Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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33412 Publications

Synthetic radiation simulations as a path to study the relativistic Kelvin-Helmholtz instability in interstellar jets

Pausch, R.ORC; Bussmann, M.ORC; Hübl, A.ORC; Schramm, U.ORC; Steiniger, K.ORC; Widera, R.ORC; Debus, A.ORC
The relativistic Kelvin-Helmholtz instability (KHI) is expected in shear flow regions of astrophysical plasma jets originating from AGNs and SNR. It generates magnetic fields that influence the jet dynamics significantly.

We present 3D3V particle-in-cell simulations of unprecedented resolution and extent that not only allow studying the plasma dynamics during the KHI but also making quantitative predictions on the emitted radiation. We present a diagnostic method that allows identifying the linear phase of the instability via a polarization anisotropy observable light years away on Earth and to quantify the growth rate of the instability.

A microscopic model, that describes the fundamental origin of the radiation signature, will be covered in detail during the talk. Technical aspects relevant for performing these large-scale simulations with the particle-in-cell code PIConGPU and for making quantitative predictions with synthetic radiation diagnostics, based on Liénard-Wiechert potentials, will be discussed, and observation limits both for interstellar jets and in lab astrophysics experiments will be covered.
Keywords: KHI, PIConGPU, radiation, synthetic diagnostics, polarization, AGN, SNR
  • Invited lecture (Conferences)
    DPG-Frühjahrstagung der Sektion Materie und Kosmos (SMuK), 18.-22.03.2019, München, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-29254
Publ.-Id: 29254


Large-scale simulations of plasma acceleration

Pausch, R.ORC; Hübl, A.ORC; Bastrakov, S.ORC; Debus, A.ORC; Garten, M.ORC; Matthes, A.ORC; Steiniger, K.ORC; Schramm, U.ORC; Widera, R.ORC; Zenker, E.; Bussmann, M.ORC
A brief presentation of the MuT/DMA activities of the Computational radiation group and solutions that might be of interest for the Matter in the Universe community.
Keywords: DMA, MUT, ARD, PIConGPU, alpaka
  • Lecture (Conference)
    "Matter and the Universe" Days 2019, 14.-15.02.2019, Hamburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-29253
Publ.-Id: 29253


From studying the self-truncated ionization injection during LWFA to hybrid LPWFA simulations

Pausch, R.ORC; Debus, A.ORC; Bussmann, M.ORC; Couperus Cabadağ, J. P.ORC; Garten, M.ORC; Heinemann, T.; Hübl, A.ORC; Martinez De La Ossa, A.; Irman, A.ORC; Kurz, T.ORC; Schöbel, S.; Steiniger, K.ORC; Schramm, U.ORC
This talk gives a brief summary of the current status of the start-to-end simulations of the hybrid LPWFA setup using PIConGPU.
Keywords: PIConGPU, hybrid, LPWFA, LWFA, PWFA
  • Lecture (others)
    hybrid collaboration meeting, 09.-11.01.2019, Hamburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-29252
Publ.-Id: 29252


T cells engrafted with a UniCAR 28/ζ outperform UniCAR BB/ζ-transduced T cells in the face of regulatory T cell-mediated immunosuppression

Kegler, A.; Koristka, S.; Bergmann, R.; Berndt, N.; Arndt, C.; Feldmann, A.; Hoffmann, A.; Bornhäuser, M.; Schmitz, M.; Bachmann, M.ORC
Adoptive transfer of chimeric antigen receptor (CAR)-equipped T cells has demonstrated astonishing clinical efficacy in hematological malignancies recently culminating in the approval of two CAR T cell products. Despite this tremendous success, CAR T cell approaches have still achieved only moderate efficacy against solid tumors. As major obstacle, engineered conventional T cells (Tconvs) face an anti-inflammatory, hostile tumor microenvironment often infiltrated by highly suppressive regulatory T cells (Tregs). Thus, potent CAR T cell treatment of solid tumors requires efficient activation of Tconvs via their engrafted CAR to overcome Treg-mediated immunosuppression. In that regard, selecting an optimal intracellular signaling domain might represent a crucial step to achieve best clinical efficiency. To shed light on this issue and to investigate responsiveness to Treg inhibition, we engrafted Tconvs with switchable universal CARs (UniCARs) harboring intracellularly the CD3ζ domain alone or in combination with costimulatory CD28 or 4-1BB. Our studies reveal that UniCAR ζ- and UniCAR BB/ζ-engineered Tconvs are strongly impaired by activated Tregs, whereas UniCARs providing CD28 costimulation overcome Treg-mediated suppression both in vitro and in vivo. Compared to UniCAR ζ- and UniCAR BB/ζ-modified cells, UniCAR 28/ζ-armed Tconvs secrete significantly higher amounts of Th1-related cytokines and, furthermore, levels of these cytokines are elevated even upon exposure to Tregs. Thus, in contrast to 4-1BB costimulation, CD28 signaling in UniCAR-transduced Tconvs seems to foster a pro-inflammatory milieu, which contributes to enhanced resistance to Treg suppression. Overall, our results may have significant implications for CAR T cell-based immunotherapies of solid tumors strongly invaded by Tregs.

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Permalink: https://www.hzdr.de/publications/Publ-29251
Publ.-Id: 29251


Investigations on stationary measurements at COSMEA-I facility - CT part

Bieberle, A.ORC; Beyer, M.; Pietruske, H.; Hampel, U.ORC; Boden, S.ORC

This repository contains reconstructed and analysed CT data obtained from the COSMEA-I test facility that is operated under stationary operating conditions. Furthermore, a full CAD drawing set is provided.

Keywords: Passive Heat Transfer; Stream Condensation; Heat Flux Probe; Process Computed Tomography
Related publications
Flow morphology and heat transfer analysis during … (Id 29452) is supplemented by this publication
  • Reseach data in the HZDR data repository RODARE
    Publication date: 2019-05-20
    DOI: 10.14278/rodare.126

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Permalink: https://www.hzdr.de/publications/Publ-29250
Publ.-Id: 29250


Thallium contamination, health risk assessment and source apportionment in common vegetables

Liu, J.; Wei, X.; Zhou, Y.; Tsang, D. C. W.; Bao, Z.; Yin, M.; Lippold, H.ORC; Yuan, W.; Wang, J.; Feng, Y.; Chen, D.
As an element with well-known toxicity, excessive thallium (Tl) in farmland soils may threaten food security and induce extreme risks to human health. Identification of key contamination sources is a prerequisite for remediation technologies. This study aims to examine the contamination level, health risks and source apportionment of Tl in common vegetables from typical farmlands distributed over a densely populated residential area in a pyrite mine city, which has been exploiting Tl-bearing pyrite minerals for over 50 years. Results showed excessive Tl levels in most of the vegetables (0.16-20.33 mg/kg) and alarming health risks induced by the vegetables via the food chain. Source apportionment of Tl contamination in vegetables was then evaluated by using the Pb isotope fingerprinting technique. Both vegetables and soils were characterized by overall low 206Pb/207Pb ratios. This indicated that a significant contribution may be ascribed to anthropogenic activities for pyrite deposit exploitation, whose raw material and slags were featured with lower 206Pb/207Pb ratios. Further calculations by the binary mixing model suggested that pyrite mining and smelting activities contributed 54-88% to the thallium contamination in vegetables. The results highlighted that Pb isotope tracing is a suitable technique for source apportionment of Tl contamination in vegetables and that contamination from pyrite mining/smelting activities urges authorities to initiate proper practices of remediation.
Keywords: Metal contamination; Isotopic analysis; Source apportionment; Food safety; Plant uptake

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Permalink: https://www.hzdr.de/publications/Publ-29249
Publ.-Id: 29249


Nitric oxide-releasing selective estrogen receptor modulators (NO-SERMs): a bifunctional approach to improve the therapeutic index

Bechmann, N.; Knieß, T.; Pietzsch, J.ORC
When using selective estrogen receptor modulators (SERMs) in cancer therapy adverse effects such as endothelial dysfunction have to be considered. Estrogens and, consequently, SERMs regulate the synthesis of vasoactive nitric oxide (•NO). We hypothesized that a bifunctional approach combining the antagonistic action of SERMs with a targeted NO-release could diminish vascular side effects. We synthesized a series of NO-releasing SERMs (NO-SERMs) and the corresponding SERMs (after NO-release) derived from a triaryl olefin lead. Compounds showed antagonistic activity for ERβ (IC50(ERβ)=0.2–2.7µM), but no interaction with ERα. Growth of ERβpositive breast cancer and melanoma cells was significantly decreased by treatment with SERM 5d. This anti-proliferative effect was diminished by the additional release of •NO by the corresponding NO-SERM 4d. Moreover, targeted release of •NO by 4d counteracted the antiproliferative effect of 5d in normal vascular tissue cells. Summarizing, the therapeutic index of SERMs might be improved by this bifunctional approach.

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  • Secondary publication expected from 17.05.2020

Permalink: https://www.hzdr.de/publications/Publ-29248
Publ.-Id: 29248


Breaking the Doping Limit in Silicon by Deep Impurities

Wang, M.ORC; Debernardi, A.; Berencen, Y.ORC; Heller, R.; Xu, C.ORC; Yuan, Y.; Xie, Y.; Böttger, R.; Rebohle, L.; Skorupa, W.; Helm, M.; Prucnal, S.; Zhou, S.ORC
n-type doping in Si by shallow impurities, such as P, As, and Sb, exhibits an intrinsic limit due to the Fermi-level pinning via defect complexes at high doping concentrations. Here, we demonstrate that doping Si with the deep chalcogen donor Te by nonequilibrium processing can exceed this limit and yield higher electron concentrations. In contrast to shallow impurities, the interstitial Te fraction decreases with increasing doping concentration and substitutional Te dimers become the dominant configuration as effective donors, leading to a nonsaturating carrier concentration as well as to an insulator-to-metal transition. First-principles calculations reveal that the Te dimers possess the lowest formation energy and donate two electrons per dimer to the conduction band. These results provide an alternative insight into the physics of deep impurities and lead to a possible solution for the ultrahigh electron concentration needed in today’s Si-based nanoelectronics.

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Permalink: https://www.hzdr.de/publications/Publ-29247
Publ.-Id: 29247


Nano-sandwiched metal hexacyanoferrate/graphene hybrid thin films for in-plane asymmetric micro-supercapacitors with ultrahigh energy density

He, Y.; Zhang, P.; Wang, M.ORC; Wang, F.; Tan, D.; Li, Y.; Zhuang, X.; Zhang, F.; Feng, X.
In-plane micro-supercapacitors (MSCs) with high power density, remarkable rate capability, and long cycling stability, exhibit promising application potential in modern electronic devices. To satisfy the fast-growing energy demands for the next-generation advanced micro-devices, increasing the energy density of MSCs is urgently desirable but still remains a great challenge. In this work, a series of in-plane asymmetric MSCs (AMSCs) are rationally constructed using a family of nano-sandwiched metal hexacyanoferrate/graphene hybrid thin films with interdigital patterns. The voltage output window of the resultant AMSCs is able to reach up to 1.8 V, delivering superior areal capacitances of up to 19.84 mF cm-2, and ultrahigh energy density of 44.6 mW h cm-3 which is among the best performances of the state-of-the-art MSCs. Moreover, the achieved AMSCs show outstanding mechanical flexibility and integration capability. Thus, this work will promote the development of novel high-performance AMSCs.

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Permalink: https://www.hzdr.de/publications/Publ-29246
Publ.-Id: 29246


Interface stability, mechanical and corrosion properties of AlCrMoNbZr/(AlCrMoNbZr)N high-entropy alloy multilayer coatings under helium ion irradiation

Zhang, W.; Wang, M.ORC; Wang, L.; Liu, C. H.; Chang, H.; Yang, J. J.; Liao, J. L.; Yang, Y. Y.; Liu, N.
High entropy alloy (HEA) coatings are promising for use as accident-tolerant fuel cladding due to their outstanding high-temperature corrosion resistance. In this work, we investigated the interface stability, mechanical properties and corrosion resistance of AlCrMoNbZr/(AlCrMoNbZr)N multilayer coatings with individual layer thickness of 5 nm, 10 nm and 50 nm, subjected to helium (He) ion irradiations: 400 keV He+ ions with fluences of 8×1015 ion/cm2 and 8×1016 ion/cm2. We determined that He bubbles are not observed in any of the multilayer coatings after a helium ion irradiation process with 400 keV He ions and a fluence as high as 8×1016 ion/cm2. Although intermixing and chemical reaction in the peak damage region of the AlCrMoNbZr/(AlCrMoNbZr)N multilayer coating with 5 nm monolayer thickness are induced by the high fluence He ion irradiation, the FCC structure remained, and no intermetallic compounds are detected. Moreover, we found that the AlCrMoNbZr/(AlCrMoNbZr)N multilayer coating with the monolayer thickness of 50 nm has better interface stability during the irradiation process. Nanoindentation tests reveal that the hardness of all multilayer coatings decreased for low and high fluences, which is mainly due to the thermal effect caused by irradiation. In addition, the electrochemical corrosion test show that AlCrMoNbZr/(AlCrMoNbZr)N multilayer coating 50 nm coatings has better corrosion resistance than AlCrMoNbZr/(AlCrMoNbZr)N multilayer coating 5 nm coatings under high fluence He irradiation. The corrosion resistance of the multilayer coating depends on the stability of the multilayer interface. Our results show that the AlCrMoNbZr/(AlCrMoNbZr)N multilayer coating with a monolayer thickness of 50 nm had better interface stability, mechanical properties and corrosion resistance than the AlCrMoNbZr/(AlCrMoNbZr)N multilayer coating with a per layer thickness of 5 nm under high fluence He irradiation. This work reveals that high-entropy alloy multilayer coatings have potential applications as an accident-tolerant fuel cladding coating in light water reactors.
Keywords: AlCrMoNbZr/(AlCrMoNbZr)N, Multilayer coating, High-entropy alloy, Ion irradiation, Interfaces, Nanoindentation, Electrochemical corrosion, Accident-tolerant fuel (ATF)

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Permalink: https://www.hzdr.de/publications/Publ-29245
Publ.-Id: 29245


Cortical microinfarcts in memory clinic patients are associated with reduced cerebral perfusion

Ferro, D.; Mutsaerts, H.; Hilal, S.; Kuijf, H.; Petersen, E. T.; Petr, J.ORC; van Veluw, S.; Venketasubramanian, N.; Yeow, T. B.; Biessels, G. J.; Chen, C.
Cerebral cortical microinfarcts (CMIs) are small ischemic lesions associated with cognitive impairment and dementia. CMIs are frequently observed in cortical watershed areas suggesting that hypoperfusion contributes to their development. We investigated if presence of CMIs was related to a decrease in cerebral perfusion, globally or specifically in cortex surrounding CMIs. In181 memory clinic patients (mean age 72 ± 9 years, 51% male) CMI presence was rated on 3 T-MRI. Cerebral perfusion was assessed from cortical gray matter of the anterior circulation using pseudo-continuous arterial spin labeling parameters cerebral blood flow (CBF) (perfusion in mL blood/100g tissue/minute) and spatial coefficient of variation (CoV) (reflecting arterial transit time (ATT)) . Patients with CMIs had a 12% lower CBF (beta=-.20) and 22% higher spatial CoV (beta= .20) (both p<.05) without a specific regional pattern on voxel based CBF analysis. CBF in a 2 cm region-of-interest around the CMIs did not differ from CBF in a reference zone in the contralateral hemisphere. These findings show that CMIs in memory clinic patients are primarily related to global reductions in cerebral perfusion, thus shedding new light on the etiology of vascular brain injury in dementia.

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Permalink: https://www.hzdr.de/publications/Publ-29244
Publ.-Id: 29244


Interaction of curium(III) with plant cells (Brassica napus)

Moll, H.ORC; Sachs, S.; Raff, J.ORC
The accumulation of radionuclides and toxic heavy metals into plants and thus into the food chain represents a potential pathway for human exposure. Hence, detailed knowledge of the fate of these elements in the ecosphere including the food chain is required for a reliable assessment of the resulting risk potential for humans and wildlife. Our aim is to explore the complex interaction of trivalent actinides with plant cells on a molecular level using curium(III) as an excellent luminescence probe.
We studied the response of canola (Brassica napus) cells to curium(III) exposure (0.7 µM). TRLFS was used as direct speciation technique to explore the Cm(III) speciation on the cells and in the supernatants. Liquid scintillation counting (LSC) was applied to measure the Cm(III) content in the supernatants. The possible release of plant cell metabolites was probed by solid phase extraction (SPE) with subsequent HPLC analysis.
The bioassociation experiments were performed in 0.154 M NaCl in a glove box over a time period up to 168 h. After defined time steps the Cm(III) concentration in the supernatants was determined as well as luminescence spectra from washed cells and the supernatants were taken. The Cm(III) concentration in the supernatants as a function of time points to a multi-stage bioassociation process on the plant cells. Red shifted Cm(III) luminescence spectra (+8.6 nm compared to Cm3+(aq)) in the supernatants indicated a Cm(III) complexation by substances that were released by the plant cells already after an exposure time of 5 h. Cell metabolites could be enriched and extracted by SPE. TRLFS studies (spectra and lifetime) showed a different Cm(III) speciation on cells compared to those found in the supernatants. To further describe the spectroscopic Cm(III) speciation in the B. napus system all spectra were evaluated with iterative transformation factor analysis (ITFA, Roßberg et al. 2003). The so obtained results (single component spectra and time-dependent species distributions) will be discussed in order to describe the fate of Cm(III) in the presence of plant cells (B. napus).
This new knowledge contributes to an improved understanding of trivalent actinide interactions with plants on a molecular level.

The authors are indebted to the U.S. Department of Energy, Office of Basic Energy Sciences, for the use of 248Cm via the transplutonium element production facilities at Oak Ridge National Laboratory; 248Cm was made available as part of collaboration between HZDR and the Lawrence Berkeley National Laboratory (LBNL). This study is part of the project TRANS-LARA which is funded by the Federal Ministry of Education and Research under contract number 02NUK051B.

Roßberg, A., Reich, T., Bernhard, G. 2003. Complexation of uranium(VI) with protocatechuic acid –
application of iterative transformation factor analysis
to EXAFS spectroscopy. Anal. Bioanal. Chem. 376, 631–638.
Keywords: curium; plant cells; Brassica napus; luminescence spectroscopy
  • Lecture (Conference)
    Envira 2019, 08.-13.09.2019, Prague, Czech Republic

Permalink: https://www.hzdr.de/publications/Publ-29243
Publ.-Id: 29243


Targeting Cyclooxygenase-2 in Pheochromocytoma and Paraganglioma: Focus on Genetic Background

Ullrich, M.ORC; Richter, S.; Seifert, V.; Hauser, S.ORC; Calsina, B.; Martínez-Montes, A. M.; Ter Laak, M.; Ziegler, C. G.; Timmers, H.; Eisenhofer, G.; Robledo, M.; Pietzsch, J.ORC
Cyclooxygenase 2 (COX-2) is a key enzyme of the tumorigenesis-inflammation interface and can be induced by hypoxia. A pseudohypoxic transcriptional signature characterizes pheochromocytomas and paragangliomas (PPGLs) of the cluster I, mainly represented by tumors with mutations in von Hippel-Lindau (VHL), endothelial PAS domain-containing protein 1 (EPAS1), or succinate dehydrogenase (SDH) subunit genes. The aim of this study was to investigate a possible association between underlying tumor driver mutations and COX-2 in PPGLs. COX-2 gene expression and immunoreactivity were examined in clinical specimens with documented mutations as well as in spheroids and allografts derived from mouse pheochromocytoma (MPC) cells. COX-2 in vivo imaging was performed in allograft mice. We observed significantly higher COX-2 expression in cluster I, especially in VHL-mutant PPGLs, however, no specific association between COX-2 mRNA levels and a hypoxia-related transcriptional signature was found. COX-2 immunoreactivity was present in about 60 % of clinical specimens as well as in MPC spheroids and allografts. A selective COX-2 tracer specifically accumulated in MPC allografts. This study demonstrates that, although, pseudohypoxia is not the major determinant for high COX-2 levels in PPGLs, COX-2 is a relevant molecular target. This potentially allows for employing selective COX-2 inhibitors as targeted chemotherapeutic agents and radiosensitizers. Moreover, available models are suitable for preclinical testing of these treatments.
Keywords: VHL; NF1; EPAS1; hypoxia-inducible factor; inflammation; radiosensitization; succinate dehydrogenase; mouse pheochromocytoma cells; immunohistochemistry; fluorescence imaging

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Permalink: https://www.hzdr.de/publications/Publ-29242
Publ.-Id: 29242


Radiumdotierte Bariumsulfat-Nanopartikel für die zukünftige Alphatherapie

Reissig, F.ORC; Pietzsch, H.-J.; Steinbach, J.; Mamat, C.ORC
1. Zielstellung: Durch die Alterung der Bevölkerung ist eine stetige Zunahme an Tumorneuerkrankungen zu verzeichnen und die Therapieoptimierung daher unabdingbar. Ein diskutierter Ansatz ist die Therapie mit Alphaemittern. Radionuklide wie 223/224Ra sind in der Lage, Tumorgewebe aufgrund ihres hohen linearen Energietransfers infolge einer Kaskade von Alpha-Zerfällen effizient zu zerstören ohne Beinflussung des gesunden Gewebes. Die stabile Fixierung von Barium- und Radiumionen kann durch Co-Fällung radiomarkierter [133Ba223/224Ra]Ba(Ra)SO4 Nanopartikel (NP) erfolgen, welche mit Alendronat funktionalisiert und anschließend mit einer targetspezifischen Einheit modifiziert werden.

