Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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Approved and published publications
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39295 Publications

Spin Wave Emission from Topological Spin Textures

Wintz, S.; Sluka, V.; Schneider, T.; Kakay, A.; Weigand, M.; Schultheiss, K.; Warnatz, T.; Mattheis, R.; Gallardo, R. A.; Roldan-Molina, A.; Landeros, P.; Tiberkevich, V.; Slavin, A.; Erbe, A.; Deac, A.; Lindner, J.; Fassbender, J.; Raabe, J.

Keywords: magnetism; spin waves; x-ray microscopy

  • Invited lecture (Conferences)
    Moscow International Symposium on Magnetism, 01.-05.07.2017, Moskau, Russische Föderation

Publ.-Id: 25988

Tailoring the gyrotropic resonance of magnetic vortices by strain

Finizio, S.; Wintz, S.; Kirk, E.; Suszka, A.; Gliga, S.; Wohlhüter, P.; Zeissler, K.; Raabe, J.

Keywords: magnetism; vortex; magnetostriction; spin dynamics

  • Lecture (Conference)
    62nd Annual Magnetism & Magnetic Materials Conference, 06.-10.11.2017, Pittsburgh, USA

Publ.-Id: 25987

Control of the magnetic vortex core dynamics in magnetostrictive microstructured elements through the Magneto-Elastic coupling

Finizio, S.; Wintz, S.; Kirk, E.; Suszka, A.; Gliga, S.; Raabe, J.

Keywords: magnetism; vortex; magneto elastic; spin dynamics

  • Lecture (Conference)
    IEEE International Magnetics Conference, 24.-28.04.2017, Dublin, Ireland

Publ.-Id: 25986

Software commissioning of a Monte-Carlo model for the double-scattering treatment head at University Proton Therapy Dresden

Eulitz, J.; Lühr, A.; Enghardt, W.; Lutz, B.

Compared to treatment planning systems (TPS) in proton therapy, Monte-Carlo simulations have the potential to describe radiation fields in patients more precisely. However, next to an accurate Monte-Carlo model of the treatment head a benchmarking with respect to dose measurements is required. The purpose of this work was to set up and validate a Monte-Carlo simulation model of the clinical proton treatment fields at the University Proton Therapy Dresden (UPTD).
A detailed model of the treatment head geometry of the UPTD in double-scattering mode was implemented using the Monte-Carlo simulation environment TOPAS. The proton beam source was optimized to match measured reference depth-dose distributions for all clinically available treatment field options. The commissioned software model was validated against an independent set of depth-dose and lateral dose validation data measured in a water phantom. A setup for the direct simulation of so-called monitor units (MU), relating dosimeter readings in the treatment head to absolute dose in a water phantom, was implemented.
Validation data on depth-dose distributions were reproduced within range differences of 0.26 mm and a relative dose uncertainty of 1% for all treatment options (i.e., comparable to measurement uncertainties). Simulated lateral dose profiles differed from validation data in lateral width and penumbra less than 0.95 mm and 0.56 mm, respectively. Measured MU values were predicted within 2% accuracy for several reference and patient treatment fields.
The commissioned Monte-Carlo model reproduced the dose validation data measured during the clinical validation of the UPTD within clinical tolerances. This enables high-precision simulations of clinical proton beams. Furthermore, it has the potential to predict absolute doses and to use patient-specific MU values, which might decrease the patient-specific measurement effort at UPTD.
This, however, requires further validation.

  • Lecture (Conference)
    Jahrestagung der BIOMEDIZINISCHEN TECHNIK und Dreiländertagung der MEDIZINISCHEN PHYSIK, 10.-13.09.2017, Dresden, Deutschland

Publ.-Id: 25985

Control of the gyration of magnetic vortices by the magneto-elastic effect

Finizio, S.; Wintz, S.; Kirk, E.; Suszka, A.; Gliga, S.; Wohlhüter, P.; Zeissler, K.; Raabe, J.

The influence of a strain-induced uniaxial magnetoelastic anisotropy on the magnetic vortex core dynamics microstructured magnetostrictive Co40 Fe40 B20 elements was investigated with time-resolved scanning transmission x-ray microscopy. The measurements revealed a monotonically decreasing eigenfrequency of the vortex core gyration with the increasing magnetoelastic anisotropy, which follows closely the predictions from in micromagnetic modeling.

Keywords: magnetism; x-ray microscopy; vortex; spin dynamics


Publ.-Id: 25984

Investigation of the LET-dependency from BeO using single photon detection for dosimetry in proton beams

Radtke, J.; Kormoll, T.; Grabs, L.; Lutz, B.; Lühr, A.; Ullrich, W.; Sponner, J.; Henniger, J.

Optically stimulated luminescence (OSL) is gaining greater importance in the field of personal dosimetry in the last few years. Its principle is based on the release of small amounts of light induced by the prior absorption of ionizing radiation. One suitable luminophore for OSL is beryllium oxide (BeO). Because of its near tissue equivalent effective atomic number of 7, it is excellent for personal dosimetry. Furthermore, the luminescence signal has a wide dose linearity ranging from the µGy region up to few Gy. For this reason, this ceramic can be used for several different areas of application. A new generation of measurement systems based on the OSL of BeO, which has a very low OSL light intensity, was developed by the radiation physics group at TU Dresden. This property allows single photon detection which is superior in contrast to other detection methods. Therefore, a single photon sensor was used as a detector. The single photon mode of the detector in combination with the so called timestamp detection method allows accessing the greatest possible information of the OSL light. This work applies the new system to dosimetry of a proton beam. Because of the LET-dependencies of the luminescence light, this presents a challenge. Common problems of solid state dosimetry are local saturation effects, which were investigated for BeO. Opportunities for correction in terms of the LET-dependency of the luminophore are being discussed. For the empirical determination of the behavior of BeO in proton beams, measurements at the medical proton therapy facility at the University Proton Therapy Dresden (UPTD) were carried out. All collected data were analyzed for LET-dependency on the response signal. For the measurements, BeO ceramics were placed at different depth infront and inside the spread out Bragg peak (SOBP). The dose read from dosimeters was analyzed with respect to the applied dose and the LET. All measurements infront of the SOBP shows no deviation of the estimated dose. The dose determination in the SOBP yielded an underestimation by 15%. This is object of current investigation.

  • Poster
    Jahrestagung der biomedizinischen Technik und Dreiländertagung der medizinischen Physik, 10.-13.09.2017, Dresden, Deutschland

Publ.-Id: 25983

Monte-Carlo simulation of proton treatment fields in patients to support treatment planning

Eulitz, J.; Lutz, B.; Oesten, H.; Wohlfahrt, P.; Enghardt, W.; Lühr, A.

