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31860 Publications
LISEL@DREAMS - The future of Accelerator Mass Spectrometry
Forstner, O.; Merchel, S.ORC; Rugel, G.; Wendt, K.
LISEL (Low energy Isobar SEparation by Lasers) is a future project at the DREAMS (DREsden Accelerator Mass Spectrometry) facility to widen the applications of AMS by extending the range of measurable (radio-) nuclides. AMS has proven to be a versatile tool capable of detecting a large number of long-lived radionuclides at the ultra-trace level i.e. isotope ratios down to 1E-16. However, being a mass spectrometric method, it is limited by the presence of strong isobaric background. To overcome this limitation, we propose to remove the isobars already at the low-energy side by laser photodetachment. This method allows to selectively neutralize isobars by laser radiation, leaving the ions of interest intact. First studies were performed at the University of Vienna and gave promising results [1,2] for the easier to be measured low-mass AMS isotopes Al-26 and Cl-36. Within the LISEL project this method will be for the first time applied to an AMS facility based on a 6 MV tandem accelerator. The first isotopes to be addressed with the new method will be Mn-53 and Fe-60. Both are currently only measurable at AMS facilities with more than 10 MV terminal voltage (currently available only at the ANU in Canberra/Australia or the LMU and TU Munich in Garching/Germany). Further on we foresee to apply this method to other rare isotopes, making LISEL@DREAMS a versatile machine for all isotopes. This will subsequently widen the applications and also the user community.
[1] Forstner, O. et al., Nucl. Instr. And Meth. B 361 (2015) p. 217-221 [2] Martschini, M. et al., Int. J. Mass Spectrom., 415 (2017) p. 9-17
Keywords: laser, AMS, accelerator mass spectrometry
  • Lecture (Conference)
    PLATAN 2019, International Conference Merger of the Poznan Meeting on Lasers and Trapping Devices in Atomic Nuclei Research and the International Conference on Laser Probing, 19.-24.05.2019, Mainz, Deutschland

Publ.-Id: 28918 - Permalink


Ultrasensitive (<1 mBq), cheap, and fast detection method for ⁷Be allowing high sample throughput
Rugel, G.; Tiessen, C. J.; Bemmerer, D.ORC; Querfeld, R.; Scharf, A.; Steinhauser, G.; Merchel, S.ORC
Beryllium-7 (T1/2 = 53.22 d), mainly measured via γ-spectrometry, is used as a (natural) radiotracer for education and science [1]. For activities < 0.1 Bq and especially for samples also containing so longer-lived ¹⁰Be (T1/2 = 1.387 Ma), accelerator mass spectrometry (AMS) is the method-of-choice.
We demonstrate that ⁷Be and ¹⁰Be can be quantified at the DREsden AMS (DREAMS) facility [2,3] on the same prepared BeO. Detection limits (⁷Be) are as low as ~ 0.6 mBq, hence, one-to-two orders of magnitude better than “standard/ordinary” and “sophisticated” decay counting (e.g. in an underground laboratory). Uncertainties for small samples are usually 6-7 % for small samples. The method is validated by γ-counting of two larger rainwater samples showing an excellent agreement with the AMS result [4].
Samples as small as tens of millilitres of rainwater can be chemically processed (after acidification) within a few hours without expensive and time-consuming ion exchange. Isobar (⁷Li) suppression by chemistry and AMS is sufficient to guarantee an ultrasensitive, cheap, and fast detection method for ⁷Be allowing high sample throughput.
The DREAMS facility allows external user access free-of-charge via a proposal system. Further information can be found at www.hzdr.de/ibc or www.ionbeamcenters.eu.

Acknowledgments
Parts of this research were carried out at the Ion Beam Centre (IBC) at the Helmholtz-Zentrum Dresden-Rossendorf e. V., a member of the Helmholtz Association. We appreciate support of Dominik Güttler, René Ziegenrücker and the DREAMS operator team during AMS-measurements, of Gyürky György (Hungarian Academy of Sciences) for providing ⁷Be for the calibration material, and of BMBF (05K16MG1) and DAAD-RISE Professional (HZDRPH-456) for funding. It was a pleasure to discuss ⁷Be-AMS with Andrew Smith (ANSTO).

References
[1] R. Querfeld, S. Merchel, G. Steinhauser, J. Radioanal. Nucl. Chem. 314 (2017) 521-527.
[2] S. Akhmadaliev et al., Nucl. Instr. Meth. B 294 (2013) 5-10.
[3] G. Rugel et al., Nucl. Instr. Meth. B 370 (2016) 94-100.
[4] C. Tiessen et al., Accelerator mass spectrometry (AMS) for beryllium-7 measurements in smallest rainwater samples, J. Radioanal. Nucl. Chem, 2019, doi: 10.1007/s10967-018-6371-6.
Keywords: Be-7, Be-10, accelerator mass spectrometry (AMS), rainwater
  • Invited lecture (Conferences)
    2nd International Conference on Radioanalytical and Nuclear Chemistry (RANC 2019), 05.-10.05.2019, Budapest, Hungary

Publ.-Id: 28917 - Permalink


Viable and active microorganisms in the deep terrestrial biosphere
Lopez-Fernandez, M.; Simone, D.; Broman, E.; Turner, E.; Wu, X.; Bertilsson, S.; Dopson, M.;
Although the continental deep biosphere is estimated to contain 2 to 19% of the earth’s total biomass, it is still one of the least understood ecosystems on the planet. A key question for the terrestrial deep biosphere is the viability and activity of the large diversity of microorganisms present. This work shows that the microbial populations in aquifers with different chemistry and depth below the surface are viable and active and their diversity decreased with depth below the surface. Quantitative PCR and high throughput 16S rRNA gene sequencing revealed no significant differences in 16S rRNA gene abundances and microbial diversity between total and viable communities. This suggested that the populations were adapted to the prevailing oligotrophic conditions and that non-viable cells are rapidly degraded and recycled into new biomass. In addition, in situ fixed RNA transcripts aligned to the three domains of life, supporting activity within these communities. Many of the SSU rRNA transcripts grouped within recently described candidate phyla or could not be mapped to known branches on the tree of life, suggesting that a large portion of the active biota in the deep biosphere remains unexplored. Despite the extremely oligotrophic conditions, mRNA transcripts revealed a diverse range of metabolic strategies carried out by different taxa. These results emphasize the need to further investigate microbial activities in the deep biosphere and the importance of unclassified and candidate phyla in this environment.
  • Lecture (Conference)
    12th International Congress of Extremophiles, 16.-20.09.2018, Ischia, Italy

Publ.-Id: 28916 - Permalink


Depth and Dissolved Organic Carbon Shape Microbial Communities in Surface Influenced but Not Ancient Saline Terrestrial Aquifers
Lopez-Fernandez, M.; Åström, M.; Bertilsson, S.; Dopson, M.;
The continental deep biosphere is suggested to contain a substantial fraction of the earth’s total biomass and microorganisms inhabiting this environment likely have a substantial impact on biogeochemical cycles. However, the deep microbial community is still largely unknown and can be influenced by parameters such as temperature, pressure, water residence times, and chemistry of the waters. In this study, 21 boreholes representing a range of deep continental groundwaters from the Äspö Hard Rock Laboratory were subjected to high-throughput 16S rRNA gene sequencing to characterize how the different water types influence the microbial communities. Geochemical parameters showed the stability of the waters and allowed their classification into three groups. These were (i) waters influenced by infiltration from the Baltic Sea with a “modern marine (MM)” signature, (ii) a “thoroughly mixed (TM)” water containing groundwaters of several origins, and (iii) deep “old saline (OS)” waters. Decreasing microbial cell numbers positively correlated with depth. In addition, there was a stronger positive correlation between increased cell numbers and dissolved organic carbon for the MM compared to the OS waters. This supported that the MM waters depend on organic carbon infiltration from the Baltic Sea while the ancient saline waters were fed by “geogases” such as carbon dioxide and hydrogen. The 16S rRNA gene relative abundance of the studied groundwaters revealed different microbial community compositions. Interestingly, the TM water showed the highest dissimilarity compared to the other two water types, potentially due to the several contrasting water types contributing to this groundwater. The main identified microbial phyla in the groundwaters were Gammaproteobacteria, unclassified sequences, Campylobacterota (formerly Epsilonproteobacteria), Patescibacteria, Deltaproteobacteria, and Alphaproteobacteria. Many of these taxa are suggested to mediate ferric iron and nitrate reduction, especially in the MM waters. This indicated that nitrate reduction may be a neglected but important process in the deep continental biosphere. In addition to the high number of unclassified sequences, almost 50% of the identified phyla were archaeal or bacterial candidate phyla. The percentage of unknown and candidate phyla increased with depth, pointing to the importance and necessity of further studies to characterize deep biosphere microbial populations.
Keywords: 16S rRNA gene, amplicon sequencing, deep subsurface, groundwaters, chemistry, microbial diversity

Publ.-Id: 28915 - Permalink


Microbial Community and Metabolic Activity in Thiocyanate Degrading Low Temperature Microbial Fuel Cells
Ni, G.; Canizales, S.; Broman, E.; Simone, D.; Palwai, V. R.; Lundin, D.; Lopez-Fernandez, M.; Sleutels, T.; Dopson, M.;
Thiocyanate is a toxic compound produced by the mining and metallurgy industries that needs to be remediated prior to its release into the environment. If the industry is situated at high altitudes or near the poles, economic factors require a low temperature treatment process. Microbial fuel cells are a developing technology that have the benefits of both removing such toxic compounds while recovering electrical energy. In this study, simultaneous thiocyanate degradation and electrical current generation was demonstrated and it was suggested that extracellular electron transfer to the anode occurred. Investigation of the microbial community by 16S rRNA metatranscriptome reads supported that the anode attached and planktonic anolyte consortia were dominated by a Thiobacillus-like population. Metatranscriptomic sequencing also suggested thiocyanate degradation primarily occurred via the ‘cyanate’ degradation pathway. The generated sulfide was metabolized via sulfite and ultimately to sulfate mediated by reverse dissimilatory sulfite reductase, APS reductase, and sulfate adenylyltransferase and the released electrons were potentially transferred to the anode via soluble electron shuttles. Finally, the ammonium from thiocyanate degradation was assimilated to glutamate as nitrogen source and carbon dioxide was fixed as carbon source. This study is one of the first to demonstrate a low temperature inorganic sulfur utilizing microbial fuel cell and the first to provide evidence for pathways of thiocyanate degradation coupled to electron transfer.
Keywords: MFC, thiocyanate degradation, extracellular electron transfer, low temperature, metatranscriptomics

Publ.-Id: 28914 - Permalink


Metatranscriptomes Reveal That All Three Domains of Life Are Active but Are Dominated by Bacteria in the Fennoscandian Crystalline Granitic Continental Deep Biosphere
Lopez-Fernandez, M.; Simone, D.; Wu, X.; Soler, L.; Nilsson, E.; Holmfeldt, K.; Lantz, H.; Bertilsson, S.; Dopson, M.;
ABSTRACT The continental subsurface is suggested to contain a significant part of the earth’s total biomass. However, due to the difficulty of sampling, the deep subsurface is still one of the least understood ecosystems. Therefore, microorganisms inhabiting this environment might profoundly influence the global nutrient and energy cycles. In this study, in situ fixed RNA transcripts from two deep continental groundwaters from the Äspö Hard Rock Laboratory (a Baltic Sea-influenced water with a residence time of < 20 years, defined as “modern marine,” and an “old saline” groundwater with a residence time of thousands of years) were subjected to metatranscriptome sequencing. Although small subunit (SSU) rRNA gene and mRNA transcripts aligned to all three domains of life, supporting activity within these community subsets, the data also suggested that the groundwaters were dominated by bacteria. Many of the SSU rRNA transcripts grouped within newly described candidate phyla or could not be mapped to known branches on the tree of life, suggesting that a large portion of the active biota in the deep biosphere remains unexplored.
Despite the extremely oligotrophic conditions, mRNA transcripts revealed a diverse range of metabolic strategies that were carried out by multiple taxa in the modern marine water that is fed by organic carbon from the surface. In contrast, the carbon dioxide- and hydrogen-fed old saline water with a residence time of thousands of years predominantly showed the potential to carry out translation. This suggested these cells were active, but waiting until an energy source episodically becomes available.
IMPORTANCE A newly designed sampling apparatus was used to fix RNA under in situ conditions in the deep continental biosphere and benchmarks a strategy for deep biosphere metatranscriptomic sequencing. This apparatus enabled the identification of active community members and the processes they carry out in this extremely oligotrophic environment. This work presents for the first time evidence of eukaryotic, archaeal, and bacterial activity in two deep subsurface crystalline rock groundwaters from the Äspö Hard Rock Laboratory with different depths and geochemical characteristics. The findings highlight differences between organic carbon fed shallow communities and carbon dioxide- and hydrogen-fed old saline waters. In addition, the data reveal a large portion of uncharacterized microorganisms, as well as the important role of candidate phyla in the deep biosphere, but also the disparity in microbial diversity when using standard microbial 16S rRNA gene amplification versus the large unknown portion of the community identified with unbiased metatranscriptomes.
Keywords: metatranscriptomes, mRNA, rRNA, deep biosphere, groundwaters

Publ.-Id: 28913 - Permalink


Investigation of viable taxa in the deep terrestrial biosphere suggests high rates of nutrient recycling
Lopez-Fernandez, M.; Broman, E.; Turner, S.; Wu, X.; Bertilsson, S.; Dopson, M.;
The deep biosphere is the largest ‘bioreactor’ on earth, and microbes inhabiting this biome profoundly influence global nutrient and energy cycles. An important question for deep biosphere microbiology is whether or not specific populations are viable. To address this, we used quantitative PCR and high throughput 16S rRNA gene sequencing of total and viable cells (i.e. with an intact cellular membrane) from three groundwaters with different ages and chemical constituents. There were no statistically significant differences in 16S rRNA gene abundances and microbial diversity between total and viable communities. This suggests that populations were adapted to prevailing oligotrophic conditions and that non-viable cells are rapidly degraded and recycled into new biomass. With higher concentrations of organic carbon, the modern marine and undefined mixed waters hosted a community with a larger range of predicted growth strategies than the ultra-oligotrophic old saline water. These strategies included fermentative and potentially symbiotic lifestyles by candidate phyla that typically have streamlined genomes. In contrast, the old saline waters had more 16S rRNA gene sequences in previously cultured lineages able to oxidize hydrogen and fix carbon dioxide. This matches the paradigm of a hydrogen and carbon dioxide-fed chemolithoautotrophic deep biosphere.
Keywords: 16S rRNA gene; deep subsurface; fracture groundwaters; propidium monoazide; viable cells; candidate phyla radiation

Publ.-Id: 28912 - Permalink


Formation of heavy clusters in ion-irradiated compounds
Kavetskyy, T.; Liedke, M. O.; Butterling, M.; Wagner, A.; Krause-Rehberg, R.; Sausa, O.; Meshi, L.; Dahan, I.; Vacik, J.; Horak, P.; Fuks, D.; Mykytenko, N.; Kiv, A.;
Ion-irradiated U(Al,Si)3 intermetallide, as an example of compounds with significantly different atomic masses of constituting atoms, was studied by slow positron beam spectroscopy in order to clarify the nature of defects accompanying the process of the ion-induced disordering of this material. The studied compound was irradiated with different Ar+ ion fluences with energy 30 keV. The formation of so-called heavy clusters (Uranium in this case) has been revealed. Such clusters affect the reliability of materials in nuclear reactors. Ion-induced creation of heavy clusters can provide important properties of similar materials.
Keywords: Intermetallic alloys and compounds; ion beam technology; positron annihilation; heavy clusters

Publ.-Id: 28910 - Permalink


Pressure-tuning the quantum spin Hamiltonian of the triangular lattice antiferromagnet Cs2CuCl4
Zvyagin, S. A.; Graf, D.; Sakurai, T.; Kimura, S.; Nojiri, H.; Wosnitza, J.; Ohta, H.; Ono, T.; Tanaka, H.;
Quantum triangular-lattice antiferromagnets are important prototype systems to investigate phenomena of the geometrical frustration in condensed matter. Apart from highly unusual magnetic properties, they possess a rich phase diagram (ranging from an unfrustrated square lattice to a quantum spin liquid), yet to be confirmed experimentally. One major obstacle in this area of research is the lack of materials with appropriate (ideally tuned) magnetic parameters. Using Cs2CuCl4 as a model system, we demonstrate an alternative approach, where, instead of the chemical composition, the spin Hamiltonian is altered by hydrostatic pressure. The approach combines high pressure electron spin resonance and magnetization measurements, allowing us not only to quasi-continuously tune the exchange parameters, but also to accurately monitor them. Our experiments indicate a substantial increase of the exchange coupling ratio from 0.3 to 0.42 at a pressure of 1.8 GPa, revealing a number of emergent field-induced phases.

Publ.-Id: 28907 - Permalink


Effect of insertion layer on electrode properties in magnetic tunnel junctions with a zero-moment half-metal
Titova, A.; Fowley, C.; Clifford, E.; Lau, Y.-C.; Borisov, K.; Betto, D.; Atcheson, G.; Hübner, R.; Xu, C.; Stamenov, P.; Coey, M.; Rode, K.; Lindner, J.; Fassbender, J.; Deac, A. M.;
Due to its negligible spontaneous magnetization, high spin polarization and giant perpendicular magnetic anisotropy, Mn₂RuₓGa (MRG) is an ideal candidate as an oscillating layer in THz spin-transfer-torque nano-oscillators. Here, the effect of ultrathin Al and Ta diffusion barriers between MRG and MgO in perpendicular magnetic tunnel junctions is investigated and compared to devices with a bare MRG/MgO interface. Both the compensation temperature, Tcomp, of the electrode and the tunneling magnetoresistance (TMR) of the device are highly sensitive to the choice and thickness of the insertion layer used. High-resolution transmission electron microscopy, as well as analysis of the TMR, its bias dependence, and the resistance-area product allow us to compare the devices from a structural and electrical point of view. Al insertion leads to the formation of thicker effective barriers and gives the highest TMR, at the cost of a reduced Tcomp. Ta is the superior diffusion barrier which retains Tcomp, however, it also leads to a much lower TMR on account of the short spin diffusion length which reduces the tunneling spin polarization. The study shows that fine engineering of the Mn₂RuₓGa/barrier interface to improve the TMR amplitude is feasible.
Keywords: Tunneling Magnetoresistance, Half-Metal, Mn-based alloys, MRAM, Spin Polarisation, Heusler alloy, Ferrimagnetic, Perpendicular Magnetic Anisotropy

Publ.-Id: 28906 - Permalink


Equiatomic quinary rare-earth rich amorphous ribbons with excellent magnetocaloric performance
Li, L.; Xu, C.ORC; Yuan, Y.; Zhou, S.
The glass forming ability, microstructure, magnetism and magnetocaloric effect (MCE) in two quinary rare-earth rich amorphous ribbons of Tm20Ho20Gd20Co20Ni20 and Tm20Ho20Gd20Co20Cu20 are reported. Both amorphous ribbons exhibit excellent glass forming ability and a table-like MCE. In addition to large magnetic entropy change of ∼14.0 J/kg-K, an extremely high refrigerant capacity of ∼790 J/kg are achieved which can almost cover the temperature range from liquid hydrogen to liquid nitrogen for the magnetic field change of 0–7 T for both ribbons. Therefore, the quinary rare-earth rich amorphous ribbons can be proposed as a new class of promising magnetic refrigeration materials.

