Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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35493 Publications

Organische Synthese einer potenten Leitverbindung zur Entwicklung neuer Radioliganden für die molekulare Bildgebung der mutierten Form der Isocitrat-Dehydrogenase 1 im Gehirn mittels Positronen-Emissions-Tomographie

Linke, Jessica

Organische Synthese einer potenten Leitverbindung zur Entwicklung neuer Radioliganden für die molekulare Bildgebung der mutierten Form der Isocitrat-Dehydrogenase 1 im Gehirn mittels Positronen-Emissions-Tomographie

Keywords: Isocitrat-Dehydrogenase 1; mIDH1; Ligand; PET; molekulare Bildgebung

  • Master thesis
    Universität Leipzig, 2021
    Mentor: Dr. Rodrigo Teodoro, Dr. Matthias Scheunemann
    80 Seiten

Publ.-Id: 32960

Large magnetic entropy change in Nd2In near the boiling temperature of natural gas

Liu, W.; Scheibel, F.; Gottschall, T.; Bykov, E.; Dirba, I.; Skokov, K.; Gutfleisch, O.

Natural gas is useful for the transition from traditional fossil fuels to renewable energies. The consumption of liquid natural gas has been rising, and the demand is predicted to double by 2040. In this context, magnetocaloric gas liquefaction, as an emerging and energy-saving technology, could be an alternative to the traditional gas-compression refrigeration. In this work, we report a large magnetic entropy change of 7.42 J/kg K under a magnetic field change of 2 T in Nd2In at 109 K, which is near the boiling temperature of natural gas of 112 K. The maximum adiabatic temperature change reaches 1.13K under a magnetic field change of 1.95 T and is fully reversible. The magnetic phase transition is confirmed to be of the first-order type with the negligible thermal hysteresis. Further investigations on the thermal expansion and the magnetostriction reveal that the magnetic transition undergoes two stages with a negligible volume change. The longitudinal strain increases with magnetic fields and then decreases. These interesting properties are useful for the practical design of a magnetocaloric natural gas liquefaction system and for the fundamental understanding of the phase transitions in other RE2In intermetallics.

Publ.-Id: 32952

Influence of microstructure on the application of Ni-Mn-In Heusler compounds for multicaloric cooling using magnetic field and uniaxial stress

Pfeuffer, L.; Gracia-Condal, A.; Gottschall, T.; Koch, D.; Faske, T.; Bruder, E.; Lemke, J.; Taubel, A.; Ener, S.; Scheibel, F.; Durst, K.; Skokov, K. P.; Manosa, L.; Planes, A.; Gutfleisch, O.

Novel multicaloric cooling utilizing the giant caloric response of Ni-Mn-based metamagnetic shape- memory alloys to different external stimuli such as magnetic field, uniaxial stress and hydrostatic pressure is a promising candidate for energy-efficient and environmentally-friendly refrigeration. However, the role of microstructure when several external fields are applied simultaneously or sequentially has been scarcely discussed in literature. Here, we synthesized ternary Ni-Mn-In alloys by suction casting and arc melting and analyzed the microstructural influence on the response to magnetic fields and uniaxial stress. By combining SEM-EBSD and stress-strain data, a significant effect of texture on the stress- induced martensitic transformation is revealed. It is shown that a <001> texture can strongly reduce the critical transformation stresses. The effect of grain size on the material failure is demonstrated and its influence on the magnetic-field-induced transformation dynamics is investigated. Temperature-stress and temperature-magnetic field phase diagrams are established and single caloric performances are characterized in terms of ΔsT and ΔTad. The cyclic ΔTad values are compared to the ones achieved in the multicaloric exploiting-hysteresis cycle. It turns out that a suction-cast microstructure and the combination of both stimuli enables outstanding caloric effects in moderate external fields which can significantly exceed the single caloric performances. In particular for Ni-Mn-In, the maximum cyclic effect in magnetic fields of 1.9 T is increased by more than 200 % to -4.1 K when a moderate sequential stress of 55 MPa is applied. Our results illustrate the crucial role of microstructure for multicaloric cooling using Ni-Mn- based metamagnetic shape-memory alloys.

Publ.-Id: 32951

Evaluation of the effective temperature change in Gd-based composite wires assessed by static and pulsed-field magnetic measurements

Beyer, L.; Weise, B.; Freudenberger, J.; Hufenbach, J. K.; Gottschall, T.; Krautz, M.

Gd cladded in a seamless 316L austenitic steel tube has been swaged into wires by the powder-in-tube (PIT) technology, resulting in an outer diameter of 1 mm, a wall thickness of approx. 100 μm and a filling factor of around 62 vol%. Such wires provide an advantageous geometry for heat exchangers and have the benefit to protect the Gadolinium, i.e. from corrosion when being in contact with a heat transfer fluid. The magnetocaloric composite has been studied by static and pulsed magnetic-field measurements in order to evaluate the performance of Gd as a core material. By the analysis of magnetization and heat capacity data, the influences of deformation-induced defects on Gadolinium are presented. The subsequent heat treatment at 773 K for 1 h in Ar atmosphere allowed restoring the magnetic properties of the wire after deformation. Data of the pulsed magnetic-field measurements on the Gd-filled PIT-wires and a Gd–core separated from the jacket are presented, with an achievable temperature change of 1.2 K for the wire and 5.2 K for the Gd in 2 T, respectively. A comparison to previously studied La(Fe, Co, Si)13-filled composite wires is included. It indicates that performance losses due to the passive matrix material cannot be overcome only by an increased adiabatic temperature change of the core material, but instead the wire components need to be chosen regarding an optimized heat capacity ratio, as well.

Publ.-Id: 32950

Correlated effects of fluorine and hydrogen in fluorinated tin oxide (FTO) transparent electrodes deposited by sputtering at room temperature

Morán-Pedroso, M.; Gago, R.; Julin, J. A.; Salas-Colera, E.; Jimenez, I.; de Andrés, A.; Prieto, C.

