Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

"Online First" included
Without submitted and only approved publications
Only approved publications

33403 Publications

Numerical simulations of convection in the titanium reduction reactor

Teimurazov, A.; Frick, P.; Weber, N.; Stefani, F.
We introduce a hydrodynamic model of convective flows in a titanium reduction reactor. The reactor retort is a cylindrical vessel with a radius of 0.75 m and a height up to 4m, filled with liquid magnesium at a temperature of 850°C. The exothermic chemical reaction on the metal surface, cooling of the side wall and heating of the lower part of the retort cause strong temperature gradients in the reactor during the process. These temperature gradients cause intensive convective flows inside the reactor. As a result of the reaction, a block of titanium sponge grows at the retort bottom and the magnesium salt, whose density is close to the density of magnesium, settles down. The process of magnesium salt settling in a titanium reduction reactor was numerically studied in a two-dimensional (full size model) and three-dimensional (30% size of the real model) non-stationary formulation. A detailed analysis was performed for configurations with and without presence of convective flow due to work of furnace heaters. It has been established that magnesium salt is settling in drops with sizes from ~3 cm to ~10 cm. It was shown that convective flow can entrain the drop and carry it with the vortex.

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-25840
Publ.-Id: 25840


A fluorescence anisotropy-based assay to characterize the GTP-binding site of tissue transglutaminase

Hauser, C.; Kasprzyk, R.; Wodtke, R.; Jemielity, J.; Löser, R.; Pietsch, M.
High activity of tissue transglutaminase (TGase 2) in various tumors is associated with both their increased metastatic and invasive potential and their resistance towards chemotherapy and radiation. This renders TGase 2 an attractive target for the development of agents that are capable of targeting the tumor-associated TGase 2 for both imaging and therapeutic approaches [1]. TGase 2 exists in two different conformations, with the closed one being the major intracellular form. It functions as a GTP-binding protein (Gh protein) at low Ca2+ levels, whereas transition to the open conformation (initiated by an increase in Ca2+ concentration) allows for the transamidase activity leading to protein-protein crosslinking [2].
Characterization of the GTP-binding activity of TGase 2 was done by means of a new fluorescence anisotropy assay using the literature known BODIPY FL-GTPγS [3]. This compound, internally quenched by an intramolecular stacking of the BODIPY and the guanosin moieties, is commonly used in fluorescence-based assays that make use of the unfolding and thereby dequenching of the fluorophore upon binding, leading to an increase in fluorescence. [3] Such behavior, however, interferes with the analysis of fluorescence anisotropy as the measured data have to be corrected [4].
To optimize the new assay, we investigated a small series of newly developed GTP- and GDP-analogues labeled with fluorescein for TGase affinity and change in fluorescence upon protein binding. All compounds show a significantly smaller increase in fluorescence intensity compared to the BODIPY FL-labeled nucleotide and – in some cases – an up to ten-fold superior binding affinity towards TGase 2. The fluorescence anisotropy assay was then validated for inhibition studies by investigation of GTP and GTPγS, which both show IC50 values (64 nM and 109 nM, respectively) that are in agreement with literature data [5,6].
Further investigations included titration of the GTP/TGase 2 interaction with CaCl2 to determine the Ca2+ concentration needed to shift TGase 2 to the extended conformation and inhibition studies with GDP and ATP as well as compounds targeting the acyltransferase domain of TGase 2.
References:
[1] Pietsch, M. et al. Bioorg. Med. Chem. Lett. 2013, 23, 6528.
[2] Kerr, C. et al. Oncogene 2016, doi: 10.1038/onc.2016.452.
[3] McEwen, D. P. et al. Methods Enzymol. 2002, 344, 403.
[4] Jameson, D. M. & Mocz, G. Methods Mol. Biol. 2005, 305, 301-322.
[5] Datta, S. et al. Biochemistry 2007, 46, 14819.
[6] Schaertl, S. et al. J. Biomol. Screen. 2010, 15, 478.
  • Poster
    Debrecen University Symposium 2017 - Transglutaminases in Medicine, 03.-05.08.2017, Debrecen, Ungarn

Permalink: https://www.hzdr.de/publications/Publ-25839
Publ.-Id: 25839


Radiosynthesis and in vitro characterisation of a potent 18F-fluorinated Nε-acryloyllysine as activity-based probe for transglutaminase 2

Wodtke, R.; Bauer, D.; Pufe, J.; Hauser, S.; Hauser, C.; Pietsch, M.; Pietzsch, J.; Löser, R.
Transglutaminase 2 (TGase 2) represents an interesting target for the development of PET tracers for functional imaging of tumours. Among the TGase 2 inhibitors described in the literature, Nα-phenylacetyl-Nε-acryloyl-L-lysine-4-(6-methylpyridin-2-yl)piperazide (1) [1] seems to be most suitable for radiotracer development as this compound exhibits both strong inhibitory potential and selectivity towards human (h) TGase 2. Extensive structure-activity relationship studies by our group revealed some potent fluorinated analogues of 1, of which compound 3 (methyl group is substituted by fluorine) is a potential candidate for PET tracer development due to its great inhibitory potency and promising pharmacokinetic properties.
For the radiosyntheses of [18F]3, 6-nitro (2a) and 6-trimethylammonio-pyridines (2b) were envisaged as precursors for direct 18F-fluorination. The fluorination reactions using [18F]fluoride were performed under various conditions. Labelling of 2a by [18F]fluoride resulted in only moderate radiochemical yields (≈20%) accompanied by the formation of two 18F-labelled side products. In contrast to this, 18F-fluorination of 2b yielded exclusively [18F]3 in high radiochemical yields (≈70%). Therefore, precursor 2b was chosen for further radiosyntheses. In vitro characterisation of [18F]3 with regards to its reactivity towards hTGase 2 as well as its selectivity and specificity was done by radio-TLC and radio-SDS-PAGE. Kinetic investigations by radio-TLC provided values for kinact/KI that are in good agreement with values obtained by fluorimetric activity assays. Incubation of whole cell lysates of different human tumour cell lines exhibiting a high expression of TGase 2 with [18F]3, followed by SDS-PAGE and measurement of the 18F activity revealed essentially a single band around the molecular mass of hTGase 2 (≈77 kDa). Accordingly, no band was observed for those tumour cells which do not express TGase 2. Further experiments with [18F]3 will include cell uptake studies in living tumour cells as well as stability, biodistribution and PET studies in mice.
[1] J. Wityak et al. ACS Med. Chem. Lett. 2012, 3, 1024-1028
  • Lecture (Conference)
    Deberecen University Symposium 2017 - Transglutaminases in Medicine, 03.-05.08.2017, Debrecen, Ungarn

Permalink: https://www.hzdr.de/publications/Publ-25838
Publ.-Id: 25838


Magnetic field dynamos and magnetically triggered flow instabilities

Stefani, F.; Albrecht, T.; Arlt, R.; Christen, M.; Gailitis, A.; Gellert, M.; Giesecke, A.; Goepfert, O.; Herault, J.; Kirillov, O.; Mamatsashvili, G.; Priede, J.; Rüdiger, G.; Seilmayer, M.; Tilgner, A.; Vogt, T.
The project A2 of the LIMTECH Alliance aimed at a better understanding of those magnetohydrodynamic instabilities that are relevant for the generation and the action of cosmic magnetic fields. These comprise the hydromagnetic dynamo effect and various magnetically triggered flow instabilities, such as the magnetorotational instability and the Tayler instability. The project was intended to support the experimental capabilities to become available in the framework of the DREsden Sodium facility for DYNamo and thermohydraulic studies (DRESDYN). An associated starting grant was focused on the dimensioning of a liquid metal experiment on the newly found magnetic destabilization of rotating flows with positive shear. In this survey paper, the main results of these two projects are summarized.

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-25837
Publ.-Id: 25837


Strategies for the radiosynthesis of potent fluorinated Nε-acryloyllysines as potential PET tracers for transglutaminase 2

Wodtke, R.; Jäckel, E.; Bauer, D.; Lohse, M.; Wong, A.; Pufe, J.; Ruiz-Gómez, G.; Hauser, C.; Hauser, S.; Steinbach, J.; Teresa Pisabarro, M. T.; Pietsch, M.; Pietzsch, J.; Löser, R.
Objectives: Various kinds of tumour entities are characterised by increased activity of transglutaminase 2 (TGase 2), which contributes to enhanced invasive potential of the tumour cells and their resistance to chemo- and radiotherapy. Therefore, this enzyme represents an interesting target for the development of PET tracers for functional imaging of tumours. Among the TGase 2 inhibitors described in the literature, Nε-acryloyllysine 1 [1] seems to be most suitable for radiotracer development as this compound exhibits both strong inhibitory potential and selectivity towards human TGase 2. Extensive structure-activity relationship studies by our group revealed some potent fluorinated analogues of 1, of which compounds 2 and 4 were identified as potential candidates for PET tracer development due to their great inhibitory potencies and promising pharmacokinetic properties.
Methods: Reference compounds 2 and 4 as well as the precursor 3 were synthesised in a modular synthetic route. For the radiosynthesis of [18F]2, thienyl and anisyl iodonium salts were envisaged as precursors for prosthetic labelling groups, which were synthesised starting from iodophenylacetates. The fluorination reactions using [18F]F- were performed under various conditions to maximise the radiochemical yield (RCY).
Results: Although a wide range of conditions for radiolabelling of the phenylacetic acid-derived iodonium salts were applied, no incorporation of [18F]F- could be observed. To identify possible reasons for this, the two other regioisomeric phenylacetic acid-derived iodonium salts were synthesised and subjected to labelling with [18F]F-. As a result of these efforts, the CH acidity of the benzylic methylene group was supposed to have a detrimental effect on the labelling reaction. In contrast to this, labelling of precursor 3 was successful with RCYs (non-isolated crude product) of up to 15%. Due to the difficult separation of 3 and [18F]4, the nitro group was reduced to the respective amino group by tin(II) chloride prior to purification by RP-HPLC.
Conclusions: After identifying fluorinated Nε-acryloyllysines as potential PET tracer candidates, strategies for their radiosynthesis were developed. While attempts for the incorporation of fluorine-18 at the non-activated phenylacetic acid moiety revealed inherent structural limitations, labelling at the 2-nitropyridine-derived precursor led to a promising PET tracer candidate.
References:
[1] J. Wityak et al. ACS Med. Chem. Lett. 2012, 3, 1024-1028
  • Open Access Logo Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 60(2017)S1, S419-S419
    DOI: 10.1002/jlcr.3508

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-25836
Publ.-Id: 25836


Improving Stability of Cathepsin B Endopeptidase Substrates as Potential Cleavage Sites in Activatable Cell-Penetrating Peptides

Kuhne, K.; Behring, L.; Birgit Belter, B.; Wodtke, R.; Steinbach, J.; Pietzsch, J.; Löser, R.
Objectives: The cysteine protease cathepsin B, whose expression in tumors correlates with increased metastasis, therapy resistance, and a generally poor prognosis, represents an excellent target for molecular imaging using radiotracers [1]. We aim to develop a cathepsin B specific, substrate-based radiotracer derived from poly-d-arginine-based activatable cell penetrating peptides [2]. With in vivo application of peptides being often limited by short biological half-life, stabilization against proteolytic degradation is a key aspect in the development of this agent.
Methods: Octapeptide substrates containing the FRET pair aminobenzoyl/dinitrophenyl (Abz/Dnp) were synthesized by solid phase peptide synthesis in high purities and good yields, using non-proteinogenic and N-methylated amino acids (AA) for stabilization. All substrates were evaluated for cleavage efficiency by cathepsin B in orientation to [3]. In vitro stability studies were performed in human serum, with analysis by UPLC-ESI-MS, using the UV absorbance of Dnp (λ = 365 nm) for quantification and subsequent ESI-MS analysis for identification of degradation products.
Results: Rapid degradation has been observed for the endopeptidase substrate Abz-Gly-Ile-Val-Arg-Ala-Lys(Dnp)-Gly-Ser-NH2 in the in vitro serum stability assay (T1/2 = 3.7 min), which was due to cleavage at the P1-P1’ cleavage site (Arg-Ala) as indicated by LC-MS analysis. In a first step, arginine was substituted by citrulline to decrease susceptibility to trypsin-like serum proteases, which increased serum stability (T1/2 = 8.9 min). The non-proteinogenic AA homoarginine, homocitrulline and O-carboxybenzylserine are being tested as further potential substitutes for arginine. Secondary cleavage sites, identified at P4-P3 (Gly-Ile) and P2’-P3’ (Lys-Gly), were suppressed by insertion of Nα-methyl-isoleucine and Nα-methyl-glycine.
Conclusions: After the optimization of the endopeptidase substrate with regards to cathepsin B-specific cleavage, substrate stabilization against other proteases is a crucial step to a peptide-based radiotracer. We have demonstrated the potential for stabilization by introduction of citrulline, with further stabilization by insertion of N-methylated and non-proteinogenic amino acids ongoing, which will pave the way to the envisaged substrate-based imaging probes.
References:
1. Löser & Pietzsch, Front. Chem. 2015, 3, 37
2. Jiang et al., PNAS 2004, 101, 17867
3. Cotrin et al., Anal. Biochem. 2004, 335, 244
  • Open Access Logo Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 60(2017)S1, S221-S221
    DOI: 10.1002/jlcr.3508

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-25835
Publ.-Id: 25835


Brain volume and perfusion changes in healthy tissue of glioblastoma patients treated with radiochemotherapy

Petr, J.
Brain volume and perfusion changes in healthy tissue of glioblastoma
patients treated with radiochemotherapy
  • Invited lecture (Conferences)
    Invited talk at Leiden University Medical Center, 17.01.2017, Leiden, Netherlands

Permalink: https://www.hzdr.de/publications/Publ-25834
Publ.-Id: 25834


Resolution and deformation issues of the partial volume correction of ASL data

Petr, J.; Mutsaerts, H.; de Vita, E.; Maus, J.; van den Hoff, J.; Asllani, I.
  • Invited lecture (Conferences)
    Invited lecture at UCL Institute of Neurology, 15.03.2016, London, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-25833
Publ.-Id: 25833


Thermal convection of liquid metal in the titanium reduction reactor

Teimurazov, A.; Frick, P.; Stefani, F.
The structure of the convective flow of molten magnesium in a metallothermic titanium reduction reactor has been studied numerically in a three-dimensional non-stationary formulation with conjugated heat transfer between liquid magnesium and solids (steel walls of the cavity and titanium block). A nonuniform computational mesh with a total of 3.7 million grid points was used. The Large Eddy Simulation technique was applied to take into account the turbulence in the liquid phase. The instantaneous and average characteristics of the process and the velocity and temperature pulsation fields are analyzed. The simulations have been performed for three specific heating regimes: with furnace heaters operating at full power, with furnace heaters switched on at the bottom of the vessel only, and with switched-off furnace heaters. It is shown that the localization of the cooling zone can completely reorganize the structure of the large-scale flow. Therefore, by changing heating regimes, it is possible to influence the flow structure for the purpose of creating the most favorable conditions for the reaction. It is also shown that the presence of the titanium block strongly affects the flow structure.

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-25832
Publ.-Id: 25832


Stability of MR Brain Perfusion Measurement Using Arterial Spin Labeling

Petr, J.; Hofheinz, F.; Platzek, I.; Schramm, G.; van den Hoff, J.
Reproducibility of ASL perfusion measurements.
  • Lecture (Conference)
    Meeting of the ASL COST Action, 03.02.2015, Les Diablerets, Switzerland

Permalink: https://www.hzdr.de/publications/Publ-25831
Publ.-Id: 25831


Transitions in a magnetized quasi-laminar spherical Couette flow

Kasprzyk, C.; Kaplan, E.; Seilmayer, M.; Stefani, F.
First results of a new spherical Couette experiment are presented. The liquid metal flow in a spherical shell is exposed to a homogeneous axial magnetic field. For a Reynolds number Re=1000, we study the effect of increasing Hartmann number Ha. The resulting flow structures are inspected by ultrasound Doppler velocimetry. With a weak applied magnetic field, we observe an equatorially antisymmetric jet instability with the azimuthal wave number m=3. As the magnetic field strength increases, this instability vanishes. When the field is increased further, an equatorially symmetric return flow instability arises. Our observations are shown to be in good agreement with linear stability analysis and non-linear flow simulations.
  • Open Access Logo Magnetohydrodynamics 53(2017)2, 393-401

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-25830
Publ.-Id: 25830


Comparison of MLAA-derived attenuation maps with and without utilisation of time-of-flight information in the attenuation estimation step

Nikulin, P.ORC; Lougovski, A.; Hofheinz, F.; Maus, J.ORC; van den Hoff, J.
INTRODUCTION
As is well known, quantitative combined PET/MR imaging depends on accurate MR-based attenuation correction (MRAC). While a mostly satisfactory state of affairs has been reached today, problems persist regarding segmentation
errors including unsatisfactory bone identification and residual systematic differences in comparison to PET/CT. Alternative or complementary strategies for attenuation correction (AC), therefore, are of considerable relevance. In this context, Maximum Likelihood reconstruction of Attenuation and Activity (MLAA) is one of the most promising approaches. As A. Rezaei et al. have shown [1], Time-Of-Flight (TOF) image reconstruction is required to eliminate possible ”crosstalk” between the estimated activity and attenuation distribution. On the other hand, it is widely believed that use of the TOF information during attenuation estimation does not result in image quality improvement and thus is unnecessary, see for example ref. [2]. However, so far this assumption has never been thoroughly tested. We address this issue in the present investigation. To this end, we have compared TOF and non-TOF versions of the attenuation estimation algorithm as part of MLAA within the framework of our previously developed Tube of response High resolution OSEM Reconstruction (THOR), see ref [3].

METHODS
MLAA is an image reconstruction algorithm, which maximizes the Likelihood function by alternately updating activity distribution and attenuation map. Maximum-Likelihood Estimation-Maximization (MLEM) is normally used for the
activity estimation and Maximum-Likelihood Transmission Reconstruction (MLTR) for the attenuation estimation. In order to investigate the potential impact of using TOF-MLTR instead of nonTOF-MLTR in the MLAA workflow both of them were implemented as a part of our THOR application. List-mode MLEM algorithm was used for activity reconstruction and accelerated by utilizing ordered subsets. For scatter correction (SC), the time-of-flight extension of the Single Scatter Simulation algorithm (SSS) was used, see ref [4]. Attenuation map reconstruction was performed by ordered subsets accelerated list-mode version of MLTR, which is equivalent to the standard sinograms based MLTR in the non-TOF case. For the initial attenuation map estimate the MR-derived outline of the scanned object was uniformly filled with the attenuation coefficient of water. During reconstruction, attenuation map estimates were augmented by a pre-computed template of the patient bed. The main difference between TOF- and nonTOF-MLTR is the way how scatter and randoms corrections are handled. TOF information allows to individually compute this correction for each event (or TOF-bin) depending on event position along the LOR, while this correction is assumed to be the same for all the events within the LOR in the non-TOF algorithm. Consequently, any differences between both MLTR versions should be most pronounced for high contrast objects as is the case, e.g., if the bladder is within the field-of-view. Therefore, two different configurations of the whole body phantom L981602 were used. The phantom in configuration A has two cylindrical air-filled inserts and one cylindrical bone-like insert. This phantom allows to assess accuracy of the attenuation map estimate under low-contrast conditions. The phantom in configuration B comprises a large spherical ”bladder” insert with high target-to-background contrast and a small ”lesion” insert with lower contrast. The attenuation map is uniform in this case, which facilitates detection of scatter-related artifacts in the MLAA reconstructed attenuation image. Transmission scans of the phantoms with the Siemens HR+ scanner were performed and used as ground-truth for the attenuation maps.

RESULTS
The whole body phantom in both configurations was scanned with the Time-Of-Flight capable Philips Ingenuity-TF PET/MR scanner (TOF resolution (FWHM): ∼600 ps). Acquired data were reconstructed with THOR MLAA and TOF-MLTR and nonTOF-MLTR, respectively. In the case of configuration A (low activity contrast, high attenuation contrast) TOF-MLTR does not improve attenuation coefficients estimate significantly. Reconstructed attenuation values differ by less than 1% for bone and less than 15% for air. The situation is different for configuration B (high activity contrast, homogeneous attenuation). Due to presence of the large hot object in the field-of-view a massive artifact appears in the transaxial plane of the reconstructed attenuation map containing the ”bladder” insert. In the coronal view this artifact appears as a rather large area of apparently reduced attenuation in the middle of the phantom. The difference between the attenuation coefficient of the water background in the central and the peripheral zones depends on the reconstruction method used. Specifically, the use of TOF-MLTR instead of nonTOF-MLTR yields twofold decrease of the artifact. On the other hand, the attenuation coefficient inside the ”bladder” is about 12% higher than the reference value with TOF-MLTR compared to a 6% overestimate with nonTOF-MLTR (where this reduced deviation probably is due to the influence of the mentioned attenuation artifact).

CONCLUSION
Our preliminary results indicate that the use of TOF-MLTR within the MLAA framework provides only small improvements in terms of attenuation map accuracy if activity contrasts are modest. However, it can distinctly decrease scatter related artifacts in the presence of high activity contrast such as is frequently observed in the pelvis region. We hypothesize the advantages of TOF-MLTR will become even more apparent with increasing TOF resolution. A more detailed investigation of the benefits of TOF-MLTR usage within the MLAA workflow is under way.