Publ.-Id: 28905 - Permalink


Flow Rate Measurement in Flows with Asymmetric Velocity Profiles by Means of Distributed Thermal Anemometry
Arlit, M.; Schroth, C.; Schleicher, E.; Hampel, U.;
Flow rate in closed conduits is one of the most frequently measured parameters in industrial processes and in gas and water supply. For an accurate measurement, flow meters typically require a fully developed symmetric flow profile with preferably no radial or tangential velocity components.
This is commonly secured by mounting flow meters in a pipe at a sufficiently long distance downstream any change in cross-section or pipe direction. In this paper, we introduce a new approach for flow rate measurement of gases or liquids that employs a novel spatially resolving fluid velocity sensor basing on thermal anemometry. The new principle allows accurate flow rate measurements for non-axisymmetric velocity profiles, even directly after pipe bends, T-junctions or other alterations in the pipe geometry. This is exemplified for air flow in three different pipe bend configurations.
Keywords: Flow rate measurement; installation effects; thermal anemometry grid sensor

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  • Secondary publication expected from 16.05.2020

Publ.-Id: 28902 - Permalink


Annual Report 2018 - Institute of Resource Ecology
Stumpf, T.; Foerstendorf, H.ORC; Bok, F.; Richter, A.
Annual Report 2018 of the scientific activities of the Institute of Resource Ecology of the Helmholtz-Zentrum Dresden-Rossendorf
  • Open Access LogoWissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-096 2019
    ISSN: 2191-8708

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Publ.-Id: 28898 - Permalink


Solvent extraction and separation of rare earth elements by diamide type ligands and the complex structure of extracted species
Shimojo, K.; Sasanuki, T.; Schöne, S.ORC; Sugita, T.; Okamura, H.; Ikeda-Ohno, A.ORC
Solvent extraction of rare earth elements using a new type of diamide ligand, DODGAA, was performed to investigate the extractability and separability of the ligand for the separation of rare earth elements. Single crystals of the DODGAA complexes with some rare earth metals were also synthesised and structurally determined by single-crystal X-ray diffraction (SC-XRD) to understand the molecular structure of extracted species.
Keywords: Rare earth elements, separation, solvent extraction, structure determination, single-crystal X-ray diffraction
  • Lecture (Conference)
    The 84th Annual Meeting of the Society of Chemical Engineering, Japan, 13.-15.03.2019, Shibaura Institute of Technology, Toyosu, Tokyo, Japan

Publ.-Id: 28896 - Permalink


Coordination chemistry of f-block metal ions with ligands bearing bio-relevant functional groups
Götzke, L.; Schaper, G.; März, J.ORC; Kaden, P.ORC; Huittinen, N.ORC; Stumpf, T.; Kammerlander, K. K. K.; Brunner, E.; Hahn, P.; Mehnert, A.; Kersting, B.; Henle, T.; Lindoy, L. F.; Zanoni, G.; Weigand, J. J.
Over recent decades there has been a great deal of interest and associated research into aspects of the f-block (lanthanide and actinide) metal chemistry of naturally-occurring ligands, such as proteins, peptides, porphyrins and related tetraaza derivatives as well as synthetically modified natural ligands and solely synthetic ligand systems incorporating bio-relevant functional groups. In this review, we present a wide-ranging overview of published work spanning the above areas, with emphasis on selected biological, medical and environmental aspects. Systems capable of discriminating between metal ions from within, or between, the lanthanide and actinide groups are also discussed including the design and synthesis of biomimetic radionuclide chelators and radionuclide decorporation agents as well as solid adsorbent materials for the uptake of radionuclides from the environment and elsewhere. Thus, the interaction of the f-group elements with a range of biopolymers, including systems based on cellulose, chitin, chitosan, humic substances as well as a range of synthetic model systems is also presented. Other applications include the synthesis of new luminescent materials, including luminescent probes and luminescent metal coordination polymers exhibiting unusual photophysical properties as well as systems showing potential for use in the development of new MRI imaging agents.
Keywords: Lanthanides Actinides Maillard products Siderophores Calix[4]arenes Porphyrins Cellulose Chitin Chitosan Humic substances Peptides Proteins

Publ.-Id: 28895 - Permalink


Radium-doped BaSO4 NPs as functionalized precursors for future targeted alpha therapy
Reissig, F.; Hübner, R.; Steinbach, J.; Pietzsch, H.-J.; Mamat, C.ORC
Although significant advances in the tailoring of BaSO4-based nanoparticles have been achieved, the synthesis of particles is strongly dependent on the use of templates, surfactants, and additives, especially when radiolabeled with 133Ba or 224Ra. Herein, direct facile preparation of radiolabeled alendronate-functionalized BaSO4 nanoparticles in an aqueous medium in a one-pot reaction is developed. Remarkably, the size of the formed BaSO4 nanoparticles can be controlled by the type of the organic solvent used. Upon the addition of alendronate, amine functionalities were introduced into the nanoparticles. Additionally, a fluorescence dye-containing alendronate was used to evidence the introduction of the alendronate during the formation of the nanoparticles. The variations in the functionalities were investigated by IR and the morphology of the resulting BASO4 nanoparticles are investigated in detail by transmission electron microscopy. DLS and TEM measurements provided an average diameter of the nanoparticles of approx. 140 nm. Radium-doped alendronate nanoparticles were successfully obtained in a one-pot labeling procedure from [224Ra]RaCl2, Na2SO4 Ba(NO3)2 and alendronate.
Keywords: Radium-223, nanoparticles, Barium sulfate, talpha-theraphy

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  • Secondary publication expected from 01.06.2020

Publ.-Id: 28892 - Permalink


Vacancy cluster in ZnO films grown by pulsed laser deposition
Wang, Z.; Luo, C.; Anwand, W.; Wagner, A.; Butterling, M.; Azizar Rahman, M.; Phillips, M. R.; Ton-That, C.; Younas, M.; Su, S.; Ling, F. C. C.;
Undoped and Ga-doped ZnO films were grown on c-sapphire using pulsed laser deposition (PLD) at the substrate temperature of 600 oC. Positron annihilation spectroscopy study (PAS) shows that the dominant VZn-related defect in the as-grown undoped ZnO grown with relative low oxygen pressure P(O2) is a vacancy cluster (most likely a VZn-nVO complex with n=2, 3) rather than the isolated VZn which has a lower formation energy. Annealing these samples at 900oC induces out-diffusion of Zn from the ZnO film into the sapphire creating the VZn, which favors the formation
of vacancy cluster containing relatively more VZn. Increasing the P(O2) during growth also lead to the formation of the vacancy cluster with relatively more VZn. For Ga-doped ZnO films, the oxygen pressure during growth has significant influence on the electron concentration and the microstructure of the VZn-related defect. Green luminescence (GL) and yellow luminescence (YL) were identified in the cathodoluminescence study (CL) study, and both emission bands were quenched after hydrogen plasma treatment.
Keywords: Vacancy cluster ZnO pulsed laser deposition positron annihilation spectroscopy photo luminescence

Publ.-Id: 28891 - Permalink


Two-Dimensional Kagome Lattices Made of Hetero Triangulenes Are Dirac Semimetals or Single-Band Semiconductors
Jing, Y.; Heine, T.ORC
Here we discuss, based on first-principles calculations, two-dimensional (2D) kagome lattices composed of polymerized heterotriangulene units, planar molecules with D3h point group containing a B, C, or N center atom and CH2, O, or CO bridges. We explore the design principles for a functional lattice made of 2D polymers, which involves control of π-conjugation and electronic structure of the knots. The former is achieved by the chemical potential of the bridge groups, while the latter is controlled by the heteroatom. The resulting 2D kagome polymers have a characteristic electronic structure with a Dirac band sandwiched by two flat bands and are either Dirac semimetals (C center), or single-band semiconductors—materials with either exclusively electrons (B center) or holes (N center) as charge carriers of very high mobility, reaching values of up to ∼8 × 103 cm2 V–1 s–1, which is comparable to crystalline silicon.
Keywords: DFT, kagome, 2D polymers, 2D COFs

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  • Secondary publication expected from 30.11.2020

Publ.-Id: 28890 - Permalink


Assessing robustness of radiomic features by image perturbation
Zwanenburg, A.; Leger, S.; Agolli, L.; Pilz, K.; Troost, E.; Richter, C.; Löck, S.;
Image features need to be robust against differences in positioning, acquisition and segmentation to ensure reproducibility. Radiomic models that only include robust features can be used to analyse new images, whereas models with non-robust features may fail to predict the outcome of interest accurately. Test-retest imaging is recommended to assess robustness, but may not be available for the phenotype of interest. We therefore investigated 18 combinations of image perturbations to determine feature robustness, based on noise addition (N), translation (T), rotation (R), volume growth/shrinkage (V) and supervoxel-based contour randomisation (C). Test-retest and perturbation robustness were compared for combined total of 4032 morphological, statistical and texture features that were computed from the gross tumour volume in two cohorts with computed tomography imaging: I) 31 non-small-cell lung cancer (NSCLC) patients; II): 19 head-and-neck squamous cell carcinoma (HNSCC) patients. Robustness was determined using the 95% confidence interval (CI) of the intraclass correlation coefficient (1, 1). Features with CI >= 0:90 were considered robust. The NTCV, TCV, RNCV and RCV perturbation chain produced similar results and identified the fewest false positive robust features (NSCLC: 0.2-0.9%; HNSCC: 1.7-1.9%). Thus, these perturbation chains may be used as an alternative to test-retest imaging to assess feature robustness.

Publ.-Id: 28889 - Permalink


Testing halophilic bacteria for their potential as pyrite biodepressants in Cu-Mo bioflotation
Luque Consuegra, G.;
Presentation outlining work up to June 2018 in the screening of halophilic bacteria as pyrite biodepressants in Cu-Mo bioflotation processes delivered in the BHT conference in TUBAF, Freiberg.
Keywords: Bioflotation, Pyrite, Halophilic bacteria, Adhesion, M.A.T.H
  • Lecture (Conference)
    BHT – Freiberger Universitätsforum, 08.06.2018, Freiberg, Deutschland

Publ.-Id: 28884 - Permalink


Time-Like Baryon Transitions studies with HADES
Ramstein, B.; Adamczewski-Musch, J.; Arnold, O.; Arnoldi-Meadows, B.; Belounnas, A.; Belyaev, A.; Biernat, J.; Blanco, A.; Blume, C.; Böhmer, M.; Bordalo, P.; Chlad, L.; Chudoba, P.; Ciepał, I.; Deveaux, C.; Dittert, D.; Dreyer, J.; Fabbietti, L.; Fateev, O.; Fonte, P.; Franco, C.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzón, J. A.; Gernhäuser, R.; Gillitzer, A.; Golubeva, M.; Greifenhagen, R.; Guber, F.; Gumberidze, M.; Harabasz, S.; Heinz, T.; Hennino, T.; Himmelreich, M.; Höhne, C.; Holzmann, R.; Ierusalimov, A.; Ivanov, V.; Ivashkin, A.; Kämpfer, B.; Kajetanowicz, M.; Kampert, K.-H.; Karavicheva, T.; Kardan, B.; Khomyakov, V.; Koenig, I.; Koenig, W.; Korcyll, G.; Kornakov, G.; Kornas, F.; Kotte, R.; Kozela, A.; Kuboś, J.; Kugler, A.; Kunz, T.; Kurepin, A.; Kurilkin, P.; Kushpil, V.; Ladygin, V.; Lalik, R.; Lebedev, A.; Linev, S.; Liu, M.; Lopes, L.; Lorenz, M.; Lykasov, G.; Mahmoud, T.; Malakhov, A.; Markert, J.; Maurus, S.; Metag, V.; Michel, J.; Mihaylov, D. M.; Mikhaylov, V.; Morozov, S.; Müntz, C.; Naumann, L.; Nowakowski, K.; Parpottas, Y.; Patel, V.; Pauly, C.; Pechenov, V.; Pechenova, O.; Pereira, A.; Petousis, V.; Petukhov, O.; Pfeifer, D.; Pietraszko, J.; Przygoda, W.; Pysz, K.; Ramos, S.; Reshetin, A.; Ritman, L.; Rodriguez-Ramos, P.; Rost, A.; Sadovsky, A.; Salabura, P.; Scheib, T.; Schuldes, H.; Schwab, E.; Scozzi, F.; Seck, F.; Sellheim, P.; Selyuzhenkov, I.; Silva, L.; Smyrski, J.; Sobiella, M.; Spataro, S.; Spies, S.; Ströbele, H.; Stroth, J.; Strzempek, P.; Svoboda, O.; Szala, M.; Taranenko, A.; Tlusty, P.; Traxler, M.; Troyan, A.; Tsertos, H.; Wagner, V.; Wendisch, C.; Wiebusch, M. G.; Wintz, P.; Wirth, J.; Włoch, B.; Zhilin, A.; Zinchenko, A.; Zumbruch, P.; Zuschke, M.;
The HADES collaboration uses the e+e− production as a probe of the resonance matter produced in collisions at incident energies of 1-3.5 GeV/nucleon at GSI. Elementary reactions provide useful references for these studies and give information on resonance Dalitz decays (R→Ne+e−). Such processes are sensitive to the structure of time-like electromagnetic baryon transitions in a kinematic range where (off-shell) vector mesons play a crucial role. Results obtained in proton-proton reactions and in a commissioning pion-beam experiment are reported and prospects for future pion beam experiments and for first hyperon Dalitz decay measurements are described. The connection with the investigations of medium effects to be continued with HADES in the next years at SIS18 and SIS100 is also discussed.

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Publ.-Id: 28881 - Permalink


Natural occurring spore-forming sulfate reducers and their influence on the bentonite barrier
Matschiavelli, N.; Kluge, S.; Podlech, C.; Standhaft, D.; Grathoff, G.; Ikeda-Ohno, A.; Warr, L. N.; Chukharkina, A.; Arnold, T.; Cherkouk, A.;
To investigate the potential influence of natural occuring microorganisms within the bentonite on its minaralogical properties, we prepared anaerobic microcosm-experiments containing bentonite and a synthetic Opalinus Clay pore-water solution. Two different Bavarian bentonites (a natural and an industrial one) were incubated for one year at 30 °C and 60 °C and analyzed for bio-geochemical parameters and microbial diversity. For stimulation of microbial activity, some set ups were supplied with organics (acetate or lactate) or H2.
Only microcosms containing the industrial bentonite show striking effects. The presence of supplemented lactate or H2 led to the dominance (up to 81 %) of spore-forming Desulfosporosinus spp. – strictly anaerobic, sulfate-redung microorganisms. The respective microcosms show an increase of ferrous iron and a simoultaneous decrease of ferric iron as well as a decrease in sulfate-concentration. Concomitantly, the redoxpotential dropped and hydrogen-sulfide was fomed – leading very likely to the formation of the observed fractures and iron-sulfur precipitations. Furthermore, lactate-containing microcosms show the formation of acetate in the same amount as lactate was consumed. The here mentioned, microbial formed metabolites could affect the dissolution bahavior of minerals and ions within the bentonite and, thus, potentially change the sealant and adsorbent properties of the bentonite barrier.
  • Lecture (others)
    MIND Project Annual Meeting 2019, 07.-09.05.2019, Stockholm, Sweden

Publ.-Id: 28880 - Permalink


Characterization of Continuous Wave Laser-Induced ThermalGradients in Magnetic Tunnel Junctions Integrated IntoMicroresonators via COMSOL Simulations
Cansever, H.; Lindner, J.; Huebner, T.; Niesen, A.; Reiss, G.; Fassbender, J.; Deac, A. M.;
Spin caloritronics investigates static and dynamic effects on magnetic structures due to spin-currents generated by thermalgradients. Here, we present COMSOL simulation results using a 2-D heat transfer module applied to Co2FeAl/MgO/CoFeB magnetictunnel junctions (MTJs) integrated into microcavity resonators. Microresonators are used in order to study the effects of temperaturegradients on single micro-/nano-objects. We find that the thermal conductivity of the insulating barrier (MgO) plays a crucialrole, influencing the overall temperature, as well as the thermal gradient over the barrier. Taking into account the microresonatorstructure around the MTJ, which is mainly made from copper, strongly affects the uniform heating of the overall stack. Nevertheless,the gradient over the barrier is relatively unaffected by the surrounding conditions. The simulation results provide insight intothe temperature profile of the whole structure and show how modifying the structure of the surrounding materials may tune andoptimize the thermal gradient magnitude and ultimately provide a path for quantifying spin-transfer torques induced by thermalgradients.
Keywords: COMSOL simulation, ferromagnetic resonance (FMR), magnetic tunnel junction (MTJ), microresonator

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  • Secondary publication expected from 05.02.2020

Publ.-Id: 28879 - Permalink


Fast-neutron-induced fission cross section of Pu(242) measured at the neutron time-of-flight facility nELBE
Kögler, T.ORC; Junghans, A. R.ORC; Beyer, R.ORC; Dietz, M.; Düllmann, C. E.ORC; Eberhardt, K.; Lorenz, C.; Müller, S. E.ORC; Nolte, R.; Reinhardt, T. P.; Schmidt, K.; Runke, J.; Schwengner, R.ORC; Takacs, M.; Vascon, A.; Wagner, A.ORC
The fast-neutron-induced fission cross section of ²⁴²Pu was measured at the neutron time-of-flight facility nELBE. A parallel-plate fission ionization chamber with novel, homogeneous, large-area ²⁴²Pu deposits on Si-wafer backings was used to determine this quantity relative to the IAEA neutron cross-section standard ²³²U(n, f ) in the energy range of 0.5 to 10 MeV. The number of target nuclei was determined from the measured spontaneous fission rate of ²⁴²Pu. This helps to reduce the influence of the fission fragment detection efficiency on the cross section. Neutron transport simulations performed with GEANT 4, MCNP 6, and FLUKA 2011 are used to correct the cross-section data for neutron scattering. In the reported energy range the systematic uncertainty is below 2.7% and on average the statistical uncertainty is 4.9%. The determined results show an agreement within 0.67(16)% to recently published data and a good accordance to current evaluated data sets.
Keywords: neutron-induced fission, plutonium, parallel plate fission ionization chambers, cross section measurements, neutron transport simulations, nuclear reactions, nucleon induced nuclear reactions, nELBE
Related publications
Fast-neutron-induced fission cross section of Pu(242) … (Id 28970) HZDR-primary research data are used by this publication

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Publ.-Id: 28878 - Permalink


Impact of radiation, systemic therapy and Treatment sequencing on survival of patients with melanoma brain metastases
Rauschenberga, R.; Bruns, J.; Brüttinga, J.; Daubner, D.; Lohaus, F.; Zimmer, L.; Forschner, A.; Zips, D.; Hassel, J. C.; Berking, C.; Kaehler, K. C.; Utikal, J.; Gutzmer, R.; Terheyden, P.; Meiss, F.; Rafei-Shamsabadi, D.; Kiecker, F.; Debus, D.; Dabrowski, E.; Arnold, A.; Garzarolli, M.; Kuske, M.; Beissert, S.; Löck, S.; Linn, J.; Troost, E. G. C.; Meier, F.;
Background
Combining stereotactic radiosurgery (SRS) and active systemic therapies (STs) achieved favourable survival outcomes in patients with melanoma brain metastases (MBMs) in retrospective analyses. However, several aspects of this Treatment strategy remain poorly understood. We Report on the Overall survival (OS) of patients with MBM treated with a combination of radiotherapy (RT) and ST as well as the Impact of the v-Raf murine sarcoma viral oncogene homolog B (BRAF)-V600 Mutation (BRAFmut) status, types of RT and ST and their sequence. Patients and methods Data of 208 patients treated with SRS or whole brain Radiation therapy (WBRT) and either immunotherapy (IT) or targeted therapy (TT) within a 6-week- interval to RT were analysed retrospectively. OS was calculated from RT to death or last follow-up. Univariate- and multivariate Cox proportional hazard analyses were performed to determine prognostic Features associated with OS.
Results
The median follow-up was 7.3 months. 139 patients received IT, 67 received TT and 2 received IT and TT within 6 weeks to RT (WBRT 45%; SRS 55%). One-year Kaplan-Meier OS rates were 69%, 65%, 33% and 18% (P < .001) for SRS with IT, SRS with TT, WBRT with IT and WBRT with TT, respectively. Patients with a BRAF mut receiving IT combined with RT experienced higher OS rates (88%, 65%, 50% and 18%). TT following RT or started before and continued thereafter was associated with improved median OS compared with to TT solely before RT (12.2 [95% confidence interval {CI} 9.3–15.1]; 9.8 [95% CI 6.9–12.6] versus 5.1 [95% CI 2.7–7.5]; P = .03).
Conclusion
SRS and IT achieved the highest OS rates. A BRAFmut appears to be a favourable prognostic factor for OS. For the combination of RT and TT, the sequence appears to be crucial. Combinations of WBRT and ST achieved unprecedentedly high OS rates and Warrant further studies.
Keywords: Melanoma; Brain metastases; Stereotactic radiosurgery; Whole brain Radiation therapy; Immunotherapies; Targeted therapy; Immune checkpoint inhibitors; BRAF inhibitors

