Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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35836 Publications

The Production of Cu Nanoparticles on Large Area Graphene by Sputtering and in-Flight Sintering

Gokhan, U. C.; Acet, M.; Tekgul, A.; Farle, M.; Atakan, S.; Lindner, J.

We have developed a simple method to synthesize Cu nanoparticles on graphene, which is a composite that is currently investigated for use as biosensors. Firstly, large area graphene (2 x 2 cm(2)) was prepared by chemical vapor deposition on Cu foils and then transferred onto SiO2 substrates by a transfer process. The Cu nanoparticles were collected on graphene/SiO2 by magnetron sputtering. The presence of graphene was verified by optical microscopy and Raman spectroscopy. The structure of graphene decorated with Cu nanoparticles was determined by scanning and transmission electron microscopy. The results show that the Cu nanoparticles acquire a cubic structure on graphene.

Keywords: Cu nanoparticle, CVD; gas phase; graphene, Magnetron Sputtering

Publ.-Id: 26433

Development of a novel active technique for bremsstrahlung source term determination in laser-plasma experiments

Molodtsova, M.; Ferrari, A.; Cowan, T.

The use of high intensity, high power lasers recently increased in research facilities all over the world. By laser-matter interactions it is possible to study new mechanisms of ion/electron acceleration, and matter under extreme conditions via pump-probe experiments. At the X-ray Free Electron Laser in Hamburg (EuXFEL) such extreme conditions will be generated and studied at the High Energy Density (HED) instrument at the Helmholtz International Beamline for Extreme Fields (HIBEF). For such experiments a wide variety of novel detectors will be needed. One of the challenges will be the detection of the bremsstrahlung radiation emitted with ultrashort pulse widths (gamma flash) down to the fs range, at every laser shot.
To characterize the gamma flash usual spectrometry techniques using pulse height analysis can not be used, because of its short pulse width as well as its high intensity (~10^10 photons). A possible approach is to measure the energy deposited by photons in a detector with a layered structure, to obtain information about the longitudinal development of the electromagnetic shower. With this data the photon spectrum can be then reconstructed by using an unfolding technique. To perform a successful unfolding, detector materials and thicknesses have to be optimized to be able to resolve the photon spectrum in the dynamic range between 50 keV and 20 MeV.
By means of FLUKA Monte Carlo simulations the development of the electromagnetic shower and the distribution of the energy deposited by the incident radiation were studied for different detector models. The model that showed the most promising set of response functions to perform a deconvolution, was chosen to realize the first prototype.
In this poster the first results of this work are presented.

  • Poster
    SATIF-13 (13th Meeting of the task-force on Shielding aspects of Accelerators, Targets and Irradiation Facilities), 10.-12.10.2016, Dresden, Deutschland
  • Open Access Logo Contribution to proceedings
    SATIF-13 (13th Meeting of the task-force on Shielding aspects of Accelerators, Targets and Irradiation Facilities), 10.-12.10.2016, Dresden, Deutschland
    Proceedings of SATIF-13: NEA

Publ.-Id: 26431

High-pressure chemistry of hydrocarbons relevant to planetary interiors and inertial confinement fusion

Kraus, D.; Hartley, N. J.; Frydrych, S.; Schuster, A. K.; Rohatsch, K.; Brown, S.; Cowan, T. E.; Cunningham, E.; Demaio-Turner, S. J.; van Driel, T.; Fletcher, L. B.; Galtier, E.; Gamboa, E. J.; Laso Garcia, A.; Gericke, D. O.; Granados, E.; Heimann, P. A.; Lee, H. J.; Macdonald, M. J.; Mackinnon, A. J.; Mcbride, E. E.; Nam, I.; Neumayer, P.; Pak, A.; Pelka, A.; Prencipe, I.; Ravasio, A.; Redmer, R.; Rödel, M.; Saunders, A. M.; Schölmerich, M.; Schörner, M.; Sun, P.; Falcone, R. W.; Glenzer, S. H.; Döppner, T.; Vorberger, J.

Diamond formation in polystyrene (C8H8)n, which is laser-compressed and heated to conditions around 150 GPa and 5,000 K, has recently been demonstrated in the laboratory [D. Kraus et al., Nat. Astron. 1, 606-611 (2017)]. Here we show an extended analysis of the acquired data and their implications for planetary physics and inertial confinement fusion. Moreover, we discuss the advanced diagnostic capabilities of adding high-quality small angle X-ray scattering and spectrally resolved X-ray scattering to the platform, which shows great prospects of precisely studying the kinetics of chemical reactions in dense plasma environments at pressures exceeding 100 GPa.

Publ.-Id: 26430

Coherent excitation of heterosymmetric spin waves with ultrashort wavelengths

Dieterle, G.; Förster, J.; Stoll, H.; Semisalova, A. S.; Finizio, S.; Gangwar, A.; Weigand, M.; Noske, M.; Fähnle, M.; Bykova, I.; Bozhko, D. A.; Musiienko-Shmarova, H. Y.; Tiberkevich, V.; Slavin, A. N.; Back, C. H.; Raabe, J.; Schütz, G.; Wintz, S.

In the emerging field of magnonics, spin waves are foreseen as signal carriers for future spintronic information processing and communication devices, owing to both the very low power losses and a high device miniaturisation potential predicted for short-wavelength spin waves. Yet, the controlled and efficient excitation of propagating nanoscale spin waves remains a challenge to be resolved. Here, we report the observation of high-amplitude, ultrashort dipole-exchange spin waves (down to 80 nm wavelength at 10 GHz frequency) in a ferromagnetic single layer system, coherently excited by the driven dynamics of a spin vortex core. We used time-resolved x-ray microscopy to directly image such propagating spin waves for a wide range of excitation frequencies. By further analysis, we found that these waves exhibit a heterosymmetric mode profile, involving regions with anti-Larmor precession sense and purely linear magnetic oscillation. In particular, this mode profile consists of dynamic vortices with laterally alternating helicity, leading to a partial magnetic flux closure over the film thickness, which is explained by a strong and unexpected mode hybridisation. The spin-wave phenomenon observed is a general effect inherent to the dynamics of sufficiently thick ferromagnetic single layer films, independent of the specific excitation method employed.

Keywords: spin wave vortex x-ray microscopy

  • Physical Review Letters 122(2019), 117202
    DOI: 10.1103/PhysRevLett.122.117202
  • Lecture (Conference)
    Intermag 2018, 23.-27.04.2018, Singapur, Singapur
  • Lecture (Conference)
    International Conference on Magnetism, 15.-20.07.2018, San Francisco, USA
  • Lecture (Conference)
    23rd International Colloquium on Magnetic Films and Surfaces, 22.-27.07.2018, Santa Cruz, USA
  • Lecture (Conference)
    9th Joint European Magnetic Symposia, 03.-07.09.2018, Mainz, Germany
  • Contribution to WWW
    arXiv:1712.00681v3 [cond-mat.mes-hall]:
  • Lecture (Conference)
    Magnonics 2019, 28.07.-01.08.2019, Carovigno, Italien


Publ.-Id: 26429

µ-RayStation 5: Expanding functionality of a clinical treatment planning system towards application for image-guided small animal radiotherapy

Tillner, F.; Nilsson, R.; Nordström, M.; Dietrich, A.; Baumann, M.; Krause, M.; Enghardt, W.; Bütof, R.

The Small Animal Image-Guided Radiation Therapy (SAIGRT) system has been developed at OncoRay by downsizing treatment technology of human radiation oncology towards small animal experiments [1,2]. The system consists of a gantry module, covered by a radiation protection housing, and a supply module. The gantry module comprises (1) a stationary unit incorporating a 3D computerised animal stage positioner and (2) a 360° rotating arm holding a 225 kV X-ray tube as radiation source, a system of flat aperture collimators for beam shaping and a flat-panel detector for X-ray imaging. Supported by dedicated software, the SAIGRT system allows for a precise and accurate, conformal irradiation and X-ray imaging of small animals using an experimental workflow resembling the patient treatment process. However, only simplified treatment planning has been applied so far, in lack of a full 3D treatment planning system (TPS).
Materials & Methods:
RayStation 5 is an advanced, clinical TPS by RaySearch Laboratories AB, which works across different external beam radiotherapy devices (e.g. linear accelerators, proton therapy). Import / export options are available for various image modalities. Furthermore, it provides versatile manual and automatic tools for contouring as well as different methods for rigid and deformable image registration. Various irradiation devices can be modelled by specifying characteristics of design features and beam shaping components (e.g. material, motion, geometry) as well as dosimetric properties of the irradiation field. For plan design, the software comprises machine-dependent functions and dose calculation engines resulting in realistic dose distributions. In addition, different features for plan evaluation and comparison are accessible. However, all tools are intended for patients and thereby not suitable for the submillimetre dimensions of small animals. For this reason, µ-RayStation 5 has been developed in collaboration with RaySearch. Based on a research version of the clinical TPS, functionality has been expanded to comply with the requirements of small animal irradiators such as the SAIGRT system.
Tools for contouring and image registration as well as the dose grid have been modified to support dimensions down to 0.1 mm. The machine model for small animal irradiators includes characteristics such as the geometry of cone-shaped beams (e.g. distances, aperture sizes), a focal spot model (e.g. 2D Gaussian distribution) and a photon energy spectrum of an X-ray tube with several hundred kV accelerating potential. Plan design is supported for 3D conformal radiotherapy using fixed beams and static arcs. Dose calculation is performed by the VMC++ Monte-Carlo engine [6]. The number of simulated histories and the dose quantity (dose to water or medium) can be selected. Monitor units have been replaced by irradiation time. The SAIGRT system was successfully modelled using a 200 kV spectrum generated from SpekCalc [3-5] showing good agreement with verification measurements.
µ-RayStation 5 provides comprehensive functionality of a clinical TPS for small animal studies allowing an efficient experimental workflow for experienced Raystation users. Flexibility of the software facilitates adaption to other small animal irradiators and expansion of usage for preclinical research in our institute especially for commencing small animal proton irradiations.
[1] Tillner et al. (2014), Z Med Phys. 24(4): 335-51
[2] Tillner et al. (2016), Phys Med Biol. 61(8): 3084-108
[3] Poludniowski GG, Evans PM (2007), Med Phys. 34(6): 2164-74
[4] Poludniowski GG (2007), Med Phys. 34(6): 2175-86
[5] Poludniowski GG et al. (2009), Phys Med Biol. 54(19): 433-8
[6] Kawrakow I, Fippel M (2000), In: The Use of Computers in Radiation Therapy, Springer: 126-8

Keywords: image-guided small animal radiotherapy

  • Lecture (Conference)
    4th Conference On Small Animal Precision Image-Guided Radiotherapy, 12.-14.03.2018, Lissabon, Portugal

Publ.-Id: 26428

4D Delivery - Treatment verification in particle therapy

Richter, C.; Jakobi, A.; Meijers, A.; Knopf, A.

4D delivery verficiation, mainly focussing on machine log-file based 4d dose reconstruction using 4D-CT and motion surrogate information

  • Invited lecture (Conferences)
    4D Treatment (Planning) Workshop, 04.-05.12.2017, Wien, Österreich

Publ.-Id: 26427

Scale dependent soil erosion dynamics in a fragile loess landscape

Baumgart, P.; Eltner, A.; Domula, A. R.; Barkleit, A.; Faust, D.

Loess landscapes provide highly fertile soils in temperate zones and thus are often under intensive agricultural use with a high susceptibility to soil degradation. Magnitudes of soil erosion on different spatio-temporal scales are hard to recognise or were even ignored due to the restricted human perception. Precise and reliable soil erosion measurements are still very scarce, especially for intense single precipitation. In this study, present-day soil erosion is investigated as a complex process on different spatial and temporal scales, such as a short-term observation on plot scale and a medium-term observation on slope scale, which lead to long-term indications for the catchment scale. Classical soil drillings, 7Be and 137Cs radionuclide tracer investigations and non-invasive unmanned aerial vehicle (UAV) photogrammetry were performed for two cultivated field sections within the Saxon Loess Province (Eastern Germany). The main findings are: (1) for a short-term intense precipitation event interrill soil erosion reaches up to 4.69 ± 0.73 mm on plot scale and mean total erosion values reach 1.45 mm on catchment scale; (2) medium-term soil erosion exhibit values up to 33 cm on slope scale within the last 50 years, indicating a strong landscape liability to agricultural use; (3) climatic pressure with increasing temperature and precipitation shifts towards seasons with bare soil surfaces favours the soil erosion process and increases the fragility of the landscape substantially. In conclusion, soil erosion is the driving factor of present-day landscape evolution in the Saxon Loess Province.

Keywords: Saxon Loess Province; Beryllium-7; Caesium-137; unmanned aerial photogrammetry (UAV)

  • Contribution to external collection
    in: Zeitschrift für Geomorphologie, Stuttgart: E. Schweizerbart'sche Verlagsbuchhandlung, 2017, 191-206
    DOI: 10.1127/zfg/2017/0409

Publ.-Id: 26423

Charakterisierung von Ba- und Ra-Verbindungen mit Calixarenen und anderen Chelatoren

Reissig, F.

Die vorliegende Arbeit beschäftigt sich mit zwei Schwerpunkten. Zum einen sollen eine Vielzahl von Derivaten eines modifizierten Calix[4]arengründgerüsts sowie ein modifiziertes Calix[6]arenderivat bezüglich ihrer komplexbildenden Eigenschaften untersucht und Komplexbildungskonstanten mit einer Methode unter der Verwendung der radioaktiven Barium- und Radiumisotope ermittelt werden. Diese Methode ist zunächst zu entwickeln und die erhaltenen Ergebnisse mit den Berechnungsmethoden, welche innerhalb der Arbeitsgruppe etabliert und bezüglich der Calix[4]arenderivate anwendbar sind, zu vergleichen. Der Komplex mit der größten Stabilität soll festgestellt werden, um ihn weiter zu modifizieren oder bei ausreichender Stabilität erste biologische Studien beginnen zu können. Zum anderen soll auf der strukturellen Grundlage von Carbazol ein zusätzlicher makrocyclischer potentieller Komplexbildner in Form eines Calix[3]carbazolderivates synthetisiert werden, welcher alternativ zu den Calix[4]aren- und Calix[6]arenderivaten verwendet werden kann. Abschließend sollen die Komplexstabiltäten der Calix[n]arene, der synthetisierten Calix[3]carbazolderivate und kommerzieller Chelatoren mit den zweifach positiv geladenen Barium- und Radiumionen untereinander verglichen werden. Da es kein natürlich vorkommendes, nicht radioaktives Radiumisotop gibt, wird aufgrund seiner chemischen Ähnlichkeit stabiles Barium als Surrogat verwendet, um nicht radioaktive Untersuchungen durchführen zu können. Die erhaltenen Erkenntnisse sollen anschließend auf Untersuchungen mit Radium übertragen werden. Auch für die radioaktiven Studien wird zunächst das radioaktive Bariumisotop Barium-133 verwendet, da es eine längere Halbwertszeit besitzt als die verfügbaren Radiumisotope.

  • Master thesis
    HTW Dresden, 2017
    Mentor: Dr. Constantin Mamat
    0081 Seiten

Publ.-Id: 26421

Bioassociation of uranium onto an extremely halophilic microorganism relevant in nuclear waste repositories in rock salt

Bader, M.

Microorganisms indigenous to rock salt must be considered for the safety analysis of a final repository for radioactive waste in a salt rock formation. Metabolic activity can cause microbial induced redox processes and influence radionuclide speciation and solubility. Additionally, passive biosorption onto living as well as dead biomass may affect the migration of radionuclides [1].
An extremely halophilic archaeon indigenous to rock salt was used for this study. Two similar strains with different origin were compared concerning their interaction processes with uranium. Halobacterium noricense DSM 15987 was originally isolated from an Austrian salt mine [2], the second strain Halobacterium putatively noricense was isolated from the Waste Isolation Pilot Plant (WIPP) [3].
[1] Lloyd, J. R. et al., Interactions of Microorganisms with Radionuclides (Eds. M. J. Keith-Roach, F. R. Livens), 313-342 (2002).
[2] Gruber, C. et al., Extremophiles, 8, Page 431-439 (2004).
[3] Swanson, J. S. et al., Status Report on the Microbial Characterization of Halite and Groundwater Samples from the WIPP - Status report Los Alamos National Laboratory, Page 1ff. (2012).

  • Lecture (Conference)
    Kompetenzzentrum Ost für Kerntechnik, 07.12.2017, Dresden, Deutschland

Publ.-Id: 26420

Topological spin textures as spin-wave emitters

Wintz, S.

The investigation of propagating spin waves is a key topic of magnetism research [1]. For the excitation of short wavelengths, it was typically necessary to either use patterned transducers with sizes on the order of the desired wavelengths (striplines or point-contacts) or to generate such spin waves parametrically by a spatially uniform double-frequency microwave signal [2]. Recently, we found a novel mechanism for the lo- cal excitation of spin waves, which overcomes the lower wavelength limit given by the minimum patterning size. This method utilizes the translation of natural topological spin textures, e.g. the gyration of spin vortex cores, to generate spin waves [3]. Yet in terms of signal transfer, spin waves excited by a 0D defect, propagating isotropically in a 2D matrix su er from a geometry induced amplitude decay. This decay is prevented when the dimensionality di erence between source and host matrix is reduced to one. Here we will show that this can be achieved in vortex pair systems with moderate uniaxial intrinsic anisotropy, where domain walls may act both as 1D channels for direc- tional wave propagation and as emitters for 2D plane waves [4]. Finally, we will address vortex core induced spin-wave excitation in single layer lms [5]. [1] A.V. Chumak et al., Nat. Phys. 11, 453 (2015). [2] A.G. Gurevich, G.A. Melkov, Magnetization Oscillations and Waves. New York CRC, 1996. [3] S. Wintz et al., Nat. Nanotechnol. 11, 948 (2016).

Keywords: spin wave vortex

  • Invited lecture (Conferences)
    DPG-Frühjahrstagung der Sektion Kondensierte Materie, 11.-16.03.2018, Berlin, Deutschland
  • Invited lecture (Conferences)
    IEEE Nanomaterials: Applications and Properties, 09.-14.09.2018, Zatoka, Ukraine
  • Invited lecture (Conferences)
    IC4N - 6th International Conference from Nanoparticles and Nanomaterials to Nanodevices and Nanosystems, 30.06.-03.07.2019, Korfu, Griechenland

Publ.-Id: 26419

Schutz von Hochleistungslasern durch Bildklassifizierung mit Deep Learning

Kelling, J.; Gebhardt, R.; Helbig, U.; Bock, S.; Schramm, U.; Juckeland, G.

Hochleistungslaser werden u. a. zur Erforschung von exotischen Materiezuständen und für medizinische Anwenden benötigt. Während des Betriebs wird der Strahlquerschnitt überwacht um destruktiv hohe Energiedichten zu erkennen und zu unterbinden. Eine Reaktion auf zufällig auftretende Fehler muss jedoch zwischen Pulsen bei 10Hz erfolgen.

Der Vorgestellte Automatisierungsansatz verwendet Deep Learning in Kombination mit einer einfachen Anomalieerkennung auf Basis bekannter physikalischer Eigenschaften des Systems. Dies ist notwendig für kurze Reaktionszeiten und um
Ergebnisse mit einer sehr kleinen Datenbasis zu erzielen.

Keywords: Bildklassifizierung; Caffe; automatische Laser-Sicherheitsabschaltung; GoogLeNet

  • Invited lecture (Conferences)
    Minds Mastering Machines, 24.-26.04.2018, Köln, Deutschland

Publ.-Id: 26418

Quantitatively consistent computation of coherent and incoherent radiation in particle-in-cell codes - a general form factor formalism for macro-particles

Pausch, R.; Debus, A.; Huebl, A.; Schramm, U.; Steiniger, K.; Widera, R.; Bussmann, M.

Quantitative predictions from synthetic radiation diagnostics often have to consider all accelerated particles.
For particle-in-cell (PIC) codes, this not only means including all macro-particles but also taking into account the discrete electron distribution associated with them.
This paper presents a general form factor formalism that allows to determine the radiation from this discrete electron distribution in order to compute the coherent and incoherent radiation self-consistently.
Furthermore, we discuss a memory-efficient implementation that allows PIC simulations with billions of macro-particles.
The impact on the radiation spectra is demonstrated on a large scale LWFA simulation.

Keywords: particle-in-cell simulations; laser plasma acceleration; far field radiation; plasma physics; radiation diagnostics

  • Contribution to proceedings
    3rd European Advanced Accelerator Concepts Workshop, 24.-29.09.2017, La Biodola, Isola d'Elba, Italien: NIM-A
  • Open Access Logo Nuclear Instruments and Methods in Physics Research A 909(2018), 419-422
    Online First (2018) DOI: 10.1016/j.nima.2018.02.020


Publ.-Id: 26417

Biomineralization of uranium(VI) by fungi - alternative for remediation approaches?

Schäfer, S.; Gerber, U.; Krawczyk-Bärsch, E.; Merroun, M. L.

