Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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33408 Publications

Microstructure characterization and strengthening mechanisms of oxide dispersion strengthened (ODS) Fe-9%Cr and Fe-14%Cr extruded bars

Chauhan, A.; Bergner, F.ORC; Etienne, A.; Aktaa, J.; de Carlan, Y.; Heintze, C.; Litvinov, D.; Hernandez-Mayoral, M.; Oñorbe, E.; Radiguet, B.; Ulbricht, A.
The collaborative study is focused on the relationship between microstructure and yield stress for an ODS Fe-9%Cr-based transformable alloy and an ODS Fe-14%Cr-based ferritic alloy. The contributions to the total room temperature yield stress arising from various strengthening mechanisms are addressed on the basis of a comprehensive description of the microstructures uncovered by means of transmission electron microscopy (TEM), electron backscatter diffraction (EBSD), small-angle neutron scattering (SANS) and atom probe tomography (APT). While these methods provide a high degree of complementarity, a reasonable agreement was found in cases of overlap of information. The derived set of microstructure parameters along with reported strengthening equations was used to calculate the room temperature yield stress. The estimates were critically compared with the measured yield stress for an extended set of alloys including data reported for Fe-Cr model alloys and steels thus covering one order of magnitude or more in grain size, dislocation density, particle density and yield stress. The comparison shows that particle strengthening, dislocation forest strengthening, and Hall-Petch strengthening are the major contributions and that a mixed superposition rule reproduces the measured yield stress within experimental scatter for the whole extended set of alloys. The wide variation of microstructures additionally underpins the conclusions and goes beyond previous work, in which one or few ODS steels and narrow microstructure variations were typically covered.
Keywords: ODS steel, Strengthening mechanisms, TEM, APT, SANS

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Permalink: https://www.hzdr.de/publications/Publ-25949
Publ.-Id: 25949


Modeling electromagnetically driven free-surface flows motivated by the Ribbon Growth on Substrate (RGS) process

Beckstein, P.; Galindo, V.ORC; Schönecker, A.; Gerbeth, G.
The Ribbon Growth on Substrate (RGS) technology is a crystallization technique that allows direct casting of silicon wafers and sheets of advanced metal-silicide compounds. With the potential of reaching high crystallization rates, it promises a very efficient approach for future photo-voltaic silicon wafer production compared to well-established processes in industry. However, a number of remaining problems, like process stability and controllability, need to be addressed for the RGS technology to eventually become a competitor in the near future. In this regard, it is very desirable to gain detailed insights into the characteristic process dynamics. To comply with this demand, we have developed a new numerical tool based on OpenFOAM (foam-extend), capable of simulating the free-surface dynamics of the melt flow under the influence of an applied alternating magnetic field. Our corresponding model thereby resolves the interaction of hydrodynamic and magnetodynamic effects in three-dimensional space. Although we currently focus on the RGS process, the modeling itself has been formulated in a more general form, which may be used for the investigation of similar problems, too. Here we provide a brief overview of these developments.
Keywords: RGS process, OpenFOAM, electromagnetic driven flow, foam-extend, free-surface

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Permalink: https://www.hzdr.de/publications/Publ-25948
Publ.-Id: 25948


Charakterisierung eines zerkleinerten Mobiltelefons mittels Mineral Liberation Analysis (MLA)

Sandmann, D.ORC
Mobiltelefone, von denen im Jahr 2016 weltweit über 1,4 Milliarden Geräte hergestellt wurden, können bis zu 60 verschiedene Elemente enthalten (TrendForce Corp., The Royal Society of Chemistry). Gegenwärtig werden allerdings nur sehr wenige der in den Mobiltelefonen enthaltenen Elemente mit Recycling-Raten von mehr als 50 % recycelt (Compound Interest). Bei den meisten Elementen liegt die Recycling-Rate bei deutlich unter 50 % und bei den Seltenen Erden, Indium, Tantal oder Gallium sogar bei unter 1 %! Ein Hauptproblem beim Recycling von Mobiltelefonen ist ihre komplexe Zusammensetzung aus vielen Einzelbauteilen. Erschwerend kommt hinzu, dass viele Elemente kommen nur in Spuren vorhanden sind und / oder sich in hoch-komplexen Materialverbunden befinden.
Um ein effektiveres Recycling der Mobiltelefone zu ermöglichen, ist es unumgänglich ihre Bauteile, das Vorkommen der Elemente darin, sowie das Zerkleinerungsverhalten möglichst detailliert zu charakterisieren.
In einer Pilotstudie wurde ein, vom Lehrstuhl für Recyclingmaschinen der TU Bergakademie Freiberg, mit einem Universal-Granulator UG300 zerkleinertes Nokia-Mobiltelefon Modell 5228 Typ RM-625 mit Hilfe von Mineral Liberation Analysis (MLA) untersucht. Die Analyse an drei Siebfraktionen des zerkleinerten Materials erfolgte mit einer MLA 650F am Helmholtz-Institut Freiberg für Ressourcentechnologie.
Eine erste manuelle Aufnahme von Rückstreuelektronenbildern zeigt unter anderem Metallphasen mit einer Kleinheit von < 0,5 µm. Nachfolgend wurden die Proben in einer automatisierten MLA-Messung mit einem Gitternetz von EDX-Spektren abgerastert (GXMAP-Modus). Insgesamt wurden bei der Analyse ca. 130 verschiedene Phasen detektiert. Mehr als 100 davon treten mit Anteilen von < 1 Gewichtsprozent auf. Ein Vergleich des Modalbestandes der drei Siebfraktionen zeigte eine Anreicherung bestimmter Bauteile in speziellen Fraktionen.

Referenzen:
Compound Interest - http://www.compoundchem.com/2015/09/15/recycling-phone-elements/
The Royal Society of Chemistry 20.03.2017 - https://www.chemistryworld.com/feature/smartphone-recycling/2500497.article
TrendForce Corp. Press Release 25.01.2017 - http://press.trendforce.com/node/view/2741.html
  • Lecture (Conference)
    Tagung 2017 „Aufbereitung und Recycling“, 08.-09.11.2017, Freiberg, Deutschland

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Permalink: https://www.hzdr.de/publications/Publ-25947
Publ.-Id: 25947


Validation of X-ray radiography for characterization of gas bubbles in liquid metals

Keplinger, O.; Shevchenko, N.; Eckert, S.
X-ray radiography has proved to be an efficient and powerful tool for the visualization of two-phase flows in non-transparent fluids, in particular in liquid metals. This paper presents a validation of the X-ray radiography by comparing measurements in water with corresponding results obtained by optical methods. For that purpose Ar bubbles were injected through a single orifice. The measurements results are compared in terms of bubble size, bubble shape and velocity. Furthermore, visualization experiments were performed in the eutectic alloy GaInSn where the image contrast between the liquid phase and the gas bubble is much stronger. Some obvious differences of the bubble dynamics in water and GaInSn are discussed.
Keywords: X-ray radiography, two-phase flows, GaInSn, water

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Permalink: https://www.hzdr.de/publications/Publ-25946
Publ.-Id: 25946


Spins in Formation

Schultheiss, H.
Spinwellen sind kollektive Anregungen magnetischer Momente eines Festkörpers. Lokal lassen sie sich auf sehr kleinen Längenskalen lenken durch ein Drehen der Magnetisierung. Damit ist es möglich, den Fluss von Spinwellen gezielt zu steuern. Dieser Vorgang könnte in der Informationstechnologie als Logik- baustein Anwendung finden.
Keywords: Spintronic, Magnonic
  • Physik Journal 09(2017), 59
  • Lecture (others)
    Physikalisches Kolloquium Universität Augsburg, 27.11.2017, Augsburg, Deutschland
  • Lecture (others)
    Physikalisches Kolloquium TU Chemnitz, 15.11.2017, Chemnitz, Deutschland
  • Lecture (others)
    Kolloquium Walther Meissner Institut, 27.1.2017, Garching, Deutschland
  • Lecture (others)
    SFB Seminar Uni Regensburg, 26.1.2017, Regensburg, Deutschland
  • Lecture (others)
    Physikalisches Kolloquium TU Dresden, 13.6.2017, Dresden, Deutschland
  • Invited lecture (Conferences)
    DPG Frühjahrstagung, 22.3.2017, Dresden, Deutschland
  • Lecture (Conference)
    633tes Wilhelm und Else Heraeus Seminar, 5.1.2017, Bad Honnef, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-25945
Publ.-Id: 25945


Magnonics: Spin waves connecting charges, spins and photons

Chumak, A. V.; Schultheiss, H.
Spin waves (SW) are the excitation of the spin system in a ferromagnetic condensed matter body. They are collective excitations of the electron system and, from a quasi-classical point of view, can be understood as a coherent precession of the electrons' spins. Analogous to photons, they are also referred to as magnons indicating their quasi-particle character. The collective nature of SWs is established by the short-range exchange interaction as well as the non-local magnetic dipolar interaction, resulting in coherence of SWs from mesoscopic to even macroscopic length scales. As one consequence of this collective interaction, SWs are 'charge current free' and, therefore, less subject to dissipation caused by scattering with impurities on the atomic level. This is a clear advantage over diffusive transport in spintronics that not only uses the charge of an electron but also its spin degree of freedom. Any (spin) current naturally involves motion and, thus, scattering of electrons leading to excessive heating as well as losses. This renders SWs a promising alternative to electric (spin) currents for the transport of spin information—one of the grand challenges of condensed matter physics.
Keywords: Magnonics, Spintronics, Photonics, Spin Waves

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Permalink: https://www.hzdr.de/publications/Publ-25944
Publ.-Id: 25944


Towards ion beam therapy based on laser plasma accelerators

Karsch, L.; Beyreuther, E.ORC; Enghardt, W.ORC; Gotz, M.; Masood, U.; Schramm, U.; Zeil, K.; Pawelke, J.ORC
Only few ten radiotherapy facilities worldwide provide ion beams, in spite of their physical advantage of better achievable tumor conformity of the dose compared to conventional photon beams. Since, mainly the large size and high costs hinder their wider spread, great efforts are ongoing to develop more compact ion therapy facilities.
One promising approach for smaller facilities is the acceleration of ions on micrometre scale by high intensity lasers. Laser accelerators deliver pulsed beams with a low pulse repetition rate, but a high number of ions per pulse, broad energy spectra and high divergences. A clinical use of a laser based ion beam facility requires not only a laser accelerator providing beams of therapeutic quality, but also new approaches for beam transport, dosimetric control and tumor conformal dose delivery procedure together with the knowledge of the radiobiological effectiveness of laser-driven beams.
Over the last decade research was mainly focused on protons and progress was achieved in all important challenges. Although currently the maximum proton energy is not yet high enough for patient irradiation, suggestions and solutions have been reported for compact beam transport and dose delivery procedures, respectively, as well as for precise dosimetric control. Radiobiological in vitro and in vivo studies show no indications of an altered biological effectiveness of laser-driven beams.
Laser based facilities will hardly improve the availability of ion beams for patient treatment in the next decade. Nevertheless, there are possibilities for a need of laser based therapy facilities in future.

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Permalink: https://www.hzdr.de/publications/Publ-25943
Publ.-Id: 25943


Tunable nonlinear optical resonances in Landau-quantized graphene

König-Otto, J. C.; Wang, Y.; Belyanin, A.; Berger, C.; de Heer, W. A.; Orlita, M.; Venanzi, T.; Pashkin, A.; Schneider, H.; Helm, M.; Winnerl, S.
Graphene has been in discussion as a candidate as a strong THz nonlinear material for a long time, because of its linear band structure [1,2]. However, an experimental demonstration of strong nonlinearities in Graphene in this spectral range is still missing. For Landau-quantized Graphene, in which the absorption is resonantly enhanced for allowed transitions between the Landau-levels, theory predicts a strongly enhanced nonlinearity, too [3]. In our joint experimental and theoretical work we study the third order nonlinearity in Landau-quantized graphene by employing a degenerate timeintegrated four-wave mixing experiment (FWM) in the mid-infrared spectral range. The free-electron laser FELBE was tuned to a photon energy of 78meV and the graphene sample was kept at 10K in a thin helium gas atmosphere. The magnetic field was set to 4.5T bringing the LL-1→LL0 and LL0→LL1 transition into resonance with the linearly polarized beams (see Fig.1a). The measured FWM signal (see Fig.1c) features a faster dynamics than the pump-probe signal (see Fig.1b) and is beyond the time resolution of our experiment. Nevertheless, we can recover the expected field dependencies of the studied third order nonlinearity in the experiment. The resonance behavior is measured by sweeping the magnetic field and is in agreement with our theoretical calculation. Furthermore, we derive a value of χ(3) from our experimental data that confirms the predicted strongly enhanced nonlinearity [4].
References
[1] S. A. Mikhailov and K. Ziegler, J. Phys.: Condens. Matter, 20, 384204, (2008)
[2] Z. Zhang and P. L. Voss, Opt. Lett., 36, 4569, (2011)
[3] X. Yao and A. Belyanin, Phys. Rev. Lett., 108, 255503, (2012)
[4] J. C. König-Otto, Y. Wang, A. Belyanin, C. Berger, W. A. de Heer, M. Orlita, A. Pashkin, H.
Schneider, M. Helm, and S. Winnerl, Nano Lett., 17, 2184, (2017)
Keywords: graphene, Landau-quantized graphene, nonlinear optics, carrier dynamics, spectroscopy
  • Lecture (Conference)
    Graphene Week 2017, 25.-29.09.2017, Athena, Hellas

Permalink: https://www.hzdr.de/publications/Publ-25942
Publ.-Id: 25942


THz Nonlinear Response of Landau-Quantized Graphene

König-Otto, J. C.; Wang, Y.; Belyanin, A.; Berger, C.; de Heer, W. A.; Orlita, M.; Pashkin, A.; Schneider, H.; Helm, M.; Winnerl, S.
The third-order nonlinear susceptibility of Landau-quantized graphene is studied by degenerate time-integrated four-wave mixing in the THz regime. The revealed resonance behavior and the observed field dependencies are in agreement with our theoretical calculations.
Keywords: graphene, Landau-quantized graphene, nonlinear optics, carrier dynamics, spectroscopy
  • Lecture (Conference)
    CLEO, 14.-19.05.2017, San Jose, USA

Permalink: https://www.hzdr.de/publications/Publ-25941
Publ.-Id: 25941


Influence of structural quality on the carrier dynamics in graphene

König-Otto, J. C.; Schneider, H.; Helm, M.; Winnerl, S.
Production of large-scale high quality graphene is a challenging task. Therefore understanding how quality will influence the properties of graphene is crucial for industrial applications. In this work we focus on the influence of defects on the carrier dynamics. To this end areas of a multilayer epitaxial graphene sample with high structural quality [1] are irradiated with different doses of low energy carbon ions. The different areas with now varying graphene quality (see D-Peaks in Raman spectra in Figure 1) are studied by a pump-probe experiment utilizing low energetic photons from a free-electron laser (photon energy 75meV). In this regime carrier relaxation is particularly slow as compared to excitation with visible light since scattering with optical phonons (energy 200meV) is efficiently suppressed [2]. The change in transmission is depicted in Figure 2 for three different structural qualities. One can directly see that the relaxation in the damaged areas is significantly faster than in the pristine graphene. This might be an indication for the presence of the intensively discussed supercollisions in graphene [3].
References
[1] C. Berger et al., Science 312, 1191 (2006).
[2] S. Winnerl et al., Phys. Rev. Lett. 107, 237401 (2011).
[3] J. C. W. Song et al., Phys. Rev. Lett. 109, 106602 (2012).
Keywords: graphene, defects, carrier dynamics
  • Poster
    Graphene2017, 28.-31.03.2017, Barcelona, Espana

Permalink: https://www.hzdr.de/publications/Publ-25940
Publ.-Id: 25940


Landau-Quantized Graphene: A Tunable Nonlinear Optical Material in the THz Range

König-Otto, J. C.; Wang, Y.; Belyanin, A.; Berger, C.; de Heer, W. A.; Orlita, M.; Pashkin, A.; Schneider, H.; Helm, M.; Winnerl, S.
Finding nonlinear optical materials for the THz and mid-infrared regimes is not straightforward. State-of-the-art devices with a high third-order optical susceptibility are often processed as complex multiquantum-well structures designed to feature one specific resonance frequency. In our work we study Landau-quantized graphene as a tunable and simple to produce nonlinear material. To this end we perform time-integrated degenerate four-wave mixing (FWM) experiments at a photon energy of 78 meV resonant to the transitions between the Landau levels LL−1, LL0 and LL1 at a magnetic field of roughly 4 T. We can recover expected scaling of the FWM-signal with the incident fields and the resonance behavior. The value of the third-order surface susceptibility in this material is in agreement with our calculations based on the density matrix formalism. We find the order of 𝜒(3) of Landau-quantized graphene to be competitive with more complex and elaborated solutions.
Keywords: graphene, Landau-quantized graphene, nonlinear optics, carrier dynamics, spectroscopy
  • Lecture (Conference)
    DPG-Frühjahrstagung, 19.-24.03.2017, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-25939
Publ.-Id: 25939


Carrier Dynamics in Graphene: Ultrafast Many-Particle Phenomena

Malic, E.; Winzer, T.; Wendler, F.; Brem, S.; Jago, R.; Knorr, A.; Mittendorff, M.; König-Otto, J. C.; Plötzing, T.; Neumaier, D.; Schneider, H.; Helm, M.; Winnerl, S.
Graphene is an ideal material to study fundamental Coulomb- and phonon-induced carrier scattering processes. Its remarkable gapless and linear band structure opens up new carrier relaxation channels. In particular, Auger scattering bridging the valence and the conduction band changes the number of charge carriers and gives rise to a significant carrier multiplication - an ultrafast many-particle phenomenon that is promising for the design of highly efficient photodetectors. Furthermore, the vanishing density of states at the Dirac point combined with ultrafast phonon-induced intraband scattering results in an accumulation of carriers and a population inversion suggesting the design of graphene-based terahertz lasers. Here, we review our work on the ultrafast carrier dynamics in graphene and Landau-quantized graphene is presented providing a microscopic view on the appearance of carrier multiplication and population inversion.
Keywords: graphene, carrier dynamics, spectroscopy

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Permalink: https://www.hzdr.de/publications/Publ-25938
Publ.-Id: 25938


“Brothers in Arms” – HIF High-Speed PIXE and MEGA Spectrometer

Renno, A.ORC; Buchriegler, J.ORC; Dreßler, S.; Hanf, D.; Munnik, F.ORC; Scharf, O.; Ziegenrücker, R.ORC
In a fast growing world with increasing demand on resources like high-tech metals as In, Ga, Ge, or rare earth elements (REE), mineralogists and economic geologists need faster and automated analytical tools to explore mineral deposits, make them accessible and define necessary initial data for all subsequent processing steps. Next to the necessary knowledge in which phases the elements of interest, ecotoxical as well as deleterious elements are concentrated, it is important to determine structural parameters like grain sizes and possible intergrowths relations of these minerals. These are typical geometallurgical analytical tasks, which are so far routinely performed by electron beam based methods of automated mineralogy, like MLA (mineral liberation analysis) or QEMSCAN, with their advantages and disadvantages. The methodological problems of these type of methods are, for example, the necessary measurement time, insufficient limits of detection (no trace element detection) and high background (electron Bremsstrahlung).

Some of these hurdles can be overcome by using alternative excitation radiation, like ions, known as particle-induced X-ray emission (PIXE) or X-rays, known as X-ray fluorescence (XRF). Combining these with a full-field detection system, such as the so-called SLcam®[1], allows the determination of trace element distributions in reasonable time over a large field of view.

The SLcam® consists of a 12 x 12 mm², X-ray sensitive pnCCD chip with 69696 pixels. A high read-out speed of up to 1000 Hz, allows the acquisition of complete X-ray spectra (2-20 keV) on each pixel simultaneously, with an energy resolution of around 160 eV (@ Mn-K even for high photon fluxes. A poly-capillary lens is used to guide the X-rays from their point of origin on the sample to the corresponding pixel on the detector-chip. Usage of a straight 1:1 lens results in a lateral resolution better than 100 µm.

The MEGA spectrometer is equipped with a laboratory-scale X-ray tube. XRF is used for the determination of major and trace element data. It’s “small”, table-top like size would in principle allow to use the set-up directly at the mining site. The so called High-Speed PIXE[2] uses a broad proton beam to excite the fluorescence radiation. Samples with a total weight of up to 10 kg and a maximum size 25 x 25 x 2.5 cm³ can be mounted in a dedicated vacuum sample chamber. The instrument is installed at the Ion Beam Center at the Helmholtz-Zentrum Dresden-Rossendorf. The advantages and disadvantages of both instruments will be presented, as well as first results of combined qualitative studies of the distribution of trace elements in representative samples to demonstrate the importance of these innovative concepts for geometallurgical research.