REFERENCES
[1] A. Rezaei, M. Defrise, G. Bal, C. Michel, M. Conti, C. Watson, and J. Nuyts, “Simultaneous reconstruction of activity and attenuation in time-of-flight PET.” IEEE transactions on Medical Imaging, vol. 31, no. 12, pp. 2224–33, dec 2012.
[2] A. Rezaei and J. Nuyts, “Simultaneous reconstruction of the activity image and registration of the CT image in TOF-PET,” IEEE Nuclear Science Symposium Conference Record, vol. 1852, p. 1852, 2016.
[3] A. Lougovski, F. Hofheinz, J. Maus, G. Schramm, E. Will, J. van den Hoff, and J. van den Hoff, “A volume of intersection approach for on-the-fly system matrix calculation in 3D PET image reconstruction,” Physics in Medicine and Biology, vol. 59, no. 3, pp. 561–577, feb 2014.
[4] C. C. Watson, “Extension of Single Scatter Simulation to Scatter Correction of Time-of-Flight PET,” IEEE Transactions on Nuclear Science, vol. 54, no. 5, pp. 1679–1686, 2007.
Keywords: PET, TOF-PET, PET/MR, MLAA, MRAC, Attenuation Correction
  • Poster
    PSMR 2017 - 6th Conference on PET-MRI and SPECT-MRI, 29.-31.05.2017, Lisbon, Portugal

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-25829
Publ.-Id: 25829


Sun - Batteries - Sun

Stefani, F.; Galindo, V.; Giesecke, A.; Weber, N.; Weier, T.
Liquid metal batteries (LMBs) are presently discussed as cheap means for the storage of wind and solar energy. Among other drivers of undesired fluid motion that could destroy the three-fluids stratification, the Tayler instability (TI) sets some upper limit for the upscalability of LMBs. We present the principles of the TI, its possible effects on LMBs, and some simple ways to suppress it. We focus on the peculiar saturation mechanism of the TI at low magnetic Prandtl numbers, which relies on the change of the hydrodynamic base state. We discuss the recently found helicity oscillations of the m=1 velocity field of the TI which, in turn, might have consequences for stellar dynamo models for which the TI had originally been discussed. We show that these helicity oscillations can be resonantly excited by certain m=2 perturbations which would result, e.g., from planetary tidal forces. It is this high sensitivity of the helicity oscillations that could empower those very weak tidal forces to synchronize the entire solar dynamo.
  • Lecture (Conference)
    International workshop on liquid metal battery fluid dynamics (LMBFD 2017), 16.-17.05.2017, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-25828
Publ.-Id: 25828


The DRESDYN project: planned experiments and present status

Stefani, F.; Eckert, S.; Gerbeth, G.; Giesecke, A.; Gundrum, T.; Räbiger, D.; Seilmayer, M.; Weier, T.
The Dresden sodium facility for dynamo and thermohydraulic studies (DRESDYN) is a platform for large-scale liquid sodium experiments devoted to fundamental geo- and astrophysical questions as well as to various applied problems related to the conversion and storage of energy. Its most ambitious part is a precession driven dynamo experiment, comprising 8 tons of liquid sodium supposed to rotate with up to 10 Hz and to precess with up to 1 Hz. Another large-scale set-up is a Tayler-Couette experiment with a gap width of 0.2 m and a height of 2 m, whose inner cylinder rotates with up to 20 Hz. Equipped with a coil system for the generation of an axial field of up to 120 mT and two different axial currents through the center and the liquid sodium, this experiment aims at studying various versions of the magnetorotational instability and their combinations with the Tayler instability. We discuss the physical background of these two experiments and delineate the present status of their technical realization. Other installations, such as a sodium loop and a test stand for In-Service-Inspection experiments, will also be sketched.
  • Lecture (Conference)
    88th GAMM Annual Meeting, 06.-10.03.2017, Weimar, Germany

Permalink: https://www.hzdr.de/publications/Publ-25827
Publ.-Id: 25827


Ultrasound propagation in bond frustrated HgCr2S4 spinel in magnetic fields

Felea, V.; Prodan, L.; Stefanet, E.; Cong, P. T.; Zherlitsyn, S.; Tsurkan, V.
Ultrasound and magnetization studies of bond frustrated spinel HgCr2S4 are performed as a function of temperature in static magnetic fields. Beside the anharmonic effect, the sound velocity shows pronounced anomaly at the antiferromagnetic (AFM) transition at TN = 23 K with an additional significant increase of the order of 0.5 % indicating a strong spin-lattice coupling. External magnetic fields enhance the ferromagnetic (FM) correlations and shift the anomalies to lower temperatures concomitantly with the reduction of the Néel temperature. The constructed H–T Phase diagram beside the long-range AFM states reveals the state with induced FM order and regimes with short-range AFM and FM correlations as well.

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-25826
Publ.-Id: 25826


Comparison of arterial spin labeling registration strategies in the multi-center GENetic frontotemporal dementia initiative (GENFI)

Mutsaerts, H. J. M. M.; Petr, J.; Thomas, D. L.; de Vita, E.; Cash, D. M.; van Osch, M. J. P.; Golay, X.; Groot, P. F. C.; Ourselin, S.; van Swieten, J.; Laforce, R.; Tagliavini, F.; Borroni, B.; Galimberti, D.; Rowe, J. B.; Graff, C.; D. Pizzini, F. B.; Finger, E.; Sorbi, S.; Castelo Branco, M.; Rohrer, J. D.; Masellis, M.; Macintosh, B. J.
Purpose: To compare registration strategies to align arterial spin labeling (ASL) with 3D T1-weighted (T1w) images, with the goal of reducing the between-subject variability of cerebral blood flow (CBF) images.
Materials and Methods: Multi-center 3T ASL data were collected at eight sites with four different sequences in the multi-center GENetic Frontotemporal dementia Initiative (GENFI) study. In a total of 48 healthy controls, we compared the following image registration options: (I) which images to use for registration (perfusion-weighted images [PWI] to the segmented gray matter (GM) probability map (pGM) (CBF-pGM) or M0 to T1w (M0-T1w); (II) which transformation to use (rigid-body or non-rigid); and (III) whether to mask or not (no masking, M0-based FMRIB software library Brain Extraction Tool [BET] masking). In addition to visual comparison, we quantified image similarity using the Pearson correlation coefficient (CC), and used the Mann-Whitney U rank sum test.Results: CBF-pGM outperformed M0-T1w (CC improvement 47.2% 6 22.0%; P < 0.001), and the non-rigid transformation outperformed rigid-body (20.6% 6 5.3%; P < 0.001). Masking only improved the M0-T1w rigid-body registration (14.5% 6 15.5%; P 5 0.007).
Conclusion: The choice of image registration strategy impacts ASL group analyses. The non-rigid transformation is promising but requires validation. CBF-pGM rigid-body registration without masking can be used as a default strategy.
In patients with expansive perfusion deficits, M0-T1w may outperform CBF-pGM in sequences with high effective spatial resolution. BET-masking only improves M0-T1w registration when the M0 image has sufficient contrast.

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-25825
Publ.-Id: 25825


Scatter correction in TOF and non-TOF PET image reconstruction in THOR

Nikulin, P.ORC; Lougovski, A.; Hofheinz, F.; Maus, J.ORC; van den Hoff, J.
INTRODUCTION
As is well known, quantitative combined PET/MR imaging depends on accurate MR-based attenuation correction (MRAC). While a mostly satisfactory state of affairs has been reached today, problems persist regarding segmentation errors including unsatisfactory bone identification and residual systematic differences in comparison to PET/CT. Alternative or complementary strategies for attenuation correction (AC), therefore, are of considerable relevance. In this context, Maximum Likelihood reconstruction of Attenuation and Activity (MLAA) is one of the most promising approaches but, as A. Rezaei et al. have shown [1], Time-Of-Flight (TOF) image reconstruction is then required to eliminate possible ”crosstalks” between the estimated activity and attenuation distribution. We are aiming at implementation of MLAA for the Philips Ingenuity-TF PET/MR scanner as part of our previously developed Tube of response High resolution OSEM Reconstruction (THOR), see ref [2]. As a prerequisite we are currently modifying THOR to make full use of the available TOF information. The most critical point in this context is accurate and computational efficient TOF Scatter Correction (TOF-SC). Here, we report on our approach to solving this issue and compare TOF-SC techniques with conventional non-TOF SC method.

METHODS
One possible implementation of TOF-SC uses a straight forward extension of Watson’s well-known Single Scatter Simulation (SSS) algorithm [3] but this approach results in about an order of magnitude increase of computational burden compared to standard SSS. Alternatively, one can use standard SSS to estimate the number of scattered events in each Line Of Response (LOR) and use an additional algorithm to estimate the shape of the time distribution of scattered events within each LOR (scatter mask). To integrate TOF-SC into our THOR reconstruction, four different approaches to scatter mask calculation have been investigated:
A. Simple scatter scaling
This approach assumes that scattered and unscattered events have identical time distribution within each single LOR.
B. Attenuation based SC
In this approach the object is modeled as a set of “scatter points” which are generated by SSS. Each scatter point is then also assumed to be a scatter source. For each detector pair and scatter point the geometric path difference from scatter source to both detectors is calculated and an effective position of the scattered event within the corresponding LOR is determined. By repeating this procedure for a large number of scatter points and post-processing the results by smoothing or using a TOF-binning technique one can compute the required scatter mask.
C. Attenuation and activity based SC
While approach B allows to properly handle the shape of the attenuating object it does not take into account the given activity distribution. To fix this issue scatter sources and scatter points should be separated. To do this in a simple and fast way we introduce a small set of “emission points” for approximation of the given activity distribution. The activity distribution/object is then described as superposition of suitable 3D Gaussian distributions around these emission
points. Calculation of the scatter masks is similar to the previous approach, but now scatter sources are determined as projections of emission points onto straight lines connecting selected scatter point and detectors. In this approach the intensity of each source is proportional to the intensity of corresponding emission point and decreases according to a Gaussian as a function of the distance between them.
D. TOF-SSS Time-Of-Flight extension of Single Scatter Simulation by Watson.

RESULTS
All four approaches have been integrated into THOR and tested in dedicated phantom and patient studies. Approach A does not yield quantitatively correct scatter distributions for big objects. Approach B is superior to A but notable artifacts remain in the presence of high-contrast. Approach C is able to eliminate part of these artifacts but requires more computation time. Approach D is the most accurate and computationally most expensive.

CONCLUSION
Our preliminary results indicate that attenuation based SC might be the best compromise between computation time and image quality for a wide range of applications.

REFERENCES
[1] A. Rezaei, M. Defrise, G. Bal, C. Michel, M. Conti, C. Watson, and J. Nuyts, “Simultaneous reconstruction of activity and attenuation in time-of-flight PET.” IEEE transactions on Medical Imaging, vol. 31, no. 12, pp. 2224–33, dec 2012.
[2] A. Lougovski, F. Hofheinz, J. Maus, G. Schramm, E. Will, J. van den Hoff, and J. van den Hoff, “A volume of intersection approach for on-the-fly system matrix calculation in 3D PET image reconstruction,” Physics in Medicine and Biology, vol. 59, no. 3, pp. 561–577, feb 2014.
[3] C. C. Watson, “Extension of Single Scatter Simulation to Scatter Correction of Time-of-Flight PET,” IEEE Transations on Nuclear Science, vol. 54, no. 5, pp. 1679–1686, 2007.
Keywords: PET, TOF-PET, Scatter Correction, TOF-SC, Single Scatter Simulation, SSS
  • Lecture (Conference)
    Seminar on PET image reconstruction, 28.-30.09.2016, Leuven, Belgium

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-25824
Publ.-Id: 25824


Effect of Brain Extraction of Low Resolution Arterial Spin Labeling (ASL) Fmri Images on Realignment and Coregistration

Liao, J.; Petr, J.; Lazar, R. M.; Marshall, R. S.; Asllani, I.
ASL is an fMRI method that maps cerebral blood (CBF), which is a key parameter of brain physiology. In ASL, flow-weighted images are computed by subtracting a “labeled” image from a contiguously acquired unlabeled control image. The difference is then converted to a CBF image using partial volume (PV) maps obtained from the segmentation of the anatomical T1w image. It follows that the quality of ASL data is dependent on the quality of motion correction and coregistration of the high-resolution T1w image to the low-resolution ASL. We tested whether applying brain-extraction on the low-resolution ASL would improve both these processes. The test was performed on 8 patients with carotid occlusive disease. Improvement in motion realignment was defined as % change averaged over the 6 degrees of freedom and across patients; improvement in coregistration was assessed as a difference in the mutual information (MI) value between the T1w and extracted and original ASL, respectively. There was a noticeable effect of brain extraction on both realignment and coregistration.
Keywords: MR neuroimaging, Brain image analysis, Rigid-body image registration, ASL
  • Contribution to proceedings
    39th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, 11.-15.07.2017, Jeju Island, Korea
  • Poster
    39th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, 11.07.2017, Jeju Island, Korea

Permalink: https://www.hzdr.de/publications/Publ-25823
Publ.-Id: 25823


SUR: a superior alternative to SUV as a surrogate of tumor glucose metabolism

van den Hoff, J.
kein Abstract verfügbar
  • Invited lecture (Conferences)
    Symposium Nuclear Medicine & Molecular Imaging, Katholieke Universiteit Leuven, 10.01.2017, Leuven, Belgien

Permalink: https://www.hzdr.de/publications/Publ-25822
Publ.-Id: 25822


Standardised Uptake Ratio (SUR): die robuste Variante des SUV

van den Hoff, J.
kein Abstract verfügbar
  • Invited lecture (Conferences)
    Jahrestagung der Bayrischen Gesellschft für Nuklearmedizin, 01.07.2016, Regensburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-25821
Publ.-Id: 25821


Magnetohydrodynamic instabilities in liquid metal batteries

Stefani, F.
The increasing deployment of strongly fluctuating renewable energies requires a corresponding large-scale expansion of electricity storage. Liquid metal batteries (LMBs) are presently discussed as a possible route of economical grid-scale energy storage. They consist of two liquid metal electrodes and a molten salt ionic conductor sandwiched between them. The density ratios allow for a stable stratification of the three layers. In the talk, we concentrate on the magnetohydrodynamic aspects of this cell type, with special focus on electro-vortex flows, the sloshing instability, and possible effects of the Tayler instability.
  • Lecture (Conference)
    XXth Winter School on Continuous Media Mechanics, 13.-16.02.2017, Perm, Russia

Permalink: https://www.hzdr.de/publications/Publ-25820
Publ.-Id: 25820


Upconverting Nanophosphors for bioimaging: Preparation Strategies for hydrophilic colloidal Stable Particles

Nsubuga, A.; Sgarzi, M.; Joshi, T.; Stephan, H.
Currently, there is a widespread interest to use neodymium containing upconverting nanophosphors (UCNPs) for bioimaging applications. The infatuation of these nanoparticles derives from their capacity for excitation in the biologically transparent window (700-1000 nm), exceptional ability to convert near infrared radiation into visible light (upconversion), which prevents autofluorescence and over-heating effect of biological tissues and capability for deep tissue, high contrast imaging related to minimum autofluorescence in this spectral range [1]. Despite the fast progress in lanthanide-doped upconversion nanoparticles, the preparation of ultrasmall, monodisperse and hydrophilic UCNPs that display intense luminescence is still a challenging issue. Only a few examples of ultrasmall and hydrophilic UCNPs have been reported [2-3]. Here, we report the elaboration, synthesis and surface modification of sub-10 nm UCNPs with an excitation wavelength of 795 nm, which are composed of a host lattice of crystalline NaYF4 doped with Nd3+ and Yb3+ as sensitizers, and Er3+,Ho3+ or Tm3+ as emitter ions. Established strategies for synthesizing UCNPs yield mainly hydrophobic particles[1]. We report the conversion of these into hydrophilic, colloidally-stable, and biocompatible by using mainly ligand exchange strategies, and the influence of the coating on the UCNPs’ photophysical properties. This study will also allow establishing information about biodistribution, pharmacokinetics and formation of protein corona for ultrasmall UCNPs.
Keywords: Upconversion, lanthanide, Sub 10 nm particles, surface functionalization, Bio imaging
  • Lecture (Conference)
    NANOTECH France 2017, 28.-30.06.2017, Paris, France

Permalink: https://www.hzdr.de/publications/Publ-25819
Publ.-Id: 25819


Time efficient scatter correction in Time-Of-Flight PET image reconstruction

Nikulin, P.ORC; Lougovski, A.; Hofheinz, F.; Maus, J.ORC; van den Hoff, J.
Aim
We are currently modifying our previously developed Tube of response High resolution OSEM Reconstruction (THOR), see ref [1], to make full use of the available Time-of-Flight (TOF) information. The most critical point in this context is accurate and computational efficient TOF Scatter Correction (TOF-SC). Here, we report on our approach to solving this issue.

Methods
Four different, partly newly developed approaches to estimation of scatter time distribution have been investigated: A. Simple scatter scaling: this approach assumes that scattered and unscattered events have identical time distribution within each single LOR. B. Attenuation based SC (new approach): in this approach the object is modeled as a set of “scatter points”. Each scatter point is also assumed to be a scatter source. C. Attenuation and activity based SC (new approach): in this approach a small set of “emission points” for approximation of the given activity distribution is introduced. Calculations are similar to B except that scatter sources are determined as projections of emission points onto straight lines connecting selected scatter point and detectors. D. TOF-SSS Time-Of-Flight extension of Single Scatter Simulation by Watson.

Results
All four approaches have been integrated into THOR and tested in dedicated phantom and patient studies. Approach A does not yield quantitatively correct scatter distributions for big objects. Approach B is superior to A but notable artifacts remain in the presence of high-contrast. Approach C is able to eliminate part of these artifacts but requires more computation time. Approach D is the most accurate and computationally most expensive.

Conclusion
Our preliminary results indicate that attenuation based SC might be the best compromise between computation time and image quality for a wide range of applications.

Literature
[1] A. Lougovski, F. Hofheinz, J. Maus, et al., Physics in Medicine
and Biology 59(3), 561 (2014)
Keywords: PET, TOF-PET, Scatter Correction, TOF-SC
  • Poster
    NuklearMedizin 2017, 26.-29.04.2017, Dresden, Germany

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-25818
Publ.-Id: 25818


Liquid metal experiments on hydromagnetic dynamos and magnetically triggered flow instabilities

Stefani, F.
The magnetic fields of planets, stars and galaxies are generated by self-excitation in moving electrically conducting fluids. Magnetic fields play, in turn, an active role in cosmic structure formation by destabilizing rotational flows that would be otherwise hydrodynamically stable. For a long time, both effects had been the subject of purely theoretical investigations. The lecture gives an overview about the recent liquid metal experiments on dynamo action and magnetically triggered instabilities. An outlook on future experiments, including a precession driven dynamo and a large-scale Tayler-Couette experiment to be set-up in the framework of the DRESDYN project, is also given.
  • Invited lecture (Conferences)
    XXth Winter School on Continuous Media Mechanics, 13.-16.02.2017, Perm, Russia

Permalink: https://www.hzdr.de/publications/Publ-25817
Publ.-Id: 25817


Time efficient scatter correction in Time-Of-Flight PET image reconstruction

Nikulin, P.ORC; Lougovski, A.; Hofheinz, F.; Maus, J.ORC; van den Hoff, J.
INTRODUCTION
As is well known, quantitative combined PET/MR imaging depends on accurate MR-based attenuation correction (MRAC). While a mostly satisfactory state of affairs has been reached today, problems persist regarding segmentation errors including unsatisfactory bone identification and residual systematic differences in comparison to PET/CT. Alternative or complementary strategies for attenuation correction (AC), therefore, are of considerable relevance. In this context, Maximum Likelihood reconstruction of Attenuation and Activity (MLAA) is one of the most promising approaches but, as A. Rezaei et al. have shown [1], Time-Of-Flight (TOF) image reconstruction is then required to eliminate possible ”crosstalks” between the estimated activity and attenuation distribution. We are aiming at implementation of MLAA for the Philips Ingenuity-TF PET/MR scanner as part of our previously developed Tube of response High resolution OSEM Reconstruction (THOR), see ref [2]. As a prerequisite we are currently modifying THOR to make full use of the available TOF information. The most critical point in this context is accurate and computational efficient TOF Scatter Correction (TOF-SC). Here, we report on our approach to solving this issue.

METHODS
One possible implementation of TOF-SC uses a straight forward extension of Watson’s well-known Single Scatter Simulation (SSS) algorithm [3] but this approach results in about an order of magnitude increase of computational burden compared to standard SSS. Alternatively, one can use standard SSS to estimate the number of scattered events in each Line Of Response (LOR) and use an additional algorithm to estimate the shape of the time distribution of scattered events within each LOR (scatter mask). To integrate TOF-SC into our THOR reconstruction, three different approaches to scatter mask calculation have been investigated which are modifications/improvements of key ideas from article [4]:
A. Simple scatter scaling
This approach assumes that scattered and unscattered events have identical time distribution within each single LOR.
B. Attenuation based SC
In this approach the object is modeled as a set of “scatter points” which are generated by SSS. Each scatter point is then also assumed to be a scatter source. For each detector pair and scatter point the geometric path difference from scatter source to both detectors is calculated and an effective position of the scattered event within the corresponding LOR is determined. By repeating this procedure for a large number of scatter points and post-processing the results by smoothing or using a TOF-binning technique one can compute the required scatter mask.
C. Attenuation and activity based SC
While approach B allows to properly handle the shape of the attenuating object it does not take into account the given activity distribution. To fix this issue scatter sources and scatter points should be separated. To do this in a simple and fast way we introduce a small set of “emission points” for approximation of the given activity distribution. The activity distribution/object is then described as superposition of suitable 3D Gaussian distributions around these emission
points. Calculation of the scatter masks is similar to the previous approach, but now scatter sources are determined as projections of emission points onto straight lines connecting selected scatter point and detectors. In this approach the intensity of each source is proportional to the intensity of corresponding emission point and decreases according to a Gaussian as a function of the distance between them.

RESULTS
All three approaches have been integrated into our THOR reconstruction and tested in phantom and patient studies. Simple scatter scaling (approach A) does not yield quantitatively correct scatter distributions for big objects such as whole body phantoms. Attenuation based SC (approach B) does not have this problem due to proper handling of the object shape, but notable artifacts appear in the presence of high-contrast such as in the pelvis/bladder region. The combined attenuation and activity based algorithm (approach C) is able to eliminate part of the latter artifacts but requires more computation time.

CONCLUSION
Our preliminary results indicate that attenuation based SC might be the best compromise between computation time and image quality for a wide range of applications. A more detailed investigation of the efficiency and accuracy of the implemented TOF-SC methods is currently in progress.

REFERENCES
[1] A. Rezaei, M. Defrise, G. Bal, C. Michel, M. Conti, C. Watson, and J. Nuyts, “Simultaneous reconstruction of activity and attenuation in time-of-flight PET.” IEEE transactions on Medical Imaging, vol. 31, no. 12, pp. 2224–33, dec 2012.
[2] A. Lougovski, F. Hofheinz, J. Maus, G. Schramm, E. Will, J. van den Hoff, and J. van den Hoff, “A volume of intersection approach for on-the-fly system matrix calculation in 3D PET image reconstruction,” Physics in Medicine and Biology, vol. 59, no. 3, pp. 561–577, feb 2014.
[3] C. C. Watson, “Extension of Single Scatter Simulation to Scatter Correction of Time-of-Flight PET,” IEEE Transations on Nuclear Science, vol. 54, no. 5, pp. 1679–1686, 2007.
[4] M. Conti, B. Bendriem, M. Casey, M. Chen, F. Kehren, C. Michel, and V. Panin, “First experimental results of time-of-flight reconstruction on an LSO PET scanner.” Physics in medicine and biology, vol. 50, no. 19, pp. 4507–4526, oct 2005.
Keywords: PET, TOF-PET, Scatter Correction, TOF-SC
  • Lecture (Conference)
    PSMR 2016 - 5th Conference on PET/MR and SPECT/MR, 23.-25.05.2016, Cologne, Germany

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-25816
Publ.-Id: 25816


DRESDYN: Liquid metal experiments on dynamo action and magnetorotational instability

Gundrum, T.; Eckert, S.; Gerbeth, G.; Stefani, F.; Steglich, C.
We report on two large-scale liquid sodium experiments on precession-driven dynamo action and magnetorotational instability that are planned in the framework of the DRESDYN project.
  • Poster
    Nuclear Astrophysics at the Dresden Felsenkeller, 26.-28.06.2017, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-25815
Publ.-Id: 25815


Can planetary tides synchronize the solar dynamo?

