Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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39129 Publications

Upgrade of the ELBE Timing System

Kuntzsch, M.; Schwarz, A.; Zenker, K.; Justus, M.; Oven, Z.; Krmpotic, L.; Legat, U.; Rojec, U.

At the ELBE accelerator center a superconducting linac is operated to drive manifold secondary radiation sources like two infrared FELs, a positron source and a THz facility. The machine uses two injectors as electron sources that are accelerated in the main linac. The user experiments demand a large variety of bunch patterns from single shot to macro pulsed and cw beam at up to 26 MHz repetition rate. At ELBE a new timing system is being developed based on the MRF hardware platform and the MRF Timing System IOC. It uses two masters and a scalable number of connected receivers to generate the desired pulse patterns for operating the machine and to control user experiments. The contribution will show the architecture of the timing system, the control interfacing and performance measurements acquired on the test bench.

Keywords: ELBE; Timing; MicroTCA

Related publications

  • Contribution to proceedings
    International Particle Accelerator Conference 2021, 24.-28.05.2021, Campinas, Brazil
    Upgrade of the ELBE Timing System
  • Poster (Online presentation)
    International Particle Accelerator Conference 2021, 24.-28.05.2021, Campina, Brazil

Publ.-Id: 32917

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

Endocytosis is a significant contributor to uranium(VI) uptake in tobacco (Nicotiana tabacum) BY-2 cells in phosphate-deficient culture

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

Endocytosis of metals in plants is a growing field of study involving metal uptake from the rhizosphere. Uranium, which is naturally and artificially released into the rhizosphere, is known to be taken up by certain species of plant, such as Nicotiana tabacum, and we hypothesize that endocytosis contributes to the uptake of uranium in tobacco. The endocytic uptake of uranium was investigated in tobacco BY 2 cells using an optimized setup of culture in phosphate-deficient medium. A combination of methods in biochemistry, microscopy and spectroscopy, supplemented by proteomics, were used to study the interaction of uranium and the plant cell. We found that under environmentally relevant uranium concentrations, endocytosis remained active and contributed to 14% of the total uranium bioassociation. Proteomics analyses revealed that uranium induced a change in expression of the clathrin heavy chain variant, signifying a shift in the type of endocytosis taking place. However, the rate of endocytosis remained largely unaltered. Electron microscopy and energy dispersive X-ray spectroscopy showed an adsorption of uranium to cell surfaces and deposition in vacuoles. Our results demonstrate that endocytosis constitutes a considerable proportion of uranium uptake in BY 2 cells, and that endocytosed uranium is likely targeted to the vacuole for sequestration, providing a physiologically safer route for the plant than uranium transported through the cytosol.

Keywords: plant cell; proteomics; radionuclide transport; heavy metal interaction; vesicle uptake

Related publications


  • Secondary publication expected

Publ.-Id: 32914

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

Related publications


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

Reconfigurable Spin-Wave Interferometer at the Nanoscale

Chen, J.; Wang, H.; Hula, T.; Liu, C.; Liu, S.; Liu, T.; Jia, H.; Song, Q.; Guo, C.; Zhang, Y.; Zhang, J.; Han, X.; Yu, D.; Wu, M.; Schultheiß, H.; Yu, H.

Spin waves with nanoscale wavelengths can transfer information free of electron transport and hence are promising for wave-based computing technologies with low-power consumption as a solution to the severe energy losses in modern electronics. Logic circuits based on the interference of spin waves have been proposed for more than a decade. However, spin-wave interference at the nanoscale has yet been realized. Here, we demonstrate experimentally the interference of spin waves with wavelengths down to 50 nm in a low-damping magnetic insulator. The constructive and destructive interference of spin waves is detected in the frequency domain using propagating spin-wave spectroscopy, which is further confirmed by the Brillouin light scattering. The interference pattern is found to be highly sensitive to the distance between two magnetic nanowires acting as spin-wave emitters. By controlling the magnetic configuration of the double-wire system, one can switch the spin-wave interferometer on and off. The observed phenomena are theoretically accounted for by the interlayer magnon-magnon coupling. Our demonstrations are thus key to the realization of spin-wave computing system based on non-volatile nanomagnets at the GHz frequencies.

Keywords: spin waves; magnetism; Brillouin spectroscopy; interferometer; interference; nanotechnologie

Publ.-Id: 32911

Nonstationary spin waves in a single rectangular permalloy microstrip under uniform magnetic excitation

Pile, S.; Stienen, S.; Lenz, K.; Narkovic, R.; Wintz, S.; Förster, J.; Mayr, S.; Buchner, M.; Weigand, M.; Ney, V.; Lindner, J.; Ney, A.

The ferromagnetic resonance modes in a single rectangular Py microstrip were directly imaged using timeresolved STXM-FMR measurements and the findings were corroborated by micromagnetic simulations. The spin wave resonance modes showed a nonstanding character, when the wave-vector is parallel to the external static magnetic field due to the highly inhomogeneous effective field inside the strip. The propagating character is observed for all the observed spin waves. The influence of the edge quality was analyzed using micromagnetic simulations.

Keywords: ferromagnetic resonance; scanning x-ray transmission microscopy; spin waves; nanostructures; micromagnetism

Related publications


Publ.-Id: 32909

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


  • Secondary publication expected

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.


Publ.-Id: 32907

Proton beam visualisation for in-beam MR imaging

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

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

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

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

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

Appendix 1

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

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

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

  • Invited lecture (Conferences) (Online presentation)
    Joint Conference of the ÖGMP, DGMP and SGSMP, 19.-21.09.2021, Online, Online
  • Contribution to proceedings
    Joint Conference of the ÖGMP, DGMP & SGSMP, 21.09.2021, online, online, 978-3-948023-16-4, 212-213

Publ.-Id: 32906

Introduction to machine learning operations for HelmholtzAI

Sultova, N.

Introduction to machine learning operations for potential usage within HelmholtzAI

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

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

Keywords: machine learning; mlops; infrastructure; version control

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


Publ.-Id: 32904

Amphiphilic ionic oligomers as functionalizable stabilizers for gene therapy nanoparticles

Schmid, M.; Mitrach, F.; Wenzel, B.; Schulz-Siegmund, M.; Hacker, M.-C.

Inorganic nano drug delivery vehicles require the use of an appropriate organic stabilizer. Examples are uncharged thiol containing macromolecules or polymers for gold NPs [1] , positively charged polyethylenimines for metals [2], or carboxylate bearing polymers for cationic calcium phosphates [3].To match a variety of demands, including ion interaction, solubility, good synthetic availability, cellular uptake and endosomal escape, we present the synthesis of amphiphilic functionalizable terpolymers. Our work is based on a broad experience in the synthesis and application of free radical synthesis of maleic anhydride-containing cooligomers. [4],[5],[6] The shown terpolymers [Fig. 1] consist of tetradecylacrylate (14), methoxy-poly(ethylenglycol) methacrylate (PEG, Mn 950) and maleic anhydride (MA). The addition of filler monomers such as 4-acryloylmorpholine (AMO) or N-vinylpyrrolidone (NVP) has also been realized. Reactive anhydride moieties allowed for accessible functionalization by amide formation e.g. with Cy5 amine as fluorescent label or with the azide linker (11-azido-3,6,9-trioxaundecan-1-amine) which renders the oligomers accessible for any kind of Cu (I) catalysed azide alkyne click reaction.

Figure 1: A Anhydride-containing terpolymer synthesis and B illustration of stabilization of in situ generated siRNA-loaded calcium phosphate nanoparticles.
Anhydride content and intactness were determined by conductometric titration. 1H-NMR was used to quantify comonomer integration and size exclusion chromatography for molecular weight analysis. Terpolymer synthesis yields ranged between 24.1 and 51.1%, and molecular weights between 4500 and 6500 Da. MA incorporation was controlled by the reaction feed and anhydride intactness in the oligomers was higher than 60% (o14PEGMA (4/4/10)). Effects of comonomer feed on integration in the resulting purified oligomers are presented. Pristine oligomers were transferred to the respective polyanionic ammonia salt. The here presented oligomers are able to stabilize siRNA bearing calciumphosphate nanoparticles, show typical amphiphilic behaviour and can be functionalized by alkyne-azide cycloaddition.
Acknowledgements: European Development Found Saxony (EFRE) and the SAB (Sächsische Aufbaubank, Saxony, Germany) for funding
1. Masse, Florence, et al.: Molecules 2019. 24 (16):
2. Norouzi, Mohammad, et al.: Nanomaterials 2020. 10 (3):
3. Zhang, Shuiquan, et al.: J. Mater. Chem. B 2020. 8 (41): 9589–9600.
4. Nawaz, Hafiz Awais, et al.: J. Mater. Chem. B 2021 (9): 2295–2307.
5. Wölk, Christian, et al.: Adv. Mater. Interfaces 2020. 7 (22): 2001168.
6. Loth, Tina, et al.: React. Funct. Polym. 2013. 73 (11): 1480–1492.

