Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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35836 Publications

Fit-for-purpose analytics for resource technology?

Dreßler, S.; Gurlit, S.; Merchel, S.; Michalak, P. P.; Renno, A. D.; Sazonov, A. M.; Schenk, F.; Sterba, J. H.

Along the value chain (exploration, mining, processing, recycling) generally solid samples of complex matrix and non-stoichiometric composition need to be analysed. Besides spatially-resolved analytics applied to technology development, bulk analytics is mainly used for characterisation of value components.
In the search of the best-suited method, there are important questions to answer at first:
1. What is already known about the sample (matrix, stability, solubility, interferences)?
2. What data are needed (quantitative, semi-quantitative or qualitative)?
3. Are the concentrations of the elements of interest at a major, minor or trace level?
4. How urgently are the data needed and what are the financial restraints?
Here, two different projects are selected to demonstrate a typical search for fit-for-purpose analytics spanning from commonly available Inductively Coupled Plasma Mass Spectrometry (ICP-MS) to more rarely applied Instrumental Neutron Activation Analysis (INAA). These are two examples of primary and secondary raw materials (intermediate goods and waste), which would open possibilities for side products of critical metals, e.g. REE, PGE, Re, Ga.
The first project deals with a natural mineral sample of molybdenite (MoS2) taken from an open pit mine in Kačaran (Armenia) in use for Mo and by-product Re mining. Rhenium is important for catalytic and petrochemical industry, metallurgy, and aviation, e.g. it is used for steel reinforcement in turbine blades for aircrafts [1,2].
The second project focus on secondary raw materials from the non-bauxitic production of aluminium and alumina in Siberia. The analysed materials were taken from different stages of the production process: The final product alumina (Al2O3), waste products like red mud (mainly calcium carbonate and SiO2), sodium salts (e.g. Na2SO4) and anode slag (carbon, Cu-Al alloy, Al) and by-products like wollastonite ceramics (CaSiO3) and soda-potash (K2CO3/Na2CO3).
Of course, there are pros and cons of every analytical method (Total Reflection X-ray Fluorescence (TXRF), ICP-MS, INAA) for different samples yielding to clear conclusions about the best-suited method for future analytical tasks. For example in the case of Re, INAA is identified as method of choice for such kind of analysis due to high sample throughput, an easy and quick sample preparation and a low detection limit (0.26 μg/g).

[1] A. Brumby, M. Verhelst, D. Cheret, Catalysis today. 2005, 106, 166-169.
[2] C. Zhan-Fang, Z. Hong, Q. Zhao-hui, Hydrometallurgy. 2009, 97, 153-157.

Keywords: Resource Technology; raw materials; INAA; Re; aluminium production

  • Poster
    GDCh-Wissenschaftsforum Chemie 2015, 30.08.-02.09.2015, Dresden, Deutschland

Publ.-Id: 21955

Herstellung und Reinigung von n.c.a. 88Y am Leipziger Zyklotron Cyclone® 18/9

Mansel, A.; Franke, K.

Die Abteilung „Reaktiver Transport“ der Forschungsstelle Leipzig beschäftigt sich mit dem Migrations-/Sorptionsverhalten von (Schad)stoffen in geologischen Formationen. In aktuellen Projekten werden partikuläre, kolloidale, gelöste und komplexierte, toxische und radiotoxische Stoffe in Batch- und Säulenstudien sowie Extraktionsverfahren für seltene Metalle untersucht. Bei der eingesetzten Radiotracertechnik kommen kurzlebige, nicht kommerziell erhältliche Radionuklide zum Einsatz. Am Leipziger Zyklotron Cyclone® 18/9 neu implementiert ist die 88Y-Herstellung (T1/2 = 106,6 d) durch Protonenbeschuss von Strontium mit natürlicher Isotopenzusammensetzung via 88Sr(p,n)88Y[1-3]. Das Target wird durch Verpressen von ca. 30 mg Strontiumcarbonat in eine Aluminiumhalterung hergestellt. Die Bestrahlung erfolgt bei einem Protonenstrom von 3 µA, einer Strahlzeit von 2 Stunden und einer Projektilenergie von ca. 12 MeV. Die chemische Aufarbeitung des bestrahlten Strontiumcarbonats erfolgte erstmals durch Ionenchromatographie mit LN-Resin-A (TrisKem Int.) aus salpetersaurer Lösung[4-5]. N.c.a. (no-carrier-added) 88Y wird mit einer radiochemischen Ausbeute von 95 % ± 4 % erhalten. Der entwickelte Trennungsgang dient zur Vorbereitung für die Produktion und Aufarbeitung des kurzlebigen Radionuklids 86Y (T1/2 = 14,7 h; Iβ+ = 31,9 %) für die Positronen-Emissions-Tomographie (PET) durch Bestrahlung von isotopenangereichertem 86Sr.

[1] S. A. Kandil, B. Scholten, K. F. Hassan, H. A. Hanafi, S. M. Qaim, J. Radioanal. Nucl. Chem. 2009, 279, 823. [2] K. Kettern, K.-H. Linse, S. Spellerberg, H. H. Coenen, S. M. Qaim, Radiochim. Acta 2002, 90, 845. [3] N. P. van der Meulen, T. N. van der Walt, G. F. Steyn, F. Szelecsenyi, Z. Kovacs, C. M. Perrang, H. M. Raubenheimer, Appl. Radiat. Isot. 2009, 67, 1320. [4] E. P. Horwitz, C. A. A. Bloomquist, J. Inorg. Nucl. Chem. 1975, 37, 425. [5] C. Pin, J. F. S. Zalduegui, Anal. Chim. Acta 1997, 339, 79.

  • Poster
    GDCh Jahrestagung 2015, Fachgruppe Nuklearchemie, 30.08.-02.09.2015, Dresden, Deutschland

Publ.-Id: 21952

Efficient Large Scale Simulation of Stochastic Lattice Models on GPUs

Kelling, J.; Ódor, G.; Heinig, K.-H.; Gemming, S.

With growing importance of nano-patterned surfaces and nano-composite materials in many applications from energy technologies to nano-electronics, a thorough understanding of the self-organized evolution of nano-structures needs to be established. Modelling and simulations of such processes can help in this endeavor and provide predictions for the turnout of manufacturing processes.

In this talk GPGPU-enabled implementations of two stochastic lattice models will be discussed, shedding light on the complications which arise when simulations of stochastic processes are to make efficient use of massively parallel GPU architectures.
A single-GPU implementation of the (2+1)-dimensional Roof-Top-model allows very precise large-scale studies of surface growth processes in the Kardar-Parisi-Zhang universality class.[1] Furthermore a multi-GPU enabled version of the 3d kinetic Metropolis lattice Monte-Carlo method[2] provides the capability to study the evolution of nano-structures both towards and out-of-equilibrium at spatio-temporal scales of experiments using only small to medium-sized GPU clusters.

[1] J. Kelling, G. Ódor Extremely large-scale simulation of a Kardar-Parisi-Zhang model using graphics cards, Physical Review E 84, 061150 (2011)
[1] J. Kelling, G. Ódor, F. Nagy, H. Schulz, K. Heinig Comparison of different parallel implementations of the 2+1-dimensional KPZ model and the 3-dimensional KMC model, The European Physical Journal - Special Topics 210, 175-187 (2012)

  • Lecture (others)
    Seminar Topical Problems, 06.05.2015, Chemnitz, Deutschland
  • Invited lecture (Conferences)
    GPU Day 2015 - The Future of Many-Core Computing in Science, 20.-21.05.2015, Budapest, Hungary
  • Lecture (others)
    Seminar, 18.11.2015, Coventry, United Kingdom

Publ.-Id: 21951

Effect of rotating magnetic field on the microstructures and physical properties of Al-Cu-Co ternary eutectic alloy

Cadirli, E.; Kaya, H.; Räbiger, D.; Eckert, S.; Gündüz, M.

The solidification microstructures and physical properties of Al-Cu-Co ternary eutectic alloy were studied in a rotating magnetic field (RMF). The RMF-driven flow was the key factor causing grain refinement and uniformity of solidification microstructures. The temperature distributions during solidification were recorded under the conditions with and without RMF. The dependence of the eutectic spacing (λ) the microhardness (HV), tensile strength (σt) and compressive strength (σc) on the RMF were investigated. Electrical resistivity (ρ) measurements of the studied alloy were also performed by using the four-point probe method and the dependence of the resistivity on temperature and RMF were determined. Besides, the enthalpy (ΔH) and the specific heat (Cp) values were determined by the DSC analysis. Important changes were found in the microstructure, microhardness, tensile strength, compressive strength and electrical resistivity of the studied alloy with increasing RMF.

Keywords: rotating magnetic field; microstructure; microhardness; tensile strength; compressive strength; electrical resistivity

Publ.-Id: 21950

Terahertz response of patterned epitaxial graphene

Sorger, C.; Preu, S.; Schmidt, J.; Winnerl, S.; Bludov, Y. V.; Peres, N. M. R.; Vasilevskiy, M. I.; Weber, H. B.

We study the interaction between polarized terahertz (THz) radiation and micro-structured large-area graphene in transmission geometry. In order to efficiently couple the radiation into the two-dimensional material, a lateral periodic patterning of a closed graphene sheet by intercalation doping into stripes is chosen. We observe unequal transmittance of the radiation polarized parallel and perpendicular to the stripes. The relative contrast, partly enhanced by Fabry-Perot oscillations reaches 20 %. The effect even increases up to 50% when removing graphene stripes in analogy to a wire grid polarizer. The polarization dependence is analyzed in a large frequency range from <80 GHz to 3 THz, including the plasmon-polariton resonance. The results are in excellent agreement with theoretical calculations based on the electronic energy spectrum of graphene and the electrodynamics of the patterned structure.

Keywords: Graphene; plasmonics

Publ.-Id: 21949

Lifetime-limited, subnanosecond terahertz germanium photoconductive detectors

Deßmann, N.; Pavlov, S. G.; Pohl, A.; Abrosimov, N. V.; Winnerl, S.; Mittendorff, M.; Zhukavin, R. K.; Tsyplenkov, V. V.; Shengurov, D. V.; Shastin, V. N.; Hübers, H.-W.

The recombination times of photo-excited free charge carriers in heavily doped and highly compensated germanium are studied by a time-resolved pump-probe experiment at a frequency of 3THz. The dominant dopant in the germanium samples is either antimony (n-Ge:Ga:Sb) or gallium (p-Ge:Sb:Ga) with compensating doping levels close to 100%. The recombination time of the free charge carriers measured by our pump-probe technique varies between 30 and 300 ps. It decreases with increasing pump pulse energy and increasing compensation due to high concentrations of Coulomb recombination centers. The recombination times at low pump powers are up to ten times shorter than those previously obtained for low-compensated n-Ge:Sb and p-Ge:Ga. The photoconductive detector made from this material shows the response time is in the order of its recombination time.

Keywords: photoconductive detector; THz detector; fast detector

Publ.-Id: 21948

SIKELOR - Silicon kerf loss recycling

Cramer, A.; Eckert, S.; Lombardi, I.; Dughiero, F.; Forzan, M.; Bojarevics, V.; Pericleous, K.; Kroschk, M.; Steinbach, H.

During slicing silicon block casts to wafers, about 50 % of the valuable material is lost into saw dust. The objective of the EU project SIKELOR is to process such silicon waste in an industrially viable and resource-friendly manner. To be competitive to virgin feedstock, maximum cumulative recycling costs of 10 $/kg are imposed as the economic goal.

Keywords: Ressources; solar silicon; recycling; electromagnetic processing of materials

  • Contribution to proceedings
    8th International Workshop on Crystalline Silicon for Solar Cells, 05.-08.05.2015, Bamberg, Deutschland
    Book of extended abstracts
  • Poster
    8th International Workshop on Crystalline Silicon for Solar Cells, 05.-08.05.2015, Bamberg, Deutschland

Publ.-Id: 21947

Ion bombardment and light irradiation driven modifications of magnetic nanostructures

Maziewski, A.; Kisielewski, J.; Kurant, Z.; Mazalski, P.; Sveklo, I.; Tahir, N.; Jakubowski, M.; Wojciechowski, T.; Wawro, A.; Fassbender, J.; Stobiecki, F.

Much attention is paid to magnetic nanostructures due to their intrigiung properties and different applications. Appearance of perpendicular magnetic anisotropy (PMA) when a magnetic layer thickness is decreased and a giant magneto-resistance effect are the most interesting effects. Tuning the magnetic domain sizes in a broad range (several orders of magnitude) by changing PMA, the geometrical parameters of the nanostructure, as well as by an applied external magnetic field is observed, see the review [1]. Patterned nanostructures with PMA are prospective for e.g.: mass memories together with magnetic ratchet memories, magnetic field sensors, spin wave applications.
A decrease of PMA as a result of the ion irradiation of the metallic ultrathin films, has been usually reported [2]. However we have recently shown that, Ga+ ion irradiation drives creation of the out-of-plane magnetization states, dependent on the ion fluence [3,4]. Irradiation with Ga+, Ar+, He+ ions results in an increase of magnetooptical effects and changes the coercivity field. We have also found that femtosecond light pulses induce: (i) reversible PMA changes which can be used to trigger magnetization oscillations [4] and (ii) irreversible PMA modifications [5] due to creation of out-of-plane magnetization states for low and high light power densities, respectively. Ion/light irradiation affecting magnetic and magnetooptical properties of nanostructures is a promising approach for new patterning purposes. Such desired modifications can be realized with fluence/energy densities lower than that reqired for the nanostructure surface etching. Moreover, using e.g. focused ion beam technique, lateral patterning can be performed with a nanometer precision. New metamaterials such as magnonic and magnetophotonic crystals or controllable transport of magnetic beads can be created in this way.

This work was supported by: National Science Center in Poland under the project HARMONIA Nr 2012/06/M/ST3/00475 and Foundation for Polish Science under the SYMPHONY project (Polish Science Team Programme, European Regional Development Fund, OPIE 2007–2013.

[1] A. Maziewski, et al., Phys. Status Solidi A, 211, 1005 (2014).
[2] H. Bernas (Ed.), Materials Science with Ion Beams, Vol. 116 (Springer-Verlag, Berlin, Berlin, 2010).
[3] A. Maziewski, et al., Phys. Rev. B 85, 054427 (2012).
[4] M. Sakamaki et al., Phys. Rev. B 86, 024418 (2012).
[4] J. Kisielewski, et al., Phys. Rev. B 85 (2012) 184429.
[5] J. Kisielewski, et al., Journal of Applied Physics 115, 053906 (2014).

Keywords: Ion bombardment and light irradiation driven modifications of magnetic nanostructures

  • Lecture (Conference)
    7th Polish Conference on Nanotechnology, 25.06.2015, Poznan, Poland

Publ.-Id: 21946

Ultrathin films: Light and ions irradiations induced changes of magnetic properties

Kisielewski, J.; Kisielewski, M.; Kurant, Z.; Mazalski, P.; Stupakiewicz, A.; Sveklo, I.; Tekielak, M.; Wawro, A.; Fassbender, J.; Maziewski, A.

When decreasing ultrathin film thickness d, an increase of the perpendicular magnetic anisotropy (PMA) occurs, resulting in the magnetization reorientation phase transition (RPT) from the in-plane to out-of-plane magnetization state below the critical thickness dRPT. The results of combined experimental, analytical, and micromagnetic simulations studies on the evolution of magnetization states and processes in ultrathin films and multilayered systems [1] will be presented. Possibilities of tuning the magnetic domain sizes in a broad range (of several orders of magnitude) by changing the geometrical parameters of the nanostructure, as well as by an applied external magnetic field will be discussed. Transitions between two- and three-dimensional magnetization distributions will be shown.
As a result of the ion irradiation of the metallic ultrathin films, a decrease of PMA was usually reported [2]. Contrariwise, Ga+ ion irradiation driven creation of the out-of-plane magnetization states, dependent on ion fluence, have been found [3]. Similarly, femtosecond light pulses of high energy density may also induce irreversible enhancement of PMA [4], while low energy density pulses can be used to trigger the magnetization oscillations, via reversible thermal changes of the magnetic anisotropy [5].
1. A. Maziewski, J. Fassbender, J. Kisielewski, M. Kisielewski, Z. Kurant, P. Mazalski, F. Stobiecki, A. Stupakiewicz, I.Sveklo, M.Tekielak, A.Wawro, and V. Zablotskii, Magnetization states and magnetization processes in nanostructures: From a single layer to multilayers, Phys. Status Solidi A, 211, 1005 (2014).
2. H. Bernas (Ed.), Materials Science with Ion Beams, Vol. 116 (Springer-Verlag, Berlin, Berlin, 2010).
3. A. Maziewski, P. Mazalski, Z. Kurant, M. O. Liedke, J. McCord, J. Fassbender, J. Ferré, A. Mougin, A. Wawro, L. T. Baczewski, A. Rogalev, F. Wilhelm, and T. Gemming, Tailoring of magnetism in Pt/Co/Pt ultrathin films by ion irradiation, Phys. Rev. B 85, 054427 (2012).
4. J. Kisielewski, W. Dobrogowski, Z. Kurant, A. Stupakiewicz, M. Tekielak, A. Kirilyuk, A. Kimel, Th. Rasing, L. T.Baczewski, A. Wawro, K. Balin, J. Szade, and A. Maziewski, Irreversible modification of magnetic properties of Pt/Co/Pt ultrathin films by femtosecond laser pulses, Journal of Applied Physics 115, 053906 (2014),
5. J. Kisielewski, A. Kirilyuk, A. Stupakiewicz, A. Maziewski, A. Kimel, Th. Rasing, L. T. Baczewski, and A. Wawro, Laser-induced manipulation of magnetic anisotropy and magnetization precession in an ultrathin cobalt wedge, Phys. Rev. B 85 (2012) 184429.

Keywords: Ultrathin films: Light and ions irradiations induced changes of magnetic properties

  • Lecture (Conference)
    50. Zakopane School of Physics Breaking Frontiers: Submicron Structures in Physics and Biology, 18.05.2015, Zakopane, Poland

Publ.-Id: 21945

Synthese und Evaluierung von [18F]NS14490 für die Bildgebung von α7 nikotinischen Acetylcholinrezeptoren im Gehirn mit Positronen-Emissions-Tomographie

Rötering, S.

