Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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Approved and published publications
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41341 Publications

Probing Defects and Spin-Phonon Coupling in CrSBr via Resonant Raman Scattering

Torres, K.; Kuc, A. B.; Maschio, L.; Pham, T.; Reidy, K.; Dekanovsky, L.; Sofer, Z.; Ross, F. M.; Klein, J.

Understanding the stability limitations and defect formation mechanisms in 2D magnets is essen- tial for their utilization in spintronic and memory technologies. Here, we correlate defects in mono- to multilayer CrSBr with their structural and vibrational properties. We use resonant Raman scattering to reveal distinct vibrational defect signatures. In pristine CrSBr, we show that bromine atoms mediate vibrational interlayer coupling, allowing for distinguishing between surface and bulk defect modes. We show that environmental exposure causes drastic degradation in monolayers, with intralayer defects forming more readily in monolayers. Through deliberate ion irradiation, we tune the formation of defect modes, which we show are strongly polarized and resonantly enhanced, reflecting the quasi-1D electronic character of CrSBr. Overall, we present a structural and vibrational study of defective CrSBr, demonstrate the air stability above the monolayer threshold, and provide further insight into the quasi-1D physics present, creating crucial understanding for defect engineering of magnetic textures.

Publ.-Id: 35188

CFD Simulation of Gas-Solid-Liquid Bubble Column

Draw, M.; Rzehak, R.

The dependence of froth flotation performance on various inter-related chemical, operational and instrumental components, makes optimizing a flotation system a very complex task. Computational Fluid Dynamics tools provide the means to study the flow inside a flotation cell by employing mathematical models that describe the interaction between the different phases of the system. The purpose of this work is to use Euler-Euler-Euler CFD simulations in OpenFOAM to validate a set of interfacial models to determine the hydrodynamics of a gas-solid-liquid flow. The combination of previously well validated baseline models for gas-liquid flows and solid-liquid flows is used for this purpose. The baseline combination includes drag, lift, wall, turbulent dispersion and virtual mass forces as well as bubble induced turbulence for gas-liquid interaction, and drag, lift, turbulent dispersion and virtual mass forces for solid-liquid interaction. Based on an extensive literature review of gas-solid-liquid experiments, the bubble column data of Rampure et al. are chosen for the numerical validation. Preliminary results show that the bubble diameter, which was not measured precisely, plays a significant role for the gas volume fraction distribution. Bubble diameter of 7 mm yields gas volume fraction profiles in agreement with the experimental data. The baseline combination yields higher particle suspension than indicated by the experimental data. This leads to a systematic study of the closure models. Choosing a model set similar to that of Rampure et al. improves the agreement of the solid distribution but deteriorates that of the gas distribution. It must be noted that, the high gas flow rate and high solid concentration likely require consideration of further aspects that are expected to have a significant effect on the flow. These may include a PIT model, a swarm corrector for the bubble and particle drag force, modifying the bubble drag force due to the existence of particles and vice versa, a solid pressure due to particle collisions and modifying the liquid viscosity due to the presence of particles. The study of the effect of these aspects is still on-going.

Keywords: Euler-Euler Simulation; Gas-Solid-Liquid; Bubble Column; Multiphase

  • Lecture (Conference)
    14th European Fluid Mechanics Conference, 13.-16.09.2022, Athen, Griechenland

Publ.-Id: 35187

Bubbly flow simulation with particle-center-averaged Euler-Euler model: Fixed polydispersity and bubble deformation

Lyu, H.; Lucas, D.; Rzehak, R.; Schlegel, F.

Bubble size and deformation are important factors for the closure models required in Euler-Euler simulations of bubbly flows. To properly simulate polydisperse bubbly flows where the bubble size spectrum may cover a range of several millimeters, several velocity groups with different sizes have to be considered. To this end, the theory for the particlecenter-averaged Euler-Euler model is generalized for the simulation with multiple bubble velocity groups. Furthermore, bubble deformation effects have been included in appropriate bubble force models. The particle-center-averaged Euler-Euler model provides additional freedom to consider the bubble shape during the conversion between the bubble number density and the gas volume fraction. Therefore, the theory is also generalized to consider an oblate ellipsoidal bubble shape in simulations. A bubbly pipe flow is used to validate the theory and to demonstrate the improvements of the proposed generalizations.

Keywords: fixed polydispersity; bubble deformation; particle-center-averaging method; Euler-Euler model


Publ.-Id: 35186

Spin wave non-reciprocity at the spin-flop transition region in synthetic antiferromagnets

Gladii, O.; Salikhov, R.; Hellwig, O.; Schultheiß, H.; Lindner, J.; Gallardo, R.

We investigate the frequency non-reciprocity in CoFeB/Ru/CoFeB synthetic antiferromagnets near the spin-flop transition region, where the magnetic moments in the two ferromagnetic layers are non-collinear. Using conventional Brillouin light scattering, we perform systematic measurements of the frequency non-reciprocity as a function of an external magnetic field. For the antiparallel alignment of the magnetic moments in the two layers, we observe a significant frequency non-reciprocity of up to a few GHz, which vanishes when the relative magnetization orientation switches into the parallel configuration at saturation. A non-monotonous dependence of the frequency non-reciprocity is found in the region where the system transitions from the antiparallel to the parallel orientation, with a maximum frequency shift around the spin-flop critical point. This non-trivial dependence of the non-reciprocity is attributed to the non-monotonous dependence of the dynamic dipolar interaction, which is the main factor that causes asymmetry in the dispersion relation. Furthermore, we found that the sign of the frequency shift changes even without switching the polarity of the bias field. These results show that one can precisely control the non-reciprocal propagation of spin waves via field-driven magnetization reorientation.

Keywords: Spin waves; Magnetization switching; Magnetization dynamics; Dipolar interaction; Magnetic multilayers; Synthetic antiferromagnets

Publ.-Id: 35185

A fluorescence anisotropy assay with guanine nucleotides provides access to functional analysis of Gαi1 proteins

Penanian, A.; Sommerfeld, P.; Kasprzyk, R.; Kühl, T.; Binbay, A.; Hauser, C.; Löser, R.; Wodtke, R.; Bednarczyk, M.; Chrominski, M.; Kowalska, J.; Jemielity, J.; Imhof, D.; Pietsch, M.

Gα proteins as part of heterotrimeric G proteins are molecular switches essential for GPCR mediated intracellular signaling. The role of the Gα subunits has been examined for decades with various guanine nucleotides to elucidate the activation mechanism and Gα protein-dependent signal transduction. Several approaches describe fluorescent ligands mimicking the GTP
function, yet lacking the efficient estimation of the proteins’ GTP binding activity and fraction of active protein. Herein, we report the development of a reliable fluorescence anisotropy-based method to determine the affinity of ligands at the GTP-binding site and to quantify the fraction of active Gαi1 protein. An advanced bacterial expression protocol was applied to produce active human Gαi1 protein, whose GTP binding capability was determined with novel fluorescently labeled guanine nucleotides acting as highaffinity Gαi1 binders compared to the commonly used BODIPY FL GTPγS. This study thus contributes a new method for future investigations of the characterization of Gαi and other Gα protein subunits, exploring their corresponding signal transduction systems and potential for biomedical applications.

Publ.-Id: 35184

Clinical use and future requirements of relative biological effectiveness: Survey among all European proton therapy centres

Heuchel, L.; Hahn, C.; Pawelke, J.; Singers Sørensen, B.; Dosanjh, M.; Lühr, A.

Background and purpose: The relative biological effectiveness (RBE) varies along the treatment field.
However, in clinical practice, a constant RBE of 1.1 is assumed, which can result in undesirable side
effects. This study provides an accurate overview of current clinical practice for considering proton
RBE in Europe.
Materials and methods: A survey was devised and sent to all proton therapy centres in Europe that treat
patients. The online questionnaire consisted of 39 questions addressing various aspects of RBE consider-
ation in clinical practice, including treatment planning, patient follow-up and future demands.
Results: All 25 proton therapy centres responded. All centres prescribed a constant RBE of 1.1, but also
applied measures (except for one eye treatment centre) to counteract variable RBE effects such as avoid-
ing beams stopping inside or in front of an organ at risk and putting restrictions on the minimum number
and opening angle of incident beams for certain treatment sites. For the future, most centres (16) asked
for more retrospective or prospective outcome studies investigating the potential effect of the effect of a
variable RBE. To perform such studies, 18 centres asked for LET and RBE calculation and visualisation
tools developed by treatment planning system vendors.
Conclusion: All European proton centres are aware of RBE variability but comply with current guidelines
of prescribing a constant RBE. However, they actively mitigate uncertainty and risk of side effects result-
ing from increased RBE by applying measures and restrictions during treatment planning. To change RBE-
related clinical guidelines in the future more clinical data on RBE are explicitly demanded.

Keywords: Relative biological effectiveness (RBE); Linear energy transfer (LET); Proton Beam Therapy; Treatment planning; Current clinical practice; Survey; Europe


Publ.-Id: 35183

Data publication: Integrated radiogenomics analyses allow for subtype classification and improved outcome prognosis of patients with locally advanced HNSCC

Rabasco Meneghetti, A.; Zwanenburg, A.; Linge, A.; Lohaus, F.; Grosser, M.; Baretton, G.; Kalinauskaite, G.; Tinhofer, I.; Guberina, N.; Stuschke, M.; Balermpas, P.; von der Grün, J.; Ganswindt, U.; Belka, C.; Peeken, J. C.; Combs, S. E.; Böke, S.; Zips, D.; Troost, E. G. C.; Krause, M.; Baumann, M.; Löck, S.

RDS data of models developed and reported for the article entitled "Integrated radiogenomics analyses allow for subtype classification and improved outcome prognosis of patients with locally advanced HNSCC". Software package version is also available in repository

Keywords: HNSCC; Radiomics; Radiogenomics; Transcriptomics; Machine Learning; Prognostic markers

Related publications

Publ.-Id: 35182

Integrated radiogenomics analyses allow for subtype classification and improved outcome prognosis of patients with locally advanced HNSCC

Rabasco Meneghetti, A.; Zwanenburg, A.; Linge, A.; Lohaus, F.; Grosser, M.; Baretton, G.; Kalinauskaite, G.; Tinhofer, I.; Guberina, N.; Stuschke, M.; Balermpas, P.; von der Grün, J.; Ganswindt, U.; Belka, C.; Peeken, J. C.; Combs, S. E.; Böke, S.; Zips, D.; Troost, E. G. C.; Krause, M.; Baumann, M.; Löck, S.

Patients with locally advanced head and neck squamous cell carcinoma (HNSCC) may benefit from personalised treatment, requiring biomarkers that characterize the tumour and predict treatment response. We integrate pre-treatment CT radiomics and whole-transcriptome data from a multicentre retrospective cohort of 206 patients with locally advanced HNSCC treated with primary radiochemotherapy to classify tumour molecular subtypes based on radiomics, develop surrogate radiomics signatures for gene-based signatures related to different biological tumour characteristics and evaluate the potential of combining radiomics features with full-transcriptome data for the prediction of loco-regional control (LRC). Using end-to-end machine-learning, we developed and validated a model to classify tumours of the atypical subtype (AUC [95% confidence interval]: 0.69 [0.53-0.83]) based on CT imaging, observed that CT-based radiomics models have limited value as surrogates for six selected gene signatures (AUC<0.60), and showed that combining a radiomics signature with a transcriptomics signature consisting of two metagenes representing the hedgehog pathway and E2F transcriptional targets improves the prognostic value for LRC compared to both individual sources (validation C-index [95% confidence interval], combined: 0.63 [0.55-0.73] vs radiomics: 0.60 [0.50-0.71] and transcriptomics: 0.59 [0.49-0.69]). These results underline the potential of multi-omics analyses to generate reliable biomarkers for future application in personalized oncology.

Keywords: HNSCC; Radiomics; Radiogenomics; Transcriptomics; Machine Learning; Prognostic markers

Related publications

Publ.-Id: 35181

Recent progress of laboratory astrophysics with intense lasers

Takabe, H.; Kuramitsu, Y.

Thanks to a rapid progress of high-power lasers since the birth of laser by T. H. Maiman in 1960, intense lasers have been developed mainly for studying the scientific feasibility of laser fusion. Inertial confinement fusion with an intense laser has attracted attention as a new future energy source after two oil crises in the 1970s and 1980s. From the beginning, the most challenging physics is known to be the hydrodynamic instability to realize the spherical implosion to achieve more than 1000 times the solid density. Many studies have been performed theoretically and experimentally on the hydrodynamic instability and resultant turbulent mixing of compressible fluids. During such activities in the laboratory, the explosion of supernova SN1987A was observed in the sky on 23 February 1987. The X-ray satellites have revealed that the hydrodynamic instability is a key issue to understand the physics of supernova explosion. After collaboration between laser plasma researchers and astrophysicists, the laboratory astrophysics with intense lasers was proposed and promoted around the end of the 1990s. The original subject was mainly related to hydrodynamic instabilities. However, after two decades of laboratory astrophysics research, we can now find a diversity of research topics. It has been demonstrated theoretically and experimentally that a variety of nonlinear physics of collisionless plasmas can be studied in laser ablation plasmas in the last decade. In the present paper, we shed light on the recent 10 topics studied intensively in laboratory experiments. A brief review is given by citing recent papers. Then, modeling cosmic-ray acceleration with lasers is reviewed in a following session as a special topic to be the future main topic in laboratory astrophysics research.

Publ.-Id: 35180

Flow‐dependent zinc corrosion in boric acid‐containing electrolytes

Harm, U.; Kryk, H.; Hampel, U.

In recent research concerning zinc dissolution studies in boric acid
electrolytes, it was shown that moderate variations of the fluid temperatures
or the boric acid concentration only cause small changes (<10%) in resulting
initial zinc corrosion rates. A stronger dependency was found, however, on the
fluid flow. Thus, a series of electrochemical measurements were carried out
using a rotating disc electrode (zinc) in boric acid electrolytes for a better
understanding of influencing parameters on the zinc corrosion rates. The main
results of these electrochemical polarization experiments (e.g., Tafel plots)
showed similar dependencies of the zinc corrosion rates as described in the
aforementioned zinc dissolution experiments. The zinc corrosion process
strongly depends on the mass transfer limitation of the dissolved oxygen to the
zinc surface (cathodic process). Increased rotation speeds (higher flow rates)
lead to extensively enhanced current densities (corrosion rates) and the
extrapolation to infinite high rotation speeds (Levich extrapolation) was used
to describe the corresponding corrosion process without transfer limitations.

Keywords: boric acid; corrosion; cyclic polarization; zinc; electrochemistry

Related publications


  • Secondary publication expected

Publ.-Id: 35179

Unraveling the spatial distribution of Eu(III) in tobacco BY-2 cells by chemical microscopy

Klotzsche, M.; Drobot, B.; Steudtner, R.; Vogel, M.; Raff, J.; Stumpf, T.

Rare earth elements (REE) have become critical components in science and industry. Their anthropogenic release into the environment and entry into the food chain poses a risk for the health of living beings. Therefore, a comprehensive understanding of the transfer and migration behaviour, the resulting localization and molecular characterization of REE in biological systems is crucial for a reasonable risk assessment and remediation strategies.

Keywords: Chemical microscopy; Europium; Luminescence; Tobacco BY-2; Plant cells; Raman microspectroscopy

  • Poster
    18th Confocal Raman Imaging Symposium, 26.-28.09.2022, Ulm, Deutschland

Publ.-Id: 35178

Quantum accurate interaction potentials for warm dense aluminum

Kumar, S.; Tahmasbi, H.; Ramakrishna, K.; Lokamani, M.; Cangi, A.

Modeling warm dense matter is relevant for various applications including the interior of gas giants and exoplanets, inertial confinement fusion, and ablation of metals. Ongoing and upcoming experimental campaigns in photon sources around the globe rely on numerical simulations which are accurate on the level of electronic structures. In that regard, density functional theory molecular dynamics (DFT-MD) simulations have been widely used to compute dynamical and thermodynamical properties of warm dense matter. However, two challenges impede further progress: (1) DFT-MD becomes computational infeasible with increasing temperature (2) finite-size effects render many computational observables inaccurate, because DFT-MD is limited to a few hundred atoms on current HPC platforms. Recently, molecular dynamics simulations using machine learning-based interatomic potentials (ML-IAP) could overcome these computational limitations. Here, we propose a method to construct ML-IAPs from DFT data based on SNAP descriptors [1]. We demonstrate our workflow for aluminum. In particular, we investigate the transferability of ML-IAPs over a large range of temperatures and pressures, which currently is a topic of active research.


[1] A. P. Thompson, L. P. Swiler, C. R. Trott, S. M. Foiles, and G. J. Tucker, Journal of
Computational Physics, 285, 316-330, 2015.

Keywords: Computational Physics; Warm Dense Matter; Machine Learning; Molecular Dynamics

  • Poster
    DFT Methods for Matter under Extreme Conditions, 21.-22.02.2022, Görlitz, Germany

Publ.-Id: 35177

Quantum-accurate interatomic potentials for aluminum at high temperatures

Kumar, S.; Tahmasbi, H.; Ramakrishna, K.; Lokamani, M.; Cangi, A.

