Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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33407 Publications

Visualization of bubble coalescence in bubble chains rising in a liquid metal

Keplinger, O.; Shevchenko, N.; Eckert, S.
Bubble coalescence in liquid metals was studied by considering the case of a bubble chain rising in the eutectic alloy GaInSn. The experiments were performed in a flat vessel with a rectangular cross section. High frame-rate X-ray radiography was used for visualizing the interaction between the bubbles. Essential process parameters such as bubble sizes, bubble shapes, velocities and distance of their closest approach are obtained from image processing. Different coalescence schemes occurring inside the bubble chain are discusses and demonstrated. The results are compared to collision cases where the bubbles bounce off each other. The material properties of the liquid metal differ significantly from those of water or other transparent fluids. In particular, the low viscosity, the high density and the high surface tension result in low values of the Mo number, Mo ≈ 2x10-13 and high Reynolds numbers of Re ~ 104. Nevertheless, the process of bubble approach, collision and coalescence was found to proceed in a qualitatively similar way as reported by previous studies for the case of water or highly viscous fluids. From the analyzed data, it was difficult to define a quantitative criterion that would allow predicting whether a pair of colliding bubbles would coalesce or bounce off. The observations indicate that the turbulent flow in the immediate vicinity of the bubbles has an important influence on whether coalescence occurs or not.
Keywords: Liquid metal; GaInSn; Bubble chain; Bubble coalescence; X-ray radiography; Two-phase flow

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Permalink: https://www.hzdr.de/publications/Publ-26500
Publ.-Id: 26500


Euler-Euler modeling and X-ray measurement of oscillating bubble chain in liquid metals

Liu, L.; Keplinger, O.; Ziegenhein, T.; Shevchenko, N.; Eckert, S.; Yan, H.; Lucas, D.
An Euler-Euler two-fluid approach was used to simulate the behavior of gas bubbles rising in a stagnant liquid metal. A single point injection in the range of moderate gas flow rates results in the formation of bubble chains undergoing distinct oscillations of the bubble trajectories. A set of interfacial closures and a shear stress transport k-ω (SST) turbulence model, namely the baseline model for bubbly flow (Rzehak, R., & Krepper, E. (2013), Nuclear Engineering and Design 265, 701-711.) was applied for simulating the transient behavior of the bubble chain. X-ray radiography measurements were conducted to establish an experimental data base for validating the numerical results. The experiments provide a visualization of the two-phase flow in a flat container and allow for determining essential bubble quantities such as the size, shape, trajectory and velocity. The comparison between numerical simulations and experimental data showed a very good qualitative and quantitative agreement with respect to the distribution of the void fraction and the dynamics of the bubble chain. Wrong results were obtained by simulations where the effect of the bubble induced turbulence (BIT) was neglected. Two BIT models were applied within this study, the baseline BIT model and the Sato BIT model. Both models showed a good agreement with the experimental observations, while the results of the baseline model were even closer to the measurements. Thus, the baseline model originally developed for the air-water system has proved to be capable of reproducing the complex transient behavior of oscillating bubble chains in liquid metals.
Keywords: Liquid metal; Bubble chain; X-ray radiography; CFD; Euler-Euler two-fluid model; Two-phase flow.

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Permalink: https://www.hzdr.de/publications/Publ-26499
Publ.-Id: 26499


Electronic proprioception

Makarov, D.
Augmented reality devices such as Smart Glasses are destined to be an integral part of our information intensive society, assisting us to acquire data and process information in an ever faster paced society. Although impressive in their realization and demonstrations, an often-neglected drawback of conventional optics-based motion detection systems is their bulkiness, energy inefficiency and the stringent requirement to be at line of sight with any object. We envision that future augmented reality systems will rely on compliant wearable and on-skin interactive electronics. When equipped with motion tracking sensory systems, electronic skins would offer complimentary information on the surrounding and enable novel means of manipulating physical or even virtual objects.
We demonstrate electronic skins capable of perceiving direction in space. Our highly compliant magnetosensory system enables real time tracking of the position of a body in space as well as the touchless manipulation of (virtual) objects based on the interaction with magnetic fields exclusively. We foresee exciting possibilities not only for business or gaming industries but also for safety and security applications, where the somatic manipulation of objects, e.g. turning regulation knobs located in a restricted environment, is undesirable or even prohibited.
  • Invited lecture (Conferences)
    Invited talk at the Microsoft, Applied Sciences Group, 04.12.2017, Redmond, USA

Permalink: https://www.hzdr.de/publications/Publ-26498
Publ.-Id: 26498


Magnetosensitive e-skins with directional perception for augmented reality

Cañón Bermúdez, G. S.; Karnaushenko, D. D.; Karnaushenko, D.; Lebanov, A.; Bischoff, L.; Kaltenbrunner, M.; Fassbender, J.; Schmidt, O. G.; Makarov, D.
Electronic skins equipped with artificial receptors are able to extend our perception beyond the modalities that have naturally evolved. These synthetic receptors offer complimentary information on our surrounding and endow us with novel means of manipulating physical or even virtual objects. Here, we realize highly compliant magnetosensitive skins with directional perception that enable magnetic cognition, body position tracking and touchless object manipulation. Transfer printing of eight high performance spin valve sensors arranged into two Wheatstone bridges onto 1.7 µm thick polyimide foils ensures mechanical imperceptibility. This resembles a new class of interactive devices extracting information from the surrounding through magnetic tags. We demonstrate this concept in augmented reality systems with virtual knob turning functions and the operation of virtual dialing pads, based on the interaction with magnetic fields. This technology will enable a cornucopia of applications from navigation, motion tracking in robotics, regenerative medicine, sports and gaming to interaction in supplemented reality.
Keywords: flexible electronics, magnetic field sensors

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Permalink: https://www.hzdr.de/publications/Publ-26497
Publ.-Id: 26497


Prediction of bubble size distributions in large-scale bubble columns using computational fluid dynamics

Besagni, G.; Inzoli, F.; Ziegenhein, T.; Lucas, D.
A precise estimation of bubble size distributions is of fundamental and practical importance to understand the fluid dynamics and to estimate the mass transfer in bubble columns. Multiphase computational fluid dynamic simulations, in the Eulerian multi-fluid framework, are able to predict the local bubble size distributions from the fluid flow conditions by using coalescence and breakage kernels. In particular, this study concerns the prediction of the bubble size distributions in the “pseudo-homogeneous” flow regime, which is characterized by a wide spectrum of bubble sizes and is generally observed in industrial applications. Reliable predictions of the “pseudo-homogeneous” flow regime are, however, limited up to now: one important drawback concerns the selection of appropriate models for the coalescence and break-up. A set of closure relations was collected at the Helmholtz-Zentrum Dresden-Rossendorf that represents the best available knowledge and may serve as a baseline model for further investigations. In this paper, the validation of this set of closure relations has been further extended to the “pseudo-homogeneous” flow regime by comparing experimental and numerical bubble size distributions at different axial positions in a large-diameter and large-scale bubble column. The results have been critically analysed and may serve as basis to improve the coalescence and break-up closures.
Keywords: Bubbly flow, bubble shape, bubble column, CFD
  • Contribution to proceedings
    14th International Conference of Multiphase Flow in Industrial Plant, 13.09.2017, Desenzano del Garda, Italy

Permalink: https://www.hzdr.de/publications/Publ-26496
Publ.-Id: 26496


Two-phase bubble column fluid dynamics: a review

Besagni, G.; Ziegenhein, T.; Inzoli, F.
We present a comprehensive literature review on the two-phase bubble column; in this review we deeply analyze the flow regimes, the flow regime transitions, the local and global fluid dynamics parameters, and the mass transfer phenomena. First, we discuss the flow regimes, the flow regime transitions, the local and global fluid dynamics parameters, and the mass transfer. We also discuss how the operating parameters (i.e., pressure, temperature, and gas and liquid flow rates), the operating modes (i.e., the co-current, the counter-current and the batch modes), the liquid and gas phase properties, and the design parameters (i.e., gas sparger design, column diameter and aspect ratio) influence the flow regime transitions and the fluid dynamics parameters. Secondly, we present the experimental techniques for studying the global and local fluid dynamic properties. Finally, we present the modeling approaches to study the global and local bubble column fluid dynamics, and we outline the major issues to be solved in future studies.
Keywords: Bubble column; flow regimes; gas holdup; bubble size distribution; multi-scale; modeling

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Permalink: https://www.hzdr.de/publications/Publ-26495
Publ.-Id: 26495


Dependency of bubble column flow regime on bubble size distribution

Ziegenhein, T.; Lucas, D.
The regime transition from homogenous to heterogeneous is one of the most important design parameters of bubble columns. As shown by Lucas et al.
(2005) the lateral lift force may have an important influence on this transition. Interactions between local and global instabilities of a bubble column were discussed by Lucas et al. (2007).
As shown experimentally by Tomiyama et al. (2002) and by numerous direct numerical simulations (e.g. Dijkhuizen et al., 2010) the lateral lift force changes its sign in dependence on the bubble size. Recently the findings of Tomiyama et al. obtained for single bubbles in a linear laminar shear flow for a system with high Morton number (high viscosity) were also confirmed for low the viscid air-water system and turbulent conditions (Ziegen-hein et al., 2017 and Ziegenhein and Lucas, 2017a). The well-known correlation of Tomiyama et al. (2002) fits very well also for these conditions, provided the Eötvös number based on the major axis is used. With the Tomiyama correlation combined with the Wellek correlation for the bubble shape the critical diameter for the change of the sign of the lift force is about 5.8 mm for the air-water system. While the Wellek-correlation is valid for contaminated water, deionized water was used in the experiments. Replacing the Wellek- correlation by a correlation based on bubble shapes that are observed in bubble columns (Ziegenhein and Lucas, 2017b) the critical diameter for the change of the sign is about 5.14 mm.
With a positive sign of the lift force coefficient – which is valid for bubbles smaller than the critical diameter a homogeneous bubbly flow is stabilized while larger bubbles destabilize the flow. Lucas et al. (2005) derived a stability criterion also for bubble size distributions that include small and large bubbles.
Experiments investigating the effect of the bubble size distribution were conducted in a high aspect ratio bubble column for air/purified water. The sparger consists of 6 holes that can be equipped with different needles. The holes are separated into two groups that hold different needle sizes to produce a certain poly-disperse flow. The total gas volume flow was fixed to 1.0 l/min for all experiments. The gas flow through the sparger group was varied to vary the partial gas fraction of the small and large bubbles. Due to this variation, the stability criterion was manipulated from ‘strong’ negative to ‘strong’ positive.


The liquid velocity profile was determined by particle tracking using microbubbles and 100 µ m PMMA particles. The bubble sizes and the gas volume fraction were determined by high-speed camera observations. Measurements were done for different height positions in
the column. Completely different flow structures and profiles were observed by only changing the bubble size. Homogeneous flow characterized by flat profiles for gas volume fraction and liquid velocity were observed for a bubble size distribution with mainly small bubbles, while a center peak characterizing the heterogeneous regime occurs for the distribution with large bubbles. Applying the stability criterion of Lucas et al. (2005) these two situations correspond to ‘strong’ negative and ‘strong’ positive meaning homogeneous and heterogeneous flow regime, respectively. Beside these extreme cases also the transition region was investigated. Here the measurements are made difficult because coalescence changes the bubble size distribution along the column height resulting in a transient behavior. In any case, the lift force seems to be the key for a local criterion on the regime transition.
Keywords: bubble size, lift force, stability
  • Poster
    15th Multiphase Flow Conference and Short Course, 14.-17.11.2017, Dresden, Germany

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Permalink: https://www.hzdr.de/publications/Publ-26494
Publ.-Id: 26494


Entwicklung simulations- und messtechnischer Methoden zur Effizienzsteigerung verfahrenstechnischer Prozesse in großtechnischen Anlagen

Reinecke, S. F.; Herrmann-Heber, R.; Mohseni, E.; Hampel, U.
Die Entsorgung und die Aufbereitung des im kommunalen und industriellen Umfeld anfallenden Abwassers zur Vermeidung der Verschmutzung und Eutrophierung von Fließgewässern ist von zentraler Bedeutung für einen nachhaltigen Umgang mit der Ressource Wasser. Die Abwasserkette umfasst im Wesentlichen den Wasserverbraucher, das Kanalnetz, die Kläranlagen und das Oberflächengewässer, in welches das gereinigte Wasser eingeleitet wird. Das allein im kommunalen Bereich anfallende Abwasser wird in 10,000 Abwasseraufbereitungsanlagen mit einem jährlichen Energieaufkommen von 4.400 GWh behandelt (Fricke, 2009). Damit tragen diese Anlagen 20% des in den Kommunen anfallenden Energieverbrauches. Davon entfallen bis zu 80% auf die biologischen Reinigungsstufen (Fricke, 2009).
Ziel dieser Forschung ist die Entwicklung einer Methodik, mit welcher basierend auf numerischen Simulationen die Optimierungspotenziale der jeweiligen Anlage aufgedeckt werden, optimierte Anlagenkonfigurationen und Betriebsweisen bestimmt bzw. bewertet werden und nach ihrer Umsetzung an der konkreten Anlage mit Hilfe innovativer Sensorik messtechnisch validiert werden. Damit soll eine grundlegende Verbesserung der Hydrodynamik von Belebungsbecken in Verbindung mit der Effizienzsteigerung der Anlage basierend auf numerischen Simulationen und innovativen Sensortechnologien möglich werden.
Weiterhin ist die Forschung in diesem Bereich auf die Entwicklung effizienter Gaseintragssysteme fokussiert. Die etablierte Technik für den Gaseintrag in kommunalen Kläranlagen sind am Boden montierte Druckbegaser mit flexiblen, perforierten Membranen. Mit dieser Begasertechnik wird jedoch nur eine begrenzte Sauerstoffeintragseffizienz von 40-60% erreicht (Wang et al. 2010). Die Sauerstoffeintragseffizienz wird maßgeblich durch die initiale Blasengröße am Begaser bestimmt. Davon hängen wiederum die Blasenverweilzeit und der Gasgehalt ab. Um eine wesentliche Steigerung der Sauerstoffeintragseffizienz zu erzielen, sind Gasblasen im Submillimeterbereich erforderlich. Nur so kann eine ausreichend große Fläche für einen effizienten Sauerstoffübergang von der Gas- in die Flüssigphase erreicht und der biologische Abbauprozess trotzdem stabil gehalten werden.
  • Lecture (others)
    TKoR Netzwerktreffen Technologie- und Kompetenzzentrum organisches Reststoffrecycling, 13.12.2017, Leipzig, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26493
Publ.-Id: 26493


GGR Biennial Critical Review: Analytical Developments Since 2014

Linge, K. L.; Bédard, L. P.; Bugoi, R.; Enzweiler, J.; Jochum, K. P.; Kilian, R.; Jingao, L.; Marin-Carbonne, J.; Merchel, S.; Munnik, F.; Morales, L. F. G.; Rollion-Bard, C.; Souders, A. K.; Sylvester, P. J.; Weis, U.
This GGR biennial critical review covers developments and innovations in key analytical methods published since January 2014, relevant to the chemical, isotopic and crystallographic characterisation of geological and environmental materials. In nine selected analytical fields, publications considered to be of wide significance are summarised, background information is provided and their importance evaluated. In addition to instrumental technologies, this review also presents a summary of new developments in the preparation and characterisation of rock, microanalytical and isotopic reference materials, including a précis of recent changes and revisions to ISO guidelines for reference material characterisation and reporting. Selected reports are provided of isotope ratio analyses by both solution-nebulisation MC-ICP-MS and laser ablation-ICP-MS, as well as of radioactive isotope geochronology by LA-ICP-MS. Most of the analytical techniques elaborated continue to provide new applications for geochemical analysis, however it is noted that instrumental neutron activation analysis has become less popular in recent years, mostly due to the reduced availability of nuclear reactors to act as a neutron source. Many of the newer applications reported here provide analysis at increasingly finer resolution. Examples include atom probe tomography, a very sensitive method providing atomic scale information, nanoscale SIMS, for isotopic imaging of geological and biological samples, and micro-XRF, which has a spatial resolution many orders of magnitude smaller than conventional XRF.
Keywords: TIMS, isotopic analysis, geochronology, ICP-MS, laser ablation, mass spectrometry, MC-ICP-MS, calibration, environmental sampling, FIB, SIMS, AMS, Ion Beam Analysis, radionuclides, INAA, reference materials, microanalysis, atom probe tomography

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Permalink: https://www.hzdr.de/publications/Publ-26492
Publ.-Id: 26492


Validation of the DYN3D-Serpent code system for SFR cores using selected BFS experiments. Part II: DYN3D calculations.

Rachamin, R.; Kliem, S.
The capability of the DYN3D-Serpent codes system to simulate highly heterogeneous sodium-cooled fast reactor cores has been studied. The BFS-73-1 and the BFS-62-3A critical assemblies were chosen for the investigation. The study was performed in two parts. In the first part of the study, a 3D full model of each of the assemblies was simulated using the Serpent Monte-Carlo (MC) code, and the basic neutronic characteristics were evaluated and compared against experimental values. In the second part of the study, which is the subject of this paper, the assemblies were modeled using the DYN3D nodal diffusion code. The few-group cross-sections for the DYN3D analysis were generated using the Serpent MC code. The generation of effective few-group cross-sections of such assemblies is quite a challenge due to the substantial heterogeneity of the assemblies configuration. Therefore, the use of homogenization techniques was considered and evaluated. Initially, the GET and SPH techniques were applied for the analysis of the BFS-73-1 assembly core fuel rods, and of selected fuel rods from the BFS-62-3A assembly. Then, the SPH method was implemented and demonstrated for a pin-by-pin calculation of the BFS-73-1 assembly. It was shown that the GET and the SPH method noticeably improve the prediction accuracy of the DYN3D code. The results of the DYN3D pin-by-pin calculation with the SPH correction agree very well with that of the full assembly Serpent results, which in turn agree very well with the experimental data.
Keywords: SFR, BFS experiments, Group constant generation, ADF, SPH, Serpent and DYN3D

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Permalink: https://www.hzdr.de/publications/Publ-26490
Publ.-Id: 26490


Eulerian multiphase flow modelling – Advanced concepts

Lucas, D.
Advanced concepts for Euler-Euler-modelling of gas-liquid flow were presented. The inhomogeneous MUSIG model is a basic framework for modelling bubbly flows. A baseline model for polydisperse bubbly flows was established at HZDR. For segragated flows the AIAD model can be used. The innovative GENTOP concept allows the consideration of different flow morphologies and transitions between them.
Keywords: Poly-disperse flows, Large interfaces, Multi-scale modelling, Flow pattern transition
  • Invited lecture (Conferences)
    Computational Fluid Dynamics in Metallurgy - Advanced Seminar, 04.-06.12.2017, Köln, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26489
Publ.-Id: 26489


Euler-Euler-modelling of poly-disperse bubbly flows

Lucas, D.
Bubbly flows occur in various industrial processes. For medium and large industrial scales the Euler-Euler approach is frequently applied in CFD-simulations. To derive the corresponding balance equations for mass, momentum and energy averaging procedures are applied and in the result information on the gas-liquid interface gets lost. Models reflecting the physics at the non-resolved scale are required to close the problem. This concerns the momentum transfer between bubbles and liquid (bubble force models), modulation of turbulence by the bubbles (BIT – bubble induced turbulence), bubble-bubble interactions (coalescence and breakup) and mass and heat transfer between the phases (boiling, condensation, heterogeneous chemical reactions). Most of these closure models sensitively depend on the bubble size and even may change their sign in dependency on the bubble size (lateral lift force). Correspondingly an appropriate modelling requires the consideration of the bubble size distribution and in general also the sub-division of the gas phase in phases representing bubbles of a specific range of sizes.
Still there is no consensus on the closure models in literature. Often closures and open parameters are tuned to obtain agreement with experimental data. To achieve a consolidation of the modelling and more reliable predictions the so-called baseline model concept was proposed by HZDR. In the baseline model all closure models including constants are well defined and the fixed model is used for the simulation of different flow situations involving bubbles in the mm-range and larger without any modification.
The lecture presents the baseline model concept, introduces the baseline model for poly-disperse bubbly flows (including the definition of closures for bubble forces, BIT, coalescence and breakup), the inhomogeneous MUSIG model for the consideration of the bubble size distribution and the modelling of phase transfer and chemical reaction. The baseline model for poly-disperse bubbly flows was validated for more than 150 single experiments. Examples for the validation are given and perspectives of the future modelling are discussed.
Keywords: CFD, Euler-Euler, bubbly flow, baseline model
  • Invited lecture (Conferences)
    ERCOFTAC Best Practice Guidance Seminar, CFD for Dispersed Multi-Phase Flows,, 20.-21.11.2017, Magdeburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26488
Publ.-Id: 26488