Publ.-Id: 28875 - Permalink


Carboranyl Analogues of Celecoxib with Potent Cytostatic Activity against Human Melanoma and Colon Cancer Cell Lines
Buzharevski, A.; Paskas, S.; Sárosi, M. B.; Laube, M.; Lönnecke, P.; Neumann, W.; Mijatovic, S.; Maksimovic-Ivanic, D.; Pietzsch, J.ORC; Hey-Hawkins, E.
Nonsteroidal anti-inflammatory drugs (NSAIDs) are the most common way of treating inflammatory disorders. Their widespread use helped reveal their other modes of action as pharmaceuticals, such as a profound effect on various cancers. Celecoxib has proven to be a very prominent member of this group with cytostatic activities. On the other hand, the highly dynamic field of drug design is constantly searching for new ways of modifying known structures to obtain more powerful and less harmful drugs. A very interesting development is the implementation of carboranes in pharmacologically active structures, mostly as phenyl mimetics. Herein we report the synthesis of three carborane-containing derivatives of the COX-2-selective NSAID celecoxib. The new compounds proved to have promising cytostatic potential against various melanoma and colorectal adenocarcinoma cell lines. Inhibited proliferation accompanied by caspase-independent apoptotic cell death was found to be the main cause of decreased cell viability upon treatment with the most efficient celecoxib analogue, 3 b (4-[5-(1,7-dicarba-closo-dodecaboranyl)-3-trifluoromethyl-1H-pyrazol-1-yl]-1-methylsulfonylbenzene).
Keywords: cancer; carboranes; celecoxib; cytotoxicity; drug discovery

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Publ.-Id: 28874 - Permalink


Simulation of the Radiation Field at the University Proton Therapy Dresden (UPTD)
Lutz, B.; Swanson, R.; Fiedler, F.; Enghardt, W.;
Radiation therapy is one of the most used treatment modalities of cancer. While most patients receive photon-therapy, a growing number of patients are treated with particles, mainly protons. Protons offers a more localised dose deposition compared to photon-therapy. This allows to reduce the dose that is applied by the primary beam to the healthy tissue outside the target volume. At the same time, the use of protons leads to a change in the composition of the radiation field, when compared to photons. For example, the out-of-field dose is dominated by secondary neutrons. Additionally, the radiation quality of protons is a function of energy. Therefore, the biological effect depends not only on the physical dose, but also on the linear energy transfer (LET). The neutron field and the LET, like other scientifically interesting quantities, are challenging to measure experimentally. Hence, a simulation that can reproduce the radiation field of a radiation treatment facility is of great value for the study of various aspects of proton therapy.
This work describes the simulation of the University Proton Therapy Dresden (UPTD) beam delivery system and treatment room.
Keywords: simulation, proton therapy, Geant4, TOPAS, double scattering
  • Lecture (Conference)
    EURADOS Annual Meeting 2019, 11.-14.02.2019, Lodz, Poland

Publ.-Id: 28873 - Permalink


Fluorine-18 labeling of S100 proteins for small animal positron emission tomography
Laube, M.; Kniess, T.; Neuber, C.; Haase-Kohn, C.; Pietzsch, J.ORC
The interaction of S100 proteins (S100s), a multigenic family of Ca2+-binding and Ca2+-modulated proteins, with pattern recognition receptors, e.g., Toll-like receptors (TLRs), the receptor for advanced glycation end products (RAGE), or scavenger receptors (SR), is hypothesized to be of high relevance in the pathogenesis of various diseases. This includes chronic inflammatory conditions, atherosclerosis, cardiomyopathies, neurodegeneration, and progression of cancers. However, data concerning the role of circulating S100s in these pathologies are scarce. One reason for this is the shortage of suitable radiolabeling methods for direct assessment of the metabolic fate of circulating S100s in vivo. We report a radiotracer approach using radiolabeling of recombinant human S100s with the positron emitter fluorine-18 (18F) by conjugation with N-succinimidyl 4-[18F]fluorobenzoate ([18F]SFB). The methodological radiochemical part focuses on an optimized and automated synthesis of [18F]SFB comprising HPLC purification to achieve higher chemical purity. The respective radioligands, [18F]fluorobenzoylated S100s ([18F]FB-S100s), were obtained with appropriate radiochemical purities, yields, and effective molar activities. Biological applications comprise cell and tissue binding experiments in vitro, biodistribution and metabolite studies in rodents in vivo/ex vivo, and dynamic positron emission tomography studies using dedicated small animal PET systems. Radiolabeling of S100s with 18F and, particularly, the use of small animal PET provide novel probes to delineate both their metabolic fate and the functional expression of their specific receptors under normal and pathophysiological conditions in rodent models of disease.
Keywords: Bolton-Hunter-type reagent; in vivo imaging; radiopharmacological characterization; 18F building block; module-assisted radiosynthesis; S100 proteins; calcium; EF-hand

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  • Secondary publication expected from 02.02.2020

Publ.-Id: 28872 - Permalink


The Inverse Trans Effect in Uranium complexes containing N-heterocyclic Carbenes
Köhler, L.; März, J.; Patzschke, M.; Kloditz, R.; Stumpf, T.;
Aim of this work was to investigate the inverse trans influence (ITI) in uranium complexes containing soft-donor ligands. Uranium(IV) and (V) complexes were synthesized by using the N-heterocylic carbene ligand iPrIm (L¹ ) and lithium bis(trimethylsilyl)amide (TMSA) as a base. The structural characterization by SC-XRD and geometry optimization of the resulting compounds [U(IV)(L¹ )₂(TMSA)Cl₃] (1) and (HL¹ )₂ [U(V)(TMSI)Cl₅] (2) (TMSI = trimethylsilylimide) confirmed the occurrence of an inverse trans influence (ITI) by means of the silylamido- or silylimido ligand.
Keywords: inverse trans influence, ITI, uranium complex, actinides
  • Lecture (others)
    Bilaterales Treffen mit AK Roesky (KIT), 10.-11.01.2019, Karlsruhe, Deutschland

Publ.-Id: 28869 - Permalink


Reversible adiabatic temperature change in the shape memory Heusler alloy NiMn0.8Ga: An effect of structural compatibility
Devi, P.; Ghorbani Zavareh, M.; Salazar Mejia, C.; Hofmann, K.; Albert, B.; Felser, C.; Nicklas, M.; Singh, S.;
The large magnetocaloric effect (MCE) observed in Ni-Mn based shape memory Heusler alloys put them forward to use in magnetic refrigeration technology. It is associated with a first-order magnetostructural (martensitic) phase transition.We conducted a comprehensive study of the MCE for the off-stoichiometric Heusler alloy Ni2.2Mn0.8Ga in the vicinity of its first-order magnetostructural phase transition. We found a reversible MCE under repeated magnetic field cycles. The reversible behavior can be attributed to the small thermal hysteresis of the martensitic phase transition. Based on the analysis of our detailed temperature dependent x-ray diffraction data, we demonstrate the geometric compatibility of the cubic austenite and tetragonal martensite phases. This finding directly relates the reversible MCE behavior to an improved geometric compatibility condition between cubic austenite and tetragonal martensite phases. The approach will help to design shape memory Heusler alloys with a large reversible MCE taking advantage of the first-order martensitic phase transition.

Publ.-Id: 28868 - Permalink


Effect of background electrolyte composition on the formation of Th(IV) nanoparticles on the muscovite (001) basal plane
Schmidt, M.ORC; Qiu, C.; Hellebrandt, S.; Eng, P. J.; Skanthakumar, S.; Steppert, M.; Soderholm, L.
Reliable long-term predictions regarding the safety of a nuclear waste disposal facility must be based on a sound understanding of the fundamental processes controlling radionuclide mobility in a subsurface environment. In particular, reactions at the water/mineral interface must be characterized on the molecular level.[1] Several actinides (An) show a tendency to form An-oxo-nanoparticles[2], which may be enhanced in the presence of mineral surfaces and even drive redox reactions.[3-6] As these reaction may, both, enhance and reduce the mobility of the actinides, it is of utmost importance to understand their mechanism and which parameters control the nanoparticle formation in environmental systems.
Recently, we have reported an unusual variability in the reactivity of ThIV on the basal plane of muscovite mica dependent on the composition of the background electrolyte.[7] In this study, based on surface X-ray diffraction [SXD; crystal truncation rod diffraction (CTR) and resonant anomalous X-ray reflectivity (RAXR)] and alpha spectrometry, it was observed that ThIV sorption from NaClO4 solution was significantly lower [< d.l. (~0.04 ThIV per area of the muscovite unit cell AUC)] than from NaCl solution (θNaCl = 0.4 Th/AUC) under otherwise identical conditions.[8] The study also revealed that the adsorbed quantity of ThIV was significantly higher in LiClO4 medium (θLiClO4 = 4.9 Th/AUC), than in NaClO4 with KClO4 intermediate between Li and Na (θKClO4 ~ 0.1 Th/AUC). In the case of LiClO4 it could be shown by RAXR, that sorption occurs in the form of small particles a few nm in size.
Here, we present a study using SXD in combination with alpha spectrometry and atomic force microscopy (AFM) aiming to identify the basis of the previously observed, unexpected effects. To probe whether anion and cation effect occur independently, ThIV sorption was studied in the presence of LiCl and KCl ([Th] = 0.1 mM, pH = 3.3, I = 0.1 M). ThIV uptake is strongest in the presence of LiCl (θLiCl = 8.8 Th/AUC), while sorption in the presence of KCl is weaker (θKCl = 3.6 Th/AUC) but still exceeds the surface occupancy previously found in NaCl media.[8] For all cations ThIV sorption is stronger when Cl- is the counterion compared to ClO4-, confirming that the cation effect is indeed independent of the background electrolyte’s anion. The influence of aqueous speciation on the sorption processes was determined using electro-spray-ionization time-of-flight mass spectrometry (ESI-TOF-MS), which finds a speciation dominated by the ThIV aquo ion in all media, indicating that any electrolyte effects must occur at the water/mineral interface. We investigated the influence of the presence of oligomers on the sorption process, by repeating experiments at higher initial [Th] = 3.0 mM. As expected ThIV sorption is significantly increased. ThIV adsorbs at a preferential height of ~6.5 Å, which can be identified as the preferred size of Th-nanochains on the mica basal plane by AFM (Fig. 1). Uptake from LiCl media is still larger than from NaCl, but only by ~32% compared to 2100% at the lower ThIV concentration. This suggests that the electrolyte cation influences the formation or aggregation of ThIV oligomers at the interface, and its influence is diminished when these are initially present.

Fig. 1. Total electron density and ThIV electron density as a function of distance from the mineral surface determined by SXD upon sorption from NaCl, KCl, and LiCl, respectively. Upper curves (grey, light blue, dark red) are total electron densities determined by CTR, lower curves (black, dark blue, light red) are ThIV electron density distributions from RAXR.

References
[1] H. Geckeis, et al., Chem. Rev., 113, 1016 (2013).
[2] K. E. Knope, et al., Chem. Rev., 113, 944 (2012).
[3] S. Hellebrandt, et al., Langmuir, 32, 10473 (2016).
[4] A. E. Hixon, et al., Environmental Science: Processes & Impacts, 20, 1306 (2018).
[5] M. Schmidt, et al., Env. Sci. Tech., 47, 14178 (2013).
[6] C. Walther, et al., Chem. Rev., 113, 995 (2013).
[7] M. Schmidt, et al., Geochim. Cosmochim. Acta, 165, 280 (2015).
[8] M. Schmidt, et al., Geochim. Cosmochim. Acta, 88, 66 (2012).
Keywords: Surface X-ray Diffraction, CTR, RAXR, AFM, Nucleation, Thorium, background electrolytes
  • Lecture (Conference)
    49èmes Journées des Actinides, 14.-17.04.2019, Erice, Italia

Publ.-Id: 28867 - Permalink


Focusing of multi-MeV, subnanosecond proton bunches from a laser-driven source
Jahn, D.; Schumacher, D.; Brabetz, C.; Kroll, F.; Brack, F.-E.; Ding, J.; Leonhardt, R.; Semmler, I.; Blazevic, A.; Schramm, U.; Roth, M.;
We report on our latest transverse focusing results of subnanosecond proton bunches achieved with a laser-driven multi-MeV ion beamline. In the frame of the LIGHT collaboration, a target normal sheath acceleration (TNSA) source based 6 m long beamline was installed. In the past years, the laser-driven proton beam was transported and shaped by this beamline. The particle beam is collimated with a pulsed high-field solenoid and rotated in longitudinal phase space with a radio-frequency cavity which leads to an energy compression with an energy spread of (2.7 +/- 1.7)% (Delta E/E-0 at FWHM) or a time compression to the subnanosecond regime. Highest peak intensities in the subnanosecond regime open up an interesting field for several applications, e.g., proton imaging, as injectors in conventional accelerators or precise stopping power measurements in a plasma. We report on achieving highest peak intensities using an installed second solenoid as a final focusing system in our beamline to achieve small focal spot sizes. We measured a focal spot size of 1.1 x 1.2 mm leading to 5.8 x 10(19) protons per s cm(2) at a central energy bin of (9.55 +/- 0.25) MeV, which can be combined with a bunch duration below 500 ps at FWHM.

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Publ.-Id: 28866 - Permalink


4He irradiation of zircon, ZrSiO4, using a micro-patterned, Si-based energy filter
Nasdala, L.; Akhmadaliev, S.; Chanmuang N., C.; Zowalla, A.; Csato, C.; Rüb, M.;
The quantitative evaluation of alpha-particle damage in the mineral zircon, ZrSiO4, using 4He irradiation experiments is difficult because the vast majority of atomic knock-ons in the target are concentrated in a narrow depth range near the ends of the He-ion trajectories. Here we present a new concept to overcome this problem, namely, tailoring the depth profile of damage by means of a micromechanically fabricated “energy filter”. Lamellae of 1.5 μm thickness, prepared from ZrSiO4 using the focused-ion-beam technique, were subjected to irradiation with 8.8 MeV 4He ions. Five irradiations with ion fluences in the range 2.5 × 1015–1 × 1017 cm-2 have resulted in mild to severe damage, as monitored by the broadening and downshift of SiO4-stretching Raman bands. Our results may provide a means for quantifying the contribution of alpha particles to the total self-irradiation damage in zircon.
Keywords: Radiation damage, Helium irradiation, Energy filter, Focused ion beam, Raman spectroscopy

Publ.-Id: 28865 - Permalink


Software in the context of luminescence dating: status, concepts and suggestions exemplified by the R package Luminescence
Kreutzer, S.; Burow, C.; Dietze, D.; Fuchs, M. C.; Fischer, M.; Schmidt, C.;
The relevance of luminescence dating is re- flected by the steadily growing quantity of published data. At the same time, the amount of data available for analysis has increased due to technological and methodological advances. Routinely, luminescence data are analysed using a mixture of commercially available soft- ware, self-written tools and specific solutions. Based on a luminescence dating literature screening we show how rarely articles report on the software used for the data analysis and we discuss potential problems arising from this. We explore the growing importance of the statistical programming language R in general and especially its reflection in recent software developments in the context of lu- minescence dating. Specifically, for the R package ‘Luminescence’ we show how the transparency, flexibility and reliability of tools used for the data analysis have been improved. We finally advocate for more transparency if unvalidated software solutions are used and we emphasise that more attention should be paid to the tools used for analysing the data.
Keywords: R, Software, Luminescence dating, Data analysis
  • Open Access LogoAncient TL 35(2017)2, 1-11

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Publ.-Id: 28863 - Permalink


Laser-induced fluorescence and hyperspectral imaging integrated in one sensor system - the inSPECtor project
Fuchs, M.; Lorenz, S.; Beyer, J.; Seidel, P.; Sharma, S. K.; Heitmann, J.; Gloaguen, R.;
Optical spectroscopy-based methods provide an immense potential for identifying rock compositions in a non-invasive and highly efficient manner, which is crucial for innovative, sustainable and acceptable technologies in raw material exploration. In principle, we employ two fundamental types from the set of light-material interactions light absorption used for hyperspectral imaging (HSI), and light emission used for laser-induced fluorescence (LiF) spectroscopy. The light spectra measured after illumination may be used as fingerprints of a sample’s composition, as long as the characteristic spectral features are known and distinguishable.
In the inSPECtor project, we develop an integrated sensor system that combines the two types of spectroscopy in order to increase the range of detectable materials and the robustness of results. HSI has already proven successful for the mapping of various minerals and also of some REEs such as Nd. However, the complexity of natural samples leads to mixed spectra with masked or only weak REE-related features complicating or even precluding a robust identification of many other REEs. Here, LiF spectroscopy provides a much more sensitive alternative as REEs show very distinct emission features characteristic transitions in REE3+ ions, as encountered in typical REE-containing minerals.
Here, we present how the inSPECtor project combines the potential of both HSI and LiF, especially for REE identification. We focus on the qualitative aspects of REE characterization in synthetic REE standards, in natural minerals and complex rocks from a range of typical REE-mineral deposits. Based on the characterization and successful identification of Nd3+, Pr3+, Sm3+, Eu3+, Yb3+, Ho3+, Dy3+, Er3+, Tb3+ and Tm3+ , we summarize required sensor specifications and illustrate needed data analyses routines.
Keywords: optical spectroscopy, spectroscopic sensors, hyperspectral imaging, laser-induced fluorescence, rare earth elements, raw material exploration
  • Poster
    9th Workshop on Hyperspectral Image and Signal Processing, 23.-26.09.2018, Amsterdam, Netherlands

Publ.-Id: 28862 - Permalink


News from the sandbox – from virtual sediment sections to full measurement models
Dietze, M.; Fuchs, M.; Kreutzer, S.;
Geomorphic concepts and hypotheses are usually formulated based on empiric data from the field or the laboratory (deduction). After translation into models they can be applied to case study scenarios (induction). However, the other way around - expressing hypotheses explicitly by models and test these by empiric data - is a rarely touched trail. There are several models tailored to investigate the boundary conditions and processes that generate, mobilise, route and eventually deposit sediment in a landscape. Thereby, the last part, sediment deposition, is usually omitted. Essentially, there is no model that explicitly focuses on mapping out the characteristics of sedimentary deposits - the material that is used by many disciplines to reconstruct landscape evolution. The R-package sandbox is a model framework that allows creating and analysing virtual sediment sections for exploratory, explanatory, forecasting and inverse research questions. sandbox is a probabilistic and rule-based model framework for a wide range of possible applications. It has been advanced and linked to another model to allow the full work flow of modelling luminescence measurements. This contribution introduces news about recent developments and shows a set of applications.
Keywords: R package, sandbox, sediments
  • Open Access LogoContribution to proceedings
    EGU General Assembly 2018, 04.-13.04.2018, Vienna, Austria
    News from the sandbox – from virtual sediment sections to full measurement models

