Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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35836 Publications

Processing of prompt gamma-ray timing data for proton range measurements at a clinical beam delivery

Werner, T.; Berthold, J.; Hueso-Gonzalez, F.; Koegler, T.; Petzoldt, J.; Roemer, K.; Richter, C.; Rinscheid, A.; Straessner, A.; Enghardt, W.; Pausch, G.

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

Keywords: proton therapy; range verification; prompt gamma ray timing

Publ.-Id: 27773

Measurement of interfacial wave dynamics in orbitally shaken cylindrical containers using ultrasound pulse-echo techniques

Horstmann, G. M.; Wylega, M.; Weier, T.

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

Keywords: Interfacial Waves; Liquid Metal Batteries; Aluminum Reduction Cells


Publ.-Id: 27772

Quaternary evolution of the Ploučnice River system (Bohemian Massif) based on fluvial deposits dated with optically stimulated luminescence and in situ-produced cosmogenic nuclides

Stor, T.; Schaller, M.; Merchel, S.; Martínek, K.; Rittenour, T.; Rugel, G.; Scharf, A.

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

Keywords: cosmogenic nuclides; optically stimulated luminescence; fluvial terraces; Bohemian Massif; Pleistocene; neotectonics

Publ.-Id: 27771

Evolution of structure and residual stress of a fcc/hex-AlCrN multi-layered system upon thermal loading revealed by cross-sectional X-ray nano-diffraction

Jäger, N.; Klima, S.; Hruby, H.; Julin, J.; Keckes, J. F.; Mitterer, C.; Daniel, R.

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

Keywords: Coating; Multilayers; Microstructure design; Residual stress; X-ray nano-diffraction

Publ.-Id: 27770

64Cu-labeled bioconjugates based on triazacyclononane bifunctional chelators for radiopharmaceutical applications

Stephan, H.; Pant, K.; Joshi, T.; Zarschler, K.

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

1. E.W. Price, C. Orvig, Chem. Soc. Rev. 2014, 43, 260. 2. G. Singh, M.D. Gott, H.-J. Pietzsch, H. Stephan, Nuclearmedicine, 2016, 55, 41.

  • Lecture (Conference)
    43rd International Conference on Coordination Chemistry, 30.07.-04.08.2018, Sendai, Japan

Publ.-Id: 27769

Radiolabelled Nanomaterials for Imaging and Treatment of Cancer

Stephan, H.

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

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

  • Lecture (others)
    Kolloquium, 26.07.2018, Tokyo, Japan

Publ.-Id: 27768

Pseudo-scalar qqbar bound states at finite temperatures within a Dyson-Schwinger-Bethe-Salpeter approach

Dorkin, S. M.; Kaptari, L. P.; Kämpfer, B.

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


Publ.-Id: 27767

Union of light ion therapy centers in Europe (ULICE EC FP7) - Objectives and achievements of joint research activities

Pötter, R.; Balosso, J.; Baumann, M.; Bert, C.; Davies, J.; Enghardt, W.; Fossati, P.; Harris, S.; Jones, B.; Krämer, M.; Mayer, R.; Mock, U.; Pullia, M.; Schreiner, T.; Dosanjh, M.; Debus, J.; Orecchia, R.; Georg, D.

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

Keywords: Particle therapy; Proton; Carbon ion; EC project

Publ.-Id: 27766

Tumor Volume, HPV Status, and Cancer Stem Cell Marker Expression as prognostic Markers for the locoregional Tumor Control in Patients with locally advanced Head and Neck Squamous Cell Carcinoma after primary Chemoradiotherapy

Linge, A.; Schmidt, S.; Krenn, C.; Lohaus, F.; Valentini, C.; von Neubeck, C.; Appold, S.; Gudziol, V.; Nowak, A.; Baretton, G.; Buchholz, F.; Baumann, M.; Krause, M.; Lock, S.

Fragestellung: Die prognostische Rolle des Tumorvolumens, des HPV-Status und der Expression des Krebsstammzellmarkers CD44 konnte kürzlich in einer Arbeit der Radioonkologie-Gruppe des Deutschen Konsortiums für Translationale Krebsforschung gezeigt werden. Ziel dieser Arbeit ist es, die prognostische Rolle dieser Marker in einer
unabhängigen Kohorte zu validieren. Methodik: Diese Studie wurde an einer monozentrischen Kohorte von 78 Patienten mit lokal fortgeschrittenen Kopf-Hals-Plattenepithel-
karzinomen der Mundhöhle, des Oropharynx und des Hypopharynx durchgeführt . Alle Patienten haben eine primäre Radiochemotherapie zwischen 1999 und 2011 mit einer medianen Gesamtdosis von 72 Gy erhalten. Der HPV-Surrogatmarker p16 und der Krebsstammzellmarker CD44 wurden immunhistochemisch untersucht . Die Genexpressionsanalyse von CD44 erfolgte mittels nanoString-Technologie. Das Tumorvolumen war von allen Patienten verfügbar und wurde durch einen Strahlentherapeuten erneut geprüft . Logistische und Cox-Regressionsmodelle wurden anhand der Fläche unter der Receiver-Operating-Characteristic-Kurve (AUC) sowie dem C-Index (ci) validiert. Der primäre Endpunkt dieser Studie ist die lokoregionale Tumorkontrolle.
Ergebnis: Das Tumorvolumen war auch in dieser Studie signifikant mit dem Endpunkt der lokoregionalen Tumorkontrolle in der univariaten Analyse assoziiert (p = 0,009). Patienten mit CD44-negativen Tumoren entwickelten kein lokoregionales Rezidiv. In der multivariaten Cox-Regressionsanalyse bezüglich der Endpunkte der lokoregionalen Tumorkontrolle und des Gesamtüberlebens konnte die unabhängige Rolle des Tumorvolumens, des N-Status und des p16-Status bestätigt werden (lokoregionale Tumorkontrolle; ci: 0,64; Gesamtüberleben; ci: 0,68). Durch die zusätzliche Berücksichtigung der Genexpression von CD44 konnte das Modell leicht verbessert werden (lokoregionale Tumorkontrolle; ci: 0,65; Gesamtüberleben; ci: 0,72) . Das auf die Marker Tumorvolumen, p16-Status und CD44-Expression basierende logistische Regressionsmodell für die lokoregionale Kontrolle nach 2 Jahren konnte ebenfalls erfolgreich validiert werden (AUC: 0,70). Schlussfolgerung: Die prognostische Rolle des Tumorvolumens, des HPV-Status und des Krebsstammzellmarkers CD44 für Patienten mit lokal fortgeschrittenen Kopf-Hals-Plattenepithelkarzinomen, die eine primäre Radiochemotherapie erhalten haben, konnte in univariaten und in multivariaten Modellen bestätigt werden.

Publ.-Id: 27765

Is Treatment Benefit caused by specialized oncology Centers in the Treatment of locally advanced Rectal Cancer?

Lattermann, A.; Löck, S.; Jentsch, C.; Weitz, J.; Krause, M.

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

Publ.-Id: 27764

p16 and CD44 as Prognostic Factors for Patients with early Squamous Cell Carcinoma of the Head and Neck Region

Schneider, M.; Linge, A.; Nowak, A.; Gudziol, V.; Olesch, F.; Lohaus, F.; Baretton, G.; Lauer, G.; Zahnert, T.; Baumann, M.; Löck, S.; Krause, M.

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

Publ.-Id: 27763

Strain and screening: Optical properties of a small-diameter carbon nanotube from first principles

Wagner, C.; Schuster, J.; Schleife, A.

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

Keywords: carbon nanotubes; optical properties; excitons; strain; first-principles calculations; density functional theory; many-body perturbation theory; screening


Publ.-Id: 27762

Influence of defect-induced deformations on electron transport in carbon nanotubes

Teichert, F.; Wagner, C.; Croy, A.; Schuster, J.

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

Keywords: carbon nanotube (CNT); defect; deformation; electronic transport; density-functional-based tight binding (DFTB)


Publ.-Id: 27761

A coronene-based semiconducting two-dimensional metal-organic framework with ferromagnetic behavior

Dong, R.; Zhang, Z.; Tranca, D. C.; Zhou, S.; Wang, M.; Adler, P.; Liao, Z.; Liu, F.; Sun, Y.; Shi, W.; Zhang, Z.; Zschech, E.; Mannsfeld, S.; Felser, C.; Feng, X.

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

Publ.-Id: 27760

Kinematic dynamo action of a precession driven flow based on the results of water experiments and hydrodynamic simulations

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

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

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

Keywords: Dynamo; DRESDYN


Publ.-Id: 27759

⁶⁰Fe and ²⁴⁴Pu on Earth – Access to the Solar Neighbourhood, Stars and the Past of Earth

Koll, D.; Faestermann, T.; Korschinek, G.; Merchel, S.; Welch, J.; Kipfstuhl, S.; Wallner, A.

Long-lived radionuclides such as ⁶⁰Fe (t1/2=2.6 Myr) or ²⁴⁴Pu (t1/2=81 Myr) are synthesised in significant quantities in stellar environments by the capture of free neutrons. ⁶⁰Fe is in addition also produced, by cosmic ray interactions with interplanetary bodies, albeit at much lower quantities. Importantly, on Earth natural production of both isotopes is negligible, making them a valuable
tracer of extraterrestrial origin. Since these two isotopes are synthesised by the slow-neutron capture process (s-process) and predominantly ejected in supernova explosions, and the rapid neutron capture process (r-process), respectively, the potential detection of both isotopes opens the possibility to connect both processes in one astrophysical production site. The only measurement technique at this time which is sensitive enough to measure lowest concentrations of both isotopes is Accelerator Mass Spectrometry (AMS).
[1] History of detecting extraterrestrial ⁶⁰Fe
Extraterrestrial ⁶⁰Fe was detected first on Earth in a ferromanganese crust by the Munich AMS group in 2004 [1,2]. These samples allowed to analyse the past ~10 Myr for its ⁶⁰Fe content. Time-profile and absolute influx indicates that these ⁶⁰Fe atoms in the deep-sea crust were produced and ejected by one or more supernovae about 2 to 3 Myr ago and subsequently incorporated in this geological archive.
This discovery triggered several other projects to confirm this finding and to look for the same signal in other reservoirs like deep-sea sediments [3,4].
Furthermore, ⁶⁰Fe was also discovered on the Moon in lunar regolith [5]. These measurements all point towards an interstellar ⁶⁰Fe entry about 2-3 Myr ago, but the signal weakens and approaches measurement background for recent times.
However, such ⁶⁰Fe measurements are extremely difficult and only two AMS facilities (TU Munich and ANU) are sensitive enough for such measurements. For these reasons, also no significantly enhanced extraterrestrial influx of contemporary ⁶⁰Fe (i.e. within the last few 10
kyr) on Earth could be reported.
[2] ⁶⁰Fe in Antarctic snow
AMS is a relative measurement for isotope ratios, here extraterrestrial ⁶⁰Fe relative to stable terrestrial Fe. One major problem in the detection of modern ⁶⁰Fe influx from space by AMS, is the presence of the highly abundant stable terrestrial iron. Combined with the short ⁶⁰Fe accumulation periods, detection of a recent extraterrestrial signal becomes extremely challenging. To overcome this limiting factors, 500 kg of pure Antarctic surface snow (i.e. with lowest terrestrial Fe content) were recovered from the Kohnen Station in Antarctica and chemically
processed for an AMS measurement. Indeed, ⁶⁰Fe was discovered in Antarctic snow and by comparison with other isotopes such as ⁵³Mn, which is dominantly produced by cosmic ray interactions with solar system objects, the origin of these ⁶⁰Fe atoms could be
deduced [6].
[3] Search for concomitant ⁶⁰Fe and ²⁴⁴Pu influx onto Earth
Recently, we have started a project to extend previous measurements of ⁶⁰Fe and ²⁴⁴Pu in several geological reservoirs. The search for the coincident influx of ⁶⁰Fe and ²⁴⁴Pu into the same terrestrial archive opens the possibility to investigate a connection between Supernova-signatures (⁶⁰Fe production) and r-process nucleosynthesis (²⁴⁴Pu is a pure r-process nuclide). For this purpose, compared to
previous studies [2,7], a substantially larger sample of the same ferromanganese crust is available for ⁶⁰Fe [2] and ²⁴⁴Pu [7]. In this multi-isotope approach, we aim for a detailed time-profile for both isotopes in the crust. Such a project has become feasible also due to a substantially improved detection efficiency in ²⁴⁴Pu measurements. In addition, we plan to extend the time-period further into the past.
[4] References
[1] K. Knie et. al. “Indication for supernova produced ⁶⁰Fe activity on Earth” Phys. Rev. Lett. 83 (1999) 18.
[2] K. Knie et. al. “⁶⁰Fe anomaly in a deep-sea manganese crust and implications for a nearby supernova source” Phys. Rev. Lett. 93 (2004) 171103.
[3] P. Ludwig et. al. “Time-resolved 2-million-year-old super-nova activity discovered in Earth's microfossil record”, Proceedings of the National Academy of Sciences 113 (2016) 9232.
[4] A. Wallner et. al. “Recent near-Earth supernovae probed by global deposition of interstellar radioactive ⁶⁰Fe” Nature 532 (2016) 69.
[5] L. Fimiani et. al. “Interstellar ⁶⁰Fe on the surface of the Moon” Phys. Rev. Lett. 116 (2016) 151104.
[6] D. Koll “Search for recent ⁶⁰Fe deposition in Antarctica with AMS” Master's Thesis TUM (2018).
[7] A. Wallner et al., “Abundance of live ²⁴⁴Pu in deep-sea reservoirs on Earth points to rarity of actinide nucleosynthesis”, Nat. Comm. 6 (2015) 5956.