Neurodegenerative Erkrankungen werden mit Veränderungen der Expressionsdichte α7 nikotinischer Acetylcholinrezeptoren in Verbindung gebracht. Dieser Rezeptor ist folglich ein interessantes Target für die molekulare Bildgebung mit Positronen-Emissions-Tomographie (PET). In der vorliegenden Arbeit werden die Synthese sowie eine Evaluierung von [18F]NS14490, ([18F]2-(1,4-Diazabicyclo[3.2.2]nonan-4-yl)-5-(1-(2-fluoroethyl)-1H-indol-6-yl)-1,3,4-oxadiazol) als neuer, potentieller Radioligand vorgestellt. Für die Radiosynthese wurden zwei Strategien verfolgt: Zum einen wurde Ethylenglykolditosylat mit [18F]Fluorethyltosylat umgesetzt und anschließend mit NS14540, einem am Indolstickstoffatom unsubstituierten Derivat zu [18F]NS14490 umgesetzt. Gleichzeitig wurden synthetisierte Präkursoren für eine direkte Radiofluorierung eingesetzt. Nach umfangreichen Arbeiten zur Isolierung und Reinigung des Radioliganden mit semipräparativer HPLC und Festphasenextraktion sowie der Formulierung folgten Untersuchungen zur Stabiltität des Radioliganden in Puffersystemem bei pH = 7 und in Schweineplasma, die Bestimmung der Lipophilie und erste Versuche zur Extraktion aus Schweineplasma.
Die In-vivo-Evaluierung des Radioliganden setzt sich aus der Bestimmung der Anreicherung des Radioliganden im Gehirn von Mäusen und Schweinen sowie der Metabolitenanalyse von Plasmaproben und Hirnhomogenaten (Maus) und in der Metabolitenanalyse von Plasmaproben (Schwein) während dynamischer PET-Aufnahmen zusammen. Der Radioligand hatte im Plasma in Mäusen eine höhere Stabilität als in Schweinen und lag im Mäusehirn nahezu unmetabolisiert vor.
Der 2. Teil dieser Arbeit beschäftigt sich mit der Aufbereitung von bestrahltem [18O]H2O zur Wiederverwendung bei der Produktion von [18F]F. 1 Liter bestrahltes [18O]H2O wurde durch Oxidation organischer Lösungsmittel mit KMnO4 und NaOH bei 50 °C oder durch Bestrahlung mit 254 nm sowie anschließender Tieftemperatur-Vakuumdestillation zur Abtrennung von Rückständen aufbereitet. Die Charakterisierung des [18O]Wassers zeigte nur geringe Restkontaminationen durch Ionen (unterer mg-l−1-Bereich) und eine nahezu abreicherungsfreie Aufbereitung. Die Durchführung von Modellexperimenten mit künstlich kontaminierten [16O]H2O gab Hinweise auf eine fast quantitative Rückgewinnung des Wassers.
Die Bestrahlung von aufbereitetem [18O]H2O und der Vergleich der Produktionsaktivitäten mit (verdünntem) [18O]Originalwasser sowie der unproblematische Einsatz des [18F]F in radiochemischen Synthesen unterstreichen die Qualität des Aufbereitungsprozesses.

Keywords: 18Fluor; α7 nikotinische Acetylcholinrezeptoren; Präkursoren; Aufbereitung von [18O]Wasser; Positronen-Emissions-Tomographie

  • Doctoral thesis
    Universität Leipzig, Fakultät für Chemie und Mineralogie, 2015
    Mentor: Prof. Dr. Thorsten Berg
    158 Seiten

Publ.-Id: 21944

On the accuracy of wire-mesh sensors in dependence of bubble sizes and liquid flow rates

Nuryadin, S.; Ignaczak, M.; Lucas, D.; Deendarlianto

An experimental study to assess the accuracy of wire-mesh sensors in dependence of bubble sizes and flow rates has been performed in a 50 mm x 50 mm transparent rectangular channel. The liquid superficial velocities were ranging from 0 m/s up to 0.62 m/s with the obtained bubble size ranging from 3 mm to 7 mm. A single wire-mesh sensor with 16 x 16 electrode wires was used with a temporal and spatial resolution of 10 kHz and 3.1 mm (lateral distance between two wires), respectively. Single bubbles with known bubble size, subsequently called reference bubble size, was injected into the test section via bubble injector approx. 25 cm upstream of the wire-mesh sensor. The bubble size measurement by using wire-mesh sensor cannot be obtained directly since it requires the information of bubble velocity which is not available only by installing a single sensor. Therefore, a stereoscopic observation was conducted to obtain the bubble velocity by tracking the successive frames as well as to study the intrusiveness of the sensor. This configuration gave an advantage that the registered bubble will be assigned with its real approach velocity and a better agreement is expected. As the result, a direct comparison of all individual bubbles with the reference bubble size showed an agreement within ±10%. However, a deceleration effect was found for low superficial and observed to disappear as the liquid superficial velocity increased then vanish at observed JL = 0.62 m/s.

Keywords: wire-mesh sensor; bubble size; bubble velocity; bubble flow

Publ.-Id: 21943

Magnetic anisotropy and magnetic Phase transitions in RFe5Al7

Gorbunov, D. I.; Yasin, S.; Andreev, A. V.; Skourski, Y.; Mushnikov, N. V.; Rosenfeld, E. V.; Zherlitsyn, S.; Wosnitza, J.

RFe5Al7 (R – Gd, Tb, Dy, Ho, Er and Tm) single crystals have been studied by measurements of magnetization, sound propagation (in static and pulsed magnetic fields up to 60 T) and specific heat. Fundamental magnetic properties have been determined and compared for all these materials. RFe5Al7 are highly anisotropic ferrimagnets. Spontaneous and field-induced magnetic phase transitions of anisotropic and exchange nature have been observed in RFe5Al7. Strong magnetoelastic interactions are manifested by pronounced acoustic anomalies at the phase transformations. The detected magnetization jumps provide important information on the R–Fe inter-sublattice exchange interactions.

Publ.-Id: 21942

Pulsed high-magnetic-field experiments: New insights into the magnetocaloric effect in Ni-Mn-In Heusler alloys

Salazar Mejia, C.; Ghorbani Zavareh, M.; Nayak, A. K.; Skourski, Y.; Wosnitza, J.; Felser, C.; Nicklas, M.

The present pulsed high-magnetic-field study on Ni50Mn35In15 gives an extra insight into the thermodynamics of the martensitic transformation in Heusler shape-memory alloys. The transformation-entropy change, ΔS, was estimated from field-dependent magnetization experiments in pulsed high magnetic fields and by heat-capacity measurements in static fields. We found a decrease of ΔS with decreasing temperature. This behavior can be understood by considering the different signs of the lattice and magnetic contributions to the total entropy. Our results further imply that the magnetocaloric effect will decrease with decreasing temperature and, furthermore, the martensitic transition is not induced anymore by changing the temperature in high magnetic fields.

Publ.-Id: 21941

Uncertainty Analysis of an Interfacial Area Reconstruction Algorithm and its application to Two Group Interfacial Area Transport Equation Validation

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) (Lucas et al., 2010; Beyer et al., 2008; Prasser et al., 2003) 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 (Ishii 2010). IATE models are still under development and the HZDR WMS experimental data provide an excellent basis for the validation and further advance of these models. The current paper is focused on the uncertainty analysis of algorithms used to reconstruct interfacial area densities from the void-fraction voxel data measured using WMS and their application towards validation efforts of two-group IATE models.
In previous research efforts, a surface triangularization algorithm has been developed in order to estimate the surface area of individual bubbles recorded with the WMS, and estimate the interfacial area in the given flow condition. In the present paper, synthetically generated bubbles are used to assess the algorithm’s accuracy. As the interfacial area of the synthetic bubbles are defined by user inputs, the error introduced by the algorithm can be quantitatively obtained. The accuracy of interfacial area measurements is characterized for different bubbles sizes and shapes, and for different WMS acquisition frequencies. It is found that while convex shapes are successfully analyzed by the reconstruction algorithm, some difficulties are faced with bubbles presenting internal cavities.
Utilizing the experimental HZDR database, 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: Wire mesh sensor; two-phase flow; interfacial area transport equation

  • Invited lecture (Conferences)
    Japan-U.S. Seminar on Two-Phase Flow Dynamics, 10.-15.05.2015, West Lafayette, USA
  • Nuclear Engineering and Design 310(2016), 620-637
    DOI: 10.1016/j.nucengdes.2016.10.038

Publ.-Id: 21940

Upbend and M1 scissors mode in in neutron-rich nuclei - consequences for r-process (n,γ) reaction rates

Larsen, A. C.; Goriely, S.; Bernstein, L. A.; Bleuel, D. L.; Bracco, A.; Brown, B. A.; Camera, F.; Eriksen, T. K.; Frauendorf, S.; Giacoppo, F.; Guttormsen, M.; Görgen, A.; Harissopulos, S.; Leoni, S.; Liddick, S. N.; Naqvi, F.; Nyhus, H. T.; Rose, S. J.; Renstrøm, T.; Schwengner, R.; Siem, S.; Spyrou, A.; Tveten, G. M.; Voinov, A. V.; Wiedeking, M.

An enhanced probability for low-energy -emission (upbend, E < 3 MeV) at high excitation energies has been observed for several light and medium-mass nuclei close to the valley of stability. Also the M1 scissors mode seen in deformed nuclei increases the γ-decay probability for low-energy γ-rays (E < 2­ - 3 MeV). These phenomena, if present in neutron-rich nuclei, have the potential to increase radiative neutron-capture rates relevant for the r-process. The experimental and theoretical status of the upbend is discussed, and preliminary calculations of (n,γ) reaction rates for neutron-rich, mid-mass nuclei including the scissors mode are shown.

Keywords: Electromagnetic strength functions; low-energy enhancement; scissors mode; neutron-capture rates; r-process

Publ.-Id: 21939

Ultrafast X-ray computed tomography for phase distribution and velocity measurements in multiphase flows

Bieberle, M.; Wagner, M.; Barthel, F.; Rabha, S.; Banowski, M.; Hampel, U.

Various flow measurement and visualization techniques are based on optical and laser-based methods. However, in many multiphase flow situations, e.g. at higher interfacial density or in flows with internals, the optical access is no longer given. Radiation based methods are in principle able to penetrate most of these systems, but are normally too slow to capture the dynamics of the flow. With ultrafast X-ray tomography a flow visualization and measurement technique has been developed, which is able to recover the dynamic phase distributions in various multiphase flow scenarios. The high imaging rate is achieved by deflecting an electron beam along a circular target, where a moving X-ray spot is generated. Tomographic projections are gathered simultaneously by a static detector ring with fast read-out. Thus, no components of the X-ray tomography system have to be rotated mechanically. The reconstructed tomography slices represent the non-superimposed phase distribution within a cross-section as a function of time. Up to 8,000 fps can be achieved in single plane mode. For velocity measurements, a second set of X-ray target and detector ring arranged at a small axial distance can be included to form the so-called dual plane mode. Although the alternating scanning of both planes reduces the frame rate by a factor of two, the benefit of combining the information from both planes to retrieve velocity information arises directly. There are different ways to extract velocity information from the two stacks of slice image data. Cross-correlation techniques offer the opportunity to retrieve time averaged as well as time resolved local or global velocities of the disperse phase. Some systems also allow the determination of single bubble or particle velocities, provided that they can be identified as the same object in both planes.

Keywords: ultrafast; X-ray CT; multiphase flows; velocity; phase distribution

  • Contribution to proceedings
    10th Pacific Symposium on Flow Visualization and Image Processing, 15.-18.06.2015, Napoli, Italia
    Proceedings of 10th Pacific Symposium on Flow Visualization and Image Processing
  • Lecture (Conference)
    10th Pacific Symposium on Flow Visualization and Image Processing, 15.-18.06.2015, Napoli, Italia

Publ.-Id: 21938

Environmental risks induced by elevated thorium contents in the complex rare earth elements deposit Strange Lake, Québec (Canada): Mineralogical investigations

Brombacher, L. C.; Kempe, U.; Möckel, R.; Heide, G.; Gutzmer, J.

The Strange Lake pluton is situated on the northern border between Québec and Labrador in northeastern Canada. The ore-body, located within a complex peralkaline granite-hosted system of pegmatites and aplites, contains elevated concentrations of both LREE and the highly coveted HREE, as well as other HFSE (high field strength elements, such as Zr, Nb, Y, Ti, and Th). The REE mineralization, however, is extremely complex and the elements of interest are variably distributed between various “exotic” minerals from different mineral classes that may also contain considerable amounts of unwanted impurities such as thorium, uranium and beryllium. Naturally occurring radioactive materials (NORM) like Th may be concentrated during beneficiation, thus constituting a serious hazard to the workers and the environment. In order to limit transportation and storage of hazardous material during production, it is of the company’s interest to separate these deleterious constituents early in or at best in advance to the extraction process. This study focuses on the characterization of the mineral phases that primarily host thorium for early recognition. Combined chemical and structural analyses indicate that there is one particular mineral phase in which Th is present in highly elevated concentrations. This mineral is best described as a metamict Th-silicate occurring in isolated, rounded grains enclosed in quartz. Further studies are required to indicate if this mineral can be separated early during minerals processing from the ore without considerable loss of valuable REE.

Keywords: rare earth elements; peralkaline complex; exotic minerals; thorium mineralogy

  • Contribution to proceedings
    Problems of use of natural resources - International forum of young scientists, 22.-24.04.2015, St. Petersburg, Russland
    Environmental risks induced by elevated thorium contents in the complex rare earth elements deposit Strange Lake, Québec (Canada): Mineralogical investigations, 978-5-94511-723-8

Publ.-Id: 21937

Improving external beam radiotherapy by combination with internal irradiation.

Dietrich, A.; Koi, L.; Zöphel, K.; Sihver, W.; Kotzerke, J.; Baumann, M.; Krause, M.

The efficacy of external beam radiotherapy (EBRT) is dose dependent, but the dose that can be applied to solid tumour lesions is limited by the sensitivity of the surrounding tissue. The combination of EBRT with systemically applied radioimmunotherapy (RIT) is a promising approach to increase efficacy of radiotherapy. Toxicities of both treatment modalities of this combination of internal and external radiotherapy (CIERT) are not additive, as different organs at risk are in target. However, advantages of both single treatments are combined, for example, precise high dose delivery to the bulk tumour via standard EBRT, which can be increased by addition of RIT, and potential targeting of micrometastases by RIT. Eventually, theragnostic radionuclide pairs can be used to predict uptake of the radiotherapeutic drug prior to and during therapy and find individual patients who may benefit from this treatment. This review aims to highlight the outcome of pre-clinical studies on CIERT and resultant questions for translation into the clinic. Few clinical data are available until now and reasons as well as challenges for clinical implementation are discussed.

Publ.-Id: 21936

Production of no-carrier-added 135La at an 18 MeV cyclotron and its purification for investigations at a concentration range down to 10-15 mol/L

Mansel, A.; Franke, K.

The production of non-commercially available 135La by proton irradiation of an isotopically enriched [135Ba]BaCO3 target at a cyclotron is described. The purification of the radionuclide was performed by a La-selective resin. 135La was separated in no-carrier-added (n.c.a) form in a nitric acid solution with a radiochemical yield of 83% ± 5% and a total activity per batch of 43 MBq ± 3 MBq. The enriched [135Ba]Ba was recycled to the carbonate form with a recovery of 90% ± 3%. On the basis of a detection limit of 1 Bq/ml, solutions of n.c.a. 135La could be measured down to the 10-15 mol/l concentration range.

Keywords: Lanthanum-135; Isotopically enriched Barium-135 target; Proton induced nuclear reaction; Chemical separation; LN-Resin-A

Publ.-Id: 21935

Co-doping GaMnP with Zinc and Carbon

Hentschel, H.; Khalid, M.; Yuan, Y.; Helm, M.; Zhou, S.

Spintronics appears to be a new and exciting field of technology, but there is still a lag of suitable materials. In principle magnetic semiconductors (DMS) would be an excellent choice, but even their highest reached Curie temperature (Tc) in GaMnAs is still too low for practical usage. Ferromagnetism in DMS is suggested to be holes according to the Zener-Model. Therefore, it is expected to increase Tc by adding additional holes, e.g. co-doping. But there is a high risk to induce more defects, especially interstitial Mn atoms. Indeed, previous investigation revealed a lower Tc in carbon codoped GaMnAs [1]. Ion Implantation followed by laser annealing might overcome this problem. We choose ferromagnetic GaMnP since it shows insulating behavior [2]. Co-doping with shallow acceptors may lead to a more pronounced change in the conductivity of GaMnP. The samples were investigated with SQUID-VSM and Hall-Effect measurement. First results do not show an increase in Tc. Structural analysis is in progress to check if more defects appear upon carbon codoping.
[1] G. M. Schott, et al., Appl. Phys. Lett. 85, 4678 (2004).
[2] M. A. Scarpulla, et al., Phys. Rev. Lett., 95, 207204 (2005).

Keywords: DMS; Co-Doping; GaMnP

  • Lecture (Conference)
    79. Jahrestagung der DPG und DPG-Frühjahrstagung, 15.-20.03.2015, Berlin, Deutschland

Publ.-Id: 21934

Carbon p Electron Ferromagnetism in SiC Single Crystal

Wang, Y.; Liu, Y.; Wang, G.; Anwand, W.; Jenkins, C. A.; Arenholz, E.; Munnik, F.; Gordan, O. D.; Salvan, G.; Zahn, D. R. T.; Chen, X.; Gemming, S.; Helm, M.; Zhou, S.

Defect induced ferromagnetism has been reported in wide-bandgap semiconductors as well as in carbon-based materials, when defects are introduced in an appropriate way. It is desirable to establish a direct relation between such ferromagnetism and defects. Here, we succeed to reveal the origin of defect-induced ferromagnetism using SiC by X-ray magnetic circular dichroism (XMCD). In addition, the theoretical model is calculated by first-principles theory. We show that the long-range ferromagnetic coupling is due to the p electrons of the nearest-neighbor carbon atoms around VSiVC divacancies. Thus, the ferromagnetism is traced down to its microscopic, electronic origin.

Keywords: XMCD; defect-induced ferromagnetism; SiC

  • Lecture (Conference)
    79. Jahrestagung der DPG und DPG-Frühjahrstagung, 15.-20.03.2015, Berlin, Germany

Publ.-Id: 21933

The PARIS cluster coupled to the BaFPro electronic module: data analysis from the NRF experiment at the γELBE facility

Wasilewska, B.; Bednarczyk, P.; Boiano, C.; Brambilla, S.; Camera, F.; Ciemala, M.; Dorvaux, O.; Giaz, A.; Jastrzab, M.; Kihel, S.; Kmiecik, M.; Maj, A.; Matea, I.; Massarczyk, R.; Mazumdar, I.; Mentana, A.; Napiorkowski, P.; Sowicki, B.; Schwengner, R.; Riboldi, S.; Zieblinski, M.

The first cluster of the constructed PARIS calorimeter was assembled and tested at the ELBE facility at HZDR, Dresden, Germany. The experiment was aimed at the evaluation of the performance of each detector separately as well as the whole PARIS cluster with discrete gamma-ray energies seen by the PARIS ranging up to 8.9 MeV. As the detectors use phoswich configuration, with 2'' x 2'' x 2'' LaBr3 (Ce) crystal coupled to 2'' x 2'' x 6'' NaI(Tl) one, great care must be taken during the data analysis process to obtain the best possible values for energy resolution. Two algorithms for data transformation from matrices created with slow vs fast pulse shaping to energy spectra were tested from which one was chosen for further analysis. An algorithm for adding back energies of -rays scattered inside the cluster was prepared, as well. Energy resolution for gamma-rays in 2­8 MeV range was estimated and is presented in this paper.

Keywords: LaBr3 detectors; NaI detectors; bremsstrahlung

Publ.-Id: 21931

Influence of calcium onto the sorption of uranium(VI) in the far-field of nuclear waste repositories

Richter, C.

