Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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31629 Publications
Preclinical imaging for establishment and comparison of orthotopic Non-Small Cell Lung Carcinoma: In search for models reflecting clinical scenarios
Aktar, R.; Dietrich, A.; Tillner, F.; Kotb, S.; Löck, S.; Willers, H.; Baumann, M.; Krause, M.; Bütof, R.;
Objectives:
Clinically relevant animal models of non-small cell lung carcinoma (NSCLC) are required for the validation of novel treatments. We compared two different orthotopic transplantation techniques as well as imaging modalities to identify suitable mouse models mimicking clinical scenarios.
Methods:
We used three genomically diverse NSCLC cell lines (NCI-H1703 adenosquamous cell carcinoma, NCI-H23 adenocarcinoma and A549 adenocarcinoma) for implanting tumour cells either as spheroids or cell suspension into lung parenchyma. Bioluminescence imaging (BLI) and contrast-enhanced cone beam computed tomography (CBCT) were performed twice weekly to monitor tumour growth. Tumour histological data and microenvironmental parameters were determined.
Results:
Tumour development after spheroid-based transplantation differs probably due to the integrity of spheroids, as H1703 developed single localized nodules, whereas H23 showed diffuse metastatic spread starting early after transplantation. A549 transplantation as cell suspension with the help of a stereotactic system was associated with initial single localized tumour growth and eventual metastatic spread. Imaging techniques were successfully applied to monitor longitudinal tumour growth: BLI revealed highly sensitive qualitative data, whereas CBCT was associated with less sensitive quantitative data. Histology revealed significant model dependent heterogeneity in proliferation, hypoxia, perfusion and necrosis.
Conclusions:
Our developed orthotopic NSCLC tumours have similarity with biological growth behavior similar to that seen in the clinic and could therefore be used as attractive models to study tumour biology and evaluate new therapeutic strategies. The use of human cancer cell lines facilitates testing of different genomic tumor profiles that may affect treatment outcomes.
Advances in knowledge:
The combination of different imaging modalities and orthotopic transplantation techniques pave the way towards representative preclinical NSCLC models for experimental testing of novel therapeutic options in future studies.
Keywords: Non-small cell lung cancer, orthotopic model, transplantation technique, preclinical imaging, microenvironment

Publ.-Id: 27590 - Permalink


Probing plutonium dioxide nanoparticles with synchrotron methods
Gerber, E.; Romanchuk, A.; Pidchenko, I.; Hennig, C.; Trigub, A.; Weiss, S.; Scheinost, A.; Kalmykov, S.; Kvashnina, K.;
INTRODUCTION

Plutonium is a chemical element of significant environmental and toxicological concern. At nuclear legacy sites, previous research has demonstrated that plutonium can migrate in colloidal form in the subsurface environment across several kilometers [1-2]. Recent spectroscopic and microscopic investigations showed that so called “colloidal Pu(IV) polymers” are in fact aggregates of PuO2 nanoparticles with diameters ~ 2 nm [3-4]. The exact stoichiometry and structure of such nanoparticles remain, however, still questionable, especially with respect to surface hydration and hydroxylation, as well as the purity of the tetravalent oxidation state considering the existence of four different oxidation states (with relatively small energy barriers III, IV, V, and VI) under environmental conditions.

RESULTS

This contribution will show first results of plutonium oxide nanoparticle studies at the large-scale facility – The European Synchrotron (ESRF) by X-ray spectroscopy and X-ray diffraction methods. Pu oxide nanoparticles were prepared by rapid chemical precipitation using precursors in the different oxidation states (Pu(III), Pu(IV), Pu(V) and Pu(VI)). These precursors were obtained by chemical reduction or oxidation of Pu stock solution. The obtained nanoparticles were characterized at the Rossendorf Beamline (ROBL) at the ESRF, dedicated to actinide science. The recently upgraded ROBL beamline provides unique opportunities to study actinide materials by several experimental techniques: high energy resolution fluorescence detection (HERFD) [5], X-ray emission spectroscopy (XES), resonant inelastic x-ray scattering (RIXS) [6], extended X-ray absorption fine structure (EXAFS) spectroscopy and X-ray diffraction (XRD) simultaneously.
We will show how the detailed information about local and electronic structure and plutonium oxidation state in different nanoparticles can be obtained using the variety of methods.
Keywords: XAFS, nanoparticles, actinides, HERFD,
  • Lecture (Conference)
    Plutonium Futures - The Science 2018, 09.-14.09.2018, San Diego, California, USA

Publ.-Id: 27589 - Permalink


Ultrafast transient absorption spectroscopy of UO22+ and [UO2Cl]+
Haubitz, T.; Tsushima, S.; Steudtner, R.; Drobot, B.; Geipel, G.; Stumpf, T.; Kumke, M. U.;
For the only water coordinated "free" uranyl(VI) aquo ion in perchlorate solution, we identified and assigned several different excited states and showed that the 3∆ state is the luminescent triplet state. With additional data from other spectroscopic methods (TRLFS, UV/Vis, and TAS), we generated a detailed Jabłoński diagram and determined rate constants for several state transitions, like the inner conversion rate constant from the 3Φ state to the 3∆ state transition to be 0.35 ps-1. In contrast to luminescence measurements, it was possible to observe the highly quenched uranyl(VI) ion in highly concentrated chloride solution by TAS and we were able to propose a dynamic quenching mechanism, where chloride complexation is followed by the charge transfer from the excited state uranyl(VI) to chloride. This proposed quenching route is supported by TD-DFT calculations.

Publ.-Id: 27588 - Permalink


Experimental platform for the investigation of magnetized-reverse-shock dynamics in the context of POLAR
Albertazzi, B.; Falize, E.; Pelka, A.; Brack, F.; Kroll, F.; Yurchak, R.; Brambrink, E.; Mabey, P.; Ozaki, N.; Pikuz, S.; van Box Som, L.; Bonnet-Bidaud, J. M.; Cross, J. E.; Filippov, E.; Gregori, G.; Kodama, R.; Mouchet, M.; Morita, T.; Sakawa, Y.; Drake, R. P.; Kuranz, C. C.; Manuel, M. J.-E.; Li, C.; Tzeferacos, P.; Lamb, D.; Schramm, U.; Koenig, M.;
The influence of a strong external magnetic field on the collimation of a high Mach number, plasma flow and its collision with a solid obstacle is investigated experimentally and numerically. The laser irradiation (I ∼ 2 × 1014 W cm−2) of a multilayer target generates a shock wave that produces a rear side plasma expanding flow. Immersed in a homogeneous 10 T external magnetic field, this plasma flow propagates in vacuum and impacts an obstacle located a few mm from the main target. A reverse shock is then formed with typical velocities of the order of 15–20 ± 5 km/s. The experimental results are compared with 2D radiative MHD simulations using the FLASH code. This platform allows investigating the dynamics of reverse shock, mimicking the processes occurring in a cataclysmic variable of polar type.
Keywords: accretion processes; high-power laser; hydrodynamics; laboratory astrophysics; polar; radiative shocks

Publ.-Id: 27587 - Permalink


Recent experiments on plasma immersion ion implantation (and deposition) using discharges inside metal tubes
Ueda, M.; Silva, C.; Marcondes, A. R.; Reuther, H.; de Souza, G. B.;
Plasma immersion ion implantation (PIII) of nitrogen inside metallic tubes of different diameters and configurations were attempted recently. PIII tests in practical size metallic tubes of SS304, ranging from 1.1 to 16 cm∅ and length of 20 cm, were carried out as a continued effort in our lab, to explore PIII inside tubes. Tubes in laying down positions and configurations including metallic lid in one side or both sides open were used, as well as, plane sample support placed 10 cm far from the tube mouth and without bias, taking advantage of plasma flowing out the tube. In particular, nitrogen and argon PIIIs were tested for tube inner wall sputtering and deposition studies, running the PIII system in the last configuration of sample support detached from the tube. During the nitrogen ion implantation runs in other cases, it was found that the final temperature of the tubes and the plasma turn-on voltages were both inversely proportional to the dimensions of the tubes, except for the smallest tube tested. High voltage glow and hollow cathode discharges were produced inside the tubes, either alternately, during the pulse or independently, depending on the tube geometry and pulser used (LIITS, a current controlled source or RUP-4, a voltage controlled one). In the case of smallest diameter of 1.1 cm∅, a suspended tube of SS304 was tested using lower power pulser (RUP-4), at its near maximum capability of 1.2 kW. In this case also, very bright plasmas were formed, mainly inside the tube and resulted in high temperature there (~700 °C). Nitrogen uptake was superior for higher temperature PIII treatments (>700 °C), combining ion implantation and thermal diffusion, which allowed the formation of TiN and Ti2N on the Ti alloy samples inside tubes with diameters ≤4 cm. In this paper, detailed discussion of results of above cited PIII tests with diversified tubes and configurations are presented, together with the analysis of the corresponding treated surfaces of the samples inside, outside and on the support detached from the tube.
Keywords: Plasma immersion ion implantation, Sputtering and deposition inside metallic tubes, TiN and Ti2N in high temperature PIII, Tubes with different dimensions and configurations

Publ.-Id: 27586 - Permalink


cupla - C++ User interface for the Platform independent Library Alpaka
Widera, R.ORC
cupla [qχɑpˈlɑʔ] is a simple user interface for the platform independent parallel kernel acceleration library alpaka. It follows a similar concept as the NVIDIA® CUDA® API by providing a software layer to manage accelerator devices. alpaka is used as backend for cupla.
  • Software in the HZDR data repository RODARE
    Publication date: 2018-06-10
    DOI: 10.14278/rodare.29
    License: LGPL-3.0

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Publ.-Id: 27585 - Permalink


Commissioning of a 4D MRI phantom for use in MR-guided radiotherapy
Schneider, S.; Dolde, K.; Engler, J.; Hoffmann, A.; Pfaffenberger, A.;
Purpose:
Systems for integrated magnetic resonance guided radiation therapy (MRgRT) provide real-time and on-line MRI guidance for unequalled targeting performance of moving tumors and organs at risk. The clinical introduction of such systems requires dedicated methods for commissioning and routine machine quality assurance (QA). The aim of the study was to develop a commissioning protocol and method for automatic quantification of target motion and geometric accuracy using a 4D MRI motion phantom.

Material and Methods:
The commissioning was performed on a clinically used 3T MR scanner. The phantom was positioned on a flat tabletop overlay using an in-house constructed base plate for a quick and reproducible setup. The torso-shaped phantom body, which was filled with mineral oil as signal generating medium, includes a 3D grid structure for image distortion analysis and a cylindrical thru-hole in which a software-controlled moving rod with a hypo-intense background gel and a decentralized hyper-intense target simulates 3D organ motion patterns. To allow for sequence optimization, MR relaxometry was performed to determine the longitudinal T1 and transverse T2 relaxation times of both target and background gel in the movable cylinder. The geometric image distortion was determined as the mean and maximum 3D Euclidean distance (∆mean, ∆max) of grid points determined by non-rigid registration of a 3D spoiled gradient echo MRI scan and a CT scan. Sinusoidal 1D/2D/3D motion trajectories, varying in amplitude and frequency, as well as an exemplary 1D MR-navigator diaphragm motion pattern extracted from a volunteer scan were scanned by means of 2D cine MRI. Target positions were automatically extracted from 2D cine MRI using an in-house developed software tool.

Results:
The base plate enabled a reproducible setup with a deviation of <1 mm in all directions. Relaxometry yielded T1/T2 values for target and background gel of 208.1±2.8 / 30.5±4.7 ms and 871 .36±36 / 13.4±1.3 ms respectively. The geometric distortion in the MRI scan increased with distance from the magnetic isocenter, with ∆mean=0.58±0.30 mm and ∆max=1.31 mm. The frequencies of the reconstructed motion patterns agreed with the pre-set values within 0.5%, whereas the reconstructed amplitudes showed a maximum deviation to the pre-set amplitudes of <0.4 mm in AP/LR direction and <0.2 mm in IS direction.

Conclusion:
A method and protocol for commissioning of a 4D MRI motion phantom on a 3T MR scanner for MRgRT was developed. High-contrast and geometrically reliable 2D cine MR images of the phantom’s moving target could be obtained. The pre-set motion parameters could be extracted with sufficient spatio-temporal accuracy from 2D cine MRI in all motion directions. The measured geometric image distortion of <1.31mm within the phantom grid confirms geometric accuracy of the clinically utilized 3D spoiled gradient echo sequence.
The method developed can be used for routine QA tests of spatio-temporally resolved MRI data in MRgRT.
Keywords: MRI, dynamic phantom, image-guided radiation therapy, commissioning

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  • Secondary publication expected from 26.10.2019

Publ.-Id: 27584 - Permalink


Microstructural degradation and creep fracture behavior of conventionally and thermomechanically treated 9% Chromium Heat Resistant steel
Vivas, J.; Capdevila, C.; Altstadt, E.ORC; Houska, M.; Sabirov, I.; San-Martín, D.
The microstructural degradation and the creep fracture behavior of conventionally and thermomechanically treated Grade 91 steel were investigated after performing Small Punch Creep Tests. A remarkable reduction in creep ductility was observed for the samples thermomechanically treated in comparison to those conventionally treated under the tested conditions of load (200 N) and temperature (700 ºC). A change in the fracture mechanism from a ductile transgranular fracture to a brittle intergranular fracture was observed when changing from the conventionally treated to the thermomechanically treated processing condition, leading to this drop in creep ductility. The change in the fracture mechanism was associated to the localized concentration of creep deformation, close to coarse M23C6 carbides, at the vicinity of prior austenite grain boundaries (PAGB) in the thermomechanically treated samples. The preferential recovery experienced at the vicinity of PAGB produced the loss of the lath structure and the coarsening of the M23C6 precipitates. The electron microscopy images provided suggest that the creep cavities nucleate in these weak recovered areas, associated to the presence of coarse M23C6. After the coalescence of the cavities the propagation of the cracks was facilitated by the large prior austenite grain size produced during the austenitization which favors the propagation of the cracks along grain boundaries triggering the intergranular brittle fracture. This fracture mechanism limits the potential use of the proposed thermomechanical processing routes.
Keywords: Creep resistant steels; thermomechanical treatment; creep fracture behavior; microstructural degradation; small punch creep tests; ausforming

Publ.-Id: 27583 - Permalink


Explicit decay heat calculation in the nodal diffusion code DYN3D
Bilodid, Y.ORC; Fridman, E.ORC; Kotlyar, D.ORC; Shwageraus, E.ORC
The residual radioactive decay heat plays an important role in some accident scenarios and, therefore, needs to be accurately calculated when performing accident analyses. The current reactor simulation codes used for accident analysis account for the residual decay heat by means of simplified models. Typically, these models rely on semi-empirical correlations which are defined over a limited range of burnup and fuel types. Therefore, the applicability of such correlations is limited and any deviation from the definition range may lead to high uncertainties, which is detrimental in evaluating safety margins.
Reactor dynamic code DYN3D was originally developed for transient and accident analysis of LWRs. In DYN3D, the residual radioactive decay heat calculation is based on the German national standard DIN Norm 25463 model. The applicability of this model is limited to a low enriched uranium dioxide fuel for light water reactors.
This paper describes a new general decay heat calculation model implemented in DYN3D. The radioactive decay rate of each nuclide in each spatial node is calculated by recently implemented depletion module and the cumulative released heat is used to obtain the spatial distribution of the decay power for every time step. Such explicit approach is based on first principles and is free from approximations and, thus, can be applied to any reactor system (e.g. thermal and fast) and fuel type. The proposed method is verified against the reference Serpent 2 Monte Carlo solutions for a range of reactor types.
Keywords: DYN3D, Decay heat, Microdepletion

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Publ.-Id: 27581 - Permalink


Comparison of radionuclide association of fungi under laboratory and natural conditions
Wollenberg, A.; Großmann, S.; Günther, A.; Raff, J.; Stumpf, T.;
The varied use of different radionuclides in medicine, industry and research and their disposal has repeat-edly led to the release of these radionuclides into the environment. Through leaching and migration, the anthropogenic released radionuclides can reach the groundwater, endangering the environment, animals and humans. However, the mobility and thus the migration behavior of radionuclides in the soil are influ-enced by the microorganisms living there.
Fungi play an important role in the microbial community of soil and can therefore have a major influence on radionuclide mobility, for example through sorption, accumulation or reduction processes. Therefore, the aim of this research is to investigate the influence of fungi on radionuclide migration in soil by using column and field experiments and to determine the potential of fungi for radiation protection precaution-ary methods or even remediation methods.
For the assessment of the suitability of fungi the first step is to investigate the molecular interactions with radionuclides under laboratory conditions to identify dominant interaction processes. Therefore binding experiments with different media were performed and the molecular binding form was investigated with time-resolved laser-induced fluorescence spectroscopy. In the next step, column experiments were carried out with soil and under natural conditions, in which the retention capacity of the fungi for radionuclide migration in the soil was investigated.
The experiments so far showed that the biochemistry of the fungi determines the metal interaction and not the surrounding environment. Furthermore, it was clearly demonstrated by column experiments, that fungi are able to retain radionuclides significantly.
Keywords: Fungi, Radionuclide, TRLFS, Column
  • Poster
    RCA-Workshop, 12.-14.06.2018, Dresden, Deutschland

Publ.-Id: 27580 - Permalink


C++ & Python API for Scientific I/O with openPMD
Koller, F.ORC; Huebl, A.ORC

openPMD is an open metadata format for open data workflows in open science. This library provides a common high-level API for openPMD writing and reading. It provides a common interface to I/O libraries and file formats such as HDF5 and ADIOS. Where supported, openPMD-api implements both serial and MPI parallel I/O capabilities.

Keywords: openPMD; Open Science; Open Data; HDF5; ADIOS; data; MPI; HPC; research; file-format; file-handling
  • Software in the HZDR data repository RODARE
    Publication date: 2018-07-07
    DOI: 10.14278/rodare.27
    License: LGPL-3.0

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Publ.-Id: 27579 - Permalink


99Tc retention on pyrite and alumina: the effect of Fe2+
Rodríguez, D.; Mayordomo, N.; Stumpf, T.; Mueller, K.;
For the safety case of a nuclear waste repository, Tc is treated very conservatively, assuming no retention by the geotechnical and geological barriers. Tc(VII), pertechnetate (TcO4-), the most dominant species in oxidizing environment is considered to be inert, hardly interacting with minerals and highly mobile. In contrast, the reduced form Tc(IV) is mainly found as solid, TcO2, and its mobility is limited.
The presence of reductants in the near-field of a nuclear waste repository, e.g. Fe2+ is expected due to canister corrosion. Therefore, most of recent studies consider Tc reductive immobilization by mineral containing reductant moieties, such as magnetite (FeIIFe2IIIO4) or mackinawite (FeS) [1,2] or pre-sorbed reductants on mineral phases, like Fe2+ on corundum (a-Al2O3), diaspore (a-AlOOH), goethite (a-FeOOH), and hematite (a-Fe2O3)[3,4].
In this work, we compare the Tc immobilization by two systems: i) pyrite (FeS2) and ii) nano particular alumina in presence of Fe2+ (ternary system).
Pyrite is capable to remove almost 100% of Tc(VII) from solution within 7 days at pH = 6.5. In a further step, we study the effect of ionic strength on the Tc immobilization under different NaCl concentrations, as the retention mechanism could be affected by the change of Tc(IV) solubility, due to different degrees of salinity [4].
Alumina is capable to retain 6.5% of Tc in the absence of reducing Fe2+. However, in the ternary system Tc retention is 100% for pH > 6.5. In this case, the improvement on the Tc reduction is not only due to Fe2+ presence, but also to the surface properties of alumina, triggering heterogeneous reduction of Tc by high Fe2+ surface coverage or possible LDH formation.

