage of spent fuel in actively cooled water pools is common practice in nuclear power plants. One possibility to improve the reliability and the economy of spent fuel storage is the substitution of active cooling components by passive heat transfer systems. Thereby, ambient air should be the ultimate heat sink. A major drawback of natural convection heat transfer to ambient is the low heat transfer coefficient. Thus, bundle heat exchangers with finned tube are commonly employed. In one of our previous studies an optimum fin design was derived for such a heat exchanger. In the present investigation this tube bundle arrangement was numerical analysed with respect to optimal tube bundle configuration, tube shape, longitudinal tube pitch, transversal tube pitch and tube row number. We found highest heat transfer performance for oval shaped tubes with an axis ratio of 1:2.1 in a staggered configuration, having longitudinal tube pitch of 73 mm, a transversal tube pitch of 52 mm and 4 tube rows.

  • Contribution to proceedings
    50th Annual Meeting on Nuclear Technology, 07.-08.05.2019, Berlin, Deutschland
    Proceedings of the 50th Annual Meeting on Nuclear Technology

Publ.-Id: 28963

Spectral Control via Multi-Species Effects in PW-Class Laser-Ion Acceleration

Huebl, A.; Rehwald, M.; Obst-Huebl, L.; Ziegler, T.; Garten, M.; Widera, R.; Zeil, K.; Cowan, T. E.; Bussmann, M.; Schramm, U.; Kluge, T.

Laser-ion acceleration with ultra-short pulse, PW-class lasers is dominated by non-thermal, intra-pulse plasma dynamics. The presence of multiple ion species or multiple charge states in targets leads to characteristic modulations and even mono-energetic features, depending on the choice of target material. As spectral signatures of generated ion beams are frequently used to characterize underlying acceleration mechanisms, thermal, multi-fluid descriptions require a revision for predictive capabilities and control in next-generation particle beam sources. We present an analytical model with explicit inter-species interactions, supported by extensive ab initio simulations. This enables us to derive important ensemble properties from the spectral distribution resulting from those multi-species effects for arbitrary mixtures. We further propose a potential experimental implementation with a novel cryogenic target, delivering jets with variable mixtures of hydrogen and deuterium. Free from contaminants and without strong influence of hardly controllable processes such as ionization dynamics, this would allow a systematic realization of our predictions for the multi-species effect.

Keywords: LPA; laser-ion acceleration; TNSA; multi-species; cryogenic target; particle-in-cell

Related publications

  • Poster
    Laser-Plasma Accelerator Workshop 2019, 06.-10.05.2019, Split, Kroatien

Publ.-Id: 28962

Revealing the Nature of Photoluminescence Emission in Metal-Halide Double Perovskites

Zelewski, S. J.; Urban, J. M.; Surrente, A.; Maude, D. K.; Kuc, A.; Schade, L.; Johnson, R. D.; Dollmann, M.; Nayak, P. K.; Snaith, H. J.; Radaelli, P. G.; Kudrawiec, R.; Nicholas, R. J.; Plochocka, P.; Baranowski, M.

Double perovskite crystals such as Cs2AgBiBr6 are expected to overcome the limitation of classic hybrid organic-inorganic perovskite crystals related to the presence of lead and the lack of structural stability. Perovskites are ionic crystals in which the carriers are expected to strongly couple to lattice vibrations. In this work we demonstrate that the photoluminescence (PL) emission in Cs2AgBiBr6 is strongly influenced by the strong electron-phonon coupling. Combining photoluminescence excitation (PLE) and Raman spectroscopy we show that the PL emission is related to a color center rather than a band-to-band transition. The broadening and the Stokes shift of the PL emission from Cs2AgBiBr6 is well explained using a Franck-Condon model with a Huang-Rhys factor of S=11.7 indicating a strong electron-phonon interaction in this material.


Publ.-Id: 28961

Effect of four lanthanides onto the viability of two mammalian kidney cell lines

Heller, A.; Barkleit, A.; Bok, F.; Wober, J.

Exposure to lanthanides (Ln) poses a serious health risk to animals and humans. Since Ln are mainly excreted with the urine, we investigated the effect of La, Ce, Eu, and Yb exposure on renal rat NRK-52E and human HEK-293 cells for 8, 24 and 48 h in vitro. Cell viability studies using the XTT assay and microscopic investigations were combined with solubility and speciation studies using ICP-MS and TRLFS. Thermodynamic modeling was applied to predict the speciation of Ln in the cell culture medium. All Ln show a concentration- and time-dependent effect on both cell lines with Ce being the most potent element. In cell culture medium, the Ln are completely soluble and most probably complexed with proteins from fetal bovine serum. The results of this study underline the importance of combining biological, chemical, and spectroscopic methods in studying the effect of Ln on cells in vitro and may contribute to the improvement of the current risk assessment for Ln in the human body. Furthermore, they demonstrate that Ln seem to have no effect on renal cells in vitro at environmental trace concentrations. Nevertheless, especially Ce has the potential for harmful effects at elevated concentrations observed in mining and industrial areas.

Keywords: f-elements; renal cells; cytotoxicity; XTT; time-resolved laser-induced fluorescence spectroscopy; thermodynamic modeling


  • Secondary publication expected

Publ.-Id: 28960

Improved axial plane distance and velocity determination for ultrafast electron beam X-ray computed tomography

Neumann, M.; Bieberle, M.; Wagner, M.; Bieberle, A.; Hampel, U.

Ultrafast electron beam X-ray computed tomography (UFXCT) has in recent years become an indispensable tool for multiphase flow studies. An essential feature of this technique is fast cross-sectional imaging in two distinct planes. Both the spatial location of focal spot path and detectors as well as the angular scanning range in UFXCT differ from that of conventional X-ray CT systems. This brings in a spatial dependence in axial scanning position and resolution. In this paper, we present an analysis of this problem, which results in an improved description of the location and shape of the imaging regions, a more accurate map of the distance between the imaging planes and finally a higher precision in the determination of axial structure velocities. The benefit of this improved approach is exemplarily demonstrated for a two-phase pipe flow around an obstacle.

Keywords: ultrafast X-ray computed tomography; phase velocity measurement


Publ.-Id: 28958

Transparent Conductive Tantalum Doped Tin Oxide as Selectively Solar-Transmitting Coating for High Temperature Solar Thermal Applications

Lungwitz, F.; Escobar-Galindo, R.; Janke, D.; Schumann, E.; Wenisch, R.; Gemming, S.; Krause, M.

The transparent conductive oxide (TCO) SnO2:Ta is developed as a selectively solar-transmitting coating for concentrated solar power (CSP) absorbers. Upon covering with an antireflective layer, a calculated absorptivity of 95 % and an emissivity of 30 % are achieved for the model configuration of SnO2:Ta on top of a perfect black body (BB). High-temperature stability of the developed TCO up to 1073 K is shown in situ by spectroscopic ellipsometry and Rutherford backscattering spectrometry. The universality of the concept is demonstrated by transforming silicon and glassy carbon from non-selective into solar-selective absorbers by depositing the TCO on top of them. Finally, the energy conversion efficiencies of SnO2:Ta on top of a BB and an ideal non-selective BB absorber are extensively compared as a function of solar concentration factor C and absorber temperature TH. Equal CSP efficiencies can be achieved by the TCO on BB configuration with approximately 50 % lower solar concentration. This improvement could be used to reduce the number of mirrors in a solar plant, and thus, the levelized costs of electricity for CSP technology.

Keywords: concentrated solar power; solar thermal electricity; solar-selective transmitter; transparent conductive oxide; high-temperature in situ characterization


Publ.-Id: 28957

Interstellar ⁶⁰Fe in Antarctica

Koll, D.; Korschinek, G.; Faestermann, T.; Gómez-Guzmán, J.; Kipfstuhl, S.; Merchel, S.; Welch, J. M.

Earth is constantly bombarded with extraterrestrial dust containing invaluable information about extraterrestrial processes, e.g. structure formation by stellar explosions or nucleosynthesis, which could be traced back by long-lived radionuclides. Here, we report the very first detection of a recent ⁶⁰Fe influx on Earth by analyzing 500 kg of snow from Antarctica by Accelerator Mass Spectrometry. By the measurement of the cosmogenically produced radionuclide ⁵³Mn, an atomic ratio of ⁶⁰Fe/⁵³Mn=0.017 was found, significantly above cosmogenic production. After elimination of possible terrestrial sources, such as global fallout, the excess of ⁶⁰Fe could only be attributed to interstellar ⁶⁰Fe from the solar neighborhood.

Keywords: AMS; supernova; ⁶⁰Fe

Publ.-Id: 28955

Critical dynamics of the Kuramoto model on sparse random networks

Juhász, R.; Kelling, J.; Ódor, G.

We consider the Kuramoto model on sparse random networks such as the Erdős-Rényi graph or its combination with a regular two-dimensional lattice and study the dynamical scaling behavior of the model at the synchronization transition by large-scale, massively parallel numerical integration. By this method, we obtain an estimate of critical coupling strength more accurate than obtained earlier by finite-size scaling of the stationary order parameter. Our results confirm the compatibility of the correlation-size and the temporal correlation-length exponent with the mean-field universality class. However, the scaling of the order parameter exhibits corrections much stronger than those of the Kuramoto model with all-to-all coupling, making thereby an accurate estimate of the order-parameter exponent hard. We find furthermore that, as a qualitative difference to the model with all-to-all coupling, the effective critical exponents involving the order-parameter exponent, such as the effective decay exponent characterizing the critical desynchronization dynamics show a non-monotonic approach toward the asymptotic value. In the light of these results, the technique of finite-size scaling of limited size data for the Kuramoto model on sparse graphs has to be treated cautiously.

Keywords: Networks; Kuramoto Model; Synchronization


Publ.-Id: 28954

Small-angle neutron scattering (SANS): Overview on principles and best practices

Bergner, F.; Ulbricht, A.

This talk provides an introduction into the method of small-angle neutron scattering (SANS), elements of good practice for the application and analysis as well as selected applications in the field of nuclear materials.

  • Lecture (Conference)
    OECD/NEA Nuclear Science Committee Preparatory meeting: Best practices for nuclear materials characterisation techniques, 11.-12.02.2019, Boulogne-Billancourt, France

Publ.-Id: 28953

Critical synchronization dynamics of the Kuramoto model on connectome and small world graphs

Ódor, G.; Kelling, J.

The hypothesis, that cortical dynamics operates near criticality also suggests, that it exhibits universal critical exponents which marks the Kuramoto equation, a fundamental model for synchronization, as a prime candidate for an underlying universal model. Here, we determined the synchronization behavior of this model by solving it numerically on a large, weighted human connectome network, containing 804092 nodes, in an assumed homeostatic state. Since this graph has a topological dimension d<4, a real synchronization phase transition is not possible in the thermodynamic limit, still we could locate a transition between partially synchronized and desynchronized states. At this crossover point we observe power-law--tailed synchronization durations, with τt≃1.2(1), away from experimental values for the brain. For comparison, on a large two-dimensional lattice, having additional random, long-range links, we obtain a mean-field value: τt≃1.6(1). However, below the transition of the connectome we found global coupling control-parameter dependent exponents 1<τt≤2, overlapping with the range of human brain experiments. We also studied the effects of random flipping of a small portion of link weights, mimicking a network with inhibitory interactions, and found similar results. The control-parameter dependent exponent suggests extended dynamical criticality below the transition point.

Keywords: networks; brain; synchronization; kuramoto model

Related publications

Publ.-Id: 28952

Framework modifications and dehydration path of a Ag+-modified, STI-type zeolite

Cametti, G.; Scheinost, A. C.; Giordani, M.; Churakov, S. V.

The effect of Ag+ incorporation into stellerite, a natural zeolite with STI framework type, was investigated by means of Single Crystal X-ray Diffraction (SC-XRD), Molecular Dynamics (MD) simulations and X-ray Absorption Fine Structure Spectroscopy (XAFS). At room temperature the complete exchange of the original extraframework ions with Ag+ provoked a distortion of the framework accompanied by symmetry reduction from orthorhombic Fmmm to monoclinic F2/m space group. Ag+ ions were strongly disordered, with occupancies ranging from 0.02 to 0.24, at partially-occupied sites within zeolitic cages. The combination of ab initio molecular dynamic simulations and XAFS spectroscopy suggested that Ag+ is coordinated by three water oxygens at 2.37 Å and by two framework oxygens at ca. 2.55 Å. The thermal stability was monitored in situ by SC-XRD (from 25 to 400°C) and by XAFS (from 25 to 650°C). Upon heating the structure transformed to three different topologies: B phase, D’ phase, observed here for the first time, and D phase. The unit-cell volume contracted from 4392.85(14) at room temperature to 3644.4(4) Å3, measured at 400°C. Possible Ag+ to Ag0 reduction could be excluded although the formation of Ag+-Ag+ clusters could not be unambiguously ruled out.

Keywords: zeolite; molecular dynamics; SC-XRD; XAFS; XANES; Ag


Publ.-Id: 28951

Directed Evolution and Engineering of Gallium-Binding Phage Clones—A Preliminary Study

Schönberger, N.; Zeitler, C.; Braun, R.; Lederer, F.; Matys, S.; Pollmann, K.

The phage surface display technology is a useful tool to screen and to extend the spectrum of metal-binding protein structures provided by nature. The directed evolution approach allows identifying specific peptide ligands for metals that are less abundant in the biosphere. Such peptides are attractive molecules in resource technology. For example, gallium-binding peptides could be applied to recover gallium from low concentrated industrial wastewater. In this study, we investigated the affinity and selectivity of five bacteriophage clones displaying different gallium-binding peptides towards gallium and arsenic in independent biosorption experiments. The displayed peptides were highly selective towards Ga3+ whereby long linear peptides showed a lower affinity and specificity than those with a more rigid structure. Cysteine scanning was performed to determine the relationship between secondary peptide structure and gallium sorption.
By site-directed mutagenesis, the amino acids of a preselected peptide sequence are systematically replaced by cysteines. The resulting disulphide bridge considerably reduces the flexibility of linear peptides. Subsequent biosorption experiments carried out with the mutants obtained from cysteine scanning demonstrated, depending on the position of the cysteines in the peptide, either a considerable increase in the affinity of gallium compared to arsenic or an increase in the affinity for arsenic compared to gallium. This study shows the impressive effect on peptide–target interaction based on peptide structure and amino acid position and composition via the newly established systematic cysteine scanning approach.

Keywords: phage surface display; gallium; metal–peptide interaction; site-directed mutagenesis; cysteine; peptide structure

Publ.-Id: 28950

Nuclear level densities and gamma-ray strength functions in samarium isotopes

Naqvi, F.; Simon, A.; Guttormsen, M.; Schwengner, R.; Frauendorf, S.; Reingold, C. S.; Burke, J. T.; Cooper, N.; Hughes, R. O.; Humby, P.; Koglin, J.; Ota, S.; Saastamoinen, A.

The gamma-strength functions and level densities of in the quasi-continuum of 147,149Sm isotopes have been extracted from particle-gamma coincidences using the Oslo method. The nuclei of interest were populated via (p,d) reactions on pure 148,150Sm targets and the reaction products were recorded by the HYPERION array. An upbend in the gSF has been observed. The systematic analysis of the gSF for a range of Sm isotopes show that the scissors mode and the upbend compete with each other. Shell model calculations show a very good agreement with the experimental gSFs and confirm the competition between the upbend and scissors mode.

Keywords: Nuclear structure; light-ion reactions; gamma spectroscopy; level densities; strength functions; shell-model calculations

Publ.-Id: 28949

A proof of principle experiment for microbeam radiation therapy at the Munich Compact Light Source

Dombrowsky, A. C.; Burger, K.; Porth, A.-K.; Stein, M.; Dierolf, M.; Günther, B.; Achterhold, K.; Gleich, B.; Feuchtinger, A.; Bartzsch, S.; Beyreuther, E.; Combs, S. E.; Pfeiffer, F.; Wilkens, J. J.; Schmid, T. E.