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Publ.-Id: 28861 - Permalink


inSPECtor - integrated spectroscopy sensor system for laser-induced fluorescence and hyperspectral imaging
Fuchs, M.; Lorenz, S.; Beyer, J.; Seidel, P.; Sharma, S. K.; Gloaguen, R.; Heitmann, J.;
The raw material sector demands for fast and non-invasive exploration technologies to reduce economic and ecologic costs as well as increasing public acceptance. Within the inSPECtor project, we develop an integrated spectroscopic sensor system that uses the light spectrum measured after illumination of a target as fingerprint of a sample's composition. The idea is to integrate information from two basic types of light-material interactions, light absorption used for hyperspectral imaging (HSI), and light emission used for laser-induced fluorescence (LiF) spectroscopy. HSI has already proven successful for various mineral identification and also allows the mapping of REEs such as Nd, which may be used as pathfinder for other REEs. However, the complexity of natural samples leads to mixed spectra with masked or weak REE-related features complicating or even precluding a robust identification of many other REEs. Here, LiF spectroscopy provides a much more sensitive alternative as REEs show very distinct emission features characteristic of the f-f type electronic transitions in REE3+ ions, as encountered in typical REE-containing minerals. We present the potential of both HSI and LiF, especially for REE identification and for raw material exploration. We focus on the qualitative and quantitative aspects of REE characterization in synthetic REE standards and in natural minerals and complex rocks from a range of typical REE-mineral deposits.
Keywords: inSPECtor, spectroscopy, laser-induced fluorescence, hyperspectral imaging
  • Open Access LogoContribution to proceedings
    EGU General Assembly 2018, 04.-13.04.2018, Vienna, Austria
    Proceedings of EGU

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Publ.-Id: 28860 - Permalink


The Need for Multi-Source, Multi-Scale Hyperspectral Imaging to Boost Non-Invasive Mineral Exploration
Gloaguen, R.; Ghamisi, P.; Lorenz, S.; Kirsch, M.; Zimmermann, R.; Booysen, R.; Andreani, L.; Jackisch, R.; Hermann, E.; Tusa, L.; Unger, G.; Contreras, C.; Khodadadzadeh, M.; Fuchs, M.;
The high demand for raw materials in our post-industrial societies contrasts the increasing difficulties to find new mineral deposits. In Europe, accessible and high-grade deposits are mostly exhausted or currently mined. Hence, future exploration must focus on the remaining, more remote locations or penetrate much deeper into the Earth's crust. Sustaining mining activities in Europe would allow the development of key technologies but also sustainable and ethical production of technological metals. Thus, we suggest to focus research on advances in multi-scale and multi-sensor remote sensing-based Earth integration techniques. The scale should range from satellite to air- and drone-borne systems and include ground validation. Multi-sensor downscaling methods involving SAR and optical data are particularly promising. We demonstrate that the integration with other sensors and/or measures such as geophysical/geochemical data as well as non-conventional remote sensing features such as textures and geometries are of interest. Thus, ultimately, our objective is to boost the competitiveness, growth, sustainability and attractiveness of the raw material sector in Europe. While we focus on the raw material sector as it is currently of strategic importance, the required methods are transferable to most environmental studies.
Keywords: Hyperspectral Imaging, Mineral Exploration
  • Open Access LogoContribution to proceedings
    IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium, 22.-27.09.2018, Valencia, Spain
    Proceedings of IGARSS 2018

Publ.-Id: 28859 - Permalink


Heavy Metal Binding Peptides – Design and Construction of new Biosorbents
Braun, R.ORC; Schönberger, N.; Bachmann, S.; Matys, S.ORC; Lederer, F.ORC; Pollmann, K.ORC
Heavy metal contaminations in both industrial and environmental waters are widely occurring. However, removal is both challenging and cost-intensive. In this study, we identified metal-binding peptide sequences using phage surface display (PSD). Fusion proteins with PSD-derived sequences were construced for further recombinant production, future scale-up and as alternative to chemical synthesis. The construction of the fusion proteins included usage of inteins and affinity tags for simplified expression and purification. Quartz crystal microbalance with dissipation monitoring (QCM-D) was used for further characterization of the peptide-metal interaction. The system developed in this study provides metal-binding peptides with high specificity and sensitivity. Being biodegradable, the constructed peptides can be used in multiple applications. The identified motifs can furthermore provide a deeper understanding of peptide-metal interaction, leading to the discovery of novel metal-interacting biomolecules and better prediction of involved amino acids.
  • Poster
    8th Peptide Engineering Meeting, 08.-10.11.2018, Berlin, Deutschland

Publ.-Id: 28858 - Permalink


Multivariate Data Assimilation for Resource Model Updating
Prior, A.; Benndorf, J.; Tolosana-Delgado, R.; van den Boogaart, K. G.;
This is just a presentation in the COSMO Day. I did not submit an abstract since I was invited speaker
  • Invited lecture (Conferences)
    COSMO Day 2018, 05.07.2018, Montreal, Canada

Publ.-Id: 28856 - Permalink


Multivariate Ensemble Based Sequential Update Of The Resource Model For Real Time Mine Settings
Prior, A.; Tolosana-Delgado, R.; Prior-Arce, A.;
Mining industry is continuously monitoring key performance indicators (KPI), and geo-metallurgical properties such as grade, fragmentation or tonnage and reconciling estimates to online capture production performance parameters. New technology is looking for monitoring also other properties as grain size.
Relevant information is obtained from sensors installed at different mining production process stages, as in a Block Evaluation or Schedule and Blending.
This study aims to develop an efficient updating framework based on Sequential Ensemble Filtering by using compositional data statistics that will be able to cope with the non-linearities of the system.
  • Poster
    POF Evaluation, 28.02.-02.03.2018, Dresden, Germany

Publ.-Id: 28855 - Permalink


Resource model updating for underground mining production settings
Prior, A.; Benndorf, J.; Mariz, C.;
This research is part of the European Union funded 'Real Time Mining' project, which aims to develop a new framework to reduce uncertainties during the extraction process in highly selective underground mining settings. A continuously self-updating resource/grade control model concept is presented and aims to improve the raw material quality control and process efficiency of any type of mining operation. Applications in underground mines include the improved control of different components of the mineralogy and geochemistry of the extracted ore utilizing available “big data” collected during production. The development of the methodology is based on two full scale case study, the copper-zinc mine Neves-Corvo in Portugal and Reiche-Zeche mine in Germany. These serve for both, for the definition of method requirements and also as a basis for defining a Virtual Asset Model (VAM), which serves for artificial sampling as benchmark for performance analysis. This contribution introduces to the updating concept, provides a brief description of the method, explains details of the test cases and demonstrates the value added by an illustrative case study.
Keywords: Underground Mining, Data Assimilation, Geostatistitcs
  • Open Access LogoContribution to proceedings
    REAL TIME MINING - Conference on Innovation on Raw Material Extraction Amsterdam 2017, 10.-11.10.2017, Amsterdam, The Netherlands

Publ.-Id: 28854 - Permalink


Tissue-type mapping of gliomas.
Raschke, F.; Barrick, T. R.; Jones, T.; Yang, G.; Ye, X.; Howe, F. A.;
PURPOSE:

To develop a statistical method of combining multimodal MRI (mMRI) of adult glial brain tumours to generate tissue heterogeneity maps that indicate tumour grade and infiltration margins.

MATERIALS AND METHODS:

We performed a retrospective analysis of mMRI from patients with histological diagnosis of glioma (n = 25). 1H Magnetic Resonance Spectroscopic Imaging (MRSI) was used to label regions of "pure" low- or high-grade tumour across image types. Normal brain and oedema characteristics were defined from healthy controls (n = 10) and brain metastasis patients (n = 10) respectively. Probability density distributions (PDD) for each tissue type were extracted from intensity normalised proton density and T2-weighted images, and p and q diffusion maps. Superpixel segmentation and Bayesian inference was used to produce whole-brain tissue-type maps.

RESULTS:

Total lesion volumes derived automatically from tissue-type maps correlated with those from manual delineation (p < 0.001, r = 0.87). Large high-grade volumes were determined in all grade III & IV (n = 16) tumours, in grade II gemistocytic rich astrocytomas (n = 3) and one astrocytoma with a histological diagnosis of grade II. For patients with known outcome (n = 20), patients with survival time < 2 years (3 grade II, 2 grade III and 10 grade IV) had a high-grade volume significantly greater than zero (Wilcoxon signed rank p < 0.0001) and also significantly greater high grade volume than the 5 grade II patients with survival >2 years (Mann Witney p = 0.0001). Regions classified from mMRI as oedema had non-tumour-like 1H MRS characteristics.

CONCLUSIONS:

1H MRSI can label tumour tissue types to enable development of a mMRI tissue type mapping algorithm, with potential to aid management of patients with glial tumours.
Keywords: Glioma; Magnetic resonance spectroscopy (MRS); Multimodal MRI; Nosologic imaging; Pattern recognition

Publ.-Id: 28845 - Permalink


Dynamics of the magnetoelastic phase transition and adiabatic temperature change in Mn1.3Fe0.7P0.5Si0.55
Fries, M.; Gottschall, T.; Scheibel, F.; Pfeuffer, L.; Skokov, K. P.; Skourski, I.; Acet, M.; Farle, M.; Wosnitza, J.; Gutfleisch, O.;
The adiabatic temperature change ΔTad of a Mn1.3Fe0.7P0.5Si0.55 Fe2P-type alloy was measured under different magnetic field-sweep rates from 0.93 Ts−1 to 2870 Ts−1. We find a field-sweep-rate independent magnetocaloric effect due to a partial alignment of magnetic moments in the paramagnetic region overlapping with the magnetocaloric effect of the first-order phase transition. Additionally, the first-order phase transition is not completed even in fields up to 20 T leading to a non-saturating behavior of ΔTad. Measurements in different pulsed fields reveal that the first-order phase transition cannot follow the fast field changes as previously assumed, resulting in a distinct field-dependent hysteresis in ΔTad.

Publ.-Id: 28844 - Permalink


Enzymes Immobilized on Carbon Nitride (C3N4) Cooperating with Metal Nanoparticles for Cascade Catalysis
Wang, Y.; Zhang, N.; Hübner, R.; Tan, D.; Löffler, M.; Facsko, S.; Zhang, E.; Ge, Y.; Qi, Z.; Wu, C.;
The exploration of effective platforms for immobilizing chemo- and biocatalysts to develop biohybrid catalysts is an attractive subject of practical interest. In this work, carbon nitride (C3N4) is used for the first time as a platform for the immobilization of metal catalyst (Pd nanoparticles) and biocatalyst (Candida antarctica lipase B, CalB) in a facile manner to prepare biohybrid catalyst. The optimal biohybrid catalyst inherits the intrinsic performance of both Pd nanoparticles and CalB, and shows high activity in the one-pot cascade reaction converting benzaldehyde to benzyl hexanoate at room temperature. With this proof of concept, it is expected that C3N4 can be utilized for immobilizing more types of chemo- and biocatalysts for perspective applications.
Keywords: biohybrid catalysts, CalB, carbon nitride, cascade reactions, Pd nanoparticles

Publ.-Id: 28842 - Permalink


Technical Note: Experimental verification of magnetic field-induced beam deflection and Bragg peak displacement for MR-integrated proton therapy.
Schellhammer, S. M.; Gantz, S.; Lühr, A.; Oborn, B. M.; Bussmann, M.; Hoffmann, A. L.;
Purpose: Given its sensitivity to anatomical variations, proton therapy is expected to benefit greatly from integration with magnetic resonance imaging for online anatomy monitoring during irradiation.
Such an integration raises several challenges, as both systems mutually interact. The proton beam will experience quasi-continuous energy loss and energy-dependent electromagnetic deflection at the same time, giving rise to a deflected beam trajectory and an altered dose distribution with a displaced Bragg peak. So far, these effects have only been predicted using Monte Carlo and analytical models, but no clear consensus has been reached and experimental benchmark data are lacking. We measured proton beam trajectories and Bragg peak displacement in a homogeneous phantom placed inside a magnetic field and compared them to simulations.
Methods: Planar dose distributions of proton pencil beams (80–180 MeV) traversing the field of a 0.95 T NdFeB permanent magnet while depositing energy in a PMMA slab phantom were measured using EBT3 radiochromic films and simulated using the Geant4 toolkit. Deflected beam trajectories and the Bragg peak displacement were extracted from the measured planar dose distributions and compared against the simulations.
Results: The lateral beam deflection was clearly visible on the EBT3 films and ranged from 1 to 10 mm for 80 to 180 MeV, respectively. Simulated and measured beam trajectories and Bragg peak displacement agreed within 0.8 mm for all studied proton energies.
Conclusions: These results prove that the magnetic field-induced Bragg peak displacement is both measurable and accurately predictable in a homogeneous phantom at 0.95 T, and allows Monte Carlo simulations to be used as gold standard for proton beam trajectory prediction in similar frameworks for MR-integrated proton therapy.
Keywords: magnetic field induced Bragg peak displacement, Monte Carlo simulation, MR guidance, proton dosimetry, proton therapy

Publ.-Id: 28841 - Permalink


SDF-1/CXCR4 expression is an independent negative prognostic biomarker in patients with head and neck cancer after primary radiochemotherapy
De-Colle, C.; Menegakis, A.; Mönnich, D.; Welz, S.; Boeke, S.; Sipos, B.; Fend, F.; Mauz, P. S.; Tinhofer, I.; Budach, V.; Abu, J. J.; Stuschke, M.; Balermpas, P.; Rödel, C.; Grosu, A. L.; Abdollahi, A.; Debus, J.; Belka, C.; Ganswindt, U.; Pigorsch, S.; Combs, S. E.; Lohaus, F.; Linge, A.; Krause, M.; Baumann, M.; Zips, D.;
Introduction: Preclinical and clinical data suggest that the chemokine pathway governed by SDF-1 and CXCR4 contributes to a resistant phenotype. This retrospective biomarker study aims to explore the specific prognostic value of SDF-1 and CXCR4 expression in locally advanced head and neck squamous cell carcinomas (HNSCC) treated with primary radiochemotherapy (RT-CT).
Material and methods: Biopsies from 141 HNSCC tumours of the oral cavity, oropharynx and hypopharynx were evaluated for SDF-1 and CXCR4 expression by immunofluorescence. SDF-1 and CXCR4 expression was correlated with clinico-pathological characteristics and outcome after RT-CT.
Results: Patients with tumours exhibiting overexpression of intracellular SDF-1 and CXCR4 have a higher risk for loco-regional relapse and a worse overall survival after RT-CT (multivariate analysis, hazard ratio 2.33, CI [1.18–4.62], p = 0.02 and hazard ratio 2.02, CI [1.13–3.59], p = 0.02, respectively). Similar results were observed when only the subgroup of HPV DNA negative patients were analysed (hazard ratio 2.23 and 2.16, p = 0.02 and p = 0.01, respectively).
Conclusions: Our data support the importance of SDF-1 and CXCR4 expression for loco-regional control and overall survival in HNSCC after primary radiochemotherapy. Prospective multivariate validation and further studies into CXCR4 inhibition to overcome radiation resistance are warranted.
Keywords: SDF-1 CXCR4 Head and neck cancer Prognostic Biomarker Primary radiochemotherapy

Publ.-Id: 28840 - Permalink


Improved effectiveness of stereotactic radiosurgery in large brain metastases by individualized isotoxic dose prescription: an in silico study
Zindler, J. D.; Schiffelers, J.; Lambin, P.; Hoffmann, A. L.;
Introduction In large brain metastases (BM) with a diameter of more than 2cm there is an increased risk of radionecrosis (RN) with standard stereotactic radiosurgery (SRS) dose prescription, while the normal tissue constraint is exceeded. The tumor control probability (TCP) with a single dose of 15Gy is only 42%. This in silico study tests the hypothesis that isotoxic dose prescription (IDP) can increase the therapeutic ratio (TCP/Risk of RN) of SRS in large BM.
Materials and methods A treatment-planning study with 8 perfectly spherical and 46 clinically realistic gross tumor volumes (GTV) was conducted. The effects of GTV size (0.5–4cm diameter), set-up margins (0, 1, and 2mm), and beam arrangements (coplanar vs non-coplanar) on the predicted TCP using IDP were assessed. For single-, three-, and five-fraction IDP dose–volume constraints of V12Gy = 10cm3, V19.2 Gy = 10cm3, and a V20Gy = 20cm3, respectively, were used to maintain a low risk of radionecrosis.
Results In BM of 4cm in diameter, the maximum achievable single-fraction IDP dose was 14Gy compared to 15Gy for standard SRS dose prescription, with respective TCPs of 32 and 42%. Fractionated SRS with IDP was needed to improve the TCP. For three- and five-fraction IDP, a maximum predicted TCP of 55 and 68% was achieved respectively (non-coplanar beams and a 1mm GTV-PTV margin).
Conclusions Using three-fraction or five-fraction IDP the predicted TCP can be increased safely to 55 and 68%, respectively, in large BM with a diameter of 4cm with a low risk of RN. Using IDP, the therapeutic ratio of SRS in large BM can be increased compared to current SRS dose prescription.
Keywords: Radiotherapy · Stereotactic · Dose prescription · Normal tissue tolerance · Large brain metastases

Publ.-Id: 28839 - Permalink


Impaired DNA damage response signaling by FUS-NLS mutations leads to neurodegeneration and FUS aggregate formation
Naumann, M.; Pal, A.; Goswami, A.; Lojewski, X.; Japtok, J.; Vehlow, A.; Naujock, M.; Günther, R.; Jin, M.; Stanslowsky, N.; Reinhardt, P.; Sterneckert, J.; Frickenhaus, M.; Pan-Montojo, F.; Storkebaum, E.; Poser, I.; Freischmidt, A.; Weishaupt, J. H.; Holzmann, K.; Troost, D.; Ludolph, A. C.; Boeckers, T. M.; Liebau, S.; Petri, S.; Cordes, N.; Hyman, A. A.; Wegner, F.; Grill, S. W.; Weis, J.; Storch, A.; Hermann, A.;
Amyotrophic lateral sclerosis (ALS) is the most frequent motor neuron disease. Cytoplasmic fused in sarcoma (FUS) aggregates are pathological hallmarks of FUS-ALS. Proper shuttling between the nucleus and cytoplasm is essential for physiological cell function. However, the initial event in the pathophysiology of FUS-ALS remains enigmatic. Using human induced pluripotent stem cell (hiPSCs)-derived motor neurons (MNs), we show that impairment of poly(ADP-ribose) polymerase (PARP)-dependent DNA damage response (DDR) signaling due to mutations in the FUS nuclear localization sequence (NLS) induces additional cytoplasmic FUS mislocalization which in turn results in neurodegeneration and FUS aggregate formation. Our work suggests that a key pathophysiologic event in ALS is upstream of aggregate formation. Targeting DDR signaling could lead to novel therapeutic routes for ameliorating ALS.