Keywords: accelerator mass spectrometry; astrophysics

  • Lecture (Conference)
    23rd Australian Institute of Physics Congress, 09.-13.12.2018, Perth, Australia


Publ.-Id: 27758

Protracted river recovery from medieval earthquakes

Stolle, A.; Schwanghart, W.; Andermann, C.; Bernhardt, A.; Fort, M.; Wittmann, H.; Merchel, S.; Rugel, G.; Adhikary, B. R.; Korup, O.

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

Keywords: accelerator mass spectrometry; cosmogenic nuclide; geomorphological risk assessment; Earthquake

  • Poster
    4th Central European Geomorphology Conference, 09.-13.10.2017, Bayreuth, Deutschland

Publ.-Id: 27757

Dynamics of nanoparticle morphology under low energy ion irradiation

Holland-Moritz, H.; Graupner, J.; Möller, W.; Pacholski, C.; Ronning, C.

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

Keywords: in situ ion beam; Monte Carlo; nanoparticles; sputtering

Publ.-Id: 27756

Comparative Hydrodynamic Analysis of Narrow and Pilot-Scale Bubble Columns with Internals

Möller, F.; Kipping, R.; Schleicher, E.; Löschau, M.; Hampel, U.; Schubert, M.

For a stable operation of exothermic processes in bubble column reactors, an appropriate heat control is required, e.g. through dense tube bundle heat exchangers installed in the column. However, their impact on flow morphology, phase distribution, mixing and mass transfer is scarcely reported and the derivation of reliable scaling approaches for bubble columns with internals is challenging. Thus, a narrow column (DN100) and a pilot-scale column (DN400) were equipped with tubes in two common patterns with triangular and square pitches to study local fluid dynamics. The results of both reactors are discussed with regard to their hydrodynamic similarity.

Keywords: Bubble column scale-up; Heat exchanger internals; Hydrodynamic similarity; Ultrafast X-ray tomography; Wire-mesh sensor


Publ.-Id: 27755

Modeling and Fitting of Three-Dimensional Mineral Microstructures by Multinary Random Fields

Teichmann, J.; Menzel, P.; Heinig, T.; van den Boogaart, K. G.

Modeling a mineral microstructure accurately in three dimensions allows to render realistic mineralogical patterns which can be used for threedimensional processing simulations and calculation of three-dimensional mineral quantities.
The present study introduces a flexible approach to model the microstructure of mineral material composed of a large number of facies. The common plurigaussian method, a valuable approach in geostatistics, can account for correlations within each facies and in principle be extended to correlations between the facies.
Assuming stationarity and isotropy, founded on a new description of this model, formulas for first- and second-order characteristics,
such as volume fraction, correlation function and cross-correlation function can be given by a multivariate normal distribution. In this particular situation, based on first- and second-order statistics, a fitting procedure can be developed which requires only numerical inversion of several one-dimensional monotone functions.
The paper describes the whole workflow; from getting the covariance structure fast from two-dimensional particle pixel images, by using Fourier transform, over model fitting to sampling and efficiently representing the resulting threedimensional microstructure by tessellations.
The applicability is demonstrated for the three-dimensional case by modeling the microstructure from a Mineral Liberation Analyzer (MLA) image data set of an andesitic basalt breccia.

Keywords: Gaussian random field; multinary random field; random closed set; plurigaussian; image processing; cross-covariance; microstructure

Publ.-Id: 27754

Frequency linewidth and decay length of spin waves in curved magnetic membranes

Otalora, J. A.; Kákay, A.; Lindner, J.; Schultheiss, H.; Thomas, A.; Fassbender, J.; Nielsch, K.

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



Publ.-Id: 27753

Multi-frequency inductive system for magnesium level detection in a titanium reduction reactor

Krauter, N.; Stefani, F.; Gundrum, T.; Wondrak, T.; Frick, P.; Khalilov, R.

The inductive measurement of the magnesium level in a titanium reduction reactor is a challenging task because the state of the art measurement techniques are hampered by the formation of titanium sponge rings within the reactor. By distorting the magnetic field between excitation and sensor coils, which is used to determine the magnesium level, these rings lead to a considerable measurement error. We present a novel approach to magnesium level detection using the existing infrastructure of the titanium reduction reactor, while considering the unknown size, position and electrical conductivity of the titanium sponge ring. Based on numerical simulations, we demonstrate how to solve the resulting inverse problem by applying a look-up-table method comprising tens of thousands of pre-calculated parameter combinations.

Keywords: Titanium; Kroll process; level detection; inductive measurements

  • Poster
    9th International Symposium on Electromagnetic Processing of Materials (EPM2018), 17.-18.10.2018, Awaji City, Japan
  • Open Access Logo IOP Conference Series: Materials Science and Engineering 424(2018), 012078
    DOI: 10.1088/1757-899X/424/1/012078

Publ.-Id: 27751

Transient Eddy Current Flow Metering: calibration-free velocity measurements for liquid metals

Krauter, N.; Stefani, F.

Most inductive techniques for the velocity measurement of liquid metals have the common problem that the measured signals depend on the electrical conductivity and the temperature of the liquid metal. This is particularly unfavourable for applications with strong temperature fluctuations or for measurements that have to be performed in different liquid metals with the same sensor. Usually these sensors have to be calibrated extensively to ensure accurate measurement results. We present a new measurement technique called Transient Eddy Current Flow Metering (TECFM) which overcomes the need for prior calibration of the sensors. Its principle relies on imprinting transient eddy current systems into the liquid metal and to track their movement as they are advected with the flow. Two kinds of sensors that use this new measurement principle have been developed: An external sensor for the contactless velocity measurement at the boundary of liquid metal flows, and an immersed sensor which allows local velocity measurements in the vicinity of the sensor. Focusing on the latter we present the results of numerical simulations as well as the results of measurements that were performed in the eutectic alloy GaInSn at room temperature and in liquid sodium at 180 °C.

Keywords: flow measurement; inductive methods; calibration-free

  • Lecture (Conference)
    9th International Symposium on Electromagnetic Processing of Materials (EPM2018), 14.-18.10.2018, Awaji City, Japan
  • Open Access Logo IOP Conference Series: Materials Science and Engineering 424(2018), 012008
    DOI: 10.1088/1757-899X/424/1/012008

Publ.-Id: 27750

Creation of silicon vacancy in silicon carbide by proton beam writing toward quantum sensing applications

Ohshima, T.; Satoh, T.; Kraus, H.; Astakhov, G.; Dyakonov, V.; Baranov, P. G.

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

Publ.-Id: 27748

Liquid structure of shock-compressed hydrocarbons at megabar pressures

Hartley, N. J.; Vorberger, J.; Döppner, T.; Cowan, T.; Falcone, R. W.; Fletcher, L. B.; Frydrych, S.; Galtier, E.; Gamboa, E. J.; Gericke, D. O.; Glenzer, S. H.; Granados, E.; Macdonald, M. J.; Mackinnon, A. J.; Mcbride, E. E.; Nam, I.; Neumayer, P.; Pak, A.; Rohatsch, K.; Saunders, A. M.; Schuster, A. K.; Sun, P.; van Driel, T.; Kraus, D.

We present ion structure results from hydrocarbons (polystyrene, polyethylene) shock compressed to pressures of up to 190 GPa, inducing rapid melting of the samples. The structure of the resulting liquid is then probed using in situ diffraction by an X-ray free electron laser beam, with precise, reliable diffraction data obtained from single shots. This is the first example of single shot diffraction from low-Z samples dynamically driven into the liquid state. The data agrees well with the structure factors calculated from ab initio simulations, demonstrating their ability to model mixed samples in this state. While the results exclude the possibility of complete carbon-hydrogen demixing at the conditions probed, they also, in contrast to previous predictions, demonstrate that diffraction is not always a sufficient diagnostic for this phenomenon.


Publ.-Id: 27747

The role of incidence angle in the morphology evolution of Ge surfaces irradiated by medium-energy Au ions

Dell’Anna, R.; Iacob, E.; Barozzi, M.; Vanzetti, L.; Hübner, R.; Böttger, R.; Giubertoni, D.; Pepponi, G.

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

Keywords: ion beam irradiation; germanium; gold ions; binary system; ripples; terraces; sponge-like structures

Publ.-Id: 27746

Investigation of the exit charge state distribution of highly charged ions transmitted through 2D materials

Creutzburg, S.; Schwestka, J.; Gruber, E.; Lehnert, T.; Leiter, R.; Kozubek, R.; Heller, R.; Klingner, N.; Kotakoski, J.; Krasheninnikov, A. V.; Kaiser, U.; Schleberger, M.; Facsko, S.; Aumayr, F.; Wilhelm, R. A.

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

Keywords: 2D materials; highly charged ions

  • Poster
    SHIM-ICACS 2018, 02.-06.07.2018, Caen, France

Publ.-Id: 27745

Creation of Surface Nanostructures in Lanthanum Fluoride Single Crystals by Irradiation with Slow Highly Charged Ions

El-Said, A. S.; Wilhelm, R. A.; Heller, R.; Facsko, S.

Slow highly charged ions (HCI) were utilized successfully for the formation of various nanostructures in the surfaces of different materials. The creation mechanism of HCI-induced nanostructures was intensively studied in alkali- and alkaline-earth fluorides. Here, we are investigating another type of fluorine-containing ionic crystals of different crystalline and electronic structure, namely lanthanum fluoride, LaF3. The single crystals were irradiated with slow (eV-keV) highly charged xenon ions (Q=26-40). After irradiation, the crystal surfaces were investigated by scanning force microscopy (SFM). The measured topographic images show nanohillocks emerging from the surface. These nanostructures were observed only after exceeding a well-defined threshold in the potential energy. The role of ion parameters for nanohillocks formation as well as a comparison with results for swift heavy ion irradiations of LaF3 single crystals are presented. Furthermore, the similarities and differences between LaF3 and other ionic fluoride crystals, in the creation of surface nanostructures, are discussed.


Publ.-Id: 27744

A versatile ion beam spectrometer for studies of ion interaction with 2D materials

Schwestka, J.; Melinc, D.; Heller, R.; Niggas, A.; Leonhartsberger, L.; Winter, H.; Facsko, S.; Aumayr, F.; Wilhelm, R. A.

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

Keywords: slow highly charged ions; 2D materials; ion spectrometer; single layer graphene


Publ.-Id: 27743

Neutralization Dynamics of Slow Highly Charged Ions in 2D Materials

Wilhelm, R.; Gruber, E.; Schwestka, J.; Heller, R.; Facsko, S.; Aumayr, F.

We review experimental and theoretical work on the interaction of slow highly charged ions with two-dimensional materials. Earlier work in the field is summarized and more recent studies on 1 nm thick amorphous carbon nanomembranes and freestanding single layer graphene by the authors are reviewed. To explain the findings, models for energy loss determination as well as qualitative model descriptions for the observed ultrafast neutralization dynamics are discussed. The results shown in this paper will be put into context with findings of nanostructure formation on two-dimensional materials, both freestanding and on substrate, as well as on surfaces of bulk insulators.

