Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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34122 Publications

Utilization of flash lamp annealing for processing of low-cost TCO layers

Mathey, A.; Prucnal, S.; Wiesenhütter, K.; Vines, L.; Lindberg, P.; Svensson, B.; Bregolin, F. L.; Skorupa, W.

Aluminum-doped zinc oxide (AZO) is one of the most promising transparent conductive oxides (TCO) characterized by low resistivity, high transparency and most of all, by low cost of fabrication. AZO thin-films were deposited on p-type Si wafers via r.f. magnetron sputtering either at room temperature or at 400 oC and subsequently annealed in the millisecond-range, utilizing flash lamp annealing (FLA). Here, we have investigated the influence of the deposition parameters and post-deposition FLA treatment on the optoelectronic properties of the AZO layer. It is shown that the millisecond range flash lamp annealing significantly enhances the electrical activation of Al and suppresses secondary phase formation during post-deposition annealing. Moreover, the optoelectronic and microstructural properties of the FLA treated samples are independent on the deposition temperature. This, in turn opens the possibility for a further, highly-desired cost reduction of the overall fabrication process. The FLA technique is cost-effective and a high-throughput alternative for processing of AZO films.

Keywords: AZO; flash lamp annealing; magnetron sputtering

  • Poster
    ION 2014 X-th International Conference on Ion Implantation and Other Applications of Ions and Electrons, 23.-26.06.2014, Kazimierz Dolny, Poland

Publ.-Id: 21252

Influence of Flash Lamp Annealing on the Optical Properties of CIGS Layer

Prucnal, S.; Jiao, F.; Reichel, D.; Zhao, K.; Cornelius, S.; Turek, M.; Pyszniak, K.; Drozdziel, A.; Skorupa, W.; Helm, M.; Zhou, S.

Copper indium gallium diselenide (CIGS) becomes more significant for solar cell applications as an alternative to silicon. The quality of the layer has a critical impact on the final efficiency of the solar cell. An influence of the post-deposition millisecond range flash lamp annealing on the optical and microstructural properties of the GIGS films was investigated. Based on the Raman and photoluminescence spectroscopy, it is shown that flash lamp annealing reduces the defect concentration and leads to an increase of the photoluminescence intensity by a factor of six compared to the nonannealed sample. Moreover, after flash lamp annealing the degradation of the photoluminescence is significantly suppressed and the absolute absorption in the wavelength range of 200-1200 nm increases by 25%.

Keywords: CIGS; flash lamp annealing; solar cells; photoluminescence

Publ.-Id: 21251

III–V semiconductor nanocrystal formation in silicon nanowires via liquid-phase epitaxy

Prucnal, S.; Glaser, M.; Lugstein, A.; Bertagnolli, E.; Stöger-Pollach, M.; Zhou, S.; Helm, M.; Reichel, D.; Rebohle, L.; Turek, M.; Zuk, J.; Skorupa, W.

Direct integration of high-mobility III-V compound semiconductors with existing Si based CMOS processing platforms presents a main challenge to increase the CMOS performance and the scaling trend. Silicon hetero-nanowires with integrated III-V segments are one of the most promising candidates for advanced nano-optoelectronics as first demonstrated using molecular beam epitaxy techniques. Here we demonstrate a novel route for InAs/Si hybrid nanowire fabrication via millisecond range liquid-phase epitaxy regrowth using sequential ion beam implantation and flash-lamp annealing. We show that such highly mismatched systems can be monolithically integrated within a single nanowire. Optical and microstructural investigations confirm the high quality hetero-nanowire fabrication coupled with the formation of atomically sharp interface between Si and InAs segments. Such hybrid systems open new routes for future high-speed and multifunctional nanoelectronic devices on a single chip.

Keywords: liquid phase epitaxy; InAs; heteronanowires; silicon; ion implantation

Publ.-Id: 21250

Optoelectronic properties of ZnO film on silicon after SF6 plasma treatment and milliseconds annealing

Prucnal, S.; Gao, K.; Zhou, S.; Wu, J.; Cai, H.; Gordan, O. D.; Zahn, D. R. T.; Larkin, G.; Helm, M.; Skorupa, W.

Zinc oxide thin film is one of the most promising candidates for the transparent conductive layer in microelectronic and photovoltaic applications, due to its low resistivity and high transmittance in the visible spectral range. In this letter we present optoelectronic and structural properties of fluorine doped ZnO films deposited at low temperature on a silicon substrate. The fluorine doping was made by post-deposition SF6 plasma treatment and activation by the millisecond range flash lamp annealing. Both the microstructural and optical investigations confirm the formation of a high-quality, highly-doped n-type ZnO layer. The current-voltage characteristics show a heterojunction between n++-ZnO and Si. Moreover, it is shown that the SF6 plasma treatment efficiently passivates the surface state and bulk defects in the ZnO film.

Keywords: ZnO; plasma immersion ion implantation; pulsed laser deposition; flash lamp annealing; SF6

Publ.-Id: 21249

The influence of different signal-to-background ratios on spatial resolution and F18-FDG-PET quantification using point spread function and time-of-flight reconstruction

Rogasch, J. M. M.; Hofheinz, F.; Lougovski, A.; Furth, C.; Ruf, J.; Großer, O. S.; Mohnike, K.; Hass, P.; Walke, M.; Amthauer, H.; Steffen, I. G.


F18-fluorodeoxyglucose positron-emission tomography (FDG-PET) reconstruction algorithms can have substantial influence on quantitative image data used, e.g., for therapy planning or monitoring in oncology. We analyzed radial activity concentration profiles of differently reconstructed FDG-PET images to determine the influence of varying signal-to-background ratios (SBRs) on the respective spatial resolution, activity concentration distribution, and quantification (standardized uptake value [SUV], metabolic tumor volume [MTV]).


Measurements were performed on a Siemens Biograph mCT 64 using a cylindrical phantom containing four spheres (diameter, 30 to 70 mm) filled with F18-FDG applying three SBRs (SBR1, 16:1; SBR2, 6:1; SBR3, 2:1). Images were reconstructed employing six algorithms (filtered backprojection [FBP], FBP + time-of-flight analysis [FBP + TOF], 3D-ordered subset expectation maximization [3D-OSEM], 3D-OSEM + TOF, point spread function [PSF], PSF + TOF). Spatial resolution was determined by fitting the convolution of the object geometry with a Gaussian point spread function to radial activity concentration profiles. MTV delineation was performed using fixed thresholds and semiautomatic background-adapted thresholding (ROVER, ABX, Radeberg, Germany).


The pairwise Wilcoxon test revealed significantly higher spatial resolutions for PSF + TOF (up to 4.0 mm) compared to PSF, FBP, FBP + TOF, 3D-OSEM, and 3D-OSEM + TOF at all SBRs (each P < 0.05) with the highest differences for SBR1 decreasing to the lowest for SBR3. Edge elevations in radial activity profiles (Gibbs artifacts) were highest for PSF and PSF + TOF declining with decreasing SBR (PSF + TOF largest sphere; SBR1, 6.3%; SBR3, 2.7%). These artifacts induce substantial SUVmax overestimation compared to the reference SUV for PSF algorithms at SBR1 and SBR2 leading to substantial MTV underestimation in threshold-based segmentation. In contrast, both PSF algorithms provided the lowest deviation of SUVmean from reference SUV at SBR1 and SBR2.


At high contrast, the PSF algorithms provided the highest spatial resolution and lowest SUVmean deviation from the reference SUV. In contrast, both algorithms showed the highest deviations in SUVmax and threshold-based MTV definition. At low contrast, all investigated reconstruction algorithms performed approximately equally. The use of PSF algorithms for quantitative PET data, e.g., for target volume definition or in serial PET studies, should be performed with caution
- especially if comparing SUV of lesions with high and low contrasts.

Keywords: FDG-PET/CT reconstruction; PSF; TOF; Spatial resolution; Metabolic tumor volume delineation; Signal-to-background ratio; Radial activity concentration profile; Gibbs artifact; Ringing artifact; Gibbs phenomenon

Publ.-Id: 21247

Spin coated targets for filamentation studies

Kraft, S.

In our presentation we report on the experimental observation of spatially modulated proton beams.

  • Lecture (Conference)
    Targert Fabrication Workshop 5, 06.-11.07.2014, St. Andrews, Great Britain

Publ.-Id: 21246

Status of laser ion acceleration at HZDR

Kraft, S.

Within the last years, numerous activities in laser particle acceleration have been taken place at the 100TW ultra-short pulse Laser system Draco at HZDR. Special emphasis was laid on developing an ion beam suitable for applications. In order to achieve high proton energies various approaches such as mass limited targets and active pre-plasma formation have been tested.

Recently, the laser is upgraded to a dual beam system delivering 30f pulses with 100TW as well as synchronized 1PW pulses. The talk will give an overview over the particle acceleration activities focussing on Laser ion acceleration as well as a current status of the laser upgrade in Dresden.

  • Invited lecture (Conferences)
    Seminar der Plasmaphysik, 12.11.2014, Darmstadt, Deutschland

Publ.-Id: 21245

Development of a compact particle therapy facility with laser driven ion beams via novel pulse powered gantry systems

Masood, U.; Baumann, M.; Bussmann, M.; Cowan, T.; Enghardt, W.; Hermannsdörfer, T.; Hofmann, K.; Kaluza, M.; Karsch, L.; Kroll, F.; Schramm, U.; Schürer, M.; Wilkens, J.; Pawelke, J.

  • Contribution to proceedings
    53th Particle Therapy Cooperative Group (PTCOG) Meeting, 08.-14.06.2014, Shanghai, China, 299

Publ.-Id: 21244

Fast measurement of 3-d dose distributions

Pawelke, J.

  • Invited lecture (Conferences)
    29th Conference on Clinical and Experimental Research in Radiation Oncology (CERRO 29), 18.-25.01.2014, Les Menuires, France

Publ.-Id: 21243

Entwicklung von Elektromagneten mit kurzen, hohen Strompulsen für die Laser basierte Protonentherapie

Schürer, M.; Hermannsdörfer, T.; Karsch, L.; Kroll, F.; Masood, U.; Pawelke, J.

  • Lecture (Conference)
    7. Tagung Feinwerktechnische Konstruktion, 05.-06.11.2013, Dresden, Deutschland
  • Contribution to proceedings
    7. Tagung Feinwerktechnische Konstruktion, 05.-06.11.2013, Dresden, Deutschland
    In: T. Nagel (Ed.): Trends in der Feinwerktechnik. Mechatronik 5, München: IGT Verlag, 13-14

Publ.-Id: 21242

Uranium sorption on montmorillonite at high ionic strengths: Surface complexation modelling

Fritsch, K.; Schmeide, K.

The current results of surface complexation modelling of U(VI) complexes on montmorillonite in NaCl and a NaCl/CaCl2/MgCl2 mixed electrolyte of high ionic strength are presented.

Keywords: uranium sorption; argillaceous rock; clay; uranium; montmorillonite; high ionic strength; surface complexation modelling

  • Lecture (others)
    7. Workshop des Verbundprojekts „Rückhaltung endlagerrelevanter Radionuklide im natürlichen Tongestein und in salinaren Systemen“, 28.-29.10.2014, Saarbrücken, Deutschland

Publ.-Id: 21240

Simulations of precessing flows in cylindrical geometry

Giesecke, A.

no abstract available

Keywords: Precession; DRESDYN; DYNAMO

  • Lecture (Conference)
    MHD Days 2014, 02.-03.12.2014, Potsdam, Germany

Publ.-Id: 21239

Radiolabelling of colloids for highly sensitive detection in transport studies Vortrag im Rahmen des BELBaR WP2 und WP4 Projekttreffens, 30.-31. Oktober, Prag

Hildebrand, H.; Schymura, S.; Kulenkampff, J.; Lippmann-Pipke, J.; Franke, K.

In dem Vortrag wurde für einen Teil des BELBaR Konsortiums ein Überblick über am HZDR/FSL vorhandene Radiomarkierungsmöglichkeiten für Kolloide bzw. Nanopartikel gegeben.

  • Lecture (others)
    Joined meeting of WP2 and WP4 within the EC project BELBaR, 30.-31.10.2014, Prag, Tschechische Republik

Publ.-Id: 21238

Cyclopeptides containing the DEKS motif as conformationally restricted collagen telopeptide analogues: synthesis and conformational analysis

Wodtke, R.; Ruiz-Gómez, G.; Kuchar, M.; Pisabarro, M. T.; Novotná, P.; Urbanová, M.; Steinbach, J.; Pietzsch, J.; Löser, R.

The collagen telopeptides play an important role for lysyl oxidase-mediated crosslinking, a process which is deregulated during tumour progression. The DEKS motif which is located within the N-terminal telopeptide of the α1 chain of type I collagen has been suggested to adopt a βI-turn conformation upon docking to its triple-helical receptor domain, which seems to be critical for lysyl oxidase-catalysed deamination and subsequent crosslinking by Schiff-base formation. Herein, the design and synthesis of cyclic peptides which constrain the DEKS sequence in a β-turn conformation will be described. Lysine-side chain attachment to 2-chlorotrityl chloride-modified polystyrene resin followed by microwave-assisted solid-phase peptide synthesis and on-resin cyclisation allowed for an efficient access to head-to-tail cyclised DEKS-derived cyclic penta- and hexapeptides. An Nε-(4-fluorobenzoyl)lysine residue was included in the cyclopeptides to allow their potential radiolabelling with fluorine-18 for PET imaging of lysyl oxidase. Conformational analysis by 1H NMR and chiroptical (electronic and vibrational CD) spectroscopy together with MD simulations demonstrated that the concomitant incorporation of a D-proline and an additional lysine for potential radiolabel attachment accounts for a reliable induction of the desired βI-turn structure in the DEKS motif in both DMSO and water as solvents. The stabilised conformation of the cyclohexapetide is further reflected by its resistance to trypsin-mediated degradation. In addition, the deaminated analogue containing allysine in place of lysine has been synthesised via the corresponding ε-hydroxynorleucine containing cyclohexapeptide. Both ε-hydroxynorleucine and allysine containing cyclic hexapeptides have been subjected to conformational analysis in the same manner as the lysine-based parent structure. Thus, both a conformationally restricted lysyl oxidase substrate and product have been synthetically accessed, which will enable their potential use for molecular imaging of these important enzymes.

Publ.-Id: 21237

Colloidal Probe Atomic Force Microscopy to determine the Floatability of Minerals in Ores

Rudolph, M.

Flotation is without a doubt one of the major processes for the separation of fine minerals and it has been applied for more than a century. A key task of a successful flotation separation is to find the proper chemical treatment to selectively hydrophobize and thus float a certain mineral phase using molecules or ions referred to as collectors, depressants, regulators and frothers. Commonly floatability is determined by microflotation tests using the Hallimond tube with pure mineral phases. This method however requires the pure mineral phase which is very often not even taken from the same deposit which is going to be processed. In this paper we present a new approach to in-situ determine and even map the floatability of finely disseminated mineral phases within cross-sections of an ore. It is based on measuring hydrophobic effects using colloidal probe atomic force microscopy with a hydrophobic polystyrene probe based on force spectroscopy with a lateral resolution of only a few nanometers. Coupled confocal Raman spectroscopy on the same locality enables the identification of the mineral phase. We present the working principles of the method and show which signals in the force spectra characteristic for hydrophobic interactions can be used to define floatability and which can then be mapped as single quantities, e.g. jump-into-contact events due to nanobubble occurrence or parameters of the long range interaction curves most probably due to capillary effects.
A finely grained silicate ore containing the valuable rare earth mineral eudialyte from southern Sweden as well as pure samples of magnetite are presented as substrates to demonstrate the capability of this new approach.
This method will not only help to find the proper flotation chemistry but it can furthermore help in researching and unravelling problems of floatability within similar mineral phases.

  • Contribution to proceedings
    International Mineral Processing Congress 2014, 20.-24.10.2014, Santiago de Chile, Chile
    Proceedings of the XXVII International Mineral Processing Congress – IMPC 2014

Publ.-Id: 21236

Subcritical bifurcation to turbulence in precessing flow

Gundrum, T.; Herault, J.; Steglich, C.; Giesecke, A.; Stefani, F.; Gerbeth, G.

Subcritical bifurcation to turbulence in precessing flow in the water mockup for the DRESDYN Experiment

Keywords: Precession driven dynamo; Subcritical bifurcation; metastable transition

  • Lecture (Conference)
    MHD Days 2014, 02.-03.12.2014, Potsdam, Deutschland

Publ.-Id: 21235

Supernova-Produced 26Al and 60Fe in Deep-Sea Sediments

Feige, J.; Wallner, A.; Fifield, L. K.; Merchel, S.; Rugel, G.; Steier, P.; Tims, S.; Winkler, S. R.; Golser, R.

Massive stars, which end their lives in a supernova (SN) explosion, eject freshly produced nuclides into the surrounding interstellar medium. Among them long-lived radionuclides, that can be deposited into terrestrial archives, if such an event occurs close to the Solar System.
About 100 samples of four deep-sea sediment cores originating from the Indian Ocean were analyzed for their content in the isotopes 26Al and 60Fe for the time range of 2-3 Myr. These nuclides are produced in SNe and the time range corresponds to an 60Fe enhancement observed in a deep-ocean crust sample (Knie et al., 2004). The method used for analysis is accelerator mass spectrometry (AMS), a very sensitive technique for the detection of long-lived radionuclides.
A clear signal of 60Fe throughout the whole measured time period was observed. This observation is in contrast to a narrow peak if originating from a direct input from a single SN. Further, no 60Fe was detected in much older or younger sediment samples. A concurring SN-signal of 26Al is, however, hidden underneath a dominant terrestrial background from continuous atmospheric and in-situ production. The resulting limits on the ratios of 60Fe/26Al were compared to nucleosynthesis models.

Keywords: AMS; supernova; radionuclide

  • Lecture (Conference)
    DPG Frühjahrstagung des Arbeitskreises Atome, Moleküle, Quantenoptik und Plasmen (AMOP), 23.-27.03.2015, Heidelberg, Deutschland

Publ.-Id: 21234

High-energy diode-pumped D2O-cooled multislab Yb:YAG and Yb:QX-glass lasers

Siebold, M.; Loeser, M.; Röser, F.; Albach, D.; Schramm, U.

We investigated the performance of multislab Yb:QX and Yb:YAG laser amplifiers using low absorption heavy-water (D2O) as coolant. We demonstrated a pulse energy of 1 J at a repetition rate of up to 10 Hz.

Keywords: Laser amplifiers; Laser cooling; Lasers, diode-pumped; Lasers, ytterbium

  • Lecture (Conference)
    Advanced Solid State Lasers (ASSL) Conference, 16.-21.11.2014, Shanghai, China
  • Contribution to proceedings
    Advanced Solid State Lasers (ASSL) Conference, 16.-21.11.2014, Shanghai, China
    Advanced Solid State Lasers 2014, OSA Technical Digest, 978-1-55752-822-3

Publ.-Id: 21233

Broadband, diode-pumped Yb-doped fused bulk silica laser

Röser, F.; Loeser, M.; Albach, D.; Siebold, M.; Schramm, U.; Grimm, S.; Brand, D.; Langner, A.; Schötz, G.; Schönfeld, D.

We successfully demonstrated cw lasing of ytterbium-doped fused bulk silica glass. We achieved a highly polarized output with a slope efficiency of 52% and a wavelength tuning range from 1005-1110 nm.

Keywords: Lasers, diode-pumped; Lasers, ytterbium; Lasers, solid-state; Laser materials

  • Lecture (Conference)
    Advanced Solid State Lasers (ASSL) Conference, 16.-21.11.2014, Shanghai, China
  • Contribution to proceedings
    Advanced Solid State Lasers (ASSL) Conference, 16.-21.11.2014, Shanghai, China
    Advanced Solid State Lasers 2014, OSA Technical Digest, 978-1-55752-822-3

Publ.-Id: 21232

Interaction of uranium with isolated microorganisms of the former uranium mine Königstein (Saxony, Germany)

Gerber, U.; Krawczyk-Bärsch, E.; Arnold, T.; Stumpf, T.

