Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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41396 Publications

Experimental investigation on the buoyancy-induced flow in a model of the Czochralski crystal growth process

Pal, J.; Franke, S.; Eckert, S.; Gerbeth, G.

Within this paper we present a model experiment focusing on investigations of the flow field in a Czochralski puller. Low melting point liquid metals as GaInSn are an important tool to investigate the flow structure for such industrial processes. The topology of the prevailing thermally-driven convection might be very complex and is mainly determined by the aspect ratio of the liquid volume and the strength of the convection described by the characteristic dimensionless Grashof number. The measurements of the fluid flow have been conducted by means of the ultrasound Doppler velocimetry (UDV) with and without the influence of external magnetic fields. Two kinds of sensor configurations were used to investigate the flow. Firstly, measurements of the radial velocity component by means of single UDV transducers were carried out shortly below the melt surface across the entire diameter of the cylindrical liquid column at various azimuthal angles. Secondly, a vertically arranged UDV array was applied at the side of the cylinder to obtain more detailed information about the radial velocities in the covered meridional plane. The results reveal the complex flow structure of natural convection in a Czochralski crucible which gains in complexity with applied external magnetic fields.

Keywords: Czochralski crystal growth process

Permalink: https://www.hzdr.de/publications/Publ-28191
Publ.-Id: 28191


The challenge of digitalising lead smelting with technology elements

Schalkwyk, R. F. Van; Reuter, M. A.; Stelter, M.

Technology elements (e.g. Te, Se, Ge) are crucial to the creation of complex products, e.g. photovoltaic cells, which also drive the circular economy. However, these elements introduce complexity when the waste materials (slags, flue dusts or electronic wastes) that contain them are treated in lead smelters. This strategy of treating wastes in lead smelters is followed to utilise existing infrastructure as far as possible. In order to address the complex metallurgy, a dynamic model of the furnaces that are operative in lead metallurgy is required. This project focuses on the laboratory measurements of thermodynamic and kinetic parameters that will be used to create a dynamic model of a Top Submerged Lance furnace.

Keywords: Top Submerged Lance furnace; Kinetics; Technology Elements; Modeling

  • Lecture (Conference)
    GDMB Lead Experts Meeting, 26.04.2018, Freiberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-28190
Publ.-Id: 28190


Digitalizing the circular economy: Behaviour of technology elements during lead smelting

Schalkwyk, R. F. Van; Reuter, M. A.; Stelter, M.

Lead pyrometallurgical infrastructure plays an important role in the circular economy, due to the application of existing lead infrastructure and smelters for processing of secondary materials (e.g. electronics, flue dusts and waste slags). However, as the proportion of non-traditional secondary feed materials to smelters increases, so does the complexity. Better understanding is required of non-traditional and minor elements in lead metallurgy, e.g. Se.
During direct lead smelting, molten metal and slag phases form and minor elements are distributed amongst these. Se typically reports to the lead bullion and is removed from the bullion during refining stages. It is important to determine the metal/slag distribution in order to understand downstream process impacts and to avoid contamination of the final product.
Equilibration experiments are carried out in a laboratory furnace to determine slag/metal distributions of minor elements. At thermodynamic equilibrium, the distribution is affected by the temperature, slag composition, oxygen potential and interactions between elements in the melt. Results from equilibrium measurements and process implications will be discussed.

Keywords: Lead; Equilibrium; Selenium; Technology Elements; Circular Economy

  • Poster
    Sustainable Minerals, 14.-15.06.2018, Namibia, Namibia

Permalink: https://www.hzdr.de/publications/Publ-28189
Publ.-Id: 28189


Two-dimensional Pd3P2S8 Semiconductors as Photocatalysts for Solar Oxygen Evolution Reaction: A Theoretical Investigation

Jing, Y.; Heine, T.

On the basis of first principles calculations, we propose Pd3P2S8 monolayer and bilayer, two-dimensional semiconductors, whose layered bulk parent crystals are experimentally reported, as promising photocatalysts for the solar-driven oxygen evolution reaction. The monolayer is kinetically and thermodynamically stable and shows a small cleavage energy of 0.35 J m−2, suggesting that it can be prepared by exfoliation from its bulk material, and exhibits a direct band gap of 2.98 eV, which can be engineered by applying strain. The Pd3P2S8 bilayer is an indirect band gap semiconductor with a slightly smaller band gap of 2.83 eV. The photoexcited holes generate favorable driving forces for promoting the specific solar-driven O2 evolution reaction. The extraordinary electronic properties, pronounced light harvesting capability in the visible and ultraviolet regions and active surface sites render the Pd3P2S8 monolayer and bilayer as compelling 2D materials with interesting application potential for photocatalytic and photoelectrocatalytic water splitting.

Permalink: https://www.hzdr.de/publications/Publ-28188
Publ.-Id: 28188


Cavitation energies can outperform dispersion interactions

He, S.; Biedermann, F.; Vankova, N.; Zhechkov, L.; Heine, T.; Hoffman, R. E.; de Simone, A.; Duignan, T. T.; Nau, W. M.

In this work we prepare Langmuir–Blodgett monolayers with a trifunctional amphiphilic anthraphane monomer. Upon spreading at the air/water interface, the monomers self-assemble into 1 nm-thin monolayer islands, which are highly fluorescent and can be visualized by the naked eye upon excitation. In situ fluorescence spectroscopy indicates that in the monolayers, all the anthracene units of the monomers are stacked face-to-face forming excimer pairs, whereas at the edges of the monolayers, free anthracenes are present acting as edge groups. Irradiation of the monolayer triggers [4 + 4]-cycloadditions among the excimer pairs, effectively resulting in a two-dimensional (2D) polymerization. The polymerization reaction also completely quenches the fluorescence, allowing to draw patterns on the monomer monolayers. More interestingly, after transferring the monomer monolayer on a solid substrate, by employing masks or the laser of a confocal scanning microscope, it is possible to arbitrarily select the parts of the monolayer that one wants to polymerize. The unpolymerized regions can then be washed away from the substrate, leaving 2D macromolecular monolayer objects of the desired shape. This photolithographic process employs 2D polymerizations and affords 1 nm-thin coatings.

Keywords: 2D polymerization; air/water interface; anthracene; fluorescence; photolithography; self-assembled monolayers

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Permalink: https://www.hzdr.de/publications/Publ-28187
Publ.-Id: 28187


PtTe Monolayer: Two-Dimensional Electrocatalyst with High Basal Plane Activity toward Oxygen Reduction Reaction

Wang, Y.; Li, Y.; Heine, T.

PtTe is a layered bulk material that was discovered in 1897. According to first-principles calculations, it is one of the few layered materials that maintains structure and metallic character when thinned down to the monolayer. Interlayer energy is small enough to allow for chemical exfoliation techniques. Our calculations show that monolayer PtTe is a candidate to substitute Pt electrodes, and we computationally studied its catalytic performance in the oxygen reduction reaction (ORR). Remarkably, the basal plane of a PtTe monolayer exhibits excellent catalytic activity toward ORR, with a positive half-wave potential (∼0.90 V) and a high four-electron reduction pathway selectivity. These characteristics suggest that it outperforms Pt electrodes as catalyst, has a reduced Pt content, high Pt utilization, and a high surface area, and is a promising candidate for fuel cell components.

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Permalink: https://www.hzdr.de/publications/Publ-28186
Publ.-Id: 28186


Target volumes in adaptive treatment of NSCLC show large discrepancies among experts

Apolle, R.; Appold, S.; Bussink, J.; Faivre-Finn, C.; Khalifa, J.; Lievens, Y.; de Ruysscher, D.; van Elmpt, W.; Troost, E. G. C.

Purpose or Objective
Target volume delineation is subject to inter-observer variability (IOV) and thus a major source of uncertainty in radiation treatment planning. IOV in the context of treatment adaptation is largely unknown. We analysed IOV of the primary gross tumour volume (GTV) and clinical target volume (CTV) in locally advanced NSCLC delineated by experts in the pre- and mid-treatment (PT and MT) setting.

Material and Methods
Five patients from routine clinical practice, who underwent repeat imaging, were selected such that a variety of features likely to prompt adaptation, e.g. atelectasis, central primary tumour, was included. Brief case reports and CT imaging data were sent to six observers, supplemented with FDG-PET studies in two cases at PT and three at MT. Observers received PT and MT imaging data at least one week apart and were asked to delineate the GTV and CTV in their own treatment planning system and to comment on their delineation process, i.e. on how GTV to CTV expansion and adaptation were performed. Delineations were rasterised on a 1mm³ grid and their compatibility assessed with the Generalised Conformity Index (CIgen). Differences in IOV between PT and MT were probed with Wilcoxon signed-rank tests and the correlation between GTV and CTV IOV evolution with Spearman rank correlation. While it is respectively impossible and very difficult for these tests to show two-sided α=0.05 significance at n=5, more powerful parametric alternatives cannot credibly be employed.

Results
A total of 109/120 delineations were received and analysed. Figure 1 shows an overview of IOV in terms of volume overlap. All but one case saw a reduction of CIgen when transitioning from PT to MT (p=0.125 for both GTVs and CTVs). Agreement in corresponding GTV and CTV delineations was generally comparable at individual time points, and there was a trend of a correlation between GTV and CTV CIgen changes (ρ=0.9, p=0.083). This behaviour is consistent with almost all observers adopting an isotropic GTV to CTV expansion of 5 mm with rare editing for anatomical boundaries at either time point. MT GTV delineations were only occasionally adopted from PT after image registration (9/28 analysed observers and cases), the remainder contoured anew. Post-transfer adaptation to changed anatomy was performed by one observer, and inclusion of PT GTV in MT CTV by two. Figure 2 shows the two cases demonstrating the most extreme changes in IOV (improvement and deterioration). In both cases large volumes of consolidated lung lead to increased IOV, but at different time points. Shortcomings of this in silico contouring challenge were incomplete FDG-PET availability and a lack of contrast-enhanced CT, both current clinical standard. Modern MRI would also have been welcomed by many.

Conclusion
Differing approaches of reacting to intra-therapeutic changes further increase IOV in target volume delineation in the adaptive setting. Consensus guidelines and in-depth analysis of per-treatment tumour shrinkage patterns are urgently needed.

Keywords: Delineation

  • Lecture (Conference)
    ESTRO 38, 26.-30.04.2019, Mailand, Italien

Permalink: https://www.hzdr.de/publications/Publ-28185
Publ.-Id: 28185


Target volume delineation for adaptive treatment in HNSCC is highly variable among experts

Apolle, R.; Bijl, H. P.; Blanchard, P.; Laprie, A.; Madani, I.; Ruffier, A.; van Elmpt, W.; Troost, E. G. C.

Purpose or Objective
Inter-observer variability (IOV) in target volume delineation is a well-documented phenomenon and a major source of uncertainty in radiation treatment (RT) planning. The increasing adoption of adaptive RT adds a dynamic component to IOV, which is largely unknown. We analysed IOV in the pre- and mid-treatment (PT and MT) setting using expert primary gross tumour volume (GTV) and clinical target volume (CTV) delineations in locally advanced HNSCC.

Material and Methods
Five patients from routine clinical practice, who underwent repeat imaging, were selected such that a variety of features likely to prompt adaptation were included. Brief case reports and CT imaging data were sent to five observers, the latter supplemented with pre-therapeutic FDG-PET in four cases. Observers received PT and MT imaging data at least one week apart and were asked to delineate the GTV and CTV in their own treatment planning system and to comment on their delineation process, i.e. on how GTV to CTV expansion and adaptation were performed. Delineations were rasterised on a 1mm³ grid and their compatibility assessed with the Generalised Conformity Index (CIgen). Differences in IOV between PT and MT were probed with Wilcoxon signed-rank tests and the correlation between GTV and CTV IOV evolution with Spearman rank correlation. While it is respectively impossible and very difficult for these tests to show two-sided α=0.05 significance at n=5, more powerful parametric alternatives cannot credibly be employed. Delineations were processed with ITK and statistical analyses performed in R.

Results
A total of 82/100 delineations were received and analysed. Figure 1 shows an overview of IOV in terms of volume overlap. All cases and volumes suffered a reduction of CIgen when transitioning from PT to MT (p=0.063 for both CTVs and GTVs). There was generally better agreement in CTV than GTV delineations at individual time points, and the correlation between GTV and CTV CIgen changes was very weak (ρ=0.5, p=0.45). This comparative robustness of CTV delineations might stem from GTV to CTV expansion practices, which overwhelmingly employed sizeable isotropic margins (mean: 7.6 mm) and additional editing for anatomical boundaries at both time points. Figure 2 shows a case in which CIgen for CTVs remains stable despite deteriorating IOV in the primary GTV. MT GTV delineations were often based on PT delineations after image registration (14/24 analysed observers and cases), the remainder contoured de novo. Post-transfer adaptation to changed anatomy was performed by two observers and inclusion of the PT GTV in the MT CTV by one. Shortcomings of this contouring challenge are a lack of MRI and contrast-enhanced CT at both time points.

Conclusion
IOV in target volume delineation increases during treatment, where a disparity in institutional adaptation practices adds to the static causes of IOV. Consensus guidelines are urgently needed and should recommend scope, frequency, and quality of MT imaging alongside adaptation strategies.

Keywords: Delineation

  • Lecture (Conference)
    ESTRO 38, 26.-30.04.2019, Mailand, Italien

Permalink: https://www.hzdr.de/publications/Publ-28184
Publ.-Id: 28184


Correction of Geometrical Effects of a Knife-Edge Slit Camera for Prompt Gamma-Based Range Verification in Proton Therapy

Petzoldt, J.; Janssens, G.; Nenoff, L.; Richter, C.; Smeets, J.

Prompt gamma (PG) based range verification can potentially reduce the safety margins in proton therapy. A knife-edge slit camera has been developed in this context using analytical PG simulations as reference for absolute range verification during patient treatment. Geometrical deviations between measurement and simulation could be observed and have to be corrected for in order to improve the range retrieval of the system. A geometrical correction model is derived from Monte Carlo simulations in water. The influence of different parameters is tested and the model is validated in a dedicated benchmark experiment. We found that the geometrical correction improves the agreement between measured and simulated PG profiles resulting in an improved range retrieval and higher accuracy for absolute range verification. An intrinsic offset of 1.4 mm between measurement and simulation is observed in the experimental data and corrected in the PG simulation. In summary, the absolute range verification capabilities of a PG camera have been improved by applying a geometrical correction model.

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Permalink: https://www.hzdr.de/publications/Publ-28183
Publ.-Id: 28183


Rare-Earth orthophosphates from atomistic simulations

Ji, Y.; Kowalski, P. M.; Kegler, P.; Huittinen, N.; Marks, N.; Vinograd, V.; Arinicheva, Y.; Neumeier, S.; Bosbach, D.

Lanthanide phosphates (LnPO4 ) are considered as a potential nuclear waste form for immobilization of Pu and minor actinides (Np, Am and Cm). In that respect, in the recent years we have applied advanced atomistic simulation methods to investigate various properties of these materials on the atomic scale. In particular, we computed several structural, thermochemical, thermodynamic and radiation damage related parameters. From a theoretical point of view, these materials turn out to be excellent systems for testing quantum mechanics-based computational methods for strongly correlated electronic systems. On the other hand, by conducting joint atomistic modeling and experimental research, we have been able to obtain enhanced understanding of the properties of lanthanide phosphates. Here we discuss joint initiatives directed at understanding the thermodynamically driven long-term performance of these materials, including long-term stability of solid solutions with actinides and studies of structural incorporation of f elements into these materials. In particular, we discuss the maximum load of Pu into the lanthanide-phosphate monazites. We also address the importance of our results for applications of lanthanide-phosphates beyond nuclear waste applications, in particular the monazite-xenotime systems in geothermometry. For this we have derived a stateof-the-art model of monazite-xenotime solubilities. Last but not least, we discuss the advantage of usage of atomistic simulations and the modern computational facilities for understanding of behavior of nuclear waste-related materials.

Keywords: Rare-earth phosphates; Atomistic simulations; Monazite; Xenotime; nuclear waste management; Ceramics; Thermodynamics; solid solutions

Permalink: https://www.hzdr.de/publications/Publ-28182
Publ.-Id: 28182


Experimental Analysis of the effect of column feed pipe configurations on the flow morphology

Döß, A.; Schubert, M.; Hampel, U.

Droplets entrained by the vapor phase can drastically reduce the separation capacity of distillation columns and cause severe corrosion problems, process instabilities as well as higher emissions due to droplet carry-over into the downstream process units.
Intensive interactions between vapor and liquid phases favor droplet formation. Feed pipe and feed inlet are prone positions for such droplet formation, depending on flow rates, phase change and pipe geometry resulting in characteristic morphologies.
Several models are available to predict the flow regime for known liquid and vapor flow rates. However, these models and flow maps are often restricted to fully developed flows in straight pipes of small diameter only and do not account for the effects of various entrance lengths, larger diameters as well as bends found in industry. Thus, an experimental analysis is performed to study the effect of column feed pipe configurations on the evolving flow regime using the wire-mesh sensor technique (Fig. 1). Wire-mesh sensors visualize the dynamic flow structure in the pipe cross-section at high spatiotemporal resolution (1 to 3 mm, up to 10,000 Hz). This work is supported by the Federal Ministry for Economic Affairs and Energy (BMWi) based on a decision by the German Bundestag (FKZ 03ET1395D).

Keywords: Two-phase flow morphology; Horizontal feed pipe; Wire-mesh sensor; Pipe configuration

  • Poster
    ProcessNet-Jahrestagung und 33. DECHEMA-Jahrestagung der Biotechnologen 2018, 10.-13.09.2018, Aachen, Deutschland
    DOI: 10.1002/cite.201855425

Permalink: https://www.hzdr.de/publications/Publ-28181
Publ.-Id: 28181


Dynamic Aeration for Improved Oxygen Mass Transfer in the Wastewater Treatment Process

Herrmann-Heber, R.; Reinecke, S.; Hampel, U.

Wastewater treatment is responsible for about 1% of the total electric energy consumption in developed countries. The dynamic aeration method, which applies oscillations to the gas flow, shows a high potential for increase of oxygen mass transfer and energy efficiency of the biological wastewater treatment process. We investigated the mass transfer of pulsed aeration modes in comparison to constant flow aeration in a test geometry in a numerical study. The effects of flow rate, pulsation frequency, bubble size and injection depth on mass transfer were studied. Gas was pulsated with a square wave pattern in on/off mode for the application in aeration basins of wastewater treatment plants. A geometry with up to 4 m aeration depth was investigated. The air supply was pulsed with frequencies in the range of 0.1 to 4 Hz. An increase of oxygen mass transfer rate by up to 24% is determined compared to continuous aeration. Moreover, comparable mass transfer rates are achieved for lower gas mass flow rates during pulsation. Thus, air demand in compression and energy consumption can be reduced when dynamic aeration is applied.

Keywords: Wastewater aeration; pulsed aeration; oxygen mass transfer; CFD

  • Open Access Logo Chemical Engineering Journal 386(2020), 122068
    Online First (2019) DOI: 10.1016/j.cej.2019.122068
    ISSN: 1385-8947
    Cited 40 times in Scopus
  • Lecture (Conference)
    14th International Conference on Gas-Liquid and Gas-Liquid-Solid Reactor Engineering (GLS-14), 30.05.-03.06.2019, Guilin, China

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Permalink: https://www.hzdr.de/publications/Publ-28180
Publ.-Id: 28180


Flow morphology in feed pipes: theoretical analysis and experimental investigation

Döß, A.; Schubert, M.; Hampel, U.; Schleicher, E.; Geipel, C.; Mehringer, C.; Flegiel, F.

