Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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32216 Publications
Quantitative predictions of LWFA simulation with PIConGPU - from improved modeling to new measurement methods via synthetic radiation diagnostics
Pausch, R.; Debus, A.; Schramm, U.; Bussmann, M.; Steiniger, K.; Widera, R.; Huebl, A.; Garten, M.; Irman, A.; Couperus, J.; Zarini, O.; Köhler, A.;
In a close interplay between particle-in-cell simulations and experimental measurements, we present new insights into the modeling of laser wakefield accelerators and discuss the arising challenges for laboratory diagnostics. These challenges were tackled by developing new methods for determining key parameters of the experiment by studying synthetic radiation diagnostics predicted by simulations.

The combination of an unprecedented experimental campaign studying the parameter dependence of beam loading during LWFA and an accompanying, extensive simulation campaign using the 3D3V particle-in-cell code PIConGPU made it possible to provide unique feedback between experiment and theory. This poster shows the step-by-step improvements through this interplay from the simulation perspective. Quantitatively more accurate methods such as the use of Gauss-Laguerre modes or a variety of ionization models are presented as well as more performant computationally procedures. Only through these improvements could the dynamics occurring in the experiment be reproduced and a deeper insight into the self-truncated ionization injection method be gained.

Moreover, this interplay also revealed the limits of current laboratory diagnostics. Synthetic in-situ radiation diagnostics in PIConGPU instigated the development of new diagnostic methods for experiments. For example, the shift of the laser focus position, compared to the vacuum, due to self-focusing in the plasma can now be quantified by spectral radiation signatures. Applying these new methods will enable an even more accurate understanding of laser plasma dynamics in experiments in the near future.
Keywords: Radiation, LWFA, aprticle-in-cell, PIConGPU
  • Poster
    The fourth annual meeting of the programme "Matter and Technologies", 12.-14.06.2018, Berlin, Deutschland
  • Lecture (Conference)
    The fourth annual meeting of the programme "Matter and Technologies", 12.-14.06.2018, Berlin, Deutschland

Publ.-Id: 27809 - Permalink


The cosmic-ray exposure history of the big iron Twannberg (IIG) meteorite
Smith, T.; Hofmann, B. A.; Leya, I.; Merchel, S.ORC; Rugel, G.; Pavetich, S.; Scharf, A.
Introduction: The Twannberg iron meteorite is one out of only six members of the group IIG. This group of iron meteorites is characterized by large amount of schreibersite (Fe,Ni) ₃P, and usually low Ni contents (Hofmann et al., 2009#). With the recent new finds (n = 1119 samples, total recovered mass: ~118 kg, up to June 30th, 2018, communication B. A. Hofmann) we have the opportunity to reinvestigate the cosmic-ray exposure history of Twannberg, with a special focus on its terrestrial age, in order to better understand the distribution of the different masses in the context of the last glaciation occurrences in Europe.
Experimental methods: The isotopic concentrations for He, Ne, and Ar have been measured by noble gas mass spectrometry at the University of Bern, following the procedures described earlier (Ammon et al., 2008#, 2009#). Analyses of the cosmogenic radionuclides (i.e., 10Be, 26Al, 36Cl, and 41Ca) have been performed at the DREsden Accelerator Mass Spectrometry facility (DREAMS, Akhmadaliev et al., 2013#) using chemical procedures previously described in Merchel et al. (1999#). In this work, we measured the cosmogenic noble gas and radionuclide concentrations in 14 and 7 Twannberg samples, respectively, from different find locations (Gruebmatt, Twannbach, and Mont Sujet, cf. Figure 1, Smith et al., 2017#).
Fig. 1. Find locations of Twannberg specimens until June 1st, 2016 (n = 570). The larger (red) squares indicate the find locations of the fragments analyzed in this work. The find location of the first mass (TW1, 15.915 kg) is indicated. Red arrow on Mont Sujet is the linear correlation of all Sujet finds and an approximation of the fall direction. LGM = last glacial maximum based on Bini et al. (2009#); OGM = Older glacial maximum (probably corresponding to Beringen/Riss) corresponding to the upper limit of the occurrence of alpine drift (see the Geological Setting section). The area south of the LGM/OGM lines was covered by alpine ice and the general direction of ice flow was from southwest to northeast. The blue arrow indicates the probable transport vector of Gruebmatt meteorites during the Beringen/Riss glaciation. Contour interval is 100 m.
Results and Discussion: First, we observe a wide range of both cosmogenic noble and radionuclide concentrations, e.g. after corrections (i.e. for trapped components, sulfur and/or phosphorus contributions, cf. Smith et al., 2017#), the cosmogenic 21Necos and 38Arcos concentrations vary by factors of 190 and 110, respectively. Based on model calculation (Ammon et al., 2008#), the observed variation of more than two orders of magnitude within all measured samples is only possible when considering a meteoroid with a minimum preatmospheric radius of ~165 cm.
Another approach is to use the cosmogenic (4He/21Ne)cos ratio as a shielding indicator; doing so, we estimate the preatmospheric radius to be ~250 cm.
To conclude, based on both the spread in cosmogenic noble gases and the (4He/21Ne)cos ratio, we infer Twannberg to have a minimum preatmospheric radius in the range of ~2 m, which, when assuming a density of ~7.8 g cm-3, would correspond to a minimal mass of ~250 tons.
Second, we calculated the cosmic-ray exposure (CRE) age of Twannberg using the well-adopted 36Cl-36Ar method (e.g. Lavielle et al., 1999#). We determined an average CRE age of 182±41 Ma. Note that this value is slightly different from the one that has been recently published in Smith et al. (2017#), due to the fact we are now using a new 41Ca half-life of 0.995×10⁵ years (Jörg et al., 2012#) instead of the previous value of 1.04×10⁵ years (Kutschera and Ahmad, 1992#). This modifies the terrestrial age (cf. below), and in return decreases the CRE age by ~5%. However, the new CRE age is still in agreement with the CRE age of 230±50 calculated previously by Hofmann et al. (2009#), as well determined using the 36Cl-36Ar method.
Third, based on new Monte-Carlo calculations, we used the 36Cl-41Ca radionuclide pair to calculate the terrestrial age of Twannberg; we found an age of 190±48 ka. Again, this age is slightly different from the one we reported in Smith et al. (2017#) since we are using here the new 41Ca half-life (cf. above). This terrestrial age, although quite surprising when considering the humid conditions in Switzerland, is 1) consistent with geological evidences (Hofmann et al., 2009; Smith et al., 2017#); and 2) indicates that the Twannberg meteorite fell most likely during or before the second last glaciation in Europe, 185-130 ka ago. This reveals that some of the masses have been glacially transported from an initial position west of Mont Sujet, in the direction of east-northeast (cf. Figure 1).
Acknowledgments: This study heavily relies on samples collected in a great effort by a joint group of meteorite enthusiasts and scientists. We particularly thank for the collaboration and samples: Marc Jost, Manuel Eggimann, Hannes Weiss, Sergey Vasiliev, Andreas Koppelt, Ernst Wyler, Gino Bernasconi, Marcel Häuselmann, and Edwin Gnos. 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. This work was supported by the Swiss National Science Foundation (SNF).
References:
Akhmadaliev S. et al. 2013. Nuclear Instruments and Methods in Physic B 294:5-10
Ammon K. et al. 2008. Meteoritics and Planetary Science 43:685-699
Ammon K. et al. 2011. Meteoritics and Planetary Science 46:785-792
Bini A. et al. 2009. Die Schweiz während des letzteiszeitlichen Maximums (LGM), Map 1:500000. Bern: Swiss Federal Office of Topography
Hofmann B. et al. 2009. Meteoritics and Planetary Science 44:187-199
Jörg G. et al. 2012. Geochimica et Cosmochimica Acta 88:51-65
Kutschera W. et al. 1992. Radiocarbon 34(3):436-446
Lavielle B. et al. 1999. Earth and Planetary Science Letters 170:93-104
Merchel S. and Herpers U. 1999. Radiochimica Acta 84:215-219
Smith T. et al. 2017. Meteoritics and Planetary Science 52:2241-2257
Keywords: AMS, cosmogenic nuclide, meteorite
  • Lecture (Conference)
    Annual Meeting of the Chinese Geoscience Union (CGU), 21.-24.10.2018, Beijing, China

Publ.-Id: 27808 - Permalink


Three-Dimensional Composition and Electric Potential Mapping of III−V Core−Multishell Nanowires by Correlative STEM and Holographic Tomography
Wolf, D.; Hübner, R.; Niermann, T.; Sturm, S.; Prete, P.; Lovergine, N.; Büchner, B.; Lubk, A.;
The nondestructive characterization of nanoscale devices, such as those based on semiconductor nanowires, in terms of functional potentials is crucial for correlating device properties with their morphological/materials features, as well as for precisely tuning and optimizing their growth process. Electron holographic tomography (EHT) has been used in the past to reconstruct the total potential distribution in three dimension but hitherto lacked a quantitative approach to separate potential variations due to chemical composition changes (mean inner potential, MIP) and space charges. In this letter, we combine and correlate EHT and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) tomography on an individual ⟨111⟩ oriented GaAs-AlGaAs core-multishell nanowire (NW). We obtain excellent agreement between both methods in terms of the determined Al concentration within the AlGaAs shell, as well as thickness variations of the few nanometer thin GaAs shell acting as quantum well tube. Subtracting the MIP determined from the STEM tomogram enables us to observe functional potentials at the NW surfaces and at the Au-NW interface, both ascribed to surface/interface pinning of the semiconductor Fermi level.
Keywords: GaAs-AlGaAs, III−V nanowire, 3D elemental mapping, functional potential, quantum well tube, tomography, holography

Publ.-Id: 27807 - Permalink


Terahertz pump-induced anisotropy and nonlinear susceptibility in graphene
Schneider, H.; König-Otto, J. C.; Mittendorff, M.; Winzer, T.; Kadi, F.; Malic, E.; Knorr, A.; Wang, Y.; Belyanin, A.; Pashkin, A.; Helm, M.; Winnerl, S.;
We report on investigations of the carrier dynamics in graphene close to the Dirac point by nonlinear terahertz spectroscopy. At terahertz frequencies and low temperatures, optical-phonon scattering is suppressed. In this case, the decay of the pump-induced anisotropy in the carrier distribution is observed to be very slow, long as several ps, which is theoretically explained by non-collinear Coulomb scattering. In Landau-quantized graphene, degenerate four-wave mixing experiments in resonance to the lowest Landau level transition allow us to investigate the induced coherent polarization and to compare its dependence on THz field strength and B-field detuning with theoretical expectations.
Keywords: graphene, nonlinear terahertz spectroscopy, nonlinear susceptibility, pump-probe
  • Poster
    34-th International Conference on the Physics of Semiconductors (ICPS 2018), 29.07.-03.08.2018, Montpellier, Frankreich

Publ.-Id: 27805 - Permalink


High-performance and room-temperature QWIPs & terahertz spectroscopy
Schneider, H.;
The topic of this seminar talk is high-performance and room-temperature quantum well photodetectors and terahertz spectroscopy.
Keywords: quantum well infrared photodetector, terahertz spectroscopy
  • Lecture (others)
    Seminarvortrag, Yunnan University, 03.05.2018, Kunming, China

Publ.-Id: 27804 - Permalink


Nonlinear THz spectroscopy of graphene and GaAs quantum wells using a free-electron laser
Schneider, H.;
This talk reviews some recent experiments using FEL-based intense narrow-band terahertz fields, in particular pump-induced optical anisotropy and nonlinear four-wave mixing in graphene, and dressing of excitons, exciton-polaritons, and intersubband transitions in GaAs quantum wells.
Keywords: nonlinear terahertz spectroscopy, graphene, interaubband, exciton
  • Invited lecture (Conferences)
    The 9th International Symposium on Ultrafast Phenomena and Terahertz Waves (ISUPTW 2018), 23.-26.04.2018, Changsha, China
  • Invited lecture (Conferences)
    International Conference on "Synchrotron and Free electron laser Radiation: generation and application" (SFR-2018), Budker Institute of Nuclear Physics, 25.-28.06.2018, Novosibirsk, Russische Föderation

Publ.-Id: 27803 - Permalink


Nonlinear THz free-electron laser spectroscopy of graphene and GaAs quantum wells
Schneider, H.;
This talk reviews some recent experiments on graphene and on GaAs quantum wells using FEL-based strong THz fields.
In graphene, we have investigated the pump-induced anisotropy of the carrier distribution upon excitation with linearly polarized light. Since optical-phonon scattering is suppressed at THz frequencies and low temperatures, we observe the decay of this anisotropy to be very slow, as long as several ps, which is theoretically explained by non-collinear Coulomb scattering. We also report on degenerate four-wave mixing experiments in Landau-quantized graphene to investigate the induced coherent polarization. In GaAs quantum wells, intense narrow-band THz fields are exploited for dressing elementary electronic excitations. We will address THz-induced dressing of excitons, exciton-polaritons, and intersubband transitions.
Keywords: Graphene, intersubband, nonlinear terahertz spectroscopy
  • Lecture (others)
    Seminarvortrag, University of California at Santa Barbara (UCSB), 05.02.2018, Santa Barbara, USA
  • Lecture (others)
    Physikalisches Kolloquium der TU Chemnitz, 13.06.2018, Chemnitz, Deutschland
  • Lecture (others)
    Seminar, Chengdu Campus of CAEP, 23.07.2018, Chengdu, China

Publ.-Id: 27802 - Permalink


Terahertz orientational relaxation and phase relaxation in graphene
Schneider, H.; König-Otto, J. C.; Mittendorff, M.; Winzer, T.; Kadi, F.; Malic, E.; Knorr, A.; Wang, Y.; Belyanin, A.; Pashkin, A.; Helm, M.; Winnerl, S.;
We report on investigations of the carrier dynamics in graphene close to the Dirac point by nonlinear terahertz spectroscopy. At terahertz frequencies and low temperatures, optical-phonon scattering is suppressed. In this case, the decay of the pump-induced anisotropy in the carrier distribution is observed to be very slow, long as several ps, which is theoretically explained by non-collinear Coulomb scattering. In Landau-quantized graphene, degenerate four-wave mixing experiments in resonance to the lowest Landau level transition allow us to investigate the induced coherent polarization and to compare its dependence on THz field strength and B-field detuning with theoretical expectations.
Keywords: graphene, nonlinear terahertz spectroscopy, nonlinear susceptibility, four-wave mixing, pump-probe
  • Lecture (Conference)
    SPIE Photonics West, Symposium on "Ultrafast Phenomena and Nanophotonics XXII", 27.01.-01.02.2018, San Francisco, USA

Publ.-Id: 27801 - Permalink


Halbleitertechnik im Osten der Republik
Skorupa, W.;
Eingeladener Vortrag anlässlich des Workshops zum 60. Gründungsjubiläum des Institutes für Halbleitertechnik an der Universität Stuttgart mit Bezug zur Ionenstrahlphysik und -technologie am Forschungsstandort Dresden-Rossendorf, jetzt Helmholtzzentrum Dresden-Rossendorf
Keywords: Halbleitertechnik, Chiptechnologie, DDR, Geschichte, Ionenstrahlphysik, Ionenstrahltechnologie
  • Invited lecture (Conferences)
    Workshop anlässlich des 60. Jahrestages des Institutes für Halbleitertechnik an der Universität Stuttgart, 01.08.2018, Stuttgart, Deutschland

Publ.-Id: 27800 - Permalink


Incorporating analytical errors in log-ratio based compositional discriminant analysis
Pospiech, S.; Tolosana-Delgado, R.;
Uncertainties in the measurement of the geochemical composition of various sample materials are rarely included for statistical analyses of the data.
In case of log-ratio methods, incorporating errors in the analysis has even not yet been done, up to the authors' knowledge.
Many calibration procedures provide relative cell-wise errors, which can be conveniently combined to deliver error assessments for any set of log-ratios.
In this contribution we incorporate all these errors in estimates of the mean vector and covariance matrix of the data on a particular log-ratio.
Thanks to the linear/bilinear relation between mean/covariance estimates among different log-ratio representations, such error-integrating estimates are affine equivariant.
These means and covariances are the building blocks of many statistical analysis.
Here we focus on developing an error-integrating Fisher rule, but the methodology can be readily applied to other linear models with compositional variables, like regression or ANOVA.
In general, results show that the incorporation of errors produce a more conservative (and honest) assessment of the discrimination direction and separability of the subpopulations considered.
The application of using cell-wise errors and its impact on interpretation of results will be shown by case studies of geochemical composition of tea plants in relation to geological source rock.
  • Open Access LogoContribution to proceedings
    IAMG2018 19th Annual Conference, 02.-08.09.2018, Olomouc, Czech Republic
    Prodeedings of IAMG2018

Publ.-Id: 27799 - Permalink


All-optical quantum thermometry based on spin-level cross-relaxation and multicenter entanglement under ambient conditions in SiC
Anisimov, A. N.; Soltamov, V. A.; Breev, I. D.; Babunts, R. A.; Mokhov, E. N.; Astakhov, G. V.; Dyakonov, V.; Yakovlev, D. R.; Suter, D.; Baranov, P. G.;
All-optical thermometry technique based on the energy level cross-relaxation in atomic-scale spin centers in SiC is demonstrated. This technique exploits a giant thermal shift of the zero-field splitting for centers in the triplet ground state, S=1, undetected by photoluminescence (so called “dark” centers) coupling to neighbour- ing spin-3/2 centers which can be optically polarized and read out (“bright” centers), and does not require radiofrequency fields. EPR was used to identify defects. The width of the cross-relaxation line is almost an order of magnitude smaller than the width of the excited state level-anticrossing line, which was used in all-optical ther- mometry and which can not be significantly reduced since determined by the lifetime of the excited state. With approximately the same temperature shift and the same sig- nal intensities as for excited state level-anticrossing, cross-relaxation signal makes it possible to increase the sensitivity of the temperature measurement by more than an order of magnitude. Temperature sensitivity is estimated to be approximately 10 mK/Hz1/2 within a volume about 1 μ3, allocated by focused laser excitation in a scanning confocal microscope. Using cross-relaxation in the ground states of “bright” spin-3/2 centers and “dark” S=1 centers for temperature sensing and ground state level anti-crossing of “bright” spin-3/2 centers an integrated magnetic field and tempera- ture sensor with submicron space resolution can be implemented using the same spin system. The coupling of individually addressable “bright” spin-3/2 centers connected by a chain of “dark” S=1 spins, could be considered in quantum information pro- cessing and multicenter entanglement under ambient conditions.
Keywords: Defects, Quantum Technology, Thermometry, Silicon Carbide

Publ.-Id: 27798 - Permalink


On-Chip THz spectrometer for bunch compression fingerprinting at fourth-generation light sources
Laabs, M.; Neumann, N.; Green, B.; Awari, N.; Deinert, J.; Kovalev, S.; Plettemeier, D.; Gensch, M.;
In this letter we present the layout and demonstrate the performance for an integrated millimeter-scale on-chip THz spectrometer. The device is based on eight Schottky-Diode detectors which are combined with narrow-band THz antennas, thereby enabling the simultaneous detection of eight frequencies in the THz range on one chip. The size of the active detector area matches the focal spot size of superradiant THz radiation utilized in bunch compression monitors of modern linear electron accelerators. The 3 dB bandwidth of the on-chip Schottky-Diode detectors is less than 10% of the center frequency and allows pulse-resolved detection at up to 5 GHz repetition rates. The performance of a first prototype device is demonstrated at a repetition rate of 100 kHz at the quasi-cw SRF linear accelerator ELBE operated with electron bunch charges between few pC and 100 pC.

Publ.-Id: 27797 - Permalink


Expression of Glypican-3 is an Independent Prognostic Biomarker in Primary Gastro-Esophageal Adenocarcinoma and Corresponding Serum Exosomes
Rahbari, M.; Pecqueux, M.; Aust, D.; Stephan, H.; Tiebel, O.; Chatzigeorgiou, A.; Tonn, T.; Rao, V.; Ziegler, N.; Greif, H.; Lin, K.; Weitz, J.; Rahbari, N. N.; Kahlert, C.;
Exosomes are nano-sized membranous vesicles of endosomal origin that carry nucleic acids, lipids and proteins. The cargo of exosomes is cell origin specific and the release of these exosomes and uptake by an acceptor cell is seen as a vital element of cell-cell communication. Here, we sought to investigate the diagnostic and prognostic value of the expression of glypican 3 (GPC3) on primary gastro-esophageal adenocarcinoma (GEA) tissue (tGPC3) and corresponding serum exosomes (eGPC3). Circulating exosomes were extracted from serum samples of 49 patients with GEA and 56 controls. Extracted exosomes were subjected to flow cytometry for the expression of eGPC3 and GPC3 expression on primary GEA tissue samples was determined by immunohistochemistry and correlated to clinicopathological parameters. We found decreased eGPC3 levels in GEA patients compared to healthy controls (p < 0.0001) and high tGPC3 expression.
This was significantly associated with poor overall survival (high vs. low eGPC3: 87.40 vs. 60.93 months, p = 0.041, high vs. low tGPC3: 58.03 vs. 84.70 months, p = 0.044). Cox regressional analysis confirmed tGPC3 as an independent prognostic biomarker for GEA (p = 0.02) and tGPC3 expression was validated in two independent cohorts. Our findings demonstrate that eGPC3 and tGPC3 can be used as potential diagnostic and prognostic biomarkers for GEA.
Keywords: Exosomes, Gastro-esophageal adenocarcinoma, Glypican-3, Prognostic biomarker, diagnostic biomarker

Publ.-Id: 27796 - Permalink


Detailed study of the Fermi surfaces of the type-II Dirac semimetallic candidates XTe2 (X = Pd, Pt)
Zheng, W.; Schönemann, R.; Aryal, N.; Zhou, Q.; Rhodes, D.; Chiu, Y.-C.; Chen, K.-W.; Kampert, E.; Förster, T.; Martin, T. M.; Mccandless, G. T.; Chan, J. Y.; Manousaki, E.; Balicas, L.;
We present a detailed quantum oscillatory study on the Dirac type-II semimetallic candidates PdTe2 and PtTe2 via the temperature and the angular dependence of the de Haas–van Alphen and Shubnikov–de Haas effects. In high-quality single crystals of both compounds, i.e., displaying carrier mobilities between 103 and 104 cm2/ Vs, we observed a large nonsaturating magnetoresistivity which in PtTe2 at a temperature T = 1.3 K leads to an increase in the resistivity up to (5×104)% under a magnetic field μ0H = 62 T. These high mobilities correlate with their light effective masses in the range of 0.04 to 1 bare electron mass according to our measurements. For PdTe2 the experimentally determined Fermi surface cross-sectional areas show excellent agreement with those resulting from band structure calculations. Surprisingly, this is not the case for PtTe2, whose agreement between calculations and experiments is relatively poor even when electronic correlations are included in the calculations. Therefore, our study provides strong support for the existence of a Dirac type-II node in PdTe2 and probably also for PtTe2. Band structure calculations indicate that the topologically nontrivial bands of PtTe2 do not cross the Fermi level ɛF. In contrast, for PdTe2 the Dirac type-II cone does intersect ɛF, although our calculations also indicate that the associated cyclotron orbit on the Fermi surface is located in a distinct kz plane with respect to that of the Dirac type-II node. Therefore, it should yield a trivial Berry phase.