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 are the beginning of the food chain, and therefore the transfer of bound uranium along this food chain could rise to a serious threat to human health. Biosorption of radionuclides especially uranium by microorganisms regulates the mobility of the metal in the environment. Thus, microorganisms could be used to clean-up contaminated soils, sediments, and waters by removing uranium and other radionuclides, due to bioremediation processes.

Keywords: Uranium; Königstein; Interaction; Microorganisms

  • Poster
    Projekttreffen TransAqua, 25.-27.11.2014, Karlsruhe, Deutschland

Publ.-Id: 21230

Kontaminationsfreie Injektion von Radiotracern für die Prozesstomographie von Transportprozessen in Geomaterialien

Kulenkampff, J.

Prozessverständnis und Modellierung von Transport in natürlichen geklüfteten oder porösen Geomaterialien (Böden, Gesteine) sind aufgrund der komplizierten geometrischen Randbedingungen auf der Mikroskala und der heterogenen Struktur und Zusammensetzung des Materials besonders schwierige Aufgaben. Gewöhnlich werden wie in weniger komplexen technischen Materialien, wie Filtern oder Reaktoren, einfache Modelle zur Beschreibung der Porzesse angewendet, die nur eine grobe Beschreibung der Prozesse erlauben und außerhalb ihres begrenzten Gültigkeitsbereichs versagen. Bei einer solchen Parametrisierung anhand von Durchbruchkurven wird das Material als Blackbox betrachtet und mit wenigen Parametern beschrieben (Abb. 1). Die Nutzung von Radioisotopen als Tracer für den mobilen Stoff ermöglicht Einblicke in den räumlich-zeitlichen Verlauf des Transports im Innern des opaken Versuchskörpers mit höchster Sensitivität und ohne chemische oder physikalische Rückwirkung auf den Prozess. Außerdem ist die einfache und selektive Detektierbarkeit geringster Konzentrationen von Radiotracern oft vorteilhaft. Präferentielle Transportwege, die Verzögerung des Transports durch Wechselwirkungen und gegebenenfalls auch die Immobilisierung der beobachteten Spezies im Versuchskörper können so erfasst werden (Abb. 2).
Es werden zylindrische Probekörper hergestellt (Durchmesser bis 30-100 mm, Länge 50-300 mm), mit Fluidanschlüssen an den Stirnflächen. Im Transportversuch wird kontinuierlich eine Trägerlösung mit Fließraten von 5 µL/min bis 5 mL/min injiziert. In Abhängigkeit vom Probenvolumen wird der Trägerlösung ein Tracerpuls (1-5 mL) hinzugefügt. Dieser Tracerpuls wird mit Positronen-Emissions-Tomographie quantitativ in seinem räumlich-zeitlichen Verlauf mit einer räumlichen Auflösung im Bereich von 1 mm erfasst. Für den Tracerpuls eingesetzte Aktivitäten betragen zwischen 1 MBq und 500 MBq. Sie werden mit einer Empfindlichkeit von 10 – 100 Bq/µL erfasst, was einer Sensitivität im picomolaren Bereich entspricht. Geeignete Radionuklide sind z.B. 18F, 124I, 64Cu, 58Co, 22Na mit Halbwertszeiten von Stunden bis Jahren. Mögliche Beobachtungszeiten sind etwa 10 Halbwertszeiten – also Tage bis Jahrzehnte.
Positronen-Emissions-Tomographie (PET) (Abb. 3) ist als höchst sensitive Methode der funktionellen medizinischen Diagnostik bekannt und wird vor allem in der Krebsdiagnostik und der biomedizinischen Forschung angewendet. Wegen des hohen Aufwandes gibt es wenige examplarische Anwendungen auf technischen Gebieten. Insbesondere wird PET in der Forschungsstelle Leipzig des HZDR seit über 10 Jahren erfolgreich für die Untersuchung von Prozessen in Geomaterialien eingesetzt (s. Literaturangaben).
Eine wichtige Rolle nimmt die zuverlässige Injektion des Tracers ein. Dabei sind Sicherheits- und Strahlenschutzaspekte zu berücksichtigen. Je nach Untersuchungsaufgabe werden unterschiedliche Pumpen eingesetzt (Schlauchpumpen, einfache Spritzenpumpen mit handelsüblichen Injektionsspritzen, HPLC-Pumpen, ISCO-Spritzenpumpen). Bei den zwei letzteren kann die Kontamination der Pumpe durch die Nutzung von Injektionsschleifen für den Radiotracer vermieden werden. Insbesondere bei langlebigen Tracern (58Co, 22Na) ist dabei aber besondere Vorsicht geboten.
Ergbebnis der Untersuchung sind zeitlich aufgelöste tomographische Darstellungen der Tracerkonzentration (Abb. 4). Hieraus lassen sich
- lokale Tracerverteilungen
- prozessabhängiges effektives Volumen
- effektiv wirksamer Anteil innere Oberfläche (bei Wechselwirkungen)
- Geschwindigkeitsverteilung
bestimmen. Gegenüber der Parametrisierung von Transportuntersuchungen durch Modellanpassung an Durchbruchkurven ergeben sich so verlässlichere real gemessenen Parametersätze und gleichzeitig eine bisher nicht erreichbare Verbesserung des Prozessverständnisses.

Richter, M., Gruendig, M., Zieger, K., Seese, A. and Sabri, O., 2005. Positron emission tomography for modelling of geochemical transport processes in clay. Radiochimica Acta, 93: 643-651.
Kulenkampff, J., Gründig, M., Richter, M. and Enzmann, F., 2008. Evaluation of positron-emission-tomography for visualisation of migration processes in geomaterials. Physics and Chemistry of the Earth, Parts A/B/C, 33(14–16): 937-942.
Wolf, M.; Kulenkampff, J.; Enzmann, F.; Gründig, M.; Richter, M.; Lippmann-Pipke, J.; Mittmann, H., 2010. 3D-Visualisierung und Quantifizierung von Fluidströmungen in Salinargestein mittels Positronen-Emissions-Tomographie. EDGG Exkursionsführer & Tagungspublikationen 244(2010), Hannover: Deutschen Gesellschaft für Geowissenschaften e.V.
Kulenkampff, J.; Gründig, M.; Korn, N.; Zakhnini, A.; Barth, T.; Lippmann-Pipke, J., 2013. Application of high-resolution positron-emission-tomography for quantitative spatiotemporal process monitoring in dense material. 7. World Congress on Industrial Process Tomography, 02.-05.09.2013, Krakow, Poland.
Bittner, L.; Kulenkampff, J.; Gründig, M.; Lippmann-Pipke, J.; Enzmann, F. , 2014. Direct Observation of Waterglass Impregnation of Fractured Salt Rock with Positron Emission Tomography. International Conference on the Performance of Engineered Barriers: Backfill, Plugs & Seals, 06.-07.02.2014, Hannover, Deutschland

  • Lecture (others)
    ISCO-Anwendertreffen, 09.12.2014, Potsdam, Deutschland

Publ.-Id: 21229

Refined reconstruction of liquid-gas interface structures for stratified two-phase flow using wire-mesh sensor

Schleicher, E.; Aydin, T. B.; Vieira, R. E.; Torres, C. F.; Pereyra, E.; Sarica, C.; Hampel, U.

Wire-mesh sensors (WMS), developed at HZDR [11], [2], are widely used to visualize two-phase flows and measure flow parameters, such as phase fraction distributions or gas phase velocities quantitatively and with a very high temporal resolution. They have been extensively applied to a wide range of two-phase gas-liquid flow problems with conducting and non-conducting liquids. However, for very low liquid loadings, the state of the art data analysis algorithms for WMS data suffer from the comparably low spatial resolution of measurements and from boundary effects, caused by e.g. flange rings - especially in the case of capacitance type WMS. In the recent past, diverse studies have been performed on two-phase liquid-gas stratified flow with low liquid loading conditions in horizontal pipes at the University of Tulsa. These tests cover oil-air flow in a 6-inch ID pipe and water-air flow in a 3-inch ID pipe employing dual WMS with 32x32 and 16x16 wires, respectively. For oil-air flow experiments, the superficial liquid and gas velocities vary between 9.2 m/s ≤ νSG ≤ 15 m/s and 0.01 m/s ≤ νSL ≤ 0.02 m/s, respectively [1]. In water-air experiments, the superficial liquid and gas velocities vary between 9.1 m/s ≤ νSG ≤ 33.5 m/s and 0.03 m/s ≤ νSL ≤ 0.2 m/s, respectively [14], [15]. In order to understand the stratified wavy structure of the flow, the reconstruction of the liquid-gas interface is essential. Due to the relatively low spatial resolution in the WMS measurements of approximately 5 mm, the liquid-gas interface recognition has always an unknown uncertainty level. In this work a novel algorithm for refined liquid-gas interface reconstruction is introduced for flow conditions where entrainment is negligible.

Keywords: Keywords Wire-mesh sensor; two-phase flow; stratified flow; liquid-gas interface recognition

Publ.-Id: 21228

Accumulation of plutonium in mammalian wildlife tissues following dispersal by accidental-release tests

Johansen, M. P.; Child, D. P.; Caffrey, E. A.; Davis, E.; Harrison, J. J.; Hotchkis, M. A. C.; Payne, T. E.; Ikeda-Ohno, A.; Thiruvoth, S.; Twining, J. R.; Beresford, N. A.

We examined the distribution of plutonium (Pu) in the tissues of mammalian wildlife inhabiting the relatively undisturbed, semi-arid former Taranaki weapons test site, Maralinga, Australia. The accumulation of absorbed Pu was highest in the skeleton, followed by muscle, liver, kidneys, and blood. Pu activity concentrations in lung tissues were elevated relative to the body average. Foetal transfer was higher in the wildlife data than in previous laboratory studies. The amount of Pu in the gastrointestinal tract was highly elevated relative to that absorbed within the body, potentially increasing transfer of Pu to wildlife and human consumers that may ingest gastrointestinal tract organs. The Pu distribution in the Maralinga mammalian wildlife generally aligns with previous studies related to environmental exposure (e.g. Pu in humans from worldwide fallout), but contrasts with the partitioning models that have traditionally been used for human worker-protection purposes (approximately equal deposition in bone and liver) which appear to under-predict the skeletal accumulation in environmental exposure conditions.

Keywords: actinides; plutonium; nuclear debris; accumulation; wildlife; radio ecology

Publ.-Id: 21227

Undesired air entrainment by vortex formation - experimental investigations on the resulting phase fraction distributions in a centrifugal pump using gamma-ray computed tomography

Schäfer, T.; Bieberle, A.; Neumann, M.; Hampel, U.

Air entrainment may occur in situations, where water is conveyed from a reservoir. There hollow vortices may form as a consequence of low liquid level and pre-existing fluid swirling. Particularly, such a situation may be prevailing in nuclear power plants, e.g. when emergency cooling water is taken from a liquid reservoir, like the condensation chamber. Presence of gas in pumps may lead to abrasion at impeller blades, strong vibrations with damaging of bearings and loss of cooling for shaft and bearings and early fatigue as a consequence. At least it will lead to decreasing pump performance even to the point of abrupt collapse of flow rate. The presented work contributes quantitative measurements, visualizations and analyses of gas-liquid phase distributions to the fundamental understanding of the effects of air entrainment in centrifugal pumps. Advanced tomographic measuring methods with high spatial resolution were applied to investigate the two-phase distribution in the impeller region of an industrial centrifugal pump.

Keywords: gamma-ray computed tomography; centrifugal pump; gas entrainment; two-phase flow

  • Poster
    East German Centre of Competence in Nuclear Technology Workshop of Doctoral Candidates, 04.12.2014, Zittau, Deutschland

Publ.-Id: 21226

Application of gamma-ray computed tomography for the analysis of gas holdup distributions in centrifugal pumps

Schäfer, T.; Bieberle, A.; Neumann, M.; Hampel, U.

In this work, gas-liquid distributions in an industrial centrifugal pump operated at various steady state conditions have been quantitatively determined. Therefore, high-resolution gamma-ray computed tomography (HireCT) has been applied, operated in time-averaging rotation-synchronized CT scanning mode. Detailed studies have been performed on a hydraulic test facility providing authentic operating conditions for industrial centrifugal pumps. The gas distribution in the centrifugal pump has been studied at defined inlet gas volumetric flow rates between 0% and 5% and for two different inlet flow regimes, namely disperse and swirling gas-liquid two-phase flow. In this way, the influence of the inlet flow boundary conditions on the performance as well as gas fraction distributions and gas holdup distribution within the impeller region could be successfully determined.

Keywords: gamma-ray computed tomography; centrifugal pump; gas entrainment; two-phase flow

Publ.-Id: 21225

Obtaining magnitude-cumulative frequency curves from rockfall scar size distribution using cosmogenic chlorine-36 in the Montsec area (Eastern Pyrenees, Spain)

Domènech, G.; Mavrouli, O.; Corominas, J.; Abellán, A.; Merchel, S.; Pavetich, S.; Rugel, G.

Magnitude-cumulative frequency (MCF) relations are commonly used components for assessing the rockfall hazard using databases of recorded events. However, in some cases, data are lacking or incomplete. To overcome this restriction, the volume distribution of the rockfall scars has been used instead. The latter may yield the temporal probability of occurrence if the time span required to generate the scars is known.
The Montsec range, located in the Eastern Pyrenees, Spain, was chosen as a pilot study area for investigating MCF distributions. This cliff, which is composed of limestones from Upper Cretaceous age, shows distinct evidences of rockfall activity, including large recent rockfall scars. These areas are identifiable by their orange colour, which contrasts in front of the greyish old stable (reference) surface of the cliff face. We present a procedure to obtain the MCF of the rockfall scars by dating an old reference cliff surface and measuring the total volume released since then. The reference cliff surface was dated using the terrestrial cosmogenic nuclide (TCN) chlorine-36 (Merchel et al., 2013). We used the Rockfall Scar Size Distribution (RSSD) obtained in Domènech et al. (2014) that considers several rockfall pattern scenarios. Scenario 1 allows for, mostly, large rockfall scar volumes, scenario 2 considers smaller occurrences and scenario 3 suggests that rockfall scars can be the result of one or several rockfall events, and thus contemplating a wider range of scar volumes.
The main steps of the methodology are: a) Obtaining the RSSD, b) Volume calculation of material lost, c) Calculation of time (T0) elapsed for the cliff to retreat (age of the old reference surface), and d) generation of the MCF curve from the RSSD. A total volume of material lost of 78900 m3 was obtained as well as an elapsed period of time of 15350 years.
The MCF curves for different rockfall scenarios are found to be well fitted by a power law with exponents -1.7, -1.1 and -1 for scenarios 1, 2 and 3, respectively. Frequencies about 0.17, 0.43 and 0.27 events/year were calculated for scenario 1, 2 and 3, respectively, considering rockfall scar volumes greater - or equal to - 0.5 m3.
Domènech G., Mavrouli O., Corominas J. and Abellán A. (2014): Calculation of the rockfall scar volume distribution using a Terrestrial Laser Scanner in the Montsec Area (Eastern Pyrenees, Spain). Geophysical Research Abstracts 16. EGU General Assembly. Vienna.
Merchel S., Braucher R., Alfimov V., Bichler M., Bourlès D.L., Reitner J.M. (2013): The potential of historic rock avalanches and man-made structures as chlorine-36 production rate calibration sites. Quat. Geochron. 18, 54-62.

Keywords: AMS; TCN; cosmogenic nuclide; hazard; rockfall

  • Lecture (Conference)
    European Geosciences Union (EGU) General Assembly, 12.-17.04.2015, Wien, Österreich

Publ.-Id: 21224

Neutron-induced fission measurements at the time-of-flight facility nELBE

Kögler, T.; Beyer, R.; Junghans, A. R.; Massarczyk, R.; Schwengner, R.; Wagner, A.

Neutron-induced fission of 242 Pu was studied at the photoneutron source nELBE. The fast neutron fission cross section was determined using actinide fission chambers in a time-of-flight experiment. Whereas the absolute normalization is missing so far, a good agreement to the present nuclear data and evaluations has been achieved in the range of 100 keV to 10 MeV.

Keywords: Neutron-induced fission; parallel plate fission ionization chambers

  • Invited lecture (Conferences)
    Scientific Workshop on Nuclear Fission dynmaics and the Emission of Prompt Neutrons and Gamma Rays, THEORY-3, 16.-18.09.2014, Opatija, Kroatien
  • Open Access Logo Contribution to proceedings
    Scientific Workshop on Nuclear Fission Dynamics and the Emission of Prompt Neutrons and Gamma-Rays, THEORY-3, 16.-18.09.2014, Opatija, Kroatien
    Physics Procedia, Amsterdam: Elsevier, 150-155
    DOI: 10.1016/j.phpro.2015.04.020

Publ.-Id: 21223

3d cfd simulation of flashing flows in a converging-diverging nozzle

Liao, Y.; Lucas, D.

Flashing of initially sub-cooled water in a converging-diverging nozzle is simulated with two-fluid model incorporating drag and non-drag forces. Phase change is assumed to be induced by interphase heat transfer. Comparison with experimental data is performed for 14 test runs under different temperature and pressure conditions. Good agreement is achieved for mass flow rate and cross-section averaged parameters. The reliability of the CFD predictions is obviously better than the ones obtained in 1D code. The transversal (radial) distribution of void fraction is however not satisfyingly reproduced. It is mainly caused by the neglect of nucleation as well as other uncertainties related to the prediction of mean bubble diameter. A poly-disperse approach with consideration of all relevant bubble dynamics is recommended for further work. For this purpose, reliable closure models and experimental data of bubble size information is required. In addition, cases characterised with large pressure-undershoot exhibit significant mechanical non-equilibrium.

Keywords: Flashing; Nozzle Flow; CFD Simulation; Two-Fluid Model

Publ.-Id: 21222

P1313 - Magnetisierbare Halbleiter und Oxide mit permanenter Magnetisierung, deren Herstellung und Verwendung

Schmidt, H.; Kaspar, T.; Bürger, D.; Skorupa, I.; Fiedler, J.

Die Erfindung beschreibt die Herstellung und den Aufbau einer Anordnung mit mindestens einer Raumladungszone, bei der sich im Bereich der Raumladungszone magnetische Polaronen stabil ausbilden. Weiterhin beschreibt die Erfindung, die Integration und die Verwendung der Anordnung in einem Spin-FET, in einem Spin-Ventil und in einer Spin-LED.

  • Patent
    DE102013209278 - Offenlegung 20.11.2014, Erteilung 18.02.2016, Nachanmeldung: WO

Publ.-Id: 21221

Baseline model for bubbly flows: Simulation of monodisperse flow in pipes of different diameters

Kriebitzsch, S.; Rzehak, R.

CFD simulations of the multiphase flow in technical equipment can provide a detailed insight into the local flow field and hence potentially be a valuable optimisation and design tool. Such simulations are feasible within the framework of interpenetrating continua, the so-called two-fluid modelling. Within this framework the interfacial transfer processes need to be modelled by suitable closure relations, many of which have been proposed in the literature. Predictions with multiphase CFD are only possible if a fixed set of closures is available that has been validated for a wide range of flow conditions and can therefore reliably be used also for unknown flow problems. To this end, a baseline model, which is applicable for adiabatic bubbly flow, has been specified recently (e.g. Rzehak and Krepper, 2013) and has been implemented into OpenFOAM (Rzehak and Kriebitzsch, 2015).
In this work we compare simulation results obtained using the baseline model with three different sets of experimental data for dispersed gas-liquid pipe flow given by Liu (1998), Shawkat et al. (2008), and Hosokawa and Tomiyama (2009). Air and water under similar flow conditions have been used in the different experiments, so that the main difference between the experiments is the variation of the pipe diameter from 25 mm to 200 mm. Overall all three experimental data sets are reasonably well reproduced by the simulation results, in particular in the bulk of the flow. The need for improved modelling of multiphase turbulence as well as wall effects manifests itself through larger differences with the experimental data in the near-wall region of the pipes.

