Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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32228 Publications
Test-retest variability of quantitative MRI perfusion measurements with ASL underclinical conditions
Petr, J.; Schramm, G.; Platzek, I.; Hofheinz, F.; van den Hoff, J.;
Ziel/Aim:
While [O-15]H2O PET is still considered the gold-standard for brain perfusion measurement, a native MRI sequence called arterial spin labeling (ASL) which offers a semi-quantitative alternative becomes increasingly relevant in the clinical setting and might be especially relevant for applications in combined PET/MR systems. For ASL, an accuracy and repeatability comparable to that of PET has been reported. A serious limitation of the respective studies is the fact that mainly young healthy subjects were used. Also, time and subject comfort were sacrificed to reach high repeatability. Our aim was to test the repeatability of ASL under realistic clinical conditions on elderly cancer patients.
Methodik/Methods:
Fifteen patients (age 55.5±12.8 years) with glioblastoma were scanned in two or more sessions (in total 21 sessions, 125±37 days apart). We used a pseudo-continuous ASL sequence with background suppression and 2D multi-slice
readout, labeling time/delay 1525/1650 ms, voxel size 2.75x2.75x6.6mm3, and standard CBF quantification (1). Mean CBF was assessed for regions corresponding to anterior cerebral artery (ACA), posterior CA, middle CA, and vertebral artery, respectively, on the contralateral side from the tumor. Repeatability index and mean relative CBF difference was assed for the two sessions for all regions.
Ergebnisse/Results:
The whole-brain mean CBF was 33.0±4.9 mL/min/100 g (45.5±6.1 mL/min/100 g in gray matter). The repeatability index was 30.4%, 34.3%, 29.7%, 31.5% and 36.8% in whole brain, ACA, MCA, PCA and VA regions, respectively. The mean relative difference between sessions for whole brain was 18.9% (range 0.4-63.0%, median 17.1%).
Schlussfolgerungen/Conclusions:
The repeatability index is close to the values measured by Heijtel (2) in healthy volunteers (27.6% for PET, 25.1% for ASL). A slight decrease in repeatability in elderly patients is to be expected. The mean gray matter perfusion is slightly lower than in (2) (48.5±5.6 in PET, 50.8±6.5 mL/min/100 g for ASL) which might be attributed to the known decline of CBF in elderly subjects. Our results thus show that pCASL measurements yield stable CBF values even under clinical conditions.
Literatur/References:
(1) Alsop, et al. Magnetic Resonance in Medicine. 2014.
(2) Heijtel, et al. NeuroImage, 92:182-92(2014).
  • Lecture (Conference)
    53. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin (DGN), 22.-25.04.2015, Hannover, Deutschland
  • Abstract in refereed journal
    Nuklearmedizin 54(2015), A22

Publ.-Id: 21860 - Permalink


A comparative study of 18F-ASEM and 18F-DBT-10, two novel PET tracers for the α7 nicotinic acetylcholine receptor, in nonhuman primates
Hillmer, A.; Zheng, M.-Q.; Scheunemann, M.; Li, S.; Lin, S.-F.; Labaree, D.; Deuther-Conrad, W.; Carson, R. E.; Brust, P.; Huang, Y.;
Introduction:
The α7 subtype of nicotinic acetylcholine receptors (nAChRs) is involved in neuropsychiatric disorders including Alzheimer’s disease, substance abuse, and schizophrenia. Recently, 18F-ASEM and 18F-DBT-10 were developed to image α7 nAChRs in vivo. We performed PET studies in nonhuman primates to directly compare the pharmacokinetic properties of these tracers.
Methods:
18F-ASEM and 18F-DBT-10 were produced via nucleophilic substitution of their respective nitro-precursors. PET data were acquired with a Focus-220 scanner in two rhesus monkeys. Bolus injection of tracer was followed by 240 min of PET acquisition, including arterial plasma assay and metabolite analysis to determine the input function. Blocking studies with cold ASEM were conducted to assess the extent of specific binding. Data were analyzed with the one- and two- tissue compartment models (1TCM & 2TCM) and multilinear analysis to measure distribution volumes (VT).
Results:
Both 18F-ASEM and 18F-DBT-10 were prepared in high specific activity and >99% radiochemical purity. Higher parent fractions of 18F-DBT-10 were found, as well as higher plasma free fraction (18F-ASEM:13±3%; 18F-DBT-10:18±2%). Tissue kinetics were faster for 18F-ASEM. The 2TCM best modeled the PET data for both radiotracers. Regional VT values were slightly higher for 18F-DBT-10, ranging from 32-53 mL/cm3 (18F-ASEM) and 35-58 mL/cm3 (18F-DBT-10) with the rank order of thalamus>frontal cortex>striatum=temporal cortex>hippocampus>occipital cortex>cerebellum. Blocking studies decreased VT values from baseline levels throughout the brain.
Conclusion:
18F-ASEM and 18F-DBT-10 both exhibit suitable properties for PET imaging of α7 nAChRs in nonhuman primates. 18F-ASEM exhibits faster kinetics and has been extended to human use (Wong et al., 2014).
  • Lecture (Conference)
    SNMMI 2015, 06.-10.06.2015, Baltimore, Maryland, USA
  • Open Access LogoAbstract in refereed journal
    Journal of Nuclear Medicine 56(2015)3, 33

Publ.-Id: 21859 - Permalink


Late Holocene environmental ice core record from Akademii Nauk ice cap (Severnaya Zemlya)
Fritzsche, D.; Opel, T.; Meyer, H.; Merchel, S.; Rugel, G.; Enamorado Baez, S. M.;
Ice cores are established as archives for environmental changes since many years. On Severnaya Zemlya, the easternmost archipelago with considerable glaciation in the Eurasian Arctic, a 724 m long ice core has been drilled on Akademii Nauk the largest ice cap there. Stable water isotope and major ions concentrations in this ice core are presented (e.g. Fritzsche et al., 2005, Opel et al., 2013). They represent more than 3000 years of regional climate and environmental history. A well‐known depth‐age relationship is necessary for a paleoclimate interpretation of the data. In a first approach the dating was performed by counting of annual cycles of stable isotopes well‐preserved in the core even though overprinted by the effect of percolating melt water from summer surface melting. The depth‐age scale produced by counting has been matched to volcanic eruption events with well‐known ages detectable in the sulphate record of the core. This approach has some disadvantages due to the fact that the pattern of stratospheric volcanic events recorded in well‐dated ice cores from Greenland and Antarctica is influenced by rather regional tropospheric eruptions as in our case probably in Iceland and Kamchatka, partly less precisely dated. The depth‐age relationship has therefore to be proofed by an independent method.
The isotope 10Be is produced by cosmic radiation in the Earth’s atmosphere. Its residence time there is about one year, shorter than it is for 14C, for which reason variability of 10Be in archives like glaciers is much higher compared to 14C. The production rate of both radionuclides is depending on the solar activity. Their concentrations were used for the reconstruction of heliomagnetic variations in the past and can be vice versa used for dating of ice cores.
Today, accelerator mass spectrometry (AMS) allows measurements of 10Be in ice cores. Its concentration is depending on the geomagnetic coordinates of the location of its production, transport and deposition mechanisms, accumulation rates etc. Therefore, local differences in 10Be concentrations are observed (Berggren et al., 2009). Here, we present 10Be concentrations measured by the team of DREsden AMS (DREAMS) (Akhmadaliev et al., 2013) in discrete Akademii Nauk ice core samples of about 300 g. Our 10Be record shows its general potential to validate our depth‐age model matching the 10Be concentration pattern to that of Greenlandic ice cores as well as 14C production reconstruction.
References
Akhmadaliev, S., Heller, R., Hanf, D., Rugel, G., and S. Merchel (2013): The new 6 MV AMS‐facility DREAMS at Dresden, Nucl. Instr. and Meth. in Phys. Res. B., 294, pp .5‐10.
doi:10.1016/j.nimb.2012.01.053.
Berggren, A.‐M., J. Beer, G. Possnert, A. Aldahan, P. Kubik, M. Christl, S. J. Johnsen, J. Abreu and B. M. Vinther (2009): A 600‐year annual 10Be record from the NGRIP ice core, Greenland, Geophys. Res. Lett., 36, L11801, doi:10.1029/2009GL038004.
Fritzsche, D., Schütt, R., Meyer, H., Miller, H., Wilhelms, F., Opel, T. and Savatyugin, L. M. (2005): A 275 year ice core record from Akademii Nauk ice cap, Severnaya Zemlya, Russian Arctic, Annals of Glaciology, 42, pp. 361‐366. doi:10.3189/172756405781812862.
Opel, T., Fritzsche, D. and Meyer, H. (2013): Eurasian Arctic climate over the past millennium as recorded in the Akademii Nauk ice core (Severnaya Zemlya) , Climate of the Past, 9 (5), pp. 2379‐2389. doi:10.5194/cp‐9‐2379‐2013.
Keywords: accelerator mass spectrometry, cosmogenic nuclide, climate, ice core
  • Lecture (Conference)
    PAST Gateways (Past Spatial and Temporal Gateways) - Third International Conference and Workshop, 18.-22.05.2015, Potsdam, Deutschland

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Publ.-Id: 21858 - Permalink


The influence of the phosphor z position on the Fermi surface of SrCo2P2: Experiment and theory
Götze, K.; Klotz, J.; Bergmann, C.; Geibel, C.; Rosner, H.; Kraft, I.; Lorenz, V.; Wosnitza, J.;
The exact crystallographic and electronic structure plays an important role for the occurrence of quantum criticality, magnetic order, and superconductivity in the family of transition-metal pnictides AT2Pn2. The pnictide-distance z is a crucial parameter for the electronic structure because the distance between the T2Pn2 layers determines whether the tetragonal crystal structure is collapsed or uncollapsed and, thereby, whether pnictide bonds are formed or not. We have investigated the influence of the P z position on the band structure of the strongly enhanced Pauli paramagnet SrCo2P2, a close relative to the superconducting iron arsenides, that is on the verge of magnetic order. The pronounced temperature dependence of the P z position influences the density of states (DOS) at the Fermi energy strongly. Therefore, we have investigated the Fermi surface of SrCo2P2 in the paramagnetic ground state with the de Haas-van Alphen effect. We compare our experimental results to band-structure calculations in order to determine the exact contribution of individual orbits to the DOS. We will also address the renormalization of the effective masses and the dimensionality of the Fermi surface.
  • Lecture (Conference)
    Frühjahrstagung der DPG 2015, 15.-20.03.2015, Berlin, Deutschland

Publ.-Id: 21857 - Permalink


Direct measurement of the magnetocaloric effect in Ni50Mn35In15 in pulsed magnetic fields
Ghorbani Zavareh, M.; Salazar Mejia, C.; Nayak, A. K.; Skourski, Y.; Wosnitza, J.; Felser, C.; Nicklas, M.;
Ferromagnetic shape-memory Heusler alloys undergo a martensitic transformation, i.e., a first-order structural transition from a cubic high-temperature phase to a low-temperature monoclinic phase. Due to a pronounced magneto-structural interaction in these compounds, a strong magnetic field can induce a metamagnetic transition and drive the system from a martensite to an austenite phase. In this case, both lattice and magnetic entropy contribute to the net magnetocaloric effect (MCE). We have measured the MCE of the shape memory Heusler alloy Ni50Mn35In15 using a set-up for direct magnetocaloric measurements in pulsed magnetic fields. The martensitic transition occurs at about 246 K in zero field and the material has a Curie temperature of 315 K. We find a saturation of the inverse MCE, related to the first-order martensitic transition, with a maximum value of -7 K. The MCE associated with the Curie temperature evolves as typical for a second-order magnetic transition. The effect is positive, nearly temperature independent and yields a value of 11 K.
  • Lecture (Conference)
    Frühjahrstagung der DPG 2015, 15.-20.03.2015, Berlin, Deutschland

Publ.-Id: 21856 - Permalink


Superconductivity and ferromagnetism in nanostructured Bi3Ni
Schönemann, R.; Herrmannsdörfer, T.; Kühne, H.; Zhang, Z.; Naumann, M.; Skrotzki, R.; Kaiser, M.; Heise, M.; Ruck, M.; Kummer, K.; Graf, D.; Wosnitza, J.;
es hat kein Abstract vorgelegen
  • Poster
    Frühjahrstagung der DPG 2015, 15.-20.03.2015, Berlin, Deutschland

Publ.-Id: 21855 - Permalink


de Haas-van Alphen oscillations in (La,Ce)TiGe3
Grasemann, J.; Uhlarz, M.; Kittler, W.; Fritsch, V.; Stockert, O.; Förster, T.; Wosnitza, J.; von Löhneysen, H.;
CeTiGe3 is one of the few Kondo-lattice compounds which order ferromagnetically (TC ≈ 14 K); LaTiGe3 may be used as its nonmagnetic reference, since both compounds crystallize in the same hexagonal perovskite structure [1, 2]. We report on angular-resolved de Haas-van Alphen oscillations in single crystals of CeTiGe3, LaTiGe3, and Ce0.1La0.9TiGe3 grown from Ge flux, measured in magnetic fields up to 13 T in a cantilever-type torque magnetometer. We found several dHvA frequencies, ranging in CeTiGe3 from 100 to 530 T and with effective masses around 0.7 m0, featuring a comparably weak angular dependence. Further, we give an interpretation of our results on the basis of DFT calculations of the electronic band structure of CeTiGe3 and LaTiGe3.
  • Poster
    Frühjahrstagung der DPG 2015, 15.-20.03.2015, Berlin, Deutschland

Publ.-Id: 21854 - Permalink


NMR of the Shastry-Sutherland lattice SrCu(BO3)2 in pulsed magnetic fields
Stern, R.; Kohlrautz, J.; Haase, J.; Kühne, H.; Green, E. L.; Wosnitza, J.;
SrCu2(BO3)2 is a quasi-two-dimensional spin system consisting of Cu2+ ions which form orthogonal spin-singlet dimers, also known as the Shastry-Sutherland lattice. This system has been studied extensively using a variety of techniques to probe the spin-triplet excitations, including recent magnetization measurements over 100 T. Spectroscopic techniques, such as nuclear magnetic resonance (NMR), can provide further insight into the spin-coupling mechanisms and excitations. We present 11B NMR spectra measured in pulsed magnetic fields up to 54 T, and compare those with prior results obtained in static magnetic fields at 41 T. Herewith, we prove the feasibility and efficacy of this technique, yielding the capability for extended studies at highest magnetic fields up to the 100 T regime that determine the spin structure in the 1/3 magnetization plateau and beyond.
  • Poster
    Frühjahrstagung der DPG 2015, 15.-20.03.2015, Berlin, Deutschland

Publ.-Id: 21853 - Permalink


Investigations on vertical gas-liquid downward pipe flows
Banowski, M.;
At the Institute of Fluid Dynamics in the Helmholtz-Zentrum Dresden-Rossendorf, two-phase downward flow experiments at a vertical pipe are performed using ultrafast X-ray tomography. For processing segmented data of co-current downward and counter-current flows, two methods for velocity estimation were developed: A morphological method and a bubble pairing one. The results agree well with expectations.
  • Contribution to proceedings
    46th Annual Meeting on Nuclear Technology - Preserving Competence in Nuclear Technology, 05.-07.05.2015, Berlin, Deutschland
  • Lecture (Conference)
    46th Annual Meeting on Nuclear Technology - Preserving Competence in Nuclear Technology, 05.-07.05.2015, Berlin, Deutschland

Publ.-Id: 21852 - Permalink


Dynamical Schwinger process in a bifrequent electric field of finite duration: survey on amplification
Otto, A.; Seipt, D.; Blaschke, D.; Smolyansky, S. A.; Kämpfer, B.;
The electron-positron pair production due to the dynamical Schwinger process in a slowly oscillating strong electric field is enhanced by the superposition of a rapidly oscillating weaker electric field. A systematic account of the enhancement by the resulting bifrequent field is provided for the residual phase space distribution. The enhancement is explained by a severe reduction of the suppression in both the tunneling and multiphoton regimes.

Publ.-Id: 21851 - Permalink


Cross-over versus first-order phase transition in holographic gravity-single-dilaton models of QCD thermodynamics
Yaresko, R.; Knaute, J.; Kämpfer, B.;
A dilaton potential is adjusted to recently confirmed lattice QCD thermodynamics data in the temperature range (0.7…3.5)Tc where Tc=155MeV is the pseudo-critical temperature. The employed holographic model is based on a gravity--single-field dilaton dual. We discuss conditions for enforcing (for the pure gluon plasma) or avoiding (for the QCD quark-gluon plasma) a first-order phase transition, but still keeping a softest point (minimum of sound velocity).

Publ.-Id: 21850 - Permalink


Instrumented flow followers for fermentation reactors – State of the art and perspectives
Reinecke, S.; Hampel, U.;
Advanced monitoring of the spatio-temporal distribution of process parameters in large-scale vessels and containers such as stirred chemical or bioreactors offers a high potential for the investigation and further optimization of plants and embedded processes. This applies especially to large-scale plants, such as industrial fermenters, biogas reactors and activated sludge basins, where the process performance including the biological processes highly depend on mixing parameters of the complex bio-substrates. Sufficient mixing is a basic requirement for a stable operation of the process and adequate process performance. However, this condition is rarely met and the process efficiency is often reduced dramatically by inhomogeneities in the agitated vessels. Without a doupt, investigation and monitoring of biochemical parameters, such as the fermentation rate, pH distribution as well as O2 and CO2 concentration is of great importance. Nevertheless, also understanding of non-biological parameters, such as fluid dynamics (flow velocity profiles, circulation times), suspension mixing (homogeneity, location of dead zones and short-circuits) and heat transfer (temperature profiles), is necessary to analyze the impact of mixing on the biological system and also to improve the process efficiency.
However, in most industrial scale applications the acquisition of these parameters and their spatial distributions in the large-scale vessels is hampered by the limited access to the process itself, because sensor mounting or cable connections are not feasible or desired. Therefore, state of the art instrumentation of such reactors is commonly limited to few spatial positions where it is doubtfully assumed that the measured parameters are representative for the whole reaction mixture.
In this work, a concept of flow following sensor particles was developed. The sensor particles allow long-term measurement of spatially distributed process parameters in the chemically and mechanically harsh environments of agitated industrial vessels. Each sensor particle comprises of an onboard measurement electronics that logs the signals of measurement devices, namely temperature, absolute pressure (immersion depth, axial position) and 3D acceleration. The whole electronics is enclosed in a robust neutrally buoyant capsule (equivalent diameter 58.2 mm; sphericity 0.91), to allow free movement with the flow.
The sensor particles were tested in pilot fermenters under comparable flow conditions of biogas fermenters. The experiments proved the applicability of the sensor particles and the robustness to resist the harsh environments of mixing processes. Moreover, the results show the capabilities of the sensor particles to monitor the internal conditions of the vessel correctly and thus deliver significant information about the flow regime. Therefore effects of liquid rheology, vessel geometry, impeller speed and axial impeller position on the macro-mixing process were properly detected. Evaluation of the impeller efficiency and the mixing processes was done based on mixing homogeneity, location of dead zones, axial velocity profiles, circulation time distributions as well as average circulation times, acceleration spectra and temperature profiles that were extracted from the measured data. Furthermore, it is shown, that parameters of mixing models such as circulation number, impeller head, PECLÉT-number and variance of suspended solid particles can be estimated from the measured data.
The main achievement of this work is therefore the development and validation of instrumented flow followers for the investigation of macro-mixing effects in agitated vessels. The sensor particles show potential for employment to real applications such as biogas fermenters or large bioreactors and to monitor and improve the mixing and heating regimes.
  • Invited lecture (Conferences)
    28th VH Yeast Conference, 13.-14.04.2015, Berlin, Deutschland
  • Contribution to proceedings
    28th International VH Yeast Conference 13th to 14th April 2015 in Berlin, 13.-14.04.2015, Berlin, Deutschland
    Proceedings of the 28th VH-Yeast Conference April 13-14, 2015 in Berlin, 109-120