Efficient separation in distillation columns driven by the thermodynamic non-equilibrium between vapor and liquid phase is achieved by high turbulence as well as large interfacial area. At the same time, intensive interactions between vapor and liquid phases result in the formation of droplets, whose entrainment by the vapor phase may drastically reduce the separation capacity. The feed pipe is a prone position for such droplet formation. Besides the flash evaporation, the evolving flow morphology in the feed pipe is decisive for the droplet generation.The flow morphology in pipes depends on fluid flow rates and properties as well as on the pipe geometry. Several models and flow regime maps for fully developed flows in small pipe diameters exist, relating operating conditions and flow morphology. However, industrial feed pipe configurations with larger diameters and bends are so far not studied.
Thus, an experimental study in feed pipes of 50 mm and 200 mm diameter is performed using the wire-mesh sensor technique (Fig. 1). The wire-mesh sensor visualizes the dynamic flow structure in the pipe cross-section at high spatiotemporal resolution (1 to 3 mm, up to 10,000 Hz). The obtained data are compared with the
state-of the art models to assess their applicability for feed pipes. This project is supported by the Federal Ministry for Economic Affairs and Energy (BMWi) based on a decision by the German Bundestag (FKZ 03ET1395D).

Keywords: Two-phase flow morphology; Horizontal feed pipe; Wire-mesh sensor

  • Lecture (Conference)
    ACHEMA 2018, Session: TERESA – Droplet entrainment and droplet reduction in mass transfer devices, 11.-15.06.2018, Fankfurt am Main, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-28179
Publ.-Id: 28179


PREFACE: American Journal of Science, Vol. 318, November, 2018

Fischer, C.; Arvidson, R. S.; (Editors)

Research in fluid-solid interaction processes has expanded tremendously over the past few decades, with key fronts ranging from fundamental understanding of reaction kinetics to detailed predictions involving the release, migration, and retention of environmentally important components. This special issue of AJS showcases the diversity and progress of this research in a series of invited papers that also illustrate core problems and solutions.
A central theme is the challenge involved in the integration of reaction processes over length and time scales that span many orders of magnitude. At one end of this spectrum, both theoretical and modeling approaches have evolved to describe the very brief interactions at the molecular scale, allowing key insights into details of reaction mechanism. At the other, modeling approaches have focused on the longer reaction times and lengths that characterize macroscopic systems. Experimental and analytical observations are also now able to map the dynamics and reactivity of reacting surfaces at the pore scale and above, providing these modeling approaches with essential feedbacks towards validation of predictions and identification of aspects where improvement is needed.
The strong coupling between the two “worlds” of experimental and simulation approaches is perhaps the most important result of the last years of research in our field. A primary motivation for this special issue was to highlight this productive interaction. A second motivation was to mark the 60th birthday of Professor Andreas Lüttge. Starting his scientific work at Tübingen University, followed by appointments at Yale University, Rice University, and now at the University of Bremen, he has continued to pursue the productive synergy of these two activities via pioneering work combining kinetic Monte Carlo simulations with complementary observations of reacting mineral surfaces.

This special issue is published in two parts. This first part begins with theoretical work by Bender and Becker, involving the kinetics of interactions between redox-sensitive plutonyl species, iron, and hydroxyl radical. This work nicely illustrates a divide-and-conquer approach, elucidating the stepwise reaction sequence involved in the formation and configuration of various complexes. In so doing, it also provides a potential framework for approaching related problems in the context of interactions at mineral surfaces. The second contribution, by Churakov and Prasianakis, combines thermodynamic calculations and kinetic simulations. Here the authors use the scale of the pore itself as a central connector to elegantly link the atomistic description of mineral surface reactivity with structural and compositional heterogeneities of real materials. The third contribution, by Kim, Marcano, Ellis, and Becker, presents experimental data on the photocatalytic role of TiO2 nanoparticles in uranyl reduction, using a diverse array of organic ligands as electron donors. This study demonstrates the importance of understanding the environmental specificity of reactions at surfaces, documenting the sensitivity of reduction efficiency to both ligand and UV wavelength. The last paper in this special issue’s first part, by Gebauer, Raiteri, Gale, and Cölfen, provides insight into current discussions concerning the birth of crystal nuclei during homogeneous precipitation in solution. They provide a nice summary of the ongoing debate, and stimulate further examination of true nature of these processes, arguing that the “critical” aspect of these clusters lies not in their size, but in their dynamics.
This last point also bears on a larger fundamental problem: how to resolve our new and increasing knowledge of the kinetics of these microscopic interactions, with the conventional thermodynamic framework that has long guided our interpretations of interactions at the mineral-fluid interface, but which is also largely macroscopic in origin. In the near future, we will announce the second part of this special issue, with a specific focus on new experimental results that challenge conventional model predictions.

  • Book (Editorship)
    New Haven, Connecticut: American Journal of Science, Yale University, 2018
    DOI: 10.2475/09.2018.01

Permalink: https://www.hzdr.de/publications/Publ-28178
Publ.-Id: 28178


Use of immobilizing individual abdominal corset in patients with upper-GI tumors treated with proton beam irradiation

Thiele, J.; Schneider, S.; Valentini, C.; Lohaus, F.; Stefanowicz, S.; Haak, D.; Krause, M.; Hoffmann, A. L.; Troost, E. G. C.

Purpose/Objective: The irradiation of tumors, which are subject to respiration-induced motion is challenging for pencil beam scanning (PBS) based proton therapy due to the interplay effect and the temporally varying tissue densities along the beam path. Here, we report on the feasibility, tolerability and setup reproducibility of an individualized immobilization device for patients with tumors in the upper abdomen, who are treated with PBS.

Material/Methods: Since January 2018, nine patients with tumors in the upper abdomen (pancreas, liver and gall bladder) have been treated with PBS at our department. All patients eligible for this study underwent the following procedure within 10-days: (1) intra-tumoral implantation of three fiducial markers for target localization, (2) design of an individualized abdominal corset for motion reduction by abdominal compression, (3) abdominal MRI scan with intravenous contrast agent (c.a.) for target volume definition and tumor motion quantification, and (4) 4D-CT scan with c.a. for treatment planning. CT simulation and irradiation was performed with a vacuum mattress (Fig.1). Before each treatment fraction, the position of the target volume was verified with orthogonal X-ray imaging. First, a 2D/2D match with the DRRs was performed and then the position of the fiducial markers was verified (tolerance level: 3-5mm). In case this tolerance level was exceeded, a CT scan was performed in-room and the dose distribution was recalculated for plan comparison; in case of clinically relevant changes in the dose distribution, a new plan was calculated.

Result: All patients tolerated the marker implantation, the abdominal corset and the treatment well with no treatment interruptions. In 4 out of the 300 applied fractions (1,3%) the tolerance level of the fiducial markers was exceeded. For these fractions, the recalculated dose distribution nevertheless showed sufficient target coverage (Fig. 2). The entire treatment fraction (including patient positioning, setup verification and dose delivery) did not exceed the standard time slot of 30 minutes.

Conclusion: This study demonstrates that PBS-based proton therapy with an abdominal corset to reduce breathing motion of GI-tumors is feasible, well-tolerated by patients and provides a reproducible setup without prolonging the daily treatment time.

Permalink: https://www.hzdr.de/publications/Publ-28177
Publ.-Id: 28177


Implementation of CT-based attenuation maps of RT positioning devices in PET/MRI - online vs offline

Täubert, L.; Pfaffenberger, A.; Berker, Y.; Beuthien-Baumann, B.; Hoffmann, A. L.; Troost, E. G. C.; Koerber, S. A.; Kachelrieß, M.; Gillmann, C.

Purpose or Objective
Integrating PET/MR hybrid imaging into radiation treatment (RT) planning has great potential to improve tumor delineation and dose prescription. Since these scans must be acquired under treatment conditions, attenuation correction of RT positioning devices is necessary. Attenuation maps can be implemented either online (directly at the PET/MRI scanner) or offline (at another PC). In this study, we compare both methods and assess their impact on PET image quality using a CT-based user-generated attenuation map of an RT table overlay.
Material and Methods
CT images of an RT table overlay (in-house construction) were acquired on a stand-alone CT (Somatom Definition Flash, Siemens Healthineers, Erlangen, Germany) at 120 kV and 360 mAs. Based on the CT images, an attenuation map of the RT table overlay was calculated via the bilinear approach [1]. The RT table overlay was then mounted onto the patient table of the PET/MRI (Biograph mMR, Siemens Healthineers) and two sets of PET-measurements were taken using an active 68Ge phantom (32 MBq, 10 min scan time). The phantom was scanned with the RT table overlay (RT scan), and without the RT table overlay (reference scan). PET reconstructions of the phantom scans were performed online at the PET/MRI scanner and offline using the e7tools (Version VA20, Siemens Healthineers) with identical reconstruction parameters. For the PET-reconstructions of the RT scan, the attenuation map of the RT table overlay was implemented. Attenuation correction accuracy was evaluated by comparing PET activities between RT and reference scans in 10 ROIs placed every 10 slices along the phantom in longitudinal direction, both for the online and the offline reconstruction methods.
Results
The RT table overlay attenuation map was successfully added to the hardware attenuation maps produced online and offline. Table 1 compares measured PET activities. For the online reconstruction, a mean percentage difference of 0.7% was found between the reference and the RT scan. For the offline reconstruction, a mean percentage difference of 1.4% was found. A systematic difference of around 500 Bq/ml was found between the online and offline reconstructions.
Conclusion
For the integration of PET/MRI in RT planning, attenuation correction of RT positioning devices is viable. The online reconstruction seems to be more accurate, but it has the disadvantage that the attenuation map must be removed from the system after every RT measurement to prevent an incorrect reconstruction of patient data that were not scanned in RT setup. Alternatively, offline reconstruction can be implemented at any PC via e7tools, and the reconstruction could be automated, thereby diminishing human error. The cause of the systematic signal difference in online and offline reconstruction needs to be investigated further.

Permalink: https://www.hzdr.de/publications/Publ-28176
Publ.-Id: 28176


Development of an anthropomorphic multimodality pelvis phantom for PET/MRI- and CT-based RT planning

Homolka, N.; Pfaffenberger, A.; Beuthien-Baumann, B.; Mann, P.; Schneider, V.; Johnen, W.; Runz, A.; Echner, G.; Hoffmann, A. L.; Troost, E. G. C.; Koerber, S. A.; Seco, J.; Gillmann, C.

Purpose
The aim of the study is the further development of an anthropomorphic multimodality pelvis phantom (ADAM, [1]) for the integration of PSMA-PET/MRI-based treatment planning of prostate cancer patients.
Materials/Methods
CT and 3T-MRI characteristics of different tissue types are mimicked using agarose gels (Agarose NEEO Ultra-Qualität Carl Roth GmbH + Co. KG, Germany) mixed with different concentrations of Gadolinium (Gd, MultiHance® 0.5 M, Bracco Imaging Deutschland GmbH) and sodium fluoride (NaF, Carl Roth GmbH + Co. KG). Gels were scanned using a 3T PET/MRI (Biograph mMR, Siemens Healthineers, Erlangen, Germany) using a saturation recovery sequence with multiple inversion times and a spin-echo sequence with multiple echo times. Based on the resulting images, T1- and T2-relaxation times were determined using in-house written software. CT scans of the agarose mixtures were performed on a stand-alone CT scanner (Somatom Definition Flash, Siemens Healthineers) at 120kV and 390 mAs.
The gels can be doped with radioactive tracers to simulate tumors in PET. Agarose mixtures that agreed best with reference values derived from literature data [2-4] were subsequently doped with patient-specific activity concentrations of 18F and 68Ga (e.g. 3kBq/ml 68Ga and 11kBq/ml 18F for the primary tumor). Organ shells (prostate with two intraprostatic lesions,
ESTRO abstract Noa Homolka, Physics Track lymph nodes and bone metastases) were printed using a 3D printer (Stratasys Objet 300 Connex 3, print material: VeroClear). The doped, liquid agarose gels were filled into the organ shells where they solidified within seconds. Organ shells were scanned at the 3T PET/MRI scanner (PET acquisition time: 10 min, MRI: T2-weighted morphological sequence).
Results
The final compositions of agarose gels are the following (given as mass fractions of agarose/NaF/Gd): Prostate (1.35%/3.2%/0.011%), tumor (2.25%/3.2%/0.0085%), lymph nodes (3.2%/1.4%/0.025%).
T1- and T2-relaxation times and CT numbers of the developed agarose gels fit well to reference values (Figure 1). Exemplary PET- and MR-images of a prostate with two intraprostatic lesions doped with 11 kBq/mL 18F are shown in Figure 2. The PET signal can be detected and the tumors appear hypointense on T2-weighted MRI.
Conclusion
Agarose gel mixtures with organ-specific MR-relaxation times at 3T and CT numbers have been developed and doped with radioactive tracers. The gels will be used in the pelvis phantom which will be central to simulate and optimize the technical workflow for the integration of PSMA-PET/MRI-based RT planning of prostate cancer patients.

Permalink: https://www.hzdr.de/publications/Publ-28175
Publ.-Id: 28175


Modelling of Complex Flow Sheets

van den Boogaart, K. G.; Kern, M.; Schach, E.; Krupko, N.; Hannula, J.; Menzel, P.; Prior, A.; Tolosana Delgado, R.

Complex multi-element ores, like the skarn ores from the AFK project and the Tellerhäuser pilot plant, are difficult to process due to their complex and fine-grained mineralogy. The valuable elements are enriched in various scales. The deposit hosts a very large, high-grade tin orebody, which is challenging to process because of the high energy consumption during grinding and the very fine-grained tin mineralisation. Traditional way of processing such ores would consist of a milling to desired liberation size, followed by a separation of cassiterite based on density or floatability properties. As it has been done historically due to the specific properties of the ore this approach however requires a selection between very intensive grinding with lots of fines, or less grinding with insufficient liberation, both approaches essentially leading to low final concentrate grades.
Unlike many other deposits, the Tellerhäuser skarn ore has a much more complex structure, which can be exploited with more advanced flow sheets. Additionally to the tin mineralization there is a substantial enrichment in multiple potential by-products. The fine-grained tin mineralization itself is locatedin lithologies (units of consistent geometallurgical, mineralogical and physical characteristics) dominated by tin free minerals. Despite a background concentration of unrecoverable tin as a trace element in the whole skarn body, the cassiterite mineralisation is localized within the ore body at mining block scale. It is thus possible to reject gangue material at various scales: Exploration based on mineralogical information allows distinguishing processable ore from gangue. A separation based on mineral groups allows to reject unmineralized skarns at various scales and to enrich preconcentrates for various by-products before cassiterite is liberated.
Applied in the right way, automated mineralogy data allows characterizing the spatial and mineralogical structure and physical properties of particles at various scales from mining blocks (selective processing), through cm-scale (sensor sorting), sub mm-scale (physical processing) down to µm scale (ultra-fine processing). This allows the prediction of potential separation behaviour of complex processing chains and thus to infer optimal separation criteria, separation thresholds, milling targets, mass streams, savings potential and environmental properties of all processing steps from mine to final concentrate.
In this way, the detailed understanding of the deposit and ore structure allows to model the different processing steps in an optimal scale and detail, combined to one flowsheet. The effect of imperfect processing behaviour can be quantified and understood in particle-level detail and used to determine suitable processing equipment.

Keywords: Automated Mineralogy; Particle Based Simulation

  • Invited lecture (Conferences)
    FAME Closure Conference, 05.-06.12.2018, London, Great Britain

Permalink: https://www.hzdr.de/publications/Publ-28174
Publ.-Id: 28174


Microbial diversity in an arid, naturally saline environment

Bachran, M.; Kluge, S.; Lopez-Fernandez, M.; Cherkouk, A.

The Arava Valley in Israel is a rock desert within the Great African Rift valley. Soil from this area is covered with a salt crust. Here, we report microbial diversity from arid, naturally saline samples collected near Ein Yahav from the Arava Valley by culture-independent as well as culture-dependent analysis. High-throughput sequencing of the hypervariable region V4 of the 16S rRNA gene revealed that the microbial community consists of halophiles from the domain Bacteria as well as Archaea. Bacterial diversity was mainly represented by the genus Salinimicrobium of the order Flavobacteriales within the phylum Bacteroidetes, from the gammaproteobacterial orders Alteromonadales and Oceanospirillales as well as representatives from the order Bacillales of the phylum Firmicutes. Archaeal diversity was dominated by euryarchaeal Halobacteria from the orders Halobacteriales, Haloferacales and Natrialbales. But more than 40 % of the sequences affiliated with Archaea were assigned to unknown or unclassified archaea. Even if taxonomic resolution of the 16S rRNA gene V4 region for Archaea is limited, this study indicates the need of further and more detailed studies of Archaea. By using culture-dependent analysis bacteria of the order Bacillales as well as archaea from all three halobacterial orders Halobacteriales, Haloferacales and Natrialbales including potentially novel species from the genera Halorubrum and Haloparvum were isolated.

Permalink: https://www.hzdr.de/publications/Publ-28173
Publ.-Id: 28173


Ultrasonic measurements of the flow field in foam and froth

Heitkam, S.; Nauber, R.; Richter, T.; Büttner, L.; Czarske, J.; Eckert, K.

In this work, the non-invasive Ultrasound-Doppler velocimetry has been used to measure the velocity distribution inside a liquid foam bulk for the first time. The foam flows upward in a transparent channel. Optical correlation algorithms and conductivity measurement provide reference data. An array of ultrasound transducers is mounted within the channel, sending bursts along the main flow axis and receiving the echoes. The penetration depth equals up to 0.2 meters. With purposely designed flows it is demonstrated, that the velocity uncertainty is below 15 percent and the spatial resolution better than 1 cm. In static experiments, the applicability to particle laden foam and froth has been estimated. These parameters allow for monitoring of industrial processes as well as scientific investigation of three-dimensional foam and froth flow on medium scales.

Keywords: Ultrasound Doppler Velocimetry; Foam flow

  • Lecture (Conference)
    ISUD 11 - 11th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering, 06.09.2018, Berlin, Germany

Permalink: https://www.hzdr.de/publications/Publ-28171
Publ.-Id: 28171


Neutron Imaging of Foam and Froth

Heitkam, S.; Lappan, T.; Rudolph, M.; Trtik, P.; Eckert, S.; Eckert, K.

The present contribution reports on the investigation of particle movement and drainage in unsteady foam and froth using Neutron Imaging (NI) (S. Heitkam et al. "Neutron imaging of froth structure and particle motion." Minerals Engineering, vol. 119, pp. 126-129, 2018.)

Froth flotation is one of the major separation processes in mining. Billions of tons per year of ore are treated by flotation worldwide. Despite the industrial relevance, measurement techniques for the observation of particle movement and liquid distribution inside the froth are limited.

In this situation, NI can reveal new insights on the mechanisms in froth flotation. NI is similar to radiography, but X-rays are replaced by neutrons. The neutrons pass through the measurement object, being partially attenuated. Then they hit a scintillator, generating photons that are observed by a high-speed camera. The advantage of NI in froth research is, that some materials (e.g. gadolinium) offer extremely high attenuation of neutrons. And also water attenuates neutrons about 30 times stronger than X-rays.

Keywords: Neutron Imaging; Foam; Froth

  • Lecture (Conference)
    EUFOAM, 10.07.2018, Liege, Belgium

Permalink: https://www.hzdr.de/publications/Publ-28170
Publ.-Id: 28170


Ultrasonic measurements of the velocity distribution inside foam

Heitkam, S.; Nauber, R.; Büttner, L.; Czarske, J.; Eckert, K.

The flowing behavior of liquid foam and froth is not yet well investigated. One reason for that is, that adequate measurement techniques are scarcely available. Also, industrial foam applications could be improved by monitoring the foam flow in the process.