Modeling warm dense matter is relevant for various applications including the interior of gas giants and exoplanets, inertial confinement fusion, and ablation of metals. Ongoing and upcoming experimental campaigns in photon sources around the globe rely on numerical simulations which are accurate on the level of electronic structures. In that regard, density functional theory molecular dynamics (DFT-MD) simulations [1] have been widely used to compute dynamical and thermodynamical properties of warm dense matter. However, two challenges impede further progress: (1) DFT-MD becomes computational infeasible with increasing temperature (2) finite-size effects render many computational observables
inaccurate, because DFT-MD is limited to a few hundred atoms on current HPC platforms. Recently, molecular dynamics simulations using machine learning-based interatomic potentials (ML-IAP) could overcome these computational limitations. Here, we propose a method to construct ML-IAPs from DFT data based on SNAP descriptors [2]. We present our results for aluminum. In particular, we investigate the transferability of ML-IAPs over a large range of temperatures and pressures, which currently is a topic of active research.


[1] G. Kresse and J. Hafner, Phys. Rev. B 47, 558 (1993).
[2] A. P. Thompson, L. P. Swiler, C. R. Trott, S. M. Foiles, and G. J. Tucker, Journal of Computational Physics, 285, 316-330, 2015.

Keywords: Computational Physics; Warm Dense Matter; Machine Learning; Transport Coefficients; Molecular Dynamics

  • Poster
    Strongly Coupled Coulomb Systems, 24.-29.07.2022, Görlitz, Germany

Publ.-Id: 35176

A snapshot review on flash lamp annealing of semiconductor materials

Rebohle, L.; Prucnal, S.; Berencen, Y.; Begeza, V.; Zhou, S.

Flash lamp annealing (FLA) is a non-equilibrium annealing method on the sub-second time scale which excellently meets the requirements of thin film processing. FLA has already been used in microelectronics, mostly after ion implantation, to activate dopants, to recrystallize amorphous semiconductor layers, and to anneal out defects. Another field of application is the formation of silicide and germanide materials for contact fabrication. However, in the last twenty years, FLA has opened up new areas of application like thin films on glass, sensors, printed electronics, flexible electronics, energy materials etc. For two years, the Helmholtz Innovation Blitzlab aims to transfer this technology to industry and application-related research.
After a short introduction, a brief overview of FLA is given, discussing the advantages and challenges of this technology. The main part displays various examples from literature and from our own research, in which FLA has been applied to semiconductors, namely to Si, Ge and GaN. In detail, the doping close or even above the solubility limit of dopants, the crystallization of Ge during FLA, the formation of NiGe for contacts, and p-type doping in GaN are addressed.

Keywords: Flash lamp annealing; Pulsed light sintering; Semiconductors; Ion implantation; Crystallization

Related publications

  • Invited lecture (Conferences)
    International Conference on Ion Implantation Technology 2022, 25.-29.09.2022, San Diego, USA
  • Open Access Logo MRS Advances 7(2022), 1301-1309
    Online First (2022) DOI: 10.1557/s43580-022-00425-w
    Cited 2 times in Scopus
  • Lecture (Conference)
    47. Nutzertreffen „Heißprozesse und RTP“, 07.-08.12.2022, München, Deutschland

Publ.-Id: 35175

Effect of laser annealing on the magnetic properties of Co/Pt based multilayers

Rasabathina, L.; Sharma, A.; Busse, S.; Böhm, B.; Samad, F.; Salvan, G.; Horn, A.; Hellwig, O.

Two modes of laser annealing, namely, Continuous Wave (CW) and Pulsed Wave (PW) mode, are used for modifying the magnetic properties of perpendicular magnetic anisotropy (PMA) multilayers in a controlled manner. For this we compare two types of samples - a PMA (Co/Pt)10 multilayer and an antiferromagnetically interlayer exchange coupled PMA (Co/Pt)4/Co/Ir/(Co/Pt)5 multilayer. Room temperature hysteresis loops using polar MOKE magnetometry are measured for the different laser annealing modes. Thus, a relationship between the applied laser parameters and the magnetic properties is extracted, which provides an opportunity to alter magnetic properties of PMA multilayer systems locally with high spatial resolution on demand.

  • Poster
    DPG conference Regensburg 2022, 08.09.2022, Regensburg, Germany

Publ.-Id: 35174

Influence of adhesion layer and sputter gas pressure on structural and magnetic properties of Co/Pt multilayers

Ehrler, R.; Uhlig, T.; Hellwig, O.

Co/Pt multilayers (MLs) are standard systems for perpendicular anisotropy layered thin films. The use of a specific underlayer, sometimes in combination with additional, very thin adhesion layers, is a common practice to define a crystalline texture for the ML on amorphous substrates. In addition, the sputter gas pressure during deposition can be used to tune the lateral heterogeneity and laminate order, which strongly affect the magnetic behavior of the system. However, the precise interplay between adhesion and sputter gas pressure, especially for the seed layer, is often neglected.

In this context, we will discuss the impact of the underlayers on the structural and magnetic properties of the Co/Pt ML system. We will emphasize the influence of an adhesion layer on the whole system and combine this with a systematic and separate variation of the sputter deposition pressure of Pt seed and Co/Pt ML. Carefully tuning these parameters enables us to exert a high degree of control on the structure of these systems, with characteristics ranging from continuous thin films to isolated grain structures.

Keywords: cobalt platin multilayer; structural properties

  • Lecture (Conference)
    DPG conference Regensburg 2022, 07.09.2022, Regensburg, Germany

Publ.-Id: 35173

Evidence for perpendicular anisotropy gradients in Co thin films on Pt seeds

Patel, G. I.; Stienen, S.; Salikhov, R.; Gallardo, R.; Fallarino, L.; Lenz, K.; Lindner, J.; Hellwig, O.

Tailoring the magnetization dynamics and anisotropy in ferromagnetic thin films by different seed layers is of great fundamental and practical importance, e.g., different seed layer materials lead to different microstructure and magnetocrystalline anisotropy energy. We have used Ta and Pt as seed layers for thin Co films and studied their broadband ferromagnetic resonance (FMR) in out-of-plane saturation as a function of Co thickness and determined the respective perpendicular magnetic anisotropy. For Ta seeds, the magnetic anisotropy decreases and shows an inverse thickness dependence. In contrast for Pt seeds the magnetic anisotropy is no longer monotonous with thickness, but shows an initial thickness dependent decrease with a distinct minimum and subsequently a steady increase again. XRD measurements show that for Pt seeds, the Co develops a well-defined hcp texture with a thickness dependent strain relaxation. As a result of this structural evolution for Co on Pt seeds our FMR measurements reveal a strong anisotropy gradient in growth direction for this system.

Keywords: cobalt; magnetic anisotropy; FMR

  • Lecture (Conference)
    DPG conference Regensburg 2022, 07.09.2022, Regensburg, Germany

Publ.-Id: 35172

Magnetostructural phase transition in Fe60V40 alloy thin films

Anwar, M. S.; Cansever, H.; Böhm, B.; Gallardo, R.; Hübner, R.; Zhou, S.; Kentsch, U.; Eggert, B.; Rauls, S.; Wende, H.; Potzger, K.; Faßbender, J.; Lenz, K.; Lindner, J.; Hellwig, O.; Bali, R.

Ferromagnetism can be induced in non-ferromagnetic alloys such as B2 Fe60Al40[1] and B2 Fe50Rh50[2] through lattice disordering. Here we study a magnetostructural transition in Fe60V40 thin films using ion-irradiation. We show that the as-grown films possess an MS of 17 kA/m and irradiation with 25 keV Ne+-ions at a fluence of 5 x 1015ions/cm2 leads to an increase of MS to ∼ 750 kA/m. A structural short-range order is observed in the as-grown films that transforms to A2 phase via ion-irradiation. Mössbauer spectroscopy and Ferromagnetic Resonance have been applied to track the variation of local magnetic ordering and dynamic behaviour respectively.

Financial support by DFG grants BA 5656/1-2 and WE 2623/14-2 is acknowledged.

[1]Ehrler, al., New J. Phys.,22,073004(2020)

[2]Eggert, al., RSC Adv.,10,14386(2020)

Keywords: iron vanadium; ion irradiation

Related publications

  • Lecture (Conference)
    DPG conference Regensburg 2022, 05.09.2022, Regensburg, Germany

Publ.-Id: 35171

Spin-orbit torque mediated coupling of terahertz light with magnon modes in heavy-metal/ferromagnet heterostructures

Salikhov, R.; Ilyakov, I.; Körber, L.; Kakay, A.; Lenz, K.; Faßbender, J.; Bonetti, S.; Hellwig, O.; Lindner, J.; Kovalev, S.

Nonvolatile and energy-efficient spin-based technologies call for new prospects to realize computation and communication devices that are able to operate at terahertz (THz) frequencies. In particular, the coupling of electro-magnetic radiation to a spin system is a general requirement for future communication units and sensors. Here we propose a layered metallic system, based on a ferromagnetic film sandwiched in between two heavy metals that allows a highly effective coupling of millimeter wavelength THz light to nanometer-wavelength magnon modes. Using single-cycle broadband THz radiation we are able to excite spin-wave modes with a frequency of up to 0.6 THz and a wavelength as short as 6 nm. Our experimental and theoretical studies demonstrate that the coupling originates solely from interfacial spin-orbit torques. These results are of general applicability to magnetic multilayered structures, and offer the perspective of coherent THz excitation of exchange-dominated nanoscopic magnon modes.

Keywords: terahertz; magnon

  • Lecture (Conference)
    DPG conference Regensburg 2022, 07.09.2022, Regensburg, Deutschland

Publ.-Id: 35169

Magnetization reversal of Co/Pt multilayer systems with weak perpendicular magnetic anisotropy

Heinig, P.; Salikhov, R.; Samad, F.; Fallarino, L.; Kakay, A.; Hellwig, O.

Perpendicular anisotropy thin film systems are well known for their highly periodic magnetic stripe domains. Here we study [Co(3.0 nm)/Pt(0.6 nm)]X multilayers in the regime of transitional in-plane to out-of-plane anisotropy. For this we vary the number of repeats X in order to tune the remanent state from purely in-plane (IP) via tilted stripe domains (tilted), i.e. with significant out-of plane as well as in-plane magnetization component, to fully out-of-plane stripe domains (OOP). Vibrating Sample Magnetometry and Magnetic Force Microscopy are used to investigate three characteristic samples with X = 6,11 and 22, which represent the three above mentioned remanent states, respectively. In contrast to fully in-plane or fully out-of-plane systems experimental data and corresponding micromagnetic simulation of the tilted magnetization regime (X=11) reveals fully reversible field regions as well as distinct points of irreversibility during an external field sweep. This collective reversal behavior seems at first sight somewhat counter intuitive for a macroscopic system and has qualitative similarities with microscopic systems, such as the Stoner Wohlfarth particle and the vortex reversal in an in-plane magnetized disk, which both show as well distinct points of irreversibility.

Keywords: tilted magnetization; weak anisotropy; Co/Pt multilayer

  • Lecture (Conference)
    DPG conference Regensburg 2022, 07.09.2022, Regensburg, Deutschland

Publ.-Id: 35168

Herausforderungen bei der TEM-Probenpräparation von neuartigen Elektroden-Materialen für Li-Ionen-Batterien

Engelmann, H.-J.; Heinig, K.-H.; Aniol, R.

Herausforderungen bei der TEM-Probenpräparation von neuartigen Elektroden-Materialen für Li-Ionen-Batterien

Keywords: TEM-Probenpräparation; FIB; TEM; Li-Ionen-Batterien

Related publications

  • Lecture (others)
    Sächsisches TEM-Präparatorentreffen, 22.09.2022, Dresden, Deutschland

Publ.-Id: 35167

Tuning up catalytical properties of electrochemically prepared nanoconical Co-Ni deposit for HER and OER

Skibinska, K.; Wojtaszek, K.; Krause, L.; Yang, X.; Marzec, M. M.; Wojnicki, M.; Żabiński, P.

Catalysts can be successfully prepared by a simple electrochemical process. Their surface composition distinguishes catalytic activity toward hydrogen and oxygen evolution reactions. In this work, uniform Co-Ni cones were synthesized using the onestep method from an electrolyte containing a crystal modifier. Electrodeposited layers were oxidized and/or reduced in the furnace at 100°C. Freshly electrodeposited coating was stored in air atmosphere for seven days. This results in an oxide layer forming on the surface of the catalyst. Changes in the surface composition, confirmed by the XPS method, strongly influenced the wettability, catalytic performance, and size of evolved hydrogen bubbles. The conical Co-Ni surface oxidized in a controlled way possesses the best catalytic activity towards hydrogen and oxygen evolution. Conversely, the spontaneously formed oxide layer decreases the catalytic performance in mentioned reactions compared with the fresh sample. The proper storage of synthesized samples is essential due to their desired catalytic applications. Proposed controlled oxidation can be an accessible way to increase nanomaterials catalytic performance.

Keywords: conical structures; wettability; catalytical properties; Hydrogen evolution reaction; Oxygen evolution reaction

Publ.-Id: 35166

Spatial magnetic imaging of non-axially symmetric vortex domains in cylindrical nanowire by transmission X-ray microscopy

Fernandez Roldan, J. A.; Bran, C.; Asenjo, A.; Vázquez, M.; Sorrentino, A.; Ferrer, S.; Chubykalo-Fesenko, O.; Del Real, R. P.

The spatial magnetization texture of a cylindrical nanowire has been determined by Transmission X-ray Microscopy (TXM) and X-ray magnetic circular dichroism (XMCD). For this purpose, nanowires with designed geometry, consisting of CoNi/Ni periodic segments, have been grown by designed electrodeposition into alumina templates. Experimental data allows one to conclude the presence of mono- and trivortex magnetic domains in CoNi segments but, unusually, these states are characterized by an asymmetric XMCD contrast across the nanowire’s section. Micromagnetic modelling shows non-trivial three-dimensional structures with ellipsoidal vortex cores and non-axially symmetric magnetization along the nanowire direction. The modelled TXM contrast of micromagnetic structures allows to correlate the experimental asymmetric XMCD contrast to the easy axis direction of the uniaxial magnetocrystalline anisotropy.

Keywords: magnetic nanowires; vortex magnetic domains; magnetic domain wall; Transmission X-ray Microscopy (TXM); X-ray magnetic circular dichroism (XMCD); CoNi; nanomagnetism; three-dimensional; cylindrical nanowire; spin texture


Publ.-Id: 35165

Photo-induced macro/mesoscopic scale ion displacement in mixed-halide perovskites: ring structures and ionic plasma oscillations

Sun, X.; Zhang, Y.; Ge, W.

Contrary to the common belief that the light-induced halide ion segregation in a mixed halide alloy occurs within the illuminated area, we find that the Br ions released by light are expelled from the illuminated area, which generates a macro/mesoscopic size anion ring surrounding the illuminated area, exhibiting a photoluminescence ring. This intriguing phenomenon can be explained as resulting from two counter-balancing effects: the outward diffusion of the light-induced free Br ions and the Coulombic force between the anion deficit and surplus region. Right after removing the illumination, the macro/mesoscopic scale ion displacement results in a built-in voltage of about 0.4 V between the ring and the center. Then, the displaced anions return to the illuminated area, and the restoring force leads to a damped ultra-low-frequency oscillatory ion motion, with a period of about 20–30 h and lasting over 100 h. This finding may be the first observation of an ionic plasma oscillation in solids. Our understanding and controlling the “ion segregation” demonstrate that it is possible to turn this commonly viewed “adverse phenomenon” into novel electronic applications, such as ionic patterning, self-destructive memory, and energy storage.

Publ.-Id: 35164

Kombinierte Bewertung von Dichte- und Größeneffekten beim Windsichten mittels Mineral Liberation Analyses (MLA)

Buchmann, M.; Heinicke, F.; Mütze, T.

Windsichten ist in der Zementindustrie ein seit Jahrzehnten bekanntes Verfahren zum Klassieren im Bereich 0,01-1,0 mm. Zusätzlich kann in entsprechenden Trockenmahlkreisläufen in Kombination mit Maschinen wie Hochdruckmahlwalzen (HPGR) der Energieverbrauch im Vergleich zu Nassanwendungen deutlich reduziert werden. Diese trocken arbeitenden Systeme sind in der Mineralaufbereitung noch nicht Stand der Technik, aber erste Prototypen wurden installiert und eine zunehmende Anzahl von Projekten beginnt, diese Alternative näher zu untersuchen.
Eine Herausforderung in diesem Bereich ist die mineralische Zusammensetzung von Erzen, die in Bezug auf Dichte und Größe eine weitaus größere Vielfalt aufweisen als Zement. Partikel mit hoher Dichte, wie z. B. eisenhaltige Partikel, haben bei gleicher Größe höhere Sinkgeschwindigkeiten als Silikatpartikel mit niedrigerer Dichte. Der vorliegende Beitrag untersucht, wie dieser Effekt bewertet werden kann. Dazu wurde eine quantitative Methode auf Basis der Mineral Liberation Analysis (MLA) entwickelt, um zweidimensionale Trennfunktionen zu berechnen. Zusätzliche statistische Analysen ermöglichen es, die Wechselwirkung von Dichte und Größe isoliert voneinander zu betrachten und so, entsprechende Effekte bei der Dimensionierung von Prozessanlagen zu berücksichtigen. In dem Beitrag werden die Methode und ausgewählte Ergebnisse für ein Eisenerz vorgestellt.