Stefani, F.; Galindo, V.; Giesecke, A.; Weber, N.; Weier, T.
While the traditional explanation of the Hale cycle of the solar magnetic field relies on intrinsic features of the solar dynamo, we presently witness an increased interest in the question of whether gravitational forces of planets could influence the length and intensity of the cycle. Although tidal forces are usually considered as much too weak to play any role, one should note the large gravitational acceleration at the tachocline that amounts to 500 m/s². This translates the apparently tiny tidal heights of the order of 1 mm to equivalent velocities of 1 m/s. Such velocities, when allowed to coherently develop in the quiet regions of the tachocline, might indeed be relevant for the dynamo.
In our quest for a viable physical mechanism that could link the weak planetary force with solar dynamo action, we focus on the helicity oscillations that were recently found in simulations of the current-driven, kink-type Tayler instability that is characterized by an m=1 azimuthal dependence. We show how these helicity oscillations can be resonantly excited by m=2 perturbations that reflect tidal oscillations. Specifically, we speculate that the 11.07 years tidal oscillation induced by the tidally dominant Venus--Earth--Jupiter system may lead to a 1:1 resonant excitation of the oscillation of the associated alpha-effect. In the framework of a reduced, zero-dimensional alpha-Omega dynamo model, including a weak non-oscillatory and a resonantly excited oscillatory part of alpha, we recover the 22.14-year cycle of the solar dynamo. We finally show that the synchronization model can produce the correct orientation of the butterfly diagram even in case that the product of the non-oscillatory part of alpha with Omega is positive.
  • Poster
    2nd Conference on Natural Dynamos, 25.06.-01.07.2017, Valtice, Czech Republic

Permalink: https://www.hzdr.de/publications/Publ-25814
Publ.-Id: 25814


Spectroscopic and microscopic approach of U(VI) sorption on Acidovorax facilis for remediation purpose

Krawczyk-Bärsch, E.; Gerber, U.; Steudtner, R.; Müller, K.; Moll, H.; Rossberg, A.; Merroun, M. L.
The Gram-negative betaproteobacterium Acidovorax facilis is a suitable candidate for in situ bioremediation of contaminated waste waters and environments [1]. For spectroscopic and microscopic studies kinetic U(VI) sorption experiments were performed under aerobic conditions at 30°C by adjusting an initial U(VI) concentration to 0.1 mM at a neutral pH range by adding UO2(NO3)2 to the batch culture.
A high-resolution image of the cellular localization of U by A. facilis was achieved by using electron microscopy (STEM/HAADF). The elemental distribution analysis of phosphorus and uranium clearly indicates that U is entirely present in the cell membrane. By cryo-Time-resolved laser-induced fluorescence spectroscopy (cryo-TRLFS) studies the spectra deconvolution indicates a fast binding of U(VI) on phosphorylic functionality groups during the first hour with a subsequent formation of Uranyl-carboxylic species in addition to the Uranyl-phosphorylic species. Compared to emission spectra of the Uranyl-lipopolysaccharide [2] we suggest an interaction of UO22+ with cell membrane components of the outer membrane of A. facilis cells, whereas lipopolysaccharide will form the most stable complex. These results support those obtained by Extended X-ray absorption fine structure spectroscopy (EXAFS), where a relative short average U-Oeq bond length of 2.35 Å were observed for the U(VI) interaction with lipopolysaccharide indicating a binding of the U(VI) via organic phosphate groups in a monodentate fashion. The strong interaction of U(VI) with phosphorylic and carboxylic groups was reinforced by in-situ attenuated total reflection Fourier-transform (ATR FT-IR) spectroscopic studies due to the presence of characteristic phosphoryl vibrations. Most of the bound U(VI) presumably remained on the cells, more precisely on the phosphorylic functionalities at the cell membrane.
[1] Gerber et al. (2016). J. Hazard. Mater. 317, 127–134.
[2] Barkleit et al. (2008). Appl. Spectrosc. 62(7), 798-802.
Keywords: Uranium, Acidovorax facilis, TRLFS, EXAFS, ATR FT-IR, STEM/HAADF
  • Lecture (Conference)
    Goldschmidt2017, 13.-18.08.2017, Paris, France

Permalink: https://www.hzdr.de/publications/Publ-25813
Publ.-Id: 25813


Laboratory experiments on dynamo action and magnetically triggered flow instabilities

Stefani, F.
Magnetic fields of planets, stars and galaxies are known to be generated by the homogeneous dynamo effect in moving electrically conducting fluids, such as liquid metals or plasmas. Once generated, magnetic fields can foster cosmic structure formation by destabilizing, via the magnetorotational instability (MRI) or the Tayler instability (TI), those rotating flows that would be otherwise hydrodynamically stable. The mutual reinforcement of dynamo action and magnetic instabilities leads to interesting concepts such as the MRI-dynamo or the Tayler-Spruit-dynamo.
For a long time, all these topics had been the subject of purely theoretical and numerical research. This situation changed in 1999 when the threshold of magnetic-field self-excitation was exceeded in the two liquid sodium experiments in Riga and Karlsruhe. Since 2006, the VKS dynamo experiment in Cadarache has successfully reproduced many features of geophysical interest such as reversals and excursions. Further liquid metal experiments in Grenoble, Madison, Maryland, Perm, Princeton, Perm, and Socorro have contributed important findings related to the alpha, beta and Omega effects as well as to various wave phenomena in magnetized rotating fluids. MRI-related research was partly successful with the observation of the helical MRI and the azimuthal MRI at the PROMISE facility at Helmholtz-Zentrum Dresden-Rossendorf (HZDR). First evidence of the current-driven Tayler instability in a liquid metal was also obtained.
The lecture gives an overview about liquid metal experiments on dynamo action and magnetically triggered flow instabilities. It concludes with an overview about future experiments, with special focus on the precession driven liquid sodium experiment and the large-scale Tayler-Couette experiment that are under construction in the framework of the DRESDYN project at HZDR.The prospects for experimental validation of the recently discussed magnetic destabilization of flows with positive shear are also discussed.
  • Invited lecture (Conferences)
    2nd Conference on Natural Dynamos, 25.06.-01.07.2017, Valtice, Czech Republic

Permalink: https://www.hzdr.de/publications/Publ-25812
Publ.-Id: 25812


Evaluation of hemodynamic impairments in healthy elderly participants and patients with high-grade unilateral carotid artery stenosis

Kaczmarz, S.; Göttler, J.; Griese, V.; Petr, J.; van de Ven, K.; Helle, M.; Kooijman, H.; Kluge, A.; Karampinos, D.; Zimmer, C.; Sorg, C.; Preibisch, C.
Internal carotid-artery stenosis (ICAS) causes complex and not yet well understood physiological impairments. We present preliminary data from an ongoing clinical study in ICAS patients and healthy, age-matched participants. The major aims were to evaluate the reliability of a multimodal MRI-protocol and investigate physiological changes. For ICAS patients, regionally impaired vascular-reactivity as well as hypo-perfusion were found. In accordance with literature, we did not find ICAS-induced changes in oxygen extraction on group level. The presented preliminary results thus imply successful application of multimodal MRI methods and are highly promising with respect to gaining a deeper insight into ICAS-related physiological changes.
Keywords: stenosis, ASL, perfusion, MRI
  • Contribution to proceedings
    25th Scientific Meeting and Exhibition of International Society for Magnetic Resonance in Medicine, 22.-27.04.2017, Honolulu, Hawaii, USA
    Proceedings of the 25th Scientific Meeting and Exhibition of International Society for Magnetic Resonance in Medicine
  • Lecture (Conference)
    25th Scientific Meeting and Exhibition of International Society for Magnetic Resonance in Medicine, 22.04.2017, Honolulu, Hawaii, USA

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-25811
Publ.-Id: 25811


Perfusion decrease during radiochemotherapy is not fully explained by volumetric gray matter changes

Petr, J.; Mutsaerts, H.; Hofheinz, F.; Asllani, I.; van Osch, M.; Platzek, I.; Seidlitz, A.; Krause, M.; van den Hoff, J.
Radiochemotherapy in brain-tumor patients was shown to cause gray matter (GM) volume and cerebral blood flow (CBF) changes. The interaction of these two effects, however, remains unclear. Here, we investigated GM volume and ASL CBF changes and their interaction in the healthy hemisphere of 38 glioblastoma patients undergoing radiochemotherapy with Temozolomide. We found a statistically significant CBF decrease with dependence on the RT-dose. PV-corrected results indicated that, while to a certain extent the apparent CBF decrease measured by ASL is caused by GM atrophy, there still remain significant CBF changes that cannot be explained by structural changes alone.
Keywords: ASL, perfusion, glioblastoma, radiochemotherapy, atrophy, partial volume
  • Contribution to proceedings
    25th Scientific Meeting and Exhibition of International Society for Magnetic Resonance in Medicine, 22.-27.04.2017, Honolulu, Hawaii, USA
    Proceedings of the 25th Scientific Meeting and Exhibition of International Society for Magnetic Resonance in Medicine
  • Poster
    25th Scientific Meeting and Exhibition of International Society for Magnetic Resonance in Medicine, 22.04.2017, Honolulu, Hawaii, USA

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-25810
Publ.-Id: 25810


Brain volume loss in glioblastoma patients following photon and proton radiochemotherapy

Petr, J.; Hofheinz, F.; Gommlich, A.; Raschke, F.; Troost, E.; Beuthien-Baumann, B.; Seidlitz, A.; Platzek, I.; Baumann, M.; Krause, M.; van den Hoff, J.
Gray matter (GM) atrophy in healthy brain tissue following radiochemotherapy was shown in brain-tumor patients in several studies. Here, we aimed to study GM and white matter (WM) changes in glioblastoma patients undergoing photon (n=43) and proton (n=12) radiochemotherapy. In photon-therapy patients, a statistically significant decrease of both GM (~2%) and WM (1.3-2.3%) volume was found with a positive influence of the RT-dose on the GM volume loss. In proton-therapy patients, no significant changes in GM and WM volumes were observed after therapy. This indicates that the proton-therapy has the potential to reduce structural GM changes in healthy tissue.
Keywords: radiochemotherapy, proton therapy, atrophy, morphometrics
  • Contribution to proceedings
    25th Scientific Meeting and Exhibition of International Society for Magnetic Resonance in Medicine, 22.-27.04.2017, Honolulu, Hawaii, USA
    Brain volume loss in glioblastoma patients following photon and proton radiochemotherapy
  • Lecture (Conference)
    25th Scientific Meeting and Exhibition of International Society for Magnetic Resonance in Medicine, 22.04.2017, Honolulu, Hawaii

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-25809
Publ.-Id: 25809


Kinetic Modeling

van den Hoff, J.
A mathematical description of the time-dependent tissue uptake and tissue clearance after injection of contrast agents or radioactively labeled tracers with suitable models (kinetic modeling) allows a detailed analysis of transport processes and metabolism in vivo. Such an analysis can provide at once quantitative information for several interesting parame- ters such as local blood volume, blood flow, distribution volumes, metabolic rates, binding potentials, and so forth. While the mathematical techniques are – with some reservations – in principle suited for data analysis in other tomographic modalities as well (notably CT and MRI), the broadest field of application is found in PET. We will focus especially on small animal PET in the following.
Keywords: PET, Kinetic Modeling, Small Animal Imaging
  • Book chapter
    Fabian Kiessling, Bernd J. Pichler, Peter Hauff: Small Animal Imaging: Basics and Practical Guide, Heidelberg: Springer International Publishing, 2017, 978-3-319-42200-8, 559-580
    DOI: 10.1007/978-3-319-42202-2_21

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-25808
Publ.-Id: 25808


Steering magnons by non-collinear spin textures

Schultheiss, K.; Wagner, K.; Kákay, A.; Schultheiss, H.
One of the grand challenges in cutting edge quantum and condensed matter physics is to harness the spin degree of electrons for information technologies. While spintronics, based on charge transport by spin polarized electrons, made its leap in data storage by providing extremely sensitive detectors in magnetic hard-drives [1], it turned out to be challenging to transport spin information without great losses [2]. With magnonics a visionary concept inspired researchers worldwide: Utilize spin waves - the collective excitation quanta of the spin system in magnetically ordered materials - as carriers for information [3-8]. Spin waves, which are also called magnons, are waves of the electrons’ spin precessional motion. They propagate without charge transport and its associated Ohmic losses, paving the way for a substantial reduction of energy consumption in computers.
While macroscopic prototypes of magnonic logic gates have been demonstrated [9,10], the full potential of magnonics lies in the combination of magnons with nano-sized spin textures. Both magnons and spin textures share a common ground set by the interplay of dipolar, spin-orbit and exchange energies rendering them perfect interaction partners. Magnons are fast, sensitive to the spins’ directions and easily driven far from equilibrium. Spin textures are robust, non-volatile and still reprogrammable on ultra short timescales. The vast possibilities offered by combining these magnetic phenomena, add value to both magnonics and the fundamental understanding of complex spin textures.
The scope of this chapter is about experimental studies on magnon transport in metallic ferromagnetic microstructures with focus on actively controlling the magnon propagation. Two inherent characteristics of magnons enable for lateral steering: the anisotropy of the magnon dispersion and its sensitivity to changes in the internal magnetic field distribution. We intend to give an idea of how these magnon features can be utilized towards realizing functionalized magnonic networks.
Keywords: spin waves, magnonics, spintronics, magneto-optics, spin textures, domain walls
  • Book chapter
    Sergej Demokritov: Spin Wave Confinement: Propagating Waves (2nd Edition), Singapore: Pan Stanford Publishing Pte. Ltd., 2017, 9789814774352

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-25807
Publ.-Id: 25807


EXILL - a high efficiency, high resolution setup for γ-spectroscopy at an intense cold neutron beam

Jentschel, M.; Blanca, A.; de France, G.; Köster, U.; Leoni, S.; Mutti, P.; Simpson, G.; Soldner, T.; Ur, C.; Urban, W.; Ahmed, S.; Astieri, A.; Augey, L.; Back, T.; Baczyk, P.; Bajoga, A.; Balabanski, D.; Belgya, T.; Benzoni, G.; Bernards, C.; Biswas, D.; Bocchi, G.; Bottoni, S.; Britton, R.; Bruyneel, B.; Burnett, J.; Cakirli, R. B.; Carroll, R.; Catford, W.; Cederwall, B.; Celikovic, I.; Cieplicka, N.; Clement, E.; Cooper, N.; Crespic, F.; Csatlos, M.; Czerwinski, M.; Danu, L.; Davies, A.; Didierjean, F.; Drouet, F.; Duchene, G.; Ducoin, C.; Eberhardt, K.; Erturk, S.; Fraile, L. M.; Gottardo, A.; Grente, L.; Grocutt, L.; Guerrero, C.; Guinet, D.; Hartig, A.-L.; Henrich, C.; Ignatov, A.; Ilieva, S.; Ivanova, D.; John, B.; John, R.; Jolie, J.; Kisyov, S.; Konstantinopoulos, T.; Korgul, A.; Krasznahorkay, A.; Kröll, T.; Kurpeta, J.; Kutiu, I.; Lalkovski, S.; Larijani, C.; Leguillon, R.; Lica, R.; Litaize, O.; Magron, C.; Mancuso, C.; Ruiz Martinez, E.; Massarczyk, R.; Mazzocchi, C.; Melon, B.; Mengoni, D.; Million, B.; Mokry, C.; Mukhopadhyay, S.; Mulholland, K.; Nannini, A.; Napoli, D. R.; Olaizola, B.; Orlandi, R.; Patel, Z.; Paziy, V.; Petrache, C.; Pfeiffer, M.; Podolyak, Z.; Ramdhane, M.; Redon, N.; Regan, P.; Regis, J. M.; Regnier, D.; Oliver, R. J.; Rudigier, M.; Runke, J.; Rzaca-Urban, T.; Saed-Samii, N.; Salsacq, M. D.; Scheck, M.; Schwengner, R.; Sengele, L.; Simpson, G.; Singh, P.; Smith, J.; Stezowski, O.; Szpak, B.; Thomas, T.; Thürauf, M.; Timaru, J.; Toml, A.; Tomandl, I.; Tornyi, T.; Townsley, C.; Tuerler, A.; Valenta, S.; Vancraeyenest, A.; Vandone, V.; Vanhoy, J.; Vedia, V.; Warr, N.; Werner, V.; Wilmsen, D.; Wilson, E.; Zerrouki, T.; Zielinska, M.
In the EXILL campaign a highly efficient array of HPGe detectors was operated at the cold neutron beam instrument PF1B of the Institut Laue-Langevin to carry out nuclear structure studies, via measurements of -rays following neutron-induced capture and fission reactions. The setup consisted of a collimation system producing a pencil beam with a thermal capture equivalent
flux of about 108 s-1 cm-2 at the target position and negligible neutron halo. The target was surrounded by an array of eight to ten anti-Compton shielded EXOGAM clover detectors, four to six
anti-Compton shielded large coaxial GASP detectors and two smaller clover detectors. The detectors were arranged in an array of rhombicuboctahedron geometry, providing the possibility to carry out very precise angular correlation and directional-polarization correlation measurements. The trigger-less acquisition system allowed an event collection rate of up to 6 × 105 Hz. From triggerless collected data it was possible to construct decay schemes and in combination with the FATIMA array of LaBr3 detectors to analyze half-lives of excited levels in the pico- to micro-second range. Precise energy and efficiency calibrations of EXILL were performed using 27Al(n,γ)28Al and 35Cl(n,γ)36Cl reactions in the energy range from 30 keV up to 10 MeV.
Keywords: neutron-induced fission; 235U; 241Pu; (n,γ)-reactions; Ge detectors; angular correlations; multiple-γ coincidences.

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-25806
Publ.-Id: 25806


Nuclear-Physics Experiments at the Bremsstrahlung Facility γELBE

Schwengner, R.; Wagner, A.
The γELBE facility at HZDR is described.
Keywords: electron accelerator, bremsstrahlung, HPGE detectors

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-25805
Publ.-Id: 25805


Modified ultrasmall nanoparticles as multimodal imaging agents for biomedical applications

Singh, G.; Licciardello, N.; Hunoldt, S.; Bergmann, R.; Zarschler, K.; Faramus, A.; de Cola, L.; Stephan, H.
Objectives
The synthesis of multimodal imaging agents is a growing research field and a lot of work is currently being done in this area because of its wide biomedical applications. The idea behind the use of nuclear and optical dual labelled imaging probes is the possibility to synergistically exploit the advantages of positron emission tomography (PET) and optical imaging. The dual labelled imaging agents combat the limitations of sensitivity, spatial and temporal resolution and also tissue penetrability [1]. The combination of the two imaging modalities may provide complementary information for improving diagnosis, allows image guided surgery as well as fluorescence microscopy of tissue biopsies.

Methods
Ultrasmall silicon nanoparticles (SiNPs) of size <5 nm are potential candidates in this perspective due to their hydrophilicity, biocompatibility, luminescence properties and the possibility to covalently functionalize their surface [2,3]. Amine-terminated ultrasmall silicon nanoparticles were prepared according to a reported method with slight modifications [4]. Here we report the functionalization of amine-terminated SiNPs with the sulfo-cyanine 5 dye (sCy5) to obtain an optical imaging probe and with biomolecules, such as single-domain antibodies (sdAb) for active targeting of a cancer biomarker. SiNPs are also modified with radiolabel such as 64Cu, coordinated to bispidines [5], to obtain a dual, nuclear and optical, probe.
Results
The renal clearance property of these biocompatible, hydrophilic ultrasmall SiNPs are the major highlights of this research. The modified particles tend to eliminate from the body within very small period of time, rendering them as excellent tools for biomedical purposes.

Conclusions
The functionalization of SiNPs with fluorescent dyes, radiotracers and targeting moieties will open the path for targeted dual imaging of cancer, possibly allowing diagnosis and therapy in in vivo systems.

References
[1] G. Singh, M. D. Gott, H.-J. Pietzsch, and H. Stephan, Nuklearmedizin 2016, 55, 41–50.
[2] M. Rosso-Vasic, E. Spruijt, Z. Popović, K. Overgaag, B. van Lagen, B. Grandidier, D. Vanmaekelbergh, D. Domínguez-Gutiérrez, L. De Cola, H. Zuilhof, J. Mater. Chem., 2009, 19, 5926-5933.
[3] C.-H. Lai, J. Hütter, C.-W. Hsu, H. Tanaka, S. Varela-Aramburu, L. De Cola, B. Lepenies, and P. H. Seeberger, Nano Lett. 2016, 16, 807−811.
[4] Y. Zhong, F. Peng, F. Bao, S. Wang, X. Ji, L. Yang, Y. Su, S.-T. Lee, Y. He, J. Am. Chem. Soc. 2013, 135, 8350- 8356.
[5] H. Stephan, M. Walther, S. Fähnemann, P. Ceroni, J. Molloy, G. Bergamini, F. Heisig, C. E. Müller, W. Kraus, and P. Comba, Chem. Eur. J., 2014, 20, 17011-17018.
Keywords: Silicon nanoparticles, Biomedical applications, Radiolabeling, Positron emission tomography, Optical imaging
  • Poster
    22nd International Symposium on Radiopharmaceutical Sciences, 14.-19.05.2017, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-25804
Publ.-Id: 25804


Synthesis of two new 11C-labelled a7 nicotinic acetylcholine receptor ligands.