Publ.-Id: 28837 - Permalink


Differential effects of α-catenin on the invasion and radiochemosensitivity of human colorectal cancer cells
Förster, S.; Hehlgans, S.; Rödel, F.; Otto, B.; Cordes, N.;
Driven by genetic and epigenetic alterations, progression, therapy resistance and metastasis are frequent events in colorectal cancer (CRC). Although often speculated, the function of cell-cell contact for radiochemosensitivity, particularly associated with E-cadherin/catenin complex, warrants further clarification. In this study, we investigated the role of the E-cadherin/catenin complex proteins under more physiological three-dimensional (3D) cell culture conditions in a panel of CRC cell lines. In contrast to floating spheroids and growth in the laminin-rich matrix, collagen type 1 induced the formation of two distinct growth phenotypes, i.e., cell groups and single cells, in 5 out of the 8 CRC cell lines.
Further characterization of these subpopulations revealed that, intriguingly, cell-cell contact proteins are important for invasion, but negligible for radiochemosensitivity, proliferation and adhesion. Despite the generation of genomic and transcriptomic data, we were unable to elucidate the mechanisms through which α-catenin affects collagen type 1 invasion. In a retrospective analysis of patients with rectal carcinoma, a low α-catenin expression trended with overall survival, as well as locoregional and distant control. Our results suggest that the E-cadherin/catenin complex proteins forming cell-cell contacts are mainly involved in the invasion, rather than the radiochemosensitivity of 3D grown CRC cells. Further studies are warranted in order to provide a better understanding of the molecular mechanisms controlling cell-cell adhesion in the context of radiochemoresistance.
Keywords: colorectal cancer, α-catenin, radiochemotherapy, E-cadherin

Publ.-Id: 28836 - Permalink


Pretherapeutic FDG–PET total metabolic tumor volume predicts response to induction therapy in pediatric Hodgkin’s lymphoma
Rogasch, J.; Hundsdoerfer, P.; Hofheinz, F.; Wedel, F.; Schatka, I.; Amthauer, H.; Furth, C.;
Background

Standardized treatment in pediatric patients with Hodgkin’s lymphoma (HL) follows risk stratification by tumor stage, erythrocyte sedimentation rate and tumor bulk. We aimed to identify quantitative parameters from pretherapeutic FDG-PET to assist prediction of response to induction chemotherapy.

Methods

Retrospective analysis in 50 children with HL (f:18; m:32; median age, 14.8 [4–18] a) consecutively treated according to EuroNet-PHL-C1 (n = 42) or -C2 treatment protocol (n = 8). Total metabolic tumor volume (MTV) in pretherapeutic FDG-PET was defined using a semi-automated, background-adapted threshold. Metabolic (SUVmax, SUVmean, SUVpeak, total lesion glycolysis [MTV*SUVmean]) and heterogeneity parameters (asphericity [ASP], entropy, contrast, local homogeneity, energy, and cumulative SUV-volume histograms) were derived. Early response assessment (ERA) was performed after 2 cycles of induction chemotherapy according to treatment protocol and verified by reference rating. Prediction of inadequate response (IR) in ERA was based on ROC analysis separated by stage I/II (1 and 26 patients) and stage III/IV disease (7 and 16 patients) or treatment group/level (TG/TL) 1 to 3.


Results

IR was seen in 28/50 patients (TG/TL 1, 6/12 patients; TG/TL 2, 10/17; TG/TL 3, 12/21). Among all PET parameters, MTV best predicted IR; ASP was the best heterogeneity parameter. AUC of MTV was 0.84 (95%-confidence interval, 0.69–0.99) in stage I/II and 0.86 (0.7–1.0) in stage III/IV. In patients of TG/TL 1, AUC of MTV was 0.92 (0.74–1.0); in TG/TL 2 0.71 (0.44–0.99), and in TG/TL 3 0.85 (0.69–1.0). Patients with high vs. low MTV had IR in 86 vs. 0% in TG/TL 1, 80 vs. 29% in TG/TL 2, and 90 vs. 27% in TG/TL 3 (cut-off, > 80 ml, > 160 ml, > 410 ml).

Conclusions

In this explorative study, high total MTV best predicted inadequate response to induction therapy in pediatric HL of all pretherapeutic FDG-PET parameters – in both low and high stages as well as the 3 different TG/TL.
Keywords: Pediatric Hodgkin’s lymphoma Early response assessment FDG-PET Metabolic tumor volume Asphericity

Publ.-Id: 28835 - Permalink


Enhancement of the effective mass at high magnetic fields in CeRhIn5
Jiao, L.; Smidman, M.; Kohama, Y.; Wang, Z. S.; Graf, D.; Weng, Z. F.; Zhang, Y. J.; Matsuo, A.; Bauer, E. D.; Lee, H.; Kirchner, S.; Singleton, J.; Kindo, K.; Wosnitza, J.; Steglich, F.; Thompson, J. D.; Yuan, H. Q.;
The Kondo-lattice compound CeRhIn5 displays a field-induced Fermi surface reconstruction at B* ≈ 30 T, which occurs within the antiferromagnetic state, prior to the quantum critical point at Bc0 ≈ 50 T. Here, in order to investigate the nature of the Fermi surface change, we measured the magnetostriction, specific heat, and magnetic torque of CeRhIn5 across a wide range of magnetic fields. Our observations uncover the field-induced itineracy of the 4f electrons, where above Bonset ≈ 17 T there is a significant enhancement of the Sommerfeld coefficient, and spin-dependent effective cyclotron masses determined from quantum oscillations. Upon crossing Bonset , the temperature dependence of the specific heat also shows distinctly different behavior from that at low fields. Our results indicate that the Kondo coupling is remarkably robust upon increasing the magnetic field. This is ascribed to the delocalization of the 4f electrons at the Fermi surface reconstruction at B*.

Publ.-Id: 28834 - Permalink


Concise Review: Prostate Cancer Stem Cells: Current Understandin
Skvortsov, S.; Skvortsova, I. I.; Tang, D. G.; Dubrovska, A.;
Prostate cancer (PCa) is heterogeneous, harboring phenotypically diverse cancer cell types. PCa cell heterogeneity is caused by genomic instability that leads to the clonal competition and evolution of the cancer genome and by epigenetic mechanisms that result in subclonal cellular differentiation. The process of tumor cell differentiation is initiated from a population of prostate cancer stem cells (PCSCs) that possess many phenotypic and functional properties of normal stem cells. Since the initial reports on PCSCs in 2005, there has been much effort to elucidate their biological properties, including unique metabolic characteristics. In this Review, we discuss the current methods for PCSC enrichment and analysis, the hallmarks of PCSC metabolism, and the role of PCSCs in tumor progression.
Keywords: Prostate • Cancer • Cancer stem cells • Heterogeneity • Metabolism

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Publ.-Id: 28833 - Permalink


Field-induced phases in a heavy-fermion U(Ru0.92Rh0.08)2Si2 single crystal
Prokes, K.; Förster, T.; Huang, Y.-K.; Mydosh, J. A.;
We report the high-field-induced magnetic phases and phase diagram of a high quality U(Ru0.92Rh0.08 )2Si2 single crystal prepared using a modified Czochralski method. Our paper, that combines high-field magnetization and electrical resistivity measurements, shows for fields applied along the c-axis direction three field-induced magnetic phase transitions at μ0Hc1 = 21.60, μ0Hc2 = 37.90, and μ0Hc3 = 38.25 T, respectively. In agreement with a microscopic up-up-down arrangement of the U magnetic moments the phase above Hc1 has a magnetization of about one-third of the saturated value. In contrast the phase between Hc2 and Hc3 has a magnetization that is a factor of 2 lower than above the Hc3 where a polarized Fermi-liquid state with a saturated moment Ms ≈ 2.1μB/U is realized. Most of the respective transitions are reflected in the electrical resistivity as sudden drastic changes. Most notably, the phase between Hc1 and Hc2 exhibits substantially larger values. As the temperature increases, transitions smear out and disappear above ≈15 K. However, a substantial magnetoresistance is observed even at temperatures as high as 80 K. Due to a strong uniaxial magnetocrystalline anisotropy, a very small field effect is observed for fields applied perpendicular to the c-axis direction.

Publ.-Id: 28832 - Permalink


Jahn-Teller effect problems via ultrasonic experiments. Application to the impurity crystal CdSe:Cr
Averkiev, N. S.; Bersuker, I. B.; Gudkov, V. V.; Zhevstovskikh, I. V.; Sarychev, M. N.; Zherlitsyn, S.; Yasin, S.; Korostelin, Y. V.; Surikov, V. T.;
Based on the data analysis of ultrasonic experiments, a novel approach has been developed to explore Jahn-Teller effect (JTE) problems in non-cubic crystals with JT centers without involving additional experimental data beyond the information about the electronic term and crystal symmetry. Distinguished from cubic crystals, the axis of symmetry of the bulk non-cubic crystal do not necessarily coincide with those of the local impurity center, thus complicating the relation between the distortions produced by the ultrasound wave and the JTE active modes. We analysed the problem with corresponding calculations for the wurtzite-type hexagonal crystal CdSe:Cr2+, in which the chromium ion substitutes the cadmium one in the tetrahedral environment, resulting in its electronic ground state 5T2(e2t2). Experimental investigation of this system by ultrasound at frequencies of 28-105 MHz in the temperature range of 4-180 K, yields a peak in the attenuation of the ultrasound below 40 K for the normal modes related to the c 11, c 44, c 55, c 55, and c 66 elastic moduli. The peak has been interpreted as the manifestation of the JTE, similar to the one, observed in cubic crystals doped with 3d ions. However, no anomalies of attenuation have been detected for the mode related to the c 33 elastic modulus, in contradiction to the theoretical predictions based on the previous method, worked out for cubic crystals. In the new method we obtained direct relations between the deformations, related to the crystal moduli, and the local JT modes, calculated the partition functions for each of the three possible JTE problems for systems with an electronic T term, T⊗e, T⊗t2 and T⊗(e + t2) revealed how these deformations alter the vibronic energy levels responsible for the relaxations in the JT centers. It emerged that in the wurtzite crystal under consideration, only in the T⊗e problem the deformation related to the elastic moduli c 33 displaces all the vibronic energy level uniformly, without relaxation possibilities, thus supporting the new method and explaining the experimental observations.

Publ.-Id: 28831 - Permalink


Changing the properties of GaAs via strain engineering in core/shell nanowires
Balaghi, L.; Bussone, G.; Grifone, R.; Hübner, R.; Grenzer, J.; Shan, S.; Fotev, I.; Pashkin, A.; Ghorbani-Asl, M.; Krasheninnikov, A.; Schneider, H.; Helm, M.; Dimakis, E.;
III-V compound semiconductors have fueled many breakthroughs in photonics owing to their direct optical band gap and the possibility to tailor it in ternary or quaternary alloys by selecting the chemical composition appropriately. More recently, III-V semiconductors in the form of free-standing nanowires have found new strengths for a wide range of future applications in nanotechnology, including nano-photonics. Here we explore the great possibilities for strain engineering in core/shell nanowires as an alternative route to tailor the optical band gap of III-V semiconductors without changing their chemical composition. In particular, we demonstrate that the GaAs core in GaAs/InxGa1-xAs or GaAs/InxAl1-xAs core/shell nanowires can sustain unusually large misfit strains that would have been impossible in equivalent thin-film heterostructures, and undergoes a significant modification of its electronic proper-ties.

Core/shell nanowires were grown in the self-catalyzed mode on SiOx/Si(111) substrates by molecular beam epitaxy [1, 2]. Strain analysis was performed using synchrotron X-ray diffraction and Raman scat-tering spectroscopy, and showed that for a thin enough core, the magnitude and the spatial distribution of the built-in misfit strain can be regulated via the composition and the thickness of the shell. Beyond a critical shell thickness, we obtain a heavily tensile-strained core and an almost strain-free shell. The tensile strain of the core exhibits a predominantly-hydrostatic character and causes the reduction of the GaAs band gap energy (Figure 1) in accordance with our theoretical predictions using deformation-potential theory and first-principle calculations. For 7 % of strain (x = 0.54), the band gap energy was reduced to 0.87 eV at 300 K, i.e. a remarkable reduction of 40 %. This is particularly important for ap-plications in optical fiber telecommunications because the emission from strained GaAs nanowires can now cover the O-band and potentially the S-band of telecommunication wavelengths.

Besides the optical band gap, a similar reduction is expected for the effective mass of free electrons in tensile-strained GaAs. The corresponding electron mobility was estimated by time-domain terahertz spectroscopy to be in the range of 4000 – 5000 cm2/V·s at 300 K (core diameter = 22 nm, x = 0.39–0.49). These values are the highest reported, even in comparison to GaAs/AlxGa1-xAs nanowires with double the core thickness. This means that high-mobility transistors could now be possible with strained GaAs nanowires.

All in all, our results demonstrate that strained GaAs in core/shell nanowires can resemble the electronic properties of InxGa1-xAs, which makes it suitable for near-infrared nano-photonics. The use of a binary alloy instead of a ternary one would be advantageous because phenomena like phase separation, surface segregation or alloy disorder that typically exist in ternary alloys and limit the performance of photonic or electronic devices, become now irrelevant.
  • Invited lecture (Conferences)
    Nanostructures for Photonics, 07.05.2018, Saint Petersburg, Russia

Publ.-Id: 28829 - Permalink


Broadband photo-excited coherent acoustic frequency combs and mini-Brillouin-zone modes in a MQW-SESAM structure
Li, C.; Gusev, V.; Dimakis, E.; Dekorsy, T.; Hettich, M.;
A multiple quantum-well semiconductor saturable absorber mirror (MQW-SESAM) structure has been investigated by femtosecond pump-probe laser spectroscopy at a central wavelength of around 1050 nm. Coherent acoustic phonons are generated and detected over a wide frequency range from ~15 GHz to ~800 GHz. In the optical absorption region, i.e., in the multiple quantum wells (In0.27Ga0.73As), acoustic frequency combs centered at ~365 GHz, with a comb spacing of ~33 GHz, are generated. Most importantly, in the transparent region, i.e., in the distributed Bragg reflector, which is formed by a non-doped long-period semiconductor GaAs/Al0.95Ga0.05As superlattice, the mini-Brillouin-zone center, as well as zone-edge acoustic modes, are observed. The mini-zone-center modes with a fundamental frequency of 32 GHz can be attributed to the spatial modulation of the pump optical interference field with a period very close to that of the distributed Bragg reflector, in combination with the periodic spatial modulation of the electrostriction coefficient in the distributed Bragg reflector. The excitation of mini-zone-edge modes is attributed to the stimulated subharmonic decay of the fundamental center modes. Their subsequent back-folding to the mini-Brillouin-zone center makes them Raman active for the probe light.
Keywords: coherent acoustic phonons; pump-probe spectroscopy; quantum well; semiconductor; superlattice; mini-Brillouin-zone; high-speed asynchronous optical sampling
  • Open Access LogoApplied Sciences 9(2019), 289

Publ.-Id: 28828 - Permalink


Structural and optical properties of pulsed-laser deposited crystalline β-Ga2O3 thin films on silicon
Berencén, Y.; Xie, Y.; Wang, M.; Prucnal, S.; Rebohle, L.; Zhou, S.;
Crystalline β-Ga2O3 thin films on (100)- and (111)-oriented Si substrates are produced by pulsed laser deposition. The as-deposited thin films are demonstrated to be polycrystalline and contain a slight deficit of oxygen atoms as measured by x-ray diffraction spectroscopy and Rutherford backscattering spectrometry, respectively. The crystallographic orientation of the Si substrate is found to play no role on the ultimate properties of the films. A direct optical band gap of 4.8 eV is determined by temperature-dependent photoluminescence excitation (PLE). Temperature-dependent PLE spectra reveal the existence of a deep acceptor level of around 1.1 eV with respect to the valence band related to self-trapped holes. We experimentally demonstrate that point defects in O-poor β-Ga2O3 thin films act as deep donors and the optical transitions are found to take place via recombination of electrons from one of the intrinsic deep donor levels with self-trapped holes located at 1.1 eV above the valence band. The 3.17 eV ultraviolet photoluminescence is proven to be related to self-trapped holes in a small polaron state between two O(II)-s sites, whereas the two blue (2.98, 2.72 eV) and the green (2.39 eV) luminescence bands are mainly originated from gallium-oxygen vacancy pairs in the (1-) charge state, gallium vacancies in the (2-) charge state and neutral oxygen interstitials, respectively.
Keywords: β-Ga2O3 thin film on Si, pulsed laser deposition, photoluminescence, substrate orientation

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Publ.-Id: 28824 - Permalink


Geological 3D model of the Thaba Chrome Mine, Bushveld Complex, South Africa
Schwäbe, A.; Gutzmer, J.; Bachmann, K.;
This 3D geologic-stratigraphic modelling project is based on comprehensive drilling data originating from the Thaba mining lease area in the Western Bushveld Complex, South Africa. The geometric shape and distribution of manifold ultramafic and mafic rock types of the cyclic units of Lower and Upper Critical Zone of the Rustenburg Layered Suite is subject of this study. These 2.06 Ga old Paleoproterozoic successions occur as layered sequences at Thaba Mine and are characterized by shallow inclination towards SE (dipping angles 15° to 27°), distinct lateral and vertical continuity of the layering and the regular stratigraphic order of the horizons.
Therewith, the requirements for the 3D geologic modelling approach are complied. The technique is called ‘Integrated Stratigraphic Modelling’ and is utilized by Maptek’s Vulcan modelling suite. The project is started by compiling a drilling database of more than 400 boreholes that host collar, survey, geology, and assay data. The present rock types of the source data are classified into five classes (chromitite, ‘silicate’, alteration, structure, burden) and a stratigraphic list of 42 horizons is developed based on the positions of chromitite horizons in the drilling data. Preparations for the modelling include modifications of original drilling data by applying the succession of horizons on the stratigraphy field in the geology table of the database.
The developed stratigraphic horizon list is utilized by the software to sequence and interpolate floor and roof positions of each horizon. In total, the model consists of 21 chromitite layers (LG1 to MG4b) and 21 mafic interlayers. Interlayer horizons with the suffix -‘SIL’ comprise all rock types between two chromitite layers. Pyroxenite, harzburgite, and norite are most dominant; the higher in the stratigraphic column the more likely are rock types that contain cumulus plagioclase, e.g. anorthosites. Altered rock types such as troctolites and serpentinites are also occurring relatively frequent, but also discordant IRUP bodies as well as dykes and pegmatitic rocks.
Chromitite layers are representing the basal parts of cyclic units with average thicknesses between a few centimeters and one meter, in some cases up to a few meters. Especially Lower Group chromitites are occurring with relative constant thicknesses over the entire study area. The farms Schilpadnest, south-west Zwartkop, and Elandskuil are parts of the study area where the layering is developed best. Middle Group chromitites and their mafic host rocks are distributed much more discontinuous on the farms Zwartkop (north-east), Roodedam, and Middellaagte.
A pronounced lateral variation of the distribution of chromitites and host rock interlayers is recognizable in different parts of the study area, particularly areas of intense faulting between the farms Zwartkop and Middellaagte plus between Middellaagte and Elandskuil. Additionally, the consistency of the modelling results is reduced in areas were dominantly short boreholes occur, especially on the north-east section of farm Zwartkop.
Keywords: -
  • Master thesis
    TU BA Freiberg, 2018
    Mentor: Jens Gutzmer
    90 Seiten