Keywords: MLA; Windsichten; Eisenerz; trockene Aufbereitung

  • Aufbereitungstechnik 63(2022)9, 52-64
    ISSN: 1434-9302

Publ.-Id: 35163

Machine learning-based quantum accurate interatomic potentials for warm dense aluminum

Kumar, S.; Tahmasbi, H.; Ramakrishna, K.; Lokamani, M.; Cangi, A.

Modeling warm dense matter is relevant for various applications including the interior of gas giants and exoplanets, inertial confinement fusion, and ablation of metals. Ongoing and upcoming experimental campaigns in photon sources around the globe rely on numerical simulations which are accurate on the level of electronic structures. In that regard, density functional theory molecular dynamics (DFT-MD) simulations [1] have been widely used to compute the dynamical and thermodynamical properties of warm dense matter. However, two challenges impede further progress: (1) DFT-MD becomes computationally infeasible with increasing temperature (2) finite-size effects render many computational observables inaccurate, because DFT-MD is limited to a few hundred atoms on current HPC platforms. Recently, molecular dynamics simulations using machine learning-based interatomic potentials (ML-IAP) could overcome these computational limitations. Here, we propose a method to construct ML-IAPs from DFT data based on SNAP descriptors [2]. We present our results for aluminum. In particular, we investigate the transferability of ML-IAPs over a large range of temperatures (1000 to 100000 K) and pressures (ambient to 800 GPa), which currently is a topic of active research. To test the transferability of the SNAP potential, we calculate thermal conductivity, viscosity, diffusion coefficient, and sound velocity in and out of the data training range.


[1]. G. Kresse and J. Hafner, Phys. Rev. B 47, 558 (1993).
[2]. A. P. Thompson, L. P. Swiler, C. R. Trott, S. M. Foiles, and G. J. Tucker, J. Comput. Phys., 285, 316-330, 2015.

Keywords: Computational Physics; Warm Dense Matter; Machine Learning; Transport Coefficients

  • Lecture (Conference)
    Multiscale Modeling of Matter under Extreme Conditions, 11.-16.09.2022, Görlitz, Germany

Publ.-Id: 35162

A single bubble rising in the vicinity of a vertical wall: A numerical study based on volume of fluid method

Yan, H.; Zhang, H.; Liao, Y.; Zhang, H.; Zhou, P.; Liu, L.

Single bubble rising in the close vicinity of a vertical wall is one of the focuses in the field of gas-liquid two-phase flow. In this work, three-dimensional direct numerical simulation based on volume of fluid (VOF) and adaptive mesh refinement method is performed to investigate the bubble rising and wake structures near a vertical wall. The bubble migration trajectory, deformation, velocity and wake structures were analyzed under various Galileo numbers and initial wall distances. Bubbles with a Galileo number of 8.8 significantly migrate away from the wall, which is driven by the repulsive force as a result of the suppression of the vortex diffusion on the bubble surface. As the Galileo number increases, the asymmetry of the shedding vortex tends to play a vital role on the repulsive force, which is exacerbated by the presence of the vertical wall. A periodic shedding of the vortex appears behind the bubble when the Galileo number reaches at 95. Meanwhile, the bubble trajectory changes from rectilinear to spiral along with a periodic oscillation. Due to the interaction between the vertical wall and the bubble wake, a transition from a rectilinear rising path to a spiral rising path is more likely to occur compared to that without a vertical wall. The presence of a vertical wall contributes to bubble-rising oscillations. A decrease of the bubble terminal velocity due to viscous effect near the vertical wall is observed for bubbles at low Galileo numbers. However, the viscous effect is less pronounced as the Galileo number increases.

Keywords: Single bubble; Migration trajectory; Wall effect; Wake structure; VOF; OpenFOAM

Publ.-Id: 35161

Data publication: FPGA Testbench for Beam-Based Feedback

Maalberg, A.; Kuntzsch, M.; Petlenkov, E.

The testbench data to compare the time response of a 4th-order regulator implemented in fixed-point with the same regulator simulated in a floating-point MATLAB model.

Related publications


Publ.-Id: 35160

Electrical Conductivity of Iron in Earth’s Core from Microscopic Ohm’s Law

Ramakrishna, K.; Vorberger, J.; Cangi, A.; Baczewski, A.; Lokamani, M.

Understanding the electronic transport properties of iron under high temperatures and pressures is essential for constraining geophysical processes. The difficulty of reliably measuring these properties calls for sophisticated theoretical methods that can support diagnostics. We present results of the electrical conductivity within the pressure and temperature ranges found in Earth's core by simulating microscopic Ohm's law using time-dependent density functional theory.

Keywords: Computational Physics; Warm dense matter; TDDFT

  • Lecture (Conference)
    Multiscale Modeling of Matter under Extreme Conditions, 13.09.2022, Görlitz, Germany

Publ.-Id: 35156

wrap up & discussion: consensus and controversial aspects of CT innovation in RT

Richter, C.

consensus and controversial aspects of CT innovation in RT

  • Invited lecture (Conferences)
    ESTRO 2022 Congress, 06.-10.05.2022, Copenhagen, Denmark

Publ.-Id: 35155

Treating Knock-On Displacements in Fluctuation Electron Microscopy Experiments

Radic, D.; Peterlechner, M.; Posselt, M.; Bracht, H.

This work investigates how knock-on displacements influence fluctuation electron microscopy (FEM) experiments. FEM experiments were conducted on amorphous silicon, formed by self-ion implantation, in a transmission electron microscope at 300 kV and 60 kV at various electron doses, two different binnings and with two different cameras, a CCD and a CMOS one. Furthermore, energy filtering has been utilized in one case. Energy filtering greatly enhances the FEM data by removing the inelastic background intensity, leading to an improved speckle contrast. The CMOS camera yields a slightly larger normalized variance than the CCD at an identical electron dose and appears more prone to noise at low electron counts. Beam-induced atomic displacements affect the 300 kV FEM data, leading to a continuous suppression of the normalized variance with increasing electron dose. Such displacements are considerably reduced for 60 kV experiments since the primary electron’s maximum energy transfer to an atom is less than the displacement threshold energy of amorphous silicon. The results show that the variance suppression due to knock-on displacements can be controlled in two ways: Either by minimizing the electron dose to the sample or by conducting the experiment at a lower acceleration voltage.

Keywords: amorphous silicon; beam damage; diffraction mapping; fluctuation electron microscopy; medium-range order

Related publications

Publ.-Id: 35154

Y(III) sorption at the orthoclase (001) surface measured by X-ray reflectivity

Neumann, J.; Lessing, J.; Lee, S. S.; Stubbs, J. E.; Eng, P. J.; Demnitz, M.; Fenter, P.; Schmidt, M.

Interactions of heavy metals with charged mineral surfaces control their mobility in the environment. Here, we investigate the adsorption of Y(III) onto the orthoclase (001) basal plane, the former as a representative of rare earth elements and an analogue of trivalent actinides and the latter as a representative of naturally abundant K-feldspar minerals. We apply in-situ high-resolution X-ray reflectivity to determine the sorption capacity and molecular distribution of adsorbed Y species as a function of Y3+ concentration and pH. We observe an inner-sphere (IS) sorption complex at a distance of ~1.5 Å from the surface and an outer-sphere (OS) complex at 3–4 Å. Based on the adsorption height of the IS complex a bidentate, binuclear binding mode, in which Y3+ binds to two terminal oxygens seems most plausible. The total Y coverages of IS and OS species are max. ~1.3 Y3+/AUC for all Y concentrations (AUC: area of the unit cell = 111.4 Ų), which is in the expected range based on the estimated surface charge of orthoclase (001).

Keywords: solid liquid interface; rare earth elements; trivalent actinides; crystal truncation rod; resonant anomalous X-ray reflectivity; feldspars

Related publications


Publ.-Id: 35153

Effect of He+ implantation on nanomechanical resonators in 3C-SiC

Jagtap, N.; Klaß, Y.; David, F.; Bredol, P.; Weig, E.; Helm, M.; Astakhov, G.; Erbe, A.

Silicon carbide (SiC) is a suitable candidate for Micro- and Nanoelectromechanical systems due to its superior mechanical properties. We would like to use it as a quantum sensor to sense small magnetic fields. It can be achieved by coupling a spin associated silicon vacancy (V_Si) in 4H-SiC with a mechanical mode of a resonator. Spin-mechanical resonance is observed when resonance frequency from V_Si matches resonance frequency of a mechanical mode.
In the initial experiments, we focus on the material modification by helium (He+) ion broad beam implantation on a strained resonator based on 3C-SiC implanted with high fluence of (1*10^14 /cm^2) and low fluence (1*10^12 /cm^2) at 14 keV. The change in resonance frequency and quality factors as a function of fluence is studied. We also show the effect on stress and higher modes of the nanomechanical resonators.

Related publications

  • Open Access Logo Lecture (others)
    NanoNet^+ Workshop 2022 - Görlitz, 04.-06.10.2022, Görlitz, Saxony, Germany

Publ.-Id: 35152

MRI-based computational model generation for cerebral perfusion simulations in health and ischaemic stroke

Józsa, T. I.; Petr, J.; Barkhof, F.; Payne, S. J.; Mutsaerts, H. J. M. M.

Cerebral perfusion models were found to be promising research tools to predict the impact of acute ischaemic stroke and related treatments on cerebral blood flow (CBF) linked to patients’ functional outcome. To provide insights relevant to clinical trials, perfusion simulations need to become suitable for group-level investigations, but computational studies to date have been limited to a few patient-specific cases. This study set out to overcome issues related to automated parameter inference, that restrict the sample size of perfusion simulations, by integrating neuroimaging data. Seventy-five brain models were generated using measurements from a cohort of 75 healthy elderly individuals to model resting-state CBF distributions. Computational perfusion model geometries were adjusted using healthy reference subjects’ T1-weighted MRI. Haemodynamic model parameters were determined from CBF measurements corresponding to arterial spin labelling perfusion MRI. Thereafter, perfusion simulations were conducted for 150 acute ischaemic stroke cases by simulating an occlusion and cessation of blood flow in the left and right middle cerebral arteries. The anatomical (geometrical) fitness of the brain models was evaluated by comparing the simulated grey and white matter (GM and WM) volumes to measurements in healthy reference subjects. Statistically significant, strong positive correlations were found in both cases (GM: Pearson’s r 0.74, P-value< 0.001; WM: Pearson’s r 0.84, P-value< 0.001). Haemodynamic parameter tuning was verified by comparing total volumetric blood flow rate to the brain in reference subjects and simulations resulting in Pearson’s r 0.89, and P-value< 0.001. In acute ischaemic stroke cases, the simulated infarct volume using a perfusion-based proxy was 197±25 ml. Computational results showed excellent agreement with anatomical and haemodynamic literature data corresponding to T1-weighted, T2-weighted, and phase-contrast MRI measurements both in healthy scenarios and in acute ischaemic stroke cases. Simulation results represented solely worst-case stroke scenarios with large infarcts because compensatory mechanisms, e.g. collaterals, were neglected. The established computational brain model generation framework provides a foundation for population-level cerebral perfusion simulations and for in silico clinical stroke trials which could assist in medical device and drug development.

Publ.-Id: 35151

Regulatory Requirements for the Translation of Radiopharmaceuticals

Kiß, O.

Regulatory Requirements for the Translation of Radiopharmaceuticals

  • Invited lecture (Conferences)
    5th GyMIC Molecular Imaging Symposium, 15.-16.09.2022, Leipzig, Deutschland

Publ.-Id: 35150

ELBE High Power RF System

Kuntzsch, M.

The ELBE accelerator at Helmholtz-Zentrum Dresden-Rossendorf has been commissioned in 2001 using klystron power amplifiers. In the course of a major machine upgrade in 2012, solid state power amplifiers have been installed to drive the superconducting cavities and to increase the maximum beam current to 1.6 mA. The talk will introduce the high power radio frequency system of the continuous wave (CW) accelerator ELBE, wrap-up the operational experience and will give an outlook to the potential successor of machine called DALI.

Keywords: ELBE; high power RF

Related publications

  • Invited lecture (Conferences)
    Power Amplifier for Particle Accelerator - PA² conference, 15.-16.11.2022, Freiburg im Breisgau, Deutschland

Publ.-Id: 35149

Frontiers of Computational Quantum Many-Body Theory

Dornheim, T.

The fundamental laws necessary for the mathematical treatment of a large part of physics and the whole of chemistry are thus completely known, and the difficulty lies only in the fact that application of these laws leads to equations that are too complex to be solved." Nearly a century has passed, yet the famous quote by Paul Dirac still gets to the heart of many research fields within theoretical physics, quantum chemistry, material science, etc. In this talk, I will show how we can use cutting-edge numerical methods on modern high-performance computing systems to effectively overcome these limitations in many cases. In this way, we get unprecedented insights into quantum many-body systems on the nanoscale going all the way from ultracold atoms like superfluid helium to warm dense matter that occurs within planetary interiors and thermonuclear fusion applications.

  • Lecture (Conference)
    International Conference of Advanced Systems Research, 14.07.2022, Wroclaw, Poland

Publ.-Id: 35148

Electronic pair alignment and roton feature in the warm dense electron gas

Dornheim, T.

The study of matter under extreme densities and temperatures as they occur e.g. in astrophysical objects and nuclear fusion applications has emerged as one of the most active frontiers in physics, material science, and related disciplines. In this context, a key quantity is given by the dynamic structure factor S(q,ω), which is probed in scattering experiments -- the most widely used method of diagnostics at these extreme conditions. In addition to its crucial importance for the study of warm dense matter, the modeling of such dynamic properties of correlated quantum many-body systems constitutes one of the most fundamental theoretical challenges of our time. Here we report a hitherto unexplained roton feature in S(q,ω) of the warm dense electron gas [1], and introduce a microscopic explanation in terms of a new electronic pair alignment model [2]. This new paradigm will be highly important for the understanding of warm dense matter, and has a direct impact on the interpretation of scattering experiments. Moreover, we expect our results to give unprecedented insights into the dynamics of a number of correlated quantum many-body systems such as ultracold helium, dipolar supersolids, and bilayer heterostructures.

[1] T. Dornheim, S. Groth, J. Vorberger, and M. Bonitz, Phys. Rev. Lett. 121, 255001 (2018)
[2] T. Dornheim, Zh. Moldabekov, J. Vorberger, H. Kählert, and M. Bonitz, arXiv:2203.12288

  • Lecture (Conference)
    Strongly Coupled Coulomb Systems (SCCS), 26.07.2022, Görlitz, Deutschland

Publ.-Id: 35147

Relation between Ga vacancies, photoluminescence and growth conditions of MOVPE prepared GaN layers

Hospodková, A.; Čížek, J.; Hájek, F.; Hubáček, T.; Pangrác, J.; Dominec, F.; Kuldová, K.; Batysta, J.; Liedke, M. O.; Hirschmann, E.; Butterling, M.; Wagner, A.

A set of GaN layers prepared by metalorganic vapor phase epitaxy under different technological conditions (growth temperature carrier gas type and Ga precursor) were investigated by varia-ble energy positron annihilation spectroscopy (VEPAS) to find a link between technological conditions, GaN layer properties and the concentration of galium vacancies (VGa). Different cor-relations between technological parameters and VGa concentration were observed for layers grown from triethyl gallium (TEGa) and trimethyl gallium (TMGa) precursors. In case of TEGa formation of VGa was significantly influenced by type of reactor atmosphere (N2 or H2), while no similar behaviour was observed for growth from TMGa. Formation of VGa was suppressed with increasing temperature for the growth from TEGa. On the contrary, enhancement of VGa concen-tration was observed for growth from TMGa with cluster formation for the highest temperature of 1100°C. From the correlation of photoluminescence results with VGa concentration determined by VEPAS it can be concluded, that yellow band in GaN is likely not connected with VGa and ad-ditionally, increased VGa concentration enhances excitonic luminescence. Probable explanation is that VGa prevents formation of some other highly efficient nonradiative defects. Possible types of such defects are suggested.

Keywords: GaN; Ga vacancy; metalorganic vapor phase epitaxy; positron annihilation spectroscopy; photoluminescence; MOVPE

Related publications

Publ.-Id: 35146

New Perspectives for Warm-dense Matter Theory: From Quantum Monte Carlo to Temperature Diagnostics

Dornheim, T.

Warm dense matter (WDM)---an extreme state that is characterized by extreme densities and temperatures---has emerged as one of the most active frontiers in plasma physics and material science. In nature, WDM occurs in astrophysical objects such as giant planet interiors and brown dwarfs. In addition, WDM is highly important for cutting-edge technological applications such as inertial confinement fusion and the discovery of novel materials.
In the laboratory, WDM is studied experimentally in large facilities around the globe, and new techniques have facilitated unprecedented insights into exciting phenomena like the formation of nano diamonds at planetary interior conditions [1]. Yet, the interpretation of these experiments requires a reliable diagnostics based on accurate theoretical modeling, which is a notoriously difficult task [2].
In this talk, I give an overview of recent ground-breaking developments in this field [3,4], which will allow for the first time to rigorously treat the intricate interplay of Coulomb coupling with thermal excitations and quantum degeneracy effects. Moreover, I show how cutting-edge quantum Monte Carlo simulation techniques will help to decisively improve density functional theory (DFT) simulations of WDM, thereby opening up unprecedented perspectives and new paradigms such as the experimental and theoretical study of nonlinear effects [5,6]. Finally, I will present a new idea to extract the exact temperature from an X-ray Thomson scattering experiment without any models or simulations [7].

