Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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32228 Publications
Towards Measuring Vacuum Birefringence
Schlenvoigt, H.-P.ORC
We will present a design study how one could detect vacuum birefringence when combining an ultra-intense optical laser and an X-ray free electron laser. By means of precision X-ray polarimetry, one may detect the polarization flip of X-ray photons induced by the ultra-strong laser fields as a signature of vacuum birefringence. We will discuss crucial experimental parameters and provide a comprehensive model to study the experimental feasibility.
Keywords: Hibef
  • Lecture (Conference)
    27th Annual International Laser Physics Workshop, 16.-20.07.2018, Nottingham, UK

Publ.-Id: 28151 - Permalink


Oxygen diffusion in bcc Fe under the influence of foreign atoms and vacancies
Wang, X.; Posselt, M.; Faßbender, J.;
A multiscale approach including Density Functional Theory (DFT) and Atomistic Kinetic Monte Carlo (AKMC) simulations is applied to investigate the diffusion of oxygen in bcc Fe under the influence of substitutional foreign atoms or solutes (Al, Si, P, S, Ti, Cr, Mn, Ni, Y, Mo, W) and vacancies. The solutes can be assumed to be immobile since their diffusion coefficient is much smaller than that of oxygen. On the other hand, the vacancy mobility must be considered in the calculations because it is comparable to that of oxygen. The most stable state of oxygen in pure bcc Fe is the octahedral interstitial configuration. Recently, jumps of oxygen in pure bcc Fe, between first-, second-, and third-neighbor octahedral interstitial sites were investigated by DFT. It was found that the first-neighbor jump is most relevant. The second-neighbor jump consists of two consecutive first-neighbor jumps whereas the barrier of the third-neighbor jump is too high to be significant for the diffusion process. In this work DFT is used to determine the modified migration barriers in the presence of solutes. It is found that Si, P, Ni, Mo and W have some effect on the migration barriers of oxygen and their interaction with O is mainly repulsive. Al, Cr and Mn have a significant influence on the barriers and they exhibit strong attractive interactions with O. The most important modification of the barriers is found for S, Ti, and Y where deep attractive states exist. The barriers for oxygen jumps near a vacancy and barriers for vacancy jumps in the environment of oxygen are also calculated by DFT. Based on the migration barriers obtained by DFT, AKMC simulations on a rigid lattice are employed to determine the diffusion coefficient of oxygen in a dilute iron alloy containing different substitutional foreign atoms. It is found that Si, P, Ni, Mo, and W have almost no influence on the diffusivity of O. The presence of Al, Cr, Mn, S, Ti, and Y causes a significant reduction of the mobility of oxygen. Another version of the AKMC code is applied to investigate the mutual influence of oxygen and vacancy diffusion as well as the migration of the oxygen-vacancy pair.
Keywords: oxygen, diffusion, bcc-Fe, Density Functional Theory, Atomistic Kinetic Monte Carlo simulations
  • Lecture (Conference)
    9th Int. Multiscale Materials Modeling conference (MMM 2018), 28.10.-02.11.2018, Osaka, Japan

Publ.-Id: 28150 - Permalink


Transmission Electron Microscopy at the Helmholtz-Zentrum Dresden-Rossendorf
Hübner, R.;
Transmission Electron Microscopy at the Helmholtz-Zentrum Dresden-Rossendorf
  • Lecture (others)
    Forschungsseminar Nanochemie, Physkalische Chemie, Technische Universität Dresden, 05.11.2018, Dresden, Deutschland

Publ.-Id: 28149 - Permalink


Operating three research infrastructures at one site: electrons & photons, ions, magnetic fields
Helm, M.;
Operating three research infrastructures at one site: electrons & photons, ions, magnetic fields
Keywords: research infrastructure, large-scale facility
  • Invited lecture (Conferences)
    Conference on International Cooperation of Science Centers, 19.10.2018, Huairou, China

Publ.-Id: 28147 - Permalink


Strategien zur Darstellung eines neuen 18F-markierten Adenosin-A2A-Rezeptorliganden zur PET-Bildgebung von Hirntumoren [1]
Lai, T. H.; Schröder, S.; Ludwig, F.-A.; Fischer, S.; Moldovan, R.-P.; Scheunemann, M.; Dukic-Stefanovic, S.; Deuther-Conrad, W.; Brust, P.;
Ziel: Auf Grundlage einer Pyrazolo[2,3-d]pyrimidin-Leitverbindung[2] wurden 21 fluorierte Derivate synthetisiert. Basierend auf den dazu ermittelten Affinitäts- und Selektivitätsdaten für den humanen Adenosin-A2A-Rezeptor wurde das potente 4-Fluorbenzyl-Derivat 1 (Ki(A2A) = 5,3 nM; Ki(A1) = 220 nM) für die 18F-Markierung zur Darstellung eines neuen potentiellen A2A Radiotracers ausgewählt. Die gewünschte Position in 1 ist jedoch nicht für eine nukleophile aromatische Substitution gegen [18F]Fluorid aktiviert, sodass die Zielstellung in der Entwicklung einer geeigneten Radiosynthese von [18F]1 besteht.

Methodik: Es wurden drei Strategien zur Radiosynthese von [18F]1 verfolgt. Ausgehend vom Trimethylammonium-Präkursor 2 erfolgte die 18F-Markierung zum [18F]Fluorbenzaldehyd [18F]3. Dieser wurde entweder direkt über eine reduktive Aminierung oder nach Reduktion und anschließender Bromierung über eine Benzylierung mit dem Pyrazolo[2,3-d]pyrimidin-Baustein 4 zu [18F]1 umgesetzt. Parallel dazu wurde die direkte 18F-Markierung des Boronsäurepinacol-Präkursors 5 bearbeitet.

Ergebnisse: Ausgehend von 2 wurde [18F]1 nach der zweistufigen Radiosynthese mit nur 1,5% radiochemischer Ausbeute in der Reaktionsmischung detektiert (Radio-HPLC). Diese konnte mittels der vierstufigen Methode auf 49% gesteigert werden. In beiden Verfahren wurde eine hohe Anzahl an 18F-Nebenprodukten nachgewiesen, welche die Isolierung von [18F]1 mittels semi-präparativer HPLC erschweren. Die direkte 18F-Markierung von 5 führte zu einer radiochemischen Ausbeute von 80-90% an [18F]1 in der Reaktionsmischung (Radio-DC/-HPLC), wobei lediglich ein 18F-Nebenprodukt (< 5%) detektiert wurde.

Schlussfolgerungen: Aufgrund dieser Ergebnisse wird ausschließlich die einstufige Strategie zur Darstellung des neuen potentiellen A2A-Radiotracers [18F]1 ausgehend von 5 weiterverfolgt. Für die geplante biologische Evaluierung (in vitro und in vivo) werden derzeit geeignete Methoden zur Isolierung, Konzentration und Formulierung von [18F]1 erarbeitet.

Referenzen:
[1] Allard et al., Immunol. Cell. Biol. 2017, 95(4), 333-339
[2] Gillespie et al., Bioorg. Med. Chem. Lett. 2008, 18, 2924-2929
Keywords: Adenosin A2A Rezeptor, Radiotracer, 18F, PET, Hirntumor
  • Lecture (Conference)
    26. Jahrestagung der AGRR, 20.-22.09.2018, Aachen, Deutschland

Publ.-Id: 28145 - Permalink


Poly-disperse simulation of flash evaporation of water inside a large vertical pipe using class method of population balance
Liao, Y.; Lucas, D.;
Flash evaporation of superheated liquid to vapour by depressurization is frequently encountered in the nature and technology, but computational fluid dynamics modelling and simulation of such scenarios is still at the embryo stage. Attempts having been made before are all based on the assumption of mono-disperse bubbles by prescribing either the size or number density, which deviates largely from the physical picture. In the present work the poly-disperse multiple-size-group approach is used for the first time to simulate the water evaporation process under pressure release transients. Complex bubble dynamics and non-equilibrium processes such as bubble nucleation, growth, coalescence and breakup as well as interfacial heat transfer are accounted for. The comparison with experimental data demonstrates that the model is effective in capturing the temporal course of vapour bubbles’ generation and growth as well as their spatial distribution. The agreement between measured and simulated cross-section averaged flow parameters such as void fraction, liquid temperature and bubble size distribution is satisfying.
Keywords: bubble coalescence; bubble nucleation; flash evaporation; interfacial heat transfer; poly-disperse

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  • Secondary publication expected from 10.05.2020

Publ.-Id: 28144 - Permalink


1-Dimensional inorganic double helices as candidates for information storage materials
Springer, M.; Kuc, A.; Vankova, N.; Heine, T.ORC
Alkali metal monopnictides contain one-dimensional chains with a double-helical structure. In this work, we report about their possible use as information storage materials. We investigated computationally fundamental properties of hetero- and homocationic systems and ways towards the application. It was shown, that the phosphorous backbone is capable of stabilising cationic chains of different composition and thus allows encoding of information.
  • Poster
    Computational Spectroscopy: Bridging Theory and Experiment, 09.-14.09.2018, Como, Italien
  • Poster
    13th HZDR PhD seminar, Ustí, 05.-07.11.2018, Ustí nad labem, Tschechische Republik
  • Poster
    JCF-Frühjahrssymposium, 20.-23.03.2019, Bremen, Deutschland

Publ.-Id: 28143 - Permalink


Theoretical and simulation study of ‘Comb’ electron beam and THz generation
Joshi, V.; Lehnert, U.; Karmakar, J.; Kumar, N.; Karmakar, B.; Tripathi, S.; Aryshev, A.; Gosh, S.; Urakawa, J.; Bhandari, R. K.; Kanjilal, D.;
A compact accelerator based super-radiant THz source is under development at Inter University Accelerator Centre (IUAC), New Delhi. The facility is based on the principle of pre-bunched Free Electron Laser (FEL) which will produce THz radiation in the range of 0.18 to 3 THz from a modulated electron beam. A photocathode electron gun will generate a short train of micro-bunches (a ‘‘comb’’ beam) driven by a fibre laser system capable of producing multi micro-pulse laser beam with variable separation (‘‘comb’’ laser pulse). Upon acceleration, the electron beam will be injected in to a compact undulator magnet tuned to the same frequency as the separation of the electron micro-bunches. The paper discusses the process of enhancement of super-radiant emission of radiation due to modulation in the comb beam and the conditions required to achieve maximum enhancement of the radiation power. The feasibility study of generating a comb beam at the photocathode and its transport through the beamline while preserving its temporal structure has been reported. To evaluate the characteristics of the radiation emitted from the comb beam, a 𝐶++ based particle tracker and Lienard–Wiechert field solver has been developed. The conceptual understanding of the emission of radiation from comb beam is shown to conform with the numerical results. The code has been used to calculate the radiation pulse energy emitted into the central cone of undulator for various comb beam configurations.
Keywords: linear accelerator; THz; THz source; radiation source; comb beam; pre-bunched beam; radiation emission; undulator radiation; super-radiant emission

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Publ.-Id: 28142 - Permalink


Dissecting spin-phonon equilibration in ferrimagnetic insulators by ultrafast lattice excitation
Maehrlein, S. F.; Radu, I.; Maldonado, P.; Paarmann, A.; Gensch, M.; Kalashnikova, A. M.; Pisarev, R. V.; Wolf, M.; Oppeneer, P. M.; Barker, J.; Kampfrath, T.;
To gain control over magnetic order on ultrafast time scales, a fundamental understanding of the way electron spins interact with the surrounding crystal lattice is required. However, measurement and analysis even of basic collective processes such as spin-phonon equilibration have remained challenging. We directly probe the flow of energy and angularmomentum in the model insulating ferrimagnet yttriumiron garnet. After ultrafast resonant lattice excitation, we observe thatmagnetic order reduces on distinct time scales of 1 ps and 100 ns. Temperature-dependentmeasurements, a spin-coupling analysis, and simulations show that the two dynamics directly reflect two stages of spinlattice equilibration. On the 1-ps scale, spins and phonons reach quasi-equilibrium in terms of energy through phonon-induced modulation of the exchange interaction. This mechanism leads to identical demagnetization of the ferrimagnet’s two spin sublattices and a novel ferrimagnetic state of increased temperature yet unchanged total magnetization. Finally, on the much slower, 100-ns scale, the excess of spin angular momentum is released to the crystal lattice, resulting in full equilibrium. Our findings are relevant for all insulating ferrimagnets and indicate that spin manipulation by phonons, including the spin Seebeck effect, can be extended to antiferromagnets and into the terahertz frequency range.
Keywords: THz control, ultra-fast, magnetism

Publ.-Id: 28141 - Permalink


Effect of anisotropic microstructure of ODS steels on small punch test results
Altstadt, E.; Bergner, F.; Das, A.; Houska, M.;
Hot rolling and hot extrusion of oxide-dispersion strengthened (ODS) ferritic steels give rise to anisotropic microstructures and mechanical properties and may provoke related phenomena such as secondary cracking. In this study, we consider the small punch (SP) test – a method, applicable in the case of small amounts of available material and well established for isotropic materials. The SP test was applied to investigate the effect of sample orientation on deformation and cracking for one hot-rolled and two hot-extruded ODS ferritic steels. Existing microstructural evidence is used to rationalize the observed anisotropic fracture behaviour. The SP test results are compared with those from existing fracture mechanics tests based on sub-sized C(T) samples. The applicability of the empirical conversion of SP-based into Charpy-based transition temperatures is evaluated. The fractographic manifestation of load drops in SP load-displacement curves is identified and the analogy to secondary cracking in fracture mechanics tests is shown.
Keywords: small punch test, ductile-to-brittle transition temperature, oxide dispersion strengthened steel, pop-ins

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  • Secondary publication expected from 17.01.2020

Publ.-Id: 28140 - Permalink


Fuzzy flow pattern identification in horizontal air-water two-phase flow based on wire-mesh sensor data
Wiedemann, P.; Döß, A.; Schleicher, E.; Hampel, U.;
Online monitoring of two-phase flow patterns is an essential need in various chemical engineering applications, since the reliability of prediction methods is limited. Therefore, the present study aims at developing a practically applicable algorithm for identifying flow patterns in horizontal gas-liquid flows on the basis of wire-mesh sensor data. Experiments were conducted in a 50mm i. d. pipe over a wide range of superficial velocities of an air-water mixture. Characteristic features involving the influence of gravity and the spatio-temporal behavior of the flows were derived from tomographic phase fraction data and used as input for fuzzy clustering. Three differently determined sets of cluster centers are compared against a reference classification by human specialist through reclassifying the measurements with the aid of defuzzyfication and, alternatively, by means of a novel visualization technique, that retains the fuzziness of the results. With respect to the latter one, best agreement is reached with cluster centers from fuzzy c-means clustering using all recorded measurements. As a special emphasis is put to the identification of transitional flow patterns, the performance of the algorithm at pseudo-dynamic operation is demonstrated, finally.
Keywords: gas-liquid flow, fuzzy c-means clustering, polar visualization technique, regime transition, wire-mesh sensor

Publ.-Id: 28139 - Permalink


Visualisation of the large scale circulation in Rayleigh-Bénard convection using contactless inductive flow tomography
Wondrak, T.; Stefani, F.; Galindo, V.; Eckert, S.;
Rayleigh-Bénard (RB) convection plays an important role in geo- and astrophysics as well as in many metallurgical applications. At sufficiently high values of the Rayleigh number, a large scale circulation (LSC) is formed whose dynamics had turned out to be surprisingly rich. In this paper, the applicability of the contactless inductive flow tomography (CIFT) for the detection of the torsional mode of the LSC is investigated. CIFT enables the three-dimensional reconstruction of flow structures in liquid metals by applying one or more magnetic fields and measuring the flow induced perturbations of those fields outside the melt. Additionally, preliminary measurements of the flow induced magnetic field with a similar sensor arrangement will be presented.
Keywords: flow measurement techniques, Rayleigh-Bénard convection
  • Lecture (Conference)
    9th international symposium on electromagnetic processing of materials (EPM2018), 14.-18.10.2018, Awaji Yumebutai International Conference Center, Japan
  • Open Access LogoIOP Conference Series: Materials Science and Engineering 424(2018), 012007
    DOI: 10.1088/1757-899X/424/1/012007

Publ.-Id: 28138 - Permalink


Real-time control of the mould flow in a model of continuous casting in frame of the TOMOCON project
Wondrak, T.; Hampel, U.; Ratajczak, M.; Glavinić, I.; Stefani, F.; Eckert, S.; van der Plas, D.; Pennerstorfer, P.; Muttakin, I.; Soleimani, M.; Abouelazayem, S.; Hlava, J.; Blishchik, A.; Kenjeres, S.;
In continuous casting, the flow structure of the liquid steel in the mould and the two-phase distribution in the submerged entry nozzle (SEN) are crucial for the quality of the produced steel. In order to effectively control the flow in the mould by electromagnetic brakes (EMBrs) and the injection of gas into the SEN, even a rough knowledge of the flow structure would be very helpful. In the framework of the TOMOCON project, the contactless inductive flow tomography (CIFT) and the mutual inductance tomography (MIT) will be integrated into a control loop for slab casters. This control loop will be developed and implemented at the Mini-LIMMCAST facility, which is available at the Helmholtz-Zentrum Dresden – Rossendorf. In this paper a short overview of this project will be given.
Keywords: continuous casting, electromagnetic brake, inductive measurement techniques, flow control
  • Lecture (Conference)
    9th international symposium on electromagnetic processing of materials (EPM2018), 14.-18.10.2018, Awaji Yumebutai International Conference Center, Japan
  • Open Access LogoIOP Conference Series: Materials Science and Engineering 424(2018), 012003
    DOI: 10.1088/1757-899X/424/1/012003

Publ.-Id: 28137 - Permalink


All-optical structuring of laser-driven proton beam profiles data sets
Obst-Huebl, L.ORC; Ziegler, T.; Brack, F.-E.; Branco, J.; Bussmann, M.; Cowan, T. E.; Curry, C. B.; Fiuza, F.; Garten, M.; Gauthier, M.; Göde, S.; Glenzer, S. H.; Huebl, A.; Irman, A.; Kim, J. B.; Kluge, T.; Kraft, S.; Kroll, F.; Metzkes-Ng, J.; Pausch, R.; Prencipe, I.; Rehwald, M.; Rödel, C.; Schlenvoigt, H.-P.; Schramm, U.; Zeil, K.

This data repository contains analyzed data files of the shown figures and simulation input files.

Please see the according README.txt files in the individual directories and the original manuscript for guidance.

