Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

"Online First" included
Approved and published publications
Only approved publications

41708 Publications

Complex antiferromagnetic structure in the intermediate-valence intermetallic Ce2RuZn4

Hartwig, S.; Prokes, K.; Hansen, T.; Ritter, C.; Gerke, B.; Pöttgen, R.; Mydosh, J. A.; Förster, T.

Abstract

Neutron powder diffraction experiments were performed on the intermediate-valence Ce2RuZn4 intermetallic compound and combined with magnetic bulk measurements including high magnetic field experiments up to 58 T. Previous theoretical studies suggest that only one (here Ce1) out of two inequivalent Ce sites ismagnetically active. Ce2RuZn4 orders antiferromagnetically at TN = 2.3 K. The magnetic structure is characterized by an incommensurate propagation vector qm = (0.384, 0.384, 1/2). Assuming that the Ce2 site does not carry any substantial moment, Ce1 magnetic moments are confined to the (110)-type planes and transversely modulated with an amplitude of 1.77(3) μB.

Involved research facilities

  • High Magnetic Field Laboratory (HLD)

Permalink: https://www.hzdr.de/publications/Publ-22341


Atomic scale interface design and characterisation

Bittencourt, C.; Ewels, C.; Krasheninnikov, A. V.

Keywords: nanotechnology

Involved research facilities

Related publications

Permalink: https://www.hzdr.de/publications/Publ-22339


Development and Validation of Advanced Theoretical Modeling for Churn-Turbulent Flows and Subsequent Transitions

Montoya Zabala, G. A.

Abstract

The applicability of CFD codes for two-phase flows has always been limited to special cases due to the very complex nature of its interface. Due to its tremendous computational cost, methods based on direct resolution of the interface are not applicable to most problems of practical relevance. Instead, averaging procedures are commonly used for these applications, such as the Eulerian-Eulerian approach, which necessarily means losing detailed information on the interfacial structure. In order to allow widespread application of the two-fluid approach, closure models are required to reintroduce in the simulations the correct interfacial mass, momentum, and heat transfer.
It is evident that such closure models will strongly depend on the specific flow pattern. When considering vertical pipe flow with low gas volume flow rates, bubbly flow occurs. With increasing gas volume flow rates larger bubbles are generated by bubble coalescence, which further leads to transition to slug, churn-turbulent, and annular flow. Considering, as an example, a heated tube producing steam by evaporation, as in the case of a vertical steam generator, all these flow patterns including transitions are expected to occur in the system. Despite extensive attempts, robust and accurate simulations approaches for such conditions are still lacking.
The purpose of this dissertation is the development, testing, and validation of a multifield model for adiabatic gas-liquid flows at high gas volume fractions, for which a multiple-size bubble approach has been implemented by separating the gas structures into a specified number of groups, each of which represents a prescribed range of sizes. A fully-resolved continuous gas phase is also computed, and represents all the gas structures which are large enough to be resolved within the computational mesh. The concept, known as GENeralized TwO Phase flow or GENTOP, is formulated as an extension to the bubble population balance approach known as the inhomogeneous MUltiple SIze Group (iMUSIG). Within the polydispersed gas, bubble coalescence and breakup allow the transfer between different size structures, while the modeling of mass transfer between the polydispersed and continuous gas allows including transitions between different gas morphologies depending on the flow situations. The calculations were performed using the computational fluid dynamic code from ANSYS, CFX 14.5, with the support of STAR-CCM+ v8.06 and v9.02. A complete three-field and four-field model, including a continuous liquid field and two to three gas fields representing bubbles of different sizes, were first tested for numerical convergence and then validated against experimental data from the TOPFLOW and MT-Loop facilities.

Keywords: CFD; GENTOP; Surface Tension; MT-Loop; TOPFLOW

Involved research facilities

  • TOPFLOW Facility
  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-063 2015
    ISSN: 2191-8708, eISSN: 2191-8716

Downloads

Permalink: https://www.hzdr.de/publications/Publ-22338


Solubility of boron, carbon, and nitrogen in transition metals: getting insight into trends from first-principles calculations

Hu, X.; Björkman, T.; Lipsanen, H.; Sun, L.; Krasheninnikov, A. V.

Abstract

Efficient chemical vapor deposition synthesis of two-dimensional (2D) materials such as graphene, boron nitride, and mixed BCN systems with tunable band gaps requires precise knowledge of the solubility and mobility of B/C/N atoms in the transition metals (TMs) used as substrates for the growth. Yet, surprisingly little is known about these quantities either from experiments or simulations. Using first-principles calculations, we systematically study the behavior of B/C/N impurity atoms in a wide range of TMs. We compute formation energies of B/C/N interstitials and demonstrate that they exhibit a peculiar but common behavior for TMs in different rows of the periodic table, as experimentally observed for C. Our simulations indicate that this behavior originates from an interplay between the unit cell volume and filling of the d- shell electronic states of the metals. We further assess the vibrational and electronic entropic contributions to the solubility, as well as the role of anharmonic effects. Finally, we calculate the migration barriers, an important parameter in the growth kinetics. Our results not only unravel the fundamental behavior of interstitials in TMs but also provide a large body of reference data, which can be used for optimizing the growth of 2D BCN materials.

Keywords: graphene; solubility; interstitials

Involved research facilities

Related publications

Permalink: https://www.hzdr.de/publications/Publ-22337


Implementation and Validation of a Surface Tension Model for the Multi-scale approach GENTOP

Montoya Zabala, G. A.; Baglietto, E.; Lucas, D.

Abstract

Multiphase flows encountered in the nuclear industry are largely of a complex nature, and knowledge of the accurate distribution of the void fraction is of utmost importance for operation of the reactor under steady, transient, and accident conditions. At high void fractions, strong coalescence leads to the formation of large deformable bubbles. An appropriate multiphase CFD modeling of these flow regimes should be able to account for both, large and small interfacial structures, also including the effect on closure modeling of the large structures. A concept known as GEneralized TwO Phase flow or GENTOP, has been developed at the Helmholtz-Zentrum Dresden-Rossendorf in order to address such flow configurations, by dealing with a resolved potentially-continuous gas field, one or more polydispersed gas fields, and a continuous liquid phase. Application of the model to churn-turbulent and slug flow in vertical pipes [1], have evidenced an important limitation related to the lack of a surface tension modeling within the free surface, which leads to an unphysical accumulation of void near the pipe wall. This work discusses the implementation of surface tension and contact angle within the GENTOP approach, as well as the validation of these models against analytical and experimental results. The validation of the surface tension has been performed against analytically calculated oscillating periods of different shapes of ethanol droplets suspended in air. Furthermore, different contact angles are analyzed for a drop of water residing on a smooth surface. Rising velocities and deformation of a single large bubble rising in a vertical pipe were finally validated against analytical solutions. The implementation of the surface tension model in the GENTOP approach demonstrated improvements on the resolution of the bubble and stability of the interface, with considerable reduction of the numerical diffusion.

Keywords: CFD; GENTOP; Surface Tension; Contact Angle; MT-Loop

  • Contribution to proceedings
    16th International Topical Meeting on Nuclear Reactor Thermalhydraulics, 30.08.-04.09.2015, Chicago, USA
    Proceedings of the 16th International Topical Meeting on Nuclear Reactor Thermalhydraulics, Chicago, USA
  • Lecture (Conference)
    16th International Topical Meeting on Nuclear Reactor Thermalhydraulics, 30.08.-04.09.2015, Chicago, USA

Permalink: https://www.hzdr.de/publications/Publ-22336


A review on mechanisms and models for the churn-turbulent flow regime

Montoya Zabala, G. A.; Lucas, D.; Baglietto, E.; Liao, Y.

Abstract

The modeling of two-phase flows has always been limited to special cases due to the very complex nature of its interface. When considering vertical pipe flows with low gas volume flow rates, bubbly flow occurs. With increasing gas volume flow rates larger bubbles are generated by bubble coalescence, which further leads to transition to slug, churn-turbulent, and annular flow. Considering, as an example, a heated tube producing steam by evaporation, as in the case of a vertical steam generator, all these flow patterns including transitions are expected to occur in the system. Despite extensive attempts, robust and accurate simulations approaches for such conditions are still lacking. This paper summarizes the state-of-the-art on the understanding of the physics behind churnturbulent flow, and transitions to and from this flow pattern. Both, benefits and limitations of the existent experimental approaches and their usefulness for model development and validation at these high void fraction conditions are discussed. Limitation of both, low-dimensional approaches (0D, 1D, and 2D), and high resolution approaches such as Direct Numerical Simulations (DNS) are analyzed. Averaging procedures, such as the Eulerian-Eulerian approach including the interfacial momentum closures which has been used in the past for simulating churn flow, are review thoroughly. Finally, possible improvements are proposed.

Keywords: churn-turbulent; CFD; multiphase; review

Permalink: https://www.hzdr.de/publications/Publ-22335


Broadband THz detection from 0.1 to 22 THz with large area field-effect transistors

Regensburger, S.; Mittendorff, M.; Winnerl, S.; Lu, H.; Gossard, A. C.; Preu, S.

Abstract

We report on ultrafast detection of radiation between 100 GHz and 22 THz by field-effect transistors in a large area configuration. With the exception of the Reststrahlenband of GaAs, the spectral coverage of the GaAs-based detectors is more than two orders of magnitude, covering the entire THz range (100 GHz - 10 THz). The temporal resolution of the robust devices is yet limited by the 30GHz oscilloscope used for read out. The responsivity roll-off towards higher frequencies is weaker than expected from an RC-roll-off model. Terahertz pulses with peak powers of up to 65 kW have been recorded without damaging the devices.

Keywords: terahertz detetector; field-effect transistor; braodband and fast THz detection

Involved research facilities

Related publications

Permalink: https://www.hzdr.de/publications/Publ-22334


From a non-magnet to a ferromagnet: Mn implantation into different TiO2 structures

Yildirim, O.; Cornelius, S.; Butterling, M.; Anwand, W.; Wagner, A.; Smekhova, A.; Fiedler, J.; Böttger, R.; Bähtz, C.; Potzger, K.

Abstract

We study effect of the initial structural order on the resulting magnetic properties of the manganese implanted TiO2 films. Different microstructures of as-grown TiO2 films, namely amorphous, polycrystalline anatase and epitaxial anatase, have been implant-doped with Mn+ up to a concentration of 5 at.%. We found that the different initial structures lead to different defect and charge carrier concentrations, and as a result, strongly influence the magnetic properties upon implantation. Depending on the initial microstructure, paramagnetism, secondary phases related magnetic properties as well as ferromagnetism could be observed in the films.

Involved research facilities

Related publications

Downloads

Permalink: https://www.hzdr.de/publications/Publ-22333


X-ray Absorption Spectroscopy for Actinide Chemistry - Basics, Experiments and Applications

Ikeda-Ohno, A.

Abstract

Synchrotron-based X-ray spectroscopy is an emerging and powerful tool for actinide chemistry. This lecture focuses particularly on X-ray absorption spectroscopy, and will provide a comprehensive overview of the basics and experiments of this technique, as well as their applications to actinide chemistry.

Keywords: X-ray absorption spectroscopy; XAS; XANES; EXAFS; synchrotron; actinide; chemistry; overview; introduction

Involved research facilities

Related publications

  • Invited lecture (Conferences)
    The ThUL School in Actinide Chemistry, 28.09.-02.10.2015, Karlsruhe, Germany

Permalink: https://www.hzdr.de/publications/Publ-22332


Targeting lysyl oxidase for molecular imaging in breast cancer

Wuest, M.; Kuchar, M.; Sharma, S. K.; Richter, S.; Hamann, I.; Wang, M.; Vos, L.; Mackey, J. R.; Wuest, F.; Löser, R.

Abstract

Introduction: Lysyl oxidase (LOX; ExPASy ENZYME entry: EC 1.4.3.13) and members of the LOX-like family, LOXL1–LOXL4, are copper-dependent enzymes that can modify proteins of the extracellular matrix. Expression of LOX is elevated in many human cancers, including breast cancer. LOX expression correlates with the level of tissue hypoxia, and it is known to play a critical role in breast cancer metastasis. The goal of the present study was to target LOX with (1) molecular probe fluorescent labeling to visualize LOX in vitro and (2) a radiolabeled peptide to target LOX in vivo in three different preclinical models of breast cancer.
Methods: Gene expression of all five members of the LOX family was analyzed at the transcript level via microarray analysis using tissue biopsy samples from 176 patients with breast cancer. An oligopeptide sequence (GGGDPKGGGGG) was selected as a substrate-based, LOX-targeting structure. The peptide was labeled with fluorescein isothiocyanate (FITC) for confocal microscopy experiments with the murine breast cancer cell line EMT-6. In vivo molecular imaging experiments were performed using a C-terminal amidated peptide, GGGDPKGGGGG, labeled with a short-lived positron emitter, fluorine-18 (18F), for positron emission tomography (PET) in three different breast cancer models: EMT6, MCF-7 and MDA-MB-231. The PET experiments were carried out in the presence or absence of β-aminopropionitrile (BAPN), an irreversible inhibitor of LOX.
Results: Immunostaining experiments using a LOX-specific antibody on EMT-6 cells cultured under hypoxic conditions confirmed the elevation of LOX expression in these cells. An FITC-labeled oligopeptide, FITC-Ava- GGGDPKGGGGG-NH2, was found to be localized in different cellular compartments under these conditions. After injection of [18F]fluorobenzoate-GGGDPKGGGGG-NH2, radioactivity uptake was visible in all three breast cancer models in vivo. Tumor uptake was reduced by predosing the animals with 2 mg of BAPN 4 h or 24 h before injection of the radiotracer.
Conclusions: The present data support further investigation into the development of LOX-binding radiolabeled peptides as molecular probes for molecular imaging of LOX expression in cancer.

Involved research facilities

  • PET-Center

Permalink: https://www.hzdr.de/publications/Publ-22331


Ultrasound Doppler flow measurements in a liquid metal column under the influence of a strong axial electric current

Starace, M.; Weber, N.; Seilmayer, M.; Kasprzyk, C.; Weier, T.; Stefani, F.; Eckert, S.

Abstract

Magnetohydrodynamic instabilities can constitute a serious hazard to the functionality of liquid metal batteries. Here we consider the Tayler instability, which appears when the electric current, passing through a conducting fluid, reaches a critical value. The experiment discussed in this article involves a column of a eutectic GaInSn alloy, along whose axis an electric current passes. Ultrasound transducers encased in a copper electrode bounding the top of the column were used to obtain the vertical component of fluid flow, once a noise suppression system had been devised. The data thus retrieved will be discussed here.

  • Magnetohydrodynamics 51(2015)2, 249-256
    ISSN: 0024-998X

Permalink: https://www.hzdr.de/publications/Publ-22330


Ion acceleration enhanced by target ablation

Zhao, S.; Lin, C.; Wang, H. Y.; Lu, H.; Tu He, X.; Chen, J.; Cowan, T. E.; Q. Yan, X.

Abstract

Laser proton acceleration can be enhanced by using target ablation, due to the energetic electrons generated in the ablation preplasma. When the ablation pulse matches main pulse, the enhancement gets optimized because the electrons' energy density is highest. A scaling law between the ablation pulse and main pulse is confirmed by the simulation, showing that for given CPA pulse and target, proton energy improvement can be achieved several times by adjusting the target ablation.

Involved research facilities

Related publications

Permalink: https://www.hzdr.de/publications/Publ-22329


Caustic structures in the spectrum of x-ray Compton scattering off electrons driven by a short intense laser pulse

Seipt, D.; Surzhykov, A.; Fritzsche, S.; Kämpfer, B.

Abstract

We study the Compton scattering of x-rays off electrons that are driven by a relativistically intense short optical laser pulse. The frequency spectrum of the laser-assisted Compton radiation shows a broad plateau in the vicinity of the laser-free Compton line due to a nonlinear mixing between x-ray and laser photons. Special emphasis is placed on how the shape of the short assisting laser pulse affects the spectrum of the scattered x-rays. In particular, we observe sharp peak structures in the plateau region, whose number and locations are highly sensitive to the laser pulse shape. These structures are interpreted as spectral caustics by using a semiclassical analysis of the laser-assisted QED matrix element.

Downloads

Permalink: https://www.hzdr.de/publications/Publ-22328


Directional Spin Wave Emission From Topological Spin Textures

Sluka, V.; Weigand, M.; Kakay, A.; Schultheiss, K.; Erbe, A.; Tyberkevych, V.; Slavin, A.; Deac, A.; Lindner, J.; Fassbender, J.; Raabe, J.; Wintz, S.

Abstract

In the present contribution we will show that in a stacked vortex pair system with uniaxial magnetic anisotropy, directional spin waves of different symmetries and dimensionalities can be excited.

Keywords: spin waves; multilayers; dipole-exchange; non-reciprocity

  • Lecture (Conference)
    13th Joint MMM/Intermag Conference, 11.-15.01.2016, San Diego, USA

Permalink: https://www.hzdr.de/publications/Publ-22327


Parameter-free determination of the exchange constant in thin films using magnonic patterning

Langer, M.; Wagner, K.; Sebastian, T.; Hübner, R.; Grenzer, J.; Wang, Y.; Kubota, T.; Schneider, T.; Stienen, S.; Linder, J.; Lenz, K.; Linder, J.; Takanashi, K.; Arias, R.; Fassbender, J.

Abstract

An all-electrical method is presented to determine the exchange constant of magnetic thin films using ferromagnetic resonance. For films of 20 nm thickness and below, the determination of the exchange constant A, a fundamental magnetic quantity, is anything but straightforward. Among others, the most common methods are based on the characterization of perpendicular standing spin-waves. These approaches are however challenging, due to (i) very high energies and (ii) rather small intensities in this thickness regime. In the presented approach, surface patterning is applied to a permalloy (Ni80Fe20) film and a CFMS (Co2Fe0.4Mn0.6Si) Heusler compound. Acting as a magnonic crystal, such structures enable the coupling of backward volume spin-waves to the uniform mode. Subsequent ferromagnetic resonance measurements give access to the spin-wave spectra free of unquantifiable parameters, and thus, to the exchange constant A with high accuracy.

Involved research facilities

Related publications

Permalink: https://www.hzdr.de/publications/Publ-22326


Breaking of axial symmetry in excited heavy nuclei as identified in GDR data

Grosse, E.; Junghans, A. R.; Massarczyk, R.

Abstract

A recent theoretical prediction of a breaking of axial symmetry in quasi all heavy nuclei is confronted to a new critical analysis of photon strength functions of nuclei in the valley of stability. For the photon strength in the isovector giant dipole resonance (IVGDR) regime a parameterization of GDR shapes by the sum of three Lorentzians (TLO) is extrapolated to energies below and above the IVGDR. The impact of non-GDR modes adding to the low energy slope of photon strength is discussed including recent data on photon scattering and other radiative processes. These are shown to be concentrated in energy regions where various model calculations predict intermediate collective strength; thus they are obviously separate from the IVGDR tail. The triple Lorentzian (TLO) ansatz for giant dipole resonances is normalized in accordance to the dipole sum rule. The nuclear droplet model with surface dissipation accounts well for positions and widths without local, nuclide specific, parameters. Very few and only global parameters are needed when a breaking of axial symmetry already in the valley of stability is admitted; a reliable prediction for electric dipole strength functions also outside of it is expected.

Involved research facilities

Related publications

Downloads

Permalink: https://www.hzdr.de/publications/Publ-22325


Post-test calculations of UPTF experiments with ANSYS CFX

Höhne, T.

Abstract

The last decade has seen an increasing use of three-dimensional CFD codes to predict steady state and transient flows in nuclear reactors because a number of important phenomena such as pressurized thermal shocks, coolant mixing, and thermal striping cannot be predicted by traditional one-dimensional system codes with the required accuracy and spatial resolution.
The nuclear industry now also recognizes that CFD codes have reached the desired level of maturity (at least for single-phase applications) for them to be used as part of the Nuclear Power Plant (NPP) design process, and it is the objective the research and development teams to assess the current capabilities of such codes in this regard, and contribute to the technology advance in respect to their verification and validation. CFD is already well-established in addressing certain safety issues in NPPs, as reported and discussed at various international workshops. The development, verification and validation of CFD codes in respect to NPP design necessitates further work on the complex physical modelling processes involved, and on the development of efficient numerical schemes needed to solve the basic equations. In parallel, it remains an overriding necessity to benchmark the performance of the CFD codes, and for this experimental databases need to be established, first for separate-effect tests but especially for full-size integral tests.
In order to validate the CFD Code ANSYS CFX for reactor safety relevant flow phenomena it is essential to use the UPTF experiments, since they are full scale tests. All other separate effect test rigs and test facilities like ROCOM (Höhne, 2000) are scaled. Scaling parameters of flow conditions are one of the still open topics for the use of CFD codes in nuclear reactor safety. Three UPTF tests were selected and post-test calculation were performed. The major focus was analyzing the qualitative flow behavior.

Keywords: UPTF; CFX; LOCA; PTS

  • Other report
    Dresden: HZDR, 2015
    25 Seiten

Permalink: https://www.hzdr.de/publications/Publ-22324


H trapping and mobility in nanostructured tungsten grain boundaries: A combined experimental and theoretical approach

González, C.; Panizo-Laiz, M.; Gordillo, N.; Tejado, E.; Munnik, F.; Guerrero, C.; Piaggi, P.; Iglesias, R.; Perlado, J. M.; González-Arrabal, R.

Abstract

The H trapping and mobility in nanostructured W grain boundaries has been studied by combining experimental and density functional theory (DFT) data. Experimental results show that nanostructured W coatings with a columnar structure and a large number of (110)/(211) interfaces retain more H than the coarsed grained W tungsten samples do. To investigate the possible influence of grain boundaries on the H retention, a complete energetic analysis has been done in a semi-coherent W(110)/W(112) interface built by DFT. Our results show that this kind of non-coherent interface largely attract points defects (both H atom and metallic monovacancy separately) and that the presence of these interfaces contribute to decrease the migration energy of the H atoms with respect to the bulk. When both W monovacancy and H atom are introduced together into the system, the HV complex results the most stable configuration suggesting an explanation to the H retention in the GB observed experimentally.