Uranium pollution of soils and waters within the environment is from big concern. A range of remediation strategies were developed using chemicals and industrial equipment. As a consequence, the conventional remediation of polluted sites is elaborated and time-consuming. Microorganisms can affect the solubility of uranium and thus they could be an appropriate alternative in bioremediation approaches. It is well described that microorganisms could interact with metals in different ways. One of these is called biomineralization, and is defined as an interaction mechanism between microorganisms and metals whereby biological produced minerals capture pollutants within stable solid phases.
We investigated natural occurring fungi which were directly isolated from the flooding water of the former uranium mine Königstein in Germany. The isolated strain KS1 Penicillium simplicissimum displayed the ability to immobilize high amounts of uranium from surrounding solutions. Metabolism-dependent uranium removal experiments revealed in different interaction mechanisms of KS1 with uranium(VI). By transmission electron microscopy (TEM) we observed that the immobilization of the soluble uranium(VI) took place by bioaccumulation within the cells and furthermore by biomineralization outside of the cells. EDX investigations resulted in amorphous phosphate-minerals inside and outside the cells. In addition, enzymatic analysis displayed organic acids which were produced by the fungi and released to the solution. The results of our investigations revealed that the isolated fungi KS1 could be a suitable candidate for further bioremediation studies. Uranium was immobilized effectively, fast and possibly within stable solid phases. Compared to conventional remediation approaches the use of microorganisms should be taken into account.

Keywords: Bioremediation; Uranium; Biomineralization

  • Invited lecture (Conferences)
    16. Remediation Colloquium Jena, 05.-06.10.2017, Jena, Germany

Publ.-Id: 26416

Nonlinear large scale flow in a precessing cylinder and its ability to drive dynamo action

Giesecke, A.; Vogt, T.; Gundrum, T.; Stefani, F.

We have conducted experimental measurements and numerical simulations of a precession driven flow in a cylindrical cavity. The study is dedicated to the precession dynamo experiment currently under construction at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) and aims at the evaluation of the hydrodynamic flow with respect to its ability to drive a dynamo. We focus on the strongly nonlinear regime in which the flow is essentially composed of the directly forced primary Kelvin mode and higher modes in terms of standing inertial waves arising from nonlinear self-interactions. We obtain an excellent agreement between experiment and simulation with regard to both, flow amplitudes and flow geometry. A peculiarity is the resonance-like emergence of an axisymmetric mode that represents a double roll structure in the meridional plane. Kinematic simulations of the magnetic field evolution induced by the time-averaged flow yield dynamo action at critical magnetic Reynolds numbers around Rm^c = 430 which is well within the range of the planned liquid sodium experiment.

Keywords: Dynamo; DRESDYN


Publ.-Id: 26415

Wechselwirkungen zwischen U(VI) und Ca-Bentonit sowie Cm(III) und CSH-Phasen unter dem Einfluss alkalischer und hochsalinarer Porenwässer

Philipp, T.; Wolter, J.-M.; Schmeide, K.; Stumpf, T.

Der Vortrag fasst den aktuellen Stand der Untersuchungen innerhalb des BMWi-Verbundprojektes GRaZ zusammen. Es werden im Wesentlichen Ergebnisse zu zwei Systemen vorgestellt: U(VI) / Ca-Bentonit, sowie Cm(III) / CSH - Phasen. Die U(VI)-Rückhaltung an Ca-Bentonit zeigt eine große Variabilität im pH-Bereich 8-13 und ist stark vom Carbonat-Gehalt abhängig. Eine Erniedrigung der U(VI)-Rückhaltung bei pH > 8 in Gegenwart von Carbonat durch Bildung schwach sorbierender Uranyl-Carbonat-Komplexe wurde nur bis zu einem bestimmten pH Wert beobachtet. Bei höherem pH wird die aquatische Speziation widerrum durch Uranyl-Hydroxo-Komplexe dominiert, was zu einer erhöhten U(VI)-Rückhaltung führt. Der zugrunde liegende Rückhaltemechanismus konnte noch nicht eindeutig geklärt werden. Erste spektroskopische Untersuchungen der Oberflächenkomplexe deuten aber darauf hin, dass Oberflächenausfällung und/oder der Bildung oligomerer Oberflächenkomplexe zur Rückhaltung beitragen.
Cm(III)-dotierte CSH-Phasen konnten erfolgreich hergestellt und mittels TRLFS characterisiert werden. Anschließende Leaching-Versuche mit 0,02 M NaHCO3 und 2,5 M NaCl zeigten, im Gegensatz zu vergleichbaren Untersuchung mit U(VI), keinerlei remobilisierung des Curiums. Grund dafür ist der Einbau des freigesetzten Curiums in bei der Alteration neu gebildete Calcit- und Vateritmineralphasen.

  • Lecture (others)
    5. Workshop des BMWi-Verbundvorhabens “Geochemische Radionuklidrückhaltung an Zementalterationsphasen (GRaZ)“, 15.11.2017, Potsdam, Deutschland

Publ.-Id: 26414

Beryllium-7 at DREAMS

Rugel, G.; Merchel, S.; Scharf, A.; Querfeld, R.; Steinhauser, G.; Tiessen, C.

Half-lives of routine AMS nuclides range from thousands to millions of years. We measured short-lived 7Be (T1/2 = 53.2 d) at the DREsden AMS-facility (DREAMS) [1] as low as 90 mBq, which can be challenging for rapid 𝛾-counting. Simultaneous determination of 7Be and 10Be (T1/2 = 1.387 Ma) via AMS is advantageous for improved understanding of production, transport, and deposition of atmospherically produced 7,9,10Be [2].
Data was normalized to a 7Be sample produced via 7Li(p,n)7Be, measured by 𝛾-counting and chemically processed to BeO (7Be/9Be ≈ 10−12). The isobar 7Li is completely eliminated by chemistry and the degrader foil technique (7Be4+, 10.2 MeV). The blank ratio of 5 × 10−16 7Be/9Be (0.8 mBq) and simple and fast chemistry allows for the measurement of rainwater samples, collected in Germany, as small as 10 ml corresponding to a few times 10−14 7Be/9Be [3,4].
Thanks to D. Bemmerer (HZDR) and G. György (ATOMKI, Hungary) for help with the 7Be normalization material.
Ref.: [1] G. Rugel et al., NIMB 370 (2016) 94. [2] A.M. Smith et al., NIMB 294 (2013) 59. [3] R. Querfeld et al., JRNC 314 (2017)521. [4] C. Tiessen et al. JRNC (submitted).

Keywords: AMS; Be-7

  • Lecture (Conference)
    DPG-Frühjahrstagung der Sektion Atome, Moleküle, Quantenoptik und Plasmen (SAMOP), 04.-09.03.2018, Erlangen, Deutschland

Publ.-Id: 26413

Effects of Heater Surface Characteristics on Bubble Sliding Induced Heat Transfers during Upward Subcooled Nucleate Boiling

Sarker, D.; Ding, W.; Hampel, U.

In the present study the effects of surface wettability and roughness on wall heat transfers during bubble sliding are investigated via isolated bubbles on a vertical heater. Bubbles were generated from artificial cavities on stainless steel heaters. The test liquid was de-gassed, de-ionized water and a borosilicate glass vessel was filled with the test liquid. By high resolution imaging technique, the bubble dynamic parameters such as temporal evolution of bubble size, bubble base diameter and bubble sliding over heater for different surface characteristics were measured. The experimental values of different bubble dynamic parameters were used in the numerical models to calculate the associated heat transfers induced by bubble sliding.

We found that with the decrease of surface wettability for similar roughness, bubble sliding distances and the bubble induced areas increase. It enhances the transient heat conduction. For rough surfaces, sliding velocities were found higher than that of smooth surfaces. It is to be noted that the wettability of these surfaces is decreased while the roughness is increased. The transient conduction heat transfers are found generally higher in this study when the surface becomes rougher. An optimal roughness of Rq=90 nm showed more than 1.4 times augmented heat transfer over the smooth surfaces due to the interaction of surface roughness with the microlayer. These kind of surfaces even transfers higher heat flux than the roughest surface, studied in this work. The contribution of microlayer evaporation beneath sliding bubbles was not found significantly influential to the total heat flux. Future work will focus on the detail understandings of surface characteristics effects on the recovery of thermal boundary layer and the microlayer behavior during bubble sliding.

Keywords: Surface characteristics; vertical heater; bubble sliding; optimal roughness; wall heat flux

  • Open Access Logo Contribution to proceedings
    17th Internationsl Topical Meeting on Nuclear Reactor Thermal Hydraulics, 03.-08.09.2017, Xi'an, China

Publ.-Id: 26412

Quantitative prediction of critical heat flux initiation in pool and flow boiling

Ding, W.; Krepper, E.; Hampel, U.

Boiling is a very efficient heat transfer mechanism with a large heat transfer coefficient and it is widely found in industrial systems. However, boiling heat transfer is limited by the critical heat flux (CHF), also termed as boiling crisis. It leads to a rapid decrease of the heat transfer coefficient in temperature controlled heat transfer or to a significant jump in heater surface temperature in power controlled heat transfer cases. While the earlier effect clearly lowers efficiency the latter may even jeopardize safety. A clear understanding of the basic mechanisms leading to CHF is still lacking. In this paper a new model of priori critical heat flux(CHF-) is derived from the bubble dynamics of nucleate boiling. It holds for pool boiling and forced convective boiling and incorporates a mutual effect model and a shear stress model. The comparison between predicted and experimental results under different thermal hydraulic conditions shows a good agreement. The model is capable to explain the initiating mechanism of the boiling crisis and impacts from different variables. It can be also implemented as a sub-model in CFD codes.

Keywords: Critical heat flux (CHF); boiling heat transfer; pool boiling; forced convective boiling; cavity activation


Publ.-Id: 26411

Numerical analysis of heat exchanger designs for passive spent fuel pool cooling to ambient air

Unger, S.; Krepper, E.; Hampel, U.

Passive cooling of spent fuel pools via natural two-phase convection of a fluid with low boiling point is a promising alternative to active cooling circuits as such a passive heat transfer system would still work in safety-critical situations, such as a station blackout. For ambient air as the ultimate heat sink the heat exchanger design plays a crucial role as driving temperature differences may be low. This paper outlines a numerical investigation on a finned oval tube bundle heat exchanger operated under natural air convection in a chimney. We studied the role of chimney geometry and heat exchanger fin geometry. With respect to the chimney we found that velocity, Nusselt number and heat transfer are enhanced by 161.3%, 31.7% and 62.5% respectively, if chimney height increases from 2 m to 16 m. With respect to the fin design we determined an optimal fin configuration with a fin height of 17 mm, fin spacing of 3 mm and fin thickness of 1.5 mm, which improves the heat transfer performance by 28.7%, the Nusselt number by 28.9% and the fin efficiency by 19.2% at a given temperature difference of 40 K. The final optimized finned tube bundle heat exchanger design achieves a volumetric heat transfer density of q_vol=3.61 kW/m³K.

Keywords: passive cooling; spent fuel pool; natural convection; heat exchanger; air cooling; design optimization

Publ.-Id: 26410

Investigation of pore and network formation in spin-on ultra low-k dielectrics by spectroscopic techniques

Koehler, N.; Liedke, M. O.; Attallah, A. G.; Butterling, M.; Anwand, W.; Wagner, A.; Krause-Rehberg, R.; Schulz, S. E.

Positronium annihilation spectroscopy has become more and more important in microelectronics industry as one of the few methods to characterize engineered nanopores in next-generation (k < 2.4) interlayer dielectrics (ILD). With the addition of infrared spectroscopy a way is found to investigate the pore and network formation during the curing process.
1. Introduction
Porous spin-on glasses are one great candidate for the integration as ultra low-k (ULK) dielectrics in Back-End of Line (BEOL) for advanced technology nodes. They offer the possibility of a structured pore network by using “Block Polymer Templated Inorganic Oxides” (USP 6,592,764) [1]. Therefore, it is possible to adjust the physical properties of these thin films [1] as well as pore size and porosity. However, these materials are also prone to dielectric damage [2,3] during the integration into back-end of Line. In addition, these material degradations will increase with porosity [3]. It follows, that beside the damage mechanism also the pore and network formation of ULK materials need to be investigated more in detail to comprehend integration damage from the very first time of appearance. This work will evaluated the formation of spin-on glasses during curing by positron annihilation spectroscopy to observe the pore formation and by Fourier Transform Infrared spectroscopy to study the network formation.
2. Experimental
2.1 Preparation of spin-on dielectrics
For preparation of spin-on ULK material a solution from SBA Materials, Inc. was used. The ULK liquid precursor consists of an amphiphilic block copolymer with silicon alkoxide esters [1]. The final thickness is supposed to be 500 nm with an initial k-value of 2.2. The solution was spin-coated on 6-inch silicon wafers with 2000 rpm for 60 s. The spin-coated samples were soft baked for 120 s at 150 °C. The curing procedure was performed with the quartz glass oven PEO 603 from ATV technologies for different curing times at 450 °C under nitrogen atmosphere. The heat ramp of curing was chosen to be 7 °C/min.
2.2 Measurement techniques of pore and network structure
Fourier Transform Infrared (FTIR) spectroscopy was used to determine the chemical and structural changes before and after different curing times. The measurements were performed in transmission mode in the mid-range from 400 to 4000 cm-1, using the Bruker Tensor 27 spectrometer. The optical response is given as absorbance and normalized to thickness as well as treated by a baseline subtraction. Thus a comparison of the different processes can be achieved. Furthermore, a deconvolution of the FTIR peaks at the oxide region (1300 cm-1 to 950 cm-1) was accomplished with the Peak-Fit Module of ORIGIN 8.5 software. As it is described in literature the oxide region is used to be deconvoluted into the following peaks: the suboxide-, network-, cage-peak [4,5] and the Si-O-C peak [6]. The area was normalized to the total area of the Si-O-Si area.
The characterization of the nanopores were carried out at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) with positron annihilation spectroscopies (PAS). For determination of different pore components the Elbe Positron Source (EPOS) was used; a pulsed positron source with high repetition rate, high intensity and choosable energies for depth profile measurements [7,8]. Furthermore, by using the The Slow-Positron System of Rossendorf (SPONSOR) Doppler broadening spectroscopy was used to acquire also information about the atomic surrounding of the pores.
Since the possibility of diffusing out of ortho-positronium (o-Ps) from film surface through open, interconnecting pores the ULK films were covered with a 20 nm thick carbon layer by evaporating using a pre-shaped carbon rod.
3. Results
Fig. 1 shows the FTIR spectrum of the uncured and cured samples after 5 min, 30 min, 60 min and 90 min at 450 °C. The curing process at 450 °C for 90 min can be considered as complete cure. The uncured sample shows the –OH absorbance peak at 3400 cm-1 and the Si-OH peak at 914 cm-1 [9], which is characteristic for spin-on glasses in sol-gel science [10]. During the curing process the methylsilsesquioxane (MSQ) based Si-OH groups condensate and cross-linking occurs to form a 3D network [11]. Besides the Si-OH peak in the uncured sample the region from 3000 cm-1 to 2800 cm-1 is more pronounced compared to the cured samples. There are located the C-Hx vibration bands, which mostly correspond to porogen to form a porous network. The region from 900 cm-1 to 700 cm-1 is called the fingerprint region, where mostly the different Si-C vibration modes are dominate [9]. The absorbance peak at 1277 cm-1 belongs to the Si-CH3 vibration band.
The two main mechanism during the curing of spin-on ULK are the cross-linking of the Si-OH groups to form a mechanically stable thin film and the porogen removal to form a porous network. The cross-linking of Si-OH to form the Si-O-Si linkage can be seen in Fig 1. in the range of 1250 cm-1 to 960 cm-1. Already after 5 min of curing the Si-O-Si region is formed almost completely and only little changes during further curing are observed. By taking a closer look at the Si-O-Si region, a shift from 1047 cm-1 to 1052 cm-1 can be observed. Within this region four peaks are overlapping: the suboxide-, network-, cage- [4,5] and the Si-O-C peak [6]. To distinguish between those peaks a deconvolution was done, where the results are shown in Fig. 2. With increasing curing time the network peak rises whereas the cage and the suboxide peak decreases. This behavior is likely due to the cross-linking of the network material and is less pronounced after 30 min of curing. The Si-O-C peak seams not to be affect by curing time.
Fig. 3 and Fig. 4 show the results from the DBS and PALS measurements. From the DBS measurements two specific line parameters can be calculated: the S- and W-parameter. The S-parameter is a measurement of the open volume and the W-parameter is a measurement of the atomic environment of the annihilation site. The mean implantation depth for the positrons is given in nanometer scale at the upper x-axes based on the density of silica. The first 20 nm (until 1.2 keV) the S- and W-parameter corresponds to the carbon capping layer and retain unchanged for all treatments. The W-parameter for the uncured sample shows the highest values. Only for 20 nm Carbon layer the W-parameter is higher. Within the first minutes of curing, the porogen is almost removed and the W-parameter decreases. From 30 min to 90 min no change in W-parameter is visible anymore. Compared to the FTIR spectra (Fig. 1) in the region of 3000 cm-1 to 2800 cm-1 no change for all curing times are visible which shows the sensitive behavior of PAS measurements for nanopore evaluations. For the cross-linking behavior (Fig. 2) the dependence on curing time can still be observed in detail by FTIR. Therefore, it can be concluded that the porogen extraction at 450 °C with a slow heating ramp is completed within the first 30 min, whereas the cross-linking of the network takes places over the complete curing time.
The calculated pore components from PALS measurements are shown in Fig. 4. Two different lifetime components were found. The upper diagrams show the diameter of the pores and the lower diagrams show the intensities of the pore components. The first pore component has a diameter of around 0.8 nm which does not change for all curing treatments and positron energies, whereas the intensities of the component 1 decrease from the uncured to the cured state. With regard to the FTIR results (Fig. 1 and Fig. 2), this pore component intensities shows the inverse behavior of the oxide region, where the network is formed. Therefore, this component is likely due to the unreacted Si-OH groups, which decreases during the curing. The second pore component arises from the pores itself and was not observed at the uncured sample. The mean diameter is about 3.4 nm, which lowers to 3 nm near the surface of the film. This can be due to the carbon capping layer deposition and needs further considerations. Also it can be seen that the pore diameter from 5 min to 30 min still increases and reaches a final value after 30 min. In addition, the intensity of the pore component 2 changes marginal. That confirms that the porogen extraction as well as the pore formation takes place within the first 30 min.
4. Summary
In this work, the pore formation of spin-on ULK materials with an initial k-value of 2.2 was studied for a thermal curing process at 450 °C with a slow heat ramp for curing. After 5 min of curing most of the porogen is extracted and the network is formed almost completely, which can be seen by PAS and FTIR. The porogen extraction as well as the pore formation appear to be complete after 30 min, whereas the remaining time is needed to form the network.
All the investigations are running right now for faster heat ramp of curing as well as for different curing temperatures to slow down the pore formation process and get a better understanding of the processes taking place inside the material during curing.
[1] P. Garrou, Solid State Technology, p. 10, Nov. 2010, Accessed 22 May 2017
[2] J.L. Shohet et al., ECS Transactions, 60 (1) p. 733-738 (2014)
[3] M.R. Baklanov et al., Journal of Applied Physics 113, p. 041101, (2013)
[4] L. Zhang et al., ECS Solid State Lett. 2 (2), p. N5 (2013)
[5] A. Grill et al., J. Appl. Phys. 94 (10), p. 6697 (2003).
[6] Y. Lin et al., J. Electrochem. Soc. 153 (7), p. F144 (2010)
[7] A. Uedono et al. Applied Surface Science, Bd. 368, pp 272-276 (2016)
[8] A. Wagner et al., Defect and Diffusion Forum, Bd. 331, pp. 25-40, (2012)
[9] B. Xie et al., Microelectron. Eng, 76 (1-4) p. 52-59 (2004)
[10] P. Eaton et al., J. Appl. Polym. Sci. 82 (8), p. 1097-4628 (2001)
[11] A. Zenasni et al., J. Electrochem. Soc. 154 (1) p. G6 –G12 (2007)

Keywords: low-k materials; dielectrics; positron annihilation spectroscopy; positron lifetime; Fourier Transform Infrared Spectroscopy; Doppler broadening spectroscopy; pores; networks

  • Poster
    2017 Advanced Metallization Conference, 13.-14.09.2017, Austin, TX, USA

Publ.-Id: 26409

Engrafting human regulatory T cells with a flexible modular chimeric antigen receptor technology

Koristka, S.; Kegler, A.; Bergmann, R.; Arndt, C.; Feldmann, A.; Albert, S.; Cartellieri, M.; Ehninger, A.; Ehninger, G.; Middeke, J. M.; Bornhäuser, M.; Schmitz, M.; Pietzsch, J.; Akgün, K.; Ziemssen, T.; Steinbach, J.; Bachmann, M. P.

As regulatory T cells (Tregs) play a fundamental role in immune homeostasis their adoptive transfer emerged as a promising treatment strategy for inflammation-related diseases. Preclinical animal models underline the superiority of antigen-specific Tregs compared to polyclonal cells. Here, we applied a modular chimeric antigen receptor (CAR) technology called UniCAR for generation of antigen-specific human Tregs. In contrast to conventional CARs, UniCAR-endowed Tregs are indirectly linked to their target cells via a separate targeting module (TM). Thus, transduced Tregs can be applied universally as their antigen-specificity is easily adjusted by TM exchange. Activation of UniCAR-engrafted Tregs occurred in strict dependence on the TM, facilitating a precise control over Treg activity. In order to augment efficacy and safety, different intracellular signaling domains were tested. Both 4-1BB (CD137) and CD28 costimulation induced strong suppressive function of genetically modified Tregs. However, in light of safety issues, UniCARs comprising a CD137-CD3z signaling domain emerged as constructs of choice for a clinical application of redirected Tregs. In that regard, Tregs isolated from patients suffering from autoimmune or inflammatory diseases were, for the first time, successfully engineered with UniCAR 137/z and efficiently suppressed patient-derived effector cells. Overall, the UniCAR platform represents a promising approach to improve Treg-based immunotherapies for tolerance induction.