Publ.-Id: 21849 - Permalink


Biosorption of U(VI) at highly saline conditions
Cherkouk, A.; Bader, M.; Drobot, B.; Müller, K.; Stumpf, T.;
For the long-term storage of radioactive waste in host rock formations with highly saline environments it is important to know how indigenous halophilic microorganisms can affect the performance of a repository. An important interaction mechanism is the soprtion of radionuclides like uranium on cell surface of microorganisms, which has an influence on U migration behaviour. Biosorption studies at highly saline conditions are also of interest for saline wastewater treatment.
The sorption of U(VI) on cells of the halophilic archaeum Halobacterium noricense DSM 15987 was studied at pH 6.0 and a NaCl concentration of 3.0 M in dependence on uranium concentration, time and temperature. Independent on the added uranium concentration (10 – 120 µM) around 90 % of the added uranium was sorbed by the cells at room temperature. Time-dependent sorption studies indicated a two-step binding process with a fast step within the first hours and a second slower one. A slightly faster sorption of added uranium could be demonstrated at higher temperatures of 50°C.
Interestingly, with increasing time, uranium concentration and temperature the cells began to form agglomerates. Live/Dead staining (LIVE/DEAD® Bac LightTM Bacterial Viabilit Kit, Molecular Probes) of cells after biosorption with uranium showed that nearly all single cells were dead whereas agglomerated cells were alive. The cell agglomeration is a stress response to protect the cells themselves from environmental challenges.
The characterization of the formed cell-uranium-complexes was even at 3M NaCl with Time-resolved Laser-induced Fluorescence Spectroscopy possible and indicated that uranium was bound to cellular carboxylic groups. The bounding of uranium not only to carboxylic groups but also to phosphate groups of the cell could be verified with Infrared Spectroscopy.
This knowledge is important in understanding microbe-radionuclide interactions at highly saline conditions in respect of geological disposal of nuclear waste and is useful for saline wastewater treatment.
  • Lecture (Conference)
    Goldschmidt Konferenz, 16.-21.08.2015, Prag, Tschechien

Publ.-Id: 21848 - Permalink


Impact of organic acids on copper minerals in Kupferschiefer ore
Kostudis, S.; Babel, B. M.; Bachmann, K.; Kutschke, S.; Pollmann, K.; Rudolph, M.; Gutzmer, J.;
The Central European Kupferschiefer constitutes one of the most important natural copper sources in Europe (Borg et al. 2012). The Kupferschiefer sensu strictu challenges conventional exploitation due to its organic load, complex mineralogy and fine dispersion of ores. Thus alternative beneficiation strategies are investigated. Bioleaching – the use of microorganisms or microbial metabolites for metal solubilisation from ore material – may serve as an efficient and environmentally benign approach. Among others leaching with microbially produced organic acids provided good results (Anjum et al 2010). In previous studies (Kostudis et al. 2015) leaching of copper from Kupferschiefer sensu strictu (Polkowice Mine, Lubin, Poland) using glutamic acid was examined. It was shown that copper is primarily released from chalcocite (Cu2S) being the main copper mineral in the shale sample. However, decrease in chalcopyrite (CuFeS2) and bornite (Cu5FeS4) content by 40 % and 37 %, respectively, has also been reported as well as formation of secondary minerals such as covellite (CuS). As the Kupferschiefer sensu strictu is constituted very complexly investigation of the single main copper minerals without the matrix is worthwhile. Thus the current study addresses the influence of organic acids on chalcocite, bornite and chalcopyrite. Experiments were performed using strewn slides prepared as thick sections. Ore samples of chalcopyrite, bornite and chalcocite were provided from Ashio/Japan; Butte/Montana/USA and Henderson Mine/Namaqualand/South Africa, respectively. The samples (fig. A) were analysed prior to and after leaching with citric and glutamic acid using mineral liberation analysis (MLA) consisting of combined SEM and ED X-ray spectrometry and a specific software for automated data acquisition (fig. B), micro-Raman spectroscopy (fig. C), and atomic force microscopy (fig. D). The presentation shows results of comprehensive mineralogical analysis of both pristine and processed copper ores.
  • Poster
    Geoanalysis Leoben 2015 - The 9th International Conference on the analysis of Geological and Environmental Materials, 09.-14.08.2015, Leoben, Österreich

Publ.-Id: 21847 - Permalink


First-in-man incorporation dosimetry of (+)-[18F]flubatine
Sattler, B.; Kranz, M.; Patt, M.; Donat, C. K.; Deuther-Conrad, W.; Hiller, A.; Smits, R.; Hoepping, A.; Brust, P.; Sabri, O.;
Objectives :
(-)-[18F]flubatine is successfully used for neuroimaging of alpha4beta2 nicotinic acetylcholine receptors in human. In this study the biokinetic of the (+) enantiomer was studied first time into humans. To assess the radiation risk by this new radioligand the biodistribution, organ doses (OD) and the effective dose (ED) were determined in 3 healthy volunteers. The results will be compared to the preclinical (mice: PET/MR piglets: PET/CT) and clinical (PET/CT) data and to the (-) enantiomer of flubatine [1].
Methods :
Whole body dosimetry was performed in 3 healthy volunteers (2 m, 1 f ; age: 58.3±5.8 y weight: 80.7±5.5 kg). The volunteers were sequentially PET-imaged up to 7h post i.v. injection of 285±13 MBq on a SIEMENS Biograph16 PET/CT-system on 9 bed positions (BP) per frame, 1.5 to 6 min/BP, CT-attenuation correction and iterative reconstruction. All relevant organs were defined by volumes of interest. Exponential curves were fitted to the time-activity-data (%ID/g, and %ID/organ). The ODs were calculated using the adult male model with OLINDA. The ED was calculated using tissue weighting factors as published in the ICRP103.
Results :
The highest OD [µSv/MBq] was received by urinary bladder (102.0 ± 29.6) and liver (53.1±29.8). The highest contribution to the ED [µSv/MBq] was by urinary bladder (4.1±1.2) and lungs (3.2±0.3). The estimated ED in humans is 23.0±1.9.
Conclusions :
The overall radiation risk was calculated to be 6.9 mSv/300MBq which is almost identically with the results of the (-)-enantiomer in humans (7.02 mSv/MBq). This is in the same magnitude as for other 18F labeled compounds too. Furthermore, the underestimation of the ED to humans based on preclinical data as mentioned in [1] could be verified for mice (12.1 µSv/MBq) and piglets (14.3 µSv/MBq) with this tracer too. This supports the use of animal image derived data for preclinical dose assessment to humans taking into account an underestimation of about 40%.
However, the risk assessment shown in this study encourages to transfer (+)-[18F]flubatine into further clinical study phases and further develop it as a clinical tool for PET brain imaging.
  • Poster
    SNMMI2015 Annual Meeting, 06.-10.06.2015, Baltimore, Maryland, USA
  • Open Access LogoAbstract in refereed journal
    Journal of Nuclear Medicine 56(2015)3, 1020

Publ.-Id: 21846 - Permalink


Preclinical dose assessment of [18F]fluspidine with PET/MRI: Enantiomeric differences in tracer kinetics cause a significant deviation in dosimetry
Kranz, M.; Sattler, B.; Wuest, N.; Deuther-Conrad, W.; Fischer, S.; Wünsch, B.; Steinbach, J.; Sabri, O.; Brust, P.;
Objectives:
[18F]fluspidine is a PET radioligand for neuroimaging of σ1 receptors. The two enantiomers have different kinetics and affinities [1]. Biodistribution, organ doses (OD) and the effective dose (ED) of (S)-(—)-fluspidine (S) and (R)-(+)-fluspidine (R) were determined in mice using PET/MRI to assess the radiation risk to humans.
Methods:
Six female CD1 mice (weight: 30.9±1.3 g) were injected i.v. with 13.2±3.0 MBq (S, n=3) or 12.6±1.4 MBq (R, n=3), respectively. A dynamic 2 h animal PET/MR study was performed. All relevant organs were defined by volumes of interest. Time- and mass-scales were adapted to the human anatomy; exponential curves were fitted to the time-activity-data (%ID/organ). The ODs were computed using the adult male model with OLINDA and the ED using tissue weighting factors (ICRP103).
Results:
For S the highest OD [µSv/MBq] was received by urinary bladder (UB) (58.0), followed by kidneys (37.6). The highest contribution to ED [µSv/MBq] was by UB (2.32) and red marrow (1.30).For R the UB received the highest OD (55.7), followed by small intestine (22.6). The highest contribution to ED was by UB (2.23) and upper large intestine (1.54). The estimated EDs (S: 12.9±0.4; R: 14.0±0.5) differ significantly (p<0.05, student's t-test).
Conclusion:
The estimated ED is well within the range of other 18F-labeled radiotracer and supports further translational research. Furthermore, we have demonstrated that the enantiomer with higher affinity and slower kinetics (R) causes a higher dosimetric burden than its counterpart (S).
References:
[1] Brust, P. et al. "Distinctive In Vivo Kinetics of the New σ1 Receptor Ligands (R)-(+)-and (S)-(–)-18F-Fluspidine in Porcine Brain." Journal of Nuclear Medicine 55.10 (2014): 1730-1736.
  • Poster
    SNMMI2015 Annual Meeting, 06.-10.06.2015, Baltimore, Maryland, USA
  • Open Access LogoAbstract in refereed journal
    Journal of Nuclear Medicine 56(2015)3, 1025

Publ.-Id: 21845 - Permalink


Application of computational fluid dynamics in nuclear reactor safety analysis research
Höhne, T.;
The last decade has seen an increasing use of three-dimensional CFD codes to predict steady state and transient flows in nuclear reactors because a number of important phenomena such as pressurized thermal shocks, coolant mixing, and thermal striping cannot be predicted by traditional one-dimensional system codes with the required accuracy and spatial resolution. CFD codes contain models for simulating turbulence, heat transfer, multi-phase flows, and chemical reactions. For this reason the long-term objective of the activities of the Helmholtz-Zentrum Dresden-Rossendorf Germany (HZDR) R&D program lies in the development of theoretical models for basic phenomena of transient, three-dimensional single and multiphase systems. Such models must be validated before they can be used with sufficient confidence in nuclear reactor safety (NRS) applications. The necessary validation is performed by comparing model results against measured data. However, in order to obtain a reliable model assessment, CFD simulations for validation purposes must satisfy strict quality criteria given in the Best Practice Guidelines (BPG). The following topical issues which are related to PWR, where CFD calculations have been performed, will be briefly discussed: Coolant mixing of the primary circuit, horizontal stratified flow phenomena in the hot leg and fibre material transport in a core under loss of coolant conditions.
Keywords: CFD, Coolant Mixing, HZDR, AIAD
  • Invited lecture (Conferences)
    INSS Symposium, 22.05.2015, Mihama-cho, Japan
  • Invited lecture (Conferences)
    CFD workshop on ICONE-23, 17.05.2015, Chiba, Japan
  • Contribution to proceedings
    INSS Symposium, 22.05.2015, Mihama-cho, Japan, 22-53

Publ.-Id: 21844 - Permalink


Investigations of electrically driven liquid metal flows using an ultrasound Doppler flow mapping system
Franke, S.; Räbiger, D.; Galindo, V.; Zhang, Y.; Eckert, S.;
This paper presents a combined experimental and numerical study of the properties of a liquid metal flow inside a cylinder driven by the application of a strong electrical current. The interaction between the electric current running through the melt and the corresponding induced magnetic field produces so-called electro-vortex flows. We consider here a configuration of two parallel pencil electrodes immersed at the free surface. Velocity measurements were performed by means of the Ultrasound Doppler method. A linear array of 25 singular transducers was used to determine the two-dimensional pattern of the vertical flow component. Numerical simulations of the magnetohydrodynamic (MHD) problem were conducted to calculate the Lorentz force, the Joule heating and the induced melt flow. Experimental and numerical results reveal a complex three-dimensional flow structure of the liquid metal flow. In particular, two pronounced downward jets are formed below both electrodes. The flow structure appears to be symmetrical with respect to two vertical cross sections being perpendicular to each other and one of the two planes contains the electrodes. The comparison between the experimental data and the numerical results shows a very good agreement.
Keywords: Liquid metal flows, electrically driven flows, velocity measurements, ultrasound Doppler method, ultrasonic transducer array

Publ.-Id: 21843 - Permalink


Evaluating Performance of Two Group Interfacial Area Transport Equation for Large Diameter Pipes
Dave, A.; Manera, A.; Beyer, M.; Lucas, D.;
In the two-fluid transport model, the coupling of mass, momentum and energy transfer between phases is highly dependent on interfacial area transfer terms. Several research efforts in the past have been focused on the development of an interfacial area transport equation model (IATE), in an attempt to eliminate the drawbacks of static flow regime maps currently used in best-estimate thermal-hydraulic system codes. The IATE attempts to model the dynamics that are involved in two phase flows by accounting for the different interaction mechanisms affecting bubble transport in the flow.
The further development and validation of IATE models has been hindered by the lack of adequate experimental data, especially in regions beyond the bubbly flow regime for large diameter pipes. At the Helmoltz Zentrum Dresden Rossendorf (HZDR) experiments utilizing wire mesh sensors have been performed over all flow regimes, establishing a database of high-resolution (in space and time) data [1]. A 195 mm diameter pipe with a 64 by 64 wire mesh sensor is utilized in the air-water experimental database used in this work. Analysis of flow conditions in the bubbly flow and churn turbulent flow regimes is presented.
The performance of the current two-group IATE model is evaluated. While the qualitative propagation of interfacial area is predicted sufficiently well, there is a discrepancy in magnitude between the model’s prediction and the experimental results. Overall, the study suggests that differences exist in the incidence of interaction mechanisms between small and large diameter pipes and further efforts are needed in order to extend the range of validity of current IATE models.
Keywords: two-phase flow, interfacial area transport, wire mesh sensor, large diameter pipe
  • Invited lecture (Conferences)
    16th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-16), 30.08.-04.09.2015, Chicago, USA
  • Contribution to proceedings
    16th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-16), 30.08.-04.09.2015, Chicago, USA
    Proceedings of NURETH-16

Publ.-Id: 21842 - Permalink


Neptunium Redox Reactions at the Iron Mineral − Water Interface
Steudtner, R.; Hübner, R.; Müller, K.; Weiss, S.; Scheinost, A. C.;
The Fe(II)-bearing secondary mineral phases siderite and magnetite form under anoxic nuclear respository conditions at the surface of corroding steel containers. Due to their redox reactivity, they control the retention of critical, long-lived radionuclides like Se, Tc and Pu (1-3). Here we show their interaction with another radionuclide of high safety concern, Np, which is more soluble and hence mobile at its oxic, pentavalent redox state in comparison to its reduced, tetravalent oxidation state. The Np(V) reactions at the mineral/water interface were investigated by macroscopic batch experiments and at the molecular level by in situ vibrational (ATR FT IR) and X-ray absorption spectroscopies (XAS). For magnetite, we could distinguish four different processes, the fast formation of a Np(V) inner-sphere sorption complex, followed by the surface reduction of Np(V) to Np(IV), which forms a tridentate Np(IV) inner-sphere sorption complex, and the precipitation of poorly ordered and/or nano-sized NpO2-like particles. The Np(IV) inner-sphere sorption complex prevails at lower pH (<6) and at shorter reaction time, while the precipitate prevails at higher pH (>7) and longer reaction time. In the siderite system, we observed neither the formation of Np(V) nor of Np(IV) sorption complexes at the mineral surface, but only the formation of NpO2 nanoparticles, pointing towards a redox reaction already in solution. Independent of the mechanism, retention of Np(V) by the two minerals was strong; even at high pH and in presence of carbonate – conditions where the retention of Np by the clay barrier becomes weak – the log Rd values remain above 3.5.

1. A. C. Scheinost et al., J. Contam. Hydrol. 102, 228-245 (2008).
2. R. Kirsch et al., Environ. Sci. Technol. 45, 7267–7274 (2011).
3. T. Kobayashi, A. C. Scheinost, D. Fellhauer, X. Gaona, M. Altmaier, Radiochim. Acta 101, 323-332 (2013).
  • Lecture (Conference)
    Goldschmidt 2015, 16.-21.08.2015, Praha, Česká republika
  • Lecture (Conference)
    GDCh-Wissenschaftsforum Chemie 2015, 30.08.-02.09.2015, Dresden, Deutschland

Publ.-Id: 21841 - Permalink


Uncertainty Analysis of an Interfacial Area Reconstruction Algorithm
Dave, A.; Manera, A.; Beyer, M.; Lucas, D.; Prasser, H.-M.;
Wire mesh sensors (WMS) are state of the art devices that allow high resolution (in space and time) measurement of 2D void fraction distribution in any two-phase flow regime. Data using WMS have been recorded at the Helmholtz Zentrum Dresden Rossendorf (HZDR) [1] for a wide combination of superficial gas and liquid velocities, providing an excellent database for advances in two-phase flow modeling. In two-phase flow, the interfacial area plays an integral role in coupling the mass, momentum and energy transport equations of the liquid and gas phase. While current models used in best-estimate thermal-hydraulic codes (e.g. RELAP5, TRACE, TRACG, etc.) are still based on algebraic correlations for the estimation of the interfacial area in different flow regimes, interfacial area transport equations (IATE) have been proposed to predict the dynamic propagation in space and time of interfacial area [2]. IATE models are still under development and the HZDR WMS experiments would provide an excellent basis for the validation and further advance of these models. The current paper is focused on the algorithms used to reconstruct interfacial area densities from the void-fraction voxel data measured using WMS.
Keywords: wire mesh sensor, two-phase flow, interfacial area transport equation, uncertainty analysis
  • Invited lecture (Conferences)
    16th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-16), 30.08.-04.09.2015, Chicago, USA
  • Contribution to proceedings
    16th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-16), 30.08.-04.09.2015, Chicago, USA
    Proceedings of NURETH-16

Publ.-Id: 21840 - Permalink


Direct Condensation and Entrainment steam experiments at the TOPFLOW-DENISE facility
Seidel, T.;
In a hypothetical Small Break Loss of Coolant Accident (SB-LOCA) in a Pressurized Water Reactor (PWR), the Reactor Pressure Vessel wall (RPV) may be exposed to thermal stress, since the Emergency Core Cooling System (ECCS) injects cold water. The loads on the primary loop and RPV walls are determined by mixing processes with the surrounding hot water and by the condensation of steam on the surface.
Computational Fluid Dynamics models are not reliable enough to contribute to reliable safety analysis. For the development and validation of CFD-models, experiments have to meet a high standard of reproducibility, measurement certainty and temporal and local resolution. The pressure tank technology of the TOPFLOW facility allows conducting such experiments at reasonable effort.
The Direct Condensation and Entrainment Installation for Steam Experiments (DENISE) is made for CFD-grade condensation experiments at up to 50 bars pressure. Subcooled water is injected into the DENISE-basin in three different configurations to generate stratified flow, jet and plunging jet (steam entrainment with a jet) experiments with condensation.
The experimental facility is presented along with the high degree of instrumentation. High speed camera, micro thermocouples, coriolis flow meters and movable thermal lances were used.
  • Contribution to proceedings
    46th Annual Meeting on Nuclear Technology, 05.-7.5.2015, Berlin, Deutschland
    Proceedings of the 46th Annual Meeting on Nuclear Technology
  • Lecture (Conference)
    46th Annual Meeting on Nuclear Technology, 05.-7.5.2015, Berlin, Deutschland

