Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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34730 Publications

Brain geometry matters in Alzheimer disease progression: a simulation study

Hoore, M.; Kelling, J.; Sayadmanesh, M.; Mitra, T.; Schips, M.; Meyer-Hermann, M.

The Amyloid cascade hypothesis (ACH) for Alzheimer's disease (AD) is modeled over the whole brain tissue with a set of partial differential equations. Our results show that the amyloid plaque formation is critically dependent on the secretion rate of amyloid β(Aβ), which is proportional to the product of neural density and neural activity. Neural atrophy is similarly related to the secretion rate of Aβ. Due to a heterogeneous distribution of neural density and brain activity throughout the brain, amyloid plaque formation and neural death occurs heterogeneously in the brain. The geometry of the brain and microglia migration in the parenchyma bring more complexity into the system and result in a diverse amyloidosis and dementia pattern of different brain regions. Although the pattern of amyloidosis in the brain cortex from in-silico results is similar to experimental autopsy findings, they mismatch at the central regions of the brain, suggesting that ACH is not able to explain the whole course of AD without considering other factors, such as tau-protein aggregation or neuroinflammation.

Keywords: Neurdegenerative disease; Alzheimer's disease; Amyloid cascade hypothesis; mult-phase model

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Permalink: https://www.hzdr.de/publications/Publ-31371
Publ.-Id: 31371


Multiscale Tomographic Analysis for Micron-Sized Particulate Samples

Ditscherlein, R.; Furat, O.; de Langlard, M.; Martins De Souza E. Silva, J.; Sygusch, J.; Rudolph, M.; Leißner, T.; Schmidt, V.; Peuker, U. A.

The three-dimensional characterization of distributed particle properties in the micro- and nanometer range is essential to describe and understand highly specific separation processes in terms of selectivity and yield. Both performance measures play a decisive role in the development and improvement of modern functional materials. In this study, we mixed spherical glass particles (0.4–5.8 μm diameter) with glass fibers (diameter 10 μm, length 18–660 μm) to investigate a borderline case of maximum difference in the aspect ratio and a significant difference in the characteristic length to characterize the system over several size scales. We immobilized the particles within a wax matrix and created sample volumes suitable for computed tomographic (CT) measurements at two different magnification scales (X-ray micro- and nano-CT). Fiber diameter and length could be described well on the basis of the low-resolution micro-CT measurements on the entire sample volume. In contrast, the spherical particle system could only be described with sufficient accuracy by combining micro-CT with high-resolution nano-CT measurements on subvolumes of reduced sample size. We modeled the joint (bivariate) distribution of fiber length and diameter with a parametric copula as a basic example, which is equally suitable for more complex distributions of irregularly shaped particles. This enables us to capture the multidimensional correlation structure of particle systems with statistically representative quantities.

Keywords: multidimensional particle characterization; multiscale X-ray tomography; parametric copula; statistical image analysis

Permalink: https://www.hzdr.de/publications/Publ-31370
Publ.-Id: 31370


Yu-Shiba-Rusinov bands in ferromagnetic superconducting diamond

Zhang, G.; Samuely, T.; Iwahara, N.; Kačmarčík, J.; Wang, C.; May, P. W.; Jochum, J. K.; Onufriienko, O.; Szabó, P.; Zhou, S.; Samuely, P.; Moshchalkov, V. V.; Chibotaru, L. F.; Rubahn, H.-G.

The combination of different exotic properties in materials paves the way for the emergence of their new potential applications. An example is the recently found coexistence of the mutually antagonistic ferromagnetism and superconductivity in hydrogenated boron-doped diamond, which promises to be an attractive system with which to explore unconventional physics. Here, we show the emergence of Yu-Shiba-Rusinov (YSR) bands with a spatial extent of tens of nanometers in ferromagnetic superconducting diamond using scanning tunneling spectroscopy. We demonstrate theoretically how a two-dimensional (2D) spin lattice at the surface of a three-dimensional (3D) superconductor gives rise to the YSR bands and how their density-of-states profile correlates with the spin lattice structure. The established strategy to realize new forms of the coexistence of ferromagnetism and superconductivity opens a way to engineer the unusual electronic states and also to design better-performing superconducting devices.

Related publications

  • Reseach data in the HZDR data repository RODARE
    Publication date: 2020-05-25
    DOI: 10.14278/rodare.341
    License: CC-BY-4.0

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Permalink: https://www.hzdr.de/publications/Publ-31369
Publ.-Id: 31369


Tailoring Magnetic Features in Zigzag-Edged Nanographenes by Controlled Diels–Alder Reactions

Ajayakumar, M.; Fu, Y.; Liu, F.; Komber, H.; Tkachova, V.; Xu, C.; Zhou, S.; Popov, A.; Liu, J.; Feng, X.

Nanographenes (NGs) with tunable electronic and magnetic properties have attracted enormous attention in the realm of carbon-based nanoelectronics. In particular, NGs with biradical character at the ground state are promising building units for molecular spintronics. However, most of the biradicaloids are susceptible to oxidation under ambient conditions and photolytic degradation, which hamper their further applications. Herein, we demonstrated the feasibility of tuning the magnetic properties of zigzag-edged NGs in order to enhance their stability via the controlled Diels–Alder reactions of peri-tetracene (4-PA). The unstable 4-PA (y0=0.72; half-life, t1/2=3 h) was transformed into the unprecedented benzo-peri-tetracenes (BPTs) by a one-side Diels–Alder reaction, which featured a biradical character at the ground state (y0=0.60) and exhibited remarkable stability under ambient conditions for several months. In addition, the fully zigzag-edged circumanthracenes (CAs) were achieved by two-fold or stepwise Diels–Alder reactions of 4-PA, in which the magnetic properties could be controlled by employing the corresponding dienophiles. Our work reported herein opens avenues for the synthesis of novel zigzag-edged NGs with tailor-made magnetic properties.

Related publications

  • Reseach data in the HZDR data repository RODARE
    Publication date: 2020-05-25
    DOI: 10.14278/rodare.343
    License: CC-BY-4.0

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Permalink: https://www.hzdr.de/publications/Publ-31366
Publ.-Id: 31366


HIF2α supports pro-metastatic behavior in pheochromocytomas/paragangliomas

Bechmann, N.; Moskopp, M. L.; Ullrich, M.; Calsina, B.; Wallace, P. W.; Richter, S.; Friedemann, M.; Langton, K.; Fliedner, S. M. J.; Timmers, H. J. L. M.; Nölting, S.; Beuschlein, F.; Fassnacht, M.; Preijbisz, A.; Pacak, K.; Ghayee, H. K.; Bornstein, S. R.; Dieterich, P.; Pietzsch, J.; Wielockx, B.; Robledo, M.; Qin, N.; Eisenhofer, G.

Mutations that drive the stabilization of hypoxia inducible factor 2α (HIF2α) and downstream pseudohypoxic signaling are known to predispose to the development of pheochromocytomas and paragangliomas (PPGLs). However, any role of HIF2α in predisposition to metastatic disease remains unclear. To assess such a role we combined gene-manipulations in pheochromocytoma cell lines with retrospective analyses of patient data and gene expression profiling in tumor specimens. Among 425 patients with PPGLs identified with mutations in tumor-susceptibility genes, those with tumors due to activation of pseudohypoxic pathways had a higher frequency of metastatic disease than those with tumors due to activation of kinase- signaling pathways, even without inclusion of patients with mutations in SDHB (18.6% vs. 4.3% in, p<0.0001). Three out of nine (33%) of patients with gain-of-function mutations in HIF2α had metastatic disease. In cell line studies, elevated expression of HIF2α enhanced cell proliferation and led to increased migration and invasion capacity. Moreover, HIF2α expression in HIF2α-deficient cells resulted in increased cell motility, diffuse cluster formation and emergence of pseudopodia indicating changes in cell adhesion and cytoskeletal remodeling. In a mouse liver metastasis model, HIF2α enhanced the metastatic load. Transcriptomics data revealed alterations in focal adhesion and extracellular matrix-receptor interactions in HIF2α-mutated PPGLs. Our translational findings demonstrate that HIF2α supports pro-metastatic behavior in PPGLs, though other factors remain critical for subsequent transition to metastasis. We identified LAMB1 and COL4A2 as new potential therapeutic targets for HIF2α-driven PPGLs. Identified HIF2α downstream targets might open a new therapeutic window for aggressive HIF2α-expressing tumors.

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  • Secondary publication expected from 14.09.2021

Permalink: https://www.hzdr.de/publications/Publ-31364
Publ.-Id: 31364


Dynamics of Bubble Formation at Micro-orifices under Constant Gas Flow Conditions

Mohseni, E.; Jose Kalayathine, J.; Reinecke, S.; Hampel, U.

Fine gas dispersion into a liquid is requested in a number of industrial applications. One way to achieve fine gas dispersion is to downsize the openings from which gas bubbles are generated. Accordingly, we have investigated the dynamics of bubble formation from submerged orifices ranging from 0.04 to 0.8 mm at a comprehensive range of gas flow rates for a system of air and deionized water. In this range of orifice size, we observe a different mechanism of bubble formation compared with millimeter-range orifices. We discuss the observations on the basis of temporal change of the bubble shape, bubble base expansion, and detachment criteria. At submillimeter orifices, the mechanism of bubble formation is highly influenced by the capillary pressure and the gas kinetic energy. The latter results in congregation of small bubbles in the vicinity of the orifice, even at very small gas flow rates. Moreover, we studied the evolution of individual forces applied to the surface of bubbles during their formation. We have found that the formation of bubbles at submillimeter orifices cannot be described with a quasi-static force balance. Finally, we present a bubbling regime map using relevant dimensionless numbers.

Keywords: Bubble Formation; Submillimeter Orifices; Bubbling Regime; Bubbling Dynamics; Stainless Steel Orifice

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Permalink: https://www.hzdr.de/publications/Publ-31363
Publ.-Id: 31363


Sorption of Europium on Diatom Biosilica as Model of a “Green” Sorbent for f-Elements

Kammerlander, K. K. K.; Köhler, L.; Huittinen, N. M.; Bok, F.; Steudtner, R.; Oschatz, C.; Vogel, M.; Stumpf, T.; Brunner, E.

Removing f-elements from anthropogenically contaminated sites is a challenging, but ecologically important task. Some of these elements are not only radioactive, but also chemically toxic and can spread through various pathways in the environment. The present work investigates f-element sorption on biogenic silica, which may be a promising “green” material for remediation. Commercially available diatomaceous earth (DE) and the cleaned cell walls of the diatom species Stephanopyxis turris (S.t.) and Thalassiosira pseudonana (T.p.) are compared with artificial mesocellular foam (MCF) as porous silica reference material. Trivalent europium was chosen as model sorptive for chemically similar trivalent actinides. Accordingly, Eu(III) in concentrations of 10-3 M and 10-5 M was sorbed on the four silica materials at varying pH values. The zeta potentials of the implemented sorbents under the same conditions were determined. With time-resolved laser-induced fluorescence spectroscopy (TRLFS), two different uptake mechanisms can be discerned, surface adsorption and incorporation/precipitation.

Keywords: biosilica; diatoms; europium; fluorescence; sorption

Permalink: https://www.hzdr.de/publications/Publ-31362
Publ.-Id: 31362


Magnetocaloric effect in GdNi2 for cryogenic gas liquefaction studied in magnetic fields up to 50 T

Taskaev, S.; Khovaylo, V.; Skokov, K.; Liu, W.; Bykov, E.; Ulyanov, M.; Bataev, D.; Basharova, A.; Kononova, M.; Plakhotskiy, D.; Bogush, M.; Gottschall, T.; Gutfleisch, O.

Natural gases have played a significant role in different sectors of the global economy. Recent analyses have shown that the world’s gas consumption doubled over the last three decades; further growth of the gas consumption is predicted, rising to be 23%–28% of the total primary energy demand by 2030. Therefore, liquefaction of natural gases rapidly gains global importance. In this context, magnetic refrigeration emerges as a modern energy-saving technique, which is an alternative to the traditional gas-compression refrigeration. This paper is devoted to the study of the magnetocaloric effect in magnetic fields up to 10 T on a representative of the Laves phase alloys, GdNi2, which is considered as a perspective material for liquefaction of natural gases. For a magnetic field change of 10 T, the magnetic entropy change ΔSm≈−17 J/kg K and the adiabatic temperature change ΔTad ≈ 6.8 K was attained around Curie temperature TC = 70 K. The maximal value of the adiabatic temperature change measured directly in pulsed magnetic fields up to 50 T is ΔTad ≈ 15 K.

Permalink: https://www.hzdr.de/publications/Publ-31361
Publ.-Id: 31361


Effect of uniaxial stress on the electronic band structure of NbP

Schindler, C.; Noky, J.; Schmidt, M.; Felser, C.; Wosnitza, J.; Gooth, J.

The Weyl semimetal NbP exhibits a very small Fermi surface consisting of two electron and two hole pockets, whose fourfold degeneracy in k space is tied to the rotational symmetry of the underlying tetragonal crystal lattice. By applying uniaxial stress, the crystal symmetry can be reduced, which successively leads to a degeneracy lifting of the Fermi-surface pockets. This is reflected by a splitting of the Shubnikov–de Haas frequencies when the magnetic field is aligned along the c axis of the tetragonal lattice. In this study, we present the measurement of Shubnikov–de Haas oscillations of single-crystalline NbP samples under uniaxial tension, combined with state-of-the-art calculations of the electronic band structure. Our results show qualitative agreement between calculated and experimentally determined Shubnikov–de Haas frequencies, demonstrating the robustness of the band-structure calculations upon introducing strain. Furthermore, we predict a significant shift of the Weyl points with increasing uniaxial tension, allowing for an effective tuning to the Fermi level at only 0.8% of strain along the a axis.

Permalink: https://www.hzdr.de/publications/Publ-31360
Publ.-Id: 31360


Adding CUDA® Support to Cling: JIT Compile to GPUs

Ehrig, S.; Hübl, A.; Naumann, A.; Vassilev, V.

Jupyter Notebooks are omnipresent in the modern scientist's and engineer's toolbox just as CUDA C++ is in accelerated computing. We present the first implementation of a CUDA C++ enabled read-eval-print-loop (REPL) that allows to interactively "script" the popular CUDA C++ runtime syntax in Notebooks. With our novel implementation, based on LLVM, Clang and CERN's C++ interpreter Cling, the modern CUDA C++ developer can work as interactively and productively as (I)Python developers while keeping all the benefits of the vast C++ computing and library ecosystem coupled with first-class performance.

Keywords: Cling; CUDA; Jupyter Notebook; interactive C++; LLVM; interactive simulation; rapid prototyping

  • Open Access Logo Lecture (Conference) (Online presentation)
    2020 Virtual LLVM Developers' Meeting, 06.-08.10.2020, Virtuell, USA

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Permalink: https://www.hzdr.de/publications/Publ-31357
Publ.-Id: 31357


Vacancy-solute clustering in Fe-Cr alloys after neutron irradiation

Konstantinovic, M. J.; Ulbricht, A.; Brodziansky, T.; Castin, N.; Malerba, L.

Origin-files, data for figure 3 and figure 4 of publication in J. Nucl. Mater.

Keywords: Neutron irradiation, FeCr alloys and steels

Related publications

  • Reseach data in the HZDR data repository RODARE
    Publication date: 2020-07-21
    DOI: 10.14278/rodare.400
    License: CC-BY-4.0

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Permalink: https://www.hzdr.de/publications/Publ-31356
Publ.-Id: 31356


Evaluation of Recyclability of a WEEE Slag by Means of Integrative X-Ray Computer Tomography and SEM-Based Image Analysis

Buchmann, M.; Borowski, N.; Leißner, T.; Heine, T.; Reuter, M.; Friedrich, B.; Peuker, U. A.

Waste of electrical and electronic equipment (WEEE) is one of the fastest growing waste streams globally. Therefore, recycling of the valuable metals of this stream plays a vital role in establishing a circular economy. The smelting process of WEEE leads to significant amounts of valuable metals and rare earth elements (REEs) trapped in the slag phase. The effective manipulation of this phase transfer process necessitates detailed understanding and effective treatment to minimize these contents. Furthermore, an adequate process control to bring these metal contents into structures that make recycling economically applicable is required. Within the present study, a typical slag from a WEEE melting process is analyzed in detail. Therefore, the material is investigated with the help of X-ray computed tomography (XCT) and scanning electron microscopy (SEM)-based mineralogical analysis (MLA) to understand the typical structures and its implications for recycling. The influencing factors are discussed, and further processing opportunities are illustrated.

Keywords: waste of electrical and electronic equipment; X-ray computed tomography; mineral liberation analysis

Permalink: https://www.hzdr.de/publications/Publ-31355
Publ.-Id: 31355


Spectral X-ray Computed Micro Tomography: 3-dimensional chemical imaging

Sittner, J.; Da Assuncao Godinho, J. R.; Renno, A.; Cnudde, V.; Boone, M.; de Schryver, T.; van Loo, D.; Merkulova, M.; Roine, A.; Liipo, J.

We present a new approach to 3-dimensional chemical imaging based on computed tomography (CT), which allows a reconstruction of the internal elemental chemistry. The method uses a conventional laboratory based CT scanner combined with a semiconductor detector (CdTe). Based on the X-ray absorption spectrum, elements in a sample can be distinguished by their K-edge energy, which is specific. Different experiments have been preformed to test the performance of the system i.e. single pure element particle measurements, element differentiation in mixtures, and mineral differentiation in a gold ore sample. The results show that the method is able to distinguish elements in the samples with K-edges in the range of 20 to 160 keV, which corresponds to an elemental range from Ag to U. Furthermore, the spectral information allows a distinction between materials, which show no variation in contrast in the reconstructed CT image.

Keywords: X-ray computed tomography; Spectral X-ray tomography; Photon counting detector; 3D imaging

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Permalink: https://www.hzdr.de/publications/Publ-31354
Publ.-Id: 31354


CFD Modeling and Experimental Validation of Top-Submerged-Lance Gas Injection in Liquid Metal

Reuter, M. A.; Akashi, M.; Kriebitzsch, S.; Meyer, B.; Obiso, D.; Eckert, S.; Richter, A.

In the present work, the dynamics of a downward gas injection into a liquid metal bath is studied using a numerical modeling approach, and validated with experimental data. As in a top-submerged-lance (TSL) smelter, gas is injected through the lance into the melt. By this means, the properties of the liquid are closer to the actual industrial process than the typically used water/glycerol–air/helium systems. The experimental activity was carried out in a quasi-2D vessel (144 x 144 x 12 mm3) filled with GaInSn, a metal alloy with eutectic at room temperature. Ar was used as the inert gas. The structure and behavior of the gas phase were visualized and quantitatively analyzed by X-ray radiography and high-speed imaging. Computational Fluid Dynamics (CFD) was applied to simulate the multiphase flow in the vessel and the Volume Of Fluid (VOF) model chosen to track the interface using a geometric reconstruction of the interface. Three different vertical lance positions were investigated, applying a gas flow rate of Qgas = 6850 cm³/min: The CFD model is able to predict the bubble detachment frequency, the average void fraction distributions, and the bubble size and hydrodynamic behavior, demonstrating its applicability to simulate such complex multiphase systems. The use of numerical models also provides a deep insight into fluid dynamics to study particular phenomena such as bubble break-up and free surface oscillations.

