Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

Electrons from laser wakefield accelerators (LWFA) can be ultrashort and quasi-monoenergetic. They have the potential to be an ideal source for advanced light sources or beam drivers for hybrid laser-plasma wakefield accelerators (LPWFA). A wide variety of injection methods have already been developed to produce high-quality LWFA electrons. However, such high-quality electron bunches may degrade upon exiting the LWFA stage.

This poster addresses quality-preserving methods for extracting electron beams from laser wakefield accelerators by adjusting the plasma density of the down ramp. By modeling different gas profiles with the fully relativistic particle-in-cell code PIConGPU, not only the final beam quality but also all relevant physical effects can be studied in detail. This allows not only to find an optimal quality-preserving down ramp but also to study the influence of changes in laser focus position on beam properties during extraction.

Axial heterostructures have diverse functionality in electronic and optoelectronic devices. Implementing such systems in freestanding semiconducting nanowires further broadens the scope of potential applications, for example: distributed Bragg reflectors, high-efficiency light-emitting diodes, and quantum dot heterostructures. The challenge, however, lies in reducing the compositional grading effect of the constituent heterostructure materials across the interfaces in nanowires grown in vapor-liquid-solid mode.
Here, our previously developed nanowire growth technique called droplet-confined alternate pulsed-epitaxy [1] (an adaptation of conventional molecular beam epitaxy), which grants precise control over the axial growth rate and droplet composition, is employed to grow Al(x)Ga(1-x)As axial insertions in self-catalyzed GaAs nanowires. A full nanowire with six insertions is shown in Figure 1 (top). High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and nanowire growth models are utilized to gain an understanding of the compositional grading mechanism and its dependence on the growth temperature (TG), the nanowire radius (RNW), and the amount of supplied Al. Figure 1 (bottom) is an example HAADF-STEM image showing two atomically resolved Al(x)Ga(1-x)As insertions embedded in a zincblende GaAs nanowire, whereas Figure 2 shows the extracted Al-content (x) axial profiles for three selected insertions with different TG and RNW (the same amount of supplied Al). We show that lower TG and/or smaller RNW result in sharper interfaces, with a more profound improvement for the AlxGa1-xAs-to-GaAs interface. In the best case, almost symmetric insertions with interface thicknesses of only 2 – 3 monolayers are achieved, approaching the absolute limit of atomically sharp interfaces.
Thermodynamics, kinetics, and nanowire geometry are all factors considered during the formation of our Al(x)Ga(1-x)As insertions. Using two existing heterostructure growth models [2, 3] to fit our experimental data we can extract valuable quantitative information regarding the interface characteristics. Our results show for the first time that not only TG, but also size effects, i.e. a decreasing RNW, play a large role in the thermodynamic stability at the liquid-solid interface, setting previously unknown limitations on the maximum attainable interface sharpness. These findings and their implications will be discussed in detail.
The functionality of our insertions is successfully tested via their employment as axial barriers in quantum dot nanowire heterostructures. By growing the quantum dot heterostructure at 350 °C, consequently sharpening the quantum dot interfaces, we observe a one order of magnitude decrease in quantum dot emission linewidth (Figure 3) in comparison to a similar system grown at 550 °C.
1. Balaghi et al., Nano Lett. 16, 4032 (2016)
2. Luna et al., Phys. Rev. Lett. 109, 126101 (2012)
3. Priante et al., Nano Lett. 16, 1917 (2016)

Axial heterostructures have diverse functionality in electronic and optoelectronic devices. Implementing such systems in freestanding semiconducting nanowires further broadens the scope of potential applications, for example: distributed Bragg reflectors, high-efficiency light-emitting diodes, and quantum dot heterostructures. The challenge, however, lies in reducing the compositional grading effect of the constituent heterostructure materials across the interfaces in nanowires grown in vapor-liquid-solid mode.
Here, our previously developed nanowire growth technique called droplet-confined alternate pulsed-epitaxy [1] (an adaptation of conventional molecular beam epitaxy), which grants precise control over the axial growth rate and droplet composition, is employed to grow Al(x)Ga(1-x)As axial insertions in self-catalyzed GaAs nanowires. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and nanowire growth models are utilized to gain an understanding of the compositional grading mechanism and its dependence on the growth temperature (TG), the nanowire radius (RNW), and the amount of supplied Al. Figure 1 (a) is an example HAADF-STEM image showing two Al(x)Ga(1-x)As insertions embedded in a zincblende GaAs nanowire, whereas Figure 1 (b) shows the extracted Al-content (x) axial profiles for three selected insertions with different TG and RNW (the same amount of supplied Al). We show that lower TG and/or smaller RNW result in sharper interfaces, with a more profound improvement for the AlxGa1-xAs-to-GaAs interface. In the best case, almost symmetric insertions with interface thicknesses of only 2 – 3 monolayers are achieved, approaching the absolute limit of atomically sharp interfaces. The fitting of our experimental data with existing heterostructure growth models [2, 3] is suggestive of different mechanisms behind the compositional grading of the two interfaces and will be discussed in detail.
The functionality of our insertions is successfully tested via their employment as axial barriers in quantum dot nanowire heterostructures. By growing the quantum dot heterostructure at 350 °C, consequently sharpening the quantum dot interfaces, we observe a one order of magnitude decrease in quantum dot emission linewidth (Figure 1 (c)) in comparison to a similar system grown at 550 °C.
[1] Balaghi et al., Nano Lett. 16, 4032 (2016)
[2] Luna et al., Phys. Rev. Lett. 109, 126101 (2012)
[3] Priante et al., Nano Lett. 16, 1917 (2016)

Für diesen eingeladenen Vortrag zum Tokyo-Dresden NMR meeting: from quantum magnets to Weyl-Dirac fermions liegt keine Kurzfassung vor.

Für diesen eingeladenen Vortrag zur International Conference on Strongly Correlated Electron Systems (SCES) 2022 liegt keine Kurzfassung vor.

Für diesen Vortrag im Rahmen der zweiten EMFL summer school "Science in High Magnetic Fields" liegt keine Kurzfassung vor.

The organosilicon pyridine-2-olates 1a–1d (RSi(pyO)₃, R = Me (a), Ph (b), Bn (c), Allyl (d); pyO = pyridine-2-olate) may serve as tripodal ligands toward CuCl with formation of complexes of the type RSi(μ²-pyO)₃CuCl (2a–2d). In addition, for R = Allyl, formation of the more stable isomer 2d′ (κO-pyO)Si(μ²-pyO)₂(μ²-Allyl)CuCl was observed. In the presence of dry air (as a source of oxygen), reactions of 1a–1d and CuCl afforded Cu(II) complexes RSi(μ²-pyO)₄CuCl (3a–3d); 3a–3c in good yield, and 3d only as a side product. Reaction of Ph₂Si(pyO)₂ (4) and CuCl in equimolar ratio afforded, depending on reaction conditions, a series of (CuCl)n-ladder-type oligonuclear Cu(I) complexes Ph₂Si(μ2-pyO)₂(CuCl)n(μ²-pyO)₂SiPh₂ (n = 2 (52), 3 (53), 4 (54)). In all of the above compounds, the pyO group is Si–O bound and, in the case of μ² coordination, Cu–N bound. All new compounds (1c, 1d, 2b, 2c, 2d, 2d′, 3b, 3c, 3d, 52, 53, 54) were characterized by single-crystal X-ray diffraction, and further characterization includes solution ¹H, ¹³C, ²⁹Si NMR spectroscopy (1c, 1d, 2b, 2c, 2d’, 53, 54), solid-state ²⁹Si (2b, 2c, 2d′, 53, 54) and ⁶³Cu NMR spectroscopy (2c, 2d′) as well as computational analyses of the isomerization of the couple 2d, 2d′.

The use of accelerated electrons from a laser wakefield accelerator (LWFA) as drivers of a plasma wakefield stage (PWFA) provides compact PWFAs that can serve as a test bed for the efficient investigation and optimization of PWFAs and their development into brightness boosters. Such hybrid accelerators have been experimentally realized at HZDR and LMU to study novel injection schemes. To better understand the microscopic, nonlinear dynamic of these accelerators, the experiments were accompanied by 3D3V particle-in-cell simulations using PIConGPU.

Here, we present the latest results from these numerical studies, covering injections due to hydrodynamic shocks, beam self-modulation and breakup, and cavity elongation - all accompanied by synthetic diagnostic methods that allow direct comparison with experimental measurements.
Challenges such as parasitic injections, shock injections, and non-ideal driver beam dynamics will be discussed. Recent technical advances in PIConGPU that enabled the execution of these large-scale simulation campaigns are briefly covered, as well as new synthetic in situ shadowgraph and radiation diagnostics.

A review of the simulation work behind the recent LPWFA publications.

Understanding the physical and chemical properties of various materials demands detailed knowledge about their shape, structure, and composition. Particularly for nanoscale materials, characterization methods with high spatial and analytical resolution are required. Due to the small wavelength of strongly accelerated electrons, transmission electron microscopy (TEM) is one of the most appropriate nanoscale analysis techniques. Moreover, due to the tremendous range of signals arising from electron-solid interaction, a broad range of analysis modes are nowadays available in a transmission electron microscope.
After introducing the advantages of TEM, the basic setup of a transmission electron microscope, and the equipment available at HZDR for performing TEM analyses, the most important modes of imaging are presented, including bright-field, dark-field, and high-resolution imaging in TEM and scanning TEM (STEM) mode. It is shown, how diffraction analysis is used to derive structure and orientation information, while energy-dispersive X-ray spectroscopy (EDXS) and electron energy-loss spectroscopy (EELS) are applied for chemical composition analysis. Using examples from various research and application fields, including e.g. information technology, resource ecology, and radiopharmacy, the various TEM analysis modes are illustrated, and their combination is shown to be essential for a comprehensive understanding of nanoscale materials.

Dielectric capacitors are widely used in pulsed power electronic devices due to their ultrahigh power densities and extremely fast charge/discharge speed. To achieve enhanced energy storage density, maximum polarization (Pmax) and breakdown strength (Eb) need to be improved simultaneously. However, these two key parameters are inversely correlated. In this study, order–disorder transition induced polar nanoregions have been achieved in PbZrO3 thin films by making use of the low-energy ion implantation, enabling us to overcome the trade-off between high polarizability and breakdown strength, which leads to the tripling of the energy storage density from 20.5 to 62.3 J/cm3 as well as the great enhancement of breakdown strength. This approach could be extended to other dielectric oxides to improve the energy storage performance, providing a new pathway for tailoring the oxide functionalities.

A overview over all large-scale simulation efforts of the laser electron acceleration team covering both recent simulations and new technical developments.

An LPWFA accelerator uses electrons from a laser wakefield accelerator stage to drive a second plasma wakefield accelerator stage. This approach makes it possible to downscale PWFAs from kilometer-sized facilities to tabletop experiments and makes the improved beam quality of PWFAs available to LWFA laboratories. The experimental realization of the hybrid accelerator at HZDR was accompanied by a simulation campaign with the fully GPU accelerated, 3D3V particle-in-cell PIConGPU. Running simulations on modern GPUs allowed reducing simulation time while modeling different experimental settings in a fully three-dimensional setup. The latter enabled studying the influence of tilted shock fronts and few-cycle probes, among others. In this talk, we will not only introduce the general concept but also discuss some of the recent results obtained using particle-in-cell simulations. Moreover, the technical innovations in PIConGPU that have enabled these new types of simulations will also be briefly addressed.

Ultra-thin InxGa1-xN/GaN quantum wells (QWs) embedded in short period superlattices (SPSs) are promising for bandgap engineering and for exploring topological insulator behavior. In order to achieve such feats, it is required to reach high In contents at thicknesses of few atomic monolayers, while avoiding plastic relaxation despite the large misfit. Previous theoretical and experimental works supported the existence of a compositional limit around 33% In in such QWs. In this work, an alternative growth model is proposed, overcoming this limit. Multi-QW (MQW) heterostructures were grown by plasma-assisted molecular beam epitaxy (PAMBE) under metal-rich conditions varying the growth temperatures of the QWs and GaN spacers. The structural quality, strain state, and composition of the QWs were investigated using aberration-corrected scanning transmission electron microscopy (HRSTEM) [1]. Experimental observations were combined with atomistic calculations across the whole compositional range, using an empirical interatomic potential as well as density functional theory. Multislice image simulations of the atomistic supercells were compared quantitatively to the HRSTEM observations using peak finding, thus resulting in the QW composition and strain with monolayer spatial resolution. The growth of monolayer-thick QWs with In-content near 50% was demonstrated and confirmed by photoluminescence measurements. The observed dependence of the QW composition on the growth temperature, and the self-limited QW thickness under metal-rich growth conditions, suggest the existence of a substitutional synthesis mechanism, comprising the surface exchange between In and Ga atoms. The proposed mechanism is promising for further increasing the composition towards binary InN/GaN QWs.