Publ.-Id: 27795 - Permalink


Experimental evidence for the microscopic mechanism of the unusual spin-induced electric polarization in GdMn2O5
Yahia, G.; Damay, F.; Chattopadhyay, S.; Baledent, V.; Peng, W.; Kim, S. W.; Greenblatt, M.; Lepetit, M.-B.; Foury-Leylekian, P.;
We report in this paper the temperature evolution of the magnetic structure of GdMn2O5, in the range 2–40 K, studied by neutron diffraction on an isotope-enriched powder. We detail a thorough analysis of the microscopic mechanisms needed to release the different magnetic frustrations that are at the origin of the polarization. In addition to the usual exchange-striction term, known to be at the origin of the polarization in this family, an additional exchange-striction effect between the Gd3+ and Mn3+ spins is found to be responsible for the very large polarization in the Gd compound.

Publ.-Id: 27794 - Permalink


Pressure-induced commensurate order in TbMn2O5 and DyMn2O5: Influence of rare-earth anisotropy and 3d-4 f exchange
Deutsch, M.; Peng, W.; Foury-Leylekian, P.; Baledent, V.; Chattopadhyay, S.; Fernandez-Diaz, M. T.; Hansen, T. C.; Forget, A.; Colson, D.; Greenblatt, M.; Lepetit, M.-B.; Petit, S.; Mirebeau, I.;
The magnetic structure of TbMn2O5 and DyMn2O5 multiferroics has been studied by high-pressure neutron diffraction in a large pressure range up to 6.6 GPa. In both cases, we observe a pressure-induced commensurate magnetic phase with propagation vector ( 1/2 0 1/2 ), growing with pressure at the expense of the ambient pressure phases. Being previously observed in YMn2O5 and PrMn2O5, this phase is most likely a generic feature of the RMn2O5 multiferroic family. A simple model is proposed to explain qualitatively the emergence of this pressure-induced phase. Differences between TbMn2O5 and DyMn2O5 behaviors at ambient and low pressures provide clues on the interaction scheme.

Publ.-Id: 27793 - Permalink


Probing the Jeff = 0 ground state and the Van Vleck paramagnetism of the Ir5+ ions in layered Sr2Co0.5Ir0.5O4
Agrestini, S.; Kuo, C.-Y.; Chen, K.; Utsumi, Y.; Mikhailova, D.; Rogalev, A.; Wilhelm, F.; Förster, T.; Matsumoto, A.; Takayama, T.; Takagi, H.; Haverkort, M. W.; Hu, Z.; Tjeng, L. H.;
We report a combined experimental and theoretical x-ray magnetic circular dichroism (XMCD) spectroscopy study at the Ir-L2,3 edges on the Ir5+ ions of the layered hybrid solid state oxide Sr2Co0.5Ir0.5O4 with the K2NiF4 structure. From theoretical simulation of the experimental Ir-L2,3 XMCD spectrum, we found a deviation from a pure Jeff = 0 ground state with an anisotropic orbital-to-spin moment ratio (Lx/2Sx = 0.43 and Lz/2S = 0.78). This deviation is mainly due to multiplet interactions being not small compared to the cubic crystal field and due to the presence of a large tetragonal crystal field associated with the crystal structure. Nevertheless, our calculations show that the energy gap between the singlet ground state and the triplet excited state is still large and that the magnetic properties of the Ir5+ ions can be well described in terms of singlet Van Vleck paramagnetism.

Publ.-Id: 27792 - Permalink


Sorption, redox reactions and (nano-)particle formation of uranium and other early actinides at mineral-water interfaces: Lessons (to be) learned from synchrotron methods
Scheinost, A. C.; Kvashnina, K. O.; Hennig, C.; Schmidt, M.; Marques Fernandes, M.;
The early actinides U, Np and Pu exhibit two to four different oxidation states within the oxic to anoxic regime of typical environmental systems, responsible for their rich and complex biogeochemistry. Due to their high surface area and catalytic activity, clay and iron oxide minerals play a crucial role in controlling the mobility of these radiotoxic elements in the environment. Understanding the underlying (geo-)chemical processes and reactions is of paramount importance for many applications from the design of nuclear waste repositories to the development of efficient remediation strategies for contaminated sites. The electronic and molecular structures of actinides, and their temporal evolution, can be studied in situ by a range of synchrotron methods, including high resolution absorption and emission spectroscopies (XES, RIXS, XANES, EXAFS), high resolution powder and single crystal X-ray diffraction and scattering (PDF) analysis, and surface sensitive techniques (CTR, RAXR). We recently upgraded The Rossendorf Beamline at ESRF to be able to apply all of these techniques to actinide samples. In this talk, I will present the different techniques and what we recently have learned about the geochemistry of uranium, neptunium and plutonium at the strongly dynamic surface of clay and Fe oxide minerals, including sorption, redox reactions, and formation of actinide Eigencolloids and of solid solutions.
Keywords: Uranium EXAFS XANES RIXS RAXR CTR Redox
  • Invited lecture (Conferences)
    URANIUM Biogeochemistry: Transformations, isotopes, and applications, 21.-26.10.2018, Ascona, Switzerland

Publ.-Id: 27791 - Permalink


Short-range quasistatic order and critical spin correlations in α-Ru1−xIrxCl3
Do, S.-H.; Lee, W.-J.; Lee, S.; Choi, Y. S.; Lee, K.-J.; Gorbunov, D. I.; Wosnitza, J.; Suh, B. J.; Choi, K.-Y.;
The magnetic ground states of the diluted α-Ru1−x IrxCl3 are systematically investigated by magnetization, specific heat, and muon spin rotation measurements. Introduction of moderate spin vacancies leads to a destabilization of the zigzag antiferromagnetic order towards a short-range ordered state. It is remarkable that the x = 0.2 sample located near a quantum critical point shows an extremely short correlation length of the magnitude of magnetic moments ζmag ∼ 1.2a (a = lattice spacing) and a power-law behavior of the magnetic susceptibility χ(T ) ∼ T−p below 14 K for μ0HIIab and below 30 K for μ0HIIc. Our work demonstrates that the α-Ru1−x IrxCl3 system hosts a short-range, quasistatic order characterized by critical spin correlations.

Publ.-Id: 27790 - Permalink


Synthesis and Pharmacological Evaluation of Identified and Putative Metabolites of the A₁ Adenosine Receptor Antagonist 8-Cyclopentyl-3-(3-fluoropropyl)-1-propylxanthine (CPFPX)
Holschbach, M. H.; Bier, D.; Sihver, W.ORC; Schulze, A.; Neumaier, B.
The A₁ adenosine receptor (A₁AR) antagonist [¹⁸F]cyclopentyl-3-(3-fluoropropyl)-1-propylxanthine ([¹⁸F]CPFPX), used in imaging human brain A₁ARs by PET, is stable in the brain but rapidly undergoes transformation into one major (M1) and several minor metabolites in blood. This report describes the synthesis of putative metabolites of CPFPX as standards for the identification of those metabolites.
Analysis by (radio)HPLC revealed that extracts of human liver microsomes incubated with n.c.a.[¹⁸F]CPFPX contained the major metabolite, M1, as well as radioactive metabolites corresponding to derivatives functionalized at the cyclopentyl moiety, but no N¹-despropyl species or metabolites resulting from functionalizations of the N³-fluoropropyl chain.
The putative metabolites displaced the binding of [³H]CPFPX to the A₁AR in pig brain cortex at Kᵢs between 1.9 and 380 nM and the binding of [³H]ZM 241385 to the A₂ᴀAR in pig striatum at Kᵢs greater than 180 nM. One metabolite, a derivative functionalized at the ω-position of the N¹-propyl chain, showed high affinity (Kᵢ 2 nM) to and very good selectivity (> 9000) for the A₁AR.

Publ.-Id: 27787 - Permalink


Code-to-code Comparison between ATHLET-CD and MELCOR for SBLOCA Severe Accident Scenario in Generic German PWR
Jobst, M.ORC; Kretzschmar, F.; Sánchez-Espinoza, V. H.; Wilhelm, P.
The evolution of a hypothetic SBLOCA severe accident scenario for a generic German PWR of type Konvoi is investigated by means of the two severe accident computer codes ATHLET-CD and MELCOR. The simulation results derived from the both codes are compared and possible reasons for deviations between the results are analyzed.
For the assessment of scenarios with core degradation, correct prediction of physical phenomena and timings, such as beginning of core degradation, time of relocation of molten core material to lower head or time of vessel failure, is of particular interest. Validation of the obtained simulation results against experimental data is very limited simply due to the fact of unavailability of full integral experiments, especially for the late in-vessel phase of severe accident scenarios. Therefore two equivalent plant models with similar geometry, initial and boundary conditions were build, one for ATHLET-CD 3.0A and one for the MELCOR 1.8.6 code. A 50 cm² cold leg SBLOCA scenario was selected for the code-to-code comparison. Due to the assumed multiple failures of safety systems, the scenario develops into a severe accident scenario with beginning of core melting approximately 3 h after beginning of the transient.
The general comparison of the main parameters between both codes shows that qualitatively good agreement is reached. Similar time spans until the start of core heat-up are predicted by both codes. Initiation of zircaloy oxidation and the total amount of produced hydrogen agree. During the late in-vessel phase more significant deviations are identified, e.g. in the process of relocation to lower head.
In a second calculation, the effectiveness of mobile pump injection to the primary circuit as additional accident management measure is investigated. The results obtained by both codes show concordantly that a commercial high power fire pump system can be applied to stop the progression of the accident, with only slight degradation of the absorber rods.
Keywords: PWR, Severe Accident, Accident Management Measures, ATHLET-CD, MELCOR
  • Contribution to proceedings
    12th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics, Operation and Safety (NUTHOS-12), 14.-18.10.2018, Qingdao, China
  • Lecture (Conference)
    12th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics, Operation and Safety (NUTHOS-12), 14.-18.10.2018, Qingdao, China

Publ.-Id: 27786 - Permalink


Synthesis, characterization and initial biological evaluation of [⁹⁹ᵐTc]Tc-tricarbonyl labeled DPA-α-MSH peptide derivatives for potential melanoma imaging
Gao, F.; Sihver, W.ORC; Bergmann, R.; Belter, B.; Bolzati, C.; Salvarese, N.; Steinbach, J.; Pietzsch, J.; Pietzsch, H.-J.
α-Melanocyte stimulating hormone (α-MSH) derivatives target the melanocortin-1 receptor (MC1R) specifically and selectively. In this study, the α-MSH derived peptide NAP-NS1 (Nle-Asp-His-D-Phe-Arg-Trp-Gly-NH₂) with and without linkers was conjugated with 5-(bis(pyridin-2-yl)methyl)amino)pentanoic acid (DPA-COOH) and labeled with [⁹⁹ᵐTc]Tc-tricarbonyl by two methods. With the one-pot method the labeling was faster than with the two-pots method, however obtaining similarly high yields. Negligible transchelation and high stability in physiological solutions was determined for the [⁹⁹ᵐTc]Tc-tricarbonyl-peptide conjugates. Coupling an ethylenglycol (EG)-based linker increased the hydrophilicity. The peptide derivatives displayed high binding affinity in murine B16F10 melanoma cells as well as in human MeWo and TXM13 melanoma cell homogenate. Preliminary in vivo studies with one of the [⁹⁹ᵐTc]Tc-tricarbonyl-peptide conjugates showed good stability in blood and both a renal and hepatobiliary excretion. Biodistribution was performed on healthy rats to gain initial insights into the potential relevance of the ⁹⁹ᵐTc-labeled peptides for in vivo imaging.
Keywords: melanocortin-1 receptor, α-MSH analogs, peptides, [⁹⁹ᵐTc]Tc-tricarbonyl labeling, radiopharmaceuticals

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Publ.-Id: 27785 - Permalink


The Potential of Reflectance and Laser Induced Luminescence Spectroscopy for Near-Field Rare Earth Element Detection in Mineral Exploration
Lorenz, S.; Beyer, J.; Fuchs, M.; Seidel, P.; Turner, D.; Heitmann, J.; Gloaguen, R.;
New energy, transport, computer and telecommunication technologies require an increasing supply of rare earth elements (REEs). As a consequence, adequate and robust detection methods become essential for the exploration and discovery of new deposits, the improved characterization of existing deposits and the future recycling of today’s high-tech products. Within this paper, we investigate the potential of combining passive reflectance (imaging and point sampling) with laser stimulated luminescence (point sampling) spectroscopic measurements across the visible, near and shortwave infrared for REE detection in non-invasive near-field mineral exploration. We analyse natural REE-bearing mineral samples from main REE-deposits around the world and focus on challenges such as the discrimination of overlapping spectroscopic features and the influence of the mineral type on detectability, feature position and mineral matrix luminescence. We demonstrate that the cross-validation of results from both methods increases the robustness and sensitivity, provides the potential for semi-quantification and enables the time- and cost-efficient detection of economically important REE, including Ce, Pr, Nd, Sm, Eu, Dy, Er, Yb and potentially also Ho and Tm.
Keywords: laser induced luminescence spectroscopy; reflectance spectroscopy; hyperspectral imaging; laser-induced fluorescence; photoluminescence; rare earth elements

Publ.-Id: 27784 - Permalink


Exploring pitfalls of 64Cu‑labeled EGFR‑targeting peptide GE11 as a potential PET tracer
Striese, F.; Sihver, W.ORC; Gao, F.; Bergmann, R.; Walther, M.; Pietzsch, J.; Steinbach, J.; Pietzsch, H.-J.
The epidermal growth factor receptor (EGFR) represents an important molecular target for both radiotracer-based diagnostic imaging and radionuclide therapy of various cancer entities. For the delivery of radionuclides to the tumor, peptides hold great potential as a transport vehicle. With respect to EGFR, the peptide YHWYGYTPQNVI (GE11) has been reported to bind the receptor with high specificity and affinity. In the present study, GE11 with β-alanine (β-Ala-GE11) was conjugated to the chelating agent p-SCN-Bn-NOTA and radiolabeled with ⁶⁴Cu for the first radio pharmacological evaluation as a potential probe for positron emission tomography (PET)-based cancer imaging. For better water solubility, an ethylene glycol-based linker was introduced between the peptide’s N terminus and the radionuclide chelator. The stability of the ⁶⁴Cu-labeled peptide conjugate and its binding to EGFR-expressing tumor cells was investigated in vitro and in vivo, and then compared with the ⁶⁴Cu-labeled EGFR-targeting antibody conjugate NOTA-cetuximab. The GE11 peptide conjugate [⁶⁴Cu]Cu-NOTA-linker-β-Ala-GE11 ([⁶⁴Cu]Cu-1) was stable in a buffer solution for at least 24 h but only 50% of the original compound was detected after 24 h of incubation in human serum. Stability could be improved by amidation of the peptide’s C terminus (β-Ala-GE11-NH₂ (2)). Binding assays with both conjugates, [⁶⁴Cu]Cu-1 and [⁶⁴Cu]Cu-2, using the EGFR-expressing tumor cell lines A431 and FaDu showed no specific binding. A pilot small animal PET investigation in FaDu tumor-bearing mice revealed only low tumor uptake (standard uptake value (SUV) < 0.2) for both conjugates. The best tumor-to-muscle ratio determined was 3.75 for [⁶⁴Cu]Cu-1, at 1 h post injection. In conclusion, the GE11 conjugates in its present form are not suitable for further biological investigations, since they presumably form aggregates.
Keywords: Epidermal growth factor receptor, ⁶⁴Cu-labeled peptide conjugates, Molecular imaging, Receptor tyrosine kinases, Positron emission tomography

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  • Secondary publication expected

Publ.-Id: 27783 - Permalink


The electronic structure and band interface of cesium bismuth iodide on a titania heterostructure using hard X-ray spectroscopy
Phuyal, D.; Jain, S. M.; Philippe, B.; Johansson, M. B.; Pazoki, M.; Kullgren, J.; Kvashnina, K. O.; Klintenberg, M.; Johansson, E. M. J.; Butorin, S. M.; Karis, O.; Rensmo, H.;
Bismuth halide compounds as a non-toxic alternative are increasingly investigated because of their potential in optoelectronic devices and their rich structural chemistry. Hard X-ray spectroscopy was applied to the ternary bismuth halide Cs3Bi2I9 and its related precursors BiI3 and CsI to understand its electronic structure at an atomic level. We specifically investigated the core levels and valence band using X-ray photoemission spectroscopy (PES), high-resolution X-ray absorption (HERFD-XAS), and resonant inelastic X-ray scattering (RIXS) to get insight into the chemistry and the band edge properties of the two bismuth compounds. Using these element specific X-ray techniques, our experimental electronic structures show that the primary differences between the two bismuth samples are the position of the iodine states in the valence and conduction bands and the degree of hybridization with bismuth lone pair (6s2) states. The crystal structure of the two layered quasiperovskite compounds plays a minor role in modifying the overall electronic structure, with variations in bismuth lone pair states and iodine band edge states. Density Functional Theory (DFT) calculations are used to compare with experimental data. The results demonstrate the effectiveness of hard X-ray spectroscopies to identify element specific bulk electronic structures and their use in optoelectronic devices

Publ.-Id: 27782 - Permalink


Sensitivity control of carbon nanotube based piezoresistive sensors by drain-induced barrier lowering
Böttger, S.ORC; Wagner, C.ORC; Lorkowski, F.ORC; Hartmann, M.ORC; Schuster, J.ORC; Hermann, S.
The superior performance of membrane-based carbon nanotube (CNT) sensors showing maximum gauge factors of up to 800 is analyzed by a device study combining technological and theoretical approaches. Drain-induced barrier lowering (DIBL) is found to contribute significantly to this high sensitivity. A high subthreshold voltage roll-off of (750±200) mV⋅V−1 and degradation of subthreshold swing is observed even for channel length of 200 nm. The piezoresistive behavior of the CNT sensor running in the DIBL regime is shown as a complex and input-voltage dependent interplay of strain-dependent Fowler-Nordheim tunneling and the intrinsic thermionic resistance change. We show, that this interplay can be controlled by the applied bias voltages 𝑉GS and 𝑉DS in such a way, that the overall sensitivity is enhanced up to 150 % with respect to the intrinsic effect. The control of the sensitivity via 𝑉DS is enabled by the DIBL effect, which appears for our CNT device at remarkably long CNT-channels.
The experimental findings are retraced by a simplified transport model, which combines a numerical device solver with an electronic model for strained carbon nanotube based field-effect transistors (CNT-FETs) covering thermionic as well as tunneling contributions. Strain dependent tunneling through the Schottky barriers (SBs) appears to be the key contribution to the strain sensitivity in our model. From the model device characteristics have been derived which reproduce the experimental findings emphasizing the significance of tunneling processes in combination with DIBL effects for the superior strain sensitivity of our device.
Keywords: carbon nanotube, CNT-FET, piezoresistive sensor, piezoresistive effect, DIBL, transport modeling

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  • Secondary publication expected from 08.06.2020