  • Poster (Online presentation)
    DPhG-Jahrestagung, 28.09.-01.10.2021, Leipzig, Deutschland

Publ.-Id: 32903

CFD-Modelling of Boiling in a Heated Pipe Including Flow Pattern Transition

Setoodeh, H.; Moonesi Shabestary, A.; Ding, W.; Lucas, D.; Hampel, U.

Flow boiling occurs when a subcooled liquid enters a heating pipe and its temperature near the heating wall exceeds the boiling onset temperature. Bubbles are generated on the heating wall and the more downstream the larger the average bubble size due to progressing evaporation and coalescence. Further downstream, the two-phase flow morphologies may change from bubbly to slug, plug, and annular flow. Since these flow patterns have a great impact on the heat and mass transfer rates, an accurate prediction of them becomes critical.
In this work, the recently developed GEneralized-TwO Phase concept (GENTOP) was used for flow patterns transition modelling and their effects on the wall heat transfer during the upward subcooled flow boiling inside a vertical heating pipe. Furthermore, a previously developed mechanistic bubble dynamics model was implemented in the GENTOP framework as a sub-model. This model is based on the force balance on a single growing bubble considering evaporation of the microlayer underneath the bubble, thermal diffusion and condensation around the bubble as well as the dynamic inclination and contact angles. It does not require a recalibration of parameters to predict the bubble dynamics. For implementing this model in the Euler-Euler (E-E) framework an extension of the current nucleation site density and heat partitioning model was required. Eventually, for a generic test case, flow boiling regimes of water in a vertical heating pipe were simulated using ANSYS CFX 18.2.

Keywords: bubble dynamics; flow boiling regimes; GENTOP; Computational Fluid Dynamics (CFD)

Publ.-Id: 32902

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

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

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

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

Publ.-Id: 32898

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

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

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

Related publications

Publ.-Id: 32897

Simulation of Flow Boiling Transition Patterns by Using GENTOP Concept and a Mechanistic Bubble Dynamics Model

Hamed Setoodeh; Wei Ding; Dirk Lucas; Uwe Hampel

Flow boiling occurs when a subcooled liquid enters a vertical heating pipe and its temperature near the heating wall exceeds the boiling onset temperature. Bubbles are generated on the heating wall. Further, along the pipe the bulk fluid temperature increases and coalescence and evaporation create large bubbles which results in two-phase flow patterns formation including bubbly, slug and annular flows.

Flow patterns transition in flow boiling is simulated by using the recently developed concept of GEneralized-TwO Phase (GENTOP) and a developed bubble dynamics model. The GENTOP concept is an extension of the inhomogeneous MUltiple SIze Group (iMUSIG) by adding a continuous gas phase in the multi-field Euler-Euler (E-E) approach. Transitions between the fields result from coalescence and breakup of the gas bubbles.

A recently developed mechanistic bubble dynamics model, which is based on the balance of forces applied on a single bubble, is implemented in the GENTOP framework as a sub-model. This model also considers the evaporation of the microlayer underneath the bubble, thermal diffusion and condensation around the bubble as well as the dynamic inclination and contact angles. In addition, it does not require a recalibration of parameters to predict the bubble dynamics and its implementation in the E-E framework needs an extension of the current nucleation site density and heat partitioning models. Finally, for a generic demonstration case, flow boiling morphological patterns in a vertical heated pipe is simulated by ANSYS CFX.

Keywords: bubble dynamics; flow boiling regimes; GENTOP; Computational Fluid Dynamics (CFD)

  • Contribution to proceedings
    19th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-19), 06.03.2022, Brussels, Belgium

Publ.-Id: 32895

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

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

Z-scan data (polarization dependent)

Matlab scripts for the fitting and simulations

FTIR transmission data


Center wavelength of OPA: 1430 nm

FWHM duration of OPA pulses: 75 fs

Pulse energy: 20 nJ

thickness of DSTMS: 0.4 mm

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

Related publications


Publ.-Id: 32894

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

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

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


Publ.-Id: 32893

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

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

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

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

Publ.-Id: 32892

Analysis of the effect of uncertainties in hydrodynamic parameters on the accuracy of the gas flow modulation technique for bubble columns

Marchini, S.; Schubert, M.; Hampel, U.

The gas flow modulation technique has recently been proposed as a novel method for determining the axial gas dispersion coefficient in bubble columns. The approach is based on a marginal sinusoidal modulation of the gas inlet flow rate that acts as a virtual tracer. Axial gas dispersion is then inversely calculated from amplitude damping and phase shift via an analytical solution of the axial dispersion model. The proposed study provides an analysis of the inherent uncertainties related to the assumptions of constant axial gas dispersion coefficient and bubble rise velocity, which are crucial for implementing the method. Besides, the sensitivity of the approach is assessed as function of the modulation parameters, the bubble rise velocity and the axial gas dispersion coefficient. Eventually, the possibility of tailoring the modulation parameters depending on the expected value of the axial gas dispersion coefficient to increase the sensitivity and to reduce the uncertainty is also assessed.

Keywords: bubble columns; bubble column reactors; axial dispersion coefficient; axial dispersion model; uncertainty analysis; sensitivity analysis


  • Secondary publication expected from 15.04.2023

Publ.-Id: 32891

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

  • Open Access Logo Journal of Fluid Mechanics 922(2021), R4
    DOI: 10.1017/jfm.2021.548
    Cited 1 times in Scopus
  • Lecture (Conference) (Online presentation)
    International Couette-Taylor Workshop 2021, 05.-09.07.2021, Enschede, Netherlands

Publ.-Id: 32890

Transport properties of systematically disordered Cr2AlC films

Salgado Cabaco, J.; Kentsch, U.; Lindner, J.; Faßbender, J.; Leyens, C.; Bali, R.; Boucher, R.

Nano-lamellar composite materials, known as MAX-phases, can possess a combination of ceramic and metallic properties. A prototype compound is Cr2AlC, formed from a unit cell of Cr2C sandwiched between atomic planes of Al, thereby imparting a goodelectrical conductivity, as well as mechanical stability, radiationand oxidationresistance [1, 2]. Theseproperties rely on the lamellar structure of the compound, and systematic introduction of defects, such as displacing or doping atoms within the layers, has the potential to tune electron transport and modify magnetic properties. An ideal tool for defect implantation is ion-irradiation, available both in the form of a broad-beam for wafer-scale processing as well as focused ion-beams for device prototyping.Here we observe the modifications to the structural, transport and magnetic behavior of 500 nm thickCr2AlC afterirradiation with Co+ions, and Ar+noble gas ions as control. The films were irradiated with 450keV of Co+ions at fluences varying from 5E12 to 5E15, and the control samples with 400 keV Ar+ions keeping the sample fluences.Structural analysis using XRD shows that ion-irradiation induces asuppression of the 0002 reflection, indicating a gradual decay of the nano-lamellar structure, see Fig.1a. Increasing ion-fluence also leads toan increase of the saturation magnetizationat 1.5K, whereby both Ar+and Co+cause an increased magnetization, respectively to 150and 190 kA.m-1, for the highest fluences used.Large variations of the transport properties are observed(Fig. 1 b).Magnetoresistance (MR) in the non-irradiated sample shows a classical B2dependency, even up to high temperatures.At Co+fluences of MR at 10 T shows a 2 orders of magnitude increase, upto 3%(10 T)at 100 K, see Fig. 1b. A similar effect also occurs for films, however with a smaller MR-increase.It appears that resistivity increases and the residual resistance ratio reduces with increasing fluence due to the introduction of disorder.Theseresults show that ion irradiation induces significant changes in the transport properties of MAX phase materials, that will be further investigated.The systematic disordering of nano-laminated MAX phase films may therefore reveal interesting disorder and spin-related transport phenomena.

