Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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32228 Publications
A semiconducting layered metal-organic framework magnet
Yang, C.; Dong, R.ORC; Wang, M.ORC; Petkov, P. S.ORC; Zhang, Z.ORC; Wang, M.; Han, P.ORC; Ballabio, M.; Bräuninger, S. A.; Liao, Z.; Zhang, J.ORC; Schwotzer, F.; Zschech, E.; Klauss, H.-H.; Cánovas, E.; Kaskel, S.ORC; Bonn, M.; Zhou, S.ORC; Heine, T.ORC; Feng, X.
The realization of ferromagnetism in semiconductors is an attractive avenue for the development of spintronic applications. Here, we report a semiconducting layered metal-organic framework (MOF), namely K3Fe2[(2,3,9,10,16,17,23,24-octahydroxy phthalocyaninato)Fe] (K3Fe2[PcFe-O8]) with spontaneous magnetization. This layered MOF features in-plane full π-d conjugation and exhibits semiconducting behavior with a room temperature carrier mobility of 15 ± 2 cm2 V−1 s−1 as determined by time-resolved Terahertz spectroscopy. Magnetization experiments and 57Fe Mössbauer spectroscopy demonstrate the presence of long-range magnetic correlations in K3Fe2[PcFe-O8] arising from the magnetic coupling between iron centers via delocalized π electrons. The sample exhibits superparamagnetic features due to a distribution of crystal size and possesses magnetic hysteresis up to 350 K. Our work sets the stage for the development of spintronic materials exploiting magnetic MOF semiconductors.

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Publ.-Id: 29493 - Permalink


Strain-induced perpendicular magnetic anisotropy and Gilbert damping of Tm3Fe5O12 thin films
Ciubotariu, O.; Semisalova, A.; Lenz, K.ORC; Albrecht, M.
In the attempt of implementing iron garnets with perpendicular magnetic anisotropy (PMA) in spintronics, the attention turned towards strain-grown iron garnets. One candidate is Tm3Fe5O12 (TmIG) which possesses an out-of-plane magnetic easy axis when grown under tensile strain. In this study, the effect of film thickness on the structural and magnetic properties of TmIG films including magnetic anisotropy, saturation magnetization, and Gilbert damping is investigated. TmIG films with thicknesses between 20 and 300 nm are epitaxially grown by pulsed laser deposition on substituted-Gd3Ga5O12(111) substrates. Structural characterization shows that films thinner than 200 nm show in-plane tensile strain, thus exhibiting PMA due to strain-induced magnetoelastic anisotropy. However, with increasing film thickness a relaxation of the unit cell is observed resulting in the rotation of the magnetic easy axis towards the sample plane due to the dominant shape anisotropy. Furthermore, the Gilbert damping parameter is found to be in the range of 0.02 ± 0.005.
Keywords: Thulium iron garnet, magnetic anisotropy, Gilbert damping
  • Poster
    Magnonics 2019, 28.07.-01.08.2019, Carovigno, Italy

Publ.-Id: 29492 - Permalink


Theranostic CAR T cell targeting: A brief review
Arndt, C.; Bachmann, M.; Bergmann, R.; Berndt, N.; Feldmann, A.; Koristka, S.;
More than 100 years ago Paul Ehrlich postulated that our immun system should be able to eliminate tumor cells. Just recently, the development of check point inhibitors, bispecific antibodies, and T cells genetically modified to express chimeric antigen receptors (CARs) underlines the true power of our immune system. T cells genetically modified with CARs can lead to complete remission of malignant hematologic diseases. However, they can also cause life-threatening side effects. In case of cytokine release syndrome, tumor lysis syndrome, or deadly side effects on the central nervous system, an emergency shut down of CAR T cells is needed. Targeting of tumor-associated antigens that are also expressed on vital tissues require a possibility to repeatedly switch the activity of CAR T cells on and off on demand and to follow the treatment by imaging. Theranostic, modular CARs such as the UniCAR system may help to overcome these problems.
Keywords: bispecific antibody, BiTE, chimeric antigen receptor, immunotherapy, T cells, UniCAR
  • Journal of Labelled Compounds and Radiopharmaceuticals 62(2019)8, 533-540
    DOI: 10.1002/jlcr.3727

Publ.-Id: 29490 - Permalink


Spatial solitons in KTaxNb1-xO3 waveguides produced by swift carbon ion irradiation and femtosecond laser ablation
He, S.; Zhang, Z.; Liu, H.; Akhmadaliev, S.; Zhou, S.; Wang, X.; Wu, P.;
We report on the fabrication of planar waveguide and ridge waveguides in a KTN crystal by using swift heavy C5+ ions irradiation and femtosecond laser ablation. The reconstructed refractive index profile of the irradiated KTN waveguide illustrates an optical well and barrier distribution. The confocal Raman spectra suggest that the enhanced tetragonality and the lattice damage occurs in the waveguide region and the optical barrier area, respectively. The optical spatial solitons at 632.8 nm are observed from the planar waveguide and the ridge waveguides with a width of 60 μm and 20 μm, respectively, at room temperature.

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  • Secondary publication expected from 26.06.2020

Publ.-Id: 29486 - Permalink


Defect-induced magnetism in SiC
Zhou, S.ORC; Chen, X.
Defect-induced magnetism describes a magnetic phenomenon in materials containing neither unpaired 3d nor 4f  electrons. Therefore, it presents a challenge to the conventional understanding of magnetism and has remained under debate for over a decade. Different from graphite and oxides which are common research venues in defect-induced magnetism, SiC is commercially available at large scale and with high quality at the microelectronic grade. Therefore, SiC presents a suitable model system for studying defect-induced ferromagnetism and exploring possible applications. Understanding and controlling defect-induced magnetism in a semiconductor like SiC opens up the possibility for producing spintronic devices based on classical semiconductor technologies. Here, we review recent studies on defect-induced magnetism in SiC. We start with a brief description about defects in SiC. Then we summarize the experimental results on defect-induced magnetism in SiC, the microscopic origin of the magnetism and the magnetic coupling mechanism. We also propose several potential applications, particularly using magnetometry as a complementary method for quantitative characterization of defects in SiC. At the end, we list the challenges from our point of view, such as controlling defects in SiC regarding their charge states, distribution and local environment, and understanding defect-induced magnetism by local and elemental selective probe techniques.

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  • Secondary publication expected from 18.07.2020

Publ.-Id: 29485 - Permalink


Spectroscopic insights into U(IV) speciation in aqueous solution
Lehmann, S.ORC; Steudtner, R.; Gerber, U.ORC; Zimmermann, T.; Brendler, V.ORC
This work is focused on uranium as the major component of the nuclear fuel cycle. It is important to predict its environmental behavior for, e.g., the safety assessment of a future repository or the remediation of the various legacies of uranium mining and milling. Typically, diluted to highly saline aquifer systems under reducing conditions with carbonates, silicates, phosphates, chlorides and sulfates as important complexing agents are to be considered. However, predictions for U(IV) speciation often suffer from a sparsely populated thermodynamic data base [1], often due to a missing spectroscopic evaluation of species stoichiometry and structure.
This work combines absorption and fluorescence spectroscopies to reveal the speciation of U(IV) in solution in concentrations down to 10⁻⁶ M uranium. The set-up for time-resolved laser-induced fluorescence was optimized to allow the determination of fluorescence decay times of U(IV) in perchloric as well as in chloric acid with 2.5 ± 0.4 ns at room temperature and 152 ± 8.3 ns at liquid nitrogen temperature. By decreasing the temperature we gained an improved fine structure with a band splitting of the main peak at 410 nm and a redshift could be observed.
By evaluation of UV-vis based titration series (pH = 0 2, [U] = 10⁻⁴-10⁻⁵ M, [SO4] from 0 to 1.9·10⁻⁵ M) in the U(IV) sulfate system, complex formation constants for USO₄²⁺ and U(SO₄)₂(aq) could be derived, yielding 6.9 ± 0.3 and 11.8 ± 0.5, respectively, when extrapolated to infinite dilution. This log K values for the 1:1 complex is close to the NEA recommendation of 6.58 whereas our value for the 1:2 complex is about one order of magnitude higher than that selected in [1]. The NEA recommendations are exclusively based on liquid-liquid extraction experiments, with higher ionic strengths (up to 2 M) and U(IV) concentrations (up to 0.1 M) as applied in this work.
The potential of direct U(IV) spectroscopy for speciation analysis at environmentally relevant uranium concentrations was proven in this study. Eventually, all acquired information will increase confidence in respective U(IV) reactive transport modelling.
The authors gratefully acknowledge funding by the German Federal Ministry of Economic Affairs and Energy under the grant 02E11334B.
[1] R. Guillaumont et al. (2003). "Update on the chemical thermodynamics of uranium, neptunium, plutonium, americium and technetium., vol. 5 of Chemical Thermodynamics." Elsevier: 960 pp.
Keywords: tetravalent uranium, photometry, thermodynamics,
  • Poster
    EGU General Assembly 2019, 07.-12.04.2019, Wien, Österreich

Publ.-Id: 29484 - Permalink


Annual Report 2018 - Institute of Ion Beam Physics and Materials Research
Faßbender, J.ORC; Helm, M.; Zahn, P.
The Institute of Ion Beam Physics and Materials Research conducts materials research for future applications in, e.g., information technology. To this end, we make use of the various possibilities offered by our Ion Beam Center (IBC) for synthesis, modification, and analysis of thin films and nanostructures, as well as of the free-electron laser FELBE at HZDR for THz spectroscopy. The analyzed materials range from semiconductors and oxides to metals and magnetic materials. They are investigated with the goal to optimize their electronic, magnetic, optical as well as structural functionality. This research is embedded in the Helmholtz Association’s programme “From Matter to Materials and Life”. Six publications from last year are highlighted in this Annual Report to illustrate the wide scientific spectrum of our institute.
  • Open Access LogoWissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-097 2019

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Publ.-Id: 29482 - Permalink


LOCA scenario-related zinc borate precipitation studies at lab scale
Harm, U.; Kryk, H.; Wiezorek, M.; Hampel, U.ORC
During the sump recirculation operation after a postulated loss-of-coolant accident (LOCA) in a pressurized water reactor (PWR), coolant spilling out of the leak in the primary cooling circuit is collected in the reactor sump and recirculated to the reactor core by residual-heat removal pumps. The long-term contact of the boric acid containing coolant with hot-dip galvanized containment internals (e.g. grating treads, strainers, support grids) may cause corrosion of the corresponding materials forming zinc borates (ZnB) dissolved in the cooling water.
Investigations regarding such zinc corrosion processes, changes of the coolant chemistry and possible resulting in-core effects are subject of joint research projects of the Helmholtz-Zentrum Dresden - Rossendorf (HZDR), TU Dresden (TUD) and Zittau/Görlitz University of Applied Sciences (HSZG). Lab-scale experiments at HZDR and TUD are focused on elucidation of physico-chemical corrosion and precipitation processes as well as resulting fouling effects at hot surfaces.
Long-term experiments of up to three weeks in a lab scale facility were conducted to simulate the simultaneous zinc dissolution (in sump) and ZnB precipitation (in hot core regions) during sump recirculation operation under boundary conditions of selected PWR LOCA scenarios. This includes LOCA-related zinc dissolution (corrosion) rates as well as experimental simulation of previously calculated scenario-related temperature courses of the coolant in the sump and area-related decay heat power courses of the reactor core. Results indicate significant precipitations of different solid ZnB products during the experiments. It turned out that the period between the start of the sump recirculation operation and the start of the ZnB precipitation as well as the precipitation rate essentially depend on the specific LOCA scenario (e.g. leak size). The ZnB precipitates usually formed dense layers on hot surfaces of electrically heated PWR cladding tubes of the lab scale facility. Additionally, flocculation or formation of solid ZnB particles inside the fluid has been observed. In most experiments, the different types of precipitates (layers, flocs or particles) were quantified and in certain cases the chemical compositions of the solid ZnB species were determined using different chemical analysis methods.
Since an influence of the ZnB precipitates on the thermal hydraulics inside the core cannot be ruled out, the results obtained at lab-scale were complemented by corresponding experiments in semi-technical test facilities of the project partner HSZG.
The investigations are supported by the German Federal Ministry for Economic Affairs and Energy under contract nos. 1501491 and 1501496.
Keywords: LOCA, loss-of-coolant accident, PWR, zinc borate, corrosion, Nuclear energy; Loss of coolant accident; corrosion; zinc release; experiments
  • Lecture (Conference)
    50th Annual Meeting on Nuclear Technology (AMNT 2019), 07.-08.05.2019, Berlin, Deutschland

Publ.-Id: 29478 - Permalink


Qualification of a Photometer Probe for Local Concentration Measurement in Dense Bubbly Flows
Hampel, U.; Kryk, H.; Kipping, R.;
Topics of current research activities within the DFG priority program SPP 1740 “Reactive Bubbly Flows” are studies on local mass transfer and reaction processes in order to gain a deeper understanding about the coupling of hydrodynamics, mass transfer and reaction kinetics in reactive bubbly flows as well as its influence on yield and selectivity in case of complex chemical reactions. Precondition for experimental investigations is the availability of sensors for local concentration measurements of components in the liquid phase. Due to limitations of currently available non-invasive measuring techniques, local concentration measurements in dense bubbly flows at technical scale pose technological challenges. Therefore, a minimal-invasive photometer probe have been qualified to measure concentrations of intermediates and products within the liquid phase of dense bubbly flows with high temporal and spatial resolution.
This work was supported by the German Research Foundation (DFG), reactive bubbly flows (SPP 1740).
Keywords: PAT, photometer, multiphase flow, hydrodynamics, mass transfer, bubbly flow, chemical reaction, concentration measurement
  • Poster
    Jahrestreffen Reaktionstechnik 2019 gemeinsam mit der Fachgruppe Mehrphasenströmungen, 27.-29.05.2019, Würzburg, Deutschland

Publ.-Id: 29477 - Permalink


Testpublikation
Frust, T.ORC; Starke, S.
Testabstract Testabstract Testabstract Testabstract Testabstract Testabstract..

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Publ.-Id: 29475 - Permalink


Multi-fluid models for gas-liquid flows: consolidation of CFD modelling
Lucas, D.;
This lecture presents the status and strategies for the consolidation of CFD-modelling in the multi-fluid framework. This is illustrated by the example of recent research on the further qualification of the baseline model for poly-disperse bubbly flows.
Keywords: CFD, multi-fluid, Euler-Euler, baseline model, bubbly flow
  • Invited lecture (Conferences)
    XIII Workshop & Summer School „Modelling of Multiphase Flows in Thermo-Chemical Systems”, 13.-15.06.2019, Wieżyca, near Gdańsk, Poland

Publ.-Id: 29469 - Permalink


Status and perspectives of CFD modelling of gas-liquid flows in the multi-fluid framework
Lucas, D.;
There is an increasing request to use CFD-methods for simulations on medium and large scale industrial applications, e.g. in chemical engineering, energy techniques and nuclear safety. For most of such applications the Euler-Euler two or multi-fluid approach is the only feasible one. Gas and liquid phases are represented by interpenetrating fields and the information on the interface gets lost during the averaging process which is applied to obtain the balance equations. To close these equations the corresponding local phenomena at the gas-liquid interfaces have to be considered by closure models. As recently discussed by Lucas et al. (2016) there is not yet consensus achieved in the community regarding the most appropriate closures which limits the reliability of CFD-simulations using the Euler-Euler approach. A so-called baseline model concept was proposed in that paper. Since the closure models have to reflect the local phenomena a case by case tuning is not meaningful and instead a fixed set of closure models should be defined for certain flow conditions and applied to different cases without any modification.

Different flow morphologies as bubbly flows, droplet flows and segregated flows with large interfaces have to be distinguished. These different approaches require different closure models. In addition for poly-disperse bubbly flows it may be necessary to divide the gas phase into sub-phases reflecting bubbles of different size respectively. At HZDR a baseline model for poly-disperse bubbly flows basing on the inhomogeneous MUSIG (iMUSIG) approach (Rzehak and Krepper, 2016) and a model for segregated flows basing on the AIAD model (Porombka and Höhne, 2016) have been established. Especially the baseline model for poly-disperse flows with fixed model formulations and model parameters was validated on a large number of experiments (more than 150) for different flow geometries, flow rates and material systems. There is already an acceptable agreement for many cases, but for some also clear deviations occur. It is the scientific challenge to identify the main reasons for these deviations and figure out a better model for the corresponding phenomenon. The baseline model strategy will be illustrated by the recent developments to improve the modelling of bubbly flows and a general strategy how to develop better models will be presented.

In many flow situations interfaces may vary over a large range of scales combining dispersed and segregated morphologies. To handle such flows the innovative GENTOP concept was developed (Hänsch et al., 2012). It combines the iMUSIG and AIAD approaches and allows also simulating transitions between the different morphologies. The well validated baseline models are thus part of GENTOP. Recently the concept was applied for a simulation of a boiling pipe which includes flow pattern transitions (Höhne et al., 2017). The second part of the lecture will report about these developments which aim to extend the range of applicability of CFD simulations.