CFD-model for industrial bubbly flows

Lucas, D.; Rzehak, R.; Ziegenhein, T.; Krepper, E.; Liao, Y.
Computational Fluid Dynamics (CFD) is an accepted tool for design and optimisation in many single-phase flow applications, e.g. in automotive or aviation industries. In principle, CFD has the same potential also for multiphase flows, but it is not yet mature for routine applications because of the complexity of such flows. For medium and large scale industrial applications the Euler-Euler approach is most suited and the interactions between the phases have to be reflected by closure models. In bubbly flows such interactions between the liquid flow field and the deformable bubble interfaces have an important influence on the flow characteristics. CFD-models should depend on local flow characteristics as e.g. shear rate, turbulence, and bubble sizes. Locally such properties may be very similar even in quite different flow situations like bubbly pipe flows, bubble columns or air-lift reactors. Instead of case by case tuning the development of a unified model for bubbly flows seems to be a promising way to increase the reliability of predictions obtained from CFD-simulations. Such a model was established at HZDR and has been applied to many different bubbly flow situations without any modification. This contribution presents this model and some examples for application to different industrial relevant bubbly flows.
Keywords: CFD, Euler-Euler, bubbly flow, polydispers, baseline
  • Contribution to proceedings
    14th International Conference on MULTIPHASE FLOW IN INDUSTRIAL PLANTS (MFIP17), 13.-15.09.2017, Desenzano del Garda, Italy
  • Lecture (Conference)
    14th International Conference on MULTIPHASE FLOW IN INDUSTRIAL PLANTS (MFIP17), 13.-15.09.2017, Desenzano del Garda, Italy

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Permalink: https://www.hzdr.de/publications/Publ-26487
Publ.-Id: 26487


Influence of the bubble size distribution on bubble column stability

Lucas, D.; Ziegenhein, T.; Schipp, J. F.
Bubble columns are widely used in industrial processes. The performance in case of chemical reactions between liquid and gaseous substances depends on characteristic parameters as interfacial area density, turbulence level, or kLa-values. Transitions between the homogeneous and the heterogeneous operating regime dramatically change such characteristic parameters and are for this reason subject of many investigations. Many of them tried to correlate the transition with the gas superficial velocity Jg or equivalent integral parameters, but there is no general valid critical value for the transition. Lucas et al. (2005) discussed the influence of the bubble size distribution on the stability of a homogeneous bubbly flow. Depending on the sign of the lateral lift force, which changes with the bubble size (Tomiyama et al., 2002), it can stabilize (positive lift force coefficient – small bubbles) or destabilize (negative lift force coefficient – large bubbles) the flow. Basing on a linear stability analysis finally a criterion was obtained for the stability of a homogeneous bubbly flow in dependence on the bubble size distribution. Indirectly it also depends on Jg since usually bubble sizes increase with increasing Jg caused by larger size of the injected bubbles and by increased coalescence. Lucas et al. (2007) discussed the complex relations between local and global instabilities that may be quite complex basing on CFD-simulations. Akbar et al. (2013) showed the influence of injection and bubble size on the flow structure in a rectangular bubble column.
The bubble size distribution clearly has an influence on the transition between the homogeneous and heterogeneous regime in bubble columns which can be explained by effects of the lateral lift force. It interacts with other phenomena like inlet induced instabilities and coalescence processes. A detailed investigation on these effects is presented in this contribution.
Keywords: bubble column, flow regime, regime transition, lift force, bubbly flow
  • Contribution to proceedings
    13th International Conference on Gas–Liquid and Gas–Liquid–Solid Reactor Engineering (GLS-13), 20.-23.08.2017, Brussels, Belgium
  • Lecture (Conference)
    13th International Conference on Gas–Liquid and Gas–Liquid–Solid Reactor Engineering (GLS-13), 20.-23.08.2017, Brussels, Belgium

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Permalink: https://www.hzdr.de/publications/Publ-26486
Publ.-Id: 26486


Simulation of flow pattern transitions in the Euler-Euler framework

Lucas, D.; Krepper, E.; Höhne, H.; Oertel, R.; Schlegel, F.
Two-phase flows occurring in nature or industrial applications frequently involve gas-liquid interfaces which vary over a wide range of scales. Simultaneously, within one flow domain there might be very small bubbles or droplets, but also large interfaces as e.g. caused by stratification due to gravity. In addition transitions between these different morphologies may occur such as bubble entrainment by jets or breaking waves, droplet generation from wave crests or the generation of large gas structures out of smaller ones by coalescence. Such flow situations are very challenging from the modelling point of view. At least for medium and large size flow domains it is not possible to resolve all interfacial scales down to the smallest ones because this would lead to a number of cells of the numerical grid which would exceed todays computing capacity by far. Consequently there will be interfaces smaller and larger than the computational grid. Clearly the smaller ones should be considered by appropriate sub-grid models while the larger ones should be simulated.
Up to now there is no CFD approach established for such flow situations. One promising approach is the so-called GENeralized TwO-Phase Flow concept (GENTOP) which was recently developed at Helmholtz-Zentrum Dresden – Rossendorf. It bases on the two-fluid multi-field approach. Beside one or several fields representing the dispersed morphologies of gas and/or liquid potentially continuous phases for gas and liquid are introduced. Interfaces between these potentially continuous fields are statistically resolved if the local volume fraction is large enough. If this is not the case, closure models for the disperse phase are applied. For this reason it is called potentially continuous phase. The coupling of the dispersed and potentially continuous fields is done basing on a population balance. The knowledge on the typical length scale of a gas or liquid structure allows its presentation in the corresponding field. Transitions can be modelled as coalescence and breakup processes which are in agreement with the involved physical phenomena.
The concept was previously implemented in the CFX-code of ANSYS and tested considering only one continuous field for liquid, but disperse fields and a potentially continuous field for gas. Demonstration cases involve the bubble entrainment by a plunging liquid jet, generation of large bubbles out of small ones due to coalescence in a bubble column, collapse of a water column with transitions from continuous to disperse morphologies of the gas in the beginning and the vice versa process in the later phase and the simulation churn-turbulent pipe flows. Recently first simulations were done for boiling in a side wall heated vertical pipe. Single phase liquid enters the pipe from below with slight sub-cooling. Steam bubbles are generated at the wall and continue to increase and coalesce producing large bubbles which migrate to the pipe center caused by the inversion of the lateral lift force. Finally large gas structures are observed in the pipe center leasing to a transition to annular flow. The simulation involves the transition between bubbly flow and churn-turbulent flow regime and a starting transition to annular flow. In the talk the GENTOP concept and selected demonstration cases with focus on the new simulations on boiling in the heated pipe are presented. Also some recent developments to implement a similar approach in OpenFOAM are presented.
Keywords: multiscale, modelling, GENTOP, CFD, two-phase, boiling
  • Invited lecture (Conferences)
    The 3rd International Conference on Numerical Methods in Multiphase Flows, ICNMMF-III, 26.-29.06.2017, Tokyo, Japan

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Permalink: https://www.hzdr.de/publications/Publ-26485
Publ.-Id: 26485


Dependency of bubble column flow regime on bubble size distribution

Ziegenhein, T.; Lucas, D.
The regime transition from homogenous to heterogeneous is one of the most important design parameters of bubble columns. The lateral lift force may have an important influence on this transition. As shown experimentally and by numerous direct numerical simulations the lateral lift force changes its sign in dependence on the bubble size. Recently the findings of Tomiyama et al. obtained for single bubbles in a linear laminar shear flow for a system with high Morton number (high viscosity) were also confirmed for low the viscid air-water system and turbulent conditions. The well-known correlation of Tomiyama et al. fits very well also for these conditions, provided the Eötvös number based on the major axis is used. With the Tomiyama correlation combined with the Wellek correlation for the bubble shape the critical diameter for the change of the sign of the lift force is about 5.8 mm for the air-water system. While the Wellek-correlation is valid for contaminated water deionized water was used in the new HZDR experiments. Replacing the Wellek- correlation by a correlation based on the observed bubble shape the critical diameter for the change of the sign is about 4.5 mm.
With a positive sign of the lift force coefficient – which is valid for bubbles smaller than the critical diameter a homogeneous bubbly flow is stabilized while larger bubbles destabilize the flow. Lucas et al. derived a stability criterion also for bubble size distributions that include small and large bubbles.
Experiments investigating the effect of the bubble size distribution were conducted in a high aspect ratio bubble column for air/purified water. The gas flow through the sparger groups was varied to modify the partial gas fraction of the small and large bubbles. Due to this variation, the stability criterion was manipulated from ‘strong’ negative to ‘strong’ positive. Measurements were done for different height positions in the column.
Completely different flow structures and profiles were observed by only changing the bubble size. Homogeneous flow characterized by flat profiles for gas volume fraction and liquid velocity were observed for a bubble size distribution with mainly small bubbles, while a center peak characterizing the heterogeneous regime occurs for the distribution with large bubbles. Applying the stability criterion of Lucas et al. these two situations correspond to ‘strong’ negative and ‘strong’ positive meaning homogeneous and heterogeneous flow regime, respectively. Beside these extreme cases also the transition region was investigated. Here the measurements are made difficult because coalescence changes the bubble size distribution along the column height resulting in a transient behavior. In any case, the lift force seems to be the key for a local criterion on the regime transition.
Keywords: bubble column, flow regime, lift force, bubbly flow, stability
  • Lecture (Conference)
    53rd European Two-Phase Flow Group Meeting, 22.-24.05.2017, Gdansk, Poland

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Permalink: https://www.hzdr.de/publications/Publ-26484
Publ.-Id: 26484


Simulation based environmental assessment of processes

Reuter, M. A.
• Background to LCA for mineral and metallurgical process evaluation
• Introduction into HSC Sim 9 - LCA tool / Link to GaBi
• Step-by-step hands-on case of a simple reactor
• Application to own case of own choice with support from lecturer
  • Invited lecture (Conferences)
    A short course in Geometallurgy, 02.-06.10.2017, Liège, Belgium

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Permalink: https://www.hzdr.de/publications/Publ-26483
Publ.-Id: 26483


SOS Metallurgy - Save our Smelters

Reuter, M. A.
Maintaining European metallurgy know-how and how to integrate metallurgy into sustainable primary and secondary raw material industry.
  • Invited lecture (Conferences)
    Europe—From Mine to Market, 28.09.2017, Dresden, Deutschland

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Permalink: https://www.hzdr.de/publications/Publ-26482
Publ.-Id: 26482


Modulation of magnetic properties at the nanometer scale in continuously graded ferromagnets

Fallarino, L.; Riego, P.; Kirby, B. J.; Miller, C. W.; Berger, A.
Ferromagnetic alloy materials with designed dopant composition depth profiles provide an efficient route for the control of magnetism at the nanometer length-scale. In this regard, cobalt-chromium and cobalt-ruthenium alloys constitute powerful model systems given that they exhibit easy to tune magnetic properties such as saturation magnetization MS and Curie temperature TC while preserving their crystalline structure in a wide composition range. In order to demonstrate this materials design potential, we have grown a series of graded Co(1-x)Cr(x) and Co(1-w)Ru(w) (10-10) epitaxial thin films, with x and w following predefined doping profiles. Structural analysis measurements verify the epitaxial nature and crystallographic quality of our entire sample sets, which were designed to exhibit in-plane c-axis orientation and thus an in-plane easy magnetic axis to suppress magnetostatic domain generation. Temperature and field-dependent magnetic depth profiles have been measured by means of polarized neutron reflectometry. In both investigated structures, TC and MS are found to vary as a function of depth in accordance with the predefined compositional depth profiles. Our Co(1-w)Ru(w) sample structures, which exhibit very steep material gradients, allow the determination of the localization limit for compositionally graded material, which we find to be of the order of 1 nm. The Co(1-x)Cr(x) systems show the expected U-shaped TC and MS depth profiles, for which these specific samples were designed. The corresponding temperature dependent magnetization profile is then utilized to control the coupling along the film depth, which even allows for a sharp onset of decoupling of top and bottom sample parts at elevated temperatures.
Keywords: ferromagnetic graded materials

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Permalink: https://www.hzdr.de/publications/Publ-26481
Publ.-Id: 26481


Opportunities & Limits of the Circular Economy

Reuter, M. A.
Metallurgy is a key enabler of a circular economy, its digitalization is the metallurgical Internet of Things (m-IoT). In short: Metallurgy is at the heart of a circular economy, as metals all have strong intrinsic recycling potentials. Process metallurgy, as a key enabler for a circular economy, will help much to deliver its goals. The first-principles models of process engineering help quantify the resource efficiency of the circular economy system, connecting all stakeholders via digitalization.
Keywords: circular economy
  • Invited lecture (Conferences)
    Strategic Materials for a Low-Carbon Future: From Scarcity to Availability / Resource Availability Conference, 02.-03.11.2017, Oxford, United Kingdom

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Permalink: https://www.hzdr.de/publications/Publ-26480
Publ.-Id: 26480


Construction and validation of a long-channel membrane test cell for representative monitoring of performance and characterization of fouling over the length of spiral-wound membrane modules

Siebdrath, N.; Ding, W.; Pietsch, E.; Kruithof, J.; Uhl, W.; Vrouwenvelder, J.
A long-channel membrane test cell (LCMTC) with the same length as full-scale elements was developed to simulate performance and fouling in nanofiltration and reverse osmosis spiral-wound membrane modules (SWMs). The transparent LCMTC enabled simultaneous monitoring of SWM performance indicators: feed channel pressure drop, permeate flux and salt passage. Both permeate flux and salt passage were monitored over five sections of the test cell and were related to the amount and composition of the accumulated foulant in these five sections, illustrating the unique features of the test cell. Validation experiments at various feed pressures showed the same flow profile and the same hydraulic behaviour as SWMs used in practice, confirming the representativeness and suitability of the test cell to study SWM operation and fouling. The importance to apply feed spacers matching the flow channel height in test cell systems was demonstrated. Biofouling studies showed that the dosage of a biodegradable substrate to the feed of the LCMTC accelerated the gradual decrease of membrane performance and the accumulation of biomass on the spacer and membrane sheets. The strongest permeate flux decline and the largest amount of accumulated biomass was found in the first 18 cm of the test cell. The LCMTC showed to be suitable to study the impact of biofilm development and biofouling control strategies under representative conditions for full-scale membrane elements.
Keywords: Feed spacer; RO spiral-wound module; NF; Permeate production; Membrane performance; Biofouling

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Permalink: https://www.hzdr.de/publications/Publ-26479
Publ.-Id: 26479


Engineering of high-temperature ferromagnetic Si1–xMnx (x ≈ 0.5) alloyed films by pulsed laser deposition: Effect of laser fluence

Pandey, P.; Drovosekov, A. B.; Wang, M.; Xu, C.; Nikolaev, S. N.; Chernoglazov, K. Y.; Savitsky, A. O.; Kreines, N. M.; Maslakov, K. I.; Cherebilo, E. A.; Mikhalevsky, V. A.; Novodvorskii, O. A.; Tugushev, V. V.; Rylkov, V. V.; Helm, M.; Zhou, S.
Thin films of Si1xMnx were deposited on Al2O3 substrate using pulsed laser deposition(PLD)technique employing time-of-flight separation of the ejected particles with different laser fluence (E = 3.8–7.6 J/cm2). Magnetic properties of these films reveal that the variation in the laser fluence has engineered several magnetic phases in Si1xMnx films: high temperature (HT) ferromagnetic (FM) phase Si1xMnx(x = 0.51–0.52) with uniformly distributed Si vacancies, and the low-temperature (LT) FM phases MnSi and Mn4Si7 with Curie temperature ≤ 40 K. At small fluence, the mesoscopic size MnSi and Mn4Si7 crystallites are formed in the upper layer of Si1xMnx films with Si excess (x ≈ 0.4–0.5), yielding to inhomogeneous magnetic phase distribution along the film growth direction, while the high and optimal fluence has resulted in uniform distribution of the HT FM phase during the film growth. The XPS, magnetotransport and ferromagnetic resonance (FMR) measurements confirm the presence of several FM phases in the samples and the amplifying role of LT FM for films grown at E ≤4.4 J/cm2.
Keywords: Si-Mn alloys High-temperature ferromagnetism Magnetic properties Ferromagnetic resonance

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Permalink: https://www.hzdr.de/publications/Publ-26478
Publ.-Id: 26478


Modeling of Reactive Mass-Transfer in Bubbly Flows

Rzehak, R.; Krauß, M.
CFD simulations of dispersed bubbly flow on the scale of technical equipment are feasible within the Eulerian two-fluid framework of interpenetrating continua. However, accurate numerical predictions rely on suitable closure models. Concerning the fluid dynamics of bubbly flows a certain degree of predictive capability has been reached recently. However, concerning mass transfer both with and without an accompanying chemical reaction only few studies have been performed to date.
The present contribution focusses on the so-called enhancement factor which describes the effect of a chemical reaction on the mass transfer. Different models available from the literature are compared. The reactive absorption of CO2 in aqueous NaOH is considered as an example. Simulations are compared with a set of experimental data reported by Darmana et al. [Chemical Engineering Science 62 (2007), 2556 - 2575]. Using an adequate model for the enhancement factor and taking into account the complete reaction network, an improved match with the data is obtained. Experimental conditions are suggested, for which further aspects of the system behavior become manifest.
Keywords: mass transfer, chemical reaction, chemisorption, enhancement factor, dispersed gas-liquid multiphase flow, Euler-Euler two-fluid model, CFD simulation
  • Lecture (Conference)
    Jahrestreffen der ProcessNet-Fachgruppen Computational Fluid Dynamics, Mischvorgänge, 16.-17.03.2017, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26477
Publ.-Id: 26477


Euler-Euler Modeling of Reactive Bubbly Flows

Rzehak, R.; Krauß, M.
CFD simulations of dispersed bubbly flow on the scale of technical equipment are feasible within the Eulerian two-fluid framework of interpenetrating continua. However, accurate numerical predictions rely on suitable closure models. To achieve predictive capability, all details of the closure models have to be fixed in advance without reference to any measured data.
Concerning the fluid dynamics of bubbly flows a baseline model has recently been proposed to this end and shown to work for a range of different applications in a unified manner [1,2]. This provides a reliable background which is well suited to add more complex physics.
Concerning mass transfer in bubbly flows both with and without an accompanying chemical reaction only few studies have been performed to date [e.g. 3 and Refs. therein]. For the mass transfer coefficient, a variety of entirely different closures have been applied in rather similar situations. To facilitate predictive applications, a standard model which is validated for a broad range of conditions yet has to be developed. The effect of a chemical reaction on the mass transfer is described by an enhancement factor which depends on the type of the reaction. As an example for which some measured data are available for comparison [4], the absorption of CO2 in NaOH is considered.

[1] Rzehak, R., Ziegenhein, T., Kriebitzsch, S., Krepper, E., and Lucas, D. (2017), Unified modeling of bubbly flows in pipes, bubble columns, and airlift columns, Chem. Eng. Sci. 157, 147-158.
[2] Rzehak, R., Krauß, M., Kovats, P., and Zähringer, K. (2017), Fluid dynamics in a bubble column: New experiments and simulations, Int. J. Multiphase Flow 89, 299-312.
[3] Rzehak, R., and Krepper, E. (2016), Euler-Euler simulation of mass-transfer in bubbly flows, Chem. Eng. Sci. 155, 459-468.
[4] Darmana, D., Henket, R., Deen, N. and Kuipers, J. (2007), Detailed modelling of hydrodynamics, mass transfer and chemical reactions in a bubble column using a discrete bubble model, Chem. Eng. Sci. 62, 2556–2575.
Keywords: mass transfer, chemical reaction, chemisorption, enhancement factor, dispersed gas-liquid multiphase flow, Euler-Euler two-fluid model, CFD simulation
  • Lecture (Conference)
    13th International Conference on Gas–Liquid and Gas–Liquid–Solid Reactor Engineering (GLS-13), 20.-23.08.2017, Brüssel, Belgien

Permalink: https://www.hzdr.de/publications/Publ-26476
Publ.-Id: 26476


Durchführung Von Euler-Euler Simulationen

Fleck, S.
Es werden Strömungssimulationen für verschieden Testfälle an Blasensäulen mit Hilfe des am HZDR entwickelten Baseline- Modells der Hydrodynamik von Blasenströmungen erstellt. Diese Simulationen werden im Anschluss ausgewertet und anhand von experimentellen Daten validiert. im Anschluss daran sind ggf etwaige Modellerweiterungen zu beachten und zu implementieren. Diese werden ausgewertet und mit den vorangegangenen Ergebnissen verglichen. Das verwendete Smulationsprogramm ist Ansys CFX.
Keywords: Strömungsmechnaik, disperse gas-flüssig Mehrphasenströmungen, Euler-Euler zwei-Fluid-Modell, CFD Simulation, Modellvalidierung, Blasensäulen
  • Study thesis
    TU Dresden, 2018
    Mentor: Prof. Dr. habil. Rüdiger Lange

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Permalink: https://www.hzdr.de/publications/Publ-26475
Publ.-Id: 26475


Guest Editorial Special Issue on Sensors for Process Imaging

Bieberle, A.; Tan, C.; Soleimani, M.; Silva, M. J. D.; (Editors)
Sustainable industrial production requires the use of advanced sensors and controls. In many industrial activities, the sensing and monitoring of processes provides valuable information for controlling and decision-making strategies as well as supporting the understanding and modeling of the phenomena involved. Since safety and efficiency requirements are continuously growing, the quality of information is becoming more and more important. A current trend to accomplish such requirements is the use of imaging sensors and systems generating and processing multidimensional data to extract key information from the processes. Further work is required to ensure that these imaging technologies are actually providing information that can be easily adapted and used in process control. This requires a holistic look at these sensing methods and data analysis.
Keywords: Special issues and sections Tomography Sensor phenomena and characterization Mechanical sensors Magnetic sensors Optoelectronic and photonic sensors Sensor systems and applications

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Permalink: https://www.hzdr.de/publications/Publ-26474
Publ.-Id: 26474