[1]A. S. Ingason, M. Dahlqvist, J. Rosen, Magnetic MAX phases from theory and experiments; a review; J. Phys.: Condens. Matter 28 (2016), 433003.[2]M. W. Barsoum, MAX Phases: Properties of Machinable Ternary Carbides and Nitrides; Weinheim: Willey-VCH (2013).[3] C. Wang, T. Yang, C. L. Tracy, C. Lu, H. Zhang, Y.-J. Hu, L. Wang, L. Qi, L. Gu, Q. Huang, J.Zhang, J. Wang, J. Xue, R. C. Ewing, Y. Wang, Disorder in Mn+1AXnphases at the atomic scale, Nature Communications 10, 622 (2019).

Related publications

  • Poster
    EuFN workshop, 27.-30.09.2021, WROCLAW, Poland

Publ.-Id: 32889

Transient behaviour of electrovortex flow in a cylindrical container

Liu, K.; Stefani, F.; Weber, N.; Weier, T.; Li, B.-W.

This study is a continuation of a combined experimental and numerical investigation of the flow of the eutectic alloy GaInSn inside a cylindrical vessel exposed to a constant electrical current. The emerging electro-vortex flow (EVF), caused by the interaction of the current, which is applied through a tapered electrode, with its own magnetic field, might have both detrimental and advantageous effects in liquid metal batteries (LMBs). While the former work was mainly concerned with time-averaged results, this paper focuses on the transient behaviour of the EVF which becomes most relevant under the influence of an external axial field. The additional Lorentz force, generated by the interaction of the imposed current with the vertical component of the geomagnetic field (bz), drives the ordinary EVF jet flow into a swirling motion. The velocity distributions and motion characteristics, such as spiral streamlines, and shortened and irregularly swinging jet regions, are investigated. The mechanism is analysed in detail for bz = −25.5 µT. The maximum angular velocity of the rotating jet region is basically linearly dependent on bz , at least for the values studied here. A good agreement between the transient simulation and experimental result is shown.


Publ.-Id: 32886

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, 182-187
  • Lecture (Conference) (Online presentation)
    Electromagnetic Processing of Materials, 14.-16.06.2021, Riga, Latvia
  • Magnetohydrodynamics 58(2022)1-2, 81-88
    DOI: 10.22364/mhd.58.1-2.8
    Cited 2 times in Scopus


Publ.-Id: 32885

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

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

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

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


Publ.-Id: 32883

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

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

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

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

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

Value of PET imaging for radiation therapy

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

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

Keywords: PET; radiation oncology; functional imaging; radiomics

Publ.-Id: 32878

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

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

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

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

Publ.-Id: 32877

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

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

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

Related publications


Publ.-Id: 32876

An open-access future for Journal of Synchrotron Radiation

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

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

Publ.-Id: 32875

Generation of Reverse Meniscus Flow by Applying An Electromagnetic Brake

Vakhrushev, A.; Kharicha, A.; Karimi-Sibaki, E.; Wu, M.; Ludwig, A.; Nitzl, G.; Tang, Y.; Hackl, G.; Watzinger, J.; Eckert, S.

A numerical study is presented that deals with the flow in the mold of a continuous slab caster under the influence of a DC magnetic field (electromagnetic brakes (EMBrs)). The arrangement and geometry investigated here is based on a series of previous experimental studies carried out at the mini-LIMMCAST facility at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR). The magnetic field models a ruler-type EMBr and is installed in the region of the ports of the
submerged entry nozzle (SEN). The current article considers magnet field strengths up to 441 mT, corresponding to a Hartmann number of about 600, and takes the electrical conductivity of the solidified shell into account. The numerical model of the turbulent flow under the applied magnetic field is implemented using the open-source CFD package OpenFOAM. Our numerical results reveal that a growing magnitude of the applied magnetic field may cause a reversal of the flow direction at the meniscus surface, which is related the formation of a ‘‘multiroll’’ flow pattern in the mold. This phenomenon can be
explained as a classical magnetohydrodynamics (MHD) effect: (1) the closure of the induced electric current results not primarily in a braking Lorentz force inside the jet but in an acceleration in regions of previously weak velocities, which initiates the formation of an opposite vortex (OV) close to the mean jet; (2) this vortex develops in size at the expense of the main vortex until it reaches the meniscus surface, where it becomes clearly visible. We also show
that an acceleration of the meniscus flow must be expected when the applied magnetic field is smaller than a critical value. This acceleration is due to the transfer of kinetic energy from smaller turbulent structures into the mean flow. A further increase in the EMBr intensity leads to the expected damping of the mean flow and, consequently, to a reduction in the size of the upper roll. These investigations show that the Lorentz force cannot be reduced to a simple
damping effect; depending on the field strength, its action is found to be topologically complex.

Keywords: continuous casting; mold flow; electromagnetic brake; numerical simulation

Publ.-Id: 32874

Resolution Enhancement for Drill-Core Hyperspectral Mineral Mapping

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

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

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

Publ.-Id: 32872

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

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

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

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

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

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

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

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


Publ.-Id: 32869

Solidification and fluid convection - the story of an inseparable couple

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

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

Keywords: solidification; double-diffusive convection; macrosegregation

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

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

Experimental validation of 4D log file-based proton dose reconstruction for interplay assessment considering amplitude-sorted 4DCTs

Spautz, S.; Jakobi, A.; Meijers, A.; Peters, N.; Löck, S.; Knopf, A. C.; Troost, E. G. C.; Richter, C.; Stützer, K.

Purpose: The unpredictable interplay between dynamic proton therapy delivery and target motion (in the thorax) can lead to severe dose distortions. A fraction-wise four-dimensional (4D) dose reconstruction workflow allows to assess the applied dose after patient treatment considering the actual beam delivery sequence extracted from machine log files, the recorded breathing pattern and the geometric information from a 4D computed tomography scan (4DCT). Such an algorithm capable of accounting for amplitude sorted 4DCTs was implemented and its accuracy as well as its sensitivity to input parameter variations was experimentally evaluated.
Methods: An anthropomorphic thorax phantom with a movable insert containing a target surrogate and a radiochromic film was irradiated with a monoenergetic field for various 1D target motion forms (sin, sin4) and peak-to-peak amplitudes (5/10/15/20/30 mm). The measured characteristic film dose distributions were compared to the respective sections in the 4D reconstructed doses using a 2D γ-analysis; γ-pass rates were derived for different dose grid resolutions (1mm/3mm) and deformable image registrations (DIR, automatic/manual) applied during the 4D dose reconstruction process. In an additional analysis, the sensitivity of reconstructed dose distributions against potential asynchronous timing of the motion and machine log files was investigated for both a monoenergetic field and more realistic 4D robustly optimized fields by artificially introduced offsets of ± 1/5/25/50/250 ms. The resulting dose distributions with asynchronized log files were compared to the those with synchronized log files by means of a 3D γ-analysis and the evaluation of absolute dose differences.
Results: The induced characteristic interplay patterns on the films were well reproduced by the 4D dose reconstruction with 2D γ-pass rates ≥95% for almost all cases with motion magnitudes ≤15 mm. In general, the γ-pass rates showed a significant decrease for larger motion amplitudes and increase when using a finer dose grid resolution but were not affected by the choice of motion form (sin, sin4). There was also a statistical trend towards the manually defined DIR for better quality of the reconstructed dose distributions in the area imaged by the film. The 4D dose reconstruction results for the monoenergetic as well as the 4D robustly optimized fields were robust against small asynchronies between motion and machine log files of up to 5 ms, which is in the order of potential network latencies.
Conclusions: We have implemented a 4D log file-based proton dose reconstruction that accounts for amplitude sorted 4DCTs. Its accuracy was proven to be clinically acceptable for target motion magnitudes of up to 15 mm. Particular attention should be paid to the synchronization of the log file generating systems as the reconstructed dose distribution may vary with log file asynchronies larger than those caused by realistic network delays.