The above mentioned approaches were first implemented and tested in the commercial CFD-code ANSYS-CFX. Presently a similar framework is established for the OpenSource code OpenFOAM. A GitLab based version control system allows a high level quality assurance and has a high potential for international co-operation. Joint efforts can be done to qualify the code system.
Keywords: CFD, multi-fluid, gas-liquid, bubbly flow, segregated flow
  • Invited lecture (Conferences)
    10th International Conference on Multiphase Flow, 19.-24.05.2019, Rio de Janeiro, Brazil
  • Contribution to proceedings
    10th International Conference on Multiphase Flow, 19.-24.05.2019, Rio de Janeiro, Brazil

Publ.-Id: 29468 - Permalink


Message from the Guest Editor of the 16th Multiphase Flow Conference Special Issue
Lucas, D.;
Selected contributions of the 16th Multiphase Flow Conference at HZDR were published in a special issue of the Open Access Journal Experimental and Computational Multiphase Flow. In this contribution an overview on the conference and a short introduction to the single papers is given.
Keywords: multiphase flow, conference
  • Open Access LogoAbstract in refereed journal
    Experimental and Computational Multiphase Flow 1(2019), 231-232
    DOI: 10.1007/s42757-019-0037-7

Publ.-Id: 29466 - Permalink


Fundamentals in GPU programming
Bieberle, A.ORC
For the 2nd TOMOCON Summer School “Process Tomography & Data Processing”, that is conducted this time in Delft, a lecture will be given about parallel data processing programming using suitable architechtures, such as graphic processing units (GPU).
Keywords: Parallelism, GPU programming, CUDA
  • Lecture (Conference)
    2nd TOMOCON Summer School “Process Tomography & Data Processing, 01.-03.07.2019, Delft, Niederlande

Publ.-Id: 29463 - Permalink


Suppressed Auger scattering and tunable light emission of Landau-quantized massless Kane electrons
But, D. B.; Mittendorff, M.; Consejo, C.; Teppe, F.; Mikhailov, N. N.; Dvoretskii, S. A.; Faugeras, C.; Winnerl, S.; Helm, M.; Knap, W.; Potemski, M.; Orlita, M.;
The Landau level laser has been proposed a long time ago as a unique source of monochromatic radiation, widely tunable in the THz and infrared spectral ranges using an externally applied magnetic field. In spite of decades of efforts, this appealing concept never resulted in the design of a reliable device. This is due to effcient Auger scattering of Landau-quantized electrons, which is an intrinsic non-radiative recombination channel that eventually gains over cyclotron emission in all materials studied so far: in conventional semiconductors with parabolic bands, but also in graphene with massless electrons. The Auger processes are favored in these systems by Landau levels (or their subsets) equally spaced in energy. Here we show that this scheme does not apply to massless Kane electrons in gapless HgCdTe alloy, in which undesirable Auger scattering is strongly suppressed and the sizeable cyclotron emission observed, for the first time in the case of massless particles. The gapless HgCdTe thus appears as a material of choice for future technology of Landau level lasers.
Keywords: Kane electrons, Landau quantization, Auger scattering, cyclotron emission

Publ.-Id: 29460 - Permalink


Holistic Data Management as a Key Towards Reproducible Science in a Diverse and Dynamic Ecosystem
Juckeland, G.ORC
Eingeladener Vortrag an der RWTH Aachen
  • Open Access LogoLecture (others)
    IT Seminar der RWTH Aachen, 12.07.2019, Aachen, Deutschland

Publ.-Id: 29459 - Permalink


Polarization-dependent near-field phonon nanoscopy of oxides: SrTiO₃, LiNbO₃, and PbZr₀.₂Ti₀.₈O₃
Wehmeier, L.; Lang, D.; Liu, Y.; Zhang, X.; Winnerl, S.; Eng, L. M.; Kehr, S. C.;
Resonant infrared near-field optical spectroscopy provides a highly material-specific response with sub-wavelength lateral resolution of about 10 nm. Here, we provide the near-field response of selected paraelectric and ferroelectric materials, i.e. SrTiO3, LiNbO3, and PbZr0:2Ti0:8O3, showing resonances in the wavelength range from 13.0 to 15.8 µm. We investigate these materials using scattering scanning near-field optical microscopy (s-SNOM) in combination with a tunable midinfrared free-electron laser (FEL). Fundamentally, we demonstrate that phonon-induced resonant near-field excitation surprisingly is possible for both p- and s-polarized incident light, a fact that is of particular interest for the nanoscopic investigation of anisotropic and hyperbolic materials. Moreover, we show that near-field spectroscopy, as compared to far-field techniques, bears substantial advantages such as lower penetration depths, stronger confinement, and a high spatial resolution. The latter permits the investigation of minute material volumes, e.g. with nanoscale changes in crystallographic structure, which we prove here via near-field imaging of ferroelectric domain structures in PbZr0.2Ti0.8O3 thin film.
Keywords: Near-field microscopy, ferroelectrica

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Publ.-Id: 29449 - Permalink


Direct Correction of Residual Symmetric Aberrations in Electron Holograms of Weak Phase Objects
Kern, F.; Linck, M.; Wolf, D.; Niermann, T.; Arora, H.; Alem, N.; Erbe, A.; Gemming, S.; Lubk, A.;
Thin TEM specimen are regarded as weak objects (WPO), if the amplitude variation of the electron wave by the specimen can be neglected and the phase modulation is very small (≪π). Large classes of topical materials can be described in this approximation, such as most 2D materials, organic semiconductor materials or biological specimen. Due to the lack of amplitude (and hence intensity) contrast, conventional TEM (CTEM) investigations on WPOs are commonly performed under a certain defocus, which transfers part of the phase information to the recorded intensity. This intermixing contrast transfer from amplitude to phase and vice versa is commonly described by the phase contrast transfer function (PCTF), while the non-mixing contrast transfer for amplitude and phase is referred to as amplitude contrast transfer function (ACTF). Due to the transfer gap in the PCTF, the CTEM contrast transfer at low spatial frequencies is degraded in defocused images of WPOs (Fig. 1). By employing electron holography, however, both amplitude and phase of the electron wave can be reconstructed without a transfer gap. Having the whole wave information also enables the a-posteriori correction of geometric aberrations as it was already proposed in D. Gabor’s seminal paper from 1948 [1]. The realization of his idea, however, remains challenging in the absence of additional knowledge about the sample, due to the lack of a criterion for a successful aberration correction.
Keywords: electron holography, ERC, density-functional calculations, all-electron, 2D materials,
  • Lecture (Conference)
    Microscopy Conference 2019, 01.-06.09.2019, Berlin, Deutschland

Publ.-Id: 29448 - Permalink


Simulation of STM images and spectroscopy of single nitrogen-doped molecules with 5-7 membered rings on Au(111) surfaces
Nikipar, S.; Ryndyk, D. A.; Gemming, S.; Moresco, F.; Cuniberti, G.; Frauenheim, T.;
We consider STM images and spectroscopy (STS) of molecules on metal surfaces. We combine DFT based atomistic tight-binding model (DFTB approach) with Green function technique, which offers a framework to consider tip, molecule and surface as one integrated system and taking into account the tip geometry. Besides, it captures the interference and interaction effects. This approach can be applied for the investigation of finite-voltage effects and describe the high-energy molecular transport states. It allows to simulate quantitatively the I(V) current-voltage spectroscopy curves and dI/dV maps in both constant current and constant height modes. We applied our methods to nitrogen-doped molecules with 5-7 membered rings on Au(111) surface and showed that the electronic properties of molecules are strongly influenced by formation of azulene-motifs. We developed the integrated open software suite for quantum nanoscale modeling (TraNaS OpenSuite, tranas.org/opensuite) for convenient calculations of large-scale molecular nanosystems on metal surfaces.
Keywords: molecular electronics, STM, conductance calculations, density-functional tight binding
  • Poster
    DPG Frühjahrstagung, 31.03.-05.04.2019, Regensburg, Deutschland

Publ.-Id: 29447 - Permalink


Electron Transport through single Mn-salen molecule: Theoretical Study
Lokamani, L.; Kilibarda, F.; Sendler, T.; Zahn, P.; Mortensen, M.; Gothelf, K. V.; Erbe, A.; Gemming, S.;
Metal-salen complexes, formed by the coordination of a metal cation and a N,N’-bis(salicylidene)ethylenediamine-based ligand, are promising candidates for molecular electronics, because of possible modulations of transport channels using different metal cations. One such candidate is Mn-salen complex.

Here, we first explore the electronic structure of single molecules using wave function (MS-CASSCF) and density-functional (DFT+U) methods. We then employ the non-equilibrium Green’s function (NEGF) technique to study electron transport through single molecules attached to gold electrodes under finite bias. We explore various docking configurations for the single molecule between the gold electrodes.

A comparison with experimental coupling constants and energy levels, obtained using mechanically controllable break junction (MCBJ) technique is also presented.
Keywords: molecular electronics, NEGF, density-functional theory, Hartree-Fock, ab-initio, complete active space, multiconfigurational approach, transport calculation
  • Lecture (Conference)
    DPG Frühjahrstagung, 31.03.-04.05.2019, Regensburg, Deutschland

Publ.-Id: 29446 - Permalink


Statistical studies of random silicon-germanium alloys using electronic structure calculations
Roscher, W.; Fuchs, F.; Wagner, C.; Schuster, J.; Gemming, S.;
Random alloys are relevant for many applications. One example is silicon-germanium which is used for high frequency devices like heterojunction-bipolar transistors. We therefore investigate the electronic structure of Si1−xGex alloys in the entire composition range 0≤ x≤ 1. For our study we use density functional theory in combination with bulk models of the alloys. To describe the band gap precisely we use the pseudopotential projector shift method as implemented in QuantumATK 18.06.

We perform a random generation of Si1−xGex structures to get statistical distributions of the electronic properties. After optimizing the structure we evaluate the band structure by averaging equivalent directions in the Brillouin zone.

The mean of the band gap is in good agreement with experimental reference data. We also demonstrate wide variations of the band gap, which are in the range of about 10 %. Further properties, such as the lattice constant and the formation energy are studied as well. Finally, we investigated also the impact of additional carbon dopants in the silicon-germanium alloy.
Keywords: Silicon nanowires, germanium nanowires, random alloys, Monte-Carlo, grand canonical potential simulations, entropy corrections, density functional calculations, mixing enthalpy, mixing entropy
  • Poster
    DPG Frühjahrstagung, 31.03.-05.04.2019, Regensburg, Deutschland

Publ.-Id: 29445 - Permalink


Understanding the formation of interlayer excitons in the case of MoS2 on GaSe.
Wagner, C.; Rahaman, M.; Zahn, D. R. T.; Gemming, S.;
The fabrication of hybrid van-der-Waals heterostructures of two-dimensional nano materials is an emerging field of study: The (weak) electronic interaction between two layers is often reasonably described by a perturbation of the physical effects of the isolated layers, such as electrostatic doping and screening of intralayer excitons. However, it turns out that this picture of the weak interaction is not exhaustive in terms of optical properties: the formation of bound excitons from electrons of one layer and the holes from another layer yields the formation of interlayer excitons. These states are measured experimentally by photoluminescence and photocurrents, e.g. in the case of MoS2 on GaSe due to type-II band alignment.

This contribution elucidates the conditions for the formation of interlayer excitons from a first-principles point of view. For this, first-principles studies of a minimal test system are conducted. One perspective is then to predict these states as a function of the heterostack in order to specifically taylor efficient solar cells.
Keywords: densit-function calculations, 2D materials, interlayer exciton, exciton, Bethe-Salpeter, two-particle excitations, 2D heterostructure
  • Lecture (Conference)
    DPG Frühjahrstagung, 31.03.-05.04.2019, Regensburg, Deutschland

Publ.-Id: 29444 - Permalink


Understanding the electron transport through NiSi2-Si interfaces
Fuchs, F.; Gemming, S.; Schuster, J.;
Metal-semiconductor interfaces are of huge importance for applications and can be found in various field-effect transistors. We study the interface between NiSi2 and silicon on the basis of density functional theory and the NEGF formalism. Different crystal orientations and strain states are investigated systematically.

We focus on the tunneling phenomena of carriers through the Schottky contact at the interface, which are crucial for the on-current in transistors. The on-current is found to be strongly dependent on strain and orientation. It will be shown that the height of the Schottky barrier determines the tunneling current. However, not all changes in the current can be traced back to the barrier height. The modification of the electronic structure matter as well, which can be modeled based on the effective mass of the tunneling carriers. We have also extracted work functions of the isolated materials which we relate to the extracted Schottky barrier heights. It will be shown that the Schottky-Mott model fails for this material system. Better approaches will be discussed in our contribution.
Keywords: one-dimensional transport, density-functional theory, electronic structure, reconfigurable electronics, RFET, silicon nanowires, nickel silicides, 1D contacts
  • Invited lecture (Conferences)
    International Workshop "Correlations and Transport in one-dimensional structures", 04.-07.07.2019, Dresden, Deutschland
  • Lecture (Conference)
    DPG-Frühjahrstagung, 31.03.-05.04.2019, Regensburg, Deutschland
  • Invited lecture (Conferences)
    Seminar Series on Topical Problems in Theoretical Physics, 20.03.2019, London, U.K.

Publ.-Id: 29443 - Permalink


Modeling the interaction of magnetically capped colloidal particles
Neumann, M.; Gemming, S.; Steinbach, G.; Erbe, A.;
Colloidal self-assembly bears significant potential for the bottom-up fabrication of advanced materials and micromechanical structures. A wide range of particles with different types of anisotropy have been recognized as promising precursors for controlled structure engineering. Here, we concentrate on particles that interact via polar fields, which are intrinsically anisotropic. More specifically, we focus on the assembly of micron-sized silica spheres which are partly covered by a thin ferromagnetic layer with an out-of-plane magnetic anisotropy. To study assemblies of such magnetic particles, we introduce a simple two-parameter model: The extended magnetization distribution is approximated by a current-carrying coil enclosed inside a hard sphere. The far field of that current reproduces the stray field of a point dipole model, the near field reflects an extended magnetization. Such a model employs only two parameters to describe the shape of the magnetization distribution: The radius and the position of the coil inside the sphere. We present stable assemblies as a function of both parameters. In the limit of very small coils the analytical solution for two particles with shifted point dipoles is correctly reproduced. By increasing the radius of the coil, we reproduce experimentally observed particle arrangements not covered by models based on single shifted dipoles.
Keywords: colloid, Janus particle, self-assembly, model potential, soft matter
  • Poster
    Frühjahrstagung der Deutschen Physikalischen Gesellschaft, 31.03.-05.04.2019, Regensburg, Deutschland

Publ.-Id: 29442 - Permalink


Characterization of irradiation-induced microstructure in reactor pressure vessel steels
Ulbricht, A.; Bergner, F.; Keiderling, U.;
SANS contributed significantly to the understanding of the behaviour of reactor pressure vessel (RPV) steels exposed to irradiation with fast neutrons. It allows macroscopically representative, statistically reliable and robust measures of size, volume fraction and number density of nmsized solute clusters to be obtained. In particular, the use of the ferromagnetic properties of the matrix allows, under certain assumptions, the exact determination of the scattering contrast and thus the absolute volume fraction. The lower detection limit in terms of volume fraction is typically about 0.005%. The A-ratio, that is the total-to-nuclear scattering ratio, can be used as one-parameter signature of the mean composition of irradiation-induced clusters. Major limitations of SANS are related to the uncertainty of the scattering contrast (cluster composition, magnetism) and to the lower detection limit. Especially because of the incoherent scattering contribution of different iron isotopes, the lower detection limit is approximately 0.5 nm in terms of radius. The unirradiated reference condition of a RPV steel exhibits a high scattering background essentially caused by different sizes of carbides and should be carefully subtracted from the investigated neutron-damaged condition.
In the present work we give an overview about major influence factors on irradiation-induced microstructural changes. Increase of neutron exposure gives rise to an increase of the volume fraction of solute clusters. This susceptibility is essentially determined by the existing alloying elements and impurities. Cu-rich precipitates are the dominant type of nanofeatures in Cubearing steels (Cu> 0.1wt%) and Mn-Ni-(Si) precipitates or their nonequilibrium precursors are the dominant type of nanofeatures in low-Cu, Mn-Ni-alloyed ferritic materials. The size of clusters remains small and does not exceed a radius of 4 nm. In recent years, research was focussed on the transferability from accelerated irradiations to real operation conditions of materials in a power reactor, for instance the effect of neutron flux on irradiation-induced damage. Here, SANS results show a clear trend. The size distribution of low flux condition is shifted towards larger radii. The effect of neutron flux on the volume fraction of irradiationinduced clusters is not so obvious. There seems to be a trend that the cluster volume fraction decreases at increasing flux. Here, the detection limits of SANS (very small clusters and/or reduced scattering contrast) and the uncertainties of the irradiation conditions possibly hide an explicit flux dependence. Differences in the A-ratio were not observed for flux pairs of one and the same material. Thus, no significant changes of cluster composition appear at different fluxes.
Strong and robust correlations between SANS-based characteristics of irradiation-induced clusters, such as (the square-root of) volume fraction and irradiation-induced changes of mechanical properties, such as Vickers hardness, yield stress or brittle/ductile transition temperature are confirmed.
Keywords: small-angle neutron scattering, irradiation-induced clusters, reactor pressure vessel steel
  • Poster
    canSAS XI workshop, 08.-11.07.2019, Freising, Deutschland

Publ.-Id: 29440 - Permalink


Flux effect on RPV materials
Ulbricht, A.;
The effect of neutron flux on the irradiation-induced microstructure and mechanical behaviour is one of the still open issues for the scientific community both for RPV steels and internals. In the case of RPV steels, more and statistically more reliable microstructural data are needed, in particular for low-Cu RPV steels irradiated up to high fluence. Within SOTERIA, suitable pairs of low-Cu RPV steels irradiated at different flux up to the same levels of fluence were identified.
This deliverable D2.1 reports about the effect of neutron flux on the neutron-irradiation-induced microstructure of RPV base and weld materials. The main methods applied are small-angle neutron scattering (SANS), positron lifetime spectroscopy (PAS), transmission electron microscopy (TEM) and atom probe tomography (APT).
Using these methods, a number of different kinds of irradiation-induced nanofeatures were detected. These comprise dislocation loops, vacancies, sub-nm vacancy clusters, solute atom clusters and segregated dislocations. Loops are insufficient in number density and vacancy clusters are too small to contribute significantly to the irradiation-induced changes of the mechanical properties, but play a role in the overall evolution of the irradiated microstructures. Solute atom clusters are decisive for irradiation hardening.
SANS and APT indicate a common trend that an increasing flux gives rise to smaller sizes and higher number densities of solute atom clusters. APT additionally shows that the clusters are more dilute at higher flux. The counteracting effects of flux on size and number density of solute atom clusters partly compensate each other and, therefore, rationalize the relative insensitivity of the mechanical properties to the neutron flux.
Keywords: reactor pressure vessel steel, low Cu, microstructure, neutron irradiation, flux effect, vacancy/solute cluster
  • Lecture (others)
    SOTERIA Final Workshop, 25.-27.06.2019, Miraflores de la Sierra, Spain

Publ.-Id: 29439 - Permalink


Emerging Noble Metal Aerogels: State of the Art and a Look Forward
Du, R.; Fan, X.; Jin, X.; Hübner, R.; Hu, Y.; Eychmüller, A.;
Noble metal aerogels (NMAs), as the most important class of noble metal foams (NMFs), appear as emerging functional porous materials in the field of materials science. Combining the irreplaceable roles of noble metals in certain scenarios, as well as monolithic and porous features of aerogels, NMAs can potentially revolutionize diverse fields, such as catalysis, plasmonics, and biology. Despite profound progress, grand challenges remain in their fabrication process, including the efficient structure control, the comprehensive understanding of the formation mechanisms, and the generality of the fabrication strategies, thus inevitably retarding the material design and optimization. This Perspective focuses on the key progress, especially of the fabrication strategies for NMAs during the last two decades, while other NMFs are also succinctly introduced. Challenges and opportunities are summarized to highlight the unexploited space and future directions in expectation of stimulating the broad interest of interdisciplinary scientists.