Keywords: dispersed gas liquid multiphase flow; Euler-Euler two-fluid model; closure relations; CFD simulation; model validation; OpenFOAM

Publ.-Id: 21220

Plasma Dynamics in ultra-short relativistic laser-solid matter interactions and synthetic diagnostics using XFELs

Huang, L. G.; Bussmann, M.; Kluge, T.; Cowan, T. E.

Abundant and complex plasma dynamics are triggered by optical ultra-short high power lasers interacting on solid targets: such as atomic ionization, hot electron generation and transportation, collisions between the charged particles, return current, bulk electron heating, ion heating and acceleration, instabilities and so on. Controlling the relative dynamic processes requires modelling of transient, non-equilibrium processes on the atomic scale. We present particle-in-cell simulations which studied enhanced ion heating in buried layer targets [1], ionization dynamics and instabilities. In order to connect the plasma dynamics seen in simulations with experiments we will discuss the role of in-situ synthetic diagnostics that mimic experimental diagnostics. As one key example we propose to use X-Ray Free Electron Lasers for probing laser-driven solid-density plasmas by small angle X-ray scattering [2] which allows for femtosecond and nanometer resolution of transient plasma processes. With these techniques, probing fundamental plasma properties will allow for direct comparison to simulations, challenging state of the art theoretical modeling of collisions, ionization, radiation transport and atomic processes.

Keywords: Plasma dynamics; ion heating; ionization; instability; XFEL probing

  • Poster
    Radiative Properties of Hot Dense Matter, 29.09.-03.10.2014, Vienna, Austria

Publ.-Id: 21219

PolCarr® - Smart carriers for advanced manufacturing in biotechnology.

Wiesenhütter, K.; Urban, B.; Müller, M.; Müller, A.-D.; Skorupa, I.; Rüb, M.; Skorupa, W.; Schmidt, O. G.; Schmidt, H.

We propose a novel concept for functionalization of carriers (PolCarr®) by surface-near electrostatic forces for diverse applications in biotechnology. PolCarr® consists of a locally doped Si wafer with an ultra-thin insulating top layer and a characteristic pattern of surface near electrostatic forces (SNEF). The selective binding of the electrically polarizable material is purely driven by SNEF. By varying the type and concentration of the dopant ions, the strength and direction of surface-near electrostatic forces can be controlled. Further on, by attaching a structured bottom electrode to PolCarr® and bias altering, SNEF can be modulated precisely in the nm-µm-mm range, permitting transport and release of the target biomaterial.

Keywords: functionalization of carriers; biotechnology; surface-near electrostatic forces; semiconductor doping; biosensors; tissue engineering

  • Lecture (others)
    Innovation Days 2014 München, Research Meets Business, 01.-02.12.2014, München, Deutschland

Publ.-Id: 21218

PolCarr: Smart carriers for advanced manufacturing in biotechnology.

Wiesenhütter, K.; Urban, B.; Müller, M.; Müller, A.-D.; Skorupa, I.; Rüb, M.; Skorupa, W.; Schmidt, O. G.; Schmidt, H.

Further development of intelligent, highly-efficient and low-cost concepts in biosensors is a prime drive of the dynamically expanding biotechnology industry. As majority of the available market for biosensors is based on the functionalization of substrates, new approaches offering carriers with superior performance i.e. with easy-to-control immobilization, modification, transport and detection of the target analytes are strongly required. Consequently, herein we propose a novel, promising concept for fabrication of the smart carriers (PolCarr) for diverse applications in biotechnology. The PolCarr substrate consists of a doped Si wafer with an ultra-thin insulating top layer and a characteristic pattern of surface near electrostatic forces (SNEF) [Baumgart 2009]. The selective binding and release of the electrically polarizable molecules onto the PolCarr medium is purely driven by SNEF [Schmidt 2013]. Though, chemical-covalent and biological immobilization mechanisms are widely used by conventional biotechnology industry, they suffer from limited control. In stark contrast, the physical interaction via SNEF offers an excellent degree of control on the mm-nm scale. By attaching a structured bottom electrode to a locally doped Si wafer and voltage altering, SNEF can be precisely modulated in the nm range. Since SNEF are characterized by excellent environmental stability, the PolCarr carriers can be successfully utilized under a broad-spectrum of environmental conditions i.e. temperature, pH and humidity. The exceptional functionality of PolCarr makes it a suitable medium for typical biotechnology processing e.g. autoclaving for sterilization, incubation for cell growth, and for cryogenic applications for shock freezing, where conventional substrates may undergo critical failure. Finally, as the PolCarr technology originates from a standard, well-established semiconductor manufacture [Skorupa and Schmidt Springer 2014], the exceptionally facile carrier processing allows for realization of significant throughput and overall cost-reduction. Based on the highly-desirable and unique features of the PolCarr technology presented above, we strongly believe that our concept constitutes a high-value solution to the challenges faced by state-of-the-art biotechnology industry and may have a decisive impact on design and development of carriers for biotechnological manufacturing [Müller in preparation].
To protect the valuable IP, patent applications were filed in 2011 and 2012. To commercialize the PolCarr technology, a spin-off company is planned.

Keywords: biotechnology; biomaterials immobilization; carrier materials; biosensors; tissue engineering; doped Si-wafer; surface-near electrostatic forces; semiconductor industry

  • Lecture (others)
    Bionection Partnering Conference for Technology Transfer in Life Sciences, 09.-10.10.2014, Dresden, Deutschland

Publ.-Id: 21217

Advanced ms-annealing concepts for semiconducting oxides for PV applications.

Wiesenhuetter, K.; Lindberg, P.; Bregolin, F. L.; Prucnal, S.; Vines, L.; Mathey, A.; Wiesenhuetter, U.; Monakhov, E. V.; Svensson, B. G.; Skorupa, W.

The demand for high performance PV devices has led to vast advances in novel concepts for highly efficient PV products to be realized. Transparent conductive oxides (TCO) is one of the materials with a great potential towards PV applications and their indium tin oxide (ITO) is an industry viable option. The excellent set of properties demonstrated by ITO are stipled by its high cost and as a result given impetus to scientists to research for cheaper materials as an alternative. Consequently, Al- and Ga-doped ZnO (AZO and GZO) were identified as attractive candidates to replace the ITO-based PV components. However, to simultaneously ensure a higher conversion of solar energy to electricity and a significant reduction of the processing costs, further improvements of the AZO characteristics need to be achieved. Herein the authors propose application of advanced, millisecond annealing technologies e.g. flash lamp annealing (FLA) for the fabrication of the enhanced quality AZO for PV industry. As it will be shown, FLA offers effective recrystallization of the as-processed AZO films, activation of the Al dopants and creation of a defect-depleted AZO/c-Si interface. Superior opto-electrical response of the fabricated semiconductor heterostructures is achieved as a result. The application of ultra-short annealing times and selective heating option lead to an extraordinary time and energy conservation, opening up novel and low cost fabrication strategies for innovative PV products.

Keywords: transparent conductive oxide; thin-films; Al-doped ZnO; millisecond flash lamp annealing; interface; PV applications

  • Invited lecture (Conferences)
    E-MRS Fall Meeting 2014, 15.-18.09.2014, Warszawa, Polska

Publ.-Id: 21216

PolCarr®: Smart carriers for advanced nano-sensors and tissue engineering applications.

Wiesenhütter, K.; Urban, B.; Müller, M.; Müller, A.-D.; Skorupa, I.; Rüb, M.; Skorupa, W.; Schmidt, O. G.; Schmidt, H.

Further development of intelligent, highly-efficient and low-cost concepts in biosensors is a prime drive of the dynamically expanding biotechnology industry. As majority of the available market for biosensors is based on the functionalization of substrates, new approaches offering carriers with superior performance i.e. with easy-to-control immobilization, modification, transport and detection of the target analytes are required. Consequently, herein we propose a novel concept for fabrication of the smart carriers (PolCarr®) for diverse applications in biotechnology e.g. nano-sensors. The PolCarr® substrate consists of a doped Si wafer with an ultra-thin insulating top layer and a characteristic pattern of surface near electrostatic forces (SNEF). The selective binding and release of the electrically polarizable molecules onto the PolCarr® medium is purely driven by SNEF. Due to the excellent control degree at both the nm- and µm-range and the superb inertness of SNEF to environmental conditions, the PolCarr® carriers are very attractive candidates for tissue engineering and regenerative medicine, as they allow for directed cell growth. The exceptional functionality of PolCarr® makes it a suitable medium for typical biotechnology processing e.g. autoclaving for sterilization. As the PolCarr® technology originates from a standard semiconductor manufacture, the exceptionally facile carrier processing offers realization of significant throughput and overall cost-reduction.

Keywords: biotechnology; biosensors; controlled cell growth; carriers; biomaterials immobilization; doped-Si wafer; semiconductors manufacturing; surface-near electrostatic forces

  • Lecture (Conference)
    E-MRS Fall Meeting 2014, 15.-18.09.2014, Warszawa, Polska

Publ.-Id: 21215

Surface solid and liquid phase processing in the ms-range using flash lamp annealing.

Wiesenhütter, K.; Schumann, T.; Prucnal, S.; Bregolin, F.; Wutzler, R.; Reichel, D.; Mathey, A.; Zichner, R.; Lindberg, P.; Vines, L.; Wiesenhütter, U.; Svensson, B. G.; Skorupa, W.

Annealing is one of the oldest methods utilized by mankind for the manufacture of materials. Over the past millennium, thermal processing has evolved from its simple form to a highly sophisticated, mature technology. However, to meet modern requirements for novel, high performance products and to respond to dynamic progress in technology, new concepts in heat treatment that allow realization of innovative materials structures with superior functionality are required. Consequently, herein we demonstrate a successful application of ultra-short millisecond flash lamp annealing (for short FLA) for surface solid and liquid phase processing of advanced materials fabricated in the form of bulk, thin-films or complex nano-heterostructures [1]. Overall principles of FLA, the state-of-the-art facilities as well as selected FLA-applications developed at the HZDR will be presented. The ms-range FLA has already proven to be a highly promising alternative to standard heating technologies e.g. furnace annealing, which cannot meet the material-manufacture-property requirements imposed by modern devices e.g. large-area electronics printed on flexible, low-thermal budget media. As FLA enables a selective surface-near high temperature heating in ultra-short cycles, the high processing efficiencies with a substantial drop of the overall fabrication costs can be achieved. The numerous advantages of ms-range FLA are already widely exploited in the semiconductor industry. However, we believe there is still plenty of room for novel innovative applications of the ms-FLA to be identified and be successfully developed.
1. W. Skorupa and H. Schmidt, Springer Series in Materials Science, 192 (2014)

Keywords: millisecond flash lamp annealing; liquid phase processing; large-area electronics; thin-films; transparent conducting oxides; Al-doped ZnO; photovoltaics

  • Poster
    4th International Conference on Advances in Solidification Processes (ICASP-4), 08.-11.07.2014, Beaumont Estates, Old Windsor, United Kingdom

Publ.-Id: 21214

Functionalization of Printed Metal-Particle Suspensions by Millisecond Thermal Processing.

Wiesenhütter, K.; Schumann, T.; Zichner, R.; Gebel, T.; Wiesenhütter, U.; Skorupa, W.

The global quest towards novel, flexible and low-cost electronic products with functionality far beyond that offered by conventional size-restricted and rigid semiconductor devices, demands a rapid development of advanced material and deposition technology concepts. One of the most promising pathways to realize this ambitious goal is printed flexible electronics (PFE). Over the past years, printing has successfully demonstrated its potential for manufacture of manifold electronic products such as flexible displays, thin-film solar cells, large-area sensors etc. Importantly, by employing bendable, inexpensive media (e.g.: polymer foils, paper-like substrates) and high-throughput roll-to-roll (R2R) processing, a significant reduction of the overall costs associated with electronic device fabrication has been achieved.
Herein, we report on a successful application of ultra-fast millisecond flash lamp annealing (FLA) as a highly-attractive technique for the functionalization of Ag- and Cu-layers screen printed on low-thermal budget PET and paper-like media for e.g. antenna applications. The effect of the FLA parameters (i.e. pulse duration and energy density), on the substrate behavior as well as on the microstructure and electrical response of the as-flashed films was studied. A significant drop of the sheet resistance of the FL-treated layers as compared to the as-printed films was observed for the selected samples. As ms-FLA permits selective, near-surface heating, a damage of the sensitive substrates was avoided. Being highly-efficient (ultra-short), “non-destructive” (suitable for low-thermal tolerance flexible media) and compatible with R2R processing, FLA offers the realization of advanced PFE products.

Keywords: printed electronics; flash lamp annealing; roll-to-roll; flexible inexpensive substrates; Ag- and Cu-based inks

  • Poster
    E-MRS Spring Meeting 2014, 26.-30.05.2014, Lille, France

Publ.-Id: 21213

Advanced AZO processing via flash lamp annealing.

Bregolin, F. L.; Lindberg, P.; Wiesenhütter, K.; Vines, L.; Prucnal, S.; Svensson, B.; Skorupa, W.

Currently, indium tin oxide (ITO) is the most widely used transparent conductive oxide due to its outstanding properties. However, because of its high cost, several alternatives are being sought to replace it. Among them, the aluminum-doped zinc oxide (AZO) films are one of the most promising candidates for PV applications due their low resistivity, high transparency and most of all, their relative low cost of fabrication.
In this work, AZO films were deposited over Si wafers via r.f. magnetron sputtering and subsequently treated by millisecond-range flash lamp annealing (FLA). The fabricated layers were then characterized by sheet resistance, photoluminescence spectroscopy, X-ray diffraction and Hall effect measurements. The influence of the deposition temperature and FLA parameters on the microstructure and optoelectronic response of the AZO layers was studied in detail. It was demonstrated that the FLA technique significantly improves the electrical conductivity of the as-deposited AZO layers due to the Al activation, the increase in crystallinity as well as the passivation of defects and grain boundaries. In particular, the room temperature sputtered AZO films subsequently treated by FLA have shown performance characteristics similar to those sputtered at 400 ºC, opening the possibility for further cost reductions in the fabrication process. The FLA technique is a cost-effective and high-throughput alternative for the processing of Si-based heterojunction solar cells.

Keywords: Transparent Conductive Oxides; Al-doped ZnO; Flash Lamp Annealig; Photovoltaics

  • Poster
    E-MRS Spring Meeting 2014, 26.-30.05.2014, Lille, France

Publ.-Id: 21212

PolCarr - Smarte Trägermaterialien für die Biotechnologie

Schmidt, H.; Wiesenhütter, K.; Teichmann, D.

Das smarte Trägermaterial PolCarr® besteht aus dotiertem Silizium und umfasst eine isolierende Deckschicht sowie eine strukturierte Rückseitenelektrode. Die Dotierung des Siliziums verursacht die Ausbildung oberflächennaher, elektrostatischer Kräfte, deren Stärke und Richtung durch die Konzentration und Spezies der implantierten Ionen auf der Nanometer- bis Millimeterlängenskale kontrolliert eingestellt wird. Elektrisch polarisierbare Zellen oder Moleküle können an PolCarr® angezogen, ausgerichtet und immobilisiert werden.

Keywords: Trägermaterialien; Biosensoren; Zellwachstumsplatten

  • Lecture (others)
    Cross Cluster Cooperation-Projekt „C3-Saxony“, IDEA CALL zum 9. Silicon Saxony Day, 03.07.2014, Dresden, Deutschland
  • Lecture (others)
    Cross Cluster Cooperation-Projekt „C3-Saxony“ IDEA CALL zum 9. Silicon Saxony Day, 03.07.2014, Dresden, Deutschland

Publ.-Id: 21211

Smart carriers for advanced nano-sensors and tissue engineering applications.

Wiesenhütter, K.; Skorupa, I.; Rüb, M.; Müller, M.; Skorupa, W.; Schmidt, O. G.; Schmidt, H.

A paramount drive of the rapidly growing biotechnology sector is the further development of intelligent, highly-efficient and inexpensive concepts for biosensors. As the key component of a biochip platform, biosensors hold a responsibility for immobilization, modification, transport and detection of a variety of biological analytes broadly utilized in health care, food industry and environmental monitoring. To augment the overall biosensor performance, much effort has been dedicated to designate the new, superior carrier materials, which permit easy-to-control immobilization of the target analytes. Consequently, herein we do propose a novel, promising concept for the smart carriers’ fabrication which is named PolCarr. PolCarr consists of doped silicon wafers and ultra-thin insulating top layers and exploits surface-near electrostatic forces (SNEF) [1-2] for the selective adsorption of electrically polarizable bioanalytes and functionalized polymers [3]. The binding and release of molecules onto the PolCarr substrate is purely driven by SNEF. By attaching a structured bottom electrode to locally doped silicon wafers and by a careful voltage altering, the SNEF can precisely be controlled on the nm-length scale, enabling realization of new, advanced products for manifold medical applications (for instance: nano-sensors). Further on, the excellent control degree at both the nm- and µm-range and the superb inertness of SNEF to environmental influences make PolCarr carriers very attractive candidates for tissue engineering and regenerative medicine, as they allow the growth of the target cells in a highly-desirable ordered manner. As PolCarr permits exceptionally facile manufacture by ion implantation and thermal dopant activation [4] and as PolCarr is compatible with well-developed standard semiconductor processing, the significant throughput and overall cost-reduction associated with the entire carrier’s production and its subsequent use as an integral part of a medical device (e.g.: biochip), can be achieved. Considering the whole benefits offered by our smart carriers, we strongly believe that the PolCarr concept can thoroughly transform traditional biosensor- and tissue engineering-oriented technologies [5]. Finally, the unique selling points of the innovative and proprietary technology offer from our point of view a high value proposition compared to state of the art technology. In order to protect the valuable intellectual property, patent applications were filed in 2011 and 2012. For the future commercialization of the technology a spin-off company is planned. The start-up team is formed by an experienced business developer and key scientists. Cooperations for the biochip development are already established. In addition, the team is supported by technology transfer partners of the Helmholtz Zentrum Dresden Rossendorf. [1] Quantitative dopant profiling in semiconductors: A Kelvin probe force microscopy model, C. Baumgart, M. Helm, H. Schmidt, Phys. Rev. B 80 (2009) 085305. [2] Kelvin probe force microscopy in the presence of intrinsic local electric fields, C. Baumgart, A.-D. Müller, F. Müller, H. Schmidt, Phys. Stat. Sol. (A) 208 (2011) 777–789. [3] Kelvin probe force microscopy for characterizing doped semiconductors for future sensor applications in nano- and biotechnology, H. Schmidt, S. Habicht, S. Feste, A.D. Müller, O.G. Schmidt, Appl. Surf. Sci. 281 (2013) 24-29 (invited). [4] Subsecond Annealing of Advanced Materials Annealing by Lasers, Flash Lamps and Swift Heavy Ions (Eds.: Wolfgang Skorupa, Heidemarie Schmidt), Springer-Verlag, ISBN: 978-3-319-03130-9 (2014). [5] Selective polyelectrolyte adsorption at novel charge patterned carrier materials for future biosensor applications, M. Müller, B. Urban, A.-D. Müller, M. Rüb, K. Wiesenhütter, I. Skorupa, O.G. Schmidt, H. Schmidt, Materials (2014), in preparation (invited).

Keywords: Biotechnology; biosensors; tissue engineering; carriers; doped Si-wafers; Surface-Near Electrostatic Forces

  • Poster
    Saxon Biotechnology Symposium 2014, Dresden, 19.03.2014, Dresden, Deutschland

Publ.-Id: 21210

Pressure-induced shift of energy levels and structural phase transition in CdSe/ZnS quantum dots

Tauch, J.; Braun, J. M.; Keller, J.; Hinz, C.; Haase, J.; Seletskiy, D. V.; Leitenstorfer, A.; Pashkin, A.