Keywords: proton therapy; log file-based dose reconstruction; pencil beam scanning; 4D dose; interplay effect

Publ.-Id: 32866

5f states in UGa2 probed by x-ray spectroscopies

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

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

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Publ.-Id: 32865

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

Creutzburg, S.

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

Related publications


Publ.-Id: 32864

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

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

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

Related publications

Publ.-Id: 32862

Autocorrelation-informed home range estimation: a review and practical guide

Simoes Silva, I. M.; Fleming, C. H.; Noonan, M. J.; Alston, J.; Folta, C.; Fagan, W. F.; Calabrese, J.

1. Modern tracking devices allow for the collection of high-volume animal tracking data at improved sampling rates over VHF radiotelemetry. Home range estimation is a key output from these tracking datasets, but the inherent properties of animal movement can lead traditional statistical methods to under- or overestimate home range areas.
2. The Autocorrelated Kernel Density Estimation (AKDE) family of estimators were designed to be statistically efficient while explicitly dealing with the complexities of modern movement data: autocorrelation, small sample sizes, and missing or irregularly sampled data. Although each of these estimators has been described in separate technical papers, here we review how these estimators work and provide a user-friendly guide on how they may be combined to reduce multiple biases simultaneously.
3. We describe the magnitude of the improvements offered by these estimators and their impact on home range area estimates, using both empirical case studies and simulations, contrasting their computational costs.
4. Finally, we provide guidelines for researchers to choose among alternative estimators and an R script to facilitate the application and interpretation of AKDE home range estimates.

Keywords: home range; tracking data; telemetry; kernel density estimation; movement process; ecology; ctmm; AKDE; autocorrelation


Publ.-Id: 32861

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

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

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

Related publications


Publ.-Id: 32860

Prompt Gamma-Ray Range Verification in Particle Therapy

Kögler, T.

Particle therapy (PT) has become a widely accepted and promising option for tumor treatment. It supplements conventional radiation therapy with MV X-rays and electrons and is becoming increasingly important for more and more applications. More than 100 clinical PT facilities are already in operation worldwide, around 40 are currently under construction and just as many are planned.
The accuracy of the prediction of the particle range in the tissue is, however, influenced by uncertainties in patient positioning, by patient movements during irradiation, by anatomical changes during one or between several fractions and by other factors that are difficult to quantify in daily clinical routine. These uncertainties are considered by conservative safety margins in the treatment planning, but these margins reduce the advantage of particle beams compared to conventional therapies in many cases. Real-time range verification is therefore a necessity in order to exploit the full potential of particle therapy.
Range verification of therapeutic ions has been investigated for over 50 years now. Many systems have been developed in this time, some devices have been tested under clinical conditions and only a few make it to clinical trials. However, so far there is no system that is used in daily clinical routine. While the first devices still made use of the annihilation radiation of the positron emitters generated in the therapy, the international community mainly concentrates on the use of prompt gamma rays today.
This talk gives an overview of the current status of prompt gamma-ray based range verification. The focus is on the three currently most promising options (Prompt Gamma Ray Imaging, Spectroscopy and Timing). The metrological fundamentals of the individual systems are presented and discussed with regard to their use in everyday clinical practice.

Keywords: Prompt Gamma Treatment Verification; Range Verification in Particle Therapy; Prompt Gamma Ray Timing; Prompt Gamma Ray Imaging; Prompt Gamma Ray Spectroscopy

Related publications

  • Lecture (others) (Online presentation)
    Heidelberg Particle Therapy Seminar, 07.07.2021, Heidelberg, Deutschland

Publ.-Id: 32859

Radiolabeled PSMA inhibitors

Neels, O.; Kopka, K.; Liolios, C.; Afshar-Oromieh, A.

Prostate-specific membrane antigen (PSMA) has shown to be a promising target for diagnosis and therapy (theranostics) of prostate cancer. An introducing overview on the regulatory status of PSMA-targeting radiopharmaceuticals in the US and Europe is given. We review developments in the field of radio- and fluorescence-guided surgery and targeted photodynamic therapy as well as multitargeting PSMA inhibitors also addressing albumin and GRPr. Technical and quality aspects of PSMA-targeting radiopharmaceuticals are described and new radiolabeling strategies are presented. Finally, insights are given into production, application and potential of alternatives beyond the commonly used radionuclides for radiolabeling PSMA inhibitors. An additional re-finement of radiopharmaceuticals is required in order to further improve dose-limiting factors like nephrotoxicity and salivary gland uptake during endoradiotherapy. The combination of ra-dionuclide therapy with therapy options of other disciplines shows a way to improve the treat-ment of patients.

Keywords: PSMA; Prostate-specific membrane antigen; PSMA inhibitor; Radiolabeling; PET; SPECT; fluorescence; endoradiotherapy; theranostics; radioguided surgery; fluorescence-guided surgery; targeted photodynamic therapy; radionuclides

Publ.-Id: 32858

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)

Related publications


Publ.-Id: 32857

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

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

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


Publ.-Id: 32856

Garnet major-element composition as an indicator of host-rock type: a machine learning approach using the random forest classifier

Schönig, J.; von Eynatten, H.; Tolosana Delgado, R.; Meinhold, G.

The major-element chemical composition of garnet provides valuable petrogenetic information about its primary host lithologies, particularly in metamorphic rocks. When facing detrital garnet, information about the bulk composition and mineral paragenesis of the initial garnet-bearing host rock is absent. This prevents the application of chemical thermobarometric techniques and calls for quantitative empirical approaches. Here we present a new garnet host-rock discrimination scheme that is based on a random forest machine-learning algorithm trained on a large dataset of 13,615 garnet analyses that covers a wide variety of garnet-bearing lithologies. Considering the out-of-bag error, the scheme correctly predicts the original garnet host-rock in (i) >95 % concerning the setting, that is mantle versus metamorphic versus igneous versus metasomatic; (ii) >84 % concerning the metamorphic facies, that is blueschist/greenschist versus amphibolite versus granulite versus eclogite/ultrahigh-pressure; and (iii) >93 % concerning the host-rock composition, that is intermediate–felsic/metasedimentary versus mafic versus ultramafic versus alkaline versus calcsilicate. The wide coverage of potential host rocks, the detailed prediction classes, the high discrimination rates, and the successfully tested real-case applications demonstrate that the introduced scheme overcomes many issues related to previous schemes. This highlights the potential of transferring the applied discrimination strategy to the broad range of detrital minerals beyond garnet, as well as many other quantitative empirical challenges in Earth sciences. For easy and quick usage, a freely accessible web app is provided that guides the user in five steps from garnet composition to prediction results including data visualization.

Publ.-Id: 32854

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

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

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

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

  • Contribution to proceedings
    Electromagnetic processing of materials 2021, 14.-16.06.2021, Riga / virtual, Latvia
    Proceedings of the 10th international conference Electromagnetic Processing of Materials, Riga: The University of Latvia Press, 978-9934-18-686-8, 1-280
  • Lecture (Conference) (Online presentation)
    Electromagnetic processing of materials 2021, 16.06.2021, Riga / virtual, Latvia
  • Magnetohydrodynamics 58(2022)1/2, 25-32
    DOI: 10.22364/mhd.58.1-2.3
    Cited 1 times in Scopus

Publ.-Id: 32853

Strong Binding of Noble Gases to [B₁₂X₁₁]⁻: a theoretical study

Wöhner, K.; Wulf, T.; Vankova, N.; Heine, T.

We systematically explore the stability and properties of [B₁₂X₁₁NG]⁻ adducts resulting from the binding of noble gas atoms to anionic [B₁₂X₁₁]⁻ clusters in the gas phase of mass spectrometers. [B₁₂X₁₁]⁻ can be obtained by stripping one X⁻ off the icosahedral closo-dodecaborate dianion [B₁₂X₁₂]²⁻. We study the binding of the noble gas atoms He, Ne, Ar, Kr and Xe to [B₁₂X₁₁]⁻ with substituents X = F, Cl, Br, I, CN. While He cannot be captured by these clusters and Ne only binds at low temperatures, the complexes with the heavier noble gas atoms Ar, Kr and Xe show appreciable complexation energies and exceed 1 eV at room temperature in the case of [B₁₂(CN)₁₁Xe]⁻. The predicted B–NG equilibrium distance in the complexes with Ar, Kr and Xe is only 0.10 to 0.25 Å longer than the sum of the covalent radii of the two corresponding atoms, and a significant charge transfer from the noble gas atom to the icosahedral B₁₂ cage is observed.