Patt, J.-T.; Deuther-Conrad, W.; Peters, D.; Brust, P.; Sabri, O.; Patt, M.
Introduction
NS-9011 (4-[5-(4-Methoxy-phenyl)-[1,3,4]oxadiazol-2-yl]-1,4-diaza-bizyclo[3.2.2]nonane) and NS-9030 (4-[5-(3-Methoxy-phenyl)-[1,3,4]oxadiazol-2-yl]-1,4-diaza-the desmethyl precursor compounds with [11C]methyltriflate. The precursor compounds showed a high reactivity towards [11C]iodomethane, unfortunately not in the desired labelling position. In order to decrease the selectivity for the undesired compound(s) [11C]methyltriflate instead of [11C]iodomethane was used. The higher reactivity of the [11C]methyltriflate in combination with elevated temperature of 60 °C and using water as solvent should result in a considerable decrease in selectivity.
Methods
The radiosynthesis was carried out in a modified TracerLab C system (GEMS) equipped with a reaction loop instead of the glass reactor in the heating zone of the module. [11C]iodomethane was subsequently passed over silver triflate at 200 °C and through the reaction loop containing the precursor solution (prepared from 0.5 – 1.0 mg precursor and 30μl of 0.5 M NaOH solution) and 30 μl of water) heated to 60 °C. The reaction mixture was transferred with eluent into a HPLC valve and injected on a ReproSil-Pur 120 C18-Aq 5μ (125 mm x 10 mm) HPLC column. An eluent composed of 10 % Ethanol (NS-9011) or 13 % Ethanol (NS-9030) and buffer solution (40 ml sodium phosphate (Braun) per 1000 ml adjusted to pH 2 with phosphorc acid was used for purification.The product peak was collected, diluted and concentrated on a Phenomenex Strata X cartridge. The radiotracer was eluted with acetone (1.5 ml). Evaporation was performed manually in a heating block (70 °C) in a stream of nitrogen. The product was dissolved in 500 μl of physiological NaCl solution. Radiochemical purity was determined on a radio-HPLC system on a ReproSil-Pur 120 C18-Aq 5μ (250 mm x 4.6 mm) HPLC column.
Results and Discussion
By applying the reaction conditions described above, despite highly favoured competing labelling sites in the precursor molecule up to 0.5 GBq of tracer compound could be synthesized. The product was obtained in high radiochemical purity (>95 %). Comparison of the UV trace of authentic standard compound and the radioactivity signal of radiotracer spiked with standard compound showed a full match of radioactivity and UV signal. The yield was sufficient for first animal experiments and the reaction conditions were not further optimized.
  • Poster
    The 22nd International Symposium on Radiopharmaceutical Sciences (ISRS 2017), 14.05.2017, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-25803
Publ.-Id: 25803


A clinical trial with (+)-[18F]Flubatine: evaluation of metabolism, plasma protein binding and parameters.

Patt, M.; Mishchenko, O.; Tiepolt, S.; Sattler, B.; Höpping, A.; Smits, R.; Becker, G. A. F.; Deuther-Conrad, W.; Steinbach, J.; Brust, P.; Sabri, O.
Introduction
(+)-[18F]Flubatine ((+)[18F]NCFHEB), the enantiomer of the recently introduced radioligand for quantificati(-)-[18F]Flubatine, was investigated in a clinical trial with patients suffering from Alzheimer’s disease compared to healthy controls. In order to be able to apply full kinetic modelling biological parameters such as plasma protein binding, amount of parent compound over time and distribution between cellular and noncellular blood components, were determined. In addition the kinetics of the tracer distribution between plasma and whole blood was assessed.
Methods
Plasma protein binding was evaluated in vitro by means of ultracentrifugation using a blood sample from each subject prior to injection. The amount of unchanged tracer over time was determined at 11 time points ranging from 3 to 270 min p.i. by radio-HPLC analysis of protein free plasma obtained by centrifugation as described previously. The distribution of radioactivity between cellular and non-cellular blood components was determined at 11 time points p.i. after separation of the blood components by centrifugation.
Results/Discussion
Plasma protein binding of (-)-[18F]Flubatine was found to be 0.140.02 (meansd) without significant difference between AD and HC groups. Metabolic degradation of (+)-[18F]Flubatine was very low: the amount of parent compound was found to be 100 and 972 % at 90 and 270 min p.i., respectively. The activity distribution between plasma and whole blood was found to be 0.820.05 and did not change with time. Kinetics for the distribution of the tracer between plasma and whole blood was determined over a time period of 1.5 h and equilibrium was found to be reached instantaneously.
Conclusions Biological parameters such as plasma protein binding, metabolism and tracer/activity distribution between plasma and whole blood were investigated within a clinical trial using (+)-[1842 subtype of nAChRs. From the biological data obtained within this study we, conclude that (+)-[18F]Flubatine is a very suitable radiotracer for the determination of the 42 nAChRs by kinetic modelling since plasma protein binding is moderate and the equilibrium between whole blood and plasma is reached instantaneously. Furthermore, metabolic degradation of the radiotracer is negligible.
  • Poster
    The 22nd International Symposium on Radiopharmaceutical Sciences (ISRS 2017), 14.-19.05.2017, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-25802
Publ.-Id: 25802


Influence of bivalent metal ions on the self-assembly of S-layer proteins from Lysinibacillus sphaericus JG-B53

Raff, J.; Liu, J.; Falke, S.; Drobot, B.; Oberthuer, D.; Kikhney, A.; Guenther, T.; Fahmy, K.; Svergun, D.; Betzel, C.
Many systems in nature are perfectly optimized for their function. Good examples therefore are surface layer (S-layer) proteins. These proteins form two-dimensional lattices acting as interfaces between prokaryotic cells and their environment and as such as selective and protecting barrier. Outstanding properties are their autocatalytic self-assembly, high physicochemical stability, many different and regular arranged functional groups and their nanoscale fine structure. Understanding the dynamic and complex process of self-assembly is not only highly interesting from a scientific point of view but also for the technical application of this group of proteins. Their use is particularly promi­sing for nanotechnology, and here especially for surface modification creating metal selective filter materials, bio-sensors or improved catalytic materials. Especially challenging within an industrial process is controlling the speed of the lattice formation and the formation of large areas of undisturbed lattices. For the examination of the structure-function relationship and the process dynamics of the protein self-assembly of the S-layer from Lysinibacillus sphaericus JG-B53 several complementary analytical techniques and methods have been applied: 1) The secondary structure of the S-layer protein was analyzed by CD spectroscopy. 2) Small-angle X-ray scattering (SAXS) was applied to gain insights into the three dimensional structure in solution. 3) The interaction with bivalent cations was followed by differential scanning calorimetry (DSC). 4) The dynamics and time-dependent assembly of S-layers was also investigated applying dynamic light scattering. 5) The two dimensional structure of the para-crystalline S-layer lattice was additionally examined by atomic force microscopy (AFM). The data obtained provide essential structural insights into the mechanism of the S-layer self-assembly, particularly with respect to the binding of the bivalent cations Mg2+ and Ca2+.
Keywords: S-layer, self-assembly, metal ions
  • Lecture (Conference)
    XXVI International Materials Research Congress (IMRC 2017), 20.-25.08.2017, Cancún, México

Permalink: https://www.hzdr.de/publications/Publ-25801
Publ.-Id: 25801


Superconductivity with broken time-reversal symmetry in ion irradiated Ba0.27K0.73Fe2As2 single crystals

Grinenko, V.; Materne, P.; Sarkar, R.; Luetkens, H.; Kihou, K.; Lee, C. H.; Akhmadaliev, S.; Efremov, D. V.; Drechsler, S.-L.; Klauss, H.-H.
Over the last years a lot of theoretical and experimental efforts have been made to find states with broken time reversal symmetry (BTRS) in multi-band superconductors. In particular, it was theoretically proposed that in the Ba1−xKxFe2As2 system either an s + is or an s + id BTRS state may exist at high doping levels in a narrow region of the phase diagram. Here we report the observation of an enhanced zero field muon spin relaxation rate below the superconducting transition temperature for a high quality crystalline sample with x ≈ 0.73. This indicates that indeed the time reversal symmetry is broken in superconducting Ba1−xKxFe2As2 at this doping level.

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-25800
Publ.-Id: 25800


Ptychographic analysis of the photorefractive effect in LiNbO3:Fe

Bernert, C.; Hoppe, R.; Wittwer, F.; Woike, T.; Schroer, C. G.
We present light induced refractive index changes in iron doped lithium niobate detected with a novel microscopy technique called ptychography. This method determines the change of the refractive index together with the intensity distribution of the writing beam from one single measurement with \SI{3}{\micro \m} spatial resolution and a sensitivity of the refractive index change of $10^{-5}$. We show that the light induced refractive index change follows exactly the intensity distribution of the writing beam.
Keywords: ptychographie, LiNbO3, LiNbO3:Fe, photorefractive effect

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-25798
Publ.-Id: 25798


Radiolabelled Nanomaterials for Imaging and Treatment of Cancer: Quo Vadis?

Stephan, H.
Novel nanomaterials (NMs) offer excellent prospects for the development of new non-invasive strategies of early diagnosis and efficient monitoring of therapeutic treatments. Thanks to their structural variability, which facilitates setting up the basic structure, modifying the periphery as well as creating complex structures, their properties allow being tailored to both diagnosis and treatment of diseases (theranostic approach) [1]. Provided with special functionalities, NMs allow the simultaneous application of different molecular imaging methods. In the field of cancer medicine, the combination of different imaging techniques such as nuclear (PET: positron emission tomography and SPECT: single-photon emission computed tomography) and near-infrared fluorescence (NIRF) imaging for tracking down tumors and metastases is particularly attractive [2].
This lecture will focus on the development and application of very small radiolabeled NMs, embracing polymeric structures [3] and inorganic particles [4]. Novel strategies will be discussed to develop stealth NMs capable of avoiding biomolecular corona formation and thus evading scavenging of NMs by the mononuclear phagocyte system, leading to eventual accumulation in the liver and spleen [5].

References
[1] J. A. Barreto, W. O’Malley, M. Kubeil, B. Graham, H. Stephan, L. Spiccia, Adv Mater 23 (2011) H18-H40.
[2] G. Singh, M. D. Gott, H.-J. Pietzsch, H. Stephan, Nuklearmedizin 55 (2016) 41-50.
[3] K. Pant, O. Sedláček, R. A. Nadar, M. Hrubý, H. Stephan, Adv Healthcare Mat 6 (2017) 1601115.
[4] K. Zarschler, L. Rocks, N. Licciardello, L. Boselli, E. Polo, K. Pombo Garcia, L. De Cola, H. Stephan, K. A. Dawson, Nanomed-Nanotechnol 12 (2016) 1663-1701.
[5] K. Pombo-García, K. Zarschler, L. Barbaro, J. A. Barreto, W. O’ Malley, L. Spiccia, H. Stephan, B. Graham
Small 10 (2014) 2516-2529.
  • Invited lecture (Conferences)
    II International Caparica Congress on Translational Chemistry, 04.-07.12.2017, Caparica (Lisbon), Portugal

Permalink: https://www.hzdr.de/publications/Publ-25797
Publ.-Id: 25797


EGFR-amplification plus gene expression profiling predicts response to combined radiotherapy with EGFR-inhibition: a preclinical trial in 10 HNSCC-tumour-xenograft models

Koi, L.; Löck, S.; Linge, A.; Thurow, C.; Hering, S.; Baumann, M.; Krause, M.; Gurtner, K.
Background and Purpose: Improvement of the results of radiotherapy by EGFR inhibitors is modest, suggesting significant intertumoral heterogeneity of response. To identify potential biomarkers, a preclinical trial was performed on ten different human squamous cell carcinoma xenografts of the head and neck (HNSCC) studying in vivo and ex vivo the effect of fractionated irradiation and EGFR inhibition. Local tumour control and tumour growth delay were correlated with potential biomarkers, e.g. EGFR gene amplification and radioresponseassociated gene expression profiles.
Material and methods: Local tumour control 120 days after end of irradiation was determined for fractionated radiotherapy alone (30f, 6 weeks) or after simultaneous EGFR-inhibition with cetuximab. The EGFR gene amplification status was determined using FISH. Gene expression analyses were performed using an in-house gene panel.
Results: Six out of 10 investigated tumour models showed a significant increase in local tumour control for the combined treatment of cetuximab and fractionated radiotherapy compared to irradiation alone. For 3 of the 6 responding tumour models, an amplification of the EGFR gene could be demonstrated. Gene expression profiling of untreated tumours revealed significant differences between amplified and non-amplified tumours as well as between responder and non-responder tumours to combined radiotherapy and cetuximab.
Conclusion: The EGFR amplification status, in combination with gene expression profiling, may serve as a predictive biomarker for personalized interventional strategies regarding combined treatment of cetuximab and fractionated radiotherapy and should, as a next step, be clinically validated.
Keywords: Keywords: Radiotherapy; Head and neck cancer; Biomarker; Cetuximab; Gene expression

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-25796
Publ.-Id: 25796


Positioning of cobalt atoms in amorphous carbon films by pre-selecting the hydrogen concentration

Gupta, P.; Williams, G. V. M.; Vajandar, S.; Osipowicz, T.; Becker, H.-W.; Heinig, K.-H.; Hübner, R.; Leveneur, J.; Kennedy, J.; Markwitz, A.
Amorphous carbon and hydrogenated amorphous carbon layers were implanted at room temperature with Co ions to investigate the role of hydrogen on the Co distribution. Amorphous carbon (a:C) and hydrogenated amorphous carbon (a:C-H) films were prepared by mass selective ion beam deposition with a 5 kV acceleration voltage using C+ and C3H6+ ions, respectively. The typically 100 nm thin films were implanted with Co using a 30 kV acceleration voltage to a fluence of 4×1016 cm-2. Raman measurements showed that Co implantation in hydrogenated amorphous carbon causes increased sp2 clustering while in amorphous carbon there is significant rehybridisation of carbon from sp3 to sp2 bonding. High resolution Rutherford backscattering measurements indicated that in the absence of hydrogen in the base matrix, the implantation profile assumes a unimodal distribution as predicted by simulations. However, in the presence of hydrogen the effects of collision cascade enhanced diffusion are significant in altering the implantation profile resulting in a bimodal distribution. The difference in the Co depth distribution between a:C and a:C-H films is explained by the change in thermal conductivity of the carbon matrix in the presence of hydrogen. The ability to position Co (magnetic atoms) in the surface region of diamond-like carbon films offers great advantages for applications in novel magnetic devices.
Keywords: Atomic positioning, Bimodal distribution, Cobalt implantation, Diamond-like carbon, Hydrogen

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-25794
Publ.-Id: 25794


Bimodale Systeme für die nukleare und optische Bildgebung

Stephan, H.; Singh, G.; Pant, K.; Steinbach, J.
Die molekulare Bildgebung hat sich als eine wertvolle Technik zum Verfolgen und zur Charakterisierung biochemischer Prozesse auf molekularer Ebene in isolierten Zellen, Geweben und höheren Organismen bis hin zur Humandiagnostik etabliert. Innerhalb des breiten Spektrums der verschiedenen Bildgebungsmodalitäten sind bimodale Systeme für die nukleare und optische Bildgebung von besonderem Interesse. Das ergibt sich vor allem aus der vergleichbaren Nachweisempfindlichkeit [1].
Es werden aussichtsreiche Systeme auf der Basis von modularen Liganden sowie nanoskaligen Materialien vorgestellt, die bifunktionelle Chelatoren zur stabilen Bindung des Positronenstrahlers 64Cu sowie Fluoreszenzfarbstoffe enthalten. Dabei handelt es sich einmal um makrocyclische Liganden auf der Basis des 1,4,7-Triazacyclonanonans (TACN) mit zusätzlichen Picolylgruppen I. Insgesamt wird mit diesen Verbindungen eine hohe thermodynamische Stabilität bei gleichzeitig schneller Komplexbildungskinetik für entsprechende Cu(II)-Komplexe erzielt [2, 3]. Weiterhin werden Liganden auf der Basis des 3,7-Diazabicyclo[3.3.1]nonans (Bispidine) II diskutiert, die ebenfalls Cu(II)-Komplexe hoher Stabilität unter milden Bedingungen (Raumtemperatur, physiologischer pH-Wert) bilden [4]. Beide Ligandsysteme gestatten die zusätzliche Funktionalisierung mit Fluoreszenzfarbstoffen sowie die Bindung an geeignete zielsuchende Moleküle zum pharmazeutischen Targeting. Damit können die konzipierten bimodalen Systeme für die nukleare (Positronen-Emissions-Tomographie) und Nah-Infrarot-Fluoreszenz (NIRF)-Bildgebung in der Diagnostik von u.a. Tumoren eingesetzt werden.


References:

[1] G. Singh et al., Nuklearmedizin 2016, 55, 41. [2] K. Viehweger et al., Bioconjugate Chem. 2014, 25, 1011. [3] K. Pant et al., Bioconjugate Chem. 2015, 26, 906. [4] H. Stephan et al., Chem. Eur. J. 2014, 20, 17011.
  • Poster
    GDCh-Wissenschaftsforum Chemie 2017, 10.-14.09.2017, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-25792
Publ.-Id: 25792


Bispidine ligands for the potential application in nuclear medicine

Comba, P.; Pietzsch, J.; Rück, K.; Starke, M.; Stephan, H.; Wadepohl, H.
Objectives
An important part of radiopharmaceuticals containing radiometals is the so-called bifunctional chelator (BFC). Bispidine ligands (3,7-diazabicyclo[3.3.1]nonane) (see Figure 1) developed in the Comba group are perfectly suited BFCs for the application in nuclear medicine. Due to their preorganisation and rigidity of the backbone with the donor atoms N3 and N7 they generally form complexes fastly and with high stability.[1]
Methods
By choosing suitable moieties at position R1 and R2 and by fine tuning of the pyridyl groups at C2 and C4,[2] bispidines can be tailored for the complexation of many different metal ions. Coupling to vector entities is performed at the ester groups at C1/5 or the hydroxyl group at C9.[3-4] One of the applications for bispidine ligands is 64CuII PET imaging (positron emission tomography).[3,5] We design bispidine ligand systems for PET and evaluate their potential in radiolabeling experiments and stability studies.
Results
First in vitro and in vivo studies show the high potential of the bispidine chelators for PET application.[3] The hexadentate ligands N2Py4, N2Py3Pdz and the isomers Hbispa1a/b with pyridyl, pyridazyl or picolinic acid groups at R1 and/or R2 (see Figure 1) are promising BFCs for 64CuII PET imaging.[6-7]
Conclusions
The hexadentate ligands shown in Figure 1 and derivatives are further investigated regarding the application in nuclear medicine.
References
[1] P. Comba, M. Kerscher, W. Schiek, Prog Inorg Chem 2007, 55, 613-704.
[2] P. Comba, S. Hunoldt, M. Morgen, J. Pietzsch, H. Stephan, H. Wadepohl, Inorg Chem 2013, 52, 8131-8143.
[3] S. Juran, M. Walther, H. Stephan, R. Bergmann, J. Steinbach, W. Kraus, F. Emmerling, P. Comba, Bioconjugate Chem 2009, 20, 347-359.
[4] H. Stephan, M. Walther, S. Fahnemann, P. Ceroni, J. K. Molloy, G. Bergamini, F. Heisig, C. E. Muller, W. Kraus, P. Comba, Chem-Eur J 2014, 20, 17011-17018.
[5] A. Roux, A. M. Nonat, J. Brandel, V. Hubscher-Bruder, L. J. Charbonniere, Inorg Chem 2015, 54, 4431-4444.
[6] C. Bleiholder, H. Borzel, P. Comba, R. Ferrari, M. Heydt, M. Kerscher, S. Kuwata, G. Laurenczy, G. A. Lawrance, A. Lienke, B. Martin, M. Merz, B. Nuber, H. Pritzkow, Inorg Chem 2005, 44, 8145-8155.
[7] P. Comba, L. Grimm, C. Orvig, K. Rück, H. Wadepohl, Inorg Chem 2016, manuscript accepted.
  • Poster
    22nd International Symposium on Radiopharmaceutical Sciences, 14.-19.05.2017, Dresden, Germany
  • Open Access Logo Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 60(2017)Suppl 1, S500
    DOI: 10.1002/jlcr.3508

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-25791
Publ.-Id: 25791


Yedoma Ice Complex of the Buor Khaya Peninsula (southern Laptev Sea)

Schirrmeister, L.; Schwamborn, G.; Overduin, P. P.; Strauss, J.; Fuchs, M. C.; Grigoriev, M.; Yakshina, I.; Rethemeyer, J.; Dietze, E.; Wetterich, S.
The composition of perennially frozen deposits holds information on the palaeo-environment during and following deposition. In this study, we investigate late Pleistocene permafrost at the western coast of the Buor Khaya Peninsula in the south-central Laptev Sea (Siberia), namely the prominent eastern Siberian Yedoma Ice Complex (IC). Two Yedoma IC exposures and one drill core were studied for cryolithological (i.e. ice and sediment features), geochemical, and geochronological parameters. Borehole temperatures were measured for 3 years to capture the current thermal state of permafrost. The studied sequences were composed of ice-oversaturated silts and fine-grained sands with considerable amounts of organic matter (0.2 to 24 wt %). Syngenetic ice wedges intersect the frozen deposits. The deposition of the Yedoma IC, as revealed by radiocarbon dates of sedimentary organic matter, took place between 54.1 and 30.1 kyr BP. Continued Yedoma IC deposition until about 14.7 kyr BP is shown by dates from organic matter preserved in ice-wedge ice. For the lowermost and oldest Yedoma IC part, infrared-stimulated luminescence dates on feldspar show deposition ages between 51.1 ± 4.9 and 44.2 ± 3.6 kyr BP. End-member modelling was applied to grain-size-distribution data to determined sedimentation processes during Yedoma IC formation. Three to five robust end-members were detected within Yedoma IC deposits, which we interpret as different modes of primary and reworked unconfined alluvial slope and fan deposition as well as of localized eolian and fluvial sediment, which is overprinted by in situ frost weathering. The cryolithological inventory of the Yedoma IC preserved on the Buor Khaya Peninsula is closely related to the results of other IC studies, for example, to the west on the Bykovsky Peninsula, where formation time (mainly during the late Pleistocene marine isotope stages (MIS) 3 interstadial) and formation conditions were similar. Local freezing conditions on Buor Khaya, however, differed and created solute-enriched (salty) and isotopically light pore water pointing to a small talik layer and thaw-bulb freezing after deposition. Due to intense coastal erosion, the biogeochemical signature of the studied Yedoma IC represents the terrestrial end-member, and is closely related to organic matter currently being deposited in the marine realm of the Laptev Sea shelf.

