Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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35836 Publications

RF Experience from 6 Years of ELBE SRF-Gun II Operation

Arnold, A.; Lu, P.; Ma, S.; Murcek, P.; Ryzhov, A.; Schaber, J.; Teichert, J.; Xiang, R.; Ciovati, G.; Kneisel, P.; Vennekate, H.

At the electron accelerator for beams with high bril-liance and low emittance (ELBE), the second version of a superconducting radio-frequency (SRF) pho-toinjector was brought into operation in 2014. After a period of commissioning, a gradual transfer to routine operation took place in 2017 and 2018, so that now more than 3400h of user beam have already been gen-erated since 2019. During this time, a total of 20 cath-odes (2 Cu, 12 Mg, 6 Cs2Te) were used, but no serious cavity degradation was observed. In this paper, we summarize the operational experience of the last 6 years of SRF gun operation, with special emphasis on main RF properties of the gun cavity.

Keywords: SRF gun; SRF; superconducting; radio frequency; ELBE

  • Open Access Logo Poster (Online presentation)
    2021 International Conference on RF Superconductivity (SRF'21), 28.06.-02.07.2021, East Lansing, Michican, USA

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Permalink: https://www.hzdr.de/publications/Publ-32919
Publ.-Id: 32919


Unusual field-induced spin reorientation in FeCr2S4: Field tuning of the Jahn-Teller state

Prodan, L.; Yasin, S.; Jesche, A.; Deisenhofer, J.; Krug Von Nidda, H.-A.; Mayr, F.; Zherlitsyn, S.; Wosnitza, J.; Loidl, A.; Tsurkan, V.

The multiferroic spinel FeCr2S4 is a benchmark material for exploring the competition of spin-orbit (SO) and Jahn-Teller (JT) coupling. Our magnetic and thermodynamic studies of stoichiometric single-crystalline samples evidence a magnetic-field-induced spin-reorientation transition in the cooperative JT state below 10 K. At 2 K, at a critical magnetic field of 4.5 T, the magnetization measured along the hard magnetization axis [111] manifests a jump to the fully saturated state accompanied by a steplike decrease of the sound velocity and an abrupt increase of the magnetostriction. All these quantities reveal a hysteretic behavior pointing towards a first-order magnetostructural transformation. Below the JT transition, the specific heat shows a complex behavior upon the application of magnetic fields depending on the crystallographic directions. The observed reduction by 20% of the magnetic anisotropy below the JT transition is attributed to the competition of the SO and JT interactions tuned by external magnetic fields. The concomitant change of the structural symmetry results in a change of the splitting of the lowest levels of the 5E doublet of the tetrahedrally coordinated Fe2+ ions.

Permalink: https://www.hzdr.de/publications/Publ-32915
Publ.-Id: 32915


Experimental Data: Endocytosis is a means of uranium(VI) uptake in tobacco (Nicotiana tabacum) BY-2 cells

John, W.; Lückel, B.; Matschiavelli, N.; Hübner, R.; Matschi, S.; Hoehenwarter, W.; Sachs, S.

The interaction of tobacco (Nicotiana tabacum) BY-2 cells with uranyl(VI) nitrate in phosphate-deficient medium was investigated. The hypothesis was that endocytosis is a means of uranium uptake in these cells. Analysis was in the form of physiological studies (growth and viability), electron microscopy, proteomics and biochemical studies.

Keywords: uranium; tobacco BY-2; endocytosis; radionuclide interaction; TEM-EDX; proteomics

  • Reseach data in the HZDR data repository RODARE
    Publication date: 2022-01-01
    DOI: 10.14278/rodare.1046
    License: CC-BY-4.0
    Embargo: 01.01.2022

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Permalink: https://www.hzdr.de/publications/Publ-32913
Publ.-Id: 32913


Intra-unitcell cluster-cluster magnetic compensation and large exchange bias in cubic alloys

Giri, B.; Sahni, B.; Salazar Mejia, C.; Chattopadhyay, S.; Zeitler, U.; Alam, A.; Nayak, A. K.

Composite quantum materials are the ideal examples of multifunctional systems, which simultaneously host more than one novel quantum phenomenon in physics. Here, we present a combined theoretical and experimental study to demonstrate the presence of an extremely large exchange bias in the range 0.8–2.7 T and a fully compensated magnetic state (FCF) in a special type of Pt and Ni-doped Mn3In cubic alloy. Here, oppositely aligned uncompensated moments in two different atomic clusters sum up to zero, which are responsible for the FCF state. Our density functional theory (DFT) calculations show the existence of several possible ferromagnetic configurations with the FCF as the energetically most stable one. The microscopic origin of the large exchange bias can be interpreted in terms of the exchange interaction between the FCF background and the uncompensated ferrimagnetic clusters stabilized due to its negligible energy difference with respect to the FCF phase. We utilize pulsed magnetic field up to 60 T and 30 T static-field magnetization measurements to confirm the intrinsic nature of exchange bias in our system. Finally, our Hall effect measurements demonstrate the importance of uncompensated noncoplanar interfacial moments for the realization of large EB. The present finding of gigantic exchange bias in a unique compensated ferrimagnetic system opens up a direction for the design of novel quantum phenomena for the technological applications.

Permalink: https://www.hzdr.de/publications/Publ-32912
Publ.-Id: 32912


A contribution to understanding the flotation behavior of lithium metal oxides and spheroidized graphite for lithium-ion battery recycling

Vanderbruggen, A.; Sygusch, J.; Rudolph, M.; Serna-Guerrero, R.

The treatment of end-of-life lithium-ion batteries (LIBs) using froth flotation has recently gained interest as a method to separate valuable lithium transition-metal oxides (LMOs) and graphite particles from the so-called “black mass” mixture. However, the flotation mechanisms of the cathode active particles have not been properly discussed so far, likely since they are generally accepted to be hydrophilic and are thus expected to remain suspended in the bulk phase and recovered in the underflow. Nevertheless, the froth phase products reported in the literature often contain more than 10% LMOs. This results in losses of cathode materials, while hampering the quality of the recovered anode components. As graphite is one of the main materials used for anode manufacturing, being categorized as a critical raw material, its recovery plays an essential role in the electric vehicle revolution.

This work provides the first fundamental study on the flotation mechanisms of the fine particulate black mass components, with the aim of properly identifying the challenges to overcome in order to drive selectivity in froth flotation separation. A series of analysis using model black mass were carried out to circumvent the influence of residual hydrophobic binder found in LIB waste. Studies of wettability with captive bubble and Washburn capillary rise methods show contact angles for LMOs varying from 14° to 52.6° depending on the technique used. Using a bubble-particle attachment set-up it was found that LMO particles can attach to air bubbles spontaneously and in measurable quantities, contrary to the commonly assumed hydrophilic character of cathode active particles. It was also observed that the typically used oil-based collectors (e.g., Escaid 110) interact with both spheroidized graphite and lithium metal oxides, increasing their hydrophobicity and promoting agglomeration. Finally, the particle agglomeration of black mass components provides another flotation mechanism for LMOs through entrapment.

Keywords: Black mass; Lithium ion batteries; Lithium transition metal oxides; Spheroidized graphite; Recycling; Froth flotation

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  • Secondary publication expected from 05.11.2022

Permalink: https://www.hzdr.de/publications/Publ-32908
Publ.-Id: 32908


Microstructure and texture development during hot-compression of Ti5321

Gu, B.; Chekhonin, P.; Xin, S. W.; Liu, G. Q.; Ma, C. L.; Zhou, L.; Skrotzki, W.

The microstructure and texture development of the metastable β‑titanium alloy Ti5321 during hot-compression were investigated by electron backscatter diffraction. Above the β-transus temperature, deformation is accompanied by continuous dynamic recrystallization leading to immediate steady state flow. The deformation below the β-transus temperature is significantly affected by α-precipitation. Dynamic globularization of the α-lamellae leads to flow softening. During hot-compression, parallel to the compression axis a 〈100〉〈111〉double fiber texture develops. With increasing temperature the intensity of 〈100〉increases, while that of <111> decreases. At all temperatures <100> is dominant.

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  • Secondary publication expected from 07.07.2022

Permalink: https://www.hzdr.de/publications/Publ-32907
Publ.-Id: 32907


Proton beam visualisation for in-beam MR imaging

Peter, J.; Schellhammer, S.; Gantz, S.; Uber, S.; van der Kraaij, E.; Smeets, J.; Karsch, L.; Pawelke, J.; Hoffmann, A. L.

Introduction
In-beam MRI is expected to improve the targeting accuracy of proton therapy for moving target volumes providing real-time anatomical images and allowing the simultaneous visualisation of the therapeutic proton beam in liquid-filled phantoms [1,2]. The aim of this contribution is to provide an overview of our previous work on MRI-based proton beam visualisation.

Materials & Methods
A 0.22 T open MR scanner was positioned at a fixed horizontal proton research beamline in a clinical proton therapy facility. Water, ethanol, petroleum and mayonnaise phantoms were irradiated with nominal proton beam energies between 190 - 225 MeV at beam currents of 1 - 64 nA. A range of pulse sequences was used for the acquisition of a horizontal slice within the beam volume. Material, sequence, beam current and energy dependence of the beam signal were evaluated.

Results
The proton beam induces a beam current and energy dependent MRI signal in liquids of low viscosity. For fixed beam current setting, the beam range in water extracted from the MR images matches the expected residual range within a few millimetres. Gradient echo-based pulse sequences appear more sensitive to the beam-induced effect than spin echo-based sequences.

Summary
The method holds potential for on-line quality assurance for MR-integrated proton therapy. The underlying image contrast mechanism requires elucidation to enable the development of specifically tailored sequences with increased sensitivity for the beam-induced effect.

Appendix 1

Figure 1: Beam current dependence of the 207 MeV beam signal in water acquired using a Time-of-Flight-Angiography sequence.


Figure 2: Inversion Recovery-Gradient Echo images of water under irradiation at a beam current of 9 nA. The dotted lines indicate the expected proton ranges.

References
[1] Schellhammer SM. Technical feasibility of MR-integrated proton therapy: Beam deflection
and image quality. Doctoral thesis, Technische Universität Dresden, 2019.
[2] Gantz S. Investigation of the physical and technical feasibility of MRI integrated proton
therapy using a horizontally scanning beam. Doctoral thesis, Technische Universität Dresden,
2021.

  • Open Access Logo Contribution to proceedings
    Joint Conference of the ÖGMP, DGMP & SGSMP, 21.09.2021, online, online, 978-3-948023-16-4, 212-213

Permalink: https://www.hzdr.de/publications/Publ-32906
Publ.-Id: 32906


Introduction to machine learning operations for HelmholtzAI

Sultova, N.

Introduction to machine learning operations for potential usage within HelmholtzAI

This presentation gives an overview of the machine learning operations landscape and our specific use case.

It further presents a detailed comparison between three potential candidates, Metaflow, MLflow and DVC and an outlook based on the gained information.

Keywords: machine learning; mlops; infrastructure; version control

  • Open Access Logo Lecture (others) (Online presentation)
    Voucher presentation at DESY, 13.07.2021, Dresden, Germany

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Permalink: https://www.hzdr.de/publications/Publ-32904
Publ.-Id: 32904


Sorption and reduction of uranium(VI) by a sulfate-reducing microorganism in synthetic Opalinus Clay pore water

Hilpmann, S.; Drobot, B.; Steudtner, R.; Bok, F.; Stumpf, T.; Cherkouk, A.

For a fully comprehensive safety concept of a nuclear repository, it is necessary to investigate not only the geological, geochemical and geophysical properties but also the influence of naturally occurring microorganisms in the deep geological layers. Clay rocks are a possible host rock formation for the long-term storage of the highly radioactive waste, with bentonite to be used as backfill material.
Various studies show that, among other sulfate-reducing microorganisms, Desulfosporosinus species are present in both clay rock and bentonite.[1,2] A phylogenetically close relative to the isolated species is Desulfosporosinus hippei DSM 8344, an anaerobic, spore-forming microorganism originally found in permafrost soils.[3] Therefore, this strain was selected to get a deeper insight into the uranium(VI) interactions with naturally occurring microorganisms from deep geological layers.
A time-dependent experiment in artificial Opalinus Clay pore water[4] (100 µM uranium(VI), pH 5.5) showed the removal of about 80 % of the uranium(VI) from the supernatants within 48 h. Corresponding live/dead images of the cells taken by fluorescence microscopy exhibit the formation of cell agglomerates and an increasing number of dead cells within the incubation time.
Further examination of the supernatants using time-resolved laser-induced fluorescence spectroscopic techniques revealed the presence of two uranium(VI) species, a lactate and a carbonate complex. The proportion of the carbonate species remained constant over the incubation period, whereas the lactate species decreased.
The comparison of UV/Vis band positions of the dissolved cell pellets with reference spectra provides clear proof of a partially reduction of uranium(VI) to uranium(IV), although bands of uranium(VI) were also still observable. Therefore, it could be that the ongoing interaction mechanism is a combined sorption-reduction process.
These findings are an important contribution to a safety concept for a nuclear repository in clay rock and provide new insights into the interactions of sulfate-reducing microorganisms with uranium(VI).

References
[1] Bagnoud et al. (2016) Nat. Commun 7, 1–10.
[2] Matschiavelli et al. (2019) Environ. Sci. Technol. 53, 10514–10524.
[3] Vatsurina et al. (2008) Int. J. Syst. Evol. Microbiol. 58, 1228–1232.
[4] Wersin et al. (2011) Appl. Geochemistry 26, 931–953.

Keywords: uranium(VI) reduction; sulfate-reducing microorganisms; clay rock

  • Lecture (Conference) (Online presentation)
    Goldschmidt 2021 Virtual, 04.-09.07.2021, Lyon, Frankreich

Permalink: https://www.hzdr.de/publications/Publ-32901
Publ.-Id: 32901


Superconductivity of highly spin-polarized electrons in FeSe probed by 77Se NMR

Molatta, S.; Opherden, D.; Wosnitza, J.; Opherden, L.; Zhang, Z. T.; Wolf, T.; von Löhneysen, H.; Sarkar, R.; Biswas, P. K.; Grafe, H.-J.; Kühne, H.

A number of recent experiments indicate that the iron-chalcogenide FeSe provides the long-sought possibility to study bulk superconductivity in the cross-over regime between the weakly coupled Bardeen-Cooper-Schrieffer (BCS) pairing and the strongly coupled Bose-Einstein condensation (BEC). We report on 77Se nuclear magnetic resonance experiments of FeSe, focused on the superconducting phase for strong magnetic fields applied along the c axis, where a distinct state with large spin polarization was reported. We determine this high-field state as bulk superconducting with high spatial homogeneity of the low-energy spin fluctuations. Further, we find that the static spin susceptibility becomes unusually small at temperatures approaching the superconducting state, despite the presence of pronounced spin fluctuations. Taken together, our results clearly indicate that FeSe indeed features an unusual field-induced superconducting state of a highly spin-polarized Fermi liquid in the BCS-BEC crossover regime.

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Permalink: https://www.hzdr.de/publications/Publ-32900
Publ.-Id: 32900


Simultaneous compression and opacity data from time-series radiography with a Lagrangian marker

Swift, D. C.; Kritcher, A. L.; Hawreliak, J. A.; Gaffney, J.; Lazicki, A.; Macphee, A.; Bachmann, B.; Döppner, T.; Nilsen, J.; Whitley, H. D.; Collins, G. W.; Glenzer, S.; Rothman, S. D.; Kraus, D.; Falcone, R. W.

Time-resolved radiography can be used to obtain absolute shock Hugoniot states by simultaneously measuring at least two mechanical parameters of the shock, and this technique is particularly suitable for one-dimensional converging shocks where a single experiment probes a range of pressures as the converging shock strengthens. However, at sufficiently high pressures, the shocked material becomes hot enough that the x-ray opacity falls significantly. If the system includes a Lagrangian marker such that the mass within the marker is known, this additional information can be used to constrain the opacity as well as the Hugoniot state. In the limit that the opacity changes only on shock heating, and not significantly on subsequent isentropic compression, the opacity of the shocked material can be determined uniquely. More generally, it is necessary to assume the form of the variation of opacity with isentropic compression or to introduce multiple marker layers. Alternatively, assuming either the equation of state or the opacity, the presence of a marker layer in such experiments enables the non-assumed property to be deduced more accurately than from the radiographic density reconstruction alone. An example analysis is shown for measurements of a converging shock wave in polystyrene at the National Ignition Facility.

Permalink: https://www.hzdr.de/publications/Publ-32899
Publ.-Id: 32899


Demonstration of an X-ray Raman Spectroscopy setup to study warm dense carbon at the High Energy Density Instrument of European XFEL

Voigt, K.; Zhang, M.; Ramakrishna, K.; Amouretti, A.; Appel, K.; Brambrink, E.; Cerantola, V.; Chekrygina, D.; Döppner, T.; Falcone, R. W.; Falk, K.; Fletcher, L. B.; Gericke, D. O.; Göde, S.; Harmand, M.; Hartley, N.; Hau-Riege, S. P.; Huang, L.; Humphries, O. S.; Lokamani, M.; Makita, M.; Pelka, A.; Prescher, C.; Schuster, A.; Smid, M.; Toncian, T.; Vorberger, J.; Zastrau, U.; Preston, T. R.; Kraus, D.

We present a proof-of-principle study demonstrating X-ray Raman Spectroscopy (XRS) from carbon samples at ambient conditions in conjunction with other common diagnostics to study warm dense matter, performed at the High Energy Density scientific instrument of the European X-ray Free Electron Laser (European XFEL). We obtain sufficient spectral resolution to identify the local structure and chemical bonding of diamond and graphite samples, using highly annealed pyrolytic graphite spectrometers. Due to the high crystal reflectivity and XFEL brightness, we obtain signal strengths that will enable accurate XRS measurements in upcoming pump-probe experiments with high repetition-rate, where the samples will be pumped with high-power lasers. Molecular dynamics simulations based on density functional theory together with XRS simulations demonstrate the potential of this technique and show predictions for high-energy-density conditions. Our setup allows simultaneous implementation of several di erent diagnostic methods to reduce ambiguities in the analysis of the experimental results, which, for warm dense matter, often relies on simplifying model assumptions. The promising capabilities demonstrated here provide unprecedented insights into chemical and structural dynamics in warm dense matter states of light elements, including conditions similar to the
interiors of planets, low-mass stars and other celestial bodies.

Permalink: https://www.hzdr.de/publications/Publ-32898
Publ.-Id: 32898


Enhanced Photoluminescence of Gold Nanoparticle-Quantum Dot Hybrids Confined in Hairy Polymer Nanofibers

Singh, S.; Raulo, A.; Singh, A.; Mittal, M.; Horechyy, A.; Hübner, R.; Formanek, P.; Srivastava, R. K.; Sapra, S.; Fery, A.; Nandan, B.

In the present work, we have studied the influence of gold nanoparticles (AuNPs) on the photoluminescence (PL) behavior of cadmium selenide (CdSe) quantum dots (QDs) confined in spatially separated soft nanoscale cylindrical domains. These cylindrical domains, in the form of hairy core-shell nanofibers, were fabricated via cooperative self-assembly of polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) block copolymer (BCP) mixed with pre-synthesized CdSe QDs and AuNPs. The CdSe QDs and AuNPs were simultaneously incorporated in the P4VP cylindrical domains of the self-assembled BCP structure. It was found that the confinement imposed by the nanometer-sized cylindrical core resulted in the localization of the CdSe QDs and AuNPs in close proximity. Notably, it was observed that the PL intensity of the CdSe QDs could be manipulated by varying the amount of AuNPs present in the cylinder core. Interestingly, in the presence of a very low fraction of AuNPs, the PL intensity of the CdSe QDs increased compared to the AuNPs-free system. However, further increase in the fraction of AuNPs led to gradual quenching of the photoluminescence intensity. The PL enhancement and quenching plausibly was due to the interplay between the energy transfer due to surface plasmon coupling and FRET/electron transfer from QDs to the AuNPs. The resulting functional nanofibers could have potential applications in sensing, bioimaging, and optoelectronic devices.

Permalink: https://www.hzdr.de/publications/Publ-32897
Publ.-Id: 32897


Data publication: Optical Kerr nonlinearity and multi-photon absorption of DSTMS measured by Z-scan method

Li, J.; Rana, R.; Zhu, L.; Liu, C.; Schneider, H.; Pashkin, O.