[1] Scharf, O., et al. (2011). Compact pnCCD-Based X-ray Camera with High Spatial and Energy Resolution: A Color X-ray Camera. Analytical Chemistry, 83(7), 2532–2538.
[2] Hanf, D., et al. (2016). A new particle-induced X-ray emission set-up for laterally resolved analysis over wide areas. Nuclear Instruments and Methods in Physics Research B, 377, 7-24.
Keywords: PIXE, High-Speed PIXE, XRF, Trace Elemenet Analysis
  • Poster
    2nd International Conference on Applied Mineralogy & Advanced Materials and 13th International Conference on Applied Mineralogy, 05.-09.06.2017, Castellaneta Marina- Taranto, Italy

Permalink: https://www.hzdr.de/publications/Publ-25937
Publ.-Id: 25937


Relevance of qualitative trace element distribution maps at answering geoscientific questions

Renno, A. D.ORC; Buchriegler, J.; Hanf, D.; Klingner, N.; Munnik, F.; Nowak, S. H.; Scharf, O.; von Borany, J.; Ziegenrücker, R.
In recent years significant efforts have been made to combine Particle Induced X-ray Emission (PIXE) techniques with the advantages of the Color X-ray Camera [1] to produce full-field PIXE images of trace element distributions in geological samples [2]. Decisive progress was made by the implementation of several image enhancement techniques [3, 4]. The ultimate objective is the installation of an analytical instrument running in routine operation. The major advantage of this new approach is the ability to gather elemental distribution maps over a large field of view (some cm²) with reasonable spatial resolution (< 100 µm) in real-time. Setting a matrix-dependent threshold value for a certain trace element concentration will allow us to reduce the measurement time compared to beam scanning based methods. This is an enormous advantage for resource technological application.
The present status of the installation at HZDR Ion Beam Center does not enable us to obtain quantitative information about trace element concentration in the single pixels of the resulting elemental distribution maps. The information content of qualitative and quantitative distribution maps is different. But it is a myth that only quantitative information is suitable of gathering information about rocks, ores and minerals. Using selected examples from petrology, economic geology and resource technology we will demonstrate the different types of qualitative information and its interpretation.
[1] O. Scharf, et al., Analytical Chemistry 83 (7) (2011) 2532–2538.
[2] D. Hanf, et al., NIM B 377, pp. 17-24 (2016).
[3] J. Buchriegler, et al. submitted (2017).
[4] S. Nowak, et al., arXiv:1705.08939, (2017).
This work has been supported by BMBF (INTRA r3 033R070) and by the EU project SPRITE (GA-No. 317 169).
Keywords: PIXE, Qualitative Analysis, Trace element analysis, element distribution map
  • Lecture (Conference)
    23rd International Conference on Ion Beam Analysis IBA-2017, 08.-13.10.2017, Shanghai, China

Permalink: https://www.hzdr.de/publications/Publ-25936
Publ.-Id: 25936


Status report of Super-SIMS for resource technology

Rugel, G.; Akhmadaliev, S.; Belokonov, G.; Böttger, R.; von Borany, J.; Gutzmer, J.; Kaever, P.; Meyer, M.; Noga, P.; Renno, A. D.ORC; Scharf, A.; Tiessen, C. J.; Voigtländer, J.; Wagner, N.; Wiedenbeck, M.; Winter, A.; Wu, H. S.; Ziegenrücker, R.
The combination of an ion source with very good spatial resolution with a tandem accelerator is a long standing idea to improve the sensitivity by orders of magnitude [1-3]. Translating this idea to reality has its challenges [e.g. 4-6]. Having a strong focus on natural, metal, and mineral resources the Helmholtz Institute Freiberg for Resource Technology installed such a system at the Ion Beam Centre at HZDR. This so-called Super-SIMS will be embedded into a system of consecutive micro-analytical methods devoted to the characterization of minerals and ores.
The secondary ion beam of the SIMS (CAMECA IMS 7f-auto) is injected into the pre-existing Dresden Accelerator Mass Spectrometry facility [7,8] which removes isobaric molecular signatures in the ion beam. The SIMS component remains as an autonomous analytical instrument with the additional option/advantage to inject the negative secondary ion beam at energies of up to 40 keV (to match the acceptance conditions) into the accelerator. A dedicated ion optical unit has been constructed and installed to focus the ion beam to the accelerator entrance.
First measurements of the performance parameters will be presented. We analyzed several matrices and mass ranges of isotopes like a P-doped Si-wafer, natural galena (PbS) and the elements between Ga and As in several natural and synthetic matrices.

[1] Purser et al. Surface and Interface Analysis 1(1), 1979, 12. [2] J. M. Anthony, D. J. Donahue, A. J. T. Jull, MRS Proceedings 69 (1986) 311-316. [3] S. Matteson, Mass Spectrom. Rev., 27 (2008) 470. [4] Ender et al. NIMB 123 (1997) 575. [5] Maden, PhD thesis, ETH Zurich 2003. [6] Fahey et al. Analytical Chemistry 88(14), 2016, 7145. [7] Akhmadaliev et al., NIMB 294 (2013) 5. [8] Rugel et al. NIMB 370 (2016) 94.
Keywords: Super-SIMS
  • Invited lecture (Conferences)
    23rd International Conference on Ion Beam Analysis IBA-2017, 08.-13.10.2017, Shanghai, China

Permalink: https://www.hzdr.de/publications/Publ-25935
Publ.-Id: 25935


The analysis of nothing and nearly nothing – some theoretical considerations about reference materials for the Super-SIMS

Renno, A. D.ORC
The Super-SIMS idea goes back to the year 1979 [1]. Since then several attempts have been made to install such instruments [2-5], although with varied success.
Most of the published data were either analysis of semiconductor materials or isotope ratios of natural materials. Having a strong focus on natural, metal, and mineral resources the Helmholtz Institute Freiberg for Resource Technology installed such a system at the Ion Beam Centre at HZDR. This new Super-SIMS will be embedded into a system of consecutive micro-analytical methods devoted to the characterization of minerals and ores. Therefore, our focus will lie on the analysis of ultra-trace elements in these natural matrices.
Despite the high precision, the accuracy of SIMS analysis can be problematic. The sensitivity factor as well as the instrumental mass fractionation vary with the chemical composition. This so-called matrix effect demands that the sample and the reference material (RM) should have exactly the same chemical composition and structure, this is difficult to achieve. Even trace elements and in the case of the Super-SIMS ultra-trace elements may affect the sensitivity factor. The compromise is the usage of matrix matched RMs.
The combination of good lateral and depth resolution of the SIMS instrument with the resulting small sample volumes / masses (sub ng-range) and the aspired detection limits in the pg/g range yield to the fact that the probability to meet one atom of the analyte in the sample volume will be < 1.
This contribution will stimulate the discussion about the concepts of detection limit, homogeneity and heterogeneity in RMs and present considerations about the design of future RMs for ultra-trace element analysis with the Super-SIMS.

[1] Purser et al. Surface and Interface Analysis 1(1), 1979, 12.; [2] S. Matteson, Mass Spectrom. Rev., 27 (2008) 470.; [3] Ender et al. NIMB 123 (1997) 575.; [4] Maden, PhD thesis, ETH Zurich 2003.;
[5] Fahey et al. Analytical Chemistry 88(14), 2016, 7145
Keywords: Super-SIMS, Reference Material
  • Lecture (Conference)
    23rd International Conference on Ion Beam Analysis IBA-2017, 08.-13.10.2017, Shanghai, China

Permalink: https://www.hzdr.de/publications/Publ-25934
Publ.-Id: 25934


Radially resolved electronic structure and charge carrier transport in silicon nanowires

Fuchs, F.; Gemming, S.; Schuster, J.
The electronic structure of silicon nanowires is studied using density functional theory. A radially resolved density of states is discussed for different nanowire diameters and crystal orientations, which allows new insight into the transport properties. Strong differences between the surface and the center of the nanowire are found, indicating that the carrier transport will mainly take place in the nanowire center. For increasing diameter the density of states in the center approaches the bulk value. We find that bulk properties such as the indirect nature of the band gap become already significant at a nanowire diameter of approximately 5 nm and beyond. Finally, the spatial characteristic of the current is visualized in terms of transmission pathways. The electron transport is found to be more localized in the nanowire center compared to the hole transport. It also depends on the crystal orientation of the wire.
Keywords: silicon nanowire, density functional theory, density of states, quantum confinement

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Permalink: https://www.hzdr.de/publications/Publ-25933
Publ.-Id: 25933


Three-dimensional velocity vector determination algorithm for individual bubble identified with Wire-Mesh Sensors

Furuya, M.; Kanai, T.; Arai, T.; Takiguchi, H.; Prasser, H.-M.; Hampel, U.; Schleicher, E.
The bubble pairing scheme was devised to quantify three-dimensional velocity of each bubble. We used two sets of Wire-Mesh Sensors to identify locations of each bubble according to bubble identification algorithm, which was developed by HZDR. The devised scheme was applied to the vertical upward air-water flow at 0.64. m/s for both air and water superficial velocities in a large diameter pipe (i.d. 224. mm). The bubble pairing scheme visualized the developing process of two-phase flow: large bubbles coalesced with each other to move toward the center, while the rest of bubbles broke up into smaller bubbles and decelerated.
Keywords: wire-mesh sensor, multiphase flow, bubbly flow, gas phase velocity measurement, bubble pairing

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Permalink: https://www.hzdr.de/publications/Publ-25931
Publ.-Id: 25931


Transglutaminase 2 als molekulares Target zur funktionellen Bildgebung von Tumoren ─ Untersuchungen zu Inhibitoren und fluorogenen Substraten

Wodtke, R.
Die TGase 2 ist ein konstitutiv exprimiertes Enzym, dessen bekannteste Funktion in der posttranslationalen Modifizierung von Proteinen durch Ca2+-abhängige Transamidierung zwischen proteingebundenen Glutaminyl-Resten und verschiedenen primären Aminen liegt. Obwohl ursprünglich namensgebend, wird diese Quervernetzungsfunktion des Proteins erst in zellulären Stresssituationen wie der Apoptose oder der Wundheilung aktiviert. Folglich erscheint es nicht überraschend, dass der TGase 2 und vor allem der Glutamyltransferase-Aktivität auch in diversen pathophysiologischen Prozessen eine große Bedeutung zukommt. Für diese Arbeit stand die Beteiligung der TGase 2 in tumorassoziierten Prozessen im Fokus. So ist bekannt, dass eine gesteigerte Expression der TGase 2 einen entscheidenden Beitrag zum Überleben, zur Resistenz gegenüber Chemo- und Strahlentherapie sowie zum Metastasierungspotential neoplastischer Zellen liefert. Dabei wurde das Enzym als ein Schlüsselprotein für die Progression zahlreicher Krebsarten identifiziert. Somit stellt das Enzym ein interessantes Target für die funktionelle Bildgebung von Tumoren mittels Positronen-Emissions-Tomographie (PET) sowie der Therapie von Tumorerkrankungen dar.
Die Zielstellungen dieser Arbeit waren durch die Entwicklung von Radiotracern für die TGase 2 motiviert, um perspektivisch mit Hilfe der nicht-invasiven Bildgebungsmodalität PET Aufschlüsse über die Relevanz des Proteins, die Bedeutung von dessen Glutamyltransferase-Aktivität in Tumoren sowie dessen molekulare Adressierbarkeit in vivo (auch im Hinblick auf therapeutische Anwendungen) zu erhalten. Dementsprechend setzt sich die vorliegende Dissertation aus zwei inhaltlichen Schwerpunkten zusammen:
• Der erste Teil befasst sich mit der Etablierung eines fluorimetrischen TGase 2-Assays einschließlich der Synthese und kinetischen Charakterisierung fluorogener Substrate als Voraussetzung für die Identifizierung und Charakterisierung von Molekülen, die zur Adressierung der TGase 2 hinsichtlich molekularer Bildgebung und therapeutischer Hemmung bestimmt sind
• Der zweite Teil beinhaltet die Entwicklung sowie enzymkinetische Charakterisierung, einschließlich Struktur-Wirkungsbeziehungen, irreversibler TGase 2-Inhibitoren als potentielle Radiotracerkandidaten. Darüber hinaus sollte eine initiale pharmakokinetische Evaluierung der Verbindungen in vitro erfolgen.

Fluorimetrischer TGase 2-Assay

Der literaturbekannte Acyldonor 2a, der durch TGase 2-vermittelte Umsetzung das stark fluoreszierende 7-Hydroxycumarin freisetzt, ist ein attraktives Substrat für Untersuchungen zur TGase 2 mittels fluorimetrischen Assays. Allerdings weist 2a nur eine geringe Löslichkeit im wässrigen Milieu auf (<10 µM). Dies schränkt sowohl die detaillierte kinetische Untersuchung der Verbindung als auch darauf beruhende Anwendungen der Verbindung ein. Daher wurden Acyldonoren auf der Basis kleiner Glutamat enthaltender Peptide entwickelt, bei denen die freie Carboxylgruppe löslichkeitsvermittelnd wirken sollte. Die Synthese der Verbindungen erfolgte mit einer modularen Synthesestrategie an einem polymeren Träger (Festphasensynthese). Alle Verbindungen konnten in ausreichenden Ausbeuten und hohen Reinheiten dargestellt werden. Die Untersuchungen zur Löslichkeit zeigten, dass die Verbindungen bis zu Konzentrationen von 250 µM im wässrigen Milieu löslich sind. Diese erheblich verbesserte Wasserlöslichkeit erlaubte die ausführliche kinetische Charakterisierung der neuartigen fluorogenen Substrate hinsichtlich ihrer TGase 2-katalysierten Hydrolyse und Aminolyse. Z-Glu(HMC)-Gly-OH (5b) erwies sich dabei als Cumarinylester mit den günstigsten Substrateigenschaften gegenüber humaner TGase 2 und kann darüber hinaus auch zur Charakterisierung weiterer Isoformen der Transglutaminase-Familie genutzt werden. Die Eignung von 5b zur Charakterisierung irreversibler Inhibitoren wurde ebenfalls demonstriert. Somit liegt nun eine verlässliche Assay-Methode zur Bewertung des Hemmpotentials und der Selektivität von TGase 2-gerichteten Inhibitoren vor.

Nε-Acryloyllysine als irreversible Inhibitoren der TGase 2

Für die Entwicklung potentieller Radiotracer wurden irreversible Inhibitoren der TGase 2 als geeigneter Ausgangspunkt erachtet. In diesem Zusammenhang wurde das Nε-Acryloyllysinpiperazid 8a in der Literatur beschrieben, das neben einem hohen inhibitorischen Potential eine ausgezeichnete Selektivität sowie vielversprechende pharmakokinetische Eigenschaften aufweist. Daher wurde dieser Inhibitor zur Leitverbindung für das Design von potentiellen Radiotracern bestimmt. Die geplanten Strukturvariationen sollten daher vor allem Funktionalisierungen mit Fluor beinhalten, die auch eine Synthese der entsprechenden Fluor-18-Analoga ermöglichen. Zusätzlich sollten Modifikationen durchgeführt werden, die das Aufdecken von Struktur-Wirkungsbeziehungen erlauben. Zu diesem Zweck wurde eine modulare Syntheseroute entworfen, die sich aus den folgenden Schritten zusammensetzt: Nε-Acryloylierung von Nα-Boc-Lysin, Amidknüpfung mit dem jeweiligen Piperazinbaustein, Boc-Entschützung und Nα-Acylierung. Die benötigten Piperazinbausteine wurden in wenigen Syntheseschritten synthetisiert oder waren kommerziell erhältlich. Mit dieser Syntheseroute konnten schließlich 56 neue Inhibitoren der TGase 2 in hohen Reinheiten hergestellt werden.
Die kinetische Charakterisierung der Verbindungen erfolgte mit dem zuvor etablierten fluorimetrischen TGase 2-Assay unter Nutzung des Acyldonors 5b. Die Charakterisierung des (R)-konfigurierten Enantiomers von 8a belegte zunächst den deutlichen Vorteil der (S)-Konfiguration am Cα-Atom des Lysyl-Restes hinsichtlich des inhibitorischen Potentials gegenüber TGase 2. Die systematisch durchgeführten Strukturvariationen ermöglichten die Aufdeckung verschiedener quantitativer Struktur-Wirkungsbeziehungen. Einige der Strukturvariationen führten sogar zu Inhibitoren mit größerem inhibitorischen Potential als das der Leitverbindung. Die beste Toleranz gegenüber der Einführung von Fluor wurde durch Substitution des H-Atoms in ortho-Position der Phenylacetylgruppe sowie der Methylgruppe am Pyridinring der Leitverbindung erreicht (Verbindungen 9b und 20).
Zur initialen pharmakokinetischen Einschätzung der TGase 2-Inhibitoren wurden die Permeabilitätseigenschaften aller Verbindungen mittels PAMPA-Methode untersucht. Dabei wurden unter anderem Inhibitoren identifiziert, die schlecht permeabel sind und somit wahrscheinlich ausschließlich die extrazelluläre TGase 2 adressieren können. Dies ist im Hinblick auf die differentielle Betrachtung von intra- und extrazellulärer TGase 2, vor allem mittels molekularer Bildgebung in vivo, von großer Bedeutung.
  • Doctoral thesis
    TU Dresden, 2017
    Mentor: Prof. Dr. Jörg Steinbach, Dr. Reik Löser
    285 Seiten

Permalink: https://www.hzdr.de/publications/Publ-25930
Publ.-Id: 25930


Simultaneous Excitation of a TE011- and a TM010-Mode in a 3.5 Cell SRF Gun Cavity

Arnold, A.; Lu, P.; Murcek, P.; Teichert, J.; Vennekate, H.; Xiang, R.; Ciovati, G.; Forehand, D.; Kneisel, P.; Turlington, L.
For future linear CW accelerators, superconducting (SC) RF guns are discussed to be the most promising solution to fulfil the demands on high average current and high brightness at the same time. But in difference to the NCRF guns, the application of static magnetic fields near the cathode to compensate for space charge forces is not possible. Instead, magnetic fields of transverse electric (TE) modes excited in parallel to the accelerating mode were proposed. Experiments at the 1st Rossendorf SRF gun using the existing fundamental mode coupler in combination with a RF diplexer have shown that this is feasible. However, since the cavity was not designed for this purpose, the mode was strongly damped by HOM couplers and cavity beam tubes and thus only low field strength could be achieved. In this contribution we will present a modified cavity design that avoids these problems and provides a separate RF coupler for the TE mode. Additionally, we will report on the first vertical test that demonstrated the functionality of the whole RF setup as well as realized significant higher field of the excited TE011 mode in parallel to the TM010 mode.
Keywords: SRF gun, superconducting RF injector, ELBE, electron source, TE mode, RF focussing, emittance compensation
  • Poster
    18th International Conference on RF Superconductivity, 17.-21.07.2017, Lanzhou, China

Permalink: https://www.hzdr.de/publications/Publ-25929
Publ.-Id: 25929


Beam Parameter Measurements of the 2nd 3.5 Cell SRF Gun for ELBE

Arnold, A.; Freitag, M.; Lu, P.; Murcek, P.; Teichert, J.; Vennekate, H.; Xiang, R.; Kneisel, P.; Ciovati, G.; Turlington, L.
In May 2014 the 1st superconducting photo injector (SRF gun) at HZDR was replaced by a new gun, featuring a new resonator and cryostat. The intention for this upgrade was to reach higher beam energy, higher bunch charge and lower emittance at the same time in order to serve user experiments at the superconducting CW accelerator ELBE. In this contribution we will report on the commissioning of the SRF gun by presenting detailed beam parameter measurements up to a bunch charge of 300 pC. Additionally, we will report the results of the first two user experiments (neutron and THz generation) that demonstrated the reliability of this gun concept.
Keywords: SRF gun, superconducting RF injector, ELBE, electron source
  • Poster
    The 59th ICFA Advanced Beam Dynamics Workshop on Energy Recovery Linacs, 18.-23.06.2017, Genf, Schweiz

Permalink: https://www.hzdr.de/publications/Publ-25928
Publ.-Id: 25928


The FLUKA Monte Carlo simulation package and its applications at the HZDR

Müller, S. E.
Vorstellung der FLUKA Monte Carlo Simulations Software und deren Anwendungen am HZDR
Keywords: FLUKA, Radiation Transport, HZDR
  • Lecture (Conference)
    VKTA KS-Klausurberatung, 08.-09.08.2017, Lohmen, Germany

Permalink: https://www.hzdr.de/publications/Publ-25927
Publ.-Id: 25927


Commissioning and RF Results of the Second 3.5 Cell Rossendorf SRF Gun

Arnold, A.; Freitag, M.; Lu, P.; Murcek, P.; Teichert, J.; Vennekate, H.; Xiang, R.; Kneisel, P.; Ciovati, G.; Turlington, L.
In May 2014 the 1st superconducting photo injector (SRF gun) at HZDR was replaced by a new gun, featuring a new resonator and cryostat. The intention for this upgrade was to reach higher beam energy, higher bunch charge and lower emittance at the same time in order to serve user experiments at the superconducting CW accelerator ELBE. In this contribution we will report on the commissioning of the SRF gun by presenting a full set of RF performance results.
Keywords: SRF gun, superconducting RF injector, ELBE, electron source
  • Poster
    The 59th ICFA Advanced Beam Dynamics Workshop on Energy Recovery Linacs, 18.-23.06.2017, Genf, Schweiz

Permalink: https://www.hzdr.de/publications/Publ-25926
Publ.-Id: 25926


Emittance Compensation for SRF Photoinjectors

Vennekate, H.
The advantages of contemporary particle injectors are high bunch charges and good beam quality in the case of normal conducting RF guns and increased repetition rates in the one of DC injectors. The technological edge of the concept of superconducting radio frequency injectors is to combine the strengths of both these sides. As many future accelerator concepts, such as energy recovery linacs, high power free electron lasers and certain collider designs, demand particle sources with high bunch charges and high repetition rates combined, applying the superconductivity of the accelerator modules to the injector itself is the next logical step. However, emittance compensation — the cornerstone for high beam quality — in case of a superconducting injector is much more challenging than in the normal conducting one. The use of simple electromagnets generating a solenoid field around the gun’s resonator interferes with its superconducting state. Hence, it requires novel and sophisticated techniques to maintain the high energy gain inside the gun cavity, while at the same time alleviating the detrimental fast transverse emittance growth of the bunch.
In the case of the ELBE accelerator at the Helmholtz-Zentrum Dresden-Rossendorf, a superconducting electron accelerator provides beam for several independent beamlines in continuous wave mode. The applications include IR to THz free electron lasers, neutron and positron generation, to Thompson backscattering with an inhouse TW laser, and hence, call for a flexible CW injector. Therefore, the development of a 3.5 cell superconducting electron gun was initiated in 1997.
The focus of this thesis lies on three approaches of transverse emittance compensation for this photoinjector: RF focusing, the installation of a superconducting solenoid close to the cavity’s exit, and the introduction of a transverse electrical mode of the RF field in the resonator. All three methods are described in theory, examined by numerical simulation, and experimentally reviewed in the particular case of the ELBE SRF Gun II at HZDR and a copy of its niobium resonator at Thomas Jefferson National Laboratory, Newport News, VA, USA.
Keywords: SRF Injector, Emittance, ELBE, Superconductivity, Accelerator Physics
  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-081 2017

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Permalink: https://www.hzdr.de/publications/Publ-25925
Publ.-Id: 25925


Development and characterization of human melanoma cell lines and xenograft models exhibiting different levels of transglutaminase 2

Hauser, S.; Aepler, J.; Pufe, J.; Wodtke, R.; Pietsch, M.; Löser, R.; Pietzsch, J.
Tissue transglutaminase (TGase 2) is involved in the progression of many different tumor entities, including malignant melanoma, via antiapoptotic processes and mechanisms supporting cellular survival, adhesion, and epithelial-mesenchymal transition [1]. Accordingly, it has been shown that TGase 2 expression is higher in metastatic and chemoresistant tumors compared to primary tumors, underlining its role during tumor progression [2]. Therefore, TGase 2 represents an interesting target for the development of selective inhibitors for theranostics of progressive malignant melanoma. In order to evaluate potent candidate compounds in vitro and in vivo, suitable transgenic melanoma cell lines and xenograft models with different TGase 2 expression and activity were developed.
A375 and MeWo cells, two human malignant melanoma cell lines with high and very low TGase 2 expression, respectively, were stably transfected with a lentiviral pHATtrick-mCherry vector (mCherry control cells) and a lentiviral pHATtrick-TGase 2 vector (TGase 2 cells). The resulting cell lines differed in their TGase 2 expression and activity, as determined by Western Blotting and fluorescence anisotropy assay [3]. Transfection and overexpression of TGase 2 did not influence cell proliferation behavior. 5×106 cells of each cell line were injected subcutaneously in athymic nude mice (NMRI-Foxn1nu) to form tumor xenografts that differed in their growth characteristics as well as in their TGase 2 expression and activity. TGase 2 activity in tumors was evaluated ex vivo by incorporation of fluorescently labeled cadaverine derivatives, which could be inhibited by a selective TGase 2 inhibitor. These results indicate that the established tumor xenograft models provide the opportunity to evaluate potent candidate substances for diagnosis and therapy of melanoma on the one hand and to investigate pathophysiological processes associated with TGase 2 in detail on the other.