Keywords: regulatory T cells; chimeric antigen receptor; immunotherapy; CD28; CD137 (4-1BB)

Publ.-Id: 26408

Assembly Behavior of Organically Interlinked Gold Nanoparticle Composite Films: A Quartz Crystal Microbalance Investigation

Daskal, Y.; Tauchnitz, T.; Güth, F.; Dittrich, R.; Joseph, Y.

Thin films based on dodecylamine stabilized gold nanoparticles interlinked with different organic molecules are prepared by automatic layer-by-layer self-assembly in a microfluidic quartz crystal microbalance (QCM) cell, to obtain an in situ insight on the film formation by ligand/linker exchange reactions. The influence of interlinking functional groups and the length of the organic linker molecule on the assembly behavior is investigated. Alkyldithiols with different lengths are compared to alkyldiamines and alkylbisdithiocarbamates with a C8 alkylic molecular backbone. The stepwise layer-by-layer assembly occurs independently of the linker molecule, while the largest frequency changes always correspond to the gold nanoparticle step.
During the solvent rinsing and ligand/linker exchange reaction step, the frequency is almost constant with slight increases or decreases dependent on the molar mass of the linker compared to the exchanged ligand. The assembly efficiency is higher for shorter molecules and for molecules with stronger interacting functional groups. The densities of the composite films are calculated from QCM data and independent thickness measurements. They reflect the higher fraction of organic material in the films comprising longer organic linkers. The plasmon resonance band of the gold nanoparticles in the final assemblies is measured with UV/vis spectroscopy. Band positions in films prepared from dithiols and diamines of comparable lengths are very similar, while the spectrum of the bisdithiocarbamate film exhibits a distinct blue-shift. This observation is explained by the longer molecular structure of the linker due to a larger binding group, in conjunction with a delocalization of particle charge on the organic molecule. Obtained results play an essential role in the understanding of thin film layer-by-layer self-assembly processes, and enable the formation of new gold nanoparticle networks with organic diamine and bisdithiocarbamate molecules.

Publ.-Id: 26407

The EPTN consensus-based atlas for CT- and MR-based contouring in Neuro-Oncology

Eekers, D.; In 'T Ven, L.; Roelofs, E.; Postma, A.; Alapetite, C.; Burnet, N.; Calugaru, V.; Compter, I.; Coremans, I.; Hoyer, M.; Lambrecht, M.; Romero, A.; Paulsen, F.; Perpar, A.; de Ruysscher, D.; Renard, L.; Vitek, P.; Weber, D.; van der Weide, H.; Whitfield, G.; Wiggenraad, R.; Nyström, P.; Timmermann, B.; Troost, E.

Purpose: To create a digital, online atlas for organs at risk (OAR) delineation in neurooncology based on high-quality computed tomography (CT) and magnetic resonance (MR) imaging.
Methods: CT and 3 Tesla (3T) MR images (slice thickness 1 mm with intravenous contrast agent) were obtained from the same patient and subsequently fused. In addition, a 7T MR without intravenous contrast agent was obtained from a healthy volunteer. Based on discussions between experienced radiation oncologists, the clinically relevant organs at risk (OARs) to be included in the atlas for neuro-oncology were determined, excluding typical head and neck OARs previously published. The draft atlas was delineated by a senior radiation oncologist, 2 residents in radiation oncology, and a senior neuro-radiologist incorporating relevant available literature. The proposed atlas was then critically reviewed and discussed by European radiation oncologists until consensus was reached.
Results: The online atlas includes one CT-scan at two different window settings and one MR scan (3T) showing the OARs in axial, coronal and sagittal view. This manuscript presents the three-dimensional descriptions of the fifteen consensus OARs for neurooncology.
Among these is a new OAR relevant for neuro-cognition, the posterior cerebellum (illustrated on 7T MR images).
Conclusion: In order to decrease inter- and intra-observer variability in delineating OARs relevant for neuro-oncology and thus derive consistent dosimetric data, we propose this atlas to be used in photon and particle therapy. The atlas is available online at and will be updated whenever required.

Keywords: Atlas for neuro-oncology; organs at risk; particle therapy; European Particle Therapy Network

Publ.-Id: 26406

Evidence on the efficacy of primary radiosurgery or stereotactic radiotherapy for drug-resistant non-neoplastic focal epilepsy in adults: a systematic review

Eekers, D.; Pijnappel, E.; Schijns, O.; Colon, A.; Hoeben, A.; Zindler, J.; Postma, A.; Hoffmann, A.; Lambin, P.; Troost, E.

Objective: Although the majority of adult epilepsy patients respond well to the current antiepileptic drug treatment (AED), 20-40% of them are drug-resistant. In these patients, resective epilepsy surgery (RES) is a curative treatment option, for which, however, only a limited number of patients is eligible. The purpose is to summarize the outcome of radiotherapy (RT) for drug-resistant non-neoplastic focal epilepsy (NNFE) and to elucidate its efficacy for seizure outcome and long-term toxicity in adults. Methods: A systematic literature search was performed in Pubmed, Ovid Medline, Cochrane library, Embase and Web of Science. The methodological quality was evaluated using an adapted QUADAS checklist. Results: Sixteen out of 170 initially identified studies were included in this systematic literature study (n=170 patients). Twelve of the 16 studies described a positive effect of RT on seizure frequency reduction, with 98 of the patients (on average 58%, range 25%-95%) reporting no or rare seizures (defined as radiotherapy-adapted Engel class [RAEC] I and II. In total, 20% (34 patients) of the patients needed subsequent surgery due to radionecrosis, cysts formation, edema, and intracranial hypertension or remaining seizures. A dose-effect model was fitted to the available response data in an attempt to derive a relationship between prescribed dose and RAEC frequency. Significance: Radiotherapy is a possible non-invasive treatment option for patients with drug-resistant focal non-neoplastic epilepsy. This systematic review showed that there is only level 4 evidence of primary RT reducing seizure frequency in adult patients. Prospective randomized trials are needed to determine its exact value compared to other treatment approaches.

Keywords: stereotactic radiotherapy; radiosurgery; epileptogenic lesions; focal epilepsy

Publ.-Id: 26405

The posterior cerebellum, a new organ at risk?

Eekers, D. B. P.; In 'T Ven, L.; Deprez, S.; Jacobi, L.; Roelofs, E.; Hoeben, A.; Lambin, P.; de Ruysscher, D.; Troost, E. G. C.

Eekers et al. (1) have recently proposed a neuro-oncology atlas which was co-authored by most centers associated in the European Proton Therapy Network (EPTN; Figure 1). With the introduction of new treatment techniques, such as integrated magnetic resonance imaging and linear accelerators (MR-linac) or particle therapy, the prediction of clinical efficacy of these more costly treatment modalities becomes more relevant. One of the side-effects of brain irradiation, being cognitive decline, is one of the toxicities most difficult to measure and predict. In order to validly compare different treatment modalities, 1) a uniform nomenclature of the organs at risk (OARs), 2) uniform atlas-based delineation [e.g., (1)], 3) long-term follow-up data with standardized cognitive tests, 4) a large patient population, and 5) (thus derived) validated normal tissue complication probability (NTCP) models are mandatory.
Apart from the Gondi model (2), in which the role of the dose to 40% of both hippocampi (HC) proves to be significantly related to cognition in 18 patients, no similar models are available. So there is a strong need for more NTCP models, on HC, brain tissue and possible other relevant brain structures.
In this review we summarize the available evidence on the role of the posterior cerebellum as a possible new organ at risk for cognition, which is deemed relevant for irradiation of brain and head and neck tumors.

Keywords: Neuro-Oncology; delineation atlas; posterior cerebellum; radiotherapy; cognition

Publ.-Id: 26404

Synthese und Charakterisierung von funktionalisierten Calix[4]arenen zur Chelatisierung von Barium und Radium

Steinberg, J.

Die Entwicklung von Ra2+-Komplexen für den Einsatz der radiopharmazeutisch interessanten Radiumnuklide Ra-223 und Ra-224 in Radiotherapeutika, beispielsweise zur Behandlung eines breiten Spektrums an Tumoren, steht im Fokus dieser Arbeit. Um einen Einbau des calciummimetischen Ra2+ in den Hydroxyapatit des Knochengewebes zu unterbinden, müssen die Radiometallkomplexe hohe Komplexstabilitäten aufweisen. Bifunktionelle Chelatoren mit einer hochaffinen Targeteinheit zum Zielgewebe sollen den Transport zum pathogenen Gewebe möglich machen. Die emittierte α-Strahlung des Radiums führt zur Zerstörung des Zielgewebes.
Vielversprechend stellen sich überbrückte und funktionalisierte p-tert-Butylcalix[4]arenderivate dar. Die erforderliche hohe Stabilität des Komplexes soll dabei besser als mit offenkettigen und einfach cyclischen Verbindungen erreicht werden, da eine definierbare Kavität selektiver und stabiler Metalle bindet. Durch die sterischen Effekte, die durch zusätzliche Modifikationen eintreten, soll der Komplex vor Dissoziation geschützt werden. Einerseits lassen die p-tert-Butyl-Gruppen der upper rim-Seite keinen Angriff auf die Metallionen zu, andererseits werden sie zusätzlich durch die sterisch anspruchsvollen Substituenten der lower rim-Seite festgehalten. Zudem sollen deprotonierbare Positionen an Funktionalisierungen gute Bindungsstellen für Ra2+ zur Komplexbildung darstellen. Aufgrund ähnlicher chemischer Eigenschaften wird Ba2+ als Surrogat für diese Untersuchungen eingesetzt, um das Komplexierungsverhalten der Calixarene zu studieren.

Keywords: Radium; Barium; Calix[4]arene

  • Diploma thesis
    TU Dresden, 2017
    Mentor: Dr. Constantin Mamat
    0120 Seiten

Publ.-Id: 26403

Desertification Susceptibility Mapping Using Logistic Regression Analysis in the Djelfa Area, Algeria

Djeddaoui, F.; Chadli, M.; Gloaguen, R.

The main goal of this work was to identify the areas that are most susceptible to desertification in a part of the Algerian steppe, and to quantitatively assess the key factors that contribute to this desertification. In total, 139 desertified zones were mapped using field surveys and photo-interpretation. We selected 16 spectral and geomorphic predictive factors, which a priori play a significant role in desertification. They were mainly derived from Landsat 8 imagery and Shuttle Radar Topographic Mission digital elevation model (SRTM DEM).
Some factors, such as the topographic position index (TPI) and curvature, were used for the first time in this kind of study. For this purpose, we adapted the logistic regression algorithm for desertification susceptibility mapping, which has been widely used for landslide susceptibility mapping. The logistic model was evaluated using the area under the receiver operating characteristic (ROC) curve. The model accuracy was 87.8%. We estimated the model uncertainties using a bootstrap method. Our analysis suggests that the predictive model is robust and stable. Our results indicate that land cover factors, including normalized difference vegetation index (NDVI) and rangeland classes, play a major role in determining desertification occurrence, while geomorphological factors have a limited impact. The predictive map shows that 44.57% of the area is classified as highly to very highly susceptible to desertification. The developed approach can be used to assess desertification in areas with similar characteristics and to guide possible actions to combat desertification.

Keywords: desertification; logistic regression; steppe; Djelfa


Publ.-Id: 26402

Pressure-induced insulator-to-metal transition in VO₂ studied by near-infrared pump – mid-infrared probe spectroscopy

Braun, J. M.; Schneider, H.; Helm, M.; Mirek, R.; Boatner, L. A.; Marvel, R. E.; Haglund, R. F.; Pashkin, A.

The strongly correlated electron material VO₂ shows an insulator-to-metal transition (IMT) when heated above Tc = 340 K accompanied by a lattice transformation from monoclinic to rutile structure. The mechanism of the temperature-driven IMT in VO₂ is very complex and involves a Peierls instability facilitated by a strong Coulomb interaction. However, the hierarchy of these processes during the IMT is still under discussion.

Ultrafast time-resolved techniques allow to study the photo-induced IMT in VO₂ that occurs on a femtosecond time scale. At sufficient pump fluences the insulating gap closes almost instantaneously due to the screening of the Coulomb repulsion [1] and the lattice evolves on a sub-picosecond timescale to a rutile structure indicating the existence of a transient monoclinic metallic phase [2].

On the other hand, application of external pressure also can induce an equilibrium monoclinic metallic phase [3]. Therefore, the mechanism of the pressure-induced IMT in VO₂ must be qualitatively different compared to the temperature-driven IMT. However, until now the information about the electronic band structure of the pressurized metallic phase remains obscure due to incompatibility of photoemission spectroscopy with high-pressure techniques.

Here we use ultrafast near-infrared pump – mid-infrared probe spectroscopy in order to unravel the changes in the electronic structure of VO₂ across the pressure-induced IMT. The nonlinear spectroscopy allows us to extract information about the response of localized and free charge carriers. In this case the non-degenerate pump-probe scheme is essential: The probe photon energy of 0.12 eV is well below the band gap (0.6 eV) at ambient conditions while the pumping with photon energies of 1.5 eV photo-excites additional charge carriers across the band gap.

The probe radiation is focused on a VO₂ single crystal inside a diamond anvil cell to a nearly diffraction limited spot. We measure the transient reflectivity change in mid-infrared induced by the near-infrared pumping. In agreement with previous studies the pump-probe traces indicate the onset of a long-living metallic state when the excitation fluence exceeds a certain threshold 𝛷th [4]. The results for three independent experimental runs of different VO₂ crystals are shown in Figure 1 together with the linear transmissivity of the probe beam. Initially the threshold grows with pressure increase, but at a critical pressure pc of 6-8 GPa a sudden drop is observed. It coincides with the vanishing of the linear transmissivity (measured without pumping) indicating the pressure-induced IMT in the sample. Remarkably, there is a remnant threshold behavior even for pressures above pc. By pumping it is still possible to enhance the conductivity of the pressure-induced metallic phase. Such behavior is fundamentally different from the temperature-driven IMT, where all t2g bands overlap with the Fermi level leading to the vanishing of the pump-probe response in the metallic phase.

We suggest that the pressure-induced changes of the threshold and linear transmission agree well to a scenario of a bandwidth-driven Mott-Hubbard transition [5]. In this scenario of a purely electronic IMT, pressure-induced increase of the bandwidth leads to a spectral weight transfer from the Hubbard bands to a quasiparticle peak at the Fermi level causing metallic conductivity and a gradual filling of the insulating gap. As a large portion of the spectral weight is still located in the Hubbard bands, the number of charge carriers still can be increased by photoexcitation.

Figure 1. Threshold fluence 𝛷th for three samples and linear transmissivity (bottom curve) as functions of pressure.

[1] D. Wegkamp et al., Phys. Rev. Lett. 2014, 113, 216401.
[2] V. R. Morrison et al., Science 2014, 346, 445.
[3] E. Arcangeletti et al., Phys. Rev. Lett. 2007, 98, 196406.
[4] C. Kübler et al., Phys. Rev. Lett. 2007, 99, 116401.
[5] J. M. Braun et al., in preparation (2017).

Keywords: ultrafast pump-probe spectroscopy; bandwidth-driven Mott-Hubbard transition; vanadium dioxide; VO₂; insulator-to-metal transition; pressure-induced metallization; high pressure; diamond anvil cell

  • Lecture (Conference)
    55th European High Pressure Research Group (EHPRG) Meeting on High Pressure Science and Technology, 03.-08.09.2017, Poznań, Poland

Publ.-Id: 26401

Pressure-Induced Metallization in VO₂ Studied by Optical Pump – THz Probe Spectroscopy

Braun, J. M.; Schneider, H.; Helm, M.; Mirek, R.; Boatner, L. A.; Marvel, R. E.; Haglund, R. F.; Pashkin, A.

We have investigated pressurized VO₂ using optical pump – THz probe spectroscopy. Distinct pump-probe signals and an excitation threshold are observed even in the metallic state. Our results are consistent with a pressure-driven Mott-Hubbard transition.

Keywords: pressure-induced metallization; bandwidth-controlled Mott-Hubbard transition; insulator-to-metal transition; high pressure; diamond anvil cell; vanadium dioxide; VO₂; optical pump - THz probe spectroscopy

  • Lecture (Conference)
    CLEO 2017 (Conference on Lasers and Electro-Optics), 14.-19.05.2017, San Jose, USA

Publ.-Id: 26400

Post-irradiation annealing behavior of oxide dispersion strengthened Fe-Cr alloys studied by nanoindentation

Duan, B.; Bergner, F.; Heintze, C.; Akhmadaliev, S.; Wang, T.

To study the nature of irradiation-induced nanofeatures in oxide dispersion strengthened (ODS) Fe-Cr alloys, post-irradiation isochronal thermal annealing up to 600 ºC was performed for 9Cr- and 14Cr-ODS alloys ion-irradiated at 300 and 500 ºC. Nanoindentation indicated hardening for all as-irradiated alloys and complete hardness recovery upon post-irradiation annealing. Candidate mechanisms of recovery were critically evaluated. Shrinkage of irradiation-induced dislocation loops via capture of thermal vacancies was found to correctly reflect the behavior of 9Cr-ODS irradiated at 300 ºC.

Keywords: ODS steel; Ion irradiation; Post-irradiation annealing; Nanoindentation; Dislocation loops


Publ.-Id: 26399

Bandwidth-controlled metallization in pressurized VO₂ revealed by optical pump – THz probe spectroscopy

Braun, J. M.; Schneider, H.; Helm, M.; Mirek, R.; Boatner, L. A.; Marvel, R. E.; Haglund, R. F.; Pashkin, A.

Vanadium dioxide (VO₂) is a classic example of a transition metal oxide showing a sharp first- order insulator-to-metal transition (IMT) around 340 K accompanied by a pronounced structural transformation. Pressure-induced metallization of VO₂ has been demonstrated by infrared spectroscopy [1] and resistivity measurements [2]. Remarkably, in contrast to the temperature-driven IMT, the crystal structure is not affected and remains monoclinic in the metallic phase [1-3].

Here we apply ultrafast optical pump – THz probe spectroscopy in order to reveal the nature of the pressure-induced IMT in a single crystal of VO₂. The probe pulses with a central frequency of 30 THz were generated by difference frequency mixing and focused down to a 35-𝜇m-spot on the sample mounted inside a diamond anvil pressure cell. Using THz radiation with photon energies far below the bandgap of VO₂ gives us an extremely sensitive probe of the dynamics of metallization [4].

Fig. 1(a) demonstrates that above a certain excitation fluence, a non-zero pump-probe signal survives on a multi-ps timescale indicating the long-lived photoinduced metallic state [4]. Here we define the threshold fluence 𝛷th as a crossing point of linearly extrapolated pump-probe signals in the low- and high-excitation regimes, as shown in Fig. 1(b). Surprisingly, the threshold behavior typical for the insulating state of VO₂ is also observed above the IMT that occurs between 6 and 8 GPa. This indicates a strongly correlated character of the pressure-induced metallic phase in which a part of the electrons remains localized - as predicted for a bandwidth-controlled Mott-Hubbard transition.

Fig. 1(c) shows that 𝛷th initially increases with pressure evidencing that the monoclinic structure stabilizes under hydrostatic compression. However, at the pressure-induced IMT, we observe a sudden drop of 𝛷th. This may be related to the partial screening of Coulomb correlations by delocalized electrons in the metallic state that lowers the critical excitation density necessary for a complete closure of the correlation gap. Our results attest to a purely electronic pressure-induced Mott-Hubbard transition in VO₂ and yield important insights into the nature of the correlated metallic state.

Figure 1: (a) Typical pump-probe response of VO₂ under a pressure of 2.9 GPa at different excitation fluences 𝛷;
(b) Amplitude of pump-probe in the metastable photoinduced state 1 ps after the excitation at different pressures;
(c) Dependence of the threshold fluence 𝛷th as a function of applied pressure. pc marks the region of the insulator-metal

[1] E. Arcangeletti et al., Phys. Rev. Lett. 98, 196406 (2007).
[2] L. Bai et al., Phys. Rev. B. 91, 104110 (2015).
[3] W.-P. Hsieh et al., Appl. Phys. Lett. 104, 021917 (2014).
[4] C. Kübler et al., Phys. Rev. Lett. 99, 116401 (2007).

Keywords: optical pump - THz probe spectroscopy; pressure-induced metallization; bandwidth-controlled Mott-Hubbard transition; insulator-to-metal transition; high pressure; diamond anvil cell; vanadium dioxide; VO₂

  • Lecture (Conference)
    Optical Terahertz Science and Technology (OTST 2017), 02.-07.04.2017, London, United Kingdom

Publ.-Id: 26398

The nature of the pressure-induced metallization in VO₂

Braun, J. M.; Schneider, H.; Helm, M.; Mirek, R.; Boatner, L. A.; Marvel, R. E.; Haglund, R. F.; Pashkin, A.