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-25790
Publ.-Id: 25790


Development of a modular micro reactor for the partial hydrocarbon oxidation

Willms, T.; Kryk, H.; Wiezorek, M.; Hampel, U.
The partial oxidation of hydrocarbons is currently the usual method for the industrial production of a variety of important products. Such processes are frequently characterized by low conversions and yields, which are mostly related to mass and heat transfer problems. Due to the reaction conditions, such processes include also important safety risks and are therefore still not sufficiently investigated. To study the influence of the residence time, oxygen concentration, initiator, additives, temperature and pressure on the product selectivity, a modular micro reactor has been developed and constructed, which permits to perform this class of reactions for the first time as a two phase process in a capillary reactor in an especially wide range of residence times, temperatures and pressures. The production of TBHP by partial oxidation of liquid isobutane is an example for the non-catalyzed oxidation of hydrocarbons with oxygen. Flow rates in the range of 15 µL/ min to 188 µL/ min for isobutane and in the range of 0.1 up to 1.5 mL/ min for oxygen were realized, using capillary lengths of up to 100 m. To characterize the two-phase flow inside the reactor, preliminary measurements of the system isobutane - nitrogen were performed in a glass capillary. Since both, initiators and reaction products are sensitive to most metals, the micro reactor and further parts of the lab facility have been coated. To analyze the reaction mixture, a GC/MS - method has been developed. The challenges of the reactor construction and their solutions are discussed.
Keywords: Micro reactor, process intensification, isobutane, hydrocarbon oxidation, Taylor flow, t-butyl hydroperoxide, multiphase flow.

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-25789
Publ.-Id: 25789


On the thermal decomposition of tert.-butyl hydroperoxide, its sensitivity to metals and its kinetics, studied by thermoanalytic methods.

Willms, T.; Kryk, H.; Oertel, J.; Hempel, C.; Hampel, U.; Knitt, F.
The decomposition of hydroperoxides like tert.-butyl hydroperoxide (TBHP) due to reactions with reactor materials (wall reactions) is an important issue in the frame of industrial processes and the analysis of such compounds. Because of the high surface-volume ratio such heterogeneous reactions are also especially important in case of thermo-analytical measurements. Therefore, the decomposition of TBHP has been studied for the first time extensively by Differential Scanning Calorimetry (DSC) using differently coated high pressure stainless steel crucibles (uncoated, gilded, silicon coated) and a medium pressure crucible. Furthermore, the interaction of such materials with TBHP has been measured for the first time by Thermal Activity Monitoring (TAM). The material of the gilded copper blowout disc turned out to be the reason for the very different DSC curves published in literature and had the highest influence compared to the crucible body material and the pressure. To protect the sample against the blowout disc, an aluminium foil has been placed below the blowout disc. This changed the shape of the DSC curve completely. It became more similar to that obtained with the medium pressure crucible. Furthermore, the reaction mechanism, kinetics and chemical aspects of the decomposition of TBHP at different conditions have been discussed and kinetics has been investigated for the first time by an overall evaluation of the DSC curves and a model free kinetics approach. Using the linear relationship between the kinetic activation parameters the published values are compared to those of the present work.
Keywords: t-butyl hydroperoxide, DSC, steel crucible, silcosteel®, gold, TAM

Downloads:

  • available with HZDR-Login
  • Secondary publication expected

Permalink: https://www.hzdr.de/publications/Publ-25788
Publ.-Id: 25788


The decomposition of tert.-butyl hydroperoxide studied by differential scanning calorimetry.

Willms, T.; Kryk, H.; Hampel, U.
Due to the investigation the oxidation of isobutane to t-butyl hydroperoxide (TBHP), studied for the first time as a two-phase process in a micro reactor at high temperatures and pressures, the prevention of the decomposition of TBHP was crucial. The observed by-products t butyl per-oxide, tert.butanol, acetone, and methanol decreasing the selectivity and thus the TBHP yield are due to the thermal decomposition of TBHP, which is influenced by the wall effect to a large extend. Therefore, the decomposition of TBHP has been studied by Differential Scanning Calorimetry (DSC) at higher temperatures using for the first time different crucible types, pressure conditions, heating rates etc.. Aluminium (low pressure) crucibles, medium pressure crucibles and differently coated high pressure stainless steel crucibles (uncoated, gilded, silicon coated) have been utilized to show the influence of the crucible material as well as of the pressure on the DSC curve. It has been found that the material of the blowout disk has an important influence on the thermal decomposition behaviour. Therefore, within further DSC studies, the sample has been protected against the gilded copper blowout disk by aluminium foil in the crucible. Kinetics of the decomposition reactions has been investigated experimentally by evaluation of the DSC curves using an nth order approach and by a model free kinetics (MFK) approach.
Keywords: differential scanning calorimetry, t-butyl hydroperoxide, crucible type, material
  • Lecture (Conference)
    22. Kalorimetrietage Braunschweig, 07.-09.06.2017, Braunschweig, Deutschland
  • Contribution to proceedings
    22. Kalorimetrietage Braunschweig, 07.-09.06.2017, Braunschweig, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-25787
Publ.-Id: 25787


Oxidation of isobutane to TBHP – a chemical process with high energy saving potential.

Willms, T.; Kryk, D. H.; Hampel, U.
Tertiary butyl hydroperoxide (TBHP), as an intermediate for the production of propylene oxide according to the Oxirane process, is currently produced at industrial scale by the partial oxidation of liquid isobutane using bubble columns or bubble tray reactors. In this process, liquid isobutane reacts with oxygen under two phase conditions at temperatures of 120 to 140 °C and pressures of 25 to 37 bars at high residence times of up to 12 hours. The conversion is limited to 35 to 50 % in order to obtain a TBHP selectivity of 50 to 60 % minimizing the formation of by-products, which are caused by the decomposition of the TBHP due to the complex reaction mechanism. Besides safety aspects, the high reaction enthalpy of the oxidation as well as heat and mass transport problems are further issues of this process. In the frame of the Helmholtz-Energy-Alliance project “Energy efficient chemical multiphase processes“, this reaction is investigated for the first time at supercritical conditions using DTBP as an initiator in a broad range of flow rates, temperatures and pressures in a micro reactor with the aim to enhance the space-time yield of the process. The advantage of micro reactors are the high surface – volume ratio for an efficient heat transfer, the related, improved – nearly inherent – safety and the resulting possibility to investigate unusual process windows, for instance within the explosive region of a reaction mixture using high oxygen concentrations. Besides two phase flow conditions, super¬critical conditions i.e. pressures above 40 bars and temperatures above 140°C are especially interesting because of the higher reaction rate and lacking mass transfer limitations. The reaction has been performed in both regimes at different conditions and the results compared. Furthermore, the influence of process parameters on the start-up time has been investigated. For all experiments, the selectivity and conversion of the reaction have been studied. Therefor, the reaction course is followed by sampling and analyzing the reaction by GC/MS and GC–TCD where analytical methods have been developed to detect a maximum of by-products and inter¬mediates.
Keywords: isobutane, oxidation, energy efficiency, t-butyl hydroperoxide, micro reactor
  • Poster
    Jahrestreffen Frankfurt I Jahrestreffen der ProcessNet-Fachgruppen Hochdruckverfahrenstechnik, Mikroverfahrenstechnik, Molekulare Modellierung, 08.-10.03.2017, Frankfurt, Deutschland
  • Contribution to proceedings
    Jahrestreffen Frankfurt I Jahrestreffen der ProcessNet-Fachgruppen Hochdruckverfahrenstechnik, Mikroverfahrenstechnik, Molekulare Modellierung, 08.-10.03.2017, Frankfurt, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-25786
Publ.-Id: 25786


Micro reactor experiments on the partial isobutane oxidation as a multiphase process - Comparison of t-butyl hydroperoxide and di-t-butyl peroxide as initiators.

Willms, T.; Kryk, H.; Hampel, U.
Tertiary butyl hydroperoxide (TBHP), as an intermediate for the production of propylene oxide according to the Oxirane process, is currently produced at industrial scale by the partial oxidation of liquid isobutane using bubble columns or bubble tray reactors. In this process, liquid isobutane reacts with oxygen at temperatures of 120 to 140 °C and pressures of 25 to 37 bars at high residence times of up to 12 hours. The conversion is limited to 35 to 50 % in order to obtain a TBHP selectivity of 50 to 60 % minimizing the formation of by-products, which are caused by the decom-position of the TBHP due to the complex reaction mechanism. Besides safety aspects, the high reaction enthalpy of the oxidation as well as heat and mass transport problems are further issues of this process. In the frame of the Helmholtz-Energy-Alliance project “Energy efficient chemical multiphase processes“, this reaction has been investigated for the first time as a Taylor-Flow process in a broad range of flow rates, temperatures and pressures in a micro reactor with the aim to enhance the space-time yield of the process. The advantages of micro reactors are the high surface – volume ratio for an efficient heat transfer and the improved, nearly inherent, safety. This permits to investigate yet unexplored process windows, for instance within the explosive region of a reaction mixture.
The reaction has been studied varying the molar ratio of the starting pro¬ducts, temperature, pressure, and initiator concentration using two different initiators, namely TBHP and di-t-butyl peroxide (DTBP). For all experiments the selectivity of the reaction products and the conversion of the reaction have been studied. The reaction course has been followed by sampling and analyzing the reaction by GC/MS where a new analytical method has been developed. The use of TBHP as initiator increases the selectivity of the reaction for the target product TBHP. The beneficial effect on the TBHP selectivity compared to DTBP might be explained on the basis of the suitable thermochemical properties of TBHP. TBHP seems to give a better selectivity since at high temperatures as they are necessary for the initiator effect of DTBP the formation of propanone already becomes important which favours the decomposition of TBHP.
Keywords: isobutane, oxidation, t-butyl hydroperoxide, t-butyl peroxide, micro reactor
  • Poster
    Jahrestreffen Reaktionstechnik 2017, 22.-24.05.2017, Würzburg, Deutschland
  • Contribution to proceedings
    Jahrestreffen Reaktionstechnik 2017, 22.-24.05.2017, Würzburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-25785
Publ.-Id: 25785


TACN Ligands – A journey through radiopharmaceutical applications

Stephan, H.; Graham, B.; Spiccia, L.
The design of tailor-made bifunctional copper radionuclide-complexing agents for nuclear medical application as well as acquisition of reliable information about the biodistribution of different materials represents an intensive and rapidly developing field of research. In this context, the tridentate macrocycle 1,4,7-triazacyclononane (TACN) is of special interest since it forms stable complexes with Cu(II) and the ligand structure can be easily modified. The introduction of further donor groups on the ligand scaffold, such as pyridine units, significantly enhances the thermodynamic stability as well as the kinetic inertness of the Cu(II) complexes formed. TACN ligands containing one or two pendant 2-picolyl arms prefer the formation of square-pyramidal coordination geometry with Cu(II). A hexadentate ligand with two picoline coordination groups as well as a carboxylic functionality, 2-[4,7-bis(2-pyridylmethyl)-1,4,7-triazacyclononan-1-yl]acetic acid (DMPTACN-COOH), enforces a six-coordinate, distorted octahedral structure. DMPTACN-based ligands rapidly chelate copper(II) radionuclides under ambient conditions and the resulting complexes show high in vivo stability. The carboxylic acid group in DMPTACN-COOH allows for the ready introduction of linker groups, such as maleimide or isothiocyanate, thereby facilitating coupling of targeting molecules and bio(nano)materials.

Examples of target-specific peptides and bio(nano)materials equipped with DMPTACN ligands for labeling with 64Cu as an ideal positron emitter are discussed. This enables tumor imaging and the biodistribution of the materials to be studied over a period of days via positron emission tomography (PET).
  • Invited lecture (Conferences)
    6th Asian Conference on Coordination Chemistry, 24.-28.07.2017, Melbourne, Australia

Permalink: https://www.hzdr.de/publications/Publ-25784
Publ.-Id: 25784


MicroTCA.4-based LLRF for the superconducting CW Linac ELBE – Status and Outlook

Kuntzsch, M.; Steinbrück, R.; Schurig, R.; Hierholzer, M.; Killenberg, M.; Schmidt, C.; Gümüs, C.; Butkowski, L.; Hoffmann, M.; Iatrou, C.; Rahm, J.; Rutkowski, I.; Grzegrzółka, M.
The superconducting linear accelerator ELBE is operated in continuous wave operation (CW). The analogue LLRF system, used since 2001, is going to be replaced by a digital solution based on µTCA.4. The new system enables a higher flexibility, better performance and more advanced diagnostics. The contribution will show the performance of the system at ELBE, the hardware and the software structure.
Further it will summarize the last steps to bring it into full user operation and give an outlook to the envisioned beam-based feedback system that will take advantage of the capabilities of the digital LLRF system.
Keywords: ELBE LLRF Feedback MicroTCA µTCA MTCA
  • Poster
    Low Level Radio Frequency Workshop 2017, 16.-19.10.2017, Barcelona, Spain

Permalink: https://www.hzdr.de/publications/Publ-25783
Publ.-Id: 25783


MicroTCA.4-based LLRF for CW operation at ELBE – Status and Outlook

Kuntzsch, M.; Steinbrück, R.; Hierholzer, M.; Killenberg, M.; Schmidt, C.; Butkowski, L.; Hoffmann, M.; Iatrou, C.; Rahm, J.; Rutkowski, I.; Grzegrzółka, M.
The superconducting linear accelerator ELBE is operated in continuous wave operation (CW). The analogue LLRF system, used since 2001, is going to be replaced by a digital solution based on µTCA.4. The new system enables a higher flexibility, better performance and more advanced diagnostics. The contribution will show the performance of the system at ELBE, the hardware and the software structure.
Further it will summarize the last steps to bring it into full user operation and give an outlook to the envisioned beam-based feedback system that will take advantage of the capabilities of the digital LLRF system.
Keywords: ELBE LLRF Feedbacks MicroTCA µTCA MTCA
  • Poster
    International Beam Instrumentation Conference, 20.-24.08.2017, Grand Rapids, USA
  • Open Access Logo Contribution to proceedings
    International Beam Instrumentation Conference, 20.-24.08.2017, Grand Rapids, USA
    MicroTCA.4-based LLRF for CW operation at ELBE – Status and Outlook

Permalink: https://www.hzdr.de/publications/Publ-25782
Publ.-Id: 25782


Optical Synchronization and Electron Bunch Diagnostic at ELBE

Kuntzsch, M.
The talk summarizes the activities at ELBE in the fields of optical synchronization and electron bunch diagnostic.
Keywords: Optical Synchronization Diagnostic ELBE
  • Invited lecture (Conferences)
    Graduiertenkolleg "Accelence", 06.07.2017, Mainz, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-25781
Publ.-Id: 25781


Active tumor pretargeting using peptide nucleic acid bioconjugates as complementary system

Zarschler, K.
The ability of early-stage diagnosis of tumor malignancies and personalized treatment ultimately relies on the availability of highly tumor-affine compounds with purposeful pharmacological profile. In this regard, monoclonal antibodies (mAbs) are particularly valuable as these molecules bind to tumor-associated epitopes with high specificity and affinity. The conventional concept of directly radiolabeled tumor-specific mAbs for radioimmunodetection (RID) and -therapy (RIT) has certainly several drawbacks, most prominently the prolonged radiation exposure of healthy tissues and organs. Fortunately, however, several of these shortcomings can be eliminated by implementing the pretargeting strategy allowing for the rational use of long circulating, high-affinity mAbs for both non-invasive cancer RID and RIT [1].
This keynote lecture will give a general overview about the pre-targeting strategy and present the different approaches for specific radionuclide delivery to pretargeted tissues. Furthermore, the different in vivo recognition systems will be introduced, with particular emphasis on synthetic complementary oligonucleotides such as peptide nucleic acid (PNA) derivatives. Regarding the latter, their synthesis as well as characterization will be described and, finally, an active tumor pretargeting approach using PNA bioconjugates will be exemplified [2].

References
[1] M. Patra, K. Zarschler, H.-J. Pietzsch, H. Stephan and G. Gasser, Chem Soc Rev 45 (2016) 6415-6431.
[2] A. Leonidova, C. Foerster, K. Zarschler, M. Schubert, H.-J. Pietzsch, J. Steinbach, R. Bergmann, N. Metzler-Nolte, H. Stephan, and G. Gasser, Chem Sci 6 (2015) 5601-5616.
  • Invited lecture (Conferences)
    2nd Internacional Caparica Christmas Congress on Translational Chemistry 2017 - IC3TC, 04.-07.12.2017, Caparica, Portugal

Permalink: https://www.hzdr.de/publications/Publ-25780
Publ.-Id: 25780


Diagnostic Tumor Imaging Using Renally Excretable Nanoparticles: Focus on Active and Passive Targeting

Zarschler, K.; Pant, K.; Neuber, C.; Pufe, J.; Steinbach, J.; Haag, R.; Pietzsch, J.; Stephan, H.
Introduction
Depending on their size, shape and surface functionalities, nanoparticles can passively extravasate and accumulate in the tumor tissue through the enhanced permeability and retention (EPR) effect. Being an accumulative process, this effect favors nanoparticles with long blood retention time. Renally excretable, ultrasmall nanoparticles with short blood half-lives are therefore less prone to passive tumor targeting as they rapidly diffuse back to the vasculature and re-enter the systemic circulation, which results in only transient intratumoral presence without substantial retention. To prevent their rapid efflux from malignant tissues by increasing the interactions between nanoparticles and tumor cells as well as by improving cellular nanoparticle uptake, the strategy of active or ligand-mediated targeting is pursued. Here, we describe the development of renally excretable dendritic polyglycerols (dPGs) functionalized with different targeting units to differentiate between active and passive tumor targeting.

Methods
Fluorescent dye labels for optical imaging and small camelid single-domain antibodies (sdAbs) as targeting units - both equipped with maleimide functionalities - were simultaneously attached in a one-pot reaction to thiol groups of the dPGs. As the presented work focusses on the epidermal growth factor receptor (EGFR) acting as a model receptor, an EGFR-specific sdAb was attached to the dPGs to obtain an active targeting probe. In parallel, a probe with similar surface characteristics but a nonspecific sdAb (passive targeting) was synthesized. Both conjugates were purified using affinity chromatography, which selectively separates the sdAb-conjugated dPGs.

Results
In vitro binding studies on different human epithelial cancer cell lines using dye-labeled sdAb-conjugated dPGs showed a high specificity, co-localization and a receptor-mediated cellular uptake of the EGFR-specific probes. Optical imaging studies using murine xenografts revealed a substantial accumulation of the EGFR-specific probes in comparison to its nonspecific counterparts and a minimum off-target accumulation of both conjugates.

Discussion and Conclusion
The direct comparison of specific and nonspecific probes with similar surface characteristics allows the straight-forward preclinical discrimination between active and potential passive tumor targeting of renally excretable nanoparticles in small animal models. Furthermore, it provides important information on the extent to which ligand-mediated targeting contributes to total nanoparticle accumulation in malignant and normal tissues.
  • Lecture (Conference)
    EANM'17 - Annual Congress of the European Association of Nuclear Medicine, 21.-25.10.2017, Wien, Österreich

Permalink: https://www.hzdr.de/publications/Publ-25779
Publ.-Id: 25779


DFO* - An Improved Chelating System for 89Zr-Immuno-PET Applications

Briand, M.; Zarschler, K.; Vugts, D.; Stephan, H.; Steinbach, J.; Gasser, G.; Mindt, T.
Objectives
The potential of 89Zr-labelled antibodies as diagnostic probes for 89Zr-immuno-PET has been demonstrated by a number of clinical trials.[1] The only chelator used thus far in the clinic is the siderophore desferrioxamine (DFO). However, DFO does not satisfy the preferred ocatadentate coordination of zirconium-89, which results in vivo into unspecific uptake of the radiometal in, e.g., the bones. This can interfere with the detection of bone metastases and leads to additional radiation dose to non-targeted tissue.
We have previously reported the development of an extended, octadentate version of DFO, termed DFO*,[2] which provides complexes with [89Zr]Zr4+ of remarkably increased stability in vitro and in vivo. [2, 3] DFO* and derivatives thereof already fulfil a number of prerequisites to become a new standard chelator for zirconium-89; however, its solubility could be improved to facilitate further its application in conjugation chemistry. We here wish to report our efforts in developing novel DFO* derivatives which display an improved water solubility.

Methods
Based on the DFO* scaffold, new derivatives containing pharmacological modifiers to improve the water solubility were synthesized. In addition, different functional groups for bioconjugation chemistry were included. LogP values of the novel bifunctional chelating agents were determined by HPLC. First bioconjugations and radiolabelling experiments with 89Zr were performed according to published procedures. [1,3]

Results
All new derivatives exhibited an increased hydrophilicity and thus, enhanced water solubility in comparison to the original DFO* (as well as DFO) system. Preliminary results on their reactivity in bioconjugations, capability of 89Zr-complexation, and stability of radiometal complexes will be reported.

Conclusions
Structural modifications provided novel derivatives of DFO* with improved water solubility which could facilitate their application in bioconjugation chemistry for the 89Zr-labelling of delicate proteins under aqueous (e.g., organic solvent free) reaction conditions.

Acknowledgements
This work is supported by the Swiss National Sciences Foundation (grant N° 205321–157216).

References
[1] G.A.M.S. Van Dongen, M.C. Huisman, R. Boellaard et al. Q. J. Nucl. Med. Mol. Imaging 2015, 59, 18-38
[2] M. Patra, A. Bauman, C. Mari et al. Chem. Commun. 2014, 50, 11523-11525
[3] D. Vugts, C. Klaver, C. Sewing et al. Eur. J. Nucl. Med. Mol. Im. 2016, doi:10.1007/s00259-016-3499-x S394: Poster 22nd International Symposium on Radiopharmaceutical Sciences
  • Poster
    22nd International Symposium on Radiopharmaceutical Sciences (ISRS 2017), 14.-19.05.2017, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-25778
Publ.-Id: 25778


Kombinierte externe und interne Bestrahlung von Tumoren: präklinischer Nachweis des kurativen Potenzials

Pietzsch, H.-J.; Dietrich, A.; Andreeff, M.; Koi, L.; Schreiner, L.; Bergmann, R.; Löck, S.; Sihver, W.; Faulhaber, D.; Kotzerke, J.; Baumann, M.; Krause, M.; Steinbach, J.
Die Therapie von Tumorerkrankungen gründet sich stadienabhängig auf die drei Säulen Chirurgie, Strahlen- und Chemotherapie. Grundprinzip der Strahlentherapie ist die gezielte Einwirkung von ionisierender Strahlung auf erkranktes Gewebe, um die Zerstörung maligner Tumorzellen zu erreichen. Neben der klassischen externen Strahlentherapie unter Verwendung von Photonen hat sich die Endoradionuklidtherapie durch Entwicklung geeigneter Targetingvektoren in den letzten Jahren zu einer zunehmend angewandten Therapieform entwickelt. Insbesondere die Radioimmuntherapie hat das Potential, auch (Mikro-) Metastasen zu zerstören. Die Kombination von externer und interner Strahlentherapie ist eine vielversprechende Behandlungsstrategie, da sie unter Schonung gesunden Gewebes potenziell die Vorteile beider Modalitäten kombiniert.