Manuscript title:
  All-optical structuring of laser-driven proton beam profiles

Authors:
  Lieselotte Obst, Tim Ziegler, Florian-Emanuel Brack, Joao Branco, Michael Bussmann, Thomas E. Cowan, Chandra B. Curry, Frederico Fiuza, Marco Garten, Maxence Gauthier, Sebastian Göde, Siegfried H. Glenzer, Axel Huebl, Arie Irman, Siegfried H. Glenzer, Axel Huebl, Arie Irman, Jongjin B. Kim, Thomas Kluge, Stephan Kraft, Florian Kroll, Josefine Metzkes-Ng, Richard Pausch, Irene Prencipe, Martin Rehwald, Christian Rödel, Hans-Peter Schlenvoigt, Ulrich Schramm, Karl Zeil

Submitted to:
  Nature Communications (2018)


Responsible for the data repository:
  Lieselotte Obst-Huebl, TU Dresden and HZDR
  Axel Huebl, TU Dresden and HZDR
  Tim Ziegler, TU Dresden and HZDR
  Thomas Kluge, HZDR

 


Related publications
All-optical structuring of laser-driven proton beam profiles (Id 28155) has used this publication of HZDR-primary research data
  • Reseach data in the HZDR data repository RODARE
    Publication date: 2018-10-30
    DOI: 10.14278/rodare.65
    License: CC-BY-4.0

Downloads:

Publ.-Id: 28136 - Permalink


Contactless inductive flow tomography for models of continuous casting and crystal growth
Ratajczak, M.; Wondrak, T.ORC; Glavinić, I.; Stefani, F.
Contactless inductive flow tomography (CIFT) enables the reconstruction of the major flow structure in electrically conducting liquids, like molten steel or silicon. It is based on the permeation of the melt by an external primary magnetic field and the subsequent induction of currents, which generate a flow-induced secondary magnetic field. The measured secondary field allows for reconstruction of the flow by solving the underlying linear inverse problem. We present results for the application of CIFT for two lab-scale model experiments of (a) continuous steel casting in the presence of an electromagnetic brake and (b) Czochalski crystal growth with a thermally driven convection. In the first scenario (a), the electromagnetic brake poses the biggest challenge, since its strong static magnetic field of about 300 mT superimposes the flow-induced field of about 100 nT, and the brake’s ferromagnetic parts distort the CIFT excitation field. We show how this can be overcome by simulations and adequate instrumentation using gradiometric induction coil sensors, which enables correct flow reconstructions in this scenario. In the second setup (b) the biggest challenges arise from the long measurement times of up to 12 hours together with thermal expansion and contraction of the setup mounting due to the intrinsic temperature gradient of the melt. Here an optimized experimental construction is necessary to enable successful measurements magnetic field measurements with Fluxgate sensors. The experimental data reveal plausible stationary and transient phenomena in accordance with numerical
flow simulations.
Keywords: metallurgy, contactless inductive flow tomography, magnetic field measurement, flow measurement
  • Contribution to proceedings
    9th world congress on industrial process tomography, 02.-6.9.2018, Bath, UK
    Proceedings of the 9th world congress on industrial process tomography, 978 0 85316 3497, 839-845
  • Lecture (Conference)
    9th world congress on industrial process tomography, 02.-6.9.2018, Bath, UK

Publ.-Id: 28135 - Permalink


Numerical aspects of contactless inductive flow tomography for crystal growth
Wondrak, T.ORC; Jacobs, R. T.; Galindo, V.; Stefani, F.
The flow structure of liquid silicon in the crucible for Czochralski (Cz) crystal growth is important for the quality of the silicon crystal. However, the high temperature and the required cleanliness of the melt represent a challenge for any flow measurement device. A promising technique to reconstruct the flow of a conducting liquid is contactless inductive flow tomography (CIFT). The procedure relies on the measurement of the flow induced perturbation of a primary magnetic field and the inversion of the corresponding integral equation system. In this paper, the numerical challenges for the application of CIFT to Cz crystal growth will be investigated. This includes the treatment of the singularities of the integral equation system as well as the selection of appropriate integration techniques. The paper concludes with numerical investigation of the expected flow induced magnetic field for a reversal of the rotation in simple model of a typical crucible.
Keywords: contactless inductive flow tomography, Czochralski crystal growth, flow measurement, liquid metal
  • Contribution to proceedings
    9th world congress on industrial process tomography, 02.-6.9.2018, Bath, UK
    Proceedings of the 9th world congress on industrial process tomography, 978 0 85316 3497, 451-456
  • Lecture (Conference)
    9th world congress on industrial process tomography, 02.-6.9.2018, Bath, UK

Publ.-Id: 28134 - Permalink


Surface nanobubbles on the carbonate mineral dolomite
Owens, C. L.ORC; Schach, E.; Rudolph, M.ORC; Nash, G. R.
Surface nanobubbles are of wide interest to a number of research fields, ranging from mineral processing to metamaterials. Their formation on hydrophobic surfaces has long been confirmed but the factors controlling their size and location are less well understood. In this work we investigate, using non-contact atomic force microscopy, the properties of surface nanobubbles on the mineral dolomite under three aqueous solutions; water, depressant and collector. Nanobubbles were observed under all three conditions, but with the highest density observed under collector conditions. Analysis of the critical angle of the bubbles suggests that the collector does not affect the surface tension of the bubbles, but instead does affect their pinning, consistent with the observed increased density.
Keywords: nanobubbles, flotation, atomic force microscopy

Publ.-Id: 28133 - Permalink


Magnon Transport in Spin Textures
Schultheiss, H.;
One of the grand challenges in cutting edge quantum and condensed matter physics is to harness the spin degree of electrons for information technologies. While spintronics, based on charge transport by spin polarized electrons, made its leap in data storage by providing extremely sensitive detectors in magnetic hard-drives, it turned out to be challenging to transport spin information without great losses. With magnonics a visionary concept inspired researchers worldwide: Utilize magnons - the collective excitation quanta of the spin system in magnetically ordered materials - as carriers for information. Magnons are waves of the electrons’ spin precessional motion. They propagate without charge transport and its associated Ohmic losses, paving the way for a substantial reduction of energy consumption in computers.
While macroscopic prototypes of magnonic logic gates have been demonstrated, the full potential of magnonics lies in the combination of magnons with nano-sized spin textures. Both magnons and spin textures share a common ground set by the interplay of dipolar, spin-orbit and exchange energies rendering them perfect interaction partners. Magnons are fast, sensitive to the spins’ directions and easily driven far from equilibrium. Spin textures are robust, non-volatile and still reprogrammable on ultrashort timescales. The vast possibilities offered by combining this toolset of magnetic phenomena, add value to both magnonics and the fundamental understanding of complex spin textures.
I will give an introduction about magnon propagation and manipulation in microstructures with non-collinear spin textures, in particular magnons propagating in nano channels formed by magnetic domain walls. Furthermore, I will address how magnons can be excited in domain wall channels by pure spin currents originating from the spin Hall effect.
References:
[1] K. Wagner, A. Kákay, K. Schultheiss, A. Henschke, T. Sebastian, and H. Schultheiss, Nature Nanotech 11, 432 (2016).
[2] K. Vogt, F. Y. Fradin, J. E. Pearson, T. Sebastian, S. D. Bader, B. Hillebrands, A. Hoffmann, and H. Schultheiss, Nat Comms 5, 3727 (2014).
Keywords: magnonics, spin waves, spin textures, domain walls, auto-oscillations
  • Invited lecture (Conferences)
    Lüscher Seminar, 08.02.2018, Klosters, Schweiz
  • Invited lecture (Conferences)
    Spin Mechanics 5 and Nano MRI 6 workshop, 16.02.2018, Chamonix, Schweiz
  • Invited lecture (Conferences)
    Nano-Magnonics Workshop, 20.02.2018, Kaiserslautern, Deutschland
  • Invited lecture (Conferences)
    International Conference on Microwave Magnetics, 25.06.2018, Exeter, England
  • Invited lecture (Conferences)
    Workshop on Advances in Brillouin Light Scattering, 13.09.2018, Perugia, Italien
  • Invited lecture (Conferences)
    International Advanced School on Magnonics, 20.09.2018, Kyiv, Ukraine

Publ.-Id: 28132 - Permalink


Ultrasmall Nanomaterials for Multimodal Cancer Imaging
Stephan, H.;
Ultrasmall nanomaterials (NMs) offer excellent prospects for the development of new non-invasive strategies of early diagnosis and efficient monitoring of therapeutic treatments. Provided with special functionalities, NMs allow the simultaneous application of different molecular imaging methods. In the field of cancer medicine, the combination of different imaging techniques such as nuclear (PET: positron emission tomography and SPECT: single-photon emission computed tomography) and near-infrared fluorescence (NIRF) imaging for tracking down tumors and metastases is particularly attractive.
This lecture will focus on the development and application of very small radiolabeled NMs, embracing inorganic particles and soft polymeric structures. Novel strategies will be discussed to develop stealth NMs capable of avoiding biomolecular corona formation and thus evading scavenging of NMs by the mononuclear phagocyte system, leading to eventual accumulation in the liver and spleen.
  • Invited lecture (Conferences)
    Kolloquium, 25.10.2018, Hamburg, Deutschland

Publ.-Id: 28130 - Permalink


Combined frequency and time domain measurements on injection-locked, constriction-based spin Hall nano-oscillators
Hache, T.; Weinhold, T.; Schultheiss, K.; Stigloher, J.; Vilsmeier, F.; Back, C.; Arekapudi, S. S. P. K.; Hellwig, O.; Fassbender, J.; Schultheiss, H.;
We demonstrate a combined frequency and time domain investigation of injection-locked, constriction-based spin Hall nano-oscillators by Brillouin light scattering (BLS) and time-resolved magneto-optical Kerr effect (TR-MOKE). This was achieved by applying an alternating current in the GHz regime in addition to the direct current which drives auto-oscillations in the constriction. In the frequency domain, we analyze the width of the locking range, the increase in intensity and reduction in linewidth as a function of the applied direct current. Then we show that the injection locking of the auto-oscillation allows for its investigation by TR-MOKE measurements, a stroboscopic technique that relies on a phase stable excitation, in this case given by the synchronisation to the microwave current. Field sweeps at different direct currents clearly demonstrate the impact of the spin current on the Kerr amplitude. Two-dimensional TR-MOKE and BLS maps show a strong localization of the auto-oscillation within the constriction, independent of the external locking.
Keywords: spin Hall, injection locking, injection-locking, TR-MOKE, Kerr-effect, Kerr, auto-oscillation, magnetism, magnetization dynamics, BLS, µBLS, Brillouin light scattering, constriction-based, nano-oscillator

Publ.-Id: 28128 - Permalink


Transition from convection rolls to large-scale cellular structures in turbulent Rayleigh-Bénard convection in a liquid metal layer
Akashi, M.; Yanagisawa, T.; Tasaka, Y.; Vogt, T.; Murai, Y.; Eckert, S.;
Turbulent Rayleigh-Bénard convection was investigated within a liquid metal layer, Prandtl number Pr = 0.03, in a square vessel having a moderate aspect ratio, Γ = 5. Laboratory experiments were performed at moderate Rayleigh numbers, 7.9 × 10^3 < Ra < 3.5 × 10^5. Ultrasonic velocity profiling (UVP) was used to visualize the spatio-temporal flow structure in two horizontal planes, while temperature fluctuations were monitored simultaneously in the fluid layer. Oscillatory roll-like structures were observed at Ra ≥ 10^4, while the transition to a fully three-dimensional cell-like structure occurs around Ra = 6 × 10^4. The transition from laminar convection to thermal turbulence manifests itself in the occurrence of unstable intermediate regimes accompanied by a stepwise increment in the horizontal scale. We propose a scaling law for the horizontal length scale as a function of the Ra number based on empirically-derived relations of the oscillation frequency and the typical flow velocity. This scaling law indicates the present results are comparable with variations of the maximum size of large scale structures in different Pr conditionsand larger aspect ratios.
Keywords: Rayleigh-Bénard convection, Thermal turbulence, Large scale structure, Liquid metal, Low Prandtl number

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Publ.-Id: 28127 - Permalink


Consequences of broken axial symmetry in heavy nuclei – an overview of the situation in the valley of stability.
Grosse, E.; Junghans, A. R.ORC; Wilson, J.
An overview on the various effects of axial symmetry breaking is presented for medium heavy and heavy nuclei covering the mass number range 70 < A <240. The discussion includes various observations for nuclei: level densities, spectroscopic features as energies and transition rates, ground state masses and finally the splitting of giant dipole resonances. Quadrupole moments and rates can be derived from models of triaxial rigid rotation or cranking for a given triaxiality parameters γ, but microscopic considerations are needed to predict these for each nucleus investigated. Respective predictions were made by recently made Hartree-Fock-Bogolyubov (HFB) calculations extended to arbitrary triaxiality by a generator coordinate method. In accord to these, various observations as reported in this overview demonstrate the importance of allowing a breaking of axial symmetry for heavy nuclei already in the valley of stability. Considering this breaking as indicated from the HFB approach surprisingly many experimental data are well described globally without the need for local fit parameters. In addition to these comparisons it will be shown that it is advantageous to consider c_γ=cos(3γ) an indicator of axiality for heavy nuclei independent of their quadrupole moment.

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Publ.-Id: 28125 - Permalink


Feasibility of proton FLASH effect tested by zebrafish embryo irradiation
Beyreuther, E.ORC; Brand, M.; Hans, S.; Hideghety, K.; Karsch, L.; Leßmann, E.; Schürer, M.; Szabo, E. R.; Pawelke, J.
Background and purpose
Motivated by first animal trials showing the normal tissue protecting effect of electron and photon Flash irradiation relative to conventional continuous beam delivery, the feasibility of proton Flash should be assessed.
Materials and methods
A setup and beam parameter settings for the treatment of zebrafish embryo with proton Flash and proton beam of conventional dose rate were established at the University Proton Therapy Dresden. Zebrafish embryos were treated with graded doses and the differential effect on embryonic survival and the induction of morphological malformations was followed for up to four days after irradiation.
Results
Beam parameters for the realization of proton Flash were set and tested with respect to controlled dose delivery to biological samples. The dose dependent embryonic survival data obtained for protons delivered as Flash and with a beam of conventional dose rate of 5 Gy/min show not significant influence of proton dose rate. Similarly, just a trend towards a protective effect of proton Flash was revealed for the induction of pericardial oedema as one type of acute radiation effect and spinal curvature as a developmental abnormality.
Conclusion
The feasibility of Flash proton irradiation was successfully shown, whereas more experiments are required to understand the absence of a clear protecting effect and therefore to figure out the limits and requirements for the Flash effect.
Keywords: proton Flash effect, proton beam therapy, normal tissue toxicity, zebrafish embryo

Publ.-Id: 28124 - Permalink


Magnon auto-oscillation under zero magnetic field
Nishida, N.; Hache, T.; Arekapudi, S. S. P. K.; Awad, A. A.; Hellwig, O.; Fassbender, J.; Schultheiss, H.;
Magnons are attractive for application in energy efficient information technology, because they propagate without any actual charge currents and they offer high frequencies up to THz range. Here we present a novel scheme for magnon generation using spin currents and domain walls.
When a charge current is applied to a heavy metallic/ferromagnetic bilayer, the spin currents originating from a spin Hall effect in the heavy metal apply a spin transfer torque on the magnetization. This allows driving efficiently auto-oscillations of magnetization [1]. We focused on domain walls as local magnon nano channels [2]. Since domain walls can be moved by electrical currents [3], they are attractive for reprogrammable nano circuits.
A 370 nm wide zigzag structure was fabricated from a Pt/CoFeB bilayer. A domain wall was generated at the apex by magnetic saturation. The magnon intensity on the remanent state was measured by Brillouin light scattering microscopy [4] with applying a dc current. The magnon excitation showed the dc current dependency. Magnons were detected only for positive dc currents. We succeeded to drive magnon auto-oscillation in the domain wall under zero magnetic field by spin transfer torque.

Reference
[1] A. N. Slavin and V. Tiberkevich, IEEE Trans. Magn. 45, 1875 (2009).
[2] K. Wagner et. al., Nat. Nanotech. 11, 432 (2016).
[3] S. S. P. Parkin et. al., Science 320, 190 (2008).
[4] T. Sebastian et. al., Front. Phys. 3, 35 (2015).
  • Lecture (Conference)
    9th Joint European Magnetic Conference, 03.-07.09.2018, Mainz, Germany

Publ.-Id: 28122 - Permalink


Magnon auto-oscillation in domain walls
Nishida, N.; Hache, T.; Arekapudi, S. S. P. K.; Awad, A. A.; Hellwig, O.; Fassbender, J.; Schultheiss, H.;
Magnons are the fundamental excitations in magnetic materials, and they can transport angular momentum without actual charge currents. Therefore, they are attractive for applications in energy efficient information technology, offering high operating frequencies up to the THz range. Here we present a novel scheme for magnon generation using spin currents and domain walls.
When a charge current is applied to a bilayer consisting of a heavy metal and a ferromagnetic metal, the spin currents originating from the spin Hall effect in the heavy metal apply a spin transfer torque on the magnetization of the ferromagnetic layer. This allows driving efficiently auto-oscillations of magnetization [1]. We focused on domain walls as local nano magnon channels [2]. Since it is possible to move domain walls by electrical currents [3], domain walls are attractive for nano-sized reprogrammable circuits.
A 370 nm wide boomerang structure was fabricated from a Pt/CoFeB bilayer (Fig.1). The sample was magnetized by applying an external magnetic field H. After the saturation, the external magnetic field was set to 0 Oe, and a dc current was applied to the sample. The magnon intensity at the apex of the boomerang structure was measured by Brillouin light scattering microscopy [4]. Figure 2 shows the dc current dependency of the magnon spectrum on the remanent state. Magnons were detected for currents between 3.6 mA and 4.5 mA, while no magnons were observed for any negative dc currents. A domain wall is generated at the apex for the remanent state because of the shape anisotropy of the boomerang structure. We succeeded to excite magnons under zero magnetic field due to the autooscillation of the magnetization by spin transfer torque.