We utilize ultrafast optical pump - THz probe spectroscopy in order to investigate the pressure-driven insulator-to-metal transition (IMT) in vanadium dioxide (VO₂). The probe pulses with central frequency of 30 THz enable a sensitive detection of the photoinduced metallization.
The threshold pump fluence necessary for generation of a metastable metallic phase has been systematically measured for pressures up to 19GPa. Initial pressure application leads to a notable increase of the threshold fluence. This contrasts the thermally-driven IMT in VO₂ where it decreases on approaching the transition temperature. Above the IMT, that occurs at approximately 6-8GPa, we observe a sharp drop of the threshold fluence. However, the clear threshold behavior characteristic for systems with cooperative electronic localization still could be observed also in the metallic state up to the highest applied pressure.
Our results support a view of the pressure-induced IMT in VO₂ as a purely electronic bandwidth-driven Mott-Hubbard transition, that does not involve any change in the crystal structure.

Keywords: pressure-induced metallization; bandwidth-controlled Mott-Hubbard transition; insulator-to-metal transition; high pressure; diamond anvil cell; vanadium dioxide; VO₂; optical pump - THz probe spectroscopy

  • Lecture (Conference)
    DPG-Frühjahrstagung 2017, 19.-24.03.2017, Dresden, Deutschland

Publ.-Id: 26397

Nanoindentation of ion-irradiated reactor pressure vessel steels – model-based interpretation and comparison with neutron irradiation

Röder, F.; Heintze, C.; Pecko, S.; Akhmadaliev, S.; Bergner, F.; Ulbricht, A.; Altstadt, E.

Ion-irradiation-induced hardening is investigated on six selected reactor pressure vessel (RPV) steels. The steels were irradiated with 5 MeV Fe2+ ions at fluences ranging from 0.01 to 1.0 displacements per atom (dpa) and the induced hardening of the surface layer was probed with nanoindentation. To separate the indentation size effect and the substrate effect from the irradiation-induced hardness profile, we developed an analytic model with the plastic zone of the indentation approximated as a half sphere. This model allows the actual hardness profile to be retrieved and the measured hardness increase to be assigned to the respective fluence. The obtained values of hardness increase versus fluence are compared for selected pairs of samples in order to extract effects of the RPV steel composition. We identify hardening effects due to increased levels of copper, manganese-nickel and phosphorous. Further comparison with available neutron-irradiated conditions of the same heats of RPV steels indicates pronounced differences of the considered effects of composition for irradiation with neutrons versus ions.

Keywords: nanoindentation; plastic zone; ion irradiation; neutron irradiation; reactor pressure vessel steel; irradiation hardening


Publ.-Id: 26396

Rapid synthesis of sub-10 nm hexagonal NaYF4-based upconverting nanoparticles using Therminol 66

Hesse, J.; Klier, D. T.; Sgarzi, M.; Nsubuga, A.; Bauer, C.; Grenzer, J.; Hübner, R.; Wislicenus, M.; Joshi, T.; Kumke, M. U.; Stephan, H.

We report a simple one-pot method for rapid preparation of sub-10 nm pure hexagonal (β-phase) NaYF4 based upconverting nanoparticles (UCNPs). Such nanocrystals are well-known for their high efficiency of energy upconversion. Using Therminol 66 as co-solvent, monodisperse UCNPs could be obtained in unusually short reaction time. By varying reaction time, reaction temperature, and the concentration of the dopants (Nd3+, Yb3+ sensitizer ions and Er3+ activator ions), it was possible to precisely control the particle size, crystalline phase, as well as the upconversion (UC) luminescence properties. The size and phase-purity of as-synthesized core and core-shell nanocrystals was assessed using complementary transmission electron microscopy (TEM), dynamic light scattering (DLS), X-ray diffraction (XRD) and small-angle X-ray scattering (SAXS) studies. In-depth photophysical evaluation of the UCNPs was pursued using steady-state as well as time-resolved luminescence spectroscopy. An enhancement in UC intensity was observed when nanocrystals, doped with optimized concentration of lanthanide sensitizer/activator ions, were further coated with an inert/active shell. This is attributed to the suppression of surface-related luminescence quenching effects.

Keywords: core-shell; lanthanides; nanocrystal synthesis; photoluminescence; upconversion

Publ.-Id: 26395

Performing clinical 18FDG-PET/MR imaging of the mediastinum using a dedicated, patient-friendly protocol

Peerlings, J.; Paulis, L.; Mitea, C.; Bakers, F.; Berbée, M.; Wierts, R.; Vöö, S.; Backes, W.; Wildberger, J.; Hoffmann, A.

To apply clinical 18FDG-PET/MRI, a trade-off between image quality (IQ), diagnostic accuracy, and patient compliance is required. This study aimed to develop a mediastinal-specific 18FDG-PET/MR protocol containing dedicated MRI-sequences able to produce robust, high-quality images with great patient compliance and diagnostic performance comparable to 18FDG-PET/CT.

In this study, 15 healthy subjects and 10 patients with mediastinal malignancies (i.e., 8 non-small cell lung cancer, 2 oesophageal cancer) received 18FDG-PET/MR imaging immediately after 18FDG-PET/CT. PET/MR-sequences (T1-VIBE, T2-HASTE) on a Siemens Biograph mMR scanner were optimized by varying the following parameters: breath-hold (BH, in end-expiration), fat saturation (SPAIR), and electrocardiogram-triggering (ECG, in end-diastole). IQ of each sequence-variation was qualitatively scored on a 5-point scale by medical experts and quantitatively assessed by calculating signal-to-noise ratios (SNR), contrast relative to muscle-tissue (CR), standardized-uptake-values (SUVs), and tumour-to-blood ratios (TBRs). Differences in CR determined contrast between adjacent tissues and tumour visibility. Diagnostic accuracy of 18FDG-PET/MRI was compared to 18FDG-PET/CT, in reference to clinical reports and histo-/cytopathological analyses.

Quantitative analysis showed that T1-VIBE images acquired with ECG-triggering presented highest SNR for soft-tissues in the mediastinum (P<0.01) with high contrast between tumours and adjacent tissue, regardless of breath-hold or free-breathing acquisition. In qualitative analyses, IQ of T1-VIBE scans using BH and ECG triggering were scored highest with good reader-agreement (κ=0.62). Quantitative and qualitative IQ of T2-HASTE was not significantly affected by BH-acquisition (P>0.9). However, qualitative IQ of both T1-VIBE and T2-HASTE deteriorated with the addition of SPAIR. Diagnostic performance of 18FDG-PET/MR was not significantly different from 18FDG-PET/CT with similar staging, SUVs, and TBRs. However, T-status was more often over-staged on 18FDG-PET/CT, while N-status was more frequently under-staged on 18FDG-PET/MR.

ECG-triggered T1-VIBE sequences acquired during short, multiple breath-holds are recommended for mediastinal imaging using 18FDG-PET/MR protocols. With dedicated protocols, 18FDG-PET/MR imaging could be implemented in thoracic oncology and aid in diagnostic evaluation, tailored treatment decision-making, and personalized patient care.

Keywords: 18F-FDG; PET/MR; PET/CT; Mediastinum; Esophageal carcinoma; Non-small cell lung cancer

Publ.-Id: 26394

Outlook on a new combined MRI/TI experiment

Seilmayer, M.; Stefani, F.; Gundrum, G.; Köppen, S.

In the project framework of DRESDYN a sodium based experiment investigating magneto rotational instability (MRI) an Tayler instability (TI) is going to be built. Since both instabilities are based on hydrodynamically stable but magnetized Taylor Couette flow, the magnetic field configuration distinguishes the different types of instabilities. The past experimental research successfully worked out helical MRI with a combination of axial and azimuthal magnetic field and azimuthal MRI with only a pure azimuthal field. In both cases the relevant field B[phi] ~ 1/r is
generated by a rather large insulated current running on the symmetry axis of the experiment. The most challenging type of instability still remains standard MRI (SMRI) which relays on pure axial magnetic field B[z]. Here the necessary high rotation rates and large dimensions do limit the experimental feasibility to trigger SMRI until now. Besides that, even a non-rotating fluid with zero velocity can be destabilized by Tayler instability. Here the current is driven through the liquid which gives a B[phi] ~ r dependence. Concluding, the aim of new experimental is to investigate the whole parameter space for the mentioned instabilities and corresponding transitions.

We like to present the latest stage of construction of a large scale liquid sodium Taylor-Couette experiment with a height of 2m and diameter of 0.8 m. In a rough approximation, the achievable boundary conditions will be up to 20 Hz rotation rate and up to 50kA of electrical current. In a more detail, there are some specific topics we like to discus.

First, there is the quasi coaxial system consisting of a central current carrying copper rod and five symmetric return paths which provides homogeneous magnetic field to the Taylor-Couette flow.
One challenging part is the design of the current distributor, which is supposed to divide the current into several equally weighted lines. Because of the individual characteristic resistance of all involved conductors an initial imbalance in the current distribution affecting the symmetry of the magnetic field is the result. So the adjustment of current distribution becomes mandatory to ensure maximum field homogeneity. An indirect access to set the current in all five return paths is to control the outflow temperature of the required water cooling. This is done by thermostatically operated valves in conjunction with the temperature dependent branch resistance. Finally, the calibrated system achieves less than 1% field in-homogeneity and works in a wide range of currents. Additional benefits of the presented approach will be the minimal stray field of the installation and cheap components.

Second, we designed a stacked magnetic field system to generate the axial component. Here 27 individual coils provide an almost homogeneous field with B[z] < 150 mT in the relevant volume. The most challenging aspect is the huge amount of electrical power (approximately 120 kW) which have to be cooled. The main advantage of the present geometry is the guaranteed access to all the sensors mounted on the outer cylinder surface. This is achieved by a special geometry to partially levitate the coil system.

[1]F. Stefani et al., PRE, 80(6), 2009.
[1]M. Seilmayer et al., PRL, 108(24), 244501, 2012.
[1]M. Seilmayer et al., IEEE Sensors Journal, DOI 10.1109/JSEN.2017.2765671, 2017.

Keywords: Experiment; Sodium; DRESDYN; Taylor-Couette

  • Poster
    GDRI DYNAMO MEETING, 26.-29.11.2017, Paris, Frankreich

Publ.-Id: 26393

Synthesis of High-Crystallinity DPP Polymers with Balanced Electron and Hole Mobility

Di Pietro, R.; Erdmann, T.; Carpenter, J. H.; Wang, N.; Shivhare, R. R.; Formanek, P.; Heintze, C.; Voit, B.; Neher, D.; Ade, H.; Kiriy, A.

We review the Stille coupling synthesis of P-(DPP2OD-T) (Poly[[2,5-di(2-octyldodecyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione-3,6-diyl]-alt-[2,2′:5′,2″-terthiophene-5,5″-diyl]]) and show that high-quality, high molecular weight polymer chains are already obtained after as little as 15 min of reaction time. The results of UV−vis spectroscopy, grazing incidence wide-angle X-ray scattering (GIWAXS), and atomic force microscopy show that longer reaction times are unnecessary and do not produce any improvement in film quality. We achieve the best charge transport properties with polymer batches obtained from short reaction times and demonstrate that the catalyst washing step is responsible for the introduction of charge-trapping sites for both holes and electrons. These trap sites decrease the charge injection efficiency, strongly reducing the measured currents. The careful tuning of the synthesis allows us to reduce the reaction time by more than 100 times, achieving a more environmentally friendly, less costly process that leads to high and balanced hole and electron transport, the latter being the best reported for an isotropic, spin-coated DPP polymer.

Publ.-Id: 26392

ns-laser driven magnetic phase transition in FeAl

Liedke, M. O.; Bali, R.; Gradauskaite, E.; Ehrler, J.; Wang, M.; Potzger, K.; Zhou, S.; Wagner, A.

FeAl alloys show temperature dependent magnetic phase transition (MPT) from a ferromagnetic disordered A2-phase to a paramagnetic ordered B2-phase. The B2-phase can be reversed back to the A2-phase, e.g, by ion irradiation. The most plausible explanation of MPT points in direction of the anti-site disorder (ASD), i.e., more Fe-Fe nearest neighbors due to disordering. However, variations of the lattice parameter, defects concentration, and secondary phases may play an important role, too. Here, we employ an excimer UV ns-laser to examine the role of ASD and defects onto magnetic properties. Three sample series with different initial order conditions were irradiated by several laser fluences: (i) as-grown semi-, (ii) Ne irradiated fully-disordered, and (iii) vacuum annealed ordered alloys. Two magnetic regimes were found depending on laser fluence: (i) in the low fluence range magnetization initially decreases, followed by (ii) subsequent monotonic increase for larger fluences. The positron annihilation spectroscopy measurements reveal changes of defects surrounding from Al- to Fe dominant, respectively, as well as of defects concentration. The results obtained by MOKE, VSM, AFM, and TEM will be discussed in detail.

Keywords: FeAl alloys; PAS; magnetic phase transition; ns-laser; anti-site disorder; positron annihilation spectroscopy

  • Lecture (Conference)
    DPG Spring Meeting 2017, 19.-24.03.2017, Dresden, Deutschland

Publ.-Id: 26391

Fe2+ ion irradiated JRQ steel investigated by nanoindentation and slow-positron Doppler broadening spectroscopy

Pecko, S.; Heintze, C.; Bergner, F.; Anwand, W.; Slugen, V.

A model reactor pressure vessel (RPV) steel, known as JRQ, was manufactured in Japan for IAEA neutron embrittlement research studies in late 80 s. This model alloy belongs to the commercially used steel of A533B-1 type and shows relatively large changes in mechanical properties after a neutron irradiation due to considerable copper content (0.15 wt%). In order to simulate neutron irradiation and investigate the hardening effect, studied specimens of JRQ steel were exposed to Fe2+ ion irradiation in five different exposures calculated using the SRIM code. The ion energy of 5 MeV, temperature at 300 °C and the flux of 1.0×1011 cm−2 s−1 were the same during the irradiations. The hardening was investigated and observed by means of nanoindentation technique and a defect profile of irradiated steels was measured by Slow-positron Doppler broadening spectroscopy (DBS). The observed increasing trend of nanohardness as a function of fluence is in good agreement with the trend observed on the basis of Vickers hardness measured for neutron-irradiated JRQ. This confirms that Cu precipitation is most likely responsible for the observed irradiation hardening and that neutron-irradiation-induced damage can be simulated using ion irradiation in the present case. We have also excluded open volume (vacancy type) defects in the crystal lattice of JRQ steel from a responsibility for the damage arising by the Fe2+ ion irradiation.

Keywords: Positron annihilation spectroscopy; Reactor pressure vessel steels; Nanoindentation; Iron irradiation

Publ.-Id: 26390

Positronium formation in nanostructured metals

Čížek, J.; Melikhova, O.; Hruška, P.; Vlček, M.; Anwand, W.; Liedke, M. O.; Novotný, M.; Bulíř, J.

Positronium formation in Au films was studied using a magnetically guided continuous slow positron beam with variable energy. Black Au film with porous morphology was compared with conventional smooth Au film. In the smooth Au film positronium is formed on the film surface only. The black Au film exhibits porous sub-surface region containing micro-cavities interconnected with surface. Positronium is formed on inner surfaces of micro-cavities in the sub-surface region and travels through interconnected cavities towards the surface. 3-gamma annihilation of ortho-positronium leaves a clear signature in two-dimensional coincidence Doppler broadening spectra. Measurements of 3-gamma annihilation contribution calculated from single gamma-ray and coincidence Doppler broadening spectra were calculated and compared.

Keywords: Positronium; slow positron beam; porous metals; Au; coincidence Doppler broadening spectroscopy; positron annihilation spectroscopy


Publ.-Id: 26389

Photon vs. proton radiochemotherapy: effects on brain tissue volume and perfusion

Petr, J.; Platzek, I.; Hofheinz, F.; Mutsaerts, H.; Asllani, I.; van Osch, M.; Seidlitz, A.; Krukowski, P.; Gommlich, A.; Beuthien-Baumann, B.; Jentsch, C.; Maus, J.; Troost, E.; Baumann, M.; Krause, M.; van den Hoff, J.

Background and Purpose: To compare the structural and hemodynamic changes of healthy brain tissue in the cerebral hemisphere contralateral to the tumor following photon and proton radiochemotherapy.

Materials and Methods: Sixty-seven patients (54.9±14.0 years) diagnosed with glioblastoma multiforme undergoing adjuvant photon (n=47) or proton (n=19) radiochemotherapy with temozolomide after tumor resection underwent T1-weighted and arterial spin labeling MRI. Changes in volume and perfusion before and 3 to 6 months after were compared between therapies.

Results: A decrease in gray matter (GM) (-2.2%, P<0.001) and white matter (WM) (-1.2%, P<0.001) volume was observed in photon-therapy patients compared to the pre-radiotherapy baseline. In contrast, for the protontherapy group, no significant differences in GM (0.3%, P=0.64) or WM (-0.4%, P=0.58) volume were observed. GM volume decreased with 0.9% per 10 Gy dose increase (P<0.001) and differed between the radiation modalities (P<0.001). Perfusion decreased in photon-therapy patients (-10.1%,
P=0.002), whereas the decrease in proton-therapy patients, while comparable in magnitude, did not reach statistical significance (-9.1%, P=0.12). There was no correlation between perfusion decrease and either dose (P=0.64) or radiation modality (P=0.94).

Conclusion: Our results show that the tissue volume decrease depends on radiation dose delivered to the healthy hemisphere and differs between treatment modalities. In contrast, the decrease in perfusion was comparable for both irradiation modalities. We conclude that proton therapy may reduce brain-volume loss when compared to photon therapy.


Publ.-Id: 26388

Positronium probing of pores in zirconia nanopowders

Prochazka, I.; Cizek, J.; Lukac, F.; Melikhova, O.; Hruska, P.; Anwand, W.; Liedke, M. O.; Konstantinova, T. E.; Danilenko, I. A.

In the present paper, conventional positron lifetime measurements on selected zirconia-based nanopowders are reported. The nanopowders were doped with various metal cations (Y3+, Eu3+, Gd3+, Lu3+ and Mg2+). Lifetime experiments were conducted in air and supplemented with mass density measurements. In a range of lifetimes, from a few ns to ≈ 70 ns, up to two individual lifetime components could be identified. Such observations confirmed positronium (Ps) formation with subsequent ortho-Ps pick-off annihilation as well as the occurrence of pores of different size. Pore sizes were estimated using a shape-free model of the correlation between pore size and ortho-Ps lifetime. The origins of pores are discussed on the basis of the ortho-Ps data in combination with the results mass density measurements.

Keywords: positron lifetime; Positronium; zirconia nanopowders; mass density measurements; defects


Publ.-Id: 26387

Microstructure, defect structure and hydrogen trapping in zirconium alloy Zr-1Nb treated by plasma immersion Ti ion implantation and deposition

Kashkarov, E.; Nikitenkov, N.; Sutygina, A.; Laptev, R.; Bordulev, Y.; Obrosov, A.; Liedke, M. O.; Wagner, A.; Zak, A.; Weiß, S.

The effect of low energy plasma immersion ion implantation and deposition of titanium on microstructure, defect structure and hydrogen trapping in zirconium alloy Zr-1Nb was studied. Defect structure and distribution were analyzed by Doppler broadening using slow positron beam. The surface microstructure after modification is represented by nanostructured Ti grains with random orientation. The gradient distribution of titanium as well as vacancy type defects were analyzed. The concentration of vacancy type defects is rising with increasing bias voltage. Gas-phase hydrogenation of the Ti-modified Zr-1Nb alloy was performed at 400 °C for 60 min. The strong interaction of hydrogen with vacancy type defects was demonstrated. Two different changes in the defect structure after hydrogenation were observed: when a titanium film is formed on the surface (after deposition at 500 V) hydrogen trapping occurs with the formation of titanium hydride phases, while in the implanted layer (deposition at 1000 and 1500 V) hydrogen is trapped due to interaction with vacancy type defects. The physical basis of Ti diffusion and its influence on the evolution of defect structure after surface modification and hydrogenation were discussed.

Keywords: Zirconium; Ion implantation; Titanium; Diffusion; Surface modification; Hydrogen trapping; Microstructure; Slow positrons; Doppler broadening; Defects

Publ.-Id: 26386

Polymer nanocomposites with silver nanoparticles formed by low-energy ion implantation: slow positron beam spectroscopy studies

Kavetskyy, T. S.; Liedke, M. O.; Srinivasan, N.; Wagner, A.; Krause-Rehberg, R.; Šauša, O.; Petkova, T.; Boev, V.; Stepanov, A. L.

Polymer nanocomposites formed by low-energy ion implantation were studied by means of positron annihilation spectroscopy with a variable-energy positron beam or slow positron beam spectroscopy. Silver ion implantation into polymethylmethacrylate (Ag:PMMA) and hybrid organic-inorganic ureasil (Ag:ureasil) was performed at different ion fluences with a constant energy of 30 keV and a current density of 1 µA/cm^2 in order to prepare Ag nanoparticles in the near-surface region of polymer matrix. Contribution of Doppler broadening slow positron beam spectroscopy technique for understanding Ag nanoparticles formation in Ag:PMMA and Ag:ureasil nanocomposite films is demonstrated.