Keywords: top-submerged-lance (TSL),; X-ray,; Computational Fluid Dynamics (CFD),; Volume Of Fluid (VOF),

Permalink: https://www.hzdr.de/publications/Publ-31353
Publ.-Id: 31353


Engineering telecom single-photon emitters in silicon for scalable quantum photonics

Hollenbach, M.; Berencen, Y.; Kentsch, U.; Helm, M.; Astakhov, G.

We create and isolate single-photon emitters with a high brightness approaching 10⁵ counts per second in commercial silicon-on-insulator (SOI) wafers. The emission occurs in the infrared spectral range with a spectrally narrow zero phonon line in the telecom O-band and shows a high photostability even after days of continuous operation. The origin of the emitters is attributed to one of the carbon-related color centers in silicon, the so-called G center, allowing purification with the ¹²C and ²⁸Si isotopes. Furthermore, we envision a concept of a highly-coherent scalable quantum photonic platform, where single-photon sources, waveguides and detectors are integrated on the same SOI chip. Our results provide a route towards the implementation of quantum processors, repeaters and sensors compatible with the present-day silicon technology.

Keywords: Signe photon source; telecommunication window; silicon photonics; quantum communication; color centers

Permalink: https://www.hzdr.de/publications/Publ-31352
Publ.-Id: 31352


Investigation of inter-fraction target motion variations in the context of pencil beam scanned proton therapy in non-small cell lung cancer patients

Den Otter, L. A.; Anakotta, R. M.; Weessies, M.; Roos, C. T. G.; Sijtsema, N. M.; Muijs, C. T.; Dieters, M.; Wijsman, R.; Troost, E. G. C.; Richter, C.; Meijers, A.; Langendijk, J. A.; Both, S.; Knopf, A.-C.

Purpose: For locally advanced-stage non-small cell lung cancer (NSCLC), inter-fraction target motion variations during the whole time span of a fractionated treatment course are assessed in a large and representative patient cohort. The primary objective is to develop a suitable motion monitoring strategy for pencil beam scanning proton therapy (PBS-PT) treatments of NSCLC patients during free breathing. Methods: Weekly 4D computed tomography (4DCT; 41 patients) and daily 4D cone beam computed tomography (4DCBCT; 10 of 41 patients) scans were analyzed for a fully fractionated treatment course. Gross tumor volumes (GTVs) were contoured and the 3D displacement vectors of the centroid positions were compared for all scans. Furthermore, motion amplitude variations in different lung segments were statistically analyzed. The dosimetric impact of target motion variations and target motion assessment was investigated in exemplary patient cases. Results: The median observed centroid motion was 3.4 mm (range: 0.2–12.4 mm) with an average variation of 2.2 mm (range: 0.1–8.8 mm). Ten of 32 patients (31.3%) with an initial motion <5 mm increased beyond a 5-mm motion amplitude during the treatment course. Motion observed in the 4DCBCT scans deviated on average 1.5 mm (range: 0.0–6.0 mm) from the motion observed in the 4DCTs. Larger motion variations for one example patient compromised treatment plan robustness while no dosimetric influence was seen due to motion assessment biases in another example case. Conclusions: Target motion variations were investigated during the course of radiotherapy for NSCLC patients. Patients with initial GTV motion amplitudes of < 2 mm can be assumed to be stable in motion during the treatment course. For treatments of NSCLC patients who exhibit motion amplitudes of > 2 mm, 4DCBCT should be considered for motion monitoring due to substantial motion variations observed. ©2020 The Authors. Medical Physics published by Wiley Periodicals LLC on behalf of American Association of Physicists in Medicine.

Keywords: free breathing; lung cancer; moving target; spencil beam scanning proton therapy; inter-fractional motion monitoring

Permalink: https://www.hzdr.de/publications/Publ-31350
Publ.-Id: 31350


Adenosine/A2B Receptor Signaling Ameliorates the Effects of Aging and Counteracts Obesity

Gnad, T.; Navarro, G.; Lahesmaa, M.; Reverte-Salisa, L.; Copperi, F.; Cordomi, A.; Naumann, J.; Hochh€Auser, A.; Haufs-Brusberg, S.; Wenzel, D.; Suhr, F.; Zenius Jespersen, N.; Scheele, C.; Tsvilovskyy, V.; Brinkmann, C.; Rittweger, J.; Dani, C.; Kranz, M.; Deuther-Conrad, W.; Eltzschig, H. K.; Niemi, T.; Taittonen, M.; Brust, P.; Nuutila, P.; Pardo, L.; Fleischmann, B. K.; Bleuher, M.; Franco, R.; Bloch, W.; Virtanen, K. A.; Pfeifer, A.

The combination of aging populations with the obesity pandemic results in an alarming rise in non-communicable diseases. Here, we show that the enigmatic adenosine A2B receptor (A2B) is abundantly expressed in skeletal muscle (SKM) as well as brown adipose tissue (BAT) and might be targeted to counteract age-related muscle atrophy (sarcopenia) as well as obesity. Mice with SKM-specific deletion of A2B exhibited sarcopenia, diminished muscle strength, and reduced energy expenditure (EE), whereas pharmacological A2B activation counteracted these processes. Adipose tissue-specific ablation of A2B exacerbated age-related processes and reduced BAT EE, whereas A2B stimulation ameliorated obesity. In humans, A2B expression correlated with EE in SKM, BAT activity, and abundance of thermogenic adipocytes in white fat. Moreover, A2B agonist treatment increased EE from human adipocytes, myocytes, and muscle explants. Mechanistically, A2B forms heterodimers required for adenosine signaling. Overall, adenosine/A2B signaling links muscle and BAT and has both anti-aging and anti–obesity potential.

Permalink: https://www.hzdr.de/publications/Publ-31349
Publ.-Id: 31349


Advanced flow profiler for two-phase flow imaging on distillation trays

Vishwakarma, V.; Schleicher, E.; Bieberle, A.; Schubert, M.; Hampel, U.

A profound knowledge of the two-phase cross-flow on large-scale distillation trays is pivotal to their efficient design and operation. For such trays, a novel flow profiler comprising of multiple dual-tip probes for simultaneous local conductivity measurements is proposed in this work. The profiler is applied for a DN800 air/water column simulator equipped with sieve trays. 3D distribution of liquid holdup and tracer-based liquid flow in the two-phase dispersion are assessed in high resolution. Non-uniform holdup is found along the dispersion height. Contrarily, the liquid flow is largely uniform and symmetric with respect to the tray centerline. Prior to measurements, the profiler design, electronic scheme, measurement principle and data processing schemes are described.

Keywords: column tray; two-phase cross-flow; 3D flow imaging; conductivity measurement; liquid holdup; tracer dispersion

Permalink: https://www.hzdr.de/publications/Publ-31348
Publ.-Id: 31348


Numerical study of the appearance of short-circuits in liquid metal batteries

Benard, S.

The report gives an overview on small-scale interface instabilities in liquid metal batteries.

  • Other
    École normale supérieure Paris-Saclay, 2020

Permalink: https://www.hzdr.de/publications/Publ-31347
Publ.-Id: 31347


Magnetoelectric coupling in a frustrated spinel studied using high-field scanning probe microscopy

Rossi, L.; Brüning, D.; Ueda, H.; Scurschii, I.; Lorenz, T.; Bryant, B.

Below its Neél temperature, the frustrated magnet CdCr2O4 exhibits an antiferromagnetic spin-spiral ground state. Such states can give rise to a sizable magnetoelectric coupling. In this report, we measure the electric polarization induced in single-crystalline CdCr2O4 by large applied magnetic field. Because the detection of a macroscopic polarization is hindered by the structural domains in the tetragonal spin-spiral phase, we have pioneered an alternative method of measuring polarization induced by high magnetic fields, using electrostatic force microscopy. This method enables us to measure polarization from nanoscale areas of the sample surface, as well as imaging how charge inhomogeneities change with magnetic field.

Permalink: https://www.hzdr.de/publications/Publ-31346
Publ.-Id: 31346


A comprehensive study of the sorption mechanism and thermodynamics of f-element sorption onto K-feldspar

Neumann, J.; Brinkmann, H.; Britz, S.; Lützenkirchen, J.; Bok, F.; Stockmann, M.; Brendler, V.; Stumpf, T.; Schmidt, M.

The mobility of heavy metal contaminants and radionuclides in the environment is directly controlled by their interactions with charged mineral surfaces, hence an assessment of their potential toxicity, e.g. in the context of nuclear waste disposal sites, requires understanding of sorption processes on the molecular level. Here, we investigate the sorption of a variety of rare earth elements (REE) and trivalent actinides (Am, Cm) on K-feldspar using batch sorption and column transport experiments, time-resolved laser-induced fluorescence spectroscopy (TRLFS), and a surface complexation model. Initially, a reliable pKa for K-feldspar’s surface deprotonation reaction was determined as 2.5 ± 0.02, in excellent agreement with a measured pHIEP of 2.8. Batch sorption experiments over a broad range of experimental conditions in terms of mineral grain size, pH, [M3+], ionic radius, solid/liquid ratio, ionic strength, and equilibration procedures were carried out to quantify macroscopic immobilization. Similar pH-dependent uptake behavior was found for all investigated trivalent REE and actinides. In parallel, spectroscopic investigations provided insight into surface speciation. Cm TRLFS spectra indicate the formation of three inner-sphere sorption complexes with increasing hydrolysis. Additionally, a ternary K-feldspar/Cm/silicate complex was found for pH > 10, and batch and spectroscopic data at low pH (< 4) point to small amounts of outer sphere sorption complexes. Based on TRLFS data, batch sorption, and titration data, a generic geochemical sorption model was developed, that describes sorption edges for all investigated M3+/K-feldspar systems satisfactorily. The derived stability constants for the binary sorption complexes (logK1-4 = −3.6, −7.7, −11.5, and −17.4, respectively) are in good agreement with previous studies on similar systems, and could successfully be used to reproduce literature data. The stability constants obtained for the surface complexes were included into the database for the Smart Kd-concept, which will further improve the safety assessment of potential repositories for radioactive waste.

Keywords: sorption; trivalent metal ions; actinides; K-feldspar; surface complexation model; TRLFS

Permalink: https://www.hzdr.de/publications/Publ-31345
Publ.-Id: 31345


Vacancy-solute clustering in Fe-Cr alloys after neutron irradiation

Konstantinovic, M. J.; Ulbricht, A.; Brodziansky, T.; Castina, N.; Malerba, L.

Vacancy-solute clustering in neutron irradiated Fe-Cr alloys with various concentrations of Cr and minor solutes (Ni, Si and P) were studied by using
coincidence Doppler broadening spectroscopy and small angle neutron scattering techniques. The results from both experiments, supported by an object kinetic Monte Carlo model, show in a very consistent way the existence and formation of vacancy-CrNiSiP clusters that play detrimental role in irradiation hardening. Similar solute cluster number density of about 30 to 50 x10^16cm-3 and an average diameter of about 1 nm were estimated for all alloys containing minor solutes, irrespectively of the chromium content. In Fe9Cr ferritic and Fe9Cr ferritic/martensitic alloys, with significantly reduced concentration of minor solute elements, the main defects are vacancy clusters, with an average cluster size size of about 10 and 2 vacancies, respectively. Large concentration of alpha'-precipitates was observed in Fe14Cr(NiSiP). However, both vacancy clusters and alpha'-precipitates provide significantly less impact to hardening in comparison to vacancy-CrNiSiP clusters. The fact that vacancy clustering in Fe9Cr ferritic alloy resembles that of pure iron suggests that Cr solutes may play lesser role in irradiation hardening of ferritic alloys and steels than previously believed.

Keywords: Neutron irradiation; FeCr alloys; Steels

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  • Secondary publication expected from 24.07.2021

Permalink: https://www.hzdr.de/publications/Publ-31344
Publ.-Id: 31344


Uranium(VI) toxicity in tobacco BY-2 cell suspension culture - a physiological study

Rajabi, F.; Jessat, J.; Garimella, J. N.; Bok, F.; Steudtner, R.; Stumpf, T.; Sachs, S.

For the first time, the physiological and cellular responses of Nicotiana tabacum (BY-2) cells to uranium (U) as an abiotic stressor was studied in a multi analytic approach combining biochemical analysis, thermodynamic modeling and spectroscopic studies. It was focused on the determination of the U threshold toxicity in tobacco BY-2 cells, the influence of U on the homeostasis of micro-macro essential nutrients as well as the effect of Fe starvation on U bioassociation in cultured BY-2 cells. Our findings showed that U interferes with the homeostasis of essential elements. The interaction of U with BY-2 cells showed a time and concentration dependent kinetic. Under Fe deficiency, less U was detected in the cells compared to Fe sufficient conditions. Interestingly, blocking of Ca channels by gadolinium chloride caused a decrease in U concentration in BY-2 cells. Spectroscopic studies evidenced changes in the U speciation in the culture media with increasing exposure time under Fe sufficient and deficient conditions. Thusly, different stress response reactions related to the Fe metabolism are assumed. It is suggested that U toxicity in BY-2 cells is highly dependent on the existence of other micro-macro elements as showed by negative synergistic effects of U and Fe on the viability of cells.

Keywords: Nicotiana tabacum cells; uranium; toxicity; physiology; bioavailability; Fe starvation; speciation; plants; plant cells

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  • Secondary publication expected from 14.01.2022

Permalink: https://www.hzdr.de/publications/Publ-31343
Publ.-Id: 31343


Band Bending and Valence Band Quantization at Line Defects in MoS2

Murray, C.; van Efferen, C.; Jolie, W.; Fischer, J. A.; Hall, J.; Rosch, A.; Krasheninnikov, A.; Komsa, H.-P.; Michely, T.

The variation of the electronic structure normal to 1D defects in quasi-freestanding MoS2, grown by molecular beam epitaxy, is investigated through high resolution scanning tunneling spectroscopy at 5K. Strong upward bending of valence and conduction bands toward the line defects is found for the 4|4E mirror twin boundary and island edges but not for the 4|4P mirror twin boundary. Quantized energy levels in the valence band are observed wherever upward band bending takes place. Focusing on the common 4|4E mirror twin boundary, density functional theory calculations give an estimate of its charging, which agrees well with electrostatic modeling. We show that the line charge can also be assessed from the filling of the boundary-localized electronic band, whereby we provide a measurement of the theoretically predicted quantized polarization charge at MoS2 mirror twin boundaries. These calculations elucidate the origin of band bending and charging at these 1D defects in MoS2. The 4|4E mirror twin boundary not only impairs charge transport of electrons and holes due to band bending, but holes are additionally subject to a potential barrier, which is inferred from the independence of the quantized energy landscape on either side of the boundary.

Keywords: 2D materials; Line defects; first-principles calculations

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  • Secondary publication expected from 30.06.2021

Permalink: https://www.hzdr.de/publications/Publ-31342
Publ.-Id: 31342


Strain robust spin gapless semiconductors/half-metals in transition metal embedded MoSe2 monolayer

Yang, Q.; Kou, L.; Hu, X.; Wang, Y.; Lu, C.; Krasheninnikov, A.; Sun, L.

The realization of spin gapless semiconductor (SGS) and half-metal (HM) behavior in two-dimensional (2D) transition metal (TM) dichalcogenides is highly desirable for their applications in spintronic devices. Here, using density functional theory calculations, we demonstrate that Fe, Co, Ni substitutional impurities can not only induce magnetism in MoSe2 monolayer, but also convert the semiconducting MoSe2 to SGS/HM system. We also study the effects of mechanical strain on the electronic and magnetic properties of the doped monolayer. We show that for all TM impurities we considered, the system exhibits the robust SGS/HM behavior regardless of biaxial strain values. Moreover, it is found that the magnetic properties of TM–MoSe2 can effectively be tuned under biaxial strain by controlling the spin polarization of the 3d orbitals of Fe, Co, Ni atoms. Our findings offer a new route to designing the SGS/HM properties and modulating magnetic characteristics of the TM–MoSe2 system and may also facilitate the implementation of SGS/HM behavior and realization of spintronic devices based on other 2D materials.

Keywords: 2D materials; first-principles simulations; magnetism

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  • Secondary publication expected from 17.06.2021

Permalink: https://www.hzdr.de/publications/Publ-31341
Publ.-Id: 31341


Reversible crystalline-to-amorphous phase transformation in monolayer MoS under grazing ion irradiation

Valerius, P.; Kretschmer, S.; V. Senkovskiy, B.; Wu, S.; Hall, J.; Herman, A.; Ehlen, N.; Ghorbani Asl, M.; Grüneis, A.; Krasheninnikov, A.; Michely, T.

By combining scanning tunneling microscopy, low-energy electron diffraction, photoluminescence and Raman spectroscopy experiments with molecular dynamics simulations, a comprehensive picture of the structural and electronic response of a monolayer of MoS2 to 500 eV Xe+ irradiation is obtained. The MoS2 layer is epitaxially grown on graphene/Ir(1 1 1) and analyzed before and after irradiation in situ under ultra-high vacuum conditions. Through optimized irradiation conditions using low-energy ions with grazing trajectories, amorphization of the monolayer is induced already at low ion fluences of 1.5 × 1014 ions cm−2 and without inducing damage underneath the MoS2 layer. The crystalline-to-amorphous transformation is accompanied by changes in the electronic properties from semiconductor-to-metal and an extinction of photoluminescence. Upon thermal annealing, the re-crystallization occurs with restoration of the semiconducting properties, but residual defects prevent the recovery of photoluminescence.

Keywords: 2D materilas; irradiation; atomistic simulations; defects

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Permalink: https://www.hzdr.de/publications/Publ-31340
Publ.-Id: 31340


Increasing the Diversity and Understanding of Semiconductor Nanoplatelets by Colloidal Atomic Layer Deposition

Reichhelm, A.; Hübner, R.; Damm, C.; Nielsch, K.; Eychmüller, A.

Nanoplatelets (NPLs) are a remarkable class of quantum confined materials with size-dependent optical properties, which are determined by the defined thickness of the crystalline platelets. To increase the variety of species, the colloidal atomic layer deposition method is used for the preparation of increasingly thicker CdSe NPLs. By growing further crystalline layers onto the surfaces of 4 and 5 monolayers (MLs) thick NPLs, species from 6 to 13 MLs are achieved. While increasing the thickness, the heavy-hole absorption peak shifts from 513 to 652 nm, leading to a variety of NPLs for applications and further investigations. The thickness and number of MLs of the platelet species are determined by high-resolution transmission electron microscopy (HRTEM) measurements, allowing the interpretation of several contradictions present in the NPL literature. In recent years, different assumptions are published, leading to a lack of clarity in the fundamentals of this field. Regarding the ongoing scientific interest in NPLs, there is a certain need for clarification, which is provided in this study.