Sorption of uranium(VI) onto orthoclase and muscovite, representing feldspars and micas as important components of the earth crust, was investigated in presence and absence of calcium under aerobic conditions. Batch experiments accompanied by time-resolved laser-induced fluorescence spectroscopy (TRLFS) were performed. A reduction of the U(VI) sorption by calcium at pH ≥ 8 due to the formation of the Ca2UO2(CO3)3 complex was observed. An evaluation of the spectroscopic results by PARAFAC indicates the formation of three surface species ≡SiO2UO20, ≡SiO2UO2OH– and ≡SiO2UO2OHCO33–. The results improve the basis for a mechanistic modeling of the sorption onto orthoclase and muscovite, which is important for long-term safety analysis of waste repositories.

  • Lecture (Conference)
    Petrus PhD Conference 2015, 22.-26.06.2015, Nancy, France

Publ.-Id: 21930

Synthesis and Biodistribution Studies of 3H- and 64Cu-labeled Dendritic Polyglycerol and Dendritic Polyglycerol Sulfate

Pant, K.; Gröger, D.; Bergmann, R.; Pietzsch, J.; Steinbach, J.; Graham, B.; Spiccia, L.; Berthon, F.; Czarny, B.; Devel, L.; Dive, V.; Stephan, H.; Haag, R.

Dendritic polyglycerol sulfate (dPGS) is a biocompatible, bioactive polymer which exhibits anti-inflammatory activity in vivo and thus represents a promising candidate for therapeutic and diagnostic applications. To investigate the in vivo pharmacokinetics in detail, dPGS with a molecular weight of ca. 10 kDa was radiolabeled with 3H and 64Cu, and evaluated by performing biodistribution studies and small animal positron emission tomography (PET). 3H-labeling was accomplished by an oxidation-reduction process with sodium periodate and [3H]-borohydride. 64Cu-labeling was achieved by conjugation of isothiocyanate- or maleimide-functionalized copper(II)-chelating ligands based on 1,4-bis(2-pyridinylmethyl)-1,4,7-triazacyclononane (DMPTACN) to an amino functionalized dPGS scaffold, followed by reaction with an aqueous solution containing 64CuCl2. Independent biodistribution by radioimaging and PET imaging studies with healthy mice and rats showed that the neutral dPG was quantitatively renally eliminated, whereas the polysulfated analogs accumulated mainly in the liver and spleen. Small amounts of the dPGS derivatives were slowly excreted via the kidneys. The degree of uptake by the reticuloendothelial system (RES) was similar for dPGS with 40% or 85% sulfation, and surface modification of the scaffold with the DMPTACN chelator did not appear to significantly affect the biodistribution profile. On the basis of our data, the applicability of bioactive dPGS as a therapeutic agent might be limited due to organ accumulation even after 3 weeks. The inert characteristics and clearance of the neutral polymer, however, underlines the potential of dPG as a multifunctional scaffold for various nanomedical applications.

Publ.-Id: 21929

Bibliotheksservices für Mitarbeiter des VKTA

Reschke, E.

VKTA-MitarbietrInnen sind externe Bibliotheksbenutzer. Im Vortrag werden die für externe Benutzer verfügbaren Bibliotheks- und Informationsservices vorgestellt.

Keywords: Library; Information services; Research Portal; eJournals; eBooks; Data bases

  • Lecture (others)
    VKTA-Leitungskreissitzung, 28.04.2015, Dresden-Rossendorf, Deutschland

Publ.-Id: 21928

K*(892)+ production in proton-proton collisions at Ebeam=3.5 GeV

Agakishiev, G.; Arnold, O.; Balanda, A.; Belver, D.; Belyaev, A. V.; Berger-Chen, J. C.; Blanco, A.; Böhmer, M.; Boyard, J. L.; Cabanelas, P.; Chernenko, S.; Dybczak, A.; Epple, E.; Fabbietti, L.; Fateev, O. V.; Finocchiaro, P.; Fonte, P.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzon, J. A.; Gernhäuser, R.; Göbel, K.; Golubeva, M.; Gonzalez-Diaz, D.; Guber, F.; Gumberidze, M.; Heinz, T.; Hennino, T.; Holzmann, R.; Ierusalimov, A.; Iori, I.; Ivashkin, A.; Jurkovic, M.; Kämpfer, B.; Karavicheva, T.; Koenig, I.; Koenig, W.; Kolb, B. W.; Kornakov, G.; Kotte, R.; Krasa, A.; Krizek, F.; Krücken, R.; Kuc, H.; Kühn, W.; Kugler, A.; Kurepin, A.; Ladygin, V.; Lalik, R.; Lang, S.; Lapidus, K.; Lebedev, A.; Liu, T.; Lopes, L.; Lorenz, M.; Maier, L.; Mangiarotti, A.; Markert, J.; Metag, V.; Michalska, B.; Michel, J.; Müntz, C.; Naumann, L.; 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.; Siebenson, J.; 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.; Vasiliev, V.; Wagner, T.; Weber, M.; Wendisch, C.; Wüstenfeld, J.; Yurevich, S.; Zanevsky, Y. V.

Results on the K*(892)+ production in proton-proton collisions at a beam energy of E = 3.5 GeV, which is hitherto the lowest energy at which this mesonic resonance has been observed in nucleon-nucleon reactions, are presented. The data are interpreted with a two-channel model that includes the 3-body production of K*(892)+ associated with the Λ- or Σ-hyperon. The relative contributions of both channels are estimated. Besides the total cross section σ(p + p -> K*(892)+ + X) = 9.5 +- 0.9 +1.1 -0.9 +- 0.7 μb, that adds a new data point to the excitation function of the K*(892)+ production in the region of the low excess energy, transverse momenta and angular spectra are extracted and compared with the predictions of the two-channel model. The spin characteristics of K*(892)+ are discussed as well in terms of the spin-alignment.

Publ.-Id: 21927

A novel inclined rotating tubular fixed bed reactor concept for enhancement of reaction rates and adjustment of flow regimes

Härting, H.-U.; Lange, R.; Larachi, F.; Schubert, M.

The inclined rotating tubular fixed bed reactor has been introduced recently as a novel reactor concept for multiphase processes, especially for heterogeneously catalyzed gas–liquid reactions with a mass transfer limitation of the gas phase (Härting et al., 2015; DOI: It is based on the adjustment of a beneficial gas–liquid distribution in the cross section of the fixed bed that allows for complete utilization of the fixed bed accompanied by periodic wetting and draining of the catalyst.
The hydrodynamics in gas–liquid co-current downflow are studied by applying a compact gamma-ray computed tomography system for different organic liquids and gas phase properties as well as various fixed bed packing materials. Four different flow regimes with stratified, sickle, annular and dispersed flow patterns are identified. Pressure drop and liquid saturation are presented as a function of reactor inclination and rotation.
Inclination of the reactor is applied to force phase separation and the superimposed rotation of the clamped fixed bed results in a favorable wetting intermittency via periodic catalyst immersion. A significant rate enhancement of the hydrogenation of alpha-methylstyrene to cumene under severe limitations of the mass transfer of the gas phase is observed in the novel reactor concept at separated flow conditions. In addition, the potential for an efficient quenching of hotspots for exothermic reactions is demonstrated.

Keywords: Heterogeneous catalysis; Hydrogenation; Process intensification; Multiphase flow; Reactor inclination; Rotating fixed bed

Publ.-Id: 21926

Triadic resonances in numerical simulations of a precessing cylinder

Giesecke, A.

In the framework of the project DRESDYN (DREsden Sodium facility for DYNamo and thermohydraulic studies) a next generation dynamo experiment is under construction at the Helmholtz-Zentrum Dresden-Rossendorf. In this experiment a fluid flow of liquid sodium in a cylindrical container, solely driven by precession, is considered as a possible source for magnetic field generation.

Precession has long been discussed as a complementary energy source for driving the geodynamo, and dynamo action generated by precession driven flows has been found in various numerical simulations in a sphere, ellipsoid, cube and cylinder. In the current study we perform hydrodynamic simulations of the three-dimensional non-linear Navier-Stokes equation in cylindrical geometry including weakly precessional forcing. The main focus is put on the development of the non-axisymmetric time-dependent instabilities that could be responsible for dynamo action like triadic resonances.

Our simulations reveal clear triads at aspect ratios and frequencies close to predictions from the linear inviscid theory with an amplitude below the forced m=1 mode so that most of the flow energy remains in the fundamental forced mode. Next step will be kinematic simulations in order to test the ability of the triades to provide for dynamo action.

Keywords: dynamo

  • Lecture (Conference)
    Stellar and Planetary Dynamos, 26.-29.05.2015, Goettingen, Germany

Publ.-Id: 21925

Low-remanence criterion for helicity-dependent all-optical magnetic switching in ferrimagnets

Hassdenteufel, A.; Schmidt, J.; Schubert, C.; Hebler, B.; Helm, M.; Albrecht, M.; Bratschitsch, R.

We demonstrate that a low-remanent sample magnetization MR is crucial for all-optical magnetic switching (AOS) in ferrimagnets and ferrimagnet heterostructures. MR may be devised by the composition of the material. However, it can also be controlled in situ by changing the sample temperature because it affects MR. We show that increasing the lattice temperature by laser pulses or a simple heating resistor enables AOS in a ferrimagnetic Tb-Fe film, which does not exhibit AOS at room temperature. We reconcile earlier contradicting results for AOS in heated and cooled magnetic films by applying the low-remanence criterion. It also applies to other existing rare-earth transition-metal (RE-TM) alloys, such as GdFeCo or Tb-Co, to ferrimagnet heterostructures, and to RE-free synthetic ferrimagnets.

Keywords: remanence; all optical magnetic switching; helicity aos

Publ.-Id: 21924

Nanoscale modulated magnetization patterns for reproducible configurational and switchable static and dynamic properties films

McCord, J.; Trützschler, J.; Langer, M.; Mattheis, R.; Fassbender, J.

Domain wall (DW) imprinting in spatially varying magnetic property thin films is a novel method to obtain thin films with new effective magnetic characteristics ranging from static to dynamic applications. In order to generate such effective material systems, light ion irradiation is an advantageous method allowing for, e. g. laterally modified exchange bias (EB) directions, making the imprinting of artificial magnetic DW patterns possible. The magnetically hybrid structures with different unidirectional anisotropy directions are unique as, e.g. a domain pattern and domain walls can be imprinted directly into the magnetic material. A reproducible nucleation and positioning of magnetic domain walls in a high density arrangement is achieved. In dependence of the applied magnetic field amplitude, the system allows for an additional defined adjustment of the magnetic configuration with varying effective magnetic anisotropy.
Extended Ni19Fe81(50nm)/Ir23Mn77(7nm) thin films with an initial unidirectional anisotropy are patterned by local He-ion irradiation in the presence of a magnetic field, which is aligned perpendicular to the initial unidirectional anisotropy, and by which hybrid magnetization patterns with two different types of modulated directions of EB are obtained. The stripe width of the patterned thin films is varied down to 500 nm by one order of magnitude, being well below the distance of the magnetic Néel wall tails. The influence of the overlapping DW structures on the effective static and dynamic magnetization properties of the thin films are investigated by complementary inductive static and dynamic methods, magneto-resistive measurement techniques, by magneto-optical microscopy, and are as well supported by matching micromagnetic simulations. By this, a complete picture of spatial and temporal evolution of magnetization is derived.
In a zig-zag or head-to-tail configuration a folded magnetization forms (Fig.1), in which the magnetization is modulated along the magnetic net direction perpendicular to the stripes. In an alternating head-to-head/tail-to-tail configuration charged DWs form, favoring a modulated magnetization with low angle head-to-head and tail-to-tail configurations. In all cases the remanent magnetization along the net-magnetization of the films increases with decreasing feature size. The fixed position of the artificial DWs leads to pronounced two staged quasi-static magnetization reversal and, accordingly, different dynamic magneto-static modes are excited in the magnetic meta-material (Fig. 2).
We show that precessional frequencies of magnetic thin films can be directly influenced by means of high density DW imprinting (up to 104 DWs/sample). The static and dynamic magnetic response is tuned by imprinting periodic DW patterns with overlapping DW structures through selective ion irradiation. Mode coupling via dynamic magnetic charges in the periodically modulated magnetization patterns is directly provoked by adjusting the micromagnetic interface density. At the transition from the saturated magnetic phase to the domain wall phase the permeability spectra exhibit a pronounced discontinuous jump in the dynamic response, making an abrupt switch between two different dynamic states achievable. We show that the controlled introduction of micromagnetic DW objects is a unique way to tailor the effective magnetic properties of magnetic thin films. Dependencies of magnetic field angle, stripe-width and orientation of EB will be discussed.

Funding from the German Science Foundation DFG through (MC9/7-2; FA314/3-2) and the Heisenberg programme of the DFG (MC9/9-1) is highly acknowledged.

Keywords: Domain Walls; Exchange Bias; Ion Irradiation

  • Lecture (Conference)
    Intermag 2015, 11.-15.05.2015, Beijing, China

Publ.-Id: 21923

Über die Lorentzkraft-getriebene dreidimensionale Strömung um eine magnetische Kugel in einem elektrischen Feld

Weier, T.; Landgraf, S.; Cierpka, C.

Im Hinblick auf die in Deutschland beschlossene Energiewende ist die effiziente Energiespeicherung für die Netzstabilität enorm wichtig. Insbesondere für die Langzeitspeicherung gibt es zur Nutzung chemischer Energieträger, vor allem von Wasserstoff und Methanol auf Wasserstoffbasis, kaum Alternativen. Die notwendigen Prozessketten sind jedoch beim Strom-zu-Strom-Wirkungsgrad alternativen Speichertechniken deutlich unterlegen. Bei der Wasserstoffelektrolyse entstehen Wasserstoff- und Sauerstoffblasen. Diese verringern die Leitfähigkeit des Elektrolyten sowie die effektive Elektrodenoberfläche, was die Effizienz limitiert. Eine signifikante Effizienzsteigerung der Wasserstoffelektrolyse wird daher durch gezielt beschleunigtes Abtragen der Wasserstoffblasen von den Elektrodenoberflächen erwartet. In diesem Zusammenhang wurde in der jüngsten Vergangenheit die Beeinflussung der wandnahen Konvektionsströmung durch elektromagnetische Volumenkräfte, d.h. Lorentzkräfte, untersucht. Dazu stand bisher der makroskopische Einfluss der Lorentzkraft auf die Gesamtströmung im Vordergrund der Arbeit. Für eine genaue Analyse der durch die Volumenkräfte hervorgerufenen Effekte muss das Geschwindigkeitsfeld in der flüssigen Phase – insbesondere um die Gasblase – vermessen werden. Im vorliegenden Beitrag werden nominell parallele elektrische und magnetische Felder betrachtet. Da die Gasblasen nicht elektrisch leitend sind, werden die elektrischen Feldlinien abgelenkt und durch das Kreuzprodukt aus magnetischer Flussdichte und elektrischer Feldstärke entsteht eine Volumenkraft in unmittelbarer Umgebung der Blase. Da die Strömung um eine reale Einzelblase (d ~ 50 mum) messtechnisch schwer zu erfassen ist, sollen die grundlegenden Phänomene an einem größeren Modell untersucht werden.
Die sich einstellende Drehströmung wurde mittels der 2D2C Particle Image Velocimetry in mehreren Ebenen charakterisiert. Anschließend wurde die dreidimensionale Strömung mittels der 3D3C Astigmatism Particle Tracking Velocimetry zeitaufgelöst vermessen, um Partikeltrajektorien im Volumen zu verfolgen. Im finalen Beitrag wird die sich einstellende Strömung anhand der 2D2C/3D3C Ergebnisse neben der Darstellung der beiden Messverfahren ausführlich diskutiert.

Keywords: Lorentzkraft; Elektrolyse; Astigmatsim Particle Tracking Velocimetry; Particle Image Velocimetry

  • Lecture (Conference)
    Lasermethoden in der Strömungsmesstechnik, 08.-10.09.2015, Dresden, Deutschland
  • Contribution to proceedings
    Lasermethoden in der Strömungsmesstechnik, 08.-10.09.2015, Dresden, Deutschland
    Proceedings der 23. GALA-Fachtagung "Lasermethoden in der Strömungsmesstechnik", 978-3-9816764-1-9, 18-1-18-8

Publ.-Id: 21922

A step closer to the CW high brilliant beam with SRF gun II

Xiang, R.; Arnold, A.; Michel, P.; Murcek, P.; Teichert, J.; Lu, P.; Vennekate, H.

In order to achieve CW electron beam with a high average current up to 1 mA and a very low emittance of 1 um, an improved superconducting photoinjector (SRF Gun II) has been installed and commissioned at HZDR since 2014. This new gun replaces the first 3.5-cell SRF gun at the SC Linac ELBE. The RF performance of the niobium cavity has been evaluated, the transverse and longitudinal beam parameters for low charge bunches have been measured, and the first beam has been guided into the ELBE beam line. The results agree with the simulation very well. The photocathode transfer system has been installed for the first high current beam test planned in 2015. In this contribution the results of the commissioning and the first beam parameters will be presented in detail.

  • Poster
    6th International Particle Accelerator Conference (IPAC'15), 03.-08.05.2015, Richmond, USA
  • Open Access Logo Contribution to proceedings
    6th International Particle Accelerator Conference (IPAC'15), 03.-08.05.2015, Richmond, USA
    Proceedings of IPAC'15, CERN: JACoW

Publ.-Id: 21921

Photocathodes for High Brightness Photo Injectors

Xiang, R.; Teichert, J.

The development of the photo-injector has become a significant technology for the future light sources and the electron-ion collider. There are a lot of opportunities to improve the electron source quality, also for the photocathodes. Especially for the high average power gun producing up to mA level of average current, the searching for the better photocathodes is a principal technical challenge. The photocathodes used in the electron gun require four important aspects: high efficiency, long life time, small transverse emittance and prompt time response. The quantum efficiency (QE) needs to be made more reliable, and the cathode material must be more robust. Thus there is a strong motivation to push the cathode R&D: one hand is to modify the present cathodes; the other hand is to search new materials.
In this presentation, we focus on the photocathode research for high brightness gun, DC or RF/SRF guns. There are several types of cathodes, such as the metallic photocathodes, the semiconductor photocathodes, and the recent superconducting (SC) cathodes and the new plasma-enhanced cathodes. The “conventional” normal conducting (NC) metallic photocathodes, such as Cu or Mg, are most robust for RF guns, but their QEs are pitifully very low, mostly on the level of 10-5. The semiconductor photocathodes, alkali antimonides, III-V GaAs(Cs), Cs2Te, have the best QE up to 1~10% but critical working environment is required. Among them, Cs2Te is relative robust and can be used in most of RF/SRF guns. And Cs2KSb achieves the highest current record 65mA in Cornell DC gun. The SC photocathodes consisting of Nb and Pb have been well investigated but the drive laser requirement is more challenging.

  • Lecture (Conference)
    LA³NET: The Laser Applications at Accelerators Conference 2015, 25.-27.03.2015, Mallorca, Spain
  • Open Access Logo Physics Procedia 77(2015), 58-65
    Online First (2015) DOI: 10.1016/j.phpro.2015.11.010

Publ.-Id: 21920

Status and running experience of the SRF gun at HZDR

Xiang, R.; Arnold, A.; Lu, P.; Murcek, P.; Teichert, J.; Vennekate, H.