References:
[1] Huang, L et al. Am J Cancer Res. 2015, 5, 2756-2776
[2] Fok, JY et al. Mol Cancer Ther 2006, 5, 1493-1503
[3] Hauser, C et al. Amino Acids 2017, 49, 567–583
  • Poster
    Debrecen University Symposium "Transglutaminases in Medicine", 03.-05.08.2017, Debrecen, Ungarn

Permalink: https://www.hzdr.de/publications/Publ-25924
Publ.-Id: 25924


Light-activated ruthenium(II) carbonyl complexes

Kubeil, M.ORC; Stephan, H.; Johnston, A.; Graham, B.; Spiccia, L.
The development of photo-activated carbon monoxide releasing molecules (photoCORMs) has received considerable attention as a new prodrug approach, since the CO is released only upon exposure to electromagnetic radiation [1]. Carbon monoxide itself has been demonstrated to exhibit several beneficial effects on biological targets such as anti-inflammation, anti-proliferation, anti-apoptosis, anti-oxidation and vasodilatory effects [2]. However, despite a large number of photoCORMs reported, relatively little information is available on the precise mechanism of CO release from most photoCORMs and even less compounds have been tested as anti-cancer agents in cells so far. Overall, a fundamental understanding of the mechanism of CO release from photoCORMs is essential for their exploitation as therapeutics.

Herein, we report the synthesis of ruthenium(II) carbonyl complexes functionalized with bidentate pyridyl (1) and tridentate diquinolyl ligands (2) and investigate the mechanism of CO release in aqueous media (before and after light-activation). The photo-induced CO release kinetics of the Ru(II) photoCORMs, as well as the identity of the intermediates and photo-activated products, will be presented [3]. Moreover, the complexes have been tested in cancer cell lines showing a reduced viability after CO release.

References
[1] U. Schatzschneider, Br. J. Pharmacol. 2015, 172, 1638. [2] R. Motterlini, L. E. Otterbein, Nat. Rev. Drug Discov. 2010. 9, 728-743. [3] M. Kubeil, R. R. Vernooij, C. Kubeil, B. R. Wood, B. Graham, H. Stephan, L. Spiccia, Inorg. Chem. 2017, 56, 5941−5952.
Keywords: ruthenium carbonyl complexes, kinetics, in vitro studies
  • Poster
    Wissenschaftsforum, 10.-14.09.2017, Berlin, Deutschland

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Permalink: https://www.hzdr.de/publications/Publ-25923
Publ.-Id: 25923


Laser-driven Ion Beam Radiotherapy (LIBRT)

Enghardt, W.; Pawelke, J.ORC; Wilkens, J. J.ORC
Laser-driven particle acceleration may promise more compact and cost effective heavy charged particle (proton and heavier ions) radiotherapy facilities and also potentially offers treatment benefits like better irradiation of moving tumours. In contrast to conventional accelerators, laser accelerators deliver short, very intense ion bunches of low repetition rate, broad energy spectra and large divergences. In addition to laser particle accelerator development, laser-driven ion beam radiotherapy (LIBRT) demands new solutions for beam transport, dosimetric control and tumour conformal dose delivery along with full characterization of radiobiological effects. Laser-driven beams are already used for radiobiological studies with cells and small animals. For irradiation of extended tumour volumes in patients, a compact light-weight gantry based on pulsed, high-field magnets has been designed, enabling the capture and transport of divergent, broad energy bunches and including a novel beam shaping and dose delivery system. High quality treatment plans could be achieved based on the axial and lateral clustering method, deliverable via such a gantry. However, laser-driven bunch parameters are still far away from therapy requirements. Beside improvement in stability and reproducibility, a considerable increase of the maximum ion energy is necessary which is expected from the ongoing development of high-repetition petawatt-class lasers.
  • Book chapter
    P.R. Bolton, K. Parodi, J. Schreiber: Applications of laser-driven particle acceleration, Boca Raton, FL, USA: CRC Press, Taylor & Francis Group, 2018, 164-180

Permalink: https://www.hzdr.de/publications/Publ-25922
Publ.-Id: 25922


Coupling and stability of interfacial waves in liquid metal batteries

Horstmann, G. M.; Weber, N.; Weier, T.
We investigate the interfacial wave coupling dynamics in liquid metal batteries and their effects to the battery's operation safety. Similar to aluminum reduction cells, liquid metal batteries can be highly susceptible to magnetohydrodynamical instabilities that excite undesired interfacial waves capable to provoke short-circuits. However, in liquid metal batteries the wave dynamics is far more complex since two metal-electrolyte interfaces are present that may step into resonance. In the first part of this paper, we present a Potential analysis of coupled gravity-capillary interfacial waves in a three-layer battery model of cylindrical shape. Analytical expressions for the amplitude ratio and the wave frequencies are derived and it is shown that the wave coupling can be completely described by two independent dimensionless parameters. We provide a decoupling criterion clarifying that wave coupling will be present in most future liquid metal batteries. In the second part, the theory is validated by comparing it with multiphase direct numerical simulations. An accompanying parameter study is conducted to analyze the system stability for differently strongly coupled interfaces. Three different coupling regimes are identified involving characteristic coupling dynamics. For strongly coupled interfaces we observe novel instabilities that may have beneficial effects on the operational safety.
Keywords: Liquid metal battery, Wave Theory, MHD, Interfacial instabilities

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Permalink: https://www.hzdr.de/publications/Publ-25921
Publ.-Id: 25921


A discrete population balance equation for binary breakage

Liao, Y.; Oertel, R.; Kriebitzsch, S.; Schlegel, F.; Lucas, D.
The numerical solution of the population balance equation is frequently achieved by means of discretization, i.e., by the method of classes. An important concern of discrete formulations is the preservation of a chosen set of moments of the distribution, e.g. numbers and mass, while remaining exible on the grid applied. As for the physical modeling of the breakup rate, two approaches exist. One type states the breakup rate of a mother particle and requires a function that describes the distribution of daughter particles. The other type gives the breakup rate between a mother and a daughter particle directly, usually under the assumption of binary breakage. The lack of an explicitly stated daughter size distribution function has implications on the formulation of the discrete equations, because existing formulations contain integrals over the daughter size distribution function. To the knowledge of the authors, no efficient formulations for this type of models exist. In the present work, a discrete formulation of the breakup terms due to binary breakage is proposed, which allows a direct implementation of both kinds of models and an efficient solution of the population balance equation, making it favorable for the coupling to computational fluid dynamics codes.
Keywords: Binary Breakup, Computational Fluid Dynamics, Incorporated Daughter Size Distribution, Method of Classes, Population Balance Equation
  • Open Access Logo International Journal for Numerical Methods in Fluids 87(2018)4, 202-215
    DOI: 10.1002/fld.4491

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Permalink: https://www.hzdr.de/publications/Publ-25920
Publ.-Id: 25920


Tomographic observation of injection procedures for fracture sealing

Kulenkampff, J.; Bittner, L.; Gründig, M.; Lippmann-Pipke, J.
Networks of micro fissures may exist in rock salt in the excavation damage zone. Though they will not affect the integrity of the barrier function as a whole it might be advantageous to seal such likely permeable structures by means of impregnation procedures. However, the lasting effect of such procedures is difficult to judge from simple measurements of the decrease of porosity and permeability, because spatial distribution and penetration depth of the impregnation agent should be known. We therefore suggest evaluating such impregnation methods with the help of tomographic laboratory methods of macroscopic samples.
The sample size should exceed the mean fracture distance. Therefore the size of standard drill cores with a diameter in the order of 100 mm is appropriate. This rather large size limits the achievable spatial resolution and thus the detectability of fractures with the otherwise well-established µCT-method. The low contrast between the density of the fracture fill and the solid material further complicates detection and segmentation of the structures. To overcome these issues, we apply positron emission tomography (PET). This tomographic modality yields quantitative images of the concentration of a positron emitting radiotracer with molecular sensitivity and a spatial resolution of 1 mm. We obtain images of the penetration of the labelled impregnation agent, as average tracer concentration over the voxel volume of 1 µL.
As prove of principle, we applied waterglass (sodium silcate) labelled with 18F as agent that was injected into an artificially fractured sylvinite core (Z2KSTh) from Staßfurt. The sample was structurally characterized before and after impregnation with µCT, and the flow field was determined with PET process tomography of propagating saturated NaCl-solution labelled with 18F. Although we achieved a significant decrease of permeability by waterglass injection, no significant structural effect could be seen with µCT. In contrast, PET showed a superficial covering of the sample surface with solid waterglass and penetration into larger voids with a penetration depth of a few millimetres (Fig. 1). This rather small effect is a consequence of the experimental conditions – low injection rate and low pressure – that were chosen to keep the setup simple. Although it was not intended here to estimate the effectiveness of waterglass impregnation as method for improving the geological barrier, we experienced the delicate interplay between reaction kinetics of waterglass solidification and local flow rate which makes its prediction difficult. However, we could prove the applicability of the visualization method which is uncomplicated to adapt to other impregnation agents and materials, higher pressure and injection rate.
Keywords: nuclear waste disposal, positron emission tomography
  • Lecture (Conference)
    Saltmech IX, 12.-14.09.2018, Hannover, Deutschland
  • Open Access Logo Contribution to proceedings
    Saltmech IX, 12.-14.09.2018, Hannover, Deutschland
    The Mechanical Behavior of Salt IX, Hannover: BGR, 978-3-9814108-6-0, 225-236

Permalink: https://www.hzdr.de/publications/Publ-25919
Publ.-Id: 25919


Evaluation of defect formation in helium irradiated Y2O3 doped W-Ti alloys by positron annihilation and nanoindentation

Richter, A.; Anwand, W.; Chen, C.-L.; Böttger, R.
Helium implanted tungsten-titanium ODS alloys are investigated using positron annihilation spectroscopy and nanoindentation. Titanium reduces the brittleness of the tungsten alloy, which is manufactured by mechanical alloying. The addition of Y2O3 nanoparticles increases the mechanical properties at elevated temperature and enhances irradiation resistance. Helium ion implantation was applied to simulate irradiation effects on these materials. The irradiation was performed using a 500 kV He ion implanter at fluences around 5 × 1015 cm−2 for a series of samples both at room temperature and at 600 °C. The microstructure and mechanical properties of the pristine and irradiated W-Ti-ODS alloy are compared with respect to the titanium and Y2O3 content. Radiation damage is studied by positron annihilation spectroscopy analyzing the lifetime and the Doppler broadening. Three types of helium-vacancy defects were detected after helium irradiation in the W-Ti-ODS alloy: small defects with high helium-to-vacancy ratio (low S parameter) for room temperature irradiation, larger open volume defects with low helium-to-vacancy ratio (high S parameter) at the surface and He-vacancy complexes pinned at nanoparticles deeper in the material for implantation at 600 °C. Defect induced hardness was studied by nanoindentation. A drastic hardness increase is observed after He ion irradiation both for room temperature and elevated irradiation temperature of 600 °C. The Ti alloyed tungsten-ODS is more affected by the hardness increase after irradiation compared to the pure W-ODS alloy.
Keywords: W-Ti-ODS alloys; He implantation; Positron annihilation spectroscopy; Nanoindentation; Vacancy defects

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Permalink: https://www.hzdr.de/publications/Publ-25918
Publ.-Id: 25918


The influence of microorganisms on subsurface, salt-based nuclear waste repositories

Swanson, J.; Cherkouk, A.; Bader, M.; Reed, D.
Subterranean salt formations have been considered by some countries, and are in use by others, for the permanent disposal of nuclear waste. Because the biogeochemistry of other deep geologic settings (e.g., granite, clay) differs significantly from subterranean salt, it is not possible to extrapolate microbial activity from one site type to the other. However, because of a lack of sufficient data, this is precisely what has been done in most safety case scenarios in salt. Thus, performance models assume the worst-case scenarios: 1) that the organisms present in rock salt will thrive on the organics present in the radioactive waste, leading to the generation of complexing agents that enhance radionuclide solubility, 2) that they will take up significant amounts of radionuclides and transport them away from the repository, and 3) that they may interact adversely with barrier components, thereby compromising their integrity. Current research being conducted by Los Alamos National Laboratory for the Waste Isolation Pilot Plant (WIPP) and by the Helmholtz-Zentrum Dresden-Rossendorf for the German concept is providing a more realistic view of the potential effects of all microorganisms, both indigenous and introduced, on salt-based nuclear waste repositories. Results suggest: 1) that the activity of repository-indigenous and introduced organisms will be constrained by the projected conditions (some combination of low water activity, high chaotropicity, anoxic atmosphere) and also by a lack of suitable organic substrates in the near-field but that organisms located in the far-field will not be as constrained; 2) that some organisms may alter brine composition in ways that may affect radionuclide solubility; 3) that the radionuclides present in some waste drums are inhibitory, but not completely lethal, at their soluble concentrations in repository brine; 4) that bioassociation of radionuclides appears to differ with oxidation state, organism, and brine composition; and 5) that microbially-induced radionuclide transformation via redox reactions may be limited to the far-field.
  • Lecture (Conference)
    Goldschmidt Konferenz, 13.-18.08.2017, Paris, Frankreich

Permalink: https://www.hzdr.de/publications/Publ-25917
Publ.-Id: 25917


Speciation of Se(IV) and Eu(III) associated with Stenotrophomonas bentonitica BII-R7 isolated from Spanish bentonites

Ruiz-Fresneda, M. A.; Gomez-Bolivar, J.; Fernandez-Cantos, M. V.; Delgado-Martín, J.; Cherkouk, A.; Moll, H.; Merroun, M. L.
Deep geological repositories (DGR) are designed to store radioactive wastes in the near future using artificial barriers like bentonites. These formations have been characterized by their high microbial diversity and activity [1]. Consequently, bentonite microbial populations would interact with radionuclides stored within DGR affecting their fate and behaviour. This study is focused on the elucidation of the mechanism involved in the interactions of Se(IV) and Eu(III) withthe bacterial strain Stenotrophomonas bentonitica BII-R7 under anaerobic and alkaline conditions using multidisciplinary approach combining microscopy, microbiology and spectroscopy. This strain was isolated from bentonites of Cabo de Gata (Almeria, Spain) [2]. The isolate BII-R7 is able to reduce Se(IV) to Se(0) under DGR relevant conditions forming Senanoparticles (Se NPs). Size, structure, morphology and cellular location of the Se NPswere analysed by STEM/HAADF, FESEM, UV-Vis spectroscopy, etc. In addition, flow cytometry studies were conducted to evaluatethe toxicity of Se(IV) on cell viability and metabolic activity.S. bentoniticais also able to interact with Eu(III) mainly by a biosorption process as indicated spectroscopic, microscopic and kinetic studies. Time-Resolved Laser-induced Fluorescence Spectroscopy (TRLFS) results also suggested that phosphoryl and carboxyl groups from the cells have an important role in the Eu(III) coordination sites.
[1] Lopez-Fernandez et al. (2014) Appl Geochem 49, 77-86.
[2] Sanchez-Castro et al. (2017) ) Int J Syst Evol Microbiol [in revision].
  • Poster
    Goldschmidt Konferenz, 13.-18.08.2017, Paris, Frankreich

Permalink: https://www.hzdr.de/publications/Publ-25915
Publ.-Id: 25915


Kooperationsprozess und strategisches Management entwickeln

Joehnk, P.
Anforderungen an das künftige Verhältnis zwischen Zuwendungsgebern, Forschungseinrichtungen und den Rechnungshöfen - Mängel im öffentlichen Sektor am Beispiel des Bundesrechnungshofs beheben
  • Science Finance 1(2017), 25-31

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Permalink: https://www.hzdr.de/publications/Publ-25914
Publ.-Id: 25914


HZDR, ZA Technischer Service, Abt. Bau- und technisches Gebäudemanagement

Oelke, M.
  • Lecture (others)
    HGF Arbeitskreis - Facility Management 2017, 16.-17.05.2017, HGF, Deutschland

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Permalink: https://www.hzdr.de/publications/Publ-25913
Publ.-Id: 25913


Gebäudeautomation im HZDR - Erfahrungsbericht

Oelke, M.
  • Lecture (others)
    HGF Arbeitskreis Facility Management, 09.-10.05.2012, HGF, Deutschland

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Permalink: https://www.hzdr.de/publications/Publ-25912
Publ.-Id: 25912


Neubau Heizwerk und Nahwärmenetz

Oelke, M.
  • Lecture (Conference)
    HGF Arbeitskreis Facility Management – 36. Tagung, 15.-16.05.2013, Kiel, Deutschland

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Permalink: https://www.hzdr.de/publications/Publ-25911
Publ.-Id: 25911


Electro-vortex flow simulation using coupled meshes

Weber, N.; Beckstein, P.; Galindo, V.; Starace, M.; Weier, T.
A numerical model for simulating electro-vortical flows in OpenFOAM is developed. Electric potential and current are solved in coupled solid-liquid conductors by a parent-child mesh technique. The magnetic field is computed using a combination of Biot-Savart’s law and induction equation. Further, a PCG solver with special regularisation for the electric potential is derived and implemented. Finally, a performance analysis is presented and the solver is validated against several test cases.