Publ.-Id: 21839 - Permalink


Near-wall measurements of the bubble- and Lorentz-force-driven convection at gas-evolving electrodes
Baczyzmalski, D.; Weier, T.; Cierpka, C.; Kähler, C. J.;
Chemical energy storage systems, e.g. in the form of hydrogen or methanol, have a great potential for the establishment of volatile renewable energy sources due to the large energy density. The efficiency of hydrogen production through water electrolysis is, however, limited by gas bubbles evolving at the electrode’s surface and can be enhanced by an accelerated bubble detachment. In order to characterize the complex multi-phase flow near the electrode, simultaneous measurements of the fluid velocities and the size and trajectories of hydrogen bubbles were performed in a water electrolyzer. The liquid phase velocity was measured by PIV/PTV, while shadowgraphy was used to determine the bubble trajectories. Special measurement and evaluation techniques had to be applied as the measurement uncertainty is strongly effected by the high void fraction close to the wall. In particular, the application of an advanced PTV scheme allowed for more precise fluid velocity measurements closer to electrode. This way, the effect of Lorentz forces on the near-wall fluid velocities was investigated. The results show a significantly increased wall parallel liquid phase velocity with increasing Lorentz forces. It is presumed that this enhances the detachment of hydrogen bubbles from the electrode surface and, consequently, decreases the fractional bubble coverage and improves the efficiency. In addition, the effect of large rising bubbles with path oscillations on the near-wall flow was investigated. These bubbles can have a strong impact on the mass transfer near the electrode and thus affect the performance of the process.
Keywords: two-phase flow, gas bubbles, water electrolysis, particle tracking, Lorentz force, MHD effect

Publ.-Id: 21838 - Permalink


18F-JHU94620, a high affinity PET radioligand for imaging of cannabinoid subtype 2 receptors (CB2R)
Moldovan, R.-P.; Deuther-Conrad, W.; Teodoro, R.; Wang, Y.; Fischer, S.; Pomper, M.; Wong, D. F.; Dannals, R. F.; Brust, P.; Horti, A. G.;
Objectives:
CB2R represents a target with increasing importance for neuroimaging due to its upregulation in various pathological conditions. Encouraged by preliminary results obtained with 11C-A-836339 (Ki = 1.2 nM) in a mouse model of acute neuroinflammation (induced by lipopolysaccharide, LPS), we designed a library of fluorinated analogs to develop a radioligand with improved CB2R binding affinity and selectivity.
Methods:
A series of fifteen analogs of A836339 was synthesized and JHU94620, selected as ligand with the highest CB2R affinity (Ki = 0.38 nM) and selectivity over CB1R (factor 1000). It was labelled from the bromo precursor by standard nucleophilic radiofluorination. For in vivo experiments, control and LPS-treated CD1 mice have been used. Metabolic stability was investigated in plasma samples (30 min p.i) by radio-HPLC. In vitro autoradiography was performed on rat spleen and pig brain using CB1, CB2, and CB1/CB2 specific ligands as competitors.
Results:
18F-JHU94620 was prepared in ~10% radiochemical yield, >98% radiochemical purity and specific activity of >150 GBq/μmol. Animal PET revealed a brain uptake comparable to 11C-A-836339. 20-30% higher uptake in LPS-treated mice was found (n=3, p<0.05). In plasma, ~10% of total radioactivity accounted for intact tracer at 30 min p.i. Binding of 18F-JHU94620 on spleen could be displaced by CB2- and CB1/CB2-specific but not by CB1-specific compounds (61%, 44%, and 107% of total binding, respectively, at 1 μM). As expected, in brain slices from healthy pig no specific binding was observed.
Conclusion:
18F-JHU94620 is a potential candidate for further studies with PET in neuroinflamation and related disorders.
  • Poster
    SNMMI2015, 05.-10.06.2015, Baltimore, Maryland, USA
  • Open Access LogoAbstract in refereed journal
    Journal of Nuclear Medicine 56(2015)3, 1048

Publ.-Id: 21837 - Permalink


Influence of thyroid hormones on brown adipose tissue activity and browning of white adipose tissues in mice
Krause, K.; Kranz, M.; Weiner, J.; Klöting, N.; Rijntjes, E.; Köhrle, J.; Zeisig, V.; Steinhoff, K.; Deuther-Conrad, W.; Fasshauer, M.; Stumvoll, M.; Sabri, O.; Blüher, M.; Hesse, V.; Brust, P.; Tönjes, A.;
Administration of thyroid hormones (TH) to mammals leads to an increase in basal metabolic rate and thermogenesis. These effects have been attributed to direct actions of TH on metabolically active tissues, such as brown adipose tissue (BAT). Furthermore, TH might stimulate “browning”, i.e. conversion of existing white fat cells to ''brite'' or ''beige'' adipocytes with features of brown adipocytes. However, the impact of TH on BAT activity and “browning” of white adipocytes has not been analyzed under well-controlled conditions in the same experimental setting.
Therefore, it was assessed how thyroid dysfunction, i.e. hyper- and hypothyroidism, affects 1) activity of BAT by 18F-FDG PET/MRI, and 2) affects gene expression of brown and beige adipose tissue differentiation markers in white adipose tissues (inguinal and epididymal, iWAT and eWAT, respectively) and interscapular BAT (iBAT) in mice. We randomized female C57BL/6NTac mice and rendered them hyper- or hyperthyroid (n = 20 per group) according to ATA guidelines (Bianco et al. Thyroid 2014). After 4 weeks of treatment, small animal PET/MR analysis revealed that hypothyroid mice had significantly decreased and hyperthyroid mice had significantly increased interscapular BAT (iBAT) 18F-FDG uptake as compared to euthyroid controls (SUV 3.5 ± 0.7 vs. 6.2 ± 0.6 and SUV 78.0 ± 2.1 vs. 6.16 ± 0.6, respectively). In addition to the findings in iBAT, hypothyroid mice also had significantly diminished glucose disposal in skeletal muscle as compared to both other groups. However, despite the iBAT of hypothyroid mice showing low metabolic activity, significantly higher levels of Ucp1 mRNA was found in iBAT when compared with hyper- and euthyroid animals (p < 0.05 for both). In accordance with these findings, other thermogenic markers including Prdm16, Fgf21, Cidea, Elovl3 and Cox7a1 were all overexpressed in the hypothyroid iBAT. In contrast, the thermogenic genes Ucp1, Prdm16, Fgf21, Cidea, Pgc1α were upregulated in eWAT in hyperthyroid mice as compared to hypothyroid and euthyroid mice. In addition, also markers for beige adipocytes (Cd137, Tmem26), and adipocyte recruitment (Zfp423) were significantly increased in the eWAT of hyperthyroid mice as compared hypo-and euthyroid mice.
In conclusion, these data suggest that TH induce both BAT activity and the thermogenic program in white adipose tissues possibly leading to the browning of white fat depots.
  • Abstract in refereed journal
    Experimental and Clinical Endocrinology & Diabetes 2(2015)123
  • Poster
    58th Symposium of the German Society of Endocrinology, 18.-21.03.2015, Lübeck, Deutschland

Publ.-Id: 21836 - Permalink


Feasibility and Importance of the alpha 7 Nicotinic Acetylcholine Receptor (alpha 7nAChR) as Target for PET Imaging
Deuther-Conrad, W.; Teodoro, R.; Scheunemann, M.; Rötering, S.; Patt, M.; Kranz, M.; Donat, C. K.; Xiong, G.; Fischer, S.; Bucerius, J.; Peters, D.; Cumming, P.; Steinbach, J.; Sabri, O.; Brust, P.;
Aim:
The α7nAChR is regarded of importance for neurodegeneration, inflammatory processes, certain types of cancer, and in the pathophysiology of atherosclerosis. Our recently developed PET radioligands [18F]NS14490 and [18F]DBT-10 showed high in vitro affinity and selectivity towards α7nAChR. We present the automated syntheses and the preclinical evaluation of both radiotracers by PET in pigs and provide evidence on their suitability for imaging of α7nAChRs in the mentioned diseases.
Materials and Methods:
[18F]NS14490 and [18F]DBT-10 were synthesized using a Tracerlab FX F-N module by direct radiofluorination using the corresponding tosylate and nitro precursors. Dynamic PET studies (~300-400 MBq) were performed in anaesthetized female piglets under control (n=3 each) and blocking conditions (n=3 each; continuous infusion of the highly selective antagonist ligand NS6740). By compartmental modeling using metabolite-corrected plasma input functions the binding parameters in 24 brain regions and on brain blood vessels were estimated. Parametric maps of the distribution volumes (VT) of [18F]NS14490 were calculated. In anticipation of human studies, for [18F]DBT-10 preclinical dose assessment and toxicity studies were performed.
Results:
[18F]NS14490 and [18F]DBT-10 were obtained with comparably high RCY (~30-40%), radiochemical purities (~92-95%) and specific activities (>150 GBq/µmol). Maximum brain uptake was reached at 3 min ([18F]NS14490 SUVmax:0.54) and 11.5 min p.i. ([18F]DBT-10 SUVmax:1.89). Comparable metabolism was observed, with 25-30% of both parent compounds in plasma at 60 min p.i. Compartmental modeling allowed reliable estimates of k3’ and binding potential, BPND. NS6740 infusion significantly reduced mean k3’ of [18F]NS14490 by 46% and mean BPND of [18F]DBT-10 by 75%. Reduction of VT on brain blood vessels by NS6740 was clearly visible in parametric maps of [18F]NS14490. SUVmax in blood vessels of 1.3-1.4 was reached at 2-4 min p.i. NS6740 reduced the SUV by 25-35% at 4 h p.i. The estimated effective dose of [18F]DBT-10 administration to humans is 12-14 μSv/MBq. DBT-10 toxicity tests did not predict harmfulness for human tracer studies.
Conclusion:
[18F]NS14490 and [18F]DBT-10 are promising PET tracers for imaging of α7nAChR. Our preclinical studies provide evidence for the detection of α7nAChRs by PET in the parenchyma and vasculature of pig brain. This further elucidates the feasibility of PET to visualize vascular α7nAChRs, which may present a tool for investigating involvement of α7nAChRs in the pathophysiology of atherosclerosis. [18F]DBT-10 is selected for further evaluation to obtain approval for translational clinical validation in humans due to its higher affinity, brain uptake, and specific binding.
  • Lecture (Conference)
    EANM 2014, 17.-22.10.2014, Göteborg, Sweden
  • Abstract in refereed journal
    European Journal of Nuclear Medicine and Molecular Imaging 41(2014), 209-210

Publ.-Id: 21835 - Permalink


(Bio)Leaching of copper from Kupferschiefer with citric acid
Kostudis, S.; Bachmann, K.; Kutschke, S.; Pollmann, K.; Gutzmer, J.;
The Central European Kupferschiefer deposit bearing copper up to five percent is the most important natural copper resource in Europe, and thus raised again interest of both industry and science. Due to the complex composition of the shale including copper and sulfide rich ores, carbonates and organic compounds there is no efficient biotechnological approach applied yet. Although promising approaches using acidophilic micoorganisms were presented [1] issues such as acid pretreatment and resulting gypsum waste remain. Thus leaching at neutral and alkalic pH ranges has been investigated using both foreign and indigenous species including yeasts [2-4]. Especially usage of microbially produced organic acids [5] has shown good results regarding copper recovery. In previous studies [4] the impact of glutamic (see figure) and citric acid on copper minerals in Kupferschiefer ore has been examined using bulk chemicals. The presentation compares those results to copper leaching with citric acid as biotechnologically produced product in fermentation broth produced by the yeast Yarrowia lipolytica.
  • Poster
    Goldschmidt2015, 16.-21.08.2015, Prag, Tschechische Republik

Publ.-Id: 21834 - Permalink


P1403 - Kapazitätsdiode, Verfahren zum Herstellen einer Kapazitätsdiode, sowie Speicher und Detektor mit einer solchen Kapazitätsdiode
Schmidt, H.; Selvaraj, L.; Bogusz, A.; Bürger, D.; Prucnal, S.; Skorupa, I.;
Die Erfindung betrifft eine Kapazitätsdiode, ein Verfahren zum Herstellen derselben, sowie einen Speicher und Detektor mit einer solchen Kapazitätsdiode, wobei die Kapazitätsdiode eine erste und eine zweite Elektrode sowie eine kontaktierend zwischen den beiden Elektroden angeordnete Schichtanordnung aufweist, und wobei die Schichtanordnung in Richtung von der ersten zu der zweiten Elektrode hin nacheinander eine Schicht aus einem ferroelektrischen Material und eine Schicht aus einem dielektrischen Material mit elektrisch geladenen Störstellen aufweist.
  • Patent
    DE102014105639 - Erteilung 05.03.2015; Nachanmeldung: WO, CN, EP, US

Publ.-Id: 21833 - Permalink


P1324 - Verfahren und Einrichtung zur Kontrolle der Reichweite von Partikelstrahlung einer Bestrahlungseinrichtung zur Strahlentherapie
Enghardt, W.; Golnik, C.; Pausch, G.; Hueso-Gonzalez, F.;
Die Erfindung betrifft Verfahren und Einrichtungen zur Kontrolle der Reichweite einer Partikelstrahlung in der Strahlentherapie über die Messung prompter Gammastrahlung mit wenigstens einem einzelne Gammaquanten nachweisenden Detektor und mindestens einem Analysator, die sich insbesondere durch ihre einfache und robuste Realisierung sowie eine durch stark reduzierte Messzeit auszeichnen, die eine Reichweitekontrolle in Echtzeit erlaubt. Dazu werden mit Hilfe des Detektors und des Analysators unter Verwendung eines Referenzsignals der Bestrahlungseinrichtung oder eines separaten Partikeldetektors Zeitverteilungen gemessen, die statistische Verteilungen der Flugzeiten von Therapiepartikeln bis zur Emission eines prompten Gammaquants, ergänzt um die Flugzeit des entsprechenden Gammaquants zum Detektor, widerspiegeln. Informationen über die Reichweite der Therapiepartikel werden im Wesentlichen aus diesen Zeitverteilungen abgeleitet.
  • Patent
    DE102013218982 - Offenlegung 26.03.2015, Nachanmeldung: WO, US, EP, JP

Publ.-Id: 21832 - Permalink


SRF Photo Injector for Electron-Laser Interaction
Lu, P.;
simulation and first results
Keywords: 1 nC simulation
  • Lecture (Conference)
    LA3NET conference: Laser applications at accelerators, 25.-27.03.2015, Mallorca, Spain

Publ.-Id: 21831 - Permalink


Beam Diagnostics of the SRF Photoinjector at HZDR, LA³NET Topical Workshop
Lu, P.;
Beam Diagnostics of the ELBE SRF Gun II
Keywords: energy spread, emittance, bunch length
  • Lecture (others)
    LA³NET Topical Workshop: Beam Diagnostics, 23.-24.03.2015, Mallorca, Spain

Publ.-Id: 21830 - Permalink


Application of Layered Double Hydroxides for 99-Tc immobilization
Shcherbina, N.; Franzen, C.; Foerstendorf, H.; Walther, C.;
99Tc is a long-lived (T1/2=2.13·105 y) fission product (FP) of the nuclear fuel cycle (NFC). As a component of nuclear wastes it remains a FP of concern for the safety assessment of a final disposal site. In the heptavalent form Tc(VII)O4-, it is well soluble, poorly sorbed and hence, a highly mobile anion in the environment. A number of strategies have been proposed to reduce 99Tc mobility by irreversible incorporation into the structure of ubiquitous mineral phases . We have recently demonstrated the incorporation of TcO4- in layered double hydroxides (LDH) that were earlier proposed for 79Se and 129I remediation in water treatment technology.
This work is focused on the interaction of 99Tc(VII) with Pyroaurite (PyA) and Hydrotalcite (HTC) - Mg-Fe and Mg-Al LDHs respectively, on simplified CO2- and O2-free conditions. Earlier experiments with Re(VII), considered to be a chemical analogue for 99Tc(VII), have demonstrated little to no uptake of Re(VII). Similar experiments with 99Tc(VII) however have shown a significant increase in 99Tc uptake on LDHs even in the concurrency with CO32- ions. Subsequent leaching experiments have revealed the irreversible character of the 99Tc(VII)-LDH compound. Modern spectroscopic methods are applied in order to understand how 99Tc is accommodated in between the brucite layers of LDHs and whether 99Tc(VII) is reduced to Tc(IV). This information will help to verify, whether LDHs can be used as a host phase for 99Tc long-term and safe storage. Additionally, these data aquired on controlled conditions can be used for modelling of 99Tc geochemical behavior in more complex repository relevant systems.
Keywords: technetium, sorption, retention
  • Poster
    Goldschmidt 2015, 16.-21.08.2015, Praha, Česká republika

Publ.-Id: 21829 - Permalink


The surface complexes of the oxoanions of Se(VI) and Tc(VII) at mineral-water interfaces
Foerstendorf, H.; Heim, K.; Franzen, C.; Jordan, N.;
79Se and 99Tc are fission products of the nuclear fuel cycle and, thus, are of concern during the safety assessment of a nuclear waste disposal site. For a comprehensive description of their mobility in the near and far field of a deep geological repository, the interactions of respective dissolved species with mineral surfaces are of special interest. In particular, the oxoanions Se(VI)O42− and Tc(VII)O4 are considered as mobile species in aquifer due to their high solubility and negative charge.
In this study, the surface reactions of these anions were studied by in situ vibrational spectroscopy which is a dedicated technique for the real time monitoring of the surface processes at the water-mineral interface [1, 2]. For the selenate anion, the formation of two different types of outer-sphere complexes was observed depending on the mineral’s surface. Although both types of sorption complexes behave like typical outer-sphere complexes in terms of macroscopic properties, the different spectral signatures clearly reflect two different molecule symmetries. From the spectra, a slightly distorted tetrahedral geometry, which is close to the aqueous species, and a bidendately coordinated species showing a C2v symmetry were derived. These surface species are denoted as “extended” and “classical” outer sphere complexes, respectively [3, 4].
In homology, spectroscopic sorption experiments with Tc(VII) were performed. The aqueous species should share the same symmetry as for Se(VI), that is a tetrahedral TcO4 ion. From preliminary results of the vibrational spectroscopic sorption experiments, mainly outer-sphere complexes were found which are obviously less specific as it was found for Se(VI).