2. Methodik
Die Synthese der BaSO4-NP wurde durch Fällung realisiert. Die Partikelgröße wurde in Abhängigkeit der Reaktionsparameter (Lösungsmittelsystem, Verhältnis der Reaktanden, Fließgeschwindigkeit bei der Zugabe des zweiten Reaktanden) untersucht. NP-Größenverteilungen wurden mittels Dynamic Light Scattering (DLS) ermittelt. Radiomarkierungen wurden unter analogen Bedingungen unter Zugabe von [133Ba]Ba2+ und [224Ra]Ra2+ durchgeführt. 224Ra wurde als [224Ra]Ra(NO3)2 aus einer 228Th-Quelle durch Ionenaustauschchromatographie separiert. 133Ba wurde als [133Ba]BaCl2 kommerziell bezogen.

3. Ergebnisse
Nach Auswertung aller Syntheseansätze wurde die Fällung der Partikel mit einem sechsfachen Bariumüberschuss in einer Ethanol/Wasser-Mischung (1/11) bei Raumtemperatur als beste Methode identifiziert. Die Einlagerung von [133Ba]Ba2+- und [224Ra]Ra2+-Ionen konnte nachgewiesen werden. Die radiomarkierten NP zeigten über 7 Tage keinen relevanten Release. Die Modifikation der Partikel mit Alendronat konnte mittels IR-Spektroskopie, EDXS-Analyse und UV/Vis-Spektroskopie nachgewiesen werden. Die Partikelgröße wurde mittels DLS (140 ± 50 nm) analysiert und durch TEM verifiziert. Die weitere Funktionalisierung der NP wurde mittels Aktivesterkupplung eines fluoreszierenden NBD-Derivates und Fluoreszenzspektroskopie nachgewiesen.

4. Schlussfolgerungen
Die Co-Fällung von Barium- und Radiumisotopen zur Gewinnung von NP definierter Größe ist ein Ausgangspunkt zukünftiger Therapieansätze. Die Funktionalisierung mit biologischen Targetmolekülen ermöglicht das zielgerichtete Aufspüren von Tumorzellen. Zukünftige Arbeiten fokussieren die Optimierung der Synthesemethode hinsichtlich der Verringerung der Partikelgröße und Ausbeute bei der Radiomarkierung sowie die anschließende Oberflächenmodifikationen bezüglich verschiedener biologischer Targets.
Keywords: Barium, Radium, Bariumsulfat, Nanopartikel
  • Lecture (Conference)
    Jahrestagung der GDCh-Fachgruppe Nuklearchemie 2019, 25.-27.09.2019, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-29241
Publ.-Id: 29241


Damage accumulation and implanted Gd and Au position in a- and c-plane GaN

Macková, A.; Malinský, P.; Jagerová, A.; Mikšová, R.; Sofer, Z.; Klímová, K.; Mikulics, M.; Böttger, R.; Akhmadaliev, S.; Oswald, J.
(0001) c-plane and (11−20) a-plane GaN epitaxial layers were implanted with 400 keV Au+ and Gd+ ions using ion implantation fluences of 5×1014, 1×1015 and 5×1015 cm-2. Rutherford Back-Scattering spectrometry in channelling mode (RBS/C) was used to follow the dopant depth profiles and the introduced disorder; the angular dependence of the backscattered ions (angular scans) in c- and a-plane GaN was measured to get insight into structural modification and dopant position in various crystallographic orientations. Defect-accumulation depth profiles exhibited differences for a- and c-plane GaN, with a-plane showing significantly lower accumulated disorder in the buried layer, accompanied by the shift of the maximum damage accumulation into the deeper layer with respect to the theoretical prediction, than c-plane GaN. Angular scans showed channelling preservation in as-implanted samples and better channelling recovery in the annealed a-plane GaN compared to cplane GaN. The angular scan widths were simulated by FLUX code as well as the half-width modifications of angular scans were discussed in connection to the damage accumulation. Photoluminescence measurement followed in detail yellow band and band edge luminescence decline after the implantation and the recovery of luminescence spectra features after annealing.
Keywords: Implanted (0001) and (11–20) GaN, Damage accumulation asymmetry in GaN, Ion implantation in semiconductors, RBS channelling, Damage-depth profiling

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Permalink: https://www.hzdr.de/publications/Publ-29240
Publ.-Id: 29240


Tc immobilization by Fe(II)-Al(III)-Cl layered double hydroxide phase

Mayordomo Herranz, N.ORC; Rodriguez Hernandez, D. M.; Roßberg, A.; Scheinost, A.ORC; Foerstendorf, H.ORC; Heim, K.; Brendler, V.ORC; Müller, K.ORC
⁹⁹Tc is a long half-life isotope (2.13×10⁵ years) that can be found in the environment due to anthropogenic sources - nuclear energy production, tests of nuclear weapons and radiopharmacy - as it is a fission product from ²³⁵U and ²³⁹Pu and the daughter of 99mTc, used for diagnosis [1].
Although Tc has several oxidation states, Tc(VII) and Tc(IV) are the more stable ones found under oxidizing and reducing conditions, respectively, but their chemical behavior differs. While the Tc(VII) main species (TcO₄⁻) is a highly mobile anion that hardly interacts with minerals, Tc(IV) is usually found as a low soluble solid (TcO₂) whose precipitation avoids the Tc migration [2]. Therefore, in order to reduce Tc mobility it is essential to understand the conditions that favor the three electrons donation step switching between these two oxidation states.
Several works report that Fe²⁺ promotes the Tc reduction, especially when found in Fe(II)-minerals or sorbed on mineral surfaces [3], [4].
If corrosion of the nuclear waste canisters occurs, Fe²⁺ will be present in the near-field of a deep geological repository. In that case, Fe²⁺ could not only act as reducing agent but also interact with different minerals, getting sorbed or forming new mineral phases.
In fact, it has been observed that when Fe²⁺ interacts with Al₂O₃, it forms Fe(II)-Al(III)-Cl, a layered double hydroxide (LDH) [5]. The LDH phases are known to retain pollutants by different mechanisms: anion exchange, incorporation, surface complexation and, in Fe(II)-Al(III)-Cl, reduction promoted by the structural Fe²⁺ [6].
Therefore, we analysed the ⁹⁹Tc retention by Fe(II)-Al(III)-Cl LDH phase under different conditions (pH, ionic strength and Tc concentration). We observed that the affinity of the Fe(II)-Al(III)-Cl LDH phase for Tc has two different trends. For pH < 6.5, Tc retention increases with increasing pH and decreasing ionic strength, being complete in water, suggesting anion exchange as the main retention mechanism. At pH > 6.5, Tc uptake is complete and independent from the ionic strength and the pH value, suggesting Tc reduction as main uptake mechanism.
This work has been performed in the frame of VESPA II project (02E11607B), supported by the German Federal Ministry for Economic Affairs and Energy (BMWi).
References:
[1] A. H. Meena and Y. Arai, Environ. Chem. Lett., vol. 15, no. 2, pp. 241–263, 2017.
[2] K. H. Lieser and C. Bauscher, Radiochim. Acta, vol. 42, pp. 205–213, 1987.
[3] T. Peretyazhko et al., Geochim. Cosmochim. Acta, vol. 72, no. 6, pp. 1521–1539, 2008.
[4] D. Cui and T. E. Eriksen, Environ. Sci. Technol., vol. 30, no. 7, pp. 2263–2269, 1996.
[5] E. J. Elzinga, Environ. Sci. Technol., vol. 46, no. 9, pp. 4894–4901, 2012.
[6] C. Forano, et al , Layered double hydroxides (LDH), vol. 5. 2013.
Keywords: Technetium, immobilization, LDH, reduction
  • Lecture (Conference)
    Gesellschaft Deutscher Chemiker Nuclearchemie 2019, 25.-27.09.2019, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-29239
Publ.-Id: 29239


⁹⁹Tc retention on Fe(II)Al(III)-Cl layered double hydroxides

Mayordomo Herranz, N.ORC; Rodriguez Hernandez, D. M.; Scheinost, A.ORC; Roßberg, A.; Brendler, V.ORC; Müller, K.ORC
To assess the safety of nuclear waste repositories, possible incidents have to be considered like canister corrosion and as a consequence the release of radionuclides.Among them,the fission product ⁹⁹Tc is of high concern due to its long half-life (2.13∙10⁵years) and the high mobility of the Tc(VII)O₄⁻ oxoanion that is barely adsorbed by common mineral phases. However, Tc migration decreases under reducing conditions due to formation of Tc(IV), whose main species is a highly insoluble solid TcO₂.Under the reducing and corrosive conditions in the near-field of the repository, Fe²⁺ will act as a reducing agent for redox sensitive radionuclides (when present in the groundwater or sorbed on mineral surfaces). Furthermore,secondary mineral phases like Fe(II)-Al(III)-Cl, a layered double hydroxide (LDH),can be formed when Fe²⁺ interacts with Al₂O₃ at circumneutral-alkaline pH [1]. LDH phases are so-called anionic clays and they are known to retain pollutants by anion exchange, incorporation, surface complexation and in the case of Fe(II)-Al(III)-Cl via reduction promoted by the structural Fe²⁺ [2]. We have analysed the ⁹⁹Tc uptake by Fe(II)-Al(III)-Cl LDH under varying pH (4 to 11), ionic strength (0 to 0.1 M) and Tc concentration(10⁻⁹to 10⁻³ M). At pH < 6.5, the solid to liquid distribution coefficient, (log Kd in mL/g),ranges from (2 to 6) and increases with decreasing ionic strength and increasing pH. At pH > 6.5, log Kd (6.5±0.3) are independent of pH and ionic strength.Tc K-edge X-ray absorption spectroscopy showed in all cases a reduction to Tc(IV) and enabled us to elucidate the surface bound speciation of Tc on a molecular level.


[1]E. J. Elzinga,”Environ. Sci. Technol., vol. 46, no. 9, pp. 4894–4901, 2012.
[2]C. Forano, U. Costantino, V. Prévot, and C. T. Gueho, Layered double hydroxides (LDH), vol. 5. 2013.
Keywords: Technetium, retention, LDH, reduction
  • Lecture (Conference)
    Goldschmidt 2019, 18.-23.08.2019, Barcelona, Spain

Permalink: https://www.hzdr.de/publications/Publ-29238
Publ.-Id: 29238


Uncovering the Origin of the Emitting States in Bi³⁺-Activated CaMO₃ (M=Zr, Sn, Ti) Perovskites: Metal-to-Metal Charge Transfer versus s-p Transitions

Back, M.; Ueda, J.; Xu, J.; Asami, K.; Amidani, L.ORC; Trave, E.; Tanabe, S.
After more than a century of studies on the optical properties of Bi³⁺ ion, the assignment of the nature of the emissions and the bands of the absorption spectra remain ambiguous. Here we report an insight into the spectroscopy of Bi³⁺-activated CaMO₃ perovskites (M=Zr, Sn, Ti), discussing the factors driving the metal-to-metal charge transfer and sp → s2 transitions. With the aim to figure out the whole scenario, a combined experimental and theoretical approach is employed. The comparison between the temperature dependence of the PL emissions with the temperature dependence of the exciton energy of the systems has led to an unprecedent evidence of the charge transfer character of the emitting states in Bi³⁺-activated phosphors. Low temperature VUV spectroscopy together with the design of the vacuum referred binding energy diagram of the luminescent center are exploited to shed light on the origin of the absorption bands. In addition, the X-ray absorption near edge structure, unambiguously confirmed the stabilization of Bi³⁺ in Ca²⁺ site in both CaSnO₃ and CaZrO₃ perovskites. This breakthrough into the understanding of the excited state origin of Bi3+ could pave the way towards the design of a new generation of effective Bi³⁺-activated phosphors.

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Publ.-Id: 29236


Plutonium retention mechanisms by magnetite under anoxic conditions: Entrapment versus sorption

Dumas, T.; Fellhauer, D.; Schild, D.; Gaona, X.; Altmaier, M.; Scheinost, A.ORC
The reliable prediction of possible plutonium migration into the geological environment is crucial for the safety assessment of radioactive waste repositories. Fe(II)-bearing corrosion products like magnetite, which form on the surface of steel waste containers, can effectively contribute to the retardation of the potential radionuclide release by sorption and redox reactions, eventually followed by formation of secondary precipitates. A retardation process even more efficient - especially when considering the required long time scales for nuclear waste reposition - is structural incorporation by magnetite, as has been demonstrated for Tc and U. Here we show that this mechanism might not be as relevant for Pu retention: after a rapid reduction of Pu(V) to Pu(III) in acidic Fe(II)/Fe(III) solution, base-induced magnetite precipitation (pHexp ≈ 12.5) leads only to a partial (≈ 50%) incorporation, while the other half remains at the surface by forming tridentate sorption complexes. Neither solid nor sorbed Pu(IV) species were observed in the starting solution and after precipitation. With Fe(II)-inforced re-crystallization at pHexp = 6.5, a process potentially mimicking long-term, thermodynamically controlled aging, the equilibrium between both Pu species is even further shifted towards the sorption complex. A detailed analysis of the incorporated species by Pu LIII-edge X-ray absorption fine-structure (XAFS) spectroscopy shows a pyrochlore-like coordination environment (split eight-fold oxygen coordination shell with Pu-O distances of 2.22 and 2.45 Å, and an edge-sharing linkage to Fe-octahedra with Pu-Fe distances of 3.68 Å), which is embedded in the magnetite matrix (Pu-Fe distances of 3.93, 5.17 and 5.47 Å). This suggests that the reason for the partial incorporation is the structural incompatibility of the large Pu(III) ion for the octahedral Fe site in magnetite. The adoption of a pyrochlore-like local environment within the magnetite long-range structure might be induced by the rapid coprecipitation rather than being a thermodynamically stable state (kinetic entrapment). For the sake of conservatism, safety assessments should rely on the formation of the Pu(III) sorption complex only.
Keywords: solid solutions radioactive waste disposal plutonium magnetite EXAFS XANES XPS

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Experiments on the magnetic enrichment of rare-earth metal ions in aqueous solutions in a microflow device

Kolczyk-Siedlecka, K.; Wojnicki, M.; Yang, X.ORC; Mutschke, G.ORC; Zabinski, P.
An attempt is made to achieve a continuous enrichment of rare-earth metal ions from aqueous solutions in a microflow device by applying magnetic forcing. An aqueous solution containing holmium(III) ions is pumped through a small channel which was exposed to a strong inhomogeneous magnetic field. At the outflow, the near- and far-field parts of the flow are separated and analyzed using UV-Vis spectroscopy. The relative change of ion concentration is determined from the measured absorbance. Results are reported for three different types of flow cells at different flow rates and magnetic field strengths and for a cascaded application of cells. The change of concentration is found to be small, and no clear trend can currently be stated due to the error margin of the concentration measurement.
Keywords: microflow, spectrophotometry, rare-earth elements, magnetic field, continuous separation

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Publ.-Id: 29233


Surface nanobubbles on the rare earth fluorcarbonate mineral synchysite

Owens, C. L.ORC; Schach, E.; Heinig, T.; Rudolph, M.ORC; Nash, G. R.
Surface nanobubbles have been identified to play an important role in a range of industries from mineral processing to food science. The formation of surface nanobubbles is of importance for mineral processing in the extraction of complex ores, such as those containing rare earth elements. This is due to the way minerals are extracted utilising froth flotation. In this study, surface nanobubbles were imaged using non-contact atomic force microscopy on a polished cross section containing rare earth minerals. Nanobubbles were found on synchysite under reagent conditions expected to induce hydrophobicity in rare earth minerals, which is required for efficient processing.

Synchysite –(Ce) is a rare earth fluorcarbonate mineral containing over 30% rare earth elements. Relatively little research has been conducted on synchysite, with only a few papers on its surface behaviour and flotation. The resulting nanobubbles were analysed and showed an average contact angle of 24 degrees± 8. These are in line with contact angles found on dolomite and galena by previous studies.
Keywords: non-contact atomic force microscopy; synchysite; bastnäsite; rare earth elements; fluorcarbonate; surface nanobubbles; carbonatite

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Publ.-Id: 29231


Refinement of Hounsfield look-up table translating CT number into proton stopping power by retrospective application of patient-specific direct stopping-power prediction from dual-energy CT

Wohlfahrt, P.ORC; Möhler, C.; Enghardt, W.; Krause, M.ORC; Kunath, D.; Menkel, S.; Troost, E. G. C.ORC; Greilich, S.; Richter, C.ORC
Background and Purpose:
Proton treatment planning relies on an accurate determination of stopping-power ratio (SPR) from x-ray computed tomography (CT). A clinically applicable refinement of the heuristic CT-based SPR prediction using a state-of-the-art Hounsfield look-up table (HLUT) is proposed, which incorporates patient-specific SPR information obtained from dual-energy CT (DECT) in a retrospective patient-cohort analysis.

Material and Methods:
SPR datasets of 25 brain-tumor, 25 prostate-cancer and three non-small cell lung-cancer (NSCLC) patients were directly derived from clinical DECT scans with the DirectSPR approach. Based on the median frequency distribution of voxelwise correlations between CT number and SPR within the irradiated volume, a piecewise linear function was specified (DirectSPR-based adapted HLUT). Differences in dose distribution and proton range were assessed for the non-adapted and adapted HLUT compared with the DirectSPR method.

Results:
The application of the DirectSPR-based adapted HLUT instead of the non-adapted one reduced systematic range deviations from 1.2% (1.1 mm) to -0.1% (0.0 mm) for brain-tumor, 1.7% (4.1 mm) to 0.2% (0.5 mm) for prostate-cancer and 2.0% (2.9 mm) to -0.1% (0.0 mm) for NSCLC patients. Due to the intra- and inter-patient tissue variability, range deviations larger than 1% are still present for the adapted HLUT.

Conclusions:
The incorporation of patient-specific correlations between CT number and SPR, derived from a retrospective application of DirectSPR to a broad patient cohort, improves the accuracy of the current state-of-the-art HLUT approach. The DirectSPR-based adapted HLUT has been clinically implemented at our institution, which represents a further step toward full integration of the DECT-based DirectSPR method for treatment planning in proton therapy.
Keywords: dual-energy CT; proton range prediction; proton therapy

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Synthesis of Mg and Zn diolates and their use in metal oxide deposition

Frenzel, P.; Preuß, A.; Bankwitz, J.; Georgi, C.; Ganss, F.; Mertens, L.; Schulz, S.; Hellwig, O.; Mehring, M.; Lang, H.
The synthesis of complexes [M(OCHMeCH₂NMeCH₂)₂] (5, M = Mg; 7, M = Zn) is described. Treatment of MeHNCH2CH2NMeH (1) with 2-methyloxirane (2) gave diol (HOCHMeCH₂NMeCH₂)₂ (3), which upon reaction with equimolar amounts of MR₂ (4, M = Mg, R = Bu; 6, M = Zn, R = Et) gave 5 and 7. The thermal behavior and vapor pressure of 5 and 7 were investigated to show whether they are suited as CVD (= chemical vapor deposition) and/or spin-coating precursors for MgO or ZnO layer formation. Thermogravimetric (TG) studies revealed that 5 and 7 decompose between 80–530 °C forming MgO and ZnO as evidenced by PXRD studies. In addition, TG-MS-coupled experiments were carried out with 7 proving that decomposition occurs by M–O, C–O, C–N and C–C bond cleavages, as evidenced from the detection of fragments such as CH𔔢N+, C₂H𔔢N+, C₂H₅N+, CH₂O+, C₂H₂O+ and C₂H₃O+. The vapor pressure of 7 was measured at 10.4 mbar at 160 °C, while 5 is non-volatile. The layers obtained by CVD are dense and conformal with a somewhat granulated surface morphology as evidenced by SEM studies. In addition, spin–coating experiments using 5 and 7 as precursors were applied. The corresponding MO layer thicknesses are between 7–140 nm (CVD) or 80 nm and 65 nm (5, 7; spin-coating). EDX and XPS measurements confirm the formation of MgO and ZnO films, however, containing 12–24 mol% (CVD) or 5–9 mol% (spin-coating) carbon. GIXRD studies verify the crystalline character of the deposited layers obtained by CVD and the spin-coating processes.