Z-scan data (polarization dependent)

Matlab scripts for the fitting and simulations

FTIR transmission data

------------------------------------------

Center wavelength of OPA: 1430 nm

FWHM duration of OPA pulses: 75 fs

Pulse energy: 20 nJ

thickness of DSTMS: 0.4 mm

'OA' means open aperture 'CA' meams close aperture

Related publications

  • Reseach data in the HZDR data repository RODARE
    Publication date: 2021-07-13
    DOI: 10.14278/rodare.1062
    License: CC-BY-4.0

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-32894
Publ.-Id: 32894


Optical Kerr nonlinearity and multi-photon absorption of DSTMS measured by Z-scan method

Li, J.; Rana, R.; Zhu, L.; Liu, C.; Schneider, H.; Pashkin, O.

We investigate the optical Kerr nonlinearity and multi-photon absorption (MPA) properties of 4-N, N-dimethylamino-4’-N’-methyl-stilbazolium 2, 4, 6- trimethylbenzene-sulfonate (DSTMS) excited by femtosecond pulses at a wavelength of 1.43 μm, which is optimal for terahertz generation via difference frequency mixing. The MPA and the optical Kerr coefficients of DSTMS at 1.43 μm are strongly anisotropic indicating a dominating contribution from cascaded 2nd-order nonlinearity.

Related publications

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  • Secondary publication expected from 09.08.2022

Permalink: https://www.hzdr.de/publications/Publ-32893
Publ.-Id: 32893


Investigations on axial gas dispersion coefficients in bubble columns using gas flow modulation

Marchini, S.; Döß, A.; Bieberle, A.; Schubert, M.; Hampel, U.

Gas-liquid contactors, such as bubble columns, are subject to dispersion phenomena in both gas and liquid phase. The Axial Dispersion Model (ADM) is the most widely used theoretical approach to account for the effects of dispersion [1].
A reliable quantification of the axial dispersion coefficients is crucial for process performance assessment as well as design and optimization of such contactors. Conventional approaches for determining axial dispersion coefficients rely on tracer substances. However, such methods are hardly universally applicable, may cause detrimental impurities or process downtimes and can even alter the physical properties of the system.
To overcome these issues, Döß et al. [2] introduced a novel non-invasive approach for determining the axial gas dispersion coefficient in bubble columns. Instead of a tracer substance, a marginal sinusoidal modulation is superimposed to the gas inlet flow rate and used as a virtual tracer. This modulation introduces a sinusoidal variation of the gas holdup in time, called gas density wave. Along the column, the gas density wave is damped in amplitude and is shifted in phase, due to gas dispersion. Amplitude damping and phase shift can be measured and related to the value of the axial dispersion coefficient via a dispersion model. A schematic sketch of the working principle is provided in Figure 1.
Döß et al. [2] successfully used sinusoidal-resolved gamma-ray densitometry to investigate the amplitude damping and phase shift. The deviation caused by the statistical behaviour of the gamma-ray photons was reduced by increasing the measurement time.As the operation of gamma-ray sources may be challenging for industrial applicability, this study assesses the possibility of using alternative non-radiative techniques to measure the gas density wave. Several measurement techniques and different gas modulation schemes in terms of initial modulation amplitude and frequency have been studied to ensure detectable amplitude and phase changes at chosen axial positions, while not altering the hydrodynamic behaviour. Uncertainties associated with the axial dispersion coefficient have been evaluated in comparison to gamma-ray densitometry.

  • Lecture (Conference) (Online presentation)
    European Chemical Engineering Conference, 20.-24.09.2021, Berlin, Germany

Permalink: https://www.hzdr.de/publications/Publ-32892
Publ.-Id: 32892


Convective, absolute and global azimuthal magnetorotational instabilities

Mishra, A.; Mamatsashvili, G.; Galindo, V.; Stefani, F.

We study the convective and absolute forms of azimuthal magnetorotational instability (AMRI) in a cylindrical Taylor–Couette (TC) flow with an imposed azimuthal magnetic field. We show that the domain of the convective AMRI is wider than that of the absolute AMRI. Actually, it is the absolute instability which is the most relevant and important for magnetic TC flow experiments. The absolute AMRI, unlike the convective one, stays in the device, displaying a sustained growth that can be experimentally detected. We also study the global AMRI in a TC flow of finite height using direct numerical simulation and find that its emerging butterfly-type structure – a spatio-temporal variation in the form of axially upward and downward travelling waves – is in a very good agreement with the linear analysis, which indicates the presence of two dominant absolute AMRI modes in the flow giving rise to this global butterfly pattern.

Keywords: absolute/convective instability; Taylor-Couette flow

Permalink: https://www.hzdr.de/publications/Publ-32890
Publ.-Id: 32890


Flow Reconstruction in a Rayleigh-Bénard Convection Cell with an Aspect Ratio 0.5 by Contactless Inductive Flow Tomography

Mitra, R.; Sieger, M.; Galindo, V.; Schindler, F.; Stefani, F.; Wondrak, T.

The time dependent behaviour of the large-scale circulation in a Rayleigh-Bénard convection cell exhibits a rich set of different three-dimensional flow features like rotations or torsional modes. In this paper, the applicability of the contactless inductive flow tomography (CIFT) to visualise these flow features in a cylindrical cell filled with GaInSn is investigated numerically. The simulated flow in the cylinder with a diameter of 320 mm and a height of 640 mm serves as a basis to investigate the quality of the reconstructed velocity field by CIFT.

Keywords: Rayleigh-Bénard convection; Large-scale circulation; Liquid metal flow; Contactless inductive flow tomography

Related publications

  • Open Access Logo Contribution to proceedings
    Electromagnetic Processing of Materials, 14.-16.06.2021, Riga, Latvia
    Proceedings of the 10th international conference in Electromagnetic Processing of Materials, Riga: The University of Latvia Press, 978-9934-18-686-8, 182-187
  • Lecture (Conference) (Online presentation)
    Electromagnetic Processing of Materials, 14.-16.06.2021, Riga, Latvia

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Permalink: https://www.hzdr.de/publications/Publ-32885
Publ.-Id: 32885


Radiative characterization of supersonic jets and shocks in a laser-plasma experiment

Bohlin, H.; Brack, F.-E.; Cervenak, M.; Chodukowski, T.; Cikhardt, J.; Dostál, J.; Dudžák, R.; Hubner, J.; Huo, W.; Jelinek, S.; Klír, D.; Kroll, F.; Krupka, M.; Krůs, M.; Pisarczyk, T.; Rusiniak, Z.; Schramm, U.; T.-H, N.-B.; Weber, S.; Zaraś-Szydłowska, A.; Zeil, K.; Kumar, D.; Schlegel, T.; Tikhonchuk, V.

The interaction of supersonic laser-generated plasma jets with a secondary gas target was studied experimentally. The plasma parameters of the jet, and the resulting shock, were characterized using a combination of multi-frame interferometry/shadowgraphy, and x-ray diagnostics, allowing for a detailed study of their structure and evolution. The velocity was obtained with an x-ray streak camera, and filtered x-ray pinhole imaging was used to infer the electron temperature of the jet and shock. The topology of the ambient plasma density was found to have a significant effect on the jet and shock formation, as well as on their radiation characteristics. The experimental results were compared with radiation hydrodynamic simulations, thereby providing further insights into the underlying physical processes of the jet and shock formation and evolution.

Keywords: Supersonic jets; Shocks; Laser Plasma; X-ray imaging; Hydrodynamic

Permalink: https://www.hzdr.de/publications/Publ-32883
Publ.-Id: 32883


On the study of hydrodynamic instabilities in the presence of background magnetic fields in high-energy-density plasmas

Manuel, M. J.-E.; Khiar, B.; Rigon, G.; Albertazzi, B.; Klein, S. R.; Kroll, F.; Brack, F.-E.; Michel, T.; Mabey, P.; Pikuz, S.; Williams, J. C.; Koenig, M.; Casner, A.; Kuranz, C. C.

Blast-wave-driven hydrodynamic instabilities are studied in the presence of a background B-field through experiments and simulations in the high-energy-density (HED) physics regime. In experiments conducted at the Laboratoire pour l’utilisation des lasers intenses (LULI), a laser-driven shock-tube platform was used to generate a hydrodynamically unstable interface with a prescribed sinusoidal surface perturbation, and short-pulse x-ray radiography was used to characterize the instability growth with and without a 10-T B-field. The LULI experiments were modeled in FLASH using resistive and ideal magnetohydrodynamics (MHD), and comparing the experiments and simulations suggests that the Spitzer model implemented in FLASH is necessary and sufficient for modeling these planar systems. These results suggest insufficient amplification of the seed B-field, due to resistive diffusion, to alter the hydrodynamic behavior. Although the ideal-MHD simulations did not represent the experiments accurately, they suggest that similar HED systems with dynamic plasma-β (=2*μ_0*ρ*v^2/B^2) values of less than ∼100 can reduce the growth of blast-wave-driven Rayleigh–Taylor instabilities. These findings validate the resistive-MHD FLASH modeling that is being used to design future experiments for studying B-field effects in HED plasmas.

Keywords: Shock waves; Nebulae; Supernovae; Radiography; Magnetohydrodynamics; High pressure instruments; Magnetic fields; Fluid instabilities; Electromagnetic coils

Permalink: https://www.hzdr.de/publications/Publ-32882
Publ.-Id: 32882


robust training, adversarial examples and what it tells us about modern medical ML classifiers

Steinbach, P.

Undoubtedly, the advent of deep learning for image classification or pattern recognition has created a ecosystem stir in the
medical domain of unprecedented extension. In this talk, I'd like to discuss the question how adversarial examples can help us
quantify the quality of a Deep Learning trained classifyer. With this approach, I'd like to underline how observations and
methods from commercial applications can or cannot be transferred to medical applications. The slidedeck is meant to motivate a discussion on what we expect machine learning to leverage and how this relates to clinical applications with robustness of solutions in mind.

Keywords: robust AI; robust ML; adversarial examples; adversarial attacks; medical imaging; radiology

  • Open Access Logo Invited lecture (Conferences) (Online presentation)
    EMPAIA Committee “Validation of AI solutions”, 24.06.2021, virtuell, Germany
    DOI: 10.6084/m9.figshare.14838330.v1

Permalink: https://www.hzdr.de/publications/Publ-32881
Publ.-Id: 32881


Update of the EPTN atlas for CT- and MR-based (3T and 7T) contouring in Neuro-Oncology

Eekers, D. B. P.; Di, P. D.; Roelofs, E.; Postma, A.; Dijkstra, J.; Ajithkumar, T.; Alapetite, C.; Blomstrand, M.; Burnet, N. G.; Calugaru, V.; Compter, I.; Coremans, I. E. M.; Harrabi, S.; Iannalfi, A.; Klaver, Y. L. B.; Lambrecht, M.; Méndez Romero, A.; Paulsen, F.; Timmermann, B.; Vitek, P.; van der Weide, H. L.; Whitfield, G. A.; Nyström, P.; Zindler, J.; De, R. D.; Langendijk, J.; Weber, D. C.; Troost, E. G. C.

Background and purpose:To update the digital online atlas for organs at risk (OARs) delineation in neuro-oncology based on high-quality computed tomography (CT) and magnetic resonance (MR) imaging withnew OARs.Materials and methods:In this planned update of the neurological contouring atlas published in 2018, tennew clinically relevant OARs were included, after thorough discussion between experienced neuro-radiation oncologists (RTOs) representing 30 European radiotherapy-oncology institutes. Inclusion wasbased on daily practice and research requirements. Consensus was reached for the delineation after crit-ical review. Contouring was performed on registered CT with intravenous (IV) contrast (soft tissue & bonewindow setting) and 3 Tesla (T) MRI (T1 with gadolinium & T2 FLAIR) images of one patient (1 mm slices).For illustration purposes, delineation on a 7 T MRI without IV contrast from a healthy volunteer wasadded. OARs were delineated by three experienced RTOs and a neuroradiologist based on the relevant lit-erature.Results:The presented update of the neurological contouring atlas was reviewed and approved by 28experts in the field. The atlas is available online and includes in total 25 OARs relevant to neurooncology, contoured on CT and MRI T1 and FLAIR (3 T & 7 T). Three-dimensional (3D) rendered films arealso available online.Conclusion:In order to further decrease inter- and intra-observer OAR delineation variability in the fieldof neuro-oncology, we propose the use of this contouring atlas in photon and particle therapy, in clinicalpractice and in the research setting. The updated atlas is freely available onwww.cancerdata.org.

Keywords: Atlas for neuro-oncology; Brain; Organs at risk; Particle therapy; Radiotherapy; European Particle Therapy Net

Permalink: https://www.hzdr.de/publications/Publ-32880
Publ.-Id: 32880


Simultaneous localisation and mapping for laparoscopic liver navigation: a comparative evaluation study

Docea, R.; Pfeiffer, M.; Bodenstedt, S.; Kolbinger, F.; Höller, L.; Wittig, I.; Hoffmann, R.; Troost, E. G. C.; Riediger, C.; Weitz, J.; Speidel, S.

Computer-Assisted Surgery (CAS) aids the surgeon by enriching the surgical scene with additional information
in order to improve patient outcome. One such aid may be the superimposition of important structures (such as
blood vessels and tumors) over a laparoscopic image stream. In liver surgery, this may be achieved by creating
a dense map of the abdominal environment surrounding the liver, registering a preoperative model (CT scan)
to the liver within this map, and tracking the relative pose of the camera. Thereby, known structures may be
rendered into images from the camera perspective. This intraoperative map of the scene may be constructed, and
the relative pose of the laparoscope camera estimated, using Simultaneous Localisation and Mapping (SLAM).
The intraoperative scene poses unique challenges, such as: homogeneous surface textures, sparse visual features,
specular reflections and camera motions specific to laparoscopy. This work compares the efficacies of two state-of-
the-art SLAM systems in the context of laparoscopic surgery, on a newly collected phantom dataset with ground
truth trajectory and surface data. The SLAM systems chosen contrast strongly in implementation: one sparse and
feature-based, ORB-SLAM3,1–3 and one dense and featureless, ElasticFusion.4 We find that ORB-SLAM3 greatly
outperforms ElasticFusion in trajectory estimation and is more stable on sequences from laparoscopic surgeries.
However, when extended to give a dense output, ORB-SLAM3 performs surface reconstruction comparably to
ElasticFusion. Our evaluation of these systems serves as a basis for expanding the use of SLAM algorithms in
the context of laparoscopic liver surgery and Minimally Invasive Surgery (MIS) more generally.

Permalink: https://www.hzdr.de/publications/Publ-32879
Publ.-Id: 32879


Value of PET imaging for radiation therapy

Lapa, C.; Nestle, U.; Albert, N.; Baues, C.; Beer, A.; Buck, A.; Budach, V.; Bütof, R.; Combs, S.; Derlin, T.; Eiber, M.; Fendler, W.; Furth, C.; Gani, C.; Gkika, E.; Grosu, A.; Henkenberens, C.; Ilhan, H.; Löck, S.; Marnitz-Schulze, S.; Miederer, M.; Mix, M.; Nicolay, N.; Niyazi, M.; Pöttgen, C.; Rödel, C.; Schatka, I.; Schwarzenboeck, S.; Todica, A.; Weber, W.; Wegen, S.; Wiegel, T.; Zamboglou, C.; Zips, D.; Zöphel, K.; Zschaeck, S.; Thorwarth, D.; Troost, E. G. C.

This comprehensive review written by experts in their field gives an overview on the current status of incorporating positron emission tomography (PET) into radiation treatment planning. Moreover, it highlights ongoing studies for treatment individualisation and per-treatment tumour response monitoring for various primary tumours. Novel tracers and image analysis methods are discussed. The authors believe this contribution to be of crucial value for experts in the field as well as for policy makers deciding on the reimbursement of this powerful imaging modality.

Keywords: PET; radiation oncology; functional imaging; radiomics

Permalink: https://www.hzdr.de/publications/Publ-32878
Publ.-Id: 32878


ROCOCO Performance Score translates dosimetric differences into clinically relevant endpoints: comparing IMPT to VMAT in pilocytic astrocytoma

In, ’. V. L.; Roelofs, E.; Cubillos, M. M.; Compter, I.; Klaver, Y.; Smeenk, R.; Janssens, G. O.; Kaanders, J. H. A. M.; Fajardo, R. D.; Oldenburger, F.; De, R. D.; Troost, E. G. C.; Eekers, D.

Background and purpose: Proton therapy is expected to outperform photon-based treatment regarding organs at risk (OAR) sparing but to date there is no method to practically measure clinical benefit. Here, we introduce the novel ROCOCO Performance Scoring System (RPSS) translating dose differences
into clinically relevant endpoints and apply this to a treatment plan comparison of volumetric modulated arc therapy (VMAT) and intensity modulated proton therapy (IMPT) in 20 pilocytic astrocytoma patients.
Material and methods: The RPSS was developed on the basis of expert-based weighting factors and toxicity scores per OAR. The imaging datasets of 20 pilocytic astrocytoma patients having undergone radiotherapy were included in this in silico dosimetric comparison trial as proof of principle. For each of these patients, treatment plans to a total dose of 54 Gy (RBE) were generated for VMAT and IMPT and these were compared regarding radiation dose to the clinical target volume (CTV) and OARs. The RPSS was calculated for each treatment plan comparing VMAT and IMPT.
Results: In 40 analysed treatment plans, the average and low dose volumes to various OARs were significantly reduced when using IMPT compared to VMAT (p < 0.05). Using the RPSS, a significant difference between both treatment modalities was found, with 85% of the patients having a lower RPSS in favour of the IMPT plan.
Conclusion: There are dosimetric differences between IMPT and VMAT in pilocytic astrocytoma patients. In absence of clinically validated NTCP models we introduce the RPSS model in order to objectively compare treatment modalities by translating dosimetric differences in potential clinical differences.

Keywords: Low grade glioma; Pilocytic astrocytoma; Organ at risk; Proton therapy; Cognition; Scoring system

Permalink: https://www.hzdr.de/publications/Publ-32877
Publ.-Id: 32877


Formation of plutonium (IV) silicate species in very alkaline reactive media

Estevenon, P.; Dumas, T.; Lorenzo Solari, P.; Welcomme, E.; Szenknect, S.; Mesbah, A.; Kvashnina, K. O.; Moisy, P.; Poinssot, C.; Dacheux, N.

The formation of stable plutonium (IV) silicate colloidal suspension has been identified in very alkaline reactive media (pH ≥ 13). XAS measurements allowed to observe that these species exhibit a structure similar to those reported at (IV) oxidation state, like for thorium, uranium and neptunium silicates counterparts. These colloids can be stabilized in aqueous solution at concentrations around 10 2 mol·L 1 and successive filtration process allowed to evaluate that most of these silicates had a size ranging between 3 and 6 nm. This result may bring new outlooks on the behavior of plutonium in silicate ions rich reactive media

Downloads:

  • Secondary publication expected from 28.07.2022

Permalink: https://www.hzdr.de/publications/Publ-32876
Publ.-Id: 32876


An open-access future for Journal of Synchrotron Radiation

Kvashnina, K.; Amemiya, Y.; Bhattacharyya, D.; Lindau, I.; Allen, A.

The entire Journal of Synchrotron Radiation (JSR) editorial team would like to take this opportunity to inform all our readers, authors and supporters about the coming transition to open access. All papers submitted to JSR after 1 October 2021, will be for open-access publication. By taking this step, JSR is supporting a journey towards open science in general.

Permalink: https://www.hzdr.de/publications/Publ-32875
Publ.-Id: 32875


Resolution Enhancement for Drill-Core Hyperspectral Mineral Mapping

Contreras Acosta, I. C.; Khodadadzadeh, M.; Gloaguen, R.

Drill-core samples are a key component in mineral exploration campaigns, and their rapid and objective analysis is becoming increasingly important. Hyperspectral imaging of drill-cores is a non-destructive technique that allows for non-invasive and fast mapping of mineral phases and alteration patterns. The use of adapted machine learning techniques such as supervised learning algorithms allows for a robust and accurate analysis of drill-core hyperspectral data. One of the remaining challenge is the spatial sampling of hyperspectral sensors in operational conditions, which does not allow us to render the textural and mineral diversity that is required to map minerals with low abundances and fine structures such as veins and faults. In this work, we propose a methodology in which we implement a resolution enhancement technique, a coupled non-negative matrix factorization, using hyperspectral, RGB images and high-resolution mineralogical data to produce mineral maps at higher spatial resolutions and to improve the mapping of minerals. The results demonstrate that the enhanced maps not only provide better details in the alteration patterns such as veins but also allow for mapping minerals that were previously hidden in the hyperspectral data due to its low spatial sampling.

Keywords: resolution enhancement; sampling enhancement; hyperspectral; high-spatial resolution multi-spectral; drill-cores; mineral mapping; machine learning

Permalink: https://www.hzdr.de/publications/Publ-32872
Publ.-Id: 32872


Comparative High-Field Magnetization Study of (Sm,Er)2Fe17 and Er2Fe17 Compounds and their Nitrides

Ivanov, L.; Paukov, M.; Tereshina, I.; Veselova, S.; Akimova, O.; Verbetsky, V.; Gorbunov, D.