[1] Foerstendorf, H. et al. (2012) J. Colloid Interface Sci. 377, 299–306. [2] Müller, K. et al. (2015) Environ. Sci. Technol. 49, 2560–2567. [3] Jordan, N. et al. (2011) Geochim. Cosmochim. Acta 75, 1519–1530. [4] Jordan, N. et al. (2013) Geochim. Cosmochim. Acta 103, 63–75.
  • Lecture (Conference)
    Goldschmidt 2015, 16.-21.08.2015, Prague, Czech Republic

Publ.-Id: 21828 - Permalink


Über die zeitlich aufgelöste Messung von Geschwindigkeiten mittels schneller Röntgentomographie
Hoppe, D.;
Für die Bestimmung von Geschwindigkeiten am schnellen Röntgentomographen Rofex eignet sich die Methode der Kreuzkorrelation. Weil dabei manchmal relativ große Integrationsintervalle notwendig sind, kann es zur entsprechend schlechten zeitlichen Auflösung der Geschwindigkeiten kommen. Gezeigt wird, dass mit geeignetem Vorwissen über das sich bewegende Medium oder Objekt trotzdem zumindest regional relativ hohe zeitliche Auflösungen erreichbar sind.
Keywords: Kurzzeit-Kreuzkorrelation, Messebenen, Blasenströmung, Rofex

Publ.-Id: 21827 - Permalink


3D-Röntgentomographie-gestützte Verfolgung von Blasen in flüssigemSchaum
Hoppe, D.;
Durch schnelle Röntgentomographie auf der Grundlage eines magnetisch abgelenkten Elektronenstrahls ist es möglich, 2D-Abbildungen von fluiden Medien zu erzeugen. 3D-Abbildungen wären zwar wünschenswert, sind aber vorerst noch nicht mit vertretbarem Aufwand realisierbar. Trotzdem soll bereits jetzt versucht werden, methodische Studien zur Bestimmung von Geschwindigkeiten in röntgentomographischen 3D-Abbildungen durchzuführen. Speziell werden dynamische Vorgänge in flüssigem Schaum betrachtet.
Keywords: Schaum, Tomographie, Geschwindigkeit, Korrelation

Publ.-Id: 21826 - Permalink


Editorial
Gutzmer, J.; Klossek, A.; Schulz, T.;
Der effiziente und sorgsame Umgang mit natürlichen Ressourcen bleibt ein Thema von globaler Tragweite. Unabhängig vom Tagespreis steigt der Rohstoffhunger der Welt ungebremst; die Qualität, der für eine Nutzung verfügbaren, primären und sekundären Rohstoffe nimmt dagegen stetig ab. Deshalb ist es wichtig, die Gesellschaft nicht nur für eine Energie-, sondern auch für eine Rohstoffwende mit allen daraus resultierenden Folgen zu sensibilisieren. Vier Jahre nach der Gründung der ersten Knowledge & Innovation Communities (KICs) in den Bereichen Klimaschutz, erneuerbare Energien sowie Informations- und Kommunikationstechnologien rief das Europäische Institut für Innovation und Technologie (EIT) nun ein neues KIC für die mineralischen und metallischen Rohstoffe ins Leben. „EIT Raw Materials“, das weltweit größte Ressourcenkonsortium umfasst mehr als 100 führende Unternehmen, Universitäten und Forschungsinstitute aus 22 europäischen Ländern. Sein Ziel wird es in den kommenden Jahren sein, ein pan-europäisches Netzwerk für die langfristige Zusammenarbeit von Bildung, Forschung und Wirtschaft entlang der gesamten Rohstoff-Wertschöpfungskette zu erschaffen.
Keywords: KIC Knowledge and Innovatione Community, EIT Raw Materials, Rohstoff-Wertschöpfungskette, Netzwerk, Rohstoffsektor, Rohstoffwende, Europa
  • Open Access LogoReSource (2015)28, 1

Publ.-Id: 21825 - Permalink


Kooperationspartnerschaft: Die Helmholtz-Gemeinschaft und die TU Bergakademie; Zeitschrift ACAMONTA 2014
Meyer, B.; Sauerbrey, R.; Gutzmer, J.;
Das Helmholtz-Institut Freiberg für Ressourcentechnologie (HIF) wurde als nationales Rohstoff-Institut im Jahr 2011 durch das Bundesministerium für Bildung und Forschung (BMBF) gegründet. Es erforscht und entwickelt Technologien für die nachhaltige Versorgung der deutschen Volkswirtschaft mit dringend benötigten mineralischen, insbesondere metallhaltigen Rohstoffen. Das HIF war von Anfang an als ein an das Helmholtz-Zentrum Dresden-Rossendorf (HZDR) angegliedertes Helmholtz-Institut mit Standort Freiberg geplant. Denn so profitiert das HIF sowohl von den Ressourcenkompetenzen der TU Bergakademie Freiberg als auch von der strukturellen Kompetenz des HZDR. Im Folgenden wird die Einbindung des HIF in die Helmholtz-Gemeinschaft Deutscher Forschungszentren und in die Bergakademie dargestellt sowie einige Beispiele aus der gemeinsame Zusammenarbeit beschrieben.
Keywords: ACAMONTA, Freunde und Förderer der TU Bergakademie Freiberg, Helmholtz-Institut Freiberg für Ressourcentechnologie, Kooperation, Rohstoffstrategie, Rohstoffversorgung
  • ACAMONTA Zeitschrift für Freunde und Förderer der Technischen Universität Bergakademie Freiberg 21(2015), 20-23

Publ.-Id: 21824 - Permalink


Reduced pulmonary blood flow in regions of injury 2 hours after acid aspiration in rats
Richter, T.; Bergmann, R.; Musch, G.; Pietzsch, G.; Koch, T.;
Background
Aspiration-induced lung injury can decrease gas exchange and increase mortality. Acute lung injury following acid aspiration is characterized by elevated pulmonary blood flow (PBF) in damaged lung areas in the early inflammation stage. Knowledge of PBF patterns after acid aspiration is important for targeting intravenous treatments. We examined PBF in an experimental model at a later stage (2 hours after injury).

Methods
Anesthetized Wistar-Unilever rats (n = 5) underwent unilateral endobronchial instillation of hydrochloric acid. The PBF distribution was compared between injured and uninjured sides and with that of untreated control animals (n = 6). Changes in lung density after injury were measured using computed tomography (CT). Regional PBF distribution was determined quantitatively in vivo 2 hours after acid instillation by measuring the concentration of [68Ga]-radiolabeled microspheres using positron emission tomography.

Results
CT scans revealed increased lung density in areas of acid aspiration. Lung injury was accompanied by impaired gas exchange. Acid aspiration decreased the arterial pressure of oxygen from 157 mmHg [139;165] to 74 mmHg [67;86] at 20 minutes and tended toward restoration to 109 mmHg [69;114] at 110 minutes (P < 0.001). The PBF ratio of the middle region of the injured versus uninjured lungs of the aspiration group (0.86 [0.7;0.9], median [25%;75%]) was significantly lower than the PBF ratio in the left versus right lung of the control group (1.02 [1.0;1.05]; P = 0.016).

Conclusions
The PBF pattern 2 hours after aspiration-induced lung injury showed a redistribution of PBF away from injured regions that was likely responsible for the partial recovery from hypoxemia over time. Treatments given intravenously 2 hours after acid-induced lung injury may not preferentially reach the injured lung regions, contrary to what occurs during the first hour of inflammation.
Keywords: Acute lung injury; Respiratory aspiration; Positron emission tomography; Pulmonary circulation; Pulmonary perfusion; Adult respiratory distress syndrome

Publ.-Id: 21823 - Permalink


Determination of gamma-ray widths in 15N using nuclear resonance fluorescence
Szücs, T.; Bemmerer, D.; Caciolli, A.; Fülöp, Z.; Massarczyk, R.; Michelagnoli, C.; Reinhardt, T. P.; Schwengner, R.; Takács, M. P.; Ur, C. A.; Wagner, A.; Wagner, L.;
Background: The stable nucleus 15N is the mirror of 15O, the bottleneck in the hydrogen burning CNO cycle. Most of the 15N level widths below the proton emission threshold are known from just one nuclear resonance fluorescence (NRF) measurement, with limited precision in some cases. A recent experiment with the AGATA demonstrator array determined level lifetimes using the Doppler Shift Attenuation Method (DSAM) in 15O. As a reference and for testing the method, level lifetimes in 15N have also been determined in the same experiment.
Purpose: The latest compilation of 15N level properties dates back to 1991. The limited precision in some cases in the compilation calls for a new measurement in order to enable a comparison to the AGATA demonstrator data. The widths of several 15N levels have been studied with the NRF method.
Method: The solid nitrogen compounds enriched in 15N have been irradiated with bremsstrahlung. The g-rays following the deexcitation of the excited nuclear levels were detected with four HPGe detectors.
Results: Integrated photon-scattering cross sections of ten levels below the proton emission threshold have been measured. Partial gamma-ray widths of ground-state transitions were deduced and compared to the literature. The photon scattering cross sections of two levels above the proton emission threshold, but still below other particle emission energies have also been measured, and proton resonance strengths and proton widths were deduced.
Conclusions: Gamma and proton widths consistent with the literature values were obtained, but with greatly improved precision.
Keywords: 15N, gamma-ray widths, proton widths, NRF

Publ.-Id: 21822 - Permalink


Long-lived cosmogenic radionuclides: Determination by accelerator mass spectrometry and model applications
Merchel, S.; Enamorado Baez, S. M.; Pavetich, S.; Rugel, G.; DREAMS-Users; DREAMS-Friends;
Introduction: Long-lived radionuclides with half-lives of 0.1-16 Ma (Tab. 1) have nowadays thousands of exciting applications, especially within environmental and geosciences. In nature, the so-called cosmogenic nuclides (CNs) are products of nuclear reactions induced by primary and secondary cosmic rays. Hence, they can be found in extraterrestrial material such as meteorites - originating from the asteroid belt, the Moon or Mars - and lunar samples in higher concentrations (e.g. ~1010 10Be atoms/g or < 0.5 mBq/g). A combination of several CNs is used to reconstruct the exposure history of this unique material while in space (irradiation age) and on Earth (terrestrial age).
Though, in terrestrial material the concentrations are typically only on the order of 104-109 atoms/g (i.e. μBq/g - nBq/g) for 10Be produced in the Earth’s atmosphere, so-called atmospheric or meteoric 10Be, transported to the surface and further absorbed and incorporated at and in, e.g. sediments or ice. Some of the lowest 10Be concentrations (~103 atoms/g), produced in-situ by neutron- and muon-induced nuclear reactions from e.g. oxygen and silicon in quartz, can be found in samples taken from the Earth’s surface. The concentrations of atmospheric or in-situ produced CNs record information to reconstruct sudden geomorphological events such as volcanic eruptions, rock avalanches, tsunamis, meteor impacts, earthquakes and glacier movements. Additionally, glacier movements and data from ice cores give hints for the reconstruction of historic climate changes and providing information for the validation of climate model predicting future changes. Slower processes such as sedimentation, river incision and erosion rates can also be investigated and last but not least, indirect dating of bones as old as several Ma’s is possible.
Anthropogenic production by release from nuclear reprocessing, accidents and weapons testing led to increased levels of CNs in surface water and soil (129I,…), ice (36Cl,…) and of course, material from nuclear installations themselves (41Ca,…).
Some of the CNs can be further used as natural or artificial tracers to follow pathways in oceanography, to date and identify sources of groundwater, to perform retrospective dosimetry and to study aspects in radioecology, phytology, nutrition, toxicology and pharmacology.
Method: Today, the analytical method of choice for long-lived cosmogenic radionuclides – especially non-gamma-active ones - is accelerator mass spectrometry (AMS). In contrast to decay counting, AMS scientists do not wait for the disintegration of the radioactive nucleus. In fact, the not-yet-decayed radionuclides are identified more efficiently by mass spectrometry. The main advantage of using a high-energy accelerator for mass spectrometry is the nearly complete elimination of background and interfering signals, resulting from molecular ions and ions with similar masses e.g. isobars. Thus, AMS generally provides much lower detection limits in comparison to conventional mass spectrometry. Our DREAMS (DREsden AMS) system (Akhmadaliev et al., 2013) offers excellent measurement capabilities also for external users.

Table 1. Radionuclides measured by AMS at DREAMS.
Nuclide t1/2 [Ma] Nuclide ratios of samples [10-12]
(machine blank level)
10Be 1.387 0.01-300 (5x10-16) 10Be/9Be
26Al 0.705 0.001-60 (8x10-16) 26Al/27Al
36Cl 0.301 0.007-700 (2x10-16) 36Cl/35Cl
41Ca 0.104 0.02-9000 (8x10-15) 41Ca/40Ca
129I 15.7 artificial samples (3x10-14) 129I/127I
actinides under development

The benefits from using AMS are obvious and manifold: Smaller sample sizes, easier and faster sample preparation, higher sample throughput and the redundancy for radiochemistry laboratories are largely reducing costs. Lower detection limits widen applications to shorter and longer time-scales and to sample types that could never be investigated before. Nevertheless, basic but accurate radiochemical sample separation is an essential prerequisite for AMS measurements.
Model applications: Some of the first successful CN-projects performed at DREAMS had been:
• Dating of marine sediments (with ANU, ETH, TANDAR, TUM & VERA) by 10Be & 26Al and search for supernova-origin 60Fe (by AMS at ANU & TUM)
• Growth rates of deep-sea manganese nodules by 10Be and 26Al (with Senckenberg)
41Ca-determination in water and concrete from a nuclear power plant by LSC and AMS (with VKTA)
• Reconstruction of meteorites’ history by 10Be, 26Al, 36Cl, 41Ca (with U Poznan & Bern, MPI Mainz,…).

Acknowledgments
Thanks to all brave DREAMS-users working with a newly installed AMS-facility and for help from colleagues at other AMS-facilities (ANSTO, ANU, ASTER, ETH, VERA…) with cross-measurements and setting-up the time-of-flight-system for future actinide measurements.

References
Akhmadaliev et al. (2013) Nucl. Instr. Meth. Phys. Res. B 294, 5-10.
Keywords: accelerator mass spectrometry, cosmogenic radionuclides, tracer
  • Lecture (Conference)
    ENVIRA2015 International Conference on Environmental Radioactivity: New Challenges with New Technologies, 21.-25.09.2015, Thessaloniki, Greece

Publ.-Id: 21821 - Permalink


Sponge-like Si-SiO2 nanocomposite as photovoltaic absorber: Synthesis by solid vs. liquid state decomposition of SiOx
Schumann, E.; Heinig, K.-H.; Hübner, R.; Carcelen, V.; Krause, M.; Gemming, S.;
Absorber layers consisting of nanostructured Si are candidates to improve the efficiency of thin film Si solar cells. Si-SiO2 nanocomposites with sponge-like Si embedded in SiO2 are promising materials due to a widened band gap and a maintained electrical interconnectivity. These structures can be formed upon isothermal or rapid thermal annealing of SiOx films (x<1), which leads to phase separation into a percolated network of Si nanowires embedded in SiO2, tentatively accompanied by crystallization of the Si. SiOx layers have been grown by ion beam sputter deposition as well as by reactive magnetron sputtering. Phase separation into Si-SiO2 nanocomposites has been achieved by classical thermal oven treatment, which has been compared to a very rapid thermal processing by scanning a diode laser line source. Compositional and structural characterization has been performed by Rutherford backscattering spectroscopy, energy filtered transmission electron microscopy, and Raman spectroscopy. The two sputter techniques of SiOx lead to distinct nanostructures during the classical thermal treatment throughout a phase separation in the solid state. In contrast, the decomposition with laser treatment occurs in the liquid state.
Keywords: sponge-like, nanostructure, nanocomposite, silicon, siliconoxide, photovoltaic
  • Poster
    79. DPG-Jahrestagung und DPG-Frühjahrstagung der Sektion Kondensierte Materie, 15.-20.03.2015, Berlin, Deutschland

Publ.-Id: 21820 - Permalink


Tailoring the electrical properties of a TiO2 layer by ion-beam irradiation for memristive applications
Blaschke, D.; Bogusz, A.; Huebner, R.; Nierobisch, F.; Rana, V.; Zahn, P.; Gemming, S.;
Reactively sputtered TiO2 thin films on Pt/Ti/SiO2/Si substrates were irradiated with low energy Ar+ ions of different energies to create surface or bulk modifications in the material. Furthermore, the fluence was varied to optimize the level of the modifications, which are e.g. amorphization, surface smoothing, and preferential sputtering of oxygen. These effects were detected by TEM, AFM and supported by TRIDYN simulations, respectively.
The impact of these changes on the electrical properties of the TiO2 layers was monitored by I-V and C-V measurements in top-bottom geometry with Pt, as well as Ti/Pt top contacts. The results indicate a transition from a Schottky-like behavior of the Pt/TiO2 interface to an ohmic one with increasing fluence, which is very similar to the behavior of a Ti/TiO2 interface. Furthermore, the capacity of the complete MIM stack increases with fluence, which points to a reduced effective thickness of the dielectric TiO2 layer after irradiation.

The project is funded by the Initiative and Networking Fund of the Helmholtz Association (Virtual Institute Memriox, VH-VI-422).
Keywords: TiO2, resistive switching, Ar+ irradiation
  • Lecture (Conference)
    79. DPG-Jahrestagung und DPG-Frühjahrstagung, 15.-20.03.2015, Berlin, Deutschland

Publ.-Id: 21819 - Permalink


Structural and electrical characterization of Ar+ irradiated TiO2 thin films
Blaschke, D.; Agnieszka, B.; Huebner, R.; Munnik, F.; Heller, R.; Scholz, A.; Nierobisch, F.; Rana, V.; Zahn, P.; Gemming, S.;
Transition metal oxide thin films, like TiO2, which show a redox-based switching process between two or more resistance levels, are promising candidates for future memory storage devices.
They are extensively studied to get a better understanding of the role of mobile oxygen ions and/or oxygen vacancies for structural changes and electronic transport inside the films.
A defective, nonstoichiometric TiO2-x layer can act as a reservoir for oxygen vacancies and improves the switching characteristics. Such a layer was introduced into the virgin TiO2 film by low energy Ar+ irradiation with different energies and fluencies to modulate the depths and level of the defective region. The impact of the irradiation to the surface morphology and crystal structure was monitored by AFM and TEM measurements and was found to be surface smoothing and amorphization. The role of the preferential sputtering of oxygen to the stoichiometry of the film was investigated with TRIDYN simulations. Electrical properties of the irradiated films were characterized by I-V and C-V measurements and are related to the structural changes caused by the Ar+ irradiation.