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Permalink: https://www.hzdr.de/publications/Publ-25910
Publ.-Id: 25910


Facile Silylation of Cyclitols using Silyl-bis(triflates)

Topp, A.; Köckerling, M.ORC; Reinke, H.; Miethchen, R.; Mamat, C.ORC
Novel silylated diols and polyols were prepared using a recently developed synthesis route with bifunctionalized silyl triflates. These silyl derivatives include two triflate functions, which allow a selective protection of two hydroxy groups. Moreover, the conformation of the silyl chain in the silane backbone led to exceptional UV properties.
Keywords: Silyl-bis(triflates), Cyclitols, Silylation, Protecting group, Carbohydrates

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Permalink: https://www.hzdr.de/publications/Publ-25909
Publ.-Id: 25909


Electrovortex flow in metal melts: Experiment and simulation

Kelley, D. H.; Ashour, R. F.; Salas, A.; Weber, N.; Weier, T.
Materials processing of molten metals often makes use of electrochemical techniques in which large electrical currents pass through the melt. Those currents can cause the melt to flow, both by interacting with Earth’s magnetic field and by interacting with magnetic fields induced by the currents themselves—“electrovortex flow". We present experimental and numerical measurements of the motion of a lead-bismuth melt in which electrovortex flow, flow driven by Earth’s magnetic field, and flow driven by thermal convection all compete and interact. We identify regimes in which the various mechanisms dominate, then consider their implications for materials processing and for liquid metal batteries.
Keywords: liquid metal batteries, electro-vortex flows
  • Lecture (Conference)
    TMS 2018 Annual Meeting & Exhibition, 11.-15.03.2018, Phoenix, Arizona, USA

Permalink: https://www.hzdr.de/publications/Publ-25908
Publ.-Id: 25908


Critical length scales for flow phenomena in liquid metal batteries

Kelley, D. H.; Weier, T.
Liquid metal batteries, a new technology for grid-scale energy storage, are composed of three liquid layers and therefore subject to a wide variety of fluid dynamical phenomena, both beneficial and detrimental. Some, like thermal convection and electrovortex flow, drive finite flow regardless of the size, current density, and temperature of the battery. Others, like the Tayler instability and the metal pad instability, occur only in certain parameter regimes - almost always dependent on length scale. I will discuss critical length scales, considering implications for battery design in light of fundamental fluid dynamics.
Keywords: liquid metal batteries
  • Lecture (Conference)
    70th Annual Meeting of the APS Division of Fluid Dynamics, 19.-21.11.2017, Denver, CO, USA

Permalink: https://www.hzdr.de/publications/Publ-25906
Publ.-Id: 25906


Transitions between electromagnetic flow states in liquid metal batteries

Kelley, D. H.; Ashour, R. F.; Weber, N.; Salas, A.; Weier, T.
High temperature batteries for stationary energy storage typically involve large electrical currents running through liquid electrodes and/or electrolytes. Those currents, in combination with Earth's magnetic field or the magnetic fields produced by the currents themselves, impose forces on the liquid layers that can drive flow and change battery performance. We report on experiments and simulations studying flow driven by electromagnetic forces in the molten electrodes of liquid metal batteries, with and without thermal convection. Our measurements and simulations reveal transitions between azimuthal and poloidal circulation. The implications of both types of flow for battery performance will be discussed.
Keywords: liquid metal battery, electro-vortex flows
  • Lecture (Conference)
    High Temperature Batteries for Stationary Energy Storage Workshop, 19.-20.09.2017, Trondheim, Norwegen

Permalink: https://www.hzdr.de/publications/Publ-25905
Publ.-Id: 25905


Structure and energetics of Y-Ti-O nanoclusters in bcc Fe

Vallinayagam, M.; Posselt, M.; Faßbender, J.ORC
Nanostructured Ferritic Alloys (NFA) are considered as promising candidates for the structural materials of future fusion and fission reactors [1]. They consist of a ferritic or ferritic/martensitic Fe-Cr matrix with a high dispersion of nanometer size yttria-based oxide particles. In this research project (started in November 2016) the nature of nanometer-size yttria-based oxide clusters in a bcc Fe matrix shall be investigated by DFT calculations. The main goal of these studies is the better understanding of the nucleation as well as the structure and composition of the nanoclusters. The investigations shall clarify the conditions for the formation of nonstoichiometric clusters that are coherent with the bcc lattice and for the formation of oxide phases (in particular Y2O3 and Y2Ti2O7). The energetics of the different structures shall be determined and compared. Furthermore, the interaction of the nanoparticles with intrinsic point defects and He atoms shall be studied. Preliminary studies and their results on structure and energetics of certain Y-Ti-O nanoclusters will be presented on the poster. Two models are considered: (i) clusters consisting of Y, Ti, and O atoms on substitutional or defect sites of the bcc lattice [2-4], and (ii) cluster consisting of parts of the bixbyite (Y2O3) or pyrochlore (Y2Ti2O7) structure embedded in bcc Fe [5].
[1] G. R. Odette, JOM-J. Min. Met. Mat. S. 66, 2427 (2014)
[2] D. Murali, B.K. Panigrahi, M.C. Valsakumar, S. Chandra, C.S. Sundar, B. Raj, J. Nucl. Mater. 403, 113 (2010)
[3] A. Claisse, P. Olsson, Nucl. Instr. Meth. B 303, 18 (2013)
[4] M. Posselt, D. Murali, B. K. Panigrahi, Model. Simul. Mater. Sc. 22, 085003 (2014)
[5] L. Barnard, G. R. Odette, I. Szlufarska, D. Morgan. Acta Mater. 60 (2012) 935 (2012)
Keywords: oxide nanoclusters, bcc Fe, nanoferritic alloy, DFT
  • Poster
    NSF/CECAM School on Computational Materials Science: From Basics to Applications, 17.-27.07.2017, Lausanne, Switzerland

Permalink: https://www.hzdr.de/publications/Publ-25904
Publ.-Id: 25904


Influence of foreign atoms on the diffusion of oxygen in bcc Fe

Wang, X.; Posselt, M.; Faßbender, J.ORC
In this research project (started in September 2016) the diffusion of foreign atoms in bcc Fe shall be investigated by first-principle methods and kinetic Monte Carlo simulations. The focus of the present work is on the diffusion of oxygen under the influence of other foreign atoms such as Al, Cr, Si, Ti, and Y. Oxygen plays e.g. an important role in the formation and evolution of nanoclusters in nanostructured ferritic Fe-Cr alloys which are considered as promising candidates for structural materials of future fusion and fission reactors [1]. In bcc Fe the most stable site of oxygen is the octahedral interstitial position and the tetrahedral interstitial position is the saddle point for the migration [2-5]. The presence of foreign atoms and intrinsic point defects modifies the migration path [5-7]. Using DFT calculations the binding energy between oxygen and a foreign atom is determined for different neighbor distances. Then the modified migration barriers are calculated, i.e. for the O jump between the first and the second neighbor of a foreign atom, etc. The results shall be used in kinetic Monte Carlo simulations of the whole diffusion process and for the determination of the corresponding diffusion coefficient in dependence on the concentration of foreign atoms. Finally, the calculated diffusion coefficient shall be compared with the few existing experimental data on oxygen diffusion in dilute iron alloys.
[1] G. R. Odette, JOM-J. Min. Met. Mat. S. 66, 2427 (2014)
[2] C.L. Fu, M. Krcmar, G.S. Painter, X.-Q. Chen, Phys. Rev. Lett. 99, 225502 (2007)
[3] D. Murali, B.K. Panigrahi, M.C. Valsakumar, S. Chandra, C.S. Sundar, B. Raj, J. Nucl. Mater. 403, 113 (2010)
[4] A. Claisse, P. Olsson, Nucl. Instr. Meth. B 303, 18 (2013)
[5] S.L. Shang, H.Z. Fang, J. Wang, C.P. Guo, Y. Wang, P.D. Jablonski, Y. Du, Z.K. Liu, Corrosion Sci. 83, 94 (2014)
[6] P. Liu, W. Xing, X. Cheng, D. Li, Y. Li, X.-Q. Chen, Phys. Rev. B 90, 024103 (2014)
[7] C. Barouh, T. Schuler, C.-C. Fu, T. Jourdan, Phys. Rev. B 92, 104102 (2015)
Keywords: diffusion, oxygen, bcc Fe, DFT, foreign atoms
  • Poster
    NSF/CECAM School on Computational Materials Science: From Basics to Applications, 17.-27.07.2017, Lausanne, Switzerland

Permalink: https://www.hzdr.de/publications/Publ-25903
Publ.-Id: 25903


Balanced 20 kA DC Distributor for Magnetized Taylor Couette Systems Utilizing Thermostatic Controlled Water Valves with CO2 Adsorption Charge Sensors as Current Controller

Seilmayer, M.; Krauter, N.
A quasi coaxial system consisting of a central current carrying copper rod and five symmetric return paths takes up to 20 kA and provides a homogeneous magnetic field B[phi] to a Taylor-Couette flow. One challenging part of the system is the design of the current distributor, which is supposed to divide the return current into several equally weighted lines. The individual components like the copper rods as well as all electrical contacts provide a characteristic resistance, each in the same magnitude of several micro Ohm. By initial installation this will support an imbalance in the current distribution affecting the symmetry of the magnetic field. So the adjustment of current distribution becomes mandatory to ensure maximum field homogeneity. Controlling the outflow temperature of the required water cooling offers an indirect access to set the current by thermostatically operated valves with CO2 adsorption charge in conjunction with the temperature dependent branch resistance. A numerical investigation proves that a stable current distribution can be achieved by a couple of paralleled thermal controlled heater valves with proportional characteristics. Finally, recent ironless Hall-effect current sensors help to calibrate the system so that the current homogeneity differs less than 1% from optimal state in a wide range of currents.
Keywords: Magnetic Fields, High Current, Magnetized Taylor Couette, PROMISE, MRI, AMRI, HMRI

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Permalink: https://www.hzdr.de/publications/Publ-25902
Publ.-Id: 25902


Characterization of U(VI) sequestration by Acidovorax facilis - a spectroscopic and microscopic approach

Krawczyk-Bärsch, E.; Gerber, U.; Müller, K.; Moll, H.; Rossberg, A.; Steudtner, R.; Merroun, M. L.
To improve bioremediation strategies based on a better understanding of binding mechanisms on the molecular level, we applied U(VI) interaction experiments with Acidovorax facilis. This is a facultative aerobic, chemoorganotrophic gram-negative betaproteobacterium, ubiquitously distributed in the nature including uranium-contaminated sites. Our study combines a variety of microscopic and spectroscopic techniques in order to elucidate the interaction process of U(VI) with A. facilis. Kinetic U(VI) sorption experiments were performed under aerobic conditions at 30°C by adjusting an initial U(VI) concentration to 0.1 mM at a pH of 5 by adding UO2(NO3)2 to the batch culture.
The results showed that different cell compartments play a major role in the sequestration of U(VI). Our findings clearly point out that the local coordination of U(VI) on functional groups of the cell membrane components of A. facilis depends upon time incubation. U(VI) biosorption by outer membrane lipopolysaccharide (LPS) containing phosphoryl residues was observed by TRLFS within the first hours of contact between the cells and U(VI). By increasing the incubation time up to 24 h the implication of carboxyl groups within the cell wall peptidoglycan (PGN) was proved in addition to phosphoryl groups. These results support those obtained by EXAFS, where a relative short average U-Oeq bond length of 2.35 Å was observed, indicating a binding of the U(VI) via organic phosphate groups (from LPS) in a monodentate fashion. The strong interaction of U(VI) with phosphorylic and carboxylic groups was reinforced by ATR FT-IR spectroscopic studies due to the presence of characteristic phosphoryl vibrations. Most of the bound U(VI) presumably remained on the cells, more precisely on the phosphorylic functionalities at the cell membrane. In addition to these functional groups located at the cell surfaces, U is coordinated also, but with low degree, to phosphoryl groups of the intracellular polyphosphate granules as was indicated by STEM analysis.

U. Gerber et al., Journal of Hazardous Materials 317(2016), 127-134.
E. Krawczyk-Bärsch, U. Gerber et al., Journal of Hazardous Materials (2017), under review.
Keywords: Uranium, Bioremediation, STEM, TRLFS, EXAFS, ATR FT-IR
  • Invited lecture (Conferences)
    16. Remediation Colloquium, 05.-06.10.2017, Jena, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-25901
Publ.-Id: 25901


Digitalizing the Circular Economy

Reuter, M. A.
The background of the talk is presented in the recent paper “Digitalizing the Circular Economy”: http://link.springer.com/article/10.1007/s11663-016-0735-5. While this paper provides the overall picture, the focus of the talk will be to show with various brief example how FACT Sage was used during the design and optimization of Outotec-Ausmelt's Top Submerged Lance (TSL) smelting technology (see paper for details), for both primary and secondary materials covering Cu, Pb, Ni, Sn, Zn-residues (jarosite/Goethite for In/Ge/Ag etc. recovery), copper scrap & ewaste, PGMs etc. processing. The talk will thus give a brief overview of the technology, its position in the bigger system of industrial applications and then how for example metal recovery and slag chemistry where optimized using FACT. The talk will end also showing how the FACT knowledge flows into work described in the following blog the presenter was involved in: https://www.fairphone.com/en/2017/02/27/recyclable-fairphone-2/ .
  • Invited lecture (Conferences)
    GTT Annual Workshop 2017 / GTT Users' Meeting 2017, 28.-30.06.2017, Herzogenrath, Deutschland

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Permalink: https://www.hzdr.de/publications/Publ-25900
Publ.-Id: 25900


GPU-Accelerated Kinetic Lattice Monte Carlo for Experimental-Scale Studies

Kelling, J.; Heinig, K. H.; Weigel, M.; Gemming, S.
Micro- and nano-structured materials, including composites, are crucial for future energy technologies. Key processes during production and life-time are governed by self-organization in phase separation processes at the micro and nano scale.
Examples include nano-structured Silicon thin film absorber layers in solar cells providing tailored band-gaps [1] on top of reduced production cost. In the case of micro-patterned electrolyte-matrices, used in a range of fuel cell technologies, both production and aging are governed by phase separation and affect the efficiency and lifetime of large industrial installations.

Simulations of these out-of-equilibrium, inhomogeneous real world systems provide important insights, finding reaction pathways for self-organization and self-alignment of nanostructures. To this end, 3D kinetic Metropolis lattice Monte Carlo simulations can be used to model physical systems at experimental scales in an atomistic way, thereby side-stepping many caveats connected with the alternative phase-field simulations.

These same long-time and large-scale simulations also provide important insights into more fundamental physical problems. The question of super-universality, that is if and how different types of quenched disorder affect universal properties, is still under investigation even for fundamental models like Ising [2], realization of which can be found in important complex magnetic systems, apart from binary mixtures.

We propose massively parallel simulation techniques using the architecture of modern graphics processing units (GPUs) to address these problems, ranging from the kinetic Metropolis Monte Carlo to any Potts models with quenched disorder.
While pioneering work in this area [3] focused on efficient but correlated stochastic cellular automaton implementations, our simulations can be virtually correlation-free [4].

Here, we present two implementations for large-scale simulations on GPUs: One is optimized to offer fast time-to-solution on experimental-scale simulations [5], the other provides highly efficient parameter studies or large sample sizes for large-scale simulations [6]. Harnessing the compute power of modern (multi-)GPU installations leads to increased energy efficiency as well as reduced time-to-solution.

[1] Apl. Phys. Lett. 103, 133106 (2013); Appl. Phys. Lett. 103, 203103 (2013); Nanolett. 16, 1942 (2016)
[2] e.g. EPL 117, 10012 (2017); Phys. Rev. B 88 042129 (2013); Phys. Rev. B 78 224419 (2012); J. Phys. A 24 L1087 (1991)
[3] J. Comp. Phys. 228, 4469 (2009); Phys. Proc. 15 92 (2001)
[4] http://arxiv.org/abs/1705.01022 ; https://arxiv.org/abs/1701.03638
[5] EPJST 210, 175 (2012)
[6] Phys. Rev. E 94 022107 (2016)
Keywords: Kinetic Lattice Monte-Carlo, GPU, Non-equilibrium, Selforganization
  • Lecture (others)
    TYC@Imperial, 16.10.2017, London, England
  • Lecture (Conference)
    2017 MRS Fall Meeting, 26.11.-01.12.2017, Boston, USA
  • Lecture (others)
    Forschungsseminar des Instituts für Wissenschaftliches Rechnen, 03.02.2020, Dresden, Germany

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Permalink: https://www.hzdr.de/publications/Publ-25899
Publ.-Id: 25899


Decoupling the two roles of liquid Ga droplets in the self-catalyzed growth of GaAs nanowires on SiOx/Si(111) substrates

Tauchnitz, T.; Nurmamytov, T.; Hübner, R.; Engler, M.; Facsko, S.; Schneider, H.; Helm, M.; Dimakis, E.
Liquid Ga droplets play a double role in the self-catalyzed growth of GaAs nanowires on Si(111) substrates covered with a native SiOx layer: they induce the formation of nano-sized holes in SiOx and drive the nanowire growth directly onto the underlying Si. The independent control of the two mechanisms is a prerequisite for mastering the growth of nanowires, but it is challenging in a conventional growth procedure where they both take place under the same droplets. As a result, serious growth implications occur, i.e. an uncontrolled number density/yield of vertical nanowires, a broad nanowire length distribution, and growth reproducibility issues.
To resolve those issues, we have developed a three-step in-situ surface modification procedure (SMP) of the SiOx/Si(111) substrates, which decouples the droplet-assisted hole formation in SiOx from the droplet-assisted growth of GaAs nanowires. Step-1 concerns the first thermal annealing of the substrate, during which extremely small pinholes are created in the SiOx layer. Ga deposition and droplet formation takes place at a lower substrate temperature in step-2. Depending on the substrate temperatures in both steps 1 and 2, the number density of Ga droplets can be varied deliberately from 107 to 1010 cm-2. Step-3 concerns the second thermal annealing of the substrate, during which all Ga droplets are evaporated completely from the substrate surface and an identical number of nano-sized holes of controlled size develop at their place. After the SMP, GaAs nanowires are always grown under identical conditions (Tgr=615°C, V/III=11) without pre-deposition of Ga. We found that different types of GaAs structures (vertical nanowires, inclined nanowires, or faceted islands) can nucleate inside the SMP-induced SiOx holes depending on the size of the latter (e.g. the nucleation of vertical nanowires is favored in 8 nm wide holes).
After careful selection of the SMP parameters (substrate temperatures and annealing durations), it is possible (i) to precisely control of the number density of vertical GaAs nanowires from 106 cm-2 to 109 cm-2 without changing the growth temperature or beam fluxes, (ii) to control the size of the SiOx holes in favor of high yields of vertical nanowires (up to 80 % of the total GaAs structures), (iii) to reproduce the wide range of nanowire number densities as well as the high yield values also on substrates from different batches, (iv) to obtain exceptionally narrow nanowire length distributions (below 1 % for 3 µm long nanowires), and (v) to control the nanowire diameter independent of the nanowire length and number density by changing only the V/III ratio.
  • Poster
    Nanowire Week 2017, 29.05.-02.06.2017, Lund, Sweden

Permalink: https://www.hzdr.de/publications/Publ-25898
Publ.-Id: 25898


Ga droplets on SiOx/Si(111) substrates: nucleation and etching

Tauchnitz, T.; Nurmamytov, T.; Hübner, R.; Schneider, H.; Helm, M.; Dimakis, E.
Liquid Ga droplets have been widely used in molecular beam epitaxy to induce the nucleation of nanostructures as well as to remove surface oxides from the substrate prior to epitaxial growth. In this work, we have employed Ga droplets to etch nanoholes into the native surface oxide of Si(111) substrates for the subsequent growth of III-V nanostructures. To that end, we studied the nucleation kinetics of Ga droplets on SiOx and the interaction between Ga adatoms/droplets and SiOx.
For given Ga flux and deposition time, we found that the number density of Ga droplets depends not only on the substrate temperature during deposition, but also on the annealing history of the substrate. This is attributed to the dependence of Ga adatom diffusivity on the surface morphology and/or the composition of the native oxide layer, both of which can be modified during the annealing. With an appropriate selection of substrate temperatures for the annealing and the Ga deposition steps, it was possible to vary deliberately the number density of Ga droplets within four orders of magnitude, i.e. 107-1010 cm-2. Interestingly, the droplet size and contact angle were found to be independent of the number density. This finding implies that low number densities of droplets are accompanied by an extensive loss of Ga atoms from the substrate surface. We discuss various explanations, such as desorption of Ga adatoms from the SiOx surface or reaction of Ga adatoms with SiOx and formation of volatile Ga2O.
All Ga droplets induce local modifications in the SiOx surface that evolve into nanoholes during a subsequent thermal annealing (which also results in complete evaporation of the Ga droplets). Depending on their size (which is a function of annealing temperature and duration), nanoholes can accommodate the nucleation of nanostructures on the underlying Si surface. As an example, we demonstrate the epitaxial growth of GaAs nanowires in the self-catalyzed mode. The number density of nanowires was controlled precisely and reproducibly within the range of 107-109 cm-2, whereas their length distribution was exceptionally narrow.
  • Poster
    19th European Workshop on Molecular Beam Epitaxy, 19.-22.03.2017, Korobitsyno, St. Petersburg, Russia

Permalink: https://www.hzdr.de/publications/Publ-25897
Publ.-Id: 25897


Aqueous Gold Overgrowth of Silver Nanoparticles: Merging the Plasmonic Properties of Silver with the Functionality of Gold

Mayer, M.; Steiner, A. M.; Röder, F.; Formanek, P.; König, T. A. F.; Fery, A.
To date, it has not been possible to combine the high optical quality of silver particles with good chemical stability and synthetic convenience in a fully aqueous system, while simultaneously allowing chemical surface functionalization. We present a synthetic pathway for future developments in information, energy and medical technology where strong optical/electronic properties are crucial. Therefore, the advantages inherent to gold are fused with the plasmonic properties of silver in a fully aqueous Au/Ag/Au core-shell-shell system. These nanoparticles inherit low dispersity from their masked gold cores, yet simultaneously exhibit the strong plasmonic properties of silver. Protecting the silver surface with a sub-skin depth gold layer enables oxidant stability and functionality without altering the Ag-controlled optical properties. This combines both worlds - optical quality and chemical stability - and furthermore it is not limited to a specific particle shape.