Development of innovative techniques for flow measurement in liquid sodium and lead-bismuth eutectic (LBE)

Eckert, S.; Wondrak, T.; Franke, S.; Krauter, N.; Ratajczak, M.; Stefani, F.; Timmel, K.
In this talk a short overview about recent developments of measurement techniques for liquid metal with special focus on liquid metal cooled nuclear reactors is given.
  • Lecture (Conference)
    2nd Sino-German Symposium on Fundamentals of Advanced Nuclear Savety Technology (SG-FANS), 12.-15.09.2017, Karlsruhe, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26473
Publ.-Id: 26473


Measuring techniques for experimental investigations and monitoring of liquid metal flows

Wondrak, T.
In this talk a short overview about different measurement techniques for liquid metals is given with a special focus on the application of liquid metal cooled nuclear reactors. This includes inductive methods, like the phase shift sensor and the and the contactless inductive flow tomography, as well as ultrasound techniques, like ultrasound Doppler velocimetry and the ultrasound transit time technique.
Keywords: liquid metal, flow measurement, inductive methods, ultrasound techniques
  • Invited lecture (Conferences)
    Heavy metal summer school, 12.-16.06.2017, Mol, Belgien

Permalink: https://www.hzdr.de/publications/Publ-26472
Publ.-Id: 26472


Numerische Untersuchungen zur Hydrodynamik und zum Stofftransport in Blasensäulen zur Validierung des Baseline-Modells

Kappelt, C.
Die Anwendung von Computational Fluid Dynamics (CFD)-Methoden hat inzwischen einen hohen Entwicklungsstand erreicht, so dass sie für viele verschiedene Strömungsprobleme eingesetzt werden.
In der Industrie findet die numerische Berechnung zum Beispiel Anwendung bei der Prozessoptimierung oder beim Scale-up. Im groÿtechnischen Maÿstab sind Zwei-Phasen-Simulationen mit Hilfe der Euler-Euler Beschreibung möglich.
Für die Simulation von Blasensäulen wird am Helmholtz-Zentrum Dresden-Rossendorf ein geeignetes Modell basierend auf dem Euler-Euler-Ansatz zur Schlieÿung von Hydrodynamik und Stofftransport entwickelt. Das Ziel dabei ist, dass das Modell ein breites Anwendungsgebiet abdeckt und für die verschiedenen Fälle validiert ist. Für die Validierung werden Simulationsrechnungen durchgeführt und mit experimentellen Daten verglichen. Die vorliegende Masterarbeit soll einen Teil zur Validierung des entwickelten Modells beitragen. Die Arbeit befasst sich mit der Absorption von Sauerstoff in Wasser in einer Blasensäule.
Keywords: Stofftransport, disperse gas-flüssig Mehrphasenströmungen, Euler-Euler zwei-Fluid-Modell, CFD Simulation, Modellvalidierung
  • Master thesis
    Hochschule Anhalt, Köthen, 2017
    Mentor: Prof. Dr. Stefan Wollny

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Permalink: https://www.hzdr.de/publications/Publ-26471
Publ.-Id: 26471


Recent developments on inductive measurement techniques for liquid metals

Wondrak, T.
There is a growing interest in determining the flow properties of metal or semiconductor melts, such as flow rate, flow structure and gas distribution. Typical applications are melt refining, continuous steel casting, silicon crystal growth or cooling of the receiver of a concentrated solar thermal power plant. However, the opaqueness prevents the use of well established optical methods. Additionally, the high temperatures (e. g. 1500°C for liquid steel or liquid silicon) and the corrosiveness of those fluids demand for contactless measurement techniques. By exploiting the high electrical conductivity of those melts inductive methods can be used. In this talk several inductive measurement techniques will be presented including transient eddy current flow meter, contactless inductive flow tomography and mutual inductance tomography. Additionally, a short overview about ultrasound techniques will be given which can be used to verify the inductive methods.
Keywords: liquid metal, inductive sensors, flow measurement
  • Invited lecture (Conferences)
    Guest colloquium of the research training group Lorentz force velocimetry and Lorentz force eddy current testing, 19.12.2017, Ilmenau, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26470
Publ.-Id: 26470


Functionalized DNA Origami Nanostructures for Molecular Electronics

Bayrak, T.; Ye, J.; Oktem, G.; Teschome, B.; Kiriy, A.; Seidel, R.; Erbe, A.
The DNA origami method provides a programmable bottom-up approach for creating nanostructures of any desired shape, which can be used as scaffolds for nanoelectronics and nanophotonics device fabrications. This technique enables the precise positioning of metallic and semiconducting nanoparticles along the DNA nanostructures. In this study, two nanostructures i.e. DNA origami nanotube and DNA origami molds are used for the fabrication of nanoelectronic devices. To this end, the DNA origami nanotubes are modified to assemble 14 gold nanoparticles (AuNPs) along with them. Then electroless gold deposition is used to selectively grow the AuNPs and create eventually continues nanowires. Similarly, AuNPs are also grown within the DNA origami molds. In order to investigate the transport properties of the so-fabricated two nanostructures, a method is developed using electron beam lithography. Additionally, the assembly of heterogeneous nanostructures, i.e. AuNPs and semiconductor quantum dots (QDs), on a single DNA origami nanotube is demonstrated and further metalized, thus representing a first step toward the future fabrication of DNA origami-templated quantum dot transistors.
  • Lecture (Conference)
    IHRS Nanonet Annual Workshop, 16.-18.08.2017, Klingenberg, Germany

Permalink: https://www.hzdr.de/publications/Publ-26469
Publ.-Id: 26469


Functionalized DNA Origami Nanostructures for Molecular Electronics

Bayrak, T.; Teschome, B.; Schonherr, T.; Erbe, A.
The DNA origami method provides a programmable bottom-up approach for creating nanostructures of any desired shape, which can be used as scaffolds for nanoelectronics and nanophotonics device fabrications. This technique enables the precise positioning of metallic and semiconducting nanoparticles along the DNA nanostructures. In this study, two nanostructures i.e. DNA origami nanotube and DNA origami molds are used for the fabrication of nanoelectronic devices. To this end, the DNA origami nanotubes are modified to assemble 14 gold nanoparticles (AuNPs) along with them. Then electroless gold deposition is used to selectively grow the AuNPs and create eventually continues nanowires. Similarly, AuNPs are also grown within the DNA origami molds.6 In order to investigate the transport properties of the so-fabricated two nanostructures, a method is developed using electron beam lithography. Additionally, the assembly of heterogeneous nanostructures, i.e. AuNPs and semiconductor quantum dots (QDs), on a single DNA origami nanotube is demonstrated and further metalized, thus representing a first step toward the future fabrication of DNA origami-templated quantum dot transistors.
  • Poster
    Future Trends in DNA based Nanotechnology, 29.05.-02.06.2017, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-26468
Publ.-Id: 26468


Functionalized DNA Origami Mold Nanostructures for Molecular Electronics

Bayrak, T.; Ye, J.; Helmi, S.; Teschome, B.; Schonherr, T.; Seidel, R.; Erbe, A.
The DNA origami method provides a programmable bottom-up approach for creating nanostructures of any desired shape, which can be used as scaffolds for nanoelectronics and nanophotonics device fabrications. This technique enables the precise positioning of metallic and semiconducting nanoparticles along the DNA nanostructures. In this study, DNA origami molds are used for the fabrication of nanoelectronic devices. To this end, electroless gold deposition is used to selectively grow the AuNPs and create eventually continues nanowires within the DNA origami molds. In order to investigate the transport properties of the so-fabricated nanostructures, a method is developed using electron beam lithography and 1D DNA origami-based metallic wires were electrically characterized from room temperature to 4.2K. Additionally, the assembly of heterogeneous nanostructures, i.e. AuNPs and semiconductor quantum dots (QDs), on a single DNA origami structure is demonstrated and further metalized, thus representing a first step toward the future fabrication of DNA origami-templated quantum dot transistors.
Keywords: DNA Origami, Charge Transport, Low Temperature Electrical Characterization
  • Lecture (Conference)
    2017 MRS Fall Meeting, 26.11.-01.12.2017, Boston, United States of America

Permalink: https://www.hzdr.de/publications/Publ-26467
Publ.-Id: 26467


Single-shot high dynamic range pulse contrast measurements at the Draco laser system in combination with plasma mirrors

Bock, S.; Oksenhendler, T.; Pueschel, T.; Helbig, U.; Gebhardt, R.; Moeller, D.; Metzkes, J.; Obst, L.; Schlenvoigt, H. P.; Pausch, R.; Lötfering, J. J.; Zeil, K.; Irman, A.; Bizouard, P.; Albert, O.; Schramm, U.
We report on high pulse contrast operation modes of the Draco laser with focus on the on-shot characterization of the few-ps-contrast by novel techniques based on tilted beam self-referenced spectral interferometry with 108 dynamic range.
  • Lecture (Conference)
    Ultrafast Optics Conference XI, 08.-13.10.2017, Jackson Hole, WY, United States of America

Permalink: https://www.hzdr.de/publications/Publ-26465
Publ.-Id: 26465


First demonstration of multi-MeV proton acceleration from a cryogenic hydrogen ribbon target

Kraft, S.; Obst, L.; Metzkes-Ng, J.; Schlenvoigt, H.-P.; Zeil, K.; Michaux, S.; Chatain, D.; Perin, J.-P.; Chen, S. N.; Fuchs, J.; Gauthier, M.; Cowan, T. E.; Schramm, U.
We show efficient laser driven proton acceleration up to 14\,MeV from a 50\,$\mu$m thick cryogenic hydrogen ribbon. Pulses of the short pulse laser ELFIE at LULI with a pulse length of $\approx 350$\,fs at an energy of 8\,J per pulse are directed onto the target. The results are compared to proton spectra from metal and plastic foils with different thicknesses and show a similar good performance both in maximum energy as well as in proton number. Thus, this target type is a promising candidate for experiments with high repetition rate laser systems.

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Permalink: https://www.hzdr.de/publications/Publ-26464
Publ.-Id: 26464


On-shot characterization of single plasma mirror temporal contrast improvement

Obst, L.ORC; Metzkes-Ng, J.; Bock, S.; Cochran, G. E.ORC; Cowan, T. E.ORC; Oksenhendler, T.; Poole, P. L.ORC; Prencipe, I.; Rehwald, M.ORC; Rödel, C.; Schlenvoigt, H.-P.ORC; Schramm, U.ORC; Schumacher, D. W.ORC; Ziegler, T.; Zeil, K.ORC
We report on the setup and commissioning of a compact recollimating single plasma mirror (PM) for temporal contrast enhancement at the Draco 150 TW laser during laser-proton acceleration experiments. The temporal contrast with and without PM is characterized single-shot by means of self-referenced spectral interferometry with extended time excursion at unprecedented dynamic and temporal range. This allows for the first single-shot measurement of the PM trigger point, which is interesting for the quantitative investigation of the complex pre-plasma formation process at the surface of the target used for proton acceleration. As a demonstration of high contrast laser plasma interaction we present proton acceleration results with ultra-thin liquid crystal targets of similar to 1 mu m down to 10 nm thickness. Focus scans of different target thicknesses show that highest proton energies are reached for the thinnest targets at best focus. This indicates that the contrast enhancement is effective such that the acceleration process is not limited by target pre-expansion induced by laser light preceding the main laser pulse.
Keywords: laser plasma interaction, plasma mirrors, laser proton acceleration

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Permalink: https://www.hzdr.de/publications/Publ-26463
Publ.-Id: 26463


MHz repetition rate Yb:YAG disk laser-amplifier for transform limited pulses, tunable between 10 ps and 100 ps

Siebold, M.; Loeser, M.; Bernert, C.; Albach, D.; Schramm, U.
We present an Yb:YAG laser system for transform limited pulses with variable tuning range between 10ps and 100ps. The spectral bandwidth of fs pulses is narrowed by an intra-cavity grating monochromator in a regenerative amplifier.

Permalink: https://www.hzdr.de/publications/Publ-26461
Publ.-Id: 26461


Optical probing of high intensity laser interaction with micron-sized cryogenic hydrogen jets

Ziegler, T.ORC; Rehwald, M.ORC; Obst, L.ORC; Bernert, C.; Brack, F.; Curry, C. B.ORC; Gauthier, M.ORC; Glenzer, S. H.; Göde, S.; Kazak, L.; Kraft, S. D.ORC; Kuntzsch, M.; Loeser, M.; Metzkes-Ng, J.ORC; Rödel, C.; Schlenvoigt, H.-P.ORC; Schramm, U.ORC; Siebold, M.ORC; Tiggesbäumker, J.; Wolter, S.; Zeil, K.
Probing the rapid dynamics of plasma evolution in laser-driven plasma interactions provides deeper understanding of experiments in the context of laser-driven ion acceleration and facilitates the interplay with complementing numerical investigations. Besides the microscopic scales involved, strong plasma (self-)emission, predominantly around the harmonics of the driver laser, often complicates the data analysis. We present the concept and the implementation of a stand-alone probe laser system that is temporally synchronized to the driver laser, providing probing wavelengths beyond the harmonics of the driver laser. The capability of this system is shown during a full-scale laser proton acceleration experiment using renewable cryogenic hydrogen jet targets. For further improvements, we studied the influence of probe color, observation angle of the probe and temporal contrast of the driver laser on the probe image quality.
Keywords: plasma diagnostic probes, laser-produced plasmas, plasma diagnostic, particle accelerator ion sources

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Permalink: https://www.hzdr.de/publications/Publ-26460
Publ.-Id: 26460


Laser-driven ion acceleration via TNSA in the relativistic transparency regime

Poole, P.ORC; Obst, L.ORC; Cochran, G.ORC; Metzkes, J.; Schlenvoigt, H.ORC; Prencipe, I.; Kluge, T.ORC; Cowan, T. E.ORC; Schramm, U.ORC; Schumacher, D.ORC; Zeil, K.
We present an experimental study investigating laser-driven proton acceleration via Target Normal Sheath Acceleration (TNSA) over a target thickness range spanning the typical TNSA-dominant region (~1 μm) down to below the relativistic laser-transparency regime (< 40 nm), enabled by freely adjustable target film thickness using liquid crystals along with high contrast (via plasma mirror) laser interaction (~ 2.65 J, 30 fs, I > 1 × 10^21 W/cm^2). Thickness dependent maximum proton energies scale well with TNSA models down to the thinnest targets, while those under ~ 40 nm indicate transparency-enhanced TNSA via differences in light transmission, maximum proton energy, and proton beam spatial profile. Oblique laser incidence (45°) allowed additional diagnostics to be fielded to diagnose the interaction quality: a suite of ion energy and spatial distribution diagnostics in the laser axis and both front and rear target normal directions as well as reflected and transmitted light measurements on-shot collectively verify the dominant acceleration mechanism as TNSA from high contrast interaction, even for ultra-thin targets. Additionally, 3D particle-in-cell simulations support the experimental observations of target-normal-directed proton acceleration from ultra-thin films.
Keywords: laser proton acceleration, laser plasma interaction
  • Open Access Logo New Journal of Physics 20(2018), 13019
    DOI: 10.1088/1367-2630/aa9d47
  • Poster
    European Physical Society Division of Plasma Physics Conference 2018, 02.07.2018, Prag, Tschechische Republik

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Permalink: https://www.hzdr.de/publications/Publ-26459
Publ.-Id: 26459


Laser proton acceleration from liquid crystal films of different thicknesses with ultra-high laser contrast

Obst, L.ORC; Poole, P.ORC; Metzkes, M.; Kluge, T.ORC; Cochran, G.ORC; Schlenvoigt, H.ORC; Kraft, S. D.; Prencipe, I.; Rehwald, M.ORC; Schumacher, D.ORC; Schramm, U.ORC; Zeil, K.
We present an experimental study which shows a possible pathway towards the robust and reliable generation of applicable, energetic, high-quality laser-driven proton beams at high repetition rates. This is enabled through the combination of ultra-high contrast laser pulses and liquid crystal film targets, which can be generated and characterized in situ within a thickness range from 10 μm to 10 nm at low cost.
Pulses from our in-house Ti:Sa laser (~3 J, 30 fs, I~10^20 W/cm^2) incident obliquely on target in order to distinguish between ion acceleration mechanisms. Increasing target normal proton energy cut-offs are observed for decreasing thicknesses, with > 25 MeV protons recorded for ultra-thin (< 50 nm) targets. The results are in agreement with the dominance of target normal sheath acceleration (TNSA) down to ultra-thin target thicknesses, in line with the observed robustness of the acceleration performance.
Keywords: laser plasma interaction, laser proton acceleration
  • Poster
    3. Annual MT Meeting, 31.01.-01.02.2017, Darmstadt, Deutschland
  • Lecture (Conference)
    SPIE Optics & Optoelectronics 2017, 24.-28.4.2017, Prag, Tschechische Republik

Permalink: https://www.hzdr.de/publications/Publ-26458
Publ.-Id: 26458


Metabolism-dependent bioaccumulation of uranium by Rhodosporidium toruloides isolated from the flooding water of a former uranium mine

Gerber, U.; Hübner, R.; Rossberg, A.; Krawczyk-Bärsch, E.; Merroun, M. L.
Remediation of former uranium mining sites represents one of the biggest challenges worldwide that have to be solved in this century. The former uranium mine Königstein (Germany) displays one of these sites and is currently remediated by controlled flooding of the underground. The flooding water is cleaned up by a conventional chemical waste water treatment plant. During the last years, the search of alternative strategies involving environmentally sustainable treatments has started. Bioremediation, the use of microorganisms to clean up polluted sites in the environment, is considered one of the best alternative. By means of culture-dependent methods, we isolated an indigenous yeast strain, KS5 (Rhodosporidium toruloides), directly from the flooding water and investigated its interactions with uranium(VI). Our results highlight distinct adaptive mechanisms towards high uranium concentrations on the one hand, and complex interaction mechanisms on the other. The cells of the strain KS5 exhibit high uranium tolerance being able to grow up to 5 mM, and also high ability to accumulate this radionuclide (350 mg uranium/g dry biomass in 48 hours). The removal of uranium by KS5 displays a temperature- and cell viability-dependent process. By STEM investigations we observed that uranium was removed by two mechanisms, inactive biosorption and active bioaccumulation. EXAFS analysis revealed that the molecular speciation of uranium associated with the cells is similar to that of meta-autunite-like minerals. The present study highlights the potential of KS5 as a representative of indigenous species which might play a key role in bioremediation of uranium-contaminated sites.
Keywords: Bioremediation, Uranium, Rhodosporidium toruloides, Bioaccumulation, Biosorption

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Permalink: https://www.hzdr.de/publications/Publ-26457
Publ.-Id: 26457


Making spectral shape measurements in inverse Compton scattering a tool for advanced diagnostic applications

Krämer, J. M.ORC; Jochmann, A.; Budde, M.; Bussmann, M.; Couperus, J. P.; Cowan, T. E.; Debus, A.; Köhler, A.; Kuntzsch, M.; Laso García, A.; Lehnert, U.; Michel, P.; Pausch, R.; Zarini, O.; Schramm, U.; Irman, A.
Interaction of relativistic electron beams with high power lasers can both serve as a secondary light source and as a novel diagnostic tool for various beam parameters. For both applications, it is important to understand the dynamics of the inverse Compton scattering mechanism and the dependence of the scattered light’s spectral properties on the interacting laser and electron beam parameters. Measurements are easily misinterpreted due to the complex interplay of the interaction parameters. Here we report the potential of inverse Compton scattering as an advanced diagnostic tool by investigating two of the most influential interaction parameters, namely the laser intensity and the electron beam emittance. Established scaling laws for the spectral bandwidth and redshift of the mean scattered photon energy are refined. This allows for a quantitatively well matching prediction of the spectral shape. Driving the interaction to a nonlinear regime, we spectrally resolve the rise of higher harmonic radiation with increasing laser intensity. Unprecedented agreement with 3D radiation simulations is found, showing the good control and characterization of the interaction. The findings advance the interpretation of inverse Compton scattering measurements into a diagnostic tool for electron beams from laser plasma acceleration.