Reference
[1] A. N. Slavin and V. Tiberkevich, IEEE Trans. Magn. 45, 1875 (2009).
[2] K. Wagner et. al., Nat. Nanotech. 11, 432 (2016).
[3] S. S. P. Parkin et. al., Science 320, 190 (2008).
[4] T. Sebastian et. al., Front. Phys. 3, 35 (2015).
  • Lecture (Conference)
    International Conference on Magnetism, 15.-20.07.2018, San Francisco, USA

Publ.-Id: 28121 - Permalink


Magnon auto-oscillation in domain walls by spin transfer torque
Nishida, N.; Hache, T.; Arekapudi, S. S. P. K.; Hellwig, O.; Fassbender, J.; Schultheiss, H.;
磁性体の基本励起状態であるマグノンは非電荷でTHz帯までの励起が可能であることから、省エネルギーかつ高速な情報デバイスへの応用が期待されている。Ptと強磁性金属の二層構造に電荷を流すと、スピンホール効果によりPt層でスピン流が生成され、強磁性層に注入される。スピン流から磁化にスピントランスファートルクが印加されることにより、磁化の自励発振[1]が駆動され、マグノンが励起される。我々は微細なマグノンチャネルとして磁壁[2]に着目し、磁壁中のマグノン励起について調べた。

図1に示すように、PtとCoFeBの二層膜から成る線幅370 nmの折れ線構造を作製し、y方向に着磁した。試料に直流電流を印加し、ブリルアン散乱分光装置を用いて折れ線の頂点におけるマグノン強度を測定した。図2にマグノン強度の電流依存性を示す。図2(a)に示すように、y方向に1.0 kOeの外部磁場を印加した場合には、2.3 mAから5.0 mAの電流値の範囲においてマグノンの励起が検出された。一方、電流の印加方向を反転させるとマグノンは検出されなかった。図2(b)に、y方向に試料を着磁した後に外部磁場を0 kOeにし、残留磁化状態において測定した結果を示す。1.0 kOeの外部磁場を印加した場合と同様に、正の電流を印加した場合のみマグノンの励起が検出された。残留磁化状態では形状磁気異方性により、試料頂点に磁壁が生成される。スピントランスファートルクを用いた磁壁中の磁化の自励発振により、ゼロ磁場下においてマグノンの励起に成功した。

参考文献
[1] A. N. Slavin and V. Tiberkevich, IEEE Trans. Magn. 45, 1875 (2009).
[2] K. Wagner et al., Nat. Nanotech. 11, 432 (2016).

Magnons are the fundamental excitations in magnetic materials and are attractive for applications in information technology devices. They do not involve charge transport and the associated waste heat and offer high operating frequencies up to the THz range. When a charge current is applied to a bilayer consisting of Pt and a ferromagnetic metal, the spin currents originating from the spin Halle effect in the Pt layer generate a spin transfer torque to the magnetizations in the ferromagnetic layer. This allows to efficiently drive auto-oscillations of magnons[1]. We focused on domain walls as local nano magnon channels[2], and investigated the magnon auto-oscillation in the domain walls.

As shown in Fig. 1, a zigzag structure was fabricated from a Pt/CoFeB bilayer. The width was set to be 370 nm. The sample was magnetized to the y direction and a dc current was applied to the sample. The magnon intensity at the corner was measured by Brillouin Light Scattering microscopy. Figure 2 shows the dc current dependency of the magnon intensity measured at the corner. As shown in Fig. 2(a), in the case that an external magnetic field of 1.0 kOe was applied to the y direction, the magnons were detected when the dc current was between 2.3 mA and 5.0 mA. While there were no magnons in the case of the reversed dc current direction. Figure 2(b) shows the magnon intensity at the remanence state after saturation to y direction. There were also no magnon in the case of the reversed dc current. The domain wall is generated at the corner under the remanence state because of a shape anisotropy. We succeeded to excite magnons under zero magnetic field due to the auto-oscillation of the magnetizations by spin transfer torque.

Reference
[1] A. N. Slavin and V. Tiberkevich, IEEE Trans. Magn. 45, 1875 (2009).
[2] K. Wagner et al., Nat. Nanotech. 11, 432 (2016).
  • Poster
    The Physical Society of Japan, 73rd Annual Meeting, 22.-25.03.2018, Noda, Chiba, Japan

Publ.-Id: 28120 - Permalink


The importance of calcium, magnesium and iron ions in the scheelite-calcite flotation system - application to the Mittersill ore
Chukwuma, O. C.;
The specific objectives of this research are:
(i) Investigating the effect of calcium and magnesium ions in the scheelite-calcite flotation system, quantifying their impact and the underpinning mechanisms
(ii) Validating the hypothesis that iron ions mixed with sodium silicate depresses calcite.
Keywords: Scheelite Water hardness Hydrosol of iron ions and sodium silicate
  • Master thesis
    HZDR - HIF, 2018
    Mentor: Nathalie Kupka

Publ.-Id: 28119 - Permalink


A simple route to synchronized nucleation of self-catalyzed GaAs nanowires on silicon for sub-Poissonian length distributions
Tauchnitz, T.ORC; Berdnikov, Y.; Dubrovskii, V. G.ORC; Schneider, H.; Helm, M.; Dimakis, E.ORC
We demonstrate a simple route to grow ensembles of self-catalyzed GaAs nanowires with a remarkably narrow statistical distribution of lengths on natively oxidized Si(111) substrates. The fitting of the nanowire length distribution with a theoretical model reveals that the key requirements for narrow length distributions are the synchronized nucleation of all nanowires on the substrate and the absence of beam shadowing from adjacent nanowires. Both requirements are fulfilled by controlling the size and number density of the openings in SiOx, where the nanowires nucleate. This is achieved by using a pre-growth treatment of the substrate with Ga droplets and two annealing cycles. The narrowest nanowire length distributions are markedly sub-Poissonian, which validates the theoretical predictions about temporally anti-correlated nucleation events in individual nanowires, the so-called nucleation antibunching. Finally, the reproducibility of sub-Poissonian length distributions attests the reliability of our growth method.
Keywords: substrate for nanowires, nucleation antibunching, nucleation delay, nanowire nucleation

Publ.-Id: 28118 - Permalink


Excitation of whispering gallery magnons in a magnetic vortex
Schultheiss, K.; Verba, R.; Wehrmann, F.; Wagner, K.; Körber, L.; Hula, T.; Hache, T.; Kákay, A.; Awad, A. A.; Tiberkevich, V.; Slavin, A. N.; Fassbender, J.; Schultheiss, H.;
We present the generation of whispering gallery magnons with unprecedented high wave vectors via nonlinear 3-magnon scattering in a μm-sized magnetic vortex state disc. These modes exhibit a strong localisation at the perimeter of the disc and practically zero amplitude in an extended area around the vortex core. They originate from the splitting of the fundamental radial magnon modes, which can be resonantly excited in a vortex texture by an out-of-plane microwave field. We shed light on the basics of this non-linear scattering mechanism from experimental and theoretical point of view. Using Brillouin light scattering (BLS) microscopy, we investigated the frequency and power dependence of the 3-magnon splitting. The spatially resolved mode
profiles give evidence for the localisation at the boundaries of the disc and allow for a direct determination of the modes wavenumber.
Keywords: magnons, spin wave, nonlinear magnetization dynamics, magnetic vortex, Brillouin light scattering
  • Open Access LogoPhysical Review Letters 122(2019), 097202
    DOI: 10.1103/PhysRevLett.122.097202
  • Invited lecture (Conferences)
    International Conference on Magnetism, 19.07.2018, San Francisco, USA
  • Lecture (Conference)
    Joint European Magnetic Symposia (JEMS), 04.09.2018, Mainz, Deutschland

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Publ.-Id: 28116 - Permalink


Steering magnons by noncollinear spin textures
Schultheiss, K.; Wagner, K.; Kákay, A.; Schultheiss, H.;
One of the grand challenges in cutting edge quantum and condensed matter physics is to harness the spin degree of electrons for information technologies. While spintronics, based on charge transport by spin polarized electrons, made its leap in data storage by providing extremely sensitive detectors in magnetic hard-drives [1], it turned out to be challenging to transport spin information without great losses [2]. With magnonics, a visionary concept inspired researchers worldwide: Utilize spin waves-the collective excitation quanta of the spin system in magnetically ordered materials-as carriers for information [3-8]. Spin waves, which are also called magnons, are waves of the electrons’ spin precessional motion. They propagate without charge transport and its associated Ohmic losses, paving the way for a substantial reduction of energy consumption in computers. While macroscopic prototypes of magnonic logic gates have been demonstrated [9, 10], the full potential of magnonics lies in the combination of magnons with nano-size spin textures. Both magnons and spin textures share a common ground set by the interplay of dipolar, spin-orbit, and exchange energies, rendering them perfect interaction partners. Magnons are fast, sensitive to the spins’ directions, and easily driven far from equilibrium. Spin textures are robust, nonvolatile, and still reprogrammable on ultrashort timescales. The vast possibilities offered by combining these magnetic phenomena add value to both magnonics and the fundamental understanding of complex spin textures. The scope of this chapter is about experimental studies on magnon transport in metallic ferromagnetic microstructures with focus on actively controlling the magnon propagation. Two inherent characteristics of magnons enable for lateral steering: the anisotropy of the magnon dispersion and its sensitivity to changes in the internal magnetic field distribution. We intend to give an idea of how these magnon features can be utilized toward realizing functionalized magnonic networks. © 2017 Pan Stanford Publishing Pte. Ltd.
Keywords: magnons, spin waves, spin textures, propagation, Brillouin light scattering
  • Book chapter
    Sergej O. Demokritov: Spin Wave Confinement: Propagating Waves, Second Edition, Singapore: Pan Stanford Publishing Pte. Ltd., 2017, 978-135161721-5;978-981477435-2, 261-294
    DOI: 10.1201/9781315110820

Publ.-Id: 28115 - Permalink


Why are hot-rolled ODS steels more prone to secondary cracking than hot-extruded ODS steels?
Das, A.ORC; Viehrig, H.-W.ORC; Altstadt, E.ORC; Bergner, F.ORC; Hoffmann, J.ORC
Secondary cracks are known to absorb energy, retard primary crack propagation and initiate at lower loads than primary cracks. They are observed more often in hot-rolled than in hot-extruded ODS steels. In this work, the microstructural factors responsible for the same are investigated. A better understanding of these factors can lead to tailoring of improved ODS steels. Fracture toughness testing of 13Cr ODS steel in hot-rolled and in hot-extruded form were carried out. The fracture behaviour of secondary cracks was investigated using scanning electron and electron backscatter microscope. Crystallographic texture and grain morphology plays a predominant role in preventing secondary cracks in hot-extruded ODS steels. At lower temperatures, secondary cracks occur predominantly via transgranular cleavage. The fracture mode changes to ductile and intergranular at higher temperatures.
Keywords: ODS steel; nanostructured ferritic alloys; fracture behaviour; anisotropy; secondary cracking; delamination
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  • Poster
    NuMat2018: The Nuclear Materials Conference, 15.10.2018, Seattle, USA

Publ.-Id: 28114 - Permalink


Diverse Effects of Phospholipase A2 Receptor Expression on LNCaP and PC-3 Prostate Cancer Cell Growth in vitro and in vivo
Friedemann, M.; Nacke, B.; Hagelgans, A.; Jandeck, C.; Bechmann, N.; Ullrich, M.; Belter, B.; Neuber, C.; Sukocheva, O.; Pietzsch, J.ORC; Menschikowski, M.
Physiological and pathophysiological functions of the phospholipase A2 receptor 1 (PLA2R1) are still not completely understood. To elucidate PLA2R1’s function in prostate carcinoma, the receptor was ectopically overexpressed in LNCaP with silenced PLA2R1, and diminished in PC-3 cells with constitutively increased PLA2R1 expression relative to normal prostate epithelial cells. LNCaP cells were transfected to overexpress PLA2R1 (LNCaP-PLA2R1) and compared to control vector transfected cells (LNCaP-Ctrl). Alternatively, a CRISPR/Cas9-knockdown of PLA2R1 was achieved in PC-3 cells (PC-3 KD) and compared to the corresponding control-transfected cells (PC-3 Ctrl). The impact of PLA2R1 expression on proliferative and metastatic parameters was analysed in vitro. A pilot in vivo study addressed the effects of PLA2R1 in mice xenografted with transfected LNCaP and PC-3 cells. Cell viability/proliferation and motility were significantly increased in LNCaP-PLA2R1 and PC-3 Ctrl compared to LNCaP-Ctrl and PC-3 KD cells, respectively. However, levels of apoptosis, clonogenicity and cell invasion were reduced in LNCaP-PLA2R1 and PC-3 Ctrl cells. Gene expression analysis revealed an up-regulation of fibronectin 1 (FN1), TWIST homolog 1 (TWIST1), and cyclin-dependent kinase 6 (CDK6) in LNCaP-PLA2R1. In LNCaP xenografts, PLA2R1-dependent regulation of clonogenicity appeared to outweigh the receptor’s pro-oncogenic properties, resulting in decreased tumour growth, supporting the tumour-suppressive role of PLA2R1. Alternatively, PC-3 Ctrl xenografts exhibited faster tumour growth compared to PC-3 KD cells, suggesting a pro-oncogenic effect of endogenous PLA2R1 expression. The differential growth-regulatory effects of PLA2R1 may be mediated by FN1, TWIST1, and CDK6 expression, although further investigation is required.

Publ.-Id: 28113 - Permalink


Electrochemical studies on zinc in boric acid containing electrolytes
Harm, U.; Kryk, H.; Hampel, U.;
During the sump recirculation phase after a leak in the primary cooling circuit of a pressurized water reactor (PWR), corrosion of hot-dip galvanized containment internals (e.g. grating treads, supporting grids of sump strainers) in the boric acid containing coolant may occur, which could later cause problems due to the possible precipitation of formed zinc borates (fouling) at hot regions of the reactor core [1, 2].
Beside other safety related investigations, generic zinc corrosion studies in boric acid electrolytes were conducted to investigate the dependency of the zinc corrosion rates in PWR coolants on different boundary conditions (fluid temperatures, pH, boric acid concentration, flow conditions nearby the zinc surface).
Corrosion experiments with dipped zinc sheets in stirred boric acid solutions already had shown that moderate variations of the fluid temperatures or the boric acid content only caused small changes in resulting zinc corrosion rates, but an increase of flow rates or turbulences often led to significantly increased corrosion rates [2].
For a better understanding of these results, additionally, some series of electrochemical measurements were carried out using a rotating disc electrode (zinc) as working electrode, a platinum counter electrode and tempered aqueous boric acid solutions (plus 0.1 M Na2SO4 as conducting salt) as electrolyte. Linear anodic and cathodic polarization was realized (up to potentials of 200 mV different from the free corrosion potential) under variation of fluid temperature (20 to 60 °C), boric acid content (1000 to 3000 ppm boron), pH (4.7 to 7) and the rotation speed.
First results of these experiments (e.g. comparing tafel plots) showed similar dependencies of the zinc corrosion rates than described above for the zinc dissolution experiments. The cathodic polarization curves mostly showed a plateau of the current densities with increasing cathodic polarization (overvoltage) indicating a strong control of the cathodic reaction (and thus the corrosion process as a whole) by the transport limitation of the dissolved oxygen to the zinc surface. Comparison of the tafel plots resulting from measurements at different rotation speeds (similar otherwise conditions) also demonstrated a strong increase of the zinc corrosion rates with increasing flow rates. For example, calculated zinc corrosion rates for infinite high rotation speeds (Levich extrapolation) usually are more than ten times higher compared to those of similar experiments without rotation. Therefore, also these results of the electrochemical investigations confirm the earlier results of a transport controlled corrosion process (see above) and may help to quantify the possible ranges of resulting corrosion rates at different boundary conditions.
This work is funded by the German Federal Ministry of Economic Affairs and Energy (BMWi) with the grant number 1501496 on the basis of a decision by the German Bundestag.

[1] Seeliger, A.; Alt, S.; Kästner, W.; Renger, S.; Kryk, H.; Harm, U.: Zinc corro¬sion after loss-of-coolant accidents in pressurized water reactors - thermo- and fluid-dynamic effects. Nuclear Engine-ering and Design, 2016, 305, 489-502
[2] Harm, U.; Kryk, H.; Hampel, U.: Generic Zinc Corrosion Studies at PWR LOCA Conditions. Annual Meeting on Nuclear Technology (AMNT 2017), 2017
Keywords: Nuclear energy; corrosion; zinc release; electrochemistry; experiments
  • Poster
    Electrochemistry 2018, 24.-26.09.2018, Ulm (Universität Ulm), Deutschland

Publ.-Id: 28112 - Permalink


Impact of membrane biofouling in the sequential development of performance indicators: feed channel pressure drop, permeability, and salt rejection
Siebdrath, N.; Farhat, N.; Ding, W.; Kruithof, J.; Vrouwenvelder, J. S.;
Biofouling development is affected by a variety of factors that change over the length of membrane modules in pressure vessels. Spatially resolved biofouling formation was studied under conditions representative to practice using a validated one-meter Long Channel Membrane Test Cells (LCMTCs), enabling the monitoring of permeability and salt rejection for five segments over the test cell length. Biofouling was induced by dosing an easily assimilable substrate to the feed water. The impact of biofouling on membrane performance was investigated spatially resolved as indicated in feed channel pressure drop over four LCMTCs and as indicated in permeability and salt rejection over five segments of each LCMTC. Results showed that all membrane performance indicators: feed channel pressure drop, permeability and salt rejection were impacted by biofouling formation. The feed channel pressure (FCP) drop increase was impacted earliest and strongest followed by permeability and salt rejection decline, underlining that FCP drop is a sensitive biofouling monitoring indicator. Spatially resolved biofouling investigations revealed that most biofouling was formed in the lead sections of membrane installations with a decreasing gradient over length, linked to substrate availability in the system. In this study, FCP drop played a crucial role: the severe FCP drop increase at the lead parts of the membrane installation caused performance losses in flux and salt rejection at the tail parts of the membrane installation. Minimizing the effect of biofouling on membrane performance should be pursued by a combination of strategies involving (i) early detection and preventive cleaning, (ii) substrate limitation for delaying biofouling built-up and (iii) optimized (early) cleaning procedures for more effective biofilm removal.
Keywords: Biofouling, Reverse Osmosis, Feed channel pressure drop, Permeability, Salt rejection, Long channel membrane test cell.

Publ.-Id: 28111 - Permalink


Role of surface characteristics on bubble growth during subcooled nucleate boiling on vertical heaters.
Sarker, D.; Ding, W.; Hampel, U.;
Bubble growth dynamics is one of the key issues of the nucleate boiling heat transfer. There are few attempts to include the role of heater surface characteristics in the bubble growth models. The present work is focused on qualitatively assessing such effects on the bubble growth by a microlayer thickness constant, C_eff. A competent bubble growth model and high resolution experimental data of the steam bubble growth from our former studies have assisted this investigation. The bubble growth model is formulated considering the evaporation of microlayer beneath the bubble base, heat diffusion at the bubble surface and condensation at the bubble cap. We have found that the values of C_eff are lower and the growth rates of bubble prior to departure are greater at the root mean square roughness height of around Sq≈0.13 μm for low- and well-wetting surfaces. Finally, a generalized equation of C_eff is proposed which comprise the effects of surface roughness and wettability on the bubble growth. The findings are useful for improving the bubble growth models and in designing the heater surface in future.
Keywords: bubble growth model; surface wettability; optimal roughness height; microlayer evaporation.