In order to achieve a high average current up to 1 mA with a low emittance of 1 mm
mrad at 77 pC, an improved SRF gun has been installed and commissioned at HZDR since 2014. This new gun replaces the first 3.5-cell SRF gun at the superconducting linear accelerator ELBE which had been in operation since 2007. The new gun has been tested first with a Cu photocathode. The RF performance of the niobium cavity has been evaluated, the transverse and longitudinal beam parameters for low charge bunches have been measured, and the first beam has been guided into the ELBE beamline. The photocathode transfer system is also installed for the first high current beam test in 2015. In this contribution the status of the gun and the results of this first measurement period will be presented in detail.

  • Lecture (Conference)
    DPG Frühjahrstagung 2015, 09.-13.03.2015, Wuppertal, Deutschland

Publ.-Id: 21919

The Tayler instability at low magnetic Prandtl numbers: between chiral symmetry breaking and helicity oscillations

Weber, N.; Galindo, V.; Stefani, F.; Weier, T.

The Tayler instability is a kink-type, current driven instability that plays an important role in plasma physics but might also be relevant in liquid metal applications with high electrical currents. In the framework of the Tayler-Spruit dynamo model of stellar magnetic field generation, the question of spontaneous helical (chiral) symmetry breaking during the saturation of the Tayler instability has received considerable interest. Focusing on fluids with low magnetic Prandtl numbers, for which the quasistatic approximation can be applied, we utilize an integro-differential equation approach in order to investigate the saturation mechanism of the Tayler instability. Both the exponential growth phase and the saturated phase are analyzed in terms of the action of the α and β effects of mean-field magnetohydrodynamics. In the exponential growth phase we always find a spontaneous chiral symmetry breaking which, however, disappears in the saturated phase. For higher degrees of supercriticality, we observe helicity oscillations in the saturated regime. For Lundquist numbers in the order of one we also obtain chiral symmetry breaking of the saturated magnetic field.

Keywords: Tayler instability; chiral symmetry breaking; helicity oscillation; Tayler Spruit dynamo

Publ.-Id: 21917

Validation of high-resolution gamma-ray computed tomography for quantitative gas holdup measurements in centrifugal pumps

Bieberle, A.; Schäfer, T.; Neumann, M.; Hampel, U.

In this paper, the capability of high-resolution gamma-ray computed tomography (HireCT) for quantitative gas-liquid phase distribution measurements in fluid machines is experimentally investigated. The object of interest thereby is an industrial centrifugal pump, which operates under two-phase flow conditions. The HireCT-System comprises a collimated 137Cs isotopic source, a radiation detector arc with a multi-channel signal processing unit, and a rotary unit enabling CT scans of objects with diameters of up to 700 mm. The accuracy of gas holdup measurement was validated on a sophisticated modular test mockup replicating defined gas-liquid distributions, which are expectable in impeller chambers of industrial centrifugal pumps under two-phase operation. Stationary as well as rotation-synchronized CT scanning techniques have been analyzed, which are both used to obtain sharply resolved gas phase distributions in rotating structures as well as non-rotating zones. A measuring accuracy of better than 1% for various distributed static gas holdups in the rotating frame has been verified with the modular test mockup using HireCT.

Keywords: Two-phase flow; gamma-ray computed tomography; gas holdup and centrifugal pump

Publ.-Id: 21916

Investigations of the interactions of subsurface living microorganisms with uranium

Gerber, U.; Krawczyk-Bärsch, E.; Anrold, T.

Actually the former uranium mine Königstein (Saxony, Germany) is in process of controlled flooding. Despite the high uranium concentrations of up to 14 mg/L and the low pH of 3,0 a high biodiversity was detected within this flooding water. Microorganisms are very important for bioremediation of uranium contaminated environments from activities such as uranium mining and extraction or fuel fabrication. Due to their ability to interact with radionuclides and heavy metals microorganisms could help to clean up the contaminated water in Königstein. With a culture dependent method it was possible to isolate different microorganisms from the flooding water. Tolerance tests displayed high resistances to uranium of these natural isolates. Furthermore uranium immobilization experiments show high rates of uranium binding to the cells. Some of the isolates are able to remove nearly 100% of the initial added uranium. TEM analysis showed two different interaction mechanisms, biosorption to the cell membrane and bioaccumulation within the cell.

Keywords: Uranium immobilization; Bioremediation; Königstein

  • Lecture (others)
    3. Workshop – TransAqua, 20.-21.04.2015, Bremen, Deutschland

Publ.-Id: 21915

Lithological control on gas hydrate saturation as revealed by signal classification of NMR logging data

Bauer, K.; Kulenkampff, J.; Henninges, J.; Spangenberg, E.

In this paper, nuclear magnetic resonance (NMR) downhole logging data are analyzed with a new strategy to study gas hydrate-bearing sediments in the Mackenzie Delta (NW Canada). In NMR logging, T2 distribution curves are usually used to determine single-valued parameters such as apparent total porosity or hydrocarbon saturation. Our approach analyzes the entire T2 distribution curves as quasi-continuous signals to characterize the rock formation. We apply self-organizing maps, a neural network clustering technique, to sub-divide the data set of NMR curves into classes with a similar and distinctive signal shape. The method includes (1) preparation of data vectors, (2) unsupervised learning, (3) cluster definition, and (4) classification and depth mapping of all NMR signals. Each signal class thus represents a specific pore size distribution which can be interpreted in terms of distinct lithologies and reservoir types. A key step in the interpretation strategy is to reconcile the NMR classes with other log data not considered in the clustering analysis, such as gamma ray, hydrate saturation and other logs. Our results defined six main lithologies within the target zone. Gas hydrate layers were recognized by their low signal amplitudes for all relaxation times. Most important, two sub-types of hydrate-bearing shaly sands were identified. They show distinct NMR signals and differ in hydrate saturation and gamma ray values. An inverse linear relationship between hydrate saturation and clay content was concluded. Finally, from the interpretations of the classified NMR signals we infer a non-cementing, pore-filling growth habit for the gas hydrates.

Keywords: gas hydrates; NMR logging; self-organizing maps; shaliness; Mackenzie Delta

Publ.-Id: 21914

Investigations of the interactions of subsurface living microorganisms with uranium

Gerber, U.; Krawczyk-Bärsch, E.; Arnold, T.; Kothe, E.

Actually the former uranium mine Königstein (Saxony, Germany) is in process of controlled flooding. Despite the high uranium concentrations of up to 14 mg/L and the low pH of 3,0 a high biodiversity was detected within this flooding water. Microorganisms are very important for bioremediation of uranium contaminated environments from activities such as uranium mining and extraction or fuel fabrication. Due to their ability to interact with radionuclides and heavy metals microorganisms could help to clean up the contaminated water in Königstein. With a culture dependent method it was possible to isolate different microorganisms from the flooding water. Tolerance tests displayed high resistances to uranium of these natural isolates. Furthermore uranium immobilization experiments show high rates of uranium binding to the cells. Some of the isolates are able to remove nearly 100% of the initial added uranium. TEM analysis showed two different interaction mechanisms, biosorption to the cell membrane and bioaccumulation within the cell.

Keywords: Uranium immobilization; Bioremediation; Königstein

  • Lecture (Conference)
    2. Projektstatusgespräch zu BMBF-geförderten Forschungs- und Entwicklungsvorhaben auf dem Gebiet der "Nuklearen Sicherheits- und Entsorgungsforschung sowie Strahlenforschung", 25.-26.03.2015, Dresden, Deutschland

Publ.-Id: 21913

Structural and electrical properties of sulfur doped Si by ion implantation

Liu, F.; Prucnal, S.; Gao, K.; Khalid, M.; Skorupa, W.; Helm, M.; Zhou, S.

Hydoping Si with chalcogens is one of the effective approaches to form an intermediate band (IB). This IB material is a candidate of infrared photodetectors and intermediate band solar cells. However, the chalcogens have relatively low solid solubility limit in Si. We prepared sulfur doped silicon to above the Mott insulator concentration by ion implantation followed by pulsed laser annealing. The degree of crystalline lattice recovery in implanted layers and the lattice location of sulfur in Si were analyzed by Rutherford backscattering spectrometry / Channeling. Our results show that S atoms are occupying substitutional lattice sites in Si. We also observe an insulator-to-metal transition in silicon hyperdoped with sulfur to concentrations well above the maximum solubility limit of about 3×1016 cm-3[1]. Analyzing temperature-dependent conductivity data, we find that a transition from insulating to metallic conduction occurs at a peak sulfur concentration of around 1×1021 cm-3.

Keywords: Hydoping; sulfur; insulator-to-metal transition; lattice location

  • Lecture (Conference)
    DPG 2015 Spring Meeting, 15.-20.03.2015, Berlin, Germany

Publ.-Id: 21912

A review of graphite beneficiation techniques

Chehreh Chelgani, S.; Rudolph, M.; Kratzsch, R.; Sandmann, D.

Graphite as a naturally occurring crystalline carbon is required for many different applications such as batteries, refractories, electrical products, pencils, etc. Many new graphite deposits are currently being extracted to help meet the growing demand. It is among the list of critical raw materials by the European Union. Graphite ore is mostly beneficiated using flotation separation techniques. The increasing demand for high grade graphite products with up to 99.99% carbon has led to develop various methods to remove impurities even to ppm range. This paper considers separation and purification techniques that are currently employed for graphite mineral beneficiation and identifies areas in need of further research.

Keywords: Graphite; Liberation; Flotation; Leaching; Roasting; Microwave; Kish

Publ.-Id: 21911

Radiosynthesis of a [18F]-quinuclidine 1,2,3-thiazole derivative as PET radioligand for neuroimaging of the α7 nicotinic acetylcholine receptor

Sarasamkan, J.; Fischer, S.; Scheunemann, M.; Brust, P.; Vajragupta, O.

The α7 nicotinic acetylcholine receptor (α7nAChR) is well recognized as a key receptor involved in memory formation and cognition which implicates its involvement in the pathophysiology of neurodegenerative disorders. Currently, this receptor subtype is one of the most attractive targets for neuroimaging to monitor the etiology and progression of brain diseases such as schizophrenia and Alzheimer’s disease (AD). Therefore, a new PET radioligand selective to α7nAChR was developed in this study. The structure of the developed ligand is based on a novel potent and selective α7nAChR agonist, 3-(4-hydroxyphenyl-1,2,3-triazol-1-yl) quinuclidine (QND8) which demonstrated cognitive enhancement in mice [1].
Materials and methods
The structure of the radioligand (18F-QND) was modified from QND8 by replacing the hydroxyl (OH) group with fluorine. After synthesis of the starting quinuclidine azide and aryl alkyne, F-QND and its precursor were synthesized by copper-catalyzed azide-alkyne cycloaddition (CuAAC) or click chemistry. Their structures were confirmed by 1H-NMR, 13C-NMR and mass spectrometry (MS). 18F-QND was radiolabeled by nucleophilic substitution of the nitro precursor. Altered amounts of kryptofix and various conditions (solvent and temperature) were chosen to improve the radiolabeling yield. The radiolabeled compound was separated and purified by chromatography. The radiochemical yield and radiochemical purity were analyzed by radio-thin layer chromatography and radio-high performance liquid chromatography. Non-radioactive references were used to confirm the stereochemistry of the nitro-precursor and F-QND.
The chemical yields of the nitro-precursor (NO2-QND) and the reference standard (F-QND) were 21% and 11%, respectively, with purity higher than 95%. The radiolabeling yield of 18F-QND was 7% with radiochemical purity > 98% and specific activity of 65 GBq/µmol. The stereochemistry study approved that both compounds were optically active. Therefore, the developed radiochemical processes can be applied for the radiosynthesis of further 18F-QND-derivatives.
Radiosynthesis of 18F-QND was accomplished by nucleophilic substitution of the phenyl-nitro compound. However, at high temperature racemization currently cannot be excluded.
1. Chalon S, Guilloteau D, PIN F, Routier S, Suzenet F, Vercouillie J. Centre National De La Recherche Scientifique (C.N.R.S). Patent WO2012143526A1, Oct. 6, 2012.

  • Poster
    EANM 2015 - Annual Congress of the European Association of Nuclear Medicine, 10.-14.10.2015, Hamburg, Deutschland
  • Abstract in refereed journal
    European Journal of Nuclear Medicine and Molecular Imaging 42(2015), 279

Publ.-Id: 21910

Robust increase of the translocator protein 18 kDa (TSPO), demonstrated with radiotracer [123I]CLINDE, in an adult rat model of Traumatic Brain Injury

Donat, C. K.; Gaber, K.; Meixensberger, J.; Brust, P.; Pinborg, L. H.; Mikkelsen, J. D.

Traumatic brain injury (TBI) can result in long-term disability, but the mechanisms are not fully elucidated. Neuroinflammation is part of these secondary injury mechanisms, and is therefore regarded as a potential target for treatment and diagnostics employing molecular imaging techniques. TSPO, a protein in the mitochondrial membrane, is robustly upregulated in response to injury and neuroinflammation, making it a marker. We therefore hypothesize that TSPO is time-dependently upregulated after TBI. This was investigated in a rat model of TBI, employing the TSPO-selective and clinically relevant radioligand [123I]CLINDE.
Adult male Sprague-Dawley rats were randomized into four groups (survival time: 6, 24, 72 h and 28 d). Animals were anaesthetized and subjected to either sham injury, craniotomy or mild-to-moderate (2 mm impact depth at 4 m/sec) controlled cortical impact injury (CCI). Drug/surgery-naïve animals were included in the study. Frozen coronal sections were cut and TSPO binding was assessed in the vicinity of the injury (M1 motor cortex, 3.5 mm posterior and +4.0 mm lateral to bregma) with in vitro autoradiography.
Binding of [123I]CLINDE was nearly uniform and displaceable (10 µMol/L PK1195) in the brains of naïve and sham-operated animals.
At 24 h, injured animals exhibited a significant increase in binding in the whole ipsilateral hemisphere (49%) and the ipsilateral M1 cortex (201%). Interestingly, CCI also resulted in an elevated binding in the contralateral M1 cortex (38%). [123I]CLINDE binding was maximally increased at 72 h after CCI in the whole ipsilateral hemisphere (368 %) and M1 cortex (1076%). Again, TBI significantly increased binding in the contralateral whole hemisphere (29%) and M1 cortex (32%).
Craniotomy, without TBI, produced a significant increase in TSPO at 24 h in the ipsilateral M1 cortex (42%) and at 72h in the ipsilateral hemisphere (232%) and M1 cortex (598%). At 6 h and 28 d, [123I]CLINDE binding was not significantly different between the groups.
[123I]CLINDE binding, reflecting TSPO, was significantly increased after experimental TBI, which corresponds to the time-course of the inflammatory response. This makes [123I]CLINDE a suitable radiotracer for the assessment brain injury in TBI and the monitoring of anti-inflammatory (pharmaco)therapies.

  • Poster
    60th Annual Meeting of the German Society for Neuropathology and Neuroanatomy, 26.-28.08.2015, Berlin, Deutschland

Publ.-Id: 21909

Low-energy magnetic radiation: Deviations from GOE

Frauendorf, S.; Schwengner, R.; Wimmer, K.

A pronounced spike at low energy in the strength function for magnetic radiation (LEMAR) is found by means of Shell Model calculations, which explains the experimentally observed enhancement of the dipole strength. LEMAR originates from statistical low-energy M1-transitions between many excited complex states. Re-coupling of the proton and neutron high-j orbitals generates the strong magnetic radiation. LEMAR is closely related to Magnetic Rotation. LEMAR is predicted for nuclides participating in the r-process of element synthesis and is expected to change the reaction rates. An exponential decrease of the strength function and a power law for the size distribution of the B(M1) values are found, which strongly deviate from the ones of the GOE of random matrices, which is commonly used to represent complex compound states.

Keywords: Magnetic dipole radiation; nuclearstructure; nuclear shell model; Gaussian Orthogonal Ensemble

Publ.-Id: 21908

Operational Experience at ELBE

Michel, P.; Lehnert, U.; Seidel, W.

The ELBE center for high power radiation sources is the largest user facility in the Helmholtz-Zentrum Dresden-Rossendorf. The facility is based on a 36 MeV superconducting RF Linac which can be operated up to 1.6 mA in cw mode. The electron beam is used to generate secondary radiation, such as infrared light (Free Electron Lasers), coherent THz radiation, MeV-Bremsstrahlung, fast neutrons and positrons for a wide range of basic research like semiconductor physics, nuclear astrophysics and radio biological investigations. Two high power laser systems (500 TW Ti:Sa laser, 2 PW diode pumped laser) are under construction for laser acceleration experiments and X-ray generation by Thomson scattering. The FELs are in operation since 2004 (mid-IR FEL, 4-22µm) and 2006 (far-IF FEL, 20-250µm). The fundamental features of the ELBE IR FELs, the FEL instrumentation and advanced beam diagnostics for the photon beam are described. During ten years of user operation experiences and statistical data were collected.

Keywords: ELBE; FEL; FELBE; operational Experience

  • Contribution to proceedings
    SPIE, Advances in X-ray Free-Electron Lasers Instrumentation, 13.-16.04.2015, Prague, Czechia
    Proceedings of SPIE 9512
    DOI: 10.1117/12.2181503
  • Lecture (Conference)
    SPIE, Advances in X-ray Free-Electron Lasers Instrumentation, 13.-16.04.2015, Prague, Czechia

Publ.-Id: 21906

Use of AC magnetic fields for flow control in solidifying metallic alloys

Räbiger, D.; Vogt, T.; Gerbeth, G.; Eckert, S.

AC magnetic fields unlock an enormous potential to realize a variety of flow structures in molten metals, which makes the electromagnetic stirring attractive for controlling the melt flow during solidification. We present an experimental study concerning the solidification of AlSi alloys exposed to a pulsed rotating magnetic field. Isothermal flow measurements were carried out in order to understand the flow structures resulting from the application of time-modulated magnetic fields. These investigations revealed transient flow regimes showing distinct inertial oscillations and coherent vortex structures. An intense melt flow with periodic reversals of the flow direction at the solidification front can be created by a suitable choice of the magnetic field parameters. Such resonant states of the flow pattern have been proven to provide beneficial conditions for solidification processes. Optimized flow conditions realized in a solidifying melt result in a significant grain refinement without provoking the formation of harmful segregation freckles.

  • Lecture (Conference)
    TMS 2016 145th ANNUAL MEETING & EXHIBITION, 15.-19.03.2015, Orlando, USA

Publ.-Id: 21905

Melt flow and grain refinement in Al-Si alloys solidified under the influence of applied electric currents

Räbiger, D.; Zhang, Y.; Galindo, V.; Franke, S.; Eckert, S.

The application of electric currents during solidification can cause grain refinement in metallic alloys. However, the knowledge about the mechanisms underlying the decrease in grain size remains fragmentary. This study considers the solidification of Al Si alloys under the influence of electric currents for the configuration of two parallel electrodes at the free surface. Solidification experiments were performed under the influence of both direct currents (DC) and rectangular electric current pulses (ECP). The interaction between the applied current and its own induced magnetic field causes a Lorentz force which produces an electro-vortex flow. Numerical simulations were conducted to calculate the Lorentz force, the Joule heating and the induced melt flow. The numerical predictions were confirmed by isothermal flow measurements in eutectic GaInSn. The results demonstrate that the grain refining effect observed in our experiments can be ascribed solely to the forced melt flow driven by the Lorentz force.