[1] I. G. Vasileiadis, L. Lymperakis, A. Adikimenakis, A. Gkotinakos, V. Devulapalli, C. H. Liebscher, M. Androulidaki, R. Hübner, Th. Karakostas, A. Georgakilas, Ph. Komninou, E. Dimakis and G. P. Dimitrakopulos, Sci. Rep., 11, 20606 (2021)

Novel transistor concepts based on semiconductor nanowires promise high performance, lower energy consumption and better integrability in various platforms in nanoscale dimensions. Concerning the intrinsic transport properties of electrons in nanowires, relatively high mobility values that approach those in bulk crystals have been obtained only in core/shell heterostructures, where electrons are confined inside the core and, thus, their scattering on the nanowire surface is suppressed.
Here, we demonstrate that the large strain in core/shell nanowires with significant lattice-mismatch between the core and the shell can affect the effective mass and the scattering of electrons in a way that boosts their mobility to higher levels compared to results obtained by any other means. Specifically, we use GaAs/InAlAs core/shell nanowires with a lattice mismatch in the range of 3%, grown on Si substrates by molecular beam epitaxy. Overgrown with an 80-nm-thick shell, the 22-nm-thick core is hydrostatically tensile-strained as found by both Raman scattering and photoluminescence measurements [1, 2]. The transport properties and dynamics of electrons were probed at room temperature by optical-pump THz-probe spectroscopy, which is an established contactless method that circumvents challenges in the fabrication of electrical contacts on nanowires. We found that the mobility of electrons inside the strained GaAs core undergoes a remarkable enhancement despite the small core thickness, becoming 30 – 50 % higher than in unstrained GaAs/AlGaAs nanowires or bulk GaAs [2]. Our studies are extended to modulation-doped GaAs/InAlAs nanowires and the results will be presented.
The reported strain-induced mobility enhancement is of major importance for the realization of transistors with high speed and low power consumption, having the potential to trigger major advancements in high-performance nanowire electronic devices monolithically integrated in Si platforms.

[1] L. Balaghi, G. Bussone, R. Grifone, R. Hübner, J. Grenzer, M. Ghorbani-Asl, A. V. Krasheninnikov, H. Schneider, M. Helm, E. Dimakis, Nat Commun 10, 2793 (2019).
[2] L. Balaghi, S. Shan, I. Fotev, F. Moebus, R. Rana, T. Venanzi, R. Hübner, T. Mikolajick, H. Schneider, M. Helm, A. Pashkin, E. Dimakis, Nat Commun 12, 6642 (2021).

Overview on in vitro experiment possibilities and Flash experiments

Overview over preclinical proton flash experiments

Background and Aims

A prominent explanation of the FLASH effect is the oxygen depletion hypothesis, in which the radiolysis of water or cytoplasm produces radicals that react with the O2 dissolved in the water or cytoplasm. This would result in an oxygen depletion leading to a hypoxic target and hence radiation protection effect based on the Oxygen Enhancement Ratio. The presented study aims to investigate the impact of beam pulse structure on oxygen depletion and its correlation with biological endpoints.
Methods

O2 depletion was measured using 30 MeV electron irradiation on a sealed water target. Read-out was performed using TROXSP5 sensors. The beam pulse structure was altered to assess 4 different regimes of average and beam pulse dose rate.
At clinical doses, not enough O2 was consumed to explain a FLASH effect due to radiation-induced hypoxia. The amount of O2 depleted per dose depends on the dose rate, and slightly less O2 is removed at higher dose rates, suggesting radical-radical reactions as a possible mechanism of the FLASH effect. Furthermore, our results regarding the pulse structures showed that the average dose rate seems to dominate the pulse dose rate in terms of radical production and O2 depletion. The direct comparison of the depletion measurements presented here with biological experiments on zebrafish embryos from another study also showed that there was a strong correlation between O2 depletion and biological radiation response (FIG 1). The results emphasize that the FLASH effect in biological tissues is likely to be explained by decreased effective radical production at high dose rates.
Conclusions

In the tested beam parameters, the mean dose rate has the most pronounced effect on O2 depletion. Depletion measurements showed a clear correlation with biological data, from which FLASH effects can be largely explained by changes in radical production.

Background and Aims
The Flash effect, i.e. the radiobiological observation of normal tissue sparing but efficient tumor killing by
ultra-high dose rate (UHDR) irradiation, promise great benefits for cancer patient treatment. The translation
process of the Flash effect should be accompanied by systematic studies on the necessary beam parameters
for each clinical applied radiation. Using the zebrafish embryo model, the influence of partial oxygen level
(https://doi.org/10.1016/j.radonc.2021.02.003), electron pulse structure and dose were studied thoroughly.
To investigate a similar range of proton beam parameters UHDR experiments at different accelerators, but
under comparable conditions, are required.
Methods
To cover a broad range of proton dose rates, experiments have been prepared at the University Proton
Therapy Dresden (UPTD) and at the Draco laser accelerator (Helmholtz-Zentrum Dresden-Rossendorf)
providing quasi-continuous and single-shot proton beam delivery in the range of 0.12 to 10^9 Gy/s. To fulfil
the requirements of the model, i.e., irradiating a sufficiently high number of embryos at low oxygen level,
dedicated setups were established that also allow for the online measurement of oxygen partial pressure
and cope with the geometric restrictions of the respective accelerator.
Results
A comparison experiment at UPTD reveal a significant protecting Flash effect in both setups for zebrafish
embryo treated with 300 Gy/s relative to conventional proton dose rate. Moreover, a higher protection of
the embryos was indicated comparing the embryo length after irradiation with 10^9 Gy/s and conventional
proton dose rate, respectively.
Conclusions
Experimental setups have been established that allow for systematic proton dose rate studies using the
zebrafish embryo model at the clinical cyclotron of UPTD and at the Draco laser accelerator. Therewith, the
experimental possibilities at the Dresden platform for UHDR radiobiology are extended providing electron
and proton dose rates up to 10^9 Gy/s.

The recent rediscovery of the “Flash Effect” revived the interest in high and ultra-high dose-rate radiation
effects throughout the radiobiology community, promising protection of normal tissue, while simultaneously
not altering tumour control. Systematic preclinical studies at (modified) clinical accelerators resulted in a recipe
of necessary beam parameters for the induction of electron Flash effect (doi:10.3389/fonc.2019.01563), whereas
for protons the optimal parameter setting is still under investigation. Expanding the clinical parameter range
the “Dresden platform for high-dose rate radiobiology” enables electron and proton experiments with doserates
of up to 109 Gy/s and more flexible beam pulse structures.
For systematic studies of the available electron and proton beam parameters, the zebrafish embryo model was
irradiated under similar conditions at the different accelerators. The irradiation setup was adapted with respect
to model requirements, i.e. a certain partial oxygen pressure, and the respective beam parameters.
Making use of the flexible pulse structure of the research electron accelerator ELBE, the mean dose rate was
identified as the factor that defines the electron Flash effect with decreasing radiation damage for electron
mean dose rate from 0.1 to 10^5 Gy/s. To cover a similar range of dose rates for protons, irradiations at the
University Proton Therapy Dresden (UPTD) were combined with proton treatment at the laser proton
accelerator DRACO. In doing so, the effects of proton dose rates in the range of 0.1 to 10^9 Gy/s could be
investigated.
To sum up, using the zebrafish embryo model as showcase the possibilities of the “Dresden platform” were
demonstrated, which opens the possibility for systematic studies on the mechanisms of the Flash effect in
tissue, on physico-chemical or molecular level.

The Need for a Research Room in a Proton Therapy Centre – Dresden perspective

Purpose/Objective
In a previous experiment at the HZDR research electron accelerator ELBE high mean dose rates of 105 Gy/s in combination with partial oxygen pressure below 5 mmHg protect zebrafish embryo from radiation damage compared to continuous reference irradiation (mean dose rate of 0.11 Gy/s) and higher oxygen pressure (Pawelke et al. Radiother Oncol 2021). However, the influence of beam pulse structure on the radiation response remains unanswered and should be resolved in an upcoming experiment.
Material/Methods
In addition to the Flash and the reference regime, the ELBE accelerator was used to mimic the pulse structure of a clinical electron linac delivering a dose of 28 Gy by 5 pulses at a frequency of 250 Hz. For comparison, a fourth regime of similar mean dose rate, but continuous beam (280 Gy/s) mimicking FLASH irradiation at a isochronous proton cyclotron (Beyreuther et al. Radiother Oncol 2019) was applied. Wild type zebrafish embryo (24 hpf) were irradiated and the radiation induced malformation were studied during the four day follow up for all four regimes. Zebrafish embryo irradiation was performed under low oxygen pressure and the depletion of depletion during irradiation was measured online.
Results
Compared to the reference regime a protecting Flash effect was found the three other pulse regimes for endpoints, except embryo survival. Analysing the radiation induced malformation more detailed significant correlations to mean and pulse dose rate are revealed. Surprisingly, the beam delivery in macro pulses (Linac regime) reduces the Flash effect relative to delivery at the same pulse dose rate but in a single pulse.
Conclusion.
The ELBE electron accelerator can be applied to study the influence of beam dose rate and pulse structure on the Flash effect by varying both parameters over several orders of magnitude. Hence, ELBE is an ideal tool for systematic studies on optimal electron beam parameters for Flash, including pulse structures that are relevant for clinical application.

Ultra-high dose rate radiobiology at the "Dresden platform for high dose-rate radiobiology"

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A lot of ecological theory relies on ordinary differential-equation models that assume well-mixed systems and do not incorporate any information about the spatial distribution of organisms. However, ecosystems present spatial heterogeneities at different scales that can impact individual fitness and, ultimately, population dynamics. I will present an alternative approach to describe the spatiotemporal dynamics of a population of interacting agents. To this end, I will consider a system with nonlinear birth-death rates and positive and negative inter-individual interactions acting at different spatial ranges. I will first describe the stochastic, individual-level rules that govern the reproduction and death of each individual. Then, using field-theory techniques, I will derive a non-local partial differential equation for the population density and compare its predictions with those obtained assuming well-mixed populations. Finally, I will discuss the ecological relevance of our results and how this approach can be extended to more complex scenarios.

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We parameterize the core of compact spherical star configurations
by a mass ($m_x$) and a radius ($r_x$)
and study the resulting admissible areas in the total-mass -- total-radius plane.
The employed fiducial equation-of-state models of the corona at radii $r \ge r_x$ and
pressures $p \le p_x = p(r = r_x)$ are that (i) of constant sound velocity and (ii)
a proxy of DY$\Delta$ DD-ME2 provided by Buchdahl's exactly solvable ansatz.
The core ($r < r_x$) may contain any type of material,
e.g.\ Standard-Model matter with unspecified equation of state or/and
an unspecified Dark-Matter admixture.
Employing a toy model for the cool equation of state with first-order phase transition
we discuss also the mass-radius relation of compact stars with an admixture of Dark Matter
in a Mirror-World scenario.

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Pathological complete response (pCR) has been correlated with overall survival in several
cancer entities including colorectal cancer. Novel total neoadjuvant treatment (TNT) in rectal cancer
has achieved pathological complete response in one‐third of the patients. To define better treatment
options for nonresponding patients, we used patient‐derived organoids (PDOs) as avatars of the
patient´s tumor to apply both photon‐ and proton‐based irradiation as well as single and combined
chemo(radio)therapeutic treatments. While response to photon and proton therapy was similar,
PDOs revealed heterogeneous responses to irradiation and different chemotherapeutic drugs.
Radiotherapeutic response of the PDOs was significantly correlated with their ability to repair
irradiation‐induced DNA damage. The classical combination of 5‐FU and irradiation could not
sensitize radioresistant tumor cells. Ataxia‐telangiectasia mutated (ATM) kinase was activated
upon radiation, and by inhibition of this central sensor of DNA damage, radioresistant PDOs were
resensitized. The study underlined the capability of PDOs to define nonresponders to irradiation
and could delineate therapeutic approaches for radioresistant patients.

This study aims to elucidate a soft computing approach for quantitative assessment of the 1
scoring grade or rubrics for students in an outcome based education system. The intended approach 2
resorts to a fuzzy membership based assessment of the different parameters of the scoring system, 3
thereby yielding a novel and humanly assessment technique. The selection of the membership 4
functions is based on the human behavior so as to make a realistic representation of the scoring 5
strategy. The novelty of the proposed strategy lies in assigning fuzzy membership based weighted 6
scores instead of simply assigning score bands to rubric categories, as is performed in normal rubrics 7
based assessment. Comparative results demonstrated on a case study of Indian education scenario 8
reveal the effectiveness of the proposed strategy over other fuzzy membership and normal rubrics 9
based assessment procedures.