Electronic band structure of CdSe/ZnS quantum dots under high pressures is studied using fluorescence spectroscopy. We observe a strong blue shift of about 50 meV/GPa for the emission line at 655 nm. At moderate pressures (below 3 GPa) this shift is linear and it is dominated by increase of the fundamental band gap of CdSe under pressure [1]. In contrast to bulk CdSe where the fluorescence is quenched above 3 GPa as a results of the phase transition into the rock-salt structure, the CdSe/ZnS quantum dots remain structurally stable up to 6.5 GPa. The shift of the fluorescence line below this pressure is strongly nonlinear with tendency to saturation. This behavior can be well described using the Murnaghan equation of state giving the deformation potential value of -3.5 eV.
The remarkably high pressure of the structural phase transition in the studied CdSe/ZnS quantum dots exceeds previously reported values for CdSe nanocrystals [2] and bulk CdSe [1]. Presumably, the wurtzite structure of the quantum dots is stabilized by the ZnS shell. This structural robustness together with the high fluorescence yield and the large pressure coefficient of the wavelength shift make CdSe quantum dots a promising alternative to bulk ruby crystals for precise pressure calibration at moderate pressures.

[1] W. Shan et al., Appl. Phys. Lett. 84, 67 (2004).
[2] S. H. Tolbert and A. P. Alivisatos, J. Chem. Phys. 102, 4642 (1995).

Keywords: quantum dots; high pressure; structural phase transition

  • Poster
    Pressure and Strain Effects in Correlated Electron Materials, 06.-10.10.2014, Dresden, Germany

Publ.-Id: 21209

Above Room Temperature Ferromagnetism in Co- and V-Doped TiO2 — Revealing the Different Contributions of Defects and Impurities

Semisalova, A. S.; Mikhailovsky, Yu. O.; Smekhova, A.; Orlov, A. F.; Perov, N. S.; Gan’shina, E. A.; Lashkul, A.; Lahderanta, E.; Potzger, K.; Yildirim, O.; Aronzon, B.; Granovsky, A. B.

We report recent experimental results on themagnetic, magnetotransport, and magneto-optical properties of Co- and V-doped TiO2−δ magnetic oxides at the doping level around 1 at. %. The samples were prepared using rf magnetron sputtering in identical conditions that allows to compare the mechanisms of above-room-temperature ferromagnetism observed in both cases of doping. In spite of the comparable values of magnetic moment around 1 ÷ 2.5 μB per 3d impurity derived from macroscopic magnetic measurements for both systems, the magneto-optical response of TiO2−δ :V was at least 2 orders of magnitude weaker. The anomalous Hall effect was absent in V-doped TiO2−δ, and no appreciable magnetic moment on V impurities was found by X-ray magnetic circular dichroism (XMCD) technique in contrast to Co-doped TiO2−δ. The obtained experimental data indicate dissimilar origin of intrinsic ferromagnetismin TiO2−δ:Co and TiO2−δ:V.

Keywords: Doped TiO2; Magnetic semiconductors; Oxygen vacancy; Defect-induced ferromagnetism

Publ.-Id: 21207

Ultrafast dynamics in CeTe3 across the pressure-induced charge-density-wave transition

Tauch, J.; Schäfer, H.; Obergfell, M.; Demsar, J.; Giraldo, P.; Fisher, I. R.; Pashkin, A.

Time-resolved optical spectroscopy is a powerful tool for studying ultrafast dynamics of quasiparticles and phonons in strongly correlated electronic systems. In particular, this technique has been efficiently utilized for investigation of charge-density-wave (CDW) compounds [1-3]. In all these studies the system has been tuned across the boundary of the CDW phase by temperature variation. However, application of external (or chemical) pressure can also lead to a suppression of a CDW state caused by an impairment of the Fermi surface nesting [4].
Here, we combine femtosecond time-resolved optical spectroscopy and a diamond anvil cell technology to study the electron and lattice dynamics in tri-telluride compound CeTe3. The optical pump-probe measurements (400 nm pump and 800 nm probe wavelength, respectively) are performed on single crystals mounted inside the pressure cell. CsI has been used as a pressure transmitting medium. Around pressures of 4 GPa we observe a gradual vanishing of the relaxation process related to the recombination of the photoexcited quasiparticles. The coherent oscillations of the phonon modes coupled to the CDW order parameter demonstrate even more dramatic suppression with increasing pressure . These observations clearly indicate a transition into the metallic state of CeTe3 induced by the external pressure.

[1] J. Demsar et al., Phys. Rev. Lett. 83, 800 (1999).
[2] J. Demsar et al., Phys. Rev. B 66, 041101 (2002).
[3] R.V. Yusupov et al., Phys. Rev. Lett. 101, 246402 (2008).
[4] A. Sacchetti et al., Phys. Rev. Lett. 98, 026401 (2007).

Keywords: Time-resolved optical spectroscopy; high pressure; charge-density-waves

  • Poster
    Pressure and Strain Effects in Correlated Electron Materials, 06.-10.10.2014, Dresden, Germany

Publ.-Id: 21206

Simulation and Experimental Verification of Prompt Gamma-ray Emissions during Proton Irradiation

Schumann, A.; Petzoldt, J.; Dendooven, P.; Enghardt, W.; Golnik, C.; Hueso-González, F.; Kormoll, T.; Pausch, G.; Roemer, K.; Fiedler, F.

Irradiation with protons and light ions offers new possibilities for tumor therapy but has a strong need for novel imaging modalities for treatment verification. The development of new detector systems, which can provide an in vivo range assessment or dosimetry, requires an accurate knowledge of the secondary radiation field and reliable Monte Carlo simulations. This paper presents multiple measurements to characterize the prompt γ-ray emissions during proton irradiation and benchmarks the latest Geant4 code against the experimental findings. Within the scope of this work, the total photon yield for different target materials, the energy spectra as well as the γ-ray depth profile were assessed. Experiments were performed at the superconducting AGOR cyclotron at KVI-CART, University of Groningen. Properties of the γ-ray emissions were experimentally determined. The prompt γ-ray emissions were measured utilizing a conventional HPGe detector system (Clover) and quantitatively compared to simulations. With the selected physics list QGSP BIC HP, Geant4 strongly verestimates the photon yield in most cases, sometimes up to 50 %. The shape of the spectrum and qualitative occurrence of discrete γ lines is reproduced accurately. A sliced phantom was designed to determine the depth profile of the photons. The position of the distal fall-off in the simulations agrees with the measurements, albeit the peak height is also overestimated. Hence, Geant4 simulations of prompt γ-ray emissions from irradiation with protons are currently not as reliable as simulating electromagnetic processes. Deviations from experimental findings were observed and quantified. Although there has been a constant improvement of Geant4 in the hadronic sector, there still remains a gap to close.

Keywords: proton therapy; prompt gamma imaging; Geant4

Publ.-Id: 21205

HADES results in elementary reactions

Ramstein, B.; Adamczewski-Musch, J.; Arnold, O.; Atomssa, E. T.; Behnke, C.; Berger-Chen, J. C.; Biernat, J.; Blanco, A.; Blume, C.; Böhmer, M.; Bordalo, P.; Chernenko, S.; Deveaux, C.; Dybczak, A.; Epple, E.; Fabbietti, L.; Fateev, O.; Fonte, P.; Franco, C.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzón, J. A.; Gill, K.; Golubeva, M.; Guber, F.; Gumberidze, M.; Harabasz, S.; Hennino, T.; Hlavac, S.; Höhne, C.; Holzmann, R.; Ierusalimov, A.; Ivashkin, A.; Jurkovic, M.; Kämpfer, B.; Karavicheva, T.; Kardan, K.; Koenig, I.; Koenig, W.; Kolb, B. W.; Korcyl, G.; Kornakov, G.; Kotte, R.; Krása, A.; Krebs, E.; Kuc, H.; Kugler, A.; Kunz, T.; Kurepin, A.; Kurilkin, A.; Kurilkin, P.; Ladygin, V.; Lalik, R.; Lapidus, K.; Lebedev, A.; Lopes, L.; Lorenz, M.; Mahmoud, T.; Maier, L.; Mangiarotti, A.; Markert, J.; Metag, V.; Michel, J.; Müntz, C.; Münzer, R.; Naumann, L.; Palka, M.; Parpottas, Y.; Pechenov, V.; Pechenova, O.; Petousis, V.; Pietraszko, J.; Przygoda, W.; Rehnisch, L.; Reshetin, A.; Rost, A.; Rustamov, A.; Sadovsky, A.; Salabura, P.; Scheib, T.; Schmidt-Sommerfeld, K.; Schuldes, H.; Sellheim, P.; Siebenson, J.; Silva, L.; Sobolev, Y. G.; Spataro, S.; Ströbele, H.; Stroth, J.; Strzempek, P.; Sturm, C.; Svoboda, O.; Tarantola, A.; Teilab, K.; Tlusty, P.; Traxler, M.; Tsertos, H.; Vasiliev, T.; Wagner, V.; Wendisch, C.; Wirth, J.; Wüstenfeld, J.; Zanevsky, Y.; Zumbruch, P.

Recent results obtained with the HADES experimental set-up at GSI are presented with a focus on dielectron production and strangeness in pp and quasi-free np reactions. Perspectives related to the very recent experiment using the pion beam at GSI are also discussed.

Publ.-Id: 21204

Transmutation von Transuranen unter den Randbedingungen des Kernenergieausstiegs – Ist das technisch machbar?

Merk, B.; Rohde, U.

Die deutsche Regierung hat den Ausstieg aus der Kernenergie beschlossen, aber der Umgang mit den hochradioaktiven Abfällen ist noch nicht geklärt. Partitionierung und Transmutation (P&T) kann als technologische Option im Prozess des Umgangs mit hochradioaktiven Abfällen betrachtet werden, dazu wurde eine umfangreiche Studie durchgeführt. In diesem Rahmen wurden auch Ziele für P&T unter der Maßgabe des Kernenergieausstiegs diskutiert. In den vorliegenden Simulationsrechnungen wird analysiert inwieweit diese Ziele unter dem Einsatz von Salzschmelzenreaktoren mit schnellem Neutronenspektrum erreicht werden können. Er wird gezeigt, dass eine effiziente Transmutation aller in Deutschland zum Abschaltzeitpunkt existierenden Transurane mit 3 bis 4 Anlagen in 45 bis 60 Jahren machbar wäre. Ferner wird eine detaillierte Bilanzierung verschiedener Inventare zum tieferen Verständnis der Vorgänge in der Transmutation präsentiert.
The German government has decided for the nuclear phase out, but a decision on a strategy for the management of the highly radioactive waste is not defined yet. Partitioning and Transmutation (P&T) could be considered as a technological option in the process of management of highly radioactive waste management, therefore a wide study has been conducted. In this group objectives for P&T und the boundary conditions of the phase out have been discussed. The fulfillment of the given objectives is analyzed using simulations of molten salt reactors with fast neutron spectrum. It is shown that the efficient transmutation of all existing transuranium isotopes would be possible in 3 to 4 reactors in a time frame of 45 to 60 years. Further on a detailed balance of different isotopic inventories is given to allow a deeper understanding of the processes during transmutation.

Keywords: nuclear; nuclear reactor; molten salt; molten salt reactor; transmutation; nuclear waste management; nuclear phase out

  • Contribution to proceedings
    Jahrestagung Kerntechnik, 05.05.2015, Berlin, Deutschland

Publ.-Id: 21203

Two-dimensional and tubular structures of misfit compounds: Structural and electronic properties

Lorenz, T.; Joswig, J.-O.; Seifert, G.

Misfit layer compounds are structures that consist of two sublattices differing in at least one of their lattice constants. The two different layers are stacked either an alternating or in a more complex series resulting in mono- or multi-layer misfit compounds. To date, planar and bent misfit structures, such as tubes, scrolls or nanoparticles, have been synthesized and interesting magnetic and physical properties have been observed as a result of their special structures. Based on these observations, we present an overview of such misfit systems and summarize and discuss their electronic structure as well as the interlayer bonding behaviour, which is not completely understood yet. Furthermore, a more detailed insight into the SnS–SnS2 system is given, which was the first tubular misfit compound that has been synthesized and extensively investigated.

Keywords: 2D layered materials; misfit layer compounds

Publ.-Id: 21202

Optical properties of triangular molybdenum disulfide nanoflakes

Wendumu, T. B.; Seifert, G.; Lorenz, T.; Joswig, J.-O.; Enyashin, A.

The results from calculations of optical and electronic properties of triangular MoS2 nanoflakes with edge lengths ranging from 1.6 to 10.4 nm are presented. The optical spectra were calculated using the time-dependent extension of the density-functional tight-binding method (TD-DFTB). The size effect in the optical absorption spectra is clearly visible. With decreasing length of the nanoflakes edges, the long-wavelength absorption in the range of visible light is shifted toward short-wavelength absorption, confirming a quantum-confinement-like behavior of these flakes. In contrast, the edges of the nanoflakes exhibit a distinct metallic-like behavior. The relation of the absorption properties to the observed photoluminescence of MoS2 nanoflakes is discussed in a qualitative manner.

Keywords: Molybdenum disulfide; Nano-flakes

  • The Journal of Physical Chemistry Letters 5(2014)21, 3636-3640
    DOI: 10.1021/jz501604j

Publ.-Id: 21201

Linear thermal expansion, thermal diffusivity and melting temperature of Am-MOX and Np-MOX

Prieur, D.; Belin, R. C.; Manara, D.; Staicu, D.; Richaud, J.-C.; Vigier, J.-F.; Scheinost, A. C.; Somers, J.; Martin, P.

The thermal properties of Np- and Am-MOX solid solutions were investigated. The linear thermal expansion was investigated with high temperature X-ray diffraction from room temperature to 1973 K. No significant difference was observed between the Np and the Am doped MOX. The thermal conductivity of Am-MOX is about 10% higher than that of Np-MOX. The melting temperatures of Np-MOX and Am-MOX were measured using a laser heating setup and are equal to 3020 ± 30 K and 3005 ± 30 K, respectively.

Keywords: Transmutation; minor actinides; MOX; XANES; XRD; thermal conductivity; laser melting

Publ.-Id: 21200

Drag and turbulence modelling for free surface flows within the two-fluid Euler-Euler framework

Porombka, P.; Höhne, T.

Two-phase flows are regularly involved in the heat and mass transfer in industrial processes. To ensure the safety and efficiency of such processes, an accurate prediction of the flow field and phase distribution by means of Computational Fluid Dynamics (CFD) is required. Nowadays, Direct numerical simulations (DNS) of large-scale two-phase flow problems are not feasible due to the computational costs involved. Therefore the Euler-Euler framework is often employed for large-scale simulations which involves macro-scale modelling of turbulence, mass and momentum transfer. The research activities at Helmholtz-Zentrum Dresden - Rossendorf (HZDR) focus on general closure models for multiphase flows that are closer to physics and include less empiricism. As part of this effort an Algebraic Interfacial Area Density model (AIAD) is developed for the morphology detection in the two-fluid Euler-Euler approach. Drag models for free surface flows are often based on experimental correlations, their applicability thus being limited to certain flow regimes. In this paper a modified free-surface drag model based on local shear stress is investigated that avoids this limitation. For this purpose the algebraic morphology detection mechanism of the AIAD model is revised. In DNS of free surface flow a dampening of the gas side turbulent fluctuations in the near surface region was found by previous investigators. This effect has also been accounted for in Euler-Euler simulations by means of dampening functions. In this work the significance of turbulence dampening in case of free surface flows is examined quantitatively for the k-omega turbulence model. For this purpose steady-state simulations of countercurrent stratified air-water flow have been performed using the commercial CFD code ANSYS CFX. The results are here presented and compared to experimental data. The revised morphology detection mechanism is seen as an improvement with respect to the detection of sharp interfaces. Satisfactory quantitative agreement is achieved for the modified free surface drag model based on experimental pressure difference, liquid levels and interfacial shear stress. Furthermore, it is demonstrated that turbulence dampening has to be accounted for in the k-omega model to qualitatively reproduce the mean flow and turbulence quantities from the experiment. More CFD grade experimental data is required for further model validation.

Keywords: CFD; two-phase flow; drag modelling; free surface; turbulence dampening; AIAD

Publ.-Id: 21199

Closures for simulation of gas-liquid flows in solid foam structures

Subramanian, K.; Baldota, R.; Schubert, M.; Lucas, D.; Hampel, U.

Ceramic foam packings are promising alternatives for packing internals used in chemical engineering processes due to their high porosity and high specific surface area, which results in low pressure drop and high catalytically utilization of the packing. The aim of this work is to perform three-dimensional Computational Fluid Dynamics (CFD) simulations of the evolving gas-liquid flow patterns considering ceramic foams as column internals and to validate them with experimental X-ray tomographic studies. The closures from trickle bed studies are modified according to the ceramic foam specifications considering the flow domain as porous.

Keywords: Multiphase flow; CFD; Ceramic foams; X-ray tomography

  • Lecture (Conference)
    ISCRE 23 & APCRE 7, 07.-10.09.2014, Bangkok, Thailand

Publ.-Id: 21198

Speciation of uranium in compartments of living cells

Geipel, G.; Viehweger, K.

Depleted uranium used a ammunition corrodes in the environment forming mineral phases and then dissolved uranium species like uranium carbonates (Schimmack et al. 2007) and hydroxides. These hydroxide species were contacted with plant cells (canola). After 24 h contact time the cells were fractionated and the uranium speciation in the fraction was determined by TRLFS (time resolved laser-induced fluorescence spectroscopy) at room temperature as well at 150K. It could be shown that the uranium speciation in the fractions is different to that in the nutrient solution. Comparison of the emission bands with literature data allows assignment of the uranium binding forms.

Keywords: Uranium; plant cells; Spectroscopy


Publ.-Id: 21197

Evolution of Spin Wave Modes in Periodically Perturbed Thin Films

Langer, M.; Gallardo, R.; Banholzer, A.; Jansen, A.; Schneider, T.; Wagner, K.; Demidov, V.; Demokritov, S. O.; Landeros, P.; Lenz, K.; Lindner, J.; Fassbender, J.

Periodic perturbations of a magnetic thin film lead to a dipolar contribution proportional to –k (for ultrathin films: k•d << 1) in the dispersion relation of backward volume spin waves additional to the exchange term, which goes quadratically with k. If the scattering condition is fulfilled, meaning the k-vector matches a multiple of the reciprocal lattice vector g0 = 2π/a0, spin waves can scatter into excited magnonic states. This process is referred to as two-magnon scattering (TMS).
In this work, TMS is investigated by introducing periodic defects by Cr+ ion beam irradiation on the surface of a d = 30 nm thick permalloy (Ni80Fe20) film. Patterning was achieved using a PMMA mask, which was pre-structured by electron beam lithography (EBL) and subsequently exposed to a low energy Cr ion beam. Selecting ion energy and fluence, the effective depth of such perturbations can be controlled to investigate the transition from a surface perturbed thin film towards a full magnonic crystal.
The FMR spectra f(H) (see Fig.1) of different samples with varying perturbation depth h and a periodicity a0 ranging from 200 nm to 400 nm have been measured showing mode splitting at each crossing point of higher spin wave modes with the uniform mode due to TMS. Moreover, brillouin light scattering (BLS) measurements have been performed to directly measure the dispersion relation of such periodically perturbed film.
In a further experiment, the evolution of FMR mode splitting dependent on the perturbation depth h was investigated performing multi-step reactive Ar+ ion beam etching (RIBE) of surface steps on a 30 nm permalloy film.
Theoretical calculations based on a perturbation theory[1,2] are accompanied and reveal a good agreement of experiment and theory (see Fig.1). Amongst that, numerical simulations of the FMR spectra were carried out using the MuMax3 code allowing for deeper understanding of the micromagnetic structure of the observed magnonic modes, such as the visualization of the dynamic magnetization.
This work has been supported by DFG grant no. LE2443/5-1.
[1] P. Landeros and D. L. Mills, Phys. Rev. B 85, 054424 (2012).
[2] R. A. Gallardo, A. Banholzer, K. Wagner, M. Körner, K. Lenz, M. Farle, J. Lindner, J. Fassbender and P. Landeros, New J. Phys 16, 023015 (2013).
[3] M. Körner, K. Lenz, R. A. Gallardo, M. Fritzsche, A. Mücklich, S. Facsko, J. Lindner and J. Fassbender, Phys. Rev. B 88, 054405 (2103).