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Permalink: https://www.hzdr.de/publications/Publ-26453
Publ.-Id: 26453


Infrared nanoscopy down to liquid helium temperatures

Lang, D.; Döring, J.; Nörenberg, T.; Butykai, Á.; Kézsmárki, I.; Schneider, H.; Winnerl, S.; Kehr, S. C.; Eng, L. M.; Helm, M.
We introduce a scattering-type scanning near-field infrared microscope (s-SNIM) for the local scale near-field sample analysis and spectroscopy from room (RT) down to liquid helium (LHe) temperatures. The extension of s-SNIM down to T=5K is in particular crucial for low-temperature phase transitions, e.g. for the examination of superconductors, as well as low energy excitations. The LT s-SNIM performance is tested with CO2-IR excitation at T=7K using a bare Au reference and a structured Si/SiO2-sample. Furthermore, we quantify the impact of local laser heating under the s-SNIM tip apex by monitoring the light-induced ferroelectric-to-paraelectric phase transition of the skyrmion-hosting multiferroic material GaV4S8 at T=42K. We apply LT s-SNIM to study the spectral response of GaV4S8 and its lateral domain structure in the ferroelectric phase by the mid-IR to THz free-electron laser-light source FELBE at the Helmholtz-Zentrum Dresden-Rossendorf, Germany. Notably, our s-SNIM is based on a non-contact atomic force microscope (AFM), and thus can be complemented in-situ by various other AFM techniques, such as topography profiling, piezo-response force microscopy (PFM) and/or Kelvin-probe force microscopy (KPFM). The combination of these methods support the comprehensive study of the mutual interplay in the topographic, electronic and optical properties of surfaces from room temperature down to 5K.
Keywords: near-field microscopy, free-electron laser, mid-infrared, low temperature, phase transition, scanning force micropscopy

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Permalink: https://www.hzdr.de/publications/Publ-26447
Publ.-Id: 26447


Development of an efficient high-current ion source for Accelerator Mass Spectrometry

Bregolin, F. L.; Hofsäss, H.; Rugel, G.; Akhmadaliev, S.; Merchel, S.; Feige, J.
A new high-current negative ion source for Accelerator Mass Spectrometry (AMS) is being built to quantify the ratios of long-lived cosmogenic radionuclides in micrometeorites, which are of great astrophysical interest. Measuring these extremely small ratios is at the technological limits of present AMS systems. The new source is designed specifically to provide a higher AMS detection sensitivity by having an optimal ion-optics design, incorporating new concepts for the construction and operation of the Cs ionizer, optimized Cs ion beam currents and Cs vapor transport. The operation with higher cathode, extraction and pre-acceleration voltages than usual is possible. Moreover, its design is modular providing ease of access and simplifying maintenance while having better mechanical stability at the same time. Several operational parameters can be controlled and measured during operation to achieve a higher ion source performance. Detailed ion-optics simulations of the ion source are compared with test measurements, and the design optimized based on its results. The authors would like to thank the Federal Ministry of Education and Research of Germany for its financial support (project 05K2016), and the HZDR’s Ion Beam Center for its essential contribution to the realization of this project.
Keywords: AMS, ion source, micrometeorites
  • Poster
    DPG Frühjahrstagung des Arbeitskreises Atome, Moleküle, Quantenoptik und Plasmen (AMOP), 04.-09.03.2018, Erlangen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26446
Publ.-Id: 26446


Nachweis von Beryllium-10 aus exotischen Zerfällen mit Hilfe von Beschleunigermassenspektrometrie (AMS)

Forstner, O.; Merchel, S.; Lachner, J.; IS541 Kollaboration
Der Ein-Neutronen Halokern 11Be geht über einen Beta-Minus-Zerfall in 11B über (t1/2 = 13,76 s). In seltenen Fällen jedoch erfolgt über eine anschließende Emission eines Protons die Umwandlung zu 10Be. Ziel dieser Studie ist es, das nach theoretischen Vorhersagen bei unter 10−7 liegende Verzweigungsverhältnis dieses raren Zerfallskanals zu messen. Mit Hilfe der Möglichkeiten der AMS zur Messung extrem niedriger Isotopenverhältnisse ist dies erstmalig experimentell gelungen und wurde zu 8,3(0,9) × 10−6 bestimmt [1].
Zur Bestimmung dieser Rate wurde an ISOLDE / CERN ein Strahl radioaktiver 11Be Ionen produziert und in Kupfer-Targets implantiert. Daraus wurde chemisch Beryllium extrahiert und mittels AMS das Verhältnis 10Be/9Be bestimmt sowie die Menge des implantierten 10Be berechnet. Aufgrund des niedrigen Verzweigungsverhältnisses und der daraus resultierenden niedrigen Zahl von entstehenden 10Be-Atomen ist eine möglichst hohe Effizienz und niedriger Untergrund im 9Be-Trägermaterial [2] essentiell. Für die Datenanalyse wurde besonderes Augenmerk auf die Methodik der Produktion gelegt, um mögliche systematische Fehler ausschließen zu können.
[1] K. Riisager, et al., Phys. Lett. B 732 (2014) 305
[2] S. Merchel, et al., Nucl. Instr. and Meth. B 266 (2008) 4291
Keywords: AMS, Protonenemission, Implantation
  • Invited lecture (Conferences)
    DPG Frühjahrstagung des Arbeitskreises Atome, Moleküle, Quantenoptik und Plasmen (AMOP), 04.-09.03.2018, Erlangen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26445
Publ.-Id: 26445


Ion irradiation effects on a magnetic Si/Ni/Si trilayer and lateral magnetic-nonmagnetic multistrip patterning by focused ion beam

Dev, B. N.; Banu, N.; Fassbender, J.; Grenzer, J.; Schell, N.; Bischoff, L.; Grötzschel, R.; McCord, J.
Fabrication of a multistrip magnetic/nonmagnetic structure in a thin sandwiched Ni layer [Si(5 nm)/Ni(15 nm)/Si] by a focused ion beam (FIB) irradiation has been attempted. A control experiment was initially performed by irradiation with a standard 30 keV Ga ion beam at various fluences. Analyses were carried out by Rutherford backscattering spectrometry, X-ray reflectivity, magnetooptical Kerr effect (MOKE) measurements and MOKE microscopy. With increasing ion fluence, the coercivity as well as Kerr rotation decreases. A threshold ion fluence has been identified, where ferromagnetism of the Ni layer is lost at room temperature and due to Si incorporation into the Ni layer, a Ni0.68Si0.32 alloy layer is formed. This fluence was used in FIB irradiation of parallel 50 nm wide stripes, leaving 1 mu m wide unirradiated stripes in between. MOKE microscopy on this FIB-patterned sample has revealed interacting magnetic domains across several stripes. Considering shape anisotropy effects, which would favour an alignment of magnetization parallel to the stripe axis, the opposite behaviour is observed. Magneto-elastic effects introducing a stress-induced anisotropy component oriented perpendicular to the stripe axis are the most plausible explanation for the observed behaviour.
Keywords: ion irradiation, ion beam analysis, magnetism

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Permalink: https://www.hzdr.de/publications/Publ-26444
Publ.-Id: 26444


Presentation "HIF Introduction", "Re-Mining @ HIF - Resources from mining dumps" and "Biotechnology@HIF" at the Indian Institute of Technology Delhi

Büttner, P.; Jain, R.
The presentation shows the Re-Mining activities at the Helmholtz Institute Freiberg for Resource Technology until the Year 2016. Examples of the Research and fields of interest for potential cooperation were presented as well. Also a overview of the HIF was given and the Biotechnology was introduced.
Keywords: 3D modelling, Altenberg, Automated mineralogy, Cassiterite, Erzgebirge, Geometallurgy, Mine waste, Mineral liberation analysis, MLA, Processing, Re-mining, Re-processing, Recycling, Remediation, Remining, Reprocessing, Spatial modelling, Tailing, Tailing storage facility, Tin, Tin recovery, TSF, Zero waste approach, Biotechnology, HIF, Bioleaching, Biomembrane, Bioflotation
  • Lecture (others)
    Meeting with the Biogroup from the Indian Institute of Technology Delhi (IIT), 05.06.2017, New Delhi, India

Permalink: https://www.hzdr.de/publications/Publ-26443
Publ.-Id: 26443


Exploring the resource potential of TSF‘s

Gutzmer, J.; Osbahr, I.; Leißner, T.; Satgé, L.; Unger, G.; Büttner, P.
The keynote presentation was given at the EIT Raw Materials Workshop “ReMining and Process Residues”
in Berlin, 18-19 January 2017. The presentation illustrates why and how Tailing Storage Facilities (TSF) are being under exploration today. The example of the Tiefenbachhalde Altenberg shows the approach of the Helmholtz Institute Freiberg for Resource Technology. A 3D-model of the relevant processing parameters was created, to give an estimation of the re-mining potential for valuable metals.
Keywords: 3D modelling, Altenberg, Automated mineralogy, Cassiterite, Erzgebirge, Geometallurgy, Mine waste, Mineral liberation analysis, MLA, Processing, Re-mining, Re-processing, Recycling, Remediation, Remining, Reprocessing, Spatial modelling, Tailing, Tailing storage facility, Tin, Tin recovery, TSF, Zero waste approach
  • Invited lecture (Conferences)
    Workshop “ReMining and Process Residues”, 18.-19.01.2017, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26442
Publ.-Id: 26442


Removal and recovery of uranium by waste digested activated sludge in fed-batch stirred tank reactor

Jain, R.; Peräniemi, S.; Jordan, N.; Vogel, M.; Weiss, S.; Foerstendorf, H.; Lakaniemi, A. M.
This study demonstrated the removal and recovery of uranium(VI) in a fed-batch stirred tank reactor (STR) using waste digested activated sludge (WDAS). The batch adsorption experiments showed that WDAS can adsorb 200 (± 9.0) mg of uranium per g of WDAS. The maximum adsorption of uranium was achieved even at an acidic initial pH of 2.7 which increased to pH of 4.0 in the equilibrium state. Desorption of uranium from WDAS was successfully demonstrated by releasing more than 95% uranium using both acidic (0.5 M HCl) and alkaline (1.0 M Na2CO3) eluents. Due to the fast kinetics of uranium adsorption onto WDAS, the fed-batch STR was successfully operated at hydraulic retention time of 15 minutes. Twelve consecutive uranium adsorption steps with average uranium adsorption efficiency of 91.5% required only two desorption steps to elute more than 95% of uranium from WDAS. Uranium was shown to interact predominantly with the phosphoryl and carboxyl groups of the WDAS, as revealed by in situ infrared spectroscopy and time-resolved laser-induced fluorescence spectroscopy. This study provided a proof-of-concept of the use of fed-batch STR process based on WDAS for the removal and recovery of uranium.
Keywords: Adsorption, desorption, STR, infrared spectroscopy, TRLFS, sludge

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Permalink: https://www.hzdr.de/publications/Publ-26441
Publ.-Id: 26441


Defining the recovery potential for residual ore minerals from flotation tailings based on automated mineralogy data

Büttner, P.; Osbahr, I.; Zimmermann, R.; Leißner, T.; Satge, L.; Gutzmer, J.
The extraction of valuable (ore) minerals from fine-grained flotation tailings is a commercially interesting but technologically challenging endeavor that needs to be supported by a full technical and economic feasibility study. A novel approach to such the technological assessment is introduced here. It is illustrated by the example of an historic tailing storage facility containing ca. 0.2 weight percent of Sn as cassiterite. Mineral processing test work identified flotation as a suitable technology route to recover the residual cassiterite. The viability of flotation was attributed to three material parameters, namely grade, liberation and grain size of cassiterite. These parameters were quantified for a set of ten exploration drill cores by chemical assay and mineral liberation analysis. For each of the three relevant parameters an optimum range was defined by a weighting function that was applied to the data set. The data was then geo-referenced and combined to construct a 3-D model illustrating a depreciated grade, i.e., the amount of tin (as cassiterite) that could realistically be recovered from the tailings storage facility.
Keywords: 3D modelling, Altenberg, Automated mineralogy, Cassiterite, Erzgebirge, Geometallurgy, Mine waste, Mineral liberation analysis, MLA, Processing, Re-mining, Re-processing, Recycling, Remediation, Remining, Reprocessing, Spatial modelling, Tailing, Tailing storage facility, Tin, Tin recovery, TSF, Zero waste approach
  • Contribution to proceedings
    Process Mineralogy '17, 20.-22.03.2017, Cape Town, South Africa
    Process Mineralogy '17 - conference proceedings
  • Lecture (Conference)
    Process Mineralogy '17, 20.-22.03.2017, Cape Town, South Africa

Permalink: https://www.hzdr.de/publications/Publ-26440
Publ.-Id: 26440


Recovery potential of flotation tailings assessed by spatial modelling of automated mineralogy data

Büttner, P.; Osbahr, I.; Zimmermann, R.; Leißner, T.; Satge, L.; Gutzmer, J.
The extraction of ore minerals from fine-grained flotation tailings is a commercially interesting but technologically challenging endeavor that needs to be supported by a full technical and economic feasibility study. A novel approach to such an assessment is introduced here. It is illustrated by the example of a historic tailing storage facility containing on average 0.2. wt% of Sn as cassiterite. Mineral processing test work identified flotation as a suitable technology route to recover this cassiterite. The viability of flotation was attributed to three material parameters, namely grade, liberation and particle size of cassiterite. These parameters were quantified for a set of ten exploration drill cores by chemical assay and mineral liberation analysis. For each of the three relevant parameters a suitable weighting function was defined that was applied to the entire data set. The data was then geo-referenced and combined to construct a 3D model illustrating a depreciated grade, i.e., the amount of cassiterite-bound tin that can realistically be recovered from the tailings. Results of the case study illustrate the importance of combining chemical grade data with quantitative mineralogical and microfabric information in any effort to objectively assess the residual value contained in industrial tailings or any other residue considered for re-processing.
Keywords: 3D modelling, Altenberg, Automated mineralogy, Cassiterite, Erzgebirge, Geometallurgy, Mine waste, Mineral liberation analysis, MLA, Processing, Re-mining, Re-processing, Recycling, Remediation, Remining, Reprocessing, Spatial modelling, Tailing, Tailing storage facility, Tin, Tin recovery, TSF, Zero waste approach

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Permalink: https://www.hzdr.de/publications/Publ-26439
Publ.-Id: 26439


Partial Isobutane Oxidation to tert-Butyl Hydroperoxide in a Micro Reactor - Comparison of DTBP and Aqueous TBHP as Initiator

Willms, T.; Kryk, H.; Hampel, U.
The oxidation of isobutane has been investigated for the first time in a micro reactor in a wide range of process conditions comparing the initiator of DTBP and TBHP as initiator on the reaction. DTBP as initiator led to nearly the double conversion, compared to the same con-centration of TBHP, but the selectivity of TBHP using TBHP as initiator was higher. Using aqueous TBHP, the conversions reached up to 6 % in case of supercritical conditions but stayed below 2 % in case of two phase flow experiments. With TBHP in decane as initiator, a conversion of about 18 % was reached, but nearly no TBHP was formed. It seems that the silicon layer of the micro reactor was not stable under such experimental conditions due to the formation of high local formic acid concentrations. In the present work, for the first time, a conversion level near to that of the industrial batch process has been reached in a micro reactor for the isobutane oxidation.
Keywords: isobutane oxidation, micro reactor, two phase flow, t-butyl hydroperoxide, t-butyl peroxide

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Permalink: https://www.hzdr.de/publications/Publ-26438
Publ.-Id: 26438


A comparative study of machine learning methods for time-To-event survival data for radiomics risk modelling

Leger, S.; Zwanenburg, A.; Pilz, K.; Lohaus, F.; Linge, A.; Zöphel, K.; Kotzerke, J.; Schreiber, A.; Tinhofer, I.; Budach, V.; Sak, A.; Stuschke, M.; Balermpas, P.; Rödel, C.; Ganswindt, U.; Belka, C.; Pigorsch, S.; Combs, S.; Mönnich, D.; Zips, D.; Krause, M.; Baumann, M.; Troost, E.; Löck, S.; Richter, C.
Radiomics applies machine learning algorithms to quantitative imaging data to characterise the tumour phenotype and predict clinical outcome. For the development of radiomics risk models, a variety of different algorithms is available and it is not clear which one gives optimal results. Therefore, we assessed the performance of 11 machine learning algorithms combined with 12 feature selection methods by the concordance index (C-Index), to predict loco-regional tumour control (LRC) and overall survival for patients with head and neck squamous cell carcinoma. The considered algorithms are able to deal with continuous time-to-event survival data. Feature selection and model building were performed on a multicentre cohort (213 patients) and validated using an independent cohort (80 patients). We found several combinations of machine learning algorithms and feature selection methods which achieve similar results, e.g., MSR-RF: C-Index = 0.71 and BT-COX: C-Index = 0.70 in combination with Spearman feature selection. Using the best performing models, patients were stratified into groups of low and high risk of recurrence. Significant differences in LRC were obtained between both groups on the validation cohort. Based on the presented analysis, we identified a subset of algorithms which should be considered in future radiomics studies to develop stable and clinically relevant predictive models for time-to-event endpoints.

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Permalink: https://www.hzdr.de/publications/Publ-26437
Publ.-Id: 26437


Screening and selection of technologically applicable microorganisms for recovery of rare earth elements from fluorescent powder

Hopfe, S.; Konsulke, S.; Barthen, R.; Lehmann, F.; Kutschke, S.; Pollmann, K.
Rare Earth Elements (REE) are essential elements in many new technology products. Nevertheless, recycling is poorly established and no environmentally friendly strategies are applied. Modern biotechnologies like bioleaching can contribute to overcome the current limitations. In this study, we tested different microorganisms to mobilize REE from used fluorescent phosphor (FP), as an exemplary REE containing waste product. Beneath, classical acidophilic microorganisms, various heterotrophic ones, producing organic acids or metal complexing metabolites, or having a high metal tolerance, were investigated. The three organic acids producing strains Komatogateibacter xylinus, Lactobacillus casei, and Yarrowia lipolytica leached larger amounts of REE. Besides the COOH-functionality, also other biotic processes contribute to metal leaching, as comparison with indirect leaching approaches showed. Preferably the red dye yttrium europium oxide (YOE) was leached from REE components of FP. The results provide the basis for the development of an environmentally friendly recycling process for REE from waste materials.
Keywords: Rare Earth Elements, Fluorescent phosphor, bioleaching, heterotrophic microorganisms, recycling

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Permalink: https://www.hzdr.de/publications/Publ-26436
Publ.-Id: 26436


Morphological stripe-bubble transition in remanent magnetic domain patterns of Co/Pt multilayer films and its dependence on Co thickness

Chesnel, K.; Westover, A. S.; Cardon, K. H.; Dodson, B.; Healey, M.; Newbold, B.; Hindman, L.; Montealegre, D.; Metzner, J.; Fallarino, L.; Böhm, B.; Schneider, T.; Samad, F.; Hellwig, O.
We report a phase transition in the topology of the magnetic domain pattern exhibited by ferromagnetic Co/Pt multilayer films at remanence. We found that the remanent magnetic domain pattern topology and density strongly depend on the magnetic history, in particular on the magnitude of the previously applied field. The magnetic pattern, which generally forms a maze of stripe domains, transforms into a bubble pattern and the domain density drastically increases when the magnitude of the previously applied field approaches a specific value, typically 70-90% of the saturation field value. We mapped out this topological phase transition as a function of the previously applied field magnitude as well as Co thickness. This led to the estimate of most favorable conditions to maximize magnetic domain density.
Keywords: Bubble domains in multilayer structures
  • Open Access Logo Physical Review B 98(2018), 224404

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Permalink: https://www.hzdr.de/publications/Publ-26435
Publ.-Id: 26435


Nanoscale Magnetic Localization in Exchange Strength Modulated Ferromagnets

Kirby, B. J.; Fallarino, L.; Riego, P.; Maranville, B. B.; Miller, C. W.; Berger, A.
Although ferromagnetism is in general a long-range collective phenomenon, it is possible to induce local spatial variations of magnetic properties in ferromagnetic materials. For example, systematic variation of the exchange coupling strength can be used to create systems that behave as if they are composed of virtually independent segments that exhibit “local” Curie temperatures. Such localization of thermodynamic behavior leads to boundaries between strongly and weakly magnetized regions that can be controllably moved within the material with temperature. The utility of this interesting functionality is largely dependent on the inherent spatial resolution of magnetic properties, specifically the distance over which the exchange strength and corresponding properties behave locally. To test the degree to which this type of localization can be realized in materials, we have fabricated epitaxial films of Co1−xRux alloy featuring a nanometer-scale triangular wavelike concentration depth profile. Continuous nanoscale modulation of the local Curie temperature was observed using polarized neutron reflectometry. These results are consistent with mean-field simulations of spin systems that encompass the possibility of delocalized exchange coupling and show that composition grading can be used to localize magnetic properties in films down to the nanometer level. Since this is demonstrated here for an itinerant metal, we assert that for virtually any modulated magnetic material system, collective effects can be suppressed to length scales smaller than about 3 nm, so that magnetic behavior overall can be well described in terms of local material properties.
Keywords: Graded ferromagnetic thin films

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Permalink: https://www.hzdr.de/publications/Publ-26434
Publ.-Id: 26434


The Production of Cu Nanoparticles on Large Area Graphene by Sputtering and in-Flight Sintering

Gokhan, U. C.; Acet, M.; Tekgul, A.; Farle, M.; Atakan, S.; Lindner, J.
We have developed a simple method to synthesize Cu nanoparticles on graphene, which is a composite that is currently investigated for use as biosensors. Firstly, large area graphene (2 x 2 cm(2)) was prepared by chemical vapor deposition on Cu foils and then transferred onto SiO2 substrates by a transfer process. The Cu nanoparticles were collected on graphene/SiO2 by magnetron sputtering. The presence of graphene was verified by optical microscopy and Raman spectroscopy. The structure of graphene decorated with Cu nanoparticles was determined by scanning and transmission electron microscopy. The results show that the Cu nanoparticles acquire a cubic structure on graphene.
Keywords: Cu nanoparticle, CVD; gas phase; graphene, Magnetron Sputtering

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Permalink: https://www.hzdr.de/publications/Publ-26433
Publ.-Id: 26433


Development of a novel active technique for bremsstrahlung source term determination in laser-plasma experiments

Molodtsova, M.; Ferrari, A.; Cowan, T.
The use of high intensity, high power lasers recently increased in research facilities all over the world. By laser-matter interactions it is possible to study new mechanisms of ion/electron acceleration, and matter under extreme conditions via pump-probe experiments. At the X-ray Free Electron Laser in Hamburg (EuXFEL) such extreme conditions will be generated and studied at the High Energy Density (HED) instrument at the Helmholtz International Beamline for Extreme Fields (HIBEF). For such experiments a wide variety of novel detectors will be needed. One of the challenges will be the detection of the bremsstrahlung radiation emitted with ultrashort pulse widths (gamma flash) down to the fs range, at every laser shot.
To characterize the gamma flash usual spectrometry techniques using pulse height analysis can not be used, because of its short pulse width as well as its high intensity (~10^10 photons). A possible approach is to measure the energy deposited by photons in a detector with a layered structure, to obtain information about the longitudinal development of the electromagnetic shower. With this data the photon spectrum can be then reconstructed by using an unfolding technique. To perform a successful unfolding, detector materials and thicknesses have to be optimized to be able to resolve the photon spectrum in the dynamic range between 50 keV and 20 MeV.
By means of FLUKA Monte Carlo simulations the development of the electromagnetic shower and the distribution of the energy deposited by the incident radiation were studied for different detector models. The model that showed the most promising set of response functions to perform a deconvolution, was chosen to realize the first prototype.
In this poster the first results of this work are presented.
  • Poster
    SATIF-13 (13th Meeting of the task-force on Shielding aspects of Accelerators, Targets and Irradiation Facilities), 10.-12.10.2016, Dresden, Deutschland
  • Open Access Logo Contribution to proceedings
    SATIF-13 (13th Meeting of the task-force on Shielding aspects of Accelerators, Targets and Irradiation Facilities), 10.-12.10.2016, Dresden, Deutschland
    Proceedings of SATIF-13: NEA

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Permalink: https://www.hzdr.de/publications/Publ-26431
Publ.-Id: 26431


High-pressure chemistry of hydrocarbons relevant to planetary interiors and inertial confinement fusion

Kraus, D.; Hartley, N. J.; Frydrych, S.; Schuster, A. K.; Rohatsch, K.; Brown, S.; Cowan, T. E.; Cunningham, E.; Demaio-Turner, S. J.; van Driel, T.; Fletcher, L. B.; Galtier, E.; Gamboa, E. J.; Laso Garcia, A.; Gericke, D. O.; Granados, E.; Heimann, P. A.; Lee, H. J.; Macdonald, M. J.; Mackinnon, A. J.; Mcbride, E. E.; Nam, I.; Neumayer, P.; Pak, A.; Pelka, A.; Prencipe, I.; Ravasio, A.; Redmer, R.; Rödel, M.; Saunders, A. M.; Schölmerich, M.; Schörner, M.; Sun, P.; Falcone, R. W.; Glenzer, S. H.; Döppner, T.; Vorberger, J.
Diamond formation in polystyrene (C8H8)n, which is laser-compressed and heated to conditions around 150 GPa and 5,000 K, has recently been demonstrated in the laboratory [D. Kraus et al., Nat. Astron. 1, 606-611 (2017)]. Here we show an extended analysis of the acquired data and their implications for planetary physics and inertial confinement fusion. Moreover, we discuss the advanced diagnostic capabilities of adding high-quality small angle X-ray scattering and spectrally resolved X-ray scattering to the platform, which shows great prospects of precisely studying the kinetics of chemical reactions in dense plasma environments at pressures exceeding 100 GPa.