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Permalink: https://www.hzdr.de/publications/Publ-25896
Publ.-Id: 25896


Radiotracer Application at Dresden University and Fraunhofer Institute for Nondestructive Material Testing (Dresden)

Zeuner, A.; Krueger, P.; Jentsch, T.
In 1957, the Faculty of Nuclear Technology was founded at the Dresden University of Technology. One of the aims of this faculty was to develop methods of radio tracer usage and to apply these methods at technical scale. The group "Technical Isotope Application" performed a lot of measurements in industrial plants. This group worked under different names up to 2005. Since about 2000, some capabilities have been transferred to the Fraunhofer Institute of Non-Destructive Testing, Dresden branch. In the following, an overview is given on working fields or investigated equipments, resp.
1. Application and development of radionuclide generators
Radiotracer investigations are done preferably by using short-lived radionuclides. As in nuclear medicine, the application of radionuclide generators (Mo-99/Tc-99m and Snl13/ Inl13m) has advantages also in technological applications, especially the long usability of the generator system. For dedicated purposes, namely the investigation of high temperature processes, a new generator system (Ba-140/La-140) was developed and applied.
2. Work on further development of radio tracer
- In many papers, the momentum method was explored. This method has the advantage, that a residence time distribution is interpreted without any model assumptions. The mean residence time and other parameters are calculated only from statistical moments and applied to
material transport processes.
- Activity estimation is an important part prior an investigation will be accepted by the radiation protection authorities. A computer program is developed based on the plant values and on the expected worst residence time distribution.
- During radiotracer measurements, the residual pulse density sometimes does not decrease to the original background. With the assumption, that the residual pulse density is caused by deposition of radioactive material near the detector, correction procedures were developed and used.
3. Working fields
Open radionuclides:
Residence time measurements in
- Water, waste water, filtration
- Gas exchange and reactions in gas phase; fluid beds
- Conveyers, dryers, rotary kilns, mills
- Plants for chemical fibres, polymers; in extruders and others
- Estimation of oil consumption of cumbustion engines
- Particle tracking in a screw conveyer by activated glass balls
- Investigation of mixing processes Application of sealed sources
- Estimation of ash content and heat value of brown coal
- Estimation of sedimentation in a smoke channel of a thermal cracker
- Steam estimation in streaming hot water
  • Poster
    The 6th International Conference on Tracers and Tracing Methods, TRACER 6, 06.-08.06.2011, Oslo, Norge

Permalink: https://www.hzdr.de/publications/Publ-25895
Publ.-Id: 25895


What Ga droplets can and cannot do in the growth of GaAs nanowires on Si

Tauchnitz, T.; Balaghi, L.; Hübner, R.; Bischoff, L.; Schneider, H.; Helm, M.; Dimakis, E.
The central role of liquid Ga droplets in the self-catalyzed growth of free-standing GaAs nanowires on Si(111) substrates will be overviewed, including our recent findings. Initially, Ga droplets interact with the surface oxide layer that typically covers a Si substrate and create nanoholes. The nucleation of GaAs nanowires takes place there, in direct contact with the underlying Si. Using a sequence of Ga deposition and substrate annealing steps, the number density of nanowires can be controlled from 107 to 109 cm-2 without the need for pre-patterned substrates. During the growth of nanowires, the Ga droplet on their apex captures Ga adatoms and As4 molecules efficiently and, thus, enhances the local growth rate in favor of the axial elongation of the nanowires. The contact angle of the droplet with the underlying nanowire determines the phase of the growing crystal. Long segments of pure zinc blende phase are possible, whereas wurtzite has been demonstrated only for short segments. On the other hand, Ga-catalyzed growth has certain inherent limitations. Those concern the axial growth of ternary alloys, the abruptness of axial hetero-interfaces and the ability for defect-free interruptions of the axial growth. Most of those limitations are related to the solubility properties of other elements (i.e. In, Al, As) in Ga droplets. As a method of probing and controlling the growth processes inside the droplets, the droplet-confined alternate pulsed epitaxy is introduced.
  • Invited lecture (Conferences)
    19th European Workshop on Molecular Beam Epitaxy, 19.-22.03.2017, Korobitsyno, St. Petersburg, Russia

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Publ.-Id: 25894


Selective mass enhancement close to the quantum critical point in BaFe2(As1−xPx)2

Grinenko, V.; Iida, K.; Kurth, F.; Efremov, D. V.; Drechsler, S.-L.; Cherniavskii, I.; Morozov, I.; Hänisch, J.; Förster, T.; Tarantini, C.; Jaroszynski, J.; Maiorov, B.; Jaime, M.; Yamamoto, A.; Nakamura, I.; Fujimoto, R.; Hatano, T.; Ikuta, H.; Hühne, R.
A quantum critical point (QCP) is currently being conjectured for the BaFe2(As1−xPx)2 system at the critical value xc ≈ 0.3. In the proximity of a QCP, all thermodynamic and transport properties are expected to scale with a single characteristic energy, given by the quantum fluctuations. Such a universal behavior has not, however, been found in the superconducting upper critical field Hc2. Here we report Hc2 data for epitaxial thin films extracted from the electrical resistance measured in very high magnetic fields up to 67 Tesla. Using a multi-band analysis we find that Hc2 is sensitive to the QCP, implying a significant charge carrier effective mass enhancement at the doping-induced QCP that is essentially band-dependent. Our results point to two qualitatively different groups of electrons in BaFe2(As1−xPx)2. The first one (possibly associated to hot spots or whole Fermi sheets) has a strong mass enhancement at the QCP, and the second one is insensitive to the QCP. The observed duality could also be present in many other quantum critical systems.

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Interactions of natural occurring microorganisms with uranium(VI)

Gerber, U.; Schäfer, S.; Krawczyk-Bärsch, E.
The uranium waste mine Königstein (Saxony, Germany) is heavily polluted with heavy metals, especially with uranium. Despite the high concentrations of heavy metals, the mine is a reservoir for many different microorganisms that have evolved special strategies to survive in these extreme environments. Their ubiquitous occurrence is of fundamental interest to understand the migration behavior of radionuclides within the biosphere.
Furthermore, microorganisms could be used to clean-up contaminated soils, sediments, and waters by removing uranium and other radionuclides, due to bioremediation processes.
Keywords: Bioremediation, Uranium(VI), microorganisms
  • Lecture (others)
    Im Rahmen einer Vorlesung der Universidad Tenica Federico Santa Maria, 27.07.2017, Valparaiso, Chile

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Publ.-Id: 25892


Evaporation-assisted magnetic separation of rare earth ions in aqueous solutions

Lei, Z.; Fritzsche, B.; Eckert, K.ORC
This work aims to answer the question of why an enrichment of paramagnetic ions can be observed in a magnetic field gradient despite the presence of a counteracting Brownian motion. For that purpose, we study a rare earth chloride (DyCl3) solution in which weak evaporation is adjusted by means of small differences in the vapor pressure. The temporal evolution of the refractive index field of this solution, as a result of heat and mass transfer, is measured by means of a Mach-Zehnder interferometer. We develop a numerical algorithm which splits the refractive index field into two parts, one space-dependent and conservative and the other time-dependent and transient. By using this algorithm in conjunction with a numerical simulation of the temperature and concentration field, we are able to show that 90\% of the refractive index in the evaporation-driven boundary layer is caused by an increase in the concentration of Dy(III) ions. A simplified analysis of the gravitational and magnetic forces, entering the Rayleigh number, leads to a diagram of the system's instability. Accordingly, the enrichment layer of elevated Dy(III) concentration is placed in a spatial zone dominated by a field gradient force. This leads to the unconditional stability of this layer in the present configuration. The underlying mechanism is the levitation and reshaping of the evaporation-driven boundary layer by the magnetic field gradient.
Keywords: magnetic separation, rare earth salt; paramagnetism; interferometer; field gradient force

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General Evolution Equation for the Specific Interfacial Area of Dendrites During Alloy Solidification

Neumann-Heyme, H.; Eckert, K.ORC; Beckermann, C.
The specific area of the solid-liquid interface of an assembly of dendrites is an important integral measure of the morphology of the microstructure forming during alloy solidification. It represents the inverse of a characteristic length scale and is needed for the prediction of solidification defects and material properties. In the present study, the evolution of the interfacial area of dendrites is analysed using 3D phase-field simulations. A general evolution equation is developed for the specific interfacial area as a function of time and solid volume fraction that accounts for the effects of growth, curvature-driven coarsening and interface coalescence. The relation is validated using data from previously performed synchrotron X-ray tomography and isothermal coarsening experiments. It is found to be valid for arbitrary and even varying cooling rates and for a wide range of binary alloys. The rate constant in the evolution equation is successfully related to alloy properties.
Keywords: Dendritic solidification; Interfacial area; Phase-field simulation; Synchrotron X-ray tomography experiments

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Publ.-Id: 25890


A new degree of freedom for electron holography

Röder, F.; Lubk, A.; Houdellier, F.; Denneulin, T.; Snoeck, E.; Hÿtch, M. J.
Off-Axis Electron Holography permits the direct reconstruction of amplitude and phase of electron waves elastically scattered by an object (see, e.g., [1]). The technique employs the Möllenstedt biprism to mutually incline an object modulat-ed wave and a plane reference wave to form an interference pattern at the detec-tor plane. Limited coherence of the electron beam in presence of aberrations at-tenuates high spatial frequencies of the object exit wave spectrum, which is de-scribed by the sideband envelope function. We explore an extension of the con-ventional electron holography set-up given by deliberately tilting the reference wave independent from the object wave. This allows the transfer of spatial fre-quencies beyond the conventional sideband information limit as predicted by a generalized transfer theory for Off-Axis Electron Holography [2]. This is based on the idea that a reference wave tilted by q0 compensates the wave aberration for the spatial frequency q0 of the object wave spectrum. Thus, an off-axis hologram series with varying reference wave tilt allows in principle a linear synthesis of an effective coherent aperture with a radius reaching out beyond the conventional information limit. Furthermore, an object-independent measurement of aberra-tions as well as strain measurements by dark-field electron holography can be realized using this setup. The experimental realization of an arbitrarily tilted refer-ence wave is challenging and could be realized for the first time at the Hitachi HF3300C I2TEM at CEMES Toulouse for one direction [3]. We used an additional biprism placed in the illumination system. Three condenser lenses were adjusted to provide a demagnified image of the condenser biprism at the sample plane under parallel illumination. The pre-specimen deflectors were adapted to maintain the incident wave vector of the object wave and to realize a tilt of the reference wave as a function of the condenser biprism voltage. Finally, we have experimen-tally shown that dark-field holography can be conducted with an object-independent reference alleviating the need for a uniform area of known structure.

[1] H. Lichte, M. Lehmann, Rep. Prog. Phys. 71 (2008) 016102.
[2] F. Röder, A. Lubk, Ultramicoscopy 152 (2015) 63-74.
[3] F. Röder, F. Houdellier,T. Denneulin, E. Snoeck, M.J. Hÿtch, Ultramicoscopy 161 (2016) 23–40.
Keywords: electron holography, tilted reference wave, aperture systhesis, dark-field
  • Invited lecture (Conferences)
    PICO 2017 - Forth Conference on Frontiers of Aberration Corrected Electron Microscopy, 30.04.-04.05.2017, Kasteel Valsbroek, The Netherlands

Permalink: https://www.hzdr.de/publications/Publ-25889
Publ.-Id: 25889


Micro-flow magnetic separation of rare earth metals ions in aqueous solutions

Kolczyk, K.; Wojnicki, M.; Yang, X.; Mutschke, G.; Kutyla, D.; Kowalik, R.; Zabinski, P.
Due to application in many modern technologies, rare earth elements (REE) nowadays attract higher and higher interest. These metals are produced both from primary and secondary sources in hydrometallurgical processes which are often complicated and costly. The most problematic step of production is the separation of ions. Due to these reasons it is desirable to improve the current processes.
Here, High Magnetic Gradient Separation (HGMS) appears to be attractive. It utilizes the different magnetic properties of rare earth metal ions to achieve separation by attraction or repulsion in an inhomogeneous magnetic field [1][2].
The present work investigates the separation of REE ions in aqueous solutions based on their magnetic properties. The experiments were carried out in micro-flow cells produced by a 3D printing technology (Fig. 1). The cells consist of a spiral channel next to which a spiral of an iron wire is arranged. The inhomogeneous magnetic field in the cross section of channel is created by the placement of the cell in a laboratory electromagnet. During the flow of the solution the metal ions experience a force from the gradient magnetic field. At the outflow, the near-wire and the far-wire half of the solution are collected and analyzed. Different solutions consisting of a single species and of mixtures of metals ions were investigated at different flow rates, and the concentrations were analyzed by UV/VIS spectrometry.
The results will be presented in detail at the conference. The conducted experiments state a preliminary determination of the influence of a gradient magnetic field on the transport of ions in aqueous solutions in the flow state.

[1] K. Kołczyk, M. Wojnicki, D. Kutyła, R. Kowalik, P. Żabiński, A. Cristofolini, Archives of Metallurgy and Materials, 61 (2016) 1919–1924.
[2] K. Kolczyk, D. Kutyla, M. Wojnicki, A. Cristofolini, R. Kowalik, P. Zabinski, MAGNETOHYDRODYNAMICS 52 (2016) 541-547.
Keywords: magnetic separation, rare earth metals, aqueous solution, microfluidics UV/VIS spectrometry
  • Lecture (Conference)
    International Conference on Magneto-Science 2017, 23.-27.10.2017, Reims, Frankreich

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Contactless manipulation of fluids and measurement of concentration changes in microfluidic systems by imposed magnetic fields

Uhlemann, M.; Hähnel, V.; Kahn, F.; Mutschke, G.; König, J.; Fritsch, I.
New technologies based on transport, actuation and manipulation of fluids and objects in the micro- and nanometer scale are rapidly developing. The enormous scientific and technological interest focuses on lab-on-a-chip approaches which are applicable in analytics and monitoring in medicine, in biology and in the environmental sector. Avoiding mechanical forces, alternative pumping concepts gain in importance.
Contactless external driving forces such magnetic fields and field gradients for fluid manipulation and electrochemical and analytical approaches are of interest.
Several microfluidic approaches were employed to prove the concept of fluid manipulation by overlaying magnetohydrodynamic (MHD) effects generated by the Lorentzforce (FL) and the magnetic field gradient force (FB) [1]. For this purpose suitable microstructures were designed and applicable materials were chosen to generate high magnetic field gradients in the immediate vicinity of the surface of the microfluidic chip. These are generated by magnetic field gradient templates consisting of μm-thin CoFe stripes which are saturated by a permanent NdFeB magnet. They were employed to manipulate liquids with paramagnetic ions (e.g. Mn2+). Potential time transients as a measure for concentration changes between the electrodes with and without superimposed magnetic field gradients are recorded and the enrichment [2] is detected by fluorescence microscopy supported by magnetic field gradient simulation.
For driving fluid flow the redox system K3Fe(CN)6/K4Fe(CN)6 which is commonly used for redox-MHD [3] was used and superimposed by high magnetic field gradients generated by the same method. Then, a fluid flow can be controlled by on-off-switching of the cell current originating from the electrodes which is generating a Lorentz force. In combination with the magnetic field gradient template a desired change of velocity and flow direction is realized as well as localized enrichment of ions. To clarify the impact of the magnetic field gradient, the template can be positioned in different orientation and distances in between the electrodes facing each other to reduce or enhance the fluid flow. Video microscopy and particle velocity measurements illustrate and quantify the effects further supported by numerical simulations.
Keywords: Redox-reaction, microfluidics, magnetic fields, Lorentz force, Kelvin force, PIV, numerical simulation
  • Lecture (Conference)
    International Conference on Magneto-Science 2017, 23.-27.10.2017, Reims, Frankreich

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Publ.-Id: 25887


Numerical simulation of mass transfer and convection near a hydrogen bubble during water electrolysis in magnetic fields

Mutschke, G.; Bazcyzmalski, D.; Karnbach, F.; Uhlemann, M.; Yang, X.; Eckert, K.; Fröhlich, J.; Cierpka, C.
Hydrogen produced from wind or solar power could be used easily for storing energy also at large scale, thus allowing to bridge the gap between supply and demand of renewable energy with respect to time and place. When splitting water by electrolysis, a deeper look at local phenomena near single bubbles at the electrode might be helpful to improve our understanding of the process. In the recent literature, magnetic fields are discussed with respect to the bubble departure, thereby possibly influencing the efficiency of the process [1-7].
The contribution will present numerical simulations resolving in detail local phenomena near a single hydrogen bubble at the cathode during the electrolysis of water in external magnetic fields. The modeling is supported by data of recent experiments on hydrogen single bubbles evolving at a platinum micro-electrode [7-9]. The results will provide insight into the local and temporal behavior of electrolyte convection, species concentration and mass transfer during electrolysis. Furthermore, the influence of the Lorentz force caused by vertical and horizontal magnetic fields on the departure will be discussed in detail (see Figs. 1 and 2).

[1] X. Yang et al., Langmuir 31 (2015) 8184-8193.
[2] D. Fernandez et al., Langmuir 30 (2014) 13065-13074.
[3] H. Liu et al., J. Electroanal. Chem. 754 (2015) 22-29.
[4] H. Liu et al., Can. J. Chem. Eng. 9999 (2015) 1-8.
[5] D. Baczyzmalski et al., Exp. Fluids 56 (2015) 162ff.
[6] J. Koza et al., Electrochem. Comm. 10 (2009) 425-429.
[7] F. Karnbach et al., J. Phys. Chem. C 120 (2016) 15137-15146.
[8] D. Baczyzmalski et al., J. Electrochem. Soc. 163 (2016) E248-E257.
[9] G. Mutschke et al., Magnetohydrodynamics 53 (2017) 193-198.
[10] D. Baczyzmalski et al., submitted to Phys. Rev. Fluids (2017).
Keywords: electrolysis, hydrogen evolution, magnetic field, Lorentz force, mass transfer, convection, numerical simulation
  • Poster
    International Conference on Magneto-Science 2017, 23.-27.10.2017, Reims, Frankreich

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Publ.-Id: 25886


Growth and detachment of single hydrogen bubbles in a magnetohydrodynamic shear flow

Baczyzmalski, D.; Karnbach, F.; Mutschke, G.; Yang, X.; Eckert, K.; Uhlemann, M.; Cierpka, C.
This study investigates the effect of a magnetohydrodynamic (MHD) shear flow on the growth and detachment of single sub-millimeter-sized hydrogen gas bubbles. These bubbles were electrolytically generated at a horizontal Pt microelectrode (100 μm in diameter) in an acidic environment (1 M H2SO4). The inherent electric field was superimposed by a homogeneous electrode-parallel magnetic field of up to 700 mT to generate Lorentz forces in the electrolyte, which drive the MHD flow. The growth and motion of the hydrogen bubble was analyzed by microscopic high-speed imaging and measurements of the electric current, while particle tracking velocimetry (μPTV) and particle image velocimetry (μPIV) were applied to measure the surrounding electrolyte flow. In addition, numerical flow simulations were performed based on the experimental conditions. The results show a significant reduction of the bubble growth time and detachment diameter with increasing magnetic induction, which is known to improve the efficiency of water electrolysis. In order to gain further insight into the bubble detachment mechanism, an analysis of the forces acting on the bubble was performed. The strong MHD-induced drag force causes the bubble to slowly slide away from the center of the microelectrode before its detachment.
This motion increases the active electrode area and enhances the bubble growth rate. The results further indicate that at large current densities the coalescence of tiny bubbles formed at the foot of the main bubble might play an important role for the bubble detachment.
Moreover, the occurrence of Marangoni stresses at the gas-liquid interface is discussed.
Keywords: electrolysis, hydrogen evolution, magnetic field, Lorentz force, PIV, numerical simulation

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Probing the Impact of the Initiator Layer on Grafted-from Polymer Brushes: A Positron Annihilation Spectroscopy Study

Panzarasa, G.; Aghion, S.; Marra, G.; Wagner, A.; Liedke, M. O.; Elsayed, M.; Krause-Rehberg, R.; Ferragut, R.; Consolati, G.
Grafting-from is the technique of choice to obtain polymer brushes. It is based on the growth of polymer chains directly from an initiator-functionalized surface, and its development gained momentum thanks to recent advances in controlled polymerization techniques. However, despite the great amount of work that has been performed on this subject, the influence exerted by the initiator layer on the characteristics of the resulting brushes has been almost completely overlooked. Our group has already demonstrated that positron annihilation spectroscopy (PAS) is a valuable analytical tool for the study of polymer brushes. Here, we applied this technique to show that differences in the organization of the initiator layer dramatically reflect on the characteristics of polymer brushes. Brushes made by surface-initiated atom transfer radical polymerization (ATRP) of a pH-responsive polymer, poly(dimethylaminoethyl methacrylate) (PDMAEMA), were investigated also in terms of the effects of protonation and of the incorporation of silver nanoparticles inside the brushes, shining a new light on the internal structure of such complex, fascinating systems.
Keywords: Grafting-from polymer brushes positron annihilation spectroscopy surface-initiated atom transfer radical polymerization (ATRP)

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Publ.-Id: 25884


Modeling in vivo relative biological effectiveness in particle therapy for clinically relevant endpoints

Lühr, A.; von Neubeck, C.; Helmbrecht, S.; Baumann, M.; Enghardt, W.; Krause, M.
Background
The relative biological effectiveness (RBE) of particle therapy compared to photon radiotherapy is known to be variable but the exact dependencies are still subject to debate. In vitro data suggested that the RBE is to a large extend independent of ion type if parametrized by the beam quality Q. This study analyzed the RBE dependence of pre-clinical data on late toxicity with an emphasis on the beam quality.
Material and Methods
Published pre-clinical RBE dose-response data of the spinal cord following one and two fractions of photon and carbon ion irradiation were compiled. The beam quality for each treatment condition was obtained from Monte Carlo simulations. The αp and βp parameters of the linear-quadratic (LQ) model for particle irradiation were determined from the pre-clinical data and provided as a function of Q. An introduced model proposed αp to increase linearly with Q and βp to remain constant. RBE values predicted by the model were compared to the published data.
Results
The αp parameter was highly correlated with Q (R2 = 0.96) with a linear slope of 0.019 Gy-1. No significant variation of βp with Q was found. RBE and Q were also highly correlated (R2 = 0.98) for one and two fractions. The (extrapolated) RBE at Q = 0 (theoretical photon limit) for one and two fractions was 1.22 and significantly larger than 1 (p = 0.004). The model reproduced the dependence of RBE on fractionation well.
Conclusion
Fraction dose and beam quality Q were sufficient to describe the RBE variability for a late toxicity model within a carbon ion treatment field. Assuming the independence of the identified RBE parameters on the ion type might suggest the translation of variable (pre-) clinical RBE data from carbon ion to proton therapy.