The project is funded by the Initiative and Networking Fund of the Helmholtz Association (Virtual Institute Memriox, VH-VI-422).
Keywords: TiO2, resistive switching, Ar irradiation
  • Poster
    79. DPG-Jahrestagung und DPG-Frühjahrstagung, 15.-20.03.2015, Berlin, Deutschland

Publ.-Id: 21818 - Permalink


Simultaneous measurement of AMR and observation of magnetic domains with dual Kerr microscopy
Osten, J.; Lenz, K.; Lindner, J.; Fassbender, J.ORC
Anisotropic magneto resistance (AMR) sensors are widely used in daily life. But the influence of magnetic domains on the AMR is still not fully understood. AMR depends on the direction of the magnetization. For the understanding of the AMR it is therefore important to know about the domain structure. Dual Kerr microscopy is used for the observation of the magnetic domains while at the same time the AMR is measured. Dual Kerr microscopy means that it is possible to measure two magnetization directions at the same time. These two sensitivity directions make it possible to calculate quantitative Kerr images for a complete loop. The investigated samples were magnetic stripe patterned permalloy. The patterning was archived with Cr-Implantation. In addition to the measured resistance the AMR is calculated from the quantitative Kerr images. We also compare the field dependence of the AMR by variation of the magnetic field angle.Our measurements show a clear dependence of the AMR on the magnetic domain types. This work is supported by DFG grant FA316/3-2.
Keywords: Kerr microscopy, AMR
  • Lecture (Conference)
    79. DPG-Jahrestagung und DPG-Frühjahrstagung, 15.-20.03.2015, Berlin, Deutschland

Publ.-Id: 21817 - Permalink


Magnetic Anisotropy in (Cr0.5Mn0.5)2GaC MAX Phase
Salikhov, R.; Semisalova, A. S.; Petruhins, A.; Ingason, A. S.; Rosen, J.; Wiedwald, U.; Farle, M.;
Magnetic MAX phase (Cr0.5Mn0.5)2GaC thin films grown epitaxially on a MgO(111) substrates were studied by ferromagnetic resonance (FMR) at temperatures between 110 K and 300 K. The spectroscopic splitting factor g = 2.00 ± 0.01 measured at all temperatures indicates pure spin magnetism in the sample. At all temperatures we find the magnetocrystalline anisotropy energy to be negligible which is in agreement with the identified pure spin magnetism.
Keywords: Magnetic MAX Phase, Ferromagnetic Resonance, g-factor, Magnetic Anisotropy

Publ.-Id: 21816 - Permalink


Accuracy of parenchymal cerebral blood flow measurements using pseudo-continuous arterial spin labeling in healthy volunteers
Ambarki, K.; Wåhlin, A.; Zarrinkoob, L.; Wirestam, R.; Petr, J.; Malm, J.; Eklund, A.;
Background and Purpose: Arterial spin-labeling method for CBF assessment is widely available but its accuracy is not fully established. We investigated the accuracy of a whole brain arterial spin-labeling technique for assessment of the mean parenchymal CBF (pCBF) and the effect of ageing in healthy volunteers. Phase-contrast MRI was used as the reference method.
Materials and Methods: Ninety-two healthy volunteers were included: 49 young (age range 20-30y) and 43 elderly (65-80y). Arterial spin-labeling pCBF values were averaged over the whole brain to quantify mean pCBFASL.
Total CBF was assessed with phase-contrast MRI as the sum of flow in the internal carotids and vertebral arteries, and subsequent division by brain volume returned the pCBFPCMRI. Accuracy was considered as good if there was less than 5 mL/min/100g in systematic difference against the reference method and if the 95% limits of agreement interval are equal or better than ±10 mL/min/100g
Results: pCBFASL was correlated with pCBFPCMRI (r=0.73, P<0.001).
Significant differences were observed between pCBFASL and pCBFPCMRI in young (P=0.001) as well as in elderly (P<0.001), and the systematic differences were -4±14 mL/min/100g (mean ± 2SD) in young and +6±12 mL/min/100g in elderly. Young subjects showed higher pCBF than elderly for both pCBFPCMRI (Young:57±8, Elderly:54±7 mL/min/100g, P=0.05) and pCBFASL (Young:60±10, Elderly:48±10 mL/min/100g, P<0.001).
Conclusion: Regarding accuracy of the arterial spin-labeling, limits of agreements were too wide while the systematic overestimation in young and underestimation in elderly was close to acceptable. Age-related decrease in pCBF was augmented in arterial spin-labeling compared to phase contrast MRI.
Keywords: ASL-arterial spin-labeling; HE-healthy elderly; HY-healthy young; PCASL-pseudocontinuous ASL; PCBF-parenchymal CBF; PCMRI-phase-contrast MRI; VA-vertebral artery

Publ.-Id: 21815 - Permalink


Partial Volume Correction of Cerebral Perfusion Estimates Obtained by Arterial Spin Labeling
Ambarki, K.; Petr, J.; Wåhlin, A.; Wirestam, R.; Zarrinkoob, L.; Malm, J.; Eklund, A.;
Arterial Spin labeling (ASL) is a fully noninvasive MRI method capable to quantify cerebral perfusion. However, gray (GM) and white matter (WM) ASL perfusions are difficult to assess separately due to limited spatial resolution increasing the partial volume effects (PVE). In the present study, ASL PVE correction was implemented based on a regression algorithm in 22 healthy young men. PVE corrected perfusion of GM and WM were compared to previous studies. PVE-corrected GM perfusion was in agreement with literature values. In general, WM perfusion was higher despite the use of PVE correction.
Keywords: MRI; cerebral perfusion; gray and white matter; arterial spin labeling and healthy
  • Contribution to proceedings
    16. NBC & 10. MTD 2014 joint conferences, 14.-16.10.2014, Gothenburg, Sweden
    16th Nordic-Baltic Conference on Biomedical Engineering, IFMBE Proceedings: Springer International Publishing, 978-3-319-12966-2, 17-19
    DOI: 10.1007/978-3-319-12967-9_5
  • Lecture (Conference)
    16th Nordic-Baltic Conference on Biomedical Engineering, 14.-16.10.2014, Gothenburg, Sweden

Publ.-Id: 21814 - Permalink


Evidence of U(VI) sorption on Acidovorax facilis by TRLFS and EF-TEM/EELS
Krawczyk-Bärsch, E.; Gerber, U.; Steudtner, R.; Lünsdorf, H.; Arnold, T.;
Acidovorax facilis, an aerobic Gram-negative Betaproteobacteria which is commonly found in soil, was used for U(VI) sorption experiments. Experiments were performed in batch cultures under aerobic conditions at 25 °C using nutrient broth. For U(VI) sorption experiments UO2(NO3)2 was added to the culture to achieve an initial U concentration of 0.05 and 0.1 M, respectively, at a neutral pH range. The duration of the sorption experiments were limited to 8 h and 48 h, respectively. By time-resolved laser fluorescence spectroscopy (TRLFS) the measured emission spectrum of the cells is characterized by four emission bands with peak maxima at 497.8, 519.5, 544.1 and 568.6 nm ± 0.5 nm. In addition, the spectra of the Uranyl-lipopolysaccharide-complexes R-O-PO3-UO2 and [R-O-PO3]2-UO22-, reported by Barkleit et al. (2008), were used for comparison. They show only a small deviation from those observed in our studies. Hence, it can be concluded that phosphoryl groups are the main binding sites for uranyl, located in the lipopolysaccharide (LPS) unit in the outer membrane by Gram-negative Acidovorax facilis cells. After the U(VI) biosorption experiments, Acidovorax facilis cells were prepared for Energy-filtered transmission electron microscopy (EF-TEM) and electron energy-loss spectroscopy (EELS). The results provide microscopically and spectroscopically evidence of U(VI) sorbed at the outer membrane of Acidovorax facilis cells by showing high electron density and U ionization intensity peaks.
Keywords: Acidovorax facilis, uranium, sorption, TRLFS, EF-TEM
  • Lecture (Conference)
    Goldschmidt Conference, 16.-21.03.2015, Prague, Czech

Publ.-Id: 21813 - Permalink


Estimating the influence of magnetization transfer effects on cerebral blood flow quantification in pseudo-continuous arterial spin labeling
Petr, J.; Schramm, G.; Hofheinz, F.; Maus, J.; van den Hoff, J.;
The magnetization transfer (MT) effects were studied in pseudo-continuous ASL (pCASL). The MT exchange rate was obtained from two pCASL sequences with and without labeling acquired at multiple delays. A mean white-matter MT exchange rate was obtained and the exchange rate in blood was derived from it. Effect on CBF quantification was then calculated using the standard pCASL quantification model for different distances from the labeling plane and different blood velocities in the arteries. CBF underestimation of up to 6% was shown in the slices closest to the labeling plane if the MT effects were ignored
  • Contribution to proceedings
    Annual Meeting of the International Society for Magnetic Resonance in Medicine, ISMRM 2014, 10.-16.05.2014, Milano, Italy
    Proceedings of the International Society for Magnetic Resonance in Medicine, 2677
  • Lecture (Conference)
    Annual Meeting of the International Society for Magnetic Resonance in Medicine, ISMRM 2014, 10.-16.05.2014, Milano, Italy

Publ.-Id: 21812 - Permalink


Linear Instability Analysis of 3D Magnetohydrodynamic Flow by Direct Numerical Simulation
Grants, I.; Gerbeth, G.;
Direct numerical simulation (DNS) is normally used to study turbulent flows. Though, it may be also very useful for linear instability analysis of complex laminar flows. given an essentially three-dimensional basic flow the number of coupled active degrees of freedom may easily exceed 105. Calculation of the full spectrum is hardly possible if meaningful in such cases. Only a few leading modes are needed for the linear instability anaxix. Iteration techniques such as Arnold iteration may be used to find an isolated eigenvalue. A separate effort, however, is then needed to verify that this eigenvalue really has the maximum real part.
Our study demonstrates that the linear instabiolity problem can be effectively solved by means of DNS. The most straight-forward approach would be to calculate the transient equations long enough to ensure that only the leading eigenmode survives. There is, however, a more efficient way to find few leading eigenvalues and eigenmodes. this method approximates n+1 equidistant flow "snapshot" by n modes that vary exponentially in thime. We describe the numberical implementation of this method coupled with DNS and demonstrate it on an example of three-dimensional magnetohydrodynamic flow. This flow models meld motion in the Cxochralski crystal growth process with a horizontal magnetic field (HMF).
  • Contribution to proceedings
    ERCOFTAC WORKSHOP Direct and Large-Eddy Simulation 9 (DLES 9), 03.-05.04.2013, Dresden, Deutschland
    ERCOFTAC Series Volume 20: Springer, 978-3-319-14447-4, 561-567
    DOI: 10.1007/978-3-319-14448-1_71

Publ.-Id: 21811 - Permalink


Topological spin textures as emitters for multidimensional spin wave modes

Sluka, V.; Weigand, M.; Kakay, A.; Schultheiss, K.; Erbe, A.; Tyberkevych, V.; Slavin, A.; Deac, A.; Lindner, J.; Fassbender, J.ORC; Raabe, J.; Wintz, S.
In the present contribution we will show that in a stacked vortex pair system with uniaxial magnetic anisotropy, spin waves of different symmetries and dimensionalities can be excited.
  • Lecture (Conference)
    International Colloquium on Magnetic Films and Surfaces, 12.-17.07.2015, Krakow, Poland

Publ.-Id: 21810 - Permalink


Radiative particle-in-cell simulations -from plasma dynamics to electromagnetic spectra
Pausch, R.; Debus, A.; Huebl, A.; Steiniger, K.; Widera, R.; Bussmann, M.;
We present PIConGPU a fully-relativistic, 3D3V particle-in-cell code running on multiple GPGPUs. Its parallelization and its application in predicting far field radiation during laser-plasma interactions are discussed during the talk.
Keywords: PIConGPU, radiation, GPU
  • Lecture (Conference)
    First MT Student Retreat, 23.-24.02.2015, Hamburg, Deutschland

Publ.-Id: 21809 - Permalink


Characterizing the Kelvin-Helmholtz instability in interstellar jets using radiation
Pausch, R.; Debus, A.; Huebl, A.; Steiniger, K.; Widera, R.; Bussmann, M.; Schramm, U.;
We present a new diagnostic method to determine the presence of the Kelvin-Helmholtz instability (KHI) in interstellar jets and measuring its main property, the exponential growth rate, using radiation observable on Earth.

Our findings are based on simulations of the relativistic KHI using the 3D3V particle-in-cell code PIConGPU. With its in-situ computation of the emitted far field radiation, we determined angularly resolved radiation spectra for all billions of particles simulated.

We will explain how measuring the electromagnetic radiation from particle jet allows for identifying the stages of the instability and provides a method to settle the question whether the KHI occurs in astro-physical particle jets or not. By identifying these stages, determining the characteristic growth rate of the KHI becomes possible thus providing quantitative insides to the jet dynamics using only the radiation observed on Earth.
Keywords: PIConGPU, KHI, radiation
  • Lecture (Conference)
    79. DPG-Jahrestagung und DPG-Frühjahrstagung, 09.-13.03.2015, Wuppertal, Deutschland

Publ.-Id: 21808 - Permalink


Evolution of Spin Wave Modes in Periodically Perturbed Thin Films
Langer, M.; Gallardo, R.; Banholzer, A.; Schneider, T.; Wagner, K.; Landeros, P.; Lenz, K.; Lindner, J.; Fassbender, J.ORC
The transition from a continuous thin film to a magnonic crystal is studied by ferromagnetic resonance (FMR). Ion irradiation as well as reactive ion beam etching were used to realize a periodic modulation of the sample surface after patterning by electron beam lithography. Mode-splitting in the FMR spectra has been investigated dependent on the size of the perturbations and compared to available analytical perturbation theory. Numerical simulations have been carried out to identify the spin waves corresponding to the mode spectra as well as to understand deviations between measurement and analytical theory for large perturbations. This work is supported by DFG grant LE2443/5-1.
  • Lecture (Conference)
    79. DPG-Jahrestagung und DPG-Frühjahrstagung, 15.-20.03.2015, Berlin, Deutschland

Publ.-Id: 21807 - Permalink


Radiation as synthetic spectral diagnostics in the particle- in-cell code PIConGPU
Pausch, R.; Debus, A.; Huebl, A.; Steiniger, K.; Widera, R.; Bussmann, M.; Schramm, U.;
We present in-situ computation of relativistic radiation in the particle- in-cell code PIConGPU that can give both qualitative and quantitative agreement with analytical models and thus has predictive capabilities. This new kind of synthetic spectral diagnostics can be used to infer plasma dynamics with high spatial and temporal resolution.

Our method is based on the far field approximation of Liénard-Wiechert potential. Its direct integration with the highly-scalable GPU framework of PIConGPU allows computing the spectrally and angu- larly resolved radiation for thousands of frequencies, ranging from infrared to x-rays, hundreds of detector positions and billions of particles efficiently. Recent updates allow studying polarization and improve time resolution thus extending the range of applications.

These capabilities are demonstrated using recent simulations of laser wakefield acceleration (LWFA), high harmonics generation during target normal sheath acceleration (TNSA) and the Kelvin-Helmholtz in- stability (KHI).
Keywords: Radiation, Laser Plasma, PIConGPU, GPU, TNSA, KHI, HHG
  • Lecture (Conference)
    DPG-Frühjahrstagung, 09.-13.03.2015, Wuppertal, Deutschland

Publ.-Id: 21806 - Permalink


Plasmonic Superlensing in Doped GaAs
Fehrenbacher, M.; Winnerl, S.; Schneider, H.; Doring, J.; Kehr, S.; Eng, L.; Huo, Y.; Schmidt, O.; Yao, K.; Liu, Y.; Helm, M.;
We demonstrate a semiconductor based broadband near-field superlens in the mid-infrared regime. Here, the Drude response of a highly doped n-GaAs layer induces a resonant enhancement of evanescent waves accompanied by a significantly improved spatial resolution at radiation wavelengths around lambda = 20 mu m, adjustable by changing the doping concentration. In our experiments, gold stripes below the GaAs superlens are imaged with a lambda/6 subwavelength resolution by an apertureless near-field optical microscope utilizing infrared radiation from a free-electron laser. The resonant behavior of the observed superlensing effect is in excellent agreement with simulations based on the Drude-Lorentz model. Our results demonstrate a rather simple superlens implementation for infrared nanospectroscopy.
Keywords: Superlens, diffraction limit, surface plasmons, near-field microscopy, semiconductor

Publ.-Id: 21805 - Permalink


Determination of the Exchange Stiffness Constant in Ultrathin Magnetic Films by Ferromagnetic Resonance
Langer, M.; Wagner, K.; Sebastian, T.; Schultheiss, H.; Lenz, K.; Lindner, J.; Fassbender, J.ORC
In ultrathin magnetic films of 10 — 20 nm thickness, it is hardly possible to determine the exchange constant A using conventional techniques, such as Brillouin light scattering. In this work, a method is presented allowing for analytical determination of the exchange constant A in ultrathin magnetic films. Periodical surface modulations are introduced by electron beam lithography with subsequent sub-nanometer etching. The periodical stray field induces two-magnon scattering leading to a coupling of the uniform excitation with higher in-plane spin waves. An analytical model is presented, that can be used to precisely calculate the exchange constant A under usage of the measured ferromagnetic
resonance spectra (frequency versus field dependence). This work is supported by DFG grant LE2443/5-1.
  • Poster
    79. DPG-Jahrestagung und DPG-Frühjahrstagung, 15.-20.03.2015, Berlin, Deutschland

Publ.-Id: 21804 - Permalink


Study of the quasi-free np→npπ+π− reaction with a deuterium beam at 1.25 GeV/nucleon
Agakishiev, G.; Balanda, A.; Belver, D.; Belyaev, A. V.; Blanco, A.; Böhmer, M.; Boyard, J. L.; Braun-Munzinger, P.; Cabanelas, P.; Castro, E.; Chernenko, S.; Christ, T.; Destefanis, M.; Díaz, J.; Dohrmann, F.; Dybczak, A.; Fabbietti, L.; Fateev, O. V.; Finocchiaro, P.; Fonte, P.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzón, J. A.; Gernhäuser, R.; Gil, A.; Gilardi, C.; Göbel, K.; Golubeva, M.; González-Díaz, D.; Guber, F.; Gumberidze, M.; Hennino, T.; Holzmann, R.; Ierusalimov, A.; Iori, I.; Ivashkin, A.; Jurkovic, M.; Kämpfer, B.; Karavicheva, T.; Kirschner, D.; Koenig, I.; Koenig, W.; Kolb, B. W.; Kotte, R.; Krizek, F.; Krücken, R.; Kühn, W.; Kugler, A.; Kurepin, A.; Kurilkin, A.; Kurilkin, P.; Ladygin, V.; Lang, S.; Lange, J. S.; Lapidus, K.; Liu, T.; Lopes, L.; Lorenz, M.; Maier, L.; Mangiarotti, A.; Markert, J.; Metag, V.; Michalska, B.; Michel, J.; Morinière, E.; Mousa, J.; Müntz, C.; Naumann, L.; Otwinowski, J.; Pachmayer, Y. C.; Palka, M.; Parpottas, Y.; Pechenov, V.; Pechenova, O.; Pietraszko, J.; Przygoda, W.; Ramstein, B.; Reshetin, A.; Rustamov, A.; Sadovsky, A.; Salabura, P.; Schmah, A.; Schwab, E.; Sobolev, Y. G.; Spataro, S.; Spruck, B.; Ströbele, H.; Stroth, J.; Sturm, C.; Tarantola, A.; Teilab, K.; Tlusty, P.; Traxler, M.; Trebacz, R.; Tsertos, H.; Wagner, V.; Vasiliev, T.; Weber, M.; Wisniowski, M.; Wojcik, T.; Wüstenfeld, J.; Yurevich, S.; Zanevsky, Y.; Zhou, P.;
The tagged quasi-free np→npπ+π− reaction has been studied experimentally with the High Acceptance Di-Electron Spectrometer (HADES) at GSI at a deuteron incident beam energy of 1.25 GeV/nucleon (s√∼ 2.42 GeV/c for the quasi-free collision). For the first time, differential distributions for π+π− production in np collisions have been collected in the region corresponding to the large transverse momenta of the secondary particles. The invariant mass and angular distributions for the np→npπ+π− reaction are compared with different models. This comparison confirms the dominance of the t-channel with ΔΔ contribution. It also validates the changes previously introduced in the Valencia model to describe two-pion production data in other isospin channels, although some deviations are observed, especially for the π+π− invariant mass spectrum. The extracted total cross section is also in much better agreement with this model. Our new measurement puts useful constraints for the existence of the conjectured dibaryon resonance at mass M∼ 2.38 GeV and with width Γ∼ 70 MeV.

Publ.-Id: 21803 - Permalink


Pulsed magnetic field spectroscopy up to 70 T on the dilute nitride GaAsN
Eßer, F.; Schneider, H.; Winnerl, S.; Drachenko, O.; Patanè, A.; Helm, M.;
Magnetic fields above 45 T offer great opportunities as a tool for materials research but can only be realized in the pulsed regime. We use pulsed magnetic fields up to 70 T for spectroscopic investigations of the dilute nitride GaAsN. This material is a promising candidate for optical applications because of the possibility for tuning its band gap by the nitrogen content. Our studies focus on the exploration of the band structure and in particular on the determination of the effective mass. Cyclotron-resonance spectroscopy indicates that the effective mass is not strongly affected by nitrogen in comparison to previous publications. Our magneto-photoluminescence investigations reveal the formation of localized and delocalized states as a result of the nitrogen incorporation. Delocalized states undergo transitions to localized ones in very high magnetic fields. This result is in good agreement with a pressure dependent study [1].