In this work, the ultrasound Doppler velocimetry is used to measure the velocity distribution inside liquid foam. (Nauber et al. “Ultrasonic measurements of the bulk flow field in foams.”, Physical Review E, vol. 97 (1), pp 013113, 2018). To that end, an array of five ultrasound transducers is positioned inside a foam channel. One transducer sends pulses into the foam and the others receive the echoes. Sound pulses are reflected at moving particles and air-liquid interfaces. The echoes reveal the longitudinal velocity distribution along the beam axis. Multiplexing of the array allows for 2D-1C measurement.

Keywords: Ultrasound Doppler Velocimetry; Foam flow

  • Lecture (Conference)
    EUFOAM, 10.07.2018, Liege, Belgium

Permalink: https://www.hzdr.de/publications/Publ-28169
Publ.-Id: 28169


Phase-resolving simulation of dense bubble clusters under periodic shear

Heitkam, S.; Fröhlich, J.

The paper studies the response of a cluster of bubbles to osmotic pressure, and steady and oscillatory shearing by resolved numerical simulations. In contrast to other investigations, the movement of the interstitial fluid is fully resolved. To that end, an immersed-boundary method is employed, yielding the trajectory of each bubble and the flow and pressure field of the fluid. Additionally, a physically motivated collision model ensures realistic bubble interactions. Furthermore, a suitable numerical configuration is proposed which allows imposing osmotic pressure and shear in a way that integrates well into the simulation without generating artefacts. This method allows for the realistic investigation of the compression of bubbles across the jamming limit, demonstrating the influence of the inertia of the interstitial fluid. Applying oscillatory shearing with varying osmotic pressure, shear stress and frequency, the occurrence of shear bands is demonstrated and the influence on rheometric measurements is discussed.

Keywords: Bubbles; Simulation; Rheology; Foam

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Permalink: https://www.hzdr.de/publications/Publ-28168
Publ.-Id: 28168


Improving the range accuracy in particle therapy: Wrap up of the workshop

Richter, C.

Summary of the workshop results

  • Lecture (Conference)
    2ND ESTRO PHYSICS WORKSHOP - SCIENCE IN DEVELOPMENT, 26.-27.10.2018, Malaga, España

Permalink: https://www.hzdr.de/publications/Publ-28167
Publ.-Id: 28167


Improving range accuracy in particle therapy: Introduction of the workshop

Richter, C.

Introduction of the workshop

  • Lecture (Conference)
    2ND ESTRO PHYSICS WORKSHOP - SCIENCE IN DEVELOPMENT, 26.-27.10.2018, Malaga, España

Permalink: https://www.hzdr.de/publications/Publ-28166
Publ.-Id: 28166


Hochpräzisions-Strahlentherapie: Mit Protonen gegen Krebs

Richter, C.

Überblicksvortrag

  • Invited lecture (Conferences)
    50. Kraftwerkstechnisches Kolloquium, 23.-24.10.2018, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-28165
Publ.-Id: 28165


Dual-energy CT for automatic organ at risk segmentation in brain tumor patients using a multi-atlas and deep-learning approach

van der Heyden, B.; Wohlfahrt, P.; Troost, E.; Terhaaf, K.; Eekers, D.; Richter, C.; Verhaegen, F.

In radiotherapy, computed tomography (CT) datasets are frequently used to calculate radiation treatment plans to interpret dose evaluation metrics in healthy surrounding organs that need to be spared, the organs at risk (OARs). Based on CT scan and/or magnetic resonance images, the OARs have to be delineated by hand which is one of the most time-consuming tasks in the clinical radiotherapy workflow. Recent multi-atlas (MA) or deep learning (DL) based methods aim to improve the clinical workflow by automatically segment the OARs on a CT dataset. However, no studies investigated the performance of these MA or DL methods on dual-energy CT datasets which have been shown to improve the image quality compared to 120 kVp single-energy CT. In this study, the in-house developed MA method and the DL method (two-step three dimensional U-net) are described first. Then, the performance of both approaches (MA and DL) was quantitatively and qualitatively evaluated on various dual-energy CT datasets, more specifically on pseudo-monoenergetic CT dataset that were generated between 40 keV and 170 keV.

Permalink: https://www.hzdr.de/publications/Publ-28164
Publ.-Id: 28164


Log file based dose reconstruction and accumulation for 4D adaptive pencil beam scanned proton therapy in a clinical treatment planning system: Implementation and proof-of-concept

Meijers, A.; Jakobi, A.; Stützer, K.; Marmitt, G.; Both, S.; Langendijk, J.; Richter, C.; Knopf, A.

Background and Purpose
Motion induced uncertainties hamper the clinical implementation of pencil beam scanning proton therapy (PBS-PT). Prospective pre-treatment evaluations only provide multi-scenario predictions without giving a clear conclusion for the actual treatment. Therefore, in this proof-of-concept study we present a methodology for a fraction-wise retrospective 4D dose reconstruction and accumulation aiming at the evaluation of treatment quality during and after treatment.
Material and Methods
We implemented an easy-to-use, script-based 4D dose assessment of PBS-PT for patients with moving tumours in a commercially available treatment planning system. This 4D dose accumulation uses treatment delivery log files and breathing pattern records of each fraction as well as weekly repeated 4D-CT scans acquired during the treatment course. The approach was validated experimentally and was executed for an exemplary data set of a lung cancer patient.
Results
The script-based 4D dose reconstruction and accumulation was implemented successfully, requiring minimal user input and a reasonable processing time (around 10 minutes for a fraction dose assessment). An experimental validation using a dynamic CIRS thorax phantom confirmed the precision of the 4D dose reconstruction methodology. In a proof-of-concept study, the accumulation of 33 reconstructed fraction showed a linear increase of D98 values. Projected treatment course D98 values revealed a CTV under dosage after fraction 25. This loss of target coverage was confirmed in a DVH comparison of the nominal, the projected (after 16 fractions) and the accumulated (after 33 fractions) dose distribution.
Conclusions
The presented method allows for the assessment of the conformity between planned and delivered dose as the treatment course progresses. The implemented approach considers the influence of changing patient anatomy and variations in the breathing pattern. This facilitates treatment quality evaluation and supports decisions regarding plan adaptation. In a next step, this approach will be applied to a larger patient cohort to investigate its capability as 4D quality control and decision support tool for treatment adaptation.

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Permalink: https://www.hzdr.de/publications/Publ-28163
Publ.-Id: 28163


Large refrigerant capacity induced by table-like magnetocaloric effect in amorphous Er0.2Gd0.2Ho0.2Co0.2Cu0.2 ribbons

Li, L.; Xu, C.; Yuan, Y.; Zhou, S.

The microstructure, magnetism, and magnetocaloric properties in melt-spun Er0.2Gd0.2Ho0.2Co0.2 Cu0.2 ribbons were reported. The ribbons are fully amorphousized and all the constituent elements are distributed uniformly. The large table-like magnetocaloric effect (MCE) from 25 to 75 K has been observed, resulting in a large value of refrigerant capacity (RC). With the magnetic field change (μ0H) of 0–5 T, the values of maximum magnetic entropy change (−Smax M ) reaches 11.1 J/kg K, and the corresponding value of RC are as large as 806 J/kg, make the amorphous Er0.2Gd0.2Ho0.2Co0.2Cu0.2 ribbons extremely attractive for cryogenic magnetic refrigeration.

Keywords: Table-like magnetocaloric effect; Er0.2Gd0.2Ho0.2Co0.2Cu0.2 amorphous ribbons; large refrigeration capacity

Permalink: https://www.hzdr.de/publications/Publ-28162
Publ.-Id: 28162


Dual-energy computed tomography for improved delineation in postoperative brain-tumor patients

Wohlfahrt, P.; Agolli, L.; Pilz, K.; Richter, C.; Troost, E.

Purpose/Objective:

The clinical use of dual-energy CT (DECT) contributes to an improved accuracy in proton treatment planning compared to single-energy CT (SECT) as demonstrated in recent studies. A precise delineation of tumor volumes and organs at risk (OARs) is essential in particular for emerging high-conformal treatment techniques. Since DECT provides additional tissue information and allows for the generation of various tissue contrasts, we assessed its influence on the intra- and inter-observer delineation variability.
Material/Methods:
Two cohorts of 10 postoperative brain-tumor patients each, receiving either a 120kVp SECT or 80/140kVp DECT scan with identical total dose, were evaluated. Pseudo-monoenergetic CT (MonoCT) datasets of 50, 60, 70 and 79keV, representing several tissue contrasts, were derived from DECT scans processed in syngo.via (Siemens Healthineers). Three radiation oncologists with different levels of experience in neuro-oncology delineated the postoperative tumor bed volume (TBV) and OARs (brainstem, parotid and lacrimal glands, eyes, lenses, optic nerves, and chiasm) on each dataset, at least two-weeks apart per patient. Relevant image information was blinded. The delineations on SECT datasets were repeated once to assess the intra-observer variability. Finally, the delineation was also performed on T1/T2 MR scans as clinical reference.
The contour conformity was quantified by the Jaccard index (JI) and Hausdorff distance (HD) between the intersection and union of the respective contours (Fig. 1).
Results:
The median inter-observer TBV conformity (Fig. 2A) was almost independent from the CT dataset (HD=6-9mm, JI=61-66%) and comparable to MR scans (HD=6-7mm, JI = 66-67%). The consistency of brainstem contours (Fig. 2B) was best at the lowest energy of MonoCT datasets (median HD=2.8mm, JI=81%). In contrast, the contour conformity of the parotid glands (Fig. 2C) gained slightly from an increased energy (median HD reduction of 0.6mm, JI increase of 1%) and also led to better results as MR scans. For these OARs, using the most suitable MonoCT instead of SECT resulted in smaller interobserver variations. No relevant differences between SECT and MonoCT were determined for the other OARs, potentially due to their small volume.
The intra-observer TBV variability obtained on SECT did not depend on clinical experience. However, the contouring of less experienced clinicians is more affected by different image contrasts introduced by MonoCT of different energies (Fig. 2D).
Conclusion:
For postoperative brain-tumor patients, DECT-derived MonoCT datasets can improve the intra- and inter-observer delineation conformity compared to the currently used SECT. Moreover, they in part led to similar or better results as the gold standard MR. The most suitable image contrast to meet individual delineation requirements of anatomical structures can be chosen after CT acquisition. Future studies need to show whether the advantages can also be translated to other tumor entities and body regions.

  • Lecture (Conference)
    ESTRO 38, 26.-30.04.2019, Milano, Italia
  • Open Access Logo Abstract in refereed journal
    Radiotherapy and Oncology 133(2019), S559-S560
    DOI: 10.1016/S0167-8140(19)31432-X

Permalink: https://www.hzdr.de/publications/Publ-28161
Publ.-Id: 28161


Glassy formation ability, magnetic properties and magnetocaloric effect in Al27Cu18Er55 amorphous ribbon

Li, L.; Xu, C.; Yuan, Y.; Zhou, S.

In this work, we have fabricated the Al27Cu18Er55 amorphous ribbon with good glassy formation ability by melt-spinning technology. A broad paramagnetic (PM) to ferromagnetic (FM) transition (second ordered) together with a large reversible magnetocaloric effect (MCE) in Al27Cu18Er55 amorphous ribbon was observed around the Curie temperature TC 11 K. Under the magnetic field change (DH of 0–7 T, the values of MCE parameter of the maximum magnetic entropy change (DSM max) and refrigerant capacity (RC) for Al27Cu18Er55 amorphous ribbon reach 21.4 J/kg K and 599 J/kg, respectively. The outstanding glass forming ability as well as the excellent magneto-caloric properties indicate that Al27Cu18Er55 amorphous could be a good candidate for low temperature magnetic refrigeration.

Keywords: Al27Cu18Er55 amorphous ribbon; Magnetocaloric effect; Magnetic properties; Magnetic refrigeration

Permalink: https://www.hzdr.de/publications/Publ-28160
Publ.-Id: 28160


Range verification in proton therapy: Can prompt-gamma imaging identify the source of deviation?

Khamfongkhruea, C.; Janssens, G.; Petzoldt, J.; Smeets, J.; Pausch, G.; Richter, C.

Purpose/ Objective
In-vivo prompt-gamma imaging (PGI) is a promising method for directly assessing deviations in the proton range during proton therapy. However, several effects that can cause range shifts in patients need to be distinguished, e.g. global errors in CT conversion to stopping power ratio (SPR), variations in patient setup, and changes in the patient anatomy. Here, we evaluate if the source of range deviation in proton pencil-beam scanning (PBS) can be distinguished based on PGI information using a slit camera [1].
Material and Methods
For a virtual head-and-neck tumor in an anthropomorphic head phantom, a PBS treatment plan with simultaneous integrated boost (3 beams, 70Gy and 57Gy in 33 fractions) was generated. For all PBS spots in the investigated beam, PGI profiles were simulated using a verified analytical model of the slit camera [2, 3] for the reference scenario as well as for different error scenarios: SPR change of ±1.0, ±2.0 and ±3.5%, setup error in beam direction of ±1mm and ±3mm, and 10 scenarios of realistic anatomical changes (Fig. 1). A decision-tree approach was proposed to classify different groups of error sources. This included preceding filtering of PBS spots containing reliable PGI information for range verification. For simplification and better hypothesis generation, the head phantom was first overridden with water density. Afterwards, the real phantom anatomy including all heterogeneities was analyzed. It was evaluated whether the different error scenarios could be classified correctly.

Results
An automated filter to identify reliable PBS spots was developed, e.g. assuring that the spot position is within the effective field of view (FOV) of the camera and that the fall-off of the PGI profile is completely included in the FOV – even in case of range shifts. For subsequent decision-tree-based error source classification (Fig. 2), the following parameters were selected: The coefficient of determination (R2), the slope and intercept of the linear regression between range shift and penetration depth as well as the 2D range shift map. With this approach, 27 of 30 error scenarios could be identified correctly. However, the three error scenarios with anatomical changes in the nasal cavity could not be identified because the automated filtering approach had removed most relevant spots in this region.
Conclusion
An automated classification approach was introduced to identify the source for range deviation solely from prompt-gamma information. Based on phantom data, including simulation of realistic anatomical variation, the results are promising. Further refinement of this initial approach might be beneficial. An extension of the validation with patient CT data is in preparation. In the future, an application of the approach on clinically measured PGI data is planned. Also other classification methods could be evaluated.

  • Lecture (Conference)
    ESTRO 38, 26.-30.04.2019, Milano, Italia
  • Open Access Logo Abstract in refereed journal
    Radiotherapy and Oncology 133(2019), S296-S297
    DOI: 10.1016/S0167-8140(19)30986-7

Permalink: https://www.hzdr.de/publications/Publ-28159
Publ.-Id: 28159


Neutronen-Imaging von partikelbeladenen Schäumen

Heitkam, S.; Rudolph, M.; Lappan, T.; Sarma, M.; Eckert, S.; Trtik, P.; Lehmann, E.; Vontobel, P.; Eckert, K.

Die Flotation ist ein Trennverfahren mit großer industrieller Bedeutung, beispielsweise in der Gewinnung von Elementen aus Erzen. Dabei werden die Erze gemahlen und in Wasser suspendiert. Durch Zugabe geeigneter oberflächenaktiver Substanzen werden die gewünschten Partikel selektiv hydrophobisiert. Dadurch haften sie an eingebrachten Gasblasen an, werden an die Oberfläche transportiert und dort in sich bildenden Schaum eingelagert. Der Schaum wird abgezogen und man erhält gewünschte Partikel in hoher Konzentration.

Keywords: Neutron Imaging; Froth flotation

  • Lecture (Conference)
    Dechema Jahrestreffen, 06.03.2018, Bremen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-28158
Publ.-Id: 28158


p-type co-doping effect in (Ga,Mn)As: Mn lattice location and magnetic phase transition

Xu, C.; Yuan, Y.; Wang, M.; Zhou, S.; Helm, M.

III-Mn-V based diluted magnetic semiconductors offer an opportunity to explore various aspects of carrier transport in the presence of cooperative phenomena [1]. In this work, we demonstrate the efficiency of an alternative approach to control the carrier state through involving one magnetic impurity Mn and one electrically active dopant Zn. Mn-doped and Zn co-doped GaAs films have been prepared by combining ion implantation and pulsed laser melting, followed by a systematic investigation on the magnetic and transport properties of (Ga,Mn)As by varying Mn concentration as well as by Zn co-doping. Changes of electrical, magnetic and magneto-transport behavior of the investigated (Ga,Mn)As were observed after co-doping with Zn. The changes are caused by interstitial Mn atoms which are transferred from substitutional sites or formation of Mn-Zn dimers.

Keywords: Dilute ferromagnetic semiconductor; ion implantation; co-doping; magnetic properties

Related publications

  • Lecture (Conference)
    Deutsche Physikalische Gesellschaft 2018, 11.-16.03.2018, Berlin, Deutschland
  • Lecture (Conference)
    Ion Implantation and other Applications of Ions and Electrons 2018, 18.06.-21.11.2018, Kazimierz Dolny, Poland

Permalink: https://www.hzdr.de/publications/Publ-28157
Publ.-Id: 28157


Tracking of particles in froth using neutron imaging

Heitkam, S.; Lappan, T.; Eckert, S.; Trtik, P.; Eckert, K.

In this study, neutron imaging is employed to investigate the movement of hydrophobic particles in a rising froth column. A cylindrical batch-flotation cell is mounted to a rotary stage, allowing for three-dimensional analysis. Gadolinium particles of 200 μm diameter are hydrophobized and floated by means of small air bubbles. The generated froth is investigated by neutron imaging. Using particle-tracking and a reconstruction algorithm for the third dimension, the movement of particles in the froth is analyzed. Varying the concentration of the frother sodium oleate, different froth stabilities are compared. It has been found, that with decreasing froth stability bubble rupture leads to higher horizontal diffusion of particles and to higher agglomeration of particles.

Keywords: Froth; Particle laden Foam; Particle Tracking; Neutron Radiography; Neutron Imaging

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Permalink: https://www.hzdr.de/publications/Publ-28156
Publ.-Id: 28156


All-optical structuring of laser-driven proton beam profiles

Obst-Hübl, L.; Ziegler, T.; Brack, F.-E.; Branco, J.; Bussmann, M.; Cowan, T. E.; Curry, C. B.; Fiuza, F.; Garten, M.; Gauthier, M.; Göde, S.; Glenzer, S. H.; Huebl, A.; Irman, A.; Kim, J. B.; Kluge, T.; Kraft, S.; Kroll, F.; Metzkes-Ng, J.; Pausch, R.; Prencipe, I.; Rehwald, M.; Rödel, C.; Schlenvoigt, H.-P.; Schramm, U.; Zeil, K.

Extreme field gradients intrinsic to relativistic laser-interactions with thin solid targets enable compact MeV proton accelerators with unique bunch characteristics. Yet, direct control of the proton beam profile is usually not possible. Here we present a readily applicable all-optical approach to imprint detailed spatial information from the driving laser pulse onto the proton bunch. In a series of experiments, counter-intuitively, the spatial profile of the energetic proton bunch was found to exhibit identical structures as the fraction of the laser pulse passing around a target of limited size.
Such information transfer between the laser pulse and the naturally delayed proton bunch is attributed to the formation of quasi-static electric fields in the beam path by ionization of residual gas. Essentially acting as a programmable memory, these fields provide access to a higher level of proton beam manipulation.