Microbeam radiation therapy (MRT), a preclinical form of spatially fractionated radiotherapy, uses an array of microbeams of hard synchrotron X-ray radiation. Recently, compact synchrotron X-ray sources got more attention as they provide essential prerequisites for the translation of MRT into clinics while overcoming the limited access to synchrotron facilities. At the Munich Compact Light Source (MuCLS), a beamline at one of these novel compact X-ray sources, a proof of principle experiment was conducted applying MRT to a xenograft tumor mouse model. First, subcutaneous tumors derived from the established squamous carcinoma cell line FaDu were irradiated at a conventional X-ray tube using broadbeam geometry to determine a suitable dose range for the tumor growth delay.
For irradiations at the MuCLS, FaDu tumors were irradiated with broadbeam and microbeam irradiation at integral doses of either 3 or 5 Gy and tumor growth delay was measured. Microbeams had a width of 50 µm and a center-to-center distance of 350 µm with peak doses of either 21 or 35 Gy. A dose rate of up to 5 Gy/min was delivered to the tumor. Both doses and modalities delayed the tumor growth compared to a sham-irradiated tumor. The irradiated area and microbeam pattern were verified by staining of the DNA double-strand break marker γH2AX. This study demonstrates for the first time that microbeam radiation therapy can be successfully performed in vivo at the MuCLS.

Keywords: MRT; microbeam; compact source; tumor; X-rays; growth delay

Publ.-Id: 28948

Time dependence of the bioassociation behavior of U(VI) and Eu(III) with Brassica napus cells

Jessat, J.; Sachs, S.; Moll, H.; Steudtner, R.; Bok, F.; Stumpf, T.

For both the remediation of contaminated sites and the safety assessment of nuclear waste repositories detailed knowledge about the transfer of radionuclides (RN) into the food chain is of central concern. The association of RN with plants and their interaction with released metabolites influences whose fate in the environment. We studied the time and concentration dependent bioassociation of U(VI) and Eu(III) as an analogue for trivalent actinides with Brassica napus cells. The aim was to determine the effect of both heavy metals on the cell viability and the influence of the cell metabolism on the speciation and bioavailability of both metals. Due to the exposure of the cells with Eu(III) and U(VI) a time and concentration dependent bioassociation behavior was observed. At 200 µM U(VI) a multistage bioassociation process occurred resulting in a detachment of bioassociated U(VI) back into the medium. This change in the U(VI) speciation in the medium was observed by time-resolved laser-induced fluorescence spectroscopy. The occurrence of three different U(VI) species in the medium over the exposure time (Fig. 1) indicates the release of plant cell metabolites, that can act as ligands for U(VI) complexation and may impact its transfer in the environment. Model calculations for the speciation of U(VI) in the initial medium were performed on basis of the literature [1]. In order to identify possible plant cell metabolites, experiments on the enrichment and chromatographic separation of metabolites were carried out. In addition, the U(VI) complexation by relevant metabolites was studied.

[1] Sachs (2017) Environ. Sci. Technol. 51, 10843-10849.

Keywords: brassica napus; spectroscopy; species; TRLFS; bioassociation; metabolite; plant cells; Uranium; Europium

  • Poster
    Goldschmidt 2019, 18.-23.08.2019, Barcelona, Spain
  • Lecture (Conference)
    Goldschmidt 2019, 18.-23.08.2019, Barcelona, Spain

Publ.-Id: 28947

In vitro and in vivo Human Metabolism of (S)-[18F]Fluspidine – a Radioligand for Imaging σ1 Receptors with Positron Emission Tomography (PET)

Ludwig, F.-A.; Fischer, S.; Houska, R.; Hoepping, A.; Deuther-Conrad, W.; Schepmann, D.; Patt, M.; Meyer, P.; Hesse, S.; Becker, G.-A.; Zientek, F. R.; Steinbach, J.; Wünsch, B.; Sabri, O.; Brust, P.

(S)-[18F]fluspidine ((S)-[18F]1) has recently been explored for PET imaging of sigma-1 receptors in humans. In the current report, we have used plasma samples of healthy volunteers to investigate the radiometabolites of (S)-[18F]1 and elucidate their structures with LC-MS/MS. For the latter purpose additional in vitro studies were conducted by incubation of (S)-[18F]1 and (S)-1 with human liver microsomes (HLM). In vitro metabolites were characterized by interpretation of MS/MS fragmentation patterns from collision-induced dissociation or by use of reference compounds. Thereby, structures of corresponding radio-HPLC-detected radiometabolites, both in vitro and in vivo (human), could be identified. By incubation with HLM, mainly debenzylation and hydroxylation occurred, beside further mono- and di-oxygenations. The product hydroxylated at the fluoroethyl side chain was glucuronidated. Plasma samples (10, 20, 30 min p.i., n=5-6), obtained from human subjects receiving 250-300 MBq (S)-[18F]1 showed 97.2%, 95.4%, and 91.0% of unchanged radioligand, respectively. In urine samples (90 min p.i.) the fraction of unchanged radioligand was only 2.6% and three major radiometabolites were detected. The one with the highest percentage, also found in plasma, matched the glucuronide formed in vitro. Only a small amount of debenzylated metabolite was detected. In conclusion, our metabolic study, in particular the high fractions of unchanged radioligand in plasma, confirms the suitability of (S)-[18F]1 as PET radioligand for sigma-1 receptor imaging.

Keywords: Sigma-1 receptors (S1R); fluspidine; positron emission tomography (PET); radiometabolites; liquid chromatography-mass spectrometry (LC-MS); liver microsomes

Publ.-Id: 28946

Selective histone deacetylase inhibitors as prospective radiotracers for PET imaging

Clauß, O.; Scheunemann, M.; Hansen, F. K.; Brust, P.

The class I histone deacetylases (HDACs) 1, 2 and 3 are overexpressed in several types of cancer, neurodegenerative diseases and inflammation. The catalyzed deacetylation of lysine residues on histones represents a key epigenetic modification that modulates the chromatin and thus influence the gene expression and transcription. Inhibition of zinc-dependent HDACs relaxes the chromatin structure and can result in transcriptional activation and anticancer effects, e.g. induction of apoptosis. Consequently, radiolabelled HDAC inhibitors have emerged as a potential tool for the diagnostic imaging of tumors by positron emission tomography (PET).
The aim of this work is the development of novel highly affine and selective fluorine containing derivatives of a class I selective HDAC inhibitor to obtain the corresponding 18-fluorine PET radiotracers with an ortho-aminoanilide as zinc-binding motif for targeting class I HDACs in tumors. A series of fluorinated reference compounds will be synthesized and the binding affinities and selectivities towards the HDAC isoforms 1, 2 and 3 will be determined. Our strategy is mainly focused on the medicinal chemistry of fluorine-containing derivatives, which are suitable for direct and indirect nucleophilic radiofluorination. For the most promising compounds, precursors for radiolabeling will be synthesized and a fully automated procedure will be established. The evaluation of physicochemical properties, e.g. stability and lipophilicity of the radiolabelled compounds will be assessed and further in vitro and in vivo investigations performed.

Keywords: Histone deacetylase inhibitors; Positron emission tomography; Fluorinated compounds

  • Poster
    NCT Retreat 2019, 09.-10.05.2019, Heidelberg, Deutschland

Publ.-Id: 28945

Instability of precession driven Kelvin modes: Evidence of a detuning effect

Herault, J.; Giesecke, A.; Gundrum, T.; Stefani, F.

We report an experimental study of the instability of a nearly resonant Kelvin mode forced by precession in a cylindrical vessel. The instability is detected above a critical precession ratio via the appearance of peaks in the temporal power spectrum of pressure fluctuations measured at the end walls of the cylinder. The corresponding frequencies can be grouped into frequency sets satisfying resonance conditions with the forced Kelvin mode. We show that one set forms a triad that is associated with a parametric resonance of Kelvin modes. We observe a significant frequency variation of the unstable modes with the precession ratio, which can be explained by a detuning mechanism due to the slowdown of the background flow. By introducing a semianalytical model, we show that the departure of the flow from the solid body rotation leads to a modification of the dispersion relation of Kelvin modes and to a detuning of the resonance condition. The second frequency set includes a very low frequency and does not exhibit the properties of a parametric resonance between Kelvin modes. Interestingly, this frequency set always emerges before the occurrence of the triadic resonances, i.e., at a lower precession ratio, which implies that it may correspond to a different type of instability. We discuss the relevance of an instability of a geostrophic mode described by Kerswell [Kerswell, J. Fluid Mech. 382, 283 (1999)], although other mechanisms cannot be completely ruled out.

Keywords: Precession; Dynamo; DRESDYN


Publ.-Id: 28944

Limited importance of EphrinA1–ligand, Src kinase, and focal adhesion kinase in EphA2-mediated regulation of metastasis in Mel-Juso and A375 human melanoma cells

Neuber, C.; Herwig, N.; Pietzsch, J.; Belter, B.

EphA2 receptor tyrosine kinase fulfils various functions in the development of cancers. Here we analyzed how regulation of EphA2 receptor influences metastatic properties in human melanoma cells in vitro and lung metastasis in vivo. Further, we investigated whether the effects are mediated by Src kinase/focal adhesion kinase (FAK) signaling downstream of EphA2. Therefore, as model Mel-Juso and A375 melanoma cell lines showing different intrinsic EphA2 expression levels were used. To regulate EphA2 expression and activity, we used RNA interference, transgeneic EphA2 overexpression, and stimulation of EphA2 activity by adding EphrinA1. Adhesion to fibronectin was increased in EphA2-silenced cells and decreased in EphA2-overexpressing cells. Migration and planar motility were unaffected in Mel-Juso cells, but increased in EphA2-silenced A375 cells and decreased in EphA2-overexpressing A375 cells. Adhesion and migration were unaffected by EphrinA1-stimulation, indicating ligand-independent mechanisms. In vivo we detected increased lung metastasis in mice inoculated with EphA2-overexpressing Mel-Juso cells, substantiating the pro-metastatic effects of EphA2 in melanoma. Activity of Src kinase and FAK were unaffected in EphA2-silenced cells and in response to EphrinA1-stimulation. However, in EphA2-overexpressing A375 cells Src phosphorylation was increased, indicating enhanced Src activity. Together, these data suggest that EphA2 receptor promotes malignancy ligand-independently by mechanisms different from Src kinase/FAK signaling.

Keywords: Cellular adhesion; cellular migration; Eph receptor tyrosine kinases; Ephrins; malignant skin cancer; metastatic melanoma; RNA interference


  • Secondary publication expected

Publ.-Id: 28943

Regulation of A375 melanoma cell adhesion and migration by EphB4 and EphrinB2 –insights from co-culture experiments

Neuber, C.; Laube, M.; Mamat, C.; Belter, B.; Pietzsch, J.

BACKGROUND: Malignant melanoma is the most malignant skin neoplasm due to early metastasis and resistance to currently available therapies. Inflammatory tumor infiltrate, particularly macrophages, are of outstanding importance for melanoma progression and therapy response. EphB4 receptor and its preferred ligand EphrinB2 are also associated with melanoma progression, metastasis, and therapy resistance.
OBJECTIVE: The aim of our study was to systematically investigate the role of EphB4 for melanoma cell adhesion and migration, also in the presence of macrophages, considering experimental i) EphB4 overexpression, ii) EphB4 activation, iii) inhibition of EphB4 and EphrinB2 interaction, and iv) inhibition of EphB4 and downstream signaling.
RESULTS: Overexpression of EphB4 resulted in increased A375 melanoma cell adhesion showing EphrinB2 reverse signaling rather than EphB4 forward signaling being responsible. By contrast, A375 melanoma cell migration was not affected by EphB4 overexpression and effects due to modulation of EphB4/EphrinB2 signaling were inconsistent. In co-culture experiments macrophages (HL-60(M)) showed substantial influence on adhesion and migration of A375 cells. However, HL-60(M)-mediated effects could not be assigned to EphB4/EphrinB2 signaling but rather to cytokine signaling pathways.
CONCLUSIONS: Under the used experimental settings EphB4 is important for adhesion but not for the migration of A375 melanoma cells. Macrophages influenced adhesion and migration of melanoma cells but without significant involvement of EphB4/EphrinB2 signaling.

Keywords: Eph receptor tyrosine kinases; Ephrin ligands; malignant melanoma; metastasis; tumor microenvironment; tyrosine kinase inhibitors


  • Secondary publication expected

Publ.-Id: 28942

Linear damped interfacial wave theory for an orbitally shaken upright circular cylinder

Horstmann, G. M.; Herreman, W.; Weier, T.

We present a new theoretical model describing gravity-capillary waves in orbitally shaken cylindrical containers. Our model can account for both one-layer free surface and two-layer interfacial wave systems. A set of modal equations for irrotational waves is formulated that we complement with viscous damping rates to incorporate energy dissipation. This approach allows us to calculate explicit formulas for the phase shifts between wave and shaker which are practically important for the mixing efficiency in orbitally shaken bioreactors. Resonance dynamics are described using eight dimensionless numbers revealing a variety of different effects influencing the forced wave amplitudes. As an unexpected result, the model predicts the formation of novel spiral wave patterns resulting from a damping-induced symmetry breaking mechanism. For validation we compare theoretical amplitudes, fluid velocities and phase shifts with three different and independent experiments and - when using the slightly deviating experimental values of the resonance frequencies - find a good agreement within the theoretical limits.


Publ.-Id: 28941

Zeit- und Konzentrationsabhängigkeit des Bioassoziationsverhaltens von U(VI) und Eu(III) mit Brassica napus-Zellen

Jessat, J.; Sachs, S.; Moll, H.; Steudtner, R.; Bok, F.; Stumpf, T.

Sowohl im Hinblick auf die Sanierung radioaktiv kontaminierter Flächen als auch für die Sicherheitsbeurteilung von potentiellen Endlagern für radioaktive Abfälle wird detailliertes Wissen über das Transferverhalten von Radionukliden (RN) in der Umwelt benötigt, da diese in die Nahrungskette gelangen können und damit ein Gesundheitsrisiko für Menschen darstellen. Die Bioassoziation von RN mit Pflanzen und ihre Wechselwirkung mit in den Boden freigesetzten Pflanzenmetaboliten kann deren Verbleib in der Umwelt beeinflussen. Es ist bekannt, dass die Aufnahme und Vertei-lung der RN in Pflanzen und damit ihre Bioverfügbarkeit signifikant von der vorliegenden Metallspeziation bestimmt wird [1]. Es wurden die Zeit- und Konzentrationsabhängigkeit des Bioassoziationsverhaltens von U(VI) und Eu(III) als Analogon für dreiwertige Actinide mit Brassica napus (Raps)-Zellen untersucht. Ziel dieser Arbeiten war es, den Effekt beider Schwermetalle auf die Zellvitalität sowie den Einfluss des Zellmetabolismus auf die Speziation beider Metalle zu bestimmen. Es konnte ein zeit- und konzentrationsabhängiges Bioassoziationsverhalten bei Exposition der Zellen mit U(VI) und Eu(III) beobachtet werden. In Gegenwart von 200 µM U(VI) tritt ein mehrstufiger Bioassoziationsprozess auf, bei dem es zur Freisetzung des zuvor bioassoziierten U(VI) in das umgebende Nährmedium kommt. Damit einhergehend konnte mittels zeitaufgelöster laser-induzierter Fluoreszenzspektroskopie eine Speziationsveränderung nachvollzogen werden. Dabei wurden drei unterschiedliche U(VI)-Spezies (s. Abb. 1) im Nährmedium nachgewiesen, die Hinweise auf die Freisetzung von Pflanzenzellmetaboliten liefern. Diese können als Liganden für die U(VI)-Komplexierung fungieren und damit einen Einfluss auf das Transferverhalten von U(VI) in der Umwelt haben. Die U(VI)-Speziation im Ausgangsnährmedium wurde in Anlehnung an die Literatur thermodynamisch modelliert [2]. Um mögliche Metabolite zu identifizieren, wurden Experimente zur Anreicherung und chromatographischen Trennung von Metaboliten durchgeführt. Zudem wurde die U(VI)-Komplexierung mit relevanten Metaboliten untersucht.

[1] S. Ebbs et al., J. Exp. Bot. 1998, 49, 1183-1190. [2] S. Sachs et al., Environ. Sci. Technol. 2017, 51, 10843-10849.

Keywords: Pflanzen; Brassica napus; Raps; Metabolite; Suspensionszellen; Uran; Europium; Toxizität; Speziation; Komplexierung

  • Lecture (Conference)
    Jahrestagung der Fachgruppe Nuklearchemie 2019, 25.-27.09.2019, Dresden, Deutschland

Publ.-Id: 28940

Mass separated Focused Ion Beams from Liquid Metal Alloy Ion Sources

Bischoff, L.; Mazarov, P.; Pilz, W.; Klingner, N.; Bauerdick, S.; Gierak, J.