The alpaka library is a header-only C++17 abstraction library for development across hardware accelerators (CPUs, GPUs, FPGAs). Its aim is to provide performance portability across accelerators through the abstraction (not hiding!) of the underlying levels of parallelism. In this poster we will show the concepts behind alpaka, how it is mapped to the various underlying hardware models, and show the features introduced over the last year. In addition, we will also present the software ecosystem surrounding alpaka.

The alpaka library is a header-only C++17 abstraction library for development across hardware accelerators (CPUs, GPUs, FPGAs). Its aim is to provide performance portability across accelerators through the abstraction (not hiding!) of the underlying levels of parallelism. In this talk we will show the concepts behind alpaka, how it is mapped to the various underlying hardware models, and show the features introduced over the last year. In addition, we will also (shortly) present the software ecosystem surrounding alpaka.

This session was part of ISTE, IET and University of Mumbai approved one week Faculty Development Program on "Quantum Computing" which was conducted in hybrid mode from 12'h Dec 2022 to 17'h Dec 2022.

We present a novel class of approximations for variational losses, being applicable for the training of physics-informed neural nets (PINNs). The formulations reflect classic Sobolev space theory for partial differential equations and their weak formulations.
The loss computation rests on an extension of \emph{Gauss-Legendre cubatures}, we term \emph{Sobolev cubatures}, replacing \emph{automatic differentiation (A.D.)}. We prove the runtime complexity for training the resulting Sobolev-PINNs (SC-PINNs) to be less than required by PINNs relying on A.D. On top of one-to-two order of magnitude speed-up the SC-PINNs are demonstrated to achieve closer solution approximations for prominent forward and inverse (non-linear) PDE problems compared to established PINNs.

Recent years witnessed various supervised learning frameworks relying on trainable quantum circuits as a result of advancement of quantum machine learning. The variational quantum classifier classifies data using a Variational Quantum Circuit (VQC) with an ansatz. The primary goal of the quantum supervised learning classifiers is to use the quantum feature map to transform data from distinct classes to different places in Hilbert space. However, it is not feasible to do feature selection beforehand, and for high-dimensional data using specific features to embed in the ansatz leads to data loss and error in classification. Hence, often data reduction technique like Shannon map is used on the data before uploading it to the quantum circuit. To obviate the data reduction before feeding to the circuit, dense parameterized quantum circuits with lesser number trainable parameters have been proposed without compromising the classification accuracy. The proposed quantum supervised learning framework is an improvement over established work on supervised quantum classifications. To show the effectiveness of the proposed densed quantum circuit, extensive experiments have been performed on IRIS data set and results show that it outperforms the previous quantum supervised classification frameworks in terms of classifications accuracy and complexity of the frameworks.

The Prompt Gamma-Ray (PG) Timing technique (PGT) is a promising candidate for online proton treatment verification as it is small, light-weight, gantry-integrable, and it introduces no additional dose to patients. We report on the first evaluation of the PGT system under clinically relevant conditions.
To this end, the CIRS Proton Therapy Dosimetry Head phantom was irradiated with clinically realistic glioblastoma treatment plans. Time-of-flight distributions of PG were acquired with inorganic scintillators of different sizes (Ø1″×1″, Ø2″×1″, Ø2″×2″). Fast dedicated plug-on spectrometers with throughput rates up to 1×10⁶ s⁻¹ and integrated pile-up rejection were used to enable high-resolution time and energy spectroscopy.
While maximizing the detection efficiency, the 2″-detectors show the expected reduced time resolution and worse gain stability compared to the 1″×1″ crystals. Doubling the acceptance of stabilized voltage dividers from 4 to 8 TeV/s improves the gain stability and significantly reduces the gain drift caused by extreme load changes during pencil beam scanning. With active pile-up rejection, the overall count rate was reduced from 700×10³ s⁻¹ to a maximum of 450×10³ s⁻¹. The limited number of processable PG with less than 100 events per treatment spot per detector was identified as the main factor inhibiting clinical application. These findings imply that further development of the PGT setup is necessary for a successful translation into clinical application. We propose strategies for such a development, including the use of larger crystals, or higher segmentation, small ring collimators, and spot aggregation, and report on the first results acquired by applying these methods.

We present a computational scheme that derives a global polynomial level set parametrisation for smooth closed surfaces from a regular
surface-point set and prove its uniqueness. This enables us to approximate a broad class of smooth surfaces by affine algebraic varieties. From such a
global polynomial level set parametrisation, differential-geometric quantities like mean and Gauss curvature can be efficiently and accurately computed. Even 4th-order terms such as the Laplacian of mean curvature are approximates with high precision. The accuracy performance results in a gain of computational efficiency, significantly reducing the number of surface points required compared to classic alternatives that rely on surface meshes or embedding grids. We mathematically derive and empirically demonstrate the strengths and the limitations of the present approach, suggesting it to be applicable to a large number of computational tasks in numerical differential geometry.

This paper assesses and reports the experience of ten teams working to port,validate, and benchmark several High Performance Computing applications on a novel GPU-accelerated Arm testbed system. The testbed consists of eight NVIDIA Arm HPC Developer Kit systems built by GIGABYTE, each one equipped with a server-class Arm CPU from Ampere Computing and A100 data center GPU from NVIDIA Corp. The systems are connected together using Infiniband high-bandwidth low-latency interconnect. The selected applications and mini-apps are written using several programming languages and use multiple accelerator-based programming models for GPUs such as CUDA, OpenACC, and OpenMP offloading. Working on application porting requires a robust and easy-to-access programming environment, including a variety of compilers and optimized scientific libraries. The goal of this work is to evaluate platform readiness and assess the effort required from developers to deploy well-established scientific workloads on current and future generation Arm-based GPU-accelerated HPC systems. The reported case studies demonstrate that the current level of maturity and diversity of software and tools is already adequate for large-scale production deployments.

Interfaces between clay and cementitious materials are studied in the context of deep disposal of radioactive waste. Contrasting porewater chemistries lead to transport and chemical reactions that modify the pore network and affect transport. Research efforts were directed towards mineralogical and physical characterisation of interface regions (e.g. Mäder et al. 2017, Swiss J. Geosci. 110, 307) but little evidence exists on direct observations of transport behaviour across complex skins. We aim at providing evidence on how mineralogical-physical changes at such an interface affect transport of water and solutes, and linking mineralogical-physical characterisation.
A core was recovered at the Mont Terri rock laboratory (CI Experiment), containing a physically preserved interface between Opalinus Clay and Portland cement (PC) concrete reacted for 10 years. A long-term transport experiment was set up by injecting a synthetic claystone pore water into the core on the clay side, and forcing advection/diffusion across the interface and out of the cement side.
Before injection, the core was tomographed by X-ray CT; the clay part showed pre-existing bedding-parallel weak jointing and the PC concrete contains aggregates and gas pores. Figure 1 (left) shows the core skeleton during the infiltration, i.e. only the aggregates in the concrete and the dense Opalinus Clay.
A series of X-ray CT scans over time showed the change in porosity, while PET (positron emission tomography) directly images the mobile phase in 3D, and its penetration as a function of time (Kulenkampff et al., 2016, Solid Earth, 7, 1217). The sample was monitored frequently by high resolution X-ray CT during the first 4 months. 124I was used as PET tracer in the infiltrating synthetic claystone pore water, and the chosen dose allowed for continuous PET scanning during two weeks. Figure 1 (right) shows the flow observed by PET superimposed to the skeleton of the core. PET captured some preferential flow across claystone along some remaining joints, a large spreading of the tracer plume at the clay/cement interface, and some preferential flow across the PC.
The mineralogical and chemical changes coupled to the time-resolved 3D X-ray CT and PET scans (imaging both the stationary and the mobile phase) provide detailed information of coupled processes in complex porous media, e. g. how the dissolution of hydroxide cement phases and the precipitation of carbonates are influenced by advection/diffusion and vice versa.
Partial funding from the European Union's (Euratom) Horizon 2020 Programme under grant agreement 662147 – Cebama is acknowleged, and contributions by Nagra and the Mont Terri Consortium (CI Experiment) to Uni Bern.

In this talk we show the benefits of using performance portability layers such as alpaka in real-world HPC applications. Using PIConGPU and the CMS Patatrack experiment as examples we demonstrate the minimal porting effort achieved by using alpaka when encountering new and previously unknown hardware architectures.

In this talk we first introduce the concept of heterogeneous computing systems and then show the difficulties that lie in programming them. We present the different workload patterns that are suitable for different hardware types. In the end propose the alpaka kernel abstraction library as a possible solution to these challenges.

In this talk the kernel abstraction library alpaka is briefly introduced. Afterwards the technical details of the alpaka SYCL back-end are presented.

We present a novel approach for an event generator inherently using exact QED descriptions to predict the results of high-energy electron-photon scattering experiments that can be performed at modern X-ray free-electron laser facilities. Our event generator makes use of the fact, that the classical nonlinearity parameter barely approaches unity in high-frequency regimes accessible at these facilities, while this parameter range is outside of the application window of existing QED-PIC codes. This constraint on the parameter range allows for an approximation which is capable of taking the finite bandwidth of the X-ray laser into account in the description of the interaction.
We investigate the application of the new first-principle method to the generation of events in energy-driven electromagnetic cascades, which complements the studies on intensity-driven cascades at optical laser experiments.

While the high frequency of modern x-ray free-electron lasers has the benefit of requiring less energy of a seed electron for triggering the development of a QED cascade, the non-linearity parameter obeys a_0 < 1, in contrast to high-intensity optical lasers. Accordingly, we analyse the phenomenon of multi-photon effects in trident pair production in pulsed x-ray laser fields at such values of a_0. The impact of the energy spectrum and its temporal structure and the coherence of the laser field on the emergent particle distribution at the onset of further cascading is discussed. Besides the evolution of mean multiplicities in the course of an energy-powered cascade, we seek characteristic fluctuation patterns.

The accurate modelling of laser-matter interaction is a very challenging task. Especially, the generation of scattering events to mimic statistical particle distributions seen in experiments have demanding requirements on the computational methods and implementations. With this talk, we introduce the complicated structure of strong-field QED and formulate the fundamental building blocks for Monte-Carlo event generation using this theory, where a key feature is the dynamical coupling of the laser field to the scattering processes. This type of coupling can not be addressed with state-of-the-art event generators used to model processes from the standard model of particle physics. Therefore, we introduce a new implementation of e Monte-Carlo event generator, written in the Julia programming language. Furthermore, we introduce some key language features of Julia, which may come in handy for implementations of future event generators in general, where especially the capabilities of distributed computing will be highlighted.

The discovery of superconductivity in the quantum critical Kondo-lattice system YbRh₂Si₂ at an
extremely low temperature of 2 mK has inspired efforts to perform high-resolution electrical
resistivity measurements down to this temperature range in highly conductive materials. Here we
show that control over the sample geometry by microstructuring using focused-ion-beam
techniques allows to reach ultra-low temperatures and increase signal-to-noise ratios (SNRs)
tenfold, without adverse effects to sample quality. In five experiments we show four-terminal
sensing resistance and magnetoresistance measurements which exhibit sharp phase transitions at
the Néel temperature, and Shubnikov–de-Haas (SdH) oscillations between 13 T and 18 T where we
identified a new SdH frequency of 0.39 kT. The increased SNR allowed resistance fluctuation
(noise) spectroscopy that would not be possible for bulk crystals, and confirmed intrinsic 1/ f -type
fluctuations. Under controlled strain, two thin microstructured samples exhibited a large increase
of T̀N from 67 mK up to 188 mK while still showing clear signatures of the phase transition and
SdH oscillations. Superconducting quantum interference device-based thermal noise spectroscopy
measurements in a nuclear demagnetization refrigerator down to 0.95 mK, show a sharp
superconducting transition at T̀c = 1.2 mK. These experiments demonstrate microstructuring as a
powerful tool to investigate the resistance and the noise spectrum of highly conductive correlated
metals over wide temperature ranges.

Consolidating a microscopic understanding of magnetic properties is crucial for a rational design of magnetic materials with tailored characteristics. The interplay of 3d and 4f magnetism in rare-earth transition metal antimonides is an ideal platform to search for such complex behavior. Here the synthesis, crystal growth, structure, and complex magnetic properties are reported of the new compound Pr₃Fe₃Sb₇ as studied by magnetization and electrical transport measurements in static and pulsed magnetic fields up to 56 T, powder neutron diffraction, and Mößbauer spectroscopy. On cooling without external magnetic field, Pr₃Fe₃Sb shows spontaneous magnetization, indicating a symmetry breaking without a compensating domain structure. The Fe substructure exhibits noncollinear ferromagnetic order below the Curie temperature T_C ≈ 380 K. Two spin orientations exist, which approximately align along the Fe–Fe bond directions, one parallel to the ab plane and a second one with the moments canting away from the c axis. The Pr substructure orders below 40 K, leading to a spin-reorientation transition (SRT) of the iron substructure. In low fields, the Fe and Pr magnetic moments order antiparallel to each other, which gives rise to a magnetization antiparallel to the external field. At 1.4 K, the magnetization approaches saturation above 40 T. The compound exhibits metallic resistivity along the c axis, with a small anomaly at the SRT.