Keywords: polymers; nanocomposites; PMMA; ureasil; ion implantation; silver nanoparticles; positron annihilation; slow positrons

  • Book chapter
    Janez Bonca and Sergei Kruchinin: NATO Science for Peace and Security Series A: Chemistry and Biology, P.O.Box 17, 3300 AA Dordrecht, The Netherlands: AK/Nato Publishing Unit, Springer, 2018, 293-300
    DOI: 10.1007/978-94-024-1304-5_21

Publ.-Id: 26385

Kinetic modeling of the new σ1 receptor ligand (-)-[18F]Fluspidine in the human brain.

Becker, G. A.; Meyer, P. M.; Patt, M.; Hesse, S.; Luthardt, J.; Patt, J.; Rullmann, M.; Fischer, S.; Kluge, A.; Steinbach, J.; Wünsch, B.; Brust, P.; Sabri, O.

Der Abstract wird nachgereicht.

  • Abstract in refereed journal
    Nuklearmedizin 57(2018)-V9

Publ.-Id: 26384

EPR studies of the triangular-lattice antiferromagnet Cs2CuBr4

Schulze, E.; Ponomaryov, A. N.; Wosnitza, J.; Tanaka, H.; Zvyagin, S. A.

The spin dynamics of the spin-1/2 triangular-lattice antiferromagnet Cs2CuBr4 is probed by means of high-frequency electron paramagnetic resonance (EPR) spectroscopy. Temperature dependences of EPR parameters are studied in a broad temperature range between 1.4 and 200 K for different orientations of the applied magnetic field. In the high-temperature regime (T >> J/kB), an unusually broad and anisotropic resonance line is detected, suggesting a sizeable Dzyaloshinskii–Moriya interaction. Employing the theory of exchange narrowing, the ratio of the Dzyaloshinskii–Moriya vector components, Dc/Da ≈ 0.3, is estimated.

  • Open Access Logo Low Temperature Physics 43(2017), 1642-1646
  • Poster
    DPG-Frühjahrstagung der Sektion Kondensierte Materie (SKM) gemeinsam mit der European Physical Society (CMD), 11.-16.03.2018, Berlin, Deutschland


Publ.-Id: 26383

Entwicklung von F-18-markierten Radioliganden zur molekularen Bildgebung des A2A Adenosinrezeptors

Lai, T. H.; Moldovan, R.-P.; Schröder, S.; Dukic-Stefanovic, S.; Ludwig, F.-A.; Fischer, S.; Deuther-Conrad, W.; Steinbach, J.; Brust, P.

Ziel: Adenosinrezeptoren wurden jüngst als potentielle neue Targets bei der Immuntherapie von Hirntumoren identifiziert. [1] Die Autoren haben sich das Ziel gesetzt, hochaffine und selektive Radioliganden für den A2A-Rezeptor-Subtyp zu entwickeln, mit deren Hilfe Hirntumoren bildgebend molekular charakterisiert und entsprechende adjuvante Therapien verbessert werden können.

Methodik: Basierend auf einer Pyrazolo[2,3-d]pyrimidin Leitverbindung [2] wurden 21 fluorierte Derivate synthetisiert. Die Bindungsaffinitäten zum A2A- und zum A1-Rezeptor wurden mittels CHO-Zellen bestimmt, welche die relevanten humanen Rezeptoren hoch exprimieren. Zwei Derivate mit hoher Affinität und Selektivität wurden ausgewählt, um entsprechende Präkursoren zu synthetisieren, welche für die Radiofluorierung durch aromatische nukleophile Substitution eingesetzt werden.

Ergebnisse: Strukturelle Modifikationen der Leitverbindung führten zu neuen Derivaten mit Affinitäten zwischen 0,93 nM und 369 nM (A2A) bzw. zwischen 31,3 nM und 2298 nM (A1). Das 4 Fluorbenzylderivat 1 (Ki(A2A) = 5,3 nM; Ki(A1) = 220 nM) und das 1-Brom-3-fluorbenzylderivat 2 (Ki(A2A) = 2,4 nM; Ki(A1) = 162 nM) wurden für die Radiofluorierung ausgewählt. Die Herstellung von [18F]1 erfolgte in ersten Experimenten über ein zweistufiges Verfahren ausgehend von 4 [18F]Fluorbenzaldehyd durch reduktive Aminierung mit dem Pyrazolo[2,3-d]pyrimidin-Baustein. Die Radiofluorierung von 2 wird unter Verwendung des entsprechenden Nitro-Präkursors realisiert.

Schlussfolgerung: Es wurden zwei fluorierte Pyrazolo[2,3-d]pyrimidin-Derivate mit hoher Affinität und Selektivität zum A2A-Rezeptor synthetisiert, welche die weitere Entwicklung für effiziente F-18-Markierungsverfahren und erste präklinische Untersuchungen rechtfertigen.

[1] Allard et al., Immunol Cell Biol. 2017, 95(4), 333-339.
[2] Gillespie et al., Bioorg. Med. Chem. Lett. 2008, 18, 2924–2929.

  • Lecture (Conference)
    Nuklearmedizin 2018 - 56. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 18.-21.04.2018, Bremen, Deutschland
  • Lecture (Conference)
    Nuklearmedizin 2018, 18.-21.04.2018, Bremen, Deutschland

Publ.-Id: 26382

Nonlinear THz spectroscopy of low-dimensional materials

Helm, M.; König-Otto, J.; Schmidt, J.; Dimakis, E.; Winnerl, S.; Schneider, H.

Thanks to the development of powerful THz sources, both table-top and accelerator-based, highly nonlinear THz investigations of materials are possible today. Here we will present two recent examples of nonlinear spectroscopy on low-dimensional materials: resonant four-wave mixing in graphene under a magnetic field, and nonlinear THz spectroscopy of intersubband transitions in a semiconductor quantum well.
Graphene is predicted to be a highly nonlinear material due to its linear dispersion. Clear experimental observations are relatively scarce, however. In a magnetic field, the band structure splits up into non-equidistant Landau levels, giving rise to resonant behavior of the optical properties. We demonstrate resonantly enhanced four-wave-mixing (FWM) at a photon energy of 78 meV, resonant at a magnetic field of B = 4.5 T. The chi(3) character is clearly demonstrated by the power dependence of the four-wave-mixing signal and the narrower line shape as compared to the linear absorption. The FWM signal, proportional to the induced microscopic polarization, decays faster than the also measured pump-probe signal, beyond the time resolution of the experiment (4 ps).
Intersubband transitions in quantum wells, due to their similarities to atomic transitions, have been a playground for many fundamental optical and quantum mechanical effects as well as for novel devices for three decades. Nonlinear or quantum optical effects such as dressed states or electromagnetically induced transparency (EIT) were demonstrated, however, only in the mid-infrared range or probed in the near infrared. Here we employ our THz free-electron laser (FEL) in combination with THz time-domain spectroscopy to realize a true narrow-band pump – broad-band probe experiment: While pumping the 2-3 intersubband transition in a single GaAs/AlGaAs quantum well (at 3.5 THz = 15 meV), we probe the entire THz absorption up to 4 THz (including 1-2 and 2-3 transitions). The experiment allows one to extract the transmission change vs pump-probe time delay as well as the complete spectral shape of the transmission change at a specific time delay. We will discuss the observed spectra, including indications for the Autler-Townes splitting on the 1-2 transition.

Keywords: four-wave mixing; graphene; free-electron laser; pump-prbe; GaAs; quantum well; intersubband transition; Autler-Townes

  • Invited lecture (Conferences)
    MTSA 2017 & TeraNano-8, 19.-23.11.2017, Okayama, Japan

Publ.-Id: 26381

[18F]DBT10 als alpha7-Nikotinrezeptor-PET-Tracer von Schlaganfall assoziierter Neuroinflammation

Barthel, H.; Deuther-Conrad, W.; Patt, M.; Nitzsche, B.; Teodoro, R.; Härtig, W.; Luthardt, J.; Grunwald, T.; Brust, P.; Sabri, O.

Nach ischämischem Schlaganfall treten neuroinflammatorische Prozesse auf, die therapeutische Targets darstellen, jedoch bisher nicht adäquat in vivo darstellbar sind. Während dieser Prozesse werden unter anderem alpha7-Nikotinrezeptoren (nAChRs) verstärkt exprimiert. [18F]DBT10 ist ein neuer alpha7-nAChR-Tracer, welcher in der vorliegenden Studie erstmals diesbezüglich untersucht werden sollte.

Bei zehn erwachsenen Merino-Schafen wurde die linke A. cerebri media permanent okkludiert (pMCAO; Tag 1). Vor dem Eingriff sowie 4h, 7 und 14 Tage nach pMCAO wurden [18F]DBT10-Hirn-PET/MRT-Messungen (Siemens mMR, ca. 300MBq, 2h dynamisch, arterielle Blutproben, Blut-Metaboliten-HPLC) durchgeführt. Anhand direkt vorhergehender [15O]H2O-PET und simultaner Schlaganfall-MRT wurden die Schlaganfall-Kompartimente segmentiert. Direkt nach der PET/MRT am Tag 14 erfolgte ex vivo eine autoradiographische (AR) und histopathologische Hirnaufarbeitung. Zusätzlich zu den pMCAO-Schafen wurden Kontrollschafe (nicht-operiert, Schein-OP) untersucht.

[18F]DBT10 im Blut wurde mit einer HWZ von 18min metabolisiert, schnell aus dem Zerebellum ausgewaschen und erreichte in kortikalen Hirn-VOIs bei 60min p.i. ein Plateau. Die Kontrollschafe in die vor dem Eingriff zeigten keine [18F]DBT10-Auffälligkeiten. In den pMCAO-Schafen fanden sich Infarkt-bezogene [18F]DBT10-PETSpeicherdefizite nach 4h und am Tag 7 (SUVRs110-120min p.i. = 0,94±0,04 und 0,90±0,17), am Tag 14 jedoch eine intensive Mehranreicherung im Randbereich des Infarktes (SUVR110-120min p.i. =1,82±0,72; p<0,01). Diese ließ sich in der AR reproduzieren und korrelierte histopathologisch mit Mikroglia-Aktivierung und Makrophagen-Infiltration.

Aus diesen Ergebnissen wird geschlussfolgert, dass [18F]DBT10 ein vielversprechender PET-Tracer zur Erfassung von alpha7-nAChR-assoziierter Neuroinflammation nach ischämischem Hirninfarkt ist. Weitere Untersuchungen sollen unter anderem der kinetischen Modellierung des Tracer-Verhaltens dienen.

  • Lecture (Conference)
    56. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 18. – 21.04.2018, 18.-21.04.2018, Bremen, Deutschland

Publ.-Id: 26380

Monte-Carlo-Simulation und Berechnung der spezifischen absorbierten Strahlenenergiefraktionen (SAF) für ein VOXEL Phantom eines Ferkels für die Inkorporationsdosimetrie

Sattler, B.; Kranz, M.; Desbrée, A.; Rullmann, M.; Patt, M.; Deuther-Conrad, W.; Steinbach, J.; Sabri, O.; Brust, P.

Ziel: Vor erstmaliger Anwendung neuartiger Radiopharmaka im Menschen muss präklinisch eine Abschätzung der inneren Strahlenexposition des Menschen am Tiermodell erfolgen. Hierfür stehen computergenerierte VOXEL Phantome (VP) unterschiedlicher Tiermodelle zur Verfügung. Die Verschiedenen, teils regulatorisch für die klinische Anwendung zugelassenen Softwaretools für die Inkorporationsdosimetrie nutzen Implementationen dieser VP für die präklinische und klinische Dosimetrie. Basierend auf den anatomischen und geometrischen Verhältnissen enthalten die VP die in Zielorganen und Organsystemen absorbierte spezifische Fraktion der von Quellorganen ausgehenden/emittierten Strahlenenergie (specific absorbed fraction, SAF). Diese sind grundlegend für die in Organen und Organsystemen absorbierten Dosis (OD) nach dem MIRD Schema und werden durch Monte-Carlo-Simulation (MC) berechnet. Eigene Arbeiten haben gezeigt, dass im Vergleich zur Verwendung von Kleintieren mit Ferkeln eine den Verhältnissen am Menschen vergleichbarere Abschätzung der Strahlenexposition möglich ist. Daher wurde ein VP für Ferkel erstellt und dessen SAFs durch MC berechnet.
Methodik: Ein 12 kg Ferkel (8 Wochen) wurde nach i.v. Injektion von [18F]Flubatine (185.4 MBq) bis zu 4,5 h p.i. in einem PET/CT (SIEMENS Biograph 16) gemessen und die List-Mode Daten nach Standardkorrekturen rekonstruiert. Unter Nutzung der PET bzw. CT Daten und der Software ROVER (ABX, Radeberg) wurden 18 Organe vorwiegend manuell segmentiert und als DICOM Structure Set exportiert. Mit der Software OEDIPE [1] erfolgte die Zuordnung der Gewebeeigenschaften der segmentierten Organe nach ICRU [2]. Anschließend erfolgt die Simulation in MCNPX (v.2.6.0) mit 20 Millionen Events als Abbruchkriterium.
Ergebnisse: Mit OEDIPE gelingt unter Verwendung des Ergebnisses der MC-Simulation die Erzeugung der SAFs für ein VP des Ferkels. Für 28 Radionuklide wurden SAFs (mGy/MBq*s) für Gehirn, Leber, Gallenblase, Nieren, Dünn- und Dickdarm, Lunge, Herz, Pankreas, rotes Knochenmark, Milz, Magen, Schilddrüse, Thymus, Blase, Skelett, Wirbelsäule und Restkörper berechnet.
Schlussfolgerung: Unter Nutzung von OEDIPE wurde erstmals ein VP des Ferkels erzeugt und durch MC-Simulation die SAFs berechnet. Dieses VP steht der Implementation in verschiedenen am Markt verfügbare Softwaretools zur Verfügung. Seine Anwendbarkeit für die präklinische Inkorporationsdosimetrie wird nunmehr durch den Vergleich mit anderen, bereits implementierten VP weiter untersucht.

Keywords: Monte-Carlo; PET; Dosimetry; VOXEL Phantom

  • Abstract in refereed journal
    Nuklearmedizin 57(2018), V112
  • Lecture (Conference)
    56. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 18.-21.04.2018, Bremen, Deutschland

Publ.-Id: 26379

Characterizing mineral wettabilities on a microscale by colloidal probe atomic force microscopy

Babel, B. M.; Rudolph, M.

For finely intergrown ores the characterization of reagent-mineral interactions in flotation systems holds difficult challenges for the applicability of standard techniques like hallimond tube tests or contact angle experiments or renders them impossible while other techniques might not work in an aqueous environment. We present the utilization of an atomic force microscope with a hydrophobic colloidal probe to characterize the wettabilities of individual mineral grains on a microscale. The sulfidic ore sample containing chalcopyrite, pyrite and quartz is investigated in an aqueous environment. The mineralogy of the sample is characterized by SEM+EDX and its wettability by contact angle measurements. Force mappings on the respective minerals are performed and allow a distinction between quartz, chalcopyrite and pyrite with the resulting force distributions. An additional focus in this paper lies on the heterogeneities within one mineral surface domain and the applicability for grain mappings.

Keywords: hydrophobic interaction; atomic force microscopy; wettabilities; adhesion imaging; flotation

  • Open Access Logo Minerals Engineering 121(2018), 212-219
    Online First (2018) DOI: 10.1016/j.mineng.2018.02.003
  • Lecture (Conference)
    NanoScientific Forum Europe, 10.-12.10.2018, Freiberg, Deutschland


Publ.-Id: 26378

Versatile Tri(pyrazolyl)phosphanes as Phosphorus Precursors for the Synthesis of Highly Emitting InP/ZnS Quantum Dots - Tri(pyrazolyl)phosphane als Vorstufen für die Synthese von stark emittierenden InP/ZnS-Quantenpunkten

Panzer, R.; Guhrenz, C.; Haubold, D.; Hübner, R.; Gaponik, N.; Eychmüller, A.; Weigand, J. J.

Tri(pyrazolyl)phosphanes (5R1,R2) are utilized as an alternative, cheap and low-toxic phosphorus source for the convenient synthesis of InP/ZnS quantum dots (QDs). From these precursors, remarkably long-term stable stock solutions (>6 months) of P(OLA)3 (OLAH=oleylamine) are generated from which the respective pyrazoles are conveniently recovered. P(OLA)3 acts simultaneously as phosphorus source and reducing agent in the synthesis of highly emitting InP/ZnS core/shell QDs. These QDs are characterized by a spectral range between 530-620 nm and photoluminescence quantum yields (PL QYs) between 51-62 %. A proof-of-concept white light-emitting diode (LED) applying the InP/ZnS QDs as a color-conversion layer was built to demonstrate their applicability and processibility.
Tri(pyrazolyl)phosphane werden als alternative kostengünstige und weniger toxische Phosphorquelle in der Synthese von InP/ZnS-Quantenpunkten (QDs) eingesetzt. Ausgehend von ihnen können langzeitstabile (>6 Monate) P(OLA)3-Stammlösungen (OLAH=Oleylamin) synthetisiert werden, aus denen sich die entsprechenden Pyrazole einfach zurückgewinnen lassen. P(OLA)3 fungiert in der Synthese von stark emittierenden InP/ZnS-QDs sowohl als Phosphorquelle als auch als Reduktionsmittel. Die erhaltenen Kern/Schale-Partikel zeichnen sich durch hohe Photolumineszenz-Quantenausbeuten von 51–62 % in einem Spektralbereich von 530-620 nm aus. Die Verarbeitung und Anwendung dieser InP/ZnS-QDs als Farbkonversionsschicht wurde anhand des Einsatzes in einer weißen Leuchtdiode demonstriert.

Keywords: hot injection; oleylamine; phosphorus; quantum dots; waste prevention; Heißinjektion; Oleylamin; Phosphor; Ressourcen-Schonung; Quantenpunkte

Publ.-Id: 26377

Extremely high magnetoresistance and conductivity in the type-II Weyl semimetals WP2 and MoP2

Kumar, N.; Sun, Y.; Xu, N.; Manna, K.; Yao, M.; Süss, V.; Leermakers, I.; Young, O.; Förster, T.; Schmidt, M.; Borrmann, H.; Yan, B.; Zeitler, U.; Shi, M.; Felser, C.; Shekhar, C.

The peculiar band structure of semimetals exhibiting Dirac and Weyl crossings can lead to spectacular electronic properties such as large mobilities accompanied by extremely high magnetoresistance. In particular, two closely neighboring Weyl points of the same chirality are protected from annihilation by structural distortions or defects, thereby significantly reducing the scattering probability between them. Here we present the electronic properties of the transition metal diphosphides, WP2 and MoP2, which are type-II Weyl semimetals with robust Weyl points by transport, angle resolved photoemission spectroscopy and first principles calculations. Our single crystals of WP2 display an extremely low residual low-temperature resistivity of 3 nΩ cm accompanied by an enormous and highly anisotropic magnetoresistance above 200 million % at 63 T and 2.5 K. We observe a large suppression of charge carrier backscattering in WP2 from transport measurements. These properties are likely a consequence of the novel Weyl fermions expressed in this compound.

Publ.-Id: 26376

Simulation of a counter-current horizontal gas/liquid flow experiment at the WENKA channel using a droplet entrainment model

Höhne, T.; Gabriel, S.

One drawback today in simulating horizontal wavy two-phase flows is that there is no treatment of droplet formation mechanisms at the liquid surface. For self-generating waves and slugs, the interfacial momentum exchange and the turbulence parameters have to be modelled correctly. Furthermore, understanding and considering the mechanism of droplet entrainment for heat and mass transfer processes is of great importance in the nuclear industry.
Therefore a step of improvement of modelling liquid/gas interfaces is the consideration of droplet entrainment mechanisms. The proposed entrainment model assumes that due to liquid turbulence the interface gets rough and wavy leading to the formation of droplets. The new approach is validated against existing horizontal two-phase flow data from the WENKA (Water ENtraninment Channel KArlsruhe) channel.
Tests were carried out for water and air at ambient pressure and temperature. High speed videometry was applied to obtain velocities from flow pattern maps of the rising and falling fluid. In the horizontal part of the channel with partially reversed flow the fluid velocities were measured by planar particle image velocimetry. The test MP 28 with droplet generation at the reversed flow conditions was utilized to compare it with the simulation data. The agreement of the experimental findings and CFD results is acceptable. Also the droplet mass flow was compared and showed the applicability of the droplet entrainment model. Further work is necessary to validate the model for different flow conditions.

Keywords: CFD; horizontal flow; AIAD; droplet entrainment; two-phase flow; HAWAC; HZDR; OVM; PIV; Isokinetic Sampling Probe; WENKA


Publ.-Id: 26375

The γ-ray angular distribution in fast neutron inelastic scattering from iron

Beyer, R.; Dietz, M.; Bemmerer, D.; Junghans, A. R.; Kögler, T.; Massarczyk, R.; Müller, S.; Schmidt, K.; Schwengner, R.; Szücs, T.; Takacs, M. P.; Wagner, A.