Keywords: Fusion; H trapping

Involved research facilities

Related publications

Permalink: https://www.hzdr.de/publications/Publ-22323


The first four years of the AMS-facility DREAMS: Status and developments for more accurate radionuclide data

Rugel, G.; Pavetich, S.; Akhmadaliev, S.; Enamorado Baez, S. M.; Scharf, A.; Ziegenrücker, R.; Merchel, S.

Abstract

DREAMS, the DREsden AMS-facility, is performing routine accelerator mass spectrometry of 10Be, 26Al, 36Cl, 41Ca, and 129I for diverse kinds of applications. All DREAMS data is normalised directly to primary standards or traceable via cross-calibration of secondary standards to those.
Recent technical developments such as a low-memory ion source for 36Cl and 129I and sophisticated tuning strategies for 129I led to improved accuracy data.Tests of ion source output have been performed with different metal binders, sample-to-binder mixing ratios, and compaction pressures in order to find optimal parameters. The highest and most stable outputs have been obtained for 10Be, 26Al, and 41Ca for the following binders and mixing ratios (by weight): BeO:Nb, 1:4; Al2O3:Ag, 1:1; CaF2:Ag, 1:4. Higher beam currents generally result in reduced statistical uncertainty. Cross-contamination and long-term memory seem to be underestimated problems asking for further tests and improvements such as the development of low-level in-house-standards.

Keywords: accelerator mass spectrometry; cosmogenic nuclides

Involved research facilities

Related publications

Permalink: https://www.hzdr.de/publications/Publ-22322


Terahertz spectroscopy of 0D and 2D semiconductors with a free-electron laser

Schneider, H.

Abstract

This talk reviews recent experimental studies carried out using the free-electron laser (FEL) facility FELBE in Dresden, Germany. Intense, nearly transform-limited ps pulses in the mid-infrared and terahertz (THz) regimes provide unique research opportunities to study novel materials and devices.

Keywords: free-electron laser; terahertz spectroscopy

Involved research facilities

Related publications

  • Lecture (others)
    Seminar, Xi'an University of Technology, 04.05.2015, Xi'an, China
  • Lecture (others)
    Seminar, CAEP, 07.05.2015, Mianyang, China

Permalink: https://www.hzdr.de/publications/Publ-22321


Spin-based nanoelectronic devices for mobile Information-Communication Technology

Deac, A. M.

Abstract

Abstract
Perhaps the best known (or most successfully implemented) spin-based device is the hard-disk read-head. Indeed, the discovery of giant magnetoresistance enabled a paradigm shift in the miniaturization of magnetic storage technology, which was disruptive enough to earn its discoverers a Nobel price [1]. More recently, it has been demonstrated that non-volatile, ultra-fast spin-based memory bit devices can be designed so that they can scale down to more than one fifth of all other available technologies, including SRAM [2]. Other spin-based nanoelectronics devices currently under consideration - which will be discussed here - range from tuneable radio-frequency oscillators to magnetic field sensors, negative resistors, amplifiers, write heads and random number generators. [1] http://www.nobelprize.org/nobel_prizes/physics/laureates/2007/index.html [2] http://www.avalanche-technology.com/technology/ram

Biography
Alina Deac is currently the leader of the Spintronics Group at the Helmholtz-Zentrum Dresden - Rossendorf in Dresden, Germany. During the last 15 years, her research has been focused on spin-torque induced phenomena and their potential applications for mobile ICT devices. After obtaining her PhD in Physics at the Universite Joseph Fourier Grenoble, France in 2005, she pursued her career by working with top-notch institutions in Japan, US and Switzerland. She is a Senior Member of the IEEE Magnetics Society and an expert in the field of spintronics for the EU.

Keywords: spintronics; magnetic storage; information-communication technology

Involved research facilities

Related publications

  • Invited lecture (Conferences)
    SEMICON Europa 2015, 06.-08.10.2015, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-22317


In Situ Tuning the Conductance of Single Molecular Diarylethene Switches

Sendler, T.; Luka-Guth, K.; Wieser, M.; Lokamani, M.; Wolf, J.; Huhn, T.; Scheer, E.; Kerbusch, J.; Gemming, S.; Erbe, A.

Abstract

A major goal of molecular electronics is the development and implementation of molecular electronic devices such as single molecular switches. In this work we present a detailed study of single diarylethene molecules that were in situ switched from their non-conductive to conductive state in the presence of gold nanoelectrodes via controlled light irradiation. The molecules were dissolved in two different solvents and measured with two different side-groups. Histograms of conductance traces were taken and complemented by extracting the relative position of the current carrying molecular level and its level broadening from current-voltage characteristics by means of the single level transport model. The obtained results show a clear light-induced ring forming isomerization, which is almost independent of the side-groups, while electron withdrawing side groups lead to a reduction of conductance, a decrease of the level broadening and an increased difference between the molecular level and the Fermi energy of the metals. Quantum chemical calculations of the light-induced switching processes correlate these observations with the fundamentally different low-lying electronic states of the opened and closed forms and their comparably small modification by the electron-withdrawing substituents.

  • Poster
    Annual Workshop IHRS NanoNet 2014, 29.-30.09.2014, Lohmen/Bastei, Deutschland
  • Poster
    DCCMS Annual Workshop and General Assembly 2014, 20.10.2014, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-22316


Spin-based nanoelectronic devices for mobile Information-Communication Technology

Deac, A. M.

Abstract

Perhaps the best known (or most successfully implemented) spin-based device is the hard-disk read-head. Indeed, the discovery of giant magnetoresistance enabled a paradigm shift in the miniaturization of magnetic storage technology, which was disruptive enough to earn a Nobel for the two researchers who carried out the initial studies [1]. In a nutshell, giant magnetoresistance refers to the fact that the electrical properties of a multilayer containing at least two magnetic layers depend on the orientation of their magnetic moment. For instance, if the magnetic layers are cobalt, iron or nickel (or their alloys), the resistance of the structure is maximum when the magnetic moments are antiparallel to each other, and minimum when they are parallel.

More recently, it has been demonstrated the inverse phenomenon can also be observed: the relative orientation of the magnetic moments of two ferromagnetic layers can be manipulated by applying an electrical bias (i.e. a current or a voltage) across the structure. This is a consequence of spin-momentum transfer between the conduction electrons and the magnetization of the layer they are travelling across, which effectively induces a torque on the magnetization, the so-called ‘spin-transfer torque’ or ‘spin-torque’ [2-6]. Two main effects can be induced exploiting this torque: the magnetic moment of a given layer can be switched to a chosen direction – for instance, from parallel to antiparallel to the magnetization of the second layer – or it can be induced to gyrate around a given direction for as long as the electrical bias is applied.

Spin-transfer switching as the first spin-transfer induced phenomenon to be demonstrated experimentally, with the first report published at the end of 2000 [5]. Today, spin-transfer switching is the write scheme for non-volatile, ultra-fast Spin-Transfer Torque Random Access Memory (STT-RAM) bit devices. STT-RAM can be designed so that they can scale down to more than one fifth of all other available technologies, including SRAM [7,8]. Spin-transfer driven precession, first demonstrated in 2003 [6], has been suggested as working principle for other spin-based nanoelectronics devices currently under consideration, which range from tuneable, low input power radio-frequency oscillators wireless communication, to magnetic field sensors, negative resistors, amplifiers, write heads and random number generators. Indeed, the frequency of such devices can be adjusted simply by changing the applied bias, and they provide sufficient power [9] while at the same time being about 50 times smaller than present devices used in mobile telecommunication [10]. Moreover, novel materials hold the promise of pushing the frequency limit beyond what present-day technology can achieve [11]. Possible applications include anti-collision systems for cars, remote hospitals and immersive audio-video entertainment systems.

[1] http://www.nobelprize.org/nobel_prizes/physics/laureates/2007/index.html
[2] J. C. Slonczewski, J. Magn. Magn. Mater. 159, L1 (1996).
[3] L. Berger, Phys. Rev. B 54, 9353 (1996).
[4] M. D. Stiles, A. Zangwill, Phys. Rev. B 66, 014407 (2002).
[5] J. A. Katine, F. J. Albert, R. A. Buhrman et al., Phys. Rev. Lett. 84, 3149 (2000).
[6] S. I. Kiselev, J. C. Sankey, I. N. Krivorotov et al., Nature (London) 425, 380 (2003).
[7] http://www.avalanche-technology.com/technology/ram
[8] http://www.everspin.com/
[9] A. Deac, A. Fukushima, H. Kubota, et al., Nature Phys. 4, 803 (2008).
[10] P. Villard, U. Ebels, D. Houssameddine, et al., IEEE J. Solid-State Circuits 45, 214
(2010).
[11] S. Mizukami, F. Wu, A. Sakuma, et al., Phys. Rev. Lett. 106, 117201 (2011).

Keywords: spintronics; wireless communication; magnetic data storage

Involved research facilities

Related publications

  • Invited lecture (Conferences)
    The 12th Japanese-German Frontiers of Science (JGFoS) Symposium, 01.-04.10.2015, Kyoto, Japan

Permalink: https://www.hzdr.de/publications/Publ-22315


Spin-Torque Devices Based on MgO-Based Magnetic Tunnel Junctions

Deac, A. M.

Abstract

Spin-torque nano-oscillators (STNOs) are novel devices which may be exploited for wireless communication applications [1-3]. In particular, it has recently been demonstrated that STNOs utilizing an in-plane magnetized polarizer (also acting as read-out layer) and out-of-plane magnetized free layer allow for the full parallel-to-antiparallel resistance variation to be exploited in the limit of 90° precession angle, thereby maximizing the output power [1]. However, for this specific geometry, steady-state precession can only be sustained if the spin-transfer torque exhibits an asymmetric dependence on the angle between the free and the polarizing layer, such as in the case of fully metallic devices [1]. Nevertheless, it has recently been reported that dynamics have been experimentally observed in similarly designed MgO-based magnetic tunnel junctions (MTJs) under constant applied electrical current, in spite of the fact that such devices do not exhibit any asymmetry in the spin-torque angular dependence [4,5]. These results have so far been interpreted based on the formalism for metallic devices.

Here, we explore potential mechanisms for sustaining steady-state precession in MgO-based STNOs with this specific geometry. To this end, we analytically and numerically solve the Landau-Lifshitz-Gilbert-Slonczewski equation under a constant perpendicular applied current and field. We take into account both the angular and the bias dependence of the resistance of the nanopillar in order to convert the current into voltage, which is the relevant parameter in an MgO-MTJ. The field-like torque is neglected. We demonstrate that the angular dependence of the resistance introduces sufficient asymmetry of the in-plane spin-torque term to sustain precession in this system, but the bias dependence of the resistance gradually quenches this asymmetry as the current is increased and consequently suppresses precession above a given threshold. We furthermore prove that in an STNO with circular cross-section an external field is required to observe steady-state dynamics, but this constraint is lifted when introducing an in-plane easy axis, which opens new avenues to be explored for designing devices for mobile communication.

[1] W. H. Rippard, A. M. Deac, M. R. Pufall, et al., Physical Review B 81, 014426 (2010).
[2] A. M. Deac, A. Fukushima, H. Kubota, et al., Nature Physics 4, 308 (2008).
[3] S. I. Kiselev, J. C. Sankey, I. N. Krivorotov, et al., Nature 425, 380 (2003).
[4] H. Kubota, K. Yakushiji, A. Fukushima, et al., Applied Physics Express 6, 103003 (2013).
[5] T. Taniguchi, H. Arai, S. Tsunegi, et al., Applied Physics Express 6, 123003 (2013).

Keywords: magnetism; magnetic tunnel junctions; spin-transfer torque

Involved research facilities

Related publications

  • Invited lecture (Conferences)
    Spin Dynamics in Nanostructures Gordon Research Conference Nanoscale Spintronics with Magnons, Phonons, and Photons, 26.-31.07.2015, The Hong Kong University of Science and Technology, China

Permalink: https://www.hzdr.de/publications/Publ-22314


International research environment and career development

Deac, A. M.

Abstract

This talk provides mentoring for students seeking an international career.

Keywords: carrer development

  • Invited lecture (Conferences)
    Spin Dynamics in Nanostructures (GRS) Gordon Research Seminar Interplay of Spin, Charge and Lattice Dynamics, 25.-26.07.2015, The Hong Kong University of Science and Technology, China

Permalink: https://www.hzdr.de/publications/Publ-22313


Zero-field precession and suppression of the output power due to the biasdependence of the TMR in MgO-based spin-torque oscillators Alina Maria Deac

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

Abstract

Spin-torque nano-oscillators (STNOs) are novel devices which may be exploited for wireless
communication applications [1-3]. In particular, it has recently been demonstrated that STNOs utilizing an in-plane magnetized polarizer (also acting as read-out layer) and out-of-plane magnetized free layer allow for the full parallel-to-antiparallel resistance variation to be exploited in the limit of 90° precession angle, thereby maximizing the output power [1]. However, for this specific geometry, steady-state precession can only be sustained if the spin-transfer torque exhibits an asymmetric dependence on the angle between the free and the polarizing layer, such as in the case of fully metallic devices [1]. Nevertheless, it has recently been reported that dynamics have been experimentally observed in similarly designed MgO-based magnetic tunnel junctions (MTJs) under constant applied electrical current, in spite of the fact that such devices do not exhibit any asymmetry in the spin-torque angular dependence [4,5]. These results have so far been interpreted based on the formalism for metallic devices.

Here, we explore potential mechanisms for sustaining steady-state precession in MgO-based STNOs with this specific geometry. To this end, we analytically and numerically solve the Landau-Lifshitz-Gilbert-Slonczewski equation under a constant perpendicular applied current and field. We take into account both the angular and the bias dependence of the resistance of the nanopillar in order to convert the current into voltage, which is the relevant parameter in an MgO-MTJ. The field-like torque is neglected. We demonstrate that the angular dependence of the resistance introduces sufficient asymmetry of the in-plane spin-torque term to sustain precession in this system, but the bias dependence of the resistance gradually quenches this asymmetry as the current is increased and consequently suppresses precession above a given threshold. We furthermore prove that in an STNO with circular cross-section an external field is required to observe steady-state dynamics, but this constraint is lifted when introducing an in-plane easy axis, which opens new avenues to be explored for designing devices for mobile communication.

[1] W. H. Rippard, A. M. Deac, M. R. Pufall, et al., Physical Review B 81, 014426 (2010).
[2] A. M. Deac, A. Fukushima, H. Kubota, et al., Nature Physics 4, 308 (2008).
[3] S. I. Kiselev, J. C. Sankey, I. N. Krivorotov, et al., Nature 425, 380 (2003).
[4] H. Kubota, K. Yakushiji, A. Fukushima, et al., Applied Physics Express 6, 103003 (2013).
[5] T. Taniguchi, H. Arai, S. Tsunegi, et al., Applied Physics Express 6, 123003 (2013).

Keywords: magnetism; spin-transfer torque; magnetic tunnel junction

Involved research facilities

Related publications

  • Invited lecture (Conferences)
    20th International Conference on Magnetism, 06.-10.07.2015, Barcelona, Spain
  • Poster
    12th Japanese-German Frontiers of Science Symposium 2015, 01.-04.10.2015, Kyoto, Japan

Permalink: https://www.hzdr.de/publications/Publ-22312


Atomic transport during solid-phase epitaxial recrystallization of amorphous germanium

Radek, M.; Bracht, H.; Mccallum, J. C.; Johnson, B. C.; Posselt, M.; Liedke, B.

Abstract

The atomic mixing of matrix atoms during solid-phase-epitaxy (SPE) is studied by means of isotopically enriched germanium (Ge) multilayer structures grown by molecular beam epitaxy on natural Ge wafers. The entire isotope structure and parts of the natural Ge wafer were preamorphized by Ge implantation. Recrystallization of the amorphous Ge layer is performed at temperatures between 350 ˚C and 450 ˚C. The position of the amorphous/crystalline (a/c) interface was monitored during SPE regrowth using a time-resolved-reflectivity (TRR) system. The SPE process was stopped before the a/c interface reached the surface, i.e, before the recrystallization of the amorphous layer was completed. Secondary-ion-mass-spectrometry (SIMS) was applied to determine the self-atom distribution within the amorphous and recrystallized part of each sample. An upper limit of 0.5 nm is determined for the displacement length of the matrix atoms. This small displacement length is consistent with theoretical models and atomistic simulations of SPE predicting that bond-switching with nearest-neighbours across the a/c interface controls the SPE regrowth.

Keywords: Germanium; Solid-phase epitaxial recrystallization; atomic transport; isotope multilayers

Involved research facilities

Related publications

  • Poster
    28th International Conference on Defects in Semiconductors (ICDS 2015), 27.-31.07.2015, Espoo, Finland

Permalink: https://www.hzdr.de/publications/Publ-22311


Characterisation and properties of f-element complexes with amide and amidine ligands

März, J.; Schmid, M.; Ikeda-Ohno, A.

Abstract

The lanthanide (Ln) complexes with N-chelating ligands have attracted considerable attentions because of their unique tuneable steric and electronic properties.[1] Amongst such Ln complexes with N-chelating ligands, amide-based complexes are known to offer a wide range of applications, e.g., as efficient luminescent agents employed in bio-analytical fields.[2] Furthermore, amidine-based complexes enable the Ln metals to stabilise in exotic oxidation states (i.e., di- and tetravalent) with remarkable catalytic activity.[3]
These unique properties of amide- and amidine-based complexes of f-elements motivate us to perform the present study focusing on the synthesis and characterisation of the f-element complexes with newly synthesised amide- and amidine ligands shown in Figure 1. The aim of this study is to investigate the physical/chemical properties (e.g., optical properties) of f-elements (i.e., Ln and actinides (An)) complexed with the amide- and amidine ligands and compare their properties between Ln and An, and between solid and solution states, by means of single-crystal X-ray diffraction, X-ray absorption spectroscopy, etc. A comprehensive overview of the amide- and amidine complexes of f-elements will be presented particularly in terms of structural point of view.

References
1 A. A. Trifonov, Coord. Chem. Rev. 2010, 254, 1327 –1347.
2 e.g., Y. Tang et al., Inorg. Chem. Commun. 2005, 8, 1018-1021; J. Xu et al., J. Am. Chem. Soc. 2011, 133, 19900–19910.
3 F. T. Edelmann, Chem. Soc. Rev. 2009, 38, 2253-2268.

Keywords: lanthanide; actinide; complex; amide; amidine; single-crystal XRD

  • Poster
    International conference on f-elements, 06.-09.09.2015, Oxford, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-22310


Dilute ferromagnetic InMnP

Khalid, M.; Weschke, E.; Skorupa, W.; Helm, M.; Zhou, S.

Abstract

We have synthesized a new magnetic semiconductor,InMnP, by Mn ion implantation and pulsed laser annealing [1, 2]. Clear ferromagnetic hysteresis loops and a perpendicular magnetic anisotropy are observed up to a Curie temperature of 42 K. Large values of negative magnetoresistance and magnetic circular dichroism as well as anomalous Hall effect are further evidences of a ferromagnetic order in InMnP. An effort is made to understand the transport mechanism in InMnP using the theoretical models. We find that the valence band of InP does not merge with the impurity band of the heavily doped InMnP (8 %). Our results suggest that impurity band conduction is a characteristic of Mn‐doped InP and GaP which have deep Mn‐ cceptor levels. [1] M. Khalid, et al., Phys. Rev. B 89, 121301(R) (2014) [2] M. Khalid, et al., J. Appl. Phys. 117, 043906 (2015).

Involved research facilities

Related publications

  • Poster
    20th International Conference on Mangetism, 05.-10.07.2015, Barcelona, Spain

Permalink: https://www.hzdr.de/publications/Publ-22309


Mid-infrared ridge waveguide in MgO:LiNbO3 crystal produced by combination of swift O5+ ion irradiation and precise diamond blade dicing

Cheng, Y.; Lv, J.; Akhmadaliev, S.; Zhou, S.; Kong, Y.; Chen, F.

Abstract

We report on the fabrication of ridge waveguide operating at mid-infrared wavelength in MgO:LiNbO3 crystal by using O5+ ion irradiation and precise diamond blade dicing. The waveguide shows good guiding properties at the wavelength of 4 μm along the TM polarization. Thermal annealing has been implemented to improve the waveguiding performances. The propagation loss of the ridge waveguide has been reduced to be 1.0 dB/cm at 4 μm after annealing at 310 °C. The micro-Raman spectra indicate that the microstructure of the MgO:LiNbO3 crystal has no significant change along the ion track after swift O5+ ion irradiation.

Keywords: Optical waveguide; MgO:LiNbO3 crystal; Ion irradiation; Diamond blade dicing; Mid-infrared waveguides

Involved research facilities

Related publications

Permalink: https://www.hzdr.de/publications/Publ-22308


Enhancing Robustness and Applicability of Contactless Inductive Flow Tomography

Ratajczak, M.; Wondrak, T.; Zürner, T.; Stefani, F.

Abstract

Measuring the flow velocity in hot, chemically aggressive and opaque melts is a challenging task even for today’s measurement techniques. The contactless inductive flow tomography (CIFT) could provide a solution by applying magnetic fields to an electrically conducting melt and measuring the small flow-induced magnetic perturbances outside of the container. In this paper we will demonstrate how the robustness of CIFT can be enhanced by means of excitation with time-harmonic magnetic fields, making it more insensitive to the ubiquitous changes of the environmental magnetic field. Further we will show how the problem of an electrically conducting container can be treated, which is necessary, e.g., for industrial application in continuous casting.