Ziel dieses Projektes war es, im Tiermodell zu überprüfen, ob eine interne Bestrahlung mit Hilfe des anti-EGFR-gerichteten, 90Y-markierten Antikörpers Cetuximab (C225) eine lokale Tumorkontrolle nach vorhergehender externer Bestrahlung bei verringerter Dosis ermöglicht.

Cetuximab wurde mit dem bifunktionellen Chelator p-SCN-Bn-CHX-A‘‘-DTPA funktionalisiert und nach 90Y-Markierung in einem Kopf-Hals-Plattenepithelkarzinom-Xenograftmodell (FaDu) eingesetzt. Die externe Bestrahlung erfolgte nach klinisch relevanten Protokollen mit 30 Bestrahlungsfraktionen (fx) verteilt über 6 Wochen. Nach 10 Fraktionen wurden jeweils 2,3 MBq des 90Y-markierten Cetuximab-Konjugats injiziert.
Die kombinierte Anwendung von externer und interner Bestrahlung erhöhte massiv die Wahrscheinlichtkeit einer lokalen Tumorkontrolle im Vergleich zur externen Bestrahlung allein oder in Kombination mit unmarkiertem Cetuximab.
In der Gruppe mit der niedrigsten externen Strahlendosis (1 Gy/Fraktion, Gesamtdosis = 30 Gy,) plus 90Y-Cetuximab wurden alle Tumore noch permanent kontrolliert (Beobachtungszeitraum = 120 d). Im Gegensatz dazu betrug die gesamte externe Strahlendosis, die notwendig ist um 50% der Tumore ohne zusätzliche Gabe von 90Y-Cetuximab zu heilen, 63,9 Gy (58,7, 73,9).

Unsere Ergebnisse zeigen, dass die kombinierte Anwendung von radiomarkierten Therapeutika nach fraktionierter externer Strahlentherapie ein bemerkenswertes Potenzial hat, das Behandlungsergebnis zu verbessern. Eine effiziente Aufnahme des Y-90-markierten Cetuximab-Konjugates ist die Voraussetzung für den Erfolg der kombinierten Strahlentherapie.
  • Lecture (Conference)
    Wissenschaftsforum Chemie, 10.-14.09.2017, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-25777
Publ.-Id: 25777


Recovery of iron and lead from a secondary lead smelter matte by magnetic separation

Kukurugya, F.; Rahfeld, A.; Möckel, R.; Nielsen, P.; Horckmans, L.; Spooren, J.; Broos, K.
A secondary Pb smelter matte containing ca. 50 wt.% Fe (as FeS, Fe3O4, FeO and metallic Fe), shows good potential for being used as a secondary Fe source. However, requirements for Fe ore are: Fe content >60% and absence of sulphide phases. Therefore, further pre-treatment steps are necessary to increase the Fe content in the matte. Dry low intensity, wet low intensity and wet high intensity magnetic separation experiments were performed on different particle size fractions of the matte. Mineral liberation analysis (MLA) was performed to explain different behaviour of Pb in the different size fractions during magnetic separation. Moreover, oxidizing roasting at 600°C was performed to transform FeS to Fe2O3. Results show that by combining low and high intensity magnetic separation and oxidizing roasting, material containing up to 61 wt% Fe (as oxide) can be recovered in the magnetic fraction representing circa 50% of the initial weigth of the sample.
Keywords: matte, MLA, LIMS, WLIMS, WHIMS, recycling

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-25776
Publ.-Id: 25776


Upgrade of the Superconducting CW Linac ELBE From Klystrons zu Silid State Amplifiers

Büttig, H.
Overview on the status of ELBE and the activities to upgrade ELBE within the HSQ project.
Keywords: Solid state RF power amplifiers Resonant ring
  • Invited lecture (Conferences)
    Graduiertenkolleg Seminar Uni Mainz und Uni Darmstadt, 06.07.2017, Mainz, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-25775
Publ.-Id: 25775


Polyethyleneimine Methylphosphonate : towards the design of a new class of macromolecular actinide chelating agent in case of human exposition

Lahrouch, F.; Sofronov, O.; Creff, G.; Rossberg, A.; Hennig, C.; Den Auwer, C.; Di Giorgio, C.
The use of uranium and to a minor extent plutonium as fuel for nuclear energy production or as components in military applications is under increasing public pressure. Uranium is weakly radioactive in its natural isotopy but its chemical toxicity, combined with its large scale industrial utilization, makes it a source of concern in terms of health impact for workers and possibly the general population. Plutonium is an artificial element that exhibits both chemical and radiological toxicities.
So far, uranium (under its form uranyl, U(VI)) or plutonium (as Pu(IV)) decorporation or protecting strategies based on molecular design have been of limited efficiency to remove the actinide once incorporated after human exposure. In all cases, after human exposure, plutonium and uranium are retained in main target organs (liver, kidneys) as well as skeleton although they exhibit differences in their biodistribution. Polymers could represent an alternative strategy as their tropism for specific target organs has been reported. We recently reported a methylcarboxylated polyethyleneimine (PEIMC) as a potential uranium decorporation agent. In this report, we extend our work and report on the ability of methylphosphonated polyethyleneimine (PEI-MP) to act as a new class of uranyl and plutonium chelating agent. As a first step, thorium (Th(IV)) was used as a chemical surrogate of plutonium because of the difficulty of handling the latter in the laboratory. For both cations, U(VI) and Th(IV), the uptake curve of PEI-MP was recorded. The functionalized PEI-MP exhibits a maximum loading capacity comprised of between 0.56 and 0.80 mg of uranium (elemental) and 0.15 - .20 mg of thorium (elemental) per milligram of PEI-MP. Complexation sites of U(VI) and Th(IV) in model conditions close to physiological pH were then characterized with a combination of Fourier transformed Infra Red (FT-IR) and Extended X-Ray Absorption Fine Structure (EXAFS). Although both cations exhibit different coordination modes, similar structural parameters with phosphonate functions were obtained. For example, the coordination sites are composed of fully monodentate phosphonate functions of the polymer chains.
Keywords: Polyethyleneimine Methylphosphonate, macromolecular actinide chelating agent, FT-IR, EXAFS, uranium, thorium

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-25774
Publ.-Id: 25774


Structural characterization of Am(III) and Pu(III)-DOTA complexes

Audras, M.; Berthon, L.; Berthon, C.; Guillaumont, D.; Dumas, T.; Illy, M. C.; Martin, N.; Zilbermann, I.; Ben-Eliyahu, Y.; Moissev, Y.; Bettelheim, A.; Camelli, S.; Hennig, C.; Moisy, P.
The complexation of DOTA ligand (1,4,7,10-tetrazacyclodecane-1,4,7,10-tetraacetic acid) with two trivalent actinides (Am3+ and Pu3+) was investigated by UV-visible spectrophotometry, Nuclear Magnetic Resonance (NMR) spectroscopy and extended X-ray absorption fine structure (EXAFS) in conjunction with computational methods. The complexation process of these two cations is similar to what has been previously observed with lanthanides(III) of similar ionic radius. The complexation takes places in different steps and ends up with the formation of a (1:1) complex [(An(III)DOTA)(H2O)]- where the cation is bonded to the nitrogen atoms of the ring, the four carboxylate arms and a water molecule is completing the coordination sphere. Nevertheless, the formation of An(III)-DOTA complexes is faster than the Ln(III)-DOTA systems of equivalent ionic radius. Furthermore, it is found that An-N distances are slightly shorter than Ln-N distances. Theoretical calculations have shown that the slightly higher affinity of DOTA toward Am over Nd is correlated with slightly enhanced Ligand-to-metal charge donation arising from oxygen and nitrogen atoms.
Keywords: DOTA, UV-visible spectrophotometry, NMR, EXAFS, DFT calculations, Americium, Plutonium, lanthanides

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-25773
Publ.-Id: 25773


Purely Antiferromagnetic Magnetoelectric Random Access Memory

Kosub, T.
Magnetic random access memory schemes employing magnetoelectric coupling to write binary information promise outstanding energy efficiency1. We propose and demonstrate a purely antiferromagnetic magnetoelectric random access memory (AF-MERAM)2 that offers a remarkable 50 fold reduction of the writing threshold compared to state-of-the-art ferromagnet-based counterparts2,3, is robust against magnetic disturbances and exhibits no ferromagnetic hysteresis losses. Using the magnetoelectric antiferromagnet Cr2O3, we demonstrate reliable isothermal switching via gate voltage pulses and all-electric readout at room temperature [Figure 1], The basics of RAM operation - writing, storage and reading information - are demonstrated repeatedly. Furthermore, the all-electric writing and read out interfaces can be harnessed for in-depth studies of the magnetoelectric selection processes in these thin film elements, which turn out to be markedly deviant from the theory of the linear magnetoelectric effect.

While omitting the ferromagnet enables the large improvement in the writing threshold over conventional exchange biased MERAM2,3, it also eliminates all possibilities for conventional magnetoresistive read out, such as the AMR/GMR/TMR effects. Thus, a key aspect of the AF-MERAM functionality is its new all-electric read out of the pure Hall resistance4. This method is both ultra-sensitive to tiny net magnetization in metallic antiferromagnets and to boundary magnetism between nonmagnetic metals and magnetic insulators, suggesting its considerable applicability to the growing fields of antiferromagnetic spintronics and insulator spintronics.

Access to the pure Hall resistance is enabled by a new electric measurement scheme called Resistance Tensormetry, which determines electrical resistance not as a scalar quantity peculiar to the used measurement layout but instead as a tensor quantity including diagonal and off-diagonal (Hall) components. Since electrical resistance is one of the most crucial material properties for both science and technology, the more comprehensive view provided by resistance tensormetry is highly relevant for emergent topics and materials. Via µΩ level sensitivity and tensor resolution, previously unattainable figures are now open to experimental scrutiny.

1. Matsukura, F., Tokura, Y. & Ohno, H., Nat. Nano. 10, 209–220 (2015).
2. Kosub, T. et al., Nat. Commun. 7, 13985 (2017).
3. He, X. et al., Nat. Mater. 9, 579–585 (2010).
4. Kosub, T., Kopte, M., Radu, F., Schmidt, O. G. & Makarov, D., Phys. Rev. Lett. 115, 097201 (2015).
  • Invited lecture (Conferences)
    Spin X Seminar Mainz/Kaiserslautern, 08.06.2017, Mainz, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-25772
Publ.-Id: 25772


Biasing in MC transport calculations

Müller, S. E.ORC
The method of biasing in radiation transport simulations is described.
Keywords: Radiation transport, variance reduction, biasing, simulation
  • Lecture (others)
    Mu2e software and simulations workshop, 21.06.2017, Batavia, USA

Permalink: https://www.hzdr.de/publications/Publ-25771
Publ.-Id: 25771


The use of FLUKA in the Mu2e experiment

Müller, S. E.ORC
The use of FLUKA in the mu2e experiment
Keywords: FLUKA, mu2e
  • Lecture (others)
    Mu2e Sotware and Simulation Meeting, 07.06.2017, Batavia, USA

Permalink: https://www.hzdr.de/publications/Publ-25770
Publ.-Id: 25770


LaFeOxNy perovskite thin films: Nitrogen location and its effect on morphological, optical and structural properties

Haye, E.; Bruyère, S.; André, E.; Boulet, P.; Barrat, S.; Capon, F.; Miska, P.; Migot, S.; Carteret, C.; Coustel, R.; Gendarme, C.; Munnik, F.
This paper reports on the first study of chemical, optical, and structural properties of lanthanum ferrite oxynitride thin films deposited by reactive magnetron sputtering. Thin films were deposited in a Ar/O2/N2 mixture as reactive plasma, from two elemental La and Fe targets, at room and high temperature (25 and 800°C). Films deposited at room temperature are amorphous and have been flash annealed to crystallize the perovskite. Oxynitride properties were investigated and compared to oxide films deposited in Ar/O2 gas mixture. All oxide and oxynitride films present an orthorhombic structure. However, nitrogen doping limited to 1-1.5% leads to lattice expansion (4%), bandgap narrowing, a lower electrical resistivity in range [25-350°C] , and modification of Infrared and Raman spectra. Electron Energy Loss Spectroscopy measurements clearly show the presence of two nitrogen sites with an “active” intra-granular nitrogen associated to an enhancement of the physical properties.
Keywords: Oxynitride perovskite, Thin film, LaFeO3, Nitrogen doping

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-25769
Publ.-Id: 25769


Preliminary combination of the KLOE08, KLOE10 KLOE12 ISR measurements

Keshavarzi, A.; Müller, S. E.ORC; Teubner, T.; Venanzoni, G.
Preliminary combination of the KLOE08, KLOE10 KLOE12 ISR measurements
Keywords: KLOE, g-2, hadronic contribution
  • Invited lecture (Conferences)
    First Workshop of the muon g-2 Theory Initiative, 04.06.2017, St. Charles, USA

Permalink: https://www.hzdr.de/publications/Publ-25768
Publ.-Id: 25768


Irradiation study of UV Silicon Photomultipliers for the Mu2e calorimeter

Baccaro, S.; Cemmi, A.; Cordelli, M.; Diociaiuti, E.; Donghia, R.; Ferrari, A.; Giovannella, S.; Loreti, S.; Miscetti, S.; Müller, S.; Pillon, M.; Sarra, I.
The Mu2e calorimeter is composed of 1400 un-doped CsI crystals, coupled to large area UV extended Silicon Photomultipliers (SiPMs), arranged in two annular disks. This calorimeter has to provide precise information on energy, timing and position resolutions. It should also be fast enough to handle the high rate background and it must operate and survive in the high radiation environment. Simulation studies estimated that, in the highest irradiated regions, each photo-sensor will absorb a dose of 20 krad and will be exposed to a neutron fluency of 5.5E11 n(1MeV)/cm2 in three years of running, with a safety factor of 3 included. At the end of 2015, we have concluded an irradiation campaign at the Frascati Neutron Generator (FNG, Frascati, Italy) measuring the response of two different 16 array models from Hamamatsu, which differ for the protection windows and a SiPM from FBK. In 2016, we have carried out two additional irradiation campaigns with neutrons and photons at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR, Dresden, Germany) and at the Calliope gamma irradiation facility at ENEA-Casaccia, respectively. A negligible increment of the leakage current and no gain change have been observed with the dose irradiation. On the other hand, at the end of the neutron irradiation, the gain does not show large changes whilst the leakage current increases by around a factor of 2000. In these conditions, the too high leakage current makes problematic to bias the SiPMs, thus requiring to cool them down to a running temperature of ~0 C.
Keywords: Calorimeters; Photon detectors for UV, visible and IR photons (solid-state), PIN diodes, APDs, Si-PMTs, G-APDs, CCDs, EBCCDs, EMCCDs
  • Lecture (Conference)
    14th Topical Seminar on Innovative Particle and Radiation Detectors, 03.-06.10.2016, Siena, Italy
  • Open Access Logo Contribution to proceedings
    14th Topical Seminar on Innovative Particle and Radiation Detectors (IPRD16), 03.-06.10.2016, Siena, Italy
    Irradiation study of UV Silicon Photomultipliers for the Mu2e calorimeter: Journal of Instrumentation 12 (2017), IOP Pub.
    DOI: 10.1088/1748-0221/12/02/C02022

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-25767
Publ.-Id: 25767


Measurement techniques for liquid metals

Ratajczak, M.; Hernández, D.; Richter, T.; Otte, D.; Buchenau, D.; Krauter, N.; Wondrak, T.
The measurement of flow properties of liquid metals, such as flow rate, flow structure and gas distribution, is a challenging task due to the opaqueness, the high temperatures (e. g. 1500 ◦ C for liquid steel or liquid silicon) and the corrosiveness of those fluids. In this paper a short review about the recent developments of measurement techniques in the framework of the Helmholtz Alliance Liquid Metal Technologies (LIMTECH) is presented which focuses on the development of contactless inductive measurement techniques exploiting the high electrical conductivity of those melts. These measurement techniques include the contactless inductive flow tomography (CIFT), which is able to reconstruct the mean three-dimensional velocity structure in liquid melts, local Lorentz force velocimetry (local LFV), which enables the local assessment of flows close to the wall, and inductive methods for bubble detection, which are based on mutual inductance tomography (MIT). Additionally, a short overview of contactless inductive flow rate measurement techniques is given. Furthermore, an ultrasound technique called ultrasound transit-time technique (UTTT) will be presented which enables the measurement of position and size of bubbles in large vessels.

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-25766
Publ.-Id: 25766


Energy Transfer Kinetics in Photosynthesis as an Inspiration for Improving Organic Solar Cells

Nganou, C.; Lackner, G.; Teschome, B.; Deen, M. J.; Adir, N.; Pouhe, D.; Lupascu, D. C.; Mkandawire, M.
Clues to designing highly efficient organic solar cells may lie in understanding the architecture of light-harvesting systems and exciton energy transfer (EET) processes in very efficient photosynthetic organisms. Here, we compare the kinetics of excitation energy tunnelling from the intact phycobilisome (PBS) light-harvesting antenna system to the reaction center in photosystem II in intact cells of the cyanobacterium Acaryochloris marina with the charge transfer after conversion of photons into photocurrent in vertically aligned carbon nanotube (va-CNT) organic solar cells with poly(3-hexyl)thiophene (P3HT) as the pigment. We find that the kinetics in electron hole creation following excitation at 600 nm in both PBS and va-CNT solar cells to be 450 and 500 fs, respectively. The EET process has a 3 and 14 ps pathway in the PBS, while in va-CNT solar cell devices, the charge trapping in the CNT takes 11 and 258 ps. We show that the main hindrance to efficiency of va-CNT organic solar cells is the slow migration of the charges after exciton formation.
Keywords: Acaryochloris marina carbon nanotubes chromophore exciton photosynthesis photovoltaic polarons solar energy conversion

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-25765
Publ.-Id: 25765


First application of the Oslo method in inverse kinematics - Nuclear level densities and gamma-ray strength functions of 87Kr

Ingeberg, V. W.; Siem, S.; Wiedeking, M.; Sieja, K.; Zeiser, F.; Bleuel, D. L.; Brits, C. P.; Bucher, D. T.; Dinoko, T. S.; Easton, J. L.; Görgen, A.; Jones, P.; Kheswa, B. V.; Khumalo, N. A.; Larsen, A. C.; Lawrie, E. A.; Lawrie, J. J.; Majola, S. N. T.; Malatji, K. L.; Makhathini, L.; Maqabuka, B.; Negi, D.; Noncolela, S. P.; Papka, P.; Sahin, E.; Schwengner, R.ORC; Tveten, G. M.; Zikhali, B. R.
A novel technique for extracting the gamma-ray strength function (SF) and nuclear level density (NLD) from inverse kinematics experiments is presented, which allows for measurements of these properties, across a vast range of previously inaccessible nuclei. Proton-gamma coincidence events from the d(86Kr, p)87Kr reaction were measured at iThemba LABS and the SF and NLD in 87 Kr obtained with the Oslo Method.The SF and NLD are important parameters in Hauser-Feshbach calculations to constrain (n,gamma) cross sections of nuclei for which these cannot be measured directly. The extracted SF and NLD are used as input in Hauser-Feshbach calculations to constrain the 86Kr(n,gamma)87Kr cross section which is important for the 87Rb production in the s-process. The nature of the low-energy region of the SF is explored through comparison to shell model calculations with the LNPS-SDG interaction.
Keywords: Nuclear structure, nuclear reactions, (d,p) recation, inverse kinematics, gamma-ray strength function, level density, shell model, Hauser-Feshbach model, s-process.

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-25764
Publ.-Id: 25764


Single bubble rise in GaInSn in a horizontal magnetic field

Richter, T.; Keplinger, O.; Shevchenko, N.; Wondrak, T.; Eckert, K.; Eckert, S.; Odenbach, S.
The rise of single gas bubbles of moderate size in a liquid metal was studied in a flat container filled with the eutectic alloy GaInSn. The bubble motion is affected by a homogeneous horizontal magnetic field which is perpendicular to the width side of the fluid container. Measurements of the bubble trajectory, bubble velocity and deformation were performed by means of a combination of ultrasound transit time technique and X-ray radiography. In the hydrodynamic case without a magnetic field, the bubbles show the typical zig-zag movement whose attenuation can be observed for sufficiently high magnetic fields of B > 270 mT. The bubble trajectory becomes straight at a field strength of about 500 mT. A damping of the zig-zag path does not result in case of small magnetic fields applied. In this parameter range, even an increase of the amplitude of the lateral path oscillation is observed. Furthermore, this study revealed a discontinuity in the bubble path, which is called as ”initial path instability” on the basis of its occurrence in the early stage of the bubble rise shortly after the bubble injection. This instability is characterized by an extreme inclination of the ellipsoidal bubble which often leads to a bubble “somersault”. This instability is suppressed by a suffciently high enough magnetic field. The reason for this instability and the magnetic field effect thereon are qualitatively discussed.

Downloads:

  • available with HZDR-Login
  • Secondary publication expected

Permalink: https://www.hzdr.de/publications/Publ-25763
Publ.-Id: 25763


A Review of Surfactant Role in Soil Clogging Processes at Wastewater Exfiltration Locations in Sewers

Nikpay, M.; Krebs, P.; Ellis, B.
Wastewater contains significant sources of pollutants and contaminants. often the failure of a pipe, inadequate sealing or corrupt pipe-connections cause the loss of raw sewage, which percolates into the nearby soil. As a consequence, a colmation layer in conjunction with soil clogging is developing, which regulates the exfiltration rate. Recently, literature has emerged that offers findings about the effects of wastewater surfactants on the change of physical properties of the soil. A survey of published literature in this field provides information highlighting the influential mechanisms of surfactants in soil clogging through physical, chemical and biological processes. Therefore, to provide a comprehensive approach, this review describes the adsorption mechanisms of surfactants on organic and inorganic particles, at gas-bubbles and at biomass.
We also provided our own input to the description of the adsorption of surfactants at fluid/fluid and fluid/solid interfaces in porous media associated with the clogging process.