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Permalink: https://www.hzdr.de/publications/Publ-26430
Publ.-Id: 26430


Coherent excitation of heterosymmetric spin waves with ultrashort wavelengths

Dieterle, G.; Förster, J.; Stoll, H.; Semisalova, A. S.; Finizio, S.; Gangwar, A.; Weigand, M.; Noske, M.; Fähnle, M.; Bykova, I.; Bozhko, D. A.; Musiienko-Shmarova, H. Y.; Tiberkevich, V.; Slavin, A. N.; Back, C. H.; Raabe, J.; Schütz, G.; Wintz, S.
In the emerging field of magnonics, spin waves are foreseen as signal carriers for future spintronic information processing and communication devices, owing to both the very low power losses and a high device miniaturisation potential predicted for short-wavelength spin waves. Yet, the controlled and efficient excitation of propagating nanoscale spin waves remains a challenge to be resolved. Here, we report the observation of high-amplitude, ultrashort dipole-exchange spin waves (down to 80 nm wavelength at 10 GHz frequency) in a ferromagnetic single layer system, coherently excited by the driven dynamics of a spin vortex core. We used time-resolved x-ray microscopy to directly image such propagating spin waves for a wide range of excitation frequencies. By further analysis, we found that these waves exhibit a heterosymmetric mode profile, involving regions with anti-Larmor precession sense and purely linear magnetic oscillation. In particular, this mode profile consists of dynamic vortices with laterally alternating helicity, leading to a partial magnetic flux closure over the film thickness, which is explained by a strong and unexpected mode hybridisation. The spin-wave phenomenon observed is a general effect inherent to the dynamics of sufficiently thick ferromagnetic single layer films, independent of the specific excitation method employed.
Keywords: spin wave vortex x-ray microscopy
  • Physical Review Letters 122(2019), 117202
    DOI: 10.1103/PhysRevLett.122.117202
  • Lecture (Conference)
    Intermag 2018, 23.-27.04.2018, Singapur, Singapur
  • Lecture (Conference)
    International Conference on Magnetism, 15.-20.07.2018, San Francisco, USA
  • Lecture (Conference)
    23rd International Colloquium on Magnetic Films and Surfaces, 22.-27.07.2018, Santa Cruz, USA
  • Lecture (Conference)
    9th Joint European Magnetic Symposia, 03.-07.09.2018, Mainz, Germany
  • Contribution to WWW
    arXiv:1712.00681v3 [cond-mat.mes-hall]: https://arxiv.org/abs/1712.00681
  • Lecture (Conference)
    Magnonics 2019, 28.07.-01.08.2019, Carovigno, Italien

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Permalink: https://www.hzdr.de/publications/Publ-26429
Publ.-Id: 26429


µ-RayStation 5: Expanding functionality of a clinical treatment planning system towards application for image-guided small animal radiotherapy

Tillner, F.; Nilsson, R.; Nordström, M.; Dietrich, A.; Baumann, M.; Krause, M.; Enghardt, W.; Bütof, R.
Introduction:
The Small Animal Image-Guided Radiation Therapy (SAIGRT) system has been developed at OncoRay by downsizing treatment technology of human radiation oncology towards small animal experiments [1,2]. The system consists of a gantry module, covered by a radiation protection housing, and a supply module. The gantry module comprises (1) a stationary unit incorporating a 3D computerised animal stage positioner and (2) a 360° rotating arm holding a 225 kV X-ray tube as radiation source, a system of flat aperture collimators for beam shaping and a flat-panel detector for X-ray imaging. Supported by dedicated software, the SAIGRT system allows for a precise and accurate, conformal irradiation and X-ray imaging of small animals using an experimental workflow resembling the patient treatment process. However, only simplified treatment planning has been applied so far, in lack of a full 3D treatment planning system (TPS).
Materials & Methods:
RayStation 5 is an advanced, clinical TPS by RaySearch Laboratories AB, which works across different external beam radiotherapy devices (e.g. linear accelerators, proton therapy). Import / export options are available for various image modalities. Furthermore, it provides versatile manual and automatic tools for contouring as well as different methods for rigid and deformable image registration. Various irradiation devices can be modelled by specifying characteristics of design features and beam shaping components (e.g. material, motion, geometry) as well as dosimetric properties of the irradiation field. For plan design, the software comprises machine-dependent functions and dose calculation engines resulting in realistic dose distributions. In addition, different features for plan evaluation and comparison are accessible. However, all tools are intended for patients and thereby not suitable for the submillimetre dimensions of small animals. For this reason, µ-RayStation 5 has been developed in collaboration with RaySearch. Based on a research version of the clinical TPS, functionality has been expanded to comply with the requirements of small animal irradiators such as the SAIGRT system.
Results:
Tools for contouring and image registration as well as the dose grid have been modified to support dimensions down to 0.1 mm. The machine model for small animal irradiators includes characteristics such as the geometry of cone-shaped beams (e.g. distances, aperture sizes), a focal spot model (e.g. 2D Gaussian distribution) and a photon energy spectrum of an X-ray tube with several hundred kV accelerating potential. Plan design is supported for 3D conformal radiotherapy using fixed beams and static arcs. Dose calculation is performed by the VMC++ Monte-Carlo engine [6]. The number of simulated histories and the dose quantity (dose to water or medium) can be selected. Monitor units have been replaced by irradiation time. The SAIGRT system was successfully modelled using a 200 kV spectrum generated from SpekCalc [3-5] showing good agreement with verification measurements.
Conclusion:
µ-RayStation 5 provides comprehensive functionality of a clinical TPS for small animal studies allowing an efficient experimental workflow for experienced Raystation users. Flexibility of the software facilitates adaption to other small animal irradiators and expansion of usage for preclinical research in our institute especially for commencing small animal proton irradiations.
References:
[1] Tillner et al. (2014), Z Med Phys. 24(4): 335-51
[2] Tillner et al. (2016), Phys Med Biol. 61(8): 3084-108
[3] Poludniowski GG, Evans PM (2007), Med Phys. 34(6): 2164-74
[4] Poludniowski GG (2007), Med Phys. 34(6): 2175-86
[5] Poludniowski GG et al. (2009), Phys Med Biol. 54(19): 433-8
[6] Kawrakow I, Fippel M (2000), In: The Use of Computers in Radiation Therapy, Springer: 126-8
Keywords: image-guided small animal radiotherapy
  • Lecture (Conference)
    4th Conference On Small Animal Precision Image-Guided Radiotherapy, 12.-14.03.2018, Lissabon, Portugal

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Permalink: https://www.hzdr.de/publications/Publ-26428
Publ.-Id: 26428


4D Delivery - Treatment verification in particle therapy

Richter, C.; Jakobi, A.; Meijers, A.; Knopf, A.
4D delivery verficiation, mainly focussing on machine log-file based 4d dose reconstruction using 4D-CT and motion surrogate information
  • Invited lecture (Conferences)
    4D Treatment (Planning) Workshop, 04.-05.12.2017, Wien, Österreich

Permalink: https://www.hzdr.de/publications/Publ-26427
Publ.-Id: 26427


Scale dependent soil erosion dynamics in a fragile loess landscape

Baumgart, P.; Eltner, A.; Domula, A. R.; Barkleit, A.ORC; Faust, D.
Loess landscapes provide highly fertile soils in temperate zones and thus are often under intensive agricultural use with a high susceptibility to soil degradation. Magnitudes of soil erosion on different spatio-temporal scales are hard to recognise or were even ignored due to the restricted human perception. Precise and reliable soil erosion measurements are still very scarce, especially for intense single precipitation. In this study, present-day soil erosion is investigated as a complex process on different spatial and temporal scales, such as a short-term observation on plot scale and a medium-term observation on slope scale, which lead to long-term indications for the catchment scale. Classical soil drillings, 7Be and 137Cs radionuclide tracer investigations and non-invasive unmanned aerial vehicle (UAV) photogrammetry were performed for two cultivated field sections within the Saxon Loess Province (Eastern Germany). The main findings are: (1) for a short-term intense precipitation event interrill soil erosion reaches up to 4.69 ± 0.73 mm on plot scale and mean total erosion values reach 1.45 mm on catchment scale; (2) medium-term soil erosion exhibit values up to 33 cm on slope scale within the last 50 years, indicating a strong landscape liability to agricultural use; (3) climatic pressure with increasing temperature and precipitation shifts towards seasons with bare soil surfaces favours the soil erosion process and increases the fragility of the landscape substantially. In conclusion, soil erosion is the driving factor of present-day landscape evolution in the Saxon Loess Province.
Keywords: Saxon Loess Province, Beryllium-7, Caesium-137, unmanned aerial photogrammetry (UAV)
  • Contribution to external collection
    in: Zeitschrift für Geomorphologie, Stuttgart: E. Schweizerbart'sche Verlagsbuchhandlung, 2017, 191-206
    DOI: 10.1127/zfg/2017/0409

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Permalink: https://www.hzdr.de/publications/Publ-26423
Publ.-Id: 26423


Charakterisierung von Ba- und Ra-Verbindungen mit Calixarenen und anderen Chelatoren

Reissig, F.
Die vorliegende Arbeit beschäftigt sich mit zwei Schwerpunkten. Zum einen sollen eine Vielzahl von Derivaten eines modifizierten Calix[4]arengründgerüsts sowie ein modifiziertes Calix[6]arenderivat bezüglich ihrer komplexbildenden Eigenschaften untersucht und Komplexbildungskonstanten mit einer Methode unter der Verwendung der radioaktiven Barium- und Radiumisotope ermittelt werden. Diese Methode ist zunächst zu entwickeln und die erhaltenen Ergebnisse mit den Berechnungsmethoden, welche innerhalb der Arbeitsgruppe etabliert und bezüglich der Calix[4]arenderivate anwendbar sind, zu vergleichen. Der Komplex mit der größten Stabilität soll festgestellt werden, um ihn weiter zu modifizieren oder bei ausreichender Stabilität erste biologische Studien beginnen zu können. Zum anderen soll auf der strukturellen Grundlage von Carbazol ein zusätzlicher makrocyclischer potentieller Komplexbildner in Form eines Calix[3]carbazolderivates synthetisiert werden, welcher alternativ zu den Calix[4]aren- und Calix[6]arenderivaten verwendet werden kann. Abschließend sollen die Komplexstabiltäten der Calix[n]arene, der synthetisierten Calix[3]carbazolderivate und kommerzieller Chelatoren mit den zweifach positiv geladenen Barium- und Radiumionen untereinander verglichen werden. Da es kein natürlich vorkommendes, nicht radioaktives Radiumisotop gibt, wird aufgrund seiner chemischen Ähnlichkeit stabiles Barium als Surrogat verwendet, um nicht radioaktive Untersuchungen durchführen zu können. Die erhaltenen Erkenntnisse sollen anschließend auf Untersuchungen mit Radium übertragen werden. Auch für die radioaktiven Studien wird zunächst das radioaktive Bariumisotop Barium-133 verwendet, da es eine längere Halbwertszeit besitzt als die verfügbaren Radiumisotope.
  • Master thesis
    HTW Dresden, 2017
    Mentor: Dr. Constantin Mamat
    0081 Seiten

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Permalink: https://www.hzdr.de/publications/Publ-26421
Publ.-Id: 26421


Bioassociation of uranium onto an extremely halophilic microorganism relevant in nuclear waste repositories in rock salt

Bader, M.
Microorganisms indigenous to rock salt must be considered for the safety analysis of a final repository for radioactive waste in a salt rock formation. Metabolic activity can cause microbial induced redox processes and influence radionuclide speciation and solubility. Additionally, passive biosorption onto living as well as dead biomass may affect the migration of radionuclides [1].
An extremely halophilic archaeon indigenous to rock salt was used for this study. Two similar strains with different origin were compared concerning their interaction processes with uranium. Halobacterium noricense DSM 15987 was originally isolated from an Austrian salt mine [2], the second strain Halobacterium putatively noricense was isolated from the Waste Isolation Pilot Plant (WIPP) [3].
[1] Lloyd, J. R. et al., Interactions of Microorganisms with Radionuclides (Eds. M. J. Keith-Roach, F. R. Livens), 313-342 (2002).
[2] Gruber, C. et al., Extremophiles, 8, Page 431-439 (2004).
[3] Swanson, J. S. et al., Status Report on the Microbial Characterization of Halite and Groundwater Samples from the WIPP - Status report Los Alamos National Laboratory, Page 1ff. (2012).
  • Lecture (Conference)
    Kompetenzzentrum Ost für Kerntechnik, 07.12.2017, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26420
Publ.-Id: 26420


Topological spin textures as spin-wave emitters

Wintz, S.
The investigation of propagating spin waves is a key topic of magnetism research [1]. For the excitation of short wavelengths, it was typically necessary to either use patterned transducers with sizes on the order of the desired wavelengths (striplines or point-contacts) or to generate such spin waves parametrically by a spatially uniform double-frequency microwave signal [2]. Recently, we found a novel mechanism for the lo- cal excitation of spin waves, which overcomes the lower wavelength limit given by the minimum patterning size. This method utilizes the translation of natural topological spin textures, e.g. the gyration of spin vortex cores, to generate spin waves [3]. Yet in terms of signal transfer, spin waves excited by a 0D defect, propagating isotropically in a 2D matrix su er from a geometry induced amplitude decay. This decay is prevented when the dimensionality di erence between source and host matrix is reduced to one. Here we will show that this can be achieved in vortex pair systems with moderate uniaxial intrinsic anisotropy, where domain walls may act both as 1D channels for direc- tional wave propagation and as emitters for 2D plane waves [4]. Finally, we will address vortex core induced spin-wave excitation in single layer lms [5]. [1] A.V. Chumak et al., Nat. Phys. 11, 453 (2015). [2] A.G. Gurevich, G.A. Melkov, Magnetization Oscillations and Waves. New York CRC, 1996. [3] S. Wintz et al., Nat. Nanotechnol. 11, 948 (2016).
Keywords: spin wave vortex
  • Invited lecture (Conferences)
    DPG-Frühjahrstagung der Sektion Kondensierte Materie, 11.-16.03.2018, Berlin, Deutschland
  • Invited lecture (Conferences)
    IEEE Nanomaterials: Applications and Properties, 09.-14.09.2018, Zatoka, Ukraine
  • Invited lecture (Conferences)
    IC4N - 6th International Conference from Nanoparticles and Nanomaterials to Nanodevices and Nanosystems, 30.06.-03.07.2019, Korfu, Griechenland

Permalink: https://www.hzdr.de/publications/Publ-26419
Publ.-Id: 26419


Schutz von Hochleistungslasern durch Bildklassifizierung mit Deep Learning

Kelling, J.; Gebhardt, R.; Helbig, U.; Bock, S.; Schramm, U.; Juckeland, G.
Hochleistungslaser werden u.a. zur Erforschung von exotischen Materiezuständen und für medizinische Anwenden benötigt. Während des Betriebs wird der Strahlquerschnitt überwacht um destruktiv hohe Energiedichten zu erkennen und zu unterbinden. Eine Reaktion auf zufällig auftretende Fehler muss jedoch zwischen Pulsen bei 10Hz erfolgen.

Der Vorgestellte Automatisierungsansatz verwendet Deep Learning in Kombination mit einer einfachen Anomalieerkennung auf Basis bekannter physikalischer Eigenschaften des Systems. Dies ist notwendig für kurze Reaktionszeiten und um
Ergebnisse mit einer sehr kleinen Datenbasis zu erzielen.
Keywords: Bildklassifizierung, Caffe, automatische Laser-Sicherheitsabschaltung, GoogLeNet
  • Invited lecture (Conferences)
    Minds Mastering Machines, 24.-26.04.2018, Köln, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26418
Publ.-Id: 26418


Quantitatively consistent computation of coherent and incoherent radiation in particle-in-cell codes - a general form factor formalism for macro-particles

Pausch, R.; Debus, A.; Huebl, A.; Schramm, U.; Steiniger, K.; Widera, R.; Bussmann, M.
Quantitative predictions from synthetic radiation diagnostics often have to consider all accelerated particles.
For particle-in-cell (PIC) codes, this not only means including all macro-particles but also taking into account the discrete electron distribution associated with them.
This paper presents a general form factor formalism that allows to determine the radiation from this discrete electron distribution in order to compute the coherent and incoherent radiation self-consistently.
Furthermore, we discuss a memory-efficient implementation that allows PIC simulations with billions of macro-particles.
The impact on the radiation spectra is demonstrated on a large scale LWFA simulation.
Keywords: particle-in-cell simulations laser plasma acceleration far field radiation plasma physics radiation diagnostics
  • Contribution to proceedings
    3rd European Advanced Accelerator Concepts Workshop, 24.-29.09.2017, La Biodola, Isola d'Elba, Italien: NIM-A
  • Nuclear Instruments and Methods in Physics Research A 909(2018), 419-422
    DOI: 10.1016/j.nima.2018.02.020

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  • Secondary publication expected

Permalink: https://www.hzdr.de/publications/Publ-26417
Publ.-Id: 26417


Biomineralization of uranium(VI) by fungi - alternative for remediation approaches?