The optical and electrical properties of fluorinated tin oxide (FTO) films deposited at room temperature by sputtering have been investigated varying the fluorine content and the hydrogen atmosphere. The complex behavior of the obtained films is disclosed using a wide set of characterization techniques that reveals the combined effects of these two parameters on the generated defects. These defects control the electrical transport (carrier density, mobility and conductivity), the optical properties (band gap and defects-related absorption and photoluminescence) and finally promote the amorphization of the samples. H₂ in the sputtering gas does not modify the H content in the films but induces the partial reduction of tin (from Sn4+ to Sn2+) and the consequent generation of oxygen vacancies with shallow energy levels close to the valence band. A variation of up to four orders of magnitude in electrical conductivity is reported in samples with the appropriate fluorine doping and hydrogen fraction in the sputtering gas, maintaining excellent optical transparency. Optimized room temperature grown electrodes reach sheet resistance ~20 Ω/□ and transparency >90%. This room temperature deposition process enables film preparation on flexible organic substrates, such as polyethylene terephthalate (PET), with identical performance of doubtless interest in flexible and large scale electronics.

Keywords: Transparent conductive materials; Fluorinated tin oxide; Room temperature film preparation

Publ.-Id: 32947

UDV methods for characterizing flows in liquid metal batteries

Cheng, J.; Wang, B.; Mohammad, I.; Horstmann, G. M.; Kelley, D.

We present ultrasound measurements from a laboratory model of a liquid metal battery (LMB). Two major flow
drivers interact within LMBs: thermal gradients due to the presence of internal heating, and electrovortex flow
(EVF) driven by diverging current densities. The product of these interactions remains poorly characterized. We
approach this problem with ultrasonic Doppler velocimetry (UDV) combined with a laboratory model of an LMB
fluid layer. Using ultrasound probes placed around a liquid gallium vessel, we elucidate typical velocities, flow
structures, and flow statistics in a representative volume of the flow field. UDV measurements reveal that pure
convection takes the form of the recently-discovered ‘jump rope vortex,’ with a characteristic frequency visible in
velocity statistics. They also indicate that EVF goes through stable, unstable, and oscillatory flow regimes. In
progress is an approach for training physics-informed neural networks (PINNs) on UDV data, allowing us to
reconstruct flow in regions where no probe measurements have taken place by leveraging the equations of motion.

  • Contribution to proceedings
    13th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering (ISUD 2021), 13.-15.06.2021, Zürich, Schweiz

Publ.-Id: 32944

Hydrodynamic and efficiency data pertaining to an air-water column mockup (of 0.8 m internal diameter) equipped with sieve trays

Vishwakarma, V.; Marchini, S.; Schleicher, E.; Schubert, M.; Hampel, U.
DataCollector: Vishwakarma, Vineet; DataCollector: Marchini, Sara; RelatedPerson: Schleicher, Eckhard; ContactPerson: Schubert, Markus; Supervisor: Hampel, Uwe

The hydrodynamic data including effective froth height, liquid holdup and tracer flow and patterns related to an operational sieve tray inside a 0.8 m diameter air-water column simulator are provided here. These data were obtained via an advanced multiplex flow profiler at several gas and liquid loadings. The generated data were examined for predicting the tray efficiency using mathematical models. For model validation, the stripping of isobutyl acetate from the aqueous solution over the tray was employed, and the liquid samples at several tray locations were analyzed via UV spectroscopy. The resulting efficiencies and related information are provided here, too. All raw data files, data processing scripts and supporting information with proper indexing and sequencing are uploaded. All these data are intended for non-commercial use only.

Keywords: Column tray; two-phase crossflow; 3D liquid holdup; effective froth height; tracer-response analysis; tray efficiency calculations

  • Reseach data in the HZDR data repository RODARE
    Publication date: 2021-07-21
    DOI: 10.14278/rodare.1071


Publ.-Id: 32942

Superconducting solenoid field measurement and optimization

Ma, S.; Arnold, A.; Ryzhov, A.; Murcek, P.; Zwartek, P.; Schaber, J.; Qian, H.; Teichert, J.; Xiang, R.

The solenoid is a significant part of an electron injector to provide a proper focusing, and preserve the beam projected emittance. A superconducting solenoid is applied for the SRF photoinjector at HZDR. The solenoid itself can degrade electron beam quality due to magnetic field imperfections like multipole components. In order to determine the field aberrations in the solenoid, we measured the superconducting solenoid magnetic field in the cryomodule. A simple and effective method is used to analyze the multipole field components, which will be presented in this paper.

Keywords: solenoid; magnetic field

  • Open Access Logo Contribution to proceedings
    12th International Particle Accelerator Conference (IPAC’21), 24.-28.05.2021, Brasília, Brazil
    Proceedings of IPAC’21: JACoW

Publ.-Id: 32938

High-entropy carbons: From high-entropy aromatic species to single-atom catalysts for electrocatalysis

Ding, J.; Wu, D.; Zhu, J.; Rodríguez-Hernández, F.; Chen, Y.; Lu, C.; Zhou, S.; Zhang, J.; Tranca, D.; Zhuang, X.

Single-atom catalysts (SACs) have rapidly entered the field of nanomaterials and demonstrated great potential for energy devices in recent years. Of all types of SACs, porous carbon-based SACs are the most popular species because of their excellent conductivity, large specific surface area, and easily tunable heteroatom and metal components. However, most of the reported cases focus on the metal centers and their coordination environments, while they do not pay much attention to carbon precursors and carbon transformation during high-temperature treatment. In this work, we use a high-entropy aromatic molecule, azulene, for rational synthesis of azulene-enriched, sandwich-like polymer nanosheets and corresponding single-Fe-dispersed porous carbon nanosheets. The azulene-based metal-free polymer nanosheets exhibit a narrow band gap and temperature-dependent magnetism. As proof-of-concept electrocatalysts for CO2 reduction, the prepared carbon nanosheets exhibit high activity and stability. Operando X-ray absorption spectroscopy and density functional theory studies reveal the high activity of Fe-N coordination sites in the presence of 5/7-membered carbon ring-based topological defects in the carbon skeleton. Taken together, this work provides a new method of synthesizing high-entropy carbons using azulene-based high-entropy molecule as precursor and paves the way toward high-efficiency SACs with rich topological defects for energy conversion.

Keywords: High-entropy aromatic molecule; Topological defect; Single-atom catalyst; Porous carbon nanosheet; Carbon dioxide conversion


  • Secondary publication expected from 14.07.2022

Publ.-Id: 32934

QE and life time of Cs2Te photocathodes on copper for SRF gun-II at HZDR

Xiang, R.; Arnold, A.; Ma, S.; Murcek, P.; Ryzhov, A.; Schaber, J.; Teichert, J.