Publ.-Id: 28823 - Permalink


A new single crystal diffractometer at BM20/ESRF
Hennig, C.; Ikeda-Ohno, A.; Radoske, T.; Scheinost, A. C.;
The Institute of Resource Ecology / Helmholtz-Zentrum Dresden-Rossendorf operates since 20 years the Rossendorf Beamline (ROBL/BM20) at the European Synchrotron Radiation Facility (ESRF). The ESRF will interrupt the user operation for a large upgrade between January 2019 and July 2020. This time will be used to refurbish the existing experiments and to extend the experimental capacities including a diffractometer for single crystal diffraction.
This diffractometer intends to fill the gap between small molecule and large molecule crystallography. The photon flux of up to 1012 photons/sec allow the structure determination of small single crystals. The analysis of complex intergrown crystals and electron density studies is possible. The energy range of 5-35 keV allows the use of anomalous dispersion. In-situ experiments will be supported.
The objective requires the combination of a large detector, precise sample position and sufficient space for additional equipment. The diffractometer consists of an adjustable granite table with a metal frame which carry the detector. It follows a design of SNBL/ESRF and is manufactured by Instrument Design Technology Ltd/UK. The Bragg reflexes will be registered with a silicon Pilatus3 X 2M single photon counting detector. Samples will be mounted on a kappa goniometer. A microscope will be placed in a large distance 170 mm from the crystal, which allows to install a cryo cooler (80-400 K), a heater (1200 K), and a Vortex X90 CUBE silicon drift detector with a FalconX1 processor. The data extraction with will be performed with CRYSALIS. Individual components are already tested with X-ray beam.
The new single crystal diffractometer will be accessible starting from August 2020.
Keywords: single crystal diffraction, small molecule and large molecule crystallography, SCXRD, Rossendorf Beamline
  • Lecture (Conference)
    Annual Meeting of the German Crystallographic Society, 25.-28.03.2019, Leipzig, Germany
  • Abstract in refereed journal
    Zeitschrift für Kristallographie Supplement 39(2019), S16-04

Publ.-Id: 28822 - Permalink


Multivariate geochemical classification of chromitite seams in the Bushveld Complex, South Africa
Bachmann, K.; Menzel, P.; Tolosana-Delgado, R.; Schmidt, C.; Hill, M.; Gutzmer, J.;
The Bushveld Complex, the largest layered mafic-ultramafic intrusion worldwide, is host of numerous, laterally continuous and chemically similar chromitite seams. Based on their stratigraphic position the seams are subdivided into a lower, middle and upper group (LG, MG and UG). Within these groups the seams are numbered successively – from the base to the top of each group. Attempts of discriminating between single seams based on their composition have failed – mainly due to the significant overlap of compositional fields, e.g. of chromitite mineral assemblages and chromite mineral chemistry between (neighboured) seams. In this contribution a tailored and easy to use multivariate classification scheme for the chromitite seams is proposed, based on a comprehensive classification routine for the LG and MG chromitites. This routine allows a clear attribution with known uncertainty of eight distinct chromitite seams. The study was carried out at the Thaba Mine, a chromite mine located on the western limb of the Bushveld Complex. The classification is based on a large geochemical database (N = 1205) from Thaba Mine. It comprises of a hierarchical discrimination approach relying on linear discriminant analysis and involves five distinct steps. Using default homogeneous prior probabilities, classification results are excellent for the first discrimination steps (LGs vs. MGs, 97 %; LG-6 vs. LG-6A, 94 %) and very good for the following steps (MG-1/2 vs. MG-3/4, 86 %; MG-1 vs. MG-2, 92 %; MG-3 vs. MG-4, 93 %; MG-4 vs. MG-4Z, 97 %; MG-4 vs. MG-4A, 88 %). The classification scheme was tested using the same sample set as a training set with unknown composition. Overall classification results for unknown samples belonging to one of the seams are 81 %. Hence, the classification scheme is at least valid for the Thaba mine. The approach may, however, be extended across the entire Bushveld, provided that an appropriate geochemical data set is available.
Keywords: Linear discriminant analysis, PGE, Thaba Mine, Lower group chromitites, Middle group chromitites, compositional data analysis

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  • Secondary publication expected from 27.02.2020

Publ.-Id: 28821 - Permalink


Variations in Composition, Texture, and Platinum Group Element Mineralization in the Lower Group and Middle Group Chromitites of the Northwestern Bushveld Complex, South Africa
Kaufmann, F. E. D.; Hoffmann, M. C.; Bachmann, K.; Veksler, I. V.; Trumbull, R. B.; Hecht, L.;
Small-scale variations in mineral chemistry, textures and platinum group element (PGE) mineralization were investigated in the Lower and Middle Group chromitite layers LG6, LG6a, MG1, MG2, MG2 II from vertical drill core profiles at the Thaba mine in the northwestern limb of the Bushveld Complex. We present detailed geochemical profiles of chromite composition and chromite crystal-size distribution curves to shed light on the processes of chromite accumulation and textural modification as well as mineralization. Multiple samples within each layer were assayed for platinum-group element concentrations and the respective platinum-group mineral association was determined by mineral liberation analysis (MLA).
There is strong evidence for post-cumulus changes in the chromitites. The crystal size distribution curves suggest that the primary chromite texture was coarsened by a combination of adcumulus growth and textural equilibration, while compaction of the crystal mush played only a minor role. Mineral compositions were also modified by post-cumulus processes, but because of the very high modal amount of chromite and its local preservation in orthopyroxene oikocrysts, that phase retained much primary information. Vertical variations of chromite composition within chromitite layers, and from one layer to another do not support the idea of chromite accumulation from crystal-rich slurries nor crystal settling from a large magma chamber. Instead, we favor a successive buildup of chromitite layers by repeated injections of relatively thin layers of chromite-saturated magmas, with in-situ crystallization occurring at the crystal mush-magma interface. The adcumulus growth of chromite grains to form massive chromitite required addition of Cr to the layers, which we attribute to downward percolation from the overlying magma.
The PGE concentrations are elevated in all chromitite layers compared to adjacent silicate rocks, and show a systematic increase upwards from LG6 (ave. 807 ppb Ir+Ru+Rh+Pt+Pd+Au) to MG2 II (ave. 2062 ppb). There are also significant internal variations in all layers, with enrichments at hanging and/or footwalls. The enriched nature of chromitites in PGE compared to host pyroxenites is a general feature, independent of the layer thickness. The MLA results distinguish two principal groups of PGE mineral associations: the LG6, LG6 and MG1 are dominated by the malanite series, laurite and PGE sulfarsenides, while the MG2 and MG2 II layers are characterized by laurite and PGE sulfides, as well as Pt-Fe-Sn and PGE-Sb-Bi-Pb alloys. Differences in the PGE associations are attributed to post-cumulus alteration of the MG2 and MG2 II layer, while the chromitites below, particularly LG6 and LG6a, contain the primary association.
Keywords: Bushveld Complex, chromitites, PGE mineralization, crystal size distribution, Thaba Mine, MLA

Publ.-Id: 28820 - Permalink


On defects role in enhanced perpendicular magnetic anisotropy in Pt/Co/Pt, induced by ion irradiation
Jakubowski, M. M.; Liedke, M. O.ORC; Butterling, M.; Dynowska, E.; Sveklo, I.; Milińska, E.; Kurant, Z.; Böttger, R.; von Borany, J.; Maziewski, A.; Wagner, A.; Wawro, A.
Modifications of magnetic and magneto-optical properties of Pt/Co(dCo)/Pt upon Ar+ irradiation (with energy 1.2, 5 and 30 keV) and fluence, F at the range from 2e13-2e16 Ar+/cm^2) were studied. Two ‘branches’ of increased perpendicular magnetic anisotropy (PMA) and enhanced magneto-optical response are found on two-dimensional (dCo, F) diagrams. The difference in F between ‘branches’ is driven by ion energy. Structural features correlated with magnetic properties have been analysed thoroughly by X-ray diffraction, Rutherford backscattering spectrometry and positron annihilation spectroscopy. Experimental results are in agreement with TRIDYN numerical calculations of irradiation-induced layers intermixing. Our work discusses particularly structural factors related to crystal lattice defects and strain, created and modified by irradiation, co-responsible for the increase in PMA.
Keywords: thin films; magnetic measurements; vacancy formation; Rutherford backscattering, RBS; atom, molecule, and ion impact; positron spectroscopies

Publ.-Id: 28819 - Permalink


[11C]-Methionine-PET/MRI is superior to MRI alone for detecting residual tumor burden in glioblastoma multiforme undergoing radical radiochemotherapy – analysis of a prospective trial
Beuthien-Baumann, B.; Seidlitz, A.; Platzek, I.; Petr, J.; Kotzerke, J.; Jentsch, C.; Löck, S.; Zessin, J.; Krex, D.; Zöphel, K.; Schackert, G.; van den Hoff, J.; Baumann, M.; Krause, M.;
kein Abstrakt vorhanden
Keywords: [11C]Methionin, Glioblastoma, Positronen-Emissions-Tomographie
  • Abstract in refereed journal
    European Journal of Nuclear Medicine and Molecular Imaging 45(2018)S1, OP-088

Publ.-Id: 28817 - Permalink


Contact of a tumour with the pleura is not associated with regional recurrence following stereotactic ablative radiotherapy for early stage non-small cell lung cancer
Wink, K. C. J.; Löck, S.; Rossi, M.; van Baardwijk, A.; Belderbos, J.; de Ruysscher, D.; Troost, E. G. C.;
Background and purpose: The aim was to investigate the incidence of isolated regional failure following stereotactic ablative radiotherapy (SABR) and risk factors for recurrence. Materials and methods: Early stage non-small cell lung cancer (NSCLC) patients treated with SABR were included in this retrospective cohort study, with isolated regional recurrence (IRR) as primary endpoint, distant recurrence (DR) and overall survival (OS) as secondary endpoints. Survival analyses were performed using the cumulative incidence function (IRR and DR) or the Kaplan–Meier method (OS) and Cox proportional hazards modelling for univariate and multivariate analyses. The prognostic effect of contact between the tumour and the pleura was investigated using the CT scans used for SABR planning. Results: A total of 554 patients were included, of whom 494 could be analysed for IRR. The median follow-up for surviving patients was 48.1 months. Twenty-one patients developed an IRR (4%). The cumulative incidence of IRR and DR after 1-, 2-, and 5 years was 2%, 3%, 7% and 8%, 15% and 21%, respectively. Two year OS was 71%. The presence and type of pleural contact was not associated with any of the studied outcomes. Conclusion: The presence, type and length of pleural contact as surrogate for visceral pleural invasion were not predictive for outcome. Further studies focussing on risk factors for occult nodal involvement, (I)RR, distant metastases and mortality in early stage NSCLC are warranted for the development of risk adapted diagnostic, treatment and follow-up strategies as more younger, operable and fitter patients receive SABR. © 2018 Elsevier B.V.
Keywords: Early stage NSCLC, Isolated regional recurrence, Radiotherapy, SABR, Visceral pleural invasion

Publ.-Id: 28814 - Permalink


Influence of microscopic precipitate structures on macroscopic pattern formation in reactive flows in a confined geometry
Balog, E.; Bittmann, K.; Schwarzenberger, K.; Eckert, K.; de Wit, A.; Schuszter, G.;
Thanks to the coupling between chemical precipitation reactions and hydrodynamics, new dynamic phenomena may be obtained and new types of materials can be synthesized. Here we experimentally investigate how the characteristic microscopic crystal properties affect the macroscopic pattern obtained. To shed light on such interactions, different reactant solutions are radially injected into a calcium chloride solution at different volumetric flow rates in a confined geometry. Depending on the reactants used and the flow conditions, deformed precipitate membranes have been observed due to reaction-driven viscous fingering. In such cases we show that upon injection a large number of small particles is produced in situ by the reaction at the miscible interface between the two reactant solutions. Therefore, a colloidal gel composed of those tiny particles is pushed forward by the injected aqueous solution giving rise to a viscosity gradient-driven hydrodynamic instability.

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Publ.-Id: 28812 - Permalink


Multiphase Flow Imaging - From Fundamentals to Applications
Hampel, U.;
The invited lecture discusses fundamentals and applications of tomographic imaging for multiphase flow measurement. A focus is given to the fields of oil and gas production, chemical engineering and nuclear engineering. Th etals addresses open quesions and future needs and exemplarily demonstrates the use of tomographic imaging techniques in fundmental and engineering research at HZDR.
Keywords: multiphase flow, flow measurement, flow imaging, tomograpy, chemical engineering, nuclear engineering, oil and gas production
  • Invited lecture (Conferences)
    SPIE Student Chapter, 12.02.2019, Dresden, Deutschland

Publ.-Id: 28811 - Permalink


Predictive Geometallurgy
Gutzmer, J.; Birtel, S.; Büttner, P.; Bachmann, K.; Kern, M.; Frenzel, M.;
For centuries the German proverb “Vor der Hacke ist es duster” has aptly described the lack of knowledge about ore volumes, grades and beneficiation characteristics during the incremental progress of mining operations. Although much progress has been made constraining ore volumes and grades by following rigorous exploration drilling programs and applying appropriate geostatistical and spatial modelling tools, there still remains considerable technical risk when exploration turns into exploitation. This is illustrated by the observation that ca. 70% of mines perform below the prediction of their feasibility study (Wood, 2018). This underperformance is usually attributed to deficiencies in the collection of tangible geoscientific data needed to design the mine and the minerals processing plant (Wood, 2018).
Geometallurgy is an interdisciplinary approach that aims to connect the data available from geosciences with the information required to predict the performance of technologies used for ore extraction and mineral beneficiation. Tangible resource characteristics – beyond grade and tonnage - are quantified to create a model that links the geology of an ore deposit with the performance achieved during mining, mineral processing and extractive metallurgy. Successful geometallurgical programs may thus be used to mitigate the risk of production planning and plant design. However, the tools of geometallurgy have thus far mostly been used by the mining industry to improve metal recoveries and to monitor process efficiency of mineral processing plants only.
Present research goes beyond these current applications of geometallurgy. Predictive geometallurgical models for complex ore bodies and even anthropogenic raw materials are being developed by interdisciplinary teams including expertise in exploration, resource characterization, minerals processing, geostatistics and spatial modelling. Case studies will be presented in this contribution that illustrate the approach taken. These examples include (1) the recovery of Sn from a historic flotation tailings storage facility; (2) the recovery of PGE as a by-product of chromite exploitation; and (3) the intelligent use of quantitative mineral abundance and mineral association data to predict the prospects of success of sensor-based sorting.
Results obtained in the three case studies illustrate the prospects of increasing resource and energy efficiency in the mining industry. Innovative approaches are of general applicability and can be easily extended to other metals and ore deposit types. The results clearly illustrate the value of conducting comprehensive geometallurgical assessments already during the latter stages of exploration; the initial process of constructing a predictive geometallurgical model will, of course, benefit greatly from regular follow-up during the phase of active exploitation.
Keywords: geometallurgy, geosciences, minerals processing, metallurgy
  • Invited lecture (Conferences)
    4th GOOD Meeting, 23.-25.01.2019, Bremen, Germany
  • Contribution to proceedings
    4th GOOD Meeting, 23.-25.01.2019, Bremen, Germany
    4th GOOD Meeting Abstract Volume, Bremen

Publ.-Id: 28808 - Permalink


Corrigendum to “Synchrotron tomographic quantification of the influence of Zn concentration on dendritic growth in Mg-Zn alloys” [Acta Mater. 156 (2018) 287-296]
Phillion, A.; Shuai, S.; Guo, E.; Wang, J.; Jing, T.; Ren, Z.; Neumann-Heyme, H.; Beckermann, C.; Lee, P.;
In solidification science, the solid-liquid interfacial area density is a key metric that characterizes the overall semi-solid morphology in a general sense. This interfacial area density can be defined in two different ways... [Abstract not available for Corrigenda]

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Publ.-Id: 28807 - Permalink


Geometric reconstruction of 3D dendrite evolution from 2D transmission radiography data by a simple phase-field method
Neumann-Heyme, H.;
For the in-situ observation of dynamical processes radiographic imaging possess significant advantages over tomographic reconstruction in terms of e.g. time resolution and data handling. However, on the other hand essential spatial information is lost in the projected 2D image. The proposed method demonstrates, how in the case of continuously growing, coherent structures such as dendrites their time evolution can be utilized in recovering the 3D morphology. In addition, the reconstruction incorporates some prior knowledge including the smoothness and preferential growth directions of the interface. The capabilities of the method are assessed for different situations based on simulated experiments of dendritic growth. Finally, the reconstruction of evolving dendrites from flat sample synchrotron experiments is shown.
  • Lecture (Conference)
    55th Annual Technical Meeting of the Society of Engineering Science (SES2018), 10.-12.10.2018, Madrid, Spain

Publ.-Id: 28806 - Permalink


4D particle tracking velocimetry to analyze bubble-particles collisions and flotation recovery at low Stokes numbers
Sommer, A.-E.ORC; Heitkam, S.; Eckert, K.ORC
Froth flotation is a fundamental technique to separate minerals. Hydrophobized target particles attach to the fluidic interface of gas bubbles rising in a suspension. The success of the process depends on both the surface chemistry for the hydrophobization of particles and the hydrodynamics for an encounter between bubble and particle. In the first part of the talk on overview about flotation research and modeling is given.
The second part of the talk is devoted to own research on the hydrodynamics in model cells. To quantify this performance in terms of recovery, the number of target particles at various times in a reference volume is measured. One of the remaining challenges in this field is the flotation of fine particles with a size below 10 µm. Caused by their small inertia, the particles follow the streamlines around the bubble and no collision occurs [1]. This work focuses on the measurement of the collision probability of particles with a small inertia at the bubble surface to advance our understanding of relevant microprocesses and its influence on the flotation recovery. With a 4D particle tracking velocimetry device the particle and bubble trajectories were measured simultaneously with a high temporal (1000 fps) and spatial resolution (0.03 mm/pixels). We developed an algorithm to evaluate the flotation recovery based on the collision and attachment probability [2]. The three-phase flow within a rectangular bubble column consisted of fluorescent polystyrene particles (33 µm, 1.05 g/cm3), a bubble chain (1-7 mm) and deionized water with methanol. The variation of the bubble diameter and methanol concentration led to a change of the fluid flow around the bubble (Re = 100 - 1200) and the particle hydrophobization. The results show the preferred collision of the particles at the rear of the bubble due to a higher acceleration within the vortices in the wake.