The angular distribution of γ-rays emitted after inelastic scattering of fast neutrons from iron was determined at the nELBE neutron time-of-flight facility. An iron sample of natural isotopic composition was irradiated by a continuous photo-neutron spectrum in the energy range from about 0.1 up to 10 MeV. The de-excitation γ-rays of the four lowest excited states of ⁵⁶Fe and the first excited state of ⁵⁴Fe were detected using a setup of five high-purity germanium (HPGe) detectors and five LaBr₃ scintillation detectors positioned around the sample at 30°, 55°, 90°, 125° and 150° with respect to the incoming neutron beam. The resulting angular distributions were fitted by Legendre polynomials up to 4th order and the angular distribution coefficients a₂ and a₄ were extracted. The angular distribution coefficients of three transitions in ⁵⁶Fe are reported here for the first time. The results are applied to a previous measurement of the inelastic scattering cross section determined using a single HPGe detector positioned at 125°. Using the updated γ-ray angular distribution, the previous cross section results are in good agreement with reference data.

Keywords: nELBE; neutron time-of-flight; angular distribution; iron


Publ.-Id: 26374

Uranium(VI) complexes with a calix[4]arene-based 8-hydroxyquinoline ligand: Thermodynamic and structural characterization based on calorimetry, spectroscopy, and liquid-liquid extraction

Bauer, A.; Jäschke, A.; Schöne, S.; Barthen, R.; März, J.; Schmeide, K.; Patzschke, M.; Kersting, B.; Fahmy, K.; Oertel, J.; Brendler, V.; Stumpf, T.

The environmental aspects of ore processing and waste treatment call for an optimization of applied technologies. There, understanding of the structure and complexation mechanism on a molecular scale is indispensable. Here, the complexation of U(VI) with a calix[4]arene-based 8-hydroxyquinoline ligand was investigated by applying a wide range of complementary methods. In solution, the formation of two complex species was proven with stability constants of log ß1:1 = 5.94±0.02 and log ß2:1 = 6.33±0.01, respectively. The formation of the 1:1 complex was found to be enthalpy driven (∆H1:1 = (– 71.5±10.0) kJ mol–1; T∆S1:1 = (–37.57±10.0) kJ mol–1), whereas the second complexation step was found to be endothermic and entropy driven (∆H2:1 = (32.8±4.0) kJ mol–1; T∆S2:1 = (68.97±4.0) kJ mol–1). Moreover, the molecular structure of [UO2(H6L)(NO3)](NO3) (1) was determined by single-crystal X-ray diffraction. Concluding, radiotoxic U(VI) was separated from a Eu(III)-containing solution by the calix[4]arene-based ligand in solvent extractions.

Keywords: calixarene; liquid-liquid extraction; density functional theory; calorimetry; spectroscopic properties; chelate; uranium; X-ray crystal

Publ.-Id: 26373

Investigations of the Effects of the Variation of Fuel Assembly Positions in a core of a PWR

Konheiser, J.; Müller, S. E.; Seidl, M.

This work shows the impact of possible variations of the core geometry on the signal values of the ex-core instrumentation of a pressurized water reactor (PWR). Based on the potential influence on the signals, neutron fluxes have been determined for selected fuel assembly displacements using stationary Monte Carlo calculations. First, critical calculations were carried out for the chosen core configurations and corresponding surface sources on the core barrel were determined. In a second step transport calculations for the ionization chambers were performed using the surface sources. Typical data of a German PWR were used for the investigations.
Variation of fuel assembly positions in the outer region of the core were studied, which were directly opposite to the ex-core instrumentation. An increase of the neutron flux at the chambers of up to 4% has been calculated for a change in position of 1 mm between some fuel assemblies. The reason is an improved moderation of neutrons because of the larger water gap. This causes an increase in local power which leads to a greater leakage of neutrons over the core barrel. In addition, a dependence of this effect as a function of cycle burnup was analyzed.

Keywords: PWR type reactor; Monte Carlo calculation; safety analysis; ex-core instrumentation

  • Lecture (others)
    17. AAA Workshop, 04.12.2017, Garching, Germany

Publ.-Id: 26372

Coupling of ferromagnetism and structural phase transition in V2O3/Co bilayers

Wang, C.; Xu, C.; Wang, M.; Yuan, Y.; Liu, H.; Dillemans, L.; Homm, P.; Menghini, M.; Locquet, J.-P.; Haesendonck, C. V.; Zhou, S.; Ruan, S.; Zeng, Y.-J.

Interfacial coupling in hybrid magnetic heterostructures is being considered as a unique opportunity for functional material design. Here, we present the temperature dependence of magnetic properties of V2O3/Co bilayers influenced by the structural phase transition that is accompanied by a metal–insulator transition in V2O3. Both the coercivity and the magnetization of Co layer are strongly affected by the interfacial stress due to the magnetostrictive effect in the ferromagnetic film. The observed change in coercivity is as large as 59% in a narrow temperature range. The changes in the magnetic properties are reproducible and reversible, which are of importance for potential applications.

Keywords: metal–insulator transition; magnetostrictive coupling; structural phase transition; heterostructure


Publ.-Id: 26371

An orthotopic xenograft model for high-risk non-muscle invasive bladder cancer in mice: influence of mouse strain, tumor cell count, dwell time and bladder pretreatment

Huebner, D.; Rieger, C.; Bergmann, R.; Ullrich, M.; Meister, S.; Toma, M.; Wiedemuth, R.; Temme, A.; Novotny, V.; Wirth, M. P.; Bachmann, M.; Pietzsch, J.; Fuessel, S.

Background: Novel theranostic options for high-risk non-muscle invasive bladder cancer are urgently needed. This requires a thorough evaluation of experimental approaches in animal models best possibly reflecting human disease before entering clinical studies. Although several bladder cancer xenograft models were used in the literature, the establishment of an orthotopic bladder cancer model in mice remains challenging.
Methods: Luciferase-transduced UM UC 3LUCK1 bladder cancer cells were instilled transurethrally via 24G permanent venous catheters into athymic NMRI and BALB/c nude mice as well as into SCID-beige mice. Besides the mouse strain, the pretreatment of the bladder wall (trypsin or poly-L-lysine), tumor cell count (0.5×106 – 5.0×106) and tumor cell dwell time in the murine bladder (30 min – 2 h) were varied. Tumors were morphologically and functionally visualized using bioluminescence imaging (BLI), magnetic resonance imaging (MRI), and positron emission tomography (PET).
Results: Immunodeficiency of the mouse strains was the most important factor influencing cancer cell engraftment, whereas modifying cell count and instillation time allowed fine-tuning of the BLI signal start and duration – both representing the possible treatment period for the evaluation of new therapeutics. Best orthotopic tumor growth was achieved by transurethral instillation of 1.0×106 UM UC 3LUCK1 bladder cancer cells into SCID-beige mice for 2 h after bladder pretreatment with poly-L-lysine. A pilot PET experiment using 68Ga-cetuximab as transurethrally administered radiotracer revealed functional expression of epidermal growth factor receptor as representative molecular characteristic of engrafted cancer cells in the bladder.
Conclusions: With the optimized protocol in SCID-beige mice an applicable and reliable model of high-risk non-muscle invasive bladder cancer for the development of novel theranostic approaches was established.

Keywords: bioluminescence; luciferase; orthotopic xenograft models; small animal multimodal imaging; magnetic resonance imaging; optical imaging; positron emission tomography; transurethral instillation; UM-UC-3 cell line; urothelial carcinoma

Publ.-Id: 26370

Nitric oxide-releasing selective cyclooxygenase-2 inhibitors as promising radiosensitizers in melanoma cells in vitro

Bechmann, N.; Hauser, S.; Hofheinz, F.; Kniess, T.; Pietzsch, J.

Expression of cyclooxygenase-2 (COX-2) and subsequent higher availability of eicosanoids are important modulators of tumor radioresistance. Additionally, elevated COX-2 protein is closely associated with hypoxia, which itself is a key promoter of tumor radioresistance. In this regard, selective COX-2 inhibitors (coxibs) containing a nitric oxide (NO)-releasing moiety (NO-coxibs) are hypothesized to act as bifunctional radiosensitizers. Therefore, novel NO-coxibs with a (pyrazolyl)benzenesulfonamide lead were investigated in vitro. As model, two human melanoma cell lines were exposed to several doses of X-ray in presence or absence of the novel NO-coxibs or the corresponding coxib during irradiation. Cells were examined in clonogenic cell survival assays to determine radiosensitizing effects under both normoxic and hypoxic conditions. COX-2 protein expression of two melanoma cell lines with a dissimilar baseline COX-2 synthesis was increased by irradiation and, furthermore, by experimental hypoxia. Radiosensitivity of both cell lines was significantly enhanced by the novel NO-coxibs and, to a lesser extent, also by the corresponding coxib. Moreover, the most potent NO-coxib 5 significantly increased the radiosensitivity of both cell lines also under hypoxic conditions. By administration of 5 the required radiation dose for 10% survival could be reduced from 6.6 Gy (DMSO control) to 5.2 Gy (p<0.01) for the ‘COX-2-positive’ A2058 cells and from 4.2 Gy (DMSO control) to 3.2 Gy for the ‘COX-2-negative’ Mel-Juso cells. The results confirm the auspicious bifunctional approach of the novel NO-coxibs as potential adjuvant radiosensitizers under normoxic and hypoxic conditions in vitro. Further studies are necessary to confirm the promising findings in vivo.

Keywords: Chemoradiotherapy; malignant melanoma; radiosensitization; multi-target approach; carbonic anhydrase-IX; CoCl2-induced hypoxia

  • Open Access Logo Annals of Radiation Therapy and Oncology 1(2017)2, 1010

Publ.-Id: 26369

Energy balance of the carbon dioxide injection facility in Ketzin, Germany

Wiese, B. U.; Nimtz, M.

Injection of 67 kt carbon dioxide was carried out between 2008 and 2013 at the test site for geological storage in
Ketzin, Germany. The source carbon dioxide was delivered in liquid phase. The injection facility has had a three
step process chain: (i) pressure increase by a liquid pump, (ii) temperature increase by ambient air vaporizers
and (iii) temperature increase by an electrical vaporizer including phase change to gaseous conditions. The
ambient vaporizers reduced electrical power demand but the weather dependence induced some kind of uncertainty,
further their power could not be measured. In the cases when the carbon dioxide was evaporated
within the ambient vaporizers, the heat demand increased such that the driving temperature was not enough for
full vaporization. However, the gas to liquid ratio is unknown wherefore the heating power can not be calculated
over the ambient vaporizer. This is addressed, as the electric energy consumption was most reduced during the
two phase operation.
For these intervals, two phase gas–liquid conditions prevailed in the pipeline. Unlike conjectured, flow
conditions remained stable and did not vary significantly from single phase behavior. The current work – for the
first time – presents a detailed analysis of energy input and losses of the carbon dioxide injection process based
on field data and simulations. A modified process chain is proposed to switch the electric energy demand to an
ambient heat source, reducing the electrical energy use per ton carbon dioxide by up to 90 %. The work provides
insight for planning future injection devices that involve liquid carbon dioxide in the process chain.

Keywords: CCS; Injection facility; Storage; Carbon dioxide; Ketzin; Ambient air heat exchanger; Vaporization

Publ.-Id: 26368

Chemical analysis of solid-liquid interfaces by in-situ Rutherford Backscattering Spectrometry

Baghban Khojasteh Mohammadi, N.; Heller, R.

Solid-liquid interfaces are important locations for various reactions to occur in biological, chemical and physical processes [1-3]. Recently, an experimental setup for in-situ Rutherford Backscattering Spectrometry (RBS) technique has been installed at the 2 MV Van-de-Graaff accelerator at Ion Beam Center (IBC) of the Helmholtz-Zentrum Dresden-Rossendorf to analyze solid-liquid interfaces as well as to conduct electro-chemistry experiments. The focus of the project is to perform experiments in different fields utilizing this quantitative, non-destructive and standard free ion beam analysis technique for solid-liquid interfaces. A Si3N4 window separates the liquid in the cell from vacuum in the beam line. He+ beam with E = 1.7 MeV is employed to bombard the samples. For feasibility tests, the cell was filled with air, Ne, He, Xe and DIH2O respectively and RBS and Particle Induced X-Ray Emission Spectroscopy (PIXE) spectra were recorded. To examine the efficiency of the technique, ion backscattering studies of the solid-liquid using 0.1M solutions of Cu(NO3) and AgNO3 have been performed and are compared to the literature [4].
[1] Kötz et al., Electrochimica acta. 31 (1986) 169.
[2] Morita et al., Radiation Physics and Chemistry. 49 (1997) 603.
[3] Hodnik et al., Accounts of chemical research. 49 (2016) 2015.
[4] Forster et al., Nuclear Instruments and Methods in Physics Research Section B. 28 (1987) 385.

Keywords: solid-liquid; interface analysis; in-situ RBS

  • Poster
    DPG Spring Meeting of the Condensed Matter Section (SKM), 11.-16.03.2018, Berlin, Deutschland

Publ.-Id: 26367

Potential of asphericity as a novel diagnostic parameter in the evaluation of patients with Ga-68-PSMA-HBED-CC PET-positive prostate cancer lesions

Meissner, S.; Janssen, J.; Prasad, V.; Brenner, W.; Diederichs, G.; Hamm, B.; Hofheinz, F.; Makowski, M.

Background: The aim of this study was to evaluate the diagnostic value of the asphericity (ASP) as a novel quantitative parameter, reflecting the spatial heterogeneity of tracer uptake, in the staging process of patients with Ga-68-PSMA-HBED-CC positron emission tomography (PET)-positive prostate cancer (PC). In this study, 37 patients (median age 72 years, range 52-82 years) with newly diagnosed PC, who received a Ga-68-PSMA-HBED-CC PET fused with computed tomography (Ga-68-PSMA-PET/CT), a magnetic resonance imaging (MRI) of the prostate, and a core needle biopsy (within 74.2 8 +/- 80.2 days) with an available Gleason score (GSc) were extracted from the local database. The ASP and the viable tumor volume (VTV) was calculated using the rover software (ABX GmbH, Radeberg, Germany), a segmentation tool for automated tumor volume delineation. Additionally, parameters including total lesion binding rate (TLB), maximum, mean and peak standardized uptake value (SUVmax/mean/peak), prostate-specific antigen (PSA), D'Amico classification, and prostate imaging reporting and data system (PI-RADS) were analyzed.

Results: The ASP mean differed significantly (p = 0.05) between the different GSc groups: GSc 6-7: 11.9 +/- 4.8%, GSc 8: 25.5 +/- 4.8%, GSc
9-10: 33.3 +/- 6.8%. A significant correlation between ASP and GSc (rho = 0.88; CI 0.78-0.94; p < 0.05) was measured. The ASP enabled an independent (p > 0.05) prediction of the GSc. A moderate correlation was measured between ASP and the D'Amico classification (rho = 0.6; CI 0.32-0.78; p < 0.05). The VTV showed a moderate correlation with the SUVmax (rho = 0.58; CI 0.32-0.76; p < 0.05) and the GSc (rho = 0.51; CI 0.23-0.72; p < 0.05).

Conclusion: The asphericity in Ga-68-PSMA-PET could represent a promising novel quantitative parameter for an improved non-invasive tumor staging of patients with PC.

Keywords: Prostatic neoplasms; Positron emission tomography computed tomography; Gleason score,Asphericity; Histopathol

Publ.-Id: 26366

Drone-borne mineral exploration in Central-West Greenland

Zimmermann, R.; Rosa, D.; Gloaguen, R.

During the last two field seasons, two different type of Unmanned Aerial Systems were tested and evaluated for mineral mapping in Central-West Greenland. A fixed wing system turned out to be more suitable as large areas can be covered faster and more efficiently.
In 2017, a sensefly ebeePlus fixed-wing system with a 4 channel multispectral Sequoia camera (4 channels in VIS-NIR with 1.2 MP + 16 MP RGB camera) was deployed. Flight altitude was set to achieve 11cm ground sampling distance (GSD). Processing followed in-house routines using Structure-from-Motion photogrammetry to get Digital Surface Models (DSM) and geometrically corrected orthomosaics. In total 6.4 km2 of the VMS showings in Kangiusap Kuua at Svartenhuk were covered. The VMS showings are hosted in the Nukavsak Fm of the Paleoproterozoic Karrat group. In certain stratigraphic horizon within the meta-turbidites, basalt flows with associated sulphide-rich sea-floor alteration occur. Flight plans were set to cover both alteration and host-rock. A validation dataset includes sampling and spectral characterisation of selected hand specimen.
Gossans are easily mappable by integrated morphological and spectral analysis as they form ridges with a distinct iron feature. Moreover, traces of fractures and faults, their spatial distribution and relation to the altered horizon is retrieved.
This further highlights the capability of drone-borne application for high-resolution reconnaissance mapping within short turn-around times. Intermediate insights from the project Multi-sensor drones for geological mapping (MULSEDRO) will facilitate the application of drones under unfavourable conditions.

  • Lecture (Conference)
    33rd Nordic Geological Winter Meeting, 10.-12.01.2018, København, Danmark

Publ.-Id: 26365

Chelation of heavy group 2 (radio)metals by p-tert-butylcalix[4]arene-1,3-crown-6 and logK determination via NMR

Bauer, D.; Gott, M.; Steinbach, J.; Mamat, C.

A crown-bridged calix[4]arene scaffold was investigated as lead compound for the ligation of heavy alkaline earth metals such as strontium and barium, which appear to be useful for radiopharmaceutical applications in diagnosis as well as in radiotherapy. The ability of p-tert-butylcalix[4]arene-1,3-crown-6 (1) in particular to chelate cations, such as group 1 and 2 metal ions or ammonium ions is well known. Also, the manifold possibilities of structural modification on the upper- and lower-rim as well as on the crown itself produce properties that may lead to a highly selective and effective chelating agent. In this work, titration experiments of the perchlorate salts of Ba2+, Sr2+ and Pb2+ with ligand 1 were performed to determine their stability constants (logK = 4.7, 4.3, and 3.3, respectively) by 1H NMR measurements in acetonitrile-d3.


Publ.-Id: 26364

Feasible device architectures for ultra-scaled CNTFETs

Pacheco-Sanchez, A.; Fuchs, F.; Mothes, S.; Zienert, A.; Schuster, J.; Gemming, S.; Claus, M.

Feasible device architectures for ultra-scaled CNTFETs are studied down to 5.9 nm using a multiscale simulation approach covering electronic quantum transport simulations and TCAD numerical device simulations. Schottky-like and ohmic-like contacts are considered. The simplified approach employed in the numerical device simulator is critically evaluated and verified by means of comparing the results with electronic quantum simulation results of an identical device. Different performance indicators such as the switching speed, switching energy, the subthreshold slope, Ion/Ioff-ratio, among others, are extracted for different device architectures. These values guide the evaluation of the technology for different application scenarios. For high-performance logic applications, the buried gate CNTFET is claimed to be the most suitable structure.

Keywords: CNTFETs; Logic gates; Numerical models; Computer architecture; Performance evaluation; Electric potential; Effective mass


Publ.-Id: 26363

Investigation of the environmental impact of nanoparticles using smart radiolabeling

Schymura, S.; Fricke, T.; Hildebrand, H.; Steudtner, R.; Hübner, R.; Mansel, A.; Franke, K.

The investigation of the environmental impact of nanoparticles is greatly hindered by a lack of suitable detection methods, especially at the low, environmentally relevant concentrations. The radiolabeling of nanoparticles can overcome these setbacks and provides a possibility of detecting nanoparticles at minimal concentrations against high elemental and particle backgrounds.
In addition to that the sophisticated use of different labeling strategies allows the direct measurement of processes such as dissolution and their relevant in, for example, plant uptake. Using different labeling stragies we produce radiolabeled CeO2 nanoparticles with different radioactivity release kinetics upon dissolution. This enabled us to measure the uptake and translocation of CeO2 nanoparticles in plants and to identify the predominant uptake pathway in the form of particles, as opposed to an uptake of their dissolved remains.

Keywords: Radiomarkierung; radiolabeling; Nanopartikel; nanoparticles; Umwelt; environment; Pflanzen; plants

  • Lecture (Conference)
    13th Cycleur – European Network of Cyclotron Research Centers – Workshop, 23.-24.11.2017, Lissabon, Portugal

Publ.-Id: 26360

Novel Humanized and Highly Efficient Bispecific Antibodies Mediate Killing of Prostate Stem Cell Antigen-Expressing Tumor Cells by CD8+ and CD4+ T Cells

Feldmann, A.; Arndt, C.; Töpfer, K.; Stamova, S.; Krone, F.; Cartellieri, M.; Koristka, S.; Michalk, I.; Lindemann, D.; Schmitz, M.; Temme, A.; Bornhäuser, M.; Ehninger, G.; Bachmann, M.

Prostate cancer is the most common noncutaneous malignancy in men. The prostate stem cell Ag (PSCA) is a promising target for immunotherapy of advanced disease. Based on a novel mAb directed to PSCA, we established and compared a series of murine and humanized anti-CD3–anti-PSCA single-chain bispecific Abs. Their capability to redirect T cells for killing of tumor cells was analyzed. During these studies, we identified a novel bispecific humanized Ab that efficiently retargets T cells to tumor cells in a strictly Ag-dependent manner and at femtomolar concentrations. T cell activation, cytokine release, and lysis of target cells depend on a cross-linkage of redirected T cells with tumor cells, whereas binding of the anti-CD3 domain alone does not lead to an activation or cytokine release. Interestingly, both CD8+ and CD4+ T cells are activated in parallel and can efficiently mediate the lysis of tumor cells. However, the onset of killing via CD4+ T cells is delayed. Furthermore, redirecting T cells via the novel humanized bispecific Abs results in a delay of tumor growth in xenografted nude mice.