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  • Secondary publication expected from 05.05.2020

Publ.-Id: 28110 - Permalink


Investigations on the effects of heater surface characteristics on the bubble waiting period during nucleate boiling at low subcooling
Sarker, D.; Ding, W.; Franz, R.; Varlamova, O.; Kovats, P.; Zähringer, K.; Hampel, U.;
In nucleate boiling the ‘bubble waiting period’, that is, the time duration between the departure of a grown bubble and the start of the formation of a new bubble from a cavity, plays a crucial role for the total heat transfer. Experiments were performed to study the influence of the heater surface characteristics on this parameter. A femtosecond pulsed laser was used to produce nano- and micro-patterned surfaces with roughness in the range of micrometers on stainless steel heater surfaces. Boiling experiments were conducted on a vertically oriented heater at atmospheric pressure and with degassed deionized water. Bubble generation, departure, sliding, detachment and inception of the next bubble have been recorded by high-resolution optical shadowgraphy. Bubble waiting periods were found to be longer for low-wettability smooth and rough surfaces. High-wettability rough surfaces showed a shorter bubble waiting period. The shortest (approximately 3 ms) and the longest (approximately 30 ms) bubble waiting periods were found for well-wetting surfaces with Sq = 0.18 µm and for low-wetting surfaces with 0.12 µm, respectively. These corresponding roughness heights are denoted as ‘optimal roughness heights’.
Keywords: Bubble waiting periodSurface wettabilityRoughnessVertical heaterNucleate boiling

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  • Secondary publication expected from 06.10.2019

Publ.-Id: 28109 - Permalink


Microbial and vegetal life in the near- and far-field of a nuclear waste repository
Raff, J.; Krawczyk-Bärsch, E.;
One of the so far unanswered question related to a nuclear waste repositiory is how big is the influence of biosystems on the safety of such a repository. Although this question can not be answered at this time, ongoing researches adress the questions of who lives in the possible host rocks, how do these organisms interact with radionuclides and what is their impact on the geochemical conditions there during the operation of a repository. This includes also researches on the microbial diversity in backfill materials such as bentonite and the microbial influence on their properties, e.g. swelling capacity and hydraulic conductivity. In addition, various procaryotic and eucaryotic organisms in the far-field of a repository, namely bacteria, fungi and plants, are currently being investigated for their interaction with radionuclides and their influence on radionuclide migration. The latter includes also a possible radionuclide entry into the food chain. The goal is to identify dominant processes and to understand them on a molecular level. Ultimately, this will allow to derive biological parameters which are suitable to be included in the radionuclide transport modeling. Identified processes will also be considered for the development of remediation concepts for the purification of contaminated water and soil.
In the second part of the talk, the interaction of uranium and neptunium with bacteriogenic iron oxides precipitates, formed by the ferrous oxidizing and stalk-forming bacterium Gallionella ferruginea from a granitic host rock, is presented in more detail. This work shows that bacteriogenic iron oxides have a high potential to immobilize radionuclides in nuclear waste repositories.
Keywords: nuclear waste repositiory, biogeochemistry, migration
  • Lecture (others)
    Scientific Seminar, 11.10.2018, Cadarache, Frankreich

Publ.-Id: 28108 - Permalink


Molekulare Geochemie für das nukleare Endlager
Schmidt, M.ORC
In diesem Überblicksvortrag werden wissenschaftliche Fragestellungen zur Endlagerung hochradioaktiver Abfälle diskutiert. Die Komplexität des geotechnischen und -chemischen Systems inbesondere im Bezug zur Rückhaltung der minoren Actiniden und Plutonium wird dargestellt, um die Notwendigkeit für ein molekulares Prozessverständnis darzulegen. Letztlich wird an Beispielen diskutiert wie dieses Prozessverständnis erhalten werden kann und wie es zur Langzeitsicherheitsanalyse beiträgt.
Keywords: Endlager, Geochemie, Actiniden, molekulares Prozessverständnis
  • Invited lecture (Conferences)
    50. Kraftwerkstechnisches Kolloquium, 23.-24.10.2018, Dresden, Deutschland

Publ.-Id: 28107 - Permalink


Experimental assessment of inter-centre variation and accuracy in SPR prediction within the EPTN
Peters, N.; Wohlfahrt, P.; Bolsi, A.; de Marzi, L.; Ellerbrock, M.; Fracchiolla, F.; Free, J.; Gomà, C.; Góra, J.; Kajdrowicz, T.; Mackay, R.; Molinelli, S.; Nørrevang, O.; Rinaldi, I.; Rompokos, V.; Dahlgren, C. V.; van der Tol, P.; Vermeren, X.; Richter, C.;
Purpose/Objective:
The standard approach for CT-number to stopping-power-ratio (SPR) conversion in particle therapy is the use of a heuristic stepwise translation, a so-called Hounsfield look-up table (HLUT). It is defined by each treatment facility individually and depends on both the calibration method and CT scan protocol. A recent survey has shown broad variability in these parameters [1], making a simple comparison on HLUT level unfeasible. Hence, we present a comprehensive experimental evaluation of inter-centre variation and absolute accuracy in SPR prediction within the European Particle Therapy Network.

Material/Methods:
A head and a body phantom with 17 tissue surrogate inserts were scanned consecutively at the participating centres using their individual clinical scan protocol. The inserts were tissue-equivalent concerning particles; their composition and SPR were blinded for the participants. The SPR calculation was performed using each centre’s CT scan and HLUT (Fig.1).The inter- centre variation and absolute accuracy in SPR prediction were quantified for each tissue surrogate individually and then summarised into the relevant tissue groups: lung, soft tissues and bones. Finally, to evaluate the integral effect on range prediction for typical clinical beams traversing different tissues, for three simplified beam paths the determined SPR deviations were accumulated according to their respective tissue distribution. So far, data from 9 out of 17 participating centres was available.


Results:
A 2σ inter-centre variation in SPR prediction of 5.7% and 5.5% relative to water was determined for the bone inserts in the head and body setup, respectively. Comparable results were achieved for the lung tissue surrogates (6.4% and 2.2%). In the soft tissue region an overall higher accuracy was achieved with a variation below 0.9% in both setups and a mean SPR prediction accuracy below 0.5%. In the head setup, both lung tissues and bones were overestimated in most centres, while in the body setup the bones were underestimated (Fig. 2A). For the three exemplary beam paths, inter-centre variations in relative range were 1.5% on average. In specific centres, range deviations from reference exceeded 1.5% (Fig 2B).

Conclusion:
Large inter-centre variations in SPR prediction were observed in low- and high density tissue surrogates. The differences in deviation for bone between the two setups indicate a strong influence of scanning parameters such as the level of beam hardening correction, potentially resulting in range shifts of clinical relevance. As the study allows for a direct attribution of the measured deviations to the calibration methods and scan protocols used by the individual centres, it stresses the need for inter-centre standardisation. While this work addresses the accuracy in SPR prediction under idealised study conditions, a direct conclusion on overall range accuracy in patients is not possible. The study is currently still ongoing.

[1] Taasti et al. 2018, phiRO 6 25-30
  • Lecture (Conference)
    European Society for Radiation & Oncology Congress 2019 ESTRO 38, 26.-30.04.2019, Milano, Italia

Publ.-Id: 28106 - Permalink


Industrial flowsheeting and thermo-economic assessment
Reuter, M. A.; Llamasa, A. A.;
Session 2 was organised by the SOCRATES project. SOCRATES studies the development of near-zero waste processes for the recycling of low-grade metal containing industrial waste streams, such as bottom ashes, copper tailings and slags and sludges from the non-ferrous industry, commonly deposited in industrial landfills and tailing ponds. Markus Reuter and Alejandro Abadias (Helmholtz-Zentrum Dresden-Rossendorf, Germany) illustrated how novel near-zero waste flowsheets for the treatment of these residues are assessed within the SOCRATES project. Focus of the session was on the primary copper production flowsheet (from rock to metal), in which two scenarios were compared, being production of copper without treatment of wastes and with additional metal recovery from wastes (slags and drosses). The analysis was performed through composing a mass and energy balance of the flowsheet and performing an exergy analysis and life cycle assessment.
Keywords: near-zero waste, recycling, SOCRATES
  • Lecture (others)
    Summer school 2018: “To mine or not to mine”, 10.-12.09.2018, Leuven, Belgien

Publ.-Id: 28105 - Permalink


The limits of the Circular Economy
Reuter, M. A.;
-> Circular Economy (CE) - The origins
-> Circular Economy Engineering (CEE)
-> Metallurgical Internet-of-Things (m-IoT) - Comprehensive flowsheets that integrate product design with physical separation and process metallurgy
-> informing Resource Efficiency (iRE)
Fairphone / Plasma furnace for battery smelting
Keywords: Circular Economy, Circular Economy Engineering, Metallurgical Internet-of-Things, Resource Efficiency, Fairphone
  • Lecture (others)
    Circular Economy of EV Batteries - Workshop, 24.-25.05.2018, Espoo, Finnland

Publ.-Id: 28104 - Permalink


Process Model Based LCA Using HSC Chemnistry Software
Reuter, M. A.; Roine, A.;
The process industry defines the initial LCA values that are used for raw materials in the manufacturing industry. Plant vs Factory!
If we are talking about the circular economy and the whole value chain, then we must also take into account the effect of the process industry and recycling. This is the only way to minimize total environmental footprints.
Keywords: circular economy, recycling, environmental footprints
  • Lecture (others)
    LCA Course SusCriMat - Winterschool, 15.-19.01.2018, Les Diablerets, Schweiz

Publ.-Id: 28103 - Permalink


Urban Mining: Dream or Reality – The Limits and opportunities of the Circular Economy
Reuter, M. A.;
The circular economy will play an important role in shaping a resource-efficient society. Enabling this transformation from a linear to a circular economy requires precise quantification of resource efficiency and thus the economic viability of the system.

Based on the development of simulation tools of classical minerals processing and process metallurgy, the HSC Sim (www.outotec.com) simulation platform could be further developed, gleaning from many academically published works of the authors. This permits the simulation of the circular economy system and to subsequently calculate its resource efficiency. It for example also enables the estimation of a simulation-based recycling index of a product from the "Bill of Material" and "Full Material Declaration". It is a unique methodology for "Design for Recycling".

Figure 1 shows that a key to this simulation is a detailed understanding of the mineralogy as well as the limits of the circular economy system and its many products, materials and systems. In addition, a detailed understanding and quantification of the thermodynamic properties of the system is key to understanding its economics. With this approach, we will show the actual losses of the "circular economy" system and thus illuminate the limits and hence explore in detail if Urban Mining is a dream or economic reality.
Keywords: Fairphone, recycling, circular economy
  • Invited lecture (Conferences)
    EuroScience Open Forum, 09.-14.07.2018, Toulouse, Frankreich

Publ.-Id: 28102 - Permalink


Bubble Generation by Micro-Orifices with Application on Activated Sludge Wastewater Treatment
Mohseni, E.ORC; Herrmann-Heber, R.; Reinecke, S. F.; Hampel, U.

We studied the initial gas dispersion performance of diffuser concepts based on micro-orifices and needles with very fine orifice diameters in the range from 30 µm to 200 µm, as such diffusers are currently in discussion for energy-efficient wastewater treatment plants. To evaluate the performance of these micro-orifices, we compared them with industrial rubber membrane diffusers with respect to Sauter mean bubble diameter, pressure drop, frequency of bubble formation, oxygen transfer rate, and power demand for air compression. Our study revealed that, in comparison with rubber membrane diffusers bubbles generated from the micro-orifices transfer up to 82% more oxygen content into the continuous phase at up to 75% less power demand. Moreover, these micro-orifices are able to produce bubble sizes in the same range as the needle diffusers at 60% less pressure drop and 60% higher bubble generation frequency. Therefore, we also expect an improvement in the oxygen transfer coefficient KLa and standard oxygen transfer efficiency SOTE compared to commercial rubber membrane diffusers.

Keywords: Bubble Generation, Micro-orifices, Aeration, Biological Wastewater Treatment, Rubber Membrane Diffusers, Oxygen Transfer
Related publications
Bubble Generation by Micro-Orifices with Application on … (Id 28585) is documented by this publication
  • Reseach data in the HZDR data repository RODARE
    Publication date: 2018-10-23
    DOI: 10.14278/rodare.63

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Publ.-Id: 28100 - Permalink


ASTEC model of the THS-15 test facility and first simulation results
Jobst, M.;
In the framework of the NuWaMa project (Expansion of a German-Czech Collaboration in the Field of Nuclear Waste Management), a research stay at ÚJV Řež (Czech Republic) took place during May 2018 (from 1st of May till 31st of May). The objective of the research stay was the development of a numerical model of the thermal-hydraulic test facility THS-15, which had been put in operation at the ÚJV site in Řež recently in order to investigate phenomena related to ex-vessel cooling for in-vessel retention of molten corium. Assessing the performed experiments with the help of the numerical model is an important contribution to a comprehensive under-standing of the observed phenomena. The current state of the ASTEC model and the first calculation results are presented.
Keywords: VVER; in-vessel melt retention; THS-15 test facility; ASTEC; numerical simulation; critical heat flux
  • Lecture (Conference)
    ASTEC Users' Club Meeting, 09.-11.10.2018, Aix-en-Provence, République française

Publ.-Id: 28099 - Permalink


Ideal flow regimes of gas spargers: Towards optimal gas bubble generation for biological wastewater treatment
Mohseni, E.ORC; Reinecke, S.; Hampel, U.
Gas bubble dispersion is involved within a large number of chemical, biochemical, and other processes. Of particular importance is the dispersion of air bubbles in the activated sludge process in biological wastewater treatment plants. This is an expensive procedure, which is responsible for the largest share of energy bill in the whole WWTP in the range 45% to 75%. The rubber membrane diffusers, which are currently used for aeration in the treatment facilities, offer relatively low standard oxygen transfer efficiency in range of 40-60 %, which is mainly due to generation of large bubble sizes. Among the parameters which influence the system efficiency, bubble size is of great importance, since it directly influences the gas holdup and the bubble residence time. Moreover, bubble size determines the surface area to volume ratio, which affects the volumetric oxygen transfer coefficient and oxygen transfer rate. Bubble formation is mainly studied at openings bigger than 1 mm. Hence, the leverage of sub-millimeter orifices on volume of the final bubble is still not understood. Current endeavor focuses on bubble formation from submerged orifices under constant flow condition. Subsequently a set of experiments is design to capture the bubble generation from small orifices in the range of 20-800 μm diameter. The initial bubble size was measured by means of a high-resolution optical measurement technique. Changes in the mechanism of bubble formation and detachment within the dynamic bubbling regime were monitored and reported over a progressive trend of the volumetric gas flow rate.
Keywords: Bubble Generation, Bubbling Regime, Activated Sludge, Aeration, Biological Wastewater Treatment
  • Contribution to proceedings
    10th IWA Eastern European Young Water Professionals Conference, 10.-11.05.2018, Zagreb, Croatia

Publ.-Id: 28098 - Permalink


Optimization of the Aeration System in Municipal Wastewater Treatment Plant
Mohseni, E.ORC; Reinecke, S.; Hampel, U.
Optimal bubble generation for biological aeration process is currently under discussion. We studied bubble formation from a range of solid orifices, from 20 µm to 800 µm, submerged in water under constant flow condition. Scant experimental data is available within this range. We studied the change in the mechanism of bubble formation and detachment at different bubbling regimes. Moreover, the existing theoretical and empirical models for prediction of initial bubble size were evaluated according to the corresponding experimental data. A modified model for prediction of initial bubble size is proposed from the best fit of experimental results. Finally, we introduced another empirical model for prediction of optimal operation condition according to consumption of 95% oxygen uptake from air bubbles in water. In the later model, parameters such as pressure drop of the system, capacity of aeration basin, and available specific aeration area for oxygen transfer are adopted.
Keywords: Bubble Generation, Activated Sludge, Aeration, Biological Wastewater Treatment, Multiphase Flow
  • Poster
    12th HZDR PhD Seminar, 16.-18.10.2017, Seiffen, Germany

Publ.-Id: 28097 - Permalink


Formation and characterization of shallow junctions in GaAs made by ion implantation and ms-range flash lamp annealing
Duan, J.; Wang, M.; Vines, L.; Böttger, R.; Helm, M.; Zeng, Y. J.; Zhou, S.; Prucnal, S.;
With the demand of aggressive scaling in nanoelectronics, further progress can be realized by integration of high mobility semiconductors, such as III-V compound semiconductors, with complementary metal-oxide-semiconductor (CMOS) technology. In this study we present the formation of shallow n-p and p-n junctions in GaAs utilizing ion implantation of S and Zn, respectively, followed by millisecond-range flash lamp annealing (FLA). The distribution of implanted elements obtained by Secondary Ion Mass Spectrometry (SIMS) shows that the FLA process can effectively suppress the diffusion of dopants. Simultaneously, the ms-range annealing is sufficient to recrystallize implanted layer and to activate the dopants. Formation of p-n and n-p junctions is confirmed by current-voltage characteristics. The on/off-current ratio can reach up to 1.7×107 in the n-GaAs:Zn case.
Keywords: GaAs, shallow junction, ion implantation, flash lamp annealing

Publ.-Id: 28096 - Permalink


Jump Rope Vortex in Liquid Metal Convection
Vogt, T.; Horn, S.; Grannan, A. M.; Aurnou, J. M.;
The large-scale circulation (LSC) is the key dynamical feature of turbulent thermal convection. It is the underlying structure that shapes the appearance of geo- and astrophysical systems, such as the solar granulation or cloud streets, and the cornerstone of theoretical models. Our laboratory-numerical experiments reveal for the first time that the LSC can perform a fully three-dimensional motion resembling a twirling jump rope.
The discovery of this novel LSC mode implies that the currently accepted paradigm of a quasi-planar oscillating LSC needs to be augmented. Moreover, it provides an important link between studies in confined geometries used in experiments and simulations and the virtually unconfined fluid layers in natural settings where an agglomeration of LSCs forms larger patterns.
Keywords: thermal convection, turbulence, coherent structures, liquid metals
  • Open Access LogoProceedings of the National Academy of Sciences of the United States of America 115(2018)50, 12674-12679
    DOI: 10.1073/pnas.1812260115