Focused Ion Beam (FIB) processing has been developed into a well-established and still promising technique in nearly all fields of nano-technology in particular for direct patterning and proto-typing on the µm scale and well below. Beside new ion source developments based on gas field emission (GFIS), on ionic liquids (ILIS), on magneto-optical traps (MOTIS) or on ICP or ECR sources for Xe-FIB as well as the nearly exclusively used gallium Liquid Metal Ion Sources (LMIS), the replacement of Ga by alloys therein with an adapted FIB optics design can open bright field of new employments. Local ion implantation, ion beam mixing, ion beam synthesis or Focused Ion Beam Lithography (IBL) in the µm- or nm range can benefit from ion species purposely selected in parallel to gallium or noble gases. Therefore, exploring the Liquid Metal Alloy Ion Sources (LMAIS) potential represent a promising alternative to expand the global FIB application fields. Especially, IBL as direct, resistless and three-dimensional patterning enables a simultaneous in-situ process control by cross-sectioning and inspection. Thanks to this nearly half of the elements of the periodic table are made available in the FIB technology as a result of continuous research in this area during the last forty years. Key features of a LMAIS are long life-time, high brightness and stable ion current. Recent developments could make these sources as an alternative technology feasible for nano patterning challenges e.g. to tune electrical, optical, magnetic or mechanic properties.
In this contribution the operation principle, the preparation and testing technology as well as prospective domains for modern FIB applications will be presented. As an example we will introduce a Ga35Bi60Li5 LMAIS in detail. It enables high resolution imaging with light Li ions and sample modification with Ga or heavy polyatomic Bi clusters, all coming from one ion source.
L. Bischoff, P. Mazarov, L. Bruchhaus, and J. Gierak, Appl. Phys. Rev. 3, 021101 (2016).

Keywords: Liquid Metal Alloy Ion Source; Focused Ion Beam; Mass spectra; Cluster ions

  • Lecture (Conference)
    PicoFIB - The International Network for gas Ion Patterning and Microscopy, 13.02.2019, London, Great Britain

Publ.-Id: 28939

Compositional Multi-Point Geostatistics for Tailings Deposits - A Synthetic Case Study

Selia, S. R. R.; Tolosana-Delgado, R.; van den Boogaart, K. G.; Schaeben, H.

Currently tailings deposits have become new resources that are challenging and valuable to exploit. To properly exploit them, we require a 3D spatial characterization of their mineral content. In a natural deposit, this is achieved by sampling at several locations and applying geostatistics to estimate block values. Certain characteristics of tailings deposits make them not amenable to conventional geostatistics. In particular, it is important to consider both valuable and gangue minerals, thus we need to take the compositional nature of our variables into account. In addition, the interplay of erosional and depositional processes creates structures with certain continuity patterns that cannot be modelled by conventional variogram-based methods such as kriging.
Therefore, we use a Multi-Point Geostatistics method, Direct Sampling (DS). DS is based on selecting the event from a training image, the conceptual spatial arrangement of a variable, with the shortest distance to the data event from the simulation domain. To account for the compositional nature of our variables, the Aitchison distance is calculated. We use numerical stratigraphic modelling to obtain a variety of training images, which we feed into a modified DS to deal with multiple training images at once.
We tested the proposal on a multi-source synthetic tailings deposit produced by numerical stratigraphic processes. Each grid of the model contains information about the content of several sediment species summing to 100%. Hard data are sampled on the model at certain locations and along with several unique training images we recreate the full 3D spatial distribution of the properties.

Keywords: Conditional simulation; Tailings Characterization; Remining

  • Lecture (Conference)
    5th International Young Earth Scientist Network (YES) Congress 2019, 09.-13.09.2019, Berlin, Germany

Publ.-Id: 28938

Radiochemical and radiopharmacological characterization of a 64Cu-labeled α-MSH analog conjugated with different chelators

Gao, F.; Sihver, W.; Bergmann, R.; Walther, M.; Stephan, H.; Belter, B.; Neuber, C.; Haase-Kohn, C.; Bolzati, C.; Pietzsch, J.; Pietzsch, H.-J.

Radiolabeled α-melanocyte stimulating hormone (α-MSH) derivatives have a high potential for diagnosis and treatment of melanoma, due to high specificity and binding affinity to the melanocortin-1 receptor (MC1R). Hence, the α-MSH-derived peptide NAP-NS1 with a β-Ala linker (ε-Ahx-beta-Ala-Nle-Asp-His-D-Phe-Arg-Trp-Gly-NH2) was conjugated to different chelators: either to NOTA (p-SCN-Bn-1,4,7-triazacyclononane-1,4,7-triacetic acid), to a hexadentate bispidine carbonate derivative (dimethyl-9-(((4-nitrophenoxy)carbonyl)oxy)-2,4-di(pyridin-2-yl)-3,7-bis(pyridin-2-ylmethyl)-3,7-diazabicyclo[3.3.1]nonane-1,5-dicarboxylate) or to DMPTACN (p-SCN-Ph-bis(2-pyridyl-methyl)-1,4,7-triaza-cyclononane), labeled with 64Cu and investigated in terms of radiochemical and radiopharmacological properties.
For the three 64Cu-labeled conjugates negligible transchelation, suitable buffer and serum stability, as well as appropriate water solubility was determined. The three conjugates exhibited high binding affinity (low nanomolar range) in murine B16F10, human MeWo and human TXM13 cells. The Bmax values of [64Cu]Cu-bispidine-NAP-NS1 ([64Cu]Cu-2) and [64Cu]Cu-DMPTACN-NAP-NS1 ([64Cu]Cu-3) were higher than those of [64Cu]Cu-NOTA-NAP-NS1 ([64Cu]Cu-1), implying that different charged chelate units might have an impact on binding capacity. Preliminary in vivo biodistribution studies suggested the main excretion pathway of [64Cu]Cu-1 and [64Cu]Cu-3 to be renal, while that of [64Cu]Cu-2 seemed to be both renal and hepatobiliary. An initial moderate uptake in the kidney decreased clearly after 60 min. All three 64Cu-labeled conjugates should be considered for further in vivo investigations using a suitable xenograft mouse model.

Keywords: copper chelators; melanocortin-1 receptor; α-MSH; malignant melanoma; molecular imaging; radiopharmaceuticals; radiotracer; PET

  • Journal of Labelled Compounds and Radiopharmaceuticals 62(2019)8, 495-509
    DOI: 10.1002/jlcr.3728

Publ.-Id: 28937

Influence of calcium on uranium and neptunium sorption on clay minerals at (hyper)alkaline conditions

Philipp, T.; Schmeide, K.; Stumpf, T.

Our previous experiments have shown that U(VI) is retained very strongly by Ca-bentonite in the pH range 10-12. Different spectroscopic techniques (site-selective TRLFS, EXAFS) have proven that the underlying retention mechanism under the given conditions was adsorption (not precipitation) despite the negative mineral surface charge and the anionic character of prevailing aqueous U(VI) species. It was hypothesized that attachment is facilitated by mediating calcium cations which are present in the solution. Therefore, the influence of calcium on the sorption of U(VI), Np(V) and Np(VI) at alkaline conditions was systematically studied. These radionuclides were selected as their aqueous speciation at high pH values is characterized by the predominance of anionic hydroxide species. Furthermore the adsorption of 45Ca on clay minerals and the resulting effect on the mineral surface charge was examined.
It was found that 45Ca adsorbed almost completely on Ca-bentonite between pH 8 and 13. Zeta potential measurements showed a partial compensation of the strongly negative surface charge of Ca-bentonite upon introduction of calcium. Hence, calcium is present at the surface, offering possible sorption sites for anionic uranium and neptunium species. Batch sorption experiments at different calcium concentrations revealed enormous effects on the retention of U(VI), Np(V) and Np(VI) between pH 10 and 13. Exemplarily shown for U(VI) in the figure below, the strong retention could not be observed in the experiment with kaolinite, where calcium was completely absent. Consequently, calcium is a crucial factor for the safety assessment of deep geological radioactive waste repositories, where (hyper)alkaline conditions evolve due to cement degradation.

Keywords: Calcium; U(VI); Np(V); Np(VI); adsorption; surface charge

  • Lecture (Conference)
    2nd International Conference on Radioanalytical and Nuclear Chemistry, 05.-10.05.2019, Budapest, Ungarn

Publ.-Id: 28936

Plasmonic field guided patterning of ordered colloidal nanostructures

Huang, X.-P.; Chen, K.; Qi, M.-X.; Zhang, P.-F.; Li, Y.; Winnerl, S.; Schneider, H.; Yang, Y.; Zhang, S.

Nano-patterned colloidal plasmonic metasurfaces are capable of manipulation of light at the subwavelength scale. However, achieving controllable lithography-free nano-patterning for colloidal metasurfaces still remains a major challenge, limiting their full potential in building advanced plasmonic devices. Here, we demonstrate plasmonic field guided patterning (PFGP) of ordered colloidal metallic nano-patterns using orthogonal laser standing evanescent wave (LSEW) fields. We achieved colloidal silver nano-patterns with a large area of 30 mm² in <10 min by using orthogonal LSEW fields with a non-focused ultralow fluence irradiation of 0.25 W cm⁻². The underlying mechanism of the formation of the nanopatterns is the light-induced polarization of the nanoparticles (NPs), which leads to a dipole-dipole interaction for stabilizing the nano-pattern formation, as confirmed by polarization-dependent surface-enhanced Raman spectroscopy. This optical field-directed self-assembly of NPs opens an avenue for designing and fabricating reconfigurable colloidal nano-patterned metasurfaces in large areas.

Keywords: ordered colloidal nanostructures; plasmonic field guided patterning; polarization stabilizing

Publ.-Id: 28934

Fluorescent Mouse Pheochromocytoma Spheroids Expressing Hypoxia-Inducible Factor 2 alpha: Morphologic and Radiopharmacologic Characterization

Seifert, V.; Liers, J.; Kniess, T.; Richter, S.; Bechmann, N.; Feldmann, A.; Bachmann, M.; Eisenhofer, G.; Pietzsch, J.; Ullrich, M.

BACKGROUND: Pheochromocytomas and paragangliomas (PPGLs) are rare catecholamine-producing tumors arising from chromaffin tissue. In a PPGL subgroup, dysregulation of hypoxia signaling pathways, in particular mediated through stabilization of hypoxia-inducible factor 2 alpha (HIF2α), have been suggested to drive tumorigenesis through altering downstream transcriptional activity.
OBJECTIVE: This study evaluated the use of mCherry-transgenic mouse pheochromocytoma (MPCmCherry) spheroids as in vitro models for investigating consequences of HIF2α expression on aggregation behavior, morphology, growth, glucose consumption, amino acid uptake, and somatostatin type 2 receptors under stable hypoxic conditions.
METHODS: MPCmCherry spheroids were monitored using confocal laser scanning microscopy. Hypoxic regions were detected using pimonidazole. Radiotracer incubation was performed using 2 [18F]fluoro-2-deoxyglucose ([18F]FDG), O 3 (2[18F]fluoroethoxy)-4 hydroxyphenylalanine ([18F]OFED), and [68Ga]Ga (Tyr3)octreotate ([68Ga]Ga-DOTA-TATE).
RESULTS: Both HIF2α-expressing and empty vector (EV) control spheroids showed regions of stable cellular hypoxia. Expression of HIF2α in MPCmCherry spheroids was associated with less symmetric morphology, faster growth, and decreased uptake of [68Ga]Ga DOTA-TATE (somatostatin type 2 receptors) compared to controls, whereas, uptake of [18F]FDG (glucose transporter 1 and hexokinases) and [18F]OFED (system L amino acid transporter 1) remained unaffected.
CONCLUSIONS: The recent study proved MPCmCherry spheroids to be complex three-dimensional tumor cell models for investigating morphologic and metabolic consequences of dysregulated hypoxia pathways under hypoxic conditions.

Keywords: Amino acid transporters; Confocal laser scanning microscopy; Neuroendocrine tumors; Paraganglioma; Pimonidazole; Positron emitters; Radiotracer uptake; Somatostatin receptors


  • Secondary publication expected from 30.12.2020

Publ.-Id: 28933

Investigation of [18F]FESCH for PET imaging of the adenosine A2A receptor in a rotenone-based mouse model of Parkinson´s disease and development of a two-step one-pot radiolabeling strategy

Schröder, S.; Lai, T. H.; Kranz, M.; Toussaint, M.; Shang, Q.; Dukic-Stefanovic, S.; Pan-Montojo, F.; Brust, P.

Rotenone-treated mice are regarded as a model for Parkinson´s disease (PD). Increased availability of the adenosine A2A receptor (A2AR) has been found in the striatum of patients with PD and dyskinesias [1]. The aim of this study was to investigate whether similar alterations are found in the mouse model of PD using small animal PET/MR imaging. For that purpose, [18F]FESCH [2] was the radiotracer of choice due to its high A2AR specificity and excellent PET imaging properties [2-5]. Furthermore, we intended to develop a simplified one-pot strategy for the radiosynthesis of [18F]FESCH.
The published two-step procedures for the radiosynthesis of [18F]FESCH start with the nucleophilic 18F-labeling of ethane-1,2-diol bis(3,4-dibromobenzenesulfonate) [4] or ethane-1,2-diol bis(4-methylbenzenesulfonate) [2]. The respective [18F]fluoroethyl synthon is isolated either by semi-preparative HPLC [4] or cartridge [2] and, only then, reacted with the phenol precursor desmethyl SCH442416. In our novel one-pot approach, desmethyl SCH442416 was treated with 40% TBAOHaq. to generate the activated phenolate which was directly reacted with the non-isolated 2-[18F]fluoroethyl tosylate in MeCN at 120 °C for 10 min (see Figure 1). [18F]FESCH was purified by semi-preparative HPLC, concentrated using solid-phase extraction on a pre-conditioned RP cartridge and eluted with absolute EtOH. After evaporation of the solvent at 75 °C, the radiotracer was finally formulated in isotonic saline ready for injection. [18F]FESCH (5.0±1.8 MBq) was administered to C57BL/6JRj mice (control n=5, rotenone-treated n=7, 18 month, 28-35 g) and whole body scans were performed for 60 min in listmode with a Mediso nanoScan® PET/MR scanner followed by dynamic reconstruction. Time-activity curves (TACs) were generated for regions of interest such as striatum (Figure 1) and cerebellum as reference region.
The herein described one-pot strategy provided [18F]FESCH (Ki hA2A=0.6 nM) with an overall radiochemical yield of 16.1±1.5% (n=9, EOB), a radiochemical purity of ≥98% and compared to the published two-pot procedure with a notably increased molar activity of 116±18.5 GBq/µmol (n=7, EOS). The PET images over 60 min showed high uptake of [18F]FESCH in the striatum (Figure 1) which is consistent with the known A2AR distribution pattern in the brain. Although not significant, slightly higher striatal A2AR binding was found in rotenone-treated mice.
The radiotracer [18F]FESCH proved to be suitable for in vivo imaging of the adenosine A2A receptor in the mouse brain. Since the increased A2AR availability appears to be related to dyskinesia, it has to be proven whether the investigated mouse model of PD reflects this aspect.
The European Regional Development Fund (ERDF) and Sächsische Aufbaubank (SAB) are acknowledged for financial support (Project No. 100226753).
[1] Ramlackhansingh et al., Neurology, 76, 2011
[2] Khanapur et al., J. Med. Chem., 57, 2014
[3] Shinkre et al., Bioorg. Med. Chem. Lett., 20, 2010
[4] Bhattacharjee et al., Nucl. Med. Biol., 38, 2011
[5] Khanapur et al., J. Nucl. Med., 58, 2017

  • Open Access Logo Poster
    23rd International Symposium on Radiopharmaceutical Sciences (ISRS 2019), 26.-31.05.2019, Beijing, China
    DOI: 10.1002/jlcr.3725

Publ.-Id: 28932

Entwicklung einer Eintopf-Radiosynthese von F-18-FESCH für die PET-Bildgebung des Adenosin-A2A-Rezeptors im Rotenon-basierten Parkinson-Mausmodel

Schröder, S.; Lai, T. H.; Deuther-Conrad, W.; Dukic-Stefanovic, S.; Kranz, M.; Toussaint, M.; Shang, Q.; Pan-Montojo, F.; Brust, P.