Publ.-Id: 27781 - Permalink


Investigation of upstream and downstream flow conditions in a swirling inline fluid separator – experiments with a wire-mesh sensor and CFD studies
Sahovic, B.; Atmani, H.; Wiedemann, P.; Schleicher, E.; Legendre, D.; Climent, E.; Zamanski, R.; Pedrono, A.; Hampel, U.ORC
Wire-mesh sensors have been developed to measure gas-liquid distributions in two-phase flows at high speed. In a wire-mesh sensor, a wire electrode grid is formed in the flow cross-section by wires running in two planes of a small axial distance. Its functional principle is based on the measurement of either electrical conductivity (conductivity wire-mesh sensor) or relative permittivity (capacitance wire-mesh sensor) in the electrode crossings. Repeated scanning gives high speed sequences of cross-sectional phase indicator distributions. The sampling frequency can be very high. Thus, for a wire- mesh sensor with 2 × 16 wire electrodes (16 × 16 crossings or image pixel in a square cross-section) 10,000 frames per second can be scanned. The high acquisition speed together with the small wire spacing of typically 3 to 4 mm allows to image gas bubbles in many slices, such that the size and shape of the bubbles and the interfacial area can be resolved, but only in case of very large bubbles. The technical challenge of wire-mesh sensor imaging is the high amount of data, which need to be analyzed by automated computer algorithms.
We used the wire-mesh sensor to study the flow conditions upstream a swirling device, which is used in the oil and gas industry as a separator. Our particular objective was the analysis of the correlation of upstream flow patterns with the shape of the swirling gas cores downstream the swirl. The upstream flow regimes depend on the gas and liquid superficial velocities and can range from bubble flow, via churn flow towards annular flow in vertical pipe orientation. The flow pattern and especially its transition have an impact on the shape and interface stability of the swirling gas core downstream. Hence the wire-mesh data can be used as a predictor for expected hollow vortex variations and can be used for automatic control of the swirling device. To assess the relationship between wire-mesh data and vortex shape we used a high-speed camera to record the downstream interface development at 200 Hz frame rate. As automatic control requires a good process model we intend to use an original computational fluid dynamics (CFD) coupling a Volume-of-Fluid (VoF) method for interface resolution and an Immersed Boundary Method (IBM) for the separator description. For that we performed first CFD studies which give key indications of required model improvements and future numerical research work.
Keywords: Computational fluid dynamics, gas-liquid flow, inline flow splitter, swirling element, wire-mesh sensor
  • Lecture (Conference)
    9th World Congress on INDUSTRIAL PROCESS TOMOGRAPHY, 02.-06.09.2018, Bath, England

Publ.-Id: 27780 - Permalink


Comparative study of the effects of seven lanthanides onto 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 these elements are mainly excreted with urine, we investigated the effect of Ln in concentrations of 10⁻⁹ – 10⁻³ M on normal rat kidney cells (NRK-52E) and human embryonal kidney cells (HEK-293) after 24 and 48 h, respectively. Cell viability was measured using the XTT test and cell morphology was studied with light microscopy as well as fluorescence microscopy after immuno-chemical staining. Solubility of the Ln in the cell culture medium was determined with ICP-MS and Ln speciation was investigated using TRLFS as well as thermodynamic modelling.
The results from cell culture experiments demonstrate that the effect of Ln onto the cell viability are concentration- and time-dependent as well as cell line- and element-specific. Dose-response curves of all Ln reveal no cytotoxicity up to 10⁻⁴ M, whereas higher concentrations cause gradual loss of cell viability in both cell lines. Effective concentrations, for which cell viability was reduced to 50 % (EC50), were calculated. In general, first and last elements of the Ln family affect the cell viability more than Ln in the middle of the series. However, Ce exhibits the significantly strongest effect of all Ln. Besides the loss of cell viability, exposed cells undergo morphological changes like rounding and shrinking prior to cell death. Comparing both cell lines reveals NRK-52E being significantly more sensitive to Ln exposure than HEK-293.
ICP-MS measurements of Ln supplemented cell culture medium after filtration through 0.45 μm filters demonstrate that the Ln are 100 % soluble. Furthermore, TRLFS results reveal that Ln speciation in the cell culture medium is most probably dominated by a complex species formed with a protein from FBS. Due to a huge lack of complex formation and solubility constants of Ln with constituents from cell culture media as well as the unknown and variable composition of FBS, thermodynamic modelling failed to reproduce the experimental results and predicts a speciation dominated by several carbonate and phosphate species instead.
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 can contribute to the improvement of current risk assessment for Ln in the human body.
Keywords: lanthanides, mammalian kidney cell
  • Poster
    10th International Conference on f-Elements (ICFE-10), 03.-06.09.2018, Lausanne, Schweiz

Publ.-Id: 27779 - Permalink


Investigation of structural models for O-Y and O-Y-Ti clusters in bcc Fe: A DFT study
Vallinayagam, M.; Posselt, M.; Faßbender, J.;
Six different structural models for atomic clusters in bcc Fe are investigated by density functional theory (DFT) calculations. Results for clusters with identical numbers of constituents (O, Y, Ti, and vacancies) are compared. It is found that the data on the stability or energetics of the relaxed clusters are comparable although their atomic configurations are often different. This contradicts the prevailing opinion in the related theoretical literature that favors the so-called structure matching model. In all studied cases, the absolute value of the total binding energy per cluster constituent becomes lower if Y is partially replaced by Ti. Therefore the driving force for the growth of O–Y clusters should be higher than that of O–Y–Ti clusters. This may be correlated with the experimental observation that the presence of Ti leads to a reduction of the size of the oxide clusters in nanostructured ferritic alloys and to a higher dispersion. Not only cage-like clusters but also clusters with oxygen in the center (cage) are investigated. In the absence of Ti, clusters with oxygen in the center attain more stability that cage-like clusters and the opposite holds for clusters with Ti. It is also shown that adding O atoms to cage-like clusters leads to structures with O in the center. In the present comprehensive DFT study only clusters with dimensions below 1 nm could be treated. This is still below or close to the limit of the experimental resolution of methods allowing for a simultaneous determination of atomic structure and composition of the clusters. These small clusters may be considered as nuclei for further structural evolution and growth during which a selection of the most favored cluster structures could occur.
Keywords: First-principle calculations, Atomic clusters in bcc Fe, Nanostructures ferritic

Publ.-Id: 27778 - Permalink


Microreactor Studies for Efficient Organic Oxidation Processes
Willms, T.; Kryk, H.; Hampel, U.;
The industrially important partial oxidation of hydrocarbons is frequently characterized by low conversions and yields, which are mostly related to mass and heat transfer problems. Due to the reaction conditions, such processes include also important safety risks and are still not sufficiently investigated. To study the influence of the process parameters on the product selectivity, a lab facility including a silicon-coated micro reactor of stainless steel has been developed and constructed. Due to its modular construction (e.g. replaceable capillary), it permits for the first time to perform catalyzed and non-catalyzed oxidations of hydrocarbons with oxygen as a two-phase process in a capillary reactor in a wide range of residence times (some mins to 24 h), temperatures and pressures.
As an example the oxidation of isobutane to tertiary butyl hydroperoxide (TBHP) is studied. TBHP, as an intermediate for the production of propylene oxide according to the Oxirane process, is currently produced at industrial scale by the partial oxidation of liquid isobutane at temperatures of 120 to 140 °C and pressures of 25 to 37 bars at high residence times of up to 12 hours using bubble columns or bubble tray reactors. The conversion is limited to 35 to 50 % in order to obtain a TBHP selectivity of 50 to 60 % minimizing the formation of by-products, which are caused by the decomposition of the TBHP due to the complex reaction mechanism. Besides safety aspects, the high reaction enthalpy of the oxidation as well as heat and mass transport problems are further issues of this process. In the frame of the Helmholtz-Energy-Alliance project “Energy efficient chemical multiphase processes“, this reaction has been investigated for the first time as a Taylor-Flow process in a micro reactor with the aim to enhance the space-time yield of the process. The advantages of micro reactors are the high surface – volume ratio for an efficient heat transfer and the improved, nearly inherent, safety. This permits to investigate yet unexplored process windows, for instance within the explosive region of a reaction mixture.
The reaction has been studied varying flow rates, temperature, pressure, the molar ratio of the starting products using two different initiators, namely TBHP and di-t-butyl peroxide (DTBP). For all experiments the selectivity of the reaction products and the conversion of the reaction have been studied by sampling and analyzing the reaction by GC/MS. The use of TBHP as initiator increased the selectivity of the reaction for the target product TBHP. TBHP as initiator seems to give a better selectivity since at high temperatures as they are necessary for DTBP, the formation of propanone already becomes important which favours the decomposition of TBHP. The replacement of the initiator diluent water by decane resulted in a very fast reaction and the highest non-catalyzed isobutane conversion (~18 %) obtained ever in a microreactor but the selectivity of TBHP dropped to zero. In this experiment the coating of the capillary was damaged, so a more stable material will be necessary.
  • Poster
    6th International Congress on GREEN PROCESS ENGINEERING, 03.-06.06.2018, Toulouse, France
  • Catalysis Today (2019)
    Online First (2019) DOI: 10.1016/j.cattod.2019.05.008

Publ.-Id: 27777 - Permalink


Entwicklung und Synthese neuartiger fluorhaltiger Liganden zur molekularen Bildgebung des Adenosin A2B-Rezeptors im Gehirn mittels Positronen-Emissions-Tomographie
Lindemann, M.ORC
Der G-Protein-gekoppelte A2B-Rezeptor unterscheidet sich von den anderen Adenosinrezeptorsubtypen (A1, A2A, A3) durch die niedrige Affinität zu seinem endogenen Liganden Adenosin. Es wird beschrieben, dass der Rezeptor in verschiedenen pathologischen Prozessen, die durch eine erhöhte Adenosinkonzentration ausgezeichnet sind, wie beispielsweise bei Entzündungen (Inflammation), Hypoxie oder auch Krebs, eine wichtige Rolle spielt. Ziel dieser Arbeit ist die Entwicklung eines Fluor-18 markierten Radioliganden für die molekulare Bildgebung des A2B-Rezeptors im Organismus bzw. im speziellen des Gehirns mittels PET. Es soll damit der Einfluss des Rezeptors bei neurodegenerativen, neuroinflammatorischen und neuroonkologischen Erkrankungen untersucht werden. Die hier erstellte Arbeit basiert auf drei verschiedenen Leitstrukturen: den Pyrazinen (PA), Pyrimidinen (PYM) und Xanthinen (PXS). Für die ersten beiden Strukturklassen wurden zunächst die Leitverbindung und verschiedene fluorierte Derivate dargestellt. Für die Xanthine wurden zwei verschiedene Derivate synthetisiert. Alle Verbindungen wurden hinsichtlich ihrer Affinität und Selektivität gegenüber den Adenosinrezeptorsubtypen untersucht. Für die Klasse der Pyrazine wurde die bis dahin beste Verbindung PA51 ausgewählt. Trotz geringer Defizite gegenüber der Selektivität zu den anderen Adenosinrezeptorsubtypen, sollte PA51 zur Untersuchung der Hirngängigkeit der Verbindungsklasse genutzt werden. Nach erfolgreicher manueller Radiomarkierung und Transfer in eine automatisierte Radiosynthese, wurde die In-vivo-Gehirnaufnahme (Autoradiographie, PET) und der In-vivo-Metabolismus von [18F]PA51 in Mäusen untersucht. Bei In-vivo- Verteilungsstudien in Mäusen wurde eine homogene Verteilung des Radiotracers im Gehirn bestimmt. Des Weiteren wurden Gehirn- und Plasmaproben zu unterschiedlichen Zeitpunkten mit verschiedenen Methoden (RP-HPLC und MLC) auf enthaltene Radiometabolite untersucht. Nach 30 min p.i. konnten 70% an intaktem Radiotracer und ein Hauptradiometabolit mit einem Anteil von 30% im Gehirn nachgewiesen werden. Dessen Struktur konnte durch Synthese einer nichtradioaktiven Vergleichssubstanz aufgeklärt werden. Auf Grund dieser Ergebnisse ist die Substanzklasse der Pyrazine nicht geeignet als PET Radiotracer. Im Vergleich zu den Pyrazinen sind die Pyrimidinderivate in der Literatur als metabolisch stabiler beschrieben. Aus diesem Grund wurde zunächst die Leitverbindung PYM80, unter leichter Modifizierung der beschriebenen siebenstufigen Syntheseroute, dargestellt. Die fluorierte Verbindung PYM81 wurde über eine neu entwickelte sechsstufige Syntheseroute dargestellt. Diese weist eine hohe Affinität und Selektivität zum A2B-Rezeptor auf, weshalb PYM81 großes Potential für die Anwendung als neuartiger fluorierter Radioligand für die molekulare Darstellung des A2B-Rezeptors mittels PET besitzt. Als dritte Strukturklasse wurden zwei Xanthinderivate PXS7-1 und PXS7-2 dargestellt. Diese Strukturen basieren auf dem literaturbekannten, hochaffinen und selektiven Liganden PSB-603. Durch Reduzierung des sterisch anspruchsvollen Sulfonamidrestes sollten die molare Masse und die stark polaren Eigenschaften dieser Verbindungsklasse gesenkt werden. An Stelle der sterisch anspruchsvollen Sulfonamidreste sollten kleine Substituenten wie 4-Fluorpiperidin oder 4-Amino-2-fluorpyridin eingeführt werden. Diese beiden Verbindungen zeigten moderate Affinitäten und Selektivitäten gegenüber dem A2B-Rezeptor, weshalb weitere strukturelle Modifizierungen, zur Steigerung der Affinität und Selektivität zum A2B-Rezeptor, folgen sollen.

The G protein-coupled A2B receptor differs from other adenosine receptor subtypes (A1, A2A, A3) by its low affinity towards the endogenous ligand adenosine. It is suggested to be involved in various pathological processes accompanied by increased levels of adenosine, e.g. inflammation, hypoxia, and cancer. In this work, the development and synthesis of a fluorine-18 labelled radioligand with the particular aim for the imaging of the A2B receptor is described, to enable the investigation of the function and expression of A2B receptor in the organism and the influence of neurodegenerative, neuroinflammatory and neurooncological processes with PET. This work is based on three different lead structures: pyrazines (PA), pyrimidines (PYM), and xanthines (PXS). For the first two structure classes, the syntheses of the lead and different fluorinated compounds were performed. For the xanthines two different molecules were synthesized. The binding affinities for the different adenosine receptor subtypes were determined for each compound. To check the brain penetration of the pyrazine class, the best candidate so far, PA51 (although lacking selectivity), was labeled with 18-fluorine. After transfer of the manual radiolabeling procedure to the automated synthesis module, the in vivo brain uptake and the in vivo metabolism studies of [18F]PA51 in mice were performed. The in vivo brain uptake studies (brain sampling, autoradiography and PET) showed a homogeneous distribution of [18F]PA51. After different time intervals, brain and plasma samples were investigated by using different methods for metabolite analytics, showing only 70% of intact radiotracer in the brain 30 min p.i. A main brain radiometabolite with an amount of 30% after 30 min p.i. was structurally identified by use of a synthesized nonradioactive reference compound. In summary, this compound class is not suitable for the use as PET radiotracer, because of the fast metabolism of the compound and the formation of a brain-penetrable radiometabolite. The pyrimidine derivatives are described in literature as more metabolically stable as the pyrazines. For this compound class, the lead compound PYM80 was synthesized in a slightly modified seven-step synthesic route. A fluorinated derivative, PYM81, was synthesized over a newly developed six-step synthesic route. The compound showed good affinity and selectivity towards the A2B receptor. Therefor PYM81 has a high potential as a novel fluorinated radioligand for the molecular imaging of the A2B receptor with PET. As third class, xanthine derivatives were synthesized because of the highly affine and selective lead compound PSB-603. Due to the high molar mass and high polarity of these compounds the sulfonamide group was modified. Instead of this group, a small 4-amino-2-fluoropyridine or 4-fluoropiperidine groups was introduced to form derivatives PXS7-1 and PXS7-2. The compounds showed moderate affinities and selectivities for the A2B receptor. In conclusion, various fluorinated compounds were synthesized and showed different affinities and selectivities for the A2B receptor and its subtypes. Furthermore, the synthesis of additional fluorinated structures with the pyrimidine lead structure is required to enhance affinity and selectivity. For a first checkup of the brain uptake of this compound class, PYM81 needs to be radiolabeled with fluorine-18 because of the literature described higher metabolic stability in comparison to the pyrazine derivatives. PYM81 and the class of pyrimidines had a high potential as novel ligands for imaging the A2B receptor with PET in the brain.
Keywords: A2B-Rezeptor, 18-Fluor, Pyrazine, Pyrimidine, Xanthine, Pyrido[2,3-d]pyrimidin-2,4(1H,3H)dione, Positronen-Emissions-Tomographie
  • Doctoral thesis
    Universität Leipzig, 2018
    Mentor: Prof. Dr. P. Brust, Dr. B. Wenzel
    274 Seiten

Publ.-Id: 27776 - Permalink


Structural Properties of Al–O Monolayers in SiO₂ on Silicon and the Maximization of their Negative Fixed Charge Density
Hiller, D.; Göttlicher, J.; Steininger, R.; Huthwelker, T.; Julin, J.ORC; Munnik, F.; Wahl, M.; Bock, W.; Schoenaers, B.; Stesmans, A.; König, D.
Al₂O₃ on Si is known to form an ultra-thin interfacial SiO₂ during deposition and subsequent annealing, which creates a negative fixed charge (Qfᵢₓ) that enables field-effect passivation and low surface recombination velocities in Si solar cells. Various concepts were suggested to explain the origin of this negative Qfᵢₓ. In this study we investigate Al–O monolayers (MLs) from atomic layer deposition (ALD) sandwiched between deliberately grown/deposited SiO₂ films. We show that the Al-atoms have an ultra-low diffusion coefficient (~4×10⁻¹⁸ cm²/s at 1000°C), are deposited at a constant rate of ~5×10¹⁴ Al-atoms/cm²/cycle from the first ALD-cycle on, and are tetrahedral O-coordinated, since the adjacent SiO₂ imprints its tetrahedral near-order and bond length into the Al–O MLs. By variation of the tunnel-SiO₂ thickness and the number of Al–O MLs, we demonstrate that the tetrahedral coordination alone is not sufficient for the formation of Qfᵢₓ but that a SiO₂ /Al₂O₃ interface within a tunneling distance from the substrate must be present. The Al-induced acceptor states at these interfaces have energy levels slightly below the Si valence band edge and require charging by electrons from either the Si substrate or from Si/SiO₂ dangling bonds to create the negative Qfᵢₓ. Hence, tunneling imposes limitations for the SiO₂ and Al₂O₃ layer thicknesses. In addition, Coulomb repulsion between the charged acceptor states results in an optimum number of Al–O MLs, i.e., separation of both interfaces. We achieve maximum negative Qfᵢₓ of ~5×10¹² cm⁻² (comparable to thick ALD-Al₂O₃ on Si) with ~1.7 nm tunnel-SiO₂ and just 7 ALD-Al₂O₃ cycles (~8 Å) after optimized annealing at 850°C for 30 s. The findings are discussed in the context of a passivating, hole-selective tunnel contact for high-efficiency Si solar cells.
Keywords: atomic layer deposition, aluminum oxide, silicon oxide, negative fixed charge, silicon surface passivation, hole-selective contact

Publ.-Id: 27775 - Permalink


Modification of magnetic properties of Pt/Co/Pt Films by Ga+ Ion irradiation: Focused versus uniform irradiation
Sveklo, I.; Mazalski, P.; Jaworowicz, J.; Jamet, J.-P.; Vernier, N.; Mougin, A.; Ferre, J.; Kisielewski, M.; Zablotskii, V.; Bourhis, E.; Gierak, J.; Postava, K.; Fassbender, J.; Kanak, J.; Maziewski, A.;
30 keV Ga+ irradiation-induced changes of magnetic and magneto-optical properties of sputtered Pt/Co/Pt ultrathin trilayers films have been studied as a function of the ion fluence. Out-of-plane magnetic anisotropy states with enhanced magneto-optical e ects were evidenced for specific values of cobalt thickness and irradiation fluence. Results obtained after uniform or quasi-uniform focused ion beam irradiation on either out-of-plane or in-plane magnetized sputtered pristine trilayers are compared. Similar irradiation-induced magnetic changes are evidenced in quasi-uniformly focused ion beam or uniformly irradiated films, grown either by sputtering or molecular beam epitaxy. We discuss on plausible common mechanisms underlying the observed effects.
Keywords: ion irradiation, magnetism, perpendicular anisotropy

Publ.-Id: 27774 - Permalink


Processing of prompt gamma-ray timing data for proton range measurements at a clinical beam delivery
Werner, T.; Berthold, J.; Hueso-Gonzalez, F.; Koegler, T.; Petzoldt, J.; Roemer, K.; Richter, C.; Rinscheid, A.; Straessner, A.; Enghardt, W.; Pausch, G.;
In proton therapy, patients benefit from the precise deposition of the dose in the tumor volume due to the interaction of charged particles with matter. Currently, the determination of the proton stopping point in the patient’s body during the treatment is not a clinical standard. The resulting range uncertainties cause broad safety margins around the tumor, which limit the actual potential of proton therapy.To overcome this obstacle, different methods are under investigation aiming at the verification of the proton range in real time during the irradiation.One approach is the Prompt Gamma-ray Timing (PGT) method, where the range of the primary protons is derived from the time-resolved emission profiles (PGT spectra)of promptly emitted gamma rays, which are produced along the particle track in the tissue. After verifying this novel technique in an experimental environment but far away from treatment conditions, the translation of PGT into clinical practice is intended. Therefore, new hardware was extensively tested and characterized in a close-to-clinical scenario using short irradiation times of 20 ms and clinical beam currents of 2 nA. Experiments were carried out in the treatment room of the University Proton Therapy Dresden. A pencil beam scanning plan was delivered to a target without and with embedded cylindrical air cavities of down to 5 mm thickness. The induced range shifts of the proton beam due to the material variation could be identified from the corresponding PGT spectra, comprising events collected during the delivery of a whole layer. Additionally, an assignment of the PGT data to the individual pencil beam spots allowed a spot-wise analysis of the variation of the PGT distribution mean and width indicating range shifts induced by the different air cavities. Furthermore, the paper presents a comprehensive software framework which standardizes future PGT analysis methods and calibration algorithms for technical limitations that have been encountered in the presented clinical-like experiments
Keywords: proton therapy, range verification, prompt gamma ray timing