  • Contribution to proceedings
    IEEE Sensors 2015, 01.-04.11.2015, Busan, Südkorea
    Proceedings of IEEE Sensors 2015, 662-665
  • Lecture (Conference)
    IEEE Sensors 2015, 01.-04.11.2015, Busan, Südkorea

Permalink: https://www.hzdr.de/publications/Publ-22307


Ferromagnetism induced by vacancy clusters in Silicon

Liu, Y.; Zhang, X. H.; Yuan, Q.; Han, J. C.; Zhou, S. Q.; Song, B.

Abstract

Defect-induced ferromagnetism provides an alternative for organic and semiconductor spintronics. Though it is weak, it can be stable above room temperature. Till now it has been confirmed at least in oxides [1, 2] and carbon based materials [3, 4]. Interestingly, the relation between magnetism and defects in Silicon was demonstrated decades ago [5]. Since then, some progresses were made [6-9] and push forward the research of magnetic Mn doped Si a lot but it is drawn little attention itself. Here, with the latest growth purifying technique and sensitive measurements, we investigated the magnetism in Silicon after neutron irradiation and try to correlate the observed magnetism to particular defects in Si.

Keywords: defect-induced ferromagnetism; silicon; neutron irradiation; semiconductors

  • Poster
    28th International Conference on Defects in Semiconductors, 27.-31.07.2015, Espoo, Finland

Permalink: https://www.hzdr.de/publications/Publ-22306


Strong Auger scattering in Landau-quantized graphene evidenced by circularly polarized pump-probe spectroscopy

Winnerl, S.; Mittendorff, M.; Wendler, F.; Malic, E.; Knorr, A.; Schneider, H.; Helm, M.

Abstract

While the carrier dynamics in graphene in absence of magnetic fields is well researched in a large spectral range ranging from UV to THz, the dynamics in Landau quantized graphene is almost unexplored. We investigate the carrier dynamics within the system of Landau levels (LLs) of index n = -1, n = 0 and n = 1 by pump-probe experiments complemented by microscopic modelling. Using circularly polarized terahertz radiation (at 18 THz) allows one to selectively excite the two energetically degenerate transitions LL-1 → LL0 and LL0 → LL1, respectively (at B  4 T). While three of the four possible configurations give intuitive results (bleaching, when pumping and probing with the same polarization, induced absorption with opposite polarizations), surprisingly, one configuration counterintuitively leads to bleaching while pumping and probing with opposite polarizations (Fig. 1 lower panel). This implies that even though LL0 is being optically pumped, its population decreases [1] ! Calculations show that LL0 is actually depleted by strong Auger scattering. Note that the two configurations shown in the Figure are distinguishable only because of the slight (n-type) doping of the graphene sample.
We discuss the role of carrier-carrier and carrier-phonon scattering in Landau quantized graphene and provide an outlook on the application potential of this system for tunable THz lasers.

Keywords: Graphene; Landau levels; carrier relaxation; pump-probe; free electron laser

Involved research facilities

Related publications

  • Lecture (Conference)
    Electronic Properties Of Two-Dimensional Electron Systems (EP2DS-21), 26.-31.07.2015, Sendai, Japan

Permalink: https://www.hzdr.de/publications/Publ-22305


Effect of an upward magnetic field on nanosized sulfide precipitation in ultra-low carbon steel

Duan, K. J.; Zhang, L.; Yuan, X. Z.; Han, S. S.; Liu, Y.; Huang, Q. S.

Abstract

An induction levitation melting (ILM) refining process is performed to remove most microsized inclusions in ultra-low carbon steel (UCS). Nanosized, spheroid shaped sulfide precipitates remain dispersed in the UCS. During the ILM process, the UCS is molten and is rotated under an upward magnetic field. With the addition of Ti additives, the spinning molten steel under the upward magnetic field ejects particles because of resultant centrifugal, floating, and magnetic forces. Magnetic force plays a key role in removing sub-micrometer-sized particles, composed of porous aluminum titanate enwrapping alumina nuclei. Consequently, sulfide precipitates with sizes less than 50 nm remain dispersed in the steel matrix. These findings open a path to the fabrication of clean steel or steel bearing only a nanosized strengthening phase.

Keywords: ultra-low carbon steel; magnetic field; sulfide precipitation; induction levitation; titanium

Permalink: https://www.hzdr.de/publications/Publ-22304


Comparative study of ultrafast X-ray tomography and wire-mesh sensors for vertical gas-liquid pipe flows

Banowski, M.; Beyer, M.; Szalinski, L.; Lucas, D.; Hampel, U.

Abstract

At the Institute of Fluid Dynamics of the Helmholtz-Zentrum Dresden-Rossendorf the wire-mesh sensor and the ultrafast X-ray tomography were developed to investigate two-phase flows with high spatial and temporal resolution. In the TOPFLOW facility, a test section was constructed for a comparative study of wire-mesh sensors and ultrafast X-ray tomography. Due to a minimum vertical distance between X-ray and wire-mesh positions, the results can be compared directly neglecting flow developing effects. Varying water and air superficial velocities in a wide range, flow regimes from bubble flow via slug flow to annular flow were investigated. Four typical experimental results are presented and discussed in this paper. Finally, the application ranges for both measurement techniques are briefly discussed.

Keywords: X-ray tomography; Wire-mesh sensor; vertical pipe; two-phase flow

Involved research facilities

  • TOPFLOW Facility
  • Contribution to proceedings
    7th International Symposium on Process Tomography, 01.-03.09.2015, Dresden, Deutschland
  • Lecture (Conference)
    7th International Symposium on Process Tomography, 01.-03.09.2015, Dresden, Deutschland
  • Flow Measurement and Instrumentation 53(2017), 95-106
    Online First (2016) DOI: 10.1016/j.flowmeasinst.2016.02.001
    Cited 61 times in Scopus

Permalink: https://www.hzdr.de/publications/Publ-22303


In-situ observation of 3D particle assembly

Josten, E.; Wetterskog, E.; Glavic, A.; Boesecke, P.; Rücker, U.; Bergström, L.; Brückel, T.

Abstract

The self-assembly of magnetic nanoparticles has a high potential for future applications [1], as it allows mass production processes of very small structures without the use of expensive equipment. The process itself is complex, including several interactions between nanoparticles, solvent, and substrate. A deeper understanding is the key for a better control of the self-organization process.

The present work adds a novel quantitative contribution to the study of the kinetics in 3D long range ordered nanoparticle superstructures. These superstructures have been investigated in-situ during the self-assembly using an optimized GISAXS setup to explore the dynamic growthmodes during deposition. The nanoparticles investigated are well-characterized γ-Fe2O3 nanospheres [2,3], which have been deposited on a substrate to form an ensemble of highly ordered superstructures (mesocrystals) [4].

The time-dependent GISAXS study of the self-assembly process, carried out at the ID01 beamline at ESRF, resulted in an understanding of how the structures evolve with time and how the evaporation can be controlled by external parameters. The in-situ cell (fig.1), which was developed to monitor the structure as well as the height and shape of the droplet, was employed for additional control of the process parameters and the possibility of an accurate identification of key physical parameters governing the process. The time evolution of the ordering process was analyzed by fitting position and width of multiple peaks for all recorded GISAXS patterns (for example fig.2). New insights into the drying and self-assembly process of an ensemble of 3D highly ordered superstructures were obtained and evaporation time-dependent stages of the mesocrystal growth and their spatial positions were identified [5].

Keywords: magnetic nanoparticles; in-situ GISAXS; self-assembly; X-ray scattering; mesocrystals

  • Lecture (Conference)
    GISAS2015, 08.-11.09.2015, Nice, Frankreich
  • Poster
    GISAXS2016 workshop, 16.-18.11.2016, Hamburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-22302


Reduction of phase noise in nanowire spin orbit torque oscillators

Yang, L.; Verba, R.; Tiberkevich, V.; Schneider, T.; Smith, A.; Duan, Z.; Youngblood, B.; Lenz, K.; Lindner, J.; Slavin, A. N.; Krivorotov, I. N.

Abstract

Spin torque oscillators (STOs) are compact, tunable sources of microwave radiation that serve as a test bed for studies of nonlinear magnetization dynamics at the nanometer length scale. In particular, the spin torque in an STO can be created by spin-orbit interaction, but low spectral purity of the microwave signals generated in spin orbit torque oscillators hinders practical applications of these magnetic nanodevices. Here we demonstrate a method for decreasing the phase noise of spin orbit torque oscillators based on Pt/Ni80Fe20 nanowires. We experimentally demonstrate that tapering of the nanowire, which serves as the STO active region, significantly decreases the spectral linewidth of the generated signal. We explain the observed linewidth narrowing in the framework of Ginzburg-Landau auto-oscillator model. The model reveals that spatial non-uniformity of the spin current density in the tapered nanowire geometry hinders the excitation of higher order spin-wave modes, thus stabilizing the single-mode generation regime. This non-uniformity also generates a restoring force acting on the excited self-oscillatory mode, which reduces thermal fluctuations of the mode spatial position along the wire. Both these effects improve the STO spectral purity.

Keywords: n.n

Involved research facilities

Related publications

Permalink: https://www.hzdr.de/publications/Publ-22301


Stability of MR brain-perfusion measurement using arterial spin labeling

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

Abstract

Arterial spin labeling (ASL) is an MR technique for assessment of cerebral blood flow (CBF) that does not require use of contrast agents which makes it a less invasive alternative to the 15O-H2O-PET measurement. The repeatability of ASL has been studied extensively but mainly in young healthy volunteers. We have tested repeatability of ASL under realistic clinical conditions in elderly brain tumor patients acquired with a Philips Ingenuity TF PET/MR in the context of an ongoing 11C-Methionine PET/MR study. Twenty three patients (age 54.8±13.0 y) were scanned on two or more session. The patients underwent 6 weeks of concurrent radiochemotherapy with Temozolomide between the first session and second measurement. The mean relative difference of gray matter CBF was 18.6% between the first two session and 13.0% for the second session and further on. The mean gray matter CBF was 46.6±7.2 mL/min/100 g on the first sessions and there was a significant decrease of 9.8% between first and second session (p=0.027). In summary, the ASL presents measurement of CBF with reasonable repeatability also in elderly patients under clinical conditions when it is not possible to control for all sources of variation. Significant decrease of CBF in healthy tissue was observed after the radiochemotherapy. Prospectively, the ASL data together with the also acquired 11C-Methionine PET will be evaluated regarding their separate and combined ability to predict patient outcome and effectiveness of the performed radiochemotherapy.

Involved research facilities

  • PET-Center
  • Lecture (Conference)
    PSMR 2015: 4th Conference on PET/MR and SPECT/MR, 17.-21.05.2015, La Biodola, Isola d’Elba, Italy
  • Open Access Logo Abstract in refereed journal
    EJNMMI Physics 2(2015)Suppl. 1, A67
    DOI: 10.1186/2197-7364-2-S1-A67

Permalink: https://www.hzdr.de/publications/Publ-22300


Measuring the Influence of Vessel Geomery on PCASL Labeling Efficiency

Petr, J.; Schramm, G.; van den Hoff, J.

Abstract

TARGET AUDIENCE: Clinicians and researcher interested in efficient planning of the pseudo-continuous arterial spin labeling (ASL).
PURPOSE: The labeling efficiency of pseudo-continuous ASL1 (pCASL) and its inter- and intra-subject reproducibility is a crucial point for reliable cerebral-blood-flow (CBF) measurements with ASL. Potential causes of varying labelling efficiency are, for example, B0 field inhomogeneity2, blood velocity3, or labeling-plane positioning3. The common recommendation is to position the labeling plane on a straight part of the vessel and perpendicular to them6. However, it is not always possible to avoid tortuous parts of the vessels if angiography is not available. Here, we study the effect of vessel geometry on the labeling efficiency both trough simulations and experiments.
METHODS: Simulations: Labeling efficiency was calculated for three cases of vessels geometry using numerical simulations as described by Wu4. Blood velocities between 1 and 40 cm/s were investigated and laminar flow was assumed. First, efficiency was calculated for a plane perpendicular to a straight vessel and angulated at 12.5°, 22.5°, or 45°. Second, a simple bend of the vessel was assumed with a length of the horizontal section of 0, 5, or 10 mm and the labeling plane positioned on the center of it and 2, 6, or 12 mm below (see Fig. 1a). Third, the bend was rotated 0°, 12.5°, 22.5°, or 45° so that the labeling plane intersected the vessel three times (Fig. 1b). Acquisitions: Five healthy young volunteers (age 31.8±3.9 y) were scanned at 3T using an eight-channel head-coil. A 3D TFE T1-weighted sequence and five pCASL sequences (pCASL1-pCASL5) with different position of the labeling plane were acquired. The T1-weighted sequence had voxel size 1×1×1 mm3. The common parameters of the pCASL sequence were: TR/TE = 3765/11 ms, FOV = 220×220 mm2,
pixel size = 2.75×2.75×6 mm3, 17 slices (0.6 mm gap), flip angle = 90°, 20 averages, background suppression with 2 pulses, 2D multi-slice EPI readout, labeling with a Hanning RF-pulse with duration 0.5 ms, tip angle 18°, and inter-pulse pause 0.5 ms, labeling time/post-labeling delay 1525/1650 ms. A reference image was acquired 5000 ms after saturation. For pCASL1, the labeling plane was set parallel with the imaged slices and the gap
was set in a way that the labeling plane intersected vertebral arteries (VA) at the level of siphon. The labeling plane was placed as parallel to the horizontal section of the VAs as possible (Fig. 1c). For pCASL2,3, the labeling plane was positioned 6 and 12 mm lower, respectively, than in pCASL1 (Fig. 1c). In pCASL4, 5 the labeling plane was positioned as in pCASL3 and rotated in the sagittal plane -30° and 30° with the center of rotation in the internal
carotid arteries (ICA), see Fig. 1c.
Preprocessing: The dynamics of all sequences were aligned with the first dynamics of pCASL1, thus coregistering the sequences and compensating for motion within each sequence. The T1-weighted image was aligned to the mean control image and segmented to obtain partial volume fractions for gray matter (GM). CBF was quantified according to the ASL white-paper6. Mean CBF (GM > 70%) in the vascular territories corresponding to the anterior cerebral artery (ACA), posterior cerebral artery (PCA), middle cerebral artery (MCA), and vertebral artery (VA) were computed for each sequence and subject. For pCASL1,2,4,5, the relative difference of the
mean CBF for each region was calculated relative to pCASL3 which was considered optimal as it contained no twists or angulations.
RESULTS: According to the numerical simulations, the decrease in labeling efficiency due to plane angulation is under 5% for most blood velocities and angle up to 30°, but it can go up to 10% for 45° angulation (Fig. 2c). For a bend in the vessel (Fig. 1a) of length 10 mm, the labeling efficiency can be decreased 20-25% (Fig. 2b). With increasing distance of the labeling plane, the decrease is only about 10% at 2mm (Fig. 2a), under 3% at 6mm and under 1% at 12 mm distance. For multiple intersections (Fig. 1b), the labeling efficiency decreased 25-30% regardless of the examined angle. The mean relative difference from sequence pCASL3 for different vascular territories is displayed in Tab. 2.
DISCUSSION: The experiments confirmed that labeling plane shift (pCASL1,2 in Tab. 1) or angulation up to 30° on ICA (pCASL4,5) produced less than 4% change of CBF in the ACA and MCA regions. Positioning the labeling plane on a section of VA parallel with it (pCASL1) caused 5.0% and 14.7% CBF decrease in PCA and VA regions respectively, although only in VA the change was significant. By increasing the distance from the bend (pCASL2), the CBF decrease became lower and not significant. Significant decrease of CBF of 8.4% and 16.9% in both PCA and VA regions, respectively, was achieved by positioning the labeling plane in a way to intersect VA at siphon multiple times. More significant decrease was expected from the simulations. The reason can be, that the actual vessel geometry was different from the worst modeled case. More measurements need to be done to find out why the decrease was lower in PCA than in VA. There are several limitations in this study. The magnetization transfer effects on the label were not taken into account5. Laminar flow profile was assumed, however the vessel thickness with regards to gradient fields was neglected for simplicity. By angulating the labeling plane, it is possible that it can intersect the imaged volume and thus directly or by magnetization transfer effects lower the measured perfusion signal. To minimize influence of this, the pixels where minimal-maximal intensity difference for all sequences was more than 10% were excluded from the analysis.
CONCLUSION: Reasonable angulation of the labeling plane causes only insignificant changes in labeling efficiency and measured CBF. On the other hand, twist and loops of the vessels as well as multiple crossing of the vessels by a labeling plane can cause significant changes of up to 25% and possibly even more, although this has been experimentally demonstrated only in VA region and not in PCA region.
REFERENCES:
1. W Dai, et al. Magn Reson Med, 2008;60(6):1488–97.
2. H Jahanian, et al. NMR in Biomedicine, 2011;24(10):1202–9.
3. S Aslan, et al. Magn Reson Med, 2010;63(3):765–71.
4. WC Wu, et al. Magn Reson Med, 2007;58(5):1020–7.
5. L Hernandez-Garcia, et al. NMR in Biomedicine, 2007;20(8):733–42.
6. Alsop, et al. Magn Reson Med, 2014; DOI: 10.1002/mrm.25197.

Involved research facilities

  • PET-Center
  • Poster
    23rd Annual Meeting of the International Society for Magnetic Resoonance in Medicine (ISMRM), 30.05.-05.06.2015, Toronto, Canada
  • Contribution to proceedings
    23rd Annual Meeting of the International Society for Magnetic Resonance in Medicine (ISMRM), 30.05.-05.06.2015, Toronto, Canada
    ISMRM '15: Proceedings of the 23rd Scientific Meeting and Exhibition of International Society for Magnetic Resonance in Medicine, 2952

Permalink: https://www.hzdr.de/publications/Publ-22299


An implementation of dead-time corrections in microbeam measurements on a pixel by pixel basis

Munnik, F.

Abstract

In microbeam measurements on inhomogeneous samples large variations in count-rate can occur. These variations result in variations in dead-time that have to be used to correct elemental distribution maps. However, the dead-time is usually not available on a pixel by pixel basis. In this work, a simple model is proposed to calculate the dead-time for each pixel. Measurements to determine the dead-time per event, needed in the model, are presented and the dead-time corrections are presented for real samples.

Involved research facilities

Related publications

  • Poster
    Workshops für Ionenstrahlen und Nanostrukturen, 22.-24.07.2015, Heidelberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-22298


Ionenstrahlanalyseverfahren in der Materialforschung

Schmidt, B.; Wetzig, K.

Abstract

Der Schwerpunkt der Materialanalyse mittels Ionenstrahlen ist die Bestimmung der Zusammensetzung und Struktur von oberflächennahen Festkörperschichten im Tiefenbereich von wenigen nm bis zu einigen µm. Charakteristisch für die verschiedenen Ionenstrahlanalysetechniken sind die Verwendung geeigneter Ionenstrahlen (z. B. Ionenart, Ionenenergie und -strom, Strahlfokus usw.), die Art der Ionen-Festkörper-Wechselwirkung (und deren Wirkungsquerschnitt), die entstehende Strahlungsart (z. B. gesputterte Sekundärionen, gestreute Ionen sowie Ionen-induzierte Photonen- und Elektronenemission). Die Vielzahl der Ionenstrahl-analyseverfahren kann bezüglich der verwendeten Ionenenergien in drei Gruppen eingeteilt werden [1]: 1) niedrige Ionenenergien von einigen keV, 2) mittlere Ionenenergien im Bereich 30-300 keV, und 3) hohe Ionenenergien im Bereich ~0,5-100 MeV. Schwere Ionen (Mi > Moxygen) für eine hinreichende Sputterausbeute an Targetatomen sind notwendig im weit verbreiteten Verfahren der Sekundärionen-Massen-Spektrometrie (SIMS). Leichte Ionen (M < 10, meistens H+, He+) werden in einem breiten Energiebereich für verschiedene Ionenstreuverfahren (LEIS, MEIS, RBS) sowie verschiedene Verfahren der Ionen-induzierten Photonenemission (PIXE, PIGE) eingesetzt. Dagegen werden schwerere, hochenergetische Ionen (z. B. N, O, Cl usw.) hauptsächlich für NRA und ERDA verwendet.
Im Vortrag werden die verschiedenen Ionenstrahlanalyseverfahren mit ihren charakteristischen Analyseparametern und Einsatzgebieten kurz vorgestellt und miteinander verglichen. Dabei wird besonders auf die hochauflösende Tiefen-profilierung für Dotierungsprofile in Halbleitern und die Elementanalyse von Dünnschichtsystemen eingegangen. Hierfür sind besonders die modernen Mikroelektronik- und Dünnschichttechnologien mit Forderungen nach immer dünneren Schichtsystemen und somit nach steigender Tiefenauflösung sowie kleineren Nachweisgrenzen die treibende Kraft. Weiterhin werden ausgewählte Beispiele für den Einsatz von Ionenstrahlanalyseverfahren in anderen Gebieten der Materialwissenschaften, z. B. in der Kunst und Archäometrie sowie in der Medizin diskutiert.

Involved research facilities

Related publications

  • Invited lecture (Conferences)
    18. Tagung Festkörperanalytik, 06.07.2015, Wien, Österreich

Permalink: https://www.hzdr.de/publications/Publ-22297


Probing defect driven tunable spontaneous magnetization in paramagnetic Zn0.95Co0.05O epitaxial films by X-ray absorption investigations

Satyarthi, P.; Ghosh, S.; Wang, Y.; Zhou, S.; Kumar, P.; Kanjilal, D.; Olivi, L.; Bürger, D.; Skorupa, I.; Schmidt, H.; Srivastava, P.