Schäfer, S.; Gerber, U.; Krawczyk-Bärsch, E.; Merroun, M. L.
Uranium pollution of soils and waters within the environment is from big concern. A range of remediation strategies were developed using chemicals and industrial equipment. As a consequence, the conventional remediation of polluted sites is elaborated and time-consuming. Microorganisms can affect the solubility of uranium and thus they could be an appropriate alternative in bioremediation approaches. It is well described that microorganisms could interact with metals in different ways. One of these is called biomineralization, and is defined as an interaction mechanism between microorganisms and metals whereby biological produced minerals capture pollutants within stable solid phases.
We investigated natural occurring fungi which were directly isolated from the flooding water of the former uranium mine Königstein in Germany. The isolated strain KS1 Penicillium simplicissimum displayed the ability to immobilize high amounts of uranium from surrounding solutions. Metabolism-dependent uranium removal experiments revealed in different interaction mechanisms of KS1 with uranium(VI). By transmission electron microscopy (TEM) we observed that the immobilization of the soluble uranium(VI) took place by bioaccumulation within the cells and furthermore by biomineralization outside of the cells. EDX investigations resulted in amorphous phosphate-minerals inside and outside the cells. In addition, enzymatic analysis displayed organic acids which were produced by the fungi and released to the solution. The results of our investigations revealed that the isolated fungi KS1 could be a suitable candidate for further bioremediation studies. Uranium was immobilized effectively, fast and possibly within stable solid phases. Compared to conventional remediation approaches the use of microorganisms should be taken into account.
Keywords: Bioremediation, Uranium, Biomineralization
  • Invited lecture (Conferences)
    16. Remediation Colloquium Jena, 05.-06.10.2017, Jena, Germany

Permalink: https://www.hzdr.de/publications/Publ-26416
Publ.-Id: 26416


Nonlinear large scale flow in a precessing cylinder and its ability to drive dynamo action

Giesecke, A.; Vogt, T.; Gundrum, T.; Stefani, F.
We have conducted experimental measurements and numerical simulations of a precession driven flow in a cylindrical cavity. The study is dedicated to the precession dynamo experiment currently under construction at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) and aims at the evaluation of the hydrodynamic flow with respect to its ability to drive a dynamo. We focus on the strongly nonlinear regime in which the flow is essentially composed of the directly forced primary Kelvin mode and higher modes in terms of standing inertial waves arising from nonlinear self-interactions. We obtain an excellent agreement between experiment and simulation with regard to both, flow amplitudes and flow geometry. A peculiarity is the resonance-like emergence of an axisymmetric mode that represents a double roll structure in the meridional plane. Kinematic simulations of the magnetic field evolution induced by the time-averaged flow yield dynamo action at critical magnetic Reynolds numbers around Rm^c = 430 which is well within the range of the planned liquid sodium experiment.
Keywords: Dynamo, DRESDYN

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Permalink: https://www.hzdr.de/publications/Publ-26415
Publ.-Id: 26415


Wechselwirkungen zwischen U(VI) und Ca-Bentonit sowie Cm(III) und CSH-Phasen unter dem Einfluss alkalischer und hochsalinarer Porenwässer

Philipp, T.; Wolter, J.-M.; Schmeide, K.; Stumpf, T.
Der Vortrag fasst den aktuellen Stand der Untersuchungen innerhalb des BMWi-Verbundprojektes GRaZ zusammen. Es werden im Wesentlichen Ergebnisse zu zwei Systemen vorgestellt: U(VI) / Ca-Bentonit, sowie Cm(III) / CSH - Phasen. Die U(VI)-Rückhaltung an Ca-Bentonit zeigt eine große Variabilität im pH-Bereich 8-13 und ist stark vom Carbonat-Gehalt abhängig. Eine Erniedrigung der U(VI)-Rückhaltung bei pH > 8 in Gegenwart von Carbonat durch Bildung schwach sorbierender Uranyl-Carbonat-Komplexe wurde nur bis zu einem bestimmten pH Wert beobachtet. Bei höherem pH wird die aquatische Speziation widerrum durch Uranyl-Hydroxo-Komplexe dominiert, was zu einer erhöhten U(VI)-Rückhaltung führt. Der zugrunde liegende Rückhaltemechanismus konnte noch nicht eindeutig geklärt werden. Erste spektroskopische Untersuchungen der Oberflächenkomplexe deuten aber darauf hin, dass Oberflächenausfällung und/oder der Bildung oligomerer Oberflächenkomplexe zur Rückhaltung beitragen.
Cm(III)-dotierte CSH-Phasen konnten erfolgreich hergestellt und mittels TRLFS characterisiert werden. Anschließende Leaching-Versuche mit 0,02 M NaHCO3 und 2,5 M NaCl zeigten, im Gegensatz zu vergleichbaren Untersuchung mit U(VI), keinerlei remobilisierung des Curiums. Grund dafür ist der Einbau des freigesetzten Curiums in bei der Alteration neu gebildete Calcit- und Vateritmineralphasen.
  • Lecture (others)
    5. Workshop des BMWi-Verbundvorhabens “Geochemische Radionuklidrückhaltung an Zementalterationsphasen (GRaZ)“, 15.11.2017, Potsdam, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26414
Publ.-Id: 26414


Beryllium-7 at DREAMS

Rugel, G.; Merchel, S.; Scharf, A.; Querfeld, R.; Steinhauser, G.; Tiessen, C.
Half-lives of routine AMS nuclides range from thousands to millions of years. We measured short-lived 7Be (T1/2 = 53.2 d) at the DREsden AMS-facility (DREAMS) [1] as low as 90 mBq, which can be challenging for rapid 𝛾-counting. Simultaneous determination of 7Be and 10Be (T1/2 = 1.387 Ma) via AMS is advantageous for improved understanding of production, transport, and deposition of atmospherically produced 7,9,10Be [2].
Data was normalized to a 7Be sample produced via 7Li(p,n)7Be, measured by 𝛾-counting and chemically processed to BeO (7Be/9Be ≈ 10−12). The isobar 7Li is completely eliminated by chemistry and the degrader foil technique (7Be4+, 10.2 MeV). The blank ratio of 5 × 10−16 7Be/9Be (0.8 mBq) and simple and fast chemistry allows for the measurement of rainwater samples, collected in Germany, as small as 10 ml corresponding to a few times 10−14 7Be/9Be [3,4].
Thanks to D. Bemmerer (HZDR) and G. György (ATOMKI, Hungary) for help with the 7Be normalization material.
Ref.: [1] G. Rugel et al., NIMB 370 (2016) 94. [2] A.M. Smith et al., NIMB 294 (2013) 59. [3] R. Querfeld et al., JRNC 314 (2017)521. [4] C. Tiessen et al. JRNC (submitted).
Keywords: AMS, Be-7
  • Lecture (Conference)
    DPG-Frühjahrstagung der Sektion Atome, Moleküle, Quantenoptik und Plasmen (SAMOP), 04.-09.03.2018, Erlangen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26413
Publ.-Id: 26413


Effects of Heater Surface Characteristics on Bubble Sliding Induced Heat Transfers during Upward Subcooled Nucleate Boiling

Sarker, D.; Ding, W.; Hampel, U.
In the present study the effects of surface wettability and roughness on wall heat transfers during bubble sliding are investigated via isolated bubbles on a vertical heater. Bubbles were generated from artificial cavities on stainless steel heaters. The test liquid was de-gassed, de-ionized water and a borosilicate glass vessel was filled with the test liquid. By high resolution imaging technique, the bubble dynamic parameters such as temporal evolution of bubble size, bubble base diameter and bubble sliding over heater for different surface characteristics were measured. The experimental values of different bubble dynamic parameters were used in the numerical models to calculate the associated heat transfers induced by bubble sliding.

We found that with the decrease of surface wettability for similar roughness, bubble sliding distances and the bubble induced areas increase. It enhances the transient heat conduction. For rough surfaces, sliding velocities were found higher than that of smooth surfaces. It is to be noted that the wettability of these surfaces is decreased while the roughness is increased. The transient conduction heat transfers are found generally higher in this study when the surface becomes rougher. An optimal roughness of Rq=90 nm showed more than 1.4 times augmented heat transfer over the smooth surfaces due to the interaction of surface roughness with the microlayer. These kind of surfaces even transfers higher heat flux than the roughest surface, studied in this work. The contribution of microlayer evaporation beneath sliding bubbles was not found significantly influential to the total heat flux. Future work will focus on the detail understandings of surface characteristics effects on the recovery of thermal boundary layer and the microlayer behavior during bubble sliding.
Keywords: Surface characteristics, vertical heater, bubble sliding, optimal roughness, wall heat flux
  • Open Access Logo Contribution to proceedings
    17th Internationsl Topical Meeting on Nuclear Reactor Thermal Hydraulics, 03.-08.09.2017, Xi'an, China

Permalink: https://www.hzdr.de/publications/Publ-26412
Publ.-Id: 26412


Quantitative prediction of critical heat flux initiation in pool and flow boiling

Ding, W.; Krepper, E.; Hampel, U.
Boiling is a very efficient heat transfer mechanism with a large heat transfer coefficient and it is widely found in industrial systems. However, boiling heat transfer is limited by the critical heat flux (CHF), also termed as boiling crisis. It leads to a rapid decrease of the heat transfer coefficient in temperature controlled heat transfer or to a significant jump in heater surface temperature in power controlled heat transfer cases. While the earlier effect clearly lowers efficiency the latter may even jeopardize safety. A clear understanding of the basic mechanisms leading to CHF is still lacking. In this paper a new model of priori critical heat flux(CHF-) is derived from the bubble dynamics of nucleate boiling. It holds for pool boiling and forced convective boiling and incorporates a mutual effect model and a shear stress model. The comparison between predicted and experimental results under different thermal hydraulic conditions shows a good agreement. The model is capable to explain the initiating mechanism of the boiling crisis and impacts from different variables. It can be also implemented as a sub-model in CFD codes.
Keywords: Critical heat flux (CHF), boiling heat transfer, pool boiling, forced convective boiling, cavity activation

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Permalink: https://www.hzdr.de/publications/Publ-26411
Publ.-Id: 26411


Numerical analysis of heat exchanger designs for passive spent fuel pool cooling to ambient air

Unger, S.; Krepper, E.; Hampel, U.
Passive cooling of spent fuel pools via natural two-phase convection of a fluid with low boiling point is a promising alternative to active cooling circuits as such a passive heat transfer system would still work in safety-critical situations, such as a station blackout. For ambient air as the ultimate heat sink the heat exchanger design plays a crucial role as driving temperature differences may be low. This paper outlines a numerical investigation on a finned oval tube bundle heat exchanger operated under natural air convection in a chimney. We studied the role of chimney geometry and heat exchanger fin geometry. With respect to the chimney we found that velocity, Nusselt number and heat transfer are enhanced by 161.3%, 31.7% and 62.5% respectively, if chimney height increases from 2 m to 16 m. With respect to the fin design we determined an optimal fin configuration with a fin height of 17 mm, fin spacing of 3 mm and fin thickness of 1.5 mm, which improves the heat transfer performance by 28.7%, the Nusselt number by 28.9% and the fin efficiency by 19.2% at a given temperature difference of 40 K. The final optimized finned tube bundle heat exchanger design achieves a volumetric heat transfer density of q_vol=3.61 kW/m³K.
Keywords: passive cooling, spent fuel pool, natural convection, heat exchanger, air cooling, design optimization

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Permalink: https://www.hzdr.de/publications/Publ-26410
Publ.-Id: 26410


Investigation of pore and network formation in spin-on ultra low-k dielectrics by spectroscopic techniques

Koehler, N.; Liedke, M. O.; Attallah, A. G.; Butterling, M.; Anwand, W.; Wagner, A.; Krause-Rehberg, R.; Schulz, S. E.
Positronium annihilation spectroscopy has become more and more important in microelectronics industry as one of the few methods to characterize engineered nanopores in next-generation (k < 2.4) interlayer dielectrics (ILD). With the addition of infrared spectroscopy a way is found to investigate the pore and network formation during the curing process.
1. Introduction
Porous spin-on glasses are one great candidate for the integration as ultra low-k (ULK) dielectrics in Back-End of Line (BEOL) for advanced technology nodes. They offer the possibility of a structured pore network by using “Block Polymer Templated Inorganic Oxides” (USP 6,592,764) [1]. Therefore, it is possible to adjust the physical properties of these thin films [1] as well as pore size and porosity. However, these materials are also prone to dielectric damage [2,3] during the integration into back-end of Line. In addition, these material degradations will increase with porosity [3]. It follows, that beside the damage mechanism also the pore and network formation of ULK materials need to be investigated more in detail to comprehend integration damage from the very first time of appearance. This work will evaluated the formation of spin-on glasses during curing by positron annihilation spectroscopy to observe the pore formation and by Fourier Transform Infrared spectroscopy to study the network formation.
2. Experimental
2.1 Preparation of spin-on dielectrics
For preparation of spin-on ULK material a solution from SBA Materials, Inc. was used. The ULK liquid precursor consists of an amphiphilic block copolymer with silicon alkoxide esters [1]. The final thickness is supposed to be 500 nm with an initial k-value of 2.2. The solution was spin-coated on 6-inch silicon wafers with 2000 rpm for 60 s. The spin-coated samples were soft baked for 120 s at 150 °C. The curing procedure was performed with the quartz glass oven PEO 603 from ATV technologies for different curing times at 450 °C under nitrogen atmosphere. The heat ramp of curing was chosen to be 7 °C/min.
2.2 Measurement techniques of pore and network structure
Fourier Transform Infrared (FTIR) spectroscopy was used to determine the chemical and structural changes before and after different curing times. The measurements were performed in transmission mode in the mid-range from 400 to 4000 cm-1, using the Bruker Tensor 27 spectrometer. The optical response is given as absorbance and normalized to thickness as well as treated by a baseline subtraction. Thus a comparison of the different processes can be achieved. Furthermore, a deconvolution of the FTIR peaks at the oxide region (1300 cm-1 to 950 cm-1) was accomplished with the Peak-Fit Module of ORIGIN 8.5 software. As it is described in literature the oxide region is used to be deconvoluted into the following peaks: the suboxide-, network-, cage-peak [4,5] and the Si-O-C peak [6]. The area was normalized to the total area of the Si-O-Si area.
The characterization of the nanopores were carried out at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) with positron annihilation spectroscopies (PAS). For determination of different pore components the Elbe Positron Source (EPOS) was used; a pulsed positron source with high repetition rate, high intensity and choosable energies for depth profile measurements [7,8]. Furthermore, by using the The Slow-Positron System of Rossendorf (SPONSOR) Doppler broadening spectroscopy was used to acquire also information about the atomic surrounding of the pores.
Since the possibility of diffusing out of ortho-positronium (o-Ps) from film surface through open, interconnecting pores the ULK films were covered with a 20 nm thick carbon layer by evaporating using a pre-shaped carbon rod.
3. Results
Fig. 1 shows the FTIR spectrum of the uncured and cured samples after 5 min, 30 min, 60 min and 90 min at 450 °C. The curing process at 450 °C for 90 min can be considered as complete cure. The uncured sample shows the –OH absorbance peak at 3400 cm-1 and the Si-OH peak at 914 cm-1 [9], which is characteristic for spin-on glasses in sol-gel science [10]. During the curing process the methylsilsesquioxane (MSQ) based Si-OH groups condensate and cross-linking occurs to form a 3D network [11]. Besides the Si-OH peak in the uncured sample the region from 3000 cm-1 to 2800 cm-1 is more pronounced compared to the cured samples. There are located the C-Hx vibration bands, which mostly correspond to porogen to form a porous network. The region from 900 cm-1 to 700 cm-1 is called the fingerprint region, where mostly the different Si-C vibration modes are dominate [9]. The absorbance peak at 1277 cm-1 belongs to the Si-CH3 vibration band.
The two main mechanism during the curing of spin-on ULK are the cross-linking of the Si-OH groups to form a mechanically stable thin film and the porogen removal to form a porous network. The cross-linking of Si-OH to form the Si-O-Si linkage can be seen in Fig 1. in the range of 1250 cm-1 to 960 cm-1. Already after 5 min of curing the Si-O-Si region is formed almost completely and only little changes during further curing are observed. By taking a closer look at the Si-O-Si region, a shift from 1047 cm-1 to 1052 cm-1 can be observed. Within this region four peaks are overlapping: the suboxide-, network-, cage- [4,5] and the Si-O-C peak [6]. To distinguish between those peaks a deconvolution was done, where the results are shown in Fig. 2. With increasing curing time the network peak rises whereas the cage and the suboxide peak decreases. This behavior is likely due to the cross-linking of the network material and is less pronounced after 30 min of curing. The Si-O-C peak seams not to be affect by curing time.
Fig. 3 and Fig. 4 show the results from the DBS and PALS measurements. From the DBS measurements two specific line parameters can be calculated: the S- and W-parameter. The S-parameter is a measurement of the open volume and the W-parameter is a measurement of the atomic environment of the annihilation site. The mean implantation depth for the positrons is given in nanometer scale at the upper x-axes based on the density of silica. The first 20 nm (until 1.2 keV) the S- and W-parameter corresponds to the carbon capping layer and retain unchanged for all treatments. The W-parameter for the uncured sample shows the highest values. Only for 20 nm Carbon layer the W-parameter is higher. Within the first minutes of curing, the porogen is almost removed and the W-parameter decreases. From 30 min to 90 min no change in W-parameter is visible anymore. Compared to the FTIR spectra (Fig. 1) in the region of 3000 cm-1 to 2800 cm-1 no change for all curing times are visible which shows the sensitive behavior of PAS measurements for nanopore evaluations. For the cross-linking behavior (Fig. 2) the dependence on curing time can still be observed in detail by FTIR. Therefore, it can be concluded that the porogen extraction at 450 °C with a slow heating ramp is completed within the first 30 min, whereas the cross-linking of the network takes places over the complete curing time.
The calculated pore components from PALS measurements are shown in Fig. 4. Two different lifetime components were found. The upper diagrams show the diameter of the pores and the lower diagrams show the intensities of the pore components. The first pore component has a diameter of around 0.8 nm which does not change for all curing treatments and positron energies, whereas the intensities of the component 1 decrease from the uncured to the cured state. With regard to the FTIR results (Fig. 1 and Fig. 2), this pore component intensities shows the inverse behavior of the oxide region, where the network is formed. Therefore, this component is likely due to the unreacted Si-OH groups, which decreases during the curing. The second pore component arises from the pores itself and was not observed at the uncured sample. The mean diameter is about 3.4 nm, which lowers to 3 nm near the surface of the film. This can be due to the carbon capping layer deposition and needs further considerations. Also it can be seen that the pore diameter from 5 min to 30 min still increases and reaches a final value after 30 min. In addition, the intensity of the pore component 2 changes marginal. That confirms that the porogen extraction as well as the pore formation takes place within the first 30 min.
4. Summary
In this work, the pore formation of spin-on ULK materials with an initial k-value of 2.2 was studied for a thermal curing process at 450 °C with a slow heat ramp for curing. After 5 min of curing most of the porogen is extracted and the network is formed almost completely, which can be seen by PAS and FTIR. The porogen extraction as well as the pore formation appear to be complete after 30 min, whereas the remaining time is needed to form the network.
All the investigations are running right now for faster heat ramp of curing as well as for different curing temperatures to slow down the pore formation process and get a better understanding of the processes taking place inside the material during curing.
References
[1] P. Garrou, Solid State Technology, p. 10, Nov. 2010, Accessed 22 May 2017
[2] J.L. Shohet et al., ECS Transactions, 60 (1) p. 733-738 (2014)
[3] M.R. Baklanov et al., Journal of Applied Physics 113, p. 041101, (2013)
[4] L. Zhang et al., ECS Solid State Lett. 2 (2), p. N5 (2013)
[5] A. Grill et al., J. Appl. Phys. 94 (10), p. 6697 (2003).
[6] Y. Lin et al., J. Electrochem. Soc. 153 (7), p. F144 (2010)
[7] A. Uedono et al. Applied Surface Science, Bd. 368, pp 272-276 (2016)
[8] A. Wagner et al., Defect and Diffusion Forum, Bd. 331, pp. 25-40, (2012)
[9] B. Xie et al., Microelectron. Eng, 76 (1-4) p. 52-59 (2004)
[10] P. Eaton et al., J. Appl. Polym. Sci. 82 (8), p. 1097-4628 (2001)
[11] A. Zenasni et al., J. Electrochem. Soc. 154 (1) p. G6 –G12 (2007)
Keywords: low-k materials, dielectrics, positron annihilation spectroscopy, positron lifetime, Fourier Transform Infrared Spectroscopy, Doppler broadening spectroscopy, pores, networks
  • Poster
    2017 Advanced Metallization Conference, 13.-14.09.2017, Austin, TX, USA

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Engrafting human regulatory T cells with a flexible modular chimeric antigen receptor technology

Koristka, S.; Kegler, A.; Bergmann, R.; Arndt, C.; Feldmann, A.; Albert, S.; Cartellieri, M.; Ehninger, A.; Ehninger, G.; Middeke, J. M.; Bornhäuser, M.; Schmitz, M.; Pietzsch, J.; Akgün, K.; Ziemssen, T.; Steinbach, J.; Bachmann, M. P.
As regulatory T cells (Tregs) play a fundamental role in immune homeostasis their adoptive transfer emerged as a promising treatment strategy for inflammation-related diseases. Preclinical animal models underline the superiority of antigen-specific Tregs compared to polyclonal cells. Here, we applied a modular chimeric antigen receptor (CAR) technology called UniCAR for generation of antigen-specific human Tregs. In contrast to conventional CARs, UniCAR-endowed Tregs are indirectly linked to their target cells via a separate targeting module (TM). Thus, transduced Tregs can be applied universally as their antigen-specificity is easily adjusted by TM exchange. Activation of UniCAR-engrafted Tregs occurred in strict dependence on the TM, facilitating a precise control over Treg activity. In order to augment efficacy and safety, different intracellular signaling domains were tested. Both 4-1BB (CD137) and CD28 costimulation induced strong suppressive function of genetically modified Tregs. However, in light of safety issues, UniCARs comprising a CD137-CD3z signaling domain emerged as constructs of choice for a clinical application of redirected Tregs. In that regard, Tregs isolated from patients suffering from autoimmune or inflammatory diseases were, for the first time, successfully engineered with UniCAR 137/z and efficiently suppressed patient-derived effector cells. Overall, the UniCAR platform represents a promising approach to improve Treg-based immunotherapies for tolerance induction.
Keywords: regulatory T cells; chimeric antigen receptor; immunotherapy; CD28; CD137 (4-1BB)

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Assembly Behavior of Organically Interlinked Gold Nanoparticle Composite Films: A Quartz Crystal Microbalance Investigation

Daskal, Y.; Tauchnitz, T.; Güth, F.; Dittrich, R.; Joseph, Y.
Thin films based on dodecylamine stabilized gold nanoparticles interlinked with different organic molecules are prepared by automatic layer-by-layer self-assembly in a microfluidic quartz crystal microbalance (QCM) cell, to obtain an in situ insight on the film formation by ligand/linker exchange reactions. The influence of interlinking functional groups and the length of the organic linker molecule on the assembly behavior is investigated. Alkyldithiols with different lengths are compared to alkyldiamines and alkylbisdithiocarbamates with a C8 alkylic molecular backbone. The stepwise layer-by-layer assembly occurs independently of the linker molecule, while the largest frequency changes always correspond to the gold nanoparticle step.
During the solvent rinsing and ligand/linker exchange reaction step, the frequency is almost constant with slight increases or decreases dependent on the molar mass of the linker compared to the exchanged ligand. The assembly efficiency is higher for shorter molecules and for molecules with stronger interacting functional groups. The densities of the composite films are calculated from QCM data and independent thickness measurements. They reflect the higher fraction of organic material in the films comprising longer organic linkers. The plasmon resonance band of the gold nanoparticles in the final assemblies is measured with UV/vis spectroscopy. Band positions in films prepared from dithiols and diamines of comparable lengths are very similar, while the spectrum of the bisdithiocarbamate film exhibits a distinct blue-shift. This observation is explained by the longer molecular structure of the linker due to a larger binding group, in conjunction with a delocalization of particle charge on the organic molecule. Obtained results play an essential role in the understanding of thin film layer-by-layer self-assembly processes, and enable the formation of new gold nanoparticle networks with organic diamine and bisdithiocarbamate molecules.