Keywords: Spin Waves; Magnons; Manonics; Magnetization Dynamics; Ferromagnetic Resonance; FMR; Ion Irradiation; Micromagnetic Simulation

  • Lecture (Conference)
    59th Annual Magnetism and Magnetic Materials Conference (MMM) 2014, 03.-07.11.2014, Honolulu, Hawaii, USA

Publ.-Id: 21196

Underground nuclear astrophysics for the Sun, and for the Big Bang (updated)

Bemmerer, D.

After the resolution of the solar neutrino problem in 2002, the study of the Sun has now entered a precision era, and an entirely new dilemma has come up: New elemental abundance data from Fraunhofer line analyses are in contradiction with helioseismological observables. Observations of 13N and 15O neutrinos from the Sun may address this so-called solar abundance problem, but their interpretation will require precise nuclear reaction data. Due to the low cross sections involved, such data can only be provided by experiments in an underground low-background setting. Work at the world's only underground accelerator, the 0.4 MV LUNA machine in Gran Sasso (Italy), on solar fusion reactions and on the Big Bang production of lithium-6 and -7 will be reviewed. In addition, some surface-based data on radiative capture reactions on 12C, 14N, and 40Ca will be shown. The status and working program of the planned higher-energy underground accelerator at the Dresden Felsenkeller in Germany will be discussed.

Keywords: Felsenkeller; Underground nuclear astrophysics; Big Bang nucleosynthesis

  • Invited lecture (Conferences)
    Joint Institute for Nuclear Astrophysics Seminar, 10.11.2014, South Bend, Indiana, USA
  • Lecture (others)
    Seminar, 14.11.2014, Seattle, Washington, USA

Publ.-Id: 21195

A new study of the 22Ne(p,γ)23Na reaction deep underground: Feasibility, setup, and first observation of the 186 keV resonance

Cavanna, F.; Depalo, R.; Menzel, M.-L.; Aliotta, M.; Anders, M.; Bemmerer, D.; Broggini, C.; Bruno, C. G.; Caciolli, A.; Corvisiero, P.; Davinson, T.; Di Leva, A.; Elekes, Z.; Ferraro, F.; Formicola, A.; Fülöp, Z.; Gervino, G.; Guglielmetti, A.; Gustavino, C.; Gyürky, G.; Imbriani, G.; Junker, M.; Menegazzo, R.; Prati, P.; Rossi Alvarez, C.; Scott, D. A.; Somorjai, E.; Straniero, O.; Strieder, F.; Szücs, T.; Trezzi, D.

The 22Ne(p,γ)23Na reaction takes part in the neon-sodium cycle of hydrogen burning. This cycle is active in asymptotic giant branch stars as well as in novae and contributes to the nucleosythesis of neon and sodium isotopes. In order to reduce the uncertainties in the predicted nucleosynthesis yields, new experimental efforts to measure the 22Ne(p,γ)23Na cross section directly at the astrophysically relevant energies are needed. In the present work, a feasibility study for a 22Ne(p,γ)23Na experiment at the Laboratory for Underground Nuclear Astrophysics (LUNA) 400\,kV accelerator deep underground in the Gran Sasso laboratory, Italy, is reported. The ion beam induced γ-ray background has been studied. The feasibility study led to the first observation of the Ep = 186\,keV resonance in a direct experiment. An experimental lower limit of 0.12\,×\,10−6\,eV has been obtained for the resonance strength. Informed by the feasibility study, a dedicated experimental setup for the 22Ne(p,γ)23Na experiment has been developed. The new setup has been characterized by a study of the temperature and pressure profiles. The beam heating effect that reduces the effective neon gas density due to the heating by the incident proton beam has been studied using the resonance scan technique, and the size of this effect has been determined for a neon gas target.

Keywords: LUNA; underground nuclear astrophysics; asymptotic giant branch stars; novae

Publ.-Id: 21194

Process-based forward numerical ecological modelling for carbonate sedimentary basins

Clavera-Gispert, R.; Carmona, A.; Gratacós, O.; Tolosana-Delgado, R.

Nowadays, numerical modelling is a significant tool used both by researchers and the industry in the study of sedimentary basins, since it allows to quantify the simulated processes and to determine interactions among them. One of such programs is SIMSAFADIM-CLASTIC, a 3D forward-model process-based code to simulate the sedimentation in a marine basin at geological scale. It models the fluid flow, siliciclastic transport and sedimentation, and carbonate production. In this article, we present the last improvements in carbonate production, in particular the usage of Generalized Lotka-Volterra equations, that include logistic growth and interaction among species. Logistic growth is linked to environment parameters such as water depth, energy of the medium, and slope to the model the growing of species. The environmental parameters are factorized and combined to obtain an environment parameter that is applied to compute the modelled species development. The interaction among species is quantified using the community matrix that captures the beneficial or detrimental effects of the presence of each species on the other. A theoretical example of a carbonate ramp is computed to model the interaction among carbonate and siliciclastic sediment, the affection of environmental parameters to the modelled species, and the interaction among species. The distribution of the modelled species associations in the theoretical example is compared with Asmari Formation in Iran and Ragusa Platform in Italy.

Keywords: Forward-Model; process-based; sedimentary basin; ecological model; carbonate production; SIMSAFADIM-CLASTIC


  • Secondary publication expected

Publ.-Id: 21193

Measurement of the analysing power in proton-proton elastic scattering at small angles

Bagdasarian, Z.; Chiladze, D.; Dymov, S.; Kacharava, A.; Macharashvili, G.; Barsov, S.; Gebel, R.; Gou, B.; Hartmann, M.; Keshelashvili, I.; Khoukaz, A.; Kulessa, P.; Kulikov, A.; Lehrach, A.; Lomidze, N.; Lorentz, B.; Maier, R.; Mchedlishvili, D.; Merzliakov, S.; Mikirtychyants, S.; Nioradze, M.; Ohm, H.; Papenbrock, M.; Prasuhn, D.; Rathmann, F.; Serdyuk, V.; Shmakova, V.; Stassen, R.; Stockhorst, H.; Strakovsky, I. I.; Ströher, H.; Tabidze, M.; Täschner, A.; Trusov, S.; Tsirkov, D.; Uzikov, Y.; Valdau, Y.; Wilkin, C.; Workman, R. L.

The proton analysing power in p→p elastic scattering has been measured at small angles at COSY-ANKE at 796 MeV and five other beam energies between 1.6 and 2.4 GeV using a polarised proton beam. The asymmetries obtained by detecting the fast proton in the ANKE forward detector or the slow recoil proton in a silicon tracking telescope are completely consistent. Although the analysing power results agree well with the many published data at 796 MeV, and also with the most recent partial wave solution at this energy, the ANKE data at the higher energies lie well above the predictions of this solution at small angles. An updated phase shift analysis that uses the ANKE results together with the World data leads to a much better description of these new measurements.

Publ.-Id: 21192

High-performance QWIPs and time-resolved terahertz spectroscopy with a free-electron laser

Schneider, H.

There is no abstract.

  • Lecture (others)
    Seminar, Kunming Institute of Physics, 17.10.2014, Kunming, China

Publ.-Id: 21190

Microstructural changes in highly irradiated 15Kh2MFA steel

Gillemot, F.; Horváth, A.; Horváth, M.; Kovács, A.; Radiguet, B.; Cammelli, S.; Pareige, P.; Hernandez-Mayoral, M.; Ulbricht, A.; Kresz, N.; Oszwald, F.; Török, G.

15Kh2MFA-type steel forgings were irradiated in an accelerated surveillance position of a power reactor, up to about 1 × 1021 n/cm2, E> 1 MeV with medium flux. This steel is a Cr-Mo-V-type low-copper reactor pressure vessel material. 15Kh2MFA was microstructurally tested as received and in three different irradiation states within the frame of the LONGLIFE project. The following microstructural tests were performed: metallography, fractography, transmission electron microscopy, small angle neutron scattering, and atom-probe tomography. The aim of the current paper is to summarize the results that were evaluated by the six European institutes performing the study. The SANS tests show that the cluster volume fraction growth is nearly linear as a function of the fluence, and atom-probe tomography concludes that vanadium carbide precipitations were already originally present in the as-received steel. During irradiation these precipitates are enriched with Mo, Cu, and Cr. At the highest dose Mn, Si, and Ni are also attached to these clusters.

Keywords: Clusters; Dislocations; Irradiation; Microstructural testing; Precipitations

  • Contribution to proceedings
    26th International Symposium - Effects of Radiation on Nuclear Materials, 12.-13.06.2013, Indianapolis, US
    Effects of Radiation on Nuclear Materials: 26th Volume, ASTM STP 1572, West Conshohocken, PA, USA: ASTM International, 978-0-8031-7589-1, 45-56
    DOI: 10.1520/STP157220130098

Publ.-Id: 21189

Quantitative differentiation of sulfur in different oxidation states (-II and +VI) by WD-XRF

Uhlig, S.; Möckel, R.; Pleßow, A.

Sulfur is one of the most abundant non-metals in the Earth’s crust and a key component of sulfidic ores. A number of methods for the determination of the total sulfur content in geochemical samples are available in the literature. However, sulfur appears in numerous oxidation states. Sulfide (-II) and sulfate (+VI) are the most common ones, but options for a analytical chemical differentiation between them are quite limited. This distinction could be achieved by combustion with stepwise adjustable decomposition temperatures (Brumsack 1981) or by classical wet-chemical methods (e.g., Kokkonen et al. 1987), but these methods require special efforts and can not be implemented during high throughput routine analyses.
Selective separation of different oxidation states by WD-XRF has been reported for sulfur (Perino et al. 2002), aluminium and silicon (Perino et al. 2002), iron (Finkelshtein and Chubarov 2010), and chromium (Malherbe and Claverie 2013). Referring to these known methods, two techniques for the quantitative differentiation between the most common sulfur species were developed, respectively improved that are based on a routine WD-XRF measurement. The first method is predicated on the exact position of the Kα1,2 peak in the XRF spectra, depending on the sulfide and sulfate content. The second option is based on the Kβ’/Kβ-ratio. As opposed to sulfides, sulfates show a Kβ’ satellite peak and its area and height depend on the sulfate concentration.
Both methods provide simple and time-saving options to differentiate between sulfide and sulfate, because the separation of the different oxidation states can be done during a routine WD-XRF measurement without any special efforts. Furthermore, samples with high amounts of fluorine, which could cause damages of technical devices, can be measured without any problems in the vacuum of the spectrometer. We aware that our research results may have two limitations. The first relates to the sulfur content. The method can not be used for samples with concentrations of the sulfatic and/or sulfatic component smaller than 10 g kg-1. The second one is the overlap of the lead (Pb) Mβ peak and the sulfur Kβ’ satellite peak. Samples with detectable lead amounts can only be investigated by the so-called Kα method.
We are currently in the process of a validation of our results by a second, independent method to further advance our investigations. Samples from Saxon mining dump drill holes appear suitable. Their total sulfur content and sulfide and sulfate concentration vary with depth. Suitable applications of these techniques are the high throughput routine analyses of samples that contain or consist of sulfidic ores.
Brumsack, H.-J., 1981. A Simple Method for the Determination of Sulfide- and Sulfate-Sulfur in Geological Materials by Using Different Temperatures of Decomposition. Fresenius' Journal of Analytical Chemistry, 307, 206.
Finkelshtein, A.L. and Chubarov, V.M., 2010. X-ray fluorescence determination of the FeO/Fe2O3tot ratio in igneous rocks. X-Ray Spectrometry, 39 (1), 17–21.
Kokkonen, P., Palko, M., and Lajunen, Lauri H. J., 1987. Indirect determination of sulfate and sulfide by flame atomic absorption spectrometry. Atomic Spectroscopy, 8 (3), 98–100.
Malherbe, J. and Claverie, F., 2013. Toward chromium speciation in solids using wavelength dispersive X-ray fluorescence spectrometry Cr Kbeta lines. Analytica Chimica Acta (773), 37–44.
Perino, E., et al., 2002. Determination of oxidation states of aluminium, silicon and sulfur. X-Ray Spectrometry, 31 (2), 115–119.

Keywords: sulfur oxidation state; WD-XRF

  • Lecture (Conference)
    CANAS - Colloquium Analytische Atomspektroskopie, 08.-10.03.2015, Leipzig, Deutschland

Publ.-Id: 21188

P1315 - Energiespeicheranordnung, deren Verwendung und Energiespeicherzellenanordnung

Galindo, V.; Gerbeth, G.; Stefani, F.; Weber, N.; Weier, T.

Gemäß verschiedenen Ausführungsformen wird eine Energiespeicheranordnung bereitgestellt, wobei diese Folgendes aufweisen kann: mindestens eine elektrochemische Zelle, wobei die mindestens eine elektrochemische Zelle eine im Betrieb flüssige Anode, einen im Betrieb flüssigen Elektrolyten und eine im Betrieb flüssige Kathode aufweist; eine außerhalb der mindestens einen elektrochemischen Zelle angeordnete Magnetfelderzeugungsstruktur zum Erzeugen eines Magnetfeldes, wobei die Magnetfelderzeugungsstruktur derart eingerichtet ist, dass das erzeugte Magnetfeld die mindestens eine elektrochemische Zelle durchdringt.

  • Patent
    DE102013112555 - Erteilung 06.11.2014, Nachanmeldung: WO, CN, EP, US

Publ.-Id: 21187

Level-set reconstruction algorithm for ultrafast limited angle X-ray computed tomography of two-phase flows

Bieberle, M.; Hampel, U.

Tomographic image reconstruction is based on recovering an object distribution from its projections, which have been acquired from all angular views around the object. If the angular range is limited to less than 180° of parallel projections, typical reconstruction artefacts arise when using standard algorithms. To compensate for this, specialized algorithms using a priori information about the object need to be applied.
The application behind this work is ultrafast limited angle X-ray computed tomography of two-phase flows. Here, only a binary distribution of the two phases needs to be reconstructed, which reduces the complexity of the inverse problem. To solve it, a new reconstruction algorithm (LSR) based on the level set method is proposed. It includes one force function term accounting for matching the projection data and one incorporating a curvature dependent smoothing of the phase boundary. The algorithm has been validated using simulated as well as measured projections of known structures and its performance has been compared to the algebraic reconstruction technique (ART) and a binary derivative of it. The validation as well as the application of the level set reconstruction on a dynamic two-phase flow demonstrated its applicability and its advantages over other reconstruction algorithms.

Keywords: Level set method; X-ray CT; image reconstruction; two-phase flow; ultrafast

Publ.-Id: 21186

X-ray Absorption Spectroscopy of Nuclear Materials at the Rossendorf Beamline, ESRF

Scheinost, A. C.; Prieur, D.; Smith, A.; Martin, P. M.; Lebreton, F.; Belin, R. C.

The Rossendorf Beamline is a dedicated X-ray absorption spectroscopy beamline for research on actinides. Embedded in the Helmholtz research program Safety of Nuclear Waste Disposal, inhouse research deals with the chemical behavior of actinides and fission products in the context of nuclear waste disposal, encompassing both near-field and far-field retention mechanisms. In the framework of European research programs, e.g. ACTINET, TALISMAN, ESRF, there is also a vivid body of research conducted on nuclear materials in the context of GenIV fuels, minor actinide transmutation, and the behavior of fuels under operational and accident conditions. In this talk I will focus on the latter aspect, presenting results from collaborations with CEA and ITU on a variety of topics including the oxidation state and local structure of Am in uranium dioxide and MOX fuels, self-irradiation effects of minor actinides in fuel matrices, and structure and oxidation state of U in sodium uranates.

Keywords: ROBL; XANES; Actinet; Talisman; Nuclear fuel

  • Invited lecture (Conferences)
    NES Colloquium, 19.11.2014, Villigen, Schweiz

Publ.-Id: 21185

Characterizing intra-exciton Coulomb scattering in terahertz excitations

Zybell, S.; Bhattacharyya, J.; Winnerl, S.; Eßer, F.; Helm, M.; Schneider, H.; Schneebeli, L.; Böttge, C. N.; Kira, M.; Koch, S. W.; Andrews, A. M.; Strasser, G.

An intense terahertz field is applied to excite semiconductor quantum wells yielding strong non-equilibrium exciton distributions. Even though the relaxation channels involve a complicated quantum kinetics of Coulomb and phonon effects, distinct relaxation signatures of Coulomb scattering are identified within time-resolved photoluminescence by comparing the experiment with a reduced model that contains all relevant microscopic processes. The analysis uncovers a unique time scale for the Coulomb scattering directly from experiments and reveals the influence of phonon relaxation as well as radiative decay.

Keywords: Exciton dynamics; GaAs quantum well; terahertz; intra-exciton transition; Coulomb scattering

Publ.-Id: 21184

Uranyl(VI) binding by bis(2-hydroxyaryl)diimine and bis(2-hydroxyaryl)diamine ligand derivatives. Synthetic, X-ray, DFT and solvent extraction studies

Jeazet, H. B. T.; Gloe, K.; Doert, T.; Mizera, J.; Kataeva, O. N.; Tsushima, S.; Bernhard, G.; Weigand, J. J.; Lindoy, L. F.; Gloe, K.

The interaction of uranyl(VI) nitrate with a series of bis(2-hydroxyaryl)imine and bis(2-hydroxyaryl)amine derivatives (H2L1- H2L7) incorporating 1,3-dimethylenebenzene or 1,3-dimethylenecyclohexane bridges between nitrogen sites is reported. Crystalline complexes of type [UO2(H2L)(NO3)2] (where H2L is H2L1 -H2L4) were isolated from methanol. X-ray structures of the complexes of H2L1, H2L2 and H2L4 show that each of these neutral ligands bind to their respective UO22+ centres in a bidentate fashion in which coordination only occurs via each ligand's hydroxy functions. Two bidentate nitrate anions complete the metal's coordination sphere in each complex to yield hexagonal bipyramidal coordination geometries. A DFT investigation of [UO2(H2L1)(NO3)2] in a simulated methanol environment is in accord with this complex maintaining its solid state conformation in solution. Solvent extraction experiments (water/chloroform) employing H2L1 - H2L7 in the organic phase and uranyl(VI) nitrate in the aqueous phase showed that both amine derivatives, H2L8 and H2L9, yielded enhanced extraction of UO22+ over the corresponding imine derivatives, H2L1 and H2L2. These results were further compared with those obtained for the corresponding Schiff bases incorporating 1,2-phenylene and 1,2-cyclohexane bridged ligands, H2L6 and H2L7; these more rigid systems also yielded enhanced extraction of UO22+ relative to the more flexible Schiff bases H2L1 - H2L5. A very significant synergistic enhancement of the extraction of UO22+ by H2L1‐H2L4 and H2L7 was observed in the presence of a 10-fold excess of octanoic acid; the influence of pH on extraction efficiency was also investigated. A parallel set of experiments employing H2L1 - H2L9 as extractants for europium(III) nitrate indicated a clear uptake preference for UO22+ over Eu3+ in all cases; separation of the uranyl ion from the rare earths is important in mineral processing;

Keywords: Uranyl(VI); Schiff base; Europium(III); X-ray; Solvent extraction; Density functional theory

Publ.-Id: 21183

Dual-modality Impedance Wire-Mesh Sensor for Investigation of Multiphase Flows

Dos Santos, E. N.; Da Silva, M. J.; Morales, R. E.; Reinecke, S.; Schleicher, E.; Hampel, U.