Publ.-Id: 28095 - Permalink


The role of open-volume defects in the annihilation of antisites in a B2-ordered alloy
Ehrler, J.; Liedke, M. O.; Cizek, J.; Boucher, R.; Butterling, M.; Zhou, S.; Böttger, R.; Hirschmann, E.; Trinh, T. T.; Wagner, A.; Lindner, J.; Fassbender, J.; Leyens, C.; Potzger, K.; Bali, R.;
The atomic arrangement in certain B2-ordered alloys, such as Fe60Al40, determines intrinsic material properties like magnetism. Here we have investigated the influence of open-volume defects on the atomic ordering process at elevated temperatures in Fe60Al40 thin films. A dependence of the ordering process on the type and concentration of defects is observed by positron annihilation spectroscopy combined with ab-initio calculations. Comparing the lifetimes of positrons in the alloy for different annealing and irradiation treatments reveals the role of mono-vacancies, triple defects as well as large vacancy clusters: The rate of atomic ordering to the ordered B2 state is increased in the presence of mono-vacancies whereas triple defects and vacancy complexes decrease the ordering rate. Furthermore, an agglomeration of vacancies during annealing to di-vacancies and larger vacancy clusters is observed. The distribution of open-volume defects can be modified in such a way as to control the thermal stability via ion-irradiation and thermal pre-treatments.
Keywords: Order-disorder phenomena, Vacancies, Lattice defects, Reordering, Positron Annihilation Spectroscopy

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  • Secondary publication expected from 26.06.2020

Publ.-Id: 28092 - Permalink


Microstructure, strengthening mechanisms & properties of ODS alloys developed under MatISSE project
Chauhan, C.; Bergner, F.; Etienne, A.; Aktaa, J.; de Carlan, Y.; Heintze, C.; Litvinov, D.; Hernandez-Mayoral, M.; Oñorbe, E.; Radiguet, B.; Ulbricht, A.;
The invited talk aims at summarizing results from a publication that received the best paper award 2017 of the Journal of Nuclear Materials. Microstructure, strengthening mechanisms and properties of ODS alloys are addressed.
Keywords: ODS alloys, microstructure characterization, strengthening mechanisms
  • Invited lecture (Conferences)
    NuMat2018: The Nuclear Materials Conference, 14.-18.10.2018, Seattle, USA

Publ.-Id: 28091 - Permalink


High Energy Fast X-ray Tomography
Barthel, F.; Windisch, D.; Hampel, U.;
Ultrafast X-ray computed tomography with ROFEX scanners has become a common tool for investigations of multiphase phenomena in science and industrial application within recent years. Though being very successful in giving unprecedented insights into dynamic processes, ROFEX scanners yet have some limitations in terms of permissible sizes and density of the investigated objects. Due to the limited penetration capability of X-rays at photon energy of up to 150 keV experimental mock-ups need to be made out of light construction materials and many experimental setups had to be scaled down from their real size to fit into the scanner. Often this limits the transferability of results to larger industrial facilities.
This contribution introduces the new High-Energy Computed Tomography scanner of Rossendorf (HECToR) as the next step towards improved industrial applicability. The facility utilizes a 1 MeV electron accelerator with a continuous beam power of up to 100 kW. The functional principle has been adapted from the ROFEX scanners. HECToR is able to scan objects with a maximum diameter of 400 mm at a temporal resolution of up to 5000 frames per second and with a spatial resolution of 3 mm at best conditions. The paper introduces the scanner concept, its components and presents first dynamic studies on generic two-phase flows in steel vessels. Furthermore, the imaging characteristics are discussed in detail.
Keywords: ROFEX, ultrafast X-ray CT, high energy, HECToR
  • Contribution to proceedings
    9th World Congress on Industrial Process Tomography, 02.-06.09.2018, Bath, UK
    Proceedings of the 9th world cogress on industrial process tomography
  • Lecture (Conference)
    9th World Congress on Industrial Process Tomography, 02.-06.09.2018, Bath, UK

Publ.-Id: 28090 - Permalink


Review Article: Review of electrohydrodynamical ion sources and their applications to focused ion beam technology
Gierak, J.; Mazarov, P.; Bruchhaus, L.; Jede, R.; Bischoff, L.;
In this article, the authors review, compare, and discuss the characteristics and applicative potential of a variety of nongallium ion liquid metal ion sources they have developed and successfully applied to nanopatterning. These sources allow generating on-demand ion beams and are promising for extending focused ion beams applications. They detail the operating characteristics of such sources capable to emit metal projectiles ranging from atomic ions with different charge states to polyatomic ions and to large metal clusters having sizes up to a few nanometers. They highlight their interest and relevance to current nanoscience challenges in terms of ultimate patterning or bottom-up nanofabrication capabilities.
Keywords: Liquid Metal Ion Source, nongallium, nanoscience
  • Open Access LogoJournal of Vacuum Science & Technology B 36(2018)6, 06J101-1-06J101-6
    DOI: 10.1116/1.5047150

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Publ.-Id: 28088 - Permalink


Forschungsdatenmanagement am Helmholtz-Zentrum Dresden-Rossendorf und am Helmholtz-Zentrum Berlin (RDM@DB)
Konrad, U.ORC; Görzig, H.; Juckeland, G.
Das BMBF Verbundprojekt RDMatDB wird im Rahmen der Förderrichtlinie "Erforschung des Managements von Forschungsdaten in ihrem Lebenszyklus“ realisiert. Ziel des Projektes ist es, Forschungsdaten-Management-Lösungen zu entwickeln, die das HZDR und HZB als Betreiber von Infrastrukturen in die Lage versetzen, die sich aus den FAIR-Prinzipien des Datenmanagements ergebenden Anforderungen zu erfüllen. Im dem Vortrag auf der BMBF-Veranstaltung "Forschungsdatenmanagement - künftige Entwicklungen und aktuelle Fragen der Wissenschaft" wird das Projekt und die Perspektiven vorgestellt.
Keywords: The BMBF joint project RDMatDB of the HZDR and HZB is implemented within the scope of the funding program "Research on the management of research data in its life cycle ". The goal of the project is to develop research data management solutions which the HZDR and HZB consider to meet the requirements of the FAIR data management principles. The project and perspectives are presented at the BMBF event "Research Data Management - Future Developments and Current Issues of Science".
  • Invited lecture (Conferences)
    Forschungsdatenmanagement - künftige Entwicklungen und aktuelle Fragen der Wissenschaft, 17.-18.10.2018, Berlin, Deutschland
    DOI: 10.14278/rodare.62

Publ.-Id: 28087 - Permalink


Influence of the magnetic field on the stability of the multiferroic conical spin arrangement of Mn0.80Co0.20WO4
Urcelay-Olabarria, I.; Ressouche, E.; Ivanov, V. Y.; Skumryev, V.; Wang, Z.; Skourski, Y.; Balbashov, A. M.; Popov, Y. F.; Vorob'En, G. P.; Qureshi, N.; Garcia-Munoz, J. L.; Mukhin, A. A.;
The evolution of the low temperature antiferromagnetic conical (characterized by two, commensurate and incommensurate propagation vectors), and the high temperature collinear spin arrangements of the 20% Co-doped MnWO4 multiferroic has been studied in the presence of magnetic field up to 60 T by means of macroscopicmagnetic and pyroelectricmeasurements, and by neutron diffraction experiments in fields up to 12 T on a single crystal. The complete magnetoelectric phase diagrams for magnetic fields along distinct magnetic directions with respect to the spin structure have been constructed up to magnetic field values exceeding those necessary to induce a spin-flip transition into the paramagnetic state. The differences in the topology of the diagrams are discussed. The obtained results might be common for other magnetic materials possessing conical antiferromagnetic structures.

Publ.-Id: 28085 - Permalink


Anomalous Hall effect in Weyl semimetal half-Heusler compounds RPtBi (R = Gd and Nd)
Shekhar, C.; Kumar, N.; Grinenko, V.; Singh, S.; Sarkar, R.; Luetkens, H.; Wu, S.-C.; Zhang, Y.; Komarek, A.; Kampert, E.; Skourski, Y.; Wosnitza, J.; Schnelle, W.; Mccollam, A.; Zeitler, U.; Kübler, J.; Yan, B.; Klauss, H.-H.; Parkin, S. P.; Felser, C.;
Topological materials ranging from topological insulators to Weyl and Dirac semimetals form one of the most exciting current fields in condensed-matter research. Many half-Heusler compounds, RPtBi (R = rare earth), have been theoretically predicted to be topological semimetals. Among various topological attributes envisaged in RPtBi, topological surface states, chiral anomaly, and planar Hall effect have been observed experimentally. Here, we report an unusual intrinsic anomalous Hall effect (AHE) in the antiferromagnetic Heusler Weyl semimetal compounds GdPtBi and NdPtBi that is observed over a wide temperature range. In particular, GdPtBi exhibits an anomalous Hall conductivity of up to 60 Ω−1·cm−1 and an anomalous Hall angle as large as 23%.Muon spin-resonance (μSR) studies of GdPtBi indicate a sharp antiferromagnetic transition (TN) at 9 K without any noticeable magnetic correlations above TN. Our studies indicate that Weyl points in these half-Heuslers are induced by a magnetic field via exchange splitting of the electronic bands at or near the Fermi energy, which is the source of the chiral anomaly and the AHE.
  • Proceedings of the National Academy of Sciences of the United States of America 115(2018)37, 9140-9144
    DOI: 10.1073/pnas.1810842115

Publ.-Id: 28084 - Permalink


Low-Temperature Magnetic Hysteresis in Nd(Pr)-Fe-B Nanostructured Alloys with Nd2Fe14B Type Main Phase Composition
Neznakhin, D. S.; Politova, G. A.; Ivanov, L. A.; Volegov, A. S.; Gorbunov, D. I.; Tereshina, I. S.; Kudrevatykh, N. V.;
Magnetic hysteresis properties of nanostructured industrially manufactured Nd-Fe-B and Pr-Fe-B alloys on the base of a tetragonal Nd2Fe14B (2-14-1) hard magnetic phase (MQP-B, MQP-B+ and MQP-16-7 brands) have been investigated at 4.2 K in magnetic fields up to 58 T. The chemical composition of the alloys given in the certificates was defined more precisely. The grain sizes of the main 2-14-1 phase were determined. The average grain size is much smaller than a critical single domain diameter. Coercivity, remanence magnetization, saturation magnetization and maximal magnetic energy product were determined at 4.2 K and compared with those obtained at room temperature.

Publ.-Id: 28083 - Permalink


Millisecond Dynamics of the Magnetocaloric Effect in a First- and Second-Order Phase Transition Material
Döntgen, J.; Rudolph, J.; Gottschall, T.; Gutfleisch, O.; Hägele, D.;
The millisecond-dynamics of the magnetocaloric effect in Gd and La-Fe-Si-Mn, which exhibit first- and second-order phase-transitions, respectively, are investigated. Direct measurements of the adiabatic temperature change ΔT are obtained from modulation infrared thermometry with field-cycling frequencies exceeding 1 kHz at amplitudes of up to 45 mT. The peak amplitude of ΔT(T) shows a dependence on sample thickness and decreases with increasing modulation frequency for both materials despite a frequency independent susceptibility of Gd. The adiabatic DT depends quadratically on the external field for Gd while La-Fe-Si-Mn shows a peculiar bucket-shaped curve for temperatures below the peak maximum. A comparative study of non-caloric samples shows that dissipative heating by eddy currents or magnetic hysteresis does not explain the observed behavior. The transient ΔT(t) instead suggests a mechanism involving strong temperature gradients at the ferromagnetic–paramagnetic boundaries and underlines the importance of further dynamical studies for a fundamental understanding of the magnetocaloric effect in first-order materials.

Publ.-Id: 28082 - Permalink


Molecular interaction of fungi with uranium
Wollenberg, A.; Merroun, M.; Günther, A.; Raff, J.; Stumpf, T.;
The radioactive and toxic element uranium is mined in large quantities, for example for industrial or research purposes, and subsequently stored as waste. This increases the risk of anthropogenic release into the environment, where it can enter the groundwater and thus the food chain through leaching and migration. However, the surrounding microbial community can influence the migration behavior of uranium. An important part of this community are fungi that can interact with uranium through various processes such as sorption, accumulation or mineralization. These processes can restrict the mobility of uranium and prevent migration into the waterways and subsequently the food chain.
The aim of this study is to investigate the potential of fungi for precautionary radiation protection methods or even bioremediation procedures for contaminated soils. In assessing the suitability of fungi, the first task is to investigate the molecular interactions with uranium in detail. For this purpose, binding experiments with the two fungi Schizophyllum commune and Leucoagaricus naucinus are conducted in various media to determine the influence of the environment on the uranium binding behavior of fungi. Time-resolved laser-induced fluorescence spectroscopy was used to investigate the speciation of fungal bound uranium. Furthermore, the location of bound uranium was determined using transmission electron microscopy with energy dispersive X-ray spectroscopy. In addition, microcosm experiments were carried out with soil to investigate the interactions of fungi with uranium under natural conditions.
The results so far show that the uranium binding of the fungi is very different but largely independent of the surrounding medium. This suggests that the interactions are mainly determined by the biochemistry of fungi.
Keywords: Fungi, Uranium, Interaction
  • Poster
    International conference Uranium biogeochemistry, 21.-26.10.2018, Ascona, Switzerland

Publ.-Id: 28081 - Permalink


Optimal beam loading in a nanocoulomb-class laser wakefield accelerator
Couperus, J. P.ORC
Laser plasma wakefield accelerators have seen tremendous progress in the last years, now capable of producing electron beams in the GeV energy range. The inherent few-femtoseconds short bunch duration of these accelerators leads to ultra-high peak-currents. Reducing the energy spread found in these accelerators, while scaling their output to hundreds of kiloampere peak current would stimulate the next generation of radiation sources covering high-field THz, high-brightness X-ray and -ray sources, compact free-electron lasers and laboratory-size beam-driven plasma accelerators. At such high currents, an accelerator operates in the beam loaded regime where the accelerating field is strongly modified by the self-fields of the injected bunch, potentially deteriorating key beam parameters. However, if appropriately controlled, the beam loading effect can be employed to improve the accelerator’s performance, specifically to reduce the energy spread.

In this thesis the beam-loading effect is systematically studied at a quasi-monoenergetic nanocoulomb-class laser wakefield accelerator. For this purpose, a tailored scheme of the self-truncated ionisation injection process is introduced for the non-linear bubble regime. This scheme facilitates stable and tunable injection of high-charge electron bunches within a short and limited time-frame, ensuring low energy spread right after injection. Employing a three millimetres gas-jet acceleration medium and a moderate 150 TW short pulse laser system as driver, unprecedented charges of up to 0.5 nC within a quasi-monoenergetic peak and energies of ~0.5 GeV are achieved. Studying the beam loading mechanism, it is demonstrated that at the optimal loading condition, i.e. at a specific amount of injected charge, performance of the accelerator is optimised with a minimisation of the energy spread. At a relative energy spread of only 15%, the associated peak current is around 10 kA, while scaling this scheme to operate with a petawatt driver laser promises peak-currents up to 100 kA.
Keywords: beam loading; plasma acceleration; electron acceleration; LWFA; laser wakefield acceleration; LPA
  • Open Access LogoWissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-093 2018

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Publ.-Id: 28080 - Permalink


Experimental investigation of bubble breakup in bubble chains rising in a liquid metal
Keplinger, O.; Shevchenko, N.; Eckert, S.;
The process of bubble breakup in a liquid metal was studied by X-ray radiography and high-speed video imaging. Argon gas bubbles were injected through a single orifice at the bottom of a rectangular vessel filled with the eutectic GaInSn alloy. Moderate gas flow rates were applied at isothermal conditions resulting in the formation of bubble chains. The bubble breakup events observed in the chosen experimental geometry were mainly initiated by bubble collisions or by the effect of local shear flow. We present experimental results accompanied by statistical analysis of the bubble breakup frequency, number of daughter bubbles and their size distribution, bubble velocities before and after the breakup process for a broad range of Argon gas flow rates.
Keywords: Liquid metal; Two-phase flow; Bubble chain; Bubble breakup; X-ray radiography.

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  • Secondary publication expected from 04.04.2020

Publ.-Id: 28079 - Permalink


Bubble motion in liquid metal with and without a magnetic field
Keplinger, O.; Shevchenko, N.; Eckert, S.;
Liquid metal two-phase flows are widely used in metallurgical processes. For example Argon gas bubbles are injected into a bulk liquid to enhance mixing and homogenization of the melt. Also the Argon gas bubbles remove undesired inclusions by transporting them towards the slag layer at the free surface improving the melt cleanliness. This process is highly dependent both on the properties of the inclusions and on the size and surface characteristics of the dispersed gas phase. The bubble size distribution and interfacial area inside the melt are strongly influenced by the bubble coalescence and breakup which are controlled by the turbulent flow that develops inside the melt. In order to improve the final product quality an external magnetic field is applied to control the fluid motion and bubble behavior. Despite an increasing number of numerical and experimental studies on bubble rise in liquid metals only few experimental data on bubble rise in the presence of a magnetic field exists. These works are mainly focused on investigations of single bubbles in the absence of turbulence. Since bubble rising dynamics in a bubble chain or cluster is often affected by bubble-wake and bubble-bubble interactions direct investigation of bubble chains and clusters rising in liquid metals under the influence of magnetic field becomes crucial.
Bubble chain ascending in non-transparent liquid metal under the influence of magnetic field was examined by X-ray radiography through high-speed video imaging. The Argon gas bubbles were injected through a single bevel-shaped nozzle positioned in the middle at the bottom of a flat Plexiglas vessel. The vessel was filled with eutectic GaInSn alloy at isothermal conditions. We present experimental results accompanied by statistical analysis of the bubble size distribution, shape deformation, velocities, etc. for Argon gas flow rates lying in the range 150-1200 cm³ /min. In general, the increase of the gas flow rate leads to increase in bubble size and velocity. In turn, the velocity shows periodic oscillations related to the zig-zag motion of the bubbles. Both the velocity and oscillation amplitude decrease with increasing the magnetic field strength. Bubble pairing regime appears at higher gas flow rates for bubbles moving in the magnetic field: at 400 cm³ /min against 300 cm³ /min for bubbles moving without magnetic field. Therefore, the appearance of bubble coalescence and breakup is also shifted to higher gas flow rates. The integral gas distribution for bubbles moving without magnetic field is symmetrical due to the bubble chain oscillation in the observation plane. In contrast, the bubbles move almost along the same bubble path in a magnetic field leading to the asymmetry of gas distribution. Further image processing reveals that the major axis of the ellipses fitted to the bubbles at moderate gas flow rates (≤400 cm³ /min) is aligned almost parallel to the bottom of the vessel in the presence of the highest magnetic field used in our experiments (for B ~270 mT). Also the bubble shape oscillations are damped with increasing magnetic field at moderate gas flow rates (≤400 cm³ /min) when the turbulence is strongly suppressed.
Keywords: Liquid metal; Two-phase flow; Bubble chain; Magnetic field; X-ray radiography.
  • Poster
    16th Multiphase Flow Conference & Short Course, 13.-16.11.2018, Helmholtz-Zentrum Dresden-Rossendorf, Germany