Publ.-Id: 27773 - Permalink


Measurement of interfacial wave dynamics in orbitally shaken cylindrical containers using ultrasound pulse-echo techniques
Horstmann, G. M.ORC; Wylega, M.; Weier, T.
We present a novel experiment on interfacial wave dynamics in orbitally shaken cylindrical vessels containing two- and three fluid layers. The experiment was designed as a hydrodynamical model for both aluminum reduction cells and liquid metal batteries to gain new insights into the rotational wave motion driven by the metal pad roll instability. Different options are presented to realize stable and measurable multi-layer stratifications. We introduce a new acoustic measurement procedure allowing to reconstruct wave amplitudes also in opaque liquids by tracking ultrasonic pulse echoes reflected on the interfaces. Measurements of resonance curves and phase shifts were conducted for varying interface positions. A strong influence of the top and bottom walls were observed, considerably reducing wave amplitudes and eigenfrequencies, when the interface is getting close. Finally, measured resonance curves were successfully compared with an existing forced wave theory that we extended to two-layer interfacial waves.
The comparison stresses the importance to carefully control the boundary condition at the contact line.
Keywords: Interfacial Waves,Liquid Metal Batteries, Aluminum Reduction Cells

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  • Secondary publication expected from 01.03.2020

Publ.-Id: 27772 - Permalink


Quaternary evolution of the Ploučnice River system (Bohemian Massif) based on fluvial deposits dated with optically stimulated luminescence and in situ-produced cosmogenic nuclides
Stor, T.; Schaller, M.; Merchel, S.ORC; Martínek, K.; Rittenour, T.; Rugel, G.; Scharf, A.
The Ploučnice River system, located in the central Bohemian Massif, is draining an area not covered by continental ice sheets, but instead archiving the fluvial deposits. The fluvial style changes from a high-energy braided to a long-bend meandering river in the upper terrace levels (36 to 31 m above present floodplain). The middle terrace levels (22 to 16 m above present floodplain) indicate a fluvial style changing from a high- to medium-energy braided river. In the lower terrace levels (13 to 7 m above present floodplain), the terrace deposits indicate high-energy braided to long-bend meandering river environments. To provide greater details on the timing of fluvial terrace formation, this study applied ²⁶Al and ¹⁰Be isochron burial and optically stimulated luminescence (OSL) dating methods to terraces of the Ploučnice River system. Terraces found at 36 m, 31 m and 16 m above present floodplain are dated with isochron burial dating whereas terraces 22 m, 13 m and 7 m above present floodplain are dated with OSL. Due to differences in age results between the two dating methods, we establish two different evolution models: The first is based on isochron burial and OSL dating and the second model is on the OSL dating results only. The time span represented by the river terraces remains unclear and varies from Eburonian to Eemian (1680 to 56 ka) or from Elsterian to Eemian (138 to 56 ka), respectively. The former river evolution model is based on tectonic activity at least since 1000 ka. Morphotectonic analysis recognized new lineaments of which the general direction corresponds with the main direction of the Ohře fault zone (NE to ENE-striking) and Lužice fault zone (NW-striking). Based on dated terrace ages of 1153 ka at 14 m above present floodplain and 138 ka at 19 m above present floodplain, we suppose a normal fault being active from at least 1153 ka. The second river evolution model assumes possible remobilization of clasts analyzed by isochron burial dating before their final deposition. From three OSL ages we calculated a mean incision rate and estimated an age of upper terrace levels at 34 m above present floodplain to be 248 ka (Saalian age). As remobilization of clasts in high-energy fluvial and glaciofluvial environments is very likely, age determination is challenging. Nevertheless, we interpret the terrace record in the Ploučnice River system as a product of Quaternary climatic changes influenced by tectonic processes.
Keywords: cosmogenic nuclides, optically stimulated luminescence, fluvial terraces, Bohemian Massif, Pleistocene, neotectonics

Publ.-Id: 27771 - Permalink


Evolution of structure and residual stress of a fcc/hex-AlCrN multi-layered system upon thermal loading revealed by cross-sectional X-ray nano-diffraction
Jäger, N.; Klima, S.; Hruby, H.; Julin, J.ORC; Keckes, J. F.; Mitterer, C.; Daniel, R.
Understanding the influence of process conditions and coating architecture on the microstructure and residual stress state of multi-layered coatings is essential for the development of novel thermally and mechanically stable coatings and requires advanced depth resolving characterization techniques. In this work, an arc-evaporated multi-layered coating, consisting of alternating Al₇₀Cr₃₀N and Al₉₀Cr₁₀N sublayers with an individual layer thickness between 120 nm and 380 nm, was investigated. The as-deposited state of the multi-layered coating and the state after vacuum annealing at 1000 ◦C for 30 min was studied along its cross-section by synchrotron X-ray nano-diraction using a beam with a diameter of 50 nm. The results revealed sublayers with alternating cubic and hexagonal phase, causing repeated interruption of the grain growth at the interfaces. The in-plane residual stress depth distribution across the coating thickness could be tuned in a wide range between pronounced compressive and slight tensile stress by combining the effects of the coating architecture and the modulated incident particle energy controlled by the substrate bias voltage ranging from −30 V to −250 V . This resulted in an oscillatory stress profile fluctuating between −2 GPa and −4.5 GPa or pronounced stress gradients with values between −4 GPa and 0.5 GPa. Finally, the decomposition routes of the metastable cubic Al₇₀Cr₃₀N phase could be controlled by the Al₉₀Cr₁₀N sublayers which acted as nucleation sites and governed the texture of the decomposition products as Cr₂N. The results demonstrate that the cross sectional combinatorial approach, relying on a sophisticated multi-layer architecture combining various materials synthesized under tailored conditions, allowed for resolving structural variations and stress proles in the individual layers within the complex architecture and pioneers the path for knowledge-based development of multi-layered coatings with predefined microstructure and a dedicated stress design.
Keywords: Coating, Multilayers, Microstructure design, Residual stress, X-ray nano-diffraction

Publ.-Id: 27770 - Permalink


64Cu-labeled bioconjugates based on triazacyclononane bifunctional chelators for radiopharmaceutical applications
Stephan, H.; Pant, K.; Joshi, T.; Zarschler, K.;
The development of multi-functional complexing agents for radiometal nuclides for nuclear medical application represents an intensively studied and rapidly evolving field of research. In this context, multifunctionalisable ligands that can form highly stable metal complexes are of particular interest. Their use enables the simultaneous introduction of radiolabels for nuclear imaging and vector molecules for pharmaceutical targeting.1-2
The tridentate azamacrocycle 1,4,7-triazacyclononane (TACN) is one such ligand that is of special interest for the development of bifunctional chelating agents (BFCAs), TACN forms stable Cu(II)complexes and the azamacrocyclic ligand structure can be easily modified. The introduction of further donor groups on the ligand scaffold, such as pyridine units, significantly enhances the thermodynamic stability as well as the kinetic inertness of the Cu(II) complexes formed. These ligands mostly form Cu(II) complexes with square-pyramidal and distorted octahedral coordination geometry.
Examples of target-specific conjugates (peptides, antibody fragments) and bio(nano)materials equipped with appropriate BFCAs based on TACN (Figure 1), suitable for labeling with 64Cu, will be presented. This enables tumor imaging and biodistribution studies of the materials over a period of days via positron emission tomography (PET).

1. E.W. Price, C. Orvig, Chem. Soc. Rev. 2014, 43, 260. 2. G. Singh, M.D. Gott, H.-J. Pietzsch, H. Stephan, Nuclearmedicine, 2016, 55, 41.
  • Lecture (Conference)
    43rd International Conference on Coordination Chemistry, 30.07.-04.08.2018, Sendai, Japan

Publ.-Id: 27769 - Permalink


Radiolabelled Nanomaterials for Imaging and Treatment of Cancer
Stephan, H.;
Novel nanomaterials (NMs) offer excellent prospects for the development of new non-invasive strategies of early diagnosis and efficient monitoring of therapeutic treatments. Thanks to their structural variability, which facilitates setting up the basic structure, modifying the periphery as well as creating complex structures, their properties allow being tailored to both diagnosis and treatment of diseases (theranostic approach) [1]. Provided with special functionalities, NMs allow the simultaneous application of different molecular imaging methods. In the field of cancer medicine, the combination of different imaging techniques such as nuclear (PET: positron emission tomography and SPECT: single-photon emission computed tomography) and near-infrared fluorescence (NIRF) imaging for tracking down tumors and metastases is particularly attractive [2].
This lecture will focus on the development and application of very small radiolabeled NMs, embracing polymeric structures [3] and inorganic particles [4]. Novel strategies will be discussed to develop stealth NMs capable of avoiding biomolecular corona formation and thus evading scavenging of NMs by the mononuclear phagocyte system, leading to eventual accumulation in the liver and spleen [5].

References
[1] J. A. Barreto, W. O’Malley, M. Kubeil, B. Graham, H. Stephan, L. Spiccia, Adv Mater 23 (2011) H18-H40.
[2] G. Singh, M. D. Gott, H.-J. Pietzsch, H. Stephan, Nuklearmedizin 55 (2016) 41-50.
[3] K. Pant, O. Sedláček, R. A. Nadar, M. Hrubý, H. Stephan, Adv Healthcare Mat 6 (2017) 1601115.
[4] K. Zarschler, L. Rocks, N. Licciardello, L. Boselli, E. Polo, K. Pombo Garcia, L. De Cola, H. Stephan, K. A. Dawson, Nanomed-Nanotechnol 12 (2016) 1663-1701.
[5] K. Pombo-García, K. Zarschler, L. Barbaro, J. A. Barreto, W. O’ Malley, L. Spiccia, H. Stephan, B. Graham
Small 10 (2014) 2516-2529.
  • Lecture (others)
    Kolloquium, 26.07.2018, Tokyo, Japan

Publ.-Id: 27768 - Permalink


Pseudo-scalar qqbar bound states at finite temperatures within a Dyson-Schwinger-Bethe-Salpeter approach
Dorkin, S. M.; Kaptari, L. P.; Kämpfer, B.;
The combined Dyson-Schwinger--Bethe-Salpeter equations are employed at non-zero temperature. The truncations refer to a rainbow-ladder approximation augmented with an interaction kernel which facilitates a special temperature dependence. At low temperatures, T→0, we recover a quark propagator from the Dyson-Schwinger (gap) equation which delivers, e.g. mass functions B, quark renormalization wave function A, and two-quark condensate $\la q \bar q \ra$ smoothly interpolating to the T=0 results, despite the broken O(4) symmetry in the heat bath and discrete Matsubara frequencies. Besides the Matsubara frequency difference entering the interaction kernel, often a Debye screening mass term is introduced when extending the T=0 kernel to non-zero temperatures. At larger temperatures, however, we are forced to drop this Debye mass in the infra-red part of the longitudinal interaction kernel to keep the melting of the two-quark condensate in a range consistent with lattice QCD results. Utilizing that quark propagator for the first few hundred fermion Matsubara frequencies we evaluate the Bethe-Salpeter vertex function in the pseudo-scalar qq¯ channel for the lowest boson Matsubara frequencies and find a competition of qq¯ bound states and quasi-free two-quark states at T=O (100 MeV). This indication of pseudo-scalar meson dissociation below the anticipated QCD deconfinement temperature calls for an improvement of the approach, which is based on an interaction adjusted to the meson spectrum at T=0.

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Publ.-Id: 27767 - Permalink


Union of light ion therapy centers in Europe (ULICE EC FP7) - Objectives and achievements of joint research activities
Pötter, R.; Balosso, J.; Baumann, M.; Bert, C.; Davies, J.; Enghardt, W.; Fossati, P.; Harris, S.; Jones, B.; Krämer, M.; Mayer, R.; Mock, U.; Pullia, M.; Schreiner, T.; Dosanjh, M.; Debus, J.; Orecchia, R.; Georg, D.;
Under the umbrella of the European Network for Light Ion Therapy (ENLIGHT), the project on Union of Light Ion Centers in Europe (ULICE), which was funded by the European Commission (EC/FP7), was carried out from 2009 to 2014. Besides the two pillars on Transnational Access (TNA) and Networking Activities (NA), six work packages formed the pillar on Joint Research Activities (JRA). The current manuscript focuses on the objectives and results achieved within these research work packages: "Clinical Research Infrastructure", "Biologically Based Expert System for Individualized Patient Allocation", "Ion Therapy for Intra-Fractional Moving Targets", "Adaptive Treatment Planning for Ion Radiotherapy", "Carbon Ion Gantry", "Common Database and Grid Infrastructures for Improving Access to Research Infrastructures". The objectives and main achievements are summarized. References to either publications or open access deliverables from the five year project work are given. Overall, carbon ion radiotherapy is still not as mature as photon or proton radiotherapy. Achieved results and open questions are reflected and discussed in the context of the current status of carbon ion therapy and particle and photon beam therapy. Most research topics covered in the ULICE JRA pillar are topical. Future research activities can build upon these ULICE results. Together with the continuous increase in the number of particle therapy centers in the last years ULICE results and proposals may contribute to the further growth of the overall particle therapy field as foreseen with ENLIGHT and new joint initiatives such as the European Particle Therapy Network (EPTN) within the overall radiotherapy community.
Keywords: Particle therapy; Proton; Carbon ion; EC project

Publ.-Id: 27766 - Permalink


Tumor Volume, HPV Status, and Cancer Stem Cell Marker Expression as prognostic Markers for the locoregional Tumor Control in Patients with locally advanced Head and Neck Squamous Cell Carcinoma after primary Chemoradiotherapy
Linge, A.; Schmidt, S.; Krenn, C.; Lohaus, F.; Valentini, C.; von Neubeck, C.; Appold, S.; Gudziol, V.; Nowak, A.; Baretton, G.; Buchholz, F.; Baumann, M.; Krause, M.; Lock, S.;
Fragestellung: Die prognostische Rolle des Tumorvolumens, des HPV-Status und der Expression des Krebsstammzellmarkers CD44 konnte kürzlich in einer Arbeit der Radioonkologie-Gruppe des Deutschen Konsortiums für Translationale Krebsforschung gezeigt werden. Ziel dieser Arbeit ist es, die prognostische Rolle dieser Marker in einer
unabhängigen Kohorte zu validieren. Methodik: Diese Studie wurde an einer monozentrischen Kohorte von 78 Patienten mit lokal fortgeschrittenen Kopf-Hals-Plattenepithel-
karzinomen der Mundhöhle, des Oropharynx und des Hypopharynx durchgeführt . Alle Patienten haben eine primäre Radiochemotherapie zwischen 1999 und 2011 mit einer medianen Gesamtdosis von 72 Gy erhalten. Der HPV-Surrogatmarker p16 und der Krebsstammzellmarker CD44 wurden immunhistochemisch untersucht . Die Genexpressionsanalyse von CD44 erfolgte mittels nanoString-Technologie. Das Tumorvolumen war von allen Patienten verfügbar und wurde durch einen Strahlentherapeuten erneut geprüft . Logistische und Cox-Regressionsmodelle wurden anhand der Fläche unter der Receiver-Operating-Characteristic-Kurve (AUC) sowie dem C-Index (ci) validiert. Der primäre Endpunkt dieser Studie ist die lokoregionale Tumorkontrolle.
Ergebnis: Das Tumorvolumen war auch in dieser Studie signifikant mit dem Endpunkt der lokoregionalen Tumorkontrolle in der univariaten Analyse assoziiert (p = 0,009). Patienten mit CD44-negativen Tumoren entwickelten kein lokoregionales Rezidiv. In der multivariaten Cox-Regressionsanalyse bezüglich der Endpunkte der lokoregionalen Tumorkontrolle und des Gesamtüberlebens konnte die unabhängige Rolle des Tumorvolumens, des N-Status und des p16-Status bestätigt werden (lokoregionale Tumorkontrolle; ci: 0,64; Gesamtüberleben; ci: 0,68). Durch die zusätzliche Berücksichtigung der Genexpression von CD44 konnte das Modell leicht verbessert werden (lokoregionale Tumorkontrolle; ci: 0,65; Gesamtüberleben; ci: 0,72) . Das auf die Marker Tumorvolumen, p16-Status und CD44-Expression basierende logistische Regressionsmodell für die lokoregionale Kontrolle nach 2 Jahren konnte ebenfalls erfolgreich validiert werden (AUC: 0,70). Schlussfolgerung: Die prognostische Rolle des Tumorvolumens, des HPV-Status und des Krebsstammzellmarkers CD44 für Patienten mit lokal fortgeschrittenen Kopf-Hals-Plattenepithelkarzinomen, die eine primäre Radiochemotherapie erhalten haben, konnte in univariaten und in multivariaten Modellen bestätigt werden.
  • Abstract in refereed journal
    Strahlentherapie und Onkologie (2018)194, S52-S53

Publ.-Id: 27765 - Permalink


Is Treatment Benefit caused by specialized oncology Centers in the Treatment of locally advanced Rectal Cancer?
Lattermann, A.; Löck, S.; Jentsch, C.; Weitz, J.; Krause, M.;
Fragestellung: Spezialisierte Krebszentren wurden mit dem Ziel einer hochqualitativen Versorgung von Krebspatienten errichtet. Ein entsprechender Benefit wurde bzgl . Patienten mit lokal fortgeschrittenen Rektumkarzinomen bisher nur unzureichend dokumentiert. In der aktuellen Auswertung stellt sich die Frage, inwieweit jene Patienten von
der Behandlung in spezialisierten Krebszentren profitieren. Methodik: Zwischen 2006 und 2013 erhielten insgesamt 131 Patienten mit neu diagnostizierten und histologisch gesicherten Rektumkarzinomen (UICC II, III) eine neoadjuvante Radiochemotherapie. Die nachfolgende Resektion erfolgte in der vom Patienten ausgewählten
Klinik. Anschließend wurde eine adjuvante Chemotherapie durchgeführt. Ein Zentrums-Effekt hinsichtlich des Gesamt- und rezidivfreien Überlebens wurde statistisch mittels Chi-Quadrat- bzw. Log-Rank-Test beurteilt .
Ergebnis: Bei den rekrutierten Patienten fanden sich nach einer medianen Nachbeobachtungszeit von 57 Monaten 8 Patienten (6 %) mit Lokalrezidiv (LR) .
Die operative Behandlung erfolgte im Median 7 Wochen nach beendeter Radiochemotherapie. 3 von 89 Patienten (3,4 %), welche an einem Universitätsklinikum operiert wurden und 5 von 42 Patienten (11,9 %), bei denen die Resektion an einem externen Haus stattfand bekamen ein LR diagnostiziert (p = 0,057). Initial wiesen 7 von 8 Patienten mit späterem LR ein cT4 bzw. cN+ und nur 1 von 8 Patienten ein cT3 bzw . cN0 Stadium auf. Bei allen 8 Patienten wurde bildmorphologisch vor Therapie eine Tumorinfiltration der mesorektalen Faszie beschrieben . 88 % der Patienten mit späterem LR hatten für das präoperative Staging ein CT oder MRT des Beckens erhalten. Bei keinem dieser Patienten zeigte sich eine Änderung des Tumorstadiums. Bei fortbestehendem Infiltrationsverdacht im präoperativen Staging wurde am Universitätsklinikum multiviszeral in Kombination mit anderen Fachrichtungen (Gynäkologie, Urologie), reseziert. Bei allen extern operierten Patienten fand letztendlich eine Standardresektion des Mesorektums, jedoch ohne Beachtung der infiltrierten Organe statt. Entsprechende LR zeigten sich bei allen 8 Patienten genau an jener Stelle, welche als initial infiltrierend beschrieben wurde. Die Zeit von Therapiebeginn bis zur Diagnose des LR betrug bei extern operierten Patienten im Median 21 Wochen, bei intern resezierten 30 Wochen (p = 0,41 Log-Rank Test). Das mediane Überleben betrug bei Patieten mit LR und extern durchgeführter Operation im Median 44 Wochen, bei intern operierten Patienten 87 Wochen (p = 0,043 Log-Rank Test) . Schlussfolgerung: Patienten mit lokal fortgeschrittenen Rektumkarzinomen und fehlendem Ansprechen auf eine neoadjuvante Radiochemotherapie sollten an spezialisierten Zentren mit der Möglichkeit einer multiviszeralen Resektion operiert werden .
  • Abstract in refereed journal
    Strahlentherapie und Onkologie 194(2018), S156-S157