Electrochemiluminescence (ECL) represents a widely explored technique to generate light, in which the emission intensity relies critically on the charge-transfer reactions between electrogenerated radicals. Two types of charge-transfer mechanisms have been postulated for ECL generation, but the manipulation and effective probing of these routes remain a fundamental challenge. Here, we demonstrate the design of quantum dot (QD) aerogels as novel ECL luminophores via a versatile water-induced gelation strategy. The strong electronic coupling between adjacent QDs enables efficient charge transport within the aerogel network, leading to the generation of highly efficient ECL based on the selectively improved interparticle chargetransfer route. This mechanism is further verified by designing CdSe-CdTe mixed QD aerogels, where the two mechanistic routes are clearly decoupled for ECL generation. We anticipate our work will advance the fundamental understanding of ECL and prove useful for designing next-generation QD-based devices.

Magnetic shape memory alloys are known to undergo stress- and temperature-driven phase changes. Here we study the specific case of a NiMnGa Heusler alloy that has an austenitic phase at room temperature. Upon cooling or the application of mechanical pressure, the austenite can transform into martensite, allowing for large reversible strain cycling and making such alloys to promising actuating materials. In order to shed more light on the mechanical switching behavior and possible dissipative processes, we probe the nano-scale plasticity of 0.5 and 2 µm thick epitaxial NiMnGa films with nanoindentation. A distinct pop-in signature is seen as the first departure from Hertzian elastic contact mechanics at small film thicknesses. This pop-in behavior persists across four orders of loading rates and over a broad temperature regime from 40°C to -30°C, which encompasses the transformation temperature to martensite. The statistics of the incipient plastic events are well described by a Weibull distribution. Atomic force microscopy reveals surface signatures around indents that indicate residual martensite, which is further confirmed with transmission electron microscopy imaging of the structure underneath indents. Instead of the expected modulated martensite (14M, 10M) that forms during a temperature-driven phase change, regions underneath indents contain non-modulated (NM) martensite. NM martensite exhibits a higher spontaneous strain and often forms at lower temperatures and higher strains. Therefore, it is concluded that the pop-in signature during nanoindentation originates from an athermal martensitic transformation, where the confinement effects result in huge and complex deformation inducing a partly irreversible transition to NM martensite.

Structural martensitic transformations enable various applications, which range from high stroke actuation and sensing to energy efficient magnetocaloric refrigeration and thermomagnetic energy harvesting. All these emerging applications benefit from a fast transformation, but up to now the speed limit of martensitic transformations has not been explored. Here, we demonstrate that a martensite to austenite transformation can be completed in under ten nanoseconds. We heat an epitaxial Ni-Mn-Ga film with a laser pulse and use synchrotron diffraction to probe the influence of initial sample temperature and overheating on transformation rate and ratio. We demonstrate that an increase of thermal energy drives this transformation faster. Though the observed speed limit of 2.5 x 1027 (Js)-1 per unit cell leaves plenty of room for a further acceleration of applications, our analysis reveals that the practical limit will be the energy required for switching. Our experiments unveil that martensitic transformations obey similar speed limits as in microelectronics, which are expressed by the Margolus–Levitin theorem.
[1] S. Schwabe, K. Lünser, D. Schmidt, K. Nielsch, P. Gaal and S. Fähler, https://arxiv.org/abs/2202.12581

Depending on composition and chemical order, Ni-Mn-based Heusler alloys exhibit interesting functional properties, which render them useful for magnetic shape memory applications or as magnetocaloric materials. This is linked to the presence of hierarchically twinned modulated structures in martensite, which can be interpreted as adaptive, self-organized arrangement of [110]-aligned nanotwins consisting of non-modulated tetragonal building blocks as was shown previously for the paradigmatic case of stoichiometric Ni2MnGa [1]. A band-Jahn-Teller-type reconstruction of the Fermi surface which in particular softens the [110] transversal acoustic phonons leads to a downhill transformation path from cubic austenite to nanotwinned martensite [2]. The twin interfaces are subject to competing repulsive and attractive interactions related to the frustrated antiferromagnetic coupling between neighboring Mn atoms [3].
Based on recent first-principles calculations in the framework of density functional theory, the present contribution explores the signatures of the interdependence of magnetism, chemical order and nanotwinning in Ni-Mn-based Heusler systems beyond Ni-Mn-Ga and their relevance for the functional properties. Particular emphasis will be made on off-stoichiometric compositions suitable for magnetocaloric purposes.

In situ measurements using RBS, ERD, and SE are less explored in characterizing solar absorber materials at high temperatures [1, 2]. In the present work, we report the W/WAlSiN/SiON/SiOO₂ based spectrally selective solar absorber coating with excellent optical, compositional and structural properties at high temperatures [3, 4]. We have carried out in situ Rutherford backscattering spectrometry, elastic recoil detection and spectroscopic ellipsometry measurements at three different temperatures at 450°C, 650°C, and 800°C. An optical model describing perfectly the reflectance and ellipsometric data was developed. Further, the microstructural properties of the solar absorber coating are evaluated using cross-sectional transmission electron microscopy before and after annealing. Our data obtained before and after the heating experiments demonstrate excellent compositional, optical and structural stability of the coatings under the applied conditions. Furthermore, in situ ellipsometry showed the conservation of the optical properties of the W/WAlSiN/SiON/SiOO₂ based spectrally selective solar absorber up to 800 °C, which is crucial for high-temperature applications.
[1] Ramón Escobar Galindo, Matthias Krause, K. Niranjan and Harish Barshilia, in Sustainable Material Solutions for Solar Energy Technologies (ed. Mariana Fraga, Delaina Amos, Savas Sonmezoglu, Velumani Subramaniam, Elsevier, 2021).
[2] Lungwitz, F. et al. Transparent conductive tantalum doped tin oxide as selectively solar-transmitting coating for high temperature solar thermal applications, Solar Energy Mater. Solar Cells 196, 84-93, doi:10.1016/j.solmat.2019.03.012 (2019).
[3] K. Niranjan, A. Soum-Glaude, A. Carling-Plaza, S. Bysakh, S. John, H.C. Barshilia, Extremely high temperature stable nanometric scale multilayer spectrally selective absorber coating: Emissivity measurements at elevated temperatures and a comprehensive study on ageing mechanism, Solar Energy Mater. Sol. Cells 221 (2021) 110905, doi:10.1016/j.solmat.2020.110905.
[4] K. Niranjan, A.C. Plaza, T. Grifo, M. Bordas, A. Soum-Glaude, H.C. Barshilia, Performance evaluation and durability studies of W/WAlSiN/SiON/SiOO₂ based spectrally selective solar absorber coating for high-temperature applications: A comprehensive study on thermal and solar accelerated ageing, Solar Energy 227 (2021) 457–467, doi:10.1016/j.solener.2021.09.026.

In situ Rutherford Backscattering Spectrometry (RBS) and Spectroscopic Ellipsometry (SE) were applied to study the compositional and optical stability of a WAlSiN-based solar-selective coating (SSC) at high temperatures in vacuum. The samples were exposed to heating-cooling cycles between quasi room temperature and stepwise-increased high temperatures of 450 °C, 650 °C, and 800 °C, respectively. In situ RBS revealed full compositional stability of the SSC during thermal cycling. In situ SE indicated full conservation of the optical response at 450 °C and 650 °C, and minimal changes at 800 °C. The analysis of the ex situ optical reflectance spectra after the complete thermal cycling gave an unchanged solar absorptance of 0.94 and a slightly higher calculated thermal emittance at 800 °C of 0.16 compared to 0.15 after deposition. Cross-sectional element distribution analysis performed in scanning transmission electron microscopy mode confirmed the conservation of the SSC’s microstructure after the heating – cooling cycles. The study demonstrates compositional, optical, and structural stability of the WAlSiN-based solar-selective coating at temperatures targeted for the next generation of concentrated solar power plants.

Purpose: PET-derived metabolic tumor volume (MTV) and total lesion glycolysis of the primary tumor are known to be prognostic of clinical outcome in head and neck cancer (HNC). Including evaluation of lymph node metastases can further increase the prognostic value of PET but accurate manual delineation and classification of all lesions is time-consuming and prone to inter-observer variability. Our goal, therefore, was development and evaluation of an automated tool for MTV delineation/classification of primary tumor and lymph node metastases in PET/CT investigations of HNC patients.

Methods: Automated lesion delineation was performed with a residual 3D U-Net convolutional neural network (CNN) incorporating a multi-head self-attention block. 698 [18F]FDG PET/CT scans from 3 different sites and 5 public databases were used for network training and testing. An external dataset of 181 [18F]FDG PET/CT scans from 2 additional sites was employed to assess the generalizability of the network. In these data, primary tumor and metastases were interactively delineated and labeled by two experienced physicians. Performance of the trained network models was assessed by 5-fold cross-validation in the main dataset and by pooling results from the 5 developed models in the external dataset. The Dice similarity coefficient (DSC) for individual delineation tasks and the primary tumor/metastasis classification accuracy were used as evaluation metrics. Additionally, a survival analysis using univariate Cox regression was performed comparing achieved group separation for manual and automated delineation, respectively.

Results: In the cross-validation experiment, delineation of all malignant lesions with the trained U-Net models achieves DSC of 0.885, 0.805, and 0.870 for primary tumor, LN metastases, and the union of both, respectively. In external testing, the DSC reaches 0.850, 0.724, and 0.823 for primary tumor, LN metastases, and the union of both, respectively. The voxel classification accuracy was 98.0% and 97.9% in cross-validation and external data, respectively. Univariate Cox analysis in the cross-validation and the external testing reveals that manually and automatically derived total MTVs are both highly prognostic with respect to overall survival, yielding essentially identical hazard ratios (HR) (HRman = 1.9; p < 0.001 vs. HRcnn = 1.8; p < 0.001 in cross-validation and HRman = 1.8; p = 0.011 vs. HRcnn = 1.9; p = 0.004 in external testing).

Conclusion: To the best of our knowledge, this work presents the first CNN model for successful MTV delineation and lesion classification in HNC. In the vast majority of patients, the network performs satisfactory delineation and classification of primary tumor and lymph node metastases and only rarely requires more than minimal manual correction. It is thus able to massively facilitate study data evaluation in large patient groups and also does have clear potential for supervised clinical application.

The α↔ϵ, α→γ and γ→ϵ transformations have been characterised in diamond anvil cells under hydrostatic compression conditions. In situ x-ray diffraction of single or oligo-crystals and ex situ SEM-EBSD measurements have been analyzed with multi-grain techniques. The mechanisms of α ↔ ϵ transitions are martensitic, following Burgers paths whiwh requires a high plastic activity. A memory effect of the reversion exists in the vast majority of the sample: the starting orientation of α-Fe single crystal is recovered. Small grains of α-Fe exhibit a new orientation compatible with Burgers path, possibly associated to twinning in ϵ-Fe. Close to the α − γ − ϵ-Fe triple point (8.7
GPa, 750 K), the α → γ transformation undergoes via diffusion and recrystallization of γ-Fe, and γ → ϵ transformation is martensitic but involves no plasticity. As a result, the microstuctures in ϵ-Fe produced by a direct α → ϵ transformation and by α → γ → ϵ transitions path are very different.

Deep Learning based approaches for automated analysis of tomographic image data are drawing ever increasing attention in Radiology and Nuclear Medicine. With the advent of the new generation of PET scanners with massively enlarged axial field of view (“total body PET”) the importance of integrating such approaches into clinical workflows will further increase. In the present study we report on our application of a convolutional neural network (CNN) for automated survival analysis in head and neck cancer (HNC): PET parameters such as metabolic tumor volume (MTV), total lesion glycolysis, and asphericity of the primary tumor are known to be prognostic of clinical outcome in HNC patients. Additionally including evaluation of lymph node metastases further increases the prognostic value of PET. However, accurate manual delineation and classification of all lesions is time consuming and incompatible with clinical routine. Our goal, therefore, was development and evaluation of an automated tool for MTV delineation/classification of primary tumor and lymph node metastases in HNC in PET.