Keywords: CdSe; colloidal atomic layer deposition; nanoplatelets

Permalink: https://www.hzdr.de/publications/Publ-31339
Publ.-Id: 31339


Unraveling Structure and Device Operation of Organic Permeable Base Transistors

Darbandy, G.; Dollinger, F.; Formánek, P.; Hübner, R.; Resch, S.; Roemer, C.; Fischer, A.; Leo, K.; Kloes, A.; Kleemann, H.

Organic permeable base transistors (OPBTs) are of great interest for flexible electronic circuits, as they offer very large on-current density and a record-high transition frequency. They rely on a vertical device architecture with current transport through native pinholes in a central base electrode. This study investigates the impact of pinhole density and pinhole diameter on the DC device performance in OPBTs based on experimental data and TCAD simulation results. A pinhole density of NPin = 54 μm−2 and pinhole diameters around LPin = 15 nm are found in the devices. Simulations show that a variation of pinhole diameter and density around these numbers has only a minor impact on the DC device characteristics. A variation of the pinhole diameter and density by up to 100% lead to a deviation of less than 4% in threshold voltage, on/off current ratio, and sub-threshold slope. Hence, the fabrication of OPBTs with reliable device characteristics is possible regardless of statistical deviations in thin film formation.

Keywords: organic permeable base transistors; organic electronics; technology computer-aided design simulation

Permalink: https://www.hzdr.de/publications/Publ-31338
Publ.-Id: 31338


Phase coherence and phase jumps in the Schwabe cycle

Stefani, F.; Beer, J.; Giesecke, A.; Gloaguen, T.; Seilmayer, M.; Stepanov, R.; Weier, T.

Guided by the working hypothesis that the Schwabe cycle of solar activity is synchronized by the 11.07 years alignment cycle of the tidally dominant planets Venus, Earth and Jupiter, we reconsider the phase diagrams of sediment accumulation rates in lake Holzmaar, and of methanesulfonate (MSA) data in the Greenland ice core GISP2, which are available for the period 10000-9000 cal. BP. Since some half-cycle phase jumps appearing in the output signals are, very likely, artifacts of applying a biologically substantiated transfer function, the underlying solar input signal with a dominant 11.04 years periodicity can be considered as mainly phase-coherent over the 1000 years period in the early Holocene. For more recent times, we show that the re-introduction of a hypothesized “lost cycle” at the beginning of the Dalton minimum would lead to a real phase jump. Similarly, by analyzing various series of 14C and 10Be data and comparing them with Schove’s historical cycle maxima, we support the existence of another “lost cycle” around 1565, also connected with a real phase jump. Viewed synoptically, our results lend greater plausibility to the starting hypothesis of a tidally synchronized solar cycle, which at times can undergo phase jumps, although the competing explanation in terms of a non-linear solar dynamo with increased coherence cannot be completely ruled out.

Keywords: Solar cycle; Synhcronization

Permalink: https://www.hzdr.de/publications/Publ-31336
Publ.-Id: 31336


Data set on DBTTs from SPT and CVN

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

The data set is related to a manuscript entitled "Use of the small punch test for the estimation of ductile-to-brittle transition temperature shift of irradiated steels". Contents raw data of small punch tests, evaluation data of small punch tests and Charpy impact tests, correlation and regression analysis.

Keywords: small punch test; Charpy impact test; ductile-to-brittle-transition temperature; reactor pressure vessel steel; neutron irradiation

  • Reseach data in the HZDR data repository RODARE
    Publication date: 2020-07-16
    DOI: 10.14278/rodare.396

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Permalink: https://www.hzdr.de/publications/Publ-31334
Publ.-Id: 31334


DGN-Handlungsempfehlung (S1-Leitlinie): PSMA-Liganden-PET/CT in der Diagnostik des Prostatakarzinoms

Afshar-Oromieh, A.; Eiber, M.; Fendler, W.; Schmidt, M.; Rahbar, K.; Ahmadzadehfar, H.; Umutlu, L.; Hadaschik, B.; Hakenberg, O. W.; Formara, P.; Kurth, J.; Neels, O.; Wester, H. J.; Schwaiger, M.; Kopka, K.; Haberkorn, U.; Hermann, K.; Krause, B. J.

Das Ziel der vorliegenden Leitlinie ist es, den Arzt bei der Indikationsstellung, der standardisierten Durchführung, der Interpretation und der Dokumentation der Befunde einer Positronen-Emissions-Tomographie/Computertomographie (PET/CT) mit PSMA-Liganden bei Patienten mit Prostatakarzinom zu unterstützen. Es werden Empfehlungen zu Patientenselektion, Bilderfassung, Interpretation und Befundung ausgesprochen sowie Limitationen der PSMA-Liganden-PET/CT präsentiert. Die Leitlinie basiert auf einer Zusammenführung wissenschaftlicher Veröffentlichungen, Empfehlungen der Autoren und evidenzbasierter Daten.

  • Open Access Logo PSMA-Liganden-PET/CT in der Diagnostik des Prostatakarzinoms 10(2019) 031-055

Permalink: https://www.hzdr.de/publications/Publ-31331
Publ.-Id: 31331


Nature of Magnetic Excitations in the High-Field Phase of α-RuCl3

Ponomaryov, O.; Zviagina, L.; Wosnitza, J.; Lampen-Kelley, P.; Benerjee, A.; Yan, J.-Q.; Bridges, C. A.; Mandrus, D. G.; Nagler, S. E.; Zvyagin, S.

We present comprehensive electron spin resonance (ESR) studies of in-plane oriented single crystals of α-RuCl3, a quasi-two-dimensional material with honeycomb structure, focusing on its high-field spin dynamics. The measurements were performed in magnetic fields up to 16 T, applied along the [110] and [100] directions. Several ESR modes were detected. Combining our findings with recent inelastic neutronand Raman-scattering data, we identified most of the observed excitations. Most importantly, we show that the low-temperature ESR response beyond the boundary of the magnetically ordered region is dominated by single- and two-particle processes with magnons as elementary excitations. The peculiarities of the excitation spectrum in the vicinity of the critical field are discussed.

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Permalink: https://www.hzdr.de/publications/Publ-31328
Publ.-Id: 31328


Earthquake-induced deformation structures in glacial sediments—evidence on fault reactivation and instability at the Vaalajärvi fault in northern Fennoscandia

Ojala, A. E. K.; Mattila, J.; Middleton, M.; Ruskeeniemi, T.; Palmu, J.-P.; Nordbäck, N.; Kirsch, M.; Lorenz, S.; Zimmermann, R.; Andreani, L.; Jackisch, R.; Unger, G.; Gloaguen, R.; Sutinen, R.

Late and postglacial reverse faults and seismically-induced landslides are characteristic features of deglaciated terrain in the northern Fennoscandia. The main focus of this study was to investigate the rupturing history of the reverse Vaalajärvi fault complex in Sodankylä, Finland, based on remote sensing, on-site geophysics and sedimentology in excavations trenched across the faulted terrain. In addition to the previously known NNW–SSE-trending Vaalajärvi segment, we discovered six new SW–NE-trending fault segments that probably belong to the same Vaalajärvi ‘postglacial’ fault complex. Our analysis indicate that the Vaalajärvi fault segment was triggered by stress change caused by ruptures on the surrounding SW–NE-trending reverse faults. In total, at least two to three slip events have taken place in different segments of the Vaalajärvi complex since the Early Weichselian with the most recent event(s) being postglacial in timing. By using the scaling laws of fault surface rupture length and offset and under different scenarios of which segments or systems ruptured in a single or separate event, we estimate that the Vaalajärvi complex potentially hosted an earthquake that ranged between Mw ≈ 6.7–7.0. This magnitude is comparable to the landslide-inferred magnitudes in the Vaalajärvi area.

Keywords: Postglacial fault; Paleoseismology; Moment magnitude; LiDAR; Vaalajärvi; Finland

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  • Secondary publication expected from 21.04.2021

Permalink: https://www.hzdr.de/publications/Publ-31327
Publ.-Id: 31327


Halogen Bonded Assemblies of Arylene-imides and -diimides: Insight from Electronic, Structural and Computational studies

Mandal, K.; Bansal, D.; Kumar, Y.; Khan, R.; Shukla, J.; Mukhopadhyay, P.

Halogen bonding interactions in electron deficient π-scaffolds has largely been underexplored. Herein, we have studied the halogen bonding properties of arylene-imide/-diimide-based electron deficient scaffolds. We probed the influence of: scaffold size, e.g. from small phthalimide (PTMI), moderately-sized pyromelliticdiimide (PMDI) or naphthalenediimides (NDIs) to large perylenediimide (PDI); axial-group modifications; varied number of halogens, etc. on the halogen bonding and its self-assembly in a set of nine molecules. The structural modification leads to tunable optical as well as redox property. Gratifyingly, we realized single crystals of all the nine systems, which revealed Br∙∙∙O, Br∙∙∙Br or Br∙∙∙π halogen bonding interactions, with few systems capable of forming all the three-types. These interactions lead to halogen bonded rings (up to 12-membered), which propagate to form stacked 1D-, 2D- or corrugated sheets. We also identified few outliers, e.g. molecule which prefer C-H∙∙∙O hydrogen bonding over halogen bonding; or a non-centrosymmetric organization over the centrosymmetric ones. Computational studies based on Atoms in Molecules (AIM) and Natural Bond Orbital (NBO) analysis provided
further insight into the halogen bonding interactions. This study can lead to a predictive design tool-box to further explore related systems on surfaces reinforced by these weak directional forces.

Permalink: https://www.hzdr.de/publications/Publ-31326
Publ.-Id: 31326


Benchmarking of Computational Fluid Dynamics Codes for Reactor Vessel Design

Krause, M.; Smith, B.; Höhne, T.; In, W. K.

Computational Fluid Dynamics (CFD) codes have reached a level of maturity, at least for single-phase applications, to be utilized in the design process of Nuclear Power Plant (NPP) components, such that advanced NPPs over the past years have increasingly utilized CFD codes in their design. A recently completed Cooperative Research Project (CRP) addressed the application of CFD codes to the process of optimizing the design of components in Pressurized Water-cooled Reactors (PWRs). Following several initiatives within the IAEA where CFD codes have been applied to situations of interest in nuclear reactor technology, this CRP aimed to contribute to a consistent application of CFD codes by establishing a common platform to assess their capabilities and level of qualification.

Eleven participant organizations from nine Member States performed simulations against four “CFD-grade” experiments performed to investigate key phenomena for CFD simulations. Two are based on test data from the ROCOM (ROssendorf COolant Mixing) facility at HZDR in Germany, and another two are based on rod-bundle experiments in the OFEL (Omni Flow Experimental Loop) facility at KAERI in Korea.

This paper outlines the objectives of the CRP, provides a description of the test facilities and experiments, and discusses selected results obtained for the four above benchmark exercises.

Keywords: Computational Fluid Dynamics; Reactor Design; CFD benchmark

  • Other report
    Wien: IAEA, 2020
    63 Seiten

Permalink: https://www.hzdr.de/publications/Publ-31324
Publ.-Id: 31324


Protecting-Group-Directed Diastereo- and Enantioselective Approach to Substituted Chiral Tetrahydropyrroloquinolines.

Chaudhari, T.; Mallampudi, N.; Bansal, D.; Mohapatra, D.; Tandon, V.

A novel synthetic method for chiral tricyclic tetrahydropyrroloquinolines following a protecting‐group‐directed domino reaction consisting of Michael addition and Mannich cyclization under mild reaction conditions was developed.

Permalink: https://www.hzdr.de/publications/Publ-31323
Publ.-Id: 31323


Evaluation of tube size variations to improve resolution in tube-of-response based image reconstruction for ⁶⁸Ga PET

Maus, J.; Nikulin, P.; Hofheinz, F.; Kotzerke, J.; van den Hoff, J.

Ga68-labeled tracers like Ga68-PSMA or Ga68-DOTATOC play a relevant role in clinical PET, but the substantial positron range of Ga68 (mean/max range in water: 2.7/8 mm) deteriorates spatial resolution. Integration of isotope-specific resolution recovery into iterative reconstruction should therefore be considered. In our in-house PET image reconstruction – THOR – this is possible by adjusting the tube diameter in the used tube-of-response projector. We have, therefore, investigated the potential of tube diameter optimization on achievable image resolution for Ga68.

We performed measurements with a resolution phantom at three different target-to-background ratios (20:1, 10:1, 5:1) for F18 and Ga68, respectively (Philips Ingenuity-TF PET/MR). All measurements were reconstructed with the vendor reconstruction as well as with THOR using different tube diameters and voxel sizes (2mm, 4mm). Image resolution, noise level, and magnitude of Gibbs artifacts (GA) were derived. The optimal tube diameters for F18 and Ga68 were determined respectively and applied to exemplary clinical Ga68 PSMA data.

The vendor reconstruction yields a resolution (FWHM) of [6.7+/-0.2] mm for Ga68 which is ~10% worse than for F18 while THOR yielded [5.0+/-0.4] mm using the default – F18-optimized – tube size which is ~14% worse than for F18. Increasing the tube diameter in THOR by up to 30% is possible for Ga68 (but not for F18) without causing notable GAs. This improves the achieved resolution by ~8% to ~4.6 mm. This is only slightly worse than the THOR result for F18 and much better than the resolution achievable for Ga68 with the vendor reconstruction. First clinical examples also demonstrate the beneficial effects of an isotope-specific tube size, exhibiting visually superior image quality.

Our preliminary results indicate that an isotope-dependent tube diameter does improve image resolution for challenging isotopes like Ga-68 without introducing notable GAs that often plaque resolution recovery attempts.

Keywords: positron emission tomography; PET; Ga68; positron range; image reconstruction; tube-of-response; nuclear medicine

  • Open Access Logo Poster (Online presentation)
    58. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 07.07.2020, Leipzig, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-31322
Publ.-Id: 31322


Multi Geometry Critical Heat Flux Observation facility (MORENA): Investigation of Critical Heat Flux (CHF) at 3 K and 5 K subcooled flow boiling - Infrared thermography (IR) data set

Geißler, T.; Franz, R.; Hampel, U.

Experiments have been conducted to investigate the boiling heat transfer and local development of Critical Heat Flux (CHF) at subcooled flow boiling in a heated vertical tube. This data set contains the raw and processed Infrared thermography (IR) data along with measured operational data of the experimental facility for 3 K and 5 K subcooled flow boiling.

Keywords: Critical Heat Flux (CHF); Subcooled flow boiling; Infrared thermography

  • Reseach data in the HZDR data repository RODARE
    Publication date: 2020-07-14
    DOI: 10.14278/rodare.394

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Permalink: https://www.hzdr.de/publications/Publ-31320
Publ.-Id: 31320


Berührungslose induktive Strömungstomographie für Modelle des kontinuierlichen Stranggießens von Stahl

Ratajczak, M.

Das Stranggießen von Stahl ist mit 96% Marktanteil das weltweit wichtigste Verfahren zur Stahlherstellung. Im Gießprozess beeinflusst das Strömungsprofil in der Kokille entscheidend die Qualität des resultierenden Stahls. Um eine möglichst optimale Strömung zu erhalten, werden Aktuatoren eingesetzt, die die Strömung kontaktlos mithilfe der Lorentzkraft beeinflussen. Diese Aktuatoren würden auch eine Regelung der Strömung ermöglichen, wenn eine geeignete Messtechnik vorhanden wäre. Allerdings messen bisher verfügbare Messtechniken für heiße Schmelzen vor allem lokal in der Nähe der Randgebiete der Strömung und sind oft in ihrer zeitlichen Auflösung limitiert. Eine neue infrage kommende Messtechnik ist die berührungslose induktive Strömungstomographie (contactless inductive flow tomography, CIFT), die aus der gemessenen strömungsinduzierten Verzerrung eines angelegten Magnetfeldes die dreidimensionale Strömung rekonstruieren kann.

In dieser Arbeit wird anhand eines 1:8-Labormodells einer Stranggusskokille und numerischen Simulationen untersucht, ob CIFT bei Anlagen mit elektromagnetischen Bremsen eingesetzt werden kann. Besondere Herausforderungen entstehen aufgrund der Verzerrung des CIFT-Anregungsmagnetfeldes durch die ferromagnetische Bremse, der großen Dynamik von 6 Größenordnungen zwischen dem Magnetfeld der Bremse und dem strömungsinduzierten Magnetfeld sowie intrinsischen Strömungsoszillationen mit einer charakteristischen Frequenz im Bereich der üblicherweise verwendeten CIFT-Anregungsfrequenzen. Es wird dargelegt, dass sich CIFT in derartigen Aufbauten einsetzen lässt, wenn (a) eine geeignete Anregungsmagnetfeldstruktur erzeugt werden kann, (b) gradiometrische Induktionsspulen als Magnetfeldsensoren eingesetzt werden und (c) die Anregungsfrequenz in einem optimalen, schmalen Bereich gewählt wird. Diese Messungen werden erst durch in dieser Arbeit angefertigte theoretische und experimentell validierte Analysen der Induktionsspulen möglich, wofür Schwerpunkte auf deren Modellierung, Design und Messunsicherheit gelegt wurden. Außerdem werden für dieses Stranggussmodell erstmals experimentelle Ergebnisse mit horizontal anstatt vertikal orientierten Anregungsmagnetfeldern präsentiert.

Um die Skalierbarkeit von CIFT in Richtung industrieller Anlagen zu demonstrieren, werden zum einen neue Rekonstruktionen in einem heißen 1:2-Labormodell einer Kokille vorgestellt. Andererseits wird die in industriellen Kokillen typischerweise aufgebrachte ferromagnetische Nickelbeschichtung und ihre Auswirkung auf CIFT mit numerischen Simulationen quantifiziert. Diese Beschichtung stellt aufgrund ihrer zeitlich und räumlich schwankenden Permeabilität eines der größten Hindernisse für die Anwendung von CIFT im industriellen Stahlguss dar. Für dieses Szenario werden neue Anregungsgeometrien untersucht und erste Rekonstruktionen gezeigt.

Keywords: CIFT; contactless inductive flow tomography; kontinuierliches Stranggießen; magnetische Bremse

  • Doctoral thesis
    TU Dresden, 2020
    Mentor: Prof. Dr.-Ing. Dr. h.c. habil. Uwe Hampel
    179 Seiten

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Permalink: https://www.hzdr.de/publications/Publ-31319
Publ.-Id: 31319


Superconductivity with broken time-reversal symmetry inside a superconducting s-wave state

Grinenko, V.; Sarkar, R.; Kihou, K.; Lee, C. H.; Morozov, I.; Aswartham, S.; Büchner, B.; Chekhonin, P.; Skrotzki, W.; Nenkov, K.; Hühne, R.; Nielsch, K.; Drechsler, S.-L.; Vadimov, V. L.; Silaev, M. A.; Volkov, P. A.; Eremin, I.; Luetkens, H.; Klauss, H.-H.