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-25762
Publ.-Id: 25762


Liquid metal based magnetic cooling: velocity measurements

Lei, Z.; Raebiger, D.; Eckert, S.; Eckert, K.ORC
Heat transfer enhancement in a segment of the active magnetic regenerator (AMR), consisting of a magnetocaloric material (Gadolinium) and a heat transfer fluid in between, which is periodically magnetized and demagnetized, is investigated in this work. After giving a brief account on how magnetohydrodynamic (MHD) convection can be used to enhance the heat transfer from flat plate gadolinium toward the heat transfer fluid we apply two different techniques for MHD flow generation. In the first approach, an electric current I was injected into an electrically conducting, aqueous heat transfer fluid (NaOH). A heat transfer enhancement of about 40% (I=3mA) was found by means of a Mach-Zehnder interferometer. In the second approach, a liquid metal (GaInSn) was used which is potentially an interesting candidate for a heat transfer fluid in an AMR operating with high cycling frequency. Velocity measurements by means of ultrasound doppler velocimetry with a quasi uniform static magnetic field (220mT) in the gadolinium channel are presented.
  • Open Access Logo Magnetohydrodynamics 53(2017)2, 403-410

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-25761
Publ.-Id: 25761


Ultrasonic measurements of the bulk flow field in foams

Nauber, R.; Büttner, L.; Eckert, K.ORC; Fröhlich, J.; Czarske, J.; Heitkam, S.ORC
The flow field of moving foams is relevant for basic research and for the optimization of industrial processes such as froth flotation. However, no adequate measurement technique exists for the local velocity distribution inside the foam bulk. We have investigated the ultrasound Doppler velocimetry (UDV), providing the first two-dimensional, non-invasive velocity measurement technique with an adequate spatial (10 mm) and temporal resolution (2.5 Hz) that is applicable to medium scale foam flows. The measurement object is dry aqueous foam flowing upward in a rectangular channel. An array of ultrasound transducers is mounted within the channel, sending pulses along the main flow axis and receiving echoes from the foam bulk. This results in a temporally and spatially resolved, planar velocity field up to a measurement depth of 200 mm, which is approximately one order of magnitude larger than those of optical techniques. A comparison with optical reference measurements of the surface velocity of the foam allows to validate the UDV results. At 2.5 Hz frame rate an uncertainty below 15 percent and an axial spatial resolution better than 10 mm is found. Therefore, UDV is a suitable tool for monitoring of industrial processes as well as the scientific investigation of three-dimensional foam flows on medium scales.

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-25760
Publ.-Id: 25760


Demonstration of a beam loaded nanocoulomb-class laser wakefield accelerator

Couperus, J. P.ORC; Pausch, R.; Köhler, A.; Zarini, O.; Krämer, J. M.; Garten, M.; Huebl, A.; Gebhardt, R.; Helbig, U.; Bock, S.; Zeil, K.; Debus, A.; Bussmann, M.; Schramm, U.; Irman, A.
Laser-plasma wakefield accelerators have seen tremendous progress, now capable of producing quasi-monoenergetic electron beams in the GeV energy range with few-femtoseconds bunch duration. Scaling these accelerators to the nanocoulomb range would yield hundreds of kiloamperes peak-current and stimulate the next generation of radiation sources covering high-field THz, high-brightness X-ray and γ-ray sources, compact FELs and laboratory-size beam-driven plasma accelerators. However, accelerators generating such currents operate in the beam loading regime where the accelerating field is strongly modified by the self-fields of the injected bunch, potentially deteriorating key beam parameters.
Here we demonstrate that, if appropriately controlled, the beam loading effect can be employed to improve the accelerator's performance. Self-truncated ionization injection enabled loading of unprecedented charges of about 0.5 nC within a mono-energetic peak. As the energy balance is reached, we show that the accelerator operates at the theoretically predicted optimal loading condition and the final energy spread is minimized.
Keywords: LWFA beam loading

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-25759
Publ.-Id: 25759


Multidisciplinary characterization of U(VI) sequestration by Acidovorax facilis for bioremediation purposes

Krawczyk-Bärsch, E.; Gerber, U.; Müller, K.; Moll, H.; Rossberg, A.; Steudtner, R.; Merroun, M.
The contamination of the environment by U may affect plant life and consequently may have an impact on animal and human health. The present work describesU(VI) sequestration by Acidovorax facilis using a multidisciplinary approach combining wet chemistry, transmission electron microscopy, and spectroscopy methods (e.g.cryo-time resolved laser-induced fluorescence spectroscopy, extended X-ray absorption fine structure spectroscopy, and in-situ attenuated total reflection Fourier transform infrared spectroscopy). This bacterial strain is widely distributed in nature including U-contaminated sites. In kinetic batch experiments cells of A. facilis were contacted for 5 minutes to 48 hours with 0.1 mM U(VI). The results show that the local coordination of U species associated with the cells depends upon time contact. U is bound mainly to phosphate groups of lipopolysaccharide (LPS) at the outer membrane within the first hour. And, that both, phosphoryl and carboxyl functionality groups of LPS and peptidoglycan of A. facilis cells may effectuate the removal of high U amounts from solution at 24-48 hours of incubation. It is clearly demonstrated that A. facilis may play an important role in predicting the transport behaviour of U in the environment and that the results will contribute to the improvement of bioremediation methods of U-contaminated sites.
Keywords: Uranium, Acidovorax facilis, spectroscopy, bioremediation

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-25758
Publ.-Id: 25758


Development and validation of a gene signature for patients with head and neck carcinomas treated by postoperative radio(chemo)therapy

Schmidt, S.; Linge, A.; Zwanenburg, A.; Leger, S.; Lohaus, F.; Krenn, C.; Appold, S.; Gudziol, V.; Nowak, A.; von Neubeck, C.; Tinhofer, I.; Budach, V.; Sak, A.; Stuschke, M.; Balermpas, P.; Rödel, C.; Bunea, H.; Grosu, A.-L.; Abdollahi, A.; Debus, J.; Ganswindt, U.; Belka, C.; Pigorsch, S.; Combs, S. E.; Mönnich, D.; Zips, D.; Baretton, G. B.; Buchholz, F.; Baumann, M.; Krause, M.; Löck, S.
The aim of this study was to identify and independently validate a novel gene signature predicting loco-regional tumor control (LRC) for treatment individualization of patients with locally advanced head and neck squamous cell carcinomas (HNSCC) who are treated with postoperative radio(chemo)therapy (PORT-C). Gene expression analyses were performed using nanoString technology on a multicenter training cohort of 195 patients and an independent validation cohort of 142 patients. The analyzed gene set was composed hypothesis-driven and included genes with previously reported association to radio(chemo)sensitivity or resistance to radio(chemo)therapy. Gene selection and model building were performed within a specifically developed statistical framework comparing several machine-learning algorithms. This procedure identified a 7-gene signature for HPV16 DNA negative tumors consisting of the genes: SERPINE1, INHBA, P4HA2, ACTN1, HILPDA, CD24 and TCF3. The 7-gene signature was used to fit a multivariable Cox model to the training data (concordance index, ci=0.84), which was successfully validated (ci=0.71). Thus, the signature showed improved performance compared to a clinical model (ci=0.66) and to a previously published model including hypoxia-associated genes and cancer stem cell markers (ci=0.65). Furthermore, the signature was used to stratify patients into groups with low and high risk of recurrence. Significant differences in LRC between these groups were found in training and validation (p<0.001). A prospective validation is planned in an ongoing prospective clinical trial of the DKTK-ROG before potential application in clinical trials for patient stratification.
Keywords: Radiochemotherapy, HNSCC, Biomarker, Loco-regional control, Gene signature, HPV status

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-25757
Publ.-Id: 25757


Laser spectroscopy measurement of the 2s-hyperfinesplitting in lithium-like bismuth

Sánchez, R.; Lochmann, M.; Jöhren, R.; Andelkovic, Z.; Anielski, D.; Botermann, B.; Bussmann, M.; Dax, A.; Frömmgen, N.; Geppert, C.; Hammen, M.; Hannen, V.; Kuehl, T.; Litvinov, Y.; Coto, R. L.; Stoehlker, T.; Thompson, R.; Vollbrecht, J.; Wen, W.; Weinheimer, C.; Will, E.; Winters, D.; Noertershaeuser, W.
We have recently reported on the first direct measurement of the 2s hyperfine transition in lithium-like bismuth (209Bi80+) at the GSI Helmholtz Centrefor Heavy Ion Research (GmbH) in Darmstadt, Germany. Combined with a newmeasurement of the 1s hyperfine splitting in hydrogen-like (209Bi82+) the so-called specific difference Δ’E = -61.37(36) meV could be determined and was found to bein good agreement with its prediction from strong-field bound-state QED. Here wereport on additional investigations performed to estimate systematic uncertainties of these results and on details of the experimental setup. We show that the dominating uncertainty arises from insufficient knowledge of the ion beam velocity which is determined by the electron-cooler (voltage). Two routes to obtain a cooler-voltage calibration are discussed and it is shown that agreement can be reached either of the experimental Δ’E with the theoretical result, or between the two measurements of the hyperfine splitting in hydrogen-like bismuth, but not both at the same time.
Keywords: qed, spectroscopy, bismuth, hyperfine, lithium-like, storage ring, laser

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-25756
Publ.-Id: 25756


Structure and energetics of Y-Ti-O nanoclusters in bcc Fe

Vallinayagam, M.; Posselt, M.; Faßbender, J.ORC
Nanostructured Ferritic Alloys (NFA) are considered as promising candidates for the structural materials of future fusion and fission reactors [1]. They consist of a ferritic or ferritic/martensitic Fe-Cr matrix with a high dispersion of nanometer size yttria-based oxide particles. In this research project (started in November 2016) the nature of nanometer-size yttria-based oxide clusters in a bcc Fe matrix are investigated by DFT calculations. The main goal of these studies is the better understanding of the nucleation as well as the structure and composition of the nanoclusters.
The investigations shall clarify the conditions for the formation of nonstoichiometric clusters that are coherent with the bcc lattice and for the formation of oxide phases (in particular Y2O3 and Y2Ti2O7). Three models are considered: (i) clusters consisting of Y, Ti atoms on bcc lattice sites and O on octahedral site [2-4], termed as On-Lattice (OL) model, (ii) cluster consisting of parts of the bixbyite (Y2O3) or pyrochlore (Y2Ti2O7) structure embedded in bcc Fe [5] termed as Structure Matching (SM) model, and (iii) substituting O also on Fe site, termed as OFe model. In all cases vacancies are introduced into the simulation cell in order to provide additional volume for O atoms. We studied clusters of different sizes in the framework of the three models. Our results show that all three models lead to almost the same energy for considered cluster configurations. This revises the statement of Barnard et al. [5] who claimed that clusters with SM configuration are generally favored energetically.
[1] G. R. Odette, JOM-J. Min. Met. Mat. S. 66, 2427 (2014)
[2] D. Murali, B.K. Panigrahi, M.C. Valsakumar, S. Chandra, C.S. Sundar, B. Raj, J. Nucl. Mater. 403,
113 (2010)
[3] A. Claisse, P. Olsson, Nucl. Instr. Meth. B 303, 18 (2013)
[4] M. Posselt, D. Murali, B. K. Panigrahi, Model. Simul. Mater. Sc. 22, 085003 (2014)
[5] L. Barnard, G. R. Odette, I. Szlufarska, D. Morgan. Acta Mater. 60 (2012) 935 (2012)
Keywords: DFT, Y-Ti-O nanoclusters in bcc-Fe, structure and energetics
  • Lecture (Conference)
    4th International Workshop on ODS materials, 26.-28.06.2017, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-25755
Publ.-Id: 25755


Influence of foreign atoms on the diffusion of oxygen in bcc Fe

Wang, X.; Posselt, M.; Faßbender, J.ORC
Iron-based ferritic alloys are widely used in industrial applications. They contain varying concentrations of foreign atoms or solutes, most of which are purposely included in order to improve the mechanical properties, the corrosion and radiation resistance as well as the high-temperature stability. The diffusion of the solutes plays a crucial role in determining all these properties during fabrication and processing, and also influences the behavior of the materials in the various applications. In many cases the diffusion proceeds via bcc lattice sites by means of intrinsic point defects, i.e. vacancies and self-interstitial atoms, and in some cases via interstitial sites. Solute diffusion determines the micro- and nanostructure obtained after heat treatments, and the detailed knowledge of the atomistic diffusion mechanisms is necessary to obtain the desired properties. Moreover, micro- and nanostructure evolution under irradiation is controlled by atomic diffusion.
In this research project (started in September 2016) the diffusion of foreign atoms in bcc Fe shall be investigated by first-principle methods and kinetic Monte Carlo simulations. The focus of the present work is on the diffusion of oxygen under the influence of other foreign atoms such as Al, Cr, Ti, and Y. Oxygen plays an important role in the formation and evolution of a high dispersion of nanometer-size particles containing Y, Ti, and O in ODS steels which are considered as promising candidates for structural materials of future fusion and fission reactors [1]. The presence of foreign atoms and intrinsic point defects modifies the original migration path of oxygen [2-4]. Using DFT calculations the binding energy between oxygen and a foreign atom for different neighbor distances and the modified migration barriers, i.e. for the O jump between the first and the second neighbor of a foreign atom, etc are calculated.
[1] G. R. Odette, JOM-J. Min. Met. Mat. S. 66, 2427 (2014)
[2] S.L. Shang, H.Z. Fang, J. Wang, C.P. Guo, Y. Wang, P.D. Jablonski, Y. Du, Z.K. Liu, Corrosion
Sci. 83, 94 (2014)
[3] P. Liu, W. Xing, X. Cheng, D. Li, Y. Li, X.-Q. Chen, Phys. Rev. B 90, 024103 (2014)
[4] C. Barouh, T. Schuler, C.-C. Fu, T. Jourdan, Phys. Rev. B 92, 104102 (2015)
Keywords: DFT, diffusion of oxygen in bcc-Fe
  • Lecture (Conference)
    4th International Workshop on ODS materials, 26.-28.06.2017, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-25754
Publ.-Id: 25754


Simulations of a precession driven flow in a cylindrical cavity

Giesecke, A.; Vogt, T.; Gundrum, T.; Stefani, F.; Herault, J.
The project DRESDYN (DREsden Sodium facility for DYNamo and thermohydraulic studies) conducted at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) provides a new platform for a variety of liquid sodium experiments devoted to problems of geo- and astrophysical magnetohydrodynamics [1]. The most ambitious experiment will be a dynamo experiment which consists of a large precessing cylindrical cavity filled with liquid sodium. The experiment is motivated by the idea of a precession-driven flow as a complementary energy source for the geodynamo [2] or the ancient lunar dynamo [3].

Our presentation addresses corresponding hydrodynamic simulations that provide characteristic properties of the precession-driven flow such as amplitudes or helicity and their implications for the dynamo effect. Our results show that the primary response of the fluid to the precession is an azimuthally rotating inertial wave, called Kelvin mode [4]. Increasing the precession ratio the fundamental Kelvin mode becomes unstable which goes along with the emergence of two free inertial waves due to a parametric resonance caused by the periodic perturbation of the primary flow [5]. The free inertial waves only exist within a narrow range of rather small precession ratios because increasing non-linear interactions give rise to the formation of an azimuthal circulation flow which alters the resonance condition (detuning effect) [6].

For large precession ratios, instead, we find a clear signature of Kelvin modes with the frequency of the forcing and higher azimuthal and/or axial wave numbers. In the turntable frame these Kelvin modes correspond to standing inertial waves that are caused by non-linear self-interaction of the fundamental forced mode. The contributions of these modes provide a breaking of the parity with respect to the equatorial plane which has proven to be beneficial for dynamo action [7].

Further considerations on the dynamo-ability of the precession driven flow require larger Reynolds numbers which are numerically no longer accessible. Therefore, they have to be based solely on data from the downscaled water experiment that currently is running at HZDR in preparation for the large liquid sodium facility (see contribution of T. Vogt). Comparisons of our simulations with experimental data from Ultrasonic Doppler Velocimetry (UDV) measurements at similar Reynolds number show a surprisingly good consistency thus providing a basis for the development of flow models at larger Reynolds numbers for future kinematic dynamo models.

[1] Stefani, F. et al., Magnetohydrodynamics, 48 (1), 103--114, 2012.
[2] Malkus, W. V. R., Science, 160, 259--264, 1968.
[3] Noir, J., and D. C{\'e}bron, J. Fluids Mech., 737, 412--439, 2013.
[4] Thomson W, Phil. Mag. J. Sci. 10 (61), 155--168, 1880.
[5] Kerswell, R. R., J. Fluids Mech., 382, 283--306, 1999.
[6] Herault, J. et al., Phys. Rev. Fluids, in preparation, 2017.
[7] Tilgner, A., Phys. Fluids, 17 (3), 034, 104, 2005.
Keywords: Dynamo DRESDYN precession
  • Lecture (Conference)
    Natural Dynamos, 26.-30.06.2017, Valtice, Tschechien

Permalink: https://www.hzdr.de/publications/Publ-25753
Publ.-Id: 25753


Structural elucidation of U(VI)-isosaccharinic acid complexes under acidic conditions: spectroscopic and theoretical investigations

Brinkmann, H.; Moll, H.; Patzschke, M.; Rossberg, A.; Stumpf, T.
The alkaline degradation of cellulosic material present in low and intermediate level waste leads to the formation of water soluble organic compounds. α-Isosaccharinic acid (ISA) as main degradation product can act as complexing agent for radionuclides. This may affect the mobility as well as the sorption behavior adversely. Studies regarding to the interaction of ISA with U(VI) are scarce. Hence, the aim of this study is to describe the U(VI)-ISA complexes formed under acidic conditions on a molecular level. Since U(VI) can coordinate to different binding sites of the polyhydroxy carboxylic acid, the number of possible complexes is large. To elucidate the number and structure of those U(VI)-ISA species, different spectroscopic methods were applied to obtain information from the metal and from the ligand.
UV-vis measurements lead to the conclusion that three complexes are formed and that both, the carboxylic as well as hydroxylic groups, are involved. Attenuated total reflection-Fourier-transformation-infrared spectroscopy (ATR-FTIR) and extended X-ray absorption fine structure-spectroscopy (EXAFS) offer structural information of the formed complexes. DFT-calculations provide data of optimized structures (e.g. figure below: [UO2(ISA)2(H2O)2]), which were used to underpin experimental results in order to identify the formed U(VI)-ISA species.
These results are the basis for further investigations under neutral and alkaline conditions. Moreover, this study helps to elucidate the U(VI) speciation in long term tissue degradation experiments in the presence of microorganisms.
Keywords: Uranium, Isosaccharinic acid, UV-vis, IR, DFT, EXAFS
  • Lecture (Conference)
    Goldschmidt 2017, 13.-18.08.2017, Paris, Frankreich

Permalink: https://www.hzdr.de/publications/Publ-25752
Publ.-Id: 25752


Σ0-production in proton nucleus collisions near threshold

Adamczewski-Musch, J.; Agakishiev, G.; Arnold, O.; Atomssa, E. T.; Behnke, C.; Berger-Chen, J. C.; Biernat, J.; Blanco, A.; Blume, C.; Böhmer, M.; Bordalo, P.; Chernenko, S.; Deveaux, C.; Dybczak, A.; Epple, E.; Fabbietti, L.; Fateev, O.; Fonte, P.; Franco, C.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzon, J. A.; Gill, K.; Golubeva, M.; Guber, F.; Gumberidze, M.; Harabasz, S.; Hennino, T.; Hlavac, S.; Höhne, C.; Holzmann, R.; Ierusalimov, A.; Ivashkin, A.; Jurkovic, M.; Kämpfer, B.; Karavicheva, T.; Kardan, B.; Koenig, I.; Koenig, W.; Kolb, B. W.; Korcyl, G.; Kornakov, G.; Kotte, R.; Krasa, A.; Krebs, E.; Kuc, H.; Kugler, A.; Kunz, T.; Kurepin, A.; Kurilkin, A.; Kurilkin, P.; Ladygin, V.; Lalik, R.; Lapidus, K.; Lebedev, A.; Lopes, L.; Lorenz, M.; Mahmoud, T.; Maier, L.; Maurus, S.; Mangiarotti, A.; Markert, J.; Metag, V.; Michel, J.; Müntz, C.; Münzer, R.; Naumann, L.; Palka, M.; Parpottas, Y.; Pechenov, V.; Pechenova, O.; Petousis, V.; Pietraszko, J.; Przygoda, W.; Ramstein, B.; Rehnisch, L.; Reshetin, A.; Rost, A.; Rustamov, A.; Sadovsky, A.; Salabura, P.; Scheib, T.; Schmidt-Sommerfeld, K.; Schuldes, H.; Sellheim, P.; Siebenson, J.; Silva, L.; Sobolev, Y. G.; Spataro, S.; Ströbele, H.; Stroth, J.; Strzempek, P.; Sturm, C.; Svoboda, O.; Tarantola, A.; Teilab, K.; Tlusty, P.; Traxler, M.; Tsertos, H.; Vasiliev, T.; Wagner, V.; Wendisch, C.; Wirth, J.; Wüstenfeld, J.; Zanevsky, Y.; Zumbruch, P.
We have studied the production of Σ0 baryons in the nuclear reaction p (3.5 GeV) + Nb. The measurement has been performed with the HADES detector at GSI, Darmstadt. Σ0->Λγ decays were identified via the decay Λ->pπ- coincident to e+e- pairs from external and internal (Dalitz decay) gamma conversion. The differential cross section integrated over the detector acceptance, i.e. within the rapidity interval 0.5 < y < 1.1, has been extracted to be 2.3 +- 0.2 (stat) +- 0.6 (sys) +- 0.2 (norm) mb and the total cross section is obtained by using different extrapolation methods to 5.8 +- 0.5 (stat) +- 1.4 (sys) +- 0.6 (norm) +- 1.7 (extrapol) mb. The Λ/Σ0 ratio is estimated for the full phase space to be 2.6 +- 0.2 (stat) +- 0.8 (sys) +- 0.7 (extrapol). The obtained rapidity and momentum distributions are compared to predictions from transport model calculations. The Σ0 cross section is discussed in the context of statistical particle production in nuclear reactions.