Keywords: Boron; Anions; Complexation; Cluster chemistry; Group 17 compounds


Publ.-Id: 32852

Concept of High-Power CW IR-THz Source for the Radiation Source ELBE Upgrade

Evtushenko, P.; Lehnert, U.; Michel, P.; Cowan, T.

The Radiation Source ELBE at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) is a user facility based on a 1 mA - 40 MeV CW SRF LINAC. Presently HZDR is considering upgrade options for the ELBE or its replace- ment with a new CW, SRF LINAC-based user facility. A part of the user requirements is the capability to generate IR and THz pulse in the frequency range from 0.1 through 30 THz, with pulse energies in the range from 100 J through a few mJ, at the repetition rate between 100 kHz and 1 MHz. This corresponds to the pulse energy in- crease, dependent on the wavelength, by a factor from 100 through 1000. In this contribution, we outline key aspects of a concept, which would allow to achieve such parameters. These aspects are: 1 - use of a beam with longitudinal density modulation and bunching factor of about 0.5 at the fundamental frequency; 2 - achieving the density modulation through the mechanism similar to the one used in optical klystron (OK); 3 – generating the necessary for the modulation optical beam by an FEL oscillator, and 4 - using two electron injectors. First injec- tor would provide a beam for the FEL oscillator. Second high charge injector would provide the beam for the high pulse energy generation for users. All-in-all the concept of the new radiation source is very similar to an OK, but operating with two beams simultaneously.

Keywords: ELBE; THz; superradiant; undulator radiation; high power; SRF linac

Related publications


Publ.-Id: 32851

Design of High-Power CW IR-THz Source for the Radiation Source ELBE Upgrade

Evtushenko, P.; Lehnert, U.; Michel, P.; Cowan, T.

The Radiation Source ELBE at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) is a user facility based on a 1 mA - 40 MeV CW SRF LINAC. Presently HZDR is considering upgrade options for the ELBE or its replace- ment with a new CW, SRF LINAC-based user facility. A part of the user requirements is the capability to generate IR and THz pulse in the frequency range from 0.1 through 30 THz, with pulse energies in the range from 100 J through a few mJ, at the repetition rate between 100 kHz and 1 MHz. This corresponds to the pulse energy in- crease, dependent on the wavelength by a factor from 100 through 1000. In this contribution, we outline key aspects of a concept, which would allow to achieve such parame- ters. Such key aspects are: 1 - use of a beam with longitu- dinal density modulation and bunching factor of about 0.5 at the fundamental frequency; 2 - achieving the density modulation through the mechanism similar to the one used in optical klystron (OK) and HGHG FEL; 3 - gener- ating necessary for the modulation optical beam by an FEL oscillator, and 4 - using two electron injectors, where one injector provides beam for the FEL oscillator while second high charge injector provides beam for the high energy per pulse generation for user experiments. All-in- all the concept of the new radiation source is very similar to an OK, but operating with two beams simultaneously.

Keywords: Superradiant Undulator; THz; SRF LINAC; Undulator radiation; modulated beam

Related publications

  • Open Access Logo Contribution to proceedings
    10th International Particle Accelerator Conference - IPAC 19, 19.-24.05.2019, Melbourne, Australia
    IAPC2019 Proceedings, 1702-1704
    DOI: 10.18429/JACoW-IPAC2019-TUPRB012


Publ.-Id: 32850

Probing the local coordination of hexavalent uranium and the splitting of 5f orbitals induced by chemical bonding.

Amidani, L.; Retegan, M.; Volkova, A.; Popa, K.; Martin, P. M.; Kvashnina, K.

We report here the first detailed experimental and theoretical investigation of hexavalent uranium in various local configurations with high-energy-resolution fluorescence-detected X-ray absorption near-edge structure at the M4 edge. We demonstrate the pronounced sensitivity of the technique to the arrangement of atoms around the absorber and provide a detailed theoretical interpretation revealing the nature of spectral features. We show that for all local configuration analyzed, the main peak corresponds to non-bonding 5f orbitals, and the highest energy peak corresponds to anti-bonding 5f orbitals. Our findings are in agreement with the accepted interpretation of uranyl spectral features and embed the latter in the broader field of view where the spectra of a larger variety of U6+-containing samples are interpreted on the same theoretical ground.


Publ.-Id: 32849

To form or not to form: PuO2 nanoparticles at acidic pH

Gerber, E.; Romanchuk, A. Y.; Weiss, S.; Kuzenkova, A.; Hynault, M.; Bauters, S.; Egorov, A.; Butorin, S. M.; Kalmykov, S. N.; Kvashnina, K. O.

Properties of the PuO2 nanoparticles (NPs) formed under acidic conditions (pH 1-4) are explored in this study at the atomic scale. High-resolution transmission electron microscopy (HRTEM) was applied to characterize the crystallinity, morphology and size of the precipitates. It was found that 2 nm crystalline NPs are formed with a crystal structure similar to bulk PuO2. High energy resolution fluorescence detected (HERFD) X-ray absorption spectroscopy at the Pu M4 edge has been used to identify the Pu oxidation states and recorded data are analyzed using the theory based on the Anderson Impurity Model (AIM). The experimental data obtained on NPs show that Pu(IV) oxidation state dominates in all NPs formed at pH 1-4. However, the suspension at pH 1 demonstrate the presence of Pu(III) in addition to the Pu(IV), which is associated with redox dissolution of PuO2 NPs under acidic conditions. As shown by UV-Vis the contribution of Pu(III) in the HERFD spectrum for the sample at pH 1 originates from the solution rather than from NPs themselves. We discuss in detail the mechanism that affects the PuO2 NP synthesis under acidic conditions and compare it with one in neutral and alkaline conditions. Future investigations of plutonium chemistry will fundamentally benefit from the insights this work provides and further applied to various environmental and technological applications

Related publications

Publ.-Id: 32848

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

Related publications

Publ.-Id: 32847

HERFD-XANES and RIXS study on the electronic structure of trivalent lanthanides across a series of isostructural compounds

Zasimov, P. V.; Amidani, L.; Retegan, M.; Walter, O.; Caciuffo, R.; Kvashnina, K. O.

We performed a systematic study of the complexes of trivalent lanthanide cations with the hydridotris(1-pyrazolyl)borato (Tp) ligand (LnTp3; Ln = La, Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb, and Lu) using both high-energy-resolution fluorescence-detected X-ray absorption near-edge structure (HERFD-XANES) and resonant inelastic X-ray scattering (RIXS) at the lanthanide L3 absorption edge. Here, we report the results obtained and we discuss them against simulations performed with the density functional theory and atomic multiplet theory computational approaches. The spectral shape and the elemental trends observed in the experimental HERFD-XANES spectra are well reproduced by density functional theory calculations, whilst the pre-edge energy interval is well better described by atomic multiplet theory. The RIXS data show a generally rather complex pattern that originates from the intra-atomic electron-electron interactions in the intermediate and final states, as demonstrated by the good agreement obtained with simulations considering exclusively the atomic configuration. Guided by theoretical predictions, we discuss possible origins of the observed spectral features and the trends in energy splitting across the series. The insight in the electronic structure of trivalent lanthanides compounds demonstrated here and obtained with advanced X-ray spectroscopies coupled with theoretical simulations can be applied to any lanthanide-bearing compound and be of great interest for all research fields involving lanthanides

Related publications

Publ.-Id: 32846

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

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

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

Related publications


Publ.-Id: 32845

Towards The Bottom of The Periodic Table

Kvashnina, K.

Towards the Bottom of the Periodic Table

Related publications

  • 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.

Related publications

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


Publ.-Id: 32843

Bubble coalescence and breakup mechanism in a vertical pipe with an obstacle

Liao, Y.; Sibel, T.-K.; Martin, N.-K.; Lucas, D.