Magnetic properties of the R2Fe17 compounds are sensitive to the atomic substitutions and interstitial absorption of nitrogen. In our work, both were combined and their effect on the magnetization behavior of Er2Fe17 compound in magnetic fields up to 58 T was studied. Er2Fe17N2, Sm1.2Er0.8Fe17N2 and Sm1.8Er0.2Fe17N2.1 nitrides were prepared. Magnetization measurements were carried out, mainly on powder samples (excluding Er2Fe17 single crystal). Nanopowders of Sm1.2Er0.8Fe17N2 were obtained by mechanical grinding. The grinding time was varied from 0 to 60 minutes. The strength of the inter-sublattice coupling in samples is estimated by analyzing high-field magnetization data.

Permalink: https://www.hzdr.de/publications/Publ-32871
Publ.-Id: 32871


Magnetocaloric properties and specifics of the hysteresis at the first-order metamagnetic transition in Ni-doped FeRh

Chirkova, A. M.; Skokov, K. P.; Scurschii, I.; Scheibel, F.; Karpenkov, A. Y.; Volegov, A. S.; Baranov, N. V.; Nielsch, K.; Schultz, L.; Müller, K.-H.; Woodcock, T. G.; Gutfleisch, O.

Measurements of the magnetization in quasistatic and pulsed magnetic fields with different sweep rates, measurements of the specific heat in various magnetic fields, and direct measurements of the adiabatic temperature change have been employed to study the metamagnetic phase transition from an antiferromagnetic (AF) to the ferromagnetic (FM) state in an (Fe0.98Ni0.02)49Rh51 alloy with a critical AF-FM transition temperature, Ttr, reduced to 266 K. Based on the obtained results, a magnetic phase diagram for this alloy has been constructed. The AF-FM transition induced by the magnetic field below 10 K is found to occur in a steplike fashion in contrast to smooth behavior at 10K < T < Ttr. The adiabatic temperature change ΔTad in the magnetic field of 2 T exceeds 6.5 K in pulsed fields (∼100 T/s) and in the Halbach setup (∼0.5 T/s), which is in agreement with the estimation from the S-T diagram constructed based on the specific heat measurements. The reversible ΔTad reaches −4.6 K under cyclic conditions in the Halbach setup (2 T). A complete transformation to the FM state in the whole temperature range requires a magnetic field of 14 T. Direct measurements of ΔTad in pulsed fields of 14 T revealed an irreversible part of the magnetocaloric effect associated with the presence of magnetic hysteresis and respective losses during the magnetization process.

Permalink: https://www.hzdr.de/publications/Publ-32870
Publ.-Id: 32870


Development of a high-speed ultrasonic tomography system for measurements of rising bubbles in a horizontal cross-section

Murakawa, H.; Tomoyuki, S.; Eckert, S.

The present study deals with high-speed ultrasonic tomography (UT) as a powerful tool to characterize the behavior of multiphase flows. A major goal of the work is to improve the temporal resolution for the detection of transit flow structures and time-dependent phenomena such as the incidence of rising gas bubbles. A special transducer with a wide divergence angle of 110° and a vertical height of the measurement volume of approx. 4 mm was developed and tested. The system thus enables the acquisition of cross-sectional images at a frame rate of up to 1,000 frames/s. Scatter noise was eliminated using a time series filtering method. This UT system was applied to a chain of gas bubbles rising in a cylindrical container with an internal diameter of 50 mm. The measurement system provides qualitative observations of the turbulent dynamics of bubbly flows including bubble-bubble interactions, such as the coalescence of individual bubbles.

Keywords: full-matrix capture; reflection mode; time-series filtering; pseudo three-dimensional image; bubble column

Downloads:

  • Secondary publication expected from 09.06.2022

Permalink: https://www.hzdr.de/publications/Publ-32869
Publ.-Id: 32869


Solidification and fluid convection - the story of an inseparable couple

Eckert, S.; Anders, S.; Shevchenko, N.; Keplinger, O.; Kao, A.

In numerous processes in nature and technology, convection is caused by density differences resulting from temperature and concentration gradients. If the rates of diffusion of the two variables differ, this is called double-diffusive convection. Solidification processes under the influence of gravitational forces almost always occur in combination with convective flows. In nature, double-diffusive convection is responsible for magma flow in the mantle of planets or occurs during freezing of seawater. Thermo-solutal convection in industrial castings may result in a composition variation over distances comparable to the size of the solidification domain due to transport of rejected solute by fluid flow, the phenomenon being known as macrosegregation. This paper is dedicated to the interplay between solidification and convection, which are usually closely coupled, interacting in many different ways and thus can lead to very complex phenomena. Results from various experiments conducted both in metals and transparent analogues are presented and discussed.

Keywords: solidification; double-diffusive convection; macrosegregation

  • Invited lecture (Conferences) (Online presentation)
    TMS 2021, annual Meeting & Exhibition, 15.-18.03.2021, virtual, online, USA

Permalink: https://www.hzdr.de/publications/Publ-32868
Publ.-Id: 32868


Investigate utilization of machine-learning methods to derive drag models for Euler-Euler simulations from DNS data

Patel, H.

Multiphase flow plays a vital role in many industrial applications. DNS simulations provide an insight
into the complexity of multiphase flows but are limited due to very high computational costs. Instead,
Euler-Euler (E-E) simulations provide a reliable prediction for a wide range of engineering applications.
E-E simulations are highly dependent on the choice of closure models for the interaction terms. Modeling
of interfacial drag force is one of the main aspect of E-E simulations. In this thesis an attempt has been
made to develop a drag model for E-E simulations by analyzing the DNS data using machine learning
techniques. The entire work was carried out at HZDR (Helmholtz Zentrum Dresden Rossendorf).

  • Master thesis
    TU Dresden, 2021
    Mentor: Dr. Fabian Schlegel
    73 Seiten

Permalink: https://www.hzdr.de/publications/Publ-32867
Publ.-Id: 32867


5f states in UGa2 probed by x-ray spectroscopies

Kolomiets, A. V.; Paukov, M.; Valenta, J.; Chatterjee, B.; Andreev, A. V.; Kvashnina, K. O.; Wilhelm, F.; Rogalev, A.; Drozdenko, D.; Minarik, P.; Kolorenc, J.; Richter, M.; Prchal, J.; Havela, L.

The 5f -based ferromagnet UGa2 with the Curie temperature TC = 125K was investigated by x-ray absorption
spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) experiments at the U–M4,5 and Ga–K
edges. The position of the U–M4 white line, determined in the high-energy resolution fluorescence detection
XAS, suggests that UGa2 is neither a localized 5f 2 nor an itinerant system with 5f occupancy close to n5f = 3.
The analysis of the acquired M4,5XANES and XMCD spectra indicates the 5f occupancy close to 2.5 and a
large orbital magnetic moment of the uranium 5f states (3.18 μB) that is partly compensated by the antiparallel
spin moment (1.31 μB). Thus, the total 5f magnetic moment of 1.87 μB is obtained, which is smaller than
the known bulk magnetization of 3.0 μB per formula unit, while the magnetic moments of the Ga atoms are
negligible. Several methods based on density-functional theory were applied and the obtained results were
compared with XAS spectral features, the Sommerfeld coefficient of the electronic specific heat, and the size of
the U moments and 5f occupancies. A clear correlation is revealed between the U–M4 white-line position of three
metallic uranium compounds and the calculated uranium ionicity. It is demonstrated that only electronic structure
methods taking appropriate care of orbital magnetism and related atomic multiplet effects can successfully
describe all considered properties

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Permalink: https://www.hzdr.de/publications/Publ-32865
Publ.-Id: 32865


Research data: Neutralization dynamics and kinetic energy loss of highly charged ions transmitted through graphene

Creutzburg, S.

This depository contains research data (measured ESA spectra and evaluated data) for highly charged ion transmission though graphene. 

Related publications

  • Reseach data in the HZDR data repository RODARE
    Publication date: 2021-07-05
    DOI: 10.14278/rodare.1052

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-32864
Publ.-Id: 32864


Peeling graphite layer by layer reveals the charge exchange dynamics of ions inside a solid

Niggas, A.; Creutzburg, S.; Schwestka, J.; Wöckinger, B.; Gupta, T.; Grande, P. L.; Eder, D.; Marques, J. P.; Bayer, B. C.; Aumayr, F.; Bennett, R.; Wilhelm, R. A.

Over seventy years ago, Niels Bohr described how the charge state of an atomic ion moving through a solid changes dynamically as a result of electron capture and loss processes, eventually resulting in an equilibrium charge state. Although obvious, this process has so far eluded direct experimental observation. By peeling a solid, such as graphite, layer by layer, and studying the transmission of highly charged ions through single-, bi- and trilayer graphene, we can now observe dynamical changes in ion charge states with monolayer precision. In addition we present a new first-principles approach based on the virtual photon model for interparticle energy transfer to corroborate our findings. Our model that uses a Gaussian shaped dynamic polarisability rather than a spatial delta function is a major step in providing a self-consistent description for interparticle de-excitation processes at the limit of small separations.

Related publications

Permalink: https://www.hzdr.de/publications/Publ-32862
Publ.-Id: 32862


Behavior of implanted Xe and Kr in nanodiamond and thin graphene stacks: experiment and modeling

Shiryaev, A. A.; Trigub, A. L.; Voronina, E. N.; Kvashnina, K. O.; Bukhovets, V. L.

Implantation and subsequent behaviour of heavy noble gases (Ar, Kr, Xe) in few-layer graphene sheets and in nanodiamonds
is studied both using computational methods and experimentally using X-ray absorption spectroscopy. For the first time the
Xe-vacancy (Xe-V) defect is experimentally confirmed as a main site for Xe in the diamond. It is shown that noble gases in
thin graphene stacks distort the layers, forming bulges. The energy of an ion placed in between flat graphene sheets is
notably lower than in domains with high curvature. However, if the ion is trapped in the curved domain, considerable
additional energy is required to displace it.

  • Physical Chemistry Chemical Physics 23(2021), 21729-21737
    Online First (2021) DOI: 10.1039/D1CP02600C

Downloads:

  • Secondary publication expected from 02.09.2022

Permalink: https://www.hzdr.de/publications/Publ-32860
Publ.-Id: 32860


Data and code for: Experimental evidence that effects of megaherbivores on mesoherbivore space use are influenced by species' traits

Wells, H. B. M.; Crego, R. D.; Opedal, Ø. H.; Khasoha, L. M.; Alston, J. M.; Reed, C. G.; Weiner, S.; Kurukura, S.; Hassan, A. A.; Namoni, M.; Ekadeli, J.; Kimuyu, D.; Young, T. P.; Kartzinel, T. R.; Palmer, T. M.; Pringle, R. M.; Goheen, J. R.

Data and code that can be used to reproduce the analyses underlying "Experimental evidence that effects of megaherbivores on mesoherbivore space use are influenced by species’ traits" by Wells et al. (2021) https://doi.org/10.1111/1365-2656.13565

  • Reseach data in the HZDR data repository RODARE
    Publication date: 2021-07-03
    DOI: 10.14278/rodare.1050

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-32857
Publ.-Id: 32857


Rational Design of Two-dimensional Binary Polymers from Heterotriangulenes for Photocatalytic Water Splitting

Zhou, Z.; Springer, M.; Geng, W.; Zhu, X.; Li, T.; Li, M.; Jing, Y.; Heine, T.

Based on first principles calculations, we report the design of three two-dimensional (2D) binary honeycomb-kagome polymers composed of B- and N-centered heterotriangulenes in the same plane with a periodically alternate arrangement as in hexagonal boron nitride. The 2D binary polymers with donor-acceptor characteristics, are semiconductors with a direct band gap of 1.98-2.28 eV. The enhanced in-plane electron conjugation contributes to high charge carrier mobilities for both electrons and holes, about 6.70 and 0.24 × 103 cm2 V-1 s-1, respectively, for the 2D binary polymer with carbonyl bridges (2D CTPAB). With appropriate band edge alignments to match the water redox potentials and pronounced light adsorption for the ultraviolet and visible range of spectra, 2D CTPAB is predicted to be an effective individual photocatalyst to promote overall water splitting.

Permalink: https://www.hzdr.de/publications/Publ-32856
Publ.-Id: 32856


Challenges in Contactless Inductive Flow Tomography for Rayleigh-Bénard Convection Cells

Sieger, M.; Mitra, R.; Schindler, F.; Vogt, T.; Stefani, F.; Eckert, S.; Wondrak, T.

Contactless inductive flow tomography (CIFT) can reconstruct the complex 3-dimensional flow structure of the large scale circulation in liquid metal filled Rayleigh-Bénard (RB) convection cells. The method relies on the precise measurement of weak magnetic fields induced by currents in the conducting liquid arising from the fluid motion in combination with primary excitation fields. The velocity distribution is reconstructed from the magnetic field measurements by solving a linear inverse problem using the Tikhonov regularization and L-curve method. A number of technical challenges have to be overcome to reach the desired accuracy of the measurement signals. In this paper we will describe our design of a new CIFT set-up for a large RB vessel with a diameter of 320 mm and a height of 640 mm. We outline the major factors perturbing the measurement signal of several tens of nanoteslas and describe solutions to decrease mechanical drifts by thermal expansion to a sub-critical level to enable CIFT measurements for high-Rayleigh number flows.

Keywords: contactless inductive flow tomography; large scale circulation; liquid metal flow; Rayleigh-Bénard convection

Related publications

  • Contribution to proceedings
    Electromagnetic processing of materials 2021, 14.-16.06.2021, Riga / virtual, Latvia
    Proceedings of the 10th international conference Electromagnetic Processing of Materials, Riga: The University of Latvia Press, 978-9934-18-686-8, 1-280
  • Lecture (Conference) (Online presentation)
    Electromagnetic processing of materials 2021, 16.06.2021, Riga / virtual, Latvia

Permalink: https://www.hzdr.de/publications/Publ-32853
Publ.-Id: 32853


Emergence of cobalt oxide nano-assemblies: X-ray in situ studies bridging the molecular- and macro- length scales

Grote, L.; Zito, C. A.; Frank, K.; Dippel, A.-C.; Reisbeck, P.; Pitala, K.; Kvashnina, K. O.; Bauters, S.; Detlefs, B.; Ivashko, O.; Pandit, P.; Rebber, M.; Harouna-Mayer, S. Y.; Nickel, B.; Koziej, D.

The key to fabricate complex, hierarchical materials is the control of chemical reactions at various length scales. The classical model of nucleation and growth fails to provide sufficient information. Here, we illustrate how modern X-ray spectroscopic and scattering in situ studies bridge the molecular- and macro- length scales for an assembly of CoO polyhedral shape nanocrystals. By combining high energy-resolution fluorescence-detected X-ray absorption near edge structure (HERFD-XANES) measurements and FEFF simulation, we directly access the molecular level of the reaction. We reveal that initially Co(acac)3 rapidly reduces to Co(acac)2 and coordinates to oxygen atoms of two solvent molecules, forming a bis-adduct of the square-planar Co(acac)2 with octahedral coordination. Unlike a classical nucleation and growth mechanism, we observe that nuclie as small as 2 nm assemble into superstructures of 20 nm. The individual nanoparticles and assemblies continue growing at a similar pace. The final assemblies are smaller than 100 nm and maintain their spherical shape, while the nanoparticles reach a size of 6 nm and adopt various polyhedral, edgy shapes. Our work thus provides a comprehensive perspective on the emergence of nano-assemblies in solution

Permalink: https://www.hzdr.de/publications/Publ-32847
Publ.-Id: 32847


Valence fluctuations in the 3D+3 modulated Yb3Co4Ge13 Remeika Phase

Feig, M.; Akselrud, L.; Motylenko, M.; Bobnar, M.; Wagler, J.; Kvashnina, K. O.; Rafaja, D.; Leithe-Jasper, A.; Gumeniuk, R.

Yb3Co4Ge13 is the first example of a Remeika phase with a 3D + 3 [space group
P43n(a,0,0)000(0,a,0)000(0,0,a)000; a = 8:72328(1) Å, Q1 = Q2 = Q3 = 0:4974(2)]
modulated crystal structure. A slight shift of the composition towards higher Ybcontent
(i:e: Yb3:2Co4Ge12:8) leads to the disappearance of the satellite reflections and
stabilization of the disordered primitive cubic [space group Pm3n, a = 8:74072(2) Å]
Remeika prototype structure. The stoichiometric structurally modulated germanide is
a metal with hole-like charge carriers, where Yb-ions are in a temperature dependent
intermediate valence state of +2:60+2:66 for the temperature range 85-293 K. The
valence fluctuations have been investigated by means of temperature dependent X-ray
absorption spectroscopy, magnetic susceptibility and thermopower measurements

Downloads:

  • Secondary publication expected from 13.09.2022

Permalink: https://www.hzdr.de/publications/Publ-32845
Publ.-Id: 32845


Towards The Bottom of The Periodic Table

Kvashnina, K.

Towards the Bottom of the Periodic Table

  • Invited lecture (Conferences) (Online presentation)
    Monday Meetings, 22.03.2021, Washington State University, USA

Permalink: https://www.hzdr.de/publications/Publ-32844
Publ.-Id: 32844


XAS Towards the Bottom of the Periodic Table

Kvashnina, K.

Understanding the mechanisms of different chemical reactions with actinides (An) at the atomic level is a key step towards safe disposal of nuclear wastes and towards the identification of physical-chemical processes of radionuclides in the environment. X-ray absorption spectroscopy in high energy resolution fluorescence detection (HERFD) mode at the An M4,5 edges is now a common technique to probe the electronic structure and the An 5f states. I will provide an overview of the recently performed studies on Uranium, Thorium and Plutonium-containing materials at the European Synchrotron (ESRF) in Grenoble (France). I will show how the detailed information about the An oxidation state, electron-electron interactions, hybridization between molecular orbitals can be obtained by a combination of experimental data and electronic structure calculations. It might be of interest for fundamental research in chemistry and physics of actinides as well as for applied science.

Reading:
[1] K. O. Kvashnina, S. M. Butorin, P. Martin, and P. Glatzel, “Chemical State of Complex Uranium Oxides,” Phys. Rev. Lett., vol. 111, no. 25, p. 253002, Dec. 2013, doi: 10.1103/PhysRevLett.111.253002.

[2] K. O. Kvashnina, Y. O. Kvashnin, and S. M. Butorin, “Role of resonant inelastic X-ray scattering in high-resolution core-level spectroscopy of actinide materials,” J. Electron Spectros. Relat. Phenomena, vol. 194, pp. 27–36, Jun. 2014, doi: 10.1016/j.elspec.2014.01.016.

[3] S. M. Butorin, K. O. Kvashnina, J. R. Vegelius, D. Meyer, and D. K. Shuh, “High-resolution X-ray absorption spectroscopy as a probe of crystal-field and covalency effects in actinide compounds,” Proc. Natl. Acad. Sci., vol. 113, no. 29, pp. 8093–8097, Jul. 2016, doi: 10.1073/pnas.1601741113.

[4] K. O. Kvashnina et al., “A Novel Metastable Pentavalent Plutonium Solid Phase on the Pathway from Aqueous Plutonium(VI) to PuO 2 Nanoparticles,” Angew. Chemie Int. Ed., vol. 58, no. 49, pp. 17558–17562, Dec. 2019, doi: 10.1002/anie.201911637.

[5] E. Gerber et al., “The missing pieces of the PuO 2 nanoparticle puzzle,” Nanoscale, vol. 12, no. 35, pp. 18039–18048, 2020, doi: 10.1039/D0NR03767B.

[6] I. Pidchenko, J. März, M. O. J. Y. Hunault, S. Bauters, S. M. Butorin, and K. O. Kvashnina, “Synthesis, Structural, and Electronic Properties of K 4 Pu VI O 2 (CO 3 ) 3(cr) : An Environmentally Relevant Plutonium Carbonate Complex,” Inorg. Chem., vol. 59, no. 17, pp. 11889–11893, Sep. 2020, doi: 10.1021/acs.inorgchem.0c01335.

[7] L. Amidani et al., “The Application of HEXS and HERFD XANES for Accurate Structural Characterisation of Actinide Nanomaterials: The Case of ThO 2,” Chem. – A Eur. J., vol. 27, no. 1, pp. 252–263, Jan. 2021, doi: 10.1002/chem.202003360.

[8] E. Gerber et al., “Insight into the structure–property relationship of UO 2 nanoparticles,” Inorg. Chem. Front., p. accepted, 2021, doi: 10.1039/D0QI01140A.

  • Open Access Logo Invited lecture (Conferences) (Online presentation)
    GlobalXAS, 04.02.2021, Washington, USA

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-32843
Publ.-Id: 32843


X-ray Spectroscopy for Actinide Science

Kvashnina, K.