Publ.-Id: 26359

Retargeting of T Cells to Prostate Stem Cell Antigen ExpressingTumor Cells: Comparison of Different Antibody Formats

Feldmann, A.; Stamova, S.; Bippes, C. C.; Bartsch, H.; Wehner, R.; Schmitz, M.; Temme, A.; Cartellieri, M.; Bachmann, M.

BACKGROUND. Prostate cancer (PCa) is the most common malignant disease in men. Novel treatment options are needed for patients after development of metastatic, hormone-refractory disease or for those who have failed a local treatment. The prostate stem cell antigen (PSCA) is expressed in >80% of primary PCa samples and bone metastases. Its expression is increased both in androgen-dependent and independent prostate tumors, particularly in carcinomas of high stages and Gleason scores. Therefore, PSCA is an attractive target for immunotherapy of PCa by retargeting of T cells to tumor cells.
METHODS. Aseries of different bispecific antibody formats for retargeting of T cells to tumor cells were described but, only very limited data obtained by side by side comparison of the different antibody formats are available. We established two novel bispecific antibodies in different formats. The functionality of both constructs was analyzed by FACS and chromium release assays. In parallel, the release of pro-inflammatory cytokines was determined by ELISA.
RESULTS AND CONCLUSIONS. Irrespective of the underlying antibody format, both novel bispecific antibodies cause an efficient killing of PSCA-positive tumor cells by preand non-pre-activated T cells. Killing and release of pro-inflammatory cytokines requires an antigen specific cross-linkage of the T cells with the target cells.

Keywords: single chain bispecific antibodies; prostate cancer; T cell targeting; immunotherapy

Publ.-Id: 26358

Retargeting of Human Regulatory T Cells by Single-Chain Bispecific Antibodies

Koristka, S.; Cartellieri, M.; Theil, A.; Feldmann, A.; Arndt, C.; Stamova, S.; Michalk, I.; Töpfer, K.; Temme, A.; Kretschmer, K.; Bornhäuser, M.; Ehninger, G.; Schmitz, M.; Bachmann, M.

Bispecific Abs hold great potential for immunotherapy of malignant diseases. Because the first components of this new drug class are now entering clinical trials, all aspects of their mode of action should be well understood. Several studies proved that CD8+ and CD4+ effector T cells can be successfully redirected and activated against tumor cells by bispecific Abs both in vitro and in vivo. To our knowledge, this study provides the first evidence that bispecific Abs can also redirect and activate regulatory T cells against a surface Ag, independently of their TCR specificity. After cross-linking, via a bispecific Ab, redirected regulatory T cells upregulate the activation markers CD69 and CD25, as well as regulatory T cell-associated markers, like CTLA-4 and FOXP3. The activated regulatory T cells secrete the immunosuppressive cytokine IL-10, but, in contrast to CD8+ and CD4+ effector T cells, almost no inflammatory cytokines. In addition, the redirected regulatory T cells are able to suppress effector functions of activated autologous CD4+ T cells both in vitro and in vivo. Therefore, the potential risk for activation of regulatory T cells should be taken into consideration when bispecific Abs are applied for the treatment of malignant diseases. In contrast, an Ag/tissue-specific redirection of regulatory T cells with bispecific Abs holds great potential for the treatment of autoimmune diseases and graft rejection.

Publ.-Id: 26357

Retargeting of regulatory T cells to surface-inducible autoantigen La/SS-B

Koristka, S.; Cartellieri, M.; Arndt, C.; Bippes, C. C.; Feldmann, A.; Michalk, I.; Wiefel, K.; Stamova, S.; Schmitz, M.; Ehninger, G.; Bornhäuser, M.; Bachmann, M.

The nuclear autoantigen La can be detected on the surface of dying cells. Here we present an assay which enables us to show that La protein is not limited to the surface of dying cells but will be released upon stress-induced cell death. As released La protein tightly binds to the surface of neighboring intact cells we asked the question whether or not La protein could serve as a stress-inducible target e.g. for redirecting of regulatory T cells (Tregs) into damaged tissues to downregulate an immune response. In order to provide first proof of concept we developed a novel fully humanized single-chain bispecific antibody (bsAb) which on the one hand is directed to the La antigen and on the other hand to the CD3 complex of T cells. A cross-linkage of Tregs with La-decorated target cells mediated by this bsAb resulted indeed in the activation of the Tregs in a target-dependent manner. Moreover, such bsAb activated Tregs displayed a potent suppressive capacity and negatively influenced proliferation, expansion and cytokine production of autologous CD4+ and CD8+ Teff cells.

Keywords: La/SS-B; Regulatory T cells; Single-chain bispecific antibodies; Immunotherapy

Publ.-Id: 26356

Interaction of uranyl ion and DNA

Tsushima, S.; Takao, K.; Mochizuki, Y.; Rossberg, A.; Komeiji, Y.

Abstract for this presentation is only available in Japanese.

  • Poster
    Annual meeting of the Japanese Society for Extremophiles, 11.-12.11.2017, Tsukuba, Japan

Publ.-Id: 26355

Effect of isotropic stress on dislocation bias factor in bcc iron: an atomistic study

Bakaev, A.; Terentyev, D.; Chang, Z.; Posselt, M.; Olsson, P.; Zhurkin, E. E.

The effect of externally applied stress on the dislocation bias factor (BF) in bcc iron has been studied using a combination of atomistic static calculations and finite element integration. Three kinds of dislocations were considered, namely, a0/2〈1 1 1〉{1 1 0} screw, a0/2〈1 1 1〉{1 1 0} edge and a0〈1 0 0〉{0 0 1} edge dislocations. The computations reveal that the isotropic crystal expansion leads to an increasing or constant dislocation bias, depending on the Burgers vector and type of dislocation. On the other hand, compressive stress reduces the dislocation bias for all the dislocations studied. Variation of the dislocation BF depending on dislocation type and Burgers vector is discussed by analysing the modification of the interaction energy landscape and the capture efficiency values for the vacancy and self-interstitial atom.

Keywords: dislocation bias factor; external stress; Ferritic steels; molecular statics

Publ.-Id: 26354

Combinatorial antigen recognition with balanced signaling promotes selective tumor eradication by engineered T cells

Kloss, C. C.; Condomines, M.; Cartellieri, M.; Bachmann, M.; Sadelain, M.

Current T-cell engineering approaches redirect patient T cells to tumors by transducing them with antigen-specific T-cell receptors (TCRs) or chimeric antigen receptors (CARs) that target a single antigen. However, few truly tumor-specific antigens have been identified, and healthy tissues that express the targeted antigen may undergo T cell–mediated damage. Here we present a strategy to render T cells specific for a tumor in the absence of a truly tumor-restricted antigen. T cells are transduced with both a CAR that provides suboptimal activation upon binding of one antigen and a chimeric costimulatory receptor (CCR) that recognizes a second antigen. Using the prostate tumor antigens PSMA and PSCA, we show that co-transduced T cells destroy tumors that express both antigens but do not affect tumors expressing either antigen alone. This ‘tumor-sensing’ strategy may help broaden the applicability and avoid some of the side effects of targeted T-cell therapies.

  • Open Access Logo Nature Biotechnology 31(2013), 71-75
    Online First (2012) DOI: 10.1038/nbt.2459

Publ.-Id: 26353

Redirection of T cells with a first fully humanized bispecific CD33–CD3 antibody efficiently eliminates AML blasts without harming hematopoietic stem cells

Arndt, C.; von Bonin, M.; Cartellieri, M.; Feldmann, A.; Koristka, S.; Michalk, I.; Stamova, S.; Bornhäuser, M.; Schmitz, M.; Ehninger, G.; Bachmann, M.

Redirection of T cells with a first fully humanized bispecific
CD33–CD3 antibody efficiently eliminates AML blasts without
harming hematopoietic stem cells

Publ.-Id: 26352

Elastic moduli of the distorted Kagome-lattice ferromagnet Nd3Ru4Al12

Suzuki, T.; Mizuno, T.; Takezawa, K.; Kamikawa, S.; Andreev, A. V.; Gorbunov, D. I.; Henriques, M. S.; Ishii, I.

The distorted kagome-lattice compound Nd3Ru4Al12 has the hexagonal structure. This compound is reported as a ferromagnet in which spins are aligned along the c-axis with the Curie temperature Tc = 39 K. The nature of localized f-electrons is expected in Nd3Ru4Al12, and magnetic anisotropy can be attributed to a crystal electric field (CEF) effect. We performed ultrasonic measurements on a Nd3Ru4Al12 single-crystalline sample in order to investigate the phase transition at TC and the CEF effect. All longitudinal and transverse elastic moduli increase monotonically with decreasing temperature, and no clear elastic softening due to a quadrupole interaction is detected under the hexagonal CEF. This result is in contrast to an isomorphic compound Dy3Ru4Al12 with a remarkable elastic softening of the transverse modulus C44. At the ferromagnetic phase transition, the moduli show obvious elastic anomalies, suggesting characteristic couplings between a strain and a magnetic order parameter.

Publ.-Id: 26351

Magnetohydrodynamic instabilites in aluminium reduction cells

Weber, N.; Herreman, W.; Horstmann, G.; Nore, C.; Weier, T.

Übersicht über Theorie und numerische Simulation von Aluminium-Reduktionszellen.

  • Lecture (others)
    Aluminium-Reduktions-Treffen, 16.11.2017, Wuppertal, Deutschland

Publ.-Id: 26350

Magnetic nanomaterials

Josten, E.; Glavic, A.; Meertens, D.; Wetterskog, E.; Bersgtröm, L.; Brückel, T.; Lindner, J.

Magnetic nanomaterials and their assembly in highly correlated structures are of great interest for future applications as e.g. spin-based data storage media or as material for magnon-spintronics. These systems exhibit unique physical properties like superparamagnetism or symmetry breaking emerging due to their limited size. Individual nanomaterials can be combined as building blocks for so called superstructures where the combination of the different functionalities creates a novel multi-functional system.
Recently, more and more well-defined nanoobjects became available and the advances in measurement methods allow a characterization of these systems. For example, single micrometer-sized three-dimensional magnetic nanoparticle assemblies are available, exhibiting a high degree of structural order close to that of an atomic crystal [1,2]. These systems provide a good basis for the magnetic investigation of nanoparticle superstructures.
The work to be presented focuses on the fundamental structural and magnetic research on such objects and their functionalization. For the investigation we make use of different complementary measurement methods like small angle x-ray and neutron scattering or using microresonators, which provide the necessary sensitivity for the investigation of magnetic properties of a single nano- or micrometer-sized object using ferromagnetic resonance (FMR) [3].

Keywords: nanoparticles; scattering

  • Invited lecture (Conferences)
    JCNS Workshop 2017, 10.-13.10.2017, Tutzing, Deutschland

Publ.-Id: 26349

Highly ordered 3D nanoparticle superlattices investigated by microresonator ferromagnetic resonance

Josten, E.; Narkowicz, R.; Kakay, A.; Meertens, D.; Lennart, B.; Brückel, T.; Fassbender, J.; Lindner, L.

Magnetic nanoparticles and their assembly into highly correlated superstructures are of great interest for future applications, e.g. as material for magnon-spintronic. These systems are not only distinguished by the obvious miniaturization but by their novel physical properties emerging due to their limited size and ordered arrangement. These superstructures are formed from nanometer-sized building blocks ordered like atoms in a crystal, which render them a new class of materials.
Recently, single micrometer-sized three-dimensional magnetic nanoparticle assemblies became available, exhibiting a high degree of structural order close to that of an atomic crystal. These systems provide a good basis for the magnetic investigation of nanoparticle superstructures.

Novel microresonators, provide the necessary sensitivity for the investigation of magnetic properties of nano- and micrometer-sized objects using ferromagnetic resonance (FMR) [1,2]. Due to the much higher filling factor as compared to conventional microwave cavities, they offer several orders of magnitude increased sensitivity gain. A focused ion beam was used to isolate an individual 3D mesocrystal from an ensemble and to transfer it into the microresonator loop (Fig. 1). The FMR study reveals the magnetic anisotropy of the single mesocrystal (Fig. 2), which is corroborated by micromagnetic simulations. It was possible for us to functionalize the system and to set the magnetic easy axis of the mesocrystal via pre-defining their shape.

Keywords: nanoparticle

  • Lecture (Conference)
    INTERMAG Europe 2017, 24.-28.04.2017, Dublin, Irland

Publ.-Id: 26348

Direct measurement of the flow field with GeoPET as the starting point for reactive transport modelling

Kulenkampff, J.; Karimzadeh, L.; Eichelbaum, S.; Lippmann-Pipke, J.; Fischer, C.

We present a RTM workflow which is based on the direct experimental derivation of effective volume and velocity vector field from sequential positron emission tomograms (PET) of the tracer transport in geologic materials. The focus on tracer concentration incorporates unconstrained upscaling from molecular sensitivity to the millimeter scale. This workflow allows minimizing deviations from the experiment and computational expenses.

Keywords: tracer; dynamics of flow; process tomography; reactive transport

  • Lecture (Conference)
    Computational Methods in Water Resources (CMWR), 03.-07.06.2018, Saint Malo, France

Publ.-Id: 26347

Felsenkeller 5 MV underground accelerator: Towards the Holy Grail of Nuclear Astrophysics 12C(α,γ)16O

Bemmerer, D.

Underground ion accelerator laboratories such as the LUNA 0.4 MV accelerator in Italy are indispensable in order to precisely measure charged particle induced nuclear reaction cross sections. The rock overburden attenuates the cosmic ray induced background and enables the measurement of very low interaction rates. The first of the new generation of higher-energy underground accelerators is the Felsenkeller 5 MV machine in Dresden/Germany, under construction and due to open late 2017. The cross sections of several nuclear reactions relevant to nucleosynthesis in a supernova and/or its precursor are not well known, with effects on the nucleosynthetic output of these events. Of these reactions, it is planned to study the 12C(alpha,gamma), 22Ne(alpha,gamma), 40Ca(alpha,gamma), and several other cases at Felsenkeller. The scientific motivation and state of work will be reviewed. It is hoped that the Felsenkeller accelerator will be widely used, including researchers from as many German universities as possible.

Keywords: Underground nuclear astrophysics; Felsenkeller; Helium burning

  • Invited lecture (Conferences)
    Arbeitstreffen Kernphysik, 02.-09.03.2017, Schleching, Deutschland
  • Lecture (Conference)
    Workshop on Nuclear Astrophysics at the Dresden Felsenkeller, 26.-28.06.2017, Dresden, Deutschland
  • Lecture (Conference)
    Nuclear Physics in Astrophysics VIII, 20.06.2017, Catania, Italien
  • Invited lecture (Conferences)
    16th International Symposium on Capture Gamma-Ray Spectroscopy and Related Topics (CGS16), 19.09.2017, Shanghai, China

Publ.-Id: 26346

Molecular encapsulator on the surface of magnetic nanoparticles. Controlled drug release from calcium Ferrite/Cyclodextrin–tethered polymer hybrid

Ramasamy, S.; Reuther, H.; Adyanpuram, M. N. M. S.; Enoch, I. V. M. V.; Potzger, K.; Samathanam, B.

Magnetic nanoparticles (MNPs) are intriguing due to their potency to deliver anti-cancer drugs. This paper presents the inference from our experimental attempts to add merit to the concept of magnetic drug carrier, by designing calcium ferrite nanoparticles and coating them with a biocompatible dextran tethered with a hydrophobic cavity-containing molecule, β-cyclodextrin (β-CD). The size, crystal system, and the morphology of the MNPs are studied. The magnetic properties are explored using vibrating sample magnetometry, SQUID and Mössbauer spectroscopy. The roughly 75 nm MNPs, encapsulated with the β-CD–dextran conjugate allows a slow and sustained in vitro release of the loaded anti-cancer drug, Camptothecin, from the polymer shell. The study of cytotoxicity reveals that the loaded Camptothecin retains its potency as efficient as an effective carrier of the anti-cancer drug. Further, the toxicity of the nanomaterial is tested on an organism which is highly sensitive to toxicity i.e., brine shrimp (Artemia salina). The polymer coating brings down the toxicity of the MNPs.

Keywords: Cyclodextrin; Drug release; Host-guest interface; Magnetic nanoparticles; Surface functionalization


Publ.-Id: 26345

Felsenkeller 5 MV underground accelerator: Muon, neutron, 𝛾-ray background and project status

Bemmerer, D.

Motivated by the success of the world's only underground ion accelerator, LUNA 0.4 MV in Italy, a project for a higher-energy underground accelerator is underway in Dresden. A 5\,MV Pelletron accelerator with double charging chains and provision for intensive ^1H^+, ^4He^+, and ^{12}C^+ beams based on external and internal ion sources is currently being installed in the Felsenkeller underground site in Dresden. Civil construction work in Felsenkeller will be completed in August 2017. The nine Felsenkeller tunnels are shielded from cosmic rays by 45\,m rock overburden, attenuating the background in radiation detectors. New data on the muon, neutron, and $\gamma$ background in Felsenkeller will be shown, and used for a discussion on the feasibility of low-background experiments there. The new accelerator will be open for outside users, and its most important experimental capabilities will be summarized.

Keywords: Underground Nuclear Astrophysics; Felsenkeller

  • Lecture (Conference)
    Frühjahrstagung, 30.03.2017, Münster, Deutschland

Publ.-Id: 26344

Recent progress on hydrogen and helium burning at the LUNA 400 kV underground accelerator

Bemmerer, D.

n-beam radiative-capture experiments at low astrophysical energies require experiments in ultra-low background conditions. The Laboratory for Underground Nuclear Astrophysics (LUNA) 0.4\,MV accelerator at INFN Gran Sasso, Italy, is so far the only underground ion accelerator in the world. Recent progress at LUNA regarding the $^{22}$Ne(p,$\gamma$)$^{23}$Na [1,2], $^{22}$Ne($\alpha$,$\gamma$)$^{26}$Mg, and $^{17}$O(p,$\alpha$)$^{14}$N [3] reactions will be reviewed. The project for the new, 3.5 MV LUNA-MV accelerator is on track and will be summarized.

Keywords: Nuclear Astrophysics; Hydrogen burning

  • Lecture (Conference)
    Frühjahrstagung, 27.03.2017, Münster, Deutschland

Publ.-Id: 26343

Constraining the 7Be(p,gamma)8B S -factor with the new precise 7Be solar neutrino flux from Borexino

Takács, M. P.; Bemmerer, D.; Junghans, A. R.; Zuber, K.

Among the solar fusion reactions, the rate of the 7Be(p,γ)8B reaction is one of the most difficult to determine rates. In a number of previous experiments, its astrophysical S-factor has been measured at E = 0.1-2.5 MeV center-of-mass energy. However, no experimental data is available below 0.1 MeV. Thus, an extrapolation to solar energies is necessary, resulting in significant uncertainty for the extrapolated S-factor. On the other hand, the measured solar neutrino fluxes are now very precise. Therefore, the problem of the S-factor determination is turned around here: Using the measured 7Be and 8B neutrino fluxes and the Standard Solar Model, the 7Be(p,γ)8B astrophysical S-factor is determined at the solar Gamow peak. In addition, the 3He(α,γ)7Be S-factor is redetermined with a similar method.

Keywords: Nuclear Astrophysics; Solar neutrinos; Nuclear reaction rate; Solar fusion

Publ.-Id: 26342

LUNA: Status and Prospects

Broggini, C.; Bemmerer, D.; Caciolli, A.; Trezzi, D.

The essential ingredients of nuclear astrophysics are the thermonuclear reactions which shape the life and death of stars and which are responsible for the synthesis of the chemical elements in the Universe. Deep underground in the Gran Sasso Laboratory the cross sections of the key reactions responsible for the hydrogen burning in stars have been measured with two accelerators of 50 and 400 kV voltage right down to the energies of astrophysical interest. As a matter of fact, the main advantage of the underground laboratory is the reduction of the background. Such a reduction has allowed, for the first time, to measure relevant cross sections at the Gamow energy. The qualifying features of underground nuclear astrophysics are exhaustively reviewed before discussing the current LUNA program which is mainly devoted to the study of the Big-Bang nucleosynthesis and of the synthesis of the light elements in AGB stars and classical novae. The main results obtained during the study of reactions relevant to the Sun are also reviewed and their influence on our understanding of the properties of the neutrino, of the Sun and of the Universe itself is discussed. Finally, the future of LUNA during the next decade is outlined. It will be mainly focused on the study of the nuclear burning stages after hydrogen burning: helium and carbon burning. All this will be accomplished thanks to a new 3.5 MV accelerator able to deliver high current beams of proton, helium and carbon which will start running under Gran Sasso in 2019. In particular, we will discuss the first phase of the scientific case of the 3.5 MV accelerator focused on the study of 12C+12C and of the two reactions which generate free neutrons inside stars: 13C(α,n)16O and 22Ne(α,n)25Mg.

Keywords: Nuclear Astrophysics; LUNA; Laboratory Underground for Nuclear Astrophysics

Publ.-Id: 26341

Modification of surface properties of solids by femtosecond LIPSS writing: comparative studies on silicon and stainless steel

Varlamova, O.; Hoefner, K.; Ratzke, M.; Reif, J.; Sarker, D.