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The EPTN consensus-based atlas for CT- and MR-based contouring in Neuro-Oncology

Eekers, D.; In 'T Ven, L.; Roelofs, E.; Postma, A.; Alapetite, C.; Burnet, N.; Calugaru, V.; Compter, I.; Coremans, I.; Hoyer, M.; Lambrecht, M.; Romero, A.; Paulsen, F.; Perpar, A.; de Ruysscher, D.; Renard, L.; Vitek, P.; Weber, D.; van der Weide, H.; Whitfield, G.; Wiggenraad, R.; Nyström, P.; Timmermann, B.; Troost, E.
Purpose: To create a digital, online atlas for organs at risk (OAR) delineation in neurooncology based on high-quality computed tomography (CT) and magnetic resonance (MR) imaging.
Methods: CT and 3 Tesla (3T) MR images (slice thickness 1 mm with intravenous contrast agent) were obtained from the same patient and subsequently fused. In addition, a 7T MR without intravenous contrast agent was obtained from a healthy volunteer. Based on discussions between experienced radiation oncologists, the clinically relevant organs at risk (OARs) to be included in the atlas for neuro-oncology were determined, excluding typical head and neck OARs previously published. The draft atlas was delineated by a senior radiation oncologist, 2 residents in radiation oncology, and a senior neuro-radiologist incorporating relevant available literature. The proposed atlas was then critically reviewed and discussed by European radiation oncologists until consensus was reached.
Results: The online atlas includes one CT-scan at two different window settings and one MR scan (3T) showing the OARs in axial, coronal and sagittal view. This manuscript presents the three-dimensional descriptions of the fifteen consensus OARs for neurooncology.
Among these is a new OAR relevant for neuro-cognition, the posterior cerebellum (illustrated on 7T MR images).
Conclusion: In order to decrease inter- and intra-observer variability in delineating OARs relevant for neuro-oncology and thus derive consistent dosimetric data, we propose this atlas to be used in photon and particle therapy. The atlas is available online at www.cancerdata.org and will be updated whenever required.
Keywords: Atlas for neuro-oncology, organs at risk, particle therapy, European Particle Therapy Network

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Evidence on the efficacy of primary radiosurgery or stereotactic radiotherapy for drug-resistant non-neoplastic focal epilepsy in adults: a systematic review

Eekers, D.; Pijnappel, E.; Schijns, O.; Colon, A.; Hoeben, A.; Zindler, J.; Postma, A.; Hoffmann, A.; Lambin, P.; Troost, E.
Objective: Although the majority of adult epilepsy patients respond well to the current antiepileptic drug treatment (AED), 20-40% of them are drug-resistant. In these patients, resective epilepsy surgery (RES) is a curative treatment option, for which, however, only a limited number of patients is eligible. The purpose is to summarize the outcome of radiotherapy (RT) for drug-resistant non-neoplastic focal epilepsy (NNFE) and to elucidate its efficacy for seizure outcome and long-term toxicity in adults. Methods: A systematic literature search was performed in Pubmed, Ovid Medline, Cochrane library, Embase and Web of Science. The methodological quality was evaluated using an adapted QUADAS checklist. Results: Sixteen out of 170 initially identified studies were included in this systematic literature study (n=170 patients). Twelve of the 16 studies described a positive effect of RT on seizure frequency reduction, with 98 of the patients (on average 58%, range 25%-95%) reporting no or rare seizures (defined as radiotherapy-adapted Engel class [RAEC] I and II. In total, 20% (34 patients) of the patients needed subsequent surgery due to radionecrosis, cysts formation, edema, and intracranial hypertension or remaining seizures. A dose-effect model was fitted to the available response data in an attempt to derive a relationship between prescribed dose and RAEC frequency. Significance: Radiotherapy is a possible non-invasive treatment option for patients with drug-resistant focal non-neoplastic epilepsy. This systematic review showed that there is only level 4 evidence of primary RT reducing seizure frequency in adult patients. Prospective randomized trials are needed to determine its exact value compared to other treatment approaches.
Keywords: stereotactic radiotherapy, radiosurgery, epileptogenic lesions, focal epilepsy

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The posterior cerebellum, a new organ at risk?

Eekers, D. B. P.; In 'T Ven, L.; Deprez, S.; Jacobi, L.; Roelofs, E.; Hoeben, A.; Lambin, P.; de Ruysscher, D.; Troost, E. G. C.
Eekers et al. (1) have recently proposed a neuro-oncology atlas which was co-authored by most centers associated in the European Proton Therapy Network (EPTN; Figure 1). With the introduction of new treatment techniques, such as integrated magnetic resonance imaging and linear accelerators (MR-linac) or particle therapy, the prediction of clinical efficacy of these more costly treatment modalities becomes more relevant. One of the side-effects of brain irradiation, being cognitive decline, is one of the toxicities most difficult to measure and predict. In order to validly compare different treatment modalities, 1) a uniform nomenclature of the organs at risk (OARs), 2) uniform atlas-based delineation [e.g., (1)], 3) long-term follow-up data with standardized cognitive tests, 4) a large patient population, and 5) (thus derived) validated normal tissue complication probability (NTCP) models are mandatory.
Apart from the Gondi model (2), in which the role of the dose to 40% of both hippocampi (HC) proves to be significantly related to cognition in 18 patients, no similar models are available. So there is a strong need for more NTCP models, on HC, brain tissue and possible other relevant brain structures.
In this review we summarize the available evidence on the role of the posterior cerebellum as a possible new organ at risk for cognition, which is deemed relevant for irradiation of brain and head and neck tumors.
Keywords: Neuro-Oncology, delineation atlas, posterior cerebellum, radiotherapy, cognition

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Synthese und Charakterisierung von funktionalisierten Calix[4]arenen zur Chelatisierung von Barium und Radium

Steinberg, J.
Die Entwicklung von Ra2+-Komplexen für den Einsatz der radiopharmazeutisch interessanten Radiumnuklide Ra-223 und Ra-224 in Radiotherapeutika, beispielsweise zur Behandlung eines breiten Spektrums an Tumoren, steht im Fokus dieser Arbeit. Um einen Einbau des calciummimetischen Ra2+ in den Hydroxyapatit des Knochengewebes zu unterbinden, müssen die Radiometallkomplexe hohe Komplexstabilitäten aufweisen. Bifunktionelle Chelatoren mit einer hochaffinen Targeteinheit zum Zielgewebe sollen den Transport zum pathogenen Gewebe möglich machen. Die emittierte α-Strahlung des Radiums führt zur Zerstörung des Zielgewebes.
Vielversprechend stellen sich überbrückte und funktionalisierte p-tert-Butylcalix[4]arenderivate dar. Die erforderliche hohe Stabilität des Komplexes soll dabei besser als mit offenkettigen und einfach cyclischen Verbindungen erreicht werden, da eine definierbare Kavität selektiver und stabiler Metalle bindet. Durch die sterischen Effekte, die durch zusätzliche Modifikationen eintreten, soll der Komplex vor Dissoziation geschützt werden. Einerseits lassen die p-tert-Butyl-Gruppen der upper rim-Seite keinen Angriff auf die Metallionen zu, andererseits werden sie zusätzlich durch die sterisch anspruchsvollen Substituenten der lower rim-Seite festgehalten. Zudem sollen deprotonierbare Positionen an Funktionalisierungen gute Bindungsstellen für Ra2+ zur Komplexbildung darstellen. Aufgrund ähnlicher chemischer Eigenschaften wird Ba2+ als Surrogat für diese Untersuchungen eingesetzt, um das Komplexierungsverhalten der Calixarene zu studieren.
Keywords: Radium, Barium, Calix[4]arene
  • Diploma thesis
    TU Dresden, 2017
    Mentor: Dr. Constantin Mamat
    0120 Seiten

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Desertification Susceptibility Mapping Using Logistic Regression Analysis in the Djelfa Area, Algeria

Djeddaoui, F.; Chadli, M.; Gloaguen, R.
The main goal of this work was to identify the areas that are most susceptible to desertification in a part of the Algerian steppe, and to quantitatively assess the key factors that contribute to this desertification. In total, 139 desertified zones were mapped using field surveys and photo-interpretation. We selected 16 spectral and geomorphic predictive factors, which a priori play a significant role in desertification. They were mainly derived from Landsat 8 imagery and Shuttle Radar Topographic Mission digital elevation model (SRTM DEM).
Some factors, such as the topographic position index (TPI) and curvature, were used for the first time in this kind of study. For this purpose, we adapted the logistic regression algorithm for desertification susceptibility mapping, which has been widely used for landslide susceptibility mapping. The logistic model was evaluated using the area under the receiver operating characteristic (ROC) curve. The model accuracy was 87.8%. We estimated the model uncertainties using a bootstrap method. Our analysis suggests that the predictive model is robust and stable. Our results indicate that land cover factors, including normalized difference vegetation index (NDVI) and rangeland classes, play a major role in determining desertification occurrence, while geomorphological factors have a limited impact. The predictive map shows that 44.57% of the area is classified as highly to very highly susceptible to desertification. The developed approach can be used to assess desertification in areas with similar characteristics and to guide possible actions to combat desertification.
Keywords: desertification; logistic regression; steppe; Djelfa

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Pressure-induced insulator-to-metal transition in VO₂ studied by near-infrared pump – mid-infrared probe spectroscopy

Braun, J. M.; Schneider, H.; Helm, M.; Mirek, R.; Boatner, L. A.ORC; Marvel, R. E.; Haglund, R. F.; Pashkin, A.
The strongly correlated electron material VO₂ shows an insulator-to-metal transition (IMT) when heated above Tc = 340 K accompanied by a lattice transformation from monoclinic to rutile structure. The mechanism of the temperature-driven IMT in VO₂ is very complex and involves a Peierls instability facilitated by a strong Coulomb interaction. However, the hierarchy of these processes during the IMT is still under discussion.

Ultrafast time-resolved techniques allow to study the photo-induced IMT in VO₂ that occurs on a femtosecond time scale. At sufficient pump fluences the insulating gap closes almost instantaneously due to the screening of the Coulomb repulsion [1] and the lattice evolves on a sub-picosecond timescale to a rutile structure indicating the existence of a transient monoclinic metallic phase [2].

On the other hand, application of external pressure also can induce an equilibrium monoclinic metallic phase [3]. Therefore, the mechanism of the pressure-induced IMT in VO₂ must be qualitatively different compared to the temperature-driven IMT. However, until now the information about the electronic band structure of the pressurized metallic phase remains obscure due to incompatibility of photoemission spectroscopy with high-pressure techniques.

Here we use ultrafast near-infrared pump – mid-infrared probe spectroscopy in order to unravel the changes in the electronic structure of VO₂ across the pressure-induced IMT. The nonlinear spectroscopy allows us to extract information about the response of localized and free charge carriers. In this case the non-degenerate pump-probe scheme is essential: The probe photon energy of 0.12 eV is well below the band gap (0.6 eV) at ambient conditions while the pumping with photon energies of 1.5 eV photo-excites additional charge carriers across the band gap.

The probe radiation is focused on a VO₂ single crystal inside a diamond anvil cell to a nearly diffraction limited spot. We measure the transient reflectivity change in mid-infrared induced by the near-infrared pumping. In agreement with previous studies the pump-probe traces indicate the onset of a long-living metallic state when the excitation fluence exceeds a certain threshold 𝛷th [4]. The results for three independent experimental runs of different VO₂ crystals are shown in Figure 1 together with the linear transmissivity of the probe beam. Initially the threshold grows with pressure increase, but at a critical pressure pc of 6-8 GPa a sudden drop is observed. It coincides with the vanishing of the linear transmissivity (measured without pumping) indicating the pressure-induced IMT in the sample. Remarkably, there is a remnant threshold behavior even for pressures above pc. By pumping it is still possible to enhance the conductivity of the pressure-induced metallic phase. Such behavior is fundamentally different from the temperature-driven IMT, where all t2g bands overlap with the Fermi level leading to the vanishing of the pump-probe response in the metallic phase.

We suggest that the pressure-induced changes of the threshold and linear transmission agree well to a scenario of a bandwidth-driven Mott-Hubbard transition [5]. In this scenario of a purely electronic IMT, pressure-induced increase of the bandwidth leads to a spectral weight transfer from the Hubbard bands to a quasiparticle peak at the Fermi level causing metallic conductivity and a gradual filling of the insulating gap. As a large portion of the spectral weight is still located in the Hubbard bands, the number of charge carriers still can be increased by photoexcitation.

Figure 1. Threshold fluence 𝛷th for three samples and linear transmissivity (bottom curve) as functions of pressure.

[1] D. Wegkamp et al., Phys. Rev. Lett. 2014, 113, 216401.
[2] V. R. Morrison et al., Science 2014, 346, 445.
[3] E. Arcangeletti et al., Phys. Rev. Lett. 2007, 98, 196406.
[4] C. Kübler et al., Phys. Rev. Lett. 2007, 99, 116401.
[5] J. M. Braun et al., in preparation (2017).
Keywords: ultrafast pump-probe spectroscopy, bandwidth-driven Mott-Hubbard transition, vanadium dioxide, VO₂, insulator-to-metal transition, pressure-induced metallization, high pressure, diamond anvil cell
  • Lecture (Conference)
    55th European High Pressure Research Group (EHPRG) Meeting on High Pressure Science and Technology, 03.-08.09.2017, Poznań, Poland

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Pressure-Induced Metallization in VO₂ Studied by Optical Pump – THz Probe Spectroscopy

Braun, J. M.; Schneider, H.; Helm, M.; Mirek, R.; Boatner, L. A.ORC; Marvel, R. E.; Haglund, R. F.; Pashkin, A.
We have investigated pressurized VO₂ using optical pump – THz probe spectroscopy. Distinct pump-probe signals and an excitation threshold are observed even in the metallic state. Our results are consistent with a pressure-driven Mott-Hubbard transition.
Keywords: pressure-induced metallization, bandwidth-controlled Mott-Hubbard transition, insulator-to-metal transition, high pressure, diamond anvil cell, vanadium dioxide, VO₂, optical pump - THz probe spectroscopy
  • Lecture (Conference)
    CLEO 2017 (Conference on Lasers and Electro-Optics), 14.-19.05.2017, San Jose, USA

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Publ.-Id: 26400


Post-irradiation annealing behavior of oxide dispersion strengthened Fe-Cr alloys studied by nanoindentation

Duan, B.; Bergner, F.ORC; Heintze, C.; Akhmadaliev, S.; Wang, T.
To study the nature of irradiation-induced nanofeatures in oxide dispersion strengthened (ODS) Fe-Cr alloys, post-irradiation isochronal thermal annealing up to 600 ºC was performed for 9Cr- and 14Cr-ODS alloys ion-irradiated at 300 and 500 ºC. Nanoindentation indicated hardening for all as-irradiated alloys and complete hardness recovery upon post-irradiation annealing. Candidate mechanisms of recovery were critically evaluated. Shrinkage of irradiation-induced dislocation loops via capture of thermal vacancies was found to correctly reflect the behavior of 9Cr-ODS irradiated at 300 ºC.
Keywords: ODS steel; Ion irradiation; Post-irradiation annealing; Nanoindentation; Dislocation loops

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Bandwidth-controlled metallization in pressurized VO₂ revealed by optical pump – THz probe spectroscopy

Braun, J. M.; Schneider, H.; Helm, M.; Mirek, R.; Boatner, L. A.ORC; Marvel, R. E.; Haglund, R. F.; Pashkin, A.
Vanadium dioxide (VO₂) is a classic example of a transition metal oxide showing a sharp first- order insulator-to-metal transition (IMT) around 340 K accompanied by a pronounced structural transformation. Pressure-induced metallization of VO₂ has been demonstrated by infrared spectroscopy [1] and resistivity measurements [2]. Remarkably, in contrast to the temperature-driven IMT, the crystal structure is not affected and remains monoclinic in the metallic phase [1-3].

Here we apply ultrafast optical pump – THz probe spectroscopy in order to reveal the nature of the pressure-induced IMT in a single crystal of VO₂. The probe pulses with a central frequency of 30 THz were generated by difference frequency mixing and focused down to a 35-𝜇m-spot on the sample mounted inside a diamond anvil pressure cell. Using THz radiation with photon energies far below the bandgap of VO₂ gives us an extremely sensitive probe of the dynamics of metallization [4].

Fig. 1(a) demonstrates that above a certain excitation fluence, a non-zero pump-probe signal survives on a multi-ps timescale indicating the long-lived photoinduced metallic state [4]. Here we define the threshold fluence 𝛷th as a crossing point of linearly extrapolated pump-probe signals in the low- and high-excitation regimes, as shown in Fig. 1(b). Surprisingly, the threshold behavior typical for the insulating state of VO₂ is also observed above the IMT that occurs between 6 and 8 GPa. This indicates a strongly correlated character of the pressure-induced metallic phase in which a part of the electrons remains localized - as predicted for a bandwidth-controlled Mott-Hubbard transition.

Fig. 1(c) shows that 𝛷th initially increases with pressure evidencing that the monoclinic structure stabilizes under hydrostatic compression. However, at the pressure-induced IMT, we observe a sudden drop of 𝛷th. This may be related to the partial screening of Coulomb correlations by delocalized electrons in the metallic state that lowers the critical excitation density necessary for a complete closure of the correlation gap. Our results attest to a purely electronic pressure-induced Mott-Hubbard transition in VO₂ and yield important insights into the nature of the correlated metallic state.

Figure 1: (a) Typical pump-probe response of VO₂ under a pressure of 2.9 GPa at different excitation fluences 𝛷;
(b) Amplitude of pump-probe in the metastable photoinduced state 1 ps after the excitation at different pressures;
(c) Dependence of the threshold fluence 𝛷th as a function of applied pressure. pc marks the region of the insulator-metal
transition.