Gegenstand der Studie ist es, das Expressionsmuster des Adenosin-A2A-Rezeptors im Gehirn von Wildtyp(WT)- und Parkinsonmodel-Mäusen mittels KleintierPET/MRT zu untersuchen. Zu diesem Zweck wurde F-18-FESCH (1) als geeigneter A2A-Radiotracer ausgewählt, wobei eine vereinfachte Methode zur Radiosynthese entwickelt werden sollte.
In der publizierten zweistufigen Radiosynthese von F-18-FESCH wird das verwendete F-18-Fluorethylsynthon mittels Festphasenextraktion (1) oder semi-präparativer HPLC (2) isoliert und erst dann mit dem Phenol-Präkursor umgesetzt. In der hier entwickelten Eintopf-Methode wurde der Phenol-Präkursor mittels TBAOHaq. deprotoniert und direkt zur Reaktionsmischung des F-18-Fluorethylsynthons zugegeben. Die F-18-Fluorethylierung erfolgte in MeCN bei 120°C für 10 min. F-18-FESCH wurde mittels semi-präparativer HPLC isoliert, über eine RP18-Kartusche konzentriert und in 0,9%iger NaClaq. formuliert. Der Radiotracer (4-8 MBq) wurde C57BL/6JRj-Mäusen (WT n=5, Rotenon-behandelt n=7, 18 Monate) appliziert und Ganzkörperscans mit einem Mediso nanoScan® PET/MRT aufgenommen.
F-18-FESCH (Ki hA2A=0,6 nM) wurde mit einer radiochemischen Ausbeute von 16,1±1,5% (n=9, EOB), einer radiochemischen Reinheit von ≥98% und einer im Vergleich zur Literatur deutlich gesteigerten molaren Aktivität von 116±18,5 GBq/µmol (n=7, EOS) bereitgestellt. Die summierten PET-Bilder (1 h) zeigen eine erhöhte Anreicherung von F-18-FESCH im Striatum, wobei kein signifikanter Unterschied zwischen den WT- und Rotenon-behandelten Mäusen detektiert wurde.
F-18-FESCH ist zur PET-Bildgebung des A2A-Rezeptors im Maushirn geeignet. Die ersten Ergebnisse der PET-Studie im Parkinson-Mausmodel weisen auf keine veränderte A2A-Rezeptordichte hin.
(1) Khanapur et al., J. Med. Chem., 57, 2014
(2) Bhattacharjee et al., Nucl. Med. Biol., 38, 2011

  • Open Access Logo Poster
    57. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin e.V.(NuklearMedizin 2019), 03.-06.04.2019, Bremen, Deutschland


Publ.-Id: 28931

Experimental and theoretical investigation of the boiling heat transfer in a low pressure natural circulation system

Viereckl, F.; Schleicher, E.; Schuster, C.; Lippmann, W.; Hurtado, A.

The implementation of passive safety systems in nuclear reactors provide the opportunity to enhance the nuclear safety. On the other hand, an accurate and reliable prediction of the heat removal behavior is not ensured because the operating conditions of certain types of passive systems like containment cooling systems differ from the validity ranges of the established heat transfer correlations. Therefore, a generic and detailed investigation is still necessary for passive systems.
Against this background, the test facility GENEVA was erected at Technische Universität Dresden in 2012. Since the commissioning, generic experiments concerning the system and stability behavior of this facility, which emulates a low pressure and low flow (LPLF) natural circulation system, were provided. Nevertheless, the investigation of the heat transfer behavior remained an open issue. On this account, the instrumentation in the heat transfer region inside GENEVA was improved to gather the necessary temperature and void fraction profiles.
The performed experiments provide a generic and wide database concerning boiling in a LPLF natural circulation systems. Within this paper, the development of the wall and bulk fluid temperature as well as the axial and center line void fraction profile in a slightly inclined tube for different heat flow rates are discussed. Furthermore, flow patterns could be identified on behalf of the void fraction measurements. To conclude the experimental analysis, the development of the heat transfer coefficient was estimated.
These experimental data provide the basis for a simulation with the lumped-parameter thermal-hydraulic code ATHLET and serve as validation reference. However, the comparisons between the experimental and computational results show insufficient agreements. Mainly, the simulation misses the saturation point of the experiments, which leads to great differences of the void fraction values. Moreover, inaccuracies appear as well with the heat transfer coefficient.
The experimental and computational results that are discussed in this paper provide the basis for the advancement not only of heat transfer correlations but also of flow pattern maps within the range of low pressure natural circulation system. In summary, this investigation contributes to the general purpose to enhance nuclear safety by providing an accurate and reliable prediction of the heat removal capacity of passive systems.

Keywords: flow patterns; GENEVA; heat transfer coefficient; low pressure natural circulation; nuclear safety; passive systems


Publ.-Id: 28930

Deterministic field-free skyrmion nucleation at a nano-engineered injector device

Finizio, S.; Zeissler, K.; Wintz, S.; Mayr, S.; Weßels, T.; Huxtable, A. J.; Burnell, G.; Marrows, C. H.; Raabe, J.

Magnetic skyrmions are topological solitons that exhibit an increased stability against annihilation [1, 2], and can be displaced with low current densities [3], making them a promising candidate as an information carrier [1]. In order to demonstrate a viable skyrmion-based memory device, it is necessary to reliably and reproducibly nucleate, displace, detect, and delete the magnetic skyrmions. While the skyrmion displacement [4–7] and detection [8, 9] have both been investigated in detail, much less attention has been dedicated to the study of the sub-ns dynamics of the skyrmion nucleation and deletion processes. Only limited studies on the statics [10, 11] and above-ns dynamics [12] have been performed, leaving still many open questions on the dynamics of the nucleation process. Furthermore, the vast majority of the presently existing studies focus on the nucleation from random natural pinning sites [10, 12], or from patterned constrictions in the magnetic material itself [10, 11], which limit the functionality of the skyrmion-based device. Those limitations can be overcome by the fabrication of a dedicated injector device on top of the magnetic material [13]. In this study, we investigate the nucleation of magnetic skyrmions from a dedicated nano-engineered injector, demonstrating the reliable magnetic skyrmion nucleation at the remnant state. The sub-ns dynamics of the skyrmion nucleation process were also investigated, allowing us to shine light on the physical processes driving the nucleation.

Keywords: skyrmion; nucleation; x-ray microscopy

Publ.-Id: 28928

Zero-field dynamics stabilized by in-plane shape anisotropy in MgO-based spin-torque oscillators

Kowalska, E.; Kákay, A.; Fowley, C.; Sluka, V.; Lindner, J.; Fassbender, J.; Deac, A. M.

Here, we demonstrate numerically that shape anisotropy in MgO-based spin-torque nano-oscillators consisting of an out-of-plane magnetized free layer and an in-plane polarizer is necessary to stabilize out-of-plane magnetization precession without the need of external magnetic fields. As the in-plane anisotropy is increased, a gradual tilting of the magnetization towards the in-plane easy direction is introduced, favouring zero-field dynamics over static in-plane states. Above a critical value, zero-field dynamics are no longer observed. The optimum ratio of in-plane shape to out-of-plane uniaxial anisotropy, for which large angle out-of-plane zero-field dynamics occur within the widest current range, is reported.

Keywords: spin-torque nano-oscillator (STNO); MgO-based magnetic tunnel junctions; tunnel magnetoresistance (TMR); spin dynamics

Related publications


Publ.-Id: 28927

Spectroelectrochemical studies of the Tc(VII) reduction in aqueous electrolyte media

Rodriguez, D.; Mayordomo, N.; Brendler, V.; Müller, K.; Stumpf, T.

99Tc, a weak β-particle-emitter with a half-life of 2.13×105 years, is a strongly relevant fission product. Under repository conditions it has two main oxidation states: Tc(VII), as pertechnetate TcO4, a highly water-soluble anion not significantly sorbed on minerals or sediments, and Tc(IV), mostly found as TcO2, a solid with a low solubility product and, thus, a lower mobility [1].

However, in 2004 Lukens et. al. [2] reported the existence of non-pertechnetate species in the Hanford waste tanks and identified them as Tc(I) – carbonyl complexes. In further reports of the Pacific Northwest National Laboratory [3–7] the synthesis of Tc(I) carbonyl and nitrosyl complexes, relevant to the Hanford Site and their characterization by XAS and NMR is fully explained. More recently, Chatterjee et. al. [8] succeeded to stabilize Tc(VI) species to study them by spectroscopic methods (UV-vis, EPR and XPS). These works show the importance of extending the current knowledge of Tc fundamental chemistry and the need for more thermodynamic information on low-valent Tc oxidation states in order to determine the reduction mechanism from Tc(VII) to Tc(IV), which is not yet fully understood.

As a first approach, we have studied the reduction of 1 mM Tc(VII) in 1M HNO3 by applying a series of negative potentials (from -100 to -500 mV) to the solution for 30 minutes each. After this time, an aliquot was taken to measure the UV-vis spectra, as shown in figure 1. Additionally, after applying -550 mV, the solution was sealed and left at rest for 24 hours to evaluate the stability of the product formed.

Figure 1-A shows a peak around 265 nm that corresponds to Tc(VII) [9,10]. The intensity of the band decreases with decreasing the potential, which implies that Tc(VII) concentration in solution decreases due to its reduction, as expected for low potential values. The spectra of the solution after 24 hours shows that Tc(VII) is formed again, although the initial concentration is not reached.

Figure 1-B shows two signals that may correspond to the formation of other Tc oxidation states. According to Alliot et. al. [10], the peak around 500 nm could be assigned to the Tc(IV) formation, although it would not fully explain the increase of the signal 24 hours after the experiment. On the other hand, the three peaks formed around 370 nm after V = -350 mV most probably account for the reduction of the nitric acid, as they maintain their shape after 24 hours and, if they were non common Tc species like Tc(V) or Tc(VI), they should have disproportionated to Tc(VII) in a short time.

Even though these results are very interesting, it is necessary to combine spectroscopic and electrochemical methods and to carry out the measurements at the same time in order to obtain a clear understanding on the reduction. Moreover, in order to avoid the uncertainty due to the reaction of the electrolyte, a systematic selection of anions and cations must be done. Therefore, we have studied the reduction of Tc(VII) in 1 M of aqueous sodium nitrate (NaNO3), sodium perchlorate (NaClO4), sodium bicarbonate (NaHCO3) and sodium chloride (NaCl) by cyclic voltammetry and differential pulse voltammetry coupled with UV – vis.

This work has been developed in the frame of VESPA II project (02E11607B), supported by the German Federal Ministry for Economic Affairs and Energy (BMWi).

1 A. H. Meena and Y. Arai, Environ. Chem. Lett. 15, 241 (2017).
2 W. W. Lukens, D. K. Shuh, N. C. Schroeder and K. R. Ashley, Environ. Sci. Technol. 38, 229 (2004).
3 T. Levitskaia, A. Anderson, S. Chatterjee, H. Cho, B. M. Rapko, J. Peterson, E. D. Walter and N. M. Washton, Speciation and Oxidative Stability of Alkaline Soluble, Non-Pertechnetate Technetium, Richland, Washington, 2014.
4 T. Levitskaia, A. Andersen, S. Chatterjee, G. B. Hall, E. D. Walter and Was, Spectroscopic Properties of Tc(I) Tricarbonyl Species Relevant to the Hanford Tank Waste, Richland, Washington, 2015.
5 G. B. Hall, S. D. Chatterjee, T. G. Levitskaia, T. J. Martin, N. A. Wall and E. D. Walter, Synthesis and Characterization of Tc(I) Carbonyl Nitrosyl Species Relevant to the Hanford Tank Waste: FY 2016 Status Report, Richland, Washington, 2016.
6 R. J. Serne, J. V Crum, B. J. Riley and T. G. Levitskaia, Options for the Separation and Immobilization of Technetium, Richland, Washington, 2016.
7 S. Chatterjee, A. Andersen, Y. Du, M. H. Engelhard, G. B. Hall, T. G. Levitskaia, W. W. Lukens, V. Shutthanandan, E. D. Walter and N. M. Washton, Characterization of Non- Pertechnetate Species Relevant to the Hanford Tank Waste, Richland, Washington, 2017.
8 S. Chatterjee, G. B. Hall, I. E. Johnson, Y. Du, E. D. Walter, N. M. Washton and T. G. Levitskaia, Inorg. Chem. Front. 5, 2081 (2018).
9 J. Paquette and W. E. Lawrence, Can. J. Chem. 63, 2369 (1985).
10 I. Alliot, C. Alliot, P. Vitorge and M. Fattahi, Environ. Sci. Technol. 43, 9174 (2009).

Keywords: Electrochemical reduction; technetium; electrolytes; aqueous chemistry

  • Poster
    17th international conference on the chemistry and migration behavior of actinides and fission products in the geosphere, 15.-21.09.2019, Kyoto, Japan

Publ.-Id: 28926

Terahertz-Field-Induced Time Shifts in Atomic Photoemission

Schmid, G.; Schnorr, K.; Augustin, S.; Meister, S.; Lindenblatt, H.; Trost, F.; Liu, Y.; Stojanovic, N.; Al-Shemmary, A.; Golz, T.; Treusch, R.; Gensch, M.; Kübel, M.; Foucar, L.; Rudenko, A.; Ullrich, J.; Schröter, C. D.; Pfeifer, T.; Moshammer, R.

Time delays for atomic photoemission obtained in streaking or reconstruction of attosecond bursts by interference of two-photon transitions experiments originate from a combination of the quantum mechanical Wigner time and the Coulomb-laser coupling. While the former was investigated intensively theoretically as well as experimentally, the latter attracted less interest in experiments and has mostly been subject to calculations. Here, we present a measurement of the Coulomb-laser coupling-induced time shifts in photoionization of neon at 59.4 eV using a terahertz (THz) streaking field (λ = 152 μm). Employing a reaction microscope at the THz beamline of the free-electron laser in Hamburg (FLASH), we have measured relative time shifts of up to 70 fs between the emission of 2p photoelectrons (∼38 eV) and lowenergetic (<1 eV) photoelectrons. A comparison with theoretical predictions on Coulomb-laser coupling reveals reasonably good agreement.

Publ.-Id: 28925

Singlet ground state in the alternating spin-1/2 chain compound NaVOAsO4

Arjun, U.; Ranjith, K. M.; Koo, B.; Sichelschmidt, J.; Skourski, Y.; Baenitz, M.; Tsirlin, A. A.; Nath, R.

We present the synthesis and a detailed investigation of structural and magnetic properties of polycrystalline NaVOAsO4 by means of x-ray diffraction, magnetization, electron spin resonance (ESR), and 75As nuclear magnetic resonance (NMR) measurements as well as density-functional band structure calculations. Temperature-dependent magnetic susceptibility, ESR intensity, and NMR line shift could be described well using an alternating spin-1/2 chain model with the exchange coupling J/kB ≃ 52 K and an alternation parameter α ≃ 0.65. From the high-field magnetization measured at T = 1.5 K, the critical field of the gap closing is found to be Hc ≃ 16 T, which corresponds to the zero-field spin gap of Δ0/kB ≃ 21.4 K. Both NMR shift and spin-lattice relaxation rate show an activated behavior at low temperatures, further confirming the singlet ground state. The spin chains do not coincide with the structural chains, whereas the couplings between the spin chains are frustrated. Because of a relatively small spin gap, NaVOAsO4 is a promising compound for further experimental studies under high magnetic fields.

Publ.-Id: 28924

Gaussian and critical scalings in the magnetoconductivity fluctuations of Y3Ba5Cu8O18 superconductor

Dias, F. T.; Vieira, V. N.; Oliveira, C. P.; Silva, D. L.; Mesquita, F.; Lima, J. R.; Wolff-Fabris, F.; Kampert, E.; Pureur, P.