Automated delineation of the HNC cancer lesions was per- formed with a residual 3D U-Net convolutional neural network (CNN). 698 FDG PET/CT scans from 3 different sites and 4 public databases were used for network training and testing. In these data, primary tumor and metastases were manually delineated (with assistance of semi-automatic tools) and accordingly labeled by an experienced physician. Performance of the trained network models was assessed by 5-fold cross validation using the Dice similarity coefficient for individual delineation tasks.

Additionally, survival analysis using univariate Cox regression was performed. Delineation of all malignant lesions with the trained U-Net model achieves a Dice coefficient of 0.866 when not dis-
criminating between primary tumor and lymph nodes. Treating primary tumor and lymph node metastases as distinct classes yields Dice coefficients of 0.835 and 0.757 for the respective delin-
eations. The univariate Cox analysis reveals that, both, manually as well as automatically derived total MTVs are highly prognostic with similar hazard ratios (HR) with respect to overall survival
(HR=1.8; P<0.001 and HR=1.7; P<0.001, respectively). To the best of our knowledge, our work represents the first CNN model for successful MTV delineation and lesion classification in HNC. The network quickly performs usually satisfactory delineation and classification of primary tumor and lymph node metastases in HNC using FDG-PET data alone with only minimal sporadic manual corrections required. It is able to massively facilitate study data evaluation in large patient groups and also does have clear potential for clinical application.

The majority of technical separation processes for fluid mixtures utilize the principle of rectification. If a two-phase mixture is fed into the column, possibly undesirable flow morphologies or severe droplet carry-over may occur, which detrimentally affect separation efficiency and equipment integrity. Currently, the two-phase flow behavior in feed pipes is hardly predicable and mostly based on empirical or heuristic methods, which do not properly account for a broad range of possible fluid properties and plant dimensions. As a consequence, costly safety margins are applied. Feed pipes to separation columns are often characterized by horizontal inlet nozzles, small length-to-diameter ratios and complex routing, involving elbows or bends. The pipe lengths are too short to enable the two-phase flow to fully develop, which thus, enters the column with unknown flow morphology. Since developing flows have rarely been studied, today’s engineering practice relies on existing predictive methods for fully developed two-phase flows. Graphical methods can hardly represent gradual transitions between flow regimes. Analytical models provide only simplified flow representations of the two-phase flow that have not yet been qualified for developing pipe flow. In this work, a comprehensive experimental database of horizontal water-air flows in two test sections with nominal pipe diameters of D = 50 mm and D = 200 mm and feed pipe lengths in the range 10 < L/D < 75 was established. This way, the data cover developing pipe flows with entrance lengths typical for two-phase feeds of separation columns and more developed flows that are comparable with the extensively studied reference system water-air. A particular focus was put on the effect of pipe bends on the flow morphology up- and downstream. The flow morphology was captured using imaging wire-mesh sensors. A 4D fuzzy algorithm was applied to objectively identify the flow two-phase morphologies. Based on their fuzzy representation, the flow morphologies were classified and a novel 2D visualization technique is proposed to discuss the flow development along the feed pipes. Undesired flow morphologies (intermittent flow and entrainment) during the operation of two-phase feeds are hardly predictable by conventional design tools. The inception of intermittent flows was analyzed using the experimental data. Consequently, the inception criteria based on the required liquid levels for fully developed intermittent flows were adapted for short entrance lengths. The characteristic dynamics of flow morphologies that are known to cause the onset of entrainment were analyzed. Based on wave frequencies, a predictive criterion for the susceptibility of wavy flows for the onset of entrainment is introduced and applied to straight feed pipes and horizontal 90° bends. Among the dozens available, 66 reduced-order models for the prediction of the void fraction were tested for straight feed pipes and horizontal 90° pipe bends. Thereof, the ones most suitable for variable operating conditions and pipe geometries were identified and adapted. Complementary 3D simulations were performed to verify the applicability of numerical codes (VoF, AIAD) for flows with free interfaces. The flow morphologies were successfully reproduced at macroscopic scale, however, the simulation results rank behind reduced-order models considering their quantitative predicting capabilities.

The transparent conductive tantalum doped tin oxide is a potential candidate for applications in concentrated solar power technology, dye-sensitized solar cells and dynamic random access memories [1], [2], [3]. In all these fields, high-temperature stability in air is mandatory to preserve its functionality. In this work we demonstrate the compositional and structural in-air-stability of SnO₂:Ta thin films at 650 °C and 800 °C for 12 hours. While the element composition and optical spectra were unchanged and the X-ray diffractograms revealed the conservation of a single-phase rutile-type crystal structure, some strong Raman lines of SnO₂:Ta underwent substantial changes upon tempering. Quantum ab initio calculations of pristine and Ta-doped SnO₂ with systematically varied point defects indicated that preferentially Sn vacancies and excess O atoms are responsible for these strong and unexpected Raman signatures. These defects are partially healed during high-temperature exposure, but that does not affect the functionality of SnO₂:Ta as transparent conductor under these harsh conditions. This study provides a comprehensive understanding of crystal and defect structure of Ta-doped SnO₂ prior to and after high temperature treatment in air for the first time and encourages its application in different fields where high-T stability, transparency and conductivity are required.
[1] F. Lungwitz et al., Transparent conductive tantalum doped tin oxide as selectively solar-transmitting coating for high temperature solar thermal applications, Solar Energy Mater. Solar Cells 199, 84 (2019), doi: 10.1016/j.solmat.2019.03.012
[2] R. Ramarajan, et al. Large-area spray deposited Ta-doped SnO₂ thin film electrode for DSSC application, Solar Energy 211, 547-559 (2020), doi:10.1016/j.solener.2020.09.042.
[3] C. J. Cho, et al. Ta-Doped SnO₂ as a reduction-resistant oxide electrode for DRAM capacitors, Journal of Materials Chemistry C 5, 9405-9411 (2017), doi:10.1039/c7tc03467a
Financial support by the EU, grant No. 645725, project FRIENDS2, is gratefully acknowledged.

Aim: Image derived PET parameters such as metabolic tumor volume (MTV), total lesion glycolysis, and tumor asphericity of the primary tumor have been shown to be prognostic of clinical outcome of patients with head and neck cancer (HNC). Evaluation of lymph node metastases in addition to the primary tumor further increases the prognostic value of PET. Such analysis requires, however, accurate delineation and classification of all lesions which is very time-consuming when performed manually. The goal of this study is development of an automated tool for MTV delineation of primary tumor and lymph node metastases in HNC in PET/CT.

Methods: Automated delineation of the HNC cancer lesions was performed with a residual 3D U-Net convolutional neural network (CNN). 698 FDG PET/CT scans from 3 different sites and 4 public databases were used for network training (N=558) and testing (N=140). In these data, primary tumor and metastases were manually delineated and accordingly labeled by an experienced physician. This manual delineation served as the ground truth for network training. Performance of the trained network model was assessed in the test data using the Dice similarity coefficient for primary tumor, metastases, and the union of all lesions, respectively.

Results: The derived U-Net model is capable of accurate delineation of malignant lesions achieving a Dice coefficient of 0.847 for indiscriminative segmentation. Treating primary tumor and lymph node metastases as distinct classes yields Dice coefficients of 0.840 and 0.714 for the respective delineations.

Conclusions: In this work, we present the first CNN model for MTV delineation and classification in HNC. The developed network model allows to quickly perform satisfactory delineation of (and discrimination between) primary tumor and lymph node metastases in HNC with only minimal manual corrections possibly required. It thus is able to improve and to accelerate study data evaluation in quantitative PET and does also have potential for clinical application.

Triboscopy focuses on the analysis of the temporal evolution of a tribological system, combining local and time-resolved information, most commonly the evolution of friction. In this work, this technique is applied on measurements, which were carried out with a custom-built ultrahigh vacuum tribometer in ball-on-disc configuration. Based on these experiments, an extended classification to distinguish different triboscopic features is suggested, depending on the persistence in both track position and time: UNIFORM, GLOBAL, LOCAL, and SPORADIC. Further, a filter technique for quantifying triboscopic data regarding this classification is introduced. The new and improved triboscopic techniques are applied to various dry friction measurements of hydrogen-free carbon coatings under varying humidity and pressure. The resulting specific triboscopic features are correlated to wear phenomena, such as counter body coating abrasion, inhomogeneities in the wear track, non-uniform track wear, stick-slip and debris in the contact area, demonstrating the increased analysis and monitoring capabilities when compared to conventional friction curves and wear track images.

Vacuum environments provide challenging conditions for tribological systems. MoS₂ is one of the materials commonly known to provide low friction for both ambient and vacuum conditions. However, it also exhibits poor wear resistance and low ability to withstand higher contact pressures. In search of wear-resistant alternatives, superhard hydrogen-free tetrahedral amorphous carbon coatings (ta-C) are explored in this study. Although known to have excellent friction and wear properties in ambient atmospheres, their vacuum performance is limited when self-paired and with steel. In this study, the influence of the paired material on the friction behavior of ta-C is studied using counterbodies made from brass, bronze, copper, silicon carbide, and aluminum oxide, as well as from steel and ta-C coatings as reference materials. Brass was found to be the most promising counterbody material and was further tested in direct comparison to steel, as well as in long-term performance experiments. It was shown that the brass/ta-C friction pair exhibits low friction (µ < 0.1) and high wear in the short term, irrespective of ambient pressure, whereas in the long term, the friction coefficient increases due to a change in the wear mechanism. Al₂O₃ was identified as another promising sliding partner against ta-C, with a higher friction coefficient than that of brass (µ = 0.3), but considerably lower wear. All other pairings exhibited high friction, high wear, or both.

The forward and reverse phase transformation from face-centered cubic (fcc) to hexagonal
close-packed (hcp) in the equiatomic high-entropy alloy (HEA) CrMnFeCoNi has been investigated
with diffraction of high-energy synchrotron radiation. The forward transformation has been induced
by high pressure torsion at room and liquid nitrogen temperature by applying different hydrostatic
pressures and large shear strains. The volume fraction of hcp phase has been determined by Rietveld
analysis after pressure release and heating-up to room temperature as a function of hydrostatic
pressure. It increases with pressure and decreasing temperature. Depending on temperature, a
certain pressure is necessary to induce the phase transformation. In addition, the onset pressure
depends on hydrostaticity; it is lowered by shear stresses. The reverse transformation evolves over
a long period of time at ambient conditions due to the destabilization of the hcp phase. The effect
of the phase transformation on the microstructure and texture development and corresponding
microhardness of the HEA at room temperature is demonstrated. The phase transformation leads
to an inhomogeneous microstructure, weakening of the shear texture, and a surprising hardness
anomaly. Reasons for the hardness anomaly are discussed in detail.

Few-cycle shadowgraphy is a valuable diagnostic for laser-plasma accelerators for obtaining insight into the $\mu$m- and fs-scale relativistic plasma dynamics. To enhance the understanding of experimental shadowgrams, we developed a synthetic shadowgram diagnostic within the fully relativistic particle-in-cell code PIConGPU.
In the shadowgraphy diagnostic, the probe laser is propagated through the plasma using PIConGPU, and then extracted and propagated onto a virtual CCD using an in-situ plugin for PIConGPU based on Fourier optics. The in-situ approach circumvents performance limitations of a post-processing workflow, like storing and loading large output files that result from large-scale laser-plasma simulations.
This poster presents the in-situ plugin and first synthetic shadowgrams from laser wakefield accelerator simulations that are generated by the plugin.

Extending 2D structures into 3D space has become a general trend in multiple disciplines, including electronics, photonics, plasmonics, superconductivity and magnetism [1,2]. This approach provides means to modify conventional or to launch novel functionalities by tailoring curvature and 3D shape of magnetic thin films and nanowires [2,3]. In this talk, we will address fundamentals of curvature-induced effects in magnetism and review current application scenarios. In particular, we will demonstrate that curvature allows tailoring fundamental anisotropic and chiral magnetic interactions [4] and enables fundamentally new non-local chiral symmetry breaking effect [5]. Application potential of geometrically curved magnetic architectures is currently being explored as mechanically reshapeable magnetic field sensors for automotive applications, memory, spin-wave filters, high-speed racetrack memory devices as well as on-skin interactive electronics relying on thin films [6,7] as well as printed magnetic composites [8,9].