Publ.-Id: 28078 - Permalink


Deep-learning based estimation of loco-regional control for patients with locally advanced HNSCC
Starke, S.; Leger, S.; Zwanenburg, A.; Pilz, K.; Lohaus, F.; Linge, A.; Zöphel, K.; Kotzerke, J.; Schreiber, A.; Tinhofer, I.; Budach, V.; Stuschke, M.; Balermpas, P.; Rödel, C.; Ganswindt, U.; Belka, C.; Pigorsch, S.; Combs, S. E.; Mönnich, D.; Zips, D.; Krause, M.; Baumann, M.; Richter, C.; Troost, E. G. C.; Löck, S.;
Purpose/Objective: In order to improve radiotherapy outcomes, further treatment personalisation is considered beneficial. Radiomics analyses aim to predict treatment outcomes based on medical imaging data. Commonly, hand-crafted imaging features are used that require domain knowledge and further feature selection steps. This may cause relevant information to be lost. Deep convolutional neural networks (CNNs) on the other hand can act as automatic feature detectors and are able to learn highly nonlinear relationships directly from imaging data, thus addressing the drawbacks of conventional radiomics approaches and enabling end-to-end learning. We investigated whether CNNs are capable of quantifying loco-regional tumour control (LRC) based on CT imaging of patients with locally advanced head and neck squamous cell carcinoma (HNSCC).
Material/Methods: A multicentre cohort consisting of 302 patients with locally advanced HNSCC was collected and divided into an exploratory and a validation cohort (207 and 95 patients, respectively). All patients received a non-contrast-enhanced CT scan for treatment-planning and were treated by primary radio(chemo)therapy. 9725 transverse CT slices from the exploratory cohort were used to train a CNN with eight convolutional layers. For every patient (with one exception) we used 23 CT slices cranial and caudal of the slice with the largest tumour area, resulting in 47 slices per patient. Discriminative performance was evaluated using 4465 slices of the validation data set. The hazard of loco-regional recurrence was estimated by the CNN maximising the likelihood of the Cox proportional hazards model, which allows for incorporation of nonlinear relationships between the imaging features and the hazard prediction. The final hazard for every patient was obtained by averaging the results of the individual slices. The prognostic value of the model was evaluated by the concordance index (C-Index). Patients were stratified into groups of low and high risk of recurrence using the median hazard in the exploratory cohort.
Results: The validation of our CNN model revealed a C-Index of 0.68 (95% confidence interval: 0.57-0.79) for the prognosis of LRC. The estimated hazards were used to stratify patients into two risk groups. LRC significantly differed between these groups, both in the exploratory and the validation cohort (log-rank p<0.0001 and p=0.0005, respectively). Compared to previously published results with an average validation C-Index of 0.62 based on conventional radiomics [1], prognostic performance was slightly improved.
Conclusions: We showed that CNNs are capable of automatically stratifying patients with locally advanced HNSCC into high and low-risk groups for loco-regional tumour recurrence. The obtained results suggest that deep-learning based approaches can become useful for non-invasively evaluating individual recurrence risks encouraging future research in this area.
[1] Leger et al. Sci Rep 7: 13206 (2017).
Keywords: Deep-learning, HNSCC, loco-regional control, Radiomics
  • Lecture (Conference)
    ESTRO 38, 26.-30.04.2019, Mailand, Italien

Publ.-Id: 28076 - Permalink


Highly compliant planar Hall effect sensor with sub 200 nT sensitivity
Granell, P.; Wang, G.; Canon Bermudez, G. S.; Kosub, T.; Golmar, F.; Steren, L.; Fassbender, J.; Makarov, D.;
Being a facet of flexible electronics, mechanically reshapeable magnetic field sensorics enable novel device ideas for soft robotics, interactive devices for virtual- and augmented reality and point of care diagnostics. These applications demand mechanically compliant yet robust sensor devices revealing high sensitivity to small magnetic fields. To push the detection limit of highly compliant and linear magnetic field sensors to be in the sub-µT range, we explore a new fundamental concept for magnetic field sensing, namely the planar Hall effect in magnetic thin films. With their remarkable bendability down to 1 mm, these compliant planar Hall effect sensors allow for an efficient detection of magnetic fields as small as 20 nT. We demonstrate the application potential of these devices as a direction (angle) as well as proximity (distance) sensors of tiny magnetic fields emanating from magnetically functionalized objects. With their intrinsic linearity and simplicity of fabrication, these compliant planar Hall effect sensors have the potential to become a standard solution for low field applications of shapeable magnetoelectronics in point of care applications and on-skin interactive electronics.
Keywords: Flexible electronics, shapeable magnetoelectronics, planar Hall effect

Publ.-Id: 28075 - Permalink


Electronic-skin compasses for geomagnetic field driven artificial magnetoception and interactive electronics
Cañón Bermúdez, G. S.; Fuchs, H.; Bischoff, L.; Fassbender, J.; Makarov, D.;
Magnetoception is the ability to detect and respond to magnetic fields that allows certain organisms to orientate themselves with respect to the Earth’s magnetic field for navigation purposes. The development of an artificial magnetoception, which is based solely on an interaction with geomagnetic fields and can be used by humans, has, however, proved challenging. Here we report a compliant and mechanically robust electronic-skin compass system that allows a person to orient with respect to Earth’s magnetic field. The compass is fabricated on 6-μm-thin polymeric foils and accommodates magnetic field sensors based on the anisotropic magnetoresistance effect. The response of these compliant sensors is tailored to be linear and possess maximum sensitivity around the earth’s magnetic field by using geometric conditioning. Our approach can also be a used to create interactive devices for virtual and augmented reality applications, and we illustrate the potential of this by using our electronic-skin compass in the touchless-control of virtual units in a game engine.
Keywords: Flexible electronics, magnetic sensors, geomagnetic field, magnetoception, virtual reality

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Publ.-Id: 28074 - Permalink


Improving landslide susceptibility mapping using morphometric features in the Mawat area, Kurdistan Region, NE Iraq: Comparison of different statistical models
Othman, A. A.; Gloaguen, R.; Andreani, L.ORC; Rahnama, M.
Susceptibility mapping provides information about vulnerable locations and thus helps to potentially decrease infrastructure damage due to mass wasting. During the past decades, expansion of settlements into areas prone to landslides in Iraq has highlighted the importance of accurate landslide susceptibility studies. The main goal of this research is to implement selected morphometric parameters to improve prediction of landslide susceptibility in the Zagros Mountain region. We used the Mawat area, in the Kurdistan Region (NE Iraq) to test the added value of morphometric indicators. Sixteen morphometric factors, mainly derived from a Digital Elevation Model (DEM), extracted using the stereo-ability of the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) satellite, as well as geological and environmental predictive factors, were appraised. We evaluated and compared Frequency Ratio (FR), Weight of Evidence (WOE), Logistic Regression (LR) and Probit Regression (PR) approaches in combination with morphometric indices to determine the Landslide Susceptibility (LS). The areas under the curve (AUC) of the Prediction Rate Curve (PRC), Relative landslide density Index (R index), and True Positive Percentage (TPP) for the four models show that all models perform similarly, and the focus should be on careful selection of the predictive factors, which is far more important than the methods used. Results indicate that lithology and slope aspects are the more dominant factors that lead to detect possible occurrence of landslides. Furthermore, this work demonstrates that the hypsometric integral performs better than the commonly used slope curvature as a predictor and thus increases the prediction accuracy of the susceptibility map. We argue that the use of adequate morphometric parameters can increase the efficiency of the LS mapping in other regions of the world.
Keywords: Frequency ratio, Weight of evidence, Logistic regression, Probit regression, Landslide susceptibility (LS), Iraq

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Publ.-Id: 28073 - Permalink


Beyond a phenomenological description of magnetostriction
Reid, A. H.; Shen, X.; Maldonado, P.; Chase, T.; Jal, E.; Granitzka, P. W.; Carva, K.; Li, R. K.; Li, J.; Wu, L.; Vecchione, T.; Liu, T.; Chen, Z.; Higley, D. J.; Hartmann, N.; Coffee, R.; Wu, J.; Dakovski, G. L.; Schlotter, W. F.; Ohldag, H.; Takahashi, Y. K.; Mehta, V.; Hellwig, O.; Fry, A.; Zhu, Y.; Cao, J.; Fullerton, E. E.; Stöhr, J.; Oppeneer, P. M.; Wang, X. J.; Dürr, H. A.;
Magnetostriction, the strain induced by a change in magnetization, is a universal effect in magnetic materials. Owing to the difficulty in unraveling its microscopic origin, it has been largely treated phenomenologically. Here, we show how the source of magnetostriction—the underlying magnetoelastic stress—can be separated in the time domain, opening the door for an atomistic understanding. X-ray and electron diffraction are used to separate the sub-picosecond spin and lattice responses of FePt nanoparticles. Following excitation with a 50-fs laser pulse, time-resolved X-ray diffraction demonstrates that magnetic order is lost within the nanoparticles with a time constant of 146 fs. Ultrafast electron diffraction reveals that this demagnetization is followed by an anisotropic, three-dimensional lattice motion. Analysis of the size, speed, and symmetry of the lattice motion, together with ab initio calculations accounting for the stresses due to electrons and phonons, allow us to reveal the magnetoelastic stress generated by demagnetization.

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Publ.-Id: 28072 - Permalink


Measuring the thermal properties of anisotropic materials using beam-offset frequency domain thermoreflectance
Rahman, M.; Shahzadeh, M.; Braeuninger-Weimer, P.; Hofmann, S.; Hellwig, O.; Pisana, S.;
Thermoreflectance techniques have become popular to measure the thermal properties of thin films such as thermal conductivity and thermal boundary conductance (TBC). Varying the focused spot sizes of the beams increases the sensitivity to in-plane heat transport, enabling the characterization of thermally anisotropic materials. However, this requires realignment of the optics after each spot size adjustment. Offsetting the probe beam with respect to the pump beam and modulating over a wide range of frequencies (5 kHz to 50 MHz) yield better sensitivity to the thermophysical properties of anisotropic materials without varying the spot sizes. We demonstrate how beam-offset frequency domain thermoreflectance can be used to measure the in- and out-of-plane thermal conductivity as well as the TBC simultaneously from a single data set by working at reduced spot sizes. Lowering the laser spot size allows us to detect signals over a wide range of frequencies and use larger beam offsets, thanks to the increase in the thermoreflectance signal. We measure the anisotropic thermal properties of a range of materials, including single layer Graphene on SiO2, which is of interest for novel electronic devices.
Keywords: Graphene, Thermal conductivity, Optical metrology, Metal oxides, Frequency domain thermoreflectance

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Publ.-Id: 28071 - Permalink


Chemical-vapor deposited ultra-fast diamond detectors for temporal measurements of ion bunches
Jahn, D.; Träger, M.; Kis, M.; Brabetz, C.; Schumacher, D.; Blaević, A.; Ciobanu, M.; Pomorski, M.; Bonnes, U.; Busold, S.; Kroll, F.; Brack, F.-E.; Schramm, U.; Roth, M.;
This article reports on the development of thin diamond detectors and their characterization for their application in temporal profile measurements of subnanosecond ion bunches. Two types of diamonds were used: a 20 μm thin polycrystalline chemical vapor deposited (CVD) diamond and a membrane with a thickness of (5 ± 1) μm etched out of a single crystal (sc) CVD diamond. The combination of a small detector electrode and an impedance matched signal outlet leads to excellent time response properties with a signal pulse resolution (FWHM) of τ = (113 ± 11) ps. Such a fast diamond detector is a perfect device for the time of flight measurements of MeV ions with bunch durations in the subnanosecond regime. The scCVD diamond membrane detector was successfully implemented within the framework of the laser ion generation handling and transport project, in which ion beams are accelerated via a laser-driven source and shaped with conventional accelerator technology. The detector was used to measure subnanosecond proton bunches with an intensity of 10^8 protons per bunch

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Publ.-Id: 28070 - Permalink


A multicaloric cooling cycle that exploits thermal hysteresis
Gottschall, T.; Gràcia-Condal, A.; Fries, M.; Taubel, A.; Pfeuffer, L.; Manosa, L.; Planes, A.; Skokov, K. P.; Gutfleisch, O.;
The giant magnetocaloric effect, in which large thermal changes are induced in a material on the application of a magnetic field, can be used for refrigeration applications, such as the cooling of systems from a small to a relatively large scale. However, commercial uptake is limited. We propose an approach to magnetic cooling that rejects the conventional idea that the hysteresis inherent in magnetostructural phase-change materials must be minimized to maximize the reversible magnetocaloric effect. Instead, we introduce a second stimulus, uniaxial stress, so that we can exploit the hysteresis. This allows us to lock-in the ferromagnetic phase as the magnetizing field is removed, which drastically removes the volume of the magnetic field source and so reduces the amount of expensive Nd–Fe–B permanent magnets needed for a magnetic refrigerator. In addition, the mass ratio between the magnetocaloric material and the permanent magnet can be increased, which allows scaling of the cooling power of a device simply by increasing the refrigerant body. The technical feasibility of this hysteresis-positive approach is demonstrated using Ni–Mn–In Heusler alloys. Our study could lead to an enhanced usage of the giant magnetocaloric effect in commercial applications.

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Publ.-Id: 28069 - Permalink


High-frequency measurements of thermophysical properties of thin films using a modified broad-band frequency domain thermoreflectance approach
Shahzadeh, M.; Rahman, M.; Hellwig, O.; Pisana, S.;
In this work, we present the implementation of a new method to perform high-frequency thermoreflectance measurements on thin films. The so-called differential broad-band frequency domain thermoreflectance method follows broad-band frequency domain thermoreflectance developed previously [Regner et al., Rev. Sci. Instrum. 84 (6), 064901 (2013)], without the use of expensive electro-optic modulators. Two techniques are introduced to recover the thermal phase of interestand to separate it from the unwanted instrumental contributions to the recorded phase. Measuring a differential thermal phase by either varying the spot size or offsetting the pump and probe beams, the thermophysical properties of materials can be extracted. This approach enables the study of nanoscale heat transport where non-equilibrium phenomena are dominating.
Keywords: Thin films, Materials properties, Thermal conductivity, Optical metrology, Frequency domain thermoreflectance

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Publ.-Id: 28068 - Permalink


Single-crystal neutron diffraction study of hexagonal multiferroic YbMnO3 under a magnetic field
Chattopadhyay, S.; Simonet, V.; Skumryev, V.; Mukhin, A. A.; Ivanov, V. Y.; Aroyo, M. I.; Dimitrov, D. Z.; Gospodinov, M.; Ressouche, E.;
We report a single-crystal neutron diffraction study of the magnetic structure of the multiferroic compound YbMnO3, a member of the hexagonal manganite family, in zero field and under a magnetic field applied along the c axis. We propose a scenario for the zero-field magnetic ordering and for the field-induced magnetic reorientation of the Mn atom and of the two Yb atoms on distinct crystallographic sites, compatible with the macroscopic measurements, as well as with previous powder neutron diffraction experiments and results from other techniques (optical second-harmonic generation and Mössbauer spectroscopy). Our study should contribute to settling some debated issues regarding the magnetic properties of thismaterial as part of a broader investigation of the entire hexagonal RMnO3 (R = Dy, Ho, Er, Tm, Yb, Lu, Y) family.

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Publ.-Id: 28067 - Permalink


Ultrafast laser generated strain in granular and continuous FePt thin films
von Reppert, A.; Willig, L.; Pudell, J.-E.; Rössle, M.; Leitenberger, W.; Herzog, M.; Ganss, F.; Hellwig, O.; Bargheer, M.;
We employ ultrafast X-ray diffraction to compare the lattice dynamics of laser-excited continuous and granular FePt films on MgO (100) substrates. Contrary to recent results on free-standing granular films, we observe in both cases a pronounced and long-lasting out-of-plane expansion. We attribute this discrepancy to the in-plane expansion, which is suppressed by symmetry in continuous films. Granular films on substrates are less constrained and already show a reduced out-of-plane contraction. Via the Poisson effect, out-of-plane contractions drive in-plane expansion and vice versa. Consistently, the granular film exhibits a short-lived out-of-plane contraction driven by ultrafast demagnetization which is followed by a reduced and delayed expansion. From the acoustic reflections of the observed strain waves at the film-substrate interface, we extract a 13% reduction of the elastic constants in thin 10 nm FePt films compared to bulk-like samples.
Keywords: Epitaxy, Poisson's ratio, Magnetic devices, Magnetic materials, Stress strain relations, Thin films, Ultrafast X-ray diffraction, Lattice dynamics, Phonons, Elastic modulus

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Publ.-Id: 28066 - Permalink


Detectability and structural stability of a liquid fiducial marker in fresh ex vivo pancreas cancer resection specimen on CT and 3T MRI
Schneider, S.; Aust, D.; Brückner, S.; Welsch, T.; Hampe, J.; Troost, E.; Hoffmann, A.;
Objectives
The aim of this study was to test the visibility of a new liquid fiducial marker injected in ex vivo pancreas tissue on magnetic resonance imaging (MRI) and computed tomography (CT). Furthermore, its injection performance using different needle sizes was investigated as well as its structural stability after fixation in formaldehyde.
Material and Methods
Liquid fiducial markers with a volume of 20-100 µL were injected into the freshly resected pancreas of three patients (two males age 69 and 72, one female age 68) with suspected adenocarcinoma of the pancreatic head. Injection was performed under X-ray guidance using a high precision unit dose injector with different needle sizes (18G, 22G, 25G). While cooled on ice, the specimens were scanned on MRI and CT with routine clinical sequences. Signal threshold based segmentation was performed manually on CT. The marker volume visible on CT was compared to the actually injected volume as a measure of potential marker backflow. After rigid registration of the MR images to the CT data set, marker detectability was assessed by searching for the corresponding hypointense structure in the respective segmentation.
Results
Markers with a volume of ≥ 20 µL were easily detected as hyperintense structures on X-ray and CT. In clinically used T1- and T2-weighted 3T MRI sequences, all marker sizes ranging from 20µL – 100µL were visible as hypointensity. Since most markers were non-spherical however, MRI visibility was relatively poor and their differentiation from hypointensities caused by air cavities or surgical clips was challenging and only feasible with a reference CT. Marker backflow was observed when injected with an 18G needle, which was prevented by injection using a smaller 22G and 25G needle. The marker was stable after 24h fixation in formaldehyde where only small volume degradations were observed (6.6±13.0%) and with the exception of one instance no wash out occurred.
Conclusion
The liquid fiducial marker with injected volumes of 20µL – 100µL, injected in an ex vivo pancreatic cancer resection specimen, was visible as hyperintensity on kV X-ray, CT and hypointensity on MRI and stable over a period of 24 hours in formaldehyde. Since most injected markers were non-spherical, a marker size of ≥50µL is recommended for the clinically used MRI sequences. Most likely, in vivo marker injection will result in more spherical forms due to persisting metabolism, and this in turn will enhance MRI visibility in an hyper intense structure.
Keywords: Liquid fiducial marker, pancreatic adenocarcinoma, MRI visibility, ex vivo