Abstract

In order to address existing unresolved issues related to intrinsic and extrinsic origins of ferromagnetism in Zn1−xCoxO based diluted magnetic semiconductors for varying x, the present work aims to investigate the tunable ferromagnetism triggered in paramagnetic Zn0.95Co0.05O films using 500 KeV inert xenon ion irradiation of different fluences. The origin of ferromagnetism in post irradiated Zn0.95Co0.05O films is understood from different densities of bound magnetic polarons (BMPs) formation through correlated spins of tetrahedrally substituted Co2+ ions and anionic vacancies. The alteration in crystallographic positions of Zn, Co cations, and O anions in the tetrahedral environment as analyzed from Zn and Co K-edgeX-ray absorption and O 1s photoemission is a crucial factor for the stabilization of different density of BMPs. Magnetic field and temperature dependence of X-ray magnetic circular dichroism at the Co L2,3 edge provide experimental evidence of purely paramagnetic contribution from well localized Co2+ ions of Co sublattice for paramagnetic Zn0.95Co0.05O film. The paramagnetic Co2+ ions of Co sublattice persist in irradiated films, which reveal BMPs formation as the origin of ferromagnetism.

Keywords: Diluted magnetic semiconductors; X-ray absorption; Spintronics

Involved research facilities

Related publications

Permalink: https://www.hzdr.de/publications/Publ-22296


Identification and quantification of PGMs by combining MLA and EPMA with a new approach to the offline overlap correction of major and trace PGE concentrations

Osbahr, I.; Krause, J.; Bachmann, K.; Gutzmer, J.

Abstract

The identification and accurate characterisation of platinum-group minerals (PGMs) is usually a very cumbersome procedure due to their small grain size (typically below 10 µm) and inconspicuous appearance under reflected light. A novel strategy for finding and quantifying PGMs by combining mineral liberation analysis (MLA), a point logging system and electron probe microanalysis (EPMA) was thus developed.
As a first step, the PGMs are identified using the MLA. Grains identified as PGMs are then marked and coordinates recorded with the point logger are then transferred to the EPMA. Case studies e.g. from the platiniferous reefs (Merensky Reef and UG2) of the Bushveld Complex (South Africa) illustrate that the combination of MLA, point logger and EPMA results in the identification of a significantly (up to 20 times) higher number of PGM grains than by careful reflected light microscopy.
The analysis of PGEs as major elements in PGMs or as trace elements in e.g. base metal sulfides by EPMA requires considerable effort. Due to the often significant overlaps between the X-ray spectra of almost all platinum-group and associated elements, X-ray lines suitable for quantitative analysis need to be carefully selected. As peak overlaps cannot be avoided completely, an offline overlap correction based on weight proportions has been developed. A reliable overlap correction is of particular importance e.g. in Ru-sulfides as laurite if the overlapped element is a trace element (Rh) and the overlapping element is a major constituent (Ru). Results obtained with the procedure attain acceptable totals and atomic proportions, indicating that the applied corrections are appropriate.

Keywords: Mineral Liberation Analyser; Electron Probe Microanalyser; Offline Overlap Correction; Platinum-Group Minerals

  • Poster
    Goldschmidt2015, 16.-21.08.2015, Prag, Tschechien

Permalink: https://www.hzdr.de/publications/Publ-22295


A novel approach for efficient identification and accurate chemical characterisation of platinum-group minerals by combining Electron Probe Microanalysis and Mineral Liberation Analysis

Osbahr, I.; Krause, J.; Bachmann, K.; Gutzmer, J.

Abstract

The identification and accurate characterisation of platinum-group minerals (PGMs) is usually a very cumbersome procedure due to their small grain size (typically below 10 µm) and inconspicuous appearance under reflected light. A novel strategy for finding PGMs and quantifying their composition was developed. It combines SEM-based automated mineralogy, in this study mineral liberation analyser (MLA) Quanta 650F by FEI, a point logging system (JEOL) and a FE-EPMA (JEOL JXA-8530F). Thin sections from a layered intrusion (UG2) in the Bushveld Complex and from two Uralian-Alaskan-type complexes in the Ural Mountains, Russia, were investigated as case studies.
As a first step, the PGMs are identified using the MLA. Grains identified as PGMs are then marked and coordinates recorded and transferred to the EPMA. Case studies illustrate that by introducing MLA for the efficient and largely automated identification of PGM grains in polished thin sections, up to 20 times more PGM grains were identified, whilst shortening time needed and avoiding the effects of human error invariably associated with reflected light microscopy. This is mainly due to the facts that (a) PGM with grain sizes < 5µm are reliably identified and (b) PGM and closely associated base metal sulfides and sulfosalts are well differentiated with the MLA. The analysis of PGMs by EPMA requires considerable effort due to the often significant overlaps between the X-ray spectra of almost all platinum-group and associated elements (e.g. OsMβ on IrMα and AuMβ on HgMα). X-ray lines suitable for quantitative analysis need to be carefully selected. As peak overlaps cannot be avoided completely, an offline overlap correction based on weight proportions has been developed. Considerable variations in the repeatedly determined overlap factors illustrate the need for a re-determination of the overlap factors with each calibration. Results obtained with the procedure proposed in this study attain acceptable totals and atomic proportions, indicating that the applied corrections are appropriate.

Keywords: Mineral Liberation Analyser; Electron Probe Microanalyser; Platinum-Group Minerals; Platinum-group Elements; offline overlap correction

  • Poster
    Geoanalysis 2015 - The 9th International Conference on the Analysis of Geological and Environmental Materials, 09.-14.08.2015, Leoben, Österreich

Permalink: https://www.hzdr.de/publications/Publ-22294


Working with uncertainty in adaptive process optimisation

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

Abstract

This contribution is concerned with adaptive processing decisions, where the process parameters are optimally adapted to the varying properties of the material input stream. Our starting point is the geometallurgical paradigm that the varying properties of the input stream are considered known e.g. from a geometallurgical model of the mined ore body, and optimal processing parameters are computed from them, by finding the parameter seaming optimal in a computer simulation.
This approach however has to work with a lot of uncertainties: The prediction of the geometallurgical ore parameters can only be done with some geostatistical uncertainty. The parameters themselves are only proxies for true ore properties. Model prediction can differ relevantly from actual process results, due to model simplifications. Due to these uncertainties the computed processing choices can turn out to be inferior to simple non-adaptive processing.
We systematically analysed this effect, by modelling this uncertainty effect mathematically and in computer simulations.
The most important findings are:
(a) Processing choices not taking into account the uncertainty sometimes even perform worse than simple non-adaptive processing, for the sole reason of ignoring the uncertainty effect.
(b) Ore properties, not adequately reflected in the ore description, might require different approaches, in which the observed processing behaviour feeds back into process control.
(c) Bayesian decision theory allows computing optimal processing choices combining the information from the mine (geostatistical predictions) and from the process feedback. These choices give much more robust choices and do not suffer from the drawbacks described for the simple approach we started from.
This new approaches can substantially improve the performance of adaptive processing in existing plants.

Keywords: Geometallurgy; Adpative Processing; Bayesian Optimisation

  • Lecture (Conference)
    IMPC 2016, XXVIII International Mineral Processing Congress, 11.-15.09.2016, Québec, Canada
  • Contribution to proceedings
    IMPC 2016, XXVIII International Mineral Processing Congress, 11.-15.09.2016, Quebec, Canada
    IMPC 2016: XXVIII International Mineral Processing Congress Proceedings: Canadian Institute of Mining, Metallurgy and Petro, 978-1-926872-29-2

Permalink: https://www.hzdr.de/publications/Publ-22293


Programme IAMG 2015 Freiberg, Germany, September 5-13, 2015, The 17th Annual Conference of the International Association for Mathematical Geosciences

Schaeben, H.; Tolosana Delgado, R.; van den Boogaart, K. G.; van den Boogaart, R.; (Editors)

Abstract

Das ist das Programmheft der IAMG2015 Konferenz

  • Book (Editorship)
    Freiberg: IAMG Office, 2015
    40 Seiten

Permalink: https://www.hzdr.de/publications/Publ-22292


Proceedings IAMG 2015 Freiberg, Germany, September 5-13, 2015, The 17th Annual Conference of the International Association for Mathematical Geosciences

Schaeben, H.; Tolosana Delgado, R.; van den Boogaart, K. G.; van den Boogaart, R.; (Editors)

Abstract

These are the proceedings with the long Abstracts of the IAMG 2015 conference

Keywords: Mathematical Geosciences; Mathematical Geology; Geoinformatics

  • Book (Editorship)
    Freiberg: IAMG Office, 2015
    1372 Seiten
    ISBN: 978-3-00-050337-5

Permalink: https://www.hzdr.de/publications/Publ-22291


Short Abstracts IAMG 2015 Freiberg, Germany, September 5-13, 2015, The 17th Annual Conference of the International Association for Mathematical Geosciences

Schaeben, H.; Tolosana Delgado, R.; van den Boogaart, K. G.; van den Boogaart, R.; (Editors)

Abstract

This is the shorts abstracts volume of the IAMG2015 Conference

Keywords: Mathematical Geosciences; Mathematical Geology; Geoinformatics

  • Book (Editorship)
    Freiberg: IAMG Office, 2015
    249 Seiten

Permalink: https://www.hzdr.de/publications/Publ-22290


Two-photon quantum well infrared photodetectors below 6 THz

Franke, C.; Walther, M.; Helm, M.; Schneider, H.

Abstract

Two-photon quantum well infrared photodetectors (QWIPs) are nonlinear detectors for the mid-infrared and terahertz regimes optimized for resonant two-photon absorption. Here we present first results on two-photon QWIP samples based on the GaAs/AlGaAs material system with intersubband energies between 25 and 12 meV (6 to 3 THz) confirmed by photocurrent spectra. The dark current showed large discontinuities, presumably caused by impact ionization. We performed interferometric autocorrelation experiments at the free-electron laser FELBE and observed nonlinear interferograms for all samples.

Keywords: quantum well infrared photodetector; QWIP; interferometric autocorrelation; nonlinear optics; two-photon absorption

Involved research facilities

Related publications

Permalink: https://www.hzdr.de/publications/Publ-22289


Innovative once-through thorium fuel cycle for the PTVM LWR concept

Rachamin, R.; Fridman, E.; Galperin, A.

Abstract

An advanced once-through thorium fuel cycle for the novel reactor concept, termed the pressure tube light water reactor with variable moderator control (PTVM LWR), is proposed. The main innovation of the concept is described. The PTVM LWR makes use of a seed-blanket geometry, whereby the core is divided into separated regions of thorium fuel channel assemblies (blanket) and low-enriched uranium fuel channel assemblies (seed). A scheme based on two separate fuel flow routes (i.e., seed route and blanket route) is proposed. Neutronic analysis indicates that the novel scheme has the potential to utilize both seed and blanket in an efficient manner.

Keywords: pressure tube reactor; “breed & burn”; moderator variation; seed-blanket geometry; once-through thorium fuel cycle

  • Open Access Logo Contribution to proceedings
    Thorium Energy Conference 2015 (ThEC15), 12.-15.10.2015, Mumbai, India
  • Poster
    Thorium Energy Conference 2015 (ThEC15), 12.-15.10.2015, Mumbai, India

Permalink: https://www.hzdr.de/publications/Publ-22288


Liquid metal modelling of continuous steel casting

Gerbeth, G.; Wondrak, T.; Stefani, F.; Shevchenko, N.; Eckert, S.; Timmel, K.

Abstract

Model experiments with low melting point liquid metals are an important tool to investigate the flow structure and related transport processes in melt flows relevant for metallurgical applications. We present recent results from the three LIMMCAST facilities working either with room-temperature alloy GaInSn or with the alloy SnBi at temperatures of 200-350°C. The main value of cold metal laboratory experiments consists in the capabilities to obtain quantitative flow measurements with a reasonable spatial and temporal resolution, which is essential for code validation. Experimental results are presented covering the following phenomena: contactless electromagnetic tomography of the flow in the mold, flow monitoring by ultrasonic sensors, mold flow under the influence of an electromagnetic brake, injection of argon bubbles through the stopper rod, X-ray visualization of gas bubble two-phase flow in the nozzle and in the mold.

Keywords: Continuous casting; physical modeling; flow measurements; magnetic field; flow control; electromagnetic brake

  • Invited lecture (Conferences)
    6th Baosteel Biannual Academic Conference and the 10th CSM Steel Congress, 21.-23.10.2015, Shanghai, China
  • Contribution to proceedings
    The 10th CSM Steel Congress and the 6th Baosteel Biennial Academic Conference, 21.-23.10.2015, Shanghai, China
    Proceedings of the 10th CMS Steel Congress & the 6th Baosteel Biennial Academic Conference: Metallurgical Industry Press, Book of Abstracts: 978-7-5024-7006-7, 8-13

Permalink: https://www.hzdr.de/publications/Publ-22287


Experimentelle Modellierung von Stranggussprozessen mit niedrig schmelzenden Legierungen

Timmel, K.; Wondrak, T.; Röder, M.; Shevchenko, N.; Miao, X.; Stefani, F.; Eckert, S.

Abstract

Die Strömung der Metallschmalze beim kontinuierlichen Stranggießen hat wesentlichen Einfluss auf das erreichte Gussergebnis. Probleme entstehen beispielsweise durch Einschlüsse von Oxiden, intermetallischen Verbindungen oder Gasblasen, die durch eine unkontrollierte Strömung in die Erstarrungszone gelangen. Die Untersuchung und Optimierung der Strömungsvorgänge erfolgte bisher vorwiegend anhand von numerischen Simulationen sowie Wassermodellen und lieferte bereits viele Erkenntnisse. Aufgrund der Materialeigenschaften sind jedoch Wassermodelle in ihrer Anwendung begrenzt und können nicht alle im Prozess auftretende physikalische Phänomene abdecken, wie z. B. Temperaturgradienten in der Schmelze, Interaktion mit elektromagnetischen Feldern oder Mehrphasenströmungen. In diesen Fällen unterscheiden sich die Kennzahlen z.T. um mehrere Größenordnungen.
Am Helmholtz-Zentrum Dresden-Rossendorf stehen drei Anlagen zur Verfügung, welche sich mit der Modellierung des Stranggussprozesses unter der Verwendung niedrigschmelzender Legierungen befassen. Die Anlagen unterscheiden sich z.T. in der Ausrichtung ihrer Untersuchungsschwerpunkte und ergänzen sich so gegenseitig ideal. Das Mini-LIMMCAST Experiment arbeitet mit einer bei Raumtemperatur flüssigen Legierung und ist sehr flexibel aufgebaut. Viele unterschiedliche Untersuchungen können und sind hier bereits durchgeführt worden. Die große LIMMCAST-Anlage ist insbesondere für einen längeren kontinuierlichen Betrieb ausgelegt und operiert im Temperaturbereich von 200 – 350 °C. Die dritte Anlage X-LIMMCAST ist speziell für die Röntgenbildgebung und die Visualisierung der Zweiphasenströmung mit Gasblasen konzipiert. Die Flexibilität der Anlagen erlaubt eine Anpassung an konkrete Gegebenheiten.
Neben den experimentellen Anlagen müssen für einen sinnvollen Betrieb auch entsprechende Messtechniken zu Erfassung der Strömungsvorgänge in flüssigen Metallen zur Verfügung stehen. Für die Geschwindigkeitsmessung sind dazu in den Versuchen die Ultraschall-Doppler-Velocimetry, die kontaktlose, induktive Strömungstomographie und die Potentialsondenmethode zum Einsatz gekommen. Für die Auflösung der Zweiphasenströmung sind wiederum eine tomographische Methode als auch die Röntgenbildgebung verwendet worden. Ziel ist neben einem tieferen Verständnis des Prozesses, die Bereitstellung eine breiteren Datenbasis für die Validierung numerischer Modelle.
Es sollen in diesem Beitrag die drei Versuchsanlagen und ausgewählte Messtechniken beispielhaft anhand von Messergebnissen vorgestellt werden.

Keywords: Stranggießen; Flüssigmetallmodell; Strömungsmessung; elektromagnetische Strömungsbeeinflussung; Zweiphasenströmung

  • Lecture (Conference)
    WERKSTOFFWOCHE, 14.-17.09.2015, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-22286


Dipole strength distribution of 74Ge

Massarczyk, R.; Schwengner, R.; Bernstein, L. A.; Anders, M.; Bemmerer, D.; Beyer, R.; Elekes, Z.; Hannaske, R.; Junghans, A. R.; Kögler, T.; Röder, M.; Schmidt, K.; Wagner, A.; Wagner, L.

Abstract

The dipole strength distribution of 74Ge was studied in photon-scattering experiments using bremsstrahlung produced with electron beams of energies of 7.0 and 12.1 MeV at the linear accelerator ELBE. We identified 94 levels with spin J = 1 up to an excitation energy of 8.9 MeV and analyzed the strength in the quasi-continuum of states. Simulations of statistical gamma-ray cascades were performed to estimate intensities of inelastic transitions and to correct the intensities of the ground-state transitions for their branching ratios. The photoabsorption cross section below the neutron-separation energy derived in this way is combined with the photoabsorption cross section obtained from an earlier (gamma, n) experiment and compared with phenomenological approximations.

Keywords: Nuclear resonance fluorescence; photon scattering; bremsstrahlung; photoabsorption cross section

Involved research facilities

Related publications

Permalink: https://www.hzdr.de/publications/Publ-22285


Nanofabrication of self-organized periodic ripples by ion beam sputtering

Iacob, E.; Dell’Anna, R.; Giubertoni, D.; Demenev, E.; Secchi, M.; Böttger, R.; Pepponi, G.

Abstract

Ion beam sputtering of solid surfaces with ions of low keV energies can produce self-organized periodic ripple patterns of nanometer size on the surface of semiconductors, metals and insulators, therefore looking to be a single-step, cost-effective method to fabricate surface topographies over large areas for various electronic and bio-devices.
To date, a comprehensive theoretical understanding of the ripple development is still missing, and the achievement of the application-specific surface topography still relay on properly tuning different ion-beam parameters, since the experiments have highlighted the dependence of ripple characteristics on them.
The success of technological applications often requires an a-priori defined ratio of ripple height to wavelength. Here we discuss how to obtain regular ripples of height h~10 nm and wavelength λ<=50 nm on silicon surfaces. Xe+ and O+ ions were used to also investigate the role of the surface chemical reactivity.
The results show the development of regular ripples with wavelengths of ~40 nm and heights of ~2 nm superimposed on a less regular periodic topography for O+ bombardment on Si; the Xe+ on Si bombardment produced structures of regularity below the expected values. We discuss the gained insights and the best recipe for the required nano-patterns.

Keywords: ion bombardment; self-organization; silicon; ripples

Involved research facilities

Related publications

Permalink: https://www.hzdr.de/publications/Publ-22284


Nanoporous Ge surface decomposition under ion bombardment: towards settling the dispute about driving forces

Böttger, R.; Liedke, B.; Liedke, M. O.; Heinig, K.-H.; Bischoff, L.

Abstract

First detailed studies of the nanoporous decomposition of Ge under ion irradiation date back more than 30 years. Irradiated Ge alters its (near-)surface morphology into a nanostructure, which remains stable after irradiation even under thermal treatment up to several hundred degrees Celsius. In recent years, this peculiar transformation of Ge has been studied extensively. However, a conclusive assessment of the driving force for the nanoporous Ge decomposition has not been reached yet.

We show that hole patterns and sponge-like layers of irradiated Ge surfaces originate from the same driving force, namely the kinetics of irradiation-induced defects in amorphous Ge layers. Ge hole patterns reported earlier for irradiation with low ion energies around 5 keV were reproduced for low energy Bi+ but also for Ge+ self-irradiation, which proves that the dominating driving force for morphology evolution cannot originate from the implanted impurities. At higher ion energies up to 100 keV the well-known formation of sponge-like Ge surface layers after heavy ion irradiation was found for Bi+ irradiation and Ge+ self-irradiation, too. The transition from smooth surfaces via hole patterns to sponge-like morphologies with increasing ion energy has been studied in detail. A model based on the kinetics of ion beam-induced defects was developed and implemented in 3D kinetic Monte Carlo simulations, which reproduce the transition from hole patterns to sponge-like layers with increasing ion energy. Finally, the proposed defect kinetics driven mechanism is undergird by a systematic positron annihilation spectroscopy investigation.
The authors acknowledge financial funding by the German Research Foundation via the Research Unit 845 “Selforganized nanostructures induced by low-energy ion beam erosion.”

Keywords: porous germanium; ion irradiation; defect kinetic; kinetic Monte-Carlo

Involved research facilities

Related publications

  • Lecture (Conference)
    Workshop Ionenstrahlen und Nanostrukturen, 22.-24.07.2015, Heidelberg, Deutschland
  • Lecture (Conference)
    8th International Workshop on Nanoscale Pattern Formation at Surfaces, 12.-16.07.2015, Krakow, Poland
  • Lecture (Conference)
    The 19th International Conference on Surface Modification of Materials by Ion Beams, 22.-27.11.2015, Chiang Mai, Thailand

Permalink: https://www.hzdr.de/publications/Publ-22283


Interactions of natural occurring eukaryotic microorganisms isolated from the uranium mine Königstein (Saxony, Germany) with U(VI)

Gerber, U.; Krawczyk-Bärsch, E.; Arnold, T.; Merroun, M. L.