We have studied the superconducting transition and the magnetoconductivity fluctuations in the polycrystalline Y3Ba5Cu8O18 (Y358) superconductor under magnetic fields upto 1 T. A two-step superconducting transition could be observed as a consequence of the granular structure of the sample, which is strongly affected by the applied magnetic field. Gaussian and genuine critical 3D-XY-E fluctuation regimes were identified. A critical scaling regime beyond 3D-XY was identified for magnetic fields upto 0.25 T, corresponding to the averaged exponent 0.19 and suggesting the occurrence of the weak first-order character of the superconducting transition. In the approximation to the zero resistance a power law regime could be observed, corresponding to the averaged exponent 2.37, which are smaller than previously reported for the Y358 system. Our results are discussed in terms of the Y358 and Yba2Cu3O7−δ (Y123) results in the literature.

Publ.-Id: 28923

Magnetization beyond the Ising limit of Ho2Ti2O7

Opherden, L.; Herrmannsdörfer, T.; Uhlarz, M.; Gorbunov, D. I.; Miyata, A.; Portugall, O.; Ishii, I.; Suzuki, T.; Kaneko, H.; Suzuki, H.; Wonsitza, J.

We report that the local Ising anisotropy in pyrochlore oxides—the crucial requirement for realizing the spin-ice state—can be broken by means of high magnetic fields. For the case of the well-established classical spin-ice compound Ho2Ti2O7 the magnetization exceeds the angle-dependent saturation value of the Ising limit using ultrahigh fields up to 120 T. However, even under such extreme magnetic fields full saturation cannot be achieved. Crystal-electric-field calculations reveal that a level crossing for two of the four ion positions leads to magnetization steps at 55 and 100 T. In addition, we show that by using a field sweep rate in the range of the spin-relaxation time the dynamics of the spin system can be probed. Exclusively at 25 ns/T, a new peak of the susceptibility appears around 2 T. We argue, this signals the crossover between spin-ice and polarized correlations.


Publ.-Id: 28922

Electronic band structure and proximity to magnetic ordering in the chiral cubic compound CrGe

Klotz, J.; Götze, K.; Förster, T.; Bruin, J. A. N.; Wosnitza, J.; Weber, K.; Schmidt, M.; Schnelle, W.; Geibel, C.; Rößler, U. K.; Rosner, H.

CrGe belongs to the family of cubic B20 intermetallics. From experimental investigations by susceptibility and de Haas-van Alphen (dHvA) measurements and from calculations of its electronic band structure by densityfunctional theory (DFT), CrGe is found to form a metallic paramagnetic ground state. Combining dHvA and DFT data, a detailed picture of the Fermi surface of CrGe is provided. The proximity to a magnetic longrange ordering in CrGe is suggested from a prominent thermal magnetic susceptibility. The possibility to induce magnetic long-range order in CrGe is discussed based on calculated properties for CrGe substituting Ge by As or Sn, and from a comparison with MnGe and the alloy series Cr1−xMnxGe. Owing to the noncentrosymmetric and nonsymmorphic crystal structure of CrGe, in absence of broken time reversal symmetry, its band structure is marked by forced nodal lines at the Fermi edge. Moreover, this material hosts degenerate unconventional electronic quasiparticles. In particular, CrGe exhibits a sixfold degeneracy of fermions crossing within about 5 meV of the Fermi energy at the R point of the Brillouin zone.


Publ.-Id: 28921

Magnetic phase diagram and crystal-field effects in the kagome-lattice antiferromagnet U3Ru4Al12

Gorbunov, D. I.; Ishii, I.; Nomura, T.; Henriques, M. S.; Andreev, A. V.; Uhlarz, M.; Suzuki, T.; Zherlitsyn, S.; Wosnitza, J.

We report on the magnetic phase diagram of the distorted kagome-lattice antiferromagnet U3Ru4Al12 determined through measurements of magnetic and elastic properties. For field applied along the [100] and [120] axes of the hexagonal crystal structure, we find pronounced anomalies in the magnetization and elastic moduli that signal the existence of unknown magnetic phases. Our crystal-electric-field (CEF) analysis evidences interlevel quadrupolar interactions between the ground-state singlet and the first excited doublet. These interactions lead to a large softening of the shear elastic modulus C44. The large number of phases and pronounced elastic
softening suggest that geometric frustrations and CEF effects play an important role in the physical properties of U3Ru4Al12.


Publ.-Id: 28920

U2Ni2Sn and the origin of magnetic anisotropy in uranium compounds

Maskova, S.; Andreev, A. V.; Skourski, Y.; Yasin, S.; Gorbunov, D. I.; Zherlitsyn, S.; Nakotte, H.; Kothapalli, K.; Nasreen, F.; Cupp, C.; Cao, H. B.; Kolomiets, A.; Havela, L.

U2Ni2Sn is a member of a large family of intermetallic compounds with the tetragonal Mo2FeB2 crystal structure. It orders antiferromagnetically at 25 K with propagation vector q = (0, 0, 1/2 ). Magnetization, magnetoacoustic, and neutron-diffraction experiments on a single crystal provide evidence that the uranium moments align parallel to the c axis with the anisotropy energy of ≈170 K, indicating that U2Ni2Sn can be classified as an Ising system. The results are at variance with previous studies on polycrystals, which indicated different magnetic structure, and which were incompatible with the 5 f -5 f two-ion anisotropy model dominant in most U band systems. High-field magnetization studies exhibit a weak linear response for fields along the basal plane up to the highest field applied (60 T), while the c-axis magnetization curve exhibits three metamagnetic transitions at approximately 30, 39, and 50 T. The U magnetic moments of 0.87μB, the low magnetic entropy, and the enhanced Sommerfeld coefficient γ = 187 mJ/mol f.u.K2 suggest that U2Ni2Sn can be classified as an itinerant antiferromagnet with strong electron-electron correlations.

Publ.-Id: 28919

LISEL@DREAMS - The future of Accelerator Mass Spectrometry

Forstner, O.; Merchel, S.; Rugel, G.; Wendt, K.

LISEL (Low energy Isobar SEparation by Lasers) is a future project at the DREAMS (DREsden Accelerator Mass Spectrometry) facility to widen the applications of AMS by extending the range of measurable (radio-) nuclides. AMS has proven to be a versatile tool capable of detecting a large number of long-lived radionuclides at the ultra-trace level i.e. isotope ratios down to 1E-16. However, being a mass spectrometric method, it is limited by the presence of strong isobaric background. To overcome this limitation, we propose to remove the isobars already at the low-energy side by laser photodetachment. This method allows to selectively neutralize isobars by laser radiation, leaving the ions of interest intact. First studies were performed at the University of Vienna and gave promising results [1,2] for the easier to be measured low-mass AMS isotopes Al-26 and Cl-36. Within the LISEL project this method will be for the first time applied to an AMS facility based on a 6 MV tandem accelerator. The first isotopes to be addressed with the new method will be Mn-53 and Fe-60. Both are currently only measurable at AMS facilities with more than 10 MV terminal voltage (currently available only at the ANU in Canberra/Australia or the LMU and TU Munich in Garching/Germany). Further on we foresee to apply this method to other rare isotopes, making LISEL@DREAMS a versatile machine for all isotopes. This will subsequently widen the applications and also the user community.
[1] Forstner, O. et al., Nucl. Instr. And Meth. B 361 (2015) p. 217-221 [2] Martschini, M. et al., Int. J. Mass Spectrom., 415 (2017) p. 9-17

Keywords: laser; AMS; accelerator mass spectrometry

  • Lecture (Conference)
    PLATAN 2019, International Conference Merger of the Poznan Meeting on Lasers and Trapping Devices in Atomic Nuclei Research and the International Conference on Laser Probing, 19.-24.05.2019, Mainz, Deutschland
  • Lecture (Conference)
    Ion Beam Physics Workshop, 24.-26.06.2019, Dresden, Deutschland

Publ.-Id: 28918

Ultrasensitive (<1 mBq), cheap, and fast detection method for ⁷Be allowing high sample throughput

Rugel, G.; Tiessen, C. J.; Bemmerer, D.; Querfeld, R.; Scharf, A.; Steinhauser, G.; Merchel, S.

Beryllium-7 (T1/2 = 53.22 d), mainly measured via γ-spectrometry, is used as a (natural) radiotracer for education and science [1]. For activities < 0.1 Bq and especially for samples also containing so longer-lived ¹⁰Be (T1/2 = 1.387 Ma), accelerator mass spectrometry (AMS) is the method-of-choice.
We demonstrate that ⁷Be and ¹⁰Be can be quantified at the DREsden AMS (DREAMS) facility [2,3] on the same prepared BeO. Detection limits (⁷Be) are as low as ~ 0.6 mBq, hence, one-to-two orders of magnitude better than “standard/ordinary” and “sophisticated” decay counting (e.g. in an underground laboratory). Uncertainties for small samples are usually 6-7 % for small samples. The method is validated by γ-counting of two larger rainwater samples showing an excellent agreement with the AMS result [4].
Samples as small as tens of millilitres of rainwater can be chemically processed (after acidification) within a few hours without expensive and time-consuming ion exchange. Isobar (⁷Li) suppression by chemistry and AMS is sufficient to guarantee an ultrasensitive, cheap, and fast detection method for ⁷Be allowing high sample throughput.
The DREAMS facility allows external user access free-of-charge via a proposal system. Further information can be found at or

Parts of this research were carried out at the Ion Beam Centre (IBC) at the Helmholtz-Zentrum Dresden-Rossendorf e. V., a member of the Helmholtz Association. We appreciate support of Dominik Güttler, René Ziegenrücker and the DREAMS operator team during AMS-measurements, of Gyürky György (Hungarian Academy of Sciences) for providing ⁷Be for the calibration material, and of BMBF (05K16MG1) and DAAD-RISE Professional (HZDRPH-456) for funding. It was a pleasure to discuss ⁷Be-AMS with Andrew Smith (ANSTO).

[1] R. Querfeld, S. Merchel, G. Steinhauser, J. Radioanal. Nucl. Chem. 314 (2017) 521-527.
[2] S. Akhmadaliev et al., Nucl. Instr. Meth. B 294 (2013) 5-10.
[3] G. Rugel et al., Nucl. Instr. Meth. B 370 (2016) 94-100.
[4] C. Tiessen et al., Accelerator mass spectrometry (AMS) for beryllium-7 measurements in smallest rainwater samples, J. Radioanal. Nucl. Chem, 2019, doi: 10.1007/s10967-018-6371-6.

Keywords: Be-7; Be-10; accelerator mass spectrometry (AMS); rainwater

  • Invited lecture (Conferences)
    2nd International Conference on Radioanalytical and Nuclear Chemistry (RANC 2019), 05.-10.05.2019, Budapest, Hungary

Publ.-Id: 28917

Viable and active microorganisms in the deep terrestrial biosphere

Lopez-Fernandez, M.; Simone, D.; Broman, E.; Turner, E.; Wu, X.; Bertilsson, S.; Dopson, M.

Although the continental deep biosphere is estimated to contain 2 to 19% of the earth’s total biomass, it is still one of the least understood ecosystems on the planet. A key question for the terrestrial deep biosphere is the viability and activity of the large diversity of microorganisms present. This work shows that the microbial populations in aquifers with different chemistry and depth below the surface are viable and active and their diversity decreased with depth below the surface. Quantitative PCR and high throughput 16S rRNA gene sequencing revealed no significant differences in 16S rRNA gene abundances and microbial diversity between total and viable communities. This suggested that the populations were adapted to the prevailing oligotrophic conditions and that non-viable cells are rapidly degraded and recycled into new biomass. In addition, in situ fixed RNA transcripts aligned to the three domains of life, supporting activity within these communities. Many of the SSU rRNA transcripts grouped within recently described candidate phyla or could not be mapped to known branches on the tree of life, suggesting that a large portion of the active biota in the deep biosphere remains unexplored. Despite the extremely oligotrophic conditions, mRNA transcripts revealed a diverse range of metabolic strategies carried out by different taxa. These results emphasize the need to further investigate microbial activities in the deep biosphere and the importance of unclassified and candidate phyla in this environment.

  • Lecture (Conference)
    12th International Congress of Extremophiles, 16.-20.09.2018, Ischia, Italy

Publ.-Id: 28916

Depth and Dissolved Organic Carbon Shape Microbial Communities in Surface Influenced but Not Ancient Saline Terrestrial Aquifers

Lopez-Fernandez, M.; Åström, M.; Bertilsson, S.; Dopson, M.

The continental deep biosphere is suggested to contain a substantial fraction of the earth’s total biomass and microorganisms inhabiting this environment likely have a substantial impact on biogeochemical cycles. However, the deep microbial community is still largely unknown and can be influenced by parameters such as temperature, pressure, water residence times, and chemistry of the waters. In this study, 21 boreholes representing a range of deep continental groundwaters from the Äspö Hard Rock Laboratory were subjected to high-throughput 16S rRNA gene sequencing to characterize how the different water types influence the microbial communities. Geochemical parameters showed the stability of the waters and allowed their classification into three groups. These were (i) waters influenced by infiltration from the Baltic Sea with a “modern marine (MM)” signature, (ii) a “thoroughly mixed (TM)” water containing groundwaters of several origins, and (iii) deep “old saline (OS)” waters. Decreasing microbial cell numbers positively correlated with depth. In addition, there was a stronger positive correlation between increased cell numbers and dissolved organic carbon for the MM compared to the OS waters. This supported that the MM waters depend on organic carbon infiltration from the Baltic Sea while the ancient saline waters were fed by “geogases” such as carbon dioxide and hydrogen. The 16S rRNA gene relative abundance of the studied groundwaters revealed different microbial community compositions. Interestingly, the TM water showed the highest dissimilarity compared to the other two water types, potentially due to the several contrasting water types contributing to this groundwater. The main identified microbial phyla in the groundwaters were Gammaproteobacteria, unclassified sequences, Campylobacterota (formerly Epsilonproteobacteria), Patescibacteria, Deltaproteobacteria, and Alphaproteobacteria. Many of these taxa are suggested to mediate ferric iron and nitrate reduction, especially in the MM waters. This indicated that nitrate reduction may be a neglected but important process in the deep continental biosphere. In addition to the high number of unclassified sequences, almost 50% of the identified phyla were archaeal or bacterial candidate phyla. The percentage of unknown and candidate phyla increased with depth, pointing to the importance and necessity of further studies to characterize deep biosphere microbial populations.

Keywords: 16S rRNA gene; amplicon sequencing; deep subsurface; groundwaters; chemistry; microbial diversity

Publ.-Id: 28915

Microbial Community and Metabolic Activity in Thiocyanate Degrading Low Temperature Microbial Fuel Cells

Ni, G.; Canizales, S.; Broman, E.; Simone, D.; Palwai, V. R.; Lundin, D.; Lopez-Fernandez, M.; Sleutels, T.; Dopson, M.

Thiocyanate is a toxic compound produced by the mining and metallurgy industries that needs to be remediated prior to its release into the environment. If the industry is situated at high altitudes or near the poles, economic factors require a low temperature treatment process. Microbial fuel cells are a developing technology that have the benefits of both removing such toxic compounds while recovering electrical energy. In this study, simultaneous thiocyanate degradation and electrical current generation was demonstrated and it was suggested that extracellular electron transfer to the anode occurred. Investigation of the microbial community by 16S rRNA metatranscriptome reads supported that the anode attached and planktonic anolyte consortia were dominated by a Thiobacillus-like population. Metatranscriptomic sequencing also suggested thiocyanate degradation primarily occurred via the ‘cyanate’ degradation pathway. The generated sulfide was metabolized via sulfite and ultimately to sulfate mediated by reverse dissimilatory sulfite reductase, APS reductase, and sulfate adenylyltransferase and the released electrons were potentially transferred to the anode via soluble electron shuttles. Finally, the ammonium from thiocyanate degradation was assimilated to glutamate as nitrogen source and carbon dioxide was fixed as carbon source. This study is one of the first to demonstrate a low temperature inorganic sulfur utilizing microbial fuel cell and the first to provide evidence for pathways of thiocyanate degradation coupled to electron transfer.

Keywords: MFC; thiocyanate degradation; extracellular electron transfer; low temperature; metatranscriptomics

Publ.-Id: 28914

Metatranscriptomes Reveal That All Three Domains of Life Are Active but Are Dominated by Bacteria in the Fennoscandian Crystalline Granitic Continental Deep Biosphere

Lopez-Fernandez, M.; Simone, D.; Wu, X.; Soler, L.; Nilsson, E.; Holmfeldt, K.; Lantz, H.; Bertilsson, S.; Dopson, M.