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Residual gammaH2AX foci in head and neck squamous cell carcinomas as predictors for tumour radiosensitivity: Evaluation in pre-clinical xenograft models and clinical specimens

Meneceur, S.; Löck, S.; Gudziol, V.; Hering, S.; Bütof, R.; Rehm, M.; Baumann, M.; Krause, M.ORC; von Neubeck, C.
Background and purpose: Predictive biomarkers can be instrumental to treatment individualisation of cancer patients and improve therapy outcome. Residual γH2AX foci represent a promising biomarker to predict tumour radiosensitivity. In this pre-clinical study, the slope of the dose–response curve was evaluated for its predictive relevance in head and neck squamous cell carcinoma xenografts (HNSCC). Additionally, the feasibility of the translated assay was tested in a clinical setting in patient derived HNSCC samples, and associations between residual γH2AX foci and clinical parameters were analysed. Materials and methods: Seven HNSCC xenografts models (FaDu, SAS, SKX, UT-SCC-5, UT-SCC-14, UT-SCC-45, XF354)were used. Tumour bearing NMRI nude mice were randomly distributed to five treatment arms (0–8 Gy). Residual γH2AX foci (24 h post irradiation)were counted by visual scoring in a micromilieu dependent manner (assessed with BrdU and pimonidazole). The local tumour control values measured as TCD 50 (tumour control dose 50%)have previously been published. Patient derived HNSCC biopsies were cultivated ex vivo for 24 h including 4 h of pimonidazole and BrdU treatment, subsequently irradiated with 0–8 Gy and fixed after 24 h. Results: In the pre-clinical study, the dose–response curve slopes negatively correlated with the tumour control dose after fractionated irradiation (TCD 50,fx , R 2 = 0.63, p = 0.032)and after single dose irradiation under homogeneous hypoxia (TCD 50,SD,clamp , R 2 = 0.66, p = 0.027). The γH2AX assay in clinical HNSCC samples showed a dose–response relationship, with the values of the slopes ranging from 0.099 Gy −1 to 0.920 Gy −1 (coefficient of variation = 52.8%). Slopes derived from patients were in the same ranges as the sensitive, moderate and resistant models of the pre-clinical study. Statistical analysis revealed a significant negative correlation between the slope and the patients’ age (R 2 = 0.65, p = 0.001). Conclusion: These results further support the promise of the slope of the residual γH2AX foci dose–response as a biomarker for radiosensitivity. In the clinical samples, the variation in the slopes reveals patients’ specific repair capacities, which could hold potential value for treatment individualisation. © 2019 Elsevier B.V.
Keywords: Clinical specimens, HNSCC, Predictive biomarker, Radiosensitivity, Xenograft modelsγH2AX

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Publ.-Id: 29228


Cancer stem cells in radiation response: current views and future perspectives in radiation oncology

Peitzsch, C.; Kurth, I.; Ebert, N.; Dubrovska, A.; Baumann, M.
Purpose: Despite technological improvement and advances in biology-driven patient stratification, many patients still fail radiotherapy resulting in loco-regional and distant recurrence. Tumor heterogeneity remains a key challenge to effective cancer treatment, and reliable stratification of cancer patients for prediction of outcomes is highly important. Intratumoral heterogeneity is manifested at the different levels, including different tumorigenic properties of cancer cells. Since John Dick et al. isolated leukemia initiating cells in 1990, the populations of tumor initiating or cancer stem cells (CSCs) were identified and characterized also for a broad spectrum of solid tumor types. The properties of CSCs are of considerable clinical relevance: CSCs have self-renewal and tumor initiating potential, and the metastases are initiated by the CSC clones with the ability to disseminate from the primary tumor site. Conclusion: Evidence from both, experimental and clinical studies demonstrates that the probability of achieving local tumor control by radiation therapy depends on the complete eradication of CSC populations. The number, properties and molecular signature of CSCs are highly predictive for clinical outcome of radiotherapy, whereas targeted therapies against CSCs combined with conventional treatment are expected to provide an improved clinical response and prevent tumor relapse. In this review, we discuss the modern methods to study CSCs in radiation biology, the role of CSCs in personalized cancer therapy as well as future directions for CSC research in translational radiooncology.
Keywords: Cancer stem cells; model systems; radiosensitivity

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Publ.-Id: 29227


Widely tunable GaAs bandgap via strain engineering in core/shell nanowires with large lattice mismatch

Balaghi, L.; Bussone, G.; Grifone, R.; Hübner, R.; Grenzer, J.; Ghorbani-Asl, M.; Krasheninnikov, A.; Schneider, H.; Helm, M.; Dimakis, E.
The realization of photonic devices for different energy ranges demands materials with different bandgaps, sometimes combined even within the same device as in multi-junction photovoltaic cells. The optimal solution in terms of integration, device performance and device economics would be a simple material system with widely tunable bandgap and compatible with the mainstream silicon technology. Here, we show that gallium arsenide nanowires grown epitaxially on silicon substrates exhibit a sizeable reduction of their bandgap by up to 40% when overgrown with lattice-mismatched indium gallium arsenide or indium aluminium arsenide shells. Specifically, we demonstrate that the gallium arsenide core sustains unusually large tensile strain with hydrostatic character and its magnitude can be engineered via the composition and the thickness of the shell. The resulted bandgap reduction renders gallium arsenide nanowires suitable for photonic devices across the near-infrared range, including telecom photonics at 1.3 and potentially 1.55 μm, with the additional possibility of monolithic integration in silicon-CMOS chips.

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Publ.-Id: 29226


Advanced Methods for Temporal Reconstruction of Modulated Electron Bunches

Zarini, O.ORC; Köhler, A.ORC; Couperus Cabadağ, J. P.ORC; Pausch, R.ORC; Kurz, T.ORC; Schöbel, S.; Meißner, H.; Bussmann, M.ORC; Schramm, U.ORC; Irman, A.ORC; Debus, A.ORC
We describe optimizations of phase-retrieval algorithms for the reconstruction of the temporal structure of highly modulated electron bunches from coherent transition radiation (CTR) spectra. Synthetic data is used to quantitatively analyze capabilities and limitations of the approach taking into account realistic bandwidth constraints of ultra-broadband spectrometers. Established algorithms are combined with information from independent channels as charge calibrated electron spectra and absolute intensity calibration of the spectrometer. With this set of data, in principle available in experiments, we demonstrate a promising fidelity for the detailed analysis of substructured laser wakefield accelerated electron bunches.
Keywords: Electron bunch duration, reconstruction algorithm, transition radiation
  • Contribution to proceedings
    Advanced Accelerator Concepts Workshop (AAC2018), 12.-17.08.2018, Breckenridge, Colorado, USA: IEEE, 978-1-5386-7721-6
    DOI: 10.1109/AAC.2018.8659388

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Publ.-Id: 29225


Synthesis and in vitro evaluation of 8-pyridinyl substituted benzo[e]imidazo[2,1-c][1,2,4]triazines as phosphodiesterase 2A (PDE2A) inhibitors

Ritawidya, R.; Ludwig, F.-A.; Briel, D.; Brust, P.ORC; Scheunemann, M.
Phosphodiesterase 2A (PDE2A) is highly expressed in distinct areas of the brain which are known to be related to neuropsychiatric diseases. The development of suitable PDE2A tracers for Positron Emission Tomography (PET) would permit the in vivo imaging of the PDE2A and evaluation of disease- mediated alterations of its expression. A series of novel fluorinated PDE2A inhibitors on the basis of a benzoimidazotriazine (BIT) scaffold was prepared leading to a promising inhibitor for further development of a PDE2A PET imaging agent. BIT derivatives (BIT1-9) were obtained by a seven-step synthesis route and their inhibitory potency towards PDE2A and selectivity over other PDEs have been evaluated. BIT1 demonstrated much higher inhibition than other BIT derivatives (82.9% inhibition of PDE2A at 10 nM). BIT1 displayed an IC50 for PDE2A of 3.33 nM with 16-fold selectivity over PDE10A. This finding revealed that a derivative bearing both a 2-fluoro-pyridin-4-yl and 2-chloro-5-methoxy-phenyl unit at 8- and 1-position, respectively, appeared to be the most potent inhibitor. In vitro studies of BIT1 using mouse liver microsomes (MLM) disclosed BIT1 as a suitable ligand for 18F-labeling. Nevertheless, future in vivo metabolism studies are required.
Keywords: Phosphodiesterase 2A (PDE2A); positron emission tomography (PET); benzoimidazotriazine (BIT); fluorinated; mouse liver microsomes (MLM)

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Publ.-Id: 29224


Experimental investigations of bubble chains in a liquid metal under the influence of a horizontal magnetic field

Keplinger, O.; Shevchenko, N.ORC; Eckert, S.ORC
We present an experimental study on bubble chains ascending in the eutectic GaInSn alloy under the influence of a horizontal magnetic field. Argon gas bubbles are injected through a single nozzle positioned in the middle at the bottom of a flat Plexiglas vessel. Bubble size distribution, shape deformation, velocities, etc. are obtained by post-processing of X-ray radiographs measured with a high-speed video-camera for a wide range of Argon gas flow rates. In the case without a magnetic field, the typical zigzag movement of the rising bubbles is observed. This movement and the integrity of the bubble chain are significantly disturbed with increasing gas flow by the turbulent flow in the liquid metal. The main effect of the magnetic field consists in a stabilization of the bubble trajectories. The application of a magnetic field at moderate field strength dampens the turbulent fluctuations in the bubble wake and stabilizes the zigzag movement. The application of a sufficiently strong magnetic field suppresses the zig-zag motion of the bubbles and forces them to follow a straight path. The rising velocity is gradually reduced with increasing magnetic field strength. The motion of the individual bubbles within the chain becomes highly correlated. Ellipsoidal bubbles tend to align their major axes along the magnetic field lines.
Keywords: Liquid metal; Two-phase flow; Bubble chain; Horizontal magnetic field; X-ray radiography.

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Publ.-Id: 29223


Measuring sub-femtosecond temporal structures in multi-ten kiloampere electron beams

Zarini, O.ORC
In laser wakefield acceleration, an ultra-short high-intensity laser pulse excites a plasma wave, which can sustain accelerating electric fields of several hundred GV/m.
This scheme advances a novel concept for compact and less expensive electron accelerators, which can be hosted in a typical university size laboratory. Furthermore, laser wakefield accelerators (LWFA) feature unique electron bunch characteristics, namely micrometer size with duration ranging from several fs to tens of fs. Precise knowledge of the longitudinal profile of such ultra-short electron bunches is essential for the design of future table-top X-ray light-sources and remains a big challenge due to the resolution limit of existing diagnostic techniques.

Spectral measurement of broadband coherent and incoherent transition radiation (TR) produced when electron bunches passing through a metal foil is a promising way to analyze longitudinal characteristics of these bunches. Due to the limited reproducibility of the electron source this measurement highly requires single-shot capability.
An ultra-broadband spectrometer combines the TR spectrum in UV/NIR (200-1000 nm), NIR (0.9-1.7 µm) and mid-IR (1.6-12 µm). A high spectral sensitivity, dynamic bandwidth and spectral resolution are realized by three optimized dispersion and detection systems integrated into a single-shot spectrometer.
A complete characterization and calibration of the spectrometer have been done concerning wavelengths, relative spectral sensitivities, and absolute photometric sensitivities, also taking into account for the light polarization.
The TR spectrometer is able to characterize electron bunches with charges as low as 1pC and can resolve time-scales of 0.4 fs. Electron bunches up to 16 fs (rms width) can be reconstructed from their TR spectrum.

In the presented work, the self-truncated ionization induced injection (STII) scheme has been explored to study the relevant beam parameters especially its longitudinal bunch profile and the resulting peak current.
Proper focusing of a high power laser pulse into a supersonic gas-jet target and tailoring the conditional laser and plasma density and taking advantage of the relativistic self-focusing effects are investigated in this PhD thesis in order to study the final beam parameters as well as the consequent beam loading effects by producing nC-class mono-energetic electron beams.

In the experiment at HZDR, the DRACO 100TW Ti:Sa based laser system is used in conjunction with a He-N₂ mixed, supersonic gas-jet target. Under optimized conditions, mono-energetic electron bunches are accelerated, which are massively loaded up to several 100 pC at 300 MeV peak energy with a narrow energy spread of a few 10 MeV. Reconstruction results of TR spectra, measured by TR spectrometer, show that the shortest electron bunch duration is at about 13 fs FWHM corresponding to a peak current as high as 20 kA.
Such peak current is about one order of magnitude higher than those generated by conventional RF linear accelerator. This landmarks a significant finding of this thesis.
Keywords: Laser wakefield acceleration, laser plasma accelerator, self-truncated ionization injection, high peak current, high bunch charge, beam loading, bunch duration measurement, coherent transition radiation, broadband spectrometer, infrared spectrometer, prism spectrometer, echelle spectrometer, phase reconstruction algorithm, Foldwrap reconstruction algorithm, PIConGPU
  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-100 2019

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Recent application of the solid targetry system

Mansel, A.; Franke, K.
The solid targetry system was used both, at port 4 directly mounted at the yoke and at the beamline at port 3. We will give an overview about the purification or separation of n.c.a. radionuclides like Sr-85, V-48, Cu-64, Cr-51, Co-56, Y-88, La-135, Zr-89, Ce-139 and Pb-203.
  • Lecture (Conference)
    14th CYCLEUR workshop 2019, 08.-10.05.2019, Dresden, Germany

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Publ.-Id: 29221


Competence Center for Ion Beams in Materials Research and Medicine

Faßbender, J.ORC
Competence Center for Ion Beams in Materials Research and Medicine
Keywords: ion beams, high-energy, materials research, user facility
  • Invited lecture (Conferences)
    Competence Center for Ion Beams in Materials Research and Medicine, 02.05.2019, München, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-29220
Publ.-Id: 29220


Pool CFD Modelling: Lessons from the SESAME Project

Moreau, V.; Profir, M.; Alamberti, A.; Frignani, M.; Merli, F.; Belka, M.; Frybort, O.; Melichar, T.; Tarantino, M.; Franke, S.; Eckert, S.ORC; Class, A.; Yanez, J.; Grishchenko, D.; Jeltsov, M.; Kudinov, P.; Roelofs, F.; Zwijsen, K.; Visser, D. C.; Badillo, A.; Niceno, B.; Martelli, D.
The Computational Fluid-Dynamics (CFD) modelling of Heavy Liquid Metal (HLM) flows in pool configuration is investigated.
We describe how the argument is treated within the SESAME project in its specific work package. The work package structure, based on a systematic approach of redundancy and diversification, is explained along with its motivation. The main achievements obtained and the main lessons learned are illustrated.
The paper focuses on the strong coupling between experimental activity and CFD simulation performed within the SESAME project. Two HLM fluids are contemplated: pure lead and Lead-Bismuth Eutectic. The objective is to make CFD a valid instrument in support to the design of safe and innovative Gen-IV nuclear plants.
Some effort has also been devoted to a highly challenging and innovative approach, the Proper Orthogonal Decomposition (POD) with Galerkin projection modelling, potentially able to cover some CFD applications at a much lower computational cost.
To reach sufficient maturity, the method requires however input from sufficiently complex CFD simulations such as those produced in the present context.
Dedicated experimental campaigns on heavily instrumented facilities have been conceived with the specific objective to build a series of datasets suited for the calibration and CFD modelling validation. In pool configuration, the attention is focused on the balance between conductive and convective heat transfer phenomena, on transients representative of incidental scenarios and on the possible occurrence of solidification phenomena. Four test sections have been selected for the dataset production: (i) the CIRCE facility from ENEA, (ii) the TALL-3D pool test section from KTH, (iii) the TALL-3D Solidification Test Section (STS) from KTH and (iv) the SESAME Stand facility from CVR. While CIRCE and TALL-3D were existing facilities, the STS and SESAME Stand facility have been conceived, built and operated within the project, heavily relying on the use of CFD support. We give an outlook on the work performed, the results achieved and remaining or new uncovered issues.
Keywords: GenIV reactors, Pool-type configuration, Heavy liquid metals, CFD

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Publ.-Id: 29219


Adjuvant drug-assisted bone healing: Part III – Further strategies for local and systemic modulation

Rothe, R.; Schulze, S.; Neuber, C.; Hauser, S.ORC; Rammelt, S.; Pietzsch, J.ORC
In this third in a series of reviews on adjuvant drug-assisted bone healing, further approaches aiming at influencing the healing process are discussed. Local and systemic modulation of bone metabolism is persued with use of a number of drugs with completely different indications, which are characterized by a pleiotropic spectrum of action. These include drugs used to treat lipid disorders (HMG-CoA reductase inhibitors), hypertension (ACE inhibitors), osteoporosis (bisphosphonates), cancer (proteasome inhibitors) and others. Potential applications to enhance bone healing are discussed.
Keywords: bisphosphonates; bone metabolism; critical-size bone defects; small molecules; statins; strontium; Wnt signaling
  • Clinical Hemorheology and Microcirculation 73(2019), 439-488
    DOI: 10.3233/CH-199104

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Permalink: https://www.hzdr.de/publications/Publ-29218
Publ.-Id: 29218


Adjuvant drug-assisted bone healing: Part II – Modulation of angiogenesis

Rothe, R.; Schulze, S.; Neuber, C.; Hauser, S.ORC; Rammelt, S.; Pietzsch, J.ORC
The treatment of critical-size bone defects following complicated fractures, infections or tumor resections is a major challenge. The same applies to fractures in patients with impaired bone healing due to systemic inflammatory and metabolic diseases. Despite considerable progress in the development and establishment of new surgical techniques, the design of bone graft substitutes and imaging techniques, these scenarios still represent unresolved clinical problems. However, the development of new active substances gives cause for hope. This work discusses therapeutic approaches that influence angiogenesis or hypoxic situations in healing bone and surrounding tissue. In particular, the literature on sphingosine-1-phosphate receptor modulators and nitric oxide (NO•) donors, including bi-functional (hybrid) compounds like NO•-releasing cyclooxygenase-2 inhibitors, was critically reviewed with regard to their local and systemic mode of action.
Keywords: critical-size bone defects; neovascularization; nitric oxide donors; signaling; small molecules; sphingosine-1-phosphate receptor
  • Open Access Logo Clinical Hemorheology and Microcirculation 73(2019), 409-438
    DOI: 10.3233/CH-199103

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Permalink: https://www.hzdr.de/publications/Publ-29217
Publ.-Id: 29217


Adjuvant drug-assisted bone healing: Part I – Modulation of inflammation

Rothe, R.; Schulze, S.; Neuber, C.; Hauser, S.ORC; Rammelt, S.; Pietzsch, J.ORC
Critical-size bone defects after compound fractures, infection, or tumor resection are challenging to treat. The same is true for fractures in patients with impaired bone healing due to metabolic diseases and cancer. Despite considerable progress over the last decade in surgical techniques, material design, and dedicated imaging approaches, these scenarios represent unsolved clinical problems. The high socioeconomic burden of such conditions justifies increasing interest in novel osteoinductive drugs for adjuvant therapeutic approaches. There is an increasing body of experimental and clinical literature on potentially promising effects of growth factors, anti-resorptive, and anabolic agents. The true clinical efficacy of these, however, is discussed controversially. Therefore, we aimed to critically examine the hypothesis that targeted adjuvant therapies have the potential to enhance bone regeneration in critical-size bone defects and under systemic conditions that impair bone healing. This first approach to the topic deals with small molecule drugs and compounds that influence the immune response and inflammatory processes. In particular, literature reporting on selective cyclooxygenase-2 inhibitors has been reviewed with respect to their local and systemic mode of action and to stimulate further research on bone healing under critical conditions.
Keywords: biomaterials; critical-size bone defects; cyclooxygenase-2; innate immunity; prostanoids; signaling; small molecules
  • Clinical Hemorheology and Microcirculation 73(2019), 381-408
    DOI: 10.3233/CH-199102

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Permalink: https://www.hzdr.de/publications/Publ-29216
Publ.-Id: 29216


Experimental and computational studies of the influence of grain boundaries and temperature on the radiation-induced damage and hydrogen behavior in tungsten

Panizo-Laiz, M.; Díaz-Rodríguez, P.; Rivera, A.; Valles, G.; Martín-Bragado, I.; Perlado, J. M.; Munnik, F.ORC; González-Arrabal, R.
We study the influence of grain boundaries on radiation-induced vacancies, as well as, on the hydrogen (H) behavior in tungsten (W) samples with different grain sizes in the temperature range from 300 K to 573 K, both experimentally and by computer simulations. For this purpose, coarse-grained and nanostructured W samples were sequentially irradiated with carbon (C) and H ions at energies of 665 keV and 170 keV, respectively. A first set of the implanted samples was annealed at 473 K and a second set at 573 K. Object kinetic Monte Carlo simulations were performed to account for experimental outcomes. Results show that the number of vacancies for nanostructured W is always larger than for single crystal W samples in the whole studied temperature range and that the number of vacancies is only reduced in samples with a large density of grain boundaries and at temperatures high enough to activate the vacancy motion (around 573 K). Results also indicate that the migration of H along vacancy free grain boundaries is more effective than along the bulk, and that the retained H is trapped in vacancies located within the grains. These results are used to explain the experimental outcomes.