Keywords: low energy ions; highly charged ions; 2D materials

Publ.-Id: 27742

Working in stealth mode: Towards the development of biomolecular corona-resistant hydrophilic nanomaterials for biomedical applications

Joshi, T.; Nsubuga, A.; Zarschler, K.; Stephan, H.

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

  • Invited lecture (Conferences)
    256th ACS National Meeting in Boston, MA, 19.-23.08.2018, Boston, USA

Publ.-Id: 27741

Development of biomolecular corona-resistant nanomaterials suitable for biological applications

Joshi, T.; Nsubuga, A.; Zarschler, K.; Stephan, H.

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

  • Invited lecture (Conferences)
    10th International Symposium on Nano & Supramolecular Chemistry, 09.-12.07.2018, Dresden, Germany

Publ.-Id: 27740

Wetting fraction in a tubular reactor with solid foam packing and gas/liquid co-current downflow

Mohammmed, I.; Hampel, U.

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

Keywords: Multiphase; Solid Foam; Wetting; Electrocemical Methode; Gas/Liquid; Pre-wetting mode

Publ.-Id: 27739

In situ Structural Study of Sb(V) Adsorption on Hematite (1-102) Using X-ray Surface Scattering

Qiu, C.; Majs, F.; Douglas, T.; Schmidt, M.; Trainor, T.

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

Keywords: Sb(V); hematite; crystal truncation rod


Publ.-Id: 27738

Nonlinear THz Spectroscopy of Two-Dimensional Systems

Helm, M.; König-Otto, J.; Schmidt, J.; Dimakis, E.; Winnerl, S.; Schneider, H.

Nonlinear THz experiments using a free-electron laser are presented on Landau quantized graphene as well as on intersubband transitions in a single GaAs quantum well.

Keywords: terahertz; free electron laser; graphene; Landau Levels; intersubband; GaAs; quantum well

  • Invited lecture (Conferences)
    Frontiers of photonics, plasmonics and electronics with 2D nanosystems, 14.-20.07.2018, Erice, Italy
  • Invited lecture (Conferences)
    Advanced Electromagnetics Symposium (AES 2018), 24.06.-01.07.2018, Marseille, France

Publ.-Id: 27737

CFD modeling of condensation inside emergency condensers of passive heat removal systems

Moonesi Shabestary, A.; Lucas, D.; Krepper, E.

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

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

  • Lecture (Conference)
    International Conference on Nuclear Engineering (ICONE 2018), 22.-26.07.2018, London, United Knigdom Britain

Publ.-Id: 27736

Realizing Quantum free-electron lasers: A critical analysis of experimental challenges and theoretical limits

Debus, A.; Steiniger, K.; Kling, P.; Carmesin, M.; Sauerbrey, R.

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

Keywords: Quantum free-electron laser; free-electron laser; FEL; QFEL


Publ.-Id: 27735

Design of high-temperature solar-selective coatings based on aluminium titanium oxynitrides AlyTi1-y(OxN1-x). Part 2: Experimental validation and durability tests at high temperature

Escobar-Galindo, R.; Guillén, E.; Heras, I.; Rincón-Llorente, G.; Alcón-Camas, M.; Lungwitz, F.; Munnik, F.; Schumann, E.; Azkona, I.; Krause, M.

The durability of two solar-selective aluminium titanium oxynitride multilayer coatings was studied under conditions simulating realistic operation of central receiver power plants. The coatings were deposited by cathodic vacuum arc applying an optimized design concept for complete solar-selective coating (SSC) stacks. Compositional, structural and optical characterization of initial and final stacks was performed by scanning electron microscopy, elastic recoil detection, UV-Vis-NIR-IR spectrophotometry and X-Ray diffraction. The design concept of the solar selective coatings was validated by an excellent agreement between simulated and initial experimental stacking order, composition and optical properties.

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

Keywords: Solar selective coatings; thermal stability; optical properties; concentrated solar power; optical simulation; oxynitrides


Publ.-Id: 27734

Cluster tool for in situ processing and comprehensive characterization of thin films at high temperatures

Wenisch, R.; Lungwitz, F.; Hanf, D.; Heller, R.; Zscharschuch, J.; Hübner, R.; von Borany, J.; Abrasonis, G.; Gemming, S.; Escobar Galindo, R.; Krause, M.

A new cluster tool for in situ real-time processing and depth-resolved compositional, structural and optical characterization of thin films at temperatures from -100 to 800 °C is described. The implemented techniques comprise magnetron sputtering, ion irradiation, Rutherford backscattering spectrometry, Raman spectroscopy and spectroscopic ellipsometry. The capability of the cluster tool is demonstrated for a layer stack MgO/ amorphous Si (~60 nm)/ Ag (~30 nm), deposited at room temperature and crystallized with partial layer exchange by heating up to 650°C. Its initial and final composition, stacking order and structure were monitored in situ in real time and a reaction progress was defined as a function of time and temperature.

Keywords: Cluster tool; thin films; in situ; high temperature; Rutherford backscattering; Raman spectroscopy; ellipsometry; metal-induced crystallization

  • Open Access Logo Analytical Chemistry 90(2018), 7837-7842
    Online First (2018) DOI: 10.1021/acs.analchem.8b00923
  • Lecture (Conference)
    16th International Conference on Plasma Surface Engineering, 16.-21.09.2018, Garmisch - Partenkirchen, Deutschland
  • Lecture (Conference)
    XV Congreso Nacional de Materiales/ Iberian Meeting on Materials Science, 04.-06.07.2018, Salamanca, Spanien


Publ.-Id: 27732

Performance study of a real-size mosaic high-rate MRPC

Lyu, P.; Han, D.; Wang, Y.; Guo, B.; Wang, F.; Chen, X.; Yu, Y.; Li, Y.; Naumann, L.; Lazo Garcia, A.; Stach, D.; Fan, X.

Towards the future CMS RPC upgrade, a real-size mosaic high-rate MRPC has been designed and developed by Tsinghua University. The prototype is a 5-gap counter composed of the low-resistive glass. Because the maximum size of this glass cannot exceed 330×280mm², 6 regions of glass stacks are mosaicked together in order to achieve a large active area. This prototype was tested in HZDR-ELBE with 30 MeV e-beam. It shows an efficiency above 95% at the rate of 2 kHz/cm². The time resolution is around 55 ps, and the cluster size is below 1.5. The performance is almost unaffected by increasing the rate to 11 kHz/cm². This design is proved to be fully capable of the CMS upgrade requirement by this HZDR beam test. The mosaic technology will make the high-rate MRPC a good choice in large-area timing systems.

Keywords: Performance of High Energy Physics Detectors; Resistive-plate chambers; Instrumentation and methods for time-of-flight (TOF) spectroscopy

Publ.-Id: 27731

Nonlinear Breit-Wheeler process in short laser double-pulses

Titov, A. I.; Kämpfer, B.; Takabe, H.

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


Publ.-Id: 27730

Low-temperature nanospectroscopy of the structural ferroelectric phases in single-crystalline barium titanate

Döring, J.; Lang, D.; Wehmeier, L.; Kuschewski, F.; Nörenberg, T.; Kehr, S. C.; Eng, L. M.

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

Keywords: s-SNIM; infrared nanospectroscopy; FEL; phase transition; low temperature

Publ.-Id: 27729

Polyethyleneimine Methylenecarboxylate: a macromolecular DTPA analogue to chelate plutonium(IV)

Lahrouch, F.; Siberchiot, B.; Leost, L.; Aupiais, J.; Rossberg, A.; Hennig, C.; Den Auwer, C.; Di Giorgio, C.

Up until now, molecular chelating agents, such as the diethylenetriamine pentaacetic acid (DTPA) have been the standard methode for actinide human decorporation. Active mainly in blood serum, their distribution within the body is thus limited. In order to treat a wider range of organs affected by plutonium contamination, a potential new class of macromolecular decorporation agents is being studied. Polyethyleneimine methylenecarboxylate (PEI-MC) is one such example. It is being considered here because of its capacity for targeting the liver and bones.

Keywords: Polyethyleneimine methylenecarboxylate; actinides; decorporation; EXAFS

Publ.-Id: 27728

Superconductivity and magnetism in noncentrosymmetric LaPtGe3 and CePtGe3

Feig, M.; Nicklas, M.; Bobnar, M.; Schelle, W.; Schwarz, U.; Leithe-Jasper, A.; Hennig, C.; Gumeniuk, R.

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

Keywords: CePtGe3; LaPtGe3; superconductor; magnetic moment; XRD

Publ.-Id: 27727

Combination of X-ray spectroscopy and X-ray diffraction at the Rossendorf Beamline / ESRF

Hennig, C.

The beamline will be refurbished in 2019, which includes the installation of additional experiments: (1) a spectrometer for high-resolution X-ray absorption near-edge structure spectroscopy (HR-XANES) and X-ray emission spectroscopy (XES), (2) a 6-circle diffractometer for crystal truncation rod (CTR) / Resonant anomalous X-ray reflectivity (RAXR) and high-resolution powder diffraction (HR-PXRD), (3) a diffractometer with a Pilatus X 2M detector for single-crystal diffraction (SC-XRD) and in-situ powder diffraction. The above mentioned experiments have been developed and tested in the last two years. The concept of the beamline and some typical experimental results will be presented.


  • Lecture (others)
    Ghent University, Department of Chemistry, 10.07.2018, Gent, Belgium

Publ.-Id: 27726

From bentonite to rock salt – microbial studies for nuclear waste disposal

Cherkouk, A.

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

  • Invited lecture (Conferences)
    THEMENFELD-KOLLOQUIUM „ENERGIE“, Topic: Results and outcomes of European programme on Microbiology In Nuclear waste Disposal (MIND) – View s and perspectives over future research, 19.09.2018, Berlin, Deutschland

Publ.-Id: 27725

Applying accelerator and microscopy methods for investigating radionuclides at Australia's former nuclear test sites

Child, D. P.; Johansen, M. P.; Hotchkis, M. A. C.; Howard, D. L.; Howell, N.; Young, E.; Davis, J.; Ikeda-Ohno, A.

The radiological residues at the former British nuclear weapons testing sites in Australia at Maralinga, Emu and the Montebello Islands are of ongoing interest in terms of environmental fate, transport, and uptake of radioactive contamination into the biosphere. The physical and chemical characteristics of these residues govern their mobility in the various environmental zones in which they reside (surface soil, ocean sediment, active beach zones) and availability of the radiological components for uptake into living organisms. At the Taranaki site, Maralinga, substantial body burdens of Pu were observed in mammals and the pattern of organ uptake was found to match that reported for exposure to respirable radioactive particles bearing refractory Pu. In order to fully deconvolute the disposition and radio-ecological impact of the contamination at these sites it was necessary to study in detail the radioactive particle composition.
Plutonium often occurs in particulate forms at nuclear accident and test sites. Such particles require advanced techniques for characterisation including Accelerator Mass Spectrometry (AMS), Scanning electron microscopy and synchrotron X-ray fluorescence microscopy (XFM). Many such particles have core-shell structures where the surface is dominated by lighter elements sourced from local soils and the Pu concentrated in the interior. Particles formed during nuclear detonations and accidents can have complex structures and compositions which may be susceptible to variable leaching and weathering rates. Modelling results suggest that for respirable-sized Pu-bearing particles (that can be inhaled and lodged in the lung), most of the alpha emissions escape the particle and are deposited in the surrounding tissue. We are currently using advanced techniques to compare the radionuclide forms from the inland sites (Maralinga and Emu) with the marine site (Montebello Islands) to compare leaching and dose implications. The characteristics of the particles will largely determine the overall potential implications for long term fate of radiological contamination at the sites.

Keywords: Accelerator mass spectrometry; X-ray fluorescence microscopy; synchrotron; nuclear tests; Australia; radioactive contaminant

  • Lecture (Conference)
    VIII INTERNATIONAL CONFERENCE Semipalatinsk Test Site: Legacy and Prospects for Scientific and Technical Potential Development, 11.09.2018, Kurchatov, Republic of Kazakhstan

Publ.-Id: 27724

Solving the Dyson–Schwinger Equation at Zero and Finite Temperatures

Dorkin, S. M.; Kaptari, L. P.; Kämpfer, B.

The properties of the solutions of the truncated Dyson–Schwinger equation for the quark propagator at finite temperatures within the rainbow-ladder approximation are analysed in some detail.


Publ.-Id: 27723

Phase structures emerging from holography with Einstein gravity - dilaton models at finite temperature

Zöllner, R.; Kämpfer, B.