Abstract

Despite high uranium concentrations (up to 14 mg L-1) and low pH (2.5 - 3.0) a high microbial diversity was detected by culture independent methods in the flooding water of the former uranium mine Königstein (Saxony, Germany). In this study we used culture dependent techniques for the isolation of eukaryotic microorganisms from the flooding water. It was possible to isolate different eukaryotic fungi with a glucose riche medium. The microbial isolates identified by 16S rDNA and 18S rDNA analysis were tested for their uranium tolerance abilities by the determination of the minimal inhibitory concentration (MIC) on solid media. The results showed high tolerances of uranium (up to 6 mM) on solid agar plates. Based on these results isolate KS5 (Rhodosporidium toruloides) and one reference organism DSM 10134 (Rhodosporidium toruloides) were selected for further uranium interaction experiments. Uranium biosorption tests indicated that the cells of the strain KS5 remove high amounts of uranium (120 mg uranium/ 1 g dry biomass). Temperature dependent biosorption tests with a U(VI) concentration of 100 µM showed significant differences: KS5 revealed twice as much uranium removal at 30°C compared to at 4°C (s. Fig. 1). Since active processes, e.g., bioaccumulation do not occur at low temperature, only minor amounts of U(VI) are taking up in the cytoplasm of the cells. Hence, U(VI) is preferentially sorbed on the cell membrane by the passive process of biosorption.
In order to test the uranium tolerance quantitatively in liquid media flow cytometry experiments with the strains KS5 and DSM 10134 were performed. For this purpose live-dead staining were done to test the cell viability. The cells were stained with Propidium Iodid (PI - non viable cells) and Fluorescein Diacetate (FDA - viable cells). Furthermore the oxidative stress response was measured with the fluorescent dye 3,3'-Dihexyloxacarbocyanine Iodide (DiOC6 - cell membrane of living cells). The results showed that the isolate KS5 are able to tolerate higher U(VI) concentrations compared to the reference culture DSM 10134. More than 50 % of the KS5 cells are viable at an initial U(VI) concentration of 100 µM. In contrast less than 10 % of the reference cells are viable at the same uranium concentration. The results of the oxidative stress response showed a slight difference to the cell viability test. The isolate KS5 showed that nearly 50 % of the cells are active, like the cell viability test. Whereas the results for the reference DSM 10134 revealed that more than 30 % of the cells are active and exhibit an active membrane potential, in contrast to the results of the cell viability test. This can be explained by the stress response in the presence of heavy metals. Some cells produce mechanic-sensitive receptors which are permeable for Propidium Iodide, resulting in a wrong fluorescent staining signal. Thus, it would be an asset to combine both methods, like cell viability test and oxidative stress response tests.
Summarizing the results of this study, we were able to prove that eukaryotic microorganisms within a uranium-contaminated environment exhibit adaption mechanisms against high U(VI) concentrations. The expensive chemical treatment of the flooding water in Königstein could take a long time probably for the next 100 years. For that reason, these isolated eukaryotic microorganisms might play an important role in the bioremediation of radionuclides within the waste water treatment in Königstein.

Keywords: Uranium; Bioremediation; Biosorption; Tolerance

  • Lecture (others)
    Remediation Symposium 2015, 30.09.-01.10.2015, Jena, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-22282


Stratified and Segregated Flow Modelling - AIAD

Höhne, T.

Abstract

Today: Limits in simulating stratified & segregated two phase flow
Algebraic Interfacial Area Density Model (AIAD)
Free Surface Drag
Turbulence Damping
Sub-grid wave turbulence (SWT)
Verification and Validation is going on – more experimental data are required for the validation

Keywords: AIAD; Free Surface Drag; Sub-grid wave turbulence (SWT)

  • Contribution to proceedings
    13th Short Course “Multiphase Flow: Simulation,Experiment and Application”, 24.-26.11.2015, Dresden, Deutschland
  • Lecture (Conference)
    13th Short Course “Multiphase Flow: Simulation,Experiment and Application”, 24.-26.11.2015, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-22281


IAEA CRP Benchmark of ROCOM Boron Dilution and PTS test cases

Höhne, T.

Abstract

The last decade has seen an increasing use of three-dimensional CFD codes to predict steady state and transient flows in nuclear reactors because a number of important phenomena such as pressurized thermal shocks, coolant mixing, and thermal striping cannot be predicted by traditional one-dimensional system codes with the required accuracy and spatial resolution.

The nuclear industry now also recognizes that CFD codes have reached the desired level of maturity (at least for single-phase applications) for them to be used as part of the NPP design process, and it is the objective of a IAEA CRP to assess the current capabilities of such codes in this regard, and contribute to the technology advance in respect to their verification and validation. CFD is already well-established in addressing certain safety issues in NPPs, as reported and discussed at various international workshops. The development, verification and validation of CFD codes in respect to NPP design necessitates further work on the complex physical modelling processes involved, and on the development of efficient numerical schemes needed to solve the basic equations. In parallel, it remains an overriding necessity to benchmark the performance of the CFD codes, and for this experimental databases need to be established, both for separate-effect tests and for full-size integral tests.

At the IAEA it was decided to set up a benchmark of ROCOM boron dilution and PTS test cases. All the test data had previously been opened, so only an ‘open’ benchmark exercise could be contemplated. Two sets of test data could be made available, relating to Pressurized Thermal Shock (PTS) and boron dilution (pump start-up). The ROCOM facility is at 1:5 scale, based on the 4-loop Konvoi reactor concept. There are 4000 measuring points by means of the Wire-Mesh Sensor (WMS) measurement technique, for which data collection is available up to a frequency of 10 kHz. It was noted that each experiment had been repeated five times to ensure authenticity of the data. In both cases, initial and boundary conditions are specified. Data have been recorded at P1 and P2 confidence levels. A CAD file of the test geometry is also available – it has recently been updated. All test data are available in tabular form, for ease of interpretation.

The Benchmark will help to analyze the CFD code capabilities for CFD in nuclear reactor design applications.

Keywords: IAEA; ROCOM; Benchmark; PTS; Boron Dilution

  • Contribution to proceedings
    25th SYMPOSIUM of AER on VVER Reactor Physics and Reactor Safety, 13.-16.10.2015, Balatongyörök, Ungarn
  • Lecture (Conference)
    25th SYMPOSIUM of AER on VVER Reactor Physics and Reactor Safety, 13.-16.10.2015, Balatongyörök, Ungarn

Permalink: https://www.hzdr.de/publications/Publ-22280


Distribution of Sb minerals in the Cu and Zn flotation of Rockliden massive sulphide ore in north-central Sweden

Minz, F. E.; Bolin, N.-J.; Lamberg, P.; Bachmann, K.; Gutzmer, J.; Wanhainen, C.

Abstract

The Rockliden massive sulphide Zn-Cu deposit contains minor amounts of Sb minerals. The Sb mineralogy is complex in terms of composition, micro textures and mineral associations. The main Sb minerals comprise tetrahedrite, bournonite, gudmundite and Sb-Pb sulphides such as meneghinite. The presence of these minerals is especially critical to the quality of the Cu-Pb concentrate. To study how they are distributed in a simplified flotation circuit and what controls their process behaviour Sb-rich drill core samples were selected from the Rockliden deposit and a standard laboratory flotation test was run on the composite samples. Scanning electron microscope-based automated mineralogy was used to measure the Sb mineralogy of the test products, and the particle tracking technique was applied to mass balance the different liberation classes to finally trace the distribution of liberated and locked Sb minerals. The mineralogical factors controlling the distribution of Sb minerals are mineral grain size, the degree of liberation, and associated minerals. Similarities in the distribution of specific particle types from the tested composites point towards systematics in the behaviour of particles and predictability of their distribution which is suggested to be used in a geometallurgical model of the deposit.

Keywords: Sulphide ores; Antimony; Liberation analysis; Particle tracking; Froth flotation

Downloads

Permalink: https://www.hzdr.de/publications/Publ-22279


Turbulence treatment at the interface of horizontal gas-liquid flows

Höhne, T.

Abstract

Stratified two-phase flows are relevant in many industrial applications, e.g. pipelines, horizontal heat exchangers and storage tanks. The numerical simulation of free surface flows can be performed using phase-averaged multi-fluid models, like the homogeneous and the two-fluid approaches, or non-phase-averaged variants. The approach shown in this paper within the two-fluid framework is the Algebraic Interfacial Area Density (AIAD) model. It allows the macroscopic blending between different models for the calculation of the interfacial area density and improved models for momentum transfer in dependence on local morphology. A further step of improvement of modelling the turbulence was the consideration of sub-grid wave turbulence (SWT) that means waves created by Kelvin-Helmholtz instabilities that are smaller than the grid size. A first CFD validation of the approach was done for an adiabatic case of the HAWAC channel. More verification and validation of the approach is necessary – more CFD grade experimental data are required for the validation.

Keywords: CFD; horizontal annular flow; AIAD; droplet entrainment; two-phase flow

  • Contribution to proceedings
    Turbulence, Heat and Mass Transfer 8, 15.-18.09.2015, Sarajevo, Bosnien Herzogowina
  • Lecture (Conference)
    Turbulence, Heat and Mass Transfer 8, 15.-18.09.2015, Sarajevo, Bosnien Herzogowina
  • Book chapter
    K. Hanjalic, T. Miyauchi, D. Borello, M. Hadzabdic and P. Venturini: Turbulencem Heat and Mass Transfer 8, New York: Begell Haus Inc., 2015, 978-1-56700-427-4, 141-145

Permalink: https://www.hzdr.de/publications/Publ-22278


Numerical modeling of horizontal annular flows using a droplet entrainment model

Höhne, T.

Abstract

One limitation in current simulating horizontal annular flows is the lack of treatment of droplet formation mechanisms. For self-generating annular flows in horizontal pipes, the interfacial momentum exchange and the turbulence parameters have to be modelled correctly. Furthermore the understanding of the mechanism of droplet entrainment in annular flow regimes for heat and mass transfer processes is of great importance in the chemical and nuclear industry.

A new entrainment model within the AIAD framework is proposed. It assumes that due to liquid turbulence the interface gets rough and wavy and forms droplets. The new approach is validated with HZDR annular flow experiments. Important phenomena like the pressure drop, the wave pumping effect, the droplet entrainment, the liquid film formation and the transient flow behavior could be calculated, analyzed and some of the phenomena compared with the measurement.

Keywords: CFD; horizontal annular flow; AIAD; droplet entrainment; two-phase flow

  • Contribution to proceedings
    The 16th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-16), 30.08.-04.09.2015, Chicago, USA
  • Lecture (Conference)
    The 16th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-16), 30.08.-04.09.2015, Chicago, USA

Permalink: https://www.hzdr.de/publications/Publ-22277


Sediment Generation in humid Mediterranean setting: Grain-size and Source-rock Control on Sediment Geochemistry and Mineralogy (Sila Massif, Calabria)

von Eynatten, H.; Tolosana-Delgado, R.; Karius, V.; Bachmann, K.; Caracciolo, L.

Abstract

Grain-size control on sediment composition is investigated in modern proximal sediment from the Sila Massif, where basic to felsic intrusive rocks are exposed in a Mediterranean humidtemperate upland climate. Samples were taken from small creeks and weathering profiles from three areas reflecting different bed rock composition. Samples were separated into eleven grain size fractions from very coarse sand to clay and analyzed by (i) X-ray fluorescence for chemical composition, and (ii) X-ray diffraction and Mineral Liberation Analysis for mineralogical composition. The chemical composition vs. grain size relations were modelled by compositional linear regression. Mineralogical composition from selected samples is used to substantiate the interpretations based on geochemistry. Results reveal a high degree of chemical weathering with chemical index of alteration (CIA) up to 92. High CIA values are restricted to the fine-grained fractions, while sand-sized sediment average at low to moderate CIA values (~ 60). Although strongly weathered, the three sample suites reflecting basic to felsic plutonic bed rock can be effectively discriminated across all grain-size classes using trace elements such as V, Rb, and Sr. Linear trend modelling and mineralogical data reflect similar patterns for all sample suites implying similar processes independent of source rock composition. This includes overall decrease of quartz and K-feldspar over the entire grain-size range from coarse to fine, which is contrasted by overall increase of sheet silicates from coarse to fine. Among the latter, increase of clay minerals strongly outpaces the increase of micas in silt to clay fractions. A more complex behaviour is shown by plagioclase, which is most abundant in intermediate grain-size fractions for all sample suites. This is caused by initial hydrolysis along cleavage planes and subsequent breakage of plagioclase crystals into smaller fragments. Towards finer grain size, intense hydrolysis has destroyed almost all feldspars. In contrast to a similar study in glacial setting Si/Al ratios constantly decrease with decreasing grain size, reflecting the cumulative effects of minor mechanical forces, quartz leaching, and intense hydrolysis.

Keywords: geochemistry; mineralogy; chemical weathering; comminution; provenance; compositional linear regression

  • Sedimentary Geology (2015)

Permalink: https://www.hzdr.de/publications/Publ-22276


Entwicklung und Anwendung analytischer Methoden in der Kupferschiefer Aufbereitung

Rahfeld, A.; Möckel, R.; Gutzmer, J.

Abstract

Kupferschiefer ist eine Ressource mit großer Bedeutung in Europa. Im Zuge neuer Entwicklungen in der Aufbereitungstechnik, einer gesteigerten Ressourcen- und Energieeffizienz und einem Interesse an alternativen Verfahren, besteht die Nachfrage nach detaillierten geochemischen und mineralogischen Informationen. Dementsprechend werden analytische Methoden benötigt die in der Lage sind Kupferschiefer nicht nur zu charakterisieren sondern auch durch Zerkleinerung, Flotation und Biolaugung hervorgerufene Änderungen nachzuweisen.
Klassische analytische Verfahren sind gänzlich ungeeignet für die Analyse von Kupferschiefer, aufgrund seiner komplexen Zusammensetzung bestehend aus einem hohen Anteil an Sulfiden und organischem Kohlenstoffverbindungen, sowie seines außergewöhnlich feinkörnigen Aufbaus der Matrix aus Tonen und Karbonaten. Nur der Einsatz moderner quantitativer Analysemethoden aus der Erz - und Gesteinsmineralogie und die Entwicklung neuer Vorgehensweisen ermöglicht eine verlässliche Untersuchung des Materials. Zum Einsatz kommen hierbei quantitative Röntgendiffraktometrie (QXRD), automatisierte Mineralidentifikation (MLA), Röntgenfluoreszenz (XRF), Atomemissionsspektrometrie (ICP-OES) und Neutronenaktivierung (INAA).

Keywords: Analytik Kupferschiefer Aufbereitung

  • Poster
    Jahrestagung Aufbereitung und Recycling 2015, 11.-12.11.2015, Freiberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-22275


Pulsed high-field magnets – An efficient way of shaping laser accelerated proton beams for application

Kroll, F.; Bagnoud, V.; Blažević, A.; Brabetz, C.; Busold, S.; Deppert, O.; Jahn, D.; Karsch, L.; Kraft, S.; Masood, U.; Roth, M.; Schumacher, D.; Schramm, U.

Abstract

Compact laser-driven proton accelerators are a potential alternative to complex, expensive conventional accelerators, enabeling unique beam properties, like ultra-high pulse dose. Nevertheless, they still require substantial development in reliable beam generation and transport.

We present experimental studies on capture, shape and transport of laser and conventionally accelerated protons via pulsed high-field magnets. These magnets, common research tools in the fields of solid state physics, have been adapted to meet the demands of laser acceleration experiments.Our work distinctively shows that pulsed magnet technology makes laser acceleration more suitable for application and can facilitate compact and efficient accelerators, e.g. for material research as well as medical and biological purposes.

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

Permalink: https://www.hzdr.de/publications/Publ-22274


A laser-driven ion beamline for generating well-defined ultra-short ion bunches at highest intensities

Kroll, F.; Busold, S.; Schumacher, D.; Brabetz, C.; Jahn, D.; Deppert, O.; Kraft, S.; Schramm, U.; Cowan, T. E.; Blažević, A.; Bagnoud, V.; Roth, M.

Abstract

The LIGHT collaboration [1] has installed a laser-driven ion beamline at GSI Helmholtz Center for Heavy Ion Research. For the first time it is now possible to study the feasibility and potential of shaping laser-driven ion beams for future applications. We report on the temporal recompression of a laser-accelerated ion bunch.
In the presented experiment (c.f. Fig. 1), a dedicated arm of the high-power laser PHELIX was used to drive a TNSA proton source using gold and titanium foils. The 650 fs short, 20 J laser pulse produces the typical exponentially decaying energy spectrum with about 10^10 particles at an energy of 10±0.5 MeV and energy cut-off at 28.4 MeV. The protons are captured by a pulsed high-field solenoid, energy selected and modulated in a conventional radiofrequency cavity and transported along a drift line to the end station by means of permanent magnetic quadrupoles. However, the long drift between the laser target and the cavity introduces a temporal spread-out of the polychromatic beam.
Most recently, we accomplished a recompression of the ion bunch by a well-chosen acceleration voltage of the rf cavity achieving phase-focusing in the following 3.5 meter long drift behind the cavity. At the end station we measured a central energy of 7.8 MeV; up to 5×10^8 protons could be temporally compressed to a bunch with duration of 462±40 ps (FWHM). The bunches show a moderate energy spread between 10 % and 15 % and are available at 6 m distance to the source, thus well separated from the harsh laser-acceleration environment. Such well-defined sub-nanosecond intense ion bunches are ideal for the generation and study of warm dense matter and can probe transient phenomena with unprecedented time resolution.
Fig. 1. LIGHT beamline experiment setup: a) TNSA proton source driven by the PHELIX laser and captured by the high-field solenoid b). The transported particles are rotated in longitudinal phase space by the cavity c). The permanent magnetic quadrupole doublets d), e) and optionally f) transport the beam towards the end station g) where the beam was diagnosed.
References
[1] S. Busold et al., Nucl. Instr. Meth. Phys. Res. A 740, 94 (2014).

  • Lecture (Conference)
    Laser Plasma Acceleration Workshop 2015, 10.-15.05.2015, Deshaies, Guadeloupe, Frankreich

Permalink: https://www.hzdr.de/publications/Publ-22273


Towards highest peak intensities for ultra-short MeV-range ion bunches

Busold, S.; Schumacher, D.; Brabetz, C.; Jahn, D.; Kroll, F.; Deppert, O.; Schramm, U.; Cowan, T. E.; Blažević, A.; Bagnoud, V.; Roth, M.

Abstract

A laser-driven, multi-MeV-range ion beamline has been installed at the GSI Helmholtz center for heavy ion research. The high-power laser PHELIX drives the very short (picosecond) ion acceleration on μm scale, with energies ranging up to 28.4MeV for protons in a continuous spectrum. The necessary beam shaping behind the source is accomplished by applying magnetic ion lenses like solenoids and quadrupoles and a radiofrequency cavity. Based on the unique beam properties from the laser-driven source, high-current single bunches could be produced and characterized in a recent experiment: At a central energy of 7.8MeV, up to 5×10^8 protons could be re-focused in time to a FWHM bunch length of τ=(462±40) ps via phase focusing. The bunches show a moderate energy spread between 10% and 15% (ΔE/E0 at FWHM) and are available at 6m distance to the source und thus separated from the harsh laser-matter interaction environment. These successful experiments represent the basis for developing novel laser-driven ion beamlines and accessing highest peak intensities for ultra-short MeV-range ion bunches.

Permalink: https://www.hzdr.de/publications/Publ-22272


Radiolabelling - A versatile tool for tracking nanoparticle release, uptake and transport

Schymura, S.; Hildebrand, H.; Fricke, T.; Holzwarth, U.; Bellido, E.; Ojea-Jiménez, I.; Cydzik, I.; Kulenkampff, J.; Kozempel, J.; Dalmiglio, M.; Bulgheroni, A.; Cotogno, G.; Simonelli, F.; Gibson, N.; Franke, K.; Lippmann-Pipke, J.

Abstract

A major challenge in nanosafety research is the sensitve detection of nanoparticles at environmentally relevant concentration in the complex systems involved. It is said that many studies in the field of nanosafety research „do not offer any kind of clear statement on the safety of nanomaterials“, in part because of the unrealistically high concentrations used. The radiolabelling of nanoparticles can help overcoming this obstacle as it provides an easy way of reliably detecting nanoparticles in minute concentrations despite the complexity of the matrix.

We have developed various methods of introducing radiotracers into some of the most common nanoparticles, such as Ag, carbon, CeO2, Silica and TiO2 nanoparticles. The labelling techniques are the synthesis of the nanoparticles using radioactive starting materials, the binding of the radiotracer to the nanoparticles, the activation of the nanoparticles using proton irradiation, the recoil labelling utilizing the recoil of a nuclear reaction to introduce a radiotracer into the nanoparticles, and the in-diffusion of radiotracers into the nanoparticles at elevated temperatures. Using these methods we have produced [105/110mAg]Ag0, [124/125/131I]CNTs, [139Ce]CeO2, [48V]TiO2, [7Be]MWCNT, [7Be]SiO2, [44/45Ti]TiO2, etc.. All the particles were evaluated for radiolabel stability and alteration of the particle properties.

Using the so-labelled nanoparticles we achieved to measure the release of nanoparticles from surface coatings, the transport of nanoparticles in porous media, the interaction of nanoparticles with complex media such as sewage sludge and the uptake of nanoparticles in plants. The easy quantification of nanoparticle fractions inside the various systems allows the extraction of crucial information in order to understand and evaluate the different processes involved.

Keywords: Nanopartikel/Nanoparticle; Radiomarkierung/Radiolabelling

  • Lecture (Conference)
    10th International Conference on the Environmental Effects of Nanoparticles and Nanomaterials, 06.-10.09.2015, Wien, Österreich

Permalink: https://www.hzdr.de/publications/Publ-22271


Flash-Lamp-Enhanced Atomic Layer Deposition of Thin Films

Henke, T.; Knaut, M.; Hossbach, C.; Geidel, M.; Rebohle, L.; Albert, M.; Skorupa, W.; Bartha, J.