[1] Yoon and Luttrell, Mineral Processing and Extractive Metallurgy Review 5, 101 (1989).
[2] AE Sommer, M Nikpay, S Heitkam, M Rudolph, K Eckert, Minerals Engineering 124, 116-122 (2018)
Keywords: flotation, particle image velocimetry
  • Invited lecture (Conferences)
    Permsker Wissenschaftliche Lesung, 24.-28.9.2018, Perm, Rusland

Publ.-Id: 28805 - Permalink


Coarsening and refinement phenomena in dendritic solidification
Neumann-Heyme, H.; Eckert, K.; Beckermann, C.;
Curvature-driven interface motion plays an important role in the formation of the final microstructure during dendritic solidification. Usually, such motion results in a coarser microstructure via coalescence or retraction of dendrite sidebranches \cite{ref1}. Under certain conditions, however, the microstructure can be refined due to curvature-driven pinching events that lead to dendrite fragmentation. Such pinching events are a strong function of the size and shape of the initial dendrite structure \cite{ref2}. In the present study, two- and three-dimensional phase-field simulations are performed to investigate coarsening and refinement phenomena during directional solidification of alloys. The phase-field model is solved using a finite element library that permits adaptive mesh refinement and exhibits wide parallel scalability on supercomputing facilities. A semi-implicit time integration scheme is used to allow for adaptive time stepping, which is important in particular, since curvature-driven interface motion occurs on significantly larger time scales than the initial growth. The present talk will focus on some characteristics of the applied model and physical insights that were obtained.
  • Lecture (Conference)
    5th GAMM Workshop on Phase-Field Modeling, 08.-09.02.2018, TU Dresden, Germany

Publ.-Id: 28804 - Permalink


Evaluation of Brain Nuclear Medicine Imaging Tracers in a Murine Model of Sepsis-Associated Encephalopathy
Szöllősi, D.; Hegedűs, N.; Veres, D. S.; Futó, I.; Horváth, I.; Kovács, N.; Martinecz, B.; Dénes, Á.; Seifert, D.; Bergmann, R.; Lebeda, O.; Varga, Z.; Kaleta, Z.; Szigeti, K.; Máthé, D.;
Purpose: The purpose of this study was to evaluate a set of widely used nuclear medicine imaging agents as possible methods to study the early effects of systemic inflammation on the living brain in a mouse model of sepsis-associated encephalopathy (SAE). The lipopolysaccharide (LPS)-induced murine systemic inflammation model was selected as a model of SAE.
Procedures: C57BL/6 mice were used. A multimodal imaging protocol was carried out on each animal 4 h following the intravenous administration of LPS using the following tracers: [99mTc][2,2-dimethyl-3-[(3E)-3-oxidoiminobutan-2-yl]azanidylpropyl]-[(3E)-3-hydroxyiminobutan-2-yl]azanide ([99m
Tc]HMPAO) and ethyl-7-[125I]iodo-5-methyl-6-oxo-4H-imidazo[1,5-a][1,4]ben-zodiazepine-3-carboxylate ([125I]iomazenil) to measure brain perfusion and neuronal damage, respectively; 2-deoxy-2-[18F]fluoro-D-glucose ([18F]FDG) to measure cerebral glucose uptake.
We assessed microglia activity on another group of mice using 2-[6-chloro-2-(4-[125I]iodo-phenyl)-imidazo[1,2-a]pyridin-3-yl]-N-ethyl-N-methyl-acetamide ([125I]CLINME). Radiotracer uptakes were measured in different brain regions and correlated. Microglia activity was also assessed using immunohistochemistry. Brain glutathione levels were measured to investigate oxidative stress.
Results: Significantly reduced perfusion values and significantly enhanced [18F]FDG and [125I]CLINME uptake was measured in the LPS-treated group. Following perfusion compensation, enhanced [125I]iomazenil uptake was measured in the LPS-treated group’s hippocampus and cerebellum. In this group, both [18F]FDG and [125I]iomazenil uptake showed highly negative correlation to perfusion measured with ([99mTc]HMPAO uptake in all brain regions. No significant differences were detected in brain glutathione levels between the groups. The CD45 and P2Y12 double-labeling immunohistochemistry showed widespread microglia activation in the LPS-treated group.
Conclusions: Our results suggest that [125I]CLINME and [99mTc]HMPAO SPECT can be used to detect microglia activation and brain hypoperfusion, respectively, in the early phase (4 h post injection) of systemic inflammation. We suspect that the enhancement of [18F]FDG and [125I]iomazenil uptake in the LPS-treated group does not necessarily reflect neural hypermetabolism and the lack of neuronal damage. They are most likely caused by processes emerging during neuroinflammation, e.g., microglia activation and/or immune cell infiltration.
Keywords: Systemic infection, Neuroinflammation, Microglia activation, LPS, [99mTc]HMPAO, [18F]FDG, [125I]iomazenil, [125I]CLINME, SPECT/CT, PET/MRI

Publ.-Id: 28803 - Permalink


Effects of electron beam generated lattice defects on the periodic lattice distortion structure in 1T-TaS2 and 1T-TaSe2 thin layers
Kinyanjui, M. K.; Björkman, T.; Lehnert, T.; Köster, J.; Krasheninnikov, A.ORC; Kaiser, U.
We have investigated the influence of electron beam generated defects on the structure of periodic lattice distortions (PLDs) which accompany charge density wave modulations in 1T -TaS2 and 1T -TaSe2 . Lattice defects were generated through irradiation with high-energy electrons in a transmission electron microscope (TEM). Using atomically resolved high-resolution TEM imaging, we investigate the PLD structure and the changes in this structure with prolonged exposure to the electron beam. We observe the formation of dislocationlike topological defects in the PLD structure. Prolonged exposure to the electron beam also leads to an increase in density of these defects. This is also accompanied by an increase in structural disorder of the PLD. Density functional theory calculations were also performed in order to understand sulfur (S) and selenium (Se) vacancy defect formation in 1T -TaSe2 and 1T -TaS2 and their effects on the PLD structure. The formation energy of Se/S vacancies was calculated to be lowest for the highly displaced S/Se atoms in the vicinity of PLD maxima. Vacancies formed at the less displaced sites near the PLD minima were found to have lower formation energy. The calculations also showed that an increase in the S/Se vacancies leads to the formation of dislocations and an increase in disorder in the PLD structures. This supports the experimental observations.
Keywords: TEM, 2D materials, first-principles calculations

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Publ.-Id: 28802 - Permalink


Characterization of continuous wave laser-induced thermal gradients in magnetic tunnel junctions integrated into microresonators via COMSOL simulations
Cansever, H.ORC; Lindner, J.; Huebner, T.; Niesen, A.; Reiss, G.; Fassbender, J.; Deac, A. M.
Spin caloritronics still is a vivid field and aims to investigate static and dynamic effects on magnetic structures due to spin-currents generated by thermal gradients [1]. In magnetic tunnel junctions, magnetization dynamics can be induced by bias voltage as well as thermal gradients [2]. In most research, COMSOL simulations are used to estimate the overall temperature of the magnetic tunnel junction as well as the thermal gradient over the insulating barrier [3-5]. Here, we perform COMSOL simulations using the 2D heat transfer module for specific Co2FeAl/MgO(2nm)/CoFeB magnetic tunnel junctions which are integrated into so-called microresonators [6]. Microresonators have been recently used as alternative approach to investigate the magnetization dynamics of the free-layer within magnetic tunnel junctions, induced by a thermal gradient by means of its ferromagnetic resonance response [6]. Utilizing microresonators for ferromagnetic resonance detection allow for the detection of signals from micron/nano-sized object under laser heating in terms of linewidth and resonance field and thus provide the possibility to detect influences of a thermal gradient on the magnetization dynamics far below the threshold of magnetic switching. The heat diffusion over all layers are modeled by starting with a 2D (vertical) rectangular shape in which we consider the MTJ stack with the MgO-substrate and backside metallization as part of the microresonators shown in Fig 1. Moreover, we consider an air ‘layer’ and the metal-contacts defining the microresonator on top of the MgO-substrate. Upon rotation of this two-dimensional shape around the central vertical z-axis of the MTJ, we obtain a 3D cylinder in which the heat profile is simulated (see Fig 2). The simulation parameters for the materials were chosen similar to those in [3,4]. In the simulation, the fundamental properties of layers i.e. thermal conductivity, heat capacity and material density are used to obtain a temperature profile of the magnetic structure. According to the simulation results, the thermal conductivity of the insulating barrier (MgO) and top metal thicknesses influence the thermal gradient, while uniform heating is strongly affected by the surrounding material of the microresonator which is mainly made from copper (high thermal conductivity). The simulation results provide insight into the heat profile of the whole structure and in particular demonstrate that not only changing the magnetic object itself but also modifying the structure of the surrounding materials yields a handle to tune and optimize the thermal gradient.
Figure 1. 2D sketch of MTJ structure integrated into a microresonator for COMSOL modelling. Heat source, i.e. cw- laser is applied to magnetic layers through the top-metal. The temperature of the bottom of the whole structure is set to 293.15 K.
Figure 2. (a) Temperature profile across the MTJ integrated in a microresonator with the applied power of 145 mW inset (b) 3D cylindrical image of MTJ structure.


[1] Bauer G E W, Saitoh E and van Wees B J 2012 Nat. Mater. 11 391
[2] Jia X, Xia K and Bauer G E W 2011 Phys. Rev. Lett.107 176603
[3] Walter M et al 2011 Nat. Mater. 10 742
[4] Huebner T, Boehnke A, Martens U, Thomas A, Schmalhorst J M, Reiss G, Münzenberg M and Kuschel T 2016 Phys. Rev. B 93 224433
[5] T Huebner et al 2018 J. Phys. D: Appl. Phys. 51 224006
[6] H Cansever et al 2018 J. Phys. D: Appl. Phys. 51 224009
Keywords: COMSOL Simulation, magnetic tunnel junction, microresonator, ferromagnetic resonance
  • Lecture (Conference)
    Joint MMM-Intermag Conference 2019 Washington D.C., 14.-18.01.2019, Washington D.C., The United States of America

Publ.-Id: 28800 - Permalink


The new Felsenkeller 5 MV underground accelerator: Status and Program
Bemmerer, D.;
Experimental nuclear astrophysics aims to study, in the laboratory, the nuclear reactions taking place in stars. However, at the energies relevant to stellar burnings, the relevant cross sections are strongly reduced by the repulsive Coulomb barrier. As a result, ion beam experiments in underground laboratories shielded from cosmic ray effects are needed in order to gain precise data. The Felsenkeller 5 MV accelerator, below 45 m rock in Dresden, is the first such accelerator on the MV scale in Europe. The laboratory was jointly built by HZDR and TU Dresden and opened in 2018. Both an internal and an external ion source have already been tested successfully underground. The accelerator itself is under commissioning, as well as a high-sensitivity radioactivity counting setup by TU Dresden. The talk will summarise the science case and the status for the new laboratory.
Keywords: Nuclear Astrophysics
  • Invited lecture (Conferences)
    Institutsseminar (Kolloquium), 24.01.2019, Dresden, Deutschland

Publ.-Id: 28797 - Permalink


Felsenkeller 5 MV underground ion accelerator status December 2018
Bemmerer, D.;
I review the status of the Felsenkeller 5 MV underground accelerator in view of the CELLAR network of underground labs.
Keywords: Nuclear Astrophysics, Low-Level Radioactivity Measurements
  • Lecture (Conference)
    CELLAR / JEILORA Meeting, 05.-07.12.2018, Monaco, Monaco

Publ.-Id: 28796 - Permalink


Nuclear Astrophysics: Nucleosynthesis and Chemical Evolution Studies
Bemmerer, D.;
I review Nuclear Astrophysics: Nucleosynthesis and Chemical Evolution Studies.
Keywords: Nuclear Astrophysics
  • Invited lecture (Conferences)
    Astroparticle Physics in Germany: Status and Perspectives, 19.09.2018, Mainz, Deutschland

Publ.-Id: 28795 - Permalink


Felsenkeller 5 MV underground accelerator at the 5th International Solar Neutrino Conference
Bemmerer, D.;
I review the status of the 5 MV underground accelerator at Felsenkeller, Dresden/Germany.
Keywords: Underground physics, Nuclear Astrophysics
  • Invited lecture (Conferences)
    5th International Solar Neutrino Conference, 13.06.2018, Dresden, Deutschland

Publ.-Id: 28794 - Permalink


Felsenkeller 5 MV underground ion accelerator for nuclear astrophysics
Bemmerer, D.; Cowan, T. E.; Grieger, M.; Hensel, T.; Junghans, A. R.; Koppitz, M.; Ludwig, F.; Rimarzig, B.; Reinicke, S.; Schwengner, R.; Stöckel, K.; Szücs, T.; Takács, M. P.; Turkat, S.; Wagner, A.; Zuber, K.;
A 5 MV Pelletron accelerator with both an internal and an external ion source providing for intensive 1H+, 4He+, and 12C+ beams is being installed in the Felsenkeller underground site in Dresden, shielded from cosmic rays by 45 m rock overburden. Civil construction has recently been completed. The technical features of the new laboratory, test results, and the scientific program will be summarized. In addition to in-house research by HZDR and TU Dresden, the new accelerator will be open for outside users, both from Germany and worldwide.
Keywords: Nuclear astrophysics, Felsenkeller
  • Lecture (Conference)
    Frühjahrstagung Hadronen und Kerne, 26.02.2018, Bochum, Deutschland

Publ.-Id: 28793 - Permalink


Improved astrophysical rate for the 18O(p,α)15N reaction by underground measurements
Bruno, C. G.; Aliotta, M.; Descouvemont, P.; Best, A.; Davinson, T.; Bemmerer, D.; Boeltzig, A.; Broggini, C.; Caciolli, A.; Cavanna, F.; Chillery, T.; Ciani, G. F.; Corvisiero, P.; Depalo, R.; Di Leva, A.; Elekes, Z.; Ferraro, F.; Formicola, A.; Fülöp, Z.; Gervino, G.; Guglielmetti, A.; Gustavino, C.; Gyürky, G.; Imbriani, G.; Junker, M.; Lugaro, M.; Marigo, P.; Menegazzo, R.; Mossa, V.; Pantaleo, F. R.; Piatti, D.; Prati, P.; Stöckel, K.; Straniero, O.; Strieder, F.; Szücs, T.; Takács, M. P.; Trezzi, D.;
The 18O(p,α)15N reaction affects the synthesis of 15N, 18O and 19F isotopes, whose abundances can be used to probe the nucleosynthesis and mixing processes occurring deep inside asymptotic giant branch (AGB) stars. We performed a low-background direct measurement of the 18O(p,α)15N reaction cross-section at the Laboratory for Underground Nuclear Astrophysics (LUNA) from center of mass energy E_CM= 340 keV down to E_CM = 55 keV, the lowest energy measured to date corresponding to a cross-section of less than 1 picobarn/sr. The strength of a key resonance at center of mass energy E_r = 90 keV was found to be a factor of 10 higher than previously reported. A multi-channel R-matrix analysis of our and other data available in the literature was performed. Over a wide temperature range, T=0.01-1.00 GK, our new astrophysical rate is both more accurate and precise than recent evaluations. Stronger constraints can now be placed on the physical processes controlling nucleosynthesis in AGB stars with interesting consequences on the abundance of 18O in these stars and in stardust grains, specifically on the production sites of oxygen-rich Group II grains.
Keywords: Stellar hydrogen burningHydrostatic stellar nucleosynthesis

Publ.-Id: 28791 - Permalink


Hyperspectral Feature Extraction Using Sparse and Smooth Low-Rank Analysis
Rasti, B.; Ghamisi, P.; Ulfarsson, M. O.;
In this paper, we develop a hyperspectral feature extraction method called sparse and smooth low-rank analysis (SSLRA). First, we propose a new low-rank model for hyperspectral images (HSIs) where we decompose the HSI into smooth and sparse components. Then, these components are simultaneously estimated using a nonconvex constrained penalized cost function (CPCF). The proposed CPCF exploits total variation penalty, ℓ1 penalty, and an orthogonality constraint. The total variation penalty is used to promote piecewise smoothness, and, therefore, it extracts spatial (local neighborhood) information. The ℓ1 penalty encourages sparse and spatial structures. Additionally, we show that this new type of decomposition improves the classification of the HSIs. In the experiments, SSLRA was applied on the Houston (urban) and the Trento (rural) datasets. The extracted features were used as an input into a classifier (either support vector machines (SVM) or random forest (RF)) to produce the final classification map. The results confirm improvement in classification accuracy compared to the state-of-the-art feature extraction approaches.

Downloads:

Publ.-Id: 28790 - Permalink


The IR-truncated PT-symmetric V = ix3 model and its asymptotic spectral scaling graph
Günther, U.ORC; Stefani, F.
The PT-symmetric V = ix3 model over the real line is infra-red (IR) truncated and considered as Sturm-Liouville problem over a finite interval. Structures hidden in the Airy function setup of the V = ix3 model are combined with WKB techniques developed by Bender and Jones in 2012 for the derivation of the real part of the spectrum of theV = ix3 model. Via WKB and Stokes graph analysis, the location of the complex spectral branches of the ix3 model as well as those of more general V = -(ix)2n+1 models over finite intervals are obtained. Splitting the related action functions into purely real scale factors and scale invariant integrals allows to extract underlying asymptotic spectral scaling graphs. These (structurally very simple) scaling graphs are geometrically invariant and cutoff-independent so that the IR limit can be formally taken. Moreover an increasing length scale can be associated with a spectral UV-IR renormalization group flow on this scaling graph. It is shown that the eigenvalues of the IR-complete V = ix3 model can be bijectively mapped onto a finite segment of the scaling graph asymptotically approaching a (scale invariant) PT phase transition region. In this way, a simple heuristic picture and complementary explanation for the unboundedness of projector norms and C-operator for the ix3 model are provided and the lack of quasi-Hermiticity of the ix3 Hamiltonian over the real line appears physically plausible. Possible directions of further research are briefly sketched.
Keywords: PT Quantum Mechanics, PT phase transition, spectral branch points, exceptional points, ix3 model, WKB techniques, IR truncation, IR completion, asymptotic spectral scaling graphs, spectral UV-IR renormalization group flow
  • Invited lecture (Conferences)
    Discrete-18, organized by CERN and the Austrian Academy of Sciences, 26.-30.11.2018, Wien, Österreich

Publ.-Id: 28787 - Permalink


The IR-truncated PT-symmetric V = ix3 model and its asymptotic spectral scaling graph
Günther, U.ORC; Stefani, F.
The PT-symmetric quantum mechanical V = ix3 model over the real line is infra-red (IR) truncated and considered as Sturm-Liouville problem over a finite interval of the real line. Via WKB and Stokes graph analysis, the location of the complex spectral branches of the V = ix3 model as well as those of more general V = -(ix)2n+1 models over finite intervals are obtained. Underlying asymptotic spectral scaling graphs are extracted which are scale-invariant so that the IR completion can be performed. Implications for the V = ix3 model over the full real line are discussed.
Keywords: PT Quantum Mechanics, PT phase transition, spectral branch points, exceptional points, ix3 model, WKB techniques, IR truncation, asymptotic spectral scaling graphs
  • Invited lecture (Conferences)
    Analytic and algebraic methods in physics XV, 10.-13.09.2018, Prague, Czech Republic

Publ.-Id: 28786 - Permalink


The IR-truncated PT-symmetric V=ix3 model and its asymptotic spectral scaling graph
Günther, U.ORC; Stefani, F.
The PT-symmetric V=ix3 model over the real line is IR truncated and considered as Sturm-Liouville problem over a finite interval. Combining structures hidden in the Airy function setup of the V=ix model with WKB techniques developed by Bender and Jones in 2012 for the derivation of the real part of the spectrum of the ix3 model, a WKB and Stokes graph analysis for the complex spectral branches of the ix3 model as well as those of more general V=-(ix)2n+1 models over finite intervals is performed. Complementary insights into the spectra of these models are obtained by splitting the spectral branch-structure into purely real scale factors and asymptotic spectral scaling graphs. It turns out that the corresponding (structurally very simple) scaling graphs are geometrically invariant and cutoff-independent so that the infra-red (IR) limit can be formally taken. These graphs have invariantly existing PT phase transition regions. In this way, a simple heuristic picture and complementary explanation for the unboundedness of the C-operator and the lack of quasi-Hermiticity of the ix3 Hamiltonian over the real line is provided.
Keywords: PT-symmetric Quantum Mechanics, PT phase transition, spectral branch points, exceptional points, ix3 model, WKB techniques, IR truncation, C-operator, unboundedness, quasi-Hermiticity
  • Invited lecture (Conferences)
    Pseudo-Hermitian Hamiltonians in Quantum Physics (PHHQP) XVIII, 04.-13.06.2018, Bangalore, India