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

Publ.-Id: 27722

Phytotoxicity of polymetallic mine wastes from southern Tuscany and Saxony

Franzaring, J.; Ancora, S.; Paoli, L.; Fongoh, A. H.; Büttner, P.; Fangmeier, A.; Schlosser, S.; Monaci, F.

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

Keywords: Mine wastes; Phytoremediation; Heavy metals; Oilseed rape; Buckwheat; Soil amendment

Publ.-Id: 27721

Stability of melt flow during magnetic sonication in a floating zone configuration

Grants, I.; Gerbeth, G.

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

Publ.-Id: 27720

High-speed X-ray CT imaging of a strongly cavitating nozzle flow

Bauer, D.; Barthel, F.; Hampel, U.

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

Keywords: Cavitation Flow; ROFEX; Ultrafast X-ray CT

Publ.-Id: 27719

The constancy of galactic cosmic rays as recorded by cosmogenic nuclides in iron meteorites

Smith, T.; Merchel, S.; Pavetich, S.; Rugel, G.; Scharf, A.; Leya, I.

We measured the He, Ne, and Ar isotopic concentrations and the ¹⁰Be, ²⁶Al, ³⁶Cl, and ⁴¹Ca concentrations in 56 iron meteorites of groups IIIAB, IIAB, IVA, IC, IIA, IIB, and one ungrouped. From ⁴¹Ca and ³⁶Cl data we calculated terrestrial ages of zero for six samples, indicating recent falls, up to 562+86 ka. Three of the studied meteorites are falls. The data therefore confirm that terrestrial ages for iron meteorites can be as long as a few hundred thousand years even in relatively humid conditions. The ³⁶Cl-³⁶Ar cosmic ray exposure (CRE) ages range from 4.3+0.4 Ma to 652+99 Ma. By including literature data, we established a consistent and reliable CRE age database for 67 iron meteorites. The improved quality of the CRE ages enables us to study structures in the CRE age histogramm more reliably. At first sight, the CRE age histogram shows peaks at about 400 Ma and 630 Ma. After correction for pairing, the updated CRE age histogram consists of 41 individual samples and shows no indications for periodic structures, especially not if one considers each group separately. Our study therefore clearly contradicts the popular hypothesis of periodic GCR intensity variations (Shaviv 2002,2003) but confirms other studies arguing that there are no periodic structures in the CRE age histogram (e.g., Rahmstorf et al. 2004; Jahnke 2005). Consequently, the data contradict the hypothesis that periodic GCR intensity variations might have triggered periodic Earth climate changes. The ³⁶Cl-³⁶Ar CRE ages are on average 40% lower than the ⁴¹K-K CRE ages (e.g., Voshage 1967). This offset can either be due to an offset in the ⁴¹K-K dating system or due to a significant lower GCR intensity in the time interval 195 Ma to 656 Ma compared to the recent past. A 40% lower GCR intensity, however, could increase the Earth temperature by up to 2°C, which seems unrealistic and leaves an ill-defined ⁴¹K-K CRE age system the most likely explanation. Finally, we present new ²⁶Al/²¹Ne and ¹⁰Be/²¹Ne production rate ratios of 0.32+0.01 and 0.33+0.02, respectively, which we consider as reliable and robust.

Keywords: Galactic cosmic-ray fluence; iron meteorites; exposure age histograms; climate changes

  • Meteoritics & Planetary Science 54(2019), 2951-2976
    Online First (2019) DOI: 10.1111/maps.13417

Publ.-Id: 27718

Stellar and thermal neutron capture cross section of ⁹Be

Wallner, A.; Bichler, M.; Coquard, L.; Dillmann, I.; Forstner, O.; Golser, R.; Heil, M.; Käppeler, F.; Kutschera, W.; Martschini, M.; Mengoni, A.; Merchel, S.; Michlmayr, L.; Priller, A.; Steier, P.; Wiescher, M.

The neutron capture cross section of ⁹Be for stellar energies was measured via the activation technique using the Karlsruhe Van de Graaff accelerator in combination with accelerator mass spectrometry at the Vienna Environmental Research Accelerator. To characterize the energy region of interest for astrophysical applications, activations were performed in a quasi-stellar neutron spectrum of kT = 25 keV and for a spectrum at En = 473+53 keV. Despite of the very small cross section, the method used provided the required sensitivity for obtaining fairly accurate results of 10.4+0.6 and 8.4+1.0 µb, respectively. With these data it was possible to constrain the cross section shape up to the first resonances at 622 and 812 keV, thus allowing for the determination of Maxwellian averaged cross sections at thermal energies between kT = 5 and 100 keV. In addition, we report a new experimental cross section value at thermal energy of s th = 8.31+0.52 mb.

Keywords: accelerator mass spectrometry; stellar nuclear reactions; supernova

Publ.-Id: 27717

Development of a novel target module redirecting UniCAR T cells to Sialyl Tn-expressing tumor cells

Loureiro, L.; Feldmann, A.; Bergmann, R.; Koristka, S.; Berndt, N.; Arndt, C.; Pietzsch, J.; Novo, C.; Videira, P.; Bachmann, M.

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

Keywords: Immunotherapy; CAR T cell therapy; Sialyl-Tn (STn)

Publ.-Id: 27716

Euler-Euler Modeling of Mass Transfer and Chemical Reaction

Rzehak, R.

Work done at HZDR on Euler-Euler simulation including mass transfer and chemical reaction is presented.

Keywords: mass transfer; chemical reaction; chemisorption; enhancement factor; dispersed gas-liquid multiphase flow; Euler-Euler two-fluid model; CFD simulation

  • Invited lecture (Conferences)
    Lectures on multiphase CFD, 06.-08.06.2018, Changsha, China

Publ.-Id: 27715

Baseline Model for Simulation of Bubbly Flows

Rzehak, R.

An overview of the HZDR-baseline Model for Simulation of Bubbly Flows is given.

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

  • Invited lecture (Conferences)
    Lectures on multiphase CFD, 06.-08.06.2018, Changsha, China

Publ.-Id: 27714

Speciation of actinides in environmentally relevant systems by advanced synchrotron techniques

Pidchenko, I.; Suksi, J.; Tullborg, A.; Scheinost, A.; Kvashnina, K. O.

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

  • Poster
    Goldschmidt 2018, 12.-27.08.2018, Boston, USA

Publ.-Id: 27713

Evidence of the negative thermal expansion of the UO2.00 fluorite local structure

Martin, P. M.; Prieur, D.; Epiphano, E.; Dardenne, K.; Rothe, J.; Hennig, C.; Scheinost, A. C.; Neuville, D.

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

Keywords: thermal contraction; UO2; XAFS

  • Lecture (Conference)
    NuMat 2018, 14.-18.10.2018, Seattle, USA

Publ.-Id: 27712

A baseline closure concept for simulating bubbly flow with phase change: interfacial heat transfer coefficient

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

In line with the best practice guidelines for computational fluid dynamics in nuclear reactor safety, Helmholtz-Zentrum Dresden – Rossendorf proposed an Euler-Euler baseline closure concept some years ago. Simulations with a fixed set of closures may help to identify model inadequacy and facilitate the further improvement. Currently, the baseline model concerns interfacial momentum and turbulent kinetic energy exchange as well as bubble coalescence and breakup. It has been tested for a wide range of isothermal applications with different geometrical configurations and material systems. In the present work, the baseline model is extended to non-isothermal flows by including a heuristic model for interfacial heat transfer coefficient. The extended baseline model is validated for both bubble-growing in superheated liquid and -condensing in sub-cooled liquid. The baseline model proposal is independent on the use of a certain CFD code. The presented simulation is carried out with the commercial software ANSYS CFX by employing the best practice guidelines. The simulated liquid temperature, gas volume fraction, vapor bubble size and velocity are compared with the measured ones. The effectivity of the model is demonstrated by the general good agreement.

  • Contribution to proceedings
    CFD4NRS-7 OECD-NEA & IAEA Workshop, 04.-06.09.2018, Shanghai, China
  • Lecture (Conference)
    CFD4NRS-7 OECD-NEA & IAEA Workshop, 04.-06.09.2018, Shanghai, China
  • Open Access Logo Nuclear Engineering and Design 348(2019), 1-13
    DOI: 10.1016/j.nucengdes.2019.04.007


Publ.-Id: 27711

Cfd modelling of flashing instability in natural circulation cooling systems

Liao, Y.; Schuster, C.; Hu, S.; Lucas, D.

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

  • Contribution to proceedings
    26th International Conference on Nuclear Engineering, ICONE26, 23.-26.07.2018, Hammersmith, London, England
  • Lecture (Conference)
    26th International Conference on Nuclear Engineering, ICONE26, 23.-26.07.2018, Hammersmith, London, England

Publ.-Id: 27710

Simulations of ultrafast X-ray laser experiments

Fortmann-Grote, C.; Andreev, A. A.; Appel, K.; Branco, J.; Briggs, R.; Bussmann, M.; Buzmakov, A.; Garten, M.; Grund, A.; Huebl, A.; Jurek, Z.; Loh, N. D.; Nakatsutsumi, M.; Samoylova, L.; Santra, R.; Schneidmiller, E. A.; Sharma, A.; Steiniger, K.; Yakubov, S.; Yoon, C.; Yurkov, M. V.; Zastrau, U.; Ziaja-Motyka, B.; Mancuso, A. P.

Simulations of experiments at modern light sources, such as optical laser laboratories, synchrotrons, and free electron lasers, become increasingly important for the successful preparation, execution, and analysis of these experiments investigating ever more complex physical systems, e.g. biomolecules, complex materials, and ultra-short lived states of matter at extreme conditions. We have implemented a platform for complete start-to-end simulations of various types of photon science experiments, tracking the radiation from the source through the beam transport optics to the sample or target under investigation, its interaction with and scattering from the sample, and registration in a photon detector. This tool allows researchers and facility operators to simulate their experiments and instruments under real life conditions, identify promising and unattainable regions of the parameter space and ultimately make better use of valuable beamtime. In this paper, we present an overview about status and future development of the simulation platform and discuss three applications: 1.) Single-particle imaging of biomolecules using x-ray free electron lasers and optimization of x-ray pulse properties, 2.) x-ray scattering diagnostics of hot dense plasmas in high power laser-matter interaction and identification of plasma instabilities, and 3.) x-ray absorption spectroscopy in warm dense matter created by high energy laser-matter interaction and pulse shape optimization for low-isentrope dynamic compression.

Keywords: XFEL; ultrafast; simulation; imaging; scattering; X-ray; biomolecules; warm dense matter

  • Contribution to proceedings
    SPIE Optics + Optoelectronics (2017), 20.06.2017, Praha, Česká republika
    SPIE 10237, Advances in X-ray Free-Electron Lasers Instrumentation IV, 978-1-5106-0975-4; 978-1-5106-0976-1
    DOI: 10.1117/12.2270552

Publ.-Id: 27709

Challenges in predicting the role of water chemistry in flotation through simulation with an emphasis on the influence of electrolytes

Michaux, B.; Rudolph, M.; Reuter, M. A.

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

Keywords: Water chemistry; Electrolytes; Solution thermodynamics; Flotation; Flotation kinetics

Publ.-Id: 27708

Reprocessing of a southern Chilean Zn tailing by flotation - a case study

Babel, B.; Penz, M.; Schach, E.; Böhme, S.; Rudolph, M.

The reprocessing of tailings can have economic and environmental benefits compared to the processing of primary ore deposits. In this paper we present the characterization of a tailings dam in southern Chile by means of mineralogical and geochemical investigations focusing on sphalerite and trace elements with the aim to investigate a potential reprocessing. The assessment is followed by a flotation study, focusing on the recovery of sphalerite with a high selectivity towards sulfidic and non-sulfidic gangue minerals. An in-depth analysis of a selected test based on mineral liberation analysis data is used to refine the liberation, concentration and flotation weighting function for future investigations.

Keywords: Geometallurgy; Flotation; Sphalerite; Tailings; Reprocessing

Publ.-Id: 27707

Bioremediation of uranium contaminated sites from former mining activities by microorganisms – a microscopic and spectroscopic approach.

Krawczyk-Bärsch, E.; Gerber, U.; Steudtner, R.; Müller, K.; Moll, H.; Rossberg, A.; Merroun, M. L.