Monte-Carlo (MC) simulations may allow for reducing range margins and applying variable relative-biological-effectiveness (RBE) models in proton therapy. Here, an approach is presented to support treatment planning of patients by highlighting regions with increased dose uncertainties originating from dose calculation and the assumption of a constant RBE of 1.1.
A software framework was developed and experimentally validated, which simulates proton plans at the University Proton Therapy Dresden (UPTD) using the MC tool TOPAS. It is based on a commissioned model of the UPTD treatment head in double-scattering mode. Clinical treatment plans and computed tomography datasets were imported in DICOM format. MC-based dose distributions were compared with dose distributions received from the clinically applied treatment planning system (TPS) XIO, Elekta. Obtained dose, linear-energy-transfer (LET), and modelled RBE maps (using experimental in vitro data) were imported into the TPS RayStation, RaySearch for plan evaluation.
TPS doses above the 95% iso dose level are reproduced within gamma pass rates GPR ≥ 98%, when applying 1 mm local and 2 % dose gamma criterion. Dose differences reached values up to 8 Gy for field volumes up to 4 cm 3 , particularly at regions with high-density gradients (e.g. bone and air cavities) and at the field edges. LET and variable RBE hot spots were obtained at (distal) field edges while at the field center RBE values below 1.1 were predicted. Clinical dose values differed by up to 10 Gy using either the assumption of a constant or a variable RBE.
The treatment planning and delivery workflow at UPTD was mapped in a MC simulation. In general, good agreement between TPS and MC clinical dose values was found. However, relevant clinical dose differences were obtained and emphasise the necessity of using MC to enhance the physical and biological dose prediction in patients.

  • Lecture (Conference)
    Jahrestagung der biomedizinischen Technik und Dreiländertagung der medizinischen Physik, 10.-13.09.2017, Dresden, Deutschland

Publ.-Id: 25982

Experimental verification of particle-range prediction in biological tissue by single- and dual-energy computed tomography

Möhler, C.; Russ, T.; Wohlfahrt, P.; Elter, A.; Runz, A.; Richter, C.; Greilich, S.

We introduce a hybrid experimental setup to accurately measure x-ray and ion absorption in tissue or other materials. With this setup using a 3D-printed sample container, the stopping-power ratio (SPR) of homogeneous materials can be measured with an uncertainty of below 0.1%. A total of 40 homogeneous porcine and bovine soft-tissue samples were prepared for measurement, comprising five samples each of eight tissue types (three different muscle and fatty tissues, liver, lung). Using a standard stoichiometric calibration for single-energy CT (SECT) as well as a state-of-the-art dual-energy CT (DECT) approach, SPR was predicted for all tissues and then compared to the measured reference. With the SECT approach, the SPR of all tissues, excluding lung due to its large heterogeneity, was underestimated by up to -3% with a mean (absolute) error of -1.5% (1.5%). In contrast, the DECT-based SPR prediction showed no significant bias with a mean error below the measurement uncertainty of 0.1% and a mean absolute error of 0.2%. In this study, the potential of DECT to decrease range uncertainty could thus be confirmed in biological tissue.

Keywords: proton and ion radiation therapy; treatment planning; stopping-power ratio; range verification

Publ.-Id: 25981

Die Energiewende braucht verlässliche Rahmenbedingungen für den Metallerzbergbau - The energy transition needs a reliable framework for metal ore mining

Wellmer, F. W.; Gutzmer, J.; Kullik, J.; Erlach, B.

Mit dem Projekt Energiesysteme der Zukunft (ESYS) wollen acatech – Deutsche Akademie der Technikwissenschaften, die Nationale Akademie der Wissenschaften Leopoldina und die Union der deutschen Akademien der Wissenschaften Impulse für die mittel- bis langfristige Umsetzung der Energiewende in Deutschland setzen. Im Rahmen des Projekts haben Wissenschaftler(innen) unterschiedlicher Fachrichtungen auch die Stellungnahme Rohstoffe für die Energiewende – Wege zu einer sicheren und nachhaltigen Versorgung (acatech et al. 2017) verfasst. Sie zeigt Handlungsoptionen für eine langfristige und nachhaltige Versorgung mit den für die Energiewende erforderlichen Rohstoffen auf. Die wissenschaftlichen Grundlagen der Handlungsoptionen sind in der Publikation Rohstoffe für die Energieversorgung der Zukunft: Geologie – Märkte – Umwelteinflüsse (Angerer et. al. 2016) dargestellt.
Martin David, Magdalena Wallkamm und Alena Bleicher haben sich in GAIA mit beiden Publikationen auseinandergesetzt (David et al. 2017). Ihre wesentliche Kritik lautet: ESYS habe eine überwiegend technologische (Umwelt-)Perspektive, während andere gesellschaftliche Fragen zu kurz kämen. Wir gehen im Folgenden auf die Kritikpunkte ein.

Keywords: energy transition; metals; mining; rare earths; social-license to operate

Publ.-Id: 25980

Cues to greater recycling efficiency-characterization of a crushed mobile phone by mineral liberation analysis

Sandmann, D.; Jäckel, H.-G.; Gutzmer, J.

In 2016 more than 1.35 billion smartphones have been manufactured (TrendForce Corp. 2017). Smartphones can contain up to 60 different elements and the summarized metal weight of the 2016 production is very likely more than 50,000 tons (The Royal Society of Chemistry 2017, 911Metallurgist 2013). However, at present, very few of the elements contained in these devices are recycled at recycling rates of more than 50%. For most elements, the recycling rates are significantly lower than 50%, and the recycling rates of rare earths, indium, tantalum or gallium are even below 1% (Compound Interest 2015)! The major challenge of mobile phone recycling is the complex composition of the devices made of many individual components. This is aggravated by the fact that many elements occur in traces only and / or are located in highly complex material composites.
To enable more effective recycling of mobile phones, it is imperative to characterise their components, the presence of elements in it, as well as the crushing behaviour as detailed as possible.
In a pilot study, a Nokia mobile phone Model 5228 Type RM-625, crushed with a Universal Granulator UG300 by colleagues of the Professorship of recycling machines of the TU Bergakademie Freiberg, was examined by Mineral Liberation Analysis (MLA). The analysis on three sieve fractions of the comminuted material was carried out with an MLA 650F at the Helmholtz Institute Freiberg for Resource Technology. The samples were scanned in an automated MLA measurement with a grid of EDX spectra (GXMAP mode). A total of 130 different phases were detected during the analysis. More than 100 of these phases occur at levels <1 % by weight. This strongly illustrates the very complex composition of mobile phones and the need for detailed analytical characterisation. A comparison of the modal content of the three sieve fractions showed an enrichment of certain components in specific fractions.


911Metallurgist (2013) - Mining & iPhone Recycling, [accessed 2017 Aug 15].
Compound Interest (2015) - The Recycling Rates of Smartphone Metals, [accessed 2017 Aug 15].
The Royal Society of Chemistry (2017) - Getting the metals out of old phones, [accessed 2017 Aug 15].
TrendForce Corp. (2017) - Press Release. TrendForce Reports Global Smartphone Production Volume Totaled 1.36 Billion Units; Samsung Held On as Leader While OPPO and Vivo Burst into Global Top Five, [accessed 2017 Aug 15].


Publ.-Id: 25979

Enhancing Charge Carrier Lifetime in Metal Oxide Photoelectrodes through Mild Hydrogen Treatment

Jang, J.; Friedrich, D.; Müller, S.; Lamers, M.; Hempel, H.; Lardhi, S.; Cao, Z.; Harb, M.; Cavallo, L.; Heller, R.; Eichberger, R.; van de Krol, R.; Abdi, F. F.