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Towards Reconfigurable Field Effect Transistors: Controlled Nickel Silicidation using Flash Lamp Annealing

Khan, M. B.; Deb, D.; Georgiev, Y. M.; Prucnal, S.; Voelskow, M.; Erbe, A.
Classical scaling down of CMOS technology is reaching its end in the next few years. To facilitate further the enhancement in the complexity and performance of electronic circuits without increasing the chip area, devices with new materials, new architectures, enhanced functionality and new computation principles have gained importance. Our work focuses on fabricating devices with new architectures and enhanced functionality i.e. devices which can be reconfigured as a p- or n-channel field effect transistor (FET). These reconfigurable FETs are based on Silicon (Si) nanowires (NWs), which are silicided at both ends to form Si-NiSi2-Si Schottky junctions. Formation of NiSi2 is a pre-requisite for proper functioning of these devices since fermi level of NiSi2 aligns itself near the mid-bandgap of Si, thereby enabling tuning of band by application of electrostatic potential for its function as a p/n FET [1]. Moreover, control over silicide length is also important to scale the Si channel and to have symmetric contacts on both sides of the nanowire [2]. These issues are the focus of our recent work.
In this paper, we report on comparison between silicidation of undoped Si NWs using rapid thermal annealing (RTA) and flash lamp annealing (FLA). The nanowires are fabricated on silicon on insulator (SOI) substrates by a top down process based on electron beam lithography (EBL) and subsequent inductively coupled plasma (ICP) etching. Hydrogen silsesquioxane (HSQ), a negative tone EBL resist, is used to provide high quality sub-15nm lithographic nanowire patterns, which are transferred into SOI by optimised ICP etching based on C4F8/SF6/O2 mixed gas chemistry. Subsequently, nickel (Ni) is sputtered at lithographically defined areas followed by RTA, which yields atomically sharp NiSi2-Si Schottky junctions. However, the main drawback of this silicidation process is the poor control over Ni silicide phase formation and the progression length of the silicidation along the Si NWs (Fig. 1). These effects lead to an inhomogeneous silicidation process, which prevents symmetric Si channel formation and downscaling.
To provide better control over the silicidation process, a ms-range FLA is investigated as a potential replacement of RTA. Initially, the FLA was performed for 3, 6 and 20 ms on bulk silicon by either flashing the front (f-FLA) or rear (r-FLA) side of the samples. Formation of NiSi and the composition was investigated by micro-Raman (Fig. 2) and Rutherford Backscattering Spectrometry (RBS) (Fig. 3). It is shown that after 6 and 20 ms annealing 50 nm Ni is fully converted to stoichiometric NiSi with atomically sharp interface between NiSi and Si. Cubic NiSi displays Raman active phonon modes at 193 and 217 cm-1, which suggests that the fabricated layer is tensile strained. These preliminary results on bulk Si suggest that the FLA promises to provide better control over silicidation process of the nanowires, thereby enhancing the performance of reconfigurable FETs. Results on silicidation of nanowires will be presented at the conference.
Keywords: Silicon nanowire; silicidation; reconfigurable transistor; Schottky junction
  • Poster
    Micro and nanoengineering, 18.-22.09.2017, Braga, Portugal

Permalink: https://www.hzdr.de/publications/Publ-25882
Publ.-Id: 25882


Electrical Characterization of sub-20 nm Silicon Nanowires Fabricated using Electron Beam Lithography and Inductively Coupled Plasma Etching

Khan, M. B.; Deb, D.; Georgiev, Y. M.; Fuchs, F.; Schuster, J.; Erbe, A.
Scaling down of CMOS faces strong challenges due to which new materials, enhanced functionality and new device concepts have gained importance. These concepts include undoped silicon nanowire based reconfigurable devices which can be programmed as p-FET or n-FET by controlling the electrostatic potential applied across gate. In this work, electrical characterization of undoped sub-20 silicon nanowires (SiNWs) is reported. SiNWs are fabricated on intrinsic SOI substrates in <110> and <100> crystal directions by a top down approach. Hydrogen silsesquioxane (HSQ), a negative tone electron beam resist is used for nano- patterning as well as hard mask for etching. Nanowire etching process is optimized using an inductively coupled plasma (ICP) source and C4F8/SF6/O2 mixed gas recipe at 18 oC. These NWs are oxidized to form a SiO2 shell and subsequently silicidized. For silicidation the SiO2 shell is wet etched at pre-defined positions followed by Nickel(Ni) sputtering and diffusion which yield silicide-silicon(Schottky) junctions. Ni is used for silicidation to selectively control the charge carriers injection at the junctions. Different transport and silicidation progress was observed in <110> and <100> crystal directions.
Keywords: Silicon nanowire; etching; lithography; schottky barrier devices
  • Lecture (Conference)
    Deutsche Physikalische Gesellschaft, 19.-24.03.2017, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-25881
Publ.-Id: 25881


Electromagnetically excited flows and instabilities in liquid metal batteries

Weier, T.; Horstmann, G. M.; Landgraf, S.; Nimtz, M.; Salas, A.; Starace, M.; Stefani, F.; Weber, N.
We will provide an overview of the liquid metal battery (LMB) related activities at the Helmholtz-Zentrum Dresden - Rossendorf (HZDR) with a focus on magnetohydrodynamic aspects of future large scale LMBs. High current densities together with a large cross section will result in substantial currents accompanied by considerable magnetic fields. Thus electromagnetically driven flows and instabilities should be taken into account for large enough installations. While beneficial effects of mild electromagnetically driven flows are to be expected for the cathodes, the thin electrolyte layers have to be protected against violent motion.

The Tayler instability (TI) can be understood as a generic case of a current driven instability under perfectly uniform current, i.e., ideal conditions. In this sense it constitutes sort of an upper bound for a current bearing fluid to remain at rest. Modifying the magnetic field distribution in the cell is an effective means to suppress the TI.
Different field configurations to achieve TI suppression and their relative merits will be discussed and related to TI saturation mechanisms.
Non-uniform current distributions are more typical for real settings. They give rise to rotational Lorentz force distributions and will thereby also generate electro-vortex flows (EVFs). In terms of LMBs the concrete shape of the current collectors plays a crucial role in whether EVFs exist and how they might interact with the TI. We will conclude with electromagnetically exited interface instabilities and discuss similarities to and differences from sloshing modes known from aluminium reduction cells.
Keywords: liquid metal batteries, Tayler instability, electro-vortex flows, interfacial instabilities
  • Lecture (Conference)
    High Temperature Batteries for Stationary Energy Storage Workshop, 19.-20.09.2017, Trondheim, Norwegen

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Publ.-Id: 25880


Arrival time and Intensity Binning at high quasi-cw repetition rates: the big data challenge

Green, B.; Kovalev, S.; Deinert, J.; Wang, Z.; Awari, N.; Chen, M.; Germanskiy, S.; Gensch, M.
  • Lecture (Conference)
    ARD-ST3 annual meeting, 19.-21.07.2017, Zeuten, DESY, Germany

Permalink: https://www.hzdr.de/publications/Publ-25879
Publ.-Id: 25879


Experimental investigation of pilot scale bubble column reactor with various internals using fine wire-mesh sensors

Lavetty, C.
In this master thesis the hydrodynmamic behavior of a bubble column reactor with various dense heat exchanging tube patterns and tube sizes has been investigated using fine wire-mesh sensors. With the special design of the wire-mesh sensors it was possible to manufacture one set of sensors while using different inlets to mimic the specific tube pattern. A three level wire-mesh sensor with a 64x64x64 grid was used in order to asses the local and global hydrodynamics, such as, bubbles size distribution, gas velocity profile, phase holdup and its distribution. For the first time, with this technique it is possible to gain insights in the flow behaviour within complex geometries, e.g. sub-channels of the tube bundle. Therfore, regime maps were generated covering all hydrodynamic flow regimes, namely, bubbly, transition and churn-turbulent flow regime. Du to the insertion of the tube bundle within the reactor, the radial holdup profile changes drastically compared to the empty counterpart. It reveals zones of liquid up flow within the sub-channel and liquid downflow within the viscinity of the tube due to additional wall brought into the system. Furthermore, a correlation has been developed in order to describe the overall holdup in dependence on tube size and pattern for the current investigations as well as for past investigations.
  • Master thesis
    University of Edinbourgh, 2018
    Mentor: Möller, Felix
    108 Seiten

Permalink: https://www.hzdr.de/publications/Publ-25878
Publ.-Id: 25878


Numerical Optimization of Finned Heat Exchanger Using Ansys CFX

Ayob, A. A.; Unger, S.
his report investigates the effect of tube geometry and different fin parameters towards heat transfer and flow properties in a heat exchanger using Ansys CFX for a single phase system. The purpose of this study was focused on improving heat transfer efficiency around a single tube within a heat exchanger. Stainless steel was used as the construction material for the tube and the flowing medium is air at ambient conditions. Tube length was kept constant at 212 mm. The temperature of the tube wall was kept constant at 330.15 K and inlet air temperature at 300.15 K. Inlet air velocity was varied from 0.5 m/s to 5 m/s to observe how the structure performed at different Reynolds number. The main results that were observed were “goodness” factor (ratio of Colburn number to friction factor), pressure drop (∆P), increase in air temperature (∆T), efficiency, and average heat transfer coefficient (HTC).
An initial simulation was modelled and compared to literature. This was done to ensure that it was performing as intended. The accuracy of Ansys CFX was studied to ensure that changing the software properties such as mesh, residual target and turbulence model would not have much impact on the results. It was decided that manipulating software properties changed the results by less than 5% would suffice. The effect of tube geometry was studied by changing the shape from annular to oval shaped and by changing the outer diameter of oval tubes from 27mm to 16 mm. From the results, it was concluded that an oval tube with 16 mm outer diameter was the best design as it gave the lowest pressure drop (0.05 – 1.9 Pa) and highest “goodness” factor (0.4), even though it had the lowest value for heat transfer coefficient. The 16 mm oval tube was used for the simulation of different fin parameters The fin parameters varied were fin thickness, fin height, and fin pitch. Only one parameter was manipulated while other parameters were maintained at a constant value. The fin height was manipulated from 6mm to 46mm. It was observed that a smaller fin height would give efficiencies up to 96%, lower pressure drop but the lowest “goodness” factor. At low air velocities, a 6 mm fin height had a lower value for ∆T compared to 46 mm tall fin by 58%. The difference decreases to 0.016% when air velocity reaches 5 m/s. Next, f in thickness was changed from 0.25 mm to 4mm. The results showed that increasing the fin thickness increases the average heat transfer coefficient and ∆T but resulted in higher ∆P. When air velocity is low, the difference in ∆T was 53%. This decreased with increasing velocity. Lastly, fin pitch was manipulated from 0.25 mm to 6 mm. It was found that a fin pitch value of 0.25-1 mm reduced the amount of air able to flow between the fins. At low velocities of around 0.5 m/s, increasing the fin pitch beyond 4 mm had a negative effect on HTC and ∆T. This value changes when air velocity exceeds 3 m/s, where a fin pitch larger than 2 mm had lower values for average heat transfer coefficient and ∆T.
  • Master thesis
    The University of Edinburgh, 2017
    Mentor: Sebastian Unger

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Publ.-Id: 25877


Transformation of biomass components to high-value products: reductive amination of ethyl levulinate with amines

Shumilov, V. V.; Salmi, T.; Murzin, D.; Hupa, L.; Eränen, K.; Kumar, N.; Sulman, E.; Schubert, M.; Boden, S.; Hampel, U.
Transformation of biomass components to high-value products used in industry over structured catalysts is the idea behind this project. Synthesis of 5-Methyl-1-Hydroxyethyl-2-Pyrrolidone by reductive amination of ethyl levulinate using 3-aminopropanol as the alkyl amine in the presence of hydrogen was performed. Reactor which uses porous ceramic monolith as a catalytic carrier was studied.

For the development of a new catalytic system, alumina was chosen as a carrier material and sponge replica technique was used for its production. Porous ceramics with different pore types and sizes are widely applied in chemical industry. The unique properties of porous materials allow to carry out a spectrum of well-established and recent applications, such as molten metal filtration, catalysis, refractory and thermal insulation, hot gas filtration. Porous form is perfect for heterogeneous catalysis because of high surface area, which enables liquid (or gas) to contact the catalyst intensively.

Alpha-Alumina is a strong material the surface area of which is low and so to enlarge surface area covering of the foam with a layer of gamma-alumina which has a much bigger surface area was performed.

Two methods of gamma-alumina coating were performed. One of them is covering alpha-alumina frame with gamma-alumina slurry. This method is limited by the pore size, as the smallest pores will be blocked after slurry adding. The second method is a hot water solution deposition where sedimentation of gamma-alumina from its salt takes place.

Pt and Ru in the form of nanoparticles were successfully deposited on the surface of the porous structure. Catalysts were characterized by nitrogen desorption, SEM, EDXA, TEM and other methods. Reactor represents a tube with a diameter about 20 mm and length about 350 mm into which porous catalyst is placed.

Reductive amination of ethyl levulinate using 3-aminopropanol as the alkyl amine which was performed. Ethyl levulinate is a product of levulinic acid transformation. Levulinic acid is a well-known precursor for pharmaceuticals, plasticizers and other additives. It is a building block or starting material for a wide range of compounds.
  • Lecture (Conference)
    10th World Congress of Chemical Engineering, 01.-05.10.2017, Barcelona, Spain

Permalink: https://www.hzdr.de/publications/Publ-25876
Publ.-Id: 25876


Development of structured reactors for transformation of biomass components to high-value products - green process industry

Salmi, T.; Shumilov, V. V.; Eränen, K.; Kumar, N.; Hupa, L.; Murzin, D.; Boden, S.; Schubert, M.; Hampel, U.; Sulman, E.
Transformation of biomass components to high-value products used in industry over structured catalysts is the idea behind this project. Synthesis of 5-Methyl-1-Hydroxyethyl-2-Pyrrolidone by reductive amination of ethyl levulinate using 3-aminopropanol as the alkyl amine in the presence of hydrogen was performed. Reactor which uses porous ceramic monolith as a catalytic carrier was studied.

For the development of a new catalytic system, alumina was chosen as a carrier material and sponge replica technique was used for its production. Porous ceramics with different pore types and sizes are widely applied in chemical industry. The unique properties of porous materials allow to carry out a spectrum of well-established and recent applications, such as molten metal filtration, catalysis, refractory and thermal insulation, hot gas filtration. Porous form is perfect for heterogeneous catalysis because of high surface area, which enables liquid (or gas) to contact the catalyst intensively.

Alpha-Alumina is a strong material the surface area of which is low and so to enlarge surface area covering of the foam with a layer of gamma-alumina which has a much bigger surface area was performed.

Two methods of gamma-alumina coating were performed. One of them is covering alpha-alumina frame with gamma-alumina slurry. This method is limited by the pore size, as the smallest pores will be blocked after slurry adding. The second method is a hot water solution deposition where sedimentation of gamma-alumina from its salt takes place.

Pt and Ru in the form of nanoparticles were successfully deposited on the surface of the porous structure. Catalysts were characterized by nitrogen desorption, SEM, EDXA, TEM and other methods. Reactor represents a tube with a diameter about 20 mm and length about 350 mm into which porous catalyst is placed.

Reductive amination of ethyl levulinate using 3-aminopropanol as the alkyl amine which was performed. Ethyl levulinate is a product of levulinic acid transformation. Levulinic acid is a well-known precursor for pharmaceuticals, plasticizers and other additives. It is a building block or starting material for a wide range of compounds.
  • Poster
    10th International Symposium on Catalysis in Multiphase Reactors and Multifunctional Reactors, 07.-10.07.2017, Qingdao, China

Permalink: https://www.hzdr.de/publications/Publ-25875
Publ.-Id: 25875


Quasi-two-dimensional nonlinear evolution of helical magnetorotational instability in a magnetized Taylor-Couette flow

Mamatsashvili, G.; Stefani, F.; Guseva, A.; Avila, M.
Magnetorotational instability (MRI) is one of the fundamental processes in astrophysics, driving angular momentum transport and mass accretion in a wide variety of cosmic objects. Despite a lot of theoretical, numerical and experimental efforts over the last decades, its saturation mechanism and amplitude, which sets angular momentum transport rate, remains not well understood, especially in the limit of high resistivity, or small magnetic Prandtl numbers typical to interiors of protoplanetary disks, liquid cores of planets and liquid metals in laboratory.
We investigate the nonlinear development and saturation properties of the helical magnetorotational instability (HMRI), a relative of standard magnetorotational instability with only axial magnetic field, in magnetized Taylor-Couette flow using direct numerical simulations. From the linear theory of HMRI, it is known that the Elsasser number, or interaction parameter plays a special role for its dynamics and determines the growth rate. We show that this parameter is also important in the present nonlinear problem. With increasing its value, a sudden transition (bifurcation) from weakly nonlinear, where the system is slightly above the linear stability threshold, to turbulent regime occurs. The energy spectra corresponding to these two regimes, also differ qualitatively. Remarkably, the nonlinear states in these cases remain mostly axisymmetric and in fact represents a type of sustained two-dimensional magnetohydrodynamic turbulence driven by HMRI. Although the contribution of non-axisymmetric modes increases with the Elsasser number, their total energy still remains more than order of magnitude smaller than that of the axisymmetric ones.
Keywords: MHD, helical magnetorotational instability, turbulence, Taylor-Couette flow, numerical simulations

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Publ.-Id: 25874


Nonlinear transverse cascade and sustenance of MRI-turbulence in Keplerian disks with an azimuthal magnetic field

Gogichaishvili, D.; Mamatsashvili, G.; Horton, W.; Chagelishvili, G.; Bodo, G.
We investigate magnetohydrodynamic turbulence driven by the magnetorotational instability (MRI) in Keplerian disks with a nonzero net azimuthal magnetic field using shearing box simulations.
As distinct from most previous studies, we analyze turbulence dynamics in Fourier (${\bf k}$-) space to understand its sustenance.
The linear growth of MRI with azimuthal field has a transient character and is anisotropic in Fourier space, leading to anisotropy of nonlinear processes in Fourier space. As a result, the main nonlinear process appears to be a new type of angular redistribution of modes in Fourier space -- the \emph{nonlinear transverse cascade} -- rather than usual direct/inverse cascade. We demonstrate that the turbulence is sustained by interplay of the linear transient growth of MRI (which is the only energy supply for the turbulence) and the transverse cascade. These two processes operate at large length scales, comparable to box size and the corresponding small wavenumber area, called \emph{vital area} in Fourier space is crucial for the sustenance, while outside the vital area direct cascade dominates. The interplay of the linear and nonlinear processes in Fourier space is generally too intertwined for a vivid schematization. Nevertheless, we reveal the \emph{basic subcycle} of the sustenance that clearly shows synergy of these processes in the self-organization of the magnetized flow system. This synergy is quite robust and persists for the considered different aspect ratios of the simulation boxes. The spectral characteristics of the dynamical processes in these boxes are qualitatively similar, indicating the universality of the sustenance mechanism of the MRI-turbulence.
Keywords: Magnetorotational instability, turbulence, nonmodal growth, accretion disks

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Publ.-Id: 25873


THz timing tool: status report

Gensch, M.
  • Lecture (Conference)
    EUCALL annual meeting, 07.-09.06.2017, Grenoble, France

Permalink: https://www.hzdr.de/publications/Publ-25872
Publ.-Id: 25872


Big Data Challenge @ TELBE

Gensch, M.
  • Lecture (Conference)
    LEAPS-IT Meeting, 26.-29.06.2017, Grenoble, France

Permalink: https://www.hzdr.de/publications/Publ-25871
Publ.-Id: 25871


Follow up on THz Radiation Sources

Gensch, M.
  • Invited lecture (Conferences)
    ARD-ST3 annual meeting, 19.-21.07.2017, Zeuthen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-25870
Publ.-Id: 25870


High-field High-repetition-rate superradiant compact THz sources for the coherent control of matter

Gensch, M.
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  • Invited lecture (Conferences)
    THz source @ TRIUMF workshop, 05.-07.07.2017, Vancouver, Canada

Permalink: https://www.hzdr.de/publications/Publ-25869
Publ.-Id: 25869


High-field Repetition-Rate THz Sources for the selective coherent control of Matter

Gensch, M.
The past 10 years have seen a growing number of THz sources coming into operation worldwide that are based on superradiant emission from ultra-short highly charged electron bunches [1]. The superradiant principle allows generating carrier-envelope stable THz pulses with high pulse energy and a large variety of different THz waveforms. If superconducting radiofrequency accelerator technology is used then the THz pulses can be generated with a unique combination of high-THz fields and high repetition-rates. The challenges and scientific opportunities of superradiant THz sources for the coherent THz control of Matter are discussed based on the experiences from two pilot facilities: TELBE [2], the worldwide first THz user facility based on superradiant THz emission from a compact quasi-cw SRF driven linear accelerator and THz-FLASH [3,4] the worldwide first facility that operates as a afterburner of the SRF accelerator-driven FLASH XUV SASE FEL. Based on example benchmark experiments the meanwhile achievable time resolution and dynamic range of multicolor ultra-fast experiments is presented. As will be shown novel pulse-resolved detection schemes opera-ting at high repetition rates in the few 100 kHz regime allow to achieve time-resolution of better than 30 fs and a dynamic range of better than 106 [5]. Limits in pulse energy and frequency range inflicted by the specific accelerator designs are discussed.