ABSTRACT The continental subsurface is suggested to contain a significant part of the earth’s total biomass. However, due to the difficulty of sampling, the deep subsurface is still one of the least understood ecosystems. Therefore, microorganisms inhabiting this environment might profoundly influence the global nutrient and energy cycles. In this study, in situ fixed RNA transcripts from two deep continental groundwaters from the Äspö Hard Rock Laboratory (a Baltic Sea-influenced water with a residence time of < 20 years, defined as “modern marine,” and an “old saline” groundwater with a residence time of thousands of years) were subjected to metatranscriptome sequencing. Although small subunit (SSU) rRNA gene and mRNA transcripts aligned to all three domains of life, supporting activity within these community subsets, the data also suggested that the groundwaters were dominated by bacteria. Many of the SSU rRNA transcripts grouped within newly described candidate phyla or could not be mapped to known branches on the tree of life, suggesting that a large portion of the active biota in the deep biosphere remains unexplored.
Despite the extremely oligotrophic conditions, mRNA transcripts revealed a diverse range of metabolic strategies that were carried out by multiple taxa in the modern marine water that is fed by organic carbon from the surface. In contrast, the carbon dioxide- and hydrogen-fed old saline water with a residence time of thousands of years predominantly showed the potential to carry out translation. This suggested these cells were active, but waiting until an energy source episodically becomes available.
IMPORTANCE A newly designed sampling apparatus was used to fix RNA under in situ conditions in the deep continental biosphere and benchmarks a strategy for deep biosphere metatranscriptomic sequencing. This apparatus enabled the identification of active community members and the processes they carry out in this extremely oligotrophic environment. This work presents for the first time evidence of eukaryotic, archaeal, and bacterial activity in two deep subsurface crystalline rock groundwaters from the Äspö Hard Rock Laboratory with different depths and geochemical characteristics. The findings highlight differences between organic carbon fed shallow communities and carbon dioxide- and hydrogen-fed old saline waters. In addition, the data reveal a large portion of uncharacterized microorganisms, as well as the important role of candidate phyla in the deep biosphere, but also the disparity in microbial diversity when using standard microbial 16S rRNA gene amplification versus the large unknown portion of the community identified with unbiased metatranscriptomes.

Keywords: metatranscriptomes; mRNA; rRNA; deep biosphere; groundwaters

Publ.-Id: 28913

Investigation of viable taxa in the deep terrestrial biosphere suggests high rates of nutrient recycling

Lopez-Fernandez, M.; Broman, E.; Turner, S.; Wu, X.; Bertilsson, S.; Dopson, M.

The deep biosphere is the largest ‘bioreactor’ on earth, and microbes inhabiting this biome profoundly influence global nutrient and energy cycles. An important question for deep biosphere microbiology is whether or not specific populations are viable. To address this, we used quantitative PCR and high throughput 16S rRNA gene sequencing of total and viable cells (i.e. with an intact cellular membrane) from three groundwaters with different ages and chemical constituents. There were no statistically significant differences in 16S rRNA gene abundances and microbial diversity between total and viable communities. This suggests that populations were adapted to prevailing oligotrophic conditions and that non-viable cells are rapidly degraded and recycled into new biomass. With higher concentrations of organic carbon, the modern marine and undefined mixed waters hosted a community with a larger range of predicted growth strategies than the ultra-oligotrophic old saline water. These strategies included fermentative and potentially symbiotic lifestyles by candidate phyla that typically have streamlined genomes. In contrast, the old saline waters had more 16S rRNA gene sequences in previously cultured lineages able to oxidize hydrogen and fix carbon dioxide. This matches the paradigm of a hydrogen and carbon dioxide-fed chemolithoautotrophic deep biosphere.

Keywords: 16S rRNA gene; deep subsurface; fracture groundwaters; propidium monoazide; viable cells; candidate phyla radiation

Publ.-Id: 28912

Focused ion beams in biology: How the Helium Ion Microscope and FIB/SEMs help reveal nature’s tiniest structures

Wolff, A.; Klingner, N.; Thompson, W.; Zhou, Y.; Lin, J.; Peng, Y. Y.; Ramshaw, J. A. M.; Xiao, Y.

Focused Ion Beams such as the Helium Ion Microscope (HIM) as well as FIB/SEMs have sparked great interest within the biological sciences in recent years. The HIM allows high resolution imaging of uncoated non-conductive samples while the FIB/SEM (FIB/SEMs combine a focused ion beam with a Scanning Electron Microscope (SEM)) allows to prepare TEM lamellae, 3D reconstruct the sample or reveal sub surface structures with nanometre precision. FIB/SEMs have become the “go to” tool in the materials sciences and semiconductor industry. Despite these unique capabilities, it is not yet fully established in the biological sciences [1-5]. This is predominantly due to the heat-induced damage from the ion beam when processing soft materials including biological samples.

This presentation shows how the HIM as well as FIB/SEMs can be used in biological sciences to reveal nature’s tiniest structures (Figure 1). The presented work then focuses on the underlying ion-solid interactions and the effect of processing parameters on heating induced by ion beams. The work presented here deals with gallium ion solid interactions, however the broader results are applicable to any type of FIB including the helium ion microscope (HIM) and plasma FIBs. The interactions of gallium ions in skin were simulated using Monte Carlo methods. The program SRIM [6] was used to obtain theoretical results which permit estimation of the ion beam induced temperature increases, using the physical principles of Fourier’s law of conductive heat transfer. The model suggests that the ion beam induced increase in temperature can be reduced by:
1. Reducing the local dose rate (smaller aperture/ion beam current)
2. Reducing the local dose (smaller aperture/ion beam current, introducing beam blur, reducing the beam overlap)
The technique was tested on collagen, a soft biological material which is commonly used in biomedical applications. Collagen was chosen as a suitable test sample as it loses its fibrillary structure when denaturated by heat, permitting damage to easily be recognized. Cross-sections and TEM lamellas were prepared from non-embedded collagen with conventional FIB processing parameters (see Figure 2 left) as well as heat reducing FIB parameters (see Figure 1 right).
The results also show that heat damage can be prevented by reducing the local dose rate and area underneath the ion beam. A TEM comparison of a microtome prepared lamella and a FIB prepared lamella (using heat reducing parameters) shows that the fibrillar structures can be maintained, and heat damage avoided. The approach described here can be used to determine suitable parameters for other soft materials.

The authors acknowledge scientific and technical assistance of Peter Hines, Jamie Riches, Rachel Hancock, and Ning Liu and the facilities at the Australian Microscopy & Microanalysis Research Facility (AMMRF) at the Central Analytical Research Facility (CARF), Queensland University of Technology, Brisbane, Australia.


[1] Drobne et al, ‘Surface Damage Induced by FIB Milling and Imaging of Biological Samples is Controllable’; Microscopy Research and Technique 70; 895-903 (2007)
[2] Earl et al, ‘Characterization of dentine structure in three dimensions using FIB-SEM’; Journal of Microscopy 240, Pt 1, 1-5 (2010)
[3] Schneider et al; ‘Serial FIB/SEM imaging for quantitative 3D assessment of the osteocyte lacuna-canalicular network’; Bone 49, 304-311 (2011)
[4] Stokes et al; ‘A New Approach to Study Biological and Soft Materials Using Focused Ion Beam Scanning Electron Microscopy (FIB/SEM)’; Journal of Physics: Conference Series 26; 50-53 (2006)
[5] Bandara et al.; ‘Bactericidal Effects of Natural Nanotopography of Dragonfly Wing on Escherichia coli’ ACS Applied Materials & Interfaces 2017 9 (8), 6746-6760
[6] Ziegler et al,

  • Invited lecture (Conferences)
    Microscience Microscopy Congress 2019, 01.-04.07.2019, Manchester, United Kingdom
  • Lecture (Conference)
    Microscopy & Microanalysis 2019, 04.-08.08.2019, Portland, United States of America
    DOI: 10.1017/S1431927619005051
  • Lecture (Conference)
    AVS 66th International Symposium & Exhibition, 20.-25.10.2019, Columbus, United States of America

Publ.-Id: 28911

Formation of heavy clusters in ion-irradiated compounds

Kavetskyy, T.; Liedke, M. O.; Butterling, M.; Wagner, A.; Krause-Rehberg, R.; Sausa, O.; Meshi, L.; Dahan, I.; Vacik, J.; Horak, P.; Fuks, D.; Mykytenko, N.; Kiv, A.

Ion-irradiated U(Al,Si)3 intermetallide, as an example of compounds with significantly different atomic masses of constituting atoms, was studied by slow positron beam spectroscopy in order to clarify the nature of defects accompanying the process of the ion-induced disordering of this material. The studied compound was irradiated with different Ar+ ion fluences with energy 30 keV. The formation of so-called heavy clusters (Uranium in this case) has been revealed. Such clusters affect the reliability of materials in nuclear reactors. Ion-induced creation of heavy clusters can provide important properties of similar materials.

Keywords: Intermetallic alloys and compounds; ion beam technology; positron annihilation; heavy clusters

Publ.-Id: 28910

Probing dense baryon-rich matter with virtual photons

Adamczewski-Musch, J.; Arnold, O.; Behnke, C.; Belounnas, A.; Belyaev, A.; Berger-Chen, J. C.; Biernat, J.; Blanco, A.; Blume, C.; Böhmer, M.; Bordalo, P.; Chernenko, S.; Chlad, L.; Deveaux, C.; Dreyer, J.; Dybczak, A.; Epple, E.; Fabbietti, L.; Fateev, O.; Filip, P.; Fonte, P.; Franco, C.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzon, J. A.; Gernhäuser, R.; Golubeva, M.; Greifenhagen, R.; Guber, F.; Gumberidze, M.; Harabasz, S.; Heinz, T.; Hennino, T.; Hlavac, S.; Höhne, C.; Holzmann, R.; Ierusalimov, A.; Ivashkin, A.; Kämpfer, B.; Karavicheva, T.; Kardan, B.; Koenig, I.; Koenig, W.; Kolb, B. W.; Korcyl, G.; Kornakov, G.; Kotte, R.; Kühn, W.; Kugler, A.; Kunz, T.; Kurepin, A.; Kurilkin, A.; Kurilkin, P.; Ladygin, V.; Lalik, R.; Lapidus, K.; Lebedev, A.; Lopes, L.; Lorenz, M.; Mahmoud, T.; Maier, L.; Mangiarotti, A.; Markert, J.; Maurus, S.; Metag, V.; Michel, J.; Mihaylov, D. M.; Morozov, S.; Müntz, C.; Münzer, R.; Naumann, L.; Nowakowski, K. N.; Palka, M.; Parpottas, Y.; Pechenov, V.; Pechenova, O.; Petukhov, O.; Pietraszko, J.; Przygoda, W.; Ramos, S.; Ramstein, B.; Reshetin, A.; Rodriguez-Ramos, P.; Rosier, P.; Rost, A.; Sadovsky, A.; Salabura, P.; Scheib, T.; Schuldes, H.; Schwab, E.; Scozzi, F.; Seck, F.; Sellheim, P.; Siebenson, J.; Silva, L.; Sobolev, Y. G.; Spataro, S.; Ströbele, H.; Stroth, J.; Strzempek, P.; Sturm, C.; Svoboda, O.; Szala, M.; Tlusty, P.; Traxler, M.; Tsertos, H.; Usenko, E.; Wagner, V.; Wendisch, C.; Wiebusch, M. G.; Wirth, J.; Zanevsky, Y.; Zumbruch, P.

Quantum chromodynamics (QCD) supports the existence of a novel state of strongly interacting matter with temperatures above kT = 50 MeV and densities several times higher than those in nuclei. Such matter can be created in the laboratory as a transient state by colliding heavy ions at relativistic energies. The thermal electromagnetic radiation emitted from the dense stage of these collisions has been used to probe microscopic properties of the produced medium. The spectral distribution of virtual photons – manifesting themselves as di-electron pairs – shows a nearly exponential shape which indeed points to an emitting source of temperature in excess of 70 MeV/k and to a strong modification of the properties of its constituents. Regarding bulk properties, this medium is similar to the dense matter formed in the final state of a neutron star merger, as apparent from its recent multi-messenger observation.


Publ.-Id: 28909

Pressure-tuning the quantum spin Hamiltonian of the triangular lattice antiferromagnet Cs2CuCl4

Zvyagin, S. A.; Graf, D.; Sakurai, T.; Kimura, S.; Nojiri, H.; Wosnitza, J.; Ohta, H.; Ono, T.; Tanaka, H.

Quantum triangular-lattice antiferromagnets are important prototype systems to investigate phenomena of the geometrical frustration in condensed matter. Apart from highly unusual magnetic properties, they possess a rich phase diagram (ranging from an unfrustrated square lattice to a quantum spin liquid), yet to be confirmed experimentally. One major obstacle in this area of research is the lack of materials with appropriate (ideally tuned) magnetic parameters. Using Cs2CuCl4 as a model system, we demonstrate an alternative approach, where, instead of the chemical composition, the spin Hamiltonian is altered by hydrostatic pressure. The approach combines high pressure electron spin resonance and magnetization measurements, allowing us not only to quasi-continuously tune the exchange parameters, but also to accurately monitor them. Our experiments indicate a substantial increase of the exchange coupling ratio from 0.3 to 0.42 at a pressure of 1.8 GPa, revealing a number of emergent field-induced phases.

Publ.-Id: 28907

Effect of insertion layer on electrode properties in magnetic tunnel junctions with a zero-moment half-metal

Titova, A.; Fowley, C.; Clifford, E.; Lau, Y.-C.; Borisov, K.; Betto, D.; Atcheson, G.; Hübner, R.; Xu, C.; Stamenov, P.; Coey, M.; Rode, K.; Lindner, J.; Fassbender, J.; Deac, A. M.

Due to its negligible spontaneous magnetization, high spin polarization and giant perpendicular magnetic anisotropy, Mn₂RuₓGa (MRG) is an ideal candidate as an oscillating layer in THz spin-transfer-torque nano-oscillators. Here, the effect of ultrathin Al and Ta diffusion barriers between MRG and MgO in perpendicular magnetic tunnel junctions is investigated and compared to devices with a bare MRG/MgO interface. Both the compensation temperature, Tcomp, of the electrode and the tunneling magnetoresistance (TMR) of the device are highly sensitive to the choice and thickness of the insertion layer used. High-resolution transmission electron microscopy, as well as analysis of the TMR, its bias dependence, and the resistance-area product allow us to compare the devices from a structural and electrical point of view. Al insertion leads to the formation of thicker effective barriers and gives the highest TMR, at the cost of a reduced Tcomp. Ta is the superior diffusion barrier which retains Tcomp, however, it also leads to a much lower TMR on account of the short spin diffusion length which reduces the tunneling spin polarization. The study shows that fine engineering of the Mn₂RuₓGa/barrier interface to improve the TMR amplitude is feasible.

Keywords: Tunneling Magnetoresistance; Half-Metal; Mn-based alloys; MRAM; Spin Polarisation; Heusler alloy; Ferrimagnetic; Perpendicular Magnetic Anisotropy

Publ.-Id: 28906

Equiatomic quinary rare-earth rich amorphous ribbons with excellent magnetocaloric performance

Li, L.; Xu, C.; Yuan, Y.; Zhou, S.

The glass forming ability, microstructure, magnetism and magnetocaloric effect (MCE) in two quinary rare-earth rich amorphous ribbons of Tm20Ho20Gd20Co20Ni20 and Tm20Ho20Gd20Co20Cu20 are reported. Both amorphous ribbons exhibit excellent glass forming ability and a table-like MCE. In addition to large magnetic entropy change of ∼14.0 J/kg-K, an extremely high refrigerant capacity of ∼790 J/kg are achieved which can almost cover the temperature range from liquid hydrogen to liquid nitrogen for the magnetic field change of 0–7 T for both ribbons. Therefore, the quinary rare-earth rich amorphous ribbons can be proposed as a new class of promising magnetic refrigeration materials.

Publ.-Id: 28905

Comparison of the stability of U(VI) and Cm(III) doped calcium (aluminum) silicate hydrate (C-(A)-S-H) phases at saline conditions

Wolter, J.-M.; Schmeide, K.; Huittinen, N.; Bok, F.; Weiss, S.; Brendler, V.; Stumpf, T.