[1] D. Kraus et al., Nature Astronomy 1, 606-611 (2017)
[2] M. Bonitz et al., Physics of Plasmas 27, 042710 (2020)
[3] T. Dornheim et al., Physics Reports 744, 1-86 (2018)
[4] T. Dornheim et al., Physical Review Letters 121, 255001 (2018)
[5] T. Dornheim et al., Physical Review Letters 125, 085001 (2020)
[6] Zh. Moldabekov et al., Journal of Chemical Theory and Computation 18, 2900-2912 (2022)
[7] T. Dornheim et al., arXiv:2206.12805

  • Invited lecture (Conferences)
    Multiscale Modeling of Matter under Extreme Conditions, 12.09.2022, Görlitz, Deutschland

Publ.-Id: 35145

Data publication: Bubble size distribution and electrode coverage at porous nickel electrodes in a novel 3-electrode flow-through cell

Rox, H.; Bashkatov, A.; Yang, X.; Loos, S.; Mutschke, G.; Gerbeth, G.; Eckert, K.

Porous materials are frequently used as e.g. electrodes or porous transport layers in various types of electrolyzers. A better understanding of the bubble dynamics on porous electrodes is especially important to optimize new electrolyzer designs like membraneless electrolyzers. The developed 3-electrode cell was optimized with regard to the analysis of the bubble nucleation, growth and detachment on the applied working electrode. Noteworthy in this regard is the 2-dimensional optical measurement system to characterize the bubble dynamics from the side and top. The cell provides a platform to run parametric studies in alkaline electrolytes. The present data set compares three different expanded nickel metals at applied current densities of |j|= 10, 20, 50, 100 or 200 mA/cm² and flow rates of ̇ = 0 or 5 ml/min. As electrolyte 1 M KOH is used. An overview of all performed experiments and the main parameters (current density j and flow rate ) is given in the file Overview of all performed experiments.pdf. The data is analyzed as described in the corresponding journal publication Bubble size distribution and electrode coverage at porous nickel electrodes in a novel 3-electrode flow-through cell. For each parameter set 3 data sets are given to ensure statistical confidence. Each data set, stored as .hdf5-file, is structured in groups as follows:

  • Electrochemical Measurement Data
  • Sideview Raw Images
  • Topview Raw Images
  • Results
    • Detected Bubbles
    • Electrode Coverage

In the attributes assigned to the groups in the .hdf5-file all relevant metadata is given, including the experimental parameters, used devices and characteristics of the mounted WE. In addition to exemplary data sets for all three electrodes, the CAD files of the experimental setup used and sample videos of the raw images are also provided within this data publication. The remaining data sets of all measurements performed can be made available upon request.

Keywords: bubble dynamics; alkaline electrolysis; porous electrodes; membraneless electrolyzer; machine learning; additive manufacturing

Related publications


Publ.-Id: 35144

Automatic detection and classification of treatment deviations in proton therapy from realistically simulated prompt gamma imaging data

Pietsch, J.; Khamfongkhruea, C.; Berthold, J.; Janssens, G.; Stützer, K.; Löck, S.; Richter, C.


A clinical study regarding the potential of range verification in proton therapy by prompt gamma imaging (PGI) is carried out at our institution. Manual interpretation of the detected spot-wise range shift information is time-consuming, highly complex, and therefore not feasible in a broad routine application.


Here, we present an approach to automatically detect and classify treatment deviations in realistically simulated PGI data for head and neck cancer (HNC) treatments using convolutional neural networks (CNNs) and conventional machine learning (ML) approaches.


For 12 HNC patients and one anthropomorphic head phantom (n=13), pencil beam scanning (PBS) treatment plans were generated and one field per plan was assumed to be monitored with the IBA slit camera. In total, 386 scenarios resembling different relevant or non-relevant treatment deviations were simulated on planning and control CTs and manually classified into 7 classes: non-relevant changes (NR) and relevant changes (RE) triggering treatment intervention due to range prediction errors (±RP), setup errors in beam direction (±SE), anatomical changes (AC), or a combination of such errors (CB). PBS spots with reliable PGI information were considered with their nominal Bragg peak position for the generation of two 3D spatial maps of 16⨯16⨯16 voxels containing PGI-determined range shift and proton number information. Three complexity levels of simulated PGI data were investigated: (I) optimal PGI data, (II) realistic PGI data with simulated Poisson noise based on the locally delivered proton number, and (III) realistic PGI data with an additional positioning uncertainty of the slit camera following an experimentally determined distribution.
For each complexity level, 3D-CNNs were trained on a data subset (n=9) using patient-wise leave-one-out cross-validation and tested on an independent test cohort (n=4). Both the binary task of detecting RE and the multi-class task of classifying the underlying error source were investigated. Similarly, four different conventional ML classifiers (logistic regression, multi-layer perceptron, random forest, support vector machine) were trained using five previously established handcrafted features extracted from the PGI data and used for performance comparison.


On the test data, the CNN ensemble achieved a binary accuracy of 0.95, 0.96, and 0.93 and a multi-class accuracy of 0.83, 0.81, and 0.76 for the complexity levels (I), (II), and (III), respectively. In the case of binary classification, the CNN ensemble detected treatment deviations in the most realistic scenario with a sensitivity of 0.95 and a specificity of 0.88. The best performing ML classifiers showed a similar test performance.


This study demonstrates that CNNs can reliably detect relevant changes in realistically simulated PGI data and classify most of the underlying sources of treatment deviations. The CNNs extracted meaningful features from the PGI data with a performance comparable to ML classifiers trained on previously established handcrafted features. These results highlight the potential of a reliable, automatic interpretation of PGI data for treatment verification, which is highly desired for broad clinical application and a prerequisite for the inclusion of PGI in an automated feedback loop for online adaptive proton therapy.

Keywords: range verification; prompt gamma imaging; proton therapy; artificial intelligence; machine learning

Publ.-Id: 35143

A High-Order-Integration Scheme for Global Polynomial Representations of Closed Surfaces

Zavalani, G.; Hecht, M.

We provide a novel high-order integration scheme crossing the limitations of established curved triangle techniques, that can be applied to a broad class of surfaces, providing a high-order approximation of the integrand and the geometry of the surface. This approach relies on recent results of multivariate interpolation which enable a global polynomial level set to be used to implicitly represent a broad class of closed surfaces.

Keywords: high-order integration; global polynomial level set; multivariate interpolation; curved triangles; closed surfaces

  • Poster
    11th Conference on Applied Mathematics and Scientific Computing, 05.-09.09.2022, Brijuni, Croatia

Publ.-Id: 35140

Recommendations on compiling test datasets for evaluating artificial intelligence solutions in pathology

Homeyer, A.; Geißler, C.; Ole Schwen, L.; Zakrzewski, F.; Evans, T.; Strohmenger, K.; Westphal, M.; David Bülow, R.; Kargl, M.; Karjauv, A.; Munné-Bertran, I.; Orge Retzlaff, C.; Romero-López, A.; Sołtysiński, T.; Plass, M.; Carvalho, R.; Steinbach, P.; Lan, Y.-C.; Bouteldja, N.; Haber, D.; Rojas-Carulla, M.; Vafaei Sadr, A.; Kraft, M.; Krüger, D.; Fick, R.; Lang, T.; Boor, P.; Müller, H.; Hufnagl, P.; Zerbe, N.

Artificial intelligence (AI) solutions that automatically extract information from digital histology images have shown great promise for improving pathological diagnosis. Prior to routine use, it is important to evaluate their predictive performance and obtain regulatory approval. This assessment requires appropriate test datasets. However, compiling such datasets is challenging and specific recommendations are missing. A committee of various stakeholders, including commercial AI developers, pathologists, and researchers, discussed key aspects and conducted extensive literature reviews on test datasets in pathology. Here, we summarize the results and derive general recommendations on compiling test datasets. We address several questions: Which and how many images are needed? How to deal with low-prevalence subsets? How can potential bias be detected? How should datasets be reported? What are the regulatory requirements in different countries? The recommendations are intended to help AI developers demonstrate the utility of their products and to help pathologists and regulatory agencies verify reported performance measures. Further research is needed to formulate criteria for sufficiently representative test datasets so that AI solutions can operate with less user intervention and better support diagnostic workflows in the future.

Keywords: machine learning; pathology; test datasets

Publ.-Id: 35139

Accurate temperature diagnostics for matter under extreme conditions

Dornheim, T.; Böhme, M.; Kraus, D.; Döppner, T.; Preston, T.; Moldabekov, Z.; Vorberger, J.

The experimental investigation of matter under extreme densities and temperatures as they occur for example in astrophysical objects and nuclear fusion applications constitutes one of the most active frontiers at the interface of material science, plasma physics, and engineering. The central obstacle is given by the rigorous interpretation of the experimental results, as even the diagnosis of basic parameters like the temperature T is rendered highly difficult by the extreme conditions. In this work, we present a simple, approximation-free method to extract the temperature of arbitrarily complex materials from scattering experiments, without the need for any simulations or an explicit deconvolution. This new paradigm can be readily implemented at modern facilities and corresponding experiments will have a profound impact on our understanding of warm dense matter and beyond, and open up a gamut of appealing possibilities in the context of thermonuclear fusion, laboratory astrophysics, and related disciplines.

Related publications

Publ.-Id: 35138

Physical insights from imaginary-time density--density correlation functions

Dornheim, T.; Moldabekov, Z.; Tolias, P.; Böhme, M.; Vorberger, J.

The accurate theoretical description of the dynamic properties of correlated quantum many-body systems such as the dynamic structure factor S(q,ω) constitutes an important task in many fields. Unfortunately, highly accurate quantum Monte Carlo methods are usually restricted to the imaginary time domain, and the analytic continuation of the imaginary time density--density correlation function F(q,τ) to real frequencies is a notoriously hard problem. In this work, we argue that no such analytic continuation is required as F(q,τ) contains, by definition, the same physical information as S(q,ω), only in an unfamiliar representation. Specifically, we show how we can directly extract key information such as the temperature or quasi-particle excitation energies from the τ-domain, which is highly relevant for equation-of-state measurements of matter under extreme conditions. As a practical example, we consider \emph{ab initio} path integral Monte Carlo results for the uniform electron gas (UEG), and demonstrate that even nontrivial processes such as the \emph{roton feature} of the UEG at low density straightforwardly manifest in F(q,τ). In fact, directly working in the τ-domain is advantageous for many reasons and holds the enticing promise for unprecedented agreement between theory and experiment.

Publ.-Id: 35137

Ab Initio Static Exchange-Correlation Kernel across Jacob’s Ladder without Functional Derivatives

Moldabekov, Z.; Böhme, M.; Vorberger, J.; Blaschke, D.; Dornheim, T.

The electronic exchange-correlation (XC) kernel constitutes a fundamental input for the estimation of a gamut of material properties such as the dielectric characteristics, the thermal and electrical conductivity, the construction of effective potentials, or the response to an external perturbation. In practice, no reliable method has been known that allows to compute the kernel of real materials. In this work, we overcome this long-standing limitation by introducing a new, formally exact methodology for the computation of the static XC kernel of arbitrary materials exclusively within the framework of density functional theory (DFT) -- no external input apart from the usual XC-functional is required. As a first practical demonstration of the utility and flexibility of our methodology, we compare our new results with exact quantum Monte Carlo (QMC) data for the archetypical uniform electron gas model at both ambient and warm dense matter conditions. This gives us unprecedented insights into the performance of different XC-functionals, and has important implications for the development of new functionals that are designed for the application at extreme temperatures. In addition, we obtain new DFT results for the XC kernel of warm dense hydrogen as it occurs in fusion applications and astrophysical objects such as planetary interiors. The observed excellent agreement to the recent QMC results by Böhme \emph{et al.}~[Phys.~Rev.~Lett.~\textbf{129}, 066402 (2022)] clearly demonstrates that our framework is capable to even capture nontrivial effects such as XC-induced isotropy breaking in the density response of hydrogen at large wave numbers. Our method can easily be applied using standard DFT codes and will open up new avenues for the computation of the properties of real materials.

Related publications

Publ.-Id: 35136

Numerical design optimization of recuperator designs for sCO2 power cycle by CFD

Guille-Bourdas, A. F.

As a part of my graduation internship in engineering and master’s degree, I work in the Helmholtz Zentrum Dresden-Rosseendorf institute for an internship of 6-months. I am a part of a team consisting of my supervisor, Dr. Sebastian Unger and a PhD student, Mrs. Malini Bangalore. The latter studies a thermal energy storage (TES). The storage would store electricity as heat from renewable energy sources when the supply in electricity is higher than the demand. In case of residual load demand, the stored thermal energy would be released to a power cycle and supply the electrical grid. Therefore, a heat exchanger , connecting the thermal storage system to the power cycle, needs to ben designed and here is where I intervene.
Before I came, it was already decided, that the power cycle uses supercritical fluid as working fluid and working fluid in the thermal energy storage circuit, more specifically the hot fluid, is CO2 at atmospheric pressure. It was also decided that the heat exchanger type is a printed circuit heat exchanger (PCHE), that the heat transfer rate is set to 10 MW and the hot fluid inlet temperature is 600 °C. However, to completely determine the geometry of the PCHE, the boundary conditions, i.e. temperature, pressure and mass flow rates in hot and cold channels, need to be determined.
To that end, a review of cycles and their modelling is made. It helps to calculate the boundary conditions for the cold side. Then, a cost-optimization analysis of the PCHE leads to determine the boundary conditions of the hot fluid. Indeed, as the hot fluid is CO2 at atmospheric pressure, even the smaller pressure drop has a significant impact on the operation cost of the PCHE. Therefore, a reference case may be determined.
Finally, CFD simulations were conducted on the reference case geometry. Furthermore, the behaviour of the PCHE is examined, when the mass flow rate is changed, e.g. because of different system operation. Finally, the CFD simulation results are compared to existing correlations.

  • Master thesis
    Universite de Poitiers, 2022
    Mentor: Sebastian Unger
    91 Seiten

Publ.-Id: 35135

Online-adaptive particle therapy: Current status and vision for the future

Richter, C.

Online-adaptive particle therapy: Current status and vision for the future
Richter, Christian

  • Lecture (Conference)
    DGMP Konferenz, 21.-24.09.2022, Aachen, Deutschland

Publ.-Id: 35134

Prompt gamma particle imaging

Richter, C.

The lecture will give an overview of the utilization of prompt-gamma (PG) radiation, emitted from the
patient’s body during fractionated particle therapy treatment, for range and treatment verification.
After the nuclear physics basics of the emission of prompt gamma rays have been refreshed, the three
fundamental approaches for PG-based particle range determination will be discussed, which use
either spatial, temporal or spectroscopic information of PG - namely prompt gamma imaging (PGI),
prompt gamma timing (PGT) and prompt gamma spectroscopy (PGS), respectively. Special emphasis
will be on the interpretation of the complex PG data for the distinction of clinically relevant from
irrelevant treatment deviations, necessary for the clinical application of PG for treatment intervention in an online-adaptive PT realization. Results from the evaluation of clinically acquired PGI data will be

  • Lecture (Conference)
    RAPTOR school - loop requirements, 04.-09.09.2022, Ljubljana, Slovenia

Publ.-Id: 35133

Next-generation radiation therapy: Towards near-realtime adaptive proton therapy

Richter, C.

Next-generation radiation therapy: Towards near-realtime adaptive proton therapy

  • Lecture (Conference)
    2nd Meeting Strategic Advisory Board Helmholtz Health, 23.05.2022, Heidelberg, Deutschland

Publ.-Id: 35132

Highlights der Medizinphysik

Richter, C.

Highlights in der Medizinphysik

  • Open Access Logo Lecture (Conference)
    100 Jahre Strahlentherapie in Dresden, 21.06.2022, Dresden, Deutschland

Publ.-Id: 35131

Dual-Energy CT in Radiation Oncology

Richter, C.; Wohlfahrt, P.

In radiation oncology, CT imaging is of crucial importance for consistent and accurate delineation of target and organ-at-risk structures as well as for highly precise treatment planning and prediction of the deposited dose. Even though the potential benefit of dual-energy CT for those purposes was identified early, its implementation in clinical practice is still in an early stage. Here, we want to give an overview of current and potential future applications of dual-energy CT in the field of radiation oncology. Since the next generation of X-ray computed tomography with a photon-counting detector technology is rising at the horizon, we also want to give an outlook on radiotherapeutic applications that will benefit or even become possible for the first time with this technological evolution.

  • Book chapter
    Hatem Alkadhi, André Euler, David Maintz, Dushyant Sahani: Spectral Imaging, Switzerland: Springer, 2022, 978-3-030-96285-2, 333-346
    DOI: 10.1007/978-3-030-96285-2

Publ.-Id: 35130

The Chemical Journey of Europium(III) through Winter Rye (Secale cereale L.) – Understanding through Mass Spectrometry and Chemical Microscopy

Stadler, J.; Vogel, M.; Steudtner, R.; Drobot, B.; Kogiomtzidis, A.; Weiss, M.; Walther, C.