In general, magnetism and superconductivity are antagonistic to each other. However, there are several families of superconductors in which superconductivity coexists with magnetism, and a few examples are known where the superconductivity itself induces spontaneous magnetism. The best known of these compounds are Sr2RuO4 and some non-centrosymmetric superconductors. Here, we report the finding of a narrow dome of an s + is' superconducting phase with apparent broken time-reversal symmetry (BTRS) inside the broad s-wave superconducting region of the centrosymmetric multiband superconductor Ba1−xKxFe2As2 (0.7 ≲ x ≲ 0.85). We observe spontaneous magnetic fields inside this dome using the muon spin relaxation (μSR) technique. Furthermore, our detailed specific heat study reveals that the BTRS dome appears very close to a change in the topology of the Fermi surface. With this, we experimentally demonstrate the likely emergence of a novel quantum state due to topological changes of the electronic system

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Permalink: https://www.hzdr.de/publications/Publ-31318
Publ.-Id: 31318


Femtosecond laser produced periodic plasma in a colloidal crystal probed by XFEL radiation

Mukharamova, N.; Lazarev, S.; Meijer, J.-M.; Gorobtsov, O. Y.; Singer, A.; Chollet, M.; Bussmann, M.; Dzhigaev, D.; Feng, Y.; Garten, M.; Huebl, A.; Kluge, T.; Kurta, R. P.; Lipp, V.; Santra, R. J.; Sikorski, M.; Song, S.; Williams, G.; Zhu, D.; Ziaja-Motyka, B.; Cowan, T. E.; Petukhov, A. V.; Vartanyants, I. A.

With the rapid development of short-pulse intense laser sources, studies of matter under extreme irradiation conditions enter further unexplored regimes. In addition, an application of X-ray Free-Electron Lasers (XFELs) delivering intense femtosecond X-ray pulses, allows to investigate sample evolution in IR pump - X-ray probe experiments with an unprecedented time resolution. Here we present a detailed study of the periodic plasma created from the colloidal crystal. Both experimental data and theory modeling show that the periodicity in the sample survives to a large extent the extreme excitation and shock wave propagation inside the colloidal crystal. This feature enables probing the excited crystal, using the powerful Bragg peak analysis, in contrast to the conventional studies of dense plasma created from bulk samples for which probing with Bragg diffraction technique is not possible. X-ray diffraction measurements of excited colloidal crystals may then lead towards a better understanding of matter phase transitions under extreme irradiation conditions.

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Permalink: https://www.hzdr.de/publications/Publ-31317
Publ.-Id: 31317


The fate of anthropogenic nanoparticles, nTiO2 and nCeO2, in waste water treatment

Lange, T.; Schneider, P.; Schymura, S.; Franke, K.

Wastewater treatment is one of the main end-of-life scenarios, as well as a possible reentry point into the environment, for anthropogenic nanoparticles (NP). These can be released from consumer products such as sunscreen or antibacterial clothing, from health-related applications or from manufacturing processes such as the use of polishing materials (nCeO2) or paints (nTiO2). The use of NP has dramatically increased over recent years and initial studies have examined the possibility of toxic or environmentally hazardous effects of these particles, as well as their behavior when released. This study focuses on the fate of nTiO2 and nCeO2 during the wastewater treatment process using lab scale wastewater treatment systems to simulate the NP mass flow in the wastewater treatment process. The feasibility of single particle mass spectroscopy (sp-ICP-MS) was tested to determine the NP load. The results show that nTiO2 and nCeO2 are adsorbed to at least 90 percent of the sludge. Furthermore, the results indicate that there are processes during the passage of the treatment system that lead to a modification of the NP shape in the effluent, as NP are observed to be partially smaller in effluent than in the added solution. This observation was made particularly for nCeO2 and might be due to dissolution processes or sedimentation of larger particles during the passage of the treatment system.

Keywords: synthetic nanoparticles; nTiO₂ and nCeO₂; waste water treatment; sp-ICP-MS nanoparticles tracking

Permalink: https://www.hzdr.de/publications/Publ-31316
Publ.-Id: 31316


Polarization tunability in multiferroic DyMn2O5: Influence of Y and Eu co-doping and 3d-4f exchange

Yang, L.; Wang, Changan; Zeng, M.; Hou, Z.; Fan, Z.; Chen, D.; Qin, M.; Lu, X.; Li, Q.; Gao, X.

Coupling effects among spin, charge, and lattice in a strongly correlated system are critical for next generation spintronic and data storage devices. However, the complex effects are elusive and difficult to distinguish their contributions to polarization modulation. Here we tailored the polarization by co-doping of non-magnetic Y and Eu at A-sites in DyMn2O5. The structure, specific heat, magnetism, and ferroelectricity of the polycrystalline Dy1-x(Eu0.24Y0.76)xMn2O5 ceramics were comprehensively explored. Interestingly, the co-doping does not cause lattice distortion of DyMn2O5, and all the ceramics are orthorhombic structures, while the independent Dy3+ spin order and the Dy3+-Mn3+ coupling can be suppressed. With increasing the co-doping content x, the spins related properties associated with the Dy3+-Mn4+-Dy3+ sub-lattice are progressively inhibited, while they keep less disturbance in the Mn3+-Mn4+-Mn3+ block. Moreover, the spin coupling of Dy3+-Mn3+ ions is stronger again the magnetic field than that of Dy3+-Mn3+. Our results enhance the understanding of ferrielectricity in DyMn2O5, and provide a method for controlling the polarization in the multiferroic manganite coexisting 3d and 4f elements.

Keywords: DyMn2O5; Multiferroicity; Ferrielectricity; Manganite

Permalink: https://www.hzdr.de/publications/Publ-31312
Publ.-Id: 31312


Probing the local atomic structure of In and Cu in sphalerite by XAS spectroscopy enhanced by reverse Monte-Carlo algorithm

Trigub, A. L.; Trofimov, N. D.; Tagirov, B. R.; Nickolsky, M. S.; Kvashnina, K. O.

The distortion of the atomic structure around In and Cu atoms in sphalerite ZnS was explored by reverse Monte Carlo (RMC) method applied to the Extended x-ray absorption fine structure (EXAFS) interpretation. Parameters of the local atomic structure (interatomic distances) around dopants in synthetic In- and In-Cu-bearing sphalerites were determined by fitting In and Cu K-edge EXAFS spectra using evolutionary algorithm (EA) of the RMC method. These data were complemented with quantum chemical Density Functional Theory (DFT) calculations and theoretical modeling of XANES spectra. The RMC-EXAFS method showed that the three coordination shells of In-bearing sphalerite are characterized by almost symmetrical Gaussian type peaks, which shapes are close to the one of pure sphalerite. This shape of the peaks is characteristic of symmetrical undisturbed structural environment of In in the sphalerite solid solution which is formed via the charge compensation schemes 3Zn2+↔2In3++□, where □ is a Zn vacancy. However, in case of (In,Cu)-bearing sphalerites formation of solid solution state follows the charge compensation scheme 2Zn2+↔Cu++In3+. In this case some splitting of the RDF peaks are observed, the splitting rate correlates with impurities concentrations. In contrast to In, the local atomic structure around Cu is not symmetric. The 2nd coordination shell around Cu (which consists of 12 metal atoms) can be described by three distinct Gaussian contributions. This splitting of interatomic distances in the 2nd coordination shell points out on the significant distortion of the ZnS crystal structure around Cu. The theoretical calculation of Cu K-edge XANES based on the distorted structural environment near Cu provides better agreement with the experiment than the symmetrical atomic model. According to our DFT calculations, considerable splitting of the 2nd coordination shell (up to 0.1 Å for Cu) occurs in the case of close positions of the impurity atoms or the Zn vacancy. The DFT calculations showed that the geometries with the close arrangement (clustering) of the impurities – In and Cu atoms, or the In atom and a vacancy, are energetically more favorable than the random distribution of the defects. However, as no heavy In atoms were detected in the 2nd shell of Cu, and the 2nd shell of In is almost undisturbed, we conclude that the defects are distributed randomly (or at least not close to each other). The disagreement of RMC-EXAFS fittings with results of DFT calculations, according to which the closest arrangement of dopants is the most stable configuration, can be explained by the presence of other defects of the sphalerite crystal lattice which were not considered in the DFT calculations.

Permalink: https://www.hzdr.de/publications/Publ-31311
Publ.-Id: 31311


Modelling thermal-hydraulic effects of zinc borate deposits in the PWR core after LOCA - Experimental strategies and test facilities

Kästner, W.; Alt, S.; Seeliger, A.; Zacharaias, F.; Harm, U.; Illgen, R.; Hampel, U.; Kryk, H.

The German software tool ATHLET (Analysis of THermohydraulics of Leaks and Transients) is continuously being developed for the simulation of the nuclear power plant behaviour in the event of transients and accidents. The focus of a current joint research project named „ATHLET Modul Zinkborat“ (AZora) is the development and validation of an ATHLET module on the basis of the current state of research on chemical long-term effects according to PWR LOCA. The module is intended to simulate thermohydraulic effects of zinc borate precipitations in the reactor core originating from long-term corrosion processes in the reactor sump during sump recirculation operation after postulated loss-of-coolant accidents in PWR. To develop and validate the sub-models, generic experiments at lab-scale as well as at semi-technical scale are planned to be carried out in unique test facilities. The structure of the module as well as the experimental strategies and the related facilities are described in the article.

Keywords: loss-of-coolant accident; LOCA; pressurized water reactor; nuclear safety research; zinc borate; corrosion; simulation; chemical effects

  • atw - International Journal for Nuclear Power 65(2020)6/7, 341-345

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  • Secondary publication expected from 09.07.2021

Permalink: https://www.hzdr.de/publications/Publ-31310
Publ.-Id: 31310


Numerical simulations of short-circuits appearance in liquid metal batteries

Benard, S.

The mid-term report gives an overview on S. Bénards work at HZDR concerning local short-circuits in liquid metal batteries.

  • Other report
    Paris: École normale supérieure Paris-Saclay, 2020

Permalink: https://www.hzdr.de/publications/Publ-31308
Publ.-Id: 31308


Microfocus X-ray tomography data set of boiling flow in vertical rod bundle with spacer grid at constant heat flux condition

Tas-Köhler, S.; Franz, R.; Boden, S.; Hampel, U.

The test section of the rod bundle experimental facility at HZDR consists of a vertically aligned PMMA channel with an upward flow of the working fluid. The cross-section of the channel is quadratic (inner edge length: 37 mm) and contains nine directly electrically heated rods (material: titanium-alloy, diameter: 10 mm, wall thickness: 0.3 mm) which are arranged in an orthogonal 3 by 3 matrix (rod axis distance: 12.8 mm). Circa 190 mm downstream of the start of the heating zone a 30 mm long spacer for the rods with tilted flow guiding vanes is mounted. These vanes are aimed to increase lateral flow velocities within the subchannels. Working fluid was octafluorocyclobutane (CAS 115-25-3, RC318). The experimental facility is comprehensively instrumented for measurement of flow, temperature and pressure/pressure difference. For non-invasive three-dimensional high-resolution measurement of a temporally averaged volumetric void fraction within the working fluid flowing around the heating rods in the subchannels an X-ray computer tomography measurement system was set up.
The presented dataset contains measurement data of the experimental facility's instrumentation and tomographic void fraction data of experiments with four different configurations of the flow guiding vanes (without vanes, 20°, 29°, 40°) for four different flow velocities between 0.4 m/s and 1.3 m/s at a heat flow density of 85.7 kW/m².

Keywords: X-Ray Computed Tomography; Phase fraction; Rod bundle; Boiling flow

  • Reseach data in the HZDR data repository RODARE
    Publication date: 2020-07-08
    DOI: 10.14278/rodare.378

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Permalink: https://www.hzdr.de/publications/Publ-31307
Publ.-Id: 31307


Validierung eines Open-source-Modells für die Simulation von PEM-Brennstoffzellen und Anwendung auf eine luftatmende Brennstoffzelle

Knüpfer, L.

Die vorliegende Arbeit beschäftigt sich mit der dreidimensionalen und mehrphasigen CFD-Simulation von PEM-Brennstoffzellen. Dabei wird die Validierung eines in OpenFOAM implementierten Modells zur Gesamtzellensimulation anhand von drei, von verschiedenen Forschungsgruppen vorgestellten, Experimenten durchgeführt.
Aufbauend auf der Modellvalidierung wird die Anwendbarkeit des Modells auf eine luft-atmende Brennstoffzelle überprüft. In diesem Zusammenhang wird der Einfluss der Orientierung auf die Transportprozesse in einer luftatmenden Brennstoffzelle mit zylindrischer Form untersucht. Dafür wird sowohl die Brennstoffzelle, als auch deren Umgebung beachtet. Die bei variierender Orientierung auftretenden Unterschiede von Naturkonvektion, Temperatur und Massenverteilung von Wasser und Sauerstoff werden dargestellt und diskutiert. Zusätzlich wird auf die Grenzen des verwendeten Modells und mögliche Verbesserungen hingewiesen.

  • Diploma thesis
    TU Dresden, 2020

Permalink: https://www.hzdr.de/publications/Publ-31305
Publ.-Id: 31305


Heavy ion irradiation damage in Zr3(Al0.9Si0.1)C2 MAX phase

Qarra, H. H.; Knowles, K. M.; Vickers, M. E.; Zapata-Solvas, E.; Akhmadaliev, S.

A Zr3(Al0.9Si0.1)C2 MAX phase-based ceramic with 22 wt.% ZrC and 10 wt.% Zr5Si3 has been irradiated with 52 MeV I9+ ions at room temperature, achieving a maximum dose of 8 displacements per atom (dpa). The response of this MAX phase-rich material to irradiation has been studied using scanning electron microscopy, transmission electron microscopy and X-ray diffraction techniques. Post-irradiation examination of the material revealed a number of crystalline changes to the MAX phase. At low doses, Zr3(Al0.9Si0.1)C2 maintained a high degree of crystallinity, while at the highest doses, its degree of crystallinity was reduced significantly. A number of radiation-induced phase transformations were observed, including the decomposition of Zr3(Al0.9Si0.1)C2 into ZrC and other phases, and the formation of β-Zr3(Al,Si)C2, a MAX phase with a rearranged stacking sequence. Microstructural examination revealed that the majority of the extended defects in Zr3(Al0.9Si0.1)C2 lie in the (0001) basal planes. Analysis of X-ray diffraction profiles after heat treating the 8 dpa-irradiated material for 1 h at 300 °C and at 600 °C showed that there were only subtle changes to the profiles relative to that of the 8 dpa-irradiated material which had not been heat treated. Overall, the experimental results of this study show that the Zr3(Al0.9Si0.1)C2 MAX phase responds less well to irradiation relative to other MAX phases irradiated with high energy heavy ions at room temperature.

Permalink: https://www.hzdr.de/publications/Publ-31304
Publ.-Id: 31304


Two types of alternating spin-1/2 chains and their field-induced transitions in ε-LiVOPO4

Mukharjee, P. K.; Ranjith, K. M.; Baenitz, M.; Scurschii, I.; Tsirlin, A. A.; Nath, R.

Thermodynamic properties, 31P nuclear magnetic resonance (NMR) measurements, and density-functional band-structure calculations for ε-LiVOPO4 are reported. This quantum magnet features a singlet ground state and comprises two types of alternating spin-1/2 chains that manifest themselves by the double maxima in the susceptibility and magnetic specific heat, and by the two-step magnetization process with an intermediate 1/2-plateau. From thermodynamic data and band-structure calculations, we estimate the leading couplings of J1 ≃ 20 K and J2 ≃ 60 K and the alternation ratios of α1 = J’1/J1 ≃ 0.6 and α2 = J’2/J2 ≃ 0.3 within the two chains, respectively. The zero-field spin gap Δ0/kB ≃ 7.3 K probed by thermodynamic and NMR measurements is caused by the J1-J’1 spin chains and can be closed in the applied field of μ0Hc1 ≃ 5.6 T, giving rise to a field-induced long-range order. The NMR data reveal predominant three-dimensional spin-spin correlations at low temperatures. Field-induced magnetic ordering transition observed above Hc1 is attributed to the Bose-Einstein condensation of triplons in the sublattice formed by the J1-J’1 chains with weaker exchange couplings.

Permalink: https://www.hzdr.de/publications/Publ-31303
Publ.-Id: 31303


Polar structure formation in solid solution of strontium substituted fluorapatite-gelatin composites: from structural and morphogenetic aspects to pyroelectric properties

Knaus, J.; Sommer, M.; Duchstein, P.; Gumeniuk, R.; Akselrud, L. G.; Sturm, S.; Auffermann, G.-D.; Hennig, C.; Zahn, D.; Hulliger, J.; Sturm, E. V.

Strontium substituted apatite-(CaF)-gelatin composites have been synthesized within a gelatin gel using the dou-ble diffusion technique. All experimental parameters were kept constant while systematically varying the strontium/ calcium molar ratio in solution. The effect of the presence of strontium ions in the growth solution on composition, morphogenesis and morphology as well as pyroelectric properties of synthetic aggregates was systemically analyzed. It was shown that stron-tium ions significantly inhibit the growth process of composite aggregates and increase growth anisotropy along [0001], which were also confirmed and explained by molecular dynamic simulations. Furthermore, it was observed the promotion of the crystal branching processes and spherulite formation. Pyroelectric microscopy (SPEM) measurements on mixed substi-tuted apatite-(CaSrF)-gelatin composite aggregates showed an increase in polar properties, suggesting a lowering of the crys-tal symmetry. This was verified by Rietveld refinement of synchrotron pXRD, which revealed the non-centrosymmetric P63apatite crystal structure. These data could shed new light on understanding piezoelectric and pyroelectric properties of apa-tite based biological hard tissues.

Keywords: apatite,strontiumsubstitution,composite,morphogenesis,crystalstructure,polarity

Permalink: https://www.hzdr.de/publications/Publ-31301
Publ.-Id: 31301


ROBL-II at ESRF: A synchrotron toolbox for actinide research

Scheinost, A.; Claußner, J.; Exner, J.; Feig, M.; Findeisen, S.; Hennig, C.; Kvashnina, K.; Naudet, D.; Prieur, D.; Roßberg, A.; Schmidt, M.; Qiu, C.; Colomp, P.; Cohen, C.; Dettona, E.; Dyadkin, V.; Stumpf, T.