This work has been developed in the frame of VESPA II project (02E11607B), supported by the German Federal Ministry of Economy and Energy (BMWi).
Keywords: Technetium, sorption, pyrite, alumina, iron
  • Lecture (Conference)
    The 10th International Symposium on Technetium and Rhenium – Science and Utilization, 03.-06.10.2018, Moscow, Russia

Publ.-Id: 27578 - Permalink


Amphiphilic Siderophore Marinobactin for Froth Flotation Process
Schrader, S.; Kutschke, S.; Rudolph, M.; Pollmann, K.;
The consumption of metallic raw materials increased in the last years. The coverage of demand is getting more difficult, because both primary and secondary raw materials become more and more complex. To find a solution, some new ways have to be gone, like the combination of biotechnology with classic processing methods.
The idea of this work is the biotechnological production of siderophores for the application in the classic froth flotation process. Siderophores are small organic molecules with a high affinity for binding Fe(III) and to form strong complexes also with other metals. They are produced by microorganisms (aerobic bacteria and fungi) and some plants to equalize the low bioavailability of iron in their environment. Especially the group of amphiphilic siderophores are very interesting. The hydrophilic part, carrying hydroxamate groups, is responsible for the binding of the metals. Flotation agents produced by the chemical industry with the same functional groups have already been applied successfully in this processing method. It can be suggested siderophores carrying the same functional groups, also work well as collectors. The fatty acid tail, that is representing the hydrophobic part, gets in contact with the bubble and spares additional chemicals and further working steps for making the target mineral particles hydrophobic.
This work includes on the one hand the biotechnological production of the marine siderophore marinobactin for the first time using a bioreactor and optimized conditions to make the production more efficient. On the other hand, the produced siderophore is tested in different froth flotation micro scale experiments like “Bubble-pick-up-test” and micro flotation in the Halimond Tube. These results show for the first time that amphiphilic siderophores are working in the froth flotation process and supply first concepts about the required concentration of siderophores in this processing process. In addition, the results also include interaction studies of different metals.
The application of amphiphilic siderophores as biochemicals in the froth flotation process can change the classic processing method in a more sustainable process – the bioflotation process. This will reduce the usage of other chemical agents. Moreover the specific metal binding of siderophores changes flotation in a more purposeful and efficient process.
Keywords: Bioflotation, Flotation, Siderophore, Marinobactin
  • Lecture (Conference)
    Applied Biotechnology in Mining, 25.-27.04.2018, Dnipro, Ukraine

Publ.-Id: 27577 - Permalink


Re-irradiation of recurrent gliomas: pooled analysis and validation of an established prognostic score-report of the Radiation Oncology Group (ROG) of the German Cancer Consortium (DKTK)
Combs, S.; Niyazi, M.; Adeberg, S.; Bougatf, N.; Kaul, D.; Fleischmann, D.; Gruen, A.; Fokas, E.; Rodel, C.; Eckert, F.; Paulsen, F.; Oehlke, O.; Grosu, A.; Seidlitz, A.; Lattermann, A.; Krause, M.; Baumann, M.; Guberina, M.; Stuschke, M.; Budach, V.; Belka, C.; Debus, J.; Kessel, K.;
The heterogeneity of high-grade glioma recurrences remains an ongoing challenge for the interdisciplinary neurooncology team. Response to re-irradiation (re-RT) is heterogeneous, and survival data depend on prognostic factors such as tumor volume, primary histology, age, the possibility of reresection, or time between primary diagnosis and initial RT and re-RT. in the present pooled analysis, we gathered data from radiooncology centers of the DKTK Consortium and used it to validate the established prognostic score by Combs et al. and its modification by Kessel et al. Data consisted of a large independent, multicenter cohort of 565 high-grade glioma patients treated with re-RT from 1997 to 2016 and a median dose of 36 Gy. Primary RT was between 1986 and 2015 with a median dose of 60 Gy. Median age was 54 years; median follow-up was 7.1 months. Median OS after re-RT was 7.5, 9.5, and 13.8 months for WHO IV, III, and I/II gliomas, respectively. All six prognostic factors were tested for their significance on OS. Aside from the time from primary RT to re-RT (P = 0.074) and the reresection status (P = 0.101), all factors (primary histology, age, KPS, and tumor volume) were significant. Both the original and new score showed a highly significant influence on survival with P < 0.001. Both prognostic scores successfully predict survival after re-RT and can easily be applied in the routine clinical workflow. Now, further prognostic features need to be found to even improve treatment decisions regarding neurooncological interventions for recurrent glioma patients.
Keywords: Outcome, prognostic score, recurrent glioma, re-irradiation

Publ.-Id: 27576 - Permalink


The state of platinum in pyrite studied by X-ray absorption spectroscopy of synthetic crystals
Filimonova, O.; Nickolsky, M. S.; Trigub, A. L.; Chareev, D. A.; Kvashnina, K. O.; Kovalchuk, E. V.; Vikentyev, I. V.; Tagirov, B. R.;
Pyrite (FeS2) is a typical container of Pt in many types of ores of magmatic and hydrothermal origin, and in some carbon-rich ores of sedimentary-diagenetic origin. Knowledge of the state of Pt disseminated in the matrix of pyrite, including local atomic environment (type of atoms in the nearest and distant coordination spheres, coordination numbers, interatomic distances) and valence state, is necessary for physical-chemical modeling of platinum group elements mineralization and for improvement of Pt ores extraction and processing technologies.
Here we report results of investigation of local atomic structure of synthetic Pt-bearing pyrites using X-ray absorption spectroscopy (XAS). Synthesis experiments, performed at 650 °C in Pt45 saturated system by means of salt flux method, yielded crystals of pyrite with concentration of Pt up to 7 wt.%. SEM and EPMA analyses show that the distribution of Pt within the pyrite grains is of zonal character, but within the distinct zones Pt is distributed homogeneously. Direct correlation between the concentrations of Pt and S and inverse correlation between the concentrations of Pt and Fe were observed in the synthesized pyrite grains. The slopes of the correlation lines correspond to the formation of the solid solutions in the Pt-Fe-S system, and/or to the formation of PtS2. The XAS experiments revealed the existence of two forms of Pt in pyrite. The main form is the solid solution Pt(II) which isomorphically substitutes for Fe. The Pt-S distance in the first coordination sphere increases by ~0.10 Å relative to the Fe-S distance in pyrite, whereas the 3rd coordination sphere is similar to that of pure pyrite. The second, Pt-rich form, was identified by means of HRTEM as nano-sized inclusions of PtS2. Heating experiment with in situ registration of X-ray absorption spectra resulted in partial decomposition of PtS2 nano-sized inclusions with the formation of the solid solution (Fe1-xPtx)S2. Therefore, the PtS2 nano-sized particles can be considered as a quench product. Our data demonstrate that both forms - Pt solid solution and PtS2 nano-sized inclusions (at high Pt content) can present in natural Pt-bearing pyrites.

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  • Secondary publication expected from 28.03.2020

Publ.-Id: 27574 - Permalink


Towards the bottom of the periodic table
Kvashnina, K. O.;
Actinide and lanthanide chemistry is currently experiencing a renaissance, due to the prospects of obtaining novel materials relevant for applications in chemical synthesis, electronics, materials science, nanotechnology, biology and medicine. Most of the fascinating properties of the lanthanide and actinide materials are related to the partially filled 4f/5f valence shell and in contrast to the rest of the periodic table, are poorly understood. This contribution will provide a brief overview of applications of advanced X-ray techniques that have recently become available for studying the electronic structure of actinide and lanthanide materials at The European Synchrotron (ESRF).
  • Invited lecture (Conferences)
    Les Midis Minatec, 08.06.2018, Grenoble, France

Publ.-Id: 27573 - Permalink


Atomic scale reversible opto-structural switching of few atom luminescent silver clusters confined in LTA zeolites
Aghakhani, S.; Grandjean, D.; Baekelant, W.; Coutiño-Gonzalez, E.; Fron, E.; Kvashnina, K.; Roeffaers, M. B. J.; Hofkens, J.; Lievens, B. F.; Sels, P.;
Luminescent silver clusters (AgCLs) stabilized inside partially Ag exchanged Na LTA zeolites show a remarkable reversible on–off switching of their green-yellowish luminescence that is easily tuned by a hydration and dehydration cycle, making them very promising materials for sensing applications. We have used a unique combination of photoluminescence (PL), UV-visible-NIR Diffuse Reflectance (DRS), X-ray absorption fine structure (XAFS), Fourier Transform-Infrared (FTIR) and electron spin resonance (ESR) spectroscopies to unravel the atomic-scale structural changes responsible for the reversible optical behavior of the confined AgCLs in LTA zeolites. Water coordinated, diamagnetic, tetrahedral AgCLs [Ag4(H2O)4]2+ with Ag atoms positioned along the axis of the sodalite six-membered rings are at the origin of the broad and intense green-yellowish luminescence in the hydrated sample. Upon dehydration, the luminescent [Ag4(H2O)4]2+ clusters are transformed into non-luminescent (dark), diamagnetic, octahedral AgCLs [Ag6(OF)14]2+ with Ag atoms interacting strongly with zeolite framework oxygen (OF) of the sodalite four-membered rings. This highly responsive on–off switching reveals that besides quantum confinement and molecular-size, coordinated water and framework oxygen ligands strongly affect the organization of AgCLs valence electrons and play a crucial role in the opto-structural properties of AgCLs.

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  • Secondary publication expected from 04.06.2019

Publ.-Id: 27571 - Permalink


Flow Structures in a Weakly Turbulent Rayleigh-Bénard Convection affected by a Horizontal Magnetic Field
Vogt, T.; Yanagisawa, T.; Ishimi, W.; Tasaka, Y.; Eckert, S.;
MHD Rayleigh-Bénard convection was studied experimentally using the eutectic metal alloy GaInSn inside a box having a square horizontal cross section and an aspect ratio of 5. Flow measurements were performed by means of ultrasound Doppler velocimetry that can capture time variations of instantaneous velocity profiles. Applying a horizontal magnetic field organizes the convective motion into a flow pattern of quasi-two dimensional rolls arranged parallel to the magnetic field [1], [2]. If the Rayleigh number (Ra) is increased over a certain threshold Ra/Q, whereby Q is the Chandrasekhar number, the flow undergoes a transition to turbulence. Besides the primary convection rolls the measurements reveal regular flow oscillations arising from 2D and 3D deformations of the rolls, Ekman-pumping induced flow as well as smaller side vortices that develop around the convection rolls [3]. Our findings demonstrate the importance to take 3D flow effects into account in order to explain the observed flow structures, which are often considered as quasi 2D. The comparison between the experiments and accompanying direct numerical simulations shows a very good agreement.
  • Lecture (Conference)
    INTERNATIONAL CONFERENCE ON RAYLEIGH BÉNARD TURBULENCE, 14.-18.05.2018, Enschede, Netherlands
  • Open Access LogoContribution to proceedings
    INTERNATIONAL CONFERENCE ON RAYLEIGH BÉNARD TURBULENCE, 14.-18.05.2018, Enschede, Netherlands

Publ.-Id: 27570 - Permalink


Large-scale circulations of turbulent Rayleigh-Bénard convection in a finite liquid metal layer
Akashi, M.; Tasaka, Y.; Yanagisawa, T.; Vogt, T.; Murai, Y.; Eckert, S.;
Large-scale circulations of Rayleigh-Bénard convection in a finite liquid metal layer were examined experimentally by means of ultrasonic Doppler velocimetry. The fluid layer with aspect ratio of five and L = 40 mm in height was filled with eutectic alloy of GaInSn (Prandtl number, Pr = 0.03), and multiple ultrasonic transducers for the velocimetry were mounted in the side wall of the vessel to capture 3D structures of the convection.
  • Lecture (Conference)
    International Conference on Rayleigh Bénard Turbulence, 14.-18.05.2018, Enschede, Netherlands
  • Open Access LogoContribution to proceedings
    International Conference on Rayleigh Bénard Turbulence, 14.-18.05.2018, Enschede, Netherlands

Publ.-Id: 27569 - Permalink


LSC Oscillations in a Liquid Metal
Vogt, T.; Horn, S.; Grannan, A.; Aurnou, J.;
We present experimental results of liquid metal Rayleigh Bénard convection in a Gamma = D/H = 2 cylindrical tank. The tank is filled with liquid gallium that has a Prandtl-number Pr = 0.03. Ultrasound Doppler velocimetry is used in this study to measure the instantaneous velocity distribution along four different measuring lines. This technique is a useful tool to measure the velocities in opaque fluids, such as liquid metals non-invasively. Furthermore, a total number of 29 thermocouples is used to monitor the temperature in the experiment. Thus, the experimental set-up allows for a simultaneous analysis of the velocity and temperature field. We observed a strong oscillatory behaviour of the LSC in both, the velocity and temperature signal whose characteristic behaviour remains unchanged over the investigated range of 7x10^4 < Ra < 6x10^6. We analysed the three dimensional structure of the oscillation and compare the results to direct numerical simulation, which are in excellent agreement to the experimental observation.
  • Lecture (Conference)
    INTERNATIONAL CONFERENCE ON RAYLEIGH BÉNARD TURBULENCE, 14.-18.05.2018, Enschede, Netherlands
  • Open Access LogoContribution to proceedings
    INTERNATIONAL CONFERENCE ON RAYLEIGH BÉNARD TURBULENCE, 14.-18.05.2018, Enschede, Netherlands

Publ.-Id: 27568 - Permalink


Controlling the lability of uranyl(VI) through intramolecular π-π Stacking
Mashita, T.; Tsushima, S.; Takao, K.;
A reaction of UO22+ with cyclohexyldiphenylphosphine oxide (OPCyPh2) in ethanol resulted in a perchlorate salt of the 4-fold homoleptic complex, [UO2(OPCyPh2)4](ClO4)2·EtOH. X-ray structure determination revealed that UO2(OPCyPh2)42+ shows a highly symmetric molecular structure supported by the intramolecular π-π stacking interactions between phenyl groups of the neighbouring OPCyPh2 in the equatorial plane of UO22+. To clarify if the reactivity of UO22+ is affected by such a unique coordination structure, the ligand exchange kinetics of [UO2(OPCyPh2)4]2+ in non-coordinating solvents has been studied by NMR line-broadening method. In CD2Cl2 and CD3NO2 solutions, both signals of coordinated and free OPCyPh2 appeared distinctively even at 298 K, while 2D EXSY experiment provided an evidence that the chemical exchange between [UO2(OPCyPh2)4]2+ and free OPCyPh2 occurs in these systems. Thus, this ligand exchange reaction is quite slow in the NMR time-scale. The dependencies of the apparent first-order rate constant (kobs) on temperature and the free OPCyPh2 concentration suggested that this ligand exchange reaction involves associative and dissociative mechanisms both governed by large negative ΔS‡ terms predominantly. Compared with kinetic data of ligand exchange reactions of other UO22+ complexes reported so far, the lability of UO22+ in [UO2(OPCyPh2)4]2+ is found to be significantly suppressed due to the intramolecular π-π stacking interactions as observed in the crystal structure. The DFT calculations successfully reproduced the intramolecular π-π stacking in [UO2(OPCyPh2)4]2+ by considering the empirical dispersion corrections, and provided theoretical rationales to the A and D mechanisms of the ligand exchange reaction of [UO2(OPCyPh2)4]2+.

Publ.-Id: 27567 - Permalink


Dynamic Imaging Based Structure Tracking with Ultrafast X-Ray Tomography
Windisch, D.ORC; Bieberle, M.; Bieberle, A.; Hampel, U.ORC
A common problem in experimental multiphase flow studies is the tracking of structures in the flow domain. Such may be for example particles, bubbles and waves. Ultrafast electron beam X-ray computed tomography (UFXRCT) is a fast cross-sectional imaging technique, which is applicable to opaque multiphase flows. However, as it is a 2D imaging technique, we can only obtain statistical information about properties of moving structures in the given axial planes so far. To progress towards tracking of structures we now devised a novel approach for dynamic imaging-based structure tracking. For that the tomography scanner follows the structure of interest by controlled positioning basing on real-time image data analysis. This approach is described in the following.
Keywords: ultrafast X-ray CT, structure tracking, real-time control
  • Open Access LogoContribution to proceedings
    9th World Congress on Industrial Process Tomography (WCIPT9), 02.-06.09.2018, Bath, United Kingdom
  • Lecture (Conference)
    9th World Congress on Industrial Process Tomography (WCIPT9), 03.09.2018, Bath, United Kingdom

Publ.-Id: 27566 - Permalink


Cerebrovascular Reactivity during Prolonged Breath-Hold in Experienced Freedivers
Keil, V.; Eichhorn, L.; Mutsaerts, H.; Träber, F.; Block, W.; Mädler, B.; van de Ven, K.; Siero, J.; Macintosh, B.; Petr, J.; Fimmers, R.; Schild, H.; Hattingen, E.;
BACKGROUND AND PURPOSE:
Experienced freedivers can endure prolonged breath-holds of up to eleven minutes despite severe hypoxemia and are therefore ideal subjects to study apnea-induced cerebrovascular reactivity (CVR). This multi-parametric study investigates CBF, the spatial coefficient of variation (ASL-sCoV), as a correlate of arterial transit time, and brain metabolism dynamics during prolonged apnea.

MATERIALS AND METHODS:
Fifteen male freedivers (median age: 36.0, CI 32.0–50.0, years; median previous prolonged breath-holds >2.5 mins.: 384, CI 24.0–4,536) underwent repetitive 3T pseudo-continuous arterial spin labeling and 31P-/1H-MR spectroscopy scans before, during and after a five-minute breath-hold (split into early and late phases) and gave temporally matching venous blood gas samples. CVR was temporally and regionally compared to blood gases and previous experience.

RESULTS:
ASL-sCoV decreased during the early breath-hold phase (-30.0%, P=.002), whereas CBF remained almost stable during this phase and increased in the late phase
(+51.8%; P<.0001). CVR differed between the anterior and the posterior circulation during all phases (e.g. late breath-hold: MCA 57.3±14.2 vs. PCA 42.7±10.8 mL/100 g/min.;
P=.001). There was an association between breath-hold experience and lower CBF (1,000 previous breath-holds reduced WM CBF by 0.6 mL/100 g/min.; CI 0.15 –1.1 mL/100 g/min., P=.01). While breath-hold caused peripheral lactate rise (+18.5 %) and hypoxemia (SpO2 -24.0%), cerebral lactate and ATP remained within physiological ranges, despite early signs of oxidative stress (-6.4% phosphocreatine/(ATP+ADP); P=.02).

CONCLUSIONS:
The CVR responses to prolonged apnea are complex, but guarantee the maintenance of a physiological brain metabolism in trained individuals for at least five minutes.