Publ.-Id: 27764 - Permalink


p16 and CD44 as Prognostic Factors for Patients with early Squamous Cell Carcinoma of the Head and Neck Region
Schneider, M.; Linge, A.; Nowak, A.; Gudziol, V.; Olesch, F.; Lohaus, F.; Baretton, G.; Lauer, G.; Zahnert, T.; Baumann, M.; Löck, S.; Krause, M.;
Fragestellung: Die kurativ intendierte Therapie von Patienten mit operablen Kopf-Hals-Plattenepithelkarzinomen erfolgt entsprechend der TNM-Klassifikation: Patienten mit lokal fortgeschrittenen, aber funktionell operablen Kopf-Hals-Tumoren erhalten eine postoperative Radio(chemo)therapie, während bei Patienten mit Tumoren im UICC Stadium I und II eine alleinige Operation durchgeführt wird . Dennoch sprechen die Patienten trotz gleichem Tumorstadium und gleicher Histologie heterogen auf die Standardtherapien an . Für atienten mit lokal fortgeschrittenen Tumoren konnte in einer multizentrischen Studie der Radioonkologie-Gruppe des Deutschen Konsortiums für Translationale Radioonkologie (DKTK-ROG) gezeigt werden, dass der HPV-Status und weitere Biomarker, wie beispielsweise Krebsstammzellmarker und Hypoxie-assoziierte Gensignaturen, wichtige Prognosefaktoren für die lokoregionale Tumorkontrolle nach postoperativer Radiochemotherapie darstellen . Diese Studie hat das Ziel zu untersuchen, ob dieselben prognostischen Faktoren auch für Patienten mit lokal begrenzten Tumoren relevant sind, die eine alleinige Operation erhalten.
Methodik: In dieser retrospektiven, monozentrischen Studie wurden 174 Patienten mit einem zwischen 2005 bis 2014 diagnostizierten lokal begrenzten Plattenepithelkarzinom (Mundhöhle, Oropharynx, Hypopharynx) eingeschlossen, die eine alleinige Operation in kurativer Intention erhalten haben . Die Proteinexpressionen des HPV-Surrogatmarkers 16 und des Krebsstammzellmarkers CD44 wurden immunhistochemisch bestimmt . Der HPV DNA Nachweis erfolgte mittels eines PCR-basierten Arrays. Enexpressionsanalysen des Markers CD44 sowie von Hypoxie-assoziierten Gensignaturen wurden mittels nanoString-Technologie durchgeführt . Endpunkte waren die lokale Tumorkontrolle (LK) und die regionale Tumorkontrolle (RK) . Ergebnisse: Alle Patienten mit p16-positiven Tumoren zeigten eine vollständige RK im Vergleich zu den Patienten mit p16-negativen Tumoren (p = 0,102) . Es konnten aber nur 27,3 % der p16-positiven Tumoren positiv für HPV DNA getestet werden (22,7 % HPV16 DNA; 4,5 % HPV33 DNA) . Patienten mit CD44-positiven Tumoren zeigten eine schlechtere LK als Patienten mit CD44-negativen Tumoren, insbesondere war eine hohe CD44-Positivität der Tumorzellen (>65 % der Tumorzellen) signifikant mit dem Auftreten von Lokalrezidiven assoziiert (p = 0,005) . Eine erhöhte CD44-Genexpression zeigte ebenfalls eine signifikant schlechtere LK (p = 0,036) . Die Analyse von Hypoxie-assoziierten Gensignaturen zeigte jedoch keinen Einfluss auf die Endpunkte.
Schlussfolgerung: Diese Analysen zeigen, dass p16 und CD44 auch bei lokal begrenzten Tumoren potentielle prognostische Biomarker darstellen und, nach erfolgreicher Validierung in der aktuell rekrutierenden HNbioSUR-Studie, möglicherweise für die Individualisierung der Therapie eingesetzt werden können.
  • Abstract in refereed journal
    Strahlentherapie und Onkologie 194(2018), S132

Publ.-Id: 27763 - Permalink


Strain and screening: Optical properties of a small-diameter carbon nanotube from first principles
Wagner, C.ORC; Schuster, J.ORC; Schleife, A.ORC
Carbon nanotubes (CNTs) are a one-dimensional material system with intriguing physical properties that lead to emerging applications:One example is their optical-absorption spectrum, that is highly strain dependent, while, at the same time, CNTs are unusually strain-resistant compared to bulk materials.It is a largely open question, as to what extent this effect is attributed to the physics of strain-dependent (i) electronic single-particle transitions, (ii) dielectric screening, or (iii) atomic geometries including CNT radii.To explain the influence of strain on the screened Coulomb interaction in one-dimensional systems, we report on cutting-edge first-principles theoretical spectroscopy of the strain-dependent electronic structure and optical properties of an (8,0) CNT.Quasiparticle effects are taken into account using Hedin's $GW$ approximation and excitonic effects are described by solving a Bethe-Salpeter-equation for the optical-polarization function.This provides an accurate description of the electron-electron interaction and the influence of strain on dielectric screening as well as electronic structure and optical absorption.We interpret our thoroughly converged first-principles data in terms of an existing scaling relation and facilitate wide-spread use of this relation: We show that it captures strain-dependent optical absorption with satisfactory accuracy, as long as screening, the quasiparticle band gap, and effective electron and hole masses of the strained system are known.
Keywords: carbon nanotubes, optical properties, excitons, strain, first-principles calculations, density functional theory, many-body perturbation theory, screening

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Publ.-Id: 27762 - Permalink


Influence of defect-induced deformations on electron transport in carbon nanotubes
Teichert, F.ORC; Wagner, C.ORC; Croy, A.ORC; Schuster, J.ORC
We theoretically investigate the influence of defect-induced long-range deformations in carbon nanotubes on their electronic transport properties. To this end we perform numerical ab-initio calculations using a density-functional-based tight-binding (DFTB) model for various tubes with vacancies. The geometry optimization leads to a change of the atomic positions. There is a strong reconstruction of the atoms near the defect (called "distortion") and there is an additional long-range deformation. The impact of both structural features on the conductance is systematically investigated. We compare short and long CNTs of different kinds with and without long-range deformation. We find for the very thin (9,0)-CNT that the long-range deformation additionally affects the transmission spectrum and the conductance compared to the short-range lattice distortion. The conductance of the larger (11,0)- or the (14,0)-CNT is overall less affected implying that the influence of the long-range deformation decreases with increasing tube diameter. Furthermore, the effect can be either positive or negative depending on the CNT type and the defect type. Our results indicate that the long-range deformation must be included in order to reliably describe the electronic structure of defective, small-diameter armchair tubes.
Keywords: carbon nanotube (CNT), defect, deformation, electronic transport, density-functional-based tight binding (DFTB)

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Publ.-Id: 27761 - Permalink


A coronene-based semiconducting two-dimensional metal-organic framework with ferromagnetic behavior
Dong, R.; Zhang, Z.; Tranca, D. C.; Zhou, S.; Wang, M.; Adler, P.; Liao, Z.; Liu, F.; Sun, Y.; Shi, W.; Zhang, Z.; Zschech, E.; Mannsfeld, S.; Felser, C.; Feng, X.;
Metal–organic frameworks (MOFs) have so far been highlighted for their potential roles in catalysis, gas storage and separation. However, the realization of high electrical conductivity (>10^−3  S cm^−1) and magnetic ordering in MOFs will afford them new functions for spintronics, which remains relatively unexplored. Here, we demonstrate the synthesis of a two-dimensional MOF by solvothermal methods using perthiolated coronene as a ligand and planar iron-bis(dithiolene) as linkages enabling a full π-d conjugation. This 2D MOF exhibits a high electrical conductivity of ~10 S cm−1 at 300 K, which decreases upon cooling, suggesting a typical semiconductor nature. Magnetization and 57Fe Mössbauer experiments reveal the evolution of ferromagnetism within nanoscale magnetic clusters below 20 K, thus evidencing exchange interactions between the intermediate spin S = 3/2 iron(III) centers via the delocalized π electrons. Our results illustrate that conjugated 2D MOFs have potential as ferromagnetic semiconductors for application in spintronics.

Publ.-Id: 27760 - Permalink


Kinematic dynamo action of a precession driven flow based on the results of water experiments and hydrodynamic simulations
Giesecke, A.; Vogt, T.; Gundrum, T.; Stefani, F.;
The project DRESDYN (DREsden Sodium facility for DYNamo and thermohydraulic studies) conducted at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) provides a new platform for a variety of liquid sodium experiments devoted to problems of geo- and astrophysical magnetohydrodynamics. The most ambitious experiment within this project is a precession driven dynamo experiment that currently is under construction. It consists of a cylinder filled with liquid sodium that simultaneously rotates around two axes. The experiment is motivated by the idea of a precession-driven flow as a complementary energy source for the geodynamo or the ancient lunar dynamo.

In the present study we address numerical and experimental examinations in order to identify parameter regions where the onset of magnetic field excitation will be most probable. Both approaches show that in the strongly nonlinear regime the flow is essentially composed of the directly forced primary Kelvin mode and higher modes in terms of standing inertial waves that arise from nonlinear self-interactions. A peculiarity is the resonance-like emergence of an axisymmetric mode that represents a double roll structure in the meridional plane, which, however, only occurs in a very limited range of the precession ratio. This axisymmetric mode turns out to be beneficial for dynamo action, and kinematic simulations of the magnetic field evolution induced by the time-averaged flow exhibit magnetic field excitation at critical magnetic Reynolds numbers around Rm c ≈430, which is well within the range of the planned liquid sodium experiment.
Keywords: Dynamo, DRESDYN

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Publ.-Id: 27759 - Permalink


⁶⁰Fe and ²⁴⁴Pu on Earth – Access to the Solar Neighbourhood, Stars and the Past of Earth
Koll, D.; Faestermann, T.; Korschinek, G.; Merchel, S.ORC; Welch, J.; Kipfstuhl, S.; Wallner, A.
Long-lived radionuclides such as ⁶⁰Fe (t1/2=2.6 Myr) or ²⁴⁴Pu (t1/2=81 Myr) are synthesised in significant quantities in stellar environments by the capture of free neutrons. ⁶⁰Fe is in addition also produced, by cosmic ray interactions with interplanetary bodies, albeit at much lower quantities. Importantly, on Earth natural production of both isotopes is negligible, making them a valuable
tracer of extraterrestrial origin. Since these two isotopes are synthesised by the slow-neutron capture process (s-process) and predominantly ejected in supernova explosions, and the rapid neutron capture process (r-process), respectively, the potential detection of both isotopes opens the possibility to connect both processes in one astrophysical production site. The only measurement technique at this time which is sensitive enough to measure lowest concentrations of both isotopes is Accelerator Mass Spectrometry (AMS).
[1] History of detecting extraterrestrial ⁶⁰Fe
Extraterrestrial ⁶⁰Fe was detected first on Earth in a ferromanganese crust by the Munich AMS group in 2004 [1,2]. These samples allowed to analyse the past ~10 Myr for its ⁶⁰Fe content. Time-profile and absolute influx indicates that these ⁶⁰Fe atoms in the deep-sea crust were produced and ejected by one or more supernovae about 2 to 3 Myr ago and subsequently incorporated in this geological archive.
This discovery triggered several other projects to confirm this finding and to look for the same signal in other reservoirs like deep-sea sediments [3,4].
Furthermore, ⁶⁰Fe was also discovered on the Moon in lunar regolith [5]. These measurements all point towards an interstellar ⁶⁰Fe entry about 2-3 Myr ago, but the signal weakens and approaches measurement background for recent times.
However, such ⁶⁰Fe measurements are extremely difficult and only two AMS facilities (TU Munich and ANU) are sensitive enough for such measurements. For these reasons, also no significantly enhanced extraterrestrial influx of contemporary ⁶⁰Fe (i.e. within the last few 10
kyr) on Earth could be reported.
[2] ⁶⁰Fe in Antarctic snow
AMS is a relative measurement for isotope ratios, here extraterrestrial ⁶⁰Fe relative to stable terrestrial Fe. One major problem in the detection of modern ⁶⁰Fe influx from space by AMS, is the presence of the highly abundant stable terrestrial iron. Combined with the short ⁶⁰Fe accumulation periods, detection of a recent extraterrestrial signal becomes extremely challenging. To overcome this limiting factors, 500 kg of pure Antarctic surface snow (i.e. with lowest terrestrial Fe content) were recovered from the Kohnen Station in Antarctica and chemically
processed for an AMS measurement. Indeed, ⁶⁰Fe was discovered in Antarctic snow and by comparison with other isotopes such as ⁵³Mn, which is dominantly produced by cosmic ray interactions with solar system objects, the origin of these ⁶⁰Fe atoms could be
deduced [6].
[3] Search for concomitant ⁶⁰Fe and ²⁴⁴Pu influx onto Earth
Recently, we have started a project to extend previous measurements of ⁶⁰Fe and ²⁴⁴Pu in several geological reservoirs. The search for the coincident influx of ⁶⁰Fe and ²⁴⁴Pu into the same terrestrial archive opens the possibility to investigate a connection between Supernova-signatures (⁶⁰Fe production) and r-process nucleosynthesis (²⁴⁴Pu is a pure r-process nuclide). For this purpose, compared to
previous studies [2,7], a substantially larger sample of the same ferromanganese crust is available for ⁶⁰Fe [2] and ²⁴⁴Pu [7]. In this multi-isotope approach, we aim for a detailed time-profile for both isotopes in the crust. Such a project has become feasible also due to a substantially improved detection efficiency in ²⁴⁴Pu measurements. In addition, we plan to extend the time-period further into the past.
[4] References
[1] K. Knie et. al. “Indication for supernova produced ⁶⁰Fe activity on Earth” Phys. Rev. Lett. 83 (1999) 18.
[2] K. Knie et. al. “⁶⁰Fe anomaly in a deep-sea manganese crust and implications for a nearby supernova source” Phys. Rev. Lett. 93 (2004) 171103.
[3] P. Ludwig et. al. “Time-resolved 2-million-year-old super-nova activity discovered in Earth's microfossil record”, Proceedings of the National Academy of Sciences 113 (2016) 9232.
[4] A. Wallner et. al. “Recent near-Earth supernovae probed by global deposition of interstellar radioactive ⁶⁰Fe” Nature 532 (2016) 69.
[5] L. Fimiani et. al. “Interstellar ⁶⁰Fe on the surface of the Moon” Phys. Rev. Lett. 116 (2016) 151104.
[6] D. Koll “Search for recent ⁶⁰Fe deposition in Antarctica with AMS” Master's Thesis TUM (2018).
[7] A. Wallner et al., “Abundance of live ²⁴⁴Pu in deep-sea reservoirs on Earth points to rarity of actinide nucleosynthesis”, Nat. Comm. 6 (2015) 5956.
Keywords: accelerator mass spectrometry, astrophysics
  • Lecture (Conference)
    23rd Australian Institute of Physics Congress, 09.-13.12.2018, Perth, Australia

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Publ.-Id: 27758 - Permalink


Protracted river recovery from medieval earthquakes
Stolle, A.; Schwanghart, W.; Andermann, C.; Bernhardt, A.; Fort, M.; Wittmann, H.; Merchel, S.ORC; Rugel, G.; Adhikary, B. R.; Korup, O.
Mountain rivers respond to strong earthquakes by rapidly aggrading to accommodate excess sediment delivered by co-seismic landslides. Detailed sediment budgets indicate that rivers need several years to decades to recover from such seismic disturbances, depending on how recovery is defined. We examine several proxies of river recovery around Pokhara, Nepal’s second largest city. We use a freshly exhumed cohort of floodplain trees in growth position as a geomorphic marker of rapid sedimentation that formed a fan covering 148 km² in a Lesser Himalayan basin with tens of meters of debris. Radiocarbon dates of these buried trees are consistent with those of nearby valley fills linked to major Himalayan earthquakes during medieval times, and offer benchmarks for estimating average rates of sedimentation and re-incision. We combine high-resolution digital elevation data, geodetic field surveys, aerial photos documenting historic channel changes, estimated removed volumes, calculated long-term denudation rates, and dated re-exhumed tree trunks to reconstruct dated geomorphic marker surfaces. The volumes of sediment lost from these surfaces require net sediment yields of up to 4200 t km² yr¹, averaged over some 650 years since the last inferred earthquake. These rates exceed density-adjusted rates of catchment-wide denudation derived from concentrations of cosmogenic ¹⁰Be in river sands. The lithological composition of active channel-bed load differs from that of local bedrock, confirming that rivers are still mainly evacuating medieval valley fills, locally incising at rates of 160 to 220 mm yr¹ in the past 50 years. Pronounced knickpoints and epigenetic gorges at tributary junctions add to the picture of a protracted fluvial response; only the distal portions of the earthquake-derived sediment wedge have been incised to near their base. Our results challenge the notion that mountain rivers recover from earthquakes within years to decades. The valley fills around Pokhara document that even highly erosive Himalayan rivers need at least centuries to millennia to adjust. Our results motivate some rethinking of post-seismic hazard appraisals and infrastructural planning in mountain regions.
Keywords: accelerator mass spectrometry, cosmogenic nuclide, geomorphological risk assessment, Earthquake
  • Poster
    4th Central European Geomorphology Conference, 09.-13.10.2017, Bayreuth, Deutschland

Publ.-Id: 27757 - Permalink


Dynamics of nanoparticle morphology under low energy ion irradiation
Holland-Moritz, H.; Graupner, J.; Möller, W.; Pacholski, C.; Ronning, C.;
If nanostructures are irradiated with energetic ions, the mechanism of sputtering becomes important when the ion range matches about the size of the nanoparticle. Gold nanoparticles with diameters of ∼50 nm on top of silicon substrates with a native oxide layer were irradiated by gallium ions with energies ranging from 1 to 30 keV in a focused ion beam system. High resolution in situ scanning electron microscopy imaging permits detailed insights in the dynamics of the morphology change and sputter yield. Compared to bulk-like structures or thin films, a pronounced shaping and enhanced sputtering in the nanostructures occurs, which enables a specific shaping of these structures using ion beams. This effect depends on the ratio of nanoparticle size and ion energy. In the investigated energy regime, the sputter yield increases at increasing ion energy and shows a distinct dependence on the nanoparticle size. The experimental findings are directly compared to Monte Carlo simulations obtained from iradina and TRI3DYN, where the latter takes into account dynamic morphological and compositional changes of the target.
Keywords: in situ ion beam, Monte Carlo, nanoparticles, sputtering

Publ.-Id: 27756 - Permalink


Frequency linewidth and decay length of spin waves in curved magnetic membranes
Otalora, J. A.; Kákay, A.; Lindner, J.; Schultheiss, H.; Thomas, A.; Fassbender, J.; Nielsch, K.;
The curvature of a magnetic membrane was presented as a means of inducing nonreciprocities in the spin-wave (SW) dispersion relation [see Otalora et al. Phys. Rev. Lett. 117, 227203 (2017) and Otalora et al. Phys. Rev. B 95, 184415 (2017)], thereby expanding the toolbox for controlling SWs. In this paper, we further complement this toolbox by analytically showing that the membrane curvature is also manifested in the absorption of SWs, leading to a difference in the frequency linewidth (or lifetime) of counterpropagating magnons. Herein, we studied the nanotubular case, predicting changes of approximately greater than 10% and up to 20% in the frequency linewidth of counterpropagating SWs for a wide range of nanotube radii ranging from 30 nm to 260 nm and with a thickness of 10 nm. These percentages are comparable to those that can be extracted from experiments on heavy metal/magnetic metal sandwiches, wherein linewidth asymmetry results from an interfacial Dzyaloshinskii-Moriya interaction (DMI). We also show that the interplay between the frequency linewidth and group velocity leads to asymmetries in the SW decay length, presenting changes between 10% and 22% for counterpropagating SWs in the frequency range of 2-10 GHz. For the case of the SW dispersion relation, the predicted effects are identified as the classical dipole-dipole interaction, and the analytical expression of the frequency linewidth has the same mathematical form as in thin films with the DMI. Furthermore, we present limiting cases of a tubular geometry with negligible curvature such that our analytical model converges to the case of a planar thin film known from the literature. Our findings represent a step forward toward the realization of three-dimensional curvilinear magnonic devices.
Keywords: FERROMAGNETIC-RESONANCE LINEWIDTH; WEAK FERROMAGNETISM; MORIYA INTERACTION; THIN-FILMS; MAGNONICS

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Publ.-Id: 27753 - Permalink


Multi-frequency inductive system for magnesium level detection in a titanium reduction reactor
Krauter, N.; Stefani, F.; Gundrum, T.; Wondrak, T.; Frick, P.; Khalilov, R.;
The inductive measurement of the magnesium level in a titanium reduction reactor is a challenging task because the state of the art measurement techniques are hampered by the formation of titanium sponge rings within the reactor. By distorting the magnetic field between excitation and sensor coils, which is used to determine the magnesium level, these rings lead to a considerable measurement error. We present a novel approach to magnesium level detection using the existing infrastructure of the titanium reduction reactor, while considering the unknown size, position and electrical conductivity of the titanium sponge ring. Based on numerical simulations, we demonstrate how to solve the resulting inverse problem by applying a look-up-table method comprising tens of thousands of pre-calculated parameter combinations.
Keywords: Titanium, Kroll process, level detection, inductive measurements
  • Poster
    9th International Symposium on Electromagnetic Processing of Materials (EPM2018), 17.-18.10.2018, Awaji City, Japan
  • Open Access LogoIOP Conference Series: Materials Science and Engineering 424(2018), 012078
    DOI: 10.1088/1757-899X/424/1/012078

Publ.-Id: 27751 - Permalink


Transient Eddy Current Flow Metering: calibration-free velocity measurements for liquid metals
Krauter, N.; Stefani, F.;
Most inductive techniques for the velocity measurement of liquid metals have the common problem that the measured signals depend on the electrical conductivity and the temperature of the liquid metal. This is particularly unfavourable for applications with strong temperature fluctuations or for measurements that have to be performed in different liquid metals with the same sensor. Usually these sensors have to be calibrated extensively to ensure accurate measurement results. We present a new measurement technique called Transient Eddy Current Flow Metering (TECFM) which overcomes the need for prior calibration of the sensors. Its principle relies on imprinting transient eddy current systems into the liquid metal and to track their movement as they are advected with the flow. Two kinds of sensors that use this new measurement principle have been developed: An external sensor for the contactless velocity measurement at the boundary of liquid metal flows, and an immersed sensor which allows local velocity measurements in the vicinity of the sensor. Focusing on the latter we present the results of numerical simulations as well as the results of measurements that were performed in the eutectic alloy GaInSn at room temperature and in liquid sodium at 180 °C.
Keywords: flow measurement, inductive methods, calibration-free
  • Lecture (Conference)
    9th International Symposium on Electromagnetic Processing of Materials (EPM2018), 14.-18.10.2018, Awaji City, Japan
  • Open Access LogoIOP Conference Series: Materials Science and Engineering 424(2018), 012008
    DOI: 10.1088/1757-899X/424/1/012008

Publ.-Id: 27750 - Permalink


Creation of silicon vacancy in silicon carbide by proton beam writing toward quantum sensing applications
Ohshima, T.ORC; Satoh, T.; Kraus, H.; Astakhov, G. V.ORC; Dyakonov, V.ORC; Baranov, P. G.
Single photon source (SPS) is a key element for quantum spintronics and quantum photonics. It is known that several color centers such as silicon vacancy (VSi), divacancy (VSiVC), carbon antisite carbon vacancy pair (CSiVC), in silicon carbide (SiC) act as SPSs. Spin (S = 3/2) in VSi in SiC can be manipulated even at room temperature and the intensity of its photoluminescence (PL) changes depending on the spin states (mS = ±3/2 or mS = ±1/2). Since PL from VSi is in the near infrared region (around 900 nm), it is expected that VSi is applied to quantum sensor especially for biological or medical applications. In this review, we discuss quantum sensing based on VSi in SiC. Also, we discuss energetic particle irradiation, especially proton beam writing (PBW), in which proton microbeams with MeV range are used, as a method to create VSi in SiC since PBW can create VSi in certain locations with micrometer accuracy and this is very useful to introduce VSi in electronic devices without the degradation of their electrical characteristics.