The SRF gun-II at HZDR has been stably applied as the electron
source for high power THz radiation since 2018, generating CW beams
with bunch charges up to 300 pC at 100 kHz. It is an excellent demonstration
that SRF guns can work reliably in a high power user facility.
In order to generate higher current beam with MHz repetition rate,
Cs2Te photocathodes are required. However, in last two experiments
with Cs2Te, the Mo substrate plugs were overheated in superconducting
rf cavity. The reason is that different thermal expansion coefficient
of Mo and Cu led to a bad thermal contact between the Mo plug and
Cu holder. Thus we decided to use Cu as new substratum of Cs2Te
cathodes. In last year we prepared several Cs2Te photocathodes on Cu
plugs and improved the vacuum of cathode transfer system in order
to achieve satisfied lifetime. In this contribution, we will present the
study result of QE and life time of Cs2Te photocathodes with different

Keywords: SRF gun; photocathode; Cs2Te

  • Open Access Logo Lecture (Conference) (Online presentation)
    DPG-Frühjahrstagung (Dortmund), 15.-19.03.2021, Dortmund, Germany

Publ.-Id: 32933

Observability of Coulomb-assisted quantum vacuum birefringence

Ahmadiniaz, N.; Bussmann, M.; Cowan, T.; Debus, A.; Kluge, T.; Schützhold, R.

We consider the scattering of an x-ray free-electron laser (XFEL) beam on the superposition of
a strong magnetic field $\bf{B}_{\rm ext}$ with the Coulomb field $\bf{E}_{\rm ext}$
of a nucleus with charge number $Z$. In contrast to Delbr\"uck scattering
(Coulomb field only), the magnetic field $\bf{B}_{\rm ext}$
introduces an asymmetry (i.e., polarization dependence) and renders the effective interaction volume quite
large, while the nuclear Coulomb field facilitates a significant momentum transfer $\Delta\bf k$.
For a field strength of $B_{\rm ext}=10^6 T$ (corresponding to an intensity of order $10^{22}~\rm W/cm^2$)
and an XFEL frequency of 24~keV, we find a differential cross section
$d\sigma/d\Omega\sim10^{-25}~Z^2/(\Delta{\bf k})^2$ in forward direction for one nucleus.
Thus, this effect might be observable in the near future at facilities such as the
Helmholtz International Beamline for Extreme Fields (HIBEF) at the European XFEL.


Publ.-Id: 32932

Two Examples for AI Communities

Juckeland, G.; Steinbach, P.

This short talk presents two approaches for building AI communities in the Dresden area. First the top down approach of Helmholtz AI, where HZDR is one of six hubs of consultants to assist and train scientists. Second with the Machine Learning Community (MLC) Dresden a bottom up approach of practitioners just sharing experience and information in regular seminars and other asynchronous communication channels.

Keywords: Helmholtz AI

  • Open Access Logo Invited lecture (Conferences) (Online presentation)
    Kick-Off of Scientific Area Network “Dimensions of Artificial Intelligence”, 16.07.2021, Dresden, Deutschland

Publ.-Id: 32923

Operational experience of photocathodes for HZDR SRF gun

Xiang, R.; Arnold, A.; Ma, S.; Murcek, P.; Teichert, J.; Schaber, J.; Zwartek, P.

The SRF gun-II at HZDR has been stably applied as the electron source for high power THz radiation since 2018, generating CW beams with bunch charges up to 300 pC at 100 kHz. It is an excellent demonstration that SRF guns can work reliably in a high power user facility.
As well known, that the quality of the photocathodes is critical for the stability and reliability of the gun operation. In last years, thank to the successful ps UV laser cleaning, Mg photocathodes were successfully used for gun operation at kHz repitition rate.
In order to satisfy user request of MHz operation, Cs2Te is still in demand. However, the Mo plugs were overheated in superconducting rf cavity due to thermal contact problem, and SRF Gun-II faced twice serious contamination in 2017. The Cs2Te could not be used in gun untill Cu is adopted in stead of Mo as new substratum. Up to now three Cs2Te cathodes on Cu plugs have been applied in the Gun-II.
In this contribution, we will present the operational aspect of the photocathodes for SRF gun, and discuss the possible improvement in the future application.

Keywords: SRF gun; photocathode

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

Publ.-Id: 32922

Review of superconducting radiofrequency gun

Xiang, Rong

The success of proposed high power free-electron lasers (FELs) and energy recovery linac (ERL) largely depends on the development of the electron source, which requires the best beam quality and CW operation. An elegant way to realize both high brilliance and high current is to com-bine the high beam quality of the normal conducting radio frequency photoinjector with the quick developing superconducting radio frequency technology, to build superconducting rf photoinjectors (SRF guns).
In last decade, several SRF gun programs based on dif-ferent approaches have achieved promising progress, even succeeded in routine operation at BNL and HZDR. In the near future SRF guns are expected to play an im-portant role for hard X-ray FEL facilities. In this contribu-tion, we will review the design concepts, parameters, and status of the major SRF gun projects.

Keywords: SRF gun

  • Open Access Logo Invited lecture (Conferences) (Online presentation)
    12th International Particle Accelerator Conference (IPAC’21), 24.-28.05.2021, virtual format, Brazil

Publ.-Id: 32921

Solving overheating of Cs2Te cathodes in the ELBE SRF gun

Arnold, A.

In 2014, the second-generation of the ELBE SRF gun replaced its predecessor, which had been in operation since 2007. In the first two years, copper and magnesium cathodes were initially used without any discernible problems. However, after switching to Cs2Te in 2017, it was found that the layers of two cathodes evaporated within a few days during RF operation in the Gun. Since this was never observed in Gun I, an extensive root cause search was conducted using a dedicated cathode test setup. The findings pointed to loose thermal contact between the cathode plug and the cathode body and ultimately resulted in a change
of the used cathode substrate from molybdenum to copper. Although this was accompanied by a lower quantum efficiency of about 5% after preparation, it stabilized to 1-2% during beam operation in the SRF gun. As of May 2020, three of these cathodes have now been successfully used for THz user beam time and a total charge of 26 C has been extracted. Together with the electrons still produced by Mg cathodes in 2019/2020, a total of 217 user shifts could be served and 2600h hours of beam time were delivered. This demonstrates the reliability of CW SRF in combination with normal conducting cathode and is so far unique in the world. During the talk, the reason for overheating, the preparation on Cu substrate as well as experiences from the past two years of user beam operation will be presented in detail.