Widespread application of solar water splitting for energy conversion is largely dependent on the progress in developing not only efficient but also cheap and scalable photoelectrodes. Metal oxides, which can be deposited with scalable techniques and are relatively cheap, are particularly interesting, but high efficiency is still hindered by the poor carrier transport properties (i.e., carrier mobility and lifetime). In this paper, a mild hydrogen treatment is introduced to bismuth vanadate (BiVO4), which is one of the most promising metal oxide photoelectrodes, as a method to overcome the carrier transport limitations. Time-resolved microwave and terahertz conductivity measurements reveal more than twofold enhancement of the carrier lifetime for the hydrogen-treated BiVO4, without significantly affecting the carrier mobility. This is in contrast to the case of tungsten-doped BiVO4, although hydrogen is also shown to be a donor type dopant in BiVO4. The enhancement in carrier lifetime is found to be caused by significant reduction of trap-assisted recombination, either via passivation of deep trap states or reduction of trap state density, which can be related to vanadium antisite on bismuth or vanadium interstitials according to density functional theory calculations. Overall, these findings provide further insights on the interplay between defect modulation and carrier transport in metal oxide photoelectrodes, which will benefit the development of low-cost, highly efficient solar energy conversion devices.

Related publications

Publ.-Id: 25977

Hydrogen calibration of GD-spectrometer using Zr-1Nb alloy

Mikhaylov, A. A.; Priamushko, T. S.; Babikhina, M. N.; Kudiiarov, V. N.; Heller, R.; Laptev, R. S.; Lider, A. M.

To study the hydrogen distribution in Zr-1Nb alloy (E(cyrillic)110 alloy) GD-OES was applied in this work. Qualitative analysis needs the standard samples with hydrogen. However, the standard samples with high concentrations of hydrogen in the zirconium alloy which would meet the requirements of the shape, size are absent. In this work method of Zr + H calibration samples production was performed at the first time. Automated Complex Gas Reaction Controller was used for samples hydrogenation. To calculate the parameters of post-hydrogenation incubation of the samples in an inert gas atmosphere the diffusion equations were used. Absolute hydrogen concentrations in the samples were determined by melting in the inert gas atmosphere using RHEN602 analyzer (LECO Company). Hydrogen distribution was studied using nuclear reaction analysis (HZDR, Dresden, Germany). RF GD-OES was used for calibration. The depth of the craters was measured with the help of a Hommel-Etamic profilometer by Jenoptik, Germany. © 2017.

Keywords: Calibration; Glow discharge optical emission spectroscopy (GD-OES); Hydrogen; Standard samples; Zirconium alloy

Related publications

Publ.-Id: 25976

Zur Ligandenentwicklung für den vesikulären Acetylcholintransporter im Gehirn

Barthel, C.

Es ist kein Abstract vorhanden.

  • Doctoral thesis
    Universität Leipzig, 2017
    Mentor: Dr. Barbara Wenzel
    203 Seiten

Publ.-Id: 25975

Holographic vector mesons in a dilaton background

Zöllner, R.; Kämpfer, B.

Within a holographic framework, we consider vector mesons riding on a gravity-dilaton background. The latter one is determined directly from a Schr\"odinger equivalent potential which delivers a proper ρ meson Regge trajectory. The mapping on the dilaton potential yields a thermodynamic phase structure with a first-order transition.

Publ.-Id: 25974

Improvements of the ELBE Control System Infrastructure and SCADA Environment

Justus, M.; Steinbrück, R.; Leege, K. W.; Schamlott, A.; Michel, P.

The ELBE Center for High-Power Radiation Sources comprises a 40 MeV c.w. electron linear accelerator, driving diverse secondary beams, both electromagnetic radiation and particles. Its control system is based on PLCs, fast data acquisition systems and the industrial SCADA system WinCC. In the past three years, requirements for availability and reliability increased, while at the same time changes of the machine configuration and instrumentation need to be handled permanently. Improvements of the control system infrastructure concerning power supply, IT and systems monitoring have been realized and are still under way. Second, along with the last major SCADA system upgrade, we implemented a more redundant SCADA infrastructure, improved long term data storage and continuously improved our standards for software development.

Keywords: ELBE; Control System

Related publications

  • Poster
    ICALEPCS 2017 - 16th International Conference on Accelerator and Large Experimental Control Systems, 08.-13.10.2017, Barcelona, Espana
  • Open Access Logo Contribution to proceedings
    ICALEPCS 2017 - 16th International Conference on Accelerator and Large Experimental Control Systems, 08.-13.10.2017, Barcelona, Espana
    16th International Conference on Accelerator and Large Experimental Physics Control Systems: JACoW Publishing, 978-3-95450-193-9, 1405-1408
    DOI: 10.18429/JACoW-ICALEPCS2017-THPHA027

Publ.-Id: 25973

Synthese und Entwicklung eines fluorierten Pyrimidingrundkörpers für weitere Radiotracerentwicklungen

Milewski, M.

Es ist kein Abstract vorhanden.

  • Bachelor thesis
    Universität Leipzig, 2017
    Mentor: Lindemann, Marcel
    52 Seiten

Publ.-Id: 25971

High-Mobility, Band-Like Charge Transport in a Semiconducting Two-Dimensional Metal-Organic Framework

Dong, R.; Han, P.; Arora, H.; Ballabio, M.; Karakus, M.; Zhang, Z.; Shekhar, C.; Adler, P.; St. Petkov, P.; Erbe, A.; Mannsfeld, S. C. B.; Felser, C.; Heine, T.; Bonn, M.; Feng, X.; Canovas, E.

Metal–organic frameworks (MOFs) are hybrid materials based on crystalline coordination polymers that consist of metal ions connected by organic ligands. In addition to the traditional applications in gas storage and separation or catalysis, the long-range crystalline order in MOFs, as well as the tunable coupling between the organic and inorganic constituents, has led to the recent development of electrically conductive MOFs as a new generation of electronic materials. However, to date, the nature of charge transport in the MOFs has remained elusive. Here we demonstrate, using high-frequency terahertz photoconductivity and Hall effect measurements, Drude-type band-like transport in a semiconducting, π–d conjugated porous Fe3(THT)2(NH4)3 (THT, 2,3,6,7,10,11-triphenylenehexathiol) two-dimensional MOF, with a room-temperature mobility up to ~ 220 cm2 V–1 s–1. The temperature-dependent conductivity reveals that this mobility represents a lower limit for the material, as mobility is limited by impurity scattering. These results illustrate the potential for high-mobility semiconducting MOFs as active materials in thin-film optoelectronic devices.

Keywords: conductive metal-organic frameworks; polymers; microelectronics

Publ.-Id: 25970

Individualized risk assessment in neuroblastoma: does the tumoral metabolic activity on 123I-MIBG SPECT predict the outcome?

Rogasch, J.; Hundsdoerfer, P.; Furth, C.; Wedel, F.; Hofheinz, F.; Krüger, P.; Lode, H.; Brenner, W.; Eggert, A.; Amthauer, H.; Schatka, I.


Risk-adapted treatment in children with neuroblastoma (NB) is based on clinical and genetic factors. This study evaluated the metabolic tumour volume (MTV) and its asphericity (ASP) in pretherapeutic 123I-MIBG SPECT for individualized image-based prediction of outcome.