Publ.-Id: 29431 - Permalink


Extending the temperature sensing range using Eu3+ luminescence up to 865 K in a single crystal of EuPO4
Sharma, S.ORC; Köhler, T.; Beyer, J.; Fuchs, M.; Gloaguen, R.; Heitmann, J.
The temperature evaluation through the measurement of emission intensities (intensity ratio method) require two distinct bands; one of which is used as a reference, and the emission intensity of other is monitored as a function of a change in temperature. Herein, we report the influence of excitation wavelengths, and a coupling scheme between lanthanoid and defect emission from the host lattice, to extend the temperature sensing range by using a single crystal of europium (III) phosphate. The temperature dependence of emission intensity was studied for different excitation wavelengths: 365 (intraconfigurational 4f2 excitation), 338 (defect excitation), and 254 nm (O2- →Eu3+ charge-transfer excitation), in the temperature range, 293--865 K. We determined the Boltzmann equilibrium among different coupling schemes using a linear regression model to infer that for an excitation at 338 nm wavelength, and evaluating the intensity ratio between defect emission and the Eu3+ 5D0,1 → 7FJ transitions, the temperature sensing range can be extended upto at least 865 K, with relative sensitivity in the range, 0.33-1.94%K-1 (at 750 K). The results showed resolution of < 1 K with an excellent reproducibility, suggesting that the thermometers can be used with high reliability.
Keywords: photoluminescence, Eu3+ doping, temperature sensing, relative sensitivity

Publ.-Id: 29430 - Permalink


Achieving optimal laser-proton acceleration through multi-parameter interaction control
Obst-Hübl, L.ORC
Relativistic laser-driven plasmas can be the source of energetic proton beams and have received increasing attention due to their high potential as compact and cost-efficient medical particle accelerators for radiation therapy. As such, exploring viable routes to scale the maximum proton energy to the medically relevant regime remains the subject of ongoing efforts in the Field. This endeavor is inherently linked to the discernment and control of seminal aspects of the acceleration process, ranging on vast temporal and spatial ranges due to highly variable plasma densities and laser intensities within one single interaction. This thesis investigates laser-proton acceleration on various physical scales and the influence of realistic laser pulse parameters, to ultimately find an optimum regime for stable proton beam production with highest particle energies. Experimental studies following this objective were primarily conducted at the high-power titanium:sapphire laser system Draco 150 TW at Helmholtz-Zentrum Dresden-Rossendorf (HZDR). Efficient on-demand control of the temporal laser pulse history was established in the form of a plasma mirror filter combined with on-shot temporal pulse contrast characterization based on an advanced spectral interferometry diagnostic. This allowed for experiments with variable pulse contrast, thus providing additional handles for proton source optimization and additionally, extending the selection of applicable interaction targets to lower thicknesses and densities. Studies with novel target technologies such as ultra-thin liquid crystal films and solid hydrogen jets were performed, each at optimized acceleration conditions, resulting in excellent proton beams with high energies and particle numbers that promise to be highly scalable with increasing laser intensities. Elaborate diagnostic suites in combination with numerical simulations delivered an improved picture of the acceleration process, which generally remains difficult to assess experimentally on the microscopic spatial and ultrafast temporal scale. As an important result, the onset of relativistic target transparency was observed for ultra-thin liquid crystal films, an operation regime that may deliver increased proton energies when optimized. Proton acceleration results from the hydrogen jet agreed well with predictive particle-in-cell simulations, thus establishing a test bed for closely linked experimental and numerical studies into advanced acceleration mechanisms, as are for example associated with target transparency. Furthermore, an unexpected proton beam structuring effect was discovered that can play a significant role in experiments with transparent or very small targets. Formerly unrecognized by the community, this effect leads to the extension of spatial and temporal interaction scales beyond the initial proton acceleration in the laser focus, that need to be considered for appropriate interpretation of proton profile signatures.
  • Doctoral thesis
    TU Dresden, 2019
    Mentor: Dr. Karl Zeil
    150 Seiten
    DOI: 10.5281/zenodo.3252952
  • Lecture (others)
    Verteidigungsvortrag, 18.06.2019, Dresden, Deutschland

Publ.-Id: 29429 - Permalink


Investigation of Bubble Plume Oscillations by Euler-Euler Simulation
Fleck, S.; Rzehak, R.;
For practical applications the Euler-Euler two-fluid model relies on suitable closure relations describing interfacial exchange processes. An ongoing effort at HZDR has led to a validated set of closures for adiabatic bubbly flows that is applicable under a rather broad range of conditions including flows in pipes and bubble columns. Up to now, however, only flows with stationary mean values have been considered. The present contribution extends the model validation to dynamic flow phenomena by considering a periodically oscillating bubble plume. Consequently, the turbulence model then runs in URANS mode. Literature data for a partially aerated flat rectangular bubble column are used for comparison. In particular, results for the plume oscillation period show good agreement between simulation and experiment.
Keywords: bubble columns, dispersed gas liquid multiphase flow, Euler-Euler two fluid model, closure relations, CFD simulation, model validation
  • Chemical Engineering Science 207(2019), 853-861
    DOI: 10.1016/j.ces.2019.07.011
  • Lecture (Conference)
    Jahrestreffen der ProcessNet-Fachgruppe „Computational Fluid Dynamics“, 19.-20.03.2019, Frankfirt/Main, Deutschland

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  • Secondary publication expected from 09.07.2020

Publ.-Id: 29428 - Permalink


Electron transport through NiSi2-Si contacts and their role in reconfigurable field-effect transistors
Fuchs, F.; Gemming, S.; Schuster, J.;
A model is presented which describes reconfigurable field-effect transistors (RFETs) with metal contacts, whose switching is controlled by manipulating the Schottky barriers at the contacts. The proposed modeling approach is able to bridge the gap between quantum effects on the atomic scale and the transistor switching. We apply the model to transistors with a silicon channel and NiSi2 contacts. All relevant crystal orientations are compared, focusing on the differences between electron and hole current, which can be as large as four orders of magnitude. Best symmetry is found for the < 110 > orientation, which makes this orientation most advantageous for RFETs. The observed differences are analyzed in terms of the Schottky barrier height at the interface. Our study indicates that the precise orientation of the interface relative to a given transport direction, perpendicular or tilted, is an important technology parameter, which has been underestimated during the previous development of RFETs. Most of the conclusions regarding the studied metal-semiconductor interface are also valid for other device architectures.
Keywords: density functional, nanowire, nanoelectronics, NanoNet, device modeling, interface, silicide, silicon

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Publ.-Id: 29427 - Permalink


Organic Iron Complexes Enhance Iron Transport Capacity along Estuarine Salinity Gradients
Herzog, S. D.; Kvashnina, K.; Persson, P.; Kritzberg, E.;
Rivers discharge a notable amount of Fe (1.5 x 109 mol yr−1) to coastal waters, but are still not considered important sources of bioavailable Fe to open marine waters. The reason is that the vast majority of riverine Fe is considered to be lost to the sediment due to aggregation during estuarine mixing. Recently however, several studies demonstrate relatively high stability of riverine Fe to salinity induced aggregation, and it has been proposed that organically complexed Fe (Fe-OM) can “survive” the salinity gradient, while Fe (oxy)hydroxides are prone to aggregation and selectively removed. In this study, we directly identified, by X-ray absorption spectroscopy, the occurrence of these two Fe phases across eight boreal rivers and confirmed a significant but variable contribution of Fe-OM in relation to Fe (oxy)hydroxides among river mouths. We further found that that Fe-OM was more prevalent at high flow conditions in spring than at low flow conditions during autumn, and that Fe-OM was more dominant in low-order streams in a catchment than at the river mouth. The stability of Fe to increasing salinity correlated well to the relative contribution of Fe-OM, i.e. confirming that organic complexes promote Fe transport capacity. This study suggests that boreal rivers may provide significant amounts of potentially bioavailable Fe to marine waters beyond the estuary, due to organic matter complexes

Publ.-Id: 29426 - Permalink


Dual-time-point 64Cu-PSMA-617-PET/CT in patients suffering from prostate cancer
Hoberück, S.; Wunderlich, G.; Michler, E.; Hölscher, T.; Walther, M.; Seppelt, D.; Platzek, I.; Zöphel, K.; Kotzerke, J.;
Regardless of its high positron energy, 68Ga-labeled PSMA ligands have become standard of care in metabolic prostate cancer imaging. 64Cu, a radionuclide with a much longer half-life (12.7 h), is available for PSMA labeling allowing imaging much later than 68Ga. In this study, the diagnostic performance of 64Cu-labeled PSMA was compared between early and late scans. Sixteen men (median age: 70 y) with prostate cancer in different stages underwent 64Cu-PSMA-617-PET/CT 2 and 22 hours post tracer injection. Pathologic and physiologic uptakes were analyzed for both points of time. Pathologic tracer accumulations occurred in 12 patients. Five patients presented with pathologic uptake in 17 different lymph nodes, two patients showed pathologic bone uptake in nine lesions, and seven patients had pathologic PSMA uptake in eight prostatic lesions. Physiologic uptake of the renal parenchyma, urine bladder, and salivary glands decreased over time, while the physiologic uptake of liver and bowel increased. In the present study, 64Cu-PSMA-617-PET demonstrated to be feasible for imaging prostate cancer for both the primary tumor site and metastases. Later imaging showed no additional, clinically relevant benefit compared with the early scans. At least the investigated time points we chose did not vindicate the additional expenditure.
Keywords: 64Cu, dual time, PET, prostate cancer, PSMA
  • Journal of Labelled Compounds and Radiopharmaceuticals 62(2019)8, 523-532
    DOI: 10.1002/jlcr.3745

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Publ.-Id: 29425 - Permalink


Spin textures and spin waves as seen by x-ray microscopy
Wintz, S.;
The investigation of spin-wave phenomena, also referred to as magnonics, plays an important role in present condensed matter research. This holds true, in particular, as spin waves are seen as signal carriers for future spintronic information processing devices, with a high potential to outperform present charge-based technologies in terms of energy efficiency and device miniaturization. Yet a successful implementation of magnonic technology will require the usage and control of spin waves with nanoscale wavelengths. Here, I will show that ferromagnetic spin textures in metallic systems can be used as nanoscale spin-wave emitters and wave guides. In particular, topological spin vortex cores prove to act as efficient and tunable generators for sub-100 nm waves, while domain walls can be utilized as quasi one-dimensional channels for spin-wave propagation and routing. The underlying spin dynamic processes were directly imaged by using time-resolved x-ray microscopy.
  • Invited lecture (Conferences)
    NAP 2019, 15.-20.09.2019, Odessa, Ukraine
  • Invited lecture (Conferences)
    Challenges & Opportunities in X-Ray Microscopy, 11.-15.02.2019, Kreuth (Schloss Ringberg), Deutschland

Publ.-Id: 29424 - Permalink


ExploreASL: a collaborative effort to process and explore multi-center ASL data
Mutsaerts, H. J.; Petr, J.; Groot, P.; Ingala, S.; Robertson, A.; Vaclavu, L.; Groote, I.; Kuijf, H.; O'Daly, O.; Zelaya, F.; Vandemaele, P.; Wink, A. M.; Kant, I.; Caan, M.; Morgan, C.; de Bresser, J.; Lysvik, E.; Schrantee, A.; Shirzadi, Z.; Kuijer, J. P. A.; Anazodo, U.; Richard, E.; Bokkers, R.; Reneman, L.; Masellis, M.; Achten, E.; Günther, M.; Macintosh, B.; Golay, X.; Hendrikse, J.; Chapell, M.; van Osch, M.; Thomas, D.; de Vita, E.; Bjornerud, A.; Nederveen, A.; Asllani, I.; Barkhof, F.;
Arterial spin labeling (ASL) has undergone significant development since its inception; yet, standardized images processing procedures remain elusive. We present ExploreASL, a robust open source ASL image processing pipeline for clinical studies. Initiated through the European COST action ASL network, this joint effort provides integration and analysis of both single- and multi-center datasets across different operating systems. ExploreASL is optimized for both native- and standard-space analyses, and provides visual and automatic quality control on all intermediate and final images, allowing exploration of ASL datasets from multiple perspectives.
  • Contribution to proceedings
    ISMRM 27th Annual Meeting & Exhibition, 11.06.2019, Montreal, Canada
    Proceedings of the ISMRM 27th Annual Meeting & Exhibition, 2705
  • Poster
    ISMRM 27th Annual Meeting & Exhibition, 11.06.2019, Montreal, Canada

Publ.-Id: 29422 - Permalink


Hemodynamic impairments in asymptomatic unilateral carotid artery stenosis are increased within individual watershed areas
Kaczmarz, S.; Goettler, J.; Petr, J.; Hansen, M. B.; Kufer, J.; Hock, A.; Sorg, C.; Zimmer, C.; Mouridsen, K.; Hyder, F.; Preibisch, C.;
Internal carotid-artery stenosis (ICAS) causes complex and not yet well understood physiological impairments, which currently limits treatment decisions. We present multimodal perfusion and oxygenation-related MRI-data from unilateral asymptomatic ICAS-patients and age-matched healthy controls. The major aim was to investigate hemodynamic impairments in ICAS within individually defined watershed areas (iWSA’s) to account for individual vascular configurations. We found statistically significant lateralization of hemodynamic parameters within iWSA’s - strongest in WM of iWSA’s. Therefore, our iWSA-based approach facilitates detection of even subtle hemodynamic changes in ICAS. Furthermore, we detected spatially widespread capillary flow heterogeneity increases which are promising future treatment indicators.
  • Contribution to proceedings
    ISMRM 27th Annual Meeting & Exhibition, 11.06.2019, Montreal, Canada
    Proceedings of the ISMRM 27th Annual Meeting & Exhibition, 3246
  • Poster
    ISMRM 27th Annual Meeting & Exhibition, 11.06.2019, Montreal, Canada

Publ.-Id: 29421 - Permalink


Recovery of cerebrovascular reactivity after asymptomatic carotid artery stenosis treatment is assessable by Breathhold-fMRI within global watershed areas
Kaczmarz, S.; Goettler, J.; Sollmann, N.; Kufer, J.; Hansen, M. B.; Hock, A.; Sorg, C.; Zimmer, C.; Mouridsen, K.; Hyder, F.; Preibisch, C.; Petr, J.;
Asymptomatic unilateral internal carotid-artery stenosis (ICAS) causes complex and currently poorly understood hemodynamic impairments which could possibly improve treatment decisions. Cerebrovascular reactivity (CVR) is an important biomarker of vascular health and can potentially serve to evaluate ICAS-treatment efficacy. We present perfusion MRI-data from a longitudinal study in 16 asymptomatic ICAS-patients before and after treatment plus 17 age-matched healthy controls. We hypothesize that CVR impairments in ICAS and their recovery after treatment can be assessed by Breathhold-fMRI analyzed by a data-driven approach. Our results demonstrate statistically significant CVR impairments within global watershed areas before treatment and significant CVR recovery after treatment.
  • Contribution to proceedings
    ISMRM 27th Annual Meeting & Exhibition, 11.06.2019, Montreal, Canada
    Proceedings of the ISMRM 27th Annual Meeting & Exhibition, 0739
  • Lecture (Conference)
    ISMRM 27th Annual Meeting & Exhibition, 11.06.2019, Montreal, Canada

Publ.-Id: 29420 - Permalink


Cerebral hypometabolism measured with intravascular T2-prepared tissue relaxation with inversion recovery (T2-TRIR) and pCASL in adults with sickle cell disease
Vaclavu, L.; Petersen, E. T.; Mutsaerts, H. J.; Petr, J.; Majoie, C. B.; Wood, J. C.; Vanbavel, E. T.; Biemond, B. J.; Nederveen, A. J.;
Cerebral metabolic rate of oxygen (CMRO2) quantifies the amount of oxygen consumed by the brain, and relies on continuous delivery of nutrients and oxygen via cerebral blood flow (CBF). In sickle cell disease (SCD), CBF is elevated to compensate for chronic anaemia. This study investigates CMRO2 in adults with SCD using T2-prepared tissue relaxation with inversion recovery (T2-TRIR). CBF increased after acetazolamide-induced vasodilation in both groups but CMRO2 reduced even further in SCD patients while it remained stable in controls. Our results suggest that cerebral shunting is exacerbated by high flow conditions.
  • Contribution to proceedings
    ISMRM 27th Annual Meeting & Exhibition, 11.06.2019, Montreal, Canada
    Proceedings of the ISMRM 27th Annual Meeting & Exhibition, 0291
  • Lecture (Conference)
    ISMRM 27th Annual Meeting & Exhibition, 11.06.2019, Montreal, Canada

Publ.-Id: 29419 - Permalink


A multi-site round robin assessment of ASL using a perfusion phantom
Oliver-Taylor, A.; Hampshire, T.; Mutsaerts, H.-J.; Clement, P.; Warnert, E.; Kuijer, J. P. A.; Baas, K.; Petr, J.; Siero, J. C. W.; Marques, J. P.; Sunaert, S.; Borra, R. J. H.; van Osch, M. J. P.; Golay, X.; Achten, E.;
Arterial Spin Labelling shows great promise for perfusion measurements; however, despite numerous volunteer reproducibility studies, comparisons have not been made using a phantom to establish differences due to the acquisition hardware and pulse sequences. We present data from a multi-site study using a perfusion phantom, targeting 3T MRI systems from a single vendor running the same software version.
  • Contribution to proceedings
    ISMRM 27th Annual Meeting & Exhibition, 11.06.2019, Montreal, Canada
    Proceedings of the ISMRM 27th Annual Meeting & Exhibition, 2653
  • Poster
    ISMRM 27th Annual Meeting & Exhibition, 11.06.2019, Montreal, Canada

Publ.-Id: 29418 - Permalink


Extra-neurite Perfusion Measurement with Combined Arterial Spin Labeling and Diffusion Weighted MRI
Asllani, I.; Petr, J.; Mutsaerts, H.-J.; Bozzali, M.; Cercignani, M.;
Introduction:
Arterial Spin Labeling (ASL) is an MRI method that uses magnetically labeled endogenous water as a tracer for measuring cerebral perfusion in vivo1. The arterial water that is usually 'labeled' at a plane positioned at the base of the brain, perpendicular to the carotids. A post-labeling delay (PLD) is introduced prior to acquisition to allow labeled water to cross the vasculature and perfuse into the tissue1. Because of signal decay due to T1 relaxation, fast acquisition schemes are employed to ensure optimal SNR. Consequently, the spatial resolution of ASL is relatively low (~ 3 x 3 x 6 mm3). As such, the measured blood flow from a given voxel reflects a mixture of signals from gray matter (GM), white matter (WM), and CSF, a phenomenon known as partial voluming (PV)2. To correct for the confounding effects of PV in ASL imaging, an algorithm (PVC) has been developed and already used by several studies2,3. The algorithm is based on GM and WM volume data obtained from the segmentation of the T1w image2, and makes no further distinction between different compartments within the same tissue type. Here, we investigated the potential of PVC ASL to map blood perfusion in the extra-neurite compartment (e.g., soma, glial cells4) and the intra-neurite (comprised of axons and axon terminals4) within the same tissue, independently. We applied the PVC algorithm using compartmental data from a diffusion weighted imaging (DWI) model, referred to as NODDI4. The underlying hypothesis was that the blood flow in the extra- and intra-neurite compartments would vary with the PLD; a short PLD acquisition would increase the flow in the extra-neurite compartment compared to the long PLD for which there should be an increased flow in the intra-neurite compartment instead.
Methods:
Theory
At any given voxel, the blood flow (fT) is given as:
fT=VFIn•fIn+VFEn•fEn+VFIso•fIs
where, VFIn, VFEn, VFIso represent respectively: the intra-neurite, extra-neurite, and non-tissue compartments obtained from NODDI4. By assuming that for each compartment blood flow is constant over a 'kernel', the equation can be re-written in vectorial form to reflect the flow at the voxel in the center of the kernel2, from which then each compartmental flow can be computed using linear regression as detailed in Asllani et al.2..