[1] E. Arcangeletti et al., Phys. Rev. Lett. 98, 196406 (2007).
[2] L. Bai et al., Phys. Rev. B. 91, 104110 (2015).
[3] W.-P. Hsieh et al., Appl. Phys. Lett. 104, 021917 (2014).
[4] C. Kübler et al., Phys. Rev. Lett. 99, 116401 (2007).
Keywords: optical pump - THz probe spectroscopy, pressure-induced metallization, bandwidth-controlled Mott-Hubbard transition, insulator-to-metal transition, high pressure, diamond anvil cell, vanadium dioxide, VO₂
  • Lecture (Conference)
    Optical Terahertz Science and Technology (OTST 2017), 02.-07.04.2017, London, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-26398
Publ.-Id: 26398


The nature of the pressure-induced metallization in VO₂

Braun, J. M.; Schneider, H.; Helm, M.; Mirek, R.; Boatner, L. A.ORC; Marvel, R. E.; Haglund, R. F.; Pashkin, A.
We utilize ultrafast optical pump - THz probe spectroscopy in order to investigate the pressure-driven insulator-to-metal transition (IMT) in vanadium dioxide (VO₂). The probe pulses with central frequency of 30 THz enable a sensitive detection of the photoinduced metallization.
The threshold pump fluence necessary for generation of a metastable metallic phase has been systematically measured for pressures up to 19GPa. Initial pressure application leads to a notable increase of the threshold fluence. This contrasts the thermally-driven IMT in VO₂ where it decreases on approaching the transition temperature. Above the IMT, that occurs at approximately 6-8GPa, we observe a sharp drop of the threshold fluence. However, the clear threshold behavior characteristic for systems with cooperative electronic localization still could be observed also in the metallic state up to the highest applied pressure.
Our results support a view of the pressure-induced IMT in VO₂ as a purely electronic bandwidth-driven Mott-Hubbard transition, that does not involve any change in the crystal structure.
Keywords: pressure-induced metallization, bandwidth-controlled Mott-Hubbard transition, insulator-to-metal transition, high pressure, diamond anvil cell, vanadium dioxide, VO₂, optical pump - THz probe spectroscopy
  • Lecture (Conference)
    DPG-Frühjahrstagung 2017, 19.-24.03.2017, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26397
Publ.-Id: 26397


Nanoindentation of ion-irradiated reactor pressure vessel steels – model-based interpretation and comparison with neutron irradiation

Röder, F.; Heintze, C.; Pecko, S.; Akhmadaliev, S.; Bergner, F.ORC; Ulbricht, A.; Altstadt, E.
Ion-irradiation-induced hardening is investigated on six selected reactor pressure vessel (RPV) steels. The steels were irradiated with 5 MeV Fe2+ ions at fluences ranging from 0.01 to 1.0 displacements per atom (dpa) and the induced hardening of the surface layer was probed with nanoindentation. To separate the indentation size effect and the substrate effect from the irradiation-induced hardness profile, we developed an analytic model with the plastic zone of the indentation approximated as a half sphere. This model allows the actual hardness profile to be retrieved and the measured hardness increase to be assigned to the respective fluence. The obtained values of hardness increase versus fluence are compared for selected pairs of samples in order to extract effects of the RPV steel composition. We identify hardening effects due to increased levels of copper, manganese-nickel and phosphorous. Further comparison with available neutron-irradiated conditions of the same heats of RPV steels indicates pronounced differences of the considered effects of composition for irradiation with neutrons versus ions.
Keywords: nanoindentation; plastic zone; ion irradiation; neutron irradiation; reactor pressure vessel steel; irradiation hardening

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Publ.-Id: 26396


Rapid synthesis of sub-10 nm hexagonal NaYF4-based upconverting nanoparticles using Therminol 66

Hesse, J.; Klier, D. T.; Sgarzi, M.; Nsubuga, A.; Bauer, C.; Grenzer, J.; Hübner, R.; Wislicenus, M.; Joshi, T.; Kumke, M. U.; Stephan, H.ORC
We report a simple one-pot method for rapid preparation of sub-10 nm pure hexagonal (β-phase) NaYF4 based upconverting nanoparticles (UCNPs). Such nanocrystals are well-known for their high efficiency of energy upconversion. Using Therminol 66 as co-solvent, monodisperse UCNPs could be obtained in unusually short reaction time. By varying reaction time, reaction temperature, and the concentration of the dopants (Nd3+, Yb3+ sensitizer ions and Er3+ activator ions), it was possible to precisely control the particle size, crystalline phase, as well as the upconversion (UC) luminescence properties. The size and phase-purity of as-synthesized core and core-shell nanocrystals was assessed using complementary transmission electron microscopy (TEM), dynamic light scattering (DLS), X-ray diffraction (XRD) and small-angle X-ray scattering (SAXS) studies. In-depth photophysical evaluation of the UCNPs was pursued using steady-state as well as time-resolved luminescence spectroscopy. An enhancement in UC intensity was observed when nanocrystals, doped with optimized concentration of lanthanide sensitizer/activator ions, were further coated with an inert/active shell. This is attributed to the suppression of surface-related luminescence quenching effects.
Keywords: core-shell; lanthanides; nanocrystal synthesis; photoluminescence; upconversion

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Permalink: https://www.hzdr.de/publications/Publ-26395
Publ.-Id: 26395


Performing clinical 18FDG-PET/MR imaging of the mediastinum using a dedicated, patient-friendly protocol

Peerlings, J.; Paulis, L.; Mitea, C.; Bakers, F.; Berbée, M.; Wierts, R.; Vöö, S.; Backes, W.; Wildberger, J.; Hoffmann, A.
Purpose:
To apply clinical 18FDG-PET/MRI, a trade-off between image quality (IQ), diagnostic accuracy, and patient compliance is required. This study aimed to develop a mediastinal-specific 18FDG-PET/MR protocol containing dedicated MRI-sequences able to produce robust, high-quality images with great patient compliance and diagnostic performance comparable to 18FDG-PET/CT.

Methods:
In this study, 15 healthy subjects and 10 patients with mediastinal malignancies (i.e., 8 non-small cell lung cancer, 2 oesophageal cancer) received 18FDG-PET/MR imaging immediately after 18FDG-PET/CT. PET/MR-sequences (T1-VIBE, T2-HASTE) on a Siemens Biograph mMR scanner were optimized by varying the following parameters: breath-hold (BH, in end-expiration), fat saturation (SPAIR), and electrocardiogram-triggering (ECG, in end-diastole). IQ of each sequence-variation was qualitatively scored on a 5-point scale by medical experts and quantitatively assessed by calculating signal-to-noise ratios (SNR), contrast relative to muscle-tissue (CR), standardized-uptake-values (SUVs), and tumour-to-blood ratios (TBRs). Differences in CR determined contrast between adjacent tissues and tumour visibility. Diagnostic accuracy of 18FDG-PET/MRI was compared to 18FDG-PET/CT, in reference to clinical reports and histo-/cytopathological analyses.

Results:
Quantitative analysis showed that T1-VIBE images acquired with ECG-triggering presented highest SNR for soft-tissues in the mediastinum (P<0.01) with high contrast between tumours and adjacent tissue, regardless of breath-hold or free-breathing acquisition. In qualitative analyses, IQ of T1-VIBE scans using BH and ECG triggering were scored highest with good reader-agreement (κ=0.62). Quantitative and qualitative IQ of T2-HASTE was not significantly affected by BH-acquisition (P>0.9). However, qualitative IQ of both T1-VIBE and T2-HASTE deteriorated with the addition of SPAIR. Diagnostic performance of 18FDG-PET/MR was not significantly different from 18FDG-PET/CT with similar staging, SUVs, and TBRs. However, T-status was more often over-staged on 18FDG-PET/CT, while N-status was more frequently under-staged on 18FDG-PET/MR.

Conclusion:
ECG-triggered T1-VIBE sequences acquired during short, multiple breath-holds are recommended for mediastinal imaging using 18FDG-PET/MR protocols. With dedicated protocols, 18FDG-PET/MR imaging could be implemented in thoracic oncology and aid in diagnostic evaluation, tailored treatment decision-making, and personalized patient care.
Keywords: 18F-FDG PET/MR PET/CT Mediastinum Esophageal carcinoma Non-small cell lung cancer

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Publ.-Id: 26394


Outlook on a new combined MRI/TI experiment

Seilmayer, M.; Stefani, F.; Gundrum, G.; Köppen, S.
In the project framework of DRESDYN a sodium based experiment investigating magneto rotational instability (MRI) an Tayler instability (TI) is going to be built. Since both instabilities are based on hydrodynamically stable but magnetized Taylor Couette flow, the magnetic field configuration distinguishes the different types of instabilities. The past experimental research successfully worked out helical MRI with a combination of axial and azimuthal magnetic field and azimuthal MRI with only a pure azimuthal field. In both cases the relevant field B[phi] ~ 1/r is
generated by a rather large insulated current running on the symmetry axis of the experiment. The most challenging type of instability still remains standard MRI (SMRI) which relays on pure axial magnetic field B[z]. Here the necessary high rotation rates and large dimensions do limit the experimental feasibility to trigger SMRI until now. Besides that, even a non-rotating fluid with zero velocity can be destabilized by Tayler instability. Here the current is driven through the liquid which gives a B[phi] ~ r dependence. Concluding, the aim of new experimental is to investigate the whole parameter space for the mentioned instabilities and corresponding transitions.

We like to present the latest stage of construction of a large scale liquid sodium Taylor-Couette experiment with a height of 2m and diameter of 0.8 m. In a rough approximation, the achievable boundary conditions will be up to 20 Hz rotation rate and up to 50kA of electrical current. In a more detail, there are some specific topics we like to discus.

First, there is the quasi coaxial system consisting of a central current carrying copper rod and five symmetric return paths which provides homogeneous magnetic field to the Taylor-Couette flow.
One challenging part is the design of the current distributor, which is supposed to divide the current into several equally weighted lines. Because of the individual characteristic resistance of all involved conductors an initial imbalance in the current distribution affecting the symmetry of the magnetic field is the result. So the adjustment of current distribution becomes mandatory to ensure maximum field homogeneity. An indirect access to set the current in all five return paths is to control the outflow temperature of the required water cooling. This is done by thermostatically operated valves in conjunction with the temperature dependent branch resistance. Finally, the calibrated system achieves less than 1% field in-homogeneity and works in a wide range of currents. Additional benefits of the presented approach will be the minimal stray field of the installation and cheap components.

Second, we designed a stacked magnetic field system to generate the axial component. Here 27 individual coils provide an almost homogeneous field with B[z] < 150 mT in the relevant volume. The most challenging aspect is the huge amount of electrical power (approximately 120 kW) which have to be cooled. The main advantage of the present geometry is the guaranteed access to all the sensors mounted on the outer cylinder surface. This is achieved by a special geometry to partially levitate the coil system.

[1]F. Stefani et al., PRE, 80(6), 2009.
[1]M. Seilmayer et al., PRL, 108(24), 244501, 2012.
[1]M. Seilmayer et al., IEEE Sensors Journal, DOI 10.1109/JSEN.2017.2765671, 2017.
Keywords: Experiment, Sodium, DRESDYN, Taylor-Couette
  • Poster
    GDRI DYNAMO MEETING, 26.-29.11.2017, Paris, Frankreich

Permalink: https://www.hzdr.de/publications/Publ-26393
Publ.-Id: 26393


Synthesis of High-Crystallinity DPP Polymers with Balanced Electron and Hole Mobility

Di Pietro, R.; Erdmann, T.; Carpenter, J. H.; Wang, N.; Shivhare, R. R.; Formanek, P.; Heintze, C.; Voit, B.; Neher, D.; Ade, H.; Kiriy, A.
We review the Stille coupling synthesis of P-(DPP2OD-T) (Poly[[2,5-di(2-octyldodecyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione-3,6-diyl]-alt-[2,2′:5′,2″-terthiophene-5,5″-diyl]]) and show that high-quality, high molecular weight polymer chains are already obtained after as little as 15 min of reaction time. The results of UV−vis spectroscopy, grazing incidence wide-angle X-ray scattering (GIWAXS), and atomic force microscopy show that longer reaction times are unnecessary and do not produce any improvement in film quality. We achieve the best charge transport properties with polymer batches obtained from short reaction times and demonstrate that the catalyst washing step is responsible for the introduction of charge-trapping sites for both holes and electrons. These trap sites decrease the charge injection efficiency, strongly reducing the measured currents. The careful tuning of the synthesis allows us to reduce the reaction time by more than 100 times, achieving a more environmentally friendly, less costly process that leads to high and balanced hole and electron transport, the latter being the best reported for an isotropic, spin-coated DPP polymer.

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Permalink: https://www.hzdr.de/publications/Publ-26392
Publ.-Id: 26392


ns-laser driven magnetic phase transition in FeAl

Liedke, M. O.; Bali, R.; Gradauskaite, E.; Ehrler, J.; Wang, M.; Potzger, K.; Zhou, S.; Wagner, A.
FeAl alloys show temperature dependent magnetic phase transition (MPT) from a ferromagnetic disordered A2-phase to a paramagnetic ordered B2-phase. The B2-phase can be reversed back to the A2-phase, e.g, by ion irradiation. The most plausible explanation of MPT points in direction of the anti-site disorder (ASD), i.e., more Fe-Fe nearest neighbors due to disordering. However, variations of the lattice parameter, defects concentration, and secondary phases may play an important role, too. Here, we employ an excimer UV ns-laser to examine the role of ASD and defects onto magnetic properties. Three sample series with different initial order conditions were irradiated by several laser fluences: (i) as-grown semi-, (ii) Ne irradiated fully-disordered, and (iii) vacuum annealed ordered alloys. Two magnetic regimes were found depending on laser fluence: (i) in the low fluence range magnetization initially decreases, followed by (ii) subsequent monotonic increase for larger fluences. The positron annihilation spectroscopy measurements reveal changes of defects surrounding from Al- to Fe dominant, respectively, as well as of defects concentration. The results obtained by MOKE, VSM, AFM, and TEM will be discussed in detail.
Keywords: FeAl alloys, PAS, magnetic phase transition, ns-laser, anti-site disorder, positron annihilation spectroscopy
  • Lecture (Conference)
    DPG Spring Meeting 2017, 19.-24.03.2017, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26391
Publ.-Id: 26391


Fe2+ ion irradiated JRQ steel investigated by nanoindentation and slow-positron Doppler broadening spectroscopy

Pecko, S.; Heintze, C.; Bergner, F.; Anwand, W.; Slugen, V.
A model reactor pressure vessel (RPV) steel, known as JRQ, was manufactured in Japan for IAEA neutron embrittlement research studies in late 80 s. This model alloy belongs to the commercially used steel of A533B-1 type and shows relatively large changes in mechanical properties after a neutron irradiation due to considerable copper content (0.15 wt%). In order to simulate neutron irradiation and investigate the hardening effect, studied specimens of JRQ steel were exposed to Fe2+ ion irradiation in five different exposures calculated using the SRIM code. The ion energy of 5 MeV, temperature at 300 °C and the flux of 1.0×1011 cm−2 s−1 were the same during the irradiations. The hardening was investigated and observed by means of nanoindentation technique and a defect profile of irradiated steels was measured by Slow-positron Doppler broadening spectroscopy (DBS). The observed increasing trend of nanohardness as a function of fluence is in good agreement with the trend observed on the basis of Vickers hardness measured for neutron-irradiated JRQ. This confirms that Cu precipitation is most likely responsible for the observed irradiation hardening and that neutron-irradiation-induced damage can be simulated using ion irradiation in the present case. We have also excluded open volume (vacancy type) defects in the crystal lattice of JRQ steel from a responsibility for the damage arising by the Fe2+ ion irradiation.
Keywords: Positron annihilation spectroscopy, Reactor pressure vessel steels, Nanoindentation, Iron irradiation

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Publ.-Id: 26390


Positronium formation in nanostructured metals

Čížek, J.; Melikhova, O.; Hruška, P.; Vlček, M.; Anwand, W.; Liedke, M. O.; Novotný, M.; Bulíř, J.
Positronium formation in Au films was studied using a magnetically guided continuous slow positron beam with variable energy. Black Au film with porous morphology was compared with conventional smooth Au film. In the smooth Au film positronium is formed on the film surface only. The black Au film exhibits porous sub-surface region containing micro-cavities interconnected with surface. Positronium is formed on inner surfaces of micro-cavities in the sub-surface region and travels through interconnected cavities towards the surface. 3-gamma annihilation of ortho-positronium leaves a clear signature in two-dimensional coincidence Doppler broadening spectra. Measurements of 3-gamma annihilation contribution calculated from single gamma-ray and coincidence Doppler broadening spectra were calculated and compared.
Keywords: Positronium, slow positron beam, porous metals, Au, coincidence Doppler broadening spectroscopy, positron annihilation spectroscopy

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Permalink: https://www.hzdr.de/publications/Publ-26389
Publ.-Id: 26389


Photon vs. proton radiochemotherapy: effects on brain tissue volume and perfusion

Petr, J.; Platzek, I.; Hofheinz, F.; Mutsaerts, H.; Asllani, I.; van Osch, M.; Seidlitz, A.; Krukowski, P.; Gommlich, A.; Beuthien-Baumann, B.; Jentsch, C.; Maus, J.; Troost, E.; Baumann, M.; Krause, M.; van den Hoff, J.
Background and Purpose: To compare the structural and hemodynamic changes of healthy brain tissue in the cerebral hemisphere contralateral to the tumor following photon and proton radiochemotherapy.

Materials and Methods: Sixty-seven patients (54.9±14.0 years) diagnosed with glioblastoma multiforme undergoing adjuvant photon (n=47) or proton (n=19) radiochemotherapy with temozolomide after tumor resection underwent T1-weighted and arterial spin labeling MRI. Changes in volume and perfusion before and 3 to 6 months after were compared between therapies.

Results: A decrease in gray matter (GM) (-2.2%, P<0.001) and white matter (WM) (-1.2%, P<0.001) volume was observed in photon-therapy patients compared to the pre-radiotherapy baseline. In contrast, for the protontherapy group, no significant differences in GM (0.3%, P=0.64) or WM (-0.4%, P=0.58) volume were observed. GM volume decreased with 0.9% per 10 Gy dose increase (P<0.001) and differed between the radiation modalities (P<0.001). Perfusion decreased in photon-therapy patients (-10.1%,
P=0.002), whereas the decrease in proton-therapy patients, while comparable in magnitude, did not reach statistical significance (-9.1%, P=0.12). There was no correlation between perfusion decrease and either dose (P=0.64) or radiation modality (P=0.94).

Conclusion: Our results show that the tissue volume decrease depends on radiation dose delivered to the healthy hemisphere and differs between treatment modalities. In contrast, the decrease in perfusion was comparable for both irradiation modalities. We conclude that proton therapy may reduce brain-volume loss when compared to photon therapy.

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Permalink: https://www.hzdr.de/publications/Publ-26388
Publ.-Id: 26388


Positronium probing of pores in zirconia nanopowders

Prochazka, I.; Cizek, J.; Lukac, F.; Melikhova, O.; Hruska, P.; Anwand, W.; Liedke, M. O.; Konstantinova, T. E.; Danilenko, I. A.
In the present paper, conventional positron lifetime measurements on selected zirconia-based nanopowders are reported. The nanopowders were doped with various metal cations (Y3+, Eu3+, Gd3+, Lu3+ and Mg2+). Lifetime experiments were conducted in air and supplemented with mass density measurements. In a range of lifetimes, from a few ns to ≈ 70 ns, up to two individual lifetime components could be identified. Such observations confirmed positronium (Ps) formation with subsequent ortho-Ps pick-off annihilation as well as the occurrence of pores of different size. Pore sizes were estimated using a shape-free model of the correlation between pore size and ortho-Ps lifetime. The origins of pores are discussed on the basis of the ortho-Ps data in combination with the results mass density measurements.
Keywords: positron lifetime, Positronium, zirconia nanopowders, mass density measurements, defects

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Publ.-Id: 26387


Microstructure, defect structure and hydrogen trapping in zirconium alloy Zr-1Nb treated by plasma immersion Ti ion implantation and deposition

Kashkarov, E.; Nikitenkov, N.; Sutygina, A.; Laptev, R.; Bordulev, Y.; Obrosov, A.; Liedke, M. O.; Wagner, A.; Zak, A.; Weiß, S.
The effect of low energy plasma immersion ion implantation and deposition of titanium on microstructure, defect structure and hydrogen trapping in zirconium alloy Zr-1Nb was studied. Defect structure and distribution were analyzed by Doppler broadening using slow positron beam. The surface microstructure after modification is represented by nanostructured Ti grains with random orientation. The gradient distribution of titanium as well as vacancy type defects were analyzed. The concentration of vacancy type defects is rising with increasing bias voltage. Gas-phase hydrogenation of the Ti-modified Zr-1Nb alloy was performed at 400 °C for 60 min. The strong interaction of hydrogen with vacancy type defects was demonstrated. Two different changes in the defect structure after hydrogenation were observed: when a titanium film is formed on the surface (after deposition at 500 V) hydrogen trapping occurs with the formation of titanium hydride phases, while in the implanted layer (deposition at 1000 and 1500 V) hydrogen is trapped due to interaction with vacancy type defects. The physical basis of Ti diffusion and its influence on the evolution of defect structure after surface modification and hydrogenation were discussed.
Keywords: Zirconium, Ion implantation, Titanium, Diffusion, Surface modification, Hydrogen trapping, Microstructure, Slow positrons, Doppler broadening, Defects

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Publ.-Id: 26386


Polymer nanocomposites with silver nanoparticles formed by low-energy ion implantation: slow positron beam spectroscopy studies

Kavetskyy, T. S.; Liedke, M. O.; Srinivasan, N.; Wagner, A.; Krause-Rehberg, R.; Šauša, O.; Petkova, T.; Boev, V.; Stepanov, A. L.
Polymer nanocomposites formed by low-energy ion implantation were studied by means of positron annihilation spectroscopy with a variable-energy positron beam or slow positron beam spectroscopy. Silver ion implantation into polymethylmethacrylate (Ag:PMMA) and hybrid organic-inorganic ureasil (Ag:ureasil) was performed at different ion fluences with a constant energy of 30 keV and a current density of 1 µA/cm^2 in order to prepare Ag nanoparticles in the near-surface region of polymer matrix. Contribution of Doppler broadening slow positron beam spectroscopy technique for understanding Ag nanoparticles formation in Ag:PMMA and Ag:ureasil nanocomposite films is demonstrated.
Keywords: polymers, nanocomposites, PMMA, ureasil, ion implantation, silver nanoparticles, positron annihilation, slow positrons
  • Book chapter
    Janez Bonca and Sergei Kruchinin: NATO Science for Peace and Security Series A: Chemistry and Biology, P.O.Box 17, 3300 AA Dordrecht, The Netherlands: AK/Nato Publishing Unit, Springer, 2018, 293-300
    DOI: 10.1007/978-94-024-1304-5_21

Permalink: https://www.hzdr.de/publications/Publ-26385
Publ.-Id: 26385


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