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Permalink: https://www.hzdr.de/publications/Publ-29215
Publ.-Id: 29215


Improvement of UniCAR T cell effectiveness against EGFR+ tumor cells by using different αEGFR targeting module formats

Jureczek, J.; Feldmann, A.ORC; Albert, S.; Bergmann, R.ORC; Berndt, N.; Arndt, C.; Koristka, S.; Bachmann, M.ORC
Since epithelial growth factor receptor (EGFR) mutations or overexpression is linked with variety of malignancies, including lung, breast, stomach, colorectal, head and neck, and pancreatic carcinomas as well as glioblastomas it is an attractive target for tailored treatment of solid cancer. Thus over the last twenty years many strategies targeting EGFR were developed and even clinically approved, including disrupting intracellular signalling involving tyrosine kinase inhibitors (TKIs) or the inhibition of ligand binding using therapeutic monoclonal antibodies like e.g. Cetuximab, Panitumumab or Necitumumab. Unfortunately, cancers treated with these targeted drugs commonly become resistant to them. These limitations justify the need of more efficient therapy options. As chimeric antigen receptor (CAR) engineered T cells highly effectively eliminate hematological malignancies already in the clinics, one idea is to redirect CAR T cells also against EGFR expressing solid cancers. However, CAR T cell therapy can lead to severe even life-threatening side effects and its effectiveness against solid tumors is still limited. Particular worrying is that EGFR is a widespread antigen commonly expressed also on healthy tissues bearing a high risk of severe on-target/off-tumor side effects due to EGFR-targeted therapies, which cannot be controlled in patients. In order to overcome these challenges our UniCAR technology might be an appropriate answer combining high anti-tumor effectiveness, tumor specificity, flexibility, and safety control mechanisms. In contrast to conventional CARs, UniCAR T cells are per se inert because UniCARs are directed against a small peptide epitope, which is not present on living cells. The redirection of UniCAR T cells to tumor cells occurs only in the presence of a tumor specific targeting module (TM). TMs, on one hand carry the specificity for a certain tumor antigen and on the other hand contain the UniCAR peptide epitope recognized by UniCARs mediating the cross-linkage of UniCAR T cells and antigen presenting tumor cells. As TMs have a very short half-life in vivo they can be used as a switch to control UniCAR T cell activity on demand in patients. In detail, UniCAR T cells are only switched on in the presence of antigen specific TMs realized by permanent TM infusion, but could be rapidly switched off when the application of the TM is stopped and the TM is eliminated. Meanwhile we successfully generated a series of different TMs against different tumor antigens and entities. Interestingly, TMs can be made of different molecules showing various structures and can flexible be exchanged in order to target any tumor antigen and overcome tumor escape variants. Commonly our TMs consist of a humanized single-chain variable fragment (scFv) derived from the variable heavy and light chain domains of a murine monoclonal antibody. In addition, we successfully generated TMs based on different monovalent and bivalent antibody derivatives, nanobodies derived from one variable camelid antibody domain, affibodies and even small peptide molecules.
Recently we demonstrated proof-of-concept for the redirection of UniCAR T cells to EGFR expressing tumor cells by a nanobody based αEGFR TM derived from the camelid αEGFR antibody 7C12. Considering that the affinity and anti-tumor efficiency of the eucaryotically expressed αEGFR nanobody based TM was limited, we therefore asked the question, whether we could further improve the therapeutic effect against EGFR positive tumor cells using the UniCAR technology. In order to answer this question, we generated a novel TM based on a scFv derived from the clinically used chimeric monoclonal antibody Cetuximab (IMC C-225). In detail, we designed a murine and humanized αEGFR scFv TM, successfully expressed them in mammalian cell lines and compared their functionality with the eucaryotic αEGFR nanobody-based TM in vitro and in vivo. In principle, we observed that both TM formats, the αEGFR nanobody as well as the scFv-based TM, are able to redirect UniCAR T cells eliminate EGFR-expressing tumor cells in an antigen-specific and TM-dependent manner. As both the murine and humanized scFv TM variants worked equally well, obviously humanization of the αEGFR scFv does not affect its functionality. However most interestingly, the tumor killing efficiency of the αEGFR scFv TM was significantly superior in comparison to the αEGFR nanobody based TM. Here, the half maximal effective TM concentration (EC50) value of scFv based TM was improved 1000-fold, from nM to pM range. Consequently, UniCAR T cells in combination with the scFv based TM efficiently eliminate also target cells expressing a low EGFR density level, while UniCAR T cells redirected by the nb based TM clearly attack only highly EGFR expressing tumor cells. Furthermore, the high anti-tumor efficacy of the αEGFR scFv TM over nb TM was manifested in experimental mice.
In summary, we successfully established different αEGFR TM formats that are able to redirect UniCAR T cells to eliminate EGFR-positive tumor cells. However, the analysed αEGFR TM formats differ with respect to their anti-tumor efficiency, which might decide whether UniCAR T cells attack target cells showing different EGFR density levels.
  • Poster
    Tumor immunology meets oncology (TIMO XV), 25.-27.04.2019, Halle, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-29214
Publ.-Id: 29214


Engineering human T cells with a novel switchable CAR technology for tumor immunotherapy

Hoffmann, A.; Feldmann, A.ORC; Kittel-Boselli, E.; Bergmann, R.ORC; Koristka, S.; Berndt, N.; Arndt, C.; Bachmann, M.ORC
With the first approvals of chimeric antigen receptor (CAR) T cell therapies by the FDA the use of genetically modified T cells in the immunotherapy of tumors has recently become a very promising approach. CAR T cells are able to recognize tumor-associated antigens (TAAs) via specific single-chain variable fragments (scFvs) in a major histocompatibility-complex (MHC)-independent manner. Although highly efficient, the inability to regulate the activity of CAR T cells can cause severe even
life-threatening side effects such as cytokine-release syndrome (CRS) and on-target, off-tumor toxicities. Modular CAR systems may overcome these limitations allowing to switch the activity of CAR T cells repeatedly “ON” and “OFF”. Alternatively or in addition, the safety of CAR T cells could also be improved by “gated” targeting strategies e.g. by splitting the signaling and costimulatory motifs to independent CARs of different specificities. Theoretically, the idea of gated targeting could be extended to include further e.g. inhibitory signals. However, the size of current CARs limit the number of specificities that can be simultaneously transduced into a T cell. We therefore developed a novel switchable modular universal artificial receptor having a minimal size. The platform was termed RevCAR system.
In order to reduce the size of the artificial receptor the original idea was to replace the extracellular scFv domain of a conventional CAR with a small peptide epitope and to engage the resulting RevCAR T cell via a bispecific target module which we termed RevTM. For proof of concept two small peptide epitopes were selected and the respective RevCARs constructed. In addition, a series of different RevTMs were constructed. On the one hand the RevTM recognized one of the two peptide epitopes on the other hand the RevTM was directed to a potential tumor associated antigen (TAA). Until now a series of such pairs of RevTMs were constructed and functionally analyzed. RevCAR T cells armed via the respective RevTM were able to specifically lyse their respective target cell in a peptide epitope specific and target specific as well as target dependent manner. These data are supported by analysis of cytokine secretion. We only observed a specific cytokine release from RevCAR T cells in the presence of both target cells and the respective RevTM. Released cytokines detected were IFN-gamma, GM-CSF, TNF, and IL-2.
Taken together these results demonstrate the high anti-tumor efficiency of the novel RevCAR platform which is characterized by a small size, an improved safety, easy controllability as well as high flexibility.
  • Poster
    Tumor immunology meets oncology (TIMO XV), 25.-27.04.2019, Halle, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-29213
Publ.-Id: 29213


cupla-docker

Ehrig, S.ORC
Dockerfiles which provide environments for building and running Cupla applications.
Keywords: Docker, Cupla, Alpaka

Permalink: https://www.hzdr.de/publications/Publ-29212
Publ.-Id: 29212


Thermal expansion of magnetron sputtered TiCxN1-x coatings studied by high-temperature X-ray diffraction

Saringer, C.; Kickinger, C.; Munnik, F.ORC; Mitterer, C.; Schalk, N.; Tkadletz, M.
The coefficient of thermal expansion (CTE) of TiCxN1-x can be adjusted by changing the value x between 0 (i.e. pure TiN) and 1 (pure TiC), which makes this material exceptionally useful as base layer to adapt the mismatch between the CTEs of substrate and coating. However, no comprehensive data on the CTE of sputtered TiCxN1-x has been reported up to now. Thus, in this work eleven coatings with compositions ranging from pure TiN to pure TiC were deposited using non-reactive magnetron sputtering. The elemental and phase composition were obtained by elastic recoil detection analysis and Raman spectroscopy, respectively. Powders of the coating material were analyzed using high-temperature X-ray diffraction between room temperature and up to 1000 °C to determine the temperature dependent lattice parameters. Subsequently, these lattice parameters were fitted using second order polynomials with coefficients linearly depending on the carbon content. Thus, a formula for the CTE of TiCxN1-x valid between 25 and 1000 °C was deduced which showed that at room temperature TiN has the highest CTE of 8.12 × 10-6 K-1. The CTE gradually decreases with increasing carbon content to 7.55 × 10-6 K-1 for pure TiC. While the value for TiC only shows a small increase with temperature, the CTE of TiN increases strongly up to 11.1 × 10-6 K-1 at 1000 °C. The presented formula for the temperature dependent CTE of sputtered TiCxN1-x coatings allows to calculate the required composition for TiCxN1-x base layers, in order to tune their thermal expansion for the use in complex multilayered coatings.
Keywords: Thermal expansion; Titanium carbonitride; High-temperature X-ray diffraction; Physical vapor deposition; Hard coatings

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Permalink: https://www.hzdr.de/publications/Publ-29211
Publ.-Id: 29211


Modeling of the FFTF isothermal physics tests with the Serpent and DYN3D codes

Nikitin, E.; Fridman, E.ORC
In this study, the isothermal physics tests performed on the fully loaded core of the Fast Flux Test Facility (FFTF) are analyzed with the Monte Carlo code Serpent and with the deterministic core simulator DYN3D. The selected tests comprise two neutron spectra measurements and a multitude of reactivity effect measurements (32 cases with control rod movements and one case for isothermal temperature coefficient). While the flux spectra are calculated only with the Monte Carlo code, the reactivity effects are evaluated with both codes, Serpent and DYN3D. The homogenized few-group cross sections for DYN3D calculations are generated with Serpent. The obtained numerical results are in a very good agreement as compared to the experimental data. Additionally, a comparison of radial power distributions is presented between DYN3D and Serpent calculations, demonstrating an adequate performance of the nodal code DYN3D. This paper provides an additional contribution to the validation of both codes for neutronic analyses of Sodium cooled Fast Reactor cores.
Keywords: Group constant generation; SFR; nodal diffusion; Monte Carlo; SPH; Serpent; DYN3D

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Permalink: https://www.hzdr.de/publications/Publ-29210
Publ.-Id: 29210


The UniCAR system: A modular CAR T cell approach to improve the safety of CAR T cells

Bachmann, M.ORC
The idea to eliminate tumor cells via our own immune system is more than a hundred years old. However, a real break through came first with the development of check point inhibitors, bispecific antibodies (bsAbs) and T cells genetically modified to express Chimeric Antigen Receptors (CARs). Eventhough the clinical application of T cells equipped with CARs can lead to a complete remission, unfortunately, their application can also cause severe or even life threatening side effects as their activity can no more be adjusted once given to the patient. For targeting of tumor cells expressing tumor associated antigens (TAAs) which are not limited to tumor cells but also accessible on healthy tissues CAR T cells should not be permanently in a killing mode but be equipped with some kind of a switch whereby the activity of CAR T cells can reversely be turned “on and off “. Moreover, in case of cytokine release syndrome (CRS), tumor lysis syndrome (TLS), or other deadly side effects the possibility of an emergency shut down of the CAR T cell activity should exist. Modular CAR variants such as the UniCAR system may fulfill these requirements.
Keywords: Immunotherapy, Chimeric antigen receptor, T cells, UniCAR, BiTE, Bispecific antibody

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Permalink: https://www.hzdr.de/publications/Publ-29209
Publ.-Id: 29209


Reconstruction of the Landscape Evolution of South Central Africa: A Case Study on Waterfalls of Northern Zambia and South-Eastern D.R. Congo

Olivotos, S.; Niedermann, S.; Mouslopoulou, V.; Merchel, S.ORC; Cotterill, F.; Flugel, T.; Gärtner, A.; Rugel, G.; Scharf, A.; Bookhagen, B.; Nadeau, M.-J.; Braucher, R.
Northern Zambia and the south-eastern Katanga Province of D.R. Congo lie within the southwest extension of the East African Rift System, which is one of the most significant present-day examples of active tectonics. Seismotectonic research in the area has been scarce, despite the fundamental impacts of neotectonics, which controls landscape evolution southwest of the Tanganyika graben. Nevertheless, the formation of the Congo-Zambezi watershed has been constrained from the combination of geological and biological evidence at ~2 Ma (Cotterill & de Wit 2011).
A preliminary Google Earth mapping has revealed two major sets of fault systems (Mweru and Upemba). Analysis of the seismicity patterns recorded within the two fault systems during the last 35 years provides indications for fault interactions over earthquake timescales, highlighting the fact that they are currently active.
This study is part of an interdisciplinary project combining DNA sequencing of selected fish groups to define molecular clocks together with surface exposure dating of key landforms using in-situ produced cosmogenic nuclides. This technique can be applied to quantify how long rocks have been exposed at “knickpoints” since they were first formed (Burbank & Anderson 2012). For that purpose, quartz-rich samples were collected from selected waterfalls with the aim of quantifying exposure ages and erosion/retreat rates. Expecting complex exposure scenarios both radionuclides ¹⁰Be and ²⁶Al and the stable noble gas ²¹Ne were combined in all samples.
Preliminary results from Northern Zambia indicate burial for at least several hundred thousand years. This specific burial may confirm the existence of a significantly deeper and larger Paleo-Lake Mweru before the modern drainage evolved (Dixey, 1944). More results are expected soon to confirm or dismiss this hypothesis. Furthermore, samples taken at different distances below the Kiubo and Luvilombo Waterfalls (D.R.C.) yield preliminary ages between ~7 and 40 ka, increasing with distance from the falls and thus reflecting waterfall retreat. Extrapolating to the original knickpoint location should enable us to estimate the age of its formation.
References
Burbank D.W. & Anderson R.S. 2012. Tectonic Geomorphology. Second Edition. Wiley‐Blackwell, Chichester.
Cotterill F.P.D. & de Wit M.J. 2011. South African Geographical Journal 114: 489-514.
Dixey F. 1944. South African Geographical Journal 47, 01: 9-45.
  • Lecture (Conference)
    GeoMünster 2019 "Earth! Past, Present, Future", 22.-25.09.2019, Münster, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-29207
Publ.-Id: 29207


Bulk analysis of meteorites using INAA at FRM II

Li, X.; Merchel, S.ORC; Lierse Von Gostomski, C.
In March 2017, the 49th German meteorite was found lying on top of a rock pile on the side of a potato field, near the city of Cloppenburg, Lower Saxony, Germany [1,2]. With two other meteorites (Oldenburg (fall in 1930), Benthullen (find in 1948 or 1951)) from the same region and meteorites from other countries, we started a program to analyze extraterrestrial samples in 2017. We have analyzed in total three chondrites, three achondrites of the HED
group (Howardite-Eucrite-Diogenite) (Dhofar 1675, NWA 2690, NWA 2698), a lunar and a Martian meteorite (NWA 7986, NWA 4925), two iron meteorites (Gibeon, yet unnamed new find from Libya/Chad in 2019) and six potential micrometeorites. The bigger samples (10-20 mg) were normally irradiated twice: for 3-5 min and for a long time up to 1 h in the rabbit position. The much smaller micrometeorites (9-38 μg) were irradiated for 24 h in the high-flux capsule irradiation position (Φth>1E14 cm-2s-1). We used the k0-method for the analysis [3].
With the high and pure thermal neutron flux at the FRM II, up to 45 elements could be determined in most samples [3]. According to the element compositions, the meteorites could be classified or earlier classifications could be confirmed. Although, the sample weights of the micrometeorites are very small and manipulating them was challenging, we could determine up to 16 elements. All of them show a rather high Fe concentration, i.e. 55-70 weight-%. However, for Ni and Ir, we can only give a detection limit of about 0.4% and 2 ng/g, respectively. Their potential origin are under discussion.
Acknowledgments
We thank A. Muszynski and M. Szyszko (Poznan, PL), A. Bischoff (Uni. Münster), D. Heinlein, J. Feige (TU Berlin) and A. Gärtner (Senckenberg Dresden) for providing and preparation of samples and the TUM-Kolleg program for financial supports.
References
1. J. Gattacceca et al., Meteorit. Planet. Sci., 2019, 54, 469-471.
2. J. Storz et al., www.paneth.eu/PanethKolloquium/2017/0075.pdf (Jan. 2019)
3. X. Li et al., J. Radioanal. Nucl. Chem. 2014, 300, 457-463.
Keywords: INAA, k0-method, meteorite, micrometeorite
  • Lecture (Conference)
    2nd International Conference on Radioanalytical and Nuclear Chemistry (RANC 2019), 05.-10.05.2019, Budapest, Hungary

Permalink: https://www.hzdr.de/publications/Publ-29206
Publ.-Id: 29206


Preliminary Report on the Study of Beam-induced Background Effects at a Muon Collider

Bartosik, N.; Bertolin, A.; Casarsa, M.; Collamati, F.; Ferrari, A.; Ferrari, A.ORC; Gianelle, A.; Lucchesi, D.; Mokhov, N.; Müller, S.ORC; Pastrone, N.; Sala, P.; Sestini, L.; Striganov, S.
Physics at a multi-TeV muon collider needs a change of perspective for the detector design due to the large amount of background induced by muon beam decays. Preliminary studies, based on simulated data, on the composition and the characteristics of the particles originated from the muon decays and reaching the detectors are presented here. The reconstruction performance of the physics processes H→bb¯ and Z→bb¯ has been investigated for the time being without the effect of the machine induced background. A preliminary study of the environment hazard due to the radiation induced by neutrino interactions with the matter is presented using the FLUKA simulation program.
Keywords: Detectors in high-intensity environments, future accelerators, muon beams, neutrino-induced radiation

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Permalink: https://www.hzdr.de/publications/Publ-29205
Publ.-Id: 29205


Vertical Organic Thin-Film Transistors with an Anodized Permeable Base for Very Low Leakage Current

Dollinger, F.; Lim, K.-G.; Li, Y.; Guo, E.; Formánek, P.; Hübner, R.; Fischer, A.; Kleemann, H.; Leo, K.
The organic permeable base transistor (OPBT) is currently the fastest organic transistor with a transition frequency of 40 MHz. It relies on a thin aluminum base electrode to control the transistor current. This electrode is surrounded by a native oxide layer for passivation, currently created by oxidation in air. However, this process is not reliable and leads to large performance variations between samples, slow production, and relatively high leakage currents. Here, for the first time it is demonstrated that electrochemical anodization can be conveniently employed for the fabrication of high-performance OPBTs with vastly reduced leakage currents and more controlled process parameters. Very large transmission factors of 99.9996 % are achieved, while excellent on/off ratios of 5 × 105 and high on-currents greater than 300 mA cm−2 show that the C60 semiconductor layer can withstand the electrochemical anodization. These results make anodization an intriguing option for innovative organic transistor design.
Keywords: aluminum oxide, anodization, organic permeable base transistors (OPBTs), organic transistors, organic thin-film transistors (OTFTs), vertical transistors

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Permalink: https://www.hzdr.de/publications/Publ-29204
Publ.-Id: 29204


The influence of microstructure on the fracture behaviour of ferritic ODS steels

Das, A.ORC
Oxide dispersion strengthened (ODS) steels are candidate materials for cladding tube and structural components in Generation IV nuclear fission reactors and as candidate materials for structural components in fusion devices. Fracture toughness is an important parameter required for the structural integrity and workability of a material. Despite having high strength at high temperatures and high irradiation swelling resistance, ODS steels have been known to possess lower fracture toughness than non-ODS ferritic martensitic steels, their immediate competitor. They also exhibit anisotropic fracture behaviour, especially for the hot-rolled and hot-extruded variants. In addition, ODS steels tend to form secondary cracks, which absorb energy but can lead to design problems.
In the present work, the microstructural features which cause low fracture toughness, anisotropic fracture behaviour and secondary cracking are investigated. This information can help manufacturers develop ODS steels with better fracture properties. Fracture toughness testing on three different batches of ODS steels are performed using miniature fracture toughness C(T) specimens using the unloading compliance method. The basic microstructure, fracture surfaces and crack propagation are investigated using techniques such as SEM, TEM and EBSD and compared with the fracture behaviour. A quantitative assessment of the microstructural parameters affecting fracture toughness is made using a critical strain based fracture toughness expression.
It was observed that the low fracture toughness of ODS steels is predominantly affected by the bond strength between the void initiating particle and the matrix. The size and inter-particle spacing of void initiating particles along with the yield stress did not dominantly affect the fracture toughness. The anisotropic fracture behaviour in ODS steels was found to be predominantly affected by the anisotropic grain morphology. Crystallographic anisotropy and anisotropy in void initiating particle distribution did not dominantly affect the fracture anisotropy. Secondary cracking favoured hot-rolled over hot-extruded specimens due to higher degree of microstructural anisotropy. Secondary cracks could stabilize primary crack propagation as well as prevent cleavage fracture at low temperatures. However, the drawback with secondary cracks was that they initiated earlier or at lower loads than the primary crack.
Keywords: fracture, fracture toughness, microstructure-mechanical property correlation, ODS steels, material characterization
  • Doctoral thesis
    University of Siegen, 2019
    Mentor: Prof. Dr.-Ing. habil. H.-J. Christ

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Permalink: https://www.hzdr.de/publications/Publ-29202
Publ.-Id: 29202


Wave-shaped polycyclic hydrocarbons with controlled aromaticity

Ma, J.ORC; Zhang, K.; Schellhammer, S.; Fu, Y.ORC; Komber, H.ORC; Xu, C.ORC; Popov, A. A.ORC; Hennersdorf, F.ORC; Weigand, J. J.ORC; Zhou, S.ORC; Pisula, W.ORC; Ortmann, F.; Berger, R.ORC; Liu, J.ORC; Feng, X.ORC
Controlling the aromaticity and electronic properties of curved π-conjugated systems has been increasingly attractive for the development of novel functional materials for organic electronics. Herein, we demonstrate an efficient synthesis of two novel wave-shaped polycyclic hydrocarbons (PHs) 1 and 2 with 64 π-electrons. Among them, the wave-shaped π-conjugated carbon skeleton of 2 is unambiguously revealed by single-crystal X-ray crystallography analysis. The wave-shaped geometry is induced by steric congestion in the cove and fjord regions. Remarkably, the aromaticity of these two structural isomers can be tailored by the annulated direction of cyclopenta[b]fluorene units. Isomer 1 (Eoptg = 1.13 eV) behaves as a closed-shell compound with weakly antiaromatic feature, whereas its structural isomer 2 displays a highly stable tetraradical character (y0 = 0.23; y1 = 0.22; t1/2 = 91 days) with a narrow optical energy gap of 0.96 eV. Moreover, the curved PH 2 exhibits remarkable ambipolar charge transport in solution-processed organic thin-film transistors. Our research provides a new insight into the design and synthesis of stable functional curved aromatics with multiradical characters.

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Permalink: https://www.hzdr.de/publications/Publ-29201
Publ.-Id: 29201


Flash Lamp Annealing: From Basics to Applications

Rebohle, L.; Prucnal, S.; Reichel, D.
The work gives a detailed introduction to the technology of flash lamp annealing, the corresponding physical background and an overview of the various applications of flash lamp annealing found in literature. It discusses a couple of issues which are relevant for process management with the focus on temperature measurement and temperature simulation. The application-related chapters include, inter alia, ultra-shallow junctions and hyperdoping in silicon, doping and superconductivity in germanium, silicon carbide, III-V semiconductors, diluted magnetic semiconductors, the crystallization of thin amorphous silicon films, semiconductor nanostructures, high-k materials, flash lamp annealing for monocrystalline, polycrystalline and thin film solar cells, transparent conducting oxides and flexible substrates.
Keywords: Thermal processing, semiconductors, flash lamp annealing, thin films, millisecond annealing

Permalink: https://www.hzdr.de/publications/Publ-29200
Publ.-Id: 29200


Measurement-Protocol Dependence of the Magnetocaloric Effect in Ni-Co-Mn-Sb Heusler Alloys

Salazar Mejia, C.; Kumar, V.; Felser, C.; Skourski, Y.; Wosnitza, J.; Nayak, A. K.
Ni-Co-Mn-Sb-based Heusler shape-memory alloys that undergo a martensitic-structural transition around room temperature are well known for exhibiting large magnetic entropy change and elastocaloric effect. Here, we report the observation of a large adiabatic temperature change of −11 K in a Ni-Co-Mn-Sb system by using direct adiabatic temperature-change measurements in pulsed magnetic fields. We show that a large magnetic cooling can be achieved in a wide temperature range spanning from 120 to 270 K by purposefully varying the chemical composition. The temperature- and field-dependent irreversibility of the effect is analyzed through a detailed experimental study of the protocol-dependent magnetocaloric effect. The present study is an important contribution towards the understanding of irreversible magnetocaloric effects in materials with magnetostructural transition.