This retrospective study included 23 children (11 girls, 12 boys; median age 1.8 years, range 0.3–6.8 years) with newly diagnosed NB consecutively examined with pretherapeutic 123I-MIBG SPECT. Primary tumour MTV and ASP were defined using semiautomatic thresholds. Cox regression analysis, receiver operating characteristic analysis (cut-off determination) and Kaplan-Meier analysis with the log-rank test for event-free survival (EFS) were performed for ASP, MTV, laboratory parameters (including urinary homovanillic acid-to-creatinine ratio, HVA/C), and clinical (age, stage) and genetic factors. Predictive accuracy of the optimal multifactorial model was determined in terms of Harrell’s C and likelihood ratio χ2.


Median follow-up was 36 months (range 7–107 months; eight patients showed disease progression/relapse, four patients died). The only significant predictors of EFS in the univariate Cox regression analysis were ASP (p = 0.029; hazard ratio, HR, 1.032 for a one unit increase), MTV (p = 0.038; HR 1.012) and MYCN amplification status (p = 0.047; HR 4.67). The mean EFS in patients with high ASP (>32.0%) and low ASP were 21 and 88 months, respectively (p = 0.013), and in those with high MTV (>46.7 ml) and low MTV were 22 and 87 months, respectively (p = 0.023). A combined risk model of either high ASP and high HVA/C or high MTV and high HVA/C best predicted EFS.


In this exploratory study, pretherapeutic image-derived and laboratory markers of tumoral metabolic activity in NB (ASP, MTV, urinary HVA/C) allowed the identification of children with a high and low risk of progression/relapse under current therapy.

Keywords: Neuroblastoma; Prognosis; 123I-MIBG; Asphericity; Metabolic tumour volume

Publ.-Id: 25969

Specific Features of the Ion-Beam Synthesis of Ge Nanocrystals in SiO2 Thin Films

Tyschenko, I. E.; Cherkov, V. A.; Volodin, V. A.; Voelskow, M.

The systematic features of the formation of Ge nanocrystals in SiO2 thin films implanted with Ge ions and then subjected to high-temperature annealing (1130°C) are studied in relation to hydrostatic pressure. It is established that annealing at atmospheric pressure is accompanied by the diffusion of Ge atoms from the implantation region to the Si substrate and does not induce the formation of Ge nanocrystals. An increase in pressure during annealing yields a deceleration in the diffusion of germanium into silicon and is accompanied by the formation of twinned lamellae at the Si/SiO2 interface (at pressures of ~103 bar) or by the nucleation and growth of Ge nanocrystals (at pressures of ~104 bar) in the SiO2 film. The results are discussed on the basis of the concept of a change in the activation volume of the formation and migration of point defects under conditions of compression.

Keywords: Ion Beam Synthesis; nanocrystals; SiO2

Related publications

Publ.-Id: 25968

The precession dynamo at HZDR -- Preliminary flow measurements and simulations

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

No abstract required

Keywords: Dynamo; Dresdyn

  • Invited lecture (Conferences)
    Max Planck Princeton Research Center for Plasma Physics Greifswald Meeting — September 2017, 19.-22.09.2017, Greifswald, Deutschland

Publ.-Id: 25967

Dynamo action from a laminar non-linear flow in a precessing cylinder

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

Within the project DRESDYN (DREsden Sodium facility for DYNamo and thermohydraulic studies) a dynamo experiment is under development in which a precession driven flow of liquid sodium will be used to excite dynamo action. In my presentation I will address preparative numerical simulations and flow measurements conducted at a small model experiment filled with water. The results provide typical flow pattern and flow amplitudes in dependence of precession ratio and Reynolds number and are used for the setup of kinematic dynamo models in order to estimate whether the particular flow is able to drive a dynamo.

In the strongly non-linear regime the flow essentially consists of the directly forced Kelvin mode superimposed by standing inertial waves caused by non-linear self-interaction of the forced mode whereas time-dependent contributions in terms of randomly distributed small-scale noise remain negligible. Most remarkable feature is the occurrence of a resonant-like axisymmetric mode around a precession ratio of Omega_prec/Omega_cyl = 0.1. Only the combination of this axisymmetric mode and the forced m=1 Kelvin mode is capable of driving a dynamo. Our simulations yield a critical magnetic Reynolds number of Rm_c=430 which is well within the regime that will be achieved in the experiment. However, the occurrence of the axisymmetric mode slightly depends on the absolute rotation rate of the cylinder and future experiments are required to indicate whether this instability will persist at the extremely large Re that will be obtained in the large scale experiment.

Keywords: Dynamo; Dresdyn

  • Poster
    MREP 2017, 11.-12.09.2017, Cambridge, Great Britain

Publ.-Id: 25966

Horizon 2020 EuPRAXIA design study

Walker, P. A.; Alesini, P. D.; Alexandrova, A. S.; Anania, M. P.; Andreev, N. E.; Andriyash, I.; Aschikhin, A.; Assmann, R. W.; Audet, T.; Bacci, A.; Barna, I. F.; Beaton, A.; Beck, A.; Beluze, A.; Bernhard, A.; Bielawski, S.; Bisesto, F. G.; Boedewadt, J.; Brandi, F.; Bringer, O.; Brinkmann, R.; Bründermann, E.; Büscher, M.; Bussmann, M.; Bussolino, G. C.; Chance, A.; Chanteloup, J. C.; Chen, M.; Chiadroni, E.; Cianchi, A.; Clarke, J.; Cole, J.; Couprie, M. E.; Croia, M.; Cros, B.; Dale, J.; Dattoli, G.; Delerue, N.; Delferriere, O.; Delinikolas, P.; Dias, J.; Dorda, U.; Ertel, K.; Pousa, A. F.; Ferrario, M.; Filippi, F.; Fils, J.; Fiorito, R.; Fonseca, R. A.; Galimberti, M.; Gallo, A.; Garzella, D.; Gastinel, P.; Giove, D.; Giribono, A.; Gizzi, L. A.; Grüner, F. J.; Habib, A. F.; Haefner, L. C.; Heinemann, T.; Hidding, B.; Holzer, B. J.; Hooker, S. M.; Hosokai, T.; Irman, A.; Jaroszynski, D. A.; Jaster-Merz, S.; Joshi, C.; Kaluza, M. C.; Kando, M.; Karger, O. S.; Karsch, S.; Khazanov, E.; Khikhlukha, D.; Knetsch, A.; Kocon, D.; Koester, P.; Kononenko, O.; Korn, G.; Kostyukov, I.; Labate, L.; Lechner, C.; Leemans, W. P.; Lehrach, A.; Li, F. Y.; Li, X.; Libov, V.; Lifschitz, A.; Litvinenko, V.; Lu, W.; Maier, A. R.; Malka, V.; Manahan, G. G.; Mangles, S. P. D.; Marchetti, B.; Marocchino, A.; Ossa, A. M. D. L.; Martins, J. L.; Massimo, F.; Mathieu, F.; Maynard, G.; Mehrling, T. J.; Molodozhentsev, A. Y.; Mosnier, A.; Mostacci, A.; Mueller, A. S.; Najmudin, Z.; Nghiem, P. A. P.; Nguyen, F.; Niknejadi, P.; Osterhoff, J.; Papadopoulos, D.; Patrizi, B.; Pattathil, R.; Petrillo, V.; Pocsai, M. A.; Poder, K.; Pompili, R.; Pribyl, L.; Pugacheva, D.; Romeo, S.; Rossi, A. R.; Roussel, E.; Sahai, A. A.; Scherkl, P.; Schramm, U.; Schroeder, C. B.; Schwindling, J.; Scifo, J.; Serafini, L.; Sheng, Z. M.; Silva, L. O.; Silva, T.; Simon, C.; Sinha, U.; Specka, A.; Streeter, M. J. V.; Svystun, E. N.; Symes, D.; Szwaj, C.; Tauscher, G.; Thomas, A. G. R.; Thompson, N.; Toci, G.; Tomassini, P.; Vaccarezza, C.; Vannini, M.; Vieira, J. M.; Villa, F.; Wahlström, C.-G.; Walczak, R.; Weikum, M. K.; Welsch, C. P.; Wiemann, C.; Wolfenden, J.; Xia, G.; Yabashi, M.; Yu, L.; Zigler, J. Z. A.