Keywords: laser plasma interaction; laser particle acceleration; novel accelerator concepts; high performance computing; high power lasers

Related publications

  • Open Access Logo Nature Communications 9(2018), 5292
    DOI: 10.1038/s41467-018-07756-z
    Cited 16 times in Scopus
  • Lecture (Conference)
    Advanced Accelerator Concepts Workshop 2018, 13.-17.08.2018, Breckenridge, USA
  • Poster
    Advanced Accelerator Concepts Workshop 2018, 13.-17.08.2018, Breckenridge, USA
  • Lecture (Conference)
    Matter and Technologies Annual Meeting, 12.-14.06.2018, Berlin, Deutschland
  • Lecture (Conference)
    Matter and Technology Meeting, 06.03.2019, Jena, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-28155
Publ.-Id: 28155


Nematicity of correlated systems driven by anisotropic chemical phase separation

Yuan, Y.; Hübner, R.; Birowska, M.; Xu, C.; Wang, M.; Prucnal, S.; Jakiela, R.; Potzger, K.; Böttger, R.; Facsko, S.; Majewski, J. A.; Helm, M.; Sawicki, M.; Zhou, S.; Dietl, T.

The origin of nematicity, i.e., in-plane rotational symmetry breaking, and in particular the relative role played by spontaneous unidirectional ordering of spin, orbital, or charge degrees of freedom, is a challenging issue of magnetism, unconventional superconductivity, and quantum Hall effect systems, discussed in the context of doped semiconductor systems such as Ga1−xMnxAs, CuxBi2Se3, and Ga(Al)As/AlxGa1−xAs quantum wells, respectively. Here, guided by our experimental and theoretical results for In1−xFexAs, we demonstrate that spinodal phase separation at the growth surface (that has a lower symmetry than the bulk) can lead to a quenched nematic order of alloy components, which then governs low-temperature magnetic and magnetotransport properties, in particular the magnetoresistance anisotropy whose theory for the C_2v symmetry group is advanced here. These findings, together with earlier data for Ga1−xMnxAs, show under which conditions anisotropic chemical phase separation accounts for the magnitude of transition temperature to a collective phase or merely breaks its rotational symmetry. We address the question to what extent the directional distribution of impurities or alloy components setting in during the growth may account for the observed nematicity in other classes of correlated systems.

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Permalink: https://www.hzdr.de/publications/Publ-28154
Publ.-Id: 28154


Modeling the gluon and ghost propagators in Landau gauge by truncated Dyson-Schwinger equations

Kaptari, L. P.; Kämpfer, B.; Zhang, P.

We suggest a framework based on the rainbow approximation with effective parameters adjusted to lattice data. The analytic structure of the gluon and ghost propagators of QCD in Landau gauge is analyzed by means of numerical solutions of the coupled system of truncated Dyson-Schwinger equations. We find that the gluon and ghost dressing functions are singular in complex Euclidean space with singularities as isolated pairwise conjugated poles. These poles hamper solving numerically the Bethe-Salpeter equation for glueballs as bound states of two interacting dressed gluons. Nevertheless, we argue that, by knowing the position of the poles and their residues, a reliable algorithm for numerical solving the Bethe-Salpeter equation can be established.

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Permalink: https://www.hzdr.de/publications/Publ-28153
Publ.-Id: 28153


Towards Measuring Vacuum Birefringence

Schlenvoigt, H.-P.

We will present a design study how one could detect vacuum birefringence when combining an ultra-intense optical laser and an X-ray free electron laser. By means of precision X-ray polarimetry, one may detect the polarization flip of X-ray photons induced by the ultra-strong laser fields as a signature of vacuum birefringence. We will discuss crucial experimental parameters and provide a comprehensive model to study the experimental feasibility.

Keywords: Hibef

  • Lecture (Conference)
    27th Annual International Laser Physics Workshop, 16.-20.07.2018, Nottingham, UK

Permalink: https://www.hzdr.de/publications/Publ-28151
Publ.-Id: 28151


Oxygen diffusion in bcc Fe under the influence of foreign atoms and vacancies

Wang, X.; Posselt, M.; Faßbender, J.

A multiscale approach including Density Functional Theory (DFT) and Atomistic Kinetic Monte Carlo (AKMC) simulations is applied to investigate the diffusion of oxygen in bcc Fe under the influence of substitutional foreign atoms or solutes (Al, Si, P, S, Ti, Cr, Mn, Ni, Y, Mo, W) and vacancies. The solutes can be assumed to be immobile since their diffusion coefficient is much smaller than that of oxygen. On the other hand, the vacancy mobility must be considered in the calculations because it is comparable to that of oxygen. The most stable state of oxygen in pure bcc Fe is the octahedral interstitial configuration. Recently, jumps of oxygen in pure bcc Fe, between first-, second-, and third-neighbor octahedral interstitial sites were investigated by DFT. It was found that the first-neighbor jump is most relevant. The second-neighbor jump consists of two consecutive first-neighbor jumps whereas the barrier of the third-neighbor jump is too high to be significant for the diffusion process. In this work DFT is used to determine the modified migration barriers in the presence of solutes. It is found that Si, P, Ni, Mo and W have some effect on the migration barriers of oxygen and their interaction with O is mainly repulsive. Al, Cr and Mn have a significant influence on the barriers and they exhibit strong attractive interactions with O. The most important modification of the barriers is found for S, Ti, and Y where deep attractive states exist. The barriers for oxygen jumps near a vacancy and barriers for vacancy jumps in the environment of oxygen are also calculated by DFT. Based on the migration barriers obtained by DFT, AKMC simulations on a rigid lattice are employed to determine the diffusion coefficient of oxygen in a dilute iron alloy containing different substitutional foreign atoms. It is found that Si, P, Ni, Mo, and W have almost no influence on the diffusivity of O. The presence of Al, Cr, Mn, S, Ti, and Y causes a significant reduction of the mobility of oxygen. Another version of the AKMC code is applied to investigate the mutual influence of oxygen and vacancy diffusion as well as the migration of the oxygen-vacancy pair.

Keywords: oxygen; diffusion; bcc-Fe; Density Functional Theory; Atomistic Kinetic Monte Carlo simulations

  • Lecture (Conference)
    9th Int. Multiscale Materials Modeling conference (MMM 2018), 28.10.-02.11.2018, Osaka, Japan

Permalink: https://www.hzdr.de/publications/Publ-28150
Publ.-Id: 28150


Transmission Electron Microscopy at the Helmholtz-Zentrum Dresden-Rossendorf

Hübner, R.

Transmission Electron Microscopy at the Helmholtz-Zentrum Dresden-Rossendorf

Related publications

  • Lecture (others)
    Forschungsseminar Nanochemie, Physkalische Chemie, Technische Universität Dresden, 05.11.2018, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-28149
Publ.-Id: 28149


Operating three research infrastructures at one site: electrons & photons, ions, magnetic fields

Helm, M.

Operating three research infrastructures at one site: electrons & photons, ions, magnetic fields

Keywords: research infrastructure; large-scale facility

Related publications

  • Invited lecture (Conferences)
    Conference on International Cooperation of Science Centers, 19.10.2018, Huairou, China

Permalink: https://www.hzdr.de/publications/Publ-28147
Publ.-Id: 28147


Review of the International Standard ISO 2975 on Tracer methods for the measurement of single-phase flows in closed conduits

Jentsch, T. B. O.; Thereska, J.; Brisset, P.

Flow rate measurement is the most applied radiotracer method for online calibration and mass balance control in industrial processing. Better than 1-2% accuracy is achievable.

ISO Standards for measurements of fluid flows with tracer methods drafted years ago have been as follows:

ISO 2975 Measurement of water flow in closed conduits-Tracer methods, which consists of 7 parts, some of them never applied and others became obsolete.
ISO 4053 Measurement of gas flow in conduits -Tracer methods, which has been withdrawn for unknown reasons in 2003 leaving a void on this subject.

It is due time to review the existing ISO 2975, in the light of new development in radiotracer methods and industrial processing market.

The Sub Committee (SC) 5 of Technical Committee (TC) 30 of International Standardization Organization (ISO) - shortly: ISO/TC 30/SC 5 - is responsible for periodically reviewing ISO standard in the field of fluid flow measurements. Currently, the SC5 consists of 25 P member states and 11 observing member states (O-members).

Every five years the ISO TC30 SC5 initiates a so-called systematic review of each ISO standard. The last one for the ISO 2975 standard was carried out in 2018.

American Society of Mechanical Engineers (ASME) has adopted the American National Standard MFC-13M – 2006, which merges both ISO 2975 and ISO 4035. This Standard defines the terms and principles needed for intelligent consideration of tracer methods for any application, it can be serving as a good model for reviewing the ISO 2975.

The International Atomic Energy Agency (IAEA) and the International Society of Tracer and Radiation Applications (ISTRA) invites experts from all over the world to participate in the reviewing process of the existing ISO standards, formulating a more comprehensive, simple and universal ISO standard in this field. The new Standard on tracer methods for the measurement of single-phase fluid (gas or liquid) flows in closed conduits, will respond to the demand of industrial end-users.

Keywords: ISO 2975; International standard; fluid flow; measurement; mass flow rate; radiotracer

  • Lecture (Conference)
    Tracer8: The 8th International Conference on Tracers and Tracing Methods, 26.-28.02.2019, Đà Nẵng‎, Vietnam

Permalink: https://www.hzdr.de/publications/Publ-28146
Publ.-Id: 28146


Strategien zur Darstellung eines neuen 18F-markierten Adenosin-A2A-Rezeptorliganden zur PET-Bildgebung von Hirntumoren [1]

Lai, T. H.; Schröder, S.; Ludwig, F.-A.; Fischer, S.; Moldovan, R.-P.; Scheunemann, M.; Dukic-Stefanovic, S.; Deuther-Conrad, W.; Brust, P.

Ziel: Auf Grundlage einer Pyrazolo[2,3-d]pyrimidin-Leitverbindung[2] wurden 21 fluorierte Derivate synthetisiert. Basierend auf den dazu ermittelten Affinitäts- und Selektivitätsdaten für den humanen Adenosin-A2A-Rezeptor wurde das potente 4-Fluorbenzyl-Derivat 1 (Ki(A2A) = 5,3 nM; Ki(A1) = 220 nM) für die 18F-Markierung zur Darstellung eines neuen potentiellen A2A Radiotracers ausgewählt. Die gewünschte Position in 1 ist jedoch nicht für eine nukleophile aromatische Substitution gegen [18F]Fluorid aktiviert, sodass die Zielstellung in der Entwicklung einer geeigneten Radiosynthese von [18F]1 besteht.

Methodik: Es wurden drei Strategien zur Radiosynthese von [18F]1 verfolgt. Ausgehend vom Trimethylammonium-Präkursor 2 erfolgte die 18F-Markierung zum [18F]Fluorbenzaldehyd [18F]3. Dieser wurde entweder direkt über eine reduktive Aminierung oder nach Reduktion und anschließender Bromierung über eine Benzylierung mit dem Pyrazolo[2,3-d]pyrimidin-Baustein 4 zu [18F]1 umgesetzt. Parallel dazu wurde die direkte 18F-Markierung des Boronsäurepinacol-Präkursors 5 bearbeitet.

Ergebnisse: Ausgehend von 2 wurde [18F]1 nach der zweistufigen Radiosynthese mit nur 1,5% radiochemischer Ausbeute in der Reaktionsmischung detektiert (Radio-HPLC). Diese konnte mittels der vierstufigen Methode auf 49% gesteigert werden. In beiden Verfahren wurde eine hohe Anzahl an 18F-Nebenprodukten nachgewiesen, welche die Isolierung von [18F]1 mittels semi-präparativer HPLC erschweren. Die direkte 18F-Markierung von 5 führte zu einer radiochemischen Ausbeute von 80-90% an [18F]1 in der Reaktionsmischung (Radio-DC/-HPLC), wobei lediglich ein 18F-Nebenprodukt (< 5%) detektiert wurde.

Schlussfolgerungen: Aufgrund dieser Ergebnisse wird ausschließlich die einstufige Strategie zur Darstellung des neuen potentiellen A2A-Radiotracers [18F]1 ausgehend von 5 weiterverfolgt. Für die geplante biologische Evaluierung (in vitro und in vivo) werden derzeit geeignete Methoden zur Isolierung, Konzentration und Formulierung von [18F]1 erarbeitet.

Referenzen:

[1] Allard et al., Immunol. Cell. Biol. 2017, 95(4), 333-339
[2] Gillespie et al., Bioorg. Med. Chem. Lett. 2008, 18, 2924-2929

Keywords: Adenosin A2A Rezeptor; Radiotracer; 18F; PET; Hirntumor

  • Lecture (Conference)
    26. Jahrestagung der AGRR, 20.-22.09.2018, Aachen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-28145
Publ.-Id: 28145


Poly-disperse simulation of flash evaporation of water inside a large vertical pipe using class method of population balance

Liao, Y.; Lucas, D.

Flash evaporation of superheated liquid to vapour by depressurization is frequently encountered in the nature and technology, but computational fluid dynamics modelling and simulation of such scenarios is still at the embryo stage. Attempts having been made before are all based on the assumption of mono-disperse bubbles by prescribing either the size or number density, which deviates largely from the physical picture. In the present work the poly-disperse multiple-size-group approach is used for the first time to simulate the water evaporation process under pressure release transients. Complex bubble dynamics and non-equilibrium processes such as bubble nucleation, growth, coalescence and breakup as well as interfacial heat transfer are accounted for. The comparison with experimental data demonstrates that the model is effective in capturing the temporal course of vapour bubbles’ generation and growth as well as their spatial distribution. The agreement between measured and simulated cross-section averaged flow parameters such as void fraction, liquid temperature and bubble size distribution is satisfying.

Keywords: bubble coalescence; bubble nucleation; flash evaporation; interfacial heat transfer; poly-disperse

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Permalink: https://www.hzdr.de/publications/Publ-28144
Publ.-Id: 28144


1-Dimensional inorganic double helices as candidates for information storage materials

Springer, M.; Kuc, A.; Vankova, N.; Heine, T.

Alkali metal monopnictides contain one-dimensional chains with a double-helical structure. In this work, we report about their possible use as information storage materials. We investigated computationally fundamental properties of hetero- and homocationic systems and ways towards the application. It was shown, that the phosphorous backbone is capable of stabilising cationic chains of different composition and thus allows encoding of information.

  • Poster
    Computational Spectroscopy: Bridging Theory and Experiment, 09.-14.09.2018, Como, Italien
  • Poster
    13th HZDR PhD seminar, Ustí, 05.-07.11.2018, Ustí nad labem, Tschechische Republik
  • Poster
    JCF-Frühjahrssymposium, 20.-23.03.2019, Bremen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-28143
Publ.-Id: 28143


Theoretical and simulation study of ‘Comb’ electron beam and THz generation

Joshi, V.; Lehnert, U.; Karmakar, J.; Kumar, N.; Karmakar, B.; Tripathi, S.; Aryshev, A.; Gosh, S.; Urakawa, J.; Bhandari, R. K.; Kanjilal, D.

A compact accelerator based super-radiant THz source is under development at Inter University Accelerator Centre (IUAC), New Delhi. The facility is based on the principle of pre-bunched Free Electron Laser (FEL) which will produce THz radiation in the range of 0.18 to 3 THz from a modulated electron beam. A photocathode electron gun will generate a short train of micro-bunches (a ‘‘comb’’ beam) driven by a fibre laser system capable of producing multi micro-pulse laser beam with variable separation (‘‘comb’’ laser pulse). Upon acceleration, the electron beam will be injected in to a compact undulator magnet tuned to the same frequency as the separation of the electron micro-bunches. The paper discusses the process of enhancement of super-radiant emission of radiation due to modulation in the comb beam and the conditions required to achieve maximum enhancement of the radiation power. The feasibility study of generating a comb beam at the photocathode and its transport through the beamline while preserving its temporal structure has been reported. To evaluate the characteristics of the radiation emitted from the comb beam, a 𝐶++ based particle tracker and Lienard–Wiechert field solver has been developed. The conceptual understanding of the emission of radiation from comb beam is shown to conform with the numerical results. The code has been used to calculate the radiation pulse energy emitted into the central cone of undulator for various comb beam configurations.

Keywords: linear accelerator; THz; THz source; radiation source; comb beam; pre-bunched beam; radiation emission; undulator radiation; super-radiant emission

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Permalink: https://www.hzdr.de/publications/Publ-28142
Publ.-Id: 28142


Dissecting spin-phonon equilibration in ferrimagnetic insulators by ultrafast lattice excitation

Maehrlein, S. F.; Radu, I.; Maldonado, P.; Paarmann, A.; Gensch, M.; Kalashnikova, A. M.; Pisarev, R. V.; Wolf, M.; Oppeneer, P. M.; Barker, J.; Kampfrath, T.

To gain control over magnetic order on ultrafast time scales, a fundamental understanding of the way electron spins interact with the surrounding crystal lattice is required. However, measurement and analysis even of basic collective processes such as spin-phonon equilibration have remained challenging. We directly probe the flow of energy and angularmomentum in the model insulating ferrimagnet yttriumiron garnet. After ultrafast resonant lattice excitation, we observe thatmagnetic order reduces on distinct time scales of 1 ps and 100 ns. Temperature-dependentmeasurements, a spin-coupling analysis, and simulations show that the two dynamics directly reflect two stages of spinlattice equilibration. On the 1-ps scale, spins and phonons reach quasi-equilibrium in terms of energy through phonon-induced modulation of the exchange interaction. This mechanism leads to identical demagnetization of the ferrimagnet’s two spin sublattices and a novel ferrimagnetic state of increased temperature yet unchanged total magnetization. Finally, on the much slower, 100-ns scale, the excess of spin angular momentum is released to the crystal lattice, resulting in full equilibrium. Our findings are relevant for all insulating ferrimagnets and indicate that spin manipulation by phonons, including the spin Seebeck effect, can be extended to antiferromagnets and into the terahertz frequency range.

Keywords: THz control; ultra-fast; magnetism

Permalink: https://www.hzdr.de/publications/Publ-28141
Publ.-Id: 28141


Effect of anisotropic microstructure of ODS steels on small punch test results

Altstadt, E.; Bergner, F.; Das, A.; Houska, M.

Hot rolling and hot extrusion of oxide-dispersion strengthened (ODS) ferritic steels give rise to anisotropic microstructures and mechanical properties and may provoke related phenomena such as secondary cracking. In this study, we consider the small punch (SP) test – a method, applicable in the case of small amounts of available material and well established for isotropic materials. The SP test was applied to investigate the effect of sample orientation on deformation and cracking for one hot-rolled and two hot-extruded ODS ferritic steels. Existing microstructural evidence is used to rationalize the observed anisotropic fracture behaviour. The SP test results are compared with those from existing fracture mechanics tests based on sub-sized C(T) samples. The applicability of the empirical conversion of SP-based into Charpy-based transition temperatures is evaluated. The fractographic manifestation of load drops in SP load-displacement curves is identified and the analogy to secondary cracking in fracture mechanics tests is shown.

Keywords: small punch test; ductile-to-brittle transition temperature; oxide dispersion strengthened steel; pop-ins

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Permalink: https://www.hzdr.de/publications/Publ-28140
Publ.-Id: 28140


Fuzzy flow pattern identification in horizontal air-water two-phase flow based on wire-mesh sensor data

Wiedemann, P.; Döß, A.; Schleicher, E.; Hampel, U.