X-ray spectroscopy is a widely used technique at synchrotron radiation sources for analyses of the electronic and structural parameters of materials. This includes the determination of the oxidation state and local symmetry of the absorbing atom. This lecture aimed at PhD students and postdocs who are interested in learning about the principles and practicalities of X-ray spectroscopy, as applied to actinide science. Experimental measurements can be performed on materials in a variety of states, including liquids and solids. The high intensity and tunability of X-rays allow the investigation of a wide range of materials, including thin films, nanoparticles, amorphous materials, solutions, disordered minerals and soils. Moreover, I will provide an overview of the advanced spectroscopic techniques, such as resonant inelastic X-ray scattering (RIXS) and high-energy-resolution fluorescence detected (HERFD) absorption spectroscopy (XAS) that are available at the synchrotrons for studies of actinide systems. I will cover basic principles of X-ray spectroscopy theory and instrumental setups and I will show several examples of the studies performed on the uranium, thorium and plutonium containing materials in the hard and tender X-ray range

  • Invited lecture (Conferences) (Online presentation)
    JDA-2021: 13th School on the Physics and Chemistry of Actinides, 22.-25.03.2021, Rennes, France

Permalink: https://www.hzdr.de/publications/Publ-32841
Publ.-Id: 32841


High energy resolution X-ray spectroscopy on uranium compounds

Kvashnina, K.

Understanding the mechanisms of different chemical reactions with uranium at the atomic level is a key step towards safe disposal of nuclear wastes and towards the identification of physical-chemical processes of radionuclides in the environment. X-ray absorption spectroscopy in high energy resolution fluorescence detection (HERFD) mode at the U L3 and M4,5 edges together with resonant inelastic X-ray scattering (RIXS) are now common techniques for probing the uranium electronic structure and for studying the physics and chemistry of uranium-containing compounds[1], [2]. I will provide an overview of the recently performed studies[3]–[5] on uranium-containing materials at the European Synchrotron (ESRF) in Grenoble (France). I will show how the detailed information about the U oxidation state and electron-electron interactions can be obtained by a combination of experimental data and electronic structure calculations. In connection with latest results, the capabilities and limitations of the HERFD and RIXS experimental methods will be discussed in details. It might be of interest for fundamental research in chemistry and physics of actinides as well as for applied science

References:
[1] K. O. Kvashnina, S. M. Butorin, P. Martin, and P. Glatzel, “Chemical State of Complex Uranium Oxides,” Phys. Rev. Lett., vol. 111, no. 25, p. 253002, Dec. 2013, doi: 10.1103/PhysRevLett.111.253002.
[2] K. O. Kvashnina, Y. O. Kvashnin, and S. M. Butorin, “Role of resonant inelastic X-ray scattering in high-resolution core-level spectroscopy of actinide materials,” J. Electron Spectros. Relat. Phenomena, vol. 194, pp. 27–36, Jun. 2014, doi: 10.1016/j.elspec.2014.01.016.
[3] N. Boulanger et al., “Enhanced Sorption of Radionuclides by Defect-Rich Graphene Oxide,” ACS Appl. Mater. Interfaces, vol. 12, no. 40, pp. 45122–45135, Oct. 2020, doi: 10.1021/acsami.0c11122.
[4] E. Gerber et al., “Insight into the structure–property relationship of UO 2 nanoparticles,” Inorg. Chem. Front., vol. 8, no. 4, pp. 1102–1110, 2021, doi: 10.1039/D0QI01140A.
[5] A. S. Kuzenkova et al., “New insights into the mechanism of graphene oxide and radionuclide interaction,” Carbon N. Y., vol. 158, pp. 291–302, Mar. 2020, doi: 10.1016/j.carbon.2019.10.003.

  • Invited lecture (Conferences) (Online presentation)
    Uranium Science, 28.06.-01.07.2021, Bristol, UK

Permalink: https://www.hzdr.de/publications/Publ-32840
Publ.-Id: 32840


Thermoelectricity and electronic properties of Y1-xCexCrB4

Flipo, S.; Rosner, H.; Bobnar, M.; Kvashnina, K.; Leithe-Jasper, A.; Gumeniuk, R.

Boron-rich materials combine chemical stability with refractory properties and, consequently, are interestingfor high-temperature thermoelectric applications. Therefore, the magnetic, electrical, and thermal transportproperties of the Y1−xCexCrB4series have been investigated here to employ the concept of correlation-enhancedthermoelectric properties. Combining x-ray diffraction and energy- or wavelength-dispersive spectrometry,we find a rather narrow stability range of Y1−xCexCrB4, only samples on the Y- and Ce-rich substitutionlimits (x=0,0.05,0.95,and 1) were obtained. Electrical resistivity data show a change from semiconducting(x=0) to metallic behavior upon Ce substitution (x0.95). From magnetic susceptibility measurements andx-ray absorption spectroscopy, we find a temperature-dependent intermediate valence state of Ce of about+3.5.However, a fit of the magnetic susceptibility data to the Coqblin-Schrieffer model yields a surprisingly highKondo temperature of about 1100 K. Together with the good thermal conductivity for the studied substitutionseries this impedes a suitable thermoelectric performance. Electronic structure calculations for YCrB4supportits narrow gap semiconducting nature in contrast to previous studies. Surprisingly, its electronic structure ischaracterized by pronounced van Hove singularities very close to the Fermi-levelEF. They originate fromnearly dispersionless Cr 3dz2−r2-derived bands in a large part of the Brillouin zone, suggesting the appearance ofelectronic instabilities upon rather small electron doping into these states

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-32839
Publ.-Id: 32839


Novel Radionuclides - Don’t Forget the Regulatory Side

Neels, O.

Recent years have seen many efforts to investigate several novel radionuclides, currently neither commercially available nor clinically used. Especially with the advent of theranostics aims are to improve therapeutic efficacy, to adapt the physical half live to the target under investigation or to improve the “matched pair” concept, i.e. eliminating differences in chemistry between a diagnostic and therapeutic radionuclides. This pre-Congress symposium will discuss, which candidates are promising, how technical and organisational advances may lead to better availability, where are major challenges, what is clinically required and desired, where are regulatory hurdles and where we currently stand in the development. The views from the producers, preclinical radiopharmaceutical researchers and the clinician will be included to provide an up to date status.

Keywords: Radionuclides; Theranostics; Accelerators; Mass separation; Radiopharmaceutical development

  • Open Access Logo Invited lecture (Conferences) (Online presentation)
    Annual Congress of the European Association of Nuclear Medicine, 11.-13.10.2021, Virtuell, Österreich
    DOI: 10.1007/s00259-021-05547-1

Permalink: https://www.hzdr.de/publications/Publ-32837
Publ.-Id: 32837


Regulatory Aspects of Cold Kit-Based Radiopharmaceuticals in the EU

Neels, O.

The cold kit approach is a fast and easy method for labeling tracers with radiometals used in Nuclear Medicine for 99mTc-radiopharmaceuticals since decades. The clinical success of some radiopharmaceutical labelled with Ga-68, a generator-based PET isotope, followed by the availability of registered generators and the development of new chelators, boosted the interest in development of cold kit-based 68Ga- radiopharmaceuticals as for 99mTc. The aluminium fluoride-18 (Al[18F]F) radiolabelling is an interesting “one-pot” method which involves the formation of 18F-metal complex trapped by a suitable chelator. This approach simplifies the 18F-labeling methodology along with the possibility to obtain a kit-based radiofluorination. In this session, the recent developments in kit-based labeling of 68Ga- radiopharmaceuticals and in Al[18F]F labeling will be discussed. Finally, since the regulatory aspect is an important issue for using cold kit preparations in clinical practice, an overview of the different regulations in European countries will be showed and discussed.

Keywords: Cold kit; radiolabeling; 68Ga-radiopharmaceuticals; Al[18F]F; regulatory aspects; PET

  • Open Access Logo Invited lecture (Conferences) (Online presentation)
    Annual Congress of the European Association of Nuclear Medicine, 20.-23.10.2021, Virtuell, Österreich
    DOI: 10.1007/s00259-021-05547-1

Permalink: https://www.hzdr.de/publications/Publ-32836
Publ.-Id: 32836


Optimization and automation of radiolabeling FAPI-74 using [18F]AlF chemistry

Laube, M.; Pietzsch, J.; Knieß, T.; Kopka, K.; Neels, O.

Aim/Introduction:
In recent years quinoline-based small molecules targeting the fibroblast activation protein alpha (FAP) have gained interest for imaging a variety of tumor entities (1). A number of radiotracers for SPECT and PET have been developed, but so far only three FAP inhibitor (FAPI) radioligands have been reported to be radiolabeled with fluorine-18 (2,3,4). This study shows the optimization and automation of the radiofluorination of FAPI-74.

Materials and Methods:
(S)-(4-Carboxymethyl-7-{2-[4-(3-{4-[2-(2-cyano-pyrrolidin-1-yl)-2-oxoethylcarbamoyl]-quinolin-6-yloxy}-propyl)-piperazin-1-yl]-2-oxo-ethyl}-[1,4,7]triazonan-1-yl)-acetic acid, commonly referred to as FAPI-74, was radiolabeled using the [18F]AlF chelation method. Starting from [18F]fluoride, the reaction with AlCl3, chelate formation and subsequent purification was initially optimized by manual syntheses. Optimization included the examination of different anion exchangers (QMA light, PSHCO3) and elution solutions (NaOAc buffer pH4, 0.9% NaCl) as well as careful adjustment of the reaction parameters time (0-20 min), temperature (r.t. to 100°C), amount of AlCl3 and NaOAc buffer pH4, solvents (DMSO, EtOH), and precursor concentration (1-350 µM). Radiochemical conversion (RCC) was determined by radio-UPLC of the crude reaction mixtures. Selected reaction mixtures were analyzed after decay using UPLC-MS to identify non-radioactive byproducts. The optimized radiosynthetic procedure was transferred to a fully automated radiosynthesizer (TRACERlab FXFN) and the final product was purified and formulated using semi-preparative HPLC and SPE.

Results:
Under optimized conditions, RCC of [18F]AlF-FAPI-74 of > 99% was still observed at precursor concentrations as low as 12 µM FAPI-74 after reaction in a 1:1 molar ratio with AlCl3 in DMSO/sodium acetate buffer at pH 4 at 80°C for 15 minutes. Transfer of optimized conditions and upscaling was successfully achieved and delivered radiochemical pure [18F]AlF-FAPI-74 formulated in EtOH suitable for further preclinical experiments. Work on a more rapid SPE-purification and full characterization according to GMP guidelines is in progress.

Conclusion:
The radiosynthesis of [18F]AlF-FAPI-74 was optimized and automated, which in the future will allow the production of large quantities and the distribution of this promising radiotracer to other (clinical) centers.
References:
(1) Altmann A et al. The latest developments in imaging fibroblast activation protein (FAP). J. Nucl. Med. 2021, 62(2) 160-167.
(2) Giesel FL et al. FAPI-74 PET/CT Using Either 18F-AlF or Cold-Kit 68Ga Labeling: Biodistribution, Radiation Dosimetry, and Tumor Delineation in Lung Cancer Patients. J. Nucl. Med. 2021, 62(2) 201-207.
(3) Jiang X et al. FAPI-04 PET/CT using [18F]AlF Labeling Strategy: Automatic Synthesis, Quality Control, and in vivo Assessment in Patient. Front. Oncol. 2021, 11:649148.

  • Open Access Logo Lecture (Conference) (Online presentation)
    Annual Congress of the European Association of Nuclear Medicine, 20.-23.10.2021, Virtuell, Österreich
    DOI: 10.1007/s00259-021-05547-1

Permalink: https://www.hzdr.de/publications/Publ-32835
Publ.-Id: 32835


Two-dimensional magneto-photoconductivity in non-van der Waals manganese selenide

Hu, L.; Cao, L.; Li, L.; Duan, J.; Liao, X.; Long, F.; Zhou, J.; Xiao, Y.; Zeng, Y.-J.; Zhou, S.

Deficient intrinsic species and suppressed Curie temperatures (Tc) in two-dimensional (2D) magnets are major barriers for future spintronic applications. As an alternative, delaminating non-van der Waals (vdW) magnets can offset these shortcomings and involve robust bandgaps to explore 2D magneto-photoconductivity at ambient temperature. Herein, non-vdW a-MnSe2 is first delaminated as quasi-2D nanosheets for the study of emerging semiconductor, ferromagnetism and magneto-photoconductivity behaviors. Abundant nonstoichiometric surfaces induce the renormalization of the band structure and open a bandgap of 1.2 eV. The structural optimization strengthens ferromagnetic super–exchange interactions between the nearest-neighbor Mn2+, which enables us to achieve a high Tc of 320 K well above room temperature. The critical fitting of magnetization and transport measurements both verify that it is of quasi-2D nature. The above observations are evidenced bymultiplemicroscopic andmacroscopic characterization tools, in line with the prediction of firstprinciples calculations. Profiting from the negative magnetoresistance effect, the self-powered infrared magneto-photoconductivity performance including a responsivity of 330.4 mA W-1 and a millisecondlevel response speed are further demonstrated. Such merits stem from the synergistic modulation of magnetic and light fields on photogenerated carriers. This provides a new strategy to manipulate both charge and spin in 2D non-vdW systems and displays their alluring prospects in magneto-photodetection.

Keywords: Manganese selenide; two dimensional non van der Waals

Permalink: https://www.hzdr.de/publications/Publ-32833
Publ.-Id: 32833


How to study nonlinear dynamics in semiconductors by terahertz wave free electron laser

Schneider, H.

This tutorial talk covers the study of nonlinear dynamics in semiconductor nanostructures in strong terahertz and mid-infrared fields involving a free-electron laser.

  • Invited lecture (Conferences) (Online presentation)
    International Symposium on Ultrafast Phenomena and Terahertz Waves (ISUPT2021), 16.-19.06.2021, Chengdu, China

Permalink: https://www.hzdr.de/publications/Publ-32832
Publ.-Id: 32832


Enhanced trion emission in monolayer MoSe2 by constructing a type-I van der Waals heterostructure

Duan, J.; Chava, P.; Ghorbani Asl, M.; Krasheninnikov, A.; Erb, D.; Hu, L.; Schneider, H.; Rebohle, L.; Erbe, A.; Helm, M.; Zeng, Y.-J.; Zhou, S.; Prucnal, S.

Trions, quasi-particles consisting of two electrons combined with one hole or of two holes with one electron, have recently been observed in transition metal dichalcogenides (TMDCs) and drawn increasing attention due to potential applications of these materials in light-emitting diodes, valleytronic devices as well as for being a testbed for understanding many-body phenomena. Therefore, it is important to enhance the trion emission and its stability. In this study, we construct a MoSe2/FePS3 van der Waals heterostructure (vdWH) with type-I band alignment, which allows for carriers injection from FePS3 to MoSe2. At low temperatures, the neutral exciton (X0) emission in this vdWH is almost completely suppressed. The ITrion/Ix0 intensity ratio increases from 0.44 in a single MoSe2 monolayer to 20 in this heterostructure with the trion charging state changing from negative in the monolayer to positive in the heterostructure. The optical pumping with circularly polarized light shows a 14% polarization for the trion emission in MoSe2/FePS3. Moreover, forming such type-I vdWH also gives rise to a 20-fold enhancement of the room temperature photoluminescence from monolayer MoSe2. Our results demonstrate a novel approach to convert excitons to trions in monolayer 2D TMDCs via interlayer doping effect using type-I band alignment in vdWH

Keywords: type-I; van der Waals heterosturcture; photoluminescence enhancement; trion/exciton intensity ratio; polarization

Permalink: https://www.hzdr.de/publications/Publ-32827
Publ.-Id: 32827


Attention based deep 3d multiple instance survival models for oropharyngeal carcinoma patients

Starke, S.; Leger, S.; Zwanenburg, A.; Löck, S.

Introduction
Attention-based convolutional neural networks (CNNs) have the capability to use multiple parts of the same image to predict outcomes of interest. Especially in the domain of medical image analysis, where whole images are typically described by a single label but the identification of important image regions is unclear, this approach allows to combine competitively performing CNNs with enhanced interpretability of the decision-making process.

Materials & Methods
We developed risk models for the prediction of overall survival (OS) for 518 patients of a publicly available oropharyngeal carcinoma (OPC) cohort. Patients were randomly split into training, validation, and test cohorts (388/30/100 patients). A baseline Cox model using clinical information only and three attention-based CNNs using different likelihood functions were trained on multiple 3D instances of the pre-treatment computed tomography (CT) images. Subsequently, patients were stratified into groups at low and high risk of death using median cutoff values based on predictions determined on the training cohort. Model performance was measured using the concordance index (C-index) and differences between Kaplan-Meier curves were assessed by the log-rank test.

Results
The baseline Cox model achieved a C-Index of 0.22 and the CNN models based on the Cox, Weibull and Lognormal likelihood functions achieved C-indices of 0.34, 0.35 and 0.35, respectively, on the test cohort. All models stratified the patients into two risk groups with a statistically significant difference in OS. Attention scores between the multiple instances of a patient were similar, suggesting that all CT instances were equally important for the network decision.

Summary
We investigated the potential of attention-based multiple-instance learning for prediction of OS on an OPC cohort. Since all attention-based CNNs generated risk groups with significantly different OS based on imaging data alone, we consider this approach promising for future validation studies.

Keywords: Deep learning; Survival analysis; Oropharyngeal carcinoma; Attention

  • Lecture (Conference) (Online presentation)
    Dreiländertagung der Medizinischen Physik, 19.-21.09.2021, digital, digital

Permalink: https://www.hzdr.de/publications/Publ-32825
Publ.-Id: 32825


THEREDA - Thermodynamic Reference Database

Moog, H. C.; Bok, F.; Freyer, D.; Gaona, X.; Thoenen, T.

Part of the process to ensure the safety of radioactive waste disposal is the predictive modeling of the solubility of all relevant toxic components in a complex aqueous solution. To ensure the reliability of thermodynamic equilibrium modeling as well as to facilitate the comparison of such calculations done by different institutions it is necessary to create a mutually accepted thermodynamic reference database. To meet this demand several institutions in Germany joined efforts and created THEREDA [1].

THEREDA is a suite of programs at the base of which resides a relational databank. Special emphasis is put on thermodynamic data along with suitable Pitzer coefficients which allow for the calculation of solubilities in high-saline solutions. Registered users may either download single thermodynamic data or ready-to-use parameter files for the geochemical speciation codes PHREEQC, Geochemist’s Workbench, CHEMAPP, or TOUGHREACT. Data can also be downloaded in a generic JSON-format to allow for the import into other codes. The database can be accessed via the world wide web: www.thereda.de

Prior to release, the released part of the database is subjected to many tests. Results are compared to results from earlier releases and among the different codes. This is to ensure that by additions of new and modification of existing data no adverse side effects on calculations are caused. Furthermore, our website offers an increasing number of examples for applications, including graphical representation, which can be filtered by components of the calculated system.

[1] H. C. Moog, F. Bok, C. M. Marquardt, V. Brendler (2015): Disposal of Nuclear Waste in Host Rock formations featuring high-saline solutions - Implementation of a Thermodynamic Reference Database (THEREDA). Appl. Geochem. (55) 72-84. http://dx.doi.org/10.1016/j.apgeochem.2014.12.016

Keywords: THEREDA; Thermodynamic Reference Database; Datenbasis; Datenbank; Pitzer; Löslichkeiten; Modellierung

  • Poster (Online presentation)
    Goldschmidt2021, 04.-09.07.2021, Lyon, Frankreich

Permalink: https://www.hzdr.de/publications/Publ-32824
Publ.-Id: 32824


Uranium carbonates removal by Layered Double Hydroxides

Padberg, G.