The Horizon 2020 Project EuPRAXIA ("European Plasma Research Accelerator with eXcellence In Applications") is preparing a conceptual design report of a highly compact and cost-effective European facility with multi-GeV electron beams using plasma as the acceleration medium. The accelerator facility will be based on a laser and/or a beam driven plasma acceleration approach and will be used for photon science, high-energy physics (HEP) detector tests, and other applications such as compact X-ray sources for medical imaging or material processing. EuPRAXIA started in November 2015 and will deliver the design report in October 2019. EuPRAXIA aims to be included on the ESFRI roadmap in 2020.

Keywords: Plasma accelerator

Related publications


Publ.-Id: 25965

Engineering of optical and electrical properties of ZnO by non-equilibrium thermal processing: The role of zinc interstitials and zinc vacancies

Prucnal, S.; Wu, J.; Berencen, Y.; Liedke, M. O.; Wagner, A.; Liu, F.; Wang, M.; Rebohle, L.; Zhou, S.; Cai, H.; Skorupa, W.

A controlled manipulation of defects in zinc oxide (ZnO) and the understanding of their electronic structure can be a key issue towards the fabrication of p-type ZnO. Zn vacancy (V-Zn), Zn interstitials (I-Zn), and O vacancy (V-O) are mainly native point defects, determining the optoelectronic properties of ZnO. The electronic structure of these defects still remains controversial. Here, we experimentally demonstrate that the green emission in ZnO comes from V-Zn-related deep acceptor and V-Zn-V-O clusters, which is accompanied by the radiative transition between the triplet and the ground singlet state with the excited singlet state located above the CB minimum. Moreover, the I-Zn is identified to be a shallow donor in ZnO, being mainly responsible for the n-type conductivity of non-intentionally doped ZnO.

Keywords: ZnO; flash lamp annealing; defects; photoluminescence; positron annihilation spectroscopy

Related publications


Publ.-Id: 25964

FEL-Based Near-Field Infrared to THz Nanoscopy

Kehr, S.; Doering, J.; Gensch, M.; Helm, M.; Eng, L. M.

Related publications

Publ.-Id: 25963

Detecting Threatening States in Laser Beams

Kelling, J.; Juckeland, G.

This poster presents our approach to automatic detection of critical failure states in the pulsed Petawatt laser systems DRACO and PENELOPE, used for investigations of exotic states of matter and medical applications. The beam shape is controlled to avoid high destructive energy densities. However, randomly occurring states threatening the device must be detected between pulses and trigger an interlock in the device firing at 10Hz.

The states we are aiming to detect are rare; thus, training data for this category is scarce. To address this, we present two approaches: First, to identify regions of interest based on physical properties of the system and apply a convolutional neural network (CNN) to to identify true positives. Secondly, using CNN-based image segmentation to localize and classify regions of interest.

Keywords: image classification; deep learning; smart laser operation

  • Poster
    Deep Learning Bootcamp 2017, 21.-25.08.2017, Dresden, Deutschland

Publ.-Id: 25962

Efficient Parallel Monte-Carlo Simulations for Large-Scale Studies of Surface Growth Processes

Kelling, J.; Ódor, G.; Weigel, M.; Gemming, G.

Lattice Monte Carlo methods are used to investigate far from and out-of-equilibrium systems, including surface growth, spin systems and solid mixtures. Such studies require observations of large systems over long times scales, to allow structures to grow over orders of magnitude, which necessitates massively parallel simulations. This talk presents work done to address the problem of parallel processing introducing correlations in Monte Carlo updates. Studies of the effect of correlations on scaling and dynamical properties of surface growth systems and related lattice gases is investigated further by comparing results obtained by correlation-free and intrinsically correlated simulations. Where the latter, based on a stochastic cellular automaton approach, are of interest because of their high efficiency. The primary subject of study is the Kardar–Parisi–Zhang surface growth in (2+1) dimensions. Key physical insights about this universality class, like precise universal exponent values and exponent relations, obtained from large-scale simulations are presented.
At the end of the talk, I will also speak about my current work at the computational science group at HZDR, which includes problems like frameworkdevelopment, image analysis and related machine learning applications.

Keywords: Lattice Monte Carlo; GPU; Surface Growth; Kardar-Parisi-Zhang

  • Lecture (Conference)
    IHRS NanoNet Annual Workshop 2017, 16.-18.08.2017, Neuklingenberg, Deutschland

Publ.-Id: 25961

Direct Measurement of the Magnetocaloric Effect in La(Fe,Si,Co)13 Compounds in Pulsed Magnetic Fields

Ghorbani Zavareh, M.; Skourski, Y.; Skokov, K. P.; Karpenkov, D. Y.; Zvyagina, L.; Waske, A.; Haskel, D.; Zhernenkov, M.; Wosnitza, J.; Gutfleisch, O.

We report on magnetization, magnetostriction, and magnetocaloric-effect measurements of polycrystalline LaFe11.74Co0.13Si1.13 and LaFe11.21Co0.65Si1.11 performed in both pulsed and static magnetic fields. Although the two compounds behave rather differently at low fields (∼5 T), they show quite similar values of the magnetocaloric effect, namely a temperature increases of about 20 K at high fields (50–60 T). The magnetostriction and magnetization also reach very similar values here. We are able to quantify the magnetoelastic coupling and, based on that, apply the Bean-Rodbell criterion distinguishing first- and second-order transitions.

Publ.-Id: 25960

Doubly dressed bosons: Exciton polaritons in a strong terahertz field

Piętka, B.; Bobrovska, N.; Stephan, D.; Teich, M.; Król, M.; Winnerl, S.; Pashkin, A.; Mirek, R.; Lekenta, K.; Morier-Genoud, F.; Schneider, H.; Deveaud, B.; Helm, M.; Matuszewski, M.; Szczytko, J.

We demonstrate the existence of a novel quasiparticle, an exciton in a semiconductor doubly dressed with two photons of different wavelengths: a near infrared cavity photon and terahertz (THz) photon, with the THz coupling strength approaching the ultrastrong coupling regime. This quasiparticle is composed of three different bosons, being a mixture of a matter-light quasiparticle. Our observations are confirmed by a detailed theoretical analysis, treating quantum mechanically all three bosonic fields. The doubly dressed quasiparticles retain the bosonic nature of their constituents, but their internal quantum structure strongly depends on the intensity of the applied terahertz field.

Keywords: ultrastrong coupling regime; dressed states; exciton polaritons

Related publications


Publ.-Id: 25959

Observation of Reactive Transport in Soil Columns with Positron Emission Tomography (GeoPET)

Kulenkampf, J.; Stoll, M.; Gründig, M.; Mansel, A.; Lippmann-Pipke, J.