[1] M. Gensch, SUPER-RADIANT LINAC-BASED THz SOURCES IN 2013, Proceedings of FEL13, New York, (2013), WEIBNO01.
[2] B. Green et al, High-field High-repetition-rate Sources for the coherent THz control of Matter, Sci. Rep. 6 (2016), 22256.
[3] M. Gensch et al, New infrared undulator beamline at FLASH, Infrared Phys. Technol.51 (2008) ,428.
[4] F. Tavella, N. Stojanovic, G. Geloni, M. Gensch, Few femtosecond timing at 4th Generation X-ray Lightsources, Nat. Photon.5 (2011), 162.
[5] S. Kovalev et al, Probing ultrafast dynamics an 4th generation lightsources with high dynamic range, Struct. Dyn. 4 (2017), 10159.
  • Invited lecture (Conferences)
    TRIUMF colloquium, 07.07.2017, Vancouver, Canada

Permalink: https://www.hzdr.de/publications/Publ-25868
Publ.-Id: 25868


Influence of the specificities of ion irradiation on the nanostructural evolution in Fe alloys: an object kinetic Monte Carlo study

Chiapetto, M.; Malerba, L.; Castin, N.; Heintze, C.; Becquart, C. S.
This work investigates the nanostructural evolution under ion irradiation in both a binary Fe-C alloy and an Fe-9%Cr-C alloy at 300°C, using an object kinetic Monte Carlo model originally developed to simulate neutron irradiation in Fe-(Cr)-C alloys. We studied the effect of specificities of ion irradiation that are expected to have an impact on the evolution of radiation-induced defect clusters as compared to neutron irradiation. The most relevant impact is due to the difference in dose-rate between neutron and ion irradiation. Moreover, the effect of two different ion irradiation regimes (continuous versus pulsed) on the nanostructure evolution material was also investigated: the presence of Cr was seen to lead to a different response over accumulated dose, the reason having been identified in the defect cluster recombination mechanism.
Keywords: kinetic Monte Carlo, Fe-Cr alloys, ion irradiation, continuous irradiation, pulsed irradiation
  • Contribution to proceedings
    NEA International Workshop on Structural Materials for Innovative Nuclear Systems (SMINS-4), 11.-14.07.2016, Manchester, UK

Permalink: https://www.hzdr.de/publications/Publ-25867
Publ.-Id: 25867


[18F]Fluorid- und [18F]FDG-PET/CT zur Beurteilung der Biomaterial-unterstützten Geweberegeneration bei einem kritischen Knochendefektmodell der Ratte

Neuber, C.; Förster, Z.; Hofheinz, F.; Rammelt, S.; Pietzsch, J.
Ziel/Aim:
Kritische Knochendefekte nach Trauma oder Tumorresektion sind eine klinische Herausforderung. Aktuelle Ansätze zur gezielten Unterstützung der Knochenregeneration schlagen den Einsatz von Biomaterialien vor, die mit einer artifiziellen extrazellulären Matrix (aEZM) aus Kollagen und Glykosaminoglykan-Derivaten beschichtet sind. Ziel dieses Pilotversuches war es, den Einfluss derartiger aEZM im Tiermodell zu charakterisieren.
Methodik/Methods:
In einen kritischen Knochendefekt im Femur adulter Ratten wurden Polycaprolacton-co-Laktid-Scaffolds implantiert, die mit Kollagen (Coll), Coll+Chondroitinsulfat (Coll/CS) oder Coll+hochsulfatierter Hyaluronsäure (Coll/s3HA) beschichtet waren. Als Negativkontrolle diente der Leerdefekt. Die Knochenneubildung und Wundheilung wurde nach 4 und 8 Wochen mittels Na[18F]F- und [18F]FDG-PET/CT beurteilt. Mittels CT wurde ein dem Defektbereich entsprechendes volume of interest definiert und der entsprechende SUVmean ermittelt. Darüber hinaus wurden die Femura ex vivo mittels µCT und histologischer Methoden charakterisiert.
Ergebnisse/Results:
Im Vergleich zum Leerdefekt führten die Scaffolds nach 4 Wochen zu einer erhöhten Na[18F]F-Anreicherung, was auf eine verstärkte initiale Knochenmineralisation schließen lässt. Unterschiede zwischen den verschiedenen aEZM wurden nicht beobachtet. Die im Vergleich zum Leerdefekt erhöhte [18F]FDG-Anreicherung nach 4 und 8 Wochen bei den Scaffolds weist auf eine vermehrte Zellaktivierung bzw. -proliferation in der Scaffold-Umgebung hin. Die Beschichtung mit Coll/CS resultierte nach 4 Wochen im größten SUVmean.
Schlussfolgerungen/Conclusions:
Die Kombination von Na[18F]F- und [18F]FDG-PET/CT gestattet die Charakterisierung der Biomaterial-unterstützten Geweberegeneration bei einem kritischen Knochendefektmodell der Ratte. Die Beschichtung mit einer aEZM aus Kollagen und Glykosaminoglykanen fördert die Knochenregeneration.
  • Contribution to proceedings
    Jahrestagung der DGN, 26.-29.04.2017, Dresden, Deutschland
    Proceedings der Jahrestagung der DGN

Permalink: https://www.hzdr.de/publications/Publ-25866
Publ.-Id: 25866


Active targeting and in vivo multimodal imaging of renally excretable polymer nanoparticles

Pant, K.; Zarschler, K.; Neuber, C.; Pufe, J.; Pietzsch, J.; Steinbach, J.; Stephan, H.; Haag, R.
Multimodal imaging represents a strategy to integrate multiple modalities on a single carrier molecule so as to increase the detection sensitivity and to obviate the need to administer compounds with different pharmacokinetics. In this regard, dendritic polyglycerols are highly biocompatible nanoscale scaffolds with multiple attachment sites, anti-fouling properties and small size (2-20 nm).1 The great versatility of the dendritic polyglycerols allows to fine tune physicochemical parameters such as the size, water solubility, surface charge that are relevant for the successful preparation of theranostic systems. Previous experiments showed that the dendritic polyglycerols (>10kDa) show a fast renal clearance with negligible uptake in the mononuclear phagocytic system (MPS) organs such as the liver and spleen.2-3 The purpose of this work to design a PET/OI dual modal construct based on dendritic polyglycerols for epidermal growth factor receptor (EGFR) targeting. In this regard, a one-pot strategy was employed for simultaneous attachment of fluorescent labels for optical imaging (cy3/cy7) and macrocyclic chelators based on a 1,4,7-triazacyclononane system for 64Cu (PET tracer) to thiol anchoring groups of the dPGs. A small camelid single-domain antibody (sdAb) representing a potential recognition agent for EGFR as targeting vector was attached (1). In parallel, a probe with similar surface characteristics but an EGFR unspecific sdAb (control) was synthesized (2). The conjugates were purified using affinity chromatography, which selectively separates the antibody-conjugated mul-timodal conjugates. In vitro and in vivo studies were conducted to assess its diagnostic potential. The in vitro results revealed a highly specific receptor mediate uptake of 1 in EGFR expressing A431 and FaDu cell lines using confocal microscopy and radio detection.
Intravenous injection of 1 and 2 on mouse xenografted models studies using PET and optical imaging revealed an overwhelming tumor accumulation of the EGFR-specific 1 in comparison to the EGFR-unspecific 2 and a minimum off-target accumulation of both conjugates. These results unveil the potential of dendritic polyglycerols as efficient multimodal platforms for theranostic applications.
Keywords: dendritic polyglycerols, cancer, biodistribution, radiolabeling, renal clearance, protein corona, biomedical applications.
  • Lecture (Conference)
    Nanotech France 2017, 28.-30.06.2017, PARIS, France

Permalink: https://www.hzdr.de/publications/Publ-25865
Publ.-Id: 25865


Comparison of lesion SUV and SUR test-retest variability in F-18 FDG PET

Hofheinz, F.; Apostolova, I.; Oehme, L.; Kotzerke, J.; van den Hoff, J.
Quantitative assessment of radiation therapy response with FDG whole body PET has attracted increasing interest in recent years. Generally, the standardized uptake value (SUV) is utilized for quantitation. In this context, the substantial SUV test-retest variability (TRV) as demonstrated in recent studies is a major concern. The goal of our study was to investigate if standard uptake ratio (SUR) exhibits a lower TRV.

34 patients with non small cell lung cancer (ACRIN 6678 trial) were included. All patients underwent two FDG PET/CT scans prior to therapy. Maximum SUV of up to seven lesions was determined. SUR was computed as ratio of tumor SUV and blood SUV (determined in the aorta) and scan-time-corrected to 75 min p.i. TRV was assessed as the 95% confidence interval of the root mean square deviation of the paired fractional differences of SUV and SUR, respectively. The effect of blood normalization and scan time correction was inspected using the ratio RTRV=TRV[SUV]/TRV[SUR]. RTRV was correlated with the group averaged value dCFmean of the quantity dCF=|1-CF|, where CF is the factor that converts paired SUV ratios into the corresponding SUR ratios. Correlation analysis was performed by successively increasing a threshold value dCFmin and restricting the computation of dCFmean and RTRV to the respective sub-group of lesions with dCF>=dCFmin.

Overall, TRV was slightly lower for SUR than for SUV. TRV[SUR] decreases while TRV[SUV] increases with increasing dCF threshold (corresponding to larger blood SUV and scan time differences between paired scans), leading to a two-fold reduction of TRV[SUR] compared to TRV[SUV] for dCF>=15%. Correlation analysis revealed a pronounced correlation between RTRV and mean dCF (Spearman's rho=-0.99, P<0.001).

SUR is superior to SUV regarding TRV by eliminating two relevant factors contributing to TRV of SUV.
  • Contribution to proceedings
    Jahrestagung der DGN, 26.-29.04.2017, Dresden, Deutschland
    Proceedings der Jahrestagung der DGN

Permalink: https://www.hzdr.de/publications/Publ-25863
Publ.-Id: 25863


Prognostische Relevanz der Asphärizität und des metabolischen Tumorvolumens beim Neuroblastom in der prätherapeutischen Iod-123-MIBG-SPECT

Rogasch, J.; Schatka, P.; Hundsdoerfer, P.; Furth, C.; Wedel, F.; Steffen, I.; Hofheinz, F.; Brenner, W.; Eggert, A.; Amthauer, H.
Ziel: Die initiale Risikostratifikation und das daraus resultierende Therapieregime erfolgen bei Kindern mit Neuroblastom (NB) anhand klinischer und genetischer Faktoren. Ziel war nun die Evaluation des Stellenwerts der Asphärizität des Uptakes (ASP) und des metabolischen Tumorvolumens (MTV) in der prätherapeutischen Iod-123-MIBG-SPECT (IMS) zur Prädiktion des Therapieverlaufes.
Methodik: Retrospektive Analyse von 21 konsekutiv untersuchten Kindern (w:10, m:11; medianes Alter, 1,8 [0,3-6,8] a), bei denen eine IMS prätherapeutisch bei neu diagnostiziertem Neuroblastom erfolgt war. Im SPECT wurde mittels halbautomatischen, hintergrundadaptierten Schwellenwerts das MTV des Primarius und die ASP als relative Abweichung der MTV-Oberfläche von einer isovolumetrischen Kugel bestimmt. Uni- und multivariate Cox Regression, ROC-Analysen zur Cut-off-Findung sowie Kaplan-Meier (KM)-Analysen mit log-rank-Test bezüglich des ereignisfreien (EFS) und Gesamtüberlebens (OS) erfolgten für ASP, MTV, genetischer Faktoren, klinische Variablen (Alter, Stadium) und Tumormarker.
Ergebnisse: Das mediane Follow-up betrug 36 [6-102] Monate. Sechs Kinder erlitten einen Progress/Rezidiv, 3 davon verstarben. Die ASP (p=0,038; Hazard Ratio [HR], 1,03 je eine Einheit) und das MTV (p=0,031; HR, 1,012) waren die alleinigen signifikanten Prädiktoren des EFS in der univariaten Cox-Analyse; nur die ASP auch in der multivariaten Analyse (p=0,034; HR, 1,046). Bei einem Cut-off von >31,6% betrug das EFS für eine hohe vs. niedrige ASP 20 vs. 87 Monate (p=0,018), für ein hohes (>46,7 ml) vs. niedriges MTV 18 vs. 88 Monate (p=0,006). In der KM Analyse sagten eine hohe ASP (p=0,012) und ein hohes MTV (p<0,001; Cut-off, >97,5 ml) zudem ein geringeres OS voraus.
Schlussfolgerungen: In dieser explorativen Studie erlaubten die prätherapeutische Bestimmung von ASP und MTV des Primarius die Trennung von Kindern mit hohem und geringerem Risiko für einen Progress bzw. ein Rezidiv unter aktuellen Therapieregimen.
Keywords: NA
  • Contribution to proceedings
    Jahrestagung der DGN, 26.-29.04.2017, Dresden, Deutschland
    Proceedings der Jahrestagung der DGN

Permalink: https://www.hzdr.de/publications/Publ-25862
Publ.-Id: 25862


Adsorption of furfural from torrefaction condensate using torrefied biomass

Doddapaneni, T. R. K.; Jain, R.; Praveenkumar, R.; Rintala, J.; Romar, H.; Konttinen, J.
Torrefaction is a biomass energy densification process that generates a major byproduct in the form of torrefaction condensate. Microbial conversion of TC could be an attractive option for energy integration within torrefaction process. However, TC contains several compounds, such as furfural, 5- hydroxymethylfurfural and guaiacol that are inhibitory to microbes. In this study, for the first time, we reported detoxification of TC, by removing the major inhibitory compound furfural, using torrefied biomass (TB) and later used the detoxified TC for anaerobic digestion. The effect of varying TB production temperature (225–300 ⁰C), TB dosage (25–250 g/L), initial pH (2–9), and contact time (1–12 h) on furfural adsorption was studied with batch adsorption experiments. Mechanism of furfural adsorption on torrefied biomass was best represented by pseudo second order kinetic model. The adsorption of furfural and other inhibitory compounds on TB was likely a hydrophobic interaction. A maximum of 60% of furfural was adsorbed from TC containing 9000 mg furfural/L using 250 g/L of TB in batch adsorption. For, column (20 mm internal diameter and 200 mm bed height), the saturation time for furfural adsorption was around 50 min. Anaerobic digestion of the detoxified TC shows that the lag phase in methane production was reduced from 25 d to 15 d for 0.2 VSsubstrate:VSinoculum loading. The study shows that TC can be effectively detoxified using TB for microbial conversion and can efficiently be integrated within the torrefied biomass pellet production process.
Keywords: Detoxification; Anaerobic digestion; pellets; torrefaction volatiles; Energy densification

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Permalink: https://www.hzdr.de/publications/Publ-25861
Publ.-Id: 25861


NMR investigations of paramagnetic effects in metal-organic complexes of trivalent and tetravalent actinides with soft-donor ligands

Radoske, T.; Adam, C.; Schöne, S.; Patzschke, M.; März, J.; Kaden, P.ORC
When NMR spectroscopy is applied to paramagnetic metal-organic complexes additional chemical shifts are observed on nuclei of the ligands that originate from electronic interactions between metal and ligand. The major two contributors to these paramagnetic chemical shifts are either due to delocalisation of unpaired electron density in molecular orbitals involving both metal and ligand orbitals (Fermi contact shift, FCS), or due to distance- and angle-dependent dipolar coupling of electron spins through space (pseudo contact shift, PCS). However, mathematical models for the treatment of paramagnetic chemical shifts are not yet applicable to actinide compounds.
Covalence is assumed to be the reason for some soft-donor ligands selectivity for the complexation of trivalent actinides over lanthanide ions. This long-kept notion was recently substantiated by evaluation of paramagnetic chemical shifts of respective Am(III) complexes1,2. The mathematical separation of contributions in complexes of the trivalent actinides, however, is hampered by the lack of a reliable diamagnetic reference in the actinide series. Furthermore, all available theories behind mathematical disentangling of contributions to the paramagnetic chemical shift, even for the lanthanide series, omit the influence of spin-orbit effects that might have a sizeable contribution as well.
To assess the chemical bonding situation via the influences on paramagnetic chemical shifts we started to study metal-organic complexes of tetravalent actinides (An(IV)) with soft-donor ligands with Th(IV) as diamagnetic reference. With increasing number of unpaired electrons throughout the series additional effects to the observed chemical shift are expected. Herein we report the first results of investigations of N-donor ligand complexes of the An(IV) series.
References
1. C. Adam, P. Kaden, B. B. Beele, U. Müllich, S. Trumm, A. Geist, P. J. Panak, M. A. Denecke, “Evidence for covalence in a N-donor complex of americium(III)”, Dalton Trans., 42, 14068-14074 (2013).
2. C. Adam, B. B. Beele, A. Geist, U. Müllich, P. Kaden, P. J. Panak, “NMR and TRLFS studies of Ln(III) and An(III) C5-BPP complexes”, Chemical Science, 6, 1548-1561 (2015).
Keywords: NMR, paramagnetic, diamagnetic reference, covalence, Fermi contact, pseudo-contact, U(IV), Th(IV), Am(III)
  • Lecture (Conference)
    Actinides 2017, 09.-14.07.2017, Sendai, Japan

Permalink: https://www.hzdr.de/publications/Publ-25860
Publ.-Id: 25860


MHD turbulence in shear flows and Keplerian disks - sustenance via interplay of linear nonmodal growth and nonlinear transverse cascade

Mamatsashvili, G.
We investigate MHD turbulence in spectrally stable shear flows, including Keplerian disk flows, threaded by a non-zero net azimuthal/toroidal magnetic field. In order to gain a deeper insight into its sustaining mechanism, we performed a set of numerical simulations in the shearing box model and based on the simulation data, analyzed in detail the turbulence dynamics in Fourier/wavenumber k-space. Classical exponential/modal instabilities are absent in such flows and linear growth of perturbations has a transient nature due to shear flow non-normality, also referred to as nonmodal growth. Similarly, in the case of Keplerian flow with a net azimuthal field in the shearing box setup, the combination of rotation, shear and magnetic field, gives rise to the magnetorotational instability (MRI), which is dominated by the effects of non-normality and hence is of transient type too. This transient growth, which serves as the only energy supply to turbulence, is strongly anisotropic in Fourier space that, in turn, leads to anisotropy of nonlinear processes in Fourier space and, as a result, the main nonlinear process appears to be not an usual direct/inverse, but rather a new type of transverse/angular redistribution of perturbation modes in Fourier space, which we refer to as the nonlinear transverse cascade. We demonstrate that the turbulence is sustained by a subtle interplay of the linear nonmodal growth (transient MRI in the case of Keplerian disks) and the nonlinear transverse cascade. Analyzing this interplay, we reveal the basic subcycle of the sustenance scheme that clearly shows synergy of the linear and nonlinear processes in the self-organization of the magnetized flow system. This synergy is quite robust and persists for the considered four simulation boxes with different aspect ratios. The spectral characteristics of the dynamical processes in these boxes are qualitatively similar, indicating the universal character of the interplay that ensures the sustenance of the turbulence. Such an interplay of linear and nonlinear processes in the turbulence sustenance proposed here exemplifies the bypass concept of subcritical turbulence in spectrally stable shear flows, elaborated in the 1990s by the hydrodynamical community. Both the linear nonmodal growth and nonlinear transverse cascade mainly operate at large length scales, comparable to the box size. Consequently, the central, small wavenumber area of Fourier space is crucial in the turbulence sustenance process and is called the vital area. Outside the vital area, both these processes are of secondary importance – the harmonics are transferred to dissipative scales by the usual nonlinear direct cascade only. In the conclusion, we discuss the application of this approach and results to the MRI-turbulence in Keplerian flows with vertical net nonzero or zero magnetic flux.
Keywords: MHD, nonmodal growth, magnetorotational instability, turbulence, accretion disks, numerical simulations
  • Invited lecture (Conferences)
    Invited seminar at the Niels Bohr Institute, University of Copenhagen, 24.-28.04.2017, Copenhagen, Denmark

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Permalink: https://www.hzdr.de/publications/Publ-25859
Publ.-Id: 25859


Nonlinear evolution of helical magnetorotational instability

Mamatsashvili, G.; Stefani, F.
We investigate the evolution of the helical magnetorotational instability in a magnetized Taylor-Couette flow from its linear growth to nonlinear saturation using numerical simulations. We show that the saturation occurs through modification (reduction) of the radial shear of the mean azimuthal velocity. The resulting saturated state is axisymmetric and represents a type of 2D MHD turbulence, whose (spectral) properties are characterized. The results are compared to the PROMISE experiment data.
Keywords: Taylor-Couette flow, helical magnetorotational instability, liquid metals, numerical simulations
  • Lecture (Conference)
    Bifurcation and instabilities in fluid dynamics, 11.-14.07.2017, Woodlands, Houston, Texas, USA

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Permalink: https://www.hzdr.de/publications/Publ-25858
Publ.-Id: 25858


Increased FDG uptake on late-treatment PET in non-tumour-affected oesophagus is prognostic for pathological complete response and disease recurrence in patients undergoing neoadjuvant radiochemotherapy

Zschaeck, S.; Hofheinz, F.; Zöphel, K.; Bütof, R.; Jentsch, C.; Schmollack, J.; Löck, S.; Kotzerke, J.; Baretton, G.; Weitz, J.; Baumann, M.; Krause, M.
Purpose

Early side effects including oesophagitis are potential prognostic factors in patients undergoing radiochemotherapy (RCT) for locally advanced oesophageal cancer (LAEC). We assessed the prognostic value of 18F-fluorodeoxyglucose (FDG) uptake within irradiated non-tumour-affected oesophagus (NTO) during restaging positron emission tomography (PET) as a surrogate for inflammation/oesophagitis.
Methods

This retrospective evaluation included 64 patients with LAEC who had completed neoadjuvant RCT and had successful oncological resection. All patients underwent FDG PET/CT before and after RCT. In the restaging PET scan maximum and mean standardized uptake values (SUVmax, SUVmean) were determined in the tumour and NTO. Univariate Cox regression with respect to overall survival, local control, distant metastases and treatment failure was performed. Independence of clinically relevant parameters was tested in a multivariate Cox regression analysis.
Results

Increased FDG uptake, measured in terms of SUVmean in NTO during restaging was significantly associated with complete pathological remission (p = 0.002) and did not show a high correlation with FDG response of the tumour (rho < 0.3). In the univariate analysis, increased SUVmax and SUVmean in NTO was associated with improved overall survival (p = 0.011, p = 0.004), better local control (p = 0.051, p = 0.044), a lower rate of treatment failure (p < 0.001 for both) and development of distant metastases (p = 0.012, p = 0.001). In the multivariate analysis, SUVmax and SUVmean in NTO remained a significant prognostic factor for treatment failure (p < 0.001, p = 0.004) and distant metastases (p = 0.040, p = 0.011).
Conclusions

FDG uptake in irradiated normal tissues measured on restaging PET has significant prognostic value in patients undergoing neoadjuvant RCT for LAEC. This effect may potentially be of use in treatment personalization.
Keywords: Oesophageal cancer Radiochemotherapy Side effects Inflammation FDG pet

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Permalink: https://www.hzdr.de/publications/Publ-25857
Publ.-Id: 25857


Nonmodal and nonlinear dynamics of helical magnetorotational instability

Mamatsashvili, G.; Stefani, F.
The helical magnetorotational instability (HMRI), a relative of standard MRI (SMRI), has become a subject of active research in recent years in connection with the experiments on magnetized cylindrical Taylor-Couette (TC) flows. It occurs in the presence of helical magnetic field, consisting of azimuthal and axial components and, like SMRI with only axial magnetic field, taps into the rotational energy of the flow. However, a main advantage of HMRI is that, being governed by the Reynolds (Re) and Hartmann (Ha) numbers, it persists even at very small magnetic Prandtl numbers typical to liquid metals, in contrast to SMRI. The linear development of HMRI has been widely studied theoretically using both classical modal and more recently by nonmodal stability analysis, where a fundamental connection between nonmodal dynamics and dissipation-induced (double-diffusive) modal instabilities, such as HMRI, has been demonstrated. A series of specially designed liquid metal TC experiments provided the first experimental evidence of HMRI and reproduced the main results of the linear theory, such as the stability threshold and propagation speed (frequency) of HMRI-wave. More importantly, these experiments revealed much richer dynamics of HMRI as a function of system parameters (Re, Ha, etc.) than that obtained from the linear analysis only. These results prompted further theoretical studies of the nonlinear development of HMRI, but detailed physics of its saturation and sustenance still remains missing, especially when comparison with the experiment is concerned.
Motivated by the existing experimental results, we investigate the evolution of HMRI, from its linear growth to nonlinear saturation using numerical simulations.
We show that depending on the Reynolds number, two regimes of saturation can be realized. At Re below a certain critical value (but higher than the instability threshold), the saturation energy linearly depends on Re and the corresponding energy spectrum is dominated by the most unstable mode and its multiple wavenumbers, while at larger Re, the energy increases with Re, but not linearly, and the related spectrum looks like turbulent spectrum, being much smoother over wavenumbers. The nonlinear state remains markedly axisymmetric (m = 0)
and at high Re can be viewed as a 2D turbulence, whose (spectral) properties are further examined.
Keywords: MHD, turbulence, nonmodal growth, instabilities, numerical simulations
  • Lecture (Conference)
    2nd Conference on Natural Dynamos, 25.06.-01.07.2017, Valtice Castle, Czech Republic