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

  • Open Access Logo Invited lecture (Conferences) (Online presentation)
    7th MT meeting (virtuell), 01.-03.02.2021, Online, Deutschland


Publ.-Id: 32920

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.

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


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.

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

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.


  • Secondary publication expected from 07.07.2022

Publ.-Id: 32907

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).

[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

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.


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.

Publ.-Id: 32899

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.

Publ.-Id: 32897

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

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

  • 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, 1-280
  • Lecture (Conference) (Online presentation)
    Proceedings of the 10th international conference on Electromagnetic Processing of Materials, 14.-16.06.2021, Riga, Latvia

Publ.-Id: 32885

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

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

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

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

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.

Publ.-Id: 32879

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

Publ.-Id: 32877

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.

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.

Publ.-Id: 32870

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

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

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


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. 

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


Publ.-Id: 32864

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)

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


Publ.-Id: 32857

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

Publ.-Id: 32847

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

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.

[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


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

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

[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

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


Publ.-Id: 32839

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

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

Publ.-Id: 32832

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:

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.

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

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

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

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

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

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


Publ.-Id: 32819

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

Publ.-Id: 32810

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

Publ.-Id: 32808

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

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


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

Publ.-Id: 32797

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

Publ.-Id: 32794

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

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.


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

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


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

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

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

Publ.-Id: 32775

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


  • Secondary publication expected from 30.06.2022

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.

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


Publ.-Id: 32761

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


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


Publ.-Id: 32748

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


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

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

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

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

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


  • Secondary publication expected from 17.05.2022

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

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.

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


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

Publ.-Id: 32734

Solution synthesis and dielectric properties of alumina thin films: understanding the role of the organic additive in film formation

Hoffmann, R. C.; Liedke, M. O.; Butterling, M.; Wagner, A.; Trouilletc, V.; Schneider, J. J.

Alumina thin films are synthesized by combustion synthesis of mixtures of aluminium nitrate (ALN) and methylcarbazate (MCZ). The interdependence of the ratio of oxidizer and reducing agent on composition, microstructure and electronic properties of the resulting oxide layers is investigated. The dielectric and insulating behaviour is improved by addition of different amounts of MCZ (MCZ : ALN = 0.67 or 2.5). In this way films (thickness ∼140 nm) with a dielectric constant κ of 9.7 and a dielectric loss tan δ below 0.015 can be achieved. Medium concentrations of MCZ (MCZ : ALN = 1.0 or 1.5) lead to films with lower performance, though. Our studies indicate two opposing effects of the organic additive. Removal of organic residues during film formation as combustion gases is potentially detrimental. Larger amounts of MCZ, however, cause condensation reactions in the precusor mixture, which improve the microstructure. The porosity of the films can be sucessfully analyzed by positron annihilation liftetime studies. In this way the impact of the organic ligand sphere on the resulting microstructure can be quantified. Samples prepared from ALN alone exhibit mesopores and also larger micropores. In contrast, the formation of mesopores can be inhibited by addition of MCZ.

Keywords: alumina; thin films; Al2O3; positron annihilation spectroscopy; combustion synthesis; dielectrics; insulator


  • Secondary publication expected from 07.06.2022

Publ.-Id: 32731

Exceptional field dependence of antiferromagnetic magnons in LiFePO4

Werner, J.; Neef, C.; Koo, C.; Ponomaryov, O.; Zvyagin, S.; Klingeler, R.

Low-energy magnon excitations in magnetoelectric LiFePO4 have been investigated by high-frequency–highfield electron spin resonance spectroscopy inmagnetic fields up to B = 58 T and frequencies up to f = 745 GHz. For magnetic fields applied along the easy magnetic axis, the excitation gap softens and vanishes at the spin-flop field of BSF = 32 T before hardening again at higher fields. In addition, for B ≲ BSF we observe a resonance mode assigned to excitations due to Dzyaloshinskii-Moriya (DM) interactions, thereby evidencing a sizable DM interaction of ≈150 μeV in LiFePO4. Both the magnetization and the excitations up to high magnetic fields are described in terms of a mean-field theory model which extends recent zero-field inelastic neutron scattering results. Our results imply that magnetic interactions as well as magnetic anisotropy have a sizable quadratic field dependence which we attribute to significant magnetostriction.

Publ.-Id: 32730

Magnetohydrodynamic effects in liquid metal batteries

Weber, N.; Benard, S.; Horstmann, G. M.; Klopper, T. S.; Landgraf, S.; Nimtz, M.; Personnettaz, P.; Stefani, F.; Weier, T.

Liquid metal batteries (LMBs) are a new technology for grid-scale energy storage. They consist of all liquid cells that operate
with liquid metals as electrodes and molten salts as electrolytes. The
liquids separate into three stably stratified layers by virtue of
density and mutual immiscibility (see the two upper left inserts in
Fig.~\ref{fig}a). This conceptually very simple and self-assembling
structure has the unique advantage to allow for an easy scale-up at
the cell level: single-cell cross sections can potentially reach
several square-meters. Such cell sizes enable highly favourable and
otherwise unattainable ratios of active to construction material
because of the cubic scaling (volume) of the former and the quadratic
scaling (surface) of the latter.

The talk will start with a general introduction to LMBs and then focus
on the fluid mechanics in these devices. Electric currents, magnetic fields, and heat
and mass transfer are tightly coupled with the cells'
electrochemistry. First a number of fluid dynamic instabilities will
be discussed in relation to operational safety. The remainder of the
talk will deal with transport phenomena in the positive
electrode. While transport in most modern battery systems is typically
dominated by diffusion and migration in micrometer-scale liquid layers
and solids, convection - with exception of the aforementioned
redox-flow batteries - rarely plays a role. This is in stark contrast
to LMBs were mediated by the fully liquid interior fluid flow can be
driven by various mechanisms. The influence of solutal convection on
the cycling behavior of a cell will be
demonstrated. Electromagnetically induced convection can be used to
improve mixing thereby mitigating diffusion

Keywords: Liquid metal batteries; wave coupling; mass transport; energy storage; Magnetohydrodynamics

  • Open Access Logo Invited lecture (Conferences) (Online presentation)
    Electromagnetic processing of materials 2021 - Summer course, 09.-11.06.2021, Riga, Lettland

Publ.-Id: 32729

Ultrasound measurement technique for the single-turn-coil magnets

Nomura, T.; Hauspurg, A.; Gorbunov, D.; Miyata, A.; Schulze, E.; Zvyagin, S.; Tsurkan, V.; Matsuda, Y. H.; Kohama, Y.; Zherlitsyn, S.