Here we investigate reactive transport in soils with GeoPET as quantitative spatiotemporal molecular imaging method. As PET directly yields tracer concentrations, the data can be utilised for parameterization and validation of reactive transport computer models.
Artificial soil columns (sand/silt/clay/Goethit, length 90 mm, diameter 40 mm) have been prepared under CO2-atmosphere. Four different experiments on one and the same soil column are shown as motion pictures from the GeoPET-observations:
1) Injection of water, labelled with [18F]KF, into the CO2-saturated column
2) Conservative transport of [18F]KF solution through the water-saturated column
3) Injection of the reactive tracer [64Cu]Cu(MCPA)2 into the unconditioned water-saturated column
4) Injection of the reactive tracer [64Cu]Cu(MCPA)2 into the preconditioned column.

The study was supported within the framework of the priority program “Biogeochemical Interfaces in Soil” by the German Science Foundation (DFG SPP 1315: KE508/19 and LI872/5).


Kulenkampff, J., Zakhnini, A., Gründig, M., and Lippmann-Pipke, J.: Quantitative experimental monitoring of molecular diffusion in clay with positron emission tomography, Solid Earth, 7, 1207-1215, 2016.
Kulenkampff, J., Gründig, M., Zakhnini, A., Gerasch, R., and Lippmann-Pipke, J.: Process tomography of diffusion, using PET, to evaluate anisotropy and heterogeneity, Clay Miner., 50, 369–375, 2015.
Kulenkampff, J., Gründig, M., Zakhnini, A., and Lippmann-Pipke, J.: Geoscientific process monitoring with positron emission tomography (GeoPET), Solid Earth, 7, 1217–1231, 2016.
Zakhnini, A., Kulenkampff, J., Sauerzapf, S., Pietrzyk, U., and Lippmann-Pipke, J.: Monte Carlo simulations of GeoPET experiments: 3D images of tracer distributions (18F, 124I and 58Co) in Opalinus Clay, anhydrite and quartz, Comput. Geosci., 57, 183–196, 2013.
Lippmann-Pipke, J., Gerasch, R., Schikora, J., and Kulenkampff, J.: Benchmarking PET for geoscientific applications: 3D quantitative diffusion coefficient estimation in clay rock, Comput. Geosci. 101, 21-27, 2017.
Stoll, M., Kulenkampff, J., Gründig, M., Lippmann-Pipke, J., and Kersten, M.: Molecular positron emission tomography imaging of Cu mobility enhanced by the herbicide 4-chloro-2-methylphenoxy-acetic acid in a soil column, submitted
Lippold, H., Karimzadeh L., Kulenkampff, J. Wissmeier, L., Stuhlfauth, C., Stoll, M., Lippmann-Pipke, L.: Effect of pH on the mobility of the herbicide MCPA in a goethite-sand matrix: 1D and 2D reactive transport modelling, to be submitted

Keywords: PET; reactive transport; soil; tomography


Publ.-Id: 25957

Origin of perpendicular magnetic anisotropy in Co/Ni multilayers

Arora, M.; Hübner, R.; Suess, D.; Heinrich, B.; Girt, E.

We studied the variation in perpendicular magnetic anisotropy of (111) textured Au/N×[Co/Ni]/Au films as a function of the number of bilayer repeats N. The ferromagnetic resonance and superconducting quantum interference device magnetometer measurements show that the perpendicular magnetic anisotropy of Co/Ni multilayers first increases with N for N≤10 and then moderately decreases for N>10. The model we propose reveals that the decrease of the anisotropy for N<10 is predominantly due to the reduction in the magnetoelastic and magnetocrystalline anisotropies. A moderate decrease in the perpendicular magnetic anisotropy for N>10 is due to the reduction in the magnetocrystalline and the surface anisotropies. To calculate the contribution of magnetoelastic anisotropy in the Co/Ni multilayers, in-plane and out-of-plane x-ray diffraction measurements are performed to determine the spacing between Co/Ni (111) and (220) planes. The magnetocrystalline bulk anisotropy is estimated from the difference in the perpendicular and parallel g factors of Co/Ni multilayers that are measured using the in-plane and out-of-plane ferromagnetic resonance measurements. Transmission electron microscopy has been used to estimate the multilayer film roughness. These values are used to calculate the roughness-induced surface and magnetocrystalline anisotropy coefficients as a function of N.

Related publications

Publ.-Id: 25956

Combining Absorption and Emission Spectroscopy for the Detection and Characterization of Rare Earth Elements

Jakob, S.; Fuchs, M.; Gloaguen, R.

In the last decade, the fast development of technology and high-tech industry distinctly increased the demand of Rare Earth Elements (REEs). The combination with the globally strongly concentrated distribution of production sites classifies REEs as critical raw materials and raises the need for the exploration of complex deposits with lower concentrations or remote locations. Spectroscopic methods are the key for an advanced, fast and non-invasive approach to reduce the economic and ecologic costs of REE characterization, not only within exploration, but along the whole raw material value chain. 
Currently, the research of spectral detection and characterization of REEs is concentrated on absorption spectroscopy. Although a considerable amount of REEs can be detected by their characteristic reflectance spectrum, the commonly low intensity of characteristic absorption limits its applicability for robust detection and characterization to a few REEs, such as Neodymium and Samarium.
In the past decades, studies were conducted to characterize REE crystals by their fluorescence properties. In contrast to absorption spectroscopy, an emission is induced in the sample using a laser with a defined excitation wavelength to maximize the response that depends on the investigated material. With emission spectroscopy, a broad set of REEs can be characterized, but still, the attribution of emission features is challenging, as it depends on crystal structure and experimental parameters.
Hereby, we propose a new approach for combining absorption and emission spectroscopy to characterize REEs and overcome the limitations of the single method. For that, we first investigated single REE crystal standards with different bindings using absorption as well as emission spectroscopy. The results can be used to create a library or decision routine for the detection of REE using combined absorption and emission spectroscopy. We will then test the proposed method on natural REE bearing samples, which are additionally characterized chemically and mineralogically to provide a proper validation. Hereby, the influence of the mineral matrix, natural crystal structure and mixed REE composition can be estimated and overcome by using lasers with different stimulation wavelengths in the UV and visible range of the spectrum. Absorption spectroscopy is conducted by point measurements with a reflectance spectrometer as well as with hyperspectral cameras. We developed the tools for processing and the analysis of the spectral data to ensure a fast and robust interpretation of the spectral features.
First results show the detectability of Dy, Er, Ho, Nd, Pr, Sm, and Tm with absorption and the detection of Er, Eu, Ho, Nd, Pr, Tb, and Yb with emission spectroscopy. Additionally, for REEs having spectral signatures in both cases, absorption features overprint the emission spectra within the broad fluorescence signal of the mineral matrix. They coincide with known and measured absorption features of the specific REEs. This, the integration of both features remarkably increases the detectability and the robustness of detection for those elements.

  • Lecture (Conference)
    10th EARSeL SIG Imaging Spectroscopy Workshop, 19.-21.04.2017, Zürich, Switzerland

Publ.-Id: 25955

Nanorattles with tailored electric field enhancement

Schnepf, M. J.; Mayer, M.; Kuttner, C.; Tebbe, M.; Wolf, D.; Dulle, M.; Altantzis, T.; Formanek, P.; Förster, S.; Bals, S.; König, T. A. F.; Fery, A.