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

Keywords: Uranium; A. facilis; sorption; TRLFS; ATR FT-IR; TEM

  • Lecture (Conference)
    19th International Conference on Heavy Metals in the Environment (ICHMET 2018),, 22.-25.07.2018, Athens, U.S.

Publ.-Id: 27706

Why do secondary cracks preferentially form in hot-rolled ODS steels in comparison with hot-extruded ODS steels?

Das, A.; Viehrig, H. W.; Altstadt, E.; Bergner, F.; Hoffmann, J.

Secondary cracks are known to absorb energy, retard primary crack propagation and initiate at lower loads than primary cracks. They are observed more often in hot-rolled than in hot extruded ODS steels. In this work, the microstructural factors responsible for this observation are investigated. Better understanding of these factors can lead to tailoring of im-proved ODS steels. Fracture toughness testing of two batches of 13Cr ODS steel, one hot-rolled and the other hot-extruded, was carried out. The fracture behaviour of secondary cracks was investigated using scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). Crystallographic texture and grain morphology play a predominant role in preventing secondary cracks in hot-extruded ODS steels. At lower temperatures, secondary cracks occur predominantly via transgranular cleavage. The fracture mode changes to ductile and intergranular at higher temperatures.

Keywords: ODS steel; fracture behaviour; anisotropy; intergranular fracture; secondary cracking; delamination

Related publications

Publ.-Id: 27705

Characterizing the Ionization Potential Depression in Dense Carbon Plasmas with High-Precision Spectrally Resolved X-ray Scattering

Kraus, D.; Bachmann, B.; Barbrel, B.; Falcone, R. W.; Fletcher, L. B.; Frydrych, S.; Gamboa, E. J.; Gauthier, M.; Gericke, D. O.; Glenzer, S. H.; Göde, S.; Granados, E.; Hartley, N. J.; Helfrich, J.; Lee, H. J.; Ravasio, A.; Nagler, B.; Schumaker, W.; Vorberger, J.; Döppner, T.

We discuss the possibility of obtaining highly precise measurements of the ionization potential depression in dense plasmas with spectrally resolved X-ray scattering, while simultaneously determining the electron temperature and the free electron density. A proof-of-principle experiment at the Linac Coherent Light Source, probing isochorically heated carbon samples, demonstrates the capabilities of this method and motivates future experiments at X-ray free electron laser facilities.


Publ.-Id: 27704

High energy resolution X-ray spectroscopy of actinide nanomaterials

Kvashnina, K. O.

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

  • Lecture (Conference)
    ATAS Workshop, 06.-09.11.2018, Nice, France

Publ.-Id: 27703

High energy resolution X-ray spectroscopy of actinide nanomaterials

Kvashnina, K. O.

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

  • Lecture (Conference)
    Advanced Techniques in Actinide Spectroscopy (ATAS2018), 06.-09.11.2018, Nice, France

Publ.-Id: 27702

The origin of low bandgap and ferroelectricity of a co-doped BaTiO3

Phuyal, D.; Das, S.; Mukherjee, S.; Jana, S.; Kvashnina, K. O.; Sarma, D. D.; Karis, O.; Rensmo, H.; Butorin, S. M.

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


Publ.-Id: 27701

Effect of time–modulated magnetic fields on the solidification structure and extrusion properties of wrought aluminium

Räbiger, D.; Resewski, C.; Müller, S.; Willers, B.; Reimers, W.; Eckert, S.

The adjustment of fine grain morphologies has been approved to be a crucial issue for improving characteristics and properties of cast and wrought aluminium alloys. Several methods are known to achieve grain refinement in solidification processes: add-on of grain refiners, rapid cooling conditions, mechanical or electromagnetic stirring or ultrasonic treatment.
AC magnetic fields provide a contactless method to control the flow inside a liquid metal and the grain size of the solidified ingot. Many studies have shown that beneficial effects like a distinct grain refinement or the promotion of a transition from a columnar to an equiaxed dendritic growth (CET) can be obtained. However, electromagnetically-driven melt convection may also produce segregation freckles on the macroscale. The achievement of superior casting structures needs a well-aimed control of melt convection during solidification.
Previous investigations considered the use of time-modulated AC magnetic fields to control the heat and mass transfer at the solidification front. It has been shown recently under laboratory conditions that an accurate tuning of the magnetic field parameters can avoid segregation effects and homogenize the mechanical properties.
This present study examines the directional solidification of commercial wrought aluminium alloys from a water-cooled copper chill. Rotating time-modulated magnetic fields were used to agitate the melt. The impact of flow on the resulting macro and micro structure are investigated. The solidified structure was reviewed in comparison to an unaffected solidified ingot and ingot prepared with chemical grain refiner. In addition results from extrusion process experiments are introduce. Our results demonstrate the potential of time–modulated magnetic fields to control the grain size, the formation of intermetallic phases and the morphology and distribution of pores.

Keywords: wrought aluminum alloy; time modulated magnetic field; bar extrusion

  • Lecture (Conference)
    The 9th International Symposium on Electromagnetic Processing of Materials, 14.-18.10.2018, Hyogo, Japan
  • Contribution to proceedings
    The 9th International Symposium on Electromagnetic Processing of Materials (EPM2018), 14.-18.10.2018, Hyogo, Japan
  • Open Access Logo IOP Conference Series: Materials Science and Engineering 424(2018), 012039
    DOI: 10.1088/1757-899X/424/1/012039

Publ.-Id: 27700

Trends in valence band electronic structure of mixed uranium oxides

Kvashnina, K. O.; Kowalski, P. M.; Butorin, S. M.; Leinders, G.; Pakarinen, J.; Bes, R.; Li, H.; Verwerft, M.

Valence band electronic structure of mixed uranium oxides (UO2, U4O9, U3O7, U3O8, b-UO3) has been studied by the resonant inelastic X-ray scattering (RIXS) technique at the U M5 edge and by computational methods. We show here that the RIXS technique and recorded U 5f - O 2p charge transfer excitations can be used to proof the validity of theoretical approximations.


Publ.-Id: 27699

Influence of Al-alloy composition on the potential of forced convection to reduce grain size and prevent macrosegregation

Räbiger, D.; Willers, B.; Eckert, S.

In addition to alloy composition, the grain size and a homogeneous phase distribution plays a major role to adjust the properties of cast and wrought aluminium alloys. To achieve grain refinement in solidification processes several methods are common: add-on of grain refiners, rapid cooling conditions, mechanical or electromagnetic stirring, or ultrasonic treatment.
The generation of an additional forced flow in the melt offers the possibility to control the grain size without chemical additives.
AC magnetic fields permit a contactless method to generate such forced flow in the liquid metal. Even more: It is possible to control the flow inside the bulk and tune the grain size of the solidified metal. Many studies have shown the complex interaction of magnetic field and melt flow and between melt flow and solidification structure. Therefore, a profound understanding of the mechanisms and well-justified flow structures in space and time are necessary to produce superior casting structures.
In this presentation experimental results are shown to understand the impact of alloy composition on the grain size and phase distribution for different flow conditions. To typify different solidification behaviors we compare various compositions. For this study pure aluminium, wrought aluminium alloy and an AlSi7-alloy was used. Our results demonstrate the restriction of meaningful implementation in low-alloy and the potential to control the grain size in wrought and cast alloys.

Keywords: grain refinement; forced convection; electromagnetic stirring; aluminium alloy; macrosegregation

  • Lecture (Conference)
    The 7th International Conference on Solidification and Gravity, 03.-06.09.2018, Miskolc - Lillafüred, Hungary
  • Contribution to proceedings
    The 7th International Conference on Solidification and Gravity, 03.-06.09.2018, Miskolc - Lillafüred, Hungary
    Proceedings of the 7th International Conference on Solidification and Gravity

Publ.-Id: 27698

Flow structure optimization and the impact on the solidification structure

Räbiger, D.; Willers, B.; Eckert, S.

The adjustment of fine grain morphologies has been approved to be a crucial issue for improving characteristics and properties of cast and wrought aluminium alloys. Several methods are known to achieve grain refinement in solidification processes: add-on of grain refiners, rapid cooling conditions, mechanical or electromagnetic stirring, or ultrasonic treatment.
AC magnetic fields provide a contactless method to control the flow inside a liquid metal and the grain size of the solidified ingot. Many studies have shown that beneficial effects like a distinct grain refinement or the promotion of a transition from a columnar to an equiaxed dendritic growth (CET) can be obtained. However, electromagnetically-driven melt convection may also produce segregation freckles on the macroscale. The achievement of superior casting structures needs a well-aimed control of melt convection during solidification, which in turn requires a detailed knowledge of the flow structures and a profound understanding of the complex interaction between melt flow, temperature and concentration field.
Previous investigations considered the use of time-modulated AC magnetic fields to control the heat and mass transfer at the solidification front [1, 2]. It has been shown recently under laboratory conditions, that an accurate tuning of the magnetic field parameters can avoid segregation effects [3] and homogenize the mechanical properties [4].
This present study examines the directional solidification of commercial cast and wrought aluminium alloys from a water-cooled copper chill. Rotating magnetic fields were used to agitate the melt. The application of different stirring strategies, e.g. time-modulated magnetic fields, reveals the impact of diverse flow conditions on the resulting macro and micro structure. The solidified structure was reviewed in comparison to an unaffected solidified ingot. Our results demonstrate the potential of magnetic fields to control the grain size and the formation of segregation freckle. In particular, time–modulated rotating fields show their capability to homogenize both the grain size distribution and phase distribution.

  • Lecture (Conference)
    The Third Russian Conference on Magnetohydrodynamics, 18.-21.06.2018, Perm, Russland

Publ.-Id: 27697

Competitive adsorption of ZrO2 nanoparticle and alkali cations (Li+ – Cs+) on muscovite (001)

Qiu, C.; Eng, P. J.; Hennig, C.; Schmidt, M.

We studied the adsorption behavior of ZrO2 nanoparticles on muscovite (001) surface in the presence of cations from the alkali series (Li+, Na+, K+, Rb+ and Cs+). The results of surface X-ray diffraction, i.e. crystal truncation rod and resonant anomalous X-ray reflectivity in combination with AFM images, shows that the sorption of ZrO2 nanoparticles is significantly affected by the binding mode of alkali ions on the muscovite (001) surface. From solutions containing alkali ions binding as outer sphere surface complexes (i.e. Li+ and Na+), higher uptake of Zr4+ is observed corresponding to the binding of larger nanoparticles, which relatively easily replaces the loosely bound alkali ions. However, Zr4+ uptake in solutions containing alkali ions binding as inner sphere surface complexes (i.e. K+, Rb+, and Cs+) is significantly lower and smaller nanoparticles are found at the interface. In addition, uptake of Zr4+ in the presence of inner sphere bound cations displays a strong linear relationship with hydration energy of the coexisting alkali ion. The linear trend can be interpreted as competitive adsorption between ZrO2 nanoparticles and inner sphere bound alkali cations, which are replaced on the surface and undergo rehydration after release to the solution. The rehydration of alkali ion gives rise to a large energy gain, which dominates the reaction energy of the competitive adsorption process. The competitive adsorption mechanism of ZrO2 nanoparticle and alkali ions is discussed comprehensively to highlight the potential relationship between the hydration effect of alkali ions and the effect of charge density of the nanoparticles.

Keywords: Surface X-ray diffraction; zirconium; muscovite; CTR; RAXR; nanoparticles; sorption


Publ.-Id: 27696

Nature does the averaging – in-situ produced ¹⁰Be, ²¹Ne, and ²⁶Al in very young river terraces

Gärtner, A.; Merchel, S.; Niedermann, S.; Braucher, R.; ASTER-Team; Steier, P.; Rugel, G.; Scharf, A.; Le Bras, L.; Linnemann, U.

The concentrations of long-lived cosmogenic nuclides (¹⁰Be, ²¹Ne, ²⁶Al) in quartz obtained from a very recent (~200 a) river terrace in Namibia are nearly constant throughout a 322 cm long depth-profile. These findings corroborate earlier hypotheses postulating a homogeneous distribution of these nuclides in freshly-deposited river terrace sediments. An averaged nuclide concentration is a crucial and generally assumed prerequisite for the determination of numerical ages of old sediments.