We investigate the implication of modified surface morphology on wettability of stainless steel (AISI 304) and silicon (100) targets covered by laser-induced periodic surface structures (LIPSS) on extended areas (10 × 10 mm2). Using multiple pulses from a Ti: Sapphire laser (790 nm/100 fs/1 kHz) at a fluence in the range of 0.35–2.1 J/cm2 on a spot of 1.13 × 10− 4 cm2, we scanned the target under the spot to cover a large area. A systematical variation of the irradiation dose by changing the scanning speed and thus dwelling time per spot results in the formation of surface patterns ranging from very regular linear structures with a lateral period of about 500–600 nm to complex patterns of 3D microstructures with several-µm feature size, hierarchically covered by nano-ripples.

Publ.-Id: 26340

Surface modifications of crystal-ion-sliced LiNbO3 thin films by low energy ion irradiations

Bai, X.; Shuai, Y.; Gong, C.; Wu, C.; Luo, W.; Böttger, R.; Zhou, S.; Zhang, W.

Single crystalline 128°Y-cut LiNbO3 thin films with a thickness of 670 nm are fabricated onto Si substrates by means of crystal ion slicing (CIS) technique, adhesive wafer bonding using BCB as the medium layer to alleviate the large thermal coefficient mismatch between LiNbO3 and Si, and the X-ray diffraction pattern indicates the exfoliated thin films have good crystalline quality. The LiNbO3 thin films are modified by low energy Ar+ irradiation, and the surface roughness of the films is decreased from 8.7 nm to 3.4 nm. The sputtering of the Ar+ irradiation is studied by scanning electron microscope, atomic force microscope and X-ray photoelectron spectroscopy, and the results show that an amorphous layer exists at the surface of the exfoliated film, which can be quickly removed by Ar+ irradiation. A two-stage etching mechanism by Ar+ irradiation is demonstrated, which not only establishes a new non-contact surface polishing method for the CIS-fabricated single crystalline thin films, but also is potentially useful to remove the residue damage layer produced during the CIS process.

Keywords: 128°Y-cut LiNbO3; Single crystalline thin films; Crystal ion slicing; BCB bonding; Ar+ irradiation

Publ.-Id: 26339

Die Bestimmung des neutroneninduzierten Spaltquerschnitts von ²⁴²Pu

Kögler, T.

Präzise neutroneninduzierte Spaltquerschnitte von Actinoiden wie den Plutoniumisotopen haben für die Entwicklung zukünftiger Transmutationstechnologien eine große Bedeutung. Die Unsicherheiten des ²⁴²Pu-Spaltquerschnitts im schnellen Bereich des Spektrums betragen derzeit etwa 21 %. Aktuelle Sensitivitätsstudien haben gezeigt, dass nur eine Reduzierung dieser Unsicherheiten auf unter 5 % verlässliche neutronenphysikalische Simulationen zulässt.
Diese anspruchsvolle Aufgabe konnte im Rahmen der vorliegenden Arbeit an der Neutronen-Flugzeitanlage nELBE durchgeführt werden. Dünne, homogene und großflächige Actinoiden-Proben wurden dem Helmholtz-Zentrum Dresden - Rossendorf innerhalb des TRAKULA-Verbundprojektes zur Verfügung gestellt. Eingesetzt in eine neu entwickelte Spaltionisationskammer ermöglichten sie eine akkurate Bestimmung des Spaltquerschnitts relativ zu ²³⁵U. Die Flächendichten der Plutoniumschichten wurden anhand der spontanen Spaltrate von ²⁴²Pu bestimmt. Aufwändige Teilchentransportsimula-
tionen (durchgeführt mit Geant 4, MCNP 6 und FLUKA) wurden genutzt, um die auftretende Neutronenstreuung zu korrigieren. Die gewonnenen Ergebnisse sind im Rahmen ihrer Unsicherheiten in guter Übereinstimmung mit aktuellen Kerndatenevaluierungen. /
Neutron induced fission cross sections of actinides like the Pu-isotopes are of relevance for the development of nuclear transmutation technologies. For ²⁴²Pu, current uncertainties are of around 21 \%. Sensitivity studies show that the total
uncertainty has to be reduced to below 5\% to allow for reliable neutron physics simulations. This challenging task was performed at the neutron time-of-flight facility of the new German National Center for High Power Radiation Sources at HZDR, Dresden. Within the TRAKULA project, thin, large and homogeneous deposits of ²³⁵U and ²⁴²Pu have been produced successfully. Using two consecutively placed fission chambers allowed the determination of the neutron induced fission cross section of ²⁴²Pu relative to ²³⁵U. The areal density of the Plutonium targets was calculated using the measured spontaneous fission rate. Experimental results of the fast neutron induced fission of ²⁴²Pu acquired at nELBE will be presented and compared to recent experiments and evaluated data. Corrections addressing the neutron scattering are discussed by using
results of different neutron transport simulations (Geant4, MCNP6 and FLUKA).

Keywords: Kernspaltung; Wirkungsquerschnitt; schnelle Neutronen; nELBE; Spaltionisationskammern; fission; cross section; fast neutrons; nELBE; fission ionization chambers

Related publications

  • Doctoral thesis
    TU Dresden, 2017
    Mentor: Dr. Arnd R. Junghans
    187 Seiten


Publ.-Id: 26338

Determination of the γ-Ray-Angular Distribution in the Inelastic Scattering of Fast Neutrons on ⁵⁶Fe at nELBE

Dietz, M.

The inelastic neutron scattering reaction on 56Fe was studied at the nELBE time-of-flight facility of HZDR. The incoming neutron energy ranges in the fast neutron spectrum from 100 keV to 10 MeV, where high precision nuclear data are needed. Regarding the recent CIELO evaluation on 56Fe, there is a great interest in improving the knowledge of inelastic scattering angular distribution and increasing the resolution on the few literature data of gamma-ray-angular distribution.
To investigate angular distributions of the emitted gamma-rays, a new detector setup has been installed. It contains five HPGe detectors and five LaBr3 scintillation detectors, which can be set under different angles. For this measurement they were positioned under 30°; 55°; 90°; 125° and 150°, relative to the beam axis. By cyclical measurement with and without the natural Fe-target the intrinsic and the neutron induced background from the setup, except the target, has been subtracted. Corrections for gamma-self-absorption inside the target and extended source effciency were achieved using GEANT4 simulations.
The gamma-ray-angular distribution data measured with the HPGe detectors are compared with data from D. L. Smith, Argonne, 1976. Due to the much better time resolution in LaBr3 detectors high resolution data have been obtained and very interesting resonant structures have been observed for the gamma-ray-angular distribution. In the end, the influence of angular distribution coeffcient a4 is demonstrated by a anisotropy correction factor for experiments, using only one detector under an angle of 125°.

Keywords: nELBE; inelastic neutron scattering; Fe-56; angular distribution

  • Master thesis
    TU Dresden, 2016
    Mentor: Arnd R. Junghans


Publ.-Id: 26336

Untersuchungen zur katalytischen Aktivität von Au(III) Verbindungen

Patzschke, M.

In diesem Betrag stellen wir von uns durchgeführte Untersuchungen zur katalytischen Aktivität verschiedener Gold(III) Verbindungen vor.

We present our investigations on the catalytic activity of Au(III) complexes in organic synthesis.

Keywords: ab initio; DFT; computational chemistry; gold chemistry; catalysis

  • Lecture (others)
    Organisch-Chemisches Kolloquium, 12.12.2017, Dresden, Deutschland

Publ.-Id: 26335

Orca for computational actinide chemistry

Patzschke, M.

The program package Orca will be introduced and the use in computational actinide chemistry will be demonstrated.

Keywords: computational chemistry; ab initio; DFT; relativistic effects

  • Invited lecture (Conferences)
    ThUL School 2017, 16.-20.10.2017, Jülich, Deutschland

Publ.-Id: 26334

Computational Spectroscopy

Patzschke, M.

In the contribution we discuss the application of computational chemistry to calculate spectroscopical parameters. We first present the foundations of computational chemistry in a very short form. We will show problems and advantages of DFT. Then we will show how spectroscopical parameters (IR,UV-VIS,NMR) can be calculated and what accuracy can be expected.

Keywords: computational chemistry; DFT; ab initio; actinides; spin-orbit coupling; relativistic effects

  • Invited lecture (Conferences)
    ThUL School 2017, 16.-20.10.2017, Jülich, Deutschland

Publ.-Id: 26333

VVER-1000 RPV lower head model related to late in-vessel phenomena in case of hypothetical severe accident

Gencheva, R.; Grudev, P.; Stefanova, A.; Jobst, M.; Wilhelm, P.

This work discusses the progress in the development of an ASTEC computational model for investigation of molten corium pool behaviour in the lower head of a VVER-1000 reactor in case of a hypothetical accident with core degradation. The model was tested with variation of characterizing parameters which could have an influence on the molten pool behaviour and respectively the response behaviour of the reactor pressure vessel wall. An accident scenario with external cooling of the RPV wall was analysed. The preliminary code results give an estimation of the thermal load on the RPV wall. The sensitivity of the model depending on RPV wall nodalization was investigated. The analysis is performed in support to the numerical investigations realized within the frames of the EU HORIZON 2020 IVMR project (grant agreement number 662157).

Keywords: VVER-1000; severe accident; RPV; lower head; in-vessel

  • Contribution to proceedings
    27th Symposium of AER on VVER Reactor Physics and Reactor Safety, 17.-20.10.2017, München, Deutschland, 205-213
  • Lecture (Conference)
    27th Symposium of AER on VVER Reactor Physics and Reactor Safety, 17.-20.10.2017, München, Deutschland

Publ.-Id: 26332

Sorption competition and kinetics of trivalent cations (Eu, Y and Cm) on corundum (α-Al2O3): a batch sorption and TRLFS study

Virtanen, S.; Meriläinen, S.; Eibl, M.; Rabung, T.; Huittinen, N.

In this study we have combined batch sorption and laser spectroscopic investigations to study the sorption of Eu(III) and Cm(III), on the aluminum oxide corundum in single- and multi-metal systems. Experiments were performed using a constant equilibrium time as a function of pH (pH-edges) or at constant pH as a function of equilibrium time (kinetic experiments) in 0.01 M NaClO4 and carbonate free conditions. The objective was to investigate how the sorption behavior of trivalent actinides and lanthanides is affected by the presence of another trivalent metal, Y(III). Our hypothesis was that the addition of higher concentrations of trivalent Y(III) together with a chemically similar trivalent metal, would affect the sorption behavior of that metal. Batch experiments show that when the concentration of competing Y(III) is high enough (1×10-4 M) to occupy most of the surface sites, there is a clear shift in the position of the Eu(III) pH-edge to higher pH. Spectroscopic studies using time-resolved laser fluorescence spectroscopy (TRLFS) clearly confirm sorption competition between the trivalent metals Cm(III) and Y(III), but they also indicate a change in the surface speciation of the trivalent actinide in the presence of the competing metal if the concentration of that competing metal is high enough.

Keywords: Sorption competition; Eu(III); Cm(III); Y(III); TRLFS; corundum; α-Al2O3


Publ.-Id: 26331

The influence of bentonite colloids on neptunium(V) migration in granitic rock

Elo, O.; Hölttä, P.; Huittinen, N.

In Finland, the repository for spent nuclear fuel (SNF) will be excavated at a depth of about 500 meters in the fractured crystalline bedrock in Olkiluoto at Eurajoki implemented by Posiva Oy. The engineered barrier systems (EBS), consisting of a solid fuel capsule, a copper-iron canister and the bentonite buffer should prevent the migration of radionuclides to the biosphere. Montmorillonite, the main mineral of bentonite, is like other aluminosilicates known to retain radionuclides, thus, preventing them from migrating from the repository with the groundwater. Bentonite erosion resulting in the formation of colloids may have a direct impact on the overall performance of the bentonite buffer. The potential relevance of colloids for radionuclide transport is highly dependent on the formation of colloids, the stability and mobility of colloids in different chemical environments, and their interaction with radionuclides [1]. Stable and mobile bentonite colloids can be formed when the glacial meltwater dilutes the groundwater. In these mildly oxic conditions, neptunium(V) will be present in its pentavalent oxidation state as the neptunyl cation (NpO2+), which is rather soluble, highly mobile and poorly adsorbed. Due to the long half-life of Np-237 (2.144·106 y), it will be a major dose contributor after 100,000 years in the SNF repository.
In our previous study, the interaction of Np(V) with Na-montmorillonite purified from MX-80 bentonite and corundum was investigated [2]. Corundum was used as a reference mineral in order to study the aluminol surface sites present on clay minerals, which are regarded as the main adsorption sites for radionuclide attachment [3]. This study aimed at investigating two processes: retardation of Np(V) on the bentonite colloids and granitic rock and the effect of the stable and mobile bentonite colloids on the migration of Np(V) in intact and crushed granitic rock columns.
The materials used in this study were colloids prepared from MX-80 Volclay type bentonite (76% montmorillonite) and Kuru Grey granite. Np(V) sorption on these materials under stagnant conditions was studied as a function of pH, solid concentration, time, and Np(V) concentration. The sorption experiments as a function of pH (3-11), were performed at a constant Np(V) concentration of 10-6 M. The sorption isotherms as a function of Np(V) concentration were conducted at concentration from 10-9 to 5·10-6 M at pH 8, 9, and 10. Solid concentrations were 0.08 g/L and 0.8 g/L for colloids and 40 g/L for granite. The samples were prepared by adding a small aliquot of colloid stock solution or crushed granite, Np-237 tracer and the background electrolyte in 20 ml polypropylene vials. The solution was buffered to the desired pH and after one week equilibration time the solid phase was separated from the liquid by centrifugation and 1 ml aliquots were taken immediately for liquid scintillation counting (Perkin Elmer Tri-Carb 3100 TR or Quantulus liquid scintillation counter). All the batch sorption studies were conducted in 10 mM NaClO4 either in carbonate-free N2-atmosphere (bentonite colloids, 0.08 g/L) or under ambient air conditions (granite and bentonite colloids 0.8 g/L).
The effect of bentonite colloids on Np(V) migration was studied in column experiments, where the column material was either crushed granite (grain size 0.01-0.1 mm) or an intact drill core of the Kuru Grey granite. The crushed granite column diameter was 1.5 cm and the length 15 cm. Drill core columns were constructed from Kuru grey granite cores which were placed inside a tube to form a flow channel (L = 28 cm, w = 4.4 cm) representing an artificial fracture formed by the 0.5 mm gap between the core and the tube [3]. In the experiments, colloid solution was injected into the water flow and the colloid breakthrough was detected by photon correlation spectroscopy (PCS) measurements. The column experiments were performed under ambient air conditions in 10 mM NaClO4 solution using flowrates of 1.5 mL/h, 0.8 mL/h, and 0.3 mL/h. The Np-tracer was injected into the flow, through an injection loop of known volume. The flow conditions in the columns were determined using chloride (36Cl-) as a conservative tracer. The effect of bentonite colloids on Np(V) transport at pH 8 and pH 10 was determined in the absence and presence of colloids (0.7 and 0.9 g/L). The colloid concentration in the collected fractions was determined by PCS and the Np(V) concentration was determined after PCS measurements from the same samples by liquid scintillation counting.
Np(V) adsorption onto MX-80 bentonite colloids and crushed Kuru Grey granite in 10 mM NaClO4 is shown as a function of pH in Figure 1a and as a function of Np concentration in Figure 1b. Sorption onto colloids was rather weak (20%) at pH 8 and higher adsorption occurred only above pH 10. According to the pH-edge results, the sorption isotherms for bentonite colloids are as expected, linear and the slopes are close to one another. The weak sorption of Np(V) on the colloids indicates that Np(V) will be mobilized as a neptunyl cation in solution. Despite the low uptake of Np(V) by the bentonite colloids, the obtained column results show that Np(V) breakthrough from the granite columns is enhanced in the presence of colloids (Figure 2).

  • Poster
    16th International Conference on Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 10.-15.09.2017, Barcelona, Spain

Publ.-Id: 26330

Complexation of trivalent actinides and lanthanides with aqueous phosphates at elevated temperatures (25-80°C)

Huittinen, N.; Jordan, N.; Lösch, H.

The incorporation of actinides in solid lanthanide phosphates crystallizing in the monazite structure has been intensely investigated in the past decades due to the relevance of these monazites as potential ceramic phases for the immobilization of specific high level radioactive waste (HLW) streams [1-3]. In recent years, understanding the incorporation behaviour of trivalent dopants in the LnPO4×nH2O rhabdophane structure, which is the hydrated phosphate precursor in the synthesis of monazites through precipitation routes and a potential secondary mineral controlling actinide solubility in dissolution and re-precipitation reactions of monazite host-phases, has been given more attention [4,5]. Despite the large interest in lanthanide phosphates and the interaction of actinides with these solids, very little data is available on the complexation of lanthanides and actinides with aqueous phosphates, even though these complexation reactions precede any aqueous synthesis of monazite ceramics and are expected to occur in natural waters as well as in the proximity of monazite-containing HLW repositories. It also suffers from an almost systematic absence of independent spectroscopic validation of the stoichiometry of the proposed complexes. Both from the perspective of aqueous rhabdophane synthesis, which is often carried out at elevated temperatures, and heat-generating HLW immobilization in monazites, the lanthanide and actinide complexation reactions with aqueous phosphates under ambient conditions should be complemented with data obtained at higher temperatures.

In the present work, time-resolved laser fluorescence spectroscopy (TRLFS) has been employed to study the phosphate complexation of Eu3+ (5×10-6 M) and Cm3+ (5×10-7 M) as a function of total phosphate concentration (0-1 M ΣPO4) in the temperature regime 25-80°C, using NaClO4 as a background electrolyte. These studies have, in a first step, been conducted in the acidic pH-range (pH = 1) to avoid precipitation of solid Eu or Cm rhabdophane. Both trivalent metal cations form a complex with the anionic H2PO4- species, i.e. EuH2PO42+ and CmH2PO42+. As expected, the complexation reaction occurs at lower total phosphate concentration when increasing the temperature. In addition, our preliminary results show the presence of a second Eu-phosphate species which is tentatively assigned to Eu(H2PO4)2+. The presence of this species will be verified with mass-spectrometric methods.
Temperature-dependent complexation constants for the identified species will be derived from the recorded luminescence emission spectra. These will be recalculated to standard conditions with the van´t Hoff equation and the Specific Ion Interaction Theory. For this, the required ion interaction coefficients have been preliminary determined at 25 °C by varying the ionic strength (0.6 to 3 M).

  • Poster
    16th International Conference on Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 10.-15.09.2017, Barcelona, Spain

Publ.-Id: 26329

Charaterization of actinide(IV) complexes with imine type ligands

Radoske, T.

The progress on the PhD thesis is presented in an oral talk. The results include complexes of tetradentate and hexadentate salen complexes with several actinides in tetravalent state.

Keywords: actinide; salen; complex; thorium; uranium; SC-XRD

  • Lecture (others)
    FENABIUM Projekttreffen, 10.05.2017, Leipzig, Deutschland

Publ.-Id: 26328

European standard on small punch testing of metallic materials

Bruchhausen, M.; Holmström, S.; Altstadt, E.; Dymacek, P.; Jeffs, S.; Lancaster, R.; Lacalle, R.; Matocha, K.; Petzova, J.

Life extension of aging nuclear power plant components requires knowledge of the properties of the service-exposed materials. For instance, in long term service the tensile and creep properties might decline and the ductile-to-brittle transition temperature (DBTT) might shift towards higher temperatures. Monitoring of structural components in nuclear power plants receives much attention – in particular in the context of lifetime extension of current plants, where the amount of material available for destructive testing is limited. Much effort has therefore been invested in the development of miniature testing techniques that allow characterizing structural materials with small amounts of material. The small punch (SP) test is one of the most widely used of these techniques. It has been developed for nuclear applications but its use is spreading to other industries.

Keywords: small punch test; tensile properties; fracture; creep; standardization

  • Contribution to proceedings
    ASME 2017 Pressure Vessels and Piping Conference PVP2017, 16.-20.07.2017, Hawaii, USA
    Proceedings of the ASME 2017 Pressure Vessels and Piping Conference PVP2017
    DOI: 10.1115/PVP2017-65396

Publ.-Id: 26327

Selective THz control of magnetic order: new opportunities from superradiant undulator sources

Kovalev, S.; Wang, Z.; Deinert, J.; Awari, N.; Chen, M.; Green, B.; Germanskiy, S.; de Oliveira, T. V. A. G.; Lee, J. S.; Deac, A.; Turchinovich, D.; Stojanovic, N.; Eisebitt, S.; Radu, I.; Bonetti, S.; Kampfrath, T.; Gensch, M.

Recent advancements of accelerator technology enable the generation of carrier-envelope-phase stable THz pulses with high-fields at adjustably high repetition rates. The appropriate choice of THz radiator allows generating narrow-band, spectrally dense, multicycle THz transients of tunable THz frequency which are ideally suited to selectively excite low-energy excitations such as magnons or phonons. They also allow one to study the frequency dependence of nonresonant THz-field interactions with various order parameters with high dynamic range. In this paper we discuss the future prospects of this new type of THz light sources for studying the coherent control of magnetic order based on recent results.

Keywords: Terahertz; THz control; magnetic order


Publ.-Id: 26326

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