Abstract

Within this work flash lamp annealing (FLA) is utilized to thermally enhance the film growth in atomic layer deposition (ALD). First, the basic principles of flash-lamp-enhanced ALD (FEALD) are presented in detail, the technology is reviewed and classified. Thereafter, results of our studies on the FEALD of aluminum-and ruthenium-based thin films are presented. These depositions were realized by periodically flashing on a substrate during the precursor exposure. It is shown that the film growth is induced by the flash heating and that the processes exhibit typical ALD characteristics. The obtained relations between flash parameters and film growth parameters are discussed with the main focus on the impact of the FLA-caused temperature profile on the film growth.
Besides, this work addresses technical challenges for the practical realization of this method and demonstrates the potential of this technology to extend the capabilities of thermal ALD.

Keywords: flash lamp annealing; atomic layer deposition; thin film

Permalink: https://www.hzdr.de/publications/Publ-22270


European activities on crosscutting thermal-hydraulic phenomena for innovative nuclear systems

Cheng, X.; Batta, A.; Bandini, G.; Roelofs, F.; van Tichelen, K.; Gerschenfeld, A.; Prasser, M.; Papukchiev, A.; Hampel, U.; Ma, W. M.

Abstract

Thermal-hydraulics is recognized as a key scientific subject in the development of innovative reactor systems. In Europe, a consortium is established consisting of 24 institutions of universities, research centers and nuclear industries with the main objectives to identify and to perform research activities on important crosscutting thermal-hydraulic issues encountered in various innovative nuclear systems. For this purpose the large-scale integrated research project THINS (Thermal-Hydraulics of Innovative Nuclear Systems) is launched in the 7th Framework Programme FP7 of European Union. The main topics considered in the THINS project are (a) advanced reactor core thermal-hydraulics, (b) single phase mixed convection, (c) single phase turbulence, (d) multiphase flow, and (e) numerical code coupling and qualification. The main objectives of the project are:

Generation of a data base for the development and validation of new models and codes describing the selected crosscutting thermal-hydraulic phenomena.
Development of new physical models and modeling approaches for more accurate description of the crosscutting thermal-hydraulic phenomena.
Improvement of the numerical engineering tools for the design analysis of the innovative nuclear systems.
This paper describes the technical tasks and methodologies applied to achieve the objectives. Main results achieved so far are summarized.

Involved research facilities

  • TOPFLOW Facility

Permalink: https://www.hzdr.de/publications/Publ-22269


Hyperspectral remote sensing for mineral mapping of structural related mineralizations around Mount Isa, Queensland, Australia

Jakob, S.; Salati, S.; Gloaguen, R.

Abstract

Alone or combined with other remote sensing data, hyperspectral mineral mapping can be used to investigate mineralizations and deposits via alteration minerals. Their kind, abundance and spatial distribution can deliver important statements about the occurrence and formation of mineralizations and their relation to structural features. The high spectral and spatial resolution of HyMap data exceeds multispectral data distinctly and makes the recognition of even smaller geological structures possible. The spectral unmixing of single endmembers can be used for the accurate mapping of specific materials or minerals.The support of hyperspectral imaging by spectral data gathered in the field and the analysis of the composition of rock samples can help to determine endmembers and to identify absorption features.
This study demonstrates the possibilities and limitations of remote sensing, especially hyperspectral data, for mineral mapping purposes, using the example of the Mount Isa Inlier. This geological area is situated in Northern Queensland, Australia, and is known for its considerable ore deposits and consequent mining of predominantly copper, zinc, lead, silver and gold. Beside hyperspectral HyMap data, multispectral Landsat 8 and SRTM digital elevation data were analyzed. A three-week field study in 2014 supported the investigations.
After preprocessing and vegetation masking the data were analyzed using Spectral Feature Fitting (SFF) and Mixture Tuned Matched Filtering (MTMF) for alteration mineral mapping. The outcomes were combined with results from decorrelation stretch, band ratioing, topographic indices and automated lineament analysis. Additional information was provided by field spectrometer measurements and the XRF and XRD analysis of rock samples.
Throughout the study, mineral mapping using remote sensing data, especially hyperspectral data, turned out to deliver high qualitative results when it is supported by additional information. In situ investigation of the observed mineralizations for validation is important and can deliver such data, for instance by the investigation of rock samples or spectral measurements. Since mineralizations and alterations are often related to structures, their analysis and consideration can provide crucial hints.
The most significant result throughout the study was the determination of a new site of gossanous, silicified ridges south of the Mount Isa mining complex. Their occurrence was validated through fieldwork observations including rock sampling and spectral measurements. The gathered information additionally supported the accurate mapping of those ridges using HyMap data, which confirmed the connection between the north-south trending ridges and the Mount Isa mine deposits. The observed ridges coincide compositionally and spectrally with the outcrops of mineralized parts of the Urquhart Shale, which form the mined Pb-Zn-Ag deposits and are probably related to structures. In samples of the new site, amounts of Pb, Zn, Ag and other metals could be detected. Contrary to the mineralized outcrops of the Urquhart Shale deposits, those ridges occur outside of the common host rock and are not mentioned as mineralizations in any available map or publication.

  • Poster
    EGU General Assembly 2015, 14.04.2015, Wien, Österreich

Permalink: https://www.hzdr.de/publications/Publ-22268


Formation of Ge-0 and GeOx nanoclusters in Ge+-implanted SiO2/Sithin-film heterostructures under rapid thermal annealing

Zatsepin, A. F.; Zatsepin, D. A.; Zhidkov, I. S.; Kurmaev, E. Z.; Fitting, H. J.; Schmidt, B.; Mikhailovich, A. P.; Lawniczak-Jablonska, K.

Abstract

The results of X-ray photoelectron spectra (XPS valence band and core levels) measurements for Ge+ implanted SiO2/Si heterostructures are presented. These heterostructures have a 30 nm thick Ge+ ion implanted amorphous SiO2 layer on p-type Si. The chemical-state transformation of the host-matrix composition after Ge+ ion implantation and rapid thermal annealing (RTA) are discussed. The XPS-analysis performed allows to conclude the formation of Ge-o and GeOx clusters within the samples under study. It was established, that the annealing time strongly affects the degree of oxidation states of Ge-atoms

Keywords: RAY PHOTOELECTRON-SPECTROSCOPY; OXYGEN; LAYERS; FILMS; SI+; CATHODOLUMINESCENCE; TRANSFORMATIONS; SIO2; XPS

Involved research facilities

Related publications

Permalink: https://www.hzdr.de/publications/Publ-22267


Modelling of the electromagnetic braking effect in the continuous casting process of steel

Timmel, K.; Willers, B.; Kratzsch, C.; Schwarze, R.; Eckert, S.; Gerbeth, G.

Abstract

It is known from industry and from scientific studies that the steel quality is significantly governed by the melt flow in the mold. Therefore, big efforts are made to adjust and to control the flow in the mold in a proper way by plant design or by the contactless, adjustable and flexible use of electromagnetic fields. These electromagnetic fields are already in industrial use for decades, but direct flow measurements about the actual effect are still rather scarce.
Three experimental facilities operating with low melting liquid metals were built at HZDR to investigate the continuous casting process of steel and to provide data for the validation of numerical simulations. The effect of the electromagnetic brake was one of the topics investigated in these low melting liquid metal experiments [1]. This paper will present new results from the LIMMCAST liquid metal experiments. Compared to previous results, the new experiments are operated in a continuous mode, providing a possibility to study the flow behavior in the stationary regime. Additional measurements focus on the behavior of the free liquid metal surface in the mold and the effect of the bulk flow on it. The paper also presents numerical results using Scale Adaptive Simulations (SAS).

Keywords: Continuous casting of steel; electro-magnetic flow control; liquid metal models; numerical simulation; scale adaptive simulations

  • Lecture (Conference)
    8th International Conference on Electromagnetic Processing of Materials (EPM2015), 12.-16.10.2015, Cannes, Frankreich
  • Contribution to proceedings
    8th International Conference on Electromagnetic Processing of Materials (EPM2015), 12.-16.10.2015, Cannes, Frankreich, 978-2-9553861-0-1, 373-376

Permalink: https://www.hzdr.de/publications/Publ-22266


Simulating Multi-Scale Physics in Solid Target Laser-Ion Acceleration

Huebl, A.; Kluge, T.; Hilz, P.; Bussmann, M.

Abstract

Laser-ion acceleration from solid targets with ultra-intense laser pulses on the fs time scale is a central research topic for next generation particle accelerators. Accompanying processes are highly non-linear and require precise knowledge about the influence of both ab-initio electro-magnetic and atomic evolution of the plasma.

Consequently, modeling the acceleration process with simulations does not only require kinetic models with very high resolution (from the order of the inverse plasma frequency to the ns acceleration process) but also self-consistent models for non-equilibrium plasma and ionization processes.

We present large scale, 3D3V simulations with the fully-relativistic particle-in-cell code PIConGPU on the ORNL Titan cluster of mass-limited droplet targets related to recent experiments levitating these in Paul-traps.
In comparison with large 2D surveys the dependence of plasma instabilities and resulting ion energies under the variation of target material and laser properties is shown.

Keywords: laser particle acceleration; ion acceleration; mass limited targets; HPC; GPU; simulation; PIConGPU

Involved research facilities

Related publications

  • Lecture (Conference)
    42nd EPS Conference on Plasma Physics 2015, 22.-26.06.2015, Lisbon, Portugal

Permalink: https://www.hzdr.de/publications/Publ-22265


Photocapacitive light sensor based on metal-YMnO3-insulator-semiconductor structures

Bogusz, A.; Choudhary, O. S.; Skorupa, I.; Bürger, D.; Lawerenz, A.; Lei, Y.; Zeng, H.; Abendroth, B.; Stäcker, H.; Schmidt, O. G.; Schmidt, H.

Abstract

Technology of light sensors, due to the wide range of applications, is a dynamically developing branch of both, science and industry. This work presents a novel concept of photodetectors based on a metal-ferroelectric-insulator-semiconductor, a structure which has not been explored yet in the field of photodetectors. Functionality of the presented light sensor exploits the effect of ferroelectric polarization, charge trapping and photocapacitive phenomena. This is accomplished by an interplay between polarization alignment, subsequent charge distribution and charge trapping processes under given illumination condition and gate voltage. Change of capacitance serves as a read out parameter indicating the wavelength and intensity of illuminating light. The operational principle of the proposed photocapacitive light sensor is demonstrated in terms of capacitance-voltage and capacitance-time characteristics of an Al/YMnO3/SiNx/p-Si structure exposed to green, red, and near infrared light. Obtained results are discussed in the terms of optical properties of YMnO3 and SiNx layers contributing to the performance of photodetectors. Presented novel concept of light sensing might serve as the basis for the development of more advanced photodetectors.

Keywords: light; sensor; photodetector; YMnO₃; photocapacitance

Permalink: https://www.hzdr.de/publications/Publ-22264


Annual Report 2014 - Institute of Ion Beam Physics and Materials Research

Fassbender, J.; Heera, V.; Helm, M.; Zahn, P.

Abstract

This past year 2014 was the year when we finally completely arrived as a “full member” in the Helmholtz Association. This is related to the successfully passed research evaluation in the framework of the Program Oriented Funding (POF), which will give us a stable and predictable funding for the next five years (2015 – 2019). This is particularly true for our large-scale user facilities, like the Ion Beam Center (IBC) and the electron accelerator ELBE with the free-electron laser. Most of our activities are assigned to the program “From Matter to Materials and Life” within the research area “Matter”, in cooperation with several other German Helmholtz Centers. Our in-house research is performed in three so-called research themes, as depicted in the schematic below. What is missing there for simplicity is a small part of our activities in the program “Nuclear Waste Management and Safety” within the research area “Energy”.

Our research and facilities were well appreciated by the evaluation committee, who made the following judgement about the Ion Beam Center:

“The Ion Beam Centre (IBC) of HZDR is an internationally leading ion-beam facility (with ion energies ranging from several eV to several tens of MeV). At both the national and international level it is one of the key players and is unique in its kind. The synergy between forefront research and user service has been leading to a very good publication output for both in-house research and user research. …
The very broad range of beam energies, the versatility of techniques and applications – both for ion beam modification of materials and for ion-beam analysis – makes the IBC unique in its kind. …
The strength of IBC is that its activities are based on a combination of forefront research and user service, which mutually interact in synergy and strengthen one another. In turn, this synergy has been leading to a very good publication output for both in-house research and user research.”
In order to make our Annual Report a bit more compact, we have decided to include only four full journal papers this year. This was also triggered by the fact that our publication activities have turned out be become more diverse, in more diverse journals than in the past, and often through longer papers, which would be too long to reprint them here. However, apart from the constantly quantitatively high publication output, we succeeded to publish in excellent journals such as Nature Physics, Nano Letters and Physical Review Letters, in fields as diverse as ion beam physics, magnetism and terahertz spectroscopy.
Two of our scientists, Dr. Artur Erbe and Dr. Alexej Pashkin obtained their Habilitation in 2014, both at University of Konstanz. For the first time, we are hosting an Emmy Noether Young Investigator Group funded by the Deutsche Forschungsgemeinschaft (DFG); the group works on the hot topic of magnonics and is headed by Dr. Helmut Schultheiß.
Finally we would like to cordially thank all partners, friends, and organizations who supported our progress in 2014. Special thanks are due to the Executive Board of the Helmholtz-Zentrum Dresden-Rossendorf, the Minister of Science and Arts of the Free State of Saxony, and the Minister of Education and Research of the Federal Government of Germany. Numerous partners from universities, industry and research institutes all around the world contributed essentially, and play a crucial role for the further development of the institute. Last but not least, the directors would like to thank again all IIM staff for their efforts and excellent contributions in 2014.

Involved research facilities

Related publications

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-060 2015
    ISSN: 2191-8708, eISSN: 2191-8716

Downloads

Permalink: https://www.hzdr.de/publications/Publ-22263


Destination and transport of engineered nanoparticles along the process wastewater – sludge – plant

Fricke, T.; Schymura, S.; Hildebrand, H.; Franke, K.

Abstract

The presence of engineered nanomaterials in various consumer products leads to a significant load of nanoparticles (NP) also in urban and industrial wastewater. Consequently, wastewater treatment plants (WWTP) play a key role in managing these NP-loaded wastewaters considering that the purified WWTP effluent must be harmless when entering the recipient and the (aquatic) environment. Up to now, there is little information or practical guidelines available to safeguard these ambitious provisions. As another product of wastewater treatment (WWT), sewage sludge is considered to act as a sink for NPs during WWT process. Quite often, sewage sludge is used as an organic fertilizer in the agriculture and horticulture. Under these purposes, it cannot be excluded that a significant amount of engineered NPs might find their way into the treated soil and finally into plants and the way back in the human food chain.
Within the project “nanoSuppe” (sludge uptake particle plant environment) guidelines for WWTP and for the usage of sewage sludge as fertilizer will be created based on laboratory studies to support WWTP companies and authorities in terms of this difficile problem. To reach this goal a strong consortium from WWTPs, related companies and a research centre is formed. The project is focused on the usage of engineered NPs like TiO2, CeO2 multiwalled carbon nanotubes (MWCNT) and quantum dots. These NPs are representatives for nanomaterials that are used in many consumer products like sunscreens, paints and also in the industry.
The process of characterization of NP from the lab into the scale of a field is one of the important focuses. It includes the radio labelling of NP as a strong detection tool, the characterization of these NP in liquid phase and sewage sludge and the uptake of NP into plants. The use of radiolabeled NPs guarantee a highly sensitive identification, localisation and quantification of NPs even at the low environmentally concentrations. It is independent of the used matrices (sewage, sludge, soil, plant) and background levels of natural NPs, colloids or substances of the same elemental composition.
Within this presentation, latest results on translocation of NPs from different matrices like tap water, sewage and sewage sludge into the plant will be shown and discussed. Furthermore the chemical and physical interactions of these matrices might have a huge impact on the destination of the NP in the different media. So the uptake of NP into the plants is limited to their availability in the media. Different approaches with four plant species such as lamb’s lettuce, sunflowers, ryegrass and red radish are under investigation. These test plants cover a wide spectrum of agricultural and horticultural interest. Lamb’s lettuce and red radish end up directly in the human food chain. Besides that ryegrass functioned as animal food for cows, goats and other animals which can end up in the food chain as well.

  • Poster
    ICCE 2015, 15th EuCheMS International Conference on Chemistry and the Environment, 20.-24.09.2015, Leipzig, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-22262


Measuring at relevant concentrations - Radiolabelling as a versatile tool for sensitive nanoparticle detection in complex systems

Hildebrand, H.; Schymura, S.; Holzwarth, U.; Bellido, E.; Ojea-Jimènez, I.; Dalmiglio, M.; Cotogno, G.; Gibson, N.; Franke, K.

Abstract

The employment of radiotracers is a versatile tool for the detection of nano-particulate materials in complex systems such as environmental samples or organisms. With the increasing usage of nanoparticles in applications outside of research laboratories, a careful risk assessment of their release into the environment becomes mandatory. However, the monitoring of nanoparticles in such complex natural systems as geological formations, ground water or organisms is nearly impossible or at least extremely laborious in terms of sample preparation using conventional methods, especially at environmentally relevant concentrations. This obstacle can be overcome by radiolabelling, which may be of crucial value in enabling such research under laboratory conditions. Radiolabelling allows to localize, to trace and to detect nanoparticles in complex media without intensive sample pre-treatment for the measurements.

We have developed various methods of introducing radiotracers into some of the most common nanoparticles, such as Ag, carbon, CeO2, Silica and TiO2 nanoparticles. The labelling techniques are the synthesis of the nanoparticles using radioactive starting materials, the binding of the radiotracer to the nanoparticles, the activation of the nanoparticles using proton irradiation, the recoil labelling utilizing the recoil of a nuclear reaction to introduce a radiotracer into the nanoparticle, and the in-diffusion of radiotracers into the nanoparticles at elevated temperatures. Using these methods we have produced [105/110mAg]Ag0 [1], [124/125/131I]CNTs, [139Ce]CeO2, [48V]TiO2 [2], [7Be]MWCNT, [7Be]SiO2 [3], [44/45Ti]TiO2 [4], etc.. The radiolabelled nanoparticles were intensively tested concerning radiolabel stability and nanoparticle properties (size, zeta potential) were compared with the original (non-labelled) material. It could be shown, that radiolabels are suitable for application in scientific studies under the individual experimental conditions and nanoparticle properties remained largely unalterd by the radiolabelling procedure.

The developed radiolabelling methods are adaptable for a wide range of other nanoparticles. The so-labelled nanoparticles can be detected at minimal concentrations well in the ng/L range even with a background of the same element and without complicated sample preparations necessary. This means that nanoparticles can be localized also in e.g. intact geological samples or during transport studies using appropriate detector arrangement.

Using our methods one can radiolabel commercial nanoparticle samples for sensitive detection in environmentally relevant trace concentrations.

[1] H. Hildebrand and K. Franke: A new radiolabeling method for commercial Ag0 nanopowder with 110mAg for sensitive nanoparticle detection in complex media, J Nanopart Res (2012) 14:1142.
[2] K. Abbas, I. Cydzik, R. Del Torchio, M. Farina, E. Forti, N. Gibson, U. Holzwarth, F. Simonelli, W. Kreyling: Radiolabelling of TiO2 nanoparticles for radiotracer studies, J Nanopart Res (2010) 12:2435–2443.
[3] U. Holzwarth, E. Bellido, M. Dalmiglio, J. Kozempel, G. Cotogno, N. Gibson: 7Be-recoil radiolabelling of industrially manufactured silica nanoparticles, J Nanopart Res (2014) 16:2574.
[4] H. Hildebrand, S. Schymura, U. Holzwarth, N. Gibson, M. Dalmiglio, K. Franke: Strategies for radiolabeling of commercial TiO2 nanopowder as a tool for sensitive nanoparticle detection in complex matrices, J Nanopart Res (2015) 17:278.

  • Lecture (Conference)
    ICCE 2015, 15th EuCheMS International Conference on Chemistry and the Environment, 20.-24.09.2015, Leipzig, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-22261


Building a New Assessment Tool for Potential Rare Earth Underground Mining Projects

Barakos, G.; Mischo, H.

Abstract

Once an ore body has been probed and outlined and initial resource indications deserve further attention, the evaluation stage has to begin to determine the potential exploitation. This analysis is a sophisticated process, let alone when it comes to underground mining projects and especially on rare earth deposits that are governed by notable boundary conditions. However, the significant numbers of the parameters to be considered and their complexity, as well as the solvency of the outcomes, often result in questioning the suitability of common evaluation methods. This has created a necessity for a new evaluation procedure that focuses on potential rare earth underground mining projects. This paper describes the construction development of an assessment tool that considers not only the mining method selection process but identifies social, economic and environmental impact factors and Rare Earth Element industry-specific criteria as well. Based on the philosophy of previous linguistic and numerical approaches, this combined tool is based on a step-by-step numerical analytical hierarchical process with weighted criteria. The purpose of building this tool is to adjust to the specifications of rare earth underground mining projects and to contribute into having accurate and secure con-clusions for if and when investment decisions should be made and minimize the potential risks regarding the viability of any mining project.

Keywords: rare earths; underground mining method selection; viability; assessment tool

  • Open Access Logo Contribution to proceedings
    7th Sustainable Development In Minerals Industry Conference (SDIMI 2015), 12.-15.07.2015, Vancouver, Canada
    Proceedings of SDIMI 2015, Vancouver: University of British Columbia

Permalink: https://www.hzdr.de/publications/Publ-22260


Setting the REE industry-specific criteria and their significant role in the viability of rare earth underground mining projects

Barakos, G.; Mischo, H.