Keywords: cosmogenic nuclides; accelerator mass spectrometry; dating; river sediments

Publ.-Id: 27695

Leveraging extreme laser-driven magnetic fields for gamma-ray generation and pair production

Jansen, O.; Wang, T.; Stark, D. J.; D'Humieres, E.; Toncian, T.; Arefiev, A. V.

he ability of an intense laser pulse to propagate in a classically over-critical plasma through the phenomenon of relativistic transparency is shown to facilitate the generation of strong plasma magnetic fields. Particle-in-cell simulations demonstrate that these fields significantly enhance the radiation rates of the laser-irradiated electrons, and furthermore they collimate the emission so that a directed and dense beam of multi-MeV gamma-rays is achievable. This capability can be exploited for electron-positron pair production via the linear Breit-Wheeler process by colliding two such dense beams. Presented simulations show that more than 103 pairs can be produced in such a setup, and the directionality of the positrons can be controlled by the angle of incidence between the beams.

Keywords: plasma channel; pair creation; high energy radiation; laser acceleration; relativistictransparency; ultra-high magneticfiel


Publ.-Id: 27694

Laser-driven strong magnetostatic fields with applications to charged beam transport and magnetized high energy-density physics

Santos, J. J.; Bailly-Grandvaux, M.; Ehret, M.; Arefiev, A. V.; Batani, D.; Beg, F. N.; Calisti, A.; Ferri, S.; Florido, R.; Forestier-Colleoni, P.; Fujioka, S.; Gigosos, M. A.; Giuffrida, L.; Gremillet, L.; Honrubia, J. J.; Kojima, S.; Korneev, P.; Law, K. F. F.; Marquès, J.-R.; Morace, A.; Mossé, C.; Peyrusse, O.; Rose, S.; Roth, M.; Sakata, S.; Schaumann, G.; Suzuki-Vidal, F.; Tikhonchuk, V. T.; Toncian, T.; Woolsey, N.; Zhang, Z.

Powerful nanosecond laser-plasma processes are explored to generate discharge currents of a few 100 kA in coil targets, yielding magnetostatic fields (B-fields) in excess of 0.5 kT. The quasi-static currents are provided from hot electron ejection from the laser-irradiated surface. According to our model, which describes the evolution of the discharge current, the major control parameter is the laser irradiance Ilasλlas2. The space-time evolution of the B-fields is experimentally characterized by high-frequency bandwidth B-dot probes and proton-deflectometry measurements. The magnetic pulses, of ns-scale, are long enough to magnetize secondary targets through resistive diffusion. We applied it in experiments of laser-generated relativistic electron transport through solid dielectric targets, yielding an unprecedented 5-fold enhancement of the energy-density flux at 60 μm depth, compared to unmagnetized transport conditions. These studies pave the ground for magnetized high-energy density physics investigations, related to laser-generated secondary sources of radiation and/or high-energy particles and their transport, to high-gain fusion energy schemes, and to laboratory astrophysics.


Publ.-Id: 27693

Transient Modelling of Wire-Mesh Sensor

de Assis Dias, F.; Schleicher, E.; Da Silva, M. J.; Hampel, U.

Wire-Mesh sensor (WMS) is a device to measure transient phase fraction distributions of multiphase fluids, e.g. in a cross-section of a pipe. It has an enormous potential to be applied in many fields, i.e. chemical, energy and oil processing. However, some questions about its operational behavior are difficult to answer with experiments only. Therefore, we present in this paper a new finite element model of a capacitive WMS that is able to solve the transient current end electric field of the system. In this way, the model is coupled with an electrical circuit to amplify the currents flowing on the receiver electrodes allowing direct comparison with experimental data. In order to validate this approach, an experiment with deionized water was carried out and compared with two models: finite element model; and an electric circuit model, where the fluid impedance is considered as a capacitor with two parallel plates.

Keywords: Finite Element Method; Numerical model; Wire-Mesh Sensor

  • Contribution to proceedings
    9th World Congress on Industrial Process Tomography, 02.-06.09.2018, Bath, United Kingdom
    9th World Congress on Industrial Process Tomography, 978-0-853-16356-5
  • Lecture (Conference)
    9th World Congress on INDUSTRIAL PROCESS TOMOGRAPHY, 02.-06.09.2018, City of Bath, England


Publ.-Id: 27692

Validation of a closure model framework for turbulent bubbly two-phase flow in different flow situations

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

In the present paper a set of closure relations for interphase momentum exchange and for bubble-induced turbulence within the Euler-Euler framework is presented and validated against a set of tests performed at the HZDR-facility MT-Loop. The facility was equipped with wire-mesh sensors that allow cross sectional distributions of gas fraction, gas velocity, and bubble sizes to be measured at different distances from the gas injection.
The radial gas fraction profile of fully developed turbulent vertical upward bubbly flow in a pipe is the result of the ratio of the radial force components of the so-called non-drag forces and can be used for model validation. However, only the ratio, not the absolute value of the bubble forces can be tested in this way. In the present paper more detailed information from the experiment is exploited by consideration of the evolution of gas fraction distribution particularly after the gas injection region. The change of cross sectional gas volume fraction distribution is the result of the action of non-drag forces.
In addition to vertical pipe flow tests further insight is obtained from the investigation of the effect of a slight tube inclination which shifts the gas distribution. Here the disturbance of the cylindrical symmetry of a vertical pipe gives hints on the absolute value of the non-drag force components.
The results show that the presented model framework at least is able to describe the phenomena qualitatively. Possible reasons for quantitative deviations are discussed and require further investigations.

Keywords: CFD; two phase flow; Euler-Euler; closure model; validation


Publ.-Id: 27691

Real space bonding and stability analysis of tetravalent f-element complexes with N-, O-donor ligands

Kloditz, R.; Radoske, T.; Patzschke, M.; Stumpf, T.

N-/O-donor ligands are promising complexing ligands for actinides in high-level liquid wastes. Especially the covalency of the An–N/O bonds and a comparison to lanthanides, e.g. Ce, is of interest for these complexes. Thus, the bond character for [M(salen)2] with M = Ce, Th, Pa, U, Np, Pu was investigated. Furthermore the stability of the complexes is compared and correlated with the bonding character.

Keywords: real-space bonding analysis; stability analysis; DFT; actinides; Schiff bases

  • Poster
    16th International Congress of Quantum Chemistry, 18.-23.06.2018, Menton, Frankreich
  • Poster
    Summer School on Modern Wavefunction Methods, 30.09.-05.10.2018, Gelsenkirchen, Deutschland

Publ.-Id: 27690

Investigation of a wetland contaminated by uranium mine tailings in Central France

Fichtner, A.; Sachs, S.; Rossberg, A.; Scheinost, A. C.; Arnold, T.; Montavon, G.; Stumpf, T.

The release of uranium from mine tailings may present a hazard to the environment, which is the reason for the monitoring of the relevant storage sites in many countries. Studying the behavior of released radionuclides at these sites serves to better estimate the local risk and can help to improve the understanding of the geochemistry of the involved contaminants, e.g. for the application in transport modelling.
The storage site Roffin, located in the Region of Auvergne, France, contains approximately 30 000 t of mill tailings from the adjacent processing plant of the same name, which operated from 1947 to 1956. After the shutdown of the plant, the responsible operator has remodeled the site several times over the decades, in order to meet updated environmental standards [1].
Recent gamma-ray surveys have shown elevated radiation levels alongside a creek downstream of the storage site, especially in a wetland area in some two hundred meters distance of the site. Drill cores taken in this area show uranium concentrations up to 2000 ppm in the upper 30 cm, with peak concentrations in a whitish,clayey layer with a thickness of about 5 cm at a depth of 20 cm. Besides this anomalous layer, the soil is of the histosol type, with very high contents of organic matter and mostly saturated with water. The goal of our study is to identify the involved uranium species in the solid and aqueous phases, in order to understand the influence of discharge history and geochemistry on the risk presented by this contamination.
Sequential extractions performed on the different layers of the soil following the protocol of Tessier et al. [2] indicate a majority of the uranium to be bound to soil organic matter. Yet scanning electron microscopy analysis (SEM) of the white layer shows the presence of particles containing high uranium concentrations with sizes around 10 μm. Energy dispersive X-ray spectra (EDS) of some of these particles give compositions corresponding to a specific mineral processed in the plant, which is Parsonsite [Pb2(UO2)(PO4)2]. Dating the soil with the C-14 of the soil organic matter and the depth profile of Cs-137 from nuclear fallout further suggests that the origin of the white layer is connected to the active period of the site. X-ray absorption spectroscopy performed on the soil shows a variable distribution of U(IV) and U(VI) in the different layers. Porewater obtained by centrifugation contains uranium concentrations up to 1000 ppb.
Further studies aim to quantify the distribution of uranium between the different solid phases of the soil, as well as the identification of the main species in the porewater.

[1] Himeur, N., Andres, C.: Bilan environnemental - Sites miniers du Puy-de-Dôme. AREVA Operational Report (2010).
[2] Tessier, A., Campbell, P.G.C., Bisson, M.: Sequential Extraction Procedure for the Speciation of Particulate Trace Metals. Anal. Chem. (1979) Issue 51, pp. 844-851.

Keywords: Uranium; wetland; mine tailing; speciation; characterization

  • Contribution to proceedings
    RadChem 2018-18th Radiochemical Conference, 13.-18.05.2018, Mariánské Lázně, Czech Republic
    Czech Chemical Society Symposium Series, 18th Radiochemical Conference, Mariánské Lázně, Czech Republic, 13-18 May 2018, Booklet of Abstracts, 214
  • Poster
    RadChem 2018-18th Radiochemical Conference, 13.-18.05.2018, Mariánské Lázně, Czech Republic
  • Poster
    8. RCA-Workshop, 12.-14.06.2018, Dresden, Deutschland
  • Poster
    International Conference Uranium Biogeochemistry, 21.-26.10.2018, Monte Veritá Ascona, Switzerland

Publ.-Id: 27689

Intensified deaeration by means of Rotating Packed Beds

Gross, K.; Bieberle, A.; de Beer, M.; Schmuhl, R.; Skiborowski, M.; Górak, A.

Metal piping and equipment corrosion related to the presence of oxygen is a severe problem in the industry. It may lead to longer down times or a replacement of the equipment, as a consequence additional maintenance effort increases the production costs.
Commonly used equipment types for the deaeration in the chemical industry are (bulky) vacuum tower de-gasifiers or forced draft degasifiers.
However, acquiring the necessary low oxygen concentrations is challenging.
Application of Rotating Packed Beds (RPBs) allows for a high removal rate of oxygen for less than <50 ppb
Equipment size reduction by a factor of 6 to 9, due to the increased volumetric gas-liquid mass transfer rates.

Keywords: Rotating Packed Beds; Process Intensification

  • Poster
    A journey through the world of salt: past, present and future, 12.07.2018, Enschede, Niederlande

Publ.-Id: 27687

Elucidating the impact of elevated temperature on the complexation of Cm(III) and Eu(III) with phosphate ions by luminescence spectroscopy

Jordan, N.; Demnitz, M.; Lösch, H.; Starke, S.; Brendler, V.; Huittinen, N.

Orthophosphate ions (H2PO4−, HPO42−, and PO43−) are ubiquitous in the environment and may originate from the natural decomposition of rocks and minerals (e.g. monazite or apatite), agricultural runoff, or from phosphate fertilizer plants. Solid phosphate monazites are one of the most important ore bodies for the recovery of REE[1], while future monazite applications may involve their use as immobilization matrices for specific HLW streams.[2] Among the inorganic ligands, phosphates are strong complexants and can be expected to influence the speciation of dissolved contaminants when present in solution. However, very little data is available on the complexation of actinides and lanthanides with aqueous phosphates, even though they precede any aqueous synthesis of monazite ceramics and are expected to occur in natural waters, in the proximity of monazite-containing high-level waste repositories as well as in the processing of rare earth elements.
The existing data also suffers from an almost complete absence of independent spectroscopic validation of the stoichiometry of the proposed complexes. Furthermore, there are no studies dealing with the impact of elevated temperatures on An/Ln complexation with aqueous phosphates, despite the relevance of high temperatures both in the proximity of heat-generating HLW repositories and in REE leaching from monazites minerals.