Keywords: Grain refinement; Al-Si alloys; External electric field

  • Lecture (Conference)
    TMS 2015 144th ANNUAL MEETING & EXHIBITION, 15.03.-19.04.2015, Orlando, USA
  • Contribution to proceedings
    TMS 2016 145th ANNUAL MEETING & EXHIBITION, 15.-19.03.2015, Orlando, USA
    DOI: 10.1002/9781119093466.ch5

Publ.-Id: 21904

Entrapped elemental selenium nanoparticles affect physicochemical properties of selenium fed activated sludge

Jain, R.; Seder-Colomina, M.; Jordan, N.; Dessi, P.; Cosmidis, J.; van Hullebusch, E. D.; Weiss, S.; Farges, F.; Lens, P. N. L.

Selenite containing wastewaters can be treated in activated sludge systems, where the total selenium is removed from the wastewater by the formation of elemental selenium nanoparticles, which are trapped in the biomass. No studies have been carried out so far on the characterization of selenium fed activated sludge flocs, which is important for the development of this novel selenium removal process. This study showed that more than 93% of the trapped selenium in activated sludge flocs is in the form of elemental selenium, both as amorphous/ monoclinic selenium nanospheres and trigonal selenium nanorods. The entrapment of the elemental selenium nanoparticles in the selenium fed activated sludge flocs leads to faster settling rates, higher hydrophilicity and poorer dewaterability compared to the control activated sludge (i.e. not fed with selenite). The selenium fed activated sludge showed a less negative surface charge density as compared to control activated sludge. The presence of trapped elemental selenium nanoparticles further affected the spatial distribution of Al and Mg in the activated sludge flocs. This study demonstrated that the formation and subsequent trapping of elemental selenium nanoparticles in the activated sludge flocs affects their physicochemical properties.

Keywords: selenium; nanoparticles; activated sludge; physicochemical; settleability; surface charge

Publ.-Id: 21902

Electron Probe Microanalysis of REE in Eudialyte Group Minerals: Challenges and Solutions

Atanasova, P.; Krause, J.; Moeckel, R.; Osbahr, I.; Gutzmer, J.

The accurate quantification of the chemical composition of eudialyte group minerals with the electron probe microanalyzer is complicated by both mineralogical and X-ray-specific challenges. These include structural and chemical variability, mutual interferences of X-ray lines, in particular of the rare earth elements, diffusive volatility of light anions and cations and instability of eudialyte group minerals under the electron beam.
A novel analytical approach has been developed to overcome these analytical challenges. The effect of diffusive volatility and beam damage is shown to be minimal when a square of 20x20 µm is scanned with a beam diameter of 6 µm at the fastest possible speed, while measuring elements critical to electron beam exposure early in the measurement sequence. Appropriate reference materials are selected for calibration considering their volatile content and composition, and supplementary offline overlap correction is performed using individual calibration factors. Preliminary results indicate good agreement with data from laser ablation inductively coupled plasma mass spectrometry demonstrating that a quantitative mineral chemical analysis of eudialyte group minerals by electron probe microanalysis is possible once all the parameters mentioned above are accounted for.

Keywords: Rare earth elements; eudialyte; electron probe microanalyzer; electron microprobe; beam conditions; diffusive volatility; interferences; reference material

Publ.-Id: 21901

Optical ridge waveguides in Yb:YAG laser crystal produced by combination of swift carbon ion irradiation and femtosecond laser ablation

Cheng, Y.; Lv, J.; Akhmadaliev, S.; Hernández-Palmero, I.; Romero, C.; Vázquez De Aldana, J. R.; Zhou, S.; Chen, F.

We report on the fabrication of optical ridge waveguides in ytterbium-doped yttrium aluminum garnet (Yb:YAG) single crystal by applying swift C5+ ion irradiation and the followed femtosecond laser ablation. The planar waveguide layer is first produced by C5+ ion irradiation and the laser ablation is used to microstructure the planar waveguide surface to construct ridge structures. The lowest propagation loss of the ridge waveguide has been determined to be ~2.1 dB/cm. From the confocal micro-fluorescence and micro-Raman spectra obtained from the waveguide regions, the intensities, positions and widths of the emission-line peaks had no obvious changes with respect to those from the bulks, which indicate that C5+ ion irradiation does not affect the bulk-related properties of the Yb:YAG crystal significantly in the waveguide regions. The results obtained in this work suggest potential applications of the Yb:YAG ridge waveguides as integrated laser sources.

Keywords: Optical ridge waveguides; Swift ion irradiation; Femtosecond laser ablation

Publ.-Id: 21900

Experimentelle Untersuchung zur Strömungsbeeinflussung mittels elektromagnetischer Bremsen beim kontinuierlichen Strangguss von Stahl

Timmel, K.

Beim kontinuierlichen Stranggießen von Stahl werden elektromagnetische Felder zur Strömungsbeeinflussung eingesetzt. In dieser Arbeit wird die Wirkung eines statischen Magnetfeldes auf die Kokillenströmung in einem Modellexperiment untersucht. Das statische Magnetfeld strukturiert die Strömung um, kann lokal die Strömungsgeschwindigkeiten erhöhen und verändert die Ausbildung und Anzahl der für Brammenkokillen typischen großskaligen Wirbel. Es zeigt sich weiterhin, dass die elektrische Leitfähigkeit der Kokillenwände einen entscheidenden Einfluss auf die Wirkung einer elektromagnetischen Bremse hat. Unter isolierenden Wänden werden räumliche Oszillationen des Flüssigmetallstrahles initiiert und es bildet sich zwischen den beiden Kokillenhälften eine asymmetrische Strömung aus. Leitfähige Wände verhindern die Oszillationen und die Kokillenströmung ist symmetrisch. Eine eindeutige bremsende Wirkung der elektromagnetischen Bremse auf den Durchfluss konnte jedoch in beiden Fällen nicht festgestellt werden.

Keywords: Continuous Casting of steel; liquid metal model; electro-magnetic brake; Ultrasonic-Doppler-Velocimetry

  • Doctoral thesis
    TU Bergakademie Freiberg, 2014
    Mentor: Prof. Dr.-Ing. Rüdiger Schwarze
    196 Seiten
  • Book (Authorship)
    Freiberg: Verlag der TU Bergakademie Freiberg, 2015
    240 Seiten


Publ.-Id: 21899

Ferromagnetic and paramagnetic magnetization of implanted GaN:Ho,Tb,Sm,Tm films

Maryško, M.; Hejtmánek, J.; Laguta, V.; Sofer, Z.; Sedmidubský, D.; Šimek, P.; Veselý, M.; Mikulics, M.; Buchal, C.; Macková, A.; Malínský, P.; Wilhelm, R. A.

The SQUID magnetic measurements were performed on the GaN films prepared by metal-organic vapour phase epitaxy and implanted by Tb3+, Tm3+, Sm3+, and Ho3+ ions. The sapphire substrate was checked by the electron paramagnetic resonance method which showed a content of Cr3+ and Fe3+ impurities. The samples 5 × 5 mm2 were positioned in the classical straws and within an estimated accuracy of 10−6 emu, no ferromagnetic moment was detected in the temperature region of 2–300 K. The paramagnetic magnetization was studied for parallel and perpendicular orientation. In the case of GaN:Tb sample, at T = 2 K, a pronounced anisotropy with the easy axis perpendicular to the film was observed which can be explained by the lowest quasi-doublet state of the non-Kramers Tb3+ ion. The Weiss temperature deduced from the susceptibility data using the Curie-Weiss (C-W) law was found to depend substantially on the magnetic field.

Publ.-Id: 21898

The inclined rotating tubular fixed bed reactor for process intensification of heterogeneous catalytic multiphase reactions

Härting, H.-U.; Lange, R.; Schubert, M.

The inclined rotating tubular fixed bed reactor has been introduced recently as a new concept for the implementation of multiphase processes, in particular for hetero-geneously catalysed gas-liquid reactions. Commonly applied trickle bed reactors (TBR) suffer from liquid maldistribution and low mass and heat transfer rates and have therefore been subject to process intensification: periodic liquid flow rate modulation at the reactor inlet was introduced, which leads to elevated space time yields in comparison to steady-state operation. However, the beneficial effects decay rapidly along the reactor length and maldistribution is not effectively curbed.
To fully utilise the positive effects of such modulation strategy, the new reactor concept is operated inclined against the vertical and rotated permanently. This operation mode ensures a wetting intermittency via periodic immersion of the whole catalyst packing, which is clamped between retaining grids. Furthermore, it allows adjusting different flow regimes, i.e. stratified flow or annular flow.
The new reactor concept enables also tuning the liquid residence time at constant gas and liquid flow rates. The wetting intermittency results in a complete utilization of the catalyst on the reactor scale and in thinner liquid films at the catalyst surface, which enhances the accessibility of the active sites for the gaseous reactants. The latter is proven by an increased space time yield compared to conventional TBR operation for the hydrogenation of α-methylstyrene to cumene.
In this presentation, the performance of the new reactor concept will be assessed based on reactive studies. Furthermore, the results will be discussed with respect to the prevailing flow regimes investigated via gamma-ray computed tomography, as well as liquid residence time and axial dispersion obtained by a stimulus-response technique using embedded wire mesh sensors.

Keywords: Hydrogenation; Heterogeneous Catalysis; Multiphase Flow; Flow Regimes

  • Lecture (Conference)
    ESCRE 2015 - European Symposium on Chemical Reaction Engineering, 27.-30.10.2015, Fürstenfeldbruck, Deutschland

Publ.-Id: 21897

Bacterial Diversity in Clay and Actinide Interactions with Bacterial Isolates in Relation to Nuclear Waste Disposal

Moll, H.; Lütke, L.; Cherkouk, A.

One potential source of radionuclides in the environment could be the accidental release from nuclear waste disposal sites. Hence the long-term safety of nuclear waste in a deep geological repository is an important issue in our society. Microorganisms indigenous to potential host rocks are able to influence the speciation and therefore the mobility of radionuclides and their retardation both by direct and indirect pathways. They can as well affect the conditions in a geologic repository (e.g., by gas generation or canister corrosion). The focus of this chapter lies on the influence of indigenous microbes on the speciation of Rn. Therefore, for the safety assessment of such a repository it is necessary to know which microorganisms are present in the potential host rocks (e.g., clay and salt) and if these microorganisms can influence the speciation of released Rn. Hence, dominant bacterial strains from potential host rocks for future nuclear waste deposition have to be investigated regarding their interaction mechanisms with soluble actinide (An) ions. This chapter will cover the following research areas. Gained knowledge concerning the bacterial diversity in e.g., Mont Terri Opalinus Clay by applying direct molecular culture-independent retrievals and cultivation experiments will be presented. Their influence on the geo-chemical behavior of selected An (e.g., uranium, and curium) will be highlighted. These investigations contribute to a better understanding of microbial interactions of An on a molecular level for an improved prediction of the safety of a planned nuclear waste repository.

Keywords: bacterial diversity; bacteria; complexation; uranium; curium; Sporomusa sp; Paenibacillus sp; TRLFS; potentiometry

  • Book chapter
    Clemens Walther, Dharmendra K. Gupta: Radionuclides in the Environment - Influence of chemical speciation and plant uptake on radionuclide migration, Heidelberg: Springer, 2015, 978-3-319-22171-7, 209-229
    DOI: 10.1007/978-3-319-22171-7_12

Publ.-Id: 21896

Helium Ion Microscopy

Hlawacek, G.; Gölzhäuser, A.

This book covers the fundamentals of Helium Ion Microscopy (HIM) including the Gas Field Ion Source (GFIS), column and contrast formation. It also provides first hand information on nanofabrication and high resolution imaging. Relevant theoretical models and the existing simulation approaches are discussed in an extra section. The structure of the book allows the novice to get acquainted with the specifics of the technique needed to understand the more applied chapters in the second half of the volume. The expert reader will find a complete reference of the technique covering all important applications in several chapters written by the leading experts in the field. This includes imaging of biological samples, resist and precursor based nanofabrication, applications in semiconductor industry, using Helium as well as Neon and many more. The fundamental part allows the regular HIM user to deepen his understanding of the method. A final chapter by Bill Ward, one of the pioneers of HIM, covering the historical developments leading to the existing tool complements the content.

Keywords: Helium Ion Microscopy; Focused ion beam; high resolution imaging; nano-fabrication; gas field ion source

  • Book (Editorship)
    Heidelberg: Springer International Publishing Switzerland, 2016
    526 Seiten
    ISBN: 9783319419886

Publ.-Id: 21895

Speciation studies of uranyl(VI) using an advanced combination of theoretical and luminescence spectroscopic methods

Drobot, B.; Tsushima, S.; Steudtner, R.; Raff, J.; Geipel, G.; Brendler, V.

Speciation constitutes the basis for actinide complexation studies. These systems can be very complex and challenging especially because of the polynuclear species. An advanced combination of theoretical and experimental methods is proposed here. Continuous wave (CW) and time-resolved laser-induced fluorescence spectroscopy (TRLFS) data of uranyl(VI) hydrolysis were analyzed using parallel factor analysis (PARAFAC). Distribution patterns of five major species were thereby derived under a fixed uranyl concentration (10-5 M) over a wide pH range from 2 to 11. UV (180 nm to 370 nm) excitation spectra were extracted for individual species. Time-dependent density functional theory (TD-DFT) calculations revealed ligand excitation (water, hydroxo, oxo) in this region and ligand-to-metal charge transfer (LMCT) responsible for luminescence. Thus excitation in the UV is extreme ligand sensitive and highly specific. Combining findings from PARAFAC and DFT the aquo complex (1:0) and four hydroxo complexes (1:1, 3:5, 3:7 and 1:3) were identified and characterized.

  • Lecture (Conference)
    Anakon 2015, 23.-26.03.2015, Graz, Östereich

Publ.-Id: 21894

Synthesis, 18F-radiolabelling and biological characterization of novel fluoroalkylated triazine derivatives for in vivo imaging of phosphodiesterase 2A in brain via positron emission tomography

Schröder, S.; Wenzel, B.; Deuther-Conrad, W.; Teodoro, R.; Egerland, U.; Kranz, M.; Scheunemann, M.; Höfgen, N.; Steinbach, J.; Brust, P.

Phosphodiesterase 2A (PDE2A) is highly and specifically expressed in particular brain regions affected by neurological disorders and in certain tumors. Development of a specific PDE2A radioligand enables molecular imaging of the PDE2A protein via positron emission tomography (PET). Herein we report on the syntheses of three novel fluoroalkylated triazine derivatives (TA2-4) and on the evaluation of their effect on the enzymatic activity of human PDE2A. The most potent PDE2A inhibitors were 18F-radiolabelled ([1818F]TA4) and investigated regarding their potential as PET radioligands for imaging of PDE2A in mouse brain. In vitro autoradiography on rat brain showed region-specific distribution of [18F]TA3 and [18F]TA4, which is consistent with the expression pattern of PDE2A protein. Metabolism studies of both [18/F]TA3 and [18F]TA4 in mice discovered a significant accumulation of two major radiometabolites of each radioligand in brain as investigated by micellar radio-chromatography. Small-animal PET/MR studies in mice using [18F]TA3 revealed a constantly increasing uptake of activity in the non-target region cerebellum, which may be caused by the accumulation of brain penetrating radiometabolites. Hence, [18F]TA3 and [18F]TA4 are exclusively suitable for in vitro investigation of PDE2A. Nevertheless, further structural modification of these promising radioligands might result in metabolically stable derivatives.

Keywords: PDE2A; Alzheimer´s disease; PET imaging in brain; micellar HPLC

Publ.-Id: 21893

Quantifying 3D tracer velocity and porosity on core scale from 3D GeoPET image sequences

Eichelbaum, S.; Lippmann-Pipke, J.; Korn, N.; Kulenkampff, J.

Flow and transport simulations in geomaterials are commonly conducted on high-resolution tomograms (µCT) of the pore structure or stochastical models that are calibrated with measured integral quantities, like break through curves (BTC). Yet, there existed virtually no method for experimental verification of the simulated velocity distribution results.
Positron emission tomography (PET) has unrivaled sensitivity and robustness for non-destructive quantitative spatio-temporal measurement of tracer concentrations in body tissue. We empowered PET for its applicability in opaque/geological media (GeoPET). Thus it is the appropriate method for experimental verification and calibration of computer simulations of pore-scale transport by means of the observed propagation of a tracer pulse, cPET(x,y,z,t).
As a principal concept, velocity and residence time distributions, as well as the tortuous pathway topology, principally can be derived directly from cPET(x,y,z,t). However, the fundamental experimental limit of finite signal to noise ratios is manifested in apparently intermittent propagation pathways, with gaps in zones where the concentration cPET falls below the significance threshold. This hampers the direct parameter estimation of velocity, v(x,y,z), and porosity distribution n(x,y,z) from cPET(x,y,z,t).

This issue is overcome to some extent by introduction of causality (continuity) into the here presented evaluation algorithm.

Likely Topics in math & comp. sciences
1) Space-Time Processes
2) Image Analysis
3) Numerical Modelling and Numerical Simulation
4) Inverse Problem solving
5) other computer sciences methods

Likely Geoscience topics:
1) Water: sea, surface and subsurface

  • Lecture (Conference)
    IAMG 2015, The 17th annual conference of the International Association for Mathematical Geosciences, 05.-13.09.2015, Freiberg, Deutschland

Publ.-Id: 21892

Electrical Conductance of DNA Oligomers — A Review of Experimental Results

Erbe, A.

the publication has no abstract

Keywords: DNA; molecular electronics

  • Book chapter
    Eugen Stulz and Guido Clever: DNA in supramolecular chemistry and nanotechnology, Chichester UK: John Wiley & Sons Limited, 2015, 978-1-118-69686-6, 94-101

Publ.-Id: 21891

Magnetic and structural studies of as grown and hydrogenated Mg2Fe based thin films

Trinh, T. T.; Liedke, M. O.; Anwand, W.; Wagner, A.; Yildirim, O.; Cornelius, S.; Grenzer, J.; Ehrler, J.; Dam, B.; Asano, K.; Potzger, K.

Due to chemochromism, Mg2Me (Me=Fe, Co, Ni) based alloys are low-cost and rare-earth-free candidates for switchable mirrors upon hydrogen loading. In order to understand the basic physical properties of Mg2Fe based thin films and its hydride, as-sputtered as well as hydrogen loaded films have been investigated using magnetometry, X-ray diffraction, 4-point probe sheet resistance technique and positron annihilation spectroscopy (PAS). The interplay of hydrogen loading, the magnetic moment, and structural properties like the sizes and chemical decoration of open volume defects in thin films detected by PAS will be presented.

Keywords: Positron; Defects; Superparamagnetism; Mg2Fe; X-Ray; RBS

  • Poster
    79. Jahrestagung der DPG und DPG-Frühjahrstagung, 15.-20.03.2015, Berlin, Deutschland

Publ.-Id: 21890

Method for constructing a mineralogical composition from a measured sample of single components

Konsulke, S.; Hopfe, S.; Tolosana-Delgado, R.; Matos Camacho, S.; van den Boogaart, K. G.