MRI protocol & image analysis
T1w (MPRAGE), NODDI, and ASL MRI images were obtained on 4 healthy participants (mean age = 44.5 ± 7.4 y, 2 men) a Siemens 3T system. To test the hypothesis that a shorter PLD would increase the signal in the extra-neurite GM compartment, ASL was acquired with a short (200ms) and long PLD (1800ms). Only results from voxels with GM content > 80% are presented.
Results:
Fig.1 shows the raw images that were used by the PVC algorithm to extract the flow from each compartment within the GM. For the long-PLD acquisition, average CBF in the extra- and intra-neurite compartments was 76 ± 10 mL/100g*min and 59 ± 8 mL/100g*min, respectively. As hypothesized, for the short-PLD, the CBF signal was contained primarily in the extra-neurite department (118 ± 17 mL/100g*min) with the intra-neurite compartment flow being essentially zero (-0.9 ± 0.6 mL/100g*min). Results from one participant are shown in Fig.2.
Supporting Image: Fig1.jpg
·Fig.1: ‘Raw’ NODDI and ASL images used by the PVC algorithm from one subject. Top row: MPRAGE and VFIn images; middle row: VFEn and VFISO; bottom row: CBF for short PLD (left) and long PLD (right).
Supporting Image: Fig2.jpg
·Fig.2: Top: Extra-neurite GM CBF from short (left) & long (right) PLD acquisitions. Bottom: axial and sagittal views of Intra-neurite CBF for long PLD with areas in blue indicating ~zero signal.

Conclusions:
We combined NODDI with PVC ASL MRI to distinguish between blood flow in the extra- and intra-neurite compartments within GM. While these initial results look promising, more work is needed to test the sensitivity of this method and its feasibility for clinical applications. For example, a larger PLD range is needed to test whether the method can be used to detect inter-neurite subcortical flow. If successful, this method could prove invaluable in mapping blood flow with high spatial specificity.
Keywords: Cerebral Blood Flow, Data analysis, fMRI CONTRAST MECHANISMS, MRI
  • Open Access LogoContribution to proceedings
    Organization for Human Brain Mapping Annual Meeting 2019, 09.-13.06.2019, Rome, Italy
  • Open Access LogoPoster
    Organization for Human Brain Mapping Annual Meeting 2019, 13.06.2019, Rome, Italy

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Publ.-Id: 29417 - Permalink


Photoelectrocatalytic degradation of emerging contaminants at WO₃/BiVO₄ photoanodes in aqueous solution
Cristino, V.; Pasti, L.; Marchetti, N.; Berardi, S.; Bignozzi, C. A.; Molinari, A.; Passabi, F.; Caramori, S.; Amidani, L.; Orlandi, M.; Bazzanella, N.; Piccioni, A.; Kesavan, J. K.; Boscherini, F.; Pasquini, L.;
WO3/BiVO4 films obtained by electrochemical deposition of BiVO4 over mesoporous WO3 were applied to the photoelectrochemical degradation of selected emerging contaminants (ketoprofen and levofloxacine) in aqueous solutions. The WO3/BiVO4 films in this work are characterized by a mesoporous morphology with a maximum photoconversion efficiency >40% extending beyond 500 nm in Na2SO4 electrolytes.
Oxygen was found to be the dominant water oxidation product (ca. 90% faradaic yield) and no evidence for the photogeneration of OH radicals was obtained. Nevertheless, both 10 ppm levofloxacine and ketoprofen could be degraded at WO3/BiVO4 junctions upon a few hours of illumination under visible light. However, while levofloxacine degradation intermediates were progressively consumed by further oxidation at the WO3/BiVO4 interface, ketoprofen oxidation byproducts, being stable aromatic species, were found to be persistent in aqueous solution even after 15 hours of solar simulated illumination. This indicates that, due to the lower oxidizing power of photogenerated holes in BiVO4 and a different water oxidation mechanism, the employment of WO3/BiVO4 in photoelectrochemical environmental remediation processes is much less universal than that possible with wider band gap semiconductors such as TiO2 and WO3.

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  • Secondary publication expected from 01.09.2020

Publ.-Id: 29416 - Permalink


Multidimensional characterization of separation processes – Part 1: Introducing kernel methods and entropy in the context of mineral processing using SEM-based image analysis
Schach, E.; Buchmann, M.; Tolosana Delgado, R.; Leißner, T.; Kern, M.ORC; van den Boogaart, K. G.; Rudolph, M.; Peuker, U. A.
An alternative method for the particle tracking approach for scanning electron microscopy-based image analysis is introduced, using kernel density estimates instead of discrete bins. This allows for information that is more robust. Uncertainties of the data are assessed using the bootstrap resampling method. The presented methodology enables the calculation of multidimensional partition curves, which can be used for a detailed analysis of separation processes. It has been found that the statistical entropy is a helpful tool to evaluate the separation efficiency of these partition maps. The methodology was applied to a density separation process of a cassiteritebearing skarn ore from the Hämmerlein deposit in the Erzgebirge region in Germany, which serves as a case study. A Sepro™ Falcon concentrator was utilized for the density separation.
Keywords: Multidimensional characterization Partition curve Separation process Mineral processing Kernel density estimation Entropy Bootstrap resampling

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  • Secondary publication expected from 28.03.2020

Publ.-Id: 29410 - Permalink


Density and Susceptibility: Geometallurgical Characterization of a Cassiterite Bearing Complex Skarn Ore From the Ore Mountains, Germany
Buchmann, M.; Schach, E.; Leißner, T.; Tolosana-Delgado, R.; Kern, M.; Krupko, N.; Rudolph, M.; Peuker, U. A.;
In mineral processing, density and magnetic susceptibility are two very fundamental properties. For the beneficiation of valuables to saleable concentrates a detailed understanding of these properties is essential. Especially when it comes to the processing of cassiterite, which is the main mineral for tin production, they become highly prominent. Due to the chemically inert character of cassiterite towards most industrial applied leaching agents, density and magnetic separation processes are mainly applied for its beneficiation. To guarantee an optimized utilization of the different operations not only cassiterite but also the different gangue minerals have to be considered.
In this study, a skarn ore is characterized by density and magnetic susceptibility. Therefore, the material was first split into different density classes by heavy liquid separation. The obtained classes were further separated by their susceptibility to finally obtain a density-susceptibility matrix. For this purpose, an isodynamic separator was used. A more detailed characterization of the materials is done via gas pycnometer, magnetic susceptibility balance and vibrating sample magnetometer to estimate the characteristics of density and susceptibility for the various classes. Further, the determination of the chemical assay and the mineral intergrowth by mineral liberation analysis helps to generate a three dimensional data base for detailed characterization of the present ore.
The objective of this study is to estimate potential material streams for a modular processing plant via characterization of the material for the entire deposit by the two afore mentioned characteristic properties. The established multidimensional data matrix, enables predictions for the separation properties of the material and contributes to the characterization of the deposit within the context of geometallurgy.
Keywords: Geometallurgy, susceptibility, density, skarn ore, cassiterite
  • Lecture (Conference)
    MPC 2018 - 29th International Mineral Processing Congress, 15.-21.09.2018, Moscow, Russian Federation

Publ.-Id: 29407 - Permalink


The smaller the valuables, the poorer the recovery – Is that always true?
Schach, E.; Leistner, T.; Rudolph, M.;
The recovery of valuables in a flotation process is known to depend on the particle size and to drop for very small particles. The lack of floatability of such particle fractions is often objected to poor particle-bubble collision efficiencies due to low inertial energies. We recently showed that very fine valuable particles do float well and that the overall flotation performance depends more on the size of the gangue particles. Those findings are in contradiction to many classic collision models in which the influence of fine gangue particles is neglected. In this study the effect of the fine gangue particles on the flotation process is investigated and discussed in more detail. Therefore flotation tests with different solid concentrations, particle size fractions and different hydrodynamic conditions are conducted, measuring the energy dissipation and analysing the obtained flotation products. In addition, the wettability of the valuables and the gangue particles is characterized.
  • Poster
    Flotation '17, 13.-16.11.2017, Cape Town, South Africa

Publ.-Id: 29405 - Permalink


Assessment of flotation kinetics modeling using information criteria; Case studies of elevated-pyritic copper sulfide and high-grade carbonaceous sedimentary apatite ores
Hassanzadehmahaleh, A.; Hoang, D. H.; Brockmann, M.;
Despite flotation kinetic modeling is well discussed in the literature, its evaluation from overfitting, the number of model parameters and model complexities have not been adequately addressed. Flotation kinetic behavior of two deposits including an elevated-pyritic (Cu/S=0.21) complex copper sulfide ore and a high-grade carbonaceous sedimentary apatite (P2O5≥25%) ore were investigated. The flotation kinetic experiments were carried out in a mechanically agitated batch flotation cell. Different flotation kinetic models including seven common empirical and initially four mathematical models were applied to the experimental data. In addition to assessment of the goodness of fit (GOF) for each model, a factor of model complexity was considered using advanced statistical techniques (i.e. Bayesian information (BIC), low of iteratedn logarithm (LILC) and Akaike information (AIC) indices). The results confirmed that flotation kinetic modeling significantly depends on the feed type. The empirical models were found more sensitive than the mathematical ones to the ore properties and the mineral types. Furthermore, the mathematical models demonstrated relatively favorable results than the practical models concerning the variation of ore properties due to the consideration of more parameters in the modeling. Finally, it was concluded that the IC indices must be applied to the process of model selection owing to consideration of GOF, the complexity of a model and model consistency. The IC was introduced as a more reliable indicator than the common regression approach for evaluating, sequential ordering and selecting the suitable flotation kinetic models. Further studies are required for model’s generalizability from a statistical point of view.
Keywords: Flotation kinetic modeling, goodness of fit, information criteria, flotation rate constant, Bayesian information

Publ.-Id: 29403 - Permalink


Lift Forces on Solid Spherical Particles in Unbounded Flows
Shi, P.; Rzehak, R.;
The present work is concerned with the lift forces acting on particles immersed in an unbounded fluid. Both mechanisms due to rotation of the particle and vorticity of the fluid flow are considered. Focus is on solid spherical particles at Reynolds numbers up to 103 which are relevant for particulate flows in chemical and minerals engineering. A comprehensive review of existing results from analytical, numerical, and experimental studies is given. In particular in the simulation area many new data have appeared in the past 10 years since the earlier review of Loth [AIAA Journal 46 (2008), 801–809]. The available correlations are critically assessed by comparison to data from experiment and direct numerical simulation. Based on the comparison new correlations are proposed and gaps or inconsistencies in the data are identified. The case of wall-bounded flows will be considered in a sequel.
Keywords: lift force, particles, shear flow, particle rotation, correlation

Publ.-Id: 29402 - Permalink


Nanoscale n++-p junction formation in GeOI probed by tip-enhanced Raman spectroscopy and conductive atomic force microscopy
Prucnal, S.; Berencen, Y.; Wang, M.; Georgiev, Y.; Erbe, A.; Khan, M. B.; Böttger, R.; Hübner, R.; Schönherr, T.; Kalbacova, J.; Vines, L.; Facsko, S.ORC; Engler, M.; Zahn, D. R. T.; Knoch, J.; Helm, M.; Skorupa, W.; Zhou, S.ORC
Ge-on-Si and Ge-on-insulator (GeOI) are the most promising materials for the next-generation nanoelectronics that can be fully integrated with silicon technology. To this day, the fabrication of Ge-based transistors with a n-type channel doping above 5 × 1019 cm−3 remains challenging. Here, we report on n-type doping of Ge beyond the equilibrium solubility limit (ne ≈ 6 × 1020 cm−3) together with a nanoscale technique to inspect the dopant distribution in n++-p junctions in GeOI. The n++ layer in Ge is realized by P+ ion implantation followed by millisecond-flashlamp annealing. The electron concentration is found to be three times higher than the equilibrium solid solubility limit of P in Ge determined at 800 °C. The millisecond-flashlamp annealing process is used for the electrical activation of the implanted P dopant and to fully suppress its diffusion. The study of the P activation and distribution in implanted GeOI relies on the combination of Raman spectroscopy, conductive atomic force microscopy, and secondary ion mass spectrometry. The linear dependence between the Fano asymmetry parameter q and the active carrier concentration makes Raman spectroscopy a powerful tool to study the electrical properties of semiconductors.
We also demonstrate the high electrical activation efficiency together with the formation of ohmic contacts through Ni germanidation via a single-step flashlamp annealing process.
Keywords: GeOI, ion implantation, flash lamp annealing, doping, TERS

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  • Secondary publication expected from 28.06.2020

Publ.-Id: 29401 - Permalink


PIConGPU: Predictive Simulations of Laser-Particle Accelerators with Manycore Hardware
Huebl, A.ORC
The presented thesis establishes simulations on modern massively parallel computing hardware to investigate relativistic laser-driven plasmas. The latter are of special interest as they may provide a compact source for energetic ion beams. Computer simulations provide valuable insight into ultrafast plasma processes, evolving in the ultrahigh intensity (I0 ≫ 1018 W/cm2) focus of the ultrashort (𝜏0=30-500 fs) laser pulses driving the interaction. Such simulations require high numerical resolution and full geometric treatment for reliable predictions, which can only be addressed with high-performance computing. The open source particle-in-cell code PIConGPU, which is developed in the framework of this thesis, answers these demands, providing speed and scalability to run on the world's largest supercomputers. PIConGPU is designed with a modular and extensible implementation, allowing to compute on current and upcoming hardware from a single code base. Furthermore, challenges arising for generated data rates, reaching 1 PByte per simulation, are resolved with scalable data reduction techniques and novel workflows, such as interactive simulations.