In this study, the complexation of Cm(III) (5×10−7 M) and Eu(III) (5×10−6 M) was investigated by means of laser-induced luminescence spectroscopy as a function of the total phosphate concentration (0–0.5 M Σ(PO4)) using NaClO4 as a background electrolyte (I = 0.5–3.1 M), in the temperature range from 25 to 80 °C. Experiments were conducted in the acidic pH range (−log[H+] = 1 and 2.5) to avoid the precipitation of solid Cm/Eu rhabdophane (MePO4×nH2O). The formation of MeH2PO42+, Me(H2PO4)2+, and Me(HPO4)+ was observed, depending on the solution pH and the total phosphate concentration.
Upon increasing both the ionic strength and temperature, complexation was found to be promoted.[3] By applying the specific ion interaction theory (SIT), the obtained conditional constants at varying ionic strengths and temperatures were extrapolated to infinite dilution (log β0). The molal standard enthalpy of reaction ΔRHm° (assumed constant between 25 to 80 °C) and molal standard entropy of reaction ΔRSm° were derived by using the Van’t Hoff equation.

The new thermodynamic data derived in this fundamental study will support the optimization of technological strategies applied to access raw materials and contribute to a fundamental process understanding necessary to critically assess the environmental fate of actinides and lanthanides.

  • Contribution to proceedings
    4th International Workshop on Advanced Techniques in Actinide Spectroscopy (ATAS 2018), 06.-09.11.2018, Nice, France
  • Lecture (Conference)
    4th International Workshop on Advanced Techniques in Actinide Spectroscopy (ATAS 2018), 06.-09.11.2018, Nice, France

Publ.-Id: 27686

Zero Overhead Modern C++ for Mapping to Any Programming Model

Huebl, A.; Matthes, A.; Worpitz, B.; Zenker, E.; Widera, R.; Juckeland, G.; Bussmann, M.

Towards exascale computing, today's HPC systems have become heterogeneous and diverse. Accounting for both host and accelerator, the TOP10 supercomputers in 11/2017 alone provided as much as 11 different computing architectures. On top of the hardware follow the accompanying programming models: from directive based, implicit and explicit descriptions up to task-based. Scientific code developers are facing a tough choice as commitment to a specific hardware and/or programming model narrows down potential target systems. With limited development resources but usually multi-decade long project lifetimes, maintaining multiple implementations of the same algorithms to widen platform support is unfeasible for most teams. Alpaka is a standard C++, compile-time meta-programming library providing a unified, explicit, parallel programming model. On typical MPI+X parallelized applications, Alpaka enables developers to describe shared-memory, in-node parallelism. Zero-overhead abstraction is achieved by compile-time specializing C++ templates to native backends (e.g. CUDA, OpenMP, TBB, ...). Alpaka stays with modern C++ as a standardized, widely supported language without introducing pre-processor or pragma-based annotations to the user directly. It naturally allows inlining, kernel fusion and code-reuse on a single-source programming paradigm. With such, abstractions and control within the final software stack are achievable without duplicating implementations leading to a maintainable code base even for large applications.

Keywords: HPC; performance portability; programming model; open source; alpaka; cuda; gpu; openpower; portability; high performance computing

  • Invited lecture (Conferences)
    Platform for Advanced Scientific Computing (PASC) Conference 2018, 02.-04.07.2018, Basel, Switzerland
    DOI: 10.5281/zenodo.1304272

Publ.-Id: 27685

Draft Genome Sequence of Bacillus safensis JG-B5T isolated from a uranium mining waste pile

Fischer, S.; Krause, T.; Jordan, N.; Lederer, F.; Jain, R.

Bacillus safensis JG-B5T was isolated from soil of the uranium mining waste pile Haberland near Johanngeorgenstadt (Saxony, Germany). We report the draft genome sequence of the bacteria strain with 3.7 Mbp, which will provide information about high metal resistant abilities. This can be useful in the bioremediation of metal and metalloid-contaminated environments.

Publ.-Id: 27684

Single Plane Compton Imaging A noval concept for radionuclide imaging

Deneva, B.; Roemer, K.; Enghardt, W.; Pausch, G.; Wagner, A.; Koegler, T.

Radionuclide imaging is a well-established and important diagnostic tool. The collected data contain physiological information as opposed to other traditional anatomical imaging techniques like X-ray computed tomography. The Anger Camera remains the primary device for nuclear medical imaging since its invention in 1957 [1]. However, despite the achieved advance in the imaging quality through the years, there are still performance limitations, resulting from the limited detection efficiency, reduced spatial resolution of highly energetic gamma rays, fixed dependency of the spatial resolution and detection efficiency from the used collimator and others. In order to overcome these limitations, the concept of “Single Plane Compton Imaging” (SPCI) has been proposed [2]. This concept, based on the idea of a “Directional Gamma Radiation Detector” [3] - [4] is now being explored experimentally.
We will present first experimental results obtained with a GAGG scintillator pixel array read out by a digital silicon photomultiplier array. The detector is operated in our laboratory and exposed to gamma radiation emitted from radioactive sources. Information about the source positions is derived from the energy spectra of coincident events in adjacent scintillator pixels.

Keywords: Anger Camera; radionuclide imaging; Single Plane Compton Imaging; GAGG

  • Poster
    Student Research Expo 2018, 4.07.2018, Dresden, Deutschland

Publ.-Id: 27683

Wide acceptance measurement of K/K+ ratio from Ni+Ni collisions at 1.91A GeV

Piasecki, K.; Herrmann, N.; Averbeck, R.; Andronic, A.; Barret, V.; Basrak, Z.; Bastid, N.; Benabderrahmane, M. L.; Berger, M.; Buehler, P.; Cargnelli, M.; Čaplar, R.; Cordier, E.; Crochet, P.; Czerwiakowa, O.; Deppner, I.; Dupieux, P.; Dželalija, M.; Fabbietti, L.; Fodor, Z.; Gasik, P.; Gašparić, I.; Grishkin, Y.; Hartmann, O. N.; Hildenbrand, K. D.; Hong, B.; Kang, T. I.; Kecskemeti, J.; Kim, Y. J.; Kirejczyk, M.; Kiš, M.; Koczon, P.; Korolija, M.; Kotte, R.; Lebedev, A.; Leifels, Y.; Le Fèvre, A.; Liu, J. L.; Lopez, X.; Mangiarotti, A.; Manko, V.; Marton, J.; Matulewicz, T.; Merschmeyer, M.; Münzer, R.; Pelte, D.; Petrovici, M.; Rami, F.; Reischl, A.; Reisdorf, W.; Ryu, M. S.; Schmidt, P.; Schüttauf, A.; Seres, Z.; Sikora, B.; Sim, K. S.; Simion, V.; Siwek-Wilczyńska, K.; Smolyankin, V.; Stoicea, G.; Suzuki, K.; Tymiński, Z.; Wagner, P.; Weber, I.; Widmann, E.; Wiśniewski, K.; Xiao, Z. G.; Xu, H. S.; Yushmanov, I.; Zhang, Y.; Zhilin, A.; Zinyuk, V.; Zmeskal, J.

The FOPI Collaboration at GSI SIS-18 synchrotron measured the charged kaons from central and semi-central collisions of Ni+Ni at the beam energy of 1.91A GeV. We present the distribution of K−/K+ ratio on the plane of energy vs polar angle in the nucleon-nucleon centre-of-mass frame, with and without the subtraction of the contribution of φ(1020) meson decays to the K− yield. The acceptance of the current experiment is substantially wider compared to the previous measurement of the same colliding system. The K−/K+ ratio is expected to be sensitive to the in-medium modifications of basic kaon properties like mass. Recent results obtained by the HADES Collaboration at 1.23A and 1.76A GeV indicate, that no mass-shift effect is needed to explain the difference between energy slopes of charged kaon spectra within uncertainties. The K−/K+ ratios obtained in this experiment, even after correction for the contribution due to the φ(1020) meson decays, decrease with increasing kinetic energy, as generally predicted in models assuming mass modifications.


Publ.-Id: 27681

Precise nuclear data of the 14N(p,γ)15O reaction for solar neutrino predictions

Wagner, L.

The 14N(p,γ)15O reaction is the slowest stage of the carbon-nitrogen-oxygen cycle of hydrogen burning and thus determines its reaction rate. Precise knowledge of its rate is required to improve the model of hydrogen burning in our sun. The reaction rate is a necessary ingredient for a possible solution of the solar abundance problem that led to discrepancies between predictions of the solar standard model and helioseismology. The solar 13N and 15O neutrino fluxes are used as independent observables that probe the carbon and nitrogen abundances in the solar core. This could settle the disagreement, if the 14N(p,γ)15O reaction rate is known with high precision. After a review of several measurements its cross section was revised downward due to a much lower contribution by one particular transition, capture to the ground state in 15O. The evaluated total relative uncertainty is still 7.5%, in part due to an unsatisfactory knowledge of the excitation function over a wide energy range.
The present work reports experimentally determined cross sections as astrophysical S- factor data at twelve energies between 0.357 – 1.292 MeV for the strongest transition, capture to the 6.79MeV excited state in 15O with lower uncertainties than before and at ten energies between 0.479 – 1.202 MeV for the second strongest transition, capture to the ground state in 15O.
In addition, an R-matrix fit is performed to estimate the impact of the new data on the astrophysical relevant energy range. The recently suggested slight S-factor enhancement at the Gamow window could not be confirmed and differences to previous measurements at energies around 1 MeV were observed. The present extrapolated zero-energy S-factors are S679(0) = (1.19±0.10) keV b and SGS(0) = (0.25±0.05) keV b and they are within the uncertainties consistent with values recommended by the latest review.

  • Doctoral thesis
    TU Dresden, 2018
    Mentor: Prof. Dr. Kai Zuber und Privatdozent Dr. Daniel Bemmerer
    111 Seiten
  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-092 2018
    ISSN: 2191-8708, eISSN: 2191-8716


Publ.-Id: 27680

twoWayGPBEFoam: An open-source Eulerian QBMM solver for monokinetic bubbly flows

Li, D.; Marchisio, D.; Hasse, C.; Lucas, D.

twoWayGPBEFoam and oneWayGPBEFoam are an open-source meso-scale Eulerian-QBMM solvers for multiphase flows, implemented within the OpenFOAM software framework. Compared with the existing macroscopic Eulerian-Eulerian (E-E) solver twoPhaseEulerFoam, it can predict the size segregation phenomenon and the size-conditioned velocities of the disperse phase. On theoretically grounds, the evolution of the disperse phase in multiphase flows is controlled by the generalized population balance equation (GPBE). The GPBE can be transformed into the moments transport equations and solved by the finite-volume method with higher-order realizable spatial-discretization schemes and time-integration schemes. In order to address the closure problems of the size-conditioned spatial flux, the size-conditioned velocities need to be modelled. In previous works on CFD-PBE coupling, the size-conditioned velocities are assumed to be identical with the disperse phase velocity predicted by the E-E method. In this work, it was modelled by the velocity polynomial approximation (VPA), for which the velocity polynomial coefficients (VPCs) can be obtained from the moments themselves. Therefore, the disperse phase momentum equation in the E-E method is discarded in this approach. Meanwhile, the continuous phase is modelled by the Navier-Stokes equations, and is fully coupled with the moments transport equations of the disperse phase by the phase fraction and the interfacial momentum exchange terms. By several test cases with both one-way and two-way coupling, we show that the results predicted by the oneWayGPBEFoam and twoWayGPBEFoam agree well with the analytical solutions and the existing experimental data.

Keywords: Computational fluid dynamics; Generalized population balance equation; Quadrature method of moments; OpenFOAM

Publ.-Id: 27678

Multiscale-modelling of gas liquid flows – GENTOP

Lucas, D.

In multiphase flows interfaces may span over a wide range of sizes. In a multi fluid approach interfaces smaller as well as larther than the typical size of the numerical grid may occur. While the small interfaces (bubbles and drops) should be represent by smeared phase volume fractions the large structures should be resolved in a CFD simulation. Also transitions between contineous and dispersed morphologies of teh phases may occur.
The lecture discusses the issues for modelling such flows and the basic ideas of the GENTOP concept. Domonstration simulations using the GENTOP concept show the cpabablities of this approach.

Keywords: multiphase; morphology; multi-scale; bubble; drop; seggregated flow; coalescence; breakup

  • Invited lecture (Conferences)
    Lectures on multiphase CFD at Central South University, School of Energy Science and Engineering, 06.-08.06.2018, Changsha, China

Publ.-Id: 27677

Two-phase flow experiments and measuring techniques @ HZDR

Lucas, D.

TOPFLOW-experiments on vertical pipes and within the TOPFLOW pressure chamber are presented. Innovative measuring techniques as wire-mesh sensors and ultrafast X-ray tomography provide detailed information on the interfacial structure in gas-liquid flows. Details on these measuring techniques are discussed and experiments on flows under adiabatic conditions as well as flows with phase transfer are presented.