Our aim is to infer the mineral composition from the chemical composition of a material. Several difficulties occur: Different mineral compositions can lead to the same chemical composition. Not all chemical compositions can be reached by compositions of certain minerals, while e.g. due to measurement errors impossible chemical compositions will typically be observed. In principle the dependency between mineral composition and chemical composition is linear. Inversion of the linear system however often leads to negative portions for some mineral components. Only the first problem is properly solved by state of the art linear end member calculation methods (see e.g. Tolosana et al. 2011).
Our algorithm computes the set of all mineral compositions leading to the chemical composition maximizing the likelihood of the observed concentrations. The measurement error for the chemical components are modelled as independent normal distributions with mean zero and standard deviation given by the measurement error reported by the lab. For any given mineral composition, the chemical composition can thus be computed by stoichiometric calculations and Maximum log-likelihood is than a weighted least squares problem. The parameter space is however constraint to the possible mineral compositions. The problem is transformed into a quadratic programming problem with linear equality and inequality constraints with a unique solution for the chemical composition. From this unique solution we can than compute all possible mineral compositions leading to the corresponding chemical composition by enumerating the corners of the simplex of equally fitting solutions.
As an example we will discuss a sample of waste material consisting of Rare Earth Elements (REE), since recycling of waste materials is getting more and more important. Rare Earth Elements (REE) are used in mostly all new technologies and until now, there is no environmentally friendly recycling-process for fluorescent phosphor. For the development of a suitable recycling method, it is important to know the composition of the materials. Due to company secrecy, in some cases only rough informations about the composition of the material can be found. In the case of fluorescent phosphor, which is collected during the recycling-process of energy saving bulbs, only the type of the dye but not the precise composition is known. Because of different restrictions in the analytical methods and the complex composition, only the elemental concentrations with relatively high measurement errors can be measured.

Keywords: End-Member Problems; Rare Earth Elements; fluorescent phosphor

  • Lecture (Conference)
    The 17th annual conference of the International Association for Mathematical Geosciences, 05.-13.09.2015, Freiberg, Deutschland
  • Contribution to proceedings
    The 17th annual conference of the International Association for Mathematical Geosciences, 05.-13.09.2015, Freiberg, Deutschland
    Proceedings of IAMG 2015, 978-3-00-050337-5

Publ.-Id: 21889

Short-lived positron emitters in beam-on PET imaging during proton therapy

Dendooven, P.; Buitenhuis, H. J. T.; Diblen, F.; Heeres, P. N.; Biegun, A. K.; Fiedler, F.; van Goethem, M.-J.; van der Graaf, E. R.; Brandenburg, S.

The only method for in-vivo dose delivery verification in proton beam radiotherapy in clinical use today is positron emission tomography (PET) of the positron emitters produced in the patient during irradiation. PET imaging during irradiation maximizes the number of detected counts and minimizes biological washout. In such a scenario, also short-lived positron emitters will be observed. We determined which short-lived positron emitters are relevant by measuring their production in the stopping of 55 MeV protons in water, carbon, phosphorus and calcium. The most copiously produced short-lived nuclides and their production rates relative to the relevant long-lived nuclides are: 12N (T1/2 = 11 ms) on carbon (9% of 11C), 29P (T1/2 = 4.1 s) on phosphorus (20% of 30P) and 38mK (T1/2 = 0.92 s) on calcium (113% of 38gK). No short-lived nuclides are produced on water. The production on PMMA and 4 tissue materials is calculated from the experimental results. The number of decays, integrated over an irradiation, is calculated as function of the duration of the irradiation. For an irradiation in (carbon-rich) adipose tissue, 12N dominates the PET image up to an irradiation duration of 70 s. On bone tissue, 12N dominates over 15O during the first 8-15 s (depending on the carbon-to-oxygen ratio). The short-lived nuclides created on phosphorus and calcium provide 2.5 times more decays than the long-lived ones during a 70 s irradiation. Bone tissue will thus be better visible in in-beam PET compared to PET imaging after an irradiation. 12N needs to be considered in PET imaging during proton beam irradiations as its large positron range blurring may noticeably degrade image quality. Investigations into the energy-dependent production of 12N, 29P and 38mK and their effect on the quality of in-vivo treatment verification in proton therapy with PET imaging are urgently needed.

Keywords: PET; dose monitoring; short lived isotopes

Publ.-Id: 21888

Spin-transfer effects in MgO-based tunnel junctions with an out-of-plane free layer and in-plane polarizer: static states and steady-state precession

Kowalska, E.; Sluka, V.; Fowley, C.; Kakay, A.; Aleksandrov, Y.; Lindner, J.; Fassbender, J.; Deac, A. M.

Spin-torque nano-oscillators (STNOs) are novel devices which may be exploited for wireless communication applications. In particular, it has recently been demonstrated that STNOs utilizing an in-plane (IP) magnetized polarizer and out-of-plane (OOP) magnetized free layer allow for the full parallel (P)-to-antiparallel (AP) resistance variation to be exploited in the limit of 90° precession angle, thereby maximizing the output power. However, for this specific geometry, steady-state precession can only be sustained if the spin-transfer torque exhibits an asymmetric dependence on the angle between the free and the polarizing layer, such as in the case of fully metallic devices. Nevertheless, it has recently been reported that dynamics have been experimentally observed in similarly designed MgO-based MTJs under constant applied electrical current, in spite of the fact that such devices do not exhibit any asymmetry in the spin-torque angular dependence. These results have so far been interpreted based on the formalism for metallic devices, including the spin-torque angular dependence. Here, we explore potential mechanisms for sustaining steady-state precession in MgO-based MTJs with an IP polarizer and an OOP free layer. To this end, we analytically and numerically solve the Landau-Lifshitz-Gilbert-Slonczewski equation for a nano-pillar MTJ with circular cross-section, under a constant perpendicular applied current and field. Since for realistic current range, the field-like torque is negligible compared to effective field acting along z axis, we take into account only the in-plane spin-torque term. To sustain steady-state precession, the energy supplied by the in-plane spin-torque term and energy dissipated through damping must compensate over a full precession period. In an MgO-MTJ, the magnitude of the STT is determined not by the current, but by the corresponding voltage across the barrier. As the magnetization of the free layer precesses around the z axis, the angle between the magnetic moments of the two layers changes and through the magnetoresistance effect the voltage changes if the Experiment is conducted at constant applied current. This cosine-like angular dependence of the MTJ resistance effectively introduces a spin-torque angle dependence asymmetry. In addition, even for a given angle, the resistance exhibits a specific bias dependence, with the resistance of the AP state decreasing approximately linearly with the bias, while remaining mostly constant in the P configuration. In this work, we demonstrate that the spin-torque angular asymmetry exhibited in such systems is sufficient to sustain STT-driven dynamics.

Keywords: spin-torque oscillators; spin-transfer torque; magnetic tunnel junctions; tunnel magnetoresistance

  • Lecture (Conference)
    The IEEE International Magnetics Conference (INTERMAG) 2015, 11.-15.05.2015, Beijing, China

Publ.-Id: 21887

Experimental investigation of interfacial structures within churn flow using a dual wire-mesh sensor

Parsi, M.; Vieira, R. E.; Torres, C. F.; Kesana, N. R.; Mclaury, B. S.; Shirazi, S. A.; Schleicher, E.; Hampel, U.

A challenging area in the field of multiphase flow is the study of churn flow. According to the multiphase flow community, churn flow has not been widely investigated in intermediate and large diameter pipes at high gas and liquid flow rates. The present work deals with an experimental study of upward vertical air–water flow in a 76.2 mm I.D. pipe. Superficial gas velocities ranging from 10 to 38 m/s and four superficial liquid velocities (0.30, 0.46, 0.61 and 0.76 m/s) were employed. The experimental data points are mostly located in churn flow and at the transition between churn and annular flow. A dual 16x16 Wire Mesh Sensor (WMS) was used to obtain the temporal/spatial variations of phase distributions over the pipe cross-section at one specific axial location (L/D = 236).
Sequences of phase distributions, axially sliced images, virtual 3-D images as well as void fraction timeseries were used to distinguish between different interfacial structures such as slugs and huge waves.
Results showed that huge waves occur with either a continuous gas core with a distinct boundary between two phases or a core with a gas–liquid mixture. Furthermore, velocities and frequencies of interfacial structures were obtained. Results are qualitatively and quantitatively consistent with the previous findings available in literature.

Keywords: churn flow; huge wave; wire mesh sensor; multiphase flow; interfacial structures

Publ.-Id: 21886

Control of intra-excitonic scattering in semiconductor quantum wells by an external magnetic field

Schneider, H.; Bhattacharyya, J.; Zybell, S.; Eßer, F.; Helm, M.; Schneebeli, L.; Böttge, C. N.; Breddermann, B.; Kira, M.; Koch, S. W.

We report on the internal dynamics of excitons in high-quality GaAs quantum wells and on the control of intra-excitonic transitions by an external magnetic field. The free-electron laser FELBE in Dresden is ideally suited for selective excitation of intra-excitonic transitions, since it provides intense, spectrally narrow transform-limited terahertz pulses in a unique continuous pulse train, which also allows us to use a synchroscan streak camera system [1]. Subsequent to the production of excitons by pulsed interband excitation, we resonantly pump the 1s-2p intra-excitonic transition which is located at around 2 THz. Coulomb-mediated transfer from the optically "dark" 2p to the radiative 2s state and relaxation into the fundamental 1s state is investigated by time-resolved photoluminescence involving the 1s and 2s excitonic levels [2]. In particular, applying an external magnetic field strongly affects the observed behavior. Detailed analysis of the experimental behavior based on a newly developed microscopic theory allows us to demonstrate the remarkable impact of magnetic fields on the Coulomb and terahertz interactions in the excitonic system, which occurs as a consequence of magnetically induced changes of excitonic orbitals and energetic detuning of excitonic levels [3]. As an interesting application, we also discuss the possibility of observing terahertz gain induced by intra-excitonic transitions.
[1] J. Bhattacharyya et al., Rev. Sci. Instrum. 82, 103107 (2011)
[2] W. D. Rice et al., Phys. Rev. Lett. 110, 137404 (2013)
[3] J. Bhattacharyya et al., Phys. Rev. B 89, 125313 (2014)

Keywords: intra-exciton transitions; GaAs quantum well; terahertz excitation; free-electron laser

  • Lecture (Conference)
    SPIE Photonics West 2015, 07.-12.02.2015, San Francisco, USA

Publ.-Id: 21885

Evolution of the interfacial magnetic anisotropy in MgO/CoFeB/Ta/Ru based multilayers as a function of annealing temperature

Aleksandrov, Y.; Fowley, C.; Kowalska, E.; Sluka, V.; Yildirim, O.; Lindner, J.; Ocker, B.; Fassbender, J.; Deac, A. M.

We report effect of the annealing temperature on the dynamic and static magnetic properties of MgO/CoFeB/Ta/Ru multilayers. The angular resolved ferromagnetic resonance measurements results show that the as-deposited film exhibits in-plane magnetic anisotropy, whereas in the annealed films the magnetic easy-axis is almost along the direction perpendicular to the plane of the layers. The extracted interfacial anisotropy energy, Ki, is maximized at an annealing temperature 225 °C, in agreement with the vibrating sample magnetometry results. Although the magnetization is not fully out-of-plane, controlling the degree of the magnetization obliquity may be advantageous for specific applications such as spin-transfer oscillators.

Keywords: FMR; PMA; CoFeB

  • Lecture (Conference)
    IEEE International Magnetics Conference (INTERMAG 2015), 11.-15.05.2015, Beijing, the People's Republic of China
  • Open Access Logo AIP Advances 6(2016)6, 065321
    Online First (2016) DOI: 10.1063/1.4954809


Publ.-Id: 21884

On the use of the SPH method in nodal diffusion analyses of SFR cores

Nikitin, E.; Fridman, E.; Mikityuk, K.

A number of recent studies successfully demonstrated the feasibility of using Monte Carlo code Serpent to generate few-group cross sections (XS) for full core nodal diffusion analyses of SFR cores. The current study investigated the potential of the SPH method, applied to correct the few-group XS produced by Serpent, to further improve the accuracy of the nodal diffusion solutions. The procedure for the generation of SPH-corrected few-group XS is presented in the paper. The performance of the SPH method was tested on a large oxide SFR core from the OECD/NEA SFR benchmark. The reference SFR core was modeled with the DYN3D and PARCS nodal diffusion codes using the SPH-corrected few-group XS generated by Serpent. The nodal diffusion results obtained with and without SPH correction were compared to the reference full-core Serpent MC solution. It was demonstrated that the application of the SPH method improves the accuracy of the nodal diffusion solutions, particularly for the rodded core state.

Keywords: Group constant generation; SFR; Monte Carlo; SPH; Serpent; DYN3D; PARCS

Publ.-Id: 21883

Spectral history model in DYN3D: Verification against coupled Monte-Carlo thermal-hydraulic code BGCore

Bilodid, Y.; Kotlyar, D.; Margulis, M.; Fridman, E.; Shwageraus, E.

This research focuses on the verification of a recently developed methodology accounting for spectral history effects in 3D full core nodal simulations. The traditional deterministic core simulation procedure includes two stages: (1) generation of homogenized macroscopic cross section sets and (2) application of these sets to obtain a full 3D core solution with nodal codes. The standard approach adopts the branch methodology in which the branches represent all expected combinations of operational conditions as a function of burnup (main branch). The main branch is produced for constant, usually averaged, operating conditions (e.g. coolant density). As a result, the spectral history effects that associated with coolant density variation are not taken into account properly. Number of methods to solve this problem (such as micro-depletion and spectral indexes) were developed and implemented in modern nodal codes. Recently, we proposed a new and robust method to account for history effects. The methodology was implemented in DYN3D and involves modification of the few-group cross section sets. The method utilizes the local Pu-239 concentration as an indicator of spectral history. The method was verified for PWR and VVER applications. However, the spectrum variation in BWR core is more pronounced due to the stronger coolant density change. The purpose of the current work is investigating the applicability of the method to BWR analysis. The proposed methodology was verified against recently developed BGCore system, which couples Monte Carlo neutron transport with depletion and thermal-hydraulic solvers and thus capable of providing a reference solution for 3D simulations. The results clearly show that neglecting the spectral history effects leads to a very large deviation (e.g. 1700 pcm in multiplication factor) from the reference solution. Application of the Pu-correction method results in a very good agreement between DYN3D and BGCore on the order of 200 pcm in kinf.

Keywords: History effects; spectral history; coupled Monte Carlo; DYN3D; BGCore

Publ.-Id: 21882

Development of indazolylpyrimidine derivatives as high-affine EphB4 receptor ligands and potential PET-radiotracers

Ebert, K.; Wiemer, J.; Caballero, J.; Köckerling, M.; Steinbach, J.; Pietzsch, J.; Mamat, C.

Due to their essential role in the pathogenesis of cancer, members of the Eph (erythropoietin-producing hepatoma cell line-A2) receptor tyrosine kinase family represent promising candidates for molecular imaging. Thus, the development and preparation of novel radiotracers for the noninvasive imaging of the EphB4 receptor via positron emission tomography (PET) is described. First in silico investigations with the indazolylpyrimidine lead compound which is known to be highly affine to EphB4 were executed to identify favorable labeling positions for an introduction of fluorine-18 to retain the affinity. Based on this, reference compounds as well as precursors were developed and labeled with carbon-11 and fluorine-18, respectively. For this purpose, a protecting group strategy was essential to generate for the prevention of unwanted methylation and to enable the introduction of fluorine-18. Further, a convenient radiolabeling strategy using [11C]methyl iodide was established which afforded the isotopically labeled radiotracer in 30-35% RCY (d.c.) which is identical with the original inhibitor molecule. A spiro ammonium precursor was prepared for radiolabeling with fluorine-18. Unfortunately, the labeling did not lead to the desired 18F-radiotracer under the chosen conditions.

Publ.-Id: 21881

Spin Waves going 3D – Chiral Effects in Curved Magnetic Nanowires

Kákay, A.; Hertel, R.

Recent progress in material science has enabled the first experimental studies concerning the static magnetization characterization of samples with tubular geometry to be carried out. Although investigating spin-wave and domain-wall dynamics remains a challenge from an experimental point of view, theory predicts that it is fundamentally different than in previously investigated flat geometries. This is a direct consequence of the specific boundary conditions in such structures. Here, we discuss the effect of the curvature on the dynamics of domain walls and spin waves. Using extensive finite element micromagnetic simulations, we demonstrate that a typical vortex-type domain wall formed in a ferromagnetic tube exhibits advantageous properties regarding the domain wall speed and stability. For topological reasons, these robust domain walls do not encounter the Walker breakdown in certain nanotubes and can propagate with velocities faster than the spin wave phase velocity. Above a critical velocity, the domain wall triggers a Cherenkov-type spin wave radiation. Note that the Spin-Cherenkov Effect is general and not specific to nanotubes. We show that this effect is present in any magnetic medium where a perturbation travels with a velocity faster than the magnonic limit. A characteristic of ferromagnetic nanotubes is that the chiral symmetry of the domain wall propagation is broken. This is attributed to the lack of local inversion symmetry due to the curved surface of the nanotube. Micromagnetic studies show that this lack of inversion symmetry leads to a non-reciprocal dispersion relation for the spin waves with regards to the sign of the propagation vector k. The split in the frequencies for spin waves traveling in opposite directions is of the order of several GHz. This effect is the largest when the nanotube radius is comparable with the wavelength of the traveling spin waves and is already present for bended thin films that form a half or even less than a half nanotube only. Moreover, we demonstrate that even in flat geometries, a similar lift of the degeneracy of the dispersion relation can be achieved if the magnetization distribution shows a non-divergence free curved pattern. This indicates that, in the presence of an external field, a set of curved surfaces of opposite bending behaves as a directional filter device in which the spin waves can propagate to a specific direction only.

Keywords: Spin waves; Curved geometries; Spin-Cherenkov effect; Magnonics

  • Invited lecture (Conferences)
    International Workshop on Magnetic Nanowires and Nanotubes, 17.-20.05.2015, Meersburg/Lake Constance, Deutschland

Publ.-Id: 21880

Spin-torque-induced dynamics at fine-split frequencies in nano-oscillators with two stacked vortices

Sluka, V.; Kákay, A.; Deac, A. M.; Bürgler, D. E.; Schneider, C. M.; Hertel, R.

The gyrotropic rotation around the equilibrium position constitutes the fundamental excitation of magnetic vortices in nanostructures. The frequency of this mode varies with material and sample geometry, but is independent of the vortex handedness and its core direction. Here, we demonstrate that this degeneracy is lifted in a spin-torque oscillator containing two vortices stacked on top of each other. When driven by spin-polarized currents, such devices exhibit a set of dynamic modes with discretely split frequencies, each corresponding to a specific combination of vorticities and relative core polarities. The fine splitting occurs even in the absence of external fields, demonstrating that such devices can function as zero-field, multi-channel, nano-oscillators for communication technologies. It also facilitates the detection of the relative core polarization and allows for the eight non-degenerate configurations to be distinguished electrically, which may enable the design of multi-state memory devices based on double-vortex nanopillars.