[1] J. Endicott, A. Patanè, D. Maude, L. Eaves, M. Hopkinson, and G. Hill, Phys. Rev. B 72, 041306(R) (2005)
Keywords: GaAsN, dilute nitride, effective mass, cyclotron-resonance, pulsed magnetic field
  • Lecture (Conference)
    79. DPG-Jahrestagung und DPG-Frühjahrstagung, 15.-20.03.2015, Berlin, Deutschland

Publ.-Id: 21802 - Permalink


THz spectroscopy of solids using a free-electron laser
Helm, M.;
I will start describing the Dresden free-electron laser FELBE as an intense, tunable, pulsed and narrowband source of infrared and THz radiation and the unique opportunities it offers for the spectroscopy of low-energy excitations in solids. In particular, the FEL can be used for nonlinear optical experiments, for time-resolved pump-probe studies, and also for near-field microscopy. I will present some recent results and will conclude with an outlook on further developments, including the superradiant THz radiation source TELBE.
Keywords: free electron laser, pump probe, spectroscopy
  • Lecture (others)
    Vortrag am Shanghai Institute for Applied Physics (SINAP), 10.03.2015, Shanghai, China

Publ.-Id: 21801 - Permalink


Topological Spin Textures in Magnetic Multilayers
Wintz, S.;
Topological spin textures, such as vortices or skyrmions, are attracting significant attention because of their intriguing fundamental properties as well as their promising applicability in memory devices or spin torque oscillators. A particular topological texture that was theoretically predicted is the two-dimensional hedgehog state, also known as ’spin meron’. It had been unclear, however, whether this kind of highly divergent magnetization structure may occur in real systems. Only recently, evidence for the existence of meron-like pair states was reported for the case of trilayer elements consisting of two ferromagnetic layers and a non-ferromagnetic interlayer [1]. On this background, a direct proof for the existence of meron-like states in trilayer elements via direct magnetic imaging will be presented. It will also be shown that in the presence of biquadratic interlayer exchange coupling, such meron-like pair states may even represent the magnetic ground state of the system. Interestingly, the highly divergent magnetization distribution induces an additional, three-dimensional torus vortex that in-turn causes a symmetry break for the possible topological pair configurations [2]. In addition the dynamic properties of vertically coupled topological spin textures will be addressed, where the focus will be set on spin wave emission processes in such systems.
References: [1] C. Phatak et al., Phys. Rev. Lett. 108, 067205 (2012). [2] S. Wintz et al., Phys. Rev. Lett. 110, 177201 (2013).
Keywords: vortex multilayer
  • Invited lecture (Conferences)
    DPG Frühjahrstagung der Sektion kondensierte Materie, 15.-20.03.2015, Berlin, Deutschland

Publ.-Id: 21800 - Permalink


Magnetic interactions in BiFe0.5Mn0.5O3 films and BiFeO3/BiMnO3 superlattices
Xu, Q.; Sheng, Y.; Khalid, M.; Cao, Y.; Wang, Y.; Qiu, X.; Zhang, W.; He, M.; Wang, S.; Zhou, S.; Li, Q.; Wu, D.; Zhai, Y.; Liu, W.; Wang, P.; Xu, Y.; Du, J.;
The clear understanding of exchange interactions between magnetic ions in substituted BiFeO3 is the prerequisite for the comprehensive studies on magnetic properties. BiFe0.5Mn0.5O3 films and BiFeO3/BiMnO3 superlattices have been fabricated by pulsed laser deposition on (001) SrTiO3 substrates. Using piezoresponse force microscopy (PFM), the ferroelectricity at room temperature has been inferred from the observation of PFM hysteresis loops and electrical writing of ferroelectric domains for both samples. Spin glass behavior has been observed in both samples by temperature dependent magnetization curves and decay of thermo-remnant magnetization with time. The magnetic ordering has been studied by X-ray magnetic circular dichroism measurements, and Fe-O-Mn interaction has been confirmed to be antiferromagnetic (AF). The observed spin glass in BiFe0.5Mn0.5O3 films has been attributed to cluster spin glass due to Mn-rich ferromagnetic (FM) clusters in AF matrix, while spin glass in BiFeO3/BiMnO3 superlattices is due to competition between AF Fe-O-Fe, AF Fe-O-Mn and FM Mn-O-Mn interactions in the well ordered square lattice with two Fe ions in BiFeO3 layer and two Mn ions in BiMnO3 layer at interfaces.

Publ.-Id: 21799 - Permalink


Evaluation of Resistive-Plate-Chamber-based TOF-PET applied to in-beam Particle Therapy Monitoring
Torres-Espellardo, I.; Diblen, F.; Rohling, H.; Solevi, P.; Gillam, J.; Watts, D.; España, S.; Vandenberghe, S.; Fiedler, F.; Rafecas, M.;
Particle therapy is a highly conformal radiotherapy technique which reduces the dose deposited to the surrounding normal tissues. In order to fully exploit its advantages, treatment monitoring is necessary to minimize uncertainties related to the dose delivery. Up to now, the only clinically feasible technique for the monitoring of therapeutic irradiation with particle beams is Positron Emission Tomography (PET).
In this work we have compared a Resistive Plate Chamber (RPC)-based PET scanner with a scintillation-crystal-based PET scanner for this application. In general, the main advantages of the RPC-PET system are its excellent timing resolution, low cost, and the possibility of building large area systems. We simulated a partial-ring scanner based on an RPC prototype under construction within the Fondazione per Adroterapia Oncologica (TERA). For comparison with the crystal-based PET scanner we have chosen the geometry of a commercially available PET scanner, the Philips Gemini TF.
The coincidence time resolution used in the simulations takes into account the current achievable values as well as expected improvements of both technologies. Several scenarios (including patient data) have been simulated to evaluate the performance of different scanners. Initial results have shown that the low sensitivity of the RPC hampers its application to hadron-beam monitoring, which has an intrinsically low positron yield compared to diagnostic PET. In addition, for in-beam PET there is a further data loss due to the partial ring configuration. In order to improve the performance of the RPC-based scanner, an improved version of the RPC detector (modifying the thickness of the gas and glass layers), providing a larger sensitivity, has been simulated and compared with an axially extended version of the crystalbased device. The improved version of the RPC shows better performance than the prototype, but the extended version of the crystal-based PET outperforms all other options.
Keywords: PET, In-beam, RPC, Particle therapy, TOF, Range deviation, Partial-ring

Publ.-Id: 21798 - Permalink


(Bio)Leaching of copper shale with organic acids
Kostudis, S.; Bachmann, K.; Babel, B. M.; Rudolph, M.; Kutschke, S.; Pollmann, K.; Gutzmer, J.;
The talk summarises PhD research activities and results with respect to (bio)leaching of copper from copper shale.
  • Invited lecture (Conferences)
    Freiberger Forschungsforum, 66. Berg-und Hüttenmännischer Tag (BHT), 17.-19.06.2015, Freiberg, Deutschland

Publ.-Id: 21797 - Permalink


Redox transformations and the disposal of radioactive waste: Influence on Se immobilization
Wieland, E.; Rojo, H.; Scheinost, A. C.; Lothenbach, B.; Tits, J.;
Safety analysis of a cement-based repository for low- and intermediate level nuclear waste (L/ILW) has shown that 79Se is an important redox-sensitive, dose-determining radio-nuclide due to its long half-life and weak retardation by common near- and far field minerals. In the sorption data bases currently used for safety analysis it is considered that 79Se is predominantly present as SeO32- in the cementitious near field because oxidizing conditions prevail during waste conditioning. With time, however, reducing conditions will establish in the near field caused by oxygen consumption in the course of metal corrosion. In these conditions Se(-II) is expected to be the dominant redox state of Se. Hence, investigations into the interaction of Se(IV) and Se(-II) with cementitious materials and the reduction of Se(IV) to Se(-II) enable us to assess the long-term fate of Se in conditions relevant to a cement-based repository.
Sorption studies with Se on cementitious materials indicate that Se(IV) and Se(-II) uptake by hydrated calcium aluminates (AFm) and calcium silicate hydrates (C-S-H) phases, the principal host phases for radionuclides in cement paste, is significant and comparable to the uptake by cement paste. The uptake mechanisms of the Se species, however, are only poorly understood. EXAFS studies on Se(IV)-loaded cement phase and wet chemistry experiments suggest that Se(IV) could be taken up into the structure of the cement phases. In the case of AFm phases, for example, anions bound in the interlayer can be replaced, at least partially, by Se(IV) and Se(-II). This explains why AFm phases are more effective in removing Se(IV) and Se(-II) from solution than C-S-H phases.
Investigations into redox transformation are ongoing and the first results already suggest that the uptake mechanism of the Se species plays an important role in the reduction of Se(IV) to Se(-II) in cementitious materials.
Keywords: nuclear waste cement selenium xas
  • Invited lecture (Conferences)
    Goldschmidt 2015, 16.-21.08.2015, Prague, Czech Republic

Publ.-Id: 21796 - Permalink


Leaching of copper from Kupferschiefer by glutamic acid and heterotrophic bacteria
Kostudis, S.; Bachmann, K.; Kutschke, S.; Pollmann, K.; Gutzmer, J.;
Polymetallic Cu–Ag ores of the Central European Kupferschiefer deposits are one of the most important sources of copper in Europe. Because the ores are typically complex and often exceptionally fine-grained the development of efficient alternatives to conventional beneficiation strategies are an important target of current research. Biomining – the use of biological components for metal extraction – may offer solutions that are both efficient and environmentally benign. As conventional bioleaching with acidophilic microorganisms is impeded by the high carbonate content of the Kupferschiefer ores, heterotrophic microorganisms and glutamic acid are investigated as a possible alternative in the present study. The focus of this investigation is solely on the recovery of copper from the Kupferschiefer sensu strictu. Bioleaching experiments were carried out using such material from the Polkowice Mine in Poland. This material is marked by high grade (3.8 wt.% Cu), complex ore mineralogy (chalcocite, bornite, chalcopyrite and covellite in significant quantity) and a gangue mineralogy that is rich in carbonate, organic carbon and clay minerals that together form a very fine-grained matrix. (Bio)leaching experiments yield best results when glutamic acid alone is used – reaching copper recoveries up to 44%. Recoveries are consistently lower in experiments in which glutamic acid and microbiological metabolites are both present. The leaching of chalcocite renders the greatest contribution to the copper recovered to the leach solution in all experiments. It can be concluded that glutamic acid solubilises copper efficiently from Kupferschiefer, mainly from chalcocite.
Keywords: sulphide ores, bacteria, bioleaching, liberation analysis, ore mineralogy

Publ.-Id: 21795 - Permalink


Biologie meets Bergbau: Biotechnologie für die Gewinnung von Kupfer
Kostudis, S.;
Der Vortrag stellt das Helmholtz-Zentrum Dresden-Rossendorf sowie das Helmholtz-Institut Freiberg für Ressourcentechnologie vor und liefert allgemeine Informationen zu biotechnologischen Prozessen in der Kupfergewinnung sowie Einlick in Arbeiten der Arbeitsgruppe Biotechnologie.
  • Lecture (others)
    Nacht der Wissenschaft und Wirtschaft zum Jubiläum, 20.06.2015, Freiberg, Deutschland

Publ.-Id: 21794 - Permalink


Identification of vancomycin interaction with Enterococcus faecalis within 30 minutes using Raman spectroscopy
Assmann, C.; Kirchhoff, J.; Beleites, C.; Hey, J.; Kostudis, S.; Pfister, W.; Schlattmann, P.; Bauer, M.; Popp, J.; Neugebauer, U.;
Vancomycin is an important glycopeptide antibiotic which is used to treat serious infections caused by Gram positive bacteria. However, during the last years a tremendous rise in vancomycin resistances, especially among enterococci, was reported, making fast diagnostic methods inevitable.
In this contribution, we apply Raman spectroscopy to systematically characterize vancomycin-enterococci interactions over a time span of 90 minutes using a sensitive E. faecalis strain and two different vancomycin concentrations above the minimal inhibitory concentration (MIC). Successful action of the drug on the pathogen could be observed already after 30 minutes of interaction time. Characteristic spectral changes are visualized with the help of multivariate statistical analysis (linear discriminant analysis and partial least squares regressions). Those changes were employed to train a statistical model to predict vancomycin treatment based on the Raman spectra. The robustness of the model was tested using data recorded by an independent operator. Classification accuracies of >90% were obtained for vancomycin concentrations in the lower range of a typical trough serum concentration recommended for most patients during appropriate vancomycin therapy.
Characterization of drug-pathogen interactions by means of label-free spectroscopic methods, such as Raman spectroscopy, can provide the knowledge base for innovative and fast susceptibility assays which could speed up microbiological analysis as well as could find applications in novel antibiotic screenings assays.
Keywords: Raman spectroscopy vancomycin, Enterococcus faecalis, bacteria-antibiotic-interaction

Publ.-Id: 21793 - Permalink


Monitoring gravitational and particle shape settling effects on MLA sampling preparation
Heinig, T.; Bachmann, K.; Tolosana-Delgado, R.; van den Boogaart, K. G.; Gutzmer, J.;
Epoxy blocks for automated mineralogy typically contain unsorted material from feeds, concentrates or tailings of the processing chain. In these cases, accuracy and precision of SEM-based analytics not only depend on stable measurement parameters and conditions but also on sample preparation. The major aim of sample preparation is the production of representative specimen mounts to generate valid information about the given samples. However, experiences in preparation indicate an influence on the analytic results of many factors such as resin type, resin viscosity, mineral grain density, grain shape and sample material/resin ratio.
This study aims at evaluating the influence of different material/resin ratios on the representativity of a mineral sample. In order to investigate possible gravitational and shape related settling effects during sample preparation, the use of homogenized Zinnwaldite ore is suitable as it provides sample material with a heterogeneous mineral composition, mineral density (Quartz – Topaz), grain shape (Mica – Quartz) and grain size. Eight specimens were prepared with equal weight aliquots of the same ore material, with increasing resin amount. These polished epoxy mounts were analyzed three times with the Mineral Liberation Analyzer (MLA) at Helmholtz Institute Freiberg for Resource Technology (HIF) to evaluate their difference in modal mineralogy, grain sizes and grain shapes. Each sample was analysed as usual on the XY plane, then polished a bit and measured again on a deeper XY plane; and finally the samples were cut along the YZ plane, remounted and measured again, thus capturing a plane orthogonal to the classical measurement plane.
First visual inspection indicates a connection between the amount of resin and the appearance of gravitational and shape related settling effects. The effects such as fractionating of grains by size and density or specific orientation of elongated grains became stronger the more resin was used. These aspects are statistically tested by comparing the frequency distributions of intersection segments between grains and families of lines (random in the XY planes, 9 equally spaced lines in the case of YZ plane observations), a way to circumvent Stereological degeneration effects. Results suggest a range of material/resin ratio that is suited for sample preparation of this particular ore type, by showing no statistical deviations between the distributions on the XY and YZ planes, hence no or very small gravitational or shape related settling effects.
  • Contribution to proceedings
    Annual Conference of the International Association of Mathematical Geosciences, 07.-10.09.2015, Freiberg, Deutschland
    Proceedings of the Annual Conference of the International Association of Mathematical Geosciences, 978-3-00-050337-5

Publ.-Id: 21792 - Permalink


Peculiar behavior of (U,Am)O2−δ compounds for high americium contents evidenced by XRD, XAS, and Raman spectroscopy
Lebreton, F.; Horlait, D.; Caraballo, R.; Martin, P.; Scheinost, A. C.; Rossberg, A.; Jégou, C.; Delahaye, T.;
In U1 xAmxO2±δ compounds with low americium content (x ≤ 20 at.%) and O/M (oxygen to metal) ratios close to 2.0, trivalent Am is charge-balanced by an equivalent amount of pentavalent U while maintaining the fluorite structure of pure U+IVO2. Up to now, it is unknown, whether this observation holds also for higher americium contents. In this study, we combined therefore X-ray diffraction with Raman and X-ray absorption spectroscopies to investigate U0.5Am0.5O2±δ. Our results indicate that americium is again only present as Am+III, while U+V remains below the amount required for charge balance. Contrary to lower americium contents, this leads to an overall oxygen hypo-stoichiometry with an average O/M ratio of 1.92(2). The cationic sublattice is only slightly affected by the coexistence of large amounts of reduced (Am+III) and oxidized (U+V) cations. Significant deviations from the fluorite structure are, however, evidenced by both EXAFS and Raman spectroscopy in the oxygen sublattice, with the coexistence of vacancies and interstitials consistent with the insertion of U6O12 cuboctahedral-type clusters (as observed in the U4O9 or U3O7 phases). These results thus highlight the specificities of uranium-americium mixed oxides, their behavior being closer to that of trivalent-lanthanide-doped UO2 than to that of U1 xPuxO2±δ MOX fuels.
Keywords: MOX fuel 4th generation nuclear reactors transmutation americium

Publ.-Id: 21791 - Permalink


Morphology and Microstructure of Si-SiO2 Nanocomposite Layers
Hübner, R.;
  • Invited lecture (Conferences)
    EFDS-Workshop "Morphologie und Mikrostruktur dünner Schichten und deren Beeinflussung", 12.03.2015, Dresden, Deutschland

Publ.-Id: 21790 - Permalink


Experimental Characterization of Vertical Downward Two-Phase Annular Flows Using Wire-Mesh Sensor
Vieira, R. E.; Parsi, M.; Mclaury, B. S.; Shirazi, S. A.; Torres, C. F.; Schleicher, E.; Hampel, U.;
Annular two-phase flow has been vastly investigated because of its large and deep involvement in industrial processes, particularly in nuclear engineering and petroleum production facilities. Much effort has been devoted to investigating upward flows involving the flow patterns, void fraction, as well as local interfacial characteristics. However, research for vertical downward two-phase flow, especially of the interfacial characteristics, are comparatively scarce. In order to gain insight on void fraction, interfacial structures and characteristics frequencies, experimental work was performed in downward annular two-phase flow with water and air as process fluids at low pressure conditions. A flow loop, including a 76 mm ID, 16.5 m long vertical pipe, has been instrumented. A state2 of-the-art instrument for two-phase flow measurements based on the fluid conductivity, namely dual Wire-Mesh Sensor (WMS) has been utilized to acquire the experimental data. A total of 43 data points have been acquired at superficial liquid velocities that ranged from 0.005 m/s to 0.10 m/s and superficial gas velocities that varied from 10 m/s to 31 m/s. The effects of liquid viscosity on the measured parameters are also investigated using two different viscosities of 1 and 10 cP. Analysis of time series void fraction data from the dual Wire-Mesh sensors allows the determination of cross-sectional averaged void fraction, local time averaged void fraction distribution, liquid phase distribution around the tube periphery, interfacial structure frequencies, pseudo 3D reconstruction as well as Probability Density Function (PDF) and Power Spectral Density (PSD). The experimental results indicate that the interfacial shape and frequencies are significantly altered by the superficial gas velocity. Comparisons between mechanistic model predictions and the acquired experimental data show a maximum absolute average relative error of approximately 7% for the cross-section void fraction.