Online monitoring of two-phase flow patterns is an essential need in various chemical engineering applications, since the reliability of prediction methods is limited. Therefore, the present study aims at developing a practically applicable algorithm for identifying flow patterns in horizontal gas-liquid flows on the basis of wire-mesh sensor data. Experiments were conducted in a 50mm i. d. pipe over a wide range of superficial velocities of an air-water mixture. Characteristic features involving the influence of gravity and the spatio-temporal behavior of the flows were derived from tomographic phase fraction data and used as input for fuzzy clustering. Three differently determined sets of cluster centers are compared against a reference classification by human specialist through reclassifying the measurements with the aid of defuzzyfication and, alternatively, by means of a novel visualization technique, that retains the fuzziness of the results. With respect to the latter one, best agreement is reached with cluster centers from fuzzy c-means clustering using all recorded measurements. As a special emphasis is put to the identification of transitional flow patterns, the performance of the algorithm at pseudo-dynamic operation is demonstrated, finally.

Keywords: gas-liquid flow; fuzzy c-means clustering; polar visualization technique; regime transition; wire-mesh sensor

Permalink: https://www.hzdr.de/publications/Publ-28139
Publ.-Id: 28139


Visualisation of the large scale circulation in Rayleigh-Bénard convection using contactless inductive flow tomography

Wondrak, T.; Stefani, F.; Galindo, V.; Eckert, S.

Rayleigh-Bénard (RB) convection plays an important role in geo- and astrophysics as well as in many metallurgical applications. At sufficiently high values of the Rayleigh number, a large scale circulation (LSC) is formed whose dynamics had turned out to be surprisingly rich. In this paper, the applicability of the contactless inductive flow tomography (CIFT) for the detection of the torsional mode of the LSC is investigated. CIFT enables the three-dimensional reconstruction of flow structures in liquid metals by applying one or more magnetic fields and measuring the flow induced perturbations of those fields outside the melt. Additionally, preliminary measurements of the flow induced magnetic field with a similar sensor arrangement will be presented.

Keywords: flow measurement techniques; Rayleigh-Bénard convection

  • Lecture (Conference)
    9th international symposium on electromagnetic processing of materials (EPM2018), 14.-18.10.2018, Awaji Yumebutai International Conference Center, Japan
  • Open Access Logo IOP Conference Series: Materials Science and Engineering 424(2018), 012007
    DOI: 10.1088/1757-899X/424/1/012007
    Cited 1 times in Scopus

Permalink: https://www.hzdr.de/publications/Publ-28138
Publ.-Id: 28138


Real-time control of the mould flow in a model of continuous casting in frame of the TOMOCON project

Wondrak, T.; Hampel, U.; Ratajczak, M.; Glavinić, I.; Stefani, F.; Eckert, S.; van der Plas, D.; Pennerstorfer, P.; Muttakin, I.; Soleimani, M.; Abouelazayem, S.; Hlava, J.; Blishchik, A.; Kenjeres, S.

In continuous casting, the flow structure of the liquid steel in the mould and the two-phase distribution in the submerged entry nozzle (SEN) are crucial for the quality of the produced steel. In order to effectively control the flow in the mould by electromagnetic brakes (EMBrs) and the injection of gas into the SEN, even a rough knowledge of the flow structure would be very helpful. In the framework of the TOMOCON project, the contactless inductive flow tomography (CIFT) and the mutual inductance tomography (MIT) will be integrated into a control loop for slab casters. This control loop will be developed and implemented at the Mini-LIMMCAST facility, which is available at the Helmholtz-Zentrum Dresden – Rossendorf. In this paper a short overview of this project will be given.

Keywords: continuous casting; electromagnetic brake; inductive measurement techniques; flow control

  • Lecture (Conference)
    9th international symposium on electromagnetic processing of materials (EPM2018), 14.-18.10.2018, Awaji Yumebutai International Conference Center, Japan
  • Open Access Logo IOP Conference Series: Materials Science and Engineering 424(2018), 012003
    DOI: 10.1088/1757-899X/424/1/012003
    Cited 4 times in Scopus

Permalink: https://www.hzdr.de/publications/Publ-28137
Publ.-Id: 28137


All-optical structuring of laser-driven proton beam profiles data sets

Obst-Huebl, L.; Ziegler, T.; Brack, F.-E.; Branco, J.; Bussmann, M.; Cowan, T. E.; Curry, C. B.; Fiuza, F.; Garten, M.; Gauthier, M.; Göde, S.; Glenzer, S. H.; Huebl, A.; Irman, A.; Kim, J. B.; Kluge, T.; Kraft, S.; Kroll, F.; Metzkes-Ng, J.; Pausch, R.; Prencipe, I.; Rehwald, M.; Rödel, C.; Schlenvoigt, H.-P.; Schramm, U.; Zeil, K.

This data repository contains analyzed data files of the shown figures and simulation input files.

Please see the according README.txt files in the individual directories and the original manuscript for guidance.

Manuscript title:
  All-optical structuring of laser-driven proton beam profiles

Authors:
  Lieselotte Obst, Tim Ziegler, Florian-Emanuel Brack, Joao Branco, Michael Bussmann, Thomas E. Cowan, Chandra B. Curry, Frederico Fiuza, Marco Garten, Maxence Gauthier, Sebastian Göde, Siegfried H. Glenzer, Axel Huebl, Arie Irman, Siegfried H. Glenzer, Axel Huebl, Arie Irman, Jongjin B. Kim, Thomas Kluge, Stephan Kraft, Florian Kroll, Josefine Metzkes-Ng, Richard Pausch, Irene Prencipe, Martin Rehwald, Christian Rödel, Hans-Peter Schlenvoigt, Ulrich Schramm, Karl Zeil

Submitted to:
  Nature Communications (2018)


Responsible for the data repository:
  Lieselotte Obst-Huebl, TU Dresden and HZDR
  Axel Huebl, TU Dresden and HZDR
  Tim Ziegler, TU Dresden and HZDR
  Thomas Kluge, HZDR

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Permalink: https://www.hzdr.de/publications/Publ-28136
Publ.-Id: 28136


Contactless inductive flow tomography for models of continuous casting and crystal growth

Ratajczak, M.; Wondrak, T.; Glavinić, I.; Stefani, F.

Contactless inductive flow tomography (CIFT) enables the reconstruction of the major flow structure in electrically conducting liquids, like molten steel or silicon. It is based on the permeation of the melt by an external primary magnetic field and the subsequent induction of currents, which generate a flow-induced secondary magnetic field. The measured secondary field allows for reconstruction of the flow by solving the underlying linear inverse problem. We present results for the application of CIFT for two lab-scale model experiments of (a) continuous steel casting in the presence of an electromagnetic brake and (b) Czochalski crystal growth with a thermally driven convection. In the first scenario (a), the electromagnetic brake poses the biggest challenge, since its strong static magnetic field of about 300 mT superimposes the flow-induced field of about 100 nT, and the brake’s ferromagnetic parts distort the CIFT excitation field. We show how this can be overcome by simulations and adequate instrumentation using gradiometric induction coil sensors, which enables correct flow reconstructions in this scenario. In the second setup (b) the biggest challenges arise from the long measurement times of up to 12 hours together with thermal expansion and contraction of the setup mounting due to the intrinsic temperature gradient of the melt. Here an optimized experimental construction is necessary to enable successful measurements magnetic field measurements with Fluxgate sensors. The experimental data reveal plausible stationary and transient phenomena in accordance with numerical
flow simulations.

Keywords: metallurgy; contactless inductive flow tomography; magnetic field measurement; flow measurement

  • Contribution to proceedings
    9th world congress on industrial process tomography, 02.-6.9.2018, Bath, UK
    Proceedings of the 9th world congress on industrial process tomography, 978 0 85316 3497, 839-845
  • Lecture (Conference)
    9th world congress on industrial process tomography, 02.-6.9.2018, Bath, UK

Permalink: https://www.hzdr.de/publications/Publ-28135
Publ.-Id: 28135


Numerical aspects of contactless inductive flow tomography for crystal growth

Wondrak, T.; Jacobs, R. T.; Galindo, V.; Stefani, F.

The flow structure of liquid silicon in the crucible for Czochralski (Cz) crystal growth is important for the quality of the silicon crystal. However, the high temperature and the required cleanliness of the melt represent a challenge for any flow measurement device. A promising technique to reconstruct the flow of a conducting liquid is contactless inductive flow tomography (CIFT). The procedure relies on the measurement of the flow induced perturbation of a primary magnetic field and the inversion of the corresponding integral equation system. In this paper, the numerical challenges for the application of CIFT to Cz crystal growth will be investigated. This includes the treatment of the singularities of the integral equation system as well as the selection of appropriate integration techniques. The paper concludes with numerical investigation of the expected flow induced magnetic field for a reversal of the rotation in simple model of a typical crucible.

Keywords: contactless inductive flow tomography; Czochralski crystal growth; flow measurement; liquid metal

  • Contribution to proceedings
    9th world congress on industrial process tomography, 02.-6.9.2018, Bath, UK
    Proceedings of the 9th world congress on industrial process tomography, 978 0 85316 3497, 451-456
  • Lecture (Conference)
    9th world congress on industrial process tomography, 02.-6.9.2018, Bath, UK

Permalink: https://www.hzdr.de/publications/Publ-28134
Publ.-Id: 28134


Surface nanobubbles on the carbonate mineral dolomite

Owens, C. L.; Schach, E.; Rudolph, M.; Nash, G. R.

Surface nanobubbles are of wide interest to a number of research fields, ranging from mineral processing to metamaterials. Their formation on hydrophobic surfaces has long been confirmed but the factors controlling their size and location are less well understood. In this work we investigate, using non-contact atomic force microscopy, the properties of surface nanobubbles on the mineral dolomite under three aqueous solutions; water, depressant and collector. Nanobubbles were observed under all three conditions, but with the highest density observed under collector conditions. Analysis of the critical angle of the bubbles suggests that the collector does not affect the surface tension of the bubbles, but instead does affect their pinning, consistent with the observed increased density.

Keywords: nanobubbles; flotation; atomic force microscopy

Permalink: https://www.hzdr.de/publications/Publ-28133
Publ.-Id: 28133


Magnon Transport in Spin Textures

Schultheiss, H.

One of the grand challenges in cutting edge quantum and condensed matter physics is to harness the spin degree of electrons for information technologies. While spintronics, based on charge transport by spin polarized electrons, made its leap in data storage by providing extremely sensitive detectors in magnetic hard-drives, it turned out to be challenging to transport spin information without great losses. With magnonics a visionary concept inspired researchers worldwide: Utilize magnons - the collective excitation quanta of the spin system in magnetically ordered materials - as carriers for information. Magnons are waves of the electrons’ spin precessional motion. They propagate without charge transport and its associated Ohmic losses, paving the way for a substantial reduction of energy consumption in computers.
While macroscopic prototypes of magnonic logic gates have been demonstrated, the full potential of magnonics lies in the combination of magnons with nano-sized spin textures. Both magnons and spin textures share a common ground set by the interplay of dipolar, spin-orbit and exchange energies rendering them perfect interaction partners. Magnons are fast, sensitive to the spins’ directions and easily driven far from equilibrium. Spin textures are robust, non-volatile and still reprogrammable on ultrashort timescales. The vast possibilities offered by combining this toolset of magnetic phenomena, add value to both magnonics and the fundamental understanding of complex spin textures.
I will give an introduction about magnon propagation and manipulation in microstructures with non-collinear spin textures, in particular magnons propagating in nano channels formed by magnetic domain walls. Furthermore, I will address how magnons can be excited in domain wall channels by pure spin currents originating from the spin Hall effect.
References:
[1] K. Wagner, A. Kákay, K. Schultheiss, A. Henschke, T. Sebastian, and H. Schultheiss, Nature Nanotech 11, 432 (2016).
[2] K. Vogt, F. Y. Fradin, J. E. Pearson, T. Sebastian, S. D. Bader, B. Hillebrands, A. Hoffmann, and H. Schultheiss, Nat Comms 5, 3727 (2014).

Keywords: magnonics; spin waves; spin textures; domain walls; auto-oscillations

Related publications

  • Invited lecture (Conferences)
    Lüscher Seminar, 08.02.2018, Klosters, Schweiz
  • Invited lecture (Conferences)
    Spin Mechanics 5 and Nano MRI 6 workshop, 16.02.2018, Chamonix, Schweiz
  • Invited lecture (Conferences)
    Nano-Magnonics Workshop, 20.02.2018, Kaiserslautern, Deutschland
  • Invited lecture (Conferences)
    International Conference on Microwave Magnetics, 25.06.2018, Exeter, England
  • Invited lecture (Conferences)
    Workshop on Advances in Brillouin Light Scattering, 13.09.2018, Perugia, Italien
  • Invited lecture (Conferences)
    International Advanced School on Magnonics, 20.09.2018, Kyiv, Ukraine
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    Magnonics 2019, 28.07.2019, Carovigno, Italien
  • Invited lecture (Conferences)
    MLZ Conference
: Neutrons for Information and Quantum Technologies, 04.06.2019, Lenggries, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-28132
Publ.-Id: 28132


Characterization of specifically metal-binding phage clones for selective recovery of cobalt and nickel

Matys, S.; Schönberger, N.; Lederer, F.; Pollmann, K.

Phage surface display (PSD) represents a powerful technique for isolating metal ion binding peptides. From a commercial pIII phage library, two specific peptide motifs—namely, CNAKHHPRC for nickel and CTQMLGQLC for cobalt—were identified using a specialized experimental set-up with sol-gel-coated glass fiber fabrics possessing ion exchange capacity. Employing single-clone binding experiments with immobilized Me2+ ions on nitrilotriacetic acid (NTA) agarose beads, adsorption isotherms were determined for both the phage clones and the reference clone without a peptide insert which clearly indicate specificity of the identified phage clones for their respective target ion. The mechanisms involved in phage binding to agarose beads could be satisfactorily described using the Freundlich model. In all experiments, two fractions of phages were reproducibly identified: those chemically eluted with glycine, and a second, smaller fraction that could be eluted only by direct incubation with the host organism E. coli ER 2738. The results demonstrate that metal ion-specific phage clones can be identified and characterized in terms of their binding strength with this experimental setup. In perspective, this approach can facilitate the identification of well suited phage clones for the further development of new element specific biosorptive materials for the recovery of heavy metals from dilute aqueous solutions, e.g. industrial waste waters.

Keywords: phage display; cobalt; nickel; adsorption isotherms; Freundlich model

Permalink: https://www.hzdr.de/publications/Publ-28131
Publ.-Id: 28131


Ultrasmall Nanomaterials for Multimodal Cancer Imaging

Stephan, H.

Ultrasmall nanomaterials (NMs) offer excellent prospects for the development of new non-invasive strategies of early diagnosis and efficient monitoring of therapeutic treatments. 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.
This lecture will focus on the development and application of very small radiolabeled NMs, embracing inorganic particles and soft polymeric structures. 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.

  • Invited lecture (Conferences)
    Kolloquium, 25.10.2018, Hamburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-28130
Publ.-Id: 28130


Nanoscale X-Ray Imaging of Spin Dynamics in Yttrium Iron Garnet

Förster, J.; Wintz, S.; Bailey, J.; Finizio, S.; Josten, E.; Dubs, C.; Bozhko, D. A.; Stoll, M.; Dieterle, G.; Träger, N.; Raabe, J.; Slavin, A. N.; Weigand, M.; Gräfe, U.; Schütz, G.

Time-resolved scanning transmission x-ray microscopy (TR-STXM) has been used for the directimaging of spin wave dynamics in thin film yttrium iron garnet (YIG) with spatial resolution inthe sub 100 nm range. Application of this x-ray transmission technique to single crystalline garnetfilms was achieved by extracting a lamella (13x5x0.185μm3) of liquid phase epitaxy grown YIG thinfilm out of a gadolinium gallium garnet substrate. Spin waves in the sample were measured alongthe Damon-Eshbach and backward volume directions of propagation at gigahertz frequencies andwith wavelengths in a range between 100 nm and 10μm. The results were compared to theoreticalmodels. Here, the widely used approximate dispersion equation for dipole-exchange spin wavesproved to be insufficient for describing the observed Damon-Eshbach type modes. For achieving anaccurate description, we made use of the full analytical theory taking mode-hybridization effectsinto account.

Keywords: Magnonics; YIG; Microscopy

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Permalink: https://www.hzdr.de/publications/Publ-28129
Publ.-Id: 28129


Combined frequency and time domain measurements on injection-locked, constriction-based spin Hall nano-oscillators

Hache, T.; Weinhold, T.; Schultheiss, K.; Stigloher, J.; Vilsmeier, F.; Back, C.; Arekapudi, S. S. P. K.; Hellwig, O.; Fassbender, J.; Schultheiss, H.

We demonstrate a combined frequency and time domain investigation of injection-locked, constriction-based spin Hall nano-oscillators by Brillouin light scattering (BLS) and time-resolved magneto-optical Kerr effect (TR-MOKE). This was achieved by applying an alternating current in the GHz regime in addition to the direct current which drives auto-oscillations in the constriction. In the frequency domain, we analyze the width of the locking range, the increase in intensity and reduction in linewidth as a function of the applied direct current. Then we show that the injection locking of the auto-oscillation allows for its investigation by TR-MOKE measurements, a stroboscopic technique that relies on a phase stable excitation, in this case given by the synchronisation to the microwave current. Field sweeps at different direct currents clearly demonstrate the impact of the spin current on the Kerr amplitude. Two-dimensional TR-MOKE and BLS maps show a strong localization of the auto-oscillation within the constriction, independent of the external locking.

Keywords: spin Hall; injection locking; injection-locking; TR-MOKE; Kerr-effect; Kerr; auto-oscillation; magnetism; magnetization dynamics; BLS; µBLS; Brillouin light scattering; constriction-based; nano-oscillator

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Permalink: https://www.hzdr.de/publications/Publ-28128
Publ.-Id: 28128


Transition from convection rolls to large-scale cellular structures in turbulent Rayleigh-Bénard convection in a liquid metal layer

Akashi, M.; Yanagisawa, T.; Tasaka, Y.; Vogt, T.; Murai, Y.; Eckert, S.

Turbulent Rayleigh-Bénard convection was investigated within a liquid metal layer, Prandtl number Pr = 0.03, in a square vessel having a moderate aspect ratio, Γ = 5. Laboratory experiments were performed at moderate Rayleigh numbers, 7.9 × 10^3 < Ra < 3.5 × 10^5. Ultrasonic velocity profiling (UVP) was used to visualize the spatio-temporal flow structure in two horizontal planes, while temperature fluctuations were monitored simultaneously in the fluid layer. Oscillatory roll-like structures were observed at Ra ≥ 10^4, while the transition to a fully three-dimensional cell-like structure occurs around Ra = 6 × 10^4. The transition from laminar convection to thermal turbulence manifests itself in the occurrence of unstable intermediate regimes accompanied by a stepwise increment in the horizontal scale. We propose a scaling law for the horizontal length scale as a function of the Ra number based on empirically-derived relations of the oscillation frequency and the typical flow velocity. This scaling law indicates the present results are comparable with variations of the maximum size of large scale structures in different Pr conditionsand larger aspect ratios.

Keywords: Rayleigh-Bénard convection; Thermal turbulence; Large scale structure; Liquid metal; Low Prandtl number

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Permalink: https://www.hzdr.de/publications/Publ-28127
Publ.-Id: 28127


Flow control in the model of a continuous caster by using Contactless Inductive Flow Tomography

Glavinic, I.; Abouelazayem, S.; Ratajczak, M.; Schurmann, D.; Eckert, S.; Stefani, F.; Hlava, J.; Wondrak, T.

The global flow pattern of liquid metal in the slab mold of a continuous caster is difficult to control, as it cannot be measured in real-time by conventional methods. Contactless inductive flow tomography (CIFT) can easily provide real-time information about the flow structure (double or single roll) and the angle of the jet coming out of the submerged entry nozzle (SEN) just from the raw sensor data. Furthermore, by solving the underlying linear inverse problem, the full velocity field can be reconstructed. This paper discusses the possibility of applying CIFT for flow pattern recognition in continuous casting, which is then used for setting an electromagnetic brake in order to control the angle of the fluid jet. The control loop will be implemented and developed for the Mini-LIMMCAST model of a continuous caster at Helmholtz-Zentrum Dresden-Rossendorf (HZDR).