Ultrasound is a powerful means to study numerous phenomena of condensed-matter physics as acoustic waves couple strongly to structural, magnetic, orbital, and charge degrees of freedom. In this paper, we present such a technique combined with single-turn coils (STCs) that generate magnetic fields beyond 100 T with the typical pulse duration of 6 μs. As a benchmark of this technique, the ultrasound results for MnCr2S4, Cu6[Si6O18]⋅6H2O, and liquid oxygen are shown. The resolution for the relative sound-velocity change in the STC is estimated as Δv/v ∼ 10−3, which is sufficient to study various field-induced phase transitions and critical phenomena.

Publ.-Id: 32728

Raw data, magnetization measurements for paper Room temperature ferromagnetism in Sb doped ZnO

Xu, C.; Zhou, S.

Raw data, magnetization measurements for samples involved in paper Room temperature ferromagnetism in Sb doped ZnO

Related publications

  • Reseach data in the HZDR data repository RODARE
    Publication date: 2021-06-08
    DOI: 10.14278/rodare.1000
    License: CC-BY-4.0


Publ.-Id: 32727

Room temperature ferromagnetism in Sb doped ZnO

Luo, C.-Q.; Zhu, S.-C.; Xu, C.; Zhou, S.; Lame, C.-H.; Ling, F. C.-C.

Using first-principle calculations, the magnetic properties of the monovacancies and the Sb-related defects including VZn, VO, SbZn, SbO, SbZn-VZn and SbZn-2VZn are studied. It is found that the isolated VZn with the charge state of 0 and −1 can contribute to ferromagnetism in ZnO material. The substitution of Sb on O sites (SbO0) also results in magnetic property. Moreover, the SbZn-2VZn complex is another defect having non-zero magnetic moment and energetically favors for the ferromagnetic state. The resultant density of states (DOS) and spin density distribution clearly show that the ferromagnetic interaction is majorly due to the O-p Zn-d and Sb-p states. To check this calculation, Sb-doped ZnO samples were grown by pulsed laser deposition with different Sb composition under P(O2) = 1.3 Pa. SQUID study showed that all of these samples are ferromagnetic at room temperature. The variation of the saturation magnetization against the Sb composition is discussed.

Related publications


  • Secondary publication expected from 09.03.2022

Publ.-Id: 32726

Real time flow control during continuous casting with Contactless Inductive Flow Tomography

Glavinic, I.; Stefani, F.; Eckert, S.; Wondrak, T.

Lack of appropriate flow measurement techniques for liquid steel during continuous casting limits the application of control strategies that could improve the quality of the end product. Contactless Inductive Flow Tomography (CIFT) is a promising measurement technique that can provide information about the flow structure in the mould to a real time controller. On this basis, electromagnetic actuators can be used to react on undesired flow conditions in the mould. However, because of their nature, these actuators pose a significant challenge for inductive measurement methods. In this work we describe the influence of an electromagnetic brake on CIFT in a laboratory environment. We also show how this influence can be fully compensated, which facilitates the viability of CIFT as a key ingredient of real time control of continuous casting.

Keywords: Contactless inductive flow tomography; Continuous casting; Electromagnetic brake

  • Open Access Logo Contribution to proceedings
    Electromagnetic processing of materials 2021, 13.-17.06.2021, Riga, Latvia
  • Lecture (Conference) (Online presentation)
    Electromagnetic processing of materials 2021, 16.06.2021, Riga, Latvia

Publ.-Id: 32723

Final Results of the Prospective Biomarker Trial PETra: [11C]-MET-Accumulation in Postoperative PET/MRI Predicts Outcome after Radiochemotherapy in Glioblastoma

Seidlitz, A.; Beuthien-Baumann, B.; Löck, S.; Jentsch, C.; Platzek, I.; Zöphel, K.; Linge, A.; Kotzerke, J.; Petr, J.; van den Hoff, J.; Steinbach, J.; Krex, D.; Schmitz-Schackert, G.; Falk, M.; Baumann, M.; Krause, M.

Purpose: This prospective trial investigates the association of time to recurrence (TTR) in glioblastoma with [11C]methionine (MET) tracer uptake before postoperative radiochemotherapy (RCT) aiming to guide radiotherapy boost regions.

Experimental Design: Between 2013 and 2016, 102 patients with glioblastoma were recruited. RCT was performed with concurrent and adjuvant temozolomide to a total dose of 60 Gy. Tumor residues in postresection PET and MRI were together defined as gross tumor volumes for radiotherapy treatment planning. [11C]methionine (MET)-PET/MRI was performed before RCT and at each follow-up.

Results: The primary hypothesis of a longer TTR for patients without increased tracer accumulation in postoperative MET-PET was confirmed in 89 patients. With 18.9 months (95% confidence interval, 9.3–28.5 months), median TTR was significantly (P < 0.001) longer for patients without (n = 29, 32.6%) as compared with 6.3 months (3.6–8.9) for patients with MET accumulation (n = 60, 67.4%) in pre-RCT PET. Although MRI often did not detect all PET-positive regions, an unfavorable impact of residual tumor in postsurgical MRI (n = 38, 42.7%) on TTR was observed [4.6 (4.2–5.1) vs. 15.5 months (6.0–24.9), P < 0.001]. Significant multivariable predictors for TTR were MRI positivity, PET-positive volume, and O6-methylguanine DNA methyltransferase (MGMT) hypermethylation.

Conclusions: Postsurgical amino acid PET has prognostic value for TTR after RCT in glioblastoma. Because of the added value of the metabolic beyond the pure structural information, it should complement MRI in radiotherapy planning if available with reasonable effort, at least in the context of maximal therapy. Furthermore, the spatial correlation of regions of recurrence with PET-positive volumes could provide a bioimaging basis for further trials, for example, testing local radiation dose escalation.