Uranium as a radionuclide and heavy metal has strong negative health effects on all living beings.
Since uranium salts display a high solubility in water, its mobility in aquifers is immense
and leads to the risk of ingestion by water consuming organisms. Sources of uranium contamination
in the environment are military and mining activities as well as leaking repositories.
The objective of this work is to analyze the uranium removal properties of two double layered
hydroxides (LDH) with different redox properties in absence and presence of carbonate. The
LDH phases selected are Ca(II)-Al(III)-Cl and Fe(II)-Al(III)-Cl, hereafter named Ca-LDH and
Fe-LDH. These LDHs play a crucial role in the geosphere, as they consist of the most abundant
elements in the earth crust. Furthermore, Ca-LDH is a product of bentonite weathering, which
is an essential process considered in repository safety management.
The first aim of this work is to synthesize and characterize Ca-LDH and Fe-LDH with respect
to their stoichiometry (inductively coupled plasma mass spectrometry, Mössbauer spectroscopy,
thermogravimetric analysis, energy-dispersive X-ray spectroscopy), their structure
(X-ray diffraction, Brunauer-Emmett-Teller theory, dynamic light scattering, scanning electron
microscopy, Raman microscopy) and their electronic state (X-ray photoelectron spectroscopy,
electrophoretic mobility).
The ultimate goal is to determine the best conditions under which uranium is removed from
solution by these LDHs. This will be achieved by analyzing the parameters that influence the
process (carbonate presence, redox processes, pH, ionic strength and uranium concentration).
In comparison to Ca-LDH, Fe(II)-LDH contains a redox active moiety, so that a different mechanism
for the interaction of these LDH phases with aqueous uranium is expected. For a comprehensive
understanding of these molecular uranium reactions occuring at the LDH phase,
various spectroscopic techniques (attenuated total reflexion Fourier-transform infrared, cryo
time-resolved laser-induced fluorescence, energy-dispersive X-ray, X-ray photelectron spectroscopy)
and microscopies (Raman microscopy, scanning electron microscopy) are applied
and combined. The synthesis of Ca-LDH and Fe-LDH was successful and structurally characterized by different
techniques (XRD, DLS, electrophoretic mobility, BET, SEM, EDXS, Raman microscopy,
XPS and Mössbauer). The stoichiometry under consideration of the corresponding oxidation
states was determined as
Ca(II)₀.₅₉Al(III)₀.₄₁Cl₀.₈₂(OH)₂ · 3.0 H2O and
Fe(II)₀.₆₀Al(III)₀.₄₀Cl₀.₈₀(OH)₂ · 1.8 H2O.
Uranium removal by Ca-LDH and Fe-LDH was evaluated as a function of pH (5.5 to 11.0),
ionic strength (H2O, 0.01 M NaCl, and 0.1 M NaCl), carbonate concentration (0, 0.013 mM,
0.2 mM, 0.24 mM and 2 mM) and U(VI) concentration (from nM to mM). As a general statement,
uranium removal was higher than 95% for pH > 6.0 for both Ca-LDH and Fe-LDH under
all studied conditions. Uranium removal decreased for pH < 6 in both LDH, as these mineral
phases are only stable under alkaline conditions. Uranium removal by Ca-LDH decreased at high ionic strength (0.1 M NaCl) and carbonate
concentration (2 mM and 20 mM). For the sorption mechanism of uranium to Ca-LDH, redox
potential measurements indicate a pH, carbonate and ionic strength dependency of the sorbed
minerals. In all studied cases, uranium associated to Ca-LDH is found as U(VI). Two different
U(VI) species are detected by ATR-IR measurements at pH 9.5 in presence of carbonate. Most
tentatively, one species is corresponding to U(VI) precipitation, which is also suggested by Raman
microscopy. The other species could be correlated to U(VI) outer-sphere complexation,
which is also supported by the lack of changes in the isoelectric point of Ca-LDH in presence
of U(VI) and the decrease of chloride content on the Ca-LDH after being in contact with U(VI).
The presence of outer-sphere complexation might be the reason of the decreased U(VI) removal
at higher ionic strengths and carbonate concentrations.
Three different species of U(VI) associated to Ca-LDH are detected by TRLFS from pH 8.0
to pH 11.0 in presence and absence of carbonate. Species 1 could be related to [UO₂(OH)₃]⁻
complexation according to uranium speciation diagrams. Species 2 identity is challenging to
hypothesize. It is assumed that U(VI) incorporation occurs due to an increased Ca concentrationin solution. Species 3 is assigned to [UO₂(CO₃)₂]²⁻ complexation. A reliable identification of
this species would need the use of additional techniques, like XAS.
In contrast, uranium removal by Fe-LDH occurs via Fe(II) promoted reduction of U(VI) to
U(IV). This is confirmed by redox potential values, the detection of Fe(III) by XPS and the
observation of Fe(III) minerals (ferrihydrite, hematite and iron aluminate) by Raman. Changes
on the Fe-LDH structure after contact with U(VI) are also observed in SEM images. The confirmation
of possible stepwise uranium removal by Fe-LDH (anion exchange followed by U(VI)
reduction) would need further verification by ATR FT-IR.
To sum up, the synthesized Ca-LDH and Fe-LDH phases are found to exhibit excellent and effective
uranium removal properties under alkaline conditions, being able to remove negatively
charged uranium species from solutions. Sorption mechanisms could be suggested in a multispectroscopic
approach as outer-sphere surface complexation and incorporaton for Ca-LDH and
as uranium reductive immobilization for Fe-LDH.
This study shows, that the examined Ca-LDH and Fe-LDH can act as a naturally occuring retention
barrier in geosphere against uranium release from repositories. Therefore, these LDH
phases can possibly be part of a technical multi-barrier system preventing uranium leaking into
the biosphere. Further experiments need to be carried out by TRLFS, ATR-IR and XAS in
order to have a comprehensive identification of the uranium sorption mechanisms on Ca-LDH
and Fe-LDH.

Keywords: uranium; Reductive immobilization; Sorption; LDH

  • Master thesis
    TU Dresden, 2021
    Mentor: Prof. Dr. Thorsten Stumpf (1. Prüfer) Dr. Natalia Mayordomo (2. Prüfer)
    65 Seiten

Permalink: https://www.hzdr.de/publications/Publ-32823
Publ.-Id: 32823


The pure paramagnetism in graphene oxide

Zhang, X.; Li, G.; Li, Q.; Shaikh, M. S.; Li, Z.

Magnetic properties of graphene and its derivatives are very fascinating because of their promising application in
spintronics. Among the graphene family materials, graphene oxide is quite typical and special for the magnetic
performance. Herein we report a systematic and detailed investigation on the magnetic properties of graphene
oxide. Compared to the previous reports on the ferromagnetism, our results show that graphene oxide is indeed
only paramagnetic. The magnetic properties can be well described by the Curie-Weiss law. This study is not only
revealing the paramagnetism in graphene oxide but also calling a revisit about the magnetic properties of graphene
oxides, graphene and the other derivatives of graphene.

Keywords: Graphene oxide; Micro-Raman; Magnetization; Paramagnetism

Permalink: https://www.hzdr.de/publications/Publ-32822
Publ.-Id: 32822


Bonding Trends in a Series of Tetravalent Th-Pu Monosalen Complexes

März, J.

Actinides (An) play an important role in chemical engineering and environmental science related to the nuclear industry or nuclear waste repositories.[1] Coordination chemistry of An using small model ligands is a useful tool to get a profound basic knowledge about fundamental physico-chemical properties of the An binding. Observed changes in e.g. the binding situation or magnetic effects among an isostructural An series with the An in the same oxidation state may deliver insight into the unique electronic An properties mainly originating from their f-electrons.
In this study we investigate the coordination chemistry of tetravalent actinides (An(IV)), which are dominant particularly under anoxic environmental conditions, using the organic salen ligand as a small N,O donor.[2] All syntheses were conducted under inert, water-free atmosphere using pyridine based solvents (Pyx). SC-XRD results prove that three isostructural complex series were achieved in each case, dependent on the solvent used. In all complexes, one salen ligand coordinates to the An (An = Th, U, Np, Pu) tetradentately with both nitrogen and deprotonated oxygen donor atoms. The vacant coordination sites are occupied by two chloro ligands for charge compensation as well as two respective solvent molecules, either pyridine (Py), 4-methylpyridine (Pic) or 3,5-lutidine (Lut), resulting in an eightfold coordination environment (see [AnCl2(salen)(Pic)2] as representatives in Figure 1).
The acquired experimental SC-XRD and IR results as well as supporting QC calculations point to a different bonding situation of the individual donor atoms to the actinide. Whereas the An–Nsalen/Pyx and the An–Cl bond lengths follow the decrease of the ionic radii, the An–Osalen bonds remarkably diverge from this behavior. These rather follow the trend of decreasing covalent radii, indicating an exceptionally strong bond here. QC calculations additionally indicate a weaker binding strength in the An–NPyx bonds compared to An–Nsalen. This explains the potential solvent exchange (e.g. to the other pyridine based solvents) and opens up the possibility of further chemical modification at these positions.

Keywords: Actinides; bonding analysis; thorium; uranium; neptunium; plutonium

  • Lecture (Conference) (Online presentation)
    Journées des Actinides, 22.-25.03.2021, Rennes, France

Permalink: https://www.hzdr.de/publications/Publ-32821
Publ.-Id: 32821


Research data: THz harmonic generation from ultraclean graphene

Deinert, J.-C.; Kovalev, S.
Project Leader: Tielrooij, Klaas-Jan; DataCollector: Kovalev, Sergey; Project Member: Soavi, Giancarlo; Project Member: Klimmer, Sebastian

Research data from the June 2021 TELBE beamtime for scientific exchange.

Keywords: Terahrtz; graphene; encapsulated graphene; nonlinear optics; harmonic generation

  • Reseach data in the HZDR data repository RODARE
    Publication date: 2021-06-22
    DOI: 10.14278/rodare.1035

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Permalink: https://www.hzdr.de/publications/Publ-32819
Publ.-Id: 32819


Effects of Substituents on the Molecular Structure and Redox Behavior of Uranyl(V/VI) Complexes with N3O2‑Donating Schiff Base Ligands

Takeyama, T.; Tsushima, S.; Takao, K.

Uranyl(VI) complexes with pentadentate N3O2-donating Schiff base ligands having various substituents at the ortho (R1) and/or para (R2) positions on phenolate moieties, R1,R2-Mesaldien2−, were synthesized and thoroughly character-ized by 1H NMR, IR, elemental analysis, and single crystal X-ray diffraction. Molecular structures of UO2(R1,R2-Mesaldien) are more or less affected by electron-donating or -withdrawing nature of the substituents. The redox be-havior of all UO2(R1,R2-Mesaldien) complexes were investigated to understand how substituents introduced onto the ligand affect redox behavior of these uranyl(VI) complexes. As a result, the redox potentials of UO2(R1,R2-Mesaldien) in DMSO increased from −1.590 V to −1.213 V with an increase in the electron-withdrawing nature of the substituents at the R1 and R2 positions. The spectroelectrochemical measurements and theoretical calculation (DFT and TD-DFT calculations) revealed that the center U6+ of each UO2(R1,R2-Mesaldien) complex undergoes one-electron reduction to afford the corresponding uranyl(V) complex, [UO2(R1,R2-Mesaldien)]−, regardless of difference in the substituents. Consequently, the redox active center of uranyl(VI) complexes seems not to be governed by the HOMO/LUMO gap, but to be determined by whether the LUMO is centered on a U 5f orbital or on one π* of a surrounding ligand.

Permalink: https://www.hzdr.de/publications/Publ-32817
Publ.-Id: 32817


Comprehensive microstructural and optical characterization of the thermal stability of aluminum-titanium oxynitride thin films after high temperature annealing in air

Escobar Galindo, R.; Heras, I.; Guillén, E.; Munnik, F.; Azkona, I.; Krause, M.

The thermal stability of two AlyTi1-y(OxN1-x) layers prepared by cathodic vacuum arc deposition with different oxygen content was studied after high temperature annealing of the samples in air. These layers were designed to be part of solar-selective coating (SSC) stacks. Compositional and microstructural characterization of the thin films was performed before and after the thermal treatment by elastic recoil detection (ERD), transmission electron microscopy and Raman spectroscopy.
AlyTi1-yN sample was stable after 2 hours of annealing at 450ºC. Initial stages of the formation of a surface oxide layer after annealing at 650 ºC were observed both by ERD and Raman analysis. Contrarily, no changes were found after 2 hours annealing treatment either at 450 and 650ºC in the composition and microstructure of AlyTi1-y(OxN1-x) sample. In both samples the formation of a surface anatase TiO2 film was reported after 2 hours annealing at 800°C. These compositional and microstructural changes were correlated with the optical properties determined by spectroscopic ellipsometry. A transition from metallic to dielectric behaviour with increasing annealing temperature was observed. These results complete the durability studies on the designed SSCs based on AlyTi1-y(OxN1-x) materials, confirming that these stacks withstand breakdown at 600ºC in air.

Keywords: Solar energy; Concentrated solar power; Solar selective coatings; Temperature stability

Permalink: https://www.hzdr.de/publications/Publ-32812
Publ.-Id: 32812


Effects of surface roughness and mineralogy on the sorption of Cm(III) on crystalline rock

Demnitz, M.; Molodtsov, K.; Schymura, S.; Schierz, A.; Müller, K.; Jankovsky, F.; Havlova, V.; Stumpf, T.; Schmidt, M.

Crystalline rock is one of the considered host rocks for a future deep geological repository for highly active radiotoxic nuclear waste. The safety assessment requires reliable information on the retention behavior of minor actinides. In this work, we applied various spatially resolved techniques to investigate the sorption of Curium onto crystalline rock (granite, gneiss) thin sections from Eibenstock, Germany and Bukov, Czech Republic. We combined Raman-microscopy, calibrated autoradiography and µTRLFS (micro-focus time-resolved fluorescence spectroscopy) with vertical scanning interferometry to study in situ the impact of mineralogy and surface roughness on Cm(III) uptake and molecular speciation on the surface. Heterogeneous sorption of Cm(III) on the surface depends primarily on the mineralogy. However, for the same mineral class sorption uptake and strength of Cm(III) increases with growing surface roughness around surface holes or grain boundaries. When competitive sorption between multiple mineral phases occurs, surface roughness becomes the major retention parameter on low sorption uptake minerals. In high surface roughness areas primarily Cm(III) inner-sphere sorption complexation and surface incorporation are prominent and in select sites formation of stable Cm(III) ternary complexes is observed. Our molecular findings confirm that predictive radionuclide modelling should implement surface roughness as a key parameter in their simulations.

Keywords: curium; luminescence; crystalline rock; granite; sorption; correlative spectroscopy

Related publications

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  • Secondary publication expected from 21.08.2022

Permalink: https://www.hzdr.de/publications/Publ-32811
Publ.-Id: 32811


Solar-selective coatings for high-temperature solar applications based on a selective transmitter on top of a black body absorber

Krause, M.; Lungwitz, F.; Mendez, A.; Hoppe, M.; Sonnenberg, J.; Garcia Valenzuela, A.; Munnik, F.; Grenzer, J.; Hübner, R.; Escobar Galindo, R.

An alternative concept to achieve solar selectivity for solar thermal materials and applications consists in the use of spectrally selective transmitter coatings.[1] These are characterized by a high transmittance in the solar range and a high reflectance in the thermal range of the electromagnetic spectrum. Suitable materials for selective transmitters are dielectric/metal/dielectric multilayers and transparent conductive oxides (TCOs).[2] The concept has a series of advantages compared to multilayer- or cermet-based solar-selective coatings (SSCs) like the easiness of manufacturing, the possibility to use standard materials as transmitter (e.g., indium tin oxide (ITO)) and absorber (e.g. Pyromark or black chrome), and the adaptability to specific requirements with respect to receiver temperature and solar concentration factor.
After a conceptual introduction, an analysis of solar plant parameters, i.e., operation temperature and solar concentration, for which this concept provides a better solar efficiency than state-of-the-art bare black body absorber, will be given.[3] We will then review the recent developments in the field, which include an excellent high-temperature in-air stability of such type of solar coatings.[4] In the second part of the talk, we will report own results toward a new TCO on black body absorber coating. Vacuum and in-air stability of the TCO SnO2:Ta at 800 °C and its structural properties before and after heat exposure are demonstrated. As potential absorber, the formation, structure, and optical properties of dense, PVD-grown CuCr2O4 thin films are studied. They are obtained in high purity from as-deposited samples by a simple in-air annealing step at 800 °C and absorb light in the whole solar range from 300 nm to 2500 nm.

[1] C.E. Kennedy, Review of Mid- to High-Temperature Solar Selective Absorber Materials, NREL Technical Reports, NREL - National Renewable Energy Laboratory, Golden, Colorado, USA, 2002.
[2] J.C.C. Fan, F.J. Bachner, Transparent heat mirrors for solar-energy applications, Applied Optics 15(4) (1976) 1012-1017.
[3] F. Lungwitz, R. Escobar-Galindo, D. Janke, E. Schumann, R. Wenisch, S. Gemming, M. Krause, Transparent conductive tantalum doped tin oxide as selectively solar-transmitting coating for high temperature solar thermal applications, Solar Energy Materials and Solar Cells 196 (2019) 84-93.
[4] H. Wang, I. Haechler, S. Kaur, J. Freedman, R. Prasher, Spectrally selective solar absorber stable up to 900 degrees C for 120 h under ambient conditions, Solar Energy 174 (2018) 305-311.

Keywords: Solar energy; Concentrated solar power; Solar selective coatings; Transparent conductive oxides; Spinel type absorber

  • Invited lecture (Conferences) (Online presentation)
    Virtual MRS Spring Meeting 2021, Symposium EN05: Materials Challenges and Opportunities in Concentrated Solar Power Technologies, 19.-23.04.2021, Virtuell, USA

Permalink: https://www.hzdr.de/publications/Publ-32810
Publ.-Id: 32810


Formation, structure, and optical properties of copper chromite thin films for high-temperature solar absorbers

Krause, M.; Sonnenberg, J.; Munnik, F.; Grenzer, J.; Hübner, R.; Garcia Valenzuela, A.; Gemming, S.

CuCr2O4 thin films grown by physical vapour deposition were studied in order to evaluate their potential as absorber material for the next generation of concentrated solar power plants. A series of Cu-Cr-O thin films was deposited by reactive ion beam sputtering. The Cr/Cu ratio in the sputter target is demonstrated as the most important parameter to achieve the intended film stoichiometry. In-air annealing at 800 °C leads to structural transformations of the as-deposited films and results in phase compositions according to those expected from the ternary Cu-Cr-O phase diagram. Tetragonal CuCr2O4 with 98.6 at.% phase purity regarding the solid film constituents is obtained for the appropriate Cr/Cu ratio in the sputter target. CuCr2O4 thin films absorb light in the entire solar spectral range from 300 nm to 2500 nm. Their energy gap is found to be < 0.5 eV, and their solar absorptance is estimated to be (0.85 +/- 0.03). The dense microstructure with good thermal conductivity, full adhesion to the substrate, and a relatively low surface roughness are discussed as technological advantages of CuCr2O4 thin films grown by physical vapour deposition.

Keywords: solar absorber; spinels; sputtering; phase transformations; optical materials

Permalink: https://www.hzdr.de/publications/Publ-32809
Publ.-Id: 32809


Environmental drivers of body size in North American bats

Alston, J.

Bergmann’s Rule—which posits that larger animals live in colder areas—is thought to influence variation in body size within species across space and time, but evidence for this claim is mixed. We tested four competing hypotheses for spatio-temporal variation in body size within bat species during the past two decades across North America. Bayesian hierarchical models revealed that spatial variation in body mass was most strongly correlated with mean annual temperature, supporting the heat conservation hypothesis (the mechanism historically believed to underlie Bergmann’s Rule). Across time, variation in body mass was most strongly correlated with net primary productivity, supporting the resource availability hypothesis. Climate change may influence body size in animals but will likely do so through both changes in mean annual temperature and in resource availability. Rapid reductions in body size alongside climate change have occurred in short-lived, fecund species, but such reductions may transpire more slowly in longer-lived species.

  • Invited lecture (Conferences) (Online presentation)
    Annual Meeting of the American Society of Mammalogists, 14.-18.06.2021, Virtual, USA

Permalink: https://www.hzdr.de/publications/Publ-32808
Publ.-Id: 32808


Dimeric and Trimeric Uranyl(VI)–Citrate Complexes: ¹⁷O-, ²³Na-, and ¹³⁹La-NMR – Helpful Probes for (Super-)Structure Determination

Kretzschmar, J.; Tsushima, S.; Drobot, B.; Steudtner, R.; Schmeide, K.; Brendler, V.; Stumpf, T.

Although being investigated for more than 70 years by various methods, the uranyl(VI)–citrate (U(VI)–Cit) system still reveals interesting structural and spectroscopic features. The aqueous chemistry of the system is complex, as evidenced by the still controversial discussions on speciation and structures.