Keywords: continuous casting; flow control; inductive measurement techniques; electromagnetic brake

  • Contribution to proceedings
    TMS2019 Annual Meeting & Exhibition, 10.03.2019, San Antonio, Texas, United States of America
  • Lecture (Conference)
    TMS2019 Annual Meeting & Exhibition, 11.03.2019, San Antonio, Texas, United States of America

Permalink: https://www.hzdr.de/publications/Publ-28126
Publ.-Id: 28126


Consequences of broken axial symmetry in heavy nuclei – an overview of the situation in the valley of stability.

Grosse, E.; Junghans, A. R.; Wilson, J.

An overview on the various effects of axial symmetry breaking is presented for medium heavy and heavy nuclei covering the mass number range 70 < A <240. The discussion includes various observations for nuclei: level densities, spectroscopic features as energies and transition rates, ground state masses and finally the splitting of giant dipole resonances. Quadrupole moments and rates can be derived from models of triaxial rigid rotation or cranking for a given triaxiality parameters γ, but microscopic considerations are needed to predict these for each nucleus investigated. Respective predictions were made by recently made Hartree-Fock-Bogolyubov (HFB) calculations extended to arbitrary triaxiality by a generator coordinate method. In accord to these, various observations as reported in this overview demonstrate the importance of allowing a breaking of axial symmetry for heavy nuclei already in the valley of stability. Considering this breaking as indicated from the HFB approach surprisingly many experimental data are well described globally without the need for local fit parameters. In addition to these comparisons it will be shown that it is advantageous to consider c_γ=cos(3γ) an indicator of axiality for heavy nuclei independent of their quadrupole moment.

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Permalink: https://www.hzdr.de/publications/Publ-28125
Publ.-Id: 28125


Feasibility of proton FLASH effect tested by zebrafish embryo irradiation

Beyreuther, E.; Brand, M.; Hans, S.; Hideghety, K.; Karsch, L.; Leßmann, E.; Schürer, M.; Szabo, E. R.; Pawelke, J.

Background and purpose
Motivated by first animal trials showing the normal tissue protecting effect of electron and photon Flash irradiation relative to conventional continuous beam delivery, the feasibility of proton Flash should be assessed.
Materials and methods
A setup and beam parameter settings for the treatment of zebrafish embryo with proton Flash and proton beam of conventional dose rate were established at the University Proton Therapy Dresden. Zebrafish embryos were treated with graded doses and the differential effect on embryonic survival and the induction of morphological malformations was followed for up to four days after irradiation.
Results
Beam parameters for the realization of proton Flash were set and tested with respect to controlled dose delivery to biological samples. The dose dependent embryonic survival data obtained for protons delivered as Flash and with a beam of conventional dose rate of 5 Gy/min show not significant influence of proton dose rate. Similarly, just a trend towards a protective effect of proton Flash was revealed for the induction of pericardial oedema as one type of acute radiation effect and spinal curvature as a developmental abnormality.
Conclusion
The feasibility of Flash proton irradiation was successfully shown, whereas more experiments are required to understand the absence of a clear protecting effect and therefore to figure out the limits and requirements for the Flash effect.

Keywords: proton Flash effect; proton beam therapy; normal tissue toxicity; zebrafish embryo

Permalink: https://www.hzdr.de/publications/Publ-28124
Publ.-Id: 28124


Domain wall-based spin-Hall nano-oscillators

Sato, N.; Schultheiß, K.; Körber, L.; Puwenberg, N.; Mühl, T.; Awad, A. A.; Arekapudi, S. S. P. K.; Hellwig, O.; Faßbender, J.; Schultheiß, H.

In the last decade, two revolutionary concepts in nanomagnetism emerged from research for storage technologies and advanced information processing. The first suggests the use of magnetic domain walls in ferromagnetic nanowires to permanently store information in domain-wall racetrack memories. The second proposes a hardware realization of neuromorphic computing in nanomagnets using nonlinear magnetic oscillations in the gigahertz range. Both ideas originate from the transfer of angular momentum from conduction electrons to localized spins in ferromagnets, either to push data encoded in domain walls along nanowires or to sustain magnetic oscillations in artificial neurones. Even though both concepts share a common ground, they live on very different timescales which rendered them incompatible so far. Here, we bridge both ideas by demonstrating the excitation of magnetic auto-oscillations inside nanoscale domain walls using pure spin currents. This Letter will shed light on the current characteristic and spatial distribution of the excited auto-oscillations.

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Permalink: https://www.hzdr.de/publications/Publ-28123
Publ.-Id: 28123


Magnon auto-oscillation under zero magnetic field

Nishida, N.; Hache, T.; Arekapudi, S. S. P. K.; Awad, A. A.; Hellwig, O.; Fassbender, J.; Schultheiss, H.

Magnons are attractive for application in energy efficient information technology, because they propagate without any actual charge currents and they offer high frequencies up to THz range. Here we present a novel scheme for magnon generation using spin currents and domain walls.
When a charge current is applied to a heavy metallic/ferromagnetic bilayer, the spin currents originating from a spin Hall effect in the heavy metal apply a spin transfer torque on the magnetization. This allows driving efficiently auto-oscillations of magnetization [1]. We focused on domain walls as local magnon nano channels [2]. Since domain walls can be moved by electrical currents [3], they are attractive for reprogrammable nano circuits.
A 370 nm wide zigzag structure was fabricated from a Pt/CoFeB bilayer. A domain wall was generated at the apex by magnetic saturation. The magnon intensity on the remanent state was measured by Brillouin light scattering microscopy [4] with applying a dc current. The magnon excitation showed the dc current dependency. Magnons were detected only for positive dc currents. We succeeded to drive magnon auto-oscillation in the domain wall under zero magnetic field by spin transfer torque.

Reference
[1] A. N. Slavin and V. Tiberkevich, IEEE Trans. Magn. 45, 1875 (2009).
[2] K. Wagner et. al., Nat. Nanotech. 11, 432 (2016).
[3] S. S. P. Parkin et. al., Science 320, 190 (2008).
[4] T. Sebastian et. al., Front. Phys. 3, 35 (2015).

Related publications

  • Lecture (Conference)
    9th Joint European Magnetic Conference, 03.-07.09.2018, Mainz, Germany

Permalink: https://www.hzdr.de/publications/Publ-28122
Publ.-Id: 28122


Magnon auto-oscillation in domain walls

Nishida, N.; Hache, T.; Arekapudi, S. S. P. K.; Awad, A. A.; Hellwig, O.; Fassbender, J.; Schultheiss, H.

Magnons are the fundamental excitations in magnetic materials, and they can transport angular momentum without actual charge currents. Therefore, they are attractive for applications in energy efficient information technology, offering high operating frequencies up to the THz range. Here we present a novel scheme for magnon generation using spin currents and domain walls.
When a charge current is applied to a bilayer consisting of a heavy metal and a ferromagnetic metal, the spin currents originating from the spin Hall effect in the heavy metal apply a spin transfer torque on the magnetization of the ferromagnetic layer. This allows driving efficiently auto-oscillations of magnetization [1]. We focused on domain walls as local nano magnon channels [2]. Since it is possible to move domain walls by electrical currents [3], domain walls are attractive for nano-sized reprogrammable circuits.
A 370 nm wide boomerang structure was fabricated from a Pt/CoFeB bilayer (Fig.1). The sample was magnetized by applying an external magnetic field H. After the saturation, the external magnetic field was set to 0 Oe, and a dc current was applied to the sample. The magnon intensity at the apex of the boomerang structure was measured by Brillouin light scattering microscopy [4]. Figure 2 shows the dc current dependency of the magnon spectrum on the remanent state. Magnons were detected for currents between 3.6 mA and 4.5 mA, while no magnons were observed for any negative dc currents. A domain wall is generated at the apex for the remanent state because of the shape anisotropy of the boomerang structure. We succeeded to excite magnons under zero magnetic field due to the autooscillation of the magnetization by spin transfer torque.

Reference
[1] A. N. Slavin and V. Tiberkevich, IEEE Trans. Magn. 45, 1875 (2009).
[2] K. Wagner et. al., Nat. Nanotech. 11, 432 (2016).
[3] S. S. P. Parkin et. al., Science 320, 190 (2008).
[4] T. Sebastian et. al., Front. Phys. 3, 35 (2015).

Related publications

  • Lecture (Conference)
    International Conference on Magnetism, 15.-20.07.2018, San Francisco, USA

Permalink: https://www.hzdr.de/publications/Publ-28121
Publ.-Id: 28121


Magnon auto-oscillation in domain walls by spin transfer torque

Nishida, N.; Hache, T.; Arekapudi, S. S. P. K.; Hellwig, O.; Fassbender, J.; Schultheiss, H.

磁性体の基本励起状態であるマグノンは非電荷でTHz帯までの励起が可能であることから、省エネルギーかつ高速な情報デバイスへの応用が期待されている。Ptと強磁性金属の二層構造に電荷を流すと、スピンホール効果によりPt層でスピン流が生成され、強磁性層に注入される。スピン流から磁化にスピントランスファートルクが印加されることにより、磁化の自励発振[1]が駆動され、マグノンが励起される。我々は微細なマグノンチャネルとして磁壁[2]に着目し、磁壁中のマグノン励起について調べた。

図1に示すように、PtとCoFeBの二層膜から成る線幅370 nmの折れ線構造を作製し、y方向に着磁した。試料に直流電流を印加し、ブリルアン散乱分光装置を用いて折れ線の頂点におけるマグノン強度を測定した。図2にマグノン強度の電流依存性を示す。図2(a)に示すように、y方向に1.0 kOeの外部磁場を印加した場合には、2.3 mAから5.0 mAの電流値の範囲においてマグノンの励起が検出された。一方、電流の印加方向を反転させるとマグノンは検出されなかった。図2(b)に、y方向に試料を着磁した後に外部磁場を0 kOeにし、残留磁化状態において測定した結果を示す。1.0 kOeの外部磁場を印加した場合と同様に、正の電流を印加した場合のみマグノンの励起が検出された。残留磁化状態では形状磁気異方性により、試料頂点に磁壁が生成される。スピントランスファートルクを用いた磁壁中の磁化の自励発振により、ゼロ磁場下においてマグノンの励起に成功した。

参考文献
[1] A. N. Slavin and V. Tiberkevich, IEEE Trans. Magn. 45, 1875 (2009).
[2] K. Wagner et al., Nat. Nanotech. 11, 432 (2016).

Magnons are the fundamental excitations in magnetic materials and are attractive for applications in information technology devices. They do not involve charge transport and the associated waste heat and offer high operating frequencies up to the THz range. When a charge current is applied to a bilayer consisting of Pt and a ferromagnetic metal, the spin currents originating from the spin Halle effect in the Pt layer generate a spin transfer torque to the magnetizations in the ferromagnetic layer. This allows to efficiently drive auto-oscillations of magnons[1]. We focused on domain walls as local nano magnon channels[2], and investigated the magnon auto-oscillation in the domain walls.

As shown in Fig. 1, a zigzag structure was fabricated from a Pt/CoFeB bilayer. The width was set to be 370 nm. The sample was magnetized to the y direction and a dc current was applied to the sample. The magnon intensity at the corner was measured by Brillouin Light Scattering microscopy. Figure 2 shows the dc current dependency of the magnon intensity measured at the corner. As shown in Fig. 2(a), in the case that an external magnetic field of 1.0 kOe was applied to the y direction, the magnons were detected when the dc current was between 2.3 mA and 5.0 mA. While there were no magnons in the case of the reversed dc current direction. Figure 2(b) shows the magnon intensity at the remanence state after saturation to y direction. There were also no magnon in the case of the reversed dc current. The domain wall is generated at the corner under the remanence state because of a shape anisotropy. We succeeded to excite magnons under zero magnetic field due to the auto-oscillation of the magnetizations by spin transfer torque.

Reference
[1] A. N. Slavin and V. Tiberkevich, IEEE Trans. Magn. 45, 1875 (2009).
[2] K. Wagner et al., Nat. Nanotech. 11, 432 (2016).

Related publications

  • Poster
    The Physical Society of Japan, 73rd Annual Meeting, 22.-25.03.2018, Noda, Chiba, Japan

Permalink: https://www.hzdr.de/publications/Publ-28120
Publ.-Id: 28120


The importance of calcium, magnesium and iron ions in the scheelite-calcite flotation system - application to the Mittersill ore

Chukwuma, O. C.

The specific objectives of this research are:

(i) Investigating the effect of calcium and magnesium ions in the scheelite-calcite flotation system, quantifying their impact and the underpinning mechanisms
(ii) Validating the hypothesis that iron ions mixed with sodium silicate depresses calcite.

Keywords: Scheelite; Water hardness; Hydrosol of iron ions and sodium silicate

  • Master thesis
    HZDR - HIF, 2018
    Mentor: Nathalie Kupka

Permalink: https://www.hzdr.de/publications/Publ-28119
Publ.-Id: 28119


A simple route to synchronized nucleation of self-catalyzed GaAs nanowires on silicon for sub-Poissonian length distributions

Tauchnitz, T.; Berdnikov, Y.; Dubrovskii, V. G.; Schneider, H.; Helm, M.; Dimakis, E.

We demonstrate a simple route to grow ensembles of self-catalyzed GaAs nanowires with a remarkably narrow statistical distribution of lengths on natively oxidized Si(111) substrates. The fitting of the nanowire length distribution with a theoretical model reveals that the key requirements for narrow length distributions are the synchronized nucleation of all nanowires on the substrate and the absence of beam shadowing from adjacent nanowires. Both requirements are fulfilled by controlling the size and number density of the openings in SiOx, where the nanowires nucleate. This is achieved by using a pre-growth treatment of the substrate with Ga droplets and two annealing cycles. The narrowest nanowire length distributions are markedly sub-Poissonian, which validates the theoretical predictions about temporally anti-correlated nucleation events in individual nanowires, the so-called nucleation antibunching. Finally, the reproducibility of sub-Poissonian length distributions attests the reliability of our growth method.

Keywords: substrate for nanowires; nucleation antibunching; nucleation delay; nanowire nucleation

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Permalink: https://www.hzdr.de/publications/Publ-28118
Publ.-Id: 28118


Excitation of whispering gallery magnons in a magnetic vortex

Schultheiss, K.; Verba, R.; Wehrmann, F.; Wagner, K.; Körber, L.; Hula, T.; Hache, T.; Kákay, A.; Awad, A. A.; Tiberkevich, V.; Slavin, A. N.; Fassbender, J.; Schultheiss, H.

We present the generation of whispering gallery magnons with unprecedented high wave vectors via nonlinear 3-magnon scattering in a μm-sized magnetic vortex state disc. These modes exhibit a strong localisation at the perimeter of the disc and practically zero amplitude in an extended area around the vortex core. They originate from the splitting of the fundamental radial magnon modes, which can be resonantly excited in a vortex texture by an out-of-plane microwave field. We shed light on the basics of this non-linear scattering mechanism from experimental and theoretical point of view. Using Brillouin light scattering (BLS) microscopy, we investigated the frequency and power dependence of the 3-magnon splitting. The spatially resolved mode
profiles give evidence for the localisation at the boundaries of the disc and allow for a direct determination of the modes wavenumber.

Keywords: magnons; spin wave; nonlinear magnetization dynamics; magnetic vortex; Brillouin light scattering

Related publications

  • Open Access Logo Physical Review Letters 122(2019), 097202
    DOI: 10.1103/PhysRevLett.122.097202
    Cited 55 times in Scopus
  • Invited lecture (Conferences)
    International Conference on Magnetism, 19.07.2018, San Francisco, USA
  • Invited lecture (Conferences)
    APS March Meeting, 04.03.2019, Boston, USA
  • Poster
    Wilhelm und Else Heraeus-Seminar “Spin Based Information Processing”, 08.01.2019, Bad Honnef, Deutschland
  • Lecture (Conference)
    Joint European Magnetic Symposia (JEMS), 04.09.2018, Mainz, Deutschland
  • Poster
    Magnonics 2019, 28.07.2019, Carovigno, Italien
  • Invited lecture (Conferences)
    Magnetics and Optics Research International Symposium, 24.06.2019, Prague, Czech Republic
  • Invited lecture (Conferences)
    Conference on Magnetism and Magnetic Materials (MMM), 06.11.2019, Las Vegas, USA

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Permalink: https://www.hzdr.de/publications/Publ-28116
Publ.-Id: 28116


Steering magnons by noncollinear spin textures

Schultheiss, K.; Wagner, K.; Kákay, A.; Schultheiss, H.

One of the grand challenges in cutting edge quantum and condensed matter physics is to harness the spin degree of electrons for information technologies. While spintronics, based on charge transport by spin polarized electrons, made its leap in data storage by providing extremely sensitive detectors in magnetic hard-drives [1], it turned out to be challenging to transport spin information without great losses [2]. With magnonics, a visionary concept inspired researchers worldwide: Utilize spin waves-the collective excitation quanta of the spin system in magnetically ordered materials-as carriers for information [3-8]. Spin waves, which are also called magnons, are waves of the electrons’ spin precessional motion. They propagate without charge transport and its associated Ohmic losses, paving the way for a substantial reduction of energy consumption in computers. While macroscopic prototypes of magnonic logic gates have been demonstrated [9, 10], the full potential of magnonics lies in the combination of magnons with nano-size spin textures. Both magnons and spin textures share a common ground set by the interplay of dipolar, spin-orbit, and exchange energies, rendering them perfect interaction partners. Magnons are fast, sensitive to the spins’ directions, and easily driven far from equilibrium. Spin textures are robust, nonvolatile, and still reprogrammable on ultrashort timescales. The vast possibilities offered by combining these magnetic phenomena add value to both magnonics and the fundamental understanding of complex spin textures. The scope of this chapter is about experimental studies on magnon transport in metallic ferromagnetic microstructures with focus on actively controlling the magnon propagation. Two inherent characteristics of magnons enable for lateral steering: the anisotropy of the magnon dispersion and its sensitivity to changes in the internal magnetic field distribution. We intend to give an idea of how these magnon features can be utilized toward realizing functionalized magnonic networks. © 2017 Pan Stanford Publishing Pte. Ltd.

Keywords: magnons; spin waves; spin textures; propagation; Brillouin light scattering

Related publications

  • Book chapter
    Sergej O. Demokritov: Spin Wave Confinement: Propagating Waves, Second Edition, Singapore: Pan Stanford Publishing Pte. Ltd., 2017, 978-135161721-5;978-981477435-2, 261-294
    DOI: 10.1201/9781315110820
    Cited 5 times in Scopus

Permalink: https://www.hzdr.de/publications/Publ-28115
Publ.-Id: 28115


Why are hot-rolled ODS steels more prone to secondary cracking than 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 the same are investigated. A better understanding of these factors can lead to tailoring of improved ODS steels. Fracture toughness testing of 13Cr ODS steel in hot-rolled and in hot-extruded form were carried out. The fracture behaviour of secondary cracks was investigated using scanning electron and electron backscatter microscope. Crystallographic texture and grain morphology plays 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; nanostructured ferritic alloys; fracture behaviour; anisotropy; secondary cracking; delamination

Related publications

  • Poster
    NuMat2018: The Nuclear Materials Conference, 15.10.2018, Seattle, USA

Permalink: https://www.hzdr.de/publications/Publ-28114
Publ.-Id: 28114


Diverse Effects of Phospholipase A2 Receptor Expression on LNCaP and PC-3 Prostate Cancer Cell Growth in vitro and in vivo

Friedemann, M.; Nacke, B.; Hagelgans, A.; Jandeck, C.; Bechmann, N.; Ullrich, M.; Belter, B.; Neuber, C.; Sukocheva, O.; Pietzsch, J.; Menschikowski, M.