  • Secondary publication expected from 31.03.2022

Publ.-Id: 32718

Exploring Data Version Control for machine learning pipelines in research

Sultova, N.

Exploration of Data Version Control as framework for managing machine learning workflows for HelmholtzAI.
The content consists of blogposts and additional code to follow along the tutorials-part.

Keywords: machine learning version control pipelines

Publ.-Id: 32717

Origin of the quasi-quantized Hall effect in ZrTe5

Galeski, S.; Ehmcke, T.; Wawrzyńczak, R.; Lozano, P. M.; Cho, K.; Sharma, A.; Das, S.; Küster, F.; Sessi, P.; Brando, M.; Küchler, R.; Markou, A.; König, M.; Swekis, P.; Felser, C.; Sassa, Y.; Li, Q.; Gu, G.; Zimmermann, M. V.; Ivashko, O.; Gorbunov, D.; Zherlitsyn, S.; Förster, T.; Parkin, S. S. P.; Wosnitza, J.; Meng, T.; Gooth, J.

The quantum Hall effect (QHE) is traditionally considered to be a purely two-dimensional (2D) phenomenon. Recently, however, a three-dimensional (3D) version of the QHE was reported in the Dirac semimetal ZrTe5. It was proposed to arise from a magnetic-field-driven Fermi surface instability, transforming the original 3D electron system into a stack of 2D sheets. Here, we report thermodynamic, spectroscopic, thermoelectric and charge transport measurements on such ZrTe5 samples. The measured properties: magnetization, ultrasound propagation, scanning tunneling spectroscopy, and Raman spectroscopy, show no signatures of a Fermi surface instability, consistent with in-field single crystal X-ray diffraction. Instead, a direct comparison of the experimental data with linear response calculations based on an effective 3D Dirac Hamiltonian suggests that the quasi-quantization of the observed Hall response emerges from the interplay of the intrinsic properties of the ZrTe5 electronic structure and its Dirac-type semi-metallic character.

Publ.-Id: 32716

Topological magnetic order and superconductivity in EuRbFe4As4

Hemmida, M.; Winterhalter-Stocker, N.; Ehlers, D.; Krug Von Nidda, H.-A.; Yao, M.; Bannies, J.; Rienks, E. D. L.; Kurleto, R.; Felser, C.; Büchner, B.; Fink, J.; Gorol, S.; Förster, T.; Arsenijevic, S.; Fritsch, V.; Gegenwart, P.

We study single crystals of the magnetic superconductor EuRbFe4As4 by magnetization, electron spin resonance (ESR), angle-resolved photoemission spectroscopy, and electrical resistance in pulsed magnetic fields up to 63 T. The superconducting state below 36.5 K is almost isotropic and is only weakly affected by the development of Eu2+ magnetic order at 15 K. On the other hand, for the external magnetic field applied along the c axis the temperature dependence of the ESR linewidth reveals a Berezinskii-Kosterlitz-Thouless topological transition below 15 K. This indicates that Eu2+ planes are a good realization of a two-dimensional XY magnet, which reflects the decoupling of the Eu2+ magnetic moments from superconducting FeAs layers.

Publ.-Id: 32715

Automated objective optimization of iterative image reconstruction protocols

Nikulin, P.; Maus, J.; Hofheinz, F.; van den Hoff, J.

The image quality achieved in iterative PET image reconstruction is influenced by several internal and user-settable parameters (number of iterations and subsets, PSF model, etc.). Typically, there are more than 3 user-settable parameters involved, interacting in a non-intuitive way. Reasonable settings typically are obtained interactively by try-and-error which is highly subjective. This proof-of-concept work proposes a method for automated reconstruction parameters optimization for a given, preselected image quality metric.

In out approach, we reconstruct images of cylindrical phantom with six "hot" sphere inserts simulating lesions of different sizes and target-to-background activity concentration ratios (20:1, 10:1, 5:1). 4 parameters of our in-house reconstruction tool THOR [1] were varied during optimization: no. of iterations and subsets, tube of response (ToR) radius, Gaussian post filter FWHM. As image quality metric we chose the weighted sum of standard deviation of contrast recovery coefficients of all 6 inserts (as a surrogate for image resolution), the image noise, and Gibbs artifacts. This metric is minimized with Bayesian optimization method using Gaussian process as a surrogate function. The reconstruction parameters resulting in the minimum metric value were chosen.

The optimization process lasted for 50 iterations. The resulting reconstruction parameters were: no. of iterations/subsets=2/21, ToR radius=2.95mm, Gaussian filter FWHM=4.0mm. The resulting images show [4.7-5.8]mm resolution and 14% noise level. Gibbs artifacts level was found to be below 3.5%.

Our framework for reconstruction protocol optimization is capable of deriving reasonable reconstruction parameters in a fully automated manner. The presented approach might also be used to improve and objectify the comparison of different image reconstruction algorithms.


[1] A. Lougovski, et al., Physics in Medicine and Biology, vol.59(3), p.561, 2014

Keywords: PET; Iterative image reconstruction; THOR; MLEM; Bayesian optimization

  • Lecture (Conference) (Online presentation)
    NuklearMedizin 2021 – hybrid, 14.-17.04.2021, Online, Online
  • Contribution to proceedings
    NuklearMedizin 2021 – hybrid, 14.-17.04.2021, Online, Online
    Nuklearmedizin 2021; 60(02): 151, eRef: Thieme Publishing Group
    DOI: 10.1055/s-0041-1726740

Publ.-Id: 32711

Simultaneous Ligand and Cation Exchange of Colloidal CdSe Nanoplatelets toward PbSe Nanoplatelets for Application in Photodetectors

Galle, T.; Spittel, D.; Weiß, N.; Shamraienko, V.; Decker, H.; Georgi, M.; Hübner, R.; Metzkow, N.; Steinbach, C.; Schwarz, D.; Lesnyak, V.; Eychmüller, A.