A combination of biochemical preparation methods with microscopic, spectroscopic, and mass spectrometric analysis techniques as contemplating state of the art application, was used for direct visualization, localization, and chemical identification of europium in plants. This works illustrates the chemical journey of europium (Eu(III)) through winter rye (Secale cereale L.), providing insight into the possibilities of speciation for Rare Earth Elements (REE) and trivalent f-elements. Kinetic experiments of contaminated plants show a maximum europium concentration in Secale cereale L. after four days. Transport of the element through the vascular bundle was confirmed with Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray analysis (EDS). For chemical speciation, plants were grown in a liquid nutrition medium, whereby Eu(III) species distribution could be measured by mass spectrometry and luminescence measurements. Both techniques confirm the occurrence of Eu malate species in the nutrition medium, and further analysis of the plant was performed. Luminescence results indicate a change in Eu(III) species distribution from root tip to plant leaves. Microscopic analysis show at least three different Eu(III) species with potential binding to organic and inorganic phosphate groups and a Eu(III) protein complex. With plant root extraction, further europium species could be identified by using Electrospray Ionization Mass Spectrometry (ESI MS). Complexation with malate, citrate, a combined malate-citrate ligand, and aspartate was confirmed mostly in a 1:1 stoichiometry (Eu:ligand). The combination of the used analytical techniques opens new possibilities in direct species analysis, especially regarding to the understanding of rare earth elements (REE) uptake in plants. This work provides a contribution in better understanding of plant mechanisms of the f-elements and their species uptake.

Keywords: Rare earth elements; plant uptake; species analysis; europium; imaging

Related publications

Publ.-Id: 35129

Personalised radiation therapy taking both the tumour and patient into consideration

Overgaard, J.; Aznar, M. C.; Bacchus, C.; Coppes, R. P.; Deutsch, E.; Georg, D.; Haustermans, K.; Hoskin, P.; Krause, M.; Lartigau, E. F.; Lee, A. W. M.; Steffen Löck J, B. V. O.; Thwaites, D. I.; van der Kogel, A. J.; van der Heide, U. A.; Valentini, V.; Baumann, M.

A look through almost 2000 abstracts submitted for the upcom-
ing ESTRO 2022 meeting together with a glance back on the 2021
papers published in Radiotherapy and Oncology gives one a good
impression of the (current) key focus areas in radiation oncology:
Almost all of this work relates to optimal delivery of radiation ther-
apy in terms of technology, quality assurance and morbidity reduc-
ing approaches. Thus, at present the research questions considered
as most relevant for radiotherapy of e.g. lung and oesophageal can-
cer are not related to tumour control, but to the late risk of cardiac
disease in the patients who are lucky to survive their cancer long
enough to develop such problems [1]. The same scenario is found
in the patient cohort that constitutes the largest indication for
radiotherapy in Europe: women with early breast cancer [2]. In
these examples, and in many other situations where radiotherapy
is applied with a curative intent, less focus has currently been
given to the aim or indication of the treatment, namely the control
of loco-regional malignant disease. Of course, since Holthusen’s
seminal paper in 1936 [3] the overall aim of radiotherapy, as stated
over and over again by all teachers in the field (including the
authors of this editorial), is uncomplicated tumour control, i.e.
loco-regional tumour control without severe normal tissue damage
(therapeutic ratio). This implies that rigorous study of the effects of
radiotherapy on normal, non-tumour, tissues is an absolute necessity. Yet, the prescription of radiotherapy in clinical practice is
done to kill tumour cells for local and loco-regional control. If the
effects of radiotherapy on tumours are shifting out of focus, it
might be taken for granted that the indication, dose, fractionation,
and potential multidisciplinary interactions in this field are fully
understood, and what remains is the fine tuning of the associated
risk of morbidity.

Publ.-Id: 35128

Ion Microprobe analysis of wear processes in ta-C coatings and contact areas on the counter bodies

Munnik, F.; Lorenz, L.; Härtwig, F.; Krause, M.

Solid lubricants, like ta-C (hydrogen-free tetrahedral amorphous carbon) coatings, are an active area of research to replace liquid lubricants. This substitution is important because of the negative environmental impact and high material consumption of liquid lubricants. The influence of soft metal counter bodies on the unlubricated friction behaviour of hydrogen-free carbon coatings has mostly been studied for doped a-C coatings so far. All these studies show that low friction and wear can only be achieved if a tribolayer is formed to protect the contact. Even with a formed tribolayer, its composition is crucial for the frictional behaviour, making the investigation of this composition essential. A study currently underway aims to identify friction-induced surface changes like material loss of the coating, material transfer between the counter body and the coating, or the formation of a tribolayer.
The current work presents Ion Beam Analysis methods to deliver laterally and depth-resolved element analysis of the wear track on the coating and the contact area of the counter bodies (CB). In a first test, a ta-C coating has been subjected to pin-on-disk tests with various metallic and ceramic CBs. He and H ion microbeams have been used to scan over the tracks and the contact areas of the CBs. Both RBS and PIXE have been used and first results are presented. It is shown that, in this case, RBS yields the more useful information. Both, a 2 MeV He ion beam and a 3 MeV H ion beam provide valuable results. The advantages of each type of ion beam depend on the sample and the information needed. As shown in this work, RBS with a 2 MeV He ion beam is useful to determine the transfer layer of a (soft) metal CB to the ta-C coating, whereas 3 MeV H RBS can be used to determine the presence of C and O on the CB because of the increased non-Rutherford cross-sections for these elements.

Related publications

  • Poster
    18th International Conference on Nuclear Microprobe Technology and Applications, 11.-16.09.2022, Ljubljana, Slovenia

Publ.-Id: 35127

In vivo assessment of tissue-specific radiological parameters with intra- and inter-patient variation using dual-energy computed tomography

Peters, N.; Kieslich, A.; Wohlfahrt, P.; Hofmann, C.; Richter, C.

Purpose/objective: Experimental in vivo determination of radiological tissue parameters of organs in the
head and pelvis within a large patient cohort, expanding on the current standard human tissue database
summarized in ICRU46.
Material/methods: Relative electron density (RED), effective atomic number (EAN) and stopping-power
ratio (SPR) were obtained from clinical dual-energy CT scans using a clinically validated DirectSPR imple-
mentation and organ segmentations of 107 brain-tumor (brain, brainstem, spinal cord, chiasm, optical
nerve, lens) and 120 pelvic cancer patients (prostate, kidney, liver, bladder). The impact of contamination
by surrounding tissues on the tissue parameters was reduced with a dedicated contour adaption routine.
Tissue parameters were characterized regarding the cohort mean value as well as the variation within
each patient (2rintra) and between patients (2rinter ). For the brain, age-dependent differences were deter-
Results: For 10 organs, including 4 structures not listed in ICRU46, the mean RED, EAN and SPR as well as
their respective intra- and inter-patient variation were determined. SPR intra-patient variation was
higher than 1.3% (1.3–4.6%) in all organs and always exceeded the inter-patient variation of the organ
mean SPR (0.6–2.1%). For the brain, a significant SPR variation between pediatric and non-pediatric
patients was determined.
Conclusion: Radiological tissue parameters in the head and pelvis were characterized in vivo for a large
patient cohort using dual-energy CT. This reassesses parts of the current standard database defined in
ICRU46, furthermore complementing the data described in literature by smaller substructures in the
brain as well as by the quantification of organ-specific inter- and intra-patient variation.

Keywords: Proton therapy; Dual-energy computed tomography; DECT; Tissue parameters

Publ.-Id: 35126

Randomisierte Studie zum Vergleich von Nebenwirkungen nach Protonen- versus Photonen- Strahlentherapie bei Patienten mit fortgeschrittenem nichtkleinzelligen Bronchialkarzinom

Troost, E. G. C.; Zschaeck, S.; Bütof, R.; Czekalla, M.; Richter, C.; Stützer, K.; Krause, M.; Baumann, M.

Bronchialkarzinome sind in Deutschland
die dritthäufigste Tumorerkrankung. Trotz
erheblicher therapeutischer Fortschritte ist
die Prognose der Lungentumoren nach
wie vor ungünstig, die relative 5-Jahres-
Überlebensrate nach Diagnose eines Bron-
chialkarzinoms beträgt lediglich 16 % [3].
Hinsichtlich der Tumorart werden nicht-
kleinzellige (NSCLC) und kleinzellige Bron-
chialkarzinome unterschieden.
Bei fortgeschrittenen NSCLC besteht
die Standardtherapie aus einer gleichzei-
tig durchgeführten Radiochemotherapie,
gefolgt von einer Immuntherapie. In
Metaanalysen konnte die Überlegenheit
der simultanen Radiochemotherapie ge-
genüber einem sequenziellen Vorgehen
gezeigt werden.

Publ.-Id: 35124

The force balance of hydrogen bubbles growing and oscillating on a microelectrode

Hossain, S. S.; Bashkatov, A.; Yang, X.; Mutschke, G.; Eckert, K.

Hydrogen evolution in acidic aqueous electrolytes was recently found to be characterized by a
carpet of microbubbles covering the microelectrode and feeding the growth of the main bubbles by
coalescence. Besides this, oscillatory behavior of the main bubbles was observed prior to departure.
Extending earlier studies, this work delivers the forces acting on the main bubble more accurately
by taking into account further geometric and electrochemical details measured during experiments.
Combining simulation work and measurements makes it possible to confirm the role of an attractive
electrical (Coulomb) force caused by the adsorption of hydrogen ions at the bubble interface and to
obtain a better understanding of the bubble dynamics observed.

Keywords: electrolysis; gas evolution; hydrogen production; force balance; Marangoni effect; adsorption at interfaces; numerical simulation; particle tracking velocimetry


Publ.-Id: 35123

Vorstoß in die Terahertz-Lücke

Deinert, J.-C.; Kovalev, S.; Gensch, M.

Der Terahertz-Frequenzbereich umfasst ein technisch wenig erschlossenes Grenzgebiet im elektromagnetischen Spektrum. Er ist aber besonders interessant, weil er viele Eigenfrequenzen verschiedener, komplexer Quantenphänomene enthält. Dafür stehen neuerdings intensive Terahertz-Pulse aus spezialisierten Elektronenbeschleunigerquellen zur Verfügung. Sie bieten nun eine einzigartige Möglichkeit, solch fundamentale Quantenprozesse im Nichtgleichgewicht zu untersuchen

Keywords: Terahertz; Elektronenbeschleuniger; Ladungsträgerdynamik; Lichtquellen; Ultrakurzzeitphysik

Related publications

Publ.-Id: 35122

A study on rare-earth Laves phases for magnetocaloric liquefaction of hydrogen

Liu, W.; Bykov, E.; Taskaev, S.; Bogush, M.; Khovaylo, V.; Fortunato, N.; Aubert, A.; Zhang, H.; Gottschall, T.; Wosnitza, J.; Scheibel, F.; Skokov, K.; Gutfleisch, O.

We are witnessing a great transition towards a society powered by renewable energies to meet the ever-stringent climate target. Hydrogen, as an energy carrier, will play a key role in building a climate-neutral society. Although liquid hydrogen is essential for hydrogen storage and transportation, liquefying hydrogen is costly with the conventional methods based on Joule-Thomas effect. As an emerging technology which is potentially more efficient, magnetocaloric hydrogen liquefaction can be a “game-changer”. In this work, we have investigated the rare-earth-based Laves phases RAl and RNi2 for magnetocaloric hydrogen liquefaction. We have noticed an unaddressed feature that the magnetocaloric effect of second-order magnetocaloric materials can become “giant” near the hydrogen boiling point. This feature indicates strong correlations, down to the boiling point of hydrogen, among the three important quantities of the magnetocaloric effect: the maximum magnetic entropy change ΔSmax m, the maximum adiabatic temperature change ΔTmax ad , and the Curie temperature TC. Via a comprehensive literature review, we interpret the correlations for a rare-earth intermetallic series as two trends: (1) ΔSmax m increases with decreasing TC; (2) ΔTmax ad decreases near room temperature with decreasing TC but increases at cryogenic temperatures. Moreover, we have developed a mean-field approach to describe these two trends theoretically. The dependence of ΔSmax m and ΔTmax ad on TC revealed in this work helps researchers quickly anticipate the magnetocaloric performance of rare-earth-based compounds, guiding material design and accelerating the discoveries of magnetocaloric materials for hydrogen liquefaction.


Publ.-Id: 35121

Enzymological characterization of ⁶⁴Cu-labeled neprilysin substrates and their application for modulating the renal clearance of targeted radiopharmaceuticals

Brandt, F.; Ullrich, M.; Wodtke, J.; Kopka, K.; Bachmann, M.; Löser, R.; Pietzsch, J.; Pietzsch, H.-J.; Wodtke, R.

The applicability of radioligands for targeted endoradionuclide therapy is limited due to radiation-induced deleterious effects to healthy tissues. This applies in particular to the kidneys as primary organs of elimination, which requires dosimetric estimates to justify internal radionuclide therapy. In this context, the targeting of enzymes of the renal brush border membrane by cleavable linkers between target molecule and radiolabel that permit the formation of fast eliminating radionuclide-carrying cleavage fragments gains increasing interest. Herein, we synthesized a small library of ⁶⁴Cu-labeled cleavable linkers and quantified their substrate potentials toward neprilysin (NEP), a highly abundant peptidase at the renal brush border membrane. This allowed for the derivation of structure-activity relationships and selected cleavable linkers were attached to the somatostatin receptor subtype 2 ligand [Tyr³]octreotate. Subsequent radiopharmacological characterization revealed that a substrate-based targeting of NEP in the kidneys with small molecules or peptides entails a certain degree of premature cleavage in the blood circulation by soluble and endothelium-derived NEP. However, for a tissue-specific targeting of NEP in the kidneys, the additional targeting of albumin in the blood by albumin-binding moieties is highlighted.

Related publications


Publ.-Id: 35120

Combined Systemic Drug Treatment with Proton Therapy: Investigations on Patient-Derived Organoids

Naumann, M.; Czempiel, T.; Jana Lößner, A.; Pape, K.; Beyreuther, E.; Löck, S.; Drukewitz, S.; Hennig, A.; von Neubeck, C.; Klink, B.; Krause, M.; William, D.; Stange, D. E.; Bütof, R.; Dietrich, A.

To optimize neoadjuvant radiochemotherapy of pancreatic ductal adenocarcinoma (PDAC),
the value of new irradiation modalities such as proton therapy needs to be investigated in relevant
preclinical models. We studied individual treatment responses to RCT using patient-derived PDAC
organoids (PDO). Four PDO lines were treated with gemcitabine, 5-fluorouracile (5FU), photon and
proton irradiation and combined RCT. Therapy response was subsequently measured via viability
assays. In addition, treatment-naive PDOs were characterized via whole exome sequencing and
tumorigenicity was investigated in NMRI Foxn1nu/nu mice. We found a mutational pattern con-
taining common mutations associated with PDAC within the PDOs. Although we could unravel
potential complications of the viability assay for PDOs in radiobiology, distinct synergistic effects
of gemcitabine and 5FU with proton irradiation were observed in two PDO lines that may lead to further mechanistical studies. We could demonstrate that PDOs are a powerful tool for translational
proton radiation research.

Keywords: patient-derived organoid; PDAC; pancreatic cancer; radiochemotherapy; 3D cell culture; proton irradiation; translational radiooncology

Publ.-Id: 35119

European Society for Radiotherapy and Oncology Advisory Committee in Radiation Oncology Practice consensus recommendations on patient selection and dose and fractionation for external beam radiotherapy in early breast cancer

Meattini, I.; Becherini, C.; Boersma, L.; Kaidar-Person, O.; Nader Marta, G.; Montero, A.; Vrou Offersen, B.; Aznar, M. C.; Belka, C.; Murray Brunt, A.; Dicuonzo, S.; Franco, P.; Krause, M.; Mairead Mackenzie, T. M.; Marrazzo, L.; Ratosa, I.; Scholten, A.; Senkus, E.; Stobart, H.; Poortmans, P.; Coles, C. E.

High-quality randomised clinical trials testing moderately fractionated breast radiotherapy have clearly shown that
local control and survival is at least as effective as with 2 Gy daily fractions with similar or reduced normal tissue
toxicity. Fewer treatment visits are welcomed by patients and their families, and reduced fractions produce substantial
savings for health-care systems. Implementation of hypofractionation, however, has moved at a slow pace. The
oncology community have now reached an inflection point created by new evidence from the FAST-Forward five-
fraction randomised trial and catalysed by the need for the global radiation oncology community to unite during the
COVID-19 pandemic and rapidly rethink hypofractionation implementation. The aim of this paper is to support
equity of access for all patients to receive evidence-based breast external beam radiotherapy and to facilitate the
translation of new evidence into routine daily practice. The results from this European Society for Radiotherapy and
Oncology Advisory Committee in Radiation Oncology Practice consensus state that moderately hypofractionated
radiotherapy can be offered to any patient for whole breast, chest wall (with or without reconstruction), and nodal
volumes. Ultrafractionation (five fractions) can also be offered for non-nodal breast or chest wall (without
reconstruction) radiotherapy either as standard of care or within a randomised trial or prospective cohort. The
consensus is timely; not only is it a pragmatic framework for radiation oncologists, but it provides a measured
proposal for the path forward to influence policy makers and empower patients to ensure equity of access to evidence-
based radiotherapy.