Cementitious materials, used in a nuclear waste repository in the form of concrete or grout to ensure mechanical stability and sealing of disposal tunnels, constitute an important containment barrier for radionuclides in the event of water intrusion into a disposal site. The immobilization potential of hardened cement paste (HCP) as well as of calcium silicate hydrate (C-S-H), as main component of HCP, towards radionuclides such as Cm(III) or U(VI) has been demonstrated in a number of studies, e.g. [1-3]. To evaluate the retention potential of cementitious materials towards radionuclides at saline conditions, U(VI) and Cm(III) doped C-S-H phases were exposed to background electrolytes with salinities comparable to those reported for pore waters of North German clay formations, which are considered as potential host rocks.
U(VI) and Cm(III) doped C-S-H phases with calcium-to-silicon (C/S) ratios ranging from 2.0 to 1.0, representing a portlandite saturated C-S-H system as well as chemically degraded cement paste, were synthesized directly in presence of either U(VI) or Cm(III). These phases were characterized by time-resolved laser-induced luminescence spectroscopy (TRLFS), infrared (IR) spectroscopy, powder X-ray diffraction (XRD), and scanning electron microscopy (SEM). Batch leaching experiments were performed for U(VI) doped CSH phases applying 2.5 M NaCl, 2.5 M NaCl/0.02 M Na2SO4, 2.5 M NaCl/0.02 M NaHCO3 or 0.02 M NaHCO3 and for Cm(III) doped CSH phases applying 2.5 M NaCl/0.02 M NaHCO3 or 0.02 M NaHCO3. The time-dependent release of Ca, Si, U or Cm from CSH phases into brines was followed up to 60 days. Leaching induced changes of the C-S-H structure and of the U(VI) or Cm(III) coordination environment were studied mainly with XRD and TRLFS or IR spectroscopy, respectively.
Generally, the high immobilization potential of C-S-H gel towards U(VI) and Cm(III), reported in the literature, was verified. In the presence of saline solutions, the C-S-H phases showed differences with regard to C-S-H stability and radionuclide release in dependence on the C/S ratio, the composition of the leaching solution and the immobilized radionuclide.
The leaching results for U(VI) doped C-S-H gel indicated that the U(VI) retention is maintained in the presence of NaCl rich solutions (2.5 M NaCl/0.02 M Na2SO4) due to the formation of a uranophane-like phase as detected by TRLFS [4]. The presence of carbonate (0.02 M) in the leaching solution, however, led in case of a C-S-H gel with a low C/S ratio (1.5, representing altered HCP) to some dissolution and thus, to a partial release of U(VI) whereby Ca2UO2(CO3)3(aq) is formed at moderate alkaline pH values. Part of the U(VI) is found to be retained in secondary CaCO3 phases after leaching. The release of U(VI) from C-S-H gel with a high C/S ratio (2.0, representing fresh HCP) due to carbonate was significantly smaller, only enhanced to a small extent due to the additional presence of 2.5 M NaCl.
The binding study of Cm(III) incorporated into C-S-H gel revealed at least two Cm(III) species: (i) Cm(III) substituted against Ca2+ from the C-S-H interlayer and (ii) Cm(III) incorporated in the polyhedral CaO plane of the C-S-H structure (c.f. Fig. 1a), which is in accordance with the literature [5]. The luminescence line narrowing effect observed in the site-selective TRLFS measurements (c.f. Fig. 1b) indicates the presence of numerous, chemically similar sorption sites for Cm(III), which can be attributed to the amorphous to semi-crystalline structure of the C-S-H gel. In addition, C-S-H gel with a C/S ratio of 2.0 showed a co-incorporation of Cm(III) into portlandite. Leaching experiments showed that Cm(III) is not mobilized by solutions with increased salinities [6]. Results obtained by XRD showed that due to contact with carbonate-containing solutions part of the C-S-H gel is converted into calcite and aragonite (C/S 1.0) or calcite and vaterite (C/S 2.0). Site-selective TRLFS showed that Cm(III) was still incorporated in C-S-H gel and portlandite and in addition, partially incorporated in secondary CaCO3 phases.
Currently, the mobilization potential of low molecular weight organic ligands, which can be released due to leaching processes from cementitious materials or might occur as degradation products of polymeric cement additives, towards radionuclides retained by C-S-H gel is studied.
The utilization of Al-bearing additives in modern concrete and the usage of tobermorite as an ion exchanger justify the study of Al-containing C-S-H gel and tobermorite with regard to radionuclide retention. Thus, we investigated the Al and U(VI) incorporation into C-S-H phases and tobermorite at different Al/Si ratios (0.025−0.2) and synthesis temperatures (25°C or 200°C) using Al additives such as Al2O3 and Al(NO3)3. The obtained phases were characterized with solid state 27Al and 29Si NMR spectroscopy, TRLFS, XRD, IR and Raman spectroscopy. Subsequently, the synthesized U(VI) and Al containing samples (tobermorite and C-S-H) were exposed to leaching solutions (2.5 M NaCl/0.02 M NaHCO3 or 0.02 M NaHCO3) for 30 days to determine the U(VI) and Al release under degradation conditions. First results indicated a preferred synthesis of tobermorite over C-S-H at hydrothermal conditions while Al was found to enter the silica chain, cross-link the sheets of tobermorite and somewhat reduce the U(VI) retention capabilities of tobermorite in the presence of carbonate.

Keywords: uranium(VI); curium(III); C-S-H; portlandite; calcite; site-selective TRLFS; luminescence line narrowing effect; high ionic strength

  • Poster
    Migration 2019 - 17th International Conference on the Chemistry and Migration Behavior of Actinides and Fission Products in the Geosphere, 15.-20.09.2019, Kyoto, Japan

Publ.-Id: 28903

Flow Rate Measurement in Flows with Asymmetric Velocity Profiles by Means of Distributed Thermal Anemometry

Arlit, M.; Schroth, C.; Schleicher, E.; Hampel, U.

Flow rate in closed conduits is one of the most frequently measured parameters in industrial processes and in gas and water supply. For an accurate measurement, flow meters typically require a fully developed symmetric flow profile with preferably no radial or tangential velocity components.
This is commonly secured by mounting flow meters in a pipe at a sufficiently long distance downstream any change in cross-section or pipe direction. In this paper, we introduce a new approach for flow rate measurement of gases or liquids that employs a novel spatially resolving fluid velocity sensor basing on thermal anemometry. The new principle allows accurate flow rate measurements for non-axisymmetric velocity profiles, even directly after pipe bends, T-junctions or other alterations in the pipe geometry. This is exemplified for air flow in three different pipe bend configurations.

Keywords: Flow rate measurement; installation effects; thermal anemometry grid sensor


Publ.-Id: 28902

Reductive immobilization of 99Tc(VII) by different crystalline phases of iron sulfide (FeS2)

Rodriguez, D.; Mayordomo, N.; Brendler, V.; Müller, K.; Schild, D.; Stumpf, T.

99Tc is a fission product with a long half-life of 2.14 × 105 years. Its migration behaviour and bioavailability strongly depends on its speciation in aqueous solution and on its oxidation state. Under aerobic conditions, Tc mainly exists as pertechnetate, TcO4, which is a highly water-soluble anion that does not significantly sorb on minerals or sediments, i.e. is considered inert and its groundwater migration is favoured. Under reducing conditions, Tc(VII) becomes Tc(IV), whose main species, TcO2, is a solid with a low solubility product and, thus, its mobility decreases.

As the presence of reductants like Fe2+ in the near-field of a nuclear waste repository is expected due to canister corrosion, several studies consider 99Tc reductive immobilization by mineral containing reductant moieties, such as magnetite (FeIIFe2IIIO4) or mackinawite (FeS) [1, 2], confirming the 99Tc(VII) reduction and subsequent 99Tc(IV) retention on the mineral surfaces.

Pyrite (cubic FeS2) is a redox sensitive sulfur mineral that has been identified as a good sorbent for Tc(VII) from soil and groundwater in both the absence [3] and presence [4] of humic substances. Under repository conditions, iron sulfide will be formed as both pyrite and marcasite (orthorhombic FeS2) as a result of corrosion processes and microbial action [5]. Moreover, iron sulfides are also accessory minerals in granitic and argillaceous rocks. Therefore, reliable data on 99Tc(VII) retention by both minerals and their mixtures is relevant for the safe disposal of nuclear waste.

We have studied the reductive immobilization of 99Tc(VII) by a synthetic mixture 60:40 marcasite – pyrite, finding that it removes almost 100% of 99Tc(VII) from solution within 7 days at pH = 6.5. This ability decreases linearly with increasing Tc concentration due to the saturation of the mineral, while an increase in the ionic strength has no significant effects. The isotherm plot has a slope of 0.5 suggesting a single reaction mechanism: sorption on one site, which would mean that the affinity of the mineral for the technetium is low [6], or precipitation of 99Tc(IV) most probably as TcO2 [7]. Figure 1 shows the SEM images of the mixture marcasite-pyrite before and after being in contact with 99Tc(VII) for 7 days at pH 6.5.

In comparison to the plain mineral, the micrographs of Tc reacted FeS2 at 2.00 μm clearly show erosion on the surface. Furthermore, the micrograph at 1.00 μm suggests deeper effects, not only the first layers of the mineral, as the morphology has obviously changed. The high surface dynamics may be induced by the incorporation of the radionuclei into the mineral. However, the flat surface of the FeS2 after the 99Tc(VII) uptake reminds to a coating that could be made of technetium polysulphides.

Although it is clear that this Tc retention is due to the reduction from 99Tc(VII) to 99Tc(IV), it has not been possible to determine so far if the 99Tc(IV) is sorbed on the mineral surface, incorporated in its structure or precipitated. As the FeS2 crystal phase as well as Tc oxidation state affect those retention mechanisms, we have also studied the immobilization of 99Tc(VII) by both pure pyrite and pure marcasite with the aim of analysing the crystal rearrangement effect and performing X-ray absorption spectroscopy for structural characterization.

This work has been developed in the frame of VESPA II project (02E11607B), supported by the German Federal Ministry of Economic Affairs and Energy (BMWi).

1 T. Kobayashi, A. C. Scheinost, D. Fellhauer, X. Gaona, M. Altmaier, Radiochim. Acta 101, 323 (2013).
2 F. R. Livens, M. J. Jones, A. J. Hynes, J. M. Charnock, J. F. W. Mosselmans, C. Hennig, H. Steele, D. Collison, D. J. Vaughan, R. A. D. Pattrick, W. A. Reed, L. N. Moyes, J. Environ. Radioact. 74, 211 (2004).
3 L. Huo, W. Xie, T. Qian, X. Guan, D. Zhao, Chemosphere 174, 456 (2017).
4 C. Bruggeman, A. Maes, J. Vancluysen, Phys. Chem. Earth 32, 573 (2007).
5 W. M. B. Roberts, A. L. Walker, A. S. Buchanan, Miner. Depos. 4, 18 (1969).
6 G. Limousin, J.-P. Gaudet, L. Charlet, S. Szenknect, V. Barthès, M. Krimissa, Appl. Geochemistry 22, 249 (2007).
7 R. Guillaumont, T. Fanghänel, V. Neck, J. Fuger, D. A. Palmer, I. Grenthe, M. A. Rand, UPDATE ON THE CHEMICAL THERMODYNAMICS OF URANIUM, NEPTUNIUM, PLUTONIUM,AMERICIUM AND TECHNETIUM, Elsevier, 2003.

Keywords: Technetium; retention; pyrite; marcasite

  • Poster
    Migration 2019 - 17th International Conference on the Chemistry and Migration Behavior of Actinides and Fission Products in the Geosphere, 15.-21.09.2019, Kyoto, Japan

Publ.-Id: 28901

Spectroscopic characterization of curium(III) protein interactions

Moll, H.; Raff, J.; Stumpf, T.

Proteins are important biomolecules in all living cells. They perform a large array of functions within organisms. To understand the speciation of actinides in living organisms, their interactions with proteins need to be explored on a molecular level.
Bacterial surface layers (S-layers) are common surface structures in many bacteria and archaea consisting of so-called surface-layer proteins (S-layer proteins) [1]. So far, we could show that S-layers proteins of Lysinibacillus sphaericus JG-A12 selectively bind several metals including U, Pd, Au, and Eu, partly with a high affinity [2]. In the present work we studied the interaction of Cm(III) with bacterial S-layer proteins of L. sphaericus JG-A12.
The formation of aqueous Cm(III) S-layer protein complexes was studied at room temperature by time-resolved laser-induced fluorescence spectroscopy (TRLFS) in 0.1 M NaCl solutions. The experiments were performed at a fixed total concentration for Cm(III) 0.88 µM and the S-layer protein of 5 g/L (39.6 µM) by varying the pH (2.0-9.0) and the type of S-layer. Based on their individual luminescence spectra and lifetimes, a specific and unspecific Cm(III) binding could be distinguished. The formation of the specific Cm3+-S-layer complex A and unspecific Cm3+-S-layer complex B depend on pH and the Ca2+ amount in the S-layer types. The influence of Ca2+ on the Cm3+ S-layer complexation was investigated by Ca2+ titration experiments. The specific Cm3+-S-layer complex A is characterized by a narrow emission band at 602.5 nm combined with a long lifetime of 310 µs. The spectroscopic EDTA titration of Cm3+-S-layer complex A showed an exchange of S-layer ligands by EDTA in the first coordination sphere of Cm(III) at EDTA concentrations of 40 µM and higher. This corresponds to a EDTA:S-layer protein ratio of 1:1.


[1] M. Sára, U.B. Sleytr, J. Bacteriol. 2000, 182,859. [2] M.L. Merroun et al., Appl. Environ. Microbiol. 2005, 71,5532.

Keywords: curium; S-layer proteins; Lysinibacillus sphaericus; luminescence spectroscopy, speciation

  • Lecture (Conference)
    Jahrestagung der Fachgruppe Nuklearchemie der GDCh 2019, 25.-27.09.2019, Dresden, Deutschland

Publ.-Id: 28900

Investigation of the availablity of sigma-1 receptors in orthotopic human glioblastoma-bearing mice with positron emission tomography (PET) using (S)-(−)-[18F]fluspidine

Toussaint, M.; Kranz, M.; Deuther-Conrad, W.; Patt, M.; Sabri, O.; Brust, P.

The sigma-1 receptor (S1R) is a chaperone protein of the mitochondrion-associated endoplasmic reticulum membrane. Its expression is dysregulated in various cancers including glioblastoma. S1R characterization in glioblastoma could help to better understand the pathophysiology of this cancer and thus help in improving diagnosis or treatment follow-up.
In this context, we aim to evaluate the potential of (S)-(−)-[18F]fluspidine to characterize S1R expression in an orthotopic glioblastoma model in mice with small animal PET/MR imaging.
Materials & Methods
11 female nude mice Rj:NMRI-Foxn1nu/nu (24-30 g) aged of 8 weeks (Janvier labs; France), underwent a stereotactic xenograft of U87 human glioblastoma cells (50 000 cells/1 µl) in the right striatum (AP:0.5, L: -2.0, DV:-3.0 mm) (Stoelting Europe, Ireland). PET scans were performed on tumor of a median size of 5.15 mm3. 3 healthy female nude mice Rj:NMRI-Foxn1nu/nu (25-30 g) were used as control group.
(S)-(-)-[18F]Fluspidine (5.6±2.5 MBq; Am: 140±50 GBq/µmol, EOS) was injected intravenously followed by 60 min dynamic PET scans (Mediso nanoScan®, PET/MRI, Hungary). 20 scans were performed and time-activity curves (TAC) from the tumor and the contralateral region were analyzed (PMOD v3.9, PMOD Technologies LLC, Switzerland). Peak-to-end ratios (peak: SUV mean from 2-9 min, end: SUV mean from 45-60 min) were used to compare regions. Paired two-tailed student t-test (p<0.05) was used for statistics.
The TACs from the striatum of healthy mice and from the contralateral side of U87 tumor bearing mice display similar profiles along with comparable peak-to-end SUV ratios (2.11±0.38 vs. 2.19±0.59).
By contrast, the profile of the average TAC of the tumor region is different from the contralateral side, with a lower initial uptake (mean SUV2-9 min p.i.: 0.95 vs. 1.1) and a higher uptake at the end of the scan (mean SUV45-60 min p.i.: 0.6 vs. 0.5). Accordingly, the peak-to-end ratio of the tumor region is significantly different from the ratio of the contralateral region (1.65±0.49 vs. 2.19±0.59, p=0.001).
The PET investigation revealed a significant difference in the pharmacokinetics of (S)-(-)-[18F]fluspidine between tumor and contralateral region, probably related to different S1R availabilities. Further investigations, such as autoradiography, will help to characterize this effect. These first results show the suitability of (S)-(-)-[18F]fluspidine for characterization of U87 S1R status.