Publ.-Id: 21789 - Permalink


On the effect of liquid viscosity on interfacial structures within churn flow: experimental study using Wire Mesh Sensor
Parsi, M.; Vieira, R. E.; Torres, C. F.; Kesana, N. R.; Mclaury, B. S.; Shirazi, S. A.; Schleicher, E.; Hampel, U.;
In the churn flow regime, periodical interfacial structures such as liquid slugs and huge waves can coexist and undoubtedly, a phase property such as liquid viscosity can dominate the behavior of these structures. Regrettably, neither are the characteristics of churn flow widely understood nor have the effects of liquid viscosity on gas-liquid flow received enough attention. A Wire Mesh Sensor (WMS) with a 16×16 spatial resolution was employed to discover the effects of liquid viscosity on the behavior of churn flow in a vertical 76.2 mm pipe. Three liquid viscosities of 1, 10, and 40 cP, and superficial liquid velocities of 0.46, 0.61, and 0.76 m/s were employed; whereas, superficial gas velocity ranged from 10 to 27 m/s. Different techniques such as Probability Density Function (PDF), and 2-D and 3-D image reconstruction methods were applied to study the flow. It was noticed that increasing liquid viscosity not only affected the flow pattern but also the appearance frequencies of interfacial structures.
Keywords: Churn Flow; Huge Wave; Wire Mesh Sensor; Multiphase Flow; Liquid Viscosity

Publ.-Id: 21788 - Permalink


Primary and Secondary Beam Stabilization at the ELBE Accelerator Facility
Justus, M.; Jainsch, R.; Kirschke, T.; Lehnert, U.; Michel, P.; Seidel, W.;
Since 2003, ELBE operates as a user facility for fundamental research and life sciences, providing highly brilliant electromagnetic radiation in a broad spectral range, as well as particle beams. The driving source is a 40 MeV, 1 mA electron LINAC in cw mode, utilizing a 13 MHz pulsed thermionic gun and Tesla acceleration technology. Infrared light from two FELs between 3 and 280μm [1] is the foremost secondary radiation used at ELBE. For its applications, different demands in beam stability are put for successful experiments. Therefore, a feedback system for the electron beam position and energy in combination with IR beam intensity feedback using FPGA technology is under development. It is aimed at suppressing beam instabilities caused by thermal behaviour, microphonics and the 50 Hz mains frequency with upper harmonics. This article depicts hardware and software details of the measurement and feedback system and provides first performance results.
Keywords: ELBE, feedback, FEL, stability
  • Open Access LogoContribution to proceedings
    ICALEPCS 2009, 12.-16.10.2009, Kobe, Japan
    Proceedings of ICALEPCS 2009, Geneva: Jacow, 978-4-9905391-0-8
  • Lecture (others)
    ICALEPCS 2009, 12.-16.10.2009, Kobe, Japan

Publ.-Id: 21787 - Permalink


A methodology to quantify the systematic uncertainty in the liquid holdup measurements with Wire Mesh Sensor
Vuong, D.; Aydin, T. B.; Torres, C. F.; Schleicher, E.; Pereyra, E.; Sarica, C.;
The systematic uncertainty in the holdup measurements of a capacitance based WMS has been experimentally evaluated, and a methodology for its quantification is proposed. Tests are conducted in laboratory and in-situ conditions for different mesh grid and pipe inclination angles, and different flow conditions in a high pressure (1.37 MPa) facility with a range of gas and liquid velocity ranges of 2.8 m/s ≤ νSg ≤ 6.9 m/s and 1 cm/s ≤ vSL ≤ 5 cm/s, respectively.
The angle between the phase interface and the sensor wires is ineffective while the pipe inclination angle plays a major role in the deviations of the holdup measurements. Using the proposed methodology, the systematic uncertainty is shown to follow a logarithmic increase as a function of the measured holdup for smaller holdup values (HL ≤ 15%) and to be lower than 1.5% for HL > 15%. This behavior is representative of the systematic uncertainty in the actual flow loop installation.
Under actual flow conditions, the holdup measurements of the trapped liquid by WMS show an Offset compared to the Canty measurements which can be corrected by using the quantified uncertainty in the laboratory tests. Furthermore, the dynamic measurements with WMS show a good agreement with the holdup of the trapped liquid volume within the quantified uncertainty bounds.
Keywords: wire mesh; systematic uncertainty; calibration; two-phase flow

Publ.-Id: 21786 - Permalink


S-layer based nanocomposites for industrial applications
Raff, J.; Matys, S.; Suhr, M.; Vogel, M.; Günther, T.; Pollmann, K.;
This book chapter gives an overview of fundamentals of bacterial S-layers and their use for the production of nano-materials subdivided in the following sections
- What are S-layer?,
- Molecular biology of S-layer proteins,
- General application potential of bacterial S-layers,
- S-layer based coatings and their production,
- New S-layer based nano-materials.
Keywords: S-layers, coatings, nano-materials
  • Book chapter
    Tijana Z. Grove, Aitziber L. Cortajarena: Protein-based Engineered Nanostructures, Heidelberg: Springer-Verlag, 2016, 978-3-319-39194-6, 245-279
    DOI: 10.1007/978-3-319-39196-0

Publ.-Id: 21785 - Permalink


Wechselwirkung von Radiometallen mit biologischen Systemen
Raff, J.; Günther, A.; Moll, H.; Vogel, M.; Drobot, B.; Stumpf, T.;
Metalle interagieren auf vielfältige Art und Weise mit lebenden Organismen. Dies wirkt sich zunächst auf die Metalle selbst aus. Eine veränderte Speziation kann beispielsweise zu einer veränderten Mobilität wie auch zu einer veränderten Bioverfügbarkeit der Metalle in der Umwelt führen. Umgekehrt haben Metalle einen direkten Einfluss auf die Vitalität von Zellen. Neben essentiellen Metallen, die grundlegende Funktionen für den Stoffwechsel erfüllen und damit lebenswichtig sind, gibt es auch toxische Metalle, die den Organismus in höherer Konzentration nachhaltig schädigen können. Radioaktive Metalle, die im Einzelfall nicht nur eine chemische sondern zusätzlich ein radiologische Toxizität aufweisen, können auf Grund der ionisierenden Strahlung Zellbestandteile schädigen oder gar zerstören. Radiometalle können hierbei natürlichen Ursprungs sein oder durch anthropogene Aktivitäten in die Umwelt gelangen. Letzteres umfasst zum Beispiel den Bergbau, die Zementproduktion, die Ausbringung von Phosphatdünger wie auch die störfallbedingte Freisetzung von Radionukliden, Atomwaffentests und die Aufbereitung und Lagerung von radioaktiven Abfällen. Eine Zusammenstellung der wichtigsten Wechselwirkungsmechanismen von Mikroorganismen mit Radiometallen in der Umwelt zeigt nebenstehende Abbildung.
Im Rahmen des Vortrags sollen unterschiedliche Mechanismen auf molekularer Ebene und an Hand von Beispielen ausführlich diskutiert werden. Des Weiteren sollen neben den verschiedenen Varianten einer chemischen Wechselwirkung auch biochemische Effekte in der Zelle berücksichtigt werden. Ziel ist es, auf Basis der unterschiedlichen Wirkungsmechanismen von Radiometallen mit biologischen Systemen, den wechselseitigen Einfluss zum einen auf das Verhalten von Radiometallen in der Umwelt und zum anderen auf den Stoffwechsel von Zellen aufzuzeigen. Die genannten Aspekte sind nicht nur für die Abschätzung der Langzeitsicherheit eines Endlagers für radioaktive Abfälle von Bedeutung, sondern auch für die generelle Abschätzung des Gefährdungspotenzials von Radiometallen für Mensch und Umwelt.
Keywords: Radiometalle, Bioliganden
  • Invited lecture (Conferences)
    GDCh-Wissenschaftsforum Chemie 2015, 30.08.-02.09.2015, Dresden, Deutschland

Publ.-Id: 21784 - Permalink


Dual-modality wire-mesh sensor for visualization of multiphase flows
Dos Santos, E. N.; Vendruscolo, T. P.; Morales, R. E. M.; Schleicher, E.; Hampel, U.; Da Silva, M. J.;
Three-phase gas-liquid-liquid flows are very common in petroleum extraction, production and transport. In this work a dual-modality measuring technique is introduced which may be well applied for gas-liquid-liquid flow visualization. Measuring principle is based on simultaneous excitation with two distinct frequencies to interrogate each crossing point of a mesh sensor which in turn are linked to conductive and capacitive parts of impedance. The developed system can operate 8 transmitter and 8 receiver electrodes at a frame repetition frequency up to 781 Hz. The system has been evaluated by measuring reference components. Deviations to references values are below 10% which considering the fast repetition frequency of measurements is suitable for flow investigation. Furthermore, the developed system was applied to visualize three-phase air-oil-water mixtures in static and dynamic (flowing) conditions, showing that the sensor is a valuable tool to investigate such flows.
Keywords: electrical permittivity; electrical conductivity, dual modality, flow measurement, multiphase flow, petroleum industry

Publ.-Id: 21783 - Permalink


An optimal model for in vivo radiobiological studies with laser driven proton beams?
Beyreuther, E.; Baumann, M.; Brüchner, K.; Karsch, L.; Krause, M.; Laschinsky, L.; Leßmann, E.; Oppelt, M.; Schürer, M.; Wetzig, K.; Pawelke, J.;
  • Poster
    1. Retreat of the National Center for Radiation Oncology (NCRO), 19.-21.03.2015, Heidelberg, Deutschland

Publ.-Id: 21782 - Permalink


In-vivo dosimetry for particle beams - Radiation Physics
Helmbrecht, S.; Iltzsche, M.; Jannusch, P.; Lutz, B.; Priegnitz, M.; Rohling, H.; Römer, K.; Schöne, S.; Schumann, A.; Weinberger, D.; Pausch, G.; Enghardt, W.; Fiedler, F.;
no abstract available
  • Poster
    National Center for Radiation Oncology - 1st Scientific Retreat, 19.-21.03.2015, Heidelberg, Deutschland

Publ.-Id: 21781 - Permalink


Transverse Emittance Compensation
Vennekate, H.; Arnold, A.; Kamps, T.; Kneisel, P.; Lu, P.; Murcek, P.; Teichert, J.; Xiang, R.;
Superconducting RF injectors are promising candidates for the particle sources of future accelerators. While machines like high power free electron lasers or energy recovery linacs are planned to be operated with large duty factors, or even continuous wave mode, to increase the beam intensity, they also demand high beam quality. As this is already determined at the very start of the generation of each particle bunch, the concept of an SRF gun becomes appealing. Transverse Emittance marks the beam quality which is of tremendous relevance for all beam optics and further more sets the level of angular resolution of any scattering experiment performed with the beam. Several concepts to enhance this quality with the lately comissioned Rossendorf SRF Gun II have been presented in recent year’s conferences. The talk will summarize the expended efforts, discuss some of the reflections on installation and operation of the used tools and present preliminary results of the recent achievements.
Keywords: SRF Gun, Emittance, ELBE
  • Lecture (Conference)
    DPG Frühjahrstagung 2015 Wuppertal, 09.-13.03.2015, Wuppertal, Deutschland

Publ.-Id: 21780 - Permalink


Experiments in bubble columns for CFD model validation
Ziegenhein, T.; Rzehak, R.; Lucas, D.;
Bubble columns are widely used in industrial application and are an actual object of research. The performance of a bubble column strongly depends on the characteristic of the flow, which can be modeled with the methods of computational fluid dynamics (CFD). A widely used CFD approach for modeling such dispersed multiphase flows is the Eulerian two-fluid approach.
With the Eulerian two-fluid approach large apparatuses can be simulated in a short time; however, the interaction between the dispersed and the continuous phases has to be modelled with closure models. The closure models refer to different forces and effects, such as drag, lift, virtual mass, turbulent dispersion, coalescence & break up and bubble induced turbulence. The usage of a proper set of closure models is an actual discussion in the scientific community (Rzehak & Krepper 2013) and proper experiments are needed for model validation.
To validate the above mentioned effects that the closure models have to cover, a wide range of experiments are needed. In addition, such experiments should allow measuring the relevant data for a model validation. The must have relevant data are the bubble size distribution, the local void fraction and the liquid velocity at different positions.
In the present study an airlift air-water bubble column, a partially aerated air-water bubble column and an air-NaCl solution bubble column is investigated. The bubble size distribution, the local void fraction and the liquid velocity will be shown at different positions in the bubble column. In addition, a comparison of the experimental results with simulations using an Euler-Euler unsteady Reynolds averaged Navier Stokes equation approach as described in Ziegenhein et al. 2015 is given.
Keywords: Bubble columns, multiphase flow, bubbly flows, particle tracking velocimetry, bubble size measurement, void fraction measurement, Airlift, break-up, coalescence
  • Poster
    Jahrestreffen der Fachgruppen Computational Fluid Dynamics und Mehrphasenströmungen, 19.-20.03.2015, Lüneburg, Deutschland

Publ.-Id: 21779 - Permalink


Prompt-Gamma-Imaging for range verification in proton therapy: Towards clinical implementation
Barczyk, S.; Golnik, C.; Priegnitz, M.; Vander Stappen, F.; Janssens, G.; Smeets, J.; Clementel, E.; Hotoiu, L.; de Xivry, J. O.; Baumann, M.; Enghardt, W.; Fiedler, F.; Krause, M.; Prieels, D.; Pausch, G.; Richter, C.;
No abstract available
  • Poster
    National Center for Radiation Oncology - 1st Scientific Retreat, 19.-21.03.2015, Heidelberg, Deutschland

Publ.-Id: 21778 - Permalink


PGI & PGT Modeling for realistic Patient Treatment Plans
Priegnitz, M.; Rohling, H.; Schumann, A.; Enghardt, W.; Pausch, G.; Fiedler, F.;
No abstract available.
  • Poster
    National Center for Radiation Oncology - 1st Scientific Retreat, 19.-21.03.2015, Heidelberg, Deutschland

Publ.-Id: 21777 - Permalink


Neutron Dose During Proton Therapy
Lutz, B.; Enghardt, W.; Pausch, G.; Fiedler, F.;
Work in progress report about the measurement of the neutron field during proton therapy at OncoRay.
  • Poster
    National Center for Radiation Oncology -- 1st Scientific Retreat, 19.-21.03.2015, Heidelberg, Deutschland

Publ.-Id: 21776 - Permalink


Experimental Characterization of Vertical Gas-Liquid Pipe Flow For Annular and Liquid Loading Conditions Using Dual Wire-Mesh Sensor
Vieira, R. E.; Parsi, M.; Torres, C. F.; Mclaury, B. S.; Shirazi, S. A.; Schleicher, E.; Hampel, U.;
In gas well production, liquid is produced in two forms, droplets entrained in the gas core and liquid film flowing on the tubing wall. For most of the gas well life cycle, the predominant flow pattern is annular flow. As gas wells mature, the produced gas flow rate reduces decreasing the liquid carrying capability initiating the condition where the liquid film is unstable and flow pattern changes from fully cocurrent annular flow to partially cocurrent annular flow. The measurement and visualization of annular flow and liquid loading characteristics is of great importance from a technical point of view for process control or from a theoretical point of view for the improvement and validation of current modeling approaches. In this experimental investigation, a Wire-Mesh technique based on conductance measurements was applied to enhance the understanding of the air-water flow in vertical pipes. The flow test section consisting of a 76 mm ID pipe, 18 m long was employed to generate annular flow and liquid loading at low pressure conditions. A 16×16 wire configuration sensor is used to determine the void fraction within the cross-section of the pipe. Data sets were collected with a sampling frequency of 10,000 Hz. Physical flow parameters were extracted based on processed raw measured data obtained by the sensors using signal processing. In this work, the principle of Wire-Mesh Sensors and the methodology of flow parameter extraction are described. From the obtained raw data, time series of void fraction, mean local void fraction distribution, characteristic frequencies and structure velocities are determined for different superficial liquid and gas velocities that ranged from 0.005 to 0.1 m/s and from 10 to 40 m/s, respectively. In order to investigate dependence of liquid loading phenomenon on viscosity, three different liquid viscosities were used. Results from the Wire-Mesh Sensors are compared with results obtained from previous experimental work using Quick Closing Valves and existing modeling approaches available in the literature.
Keywords: Wire-mesh sensor; gas-liquid flow; void fraction; phase distribution; flow visualization

Publ.-Id: 21775 - Permalink


Exploring photochemistry of uranyl(VI)
Tsushima, S.;
Photoexcited uranyl(VI) is a mild oxidant and can decompose various biological substances including large molecule like DNA. This reaction constitutes another environmental risk of uranium in addition to its radiotoxicity and chemotoxicity. There are several different mechanisms which may lead to decomposition of organic substances by photoexcited uranyl(VI). This includes hydrogen abstraction by “yl”-oxygen, decarboxylation of uranyl-bound carboxylic group, and ligand-to-metal charge transfer. These mechanisms may also compete with each other and makes mechanistic understanding far from being straightforward. In my talk, I will focus on our recent experimental and theoretical development on DNA photocleavage study. Although hydrogen abstraction is widely believed to be the key reaction in uranyl(VI)–mediated photocleavage of DNA, density functional theory calculations show that direct charge transfer from DNA to photoexcited uranyl(VI) can be an alternative pathway that leads to DNA strand break. In the oxidized state of DNA, electron deficiency is centered mainly on guanine as well as on uranyl–free phosphate, and lesser extent is distributed on adenine and thymine. Presumably there is no unique “hot spot” in DNA and upon irradiation local oxidation occurs in nucleobase or in uranyl–free phosphate in the vicinity of uranium. Oxidation of phosphate eventually leads to DNA strand break. Experiments using circular dichroism (CD) and X-ray absorption spectroscopy (XAS) are in progress.
  • Invited lecture (Conferences)
    The International Chemical Congress of Pacific Basin Societies (PACIFICHEM 2015), Symposium on Experimental and Theoretical Actinide Chemistry: From Fundamental Systems to Practical Applications, 15.-20.12.2015, Honolulu, Hawaii, USA

Publ.-Id: 21774 - Permalink


Polymer and cluster chemistry of f-elements in aqueous solutions
Ikeda-Ohno, A.;
Because of their high charge density, the aqueous chemistry of f-elements with lower valences (i.e. tri- and tetravalent) is predominantly controlled by strong hydrolysis producing a variety of hydroxide species. Interestingly enough, this strong hydrolysis often induces the intrinsic formation of polymer and nano-sized cluster complexes which are stable even in aqueous solutions. This seminar will provide a recent overview of the hydrolysis-induced polymer/cluster formation of tetravalent f-elements particularly from the viewpoint of structural chemistry, as well as the associated characterisation techniques (e.g. X-ray absorption spectroscopy or X-ray scattering).
Keywords: actinides, lanthanides, f-elements, hydrolysis, aqueous solution, polymers, clusters, characterisation
  • Invited lecture (Conferences)
    Internal seminar, Institut für Radioökologie und Strahlenschutz, Leibnitz Universität Hannover, 30.04.2015, Hannover, Germany

Publ.-Id: 21773 - Permalink


The effect of magnetic annealing on crystallographic texture and magnetic properties of Fe-2.6%Si
Salih, M. Z.; Uhlarz, M.; Pyczak, F.; Brokmeier, H.-G.; Weidenfeller, B.; Al-Hamdany, N.; Gan, W. M.; Zhong, Z. Y.; Schell, N.;
The effect of magnetic annealing on crystallographic texture ,microstructure, defects density and magnetic properties of a Fe-2.6%Si steel has been analyzed. After two stage cold rolling (75% and 60% cold rolled) with intermediate annealing process at (600 °C/1 h) the sample annealed at 600 °C for one hour during which different magnetic field of 0,7 and 14 T were applied has been investigated. The effect of defects density after cold rolling process on the recrystallization texture and magnetic properties was characterized. Heat treatments under a high external field of14 T show a drastic improvement of the magnetic properties such as significantly increased permeability. Neutron diffraction measurements were preferred for measurement of the bulk sample texture so that sufficient grain statistics were obtained. Because of its small wavelength (0.05–0.2 Å) synchrotron diffraction with high photon energy was used to evaluate the defects density by a modified Williamson–Hall plot.