Publ.-Id: 27748 - Permalink


Liquid structure of shock-compressed hydrocarbons at megabar pressures
Hartley, N. J.; Vorberger, J.; Döppner, T.; Cowan, T.; Falcone, R. W.; Fletcher, L. B.; Frydrych, S.; Galtier, E.; Gamboa, E. J.; Gericke, D. O.; Glenzer, S. H.; Granados, E.; Macdonald, M. J.; Mackinnon, A. J.; Mcbride, E. E.; Nam, I.; Neumayer, P.; Pak, A.; Rohatsch, K.; Saunders, A. M.; Schuster, A. K.; Sun, P.; van Driel, T.; Kraus, D.;
We present ion structure results from hydrocarbons (polystyrene, polyethylene) shock compressed to pressures of up to 190 GPa, inducing rapid melting of the samples. The structure of the resulting liquid is then probed using in situ diffraction by an X-ray free electron laser beam, with precise, reliable diffraction data obtained from single shots. This is the first example of single shot diffraction from low-Z samples dynamically driven into the liquid state. The data agrees well with the structure factors calculated from ab initio simulations, demonstrating their ability to model mixed samples in this state. While the results exclude the possibility of complete carbon-hydrogen demixing at the conditions probed, they also, in contrast to previous predictions, demonstrate that diffraction is not always a sufficient diagnostic for this phenomenon.

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Publ.-Id: 27747 - Permalink


The role of incidence angle in the morphology evolution of Ge surfaces irradiated by medium-energy Au ions
Dell’Anna, R.; Iacob, E.; Barozzi, M.; Vanzetti, L.; Hübner, R.; Böttger, R.; Giubertoni, D.; Pepponi, G.;
Germanium (Ge) surfaces have been irradiated with 26 keV gold (Au) ions at a constant fluence and at incidence angles varying from 0° to 85°. The evolution of the emerging nanostructures is studied by atomic force microscopy (AFM), scanning electron microscopy, x-ray photoelectron spectroscopy (XPS), and cross-sectional transmission electron microscopy. The obtained results are compared with findings reported in the literature. Periodic rippled patterns with the wave vector parallel to the projection of the ion beam direction onto the Ge surface develop between 30° and 45°. From 75° the morphology changes from parallel-mode ripples to parallel-mode terraces, and by further increasing the incidence angle the terraces coarsen and show a progressive break-up of the front facing the ion beam. No perpendicular-mode ripples or terraces have been observed. The analysis of the AFM height profiles and slope distributions shows in the 45°-85° range an angular dependence of the temporal scale for the onset of nonlinear processes. For incidence angles below 45°, the surface develops a sponge-like structure, which persists at higher incidence angles on the top and partially on the face of the facets facing the ion beam. The XPS and the energy-dispersive x-ray spectroscopy evidence the presence of Au nano-aggregates of different sizes for the different incidence angles. This study points out the peculiar behavior of Ge surfaces irradiated with medium-energy Au ions and warns about the differences to be faced when trying to build a universal framework for the description of semiconductor pattern evolution under ion-beam irradiation.
Keywords: ion beam irradiation, germanium, gold ions, binary system, ripples, terraces, sponge-like structures

Publ.-Id: 27746 - Permalink


Investigation of the exit charge state distribution of highly charged ions transmitted through 2D materials
Creutzburg, S.; Schwestka, J.; Gruber, E.; Lehnert, T.; Leiter, R.; Kozubek, R.; Heller, R.; Klingner, N.; Kotakoski, J.; Krasheninnikov, A. V.; Kaiser, U.; Schleberger, M.; Facsko, S.; Aumayr, F.; Wilhelm, R. A.;
2D materials exhibit unique electronic and optical properties due to surface and quantum confinement effects [1]. To tailor the properties of 2D materials for a specific application ion beams may be used for implantation of foreign atoms or to deliberately introduce defects. The impact of energetic particles on a solid surface can result in a strong excitation of the electronic system, which leads to damage formation [2]. Highly charged ions (HCIs) provide a large amount of potential energy stored due to the ionization of dozens of electrons. With their high charge state q less or equal than Z they resemble a moving point charge creating a strong electric field in its vicinity. Freestanding 2D materials serve as ultimately thin solid targets for classical beam foil experiments giving insights not only into the charge exchange dynamics of the ions but also into the electronic response of a solid target to an ultrafast (fs) strong electric field pulse [3,4,5]. A large electron current density is present upon ion impact on a 2D material and thus surprisingly short neutralization times of only a few femtoseconds were determined by measuring the exit charge for different energies of incident slow HCIs on single layer graphene [3,4]. Here we extend our investigations to other 2D materials beyond graphene, namely MoS2 and hBN. They exhibit different structural and electronic properties, which have an influence on the neutralization process. Charge state distributions are recorded by utilization of a setup composed of deflector plates and a microchannel plate, which allows the measurement of low charge states and even neutralized ions.
[1] W. Choi et al., Materials Today 20 (3) (2017).
[2] F. Aumayr et al., J. Phys.: Condens. Matter. 23 (2011) 393001.
[3] E. Gruber et al., Nat. Commun. 7, 13948 (2016).
[4] R. A. Wilhelm et al., Phys. Rev. Lett. 119, 103401 (2017).
[5] R. A. Wilhelm et al., Phys. Rev. Lett. 112, 153201 (2014).
Keywords: 2D materials, highly charged ions
  • Poster
    SHIM-ICACS 2018, 02.-06.07.2018, Caen, France

Publ.-Id: 27745 - Permalink


A versatile ion beam spectrometer for studies of ion interaction with 2D materials
Schwestka, J.; Melinc, D.; Heller, R.; Niggas, A.; Leonhartsberger, L.; Winter, H.; Facsko, S.; Aumayr, F.ORC; Wilhelm, R. A.ORC
We present an ultra-high vacuum setup for ion spectroscopy of freestanding two-dimensional solid targets. An ion beam of different ion species (e.g. Xe with charge states from 1 to 44 and Ar with charge states from 1 to 18) and kinetic energies ranging from a few 10 eV to 400 keV is produced in an electron beam ion source. Ions are detected after their transmission through the 2D target with a position sensitive microchannel plate detector allowing the determination of the ions exit charge state as well as the scattering angle with a resolution of approx. 0.04◦. Further, the spectrometer is mounted on a swiveling frame covering a scattering angle of ±8° with respect to the incoming beam direction. By utilizing a beam chopper we measure the time-of-flight of the projectiles and determine the energy loss when passing a 2D target with an energy uncertainty of about 2%. Additional detectors are mounted close to the target to observe emitted secondary particles and are read-out in coincidence with the position and time information of the ion detector. A signal in these detectors can also be used as a start trigger for time-of-flight measurements, which then yield an energy resolution of 1% and an approx. 1000-fold larger duty cycle. First results on the interaction of slow Xe30+ ions with a freestanding single layer of graphene obtained with the new setup are compared to recently published data where charge exchange and energy were measured by means of an electrostatic analyzer.
Keywords: slow highly charged ions, 2D materials, ion spectrometer, single layer graphene

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Publ.-Id: 27743 - Permalink


Neutralization Dynamics of Slow Highly Charged Ions in 2D Materials
Wilhelm, R.ORC; Gruber, E.ORC; Schwestka, J.; Heller, R.; Facsko, S.; Aumayr, F.ORC
We review experimental and theoretical work on the interaction of slow highly charged ions with two-dimensional materials. Earlier work in the field is summarized and more recent studies on 1 nm thick amorphous carbon nanomembranes and freestanding single layer graphene by the authors are reviewed. To explain the findings, models for energy loss determination as well as qualitative model descriptions for the observed ultrafast neutralization dynamics are discussed. The results shown in this paper will be put into context with findings of nanostructure formation on two-dimensional materials, both freestanding and on substrate, as well as on surfaces of bulk insulators.
Keywords: low energy ions; highly charged ions; 2D materials

Publ.-Id: 27742 - Permalink


Working in stealth mode: Towards the development of biomolecular corona-resistant hydrophilic nanomaterials for biomedical applications
Joshi, T.; Nsubuga, A.; Zarschler, K.; Stephan, H.;
The interaction of nanoparticles (NPs) with biomolecules depends on their surface characteristics and has a major influence on their ultimate metabolic fate. Attempts to modulate the NP-biomolecule interaction in complex biological conditions has led to intensive research on the role of NP size, shape, charge, surface structure and the capping molecules in their eventual pharmacokinetic response. Research shows that to avoid accumulation in the organs of the mononuclear phagocyte system (MPS), engineered NPs must resist nonspecific adsorption of proteins (biomolecular corona) onto their surface. To date the most common approach to make NPs corona-resistant includes formation of a hydrophilic, neutral-charged polyethylene glycol coating (PEGylation) on their surface. This route, widely used by many groups, furnishes hydrophilic NPs, but suffers from some serious drawbacks, such as, a substantial increase in the hydrodynamic diameter (Dh) after PEGylation, and the formation of anti-PEG antibodies in vivo.
Herein, we present our efforts towards tackling the problem of biomolecular corona formation. To this end, we have explored the use of amphiphilic zwitterionic polymers and low molecular weight entities as capping ligands on the surface of ultrasmall iron oxide nanoparticles (USPIONs) and lanthanide-doped upconverting nanoparticles (UCNPs). Following such surface modification, the hydrophobic NPs were rendered water-dispersible and showed reduced adsorption of serum proteins, but without any significant increase in particle size. Additionally, the availability of reactive functional groups on the surface of the modified NPs makes them ready for further functionalization with, for example, small molecules, peptides, proteins, and antibodies. The presented results highlight the usefulness of our surface functionalization strategy to produce biocompatible materials suitable for multimodal diagnostic/therapeutic applications.
  • Invited lecture (Conferences)
    256th ACS National Meeting in Boston, MA, 19.-23.08.2018, Boston, USA

Publ.-Id: 27741 - Permalink


Development of biomolecular corona-resistant nanomaterials suitable for biological applications
Joshi, T.; Nsubuga, A.; Zarschler, K.; Stephan, H.;
Nanoparticle (NP) size, shape, charge, surface structure and the capping moieties have a significant influence on their eventual pharmacokinetic behaviour. For NPs to avoid accumulation in the organs of the mononuclear phagocyte system (MPS), it is important that they resist nonspecific adsorption of proteins (biomolecular corona) onto their surface. Reported methods to make corona-resistant hydrophilic NPs mostly suffer from serious drawbacks in regards to the in vivo applications of the engineered NMs. The major ones being (1) substantial increase in the hydrodynamic diameter (Dh) of the modified NMs, and (2) the formation of anti-PEG antibodies in vivo. Herein, we will present our efforts towards tackling the problem of biomolecular corona formation in ultrasmall iron oxide nanoparticles (USPIONs) and lanthanide-doped upconverting nanoparticles (UCNPs) by using amphiphilic zwitterionic polymers and low molecular weight entities as capping ligands on the NP surface. Our studies show that such surface functionalization strategy can produce biocompatible NPs that exhibit negligible interaction with biomolecules, and are suitable for developing multimodal imaging/therapeutic agents.
  • Invited lecture (Conferences)
    10th International Symposium on Nano & Supramolecular Chemistry, 09.-12.07.2018, Dresden, Germany

Publ.-Id: 27740 - Permalink


Wetting fraction in a tubular reactor with solid foam packing and gas/liquid co-current downflow
Mohammmed, I.; Hampel, U.;
The performance of fixed bed reactors with structured catalysts depends heavily on the gas-liquid-solid contacting pattern. For a broad range of flow conditions, the liquid phase does not cover the solid surface of the packing homogeneously, which is known as partial wetting. Wetting fraction in solid foams was obtained using a modified electrochemical measurement method with adaption of limiting current technique at different pre-wetting scenarios. The external wetting fraction, which is defined as fraction of the external solid foam area covered by the liquid phase to the total external solid foam area, is directly linked to the overall rate of reaction through the overall liquid mass transfer rate.
The wetting fraction decreased with an increase of the foam density, which was related to decreasing the struts’ thickness, for more foam surface area, and consequently decreasing the wetted area. Additionally, the results indicate that better distribution of liquid and increased wetting fraction occurred when applying a spray nozzle distributor. A new wetting correlation for solid foams is proposed to estimate the wetting fraction with consideration of foam morphology and flow regime.
Keywords: Multiphase, Solid Foam, Wetting, Electrocemical Methode, Gas/Liquid, Pre-wetting mode

Publ.-Id: 27739 - Permalink


In situ Structural Study of Sb(V) Adsorption on Hematite (1-102) Using X-ray Surface Scattering
Qiu, C.; Majs, F.; Douglas, T.; Schmidt, M.; Trainor, T.;
The binding mechanism of Sb(V) on a single crystal hematite (1-102) surface was studied using crystal truncation rod X-ray diffraction (CTR) under in situ conditions. The best fit CTR model indicates Sb(V) adsorbs at the surface as an inner-sphere complex forming a binuclear tridentate binding geometry with the nearest Sb-Fe distance of 3.09(4) Å and an average Sb-O bond length of 2.08(5) Å. In this binding geometry Sb is bound at both edge-sharing and corner-sharing sites of the surface Fe-O octahedral units. The chemical plausibility of the proposed structure was further verified by bond valence analysis, which also deduced a protonation scheme for surface O groups. The stoichiometry of the surface reaction predicts the release of one OH- group at pH 5.5.
Keywords: Sb(V), hematite, crystal truncation rod

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  • Secondary publication expected

Publ.-Id: 27738 - Permalink


Nonlinear THz Spectroscopy of Two-Dimensional Systems
Helm, M.; König-Otto, J.; Schmidt, J.; Dimakis, E.; Winnerl, S.; Schneider, H.;
Nonlinear THz experiments using a free-electron laser are presented on Landau quantized graphene as well as on intersubband transitions in a single GaAs quantum well.
Keywords: terahertz, free electron laser, graphene, Landau Levels, intersubband, GaAs, quantum well
  • Invited lecture (Conferences)
    Frontiers of photonics, plasmonics and electronics with 2D nanosystems, 14.-20.07.2018, Erice, Italy
  • Invited lecture (Conferences)
    Advanced Electromagnetics Symposium (AES 2018), 24.06.-01.07.2018, Marseille, France

Publ.-Id: 27737 - Permalink


CFD modeling of condensation inside emergency condensers of passive heat removal systems
Moonesi Shabestary, A.; Lucas, D.; Krepper, E.;
Future nuclear reactor concepts are frequently equipped with a passive emergency cooling system which removes decay heat from the reactor core in case of any emergency accidents. The emergency cooling system considered here consists of slightly inclined horizontal pipes which are immersed in a tank of subcooled water. Under normal operating conditions, pipes are filled with water and no heat transfer exists between primary and secondary side of the emergency condenser. In case of an accident the level of water in the core decreases, afterward steam enters the tubes on the primary side of the emergency condensers and because of the heat transfer from the subcooled water around the pipe to the steam, steam condensation occurs inside the pipes. Therefore, the emergency condenser acts as a strong heat sink which is responsible for a quick depressurization of the reactor core. The focus of the current paper is on CFD modeling of the whole condensation process inside the inclined pipe and validation of the results with the data obtained from experiments performed in TOPFLOW facility of HZDR for a single condensation pipe at operating conditions close to the reality, i.e. at high pressure and high saturated steam temperature.

During the condensation process, different flow morphologies may occur inside the pipe. The process is initiated due to the heat flux from the pipe’s wall to the steam. Because of the phase change, a thin layer of liquid film is generated near the wall leading to annular flow. The generated liquid film stays in direct contact with steam which is on the saturation temperature and cause direct contact condensation at the interface of the steam and the liquid. Because of the gravity force, the laminar liquid film is falling, gathering at the lower part of the pipe and finally, a stratified flow occurs. Furthermore, by enhancing the condensation rate, different flow morphologies such as stratified wavy flow, slug flow, plug flow and bubbly flow occur inside the pipe. CFD modeling of combined wall condensation and direct contact condensation inside the inclined pipes and effects of the liquid film on the heat transfer coefficient is the major focus of the current paper. In the end, the CFD modeling results are validated with the experimental data.
  • Lecture (Conference)
    International Conference on Nuclear Engineering (ICONE 2018), 22.-26.07.2018, London, United Knigdom Britain

Publ.-Id: 27736 - Permalink


Realizing Quantum free-electron lasers: A critical analysis of experimental challenges and theoretical limits
Debus, A.ORC; Steiniger, K.; Kling, P.; Carmesin, M.; Sauerbrey, R.
We examine the experimental requirements for realizing a high-gain Quantum free-electron laser (Quantum FEL). Beyond fundamental constraints on electron beam and undulator, we discuss optimized interaction geometries, include coherence properties along with the impact of diffraction, space-charge and spontaneous emission.
Based on desired Quantum FEL properties, as well as current experimental capabilities, we provide a procedure for determining a corresponding set of experimental parameters.
Even for an idealized situation, the combined constraints on space-charge and spontaneous emission put strong limits on sustaining the quantum regime over several gain lengths. Guided by these results we propose to shift the focus towards seeded Quantum FELs instead of continuing to aim for self-amplified spontaneous emission (SASE). Moreover, we point out the necessity of a rigorous quantum theory for spontaneous emission as well as for space-charge in order to identify possible loopholes in our line of argument.
Keywords: Quantum free-electron laser, free-electron laser, FEL, QFEL

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  • Secondary publication expected from 15.04.2020

Publ.-Id: 27735 - Permalink


Design of high-temperature solar-selective coatings based on aluminium titanium oxynitrides AlyTi1-y(OxN1-x). Part 2: Experimental validation and durability tests at high temperature
Escobar-Galindo, R.; Guillén, E.; Heras, I.; Rincón-Llorente, G.; Alcón-Camas, M.; Lungwitz, F.; Munnik, F.; Schumann, E.; Azkona, I.; Krause, M.;
The durability of two solar-selective aluminium titanium oxynitride multilayer coatings was studied under conditions simulating realistic operation of central receiver power plants. The coatings were deposited by cathodic vacuum arc applying an optimized design concept for complete solar-selective coating (SSC) stacks. Compositional, structural and optical characterization of initial and final stacks was performed by scanning electron microscopy, elastic recoil detection, UV-Vis-NIR-IR spectrophotometry and X-Ray diffraction. The design concept of the solar selective coatings was validated by an excellent agreement between simulated and initial experimental stacking order, composition and optical properties.