One of the major issues in numerical study of bubbly flows is the prediction of bubble size. Among other physical processes coalescence and breakup represents a huge challenge. A variety of investigations on bubble coalescence and breakup in turbulent flows has been motivated, and a remarkable diversity of mechanisms has been observed. However, knowledge on the superposition of multiple mechanisms remains insufficient. The purpose of this work is to investigate the effect of a sudden change of flow fields on coalescence and breakup events. Turbulent bubbly flows in a vertical pipe with a ring obstacle are analyzed with ultrafast x-ray computed tomography and a generalized population balance model. The results show that coalescence and breakup are in equilibrium before the obstacle leading to a nearly unchanged bubble size distribution (BSD) and quasi fully-developed flow, which is destroyed by the presence of the obstacle. Immediately behind it, both the coalescence and breakup rates are enhanced due to intensified turbulence and recirculation, and as a result, the BSD becomes broader. At first, the increase in coalescence exceeds that in breakup such that the mean bubble size increases. After about ten millimeters downstream from the obstacle (L/D≈0.2), breakup overtakes coalescence and the BSD shifts to the direction of small bubble size. At L/D≈0.4, the bubble size before the obstacle is almost recovered, but it decreases further downstream. The predicted and measured BSDs agree well with each other upstream and downstream, where the bubble coalescence and breakup is majorly controlled by turbulence. Difficulties are encountered in capturing the drastic change in the region directly downstream of the obstacle in particular the rapid increase in coalescence rate. The test of turbulence single-phase flow through a sudden expansion reveals that it is difficult for a RANS model to reproduce the turbulence structure in the recirculation zone reliably, which directly affects the performance of coalescence and breakup models. Furthermore, coalescence resulting from other mechanisms such as wake entrainment or laminar shear is shown to have a minor contribution, and turbulence is dominant. Further investigations concerning bubble coalescence and breakup, turbulence as well as its effect on interfacial momentum transfer are necessary for the obstructed flow.

Keywords: bubble coalescence and breakup; computational fluid dynamics; obstacle; turbulence; vertical pipe flow

  • Contribution to proceedings
    The 19th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-19), 06.-11.03.2022, Brussels, Belgium
  • Lecture (Conference)
    The 19th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-19), 06.-11.03.2022, Brussels, Belgium

Publ.-Id: 32842

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

Related publications

  • 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.

Related publications

  • 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

Related publications


Publ.-Id: 32839

Uptake of niobium by cement systems relevant for nuclear waste disposal: impact of ISA and chloride

Cevirim-Papaioannou, N.; Jo, Y.; Franke, K.; Fuss, M.; de Blochouse, B.; Altmaier, M.; Gaona, X.

The isotope 94 of niobium (t1/2= 2.04·104 a) is produced during the operation of nuclear reactors due to the neutron activation of 93Nb, which is present in some structural components in nuclear reactor vessels. Related waste streams will be disposed of in repositories for low and intermediate level wastes (L/ILW), where cement is widely used for the stabilization of the waste and for construction purposes.
The retention of niobium by young cement was investigated in a series of sorption experiments using a combination of active (95Nb + 91mNb) and inactive (93Nb) niobium isotopes. Sorption experiments assessed also the impact of iso-saccharinic acid (ISA, main degradation product of cellulose) and chloride on Nb retention, both expected in specific L/ILW.
A pyrochlore-structure Ca-Nb(V) oxide was found to control the solubility of Nb(V) in cement pore water at pH= 13.5, defining [Nb(V)]aq = 2∙10-6 - 7·10–8 M. Sorption experiments revealed a strong uptake of Nb(V) by cement (5 ≤ log Rd ≤ 7, Rd in L·kg–1), in spite of the predominance of anionic hydrolysis species in the cement pore water. Sorption isotherms were found to be linear within 10–14 M ≤ [Nb(V)]aq ≤ 10–9 M. Calcium silicate hydrate (C-S-H) phases are defined as main sink of Nb(V) in cement, with Ca2+ playing a key role in bridging the negatively charged Nb(V) species to C-S-H. ISA significantly decreases the uptake of Nb(V) at [ISA]aq ≥ 10–4 M, reflecting the formation of stable (Ca-)Nb(V)-ISA complexes in the aqueous phase. Sorption is not affected by chloride within the investigated concentration range (10–5 M ≤ [Cl] ≤ 1.0 M).
This work represents the first experimental evidence on the uptake of niobium by young cement in the absence and presence of ISA and Cl, thus providing key inputs for the assessment of 94Nb retention in the context of the Safety Case for repositories for nuclear waste.

Keywords: niobium; cement; ISA; chloride; sorption

Publ.-Id: 32838

Novel Radionuclides - Don’t Forget the Regulatory Side

Neels, O.

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

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

Publ.-Id: 32837

Regulatory Aspects of Cold Kit-Based Radiopharmaceuticals in the EU

Neels, O.

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

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

Publ.-Id: 32836

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

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


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

Materials and Methods:

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


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


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

Publ.-Id: 32835

Resonance behavior of embedded and freestanding microscale ferromagnets

Cansever, H.; Anwar, M. S.; Stienen, S.; Lenz, K.; Narkovic, R.; Hlawacek, G.; Potzger, K.; Hellwig, O.; Faßbender, J.; Lindner, J.; Bali, R.

The ferromagnetic resonance of a disordered A2 Fe60Al40 of ferromagnetic strip, of dimensions 5 µm × 1 µm x 32 nm, has been observed in two vastly differing surroundings: in the first case, the ferromagnetic region was circumferenced by ordered B2 Fe60Al40, and in the second case it was free standing, adhering only to the oxide substrate. The embedded ferromagnet possesses a periodic magnetic domain structure, which transforms to a single domain structure in the freestanding case. The two cases differ in their dynamic response, for instance, the resonance field for the uniform (k = 0) mode at ~ 14 GHz excitation displays a shift from 209 to 194 mT, respectively for the embedded and freestanding cases, with the external magnetic field applied along the long axis. The resonant behavior of a microscopic ferromagnet can thus be finely tailored via control of its near-interfacial surrounding.

Keywords: Embedded nanomagnets; microresonator; ferromagnetic resonance; ion irradiation

Related publications

Publ.-Id: 32834

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

Related publications

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.

Related publications

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

Publ.-Id: 32832

Interfacial behavior of particle-laden bubbles under asymmetric shear flow

Eftekhari, M.; Schwarzenberger, K.; Heitkam, S.; Javadi, A.; Bashkatov, A.; Ata, S.; Eckert, K.

The interfacial properties of air bubbles have mostly been studied in quiescent fluids or in an axisymmetric flow field. To extend the knowledge to technologically relevant conditions, we investigate the behavior of surfactant- and particle-laden bubbles under asymmetric shear forces. Experiments are performed with a buoyant bubble at the tip of a capillary placed in a defined flow field. The response of the interface to the surrounding asymmetric flow is measured under successive reduction of the surface area. Profile analysis tensiometry is utilized to investigate the dynamic surface tension and the surface rheology of the surfactant- and particle-laden interfaces. The bulk flow and the interfacial mobility of the buoyant bubble are studied using microscopic particle image and tracking velocimetry. According to our findings, under asymmetric shear flow, surfactant-laden interfaces remain mobile regardless of the surfactant concentration. In contrast, particle-laden interfaces adopt a solid-like state and resist the interfacial flow at certain surface coverages. Elasticity measurements during successive reduction of the surface area indicate a significant change in the structure of the interface that changes its mobility. The immobilization of the interface is characterized by the ratio of the interfacial elasticity to shear forces. This dimensionless number provides an estimate the interfacial forces required to initiates interfacial immobility at defined flow field. Our findings can serve as a basis to model the boundary conditions and to modulate the hydrodynamics of bubbles and droplets with different adsorbed material.


Publ.-Id: 32831

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

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

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

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

Related publications

Publ.-Id: 32827

Log file-based 4D proton dose reconstruction for interplay assessment in clinical routine and simulation studies

Stützer, K.; Spautz, S.; Thiele, J.; Tschiche, M.; Troost, E. G. C.; Richter, C.

We have implemented the reconstruction of interplay-affected dose distributions from the log files of the dynamic PBS proton beam delivery and of the breathing-induced intra-fractional motion. For the first time, such an algorithm is capable to consider amplitude-sorted 4DCT phases. We have validated the reconstruction accuracy by phantom experiments for several motion patterns and magnitudes. The module is applied in combination with weekly repeat 4DCTs to routinely monitor the PBS treatments of NSCLC patients in our clinic department. Further use cases are occasional pre-treatment interplay estimations and the interplay effect evaluations within a plan comparison study investigating the benefit of 4D robustly optimized proton plans for NSCLC patients with large breathing motion (>5mm).