Publ.-Id: 28785 - Permalink


Curing processes in ultra low-k materials by positron annihilation spectroscopy
Liedke, M. O.ORC; Köhler, N.; Butterling, M.; Hirschmann, E.; Attallah, A. G.; Krause-Rehberg, R.; Schulz, S. E.; Wagner, A.
The first results on in-situ investigations of pore formation in ultra low-k dielectrics during a curing process, i.e., a porogen removal by vacuum annealing will be presented. The main focus is to obtain insight into initial stages of pore networks formation up to their full development. The in-situ annealing and Doppler broadening positron annihilation spectroscopy measurements have been conducted on our Apparatus for In-situ Defect Analysis (AIDA) - the end-station of a slow positrons beamline at HZDR. In addition, positron lifetime spectroscopy has been utilized, where mono-energetic pulsed positron beam (MePS) serves as a probe to evaluate pore sizes, their concentration and distribution as a function of curing temperature and time. The MePS facility has partly been funded by the Federal Ministry of Education and Research (BMBF) with the grant PosiAnalyse (05K2013). The AIDA system was funded by the Impulse- und Networking fund of the Helmholtz-Association (FKZ VH-VI-442 Memriox) and through the Helmholtz Energy Materials Characterization Platform (03ET7015)
Keywords: positron, low-k, curing, AIDA, defects, pores
  • Lecture (Conference)
    DPG Frühjahrstagung Berlin, 11.03.2018, Berlin, Deutschland

Publ.-Id: 28784 - Permalink


Vacancy-mediated magnetic phase-transitions
Liedke, M. O.ORC; Butterling, M.; Quintana, A.; Menéndez, E.; Ehrler, J.; Bali, R.; Hirschmann, E.; Sireus, V.; Nogués, J.; Sort, J.; Wagner, A.
Two thin film systems exhibiting vacancy mediated magnetic phase transitions will be discussed in detail, i.e., Co3O4 and Fe60Al40.
In applications, substituting electric currents, which are nowadays used to operate spintronic devices, with electric fields, would result in a reduction of both the energy consumption and cost [1]. Co3O4 is a candidate for a tunable, non-volatile energy-efficient functional material whose magnetic properties can be controlled by electric voltage. In our current investigations the as-grown Co3O4 films consist of a paramagnetic (PM) phase only, which is transformed to a ferromagnetic (FM) state by electrolyte-gated and defect-mediated O and Co transport. A negative voltage reduces Co3O4 to Co (FM: ON), resulting in a phase separated material with Co- and O-rich regions. Applying a positive bias, the process is reversed oxidizing Co back to Co3O4 (PM: OFF). We will show that atoms migration is driven by rather complex vacancy states and a clear increase of the grain boundaries volume after negative biasing assists to O transport. Moreover, concomitantly with the PM phase transition due to the positive biasing the structural defects picture reverses to a large extent as well, which manifests as reduction in volume of both vacancy clusters and grain boundaries.
B2-Fe60Al40 phase is paramagnetic, and strong ferromagnetism can be induced via disordering to the A2-Fe60Al40 phase [2]. Disordering implies the formation of anti-site defects [3], which correlates with an increased Fe coordination. The concentration and size of open volume defects can play an important role in reordering kinetics. Three different initial order states have been investigated: (i) as-grown, partially disordered Fe60Al40, (ii) the as-grown films after Ne+ irradiation, and (iii) Ne-irradiated B2-Fe60Al40. Since, reordering directly affects magnetization saturation; the extent of the diffusion process can be traced via magnetometry at slightly elevated temperature of 400 K. We show that immobile large vacancy clusters with a high thermal activation barrier are dominant in the as-grown film and hinder ordering. Ion irradiation breaks down these pinning sites, thereby strongly accelerating thermal diffusion and reordering. These results provide insights into thermal reordering processes in binary alloys, and the consequent effect on magnetic properties. Doppler broadening and positron annihilation lifetime spectroscopy have been used as a probe for both electric field driven ionic transport of Co and O via different type of defects in Co3O4 systems as well as vacancy-mediated ordering in Fe60Al40.
[1] Y. Shiota, et al. Nature Mater. 11, 39 (2012). [2] M.O. Liedke, et al., J. Appl. Phys. 117, 163908 (2015).
[3] R. Bali, et al., Nano Lett. 14, 435 (2014).
Keywords: magnetism, positron, ion, irradiation, phase transitions, defects, electrical fields
  • Invited lecture (Conferences)
    18th International Conference on Positron Annihilation (ICPA-18), 19.08.2018, Orlando, USA

Publ.-Id: 28783 - Permalink


Magnetic ordering and open volume defects – phase transitions in ion irradiated Fe60Al40 thin films
Liedke, M. O.ORC; Ehrler, J.; Bali, R.; Butterling, M.; Hirschmann, E.; Wagner, A.
Fe60Al40 exhibit the so-called disorder induced ferromagnetism, where anti-site disorder (ASD) promotes ferromagnetic A2-phase (disordered) over paramagnetic B2-phase (ordered). Both phases can be - in a controllable fashion - driven by ion irradiation or annealing, respectively. The main physical origin correlates strongly with ASD [R. Bali, et al., Nano Lett. 14, 435 (2014)]. Nevertheless, the concentration and size of open volume defects can be of crucial importance in determining the kinetics of the reordering processes. To unravel the influence of vacancy clusters, three different initial order states have been investigated: (i) as-sputtered, (ii) as-grown irradiated with Ne+ and (iii) B2 ordered films, obtained via 773 K annealing and Ne-irradiated. Open volume defects in the treated samples were investigated with Doppler broadening and positron annihilation lifetime spectroscopy. Furthermore, since the reordering directly affects Ms, the extent of the diffusion process can be traced via magnetometry at slightly elevated temperature of 400 K. We show that immobile large vacancy clusters are dominant in the as-grown films; these complexes present only in the as-sputtered film possess a high thermal activation barrier and hinder ordering. Ion irradiation breaks down these pinning defects strongly accelerating thermal diffusion and reordering. These results provide insights into thermal reordering processes in binary alloys, and the consequent effect on magnetic behavior.
Keywords: magnetism, positron, ordering, ion, irradiation, phase transition, defects
  • Lecture (Conference)
    9th Joint European Magnetic Symposia (JEMS-9), 03.09.2018, Mainz, Deutschland

Publ.-Id: 28782 - Permalink


On the use of stacks of fission-like targets for neutron capture experiments
Guerrero, C.; Lerendegui-Marco, J.; Eberhardt, K.; Düllmann, C. E.; Junghans, A.; Lommel, B.; Mokry, C.; Quesada, J. M.; Runke, J.; Thörle-Pospiech, P.; The N_Tof Collaboration;
The measurement of neutron induced reactions on unstable isotopes is of interest in many fields, from nuclear energy to astrophysics or applications; in particular transuranic isotopes are essential for the development of innovative nuclear reactors and for the management of the radioactive waste. In such measurements, the quality of the associated radioactive target is crucial for the success of the experiment, but in many cases the geometry, amount of mass and encapsulation of the target are not optimal, leading to limited results. In this work we propose to produce high quality radioactive targets for capture as a stack of thin targets using the techniques usually employed for fission measurements. In particular, we have succeeded in making a 242Pu target of nearly 100 mg by combining seven thin (~1 mg/cm2) fission-like targets with 45 mm in diameter achieving a total backing thickness of only 70 m of aluminum. The target has been shown to perform successfully in experiments at both a neutron time-of-flight facility (n_TOF at CERN) and a thermal neutron beam (BRR at KFKI), providing the most accurate data from thermal up to 250 keV to date.

Publ.-Id: 28781 - Permalink


Dual-Energy CT for more accurate stopping power prediction & Importance of range verification
Richter, C.;
Direct dual-energy CT based stopping power prediction (DirectSPR) allows the reduction of the currently clinical used range uncertainty. The clinical benefits of DirectSPR, its extensive validation and implementation will be presented together with a quantification of the range reduction potential. Furthermore, steps towards in-man validation of the SPR prediction with the IBA Prompt-Gamma-Imaging slit camera will be highlighted.
  • Invited lecture (Conferences)
    IBA Proteus User Meeting 2019, 01.-03.02.2019, Miami, USA

Publ.-Id: 28780 - Permalink


Strahlenschutzaspekte bei der Errichtung und Inbetriebnahme des kanadischen Zyklotrons TR-FLEX im Helmholtz-Zentrum Dresden-Rossendorf
Preusche, S.; Naumann, B.; Kaspari, W.;
  • Invited lecture (Conferences)
    Strahlenschutz in Medizin, Forschung und Industrie, 11.-12.12.2018, Aschaffenburg, Deutschland

Publ.-Id: 28779 - Permalink


Entwicklung von hochaffinen 18F-markierten Radiotracern zur molekularen Bildgebung des Adenosin-A2A-Rezeptors mittels Positronen-Emissions-Tomographie
Lai, T. H.; Schröder, S.; Moldovan, R.-P.; Ludwig, F.-A.; Fischer, S.; Dukic-Stefanovic, S.; Deuther Conrad, W.; Steinbach, J.; Brust, P.;
Ziel: Die Bildgebung des Adenosin-A2A-Rezeptors mittels PET gilt hinsichtlich der Frühdiagnostik neurodegenerativer und neuroonkologischer Erkrankungen als vielversprechend. Für die Entwicklung neuer 18F-Tracer basierend auf einer Pyrazolo[2,3-d]pyrimidin-Leitverbindung [1] wurden 21 fluorierte Derivate synthetisiert. Aufgrund der Affinitätswerte wurden die 2- bzw. 4-Fluorbenzylderivate 1 (Ki(hA2A) = 5,3 nM; Ki(hA1) = 220 nM) und 2 (Ki(hA2A) = 2,1 nM; Ki(hA1) = 147 nM) als potentielle A2A-Radiotracer ausgewählt.

Methodik: Für die Radiosynthese von [18F]1 wurden drei verschiedene Markierungsstrategien entwickelt. Strategien A und B erfolgten über 2 bzw. 4 Stufen unter Verwendung von [18F]Fluorbenzaldehyd. Dieser wurde für die reduktive Aminierung (A) bzw. nach Reduktion und Bromierung für die finale Benzylierung (B) verwendet. Strategie C basiert auf einer einstufigen 18F Markierung eines Boronsäurepinacol-Präkursors mit [18F]TBAF in Gegenwart von Cu(OTf)2(py)4 in DMA/n-BuOH und wurde sowohl für die Radiosynthese von [18F]1 als auch [18F]2 angewendet. Die In vitro-Evaluierung erfolgte mittels Autoradiographie in Hirnschnitten von der Maus.

Ergebnisse: Die mehrstufigen Markierungsverfahren A und B ergaben radiochemische Ausbeuten von lediglich 1,4 bzw. 10% [18F]1 (nicht isoliert). Mittels der einstufigen Strategie C konnten [18F]1 und [18F]2 mit einer RCA von 51+6 bzw. 8+1% (EOB), einer AM von 135+64 bzw. 132 GBq/μmol (EOS) und einer RCR >98% erhalten werden. In-vitro-Autoradiographiestudien zeigten nur für [18F]2 eine spezifische Bindung im Striatum, die mit A2A- Liganden blockierbar war.

Schlussfolgerung: Es wurde eine effiziente einstufige 18F-Markierung von zwei neuen hochaffinen A2A-Radiotracern etabliert. In ersten In-vitro-Studien erwies sich [18F]2 für die bildgebende Darstellung des Adenosin-A2A-Rezeptores als geeignet. Gegenstand aktueller Arbeiten sind weitere In-vitro- und In-vivo-Untersuchungen.

Literatur: [1] Gillespie et al., Bioorg Med Chem Lett 2008, 18, 2924-2929.
Keywords: Adenison, A2A, Radiotracer, 18F, PET
  • Lecture (Conference)
    Nuklearmedizin 2019 - 57. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 03.-06.04.2019, Bremen, Deutschland
    DOI: 10.1055/s-0039-1683493

Publ.-Id: 28778 - Permalink


Detection of Extraterrestrial ⁶⁰Fe in Antarctica with AMS
Koll, D.; Faestermann, T.; Korschinek, G.; Merchel, S.ORC; Welch, J. M.; Kipfstuhl, S.
The long-lived radioactive isotope ⁶⁰Fe with a half-life of 2.6 Myr is mainly produced by stellar nucleosynthesis and ejected into space by core-collapse supernovae. Former investigations by Accelerator Mass Spectrometry (AMS) showed a supernova signal on Earth 1.7-3.2 Myr ago.

Considering an enrichment of the solar neighborhood in long-lived radionuclides by previous supernovae, deposition of ⁶⁰Fe on Earth could be currently ongoing. To investigate this case, 500 kg of Antarctic snow were analyzed by Accelerator Mass Spectrometry with the 14 MV tandem accelerator and the Gas-filled Analyzing Magnet System (GAMS) at the Maier-Leibnitz-Laboratorium in Garching, Germany.

Indeed, ⁶⁰Fe was discovered in Antarctic snow and by the measurement of ⁵³Mn, which is dominantly produced by cosmic ray interactions with solar system objects, the origin of these ⁶⁰Fe atoms could be deduced.
Keywords: AMS, supernovae
  • Lecture (Conference)
    83. Jahrestagung der DPG und DPG-Frühjahrstagung der Sektion Atome, Moleküle, Quantenoptik und Plasmen (SAMOP) in Zusammenarbeit mit der Deutschen Gesellschaft für Massenspektrometrie DGMS 2019, 10.-15.03.2019, Rostock, Deutschland

Publ.-Id: 28777 - Permalink


Universal Limits of Thermopower and Figure of Merit from Transport Energy Statistics
Zahn, P.ORC
The search for new thermoelectric materials aims at improving their power and efficiency, as expressed by thermopower S and figure of merit ZT.
By considering a very general transport spectral function w(ε), expressions for the S and ZT can be derived, which contain the statistical weights of an effective distribution function only, see Ref. [1]. The assumption of a Lorentzian shape with width kBT resulting from the electron-phonon coupling allows to estimate an upper limit of S and ZT regardless the microscopic mechanisms of the transport process.
The limit of |S| is given by 1.88 in units of kB/e, which is about 160 μV/K, and the limit for ZT is about 1.11 (red dots in the figure).
The work was partially supported by the Initiative and Networking Fund of the German Helmholtz Association, International Helmholtz Research School NanoNet (VH-KO-606), the Helmholtz Exzellenznetzwerk cfaed (ExNet-0026), and the DFG Priority Program 'Nanostructured Thermoelectrics' (ZA264/3-2). We thank S. Gemming for helpful discussions.
Keywords: Thermoelectrics, Thermopower, Figure of Merit, universal limit, transport spectral function
  • Poster
    667. WE-Heraeus-Seminar 'System-oriented approach to thermoelectrics: Materials – Interfaces – Devices', 08.-11.04.2018, Bad Honnef, Deutschland

Publ.-Id: 28776 - Permalink


Burning in the Tail: Implications for a Burst Oscillation Model
Chambers, F.; Watts, A.; Keek, L.; Cavecchi, Y.; Garcia Gonzalez, F.;
Accreting neutron stars (NSs) can exhibit high-frequency modulations, known as burst oscillations, in their light curves during thermonuclear X-ray bursts. Their frequencies can be offset from the spin frequency of the NS (known independently) by several Hz, and can drift by 1-3 Hz. One plausible explanation for this phenomenon is that a wave is present in the bursting ocean that decreases in frequency (in the rotating frame) as the burst cools. The strongest candidate is the buoyant r-mode; however, models for the burning ocean background used in previous studies over-predict frequency drifts by several Hz. Using new background models (which include shallow heating, and burning in the tail of the burst) the evolution of the buoyant r-mode is calculated. The resulting frequency drifts are smaller, in line with observations. This illustrates the importance of accounting for the detailed nuclear physics in these bursts.

Publ.-Id: 28775 - Permalink


Experiments and Simulations of the Magnetized Spherical Couette Problem
Garcia Gonzalez, F.; Stefani, F.;
The magnetized spherical Couette system models experiments that are being carried out at Helmholtz-Zentrum Dresden-Rossendorf (HZDR). A liquid metal is confined within two differentially rotating spheres and immersed in a magnetic field parallel to the axis of rotation. Preliminary simulations of periodic and quasiperiodic flows, arising at the first bifurcations, will be presented. The aim is to study in detail the instabilities observed in the experiments and previous numerical studies. This study will reveal how the flow patterns depend on control parameters, reproducing thus different physical situations of the HZDR experiments.
  • Poster
    Fifty years after Roberts' MHD: Dynamos and planetary flows today, 16.-17.11.2017, London, United Kingdom

Publ.-Id: 28774 - Permalink


Experiments and Simulations of the Magnetized Spherical Couette Problem
Garcia Gonzalez, F.; Stefani, F.;
The magnetized spherical Couette system models experiments that are being carried out at Helmholtz-Zentrum Dresden-Rossendorf (HZDR). A liquid metal is confined within two differentially rotating spheres and immersed in a magnetic field parallel to the axis of rotation. Preliminary simulations of periodic and quasiperiodic flows, arising at the first bifurcations, will be presented. The aim is to study in detail the instabilities observed in the experiments and previous numerical studies. This study will reveal how the flow patterns depend on control parameters, reproducing thus different physical situations of the HZDR experiments.
  • Poster
    GDRI Dynamo meeting 2017, 27.-29.11.2017, Paris, France

Publ.-Id: 28773 - Permalink


New axisymmetric helical magnetorotational instability in dissipative rotating flows with positive shear
Mamatsashvili, G.; Stefani, F.; Hollerbach, R.; Rüdiger, G.;
We present a new type of axisymmetric magnetorotational instability which is capable of destabilizing viscous and resistive magnetized flows with radially increasing angular velocity. Using short-wavelength WKB approach, supported by 1D linear stability calculations in Taylor-Couette flow, we show that this instability works only when a combination of axial and azimuthal magnetic fields is applied and when the magnetic Prandtl number is different from one. It might have grave consequences for the stability of the equator-near parts of the solar tachocline, and for the dynamo action in this region
  • Lecture (Conference)
    MHD Days and GdRI Dynamo Meeting, 26.-28.11.2018, Dresden, Germany

Publ.-Id: 28772 - Permalink


Experiments and Simulations of the Magnetized Spherical Couette Problem
Garcia Gonzalez, F.; Stefani, F.;
The magnetized spherical Couette system models experiments that are being carried out at Helmholtz-Zentrum Dresden-Rossendorf (HZDR). A liquid metal is confined within two differentially rotating spheres and immersed in a magnetic field parallel to the axis of rotation. Preliminary simulations of periodic and quasiperiodic flows, arising at the first bifurcations, will be presented. The aim is to study in detail the instabilities observed in the experiments and previous numerical studies. This study will reveal how the flow patterns depend on control parameters, reproducing thus different physical situations of the HZDR experiments.
  • Poster
    Alexander von Humboldt Foundation Network Meeting 2018, 19.-21.02.2018, Potsdam, Deutschland

Publ.-Id: 28771 - Permalink


A Tayler-Spruit type model of a tidally synchronized solar dynamo
Stefani, F.; Giesecke, A.; Weber, N.; Weier, T.;
We consider a solar dynamo model of Tayler-Spruit type whose Omega-effect is conventionally produced by a solar-like differential rotation but whose alpha-effect is assumed to be periodically modulated by planetary tidal forcing. This resonance-like effect relies on the tendency of the current-driven Tayler instability to produce intrinsic helicity oscillations which can be synchronized by periodic tidal perturbations. Specifically, we focus on the 11.07 years alignment periodicity of the tidally dominant planets Venus, Earth, and Jupiter, whose empirical synchronization with the solar dynamo is illustrated. The typically emerging dynamo modes are dipolar fields, oscillating with a 22.14 years period or pulsating with a 11.07 years period, but also quadrupolar fields with corresponding periodicities. In the absence of any constant part of alpha, we prove the subcritical nature of this periodic Tayler-Spruit type dynamo. Phase coherent transitions between dipoles and quadrupoles, which are reminiscent of the observed behaviour during the Maunder minimum, can be easily triggered by long-term variations of dynamo parameters. Further interesting features of the model are the typical second intensity peak and the intermittent appearance of reversed helicities in both hemispheres
  • Poster
    MHD Days and GdRI Dynamo Meeting, 26.-28.11.2018, Dresden, Germany

Publ.-Id: 28770 - Permalink


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