ROBL-II provides four different experimental stations to investigate actinide and other alpha- and beta-emitting radionuclides at the new EBS storage ring of ESRF within an energy range of 3 to 35 keV. The XAFS station consists of a highly automatized, high sample throughput installation in a glovebox, to measure EXAFS and conventional XANES of samples routinely at temperatures down to 10 K, and with a detection limit in the sub-ppm range. The XES station with its 5 bent-crystal analyzer, Johann-type setup with Rowland circles of 1.0 and 0.5 m radii provides high-energy resolution fluorescence detection (HERFD) for XANES, XES, and RIXS measurements, covering both actinide L and M edges together with other elements accessible in the 3 to 20 keV energy range. The 6-circle heavy duty goniometer of XRD-1 is equipped for both high-resolution powder diffraction as well as surface-sensitive CTR and RAXR techniques. Single crystal diffraction, powder diffraction with high temporal resolution, as well as X-ray tomography experiments can be performed at a Pilatus 2M detector stage. Elaborate radioprotection features enable a safe and easy exchange of samples between the four different stations to allow the combination of several methods for an unprecedented level of information on radioactive samples for both fundamental and applied actinide and environmental research.

Keywords: XAFS; XANES; XES; XRD; RIXS; RAXR; CTR; actinides

Permalink: https://www.hzdr.de/publications/Publ-31300
Publ.-Id: 31300


Scanning transmission imaging in the helium ion microscope with a position-sensitive detector

Serralta Hurtado De Menezes, E.; Klingner, N.; de Castro, O.; Mousley, M.; Biesemeier, A.; Babeacua, C.; Eswara, S.; Duarte Pinto, S.; Wirtz, T.; Hlawacek, G.

The helium ion microscope (HIM) is an instrument for high-resolution imaging, nanofabrication, composition analysis, and material modification at the nanometer scale [1]. The npSCOPE instrument is a unique HIM prototype with three special add-ons, namely: secondary ion mass spectroscopy (SIMS), cryo-microscopy, and scanning transmission helium ion microscopy (STHIM).
In this work, we focus on STHIM. Our STHIM detection system is based on a position- and time-sensitive detector comprising a microchannel plate and a delay line readout structure. A dedicated software interface for data acquisition and post-processing allows the reconstruction of images for selected scattering directions, and the visualization of different contrast regimes for a given sample. Using STHIM, we analyzed material contrast for layered films of various thicknesses and materials. Channeling contrast in transmission for poly- and single-crystalline materials is also detected. In the case of biological samples, STHIM provides a way of identifying sub-surfaces structures that can help to localize nanomaterials for toxicology studies, as shown in Figure 1.

Keywords: Helium Ion Microscopy; Scanning transmission ion microscopy

  • Lecture (Conference) (Online presentation)
    CMD2020GEFES, 31.08.-04.09.2020, Madrid, España
  • Lecture (Conference) (Online presentation)
    Virtual Early Career European Microscopy Congress 2020, 24.-26.11.2020, København, Danmark

Permalink: https://www.hzdr.de/publications/Publ-31299
Publ.-Id: 31299


Developments in nuclear medicine – new radioisotopes in use and associated challenges: proceedings of a scientific seminar held in Luxembourg on 13 November 2019

Laßmann, M.; Neels, O.; Sjögreen Gleisner, K.; Bly, R.; Konijnenberg, M.

The European Commission organises every year, in cooperation with the Group of Experts referred to in Article 31 of the Euratom Treaty, a scientific seminar on emerging issues in radiation protection – generally addressing new research findings with potential policy and/or regulatory implications. Leading scientists are invited to present the status of scientific knowledge in the selected topic.
Based on the outcome of the scientific seminar, the Group of Experts referred to in Article 31 of the Euratom Treaty may recommend research, regulatory or legislative initiatives. The European Commission takes into account the conclusions of the Experts when setting up its radiation protection programme. The Experts' conclusions are valuable input to the process of reviewing and potentially revising European radiation protection legislation.

Keywords: Conference proceedings; Energy research; Nuclear accident; Nuclear medicine; Public health; Radiation exposure; Radiation protection

  • Open Access Logo Contribution to proceedings
    EU Scientific Seminar November 2019, 13.11.2019, Luxembourg, Luxembourg
    Proceedings of EU Scientific Seminar November 2019, 978-92-76-27010-2
    DOI: 10.2833/905722

Permalink: https://www.hzdr.de/publications/Publ-31298
Publ.-Id: 31298


Direct Characterisation of Solute Transport inUnsaturated Porous Media using 4D X-raySynchrotron Microtomography

Sharul, H.; Vahid, J.-N.; Nikolaos, K. K.; Da Assuncao Godinho, J. R.; Nghia, T. V.; Senyou, A.; Arash, A.; Holger, S.

Solute transport in unsaturated porous materials is a complex pro-cess, which exhibits some distinct features differentiating it fromtransport under saturated conditions. These features emerge mostlydue to the different transport time scales at different regions of theflow network, which can be classified into flowing and stagnantregions, predominantly controlled by advection and diffusion, re-spectively. Under unsaturated conditions, the solute breakthroughcurves show early arrivals and very long tails, and this type of trans-port is usually referred to as non-Fickian. This is the first studywhich directly characterise transport through an unsaturated porousmedium in three spatial dimensions at the resolution of 3.25μm andthe time resolution of 6s. Using advanced high-speed, high spa-tial resolution, synchrotron-based X-Ray Computed Microtomogra-phy (sCT) we obtained the first detailed information on solute trans-port through a glass-bead packing at different saturations. A largeexperimental dataset (>50TB) was produced, while imaging the evo-lution of the solute concentration with time at any given point withinthe field of view. We show that the fluids’ topology has a critical sig-nature on the non-Fickian transport, which has not been addressedin the theories of transport through unsaturated porous media. Wedemonstrate that the "fully-mixing" assumption at pore scale is notvalid, due to the significant impact of the no-slip boundary of thesolid walls. Results demonstrate that dispersivity, as a major trans-port parameter, is changing with saturation, being two-fold larger atsmaller saturations compared to that at high saturations.

Keywords: contaminant transport; X-ray microtomography; stagnant saturation; non-Fickian transport; unsaturated flow

  • Open Access Logo Proceedings of the National Academy of Sciences of the United States of America 117(2020)38, 23443-2344
    DOI: 10.1073/pnas.2011716117

Permalink: https://www.hzdr.de/publications/Publ-31297
Publ.-Id: 31297


Magnetization dynamics and mutual spin-pumping in SAFs

Sorokin, S.; Gallardo, R.; Fowley, C.; Lenz, K.; Titova, A.; Dennehy, G.; Atchenson, G.; Rode, K.; Faßbender, J.; Lindner, J.; Deac, A. M.

Primary data related to the publication in PRB: Article Link.  Pre-release version is available at: Arxiv, ResearchGate.

Some of the file are auxiliary or analisys files for faster display of the main results (like .opj, .ods files). Main raw data files are in the archives.

Keywords: Magnetization dynamics; Spin-pumping; SAFs, SAF; synthetic antiferromagnets; coupled magnetic trilayers; magnetic multilayers; ferromagnetic resonance; electrically-detected ferromagnetic resonance; FMR; ED-FMR; ST-FMR

Related publications

  • Reseach data in the HZDR data repository RODARE
    Publication date: 2019-12-09
    DOI: 10.14278/rodare.390
    License: CC-BY-4.0

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Permalink: https://www.hzdr.de/publications/Publ-31295
Publ.-Id: 31295


The influence of an applied magnetic field on the self-assembly of magnetic nanogels

Novikau, I. S.; Sanchez Romero, P. A.; Kantorovich, S. S.

Using Langevin dynamics simulations, we investigate the self-assembly of magnetic nanogels in the presence of applied magnetic fields of moderate strength. We find that even weak fields lead to drastic changes in the structure factors of both, the embedded magnetic nanoparticles and of whole nanogel particles. Nanogels assemble by uniting magnetic particle clusters forming inter-gel bridges. At zero field the average amount of such bridges for a pair of nanogels is close to one, whereas even for weak fields it fastly doubles. Rapid growth of cluster size at low values of the applied field is followed by a broad region of slow increase, caused by the mechanical constraints imposed the polymer matrix. The influence of the latter manifests itself in both, the slow growth of the magnetisation curve at intermediate fields and the slow decay of the total Zeeman energy.

Keywords: Magnetic nanogels; Self-assembly; Molecular dynamics

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  • Secondary publication expected from 01.06.2021

Permalink: https://www.hzdr.de/publications/Publ-31294
Publ.-Id: 31294


Diffusion of single active-dipolar cubes in applied fields

Kaiser, M.; Martinez, Y.; Schmidt, A. M.; Sanchez Romero, P. A.; Kantorovich, S. S.

“Active matter” refers to a class of out-of-equilibrium systems whose ability to transform environmental energy to kinetic energy is sought after in multiple fields of science and at very different length scales. At microscopic scales, an important challenge lies in overpowering the particles reorientation due to thermal fluctuations, especially in nano-sized systems, to create non-random, directed motion, needed for a wide range of possible applications. In this article, we employ molecular dynamics simulations to show that the diffusion of a self-propelling dipolar nanocube can be enhanced in a pre-defined direction with the help of a moderately strong applied magnetic field, overruling the effect of the thermal fluctuations. Furthermore, we show that the direction of diffusion is given by the orientation of the net internal magnetisation of the cube. This can be used to determine experimentally the latter in synthetically crafted active cobalt ferrite nanocubes.

Keywords: Active matter; Magnetic cubes; Molecular dynamics

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  • Secondary publication expected from 15.04.2021

Permalink: https://www.hzdr.de/publications/Publ-31293
Publ.-Id: 31293


Measuring FORCs diagrams in computer simulations as a mean to gain microscopic insight

Dobroserdova, A. B.; Sanchez Romero, P. A.; Shapochkin, V. E.; Smagin, D. A.; Zverev, V. S.; Odenbach, S.; Kantorovich, S. S.

FORCs (first-order reversal curves) diagrams prove to be an efficient experimental technique to investigate magnetic interactions in complex systems. In experiments, as a rule, it is difficult to relate actual microstructural changes to the evolution of FORCs diagrams. Here, using Molecular Dynamics simulations, we calculate FORCs for two simple models of a magnetic elastomer. The simplicity of these models allows to relate directly both, the rigidity of the matrix and the magnetoelastic coupling to the shape and intensity of FORCs diagrams.

Keywords: FORC Molecular dynamics; Magnetic elastomers; Magneto-elastic coupling

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  • Secondary publication expected from 01.05.2021

Permalink: https://www.hzdr.de/publications/Publ-31292
Publ.-Id: 31292


Unknotting of quasi-two-dimensional ferrogranular networks by in-plane homogeneous magnetic fields

Sanchez Romero, P. A.; Miller, J.; Kantorovich, S. S.; Richter, R.

Our ongoing research addresses, by means of experiments and computer simulations, the aggregation process that takes place in a shaken granular mixture of glass and magnetized ferrous alloy beads when the shaking amplitude is suddenly decreased. After this quenching, the magnetized beads form a transient network that coarsens in time into compact clusters, following a viscoelastic phase separation. Here we focus on the quasi-two-dimensional case, analyzing in computer simulations the effects of a magnetic field parallel to the system plane. Our results evidence that the field drastically changes the structure of the forming network: chains and elongated clusters parallel to the field are favored whereas perpendicular connecting structures tend to be suppressed, leading to the unknotting of the networks which are observed at zero field. Importantly, we found that moderate field strengths lead to the formation of larger clusters at intermediate time intervals than in the case of weak and strong fields. Moreover, the latter tend to limit the overall growth of the clusters at longer time scales. These results may be relevant in different systems governed by similar magnetically driven aggregation processes as, for example, in the formation of iron-rich planetesimals in protoplanetary discs or for magnetic separation systems.

Keywords: Ferrogranulate mixture; Field induced network unknotting; Susceptible dipolar hard spheres; Langevin dynamics simulations; Viscoelastic phase separation; Transient network

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  • Secondary publication expected from 01.04.2021

Permalink: https://www.hzdr.de/publications/Publ-31291
Publ.-Id: 31291


The influence of crosslinkers and magnetic particle distribution along the filament backbone on the magnetic properties of supracolloidal linear polymer-like chains

Mostarac, D.; Vaughan, L.; Sanchez Romero, P. A.; Kantorovich, S. S.

Diverse polymer crosslinking techniques allow the synthesis of linear polymer-like structures whose monomers are colloidal particles. In the case where all or part of these colloidal particles are magnetic, one can control the behaviour of these supracolloidal polymers, known as magnetic filaments (MFs), by applied magnetic fields. However, the response of MFs strongly depends on the crosslinking procedure. In the present study, we employ Langevin dynamics simulations to investigate the influence of the type of crosslinking and the distribution of magnetic particles within MFs on their response to an external magnetic field. We found that if the rotation of the dipole moment of particles is not coupled to the backbone of the filament, the impact of the magnetic content is strongly decreased.

Keywords: Supracolloidal magnetic polymers; Magnetisation; Crosslinking methods; Langevin dynamics simulations

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  • Secondary publication expected from 01.03.2021

Permalink: https://www.hzdr.de/publications/Publ-31290
Publ.-Id: 31290


Suspensions of magnetic nanogels at zero field: Equilibrium structural properties

Novikau, I. S.; Minina, E. S.; Sanchez Romero, P. A.; Kantorovich, S. S.

Magnetic nanogels represent a cutting edge of magnetic soft matter research due to their numerous potential applications. Here, using Langevin dynamics simulations, we analyse the influence of magnetic nanogel concentration and embedded magnetic particle interactions on the self-assembly of magnetic nanogels at zero field. For this, we calculated radial distribution functions and structure factors for nanogels and magnetic particles within them. We found that, in comparison to suspensions of free magnetic nanoparticles, where the self-assembly is already observed if the interparticle interaction strength exceeds the thermal fluctuations by approximately a factor of three, self-assembly of magnetic nanogels only takes place by increasing such ratio above six. This magnetic nanogel self-assembly is realised by means of favourable close contacts between magnetic nanoparticles from different nanogels. It turns out that for high values of interparticle interactions, corresponding to the formation of internal rings in isolated nanogels, in their suspensions larger magnetic particle clusters with lower elastic penalty can be formed by involving different nanogels. Finally, we show that when the self-assembly of these nanogels takes place, it has a drastic effect on the structural properties even if the volume fraction of magnetic nanoparticles is low.

Keywords: Magnetic nanogels; Magnetic self-assembly; Langevin dynamics; Structure factor

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  • Secondary publication expected from 15.03.2021

Permalink: https://www.hzdr.de/publications/Publ-31289
Publ.-Id: 31289


The structure of clusters formed by Stockmayer supracolloidalmagnetic polymers

Kantorovic, S. S.; Sanchez Romero, P. A.; Pyanzina, E. S.; Novak, E. V.

Unlike Stockmayer fluids, that prove to undergo gas-liquid transition on cooling, the system of dipolar hard or soft spheres without any additional central attraction so far has not been shown to have a critical point. Instead, in the latter, one observes diverse self-assembly scenarios. Crosslinking dipolar soft spheres into supracolloidal magnetic polymer-like structures (SMPs) changes the self-assembly behaviour. Moreover, aggregation in systems of SMPs strongly depends on the constituent topology. For Y- and X-shaped SMPs, under the same conditions in which dipolar hard spheres would form chains, the formation of very large loose gel-like clusters was observed (E. Novak et al., J. Mol. Liq. 271, 631 (2018)). In this work, using molecular dynamics simulations, we investigate the self-assembly in suspensions of four topologically different SMPs --chains, rings, X and Y-- whose monomers interact via Stockmayer potential. As expected, compact drop-like clusters are formed by SMPs in all cases if the central isotropic attraction is introduced, however, their shape and internal structure turn out to depend on the SMPs topology.

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  • Secondary publication expected

Permalink: https://www.hzdr.de/publications/Publ-31288
Publ.-Id: 31288


Atomistic simulation of PDADMAC/PSS oligoelectrolyte multilayers: overall comparison of tri- and tetra-layer systems

Sanchez Romero, P. A.; Vögele, M.; Smiatek, J.; Qiao, B.; Sega, M.; Holm, C.

By employing large-scale molecular dynamics simulations of atomistically resolved oligoelectrolytes in aqueous solutions, we study in detail the first four layer-by-layer deposition cycles of an oligoelectrolyte multilayer made of poly(diallyl dimethyl ammonium chloride)/poly(styrene sulfonate sodium salt) (PDADMAC/PSS). The multilayers are grown on a silica substrate in 0.1 M NaCl electrolyte solutions and the swollen structures are then subsequently exposed to varying added salt concentration. We investigated the microscopic properties of the films, analyzing in detail the differences between three- and four-layer systems. Our simulations provide insights into the early stages of growth of a multilayer, which are particularly challenging for experimental observations. We found rather strong complexation of the oligoelectrolytes, with fuzzy layering of the film structure. The main charge compensation mechanism is for all cases intrinsic, whereas extrinsic compensation is relatively enhanced for the layer of the last deposition cycle. In addition, we quantified other fundamental observables of these systems, such as the film thickness, water uptake, and overcharge fractions for each deposition layer.

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  • Secondary publication expected

Permalink: https://www.hzdr.de/publications/Publ-31286
Publ.-Id: 31286


Itinerant metamagnetic transition in the ferromagnet LuCo3 induced by high field: Instability of the 3d-electron subsystem

Neznakhin, D. S.; Radzivonchik, D. I.; Gorbunov, D.; Andreev, A. V.; Sebek, J.; Lukoyanov, A. V.; Bartashevich, M. I.

LuCo3 is an itinerant ferromagnet whose magnetic properties strongly depend on the position of the 3d electronic states relative to the Fermi level. Here, we report on the magnetization of a LuCo3 single crystal in pulsed magnetic fields up to 58 T. We find a field-induced phase transition just below 50 T from a low-spin to a high-spin state. The transition shows a pronounced anisotropy of the magnetization jump and hysteresis. A series of ab initio calculations based on the density functional theory show that the transition is due to a significant change in the occupancies of the Co 3d electronic states. At the same time, some features in the majority spin density of the Co 3d states are slightly modified and pass through the Fermi level when the spin state is changed, which leads to the instability of the 3d-electron subsystem. Thereby, the applied magnetic field causes a significant redistribution in the majority and minority spin states in the Co 3d subsystem, which results in the sharp change in the magnetization.

Permalink: https://www.hzdr.de/publications/Publ-31284
Publ.-Id: 31284


Enhanced magnetocaloric effect in distilled terbium and emergence of novel properties after severe plastic deformation

Tereshina-Chitrova, E. A.; Korneeva, Y. V.; Ozherelkov, D. Y.; Dolezal, P.; Tereshina, I. S.; Kaminskaya, T. P.; Gorbunov, D.; Dobatkin, S. V.; Minarik, P.

We report the magneto-structural and magnetocaloric properties study of Tb purified by distillation and further processed by severe plastic deformation (SPD). Both parent and the SPD-processed Tb contain nanosized structural elements and have a very pronounced (00 l ) texture. We observe an improved magnetocaloric effect (MCE) in the distilled nanocrystalline Tb while novel properties emerge in the sample after severe plastic deformation. The latter demonstrates zero thermal expansion over a wide temperature range while its MCE vanishes. We show that the absolutely new physical properties in Tb result from the structural transformation and modification of magnetic interactions.