Cation exchange emerged as a versatile tool to obtain a variety of nanocrystals not yet available via a direct synthesis. Reduced reaction times and moderate temperatures make the method compatible with anisotropic nanoplatelets (NPLs). However, the subtle thermodynamic and kinetic factors governing the exchange require careful control over the reaction parameters to prevent unwanted restructuring. Here, we capitalize on the research success of CdSe NPLs by transforming them into PbSe NPLs suitable for optoelectronic applications. In a two-phase mixture of hexane/Nmethylformamide, the oleate-capped CdSe NPLs simultaneously undergo a ligand exchange to NH4I and a cation exchange reaction to PbSe. Their morphology and crystal structure are well-preserved as evidenced by electron microscopy and powder X-ray diffraction. We demonstrate the successful ligand exchange and associated electronic coupling of individual NPLs by fabricating a simple photodetector via spray-coating on a commercial substrate. Its optoelectronic characterization reveals a fast light response at low operational voltages.

Publ.-Id: 32705

The contribution of hydrodynamic processes to calcite dissolution rates and rate spectra

Agrawal, P.; Bollermann, Till; Raoof, A.; Iliev, O.; Fischer, C.; Wolthers, M.

Recent measurements on the dissolution rate of nano- and micron-scale rough calcite surfaces have shown lateral variations in dissolution rate, which can be quantified using rate spectra. This study uses numerical simulations to investigates the hydrodynamic processes during such experiments to explore whether hydrodynamic effects can explain the observed dissolution rate spectra. For this purpose, we simulated the dissolution processes of nano- and micron-scale rough calcite surfaces in COMSOL Multiphysics. We imposed surface topographies and local reaction rates measured using Vertical Scanning Interferometry (VSI), and implemented the same flow rate (i.e., 6 × 10−8 m3 s−1), solution chemistry (pH 8.8, alkalinity 4.4 meq/kg-H2O and pCO2 10−3.48 bar) and flow-cell geometry as those used in the experiment. We have compared the simulated rate spectra against the experimentally measured values at a calcite surface having the same surface topography and reactive-flow conditions.

Simulations using a single dissolution rate for the rough calcite surface did not produce similarly wide dissolution rate spectra like those observed experimentally. Our results have shown that only by explicitly incorporating the rate spectra in the model the simulated and the measured rate spectra would match. Sensitivity analyses by varying chemical composition and flow velocity were performed to examine the effects of these parameters on the calculated rate spectra. This study concludes that for the reactive-flow regimes where dissolution rate spectra are observed experimentally, the chemical heterogeneity, topography of the crystal surface and the resulting heterogeneity in the free energy landscape at the surface play a major role in controlling the dissolution rate spectra. With the injection of more acidic (pH 2) solutions at higher velocities (i.e., 0.04 m s−1), we observed an increase in the hydrodynamics-induced rate variability at microscopically rough surfaces

Keywords: Calcite dissolution; Pore-scale reactive transport model; Microscopic surface experiments; Surface roughness; Hydrodynamic effects; Dissolution rate spectra

Publ.-Id: 32700

Enhancing Ferromagnetism and Tuning Electronic Properties of CrI3Monolayers by Adsorption of Transition-Metal Atoms

Yang, Q.; Hu, X.; Shen, X.; Krasheninnikov, A.; Chen, Z.; Sun, L.

Among first experimentally discovered two-dimensional (2D) ferromagnetic materials, chromium triiodide (CrI3) monolayers have attracted particular attention due to their potential applications in electronics and spintronics. However, the Curie temperature Tc of the CrI3 monolayer is below room temperature, which greatly limits practical development of the devices. Herein, using density functional theory calculation, we explore how the electronic and magnetic properties of CrI3 monolayers change upon adsorption of 3d transition-metal (TM) atoms (from Sc to Zn). Our results indicate that the electronic properties of the TM-CrI3 system can be tuned from semiconductor to metal/half-metal/spin gapless semiconductor depending on the choice of the adsorbed TM atoms. Moreover, the adsorption can improve the ferromagnetic stability of CrI3 monolayers by increasing both magnetic moments and Tc. Notably, Tc of CrI3 with Sc and V adatoms can be increased by nearly a factor of 3. We suggest postsynthesis doping of 2D CrI3 by deposition of TM atoms as a new route toward potential applications of TM-CrI3 systems in nanoelectronic and spintronic devices.

Keywords: 2D materials; adsorption; magnetic properteis


  • Secondary publication expected from 27.04.2022

Publ.-Id: 32699

Defect Agglomeration and Electron Beam-Induced Local Phase Transformations in Single-Layer MoTe₂

Köster, J.; Ghorbani Asl, M.; Lehnert, T.; Komsa, H.-P.; Kretschmer, S.; Krasheninnikov, A.; Kaiser, U.

Atom migrations in single-layer 1H-MoTe₂ are studied with Cc/Cs-corrected high-resolution transmission electron microscopy (TEM) at an electron energy of 40 keV using the electron beam simultaneously for material modification and imaging. After creating tellurium vacancies and vacancy lines, we observe their migration pathways across the lattice. Furthermore, we analyze phase transformations from the 1H- to the 1T’-phase associated with the strain-induced due to the formation of Te vacancy lines. Combining the experimental data with the results of first-principles calculations, we explain energetics and driving forces of point and line defect migration and the phase transformations due to an interplay of electron-beam-induced energy input, atom ejection, and strain spread. Our results enhance the understanding of defect dynamics in 2D transition metal dichalcogenides, which should facilitate tailoring their local optical and electronic properties.

Keywords: two-dimensional materials; transition metal dichalcogenides; transmission electron microscopy; defects; first-principles calculations


  • Secondary publication expected from 13.06.2022

Publ.-Id: 32698

Dichotomy in temporal and thermal spin correlations observed in the breathing pyrochlore LiGa1−xInxCr4O8

Lee, S.; Do, S.-H.; Lee, W.; Choi, Y. S.; van Tol, J.; Reyes, A. P.; Gorbunov, D.; Chen, W.-T.; Choi, K.-Y.

A breathing pyrochlore system is predicted to host a variety of quantum spin liquids. Despite tremendous experimental and theoretical efforts, such sought-after states remain elusive as perturbation terms and lattice distortions lead to magnetic order. Here, we utilize bond alternation and disorder to tune a magnetic ground state in the Cr-based breathing pyrochlore LiGa1−xInxCr4O8. By combining thermodynamic and magnetic resonance techniques, we provide experimental signatures of a spin-liquid-like state in x = 0.8, namely, a nearly T2-dependent magnetic specific heat and persistent spin dynamics by muon spin relaxation (μSR). Moreover, Li NMR, ZF-μSR, and ESR unveil the temporal and thermal dichotomy of spin correlations: a tetramer singlet on a slow time scale vs. a spin-liquid-like state on a fast time scale. Our results showcase that a bond disorder in the breathing pyrochlore offers a promising route to disclose exotic magnetic phases.