Publ.-Id: 35118

Biomarker signatures for primary radiochemotherapy of locally advanced HNSCC – Hypothesis generation on a multicentre cohort of the DKTK-ROG

Löck, S.; Linge, A.; Lohaus, F.; Ebert, N.; Gudziol, V.; Nowak, A.; Tinhofer, I.; Kalinauskaite, G.; Guberina, M.; Stuschke, M.; Balermpas, P.; von der Grün, J.; Grosu, A.-L.; Debus, J.; Ganswindt, U.; Belka, C.; Peeken, J. C.; Combs, S. E.; De-Colle, C.; Zips, D.; Baretton, G. B.; Krause, M.; Baumann, M.

Purpose: To develop prognostic biomarker signatures for patients with locally advanced head and neck
squamous cell carcinoma (HNSCC) treated by primary radiochemotherapy (RCTx) based on previously
published molecular analyses of the retrospective biomarker study of the German Cancer Consortium
– Radiation Oncology Group (DKTK-ROG).

Keywords: HNSCC; Biomarkers; Primary radiochemotherapy; Validation; Signature

Publ.-Id: 35117

Clinical necessity of multi-image based (4DMIB) optimization for targets affected by respiratory motion and treated with scanned particle therapy – A comprehensive review

Knopf, A.-C.; Czerska, K.; Fracchiolla, F.; Graeff, C.; Molinelli, S.; Rinaldi, I.; Rucincki, A.; Sterpin, E.; Stützer, K.; Trnkova, P.; Zhang, Y.; Chang, J. Y.; Giap, H.; Liu, W.; Schild, S. E.; Simone Ii, C. B.; Lomax, A. J.; Meijers, A.

4D multi-image-based (4DMIB) optimization is a form of robust optimization where different uncertainty
scenarios, due to anatomy variations, are considered via multiple image sets (e.g., 4DCT). In this review,
we focused on providing an overview of different 4DMIB optimization implementations, introduced var-
ious frameworks to evaluate the robustness of scanned particle therapy affected by breathing motion and
summarized the existing evidence on the necessity of using 4DMIB optimization clinically. Expected
potential benefits of 4DMIB optimization include more robust and/or interplay-effect-resistant doses for
the target volume and organs-at-risk for indications affected by anatomical variations (e.g., breathing,
peristalsis, etc.). Although considerable literature is available on the research and technical aspects of
4DMIB, clinical studies are rare and often contain methodological limitations, such as, limited patient
number, motion amplitude, motion and delivery time structure considerations, number of repeat CTs,
etc. Therefore, the data are not conclusive. In addition, multiple studies have found that robust 3D opti-
mized plans result in dose distributions within the set clinical tolerances and, therefore, are suitable for a
treatment of moving targets with scanned particle therapy. We, therefore, consider the clinical necessity
of 4DMIB optimization, when treating moving targets with scanned particle therapy, as still to be

Keywords: Proton therapy; 4D optimization; Multi-image-based optimization; Motion management

Publ.-Id: 35116

Integration of p16/HPV DNA Status with a 24-miRNA-Defined Molecular Phenotype Improves Clinically Relevant Stratification of Head and Neck Cancer Patients

Hess, J.; Unger, K.; Maihoefer, C.; Schüttrumpf, L.; Weber, P.; Marschner, S.; Wintergerst, L.; Pflugradt, U.; Baumeister, P.; Walch, A.; Woischke, C.; Kirchner, T.; Werner, M.; Sörensen, K.; Baumann, M.; Tinhofer, I.; Combs, S. E.; Debus, J.; Schäfer, H.; Krause, M.; Linge, A.; von der Grün, J.; Stuschke, M.; Zips, D.; Canis, M.; Lauber, K.; Ganswindt, U.; Henke, M.; Zitzelsberger, H.; Belka, C.

Human papillomavirus (HPV)-driven head and neck squamous cell carcinomas (HNSCC)
generally have a more favourable prognosis. We hypothesized that HPV-associated HNSCC may
be identified by an miRNA-signature according to their specific molecular pathogenesis, and be
characterized by a unique transcriptome compared to HPV-negative HNSCC. We performed miRNA
expression profiling of two p16/HPV DNA characterized HNSCC cohorts of patients treated by
adjuvant radio(chemo)therapy (multicentre DKTK-ROG n = 128, single-centre LMU-KKG n = 101).
A linear model predicting HPV status built in DKTK-ROG using lasso-regression was tested in
LMU-KKG. LMU-KKG tumours (n = 30) were transcriptome profiled for differential gene expression
and miRNA-integration. A 24-miRNA signature predicted HPV-status with 94.53% accuracy (AUC:
0.99) in DKTK-ROG, and 86.14% (AUC: 0.86) in LMU-KKG. The prognostic values of 24-miRNA-
and p16/HPV DNA status were comparable. Combining p16/HPV DNA and 24-miRNA status
allowed patient sub-stratification and identification of an HPV-associated patient subgroup with
impaired overall survival. HPV-positive tumours showed downregulated MAPK, Estrogen, EGFR,
TGFbeta, WNT signaling activity. miRNA-mRNA integration revealed HPV-specific signaling pathway
regulation, including PD−L1 expression/PD−1 checkpoint pathway in cancer in HPV-associated HNSCC.
Integration of clinically established p16/HPV DNA with 24-miRNA signature status improved
clinically relevant risk stratification, which might be considered for future clinical decision-making
with respect to treatment de-escalation in HPV-associated HNSCC.

Keywords: head and neck cancer; HNSCC; HPV; miRNA; signature; prediction; prognosis; mRNA; interaction; signaling pathways

Publ.-Id: 35115

Multiphase CFD for Nuclear Safety Research

Lucas, D.

While according to the state of the art safety analyses related to nuclear reactor thermal hydraulics are done using system codes, CFD becomes more and more important as a tool to support such analyses. Often multiphase flows are involved in the flow situations that have to be considered. For medium and large scales, as they are typical in nuclear reactor safety research, the Euler-Euler (E-E) approach is most suited and most frequently used. However, E-E-CFD is not yet mature. A consolidation of closure models is required to enable reliable predictions. The baseline model concept is a promising way to reach such a consolidation. A baseline model for poly-disperse bubbly flows is established and implemented in the OpenSource CFD package OpenFOAM (Foundation release). The sustainable development requires quality insurance and continuous maintenance of the corresponding OpenFOAM-add-ons which is enabled in the GitLab environement. An automated workflow helps efficiently to support the step-by-step improvement of the baseline model. The lecture presents the baseline model conceptand the general strategy for its further development. This is illustrated by the example of the baseline model for poly-disperse flows. Advantages as well as challenges related to the use of Open Source software in NRS are discussed.

Keywords: multiphase CFD; Euler-Euler model; OpenFOAM

  • Invited lecture (Conferences) (Online presentation)
    13th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics, Operation, and Safety (NUTHOS-13), 06.-08.09.2022, Hsinchu, Taiwan

Publ.-Id: 35114

Integration of radiation oncology teaching in medical studies by German medical faculties due to the new licensing regulations

Dapper, H.; Belka, C.; Bock, F.; Budach, V.; Budach, W.; Christiansen, H.; Debus, J.; Distel, L.; Dunst, J.; Eckert, F.; Eich, H.; Eicheler, W.; Engenhart-Cabillic, R.; Fietkau, R.; Fleischmann, D. F.; Frerker, B.; Giordano, F. A.; Grosu, A. L.; Herfarth, K.; Hildebrandt, G.; Kaul, D.; Kölbl, O.; Krause, M.; Krug, D.; Martin, D.; Matuschek, C.; Medenwald, D.; Nicolay, N. H.; Niewald, M.; Oertel, M.; Petersen, C.; Pohl, F.; Raabe, A.; Rödel, C.; Rübe, C.; Schmalz, C.; Schmeel, L. C.; Steinmann, D.; Stüben, G.; Thamm, R.; Vordermark, D.; Vorwerk, H.; Wiegel, T.; Zips, D.; Combs, S. E.

The new Medical Licensing Regulations 2025 (Ärztliche Approbationsordnung, ÄApprO) will soon be passed by the Federal Council (Bundesrat) and will be implemented step by step by the individual faculties in the coming months. The further development of medical studies essentially involves an orientation from fact-based to competence-based learning and focuses on practical, longitudinal and interdisciplinary training. Radiation oncology and radiation therapy are important components of therapeutic oncology and are of great importance for public health, both clinically and epidemiologically, and therefore should be given appropriate attention in medical education. This report is based on a recent survey on the current state of radiation therapy teaching at university hospitals in Germany as well as the contents of the National Competence Based Learning Objectives Catalogue for Medicine 2.0 (Nationaler Kompetenzbasierter Lernzielkatalog Medizin 2.0, NKLM) and the closely related Subject Catalogue (Gegenstandskatalog, GK) of the Institute for Medical and Pharmaceutical Examination Questions (Institut für Medizinische und Pharmazeutische Prüfungsfragen, IMPP). The current recommendations of the German Society for Radiation Oncology (Deutsche Gesellschaft für Radioonkologie, DEGRO) regarding topics, scope and rationale for the establishment of radiation oncology teaching at the respective faculties are
also included.

Keywords: Radiation oncology teaching; Medical studies; New licensing regulations

Publ.-Id: 35113

Targeting of p21-Activated Kinase 4 Radiosensitizes Glioblastoma Cells via Impaired DNA Repair

Blankenstein, L. J.; Cordes, N.; Kunz-Schughart, L. A.; Vehlow, A.

Glioblastoma is a devastating malignant disease with poor patient overall survival. Strong invasiveness and resistance to radiochemotherapy have challenged the identification of molecular targets that can finally improve treatment outcomes. This study evaluates the influence of all six known p21-activated kinase (PAK) protein family members on the invasion capacity and radioresponse of glioblastoma cells by employing a siRNA-based screen. In a panel of human glioblastoma cell models, we identified PAK4 as the main PAK isoform regulating invasion and clonogenic survival upon irradiation and demonstrated the radiosensitizing potential of PAK4 inhibition. Mechanistically, we show that PAK4 depletion and pharmacological inhibition enhanced the number of irradiation- induced DNA double-strand breaks and reduced the expression levels of various DNA repair proteins.
In conclusion, our data suggest PAK4 as a putative target for radiosensitization and impairing DNA repair in glioblastoma, deserving further scrutiny in extended combinatorial treatment testing.

Keywords: glioblastoma; p21-activated kinase 4; radiosensitivity; DNA repair

Publ.-Id: 35112

Efficient Production of the PET radionuclide 133La for Theranostic Purposes in Targeted Alpha Therapy using the 134Ba(p,2n)133La Reaction

Brühlmann, S. A.; Kreller, M.; Pietzsch, H.-J.; Kopka, K.; Mamat, C.; Walther, M.; Reissig, F.

Targeted Alpha Therapy is a research field of highest interest in specialized radionuclide therapy. Over the last decades, several alpha-emitting radionuclides have entered and left research topics towards their clinical translation. Especially, 225Ac provides all necessary physical and chemical properties for a successful clinical application, which has already been shown by [225Ac]Ac PSMA 617. While PSMA 617 carries the DOTA as the complexing agent, the chelator macropa as macrocyclic alternative provides even more beneficial properties regarding labeling and complex stability in vivo. Lanthanum-133 is an excellent positron-emitting diagnostic lanthanide to radiolabel macropa-functionalized therapeutics, since 133La forms a perfect matched theranostic pair of radionuclides with the therapeutic radionuclide actinium-225 which itself can optimally be complexed by macropa as well. 133La was thus produced by cyclotron-based proton irradiation of an enriched 134Ba target. The target (30 mg of [134Ba]BaCO3) was irradiated for 60 min at 22 MeV and 10-15 µA beam current. Irradiation side products in the raw target solution were identified and quantified: 135La (0.4%), 135mBa (0.03%), 133mBa (0.01%) and 133Ba (0.0004%). The subsequent work-up and anion-exchange-based product purification process took approx. 30 min and led to a total amount of (1.2 – 1.8) GBq (decay-corrected to EOB) of 133La, formulated as [133La]LaCl3. After complete decay of 133La, a remainder of ca. 4 kBq of long-lived 133Ba per 100 MBq of 133La was detected and rated as uncritical regarding personal dose and waste management. Subsequent radiolabeling was successfully performed with previously published macropa-derived PSMA inhibitors at a micromolar range (quantitative labeling at 1 µM) and evaluated by radio-TLC and radio-HPLC analyses. The scale up to radioactivity amounts that are needed for clinical application purposes would be easy to achieve by increasing target mass, beam current and/or irradiation time to produce 133La of high radionuclide purity (>99.5%) regarding labeling properties and side products.

Keywords: macropa; lanthanum-133; actinium-225; PET; targeted alpha therapy; theranostics

Publ.-Id: 35111

Fallstudie Kühlgeräterecycling

Heibeck, M.; Mütze, T.

Die Fallstudie behandelt einen großtechnischen Recyclingversuch von 100 Kühlgeräten aus dem Haushaltsbereich in einer gewerblichen Erstbehandlungsanlage. Neben der Beobachtung von Be-handlungsschritten wie z. B. der Kompressordemontage wurden die Produktfraktionen Eisen, Nichteisen und Kunststoffe für drei Kühlgerätegruppen näher analysiert. Dabei wurde ein besonde-rer Fokus auf die Analyse von Restverbunden gelegt. Die Versuchsergebnisse ermöglichen eine Unterscheidung zwischen Restverbunden, welche im Prozess gebildet wurden, und anderen, die durch den konstruktiven Aufbau bedingt sind. Dadurch können Potenziale für ein recyclinggerech-teres Design von Kühlgeräten und Herausforderungen bei der Aufschlusszerkleinerung gezeigt werden. Außerdem können beispielsweise Leiterplatten für die Demontage leichter zugänglich an-geordnet werden und Kompressoren eine einfacher und schneller lösbare Befestigung haben. Zu-dem kann ein Auslassventil beim verlustfreien Trockenlegen des Kältekreislaufes helfen.

Keywords: WEEE Erstbehandlung; Schadstoffentfrachtung; mechanische Aufbereitung; Zerkleinerung; Aufschlussgrad

  • Lecture (Conference)
    Recy & DepoTech-Konferenz 2022, 09.-11.11.2022, Leoben, Österreich

Publ.-Id: 35110

THz sources: from semiconductor antennas to relativistic electrons

Helm, M.

I will discuss some developments related to two types of THz sources: on the one hand photoconductive antennas, including recent results using the material germanium, and on the other hand I will give an overview on the accelerator based coherent infrared and THz sources operating at HZDR, and discuss plans for a successor facility.

Keywords: terahertz; photoconductive antenna; free electron laser

Related publications

  • Invited lecture (Conferences)
    47th International Conference on Infrared, Millimeter and Terahertz Waves (IRMMW-THz) 2022, 28.08.-02.09.2022, Delft, The Netherlands

Publ.-Id: 35109

Experimental comparison of Prompt Gamma-Ray Imaging and Spectroscopy under Equalized Conditions Using a Calibrated Head Phantom

Hueso-González, F.; Berthold, J.; Wohlfahrt, P.; Bortfeld, T.; Khamfongkhruea, C.; Tattenberg, S.; Zarifi, M.; Verburg, J.; Richter, C.

First studies on range verification in proton therapy using prompt gamma-ray spectroscopy (PGS) or imaging (PGI) have been recently conducted with patients. To benchmark the performance of each method, we designed a multi-center experiment between Massachusetts General Hospital and OncoRay with a shared anthropomorphic head phantom irradiated under equalized conditions. The treatment plan was delivered at clinical beam currents and doses in the respective proton therapy hospitals. Two gantry beam angles were used: horizontal and oblique (270° and 350°). Each field contained the same spot positions and energies as well as target volume in both institutions. The experimentally measured range was compared against the ground truth based on the reference stopping-power
map of the phantom. The absolute range error of PGS or PGI was 2.4 mm or -0.5 mm for the horizontal field and 1.3 mm or 2.4 mm for the oblique one, respectively. The ability to detect relative range deviations was assessed by introducing 2 mm and 5 mm plastic slabs on the ventral half of the horizontal field. The measured range shifts were 1.8 mm or 4.8 mm for PGS, and 2.0 mm or 4.2 mm for PGI, respectively. The designed set of experiments represents the first systematic comparison of prompt gamma-ray systems for proton range verification across different institutions using a ground-truth head phantom as reference, and effectively proposes a standard testing platform for benchmarking future proton range verification prototypes in reproducible conditions.

Keywords: proton therapy; prompt gamma-ray; range verification

  • Lecture (Conference)
    2022 IEEE Nuclear Science Symposium and Medical Imaging Conference, 05.-12.11.2022, Milano, Italia

Publ.-Id: 35108

Study on the degradation process of semiconductor photocathodes in particle accelerators

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

The quality of the photocathodes is critical for the stable operation of the electron sources of the accelerator-based light sources (for example X-ray FEL at DESY [1], THz at ELBE [2], etc). In this field, high quantum efficiency (QE) and long operation lifetime are the most important parameters for the ideal photocathode materials. Cs2Te photocathodes have been successfully applied in the e- guns at DESY and in the superconducting RF gun at HZDR. Recently GaN as a new photocathode candidate has been paid more and more attention because of its high QE and robustness. However, even under the extremly high vacuum environment, photocathodes lose QE slowly and change the QE distribution during the operation. In this contribution, we will present the surface study on the Cs2Te and GaN photocathodes, including the QE evolution during operation (see Fig. 1) and the XPS analysis of the 'used' photocathodes (see Fig. 2). Several possible reasons leading degradation of those photocathodes might be: 1. rest gases during operation react with the sensitive alkali-rich surface; 2. the low energy ions, ionized rest gas molecules by the electrons, reach the cathode surface and react with the surface.