[1] P. Gentile et al., Electronic materials with nanoscale curved geometries. Nature Electronics (Review) 5, 551 (2022).
[2] D. Makarov et al., New Dimension in Magnetism and Superconductivity: 3D and Curvilinear Nanoarchitectures. Advanced Materials (Review) 34, 2101758 (2022).
[3] D. Makarov et al., Curvilinear micromagnetism: from fundamentals to applications (Springer, Zurich, 2022).
[4] O. Volkov et al., Experimental observation of exchange-driven chiral effects in curvilinear magnetism. Physical Review Letters 123, 077201 (2019).
[5] D. D. Sheka et al., Nonlocal chiral symmetry breaking in curvilinear magnetic shells. Communications Physics 3, 128 (2020).
[6] J. Ge et al., A bimodal soft electronic skin for tactile and touchless interaction in real time. Nature Communications 10, 4405 (2019).
[7] G. S. Canon Bermudez et al., Electronic-skin compasses for geomagnetic field driven artificial magnetoception and interactive electronics. Nature Electronics 1, 589 (2018).
[8] M. Ha et al., Printable and Stretchable Giant Magnetoresistive Sensors for Highly Compliant and Skin-Conformal Electronics. Advanced Materials 33, 2005521 (2021).
[9] R. Xu et al., Self-healable printed magnetic field sensors using alternating magnetic fields. Nature Communications 13, 6587 (2022).

Industrial wastes and wastewaters are important secondary sources for many metals. Recovering these metals from such waste streams helps in resource recycling and reduce the environmental burden. Microbial technology offers an economical alternative to traditional metal recovery. Several bacterial and fungal species are reported for metal bioleaching from different industrial wastes. Use of fungi in bioleaching process offers a variety of advantages. The present study provides an overview of fundamental mechanisms of fungal bioleaching and methods used for the same. The case study of two different industrial wastes is also provided.

Metal recovery by bioionflotation using biosurfactants

Extending 2D structures into 3D space has become a general trend in multiple disciplines, including electronics, photonics, plasmonics, superconductivity and magnetism [1,2]. This approach provides means to modify conventional or to launch novel functionalities by tailoring curvature and 3D shape of magnetic thin films and nanowires [2,3]. In this talk, we will address fundamentals of curvature-induced effects in magnetism and discuss realizations of curved low-dimensional architectures and their characterization, which among others resulted in the experimental confirmation of exchange-driven chiral effects [4]. Geometrically curved architectures can support a new chiral symmetry breaking effect: it is essentially non-local and manifests itself even in static spin textures living in curvilinear magnetic nanoshells [5]. The field of curvilinear magnetism was extended towards curvilinear antiferromagnets, offering a novel material science platform for antiferromagnetic spinorbitronics. It was demonstrated that intrinsically achiral 1D curvilinear antiferromagnets behave as a chiral helimagnet with geometrically tunable DMI, orientation of the Neel vector and the helimagnetic phase transition [6]. Application potential of geometrically curved magnetic thin films is currently being explored as mechanically reshapeable magnetic field sensors for automotive applications, memory, spin-wave filters, high-speed racetrack memory devices as well as on-skin interactive electronics [7,8].

References:

[1] P. Gentile et al., Electronic materials with nanoscale curved geometries, Nature Electronics (Review) 5, 551 (2022).
[2] D. Makarov et al., New Dimension in Magnetism and Superconductivity: 3D and Curvilinear Nanoarchitectures, Advanced Materials (Review) 34, 2101758 (2022).
[3] D. Makarov et al., Curvilinear micromagnetism: from fundamentals to applications (Springer, Zurich, 2022). https://link.springer.com/book/10.1007/978-3-031-09086-8
[4] O. Volkov et al., Experimental observation of exchange-driven chiral effects in curvilinear magnetism, Physical Review Letters 123, 077201 (2019).
[5] D. Sheka et al., Nonlocal chiral symmetry breaking in curvilinear magnetic shells, Communications Physics 3, 128 (2020).
[6] O. Pylypovskyi et al., Curvilinear One-Dimensional Antiferromagnets, Nano Letters 20, 8157 (2020).
[7] J. Ge et al., A bimodal soft electronic skin for tactile and touchless interaction in real time, Nature Communications 10, 4405 (2019).
[8] G. S. Canon Bermudez et al., Electronic-skin compasses for geomagnetic field driven artificial magnetoception and interactive electronics, Nature Electronics 1, 589 (2018).

Extending 2D structures into 3D space has become a general trend in multiple disciplines, including electronics, photonics, plasmonics, superconductivity and magnetism [1,2,3]. This approach provides means to modify conventional or to launch novel functionalities by tailoring curvature and 3D shape of magnetic thin films and nanowires [3]. In this talk, we will address fundamentals of curvature-induced effects and discuss experimental realisations of geometrically curved low-dimensional architectures and their characterization, which among others resulted in the experimental confirmation of the exchange-driven chiral effects [4]. Geometrically curved magnetic thin films are interesting not only fundamentally. They are the key component of mechanically flexible magnetic field sensors. We will briefly outline activities on shapeable magnetoelectronics [5,6], which includes flexible, stretchable and printable magnetic field sensors for the realisation of human-machine interfaces [7,8], interactive electronics for virtual [9] and augmented [10] reality applications and soft robotics [11] to mention just a few. Very recently, self-healable magnetic field sensors for interactive printed electronics were reported [12]. The presence of the geometrical curvature in a magnetic thin film influences pinning of magnetic domain walls and in this respect it affects the sensitivity of mechanically flexible magnetic field sensors. This is an intimate link between the fundamental topic of curvilinear magnetism and application-oriented activities on shapeable magnetoelectronics. This link will be discussed in the presentation as well.

References
1. P. Gentile et al., Electronic materials with nanoscale curved geometries. Nature Electronics (Review) 5, 551 (2022).
2. D. Makarov et al., Curvilinear micromagnetism: from fundamentals to applications. (Springer, Zurich (2022)). https://link.springer.com/book/10.1007/978-3-031-09086-8
3. D. Makarov et al., New Dimension in Magnetism and Superconductivity: 3D and Curvilinear Nanoarchitectures. Advanced Materials (Review) 34, 2101758 (2022).
4. O. Volkov et al., Experimental observation of exchange-driven chiral effects in curvilinear magnetism. Physical Review Letters 123, 077201 (2019).
5. D. Makarov et al., Shapeable Magnetoelectronics. Appl. Phys. Rev. 3, 011101 (2016).
6. G. S. Canon Bermudez et al., Magnetosensitive e-skins for interactive devices. Advanced Functional Materials (Review) 31, 2007788 (2021).
7. P. Makushko et al., Flexible Magnetoreceptor with Tunable Intrinsic Logic for On-Skin Skin Touchless Human-Machine Interfaces. Adv. Funct. Mater. 31, 2101089 (2021).
8. J. Ge et al., A bimodal soft electronic skin for tactile and touchless interaction in real time. Nature Communications 10, 4405 (2019).
9. G. S. Canon Bermudez et al., Electronic-skin compasses for geomagnetic field driven artificial magnetoception and interactive electronics. Nature Electronics 1, 589 (2018).
10. G. S. Canon Bermudez et al., Magnetosensitive e-skins with directional perception for augmented reality. Science Advances 4, eaao2623 (2018).
11. M. Ha et al., Reconfigurable Magnetic Origami Actuators with On-Board Sensing for Guided Assembly. Advanced Materials 33, 2008751 (2021).
12. R. Xu et al., Self-healable printed magnetic field sensors using alternating magnetic fields. Nature Communications 13, 6587 (2022).

In this tutorial, we will review recent activities in the field of curvilinear magnetism. In particular, fundamental aspects on controling anisotropy and chiral responses via geometrical curvature will be discussed. Furthermore, activities on the realization and application scenarios of flexible, stretchable and printed magnetic field sensors will be presented.

The programmed cell death ligand (PD-L1) is expressed on a number of different tumor entities and inhibits the immune response through binding to PD-1 on T-cells. Immune checkpoint inhibitors (ICI) prevent this blockade and thus can reactivate an immune response. However, only about 30% of the patients respond to an ICI monotherapy. Therefore, clinicians are in need for a non-invasive PET/SPECT radioligand for patient stratification and therapy monitoring.

Based on the structures of non-peptidic PD-L1 inhibitors, six different radiotracers were synthesized and radiolabelled with [64Cu]Cu2+ (HZDR, 30 MeV TR-FLEX cyclotron). Binding affinities were determined on PC3 cells stably overexpressing hPD-L1. For in vivo studies, qualitative PET/CT imaging experiments (nanoSCAN PET/CT, Mediso) were performed in NMRI-FoxN1-nude mice bearing PC3-hPD-L1 and mock xenograted tumors.

Two PD-L1 inhibitors were modified with strongly water-soluble acid groups, hydrophilic linker units and a NODAGA-chelator resulting in six different radioligands. The log(D) values of the copper-64 labelled radiotracers were between –3.17 and –4.15 and binding affinities ranged between 80.5 and 533 nM. Depending on the number and the pattern of sulfonate and phosphonate groups, in vivo experiments showed drastically different pharmacokinetic profiles. The radiotracer with one sulfonate and phosphonate group and the most hydrophobic linker exhibited a short circulation time, renal clearance, good tumor uptake (SUVmax = 3.5) and a distinct contrast between the hPD-L1 and the mock tumor.

In conclusion one PD-L1 radiotracer showed a promising pharmacokinetic profile, which is currently further modified to improve the binding affinity and tumor uptake.

Aim:

The programmed cell death ligand 1 (PD-L1) is overexpressed by various cancers, resulting in a downregulation of the local immune response and therefore enabling further tumor growth.[1] Immune checkpoint inhibitors (ICIs) can reactivate the immune system, however, only 30% of the patients respond to an ICI monotherapy.[2] Since PD-L1 is heterogeneously expressed within and across tumor sites, there is an urgent clinical need for non-invasive diagnostic tools to support the therapeutic decision process. Small molecule-based radiotracers for noninvasive molecular PD-L1 imaging offer improved tissue penetration, fast blood clearance and low immunogenicity over radiolabeled antibodies.

Methods:

Based on a published small molecule PD-L1 inhibitor, 10 different radioligands were synthesized and radiolabeled with copper-64 (HZDR, 30 MeV TR-FLEX cyclotron). Binding affinities were determined on PC3 cells stably overexpressing human PD-L1. For in vivo evaluation, qualitative PET/CT imaging (nanoSCAN PET/CT, Mediso) was performed in NMRI-FoxN1-nude mice bearing PC3-hPD-L1 xenografted tumors.

Results:

Modification of the PD-L1 binding motif with strongly water-solubilizing sulfonate and phosphonate groups, different linker units and a NODAGA-chelator in 21-25 organic synthesis steps (12-13 longest linear sequence) yielded 10 different ligands [3]. The 64Cu-labelled radiotracers exhibited logD values between -3.17 and -4.15 for six ligands of the first series, with dissociation constants (Kd) between 80.5 and 532.8 nM, as determined by saturation binding assays. Depending on the number and pattern of sulfonate and phosphonate groups, the in vivo experiments showed drastically different pharmacokinetic profiles: Compounds bearing a less hydrophilic linker showed improved tumor uptake. Three sulfonates resulted in increased blood circulation times of up to 24 h due to albumin binding increased renal clearance but also low tumor uptake (SUVmax = 1.4). Substitution of one sulfonate with a phosphonate reduced the circulation time to two hours, however, accompanied by mainly hepatobiliary clearance. To achieve predominant renal clearance, a second series of four compounds bearing two phosphonate and one sulfonate groups in the solubilizer unit and larger halogens at the central aryl core for improved tumor uptake were synthesized and are currently tested in vivo.

Conclusion:

Sulfonate groups in the PD-L1 tracers increased circulation times along with renal clearance, while tracers with one phosphonate group reduced the blood circulation time but lead to a more hepatobiliary clearance. Structural modifications to increase the binding affinity and improve tumor uptake are currently ongoing.

References:

[1] M. A. Postow, M. K. Callahan, J. D. Wolchok, J. Clin. Oncol. 2015, 33, 1974-1982.
[2] S. L. Topalian, C. G. Drake, D. M. Pardoll, Cancer Cell 2015, 27, 450-461.
[3] Stadlbauer S., Krutzek F., Kopka K. EP21212444.0, December 6th 2021.

Aim/Introduction
The programmed cell death ligand 1 (PD-L1) is expressed by several cancer types and leads to a downregulation of the local immune response, therefore enabling tumour cells to evade the immune response.[1] So-called immune checkpoint inhibitors (ICI) are able to reactivate the immune system, however, only 30% of the patients respond to an ICI monotherapy.[2] Since PD-L1 is heterogeneously expressed within and across tumour sites, there is an urgent clinical need for a diagnostic, non-invasive imaging probe to support therapy decision. Small molecule-based radiotracers for PD-L1 PET or SPECT imaging fulfil these requirements due to their fast clearance, low risk of side effects and highly sensitive imaging at the molecular level.[3]

Materials & Methods
Based on a published small molecule PD-L1 inhibitor, six different radioligands were synthesized and radiolabelled with copper-64 (HZDR, 30 MeV TR-FLEX cyclotron). Binding affinities were determined on PC3 cells stably overexpressing human PD-L1 which were kindly provided by the Department of Radioimmunology. For in vivo evaluation, qualitative PET/CT imaging experiments (nanoSCAN PET/CT scanner, Mediso) were performed in NMRI-FoxN1-nude mice bearing PC3-hPD-L1 xenografted tumours.