Downloads:

  • Secondary publication expected from 01.10.2019

Publ.-Id: 27565 - Permalink


Architecture and mineral potential of the Paleoproterozoic Karrat Group, West Greenland - Results of the 2017 Season
Rosa, D.; Bernstein, S.; Dewolfe, M. Y.; Dziggel, A.; Grocott, J.; Guarnieri, P.; Kolb, J.; Partin, C. A.; Sørensen, E.-V.; Zimmermann, R.;
The main goal of the 2017 field season was to revise the geological maps of the southern area of Karrat Group exposures. This revision will encompass the 1:100 000 sheets of Maarmorilik 71V.2 Syd, Nuugaatsiaq 71V.2 Nord, Pannertooq 72V.2 Syd, and Svartenhuk 71V.1 Nord, originally compiled between 1980 and 1991. This third field season followed up on fieldwork carried out in 2015 and 2016 and, as the other two field seasons, was jointly financed by the Geological Survey of Denmark and Greenland (GEUS) and the Ministry of Mineral Resources of Greenland (MMR).
Within this framework, and since the focus of the first two seasons had been on the Paleo- proterozoic Karrat Group, the 2017 fieldwork targeted Archean rocks, namely in Panner- tooq (head of Ukkusissat Fjord), Upernivik Ø, Kigarsima/Tornit and the area south of Maarmorilik. This work led to the identification, in what was originally mapped as Archean orthogneiss, of significant paragneiss and quartzite sequences, of uncertain age. These supracrustal sequences often appear infolded with Archean orthogneiss, so some of them could possibly be unrelated to the stratigraphy of the Karrat Group. Similar infolding ob- served in the Qeqertarssuaq Formation, mapped in Kangilleq Fjord, suggests that this for- mation could possibly also be unrelated to the Karrat Group, as traditionally defined. Cor- roborating this interpretation is the fact that higher-P metamorphic assemblages, evi- denced by garnet amphibolite and kyanite micaschist, were documented in the Qeqertars- suaq Formation, but not in overlying formations. This contrasting metamorphic evolution can be interpreted as evidence for an early thermal event, prior to Qaarsukassak Formation deposition. Alternatively, the disparate metamorphic conditions could be accounted for by juxtaposition of different tectonic units during the Rinkian orogeny. T o further constrain the depositional ages of the paragneiss and quartzite (including those of the Qeqertarssuaq Formation), follow up detrital zircon geochronology is warranted. However, regardless of what the subsequent analytical work reveals, these findings appear to already imply signifi- cant revisions to the existing maps.
Within the Paleoproterozoic volcano-sedimentary succession, fieldwork allowed for the identification of the presence of the Qaarsukassak Formation (informal) in Kussinersuaq (Umiammakku Isbræ), Rinks Isbræ, Qingaarssuaq (Kangerlussuaq Fjord), Kigarsima/T ornit (Kangerluarsuk Fjord) and Kangerluarsuup Sermia. This formation hosts the stratabound mineralisation in the Rio Tinto Zinc (RTZ) Discovery area (Kangerluarsuk Fjord), where it was first defined. While no primary Zn mineralisation was observed at the defined localities, with only faint zinc zap responses obtained at Kussinersuaq, and other localities not tested for mineralisation, these findings significantly stretch the areal extent of the stratabound Zn- hosting Qaarsukassak Formation, and are therefore of economic significance. Detailed follow up photogeological mapping and interpretation of hyperspectral scenes of this min- eralisation host should consequently be carried out. Further work within the Paleoprotero- zoic Karrat Group, included the study of the mafic volcanic rocks of the Kangilleq Fm (in- formal), was aimed at recognising horizons with distinct geochemical signatures (alkaline vs. subalkaline), as identified in samples collected in previous seasons, in order to elucidate petrogenesis of the volcanic rocks.
The structural setting and metamorphism of the Prøven Igneous Complex (PIC) is key to understanding the geological evolution of the region and its lower contacts and some internal structures were studied. This work demonstrated that the PIC comprises one or more tabular intrusions. In the west, near Upernavik, the complex was emplaced close to the basement-cover contact. Farther to the east and south, it seems to have been emplaced at a higher stratigraphic position within the Paleoproterozoic sedimentary sequence. Subse- quently, the complex was displaced to the NW (north side of the PIC) and SE (south side of the PIC). Wherever it was studied, both North and South, this contact is a shear zone. The PIC contains abundant enclaves of meta-sedimentary rocks, particularly near the lower contact. The enclaves are most likely to be from a Paleoproterozoic sequence - the Karrat Group - although this assumption is unproven. In the instances where possible cross- cutting intrusive relations are found with meta-sedimentary rocks at the base of the PIC, the cross-cutting igneous rocks are late syn-tectonic biotite granite and leucogranites, rather than elements of the PIC proper. Earlier workers assumed that these late syn-tectonic granites and the PIC were part of the same magmatic event and were both late syn- tectonic. Our new field evidence from the northern contact of the PIC, consistent with re- cently published geochronology (Sanborn-Barrie et al. 2017), shows that the PIC was af- fected by intense fabric formation and folding and that its contacts with its host rocks, where we have seen them, are always concordant as a consequence of intense defor- mation. We conclude that the published interpretation that the PIC was emplaced relatively late during Rinkian orogenic evolution should be rejected (Grocott & Pulvertaft, 1990 and references therein).
  • Other report
    København, Danmark: Danmarks of Grønlands geologiske undersøgelse, 2018
    102 Seiten

Publ.-Id: 27564 - Permalink


Analysis of flow patterns in high gravity equipment using gamma-ray computed tomography
Groß, K.; Bieberle, A.; Gladyszewski, K.; Schubert, M.; Hampel, U.; Skiborowski, M.; Górak, A.; (Editors)
The capacity of today’s gas-liquid contacting equipment such as tray or packed columns is limited by the gravitational-driven liquid flow. Intensified equipment applying centrifugal force offers great potential for enhancing the mass transfer and for reducing equipment size. Yet, detailed knowledge about the liquid flow inside rotating packings is scarce due to limited accessibility with conventional measurement systems. In this study, a gamma-ray computed tomography is employed to quantify the liquid hold-up and its distribution in the moving packing.
Keywords: Flow behavior, gas-liquid flow pattern, local liquid hold-up, non-invasive flow imaging, rotating packed bed

Publ.-Id: 27563 - Permalink


Evaluation of liquid hold-up in a rotating packed bed for high gravity fluid separation using process-synchronized gamma-ray computed tomography
Groß, K.; Bieberle, A.; Gladyszewski, K.; Schubert, M.; Skiborowski, M.; Hampel, U.; Górak, A.; (Editors)
A Rotating Packed Bed (RPB) is a compact and flexible fluid separation equipment, which utilizes a centrifugal forces to achieve enhanced mass and energy transfer between a liquid and a vapour phase, brought in contact within a porous rotating packing. In order to perform a reliable design and scale-up of RPBs, detailed knowledge about the hydrodynamics and flow mechanisms within the equipment is strongly required. However, due to the non-transparent solid casing, such insight cannot be generated by common analytics. In the present study, liquid hold-up and gas-liquid phase distribution are determined in a porous metal foam packing of 450 mm diameter installed in a pilot-scale RPB using a high-energetic gamma-ray computed tomography (CT). The CT system consists of an isotopic source Cs 137 and an in-house developed radiation detector comprising 320 scintillation detector elements operated in photon counting mode in order to detect each single gamma photon. In particular, the liquid hold-up distribution and the lateral spreading behaviour is visualized and analysed relative to the motion of the rotating packing applying conventional CT scanning and a time-averaged angular-resolved CT scanning procedure, respectively.
Keywords: Fluid Separation, High Gravity Equipment, Rotating Packed Beds, Gamma-Ray Computed Tomography, Process-Synchronized Imaging
  • Contribution to proceedings
    World Congress on Industrial Process Tomography, 02.-06.09.2018, Bath, UK
  • Lecture (Conference)
    World Congress on Industrial Process Tomography, 02.-06.09.2018, Bath, UK

Publ.-Id: 27562 - Permalink


Compact high energy x-ray spectrometer based on forward Compton scattering for high intensity laser plasma experiments
Singh, S.; Versaci, R.; Laso Garcia, A.; Morejon, L.; Ferrari, A.; Molodtsova, M.; Schwengner, R.; Kumar, D.; Cowan, T.;
This article describes the design and presents recent results from testing and calibration of a forward Compton scattering gamma-ray spectrometer. The calibration was performed using a bremsstrahlung source on the photon scattering facility at the ELBE accelerator at Helmholtz-Zentrum Dresden-Rossendorf, which provides gamma-ray photons with energies up to 18 MeV. The calibration was conducted at different bremsstrahlung end point energies - 10.5, 13, 15 and 18 MeV. Experimental spectra show systematic increase in the maximum energy, photon temperature and flux. The spectrometer is effective for an energy range of 4 to 20 MeV with 20 to 30% energy resolution. The article also describes the design and shielding considerations which helped to achieve a dynamic range greater than 30 with this spectrometer. The comparison between experimental results and Monte Carlo simulations are also presented.
Keywords: bremsstrahlung, photon scattering, gamma rays, Compton spectrometer

Publ.-Id: 27561 - Permalink


Modification of the perpendicular anisotropy in synthetic antiferromagnets by global and local ion beam irradiation
Lenz, M.; Koch, L.; Samad, F.; Arekapudi, P.; Fallarino, L.; Hellwig, O.;
We investigate sputter deposited synthetic antiferromagnets consisting of Co/Pt multilayers with perpendicular anisotropy. Repeated multilayer-blocks are antiferromagnetically coupled to each other via Ru interlayers. This complex sample structure allows an exact tuning of the energy contributions perpendicular anisotropy, interlayer exchange and demagnetization: Varying repeats within the Co/Pt multilayers (X) or a different number of multilayer-blocks (N) lead to various magnetic phases and 3-dimensional textures [1].
By ion beam irradiation we can change the balance of these energy contributions due to an intermixing at the interfaces. With this we can realize various magnetic phases within one and the same sample and by local irradiation we can even achieve a lateral coexistence of different magnetic phases.
We will present our investigations of globally and locally irradiated synthetic antiferromagnet’s field reversal behaviour, using vibrating sample magnetometry and high resolution magnetic force microscopy.
[1] O. Hellwig et al., J. Magn. Magn. Mater. 319, 13 (2007)
  • Poster
    Joint European Magnetic Symposia (JEMS), 03.-07.09.2018, Mainz, Deutschland

Publ.-Id: 27560 - Permalink


Parametric resonances in periodically perturbed dynamo models
Giesecke, A.; Stefani, F.;
I present results on kinematic dynsamo models driven by an axisymmetric large scale flow impacted by periodic perturbations due to azimuthally propagating vortices. I found a strong impact on growth rates and frequencies with regimes of parametric resonances whenn the frequency of the perturbation is twice the frequency of the unperturbed case. These models behave similar to rotating mechanical systems subject to periodic distortions that are described by the Matthieu equation. A possible application are dynamo experiments like VKS dynamo in Cadarache or convection driven planetary dynamos that are influenced by tidal forces.
Keywords: dynamo DRESDYN
  • Lecture (Conference)
    Planetary-Stellar Connection: The Sun's Lesson, 07.-09.05.2018, Freiburg, Deutschland

Publ.-Id: 27559 - Permalink


Advanced correction algorithms for ultrafast X-ray computed tomography
Bieberle, M.; Wagner, M.; Gücker, F.; Neumann, M.; Hampel, U.;
Ultrafast electron beam X-ray computed tomography is a unique imaging technique for the investigation of multiphase flows. It provides high-resolution cross-sectional images at rates of up to 4,000 fps from two tomography planes, which also allows axial velocities to be determined. As is typical for such complex measurement systems, there are several physical effects leading to deviations from the ideal imaging system. On the one hand, these are deviations associated to X-ray computed tomography (CT) in general, such as photon scattering and beam hardening. On the other hand, there are several effects originating from the electron beam deflection, which are in particular related to electron beam X-ray CT. For example, some uncertainties about the final size and position of the X-ray focal spot path on the target are remaining. This paper addresses effects and corresponding practical correction algorithms for both categories. Scattering and beam hardening as interlinked phenomena are treated by correction based on fast ray-tracing in-plane simulations. The topic of focal spot path uncertainties has been analysed in detail with respect to different parameters. The problem is tackled with two approaches. The first approach searches the correct angular positions of the X-ray focal spot on the target by maximizing the grey value variance in the resulting reconstructed images. The second approach evaluates the resulting distance map between the two imaging planes by combining simulated distributions with measured values.
Keywords: correction algorithms, image reconstruction, ultrafast, X-ray CT
  • Contribution to proceedings
    9th World Congress on Industrial Process Tomography (WCIPT9), 02.-06.09.2018, Bath, United Kingdom
    Proceedings of the 9th World Congress on Industrial Process Tomography
  • Lecture (Conference)
    9th World Congress on Industrial Process Tomography (WCIPT9), 02.-06.09.2018, Bath, United Kingdom

Publ.-Id: 27558 - Permalink


Local structural effects of Eu3+ incorporation into xenotime-type solid solutions with different host cations
Xiao, B.; Lösch, H.; Huittinen, N.ORC; Schmidt, M.ORC
In this study, the effect of host cations on the local structure around the dopant site of materials from the xenotime family is systematically studied on the molecular level. A series of six Eu3+-doped xenotime-type single crystals (Tb, Y, Ho, Er Yb, and LuPO4) have been grown and spectroscopically analyzed using polarization−dependent laser−induced luminescence spectroscopy (p−TRLFS). Our results demonstrate that the structural disorder changes in a non-linear manner with a structural break between Yb3+ and Lu3+. Despite adopting identical crystal structures, the solid solutions of these materials vary significantly, and differ from monazite solid solutions. Similar Eu3+ incorporation behavior with a strongly distorted dopant site is found for the early members of the xenotime family, while LuPO4 with the largest host vs. dopant radii mismatch is anomalous in that it contains the most symmetrical lattice site. This goes along with a significantly stronger crystal field, indicating a shorter Eu – O bond distance, as well as a strong vibronic coupling to external translational lattice vibrations. The p−TRLFS analysis confirms the breakdown of the crystallographic site symmetry from D2d to C1 in YPO4, whereas a small distortion of the crystallographic site in LuPO4 results in an S4 point symmetry for the Eu3+ cation. The lattice with the smallest cation host site is no longer sufficiently flexible to make room for Eu3+ and instead “forces” the guest ion to occupy a less distorted Lu3+ site.
Keywords: Xenotime, Incorporation, TRLFS, Luminescence, Eu3+

Downloads:

  • Secondary publication expected from 05.07.2019

Publ.-Id: 27557 - Permalink


Temporal Evolution of Calcite Surface Dissolution Kinetics
Bibi, I.; Arvidson, R. S.; Fischer, C.; Luttge, A.;
This brief paper presents a rare dataset: a set of quantitative, topographic measurements of a dissolving calcite crystal over a relatively large and fixed field of view (~400 μm) and long total reaction time (>6h). Using a vertical scanning interferometer and patented fluid flow cell, surface height maps of a dissolving calcite crystal were produced by periodically and repetitively removing reactant fluid, rapidly acquiring a height dataset, and returning the sample to a wetted, reacting state. These reaction-measurement cycles were accomplished without changing the crystal surface position relative to the instrument’s optic axis, with an approximate frequency of one data acquisition per six minutes’ reaction (~10/h). In the standard fashion, computed differences in surface height over time yield a detailed velocity map of the retreating surface as a function of time. This dataset thus constitutes a near-continuous record of reaction, and can be used to both understand the relationship between changes in the overall dissolution rate of the surface and the morphology of the surface itself, particularly the relationship of a) large, persistent features (e.g., etch pits related to screw dislocations; b) small, short-lived features (e.g., so-called pancake pits probably related to point defects); c) complex features that reflect organization on a large scale over a long period of time (i.e., coalescent “super” steps), to surface normal retreat and stepwave formation. Although roughly similar in frequency of observation to anin situ AFM fluid cell, this VSI method reveals details of the interaction of surface features over a significantly larger scale, yielding insight into the role of various components in terms of their contribution to the cumulative dissolution rate as a function of space and time.

Publ.-Id: 27556 - Permalink


Self-Diffusion in Amorphous Silicon by Local Bond Rearrangements
Kirschbaum, J.; Teuber, T.; Donner, A.; Radek, M.; Bougeard, D.; Lundsgaard Hansen, J.; Nylandsted Larsen, A.; Posselt, M.; Bracht, H.; Böttger, R.;
Experiments on self-diffusion in amorphous silicon (Si) were performed at temperatures between 460 to 600° C. The amorphous structure was prepared by Si ion implantation of single crystalline Si isotope multilayers epitaxially grown on a silicon-on-insulator wafer. The Si isotope profiles before and after annealing were determined by means of secondary ion mass spectrometry. Isothermal diffusion experiments reveal that structural relaxation does not cause any significant intermixing of the isotope interfaces whereas self-diffusion is significant before the structure recrystallizes. The temperature dependence of self-diffusion is described by an Arrhenius law with an activation enthalpy Q =2.70 +- 0.11eV and preexponential factor D0=5.5(+11.1 -3.7) × 10−2 cm2 s−1. Remarkably, Q equals the activation enthalpy of hydrogen diffusion in amorphous Si, the migration of bond defects determining boron diffusion, and the activation enthalpy of solid phase epitaxial recrystallization reported in the literature. This close agreement provides strong evidence that self-diffusion is mediated by local bond rearrangements rather than by the migration of extended defects as suggested by Strauß et al. (Phys. Rev. Lett. 116, 025901 (2016)).
Keywords: amorphous Si, self-diffusion, isotope multilayers

Publ.-Id: 27555 - Permalink


Local structural analyses of the uranium and zirconium in fuel debris containing boron at the Fukushima Daiichi NPP accident
Uehara, A.; Akiyama, D.; Numako, C.; Takeda, S.; Ikeda-Ohno, A.ORC; Terada, Y.; Nitta, K.; Ina, T.; Kirishima, A.; Sato, N.
Mixtures of UO2, ZrO2 and B4C, that are one possible phase of nuclear debris remaining in the damaged reactors at the Fukushima Dai-ichi Nuclear Power Plants, were prepared at high temperature between 1200 to 1600 C, and their solid state structure was characterised by X-ray absorption spectroscopy at both U LIII- and Zr K-edges, and powder X-ray diffraction. The data were further analysed by principal component analysis.
Keywords: Nuclear fuel debris, Fukushima Dai-ichi Nuclear Power Plants, solid state, characterisation, uranium, zirconium, boron, X-ray absorption spectroscopy, X-ray diffraction
  • Lecture (Conference)
    2018 Fall Meeting, Atomic Energy Society of Japan, 05.09.2018, Okayama University, Japan

Publ.-Id: 27554 - Permalink


Design, validation and testing of new receiver coatings for concentrated solar power
Krause, M.; Heras, I.; Lungwitz, F.; Wenisch, R.; Schumann, E.; Janke, D.; Guillén, E.; Munnik, F.; Azkona, I.; Gemming, S.; Escobar-Galindo, R.;
Increasing central receiver solar plant’s operation temperature from 550°C to about 800°C would improve the energy conversion efficiency by 15 to 20%. Absorber coatings appropriate for such conditions have to outperform the state-of-the-art pigment paint Pyromark® that has an absorptivity α > 95% but a high emittance (ε ~ 80%). The development of environmentally stable solar-selective coatings (SSC) for these temperatures requires new concepts of design and thermal testing. Multilayer SSC based on [AlyTi1-y(OxN1-x)] absorbers were designed after an extensive microstructural characterization and optical simulations. Based on excellent simulation performance values of α = 88-94% and εRT = 4.8-13.6%, complete coating stacks were experimentally validated and tested in vacuum and in air up to temperatures of 800°C [1]. Thermal stability in vacuum up to 800°C is shown by in situ Rutherford backscattering spectrometry (RBS), Raman spectroscopy and spectroscopic ellipsometry (SE) for individual layers as well as for complete SSC. Regarding in-air stability, the most stable SSC fulfilled the standard performance criterion PC ≤ 5% for 300 symmetric, 3 hours long cyclic tests between 300°C and 600°C. Another promising and simpler coating concept to be presented is based on a metal-doped transparent conductive oxide acting as solar-selective transmitter on top of a blackbody. The onset of the infrared reflectivity is tuneable by variation of the parameters during reactive magnetron sputtering deposition, thus matching the specific temperature requirements during solar applications. Thermal stability up to 800°C in vacuum is demonstrated by in situ RBS and SE.

Financial support by the EU, grant No. 645725, project FRIENDS2, and the HGF via the W3 program (S.G.) is gratefully acknowledged.

[1] I. Heras, et al. , Design of high-temperature solar-selective coatings based on aluminium titanium oxynitrides [AlyTi1-y(OxN1-x)]. Part 1: Advanced microstructural characterisation and optical simulation. Solar Energy Materials and Solar Cells 176 (2018) 81-92
Keywords: Solar selective coatings, oxynitrides, TCO's, thermosolar energy, in situ analysis, cluster tool
  • Invited lecture (Conferences)
    5th European Conference in Nanofilms (ECNF), 20.-22.03.2018, Cranfield, United Kingdom

Publ.-Id: 27553 - Permalink


Percolated Si:SiO2 Nanocomposites: Oven- vs. Millisecond Laser-induced Crystallization of SiOx Thin Films
Schumann, E.; Hübner, R.; Grenzer, J.; Gemming, S.; Krause, M.ORC
Three-dimensional nanocomposite networks consisting of percolated Si nanowires in a SiOx matrix, Si:SiO2, were studied. The structures were obtained by reactive ion beam sputter deposition of SiOx (x~0.6) thin films at 450 °C and subsequent crystallization using conventional oven as well as millisecond line focus laser annealing. Rutherford backscattering spectrometry, Raman spectroscopy, X-ray diffraction, cross-sectional and energy-filtered transmission electron microscopy were applied for sample characterization. While oven annealing resulted in a mean Si wire diameter of 10 nm and a crystallinity of 72 % within the Si volume, almost single-domain Si structures with 30 nm in diameter and almost free of amorphous Si were obtained by millisecond laser application. The structural differences are attributed to the different crystallization processes: Conventional oven tempering proceeds via solid state, millisecond laser application via liquid phase crystallization of Si. The 5 orders of magnitude larger diffusion constant in the liquid phase is responsible for the three times larger Si nanostructure diameter. In conclusion, laser annealing offers not only significantly shorter process times but moreover a superior structural order of nano-Si compared to conventional heating.
Keywords: silicon; nanostructures; percolated networks; nanocomposites; thin films; laser processing; phase separation; liquid phase crystallization

Publ.-Id: 27552 - Permalink


Tiny but timely: Crystal surface reactivity constraints on diagenesis
Fischer, C.;
Quantitative variability of diagenetic alteration is a major challenge for the development of predictive concepts. Here, we focus on the nano- and microscopic variability of crystal surface reactivity as a major constraint to fluid-solid reactions. While density and distribution of defect structures play a critical role, additional important impact is provided by the interaction of surfaces with nanoparticles and colloids during precipitation reactions. Quantitative data are available from multiple surface-sensitive methods that provide mechanistic insight via reaction rate maps and rate spectra and challenge the prevailing view that crystal dissolution is simply the inverse process of continuous crystal growth at crystal dislocations, e.g., during secondary porosity formation. Mechanistic insight is available from kinetic Monte Carlo methods, e.g., about inherited reactivity. The upscaling of such simulation results to the pore scale is a challenging task that requieres novel numerical approaches. Additionally to heterogeneities of the fluid flow field, reactive transport modeling approaches need to address ultimately the variability in surface reactivity in order to provide improved predictability.
  • Lecture (Conference)
    Goldschmidt-Conference, 12.-17.08.2018, Boston, USA

Publ.-Id: 27551 - Permalink


Pulsating dissolution of crystalline matter
Fischer, C.;
The reaction of crystalline material with fluids is of relevance for natural and technical processes. A basic as¬sump-tion has been that the reaction products are continuously released from the crystal surface. New experimental and ana-lytical results show something fundamentally different: Material is released in a series of reaction pulses [1]. We present reaction rate maps that are derived from sequences of topography maps and quantify the spatial distribution of reaction rates across the crystal surface. The first (rate acceleration) and second (rate jerk) temporal derivative of the rate quantify the dynamic formation and loss of reactive surface sites. The resulting variability in nanoscale roughness is a key factor that controls kink-site distribution and density and therefore may help explain why laboratory (bulk) dissolution rates are so variable.
Applied and theoretical implications impact both the upscaling of crystal dissolution kinetics, and more importantly, the problem of how dissolution and growth are connected via the equilibrium state. These results challenge the prevailing view that crystal dissolution is simply the inverse process of continuous crystal growth at crystal dislocations. Consequently, we need to examine how macroscopic crystal equilibrium reflects continuous or discontinuous processes in the microscopic state.