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  • Secondary publication expected from 29.05.2020

Publ.-Id: 28065 - Permalink


Comparison of respiratory motion management by means of three abdominal corsets for particle therapy
Schneider, S.; Dolde, K.; Alimusaj, M.; Fluegel, B.; Hoffmann, A.; Pfaffenberger, A.;
Purpose/Objective:
Particle therapy (PT) has the potential of improving the outcome in radiotherapy (RT) due to its inverse dose profile and the superior sparing of healthy tissues surrounding the target volume compared to photon therapy. However, PT is strongly susceptible to anatomical changes, and especially for the treatment of abdominal tumours, strategies for motion management are required.
The purpose of this study was to investigate and compare the potential usability of three different abdominal corsets in PT by measuring their water equivalent ratio (WER) in proton therapy as well as by analysing their effect on the respiration-induced motion of the pancreas.
Material/Methods:
The corsets differed in terms of geometry (thickness of 2.5mm – 24mm), material (polyethylene (PE) vs. polyurethane (PU)) as well as regarding the method of construction (patient individual vs. patient independent). A healthy volunteer was scanned on a 1.5T MR scanner (Magnetom Aera, Siemens Healthineers) on two consecutive days while he was wearing each of the three respective corsets and without him wearing a corset for reference. A gradient echo sequences with radial golden angel acquisition was used and reconstructed to a 4D data set with 20 phases. The pancreas was delineated in max exhale and max inhale phase using the open-source software MITK (Fig. 1). The centre of mass was calculated as a surrogate for the respiratory motion of the pancreas in each of the four scenarios for both days.
After acquiring CT scans of the three corsets for assessment of material homogeneity and regularity of material thickness, WER measurements were performed at two different proton energies (150MeV, 200MeV) using a multi-layer ionization chamber (Giraffe, IBA Dosimetry) to measure the shift of the single beam Bragg Peak after penetrating the corset sample.
Results:
All three abdominal corsets led to reduced pancreatic motion, and the effect was largest in inferior-superior direction (Table 1). The CT revealed a perfectly homogeneous material for the two PE corsets with a constant thickness of 2.5±0.1mm and 4.9±0.1mm. In case of the PU corset the material was inhomogeneous with air inclusions throughout the whole corset. Furthermore, its thickness varied between 8.0-24.2mm in the relevant region. The WER of the two polyethylene corsets was determined to be 0.990 and 0.956, while the WER of the polyurethane corset was 0.298.
Conclusion:
While all three corsets reduce the respiratory motion to a similar amount, the material analysis revealed that the polyurethane corset is not suitable for PT due to its inhomogeneous structure and irregular thickness. On the other hand, the two PE corsets both show very stable material conditions which could, in terms of physics, easily be included in treatment planning and a fractionated treatment scheme. However, due to their different construction approach, the PE corsets have respective benefits in accuracy of fit, flexibility, cost and the time required for preparation.
  • Lecture (Conference)
    ESTRO 38, 26.-30.04.2019, Mailand, Italien

Publ.-Id: 28064 - Permalink


Ultrafast Self-Induced X-Ray Transparency and Loss of Magnetic Diffraction
Chen, Z.; Higley, D. J.; Beye, M.; Hantschmann, M.; Mehta, V.; Hellwig, O.; Mitra, A.; Bonetti, S.; Bucher, M.; Carron, S.; Chase, T.; Jal, E.; Kukreja, R.; Liu, T.; Reid, A. H.; Dakovski, G. L.; Föhlisch, A.; Schlotter, W. F.; Dürr, H. A.; Stöhr, J.;
Using ultrafast ≃2.5  fs and ≃25  fs self-amplified spontaneous emission pulses of increasing intensity and a novel experimental scheme, we report the concurrent increase of stimulated emission in the forward direction and loss of out-of-beam diffraction contrast for a Co/Pd multilayer sample. The experimental results are quantitatively accounted for by a statistical description of the pulses in conjunction with the optical Bloch equations. The dependence of the stimulated sample response on the incident intensity, coherence time, and energy jitter of the employed pulses reveals the importance of increased control of x-ray free electron laser radiation.

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Publ.-Id: 28063 - Permalink


Adaptive Micromixer Based on the Solutocapillary Marangoni Effect in a Continuous-Flow Microreactor
Bratsun, D.; Kostarev, K.; Mizev, A.; Aland, S.; Mokbel, M.; Schwarzenberger, K.; Eckert, K.;
Continuous-flow microreactors are an important development in chemical engineering technology, since the pharmaceutical production needs flexibility in reconfiguring the synthesis system rather than large volumes of product yield. Microreactors of this type have a special vessel, in which the convective vortices are organized to mix the reagents in order to increase the product output. We propose a new type of micromixer based on the intensive relaxation oscillations induced by a fundamental effect discovered recently. The mechanism of these oscillations was found to be a coupling of the solutal Marangoni effect, buoyancy and diffusion. The phenomenon can be observed in the vicinity of an air-liquid (or liquid-liquid) interface with inhomogeneous concentration of a surface-active solute. Important features of the oscillations are demonstrated experimentally and numerically. The periodicity of the oscillations is a result of the repeated regeneration of the Marangoni driving force.
This feature is used in our design of a micromixer with a single air bubble inside the reaction zone.
We show that the micromixer does not consume external energy and adapts to the medium state due to feedback. It switches on automatically each time when a concentration inhomogeneity in the reaction zone occurs, and stops to mix when the solution becomes sufficiently uniform.

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Publ.-Id: 28062 - Permalink


Information transmission by Marangoni-driven relaxation oscillations at droplets
Mokbel, M.; Schwarzenberger, K.; Aland, S.; Eckert, K.;
Marangoni-driven relaxation oscillations can be observed in many systems where concentration gradients of surface-active substances exist. In the present paper, we describe the experimentally observed coupling between relaxation oscillations at neighboring droplets in a concentration gradient. By a numerical parameter study, we evaluate the oscillation characteristics depending on relevant material parameters and the pairwise droplet distance. Based on these findings, we demonstrate that hydrodynamic interaction in multidroplet configurations can lead to a synchronization of the oscillations over the whole ensemble. This effect has the potential to be used as a novel approach for information transmission in microfluidic applications.

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Publ.-Id: 28061 - Permalink


FMISO-PET-based lymph node hypoxia adds to the prognostic value of tumor only hypoxia in HNSCC patients
Bandurska-Luque, A.; Löck, S.; Haase, R.; Richter, C.; Zöphel, K.; Abolmaali, N.; Seidlitz, A.; Appold, S.; Krause, M.; Steinbach, J.; Kotzerke, J.; Zips, D.; Baumann, M.; Troost, E.;
Purpose: This secondary analysis of the prospective study on repeat [18F]fluoromisonidazole (FMISO)-PET in patients with locally advanced head and neck squamous cell carcinomas (HNSCC) assessed the prognostic value of synchronous hypoxia in primary tumor (Tu) and lymph node metastases (LN), and evaluated whether the combined reading was of higher prognostic value than that of primary tumor hypoxia only. Methods: This analysis included forty-five LN-positive HNSCC patients. FMISO-PET/CTs were performed at baseline, weeks 1, 2 and 5 of radiochemotherapy. Based on a binary scale, Tu and LN were categorized as hypoxic or normoxic, and two prognostic parameters were defined: Tu-hypoxia (independent of the LN oxygenation status) and synchronous Tu-and-LN-hypoxia. In fifteen patients with large LN (N = 21), additional quantitative analyses of FMISO-PET/CTs were performed. Imaging parameters at different time-points were correlated to the endpoints, i.e., locoregional control (LRC), local control (LC), regional control (RC) and time to progression (TTP). Survival curves were estimated using the cumulative incidence function. Univariable and multivariable Cox regression was used to evaluate the prognostic impact of hypoxia on the endpoints. Results: Synchronous Tu-and-LN-hypoxia was a strong adverse prognostic factor for LC, LRC and TTP at any of the four time-points (p ≤ 0.004), whereas Tu-hypoxia only was significantly associated with poor LC and LRC in weeks 2 and 5 (p ≤ 0.047), and with TTP in week 1 (p = 0.046). The multivariable analysis confirmed the prognostic value of synchronous Tu-and-LN-hypoxia regarding LRC (HR = 14.8, p = 0.017). The quantitative FMISO-PET/CT parameters correlated with qualitative hypoxia scale and RC (p < 0.001, p ≤ 0.033 at week 2, respectively). Conclusions: This secondary analysis suggests that combined reading of primary tumor and LN hypoxia adds to the prognostic information of FMSIO-PET in comparison to primary tumor assessment alone in particular prior and early during radiochemotherapy. Confirmation in ongoing trials is needed before using this marker for personalized radiation oncology. © 2018 Elsevier B.V.
Keywords: FMISO-PETHypoxia, Locally advanced HNSCC, Lymph node, Prognostic biomarker

Publ.-Id: 28060 - Permalink


Irradiation effects in monazite-(Ce) and zircon: Raman and photoluminescence study of Au-irradiated FIB foils
Nasdala, L.; Akhmadaliev, S.; Artac, A.; Chanmuang, N. C.; Habler, G.; Lenz, C.;
Lamellae of 1.5 µm thickness, prepared from well-crystallised monazite-(Ce) and zircon samples using the focused-ion-beam technique, were subjected to triple irradiation with 1 MeV Au+ ions (15.6% of the respective total fluence), 4 MeV Au2+ ions (21.9%) and 10 MeV Au3+ ions (62.5%). Total irradiation fluences were varied in the range 4.5E12 -1.2E14 ions/cm2. The highest fluence resulted in amorphisation of both minerals; all other irradiations (i.e. up to 4.5E13 ions/cm2) resulted in moderate to severe damage. Lamellae were subjected to Raman and laser-induced photoluminescence analysis, in order to provide a means of quantifying irradiation effects using these two micro-spectroscopy techniques. Based on extensive Monte Carlo calculations and subsequent defect-density estimates, irradiation-induced spectroscopic changes are compared with those of naturally self-irradiated samples. The finding that ion irradiation of monazite-(Ce) may cause severe damage or even amorphisation, is in apparent contrast to the general observation that naturally self-irradiated monazite-(Ce) does not become metamict (i.e. irradiation-amorphised), in spite of high self-irradiation doses. This is predominantly assigned to the continuous low-temperature damage annealing undergone by this mineral; other possible causes are discussed. According to cautious estimates, monazite-(Ce) samples of Mesoproterozoic to Cretaceous ages have stored only about 1% of the total damage experienced. In contrast, damage in ion-irradiated and naturally self-irradiated zircon is on the same order; reasons for the observed slight differences are discussed. We may assess that in zircon, alpha decays create significantly less than 1000 Frenkel-type defect pairs per event, which is much lower than previous estimates. Amorphisation occurs at defect densities of about 0.10 dpa (displacements per lattice atom).
Keywords: Radiation damage, Heavy-ion irradiation, Focused ion beam, Raman spectroscopy, Photoluminescence

Publ.-Id: 28059 - Permalink


Site-controlled formation of single Si nanocrystals in a buried SiO₂ matrix using ion beam mixing
Xu, X.; Prüfer, T.; Wolf, D.; Engelmann, H.-J.; Bischoff, L.; Hübner, R.; Heinig, K.-H.; Möller, W.; Facsko, S.; von Borany, J.; Hlawacek, G.;
For future nanoelectronic devices—such as room-temperature single electron transistors—the site controlled formation of single Si Nanocrystal (NC) is a crucial prerequisite. Here, we report an approach to fabricate single Si NCs via medium-energy Si+ or Ne+ ion beam mixing of Si into a buried SiO₂ layer followed by thermally activated phase separation. Binary Collision Approximation and kinetic Monto Carlo methods are conducted to gain atomistic insight into the influence of relevant experimental parameters on the Si NC formation process. Energy Filtered Transmission Electron Microscopy is performed to obtain quantitative values on the Si NC size and distribution in dependence of the layer stack geometry, ion fluence and thermal budget. Employing a focused Ne+ beam from a Helium Ion Microscope, we demonstrate site-controlled self-assembly of single Si NCs. Line irradiation with a fluence of 3000Ne+/nm² and a line width of 4 nm leads to the formation of a chain of Si NCs, and a single NC with 2.2 nm diameter is subsequently isolated and visualized in a few nm thin lamella prepared by Focused Ion Beam (FIB). The Si NC is centered between the SiO₂ layers and the perpendicular to the incident Ne+ beam.
Keywords: Helium Ion Microscopy, ion beam mixing, single electron transistor, phase separation, Monte Carlo simulations

Publ.-Id: 28058 - Permalink


Smart Tomographic Sensors for Advanced Industrial Process Control - TOMOCON
Hampel, U.; Wondrak, T.; Bieberle, M.; Lecrivain, G.; Schubert, M.; Eckert, K.; Reinecke, S.;
With the recent developments in high-power massive parallel computing, process tomography has gained the required real-time capability of being employed as sensors in advanced control systems. Process tomography techniques are of great value as they provide distributed process parameters for opaque processes.
The European Training Network TOMOCON joins 27 international academic and industry partners working together in the emerging field of industrial process control using smart tomographic sensors to lay the scientific and technological fundamentals of integrating imaging sensors into industrial processes and to demonstrate its functional feasibility on lab and pilot-scale applications. Particular focus is on the training of the doctoral researchers in the fields of process tomography hardware, control systems design, industrial process design, multi-physics modelling, and human-computer interaction.
The teams are engaged in multi-disciplinary research on various tomographic imaging modalities, tomographic image processing as well as advanced multi-physics modelling of processes, sensors and actuators. Proof-of-principle demonstrations of tomography-based processes focus on important industrial processes, such as inline fluid separation, microwave drying of porous materials, continuous steel casting and ultrasound-controlled crystallization.
  • Poster
    ProcessNet-Jahrestagung und 33. DECHEMA-Jahrestagung der Biotechnologen 2018, 10.-15.09.2018, Aachen, Deutschland
  • Open Access LogoAbstract in refereed journal
    Chemie Ingenieur Technik 90(2018)9, 1238-1239
    DOI: 10.1002/cite.201855235

Publ.-Id: 28057 - Permalink


Investigation of bioreactors by smart sensor particles
Reinecke, S. F.; Hampel, U.;
Advanced monitoring of the spatio-temporal distribution of process parameters in the large-scale vessels of chemical or bioreactors, such as industrial fermenters, biogas digesters and activated sludge basins, offers a high potential for the investigation and further optimization of plants and embedded processes. However, in most industrial scale applications the acquisition of these parameters and their spatial distributions in the large-scale vessels is hampered by the limited access to the process itself, because sensor mounting or cable connections are not feasible or desired. Therefore, state of the art instrumentation of such reactors is commonly limited to few spatial positions where it is doubtfully assumed that the measured parameters are representative for the whole reaction mixture.
Instrumented sensor particles have been developed by Thiele et al. [1] for investigation of hydrodynamic and biochemical processes chemical reactors and bioreactors. The sensor particles allow autonomous long-term measurement of spatially distributed process parameters in the chemically and mechanically harsh environments of agitated industrial vessels. Each sensor particle comprises of an on-board measurement electronics that logs the signals of the embedded sensors. A buoyancy control unit enables automated taring to achieve neutral buoyancy and thus flow-following capabilities of the sensor particles [2]. Moreover, controlled floating of the sensor particles is possible to expose them for recovery from the fluid surface. The paper presents results of the sensor system validation and tests in an air-water column reactor, a pilot biogas digester and a waste water treatment plant. Moreover, ongoing developments of smart sensor particles features, i.e. magnetic position detection and inertial position tracking, are presented.
  • Lecture (Conference)
    ProcessNet-Jahrestagung und 33. DECHEMA-Jahrestagung der Biotechnologen 2018, 10.-15.09.2018, Aachen, Deutschland
  • Open Access LogoAbstract in refereed journal
    Chemie Ingenieur Technik 90(2018)9, 1268-1268
    DOI: 10.1002/cite.201855298

Publ.-Id: 28056 - Permalink


Inertial position tracking of flow following sensor particles
Reinecke, S. F.; Hampel, U.;
In this paper, a concept for inertial position tracking of flow following sensor particles based on data fusion of inertial sensors is presented. The employed data fusion technique is quaternion based and uses an extended Kalman filter algo-rithm. A generalized sensor system kinematics has been developed to test the filter algorithm where two data conditions have been considered. Eventually, first simulation results are compared which shows the performance of the filter re-garding sensor drift and noise.
  • Contribution to proceedings
    Sensoren und Messsysteme 2018 ∙ 26. – 27.06.2018 in Nürnberg, 26.-27.06.2018, Nürnberg, Deutschland
    Beiträge der 19. ITG/GMA-Fachtagung 26. – 27. Juni 2018 in Nürnberg, 978-3-8007-4683-5
  • Lecture (Conference)
    Sensoren und Messsysteme 19. ITG/GMA-Fachtagung 26. – 27. Juni 2018 in Nürnberg, 26.-27.06.2018, Nürnberg, Deutschland

Publ.-Id: 28055 - Permalink


Magnetic Communication Using High-Sensitivity Magnetic Field Detectors
Hott, M.; Hoeher, P. A.; Reinecke, S. F.;
In this article, an innovative approach for magnetic data communication is presented. For
this purpose, the receiver coil of a conventional magneto-inductive communication system is replaced by a high-sensitive wideband magnetic field sensor. The results show decisive advantages offered by sensitive magnetic field sensors, including a higher communication range for small receiver units. This approach supports numerous mobile applications where receiver size is limited, possibly in conjunction with multiple detectors. Numerical results are supported by a prototype implementation employing an anisotropic magnetoresistive sensor.
Keywords: wireless communication; magnetic induction communication; mobile sensing systems; magnetic sensors; RF-challenging environments

Publ.-Id: 28054 - Permalink


Destabilization of DNA through interstrand crosslinking by UO22+
Rossberg, A.; Abe, T.; Okuwaki, K.; Barkleit, A.; Fukuzawa, K.; Nakano, T.; Mochizuki, Y.; Tsushima, S.;
UO22+ forms an interstrand crosslink between two different strands from a single DNA, which hardly affects the hydrogen bonds between nucleobase pairs whereas it destabilizes the π–π stacking between the two nucleobases in the vicinity of UO22+– bound phosphate. Thereby, fragility of DNA backbone increases upon UO22+ binding.
Keywords: Fragment molecular orbital method, DNA, chemotoxicity, uranyl(VI), interstrand crosslink, EXAFS.