Keywords: Spin-torque; vortex; nano-oscillator; fine-split

Publ.-Id: 21879

Au-Interaction of Slp1 polymers and monolayer from Lysinibacillus sphaericus JG-B53 - QCM-D, ICP-MS and AFM as tools for biomolecule-metal studies

Suhr, M.; Raff, J.; Pollmann, K.

To obtain basic information on the sorption and recycling of gold from aqueous systems the interaction of Au(III) and Au(0) nanoparticles on S-layer proteins were investigated. The sorption of protein polymers was investigated by ICP-MS and that of proteinaceous monolayers by QCM-D. Subsequent AFM enable the imaging of the nanostructures.

Keywords: Biosorption; metals; S-layer; bacteria; nanoparticles; QCM-D; AFM; ICP-MS; gold

  • Journal of Visualized Experiments 107(2016), e53572
    Online First (2016) DOI: 10.3791/53572

Publ.-Id: 21878

First-principles calculation of defect free energies: General aspects illustrated in the case of bcc-Fe

Devaraj, M.; Posselt, M.; Schiwarth, M.

Modeling of nanostructure evolution in solids requires comprehensive data on the properties of defects such as the vacancy and foreign atoms. Since most processes occur at elevated temperatures not only the energetics of defects in the ground state but also their temperature-dependent free energies must be known. The first-principles calculation of contributions of phonon and electron excitations to free formation, binding, and migration energies of defects is illustrated in the case of bcc-Fe. First of all, the ground state properties of the vacancy, the foreign atoms Cu, Y, Ti, Cr, Mn, Ni, V, Mo, Si, Al, Co, O, and the O-vacancy pair are determined under constant volume (CV) as well as zero pressure (ZP) conditions, and relations between the results of both kinds of calculations are discussed. Second, the phonon contribution to defect free energies is calculated within the harmonic approximation using the equilibrium atomic positions determined in the ground state under CV and ZP conditions. In most cases the ZP-based free formation energy decreases monotonously with temperature, whereas for CV-based data both an increase and a decrease were found. The application of a quasi-harmonic correction to the ZP-based data does not modify this picture significantly. However, the corrected data are valid under zero-pressure conditions at higher temperatures than in the framework of the purely harmonic approach. The difference between CV- and ZP-based data is mainly due to the volume change of the supercell since the relative arrangement of atoms in the environment of the defects is nearly identical in the two cases. A simple transformation similar to the quasi-harmonic approach is found between the CV- and ZP-based frequencies. Therefore, it is not necessary to calculate these quantities and the corresponding defect free energies separately. In contrast to ground state energetics the CV- and ZP-based defect free energies do not become equal with increasing supercell size. Third, it was found that the contribution of electron excitations to the defect free energy can lead to an additional deviation of the total free energy from the ground state value or can compensate the deviation caused by the phonon contribution. Finally, self-diffusion via the vacancy mechanism is investigated. The ratio of the respective CV- and ZP-based results for the vacancy diffusivity is nearly equal to the reciprocal of that for the equilibrium concentration. This behavior leads to almost identical CV- and ZP-based values for the self-diffusion coefficient. Obviously, this agreement is accidental. The consideration of the temperature dependence of the magnetization yields self-diffusion data in very good agreement with experiments.

Keywords: First-principles calculations; Defects; Free energy; bcc-Fe

Publ.-Id: 21877

Geometallurgical assessment: beneficiation of rare earth minerals as a possible by-product from the Vergenoeg Fluorite Mine, South Africa

Birtel, S.; Kern, M.; Höfig, T.; Krause, J.; Gutzmer, J.

A systematic geometallurgical study of the rare earth mineralogy and beneficiation potential as by-product was carried out at the Vergenoeg Fluorite Mine, South Africa. For this purpose, a representative suite of samples was collected from a mining block prior to blasting. After mining, this material was tracked through the beneficiation plant by sampling all crucial steps. Whole rock geochemical analyses, quantitative mineralogical and microstructural analyses (by MLA), complemented by mineral chemistry data for relevant REE minerals, were obtained for undisturbed and processed samples. These data were used to assess the deportment of REE and to track the route of REE minerals within the beneficiation process.
Microcrystalline xenotime and monazite were found to be the two most abundant REE minerals, with all other REE minerals of only very minor quantitative importance. Process samples from the flotation circuit illustrate that the material from the cleaner circuit (B) tailing, being usually considered as waste, is strongly enriched in both monazite and xenotime. The REE minerals are well liberated, thus leading to the conclusion that it may be feasible to produce REE minerals as a future by-product by only slight modification of the current flow sheet.

Keywords: REE; MLA; mineral processing; geometallurgy

  • Contribution to proceedings
    13th SGA biennial Meeting in Nancy, France, 24.-27.08.2015, Nancy, France
    Proceedings of the 13th SGA biennial Meeting, Vol 4, Nancy, 1383-1386
  • Poster
    13th SGA biennial Meeting in Nancy, France, 24.-27.08.2015, Nancy, France

Publ.-Id: 21876

Status Report of the ELBE SRF Gun II

Arnold, A.; Lu, P.; Murcek, P.; Teichert, J.; Vennekate, H.; Xiang, R.; Eremeev, G. V.; Kneisel, P.; Stirbet, M.; Turlington, L.

As in 2007 the first 3.5 cell superconducting radio frequency (SRF) gun was taken into operation, it turned out that the specified performance has not been achieved. However, to demonstrate the full potential of this new type of electron source, a second and slightly modified SRF gun II was built in collaboration with Thomas Jefferson National Accelerator Facility (TJNAF). We will report on commissioning and recent results of the new gun, which includes in particular the characterization of the most important RF properties as well as investigations on photo cathode preparation.

Keywords: SRF gun; superconducting radio frequency electron injector; ELBE linear accelerator

  • Lecture (others)
    HOPE / SINEMP Projekttreffen im Rahmen BMBF Verbundforschungsinitiative, 11.03.2015, Wuppertal, Deutschland

Publ.-Id: 21875

Tiefseeastronomie – Chemie mit Sternenstaub

Feige, J.; Wallner, A.; Fifield, L. K.; Merchel, S.; Rugel, G.; Steier, P.; Tims, S.; Winkler, S. R.; Golser, R.

Bei der Explosion massereicher Sterne werden langlebige Radionuklide erzeugt und in den Weltraum hinausgeschleudert. Relikte naher Supernovae lassen sich nicht nur im All, sondern auch auf der Erde selbst entdecken [1]. Um Supernova-Spuren in Tiefseearchiven nachzuweisen, wurden 100 Proben aus 4 Sedimenten untersucht. Die Bohrkerne stammen aus einer Tiefe von 4 200 m des Indischen Ozeans. Sie umfassen ein Altersprofil von 1,7-3,2 Millionen Jahren, in dem sich Supernova-Radionuklide abgelagert haben.
Die Proben wurden chemisch aufbereitet, einzelne Elementfraktionen voneinander getrennt und analysiert. Mit der Beschleunigermassenspektrometrie (AMS), einer sehr sensitiven Methode zur Bestimmung extrem niedriger Konzentrationen langlebiger Radionuklide, wurden 10Be, 26Al, und 60Fe gemessen. Isotopenverhältnisse im Bereich von 10-9 (10Be/9Be) bis zu 10-16 (60Fe/Fe) konnten so quantifiziert werden.
Die Nuklide 10Be und 26Al werden kontinuierlich in der Erdatmosphäre durch hochenergetische Kernreaktionen hauptsächlich an Stickstoff, Sauerstoff und Argon gebildet und können zur Datierung der Sedimente verwendet werden. 60Fe hat keine terrestrischen Quellen, wird jedoch kurz vor und während einer Sternexplosion produziert. Da in dem gemessenen Zeitbereich eine Erhöhung dieses Eisen-Isotops festgestellt wurde, kann davon ausgegangen werden, dass es aus dem Weltall in die Tiefseesedimente eingetragen wurde.

[1] K. Knie, Phys. Rev. Lett., 2004, 93, id. 171103

Keywords: accelerator mass spectrometry; cosmogenic nuclide; supernova; astronomy

  • Invited lecture (Conferences)
    GDCh-Wissenschaftsforum Chemie 2015, 30.08.-02.09.2015, Dresden, Germany

Publ.-Id: 21874

Enhanced photoelectrochemical activity of vertically aligned ZnO-coated TiO2 nanotubes

Cai, H.; Yang, Q.; Hu, Z.; Duan, Z.; You, Q.; Sun, J.; Xu, N.; Wu, J.

Vertically aligned ZnO-TiO2 hetero-nanostructures constructed of anatase TiO2 nanotubes (NTs) and wurtzite ZnO coatings are fabricated by atomic layer deposition of ZnO coatings on electrochemical anodization formed TiO2 NTs, and their photoelectrochemical activities are studied through photoelectrochemical and electrochemical characterization. Compared with bare TiO2 NTs, the transient photocurrent increases to over 1.5-fold for the annealed ZnO-coated TiO2 NTs under visible illumination. The ZnO-coated TiO2 NTs also show a longer electron lifetime, a lower charge-transfer resistance and a more negative flat-band potential than the bare TiO2 NTs, confirming the improved photoelectrochemical activity due to the enhanced Charge separation.

Keywords: Titanium dioxide nanotubes; Zinc oxide coating; Photoluminescence; Photoelectrochemical properties

  • Lecture (Conference)
    Deutsche Physikalische Gesellschaft, 15.-20.03.2015, Berlin, Germany

Publ.-Id: 21873

Influnce of ultrathin ZnO shell thickness on the electrochemical performance of heterogeneous ZnO/TiO2 nanotube arrays

Cai, H.; Liu, F.; Wu, Jiada; Hu, Zhigao; Zhou, S.

Vertically aligned ZnO/TiO2 hetero-nanostructures are successfully fabricated by atomic layer deposition of ZnO shells on electrochemical anodization formed TiO2 nanotube (NT) arrays. The ultrathin and highly conformal ZnO shells (as thin as ~ 2.0 nm) were deposited on TiO2 NTs with precise thickness-control at atomic scale. Its thickness dependent changes in crystallographic, optical and photoelectrochemical properties of ZnO/TiO2 NTs are investigated. The photoelectrochemical activities are studied through electrochemical impendence spectroscopy, flat-band potential and transient photocurrent density measurements. The ZnO/TiO2 NTs with 10-cyle ZnO layers show a longer electron lifetime, a lower charge-transfer resistance and a more negative flat-band potential than the bare TiO2 NTs and the sample with 25-cyle ZnO layers. Consequently, the transient photocurrent of ZnO/TiO2 improves under visible illumination. The improved photoelectrochemical activity in ZnO/TiO2 hetero-nanostructures is attributed to the enhanced charge separation due to the ZnO layer covering out of TiO2 NTs. Our results also indicate that a thinner ZnO layer leads to a larger and more stable photocurrent.

Keywords: Titania nanotube; ZnO oxide shell; Heterogeneous nanostructure; Photoelectrochemical properties

  • Lecture (Conference)
    The Energy & Materials Research Conference, 25.-27.02.2015, Madrid, Spain

Publ.-Id: 21872

Quantitative analysis of PET image quality in PET/MR brain examinations

Schramm, G.; Oehme, L.; Maus, J.; Hofheinz, F.; Lougovski, A.; Petr, J.; Beuthien-Baumann, B.; Kotzerke, J.; van den Hoff, J.

According to [1] and [2] the Philips Ingenuity PET/MR (PETMR) has the same NEMA sensitivity as the Siemens ECAT HR+ standalone PET (PET). However, the NEMA sensitivity is measured without taking into account any attenuating materials such as the patient bed or MRI head coil which are present in every PET/MR brain examination. The aim of this work is to measure and compare the effective PET sensitivity and signal to noise ratios of reconstructed images (SNR) of PETMR for brain examinations under clinical conditions.
A solid 68-Ge phantom (33 MBq) was measured in PETMR and PET on the same day. The total acquisition time was 5min. The phantom was positioned in the MRI head coil in the PETMR and on a dedicated carbon head support in PET as used in clinical examinations. The ratio of prompt coincidences (PR) from the listmode files was calculated. Images were reconstructed employing parameters used in clinical routine. The SNR was calculated as mean over a 3D ROI with a diameter of 10cm divided by standard deviation.
PR was 0.52 (PETMR / PET). SNR was (8.6, 5.2, 3.7, 1.6) (PETMR) and (6.2, 3.9, 2.9,1.6) (PET) for frame durations of 300s, 100s, 50s and 10s, respectively.
Although the effective sensitivity of PETMR for brain examinations is lower than the one of PET, the resulting SNR in the reconstructed images is superior except for short frame durations. The influence on clinical quantification is currently investigated and will be reported.
[1] Zaidi et al. Design and performance evaluation of a whole-body Ingenuity TF PET-MRI system. Phys Med Biol 2011
[2] Herzog et al. NEMA NU2-2001 guided performance evaluation of four Siemens ECAT PET scanners, IEEE TMI

  • Poster
    53. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin (DGN), 22.-25.04.2015, Hannover, D
  • Abstract in refereed journal
    Nuklearmedizin 54(2015), A127

Publ.-Id: 21870

Comparison of FDG-PET based tumor-to-blood standard uptake ratio and standard uptake value with patient outcome in NSCLC

Steffen, I. G.; Hofheinz, F.; Ego, K.; Furth, C.; van den Hoff, J.; Amthauer, H.; Apostolova, I.

It has been demonstrated that the tumor-to-blood standard uptake ratio (SUR) shows a higher linear correlation with the metabolic trapping rate of 18F-fluorodeoxyglucose (FDG) in comparison to the tumor standard uptake value (SUV). The aim of this study was to compare the association of SUR and SUV with patient outcome in NSCLC.
In total 72 patients (66.3±9.4 years) with newly diagnosed, untreated NSCLC were retrospectively included. All patients underwent FDG-PET/CT with dosages ranging from 179 to 254 MBq. Primary tumors were segmented using an
adaptive tumor-to-background thresholding algorithm (ROVER, ABX, Radeberg, Germany). The blood SUV was determined from a cylindrical three-dimensional region of interest placed in the aorta and the maximum SUR (SURmax) was calculated as ratio of tumor SUVmax to blood SUV. The association of SURmax and SUVmax with progression free survival (PFS) and overall survival (OS) was analyzed using the cox proportional hazard model. 95%-confidence intervals are given for hazard ratios (HR).
Progression was observed in 47 patients (65.3%) with a median time of PFS of 10.8 months (range, 0.7-31.4 months). 33 patients died (median OS, 15.4 months [range, 0.7-32.5 months]). The median follow-up time was 20.9 months
(range, 5.2-32.5 months). SURmax was significantly correlated with SUVmax (Spearman's rho, 0.92; p<0.001). Cox regression model revealed a significant association of SURmax with PFS (HR, 1.08 [1.01-1.15]; p=0.029) and a tendency for significance with OS (HR, 1.07 [0.99-1.16]; p=0.071) whereas no significant association was observed for SUVmax neither for PFS (HR, 1.01 [0.98-1.03]; p=0.548) nor for OS (HR, 1.01 [0.98-1.04]; p=0.558).
The maximum tumor-to-blood standard uptake ratio (SURmax) showed a stronger association with patient outcome in comparison to SUVmax. These encouraging results have to be confirmed in further investigations.

  • Poster
    53. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin (DGN), 22.-25.04.2015, Hannover, Deutschland
  • Abstract in refereed journal
    Nuklearmedizin 54(2015), A121-A122

Publ.-Id: 21869

Synthese und enzymkinetische Charakterisierung von N6-Acryloyllysinpiperaziden als potentielle Radiotracer zur funktionellen Bildgebung der Transglutaminase 2 (TGase 2)

Wodtke, R.; Hauser, C.; Jäckel, E.; Wong, A.; Steinbach, J.; Pietzsch, J.; Pietsch, M.; Löser, R.

Eine erhöhte Aktivität der TGase 2 in Tumoren geht einher mit erhöhtem invasivem Potential sowie gesteigerter Chemo- und Strahlenresistenz. Daher stellt dieses Enzym ein interessantes Target für die Entwicklung von PET-Tracern zur funktionellen Bildgebung von Tumoren dar. Unter den in der Literatur beschriebenen Inhibitoren der TGase 2 erscheinen die N6-Acryloyllysin-4-arylpiperazide für die Entwicklung von Radiotracern als besonders geeignet, da sie über eine hohe inhibitorische Potenz und Selektivität sowie günstige pharmakokinetische Eigenschaften verfügen (1). Daher sollten ausgehend von dieser Verbindungsklasse Derivate dargestellt werden, die eine Funktionalisierung mit Radionukliden wie F-18 oder I-124 ermöglichen, sowie deren inhibitorisches Potential gegenüber der TGase 2 ermittelt werden.
Ausgehend von N2-Boc-Lysin wurden in einer Sequenz bestehend aus N6-Acrylierung, Amidknüpfung, Boc-Entschützung und N2-Acylierung verschiedene N2_Acyl-N6-acryloyllysin-4-pyridylpiperazide synthetisiert. Die benötigten Pyridylpiperazine wurden entweder kommerziell bezogen oder in wenigen Syntheseschritten hergestellt. Alle Zielverbindungen wurden in zwei unabhängigen enzymkinetischen Assays, welche die Transamidase- bzw. Hydrolaseaktivität der TGase 2 erfassen, evaluiert. Dabei diente N2_Phenylacetyl-N6-acryloyllysin-4-(6-methylpyridin-2-yl)piperazid als literaturbekannter Referenzinhibitor.
Mit Hilfe der umrissenen Syntheseroute konnte eine Serie von 21 N2_Acyl-N6-acryloyllysin-4-pyridylpiperaziden hergestellt werden. Die verschiedenen Substituenten wurden dabei unter Gesichtspunkten ausgewählt, die auf die Ermöglichung von Synthesen F-18- und Radioiod-basierter Tracerverbindungen abzielen. Die enzymkinetische Charakterisierung der Verbindungen deckte interessante Struktur-Wirkungsbeziehungen auf, wobei unter anderem der Ersatz der Methylgruppe im Referenzinhibitor gegen Fluor zu höherer inhibitorischer Potenz gegenüber der TGase 2 führte.
Fluorierte und iodierte N2_Acyl-N6-acryloyllysin-4-pyridylpiperazide wurden zugänglich gemacht und bezüglich ihrer Hemmwirkung an TGase 2 untersucht, wodurch die Entwicklung von Inhibitor-basierten Radiotracern zur molekularen Bildgebung dieses Enzyms ermöglicht wird. Untersuchungen zur F-18-Markierung geeigneter Kandidaten sind in Planung.
(1) Wityak et al. ACS Med. Chem. Lett. 2012, 3, 1024

  • Poster
    53. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin (DGN), 22.-25.04.2015, Hannover, Deutschland
  • Abstract in refereed journal
    Nuklearmedizin 54(2015), A105

Publ.-Id: 21868

Radioaktive Markierung von NOTA mit Tc-99m -Tricarbonyl - eine Methode zur Markierung von Antikörpern

Naumann, A.; Schubert, M.; Jentschel, C.; Wunderlich, G.; Pietzsch, H.-J.; Kotzerke, J.