Keywords: wire-mesh sensor; ultrafast X-ray tomography; pipe flow; pressure chamber; TOPFLOW

  • Invited lecture (Conferences)
    Lectures on multiphase CFD at Central South University, School of Energy Science and Engineering, 06.-08.06.2018, Changsha, China

Publ.-Id: 27676

The Institute of Fluid Dynamics at HZDR

Lucas, D.

The Institute of Fluid Dynamics within the HZDR was introduced in frame of a lecture series at Central South University inn Changsha, China. Special focus was on the activities of the CFD-department.

Keywords: HZDR; multiphase flow; CFD

  • Invited lecture (Conferences)
    Lectures on multiphase CFD at Central South University, School of Energy Science and Engineering, 06.06.2018, Changsha, China

Publ.-Id: 27675

Multiphase flow CFD activities at HZDR

Lucas, D.

The HZDR strategy on the qualification of multiphase CFD in frame of the Euler-Euler-concept is presented. The inhomogeneous MUSIG model is a basic framework for modelling bubbly flows. The baseline model for polydisperse bubbly flows was established at HZDR. For segragated flows the AIAD model can be used. The innovative GENTOP concept allows the consideration of different flow morphologies and transitions between them. Finally the HZDR activities are illustrated by several applications of multiphase CFD on industrial problem.

Keywords: CFD; MUSIG; AIAD; GENTOP; baseline; Euler-Euler

  • Lecture (others)
    Presentation at the Institute of Mechanics, Chinese Academy of Science, 12.06.2018, Beijing, China

Publ.-Id: 27674

Multi-fluid models for industrial gas-liquid flows

Lucas, D.

The HZDR concepts for Euler-Euler-modelling of gas-liquid flow are presented. The inhomogeneous MUSIG model is a basic framework for modelling bubbly flows. A baseline model for polydisperse bubbly flows was established at HZDR. For segragated flows the AIAD model can be used. The innovative GENTOP concept allows the consideration of different flow morphologies and transitions between them.

Keywords: CFD; multiphase; MUSIG; AIAD; GENTOP

  • Invited lecture (Conferences)
    DANSIS Seminar on Computational Techniques for Gas-Liquid Flows, 16.05.2018, Copenhagen, Denmark

Publ.-Id: 27673

CFD-modelling for bubbly flows in medium and large scales

Lucas, D.; Liao, Y.; Ma, T.; Krepper, E.; Ziegenhein, T.

For gas-liquid flows in large and medium scale industrial applications the Euler-Euler approach is frequently used and for many problems it is the only feasible one. During the derivation of the basic conservation equations the information on the interface gets lost and all interfacial exchange between gas and liquid has to be reflected by appropriate closure models. They have to reflect local phenomena that usually are similar in different global flow situations as bubble columns, pipe flows and others. For this reason a unified setup for closure models should be applicable without any modification for such a spectrum of flow situations. The HZDR baseline model for bubbly flows defines such a set of closures. It was applied to more than 150 different cases indicating a good overall performance, but showing also the limits of the present model. For this reason the model has to be improved continuously.
Recently a new model for bubble-induced turbulence in the RANS framework was included into the baseline model. It was developed basing on DNS of a bubbly channel flow. Other activities aim on the lateral lift force, which is closely connected to the bubble shape. Weak points in the present setup are the near wall simulation and the consideration of swarm effects. For these issues more basic research is required to improve the understanding of the phenomena and to derive better closure models. The present model also shows clear deviations from experimental findings for cases with high liquid superficial velocities which are connected with large gradients in the liquid flow field and a high turbulence level.
The focus of the presentation is on recent and ongoing activities to improve closure models and on the requirements for further improvements.

Keywords: CFD; bubbly flow; Euler-Euler; baseline

  • Lecture (Conference)
    8th European-Japanese Two-Phase Flow Group Meeting, 22.-26.04.2018, New York, USA

Publ.-Id: 27672

A systematic experimental study and dimensionless analysis of bubble plume oscillations in rectangular bubble columns

Liu, L.; Yan, H.; Ziegenhein, T.; Hessenkemper, H.; Li, Q.; Lucas, D.

Unsteady bubble plume oscillations significantly influence mixing and other transport processes occurring in bubble column reactors. In the present work, oscillations of centrally aerated bubble plumes in rectangular bubble columns were experimentally studied in water and aqueous glycerol solutions. The effects of the superficial gas velocity, aspect ratio, aerated width, needle size and the liquid viscosity on the low-frequency oscillations were investigated. The performance of the dimensionless numbers characterizing the plume oscillation published in the literature was assessed with the present experimental data. Dimensionless analysis was performed and a new empirical correlation was proposed based on the present experiments, and then validated through a large number of available experimental data in the literature. The experimental data and dimensionless analysis presented here can help in understanding the physics of the plume oscillations under various operating conditions. Further, the results can be used for validating corresponding computational models.

Keywords: Bubble plume; Gas-liquid flow; Bubble column; Plume oscillation frequency; Particle Shadow Velocimetry

Publ.-Id: 27671

Euler-Euler simulation and X-ray measurement of bubble chain in a shallow container filled with liquid metals

Liu, L.; Keplinger, O.; Ma, T.; Ziegenhein, T.; Shevchenko, N.; Eckert, S.; Yan, H.; Lucas, D.

An Euler-Euler two-fluid approach was used to simulate the behavior of gas bubbles rising in a stagnant liquid metal. A single point injection with four gas flow rates resulted in the formation of bubble chains undergoing either slight or distinct oscillations of the bubble trajectories. A set of interfacial closures with a shear stress transport (SST) k-ω turbulence models was applied for simulating the transient behavior of the bubble chain. X-ray radiography measurements were conducted to establish an experimental data base for validating the numerical results. The experiments provide a visualization of the bubble chain in a flat container and allow determining the bubble size and integral void fraction. Two bubble induced turbulence (BIT) models (Rzehak and Krepper, 2013a, Sato et al., 1981) and a modified turbulent viscosity approach (Johansen et al., 2004) were applied within this study. For all gas flow rates, the Rzehak and Sato BIT model alone predicted a steady bubble chain in contrast to the oscillating bubble plume observed in the experiments. Without a BIT model the oscillating bubble chain can be predicted but the oscillation frequency is underestimated especially for high gas flow rates. In addition, calculations without a BIT model predicted over-dispersion of the averaged gas fraction through the whole fluid container for the high gas flow rates. The best results in terms of a satisfying agreement with the experimental data were achieved by adopting a modified turbulent viscosity approach proposed by Johansen together with the Rzehak and Krepper BIT model. These findings demonstrate the significance of the turbulence model.

Keywords: Liquid metal two-phase flow; Bubble chain; X-ray radiography; Bubble induced turbulence model; CFD; Euler-Euler two-fluid model

Publ.-Id: 27670

Evaluation of Hydrodynamic Closures for Bubbly Regime CFD Simulations in Developing Pipe Flow

Shiea, M.; Buffo, A.; Baglietto, E.; Lucas, D.; Vanni, M.; Marchisio, D.

The effect of interfacial forces and relevant closures, particularly the lift and wall lubrication forces, on the predictions of Eulerian-Eulerian computational fluid dynamics simulations of bubbly flows was studied. The test case under study was a developing turbulent bubbly pipe flow, simulated by using OpenFOAM. The results show that the geometric approach to consider the wall effect leads to better agreement than a standard relation assuming asymmetric drainage around the bubble near the wall. Furthermore, the results verify the need for employing negative lift coefficients in cases with large bubbles. A sensitivity analysis on the lift coefficient highlighted the importance of investigating spatially developing flows to draw general conclusions on the applicability of closure relations.

Keywords: Bubbly Flow; Two-fluid Model; Interfacial Forces; Lift Coefficient; Wall Lubrication Force

Publ.-Id: 27669

Ion Irradiation Induced Cobalt/Cobalt Oxide Heterostructures: From Materials to Devices.

Hilliard, D.; Yildirim, O.; Fowley, C.; Arekapudi, S. S. P. K.; Cansever, H.; Böttger, R.; Hlawacek, G.; Hellwig, O.; Lindner, J.; Fassbender, J.; Deac, A.

The demand on high data transfer and storage capacities requires smaller devices to transmit or save data. Forming well-defined ferromagnetic and electrically conducting volumes within a non-magnetic and insulating matrix in the dimensions of several nanometers can pave a way to the production of such small devices. It has been demonstrated that the reduction of oxygen in Co₃O₄/Pd multilayers is possible via local proton irradiation resulting in ferromagnetic and conducting Co embedded in a nonmagnetic and insulating Co₃O₄ matrix [1]. However, the physical mechanism behind the ion irradiation-induced oxide reduction was not addressed clearly. There are two possible mechanisms suggested to play a role behind this oxide reduction. The first one is the chemical reduction of oxygen by reacting with implanted H+ ions, while the second possible mechanism is atomic displacements induced by ion irradiation. To address this issue, we analysed cobalt oxide thin films after irradiation with H+ and Ne+ ions at different doses. The irradiation parameters for Ne+ were chosen to give the same displacements per atom (dpa) as that of H+ which is required to reduce cobalt oxide. We also confined irradiated areas on the films in the range of microns to submicron, in order to ascertain the lateral distribution of oxygen after irradiation.
We prepared single layer films of CoO (6-12nm) and Co₃O₄ (10nm) capped with Pt protection layers. Broad-beam H+ irradiations were performed at 0.3 keV for ion doses ranging from 10¹⁵ to 10¹⁷ ions/cm² on unpatterned films. After irradiation the films were characterized structurally and magnetically and compared to un-irradiated films. Extended films showed approximately 7% of the Co bulk metal saturation magnetization (MS) after irradiation at a dose of 5 x 10¹⁶ ions/cm² (fig. 1a inset). The increase is more pronounced with Co₃O₄ than CoO (fig. 1a). A sample was also prepared with a striped irradiation mask of 40 μm pitch. These films showed a higher magnetization after irradiation at lower doses as compared to unpatterned films, 0.14 MA/m for a dose of 10¹⁶ ions/cm² (striped) as opposed to 0.025 MA/m (extended) for a dose of 10¹⁷ ions/cm².
Figure 1 (b) shows the effect of stripe width (0.5, 5, 10, 20 μm) on the resulting magnetization after H+ irradiation at the same energy with a dose of 10¹⁷ ions/cm². No clear correlation between stripe width and MS was seen in either oxide phase for stripes down to 0.5 μm. However, the CoO sample with 0.5 μm stripes and a thinner oxide thickness of 6 nm (gold line) as opposed to 12 nm exhibited larger MS after irradiation, indicating oxygen displacements occur in the first few nanometers of the oxide.
We also performed 5 keV Ne+ irradiations with the helium-ion microscope (HIM) varying the ion dose from 10¹⁴ to 10¹⁶ ions/cm². After Ne+ irradiations magnetic force microscopy (MFM) images were taken along with a topography image in the remnant state (fig. 2). Starting from the ion dose of 5x10¹⁴ ions/cm², a magnetic contrast could be observed by MFM, suggesting that oxygen atoms were successfully removed locally by reducing paramagnetic CoO to ferromagnetic Co. The formation of topographical bubbles was observed upon increasing the ion dose from 10¹⁵ ions/cm² to 10¹⁶ ions/cm². The lateral and horizontal sizes of the observed bubbles show a clear dependence on the ion dose with a narrow size distribution.
In conclusion, our results show that, oxygen removal by means of H+ irradiation is more efficient in Co₃O₄ films as opposed to CoO. Additionally, although there is little dependence of the resulting Ms on the pitch of the stripes (in the range of 0.5 - 20 μm), the use of a stripe mask has a more pronounced effect on the oxygen removal process as compared to the irradiations on extended films. Therefore, the physical mechanism behind the ion-irradiation induced oxide reduction process cannot purely be a chemical reaction between oxygen and hydrogen. As an outlook, the lateral size and spacing of the ferromagnetic regions generated by H+ irradiation is only limited by the resolution of EBL. This method and the successful formation of ferromagnetic regions upon Ne+ irradiation using the HIM can be exploited to print smaller, closer and synchronized contacts for nanocontact spin torque oscillators.

Keywords: oxygen reduction; oxygen removal; magnetization; CoO; Co3O4; ion beam; cobalt; cobalt oxide

  • Open Access Logo Contribution to proceedings
    Intermag 2018, 23.-27.04.2018, Marina Bay Sands Convention Center, Singapore

Publ.-Id: 27668

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