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-25751
Publ.-Id: 25751


A Facility For Pion Induced Nuclear Reaction Studies With HADES

Adamczewski-Musch, J.; Arnold, O.; Behnke, C.; Belounnas, A.; Belyaev, A.; Berger-Chen, J. C.; Biernat, J.; Blanco, A.; Blume, C.; Böhmer, M.; Bordalo, P.; Chernenko, S.; Chlad, C.; Deveaux, C.; Dreyer, J.; Dybczak, A.; Epple, E.; Fabbietti, L.; Fateev, O.; Filip, P.; Fonte, P.; Franco, C.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzon, J. A.; Gernhäuser, R.; Golubeva, M.; Guber, F.; Gumberidze, M.; Harabasz, S.; Heinz, T.; Hennino, T.; Hlavac, S.; Höhne, C.; Holzmann, R.; Ierusalimov, A.; Ivashkin, A.; Kämpfer6, B.; Karavicheva, T.; Kardan, B.; Koenig, I.; Koenig, W.; Kolb, B. W.; Korcyl, G.; Kornakov, G.; Kotte, R.; Kugler, A.; Kunz, T.; Kurepin, A.; Kurilkin, A.; Kurilkin, P.; Ladygin, V.; Lalik, R.; Lapidus, K.; Lebedev, A.; Lopes, L.; Lorenz, M.; Mahmoud, T.; Maier, L.; Mangiarotti, A.; Markert, J.; Maurus, S.; Metag, V.; Michel, J.; Mihaylov, D. M.; Morozov, S.; Müntz, C.; Münzer, R.; Naumann, L.; Nowakowski, K. N.; Palka, M.; Pechenov, V.; Pechenova, O.; Petukhov, O.; Pietraszko, J.; Przygoda, W.; Ramos, S.; Ramstein, B.; Reshetin, A.; Rodriguez-Ramos, P.; Rosier, P.; Rost, A.; Sadovsky, A.; Salabura, P.; Scheib, T.; Schmidt, C. J.; Schmidt-Sommerfeld, K.; Schuldes, H.; Schwab, E.; Scordo, A.; Scozzi, F.; Seck, F.; Sellheim, P.; Siebenson, J.; Silva, L.; Sobolev, Y. G.; Spataro, S.; Ströbele, H.; Stroth, J.; Strzempek, P.; Sturm, C.; Svoboda, O.; Tlusty, P.; Traxler, M.; Tsertos, H.; Usenko, E.; Wagner, V.; Wendisch, C.; Wiebusch, M. G.; Wirth, J.; Zanevsky, Y.; Zumbruch, P.
The combination of a production target for secondary beams, an optimized ion optical beam line setting, in-beam detectors for minimum ionizing particles with high rate capability, and an efficient large acceptance spectrometer around the reaction target constitutes an experimental opportunity to study in detail hadronic interactions utilizing pion beams impinging on nucleons and nuclei. For the 0.4 - 2.0 GeV/c pion momentum regime such a facility is located at the heavy ion synchrotron accelerator SIS18 in Darmstadt (Germany). The layout of the apparatus, performance of its components and encouraging results from a first commissioning run are presented.

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-25750
Publ.-Id: 25750


Solvent extraction: fundamental equilibrium studies of neodymium and DEHPA

Scharf, C.; Ditze, A.
This article presents equilibrium studies into the NdCl3–HCl (or NaOH)–H2O–DEHPA (di-(2-ethylhexyl) phosphoric acid)–kerosene system. The system plays a role in solvent extraction of rare earth elements from aqueous chloride solutions. Thereby neodymium is transferred into the organic phase consisting of DEHPA solved in kerosene. Measurements were taken at DEHPA concentrations between 1 and 40 vol.% and at concentrations of neodymium which prevent a gelatinous organic phase. Results are presented in tables. Three charts of process variables were evaluated which, under the assumption of ideal behaviour, should lead to slopes of 3 in double logarithmic scale in all three cases. Since the actual slopes of measured variables were 2.4, 2.5 and 3.8, ideal behaviour is only a first approximation, and non-ideal aspects need to be further studied. The plot of percentage extraction versus pH shows that neodymium is completely extracted at pH values above 1.
Keywords: solvent extraction, equilibrium system, neodymium, DEHPA, law of mass action

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-25749
Publ.-Id: 25749


Experimental study on the influence of horizontal channel vibration on the mass transfer rate of bubbles in milli-channels

Haghnegahdar, M.; Boden, S.; Hampel, U.
Millimeter-sized reactors have gained a great research interest from the industry and academia because of their advantages such as large interfacial area, high mass transfer rates, low pressure drop, and ease of scale-up over the conventional reactor technology. Optimization of the multiphase flow processes is one of main requirements of modern industry to achieve the higher efficiency and environment-friendly processes. A new design and technique for measurement of mass transfer rate of single bubbles in vibrating milli-channels is being developed with the claimed goal of process intensification [1].
In this study, the absorption rate of a single Taylor bubble of carbon dioxide in water is investigated using high resolution X-ray radiography technique in an oscillating vertical channel. The liquid-side mass transfer coefficient is calculated by measuring the changes in the size of the bubble at constant pressure. The channel is a glass pipe with 6 mm inside diameter and circular cross section. The glass channel is vibrated using a calibrated vibrator in horizontal direction. The amplitude and frequency of vibration is controlled by a wave generator accurately. The method which is used to measure the variation of the bubble size is X-ray radiography. This technique was qualified to disclose the three-dimensional shape of Taylor bubbles in capillary and enabled the acquisition of a series of high-resolution radiographic images of nearly stationary Taylor bubbles. The processed images which give volume (and also the interfacial area) of the bubble with high accuracy as a function of time, are used to evaluate the liquid side mass transfer coefficient between bubble and liquid using the mass conservation equation. The liquid phase is filtered-deionized water and the gas phase is carbon dixide.
The results for the short term dissolution of single carbon dioxide bubbles confirmed that the channel vibration causes to increase of mass transfer rate for single Taylor bubbles. The dissolution rate of bubbles increases as the frequency of vibration rises and there is a maximum value at the channel resonance frequency where large surface oscillation of bubbles exists. Furthermore, it was shown that the liquid-side mass transfer coefficient of dissolving bubbles grow up as the vibration amplitude of channel enlarges.
Keywords: vibration; mass transfer rate; milli-channels
  • Contribution to proceedings
    13th International Conference on Gas–Liquid and Gas–Liquid–Solid Reactor Engineering (GLS-13), 20.-23.08.2017, Brussels,, Belgium
  • Lecture (Conference)
    13th International Conference on Gas–Liquid and Gas–Liquid–Solid Reactor Engineering (GLS-13), 20.-23.08.2017, Brussels, Belgium

Permalink: https://www.hzdr.de/publications/Publ-25747
Publ.-Id: 25747


Experimental analysis of Taylor bubble behavior and mass transfer during lateral oscillation of a vertical milli-channel

Haghnegahdar, M.; Boden, S.; Hampel, U.
In this paper, we report on an experimental study on the influence of low-frequency horizontal vibration of a vertical millimeter-size channel with Taylor bubbles. We investigated the motion, shape and dissolution rate of individual elongated Taylor bubbles of air and CO2, which were freely rising in stationary water. Bubble size and dissolution rate were determined from microfocus X-ray radiographs. From the shrinking rate we calculated the liquid-side mass transfer coefficient. The rise velocity of bubbles and surface wave motion were analyzed using a videometric technique. The comparison of the results for the stationary and the oscillating channel showed that mechanical vibration of the channel is able to enhance the mass transfer coefficient from gas to the liquid phase by 80% to 186%, depending on the frequency and amplitude of vibration. It was found that channel oscillation causes the increase of free rise velocity of bubbles which is mainly attributed to the development of propelling interfacial waves and increase of liquid film flow rate. Furthermore, analyzing the surface wave motion of bubbles revealed that the enlargement of contact area between the phases and the increased mixing enhances the mass transfer additionally up to 30% compared to non-agitated bubbles of similar Peclet number.
Keywords: Vibration; Milli-channels; Mass transfer; Taylor bubble; Carbon dioxide

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-25746
Publ.-Id: 25746


Technetium retention by siderite under anoxic conditions

Schmeide, K.ORC; Rossberg, A.; Weiss, S.; Brendler, V.; Scheinost, A. C.
99Tc is a long-lived (t1/2 = 2.1 × 105 years) β-emitter formed during the fission of U and is of major concern for radioactive waste disposal. Its environmental mobility is primarily governed by the oxidation states VII and IV, with TcVII forming the highly mobile TcO4 aquo anion, whereas TcIV is rather immobile due to the low solubility of its hydrolysis products. Redox processes, which are able to convert TcVII into TcIV, are hence of paramount importance for the safety of radioactive waste repositories. FeII-bearing minerals, ubiquitous in nature and also forming as corrosion products of the carbon steel canisters foreseen as a possible first enclosure of radioactive waste, play a vital role in these redox reactions due to their high redox reactivity and high sorption capacity, as has been shown not only for Tc, but also for Se, U, Np and Pu.
Here we focus on the retention of TcVII by a typical FeII mineral in carbonate-rich environments, siderite (FeCO3), which we studied in the relevant pH range (7 – 12.6) under anoxic conditions by means of batch sorption experiments and by X-ray absorption spectroscopy. Sorption experiments showed that Tc retention by siderite is fast (within minutes) and efficient (log Rd ~5) across the investigated pH range and independent of ionic strength (0.1 – 1 M NaCl). Tc K-edge X-ray absorption near-edge structure (XANES) data confirmed that the Tc immobilization is due to the surface-mediated reduction of TcVII to TcIV. The local structure of TcIV as probed by extended X-ray absorption fine-structure (EXAFS) spectroscopy revealed two different species: in the pH range 7.8 to 11.5, TcO2-dimers form inner-sphere sorption complexes at the surface of siderite or of an FeII,III (hydr)oxide potentially formed during the redox reaction. At pH 11.8 to 12.6, the retention proceeds through the (near-surface) incorporation of TcIV by siderite.
In conclusion, siderite contributes effectively to the retention of Tc in the near-field of nuclear waste repositories.
Keywords: Technetium, siderite, reduction, adsorption, incorporation, technetium carbonate, X-ray absorption spectroscopy
  • Lecture (Conference)
    GeoBremen 2017, 24.-29.09.2017, Bremen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-25745
Publ.-Id: 25745


FoMICS Prize for PhD Students: Presentation "Modeling ultrafast processes in laser-driven plasmas on modern compute hardware"

Huebl, A.ORC
Conventional particle accelerators are approaching fundamental material limits which drive up machine sizes and costs. But both fundamental research and mid-energy range applications such as tumor therapy with ion beams are demanding further progress. Plasma-based accelerators driven by high-power lasers promise a fresh approach to overcome today's limits in accelerator physics. Providing a substantiation increase in accelerating gradients, this new generation of particle accelerators potentially fits on the size of a table if controlled correctly.

My PhD topic focuses on the development of open, manycore-driven particle-in-cell (PIC) simulations in order to model highly non-linear processes that happen on a time scale of atto- to pico-seconds inside this new class of particle accelerators. This includes the development of the world's fastest PIC code PIConGPU which scales up to the full size of Titan (ORNL). I am further extending the PIC algorithm to model previously unreachable multi-physics processes in high-energy density plasmas such as the interaction with XFEL laser beams at the European XFEL, enabling a new quality in predictability.
Keywords: laser plasma modeling HED atomic physics PIC GPU open source LPA ion acceleration
  • Lecture (Conference)
    Platform for Advanced Scientific Computing (PASC) Conference 2017, 26.-28.06.2017, Lugano, Schweiz

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-25744
Publ.-Id: 25744


Combining dynamic modelling codes with medium energy ion scattering measurements to characterise plasma doping

England, J.; Möller, W.; van den Berg, J. A.; Rossall, A.; Min, W. J.; Kim, J.
Plasma doping ion implantation (PLAD) is becoming increasingly important in the manufacture of advanced semiconductor device structures but a fundamental understanding of PLAD is complicated. A model of PLAD into planar substrates has been constructed using the one dimensional computer code TRIDYN to predict collision cascades and hence substrate compositional changes during implantation. Medium Energy Ion Scattering (MEIS) measurements of dopant profiles in PLAD processed samples were used to calibrate the input ion and neutral fluxes to the model. Rules could then be proposed for how post implant profiles should be modified by a cleaning step. This learning was applied to a three dimensional TRI3DYN based model for PLAD implants into FinFET like structures. Comparison of the model to dopant profile measurements made by time of flight (TOF)-MEIS revealed the angular distributions of neutral species and doping mechanisms acting in three dimensional structures.
Keywords: FinFET, Ion beam modelling, Ion-Implantation, PLAD, Plasma Doping, TRI3DYN, TRIDYN

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-25743
Publ.-Id: 25743


Spatiotemporal quantitative imaging of leaching processes with positron emission tomography (PET), improving process understanding and modelling performance

Kulenkampff, J.; Barthen, R.; Gründig, M.; Karimzadeh, L.; Lippold, H.; Schymura, S.; Lippmann-Pipke, J.
A current application that needs improved understanding of coupled reactive transport processes and fluid-rock interactions is in situ leaching of ore minerals. These processes are largely controlled by the chemical and hydrological heterogeneity of the material and the respective transport process.
We apply GeoPET as method for quantitative spatiotemporal imaging of tracer concentrations, which combines molecular sensitivity (picomolar) with suitable spatial resolution (ca. 1 mm) for elucidating heterogeneous effects on the core scale. This laboratory imaging method is virtually unique for crossing the scale from molecular processes to the macrosphere with its typical heterogeneous geoscienctific characteristics. It requires labelling the relevant substance with an appropriate positron-emitting radionuclide, like 18F or 64Cu. PET then makes use of the space-resolved detection of the decay radiation for deriving the tracer concentration.
From the time series of 3D frames of the tracer concentration of conservative flow experiments we compute the distribution of both the process-dependent effective volume and the local velocity distribution of the tracer. These experimental data are the basis of exceptionally efficient finite-element reactive transport models on the millimetre scale with a COMSOL-PhreeqC-coupling.
Our study was conducted within the framework of the French-German project “EcoMetals” which aims at the development of innovative processes for copper (and associated metals) extraction by means of biotechnology. In our showcase experiment we leached copper from pebbles that had been artificially coated with [64Cu]covellite. The PET-experiment has two stages. At first we observed the depletion of the 64Cu activity concentration in the surface layer during leaching with glutamic acid. From this, we derived local covellite leaching rates. After decay of the radionuclide we conducted a conservative flow experiment with pore water labelled with 18F. This experiment identifies strongly localized preferential flow zones. From this, we compute porosity and velocity distributions, which serve as input parameters for the numerical simulation. The simulation results are validated in comparison with observed leaching rates.
  • Lecture (Conference)
    GeoBremen2017, 24.-29.09.2017, Bremen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-25742
Publ.-Id: 25742


Roughness-induced domain structure in perpendicular Co/Ni multilayers

Lee-Hone, N. R.; Thanhoffer, R.; Neu, V.; Schäfer, R.; Arora, M.; Hübner, R.; Suess, D.; Broun, D. M.; Girt, E.
We investigate the correlation between roughness, remanence and coercivity in Co/Ni films grown on Cu seed layers of varying thickness. Increasing the Cu seed layer thickness of Ta/Cu/8×[Co/Ni] thin films increases the roughness of the films. In-plane magnetization loops show that both the remanence and coercivity increase with increasing seed layer roughness. Polar Kerr microscopy and magnetic force microscopy reveal that the domain density also increases with roughness. Finite element micromagnetic simulations performed on structures with periodically modulated surfaces provide further insight. They confirm the connection between domain density and roughness, and identify the microsocpic structure of the domain walls as the source of the increased remanence in rough films. The simulations predict that the character of the domain walls changes from Bloch-like in smooth films to Néel-like for rougher films
Keywords: Domain density, Domain structure, In-plane magnetization, Micromagnetic simulations, Modulated surfaces, Polar-Kerr, Seed layer thickness, Varying thickness

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-25741
Publ.-Id: 25741


Impact of Self-Trapped Excitons on Blue Photoluminescence in TiO2 Nanorods on Chemically Etched Si Pyramids

Saini, C. P.; Barman, A.; Banerjee, D.; Grynko, O.; Prucnal, S.; Gupta, M.; Phase, D. M.; Sinha, A. K.; Kanjilal, D.; Skorupa, W.; Kanjilal, A.
Temperature-dependent photoluminescence (PL) of titanium oxide (TiO2) shows an evolution of blue emission when exposed to 50 keV At+ ions. The origin of observed PL has been examined by X-ray absorption near-edge spectroscopy (XANES) at Ti-K,L and O-K edges, revealing the reduction of ligand field splitting owing to the formation of oxygen vacancies (OVs) by destroying TiO6 octahedral symmetry. Detailed PL and XANES analyses suggest that the fluence (ions/cm(2)) dependent increase in OVs not only boosts the conduction electrons but also increases the density of holes in localized self-trapped exciton (STE) states near the valence band. Based on these observations, we propose a model in which doped conduction electrons are recombining radiatively with the holes in STE states for blue light emission.
Keywords: titanium oxide, ion implantation, photoluminescence, X-ray absorption near-edge spectroscopy, oxygen vacancy, localized self-trapped exciton

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-25740
Publ.-Id: 25740


High-field ESR in low-D spin systems

Zvyagin, S.
  • Invited lecture (Conferences)
    L. A. Prozorova Workshop on Spin Dynamics, 17.-18.05.2017, Moscow, Russia

Permalink: https://www.hzdr.de/publications/Publ-25739
Publ.-Id: 25739


Radiotracer exchange studies for gaining direct insight into the equilibrium characteristics of elementary processes determining humic-bound metal transport

Lippold, H.
The mobility of toxic or radioactive contaminant metals in the subsurface hydrosphere can be essentially governed by their interaction with humic colloids. Predictions on migration processes need thorough consideration of kinetic aspects in the ternary system metal / humic substance / mineral surface. In reactive transport models, reversibility is commonly presumed. However, for adsorption of humic matter, strong hysteresis is observed (hardly any desorption upon dilution), and recoveries in column experiments are far from complete. Complexation of higher-valent metals with humic substances is accompanied by slow processes leading to an increase in complex inertness, i.e., a growing resistance to dissociation.
In view of these uncertainties, the aim of our studies was to elucidate the reversible / irreversible character of interactions controlling humic-bound transport. For this purpose, the principle of tracer exchange was employed to gain insight into the dynamics of equilibria within the ternary system. A radioactive probe, introduced as a reactant into pre-equilibrated systems, will represent the overall equilibrium if there is a dynamic exchange. In case of a static equilibrium, the tracer will not get involved. The chosen model system for these experiments consisted of terbium(III) (as an analogue of trivalent actinides), humic acid and kaolinite. 160Tb as a radioisotope was produced by neutron activation of 159Tb. Humic acid was radiolabelled by azo coupling with [14C]aniline.
After introducing trace amounts of [14C]humic acid into pre-equilibrated adsorption systems of kaolinite and non-labelled humic acid in the state of surface saturation, quantitative exchange was found to take place. Evidently, adsorption equilibria of humic colloids are not static, notwithstanding their size and multiple bonding, albeit an exchange time of more than 4 weeks was required. Isotope exchange of 159Tb / 160Tb on saturated humic acid was completed within a very short time frame, independently of the time of pre-equilibration 159Tb / humic acid. However, if the tracer 160Tb was introduced prior to saturation with 159Tb, the expected partial desorption of 160Tb occurred at much lower rates, decreasing with time of pre-equilibration. Inertisation phenomena are thus confined to the strongest sites of humic molecules. Analysing the time-dependent course of isotope exchange according to first-order kinetics indicated that up to 3 years are needed to attain equilibrium.
  • Lecture (Conference)
    GeoBremen 2017, 24.-29.09.2017, Bremen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-25738
Publ.-Id: 25738


The determination of the fast neutron-induced fission cross section of Pu(242) at nELBE

Kögler, T.; Beyer, R.; Junghans, A. R.; Müller, S. E.; Schwengner, R.; Wagner, A.
The fast neutron-induced fission cross section of 242Pu was determined in the range of 0.5 MeV to 10 MeV relative to 235U(n,f) at the neutron time-of-flight facility nELBE. The number of target nuclei was calculated by means of measuring the spontaneous fission rate of 242Pu. Neutron transport simulations with Geant 4 and MCNP 6 are used to correct the relative cross section for neutron scattering. The determined results are in good agreement with current experimental and evaluated data sets.
Keywords: neutron-induced fission cross section, neutron scattering corrections, fast neutrons, nELBE
  • Invited lecture (Conferences)
    Scientific Workshop on Nuclear Fission dynamics and the Emission of Prompt Neutrons and Gamma Rays, 19.-23.06.2017, Varna, Bulgaria
  • Open Access Logo Contribution to proceedings
    Scientific Workshop on Nuclear Fission dynamics and the Emission of Prompt Neutrons and Gamma Rays, 20.-22.06.2017, Varna, Bulgaria
    European Physical Journal: Web of Conferences, Vol. 169, 00009, Les Ulis Cedex A: EDP Sciences
    DOI: 10.1051/epjconf/201816900009

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-25737
Publ.-Id: 25737


Pages: [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31] [32] [33] [34] [35] [36] [37] [38] [39] [40] [41] [42] [43] [44] [45] [46] [47] [48] [49] [50] [51] [52] [53] [54] [55] [56] [57] [58] [59] [60] [61] [62] [63] [64] [65] [66] [67] [68] [69] [70] [71] [72] [73] [74] [75] [76] [77] [78] [79] [80] [81] [82] [83] [84] [85] [86] [87] [88] [89] [90] [91] [92] [93] [94] [95] [96] [97] [98] [99] [100] [101] [102] [103] [104] [105] [106] [107] [108] [109] [110] [111] [112] [113] [114] [115] [116] [117] [118] [119] [120] [121] [122] [123] [124] [125] [126] [127] [128] [129] [130] [131] [132] [133] [134] [135] [136] [137] [138] [139] [140] [141] [142] [143] [144] [145] [146] [147] [148] [149] [150] [151] [152] [153] [154] [155] [156] [157] [158] [159] [160] [161] [162] [163] [164] [165] [166] [167] [168] [169] [170] [171] [172] [173] [174] [175] [176] [177] [178] [179] [180] [181] [182] [183] [184] [185] [186] [187] [188] [189] [190] [191] [192] [193] [194] [195] [196] [197] [198] [199] [200] [201] [202] [203] [204] [205] [206] [207] [208] [209] [210] [211] [212] [213] [214] [215] [216] [217] [218] [219] [220] [221] [222] [223] [224] [225] [226] [227] [228] [229] [230] [231] [232] [233] [234] [235] [236] [237] [238] [239] [240] [241] [242] [243] [244] [245] [246] [247] [248] [249] [250] [251] [252] [253] [254] [255] [256] [257] [258] [259] [260] [261] [262] [263] [264] [265] [266] [267] [268] [269] [270] [271] [272] [273] [274] [275] [276] [277]