Cetuximab ist ein EGFR affiner Antikörper. Bei Markierungen mit Tc-99m werden hohe Temperaturen und Reduktionsmittel benötigt, um Kopplungen an Biomolekülen zu erzielen. Mit dem Komplexbildner 2,2',2''-(1,4,7-triazonane-1,4,7-triyl)triacetic acid (NOTA) ist eine schonende Komplexierung mit Tc-99m-Tricarbonyl möglich. Mit einem doppelt funktionalisierten Alexa488-Cetuximab-NOTA-Konjugat wurden Markierungsparameter angepasst und erste Zellstudien durchgeführt. Radioaktivität und Fluoreszenz konnten mit dem gleichen Antikörper parallel in der Zelle detektiert werden.
Die Markierung des Antikörpers mit Tc-99m[(CO)3(H2O)3]+ wurde durch Anpassung der Reaktionsparameter und Reinigungsverfahren optimiert. Aussagen über Ausbeute, Qualität und Stabilität wurden mit Radio-HPLC und Radio-DC getroffen. Die Integrität des Antikörpers nach der Markierung wurde über SDS-Page untersucht. Zelluläre Studien mit EGFR-positiven A431- und EGFR-negativen MDA-Zellen beinhalteten Uptake und Bindungsstudien (Gamma-Counter) bei 4°C/37°C. Die Detektion der Fluoreszenz fand über ein invers messendes Fluoreszenzmikroskop (Zeiss) statt.
Eine Komplexierung Tc-99m[(CO)3(H2O)3]+ mit NOTA konnte erzielt werden. Die Markierung des modifizierten Antikörpers zeigte eine radiochemische Reinheit von > 95%. Nach 24h konnten noch 75% des markierten Antikörpers nachgewiesen werden. Zelluläre Untersuchungen ergaben max. spezifische Aufnahmen bei A431-Zellen nach 1h (48%/0,5Mio.Zellen/2MBq) mit ca. 30% Membran gebundenem Anteil, welcher nach 24h abnimmt (1,5%/0,5Mio.Zellen/2MBq). Ein fluoreszenzmikroskopischer Bindungsnachweis konnte erbracht werden.
Eine Markierung des modifizierten Cetuximabs mit Tc-99m[(CO)3(H2O)3]+ konnte entwickelt werden. Geeignete Parameter und Reinigungsverfahren wurden etabliert. Bindungsstudien zeigten eine spezifische Anreicherung an A431-Zellen mit maximaler Aufnahme nach 1h. Die Anreicherung des modifizierten Antikörpers konnte über Fluoreszenzmikroskopie visualisiert werden.

  • Poster
    53. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin (DGN), 22.-25.04.2015, Hannover, D
  • Abstract in refereed journal
    Nuklearmedizin 54(2015), A102

Publ.-Id: 21867

Radiosynthesis of 18F-cabozantinib, a small molecule angiokinase inhibitor

Schwebe, M.; Steinbach, J.; Pietzsch, J.; Knieß, T.

Cabozantinib is a highly affine receptor tyrosine kinase (angiokinase) inhibitor (TKI) selectively targeting VEGFR-2 and c-Met. Radiolabeled cabozantinib might be a valuable probe to monitor induction of angiogenesis and the success of anti-angiogenic therapy in vivo. For this purpose, we developed 18F-cabozantinib, a potential PET tracer where the already existing fluorine atom is replaced by fluorine-18.
The radiotracer 18F-cabozantinib is obtained via a condensation of an acyl chloride precursor with 4-[18F]fluoroaniline. Briefly, 1,4-dinitrobenzene reacts with [18F]fluoride in DMSO for 5 min at 140°C to build 4-[18F]fluoronitrobenzene which subsequently is separated by SPE and eluted with methanol. Reduction with Pd/C and NaBH4 then delivered 4-[18F]fluoroaniline which is trapped on a second SPE cartridge and eluted with THF to the precursor to form 18F-cabozantinib.
1-[4-(6,7-dimethoxy-quinoline-4-yloxy)-phenylcarbamoyl]-cyclopropanecarbonyl chloride as precursor was synthesized via three steps in 48% overall yield. 4-[18F]fluoroaniline was obtained in > 50 radiochemical yield (dc) after cartridge purification. By large scale synthesis via a TracerLAB (GE) synthesizer comprising 18F-fluorination and reduction, 4-[18F]fluoroaniline was produced in a 2 GBq scale. 10 mg of the acyl chloride precursor was reacted with 2 GBq of 4-[18F]fluoroaniline in THF at ambient temperature for 15 min to build 18F-cabozantinib with > 90% radiochemical yield. Final semi-preparative HPLC purification delivered 18F-cabozantinib in radiochemical purity > 95% and a specific activity > 20 GBq/µmol.
In a multitude of experiments the optimal conditions for radiosynthesis and purification of -[18F]fluoroaniline and 18F-cabozantinib could be established. By a partly automated procedure the small molecule angiokinase inhibitor 18F-cabozantinib was successfully synthesized in high chemical and radiochemical purity in a 200 MBq scale.

  • Poster
    53. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin (DGN), 22.-25.04.2015, Hannover, Deutschland
  • Abstract in refereed journal
    Nuklearmedizin 54(2015), A100-A101

Publ.-Id: 21866

Analyse der Kalibrierung eines TOF-Scanners mit pixelliertem Flächendetektor (Gemini TF 16 BigBore)

Nemer, U.; Maus, J.; Schramm, G.; Meyer, P.; Hennig, J.; Mix, M.

An den Philips Gemini TF PET/CT-Scannern wird die SUV-Kalibrierung für die korrekte Quantifizierung über eine Zerfallsreihe mit Akquisition im Sinogramm (SM)-Format durchgeführt. Die klinische Akquisition erfolgt jedoch im
Listmode (LM)-Format. Durch eine zusätzliche SUV-Validierung (SUV-Val) soll der Unterschied zwischen beiden Formaten korrigiert werden, unter der Annahme, dass dieser über die gesamte Breite der Singles-Zählraten prozentual
konstant bleibt. In wie weit dies korrekt ist und welche quantitativen Auswirkungen dies hat, wurde untersucht.
Für die Messung wurde ein zylindrisches Phantom (V=9,3l) mittig im Scanner positioniert und über 12h gemessen. Neben der Kalibrierung im SM-Format (SM-Kalib) und der dazugehörenden SUV-Val, wurde die Zerfallsreihe wiederholt, allerdings im LM-Format (LM-Kalib). Die Rekonstruktion der TOF-Messung erfolgte im klinischen WB-Protokoll. Auf Grundlage dieser Messungen wurden Kalibrierungstabellen erstellt und an Messungen des NEMA Image Quality Phantoms und eines ebenfalls über 12h gemessenen 5,6l-Phantoms, überprüft.
Im Vergleich zur LM-Kalib verhalten sich die Kalibrierungsfaktoren bis 10 Mcps äquivalent, bei größeren Zählraten ergibt sich jedoch ein Unterschied von bis zu 15%. Die unterschiedlichen Kalibrierungstabellen resultierten beim
NEMA-Phantom in einer Abweichung von 1% im SUV-Wert des Hintergrundes und im Mittel um 2% bei den Recovery-Koeffizienten. Bei der dynamischen Messung des Brain-Phantoms ergibt sich für die SUV-Werte eine
Verteilung von [0,94-1,02] SUV (LM-Kalib) zu [0,83-1,01] SUV (SM-Kalib).
Es konnte gezeigt werden, dass im klinisch relevanten Zählratenbereich nur ein geringer Unterschied zwischen beiden Verfahren besteht. Bei höheren Zählraten kann jedoch eine größere Abweichung entstehen,die bei dynamischen
Untersuchungen mit Bolusinjektion oder kurzlebigeren Isotopen von Relevanz sein kann. In (1) wurde ebenfalls auf eine ähnliche Problematik bei den Philips PET/MR-Geräten hingewiesen, es scheint sich daher um einen systemweiten Effekt bei Philips-Geräten zu handeln.
(1) "Phantom-based evaluation of quantification accuracy of combined PET/MRI", Langner et al., DGN Jahrestagung 2013 (P43).

  • Lecture (Conference)
    53. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin (DGN), 22.-25.04.2015, Hannover, Deutschland
  • Abstract in refereed journal
    Nuklearmedizin 54(2015), A86

Publ.-Id: 21865

On the relation between blob and tube-of-response based approaches to system matrix calculation in PET

Lougovski, A.; Hofheinz, F.; Schramm, G.; Maus, J.; van den Hoff, J.

We have presented previously a model for fast on-the-fly volume-of-intersection (VOI) system matrix calculation for PET image reconstruction. The model replaces cubic voxels by spheres and the usual line of response (LOR) by a cylindrical tube of response (TOR). The use of spherically symmetric voxel makes it superficially similar to the blob model, where tracer distribution is discretized using modified Kaiser-Bessel window functions (KBWF) rather than cubic voxels. We now present an extended TOR model with radially varying tube density (eTOR) and investigate the relation between eTOR and the blob model. We also analyse under which conditions they can be mapped to each other and which density function leads to the best mapping.
We start with an analyses of circumstances under which both models generate equivalent system matrices. For that we investigate weighting functions of both models (Length of Intersection between LOR and blob and VOI between
TOR and sphere as functions of the impact parameter, respectively). We tried several candidate TOR density functions (Gaussian, difference of error functions and modified KBWF) and determined optimal parameters for the density
functions by least squares fitting of the respective TOR weighting function to the targeted weighting function of the blob model. Both, eTOR and blob models, were evaluated (using phantom data acquired on the Philips Ingenuity TF PET/MR system) regarding reconstructed resolution and noise level.
A good concordance between eTOR and blob model weighting functions can be achieved with all candidate functions. The best fit (residuals <5e-4) was obtained for KBWF. As expected, the close equivalence between the
weighting functions resulted in almost identical reconstructed resolution and noise level for all investigated voxel sizes and contrast ratios.
We analysed different density function for eTOR models and showed that all of them can be used to mimic (with high accuracy) the conventional blob model, proving a generic nature of the eTOR approach. The achieved equivalence of the weighting functions between eTOR and blob models also indicates that the conventional resampling step of the blob model might be unnecessary.

  • Lecture (Conference)
    53. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizn (DGN), 22.-25.04.2015, Hannover, Deutschland
  • Abstract in refereed journal
    Nuklearmedizin 54(2015), A85

Publ.-Id: 21864

Scan time-normalized tumor to blood standard uptake ratio (SUR) in pretherapeutic FDG PET is superior to SUV as a prognostic factor in patients with esophageal carcinoma

Hofheinz, F.; Bütof, R.; Zöphel, K.; Schütze, C.; Löck, S.; Stadelmann, T.; Schmollack, J.; Kotzerke, J.; Baumann, M.; van den Hoff, J.

Tumor SUV is widely used for quantitative assessment of tumor metabolism in FDG PET and its potential for therapy outcome prediction in various cancer diseases has been investigated in many publications. However, the SUV approach has well known limitations compromising its ability to act as a surrogate parameter of glucose consumption. Recently, we have shown that SUR overcomes most of these limitations as long as FDG kinetics in the target structure can be considered irreversible [1,2]. The aim of this work was to compare the prognostic value of SUR and SUV in patients with esophageal carcinoma.
FDG-PET/CT was performed in 103 consecutive patients ((63+/-11)y, 89 males) with newly diagnosed esophageal cancer prior to definitive radiochemotherapy. In the PET images the metabolic active volume (MTV) of the primary tumor was delineated with an adaptive threshold method. The blood SUV was determined by manually delineating the aorta in the low dose CT. SUR values were computed as ratio of tumor SUV and blood SUV. SUR values were
scan-time-normalized to 60 min p.i. as described in [2]. Kaplan-Meier analysis and univariate Cox regression with respect to overall survival (OS), locoregional control (LRC), and distant-metastases-free survival (DM) was performed
for SUVmax, SURmax and clinically relevant parameters. Additionally, a multivariate Cox regression including clinical parameters, which were univariate significant, as confounding factors was performed.
Both, SUVmax and SURmax, were prognostic factors for OS and DM, but not for LRC. With respect to OS a univariate Cox regression showed a slightly increased hazard ratio (HR) for SURmax (HR=2.2, p=0.003) compared to SUVmax (HR=1.8, p=0.01). With respect to DM HR of SURmax was notably larger than HR of SUVmax (HR=6.5, p=0.01 compared to 2.8, p=0.044). Moreover, in multivariate Cox regression only SUR was an independent prognostic factor for OS and for DM the prognostic value of SUR was notably higher than of SUV.
Our results indicate that blood- and time-normalization increases the prognostic value of lesion uptake in pretherapeutic FDG PET of patients with esophageal carcinoma. More comprehensive investigations are necessary to confirm these results.
[1] van den Hoff et al, EJNMMI Res 2013, 3:77.[2] van den Hoff et al, EJNMMI Res 2014, 4:18.

  • Lecture (Conference)
    53. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin (DGN), 22.-25.04.2015, Hannover, Deutschland
  • Abstract in refereed journal
    Nuklearmedizin 54(2015), A83-A84

Publ.-Id: 21863

Relationship between asphericity of FDG uptake in the primary tumor and histopathology in NSCLC

Apostolova, I.; Steffen, I. G.; Ego, K.; Kalinski, T.; Schultz, M.; Furth, C.; Genseke, P.; Buchert, R.; Hofheinz, F.; Amthauer, H.

Asphericity (ASP) is a novel FDG-PET-based in vivo measure of tumor heterogeneity which quantitatively characterizes the tumor's deviation from sphere shape. To better understand its biological and histopathological correlates we
investigated the relationship with histopathological features in NSCLC.
FDG-PET/CT had been performed in 76 unselected patients (66.4±9.3 years) with newly diagnosed NSCLC prior to therapy. Primary tumor resection specimens and core biopsies were used to assess histologic subtype, degree of
differentiation, and Ki-67 proliferation index. The FDG PET image of the primary tumor was delineated by an automatic algorithm based on adaptive thresholding taking local background into account. ASP and SUVmax were considered as quantitative PET measures. Their correlation with clinicopathological features was analyzed using Spearman's correlation; differences between groups were analyzed using Kruskal-Wallis and Mann-Whitney tests.
Squamous cell carcinomas (SCC) exhibited significantly higher SUVmax than adenocarcinomas (ADC, Mann-Whitney, p=0.04), whereas there was no significant effect of histological type on ASP. There was a moderate but significant correlation with Ki-67 for ASP (r=0.39, p=0.001), a weak correlation for SUVmax (r=0.28, p=0.02). Both correlations were stronger in the ADC than in the SCC subgroup. Ki-.67 > 50% was associated with higher ASP (Mann-Whitney, p=0.04) and higher SUVmax (p=0.07). Grade 3 tumors had a tendency for higher ASP (p=0.07) but not SUVmax (p=0.29). Pathological T and N stage were associated with both SUVmax (Kruskal-Wallis, p=0.004/ p=0.02) and ASP (p<0.001/p=0.06). Only SUVmax was associated with M stage (p=0.02).
Tumor asphericity (ASP) appears to depict different features of tumor biology in NSCLC than SUVmax. This is in line with our previous finding that ASP provides independent information for prognosis in patients with NSCLC.

  • Lecture (Conference)
    53. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin (DGN), 22.-25.04.2015, Hannover, D
  • Abstract in refereed journal
    Nuklearmedizin 54(2015), A75

Publ.-Id: 21862

Ga-68-DATATOC: Radiopharmakologie und Bildgebung

Bergmann, R.; Ullrich, M.; Waldron, B. P.; Seemann, J.; Ziegler, C. G.; Pietzsch, J.; Steinbach, J.; Rösch, F.

Ga-68-DOTATOC und Ga-68-DOTATATE werden intensiv in der Routinediagnostik von neuroendokrinen Tumoren und deren Metastasen eingesetzt. Der neue Radiotracer Ga-68-DATATOC (Chelator DATA (6-Amino-1,4-diazepin-triessigsäure) verknüpft mit [Tyr3]-Octreotid) kann aber im Unterschied zu den Ga-68-DOTA-Peptiden bereits bei Raumtemperatur quantitativ radiomarkiert werden. In ersten präklinischen Untersuchungen des Ga-68-DATATOC sollte dessen radiopharmakologisches Profil und Potential zur Bildgebung von neuroendokrinen Tumoren ermittelt werden.
Nach manueller Radiomarkierung mit Ga-68 und einmaliger, intravenöser Injektion des Ga-68-DATATOC, wurden dessen Bioverteilung (Ratte und Maus), -Kinetik, metabolische Stabilität und die spezifische Akkumulation (Blockierung mit Octreotide (OC)) im Somotostatin-Rezeptor-exprimierenden Maus-Phäochromozytom-Modell (MPCmCherryt) in NMRI nu/nu Mäusen untersucht. In der Kleintier-PET wurde die Tumordarstellung von Ga-68-DATATOC und Ga-68-DOTATATE verglichen.
In der PET wurden die Tumoren mit Ga-68-DATATOC bereits nach 10 min klar und kontrastreich dargestellt. Die Bioverteilung ergab eine spezifische Anreicherung im Tumor (3.73 ± 1.49 SUV) und Pankreas (0.57 ± 0.17 SUV) als
SSTR exprimierenden Organen, die durch OC blockiert (0.45 ± 0.15;0.12 ± 0.06; entsprechend) werden konnte. Über 70%ID wurden renal ausgeschieden und nur maximal 5%ID in den Nieren zurückgehalten. Der Blutspiegel von
Ga-68-DATATOC war nach einer Stunde niedriger als der von Ga-68-DOTATATE. 93,7% (Maus, 1 h) bzw. 72% (Ratte, 2 h) der Blutplasmaaktivität lagen dabei als Ga-68-DATATOC vor.
Im Unterschied zu DOTA, konnte DATA in Verbindung mit [Tyr3]-Octreotid bereits bei Raumtemperatur quantitativ mit Ga-68 radiomarkiert werden. Die Bioverteilung, Blockierungsexperimente und dynamischen PET-Untersuchungen an MPCmCherry-tumortragenden Mäusen ergaben für Ga-68-DATATOC das typische Profil eines an SSTR bindenden Radiotracers. Das schnelle Erreichen eines hohen Kontrastes zeigt auf das beachtliche Potential als diagnostisches Radiopharmakon.
(Die Arbeiten wurden von der DFG-in dem Projekt BE-2607/1-1 und ZI-1362/2-1 gefördert.).
[1] In vivo fluorescence imaging and urinary monoamines as surrogate biomarkers of disease progression in a mouse
model of pheochromocytoma. Ullrich M, Bergmann R et al. Endocrinology. 2014 Nov;155(11):4149-56.

  • Lecture (Conference)
    53. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin (DGN), 22.-25.04.2015, Hannover, Deutschland
  • Abstract in refereed journal
    Nuklearmedizin 54(2015), A33-A34

Publ.-Id: 21861

Test-retest variability of quantitative MRI perfusion measurements with ASL underclinical conditions

Petr, J.; Schramm, G.; Platzek, I.; Hofheinz, F.; van den Hoff, J.

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.
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.
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%).
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.
(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

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.

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.
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).
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.
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 Logo Abstract in refereed journal
    Journal of Nuclear Medicine 56(2015)3, 33

Publ.-Id: 21859

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.
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.
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


Publ.-Id: 21858

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

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

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

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

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

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

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

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

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

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