Numerical studies are performed on two novel targets for laser-proton acceleration with near-critical and mass-limited properties. A micrometer-scale spherical target is explored with realistic temporal laser contrast, providing an interpretation for experimental results collected at the PW-class laser system PHELIX (𝜏0=500 fs pulse length). In this study, 3D modeling with the GPU supercomputer Titan enabled the identification of pre-expansion to near-critical target conditions, which uncovers a regime of volumetric laser-electron interaction generating a highly directed proton beam. Furthermore, a novel cryogenic hydrogen jet target is researched in close collaboration to experiments at the laser system DRACO (𝜏0=30 fs). This target system provides a unique setup for the isolated investigation of multi-species effects and their influence on the generated ion energy distribution. A novel analytical model provides a link between characteristic modulations in the ion energy spectra and ensemble properties of the microscopic electron distribution. In view of a potential experimental realization, parametric scans are performed confirming the feasibility of the proposed setup.
Keywords: laser-plasma acceleration, modeling, HPC, GPU, laser-ion acceleration, exascale computing, open source, open data
  • Doctoral thesis
    TU Dresden, 2019
    Mentor: Prof. Dr. Ulrich Schramm
    171 Seiten
    DOI: 10.5281/zenodo.3266820
  • Lecture (others)
    Dissertationsverteidigung, 25.06.2019, Dresden, Deutschland

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Publ.-Id: 29400 - Permalink


Joint project: Umwandlungsmechanismen in Bentonitbarrieren - Subproject B: Einfluss von mikrobiellen Prozessen auf die Bentonitumwandlung
Matschiavelli, N.; Drozdowski, J.; Kluge, S.; Arnold, T.; Cherkouk, A.;
Concerning the deep geological disposal of high-level radioactive waste (HLW), bentonite can be used because of its high swelling capacity and its low hydraulic conductivity as geo-technical barrier and buffering material in between the waste-containing canister (technical barrier) and the surrounding host rock (geological barrier). There are still many gaps in process understanding of bentonite transformations, especially in dependence of different temperatures and pore waters. Within the joint-project UMB (“Umwandlungsmechanismen in Bentonitbarrieren”), the co-operation partner Gesellschaft für Anlagen- und Reaktorsicherheit (GRS) mbH (Repository Safety Analysis), the University of Greifswald (Institute for Geography and Geology), the Federal Institute for Geosciences and Natural Resources (BGR, section of technical mineralogy), the Technical University of Munich (TUM; chair of theoretical chemistry, quantum chemistry) and the Helmholtz-Center Dresden-Rossendorf (HZDR, Institute of Resource Ecology) are supposed to define criteria which facilitate the selection of suitable bentonites in order to use them in the deep geological repository of high-level radioactive waste. HZDR analyzed two different bentonites (B36 and SD80) regarding their microbial diversity and potential microbial activity. In dependence of repository-relevant parameters (temperature, pore water, presence of substrates), microcosm experiments were set up at the GRS, containing the respective bentonites and Opalinus Clay pore water or cap rock solution, respectively. The long-term batches were incubated one year and two years at different temperatures (25 °C, 60 °C and 90 °C) in gastight bottles. Additionally, HZDR set up B36 short-term microcosms with Opalinus Clay pore water, which incubated for three month at 30 °C with six sampling points monitoring the microbial diversity and geochemical parameters.
After one and two years of incubation at 25 °C, respectively, supplemented SD80 microcosms containing Opalinus Clay pore water showed the formation of black precipitates and fissures as well as the dominance of sulfate-reducing and spore-forming bacteria. The detected genera are able to reduce the present sulfate in order to form hydrogen sulfide. XRF spectroscopy analysis, done at the University of Greifswald, showed a decrease in sulfate concentration in the respective SD80 microcosms, supporting this surveillance. Similar observations were made for the two-year incubations. The microbial diversity of the B36 bentonite raw material is much different from the SD80 bentonite raw material. Similar to the diversity of SD80 bentonite, the microbial community of the B36 bentonite long-term incubations changed with respect to the applied pore water. Spore-forming organisms dominated the set ups which were supplied with Opalinus Clay pore water solution whereas halophilic microorganisms were found in set ups containing diluted cap rock solution. We were also successful in showing the dominance of thermophilic bacteria in Opalinus clay pore water-containing microcosms that incubated at 60 °C for two years. Additionally, we were able to enrich microorganism from Opalinus Clay pore water of both, B36 and SD80 bentonite long-term incubations. Similar to the long-term analysis, substrate-containing B36 short-term microcosms, containing Opalinus Clay pore water, showed also the dominance of spore-forming bacteria after three months of incubation. Furthermore, a slight decrease in lactate-concentration as well as an increase in ferrous iron and acetate-concentration was observed in the respective B36 microcosms. The presence of substrates and mesophilic incubation temperatures of 25 °C or 30 °C, respectively, promoted the growth of “microbial generalists” that are able to exist in a vegetative state. Extreme environmental conditions as elevated temperatures (60 °C) or high-salt concentrations promote the dominance of highly specialized microorganisms. Our data show, that the microbial diversity in the analyzed bentonites and, furthermore, the evolution of the respective microbial communities differs significantly from each other. Since not that much is known about intrinsic extremophilic microorganisms (metabolic activity and potential influence on the bentonite barrier material), our data stress the importance of further microbial investigations in order to prevent and reduce potential risks (e.g. corrosion, mineralogical changes), due to microbial activity within the repository.
  • Open Access LogoWissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-103 2019

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Publ.-Id: 29398 - Permalink


Making a cool choice: the materials library of magnetic refrigeration
Gottschall, T.; Skokov, K. P.; Fries, M.; Taubel, A.; Radulov, I.; Scheibel, F.; Benke, D.; Riegg, S.; Gutfleisch, O.;
The phase-down scenario of conventional refrigerants used in gas-vapor compressors and the demand for environmentally friendly and efficient cooling makes the search for alternative technologies more important than ever. Magnetic refrigeration utilizing the magnetocaloric effect of magnetic materials could be that alternative. However, there are still several challenges to be overcome before we have devices that are competitive with those based on the conventional gas-vapor technology. In this paper we present a rigorous assessment of the most relevant examples of 14 different magnetocaloric material families and compare them in terms of their adiabatic temperature and isothermal entropy change under cycling in magnetic-field changes of 1 and 2 T, criticality aspects and the amount of heat that they can transfer per cycle. The work is based on magnetic, direct thermometric and calorimetric measurements made under similar conditions and in the same devices. Such a wide-ranging study has not been carried out before. This data sets the basis for more advanced modelling and machine learning approaches in the near future.

Publ.-Id: 29397 - Permalink


Multiferroic spin-superfluid and spin-supersolid phases in MnCr2S4
Ruff, A.; Wang, Z.; Zherlitsyn, S.; Wosnitza, J.; Krohns, S.; Krug Von Nidda, H.-A.; Lunkenheimer, P.; Tsurkan, V.; Loidl, A.;
Spin supersolids and spin superfluids reveal complex canted spin structures with independent order of longitudinal and transverse spin components. This work addresses the question whether these exotic phases can lead to spin-driven ferroelectricity. Here we report the results of dielectric and pyrocurrent measurements of MnCr2S4 as function of temperature and magnetic field up to 60 T. This sulfide chromium spinel exhibits a Yafet-Kittel type spin structure at low temperatures. As function of external magnetic field, the manganese spins undergo a sequence of ordering patterns of the transverse and longitudinal spin components, which can be mapped onto phases as predicted by lattice-gas models including solid, liquid, super-fluid, and supersolid phases. By detailed dielectric and pyrocurrent measurements, we document a zoo of multiferroic phases with sizable ferroelectric polarization strongly varying from phase to phase. Using lattice-gas terminology, the title compound reveals multiferroic spin-superfluid and spin-supersolid phases, while the antiferromagnetic solid is paraelectric.

Publ.-Id: 29396 - Permalink


Biologische Wege zur Rohstoffsicherung – vom Nobelpreis zum Recycling
Lederer, F.;
Im Jahr 1985 entwickelte der Wissenschaftler George P. Smith eine Methode zur Identifizierung von kurzen Eiweißbruchstücken, die gezielt und selektiv ein Zielmaterial binden können. Für diese Methode der Evolution im Reagenzglas, welche auf der Verwendung von Bakteriophagen basiert, erhielt er im Jahr 2018 den Chemienobelpreis. Damals half ihm die Methode, Antikörper für bestimmte Krebszellen zu identifizieren. Die Wissenschaftler des Helmholtz-Instituts Freiberg für Ressourcentechnologie nutzen die Phage Surface Display genannte Methode für die Entwicklung hochspezifischer Bioangeln zum seletiven Recycling von Seltenen Erden aus Elektroschrott.
Keywords: Biotechnologie, Phage Surface Display, Bioangeln
  • Lecture (others)
    Lange Nacht der Wissenschaften 2019 in Dresden, 14.06.2019, Dresden, Deutschland

Publ.-Id: 29395 - Permalink


Metallgewinnung durch Mikrobiologie – Biologisch assistierte Prozesse in der Rohstofftechnologie
Lederer, F.;
Präsentation der Arbeitsbereiche Bioflotation, Biosorption und Biolaugung, die in der Abteilung Biotechnologie des HIF Schwerpunktmäßig untersucht werden. Vorstellung der Nachwuchsgruppe BioKollekt
Keywords: Phage Surface Display, BioKollekt, Bioflotation, Biolaugung, Biosorption
  • Lecture (others)
    Lehrveranstaltung Industrielle Mikrobiologie im Fachbereich Technische Mikrobiologie, 24.06.2019, Senftenberg, Deutschland

Publ.-Id: 29394 - Permalink


Fermi surface investigation of the semimetal TaAs2
Butcher, T. A.; Hornung, J.; Förster, T.; Uhlarz, M.; Klotz, J.; Sheikin, I.; Wosnitza, J.; Kaczorowski, D.;
The transversal magnetoresistance associated with the semimetal TaAs2 shows a parabolic field dependence that rises unrestrictedly to 2800 at 14 T and 1.8 K. Here, we report the results of a comprehensive quantum-oscillation study. Angular-dependent de Haas–van Alphen (dHvA) data were obtained with the method of cantilever-torque magnetometry. These were compared with the results of density-functional theory calculations, which predict a Fermi surface with two kinds of electron pockets, as well as two types of hole pockets. Only the electron pockets could be xperimentally verified, whereas no evidence for the hole pockets is present in the measured dHvA frequencies.

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Publ.-Id: 29393 - Permalink


Fermi surface studies of the skutterudite superconductors LaPt4Ge12 and PrPt4Ge12
Bergk, B.; Klotz, J.; Förster, T.; Gumeniuk, R.; Leithe-Jasper, A.; Lorenz, V.; Schnelle, W.; Nicklas, M.; Rosner, H.; Grin, Y.; Wosnitza, J.;
We report on comprehensive de Haas–van Alphen (dHvA) and electronic band-structure studies of the superconducting skutterudites LaPt4Ge12 (Tc = 8.3 K) and PrPt4Ge12 (Tc = 7.9 K). Both materials show very rich spectra of dHvA oscillations with similar and only slightly varying angular-dependent frequencies. The spectral richness can partly be rationalized by the elaborated electronic band structures resulting in several Fermi surfaces built by six different bands. The effective cyclotron masses of both superconductors lie between about 0.5 and 1.1 times the free-electron mass. Although these values are small, we find moderate mass enhancements between about 2 and 4 when comparing to the calculated masses. Our results evidence the localized character of the 4f electrons in the Pr compound and are in line with an electron-phonon mediated multiband superconductivity, largely identical for both compounds.

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Publ.-Id: 29392 - Permalink


Hole compensation effect in III-Mn-V dilute ferromagnetic semiconductors
Xu, C.ORC; Wang, M.; Yuan, Y.; Larkin, G.; Helm, M.; Zhou, S.
A systematic study of hole compensation effect on magnetic properties, which is controlled by defect compensation through ion irradiation, in (Ga,Mn)As, (In,Mn)As and (Ga,Mn)P is represented in this work. In all materials, both Curie temperature and magnetization decrease upon increasing the hole compensation, confirming the description of hole mediated
erromagnetism according to the p -d Zener model. The material dependence of Curie temperature and magnetization versus hole compensation reveals that the manipulation of magnetic properties in III-Mn-V dilute ferromagnetic semiconductors by ion irradiation is strongly influenced by the energy level location of the produced defect relative to the band edges in
emiconductors.
Keywords: dilute ferromagnetic semiconductors, the Curie temperature, magnetization, compensation effect, ion irradiation

Publ.-Id: 29391 - Permalink


Presenting Non-Invasive and Fully Acceptable Exploration Technologies - The INFACT Project
Viezzoli, A.; Roffey, S.; Wijns, C.; Fernandez, I.; Blanco, J. M.;
Despite its rich history of mining and residual mineral wealth, current conditions within the EU present a number of social, political, legislative, cost, technical and physical obstacles to raw material exploration: obstacles to be overcome by innovation, dialogue, and reform. The Innovative, Non-invasive and Fully Acceptable Exploration Technologies (INFACT) project, within the Horizon 2020 program, will work to mitigate each and every one of these obstacles.
Specific to exploration geophysics, the project will facilitate the development of innovative airborne geophysical and remote sensing technologies (less-invasive than classical exploration methods) that promise to penetrate to new depths, reach new sensitivities and resolve new parameters. The project will also set the EU as a leader on the world stage by establishing permanent infrastructure (reference sites) to drive innovation in the next generation of exploration tools: tools that are cost-effective, designed for EU conditions and its raw materials strategy, and high-performing in terms of minimum environmental impact, social acceptability, and technical performance. These reference sites will provide long-term targets over which successive new technologies can be tested against previous ones.
  • Poster
    2nd Conference on Geophysics for Mineral Exploration and Mining, 09.-12.09.2018, Porto, Portugal
    DOI: 10.3997/2214-4609.201802752

Publ.-Id: 29390 - Permalink


Investigations on potential methods for the long-term monitoring of the state of fuel elements in dry storage casks: recent results
Hampel, U.; Wagner, M.; Schmidt, S.; Fiß, D.; Reinicke, S.; Kratzsch, A.;
Until a repository is available in deep geological formations, there is a need in Germany for the safe interim storage of spent fuel elements at the power plant sites. It is assumed that considerable periods of more than 50 years will have to be taken into account. Spent fuel elements are stored in Germany in transport and storage casks of the CASTOR type.
A material-scientific question currently being investigated in depth internationally concerns the long-term integrity of the fuel rod cladding tubes during dry storage and thus the safety during transport to the final repository and during secondary packaging. The absorption of hydrogen in the cladding tube during reactor operation leads to the precipitation of hydrides. If the cladding tube temperature increases during reloading or dry storage, a radial reorientation of the hydrides is conceivable due to the tangential stresses caused by the internal rod pressure. This type of hydride arrangement considerably reduces the brittle fracture toughness. A long-term cladding tube failure is conceivable due to a long-term increase in the internal rod pressure (production of gaseous fission products) and a long-term decrease in the cladding tube temperature (reduction of brittle fracture toughness).
Due to the existing uncertainties with regard to the concrete physical processes, the question arises as to the possibility of monitoring the cask contents. Invasive procedures, such as internal probes, are mainly ruled out for reasons of licensing. On the other hand, the massive construction of the containers with a wall thickness of at least 47 cm on all sides limits the spectrum of non-invasive testing and condition monitoring procedures that can be used. Within the DCS-Monitor project, four non-invasive measuring methods are investigated with regard to their suitability for the condition monitoring of the cask inventory by simulations and experiments. For this purpose, damage scenarios of the cask inventory were assumed in a CASTOR V/19, which were identified on the basis of investigations on damage mechanisms. In the following, the recent investigation results of the project are presented.
  • Contribution to proceedings
    3rd Workshop on Safety of Extended Dry Storage of Spent Nuclear Fuel, 05.-07.06.2019, Garching, Deutschland
  • Lecture (Conference)
    3rd Workshop on Safety of Extended Dry Storage of Spent Nuclear Fuel, 05.-07.06.2019, Garching, Deutschland

Publ.-Id: 29389 - Permalink


Phase Transition Induced Carrier Mass Enhancement in 2D Ruddlesden-Popper Perovskites
Baranowski, M.; Zelewski, S. J.; Kepenekian, M.; Traoré, B.; Urban, J. M.; Surrente, A.; Maude, D. K.; Kuc, A.; Booker, E. P.; Stranks, S. D.; Plochocka, P.;
The variety of possible ways to tune the optical properties of 2D perovskites is their huge advantage, while at the same time, the mutual dependence between different tuning parameters hinder our fundamental understanding of their properties. In this work, we attempt to address this issue for (CnH2n+1NH3)2PbI4 (with n=4,6,8,10,12) using optical spectroscopy in high magnetic fields up to 67T. Our experimental results, supported by DFT calculations, clearly demonstrate that the reduced mass of the exciton increases by around 30% in the low temperature phase. This is reflected by a 2-3 fold decrease of the diamagnetic coefficient. Our studies shows that the effective mass which is essential parameter for optolectronic device operation can be tuned by the variation of organic spacers and/or moderate cooling achievable using Peltier coolers. Moreover, we show that the complex absorption features visible in absorption/transmission specta track each other in magnetic field providing strong evidence for the phonon related nature of the observed side bands.

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  • Secondary publication expected from 04.09.2020

Publ.-Id: 29386 - Permalink


Tunable large field magnetoconductance of ZnO, ZnMnO, and ZnCoO thin films
Vegesna, S. V.; Bürger, D.; Patra, R. K.; Dellith, J.; Abendroth, B.; Skorupa, I.; Schmidt, O. G.; Schmidt, H.;
Magnetoconductivity of ten ZnO, Zn1-x Cox O, and Zn1-x MnxO thin films with nominal concentrations of 2.0 at.% and 0.1 at.% of Co2+ and Mn2+ ions, respectively, has been analyzed in the temperature range from 5 K to 200 K in in-plane and out-of-plane magnetic fields up to 6 T. The formation of a highly conducting surface layer can be controlled during thin film deposition, leading to a large variation of the sheet resistance, namely, from 2 × 103 ω /□ to 1 × 10 5 ω/□ at room temperature. Depending on the thickness of the highly conducting surface layer, a single two-dimensional (2D), a single three-dimensional (3D), or a two-dimensional and three-dimensional (2D + 3D) parallel conducting model was chosen to analyze the measured magnetoconductivity of the magnetic ZnO thin films with different electron spins (S = 5 / 2 for Zn 1 - x Mn x O and S = 3 / 2 for Zn1-x Cox O) and with different Landé g -factors (isotropic for 3D Zn1-x Mnx O and 2D Zn1-x Cox O and anisotropic for 2D Zn1-x Mnx O and 3D Zn1-x Cox O).