Physiological and pathophysiological functions of the phospholipase A2 receptor 1 (PLA2R1) are still not completely understood. To elucidate PLA2R1’s function in prostate carcinoma, the receptor was ectopically overexpressed in LNCaP with silenced PLA2R1, and diminished in PC-3 cells with constitutively increased PLA2R1 expression relative to normal prostate epithelial cells. LNCaP cells were transfected to overexpress PLA2R1 (LNCaP-PLA2R1) and compared to control vector transfected cells (LNCaP-Ctrl). Alternatively, a CRISPR/Cas9-knockdown of PLA2R1 was achieved in PC-3 cells (PC-3 KD) and compared to the corresponding control-transfected cells (PC-3 Ctrl). The impact of PLA2R1 expression on proliferative and metastatic parameters was analysed in vitro. A pilot in vivo study addressed the effects of PLA2R1 in mice xenografted with transfected LNCaP and PC-3 cells. Cell viability/proliferation and motility were significantly increased in LNCaP-PLA2R1 and PC-3 Ctrl compared to LNCaP-Ctrl and PC-3 KD cells, respectively. However, levels of apoptosis, clonogenicity and cell invasion were reduced in LNCaP-PLA2R1 and PC-3 Ctrl cells. Gene expression analysis revealed an up-regulation of fibronectin 1 (FN1), TWIST homolog 1 (TWIST1), and cyclin-dependent kinase 6 (CDK6) in LNCaP-PLA2R1. In LNCaP xenografts, PLA2R1-dependent regulation of clonogenicity appeared to outweigh the receptor’s pro-oncogenic properties, resulting in decreased tumour growth, supporting the tumour-suppressive role of PLA2R1. Alternatively, PC-3 Ctrl xenografts exhibited faster tumour growth compared to PC-3 KD cells, suggesting a pro-oncogenic effect of endogenous PLA2R1 expression. The differential growth-regulatory effects of PLA2R1 may be mediated by FN1, TWIST1, and CDK6 expression, although further investigation is required.

Permalink: https://www.hzdr.de/publications/Publ-28113
Publ.-Id: 28113


Electrochemical studies on zinc in boric acid containing electrolytes

Harm, U.; Kryk, H.; Hampel, U.

During the sump recirculation phase after a leak in the primary cooling circuit of a pressurized water reactor (PWR), corrosion of hot-dip galvanized containment internals (e.g. grating treads, supporting grids of sump strainers) in the boric acid containing coolant may occur, which could later cause problems due to the possible precipitation of formed zinc borates (fouling) at hot regions of the reactor core [1, 2].
Beside other safety related investigations, generic zinc corrosion studies in boric acid electrolytes were conducted to investigate the dependency of the zinc corrosion rates in PWR coolants on different boundary conditions (fluid temperatures, pH, boric acid concentration, flow conditions nearby the zinc surface).
Corrosion experiments with dipped zinc sheets in stirred boric acid solutions already had shown that moderate variations of the fluid temperatures or the boric acid content only caused small changes in resulting zinc corrosion rates, but an increase of flow rates or turbulences often led to significantly increased corrosion rates [2].
For a better understanding of these results, additionally, some series of electrochemical measurements were carried out using a rotating disc electrode (zinc) as working electrode, a platinum counter electrode and tempered aqueous boric acid solutions (plus 0.1 M Na2SO4 as conducting salt) as electrolyte. Linear anodic and cathodic polarization was realized (up to potentials of 200 mV different from the free corrosion potential) under variation of fluid temperature (20 to 60 °C), boric acid content (1000 to 3000 ppm boron), pH (4.7 to 7) and the rotation speed.
First results of these experiments (e.g. comparing tafel plots) showed similar dependencies of the zinc corrosion rates than described above for the zinc dissolution experiments. The cathodic polarization curves mostly showed a plateau of the current densities with increasing cathodic polarization (overvoltage) indicating a strong control of the cathodic reaction (and thus the corrosion process as a whole) by the transport limitation of the dissolved oxygen to the zinc surface. Comparison of the tafel plots resulting from measurements at different rotation speeds (similar otherwise conditions) also demonstrated a strong increase of the zinc corrosion rates with increasing flow rates. For example, calculated zinc corrosion rates for infinite high rotation speeds (Levich extrapolation) usually are more than ten times higher compared to those of similar experiments without rotation. Therefore, also these results of the electrochemical investigations confirm the earlier results of a transport controlled corrosion process (see above) and may help to quantify the possible ranges of resulting corrosion rates at different boundary conditions.
This work is funded by the German Federal Ministry of Economic Affairs and Energy (BMWi) with the grant number 1501496 on the basis of a decision by the German Bundestag.

[1] Seeliger, A.; Alt, S.; Kästner, W.; Renger, S.; Kryk, H.; Harm, U.: Zinc corro¬sion after loss-of-coolant accidents in pressurized water reactors - thermo- and fluid-dynamic effects. Nuclear Engine-ering and Design, 2016, 305, 489-502
[2] Harm, U.; Kryk, H.; Hampel, U.: Generic Zinc Corrosion Studies at PWR LOCA Conditions. Annual Meeting on Nuclear Technology (AMNT 2017), 2017

Keywords: Nuclear energy; corrosion; zinc release; electrochemistry; experiments

  • Poster
    Electrochemistry 2018, 24.-26.09.2018, Ulm (Universität Ulm), Deutschland

Permalink: https://www.hzdr.de/publications/Publ-28112
Publ.-Id: 28112


Impact of membrane biofouling in the sequential development of performance indicators: feed channel pressure drop, permeability, and salt rejection

Siebdrath, N.; Farhat, N.; Ding, W.; Kruithof, J.; Vrouwenvelder, J. S.

Biofouling development is affected by a variety of factors that change over the length of membrane modules in pressure vessels. Spatially resolved biofouling formation was studied under conditions representative to practice using a validated one-meter Long Channel Membrane Test Cells (LCMTCs), enabling the monitoring of permeability and salt rejection for five segments over the test cell length. Biofouling was induced by dosing an easily assimilable substrate to the feed water. The impact of biofouling on membrane performance was investigated spatially resolved as indicated in feed channel pressure drop over four LCMTCs and as indicated in permeability and salt rejection over five segments of each LCMTC. Results showed that all membrane performance indicators: feed channel pressure drop, permeability and salt rejection were impacted by biofouling formation. The feed channel pressure (FCP) drop increase was impacted earliest and strongest followed by permeability and salt rejection decline, underlining that FCP drop is a sensitive biofouling monitoring indicator. Spatially resolved biofouling investigations revealed that most biofouling was formed in the lead sections of membrane installations with a decreasing gradient over length, linked to substrate availability in the system. In this study, FCP drop played a crucial role: the severe FCP drop increase at the lead parts of the membrane installation caused performance losses in flux and salt rejection at the tail parts of the membrane installation. Minimizing the effect of biofouling on membrane performance should be pursued by a combination of strategies involving (i) early detection and preventive cleaning, (ii) substrate limitation for delaying biofouling built-up and (iii) optimized (early) cleaning procedures for more effective biofilm removal.

Keywords: Biofouling; Reverse Osmosis; Feed channel pressure drop; Permeability; Salt rejection; Long channel membrane test cell

Permalink: https://www.hzdr.de/publications/Publ-28111
Publ.-Id: 28111


Bubble growth during subcooled nucleate boiling on a vertical heater: A mechanistic attempt to evaluate the role of surface characteristics on microlayer evaporation

Sarker, D.; Ding, W.; Hampel, U.

For the modeling of nucleate boiling heat transfer, the bubble growth dynamics is of key importance. The study reported in this paper focuses on a qualitative assessment of the role of heater surface parameters on the bubble growth and the effective microlayer thickness constant, Ceff . The latter is part of a recently derived improved bubble growth model, which we utilize in our analysis along with high-resolution experimental data of the steam
bubble growth. The bubble growth model is formulated considering the evaporation of microlayer beneath the bubble, heat diffusion at the bubble surface and condensation at the bubble cap. We found that the values of Ceff are lower and the growth rates of bubble prior to departure are greater at the root mean square roughness of around Sq=0.12 μm for low-wetting surfaces. For well-wetting surfaces Ceff and the bubble growth rates are also found lower and greater, respectively at Sq=0.15 μm. Finally, a generalized equation for Ceff is proposed which comprises the effects of surface roughness and wettability on the bubble growth. The findings are useful for improving the bubble growth models and in designing the heater surface in the future.

Keywords: bubble growth model; surface wettability; optimal roughness height; microlayer evaporation

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Permalink: https://www.hzdr.de/publications/Publ-28110
Publ.-Id: 28110


Investigations on the effects of heater surface characteristics on the bubble waiting period during nucleate boiling at low subcooling

Sarker, D.; Ding, W.; Franz, R.; Varlamova, O.; Kovats, P.; Zähringer, K.; Hampel, U.

In nucleate boiling the ‘bubble waiting period’, that is, the time duration between the departure of a grown bubble and the start of the formation of a new bubble from a cavity, plays a crucial role for the total heat transfer. Experiments were performed to study the influence of the heater surface characteristics on this parameter. A femtosecond pulsed laser was used to produce nano- and micro-patterned surfaces with roughness in the range of micrometers on stainless steel heater surfaces. Boiling experiments were conducted on a vertically oriented heater at atmospheric pressure and with degassed deionized water. Bubble generation, departure, sliding, detachment and inception of the next bubble have been recorded by high-resolution optical shadowgraphy. Bubble waiting periods were found to be longer for low-wettability smooth and rough surfaces. High-wettability rough surfaces showed a shorter bubble waiting period. The shortest (approximately 3 ms) and the longest (approximately 30 ms) bubble waiting periods were found for well-wetting surfaces with Sq = 0.18 µm and for low-wetting surfaces with 0.12 µm, respectively. These corresponding roughness heights are denoted as ‘optimal roughness heights’.

Keywords: Bubble waiting periodSurface wettabilityRoughnessVertical heaterNucleate boiling

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Permalink: https://www.hzdr.de/publications/Publ-28109
Publ.-Id: 28109


Microbial and vegetal life in the near- and far-field of a nuclear waste repository

Raff, J.; Krawczyk-Bärsch, E.

One of the so far unanswered question related to a nuclear waste repositiory is how big is the influence of biosystems on the safety of such a repository. Although this question can not be answered at this time, ongoing researches adress the questions of who lives in the possible host rocks, how do these organisms interact with radionuclides and what is their impact on the geochemical conditions there during the operation of a repository. This includes also researches on the microbial diversity in backfill materials such as bentonite and the microbial influence on their properties, e.g. swelling capacity and hydraulic conductivity. In addition, various procaryotic and eucaryotic organisms in the far-field of a repository, namely bacteria, fungi and plants, are currently being investigated for their interaction with radionuclides and their influence on radionuclide migration. The latter includes also a possible radionuclide entry into the food chain. The goal is to identify dominant processes and to understand them on a molecular level. Ultimately, this will allow to derive biological parameters which are suitable to be included in the radionuclide transport modeling. Identified processes will also be considered for the development of remediation concepts for the purification of contaminated water and soil.
In the second part of the talk, the interaction of uranium and neptunium with bacteriogenic iron oxides precipitates, formed by the ferrous oxidizing and stalk-forming bacterium Gallionella ferruginea from a granitic host rock, is presented in more detail. This work shows that bacteriogenic iron oxides have a high potential to immobilize radionuclides in nuclear waste repositories.

Keywords: nuclear waste repositiory; biogeochemistry; migration

Related publications

  • Lecture (others)
    Scientific Seminar, 11.10.2018, Cadarache, Frankreich

Permalink: https://www.hzdr.de/publications/Publ-28108
Publ.-Id: 28108


Molekulare Geochemie für das nukleare Endlager

Schmidt, M.

In diesem Überblicksvortrag werden wissenschaftliche Fragestellungen zur Endlagerung hochradioaktiver Abfälle diskutiert. Die Komplexität des geotechnischen und -chemischen Systems inbesondere im Bezug zur Rückhaltung der minoren Actiniden und Plutonium wird dargestellt, um die Notwendigkeit für ein molekulares Prozessverständnis darzulegen. Letztlich wird an Beispielen diskutiert wie dieses Prozessverständnis erhalten werden kann und wie es zur Langzeitsicherheitsanalyse beiträgt.

Keywords: Endlager; Geochemie; Actiniden; molekulares Prozessverständnis

  • Invited lecture (Conferences)
    50. Kraftwerkstechnisches Kolloquium, 23.-24.10.2018, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-28107
Publ.-Id: 28107


Experimental assessment of inter-centre variation and accuracy in SPR prediction within the EPTN

Peters, N.; Wohlfahrt, P.; Bolsi, A.; de Marzi, L.; Ellerbrock, M.; Fracchiolla, F.; Free, J.; Gomà, C.; Góra, J.; Kajdrowicz, T.; Mackay, R.; Molinelli, S.; Nørrevang, O.; Rinaldi, I.; Rompokos, V.; Dahlgren, C. V.; van der Tol, P.; Vermeren, X.; Richter, C.

Purpose/Objective:

The standard approach for CT-number to stopping-power-ratio (SPR) conversion in particle therapy is the use of a heuristic stepwise translation, a so-called Hounsfield look-up table (HLUT). It is defined by each treatment facility individually and depends on both the calibration method and CT scan protocol. A recent survey has shown broad variability in these parameters [1], making a simple comparison on HLUT level unfeasible. Hence, we present a comprehensive experimental evaluation of inter-centre variation and absolute accuracy in SPR prediction within the European Particle Therapy Network.

Material/Methods:

A head and a body phantom with 17 tissue surrogate inserts were scanned consecutively at the participating centres using their individual clinical scan protocol. The inserts were tissue-equivalent concerning particles; their composition and SPR were blinded for the participants. The SPR calculation was performed using each centre’s CT scan and HLUT (Fig.1).The inter- centre variation and absolute accuracy in SPR prediction were quantified for each tissue surrogate individually and then summarised into the relevant tissue groups: lung, soft tissues and bones. Finally, to evaluate the integral effect on range prediction for typical clinical beams traversing different tissues, for three simplified beam paths the determined SPR deviations were accumulated according to their respective tissue distribution. So far, data from 9 out of 17 participating centres was available.

Results:

A 2σ inter-centre variation in SPR prediction of 5.7% and 5.5% relative to water was determined for the bone inserts in the head and body setup, respectively. Comparable results were achieved for the lung tissue surrogates (6.4% and 2.2%). In the soft tissue region an overall higher accuracy was achieved with a variation below 0.9% in both setups and a mean SPR prediction accuracy below 0.5%. In the head setup, both lung tissues and bones were overestimated in most centres, while in the body setup the bones were underestimated (Fig. 2A). For the three exemplary beam paths, inter-centre variations in relative range were 1.5% on average. In specific centres, range deviations from reference exceeded 1.5% (Fig 2B).

Conclusion:

Large inter-centre variations in SPR prediction were observed in low- and high density tissue surrogates. The differences in deviation for bone between the two setups indicate a strong influence of scanning parameters such as the level of beam hardening correction, potentially resulting in range shifts of clinical relevance. As the study allows for a direct attribution of the measured deviations to the calibration methods and scan protocols used by the individual centres, it stresses the need for inter-centre standardisation. While this work addresses the accuracy in SPR prediction under idealised study conditions, a direct conclusion on overall range accuracy in patients is not possible. The study is currently still ongoing.

[1] Taasti et al. 2018, phiRO 6 25-30

  • Lecture (Conference)
    European Society for Radiation & Oncology Congress 2019 ESTRO 38, 26.-30.04.2019, Milano, Italia
  • Abstract in refereed journal
    Radiotherapy and Oncology 133(2019), 348-349
    DOI: 10.1016/S0167-8140(19)31087-4
    ISSN: 0167-8140

Permalink: https://www.hzdr.de/publications/Publ-28106
Publ.-Id: 28106


Industrial flowsheeting and thermo-economic assessment

Reuter, M. A.; Llamasa, A. A.

Session 2 was organised by the SOCRATES project. SOCRATES studies the development of near-zero waste processes for the recycling of low-grade metal containing industrial waste streams, such as bottom ashes, copper tailings and slags and sludges from the non-ferrous industry, commonly deposited in industrial landfills and tailing ponds. Markus Reuter and Alejandro Abadias (Helmholtz-Zentrum Dresden-Rossendorf, Germany) illustrated how novel near-zero waste flowsheets for the treatment of these residues are assessed within the SOCRATES project. Focus of the session was on the primary copper production flowsheet (from rock to metal), in which two scenarios were compared, being production of copper without treatment of wastes and with additional metal recovery from wastes (slags and drosses). The analysis was performed through composing a mass and energy balance of the flowsheet and performing an exergy analysis and life cycle assessment.

Keywords: near-zero waste; recycling; SOCRATES

  • Lecture (others)
    Summer school 2018: “To mine or not to mine”, 10.-12.09.2018, Leuven, Belgien

Permalink: https://www.hzdr.de/publications/Publ-28105
Publ.-Id: 28105


The limits of the Circular Economy

Reuter, M. A.

-> Circular Economy (CE) - The origins
-> Circular Economy Engineering (CEE)
-> Metallurgical Internet-of-Things (m-IoT) - Comprehensive flowsheets that integrate product design with physical separation and process metallurgy
-> informing Resource Efficiency (iRE)
Fairphone / Plasma furnace for battery smelting

Keywords: Circular Economy; Circular Economy Engineering; Metallurgical Internet-of-Things; Resource Efficiency; Fairphone

  • Lecture (others)
    Circular Economy of EV Batteries - Workshop, 24.-25.05.2018, Espoo, Finnland

Permalink: https://www.hzdr.de/publications/Publ-28104
Publ.-Id: 28104


Process Model Based LCA Using HSC Chemnistry Software

Reuter, M. A.; Roine, A.

The process industry defines the initial LCA values that are used for raw materials in the manufacturing industry. Plant vs Factory!
If we are talking about the circular economy and the whole value chain, then we must also take into account the effect of the process industry and recycling. This is the only way to minimize total environmental footprints.

Keywords: circular economy; recycling; environmental footprints

  • Lecture (others)
    LCA Course SusCriMat - Winterschool, 15.-19.01.2018, Les Diablerets, Schweiz

Permalink: https://www.hzdr.de/publications/Publ-28103
Publ.-Id: 28103


Urban Mining: Dream or Reality – The Limits and opportunities of the Circular Economy

Reuter, M. A.

The circular economy will play an important role in shaping a resource-efficient society. Enabling this transformation from a linear to a circular economy requires precise quantification of resource efficiency and thus the economic viability of the system.

Based on the development of simulation tools of classical minerals processing and process metallurgy, the HSC Sim (www.outotec.com) simulation platform could be further developed, gleaning from many academically published works of the authors. This permits the simulation of the circular economy system and to subsequently calculate its resource efficiency. It for example also enables the estimation of a simulation-based recycling index of a product from the "Bill of Material" and "Full Material Declaration". It is a unique methodology for "Design for Recycling".

Figure 1 shows that a key to this simulation is a detailed understanding of the mineralogy as well as the limits of the circular economy system and its many products, materials and systems. In addition, a detailed understanding and quantification of the thermodynamic properties of the system is key to understanding its economics. With this approach, we will show the actual losses of the "circular economy" system and thus illuminate the limits and hence explore in detail if Urban Mining is a dream or economic reality.