Both SSC stacks were stable in single stage tests of 12 hours at 650°C. At 800°C, they underwent a structural transformation by full oxidation and they lost their solar selectivity. During cyclic durability tests, multilayer 1, comprised of TiN, Al0.64Ti0.36N and an Al1.37Ti0.54O top layer, fulfilled the performance criterion (PC) ≤ 5% for 300 symmetric, 3 hours long cycles at 600°C in air. Multilayer 2, which was constituted of four AlyTi1-y(OxN1-x) layers, met the performance criterion for 250 cycles (750 hours), but was more sensitive to these harsh conditions. With regard to the degradation mechanisms, the coarser microstructure of multilayer 1 is more resistant against oxidation than multilayer 2 with its graded oxygen content. These results confirm that the designed SSCs based on AlyTi1-y(OxN1-x) materials withstand breakdown at 600ºC in air. Therefore, they can be an exciting candidate material for concentrated solar power applications at high temperature.
Keywords: Solar selective coatings, thermal stability, optical properties, concentrated solar power, optical simulation, oxynitrides

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Publ.-Id: 27734 - Permalink


Cluster tool for in situ processing and comprehensive characterization of thin films at high temperatures
Wenisch, R.; Lungwitz, F.; Hanf, D.; Heller, R.; Zscharschuch, J.; Hübner, R.; von Borany, J.; Abrasonis, G.; Gemming, S.; Escobar Galindo, R.; Krause, M.;
A new cluster tool for in situ real-time processing and depth-resolved compositional, structural and optical characterization of thin films at temperatures from -100 to 800 °C is described. The implemented techniques comprise magnetron sputtering, ion irradiation, Rutherford backscattering spectrometry, Raman spectroscopy and spectroscopic ellipsometry. The capability of the cluster tool is demonstrated for a layer stack MgO/ amorphous Si (~60 nm)/ Ag (~30 nm), deposited at room temperature and crystallized with partial layer exchange by heating up to 650°C. Its initial and final composition, stacking order and structure were monitored in situ in real time and a reaction progress was defined as a function of time and temperature.
Keywords: Cluster tool, thin films, in situ, high temperature, Rutherford backscattering, Raman spectroscopy, ellipsometry, metal-induced crystallization
  • Open Access LogoAnalytical Chemistry 90(2018), 7837-7842
    DOI: 10.1021/acs.analchem.8b00923
  • Lecture (Conference)
    16th International Conference on Plasma Surface Engineering, 16.-21.09.2018, Garmisch - Partenkirchen, Deutschland
  • Lecture (Conference)
    XV Congreso Nacional de Materiales/ Iberian Meeting on Materials Science, 04.-06.07.2018, Salamanca, Spanien

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Publ.-Id: 27732 - Permalink


Performance study of a real-size mosaic high-rate MRPC
Lyu, P.; Han, D.; Wang, Y.; Guo, B.; Wang, F.; Chen, X.; Yu, Y.; Li, Y.; Naumann, L.; Lazo Garcia, A.; Stach, D.; Fan, X.;
Towards the future CMS RPC upgrade, a real-size mosaic high-rate MRPC has been designed and developed by Tsinghua University. The prototype is a 5-gap counter composed of the low-resistive glass. Because the maximum size of this glass cannot exceed 330×280mm², 6 regions of glass stacks are mosaicked together in order to achieve a large active area. This prototype was tested in HZDR-ELBE with 30 MeV e-beam. It shows an efficiency above 95% at the rate of 2 kHz/cm². The time resolution is around 55 ps, and the cluster size is below 1.5. The performance is almost unaffected by increasing the rate to 11 kHz/cm². This design is proved to be fully capable of the CMS upgrade requirement by this HZDR beam test. The mosaic technology will make the high-rate MRPC a good choice in large-area timing systems.
Keywords: Performance of High Energy Physics Detectors; Resistive-plate chambers; Instrumentation and methods for time-of-flight (TOF) spectroscopy

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  • Secondary publication expected

Publ.-Id: 27731 - Permalink


Nonlinear Breit-Wheeler process in short laser double-pulses
Titov, A. I.; Kämpfer, B.; Takabe, H.;
The non-linear (strong-field) Breit-Wheeler e+e− pair production by a probe photon traversing two consecutive short and ultra short (sub-cycle) laser pulses is considered within a QED framework. The temporal shape of the pulses and the distance between them are essential for the differential cross section as a function of the azimuthal angle distribution of the outgoing electron (positron). The found effect of a pronounced azimuthal anisotropy is important for sub-cycle pulses and decreases rapidly with increasing width of the individual pulses.

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Publ.-Id: 27730 - Permalink


Low-temperature nanospectroscopy of the structural ferroelectric phases in single-crystalline barium titanate
Döring, J.; Lang, D.; Wehmeier, L.; Kuschewski, F.; Nörenberg, T.; Kehr, S. C.; Eng, L. M.;
We optically investigate the local-scale ferroelectric domain structure of tetragonal, orthorhombic, and rhombohedral barium titanate (BTO) single crystals using scattering-type scanning near-field infrared (IR) optical microscopy (s-SNIM) at temperatures down to 150 K. Thanks to the precisely tunable narrow-band free-electron laser FELBE, we are able to explore the spectral fingerprints and IR resonances of these three phases and their domain orientations in the optical IR near-field. More clearly, every structural phase is analyzed with respect to its near-field resonances close to a wavelength of 17μm when exploring the (111)-oriented BTO sample surface. Furthermore, near-field imaging at these resonances is performed, that clearly allows for the unambiguous optical identification of different domain orientations. Since our s-SNIM bases on a non-contact scanning force microscope, our s-SNIM findings are backed up by sample-topography and piezoresponse force microscopy (PFM) imaging, providing complementary information in an excellent match to the s-SNOM results.
Keywords: s-SNIM, infrared nanospectroscopy, FEL, phase transition, low temperature

Publ.-Id: 27729 - Permalink


Polyethyleneimine Methylenecarboxylate: a macromolecular DTPA analogue to chelate plutonium(IV)
Lahrouch, F.; Siberchiot, B.; Leost, L.; Aupiais, J.; Rossberg, A.; Hennig, C.; Den Auwer, C.; Di Giorgio, C.;
Up until now, molecular chelating agents, such as the diethylenetriamine pentaacetic acid (DTPA) have been the standard methode for actinide human decorporation. Active mainly in blood serum, their distribution within the body is thus limited. In order to treat a wider range of organs affected by plutonium contamination, a potential new class of macromolecular decorporation agents is being studied. Polyethyleneimine methylenecarboxylate (PEI-MC) is one such example. It is being considered here because of its capacity for targeting the liver and bones.
Keywords: Polyethyleneimine methylenecarboxylate, actinides, decorporation, EXAFS

Publ.-Id: 27728 - Permalink


Superconductivity and magnetism in noncentrosymmetric LaPtGe3 and CePtGe3
Feig, M.; Nicklas, M.; Bobnar, M.; Schelle, W.; Schwarz, U.; Leithe-Jasper, A.; Hennig, C.; Gumeniuk, R.;
LaPtGe3 and CePtGe3 crystallize with a noncentrosymmetric body-centered tetragonal (space group I4mm) BaNiSn3 type of structure. LaPtGe3 is a weakly coupled BCS-like s-wave type-I superconductor with Tc = 0:55 K, Bc ' 14 mT and Ginzburg-Landau parameter kGL = 0:044 < 1= p 2, which is obtained from the free electron model. CePtGe3 is a Curie-Weiss paramagnet with an effective magnetic moment mueff = 2:46 muB. The Ce moments show two antiferromagnetic ordering transitions at TN1 ~ 3:7 K and TN2 ~ 2:7 K and a ground state multiplet J = 5=2 splitting into three doublets (splitting energies from the ground state d1 = 46 K and d2 = 137 K). The reduced magnetic entropy at TN1 together with an enhanced Sommerfeld coeffcient suggest that the magnetic orderings in CePtGe3 originates from dominating RKKY interactions.
Keywords: CePtGe3, LaPtGe3, superconductor, magnetic moment, XRD

Publ.-Id: 27727 - Permalink


Combination of X-ray spectroscopy and X-ray diffraction at the Rossendorf Beamline / ESRF
Hennig, C.;
The beamline will be refurbished in 2019, which includes the installation of additional experiments: (1) a spectrometer for high-resolution X-ray absorption near-edge structure spectroscopy (HR-XANES) and X-ray emission spectroscopy (XES), (2) a 6-circle diffractometer for crystal truncation rod (CTR) / Resonant anomalous X-ray reflectivity (RAXR) and high-resolution powder diffraction (HR-PXRD), (3) a diffractometer with a Pilatus X 2M detector for single-crystal diffraction (SC-XRD) and in-situ powder diffraction. The above mentioned experiments have been developed and tested in the last two years. The concept of the beamline and some typical experimental results will be presented.
Keywords: EXAFS, HR-XANES, XES, CTR, RAXR, PXRD, SCXRD
  • Lecture (others)
    Ghent University, Department of Chemistry, 10.07.2018, Gent, Belgium

Publ.-Id: 27726 - Permalink


From bentonite to rock salt – microbial studies for nuclear waste disposal
Cherkouk, A.;
Clay and crystalline rock as well as rock salt formations are considered as potential host rocks for the long-term storage of high-level radioactive waste in a deep geological repository. In all three host rocks are particular microbial communities present that could potentially influence the properties of the host rock or materials used in the repository due to their metabolic activity.
Within the EU project MIND the potential influence of natural occurring microorganisms within the bentonite on the bentonite barrier, which is placed as a part of the multi barrier concept between the steel-canister (containing the HLW) and the surrounding host rock (e.g. clay rock), is currently under investigation. Therefore, microcosms were set up with two different Bavarian bentonites (a natural and an industrial one), which were supplied with an anaerobic, synthetic Opalinus-clay pore water solution under an N2/CO2-atmosphere and incubated for one year at 30 °C and 60 °C. To some set ups organics (acetate or lactate) or H2 were supplemented. During the incubation time samples were taken and analysed for several bio-geochemical parameters and the evolution of microbial diversity. Our results clearly demonstrate that natural occurring microbes affect geochemical parameters. Set ups containing the industrial bentonite supplemented with lactate show the most striking effects, which resulted in the dominance (up to 81 %) of Desulfosporosinus spp. – spore-forming, strictly anaerobic, sulphate-reducing organisms, able to survive under very harsh conditions. Concomitantly, an increase of ferrous iron and a simultaneous decrease of ferric iron were observed. Furthermore, the lactate and sulphate concentration decreased, whereas pyruvate and acetate were formed. Similar observations were also made in setups containing H2. Samples from selected batches were analysed regarding its mineralogy with Scanning Electron Microscopy (SEM), at the University of Greifswald. The SEM mapping analysis indicated a higher number of iron-sulphur accumulations in lactate-containing B25-samples compared to the raw material and samples including hydrogen or no substrate. Thus, microbial activity under the applied conditions led to an alteration of mineral phases when the conditions were favourable.
Moreover, the microbial potential in rock salt as a potential host rock for nuclear waste disposal is currently being investigated. Extremely halophilic archaea, e.g. Halobacterium species, dominate this habitat. For long-term risk assessment it is of high interest to study how these microorganisms can interact with radionuclides if released from the waste repository. Therefore, the interactions of the extremely halophilic archaeon Halobacterium noricense DSM 15987T with uranium were investigated in detail in batch experiments. A multi-spectroscopic and microscopic approach was used to decipher the interaction mechanisms on a molecular level. H. noricense DSM 15987T showed a multistage bioassociation of uranium. By using time-resolved laser-induced fluorescence spectroscopy and X-ray absorption spectroscopy the formation of U(VI) phosphate minerals, such as meta-autunite, was observed. The retardation of uranium as phosphate minerals highlight the potential significance of the microbial life in deep geological hypersaline environments and offer new insights into the microbe-actinide interactions at highly saline conditions relevant to the disposal of highly radioactive waste.
  • Invited lecture (Conferences)
    THEMENFELD-KOLLOQUIUM „ENERGIE“, Topic: Results and outcomes of European programme on Microbiology In Nuclear waste Disposal (MIND) – View s and perspectives over future research, 19.09.2018, Berlin, Deutschland

Publ.-Id: 27725 - Permalink


Applying accelerator and microscopy methods for investigating radionuclides at Australia's former nuclear test sites
Child, D. P.; Johansen, M. P.; Hotchkis, M. A. C.; Howard, D. L.; Howell, N.; Young, E.; Davis, J.; Ikeda-Ohno, A.ORC
The radiological residues at the former British nuclear weapons testing sites in Australia at Maralinga, Emu and the Montebello Islands are of ongoing interest in terms of environmental fate, transport, and uptake of radioactive contamination into the biosphere. The physical and chemical characteristics of these residues govern their mobility in the various environmental zones in which they reside (surface soil, ocean sediment, active beach zones) and availability of the radiological components for uptake into living organisms. At the Taranaki site, Maralinga, substantial body burdens of Pu were observed in mammals and the pattern of organ uptake was found to match that reported for exposure to respirable radioactive particles bearing refractory Pu. In order to fully deconvolute the disposition and radio-ecological impact of the contamination at these sites it was necessary to study in detail the radioactive particle composition.
Plutonium often occurs in particulate forms at nuclear accident and test sites. Such particles require advanced techniques for characterisation including Accelerator Mass Spectrometry (AMS), Scanning electron microscopy and synchrotron X-ray fluorescence microscopy (XFM). Many such particles have core-shell structures where the surface is dominated by lighter elements sourced from local soils and the Pu concentrated in the interior. Particles formed during nuclear detonations and accidents can have complex structures and compositions which may be susceptible to variable leaching and weathering rates. Modelling results suggest that for respirable-sized Pu-bearing particles (that can be inhaled and lodged in the lung), most of the alpha emissions escape the particle and are deposited in the surrounding tissue. We are currently using advanced techniques to compare the radionuclide forms from the inland sites (Maralinga and Emu) with the marine site (Montebello Islands) to compare leaching and dose implications. The characteristics of the particles will largely determine the overall potential implications for long term fate of radiological contamination at the sites.
Keywords: Accelerator mass spectrometry, X-ray fluorescence microscopy, synchrotron, nuclear tests, Australia, radioactive contaminant
  • Lecture (Conference)
    VIII INTERNATIONAL CONFERENCE Semipalatinsk Test Site: Legacy and Prospects for Scientific and Technical Potential Development, 11.09.2018, Kurchatov, Republic of Kazakhstan

Publ.-Id: 27724 - Permalink


Solving the Dyson–Schwinger Equation at Zero and Finite Temperatures
Dorkin, S. M.; Kaptari, L. P.; Kämpfer, B.;
The properties of the solutions of the truncated Dyson–Schwinger equation for the quark propagator at finite temperatures within the rainbow-ladder approximation are analysed in some detail.

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Publ.-Id: 27723 - Permalink


Phase structures emerging from holography with Einstein gravity - dilaton models at finite temperature
Zöllner, R.; Kämpfer, B.;
Asymptotic AdS Riemann space-times in five dimensions with a black brane (horizon) sourced by a fully back-reacted scalar field (dilaton) offer - via the holographic dictionary - various options for the thermodynamics of the flat four-dimensional boundary theory, uncovering Hawking-Page, first-order and second-order phase transitions up to a cross-over or featureless behavior. The relation of these phase structures to the dilaton potential is clarified and illustrating examples are presented. Having in mind applications to QCD we study vector mesons in the probe limit with the goal to figure out conditions for forming Regge type series of radial excitations and address the issue of meson melting.

Publ.-Id: 27722 - Permalink


Phytotoxicity of polymetallic mine wastes from southern Tuscany and Saxony
Franzaring, J.; Ancora, S.; Paoli, L.; Fongoh, A. H.; Büttner, P.; Fangmeier, A.; Schlosser, S.; Monaci, F.;
Restoration potential of mine wastes or approaches to improve soil conditions and to ameliorate phytotoxicity on these sites may be simulated in standardized greenhouse experiments. Plants can be cultivated side by side on materials from different origins in dilution series with defined admixtures of certain aggregates. Mine wastes used in the present study originated from Fenice Capanne (FC, Tuscany, Italy) and Altenberg (ALT, Saxony, Germany). Tailings of the Italian site contain high concentrations of lead, zinc, arsenic and sulphur while tin, wolfram, molybdenum and lithium are highly elevated in the German mine waste. We tested growth responses of five crop species and analyzed concentrations of various metals and nutrients in the shoot to evaluate the toxicity of the FC mine waste and found oilseed rape being the most and corn the least resistant crop. Interestingly, oilseed rape accumulated seven times higher levels of lead than corn without showing adverse effects on productivity. In a subsequent comparison of FC and ALT mine waste, we cultivated different species of buckwheat (Fagopyrum spec.), a fast growing genus that evolved in mountain areas and that has been shown to be tolerant to low pH and high concentrations of metals. We found that the FC mine waste was more toxic than the ALT substrate in F. tataricum and F. esculentum. However, lower admixtures of FC material (10%) resulted in stronger growth reductions than higher proportions (25%) of the mine waste which was primarily related to the slightly lower pH and higher availability of essential metals due to the admixture of sand. These results confirm the importance of managing the soil chemical and physical characteristics of wastelands and call for the development of assisted reclamation to prepare sites for regular biomass production.
Keywords: Mine wastes, Phytoremediation, Heavy metals, Oilseed rape, Buckwheat, Soil amendment

Publ.-Id: 27721 - Permalink


Stability of melt flow during magnetic sonication in a floating zone configuration
Grants, I.; Gerbeth, G.;
This paper considers the linear stability of a liquid metal flow driven by superimposed alternating and static axial magnetic fields in the floating zone configuration. A simple model is constructed that assumes a slight axial variation of the flow-driving radial magnetic force and a low-to-moderate skin effect. This force drives two symmetrical flow tori. Formation of the field-parallel layer is observed for a strong static field. In this regime the instability sets in as a standing azimuthal wave around the circumference of the cylindrical melt volume near its midplane. The length of this wave scales with the thickness of the parallel layer. The instability criterion may be formulated in terms of an interaction parameter reaching its critical value at around 525.
Keywords: -

Publ.-Id: 27720 - Permalink


High-speed X-ray CT imaging of a strongly cavitating nozzle flow
Bauer, D.; Barthel, F.; Hampel, U.;
Examining or imaging of internal structures in flows with cavitation is still one of the greatest challenges in this field of research. In a specially designed nozzle, a strong cavitation region (CR) is generated with a liquid core (LC) in the center, surrounded by vapour. While it is almost not feasible to visualize the inside of the CR with visible light, it is shown that with high-speed X-ray computed tomography it is possible to visualize the dynamics of the unsteady cavitational flow structures inside the CR. The observed phenomena start with a ring of cavitation and small amounts of vapour inside the LC at / near the entrance of the cavitation channel. Further downstream the cavitation is growing rapidly and cavitation structures, as string cavitation can be identified inside the LC. In addition the results are compared with former time averaged CT images of the same nozzle and with results obtained with high-speed videography.
Keywords: Cavitation Flow, ROFEX, Ultrafast X-ray CT

Publ.-Id: 27719 - Permalink


Stellar and thermal neutron capture cross section of ⁹Be
Wallner, A.; Bichler, M.; Coquard, L.; Dillmann, I.; Forstner, O.; Golser, R.; Heil, M.; Käppeler, F.; Kutschera, W.; Martschini, M.; Mengoni, A.; Merchel, S.ORC; Michlmayr, L.; Priller, A.; Steier, P.; Wiescher, M.
The neutron capture cross section of ⁹Be for stellar energies was measured via the activation technique using the Karlsruhe Van de Graaff accelerator in combination with accelerator mass spectrometry at the Vienna Environmental Research Accelerator. To characterize the energy region of interest for astrophysical applications, activations were performed in a quasi-stellar neutron spectrum of kT = 25 keV and for a spectrum at En = 473+53 keV. Despite of the very small cross section, the method used provided the required sensitivity for obtaining fairly accurate results of 10.4+0.6 and 8.4+1.0 µb, respectively. With these data it was possible to constrain the cross section shape up to the first resonances at 622 and 812 keV, thus allowing for the determination of Maxwellian averaged cross sections at thermal energies between kT = 5 and 100 keV. In addition, we report a new experimental cross section value at thermal energy of sth = 8.31+0.52 mb.
Keywords: accelerator mass spectrometry, stellar nuclear reactions, supernova

Publ.-Id: 27717 - Permalink


Development of a novel target module redirecting UniCAR T cells to Sialyl Tn-expressing tumor cells
Loureiro, L.; Feldmann, A.; Bergmann, R.; Koristka, S.; Berndt, N.; Arndt, C.; Pietzsch, J.; Novo, C.; Videira, P.; Bachmann, M.;
The development of antibody-based therapies has been driven by progress in the immune response field culminating in the development of chimeric antigen receptors (CARs) as a promising approach in cancer immunotherapy. Nevertheless, drawbacks associated with CAR T cell therapies include on-target off-tumor effects or severe toxicity. Recently, we developed a novel modular universal CAR (UniCAR) platform to increase clinical safety while maintaining the efficacy of CAR T cell therapy. UniCAR T cells are exclusively activated via a target module (TM) that allows the cross-link between UniCAR T cells and target cancer cells. Here, we describe a novel TM against the tumor-associated carbohydrate antigen sialyl-Tn (STn). The developed anti-STn TM efficiently activate and redirect UniCAR T cells to STn-expressing tumors in a highly efficient target-specific and target-dependent manner, promoting the secretion of pro-inflammatory cytokines, tumor cell lysis of breast and bladder cancer cells in vitro and of breast cancer cells in experimental mice. Additionally, PET-imaging shows that anti-STn TM is enriched at the tumor site representing the potential use of this TM in diagnostic imaging. Taken together, these data demonstrate the effective and potential use of this CAR T cell-derived modular system to target STn in different types of cancer.
Keywords: Immunotherapy, CAR T cell therapy, Sialyl-Tn (STn)

Publ.-Id: 27716 - Permalink


Euler-Euler Modeling of Mass Transfer and Chemical Reaction
Rzehak, R.;
Work done at HZDR on Euler-Euler simulation including mass transfer and chemical reaction is presented.
Keywords: mass transfer, chemical reaction, chemisorption, enhancement factor, dispersed gas-liquid multiphase flow, Euler-Euler two-fluid model, CFD simulation
  • Invited lecture (Conferences)
    Lectures on multiphase CFD, 06.-08.06.2018, Changsha, China

Publ.-Id: 27715 - Permalink


Baseline Model for Simulation of Bubbly Flows
Rzehak, R.;
An overview of the HZDR-baseline Model for Simulation of Bubbly Flows is given.
Keywords: dispersed gas liquid multiphase flow, Euler-Euler two-fluid model, closure relations, CFD simulation, model validation
  • Invited lecture (Conferences)
    Lectures on multiphase CFD, 06.-08.06.2018, Changsha, China