Nanorattles are metallic core-shell particles with core and shell separated by a dielectric spacer. These nanorattles have been identified as a promising class of nanoparticles, due to their extraordinary high electric-field enhancement inside the cavity. Limiting factors are reproducibility and loss of axial symmetry owing to the movable metal core; movement of the core results in fluctuation of the nanocavity dimensions and commensurate variations in enhancement factor. We present a novel synthetic approach for the robust fixation of the central gold rod within a well-defined box, which results in an axisymmetric nanorattle. We determine the structure of the resulting axisymmetric nanorattles by advanced transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS). Optical absorption and scattering cross-sections obtained from UV-vis-NIR spectroscopy quantitatively agree with finite-difference time-domain (FDTD) simulations based on the structural model derived from SAXS. The predictions of high and homogenous field enhancement are evidenced by scanning TEM electron energy loss spectroscopy (STEM-EELS) measurement on single-particle level. Thus, comprehensive understanding of structural and optical properties is achieved for this class of nanoparticles, paving the way for photonic applications where a defined and robust unit cell is crucial.

Publ.-Id: 25954

Ultrafast carrier dynamics in VO₂ across the pressure-induced insulator-to-metal transition

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

We utilize near-infrared pump ‒ mid-infrared probe spectroscopy to investigate the ultrafast electronic response of pressurized VO₂. Distinct pump‒probe signals and a pumping threshold behavior are observed even in the pressure-induced metallic state showing a noticeable amount of localized electronic states. Our results are consistent with a scenario of a bandwidth-controlled Mott-Hubbard transition.

Keywords: pressure-induced metallization; bandwidth-controlled Mott-Hubbard transition; insulator-to-metal transition; high pressure; diamond anvil cell; vanadium dioxide; VO₂; pump - probe spectroscopy

Publ.-Id: 25953

Local Lorentz force and ultrasound Doppler velocimetry in a vertical convection liquid metal flow

Zürner, T.; Vogt, T.; Resagk, C.; Eckert, S.; Schumacher, J.

We report velocitymeasurements in a vertical turbulent convection flow cell that is filled with the eutectic liquid metal alloy gallium-indium-tin by a combined use of local Lorentz force velocimetry (LLFV) and ultrasound Doppler velocimetry (UDV). We demonstrate the applicability of LLFV for a thermal convection flow and reproduce a linear dependence of the measured force in the range of micronewtons on the local flow velocitymagnitude. Furthermore, the presented experiment is used to explore scaling laws of the global turbulent transport of heat and momentum in this low-Prandtl-number convection flow. Our results are found to be consistent with theoretical predictions and recent direct numerical simulations.


Publ.-Id: 25952

Magnetic flow control in growth and casting of photovoltaic silicon: Numerical and experimental results

Poklad, A.; Pal, J.; Galindo, V.; Grants, I.; Heinze, V.; Meier, D.; Pätzold, O.; Stelter, M.; Gerbeth, G.

A novel, vertical Bridgman-type technique for growing multi-crystalline silicon ingots in an induction furnace is described. In contrast to conventional growth, a modified setup with a cone-shaped crucible and susceptor is used. A detailed numerical simulation of the setup is presented. It includes a global thermal simulation of the furnace and a local simulation of the melt, which aims at the influence of the melt flow on the temperature and concentration fields. Furthermore, seeded growth of cone-shaped Si ingots using either a monocrystalline seed or a seed layer formed by pieces of poly-Si is demonstrated and compared to growth without seeds. The influences of the seed material on the grain structure and the dislocation density of the ingots are discussed. The second part addresses model experiments for the Czochralski technique using the room temperature liquid metal GaInSn. The studies were focused on the influence of a rotating and a horizontally static magnetic field on the melt flow and the related heat transport in crucibles being heated from bottom and/or side, and cooled by a crystal model covering about 1/3 of the upper melt surface.

Keywords: Magnetic flow control; Crystall-Growth; Photovoltaic Silicon; Numerical Simulation

Publ.-Id: 25951

The effect of the initial microstructure in terms of sink strength on the ion-irradiation-induced hardening of ODS alloys studied by nanoindentation

Duan, B.; Heintze, C.; Bergner, F.; Ulbricht, A.; Akhmadaliev, S.; Oñorbe, E.; de Carlan, Y.; Wang, T.

Oxide dispersion strengthened (ODS) Fe-Cr alloys are promising candidates for structural components in nuclear energy production. The small grain size, high dislocation density and the presence of particle matrix interfaces may contribute to the improved irradiation resistance of this class of alloys by providing sinks and/or traps for irradiation-induced point defects. The extent to which these effects impede hardening is still a matter of debate. To address this problem, a set of alloys of different grain size, dislocation density and oxide particle distribution were selected. In this study, three-step Fe-ion irradiation at both 300 C and 500 C up to 10 dpa was used to introduce damage in five different materials including three 9Cr-ODS alloys, one 14Cr-ODS alloy and one 14Cr-non-ODS alloy. Electron backscatter diffraction (EBSD), transmission electron microscopy (TEM), small angle neutron scattering (SANS), and nanoindentation testing were applied, the latter before and after irradiation. Significant hardening occurred for all materials and temperatures, but it is distinctly lower in the 14Cr alloys and also tends to be lower at the higher temperature. The possible contribution of Cr-rich alpha’-phase particles is addressed. The impact of grain size, dislocation density and particle distribution is demonstrated in terms of an empirical trend between total sink strength and hardening.

Keywords: Oxide dispersion strengthened alloys; Ion irradiation; Nanoindentation; Hardening; Sink strength

Related publications


Publ.-Id: 25950

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

Chauhan, A.; Bergner, F.; 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


Publ.-Id: 25949

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

Beckstein, P.; Galindo, V.; 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

Publ.-Id: 25948

Charakterisierung eines zerkleinerten Mobiltelefons mittels Mineral Liberation Analysis (MLA)

Sandmann, D.

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.


Compound Interest -
The Royal Society of Chemistry 20.03.2017 -
TrendForce Corp. Press Release 25.01.2017 -

  • Lecture (Conference)
    Tagung 2017 „Aufbereitung und Recycling“, 08.-09.11.2017, Freiberg, Deutschland


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

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

Related publications

  • 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

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

Publ.-Id: 25944

Towards ion beam therapy based on laser plasma accelerators

Karsch, L.; Beyreuther, E.; Enghardt, W.; Gotz, M.; Masood, U.; Schramm, U.; Zeil, K.; Pawelke, J.

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.

Related publications


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].
[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

Related publications

  • Lecture (Conference)
    Graphene Week 2017, 25.-29.09.2017, Athena, Hellas

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

Related publications

  • Lecture (Conference)
    CLEO, 14.-19.05.2017, San Jose, USA

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].
[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

Related publications

  • Poster
    Graphene2017, 28.-31.03.2017, Barcelona, Espana

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

Related publications

  • Lecture (Conference)
    DPG-Frühjahrstagung, 19.-24.03.2017, Dresden, Deutschland

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

Related publications


Publ.-Id: 25938

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

Renno, A.; Buchriegler, J.; Dreßler, S.; Hanf, D.; Munnik, F.; Scharf, O.; Ziegenrücker, R.