For the investigation of multiphase flows, i.e. in oil production, there are only few suitable measuring techniques. For this reason, in this paper a new multichannel complex impedance measuring system using wire-mesh sensors is presented. The novel system measures amplitude and phase components of impedance (at single frequency) and is thus able to evaluate simultaneously the conductive and the capacitive parts of a fluid (complex permittivity). In the future this system can be employed for the investigation of dynamic processes in multiphase flow. The performance in measuring amplitude and phase of a signal is evaluated. First promising results for the three-phase flow are presented.

Keywords: Complex impedance measurement; multiphase flow; wire-mesh sensor

  • Lecture (Conference)
    International Conference on Imaging Systems and Techniques (IST), 14-17.10.2014, Santorini, Greece, 14.-17.10.2014, Santorini, Griechenland
  • Contribution to proceedings
    International Conference on Imaging Systems and Techniques (IST), 14-17.10.2014, Santorini, Greece, 14.-17.10.2014, Santorini, Griechenland
    Proceedings of International Conference on Imaging Systems and Techniques (IST), 14-17.10.2014, Santorini, Greece, 9781479952199, 316-319

Publ.-Id: 21181

Configurational anisotropy effects in 90 degree domain wall imprinted thin films - statics and dynamics

Trützschler, J.; Sentosun, K.; Langer, M.; Mattheis, R.; Fassbender, J.; McCord, J.

The dynamic magnetic behavior of magnetic films has gained increased attention due to the use of magnetic films for high frequency inductors and their application as microwave filters. Moreover, the excitation and modification of spin waves has led to considerable interest in the field of magnonic crystals[1]. In general, the high frequency behavior of magnetic film stacks is determined by the material’s magnetic properties and by structural patterning. Yet, dynamic magnetization modes are not only inherent to the physical structure of magnetic films, but are also strongly influenced by e.g. ripplelike magnetic domain states[2] and as well as the pure existence of domain walls (DW)[3] in magnetic films. One way to introduce DWs in a controlled way in thin films is by local ion-irradiation[4,5,6].
In order to introduce a periodic DW pattern, extended Ni19Fe81(50nm)/Ir23Mn77(7nm) films with an initial unidirectional anisotropy are patterned by local He-ion irradiation into stripe-like twodimensional structures with periodically alternating directions of exchange bias. Magnetization patterns with zigzag oriented exchange bias directions are obtained. The influence of the DW density on static and dynamic magnetization properties is investigated for a stripe period (stripe width) from 12 μm (6 μm) down to 1 μm (500 nm). By this, exactly oriented and magnetically charged 90 N´eel-type domain walls with a DW density up to 2x103/mm are imprinted in the film.
Static and dynamic magnetization properties of the thin films are analyzed by complementary methods.
In Figure 1 (a) and (c) exemplary magnetization loops are presented for a stripe period of 2 μm. Perpendicular to the stripe axis an effective exchange bias field, which is caused by the magnetic interaction of the individual exchanged biased stripes, results in a net exchange bias direction. Due to DW interactions with increasing stripe period the samples correspondingly exhibit a decrease of remanent magnetization. Applying the external magnetic field parallel to the stripe axis, a two staged reversal loop is obtained. Even down to low stripe periods and despite of the straightening of magnetization the two step magnetization process remains for low stripe widths.
The corresponding change of high frequency permeability maps (up to 5 GHz) with bias fields in accordance with the shown magnetization reversal loops are displayed in Fig. 1 (b) and (d). Increasing the external magnetic field perpendicular to the stripes two distinct precessional frequencies, corresponding to an acoustic and an optical dynamic mode, are exhibited over the whole field range (Fig. 1(b)). Applying the field parallel to the stripe axis, in the central plateaued region (Fig. 1(d)) a bi-modal dynamic behavior is observed, that transforms into a single mode with higher permeability outside the plateau region. With increasing stripe period, the precessional frequencies at zero magnetic field decrease.
The occurring magnetic configurations are verified by high resolution Kerr microscopy in the longitudinal mode, examples of which are given in Fig. 2. The displayed images for different applied field values match the situation in Fig. 1 (c) and (d). The domain imaging data proves the existence of a pronounced magnetic modulation with high stability to magnetic fields even for a highly remanent state. The domain states, shown in Fig. 2 (b, c, d), exist in a magnetic field range, which is in accordance with the plateau in the magnetization loop and the change in the permeability spectrum around zero field.
Quasi-static and dynamic behavior are explained in terms of an increased domain wall mediated configurational magnetic anisotropy that results from variable magnetic charges at the imprinted domain walls due to the zigzagged alignment of magnetization. The magnetic charges increase with the rotational magnetization process. The DW stabilization induced effect has also significant influence on the dynamic magnetic characteristics. The effect of DW orientation relative to the alignment of exchange bias will be discussed. The controlled introduction of high density and locked micromagnetic objects opens new ways to control the static and dynamic magnetic properties of continuous magnetic thin films.
Funding from the German Science Foundation DFG through the grants MC9/7-2, FA314/3-2, and the Heisenberg programme of the DFG (MC9/9-1) is highly acknowledged.
[1] A. V. Chumak, A. A. Serga, B. Hillebrands, M. P. Kostylev, Appl. Phys. Lett. 93, 022508 (2008)
[2] C. Patschureck, K. Lenz, M. O. Liedke, M. U. Lutz, T. Strache, I. M¨onch, R. Sch¨afer, L. Schultz, and J. McCord, Phys. Rev. B 86, 054426 (2012)
[3] U. Queitsch, J. McCord, A. Neudert, R. Sch¨afer, L. Schultz, K. Rott, H. Br¨uckl, J. Appl. Phys. 100, 093911 (2006)
[4] J. Fassbender, J. McCord, J. Magn. Magn. Mater. 320, 579 (2008)
[5]C. Hamann, R. Mattheis, I. M¨onch, J. Fassbender, L. Schultz, J. McCord, Magnetization dynamics of magnetic domain wall imprinted magnetic films, submitted
[6] J. Tr¨utzschler, K. Sentosun, M. Langer, I. M¨onch, R. Mattheis, J. Fassbender, J. McCord, Magnetoresistive and domain investigations of zigzag folded magnetization structures, submitted

Keywords: Magnetic Domains; Anisotropic Magneto-Resistance; Kerr-Microscopy; Ferromagnetic Resonance

  • Lecture (Conference)
    IEEE Internation Magnetics Conference - Intermag Dresden 2014, 04.-08.05.2014, Dresden, Deutschland

Publ.-Id: 21180

P1211 - Verfahren und System zur Abtrennung von Schwermetallen

Lütke, L.; Moll, H.

Die Erfindung betrifft das Gebiet der Aufreinigung schwermetallbelasteter Gewässer, sowie den Nachweis von Schwermetallen in Lösungen. Der Erfindung liegt die Aufgabe zugrunde, eine effektive Abtrennung von Uran (Schwermetallen allgemein) durch mikrobielle Zellen ohne einen zusätzlichen Immobilisierungsschritt zu erzielen. Die Lösung der Aufgabe erfolgt durch ein erfindungsgemäßes Verfahren zur Abtrennung von Schwermetallen, enthaltend die folgenden Schritte: a. Bereitstellen einer Lösung enthaltend ein Minimalmedium und metabolisch aktive Biomasse aus gramnegativen Bakterien, b. Inkontaktbringen dieser Lösung mit einer Lösung enthaltend Schwermetalle, c. Einstellen der Phosphatkonzentration auf, 0,05 mmol/l bis 0,1 mol/l, bevorzugt 0,2 mmol/l bis 0,5 mmol/l, wobei die Schritte b und c in beliebiger Reihenfolge erfolgen können. Ebenfalls erfindungsgemäß ist ein System zur Abtrennung von Schwermetallen, enthaltend ein Minimalmedium, metabolisch aktive Biomasse aus gramnegativen Bakterien und Phosphat in einer Konzentration von 0,05 mM bis 0,1 M, bevorzugt 0,2 mM bis 0,5 mM. Ebenfalls erfindungsgemäß ist die Verwendung des erfindungsgemäßen Verfahrens oder des erfindungsgemäßen Systems zur Aufreinigung schwermetallbelasteter Gewässer oder zum Nachweis von Schwermetallen in Gewässern.

  • Patent
    DE102013207197 - Offenlegung 23.10.2014

Publ.-Id: 21179

Tomographie an technischen Anlagen – für effizientere Prozesse in der Chemie- und Verfahrenstechnik

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

Tomographie an technischen Anlagen – für effizientere Prozesse in der Chemie- und Verfahrenstechnik

Keywords: tomography

  • Lecture (others)
    Vortrags-/Besichtigungsprogramm für Besuchergruppen, 02.07.2014, Dresden, Deutschland

Publ.-Id: 21178

Ultrafast X-ray computed tomography for the analysis of multiphase flows

Bieberle, M.; Hampel, U.

This presentation addresses the question, why tomographic imaging of multiphase flows is needed and explains the principle of computed tomography as well as the ultrafast X-ray computed tomography system. Examples of application are presented as well as present developments.

Keywords: X-ray computed tomography; ultrafast

  • Lecture (others)
    summer school MIMENIMA, 18.09.2014, Dresden, Deutschland

Publ.-Id: 21177

Np-237 sorption onto montmorillonite and corundum

Elo, O.; Huittinen, N.; Müller, K.; Heim, K.; Hölttä, P.; Lehto, J.

The bentonite buffer in Engineered Barrier Systems (EBS), planned for spent nuclear fuel (SNF) repositories, consists mainly of the clay mineral montmorillonite. Montmorillonite and other aluminosilicates are known to retain radionuclides found in the SNF, thus, contributing to the retention or immobilization of these metal ions in the environment. The neptunyl cation, NpO2+, is rather soluble, poorly sorbed, and readily mobile under environmental conditions making it highly relevant for research concerning SNF repository safety. In the present study we have investigated the sorption of neptunium on the clay mineral montmorillonite under carbonate free, but environmentally relevant conditions. The interaction of neptunium with α-Al2O3 (corundum) has also been investigated in order to study the aluminol surface sites present on clay minerals, which are regarded as the main adsorption sites for radionuclide attachment. We have performed batch sorption studies both as a function of pH and as a function of neptunium concentration 5×10-10 M-5×10-6 M. The NpO2+ uptake on the two different minerals is rather weak. Sorption on the mineral surfaces begins at pH 7, and at pH 8 which is the pH-value expected to prevail in the deep underground in Olkiluoto, Finland, the final disposal site for the Finnish SNF, only ~ 10% of the actinyl ion is retained. To gain insight into the surface speciation of neptunium on the two minerals, we performed in situ ATR-FT-IR spectroscopic investigations at pH 9 and 10. Upon NpO2+ sorption onto corundum and montmorillonite we observe a shift of the antisymmetric stretch vibration of the neptunyl ion from 818 cm-1 obtained for the free aquo ion to 790 cm-1. The large shift of the asymmetric stretch vibration indicates the formation of an inner-sphere bound neptunium com-plex on the mineral surface. A similar shift has previously been observed by Gückel et al. (2013) for NpO2+ sorption onto gibbsite (α-Al(OH)3). In contrast to the results obtained in Gückel et al., where neptunium desorption could not be observed after flushing the mineral film on the ATR crystal, we see a high reversibility of the sorption on both corundum and montmorillonite. This high reversibility of the sorption process speaks for a weaker bonding to the surface. In upcoming EXAFS (Extended X-ray Absorption Fine Structure) measurements, we hope to be able to find an explanation for the deviating desporption behaviour of NpO2+ on montmorillonite and corundum in comparison to gibbsite. In addition, information on structural parameters and the complexation mechanism of neptunium sorption onto montmorillonite and corundum will be obtained.

Keywords: neptunium; sorption; in situ ATR-FT-IR; montmorillonite; corundum

  • Poster
    Advanced Techniques in Actinide Spectroscopy 2014 (ATAS 2014), 03.-07.11.2014, Dresden, Germany

Publ.-Id: 21176

Site-selective TRLFS of Eu(III) doped rare earth phosphates for conditioning of radioactive wastes

Huittinen, N.; Arinicheva, Y.; Holthausen, J.; Neumeier, S.; Stumpf, T.

Crystalline ceramic materials show promise as potential waste forms for immobilization of high-level radioactive wastes. Rare earth (RE) phosphate ceramics have been found to be extremely stable over geological time scales and they show good tolerance to high radiation doses. These ceramics are able to incorporate radionuclides in well-defined atomic positions within the crystal lattice up to high (~25%) loadings, which will reduce the volume of waste in the radionuclide conditioning process. The dehydrated RE phosphates are known to crystallize in two distinct structures, depending on the ionic radius of the cation: the larger lanthanides from La3+ to Gd3+ crystallize in the nine-fold coordinated monazite structure, while the smaller lanthanides such as Lu3+ form eight-fold coordinated xenotime structures.
In the present work we have used site-selective time-resolved laser fluorescence spectroscopy (TRLFS) to investigate the structural incorporation of Eu3+, an analogue for the actinides Pu3+, Am3+ and Cm3+, in rare earth phosphate ceramics. The very narrow excitation spectra of LaPO4 and GdPO4 monazites doped with 500 ppm Eu3+ indicate that Eu3+ is fully incorporated on the host cation sites in the highly ordered ceramic materials independent of the ionic radii of the host cations. The LuPO4 xenotime phase, however, shows a very low incorporation of the Eu3+ ion within the crystal lattice. The majority of the signal in the Eu3+-LuPO4 excitation spectrum could be assigned to partly hydrated europium in the LuPO4 ceramic. In experiments where we increased the dopant concentration up to 50 % in the xenotime host matrix, a larger amount of Eu3+ incorporation within the crystal structure in relation to the hydrated species could be seen. A similar increase of the dopant concentration in the monazite phases caused a broadening of the excitation spectra as a result of local disordering of the crystal structures. This disordering, however, had no influence on the Ln3+ site symmetry in the monazites.
Our site-selective TRLFS investigations have shown that the host cation size in the monazites has very little influence on the Eu3+ incorporation into these materials. The structure of the ceramic, however, seems to play a decisive role in how well the dopant is substituted within the crystal lattice.

Keywords: rare earth phosphate ceramics; incorporation; Eu(III); site-selective TRLFS

  • Lecture (Conference)
    Advanced Techniques in Actinide Spectroscopy 2014 (ATAS 2014), 03.-07.11.2014, Dresden, Germany

Publ.-Id: 21175

A few remarks on the structure of PT quantum mechanics

Günther, U.

In the first part of the talk, starting from a historical discussion of the 2-dimensional Ising model, the Yang-Lee analysis of the zeros of the corresponding partition function and the occurrence of the Yang-Lee edge singularities the structural origin of the quantum mechanical toy model Hamiltonian with ix^3 potential is elucidated. The close relationship of this Hamiltonian to the Landau theory of phase transitions and conformal field theories (CFTs) is sketched what provides an intuitive explanation for the operator-theoretic difficulties in treating a conjectured Hermitian structure of the ix^3 model in full depth.
In the second part of the talk, the Krein space and Hilbert space metric structures of quasi-Hermitian PT-symmetric matrix models are discussed with emphasis on the underlying general Lie group structures of these metric operators. The Cartan decomposition into compact and noncompact metric components is used to show the existence of an underlying Lie triple system and its relation to the curvature of homogeneous coset spaces.
Finally, several extension schemes from finite-dimensional Lie groups toward ∞−dimensional Lie groups and Hilbert-Schmidt Lie groups are sketched.

Keywords: Yang-Lee model; Yang-Lee edge singularity; Ising model; Landau theory of phase transitions; conformal field theory; PT quantum mechanics; metric operator; Krein space; Lie groups; Cartan decomposition; Lie triple systems; homogeneous coset spaces; Hilbert-Schmidt Lie groups

  • Invited lecture (Conferences)
    14th International Workshop on Pseudo-Hermitian Hamiltonians in Quantum Physics, 05.-10.09.2014, Setif, Algeria

Publ.-Id: 21174

Validierung der Nutzbarkeit eines zweikanaligen Heißfilmanemometers in Mehrphasenströmungen durch Vergleichsmessungen mittels Particle Imaging Velocimetry

Chi, B.

Die Bestimmung der Geschwindigkeitskomponenten zur Validierung von CFD-Simulation zählt zu den elementarsten Messaufgaben in einer Blasensäule. Während besonders in einphasigen Strömungen Particle Imaging Velocimetry (PIV) und Constant Temperature Anemometry (CTA) etabliert sind, ist deren Einsatz in Zweiphasenströmung deutlich durch die auftretenden Phasenwechsel gestört.
Während der Einsatz eines PIV-Systems bereits bei geringen Gasanteilen durch fehlende optische Zugänglichkeit nicht mehr möglich ist, besteht bei CTA-Systemen, bedingt durch ihr Messprinzip, die Möglichkeit auch bei höheren Gasdurchsätzen zu messen.
Im Rahmen der Diplomarbeit sind systematische Studien zur Validierung der Nutzbarkeit eines Flüssigkeits-CTA-Systems in Mehrphasenströmung mit verschiedenen Gasgehalten durchzuführen. Die Validierung erfolgt hierbei durch parallele, zeitgemittelte Vermessung lokaler Strömungsgeschwindigkeiten mittels PIV. Um der Verfälschung von Flüssigkeits-Messdaten des CTA-Systems durch Phasenwechsel vorzubeugen, ist das Messsystem mit einer HZDR-eigenen Nadelsonde zu koppeln und entsprechend verfälschte Daten zu maskieren. Zudem ist eine vorherige Kalibrierung des CTA-Systems vorzunehmen.

Keywords: hot film anemometry; multiphase velocimetry; particle imaging velocimetry

  • Diploma thesis
    TU Dresden, 2014
    Mentor: Zalucky, J., Hampel, U.

Publ.-Id: 21173

Hydrodynamics and transport processes in structured reactor devices: Project status report

Zalucky, J.; Wagner, M.; Rabha, S. S.; Schubert, M.; Bieberle, M.; Hampel, U.

On the occasion of half-annual project status report, work package progress is presented. The first part covers the presentation of pre-liminary experiments in the x-ray investigation of multiphase hydrodynamics in solid foam packed fixed bed and packed bubble column reactors. The second part reports on pre-liminary actions in mass transfer investigations. The presentation concludes with the planed project schedule and upcoming milestones.

Keywords: ultrafast x-ray CT; solid foam reactors; multiphase hydrodynamics; mass transfer investigations

  • Lecture (others)
    Helmholtz-Energie-Allianz EECMP: Half-annular project meeting, 03.-04.04.2014, Dresden, Deutschland

Publ.-Id: 21172

Advances in multiphase hydrodynamic characterization of solid foams and cubic cell structures - Project status report

Zalucky, J.; Wagner, M.

On the occasion of annual project status report, work package progress is presented. The first part includes conventionally measured hydrodynamic characteristics such as static liquid holdup, flow maps and pressure drop measurements. Second part includes deeper data mining on ultrafast x-ray computed tomography measurements. The second part is related to actions in mass transfer investigations and reports progress and upcoming investigations with the electrochemical method.

Keywords: project status report; ultrafast x-ray computed tomography; liquid-solid mass transfer; multiphase hydrodynamics

  • Lecture (others)
    Jahrestreffen Helmholtz-Energie-Allianz "Energieeffiziente chemische Mehrphasenprozesse", 08.-09.10.2014, Hamburg, Deutschland

Publ.-Id: 21171

Pulse dynamic visualization in foam packed reactors - flow path evolution

Zalucky, J.; Rabha, S. S.; Schubert, M.; Hampel, U.