Publ.-Id: 27714 - Permalink


Speciation of actinides in environmentally relevant systems by advanced synchrotron techniques
Pidchenko, I.; Suksi, J.; Tullborg, A.; Scheinost, A.; Kvashnina, K. O.;
The disposal in deep geological repositories is a widely considered option for the management of spent nuclear fuel (SNF). SNF consists mainly of actinides (An): uranium (U), minor An and fission products which are potentially released from the SNF and may migrate then into the geologic environment. Such scenario depends on the stability of the SNF matrix and engineered geological barriers, as well as from the groundwater conditions at the disposal site. The versatile chemistry of An with their complex interaction and their low content in the natural environments require highly sensitive and non-destructive techniques for speciation and structural characterization.
We report a systematic application of X-ray absorption spectroscopies (XAS) measured at U L3 and M4 edges in the high-energy resolution fluorescence detected (HERFD) mode for the investigation of complex U systems. Here reported systems include U interaction with magnetite nanoparticles in laboratory systems and U speciation in the granite fracture coating from 86 m depth profile of the Forsmark investigation site. U M4 HERFD-XAS clearly distinguishes U(IV), U(V) and U(VI) existing simultaneously in the same sample. U(V) is the main species formed and stabilized in the structure of magnetite at environmentally relevant U concentrations even when exposed on air for several hundred days. U L3 HERFD-XAS analysis of the granite shows that a mixed U oxide with composition close to U4O9 is formed on the surface of material. This finding agrees with reducing conditions for the investigated depth profile. U4O9 may have varying content of U(IV), U(V) and U(VI) depending on chemical conditions and spectra analysis. XAS shows that up to 28% of total U can be present in U4O9 as U(VI). Sequential leaching of granite results in 24% of soluble U, preferably as U(VI), supporting preliminary XAS results. Based on the spectroscopic analysis and available chemical data structural and redox transformation pathways are proposed.
  • Poster
    Goldschmidt 2018, 12.-27.08.2018, Boston, USA

Publ.-Id: 27713 - Permalink


Evidence of the negative thermal expansion of the UO2.00 fluorite local structure
Martin, P. M.; Prieur, D.; Epiphano, E.; Dardenne, K.; Rothe, J.; Hennig, C.; Scheinost, A. C.; Neuville, D.;
The thermal properties of uranium dioxide UO2 are of significant importance in view of a safe use of the nuclear energy. Up to now, UO2 is considered as a fluorite structure (Fm-3m) from room temperature to the melting point (3147 ± 20 K), in which both interatomic distances and lattice parameters expands with the temperature. This view was challenged by more recent in situ synchrotron X-ray diffraction measurements, showing an unusual thermal shrinking of the U-O distances up to the melting point.
It was later confirmed later by neutron pair distribution function results and interpreted as a consequence of the splitting of the U-O distances due to a change in the U local symmetry from Fm-3m to Pa-3.
In contrast to these previous investigations, we used an element-specific synchrotron-based spectroscopic method (X-Ray Absorption Spectroscopy) to probe in situ the uranium local environment in UO2.00 sintered pellet sample from 50 K to 1265 K. In the whole range, the U sublattice remains locally of the fluorite type. Whereas, results collected in Ar-4% H2 atmosphere at 298, 805, 1090 and 1265 K using a dedicated furnace, shown a decrease of the first U-O bond lengths with increasing temperature. The direct determinations of U oxidation state during the measurements clearly show that neither reduction nor reduction of the UO2.00 sample occurred ensuring that the work was really done on a stoichiometric compound. Furthermore, an increase of the disorder is observed with increasing temperature which we modelled using the Einstein model. These findings are of significant importance in order to understand and predict the thermal behaviour of nuclear fuel.
Keywords: thermal contraction UO2 XAFS
  • Lecture (Conference)
    NuMat 2018, 14.-18.10.2018, Seattle, USA

Publ.-Id: 27712 - Permalink


A baseline closure concept for simulating bubbly flow with phase change: interfacial heat transfer coefficient
Liao, Y.; Krepper, E.; Lucas, D.;
In line with the best practice guidelines for computational fluid dynamics in nuclear reactor safety, Helmholtz-Zentrum Dresden – Rossendorf proposed an Euler-Euler baseline closure concept some years ago. Simulations with a fixed set of closures may help to identify model inadequacy and facilitate the further improvement. Currently, the baseline model concerns interfacial momentum and turbulent kinetic energy exchange as well as bubble coalescence and breakup. It has been tested for a wide range of isothermal applications with different geometrical configurations and material systems. In the present work, the baseline model is extended to non-isothermal flows by including a heuristic model for interfacial heat transfer coefficient. The extended baseline model is validated for both bubble-growing in superheated liquid and -condensing in sub-cooled liquid. The baseline model proposal is independent on the use of a certain CFD code. The presented simulation is carried out with the commercial software ANSYS CFX by employing the best practice guidelines. The simulated liquid temperature, gas volume fraction, vapor bubble size and velocity are compared with the measured ones. The effectivity of the model is demonstrated by the general good agreement.
  • Contribution to proceedings
    CFD4NRS-7 OECD-NEA & IAEA Workshop, 04.-06.09.2018, Shanghai, China
  • Lecture (Conference)
    CFD4NRS-7 OECD-NEA & IAEA Workshop, 04.-06.09.2018, Shanghai, China
  • Nuclear Engineering and Design 348(2019), 1-13
    DOI: 10.1016/j.nucengdes.2019.04.007

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  • Secondary publication expected from 08.04.2020

Publ.-Id: 27711 - Permalink


Cfd modelling of flashing instability in natural circulation cooling systems
Liao, Y.; Schuster, C.; Hu, S.; Lucas, D.;
Passive cooling systems driven by natural circulation are common design features of proposals for advanced reactors. The natural circulation systems are inherently more unstable than forced circulation ones due to its nonlinear nature and low driving force. Any disturbance, e.g. flashing or boiling inception, in the driving force will affect the flow which in turn will influence the driving force leading to an oscillatory behavior. Owing to safety concerns, flashing instability particularly for advanced boiling water reactors has been broadly investigated, and many test facilities have been constructed in the past. A number of numerical analyses of experimental test cases are available. Nevertheless, there exists a need to update the method from one-dimensional system codes to high-resolution computational fluid dynamics (CFD). In the present work flashing-induced instability behavior and flow pattern in the riser of the GENEVA facility, which is a downscale of a reactor containment passive cooling system, is investigated using the commercial CFD code ANSYS CFX. A two-fluid model is adopted for the unstable turbulent gas-liquid flow, and the HZDR baseline closure is used to model interphase mass, momentum, heat transfer as well as bubble-induced turbulence. The simulated fluid temperature, pressure and local void fraction at different heights of the riser are compared with the measured ones. The limitation and possibility of the CFD technique for such complex two-phase scenarios are discussed, and suggestions for improving the predictability of simulations are made.
  • Contribution to proceedings
    26th International Conference on Nuclear Engineering, ICONE26, 23.-26.07.2018, Hammersmith, London, England
  • Lecture (Conference)
    26th International Conference on Nuclear Engineering, ICONE26, 23.-26.07.2018, Hammersmith, London, England

Publ.-Id: 27710 - Permalink


Simulations of ultrafast X-ray laser experiments
Fortmann-Grote, C.; Andreev, A. A.; Appel, K.; Branco, J.; Briggs, R.; Bussmann, M.; Buzmakov, A.; Garten, M.; Grund, A.; Huebl, A.; Jurek, Z.; Loh, N. D.; Nakatsutsumi, M.; Samoylova, L.; Santra, R.; Schneidmiller, E. A.; Sharma, A.; Steiniger, K.; Yakubov, S.; Yoon, C.; Yurkov, M. V.; Zastrau, U.; Ziaja-Motyka, B.; Mancuso, A. P.;
Simulations of experiments at modern light sources, such as optical laser laboratories, synchrotrons, and free electron lasers, become increasingly important for the successful preparation, execution, and analysis of these experiments investigating ever more complex physical systems, e.g. biomolecules, complex materials, and ultra-short lived states of matter at extreme conditions. We have implemented a platform for complete start-to-end simulations of various types of photon science experiments, tracking the radiation from the source through the beam transport optics to the sample or target under investigation, its interaction with and scattering from the sample, and registration in a photon detector. This tool allows researchers and facility operators to simulate their experiments and instruments under real life conditions, identify promising and unattainable regions of the parameter space and ultimately make better use of valuable beamtime. In this paper, we present an overview about status and future development of the simulation platform and discuss three applications: 1.) Single-particle imaging of biomolecules using x-ray free electron lasers and optimization of x-ray pulse properties, 2.) x-ray scattering diagnostics of hot dense plasmas in high power laser-matter interaction and identification of plasma instabilities, and 3.) x-ray absorption spectroscopy in warm dense matter created by high energy laser-matter interaction and pulse shape optimization for low-isentrope dynamic compression.
Keywords: XFEL, ultrafast, simulation, imaging, scattering, X-ray, biomolecules, warm dense matter
  • Contribution to proceedings
    SPIE Optics + Optoelectronics (2017), 20.06.2017, Praha, Česká republika
    SPIE 10237, Advances in X-ray Free-Electron Lasers Instrumentation IV, 978-1-5106-0975-4; 978-1-5106-0976-1
    DOI: 10.1117/12.2270552

Publ.-Id: 27709 - Permalink


Challenges in predicting the role of water chemistry in flotation through simulation with an emphasis on the influence of electrolytes
Michaux, B.; Rudolph, M.; Reuter, M. A.;
As the mining industry is facing an increasing number of issues related to its fresh water consumption, a series of water-saving strategies are progressively being implemented in the processing plants, such as increasing the recirculation of process water. This recirculation is associated with a modification of the process water chemistry, which can be detrimental to the process performance, in particular flotation. This modification is, unfortunately, hardly predictable and often constitutes an obstacle to the implementation of the highly-needed water-saving strategies. However, a large amount of knowledge has been accumulated over the years to better understand how the process water chemistry can affect different parts of the flotation process, yet much of this knowledge still needs to be digitalized in a practical and suitable form to be of use in mineral processing simulators. Such digitalization requires the linking of water properties to the flotation process parameters, in particular the flotation kinetics of the different particles present in the system. This paper discusses a variety of mechanisms through which electrolytes can modify the flotation performance, and how those mechanisms translate into a modification of the flotation kinetics when this link can be made. A series of missing relationships needed for the knowledge digitalization in mineral processing simulators are being highlighted throughout this paper, hence addressing the challenge of predicting the role of electrolytes on the flotation plant performance through simulation.
Keywords: Water chemistry; Electrolytes; Solution thermodynamics; Flotation; Flotation kinetics.

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  • Secondary publication expected

Publ.-Id: 27708 - Permalink


Reprocessing of a southern Chilean Zn tailing by flotation - a case study
Babel, B.; Penz, M.; Schach, E.; Böhme, S.; Rudolph, M.;
The reprocessing of tailings can have economic and environmental benefits compared to the processing of primary ore deposits. In this paper we present the characterization of a tailings dam in southern Chile by means of mineralogical and geochemical investigations focusing on sphalerite and trace elements with the aim to investigate a potential reprocessing. The assessment is followed by a flotation study, focusing on the recovery of sphalerite with a high selectivity towards sulfidic and non-sulfidic gangue minerals. An in-depth analysis of a selected test based on mineral liberation analysis data is used to refine the liberation, concentration and flotation weighting function for future investigations.
Keywords: Geometallurgy; Flotation; Sphalerite; Tailings; Reprocessing

Publ.-Id: 27707 - Permalink


Bioremediation of uranium contaminated sites from former mining activities by microorganisms – a microscopic and spectroscopic approach.
Krawczyk-Bärsch, E.; Gerber, U.; Steudtner, R.; Müller, K.; Moll, H.; Rossberg, A.; Merroun, M. L.;
Environmental pollution by metals and radionuclides is one of the biggest challenges which have to be solved globally. For in situ remediation of uranium contaminated waste waters and environments from activities such as uranium mining and uranium processing, microorganisms could be important due to their ability to immobilize radionuclides and heavy metals. To improve bioremediation strategies based on a better understanding of binding mechanisms on the molecular level we applied uranium interaction experiments with selected microorganisms from the former uranium mining site Königstein (Germany). Acidovorax facilis, the Gram-negative Betaproteobacteria, was one of the microorganisms used for our experiments. It is an aerobic and widely distributed strain in nature and commonly found in soils but also in the mine water of uranium mines. The present work describes a multidisciplinary approach combining wet chemistry, transmission electron microscopy, and spectroscopy .The results reveal that the local coordination of uranium associated with the cells of A. facilis depends upon time of incubation. Uranium biosorption by outer membrane lipopolysaccharides containing phosphoryl residues was observed within the first hours of contact between the cells and uranium. By increasing the incubation time up to 24 h the implication of carboxyl groups within the cell wall peptidoglycan was proved in addition to phosphoryl groups. To a lower extend, uranium is also coordinated to phosphoryl groups of the intracellular polyphosphate granules. This study showed that different cell compartments play a major role in the sequestration of uranium. Our findings contribute to a better understanding of the mechanisms of microbial response to uranium and demonstrate that A. facilis may play an important role in predicting the fate and transport of uranium in uranium-contaminated sites by being a suitable candidate for bioremediation purposes.
Keywords: Uranium, A. facilis, sorption, TRLFS, ATR FT-IR, TEM
  • Lecture (Conference)
    19th International Conference on Heavy Metals in the Environment (ICHMET 2018),, 22.-25.07.2018, Athens, U.S.

Publ.-Id: 27706 - Permalink


Why do secondary cracks preferentially form in hot-rolled ODS steels in comparison with hot-extruded ODS steels?
Das, A.ORC; Viehrig, H. W.; Altstadt, E.ORC; Bergner, F.ORC; Hoffmann, J.ORC
Secondary cracks are known to absorb energy, retard primary crack propagation and initiate at lower loads than primary cracks. They are observed more often in hot-rolled than in hot extruded ODS steels. In this work, the microstructural factors responsible for this observation are investigated. Better understanding of these factors can lead to tailoring of im-proved ODS steels. Fracture toughness testing of two batches of 13Cr ODS steel, one hot-rolled and the other hot-extruded, was carried out. The fracture behaviour of secondary cracks was investigated using scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). Crystallographic texture and grain morphology play a predominant role in preventing secondary cracks in hot-extruded ODS steels. At lower temperatures, secondary cracks occur predominantly via transgranular cleavage. The fracture mode changes to ductile and intergranular at higher temperatures.
Keywords: ODS steel, fracture behaviour, anisotropy, intergranular fracture, secondary cracking, delamination
Related publications
Why are hot-rolled ODS steels more prone to secondary … (Id 28114) is an alternate identifier of this publication

Publ.-Id: 27705 - Permalink


Characterizing the Ionization Potential Depression in Dense Carbon Plasmas with High-Precision Spectrally Resolved X-ray Scattering
Kraus, D.; Bachmann, B.; Barbrel, B.; Falcone, R. W.; Fletcher, L. B.; Frydrych, S.; Gamboa, E. J.; Gauthier, M.; Gericke, D. O.; Glenzer, S. H.; Göde, S.; Granados, E.; Hartley, N. J.; Helfrich, J.; Lee, H. J.; Ravasio, A.; Nagler, B.; Schumaker, W.; Vorberger, J.; Döppner, T.;
We discuss the possibility of obtaining highly precise measurements of the ionization potential depression in dense plasmas with spectrally resolved X-ray scattering, while simultaneously determining the electron temperature and the free electron density. A proof-of-principle experiment at the Linac Coherent Light Source, probing isochorically heated carbon samples, demonstrates the capabilities of this method and motivates future experiments at X-ray free electron laser facilities.

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  • Secondary publication expected from 13.11.2019

Publ.-Id: 27704 - Permalink


High energy resolution X-ray spectroscopy of actinide nanomaterials
Kvashnina, K. O.;
This contribution will provide a brief overview of applications of advanced X-ray spectroscopic techniques that take advantage of the resonant inelastic X-ray scattering (RIXS) in the hard and tender X-ray range and have recently become available for studying the electronic structure of actinides at the synchrotron facilities. We will focus on the high-energy-resolution fluorescence detection (HERFD) X-ray absorption near edge structure (XANES) and RIXS spectroscopies at the U, Th and Pu L3 edges of actinide (hydroxo-) oxide nanoparticles [1–4]. The experiments were performed at the Rossendorf Beamline (ROBL) at the ESRF, dedicated to the actinides science, where we recently installed a novel X-ray emission spectrometer [5] with ground-breaking detection limits. We will show how the detail information about local and electronic structure of actinide nanomaterials can be obtained, including information on the electron-electron interactions, hybridization between molecular orbitals, the nature of their chemical bonding, and the occupation and the degree of the f-electron localization.
The experimental spectral features has been analyzed using a number of theoretical methods, such as the full multiple scattering (FEFF) and ab-initio finite difference method near-edge structure (FDMNES) codes. In connection with presented results, the capabilities and limitations of the experimental techniques and theoretical methods will be discussed
  • Lecture (Conference)
    ATAS Workshop, 06.-09.11.2018, Nice, France

Publ.-Id: 27703 - Permalink


High energy resolution X-ray spectroscopy of actinide nanomaterials
Kvashnina, K. O.;
Actinide nanomaterial research with cutting-edge effort in synthesis, processing and atomic-scale characterization is a fascinating and a rapidly progressing field of science. Experts around the world develop highly controllable synthesis approaches, use more sensitive characterization tools and finally improve models and theories to explain the experimental observations.
This contribution will provide an overview of advanced X-ray spectroscopic techniques that take advantage of the resonant inelastic X-ray scattering (RIXS) in the hard and tender X-ray range and have become available for studying the electronic structure of actinides at the syn-chrotron facilities1–6. We will show latest results of actinide (hydroxo-) oxide nanoparticles stud-ies obtained by high-energy-resolution fluorescence detection (HERFD) X-ray absorption near edge structure (XANES) and RIXS spectroscopies (Fig.1.) at the U, Th and Pu L3 and M4,5 edges. The experiments were performed at the Rossendorf Beamline (ROBL) at the ESRF, where we recently installed a novel X-ray emission spectrometer7 with ground-breaking detection limit. We will show how the detail information about local and electronic structure of actinide nanomaterials can be obtained, including information on the electron-electron interactions, hybridization between molecular orbitals, the nature of their chemical bonding, and the occupation and the degree of the f-electron localization. The experimental spectral features have been analyzed using a number of theoretical methods. It might be of interest for fundamental research in chemistry and physics of actinide systems as well as for the applied science
  • Lecture (Conference)
    Advanced Techniques in Actinide Spectroscopy (ATAS2018), 06.-09.11.2018, Nice, France

Publ.-Id: 27702 - Permalink


The origin of low bandgap and ferroelectricity of a co-doped BaTiO3
Phuyal, D.; Das, S.; Mukherjee, S.; Jana, S.; Kvashnina, K. O.; Sarma, D. D.; Karis, O.; Rensmo, H.; Butorin, S. M.;
We recently demonstrated a new low bandgap ferroelectric material based on BaTiO3. The co-doping of BaTiO3 exhibited robust spontaneous electrical polarization with bandgap values suitable for visible light absorption for application in optoelectronic devices. In this study, the valence and conduction bands are investigated with a combination of x-ray spectroscopies and DFT calculations. The local electronic structure and coordination of BaTi1-x(Mn1/2Nb1/2)xO3 is studied by means of x-ray absorption at the Ti K, Mn K, and O K edges. The spectroscopic evidence suggests only small distortions to the parent tetragonal ferroelectric system, reducing of the bandgap through compositional doping without compromising ferroelectricity to a large extent. The Ti K pre-edge features in particular, which are sensitive to site coordination and an indication of Ti off-centering within the Ti-O6 octahedra, shows modest changes with doping and strongly corroborates with our measured polarization values. Resonant photoemission spectroscopy results reveal newly created Mn d bands that hybridize with O 2p as well as additional valence band edge states with predominantly Mn d character. Through various x-ray spectroscopic techniques, we reveal the electronic structure that allows the compound to retain its ferroelectricity while reducing the bandgap

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  • Secondary publication expected from 19.11.2019

Publ.-Id: 27701 - Permalink


Effect of time–modulated magnetic fields on the solidification structure and extrusion properties of wrought aluminium
Räbiger, D.; Resewski, C.; Müller, S.; Willers, B.; Reimers, W.; Eckert, S.;
The adjustment of fine grain morphologies has been approved to be a crucial issue for improving characteristics and properties of cast and wrought aluminium alloys. Several methods are known to achieve grain refinement in solidification processes: add-on of grain refiners, rapid cooling conditions, mechanical or electromagnetic stirring or ultrasonic treatment.
AC magnetic fields provide a contactless method to control the flow inside a liquid metal and the grain size of the solidified ingot. Many studies have shown that beneficial effects like a distinct grain refinement or the promotion of a transition from a columnar to an equiaxed dendritic growth (CET) can be obtained. However, electromagnetically-driven melt convection may also produce segregation freckles on the macroscale. The achievement of superior casting structures needs a well-aimed control of melt convection during solidification.
Previous investigations considered the use of time-modulated AC magnetic fields to control the heat and mass transfer at the solidification front. It has been shown recently under laboratory conditions that an accurate tuning of the magnetic field parameters can avoid segregation effects and homogenize the mechanical properties.
This present study examines the directional solidification of commercial wrought aluminium alloys from a water-cooled copper chill. Rotating time-modulated magnetic fields were used to agitate the melt. The impact of flow on the resulting macro and micro structure are investigated. The solidified structure was reviewed in comparison to an unaffected solidified ingot and ingot prepared with chemical grain refiner. In addition results from extrusion process experiments are introduce. Our results demonstrate the potential of time–modulated magnetic fields to control the grain size, the formation of intermetallic phases and the morphology and distribution of pores.
Keywords: wrought aluminum alloy, time modulated magnetic field, bar extrusion
  • Lecture (Conference)
    The 9th International Symposium on Electromagnetic Processing of Materials, 14.-18.10.2018, Hyogo, Japan
  • Contribution to proceedings
    The 9th International Symposium on Electromagnetic Processing of Materials (EPM2018), 14.-18.10.2018, Hyogo, Japan
  • Open Access LogoIOP Conference Series: Materials Science and Engineering 424(2018), 012039
    DOI: 10.1088/1757-899X/424/1/012039

Publ.-Id: 27700 - Permalink


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