Abstract

To evaluate the feasibility of a future underground mining operation is a complex problem in itself, with several different parameters to be accounted for and evaluated to secure investment decisions over the viability of any potential underground mining project. This procedure gets even more complicated when it comes to exploiting rare earth deposits. Various concerns are expressed regarding the environmental impacts that an underground mining operation may cause due to the radioactivity of the rare earth elements during mining and in waste treatment. Furthermore, the fragile market and the diversified supply and demand of the different rare earth elements can significantly affect the viability of such a venture, among other factors. This paper deals with the definition and classification of the specific criteria that govern the REE mining industry. Moreover, a thorough investigation is made of how these criteria can determine not only the selection of the underground mining method to be applied, but also of the impact that they may have to the overall feasibility of any given potential project.

Keywords: rare earth elements; underground mining; sustainability; environmental impacts; balance problem

  • Open Access Logo Contribution to proceedings
    26th Annual Meeting & Conference of the Society of Mining Professors, 21.-26.06.2015, Freiberg, Deutschland
    Proceedings of the 26th Annual Meeting & Conference of the Society of Mining Professors, Backnang, Stuttgart: WIRmachenDRUCK, 978-3-86012-505-2

Permalink: https://www.hzdr.de/publications/Publ-22259


Broken vertex symmetry and finite zero-point entropy in the artificial square ice ground state

Gliga, S.; Kákay, A.; Heyderman, L. J.; Hertel, R.; Heinonen, O. G.

Abstract

We study degeneracy and entropy in the ground state of artificial square ice. In theoretical models, individual nanomagnets are typically treated as single spins with only two degrees of freedom, leading to a twofold degenerate ground state with intensive entropy and thus no zero-point entropy. Here, we show that the internal degrees of freedom of the nanostructures can result, through edge bending of the magnetization and breaking of local magnetic symmetry at the vertices, in a transition to a highly degenerate ground state with finite zero-point entropy, similar to that of the pyrochlore spin ices. We find that these additional degrees of freedom have observable consequences in the resonant spectrum of the lattice, and predict the occurrence of edge “melting” above a critical temperature at which the magnetic symmetry is restored.

Keywords: zero-point entropy; artificial spin-ice

Permalink: https://www.hzdr.de/publications/Publ-22258


Compton camera and prompt gamma ray timing: two methods for in vivo range assessment in proton therapy

Hueso-González, F.; Fiedler, F.; Golnik, C.; Kormoll, T.; Pausch, G.; Petzoldt, J.; Römer, K. E.; Enghardt, W.

Abstract

Proton beams are promising means for treating tumours. Such charged particles stop at a defined depth, where the ionization density is maximum. As the dose deposit beyond this distal edge is very low, proton therapy minimises the damage to normal tissue compared to photon therapy. Nevertheless, inherent range uncertainties cast doubts on the irradiation of tumours close to organs at risk and lead to the application of conservative safety margins. This constrains significantly the potential benefits of protons over photons. In this context, several research groups are developing experimental tools for range verification based on the detection of prompt gammas, a nuclear by-product of the proton irradiation. At OncoRay and Helmholtz-Zentrum Dresden-Rossendorf, detector components have been characterised in realistic radiation environments as a step towards a clinical Compton camera. Corresponding experimental methods and results obtained during the ENTERVISION training network are reviewed. On the other hand, a novel method based on timing spectroscopy has been proposed as an alternative to collimated imaging systems. The first tests of the timing method at a clinical proton accelerator are summarised, its applicability in a clinical environment for challenging the current safety margins is assessed, and the factors limiting its precision are discussed.

Keywords: proton therapy; range verification; in vivo dosimetry; Compton imaging; block detector; scintillation; prompt gamma ray timing

Involved research facilities

Related publications

Permalink: https://www.hzdr.de/publications/Publ-22257


Simulation studies for the in-vivo dose verification of particle therapy

Rohling, H.

Abstract

An increasing number of cancer patients is treated with proton beams or other light ion beams which allow to deliver dose precisely to the tumor. However, the depth dose distribution of these particles, which enables this precision, is sensitive to deviations from the treatment plan, as e.g. anatomical changes. Thus, to assure the quality of the treatment, a non-invasive in-vivo dose verification is highly desired. This monitoring of particle therapy relies on the detection of secondary radiation which is produced by interactions between the beam particles and the nuclei of the patient’s tissue.
Up to now, the only clinically applied method for in-vivo dosimetry is Positron Emission Tomography which makes use of the beta+-activity produced during the irradiation (PT-PET). Since from a PT-PET measurement the applied dose cannot be directly deduced, the simulated distribution of beta+-emitting nuclei is used as a basis for the analysis of the measured PT-PET data. Therefore, the reliable modeling of the production rates and the spatial distribution of the beta+-emitters is required. PT-PET applied during instead of after the treatment is referred to as in-beam PET. A challenge concerning in-beam PET is the design of the PET camera, because a standard full-ring scanner is not feasible. For instance, a double-head PET camera is applicable, but low count rates and the limited solid angle coverage can compromise the image quality. For this reason, a detector system which provides a time resolution allowing the incorporation of time-of-flight information (TOF) into the iterative reconstruction algorithm is desired to improve the quality of the reconstructed images.
Secondly, Prompt Gamma Imaging (PGI), a technique based on the detection of prompt gamma-rays, is currently pursued. Concerning the emissions of prompt gamma-rays during particle irradiation, experimental data is not sufficiently available, making simulations necessary. Compton cameras are based on the detection of incoherently scattered photons and are investigated with respect to PGI. Monte Carlo simulations serve for the optimization of the camera design and the evaluation of criteria for the selection of measured events.
Thus, for in-beam PET and PGI dedicated detection systems and, moreover, profound knowledge about the corresponding radiation fields are required. Using various simulation codes, this thesis contributes to the modelling of the beta+-emitters and photons produced during particle irradiation, as well as to the evaluation and optimization of hardware for both techniques.
Concerning the modeling of the production of the relevant beta+-emitters, the abilities of the Monte Carlo simulation code PHITS and of the deterministic, one-dimensional code HIBRAC were assessed. The Monte Carlo tool GEANT4 was applied for an additional comparison. For irradiations with protons, helium, lithium, and carbon, the depth-dependent yields of the simulated beta+-emitters were compared to experimental data. In general, PHITS underestimated the yields of the considered beta+-emitters in contrast to GEANT4 which provided acceptable values. HIBRAC was substantially extended to enable the modeling of the depth-dependent yields of specific nuclides. For proton beams and carbon ion beams HIBRAC can compete with GEANT4 for this application. Since HIBRAC is fast, compact, and easy to modify, it could be a basis for the simulations of the beta+-emitters in clinical application. PHITS was also applied to the modeling of prompt gamma-rays during proton irradiation following an experimental setup. From this study, it can be concluded that PHITS could be an alternative to GEANT4 in this context.
Another aim was the optimization of Compton camera prototypes. GEANT4 simulations were carried out with the focus on detection probabilities and the rate of valid events. Based on the results, the feasibility of a Compton camera setup consisting of a CZT detector and an LSO or BGO detector was confirmed. Several recommendations concerning the design and arrangement of the Compton camera prototype were derived. Furthermore, several promising event selection strategies were evaluated. The GEANT4 simulations were validated by comparing simulated to measured energy depositions in the detector layers. This comparison also led to the reconsideration of the efficiency of the prototype. A further study evaluated if electron-positron pairs resulting from pair productions could be detected with the existing prototype in addition to Compton events. Regarding the efficiency and the achievable angular resolution, the successful application of the considered prototype as pair production camera to the monitoring of particle therapy is questionable.
Finally, the application of a PET camera consisting of Resistive Plate Chambers (RPCs) providing a good time resolution to in-beam PET was discussed. A scintillator-based PET camera based on a commercially available scanner was used as reference. This evaluation included simulations of the detector response, the image reconstructions using various procedures, and the analysis of image quality. Realistic activity distributions based on real treatment plans for carbon ion therapy were used. The low efficiency of the RPC-based PET camera led to images of poor quality. Neither visually nor with the semi-automatic tool YaPET a reliable detectability of range deviations was possible. The incorporation of TOF into the iterative reconstruction algorithm was especially advantageous for the considered RPC-based PET camera in terms of convergence and artifacts.
The application of the real-time capable back projection method Direct TOF for the RPCbased PET camera resulted in an image quality comparable to the one achieved with the iterative algorihms. In total, this study does not indicate the further investigation of RPC-based PET cameras with similar efficiency for in-beam PET application.
To sum up, simulation studies were performed aimed at the progress of in-vivo dosimetry. Regarding the modeling of the beta+-emitter production and prompt gamma-ray emissions, different simulation codes were evaluated. HIBRAC could be a basis for clinical PT-PET simulations, however, a detailed validation of the underlying cross section models is required. Several recommendations for the optimization of a Compton Camera prototype resulted from systematic variations of the setup. Nevertheless, the definite evaluation of the feasibility of a Compton camera for PGI can only be performed by further experiments. For PT-PET, the efficiency of the detector system is the crucial factor. Due to the obtained results for the considered RPC-based PET camera, the focus should be kept to scintillator-based PET cameras for this purpose.

Keywords: Monte-Carlo Simulation; Partikeltherapie; in-vivo Reichweitenkontrolle; GEANT4; PHITS; Prompt Gamma Imaging; Compton-Kamera; Positronen-Emissions-Tomographie; Paarbildungskamera; Monte Carlo simulation; particle therapy; in-vivo range verification; GEANT4; PHITS; Prompt Gamma Imaging; Compton camera; positron emission tomography

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-062 2015
    ISSN: 2191-8708, eISSN: 2191-8716

Downloads

Permalink: https://www.hzdr.de/publications/Publ-22256


Surface modification with focused polyatomic ion beams

Bischoff, L.; Böttger, R.; Pilz, W.; Heinig, K.-H.

Abstract

In the last decades Focused Ion Beams (FIB) have evolved from a sophisticated idea to a distinguished standard technique for sample preparation for SEM and TEM, prototyping in research and development and analytics in fields like microelectronics or nanotechnology. Most of FIB systems work with Ga beams, but liquid metal ion sources (LMIS) provide a much broader spectrum of other ion species using different source materials and an ion optical column equipped with an ExB mass separator [1]. From the source tip, beside single and double charged monatomic ions also dimers, trimers and heavier projectiles are extracted, which play an increasing role due to their special properties, like shallow penetration depth, enhanced sputtering efficiency and the huge energy deposition due to the simultaneous impact of several atoms in the same point of the sample surface.
Beside others heavy elements or alloys, those containing Au but in particular Bi are very suitable for the emission of polyatomic ions. Such projectiles with masses up to about 1000 amu have an energy spread in the range of EFWHM = 30 … 150 eV, which restrict the final FIB resolution (spot size) due to chromatic aberration to 10 … 100 nm. This is a result of the complex appearance of polyatomic species in the area around the emission point.
One of the main application fields at present is SIMS, which increasingly works with polyatomic Bi beams for defined surface erosion of inorganic as well as organic specimens. Another exciting field of application is the surface modification in terms of surface patterning by heavy dimer and trimer ions (e.g. Aunm+, Binm+). Due to the enormous, surface-near energy density deposition of cluster ions a self-organization process of hexagonally ordered dot arrays on Ge and Si based on transient melt pool formation can be triggered (Fig. 1) [2].
The authors would like to thank S. Facsko and B. Schmidt from HZDR for fruitful contributions to this work.

[1] L. Bischoff, Nucl. Instr. Meth. B 2008, 266, 1846.
[2] R. Böttger, L. Bischoff, K.-H. Heinig, W. Pilz, B. Schmidt, J. Vac. Sci. Technol. B 2012, 30, 06FF12.

Keywords: Surface modification; ion; cluster; FIB; sputtering

Involved research facilities

Related publications

  • Lecture (Conference)
    Workshop Ionenstrahlen und Nanostrukturen, 22.-24.07.2015, Heidelberg, Germany

Permalink: https://www.hzdr.de/publications/Publ-22255


Polyatomic Focused Ion Beams – Origin and Applications

Bischoff, L.

Abstract

In the last four decades Focused Ion Beams (FIB) have evolved from a sophisticated idea to a distinguished standard technique for sample preparation for SEM and TEM, prototyping in research and development and analytics in fields like microelectronics or nanotechnology. Most of the FIB systems works with Ga beams, but liquid metal ion sources (LMIS) provide a much broader spectrum of other ion species using different source materials and an ion optical column equipped with an ExB mass separator [1]. From the source tip beside single and double charged monatomic ions also dimers, trimers and heavier projectiles are extracted, which play an increasing role due to their special properties, like slight penetration depth, enhanced sputtering efficiency and the huge energy deposition due to the simultaneous impact of several atoms in the same point of the surface.
Beside others heavy elements or alloys, those containing Au but in particular Bi are very appropriate for the emission of polyatomic ions. Such projectiles with masses up to about 1000 amu have an energy spread in the range of ΔEFWHM = 30 … 150 eV, which restrict the final FIB resolution (spot size) due to chromatic aberration to 10 to 100 nm. This is a result of the complex appearance of polyatomic species in the area around the emission point.
One of the main application fields at present is SIMS, which increasingly works with polyatomic Bi beams for defined surface erosion on inorganic as well as organic specimen [2]. A second exciting field of application is the surface modification in terms of surface patterning by heavy dimer and trimer ions (e.g. Aunm+, Binm+). Due to the enormous energy transfer by the cluster ions to the surface a self-organization process of hexagonal ordered dot arrays on Ge and Si could be found surprisingly for pure elemental targets at normal incidence, described by the formation of tiny melt pools [3] shown in the figure.

[1] L. Bischoff, Nucl. Instr. Meth. B 266 (2008) 1846.
[2] F. Kollmer, Appl. Surf. Sci. 231-232 (2004) 153.
[3] R. Böttger, L. Bischoff, K.-H. Heinig, W. Pilz and B. Schmidt, JVST B 30 (2012) 06FF12.

Keywords: FIB; Cluster ions; LMIS; self-assembly

Involved research facilities

Related publications

  • Lecture (Conference)
    10. Dreiländer-FIB-Workshop, 29.-30.06.2015, Halle, Germany

Permalink: https://www.hzdr.de/publications/Publ-22254


Uptake of Selenium Oxyanions by δ-alumina at elevated Temperatures

Franzen, C.; Jordan, N.

Abstract

One major process controlling the mobility and bioavailability of selenium, a long-lived fission product in nuclear waste, is the adsorption onto mineral surfaces of both the engineered and geological barrier. In this context, it is important to understand to what extent this sorption is influenced particularly by characteristic parameters as expected in deep underground repositories for high level and long-lived radioactive waste. These parameters include inter alia elevated temperatures originating from heat generating waste and natural ground heat. For the investigation of the sorption processes, δ−Al2O3 was chosen because it is omnipresent in the environment and it represents a model oxide for more complex aluminosilicates.
In the present study, a combination of macroscopic sorption experiments, electrophoretic mobility and in-situ ATR FT-IR spectroscopy measurements was used to study the interaction of selenate and selenite with aged δ-Al2O3 at different temperatures between 25°C and 60°C. From in-situ ATR FT-IR spectra, a change in the symmetry of the aqueous tetrahedral selenate anion can be derived evidencing the formation of a surface complex on δ-Al2O3. From batch experiments, we observe a decreasing sorption of both selenate and selenite upon increasing temperature.
The isoelectric point (pHIEP) of δ-Al2O3 was located at pH 9.6 at 25°C. At higher temperatures, the pHIEP was shifted towards lower pH with a value of 8.6 at 60 °C. In addition, the absolute values of the zeta potential were lowered at higher temperatures. Both findings were in good agreement with the batch experiments.
The observed decrease in selenate and selenite sorption at higher temperatures could be assigned to a change in the surface properties of δ−Al2O3.
This effect may significantly increase the mobility of these Se−species and must be taken into account in future safety assessments of nuclear waste repositories.

Keywords: selenate; selenite; sorption

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

Permalink: https://www.hzdr.de/publications/Publ-22253


Spin-transfer effects in MgO-based tunnel junctions with an out-of-plane free layer and in-plane polarizer

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

Abstract

Spin-torque nano-oscillators (STNOs) are novel devices which may be exploited for wireless communication applications [1-3]. In particular, it has recently been demonstrated that STNOs utilizing an in-plane (IP) magnetized polarizer (also acting as read-out layer) and out-of-plane (OOP) magnetized free layer allow for the full parallel (P)-to-antiparallel (AP) resistance variation to be exploited in the limit of 90° precession angle, thereby maximizing the output power [1]. However, for this specific geometry, steady-state precession can only be sustained if the spin-transfer torque exhibits an asymmetric dependence on the angle between the free and the polarizing layer, such as in the case of fully metallic devices [1]. Nevertheless, it has recently been reported that dynamics have been experimentally observed in similarly designed MgO-based MTJs under constant applied electrical current, in spite of the fact that such devices do not exhibit any asymmetry in the spin-torque angular dependence [4,5]. These results have so far been interpreted based on the formalism for metallic devices, including the spin-torque angular dependence.
Here, we explore potential mechanisms for sustaining steady-state precession in MgO-based MTJs with an IP polarizer and an OOP free layer. To this end, we analytically and numerically solve the Landau-Lifshitz-Gilbert-Slonczewski equation for a nano-pillar MTJ with circular cross-section, under a constant perpendicular applied current and field. To sustain steady-state precession, the energy supplied by the in-plane spin-torque term and energy dissipated through damping must compensate over a full precession period.
In an MgO-MTJ, the magnitude of the STT is determined by the voltage across the barrier [6]. As the magnetization of the free layer precesses around the put-of-plane direction, the angle between the magnetic moments of the two layers changes and through the magnetoresistance effect the voltage changes if the experiment is conducted at constant applied current [7,8]. This cosine-like angular dependence of the MTJ resistance effectively introduces a spin-torque angle dependence asymmetry. In addition, for a given angle, the resistance exhibits a specific bias dependence, with the resistance of the AP state decreasing approximately linearly with increasing bias, while remaining mostly constant in the P configuration. In this work, we demonstrate that the spin-torque angular asymmetry exhibited in such systems is sufficient to sustain STT-driven dynamics.
Fig. 1 shows dynamic and static phase diagrams of the STNO obtained when neglecting (Fig. 1(a) and 1(c)) and taking into account (Fig. 1(b) and 1(d)) the bias dependence of the AP state resistance. In both cases, stable dynamics occur only for positive currents (colored area), defined as electrons flowing from the free to the reference layer. In MTJs exhibiting no bias dependence of the resistance (dRAP/dV = 0 Ω/V), the onset current for steady-state dynamics (solid lines) scales linearly with the applied current. High output powers can be obtained for relatively low values of applied currents and fields for realistic MTJ parameters, which is beneficial from the point of view of applications. Introducing an experimentally realistic value of dRAP/dV affects mostly the steady-state dynamics, while most of the trends observed for static states are maintained (Fig. 1(b) and 1(d)). Indeed, in this case current-driven precession is only excited for fields lower than the effective anisotropy of the free layer (but still only for positive currents). Moreover, while the symmetry versus field sign is conserved, the onset current no longer increases linearly with the field, but rather exhibits a parabolic-like dependence.

Keywords: spin-torque nano-oscillators (STNOs); magnetic tunnel junctions (MTJs)

  • Poster
    International Colloquium on Magnetic Films and Surfaces (ICMFS 2015), 12.-17.07.2015, Cracow, Poland

Permalink: https://www.hzdr.de/publications/Publ-22252


Tomographic investigations on centrifugal pumps conveying gas-liquid two phase flow

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

Abstract

This contribution presents an investigation study of two-phase flow distribution in an industrial centrifugal pump and its effect to the hydrodynamic behaviour. Therefore, high-resolution gamma-ray computed tomography has been applied especially in the impeller region of an industrial centrifugal pump. To observe gas-liquid phase distributions within a sharply mapped impeller wheel, which rotates with up to 1900 rpm, time-averaged rotation-synchronized computed tomography as well as radiography has been applied. The accumulation of the gas phase was studied for varying injected gas volume fractions and flow regimes. Furthermore, various internally accumulated gas holdup patterns could be identified and, eventually, associated with characteristic pump performance behaviours. Moreover, the measuring method allowed gas holdup analysis in each chamber of the impeller wheel along selected streamlines. As a result, specific phase holdup profiles could be evaluated.

Keywords: gamma-ray computed tomography; centrifugal pump; two-phase flow; gas entrainment

Involved research facilities

  • TOPFLOW Facility
  • Lecture (Conference)
    7th International Symposium on Process Tomography (ISPT7), 01.-03.09.2015, Dresden, Deutschland
  • Contribution to proceedings
    7th International Symposium on Process Tomography (ISPT7), 01.-03.09.2015, Dresden, Deutschland
    Proceedings of the 7th International Symposium on Process Tomography

Permalink: https://www.hzdr.de/publications/Publ-22251


Ion microprobe PIXE and PIGE analysis of standards’ trace elements for electron microprobe calibration.

Le Bras, L.; Munnik, F.; Renno, A. D.

Abstract

The purpose of this study is, with the recorded data, to be able to calibrate microanalytical methods, in particular electron microprobe with high precision chemical data standards. Analysis on selected standards by ion microprobe Particle-Induced-X-ray-Emission (PIXE) and Particle-Induced-Gamma-ray-Emission (PIGE) are used to detect and quantify the trace and light elements present in these samples. The presence of those elements makes a specific calibration of the machines necessary.
Electron- and X-ray measurements need good standards for a good quantification of the elements of interest. Actually, certified reference materials for microanalytical methods are very rare. In addition they are mainly glass samples. Utilisation of chosen minerals fixed in a matrix instead of glasses for calibration makes possible the application of the matrix-matched principle and the detection and quantification of trace elements in natural minerals for a resource technology application.
The widespread utilisation of Smithsonian Microbeam Standards makes this study relevant. That is why a 10 sample selection has been made in this collection. The samples’ theoretical compositions in major and trace elements are very important for the achievement of the analysis. In addition to the given element concentrations [1], a bibliographic study has also been performed for each standard in order to find possible trace elements which could be detected.
The standards received from the Smithsonian Institute are composed of crushed particles (500 µm diameter). The sample preparation is also essential. It consists in the fixation of three particles with epoxy resin into a 3 mm diameter messing cylinder.
The analyses are performed with an incident proton beam of 3.5 MeV in order to acquire simultaneously X- and Gamma-ray spectra. The data analysis is performed with GeoPIXE in order to add qualitative and quantitative data about trace elements to the given composition of the major elements. Preliminary results on apatite (NMNH 104021) are in agreement with the literature and show the presence of vanadium, arsenic, strontium, yttrium and light Rare Earth Elements such as lanthanum, cerium and neodymium. These trace elements are important for mineral resources analysis. Elemental mapping is also achieved in order to check the homogeneity of the samples’ particles.