Publ.-Id: 29383 - Permalink


Fundamentals and Applications of Hybrid LWFA-PWFA
Hidding, B.; Beaton, A.; Boulton, L.; Corde, S.; Doepp, A.; Habib, F. A.; Heinemann, T.; Irman, A.; Karsch, S.; Kirwan, G.; Knetsch, A.; Manahan, G. G.; Martinez De La Ossa, A.; Nutter, A.; Scherkl, P.; Schramm, U.; Ullmann, D.;
Fundamental similarities and differences between laser-driven plasma wakefield acceleration (LWFA) and particle-driven plasma wakefield acceleration (PWFA) are discussed.
The complementary features enable the conception and development of novel hybrid plasma accelerators, which allow previously not accessible compact solutions for high quality electron bunch generation and arising applications. Very high energy gains can be realized by electron beam drivers even in single stages because PWFA is practically dephasing-free and not diffraction-limited.
These electron driver beams for PWFA in turn can be produced in compact LWFA stages. In various hybrid approaches, these PWFA systems can be spiked with ionizing laser pulses to realize tunable and high-quality electron sources via optical density downramp injection (also known as plasma torch) or plasma photocathodes (also known as Trojan Horse) and via wakefield-induced injection (also known as WII). These hybrids can act as beam energy, brightness and quality transformers, and partially have built-in stabilizing features. They thus offer compact pathways towards beams with unprecedented emittance and brightness, which may have transformative impact for light sources and photon science applications. Furthermore, they allow the study of PWFA-specific challenges in compact setups in addition to large linac-based facilities, such as fundamental beam–plasma interaction physics, to develop novel diagnostics, and to develop contributions such as ultralow emittance test beams or other building blocks and schemes which support future plasma-based collider concepts.
Keywords: plasma physics; accelerators; electron beams; light sources; photon science

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Publ.-Id: 29382 - Permalink


Which transition metal atoms can be embedded into two-dimensional molybdenum dichalcogenides and add magnetism?
Karthikeyan, J.; Komsa, H.-P.; Batzill, M.; Krasheninnikov, A. V.ORC
As compared to bulk solids, large surface-to-volume ratio of two-dimensional (2D) materials may open new opportunities for post-synthesis introduction of impurities into these systems by, e.g., vapor deposition. However, it does not work for graphene or h-BN, as the dopant atoms prefer clustering on the surface of the material instead of getting integrated into the atomic network. Using extensive first-principles calculations, we show that counterintuitively most transition metal (TM) atoms can be embedded into the atomic network of the pristine molybdenum dichalcogenides (MoDCs) upon atom deposition at moderate temperatures either as interstitials or substitutional im- purities, especially in MoTe2, which has the largest spacing between the host atoms. We further demonstrate that many impurity configurations have localized magnetic moments. By analyzing the trends in energetics and values of the magnetic moments across the periodic table, we rationalize the results through the values of TM atomic radii and the number of (s + d) electrons available for bonding, and suggest the most promising TMs for inducing magnetism in MoDCs. Our results are in line with the available experimental data and should further guide the experimental effort towards a simple post-synthesis doping of 2D MoDCs and adding new functionalities to these materials.
Keywords: 2D materials, electronic structure calcualtions

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  • Secondary publication expected from 24.06.2020

Publ.-Id: 29380 - Permalink


Analysing tumour growth delay data from animal irradiation experiments with deviations from prescribed dose
Karsch, L.; Beyreuther, E.; Eger Passos, D.; Pawelke, J.; Löck, S.;
Abstract: The development of new radiotherapy technologies is a long-term process, which requires proving the general concept although clinical requirements with respect to beam quality and controlled dose delivery may not yet be fulfilled. Exemplarily, the necessary radiobiological experiments with laser-accelerated ion beams are challenged by fluctuating beam intensities. Based on tumour-growth data and dose values obtained in an in-vivo trial comparing the biological efficacy of laser-driven and conventional Linac electrons [2], different statistical approaches for analysis were compared. In addition to the classical averaging per dose point, which excludes animals with high dose deviations, multivariable linear regression, Cox regression and a Monte-Carlo-based approach were tested as alternatives that include all animals in statistical analysis. The four methods were compared based on experimental and simulated data. All applied statistical approaches revealed a comparable radiobiological efficacy of laser-driven and conventional Linac electrons, confirming the experimental conclusion. However, in the simulation study, significant differences in dose-response were observed by all methods except for the conventional method. Thereby, these statistical approaches may allow for reducing the total number of required animals in future pre-clinical trials.
Keywords: pre-clinical studies; statistical analysis; experimental beams; radiotherapy

Publ.-Id: 29379 - Permalink


Application of Magnetism on Curved Surfaces
Makarov, D.;
Extending 2D structures into 3D space has become a general trend in multiple disciplines, including electronics, photonics, plasmonics and magnetics. This approach provides means to modify conventional or to launch novel functionalities by tailoring curvature and 3D shape. We study 3D curved magnetic thin films where new fundamental effects emerge from the interplay of the geometry of an object and topology of a magnetic sub-system. On the other hand, we explore the application potential of these 3D magnetic architectures for the realization of mechanically shapeable magnetoelectronics for automotive but also virtual and augmented reality appliances.
Keywords: flexible magnetoelectronics, virtual reality
  • Invited lecture (Conferences)
    European Forum for Science, Research and Innovation, 24.-25.06.2019, Dresden, Germany

Publ.-Id: 29375 - Permalink


A series of tetravalent Pu, Np, U and Th complexes of a salen type ligand
Radoske, T.ORC; Kaden, P.ORC; Walter, O.; Kloditz, R.; Patzschke, M.ORC; Stumpf, T.; März, J.ORC
Fundamental actinide (An) coordination chemistry is still rather scarcely explored though it can provide a deep insight into the bonding situation and bonding trends across the An series. Characteristic of actinides is their huge variety of possible oxidation states, typically ranging from +II to +VII for early An. A suitable approach to explore fundamental physical-chemical properties of actinides is to study series of isostructural An compounds in which the An possesses the same oxidation state. Changes in e.g. the binding situation or magnetic effects among the An series allow insights into their unique electronic properties mainly originating from the 5f-electrons. The tetravalent actinides (An(IV)) are particularly suitable for this kind of systematic studies, as this is the largest accessible series within the early actinides.
Against this background, we performed the current study focusing on a systematic comparison of isostructural An(IV) complexes of Th, U, Np and Pu with a salen type ligand (H2L).
All syntheses and characterizations are conducted under inert, water-free nitrogen atmosphere. SC-XRD results prove that an isostructural complex series was achieved with a molecular unit where two ligands coordinate tetradentately to the An with all oxygen and nitrogen donor atoms. The resulting eightfold coordination environment exhibits a distorted square antiprismatic coordination geometry around the An center. Moreover, the relevant complexes are characterized in solution by NMR spectroscopy displaying characteristic paramagnetic effects according to the unpaired f-electrons. Interestingly, the paramagnetic contributions to the 1H and 13C NMR chemical shifts reach their maximum with [NpL2], and are drastically lower for [PuL2]. The acquired experimental results are further supported by quantum chemical calculations to study the electronic structure of the complexes.
Keywords: tetravalent actinide complexes coordination chemistry paramagnetic effects
  • Lecture (Conference)
    49èmes Journées des Actinides, 14.-18.04.2019, Erice, Italy

Publ.-Id: 29374 - Permalink


Cerebral Oxygen Metabolism Measurements with MRI in Adults with Sickle Cell Disease: PF742
Vaclavu, L.; Petersen, E.; Mutsaerts, H.; Petr, J.; Majoie, C.; Wood, J.; Vanbavel, E.; Nederveen, A.; Biemond, B.;
MRI studies have demonstrated a high prevalence of silent cerebral infarcts (SCI) in both children and adults with sickle cell disease (SCD). SCI are associated with cognitive impairment and lesion progression in adults with SCD. Disrupted oxygen transport can contribute to cerebral ischemic lesions, despite the compensatory elevation in cerebral blood flow (CBF) in SCD. Investigating the cerebral metabolic rate of oxygen (CMRO2) may therefore give insight into the hemodynamic etiology of SCI in SCD patients. We hypothesized that CMRO2 is reduced in adult patients with SCD as a result of chronic anemia and that vasodilation can improve CMRO2 by generating an increase in blood and oxygen flow.
  • Open Access LogoPoster
    24th Annual Congress of the European Hematology Association, 13.06.2019, Amsterdam, The Netherlands
  • Open Access LogoContribution to proceedings
    24th Annual Congress of the European Hematology Association, 13.06.2019, Amsterdam, The Netherlands
    Hemasphere, 324-325
    DOI: 10.1097/01.HS9.0000561252.50212.c6

Publ.-Id: 29373 - Permalink


Using Agile Development Platforms for Continuous Integration, Code Review and Collaboration
Schlegel, F.;
The reality of scientific software development is of a more or less agile nature. As such, modern code development platforms such as GitHub or GitLab are a great fit to support this process. With their components (issues, projects, continuous integration, etc.) they match the agile development components, merge request enforce a cross-check for all code changes. While a lot of other development workflows are possible, this talk will present the best practice established for large and small projects at HZDR for using these platforms for software development projects.
  • Lecture (Conference)
    Platform for Advanced Scientific Computing (PASC) Conference 2019, 12.-14.06.2019, Zürich, Schweiz

Publ.-Id: 29372 - Permalink


Synthesis and Reactivity of Tetravalent Actinide Amidinates
Schöne, S.ORC; März, J.; Kaden, P.
A series of tetravalent actinide amidinates was synthesized and characterized in solution and in solid state. Quantum chemical calculations support findings based on bonding analysis. Furthermore the reactivity of the complexes is presented.
  • Lecture (others)
    FENABIUM Projekttreffen März 2019, 27.02.2019, Dresden, Deutschland

Publ.-Id: 29371 - Permalink


Enantiopure Tetravalent Actinide Amidinates – Synthesis and Reactivity
Schöne, S.ORC; Kloditz, R.; März, J.; Kaden, P.; Patzschke, M.; Roesky, P. W.; Stumpf, T.
In contrast to the dominant trivalent state for the lanthanide series (Ln(III)), a wide variety of oxidation states (from II to VII) of actinides (An) makes their chemistry intricate but attractive. Especially the early An thorium (Th), uranium (U), neptunium (Np), and plutonium (Pu) form highly charged cations with the oxidation state +IV (An4+), which are of particular interest for coordination chemistry due to their strong interaction with ligands.
The focus of our investigations lies in the comprehensive characterization of An(IV) complexes with ligands bearing soft donor atoms, such as nitrogen (N), both in the solid state and in solution. The present study focuses particularly on the interaction of An(IV) (Th, U, Np) with N-donor ligands of amidinate type, which could be considered as a simplified model of naturally occurring N-donor organic compounds.
Recently, the trivalent lanthanide complexes with the chiral benzamidine, (S,S)-N,N‘-Bis-(1-phenylethyl)-benzamidine ((S)-HPEBA), have been successfully synthesized.[1,2] Mono- and bis-amidinate complexes of the later lanthanides (Er, Yb, Lu) were obtained using a salt metathesis approach. Only for the larger samarium(III) a homoleptic tris-amidinate was accessible.
We have extended this approach to the tetravalent An, and successfully synthesized the first transuranic amidinate complexes. Moreover, we have obtained the first enantiopure amidinate complexes of An(IV) [AnCl((S)-PEBA)3] (An = Th, U, and Np) as well as the analogous Ce(IV) compound, a chemical analog of An(IV). The tris-amidinate complexes have been structurally characterized in solid state and in solution showing a comparable complex geometry.
Due to the presence of a Cl- ligand in the An coordination sphere, it could be speculated that the complex should be reactive. Thus, the reactivity of the complexes has been demonstrated by successful reduction with potassium graphite to homoleptic trivalent actinide amidinates [An((S)-PEBA)3] (An = U, Np).
  • Lecture (Conference)
    Journées des Actinides 2019, 14.-18.04.2019, Erice, Italien

Publ.-Id: 29370 - Permalink


Comprehensive real space bonding analysis of tetravalent f-element complexes with Schiff-base ligands
Kloditz, R.; Radoske, T.; Patzschke, M.; Stumpf, T.;
The contribution of the f-orbitals to chemical bonding leads to the rich chemistry of the actinides. This is in contrast to the lanthanides, where it is known that this contribution is less important. Of special interest is the influence of these orbitals on the bonding character of actinides and lanthanides with organic ligands reflecting natural binding motifs.
This study compares the different bonding behavior of tetravalent actinides and lanthanides with the Schiff base salen (see Fig. 1, left) by means of real-space bonding analysis. Our approach makes use of the quantum theory of atoms in molecules (QTAIM), plots of the non-covalent interactions (NCI) and density differences complemented by natural population analysis (NPA). Especially the local properties at the bond critical points (Fig. 1, right), for instance charge, density, ellipticity and others, can be used to characterize a bond’s order, strength, and covalent contribution. In addition, thermodynamic calculations on the stability of these complexes are presented since the difference in stability is a direct consequence of the different interaction strengths of the f elements.
First results reveal a strong interaction of the actinides, i.e. Th to Pu, with the oxygen of salen characterized by a high electron density concentration between the atoms. In contrast, the interaction between the actinides and the nitrogen of salen is much weaker. The delocalization index, density and Laplacian reveal a significant increase of covalency for Pa to Pu compared to Th and Ce being an indicator of the contribution of the f-electrons. Tetravalent Ce as a lanthanide analogue of Th is expected to show a similar bonding behavior, but, surprisingly, this is not the case for all investigated bonding properties.
Such a detailed analysis of the electronic properties of actinide compounds will help to improve understanding of their behavior in the environment as well as in technical processes and leads to the possibility to predict properties of unknown complexes.
Keywords: Actinides, Quantum chemistry, DFT, Bonding, Covalency
  • Lecture (Conference)
    Journees des Actinides, 14.-18.04.2019, Erice, Italien

Publ.-Id: 29369 - Permalink


Hybrid LWFA–PWFA staging as a beam energy and brightness transformer: conceptual design and simulations
Martinez De La Ossa, A.; Assmann, R. W.; Bussmann, M.; Corde, S.; Couperus Cabadağ, J. P.; Debus, A.; Döpp, A.; Ferran Pousa, A.; Gilljohann, M. F.; Heinemann, T.; Hidding, B.; Irman, A.; Karsch, S.; Kononenko, O.; Kurz, T.; Osterhoff, J.; Pausch, R.; Schöbel, S.; Schramm, U.ORC
We present a conceptual design for a hybrid laserdriven plasma wakefield accelerator (LWFA) to beam-driven plasma wakefield accelerator (PWFA). In this set-up, the output beams from an LWFA stage are used as input beams of a new PWFA stage. In the PWFA stage, a new witness beam of largely increased quality can be produced and accelerated to higher energies. The feasibility and the potential of this concept is shown through exemplary particle-in-cell simulations.
In addition, preliminary simulation results for a proof-of-concept experiment in Helmholtz-Zentrum Dresden-Rossendorf (Germany) are shown.
Keywords: laser plasma accelerator, LWFA, PWFA

Downloads:

  • Secondary publication expected from 25.06.2020

Publ.-Id: 29368 - Permalink


Dynamics of Charges in Superlong Blacklight-Emitting CaB2O4:Ce3+ Persistent Phosphor
Sharma, S. K.; Bettinelli, M.; Carrasco, I.; Beyer, J.; Gloaguen, R.; Heitmann, J.;
The optical and persistent luminescence properties of CaB2O4:Ce3+ phosphor are presented. The optical emission for excitation in the 250–340 nm wavelength region is dominated by two bands at 365 and 460 nm. Lifetime measurements suggested that the 365 nm emission band is due to interconfigurational Ce3+ 5d → 4f transitions. Upon excitation with a 254 nm UV lamp, a superlong persistent luminescence in the UVA1 region (340–400 nm, blacklight) was observed, lasting for at least 15 h, and with excellent reproducibility, which is perfectly suitable for phototherapy application. The initial-rise method was applied on the thermoluminescence glow curves to determine the trap distribution and trap depth. The results suggest that one distinct trap, with an activation energy of ∼0.52 eV, was solely responsible for the persistent luminescence in the CaB2O4:Ce3+ phosphor. The other traps had a quasi-continuous distribution, with activation energies between 0.56 and 1.15 eV. The proposed persistent luminescence and the thermoluminescence mechanisms are elucidated using experimental parameters obtained from the optical and thermoluminescence results and the theoretically calculated electronic structure of the Ce3+ ion in CaB2O4. The lowest Ce3+ 5d1 level was found to be ∼0.97 eV below the conduction band, and the persistent luminescence/thermoluminescence emission was dominated by the radiative transitions between Ce3+ energy levels, 5d → 2F5/2,7/2.
Keywords: Rare earth luminescence, long persistence, photoluminescence, thermoluminescence, mechanism

Publ.-Id: 29367 - Permalink


Nanoscale modification of one-dimensional single-crystalline cuprous oxide
Das, P.; Raibhar, M. K.; Elliman, R. G.; Möller, W.; Facsko, S.; Chatterjee, S.;
In this work we report for the first time a method to modify the surface of Cu2O nanowires in a controllable way and physically weld them into a network form, which contributes to higherelectrical conductivity as well as a strong water-repelling nature. We have used state-of-the-art theoretical calculations to support our experimental observations. We demonstrate how varying the irradiation fluence can modulate the surface and decorate the nanowire with a uniformdistribution of Cu8O nanocrystals due to referential sputtering. While several well studied joining techniques are available for carbon and metal-based nanowires, the same information forceramic nanowires is scarce at present. The current study sheds light into this and a state-of-the art 3D simulation technique predicts most of the modifications including surface modulation, oxygen depletion and welding. The welded network shows higher electrical conductivity than the unwelded assembly. With Cu2O being of p-type the current ion beam joining technique shows a novel path for fabricating p-i-n junctions or solar cell devices through bottom-up approach. Furthermore, we have explored the response of this network to moisture. Our calculation based on density functional theory predicts the hydrophilic nature of individual copper oxide nanowires both before and after irradiation. However, the network shows a strong water-repelling nature, which has been explained quantitatively using the Cassie–Baxter model.
Keywords: copper oxide, superhydrophobic, ion irradiation, nanowire, welding

Publ.-Id: 29366 - Permalink


Ab initio path integral Monte Carlo approach to the static and dynamic density response of the uniform electron gas
Groth, S.; Dornheim, T.; Vorberger, J.;
In a recent Letter [T. Dornheim et al., Phys. Rev. Lett. 121, 255001 (2018)] we have presented ab initio results for the dynamic structure factor S(q,ω) of the uniform electron gas for conditions ranging from the warm dense matter regime to the strongly correlated electron liquid. This was achieved on the basis of exact path integral Monte Carlo data by stochastically sampling the dynamic local field correction G(q,ω). In this paper we introduce in detail this reconstruction method and provide several practical demonstrations. Moreover, we thoroughly investigate the associated imaginary-time density-density correlation function F(q,τ). The latter also gives us access to the static density-response function χ(q) and static local field correction G(q), which are compared to standard dielectric theories like the widespread random phase approximation. In addition, we study the high-frequency limit of G(q,ω) and provide extensive results for the dynamic structure factor for different densities and temperatures. Finally, we discuss the implications of our findings for warm dense matter research and the interpretation of experiments.
Keywords: electron gas, warm dense matter, response function, structure factor, local field correction, quantum Monte Carlo

Downloads:

Publ.-Id: 29365 - Permalink


Selective leaching of rare earth elements (REEs) from eudialyte concentrate after sulfation and thermal decomposition of non-REE sulfates
Balinski, A.; Petya, A.; Wiche, O.; Kelly, N.; Reuter, M. A.; Scharf, C.;
Eudialyte, a sodium rich zirconosilicate, is one of the promising sources for REEs, particularly for HREEs+Y. The key challenge by hydrometallurgical processing is the prevention of silica gel formation and REE separation from resulting multi-element leach solutions. This study deals with the selective leaching of REEs from eudialyte concentrate after sulfation and thermal decomposition of non-REE sulfates. We demonstrate how to select the parameters in each process stage to achieve high yields of REEs and to separate them from Zr⁴⁺(+Hf⁴⁺), Nb⁵⁺, Al³⁺ and Fe³⁺. The best result in terms of the separation and the REE yield was achieved with the following parameters: acid addition: 15 mmol/g; roasting temperature: 750 °C; roasting time: 2 h; pulp density: 25 kg/m³; leaching temperature: 20 °C; leaching time: 24 h; stirring speed: 300 rpm. For sufficient conversion of REEs into sulfates H₂SO₄ was added in excess, approximately twice as high as the acid consumption. Water leaching at high solid/liquid ratios caused decrease in the separation factor and REE losses resulting from formation of double sulfates and gypsum.
Keywords: eudialyte concentrate, rare earth elements, separation, sulfation, selective roasting, thermal stability of sulfates, leaching, silica stability during leaching

Publ.-Id: 29363 - Permalink


Relation between topology and electronic structure of 2D polymers
Springer, M.; Kuc, A.; Heine, T.;
New 2D materials open access to a whole new world of compounds and properties. Graphene monolayer is such a material, since it has special electron transport features due to its honeycomb topology. Apart from the honeycomb net, there are many more topologies, which promise a manifold of new properties, e.g. the kagomé or the Lieb lattice. As recently shown in the case of the kagomé net, 2D polymers (covalent organic frameworks) can be designed in a way, that their geometric and electronic structures match the desired topology.[1] Other nets, e.g. the Lieb lattice, can at the moment only be realized as optical lattices or via adsorption of molecules on a surface.[2]
In this project, we want to work out the relation between topology and electronic properties. For this purpose, we employ a tight-binding model. In Fig. 1, exemplary results for the aforementioned kagomé and Lieb lattices are shown. Based on these findings, we want to propose new 2D polymers with the desired structures and new properties using density- functional theory.
[1] Y. Jing, T. Heine, J. Am. Chem. Soc. 141, 2, 743 (2019)
[2] S. Mukherjee et al., Phys. Rev. Lett. 114, 245504 (2015); S. Taie et al., Sci. Adv. 1, e1500854 (2015); M. R. Slot et al., Nat. Phys. 13, 672 (2017)
  • Poster
    Flatlands Beyond Graphene 2019, Toulouse, 02.-06.09.2019, Toulouse, France

Publ.-Id: 29360 - Permalink


Tetranuclear Cu(II)-chiral complexes: Synthesis, characterization and biological activity
Peewasan, K.; Merkel, M. P.; Zarschler, K.; Stephan, H.; Anson, C. E.; Powell, A. K.;
Tetranuclear chiral Cu(II)-Schiff-base complexes S-1 and R-1, were synthesised using enantiomerically pure (S)-H2L and (R)-H2L ligand respectively in the ratio of 1:1 of Cu(NO3)2 to (S/R)-H2L in MeOH at room temperature. A pair of polynuclear chiral Cu(II)-cluster complexes were characterized using single-crystal X-ray diffraction, elemental analysis, infrared and CD spectroscopy. The results revealed the importance of these chiral ligands encouraging the arrangement of copper metal in non-centrosymmetric polar packing. The potential of the novel Cu(II)-H2L complexes as biologically active compounds was assessed in particular regarding their anti-proliferative and anti-microbial properties.
Keywords: Metal-based drugs; Polynuclear Cu(II)-cluster; Enantiomerically pure Schiff-base ligand; Cell viability; Single-crystal X-ray diffraction

Publ.-Id: 29357 - Permalink


Bakterien als Alleskönner
Lederer, F.;
Bakterien sind Lebewesen, die unser tägliches Leben ganz entscheidend prägen. Ob Käse, Sauerkraut oder Wein - viele Delikatessen werden für uns durch diese kleinen Alleskönner produziert. Obwohl Bakterien häufig als Krankheitserreger verschrien sind, sind viele von ihnen wichtige Unterstützer unserer Gesundheit - was wir oft erst dann merken, wenn sie weg sind. Eine gesunde Darmflora aus Millionen von Bakterien ist entscheidend für die Produktion und Aufnahme vieler Vitamine in unserem Körper und für unser körperliches Wohlbefinden.
Auch in der Forschung werden Bakterien mit ihren vielen Eigenschaften gerne eingesetzt. Am Helmholtz-Zentrum Dresden-Rossendorf studiert man unter anderem ihre Fähigkeiten, sich fehlende Metalle aus der Umgebung zu besorgen und nutzt diese mikrobiellen Komplexbildner zur Rohstoffrückgewinnung aus Industrieabwässern.
Der Vortrag wird Bakterien als Alleskönner aus verschiednen Perspektiven beleuchten.
Keywords: Bakterien
  • Lecture (others)
    Seniorenakademie, 11.4.2019, Dresden, Deutschland

Publ.-Id: 29356 - Permalink


Gezieltes selektives Herauslösen von Substanzen aus Roh- und Reststoffen mit biologisch basierten Aufbereitungstechnologien
Lederer, F.;
Gast-Vorlesung an der BTU Cottbus-Senftenberg in der Fakultät Umweltwissenschaften und Verfahrenstechnik im Modul "Stoffliche Nutzung nachwachsender Rohstoffe"
Keywords: Mikrobiologie, Phage Surface Display
  • Lecture (others)
    Stoffliche Nutzung nachwachsender Rohstoffe, 17.01.2019, Cottbus, Deutschland
  • Lecture (others)
    Vorlesung im Modul "Stoffliche Nutzung nachwachsender Rohstoffe", 17.01.2019, Cottbus, Deutschland

Publ.-Id: 29355 - Permalink


Ultrafast X-ray tomography raw-data of bubbly two-phase pipe flow around a ring shaped obstacle
Neumann, M.ORC; Hampel, U.ORC

For the investigation of bubbly two-phase flow, which should serve as a future benchmark experiment for CFD code validation, an experimental study has been conducted at the Transient Two-Phase Flow (TOPFLOW) facility at Helmholtz-Zentrum Dresden – Rossendorf (HZDR) using ultrafast electron beam X-ray tomography (UFXRAY). In this study, flow obstacles were installed into a pipe to create a generic three-dimensional flow field as an advanced test case for CFD codes. UFXRAY provide valueable data of the gas phase dynamics with high temporal and spatial resolution.

The provided data set contains tomography raw-data for the experimental series L30 that uses a ring shaped flow obstacle with a blockage ratio of 0.5. 

For visualization, the data might be opend with Fiji. Therefore choose Import->Raw... In the following window specify "Image type" as 16-bit Unsigned, "Width" as 288 pixels and "Height" as 500 pixels for 2x1000Hz measurement or 200 pixels for 2x2500Hz measurement. Make sure that "Little-endian byte order" is checked. A data set contains image frames of both scvanning planes in alternating order. Therefore, if only a single scanning plane is required, the offset and gap parameters need to be set to 288000 bytes for 2x1000Hz measurement or 115200 bytes for 2x2500Hz measurement.

Keywords: ultrafast X-ray computed tomography; bubbly two-phase flow; three-dimensional flow field; two-phase pipe flow
  • Reseach data in the HZDR data repository RODARE
    Publication date: 2019-06-18
    DOI: 10.14278/rodare.124
    License: CC-BY-4.0

Downloads:

Publ.-Id: 29354 - Permalink


Ultrafast X-ray tomography raw-data of bubbly two-phase pipe flow around a semi-circular obstacle
Martin NeumannORC; Hampel, U.ORC

For the investigation of bubbly two-phase flow, which should serve as a future benchmark experiment for CFD code validation, an experimental study has been conducted at the Transient Two-Phase Flow (TOPFLOW) facility at Helmholtz-Zentrum Dresden – Rossendorf (HZDR) using ultrafast electron beam X-ray tomography (UFXRAY). In this study, flow obstacles were installed into a pipe to create a generic three-dimensional flow field as an advanced test case for CFD codes. UFXRAY provide valueable data of the gas phase dynamics with high temporal and spatial resolution.

The provided data set contains tomography raw-data for the experimental series L30 that uses a semi-circular flow obstacle with a blockage ratio of 0.5. 

For visualization, the data might be opend with Fiji. Therefore choose Import->Raw... In the following window specify "Image type" as 16-bit Unsigned, "Width" as 288 pixels and "Height" as 500 pixels for 2x1000Hz measurement or 200 pixels for 2x2500Hz measurement. Make sure that "Little-endian byte order" is checked. A data set contains image frames of both scvanning planes in alternating order. Therefore, if only a single scanning plane is required, the offset and gap parameters need to be set to 288000 bytes for 2x1000Hz measurement or 115200 bytes for 2x2500Hz measurement.

Keywords: ultrafast X-ray computed tomography; bubbly two-phase flow; three-dimensional flow field; two-phase pipe flow
  • Reseach data in the HZDR data repository RODARE
    Publication date: 2019-06-26
    DOI: 10.14278/rodare.122
    License: CC-BY-4.0

Downloads:

Publ.-Id: 29353 - Permalink


Scalable, Data Driven Plasma Simulations with PIConGPU
Huebl, A.ORC; Widera, R.ORC; Garten, M.ORC; Pausch, R.ORC; Steiniger, K.ORC; Bastrakov, S.ORC; Meyer, F.; Bastrakova, K.; Debus, A.ORC; Kluge, T.ORC; Ehrig, S.ORC; Werner, M.; Worpitz, B.; Matthes, A.ORC; Rudat, S.; Starke, S.ORC; Bussmann, M.ORC

PIConGPU is an open source, multi-platform particle-in-cell code scaling to the fastest supercomputers in the TOP500 list. We present the architecture, novel developments, and workflows that enable high-precision, fast turn-around computations on Exascale-machines. Furthermore, we present our strategies to handle extreme data flows from thousands of GPUs for analysis with in situ processing and open data formats (openPMD). PIConGPU is since recently furthermore natively controlled by a Python Jupyter interface and we research just-in-time kernel generation for C++ with our Cling-CUDA extensions.

Keywords: LPA; laser-plasma; particle-in-cell; HPC; manycore; GPU; simulation; interactive; big data
Related publications
Scalable, Data Driven Plasma Simulations with PIConGPU (Id 29350) is supplemented by this publication
  • Reseach data in the HZDR data repository RODARE
    Publication date: 2019-06-13
    DOI: 10.14278/rodare.130
    License: CC-BY-4.0

Downloads:

Publ.-Id: 29351 - Permalink


Scalable, Data Driven Plasma Simulations with PIConGPU
Huebl, A.ORC; Widera, R.ORC; Garten, M.ORC; Pausch, R.ORC; Steiniger, K.ORC; Bastrakov, S.ORC; Meyer, F.; Bastrakova, K.; Debus, A.ORC; Kluge, T.ORC; Ehrig, S.ORC; Werner, M.; Worpitz, B.; Matthes, A.ORC; Rudat, S.; Starke, S.ORC; Bussmann, M.ORC
PIConGPU is an open source, multi-platform particle-in-cell code scaling to the fastest supercomputers in the TOP500 list. We present the architecture, novel developments, and workflows that enable high-precision, fast turn-around computations on Exascale-machines. Furthermore, we present our strategies to handle extreme data flows from thousands of GPUs for analysis with in situ processing and open data formats (openPMD). PIConGPU is since recently furthermore natively controlled by a Python Jupyter interface and we research just-in-time kernel generation for C++ with our Cling-CUDA extensions.
Keywords: LPA, laser-plasma, particle-in-cell, HPC, manycore, GPU, simulation, interactive, big data
Related publications
Scalable, Data Driven Plasma Simulations with PIConGPU (Id 29351) is a supplement to this publication
  • Invited lecture (Conferences)
    Platform for Advanced Scientific Computing (PASC) Conference (PASC19), 12.-14.06.2019, Zürich, Schweiz
    DOI: 10.14278/rodare.131

Downloads:

Publ.-Id: 29350 - Permalink


AMS measurements of cosmogenic nuclide concentrations resolve mountain landscape evolution and the glacial history in the Pamir, Central Asia
Stübner, K.; Bookhagen, B.; Merchel, S.ORC; Rugel, G.; Lachner, J.
Secondary cosmic rays interact with terrestrial materials in the atmosphere and near the Earth's surface to produce cosmogenic radionuclides. The production and accumulation of cosmogenic ¹⁰Be and ²⁶Al in quartz allows geologists to investigate processes of landscape evolution such as erosion, landsliding, sediment transport and deposition on time scales of thousands to few millions of years. The Pamir mountains at the western end of the India-Asia collision zone have been in the focus of geologic research since the early 2000s. While the tectonic evolution of the Pamir is increasingly well understood, the drivers of Pamir landscape evolution remain elusive. The western Pamir is characterized by an extreme topographic relief with summit and valley elevations of 6-7 km and 2-3 km, respectively; the eastern Pamir is a low-relief plateau at ~4 km. This contrast may be attributed to higher precipitation in the western Pamir driving faster river incision and erosion compared to the arid east. Alternatively, the relief may be controlled by spatially variable, tectonically forced surface uplift. Field observations suggest that Pleistocene glaciation of the Pamir was much more extensive than modern glaciation, and that glaciation had a significant impact on the evolution of the Pamir landscape.

We use cosmogenic ¹⁰Be and ²⁶Al concentrations in moraine boulders, glacially polished bedrock and glacio-alluvial sediment deposits to determine the timing and extent of past glacial stages with the goal to better understand what controls landscape evolution in the Pamir. Our results indicate that early Holocene (~10 ka) glaciation was more extensive than previously thought, and that at that time the western Pamir was much more strongly glaciated than the east. The most widespread glaciation occurred at ≥200 ka covering most of the western Pamir and possibly also much of the east Pamir plateau. These results strengthen our hypothesis that the glacial history of the Pamir had a significant impact on its landscape evolution.
Keywords: AMS, tectonics, geomophology
  • Lecture (Conference)
    Heavy Ion Accelerator Symposium on Fundamental and Applied Science (HIAS), 09.-13.09.2019, Canberra, Australia

Publ.-Id: 29349 - Permalink


Mass transport induced asymmetry in charge/discharge behavior of liquid metal batteries
Personnettaz, P.; Landgraf, S.; Nimtz, M.; Weber, N.; Weier, T.;
Mass and charge transport in liquid metal batteries are closely intertwined because of the fully liquid interior of the cells. We found that charging and discharging cycles may show pronounced asymmetries. They are caused by the presence (charge) or absence (discharge) of solutal convection. While the direction of thermal gradients in the positive electrode of a liquid metal battery depend on boundary conditions and thermodynamics in a non-trivial manner, the solutal gradient predictably changes direction from charge to discharge. The unstable density distribution during charge drives a flow strong enough to prevent any concentration polarization. In contrast, during discharge, the stable density gradient suppresses convection and leads to a substantial mass transport overvoltage. We illustrate this scenario by experimental data, numerical simulations and a physical model.
Keywords: electrorefining, liquid electrode, liquid metal batteries, mass transport, overvoltage, solutal convection

Publ.-Id: 29348 - Permalink


Heavy ion irradiation damage in Zr2AlC MAX phase
Qarra, H. H.; Knowles, K. M.; Vickers, M. E.; Akhmadaliev, S.; Lambrinou, K.;
Zr2AlC MAX phase-based ceramic material with 33 wt% ZrC has been irradiated with 22 MeV Au7+ ions between room temperature and 600 °C, achieving a maximum nominal midrange dose of 3.5 displacements per atom. The response of the material to irradiation has been studied using scanning electron microscopy, transmission electron microscopy and X-ray diffraction. Under room temperature irradiation, the ions caused a partial amorphisation of the MAX phase. At high temperatures, irradiated Zr2AlC remained crystalline, but developed an increased density of dislocations and stacking faults in the (0001) basal planes. The irradiated material also exhibited a temperature-dependent microcracking phenomenon similar to that previously reported in other MAX phase materials.

Publ.-Id: 29346 - Permalink


Advanced characterization methods for electrical and sensoric components and devices at the micro and nanoscale
Sheremet, E.ORC; Meszmer, P.ORC; Blaudeck, T.ORC; Hartmann, S.; Wagner, C.ORC; Ma, B.; Hermann, S.; Wunderle, B.; Schulz, S. E.; Hietschold, M.; Rodriguez, R. D.; Zahn, D. R. T.
This feature article covers the nano-analysis methods for four key material characteristics: electrical and electronic properties, optical, stress and strain, and chemical composition. With the downsizing of the geometrical dimensions of electronic, optoelectronic, and electromechanical devices from the micro to the nanoscale at the one hand and the increase of functionality density at the other, the previous generation of micro-analysis methods is no longer sufficient. Therefore, the metrology of materials’ properties with nanoscale resolution has become prerequisite in materials research and development. The article shortly reviews the standard analysis methods and focuses on advanced methods with a nanoscale spatial resolution based on atomic force microscopy (AFM): current-sensing AFM (CSAFM), Kelvin probe force microscopy (KPFM), and hybrid optical techniques coupled with AFM including tip-enhanced Raman spectroscopy (TERS), photothermal-induced resonance (PTIR) characterization methods (nano-Vis, nano-IR), photo-induced force microscopy (PIFM) and photothermal microspectroscopy (PTMS). The simultaneous acquisition of multiple parameters (topography, charge and conductivity, stress and strain, chemical composition) at the nanoscale is a key for exploring new research on structure-property relationships of nanostructured materials such as carbon nanotubes (CNTs) and nano/microelectromechanical systems (N/MEMS). Advanced nanocharacterization techniques foster the design and development of new functional materials for flexible hybrid and smart applications.
Keywords: Scanning probe microscopy, Kelvin probe force microscopy, nanoanalysis, Raman spectroscopy, atomic force microscopy

Publ.-Id: 29345 - Permalink


RF Controls Towards Femtosecond and Attosecond Precision
Zenker, K.; Ludwig, F.; Branlard, J.; Butkowski, L.; Czwalinna, M. K.; Hoffmann, M.; Killenberg, M.; Lamb, T.; Mavric, U.; Mueller, J. M.; Pfeiffer, S.; Schlarb, H.; Schmidt, C.; Springer, L.; Kuntzsch, M.; Hierholzer, M.; Marjanovic, J.;
In the past two decades, radio-frequency (RF) controls have improved by two orders in magnitude achieving meanwhile sub-10 fs phase stabilities and 0.01% amplitude precision. Advances are through improved field detection methods and extensive usage of digital signal processing on very powerful field programmable gate arrays (FPGAs). The question rises, what can be achieved in the next 10 years? In this paper, a review is given of existing systems and strategies, current stability limitations of RF control systems and new technologies with the potential to achieve attosecond resolutions.
  • Open Access LogoContribution to proceedings
    10th International Particle Accelerator Conference, 19.-24.05.2019, Melbourne, Astralia: JACoW, 978-3-95450-208-0, 3414-3418
    DOI: 10.18429/JACoW-IPAC2019-THYYPLM2

Publ.-Id: 29344 - Permalink


Super-SIMS at HZDR - first steps: measurements on halogens
Rugel, G.; Renno, A. D.; Wiedenbeck, M.; Ziegenrücker, R.ORC
The integration of an ion source with very high spatial resolution with a tandem accelerator is a long-standing concept for improving analytical selectivity and sensitivity by orders of magnitude [1-3]. Translating this design concept to reality has its challenges [e.g. 4-6]. Supporting a strong focus on natural, metallic and mineral resources the Helmholtz Institute Freiberg for Resource Technology installed such a system at the Ion Beam Centre at HZDR. This so-called Super-SIMS will be at the core of a comprehensive pallet of micro-analytical methods devoted to the characterization of minerals and ores. Secondary ion beam from a CAMECA IMS 7f-auto are injected into the pre-existing 6MV Dresden Accelerator Mass Spectrometry facility [7,8], which quantitatively eliminates isobaric molecular species from the ion beam.
Our SIMS component can function as either a stand-alone device or can be used to inject the negatively charged secondary ions at energies of up to 40 keV (to match the acceptance conditions) into the accelerator.
We will present the current status of this initiative and will report first results from halogen determinations (F – I) in sphalerite and galena. These data demonstrate a systematic and significant change in the counting rates of all halogens in mineralogically clearly distinguishable areas of both minerals. Furthermore first attempts on quantification with reference materials are given in [8].