[1] Fischer, C., Luttge, A., 2018. Pulsating dissolution of crystalline matter. PNAS 115, 897-902.
  • Invited lecture (Conferences)
    Goldschmidt-Conference, 12.-17.08.2018, Boston, USA

Publ.-Id: 27550 - Permalink


Synthesis and radiofluorination of a novel monocarboxylate transporter 1 inhibitor for tumor imaging by PET
Sadeghzadeh, M.; Moldovan, R.-P.; Wenzel, B.; Fischer, S.; Teodoro, R.; Ludwig, F.-A.; Gurrapu, S.; Drewes, L. R.; Brust, P.;
Monocarboxylate transporter 1 (MCT1) is an integral plasma membrane protein that bi-directionally transports lactate and ketone bodies and is highly expressed in non-hypoxic regions of human colon, brain, breast, lung and other tumors. Accordingly, MCT1 inhibitors are regarded to be of potential clinical use. In the current study we developed a new 18F-labeled radioligand for in vivo imaging of MCT1-overexpressing brain tumors by PET.
A new fluorinated analogue of α-cyano-4-hydroxycinnamic acid (RM231) was synthesized from m-anisidine via alkylation, ortho formylation and Knoevenagel condensation in 50% overall yield. Its MCT1 inhibition activity was evaluated via [14C]lactate uptake assay on rat brain endothelial 4 cells. The mesylated precursor was similarly prepared in 52% overall yield. Radiosynthesis of [18F]RM231 was achieved by a two-step reaction, starting with the radiofluorination using [18F]-K2CO3-K222 complex followed by protective group removal via hydrolysis under optimized reaction conditions.
RM231 showed relatively high MCT1 inhibition activity (IC50 = 12 nM). The radiolabeled intermediate was obtained by an optimized procedure (acetonitrile, 5.5 mg of K222, 0.7 mg of K2CO3, 12-15 GBq of K18F, 100 ̊C, 8 min) with 44-50% yield determined by radio-HPLC analysis (N=3, non-isolated). The final product was obtained by hydrolysis with TFA in dry dichloromethane at room temperature for 10 minutes with 29% yield (radio-HPLC, non-isolated).[18F]RM231 could be obtained after separation using semi-preparative HPLC (RP C18 column; 30% ACN, 20 mM NH4CO2H). Currently, attempts are made to stabilize and formulate the final product appropriately for biological investigation. The newly developed MCT1 radioligand is anticipated to be a useful agent for imaging of the tumors with PET. Accordingly, animal studies on the new radiotracer are currently under investigation.
Keywords: Monocarboxylate transporter 1, α-Cyanocinnamic acid derivatives, Radiofluorination, Fluorine-18, Brain tumors.
  • Lecture (Conference)
    18th Radiochemical Conference, 13.-18.05.2018, Mariánské Lázně, Czeck Republic

Publ.-Id: 27549 - Permalink


Effect of beam energy straggling on resonant yield in thin gas targets: The cases 22Ne(p,gamma)23Na and 14N(p, gamma)15O
Bemmerer, D.; Cavanna, F.; Depalo, R.; Aliotta, M.; Anders, M.; Boeltzig, A.; Broggini, C.; Bruno, C.; Caciolli, A.; Corvisiero, P.; Davinson, T.; Elekes, Z.; Ferraro, F.; Formicola, A.; Fülöp, Z.; Gervino, G.; Guglielmetti, A.; Gustavino, C.; Gyürky, G.; Menegazzo, R.; Mossa, V.; Pantaleo, F. R.; Prati, P.; Scott, D. A.; Straniero, O.; Szücs, T.; Takács, M. P.; Trezzi, D.;
When deriving resonance strengths using the thick-target yield approximation, for very narrow resonances it may be necessary to take beam energy straggling into account. This applies to gas targets of a few keV width, especially if there is some additional structure in target stoichiometry or detection efficiency. The correction for this effect is shown and tested on recent studies of narrow resonances in the 22Ne(p, γ)23Na and 14N(p, γ)15O reactions.

Publ.-Id: 27548 - Permalink


Erratum: Three new low-energy resonances in the 22Ne(p,γ)23Na reaction
Cavanna, F.; Depalo, R.; Aliotta, M.; Anders, M.; Bemmerer, D.; Best, A.; Böltzig, A.; Broggini, C.; Bruno, C. G.; Caciolli, A.; Corvisiero, P.; Davinson, T.; Di Leva, A.; Elekes, Z.; Ferraro, F.; Formicola, A.; Fülöp, Z.; Gervino, G.; Guglielmetti, A.; Gustavino, C.; Gyürky, G.; Imbriani, G.; Junker, M.; Menegazzo, R.; Mossa, V.; Pantaleo, F. R.; Prati, P.; Scott, D. A.; Somorjai, E.; Straniero, O.; Strieder, F.; Szücs, T.; Takács, M. P.; Trezzi, D.;
Reported strengths of newly discovered resonances in [F. Cavanna et al., Phys. Rev. Lett. 115, 252501 (2015)] were affected by an error in the analysis. The energy straggling of the ion beam was erroneously neglected. When taking this effect into account, 18-19% higher values are found for the resonance strengths. The astrophysical implications are unchanged.

Publ.-Id: 27547 - Permalink


Phage Display Derived Short Peptides for the Recovery of Valuable Metal Ions from Water Streams
Matys, S.; Schönberger, N.; Braun, R.; Lehmann, F.; Flemming, K.; Lederer, F.; Pollmann, K.;
Since several years, the phage surface display technique (PSD) has been successfully applied for the development of new receptor-ligand pairs for medical purposes, new pharmaceuticals or the elucidation of protein-protein interactions [1,2]. A comparatively new methodological approach is the use of this technique for bioremediation [3,4]. We established the PSD as novel biotechnological platform for the selective recovery of industrial relevant elements either in ionic form or as small particles. The commercially available bacteriophage libraries Ph.D.C7C and Ph.D.12 (New England Biolabs, Inc.) were used for isolation and identification of specific nickel, cobalt and gallium ion binding peptides. From a pool of 1,2 x 10⁹ different peptide motifs, 24 phage clones for nickel, 20 for cobalt and 108 for gallium were isolated in the iterative bio-panning process. The binding strength of these phages clones was compared with the one of unmodified wild type phages by performing adsorption tests onto metal loaded agarose beads. Cross binding tests revealed for most of the nickel binding phages also binding capacities for cobalt and vice versa.


[1]. H.M.E. Azzazy, W.E. Highsmith Jr., Clinical Biochemistry. 2002, 35, 425-45:
[2] J. Pande, M.M. Szewczyk, A.K. Grover, Biotechnology Advances. 2010, 28, 849-58:
[3] S.B. Curtis, J. Hewitt, R.T.A. MacGillivray, W.S. Dunbar, Biotech. Bioeng. 2009, 102, 644-650:
[4] T. Hatanaka, A. Matsugami, T. Nonaka, H. Takagi, F. Hayashi, T. Tani, N. Ishida, Nature Comm. 2017, 8, 15670:
Keywords: phage surface display, biopanning, metal recovery
  • Poster
    4th International Conference on Bioinspired and Biobased Chemistry & Materials, 14.-17.10.2018, Nizza, Frankreich

Publ.-Id: 27546 - Permalink


Modelling of condensation inside an inclined pipe
Moonesi Shabestary, A.; Bieberle, A.; Krepper, E.; Lucas, D.; Hampel, U.;
Designs of future nuclear boiling water reactor concepts are usually equipped with a so-called emergency cooling system which is passively driven to remove heat from the core to the outside in case of an accident. The emergency cooling system consists of a bunch of slightly inclined horizontal pipes which are immersed in a tank of subcooled water. At normal operation conditions, the pipes are filled with water and no heat transfer to the secondary side of the condenser exists. In case of an accident during which the water level in the core is decreasing, steam enters the emergency pipes and due to the cold water around the pipe, the steam condenses at the inner wall of the pipes. Therefore, the emergency condenser removes the decay heat from the reactor core. In the current PANAS-project all the involved thermal hydraulic components are studied intensively. The focus of the current paper is on CFD modeling of the emergency condenser and validation of the models with data obtained from experiments performed at the TOPFLOW facility at a single condensation pipe at operating conditions close to reality, i.e. at high pressure and saturated steam.
In this paper, the inflow of the pipe is assumed as pure steam. Due to wall condensation a thin liquid film is generated near the wall leading to annular flow. The generated liquid film stays in direct contact with steam which is on saturation temperature causing direct contact condensation at the interface between steam and liquid. Because of the gravity force, the laminar liquid film is falling, gathering at the lower part of the pipe and finally a stratified flow occurs. Combining wall condensation, direct contact condensation and effects of the liquid film on the heat transfer coefficient is a major focus of this paper. Finally, the results of the simulations are validated with the experimental data.
  • Contribution to proceedings
    49th Annual Meeting on Nuclear Technology, 29.-30.05.2018, Berlin, Germany
    Modelling of condensation inside an inclined pipe

Publ.-Id: 27545 - Permalink


Complexation of europium with chondroitin sulfate
Barkleit, A.ORC; Patzschke, M.; Heim, K.; Seidler, D. G.
Glycosaminoglycans (GAGs) are linear polysaccharides and highly negatively charged. GAGs are part of proteoglycans which are major components of the extracellular matrix. They are involved in binding cations (such as sodium, potassium and calcium) and water, and also regulating the movement of molecules through the matrix. Individual functions of proteoglycans can be attributed to either the protein core or the attached GAG chain. The GAG family consists of heparin/heparan sulfate, chondroitin sulfate (CS) and dermatan sulfate (DS). CS is composed of the disaccharide unit N-acetylgalactosamine (D-GalNAc) and D-glucuronic acid which can be sulfated at the C4 and C6 of GalNAc (CS4S and CS6S). DS is defined by presence of L-iduronic acid residues and is always sulfated at C4 at the GalNAc. The ability of the lanthanide ions, like Europium (Eu), which show luminescence properties, allowed studying the binding behavior of GAGs.
The behavior of the complex formation of Eu3+/GAGs was analyzed under physiological conditions by several experimental methods such as time-resolved laser-induced fluorescence spectroscopy (TRLFS) and infrared spectroscopy (ATR-FT-IR), supplemented by theoretical calculations of the possible structures and resulting spectra.
All three GAGs (CS4S, CS6S and DS) caused an increase in luminescence intensity of the hypersensitive 7F2 emission band of Eu3+ due to complex formation, which was more pronounced for CS4S and DS compared to CS6S. The luminescence lifetimes increased with CS4S and DS up to 200-300 µs, corresponding to 2-4 remaining H2O molecules in the first coordination shell of Eu3+. With CS6S, the luminescence lifetime was even more prolonged up to ~650 µs (~1 remaining H2O).
FT-IR showed that the binding of GAGs to Eu3+ occurs not only via the carboxyl groups but also via the sulfate groups.
Even though the coordination behavior of GAGs towards Eu3+ is in general quite similar, particular differences could be identified: GAGs with C4 sulfation seem to be stronger ligands, whereas C6 sulfation seems to be sterically more ambitious since it can replace more H2O molecules from the first spherical coordination shell of Eu3+ than C4 sulfation.
  • Poster
    10th International Conference on f-Elements (ICFE-10), 03.-06.09.2018, Lausanne, Schweiz

Publ.-Id: 27544 - Permalink


Magnetic coupling effects in curvilinear nanomagnets
Makarov, D.; Volkov, O.; Kakay, A.; Fassbender, J.;
While conventionally magnetic films and structures are fabricated on flat surfaces, the topology of curved surfaces has only recently started to be explored and leads to new fundamental physics as well as applied device ideas [1]. In particular, novel effects occur when the magnetization is modulated by curvature providing a new degree of freedom that leads to new magnetization configurations and is predicted to have major implications on the spin dynamics due to topological constraints [2].
Advances in this novel field solely rely on the understanding of the fundamentals behind the modifications of magnetic responses of 3D-curved magnetic thin films. The lack of an inversion symmetry and the emergence of a curvature induced effective anisotropy and Dzyaloshinskii-Moriya interaction are characteristic of curved surfaces, leading to curvature-driven magnetochiral effects and topologically induced magnetization patterning. In addition to these rich physics, the application potential of 3D-shaped objects is currently being explored as mechanically reshapeable magnetic field sensorics [3], spin-wave filters and high-speed racetrack memory devices. The fundamentals as well as application relevant aspects of curvilinear nanomagnets will be covered in this presentation.

[1] R. Streubel, D. Makarov et al., J. Phys. D: Appl. Phys. 49, 363001 (2016).
[2] D. Sander, D. Makarov et al., J. Phys. D: Appl. Phys. 50, 363001 (2017).
[3] D. Makarov et al., Appl. Phys. Rev. 3, 011101 (2016).
Keywords: curvature effects, magnetic thin films
  • Poster
    Joint European Magnetic Symposia 2018, 03.-07.09.2018, Mainz, Germany

Publ.-Id: 27542 - Permalink


Spintronics with magnetoelectric antiferromagnetic thin films
Makarov, D.;
Thin film antiferromagnets (AF) have potential to revolutionize spintronics due to their inherently magnetic-field stable magnetic order and high-frequency operation. To explore their application potential, it is necessary to understand modifications of the magnetic properties and magnetoelectric responses of AF thin films with respect to their bulk counterparts. Considering grainy morphology of thin films, questions regarding the change of the intergranular exchange, criticality behavior and switching of the order parameter need to be addressed.
Our approach is based on the electron transport characterization of magnetic responses of thin film metallic (IrMn) and insulating (α-Cr2O3) antiferromagnets [1-3]. To access minute uncompensated surface magnetization, we rely on zero-offset Hall magnetometry [2]. To build a reliable description of the material properties, the analysis of the transport data is backed up by structural characterization and real space imaging of AF domain patterns using NV microscopy [2].
The fundamental understanding of the magnetic microstructure of magnetoelectric α-Cr2O3 thin films and the possibility to read-out its AF order parameter all-electrically allowed us to put forth a new recording concept where a magnetoelectric memory cell is addressed without using a ferromagnet [1].
[1] T. Kosub et al., Nat. Commun. 8, 13985 (2017).
[2] T. Kosub et al., Phys. Rev. Lett. 115, 097201 (2015).
[3] R. Schlitz et al., Appl. Phys. Lett. 112, 132401 (2018).
Keywords: antiferromagnets, magnetoelectric effect
  • Invited lecture (Conferences)
    2018 International Colloquium on Magnetic Films and Surfaces (ICMFS), 22.-27.07.2018, Santa Cruz, USA

Publ.-Id: 27541 - Permalink


Spintronics of thin film granular antiferromagnets
Makarov, D.;
Antiferromagnets have the potential to revolutionize spintronics due to their inherently magnetic-field stable magnetic order and high-frequency operation. There are already great advances in the field especially when bulk antiferromagnets are considered. The application potential of antiferromagnets can be explored in full only if they will be prepared in the way to be compatible with a conventional microelectronic processing. This necessarily requires the use of (i) thin film antiferromagnets and (ii) discovery of methods to address the order parameter and its modifications all-electrically.
With respect to the first challenge it is necessary to understand modifications of the magnetic properties and magneto-electric responses of thin film antiferromagnets with respect to their bulk counterparts. Typically, thin films possess grainy morphology. Hence, to determine their application potential, questions regarding the change of the intergranular exchange, criticality behavior and switching of the order parameter need to be answered. This topic will be illustrated on the specific example of thin film magnetoelectric collinear antiferromagnet α-Cr2O3 studied using zero-offset Hall magnetometry and NV microscopy [1].
To address the second challenge it is required to develop transport-based techniques to harness the responses of thin film antiferromagnets. This task is difficult as minute uncompensated surface magnetization of antiferromagnets needs to be detected, which imposes strict requirements to the sensitivity of the method. I will outline our developments of zero-offset anomalous Hall magnetometry [2] applied to study the physics of conventional metallic IrMn and insulating magnetoelectric Cr2O3 antiferromagnets.
The fundamental understanding of the magnetic microstructure of magnetoelectric α-Cr2O3 thin films and the possibility to read-out its antiferromagnetic order parameter all-electrically enabled the entirely new recording concept where a magnetoelectric memory cell can be addressed without using a ferromagnet. With this approach, we opened an appealing field of purely antiferromagnetic magnetoelectric random access memory (AF-MERAM) [1]. The key performance parameters of the Cr2O3 based AF-MERAM will be highlighted.
The essence of the AF-MERAM concept is that the read out is realized by acquiring Hall effect measurements from a thin metal layer (e.g., Pt) in proximity with the insulating Cr2O3. While this approach provides a convenient all-electric way to interface with the antiferromagnetic material, the underlying mechanism is debated to be based on either spin Hall magnetoresistance (SMR) or proximity effect. By carrying out temperature dependent anomalous Hall and magnetoresistance measurements, we found out that the signal is dominated by the SMR with a clear presence of an additional contribution. The origin of this contribution might be related to the proximity effect. These preliminary experimental results will be put forth for the discussion as well.
[1] T. Kosub, M. Kopte, R. Hühne, P. Appel, B. Shields, P. Maletinsky, R. Hübner, M. O. Liedke, J. Fassbender, O. G. Schmidt, and D. Makarov, “Purely antiferromagnetic magnetoelectric random access memory”. Nature Communications 8, 13985 (2017).
[2] T. Kosub, M. Kopte, F. Radu, O. G. Schmidt, and D. Makarov, “All-Electric access to the magnetic-field-invariant magnetization of antiferromagnets”. Phys. Rev. Lett. 115, 097201 (2015).
Keywords: antiferromagnets, spintronics
  • Invited lecture (Conferences)
    Joint European Magnetic Symposia 2018, 03.-07.09.2018, Mainz, Germany

Publ.-Id: 27540 - Permalink


Curvilinear nanomagnetism
Makarov, D.;
While conventionally magnetic films and structures are fabricated on flat surfaces, the topology of curved surfaces has only recently started to be explored and leads to new fundamental physics as well as applied device ideas [1]. In particular, novel effects occur when the magnetization is modulated by curvature providing a new degree of freedom that leads to new magnetization configurations and is predicted to have major implications on the spin dynamics due to topological constraints [2].
Advances in this novel field solely rely on the understanding of the fundamentals behind the modifications of magnetic responses of 3D-curved magnetic thin films [3]. The lack of an inversion symmetry and the emergence of a curvature induced effective anisotropy and Dzyaloshinskii-Moriya interaction are characteristic of curved surfaces, leading to curvature-driven magnetochiral effects and topologically induced magnetization patterning [4]. In addition to these rich physics, the application potential of 3D-shaped objects is currently being explored as mechanically reshapeable magnetic field sensorics [5], spin-wave filters and high-speed racetrack memory devices. The fundamentals as well as application relevant aspects of curvilinear nanomagnets will be covered in this presentation.