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Permalink: https://www.hzdr.de/publications/Publ-29199
Publ.-Id: 29199


Magnetocaloric effect of gadolinium in high magnetic fields

Gottschall, T.ORC; Kuz'Min, M. D.; Skokov, K. P.; Skourski, Y.; Fries, M.; Gutfleisch, O.; Ghorbani Asl, M.ORC; Schlagel, D. L.; Mudryk, Y.; Pecharsky, V.; Wosnitza, J.
The magnetocaloric effect of gadolinium has been measured directly in pulsed magnetic fields up to 62 T. The maximum observed adiabatic temperature change is ΔTad = 60.5 K, the initial temperature T0 being just above 300 K. The field dependence of ΔTad is found to follow the usual H2/3 law, with a small correction in H4/3. However, as H is increased, a radical change is observed in the dependence of ΔTad on T0, at H = const. The familiar caret-shaped peak situated at T0 = TC becomes distinctly asymmetric, its high-temperature slope becoming more gentle and evolving into a broad plateau. For yet higher magnetic fields, μ0H ≥ 140 T, calculations predict a complete disappearance of the maximum near TC and an emergence of a new very broad maximum far above TC.

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Permalink: https://www.hzdr.de/publications/Publ-29198
Publ.-Id: 29198


Field-induced instability of the quantum spin liquid ground state in the Jeff = 1/2 triangular-lattice compound NaYbO2

Ranjith, K. M.; Opherden, D.; Khim, S.; Sichelschmidt, J.; Luther, S.; Ehlers, D.; Yasuoka, H.; Wosnitza, J.; Tsirlin, A. A.; Kühne, H.; Baenitz, M.
Polycrystalline samples of NaYbO2 are investigated by bulk agnetization and specific-heat measurements, as well as by nuclear magnetic resonance (NMR) and electron spin resonance (ESR) as local probes. No signatures of long-range magnetic order are found down to 0.3 K, evidencing a highly frustrated spin-liquid-like ground state in zero field. Above 2 T, signatures of magnetic order are observed in thermodynamic measurements, suggesting the possibility of a field-induced quantum phase transition. The 23Na NMR relaxation rates reveal the absence of magnetic order and persistent fluctuations down to 0.3 K at very low fields and confirm the bulk magnetic order above 2 T. The H-T phase diagram is obtained and discussed along with the existing theoretical concepts for layered spin- 1/2 triangular-lattice antiferromagnets.

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Publ.-Id: 29197


Strain engineering of electronic properties of point defects inside MoS2 monolayers from first-principles calculations

Bahmani, M.; Lorke, M.; Frauenheim, T.; Faghihnasiri, M.; Kuc, A. B.ORC
Monolayers of transition metal dichalcogenides are a set of two-dimensional materials with a stable semiconducting phase and direct-bandgap, showing promising applications in various electronic and optoelectronic devices. Monolayers of transition metal dichalcogenides have shown elastic relaxations up to an enormous fraction of their ideal strength while their electronic structure being very sensitive to the applied strain. Point vacancies in monolayers of such materials are present in all laboratory samples which affect in particular their electronic properties. These findings have paved the way for using strain and defect engineering in novel applications. The electronic structure and energetics of MoS2 monolayers containing point defects under strain are investigated by means of first-principles calculations based on density functional theory. Our results indicate that strain leads to strong modifications of the defect levels and their formation energies which are of importance for the application of these materials in real devices.

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Publ.-Id: 29196


Single Plane Compton Imaging for Radionuclide and Prompt Gamma-Ray Imaging

Kögler, T.ORC; Berthold, J.; Deneva, B.; Enghardt, W.ORC; Römer, K.; Straessner, A.ORC; Wagner, A.ORC; Werner, T.; Pausch, G.ORC
The contribution reports on first attempts to prove the concept of Single Plane Compton Imaging (SPCI), which was recently proposed in [1]. SPCI combines electronic collimation as known from conventional Compton cameras with a much simpler detector design: Multiple scintillator pixels are arranged alongside in a single detection plane. Imaging information is encoded in a set of ‘conditional’ spectra meaning energy deposition distributions in single pixels obliged with the condition of a coincident detection in another (adjacent) pixel. The activity distribution is iteratively reconstructed from the measured projections (the bin contents of the conditional spectra) by using the Maximum Likelihood Expectation Maximization (MLEM) algorithm.
This concept has been approached experimentally with three distinct setups addressing the application fields of radionuclide imaging in nuclear medicine, and of prompt-gamma based range verification in radiooncology with proton beams.
The first setup consists of two Directional Gamma-Ray Detectors [2], each consisting of two monolithic CeBr3 scintillators of 2”x1” and 2”x2”, arranged facing each other in close geometry. Those were exposed to prompt gamma radiation produced by a 90 MeV proton beam in a beam-stopping polymethyl acrylate (PMMA) target.
The third setup, aiming to be applied in radionuclide imaging, is a combination of a 4×4 pixel array of about 7 × 7 × 20 mm3 GAGG scintillator pixels read out with a Philips STEK module comprising 4×4 digital silicon photomultiplier dies. Data were taken with radioactive point sources arranged in few-cm distance from the scintillator pixels. Though data analyses are not yet finished, the effects enabling imaging are clearly visible. Preliminary plots exemplify the applicability of SPCI in both applications. The experimental activities have been closely accompanied with appropriate imaging methods and modeling using the Geant4 toolkit.

Bibliography

[1] G. Pausch, C. Golnik, A. Schulz and W. Enghardt, "A Novel Scheme of Compton Imaging for Nuclear Medicine," in IEEE Nuclear Science Symposium, Medical Imaging Conference and Room-Temperature Semiconductor Detector Workshop (NSS/MIC/RTSD), Strasbourg, 2016.
[2] A. Gueorguiev, J. Preston, l. Hoy, G. Pausch, C. Herbach and J. Stein, "A novel method to determine the directionality of radiation sources with two detectors based on coincidence measurements," in IEEE Nuclear Science Symposuim & Medical Imaging Conference, Knoxville, 2010.
Keywords: proton therapy, radiotherapy, range verification, single plane Compton imaging
  • Invited lecture (Conferences)
    International Conference on Nuclear Data for Science and Technology 2019, 19.-24.05.2019, Beijing, China

Permalink: https://www.hzdr.de/publications/Publ-29195
Publ.-Id: 29195


Proton-induced Prompt Gamma-Ray Yield of Carbon for Range Verification in Hadron Therapy

Kögler, T.ORC; Buch, F.; Römer, K.; Urlaß, S.; Pausch, G.ORC; Wagner, A.ORC
With particle therapy, more and more patients around the world are benefiting from precise dose deposition in the tumor. Due to the characteristic depth dose distribution, however, hadron therapy is particularly susceptible to range inaccuracies. Particle range verification is the subject of current research, but not yet a clinical standard. To circumvent this problem, safety margins are currently being defined around the tumor volume, which nullify the potential precision of particle compared to conventional photon therapy.
The use of the prompt gamma radiation resulting from the deceleration of hadrons in tissue for range verification is a promising approach here. At present, various methods exist (for example, prompt gamma-ray imaging, prompt gamma-ray spectroscopy, prompt gamma-ray timing, prompt gamma-ray peak integration), which attempt to obtain information regarding the range from the temporal and / or spatial distribution of these high-energy photons. However, all methods are based directly or indirectly on the results of particle transport calculations. But their results show significant discrepancies compared to the experimental data [1] - [7].
Photon production cross sections are particularly important for range verification with prompt gamma radiation, although there is hardly any experimental data for the clinically relevant isotopes to check and optimize the underlying models. The importance of prompt photon yields in clinical research was therefore also the subject of the 2nd ESTRO Physics Workshop Science and Development "Improving Range Accuracy in Particle Therapy" and will soon be emphasized again in a position paper of the society.
At the University Proton Therapy Dresden, the prompt emission spectrum of homogeneous graphite targets of different thickness was determined by irradiation with 90, 150 and 226 MeV protons. The detector response of the CeBr3 scintillation detectors (placed below 55 °, 90 ° and 125 ° with respect to the beam axis) was determined by Geant 4 simulations and verified by measurements with radioactive emitters. The emission spectrum was then obtained by unfolding the detector response using two different deconvolution algorithms (gold deconvolution and spectrum stripping). Scattered protons, which were detected in a YAP / BGO-Phoswich detector below 35°, were used to determine the incident proton fluence. The yields thus obtained are in good agreement with the available experimental data.

Bibliography

[1] J. Berthold, Single Plane Compton Imaging for Range Verification in Proton Therapy - A Proof-of-Principle Study, Dresden: Technische Universität Dresden, 2018.
[2] L. Kelleter, A. Wronska, J. Besuglow, A. Konefał, K. Laihem, J. Leidner und A. Magiera, „Spectroscopic study of prompt-gamma emission for range verification in proton therapy,“ Physica Med., Bd. 34, pp. 7-17, 2017.
[3] M. Pinto, D. Dauvergne, N. Freud, J. Krimmer, J. Létang und E. Testa, „Assessment of Geant4 Prompt-Gamma Emission Yields in the Context of Proton Therapy Monitoring,“ Frontiers in Oncology, Bd. 6, 2016.
[4] J. Jeyasugiththan und S. Peterson, „Evaluation of proton inelastic reaction models in Geant4 for prompt gamma production during proton radiotherapy,“ Phys. Med. Biol., Bd. 60, p. 7617–7635, 2015.
[5] A. Schumann, J. Petzoldt, P. Dendooven, W. Enghardt, C. Golnik, F. Hueso-González, T. Kormoll, G. Pausch, K. Roemer und F. Fiedler, „Simulation and experimental verification of prompt gamma-ray emissions during proton irradiation,“ Phys. Med. Biol., Bd. 60, pp. 4197-4207, 2015.
[6] J. Verburg, Reducing Range Uncertainty In Proton Thearpy, Eindhoven: Technische Universiteit Eindhoven, 2015.
[7] J. Dudouet, D. Cussol, D. Durand und M. Labalme, „Benchmarking Geant4 nuclear models for hadron therapy with 95 MeV/nucleon carbon ions,“ Phys. Rev. C, Bd. 89, p. 054616, 2014.
Keywords: proton therapy, range verification, prompt gamma yield, spectrum stripping, gold deconvolution
  • Poster
    International Conference on Nuclear Data for Science and Technology 2019, 19.-24.05.2019, Beijing, China

Permalink: https://www.hzdr.de/publications/Publ-29194
Publ.-Id: 29194


Solubility of Se in saline solutions – towards a consistent polythermal Pitzer dataset

Bok, F.; Moog, H. C.
Selenium (with the isotope Se-79 being an important fission product) can occur in oxidation states varying between +VI and –II. Most often negatively charged species are formed rendering them extraordinarily mobile in groundwater systems. For a correct calculation of the solubilities of Se(VI) and Se(IV) phases, the Pitzer ion-ion interaction model is essential for solutions with high ionic strengths.
Beside solubility calculations – mostly relevant for low soluble earth alkali selenites – reliable thermodynamic data sets for selenium are also of importance for chemotoxicity estimations or as boundary system in S-Se-solid solutions.
The state-of-the-art thermodynamic data for Selenium are given in the OECD/NEA Chemical Thermodynamics. This compilation does not address the Pitzer ion-ion interaction model. A polythermal set of Pitzer interaction parameters was compiled by GRS. However, both compilations hold solubility data for T = 25 °C only.
Here, to enable the calculation of selenium solubility at various temperatures in high saline solutions, temperature functions for the solubility products of alkaline and earth alkaline selenium phases are presented.

The experimental solubility data of various alkaline and earth alkaline selenates and selenites have been collected. The temperature function’s parameters of the solubility products were fitted to these solubility data using the geochemical speciation code PHREEQC in combination with the parameter estimation software Ucode2014.
Beside the solubility data, also temperature function’s parameters for the relevant redox reactions have been determined. The THEREDA database was used for all auxiliary reactions. Thus, the obtained data are consistent with their actual Pitzer model.

Temperature function’s parameters for the solubility products of seven selenate and four selenite mineral phases as well as for the relevant redox reactions could be obtained. In all cases, simplified functions with only two parameters were sufficient to fit the data within the range of experimental uncertainty.
With this new temperature-dependent parameter set, the solubility of selenium(IV) and (VI) an be calculated over the temperature range (T = 0 – 100 °C) relevant for a nuclear waste disposal.
The literature on directly measured selenide solubility data is very limited and not sufficient to derive solubility products or Pitzer interaction parameters – even at 25 °C. Thus, for the Se(−II) system the solubility data for alkaline and earth alkaline solid phases were taken from thermochemical measurements. For the Pitzer interaction coefficients data from chemical analogs have been used (Br or H2S). For the selenide system, this dataset is valid for T = 25 °C only.
The new temperature functions provide a redox-enabled and self-consistent dataset for the solubility calculations of selenium within the oceanic salt system including carbonates from the binary up to ternary and some quaternary systems.
For oxidizing to light reducing conditions, this dataset is valid between T = 0 – 100 °C, for stronger reducing conditions, the dataset is valid at T = 25 °C only.
Keywords: THEREDA, Selenium, Solubility, Löslichkeit, Pitzer
  • Lecture (Conference)
    Workshop on Actinide-Brine-Chemistry and Workshop on High Temperature Aqueous Chemistry, 25.-27.06.2019, Karlsruhe, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-29193
Publ.-Id: 29193


Size effects in nanocrystalline thoria

Plakhova, T.; Romanchuk, A.; Lykhosherstova, D.; Baranchikov, A.; Dorovatovskii, P.; Svetogorov, R.; Shatalova, T.; Egorova, T.; Trigub, A.; Kvashnina, K.ORC; Ivanov, V.; Kalmykov, S.
The facile chemical precipitation method and subsequent thermal treatment were shown to be suitable for preparation of crystalline ThO2 nanoparticles (NPs) in a wide range of particle sizes (from 2.5 to 34.3 nm). The obtained NPs were investigated with X-ray diffraction, high-resolution transmission electron microscopy and X-ray absorption techniques to find out the possible size effects associated with nanocrystalline thoria. The lattice parameter of ThO2 was found to increase by up to 1.1 %, in comparison with the bulk material whose particle size decreased to 2.5 nm. The decrease in the particle size was also accompanied by a significant decrease in the Th-Th coordination number

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Permalink: https://www.hzdr.de/publications/Publ-29192
Publ.-Id: 29192


New insights into the mechanism of graphene oxide and radionuclide interaction through vacancy defects

Kuzenkova, A.; Romanchuk, A.; Trigub, A.; Maslakov, K.; Egorov, A.; Amidani, L.; Kittrelle, C.; Kvashnina, K.ORC; Toure, J.; Talyzin, A.; Kalmykov, S.
The sorption of U(VI), Am(III)/Eu(III) and Cs(I) radionuclides by graphene oxides (GOs) synthesized by Hummers’s, Brodie’s and Tour’s methods was studied through a combination of batch experiments with characterization by microscopic and spectroscopic techniques such as XPS, ATR-FTIR, HERFD-XANES, EXAFS and HRTEM. Remarkably different sorption capacity and affinity of radionuclides was found towards GOs synthesized by Hummers’s and Brodie’s methods reflecting different structure and oxidation state of these materials. Mechanism underlying GO –radionuclide interaction is determined using variety of experimental techniques. For the first time it is shown here that GO - radionuclides interaction takes place on the small holes or vacancy defects in the GO sheets. Mechanism of GO’s interaction with radionuclides was analysed and specific functional groups responsible for this interaction were identified. Therefore, new strategy to produce improved materials with high capacity for radionuclides suggests to use perforated and highly defected GO with larger proportion of carboxylic functional groups

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Permalink: https://www.hzdr.de/publications/Publ-29191
Publ.-Id: 29191


Ion Sources for Focused Ion Beams – Present Status and Prospective Developments

Bischoff, L.ORC; Mazarov, P.; Pilz, W.; Klingner, N.ORC; Gierak, J.
Focused Ion Beam (FIB) processing has been developed into a well-established, irreplaceable and still promising technique in nearly all fields of nano-technology in particular for direct patterning and proto-typing on the μm scale and well below as well as sample preparation for further investigations, using SEM or TEM.
At the moment nearly exclusively gallium Liquid Metal Ion Sources (LMIS) are used for ion beam generation. Therefore, the Liquid Metal Alloy Ion Sources (LMAIS) represent a promising new alternative research area to expand the global FIB application fields. Here, especially, IBL (Ion Beam Lithography) - a direct, resistless and threedimensional patterning - enables a simultaneous in-situ process control by crosssectioning and inspection. Thanks to this, nearly half of the elements of the periodic table are made available in the FIB technology as a result of continuous research in this area during the last forty years [1]. Key features of a LMAIS are long life-time, high brightness and stable ion current. Recent developments could make these sources as an alternative technology feasible for nano patterning challenges e.g. to tune electrical, optical, magnetic or mechanic properties. In this contribution the operation principle, the preparation and testing
technology as well as prospective domains for modern FIB applications will be presented. As an example we will introduce a Ga35Bi60Li5 LMAIS in detail. It enables high resolution imaging with light Li ions, obtained with a VELION FIB/SEM system (Raith GmbH), as well as heavy Bi ions or polyatomic clusters, all coming from one ion source [2]. Additionally, also new ion source developments based on gas field emission (GFIS), on ionic liquids (ILIS), on magneto-optical traps (MOTIS) or on ICP or ECR high current sources for Xe-FIB are presented. Combined with an optimized FIB optics design they can open a bright field of new employments. These alternative ion sources will be introduced and briefly described.
[1] L. Bischoff, P. Mazarov, L. Bruchhaus, and J. Gierak, Liquid Metal Alloy Ion Sources - An Alternative
for Focused Ion Beam Technology, Appl. Phys. Rev. 3 (2016) 021101.
[2] W. Pilz, N. Klingner, L. Bischoff, P. Mazarov, and S. Bauerdick, Lithium Ion Beams from Liquid Metal
Alloy Ion Sources, J. Vac. Sci. Technol. B 37 (2019) 021802-1.
Keywords: Ion sources, Focused Ion Beam, Nanopatterning
  • Invited lecture (Conferences)
    European FIB Network, 3rd EuFN Workshop 2019, 12.-14.06.2019, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-29190
Publ.-Id: 29190


Studying of plutonium nanoparticles with various synchrotron metods

Gerber, E.; Romanchuk, A.; Hennig, C.; Trigub, A.; Scheinost, A.ORC; Roßberg, A.; Vaughan, G.; Amidani, L.ORC; Pidchenko, I.; Weiß, S.; Kalmykov, S.; Kvashnina, K.ORC
Plutonium is one of the most significant elements among actinides due to its high radiotoxicity and long period of high-decay. The migration of plutonium in the environment is a challenging and global problem. Plutonium migrates at scale of kilometers from previously contaminated sites in the form of intrinsic colloids or “pseudocolloids”.1-2 In the last few years it was found that so called “colloidal Pu(IV) polymers” actually represents as aggregates of PuO2 nanoparticles with size ~ 2 nm.3-5 The revealing of the mechanism of these particles formation (including the consideration of different factors which may have an influence), as well as their characterization is a key to understanding the conditions for long-term storages for the nuclear waste.
With the combination of different laboratory and synchrotron techniques it was found that small (2 nm) nanoparticles are formed from Pu(III), Pu(IV), Pu(V) aqueous solutions at pH 8-12, with the crystal structure close to PuO2, and with only Pu(IV) oxidation state present. Any other Pu-O contributions except Pu(IV)-O (in oxide) were not revealed.
  • Lecture (Conference)
    XXI Mendeleev Congress on General and Applied Chemistry, 09.-13.09.2019, Saint Petersburg, Russia

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Permalink: https://www.hzdr.de/publications/Publ-29189
Publ.-Id: 29189


Minimizing betatron coupling of energy spread and divergence in laser-wakefield accelerated electron beams

Köhler, A.ORC; Pausch, R.ORC; Couperus Cabadağ, J. P.ORC; Zarini, O.ORC; Krämer, J. M.; Bussmann, M.ORC; Debus, A.ORC; Schramm, U.ORC; Irman, A.ORC
Matched beam loading in laser wakefield acceleration (LWFA), characterizing the state of flattening of the accelerating electric field along the bunch, leads to the minimization of energy spread at high bunch charges. Here, we demonstrate by independently controlling injected charge and accelerating gradients, using the self-truncated ionization injection scheme, that minimal energy spread coincides with a reduction of the normalized beam divergence. With the simultaneous confirmation of a constant beam radius at the plasma exit, deduced from betatron radiation spectroscopy, we attribute this effect to the reduction of chromatic betatron decoherence. Thus, beam loaded LWFA enables highest longitudinal and transverse phase space densities.
Keywords: Laser wakefield acceleration, laser plasma accelerator, high bunch charge, beam loading, bunch size measurement, betatron radiation, betatron spectroscopy, Transverse phase space dynamic, beam divergence, beam decoherence, betatron phase mixing, betatron decoherence
Related publications
Transverse electron beam dynamics in the beam loading regime (Id 29299) has used this publication of HZDR-primary research data
  • Lecture (Conference)
    4th European Advanced Accelerator Concepts Workshop, 15.-21.09.2019, Isola d'Elba, Italia
  • Contribution to WWW
    arXiv:1905.02240 [physics.acc-ph]: https://arxiv.org/abs/1905.02240

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Permalink: https://www.hzdr.de/publications/Publ-29188
Publ.-Id: 29188


Geometry description in the FLUKA MC transport code

Müller, S.ORC
Geometry description in the FLUKA MC transport code
Keywords: FLUKA, MU2E, CLFV
  • Lecture (others)
    MU2E SimWG meeting, 11.04.2019, Fermilab, Batavia, USA

Permalink: https://www.hzdr.de/publications/Publ-29187
Publ.-Id: 29187


Ultrafast Anisotropic Disordering in Graphite Driven by Intense Hard X-ray Pulses

Hartley, N.ORC; Grenzer, J.; Lu, W.; Huang, L.; Inubushi, Y.; Kamimura, N.; Katagiri, K.; Kodama, R.; Kon, A.; Lipp, V.; Makita, M.; Matsuoka, T.; Medvedev, N.; Nakajima, S.; Ozaki, N.; Pikuz, T.; Rode, A. V.; Rohatsch, K.; Sagae, D.; Schuster, A.; Tono, K.; Vorberger, J.; Yabuuchi, T.; Kraus, D.
We present results from the SPring-8 Angstrom Compact free electron LAser (SACLA) X-ray free electron laser (XFEL) facility, using an X-ray pump, X-ray probe scheme to observe ultrafast changes in the structure of heated graphite. The 9.8 keV XFEL beam was focused to give an intensity on the order of 10^19 W/cm2, and the evolution of the diffraction pattern observed up to delays of 300 fs. The interplanar diffraction peaks weaken significantly within 10s of femtoseconds, but in-plane diffraction orders i.e. those with Miller Index (hk0), persist up to 300 fs, with the observed signal increasing. We interpret this as nonthermal damage through the breaking of interplanar bonds, which at longer timescales leads to ablation by removal of intact graphite sheets. Post-experiment examination of the graphite samples shows damage which is comparable in size to the range of the excited photoelectrons. These results highlight the challenges of accurately modelling X-ray driven heating, as it becomes a routine approach to generating high energy density states.