  • Lecture (others) (Online presentation)
    European RayStation user meeting 2021, 30.11.-01.12.2021, Stockholm, Sweden

Publ.-Id: 32826

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

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

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

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

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

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

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

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

Publ.-Id: 32825

THEREDA - Thermodynamic Reference Database

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

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

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

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

Related publications

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

Effect of Background Electrolyte Composition on the Interfacial Formation of Th(IV) Nanoparticles on the Muscovite (001) Basal Plane

Neumann, J.; Qiu, C.; Eng, P.; Skanthakumar, S.; Soderholm, L.; Stumpf, T.; Schmidt, M.

Understanding the impact of actinide nanoparticle (NP) formation is important to assess radionuclide mobility in the environment. We combined Surface X-ray Diffraction (SXRD) and in situ AFM to investigate the previously reported unusual electrolyte effects on Th uptake on mica. At low [Th] (0.1 mM), interfacial structures show a broad Th electron density (~50 Å). A linear decrease of Th uptake with decreasing hydration enthalpy of the electrolyte cation (Li⁺, K⁺, NH₄⁺, Cs⁺) indicates a competitive effect between Th and the electrolyte cation. Na⁺ is a clear outlier from this trend. In situ AFM imaging confirms the results. Particles show a vertical size of ~1 – 2 nm and larger lateral dimensions of ~10 – 20 nm, which is typical for particles formed at interfaces (heterogeneous nucleation). At high [Th] = 1 and 3 mM, all investigated electrolytes (ACl, A = Li⁺, Na⁺, K⁺) show similar Th uptake, indicating a much smaller impact of electrolyte composition. The interfacial structures are dominated by a high Th loading at a distinct distance (~6.5 Å) from the surface. Therefore, the main retention mechanism at high [Th] is suggested to be the sorption of Th NPs aggregated from Th oligomers present in solution (homogeneous nucleation).

Keywords: CTR; RAXR; SXRD; AFM; surface X-ray diffraction; nanoparticles; nucleation; thorium

Publ.-Id: 32820

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

Related publications


Publ.-Id: 32819

Analyse eines Energiespeichersystems basierend auf geologischer Unter-grundspeicherung von CO2 und CH4

Fogel, S.; Yeates, C.; Unger, S.; Hampel, U.

Die Speicherung von überschüssiger Elektroenergie aus regenerativen Energiequellen in relevanten Größenordnungen stellt eine wesentliche technologische Hürde der Energiewende in der Bundes-republik Deutschland dar. Der nationale Strombedarf in Zeiten unzureichender regenerativer Er-zeugung kann zukünftig mit Speicherkraftwerken auf Basis von aus CO2 und Elektrolysewasser-stoff produziertem synthetischen Methan (Power-to-Gas) und methangefeuerten, hocheffizienten Kraftkreisläufen (Gas-to-Power) basierend auf dem Allam-Kreislauf gedeckt werden. Durch die Nutzung von überkritischem CO2 als Kreislaufmedium lassen sich Wirkungsgrade von bis zu 66% für den Gas-to-Power-Pfad und Gesamtwirkungsgrade des Speicherzyklus von >50% erzielen. Zur Umsetzung dieses Konzeptes sind ausreichende Speicherkapazitäten für CO2, CH4 und O2 sowie regenerative Erzeugungskapazitäten vorzuhalten. Der vorliegende Beitrag untersucht den vorge-stellten Energiespeicherzyklus unter Annahme eines geschlossenen CO2-Kreislaufs gekoppelt mit geologischer Untergrundspeicherung von CO2 und CH4 im Sinne des Carbon Capture, Utilization and Storage (CCUS). Zur technischen Bewertung des Konzeptes wurde das Potential der Speiche-rung von CO2 in Aquiferen in Deutschland analysiert und eine Studie des deutschen Energiesys-tems im Jahre 2050 für verschiedene Orientierungsszenarien durchgeführt. Mit Hilfe der erstellten Szenarien konnten die zur Erlangung einer CO2-neutralen Energiespeicherung benötigen Kapazitä-ten der regenerativen Stromerzeugung, elektrolytischen Wasserstoffbereitstellung und Rekonversi-on von CH4 sowie Speicherkapazitäten für CO2, CH4 und O2 abgeleitet werden.

  • Lecture (Conference)
    53. Kraftwerkstechnisches Kolloquium, 05.-06.10.2021, Dresden, Deutschland

Publ.-Id: 32818

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

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

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

Publ.-Id: 32817

Describing chain-like assembly of ethoxygroup-functionalized organic molecules on Au(111) using high-throughput simulations

Lokamani, M.; Kelling, J.; Ohmann, R.; Meyer, J.; Kühne, T.; Cuniberti, G.; Wolf, J.; Juckeland, G.; Huhn, T.; Zahn, P.; Moresco, F.; Gemming, S.

Due to the low corrugation of the Au(111) surface, 1,4-bis(phenylethynyl)-2,5-bis(ethoxy)benzene (PEEB) molecules can form
quasi interlocked lateral patterns, which are observed in scanning tunneling microscopy (STM) experiments at low temperatures.
We demonstrate a multi-dimensional clustering approach to quantify the anisotropic pair-wise interaction of molecules and
explain these patterns. We perform high-throughput calculations to evaluate an energy function, which incorporates the
adsorption energy of single PEEB molecules on the metal surface and the intermolecular interaction energy of a pair of PEEB
molecules. The analysis of the energy function reveals, that, depending on coverage density, specific types of pattern are
preferred which can potentially be exploited to form one-dimensional molecular wires on Au(111).

Keywords: DFTB; 1,4-bis(phenylethynyl)-2,5-bis(ethoxy)benzene (PEEB); STM; High-Throughput; Meta-Structures

Publ.-Id: 32816

Transport in tight material enlightened by process tomography

Kulenkampff, J.; Bollermann, T.; Cardenas Rivera, M. A.; Fischer, C.

The analysis of fluid transport through tight barrier materials poses two major challenges: (i) Long equilibration periods require long minimum experiment durations, and, (ii) the fluid transport frequently results in complex pattern formation. Too short measuring times may feign too small transport rates; intact homogeneous samples are often missing problematic features, e.g. fractures. Both issues are detected and analyzed by using process tomography techniques, hence providing an improved understanding of transport processes in complex materials.
We thus continuously develop and apply the positron emission tomography (PET) method for geomaterials (Kulenkampff et al., 2016). It is able to trace very low concentrations of β+-emitting radionuclides during their passage through drill cores of barrier material with reasonable resolution (1 mm) and over variable periods (hours to years). The method yields time-resolved quantitative tomographic images of the tracer concentration (e.g., in contrast to input-output experiments like common permeability measurements, diffusion cells, or break-through curves.
Our current research includes the analysis of diffusive transport in heterogeneous shales (sandy facies of the Opalinuston) (BMBF and HGF iCross project), the reactive flow in fracture-filling materials of crystalline rocks (Eurad FUTURE project), and transport in engineered barriers and the contact zone (Euratom Cebama, Eurad Magic, as well as MgO and Stroefun BMWi projects). The efforts combine flow field tomography, structural imaging and reactive transport modelling for improving process understanding and to provide a bridge from the molecular to the macroscopic scale.
The benefits include:

  • Insight into temporal stability and spatial heterogeneity of the observed transport process
  • Parameterization of local velocity distribution and effective volume, comparability with pore-scale model simulations
  • Ability to quantify multiple internal transport rates without necessity to register the delayed output signal
  • Transparent and palpable visualization of processes hidden in the opaque material
The method requires specific constraints of the experimental setup (size, fluid pressure, temperature). Nevertheless, it provides unique insight into reactive transport processes observed in potential materials for nuclear waste management.
Kulenkampff, J.; Gründig, M.; Zakhnini, A.; Lippmann-Pipke, J., Solid Earth 7, 1217-1231, DOI: 10.5194/se-7-1217-2016
Kulenkampff, J.: Geophysical Research Abstracts, Vol. 20, EGU2018-8813-1, 2018.