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Permalink: https://www.hzdr.de/publications/Publ-25856
Publ.-Id: 25856


Kinetic Modeling of the New σ1 Receptor Ligand (-)-[18F]Fluspidine in the Human Brain

Becker, G. A. F.; Meyer, P.; Patt, M.; Hesse, S.; Luthardt, J.; Patt, J.; Rullmann, M.; Fischer, S.; Kluge, A.; Steinbach, J.; Wünsch, B.; Brust, P.; Sabri, O.
Objectives:
The σ1 receptor, a transmembrane protein located at the endoplasmatic reticulum is involved in a variety of neuropsychiatric diseases, e.g. depression, schizophrenia and drug addiction. The newly developed PET tracer (-)-[18F]Fluspidine was successfully applied to quantify σ1 receptors in the porcine brain [1]. Here we present the first PET quantification of σ1 receptors with (-)-[18F] Fluspidine in humans.
Methods:
After intravenous administration of 269.6±13.3 MBq (-)-[18F]Fluspidine PET brain imaging was performed in 10 healthy subjects (age 36.6±14.8 years; gender 5F/5M) using an ECAT EXACT HR+ system in 3D-acquisition mode. 26 frames were acquired from 0-210 min post injection and motion corrected with SPM2. Kinetic modeling using 1- and 2-tissue compartment models (1TCM, 2TCM) with metabolite corrected arterial input-function was applied to the volume of interest (VOI) based tissue time-activity curves (TACs) in 43 brain regions (anatomically defined via MRI co-registration). Time ranges from 0 to 90 and 0 to 210 min were investigated. Model-based receptor parameter was the total distribution volume VT (ml/cm-3), a linear function of receptor density.
Results:
TACs of all 43 regions could be described with the 1- and 2TCM. VT in all cortical regions could be reliably estimated from 90 min PET data already. In white matter longer measurements can be necessary. The distribution volume was highest in the cerebellar cortex (31.4±6.1), low in the centrum semiovale (17.7±7.1) and ranged in cortical structures between 20.9±3.9 in the orbitofrontal and 24.9±5.7 in the posterior cingulate cortex (pcc) (2TCM, 90 min). The distribution volumes computed from 210 min data were comparable to 90 min results, e.g. in pcc 25.7±5.9 (2TCM) and 25.7±6.0 (1TCM).
Conclusions:
σ1 receptor parameters in cortical structures can be estimated with a 1- or 2TCM from 90 min (-)-[18F]Fluspidine TACs. If a model derived receptor parameter is used in a classification problem, e.g., distinguishing patients with depression from healthy controls, the final model decision should be made on the basis of the PET data of both groups.
References:
P. Brust, ..., O. Sabri, Journal of Nuclear Medicine 2014, 55, 1730-1736
  • Open Access Logo Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 60(2017)S1, S383
    DOI: 10.1002/jlcr.3508

Permalink: https://www.hzdr.de/publications/Publ-25855
Publ.-Id: 25855


Development of (S)-[18F]T1 as first PET tracer for imaging the α3β4 nicotinic acetylcholine receptor

Sarasamkan, J.; Fischer, S.; Deuther-Conrad, W.; Scheunemann, M.; Ludwig, F.-A.; Vajragupta, O.; Brust, P.
Objectives:
Neuronal nicotinic acetylcholine receptors (nAChRs) are composed of diverse subtypes which have different functional properties, distributions and pharmacological profiles. The α7, α3β4 and α4β2 nAChRs are well recognized as drug targets implicated in cognitive disorders and addiction. Therefore, to image nAChRs in vivo, subtype-selective radiotracers need to be developed.
Methods:
A novel PET radiotracer for imaging nAChRs was developed based on the design and synthesis of six racemates (T1-T6) and its enantiomers based on the structure of triazole-quinuclidine QND8. All R enantiomers were found to be selective to α7 nAChR while their S counterparts were selective to α3β4 nAChR. (S)-T1 binds selectively to α3β4 nAChR (Ki 3.09 nM) with very modest off-target binding to α1 receptor, dopamine receptors and serotonin receptors. Radiosynthesis of (S)-[18F]T1 was achieved by two-step reaction, starting with the preparation of 18F-alkyne synthon (1-ethynyl-4-[18F]fluorobenzene; [18F]2), followed by the click reaction between [18F]2 and (S)-azidoquinuclidine.
Results:
The radiosynthesis of (S)-[18F]T1 was achieved in 130 min with the overall isolated radiochemical yield of 4.3±1.3%, radiochemical purity > 99%, and molar radioactivity > 158 GBq/µmol at end of synthesis. The brain uptake and brain-to-blood ratio of this tracer in mice at 30 min after injection were 6.06% ID/g and 6.1, respectively. The tracer remained intact > 99% in brain homogenates. Only one major radiometabolite was detected in plasma and urine samples. In vitro autoradiography on pig brain slices revealed high binding of (S)-[18F]T1 to brain regions consistent with the α3β4 nAChR distribution. Selective binding of (S)-[18F]T1 was evidenced by (i) the reduction of percent labeling of this tracer in the presence of a selective α3β4 nAChR partial agonist, AT-1001 and (ii) the retention of the tracer in the presence of α7 nAChR-specific SSR180711.
Conclusions:
These findings suggest the potential of (S)-[18F]T1 for imaging the α3β4 nAChR in the brain as a promising tool for both diagnosis and therapy monitoring of neurodegenerative diseases and addiction.
Acknowledgement:
This work was supported by Thailand Research Fund (TRF) through the Royal Golden Jubilee Ph.D. Program (grant no. PHD/0272/2552) to J.S. and O.V.
References:
[1] K. Arunrungvichian, V. V. Fokin, O. Vajragupta, P. Taylor. ACS Chem Neurosci. 2015, 6, 1317-1330.
[2] J. Sarasamkan, M. Scheunemann, N. Apaijai, S. Palee, W. Parichatikanond, K. Arunrungvichian, et al. ACS Med. Chem. Lett. 2016, 7, 890- 895.
  • Open Access Logo Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 60(2017)S1, S50
    DOI: 10.1002/jlcr.3507

Permalink: https://www.hzdr.de/publications/Publ-25854
Publ.-Id: 25854


ElectroHydroDynamic emitters developments for improving Focused Ion Beam machines

Gierak, J.; Bischoff, L.; Mazarov, P.; Bruchhaus, L.; Blanchard-Desce, M.; Vaultier, M.; Lozano, P.
The patterning of samples using Focused Ion Beams (FIB) is very popular, widely used both for industrial [1] and emerging nanoscience prototyping applications [2]. This FIB technique allows 3D and direct patterning of target materials using a finely focused pencil of ions having speeds of several hundreds of km/seconds at impact with a penetration range of a few tens of nanometres. Thanks to this, local information and/or modifications can be obtained at the target surface. In what the ion nature is concerned, apart that many elements can be used in FIB technology as pure elements or in the form of alloys, gallium (Ga+ ions) is often preferred.
Traditionally for several decades FIB technology has been mainly based on gallium Liquid Metal Ion Sources (LMIS). LMIS are also known as electrohydrodynamically (EHD) driven ion emitters operating in a cone-jet mode. The very high brightness, long lifespan, small source size, and easy handling of this emitter remain its chief and most decisive advantages. On the other hand, some weaknesses are also well known that inhibit the resolution of EHD/LMIS-based FIBs. Therefore progress on ion sources operational characteristics still remains very desirable.
In this presentation we will first summarize our work aiming at understanding, optimizing and evaluating gallium LMIS “needle type” performances. In particular stable operation at lowest possible emission currents will be detailed. The gains in terms of patterning resolution and beam selectivity [3], we will evaluate, are firm evidence that progresses can still be expected from this mature technology.
We will then review and detail the advantages of Liquid Metal Alloy Ion Sources (LMAIS) that represent a promising alternative to expand the already remarkable application field and potential of FIB machines in the field of nanosciences. Indeed selecting the best suited elements transported in a focused ion beam can open new nanofabrication routes. In this presentation we will explain that nearly half of the elements of the periodic table can already be made available to the FIB technology as a result of a continuous research effort in this area [4] and how, in our opinion, nanofabrication shall now take benefit of these capabilities. Finally we will introduce our new addition to the arsenal of EHD driven devices: The Ionic Liquid Ion Sources (ILIS). ILIS are capable to produce ion beams through field-evaporation, also in the cone-jet mode, but from room temperature molten-salts [5]. The possibility of extracting both positive and negative ions at
emission current several orders of magnitude below LMIS standards is already a very appealing perspective in terms of source virtual source size and brightness. Then we will show that ILIS allows to access new ionic species thanks to the almost limitless chemical engineering latitude of molten salts. Moreover subsequent tuning can be achieved via selecting the tip polarity, the ion emission current and the ion landing energy. We will show the possibility to achieve a new kind of FIB patterning using a beam of chemically reactive ion radicals native in the transported beam. This represents a formidable perspective for FIB technology.
In conclusion we will summarize our vision on the future of FIB technology based on electrohydrodynamically (EHD) driven emitters operating in the conejet mode, both in terms of performances, versatility and on the science frontiers these might help to push.

[1] J. Orloff, Scientific American Oct. 1994, pp.74-79
[2] J. Gierak Nanofabrication 2014; Volume 1: pp. 35–52
[3] J. Gierak and R. Jede, Patent US8546768 B2, WO2010029270A1; Sept 2008
[4] L. Bischoff, P. Mazarov, L. Bruchhaus, and J. Gierak, Appl. Phys. Rev. 2016; 3: pp. 021101
[5] C. Perez-Martinez, J. Gierak, and P. C. Lozano, P106 (Invited), EIPBN Conference, May 31-
June 3, 2016, Pittsburgh, PA
Keywords: Focused Ion Beam; Liquid Metal Alloy Ion Source; Ionic Liquid Ion Source; FIB patterning
  • Lecture (Conference)
    Conference on ultracold ion and electron beams, 10.-12.07.2017, Eindhoven, The Netherlands
  • Lecture (Conference)
    61th International Conference on Electron, Ion, and Photon Beam Technology and Nanofabrication EIPBN-2017, 30.05.-02.06.2017, Orlando, USA

Permalink: https://www.hzdr.de/publications/Publ-25853
Publ.-Id: 25853


Ion-Beam-Induced Atomic Mixing in Ge, Si, and SiGe, Studied by Means of Isotope Multilayer Structures

Bracht, H.; Radek, M.; Posselt, M.; Liedke, B.; Schmidt, B.; Voelskow, M.; Bischoff, L.; Böttger, R.; Prucnal, S.; Hansen, J. L.; Larsen, A. N.; Bougeard, D.
Crystalline and preamorphized isotope multilayers are utilized to investigate the dependence of ion beam mixing in silicon (Si), germanium (Ge), and silicon germanium (SiGe) on the atomic structure of the sample, temperature, ion flux, and electrical doping by the implanted ions. The magnitude of mixing is determined by secondary ion mass spectrometry. Rutherford backscattering spectrometry in channeling geometry, Raman spectroscopy, and transmission electron microscopy provide information about the structural state after ion irradiation. Different temperature regimes with characteristic mixing properties are identified. A disparity in atomic mixing of Si and Ge becomes evident while SiGe shows an intermediate behavior. Overall, atomic mixing increases with temperature, and it is stronger in the amorphous than in the crystalline state. Ion-beam-induced mixing in Ge shows no dependence on doping by the implanted ions. In contrast, a doping effect is found in Si at higher temperature. Molecular dynamics simulations clearly show that ion beam mixing in Ge is mainly determined by the thermal spike mechanism. In the case of Si thermal spike, mixing prevails at low temperature whereas ion beam-induced enhanced self-diffusion dominates the atomic mixing at high temperature. The latter process is attributed to highly mobile Si di-interstitials formed under irradiation and during damage annealing.
Keywords: silicon; germanium; ion beam; atomic mixing; thermal spike; radiation enhanced diffusion; amorphization; recrystallization; molecular dynamics

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Permalink: https://www.hzdr.de/publications/Publ-25852
Publ.-Id: 25852


Modeling tumor control probability for spatially inhomogeneous risk of failure based on clinical outcome data

Lühr, A.; Löck, S.; Jakobi, A.; Stützer, K.; Bandurska-Luque, A.; Vogelius, I. R.; Enghardt, W.; Baumann, M.; Krause, M.
Purpose

Objectives of this work are (1) to derive a general clinically relevant approach to model tumor control probability (TCP) for spatially variable risk of failure and (2) to demonstrate its applicability by estimating TCP for patients planned for photon and proton irradiation.
Methods and Materials

The approach divides the target volume into sub-volumes according to retrospectively observed spatial failure patterns. The product of all sub-volume TCPi values reproduces the observed TCP for the total tumor. The derived formalism provides for each target sub-volume i the tumor control dose (D50,i) and slope (γ50,i) parameters at 50% TCPi. For a simultaneous integrated boost (SIB) prescription for 45 advanced head and neck cancer patients, TCP values for photon and proton irradiation were calculated and compared. The target volume was divided into gross tumor volume (GTV), surrounding clinical target volume (CTV), and elective CTV (CTVE). The risk of a local failure in each of these sub-volumes was taken from the literature.
Results

Convenient expressions for D50,i and γ50,i were provided for the Poisson and the logistic model. Comparable TCP estimates were obtained for photon and proton plans of the 45 patients using the sub-volume model, despite notably higher dose levels (on average +4.9%) in the low-risk CTVE for photon irradiation. In contrast, assuming a homogeneous dose response in the entire target volume resulted in TCP estimates contradicting clinical experience (the highest failure rate in the low-risk CTVE) and differing substantially between photon and proton irradiation.
Conclusions

The presented method is of practical value for three reasons: It (a) is based on empirical clinical outcome data; (b) can be applied to non-uniform dose prescriptions as well as different tumor entities and dose-response models; and (c) is provided in a convenient compact form. The approach may be utilized to target spatial patterns of local failures observed in patient cohorts by prescribing different doses to different target regions. Its predictive power depends on the uncertainty of the employed established TCP parameters D50 and γ50 and to a smaller extent on that of the clinically observed pattern of failure risk.
Keywords: Radiotherapy, Dose–response modeling, TCP, Inhomogeneous dose, Head and neck cancer, Proton therapy

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Permalink: https://www.hzdr.de/publications/Publ-25851
Publ.-Id: 25851


Superconducting Ferromagnetic Nanodiamond

Zhang, G.; Samuely, T.; Xu, Z.; Jochum, J. K.; Volodin, A.; Zhou, S.; May, P. W.; Onufriienko, O.; Kačmarčík, J.; Steele, J. A.; Li, J.; Vanacken, J.; Vacík, J.; Szabó, P.; Yuan, H.; Roeffaers, M. B. J.; Cerbu, D.; Samuely, P.; Hofkens, J.; Moshchalkov, V. V.
Superconductivity and ferromagnetism are two mutually antagonistic states in condensed matter. Research on the interplay between these two competing orderings sheds light not only on the cause of various quantum phenomena in strongly correlated systems but also on the general mechanism of superconductivity. Here we report on the observation of the electronic entanglement between superconducting and ferromagnetic states in hydrogenated boron-doped nanodiamond films, which have a superconducting transition temperature Tc ∼ 3 K and a Curie temperature TCurie > 400 K. In spite of the high TCurie, our nanodiamond films demonstrate a decrease in the temperature dependence of magnetization below 100 K, in correspondence to an increase in the temperature dependence of resistivity. These anomalous magnetic and electrical transport properties reveal the presence of an intriguing precursor phase, in which spin fluctuations intervene as a result of the interplay between the two antagonistic states. Furthermore, the observations of high-temperature ferromagnetism, giant positive magnetoresistance, and anomalous Hall effect bring attention to the potential applications of our superconducting ferromagnetic nanodiamond films in magnetoelectronics, spintronics, and magnetic field sensing.
Keywords: anomalous Hall effect; giant positive magnetoresistance; nanodiamond; spin fluctuations; superconductivity and ferromagnetism

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Permalink: https://www.hzdr.de/publications/Publ-25850
Publ.-Id: 25850


Structural and optical properties of Gd implanted GaN with various crystallographic orientations

Macková, A.; Malinský, P.; Jagerová, A.; Sofer, Z.; Klímová, K.; Sedmidubský, D.; Pristovsek, M.; Mikulics, M.; Lorinčík, J.; Böttger, R.; Akhmadaliev, S.
Structure, morphology, and optical properties of Gd implanted GaN epitaxial layers were studied for (0001), (11 − 20), and (11 − 22) orientations. The GaN layers grown by MOVPE on sapphire were subsequently implanted with 200 keV Gd+ ions using fluences of 5 × 1015 and 5 × 1016 cm− 2. Dopant depth profiling was accomplished by Rutherford Back-Scattering spectrometry (RBS). Structural and optical changes during subsequent annealing were characterized by RBS, Raman spectroscopy, and photoluminescence measurements. Post-implantation annealing induced a structural reorganization of GaN structure in the buried layer depending on the introduced disorder level, i.e. depending on the implantation fluence and on crystallographic orientation. The defect density depth distribution was evaluated by RBS. The surface morphology and optical properties depend on particular crystallographic orientation.
Keywords: GaN implantation; RBS channelling; Optical properties of Gd implanted GaN

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Permalink: https://www.hzdr.de/publications/Publ-25849
Publ.-Id: 25849


Interplay between magnetic domain patterning and anisotropic magnetoresistance probed by magnetooptics

Osten, J.ORC; Lenz, K.; Schultheiss, H.ORC; Lindner, J.; McCord, J.; Fassbender, J.ORC
We study the correlation between the magnetic reversal and the anisotropic magnetoresistance (AMR) response in magnetic hybrid structures that were created by local modification of magnetic properties induced by ion implantation. The stripe pattern have been investigated simultaneously by dual-wavelength Kerr microscopy and magnetoresistance measurements. We observe that the switching of the stripe pattern introduces an additional AMR maximum. The domain wall in between the stripes provides a positive resistance contribution, whereas domains at the stripe edges lead to an asymmetric AMR response. A method for calculating the AMR response from the quantitative Kerr micrographs is demonstrated that allows the reconstruction of the AMR value within a region of interest only.
Keywords: anisotropic magnetoresistance, magnetic domain

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Permalink: https://www.hzdr.de/publications/Publ-25848
Publ.-Id: 25848


Experimental and Numerical Modeling of Fluid Flow Processes in Continuous Casting: Results from the LIMMCAST-Project

Timmel, K.ORC; Kratzsch, C.; Asad, A.; Schurmann, D.; Schwarze, R.; Eckert, S.
The present paper reports about numerical simulations and model experiments concerned with the fluid flow in the continuous casting process of steel. This work was carried out in the LIMMCAST project in the framework of the Helmholtz alliance LIMTECH. A brief description of the LIMMCAST facilities used for the experimental modeling at HZDR is given here. Ultrasonic and inductive techniques and the X-ray radioscopy were employed for flow measurements or visualizations of two-phase flow regimes occurring in the submerged entry nozzle and the mold. Corresponding numerical simulations were performed at TUBAF taking into account the dimensions and properties of the model experiments. Numerical models were successfully validated using the experimental data base. The reasonable and in many cases excellent agreement of numerical with experimental data allows to extrapolate the models to real casting configurations. Exemplary results will be presented here showing the effect of electromagnetic brakes or electromagnetic stirrers on the flow in the mold or illustrating the properties of two-phase flows resulting from an Ar injection through the stopper rod.
Keywords: LIMTECH-alliance, Continuous Casting, numerical modeling, experimental modeling, liquid metal models, electromagnetic actuators, two-phase flow

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Permalink: https://www.hzdr.de/publications/Publ-25847
Publ.-Id: 25847


Arterial spin labeling spatial coefficient of variation predicts carotid occlusion side

Mutsaerts, H. J.; Petr, J.; Bokkers, R.; Hendrikse, J.; Lazar, R.; Marshall, R.; Asllani, I.
Collateral perfusion has been shown to be of key prognostic importance in carotid steno‐occlusive disease as it prevents irreversible ischemia1, 2. Arterial spin labeling ﴾ASL﴿ may provide a biomarker of collateral perfusion by measuring arterial transit time ﴾ATT﴿ in addition to cerebral blood flow ﴾CBF﴿. However, this leads to longer scanning times, lower signal‐to‐noise ratio3 and higher motion sensitivity4. We have developed a method to estimate the ATT from a single post‐labeling delay ﴾PLD﴿ ASL image using the spatial coefficient of variance ﴾CoV﴿5. Here, we investigate whether the spatial CoV lateralization through collateral perfusion can predict the side of carotid occlusion.
  • Lecture (Conference)
    34th Annual Scientific Meeting of European Society for Magnetic Resonance in Medicine and Biology, 19.10.2017, Barcelona, Spain
  • Abstract in refereed journal
    Magnetic Resonance Materials in Physics, Biology and Medicine 30(2017)Suppl 1, 198
    DOI: 10.1007/s10334-017-0633-0

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Permalink: https://www.hzdr.de/publications/Publ-25846
Publ.-Id: 25846


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