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Publ.-Id: 29186


Tunable disorder and localization in the rare-earth nickelates

Wang, C.ORC; Chang, C.-H.; Huang, A.; Wang, P.-C.; Wu, P.-C.; Yang, L.; Xu, C.ORC; Pandey, P.; Zeng, M.; Böttger, R.; Jeng, H.-T.; Zeng, Y.-J.; Helm, M.; Chu, Y.-H.; Ganesh, R.; Zhou, S.ORC
We demonstrate that transport in metallic rare-earth nickelates can be engineered by directly tuning the electronic mean free path. Using irradiation as a tool to induce disorder, we drive this system from a metallic phase into an Anderson insulator. This proceeds via an intermediate regime which shows a thermal crossover from insulating to metallic behavior. We argue that this phase falls within the paradigm of weak localization in three dimensions. We develop a theoretical model for the temperature dependence of resistivity which shows good agreement with our data. The three-dimensional weak localization picture is supported by magnetoconductivity, which scales as ∼B2 up to several tesla. Interestingly, our data indicate that this phase lies in the Mott-Ioffe-Regel regime with the mean free path approaching the lattice constant. Upon further increasing disorder, the charge carriers are localized, leading to insulating behavior at all temperatures. Our results show that irradiation provides a “clean” tuning knob for the mean free path, without altering other system parameters. This suggests promising directions for studies of Anderson localization.
Keywords: Anderson localization; Metal-insulator transition; Weak localization; Magnetoresistance
  • Physical Review Materials 3(2019)053801
    DOI: 10.1103/PhysRevMaterials.3.053801
  • Poster
    26th International Workshop on Oxide Electronics, 29.09.-02.10.2019, Kyoto, Japan

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Permalink: https://www.hzdr.de/publications/Publ-29185
Publ.-Id: 29185


Light and Heavy Ions from New Non-classical Liquid Metal Ion Sources for Advanced Nanofabrication

Mazarov, P.; Richter, T.; Bruchhaus, L.; Jede, R.; Yu, Y.; Sanabia, J. E.; Bischoff, L.ORC; Gierak, J.
Nanofabrication requirements for FIB technologies are specifically demanding in terms of patterning resolution, stability and the support of new processing techniques. Moreover the type of ion defines the nature of the interaction mechanism with the sample and thus has significant consequences on the resulting nanostructures [1]. Therefore, we have extended the technology towards the stable delivery of multiple ion species selectable into a nanometer scale focused ion beam by employing a liquid metal alloy ion source (LMAIS) [2]. This provides single and multiple charged species of different masses, resulting in significantly different interaction mechanisms. Nearly half of the elements of the periodic table are made available in the FIB technology as a result of continuous research in this area [3]. This range of ion species with different mass or charge can be beneficial for various nanofabrication applications. Recent developments could make these sources to an alternative technology feasible for nanopatterning challenges. In this contribution the operation principle, the preparation and testing process as well as prospective domains for modern FIB applications will be presented. As example we will introduce a GaBiLi LMAIS [4]. It enables high resolution imaging with light Li ions and sample modification with Ga or heavy polyatomic Bi clusters, all coming from one ion source. For sub-10 nm focused ion beam nanofabrication and microscopy, the GaBiLi-FIB or the AuSiGe-FIB could benefit of providing additional ion species in a mass separated FIB without changing the ion source.
[1] L. Bruchhaus, P. Mazarov, L. Bischoff, J. Gierak, A. D. Wieck, and H. Hövel, Comparison of technologies for nano device prototyping with a special focus on ion beams: A review, Appl. Phys. Rev. 4, 011302 (2017).
[2] L. Bischoff, P. Mazarov, L. Bruchhaus, and J. Gierak, Liquid Metal Alloy Ion Sources – An Alternative for
Focused Ion Beam Technology, Appl. Phys. Rev. 3 (2016) 021101.
[3] J. Gierak, P. Mazarov, L. Bruchhaus, R. Jede, L. Bischoff, Review of electrohydrodynamical ion sources and their applications to focused ion beam technology, JVSTB 36, 06J101 (2018).
[4] W. Pilz, N. Klingner, L. Bischoff, P. Mazarov, and S. Bauerdick, Lithium ion beams from liquid metal alloy ion sources, JVSTB 37, 021802 (2019).
Keywords: Nanofabrication, FIB technology, Liquid Metal Alloy Ion Source
  • Invited lecture (Conferences)
    AVS 66th International Symposium & Exhibition, 20.-25.10.2019, Columbus, Ohio, USA

Permalink: https://www.hzdr.de/publications/Publ-29184
Publ.-Id: 29184


Numerical simulation of an electromagnetic flow excitation in a liquid metal volume using OpenFOAM

Röhrborn, S.; Jüstel, P.; Schindler, F.; Galindo, V.ORC; Stefani, F.
To prepare an experiment on the potential resonance effect between the Rayleigh-Bénard convection and weak tidal forcing in a liquid metal, the influence of electromagnetic forcing on the eutectic metal Ga-In-Sn simulated in OpenFOAM will be the main topic of this work [1].
A modulated tidal m=2 Lorentz forcing will be produced by two opposing Helmholtz-like coils outside a Ga-In-Sn filled cylinder with an aspect ratio of one. Considering future analyses with additional Rayleigh-Bénard convection two Cu-plates installed at the bottom and the top of the volume are also taken into account for the simulation of the AC magnetic field. With a small magnetic flux density of a few mT a flow speed up to several centimeters per second can be produced. The results of the numerical simulations will be compared with experimental data.
Keywords: Magnetohydrodynamics, OpenFOAM, Rayleigh-Bénard convection, electromagnetic forcing, liquid metal
  • Lecture (Conference)
    9th European Postgraduate Fluid Dynamics Conference, 16.-19.07.2019, Ilmenau, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-29183
Publ.-Id: 29183


Electromagnetic flow excitation in a liquid metal volume using a Helmholtz-like coil setup

Jüstel, P.; Röhrborn, S.; Schindler, F.; Galindo, V.ORC; Stefani, F.
We present first results of our experiment involving electromagnetic forcing of a liquid metal volume. The experiment consist of a cylinder filled with eutectic GaInSn alloy and two magnetic coils placed on opposite sides of the cylinder. An alternating current in the coils excites Lorentz forces in the fluid, generating a flow field. Using ultrasound doppler velocimetry (UDV), we mapped this flow field. Maximum velocities of a few centimetres per second were reached. Numerical studies of the problem were also conducted and show good agreement. As a next step, the experimental setup shall be used to periodically disturb a Rayleigh-Bénard convection. The Rayleigh-Bénard flow structure occurs, when a layer of fluid is heated from below. The resulting flow is a convection roll about a horizontal axis. Point of interest is a possible resonance effect between the introduced forces and this flow structure.
Keywords: Electromagnetic forcing, liquid metal, Rayleigh-Bénard convection, resonance
  • Poster
    9th European Postgraduate Fluid Dynamics Conference, 16.07.2019, Ilmenau, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-29182
Publ.-Id: 29182


Experimental investigation of magnetorotational instability in hydromagnetic Taylor-Couette flows

Ogbonna, J. E.; Seilmayer, M.ORC; Stefani, F.
Magnetorotational instability (MRI) is believed to be largely responsible for the formation of protostars and black holes by introducing turbulence and facilitating an outward angular momentum transport in accretion disks. MRI is replicable in Taylor-Couette flows of electrically conducting fluids in the presence of externally applied magnetic fields. The Potsdam Rossendorf Magnetic Instability Experiment (PROMISE) at Helmholtz-Zentrum Dresden-Rossendorf is one of several existing facilities where an experimental approach towards understanding MRI takes place. PROMISE creates a magnetized Taylor-Couette flow of GaInSn alloy between concentric copper cylinders. Using PROMISE, the azimuthal MRI (AMRI), which is obtained when an azimuthal magnetic field is applied to the flow, have been demonstrated. The azimuthal magnetic field is induced by a strong central current along the cylinder axis. PROMISE has also shown evidence of the helical MRI (HMRI), which is obtained when an axial magnetic field is applied in addition to the azimuthal magnetic field. The axial magnetic field is induced by current through a coil wound around the outer cylinder. Recently, a symmetry breaking of AMRI due to thermal convection in the GaInSn alloy was discovered. In future, the transition from AMRI to HMRI will be investigated.
Keywords: Magnetorotational instability, Taylor-Couette flows, hydromagnetic flows
  • Lecture (Conference)
    9th European Postgraduate Fluid Dynamics Conference, 16.-19.07.2019, Ilmenau, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-29181
Publ.-Id: 29181


Solid target irradiation at the cyclotron Cyclone 18/9® at the HZDR in Leipzig

Franke, K.; Mansel, A.
Different research projects within the fields of resource ecology and neuroradiopharamceutical research make use of the cyclotron Cyclone 18/9® (IBA RadioPharma Solutions) at the HZDR in Leipzig. Aside liquid (2x F-18) and gas targets ([C-14]CH4, [C-14]CO2, [O-15]O2) two Nirta® Solid irradiation systems (IBA RadioPharma Solutions) are used. A broad spectrum of radionuclides (Ti-45, V-48, Cr-51, Co-56, Cu-64, Sr-85, Y-86, Zr-89, La-135, Ce-139, Au-194) is produced with these Nirta® Solid irradiation systems. Here we give an overview about the used target designs, irradiation parameters and target processing.
The Nirta® Solid irradiation system 1 (SIS1) is mounted at a 2m beam transfer line at port 3 of the cyclotron. The second irradiation system (SIS2) is mounted at port 4 of the cyclotron via a short tube. The cyclotron Cyclone 18/9 provides protons with an energy of 18 MeV and deuterons with energy of 9 MeV. The required energy of the incident particle for the nuclear reaction is set by the appropriate choice of the vacuum (Ti) and the entrance window (Al) of the target. SIS2 can hold coin like target disks (Ø 24 mm x 2mm). The maximal effective target size is Ø 12 mm x 1 mm. The SIS2 is used for the irradiation of metal foils, which are crimped inside the disk in between a cover and a backing plate. SIS1 can operate target capsules with a maximal effective target size of Ø 12 mm x 4 mm. This enables the irradiation of powders and pellets aside its use for metal foils. Both irradiation systems can be pre-loaded with 3 targets for consecutive irradiations. Different target materials are used for irradiation, like metal foils (Sc-45(p,n)Ti-45, Ti-48(p,n)V-48, V-nat(p,n)Cr-51, Ni-64(p,n)Cu-64, Y 89(p,n)Zr-89), metal powders (Ti-48(p,n)V-48, Pt-nat(p,n)Au-194), oxides (La-139(p,n)Ce-139), carbonates (Sr 86(p,n)Y-86) and chlorides (Rb-85(p,n)Sr-85). If required electroplating or pellet pressing is applied for target preparation. After irradiation the targets are transferred out of the vault by a conveyer system. Different techniques, like liquid/liquid extraction, liquid/solid extraction and chromatography are applied for target processing and the recovery of the enriched target material. Gamma-ray spectrometry is used to prove the radionuclidical purity of the product. The presented methods allow a straightforward and reliable production of n.c.a. radionuclides for research purposes. Irradiation parameters, target preparation and processing are easily adaptable to the experimental needs.
  • Poster
    Jahrestagung der Fachgruppe Nuklearchemie 2019, 25.-27.09.2019, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-29180
Publ.-Id: 29180


AMS at Big Accelerators: 53Mn and 60Fe in Meteorites

Rugel, G.; Faestermann, T.; Fimiani, L.; Korschinek, G.; Leya, I.; Ludwig, P.; Pavetich, S.; Smith, T.; Wallner, A.
The poster describes that big tandem accelerators are essential to measure 53Mn and 60Fe in meteorites.
Keywords: AMS Accelerator Fe-60 Mn-53 Meteorites
  • Poster
    KIMM Workshop 2019, 02.05.2019, München, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-29179
Publ.-Id: 29179


Interaction of O-Y and O-Y-Ti clusters embedded in bcc Fe with He, vacancies and self-interstitial atoms

Vallinayagam, M.; Posselt, M.ORC; Faßbender, J.ORC
Calculations based on Density Functional Theory are performed to investigate the interaction of O-Y and O-Y-Ti clusters in bcc Fe with He atoms, vacancies (V) and self-interstitial atoms (SIA). The four different cluster structures studied in our previous work (J Phys Condens Matter 31 095701) are considered. He, V and SIA are inserted on different positions inside and in the environment of the clusters, the total energy of the corresponding supercell is minimized and the binding and incorporation energy of the three kinds of defects is determined. He in the center of a cage-like (CL) cluster is more stable than on interfacial vacant sites (IVS). In CL O-Y clusters He on an IVS is more stable than in the cluster structure with oxygen in the center (OC), whereas there is no significant difference between the two kinds for clusters with Ti. Up to a distance of 1.5 times the iron lattice constant from the cluster center He is not stable on most of the octahedral and tetrahedral interstitial sites in the Fe matrix near the interface. Instead He is shifted towards positions closer to the cluster. Relaxation occurs to known IVS as well as to previously unknown interfacial interstitial sites (IIS). Moreover, two or three He atoms are placed on sites found to be stable after adding a single He. The corresponding binding and incorporation energies obtained after relaxation are nearly equal to the sum of the values for the interaction with a single He atom. However, placing He dimers or trimers in the environment of a vacancy may also lead to relatively low values of the incorporation energy. Also, barriers for jumps of He atoms between interfacial sites and the center of CL clusters are determined. In the CL O-Y cluster the barriers are lower than in the CL O-Y-Ti cluster, i.e. trapping and release of He is easier in the former than in the latter. V and SIA interaction with the clusters is also attractive. The binding energy of V strongly depends on the site where V is inserted while in all the studied cases the SIA is annihilated at the cluster-iron interface. Present results clearly demonstrate that the oxide-based nanoclusters are strong traps for irradiation induced defects which is in agreement with experimental findings.
Keywords: density functional theory calculations, oxide dispersion strengthened steels, interaction with He, vacancies and self-interstitial atoms

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Publ.-Id: 29178


Magnetic Orders and Origin of Exchange Bias in Co Clusters Embedded Oxide Nanocomposite Films

Li, H.; Wang, C.ORC; Li, D.-Y.; Pereira, L. M. C.; Homm, P.; Menghini, M.; Locquet, J.-P.; Temst, K.; Vantomme, A.; van Haesendonck, C.; van Bael, M. J.; Ruan, S.; Zeng, Y.-J.
Magnetic nanoparticles embedded oxide semiconductors are interesting candidates for spintronics in view of combining ferromagnetic (FM) and semiconducting properties. Co-ZnO and Co-V2O3 nanocomposite thin films are synthesized by Co ion implantation in crystalline thin films. Magnetic order varies with the implantation fluence in Co-ZnO, where the superparamagnetic (SPM) order appears in the low-fluence films (2×1016 and 4×1016 ions/cm2) while the FM order coexists with the SPM phase in high-fluence ones (1×1017 ions/cm2). The exchange bias (EB) effect is evident in high-fluence films, which gives an EB field of about 100 Oe at 2 K and a blocking temperature of around 100 K. In parallel, 3.5×1016 ions/cm2 Co-V2O3 hybrid thin film exhibits a clear antiferromagnetic (AFM) coupling at low temperature with a weak EB effect. The different magnetic behaviors in the two Co-implanted systems lead us to believe on one hand, that the observed EB effect in the Co-ZnO system is the result of the FM/AFM coupling between large Co nanoparticles and their CoO/Co3O4 surroundings in the (Zn,Co)O matrix. While, on the other hand, the EB effect in Co-V2O3 system originates from the interaction between FM Co nanoparticles and AFM V2O3 matrix. Detailed studies of magnetic orders as well as EB effect in magnetic nanocomposite semiconductors pave the way for their application in spintronics.
Keywords: nanocomposite, exchange bias, antiferromagnetic, superparamagnetic

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Permalink: https://www.hzdr.de/publications/Publ-29176
Publ.-Id: 29176


Thermal stability of Te-hyperdoped Si: Atomic-scale correlation of the structural, electrical, and optical properties

Wang, M.ORC; Hübner, R.; Xu, C.ORC; Xie, Y.; Berencen, Y.ORC; Heller, R.; Rebohle, L.; Helm, M.; Prucnal, S.; Zhou, S.ORC
Si hyperdoped with chalcogens (S,Se,Te) is well known to possess unique properties such as an insulator-tometal transition and a room-temperature sub-band-gap absorption. These properties are expected to be sensitive to a postsynthesis thermal annealing, since hyperdoped Si is a thermodynamically metastable material. Thermal stability of the as-fabricated hyperdoped Si is of great importance for the device fabrication process involving temperature-dependent steps such as Ohmic contact formation. Here, we report on the thermal stability of the as-fabricated Te-hyperdoped Si subjected to isochronal furnace anneals from 250 to 1200 °C. We demonstrate that Te-hyperdoped Si exhibits thermal stability up to 400 °C for 10 min, which even helps to further improve the crystalline quality, the electrical activation of Te dopants, and the room-temperature sub-band-gap absorption. At higher temperatures, however, Te atoms are found to move out from the substitutional sites with a maximum migration energy of EM = 2.3 eV forming inactive clusters and precipitates that impair the structural, electrical, and optical properties. These results provide further insight into the underlying physical state transformation of Te dopants in a metastable compositional regime caused by postsynthesis thermal annealing. They also pave the way for the fabrication of advanced hyperdoped Si-based devices.

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Publ.-Id: 29175


Controllable defect driven symmetry change and domain structure evolution in BiFeO3 with enhanced tetragonality

Chen, C.; Wang, C.ORC; Cai, X.; Xu, C.; Li, C.; Zhou, J.; Luo, Z.; Fan, Z.; Qin, M.; Zeng, M.; Lu, X.; Gao, X.; Kentsch, U.; Yang, P.; Zhou, G.; Wang, N.; Zhu, Y.; Zhou, S.ORC; Chen, D.; Liu, J.
Defect engineering has been a powerful tool to enable the creation of exotic phases and the discovery of intriguing phenomena in ferroelectric oxides. However, the accurate control of the concentration of defects remains a big challenge. In this work, ion implantation, which can provide controllable point defects, allows us to produce a controlled defect driven true super-tetragonal (T) phase with a single-domain-state in ferroelectric BiFeO3 thin films. This point-defect engineering is found to drive the phase transition from the as-grown mixed rhombohedral-like (R) and tetragonal-like (MC) phase to true tetragonal (T) symmetry and induce the stripe multi-nanodomains to a single domain state. By further increasing the injected dose of the He ion, we demonstrate an enhanced tetragonality super-tetragonal (super-T) phase with the largest c/a ratio of ∼1.3 that has ever been experimentally achieved in BiFeO3. A combination of the morphology change and domain evolution further confirms that the mixed R/MC phase structure transforms to the single-domain-state true tetragonal phase. Moreover, the re-emergence of the R phase and in-plane nanoscale multi-domains after heat treatment reveal the memory effect and reversible phase transition and domain evolution. Our findings demonstrate the reversible control of R-Mc-T-super T symmetry changes (leading to the creation of true T phase BiFeO3 with enhanced tetragonality) and multidomain-single domain structure evolution through controllable defect engineering. This work also provides a pathway to generate large tetragonality (or c/a ratio) that could be extended to other ferroelectric material systems (such as PbTiO3, BaTiO3 and HfO2) which might lead to strong polarization enhancement.