Keywords: Sigma-1 receptor; Fluspidine; Glioblastoma; Positron emission tomography

  • Poster
    1. Deutscher Krebsforschungskongress (DKFK), 04.-05.02.2019, Heidelberg, Germany
  • Open Access Logo Poster
    10th Brain tumor meeting - 2019, 23.-24.05.2019, Berlin-Buch, Deutschland


Publ.-Id: 28899

Annual Report 2018 - Institute of Resource Ecology

Stumpf, T.; Foerstendorf, H.; Bok, F.; Richter, A.

Annual Report 2018 of the scientific activities of the Institute of Resource Ecology of the Helmholtz-Zentrum Dresden-Rossendorf

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-096 2019
    ISSN: 2191-8708, eISSN: 2191-8716


Publ.-Id: 28898

Impact of temperature on the complexation of Eu(III) and Cm(III) with aqueous phosphates

Jordan, N.; Huittinen, N.; Jessat, I.; Réal, F.; Vallet, V.; Starke, S.; Demnitz, M.; Lösch, H.; Brendler, V.

The incorporation of actinides in solid lanthanide phosphates crystallizing in the monazite structure has been intensely investigated in the past decades due to the relevance of these monazites as potential ceramic phases for the immobilization of specific high level radioactive waste (HLW) streams [1-3]. In recent years, understanding the incorporation behaviour of trivalent dopants in the LnPO4×nH2O rhabdophane structure, which is the hydrated phosphate precursor in the synthesis of monazites through precipitation routes and a potential secondary mineral controlling actinide solubility in dissolution and re-precipitation reactions of monazite host-phases, has been given more attention [4,5]. Despite the large interest in lanthanide phosphates and the interaction of actinides with these solids, very little data is available on the complexation of lanthanides and actinides with aqueous phosphates, even though these complexation reactions precede any aqueous synthesis of monazite ceramics and are expected to occur in natural waters as well as in the proximity of monazite-containing HLW repositories. It also suffers from an almost systematic absence of independent spectroscopic validation of the stoichiometry of the proposed complexes. Both from the perspective of aqueous rhabdophane synthesis, which is often carried out at elevated temperatures, and heat-generating HLW immobilization in monazites, the lanthanide and actinide complexation reactions with aqueous phosphates under ambient conditions should be complemented with data obtained at higher temperatures.

In the present work, laser-induced luminescence spectroscopy (LIL) was used to study the complexation of Eu(III) (5×10 6 M) and Cm(III) (5×10 7 or 1×10 8 M) as a function of total phosphate concentration (0-0.3 M ΣPO4) in the temperature regime 25-90°C, using NaClO4 as a background electrolyte (I = 0.5 to 3.1 M). These studies have, in a first step, been conducted in the acidic pH-range (pH = 1) to avoid precipitation of solid Eu or Cm rhabdophane. Both trivalent metal cations form a complex with the anionic H2PO4 species, i.e. EuH2PO42+ and CmH2PO42+. The conditional complexation constants were found to increase upon rising ionic strength and temperature. Extrapolation of the obtained complexation constants to infinite dilution at 25 °C was performed by applying the Specific Ion Interaction Theory (SIT) [6]. The obtained log β° values for EuH2PO42+ and CmH2PO42 were 0.89 ± 0.13 and 0.45 ± 0.19, respectively, for reaction 1 below:

Me3+ + H3PO4 ⇌ MeH2PO42+ + H+ (Me = Eu or Cm) (1)

The ion-ion interaction coefficients ε(EuH2PO42+;ClO4 ) = 0.20 ± 0.08 and ε(CmH2PO42+;ClO4 ) = 0.16 ± 0.12 were derived at 25 °C. Temperature-dependent conditional complexation constants for the identified species were obtained from the recorded luminescence emission spectra. They were subsequently extrapolated to I =0 M, assuming that the ion-ion interaction parameters obtained at 25 °C are not significantly impacted by the temperature increase from 25 °C to 90 °C [6]. Using the extended van´t Hoff equation, the molal enthalpy ΔRHm° and entropy of reaction ΔRSm° values were both found to be positive.
Exactly the same combination of batch, spectroscopic, and thermodynamic studies was used at lower H+ concentrations ( log[H+] = 2.52, 3.44, and 3.65). Our results clearly showed the presence of Eu(H2PO4)2+ and Cm(H2PO4)2+ species, so far never reported in the literature. In addition Eu(HPO4)+ and Cm(HPO4)+ species were identified. Conditional complexation constants for these species will be derived and extrapolated to infinite dilution using the SIT approach.
Finally, relativistic quantum chemical investigations will be performed to shed light on the observed differences in the complexation strength of Eu(III) and Cm(III) with aqueous phosphates. They will also provide insight on the role of spin-orbit coupling and serve to probe the character of the metal water and metal phosphate bonds.

Keywords: Lanthanide; Actinide; Complexation; Luminescence spectroscopy; SIT

  • Contribution to proceedings
    Migration 2019 - 17th International Conference on the Chemistry and Migration Behavior of Actinides and Fission Products in the Geosphere, 15.-20.09.2019, Kyoto, Japan
    Proceedings of Migration 2019

Publ.-Id: 28897

Solvent extraction and separation of rare earth elements by diamide type ligands and the complex structure of extracted species

Shimojo, K.; Sasanuki, T.; Schöne, S.; Sugita, T.; Okamura, H.; Ikeda-Ohno, A.

Solvent extraction of rare earth elements using a new type of diamide ligand, DODGAA, was performed to investigate the extractability and separability of the ligand for the separation of rare earth elements. Single crystals of the DODGAA complexes with some rare earth metals were also synthesised and structurally determined by single-crystal X-ray diffraction (SC-XRD) to understand the molecular structure of extracted species.

Keywords: Rare earth elements; separation; solvent extraction; structure determination; single-crystal X-ray diffraction

  • Lecture (Conference)
    The 84th Annual Meeting of the Society of Chemical Engineering, Japan, 13.-15.03.2019, Shibaura Institute of Technology, Toyosu, Tokyo, Japan

Publ.-Id: 28896

Coordination chemistry of f-block metal ions with ligands bearing bio-relevant functional groups

Götzke, L.; Schaper, G.; März, J.; Kaden, P.; Huittinen, N.; Stumpf, T.; Kammerlander, K. K. K.; Brunner, E.; Hahn, P.; Mehnert, A.; Kersting, B.; Henle, T.; Lindoy, L. F.; Zanoni, G.; Weigand, J. J.

Over recent decades there has been a great deal of interest and associated research into aspects of the f-block (lanthanide and actinide) metal chemistry of naturally-occurring ligands, such as proteins, peptides, porphyrins and related tetraaza derivatives as well as synthetically modified natural ligands and solely synthetic ligand systems incorporating bio-relevant functional groups. In this review, we present a wide-ranging overview of published work spanning the above areas, with emphasis on selected biological, medical and environmental aspects. Systems capable of discriminating between metal ions from within, or between, the lanthanide and actinide groups are also discussed including the design and synthesis of biomimetic radionuclide chelators and radionuclide decorporation agents as well as solid adsorbent materials for the uptake of radionuclides from the environment and elsewhere. Thus, the interaction of the f-group elements with a range of biopolymers, including systems based on cellulose, chitin, chitosan, humic substances as well as a range of synthetic model systems is also presented. Other applications include the synthesis of new luminescent materials, including luminescent probes and luminescent metal coordination polymers exhibiting unusual photophysical properties as well as systems showing potential for use in the development of new MRI imaging agents.

Keywords: Lanthanides; Actinides; Maillard products; Siderophores; Calix[4]arenes; Porphyrins; Cellulose; Chitin; Chitosan; Humic substances; Peptides; Proteins

Publ.-Id: 28895

Experimental study in the heat flux of a heat exchanger for passive cooling of spent fuel pools by temperature anemometry grid sensor

Unger, S.; Arlit, M.; Beyer, M.; Hampel, U.

In commercial nuclear power plants spent fuel assemblies are usually stored in actively cooled water pools. The continuous decay heat release represents a potential risk in case of a station black out scenario. Thus two-phase passive heat removal systems are a key technology to enhance the safety of nuclear power plants. Such systems work only by the energy provided from the heat source, e.g. by the maintenance of a natural convection cooling. A heat transfer loop using air as an unlimited heat sink consists of a primary heat exchanger in the spent fuel pool water and a secondary heat exchanger located in ambient air. Thus the measurement of the heat flux, which gets transferred from the pool to the ambient air, is an important task. If one would measure heat flux, flow rates and temperatures in many positions by help of local probes, the natural flow would get strongly disturbed. For that reason we introduce a heat flux measurement around the secondary heat exchanger located in ambient air, which applies temperature and velocity measurement by an anemometric principle.
A 6.5m long flow channel with an electrical heated finned tube heat exchanger was set up at the TOPFLOW facility at HZDR. Since the tubes of a heat exchanger would be tilted in a passive heat removal system, i.e. to allow drainage of the condensed heat transfer medium, different tiled angles were adjusted to 0° (horizontal), 20°,30° and 40°. The frontal velocity was varied between 0.5 m/s and 4 m/s and three thermocouples were placed up- and downstream of the heat exchanger respectively. A novel Temperature Anemometry Grind Sensor (TAGS) was located downstream the heat exchanger. It consists of a wire grid with platinum resistance elements, which are placed in the small sub-channels of a flow straightener to generate laminar flow profiles. Two methods were used to calculate the heat flux: arithmetical average and weighting of the flow area. The results of velocity was compared with the average velocity measured by the volume flow control and out of the velocity and temperature the heat flux was calculated and compared with electrical supplied heat flux. The calculated average velocity measured by the TAGS corresponds well with the velocity measured by the volume flow controller up to approximately 3 m/s with a maximum deviation of ±5%, but underestimates the velocity measured by the volume flow controller at higher velocities. The heat flux was calculated by five methods, 1.) from the three thermocouples up- and downstream of the heat exchanger, 2.) from the average temperatures measured by the TAGS, 3.) from the weighted temperature measured by the TAGS, 4.) from the average temperature and velocity measured by the TAGS and 5.) from the weighted temperature and velocity measured by the TAGS. In this order the accuracy of methods increases compared to the electrical supplied heat flux. For the last method the maximum deviation was 6.5% for all tilt angles. This new measurement concept determines the heat flux without disturbing the flow in the loop.

Keywords: Finned Tube Heat Exchanger; Heat Flux Measurement; Heat Transfer; Passive Decay Heat Removal; Temperature Anemometry Grid Sensor; Velocity Measurement

  • Contribution to proceedings
    SWINTH-2019, 22.-25.10.2019, Livorno, Italy
  • Lecture (Conference)
    SWINTH-2019, 22.-25.10.2019, Livorno, Italy

Publ.-Id: 28893

Facile preparation of radium-doped, functionalized nanoparticles as carriers for targeted alpha therapy

Reissig, F.; Hübner, R.; Steinbach, J.; Pietzsch, H.-J.; Mamat, C.

Although significant advances in the tailoring of BaSO4-based nanoparticles have been achieved, the synthesis of particles is strongly dependent on the use of templates, surfactants, and additives, especially when radiolabeled with 133Ba or 224Ra. Herein, direct facile preparation of radiolabeled alendronate-functionalized BaSO4 nanoparticles in an aqueous medium in a one-pot reaction is developed. Remarkably, the size of the formed BaSO4 nanoparticles can be controlled by the type of the organic solvent used. Upon the addition of alendronate, amine functionalities were introduced into the nanoparticles. Additionally, a fluorescence dye-containing alendronate was used to evidence the introduction of the alendronate during the formation of the nanoparticles. The variations in the functionalities were investigated by IR and the morphology of the resulting BASO4 nanoparticles are investigated in detail by transmission electron microscopy. DLS and TEM measurements provided an average diameter of the nanoparticles of approx. 140 nm. Radium-doped alendronate nanoparticles were successfully obtained in a one-pot labeling procedure from [224Ra]RaCl2, Na2SO4 Ba(NO3)2 and alendronate.

Keywords: Radium-223; nanoparticles; Barium sulfate; talpha-theraphy


Publ.-Id: 28892

Vacancy cluster in ZnO films grown by pulsed laser deposition

Wang, Z.; Luo, C.; Anwand, W.; Wagner, A.; Butterling, M.; Azizar Rahman, M.; Phillips, M. R.; Ton-That, C.; Younas, M.; Su, S.; Ling, F. C. C.

Undoped and Ga-doped ZnO films were grown on c-sapphire using pulsed laser deposition (PLD) at the substrate temperature of 600 oC. Positron annihilation spectroscopy study (PAS) shows that the dominant VZn-related defect in the as-grown undoped ZnO grown with relative low oxygen pressure P(O2) is a vacancy cluster (most likely a VZn-nVO complex with n=2, 3) rather than the isolated VZn which has a lower formation energy. Annealing these samples at 900oC induces out-diffusion of Zn from the ZnO film into the sapphire creating the VZn, which favors the formation
of vacancy cluster containing relatively more VZn. Increasing the P(O2) during growth also lead to the formation of the vacancy cluster with relatively more VZn. For Ga-doped ZnO films, the oxygen pressure during growth has significant influence on the electron concentration and the microstructure of the VZn-related defect. Green luminescence (GL) and yellow luminescence (YL) were identified in the cathodoluminescence study (CL) study, and both emission bands were quenched after hydrogen plasma treatment.

Keywords: Vacancy cluster; ZnO; pulsed laser deposition; positron annihilation spectroscopy; photo luminescence

Publ.-Id: 28891

Two-Dimensional Kagome Lattices Made of Hetero Triangulenes Are Dirac Semimetals or Single-Band Semiconductors

Jing, Y.; Heine, T.

Here we discuss, based on first-principles calculations, two-dimensional (2D) kagome lattices composed of polymerized heterotriangulene units, planar molecules with D3h point group containing a B, C, or N center atom and CH2, O, or CO bridges. We explore the design principles for a functional lattice made of 2D polymers, which involves control of π-conjugation and electronic structure of the knots. The former is achieved by the chemical potential of the bridge groups, while the latter is controlled by the heteroatom. The resulting 2D kagome polymers have a characteristic electronic structure with a Dirac band sandwiched by two flat bands and are either Dirac semimetals (C center), or single-band semiconductors—materials with either exclusively electrons (B center) or holes (N center) as charge carriers of very high mobility, reaching values of up to ∼8 × 103 cm2 V–1 s–1, which is comparable to crystalline silicon.

Keywords: DFT; kagome; 2D polymers; 2D COFs


  • Secondary publication expected from 30.11.2020

Publ.-Id: 28890

Assessing robustness of radiomic features by image perturbation

Zwanenburg, A.; Leger, S.; Agolli, L.; Pilz, K.; Troost, E.; Richter, C.; Löck, S.

Image features need to be robust against differences in positioning, acquisition and segmentation to ensure reproducibility. Radiomic models that only include robust features can be used to analyse new images, whereas models with non-robust features may fail to predict the outcome of interest accurately. Test-retest imaging is recommended to assess robustness, but may not be available for the phenotype of interest. We therefore investigated 18 combinations of image perturbations to determine feature robustness, based on noise addition (N), translation (T), rotation (R), volume growth/shrinkage (V) and supervoxel-based contour randomisation (C). Test-retest and perturbation robustness were compared for combined total of 4032 morphological, statistical and texture features that were computed from the gross tumour volume in two cohorts with computed tomography imaging: I) 31 non-small-cell lung cancer (NSCLC) patients; II): 19 head-and-neck squamous cell carcinoma (HNSCC) patients. Robustness was determined using the 95% confidence interval (CI) of the intraclass correlation coefficient (1, 1). Features with CI >= 0:90 were considered robust. The NTCV, TCV, RNCV and RCV perturbation chain produced similar results and identified the fewest false positive robust features (NSCLC: 0.2-0.9%; HNSCC: 1.7-1.9%). Thus, these perturbation chains may be used as an alternative to test-retest imaging to assess feature robustness.

Publ.-Id: 28889

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