In co-currently downward operated packed bed reactors, pulse flow is well known for its performance enhancing effects. Though suffering from a lot higher pressure drop than trickle flow, it offers the high advantage of continuous re-wetting, liquid flow re-routing and enhanced mass transfer due to higher, liquid induced shear stress. In our contribution, the evolution of liquid flow is addressed and visualized by the used of our ultrafast X-ray computed tomography system. As novel catalyst internal, foam blocks made of silicon infiltrated silicon carbide (SiSiC) were investigated.

Keywords: Pulse flow visualization; co-current downward flow; ceramic foams; ultrafast x-ray computed tomography

  • Poster
    ProcessNET Jahrestagung, 29.09.-02.10.2014, Aachen, Deutschland

Publ.-Id: 21170

Advances in application of the limiting current technique for solid-liquid mass transfer investigations

Zalucky, J.; Rabha, S. S.; Schubert, M.; Hampel, U.

The limiting current technique has widely been used to study liquid-solid mass transfer in various reactor configurations. In the present contribution several underlying physical aspects have been investigated in order to improve the design of mass transfer experiments. Experimentally, the significant influence of electrolyte composition and hydrodynamic conditions have been studied and quantified to ensure conditions of high reproducibility. In the course of single phase COMSOL simulations, different electrode configurations have been examined with emphasis on concentration fields and electric current distribution showing a large sensitivity of the experimental configuration on the absolute current values.

Keywords: Liquid-solid mass transfer; limiting current technique; electric field simulation; ceramic solid foams

  • Poster
    2nd International Symposium on Multiscale Multiphase Process Engineering, 24.-27.09.2014, Hamburg, Deutschland
  • Contribution to proceedings
    2nd International Symposium on Multiscale Multiphase Process Engineering, 24.-27.09.2014, Hamburg, Deutschland
    Book of full-length manuscript, Fr: DECHEMA/VDI, 313-318

Publ.-Id: 21169

The Bubbles Breakup and Coalescence Rates in Bubble Columns

Azizi, S.; Schubert, M.

Bubble size distribution has important role in bubble columns in point view of available interfacial area for interphase exchange phenomena. The difficulty in determining of bubble size is due to uncertain breakup and coalescence models for using in population balance equations. Variety of mechanism and coefficients for the each of the models prevents to generalize them. Furthermore, measurement of each rate individually is not possible except for single bubble trajectory in transparent systems (mostly air-water dispersions) that some of the existing models based on it. Here, a novel algorithm demonstrated to calculate breakup and coalescence rates using the bubble size distribution, bubble rise velocity, and hold-up profiles along the bubble column.

Keywords: Bubble Column; Bubbles Breakup and Coalescence; Mechanisms; Experimental Study; Population Balance

  • Poster
    HZDR Annual PhD Seminar, 06.-08.10.2014, Altenberg, Germany

Publ.-Id: 21168

Morphological Characterization of Open-Cell Solid Foams

Mohammed, I.; Bauer, T.; Schubert, M.; Lange, R.

Reactors with a fixed-bed of catalyst particles are widely applied for continuous multi-phase processes in the petrochemical, chemical, and biochemical industry. However, the performance of these reactors often suffers from some drawbacks, such as energy consuming high-pressure drop and mass and heat transfer limitations. One solution is to replace randomly packed catalysts with structured packings, e.g open-cell solid foam catalysts as they provide high specific surface area of up to 2000 m2/m3 at high open porosities between 75 - 97%. As result, the pressure drop of the gas-liquid two-phase flow is comparatively low (Mohammed et al. 2013). Studies argued that both the bulk material and the foam morphological properties like the number and shape of the pores and struts have a strong impact on heat transfer rates and on the hydrodynamic behavior (Tekog˜lu et al., 2011). Thus, a key factor in the foam characterization is to properly define foam structural parameters and to choose an appropriate predictive morphological model. Due to the highly random, irregular and non-ideal solid foam structure it is difficult to specify one geometrical property. At same time, although several models and correlations have been proposed to calculate morphological properties, each of these correlations was proposed for specific materials and pore shape. Therefore, the goal of this study is to characterize the solid foam, and find the most suitable morphological model for the characterization of the packing, which is applicable for different solid foam shape, material, and structure. In order to distinguish the influence of the foam materials, foam samples of different materials (polyurethane, carbon, and nickel) but same foam density are investigated. Different measurements techniques (light microscopy, electron scanning microscopy, and X-ray micro tomography) were used to reveal the impact of the material. The morphological analysis indicated that polyurethane foam mimics both the carbon and the nickel foam. Furthermore, all solid foams show similar strut properties (see Fig 1) which is confirmed by tomographic measurements of window (pore) diameter and specific surface area. In the contribution, the methodology of the foam characterization and the comparison between the foam morphologies will be shown.

  • Poster
    6th International FEZA Conference, 08.-11.09.2014, Leipzig, Deutschland

Publ.-Id: 21167

Bubble Size and Velocity Measurements in Bubble Columns using Ultrafast X-ray Tomography

Lau, Y. M.; Schubert, M.

We present measurements of bubble size distribution in bubble columns using X-ray tomography. The experimental setup is an ultrafast electron beam X-ray tomographic system applied to a cylindrical bubble column with a diameter of 0.07 m. Measurements are taken placed on two planes, which are separated with an axial distance of 10 mm. The obtained reconstructed images are filtered, segmented and stacked in the time-domain to form a three-dimensional matrix of bubble objects. By cross-examining the matrices of both planes, we can identify the corresponding bubble objects and determine bubble velocities and volumes as well.

  • Lecture (Conference)
    2014 AIChE Annual Meeting, 16.-21.11.2014, Atlanta, USA

Publ.-Id: 21166

Analysis of Breakup & Coalescence Rates inside the Bubble Columns

Azizi, S.; Lau, Y. M.; Schubert, M.

The prediction of bubble size distributions (BSD) in bubble column reactors is a great challenge for the column design and for the optimization of the operating conditions to enhance the gas-liquid mass transfer rates. The implementation of population balance equations (PBE) for bubbly flows into computational fluid dynamics (CFD) codes allowed better understanding of the hydrodynamic behavior of bubble columns and better quantification of the interfacial area for the estimation of interphase transport phenomena. On the other hand, the complexity of numerical models increased with the introduction of new sub-models for the determination of the BSDs. The formulation of sink and source terms of such PBEs is a very controversial issue. These terms depend on assumption on the dominating mechanisms due to turbulence, buoyancy, wake, shear, etc. However, the unknown physical effects, the variety of constants of breakup and coalescence (B&C) kernels as well as their complex coupling with the hydrodynamics of the flow prevent to generalize existing models.
In this work, a new approach was used to determine ‘experimental’ B&C rates along the axial height of bubble columns using measured BSD data at different axial positions. The required bubble size distributions were determined by dual plane ultrafast X-ray tomography applied at several heights of the bubble column. Tomographic images are obtained at high frequencies (>1000Hz) for two measurement planes. By cross examining the images of the two planes, bubbles can be identified and the velocities, hence the sizes can be determined.
Subsequently, the liquid velocity distributions were determined by an Eulerian-Eulerian CFD model based on the multi-size group (MUSIG) poly-disperse model approach using the ‘experimental’ B&C rates. Excellent agreement was found between the measured and the predicted BSDs, gas holdups and bubble velocities. The liquid flow patterns are very important since the existing theoretical correlations for the B&C models are based on the liquid hydrodynamic properties. Accordingly, the validated hydrodynamic data from CFD simulations can be utilized to determine the dominating mechanisms for the B&C models at different axial regions of the bubble columns, and to investigate the role of B&C rates for each mechanisms.

Keywords: Breakup and Coalescence; Bubbly Flow; Bubble Column; CFD; Eulerian-Eulerian

  • Lecture (Conference)
    21st International Congress of Chemical and Process Engineering, CHISA 2014, 23.-27.08.2014, Prague, Czech Republic

Publ.-Id: 21165

Investigation of hydrodynamics and mass transfer of solid foam packings for gas-liquid applications

Mohammed, I.; Bauer, T.; Schubert, M.; Lange, R.

Chemical reactors with a fixed bed of catalyst particles are widely applied in the chemical industry. However, the performance of these reactors often suffers from some drawbacks, such as high energy consumption caused by pressure loss and low productivity due to mass and heat transfer limitations. One solution is to replace catalyst particles with catalysts packings based on solid foams with an open cell structure. Such porous structures combine large specific surface areas, high bed porosities, and interconnected pores for enhanced heat and mass transfer (Zhang et al. 2012). The performance of reactors with solid foam catalysts depends on the interaction of the fluids with the foam structure and, hence, the mass transfer to the foam surface. These two aspects are directly linked to the overall reactor performance and need to be understood in detail for reactor design. This work focuses on an experimental investigation of hydrodynamics and mass transfer. The hydrodynamics investigation was based on applying novel wire-mesh sensors to study gas and liquid distribution at high spatial resolution. The particular liquid-solid mass transfer was studied by a modified electrochemical method. The experiments are based on the measurement of electrical current under mass transfer diffusion limited condition. The experimental results of this work demonstrate clearly the potential of solid foam as suitable packing for gas-liquid applications.

  • Lecture (Conference)
    248th ACS National Meeting, 10.-14.08.2014, San Francisco, USA

Publ.-Id: 21164

Hydrodynamics, mass and heat transfer in bubble columns with vertical internals: an experimental study

Simic, N.; Breiler, K.; Schubert, M.

The objective of this study is to examine the influence of different vertical tube bundle designs on the bubble dynamics and on the mass and heat transfer rates in a bubble column. The studies in the open literature examining the performance of bubble columns with vertically inserted tube bundles have focused primarily on the coverage of the cross-sectional area of the bubble column by the tube bundle (CSA). The most frequently used coverages are the 5% and the 25% (± 3%) which mimic the heat exchangers utilized in the processes of methanol and Fischer-Tropsch syntheses. Other than that, the designs of tube bundles seem to be arbitrarily chosen and feature a number of different configurations of layouts, tube diameters and tube lengths. From the current state of research, it is thus rather difficult to draw conclusions on the optimal design of a heat exchanger suitable for use in bubble columns. Intuitively, it can be concluded that the most important design features of tube bundles affecting the flow are the distance between the tubes and the unit cell area enclosed by the tubes in their respective arrangements. Accordingly, the study aims on a systematic analysis on the effect of these geometric parameters.
The experiments are conducted in a 10-cm bubble column equipped with a perforated plate gas distributor in the air-water system. Four tube bundle designs have been chosen and arranged in the triangular and square pattern layouts, which represent the two most widely used heat exchanger designs according to TEMA (Tubular Exchange Manufacturer´s Association) and are known to affect the fluid turbulence to different extents. The volumetric mass transfer coefficient, kLa, is measured by the oxygen absorption method using a commercially available oxygen probe and the heat transfer is measured using the extended heat exchanger probe. The gas phase dynamics are obtained with the use of the in-house developed dual-plane ultrafast electron beam X-ray tomography.

Keywords: bubble column; internals; heat exchanger; tube bundle; hydrodynamics; gas holdup; bubble size distribution; mass transfer; X-ray tomography

  • Poster
    HZDR PhD Seminar 2014, 06.-08.10.2014, Altenberg, Deutschland

Publ.-Id: 21163

Langzeitspezifische Alterungseffekte in RDB-Stahl

Bergner, F.; Ulbricht, A.; Wagner, A.

Ziel des BMWi-Fördervorhabens 1501393 ist es, durch den Einsatz von Untersuchungsmethoden auf der nm-Skala einen Beitrag zur Aufklärung von Flusseffekten und von Late-Blooming-Effekten in bestrahlten RDB-Stählen zu leisten. Zur Untersuchung dieser Effekte wurde auf RDB-Stähle deutscher Reaktoren aus zwei bei der AREVA GmbH abgeschlossenen Vorhaben zurückgegriffen. Die Auswahl der Grundwerkstoffe und Schweißgüter erfolgte so, dass sich optimale Voraussetzungen für das Erreichen des Gesamtziels des Vorhabens ergeben. Die ausgewählten Untersuchungsmethoden umfassen mit der Neutronenkleinwinkelstreuung, der Atomsondentomographie und der Positronen-annihilationsspektroskopie solche Techniken, die die nm-skaligen bestrahlungsinduzierten Defekt-Fremdatom-Cluster bestmöglich und in komplementärer Weise zu detektieren und zu charakterisieren gestatten. Es wurde ein Flusseffekt auf die Größe der bestrahlungsinduzierten Fremdatomcluster, jedoch nicht auf den Volumenanteil und die mechanischen Eigenschaften gefunden. In einem Cu-armen RDB-Schweißgut wurde ein Late-Blooming-Effekt nachgewiesen, der sich in einem steilen Anstieg des Clustervolumenanteils und der Übergangstemperaturverschiebung nach einer Phase schwacher oder fehlender Zunahme niederschlägt.

The BMWi project 1501393 aimed at contributing to the clarification of flux effects and late blooming effects in irradiated RPV steels by means of experimental techniques of sensitivity at the nm scale. The investigation of these effects was focussed on RPV steels, both base metal and weld of German reactors selected according to the objectives of the present project from two previous projects performed at AREVA GmbH. The complementary techniques of small-angle neutron scattering, atom probe tomography and positron annihilation spectroscopy were applied to detect and characterize the irradiation-induced nm-scale defect-solute clusters. A flux effect on the size of the irradiation-induced clusters but no flux effect on both cluster volume fraction and mechanical properties was found. For a low-Cu RPV weld, a late blooming effect was observed, which results in a steep slope of both cluster volume fraction and transition temperature shift after an initial stage of small or no change.

Keywords: pressure vessel steel; base metal; weld metal; microstructure; irradiation effects; rate theory

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-056 2014
    ISSN: 2191-8708, eISSN: 2191-8716


Publ.-Id: 21162

Mixing efficiency of cross-bar and helical static mixer in upward gas-liquid flows

Rabha, S.; Schubert, M.; Banowski, M.; Hampel, U.

The process of dispersing gaseous phases into liquid bulks is one of the most widely used mixing processes in the chemical and process industry. The choice of an appropriate agitation system for the desired processes depends essentially on the efficiency to ensure high interfacial area at economically justifiable energy input. In this context, the static mixer technology emerges in many areas as an attractive alternative to conventional agitators such as continuous stirred tank reactors 1-3. Numerous static mixer designs, for example Helical (Kenics), SMV (Sulzer), SMX (Koch-Sulzer), LPD and ISG (Charles Ross & Son) have been proposed but only few designs are used in the industry. However, comparative performance studies of these mixers are scarce. In this contribution, the mixing capabilities of cross-bar and helical static mixers for upward gas-liquid flows will be presented at turbulent gas-liquid flow regime.

Keywords: static mixer

  • Poster
    International Symposium on Catalysis Multiphase Reactors, 07.-10.12.2014, Lyon, France

Publ.-Id: 21161

Dual Role of B7 Costimulation in Obesity-Related Nonalcoholic Steatohepatitis and Metabolic Dysregulation

Chatzigeorgiou, A.; Chung, K.-J.; Garcia-Martin, R.; Alexaki, V.-I.; Klotzsche-Von Ameln, A.; Phieler, J.; Sprott, D.; Kanczkowski, W.; Tzanavari, T.; Bdeir, M.; Bergmann, S.; Cartellieri, M.; Bachmann, M.; Nikolakopoulou, P.; Androutsellis-Theotokis, A.; Siegert, G.; Bornstein, S. R.; Muders, M. H.; Boon, L.; Karalis, K. P.; Lutgens, E.; Chavakis, T.

The low-grade inflammatory state present in obesity contributes to obesity-related metabolic dysregulation, including nonalcoholic steatohepatitis (NASH) and insulin resistance. Intercellular interactions between immune cells or between immune cells and hepatic parenchymal cells contribute to the exacerbation of liver inflammation and steatosis in obesity. The costimulatory molecules, B7.1 and B7.2, are important regulators of cell-cell interactions in several immune processes; however, the role of B7 costimulation in obesity-related liver inflammation is unknown. Here, diet-induced obesity (DIO) studies in mice with genetic inactivation of both B7.1 and B7.2 (double knockout; DKO) revealed aggravated obesity-related metabolic dysregulation, reduced insulin signalling in the liver and adipose tissue (AT), glucose intolerance, and enhanced progression to steatohepatitis resulting from B7.1/B7.2 double deficiency. The metabolic phenotype of B7.1/B7.2 double deficiency upon DIO was accompanied by increased hepatic and AT inflammation, associated with largely reduced numbers of regulatory T cells (Tregs) in these organs. In order to assess the role of B7 costimulation in DIO in a non-Treg-lacking environment, we performed antibody (Ab)-mediated inhibition of B7 molecules in wild-type mice in DIO. Antibody-blockade of both B7.1 and B7.2 improved the metabolic phenotype of DIO mice, which was linked to amelioration of hepatic steatosis and reduced inflammation in liver and AT. Conclusion: Our study demonstrates a dual role of B7 costimulation in the course of obesity-related sequelae, particularly NASH. The genetic inactivation of B7.1/B7.2 deteriorates obesity-related liver steatosis and metabolic dysregulation, likely a result of the intrinsic absence of Tregs in these mice, rendering DKO mice a novel murine model of NASH. In contrast, inhibition of B7 costimulation under conditions where Tregs are present may provide a novel therapeutic approach for obesity-related metabolic dysregulation and, especially, NASH.

Publ.-Id: 21160

Bifunctional Cyclam-Based Ligands with Phosphorus Acid Pendant Moieties for Radiocopper Separation – Thermodynamic and Kinetic Studies

Paúrová, M.; Havlíčková, J.; Pospíšilová, A.; Vetrík, M.; Císařová, I.; Stephan, H.; Pietzsch, H.-J.; Hrubý, M.; Hermann, P.; Kotek, J.

Two novel macrocyclic ligands based on trans-substituted cyclam with N-methyl and N-(4-aminobenzyl) groups as well as with two methylphosphinic (H2L1) or methylphosphonic (H4L2) acid pendant arms were synthesised and investigated in solutions. The ligands form stable complexes with transition metal ions. Both ligands show a high thermodynamic selectivity for divalent copper over nickel(II) and zinc(II) (K(CuL) is higher than K(Ni/ZnL) by about 7 orders of magnitude). Complexation is significantly faster for the phosphonate ligand H4L2 probably due to stronger coordination ability of more basic phosphonate groups, which efficiently bind the metal ion in the out-of-cage complex and helps its in-cage binding. The rate of complexation of Cu(II) by the phosphinate ligand H2L1 is comparable to that of cyclam itself and it derivatives with non-coordinating substituents. Acid-assisted decomplexation of the copper(II) complexes is relatively fast (½ 44 and 42 s in 1 M aq. HCl at 25 °C for H2L1 and H4L2, respectively). Combination of the properties is convenient for selective copper removal/purification. Thus, the title ligands were employed in preparation of ion-selective resins for radiocopper(II) separation. Glycidyl-methacrylate copolymer beads were modified with the ligands through diazotation reaction. The separation ability of the modified polymers was tested with cold copper(II) or non-carrier-added (NCA) 64Cu in the presence of a high excess of both nickel(II) and zinc(II). The experiments exhibited high overall separation efficiency leading to 60–70 % recovery of radiocopper with high selectivity over the other metal ions originally present in 900-times molar excess. The results showed the concept of chelating resins with properly tuned selectivity of complexing moieties can be employed for radiocopper separation.

Publ.-Id: 21159

Multiphase flow imaging – between physics and contemporary art

Hampel, U.; (Editor)

The presentation gives an overview over various multiphase flow imaging techniques, their functional principles, hardware and image processing aspects. Furthermore different applications on industrial and scientific flow analysis problems are being discussed.

Keywords: multiphase flow imaging; process tomography; image processing

  • Invited lecture (Conferences)
    Netherlands Process Technology Symposium NPS14, 03.-05.11.2014, Utrecht, The Netherlands

Publ.-Id: 21158

Two-phase flow measurements with ultrafast X-ray tomography

Hampel, U.; Banowski, M.; Barthel, F.; Hoppe, D.; Lucas, D.; Rabha, S.; Wagner, M.