[1] R. Streubel, D. Makarov et al., Magnetism in curved geometries. J. Phys. D: Appl. Phys. (Topical Review) 49, 363001 (2016).
[2] D. Sander, D. Makarov et al., The 2017 Magnetism Roadmap. J. Phys. D: Appl. Phys. (Topical Review) 50, 363001 (2017).
[3] R. Streubel, D. Makarov et al., Retrieving spin textures on curved magnetic thin films with full-field soft X-ray microscopies. Nat. Commun. 6, 7612 (2015).
[4] V. P. Kravchuk, D. Makarov et al., Multiplet of Skyrmion states on a curvilinear defect: Reconfigurable Skyrmion lattices. Phys. Rev. Lett. 120, 067201 (2018).
[5] D. Makarov et al., Shapeable Magnetoelectronics. Appl. Phys. Rev. (Focused Review) 3, 011101 (2016).
Keywords: curvature effects, magnetic thin films, shapeable magnetoelectronics
  • Invited lecture (Conferences)
    Invited talk at the Condensed Matter Theory seminar at the University of Utrecht, 20.06.2018, Utrecht, The Netherlands

Publ.-Id: 27539 - Permalink


Spintronics with thin film magnetoelectric antiferromagnets
Makarov, D.;
In this talk I will Review our activities on thin film Cr2O3 films, which led to the realization of antiferromagnetic magnetoelectric RAM [1-3].
[1] T. Kosub, D. Makarov et al., Nat. Commun. 8, 13985 (2017).
[2] T. Kosub, D. Makarov et al., Phys. Rev. Lett. 115, 097201 (2015).
[3] R. Schlitz, D. Makarov et al., Appl. Phys. Lett. 112, 132401 (2018).
Keywords: antiferromagnets, spintronics
  • Invited lecture (Conferences)
    2018 Gordon Research Conference entitled Multiferroic and Magnetoelectric Materials – "Effects in Multiferroics Beyond the Coupling of Magnetic and Electric Order", 05.-10.08.2018, Lewiston, Maine, USA

Publ.-Id: 27538 - Permalink


Magnetic smart skins for augmented reality
Makarov, D.;
Augmented reality gadgets are becoming common for our information intensive society assisting us to acquire and process the data. Although impressive in the realization and demonstrations, the obvious drawback of the state-of-the-art augmented and virtual reality devices relying on optical detection systems is their bulkiness, energy inefficiency and the stringent requirement for an operator to be at the line of sight of the device.
We envision that prospective augmented reality systems will strongly benefit from the recent developments in compliant on-skin electronics [1-3]. The fabrication of highly conformable gadgets requires the realization of the electronic replica of the exteroceptive sensory system of humans as well as calls for the acquiring new perception skills beyond those prescribed by the evolution. The representative example of the missing exteroceptive sense of humans is the magnetoception, which allows some of the mammals but not humans perceiving the location in space or directions based on the detection of magnetic fields. The first crucial step towards the realization of this vision was accomplished with the development of interactive magnetosensitive skins [4-6]. The key enabler for this technology is the shapeable [7] –namely, flexible [5,6], stretchable [8,9] and imperceptible [4]– magnetic field sensorics.
Here, we present the first on-skin gadgets, which replicate our natural proprioceptive sensory ability of detecting the motion. The technology is put forth to realize distributed arrays of magnetic field sensors on ultra-thin polymeric foils. Relying on this magnetically enabled electronic proprioception, we visualize the bodily motion and demonstrate the touchless manipulation of virtual objects for augmented reality systems.
Those highly conformable interactive devices possess great potential to extend the portfolio of tasks, which can be performed in virtual or augmented reality. The integration of gadgets in imperceptible electronic skins will open not only exciting possibilities for business or gaming industry but is also beneficial 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.

1. J. A. Rogers et al. Nature 477, 45 (2011).
2. S. Bauer et al., Adv. Mater. 26, 149 (2014).
3. M. Kaltenbrunner et al., Nature 499, 458 (2013).
4. M. Melzer et al., Nature Commun. 6, 6080 (2015).
5. M. Melzer et al., Adv. Mater. 27, 1274 (2015).
6. N. Münzenrieder et al., Adv. Electron. Mater. 2, 1600188 (2016).
7. D. Makarov et al., Appl. Phys. Rev. 3, 011101 (2016).
8. M. Melzer et al., Nano Lett. 11, 2522 (2011).
9. M. Melzer et al., Adv. Mater. 27, 1333 (2015).
Keywords: flexible magnetic field sensors, shapeable magnetoelectronics, virtual reality
  • Invited lecture (Conferences)
    18th International Conference on Experimental Mechanics (ICEM 2018), 01.-05.07.2018, Brussels, Belgium

Publ.-Id: 27537 - Permalink


Magnetism in curved geometries
Makarov, D.;
While conventionally magnetic films and structures are fabricated on flat surfaces, the topology of curved surfaces has only recently started to be explored and leads to new fundamental physics as well as applied device ideas. In particular, novel effects occur when the magnetization is modulated by curvature that has major implications on the spin statics and dynamics due to topological constraints.
Advances in this novel field solely rely on the understanding of the fundamentals behind the modifications of magnetic responses of 3D-curved magnetic thin films. The lack of an inversion symmetry and the emergence of a curvature induced effective anisotropy and Dzyaloshinskii-Moriya interaction are characteristic of curved surfaces, leading to curvature-driven magnetochiral effects and topologically induced magnetization patterning [1]. In addition to these rich physics, the application potential of 3D-shaped objects is currently being explored as spin filters, magnetic field sensorics and memory devices.
To this end, the initially fundamental topic of magnetism in curved geometries strongly benefited from the input of the application-oriented community, which among others explores the mechanical shapeability of curved magnetic thin films. These activities resulted in the development of shapeable magnetoelectronics [2] - spintronics on flexible, bendable and stretchable surfaces.
[1] Streubel et al., J. Phys. D: Appl. Phys. (Topical Review) 49, 363001 (2016).
[2] Makarov et al., Appl. Phys. Rev. (Focused Review) 3, 011101 (2016).
Keywords: curvature effects, magnetism, 3D shapes, magnetic thin films
  • Lecture (Conference)
    DPG Spring meeting, 11.-16.03.2018, Berlin, Germany

Publ.-Id: 27536 - Permalink


Spintronics of thin film granular antiferromagnets
Makarov, D.;
Antiferromagnets have the potential to revolutionize spintronics due to their inherently magnetic-field stable magnetic order and high-frequency operation. Their application potential can be explored in full only if antiferromagnets will be prepared to be compatible with a conventional microelectronic processing. This necessarily requires the use of (i) thin film antiferromagnets and (ii) discovery of methods to address the order parameter and its modifications all-electrically.
With respect to the first challenge it is necessary to understand modifications of the magnetic properties and magneto-electric responses of thin film antiferromagnets with respect to their bulk counterparts. Typically, thin films possess grainy morphology. Hence, to determine their application potential, questions regarding the change of the intergranular exchange, criticality behavior and switching of the order parameter need to be answered. This topic I will illustrate on the specific example of thin film magnetoelectric collinear antiferromagnet α-Cr2O3 studied using zero-offset Hall magnetometry and NV microscopy [1].
To address the second challenge it is required to develop transport-based techniques to harness the responses of thin film antiferromagnets. This task is difficult as minute uncompensated surface magnetization of antiferromagnets needs to be detected, which imposes strict requirements to the sensitivity of the method. I will outline our developments of zero-offset anomalous Hall magnetometry [2] applied to study the physics of conventional metallic IrMn and insulating magnetoelectric Cr2O3 antiferromagnets.
The fundamental understanding of the magnetic microstructure of magnetoelectric α-Cr2O3 thin films and the possibility to read-out its antiferromagnetic order parameter all-electrically enabled the entirely new recording concept where a magnetoelectric memory cell can be addressed without using a ferromagnet. With this approach, we opened an appealing field of purely antiferromagnetic magnetoelectric random access memory (AF-MERAM) [1].

[1] T. Kosub et al., Nature Communications 8, 13985 (2017).
[2] T. Kosub et al., Phys. Rev. Lett. 115, 097201 (2015).
Keywords: antiferromagnets, magnetoelectric effect, Hall measurement
  • Invited lecture (Conferences)
    International Workshop on Magneto-Electric Actuation, Magneto-ionicsand Related Phenomena in High-Surface Area Materials, 28.-30.05.2018, Gavà-Barcelona, Spain

Publ.-Id: 27535 - Permalink


Magnetic Functionalities for Flexible Interactive Electronics
Makarov, D.;
Augmented reality gadgets are becoming common for our information intensive society assisting us to acquire and process the data. Although impressive in the realization and demonstrations, the obvious drawback of the state-of-the-art augmented and virtual reality devices relying on optical detection systems is their bulkiness, energy inefficiency and the stringent requirement for an operator to be at the line of sight of the device.
We envision that prospective augmented reality systems will strongly benefit from the recent developments in compliant on-skin electronics [1-3]. The fabrication of highly conformable gadgets requires the realization of the electronic replica of the exteroceptive sensory system of humans as well as calls for the acquiring new perception skills beyond those prescribed by the evolution. The representative example of the missing exteroceptive sense of humans is the magnetoception, which allows some of the mammals but not humans perceiving the location in space or directions based on the detection of magnetic fields. The first crucial step towards the realization of this vision was accomplished with the development of interactive magnetosensitive skins [4-6]. The key enabler for this technology is the shapeable magnetoelectronics [7] –namely, flexible [5,6], stretchable [8,9] and imperceptible [4,10]– magnetic field sensorics.
Here, we present the first on-skin gadgets, which replicate our natural proprioceptive sensory ability of detecting the motion [6, 7, 10]. The technology is put forth to realize distributed arrays of magnetic field sensors on ultra-thin polymeric foils. Relying on this magnetically enabled electronic proprioception, we visualize the bodily motion and demonstrate the touchless manipulation of virtual objects for augmented reality systems.
Those highly conformable interactive devices possess great potential to extend the portfolio of tasks, which can be performed in virtual or augmented reality. The integration of gadgets in imperceptible electronic skins will open not only exciting possibilities for business or gaming industry but is also beneficial 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.

References
1. J. A. Rogers et al., Nature 477, 45 (2011).
2. S. Bauer et al., Adv. Mater. 26, 149 (2014).
3. M. Kaltenbrunner et al., Nature 499, 458 (2013).
4. M. Melzer et al., Nature Commun. 6, 6080 (2015).
5. M. Melzer et al., Adv. Mater. 27, 1274 (2015).
6. N. Münzenrieder et al., Adv. Electron. Mater. 2, 1600188 (2016).
7. D. Makarov et al., Appl. Phys. Rev. 3, 011101 (2016).
8. M. Melzer et al., Nano Lett. 11, 2522 (2011).
9. M. Melzer et al., Adv. Mater. 27, 1333 (2015).
10. G. S. Canon Bermudez et al., Science Advances 4, eaao2623 (2018).
Keywords: flexible electronics, magnetic field sensors, on-Skin electronics
  • Invited lecture (Conferences)
    6th International Conference on Superconductivity and Magnetism, 29.04.-04.05.2018, Antalya, Turkey

Publ.-Id: 27534 - Permalink


Efficient Parallel Monte-Carlo Simulations for Large-Scale Studies of Surface Growth Processes
Kelling, J.;
Lattice Monte Carlo methods are used to investigate far from and out-of-equilibrium systems, including surface growth, spin systems and solid mixtures. Applications range from the determination of universal growth or aging behaviors to palpable systems, where coarsening of nanocomposites or self-organization of functional nanostructures are of interest. Such studies require observations of large systems over long times scales, to allow structures to grow over orders of magnitude, which necessitates massively parallel simulations.

This work addresses the problem of parallel processing introducing correlations in Monte Carlo updates and proposes a virtually correlation-free domain decomposition scheme to solve it. The effect of correlations on scaling and dynamical properties of surface growth systems and related lattice gases is investigated further by comparing results obtained by correlation-free and intrinsically correlated but highly efficient simulations using a stochastic cellular automaton (SCA). Efficient massively parallel implementations on graphics processing units (GPUs) were developed, which enable large-scale simulations leading to unprecedented precision in the final results.

The primary subject of study is the Kardar–Parisi–Zhang (KPZ) surface growth in (2 + 1) dimensions, which is simulated using a dimer lattice gas and the restricted solid-on-solid model (RSOS) model. Using extensive simulations, conjectures regarding growth, autocorrelation and autoresponse properties are tested and new precise numerical predictions for several universal parameters are made.
Keywords: lattice Monte Carlo, surface growth, ballistic deposition, physical aging, Kardar–Parisi–Zhang, lattice gas, parallel processing, domain decomposition, GPU
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Publ.-Id: 27533 - Permalink


Inductive System for Reliable Magnesium Level Detection in a Titanium Reduction Reactor
Krauter, N.; Eckert, S.; Gundrum, T.; Stefani, F.; Wondrak, T.; Frick, P.; Khalilov, R.; Teimurazov, A.;
The determination of the Magnesium level in a Titanium reduction retort by inductive methods is often hampered by the formation of Titanium sponge rings which disturb the propagation of electromagnetic signals between excitation and receiver coils. We present a new method for the reliable identification of the Magnesium level which explicitly takes into account the presence of sponge rings with unknown geometry and conductivity. The inverse problem is solved by a look-up-table method, based on the solution of the inductive forward problems for several tens of thousands parameter combinations.
Keywords: titanium, Kroll process, level detection, inductive measurements

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Publ.-Id: 27532 - Permalink


Contilisant, a Tetratarget Small Molecule for Alzheimer’s Disease Therapy Combining Cholinesterase, Monoamine Oxidase Inhibition and H3R Antagonism with Sigma 1R Agonism Profile
Bautista-Aguilera, O. M.; Budni, J.; Mina, F.; Medeiros, E. B.; Deuther-Conrad, W.; Entrena, J. M.; Moraleda, I.; Iriepa, I.; López-Muñoz, F.; Marco-Contelles, J.;
Contilisant, a permeable, antioxidant and neuroprotectant agent, showing high nM affinity at H3R, excellent inhibition of the monoamine oxidases and cholinesterases, is an affine and selective S1R agonist in the nanomolar range, based on the binding affinity and functional experiment, a result confirmed by molecular modeling. In addition, Contilisant significantly restores the cognitive deficit induced by Aβ1-42 in the radial maze assay in an in vivo Alzheimer’s disease test, comparing very favorably with donepezil.
Keywords: Alzheimer’s disease, Aβ, ASS234, ChE inhibitor, Contilisant, Cognitive impairment, H3R antagonist, MAO inhibitor, Molecular modeling, Radial arm-maze test, hSigma 1R agonist, rVAChT modulator, Y-maze test.

Publ.-Id: 27531 - Permalink


Laser schaltet Magnet an und aus
Ehrler, J.ORC; Kronast, F.; Zhigilei, L. V.; Bali, R.
Mit einem Laserstrahl in einer Legierung magnetische Strukturen zu erzeugen und anschließend wieder zu löschen – das gelang einer internationalen Kooperation unter Leitung des Helmholtz-Zentrums Dresden-Rossendorf (HZDR). Durch Laserpulse veränderte sie die Anordnung der Atome, was eine Veränderung der magnetischen Eigenschaften zur Folge hatte. Da Laser in der Industrie weit verbreitet sind, könnten sich für die Materialbearbeitung, für optische Technologien oder die Datenspeicherung neue Perspektiven eröffnen.
Related publications
Laser-Rewriteable Ferromagnetism at Thin Film Surfaces (Id 27198) is cited by this publication
  • Physik in unserer Zeit (2018)

Publ.-Id: 27530 - Permalink


Environmental fate of fission products: a comprenhensive study
Mayordomo, N.; Rodríguez, D. M.; Müller, K.ORC
Assuring a safe long-term nuclear waste management implies extensive knowledge on the fundamental behaviour of fission products in the surroundings of the feasible repository. This includes the radionuclide speciation, their migration, and their possible interaction with compartments of the technical and geological barriers, and biota.
Fission products, although generated in low yield, posse radiotoxicity and their half-life can be high (10^5 years). Among them, Se and Tc are especially relevant because some of their species are assumed highly mobile in water, since their interaction with the barrier materials (like clay) is considered negligible, as they are mainly found as anionic species [1].
We carry out a comprehensive study to fill the existing gaps of knowledge about the thermodynamic parameters and the molecular level information related to Tc and Se interaction with minerals. Our approach consist on having a global view of the interaction by combining experiments and theoretical tools [2]. On one hand the experiments consists on batch sorption experiments (to obtain the trend of sorption with pH, ionic strength or time) and on spectroscopic experiments (to get the information of the interaction at a molecular level). On the other hand, the theoretical tool consists on developing complexation models that allow the prediction of fission product-mineral interaction under given conditions and that can be adapted to other environments.
In this talk we focus on the Tc(VII) interaction with alumina. Alumina has been selected not only for its model character for complex minerals, but also because of its high affinity for anions, as Se(IV) [2].

This work has been developed in the frame of VESPA II project (02E11607B), supported by the German Ministry of Economy and Energy (BMWi).

[1] K.H. Lieser, et al. Radiochim. Acta. 42 (1987) 205–213.
[2] N. Mayordomo, et al. Environ. Sci. Technol. (2018) 581–588.
Keywords: Technetium, alumina, retention
  • Invited lecture (Conferences)
    Goldschmidt 2018, 12.-17.08.2018, Boston, USA

Publ.-Id: 27529 - Permalink


The Feasibility of Studying 44Ti(α, p)47V Reaction at Astrophysical Energies
Al-Abdullah, T.; Bemmerer, D.; Elekes, Z.; Schumann, D.;
The gamma-ray lines from the decay of 44Ti have been observed by space-based gamma-ray telescopes from two supernova remnants. It is believed that the 44Ti(α, p)47V reaction dominates the destruction of 44Ti. This work presents a possible technique to determine its reaction rate in forward kinematics at astrophysically relevant energies. Several online and offline measurements in parallel with Monte Carlo simulations were performed to illustrate the feasibility of performing this reaction. The results will be discussed.