Upon complexation, a chiral center is induced in Cit’s central carbon, yielding two diastereomeric pairs of enantiomers, whereupon the 2:2 complexes exhibit syn- and anti-configured isomers. In fact, the combination of ¹⁷O-NMR (at natural abundance) and DFT calculations allowed an unambiguous discrimination. Hereby symmetry and especially deviation from regular pentagonal bipyramidal coordination geometry affect the O=U=O entities’ (Oyl) chemical shifts. In aqueous solution, the syn-isomer is favored, in contrast to the preferably crystallizing anti-isomer. Both isomers interconvert mutually with exchange rates of about 30 s¹ at −6 °C and 249 s¹ at 60 °C in acidic solution, corresponding to an activation barrier of about 24 kJ mol¹.[1]

At circumneutral conditions, above 3 mM uranyl(VI) citrate concentrations, two trimeric 3:3 U(VI)–Cit complex molecules associate upon sandwiching a metal ion (Mn+) as a O=U=O→Mn+ Lewis acid–base adduct. The coordination shell formed by the six (inner) Oyl restricts the size of the enclosed Lewis acid. Among the studied metal ions, only Na+, Ca²+, and La³+ with ionic radii close to 1.0 Å match the formed cavity, while Li+ is too small, and K+ and Rb+ are too large. This cavity constitutes an anhydrous environment that shields the Mn+ from the aqueous phase, causing the sandwiched Na+ and La³+ to resonate 25 ppm and 430 ppm up-field relative to their corresponding aquo ions, respectively.
Upon increasing Mn+ charge/radius ratio, the sandwiched Lewis acids more and more withdraw electron density from those Oyl acting as Lewis base, and thus the latter sense a remarkable de-shielding. Increasing the charge of the sandwiched cation from +1 to +3, ΔδO between signals of the coordinating Oyl and the outer Oyl increases remarkably (12, 69, and 93 ppm, respectively), as the O=U=O units become progressively polarized.[2]

Literature:

[1] J. Kretzschmar et al., Inorg. Chem. 2021, 60, 7998.
[2] J. Kretzschmar et al., Chem. Commun. 2020, 56, 13133.

Keywords: NMR spectroscopy; Uranium; U(VI); Uranyl(VI); Citrate; Complex; Chirality; Diastereomers; Sandwich complex; Lewis acid-base adduct

Related publications

  • Lecture (Conference) (Online presentation)
    GDCh Jahrestagung der Fachgruppe Magnetische Resonanz (FGMR), 27.09.-01.10.2021, online, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-32805
Publ.-Id: 32805


Bentonite alteration in batch reactor experiments with and without fertilizing agents: implications for the disposal of radioactive waste

Podlech, C.; Matschiavelli, N.; Peltz, M.; Kluge, S.; Arnold, T.; Cherkouk, A.; Meleshyn, A.; Grathoff, G.; Warr, L. N.

Bentonite is currently proposed as a potential backfill material for sealing high-level-radioactive waste in underground repositories due to its low hydraulic conductivity, self-sealing ability and high adsorption capability. High saline pore waters, high temperatures and the influence of microbes may cause mineralogical changes and affect the long-term performance of the bentonite barrier system. In this study, long-term diffusion batch experiments were carried out at 25°C and 90°C for one and two years using two different industrial bentonites (SD80 from Greece, B36 from Slovakia) and two types of aqueous solutions, which simulated a) Opalinus clay pore water with a salinity of 19 g·L-1 and b) saline cap rock solution with a salinity of 155 g·L-1. The bentonites were supplemented with and without organic substrates to study the microbial community and their potential influence on the bentonite mineralogy. Smectite alteration was dominated by metal ion substitutions, changes in layer charge and delamination during water-clay interaction. The degree of smectite alteration and changes in the microbial diversity depended largely on the respective bentonite and the experimental condition. Thus, the low charged SD80 with 17% tetrahedral charge showed nearly no structural change, whereas B36 as a medium charged smectite with 56% tetrahedral charge became more beidellitic with increasing temperature reacted in saline cap rock solution. Based on these experiments, the alteration of the smectite is mainly attributed to the nature of the bentonite, pore water chemistry and temperature. A significant microbial influence on the here analyzed parameters was not observed within the two years of experimentation, but should not be excluded, as the detected genera are known to potentially influence geochemical processes.

Permalink: https://www.hzdr.de/publications/Publ-32803
Publ.-Id: 32803


Tailoring crystalline structure of titanium oxide films for optical applications using non-biased filtered cathodic vacuum arc deposition at room temperature

Guillén, E.; Krause, M.; Heras, I.; Rincón-Llorente, G.; Escobar-Galindo, R.

Titanium oxide films were deposited at room temperature and with no applied bias using a filtered cathodic vacuum arc (FCVA) system in a reactive oxygen environment. The dependence of film growth on two process parameters, the working pressure (Pw) and the O2 partial pressure (pO2), is described in detail. The composition, morphological features, crystalline structure, and optical properties of the deposited films were systematically studied by Rutherford Back Scattering (RBS), Scanning Electron Microscopy (SEM), X-Ray diffraction (XRD), Raman Spectroscopy, UV-vis spectroscopy, and spectroscopic ellipsometry. This systematic investigation allowed the identification of three different groups or growth regimes according to the stoichiometry and to the phase structure of the titanium oxide films. RBS analysis revealed that a wide range of TiOx stoichiometries (0.6 < x < 2.2) were obtained, including oxygen-deficient, stoichiometric TiO2 and oxygen-rich films. TiO, Ti2O3, rutile-type TiO2, and amorphous TiO2 phase structures could be achieved, as confirmed both by Raman and XRD. Therefore the results showed a highly versatile approach, in which different titanium oxide stoichiometries and crystalline phases especially suited for diverse optical applications can be obtained by changing only two process parameters, in a process at room temperature and without applied bias. Of particular interest are crystalline rutile films with high density to be used in ultra-high reflectance metal-dielectric multilayered mirrors, and reduced-TiO2 rutile samples with absorption in the visible range as a very promising photocatalyst material.

Keywords: titanium oxide films; filtered cathodic vacuum arc; rutile; optical coatings

Permalink: https://www.hzdr.de/publications/Publ-32800
Publ.-Id: 32800


Data publication: Detecting bacterial cell viability in few μl solutions from impedance measurements on silicon‐based biochips

Bhat, V. J.; Vegesna, S. V.; Kiani, M.; Zhao, X.; Blaschke, D.; Du, N.; Vogel, M.; Kluge, S.; Raff, J.; Hubner, U.; Skorupa, I.; Rebohle, L.; Schmidt, H.

Der Datensatz umfasst mikroskopische Bilder und Fotos zur Bestimmung der Zelldichte sowie lebender und toter Zellen inklusive Berechnungen, Protokolle und Auswertungen dazu.

Keywords: Cell viability; Dead bacterial cells; Dead bacterial cells; Impedance biochips; Live bacterial cells; Lysinibacillus sphaericus; Membrane potential

Related publications

  • Reseach data in the HZDR data repository RODARE
    Publication date: 2021-06-23
    DOI: 10.14278/rodare.1039
    License: CC-BY-4.0

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Permalink: https://www.hzdr.de/publications/Publ-32799
Publ.-Id: 32799


Structure and luminescence of a-plane GaN on r-plane sapphire substrate modified by Si implantation

Huang, L.; Li, L.; Shang, Z.; Wang, M.; Kang, J.; Luo, W.; Liang, Z.; Prucnal, S.; Kentsch, U.; Ji, Y.; Zhang, F.; Wang, Q.; Yuan, Y.; Sun, Q.; Zhou, S.; Wang, X.

We show the structural and optical properties of non-polar a-plane GaN epitaxial films modified by Si ion implantation. Upon gradually raising Si fluences from 5*10¹³ /cm² to 5*10¹⁵ /cm², the n-type dopant concentration gradually increases from 4.6*10¹⁸ /cm² to 4.5*10²⁰ /cm², while the generated vacancy density accordingly raises from 3.7*10¹³ /cm² to 3.8*10¹⁵ /cm². Moreover, despite that the implantation enhances structural disorder, the epitaxial structure of the implanted region is still well preserved which is confirmed by Rutherford backscattering channeling spectrometry measurements. The monotonical uniaxial lattice expansion along the a direction (out-of-plane direction) is observed as a function of fluences till 1*10¹⁵ /cm², which ceases at the overdose of 5*10¹⁵ /cm² due to the partial amorphization in the surface region. Upon raising irradiation dose, a yellow emission in the as-grown sample is gradually quenched, probably due to the irradiation-induced generation of non-radiative recombination centers.

Keywords: ion implantation; GaN; defects

Permalink: https://www.hzdr.de/publications/Publ-32797
Publ.-Id: 32797


New insights into U(VI) sorption onto montmorillonite from batch sorption and spectroscopic studies at increased ionic strength

Stockmann, M.; Fritsch, K.; Bok, F.; Marques Fernandes, M.; Baeyens, B.; Steudtner, R.; Müller, K.; Nebelung, C.; Brendler, V.; Stumpf, T.; Schmeide, K.

The influence of ionic strength up to 3 mol/kg (background electrolytes NaCl or CaCl2) on U(VI) sorption onto montmorillonite was investigated as function of pHc in absence and presence of CO2. A multi-method approach combined batch sorption experiments with spectroscopic methods (time-resolved laser-induced fluorescence spectroscopy (TRLFS) and in situ attenuated total reflection Fourier-transform infrared (ATR FT-IR) spectroscopy). In the absence of atmospheric carbonate, U(VI) sorption was nearly 99% above pHc 6 in both NaCl and CaCl2 and no significant effect of ionic strength was found. At lower pH, cation exchange was strongly reduced with increasing ionic strength. In the presence of carbonate, U(VI) sorption was reduced above pHc 7.5 in NaCl and pHc 6 in CaCl2 system due to formation of aqueous UO2(CO3)x (2-2x) and Ca2UO2(CO3)3 complexes, respectively, as verified by TRLFS. A significant ionic strength effect was observed due to the formation of Ca2UO2(CO3)3 (aq), which strongly decreases U(VI) sorption with increasing ionic strength.
The joint analysis of determined sorption data together with literature data (giving a total of 213 experimental data points) allowed to derive a consistent set of surface complexation reactions and constants based on the 2SPNE SC/CE approach, yielding log K⁰ = 2.42 ± 0.04 (≡SSOUO2 +), log K⁰ = −4.49 ± 0.7 (≡SSOUO2OH), and log K⁰ = −20.5 ± 0.4 (≡SSOUO2(OH)3 2-). Ternary uranyl carbonate surface complexes were not required to describe the data. With this reduced set of surface complexes, an improved robust sorption model was obtained covering a broad variety of geochemical settings over wide ranges of ionic strengths and groundwater compositions, which subsequently was validated by an independent original dataset. This model improves the understanding of U(VI) retention by clay minerals and enables now predictive modeling of U(VI) sorption processes in complex clay rich natural environments.

Keywords: argillaceous rock; surface complexation modeling; uranium; specific ion interaction theory (SIT); ATR FT-IR; TRLFS; 2SPNE SC/CE

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  • Secondary publication expected from 28.09.2022

Permalink: https://www.hzdr.de/publications/Publ-32796
Publ.-Id: 32796


Pharmacokinetic studies of [⁶⁸Ga]Ga‑PSMA‑11 in patients with biochemical recurrence of prostate cancer: detection, differences in temporal distribution and kinetic modelling by tissue type

Strauss, D. S.; Sachpekidis, C.; Kopka, K.; Pan, L.; Haberkorn, U.; Dimitrakopoulou‑Strauss, A.

Purpose: [⁶⁸Ga]Ga-PSMA-11 is a promising radiopharmaceutical for detecting tumour lesions in prostate cancer, but knowledge of the pharmacokinetics is limited. Dynamic PET-CT was performed to investigate the tumour detection and differences in temporal distribution, as well as in kinetic modelling of [⁶⁸Ga]Ga-PSMA-11 by tissue type.
Methods: Dynamic PET-CT over the lower abdomen and static whole-body PET-CT 80–90 min p.i. from 142 patients with biochemical recurrence were retrospectively analysed. Detection rates were compared to PSA levels. Average time-activity curves were calculated from tumour lesions and normal tissue. A three-compartment model and non-compartment model
were used to calculate tumour kinetics.
Results: Overall detection rate was 70.42%, and in patients with PSA > 0.4 ng/mL 76.67%. All tumour lesions presented the steepest standardised uptake value (SUV) incline in the first 7–8 min before decreasing to different degrees. Normal tissue presented with a low uptake, except for the bladder, which accumulated activity the steepest 15–16 min. p.i.. While all tumour
lesions continuously increased, bone metastases showed the steepest decline, resulting in a significantly lower SUV than lymph node metastases (60 and 80–90 min). Transport rate from the blood and tracer binding and internalisation rate were lower in bone metastases. Heterogeneity (fractal dimension) and vascular density were significantly lower in bone metastases.
Conclusion: Even at low PSA between 0.51 and 0.99 ng/mL, detection rate was 57%. Dynamic imaging showed a time window in the first 10 min where tumour uptake is high, but no bladder activity is measured, aiding accuracy in distinction of local recurrence. Kinetic modelling provided additional information for tumour characterisation by tissue type.

Keywords: Ga-PSMA; PSMA; PSMA Kinetic; Recurrent prostate cancer

Permalink: https://www.hzdr.de/publications/Publ-32794
Publ.-Id: 32794


Cation non-stoichiometry in Fe:SrTiO3 thin films and its effect on the electrical conductivity

Morgenbesser, M.; Taibl, S.; Kubicek, M.; Schmid, A.; Viernstein, A.; Bodenmüller, N.; Herzig, C.; Baiutti, F.; de Dios Sirvent, J.; Liedke, M. O.; Butterling, M.; Wagner, A.; Artner, W.; Limbeck, A.; Tarancon, A.; Fleig, J.

The interplay of structure, composition and electrical conductivity was investigated for Fe-doped SrTiO3 thin films prepared by pulsed laser deposition. Structural information was obtained by reciprocal space mapping while solution-based inductively-coupled plasma optical emission spectroscopy and positron annihilation lifetime spectroscopy were employed to reveal the cation composition and the predominant point defects of the thin films, respectively. A severe cation non-stoichiometry with Sr vacancies was found in films deposited from stoichiometric targets. The across plane electrical conductivity of such epitaxial films was studied in the temperature range of 250 - 720 °C by impedance spectroscopy. This revealed a pseudo-intrinsic electronic conductivity despite the substantial Fe acceptor doping, i.e. conductivities being several orders of magnitude lower than expected. Variation of PLD deposition parameters causes some changes of the cation stoichiometry, but the films still have conductivities much lower than expected. Targets with significant Sr excess (in the range of several percent) were employed to improve the cation stoichiometry in the films. The use of 7 % Sr-excess targets resulted in near-stoichiometric films with conductivities close to the stoichiometric bulk counterpart. The measurements show that a fine-tuning of the film stoichiometry is required in order to obtain acceptor doped SrTiO3 thin films with bulk-like properties. One can conclude that, although RSM experiments give a first hint whether or not cation non-stoichiometry is present, conductivity measurements are more appropriate for assessing SrTiO3 film quality in terms of cation stoichiometry.

Keywords: SrTiO3 thin films; pulsed laser deposition; structure-property relations; cationic non-stoichiometry; positron annihilation spectroscopy

Permalink: https://www.hzdr.de/publications/Publ-32792
Publ.-Id: 32792


Exploring the anti-site disorder and oxygen vacancies in Sr₂FeMoO₆ thin films

Saloaro, M.; Liedke, M. O.; Angervoa, I.; Butterling, M.; Hirschmann, E.; Wagner, A.; Huhtinen, H.; Paturi, P.

To address the importance of nanoscale defects in complex magnetic oxides, we present an effective tool, variable energy positron annihilation spectroscopy, for probing the relatively small changes in anti-site disorder and oxygen vacancies of the in situ annealed double perovskite Sr₂FeMoO₆ thin films. By controlling the annealing conditions in wide pressure and temperature ranges and thus affecting the amount of nanoscale defects, we show that the magnetic properties of Sr₂FeMoO₆ thin films can be modified, particularly with the oxygen nonstoichiometry, and hence their spintronic functionality can be improved. On the basis of our findings together with proposed mechanism, we suggest that the annealing treatments can also be scaled to other complex magnetic perovskites to engineer nanoscale defects and thus improve their usability in future spintronic applications.

Keywords: spintronics; SFMO; defect engineering; oxygen vacancy; positron annihilation spectroscopy; magnetic properties; anti-site disorder

Permalink: https://www.hzdr.de/publications/Publ-32789
Publ.-Id: 32789


An Introduction to the Materials Learning Algorithms Package (MALA)

Fiedler, L.; Cangi, A.; Ellis, J. A.; Rajamanickam, S.

Density Functional Theory (DFT) is one of the most popular quantum mechanical simulation methods, since it balances sufficient accuracy with reasonable computational cost. It is often used in material science applications at ambient and extreme conditions. Nonetheless, DFT approaches its limits in terms of computational feasbility when faced with simulation problems at larger time and length scales, especially at temperatures >> 0K. Surrogate models based on neural networks can circumvent these limitations. By training a neural network to predict properties of interest (total energy, atomic forces) based on atomic configurations, predictions with DFT-like accuracy can be done at a fraction of the computational cost.
To facilitate the creation and usage of these surrogate models, the Materials Learning Algorithms package (MALA) provides modular open-source toolbox that allows users to preprocess of DFT data, train models and postprocess model predictions using only a few lines of code. MALA is jointly developed by the Center for Advanced Systems Understanding (CASUS), Sandia National Laboratories (SNL) and Oak Ridge National Laboratory (ORNL).

Keywords: Density Functional Theory; Machine Learning

Permalink: https://www.hzdr.de/publications/Publ-32788
Publ.-Id: 32788


Imaging neutron capture cross sections: i-TED proof-of-concept and future prospects based on Machine-Learning techniques.

Babiano-Suárez, V.; Lerendegui-Marco, J.; Balibrea-Correa, J.; Caballero, L.; Calvo, D.; Ladarescu, I.; Real, D.; Domingo-Pardo, C.; Calviño, F.; Casanovas, A.; Tarifeño-Saldivia, A.; Alcayne, V.; Guerrero, C.; Millán-Callado, M. A.; Rodriguez-González, T.; Barbagallo, M.; Aberle, O.; Amaducci, S.; Andrzejewski, J.; Audouin, L.; Bacak, M.; Bennett, S.; Berthoumieux, E.; Billowes, J.; Bosnar, D.; Brown, A.; Busso, M.; Caamaño, M.; Calviani, M.; Cano-Ott, D.; Cerutti, F.; Chiaveri, E.; Colonna, N.; Cortés, G.; Cortés-Giraldo, M. A.; Cosentino, L.; Cristallo, S.; Damone, L. A.; Davies, P. J.; Diakaki, M.; Dietz, M.; Dressler, R.; Ducasse, Q.; Dupont, E.; Durán, I.; Eleme, Z.; Fernández-Dominguez, B.; Ferrari, A.; Finocchiaro, P.; Furman, V.; Göbel, K.; Garg, R.; Gawlik, A.; Gilardoni, S.; Gonçalves, I. F.; González-Romero, E.; Gunsing, F.; Harada, H.; Heinitz, S.; Heyse, J.; Jenkins, D. G.; Junghans, A.; Käppeler, F.; Kadi, Y.; Kimura, A.; Knapova, I.; Kokkoris, M.; Kopatch, Y.; Krtička, M.; Kurtulgil, D.; Lederer-Woods, C.; Leeb, H.; Lonsdale, S. J.; Macina, D.; Manna, A.; Martinez, T.; Masi, A.; Massimi, C.; Mastinu, P.; Mastromarco, M.; Maugeri, E. A.; Mazzone, A.; Mendoza, E.; Mengoni, A.; Michalopoulou, V.; Milazzo, P. M.; Mingrone, F.; Moreno-Soto, J.; Musumarra, A.; Negret, A.; Ogállar, F.; Oprea, A.; Patronis, N.; Pavlik, A.; Perkowski, J.; Persanti, L.; Petrone, C.; Pirovano, E.; Porras, I.; Praena, J.; Quesada, J. M.; Ramos-Doval, D.; Rauscher, T.; Reifarth, R.; Rochman, D.; Rubbia, C.; Sabaté-Gilarte, M.; Saxena, A.; Schillebeeckx, P.; Schumann, D.; Sekhar, A.; Smith, A. G.; Sosnin, N. V.; Sprung, P.; Stamatopoulos, A.; Tagliente, G.; Tain, J. L.; Tassan-Got, L.; Thomas, T.; Torres-Sánchez, P.; Tsinganis, A.; Ulrich, J.; Urlaß, S.; Valenta, S.; Vannini, G.; Variale, V.; Vaz, P.; Ventura, A.; Vescovi, D.; Vlachoudis, V.; Vlastou, R.; Wallner, A.; Woods, P. J.; Wright, T.; Žugec, P.

i-TED is an innovative detection system which exploits Compton imaging techniques to achieve a superior signal-to-background ratio in (n, γ ) cross-section measurements using time-of-flight technique. This work presents the first experimental validation of the i-TED apparatus for highresolution time-of-flight experiments and demonstrates for the first time the concept proposed for background rejection. To this aim, the 197 Au(n, γ ) and 56 Fe(n, γ ) reactions were studied at CERN n_TOF using an i-TED demonstrator based on three position-sensitive detectors. Two C6 D6 detectors were also used to benchmark the performance of i-TED. The i-TED prototype built for this study shows a factor of ∼3 higher detection sensitivity than state-of-the-art C6 D6 detectors in the 10 keV neutron-energy region of astrophysical interest. This paper explores also the perspectives of further enhancement in performance attainable with the final i-TED array consisting of twenty position-sensitive detectors and new analysis methodologies based on Machine-Learning techniques.