Ultrafast X-ray tomography provides a means for the contactless high-resolution scanning of multiphase flows. In the current version the technique is able to scan flows in vessels of up to 160 mm diameter with scan rates of several thousand frames per second, a nominal spatial resolution of around one millimeter and in two consecutive planes. One of the main advantages is that two-phase flows in opaque and complex structures can be disclosed.
A challenging subject in the frame of ultrafast X-ray tomography is data processing and analysis. The high scanning rates yield large data sets and automated image processing must be applied to extract typical hydrodynamic parameters of interest, such as gas hold-up profiles, bubble and particle size distributions and velocities and interfacial area. On the other hand it is difficult to obtain some parameters from the continuous phase, such as continuous phase velocities or turbulence parameters. Here combination of different measurement techniques has further potential.
The presentation will provide an overview over the capacities and limits of ultrafast X-ray tomography by discussing different two-phase flow problems with increasing complexity: two-phase flow in vertical pipes, slurry bubble columns and static mixers. Moreover different image processing and data analysis techniques will be introduced and discussed in detail.

Keywords: ultrafast X-ray tomography; two-phase flow

  • Invited lecture (Conferences)
    The 52nd European Two-Phase Flow Group Meeting (ETPFGM2014), 07.-09.05.2014, Dresden, Germany

Publ.-Id: 21157

Ultrafast X-ray tomography for multiphase flow analysis

Hampel, U.; Banowski, M.; Barthel, F.; Hoppe, D.; Rabha, S. S.; Schubert, M.

Ultrafast X-ray tomography provides a means for the contactless high-resolution scanning of multiphase flows. In the current version the technique is able to scan flows in vessels of up to 195 mm diameter with scan rates of several thousand frames per second, a nominal spatial resolution of around one millimetre and in two consecutive planes. One of the main advantages is that two-phase flows in opaque and complex structures can be disclosed. A challenging subject in the frame of ultrafast X-ray tomography is data processing and analysis. The high scanning rates yield large data sets and automated image processing must be applied to extract typical hydrodynamic parameters of interest, such as gas hold-up profiles, bubble and particle size distributions, disperse phase velocities and interfacial area. On the other hand it is difficult to obtain certain parameters from the continuous phase, such as continuous phase velocities or turbulence. Here combination of different measurement techniques has further potential.

Keywords: ultrafast X-ray tomography; multiphase flow; tomographic image processing

  • Contribution to proceedings
    5th International Workshop on Process Tomography (IWPT-5), 16.-18.09.2014, Jeju, Korea
  • Invited lecture (Conferences)
    5th International Workshop on Process Tomography (IWPT-5), 16.-18.09.2014, Jeju, Korea

Publ.-Id: 21156

Reactor pressure vessel surveillance

Ballesteros, A.; Hein, H.; May, J.; Planman, T.; Todeschini, P.; Brumovsky, M.; Gillemot, F.; Chaouadi, R.; Rouden, J.; Efsing, P.; Altstadt, E.

The Euratom LONGLIFE project has proposed multiple ways of monitoring radiation embrittlement of RPVs during long-term operation. An overview is presented.

Keywords: Embrittlement; Surveillance; Reactor pressure vessel

  • Nuclear Engineering International 59(2014)724, 19-20

Publ.-Id: 21155

Surface-mediated formation of Pu(IV) nanoparticles on muscovite

Schmidt, M.; Knope, K. E.; Lee, S. S.; Stubbs, J. E.; Eng, P. J.; Bellucci, F.; Fenter, P.; Soderholm, L.

Nanoparticles have long been recognized as an important factor in actinide chemistry,[1] as well as reactive transport.[2, 3] The formation of Pu(IV) nanoparticles can be enhanced by the presence of a mineral surface[4], even if Pu is not initially present as Pu(IV).[5] Redox activity of the mineral surface is not a prerequisite for this oxidation/ polymerization reaction.[6]
Upon reaction of a solution of Pu(III) with muscovite mica the formation of Pu(IV)-oxo-nanoparticles was observed by surface x-ray scattering [crystal truncation rods (CTR) and resonant anomalous x-ray reflectivity (RAXR)] and atomic force microscopy (AFM).[6] The surface-mediated polymerization has been related to the enhanced concentration of mobile plutonium near the interface, as well as the redox equilibrium of Pu(III) and Pu(IV) under atmospheric conditions.
Here we present our recent findings demonstrating that the same mechanism is also found when Pu is initially present in its hexavalent state PuO22+, thus requiring reduction instead of oxidation to reach the tetravalent state. Surface x-ray scattering in combination with x-ray absorption near-edge spectroscopy (XANES) reveal the presence of Pu(IV) nanoparticles after 12 hours reaction time. Grazing incidence XANES shows only Pu(IV) at the interface, within the detection limits. The interfacial structure revealed by CTR and RAXR will be discussed and compared to the structures formed upon sorption of preformed Pu(IV) nanoparticles[7], as well as after surface-mediated formation of nanoparticles from trivalent plutonium.[6]
[1] Knope, K.E., et al., Chem. Rev., 2012. 113(2): 944; [2] Kersting, A.B., et al., Nature, 1999. 397: 56; [3] Novikov, A.P., et al., Science, 2006. 314: 638; [4] Powell, B.A., et al., ES&T, 2011. 45(7): 2698; [5] Kirsch, R., et al., ES&T, 2011. 45(17): 7267; [6] Schmidt, M., et al., ES&T, 2013. 47(24): 14178; [7] Schmidt, M., et al., Langmuir, 2012. 28: 2620.

Keywords: Plutonium; Redox chemistry; CTR; RAXR; AFM; XANES

  • Lecture (Conference)
    Goldschmidt 2014, 08.-13.06.2014, Sacramento, CA, USA

Publ.-Id: 21154

Interfacial Reactivity of Pu and Th at the Muscovite (001) Basal Plane

Schmidt, M.; Fenter, P.; Lee, S. S.; Bellucci, F.; Wilson, R. E.; Knope, K. E.; Soderholm, L.

The geochemistry of the actinides is of utmost importance in understanding and predicting their behavior in contaminated legacy sites as well as nuclear waste storage facilities. The unique chemistry of this group of elements including strong hydrolysis, complex redox chemistry, and the potential for polymerization reactions in combination with the actinides’ inherent radioactivity and toxicity makes studies challenging. However, especially for artificial elements like Pu and other transuranics, no natural analogues are available and homologues frequently fall short in accurately reproducing the actinides’ behavior.
We will present and discuss recent results from in situ resonant anomalous x-ray reflectivity (RAXR) and crystal truncation rod (CTR) experiments, shedding light on the inter-action of Th(IV) as well as Pu(III) and Pu(IV) with the negatively charged muscovite (001) basal plane. The example of Th(IV) demonstrates how the strong hydration of the highly charged cations prevents a close approach to the surface, instead favoring adsorption as a highly hydrated extended outer sphere complex. Subsequently, it will be shown how similar adsorption behavior in combination with the complex redox chemistry of plutonium, leads to a surface-enhanced formation of nanoparticles.
Results from surface x-ray scattering will be supplemented by ex situ alpha-spectrometry quantification and atomic force microscopy (AFM), to yield a more complete understanding of the interfacial structure.

Keywords: Plutonium; Thorium; RAXR; CTR; AFM

  • Invited lecture (Conferences)
    ActinideXAS 2014: 7th Workshop on Speciation, Techniques, and Facilities for Radioactive Materials at Synchrotron Light Sources, 20.-22.05.2014, Böttstein, Schweiz

Publ.-Id: 21153

High-temperature ferromagnetism of Si1−xMnx (x≈0.52−0.55) alloys

Rylkov, V. V.; Bugaev, A. S.; Novodvorskii, O. A.; Tugushev, V. V.; Kulatov, E. T.; Zenkevich, A. V.; Semisalova, A. S.; Nikolaev, S. N.; Vedeneev, A. S.; Shorokhova, A. V.; Aver′Yanov, D. V.; Chernoglazov, K. Y.; Gan′Shina, E. A.; Granovsky, A. B.; Wang, Y.; Panchenko, V. Y.; Zhou, S.

The paper reports on the comprehensive study of properties of nonstoichiometric Si1−xMnx alloys slightly enriched in Mn (x≈0.51–0.55) as compared to the stoichiometric monosilicide MnSi. Mosaic type Si1−xMnx films 55–70 nm in thickness were produced by the pulsed laser deposition (PLD) method onto the single crystalline Al2O3 substrates at 340 °C. The Curie temperature TC in nonstoichiometric Si1−xMnx (x≈0.52–0.55) films exceeds room temperature, while in their stoichiometric counterpart, MnSi, the TC value does not exceed ≈30 К. The consistent data on anomalous Hall effect and transverse Kerr effect prove the global character of ferromagnetic (FM) order caused by magnetic defect formation rather than the presence of FM clusters. Аt Mn content x≤0.55, the magnetization data testify to a good homogeneity in the distribution of magnetic defects without their segregation: variations of the saturation magnetization Ms do not exceed 6% in the temperature range T=10–100 К and are well described by the Bloch law. It is also revealed that textured high-quality Si1−xMnx films with x≈0.52 and ТС~300 К could be formed by PLD method in the “shadow” geometry (at lower energy of deposited atoms).

Keywords: Si–Mn alloy; High-temperature ferromagnetism; Anomalous Hall effect; Magnetic and magneto-optical properties

Publ.-Id: 21152

Analytical computation of prompt gamma ray emission and detection for proton range verification

Sterpin, E.; Janssens, G.; Smeets, J.; Vander Stappen, F.; Prieels, D.; Priegnitz, M.; Perali, I.; Vynckier, S.

A prompt gamma (PG) slit camera prototype recently demonstrated that Bragg Peak position in a clinical proton scanned beam could be measured with 1–2 mm accuracy by comparing an expected PG detection profile to a measured one. The computation of the expected PG detection profile in the context of a clinical framework is challenging but must be solved before clinical implementation. Obviously, Monte Carlo methods (MC) can simulate the expected PG profile but at prohibitively long calculation times. We implemented a much faster method that is based on analytical processing of precomputed MC data that would allow practical evaluation of this range monitoring approach in clinical conditions. Reference PG emission profiles were generated with MC simulations (PENH) in targets consisting of either 12 C, 14 N, 16 O, 31 P or 40 Ca, with 10% of 1 H. In a given geometry, the local PG emission can then be derived by adding the contribution of each element, according to the local energy of the proton obtained by continuous slowing down approximation and the local composition. The actual incident spot size is taken into account using an optical model fitted to measurements and by super sampling the spot with several rays (up to 113). PG transport in the patient/camera geometries and the detector response are modelled by convolving the PG production profile with a transfer function. The latter is interpolated from a database of transfer functions fitted to MC data (PENELOPE) generated for a photon source in a cylindrical phantom with various radiuses and a camera placed at various positions. As a benchmark, the analytical model was compared to MC and experiments in homogeneous and heterogeneous phantoms. Comparisons with MC were also performed in a thoracic CT. For all cases, the analytical model reproduced the prediction of the position of the Bragg peak computed with MC within 1 mm for the camera in nominal configuration. When compared to measurements, the shape of the profiles was well reproduced and agreement for the estimation of the position of the Bragg peak was within 2.7 mm on average (1.4 mm standard deviation). On a non-optimized MATLAB code, computation time with the analytical model is between 0.3 to 10 s depending on the number of rays simulated per spot. The analytical model can be further used to determine which spots are the best candidates to evaluate the range in clinical conditions and eventually correct for over- and under-shoots depending on the acquired PG profiles.

Keywords: prompt gamma; range monitoring; Monte Carlo

Publ.-Id: 21151

How polytypism in InAs nanowires is affected by the presence of liquid indium during the growth on silicon

Dimakis, E.; Biermanns, A.; Davydok, A.; Sasaki, T.; Geelhaar, L.; Takahasi, M.; Pietsch, U.

The self-assisted growth of vertical InAs nanowires on Si(111) substrates offers the possibil-ity to integrate monolithically the two materials, e.g. for novel transistor architectures, without the risk of contamination by foreign catalysts. However, arsenide nanowires that grow along the [111] crystallographic orientation are prone to wurtzite-zincblende polytypism, making the control of the crystal phase very challenging. In this work, we attempt to describe the dynamic relation between the growth conditions and the structural composition of the nanowires, and to identify potential ways to achieve phase-pure, particularly wurtzite, InAs nanowires.
Using in-situ X-ray scattering and diffraction measurements during the growth by molecular beam epitaxy, we were able to monitor the liquid phase of indium and the crystal structure of the growing nanowires throughout the growth process (Fig. 1). Although we used a much higher flux for arsenic than for indium as it is typically done for InAs nanowires, we directly observed the spontaneous build-up of liquid indium in the beginning of the growth process. Most im-portantly, the presence of liquid indium was associated with the simultaneous nucleation of InAs nanowires predominantly in the wurtzite phase. Since the build-up of liquid indium is driven by the surface diffusion of indium adatoms on the Si substrate under extremely arsenic-rich conditions, only a limited number of liquid indium sites were possible to form on the substrate, while their existence lasted for a limited period of time. In fact, the number and the lifetime of the liquid indium sites were the two parameters that defined the nucleation phase for the nan-owires.
After their nucleation, the nanowires continue to grow in the absence of liquid indium, and with a highly defective wurtzite structure. Numerical simulations based on a Monte Carlo ap-proach were employed to fit the ex-situ diffuse X-ray scattering measurements, showing that the structural degradation of the nanowires is due to the formation of planar stacking faults with their planes perpendicular to the growth direction. The onset of the formation of stacking faults is correlated with the transition from indium- to arsenic-rich conditions on each nanowire shortly after their nucleation.
After all, our study reveals the role of liquid indium in the nucleation and the structural com-position of InAs nanowires that grow on Si(111), implying that pure wurtzite nanowires may be obtained if the growth is performed in the continuous presence of liquid indium, i.e. the vapour-liquid-solid mode.

  • Lecture (Conference)
    Nanowire Growth Workshop, 25.08.2014, Eindhoven, The Netherlands

Publ.-Id: 21150

2nd International Workshop on Advanced Techniques for Actinide Spectroscopy (ATAS 2014) Abstract Book

Foerstendorf, H.; Müller, K.; Steudtner, R.; (Editors)

In 2012, The Institute of Resource Ecology at the Helmholtz-Zentrum Dresden Rossendorf organized the first international workshop of Advanced Techniques in Actinide Spectroscopy (ATAS). A very positive feedback and the wish for a continuation of the workshop were communicated from several participants to the scientific committee during the workshop and beyond.
Today, the ATAS workshop has been obviously established as an international forum for the exchange of progress and new experiences on advanced spectroscopic techniques for international actinide and lanthanide research. In comparison to already established workshops and conferences on the field of radioecology, one main focus of ATAS is to generate synergistic effects and to improve the scientific discussion between spectroscopic experimentalists and theoreticians.
The exchange of ideas in particular between experimental and theoretical applications in spectroscopy and the presentation of new analytical techniques are of special interest for many research institutions working on the improvement of transport models of toxic elements in the environment and the food chain as well as on reprocessing technologies of nuclear and non-nuclear waste.
Spectroscopic studies in combination with theoretical modelling comprise the exploration of molecular mechanisms of complexation processes in aqueous or organic phases and of sorption reactions of the contaminants on mineral surfaces to obtain better process understanding on a molecular level. As a consequence, predictions of contaminant’s migration behaviour will become more reliable and precise. This can improve the monitoring and removal of hazardous elements from the environment and hence, will assist strategies for remediation technologies and risk assessment.
Particular emphasis is placed on the results of the first inter-laboratory Round-Robin test on actinide spectroscopy (RRT). The main goal of RRT is the comprehensive molecular analysis of the actinide complex system U(VI)/acetate in aqueous solution independently investigated by different spectroscopic and quantum chemical methods applied by leading laboratories in geochemical research. Conformities as well as sources of discrepancies between the results of the different methods are to be evaluated, illuminating the potentials and limitations of cou-pling different spectroscopic and theoretical ap-proaches as tools for the comprehensive study of actinide molecule complexes. The test is understood to stimulate scientific discussions, but not as a competitive exercise between the labs of the community.
Hopefully, the second ATAS workshop will continue to bundle and strengthen respective research activities and ideally act as a nucleus for an international network, closely collaborating with international partners. I am confident that the workshop will deliver many exciting ideas, promote scientific discussions, stimulate new developments and collaborations and in such a way be prosperous.
This workshop would not take place without the kind support of the HZDR administration which is gratefully acknowledged. Finally, the or-ganizers cordially thank all public and private sponsors for generous funding which makes this meeting come true for scientists working on the heavy metal research field.

Thorsten Stumpf
Director of the Institute of Resource Ecology

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-054 2014
    ISSN: 2191-8708, eISSN: 2191-8716


Publ.-Id: 21149

3 × 3 rod bundle investigations, CFD single-phase numerical simulations

Lifante, C.; Krull, B.; Frank, T.; Franz, R.; Hampel, U.

The work here presented has been performed in the framework of a research project aimed to investigate two-phase (boiling) flows in pressurized water reactors (PWR). CFD investigations of a rod bundle have been conducted while a new experimental facility (ROFEX) was constructed in Helmholtz Zentrum Dresden-Rossendorf (HZDR) for the generation of quality validation data. The apparatus consists of a 3 × 3 rod bundle inside a Plexiglas vertical pipe. The results summarized in this paper are considered as a pre-investigation, being the final goal to be able to predict accurately boiling water flows under high pressure around rods. For this purpose, three steps were defined: analysis of single-phase flows in such geometry, analysis of the multiphase flow when using a refrigerant as a working fluid and, finally, the analysis of a multiphase flow using water. The single-phase approach allows gaining experience regarding the turbulence behaviour of the flow, while the multiphase investigation of the refrigerant simplifies the experimental conditions since it is possible to get boiling situations at lower pressure level. At the moment of writing this paper, the authors were focused on the first step (single-phase flows at low pressure), since this not only made possible to better understand the turbulence in that geometry, but it also resulted in valuable feedback to the experimentalists on improving the construction of the facility. In parallel, HZDR researchers have been developing a new tomography measurement technique to measure gas content in multiphase flows.

Keywords: Rod bundles

Publ.-Id: 21148

A new statistical parameter for identifying of the main transition velocities in bubble columns

Nedeltchev, S. N.; Rabha, S.; Hampel, U.; Schubert, M.

The identification of the main flow regime boundaries in bubble columns is essential since the degrees of mixing, mass and heat transfer vary with the flow regime. Most of the available methods in the literature for flow regime identification provide controversial results about the transition velocities and they are applicable mainly to pressure fluctuations. That is why, in this work a new statistical parameter was extracted from gas holdup time series (60,000 points) of the cross-sectional averaged gas holdup. The measurements were performed in a narrow (0.15 m in ID) and a large (0.4 m in ID) bubble column by means of conductivity wire-mesh sensors at very high sampling frequency (2000 Hz). The wire-mesh sensors in both columns were always installed at a height of 1.3 m above the gas distributor. Both columns were equipped with a perforated plate distributor, each with an open area of 1 %. The columns operated with an air-deionized water system at ambient conditions.
As a regime indicator, a new dimensionless statistical parameter called ‘relative maximum number of visits in a region’ Nrmax was introduced. This new parameter is a function of the difference between the maximum number of visits in a region arising from two different division schemes of the signal’s range. The identified two transition velocities were found to be independent of the different division schemes studied in this work. In both small and large bubble columns, the Nrmax profiles exhibited two well-defined local minima, which identified two transition velocities Utrans, indicating the end of the gas maldistribution regime and the onset of the churn-turbulent regime. It was found that the column diameter affects only the second transition velocity.

Keywords: flow regime identification; bubble column; maximum number of visits in a region; gas maldistribution; gas holdup fluctuations; conductivity wire-mesh sensor

Publ.-Id: 21147

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