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  • Secondary publication expected from 05.04.2020

Permalink: https://www.hzdr.de/publications/Publ-29174
Publ.-Id: 29174


High spin-wave propagation length consistent with low damping in a metallic ferromagnet

Flacke, L.; Liensberger, L.; Althammer, M.; Huebl, H.; Geprägs, S.; Schultheiß, K.ORC; Buzdakov, A.; Hula, T.; Schultheiß, H.ORC; Edwards, E. R. J.; Nembach, H. T.; Shaw, J. M.; Gross, R.; Weiler, M.
We report ultra-low intrinsic magnetic damping in Co25Fe75 heterostructures, reaching the low 10E−4 regime at room temperature. By using a broadband ferromagnetic resonance technique, we extracted the dynamic magnetic properties of several Co25Fe75-based heterostructures with varying ferromagnetic layer thickness. By estimating the eddy current contribution to damping, measuring radiative damping and spin pumping effects, we extrapolated an intrinsic damping of α0 ≤ 3.05 × 10E−4. Furthermore, using Brillouin light scattering microscopy we measured spin-wave propagation lengths of up to (21 ± 1) μm in a 26 nm thick Co25 Fe75 heterostructure at room temperature, which is in excellent agreement with the measured damping.
Keywords: spin-wave propagation; low magnetic damping; ferromagnetic resonance; Brillouin light scattering

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Permalink: https://www.hzdr.de/publications/Publ-29172
Publ.-Id: 29172


Nonlinear ferromagnetic resonance in the presence of 3-magnon scattering in magnetic nanostructures

Slobodianiuk, D. V.; Melkov, G. A.; Schultheiß, K.ORC; Schultheiß, H.ORC; Verba, R. V.
Bulk and patterned ferromagnets can exhibit various nonlinear phenomena at moderate excitation power, making them a nice test bed for study of nonlinear dynamics. We investigate nonlinear ferromagnetic resonance in magnetic nanostructures with discrete spectra of spin-wave modes in the case of allowed 3-magnon scattering processes. These processes result in the splitting of a directly driven spin-wave mode into two secondary modes if a certain excitation threshold is overcome. The 3-magnon splitting manifests itself as a characteristic distortion of the resonance curve, which can be detected in a simple ferromagnetic resonance experiment. Theoretical results are also compared to the experimental study of nonlinear spin-wave dynamics in a vortex-state magnetic disk, in which 3-magnon splitting is confirmed by direct measurements using Brillouin light scattering microscopy.
Keywords: nonlinear ferromagnetic resonance; 3-magnon scattering; spin-wave modes; magnetic vortex; Brillouin light scattering; magnetic nanoelements

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Publ.-Id: 29171


Absorption edge, Urbach tail, and electron-phonon interactions in topological insulator Bi2Se3 and band insulator (Bi0.89In0.11)2Se3

Zhu, J.ORC; Xia, Y.; Li, G.; Zhou, S.ORC; Wimmer, S.; Springholz, G.ORC; Pashkin, O.ORC; Helm, M.; Schneider, H.ORC
We employ infrared transmission spectroscopy to explore the temperature-dependent absorption edge and electron-phonon (e-ph) interaction in topological insulator Bi2Se3 and band insulator (Bi0.89In0.11)2Se3 films. Upon heating from 5 K to 300 K, the absorption edge shifts from 262 to 249 meV for Bi2Se3 and from 367 to 343 meV for (Bi0.89In0.11)2Se3. By analyzing the temperature dependence of the Urbach tail, the significant role of Raman-active phonon mode E2g in e-ph interaction is identified, which agrees well with the ab initio calculation.

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Publ.-Id: 29170


Electron-Beam-Driven Structure Evolution of Single-Layer MoTe2 for Quantum Devices

Lehnert, T.; Ghorbani Asl, M.ORC; Köster, J.; Lee, Z.; Krasheninnikov, A.ORC; Kaiser, U.
40 kV high-resolution transmission electron microscopy (TEM) experiments are performed to understand defect formation and evolution of their atomic structure in single-layer 2H MoTe2 under electron beam irradiation. We show that Te vacancies can agglomerate either in single Te-vacancy lines or in extended defects composed of column Te vacancies, including rotational trefoil-like defects, with some of them being never reported before. The formation of inversion domains with mirror twin boundaries of different types, along with the islands of the metallic T’ phase was also observed. Our first-principles calculations provide insights into the energetics of the transformations as well as the electronic structure of the system with defects and point out that some of the observed defects have localized magnetic moments. Our results indicate that various nano-scale structures, including metallic quantum dots consisting of T’-phase islands and one-dimensional metallic quantum systems such as vacancy lines and mirror twin boundaries embedded into a semiconducting host material can be realized in single-layer 2H MoTe2, and defect-associated magnetism can also be added, which may allow prospective control of optical and electronic properties of two-dimensional materials.
Keywords: Defects, 2D MoTe2, transmission electron microscopy, transition metal dichalcogenide, DFT, quantum devices

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  • Secondary publication expected from 26.04.2020

Permalink: https://www.hzdr.de/publications/Publ-29169
Publ.-Id: 29169


Impact of Extrinsic and Intrinsic Hypoxia on Catecholamine Biosynthesis in Absence or Presence of Hif2α in Pheochromocytoma Cells

Bechmann, N.; Poser, I.; Seifert, V.; Greunke, C.; Ullrich, M.ORC; Qin, N.; Walch, A.; Peitzsch, M.; Robledo, M.; Pacak, K.; Pietzsch, J.ORC; Richter, S.; Eisenhofer, G.
Abstract: Pheochromocytomas and paragangliomas (PPGLs) with activated pseudohypoxic pathways are associated with an immature catecholamine phenotype and carry a higher risk for metastasis. For improved understanding of the underlying mechanisms we investigated the impact of hypoxia and pseudohypoxia on catecholamine biosynthesis in pheochromocytoma cells naturally lacking Hif2α (MPC and MTT) or expressing both Hif1α and Hif2α (PC12). Cultivation under extrinsic hypoxia or in spheroid culture (intrinsic hypoxia) increased cellular dopamine and norepinephrine contents in all cell lines. To distinguish further between Hif1α- and Hif2α-driven effects we expressed Hif2α in MTT and MPC-mCherry cells (naturally lacking Hif2α). Presence of Hif2α resulted in similarly increased cellular dopamine and norepinephrine under hypoxia as in the control cells. Furthermore, hypoxia resulted in enhanced phosphorylation of tyrosine hydroxylase (TH). A specific knockdown of Hif1α in PC12 diminished these effects. Pseudohypoxic conditions, simulated by expression of Hif2α under normoxia resulted in increased TH phosphorylation, further stimulated by extrinsic hypoxia. Correlations with PPGL tissue data led us to conclude that catecholamine biosynthesis under hypoxia is mainly mediated through increased phosphorylation of TH, regulated as a short-term response
(24–48 h) by HIF1α. Continuous activation of hypoxia-related genes under pseudohypoxia leads to a HIF2α-mediated phosphorylation of TH (permanent status).
Keywords: hypoxia; pseudohypoxia; spheroids; HIF; EPAS1; catecholamine; pheochromocytoma and paraganglioma; phosphorylation tyrosine hydroxylase

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Permalink: https://www.hzdr.de/publications/Publ-29168
Publ.-Id: 29168


Silver Particles with Rhombicuboctahedral Shape and Effective Isotropic Interactions with Light

Steiner, A. M.; Mayer, M.; Schletz, D.; Wolf, D.; Formanek, P.; Hübner, R.; Dulle, M.; Förster, S.; König, T. A. F.; Fery, A.
Truly spherical silver nanoparticles are of great importance for fundamental studies including plasmonic applications, but their direct synthesis in aqueous media is not feasible. Using the commonly employed copper-based etching processes, an isotropic plasmonic response can be achieved by etching well-defined silver nanocubes. Whilst spherical-like shape is typically prevailing in such processes, we established that there is a preferential growth toward silver rhombicuboctahedra, which is the thermodynamically most stable product of this synthesis. The rhombicuboctahedral morphology is further evidenced by comprehensive characterization with small-angle X-ray scattering in combination with transmission electron microscopy (TEM) tomography and high-resolution TEM. We also elucidate the complete reaction mechanism based on UV-vis kinetic studies, and the postulated mechanism can also be extended to all copper-based etching processes.

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Permalink: https://www.hzdr.de/publications/Publ-29167
Publ.-Id: 29167


Carboranyl analogues of ketoprofen with cytostatic activity against human melanoma and colon cancer cell lines

Buzharevski, A.; Paskas, S.; Laube, M.ORC; Lönnecke, P.; Neumann, W.; Murganic, B.; Mijatovic, S.; Maksimovic-Ivanic, D.; Pietzsch, J.ORC; Hey-Hawkins, E.
Ketoprofen is a widely used nonsteroidal anti-inflammatory drug (NSAID) that also exhibits cytotoxic activity against various cancers. This makes ketoprofen an attractive structural lead for the development of new NSAIDs and cytotoxic agents. Recently, the incorporation of carboranes as phenyl mimetics in structures of established drugs has emerged as an attractive strategy in drug design. Herein, we report the synthesis and evaluation of four novel carborane-containing derivatives of ketoprofen, two of which are prodrug esters with an nitric oxide-releasing moiety. One of these prodrug esters exhibited high cytostatic activity against melanoma and colon cancer cell lines. The most pronounced activity was found in cell lines that are sensitive to oxidative stress, which was apparently induced by the ketoprofen analogue.

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Publ.-Id: 29166


General guideline for closure model development for gas-liquid flows in the multi-fluid framework

Lucas, D.; Krepper, E.; Liao, Y.; Rzehak, R.; Ziegenhein, T.
The two- or multi-fluid approach is frequently used for Nuclear Reactor Safety (NRS)-related simulations of gas-liquid flows. To enable reliable predictions the closure models have to reflect the involved local physical phenomena at the non-resolved scale properly. To consolidate the CFD-modelling in the frame of the multi-fluid approach the so-called baseline model strategy was recently proposed (Lucas et al., 2016). The present technical note discusses a long-term strategy for the baseline model development and ways to obtain or improve closure models. Guidelines for the model development are given by listing requirements for appropriate closure models as well as frequently made mistakes. This is illustrated by examples for recent developments done for HZDR baseline models for poly-disperse bubbly flows.
Keywords: CFD, multi-fluid model, closure models

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  • Secondary publication expected from 31.10.2020

Permalink: https://www.hzdr.de/publications/Publ-29165
Publ.-Id: 29165


A Five-MicroRNA Signature Predicts Survival and Disease Control of Patients with Head and Neck Cancer Negative for HPV Infection

Hess, J.; Unger, K.; Maihoefer, C.; Schuettrumpf, L.; Wintergerst, L.; Heider, T.; Weber, P.; Marschner, S.; Braselmann, H.; Samaga, D.; Kuger, S.; Pflugradt, U.; Baumeister, P.; Walch, A.; Woischke, C.; Kirchner, T.; Werner, M.; Werner, K.; Baumann, M.; Budach, V.; Combs, S. E.; Debus, J.; Grosu, A.-L.; Krause, M.ORC; Linge, A.; Roedel, C.; Stuschke, M.; Zips, D.; Zitzelsberger, H.; Ganswindt, U.; Henke, M.; Belka, C.
Purpose: Human papillomavirus (HPV)-negative head and neck squamous cell carcinoma (HNSCC) is associated with unfavorable prognosis, while independent prognostic markers remain to be defined.
Experimental Design: We retrospectively performed miRNA expression profiling. Patients were operated for locally advanced HPV-negative HNSCC and had received radiochemotherapy in eight different hospitals (DKTK-ROG; n = 85). Selection fulfilled comparable demographic, treatment, and follow-up characteristics. Findings were validated in an independent single-center patient sample (LMU-KKG; n = 77). A prognostic miRNA signature was developed for freedom from recurrence and tested for other endpoints. Recursivepartitioning analysis was performed on the miRNA signature, tumor and nodal stage, and extracapsular nodal spread.
Technical validation used qRT-PCR. An miRNA-mRNA target network was generated and analyzed.
Results: For DKTK-ROG and LMU-KKG patients, the median follow-up was 5.1 and 5.3 years, and the 5-year freedom from recurrence rate was 63.5% and 75.3%, respectively. A five-miRNA signature (hsa-let-7g-3p, hsamiR- 6508-5p, hsa-miR-210-5p, hsa-miR-4306, and hsa-miR-7161-3p) predicted freedom from recurrence in DKTK-ROG [hazard ratio (HR) 4.42; 95% confidence interval (CI), 1.98-9.88, P < 0.001], which was confirmed in LMU-KKG (HR 4.24; 95% CI, 1.40-12.81, P = 0.005). The signature also predicted overall survival (HR 3.03; 95% CI, 1.50-6.12, P = 0.001), recurrence-free survival (HR 3.16; 95% CI, 1.65-6.04, P < 0.001), and disease-specific survival (HR 5.12; 95% CI, 1.88-13.92, P < 0.001), all confirmed in LMU-KKG data. Adjustment for relevant covariates maintained the miRNA signature predicting all endpoints. Recursive- partitioning analysis of both samples combined classified patients into low (n = 17), low-intermediate (n = 80), high-intermediate (n = 48), or high risk (n = 17) for recurrence (P < 0.001).
Conclusions: The five-miRNA signature is a strong and independent prognostic factor for disease recurrence and survival of patients with HPV-negative HNSCC.

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Publ.-Id: 29164


Thermal Transport in MoS2 from Molecular Dynamics using Different Empirical Potentials

Xu, K.; Gabourie, A. J.; Hashemi, A.; Fan, Z.; Wei, N.; Farimani, A. B.; Komsa, H.-P.; Krasheninnikov, A.ORC; Pop, E.; Ala-Nissila, T.
Thermal properties of molybdenum disulfide (MoS2) have recently attracted attention related to fundamentals of heat propagation in strongly anisotropic materials, and in the context of potential applications to optoelec- tronics and thermoelectrics. Multiple empirical potentials have been developed for classical molecular dynamics (MD) simulations of this material, but it has been unclear which provides the most realistic results. Here, we calculate lattice thermal conductivity of single- and multilayer pristine MoS2 by employing three different thermal transport MD methods: equilibrium, nonequilibrium, and homogeneous nonequilibrium ones. We mainly use the Graphics Processing Units Molecular Dynamics code for numerical calculations, and the Large-scale Atomic/Molecular Massively Parallel Simulator code for crosschecks. Using different methods and computer codes allows us to verify the consistency of our results and facilitate comparisons with previous studies, where different schemes have been adopted. Our results using variants of the Stillinger-Weber potential are at odds with some previous ones and we analyze the possible origins of the discrepancies in detail. We show that, among the potentials considered here, the reactive empirical bond order (REBO) potential gives the most reasonable predictions of thermal transport properties as compared to experimental data. With the REBO potential, we further find that isotope scattering has only a small effect on thermal conduction in MoS2 and the in-plane thermal conductivity decreases with increasing layer number and saturates beyond about three layers. We identify the REBO potential as a transferable empirical potential for MD simulations of MoS2 which can be used to study thermal transport properties in more complicated situations such as in systems containing defects or engineered nanoscale features. This work establishes a firm foundation for understanding heat transport properties of MoS2 using MD simulations.
Keywords: 2D materials; thermal transport; atomistic simulations

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Publ.-Id: 29163


Tomonaga-Luttinger liquid in a box: electrons confined within MoS2 mirror twin boundaries

Jolie, W.; Murray, C.; Weiß, P. S.; Hall, J.; Portner, F.; Atodiresei, N.; Krasheninnikov, A.ORC; Busse, C.; Komsa, H.-P.; Rosch, A.; Michely, T.
Two- or three-dimensional metals are usually well described by weakly interacting, fermionic quasiparticles. This concept breaks down in one dimension due to strong Coulomb interactions. There, low-energy electronic excitations are expected to be bosonic collective modes, which fractionalize into independent spin- and charge-density waves. Experimental research on one-dimensional metals is still hampered by their difficult realization, their limited accessibility to measurements, and by competing or obscuring effects such as Peierls distortions or zero bias anomalies. Here we overcome these difficulties by constructing a well-isolated, one-dimensional metal of finite length present in MoS2 mirror-twin boundaries. Using scanning tunneling spectroscopy we measure the single-particle density of the interacting electron system as a function of energy and position in the 1D box. Comparison to theoretical modeling provides unambiguous evidence that we are observing spin-charge separation in real space.
Keywords: 2D materials, Tomonaga-Luttinger liquid, First-principles calculations

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Permalink: https://www.hzdr.de/publications/Publ-29162
Publ.-Id: 29162


Room temperature ferromagnetism in MoTe2 by post-growth incorporation of vanadium impurities

Coelho, P. M.; Komsa, H.-P.; Lasek, K.; Kalappattil, V.; Karthikeyan, J.; Phan, M.-H.; Krasheninnikov, A.ORC; Batzill, M.
Post-synthesis doping of 2D materials is demonstrated by incorporation of vapor-deposited transition metals into a MoTe2 lattice. Using this approach, vanadium doping of 2H-MoTe2 produces a 2D ferromagnetic semiconductor with a Curie temperature above room temperature (RT). Surprisingly, ferromagnetic properties can be induced with very low vanadium concentrations, down to ≈0.2%. The vanadium species introduced at RT are metastable, and annealing to above ≈500 K results in the formation of a thermodynamically favored impurity configuration that, however, exhibits reduced ferromagnetic properties. Doping with titanium, instead of vanadium, shows a similar incorporation behavior, but no ferromagnetism is induced in MoTe2. This indicates that the type of impurities in addition to their atomic configuration is responsible for the induced magnetism. The interpretation of the experimental results is consistent with ab initio calculations, which confirm that the proposed vanadium impurity configurations exhibit magnetic moments, in contrast to the same configurations with titanium impurities. This study illustrates the possibility to induce ferromagnetic properties in layered van der Waals semiconductors by controlled magnetic impurity doping and thus to add magnetic functionalities to 2D materials.
Keywords: 2D materials; STM; electronic structure calculations; doping

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  • Secondary publication expected from 01.04.2020

Permalink: https://www.hzdr.de/publications/Publ-29161
Publ.-Id: 29161


Efficient method for calculating Raman spectra of solids with impurities and alloys and its application to two-dimensional transition metal dichalcogenides

Hashemi, A.; Krasheninnikov, A.ORC; Puska, M.; Komsa, H.
Raman spectroscopy is a widely used, powerful, and nondestructive tool for studying the vibrational properties of bulk and low-dimensional materials. Raman spectra can be simulated using first-principles methods but due to the high computational cost calculations are usually limited only to fairly small unit cells, which makes it difficult to carry out simulations for alloys and defects. Here, we develop an efficient method for simulating Raman spectra of alloys, benchmark it against full density-functional theory calculations, and apply it to several alloys of two-dimensional (2D) transition metal dichalcogenides. In this method, the Raman tensor for the supercell mode is constructed by summing up the Raman tensors of the pristine system weighted by the projections of the supercell vibrational modes to those of the pristine system. This approach is not limited to 2D materials and should be applicable to any crystalline solid with defects and impurities. To efficiently evaluate vibrational modes of very large supercells, we adopt mass approximation, although it is limited to chemically and structurally similar atomic substitutions. To benchmark our method, we first apply it to the MoxW(1-x)S2 monolayer in the H phase where several experimental reports are available for comparison. Second, we consider MoxW(1-x)Te2 in the T' phase, which has been proposed to be a 2D topological insulator but where experimental results for the monolayer alloy are still missing. We show that the projection scheme also provides a powerful tool for analyzing the origin of the alloy Raman-active modes in terms of the parent system eigenmodes. Finally, we examine the trends in characteristic Raman signatures for dilute concentrations of impurities in MoS2.
Keywords: 2D materials; atomistic simulation

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Permalink: https://www.hzdr.de/publications/Publ-29160
Publ.-Id: 29160


Cathepsin B-Activatable Cell-Penetrating Peptides

Kuhne, K.; Behring, L.; Belter, B.; Wodtke, R.; Pietzsch, J.ORC; Löser, R.
Protease activity is increasingly drawn into the spotlight as a crucial modulator in cancer angiogenesis, invasion, and metastasis [1]. Elevated activity of multiple members of the family of cysteine cathepsins has been shown to correlate with increased metastasis and therapy resistance [2, 3]. Especially high expression levels of extracellular cathepsin B (CatB) indicate poor prognosis in neoplastic diseases, making CatB an interesting target for functional characterization of cancers by activity-based molecular imaging. It is our aim to develop such an imaging probe for CatB by combination of a polyarginine-based, activatable cell-penetrating peptide [4] (ACPP) and an optimised endopeptidase substrate for CatB. Substrate optimisation proofed to be challenging as two entirely opposite factors needed to be balanced – high stability against serum proteases to prevent premature cleavage of the activation sequence, while retaining efficient and specific endoproteolytic cleavability by CatB. We have generated a CatB-endoprotease substrate by C-terminally elongating the CatB carboxydipeptidase substrate Abz GIVR*AK(Dnp) OH [5] (Abz – amino-benzoyl, Dnp – dinitrophenyl, * – cleavage site) to the octapeptide Abz GIVR*AK(Dnp)GX CONH2, which could be used as activation site in the final ACPP. Introduction of any amino acid other than glycine at the P4’ position resulted in hysteretic kinetics for the CatB-catalysed hydrolysis of the octapeptides, which might indicate the displacement of the occluding loop from the active site upon interaction with the substrates. Using LC-ESI-MS-based analysis of serum-incubated substrates, the positions P1 and P3’ where determined to be primary determinants of serum stability. After suppression of the P3’ instability by Nα-methylation and optimisation within the positions P1-P3, we were able to increase serum half-life from < 5 min to > 24 h under concomitant improvement of kinetic substrate efficiency towards CatB. Based on this optimised CatB-endopeptidase substrate, we have synthesised a fluorescently labelled ACPP with which we were able to demonstrate CatB-dependent uptake and subsequent nucleolar accumulation of the activated peptide in human U87 MG glioma cells. Radiolabelling of the probe with copper-64 was enabled by conjugating the ACPP to NODAGA as chelating moiety. Its evaluation in vivo using PET imaging is under current investigation.

[1] Yang et al., Cancer Growth Metastasis 2009, 2, 13
[2] Aggarwal and Sloane, Proteomics Clin. Appl. 2014, 8, 427
[3] Löser and Pietzsch, Front. Chem. 2015, 3, article 37
[4] Jiang et al., PNAS, 2004, 101, 17867
[5] Cotrin et al., Anal. Biochem. 2004, 335, 244
  • Poster
    Frontiers in Medicinal Chemistry, 24.-27.03.2019, Würzburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-29159
Publ.-Id: 29159


Optical properties of ZnSxTe1-x synthesized by sulfur implantation

Zhang, X.; Xu, M.; Li, Q.; Wang, M.ORC; Akhmadaliev, S.; Zhou, S.ORC; Wu, Y.; Guo, B.
ZnSxTe1-x thin films were prepared by sulfur implantation into ZnTe grown by molecular beam epitaxy and subsequent pulsed laser melting. The chemical composition and layer thickness of the ZnSxTe1-x layer have been analyzed based on Rutherford backscattering spectrometry. Raman and photoluminescence spectroscopies were employed to reveal the optical properties of the ZnSxTe1-x layer. Raman spectra exhibit a redshift of the longitudinal optical photon modes with increasing sulfur concentration. The room temperature photoluminescence measurement indicates the appearance of the sulfur induced energy state in the bandgap.