Publ.-Id: 21772 - Permalink


Inference of phase properties from sorting experiments and MLA data
Matos Camacho, S.; Leißner, T.; Bachmann, K.; van den Boogaart, K. G.;
In the last 20 years the development of new analytical methods and devices provided the possibility of high-resolution data in almost every field of science. Information is much easier to retrieve and in a depth never known before. But often these methods are expensive and a lot of time is needed for proper data acquisition and analysis. For example, in geosciences the Mineral Liberation Analyser (MLA) provides quantitative mineralogical microstructural information. This is a scanning electron microscope with automated software for high resolution images of rock specimen and sample compounds from mineral processing. The information can be used for evaluating the effect of mineral processing on a given ore sample in order to find the optimal processing parameters of each step and predict the overall recovery and grade the requested value minerals.

For example, the magnetic susceptibility of a mineral phase determines its behaviour during magnetic separation. It can be modelled as a linear combination of the susceptibilities of each occurring mineral phase with respect to its mass fraction:
\begin{equation} \label{equ} \overline{\chi_s} = \sum_{i=1}^{n} \frac{m_i}{m_s}\chi_i. \end{equation} (chi_s: susceptibility of the whole sample, chi_i: susceptibility of the i-th mineral phase, m_s: mass of the whole sample, m_i mass of the i-th mineral phase)

Unfortunately, quite often only the susceptibility of the composition can be measured in an experiment due to several reasons, e.g. if the composition consists of too many distinct components and the contained mineral particles consist of several mineral phases. During the separation the sample is split into several classes. The susceptibility can only be measured for such a class.
But we would like to infer the susceptibility for every single mineral phase. The common approach is a linear model, which fails if we have more mineral phases than susceptibility classes found in the experiment.

Our approach uses bootstrapping for constructing new subsamples out of the measured ones. Since every particle has the given mean property, taking such subsamples is like repeating the experiment. This provides a broader base with subsamples having a much higher variability of phase compositions. We repeat this procedure for every susceptibility class.

Furthermore we often do not only have one single value for each class found in the experiment, but a set of them within a certain bounded range. Instead of using the average we arbitrarily assign one of them to each new sample. This additionally prevents us from too many linear dependent equations using (\ref{equ}). We end up in an over-determined system of linear equations. For the solution we use the Moore-Penrose inverse, giving us the possibility to compute an estimation error for every mineral phase relying on the corresponding eigenvalue.

We will discuss simulation results and apply the method to actual experimental data.
Keywords: Geometallurgy, Statistic, MLA, Linear Model
  • Lecture (Conference)
    IAMG 2015, The 17th annual conference of the International Association for Mathematical Geosciences, 05.-13.09.2015, Freiberg, Deutschland
  • Contribution to proceedings
    IAMG 2015, The 17th annual conference of the International Association for Mathematical Geosciences, 07.-10.09.2015, Freiberg, Deutschland
    Proceedings of the 17th annual conference of the International Association for Mathematical Geosciences

Publ.-Id: 21771 - Permalink


Experimental benchmark of an analytical model for prompt gamma imaging
Sterpin, E.; Janssens, G.; Smeets, J.; Vander Stappen, F.; Prieels, D.; Priegnitz, M.; Perali, I.; Vynckier, S.;
A prompt gamma (PG) slit camera prototype recently demonstrated a 1-2 mm accuracy to detect proton range shifts at clinical beam currents by comparing an expected PG detection profile to a measured one. An analytical model has been recently developed to compute the expected profile at practical speed (< 1 s). We present here its benchmark against measurements in heterogeneous phantoms.
  • Lecture (Conference)
    AAPM 2015, 57th Annual Meeting, 12.-16.07.2015, Anaheim, USA
  • Abstract in refereed journal
    Medical Physics 42(2015)6, 3726

Publ.-Id: 21770 - Permalink


Spectroscopic studies on monazite-type ceramics for the conditioning of radioactive waste: Infrared, Raman, X-ray Absorption and Site-Selective Time Resolved Laser Fluorescence Spectroscopy
Neumeier, S.; Arinicheva, Y.; Huittinen, N.; Lozano-Rodriguez, M. J.; Holthausen, J.; Modolo, G.; Scheinost, A. C.; Stumpf, T.; Bosbach, D.;
Monazite ceramics are being considered as potential waste forms for immobilization of minor actinides since they exhibit advantageous properties such as high chemical durability and radiation tolerance.
The overall objective of our study is to reveal the mechanisms of solid solution formation as well as the incorporation of the actinides into the crystal structure of the waste matrix. A fundamental understanding of these mechanisms is of great importance with regard to the long-term stability of monazites for safe nuclear waste disposal.
(La,Eu)PO4 and due to quenching effects of high Eu-contents in TRLFS measurements Eu doped (La,Gd)PO4 monazite solid solutions were synthesized by wet chemical methods. Eu serves as surrogate for trivalent actinides. Samples were characterized by XRD, Raman, IR, EXAFS and TRLFS spectroscopies. Structural refinement of XRD data as well as a linear shift of Raman and IR bands towards higher wave numbers shows a linear dependency of lattice parameters on the Eu content according to Vegard’s law. In contrast, EXAFS analysis reveals a decrease only for the La-O distances in the first coordination shell and the first metal-metal distance, while the Eu-O local coordination remains unchanged. TRLFS investigations show that the host cation size in the monazites has very little influence on the Eu3+ incorporation into these materials, but a broadening of the excitation spectra indicate a local disordering of the crystal structure around the dopant
Keywords: Monazite XRD EXAFS IR TRLFS Europium
  • Invited lecture (Conferences)
    E-MRS Spring Meeting 2015, 11.-15.05.2015, Lille, France

Publ.-Id: 21769 - Permalink


Investigating Spinodal Decomposition and Coarsening using Massively Parallel Kinetic Metropolis Lattice Monte-Carlo Simulations
Kelling, J.; Heinig, K. H.; Gemming, S.;
Nano-structured materials are important for many applications, including energy technologies. The desired structures can be created using bottom-up processes, which utilize self-assembling. By way of spinodal decomposition of a metastable phase, like SiOx into Si and SiO2, sponge-like networks of nanowires can be obtained. Understanding the coarsening kinetics of spinodal structures is crucial not only for bottom-up production, but also helps to increase the life-time of components like porous matrices in fuel cells, where suppression of coarsening has a huge economic impact.

Two theories on coarsening of spinodal structures exist: one assuming diffusion through the bulk [1], the other along interfaces [2]. Since orders of magnitude in both space and time have to be covered by simulations, numerical studies are quite demanding. Nevertheless, simulations are essential in studying systems containing size-inhomogeneities in initial nano-structures, where strongly accelerated coarsening is observed.

Here, a multi-GPU Kinetic Metropolis Lattice Monte-Carlo implementation, capable of atomistic simulations of phase-separation and coarsening at spatio-temporal experimental scales (billions of particles over millions of time-steps) is presented while laying focus on the above-mentioned applications.

[1] A. Chakrabarti, R. Toral, J.D. Gunton, Phys. Rev. B 39(7) 4386 (1989) suggesting a modified Lifschitz-Slyozov law: I.M. Lifshitz, V.V. Slyozov, J. Phys. Chem. Solids 19(1-2), 35-50 (1961)
[2] W.W. Mullins, J. Appl. Phys. 28(3), 333-339 (1957)
Keywords: Nano Structures, GPGPU, Supercomputing, Statistical Physics
  • Lecture (Conference)
    Conference of the Middle European Cooperation in Statistical Physics, 23.-25.03.2015, Esztergom, Hungary

Publ.-Id: 21768 - Permalink


Simulation of Surface Growth and Lattices Gases Using GPUs
Schulz, H.; Kelling, J.; Ódor, G.; Ódor, G.; Ferenc Nagy, M.;
Restricted solid on solid surface growth models can be mapped onto binary lattice gases. We show that efficient simulation algorithms can be realized on GPUs either by CUDA or by OpenCL programming. We consider a deposition/evaporation model following Kardar–Parisi–Zhang growth in d+1 dimensions, related to the Asymmetric Simple Exclusion Process. Up to 100 - 400 x speedup can be achieved with respect to the serial code running on a I5 core. This permits studying disorder and aging behavior in these system.
Keywords: Computational Physics, Supercomputing

Publ.-Id: 21767 - Permalink


Radiobiologial response to ultra-short pulsed MeV electron beams of ultra-high pulse dose rate
Beyreuther, E.; Gotz, M.; Karsch, L.; Laschinsky, L.; Leßmann, E.; Oppelt, M.; Schürer, M.; Pawelke, J.;
  • Poster
    1. Retreat of the National Center for Radiation Oncology (NCRO), 19.-21.03.2015, Heidelberg, Deutschland
  • Poster
    15th International Congress of Radiation Research, 25.-29.05.2015, Kyoto, Japan

Publ.-Id: 21766 - Permalink


GPGPU Powered 3D Simulations of Micro Droplets in Laser-Ion Acceleration
Huebl, A.; Kluge, T.; Hilz, P.; Bussmann, M.;
We present current large scale, full 3D particle-in-cell simulations and studies of laser-ion acceleration utilizing highly over-dense, mass and volume limited micro targets with PIConGPU. Powered by thousands of GPGPUs on Oak Ridge's supercomputer Titan, we show early results such as the influence of the target to laser spot size and the arising acceleration regimes thereof.

The simulations show the capability of PIConGPU, a highly scalable particle-in-cell code for many-core compute architectures that allows for in-situ, real time visualization and ultra-fast computation of large systems.
Keywords: mass-limited targets, PBA, GPGPU, simulation, HPC, laser-ion acceleration
  • Lecture (Conference)
    DPG-Frühjahrstagung: FV Teilchen-, Strahlen- und Medizinphysik, Arbeitskreis Beschleunigerphysik, 09.-13.03.2015, Wuppertal, Deutschland

Publ.-Id: 21765 - Permalink


Low-energy enhancement of M1 strength
Schwengner, R.; Frauendorf, S.; Larsen, A. C.;
Magnetic dipole strength functions have been deduced from averages of a large number of M 1 transition strengths calculated within the shell model for the nuclides 90 Zr, 94Mo, 95 Mo, and 96 Mo. An enhancement of M1 strength toward low transition energy has been found for all nuclides considered. Large M1 strengths appear for transitions between close-lying states with configurations including proton as well as neutron high-j orbits that re-couple their spins and add up their magnetic moments coherently. The M 1 strength function deduced from the calculated M 1 transition strengths is compatible with the low-energy enhancement found in (3He,3He') and (d,p) experiments. The present work presents an explanation of the experimental findings.
Keywords: Strength functions, magnetic dipole strength, shell model.
  • Open Access LogoJournal of Physics: Conference Series 580(2015), 012020
    DOI: 10.1088/1742-6596/580/1/012020
  • Invited lecture (Conferences)
    11th International Spring Seminar on Nuclear Physics: Shell Model and Nuclear Structure - achievements of the past two decades, 12.-16.05.2014, Ischia, Italia

Publ.-Id: 21763 - Permalink


Annual Report 2014 - Institute of Resource Ecology
Stumpf, T.; Foerstendorf, H.; Bok, F.; Richter, A.; (Editors)
The Institute of Resource Ecology (IRE) is one of the eight institutes of the Helmholtz-Zentrum Dresden – Rossendorf (HZDR).
The research activities are mainly integrated into the program “Nuclear Waste Management, Safety and Radiation Research (NUSAFE)” of the Helmholtz Association (HGF) and focused on the topics “Safety of Nuclear Waste Disposal” and “Safety Research for Nuclear Reactors”.
Additionally, various activities have been started investigating chemical and environmental aspects of processing and recycling of strategic metals, namely rare earth elements. These activities are located in the HGF program “Energy Efficiency, Materials and Resources (EMR)”. Both programs, and therefore all work which is done at IRE, belong to the research sector “Energy” of the HGF.
The research objectives are the protection of humans and the environment from hazards caused by pollutants resulting from technical processes that produce energy and raw materials. Treating technology and ecology as a unity is the major scientific challenge in assuring the safety of technical processes and gaining their public acceptance. We investigate the ecological risks exerted by radioactive and nonradioactive metals in the context of nuclear waste disposal, the production of energy in nuclear power plants, and in processes along the value chain of metalliferous raw materials. A common goal is to generate better understanding about the dominating processes essential for metal mobilization and immobilization on the molecular level by using advanced spectroscopic methods. This in turn enables us to assess the macroscopic phenomena, including models, codes, and data for predictive calculations, which determine the transport and distribution of contaminants in the environment.
  • Open Access LogoWissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-059 2015

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Publ.-Id: 21762 - Permalink


Einfluss von Biofilmen auf das Migrationsverhalten von Uran, Americium und Europium in der Umwelt
Baumann, N.; Zirnstein, I.; Arnold, T.;
Die Mechanismen von Immobilisierungsprozessen radioaktiver Schwermetall-Ionen innerhalb von Biofilmen sind noch weitgehend unerforscht. Das liegt an der Komplexität der Biofilme, welche häufig diskrete geochemische Mikromilieus bilden, die sich vom umgebenden Milieu („Bulk Solution“) in Bezug auf dessen Biozönose (der mikrobiellen Diversität), den darin herrschenden geochemischen Bedingung (z.B. Red/Ox-Potential u./o. gelöster Sauerstoffmenge), aber auch in der Konzentration möglicher Komplexbildner (z.B. Metaboliten u./o. EPS-Komponenten) deutlich unterscheiden. Alle diese Faktoren können die Speziation der Radionuklide verändern und damit auch deren Transportverhalten. Für ein besseres Prozessverständnis zu den Wechselwirkungen von Radionukliden mit natürlichen, in Uran-kontaminierten Milieus lebende Mikroorganismen und den damit verbunden Stoffen wurde die Biozönose in Biofilmen und im Grubenwasser des ehem. WISMUT-Uranbergwerkes Königstein nach klassischen mikrobiologischen- und molekularbiologischen Methoden bestimmt. Aus einem Vergleich der Chemie im Biofilm mit der Chemie der umgebenden Lösung wird der Einfluss der Biofilme auf das Migrationsverhalten von Radionukliden in der Natur beurteilt. Die Identifizierung und Quantifizierung von Prokaryoten erfolgte u.a. mit der CARD FISH Methode. Die selektive Visualisierung der EPS-Komponenten in der Matrix der Biofilme wurde mit Hilfe der Konfokalen Laser Scanning Mikroskopie (CLSM) bewerkstelligt.
Zur Untersuchung der Speziation von fluoreszierenden Schwermetall-Ionen wie U(VI) kam die zeitaufgelöste, laser-induzierte Fluoreszenzspektroskopie (TRLFS) zum Einsatz. Um diese Methode auch im mikroskopischen Bereich anwenden zu können, wurde sie weiter zum CLSM hin entwickelt: Da ein 80-MHz-MaiTai-Laser zur Verfügung stand, wurde durch im kHz-Bereich alternierendes Beugen des Anregungslaserstrahls von der Probe weg (und wieder zu ihr hin) mittels akusto-optischem Modulator (AOM) eine quasi-gepulste Laseranregung im kHz-Bereich erreicht. Durch Einbindung von Frequenzvervielfachern („Harmonixx“ von APE Berlin und „Inspire“ von Spectra-Physics) konnte so eine gepulste Anregung innerhalb eines breiten Wellenlängenbereiches (ca. 230-1090 nm) ermöglicht werden. Für die Auswertung des als äußerst schwach zu erwartenden Fluoreszenzsignales (entsprechend des mikroskopisch kleinen Anregungsraumes) wurde die Time-Correlated Single-Photon Counting Methode (TCSPC) – auch „zeitbezügliche Einzelphotonenzählungs-Methode“ – an das Laser-Anregungssystem angepasst. Die Fluoreszenzlebenszeitkurve des Fluoreszenzsignals von U(VI) Species, die sich an der Oberfläche von den Protozoen Euglena Mutabilis befanden, konnte z.B. auf diese Art mit Hilfe der TCSPC ermittelt werden.
  • Open Access LogoWissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-061 2015

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Carrier relaxation dynamics in graphene
Mittendorff, M.;
Graphene, the two-dimensional lattice of sp2-hybridized carbon atoms, has a great potential for future electronics, in particular for opto-electronic devices. The carrier relaxation dynamics, which is of key importance for such applications, is in the main focus of this thesis. Besides a short introduction into the most prominent material properties of graphene and the experimental techniques, this thesis is divided into three main parts.
The investigation of the carrier relaxation dynamics in the absence of a magnetic field is presented in Chapter 3. In the first experiment, the anisotropy of the carrier excitation and relaxation in momentum space was investigated by pump-probe measurements in the near-infrared range. While this anisotropy was not considered in all previous experiments, our measurements with a temporal resolution of less than 50 fs revealed the polarization dependence of the carrier excitation and the subsequent relaxation. About 150 fs after the electrons are excited, the carrier distribution in momentum space gets isotropic, caused by electron-phonon scattering. In a second set of two-color pump-probe experiments, the temperature of the hot carrier distribution, which was obtained within the duration of the pump pulse (about 200 fs), could be estimated. Furthermore, a change in sign of the pump-probe signal can be used as an indicator for the Fermi energy of different graphene layers. Pump-probe experiments in the far-infrared range in reflection and transmission geometry were performed at high pump power. A strong saturation of the pump-induced transmission was found in previous experiments, which was attributed to the pump-induced change in absorption. Our investigation shows the strong influence of pump-induced reflection at long wavelengths, as well as a lot smaller influence of the saturation of the pump-induced change in absorption. At a high pump power, the increase of the reflection exceeds the change in absorption strongly, which leads to negative pump-probe signals in transmission geometry.
In Chapter 4, investigations of the carrier dynamics of graphene in magnetic fields of up to 7T are presented. Even though the optical properties of Landau-quantized graphene are very interesting, the carrier dynamics were nearly unexplored. A low photon energy of 14meV allows the investigation of the intraband Landau-level (LL) transitions. These experiments revealed two main findings: Firstly, the Landau quantization strongly suppresses the carrier relaxation via optical-phonon scattering, resulting in an increased relaxation time. Secondly, a change in sign of the pumpprobe signal can be observed when the magnetic field is varied. This change in sign indicates a hot carrier distribution shortly after the pump pulse, which means that carrier-carrier scattering remains very strong in magnetic fields. In a second set of pump-probe measurements, carried out at a photon energy of 75meV, the relaxation dynamics of interband LL transitions was investigated. In particular, experiments on the two energetically degenerate LL transitions LL−1 ) LL0 and LL0 ) LL1 showed the influence of extremely strong Auger processes.
An ultrafast and extremely broadband terahertz detector, based on a graphene flake, is presented in the last chapter of this thesis. To couple the radiation efficiently to the small flake, the inner part of a logarithmic periodic antenna is connected to it. With a rise time of about 50 ps in a wavelength range of 9 μm to 500 μm, this detector is very interesting to obtain the temporal overlap in two-color pump-probe experiments with the free-electron laser FELBE. Furthermore, the importance of the substrate material, in particular for the high-speed performance, is discussed.
  • Open Access LogoWissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-057 2015

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