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

Related publications

  • Poster
    2nd International Conference on Applied Mineralogy & Advanced Materials and 13th International Conference on Applied Mineralogy, 05.-09.06.2017, Castellaneta Marina- Taranto, Italy

Publ.-Id: 25937

Relevance of qualitative trace element distribution maps at answering geoscientific questions

Renno, A. D.; 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

Related publications

  • Lecture (Conference)
    23rd International Conference on Ion Beam Analysis IBA-2017, 08.-13.10.2017, Shanghai, China

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.; 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

Related publications

  • Invited lecture (Conferences)
    23rd International Conference on Ion Beam Analysis IBA-2017, 08.-13.10.2017, Shanghai, China

Publ.-Id: 25935

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

Renno, A. D.

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

Related publications

  • Lecture (Conference)
    23rd International Conference on Ion Beam Analysis IBA-2017, 08.-13.10.2017, Shanghai, China

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

Related publications

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

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

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

Related publications

  • Poster
    18th International Conference on RF Superconductivity, 17.-21.07.2017, Lanzhou, China

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

Related publications

  • Poster
    The 59th ICFA Advanced Beam Dynamics Workshop on Energy Recovery Linacs, 18.-23.06.2017, Genf, Schweiz

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

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

Related publications

  • Poster
    The 59th ICFA Advanced Beam Dynamics Workshop on Energy Recovery Linacs, 18.-23.06.2017, Genf, Schweiz

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

Related publications

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-081 2017
    ISSN: 2191-8708, eISSN: 2191-8716


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.


[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

Publ.-Id: 25924

Light-activated ruthenium(II) carbonyl complexes

Kubeil, M.; 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.

[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

Publ.-Id: 25923

Laser-driven Ion Beam Radiotherapy (LIBRT)

Enghardt, W.; Pawelke, J.; Wilkens, J. J.

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.

Related publications

  • 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

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


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


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

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

Related publications

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

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

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

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

Publ.-Id: 25913

Gebäudeautomation im HZDR - Erfahrungsbericht

Oelke, M.

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

Publ.-Id: 25912

Neubau Heizwerk und Nahwärmenetz

Oelke, M.

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

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.


Publ.-Id: 25910

Facile Silylation of Cyclitols using Silyl-bis(triflates)

Topp, A.; Köckerling, M.; Reinke, H.; Miethchen, R.; Mamat, C.

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


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

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

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

Publ.-Id: 25905

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

Vallinayagam, M.; Posselt, M.; Faßbender, J.

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

Publ.-Id: 25904

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

Wang, X.; Posselt, M.; Faßbender, J.

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

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


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

Related publications

  • Invited lecture (Conferences)
    16. Remediation Colloquium, 05.-06.10.2017, Jena, Deutschland

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”: 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: .

  • Invited lecture (Conferences)
    GTT Annual Workshop 2017 / GTT Users' Meeting 2017, 28.-30.06.2017, Herzogenrath, Deutschland

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] ;
[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

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.

Related publications

  • Poster
    Nanowire Week 2017, 29.05.-02.06.2017, Lund, Sweden

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.

Related publications

  • Poster
    19th European Workshop on Molecular Beam Epitaxy, 19.-22.03.2017, Korobitsyno, St. Petersburg, Russia

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.

Related publications

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

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.

Related publications

  • Invited lecture (Conferences)
    19th European Workshop on Molecular Beam Epitaxy, 19.-22.03.2017, Korobitsyno, St. Petersburg, Russia

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.

Publ.-Id: 25893

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

Related publications

  • Lecture (others)
    Im Rahmen einer Vorlesung der Universidad Tenica Federico Santa Maria, 27.07.2017, Valparaiso, Chile

Publ.-Id: 25892

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

Lei, Z.; Fritzsche, B.; Eckert, K.

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


Publ.-Id: 25891

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

Neumann-Heyme, H.; Eckert, K.; 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


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

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

Publ.-Id: 25888

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

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

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

Publ.-Id: 25885

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)

Related publications

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.

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.
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.
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.


Publ.-Id: 25883

Pages: [1.] [2.] [3.] [4.] [5.] [6.] [7.] [8.] [9.] [10.] [11.] [12.] [13.] [14.] [15.] [16.] [17.] [18.] [19.] [20.] [21.] [22.] [23.] [24.] [25.] [26.] [27.] [28.] [29.] [30.] [31.] [32.] [33.] [34.] [35.] [36.] [37.] [38.] [39.] [40.] [41.] [42.] [43.] [44.] [45.] [46.] [47.] [48.] [49.] [50.] [51.] [52.] [53.] [54.] [55.] [56.] [57.] [58.] [59.] [60.] [61.] [62.] [63.] [64.] [65.] [66.] [67.] [68.] [69.] [70.] [71.] [72.] [73.] [74.] [75.] [76.] [77.] [78.] [79.] [80.] [81.] [82.] [83.] [84.] [85.] [86.] [87.] [88.] [89.] [90.] [91.] [92.] [93.] [94.] [95.] [96.] [97.] [98.] [99.] [100.] [101.] [102.] [103.] [104.] [105.] [106.] [107.] [108.] [109.] [110.] [111.] [112.] [113.] [114.] [115.] [116.] [117.] [118.] [119.] [120.] [121.] [122.] [123.] [124.] [125.] [126.] [127.] [128.] [129.] [130.] [131.] [132.] [133.] [134.] [135.] [136.] [137.] [138.] [139.] [140.] [141.] [142.] [143.] [144.] [145.] [146.] [147.] [148.] [149.] [150.] [151.] [152.] [153.] [154.] [155.] [156.] [157.] [158.] [159.] [160.] [161.] [162.] [163.] [164.] [165.] [166.] [167.] [168.] [169.] [170.] [171.] [172.] [173.] [174.] [175.] [176.] [177.] [178.] [179.] [180.] [181.] [182.] [183.] [184.] [185.] [186.] [187.] [188.] [189.] [190.] [191.] [192.] [193.] [194.] [195.] [196.] [197.] [198.] [199.] [200.] [201.] [202.] [203.] [204.] [205.] [206.] [207.] [208.] [209.] [210.] [211.] [212.] [213.] [214.] [215.] [216.] [217.] [218.] [219.] [220.] [221.] [222.] [223.] [224.] [225.] [226.] [227.] [228.] [229.] [230.] [231.] [232.] [233.] [234.] [235.] [236.] [237.] [238.] [239.] [240.] [241.] [242.] [243.] [244.] [245.] [246.] [247.] [248.] [249.] [250.] [251.] [252.] [253.] [254.] [255.] [256.] [257.] [258.] [259.] [260.] [261.] [262.] [263.] [264.] [265.] [266.] [267.] [268.] [269.] [270.] [271.] [272.] [273.] [274.] [275.] [276.] [277.] [278.] [279.] [280.] [281.] [282.] [283.] [284.] [285.] [286.] [287.] [288.] [289.] [290.] [291.] [292.] [293.] [294.] [295.] [296.] [297.] [298.] [299.] [300.] [301.] [302.] [303.] [304.] [305.] [306.] [307.] [308.] [309.] [310.] [311.] [312.] [313.] [314.] [315.] [316.] [317.] [318.] [319.] [320.] [321.] [322.] [323.] [324.] [325.] [326.] [327.] [328.] [329.] [330.]