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  • Secondary publication expected from 02.01.2020

Publ.-Id: 28053 - Permalink


HEFIB2018 – Helium and emerging focused ion beams
Hlawacek, G.ORC
Die zweite HEFIB – Helium and emerging focused ion beams Konferenz fand vom 11. bis zum 13. Juni in Dresden statt. Das ers­te Treffen unter diesem Namen fand 2016 in Luxemburg statt. Zwei Jahre später fand planmäßig die zweite HEFIB statt. Ein Teil des bewährten Organisationsteams aus Lu­xemburg und Deutschland wurde mit neu­en Mitgliedern aus Japan und den USA vervollständigt.
Keywords: Konferenzreport
  • Open Access LogoElektronenmikroskopie 44(2018), 21-22

Publ.-Id: 28052 - Permalink


Visible Light Actuated Efficient Exclusion Between Plasmonic Ag/AgCl Micromotors and Passive Beads
Wang, X.; Baraban, L.; R. Misko, V.; Nori, F.; Huang, T.; Cuniberti, G.; Fassbender, J.; Makarov, D.;
Insight is provided into the collective behavior of visible‐light photochemically driven plasmonic Ag/AgCl Janus particles surrounded by passive polystyrene (PS) beads. The active diffusion of single Janus particles and their clusters (small: consisting of two or three Janus particles and large: consisting of more than ten Janus particles), and their interaction with passive PS beads, are analyzed experimentally and in simulations. The diffusivity of active Janus particles, and thus the exclusive effect to passive PS beads, can be regulated by the number of single Janus particles in the cluster. On the simulation side, the Langevin equations of motion for self‐propelled Janus particles and diffusing passive PS beads are numerically solved using Molecular‐Dynamics simulations. The complex interactions of both subsystems, including elastic core‐to‐core interactions, short‐range attraction, and effective repulsion due to light‐induced chemical reactions are considered. This complex mixed system not only provides insight to the interactive effect between active visible light‐driven self‐propelled micromotors and passive beads, but also offers promise for implications in light‐controlled propulsion transport and chemical sensing.

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Publ.-Id: 28051 - Permalink


High-Motility Visible Light-Driven Ag/AgCl Janus Micromotors
Wang, X.; Baraban, L.; Nguyen, A.; Ge, J.; R. Misko, V.; Tempere, J.; Nori, F.; Formanek, P.; Huang, T.; Cuniberti, G.; Fassbender, J.; Makarov, D.;
Visible light‐driven nano/micromotors are promising candidates for biomedical and environmental applications. This study demonstrates blue light‐driven Ag/AgCl‐based spherical Janus micromotors, which couple plasmonic light absorption with the photochemical decomposition of AgCl. These micromotors reveal high motility in pure water, i.e., mean squared displacements (MSD) reaching 800 µm2 within 8 s, which is 100× higher compared to previous visible light‐driven Janus micromotors and 7× higher than reported ultraviolet (UV) light‐driven AgCl micromotors. In addition to providing design rules to realize efficient Janus micromotors, the complex dynamics revealed by individual and assemblies of Janus motors is investigated experimentally and in simulations. The effect of suppressed rotational diffusion is focused on, compared to UV light‐driven AgCl micromotors, as a reason for this remarkable increase of the MSD. Moreover, this study demonstrates the potential of using visible light‐driven plasmonic Ag/AgCl‐based Janus micromotors in human saliva, phosphate‐buffered saline solution, the most common isotonic buffer that mimics the environment of human body fluids, and Rhodamine B solution, which is a typical polluted dye for demonstrations of photocatalytic environmental remediation. This new knowledge is useful for designing visible light driven nano/micromotors based on the surface plasmon resonance effect and their applications in assays relevant for biomedical and ecological sciences.

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Publ.-Id: 28050 - Permalink


Control of domain structure and magnetization reversal in thick Co/Pt multilayers
Fallarino, L.; Oelschlägel, A.; Arregi, J. A.; Bashkatov, A.; Samad, F.; Böhm, B.; Chesnel, K.; Hellwig, O.;
We present a study of the magnetic properties of [Co(3.0nm)/Pt(0.6nm)]N multilayers as a function of Co/Pt bilayer repetitions N. Magnetometry investigation reveals that samples with high N exhibit two characteristic magnetization reversal mechanisms, giving rise to two different morphologies of the remanent domain pattern. For applied magnetic field angles near the in-plane field orientation, the magnetization reversal proceeds via a spontaneous instability of the uniform magnetic state resulting in perpendicular stripe domains. Conversely, for field angles close to the out-of-plane orientation, the reversal occurs via domain nucleation and propagation leading to a maze-like domain pattern at remanence. Our measurements further enable the characterization of the N-dependent energy balance between the magnetic anisotropy and magnetostatic energy contributions, revealing a gradual disappearance of the domain nucleation process during magnetization reversal for N < 14. This leads to the exclusive occurrence of an instability reversal mechanism for all field orientations as well as aligned-like stripe domains at remanence. Furthermore, a detailed study of the influence of the magnetic history allows the determination of a range of material properties and magnetic field strengths, where a lattice of bubble domains with remarkably high density is stabilized. These modulations of the ferromagnetic order parameter are found to strongly depend on N, in terms of center-to-center bubble distance as well as of bubble diameter. Moreover, such Co/Pt multilayers could be utilized to engineer field reconfigurable bubble domain lattices, which can resemble magnonic crystals.
Keywords: Co/Pt thick multilayers, Magnetic bubble domains, magnonic crystals.

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Publ.-Id: 28049 - Permalink


Crystal Structure of Regularly Th-Symmetric [U(NO3)6]2− Salts with Hydrogen Bond Polymers of Diamide Building Blocks
Takao, K.; Kazama, H.; Ikeda, Y.; Tsushima, S.;
Hexanitratouranate(IV), [U(NO3)6]2−, has been crystallized with anhydrous H+ counter cations stabilized by formation of hydrogen bond polymers with selected diamide building blocks. Thanks to the significant moderation of electrostatic interactions between the anions and cations, the molecular structure of [U(NO3)6]2− in these compounds is regularly Th-symmetric. The f-f transitions stemming from 5f2 configuration of U4+ is strictly forbidden by the Laporte selection rule in such a centrosymmetric system , so that the obtained compounds are nearly colourless in contrast to other U(IV) species usually coloured in green.

Publ.-Id: 28048 - Permalink


Towards Utilising Photocrosslinking of Polydiacetylenes for the Preparation of “Stealth” Upconverting Nanoparticles
Nsubuga, A.; Zarschler, K.ORC; Sgarzi, M.ORC; Graham, B.; Stephan, H.ORC; Joshi, T.ORC
We demonstrate a novel strategy for preparing hydrophilic upconverting nanoparticles (UCNPs) by harnessing the photocrosslinking ability of diacetylenes. Replacement of the hydrophobic oleate coating on the UCNPs with 10,12-pentacosadiynoic acid, followed by overcoating with diacetylene phospholipid and subsequent photocrosslinking under 254 nm irradiation produces water-dispersible polydiacetylene-coated UCNPs. These UCNPs resist the formation of a biomolecular corona and show great colloidal stability. Furthermore, amine groups on the diacetylene phospholipid allow for functionalisation of the UCNPs with, for example, radiolabels or targeting moieties. These results demonstrate that this new surface coating method has great potential for use in the preparation of UCNPs with improved biocompatibility.
Keywords: Crosslinking, Diacetylene, Lanthanides, Nanomaterials, Upconversion

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Publ.-Id: 28047 - Permalink


From curvilinear magnetism to shapeable magnetoelectronics (plenary)
Makarov, D.;
Extending two-dimensional structures into the three-dimensional (3D) space has become a general trend in multiple disciplines, including electronics, photonics, plasmonics and magnetics. This approach provides means to modify conventional or to launch novel functionalities by tailoring curvature and 3D shape. In the case of 3D curved magnetic thin films and nanowires the physics is driven by the interplay between exchange and magnetostatic interactions, which contain spatial derivatives in their energy functionals [1,2]. This makes both interactions sensitive to the appearance of bends and twists in the physical space. Theoretical works predict the curvature-induced effective anisotropy and effective Dzyaloshinskii-Moriya interaction resulting in a multitude of novel effects including magnetochiral effects (chirality symmetry breaking) and topologically induced magnetization patterning.
Those 3D magnetic architectures are already proven to be application relevant for life sciences, targeted delivery, realization of 3D spin-wave filters, and magneto-encephalography devices to name just a few. To this end, the initially fundamental topic of the magnetism in curved geometries strongly benefited from the input of the application-oriented community, which among others explores the shapeability aspect of the curved magnetic thin films. These activities resulted in the development of the family of shapeable magnetoelectronics [3], which already includes flexible, printable, stretchable and even mechanically imperceptible magnetic field sensorics [4,5].
The balance between the fundamental and applied inputs into the topic of magnetism in curved geometries is rather unique. This stimulates even further the development of new theoretical methods and novel fabrication/characterization techniques. The synergy will definitely enable us surpassing the exploratory research and will pave the way towards novel device concepts, where the geometry of a functional thin film will play a decisive role in determining the device performance.

References
[1] R. Streubel, D. Makarov et al., J. Phys. D: Appl. Phys. 49, 363001 (2016).
[2] D. Sander, D. Makarov et al., J. Phys. D: Appl. Phys. 50, 363001 (2017).
[3] D. Makarov et al., Appl. Phys. Rev. 3, 011101 (2016).
[4] G. S. Canon Bermudez, D. Makarov et al., Science Advances 4, eaao2623 (2018).
[5] M. Melzer, D. Makarov et al., Nat. Commun. 6, 6080 (2015).
Keywords: curvilinear magnetism, flexible electronics, magnetic field sensors
  • Invited lecture (Conferences)
    XIV International Conference on Applied Physics and Electronics, 24.-26.10.2018, Kyiv, Ukraine

Publ.-Id: 28046 - Permalink


Intelligent materials and devices
Makarov, D.;
In this invited talk I will Highlight activities of the Group FWIN-I "Intelligent materials and devices".
Keywords: anitiferromagnetic spintronics, flexible electronics, curvilinear magnetism
  • Invited lecture (Conferences)
    Advancing Science through International Cooperation: Forum of the Ukrainian Research Diaspora, 20.-22.10.2018, Kyiv, Ukraine

Publ.-Id: 28045 - Permalink


Flexible electronics: from interactive on-skin devices to in vivo applications
Makarov, D.;
In this invited talk I will Review our recent activities on flexible electronics including interactive magnetic Skins and highly compliant devices for in vivo applications.
Keywords: flexible electronics, magnetic field sensors
  • Invited lecture (Conferences)
    Seminar at the Kyiv Academic University, 19.10.2018, Kyiv, Ukraine

Publ.-Id: 28044 - Permalink


Injection locking of multiple auto-oscillation modes in a tapered nanowire spin Hall oscillator
Wagner, K.ORC; Smith, A.; Hache, T.; Chen, J.-R.; Yang, L.; Montoya, E.; Schultheiss, K.; Lindner, J.; Fassbender, J.; Krivorotov, I.; Schultheiss, H.
Spin Hall oscillators (SHO) are promising candidates for the generation, detection and amplification of high frequency signals, that are tunable through a wide range of operating frequencies. They offer to be read out electrically, magnetically and optically in combination with a simple bilayer design. Here, we experimentally study the spatial dependence and spectral properties of auto-oscillations in SHO devices based on Pt(7 nm)/ Ni80Fe20(5nm) tapered nanowires. Using Brillouin light scattering microscopy, we observe two individual self- localized spin-wave bullets that oscillate at two distinct frequencies (5.2 GHz and 5.45 GHz) and are localized at different positions separated by about 750 nm within the SHO. This state of a tapered SHO has been predicted by a Ginzburg-Landau auto-oscillator model, but not yet been directly confirmed experimentally. We demonstrate that the observed bullets can be individually synchronized to external microwave signals, leading to a frequency entrainment, linewidth reduction and increase in oscillation amplitude for the bullet that is selected by the microwave frequency. At the same time, the amplitude of other parasitic modes decreases, which promotes the single-mode operation of the SHO. Finally, the synchronization of the spin-wave bullets is studied as a function of the microwave power. We believe that our findings promote the realization of extended spin Hall oscillators accomodating several distinct spin-wave bullets, that jointly cover an extended range of tunability.
Keywords: Magnonik, auto-oscillation, magnetic auto-oscillator, spin Hall oscillator, magnetization dynamic, Brillouin-Light-Scattering

Publ.-Id: 28043 - Permalink


Giant impact of self-photothermal on light-induced ultrafast insulator-to-metal transition in VO₂ nanofilms at terahertz frequency
Zhai, Z.-H.; Chen, S.-C.; Du, L.-H.; Zhong, S.-C.; Huang, W.; Li, Z.-R.; Schneider, H.; Shi, Q.; Zhu, L.-G.;
Ultrafast detection and switching of light are key processes in high-speed optoelectronic devices. However, the performances of VO₂-based optoelectronics are strongly degraded by photothermal. The mechanism of the latter is still unclear. Here, by using femtosecond-laser (fs-laser) driven kinetic terahertz wave absorption, we quantitatively separate slow photothermal response and ultrafast photodoping response (e.g. light-induced insulator-to-metal transition) from second- to picosecond-timescales, and discover the competing interplay between them. With self-photothermal (mainly determined by fs-laser pulse repetition rate and pump fluence), the ultrafast transition time was degraded by 190% from 50 ps to 95 ps, the ultrafast transition threshold was decreased to 82% from 11mJ/cm² to 9mJ/cm², while the amplitudes of the two photoresponse are competing. Percolation theory, along with the macroscopic conductivity response, is used to explain the competing interplay. Our findings are relevant for designing and optimizing VO₂-based ultrafast optoelectronic devices.
Keywords: vanadium-dioxide, insulator-to-metal transition, photo-thermal effect

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Publ.-Id: 28042 - Permalink


Interaction of U(VI) with α-isosaccharinic acid: structural elucidation of the formed complexes and implications for the retention of U(VI) on bentonite
Brinkmann, H.; Philipp, T.; Dullies, P.; Shams Aldin Azzam, S.; Patzschke, M.; Roßberg, A.; Moll, H.; Stumpf, T.;
Low and intermediate level waste contains considerable amounts of cellulosic materials, which will be degraded relatively fast under alkaline conditions, with isosaccharinic acid (ISA), a polyhydroxy-carboxylic acid, being the main degradation product. It has been shown that the α-form is a stronger complexant for certain radionuclides compared to the β-form and that the complex formation affects the sorption as well as the solubility adversely.[1]
In the particular case of U(VI) the number of studies concerning the speciation in the presence of ISA is small. The excellent spectroscopic properties of the uranyl-entity were used to determine the speciation by UV-vis, luminescence, ATR-FTIR and EXAFS spectroscopy properly under acidic conditions. To understand the complex formation mechanism on a molecular level, the behavior of the ligand was simultaneously investigated by ATR-FTIR and NMR spectroscopy and the results were compared to theoretical data from DFT-calculations, whereby a dominant chelate binding motif via the carboxylic and the α-hydroxy-group was identified.
Whereas hydrolysis of U(VI) and carbonate-complexation can be neglected under acidic conditions, they have to be carefully considered under neutral and alkaline conditions as competitive reactions in addition to the complex formation with ISA. In this context the influence of ISA on the retention of U(VI) on bentonite was investigated. Sorption experiments were performed under anaerobic (carbonate-free) and aerobic (with carbonate) conditions between pH 8 and 13 in the presence of ISA. Time-resolved laser-induced fluorescence spectroscopy was used to determine the aqueous speciation of U(VI) and the results will be compared to measurements without ISA.

[1] Van Loon, L. R., et al., Radiochimica Acta, 1999, Vol. 86, https://doi.org/10.1524/ract.1999.86.34.183.
Keywords: uranium, isosaccharinic acid, spectroscopy, bentonite, sorption
  • Lecture (Conference)
    International conference Uranium Biogeochemistry, 21.-26.10.2018, Monte Veritá Ascona, Schweiz

Publ.-Id: 28041 - Permalink


Detailed characterization of uranyl complexes with small organic ligands on a molecular level: a spectroscopic approach
Brinkmann, H.; Heim, K.; Kaden, P.; Kloditz, R.; Moll, H.; Patzschke, M.;
The fundamental aspects of uranyl-spectroscopy (absorption, luminescence, IR), data interpretation and subsequent conclusions to interpret the U(VI)-speciation will be discussed. Furthermore, it will be explained how spectroscopy (NMR and IR) can be used to identify the binding properties of organic molecules, exemplarily explained for a polyhydroxy-carboxylic acid.
Keywords: uranium, spectroscopy, isosaccharinic acid
  • Lecture (others)
    MIND Advanced training course | Geomicrobiology in radioactive waste disposal, 08.-11.10.2018, Mol, Belgien

Publ.-Id: 28040 - Permalink


Age and provenance of detrital zircons from the Oligocene formations of the Marseille–Aubagne basins (SE France): consequences on the geodynamic and palaeogeographic evolution of the northern Gondwana margin
Villeneuve, M.; Gärtner, A.; Nury, D.; Fournier, F.; Arlhac, P.; Linnemann, U.; Caron, J. P.;
Eight samples from Oligocene sedimentary rocks of the Marseille–Aubagne basins have been analysed for their detrital zircon age spectra. These age spectra provide information about the regional evolution, from Oligocene to Archaean times. The Carboniferous Variscan and the Late Cretaceous to Eocene Pyreneo-Provençal belts represent the latest main tectonic, magmatic, and volcanic events that formed the major zircon age populations found in studied sediments. The obtained detrital zircon age record of the Marseille–Aubagne basins comprises eleven detrital zircon age clusters. They reflect the long and complex geologic history of the sediments source areas and can be ascribed to the opening of the western Mediterranean, the Variscan, Cadomian and Pan-African belts, to an unknown Mesoproterozoic event, to the Eburnean orogeny of West Africa and to the different tectono-metamorphic events that took place in Archaean times. In general, the Palaeo- and Mesozoic events are ascribed to the dispersal of Western and Eastern Gondwana and the Pangaean supercontinent cycle. Thus, the successive recycling of zircon grains from older and the incorporation of them to younger belts lead to new geodynamical models for the northern Gondwana margin evolution. Significant amounts of Mesoproterozoic detrital zircon are at odds with previous hypotheses and re-open the question of the provenance of these zircon age populations. Therefore, this tiny Tertiary basin is a natural archive which records the main geological events in SE France and its vicinity.
Keywords: U–Th–Pb zircon dating, Oligocene, Variscan, Provence, Mediterranean, Palaeogeography, Geodynamic

Publ.-Id: 28039 - Permalink


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