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Permalink: https://www.hzdr.de/publications/Publ-29158
Publ.-Id: 29158


Dipeptide-derived Alkynes as Irreversible Inhibitors of Cysteine Cathepsins

Behring, L.; Trapp, C.; Morales, M.; Wodtke, R.; Kuhne, K.; Belter, B.; Pietzsch, J.ORC; Löser, R.
Even though the C-C triple bond is largely considered as a bioinert functional group, two research groups observed the irreversible inhibition of a cysteine protease by an alkyne-functionalised substrate derivative: both EKKEBUS et al. and SOMMER et al. independently described the unexpected inactivation of de-ubiquitinating enzymes by ubiquitin or ubiquitin-like modifiers bearing propargylamine in place of C-terminal glycine by covalent targeting of the active-site cysteine residue [1, 2]. We intended to harness that finding for the design of inhibitor-based probes for the imaging of tumour-associated cysteine proteases.
All 11 human cysteine cathepsins have been linked to tumour progression. Especially high expression levels of the cathepsins B, K, L, S and X are correlated with an increased metastatic potential and poor prognosis. [3] Therefore, those enzymes represent promising targets for the therapy and imaging of tumours.
GREENSPAN et al. reported a potent, highly selective dipeptidyl nitrile-based cathepsin B inhibitor (1, structure shown above) [4]. Based on that lead compound, dipeptide alkynes were designed by isoelectronic replacement of the nitrile nitrogen atom by a methine group (2) and consecutive variation of the 2,4-difluorobenzoyl group and the amino acid-derived side chains. Formation of the C-C triple bond by reaction of the corresponding open-chain serine-derived aldehyde with the Bestmann-Ohira reagent was accompanied by partial enantiomerisation. Therefore, the synthesis was performed via Garner’s aldehyde to ensure high stereochemical purity of the final compounds.
By investigating the inhibitory potential against cathepsin B, S, L and K potent alkyne-based inhibitors were identified for all tested cathepsins, with second-order inactivation constants (kinact/KI) up to 10133 M-1s-1 and interesting selectivity profiles. Based on these promising results and considering their absent indiscriminate thiol reactivity, dipeptidyl alkynes have the potential to be translated into activity-based probes for molecular imaging in vivo. In further studies, selected inhibitors will be labelled with suitable radionuclides such as fluorine-18, which will in turn enable further pharmacological evaluations.
[1] Ekkebus et al., J. Am. Chem. Soc., 2013, 135, 2867-2870.
[2] Sommer et al., Bioorg. Med. Chem., 2013, 21, 2511-2517.
[3] Löser and Pietzsch, Front. Chem., 2015, 3, 37.
[4] Greenspan et al., J. Med. Chem., 2001, 44, 4524-4534.
  • Lecture (Conference)
    Frontiers in Medicinal Chemistry, 24.-27.03.2019, Würzburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-29157
Publ.-Id: 29157


Deciphering the Crystal Structure of a Scarce 1D Polymeric Thorium Peroxo Sulfate

Bonato, L.; Virot, M.; Dumas, T.; Mesbah, A.; Lecante, P.; Prieur, D.ORC; Le Goff, X.; Hennig, C.; Dacheux, N.; Moisy, P.; Nikitenko, S.
The preparation and structural characterization of an original Th peroxo sulfate dihydrate crystallizing at room temperature in the form of stable 1D polymeric microfibers is described. A combination of laboratory and synchrotron techniques allowed to solve the structure of Th(O2)(SO4)(H2O)2 compound which crystallizes in a new structure type in the Pna21 space group of the orthorhombic system. Particularly, peroxide ligand coordinates Th cations in a scarce μ3–η2:η2:η2 bridging mode forming an infinite 1D chain decorated with sulfato ligands exhibiting simultaneously both monodentate and bidentate coordination modes.

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Permalink: https://www.hzdr.de/publications/Publ-29156
Publ.-Id: 29156


Collective flow and correlations measurements with HADES in Au plus Au collisions at 1.23 AGeV

Kardan, B.; Adamczewski-Musch, J.; Arnold, O.; Arnoldi-Meadows, B.; Belounnas, A.; Belyaev, A.; Biernat, J.; Blanco, A.; Blume, C.; Boehmer, M.; Bordalo, P.; Chlad, L.; Chudoba, P.; Ciepal, I.; Deveaux, C.; Dittert, D.; Dreyer, J.; Fabbietti, L.; Fateev, O.; Fonte, P.; Franco, C.; Friese, J.; Froehlich, I.; Galatyuk, T.; Garzon, J. A.; Gernhaeuser, R.; Gillitzer, A.; Golosov, O.; Golubeva, M.; Greifenhagen, R.; Guber, F.; Gumberidze, M.; Harabasz, S.; Heinz, T.; Hennino, T.; Hoehne, C.; Holzmann, R.; Ierusalimov, A.; Ivanov, V.; Ivashkin, A.; Kaempfer, B.; Kajetanowicz, M.; Kampert, K.-H.; Kardan, B.; Khomyakov, V.; Koenig, I.; Koenig, W.; Korcyl, G.; Kornakov, G.; Kornas, F.; Kotte, R.; Kozela, A.; Kubos, J.; Kugler, A.; Kunz, T.; Kurilkin, P.; Kushpil, V.; Ladygin, V.; Lalik, R.; Lebedev, A.; Linev, S.; Lopes, L.; Lorenz, M.; Lykasov, G.; Mahmoud, T.; Malakhov, A.; Markert, J.; Maurus, S.; Metag, V.; Michel, J.; Mihaylov, D. M.; Mikhaylov, V.; Morozov, S.; Muentz, C.; Naumann, L.; Nowakowski, K.; Parpottas, Y.; Patel, V.; Pauly, C.; Pechenov, V.; Pechenova, O.; Pereira, A.; Petousis, V.; Petukhov, O.; Pfeifer, D.; Pietraszko, J.; Prozorov, A. P.; Przygoda, W.; Pysz, K.; Ramos, S.; Ramstein, B.; Reshetin, A.; Ritman, L.; Rodriguez-Ramos, P.; Rost, A.; Salabura, P.; Scheib, T.; Schuldes, H.; Schwab, E.; Scozzi, F.; Seck, F.; Sellheim, P.; Selyuzhenkov, I.; Silva, L.; Smyrski, J.; Sobiella, M.; Spataro, S.; Spies, S.; Strikhanov, M.; Stroebele, H.; Stroth, J.; Strzempek, P.; Svoboda, O.; Szala, M.; Taranenko, A.; Tlusty, P.; Traxler, M.; Troyan, A.; Tsertos, H.; Wagner, V.; Wendisch, C.; Wiebusch, M. G.; Wintz, P.; Wirth, J.; Wloch, B.; Zhilin, A.; Zinchenko, A.; Zumbruch, P.
The HADES experiment provides a large acceptance combined with a high mass resolution and therefore makes it possible to study dielectron and hadron production in heavy-ion collisions with unprecedented precision. With the high statistics of seven billion Au+Au collisions at 1.23 AGeV recorded in 2012 the investigation of collective effects and particle correlations is possible with unprecedented accuracy. We present multi-differential data on directed (v(1)) and elliptic (v(2)) flow, and the first measurement of triangular flow (v(3)), of protons and deuterons.

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Permalink: https://www.hzdr.de/publications/Publ-29155
Publ.-Id: 29155


Multi-differential pattern of low-mass e(+)e(-) excess from root S-NN=2.4 GeV Au+Au collisions with HADES

Harabasz, S.; Adamczewski-Musch, J.; Arnold, O.; Arnoldi-Meadows, B.; Belounnas, A.; Belyaev, A.; Biernat, J.; Blanco, A.; Blume, C.; Boehmer, M.; Bordalo, P.; Chlad, L.; Chudoba, P.; Ciepal, I.; Deveaux, C.; Dittert, D.; Dreyer, J.; Fabbietti, L.; Fateev, O.; Fonte, P.; Franco, C.; Friese, J.; Froehlich, I.; Galatyuk, T.; Garzon, J. A.; Gernhaeuser, R.; Gillitzer, A.; Golosov, O.; Golubeva, M.; Greifenhagen, R.; Guber, F.; Gumberidze, M.; Harabasz, S.; Heinz, T.; Hennino, T.; Hoehne, C.; Holzmann, R.; Ierusalimov, A.; Ivanov, V.; Ivashkin, A.; Kaempfer, B.; Kajetanowicz, M.; Kampert, K.-H.; Kardan, B.; Khomyakov, V.; Koenig, I.; Koenig, W.; Korcyl, G.; Kornakov, G.; Kornas, F.; Kotte, R.; Kozela, A.; Kubos, J.; Kugler, A.; Kunz, T.; Kurilkin, P.; Kushpil, V.; Ladygin, V.; Lalik, R.; Lebedev, A.; Linev, S.; Lopes, L.; Lorenz, M.; Lykasov, G.; Mahmoud, T.; Malakhov, A.; Markert, J.; Maurus, S.; Metag, V.; Michel, J.; Mihaylov, D. M.; Mikhaylov, V.; Morozov, S.; Muentz, C.; Naumann, L.; Nowakowski, K.; Parpottas, Y.; Patel, V.; Pauly, C.; Pechenov, V.; Pechenova, O.; Pereira, A.; Petousis, V.; Petukhov, O.; Pfeifer, D.; Pietraszko, J.; Prozorov, A. P.; Przygoda, W.; Pysz, K.; Ramos, S.; Ramstein, B.; Reshetin, A.; Ritman, L.; Rodriguez-Ramos, P.; Rost, A.; Salabura, P.; Scheib, T.; Schuldes, H.; Schwab, E.; Scozzi, F.; Seck, F.; Sellheim, P.; Selyuzhenkov, I.; Silva, L.; Smyrski, J.; Sobiella, M.; Spataro, S.; Spies, S.; Strikhanov, M.; Stroebele, H.; Stroth, J.; Strzempek, P.; Svoboda, O.; Szala, M.; Taranenko, A.; Tlusty, P.; Traxler, M.; Troyan, A.; Tsertos, H.; Wagner, V.; Wendisch, C.; Wiebusch, M. G.; Wintz, P.; Wirth, J.; Wloch, B.; Zhilin, A.; Zinchenko, A.; Zumbruch, P.
The matter formed in central heavy-ion collisions at a few GeV per nucleon is commonly understood as resonance matter, a gas of nucleons and excited baryon states with a substantial contribution from mesonic, mostly pionic excitations. Yet, in the initial phase of the reaction the system is compressed to beyond nuclear ground state density and hence substantial modifications of the hadron properties are expected to occur. The spectral distribution of virtual photons measured in Au+Au collisions at 2.4 GeV center of mass energy indicates strong medium effects beyond pure superposition of individual NN collisions. We present multi-differential distributions of low-mass electron pairs. This radiation is remarkably well described assuming emission from a thermalized system. To gain deeper understanding of the microscopic origin of the radiation, we extracted the centrality dependent true (not blue-shifted) temperature, its azimuthal distribution, as well as mass-dependent effective slope parameter. Virtual photon spectra are confronted with available model calculations.

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Permalink: https://www.hzdr.de/publications/Publ-29154
Publ.-Id: 29154


Sub-threshold strangeness production measured with HADES

Kornakov, G.; Adamczewski-Musch, J.; Arnold, O.; Arnoldi-Meadows, B.; Belounnas, A.; Belyaev, A.; Biernat, J.; Blanco, A.; Blume, C.; Boehmer, M.; Bordalo, P.; Chlad, L.; Chudoba, P.; Ciepal, I.; Deveaux, C.; Dittert, D.; Dreyer, J.; Fabbietti, L.; Fateev, O.; Fonte, P.; Franco, C.; Friese, J.; Froehlich, I.; Galatyuk, T.; Garzon, J. A.; Gernhaeuser, R.; Gillitzer, A.; Golosov, O.; Golubeva, M.; Greifenhagen, R.; Guber, F.; Gumberidze, M.; Harabasz, S.; Heinz, T.; Hennino, T.; Hoehne, C.; Holzmann, R.; Ierusalimov, A.; Ivanov, V.; Ivashkin, A.; Kaempfer, B.; Kajetanowicz, M.; Kampert, K.-H.; Kardan, B.; Khomyakov, V.; Koenig, I.; Koenig, W.; Korcyl, G.; Kornas, F.; Kotte, R.; Kozela, A.; Kubos, J.; Kugler, A.; Kunz, T.; Kurilkin, P.; Kushpil, V.; Ladygin, V.; Lalik, R.; Lebedev, A.; Linev, S.; Lopes, L.; Lorenz, M.; Lykasov, G.; Mahmoud, T.; Malakhov, A.; Markert, J.; Maurus, S.; Metag, V.; Michel, J.; Mihaylov, D. M.; Mikhaylov, V.; Morozov, S.; Muentz, C.; Naumann, L.; Nowakowski, K.; Parpottas, Y.; Patel, V.; Pauly, C.; Pechenov, V.; Pechenova, O.; Pereira, A.; Petousis, V.; Petukhov, O.; Pfeifer, D.; Pietraszko, J.; Prozorov, A. P.; Przygoda, W.; Pysz, K.; Ramos, S.; Ramstein, B.; Reshetin, A.; Ritman, L.; Rodriguez-Ramos, P.; Rost, A.; Salabura, P.; Scheib, T.; Schuldes, H.; Schwab, E.; Scozzi, F.; Seck, F.; Sellheim, P.; Selyuzhenkov, I.; Silva, L.; Smyrski, J.; Sobiella, M.; Spataro, S.; Spies, S.; Strikhanov, M.; Stroebele, H.; Stroth, J.; Strzempek, P.; Svoboda, O.; Szala, M.; Taranenko, A.; Tlusty, P.; Traxler, M.; Troyan, A.; Tsertos, H.; Wagner, V.; Wendisch, C.; Wiebusch, M. G.; Wintz, P.; Wirth, J.; Wloch, B.; Zhilin, A.; Zinchenko, A.; Zumbruch, P.
At energies below sqrt(sNN) approximate to 2.55 GeV, strange quarks cannot be produced in binary nucleon-nucleon collisions because of the higher production threshold of the lightest hadrons carrying strangeness. Hence, the investigation of sub-threshold strangeness production in heavy-ion collisions is one of the most promising probes, to access the properties of the created system, as the missing energy must be provided by the latter one. For the first time, a nearly complete set of strange particles has been reconstructed in the 40% most central Au+Au collisions at sqrt(sNN) = 2.42 GeV. The data sample includes multi-differential representations of charged and neutral particles containing strangeness (K+,-,Ks0, φ, Λ). To achieve a better understanding of strangeness production the properties of the short-lived resonances have to be investigated. The first steps in this direction are presented here, including the reconstruction of baryon resonances using a new iterative technique, comparison to microscopic transport model calculations and interpretation of the pion transverse momentum distribution.

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Permalink: https://www.hzdr.de/publications/Publ-29153
Publ.-Id: 29153


Ferromagnetic (In,Ga,Mn)As films prepared by ion implantation and pulsed laser melting

Xu, C.ORC; Wang, M.ORC; Zhang, X.; Yuan, Y.; Zhou, S.ORC
In the present work, we show the preparation of (In,Ga,Mn)As films with different Ga concentration by Mn ion implantation and pulsed laser melting. All films are confirmed to be well recrystallized by Rutherford backscattering spectrometry/channeling and to be ferromagnetic by magnetometry measurements, respectively. Their Curie temperatures depend on the Ga concentration. Our results show the perspective of ion implantation in the preparation of different III-Mn-V quaternary alloys as new members of diluted ferromagnetic semiconductors.
Keywords: Thin film, Ion implantation, Pulsed laser melting, III-V compounds

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Permalink: https://www.hzdr.de/publications/Publ-29152
Publ.-Id: 29152


Coupled dissolution-precipitation reactive transport modeling at the pore scale

Karimzadeh, L.; Fischer, C.ORC
Coupled dissolution-precipitation processes are of critical importance for the evolution of porosity and permeability in materials and for multiple applications, such as waste management, reservoir rocks, and corrosion. Here, we study the impact of saturation and fluid flow velocity with high spatial resolution, i.e., in the micrometer to submicrometer scale. Utilizing a time series of datasets of corroded crystal surfaces, collected using interferometry techniques, we analyze the impact of local fluid flow heterogeneity and resulting saturation variability. Systematically, the series of surface data is used (i) to constrain the initial topography for reactive transport modeling, and (ii) to compare the model vs. experimental results.
In this work, a reactive transport model is presented which simulates the complex chemical reaction of mineral dissolution/precipitation and subsequent pore-geometry evolution at a single pore scale [1]. We used the finite element package COMSOL Multiphysics® 5.4 for the simulation, utilizing the arbitary-Lagrangian Eulerian (ALE) method for the free-moving domain boundary.
Experimental and modeling studies have shown both the spatial [2] and temporal [3] heterogeneity of reaction rates and their impact on topography evolution at the pore scale. We expect an improved predictability of reactive transport modeling by using an approach combining the heterogeneities of surface reactivity and flow velocity at the pore scale.


[1] Karimzadeh, L., et al., 2018. Benchmark 3D reactive transport modelling of leaching of fractured calcareous sulfide ores, in: Lottermoser, B.G. (Ed.), Aachen International Mining Symposia (AIMS 2018), Aachen, Germany, p. 88 pp.
[2] Fischer, C., and Luttge, A., 2018, Pulsating dissolution of crystalline matter. PNAS 115.
[3] Fischer, C., Kurganskaya, I., and Luttge, A., 2018, Inherited control of crystal surface reactivity. Applied Geochemistry 91, 140.
  • Poster
    EGU General Assembly 2019, 08.-12.04.2019, Wien, Österreich

Permalink: https://www.hzdr.de/publications/Publ-29151
Publ.-Id: 29151


Improving fracture-flow models by experimental evidence from process tomography

Kulenkampff, J.; Karimzadeh, L.; Jankovsky, F.; Zuna, M.; Havlova, V.; Fischer, C.ORC
Advective fluid flow transport controls the migration of radionuclides in fractured crystalline rocks. Thus, the
safety assessment of deep geological repositories in crystalline rocks relies critically on fracture flow properties
and the reliability of transport modelling approaches. Here, we focus on heterogeneity and complexity of transport
processes, typically of limited predictability. In order to tackle this issue, we suggest experimental observations by
using tomographic methods, as well as feedback with and improvement of existing transport modelling approaches.
As an example, tracer propagation through fractured crystalline rock cores from the Czech Republic (Bukov URL,
depth of 500 m below the surface), was studied in collaboration between HZDR (Germany) and UJV (Czech
Republic). Spatiotemporal data of the tracer concentration during conservative transport are based on positron
emission tomography (PET), and the underlying fracture structure was characterized by microCT-imaging. The latter
yields a structural model for reactive transport modelling. The PET data sequences provide (i) the validation of
existing simulation approaches, and (ii) serve as input or the parameterization of advanced simulation concepts.
First results underscore the outlined approach. In particular, the PET measurements clearly show preferential and
localized pathways, a feature of the process that significantly reduces the effect of interactions at the fracture
surface (and thus retention by adsorption); although repeat experiments are suggesting that the identified pathways
are not constant over the experimental periods.
As a consequence of the combined experimental and simulation approach, we expect (i) advanced model concepts
based on experimental insights and (ii) an improved understanding of reactive transport processes with a focus on
temporal heterogeneity of preferential pathways.
  • Poster
    EGU General Assembly 2019, 08.-12.04.2019, Wien, Österreich

Permalink: https://www.hzdr.de/publications/Publ-29150
Publ.-Id: 29150


Photoconductive germanium antenna emitting broadband THz pulses

Pashkin, O.ORC; Singh, A.ORC; Winnerl, S.; Helm, M.; Schneider, H.ORC
The spectral range between 5 and 10 THz is hardly accessible for time-resolved THz spectroscopy due to strong phonon absorption in many polar materials utilized for the generation of THz transients. We demonstrate that non-polar germanium is a promising semiconductor for a realization of a photoconductive THz emitter with a continuous spectrum spanning well above 10 THz.
  • Invited lecture (Conferences)
    AES 2019, the 7th Advanced Electromagnetics Symposium, 24.-26.07.2019, Lisbon, Portugal

Permalink: https://www.hzdr.de/publications/Publ-29149
Publ.-Id: 29149


A correlation study of layer growth rate, thickness uniformity, stoichiometry, and hydrogen impurity level of ALD grown HfO2 thin films

Blaschke, D.; Munnik, F.ORC; Grenzer, J.; Rebohle, L.ORC; Zahn, P.ORC; Schmidt, H.; Gemming, S.ORC
Hafnium oxide was deposited from tetrakis(dimethylamino)hafnium (TDMAHf) and water by atomic layer deposition (ALD) on heated 400 Si wafers covered with native oxide in the temperature range from 100 C to 350 C. Optimized self-limiting ALD reaction and smallest hydrogen impurity level have been realized for a substrate temperature of 300 C. The stoichiometry of deposited films and hydrogen impurity level were measured by elastic recoil detection analysis. The hafnium to oxygen ratio showed the expected 1:2 value. Besides hydrogen, no other impurities could be detected.
Furthermore, a strong correlation between the growth rate per cycle (GPC), film uniformity and level of hydrogen impurities was observed. Based on this result, the easily accessible GPC can be used as a first indication for the hydrogen impurity level in ALD grown thin films.
Furthermore, the characterization of the crystal structure showed the appearance of some crystallites in an amorphous matrix already for a growth temperature of 250 C and a pure crystalline layer at a growth temperature of 350 C. The increased crystallinity with increasing growth temperature was attributed to a higher seed concentration and a constant crystal size.
Keywords: ALD, TDMAHf, HfO₂, growth rate per cycle, thickness uniformity, ERDA, H impurity level, GIXRD, AFM

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  • Secondary publication expected from 26.11.2020

Permalink: https://www.hzdr.de/publications/Publ-29148
Publ.-Id: 29148


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