Results
We designed six radioligands by modifying the PD-L1 binding motif with strongly water-solubilizing sulfonate and phosphonate groups, hydrophilic linker units and a NODAGA-chelator in 21 – 25 organic synthesis steps (12-13 longest linear sequence).[4] The copper-64 labelled radiotracers exhibited log(D) values between –3.17 and –4.15. Binding affinities (Kd) were between 80.5 and 532.8 nmol/L. Depending on the number and pattern of sulfonate and phosphonate groups, the in vivo experiments showed drastically different pharmacokinetic profiles: The radiotracer containing three sulfonates showed long circulation times of 24 h due to albumin binding, renal clearance but low tumour uptake (SUVmax = 1.4). Substitution of one sulfonate with a phosphonate improved tumour uptake (SUVmax = 3.1), reduced the circulation time to two hours but showed a more hepatobiliary clearance. The less hydrophilic radiotracer in this series with a Kd of 82.4 ± 7.42 nM, bearing one sulfonate and one phosphonate showed the most favourable pharmacokinetic profile with a short circulation time, renal clearance and an increased tumour uptake (SUVmax = 3.5).

Conclusions
The radiotracer bearing one sulfonate and one phosphonate group exhibited the best pharmacokinetic profile. This radioligand will undergo further structural modifications to increase the binding affinity and improve the tumour uptake.

References
[1] M. A. Postow, M. K. Callahan, J. D. Wolchok, J. Clin. Oncol. 2015, 33, 1974-1982.
[2] S. L. Topalian, C. G. Drake, D. M. Pardoll, Cancer Cell 2015, 27, 450-461.
[3] S. Chatterjee, W. G. Lesniak, S. Nimmagadda., Mol. Imaging 2017, 16, 1-5.
[4] S. Stadlbauer, F. Krutzek, K. Kopka, EP21212444.0, 2021.

Ziel: Der Programmed Cell Death Ligand 1 (PD-L1) ist auf verschiedenen Tumorentitäten überexprimiert und hemmt die Immunantwort durch Bindung an PD-1 auf T-Zellen. Immuncheckpoint-Inhibitoren können diese Blockade aufbrechen und die Immunantwort reaktivieren. Da nur ca. 30% der Patienten auf eine solche Therapie ansprechen, besteht klinisch ein dringender Bedarf an einem nicht-invasiven PET/SPECT-Radioliganden, um die Ansprechrate der Patienten auf diese Therapie abzuschätzen.[1]

Methoden: Basierend auf den Strukturen von nicht-peptidischen PD-L1-Inhibitoren, wurden sechs verschiedene Radioliganden synthetisiert und mit [64Cu]Cu2+ markiert (HZDR, 30 MeV TR-FLEX-Zyklotron). Bindungsaffinitäten wurden auf stabil hPD-L1 überexprimierenden PC3 Zellen bestimmt. In vivo wurden qualitative PET/CT-Bilder (nanoSCAN PET/CT, Mediso) an NMRI-FoxN1-Nacktmäusen mit PC3-hPD-L1- und mock-Tumoren aufgenommen.

Ergebnisse:

Zwei PD-L1-Inhibitoren wurden synthetisch mit stark wasserlöslichen Säuregruppen, hydrophilen Linkern und NODAGA modifiziert (Abb. 1a).[2] Die LogD7.4-Werte der [64Cu]Cu-Radioliganden lagen zwischen –3,17 und –4,15 und die Bindungsaffinitäten (KD) zwischen 80,5 und 532,8 nM. Abhängig von der Zahl und dem Substitutionsmuster der Sulfon- und Phosphonsäuregruppen, zeigte sich in vivo eine stark unterschiedliche Pharmakokinetik. Der Radioligand mit R1 = SO2Me, R2 = PO3H2 und n = 0 zeigte in vivo eine kurze Zirkulationszeit, renale Ausscheidung, gute Tumoraufnahme (SUVmax = 3.5) und einen deutlichen Kontrast zwischen hPD-L1- und mock-Tumor (Abb. 1b).
Schlussfolgerungen: Der PD-L1-Radioligand mit je einer Sulfon- und Phosphonsäuregruppe wies das beste pharmakokinetische Profil auf. Um die Bindungsaffinität und die Tumoraufnahme zu verbessern, wird das Leitmotiv derzeit weiter modifiziert.

Referenzen:

[1] Postow M. A., Callahan M. K., Wolchok J. D. J. Clin. Oncol. 2015, 33, 1974-1982.
[2] Stadlbauer S., Krutzek F., Kopka K. EP21212444.0, 2021.

Motivated by recent experimental initiatives, such as at the
Helmholtz International Beamline for Extreme Fields (HIBEF)
at the European X-ray Free Electron Laser (XFEL), we calculate
the birefringent scattering of x-rays at the combined field of
two optical (or near-optical) lasers and compare various scenarios.
%
In order to facilitate an experimental detection of quantum vacuum diffraction and
birefringence, special emphasis is placed on scenarios where the initial
and final x-ray photons differ not just in polarization, but also in
propagation direction (corresponding to scattering angles in the mrad regime)
and possibly energy.

In this article we consider resummed expressions for the heat-kernel's
trace of a Laplace operator, the latter including a potential and imposing Dirichlet semitransparent boundary conditions on a surface of codimension one in flat space.
We obtain resummed expressions that correspond to the first and second order expansion of the heat-kernel in powers of the potential.
We show how to apply these results to obtain the bulk and surface form factors of a scalar quantum field theory in $d=4$ with a Yukawa coupling to a background.
A characterization of the form factors in terms of pseudo-differential operators is given.

In this work we discuss the deformed relativistic wave equations, namely the Klein--Gordon and Dirac equations in a Doubly Special Relativity scenario.
We employ what we call a geometric approach, based on the geometry of a curved momentum space, which should be seen as complementary to the more spread algebraic one.
In this frame we are able to rederive well-known algebraic expressions, as well as to treat yet unresolved issues, to wit, the explicit relation between both equations, the discrete symmetries for Dirac particles, the fate of covariance, and the formal definition of a Hilbert space for the Klein--Gordon case.

Particle therapy (PT) used for cancer treatment can spare healthy tissue and reduce treatment toxicity. However, full exploitation of the dosimetric advantages of PT is not yet possible due to range uncertainties, warranting development of range-monitoring techniques. This study proposes a novel range-monitoring technique introducing the yet unexplored concept of simultaneous detection and imaging of fast neutrons and prompt-gamma rays produced in beam-tissue interactions. A quasi-monolithic organic detector array is proposed, and its feasibility for detecting range shifts in the context of proton therapy is explored through Monte Carlo simulations of realistic patient models. The results indicate that range shifts of 1 mm can be detected at relatively low proton intensities (6 million/spot) when spatial information obtained through imaging of both particle species are used simultaneously. This study lays the foundation for multi-particle detection and imaging systems in the context range verification in PT.

We show how to use the worldline-instanton formalism to calculate the momentum spectrum of the electron-positron pairs produced by an electric field that depends on both space and time. Using the LSZ reduction formula with a worldline representation for the propagator in a spacetime field, we make use of the saddle-point method to obtain a semiclassical approximation of the pair-production spectrum. In order to check the final result, we integrate the spectrum and compare with the results obtained using a previous instanton method for the imaginary part of the effective action.

This work presents first insights into the dynamics of free-surface release clouds from dynamically compressed polystyrene and pyrolytic graphite at pressures up to 200 GPa, where they transform into diamond or lonsdaleite, respectively. These ejecta clouds are released into either vacuum or various types of catcher systems, and are monitored with high-speed recordings (frame rates up to 10 MHz). Molecular dynamics simulations are used to give insights to the rate of diamond preservation throughout the free expansion and the catcher impact process, highlighting the challenges of diamond retrieval. Raman spectroscopy data show graphitic signatures on a catcher plate confirming that the shock-compressed PS is transformed. First electron microscopy analyses of solid catcher plates yield an outstanding number of different spherical-like objects in the size range between ten(s) up to hundreds of nanometres, which are one type of two potential diamond candidates identified. The origin of some objects can unambiguously be assigned, while the history of others remains speculative.

Ultrasonication using low frequencies of sound can increase cell organogenesis, which is beneficial for various industrial applications. This study demonstrates a novel approach of integrated phycoremediation and ultrasonication-irradiation treatment (iPUT) used for improving the degradation of sulfonamide antibiotics via a cumulative effect of combined treatments. Variable ultrasonication treatment (UT) (20 %-2 min to 40 %-10 min) was given to a model microalga, Chlamydomonas mexicana in two ways, 1) single ultrasonic treatment (SUT) and 2) multiple-intermittent ultrasonic treatments (IUT). The microalgal growth was slightly affected by SUT, while it significantly inhibited by IUT. The removal of sulfacetamide and sulfapyridine was significantly improved by >1.7-fold and >1.95-fold at 20 % of SUT and IUT treatment, respectively, compared to control. In the case of sulfamethazine, the SUT showed maximum removal (33.5 %) at 20 %, whereas IUT could achieve 27.5 % removal at the same ultrasonication conditions compared to 9.5 % removal in control. The IUT accelerated the degradation of sulfamethoxazole and sulfadimethoxine more than SUT showing a 9- fold and 12- fold increase in the removal of sulfamethoxazole and sulfadimethoxine with 20 % and 40 % treatments, respectively. The changes in microalgal cell morphology due to ultrasonication treatment were the main cause of enforced uptake and subsequent degradation of these ECs.

Fenoprofen is a widely used nonsteroidal anti-inflammatory drug (NSAID) against rheumatoid arthritis, degenerative joint disease, ankylosing spondylitis and gout. Like other NSAIDs, fenoprofen inhibits the synthesis of prostaglandins by blocking both cyclooxygenase (COX) isoforms, COX-1 the “house-keeping” enzyme and COX-2 the induced isoform from pathological stimuli. Unselective inhibition of both COX isoforms results in many side effects, but off-target effects have also been reported. The steric modifications of the drugs could afford the desired COX-2 selectivity. Furthermore, NSAIDs have shown promising cytotoxic properties. The structural modification of fenoprofen using bulky dicarba-closo-dodecaborane(12) (carborane) clusters and the biological evaluation of the carborane analogues for COX inhibition and antitumor potential showed that the carborane analogues exhibit stronger antitumor potential compared to their respective aryl-based compounds.

Functional connectivity plays an essential role in modern neuroscience. The modality sheds light on the brain's functional and structural aspects, including mechanisms behind multiple pathologies. One such pathology is schizophrenia which is often followed by auditory verbal hallucinations. The latter is commonly studied by observing functional connectivity during speech processing. In this work, we have made a step toward an in-depth examination of functional connectivity during a dichotic listening task via deep learning for three groups of people: schizophrenia patients with and without auditory verbal hallucinations and healthy controls. We propose a graph neural network-based framework within which we represent EEG data as signals in the graph domain. The framework allows one to 1) predict a brain mental disorder based on EEG recording, 2) differentiate the listening state from the resting state for each group and 3) recognize characteristic task-depending connectivity. Experimental results show that the proposed model can differentiate between the above groups with state-of-the-art performance. Besides, it provides a researcher with meaningful information regarding each group's functional connectivity, which we validated on the current domain knowledge.

Objectives: This study investigates the ability of the open-source treatment planning system (TPS) matRad to generate accurate intensity-modulated proton therapy (IMPT) plans for a real-world horizontal proton pencil beam scanning (PBS) research beamline. Initial validation for IMPT dose delivery is addressed by comparing simulation data with measurements.

Materials and Methods: The PBS delivery was modelled with Monte Carlo (MC) simulations using TOPAS version 3.7. First, base data measurements were performed to develop a proton beam model (BM) for the OncoRay horizontal PBS research beamline. Data include spot sizes in air, depth-dose profiles and a monitor unit (MU) calibration. BM data was then integrated into matRad to build base-data for IMPT treatment planning.
For initial validation of dose delivery, simple 3D box plans were generated at three depths (target beam entrance at 10, 15 and 20cm) covering energies from 115 to 195MeV. Absolute and relative doses were measured using a Semiflex 31013 ionization chamber (PTW Dosimetry) and a scintillation detector (Lynx®, IBA Dosimetry), respectively.

Results: Simulations and dose measurements showed good agreement of relative dose profiles at depths of 14.75, 18.05 and 24.05cm for field sizes of 5 x 5, 10 x 10 and 15 x 15cm2. The overall absolute difference of measured and planned target doses was ~1% (see Table 1).