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Permalink: https://www.hzdr.de/publications/Publ-32787
Publ.-Id: 32787


First Results of the 140Ce(n,gamma)141Ce Cross-Section Measurement at n_TOF

Amaducci, S.; Colonna, N.; Cosentino, L.; Cristallo, S.; Finocchiaro, P.; Krtička, M.; Massimi, C.; Mastromarco, M.; Mazzone, A.; Mengoni, A.; Valenta, S.; Aberle, O.; Alcayne, V.; Andrzejewski, J.; Audouin, L.; Babiano-Suarez, V.; Bacak, M.; Barbagallo, M.; Bennett, S.; Berthoumieux, E.; Billowes, J.; Bosnar, D.; Brown, A.; Busso, M.; Caamaño, M.; Caballero-Ontanaya, L.; Calviño, F.; Calviani, M.; Cano-Ott, D.; Casanovas, A.; Cerutti, F.; Chiaveri, E.; Cortés, G.; Cortés-Giraldo, M.; Damone, L.-A.; Davies, P.-J.; Diakaki, M.; Dietz, M.; Domingo-Pardo, C.; Dressler, R.; Ducasse, Q.; Dupont, E.; Durán, I.; Eleme, Z.; Fernández-Dominguez, B.; Ferrari, A.; Furman, V.; Göbel, K.; Garg, R.; Gawlik, A.; Gilardoni, S.; Gonçalves, I.; González-Romero, E.; Guerrero, C.; Gunsing, F.; Harada, H.; Heinitz, S.; Heyse, J.; Jenkins, D.; Junghans, A.; Käppeler, F.; Kadi, Y.; Kimura, A.; Knapova, I.; Kokkoris, M.; Kopatch, Y.; Kurtulgil, D.; Ladarescu, I.; Lederer-Woods, C.; Leeb, H.; Lerendegui-Marco, J.; Lonsdale, S.-J.; Macina, D.; Manna, A.; Martinez, T.; Masi, A.; Mastinu, P.; Maugeri, E.-A.; Mendoza, E.; Michalopoulou, V.; Milazzo, P.; Mingrone, F.; Moreno-Soto, J.; Musumarra, A.; Negret, A.; Ogállar, F.; Oprea, A.; Patronis, N.; Pavlik, A.; Perkowski, J.; Piersanti, L.; Petrone, C.; Pirovano, E.; Porras, I.; Praena, J.; Quesada, J.-M.; Ramos-Doval, D.; Rauscher, T.; Reifarth, R.; Rochman, D.; Rubbia, C.; Sabaté-Gilarte, M.; Saxena, A.; Schillebeeckx, P.; Schumann, D.; Sekhar, A.; Smith, G.; Sosnin, N.; Sprung, P.; Stamatopoulos, A.; Tagliente, G.; Tain, J.; Tarifeño-Saldivia, A.; Tassan-Got, L.; Thomas, B.; Torres-Sánchez, P.; Tsinganis, A.; Ulrich, J.; Urlaß, S.; Vannini, G.; Variale, V.; Vaz, P.; Ventura, A.; Vescovi, D.; Vlachoudis, V.; Vlastou, R.; Wallner, A.; Woods, P.; Wright, T.; Žugec, P.

An accurate measurement of the 140Ce(n,g) energy-dependent cross-section was performed
at the n_TOF facility at CERN. This cross-section is of great importance because it represents a
bottleneck for the s-process nucleosynthesis and determines to a large extent the cerium abundance in
stars. The measurement was motivated by the significant difference between the cerium abundance
measured in globular clusters and the value predicted by theoretical stellar models. This discrepancy
can be ascribed to an overestimation of the 140Ce capture cross-section due to a lack of accurate
nuclear data. For this measurement, we used a sample of cerium oxide enriched in 140Ce to 99.4%.
The experimental apparatus consisted of four deuterated benzene liquid scintillator detectors, which
allowed us to overcome the difficulties present in the previous measurements, thanks to their very
low neutron sensitivity. The accurate analysis of the p-wave resonances and the calculation of their
average parameters are fundamental to improve the evaluation of the 140Ce Maxwellian-averaged
cross-section.

Keywords: cerium; 140Ce; neutron capture; cross-section; n_TOF; MACS; nucleosynthesis

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Permalink: https://www.hzdr.de/publications/Publ-32785
Publ.-Id: 32785


Detecting bacterial cell viability in few μl solutions from impedance measurements on silicon‐based biochips

Bhat, V. J.; Vegesna, S. V.; Kiani, M.; Zhao, X.; Blaschke, D.; Du, N.; Vogel, M.; Kluge, S.; Raff, J.; Hubner, U.; Skorupa, I.; Rebohle, L.; Schmidt, H.

Using two different types of impedance biochips (PS5 and BS5) with ring top electrodes, a distinct change of measured impedance has been detected after adding 1–5 μL (with dead or live Gram‐positive Lysinibacillus sphaericus JG‐A12 cells to 20 μL DI water inside the ring top electrode. We relate observed change of measured impedance to change of membrane potential of L. sphaericus JG‐A12 cells. In contrast to impedance measurements, optical density (OD) measurements cannot be used to distinguish between dead and live cells. Dead L. sphaericus JG‐A12 cells have been obtained by adding 0.02 mg/mL of the antibiotics tetracycline and 0.1 mg/mL chloramphenicol to a batch with OD0.5 and by incubation for 24 h, 30 °C, 120 rpm in the dark. For impedance measurements, we have used batches with a cell density of 25.5 × 10⁸ cells/mL (OD8.5) and 270.0 × 10⁸ cells/mL (OD90.0). The impedance biochip PS5 can be used to detect the more resistive and less capacitive live L. sphaericus JG‐A12 cells. Also, the impedance biochip BS5 can be used to detect the less resistive and more capacitive dead L. sphaericus JG‐A12 cells. An outlook on the application of the impedance biochips for high‐throughput drug screening, e.g., against multi‐drug‐resistant Gram‐positive bacteria, is given.

Keywords: Cell viability; Dead bacterial cells; Dead bacterial cells; Impedance biochips; Live bacterial cells; Lysinibacillus sphaericus; Membrane potential

Related publications

Permalink: https://www.hzdr.de/publications/Publ-32782
Publ.-Id: 32782


Creep Properties of 9Cr and 14Cr ODS Tubes Tested by Inner Gas Pressure

Sornin, D.; Ehrnsten, U.; Mozzani, N.; Rantala, J.; Walter, M.; Hobt, A.; Aktaa, J.; Onorbe, E.; Hernandez-Mayoral, M.; Ulbricht, A.; Gicquel, S.; Frank, L.; de Carlan, Y.

Oxide-dispersion strengthened steels are promising materials for extreme service conditions including nuclear reactors core. In service conditions, nuclear fuel claddings are exposed to the fission gas pressure at temperatures about 700°C. This paper presents novel results on ODS creep properties from a round robin of inner gas pressure creep test. A gas pressure creep test, simulating fission gas loading, was designed and achieved by four different European teams. Lifetime and specific behavior of ODS steel tube are prospected. Based on a mechanical clamping achieving gas tightness, short length tubes samples are tested by different laboratories. In situ laser measurements exhibit the radial expansion of ODS steel tubes before failure. Post-mortem, geometrical characterizations are performed to determine hoop strains at failure. A consistent creep lifetime is observed by all the teams even with slightly different testing apparatus and clamping systems. Under inner gas pressure, ODS steels exhibit a typical failure by leakage associated to a very small radial expansion. This behavior results from a brutal failure (burst) without evidence of tertiary creep stage. This failure mode of ODS cladding in creep conditions is consistently observed on all samples of the study. Inner gas pressure creep tests were compared, for the first time, by four European laboratories on ODS steel tube. This technique, simulating the fission gas pressure loading, is applied on small and mechanically clamped samples. This technique shows a remarkable consistency between the different laboratories results and demonstrates to be efficient for ODS steel cladding tube qualification. The results show a correlation between the creep properties and the microstructure.

Keywords: ODS steel; Tube creep test; Inner gas pressure

Permalink: https://www.hzdr.de/publications/Publ-32777
Publ.-Id: 32777


Mechanically flexible magnetoelectronics for human-machine interfaces and soft robotics

Makarov, D.

In this presentation I review our activities on flexible, printable and stretchable functional elements for human-machine interfaces, interactive electronics, soft robotics and cancer research.

Keywords: flexible magnetic field sensors; printable magentic field sensors; flexible heater

  • Invited lecture (Conferences) (Online presentation)
    International School on Programmable Smart Sensors based on Bio-compatible Nanocomposite Materials (NanoSens), 17.-24.06.2021, Chemnitz, Germany

Permalink: https://www.hzdr.de/publications/Publ-32775
Publ.-Id: 32775


Self-discharge mitigation in a liquid metal displacement battery

Mushtaq, K.; Zhao, J.; Weber, N.; Mendes, A.; Sadoway, D. R.

Recently, a disruptive idea was reported about the discovery of a new type of battery named Liquid Displacement Battery (LDB) comprising liquid metal electrodes and molten salt electrolyte. This cell featured a novel concept of a porous electronically conductive faradaic membrane instead of the traditional ion-selective ceramic membrane. LDBs are attractive for stationary storage applications but need mitigation against self-discharge. In the instant battery chemistry, Li|LiCl-PbCl2|Pb, reducing the diffusion coefficient of lead ions can be a way forward and a solution can be the addition of PbO to the electrolyte. The latter acts as a supplementary barrier and complements the function of the faradaic membrane. The remedial actions improved the cell’s coulombic efficiency from 92% to 97% without affecting the voltage efficiency. In addition, the limiting current density of a 500 mAh cell increased from 575 to 831 mA/cm² and the limiting power from 2.53 to 3.66 W. Finally, the effect of PbO on the impedance and polarization of the cell was also studied.

Permalink: https://www.hzdr.de/publications/Publ-32771
Publ.-Id: 32771


Nonreciprocity of spin waves in magnetic nanotubes with helical equilibrium magnetization

Salazar-Cardona, M. M.; Körber, L.; Schultheiß, H.; Lenz, K.; Thomas, A.; Nielsch, K.; Kakay, A.; Otálora, J. A.

Spin waves (SWs) in magnetic nanotubes have shown interesting nonreciprocal properties in their dispersion relation, group velocity, frequency linewidth, and attenuation lengths. The reported chiral effects are similar to those induced by the Dzyaloshinskii–Moriya interaction but originating from the dipole–dipole interaction. Here, we show that the isotropic-exchange interaction can also induce chiral effects in the SW transport; the so-called Berry phase of SWs. We demonstrate that with the application of magnetic fields, the nonreciprocity of the different SW modes can be tuned between the fully dipolar governed and the fully exchange governed cases, as they are directly related to the underlying equilibrium state. In the helical state, due to the combined action of the two effects, every single sign combination of the azimuthal and axial wave vectors leads to different dispersions, allowing for a very sophisticated tuning of the SW transport. A disentangle- ment of the dipole–dipole and exchange contributions so far was not reported for the SW transport in nanotubes. Furthermore, we propose a device based on coplanar waveguides that would allow to selectively measure the exchange or dipole induced SW nonreciprocities. In the context of magnonic applications, our results might encourage further developments in the emerging field of 3D magnonic devices using curved magnetic membranes.

Keywords: spin wave; nanotube; nonreciprocity; transducer

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  • Secondary publication expected from 30.06.2022

Permalink: https://www.hzdr.de/publications/Publ-32767
Publ.-Id: 32767


An introduction to Automatic Differentiation with theory and code examples.

Schmerler, S.

An introduction to Automatic Differentiation with theory and code examples.

Permalink: https://www.hzdr.de/publications/Publ-32764
Publ.-Id: 32764


Taxonomic and Metabolic Profiling for Microbial Communities in Opalinus Clay Rocks from Deep Subsurface Biosphere

Wei, T.-S.; Kluge, S.; Schleicher, A.; Des Los Rios, A.; Cherkouk, A.

Background: Microorganisms in deep terrestrial subsurface harbor unique metabolic traits due to insufficient sunlight, oxygen and organic carbons. Previous studies reported that in the porewaters from boreholes of Opalinus clay rocks under a deep geological repository (DGR), autotrophoic H2-oxidizing sulfate-reducing bacteria (SRB)—Peptococcaceae, Desulfatialea and Desulfobulbaceae—together with other heterotrophic and fermentative bacteria were able to alleviate the H2 pressure accumulated from the process during anoxic corrosion of steel containers for nuclear wastes. Objective and Method: What remains elusive is whether these microorganisms are porewater- or rock-origin. Thus, we re-analyzed the above-mentioned porewater communities based on the amplicon sequence variant (ASV) instead of operational taxonomic unit clustering. In addition, two cores of Opalinus rocks were collected in November of 2019. The extracted DNA/RNA from these rock samples will be subjected to 16S amplicon sequencing, metagenome and metatransctriptome to investigate microbial diversity and metabolisms; microbial colonization will also be examined via scanning electron microscopy. Result: Our principal coordinates analysis indicated that the community structure of original porewaters between different boreholes were significantly distinct in the same DGR site. Moreover, the chao1 diversity index suggested that some rare biosphere may thrive in the H2-spiked communities. The differential analysis further showed that up to 213 ASVs were significantly enriched in the H2-injected porewater communities, mainly belonging to Proteobacteria, Firmicutes, Desulfobacterota, and Bacteroidota. This ASV-resolute analysis indicated that bacteria involved in this microbial loop is more complex than previously appreciated. Besides, the preliminary results showed the DNA content of newly collected Opalinus rocks was extremely low based on Qubit quantification (0.57 ± 0.07 to 0.61 ± 0.04 ng/g of clay), whereas the total RNA was not quantifiable via Qubit. Despite this, the V4 region of 16S rRNA gene was able to be amplified, indicating the presence of microorganisms with low biomass. In future, 16S amplicon sequences from rocks will be analyzed together with porewater communities. The DNA will be applied to multiple displacement amplification prior to metagenome sequencing. The understanding of microbial ecology in deep subsurface not only benefits nuclear wastes management but also underpins the notion of evolutionary and astrobiology.

Keywords: microbial ecology; metagenome; nuclear waste management; deep subsurface biosphere

  • Poster (Online presentation)
    World Microbe Forum 2021, 20.-24.06.2021, Online, USA

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Permalink: https://www.hzdr.de/publications/Publ-32761
Publ.-Id: 32761


The effect of UV-C irradiation and EDTA on the uptake of Co2+ by antimony oxide in the presence and absence of competing cations Ca2+ and Ni2+

Malinen, L.; Repo, E.; Harjula, R.; Huittinen, N.

In nuclear power plants and other nuclear facilities the removal of cobalt from radioactive liquid waste is needed to reduce the radioactivity concentration in effluents. In liquid wastes containing strong organic complexing agents such as EDTA cobalt removal can be problematic due to the high stability of the Co-EDTA complex. In this study, the removal of cobalt from NaNO3 solutions using antimony oxide (Sb2O3) synthesized from potassium hexahydroxoantimonate was investigated in the absence and presence of EDTA. The uptake studies on the ion exchange material were conducted both in the dark (absence of UV-light) and under UV-C irradiation. Ca2+ or Ni2+ were included in the experiments as competing cations to test the selectivity of the ion exchanger. Results show that UV-C irradiation noticeably enhances the cobalt sorption efficiency on the antimony oxide. It was shown that nickel decreased the sorption of cobalt to a higher extent than calcium. Finally, the sorption data collected for Co2+ on antimony oxide was modeled using six different isotherm models. The Sips model was found to be the most suitable model to describe the sorption process. The Dubinin-Radushkevich model was further used to calculate the adsorption energy, which was found to be 6.2 kJ mol-1.

Keywords: cobalt; EDTA; sorption; antimony oxide; UV-C; competing cations

Permalink: https://www.hzdr.de/publications/Publ-32756
Publ.-Id: 32756


First experiments with two new diffractometers at the Rossendorf Beamline/ESRF

Hennig, C.; Svitlyk, V.

The Institute of Resource Ecology / HZDR is operating the Rossendorf Beamline (ROBL/BM20) at the ESRF for over 20 years. A second experimental hutch with two diffractometers for single crystal, powder and surface diffraction has been constructed in the last two years. As CRG beamline provides ROBL 1/3 of its beam time via the ESRF proposal system to the user community, whereas 2/3 are reserved for in-house research.
One diffractometer is a 6-circle Huber diffractometer with Eulerian cradle geometry (XRD-1). It will be used for high-resolution powder diffraction and surface diffraction. Powder diffraction measurements will be performed with a Pilatus 100k Si or an Eiger CdTe 500k detector mounted on the detector arm. The Bragg reflexes are extracted by radial integration using a modified pyFAI code.
The diffractometer for single crystal diffraction and in situ diffraction measurements (XRD-2) is equipped with a Pilatus3 X 2M detector. Diffraction measurements can be combined simultaneously with XANES and XRF spectroscopy. The setup comprises a cryo stream cooler (80-400 K) and a heater (up to 1200 K). The diffractometer is controlled with the Pylatus software and the single crystal data extraction is performed with CrysAlisPro.
We will report the first experiments performed on the two diffractometers.

Keywords: powder diffraction; single crystal diffraction; surface diffraction

  • Poster (Online presentation)
    Conference Association Française de Cristallographie 2021, 29.06.-02.07.2021, Grenoble, France

Permalink: https://www.hzdr.de/publications/Publ-32754
Publ.-Id: 32754


Aufbau einer Versuchsanlage mit superkritischen Kohlenstoffdioxid (sCO2) als Arbeitsmedium in Kraftkreisläufen

Unger, S.; Fogel, S.; Rath, S.; Gampe, U.; Hampel, U.

Der Großteil elektrischer Energieerzeugung erfolgt durch thermische Kraftkreisläufe, welche durch eine Wärmequelle versorgt werden. Hierbei werden zwei Typen kommerzieller Anlagen betrieben, der offene direkt befeuerte Brayton oder Joule-Kreislauf (bsp. Gasturbinenkreisläufe) und der geschlossene indirekt befeuerte Rankine-Kreislauf (Dampfkreislauf). Neben diesen konventionellen Kraftkreisläufen existiert seit einigen Jahren, basierend auf den Brayton-Kreislauf, ein innovatives Konzept mit superkritischen Kohlenstoffdioxid (sCO2) als Arbeitsmedium. Zahlreiche Studien haben gezeigt, dass sCO2 Kreisläufe das Potential haben, höhere Wirkungsgrade zu erreichen, einen niedrigeren Brennstoff- und Wasserverbrauch zu erzielen (Subbaraman et al., 2011; Kacludis et al., 2012; Shelton et al., 2016). SCO2 kombiniert den Vorteil der hohen Dichte von Flüssigkeiten und die niedrige Viskosität von Gasen, sodass geringere Komponentengrößen, kleinere Footprints der Gesamtanlage und damit niedrigere Kapitalkosten möglich sind.
Bei der Prozessführung wird zwischen dem offenen und dem geschlossenen sCO2 Brayton-Kreislauf unterschieden. Bei einem geschlossenen Kreislauf wird sCO2 nahe des kritischen Punktes (ca. 31 °C und 74 bar) verdichtet, in einem Rekuperator vorgewärmt, in einem Erhitzer durch die Wärmequelle aufgeheizt, in einer Expansionsturbine entspannt, durch den Rekuperator auf der Gegenseite geführt und anschließend bis nahe des kritischen Punktes zurückgekühlt, um den Kreislauf erneut zu beginnen. Dieser Prozess kann für unterschiedlichste Wärmequellen, wie fossile Kraftstoffe, Kernenergie, industrielle Abwärme, Geothermie oder Solarstrahlung eingesetzt werden. Der offene Kreislauf adressiert dagegen höhere Temperaturen und wird üblicherweise für eine Sauerstoffverbrennung untersucht. Dabei wird ein Sauerstoff-Methan-Gemisch bei hohen Druck und hoher Temperatur verbrannt. Das Rauchgas wird dann, vermischt mit großen Mengen sCO2, in einer Turbine entspannt. Das sCO2-Wasserdampf-Gemisch wird ebenfalls in einem Rekuperator genutzt, um anschließend Wasser sowie kleine Mengen CO2 mittels Kondensation sowie Abtrennung aus dem Kreislauf zu entfernen. Der verbleibende sCO2-Strom wird erneut dem Verbrennungsprozess zugeführt. Dieser offene Kreislauf ist besonders attraktiv, um Erdgas, synthetisch erzeugte Gase oder vergaste Kohle zu nutzen. Verglichen mit dem geschlossenen Kreislauf können hier noch höhere Wirkungsgrade und Leistungsdichten erreicht werden.
Um diese Kraftwerkskonzepte sowie die dafür notwendigen Komponenten auf einer experimentellen Basis untersuchen zu können, wurde das Projekt CARBOSOLA in Zusammenarbeit mit der TU Dresden, dem DLR und der Siemens Energy AG initiiert. Inhalt dieses Projektes ist unter anderem der Aufbau einer Versuchsanlage am HZDR, zur Untersuchung von sCO2 bei bis zu 650 °C, bei gleichzeitig 300 bar und einem Massenstrom bis zu 3,3 kg/s. Die damit verbundenen Herausforderungen und Lösungen werden erläutert.