Related publications

  • Lecture (Conference)
    35th European Conference on Surface Science (ECOSS2022), 29.08.-02.09.2022, University of Luxembourg, Belval Campus, Luxembourg

Publ.-Id: 35107

Exploring nitric oxide (NO)- releasing celecoxib derivatives as modulators of radioresponse in pheochromocytoma cells

Brandt, F.; Ullrich, M.; Seifert, V.; Haase-Kohn, C.; Richter, S.; Knieß, T.; Pietzsch, J.; Laube, M.

COX-2 can be considered as a clinically relevant molecular target for adjuvant, in particular radiosensitizing treatments. In this regard, using selective COX-2 inhibitors, e.g., in combination with radiotherapy or endoradiotherapy, represents an interesting treatment option. Based on our own findings that nitric oxide (NO)-releasing and celecoxib-derived COX-2 inhibitors (COXIBs) showed promising radiosensitizing effects in vitro, we herein present the development of a series of eight novel NO-COXIBs differing in the peripheral substitution pattern and their chemical and in vitro characterization. COX-1 and COX-2 inhibition potency was found to be comparable to the lead NO-COXIBs, and NO-releasing properties were demonstrated to be mainly influenced by the substituent in 4-position of the pyrazole (Cl vs. H). Introduction of the N-propionamide at the sulfamoyl residue as a potential prodrug strategy lowered lipophilicity markedly and abolished COX inhibition while NO-releasing properties were not markedly influenced. NO-COXIBs were tested in vitro for a combination with single-dose external X-ray irradiation as well as [ 177Lu]LuCl3 treatment in HIF2α-positive mouse pheochromocytoma (MPC-HIF2a) tumor spheroids. When applied directly before X-ray irradiation or 177Lu treatment, NO-COXIBs showed radioprotective effects, as did celecoxib, which was used as a control. Radiosensitizing effects were observed when applied shortly after X-ray irradiation. Overall, the NO-COXIBs were found to be more radioprotective compared with celecoxib, which does not warrant further preclinical studies with the NO-COXIBs for the treatment of pheochromocytoma. However, evaluation as radioprotective agents for healthy tissues could be considered for the NO-COXIBs developed here, especially when used directly before irradiation.

Keywords: cancer; endoradionuclide therapy; NO donors; pheochromocytoma; (pseudo)hypoxia; radiation therapy; selective cyclooxygenase-2 inhibitors

Publ.-Id: 35106

Measurement techniques for the investigation of gas holdup and bubble size distribution in the anode circuit of PEM electrolyzers

Condriuc, I.; Kipping, R.; Schleicher, E.; Kryk, H.; Hampel, U.

The cost-effective production of large amounts of green hydrogen using a new generation of proton exchange membrane (PEM) electrolyzers generates very high gas fractions in the anode circuit, resulting from the high current densities. The volume fraction of oxygen prevails over the volume fraction of hydrogen by a factor of 20. The main goal for the separation process of oxygen from the two-phase flow mixture is a completely gas-free operation fluid before the water enters the heat exchanger. Furthermore, the local instantaneous oxygen fraction represented by partially fine dispersed bubbles related to the full oxygen amount in the anode circuit is still unknown and should be investigated. Due to the development of new separation concepts with high separation efficiency, the measurement of gas holdup and bubble size are carried out using a capacitance wire-mesh sensor (WMS), optical channel body flow sensor, and optical microscope. This poster was prepared for the H2Giga status conference and provides an overview of measurement techniques used in the project.

The authors acknowledge the financial support by the Federal Ministry of Education and Research of Germany in the programme ”H2GIGA”. Project identification number: 03HY123E.

Keywords: Capacitance wire-mesh sensor; Optical channel body flow sensor; Optical flow microscope; Gas holdup measurement; Gas-water separator

  • Poster
    H2GIGA Statuskonferenz, 07.-08.09.2022, Frankfurt am Main, Deutschland

Publ.-Id: 35105

On Curie temperature of B20-MnSi films

Li, Z.; Yuan, Y.; Begeza, V.; Rebohle, L.; Helm, M.; Nielsch, K.; Prucnal, S.; Zhou, S.

B20-type MnSi is the prototype magnetic skyrmion material. Thin films of MnSi show a higher Curie temperature than their bulk counterpart. However, it is not yet clear what mechanism leads to the increase of the Curie temperature. In this work, we grow MnSi films on Si(100) and Si(111) substrates with a broad variation in their structures. By controlling the Mn thickness and annealing parameters, the pure MnSi phase of polycrystalline and textured nature as well as the mixed phase of MnSi and MnSi1.7 are obtained. Surprisingly, all these MnSi films show an increased Curie temperature of up to around 43 K. The Curie temperature is likely independent of the structural parameters within our accessibility including the film thickness above a threshold, strain, cell volume and the mixture with MnSi1.7. However, a pronounced phonon softening is observed for all samples, which can tentatively be attributed to slight Mn excess from stoichiometry, leading to the increased Curie temperature.

Related publications

Publ.-Id: 35103

Combining Batch Experiments and Spectroscopy for realistic Surface Complexation Modelling of the Sorption of Americium, Curium, and Europium onto Muscovite

Bezzina, J. P.; Neumann, J.; Brendler, V.; Schmidt, M.

For a safe enclosure of contaminants, for instance in deep geological repositories of radioactive waste, any processes retarding metal migration are of paramount importance. This study focusses on the sorption of trivalent actinides (Am, Cm) and lanthanides (Eu) to the surface of muscovite, a mica and main component of most crystalline rocks (granites, granodiorites). Batch sorption experiments quantified the retention regarding parameters like pH (varied between 3 and 9), metal concentration (from 0.5 µM Cm to 10 µM Eu), or solid-to-liquid ratio (0.13 and 5.25 g·L-1). In addition, time-resolved laser fluorescence spectroscopy (TRLFS) using the actinide Cm(III) identified two distinct inner-sphere surface species. Combining both approaches allowed the development of a robust surface complexation model and the determination of stability constants of the spectroscopically identified species of (≡S OH)2M3+ (logKo −8.89), (≡S O)2M+ (logKo −4.11), and (≡S-O)2MOH (logKo −10.6), with all values extrapolated to infinite dilution. The inclusion of these stability constants into thermodynamic databases will improve the prognostic accuracy of lanthanide and actinide transport through groundwater channels in soils and crystalline rock systems.

Keywords: mica; trivalent actinides; retardation; TRLFS; Diffuse Double Layer Model


Publ.-Id: 35102

ExPaNDS D5.5: Dedicated websites and e-platforms with the teaching material

Knodel, O.; Padovani, A.

The purpose of this task is to coordinate with the e-platforms providers (ESRF for PaNOSC and EGI for EOSC-hub) to jointly define the prerequisites to maximise and expand the use of the platforms as appropriate. WP2, WP3 and WP4 will work closely with WP5 and WP6 to deliver a tailored specification for each of the online training modules. The output of WP5 will be a definition of the most suitable training materials in accordance with the requirements and recommendations made by the targeted e-platform providers.
A unique joint PaN training portal has been developed and deployed to provide both a training material and events catalogue (ExPaNDS) as well as an e-learning system (PaNOSC) under the domain

Keywords: PaN-training; PaN portal; ExPaNDS; e-learning; TeSS; Photon science; Neutron science; EOSC Portal

Publ.-Id: 35101

New insights into uranium(VI) reduction by a sulfate-reducing bacterium relevant to nuclear waste disposal

Hilpmann, S.; Steudtner, R.; Roßberg, A.; Kvashnina, K.; Prieur, D.; Bauters, S.; Hübner, R.; Stumpf, T.; Cherkouk, A.

For a comprehensive safety assessment of a nuclear repository, the influence of naturally occurring microorganisms from deep geological layers has to be taken into account. Clay rock represents a suitable host rock for the long-term storage of high-level radioactive waste with bentonite as backfill material. In the event of a worst-case scenario, water can enter the repository, solubilize components of the waste, and transport it into the surrounding barriers. In this case, microorganisms can interact with the radionuclides and thereby change the chemical speciation or induce redox reactions.
Desulfosporosinus species represent important members of anaerobic, sulfate-reducing bacteria present in both, clay rock and bentonite. They occur, among others, in the pore water of Opalinus Clay and in the Bavarian bentonite B25. [1,2] Desulfosporosinus hippei DSM 8344T is a close phylogenetic relative to an isolated bacterium from bentonite samples. [3] Therefore, this strain was selected to get a more profound insight into the uranium(VI) interactions, especially regarding the reduction to the less mobile uranium(IV).
Artificial Opalinus Clay pore water [4] served as background electrolyte for the reduction experiments (100 µM uranium(VI), pH 5.5), in which the uranium concentrations in the supernatants decreased rapidly. Time-resolved laser-induced fluorescence spectroscopy showed the presence of a uranyl lactate and a uranyl carbonate complex as aqueous species in the supernatant. While the proportion of the uranyl lactate complex decreased with the incubation time, the uranyl carbonate fraction remained almost constant.
UV/Vis studies of the dissolved cell pellets provided clear proof of a partial reduction of uranium(VI) to uranium(IV) of up to 39% in the samples. Therefore, a combined association-reduction process is a possible interaction mechanism.
TEM images showed the presence of uranium-containing aggregates on the cell surface. To mitigate encrustation, cells released membrane vesicles as a possible defense mechanism.
In addition, uranium(VI) reduction was confirmed by HERFD-XANES measurements. Moreover, uranium(V) could be detected as an intermediate, providing first evidence of the involvement of uranium(V) in uranium(VI) reduction by sulfate-reducing microorganisms. EXAFS measurements helped to identify different cell-related uranium species.
This study helps to improve the understanding of the complexity of uranium-microbe interactions relevant to the long-term storage of high-level radioactive waste in clay rock and therefore contributes to a safety concept for a nuclear repository in this host rock.
[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: Sulfate-reducing bacteria; Uranium(VI) reduction; Clay rock; Opalinus Clay pore water

  • Lecture (Conference)
    DECAY Days 2022, 21.-23.09.2022, St. Ursanne, Schweiz

Publ.-Id: 35100

Locating skarns with magnetic survey data, Geyer, Erzgebirge: optimizing data acquisition procedures

Ugalde, H.; Morris, W.; Madriz Diaz, Y. C.; Kirsch, M.; Gloaguen, R.; Schneider, M.; Schiffler, M.; Siemon, B.; Fréville, T.; Munschy, M.

Magnetic data can be acquired from a number of different platforms (e.g., ground, drone, helicopter) using a variety of sensors (e.g., caesium vapour-type optically pumped magnetometers, fluxgate, superconducting quantum interference devices) with different flight line configurations. To detect a magnetic anomaly associated with a mineral commodity that is not exposed but is thought to be associated with the anomalous magnetic mineral content, it is necessary to optimize the survey parameters through a complete data integration process. Prior petrophysical measurements provide insight into the physical contrast that might be expected between adjacent lithologic units and between the ore zone and the encompassing lithology. Oriented rock samples provide access to magnetic remanence data through palaeomagnetic laboratory measurements. Knowing the typical morphology of the ore zone one can compute a forward model of the expected anomalous response and determine which combination of survey parameters provides the highest probability of detecting the commodity being sought. In this study, we analyse magnetic patterns associated with thin dipping skarn bodies from the Geyer mining district in Erzgebirge, Germany. Petrophysical measurements indicate that the skarns are more magnetic than the surrounding host rock. Partially oriented samples from a bore core record a Variscan age metamorphic remanence. Forward modelling indicates that clusters of skarn bodies are required to produce a reliably detectable magnetic signal. Ground, or low elevation drone surveys are needed to detect these anomalies with standard scalar-type optically pumped magnetometer or fluxgate magnetic surveys. The enhanced spatial resolution and long-wavelength rejection of a superconducting quantum interference device-based full-tensor magnetic gradiometer provide an improvement over optically pumped magnetometers for an aircraft-based survey platform.

Keywords: Acquisition; Interpretation; Magnetics; Potential fields

Publ.-Id: 35099

HELIPORT — An Integrated Research Data Lifecycle

Knodel, O.; Pape, D.; Voigt, M.; Gruber, T.; Kelling, J.; Lokamani, M.; Müller, S.; Juckeland, G.; Kessler, A.; Hein, J.; Lee, C.-L.; Kaluza, M.; Schuller, B.

HELIPORT is a data management solution that aims at making the components and steps of the entire research experiment’s life cycle discoverable, accessible, interoperable and reusable according to the FAIR principles.
Among other information, HELIPORT integrates documentation, scientific workflows, and the final publication of the research results - all via already established solutions for proposal management, electronic lab notebooks, software development and devops tools, and other additional data sources. The integration is accomplished by presenting the researchers with a high-level overview to keep all aspects of the experiment in mind, and automatically exchanging relevant metadata between the experiment’s life cycle steps.
Computational agents can interact with HELIPORT via a REST API that allows access to all components, and landing pages that allow for export of digital objects in various standardized formats and schemas. An overall digital object graph combining the metadata harvested from all sources provides scientists with a visual representation of interactions and relations between their digital objects, as well as their existence in the first place. Through the integrated computational workflow systems, HELIPORT can automate calculations using the collected metadata.
By visualizing all aspects of large-scale research experiments, HELIPORT enables deeper insights into a comprehensible data provenance with the chance of raising awareness for data management.

Keywords: Data Management; Metadata; FAIR; Data provenance; Digital Objects; Workflows

  • Open Access Logo Poster
    German Conference for Research with Synchrotron Radiation, Neutrons and on Beams at Large Facilities, 05.-07.09.2022, Freie Universität Berlin, Germany
  • Open Access Logo Poster
    3. SaxFDM Tagung 2022, 22.09.2022, Leipzig, Deutschland
  • Open Access Logo Poster
    8. Annual MT Meeting, 26.-27.09.2022, Hamburg, Deutschland
  • Open Access Logo Poster (Online presentation)
    Helmholtz Metadata Collaboration | Conference 2022, 05.-06.10.2022, online, online
    DOI: 10.5281/zenodo.7104941
  • Open Access Logo Poster
    deRSE23 - Conference for Research Software Engineering in Germany, 20.-22.02.2023, Paderborn, Germany
    DOI: 10.5281/zenodo.7104941


Publ.-Id: 35097

Changes in Radical Levels as a Cause for the FLASH effect: Impact of beam structure parameters at ultra-high dose rates on oxygen depletion in water

Jansen, J.; Beyreuther, E.; García-Calderón, D.; Karsch, L.; Knoll, J.; Pawelke, J.; Schürer, M.; Seco, J.

The influence of different average and bunch dose rates in electron beams on the FLASH effect was investigated. The present study measures O2 content in water at different beam pulse patterns and finds strong correlation with biological data, strengthening the hypothesis of radical-related mechanisms as a reason for the FLASH effect.

Keywords: FLASH effect; oxygen depletion; pulse structure; radical reduction

Related publications

Publ.-Id: 35096

Long-term evolution of the neutron rate at the Canfranc Underground Laboratory

Orrigo, S. E. A.; Tain, J. L.; Mont-Geli, N.; Tarifeño-Saldivia, A.; Fraile, L. M.; Grieger, M.; Agramunt, J.; Algora, A.; Bemmerer, D.; Calviño, F.; Cortés, G.; de Blas, A.; Dillmann, I.; Domínguez Bugarín, A.; García, R.; Nacher, E.; Tolosa-Delgado, A.

We report results on the long-term variation of the neutron counting rate at the Canfranc Underground Laboratory, of importance for several low-background experiments installed there, including rare-event searches. The measurement campaign was performed employing the High Efficiency Neutron Spectrometry Array (HENSA) mounted in Hall A and lasted 412 live days. The present study is the first long-term measurement of the neutron rate with sensitivity over a wide range of neutron energies (from thermal up to 0.1 GeV and beyond) performed in any underground laboratory so far. Data on the environmental variables inside the experimental hall (radon concentration, air temperature, air pressure and humidity) were also acquired during all the measurement campaign. We have investigated for the first time the evolution of the neutron rate for different energies of the neutrons and its correlation with the ambient variables.

Keywords: neutron; underground laboratory; hensa; background

Publ.-Id: 35095

Optoelectronic properties of 2D perovskites and other inorganic-organic hybrid materials

Kuc, A. B.

Summary of the CRC1415 project C03 progress. Published results since the beginning of the project were shown.

  • Lecture (others)
    Retreat of CRC1415 project, 15.-17.06.2022, Lichtenwalde, Germany

Publ.-Id: 35094

Modelling TMDC/2D perovskite heterostructures for charge and energy transfer

Kuc, A. B.

Modelling of 2D TMDC/2D perovskite heterostructures is shown together with experimental data. Nonradiative energy transfer and charge transfer were found to co-exist in this type of heterostructures.

  • Lecture (Conference)
    Midterm meeting of SPP2244, 21.-23.03.2022, Dresden, Germany

Publ.-Id: 35092

Modelling van der Waals heterostructures for experimental collaborations

Kuc, A. B.

Modelling of 2D van der Waals heterostructures is discussed from the point of view of complexity and desired property investigations. Different models are shown together with appropriate approached to simulate properties of materials.