Publ.-Id: 32696

Magnetic properties of a quantum spin ladder in proximity to the isotropic limit

Zvyagin, S.; Ponomaryov, O.; Ozerov, M.; Schulze, E.; Scurschii, I.; Beyer, R.; Reimann, T.; Zviagina, L.; Green, E. L.; Wosnitza, J.; Sheikin, I.; Bouillot, P.; Giamarchi, T.; Wikara, J. L.; Turnbull, M. M.; Landee, C. P.

We report on the synthesis, crystal structure, magnetic, thermodynamic, and electron-spin-resonance properties of the coordination complex [Cu2(pz)3(4-HOpy)4](ClO)4 (pz = pyrazine; 4-HOpy = 4-hydroxypyridine). This material is identified as a spin-1/2 Heisenberg ladder system with exchange-coupling parameters Jrung/kB = 12.1(1) K and Jleg/kB = 10.5(3) K [Jrung/Jleg = 1.15(4)]. For single crystals our measurements revealed two critical fields, μ0Hc1 = 4.63(5) T and μ0Hc2 = 22.78(5) T (for H II a*), separating the gapped spin-liquid, gapless Tomonaga-Luttinger-liquid, and fully spin-polarized phase. No signature of a field-induced transition into a magnetically ordered phase was found at temperatures down to 450 mK. The material bridges an important gap by providing an excellent physical realization of an almost isotropic spin-1/2 strong-rung Heisenberg ladder system with modest exchange-coupling energy and critical-field scales.


Publ.-Id: 32694

Distinct field-induced ferroquadrupolar states for two different magnetic-field directions in DyNiAl

Ishii, I.; Suzuki, D.; Umeno, T.; Kurata, Y.; Wada, Y.; Suzuki, T.; Andreev, A. V.; Gorbunov, D.; Miyata, A.; Zherlitsyn, S.; Wosnitza, J.

The hexagonal Dy-based compound DyNiAl undergoes ferromagnetic and antiferromagnetic-type magnetic phase transitions at TC = 30 K and T1 = 15 K, respectively. To investigate the 4f -electronic state and quadrupole interactions in DyNiAl, we carried out ultrasonic measurements versus temperature and applied magnetic field. The transverse elastic moduli C44 and C66 show a prominent elastic softening originating from an interlevel ferroquadrupolar-type interaction between the ground state and excited Kramers doublets, clarified by a crystal field analysis. In magnetic fields applied along the [100] and [001] axes, we observed a field-induced phase transition. Because the quadrupole interaction is enhanced in high magnetic fields according to our calculations, we suggest a magnetic-field-induced ferroquadrupolar ordering of the electric quadrupoles Oxy and Oyz for fields applied along [100] and [001], respectively, with different quadrupolar order parameters depending on the field direction.

Publ.-Id: 32692

Easy Diagram Creation in GitLab

Huste, T.; Jandt, U.

Recently, the Helmholtz-wide software development platform (Gitlab) has been extended with the ability to create diagrams from textual descriptions. This post will help you getting started with this new feature.

Keywords: GitLab; Software; Diagrams; UML; Markdown

Publ.-Id: 32691

Aktuelle Entwicklungen aus den Radiopharmazeutischen Wissenschaften für theranostische Anwendungen - Editorial

Mamat, C.; Kopka, K.

Die klinische Bereitstellung von Radiopharmaka für diagnostische und therapeutische Zwecke ist eine der zentralen Aufgaben der konventionellen Radiopharmazie, denn sie ist das Herzstück einer jeden modernen Nuklearmedizin. Neben einem großen, aber planbaren, logistischen Aufwand ist die Versorgung mit Radiopharmaka sowohl mit radiochemischen als auch regulatorischen Herausforderungen verbunden. Das betrifft beispielsweise die zuverlässige Verfügbarkeit einzelner Radionuklide aufgrund ihrer Kurzlebigkeit und die Erfüllung obligatorischer Qualitätskontrollen.
Daneben widmen sich die Radiopharmazeutischen Wissenschaften ihrem Forschungsauftrag, der in der Erforschung neuer Radionuklide, der Entwicklung und der (prä-)klinischen Testung neuer Radiopharmaka für Diagnose und Therapie und der Weiterentwicklung der bildgebenden Verfahren SPECT und PET
sowie der hybriden Kombinationen mit MRT und CT, besteht. In diesem Sinne ist diese Ausgabe des Nuklearmediziners ganz den neuesten Entwicklungen auf dem Gebiet der Radiopharmazie gewidmet, welche sich mittlerweile über klassische Ansätze hin zu theranostischen Anwendungen in Form von diagnose-geleiteten Therapien entfaltet.

Keywords: Nuklearmedizin; Radiopharmazeutische Wissenschaften

Publ.-Id: 32690

Quenching Mechanism of Uranyl(VI) by Chloride and Bromide in Aqueous and Non-Aqueous Solutions

Haubitz, T.; Drobot, B.; Tsushima, S.; Steudtner, R.; Stumpf, T.; Kumke, M. U.

A major hindrance in utilizing uranyl(VI) luminescence as a standard analytical tool, for example, in environmental monitoring or nuclear industries, is quenching by other ions such as halide ions, which are present in many relevant matrices of uranyl(VI) speciation. Here, we demonstrate through a combination of time-resolved laser-induced fluorescence spectroscopy, transient absorption spectroscopy, and quantum chemistry that coordinating solvent molecules play a crucial role in U(VI) halide luminescence quenching. We show that our previously suggested quenching mechanism based on an internal redox reaction of the 1:2-uranyl−halide-complex holds also true for bromide-induced quenching of uranyl(VI). By adopting specific organic solvents, we were able to suppress the separation of the oxidized halide ligand X2·− and the formed uranyl(V) into fully solvated ions, thereby “reigniting” U(VI) luminescence. Time-dependent density functional theory calculations show that quenching occurs through the outer-sphere complex of U(VI) and halide in water, while the ligand-tometal charge transfer is strongly reduced in acetonitrile.

Publ.-Id: 32687

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