Keywords: superkritischen Kohlenstoffdioxid; Energieumwandlung; hohe Wirkungsgrade; CARBOSOLA

  • Lecture (Conference)
    53. KRAFTWERKSTECHNISCHES KOLLOQUIUM, 05.-06.10.2021, Dresden, Deutschland
  • Contribution to proceedings
    53. KRAFTWERKSTECHNISCHES KOLLOQUIUM, 05.-06.10.2021, Dresden, Deutschland
    Proceedings des 53. KRAFTWERKSTECHNISCHEN KOLLOQUIUMS

Permalink: https://www.hzdr.de/publications/Publ-32751
Publ.-Id: 32751


Inverting the Beamline

Steinbach, P.

In many domains of modern physics, we encounter the situation that generations of scientists have created high precision simulations of the effects under study. Today, these simulations have become essential to the scientific method. However, these
(often mechanistic) simulations of high predictive power carry with them a burden of inference. Once a forward process has been simulated, an inversion of a simulation given observed data from experiments is challenging, sometimes even impossible.

In this presentation, I'd like to provide an introduction to simulation based inference for inverting a beamline simulation at BESSY in Berlin. In this project, I studied the inversion of a beamline simulation using state-of-the-art machine learning. We will start our journey with normalizing flows, walk by conditional invertible neural networks and finish with Automatic Posterior Transformation for Likelihood-Free Inference. To stay with the metaphor: please bring your mathematical boots, wear a hat of Bayes Law and bring your best compass of statistics - otherwise you likely get lost in about a quarter of the presentation.

Keywords: beamline; simulation; normalizing flows; posterior; inverse problem; machine learning

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Permalink: https://www.hzdr.de/publications/Publ-32750
Publ.-Id: 32750


Indikatoren für Open Science: Report des Helmholtz Open Science Forum

Ferguson, L. M.; Pampel, H.; Bertelmann, R.; Dirnagl, U.; Zohbi, J.; Kapitza, D.; Keup-Thiel, E.; Konrad, U.; Lorenz, S.; Mittermaier, B.; Rechid, D.; Schuck-Zöller, S.

Open Access, Open Research Data und Open Research Software: Diese Themen prägen die aktuellen Diskussionen zu Open Science in der Helmholtz-Gemeinschaft. Doch an welchen Indikatoren lässt sich der Kulturwandel hin zu Open Science festmachen? Und welche Anreize setzen Indikatoren für die Entwicklung von Open Access? Diesen und weiteren Fragen widmete sich das virtuelle Helmholtz Open Science Forum unter dem Motto „Indikatoren für Open Science“ am 20. Januar 2021. Im Zuge der Veranstaltung wurden anhand von Impuls- und Praxisvorträgen Indikatoren für Open Science vorgestellt, untersucht und mit einem breiten Publikum aus der Helmholtz-Gemeinschaft diskutiert. Dieser Report fasst die Vorträge und Diskussionen des Forums zusammen und bietet eine Basis für weitere Entwicklungen des Themenfeldes in der Gemeinschaft.

Keywords: Open Access; Softwareentwicklung; Software Development; Indikatoren; Indicators; Helmholtz Gemeinschaft; Open Science

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Permalink: https://www.hzdr.de/publications/Publ-32748
Publ.-Id: 32748


Chirality Remote Control in Nanoporous Materials by Circularly Polarized Light

Kanj, A. B.; Bürck, J.; Vankova, N.; Li, C.; Mutruc, D.; Chandresh, A.; Hecht, S.; Heine, T.; Heinke, L.

The ability to dynamically control chirality remains a grand challenge in chemistry. Although many molecules possess chiral isomers, lacking their isolation, for instance during photoisomerization, results in racemic mixtures with suppressed enantiospecific chiral properties. Here, we present a nanoporous solid in which chirality and enantioselective enrichment is induced by circularly polarized light (CPL). The material is based on photoswitchable fluorinated azobenzenes attached to the scaffold of a crystalline metal–organic framework (MOF). The azobenzene undergoes trans-to-cis-photoisomerization upon irradiation with green light and reverts back to trans upon violet light. While each moiety in cis conformation is chiral, we show the trans isomer also possesses a nonplanar, chiral conformation. During photoisomerization with unpolarized light, no enantiomeric enrichment is observed and both isomers, R- and S-cis as well as R- and S-trans, respectively, are formed in identical quantities. In contrast, CPL causes chiral photoresolution, resulting in an optically active material. Right-CPL selectively excites R-cis and R-trans enantiomers, producing a MOF with enriched S-enantiomers, and vice versa. The induction of optical activity is reversible and only depends on the light-handedness. As shown by first-principle DFT calculations, while both, trans and cis, are stabilized in nonplanar, chiral conformations in the MOF, the trans isomer adopts a planar, achiral form in solution, as verified experimentally. This shows that the chiral photoresolution is enabled by the linker reticulation in the MOF. Our study demonstrates the induction of chirality and optical activity in solid materials by CPL and opens new opportunities for chiral resolution and information storage with CPL.

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  • Secondary publication expected from 29.04.2022

Permalink: https://www.hzdr.de/publications/Publ-32747
Publ.-Id: 32747


Hermes Project Poster

Druskat, S.; Schlauch, T.; Bertuch, O.; Juckeland, G.; Knodel, O.

The goal of this project is to support researchers in publishing their research software, in a way that makes it findable, comprehensible, citable and reusable. The key to this is the creation, curation and deposit of rich metadata with software publications. To this end, the project will conceptualize, produce and provide well-documented, adoption-ready workflows with automation interfaces and reference implementations for InvenioRDM and Dataverse.

Keywords: research software; FAIR; software publication; metadata; workflows

  • Open Access Logo Poster (Online presentation)
    Info event for the second project call of the Helmholtz Incubator Platform Helmholtz Metadata Collaboration (HMC), 15.06.2021, Berlin, Germany

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Permalink: https://www.hzdr.de/publications/Publ-32746
Publ.-Id: 32746


Heliport Project Poster

Knodel, O.; Voigt, M.; Ufer, R.; Pape, D.; Lokamani, M.; Müller, S.; Gruber, T.; Juckeland, G.; Kaluza, M. C.; Hein, J.; Kessler, A.; Eckner, E.; Schuller, B.

The HELIPORT project aims at developing a platform which accommodates the complete life cycle of a scientific project and links all corresponding programs, systems and workflows to create a more FAIR and comprehensible project description.

Keywords: Data Management; Heliport; Metadata; Data provenance; FAIR

  • Open Access Logo Poster (Online presentation)
    Info event for the second project call of the Helmholtz Incubator Platform Helmholtz Metadata Collaboration (HMC), 15.06.2021, Berlin, Germany

Permalink: https://www.hzdr.de/publications/Publ-32745
Publ.-Id: 32745


Superradiant many-qubit absorption refrigerator

Kloc, M.; Meier, K.; Hadjikyriakos, K.; Schaller, G.

We show that the lower levels of a large-spin network with a collective anti-ferromagnetic interaction and collective couplings to three reservoirs may function as a quantum absorption refrigerator. In appropriate regimes, the steady-state cooling current of this refrigerator scales quadratically with the size of the working medium, i.e., the number of spins. The same scaling is observed for the noise and the entropy production rate.

Keywords: open quantum systems; collective interactions; quantum heat engine; quantum absorbtion refrigerator; Dicke superradiance

Permalink: https://www.hzdr.de/publications/Publ-32744
Publ.-Id: 32744


Non-equilibrium boundary driven quantum systems: models, methods and properties

Gabriel, T. L.; Dario, P.; Gernot, S.

Recent years have seen tremendous progress in the theoretical understanding of quantum systems driven dissipatively by coupling them to different baths at their edges. This was possible because of the concurrent advances in the models used to represent these systems, the methods employed, and the analysis of the emerging phenomenology. Here we aim to give a comprehensive review of these three integrated research directions. We first provide an overarching view of the models of boundary driven open quantum systems, both in the weak and strong coupling regimes. This is followed by a review of state-of-the-art analytical and numerical methods, both exact, perturbative and approximate. Finally, we discuss the transport properties of some paradigmatic one-dimensional chains, with an emphasis on disordered and quasiperiodic systems, the emergence of rectification and negative differential conductance, and the role of phase transitions.

Keywords: open quantum systems; quantum transport; phase transitions; local and global master equations; chain models

Permalink: https://www.hzdr.de/publications/Publ-32743
Publ.-Id: 32743


Validation of Serpent-SUBCHANFLOW-TRANSURANUS pin-by-pin burnup calculations using experimental data from the Temelín II VVER-1000 reactor

Garcia, M.; Vocka, R.; Tuominen, R.; Gommlich, A.; Leppanen, J.; Valtavirta, V.; Imke, U.; Ferraro, D.; van Uffelen, P.; Milisdorfer, L.; Sanchez-Espinoza, V.

This work deals with the validation of a high-fidelity multiphysics system coupling the Serpent 2 Monte Carlo neutron transport code with SUBCHANFLOW, a subchannel thermalhydraulics code, and TRANSURANUS, a fuel-performance analysis code. The results for a full-core pin-by-pin burnup calculation for the ninth operating cycle of the Temelín II VVER-1000 plant, which starts from a fresh core, are presented and assessed using experimental data. A good agreement is found comparing the critical boron concentration and a set of pin-level neutron flux profiles against measurements. In addition, the calculated axial and radial power distributions match closely the values reported by the core monitoring system. To demonstrate the modeling capabilities of the three-code coupling, pin-level neutronic, thermalhydraulic and thermomechanic results are shown as well. These studies are encompassed in the final phase of the EU Horizon 2020 McSAFE project, during which the Serpent-SUBCHANFLOW-TRANSURANUS system was developed. © 2021

Keywords: Fuel-performance analysis; High-fidelity multiphysics; Monte Carlo neutron transport; Pin-level burnup; Subchannel thermalhydraulics; VVER-1000

Permalink: https://www.hzdr.de/publications/Publ-32740
Publ.-Id: 32740


Morphology-Tunable Synthesis of Intrinsic Room-Temperature Ferromagnetic γ-Fe2O3 Nanoflakes

Jia, Z.; Wang, W.; Li, Z.; Sun, R.; Zhou, S.; Leonard Deepak, F.; Su, C.; Li, Y.; Wang, Z.

Intrinsic two-dimensional (2D) magnetic materials with room-temperature ferromagnetism and air stability are highly desirable for spintronic applications. However, the experimental observations of such 2D or ultrathin ferromagnetic materials are rarely reported owing to the scarcity of these materials in nature and for the intricacy in their synthesis. Here, we report a successful controllable growth of ultrathin γ-Fe2O3 nanoflakes with a variety of morphologies tunable by the growth temperature alone using a facile chemical vapor deposition method and demonstrate that all ultrathin nanoflakes still show intrinsic room-temperature ferromagnetism and a semiconducting nature. The γ-Fe2O3 nanoflakes epitaxially grown on α-Al2O3 substrates take a triangular shape at low temperature and develop gradually in lateral size, forming eventually a large-scale γ-Fe2O3 thin film as the growth time increases due to a thermodynamic control process. The morphology of the nanoflakes could be tuned from triangular to stellated, petaloid, and dendritic crystalloids in sequence with the rise of precursor temperature, revealing a growth process from thermodynamically to kinetically dominated control. Moreover, the petaloid and dendritic nanoflakes exhibit enhanced coercivity compared with the triangular and stellated nanoflakes, and all the nanoflakes with diverse shapes possess differing electrical conductivity. The findings of such ultrathin, air-stable, and room-temperature ferromagnetic γ-Fe2O3 nanoflakes with tunable shape and multifunctionality may offer guidance in synthesizing other non-layered magnetic materials for next-generation electronic and spintronic devices.

Keywords: γ-Fe2O3 nanoflakes; morphology tunable synthesis; room-temperature ferromagnetism; coercivity; resistivity

  • ACS Applied Materials and Interfaces 13(2021)20, 24051-24061
    Online First (2021) DOI: 10.1021/acsami.1c05342

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  • Secondary publication expected from 17.05.2022

Permalink: https://www.hzdr.de/publications/Publ-32739
Publ.-Id: 32739


The response of the accumulator plants Noccaea caerulescens, Noccaea goesingense and Plantago major towards the uranium

Burger, A.; Weidinger, M.; Baumann, N.; Vesely, A.; Lichtscheidl, I.

Uranium (U) is a naturally occurring metal; its environmental levels can be increased due to processes in the nuclear industry and fertilizer production. The transfer of U in the food chain from plants is associated with deleterious chemical and radiation effects. To date, limited information is available about U toxicity on plant physiology. This study investigates the responses of metal-accumulating plants to different concentrations of U. The plants Noccaea caerulescens and Noccaea goesingense are known as metal hyperaccumulators and therefore could serve as candidates for the phytoremediation of radioactive hotspots; Plantago major is a widely used pharmaceutical plant that pioneers polluted grounds and therefore should not contain high concentrations of toxic elements. The experimental plants were grown hydroponically at U concentrations between 1 μM and 10 mM. The content of U and essential elements was analyzed in roots and leaves by ICP-MS. The amount of accumulated U was influenced by its concentration in the hydroponics. Roots contained most of the metal, whereas less was transported up to the leaves, with the exception of N. goesingense in a medium concentration of U. U also influenced the nutrient profile of the plants. We localized the U in plant tissues using EDX in the SEM. U was evenly distributed in roots and leaves of Noccaea species, with one exception in the roots of N. goesingense, where the central cylinder contained more U than the cortex. The toxicity of U was assessed by measuring growth and photosynthetic parameters. While root biomass of N. caerulescens was not affected by U, root biomass of N. goesingense decreased significantly at high U concentrations of 0.1 and 10 mM and root biomass of P. major decreased at 10 mM U. Dry weight of leaves was decreased at different U concentrations in the three plant species; a promotive effect was observed in N. caerulescens at lowest concentration offered. Chlorophyll a fluorescence was not affected or negatively affected by U in both Noccaea species, whereas in Plantago also positive effects were observed. Our results show that the impact of U on Plantago and Noccaea relates to its external concentration and to the plant species. When growing in contaminated areas, P. major should not be used for medicinal purpose. Noccaea species and P. major could immobilize U in their rhizosphere in hotspots contaminated by U, and they could extract limited amounts of U into their leaves.

Keywords: Accumulation; Chemotoxicity; Distribution; Localization; Uptake; Uranium

Permalink: https://www.hzdr.de/publications/Publ-32738
Publ.-Id: 32738


High-field spin-flop state in green dioptase

Prokhnenko, O.; Marmorini, G.; Nikitin, S. E.; Yamamoto, D.; Gazizulina, A.; Bartkowiak, M.; Ponomaryov, O.; Zvyagin, S.; Nojiri, H.; Diaz-Ortega, I. F.; Anovitz, L. M.; Kolesnikov, A. I.; Podlesnyak, A.

The high-field magnetic properties and magnetic order of the gem mineral green dioptase Cu6[Si6O18] · 6H2O have been studied by means of single-crystal neutron diffraction in magnetic fields up to 21 T and magnetization measurements up to 30 T. In zero field, the Cu2+ moments in the antiferromagnetic chains are oriented along the c axis with a small off-axis tilt. For a field applied parallel to the c axis, the magnetization shows a spin-flop-like transition at B = 12.2 T at 1.5 K. Neutron diffraction experiments show a smooth behavior in the intensities of the magnetic reflections without any change in the periodicity of the magnetic structure. Bulk and microscopic observations are well described by a model of ferromagnetically coupled antiferromagnetic XXZ spin- 1/2 chains, taking into account a change of the local easy-axis direction.We demonstrate that the magnetic structure evolves smoothly from a deformed Néel state at low fields to a deformed spin-flop state in a high field via a strong crossover around B. The results are generalized for different values of interchain coupling and spin anisotropy.

Permalink: https://www.hzdr.de/publications/Publ-32736
Publ.-Id: 32736


Joint project: Geochemical retention of radionuclides on cement alteration phases (GRaZ) - Subproject B

Schmeide, K.; Philipp, T.; Wolter, J.-M.; Kretzschmar, J.; Dullies, P.; Lippold, H.; Schymura, S.; Stumpf, T.

The report summarizes the results obtained by the Institute of Resource Ecology of the Helmholtz-Zentrum Dresden-Rossendorf within the BMWi-financed Joint Research Project “Geochemical retention of radionuclides on cement alteration phases (GRaZ)”. The project focused on the retention behavior of Ca-bentonite and cementitious material, both constituents of the geo-engineered barrier of deep geological repositories for high-level radioactive waste, towards radionuclides. Specifically, the influence of increased salinities and of hyperalkaline conditions on interaction processes in the system radionuclides – organics – clay/cementitious materials – aquifer was studied. For this purpose, complexation, sorption and desorption studies were performed at alkaline to hyperalkaline pH conditions (pH 8-13) and under variation of the ionic strength (0.1 to 4 M) applying complex solution compositions. For the U(VI) citrate system molecular structures dominating in the pH range 2-9 were studied spectroscopically (NMR, UV-Vis, FT-IR). As dominating species 2:2, 3:3, 3:2 and, above critical concentrations also 6:6 and 9:6 U(VI) citrate complexes were identified or confirmed and complex formation constants were determined. U(VI) sorption on Ca-bentonite at (hyper)alkaline conditions in mixed electrolyte solutions was studied by means of batch sorption experiments. The U(VI) retention on Ca-bentonite was shown to be very effective at pH>10, even in the presence of carbonate and despite the prevalence of anionic aqueous uranyl species. The presence of two independent U(VI) surface complexes on Ca-bentonite at pH 8-13 was shown by site-selective TRLFS and EXAFS spectroscopy. The sorption of anionic uranyl hydroxide complexes to the mineral surface was shown to be mediated by calcium cations. In further experiments, the effect of isosaccharinic acid (ISA) and polycarboxylate ether (PCE) on U(VI) and Eu(III) sorption, respectively, on Ca-bentonite was studied. An effect of ISA on U(VI) sorption on Ca-bentonite only occurs when ISA is present in very high excess to U(VI). The effect of PCE, as a commercial cement superplasticizer, on Eu(III) sorption onto Ca-bentonite was negligible already at moderate ionic strengths. The retention of U(VI) and Cm(III) by various C-(A-)S-H phases, representing different alteration stages of concrete, was studied by batch sorption experiments. Sorbed or incorporated actinide species were identified by TRLFS. The stability of U(VI) and Cm(III) doped C-(A-)S-H phases at high ionic strengths conditions was studied in solutions simulating the contact with North German claystone formation water. Potential changes of actinide speciation as well as formation of secondary phases due to leaching effects were followed spectroscopically. The results of this project show that both bentonite and cementitious material constitute an important retention barrier for actinides under hyperalkaline conditions and increased ionic strength.

Keywords: uranium; curium; europium; Ca-bentonite; site-selective TRLFS; EXAFS; speciation; C-S-H; cement; ionic strength; citric acid; complexation; NMR; surface complexation; TRLFS

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-114 2021
    ISSN: 2191-8708, eISSN: 2191-8716

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Permalink: https://www.hzdr.de/publications/Publ-32735
Publ.-Id: 32735


ALFERROCK Heat Storage Systems in the Chemical Process Industry

Hampel, U.; Unger, S.; Vishwakarma, V.; Bangalore Mohankumar, M.

Energy storage is a central element of future energy systems. In the process industry, the storage of heat is of particular importance. The talk discusses possible applications of high-temperature heat storage in thermal separation processes using the example of a new heat storage material produced from bauxite residues by the company Alferrock GmbH.

Keywords: heat storage; sensible heat storage; high-temperature heat storage; chemical industry; distillation

  • Invited lecture (Conferences) (Online presentation)
    72. BHT - Freiberger Universitätsforum, 09.-11.06.2021, Freiberg, Germany

Permalink: https://www.hzdr.de/publications/Publ-32734
Publ.-Id: 32734


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