Keywords: Fairphone; recycling; circular economy

  • Invited lecture (Conferences)
    EuroScience Open Forum, 09.-14.07.2018, Toulouse, Frankreich

Permalink: https://www.hzdr.de/publications/Publ-28102
Publ.-Id: 28102


Cost benefit and environmental life cycle assessment

Rodriguez-Garcia, G.; Molinos-Senante, M.; Gabarron, S.; Alfonsín, C.; Hospido, A.; Corominas, L.; Hernandez-Sancho, F.; Omil, F.; Feijoo, G.; Sala-Garrido, R.; Rodriguez-Roda, I.; Moreira, M. T.

This chapter evaluates the economic and environmental implications of MBR using Cost Benefit Analysis (CBA) and Life Cycle Assessment (LCA). A brief introduction to these methodologies and the main developments and achievements when applied to MBR is given before the presentation of two case studies. In the first case study, CBA and LCA were applied for the assessment of seven wastewater treatment plants using MBR and other membrane technologies. The results highlighted the benefits of removal of substances responsible for eutrophication and the relevance of the scale factor regarding electricity use, one of the main environmental and economic costs. In the second case study, LCA alone was applied for the environmental assessment of four novel MBR configurations at pilot-plant scale focusing on the removal of pharmaceutical and personal care products (PPCPs), of which only hormones were found to be relevant in terms of toxicity terms due to their higher concentrations in the influent.

  • Book chapter
    Faisal I. Hai, Kazuo Yamamoto, Chung-Hak Lee: Membrane Biological Reactors: Theory, Modeling, Design, Management and Applications to Wastewater Reuse - Second Edition, London (UK): IWA Publishing, 2019, 9781780409160
    DOI: 10.2166/9781780409177_0227

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Permalink: https://www.hzdr.de/publications/Publ-28101
Publ.-Id: 28101


Bubble Generation by Micro-Orifices with Application on Activated Sludge Wastewater Treatment

Mohseni, E.; Herrmann-Heber, R.; Reinecke, S. F.; Hampel, U.

We studied the initial gas dispersion performance of diffuser concepts based on micro-orifices and needles with very fine orifice diameters in the range from 30 µm to 200 µm, as such diffusers are currently in discussion for energy-efficient wastewater treatment plants. To evaluate the performance of these micro-orifices, we compared them with industrial rubber membrane diffusers with respect to Sauter mean bubble diameter, pressure drop, frequency of bubble formation, oxygen transfer rate, and power demand for air compression. Our study revealed that, in comparison with rubber membrane diffusers bubbles generated from the micro-orifices transfer up to 82% more oxygen content into the continuous phase at up to 75% less power demand. Moreover, these micro-orifices are able to produce bubble sizes in the same range as the needle diffusers at 60% less pressure drop and 60% higher bubble generation frequency. Therefore, we also expect an improvement in the oxygen transfer coefficient KLa and standard oxygen transfer efficiency SOTE compared to commercial rubber membrane diffusers.

Keywords: Bubble Generation; Micro-orifices; Aeration; Biological Wastewater Treatment; Rubber Membrane Diffusers; Oxygen Transfer

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Permalink: https://www.hzdr.de/publications/Publ-28100
Publ.-Id: 28100


ASTEC model of the THS-15 test facility and first simulation results

Jobst, M.

In the framework of the NuWaMa project (Expansion of a German-Czech Collaboration in the Field of Nuclear Waste Management), a research stay at ÚJV Řež (Czech Republic) took place during May 2018 (from 1st of May till 31st of May). The objective of the research stay was the development of a numerical model of the thermal-hydraulic test facility THS-15, which had been put in operation at the ÚJV site in Řež recently in order to investigate phenomena related to ex-vessel cooling for in-vessel retention of molten corium. Assessing the performed experiments with the help of the numerical model is an important contribution to a comprehensive under-standing of the observed phenomena. The current state of the ASTEC model and the first calculation results are presented.

Keywords: VVER; in-vessel melt retention; THS-15 test facility; ASTEC; numerical simulation; critical heat flux

  • Lecture (Conference)
    ASTEC Users' Club Meeting, 09.-11.10.2018, Aix-en-Provence, République française

Permalink: https://www.hzdr.de/publications/Publ-28099
Publ.-Id: 28099


Ideal flow regimes of gas spargers: Towards optimal gas bubble generation for biological wastewater treatment

Mohseni, E.; Reinecke, S.; Hampel, U.

Gas bubble dispersion is involved within a large number of chemical, biochemical, and other processes. Of particular importance is the dispersion of air bubbles in the activated sludge process in biological wastewater treatment plants. This is an expensive procedure, which is responsible for the largest share of energy bill in the whole WWTP in the range 45% to 75%. The rubber membrane diffusers, which are currently used for aeration in the treatment facilities, offer relatively low standard oxygen transfer efficiency in range of 40-60 %, which is mainly due to generation of large bubble sizes. Among the parameters which influence the system efficiency, bubble size is of great importance, since it directly influences the gas holdup and the bubble residence time. Moreover, bubble size determines the surface area to volume ratio, which affects the volumetric oxygen transfer coefficient and oxygen transfer rate. Bubble formation is mainly studied at openings bigger than 1 mm. Hence, the leverage of sub-millimeter orifices on volume of the final bubble is still not understood. Current endeavor focuses on bubble formation from submerged orifices under constant flow condition. Subsequently a set of experiments is design to capture the bubble generation from small orifices in the range of 20-800 μm diameter. The initial bubble size was measured by means of a high-resolution optical measurement technique. Changes in the mechanism of bubble formation and detachment within the dynamic bubbling regime were monitored and reported over a progressive trend of the volumetric gas flow rate.

Keywords: Bubble Generation; Bubbling Regime; Activated Sludge; Aeration; Biological Wastewater Treatment

  • Contribution to proceedings
    10th IWA Eastern European Young Water Professionals Conference, 10.-11.05.2018, Zagreb, Croatia

Permalink: https://www.hzdr.de/publications/Publ-28098
Publ.-Id: 28098


Optimization of the Aeration System in Municipal Wastewater Treatment Plant

Mohseni, E.; Reinecke, S.; Hampel, U.

Optimal bubble generation for biological aeration process is currently under discussion. We studied bubble formation from a range of solid orifices, from 20 µm to 800 µm, submerged in water under constant flow condition. Scant experimental data is available within this range. We studied the change in the mechanism of bubble formation and detachment at different bubbling regimes. Moreover, the existing theoretical and empirical models for prediction of initial bubble size were evaluated according to the corresponding experimental data. A modified model for prediction of initial bubble size is proposed from the best fit of experimental results. Finally, we introduced another empirical model for prediction of optimal operation condition according to consumption of 95% oxygen uptake from air bubbles in water. In the later model, parameters such as pressure drop of the system, capacity of aeration basin, and available specific aeration area for oxygen transfer are adopted.

Keywords: Bubble Generation; Activated Sludge; Aeration; Biological Wastewater Treatment; Multiphase Flow

  • Poster
    12th HZDR PhD Seminar, 16.-18.10.2017, Seiffen, Germany

Permalink: https://www.hzdr.de/publications/Publ-28097
Publ.-Id: 28097


Formation and characterization of shallow junctions in GaAs made by ion implantation and ms-range flash lamp annealing

Duan, J.; Wang, M.; Vines, L.; Böttger, R.; Helm, M.; Zeng, Y. J.; Zhou, S.; Prucnal, S.

With the demand of aggressive scaling in nanoelectronics, further progress can be realized by integration of high mobility semiconductors, such as III-V compound semiconductors, with complementary metal-oxide-semiconductor (CMOS) technology. In this study we present the formation of shallow n-p and p-n junctions in GaAs utilizing ion implantation of S and Zn, respectively, followed by millisecond-range flash lamp annealing (FLA). The distribution of implanted elements obtained by Secondary Ion Mass Spectrometry (SIMS) shows that the FLA process can effectively suppress the diffusion of dopants. Simultaneously, the ms-range annealing is sufficient to recrystallize implanted layer and to activate the dopants. Formation of p-n and n-p junctions is confirmed by current-voltage characteristics. The on/off-current ratio can reach up to 1.7×107 in the n-GaAs:Zn case.

Keywords: GaAs; shallow junction; ion implantation; flash lamp annealing

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Permalink: https://www.hzdr.de/publications/Publ-28096
Publ.-Id: 28096


Jump Rope Vortex in Liquid Metal Convection

Vogt, T.; Horn, S.; Grannan, A. M.; Aurnou, J. M.

The large-scale circulation (LSC) is the key dynamical feature of turbulent thermal convection. It is the underlying structure that shapes the appearance of geo- and astrophysical systems, such as the solar granulation or cloud streets, and the cornerstone of theoretical models. Our laboratory-numerical experiments reveal for the first time that the LSC can perform a fully three-dimensional motion resembling a twirling jump rope.
The discovery of this novel LSC mode implies that the currently accepted paradigm of a quasi-planar oscillating LSC needs to be augmented. Moreover, it provides an important link between studies in confined geometries used in experiments and simulations and the virtually unconfined fluid layers in natural settings where an agglomeration of LSCs forms larger patterns.

Keywords: thermal convection; turbulence; coherent structures; liquid metals

Permalink: https://www.hzdr.de/publications/Publ-28095
Publ.-Id: 28095


Magneto-structural correlations in a systematically disordered B2 lattice

Ehrler, J.; Sanyal, B.; Grenzer, J.; Zhou, S.; Böttger, R.; Wende, H.; Lindner, J.; Faßbender, J.; Leyens, C.; Potzger, K.; Bali, R.

Ferromagnetism in certain B2 ordered alloys such as Fe60Al40 can be switched on, and tuned, via antisite disordering of the atomic arrangement. The disordering is accompanied by a 1% increase in the lattice parameter. Here we performed a systematic disordering of B2 Fe60Al40 thin films, and obtained correlations between the order parameter (S), lattice parameter (a0), and the induced saturation magnetization (Ms). As the lattice is gradually disordered, a critical point occurs at 1-S=0.6 and a0=2.91 A, where a sharp increase of the Ms is observed. DFT calculations suggest that below the critical point the system magnetically behaves as it would still be fully ordered, whereas above, it is largely the increase of a0 in the disordered state that determines the Ms. The insights obtained here can be useful for achieving tailored magnetic properties in alloys through disordering.

Keywords: order-disorder; Fe60Al40; phase transition; structural properties; magnetic properties

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Permalink: https://www.hzdr.de/publications/Publ-28094
Publ.-Id: 28094


The role of open-volume defects in the annihilation of antisites in a B2-ordered alloy

Ehrler, J.; Liedke, M. O.; Cizek, J.; Boucher, R.; Butterling, M.; Zhou, S.; Böttger, R.; Hirschmann, E.; Trinh, T. T.; Wagner, A.; Lindner, J.; Fassbender, J.; Leyens, C.; Potzger, K.; Bali, R.

The atomic arrangement in certain B2-ordered alloys, such as Fe60Al40, determines intrinsic material properties like magnetism. Here we have investigated the influence of open-volume defects on the atomic ordering process at elevated temperatures in Fe60Al40 thin films. A dependence of the ordering process on the type and concentration of defects is observed by positron annihilation spectroscopy combined with ab-initio calculations. Comparing the lifetimes of positrons in the alloy for different annealing and irradiation treatments reveals the role of mono-vacancies, triple defects as well as large vacancy clusters: The rate of atomic ordering to the ordered B2 state is increased in the presence of mono-vacancies whereas triple defects and vacancy complexes decrease the ordering rate. Furthermore, an agglomeration of vacancies during annealing to di-vacancies and larger vacancy clusters is observed. The distribution of open-volume defects can be modified in such a way as to control the thermal stability via ion-irradiation and thermal pre-treatments.

Keywords: Order-disorder phenomena; Vacancies; Lattice defects; Reordering; Positron Annihilation Spectroscopy

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Permalink: https://www.hzdr.de/publications/Publ-28092
Publ.-Id: 28092


Microstructure, strengthening mechanisms & properties of ODS alloys developed under MatISSE project

Chauhan, C.; Bergner, F.; Etienne, A.; Aktaa, J.; de Carlan, Y.; Heintze, C.; Litvinov, D.; Hernandez-Mayoral, M.; Oñorbe, E.; Radiguet, B.; Ulbricht, A.

The invited talk aims at summarizing results from a publication that received the best paper award 2017 of the Journal of Nuclear Materials. Microstructure, strengthening mechanisms and properties of ODS alloys are addressed.

Keywords: ODS alloys; microstructure characterization; strengthening mechanisms

  • Invited lecture (Conferences)
    NuMat2018: The Nuclear Materials Conference, 14.-18.10.2018, Seattle, USA

Permalink: https://www.hzdr.de/publications/Publ-28091
Publ.-Id: 28091


High Energy Fast X-ray Tomography

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

Ultrafast X-ray computed tomography with ROFEX scanners has become a common tool for investigations of multiphase phenomena in science and industrial application within recent years. Though being very successful in giving unprecedented insights into dynamic processes, ROFEX scanners yet have some limitations in terms of permissible sizes and density of the investigated objects. Due to the limited penetration capability of X-rays at photon energy of up to 150 keV experimental mock-ups need to be made out of light construction materials and many experimental setups had to be scaled down from their real size to fit into the scanner. Often this limits the transferability of results to larger industrial facilities.
This contribution introduces the new High-Energy Computed Tomography scanner of Rossendorf (HECToR) as the next step towards improved industrial applicability. The facility utilizes a 1 MeV electron accelerator with a continuous beam power of up to 100 kW. The functional principle has been adapted from the ROFEX scanners. HECToR is able to scan objects with a maximum diameter of 400 mm at a temporal resolution of up to 5000 frames per second and with a spatial resolution of 3 mm at best conditions. The paper introduces the scanner concept, its components and presents first dynamic studies on generic two-phase flows in steel vessels. Furthermore, the imaging characteristics are discussed in detail.

Keywords: ROFEX; ultrafast X-ray CT; high energy; HECToR

  • Contribution to proceedings
    9th World Congress on Industrial Process Tomography, 02.-06.09.2018, Bath, UK
    Proceedings of the 9th world cogress on industrial process tomography
  • Lecture (Conference)
    9th World Congress on Industrial Process Tomography, 02.-06.09.2018, Bath, UK

Permalink: https://www.hzdr.de/publications/Publ-28090
Publ.-Id: 28090


Minor changes in neurocognition and quality of life after proton therapy for brain tumour patients

Dutz, A.; Agolli, L.; Valentini, C.; Bütof, R.; Troost, E. G. C.; Baumann, M.; Lühr, A.; Krause, M.; Löck, S.

Purpose: To investigate changes in neurocognitive function and quality of life (QoL) and their association with dosimetric parameters of various brain structures as well as clinical cofactors in adult brain tumour patients following proton beam therapy (PBT).

Material and methods: Sixty-nine adult patients with primary brain tumours who received conventionally fractionated PBT were included in this study. Neurocognitive function according to the Montreal Cognitive Assessment (MoCA) test and QoL according to general EORTC-QLQ-C30 and brain tumour specific QLQ-BN20 questionnaires were scored prospectively at baseline and within 3-month-intervals up to one year after PBT. Dose-volume parameters of the retrospectively contoured structures hippocampus, thalamus, frontal and temporal lobes, amygdala, entire cerebellum, anterior cerebellum, and posterior cerebellum were extracted. Clinical parameters comprised age, sex, diagnosis and WHO grading, tumour volume, prescribed dose, concomitant chemotherapy, tumour resection and administration of corticosteroids. MoCA scores and differences to baseline values at different time points were correlated with self-reported QoL items (Spearman correlation rs), clinical and dosimetric parameters (Mann-Whitney U test, logistic regression). A change of ≥3 points of the MoCA total score compared to baseline was considered clinically relevant. Unless otherwise stated, differences at 3 months after PBT compared to baseline are given.

Results: The MoCA total score remained stable over time for the majority of patients: Less than 10% of the patients had clinically relevant changes at respective time points. The QLQ-C30 items did not change over time. On the QLQ-BN20 symptom scale, significant increases were observed for the items hair loss (p=0.002) and seizure (p<0.042, up to 9 months after PBT). However, future uncertainty decreased significantly (p<0.042). MoCA scores were significantly correlated with self-reported QoL scores. At all time-points, MoCA total score correlated with QLQ-C30 cognitive function (rs: 0.31-0.57) and MoCA language scores with QLQ-BN20 communication deficit (rs: 0.36-0.59).
Clinically relevant differences in the MoCA total score were significantly associated with high dose parameters in the anterior, posterior and entire cerebellum (V55Gy, p<0.05), but not with clinical parameters.

Conclusion: Neurocognitive function and QoL remained stable in the majority of brain tumour patients following PBT. Self-reported QoL was in accordance with the results of the objective MoCA test. Significant associations between dose-volume parameters and clinically relevant neurocognitive changes suggest that further sparing of organs at risk in treatment planning may lead to increased neurocognitive function and QoL for brain tumour patients. New planning constraints for further potential organs at risk, such as the cerebellum [1], should be discussed.

[1] Eekers DBP et al. (2017) Clin Transl Radiat Oncol 8, 22–26.

Keywords: Quality of Life

Permalink: https://www.hzdr.de/publications/Publ-28089
Publ.-Id: 28089


Review Article: Review of electrohydrodynamical ion sources and their applications to focused ion beam technology

Gierak, J.; Mazarov, P.; Bruchhaus, L.; Jede, R.; Bischoff, L.

In this article, the authors review, compare, and discuss the characteristics and applicative potential of a variety of nongallium ion liquid metal ion sources they have developed and successfully applied to nanopatterning. These sources allow generating on-demand ion beams and are promising for extending focused ion beams applications. They detail the operating characteristics of such sources capable to emit metal projectiles ranging from atomic ions with different charge states to polyatomic ions and to large metal clusters having sizes up to a few nanometers. They highlight their interest and relevance to current nanoscience challenges in terms of ultimate patterning or bottom-up nanofabrication capabilities.

Keywords: Liquid Metal Ion Source; nongallium; nanoscience

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Permalink: https://www.hzdr.de/publications/Publ-28088
Publ.-Id: 28088


Forschungsdatenmanagement am Helmholtz-Zentrum Dresden-Rossendorf und am Helmholtz-Zentrum Berlin (RDM@DB)

Konrad, U.; Görzig, H.; Juckeland, G.

Das BMBF Verbundprojekt RDMatDB wird im Rahmen der Förderrichtlinie "Erforschung des Managements von Forschungsdaten in ihrem Lebenszyklus“ realisiert. Ziel des Projektes ist es, Forschungsdaten-Management-Lösungen zu entwickeln, die das HZDR und HZB als Betreiber von Infrastrukturen in die Lage versetzen, die sich aus den FAIR-Prinzipien des Datenmanagements ergebenden Anforderungen zu erfüllen. Im dem Vortrag auf der BMBF-Veranstaltung "Forschungsdatenmanagement - künftige Entwicklungen und aktuelle Fragen der Wissenschaft" wird das Projekt und die Perspektiven vorgestellt.
The BMBF joint project RDMatDB of the HZDR and HZB is implemented within the scope of the funding program "Research on the management of research data in its life cycle".
The goal of the project is to develop research data management solutions which the HZDR and HZB consider to meet the requirements of the FAIR data management principles.
The project and perspectives are presented at the BMBF event "Research Data Management - Future Developments and Current Issues of Science".

  • Invited lecture (Conferences)
    Forschungsdatenmanagement - künftige Entwicklungen und aktuelle Fragen der Wissenschaft, 17.-18.10.2018, Berlin, Deutschland
    DOI: 10.14278/rodare.62

Permalink: https://www.hzdr.de/publications/Publ-28087
Publ.-Id: 28087


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