Publ.-Id: 27528 - Permalink


Thermally driven convection in Li||Bi liquid metal batteries
Personnettaz, P.; Beckstein, P.; Landgraf, S.; Köllner, T.; Nimtz, M.; Weber, N.; Weier, T.;
Liquid Metal Batteries (LMBs) are a promising concept for cheap electrical energy storage at grid level. These are built as a stable density stratification of three liquid layers, with two liquid metals separated by a molten salt. In order to ensure a safe and efficient operation, the understanding of transport phenomena in LMBs is essential. With this motivation we study thermal convection induced by internal heat generation.
We consider the electrochemical nature of the cell in order to define the heat balance and the operating parameters. Moreover we develop a simple 1D heat conduction model as well as a fully 3D thermo-fluid dynamics model. The latter is implemented in the CFD library OpenFOAM, extending the volume of fluid solver, and validated against a pseudo-spectral code. Both models are used to study a rectangular 10×10 cm Li||Bi LMB cell at three different states of charge.
Keywords: liquid metal batteries, heat transfer, thermal convection, thermodynamics, OpenFOAM, volume of fluid, spurious currents

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  • Secondary publication expected from 10.09.2019

Publ.-Id: 27527 - Permalink


Using FIB/SEM's to Investigate Biological Samples
Wolff, A.; Klingner, N.ORC; Thompson, W.; Zhou, Y.; Lin, J.; Peng, Y. Y.; Ramshaw, J. A. M.; Xiao, Y.
This study focuses on gallium ion-solid interactions and their simulations to derive sets of suitable operational parameters and a technique which prevents heat damage in soft materials.
The technique is successfully demonstrated on non-resin embedded collagen,a bio material which serves as a case study for other soft tissues.
  • Poster
    The 62nd International Conference on Electron, Ion, and Photon Beam Technology and Nanofabrication, 29.05.-01.06.2018, Puerto Rico, USA
  • Lecture (Conference)
    2nd international HeFIB conference on Helium and emerging Focused Ion Beams, 11.-13.06.2018, Dresden, Germany

Publ.-Id: 27526 - Permalink


Radiopharmaceutical evaluation of novel bifunctional chelators and bioconjugates for tumor imaging and therapy
Stephan, H.;
The development of multi-functional complexing agents for radiometal nuclides with a view of nuclear medical application represents a field of research that is intensively dealt with and has rapidly been developing. In this context, ligands that form highly stable metal complexes and additionally possess several different functional groups are of particular interest. This enables the simultaneous introduction of targeting, solubilizing and, for example, fluorescent units into the relevant metal complexes. In this perspective, bifunctional chelating agents (BFCAs) based on 3,7-diazabicyclo[3.3.1]nonane (bispidine) and 1,4,7-triazacyclononane (TACN) are discussed. Examples of target-specific peptides and bio(nano)materials equipped with bispidine and TACN ligands for labeling with 64Cu as an ideal positron emitter are presented. This enables tumor imaging and the biodistribution of the materials to be studied over a period of days via positron emission tomography (PET). This lecture will also give an insight into the pre-targeting strategy using complementary oligonucleotides such as peptide nucleic acid (PNA) derivatives. The pre-targeting strategy allows for the rational use of long circulating, high affinity antibodies for both non-invasive cancer radioimmunodetection (RID) and –therapy (RIT).
  • Invited lecture (Conferences)
    IsoSiM Summer School 2018, Medical Isotope Production and Applications, 03.-07.06.2018, Harrison Hot Springs, Canada

Publ.-Id: 27525 - Permalink


An experimental investigation on the air-side heat transfer and flow resistance of finned short oval tubes at different tube tilt angles
Unger, S.; Beyer, M.; Arlit, M.; Stasch, P.; Hampel, U.;
We experimentally studied the heat transfer and flow characteristics of finned oval tubes at different Reynolds numbers, fin spacing and tube orientation and compared results with correlations from literature. As assessment parameters we used the efficiency index, the performance evaluation criterion and the global performance criterion. For tubes in horizontal orientation (main flow direction perpendicular to the tube axis) we found an improvement of Nusselt number and a reduction of friction factor, when fin spacing increases. The efficiency index and the performance evaluation criterion improve with rising fin spacing and the global performance criterion remains almost constant. A substantial impact of tilt tube angle on Nusselt number and friction factor was observed. As the tube tilt angle rises from 0° to 40° Nusselt number and friction factor strongly increase. The horizontal tube orientation outperforms the tilted orientations in all performance parameters and at all Reynolds number. Thus, the performance is highest at 0° and worst at 40° tilt angle, since the increase in pressure drop dominates over the heat transfer enhancement. Based on the experimental outcome correlations between Nusselt number, friction factor and Reynolds number, fin spacing and tube tilt angle are recommended, which can be used to design finned oval tubes.
Keywords: Finned tube heat exchanger, Heat transfer, Flow resistance, Tube tilt angle, Thermal-flow performance, Heat transfer correlation

Publ.-Id: 27523 - Permalink


Individual Response to Ionizing Radiation and Personalized Radiotherapy
Domina, E.; Philchenkov, A.; Dubrovska, A.;
Radiation therapy remains one of the most effective cancer treatments. Nevertheless, biology driven personalized radiation therapy which enables to treat the patients according to the biological characteristics of the individual tumors and normal tissues still needs to be implemented into clinic. Understanding the mechanisms of radiation response in both tumors and normal tissues is necessary to develop reliable predictive biomarkers for tumor radioresistance and normal tissue toxicity as well as to exploit new therapeutic opportunities for tumor radiosensitization. In this paper, we review the mechanisms of tumor radiosensitivity, the early and late responses of normal tissues to therapeutic radiation exposure and discuss possible implementation of these mechanisms for biology-driven personalized radiation treatment.
Keywords: ionizing radiation, DNA damage, DNA repair, cell cycle checkpoints, radiosensitivity, cancer, cancer stem cells, radiotherapy, radioresistance, marker

Publ.-Id: 27522 - Permalink


Untersuchungen zu den Wechselwirkungen zwischen unter Tage lebenden Mikroorganismen mit Uran und deren Einfluss auf das Migrationsverhalten von Uran in gefluteten Urangruben und Spektroskopische Bestimmung der Bindungsform (Speziation) trivalenter Actinide/Lanthanide in Biofluiden des menschlichen Gastrointestinaltraltes und im Blut
Arnold, T.; Barkleit, A.; Gerber, U.; Krawczyk-Bärsch, E.; Wilke, C.;
Teil A:
Es wurde gezeigt, dass das Transportverhalten von Uran in der Umwelt und an den ehemaligen Uranabbaustätten stark von der Anwesenheit und Aktivität natürlich vorkommender Mikroorganismen abhängt. Die Untersuchungen zeigten, dass die Isolate eine hohe Toleranz gegenüber Uran aufweisen und in der Lage sind, relativ hohe Mengen an Uran zu immobilisieren und aus der umgebenden Lösung zu entfernen. Durch anaerobe Versuche konnte gezeigt werden, dass die mikrobielle Reduktion von Uran(VI) allein durch die Zugabe von 10 mM Glycerin bei zukünftigen Anwendungen als in situ Biosanierungsapplikationen genutzt werden könnte. Die Ergebnisse dieser Arbeit konnten die Wechselwirkungsmechanismen zwischen natürlich vorkommenden Mikroorganismen und Uran im Detail beschreiben und neue Zusammenhänge zwischen aktivem und inaktivem Stoffwechsel der Mikroorganismen zeigen. Zusammenfassend können diese einen wertvollen Beitrag zur Entwicklung von Biosanierungsansätzen für die Behandlung von Radionuklid-kontaminierten Standorten aus der ehemaligen Bergbauindustrie leisten.
Teil B:
Im Speichel dominiert neben einem kleinen Bindungsanteil an dem Enzym alpha-Amylase die Komplexierung mit anorganischen Liganden, im Magen dominiert aufgrund des sauren pH-Wertes das Eu- bzw. Cm-Aquo-Ion, und im Darm dominiert neben anorganischen Komplexen die Bindung der Metallionen an das Glycoprotein Mucin. Die starke Komplexfähigkeit von Mucin gegenüber dreiwertigen f-Elementen könnte die Absorption dieser im menschlichen Körper unterdrücken und deren Exkretion fördern. Die Ergebnisse dieser Arbeit geben neue Einblicke in das biochemische Verhalten dreiwertiger f-Elemente und können zudem zur Einschätzung von Gesundheitsrisiken nach der Inkorporation von Radionukliden und der Entwicklung von Dekontaminationstherapien beitragen.
Keywords: Mikroorganismen, Uran, Immobilisierung, U(VI)-Reduktion, dreiwertige f-Elemente, Speziation, Biofluide, Verdauungssystem, Laserfluoreszenzspektroskopie
  • Open Access LogoWissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-098 2019
    ISSN: 2191-8708

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Publ.-Id: 27521 - Permalink


From Point to Line Defects in Two-Dimensional Transition Metal Dichalcogenides: Insights from Transmission Electron Microscopy and First-Principles Calculations
Komsa, H.-P.; Krasheninnikov, A. V.ORC
Two-dimensional (2D) transition metal dichalcogenides (TMDs) have recently received great deal of attention due to their unique properties associated with the reduced dimensionality of the system. The properties of these materials have been shown to be affected by atomic defects in the atomic network. The very structure of these materials which are composed from three atomic layers only, combined with dramatic improvements in microscopy techniques, made it possible to study the behavior of defects in these systems with unprecedented accuracy. Various point and line defects were identified, and their effects on the properties of the systems were accessed. It was demonstrated that point defects induced by electron beam irradiation coalesce in line defects, but their quasi-one dimensional atomic structure varies from member to member in the transition metal dichalcogenides family. In this review, we summarize recent experimental and theoretical findings in this area, discuss how the line structures appear due to the agglomeration of point defects, and dwell upon how line defects can be used to engineer properties of 2D TMDs. Finally, we address the challenges in this field and issues which still lack the explanation.
Keywords: 2D materials
  • Book chapter
    Vittorio Morandi, Luca Ottaviano: Carbon nanostructures book series (CARBON), EU: Springer, 2017, 71-85
    DOI: 10.1007/978-3-319-58134-7_6

Publ.-Id: 27520 - Permalink


Ring-like spatial distribution of laser accelerated protons in the ultra-high-contrast TNSA-regime
Becker, G. A.; Tietze, S.; Keppler, S.; Reislöhner, J.; Bin, J. H.; Bock, L.; Brack, F.-E.; Hein, J.; Hellwing, M.; Hilz, P.; Hornung, M.; Kessler, A.; Kraft, S. D.; Kuschel, S.; Liebetrau, H.; Ma, W.; Polz, J.; Schlenvoigt, H.-P.; Schorcht, F.; Schwab, M. B.; Seidel, A.; Zeil, K.; Schramm, U.; Zepf, M.; Schreiber, J.; Rykovanov, S.; Kaluza, M. C.;
The spatial distribution of protons accelerated from submicron-thick plastic foil targets using multi-terawatt, frequency-doubled laser pulses with ultra-high temporal contrast has been investigated experimentally. A very stable, ring-like beam profile of the accelerated protons, oriented around the target's normal direction has been observed. The ring's opening angle has been found to decrease with increasing foil thicknesses. Two-dimensional particle-in-cell simulations reproduce our results indicating that the ring is formed during the expansion of the proton density distribution into the vacuum as described by the mechanism of target-normal sheath acceleration. Here - in addition to the longitudinal electric fields responsible for the forward acceleration of the protons - a lateral charge separation leads to transverse field components accelerating the protons in the lateral direction.
Keywords: laser-plasma interaction, proton acceleration, proton beam profile, target normal sheath acceleration

Publ.-Id: 27519 - Permalink


Metal-organic complexes of tetravalent actinides with soft-donor ligands investigated by paramagnetic NMR spectroscopy
Schöne, S.ORC; Radoske, T.; Felsner, B.; Patzschke, M.ORC; März, J.ORC; Kaden, P.ORC
In NMR spectra of paramagnetic metal-organic complexes electronic interactions are the origin of additional NMR chemical shifts observed on resonances of nuclei of the ligand. The major two contributors to these hyperfine shifts are Fermi-contact shifts (FCS) and pseudo-contact shifts (PCS). FCS are due to delocalisation of unpaired electron density in molecular orbitals involving both metal and ligand orbitals and thus report on the bond properties. PCS are originating from distance- and angle-dependent dipolar coupling of electron spins through space and are therefore bearing structural information.
The paramagnetic contributions can be mathematical separated provided that a suitable diamagnetic reference is available (to subtract non-paramagnetic contributions). For the trivalent actinides no diamagnetic reference in the same series is available in milligram scale. Furthermore, all available theories behind mathematical disentangling of contributions to the paramagnetic chemical shift, even for the lanthanide series, omit the influence of spin-orbit effects that might have a sizeable contribution.[1,2]
Comparing studies of isostructural diamagnetic complexes of both f-element series of tetravalent metal ions (Ce(IV) and Th(IV)) allow for an estimation of additional influences to the chemical shifts and the effect of contributions usually omitted by commonly used mathematical theories.
We started to study paramagnetic metal-organic complexes of the tetravalent actinides (An(IV)). Throughout the 5f-series additional effects to the observed chemical shift are expected with increasing number of unpaired electrons. Assessing the chemical bonding situation is possible via the influences on NMR chemical shifts (via FCS) and structural properties of the complexes (via PCS) can be compared to SC-XRD structures. Herein we report the first results of investigations of N- and N,O-donor ligand complexes of the An(IV) series.

References
1 C. Adam, P. Kaden, B. B. Beele, U. Müllich, S. Trumm, A. Geist, P. J. Panak, M. A. Denecke, “Evidence for covalence in a N-donor complex of americium(III)”, Dalton Trans., 42, 14068-14074 (2013).
2. C. Adam, B. B. Beele, A. Geist, U. Müllich, P. Kaden, P. J. Panak, “NMR and TRLFS studies of Ln(III) and An(III) C5-BPP complexes”, Chemical Science, 6, 1548-1561 (2015).
Keywords: NMR, paramagnetic, Actinide, N-donor, FCS, PCS
  • Lecture (Conference)
    ISNSC - 10th International Symposium on Nano and Supramolecular Chemistry 2018, 09.-12.07.2018, Dresden, Deutschland

Publ.-Id: 27518 - Permalink


Paramagnetic NMR investigations in metal-organic complexes of tetravalent actinides with soft-donor ligands
Schöne, S.ORC; Radoske, T.; Felsner, B.; Patzschke, M.ORC; März, J.ORC; Kaden, P.ORC
Electronic interactions between metal and ligand are the origin of additional NMR chemical shifts observed on nuclei of the ligand in paramagnetic metal-organic complexes. The major two contributors to these paramagnetic chemical shifts are Fermi-contact shifts (FCS) and pseudo-contact shifts (PCS). FCS are due to delocalisation of unpaired electron density in molecular orbitals involving both metal and ligand orbitals and thus report on the bond properties. PCS are originating from distance- and angle-dependent dipolar coupling of electron spins through space and are therefore bearing structural information.
The mathematical separation of paramagnetic contributions in complexes relies on the availability of a suitable diamagnetic reference to subtract non-paramagnetic contributions. For the trivalent actinides no diamagnetic reference in the same series is available in milligram scale. Furthermore, all available theories behind mathematical disentangling of contributions to the paramagnetic chemical shift, even for the lanthanide series, omit the influence of spin-orbit effects that might have a sizeable contribution as well. [1,2]
Comparing isostructural diamagnetic complexes of both f-element series of tetravalent metal ions (Ce(IV) and Th(IV)) allows for an estimation of additional influences to the chemical shifts and the effect of contributions usually omitted by commonly used mathematical theories.
To assess the chemical bonding situation via the influences on NMR chemical shifts (via FCS) we started to study paramagnetic metal-organic complexes of the tetravalent actinides (An(IV)). With increasing number of unpaired electrons throughout the 5f-series additional effects to the observed chemical shift are expected. Structural properties of the complexes as derived from PCS contributions can be compared to single crystal X-ray diffraction structures. Herein we report the first results of investigations of N- and N,O-donor ligand complexes of the An(IV) series.

References
1 C. Adam, P. Kaden, B. B. Beele, U. Müllich, S. Trumm, A. Geist, P. J. Panak, M. A. Denecke, “Evidence for covalence in a N-donor complex of americium(III)”, Dalton Trans., 42, 14068-14074 (2013).
2. C. Adam, B. B. Beele, A. Geist, U. Müllich, P. Kaden, P. J. Panak, “NMR and TRLFS studies of Ln(III) and An(III) C5-BPP complexes”, Chemical Science, 6, 1548-1561 (2015).
Keywords: NMR, paramagnetic, Actinide, N-donor, FCS, PCS, structure determination, solution
  • Lecture (Conference)
    18th Radiochemical Conference - RadChem 2018, 13.-18.05.2018, Mariánské Lázně, Tschechische Rupublik
  • Contribution to proceedings
    18th Radiochemical Conference, 13.-18.05.2018, Mariánské Lázně, Tschechische Rupublik
    Czech Chemical Society Symposium Series 2

Publ.-Id: 27517 - Permalink


Nanohardening features in ion and neutron irradiated EUROFER97 and model alloys investigated with atom probe tomography
Gómez-Ferrer, B.; Heintze, C.; Dethloff, C.; Gaganidze, E.; Konstantinovic, M. J.; Malerba, L.; Pareige, P.; Pareige, C.;
Among other effects, neutron irradiation hardens ferritic/martensitic (F/M) nuclear steels; this hardening is suspected to be due to the formation of dislocation loops, alpha' phase and solute-rich clusters (SRCs). In neutron irradiated FeCr model alloys the SRCs which are made of unavoidable impurities such as P are likely to be the main contributors to the yield strength increase, together with the presence of alpha' precipitates, if any [1,2]. Ion irradiation is an extended tool used to investigate the creation and evolution of radiation damage. Since the experiments are fast they offer the possibility to tune the parameters to design model-oriented experiments. Their use is also oriented to reproduce the effects of neutrons for nuclear applications. However, the characteristics of the nano-sized features (solute concentration, density, size and size distribution) are difficult to reproduce using ions with respect to neutrons, since the increase of the sink strength due to injecte d inters titials [3,4] and the high values of damage rate [5] influence defect production and evolution.
Atom probe tomography (APT) is used in the present work to investigate the hardening nanofeatures in irradiated materials. First, an Fe14CrNiSiP model alloy has been irradiated with both Fe+ ions and neutrons up to a dose of 0.1 dpa at 300°C. At such low doses some features, such as SRCs or Cr-rich regions, are formed, thus a direct comparison can be made to highlight differences and commonalities between the two kinds of irradiation; these results can also be used for the development of models. Second, a similar investigation has been made on neutron irradiated EUROFER97 up to 15 dpa at 300°C. The presence of radiation induced segregation (RIS) and radiation enhanced features can be correlated to the model alloy providing some insights on the nature of the hardening in F/M steels.
  • Lecture (Conference)
    E-MRS 2018 Spring Meeting, 18.-22.06.2018, Strasbourg, France

Publ.-Id: 27516 - Permalink


Critical heat flux as a mass flux dependent local or global phenomenon: Theoretical analysis and experimental confirmation
Ding, W.; Geißler, T.; Krepper, E.; Hampel, U.;
In this article, we report on a theoretical analysis and experimental investigations on critical heat flux (CHF) in subcooled flow boiling. Commonly, CHF is considered as a local phenomenon. A validated CHF- concept recently developed in our group indicated that CHF may be initiated in two different ways, that is, locally and globally. We designed and conducted an experiment to verify this hypothesis. The experimental results agree well with the expectations from our CHF- modelling and confirm the two mechanisms. Following that, we continued to clarify the role of different parameters, such as channel orientation, channel length and hydraulic diameter. The new concept of CHF is useful to explain and predict CHF at conditions of low pressure and low fluid velocity.
Keywords: boiling, critical heat flux, initiation mechanisms

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  • Secondary publication expected from 30.04.2019

Publ.-Id: 27515 - Permalink


Application of an Eulerian-Eulerian CFD approach to simulate the thermohydraulics of rod bundles
Ding, W.; Krepper, E.; Sarker, D.; Hampel, U.;
The Eulerian-Eulerian computational fluid dynamics (CFD) approach is widely applied in the simulation of industrial scale thermal fluid dynamics problems, such as flow and heat transfer in fuel elements. However, the case dependency of sub models in the Eulerian-Eulerian CFD approach currently hampers its applicability. In order to reduce this dependency, a sub model to predict the bubble departure in both pool and flow boiling was developed in our group, which includes the impact of microlayer, thermal diffusion, condensation, mutual effect and force balance. Moreover, we also raised a new CHF- concept. It is currently based on correlations but we are continuously working on a transition to a fully physics-based model, which e.g. considers the dependency of boiling on the microlayer thickness, bubble base expansion speed and local shear stress. In order to implement the bubble dynamics model and CHF model into the Eulerian-Eulerian CFD framework, a new cavity activation and heat partitioning model was developed, which is not only used for bubble nucleation but also connects the nucleation boiling and CHF- in one CFD approach. However nucleation site density is strongly dependent on the surface properties, which is difficult to model without correlations.
  • Contribution to proceedings
    49th Annual Meeting on Nuclear Technology (AMNT 2018), 29.-30.05.2018, Berlin, Germany
    49th Annual Meeting on Nuclear Technology

Publ.-Id: 27514 - Permalink


Long-term quality of life in inoperable non-small cell lung cancer patients treated with conventionally fractionated compared to hyperfractionated accelerated radiotherapy - Results of the randomized CHARTWEL trial
Hechtner, M.; Krause, M.; Konig, J.; Appold, S.; Hornemann, B.; Singer, S.; Baumann, M.;
Background and purpose: To evaluate the quality of life (QoL) of patients with inoperable non-small cell lung cancer treated with conventionally fractionated radiotherapy (CF) vs. continuous hyperfractionated accelerated radiotherapy weekend-less (CHARTWEL).
Material and methods: The largest monocentric subgroup of the phase III CHARTWEL trial was analyzed up to three years after randomization. QoL was assessed with the European Organization for Research and Treatment of Cancer QoL Core Questionnaire (QLQ-C30) and lung cancer module (QLQ-LC13) and compared using linear mixed models. QoL interrelations with recurrence, metastasis, and death were explored by multi-state modeling.
Results: 160 patients (98%) provided at least one QoL assessment.
Average treatment differences of CF vs. CHARTWEL over three years were -5.4 points (95%CI [-13.6,2.8], p = 0.19) in global QoL, 11.9 ([2.8,21.0], p = 0.01) in fatigue, 13.4 ([3.5,23.3], p = 0.009) in pain, 10.5 ([1.3,19.6], p = 0.03) in dyspnea, and 5.2 ([-2.7,13.0], p = 0.19) in dysphagia. At 12 months, the probabilities of being disease-free with good, good or moderate, any global QoL, or alive were 5.1%, 20.3%, 34.2%, 54.4% under CF and 10.4%, 21.0%, 37.5%, 65.3% under CHARTWEL.
Conclusions: Over three years, QoL was similar or more favorable under CHARTWEL compared to CF. Modeling QoL together with disease states provided additional insight into treatment comparisons.
Keywords: Quality of life Non-small cell lung cancer Accelerated radiotherapy Hyperfractionation Randomized trial Multi-state model

Publ.-Id: 27513 - Permalink


Cognitive deficits following brain tumor radiation therapy
Buthut, M.; Haussmann, R.; Seidlitz, A.; Krause, M.; Donix, M.;
Brain radiation is an important treatment option for malignant and benign brain diseases. The possible acute or chronic impact of radiation therapy on cognitive performance is important for daily functioning and quality of life. A detailed evaluation of cognitive impairment is important in the context of how to control disease progression. The susceptibility of the hippocampus to radiation-induced neuronal damage and its important role in memory highlight that therapeutic strategies require precision medicine.