Permalink: https://www.hzdr.de/publications/Publ-31283
Publ.-Id: 31283


The old, unique C1 chondrite Flensburg – Insight into the first processes of aqueous alteration, brecciation, and the diversity of water-bearing parent bodies and lithologies

Bischoff, A.; Alexander, C.; Barrat, J.-A.; Burkhardt, C.; Busemann, H.; Degering, D.; Di Rocco, T.; Fischer, M.; Fockenberg, T.; Foustoukos, D.; Gattacceca, J.; Da Assuncao Godinho, J. R.; Harries, D.; Heinlein, D.; Hellmann, J.; Hertkorn, N.; Holm, A.; Jull, A. J. T.; Kerraouch, I.; King, A. J.; Koll, D.; Lachner, J.; Ludwig, T.; Merchel, S.; Mertens, C.; Neumann, W.; Pack, A.; Patzek, M.; Pavetich, S.; Morino, P.; Reitze, M. P.; Rüfenacht, M.; Rugel, G.; Schmidt, C.; Schmitt-Kopplin, P.; Schönbächler, M.; Trieloff, M.; Wallner, A.; Wimmer, K.; Wölfer, E.; Kleine, T.

On September 12, 2019 at 12:49:48 (UT) a bolide was observed by hundreds of eye-witnesses from the Netherlands, Germany, Belgium, Denmark and the UK. One day later a small meteorite stone was found by accident in Flensburg. The presence of short-lived cosmogenic radionuclides with half-lives as short as 16 days proves the recent exposure of the found object to cosmic rays in space linking it clearly to the bolide event. An exceptionally short exposure time of ~5000 years was determined. The 24.5 g stone has a fresh black fusion crust, a low density of <2 g/cm³, and a magnetic susceptibility (MS) of logχ= 4.35 (χ in 10-9 m³/kg). The rock consists of relict chondrules and clusters of sulfide and magnetite grains set in a fine-grained matrix. The most abundant phases are phyllosilicates. Carbonates (~3.9 vol.%) occur as calcites, dolomites, and a Na-rich phase. The relict chondrules (often surrounded by sulfide laths) are free of anhydrous silicates and contain abundant serpentine. Lithic clasts are also surrounded by similar sulfide laths partly intergrown with carbonates. ⁵³Mn-⁵³Cr ages of carbonates in Flensburg indicate that brecciation and contemporaneous formation of the pyrrhotite-carbonate intergrowths by hydrothermal activities happened no later than 4564.6±1.0 Ma (using D'Orbigny as Mn-Cr anchor). This corresponds to 2.6±1.0 or 3.4±1.0 Ma after CAIs, depending on the exact age CAI age. This is the oldest dated evidence for brecciation and carbonate formation, which likely occurred during parent body growth and incipient heating due to ²⁶Al.
The O isotope composition of Flensburg reveals that it plots at the ¹⁶O-rich end of the CM chondrite field and in the transition field to the CV-CK-CR chondrites. This is unexpected since the O-isotope compositions of strongly aqueously-altered chondrites are generally found to be at the ¹⁶O-poor end of the CM range. The mass-dependent Te isotopic compositionof Flensburg is slightly different from mean CM chondrites and is most similar to those of the ungrouped C2 chondrite Tagish Lake. On the other hand, the 50Ti and 54Cr isotope nomalies indicate that Flensburg is similar to CM chondrites, as do the ~10 wt.% H₂O. Yet, the bulk Zn, Cu, and Pb concentrations are about 30% lower than those of mean CM chondrites. The He, Ne and, Ar isotopes of Flensburg show no solar wind contribution; its trapped noble gas signature is similar to that of CMs with a slightly lower concentration of ²⁰Netr.
Based on the bulk H, C and N elemental abundances and isotopic compositions, Flensburg is clearly unique among the analyzed chondrites as it has the lightest bulk H and N isotopic compositions of any type 1 or 2 chondrite. The number of soluble organic compounds in Flensburg is even lower than that of the brecciated CI chondrite Orgueil.
The extraordinary significance of Flensburg is given by the observation that it represents the oldest chondrite sample, in which the contemporaneous episodes of aqueous alteration and brecciation are 81 perfectly visible. The characterization of a large variety of carbonaceous chondrites with different alteration histories is important for interpreting returned samples from the OSIRIS-REx and Hayabusa 2 missions.

Keywords: AMS; meteorite; cosmic exposure

Permalink: https://www.hzdr.de/publications/Publ-31282
Publ.-Id: 31282


Intrinsic plasticity of silicon nanowire neurotransistors: plots of the figures 1-2

Baraban, L.

Data and Figures supporting the publication

Related publications

  • Reseach data in the HZDR data repository RODARE
    Publication date: 2020-07-01
    DOI: 10.14278/rodare.388
    License: CC-BY-4.0

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Permalink: https://www.hzdr.de/publications/Publ-31280
Publ.-Id: 31280


Rapidly Switchable Universal CAR-T Cells for Treatment of CD123-Positive Leukemia

Loff, S.; Dietrich, J.; Meyer, J.-E.; Riewaldt, J.; Spehr, J.; von Bonin, M.; Gründer, C.; Swayampakula, M.; Franke, K.; Feldmann, A.; Bachmann, M.; Ehninger, G.; Ehninger, A.; Cartellieri, M.

Chimeric antigen receptor T cells (CAR-T) targeting CD19 or B cell maturation antigen (BCMA) are highly effective against B cell malignancies. However, application of CAR-T to less differentially expressed targets remains a challenge due to lack of tumor-specific antigens and CAR-T controllability. CD123, a highly promising leukemia target, is expressed not only by leukemic and leukemia-initiating cells, but also by myeloid, hematopoietic progenitor, and certain endothelial cells. Thus, CAR-T lacking fine-tuned control mechanisms pose a high toxicity risk. To extend the CAR-T target landscape and widen the therapeutic window, we adapted our rapidly switchable universal CAR-T platform (UniCAR) to target CD123. UniCAR-T efficiently eradicated CD123+ leukemia in vitro and in vivo. Activation, cytolytic response, and cytokine release were strictly dependent on the presence of the CD123-specific targeting module (TM123) with comparable efficacy to CD123-specific CAR-T in vitro. We further demonstrated a pre-clinical proof of concept for the safety-switch mechanism using a hematotoxicity mouse model wherein TM123-redirected UniCAR-T showed reversible toxicity toward hematopoietic cells compared to CD123 CAR-T. In conclusion, UniCAR-T maintain full anti-leukemic efficacy, while ensuring rapid controllability to improve safety and versatility of CD123-directed immunotherapy. The safety and efficacy of UniCAR-T in combination with TM123 will now be assessed in a phase I clinical trial (ClinicalTrials.gov: NCT04230265).

Permalink: https://www.hzdr.de/publications/Publ-31279
Publ.-Id: 31279


Development and In Vivo Application of a Water-Soluble Anticancer Copper Ionophore System Using a Temperature-Sensitive Liposome Formulation

Gaál, A.; Garay, T. M.; Horváth, I.; Máthé, D.; Szöllösi, D.; Veres, D. S.; Mbuotidem, J.; Kovacs, T.; Tóvári, J.; Bergmann, R.; Streli, C.; Szakács, G.; Mihály, J.; Varga, Z.; Szoboszlai, N.

Liposomes containing copper and the copper ionophore neocuproine were prepared and characterized for in vitro and in vivo anticancer activity. Thermosensitive PEGylated liposomes were prepared with di_erent molar ratios of 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) and hydrogenated soybean phosphatidylcholine (HSPC) in the presence of copper(II) ions. Optimal, temperature dependent drug release was obtained at 70:30 DPPC to HSPC weight ratio. Neocuproine (applied at 0.2 mol to 1 mol phospholipid) was encapsulated through a pH gradient while using unbuffered solution at pH 4.5 inside the liposomes, and 100 mM HEPES bu_er pH 7.8 outside the liposomes. Copper ions were present in excess, yielding 0.5 mM copper-(neocuproine)2 complex and 0.5 mM free copper. Pre-heating to 45 °C increased the toxicity of the heat-sensitive liposomes in short-term in vitro experiments, whereas at 72 h all investigated liposomes exhibited similar in vitro toxicity to the copper(II)-neocuproine complex (1:1 ratio). Thermosensitive liposomes were found to be more effective in reducing tumor growth in BALB/c mice engrafted with C26 cancer cells, regardless of the mild hyperthermic treatment. Copper uptake of the tumor was verified by PET/CT imaging following treatment with [64Cu]Cu-neocuproine liposomes. Taken together, our results demonstrate the feasibility of targeting a copper nanotoxin that was encapsulated in thermosensitive liposomes containing an excess of copper.

Keywords: eocuproine; themosensitive liposomal formulation; mild hyperthermia; copper nanotoxin; MRPS; in vivo antitumor effect

Permalink: https://www.hzdr.de/publications/Publ-31278
Publ.-Id: 31278


Heisenberg limit for detecting vacuum birefringence

Ahmadiniaz, N.; Cowan, T.; Sauerbrey, R.; Schramm, U.; Schlenvoigt, H.-P.; Schützhold, R.

Quantum electrodynamics predicts the vacuum to behave as a nonlinear medium, including effects such as birefringence. However, for experimentally available field strengths, this vacuum polarizability is extremely small and thus very hard to measure. In analogy to the Heisenberg limit in quantum metrology, we study the minimum requirements for such a detection in a given strong field (the pump field). Using a laser pulse as the probe field, we find that its energy must exceed a certain threshold depending on the interaction time. However, a detection at that threshold, i.e., the Heisenberg limit, requires highly nonlinear measurement schemes--while for ordinary linear-optics schemes, the required energy (Poisson or shot noise limit) is much larger. Finally, we discuss several currently considered experimental scenarios from this point of view.

Keywords: Quantum Electrodynamics; Vacuum birefringence; Heisenberg limit

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Permalink: https://www.hzdr.de/publications/Publ-31277
Publ.-Id: 31277


An overview on electrochemical simulation with OpenFOAM

Weber, N.; Weier, T.

Modelling electrochemical devices, such as fuel cells, batteries or electrolysers asks typically for coupling electrochemistry with flow simulation and mass transfer. While solvers for mass transfer and fluid dynamics are well established in the open-source CFD library OpenFOAM, electrochemistry simulations are a rather young field of application. The presentation shall give therefore an overview on different approaches on how to simulate potential and current distributions as well as the cell voltage of electrochemical devices using OpenFOAM.

  • Lecture (Conference) (Online presentation)
    OpenFOAM Conference, 13.10.2020, Online, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-31276
Publ.-Id: 31276


Status of the STM-FPGA-DAQ HLS-Cores for LaBr Peak Detection and Zero Suppression

Knodel, O.

Brief overview and status of the STM-FPGA-DAQ HLS-Cores for LaBr peak detection, moving window deconvolution and zero suppression

Keywords: Data Management; DAQ; FPGA; Mu2e

  • Invited lecture (Conferences) (Online presentation)
    Mu2e Collaboration Meeting, STM Workshop, 16.06.2020, Online, Online

Permalink: https://www.hzdr.de/publications/Publ-31275
Publ.-Id: 31275


Interprofessionelle Kooperation: Bedarf und Komplexizität bei prospektiv-nuklearmedizinischen Studien am Beispiel des DKTK-Multicenter-Trials mit [68Ga]Ga-PSMA-11

Zippel, C.; Neels, O.; Biedenstein, S.; Giesel, F. L.; Kopka, K.

Ziel/Aim: Um neue PET-Tracer in die Patientenversorgung überführen zu können, werden in der nuklearmedizinischen Forschung zunehmend prospektiv-klinische Studien mit den vielversprechendsten Radioliganden initiiert. Damit diese Studien möglichst effizient und effektiv durchgeführt werden können, bedarf es der möglichst engen Kooperation und Kommunikation von Expert*innen aus verschiedenen Berufsgruppen.

Methodik/Methods: Wir beleuchten am Beispiel der Multicenter-Studie „Ga-68-PSMA-11 in Hochrisiko-Prostatakrebs“ der Phasen-I/-II, welche wesentlichen Professionen aus forschender Klinik, Wirkstoffherstellung und Verwaltung bei der Planung, Vorbereitung und Durchführung prospektiv-nuklearmedizinischer Studien involviert sein können und welche Aufgaben diese zur Studienverwirklichung wahrnehmen. Darauf aufbauend leiten wir organisatorische Maßnahmen ab, durch die die interprofessionelle Kooperation bei prospektiven Bildgebungsstudien (auch über mehrere Prüfzentren) gefördert werden kann.

Ergebnisse/Results: In die Beispielstudie sind im engeren fachlichen Kreis Mediziner aus Nuklearmedizin/Urologie/Pathologie, MTA-Rs, Studienassistenten, Radiochemiker/-pharmazeuten, BTA/CTA, MTA und Gesundheits-/Krankenpfleger involviert. Im weiteren fachlichen Kreis sind ferner Strahlenschutzbeauftragte, Qualitätsmanager, klinische Monitore, Juristen, Datenschutzbeauftragte, Projektmanager und Studienkoordinatoren eingebunden, und dies jeweils an bis zu elf Prüfzentren in Deutschland, Österreich und der Schweiz.

Schlussfolgerungen/Conclusions: Interprofessionelle Kooperation ist für die Durchführung prospektiv-nuklearmedizinischer Studien essentiell. Hierzu bedarf es u. a. der grundlegenden Bereitschaft, sich in andere (Tätigkeits-)Rollen hineinzuversetzen und über Professionsgrenzen hinaus kooperieren zu wollen, ausreichend Zeit zum gegenseitigen Austausch, Fähigkeit/Fertigkeiten zum berufsübergreifenden Projektmanagement und eine integrale Betrachtung benötigter Expertisen mit Stärkung professionsübergreifender Kommunikation insbesondere über die Leitungsebene.

  • Lecture (Conference) (Online presentation)
    58. DGN-Jahrestagung 2020, 06.-09.07.2020, Leipzig, Deutschland
    DOI: 10.1055/s-0040-1708427

Permalink: https://www.hzdr.de/publications/Publ-31274
Publ.-Id: 31274


GMP Requirements for a Clinical Trial with 68Ga-PSMA-11 - Experience from a Multi-Centre Trial

Neels, O.

Without abstract

  • Invited lecture (Conferences)
    Annual Congress of the European Association of Nuclear Medicine, 15.-19.10.2016, Barcelona, Spanien
    DOI: 10.1007/s00259-016-3484-4

Permalink: https://www.hzdr.de/publications/Publ-31273
Publ.-Id: 31273


Molecular Imaging of Prostate Cancer: A direct comparison of the preclinical characteristics of [18F]DCFPyL and [18F]PSMA-1007 and the impact of glutamic acids on [18F]PSMA-1007

Roscher, M.; Remde, Y.; Schäfer, M.; Bauder-Wüst, U.; Giesel, F.; Neels, O.; Cardinale, J.; Kopka, K.

Aim: For the imaging of PSMA-positive prostate cancer, several fluorine-18 (18F)-labelled compounds have been developed and translated into the clinics. Next to a clinical study comparing the tracer-specific characteristics of [18F]DCFPyL and [18F]PSMA-1007 intra-individually(1), a direct comparison of their preclinical characteristics has only recently been published(2). In this work, the importance of glutamic acids in the structure of [18F]PSMA-1007 is further elucidated using derivatives with none to three glutamic acids (Glu), respectively. Furthermore, [18F]DCFPyL and [18F]PSMA-1007 are evaluated regarding their preclinical characteristics using the in vitro and in vivo methods established at DKFZ Heidelberg, Germany. Materials and Methods: The precursors for radiofluorination containing different amino acid linkers (0-3 Glu) were synthesized by means of solid phase chemistry. The radiolabeling of [18F]PSMA-1007, its derivatives, and [18F]DCFPyL were performed prior to each experiment as described(3,4). The binding affinities of non-radioactive reference compounds were determined by competitive binding assays against [68Ga]Ga-PSMA-10 in LNCaP cells. The internalization of the respective radioligands in LNCaP cells was compared. Biodistribution and pharmacokinetics were evaluated in vivo in LNCaP-tumor bearing BALB/c Nude mice using μPET. Results: The Glu variation in the linker structure resulted in similar binding affinities (Ki 3-14 nM) whereby the insertion of three Glu showed the highest Ki values. Internalization assays revealed that the insertion of Glu influences the internalization rate, whereby the insertion of two Glu ([18F]PSMA-1007) leads to the highest internalization rate (54.04±13.7%) in a total range between 27.3±3% to 54±13.7%. In comparison to [18F]PSMA-1007, a higher proportion of [18F]DCFPyL remains cell surface bound; only 27.83 ± 4.31% of the radiotracer is internalized. [18F]DCFPyL also has a slightly lower binding affinity (18.02±9.63 nM). μPET imaging showed outstanding imaging properties, especially of [18F]DCFPyL and [18F]PSMA-1007. In mice, the liver uptake is reduced by introduction of Glu linkers. The data will be analysed more detailed soon. Conclusion: Comparative cell experiments revealed a high binding affinity for all tracers and the highest internalization rate for [18F]PSMA-1007. The insertion of Glu in the linker structure plays an important role in pharmacokinetics due to the decreased lipophilicity of the respective radiotracer. Especially [18F]DCFPyL and [18F]PSMA-1007 are of excellent imaging quality. Their apparent non-inferiority is currently under further assessment in clinical trials. References: (1) Giesel F et al (2017): JNM, doi: 10.2967/jnumed.117.204669. (2) Robu S et al (2018): EJNMMI Res., 8(1):30. (3) Cardinale J et al. (2017): JNM, 58(3):425-431. (4) Chen Y et al. (2011): Clin Cancer Res., 17(24):7645-53.

  • Lecture (Conference)
    Annual Congress of the European Association of Nuclear Medicine, 13.-17.10.2018, Düsseldorf, Deutschland
    DOI: 10.1007/s00259-018-4148-3

Permalink: https://www.hzdr.de/publications/Publ-31272
Publ.-Id: 31272


Initiation Of A Prospective Clinical Multicentre Trial With Local Production Of A Short-Lived PSMA-PET Radiopharmaceutical In The D-A-CH-Region: Chances And Experiences

Neels, O.; Zippel, C.; Giesel, F. L.; Kopka, K.