[1] K. Purser et al. Surface and Interface Analysis 1(1), 1979, 12.
[2] J. M. Anthony, D. J. Donahue, A. J. T. Jull, MRS Proceedings 69 (1986) 311-316.
[3] S. Matteson, Mass Spectrom. Rev., 27 (2008) 470.
[4] Ender et al. NIMB 123 (1997) 575.
[5] C. Maden, PhD thesis, ETH Zurich 2003.
[6] A. J. Fahey et al. Analytical Chemistry 88(14), 2016, 7145.
[7] Sh. Akhmadaliev et al., NIMB 294 (2013) 5. [8] G. Rugel et al. NIMB 370 (2016) 94.
[8] R. Ziegenrücker et al., this conference.
Keywords: SIMS, Super-SIMS, AMS, accelerator, Beschleuniger, Flur, Flourine, Sphalerit, sphalerite
  • Poster
    Ion Beam Physics Workshop 2019, 24.-26.06.2019, Dresden, Deutschland

Publ.-Id: 29342 - Permalink


Continuous Documentation for Users, Developers and Maintainers
Frust, T.ORC
This talk covers the often neglected and “hated” aspect of software documentation that is indispensable in a sustainable research software development process. A good, up-to-date and easily accessible software documentation lays the foundation for broader usage and collaboration. Software documentation usually covers three different components: user documentation, instructions how to modify and contribute to the software and a low-level API documentation. When starting developing a new research software, the documentation should be considered from the very beginning. Maintaining an up-to-date software documentation with good coverage in an exascale ready scientific software stack is only achievable, if the contribution process clearly includes a check for documentation adding or updates. This check can only be automated partially and usually requires a manual review process. All contributions must be made with the understanding, that documentation is a key aspect of any contribution. Things get never cleaned up later. Recurrent tasks should be automated wherever possible to reduce the impact of manual errors, e.g. the deployment of software documentation. This talk provides a set of best practices for software documentation in science combined with concrete examples from real-world scientific software solutions.
Keywords: Documentation; Software; Best Practices; CI; CD; Continuous Integration; API
  • Open Access LogoInvited lecture (Conferences)
    Platform for Advanced Scientific Computing (PASC) Conference 2019, 12.-14.06.2019, Zürich, Schweiz
    DOI: 10.5281/zenodo.3247324

Publ.-Id: 29338 - Permalink


Entwicklung induktiver Strömungs- und Füllstandssensoren für flüssige Metalle
Krauter, N.;
In dieser Arbeit werden die Weiterentwicklung bestehender und die Entwicklung neuer Sensoren für die induktive Strömungs- und Füllstandsmessung in flüssigen Metallen sowie die zugehörigen Simulations- und Messergebnisse vorgestellt: Dabei handelt es sich um die Entwicklung und Charakterisierung eines miniaturisierten Eddy Current Flow Meters, das z.B. als Bestandteil der Sicherheitstechnik in flüssigmetallgekühlten Reaktoren zur Überwachung der Kühlmittelströmung bei hohen Umgebungstemperaturen eingesetzt werden kann. Außerdem wird das im Rahmen dieser Arbeit entwickelte Immersed Transient Eddy Current Flow Meter vorgestellt, welches eine direkte und kalibrierungsfreie Fließgeschwindigkeitsmessung ermöglicht und damit einen entscheidenden Vorteil gegenüber herkömmlichen induktiven Strömungssensoren besitzt. Anschließend werden neue Konzepte und ein Sensor für die Füllstandsüberwachung bei industriellen Prozessen, hier am Beispiel der Aluminium-Elektrolyse bei Temperaturen bis zu 1000 °C und der Titanherstellung vorgestellt.
Keywords: Induktive Messverfahren, Fließgeschwindigkeitsmessung, Füllstandsmessung
  • Doctoral thesis
    TUDpress, 2019
    Mentor: Prof. Dr. Uwe Hampel und Dr. Frank Stefani
    248 Seiten

Publ.-Id: 29336 - Permalink


Local inductive flow measurements
Krauter, N.; Stefani, F.;
An overview of current research on inductive local flow rate measurement techniques in liquid metals at the HZDR.
Keywords: Inductive Flow Measurements, Eddy Current Flow Meter, Immersed Transient Eddy Current Flow Meter
  • Lecture (Conference)
    ESFR-SMART European Workshop on Instrumentation for the Safety of Liquid Metal Facilities, 10.-12.04.2019, Dresden, Deutschland

Publ.-Id: 29335 - Permalink


Inductive Level Sensors
Krauter, N.; Stefani, F.; Zürner, T.; Wondrak, T.; Ratajczak, M.;
An overview of current research on inductive level measurement techniques in liquid metals at the HZDR.
Keywords: Eddy Current Level Sensor, Free Surface Detection, Look-Up-Table Method
  • Lecture (Conference)
    ESFR-SMART European Workshop on Instrumentation for the Safety of Liquid Metal Facilities, 10.-12.04.2019, Dresden, Deutschland

Publ.-Id: 29334 - Permalink


Simultaneous determination of flow velocity and electrical conductivity of a liquid metal using an eddy current flow meter in combination with a look-up-table method
Krauter, N.; Stefani, F.;
Eddy Current Flow Meters (ECFM) are inductive sensors that are commonly used to measure the local flow rate or flow velocity of liquid metals in the vicinity of the sensor. One disadvantage of the ECFM is, that the measured voltage signals depend on the magnetic Reynolds number i.e. they are not only depending on the flow velocity but also on the electrical conductivity of the liquid metal. For applications where the temperature (and therefore also the electrical conductivity) is fluctuating significantly, the ECFM has to be calibrated in order to be able to distinguish between the influence of the flow velocity and the temperature on the measured signals. In this paper we present a method that allows the simultaneous measurement of electrical conductivity and flow velocity by using a so called Look-Up-Table method. When using this method, there is no need to calibrate the ECFM.
Keywords: Eddy current, inductive flow measurement, look-up-table
  • Contribution to proceedings
    11th Pamir International Conference Fundamental and Applied MHD, 01.-05.07.2019, Reims, Frankreich
  • Lecture (Conference)
    11th Pamir International Conference Fundamental and Applied MHD, 01.-05.07.2019, Reims, Frankreich

Publ.-Id: 29333 - Permalink


I-BEAT: Ultrasonic method for online measurement of the energy distribution of a single ion bunch
Haffa, D.; Yang, R.; Bin, J.; Lehrack, S.; Brack, F.-E.; Ding, H.; Englbrecht, F.; Gao, Y.; Gaus, L.; Gebhard, J.; Gilljohann, M.; Götzfried, J.; Hartmann, J.; Herr, S.; Hilz, P.; Kraft, S.; Kreuzer, C.; Kroll, F.; Lindner, F. H.; Metzkes-Ng, J.; Ostermayr, T. M.; Ridente, E.; Rösch, T. F.; Schilling, G.; Schlenvoigt, H.-P.; Speicher, M.; Taray, D.; Würl, M.; Zeil, K.; Schramm, U.ORC; Karsch, S.; Parodi, K.; Bolton, P.; Schreiber, J.; Assmann, W.
the shape of a wave carries all information about the spatial and temporal structure of its source, given that the medium and its properties are known. Most modern imaging methods seek to utilize this nature of waves originating from Huygens’ principle. We discuss the retrieval of the complete kinetic energy distribution from the acoustic trace that is recorded when a short ion bunch deposits its energy in water. this novel method, which we refer to as Ion-Bunch energy Acoustic tracing (I-BeAt), is a refinement of the ionoacoustic approach. With its capability of completely monitoring a single, focused proton bunch with prompt readout and high repetition rate, I-BeAt is a promising approach to meet future requirements of experiments and applications in the field of laser-based ion acceleration. We demonstrate its functionality at two laser-driven ion sources for quantitative online determination of the kinetic energy distribution in the focus of single proton bunches
Keywords: laser ion acceleration, ion spectrometer

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Publ.-Id: 29332 - Permalink


Direct Observation of Plasma Waves and Dynamics Induced by Laser-Accelerated Electron Beams
Gilljohann, M. F.; Ding, H.; Döpp, A.; Götzfried, J.; Schindler, S.; Schilling, G.; Corde, S.; Debus, A.; Heinemann, T.; Hidding, B.; Hooker, S. M.; Irman, A.; Kononenko, O.; Kurz, T.; Martinez De La Ossa, A.; Schramm, U.ORC; Karsch, S.
Plasma wakefield acceleration (PWFA) is a novel acceleration technique with promising prospects for both particle colliders and light sources. However, PWFA research has so far been limited to a few large-scale accelerator facilities worldwide. Here, we present first results on plasma wakefield generation using electron beams accelerated with a 100-TW-class Ti:sapphire laser. Because of their ultrashort duration and high charge density, the laser-accelerated electron bunches are suitable to drive plasma waves at electron densities in the order of 1019  cm−3. We capture the beam-induced plasma dynamics with femtosecond resolution using few-cycle optical probing and, in addition to the plasma wave itself, we observe a distinctive transverse ion motion in its trail. This previously unobserved phenomenon can be explained by the ponderomotive force of the plasma wave acting on the ions, resulting in a modulation of the plasma density over many picoseconds. Because of the scaling laws of plasma wakefield generation, results obtained at high plasma density using high-current laser-accelerated electron beams can be readily scaled to low-density systems. Laser-driven PWFA experiments can thus act as miniature models for their larger, conventional counterparts. Furthermore, our results pave the way towards a novel generation of laser-driven PWFA, which can potentially provide ultralow emittance beams within a compact setup.
Keywords: laser wakefield, plasma wakefield electron acceleration, high power laser, advanced accelerator

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Publ.-Id: 29331 - Permalink


A new method for the production of CeO2-base nanograined high capacity absorbent
Bonani, W.; Walter, O.; Cologna, M.; Prieur, D.; Beck, A.; Vitova, T.; Martin, P.; Störmer, H.; Popa, K.;
Due to the broad range of applications (e.g.: catalyst, polishing agents, in fuel cells, pollutant adsorbed, in medicine), ceria is one of the most engineered oxides at nano- and micro-scale. The present research demonstrates highly reactive, nearly mono-dispersed metal oxides NPs with very large specific surface area (>300 m /g). The size of the NPs can be tailored by controlling the temperature and the pressure of the process. This research project explores applications of high quality CeO nanomaterials towards safe management of liquid radioactive wastes contributing to the environmental protection, resources, energy consumption optimisation, and circular economy.
  • Poster
    Nano Today Conference, 17.-21.06.2019, Lisbon, Portugal

Publ.-Id: 29330 - Permalink


How do actinyls interact with hyperphosphorylated yolk protein Phosvitin ?
Kumar, S.; Creff, G.; Hennig, C.; Rossberg, A.; Steudtner, R.; Raff, J.; Vidaud, C.; Oberhaensli, F. R.; Bottein, Y.; Den Auwer, C.;
We carried out a multi-techniques spectroscopic investigation to reveal the coordination geometry of actinyl ions (U(VI), Np(V)) in speciation with phosvitin protein. Like other protein molecules, phosvitin has carboxylic, phosphoryl and amide functional groups, but it has clustered serine residues and all the serine residues are phosphorylated to make it a hyperphosphorylated protein. IR spectroscopic study revealed phosphoryl groups as the main functional group interacting with uranyl ions. This was confirmed in the U(VI)-phosvitin fluorescence spectroscopic investigation and Np(V)-phosvitin UV-visible studies. Further, the existence of U(VI)-phosvitin system in a single speciation was found by the analysis of uranyl ion fluorescence decay data. Interestingly, X-ray absorption fine structure spectroscopic data for U/Np LIII edge revealed small contribution of bidentate binding present along with predominantly monodentate binding of phosphoryl groups in speciation of Uranyl ions with phosvitin protein. Signature of only bidentate binding was found in speciation of Np(V)-phosvitin system. In view of (de)phosphorylation as an important step of functional expression of various human body proteins, this study adds significant details to the molecular description of the toxicity of actinyl ions in biosphere.

Publ.-Id: 29329 - Permalink


Instant kit preparation of 68Ga-radiopharmaceuticals via the hybrid chelator DATA: clinical translation of [68Ga]Ga-DATA-TOC
Sinnes, J. P.; Nagel, J.; Waldron, B. P.; Maina, T.; Nock, B. A.; Bergmann, R. K.; Ullrich, M.; Pietzsch, J.ORC; Bachmann, M.; Baum, P. B.; Rösch, F.
PURPOSE:
The widespread use of 68Ga for positron emission tomography (PET) relies on the development of radiopharmaceutical precursors that can be radiolabelled and dispensed in a simple, quick, and convenient manner. The DATA (6-amino-1,4-diazapine-triacetate) scaffold represents a novel hybrid chelator architecture possessing both cyclic and acyclic character that may allow for facile access to 68Ga-labelled tracers in the clinic. We report the first bifunctional DATA chelator conjugated to [Tyr3]octreotide (TOC), a somatostatin subtype 2 receptor (SST2)-targeting vector for imaging and functional characterisation of SSTR2 expressing tumours.

METHODS:
The radiopharmaceutical precursor, DATA-TOC, was synthesised as previously described and used to complex natGa(III) and 68Ga(III). Competition binding assays of [natGa]Ga-DATA-TOC or [natGa]Ga-DOTA-TOC against [125I-Tyr25]LTT-SS28 were conducted in membranes of HEK293 cells transfected to stably express one of the hSST2,3,5 receptor subtypes (HEK293-hSST2/3/5 cells). First in vivo studies were performed in female NMRI-nude mice bearing SST2-positive mouse phaeochromocytoma mCherry (MPC-mCherry) tumours to compare the in vivo SST2-specific tumour-targeting of [68Ga]Ga-DATA-TOC and its overall pharmacokinetics versus the [68Ga]Ga-DOTA-TOC reference. A direct comparison of [68Ga]Ga-DATA-TOC with the well-established PET radiotracer [68Ga]Ga-DOTA-TOC was additionally performed in a 46-year-old male patient with a well-differentiated NET (neuroendocrine tumour), representing the first in human administration of [68Ga]Ga-DATA-TOC.

RESULTS:
DATA-TOC was labelled with 68Ga with a radiolabelling efficiency of > 95% in less than 10 min at ambient temperature. A molar activity up to 35 MBq/nmol was achieved. The hSST2-affinities of [natGa]Ga-DATA-TOC and [natGa]Ga-DOTA-TOC were found similar with only sub-nanomolar differences in the respective IC50 values. In mice, [68Ga]Ga-DATA-TOC was able to visualise the tumour lesions, showing standardised uptake values (SUVs) similar to [68Ga]Ga-DOTA-TOC. Direct comparison of the two PET tracers in a NET patient revealed very similar tumour uptake for the two 68Ga-radiotracers, but with a higher tumour-to-liver contrast for [68Ga]Ga-DATA-TOC.

CONCLUSION:
[68Ga]Ga-DATA-TOC was prepared, to a quality appropriate for in vivo use, following a highly efficient kit type process. Furthermore, the novel radiopharmaceutical was comparable or better than [68Ga]Ga-DOTA-TOC in all preclinical tests, achieving a higher tumour-to-liver contrast in a NET-patient. The results illustrate the potential of the DATA-chelator to facilitate the access to and preparation of 68Ga-radiotracers in a routine clinical radiopharmacy setting.
Keywords: DATA-TOC; DOTA-TOC; Gallium-68; Molecular imaging; NET; PET-CT; Somatostatin receptor

Publ.-Id: 29328 - Permalink


High-field magnetoresistance of graphite revised
Barzola-Quiquia, J.; Esquinazi, P. D.; Precker, C. E.; Stiller, M.; Zoraghi, M.; Förster, T.; Herrmannsdörfer, T.; Coniglio, W. A.;
A detailed magnetoresistance (MR) study of bulk and microflake samples of highly oriented pyrolytic graphite in a broad temperature 240 ≳ T ≳ 1 K and magnetic field μ0H ≼ 62 T range, reveals the existence of three independent phenomena, the contributions of which are observed at different temperatures and fields. The identification of the three phenomena was possible by studying the MR of samples with thickness of 25 μm to 23 nm. At temperatures T ≳ 100 K the MR is mainly given by the semiconducting stacking order regions. At lower temperatures the contribution of the internal interfaces of graphite to its MR is clearly observable. These interfaces are the origin of the commonly observed electronic phase transitions at fields 35 ≲ μ0H ≲ 55 T at T ≲ 10 K as well as a background MR in the whole field range that resembles the MR measured in granular superconductors.

Publ.-Id: 29327 - Permalink


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