Publ.-Id: 27512 - Permalink


Magnetohydrodynamic Simulation: Liquid Metal Batteries, Crystal Growth & Steel Casting
Weber, N.; Beckstein, P.; Galindo, V.; Giesecke, A.; Liu, K.; Pal, J.; Personnettaz, P.; Stefani, F.; Timmel, K.; Weier, T.;
Der Vortrag gibt einen Überblick über numerische Simulationen der Abteilung Magnetohydrodynamik am HZDR.
  • Lecture (Conference)
    OpenFOAM Stammtisch United, 24.05.2018, Dresden, Deutschland

Publ.-Id: 27511 - Permalink


Instrumentation for Liquid Metal Facilities
Gundrum, T.; Krauter, N.; Wondrak, T.; Richter, T.; Keplinger, O.; Franke, S.; Eckert, S.;
Instrumentation for Liquid Metal Facilities an overview and present work
  • Invited lecture (Conferences)
    ESFR-SMART European workshop on Liquid Metal facilities; focus on sodium facilities design & safe operation, 22.-24.05.2018, Rom, Italia

Publ.-Id: 27510 - Permalink


Quantum Criticality of an Ising-like Spin-1/2 Antiferromagnetic Chain in a Transverse Magnetic Field
Wang, Z.; Lorenz, T.; Gorbunov, D. I.; Cong, P. T.; Kohama, Y.; Niesen, S.; Breunig, O.; Engelmayer, J.; Herman, A.; Wu, J.; Kindo, K.; Wosnitza, J.; Zherlitsyn, S.; Loidl, A.;
We report on magnetization, sound velocity, and magnetocaloric-effect measurements of the Ising-like spin-1/2 quantum antiferromagnetic chain BaCo$_2$V$_2$O$_8$ as a function of temperature down to 1.3~K and applied transverse magnetic field up to 60~T. While across the Ne\'{e}l temperature of $T_N\sim5$~K anomalies in magnetization and sound velocity confirm the antiferromagnetic ordering transition, at the lowest temperature in the field-dependent measurements we find a sharp softening of sound velocity and a clear temperature minimum at $B^{c,3D}_\perp=21.4$~T, indicating suppression of the antiferromagnetic order. At higher fields, magnetocaloric-effect measurements reveal a broad temperature minimum at $B^c_\perp = 40$~T, accompanied by a broad minimum of sound velocity and a saturation-like level-off in magnetization. These features signal a quantum phase transition that is further quantified by the divergent behavior of Gr\"{u}neisen parameter $\Gamma_B \propto (B-B^{c}_\perp)^{-1}$. By contrast, at the critical field the Gr\"{u}neisen parameter converges to a constant as temperature decreases towards zero, which is a distinct characteristics of the one-dimensional transverse-field Ising quantum critical point.
Keywords: Spin chain, quantum critical point, transverse field Ising model, BaCo2V2O8, magnetization, sound velocity, magnetocaloric effects

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Publ.-Id: 27509 - Permalink


Magnetic field dependence of antiferromagnetic resonance in NiO
Wang, Z.; Kovalev, S.; Awari, N.; Chen, M.; Germanskiy, S.; Green, B.; Deinert, J.-C.; Kampfrath, T.; Milano, J.; Gensch, M.;
We report on measurements of magnetic field and temperature dependence of antiferromagnetic resonances in the prototypical antiferromagnet NiO. The frequencies of the magnetic resonances in the vicinity of 1 THz have been determined in the time-domain via time-resolved Faraday measurements after selective excitation by narrow-band superradiant terahertz (THz) pulses at temperatures down to 3 K and in magnetic fields up to 10 T. The measurements reveal two antiferromagnetic resonance modes, which can be distinguished by their characteristic magnetic field dependencies. The nature of the two modes is discussed by comparison to an eight-sublattice antiferromagnetic model, which includes superexchange between the next-nearest-neighbor Ni spins, magnetic dipolar interactions, cubic magneto-crystalline anisotropy, and Zeeman interaction with the external magnetic field. Our study indicates that a two-sublattice model is insufficient for the description of spin dynamics in NiO, while the magnetic-dipolar interactions and magneto-crystalline anisotropy play important roles.
Keywords: NiO, terahertz spectroscopy, antiferromagnetic resonance, magnetic field

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Publ.-Id: 27508 - Permalink


Towards femtosecond-level intrinsic laser synchronization at fourth generation light sources
Chen, M.ORC; Kovalev, S.ORC; Awari, N.ORC; Wang, Z.ORC; Germanskiy, S.; Green, B.; Deinert, J.-C.ORC; Gensch, M.ORC
In this Letter, the proof of principle for a scheme providing intrinsic femtosecond-level synchronization between an external laser system and fourth generation light sources is presented. The scheme is applicable at any accelerator-based light source that is based on the generation of coherent radiation from ultrashort electron bunches such as superradiant terahertz (THz) facilities or X-FELs. It makes use of a superradiant THz pulse generated by the accelerator as an intrinsically synchronized gate signal for electro-optical slicing. We demonstrate that the scheme enables a reduction of the timing instability by more than 2 orders of magnitude. This demonstration experiment thereby proves that intrinsically synchronized time-resolved experiments utilizing laser and accelerator-based radiation pulses on few tens of femtosecond (fs) to few fs timescales are feasible.
Keywords: Synchronization, THz slicing, Spectral Decoding

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Publ.-Id: 27507 - Permalink


SRF gun II - status as of April 2018
Arnold, A.; Teichert, J.; Xiang, R.; Murcek, P.;
In May 2014 the 1st superconducting photo injector (SRF gun) at HZDR was replaced by a new gun, featuring a new resonator and a new cryostat. The intention for this upgrade was to reach higher beam energy, higher bunch charge and lower emittance at the same time. With the improved parameters user experiments of the superconducting CW accelerator ELBE are to be served, that benefit from an increased average beam current at a given repetition rate of some hundred kHz. Although the cavity performance stays behind its specifications, the SRF gun has been optimized for an operation mode at 200 pC and a repetition rate of 100 kHz to generate four times more THz pulse energy then possible by ELBE's thermionic injector. Because of this significant improvement, the new gun has been recently used for first user shifts at the THz facility at ELBE. In this contribution we will report on first results and operational experiences.
Keywords: SRF gun, superconducting RF injector, ELBE, electron source
  • Lecture (others)
    HOPE II Projekttreffen im Rahmen BMBF Verbundforschungsinitiative, 16.04.2018, Mainz, Deutschland

Publ.-Id: 27506 - Permalink


Structure of 13Be studied in proton knockout from 14B
Ribeiro, G.; Nacher, E.; Tengblad, O.; Diaz Fernandez, P.; Aksyutina, Y.; Alvarez-Pol, H.; Atar, L.; Aumann, T.; Avdeichikov, V.; Beceiro-Novo, S.; Bemmerer, D.; Benlliure, J.; Bertulani, C. A.; Boillos, J. M.; Boretzky, K.; Borge, M. J. G.; Caamano, M.; Caesar, C.; Casarejos, E.; Catford, W.; Cederkall, J.; Chartier, M.; Chulkov, L.; Cortina-Gil, D.; Cravo, E.; Crespo, R.; Datta Pramanik, U.; Dillmann, I.; Elekes, Z.; Enders, J.; Ershova, O.; Estrade, A.; Farinon, F.; Fraile, L. M.; Freer, M.; Fynbo, H. O. U.; Galaviz, D.; Geissel, H.; Gernhäuser, R.; Golubev, P.; Göbel, K.; Hagdahl, J.; Heftrich, T.; Heil, M.; Heine, M.; Heinz, A.; Henriques, A.; Holl, M.; Hufnagel, A.; Ignatov, A.; Johansson, H. T.; Jonson, B.; Kalantar-Nayestanaki, N.; Kanungo, R.; Kelic-Heil, A.; Kurz, N.; Kröll, T.; Labiche, M.; Langer, C.; Le Bleis, T.; Lemmon, R.; Lindberg, S.; Machado, J.; Marganiec, J.; Movsesyan, A.; Nilsson, T.; Nociforo, C.; Panin, V.; Paschalis, S.; Perea, A.; Petri, M.; Pietri, S.; Plag, R.; Reifarth, R.; Rigollet, C.; Riisager, K.; Rossi, D.; Röder, M.; Savran, D.; Scheit, H.; Simon, H.; Sorlin, O.; Syndikus, I.; Taylor, J. T.; Thies, R.; Velho, P.; Wagner, A.; Wamers, F.; Vandebrouck, M.; Weick, H.; Wheldon, C.; Wilson, G.; Wimmer, C.; Winfield, J. S.; Woods, P.; Zhukov, M. V.; Zilges, A.; Zuber, K.;
The neutron-unbound isotope 13Be has been studied in several experiments using different reactions, different projectile energies and different experimental setups. There is, however, no real consensus in the interpretation of the data, in particular concerning the structure of the low-lying excited states. Gathering new experimental information, which may reveal the 13Be structure, is a challenge, in particular in light of its bridging role between 12Be, where the N=8 neutron-shell breaks down, and the Borromean halo nucleus 14Be. The purpose of the present study is to investigate the role of bound excited states in the reaction product 12Be after proton knockout from 14B, by measuring coincidences between 12Be, neutrons, and rays originating from de-excitation of states fed by neutron decay of 13Be. The 13Be isotopes were produced in proton-knockout from a 400 MeV/u 14B beam impinging on a CH2 target. The 12Be-n relative-energy spectrum dsigma=dEfn was obtained from coincidences between 12Be(g.s.) and a neutron, and also as threefold coincidences by adding rays, from the de-excitation of excited states in 12Be. Neutron decay from the first 5=2+ state in 13Be to the 2+ state in 12Be at 2.11 MeV is cofirmed. An energy-independence of the proton-knockout mechanism is found from a comparison with data taken with a 35 MeV/u 14B beam. A low-lying p-wave resonance in 13Be(1/2+) is confirmed by comparing proton- and neutron-knockout data from 14B and 14Be.
Keywords: radioactive beams; nuclear structure; unbound nuclei; 13Be

Publ.-Id: 27505 - Permalink


Pushing the limits of applicability of REBCO coated conductor films through fine chemical tuning and nanoengineering of inclusions
Rizzo, F.; Augieri, A.; Kursumovic, A.; Bianchetti, M.; Opherden, L.; Sieger, M.; Hühne, R.; Hänisch, J.; Meledin, A.; van Tendeloo, G.; Macmanus-Driscol, J. L.; Celentano, G.;
An outstanding current carrying performance (namely critical current density, Jc) over a broad temperature range of 10–77 K for magnetic fields up to 12 T is reported for films of YBa2Cu3O7−x with Ba2Y(Nb,Ta)O6 inclusion pinning centres (YBCO-BYNTO) and thicknesses in the range of 220–500 nm. Jc values of 10 MA cm−2 were measured at 30 K – 5 T and 10 K – 9 T with a corresponding maximum of the pinning force density at 10 K close to 1 TN m−3. The system is very flexible regarding properties and microstructure tuning, and the growth window for achieving a particular microstructure is wide, which is very important for industrial processing. Hence, the dependence of Jc on the magnetic field angle was readily controlled by fine tuning the pinning microstructure. Transmission electron microscopy (TEM) analysis highlighted that higher growth rates induce more splayed and denser BYNTO nanocolumns with a matching field as high as 5.2 T. Correspondingly, a strong peak at the B||c-axis is noticed when the density of vortices is lower than the nanocolumn density. YBCO-BYNTO is a very robust and reproducible composite system for high-current coated conductors over an extended range of magnetic fields and temperatures.

Publ.-Id: 27503 - Permalink


Anomalous Hall effect in fully compensated half-metallic Mn₂RuₓGa thin films
Fowley, C.; Rode, K.; Lau, Y. C.; Thiyagarajah, N.; Betto, D.; Borisov, K.; Atcheson, G.; Kampert, E.; Wang, Z.; Yuan, Y.; Zhou, S.; Lindner, J.; Stamenov, P.; Coey, J. M. D.; Deac, A. M.;
High-field magnetotransport is investigated in thin films of half-metallic ferrimagnet Mn₂RuₓGa. A non-vanishing Hall signal is observed over a broad temperature range, spanning the compensation temperature (155K), where the net magnetic moment is strictly zero, the Hall conductivity is 6673 Ohm⁻¹ m⁻¹ and the coercivity exceeds 9T. Molecular field modelling is used to determine the intra- and inter-sublattice exchange constants and from the spin-flop transition we infer the anisotropy of the electrically active sublattice to be 216 kJm⁻³ and predict the magnetic resonances frequencies. Exchange and anisotropy are comparable and hard-axis applied magnetic fields result in a tilting of the magnetic moments from their collinear ground state. Our analysis is applicable to collinear ferrimagnetic half-metal systems.
Keywords: Ferrimagnetism, Magnetotransport, Half-metals, Anomalous Hall effect, Magnetic anisotropy, Exchange interaction
  • Invited lecture (Conferences)
    Intermag 2018, 23.-27.04.2018, Singapore, Singapore
  • Open Access LogoPhysical Review B 98(2018), 220406(R)
    DOI: 10.1103/PhysRevB.98.220406

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Publ.-Id: 27502 - Permalink


Features of magnetization behavior in the rare-earth intermetallic compound (Nd0.5Ho0.5)2Fe14B
Kostyuchenko, N. V.; Tereshina, I. S.; Gorbunov, D. I.; Tereshina-Chitrova, E. A.; Andreev, A. V.; Doerr, M.; Politova, G. A.; Zvezdin, A. K.;
The crystal-electric field parameters are determined for the (Nd0.5Ho0.5)2Fe14B compound by analyzing experimental magnetization curves obtained in magnetic fields up to 60 T. The values of the crystal-field parameters B20, B40, B60, B44, B64 are 56.3, −73.2, −10.74, −8.9, 0 cm−1 for Nd3+ ion and 312.38, −176.78, 89.2, −88.43, 0 cm−1 for Ho3+ ion. The transition from the ferri- to the field-induced ferromagnetic state has been studied in detail.

Publ.-Id: 27501 - Permalink


Magnetic and magnetocaloric properties of single Crystal (Nd0.5Pr0.5)2Fe14B
Politova, G. A.; Tereshina, I. S.; Gorbunov, D. I.; Paukov, M. A.; Andreev, A. V.; Grechishkin, R. M.; Rogacki, K.;
In this work the magnetic and magnetocaloric properties of a (Nd0.5Pr0.5)2Fe14B single crystal have been investigated in a wide range of temperatures and magnetic fields. Magnetic phase transition temperatures (spin-reorientation transition (SRT) at TSR = 73 K and Curie point at Tc = 570 K) were determined together with the values of saturation magnetization Ms and magnetocrystalline anisotropy constants K1 and K2. In the vicinity of a spin-reorientation magnetic phase transition, the value of the magnetocaloric effect was determined as an isothermal magnetic entropy change (DSM). The universal curve of ΔS´(ʘ) around TSR under various magnetic field changes has been constructed by using a phenomenological procedure. It is found that this approach is applicable to materials with a second-order spin-reorientation phase transition.

Publ.-Id: 27500 - Permalink


Complex magnetic order in the kagome ferromagnet Pr3Ru4Al12
Henriques, M. S.; Gorbunov, D. I.; Andreev, A. V.; Fabrèges, X.; Gukasov, A.; Uhlarz, M.; Petricek, V.; Ouladdiaf, B.; Wosnitza, J.;
In the hexagonal crystal structure of Pr3Ru4Al12, the Pr atoms form a distorted kagome lattice, and their magnetic moments, are subject to competing exchange and anisotropy interactions.We performed magnetization, magnetic-susceptibility, specific-heat, electrical-resistivity, and neutron-scattering measurements. Pr3Ru4Al12 is a uniaxial ferromagnet with TC = 39 K that displays a collinear magnetic structure (in the high-temperature range of the magnetically ordered state) for which the only crystallographic position of Pr is split into two sites carrying different magnetic moments. A spin-reorientation phase transition is found at 7 K. Below this temperature, part of the Pr moments rotate towards the basal plane, resulting in a noncollinear magnetic state with a lower magnetic symmetry. We argue that unequal RKKY exchange interactions competing with the crystal electric field lead to a moment instability and qualitatively explain the observed magnetic phases in Pr3Ru4Al12.

Publ.-Id: 27499 - Permalink


CFD Modeling and Simulation of Heat and Mass Transfer in Passive Heat Removal Systems
Moonesi Shabestary, A.; Krepper, E.; Lucas, D.;
This paper is presenting the CFD-modelling and simulation of condensation inside passive heat removal systems. Designs of future nuclear boiling water reactor concepts are equipped with emergency cooling systems which are passive systems for heat removal. The emergency cooling system consists of slightly inclined horizontal pipes which are immersed in a tank of subcooled water. At normal operation conditions, the pipes are filled with water and no heat transfer to the secondary side of the condenser occurs. In the case of some accident scenarios the water level may decrease in the core, steam enters the emergency pipes and due to the subcooled water around the pipe, this steam condenses. The emergency condenser acts as a strong heat sink which is responsible for a quick depressurization of the reactor core.
This procedure acts passive i.e. without any additional external measures. The actual project is defined to model the phenomena which are occurring inside the emergency condensers. The focus of the project is on detection of different morphologies such as annular flow, stratified flow, slug flow and plug flow and also modeling of the laminar film which is occurring during the condensation near the wall.
  • atw - International Journal for Nuclear Power 63(2018)4

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  • Secondary publication expected

Publ.-Id: 27498 - Permalink


Bethe‐Strings: Exotische Anregungen in Spinsystemen
Wang, Z.; Loidl, A.;
Hans Bethe sagte 1931 in einer fundamentalen Arbeit die Existenz von stark gebundenen Zuständen von Quasiteilchen voraus. Nun konnte eine internationale Kooperation erstmals derartige Bethe‐Strings in einem Kristall nachweisen.
Keywords: Spin Kette, Quasiteilchen, String Erregungen, Hans Bethe

Publ.-Id: 27497 - Permalink


Stability and instability of hydromagnetic Taylor–Couette flows
Rüdiger, G.; Gellert, M.; Hollerbach, R.; Schultz, M.; Stefani, F.;
Decades ago S. Lundquist, S. Chandrasekhar, P. H. Roberts and R. J. Tayler first posed questions about the stability of Taylor–Couette flows of conducting material under the influence of large-scale magnetic fields. These and many new questions can now be answered numerically where the nonlinear simulations even provide the instability-induced values of several transport coefficients. The cylindrical containers are axially unbounded and penetrated by magnetic background fields with axial and/or azimuthal components. The influence of the magnetic Prandtl number Pm on the onset of the instabilities is shown to be substantial. The potential flow subject to axial fields becomes unstable against axisymmetric perturbations for a certain supercritical value of the averaged Reynolds number (with Re the Reynolds number of rotation, Rm its magnetic Reynolds number). Rotation profiles as flat as the quasi-Keplerian rotation law scale similarly but only for Pm >> 1 while for the instability instead sets in for supercritical Rm at an optimal value of the magnetic field. Among the considered instabilities of azimuthal fields, those of the Chandrasekhar-type, where the background field and the background flow have identical radial profiles, are particularly interesting. They are unstable against nonaxisymmetric perturbations if at least one of the diffusivities is non-zero. For Pm << 1the onset of the instability scales with Re while it scales with Rm for Pm >> 1. Even superrotation can be destabilized by azimuthal and current-free magnetic fields; this recently discovered nonaxisymmetric instability is of a double-diffusive character, thus excluding Pm=1 . It scales with Re for Pm -> 0 and with Rm for Pm -> infinity.
The presented results allow the construction of several new experiments with liquid metals as the conducting fluid. Some of them are described here and their results will be discussed together with relevant diversifications of the magnetic instability theory including nonlinear numerical studies of the kinetic and magnetic energies, the azimuthal spectra and the influence of the Hall effect.