Aim/Introduction: The development of innovative radiotracers targeting PSMA for non-invasive imaging of prostate cancer and successive treatment results in an increasing number of multicentre clinical trials using the most promising PSMA ligand candidates. For prospective studies with short-lived radiopharmaceuticals like [68Ga]Ga-PSMA-11, a regulatory and country-specific structure has to be established before recruitment of patients is possible. This structure allows the decentralized manufacturing of the investigational medicinal product (IMP) according to Good Manufacturing (GMP) and subsequent implementation of the respective tracer compliant with Good Clinical Practice (GCP). Materials and Methods: For the multicenter clinical trial (phases-I/-II) ,,Ga-68-PSMA-11 in high-risk prostate cancer“ (NCT03362359) within DKTK a harmonized decentralized radiotracer production in multiple radiopharmacies has been set up for the very first time in the German speaking Radiopharmacy/Nuclear Medicine Community. In this prospective clinical study Nuclear Medicine physicians, radiopharmacists, urologists, pathologists and study related experts like lawyers and study nurses out of eleven study sites within the so-called D-A-CH region (Germany-Austria-Switzerland) have been involved. The basis for the accurately specified radioactive IMP manufacturing procedure was defined by EU-GMP requirements plus national standards (e.g. Medicinal Products Act and Radiation Protection Law). Results: For the recruiting study sites the required allowances, e.g. manufacturing authorization from local authorities as well as approval from ethics committees and national regulatory bodies such as BfS and BfArM in Germany, BASG in Austria as well as BAG and Swissmedic in Switzerland, have been obtained. The challenge of manufacturing a short-lived radiopharmaceutical at each of the participating geographically different sites with identical specification by adaption of production and quality control processes and parameters according to the IMP dossier (IMPD) during the starting phase of the clinical trial under a centralized quality assurance management has been achieved. Conclusion: The initiation and establishment of a multicentre clinical trial including the manufacturing of a short-lived radiopharmaceutical IMP across local study sites is very complex, but manageable. In view of the high European and national regulatory and legal burdens and the number of involved partners it is feasible in a defined time frame. Based on the achieved structures, the decentralized manufacture of novel short-lived radiopharmaceuticals can be established in the D-A-CH region and even on a European level for further investigator initiated multicentre clinical trials. We estimate our experiences important for the development of the field Nuclear Medicine at the national and international level taking into account the new EU regulation No 536/2014. References: None.

  • Poster
    Annual Congress of the European Association of Nuclear Medicine, 12.-16.10.2019, Barcelona, Spanien
    DOI: 10.1007/s00259-019-04486-2

Permalink: https://www.hzdr.de/publications/Publ-31271
Publ.-Id: 31271


Too many regulations

Neels, O.

Without abstract

  • Invited lecture (Conferences)
    Annual Congress of the European Association of Nuclear Medicine, 12.-16.10.2019, Barcelona, Spanien
    DOI: 10.1007/s00259-019-04486-2

Permalink: https://www.hzdr.de/publications/Publ-31270
Publ.-Id: 31270


Supplementary Video sets for the publication

Baraban, L.

6 supplementary videos

Related publications

  • Reseach data in the HZDR data repository RODARE
    Publication date: 2020-06-29
    DOI: 10.14278/rodare.384
    License: CC-BY-4.0

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-31268
Publ.-Id: 31268


Inverse Solidification Induced by Active Janus Particles

Huang, T.; Misko, V. R.; Gobeil, S.; Wang, X.; Nori, F.; Schütt, J.; Fassbender, J.; Cuniberti, G.; Makarov, D.; Baraban, L.

Crystals melt when thermal excitations or the concentration of defects in the lattice is sufficiently high. Upon melting, the crystalline long-range order vanishes, turning the solid to a fluid. In contrast to this classical scenario of solid melting, here we demonstrate a counter-intuitive behavior of the occurrence of crystalline long-range order in an initially disordered matrix. This unusual solidification is demonstrated in a system of passive colloidal particles accommodating chemically active defects - photocatalytic Janus particles. The observed crystallization occurs when the amount of active-defect-induced fluctuations (which is the measure of the effective temperature) reaches critical value. The driving mechanism behind this unusual behavior is purely internal and resembles a blast-induced solidification. Here the role of "internal micro-blasts" is played by the photochemical activity of defects residing in the colloidal matrix. The defect-induced solidification occurs under non-equilibrium conditions: the resulting solid exists as long as a constant supply of energy in the form of ion flow is provided by the catalytic photochemical reaction at the surface of active Janus particle defects. Our findings could be useful for understanding of the phase transitions of matter under extreme conditions far from thermodynamic equilibrium.

Related publications

Permalink: https://www.hzdr.de/publications/Publ-31267
Publ.-Id: 31267


Intrinsic plasticity of silicon nanowire neurotransistors for dynamic memory and learning functions

Baek, E.; Ranjan Das, N.; Vittorio Cannistraci, C.; Rim, T.; Santiago Cañón Bermúdez, G.; Nych, K.; Cho, H.; Kim, K.; Baek, C.-K.; Makarov, D.; Tetzlaff, R.; Chua, L.; Baraban, L.; Cuniberti, G.

Neuromorphic architectures merge learning and memory functions within a single unit cell and in a neuron-like fashion. Research in the field has been mainly focused on the plasticity of artificial synapses. However, the intrinsic plasticity of the neuronal membrane is also important in the implementation of neuromorphic information processing. Here we report a neurotransistor made from a silicon nanowire transistor coated by an ion-doped sol–gel silicate film that can emulate the intrinsic plasticity of the neuronal membrane. The neurotransistors are manufactured using a conventional complementary metal–oxide–semiconductor process on an 8-inch (200 mm) silicon-on-insulator wafer. Mobile ions allow the film to act as a pseudo-gate that generates memory and allows the neurotransistor to display plasticity. We show that multiple pulsed input signals of the neurotransistor are non-linearly processed by sigmoidal transformation into the output current, which resembles the functioning of a neuronal membrane. The output response is governed by the input signal history, which is stored as ionic states within the silicate film, and thereby provides the neurotransistor with learning capabilities.

Related publications

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  • Secondary publication expected

Permalink: https://www.hzdr.de/publications/Publ-31265
Publ.-Id: 31265


Nanosensors-Assisted Quantitative Analysis of Biochemical Processes in Droplets

Belyaev, D.; Schütt, J.; Ibarlucea, B.; Rim, T.; Baraban, L.; Cuniberti, G.

Here, we present a miniaturized lab-on-a-chip detecting system for an all-electric and label-free analysis of the emulsion droplets incorporating the nanoscopic silicon nanowires-based field-effect transistors (FETs). We specifically focus on the analysis of β-galactosidase activity, which is an important enzyme in the glycolysis metabolic pathway. Furthermore, the efficiency of the synthesis and action of β-galactosidase can be one of the markers for several diseases, eg., cancer, hyper/hypoglycemia, cell senescence, or other disruptions in cell functioning. We measure the reaction and reaction kinetics-associated shift of the source-to-drain current I sd in the system, which is caused by the change of the ionic strength of the microenvironment. With these results, we demonstrate that the ion-sensitive FETs are able to sense the interior of the aqueous reactors; thus, the conjunction of miniature nanosensors and droplet-based microfluidic systems conceptually opens a new route toward a sensitive, optics-less analysis of biochemical processes.

Permalink: https://www.hzdr.de/publications/Publ-31264
Publ.-Id: 31264


Experimental control of laser proton acceleration beyond 50 MeV

Ziegler, T.; Bernert, C.; Bock, S.; Brack, F.-E.; Cowan, T.; Garten, M.; Gaus, L.; Gebhardt, R.; Helbig, U.; Irman, A.; Kiriyama, H.; Kluge, T.; Kraft, S.; Kroll, F.; Metzkes-Ng, J.; Nishiuchi, M.; Obst-Hübl, L.; Püschel, T.; Rehwald, M.; Schlenvoigt, H.-P.; Schramm, U.; Zeil, K.

We report on the ongoing plasma accelerator development at the HZDR, moving from plasma-acceleration studies towards real plasma-accelerators that can be controlled and applied in the lab.
We show experimental investigations of proton acceleration from laser-irradiated solid foils with the DRACO PW laser, where highest proton cut-off energies were achieved for temporal pulse shape parameters well different from that of a Fourier transform limited (FTL) pulse. Controlled spectral phase modulation of the driver laser by means of an acousto-optic programmable dispersive filter enabled us to manipulate the temporal laser pulse shape and to study the effect on proton acceleration from thin foil targets. The results show that short and asymmetric pulses generated by positive third order dispersion values are favourable for proton acceleration and can lead to maximum energies of 60 MeV for thin plastic foils. Assuming appropriate control of the spectral phase of the laser and comparable temporal contrast conditions, we believe that the presented method can be universally applied to improve the proton acceleration performance using any other laser system operated in the PW regime.

  • Lecture (Conference) (Online presentation)
    6. Annual Matter and Technology Meeting, 17.-18.06.2020, Jülich, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-31263
Publ.-Id: 31263


Synthesis, characterization and evaluation of 68Ga labelled monomeric and dimeric quinazoline derivatives of the HBED-CC chelator targeting the epidermal growth factor receptor

Liolios, C.; Shegani, A.; Roupa, I.; Kiritsis, C.; Makarem, A.; Paravatou-Petsotas, M.; Pelecanou, M.; Bouziotis, P.; Papadopoulos, M.; Kopka, K.; Pirmettis, I.

Tyrosine kinase (TK) receptors including epidermal growth factor receptors (EGFRs) are known to be overexpressed in a wide variety of solid tumors associated with poor prognosis. The HBED-CC chelator N,N′-bis[2-hydroxy-5-(carboxyethyl)benzyl]ethylenediamine-N,N′-diacetic acid 1 was coupled via one or both its propionic acid moieties with the quinazoline EGFR-TK inhibiting pharmacophore 4-amino-N-(4-((3-bromophenyl)amino)quinazolin-6-yl)butanamide 3 resulting in either a monomeric 4 or a dimeric 5 species. Ligands 4 and 5 reacted with Ga3+ generating the corresponding complexes Ga4 and Ga5. Both ligands and complexes were characterized with mass spectrometry and NMR spectroscopy and evaluated in vitro with MTT assays in A431 cells, where they showed IC50 values in the range 51.6 to 68.8 μM. Labeling of ligands 4 and 5 with the PET radionuclide 68Ga was quantitative and resulted in tracers [68Ga]Ga4 and [68Ga]Ga5 with radiochemical purities greater than 98%, which were also characterised by comparative RP-HPLC studies with Ga4 and Ga5 respectively. Radiotracers [68Ga]Ga4 and [68Ga]Ga5 were stable (in tact tracer over 98%) in the reaction mixture (120 min) and in human serum (30 min). Both tracers were evaluated in vivo with biodistribution experiments in SCID mice bearing A431 tumors presenting tumor uptake of 1.34 for [68Ga]Ga4 and 1.01 %ID/g for [68Ga]Ga5 at 5 min, which was slightly decreased at 60 min p.i. and then remained stable until 120 min p.i. To the best of our knowledge, this is the first report of monomeric and dimeric quinazoline conjugates with the chelator HBED-CC, which can serve as a basis for further development of EGFR-TKI targeting tracers.

Keywords: Epidermal growth factor tyrosine kinase (EGFR-TK); tyrosinekinase inhibitors (TKIs); Quinazoline Gallium complexes; 68Ga; HBED-CC

Permalink: https://www.hzdr.de/publications/Publ-31262
Publ.-Id: 31262


Enhanced Sorption of Radionuclides by Defect-Rich Graphene Oxide

Boulanger, N.; Kuzenkova, A. S.; Iakunkov, A.; Romanchuk, A. Y.; Trigub, A. L.; Egorov, A. V.; Bauters, S.; Amidani, L.; Retegan, M.; Kvashnina, K.; Kalmykov, S. N.; Talyzin, A. V.

Extremely defect graphene oxide (dGO) is proposed as an advanced sorbent for treatment of radioactive waste and con-taminated natural waters. dGO prepared using a modified Hummers oxidation procedure, starting from reduced graphene oxide (rGO) as a precursor, shows significantly higher sorption of U(VI), Am(III) and Eu(III) compared to standard gra-phene oxides (GO). Earlier studies revealed the mechanism of radionuclide sorption related to defects in GO sheets. There-fore, explosive thermal exfoliation of graphite oxide was used to prepare rGO with large number of defects and holes. De-fects and holes are additionally introduced by Hummers oxidation of rGO thus providing extremely defect-rich material. Analysis of characterization by XPS, TGA, FTIR shows that dGO oxygen functionalization is predominantly related to de-fects, such as flake edges and edge atoms of holes, whereas standard GO exhibits oxygen functional groups mostly on the planar surface. The high abundance of defects in dGO results in a 15-fold increase in sorption capacity of U(VI) compared to standard Hummers GO. The improved sorption capacity of dGO is related to abundant carboxylic groups attached hole edge atoms of GO flakes as revealed by synchrotron-based extended X-ray absorption fine structure (EXAFS) and high-energy resolution fluorescence detected X-Ray absorption near edge structure (HERFD-XANES) spectroscopy.

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  • Secondary publication expected from 09.09.2021

Permalink: https://www.hzdr.de/publications/Publ-31261
Publ.-Id: 31261


The state of trace elements (In, Cu, Ag) in sphalerite studied by X-ray absorption spectroscopy of synthetic minerals

Trofimov, N. D.; Trigub, A. L.; Tagirov, B. R.; Filimonova, O. N.; Evstigneeva, P. V.; Chareev, D. A.; Kvashnina, K.; Nickolsky, M. S.

The oxidation state and local atomic environment of admixtures of In, Cu, and Ag in synthetic sphalerite crystals were determined by X-ray absorption spectroscopy (XAS). The sphalerite crystals doped with In, Cu, Ag, In–Cu, and In–Ag were synthesized utilizing gas transport, salt flux, and dry synthesis techniques. Oxidation states of dopants were determined using X-ray absorption near edge structure (XANES) technique. The local atomic structure was studied by X-ray absorption fine structure spectroscopy (EXAFS). The spectra were recorded at Zn, In, Ag, and Cu K-edges. In all studied samples, In was in the 3+ oxidation state and replaced Zn in the structure of sphalerite, which occurs with the expansion of the nearest coordination shells due to the large In ionic radius. In the presence of In, the oxidation state of Cu and Ag is 1+, and both metals can form an isomorphous solid solution where they substitute for Zn according to the coupled substitution scheme 2Zn2+ ↔ Me+ + In3+. Moreover, Ag K-edges EXAFS spectra fitting, combined with the results obtained for In-and Au-bearing sphalerite shows that the Me-S distances in the first coordination shell in the solid solution state are correlated with the ionic radii and increase in the order of Cu < Ag < Au. The distortion of the atomic structure increases in the same order. The distant (second and third) coordination shells of Cu and Ag in sphalerite are split into two subshells, and the splitting is more pronounced for Ag. Analysis of the EXAFS spectra, coupled with the results of DFT (Density Function Theory) simulations, showed that the In–In and Me+–In3+ clustering is absent when the metals are present in the sphalerite solid solution. Therefore, all studied admixtures (In, Cu, Ag), as well as Au, are randomly distributed in the matrix of sphalerite, where the concentration of the elements in the “invisible” form can reach a few tens wt.%.

Permalink: https://www.hzdr.de/publications/Publ-31260
Publ.-Id: 31260


Fingerprinting mean composition of lithium polysulfide standard solutions by applying high energy resolution fluorescence detected X-ray Absorption Spectroscopy

Robba, A.; Barchasza, C.; Bučar, K.; Petric, M.; Žitnik, M.; Kvashnina, K.; Vaughan, G. B. M.; Bouchet, R.; Alloin, F.; Kavčič, M.

In a lithium/sulfur (Li/S) battery, the reduction of sulfur during discharge involves a particular mechanism, where the active material successively dissolves into the electrolyte to form lithium polysulfide intermediate species (Li2Sx), with x being a function of the state of charge. In this work, sulfur K-edge Resonant Inelastic X-ray Scattering measurements were performed for the characterization of different Li2Sx polysulfide standard solutions. High Energy Resolution Fluorescence Detected X-ray Absorption Spectroscopy allowed clear separation the pre-edge absorption peak corresponding to terminal sulfur atoms from the main absorption peak due to internal atoms, and to evaluate quantitatively the evolution of the peak area ratio as a function of the polysulfide chain length. Results of this experimental work demonstrate that the normalized area of the pre-edge is a reliable fingerprint of Li2Sx mean chain length in agreement with recent theoretical predictions. As a perspective, this work confirms that operando HERFD XAS can be used to differentiate mean polysulfide composition, which is key issue in the characterization of Li/S cells.

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  • Secondary publication expected from 25.06.2021

Permalink: https://www.hzdr.de/publications/Publ-31259
Publ.-Id: 31259


Study of nanoscopic porosity in black metals by positron annihilation spectroscopy

Melikhova, O.; Cížek, J.; Hruška, P.; Liedke, M. O.; Butterling, M.; Wagner, A.; Novotný, M.; More-Chevalier, J.

Black and smooth Al films were characterized by the variable energy positron annihilation spectroscopy (VEPAS). It was found that in smooth films positronium (Ps) is formed on the surface only while in black metal films, it is formed also in nanoscopic pores inside the film. The mean pore size increases from the substrate to the surface due to increasing film roughness.

Keywords: positron annihilation spectroscopy; positron annihilation lifetime spectroscopy; black metals; Positronium

Permalink: https://www.hzdr.de/publications/Publ-31258
Publ.-Id: 31258


A secret luminescence killer in deepest QWs of InGaN/GaN multiple quantum well structures

Hospodková, A.; Hájek, F.; Pangrác, J.; Slavická Zíková, M.; Hubáček, T.; Kuldová, K.; Oswald, J.; Vaněka, T.; Vetushka, A.; Čížek, J.; Liedke, M. O.; Butterling, M.; Wagner, A.

This work suggests new alternative explanation why a single InGaN quantum well (QW) or the deepest QWs in the multiple quantum well (MQW) structures suffer with a high non-radiative recombination rate. According to SIMS results, positron annihilation spectroscopy and photoluminescence measurements we suggest that vacancy of Ga in complex with hydrogen atoms can play a dominant role in non-radiative Shockley-Read-Hall recombination of the deepest QWs in InGaN/GaN MQW structures. Vacancy of gallium originate dominantly in GaN buffer layers grown at higher temperatures in H2 atmosphere and are transported to the InGaN/GaN MQW region by diffusion, where they are very effectively trapped in InGaN layers and form complex defects with hydrogen atoms during epitaxy of InGaN layers. Trapping of gallium vacancies is another suggested mechanism explaining why the widely used In containing prelayers help to increase the luminescence efficiency of the InGaN/GaN MQW active region grown above them. Understanding the mechanism why the luminescence efficiency is suppressed in deeper QWs may be very important for LED community and can help to develop new improved technologies for the growth of InGaN/GaN MQW active region.

Keywords: positron annihilation spectroscopy; positron annihilation lifetime spectroscopy; quantum wells; InGaN; hydrogen complexes; GaN; vacancy

Permalink: https://www.hzdr.de/publications/Publ-31257
Publ.-Id: 31257


P1819 - Verfahren zur Herstellung eines keramischen Materials mit lokal einstellbarem Permeabilitätsgradienten, dessen Anwendung in einem Beschichtungsverfahren sowie dessen Verwendung

Bürger, D.; Krüger, S.; Skorupa, I.; Schmidt, H.; Du, N.