Conclusions: Accurate MC-based BM was calculated and integrated into the TPS toolkit matRad. Absolute and relative measurements were in agreement with planned IMPT data. Full validation will be completed next months, including absolute and relative dosimetry of patient plans.

The Electron Linac for beams with high Brilliance and low Emittance (ELBE) at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) is operated using the SCADA system WinCC by Siemens. The majority of ELBE systems is connected to WinCC via industrial Ethernet and proprietary S7 communication. However, in recent years there was a demand to provide a more open and platform independent access to ELBE machine data. The Industry 4.0 standard OPC UA has been chosen to implement such an interface. We will show how we use OPC UA as a common communication layer between industrial and scientific instruments as well as proprietary and open source control system software. Our solution makes use of commercially available hard- and software, namely Simatic STEP7, Simatic WinCC v7.x by Siemens and IBH Link UA by IBHsoftec. Combining these products we designed an OPC UA based user data interface, which features encrypted communication and access control from the control room via WinCC. It is available for internal use, e.g. for feedbacks, and external use, e.g to log ELBE data along with experiment data or to provide data to ELBE operators for machine optimizations.

Ultra-high-intensity laser pulse interactions with solid density targets are of central importance for
modern accelerator physics, Inertial Confinement Fusion(ICF) and astrophysics. In order to meet
the requirements of real-world applications, a deeper understanding of the underlying plasma
dynamics, including plasma instabilities and acceleration mechanisms, is needed. X-ray radiation
plays a substantial role in plasma physics, either as an integral part of a physical system itself or
as a useful diagnostic, hence it should be included in computational models.
Therefore, we bring a Monte Carlo based X-ray radiation transport module into our Particle In
Cell simulation framework PIConGPU. It allows, among others, for Thompson scattering, e.g. for
small-angle X-ray scattering (SAXS), and Faraday effect calculation for X-ray polarimetry - as
online, in-situ diagnostics.

The small modular reactor (SMR) NuScale is modelled by Helmholtz-Zentrum Dresden Rossendorf (HZDR) in the framework of the EU H2020 McSAFER. NuScale is a SMR of integral pressurized type operated with light water driven by natural circulation. This work summarizes the reactor modelling approach with the system code ATHLET and presents the results from a boron dilution sequence, based on the Design Certification Application (DCA). Steady-state and transient results show agreement, thereby demonstrating ATHLET strong simulation capabilities on complex transients applied to SMR designs. The results show a decrease in core nominal boron concentration and subsequent reactivity insertion by the boron feedback. The reactor is tripped upon “high pressurizer pressure” setpoint and the actuation of the DHRS leads to a long term safe shutdown condition.

Research and development of small modular reactors (SMRs) is receiving increasing attention by several countries and organizations due to flexibility, cost reduction and advanced safety features. The SMR NuScale is modelled by Helmholtz-Zentrum Dresden Rossendorf (HZDR) in the framework of the EU H2020 McSAFER project. NuScale is a SMR of integral pressurized water reactor (PWR) type, operated with light water driven by natural circulation in all operation modes. This work summarizes the modelling approach of a thermohydraulic model of NuScale SMR with the system code ATHLET, that includes a state-of-the-art 3-D reactor pressure vessel (RPV). The paper presents results and discussion from a boron dilution sequence at hot full power based on the Design Certification Application (DCA) report. Simulation results show agreement at steady-state and transient calculation, thereby demonstrating ATHLET strong simulation capabilities on complex sequences in SMR designs. The results show a decrease in core nominal boron concentration and subsequent reactivity insertion by boron feedback. The reactor is tripped upon “high pressurizer pressure” function by the insertion of the control rod banks. The actuation of the decay heat removal system (DHRS) provides long term core cooling to bring the reactor to a safe shutdown condition and preservation of shutdown margin is met during the simulation thereby complying with acceptance criterion.

The micro particle separation of calcium minerals by means of selective froth flotation is a challenging task. The difficulty arises because of the similar surface properties of the minerals, and thereby similar responses to various known families of flotation collectors (selectively adsorbing surfactants). Within the scope of this study colloidal silica is investigated as a potential selectively interacting nanoparticle depressant in the flotation process of calcium minerals. The effect of the colloidal silica and its interactions with the reagent system were investigated by varying its modification and specific surface area/particle size. Single-mineral microflotation of scheelite (calcium tungstate), fluorite (calcium fluoride), calcite (calcium carbonate) and apatite (calcium fluoro phosphate) were used to determine if colloidal silica would have any effect on the minerals. First results show that colloidal silica prevents calcite from floating while scheelite, fluorite and apatite are unaffected by the presence of the reagent, regardless of the dosage.
First batch flotation tests have shown significant differences between the three modifications in terms of the significant effect on the selectivity. The same finding was made when varying the specific surface area/particle size. Further surface chemistry studies will provide more insight on the depression mechanisms of colloidal silica in calcium mineral flotation.

Die Aufbereitung komplexer Erze durch neue Verfahren oder durch den Einsatz neuer oder ungewöhnlicher Reagenzien in der Flotation kann Probleme mit sich bringen. Insbesondere wenn neue Flotationsreagenzien verwendet werden oder ein kompliziertes Fließschema erforderlich ist, lassen sich die Auswirkungen auf den Betrieb anhand von Laborversuchen nicht ausreichend bestimmen. Es ist daher ratsam, Erze im kontinuierlichen Betrieb einer Pilotanlage zu untersuchen, bevor eine Aufbereitungsanlage im industriellen Maßstab installiert wird. Üblicherweise sind konventionelle Pilotanlagen, in denen 100 bis 1.000 kg/h Erzproben verarbeitet werden, eingesetzt, um die Machbarkeit des Verfahrens vor dem industriellen Maßstab zu belegen. Daraus ergeben sich detaillierte technische Daten, die für die Entwicklung eines endgültigen Prozessablaufs und die Dimensionierung der Ausrüstung erforderlich sind. Allerdings sind diese Pilotanlagen teuer in der Errichtung und im Betrieb. Als Alternative entwickelte das Falconbridge Technology Centre (FTC) 1999 in Zusammenarbeit mit Canadian Process Technologies Inc. eine Mini-Pilotanlage. Die FTC-Mini-Pilotanlage hat zunehmend an Bedeutung gewonnen, vor allem wegen der geringeren Probenmenge im Vergleich zur konventionellen Pilotanlage. In diesem Beitrag wird anhand der Ergebnisse der Batch-Flotation einer Fallstudie der Einsatz der FTC-Mini-Pilotanlage Optimierung des Flotationsprozesses von Scheelit unter Verwendung ein neuer Drücker aufgezeigt. Die Vorteile und Grenzen des Betriebs der Mini-Pilotanlage werden erörtert und die Ergebnisse im industriellen Maßstab validiert.

The interaction of near-critical plasmas with ultra-intense laser pulses presents a promising approach to enable the development of very compact sources for high-energetic ions. However, current records for maximum proton energies are still below the required values for many applications, and challenges such as stability and spectral control remain unsolved to this day. In particular, significant effort per experiment and a high-dimensional design space renders naive sampling approaches ineffective. Furthermore, due to the strong nonlinearities of the underlying laser-plasma physics, synthetic observations by means of particle-in-cell (PIC) simulations are computationally very costly, and the maximum distance between two sampling points is strongly limited as well. Consequently, in order to build useful surrogate models for future data generation and experimental understanding and control, a combination of highly optimized simulation codes (we employ PIConGPU), powerful data-based methods, such as artificial neural networks, and modern sampling approaches are essential. Specifically, we employ invertible neural networks for bidirectional learning of parameter and observables, and autoencoder to reduce intermediate field data to a lower-dimensional latent representation.

The interaction of overdense and/or near-critical plasmas with ultra-intense laser pulses presents a promising approach to enable the development of very compact sources for high-energetic ions. However, current records for maximum proton energies are still below the required values for many applications, and challenges such as stability and spectral control remain unsolved to this day. In particular, significant effort per experiment and a high-dimensional design space renders naive sampling approaches ineffective. Furthermore, due to the strong nonlinearities of the underlying laser-plasma physics, synthetic observations by means of particle-in-cell (PIC) simulations are computationally very costly, and the maximum distance between two sampling points is strongly limited as well. Consequently, in order to build useful surrogate models for future data generation and experimental understanding and control, a combination of highly optimized simulation codes (we employ PIConGPU), powerful data-based methods, such as artificial neural networks, and modern sampling approaches are essential. Specifically, we employ invertible neural networks for bidirectional learning of parameter and observables, and autoencoder to reduce intermediate field data to a lower-dimensional latent representation.

While the interaction of ultra-intense ultra-short laser pulseswith near- and overcritical plasmas cannot be directly observed, experimentally accessible quantities (observables) often only indirectly giveinformation about the underlying plasma dynamics. Furthermore, theinformation provided by observables is incomplete, making the inverseproblem highly ambiguous. Therefore, in order to infer plasma dynamicsas well as experimental parameter, the full distribution over parameters given an observation needs to considered, requiring that models areflexible and account for the information lost in the forward process. Invertible Neural Networks (INNs) have been designed to efficiently modelboth the forward and inverse process, providing the full conditional posterior given a specific measurement. In this work, we benchmark INNsand standard statistical methods on synthetic electron spectra. First, weprovide experimental results with respect to the acceptance rate, whereour results show increases in acceptance rates up to a factor of 10. Additionally, we show that this increased acceptance rate also results in anincreased speed-up for INNs to the same extent. Lastly, we propose acomposite algorithm that utilizes INNs and promises low runtimes whilepreserving high accuracy.

Geometric curvature in nanowires and shells is established as a powerful method to tailor chiral and anisotropic responses in ferromagnets. Here, we apply the framework of curvilinear magnetism to antiferromagnetic (AFM) systems. First, we consider curvilinear AFM spin chains with the nearest-neighbor exchange and hard axis of anisotropy along the chain. Their shape is characterized by curvature K and torsion T. These functions determine the direction of the geometry-driven Dzyaloshinskii vector D and easy axis of anisotropy stemming from exchange. Furthermore, the broken translation symmetry in AFM chains arranged along space curves leads to the weakly ferromagnetic response proportional to K and T even if the magnetic texture is locally homogeneous. While the plane AFM chains possess the uniform ground state, the geometry-induced anisotropy axes and chiral response become pronounceable approaching spin-flop phase. Namely, in AFM rings the non-zero D leads to the appearance of canted state for the large enough K, while spin-flop phase splits in two phases by the value of K with different topology of the order parameter. For 3D chiral AFMs, the sample boundaries alter the width and produce an additional twist of domain walls and skyrmions near the surface.

O. V. Pylypovskyi, D. Y. Kononenko, K. V. Yershov et al, Nano Lett. 20, 8157 (2020)
O. V. Pylypovskyi, Y. A. Borysenko, J. Fassbender et al, Appl. Phys. Lett. 118, 182405 (2021)
O. V. Pylypovskyi, A. V. Tomilo, D. D. Sheka et al, Phys. Rev. B 103, 134413 (2021)
Y. A. Borysenko, D. D. Sheka, J. Fassbender et al, ArXiv:2208.02510 (2022)

Cr2O3 is the only known uniaxial antiferromagnetic material that is also magnetoelectric at room temperature. This renders Cr2O3 a technologically relevant playground for the realisation of different device ideas for prospective antiferromagnetic spintronics. We discovered the presence of flexomagnetic effects in Cr2O3, which come about due to the impact of a strain gradient on the thermodynamic properties, namely on the Neel temperature. By combining magnetotransport and Nitrogen Vacancy magnetometry characterizations, we experimentally determine the presence of the gradient of the Neel temperature in a 50-nm-thick Cr2O3 thin film and quantify that the magnetic moment, generated by this new effect, can be as high as 15 μB/nm2. Furthermore, due to good oxide-oxide heteroepitaxy and respective compressive strain, the Neel temperature in Cr2O3 thin films can be enhanced persistently up to 100degC, which is 60degC higher than the bulk transition temperature. The emergent flexomagnetism-driven ferromagnetic order parameter in antiferromagnetic thin films offers more flexibility in the design of spintronic and magnonic devices and can be of relevance for other antiferromagnetic materials.

P. Makushko, T. Kosub, O. V. Pylypovskyi et al., Nature Communications (2022), in press.

Infrared spectroscopy studies on pentacene single crystals have been performed in the frequency range of 12 meV to 3 eV in reflection and transmission configurations as a function of temperature, down to 10 K. Our results reveal the dominant contributions of the excitonic bands at the absorption edge. The singlet transitions of the Frenkel excitons at 1.78 eV with 130 meV Davydov splitting have been identified. An additional excitonic feature observed at 1.83 eV can be assigned to a charge-transfer type exciton evidenced by the strong vibrational anomalies. On the other hand, the strong feature seen at 1.67 eV does not couple to the vibrational modes suggests that electronic origin in nature.