Publ.-Id: 27496 - Permalink


Experiences with the SRF Gun II for User Operation at the ELBE Radiation Source
Teichert, J.; Arnold, A.; Bawatna, M.; Evtushenko, P. E.; Gensch, M.; Green, B. W.; Kovalev, S.; Lehnert, U.; Lu, P. N.; Michel, P.; Murcek, P.; Vennekate, H.; Xiang, R.;
The second version of the superconducting RF photoinjector (SRF Gun II) was successfully commissioned at the ELBE radiation source in 2014. The gun features an improved 3.5-cell niobium cavity combined with a superconducting solenoid integrated in the cryostat. With a Mg photocathode the SRF Gun II is able to generate bunches with up to 200 pC and with sub-ps length in CW mode with 100 kHz pulse frequency for the THz radiation facility at ELBE. In the ELBE linac, the beam is accelerated, gets a proper correlated energy spread, and is compressed in a magnetic chicane. Sub-ps pulses are obtained producing coherent diffraction radiation and superradiant undulator radiation.
Keywords: electron source, SRF gun, superconducting RF, THz radiation, coherent diffration radiation, superradiant radiation, ELBE
  • Poster
    9th International Particle Accelerator Conference IPAC´18, 29.04.-04.05.2018, Vancouver, Canada
  • Open Access LogoContribution to proceedings
    9th International Particle Accelerator Conference IPAC´18, 29.04.-04.05.2018, Vancouver, Canada
    Proceedings of the 9th International Particle Accelerator Conference IPAC´18, Genf: JACoW, 1247-1250
    DOI: 10.18429/JACoW-IPAC2018-THPMF040

Publ.-Id: 27495 - Permalink


Study of Magnesium Photocathodes for Superconducting RF Photoinjectors
Xiang, R.; Arnold, A.; Lu, P. N.; Murcek, P.; Teichert, J.; Vennekate, H.;
The superconducting RF photoinjector (SRF Gun II) has successfully served for the ELBE user facility at HZDR. The quality of photocathodes is one of the most critical issues in improving the stability and reliability for its application. Mg has a comparably low work function and shows quantum efficiency up to 0.3% after laser cleaning. But the present cleaning with a high intensity laser beam is time consuming and produces unwanted surface roughness. Thermal treatment and excimer laser cleaning are being investigated as alternative methods.
Keywords: electron source, photocathode, Mg, SRF gun, superconducting RF, laser cleaning
  • Poster
    9th International Particle Accelerator Conference IPAC´18, 29.04.-04.05.2018, Vancouver, Canada
  • Open Access LogoContribution to proceedings
    9th International Particle Accelerator Conference IPAC´18, 29.04.-04.05.2018, Vancouver, Canada
    Proceedings of the 9th International Particle Accelerator Conference IPAC´18, Genf: JACoW, 4142-4144
    DOI: 10.18429/JACoW-IPAC2018-THPMF039

Publ.-Id: 27494 - Permalink


A Cu Photocathode for the Superconducting RF Photoinjector of BERLinPro
Kühn, J.; Bürger, M.; Frahm, A.; Jankowiak, A.; Kamps, T.; Klemz, G.; Kourkafas, G.; Neumann, A.; Ohm, N.; Schmeißer, M.; Schuster, M.; Völker, J.; Murcek, P.; Teichert, J.;
The initial commissioning of the Superconducting RF (SRF) photoinjector is achieved with a Cu photocathode due to its robustness with respect to interactions with the SRF cavity of the injector. Here we present the preparation and characterization of a Cu photocathode plug and the diagnostics to insert the photocathode in the back wall of the SRF cavity. A polycrystalline bulk Cu plug was polished, particle free cleaned and characterized by x-ray photoelectron spectroscopy. During the transfer of the photocathode insert into the gun module the whole process was controlled by several diagnostic tools monitoring the insert position as well as RF, vacuum and cryogenic signals. We discuss the challenges of the photocathode transfer into an SRF cavity and how they can be tackled.
Keywords: electron source, photocathode, Cu, SRF gun, superconducting RF
  • Poster
    9th International Particle Accelerator Conference IPAC´18, 29.04.-04.05.2018, Vancouver, Canada
  • Open Access LogoContribution to proceedings
    9th International Particle Accelerator Conference IPAC´18, 29.04.-04.05.2018, Vancouver, Canada
    Proceedings of the 9th International Particle Accelerator Conference IPAC´18, Genf: JACoW, 1247-1250
    DOI: 10.18429/JACoW-IPAC2018-TUPMF002

Publ.-Id: 27493 - Permalink


Reply to “Comment on Methodological accuracy of image-based electron density assessment using dual-energy computed tomography” [Med. Phys. 44, 2429-2437 (2017)]
Möhler, C.ORC; Wohlfahrt, P.ORC; Richter, C.; Greilich, S.ORC
To the editor,
In his recent letter, Dr. Bouchard expressed his concern that our article on electron density (ED) assessment with dual-energy computed tomography (DECT) contained “some errors and speculative arguments”. We are aware that any study — no matter how carefully conducted — can exhibit erroneous aspects. In this case, however, we concluded that most of the statements and additional data provided by Dr. Bouchard in fact support the key findings of our paper, while other points raised can be attributed to a different use of concepts and to occasional overinterpretation. We therefore firmly reject his assertion. In this reply we provide our response to the criticism
raised:
Keywords: dual-energy CT, electron density, proton therapy

Publ.-Id: 27492 - Permalink


EOS at cw beam operation at Elbe
Schneider, C.; Gensch, M.; Kuntzsch, M.; Michel, P.; Seidel, W.; Kaya, K.; Al Shemmary, A.; Stojanovic, N.; Evtushenko, P.;
The ELBE accelerator is a super conduction electron cw machine located at the Helmholtz Center Dresden Rossendorf Germany with 1 mA current, now tested for up to 2 mA. Besides other important diagnostics for setting up the machine for user beam time and further improvement of the machine – a THz source is momentary under commissioning – a EOS measuring station for bunch length measurements is locate right behind the second super conducting Linac. Measuring with a crystal in the vicinity of an up to 2 mA cw beam implies higher beam loss and also higher radiation exposure of the crystal and hence also a safety risk for the UHV conditions of the super conducting cavities in the case of crystal damage. Therefore the EOS measuring principle is adapted to larger measuring distances and also for beam requirements with lower bunch charge at ELBE. A description of the setup, considerations of special boundary conditions and as well results for 13 MHz cw beam operation are presented.
  • Open Access LogoContribution to proceedings
    IPAC2014 - 5th International Particle Accelerator Conference, 15.-20.06.2014, Dresden, Germany

Publ.-Id: 27491 - Permalink


Microresonator-ferromagnetic resonance investigation of thermal spin-transfer torque in Co2FeAl/MgO/CoFeB magnetic tunnel junctions
Cansever, H.ORC; Narkowicz, R.; Lenz, K.; Fowley, C.; Ramasubramanian, L.; Yildirim, O.; Niesen, A.; Huebner, T.ORC; Reiss, G.; Lindner, J.; Fassbender, J.; Deac, A. M.
Similar to electrical currents flowing through magnetic multilayers [1,2], thermal gradients applied across the barrier of a magnetic tunnel junction may induce pure spin currents and generate ‘thermal’ spin-transfer torques large enough to induce magnetization dynamics on the free layer [3, 4]. The relation of spin current, charge current and heat current was theoretically described by Bauer et al. using Onsager’s reciprocity rule [5]. According to Onsager’s law, spin currents can be produced by bias voltages or thermal gradients and investigated in terms of spin-Seebeck effect in magnetic multilayers.
First, Hatami et al. theoretically studied the spin-Seebeck effect in spin-valves and introduced the concept of thermal spin-transfer torques. They predicted that the thermally induced spin current creates an imbalance on the interface between non-magnetic and ferromagnetic layers due to collisions (electron-electron and electron-phonon interactions) [3]. Thermal spin-transfer torques were studied experimentally within asymmetric Co/Cu/Co nanowire spin-valves which exhibit switching field changes under varying a.c. currents causing Joule heating [6]. In magnetic tunnel junctions, it was theoretically predicted that temperature differences of around 10 K over an ultrathin barrier (1 nm) can create magnetization dynamics in Fe/MgO/Fe magnetic tunnel junctions [4]. The spin-Seebeck effect has been studied on CoFeB/MgO/CoFeB magnetic tunnel junctions using different heating methods such as Joule heating, heating with Peltier elements, as well as laser heating [8-14]. Recently, it was shown that using Co2FeAl as a reference layer improves tunneling magneto-Seebeck (TMS) in magnetic tunnel junctions [7].
Here, we describe a novel experimental approach and setup to observe effects of thermal gradients within magnetic tunnel junctions with Heusler compounds by using the microresonator ferromagnetic resonance (µR-FMR) method under laser heating. Initially, microresonators (shown in figure 1) were introduced by Narkowicz et al. for electron paramagnetic resonance (EPR) experiments to achieve optimal sensitivity for small objects [8]. Detecting the FMR signal of nano- to micron-sized samples in conventional cavities (cm3) is not possible, due to the too small ferromagnetic volume, and therefore low filling factor. A planar microresonator, by definition, is a two-dimensional structure, its diameter can be tailored to match the order of the sample’s size (shown as a black ellipse in the microresonator loop in figure 1). Two stubs are attached to the inductive loop. The capacitive radial stub in first approximation may be viewed as an element to tune the loop to the operation frequency, while the rectangular stub matches the structure to the 50 Ω impedance of the microstrip feedline.

Figure 1: Layout of a planar microresonator with simulated electric field distribution at the resonance frequency. The inset shows the current and magnetic field distribution (out-of-plane direction) in the loop containing a sample (black ellipse).
We investigated magnetic tunnel junctions (MTJs) fabricated out of Co2FeAl/MgO/CoFeB stacks. The sample and microresonator fabrication consist of multiple steps of lithography, ion etching and lift-off processes. The sample is finally patterned into a 6x9 µm2 elliptical shape using electron beam lithography (EBL) and ion beam etching is used to etch down the sample to the substrate. Microresonators are then fabricated around the sample using UV lithography. For laser heating, a continuous-wave (CW) laser at 532 nm wavelength and with tunable power up to 33 mW is focused on the sample.
“Hot-FMR” measurements were performed on unpatterned multilayers between 300 K and 450 K (figure 2) to understand the effect of global heating. It is clearly seen that the FMR signal of Co2FeAl exhibits a shift with increasing temperature. As seen in the inset graph, it is difficult to quantify the changes for the CoFeB signal, due to its small intensity. Subsequent, measurements in the presence of a thermal gradient were performed on 6x9 µm2 MTJs, integrated into microresonator loops with an inner diameter of 20 µm. The MTJs were submitted to laser irradiation, up to a maximum power of 33 mW. Unlike the Hot-FMR measurements, the resonance field and linewidth did not show clear changes with increasing laser power. The results suggest that the laser power is neither sufficient to induce magnetization dynamics via thermal gradients across the barrier, nor lead to significant changes of the magnetic parameters due to global heating of the sample.
Figure 2: FMR spectra of the extended films of Co2FeAl / MgO / CoFeB measured in the in-plane direction at different temperatures
As a conclusion, the effect of a global temperature change on the resonance frequency and linewidth of Co2FeAl was analyzed. With regards to the µR-FMR results, higher laser power is needed to induce magnetization dynamics. Moreover, the lateral heat transport might reduce the vertical thermal gradients, thus similar measurements on smaller structures are required.
This study was funded by the German Research Foundation (DFG) via priority program SpinCaT (SPP 1538). We thank H. Schultheiss for helping with the optical part of the experimental setup and S. Zhou for giving the access to the VSM setup.
[1] J.C. Slonczewski, J. Magn. Magn. Mater. 159, L1, (1996).
[2] L. Berger, Phys. Rev. B 54, 9353, (1996).
[3] M. Hatami, G.E.W. Bauer, Q. Zhang and P.J. Kelly, Phys. Rev. Lett. 99, 066603 (2007).
[4] X. Jia, K. Xia and G.E.W. Bauer, Phys. Rev. Lett. 107, 176603 (2011).
[5] G.E.W. Bauer, E. Saitoh and B.J. van Wees, Nature Mater. 11, 391, (2012).
[6] H. Yu, S. Granville, D.P. Yu and J.-Ph. Ansermet, Phys. Rev. Lett. 104, 146601 (2010).
[7] A. Boehnke, U. Martens, C. Sterwerf, A. Niesen, T. Huebner, M. von der Ehe, M. Meinert, T. Kuschel, A. Thomas, C. Heiliger, M. Münzenberg M, Nature Communications 8,(1),1626, (2017).
[8] R. Narkowicz, D. Suter and R. Stonies, J. Magn. Reson.175, 275 (2005).
Keywords: thermal spin transfer torque, ferromagnetic resonance, microresonator, magnetic tunnel junctions
  • Lecture (Conference)
    INTERMAG 2018 Singapore, 23.-27.04.2018, Singapore, Singapore

Publ.-Id: 27490 - Permalink


Radiation Tests Of Aerospace Components At Elbe
Schneider, C.; Bemmerer, D.; Michel, P.; Stach, D.;
The cw electron accelerator ELBE operates mainly in the beam energy range 6 to 32 MeV and beam current range 1μA to 1mA. For most experiments a thermionic gun is used as electron source. The cw electron pulse structure so as the pulse charge is realized by applying electrical pulses with specific amplitudes and frequencies on the grid of the gun. The standard cw operation frequency is 13 MHz but can be divided sequentially by the factor 2 down to 101 kHz. For very special pulse structures a so called single pulser module exist performing different patterns also with dark current suppression via a macro pulser gate. For evaluating the performance and hardness under irradiation of e.g. aerospace components much lower doses resp. currents lower than the μA range are required. Furthermore reproducible and stable doses in a specific area for consecutively radiation of samples are necessary. In the presentation the investigations and concepts used at ELBE for the irradiation of different aerospace components are described.
  • Open Access LogoContribution to proceedings
    IPAC2017 - 8th International Particle Accelerator Conference, 14.-19.05.2017, Copenhagen, Denmark

Publ.-Id: 27489 - Permalink


Unmixing-based feature extraction for mineral mapping
Contreras, C.; Khodadadzadeh, M.; Tusa, L.; Gloaguen, R.;
Hyperspectral imaging is a well-accepted technology for mineral mapping. However, the advantage of using hyperspectral data for this purpose depends on the applied techniques. Spectral unmixing and classification algorithms have been widely applied in the literature to map and determine different minerals composition.
Generally, these two algorithms are used independently, however, in the scientific community dedicated to the field of land cover classification, new techniques have been developed in which, both classification and spectral unmixing are used complementarily. For example, spectral unmixing techniques have been used for feature extraction prior to a supervised classification. This strategy has been explored to address the problem of mixed pixels, which are dominant in hyperspectral images. Previous studies concluded that using unmixing-based features do not particularly improve classification accuracies in comparison to applying the extracted features by a classic algorithm such as the Minimum Noise Fraction (MNF). However, the advantage over this is that features extracted from spectral unmixing techniques have physical meaning since they can be interpreted as the abundances of the materials present in the scene, and they do not relegate variations of features with less significant signal-to-noise ratio, therefore, small classes are better characterized. Nevertheless, in geological remote sensing applications, the use of spectral unmixing as a feature extraction technique prior to a supervised classification has not been previously applied.
In this context, this work proposes the use of an automatic endmember extraction algorithm (e.g., Vertex Component Analysis – VCA) to further obtain the mineral abundances at a sub-pixel scale with a linear unmixing process. These features are subsequently used as inputs to a standard supervised classification technique (e.g., Support Vector Machine – SVM). The experiments are carried out on a hyperspectral VNIR/SWIR dataset of core samples. With this technique, we introduce a novel supervised approach, which, based on preliminary attempts, is expected to deliver both qualitative and quantitative improvements in the final classification accuracies.
  • Poster
    European Geosciences Union General Assembly 2018 (EGU), 08.-13.04.2018, Vienna, Austria

Publ.-Id: 27488 - Permalink


Design Of A Stripline Kicker For The Elbe Accelerator
Schneider, C.; Arnold, A.; Hauser, J.; Michel, P.; Staats, G.;
ELBE is a linac based cw electron accelerator serving different secondary beams one at a time. Depending on the user demand the bunch repetition rate may vary from single pulse up to 13 MHz. For the future different end stations should be served simultaneously, hence specific bunch patterns have to be kicked into different beam-lines. To use e.g. one bunch out of the bunch train very short kicking durations have to be realized. The variabil-ity of the bunch pattern and the frequency resp. switching time are one of the main arguments for a stripline-kicker combined with high voltage (HV)-switches as basic con-cept. A nearly homogenous field in the kicker has to be realized for uniform deflection of the electron bunch and keep the emittance growth of the bunch as low as possi-ble. Furthermore the fast switching ability of the kicker demands for a fast decay of the HV-pulse resp. its reflec-tions in the structure implying a specific design of the kicker elements. For this reason a design with two tapered active electrodes and two ground fenders was optimized in time and frequency domain with the software package CST. Additionally a first prototype was manufactured for laboratory and first beam-line tests.
  • Open Access LogoContribution to proceedings
    IPAC2017 - 8th International Particle Accelerator Conference, 14.-19.05.2017, Copenhagen, Denmark

Publ.-Id: 27487 - Permalink


Effect of DTPA on adsorption of Eu(III) onto quartz sand as a function of pH
Karimzadeh, L.; Lippold, H.;
Organic ligands are known to affect radionuclide adsorption onto mineral surfaces. Quantitative description of these ternary systems requires appropriate modelling of the constituent interaction processes, which are not yet fully understood. In this study, the effect of the decontamination agent DTPA on adsorption of Eu(III) (as an analogue of trivalent actinides) onto quartz sand was investigated in radiotracer studies with 152Eu, at a pH range from 3 to 9. The experimental results show that DTPA strongly reduces adsorption of Eu(III) and thus promotes its mobility by formation of aqueous Eu-DTPA complexes over the whole studied pH range. This behavior was successfully described by generalized two-layer surface complexation model based on the aqueous speciation of Eu(III) / DTPA as a function of pH.
Keywords: DTPA, Surface complexation modeling, Europium, Quartz sand
  • Poster
    10th International Symposium on Nano and Supramolecular chemistry, 09.-12.07.2018, Dresden, Germany

Publ.-Id: 27486 - Permalink


Recent Developments of the Liquid Metal Taylor Couette Experiment PROMISE
Seilmayer, M.; Stefani, F.; Gundrum, T.;
In the beginning of the 20th century Taylor-Couette (TC) experiments were carried out with transparent liquids like water or air, which are electrical no-conducting. With the first experiments of Donnelly [1] in the sixties, a more general approach with liquid metal experiments started to investigate the interaction between magnetic fields and the TC flows of electrically conducting fluids. Two challenges of opaque liquid metal experiments are the measurement technique to investigate the flow structure inside the liquid and the precision and strength of the magnetic field.
We like to report recent results carried out with a quasi coaxial return path, which was introduced to the PROMIS experiment in the last years. Instead of the former frame coil an axial-symmetric return path closes the electrical circuit, which improves the field symmetry inside the experiment and minimizes the stray field outside the setup. Since this arrangement consists of an electrical parallel connection of the return conductors and the parallel connection of the hydraulic cooling circuit, it must be checked whether stability problems can occur in the current distribution in the return conductors. It turned out that the current return design can be controlled by simple and cheap proportional heater valves [2].

[1] R. J. Donnelly and M. Ozima, Phys. Rev. Lett., 4(10), 497--498, 1960
[2] M. Seilmayer and N. Krauter, IEEE Sensors Journal, 18(3), 1256--1264, 201
Keywords: DRESDYN, PROMISE, MRI, AMRI, Taylor Couette, Liquid Metal
  • Lecture (Conference)
    ICTW 20: 20th International Couette-Taylor Workshop, 11.-13.07.2018, Marseille, France

Publ.-Id: 27485 - Permalink


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