Acknowledgements: Special thanks to Andreas Bartzsch, from the sample’s preparation laboratory of the Helmholtz Institute Freiberg, Germany, for his expertise.

[1] E. Jarosewich, J. A. Nelen, J. A. Norberg, Geostandards Newsletter 4 1980, p. 43-47

Keywords: Mineral standards; PIXE; PIGE; calibration; electron microprobe

Involved research facilities

Related publications

  • Lecture (Conference)
    Workshop für Ionenstrahlen und Nanostrukturen, 22.-24.07.2015, Heidelberg, Germany

Permalink: https://www.hzdr.de/publications/Publ-22249


A comprehensive study on iodine uptake by selected LDH phases via coprecipitation, anionic exchange and reconstruction

Iglesias, L.; Walther, C.; Medina, F.; Holzer, A.; Neumann, A.; Lozano-Rodriguez, M. J.; Alvarez, M. G.; Torapava, N.

Abstract

We explored the use of selected layered double hydroxides (LDHs) of different compositions and obtained by means of different routes (i.e., coprecipitation, anionic exchange and reconstruction) as iodine/iodate adsorbents. The influence of speciation (iodide vs. iodate) on iodine uptake was rather strong, resulting in much lower iodide incorporation. The Fourier transform of iodine K X-ray absorption edge data (EXAFS) of all iodate-LDHs showed a single I–O scattering path of 1.8 A ° . Thermal stability and leaching experiments showed that the incorporated iodate and iodide were rather loosely bound in the interlayer space and were easily released under heating to 180 C and leaching with Milli-Q water and brine solution.

Keywords: Iodine; Layered double hydroxide; Immobilization; Nuclear waste; Aqueous systems

Involved research facilities

Related publications

Permalink: https://www.hzdr.de/publications/Publ-22248


Coffinite, USiO4, Is Abundant in Nature: So Why Is It So Difficult To Synthesize?

Mesbah, A.; Szenknect, S.; Clavier, N.; Lozano-Rodriguez, J.; Poinssot, C.; Den Auwer, C.; Ewing, R. C.; Dacheux, N.

Abstract

Coffinite, USIO4, is the second most abundant U4+ mineral on Earth, and its formation by the alteration of the UO2 in spent nuclear fuel in a geologic repository may control the release of radionuclides to the environment. Despite its abundance in nature, the synthesis and characterization of coffinite have eluded researchers for decades. On the basis of the recent synthesis of USiO4, we can now define the experimental conditions under which coffinite is most efficiently formed. Optimal formation conditions are defined for four parameters: pH, T, heating time and U/Si molar ratio. The adjustment pf pH between 10 and 12 leads probably to the formation of a uranium (IV) hydroxo-silicate complex that acts as a precursor of uranium (IV) silicate colloids and then of coffinite. Moreover, in this pH range, the largest yield of coffinite formation (as compared with those of the two competing byproduct phases, nanometer-scale UO2 and amorphous SiO2) is obtained for 250 C, 7 days and 100% excess silica.

Keywords: coffinite; PXRD; EXAFS; XANES; Raman spectra

Involved research facilities

Related publications

Permalink: https://www.hzdr.de/publications/Publ-22247


High Conversion Th–U233 fuel for current generation of PWRs: Part III – Fuel availability and utilization considerations

Baldova, D.; Fridman, E.; Shwageraus, E.

Abstract

In the previous studies, reported in Parts I and II of the paper, the high conversion (HC) Th-U233 fuel design for current generation of PWRs was proposed and investigated in details on single fuel assembly and 3D full core levels. One of the important limitations of the previous studies was the reliance on the availability of pure U233 as a fissile driver. In reality, however, U233 will always be accompanied by other U isotopes. Part III of the paper deals with a number of fuel cycle aspects associated with the use of HC Th-U fuel in PWRs including: (1) more realistic estimation of neutronic properties and conversion performance of HC Th-U fuel by accounting for the evolution of U isotopic composition with a number of recycle stages; (2) reassessment of the HC Th-U PWR core performance through 3D full core coupled neutronic and T-H analysis; (3) demonstration of a feasible way of generating U233; and finally (4) evaluation of potential savings in available resources that can be achieved by using HC Th-U fuel cycle as compared to the current fuel cycle practices.

Keywords: High conversion; PWR; Th-U233 fuel; seed-blanket; DYN3D

Permalink: https://www.hzdr.de/publications/Publ-22246


Liquid Metal Alloy Ion Sources - an Alternative for Focused Ion Beam Technology

Bischoff, L.; Mazarov, P.; Bruchhaus, L.; Gierak, J.

Abstract

Today Focused Ion Beam (FIB) processing is nearly exclusively based on gallium Liquid Metal Ion Sources (LMIS). But, many applications in the µm- or nm range could benefit from ion species other than gallium: local ion implantation, ion beam mixing, ion beam synthesis or Focused Ion Beam Lithography (IBL). Therefore Liquid Metal Alloy Ion Sources (LMAIS) represent a promising alternative to expand remarkable the application fields for FIB. Especially the IBL process shows potential advantages over e.g. electron beam (EBL) or other lithography techniques: direct, resistless, and three-dimensional patterning, enabling a simultaneous in-situ process control by cross sectioning and inspection. Taking additionally into account that the used ion species influence significantly the physical and chemical nature of the resulting nanostructures -in particular the electrical, optical, magnetic and mechanic properties- leading to a large potential application area which can be tuned by choosing a well suited LMAIS. Nearly half of the elements of the Periodic Table are recently available in FIB technology as a result of continuous research in this area during the last forty years. Key features of a LMAIS are long life-time, high brightness and stable ion current. Recent developments could make these sources feasible for nano patterning issues as an alternative technology more in research than in industry. The authors will review existing LMAIS, working with pure elements (LMIS) other than Ga or binary or ternary alloys, their physical properties as well as the fabrication technology and prospective domains for modern FIB applications. Other emerging ion sources will be also presented and their performances discussed.

Keywords: Liquid Metal Alloy Ion Sources; Focused Ion Beam; Mass Separation

Involved research facilities

Related publications

Permalink: https://www.hzdr.de/publications/Publ-22245


Relationship Between Kolmogorov Entropy and Characteristic Mixing Length in Narrow Bubble Columns Operated in the Transition Flow Regime

Nedeltchev, S.; Schubert, M.; Donath, T.; Rabha, S.; Hampel, U.

Abstract

The mixing performance of bubble column reactors depends strongly on the prevailing flow regime. Kawase and Tokunaga (Can. J. Chem. Eng. 69, 1228-1231, 1991) introduced the characteristic mixing length L as an important mixing parameter. In the homogeneous regime the liquid mixing is at the scale of the bubble diameter, whereas in the heterogeneous regime it is at the scale of the column diameter. Our research is aimed at determining the scale of liquid mixing in the transition flow regime by using some advanced methods.
The Kolmogorov entropies (KE) were extracted from gas holdup time series measured (at 2000 Hz) by a new type of wire mesh sensor. It was found that in a relatively narrow bubble column (0.15 m in ID, clear liquid height = 2 m) operated with an air-water system in the transition flow regime the KE values could be correlated to L. The KE in the transition flow regime decreases monotonously and can be correlated to the superficial gas velocity (KE=1.5Ug^-0.38). The same exponent (-0.38) for UG was reported by Kawase and Tokunaga (1991) in their correlation for prediction of L. Therefore, the KE and L values (in a narrow bubble column) are correlated as follows: KE=222.222L.
A new parameter called maximum number of visits per region Nv-max was also introduced and in the same way was related to L in the transition flow regime.

Keywords: Narrow bubble column; Transition flow regime; Kolmogorov entropy; Mixing length; New statistical parameter

Involved research facilities

  • TOPFLOW Facility
  • Lecture (Conference)
    Jahrestreffen der Fachgruppen Mehrphasenströmungen und Wärme- und Stoffübertragung, 24.-26.03.2014, Fulda, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-22244


18F-FDG PET/MRI for therapy response assessment in sarcoma: Comparison of PET and MR imaging results

Schuler, M. K.; Platzek, I.; Beuthien-Baumann, B.; Fenchel, M.; Ehninger, G. E.; van den Hoff, J.

Abstract

Background: 18F-Fluorodeoxyglucose (FDG) positron emission tomography (PET) has proven to be of substantial benefit in imaging of sarcoma patients. We therefore investigated the feasibility and benefit of combined PET/magnetic resonance imaging (MRI). Methods: Twelve patients with sarcoma who underwent FDG PET/MRI for staging and response assessment after chemotherapy were included. Results: Based on contrast-enhanced MRI and application of Choi criteria, therapy response was classified as stable disease in 6/12 patients (50%) and as partial remission in 6/12 patients (50%). Conclusion: In sarcoma patients, response assessment using Choi criteria based on contrast-enhanced MRI in comparison to FDG PET imaging only demonstrates slight correlation.

Keywords: Cancer imaging; Choi criteria; FDG PET/MRI; Sarcoma

Involved research facilities

  • PET-Center

Permalink: https://www.hzdr.de/publications/Publ-22243


2-[18F]Fluoroethyl tosylate - a versatile tool for building 18F-based radiotracers for positron emission tomography

Knieß, T.; Laube, M.; Brust, P.; Steinbach, J.

Abstract

Positron emission tomography (PET) is a modern in vivo imaging technique and an important diagnostic modality for clinical and pre-clinical research. The incorporation of a radionuclide like fluorine-18 into a target molecule to form PET radiopharmaceuticals is a repeated challenge for radiochemists. 18F-Fluoroethylation is a well acknowledged method for 18F-radiolabeling and 2-[ 18F]fluoroethyltosylate ([ 18 F]FEts) is a preferred reagent because of its high reactivity to phenolic, thiophenolic, carboxylic and amide functions. The review will highlight the role of [ 18F]FEts in PET-chemistry, and summarize its applicability in radiotracer design. The radiolabeling conditions and pros and cons of direct and indirect radiolabeling as well the aspects of reactivity of [ 18F]FEts compared with other [ 18F]fluoroalkylating reagents will be discussed comprehensively.

Involved research facilities

  • PET-Center

Permalink: https://www.hzdr.de/publications/Publ-22242


New Methods for Flow Regime Identification in Bubble Columns and Fluidized Beds

Nedeltchev, S.

Abstract

New methods for flow regime identification were developed and applied to photon count time series measured in a bubble column (0.162 m in ID) and fluidized bed (0.438 m in ID). The signals in the bubble column (operated with an air-therminol system) were measured by means of Computed Tomography (CT), whereas the data in the fluidized bed (operated with an air-polyethylene system) were recorded by means of Nuclear Gauge Densitometry (NGD). The hidden information in the time series was extracted by means of two new parameters: entropy (bit/s) and information entropy (bit). Both of them were calculated on the basis of multiple reconstructions of the time series. In the case of the bubble column, the well-pronounced local minima were used for identification of three transition velocities (0.04, 0.08 and 0.13 m/s). They distinguished the boundaries of the bubbly flow, transition and churn-turbulent flow regimes. In the case of the fluidized bed, the minimum fluidization velocity (0.086 m/s) and minimum bubbling velocity (0.12 m/s) were also identified on the basis of the well-pronounced local minima in the profiles of the new parameters. They distinguished the boundaries of both the transition and bubbling fluidization regimes.

Keywords: Flow regime identification; Bubble column; Fluidized bed; Transition velocities; Entropy; Information entropy

Permalink: https://www.hzdr.de/publications/Publ-22241


Terahertz emission based on large-area photoconductive emitters illuminated via beam interference

Krauß, N.; Haas, M.; Niemeyer, L.; Winnerl, S.; Helm, M.; Dekorsy, T.

Abstract

The use of beam interference in combination with large-area photoconductive emitters for the generation of pulsed terahertz radiation is presented. An interference pattern with a periode twice that of the terahertz emitter is generated with a transmission phase grating, placed directly in front of the photoconductive emitter. This way, efficient terahertz generation is achieved with a single metallization layer and a single lithography step in the fabrication technology of the THz emitter.

Keywords: THz photoconductive emitter; large-area THz emitter

Permalink: https://www.hzdr.de/publications/Publ-22240


Characterization of microbiological community in natural REE-containing matrixes

Kutschke, S.; Raff, J.; Pollmann, K.

Abstract

Biochemistry of REE is very poorly understood. As microbes drive biogeochemistry in many ecosystems it can be expected with various yet unknown organisms that play a role in REE biogeochemistry. Thus these environments are a promising source for the recovery of microbes that are suitable candidates for their application in REE extraction and recycling.
The microbial community is a close metabolic network, where some of the organisms actively contribute to the carbon, nitrogen, sulfur, and phosphorus cycle and other microorganisms interact with minerals, metals, and pollutants. On the one hand such a microbial community is well adapted to environment and on other hand it is influenced by the geochemical parameters. Investigation of microbial community of REE containing matrixes has to be accompanied by (geo)-chemical analyses. Geochemical and structural soil parameters like organic compounds, ion exchange or waterholding capacity and porosity influence the microbial population. Moreover daily or seasonal changes of physical matrix properties force the microbial community to adapt. Reflection of environmental circumstances is one challenge describing natural microbial community (Xu 2006). The most sensitive describing tools are culture independent genomic methods. These genomic methods describe and characterize the majority of microorganisms including even the uncultivated microorganisms. Generated metagenomic data will be matched with already existing genomic databases. Up to now genetic methods like PCR fingerprinting techniques and fluorescence in situ hybridization used to identify and quantify microorganisms interacted with REE containing ore. Nevertheless genomic information of energetic metabolism, phosphate, sulfur and iron metabolism, quorum sensing, and genes involved in metal resistance and amino acid biosynthesis pathways were identified (Jerez 2008). As already mentioned the data base for comparative genomic is small. To extent this fundament it is necessary to extract single strains, to cultivate them and to analyze their genomes.
Jerez, C. A. (2008). "The use of genomics, proteomics and other OMICS technologies for the global understanding of biomining microorganisms." Hydrometallurgy 94(1–4): 162-169.
Xu, J. (2006). "Microbial ecology in the age of genomics and metagenomics: Concepts, tools, and recent advances." Molecular Ecology 15(7): 1713-1731.

  • Poster
    World Congress and Expo on Applied Microbiology 2015, 18.-20.08.2015, Frankfurt, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-22239


Efficient Auger scattering in Landau-quantized graphene

Wendler, F. H. F.; Mittendorff, M.; Winnerl, S.; Helm, M.; Knorr, A.; Malic, E.

Abstract

We present an analytical expression for the differential transmission of a delta-shaped light field in Landauquantized graphene. This enables a direct comparison of experimental spectra to theoretical calculations reflecting the carrier dynamics including all relevant scattering channels. In particular, the relation is used to provide evidence for strong Auger scattering in Landau-quantized graphene.

Keywords: Graphene; ultrafast spectroscopy; Landau quantization; Auger scattering

Involved research facilities

Related publications

  • Lecture (Conference)
    Photonics West Conference, 07.-12.02.2015, San Francisco, USA
  • Contribution to proceedings
    Photonics West Conference, 07.-12.02.2015, San Francisco, USA
    Proceedings of SPIE, 936105
    DOI: 10.1117/12.2075458
    Cited 4 times in Scopus

Permalink: https://www.hzdr.de/publications/Publ-22238


Theoretical Prediction of Mass Transfer Coefficients in Two-Phase and Slurry Bubble Columns

Nedeltchev, S.

Abstract

Two-phase and slurry bubble columns are characterized with high volumetric mass transfer coefficients kLa at low energy input. The design, modelling, optimization and scale-up of these reactors require precise knowledge of the mass transfer parameters. The mass transfer coefficients determine the efficiency and dimensions of (slurry) bubble columns. Nedeltchev et al. (2007) developed a correlation for prediction of mass transfer coefficients in gas-liquid bubble columns operated in the homogeneous flow regime. It was based on experimental gas holdups. On the other hand, Nedeltchev and Schumpe (2008) developed a correlation for prediction of gas holdups in gas-liquid bubble columns operated in the homogeneous regime. In this work, the theoretically calculated gas holdups were substituted in the mass transfer model (in the correlation for the interfacial area) of Nedeltchev et al. (2007) and the mass transfer coefficients were recalculated by means of a purely theoretical approach. The same gases and liquids (18 pure organic liquids, 14 adjusted liquid mixtures and tap water) were used and 263 kLa values (only in the homogeneous regime) were successfully predicted at ambient and high pressures (up to 1 MPa).
The same approach was tested in a slurry bubble column. Nedeltchev et al. (2014) predicted successfully the experimental mass transfer coefficients in a slurry bubble column based on bubble sizes which depended on the experimental gas holdups. On the other hand, Nedeltchev (2014) established a new approach for predicting the gas holdups in a slurry bubble column. When these theoretical gas holdups were substituted in the mass transfer model (in the correlations for prediction of bubble size and interfacial area), a purely theoretical kLa values in a slurry bubble column were obtained. The predictions were good not only in the homogeneous regime but also in the heterogeneous regime. The theoretical approach was applicable up to relatively high (18 %) solids concentrations. Six different liquid-solid systems were used and 66 kLa values were successfully predicted. In both mass transfer models, correction factors (a function of Eӧtvӧs numbers) were introduced due to the non-spherical (ellipsoidal) shape of the bubbles.

Keywords: Mass transfer coefficients; Penetration theory; New contact time; Gas-liquid bubble columns; Slurry bubble columns

  • Lecture (Conference)
    12th International Conference on Gas-Liquid and Gas-Liquid-Solid Reactor Engineering (GLS12), 28.06.-01.07.2015, New York, USA

Permalink: https://www.hzdr.de/publications/Publ-22237


Years: 2023 2022 2021 2020 2019 2018 2017 2016 2015


Pages: [1.] [2.] [3.] [4.] [5.] [6.] [7.] [8.] [9.] [10.] [11.] [12.] [13.] [14.] [15.] [16.] [17.] [18.] [19.] [20.] [21.] [22.] [23.] [24.] [25.] [26.] [27.] [28.] [29.] [30.] [31.] [32.] [33.] [34.] [35.] [36.] [37.] [38.] [39.] [40.] [41.] [42.] [43.] [44.] [45.] [46.] [47.] [48.] [49.] [50.] [51.] [52.] [53.] [54.] [55.] [56.] [57.] [58.] [59.] [60.] [61.] [62.] [63.] [64.] [65.] [66.] [67.] [68.] [69.] [70.] [71.] [72.] [73.] [74.] [75.] [76.] [77.] [78.] [79.] [80.] [81.] [82.] [83.] [84.] [85.] [86.] [87.] [88.] [89.] [90.] [91.] [92.] [93.] [94.] [95.] [96.] [97.] [98.] [99.] [100.] [101.] [102.] [103.] [104.] [105.] [106.] [107.] [108.] [109.] [110.] [111.] [112.] [113.] [114.] [115.] [116.] [117.] [118.] [119.] [120.] [121.] [122.] [123.] [124.] [125.] [126.] [127.] [128.] [129.] [130.] [131.] [132.] [133.] [134.] [135.] [136.] [137.] [138.] [139.] [140.] [141.] [142.] [143.] [144.] [145.] [146.] [147.] [148.] [149.] [150.] [151.] [152.] [153.] [154.] [155.] [156.] [157.] [158.] [159.] [160.] [161.] [162.] [163.] [164.] [165.] [166.] [167.] [168.] [169.] [170.] [171.] [172.] [173.] [174.] [175.] [176.] [177.] [178.] [179.] [180.] [181.] [182.] [183.] [184.] [185.] [186.] [187.] [188.] [189.] [190.] [191.] [192.] [193.] [194.] [195.] [196.] [197.] [198.] [199.] [200.] [201.] [202.] [203.] [204.] [205.] [206.] [207.] [208.] [209.] [210.] [211.] [212.] [213.] [214.] [215.] [216.] [217.] [218.] [219.] [220.] [221.] [222.] [223.] [224.] [225.] [226.] [227.] [228.] [229.] [230.] [231.] [232.] [233.] [234.] [235.] [236.] [237.] [238.] [239.] [240.] [241.] [242.] [243.] [244.] [245.] [246.] [247.] [248.] [249.] [250.] [251.] [252.] [253.] [254.] [255.] [256.] [257.] [258.] [259.] [260.] [261.] [262.] [263.] [264.] [265.] [266.] [267.] [268.] [269.] [270.] [271.] [272.] [273.] [274.] [275.] [276.] [277.] [278.] [279.] [280.] [281.] [282.] [283.] [284.] [285.] [286.] [287.] [288.] [289.] [290.] [291.] [292.] [293.] [294.] [295.] [296.] [297.] [298.] [299.] [300.] [301.] [302.] [303.] [304.] [305.] [306.] [307.] [308.] [309.] [310.] [311.] [312.] [313.] [314.] [315.] [316.] [317.] [318.] [319.] [320.] [321.] [322.] [323.] [324.] [325.] [326.] [327.] [328.] [329.] [330.] [331.] [332.] [333.] [334.] [335.] [336.] [337.] [338.] [339.] [340.] [341.] [342.] [343.] [344.] [345.] [346.] [347.] [348.] [349.] [350.] [351.] [352.]