Die Erfindung betrifft ein Verfahren zur Herstellung eines keramischen Materials mit lokal einstellbarem Permeabilitätsgradienten, dessen Anwendung in einem Beschichtungsverfahren- Materialbearbeitungsverfahren sowie dessen Verwendung. Die Aufgabe ein Material zur Verfügung zu stellen, welches zum Leiten und Isolieren von Magnetfeldern geeignet ist sowie in magnetischen Kopplungselementen verwendet werden kann, wird durch ein Verfahren zur Herstellung eines keramischen Materials mit lokal einstellbarem Permeabilitätsgradienten gelöst, wobei das Verfahren folgende Schritte umfasst: - Erzeugen eines keramischen Materials mittels Erhitzen einer Ausgangsmaterialkomposition bis zu einer Temperatur unterhalb der Schmelztemperatur der Ausgangsmaterialkomposition, - Abkühlen des erzeugten keramischen Materials auf Raumtemperatur nach einer definierten Abkühlrate zur Einstellung einer Vortex-Dichte in dem erzeugten keramischen Material, und - nachfolgende lokale Temperaturbehandlung zum Erhitzen des keramischen Materials über dessen ferroelektrische Ordnungstemperatur und zum Einstellen des lokalen Permeabilitätsgradienten.

  • Patent
    DE102018125270 - Offenlegung 16.04.2020; Nachanmeldungen: WO

Permalink: https://www.hzdr.de/publications/Publ-31256
Publ.-Id: 31256


Boosting Room-Temperature Magneto-Ionics in a Non-Magnetic Oxide Semiconductor

de Rojas, J.; Quintana, A.; Lopeandía, A.; Salguero, J.; Costa-Krämer, J. L.; Abad, L.; Liedke, M. O.; Butterling, M.; Wagner, A.; Henderick, L.; Dendooven, J.; Detavernier, C.; Sort, J.; Menéndez, E.

Voltage control of magnetism through electric field-induced oxygen motion (magneto-ionics) could represent a significant breakthrough in the pursuit for new strategies to enhance energy efficiency in magnetically actuated devices. Boosting the induced changes in magnetization, magneto-ionic rates and cyclability continue to be key challenges to turn magneto-ionics into real applications. Here, it is demonstrated that room-temperature magneto-ionic effects in electrolyte-gated paramagnetic Co3O4 films can be largely increased both in terms of generated magnetization (6 times larger) and speed (35 times faster) if the electric field is applied using an electrochemical capacitor configuration (utilizing an underlying conducting buffer layer) instead of placing the electric contacts at the side of the semiconductor (electricdouble-layer transistor-like configuration). This is due to a greater uniformity and strength of the electric field in the capacitor design. These results are appealing to widen the use of ion migration in technological applications such as neuromorphic computing or iontronics in general.

Keywords: positron annihilation spectroscopy; Co3O4; Doppler broadening; ionic transport; magnetic switch; defects

Permalink: https://www.hzdr.de/publications/Publ-31255
Publ.-Id: 31255


A New Mechanism for Void-Cascade Interaction from Non-destructive Depth-resolved Atomic-scale Measurements of Ion Irradiation-induced Defects in Fe

Agarwal, S.; Liedke, M. O.; Jones, A. C. L.; Reed, E.; Kohnert, A. A.; Uberuaga, B. P.; Wang, Y. Q.; Cooper, J.; Kaoumi, D.; Li, N.; Auguste, R.; Hosemann, P.; Capolungo, L.; Edwards, D. J.; Butterling, M.; Hirschmann, E.; Wagner, A.; Selim, F. A.

The non-destructive investigation of single vacancies and vacancy clusters in ion irradiated samples requires a depth-resolved probe with atomic sensitivity to defects. The recent development of short-pulsed positron beams provides such a probe. Here, we combine depth-resolved Doppler broadening and positron annihilation lifetime spectroscopies to identify vacancy clusters in ion irradiated Fe and measure their density as a function of depth. Despite large concentrations of dislocations and voids in the pristine samples, positron annihilation measurements uncovered the structure of vacancy-clusters and the change in their size and density with irradiation dose. When combined with TEM measurements, the study demonstrates that the increase in the density of small vacancy clusters with irradiation is associated with a remarkable reduction in the size of large voids, revealing a novel mechanism for the interaction of cascade damage with voids in ion irradiated materials, a consequence of the high porosity of the initial microstructure.

Keywords: positron annihilation spectroscopy; positron annihilation lifetime spectroscopy; Doppler broadening; irradiation; Fe; defects; vacancy clusters; TEM

Permalink: https://www.hzdr.de/publications/Publ-31254
Publ.-Id: 31254


Characterisation of micropores in plasma deposited SiOx films by means of positron annihilation lifetime spectroscopy

Hoppe, C.; Mitschker, F.; Butterling, M.; Liedke, M. O.; de Los Arcos, T.; Awakowicz, P.; Wagner, A.; Grundmeier, G.

The effect of average incorporated ion energy and impinging atomic oxygen flux on the structure and permeability of SiOx thin films by a microwave driven low-pressure discharge with additional RF bias is studied by means of positron annihilation lifetime spectroscopy (PALS) and complementary analytical approaches. The film growth and structure were controlled by the particle fluxes. Acorrelation between the pore sizes and pore size distribution as measured by positron annihilation lifetime spectroscopy (PALS) and the adjusted plasma parameters was established. The corresponding barrier performance was measured by oxygen transmission rate (OTR) and could be explained by the pore size distribution. The dominant pore size characteristic for dangling bonds within the SiOx-network was found to be in the range of 0.8 nm. The chemical composition and morphology were analysed by means of X-ray photoelectron spectroscopy (XPS), FTIR diffuse reflectance measurements (DRIFT) and atomic force microscopy (AFM). It was observed that a combination of both an increase in incorporated energy per deposited Si atom and low oxygen to silicon ratio resulted in an enhanced cross-linking of the SiOx network and thereby lead to a decrease in micropore density and to a shift of the pore size distribution function to lower values.

Keywords: positron annihilation spectroscopy; positron annihilation lifetime spectroscopy; positron; SiOx; Doppler broadening; PALS; FTIR

Permalink: https://www.hzdr.de/publications/Publ-31253
Publ.-Id: 31253


Procedures for the GMP-Compliant Production and Quality Control of [18F]PSMA-1007: A Next Generation Radiofluorinated Tracer for the Detection of Prostate Cancer

Cardinale, J.; Martin, R.; Remde, Y.; Schäfer, M.; Hienzsch, A.; Hübner, S.; Zerges, A.-M.; Marx, H.; Hesse, R.; Weber, K.; Smits, R.; Hoepping, A.; Müller, M.; Neels, O.; Kopka, K.

Radiolabeled tracers targeting the prostate-specific membrane antigen (PSMA) have become important radiopharmaceuticals for the PET-imaging of prostate cancer. In this connection, we recently developed the fluorine-18-labelled PSMA-ligand [18F]PSMA-1007 as the next generation radiofluorinated Glu-ureido PSMA inhibitor after [18F]DCFPyL and [18F]DCFBC. Since radiosynthesis so far has been suffering from rather poor yields, novel procedures for the automated radiosyntheses of [18F]PSMA-1007 have been developed. We herein report on both the two-step and the novel one-step procedures, which have been performed on different commonly-used radiosynthesisers. Using the novel one-step procedure, the [18F]PSMA-1007 was produced in good radiochemical yields ranging from 25 to 80% and synthesis times of less than 55 min. Furthermore, upscaling to product activities up to 50 GBq per batch was successfully conducted. All batches passed quality control according to European Pharmacopoeia standards. Therefore, we were able to disclose a new, simple and, at the same time, high yielding production pathway for the next generation PSMA radioligand [18F]PSMA-1007. Actually, it turned out that the radiosynthesis is as easily realised as the well-known [18F]FDG synthesis and, thus, transferable to all currently-available radiosynthesisers. Using the new procedures, the clinical daily routine can be sustainably supported in-house even in larger hospitals by a single production batch.

Keywords: [18F]PSMA-1007; fluorine-18; PSMA; automation; prostate cancer; PET

Permalink: https://www.hzdr.de/publications/Publ-31252
Publ.-Id: 31252


Effects of Alloying Elements on Surface Oxides of Hot–Dip Galvanized Steel

Gaderbauer, W.; Truglas, T.; Arndt, M.; Steck, T.; Klingner, N.; Stifter, D.; Faderl, J.; Groiß, H.

Effects of steel alloying agents on the formation of the surface oxide layer of galvanized press hardened steel after austenitization annealing were examined with various advanced microscopy and spectroscopy techniques. The main oxides on top of the original thin Al2O3 layer, originating from the primary galvanizing process, are identified as ZnO and (Mn,Zn)Mn2O4 spinel. For some of the investigated steel alloys, a non-uniform, several nanometer thick Cr-enriched additional film was found at the Al2O3 layer. At a sufficiently high concentration, Cr can act as a substitute for Al during annealing, strengthening and regenerating the original Al2O3 layer with Cr2O3. Further analysis with secondary ion mass spectrometry allowed a reliable distinction between ZnO and Zn(OH)2.

Keywords: Steel; Metal Coatings; Oxidation; AES; SIMS; TEM

Permalink: https://www.hzdr.de/publications/Publ-31251
Publ.-Id: 31251


Carbon ion radiotherapy: impact of tumor differentiation on local control in experimental prostate carcinomas

Glowa, C.; Peschke, P.; Brons, S.; Neels, O.; Kopka, K.; Debus, J.; Karger, C. P.

Background: To summarize the research activities of the “clinical research group heavy ion therapy”, funded by the German Research Foundation (DFG, KFO 214), on the impact of intrinsic tumor characteristics (grading, hypoxia) on local tumor control after carbon (12C-) ion- and photon irradiations. Methods: Three sublines of syngeneic rat prostate tumors (R3327) with various differentiation levels (highly (-H), moderately (-HI) or anaplastic (-AT1), (diameter 10 mm) were irradiated with 1, 2 and 6 fractions of either 12C-ions or 6 MV photons using increasing dose levels. Primary endpoint was local tumor control at 300 days. The relative biological effectiveness (RBE) of 12C-ions was calculated from TCD50-values (dose at 50% tumor control probability) of photons and 12C-ions and correlated with intrinsic tumor parameters. For the HI-subline, larger tumors (diameter 18 mm) were irradiated with either carbon ions, oxygen ions or photons under ambient as well as hypoxic conditions to determine the variability of the RBE under different oxygenation levels. In addition, imaging, histology and molecular analyses were performed to decipher the underlying mechanisms. Results: Experimental results revealed (i) a smaller variation of the TCD50-values between the three tumor sublines for 12C-ions (23.6 - 32.9 Gy) than for photons (38.2 - 75.7 Gy), (ii) steeper dose-response curves for 12C-ions, and (iii) an RBE that increased with tumor grading (1.62 ± 0.11 (H) vs 2.08 ± 0.13 (HI) vs 2.30 ± 0.08 (AT1)). Large HI-tumors resulted in a marked increase of TCD50, which was increased further by 15% under hypoxic relative to oxic conditions. Noninvasive imaging, histology and molecular analyses identified hypoxia as an important radioresistance factor in photon therapy. Conclusions: The dose-response studies revealed a higher efficacy of 12C-ions relative to photon therapy in the investigated syngeneic tumor model. Hypoxia turned out to be at least one important radioresistance factor, which can be partly overridden by high-LET ion beams. This might be used to increase treatment effectiveness also in patients. The results of this project served as a starting point for several ongoing research projects.

Keywords: Carbon ion radiotherapy; relative biological effectiveness (RBE); prostate tumor; hypoxia imaging

Permalink: https://www.hzdr.de/publications/Publ-31250
Publ.-Id: 31250


Diagnostic performance of 68Ga-PSMA-11 (HBED-CC) PET/CT in patients with recurrent prostate cancer: evaluation in 1007 patients

Afshar-Oromieh, A.; Holland-Letz, T.; Giesel, F. L.; Kratochwil, C.; Mier, W.; Haufe, S.; Debus, N.; Eder, M.; Eisenhut, M.; Schäfer, M.; Neels, O.; Hohenfellner, M.; Kopka, K.; Kauczor, H.-U.; Debus, J.; Haberkorn, U.

Purpose Since the clinical introduction of 68Ga-PSMA-11 PET/CT, this imaging method has rapidly spread and is now regarded as a significant step forward in the diagnosis of recurrent prostate cancer (PCa). The aim of this study was to analyse the influence of several variables with possible influence on PSMA ligand uptake in a large cohort. Methods We performed a retrospective analysis of 1007 consecutive patients who were scanned with 68Ga-PSMA-11 PET/CT (1 h after injection) from January 2014 to January 2017 to detect recurrent disease. Patients with untreated primary PCa or patients referred for PSMA radioligand therapy were excluded. The possible effects of different variables including PSA level and PSA doubling time (PSADT), PSA velocity (PSAVel), Gleason score (GSC, including separate analysis of GSC 7a and 7b), ongoing androgen deprivation therapy (ADT), patient age and amount of injected activity were evaluated. Results In 79.5% of patients at least one lesion with characteristics suggestive of recurrent PCa was detected. A pathological (positive) PET/CT scan was associated with PSA level and ADT. GSC, amount of injected activity, patient age, PSADT and PSAVel were not associated with a positive PET/CT scan in multivariate analysis. Conclusion 68Ga-PSMA-11 PET/CT detects tumour lesions in a high percentage of patients with recurrent PCa. Tumour detection is clearly associated with PSA level and ADT. Only a tendency for an association without statistical significance was found between higher GSC and a higher probability of a pathological PET/CT scan. No associations were found between a pathological 68Ga-PSMA-11 PET/CT scan and patient age, amount of injected activity, PSADT or PSAVel.

Keywords: Prostate cancer; PET/CT; positron emission tomography; PSMA; prostate-specific membrane antigen

Permalink: https://www.hzdr.de/publications/Publ-31249
Publ.-Id: 31249


Tracer uptake in mediastinal and paraaortal thoracic lymph nodes as a potential pitfall in image interpretation of PSMA ligand PET/CT

Afshar-Oromieh, A.; Sattler, L. P.; Steiger, K.; Holland-Letz, T.; Livorsi Da Cunha, M.; Mier, W.; Neels, O.; Kopka, K.; Weichert, W.; Haberkorn, U.

Purpose Since the introduction of 68Ga-PSMA-11 PET/CT for imaging prostate cancer (PC) we have frequently observed mediastinal lymph nodes (LN) showing tracer uptake despite being classified as benign. The aim of this evaluation was to further analyze such LN. Methods Two patient groups with biphasic 68Ga-PSMA-11 PET/CT at 1 h and 3 h p.i. were included in this retrospective evaluation. Group A (n = 38) included patients without LN metastases, and group B (n = 43) patients with LN metastases of PC. SUV of mediastinal/paraaortal LN of group A (n = 100) were compared to SUV of LN metastases of group B (n = 91). Additionally, 22 randomly selected mediastinal and paraaortal LN of patients without PC were immunohistochemically (IHC) analyzed for PSMA expression. Results In group A, 7/38 patients (18.4%) presented with at least one PSMA-positive mediastinal LN at 1 h p.i. and 3/38 (7.9%) positive LN at 3 h p.i. with a SUVmax of 2.3 ± 0.7 at 1 h p.i. (2.0 ± 0.7 at 3 h p.i.). A total of 11 PSMA-positive mediastinal/paraaortal LN were detected in nine patients considering both imaging timing points. SUVmax of LN-metastases was 12.5 ± 13.2 at 1 h p.i. (15.8±17.0 at 3 h p.i.). SUVmax increased clearly (> 10%) between 1 h and 3 h p.i. in 76.9% of the LN metastases, and decreased significantly in 72.7% of the mediastinal/paraaortal LN. By IHC, PSMA-expression was observed in intranodal vascular endothelia of all investigated LN groups and to differing degrees within germinal centers of 15/22 of them (68.1%). Expression was stronger in mediastinal nodes (p = 0.038) and when follicular hyperplasia was present (p = 0.050). Conclusion PSMA-positive mediastinal/paraaortal benign LN were visible in a notable proportion of patients. PSMA-positivity on the histopathological level was associated with the activation state of the LN. However, in contrast to LN metastases of PC, they presented with significantly lower uptake, which, in addition, usually decreased over time.

Keywords: Prostate cancer; PET/CT; Mediastinal; Mediastinal/paraaortal; Lymph nodes; PSMA; Prostate-specific membrane antigen; 68Ga-PSMA-11

Permalink: https://www.hzdr.de/publications/Publ-31248
Publ.-Id: 31248


Vacancy-Hydrogen Interaction in Niobium during Low-Temperature Baking

Wenskat, M.; Čižek, J.; Liedke, M. O.; Butterling, M.; Bate, C.; Haušild, P.; Hirschmann, E.; Wagner, A.; Weise, H.

A recently discovered modified low-temperature baking leads to reduced surface losses and an increase of the accelerating gradient of superconducting TESLA shape cavities. We will show that the dynamics of vacancy-hydrogen complexes at low-temperature baking lead to a suppression of lossy nanohydrides at 2 K and thus a significant enhancement of accelerator performance. Utilizing Doppler broadening Positron Annihilation Spectroscopy, Positron Annihilation Lifetime Spectroscopy and instrumented nanoindentation, samples made from European XFEL niobium sheets were investigated. We studied the evolution of vacancies in bulk samples and in the sub-surface region and their interaction with hydrogen at different temperature levels during in-situ and ex-situ annealing.

Keywords: positron annihilation spectroscopy; PALS; Doppler broadening; Nb RF cavities; superconductivity

Permalink: https://www.hzdr.de/publications/Publ-31247
Publ.-Id: 31247


Quenched-in Vacancies and Hardening of Fe–Al Intermetallics

Prochazka, I.; Vlasak, T.; Cizek, J.; Lukac, F.; Liedke, M. O.; Anwand, W.; Jiraskova, Y.; Janickovice, D.

The role of vacancies in hardening of Fe–Al intermetallic alloys were studied in the present work for a wide range of Al concentrations from 20 to 50 at%. The alloys quenched from 1000 ◦C as well as those annealed subsequently at 520 ◦C for 1 h were subject to study. Slow-positron beam experiments combined with Vicker’s microhardness tests were utilised. Hardness of Fe–Al alloys exhibited a somewhat complex dependence on Al content which could not be fully explained purely by consideration of intermetallic phases formed. This happens due to additional hardening effect caused by quenched-in vacancies. The concentrations of vacancies were estimated from positron back-diffusion data and found to rise for Al content above 25 at%. Correlation of vacancy concentrations with hardness data for the quenched and annealed alloys has revealed that hardening of alloys with a low Al content (< 30 at%) is originated predominantly by anti-phase boundaries while hardening induced by quenched-in vacancies dominates for alloys with a higher Al content (30–50 at%).

Keywords: positron annihilation spectroscopy; Doppler broadening; FeAl; defetcs; SPONSOR

Permalink: https://www.hzdr.de/publications/Publ-31246
Publ.-Id: 31246


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