  • Invited lecture (Conferences)
    Semiconductor Materials Engineering Seminar, 25.02.2022, Wroclaw, Poland

Publ.-Id: 35090

Simulation of hydrogen species diffusion and transport between and through layers of 2D materials

Kuc, A. B.

Recent experiments by Geim’s group have demonstrated transport and separation of hydrogen isotopes through the van der Waals gap in hexagonal boron nitride (h-BN) and molybdenum disulfide (MoS2) bulk layered materials. The experiments could not distinguish whether the transported particles are protons (H+) or protium (H) atoms. In one of our recent works, we reported theoretical studies, which indicate that protium atoms, rather than protons, are transported through the gap.[1] First-principles calculations combined with well-tempered metadynamics simulations at finite temperature reveal that for h-BN and MoS2, the diffusion mechanism of both protons and protium (H) atoms involves a hopping process between adjacent layers. This process is assisted by low-energy phonon shear modes. The extracted diffusion coefficient of protium matches the experiment, while for protons, it is several orders of magnitude smaller. This indicates that H atoms are responsible for the experimental observations. These results allow for a comprehensive interpretation of experimental results on the transport of H isotopes through van der Waals gaps and can help identify other materials for hydrogen isotope separation applications.
In more recent investigations, we focus on H atom diffusion between layers of transition-metal dichalcogenides (TMDCs), such as MoS2, where we investigate the impact of transition metal atom, chalcogen atom, stacking order, and moiré pattern on the diffusion coefficients. We want to learn whether the free energy barriers are lowered (resulting in higher diffusion coefficients) and whether the moiré patterns can enforce directional transport.
We use well-tempered metadynamics simulations in our studies as implemented in the cp2k code. Our approach to H atom diffusion can be extended to investigations of other species, such as Eu(III)-species diffusion in clay mineral layered materials.
[1] Y. An, A. Kuc, P. Petkov, M. Lozada-Hidalgo, T. Heine, Small 1901722 (2019) 1-7.

  • Lecture (Conference)
    Casuscon 2022, 11.-14.07.2022, Wroclaw, Poland

Publ.-Id: 35089

Modelling 2D materials for experimental collaborations

Kuc, A. B.

In this summer school, I was introducing simulations of electronic and vibrational properties of 2D materials in the form of a lecture.

  • Invited lecture (Conferences)
    2D-Mat School, 24.-29.07.2022, Bad Honnef, Germany

Publ.-Id: 35088

Investigating the influence of multiple particle properties on the separation of ultrafine particles via enhanced froth flotation

Sandbrink, J.; Rudolph, M.

One of the most important techniques to separate valuable minerals from unwanted gangue is froth flotation. It is an efficient process for particles with sizes ranging from 10 µm to 200 µm and its main separation feature is the difference in particle wettabilities. As particles are getting finer, existing flotation techniques need to be adapted and improved in order to have an efficient separation. For that reason, this project, which is part of the German research foundation priority programme DFG-SPP 2045 “MehrDimPart”, aims at developing a method for the separation of ultrafine particles based on multiple particle properties, such as size, morphology or surface energy.
A particle system consisting of ultrafine size fractions of glass particles as the valuable material and magnetite as the gangue material is used for this study. The wettability of the glass particles is modified via an esterification reaction using alcohols with differing chain length and the resulting wettability states are analysed using inverse gas chromatography as well as analytic particle solvent extraction. Information on the particle size and shape are obtained via a combination of laser diffraction and microscopic analysis. The technique of flow cytometry is introduced for multidimensional particle characterization, as it allows for simultaneous size and shape analysis. Additionally, information on the particle wettability can be obtained by fluorescent marking of particles with dyes. All flotation tests are carried out in batch mode using a novel flotation apparatus, specifically designed for the flotation of ultrafine particles by combining advantages from machine-type froth flotation and column flotation and the separation process is evaluated using multidimensional partition curves.
This investigation will help to further understand how certain particle properties influence flotation, as well as other separation processes. In this way, the separation of ultrafine particles will be more efficient, which will play an important role in the recycling of secondary materials.

Keywords: ultrafine particles; multidimensional separation; flotation; particle characterization; partition curves

  • Lecture (Conference)
    9th World Congress on Particle Technology, 18.-22.09.2022, Madrid, Spanien

Publ.-Id: 35087

Nonradiative Energy Transfer and Selective Charge Transfer in TMDC/2D perovskite Heterostructures

Kuc, A. B.

Van der Waals heterostructures are currently the focus of intense investigation; this is essentially due to the unprecedented flexibility offered by total relaxation of lattice matching requirements and their new and exotic properties compared to the individual layers. Here, we investigate hybrid transition-metal dichalcogenide (TMDC)/2D perovskite heterostructures. We present the first density functional theory (DFT) calculations of a such ensembles, which reveal a novel band alignment, where direct electron transfer is blocked by the organic spacer of the 2D perovskite. In contrast, the valence band forms a cascade from TMDC through the organic linkers to the inorganic part of the perovskite allowing a hole transfer. These predictions are supported by optical spectroscopy studies, which provide compelling evidence for both charge transfer and nonradiative transfer of the excitation (energy transfer) between the layers. Our results show that TMDC/2D perovskite heterostructures provide a flexible and convenient way to engineer the band alignment.

  • Lecture (Conference)
    Psi-k conference 2022, 22.-25.08.2022, Lausanne, Switzerland

Publ.-Id: 35086

MultiDimFlot - Multidimensional separation of ultrafine particles using a mechanical flotation cell combined with froth fractionation

Sandbrink, J.; Rudolph, M.

Froth flotation is one of the most important techniques in the mining industry for the efficient separation of particles with sizes between 10 µm and 200 µm. The separation process is based on the difference in particle wettabilities, as hydrophobic particles attach to a gas bubble and are recovered in a froth, whereas hydrophilic particles tend to stay in the pulp. Although, the wettability is the most prominent separation feature, the micro processes that occur in the pulp and in the froth zone include complex interactions between the particles and the bubbles and also other particle properties, such as size, morphology, surface energy or the dispersion state have an impact on the separation.
Low ore grades and very fine composite particles in electronic devices are forcing the industry to adapt and improve existing flotation techniques to the processing of ultrafine particles (< 10 µm), as the material needs to be milled down to finer size fractions to obtain sufficient liberation of the valuable minerals. For that reason, the project “MultiDimFlot”, which is part of the German research foundation priority programme DFG-SPP 2045 “MehrDimPart”, aims at developing a method for the separation of ultrafine particles (< 10 µm) based on multiple particle properties.
A novel separation apparatus is used that combines the advantages of a mechanical flotation cell that comes with a high particle-bubble collision rate (thus a high recovery) with those from a flotation column with a fractionating effect due to its deep froth (thus a high grade). An academic particle system, consisting of glass spheres, glass fragments and glass fibres as the valuable material and magnetite as the gangue material is used, whose particle properties are studied in depth. These investigations will help to further understand the behaviour of ultrafine particles during flotation and how certain particle properties affect the separation process. Furthermore, the possibilities and limitations of different analysis techniques, e.g. coupled SEM-EDX, flow cytometry or inverse gas chromatography are investigated for their use in ultrafine particle characterization.

Keywords: Ultrafine particles; multidimensional separation; flotation; partition curves

  • Poster
    9th World Congress on Particle Technology, 18.-22.09.2022, Madrid, Spanien

Publ.-Id: 35085

Numerical investigation of the flow inside a precession driven cylindrical cavity with additional baffles using an Immersed Boundary Method

Wilbert, M.; Giesecke, A.; Grauer, R.

In this paper we present a numerical approach to
solve the Navier-Stokes equations for arbitrary vessel geometries by
combining a Fourier-Spectral method with a direct forcing
Immersed Boundary method which allows to consider solid-fluid
The approach is applied to a paradigmatic setup motivated by the precession dynamo experiment currently
under construction at Helmholtz-
Zentrum Dresden-Rossendorf (\textit{HZDR}). The experiment
consists of a fluid filled cylinder rotating about 2 axes which
induces a precession driven flow inside the cavity. The cylinder is
also equipped with baffles at the end caps with adjustable penetration depth
to impact the flow. The numerical details as well as simulation
results for the spin-up and precession driven flow in a circular cylinder
with additional baffles are presented.
The results provide a first confirmation that the use of such
baffles in the precession dynamo experiment is a useful way of influencing the flow,
allowing more efficient driving without changing the known flow
structure too much.

Keywords: DRESDYN; Immersed Boundary Method; Spectral; Dynamo


Publ.-Id: 35084

Radiosynthesis and preclinical evaluation of an 18F-labeled tri-azolopyridopyrazine-based inhibitor for neuroimaging of the phosphodiesterase 2A (PDE2A)

Wenzel, B.; Fritzsche, S. R.; Toussaint, M.; Briel, D.; Kopka, K.; Brust, P.; Scheunemann, M.; Deuther-Conrad, W.

The cyclic nucleotide phosphodiesterase 2A is an intracellular enzyme which hydrolyzes the secondary messengers cAMP and cGMP and therefore plays an important role in signaling cas-cades. A high expression in distinct brain areas as well as in cancer cells makes PDE2A an inter-esting therapeutic and diagnostic target for neurodegenerative and neuropsychiatric diseases as well as for cancer. Aiming at a specific imaging of this enzyme in the brain with positron emis-sion tomography (PET), a new triazolopyridopyrazine-based derivative (11) was identified as a potent PDE2A inhibitor (IC50, PDE2A = 1.99 nM; IC50, PDE10A ~ 2000 nM) and has been radiofluorinated for biological evaluation. In vitro autoradiographic studies revealed that [18F]11 binds with high affinity and excellent specificity towards PDE2A in the rat brain. For the PDE2A-rich region nu-cleus caudate and putamen an apparent KD value of 0.24 nM and an apparent Bmax value of 16 pmol/mg protein were estimated. In vivo PET-MR studies in rat showed a moderate brain uptake of [18F]11 with a highest standardized uptake value (SUV) of 0.97. However, no considerable en-richment in PDE2A-specific regions in comparison to a reference region was detectable (SUVcau-date putamen = 0.51 vs. SUVcerebellum = 0.40 at 15 min p.i.). Furthermore, metabolism studies revealed a considerable uptake of radiometabolites of [18F]11 in the brain (66% parent fraction at 30 min p.i.). Altogether, despite the low specificity and the blood-brain barrier crossing of radiometab-olites observed in vivo, [18F]11 is a valuable imaging probe for the in vitro investigation of PDE2A in the brain and has potential as a lead compound for further development of a PDE2A-specific PET ligand for neuroimaging.

Keywords: PDE2A inhibitor; triazolopyridopyrazine; fluorine-18; small animal PET-MR; autoradiography; in vivo metabolism

Publ.-Id: 35082

Engineering of excitonic g-factors in van der Waals structures

Wozniak, T.; Faria Junior, P. E.; Chaves, A.; Kunstmann, J.; Kuc, A. B.

We develop a fully ab-initio based method of calculation of excitonic g-factors, which describe their energy dependence on external magnetic field, and apply it to 1L TMDs and MoSe2/WSe2 heterobilayers, obtaining excellent agreement with experimental data for intra- and interlayer excitons. A proper inclusion of stacking-dependent selection rules allows to assign the measured optical peaks to specific transitions in the band structure and regions of the samples [1]. We identify a series of magneto-PL peaks in 1L WS2 based on the calculated g-factors of excitons, trions and biexcitons, as well as four phonon replicas of the dark trion. We obtain a perfect agreement of the individual bands g-factors with the values derived from experimental data [2]. We explain the reduction of a g-factor measured in MoSe2/WS2 by the spatial confinement of the mixed exciton in the moiré potential [3].
[1] PRB 105, 235408
[2] NanoLett 21, 2519
[3] arX:2204.01813

  • Lecture (Conference)
    Psi-k conference 2022, 22.-25.08.2022, Lausanne, Switzerland

Publ.-Id: 35080

Impact of blood parameters and normal tissue dose on treatment outcome in esophageal cancer patients undergoing neoadjuvant radiochemotherapy

Bütof, R.; Häberlein, L.; Jentsch, C.; Kotzerke, J.; Lohaus, F.; Makocki, S.; Valentini, C.; Weitz, J.; Löck, S.; Troost, E. G. C.

Despite technological advances, normal tissue sparing in photon beam irradiation is still challenging. Since in esophageal cancer this may inflict damage on the lungs, heart and bone marrow, possibly impacting on outcome, the aim of this study was to investigate the association of normal tissue dose and blood parameters on the survival of patients having undergone neoadjuvant radiochemotherapy (RCTx) followed by surgery. This retrospective study included 125 patients irradiated to 40–41.4 Gy with photons or protons combined with concurrent chemotherapy. On initial and restaging 18F-FDG-PET/CT, the lungs and heart were contoured as organs at risk for which standardized uptake values (SUV) were evaluated. The mean radiation dose (Dmean) to the lungs and
heart, the volume of the lungs receiving at least 20 Gy (V20Gy_lung) and various pre- and per-treatment blood parameters were included in the Cox regression analyses. Results: The median follow-up time was 19.8 months and median overall survival 37 months (95% confidence interval: 16–58.9 months). In multivariate analysis, higher radiation doses to the lungs and heart were statistically significantly associated with decreased overall survival (Dmean_lung: p < 0.001; V20Gy_lung: p < 0.002; Dmean_heart: p = 0.005). Neither the 18F-FDG-PET nor blood parameters were predictive for overall survival. In patients with locally advanced esophageal cancer treated with RCTx, the radiation dose to the heart and lungs was significantly associated with overall survival.

Keywords: esophageal cancer; radiochemotherapy; normal tissue dose; neoadjuvant; outcome; PET; blood parameter

Publ.-Id: 35079

Deutschlands Ausstieg aus der Atomkraft - Was passiert mit dem Müll und welche Rolle spielen Mikroorganismen?

Matschiavelli, N.

Vortrag über mikrobiologische Themen in der Abteilung Biogeochemie am HZDR

  • Invited lecture (Conferences)
    Tag der Wissenschaften, 24.11.2022, Dresden, Deutschland

Publ.-Id: 35078

Fracture Mechanics Testing of Neutron Irradiated RPV Steels using Mini-C(T) Specimens

Das, A.; Chekhonin, P.; Houska, M.; Obermeier, F.; Altstadt, E.

Neutron irradiation induced embrittlement of the reactor pressure vessel (RPV) reduces the operating lifetime of nuclear reactors and leads to an increase in the transition temperature T0. Fracture mechanics testing of RPV steels before and after neutron irradiation, which reveals the shift in T0, is often limited by the shortage of irradiated material. To solve this, we tested sub-sized 0.16T C(T) specimens manufactured from already tested SE(B) standard Charpy sized specimens using the Master Curve concept. The transferability of fracture mechanics data from small to standard sized specimens forms a key part of this study. To investigate the effect of chemical composition on neutron irradiation, four western RPV steels are chosen in this study, three base and one weld metal. Fractography is performed on broken mini-C(T) specimens using scanning electron microscopy in order to determine the location of the fracture initiating particles as well as the mode of fracture. In order to make the testing procedure simpler, based on large statistical data, we studied the impact of the slow stable crack growth censoring criterion on the determination of T0. We found that the results from the small specimens are comparable to the standard specimens. RPV steels containing higher amounts of Cu, Ni and P exhibit a higher increase in T0 after irradiation. The fracture initiating particles were located at greater distances from the crack front in irradiated specimens of the weld material as compared to the unirradiated specimens. The fracture toughness of all materials remained constant for similar test temperatures irrespective of their irradiation state. Furthermore, we found that the stable crack growth censoring criterion did not influence the T0 significantly. Our results demonstrate the validity of small specimen testing and confirms the role of the impurity elements Cu and P in neutron embrittlement.

Keywords: Fracture mechanics testing; sub-sized specimen; transition temperature; reactor pressure vessel steels; Master Curve; neutron-irradiation

  • Lecture (Conference)
    The Nuclear Materials Conference 2022, 24.-28.10.2022, Ghent, Belgium

Publ.-Id: 35077

Development of Radiotracers for Imaging of the PD-1/PD-L1 Axis

Krutzek, F.; Kopka, K.; Stadlbauer, S.

Immune checkpoint inhibitor (ICI) therapy has emerged as a major treatment option for a variety of cancers. Among the immune checkpoints addressed, the programmed death receptor 1 (PD-1) and its ligand PD-L1 are the key targets for an ICI. PD-L1 has especially been proven to be a reproducible biomarker allowing for therapy decisions and monitoring therapy success. However, the expression of PD-L1 is not only heterogeneous among and within tumor lesions, but the expression is very dynamic and changes over time. Immunohistochemistry, which is the standard diagnostic tool, can only inadequately address these challenges. On the other hand, molecular imaging techniques such as positron emission tomography (PET) and single-photon emission computed tomography (SPECT) provide the advantage of a whole-body scan and therefore fully address the issue of the heterogeneous expression of checkpoints over time. Here, we provide an overview of existing PET, SPECT, and optical imaging (OI) (radio)tracers for the imaging of the upregulation levels of PD-1 and PD-L1. We summarize the preclinical and clinical data of the different molecule classes of radiotracers and discuss their respective advantages and disadvantages. At the end, we show possible future directions for developing new radiotracers for the imaging of PD-1/PD-L1 status in cancer patients.

Keywords: tumor microenvironment; PD-1/PD-L1 targeting radiotracer; immune checkpoint; molecular imaging

Publ.-Id: 35076

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