Keywords: radioactive waste disposal; geological barrier; transport experiments; positron emission tomography

  • Open Access Logo Contribution to proceedings
    Interdisziplinäres Forschungssymposium safeND, 10.-12.11.2021, Berlin, Deutschland
    Safety of Nuclear Waste Disposal, Göttingen: Copernicus Publications
    DOI: 10.5194/sand-1-293-2021

Publ.-Id: 32815

Electrical control of orbital and vibrational interlayer coupling in bi- and trilayer 2H-MoS2

Klein, J.; Wierzbowski, J.; Soubelet, P.; Brumme, T.; Maschio, L.; Kuc, A. B.; Müller, K.; Stier, A. V.; Finley, J. J.

Manipulating electronic interlayer coupling in layered van der Waals (vdW) mate- rials is essential for designing opto-electronic devices. Here, we control vibrational and electronic interlayer coupling in bi- and trilayer 2H-MoS2 using large external electric fields in a micro-capacitor device. The electric field lifts Raman selection rules and activates phonon modes in excellent agreement with ab-initio calculations. Through polarization resolved photoluminescence spectroscopy in the same device, we observe a strongly tunable valley dichroism with maximum circular polarization degree of ∼ 60% in bilayer and ∼ 35% in trilayer MoS2 that are fully consistent with a rate equation model which includes input from electronic band structure calculations. We identify the highly delocalized electron wave function between the layers close to the high symmetry Q points as the origin of the tunable circular dichroism. Our results demonstrate the possibility of electric field tunable interlayer coupling for controlling emergent spin-valley physics and hybridization driven effects in vdW materials and their heterostructures.


Publ.-Id: 32814

Towards harmonizing clinical linear energy transfer (LET) reporting in proton radiotherapy: A European multi-centric study

Hahn, C.; Ödén, J.; Dasu, A.; Vestergaard, A.; Fuglsang Jensen, M.; Sokol, O.; Pardi, C.; Bourhaleb, F.; Leite, A.; de Marzi, L.; Smith, E.; Aitkenhead, A.; Rose, C.; Merchant, M.; Kirkby, K.; Grzanka, L.; Pawelke, J.; Lühr, A.

Background: Clinical data suggest that the relative biological effectiveness (RBE) in proton therapy (PT) varies with linear energy transfer (LET). However, LET calculations are neither standardized nor available in clinical routine. Here, the status of LET calculations among European PT institutions and their comparability are assessed and a consensus for harmonized LET reporting is presented.
Materials and methods: Eight European PT institutions used suitable treatment planning systems with their centre-specific beam model to create treatment plans in a water phantom covering different field arrangements and fulfilling commonly agreed dose objectives. They employed their locally established LET simulation environments and procedures to determine the corresponding LET distributions. Dose distributions D1.1 and DRBE assuming constant and variable RBE, respectively, and LET were compared among the institutions. Inter-centre variability was assessed based on dose- and LET-volume-histogram parameters.
Results: Treatment plans from six institutions fulfilled all clinical goals and were eligible for common analysis. D1.1 distributions in the target volume were comparable among PT institutions with variability <2.7%. However, corresponding LET values varied substantially between institutions for all field arrangements (≤57.1%), primarily due to differences in LET averaging technique and considered secondary particle spectra. Consequently, DRBE using nonharmonized LET calculations increased inter-centre dose variations substantially compared to D1.1 and significantly in mean dose to the target volume of perpendicular and opposing field arrangements (p<0.05). Harmonizing LET reporting (dose-averaging, all protons, LET to water) reduced the inter-centre variability in LET to the order of 10-15% within and outside the target volume for all beam arrangements. Consequentially, inter-institutional variability in DRBE decreased to that observed for D1.1 (p>0.05).
Conclusion: Harmonizing the reported LET among PT centres is feasible and allows for consistent multi-centric analysis and reporting of tumour control and toxicity in view of a variable RBE. It may serve as basis for harmonized variable RBE dose prescription in PT.

Keywords: proton therapy; multi-centric study; linear energy transfer (LET); relative biological effectiveness (RBE)


Publ.-Id: 32813

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

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

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

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

Related publications

Publ.-Id: 32812

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

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

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

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


Publ.-Id: 32811

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

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

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

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

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

Related publications

  • 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

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

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

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

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

Related publications

Publ.-Id: 32809

Environmental drivers of body size in North American bats

Alston, J.

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

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

Publ.-Id: 32808

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.; Reed, C. G.; Weiner, S.; Kurukura, S.; Hassan, A. A.; Namoni, M.; Ekadeli, J.; Kimuyu, D. M.; Young, T. P.; Kartzinel, T. R.; Palmer, T. M.; Pringle, R. M.; Goheen, J. R.

1. The extinction of 80% of megaherbivore (>1,000 kg) species towards the end of the Pleistocene altered vegetation structure, fire dynamics, and nutrient cycling worldwide. Ecologists have proposed (re)introducing megaherbivores or their ecological analogues to restore lost ecosystem functions and reinforce extant but declining megaherbivore populations. However, the effects of megaherbivores on smaller herbivores are poorly understood.

2. We used long-term exclusion experiments and multispecies hierarchical models fitted to dung counts to test 1) the effect of megaherbivore (elephant and giraffe) presence-absence on the occurrence (dung presence) and use intensity (dung-pile density) of mesoherbivores (2–1,000 kg), and 2) the extent to which the responses of each mesoherbivore species was predictable based on their traits (diet and shoulder height) and phylogenetic relatedness.

3. Megaherbivores increased the predicted occurrence and use intensity of zebras but reduced the occurrence and use intensity of several other mesoherbivore species. The negative effect of megaherbivores on mesoherbivore occurrence was stronger for shorter species, regardless of diet or relatedness.

4. Megaherbivores substantially reduced the expected total use intensity (i.e., cumulative dung density of all species) of mesoherbivores, but only minimally reduced the expected species richness (i.e., cumulative predicted occurrence probabilities of all species) of mesoherbivores (by <1 species).

5. Simulated extirpation of megaherbivores altered use intensity by mesoherbivores, which should be considered during (re)introductions of megaherbivores or their ecological proxies. Species’ traits (in this case shoulder height) may be more reliable predictors of mesoherbivores’ responses to megaherbivores than phylogenetic relatedness, and may be useful for predicting responses of data-limited species.

Keywords: African savanna; biotic interactions; competition; elephant; facilitation; giraffe; megafauna; trophic rewilding


Publ.-Id: 32807

Daily torpor reduces the energetic consequences of habitat selection for a widespread bat

Alston, J.; Dillon, M. E.; Keinath, D. A.; Abernethy, I. M.; Goheen, J. R.

Homeothermy requires increased metabolic rates as temperatures decline below the thermoneutral zone, so homeotherms typically select microhabitats within or near their thermoneutral zones during periods of inactivity. However, many mammals and birds are heterotherms that relax internal controls on body temperature when maintaining a high, stable body temperature is energetically costly. Such heterotherms should be less tied to microhabitats near their thermoneutral zones, and because heterotherms spend more time in torpor and expend less energy at colder temperatures, heterotherms may even select microhabitats in which temperatures are well below their thermoneutral zones. We studied how temperature and daily torpor influence selection of diurnal roosts by a heterothermic bat (Myotis thysanodes). We (1) quantified the relationship between ambient temperature and daily duration of torpor, (2) simulated daily energy expenditure over a range of microhabitat (roost) temperatures, and (3) quantified the influence of roost temperature on roost selection. While warm roosts substantially reduced energy expenditure of simulated homeothermic bats, heterothermic bats modulated their use of torpor to maintain a constant level of energy expenditure over the course of a day. Daily torpor expanded the range of energetically economical microhabitats, such that roost selection was independent of roost temperature. Our work adds to a growing literature documenting functions of torpor beyond its historical conceptualization as a last-resort measure to save energy during extended or acute energetic stress.

Keywords: Bayesian hierarchical models; climate change; daily torpor; fringed myotis (Myotis thysanodes); temporal heterothermy; thermal ecology; VHF telemetry


Publ.-Id: 32806

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

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

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

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

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


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

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

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

Publ.-Id: 32805

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