Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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32221 Publications
Filling the 5-10 THz gap using Ge-based photoconductive emitter
Singh, A.; Pashkin, A.; Winnerl, S.; Helm, M.; Schneider, H.;
We present here a Ge photoconductive emitter generating THz pulses with a spectrum up to 13 THz free from any absorption lines if detected with a proper detector. Ge is a centrosymmetric non-polar crystal and hence its phonons are not IR-active. Therefore, Ge shows high and almost uniform transmission of THz radiation up to frequencies more than 20 THz besides a weak two-phonon absorption band near 10 THz [1]. Ge also has high carrier mobility required for efficient THz emission. Bowtie-like electrode structures with 10 µm electrode gap are deposited on a pure Ge substrate to fabricate the photoconductive THz emitter. The carrier lifetime in pure Ge is of the order of µs, thus it requires a pump laser with pulse repetition rate less than a MHz. A Ti:sapphire amplified laser system operating at 800 nm wavelength, 250 kHz repetition rate and ~ 65 fs pulse width is used to pump the Ge emitter and probe the radiated THz pulse using the electro optic sampling technique.
[1] A. Singh, A. Pashkin, S. Winnerl, M. Helm and H. Schneider, “Gapless broadband terahertz emission from a germanium photoconductive emitter”, ACS Photonics 5, 2718−2723 (2018).
Keywords: terahertz emitter, germanium
  • Lecture (Conference)
    Conference on Lasers and Electro-Optics (CLEO), 06.-10.05.2019, San José, USA
  • Contribution to proceedings
    Conference on Lasers and Electro-Optics (CLEO), 05.-10.05.2019, San José, USA
    Conference on Lasers and Electro-Optics OSA Technical Digest (Optical Society of America, 2019), 345 E 47TH ST, NEW YORK, NY 10017 USA: IEEE, 978-1-943580-57-6
    DOI: 10.1364/CLEO_SI.2019.STu3F.3

Publ.-Id: 29688 - Permalink


Scalable Large-Area Terahertz Emitters with Improved Electrode Design
Singh, A.; Welsch, M.; Winnerl, S.; Helm, M.; Schneider, H.;
We have systematically investigated the influence of electrode parameters on the emission efficiency of scalable large-area photoconductive THz emitters. We identify two contributions to THz emission, originating from the photoexcited carriers in the semiconductor and from the interdigitated metal electrodes acting as dipole antennae, respectively. Both contributions are optimized for maximum THz emission efficiency by varying the gap and stripe widths of the interdigitated metal electrodes. Using this approach we achieve a 50% improvement of the radiated THz electric field as compared to electrodes with equal stripe and gap widths.
Keywords: terahertz emitter, large-area emitter
  • Lecture (Conference)
    The 44th International Conference on Infrared, Millimeter and Terahertz Waves (IRMMW-THz'2019), 01.-06.09.2019, Paris, France

Publ.-Id: 29687 - Permalink


Linear and nonlinear THz spectroscopy at HZDR
Schneider, H.;
In this talk I have presented some experiments on linear and nonlinear THz spectroscopy at HZDR
Keywords: terahertz spectroscopy, free-electron laser
  • Lecture (others)
    Seminarvortrag, Harbin Institute of Technology, 22.07.2019, Harbin, China

Publ.-Id: 29686 - Permalink


Nonlinear dressing of excitons, polaritons, and intersubband transitions using a terahertz free-electron laser
Schneider, H.;
This talk reports some recent experiments making use of intense, spectrally narrow terahertz(THz) pulses from a free-electron laser (FEL) as a unique tool for nonlinear dressing of elementary transitions in the THz range.
Keywords: terahertz, free-electron laser, exciton, dressed state
  • Lecture (Conference)
    VII International Conference “Frontiers of Nonlinear Physics”, 28.06.-04.07.2019, Nizhny Novgorod, Russian Federation

Publ.-Id: 29685 - Permalink


Nonlinear terahertz spectroscopy of III-V semiconductor quantum wires and quantum wells using a free-electron laser
Schneider, H.;
This talk reviews some recent experiments using intense narrow-band terahertz (THz) fields from a free-electron laser for exploring electronic properties in semiconductor nanostructures. In n-type III-V semiconductor nanowires (NW), intense THz excitation causes a nonlinear plasmonic response, which manifests itself by a strong red shift of the plasma resonance. This nonlinearity is investigated by scattering-type scanning near-field infrared microscopy. For the NWs under study, a spectrally sharp plasma resonance, located at a photon energy of 125 meV for weak excitation, undergoes a power-dependent redshift to about 95 meV. We attribute this nonlinearity to an increase of the effective mass caused by transient carrier heating. In another experiment, we use strong narrowband THz excitation to dress the 2-3 intersubband transition in a 40 nm wide GaAs quantum well (QW). The resulting nonlinearities are explored by THz time-domain spectroscopy using synchronous broadband THz probe pulses and electro-optic sampling. Tuning the THz pump beam into resonance with the 2-3 intersubband transition, we have investigated the induced coherent signatures in the vicinity of the 1-2 intersubband transition and found evidence for mixed light-matter states in the QW giving rise to a THz Autler-Townes effect.
The presented work was conducted in collaboration with D. Lang and J. Schmidt (HZDR) who did most experiments, L. Balaghi, E. Dimakis, M. Helm, R. Hübner, D. Lang, A. Pashkin, S. Winnerl (HZDR), and S.C. Kehr, L.M. Eng (TU Dresden, Germany).
Keywords: terahertz, free-electron laser, nonlinear spectroscopy, quantum wire, quantum well
  • Invited lecture (Conferences)
    Light Conference 2019, 16.-18.07.2019, Changchun, China

Publ.-Id: 29684 - Permalink


Layer Rotation-Angle-Dependent Excitonic Absorption in van der Waals Heterostructures Revealed by Electron Energy Loss Spectroscopy
Gogoi, P. K.; Lin, Y.-C.; Senga, R.; Komsa, H.-P.; Liang, S.; Chi, W. D.; Krasheninnikov, A. V.ORC; Li, L.-J.; Breese, M. B. H.; Pennycook, S. J.; Wee, A. T. S.; Suenaga, K.
Heterostructures comprising van der Waals (vdW) stacked transition metal dichalcogenide (TMDC) monolayers are a fascinating class of two-dimensional (2D) materials. The presence of interlayer excitons, where the electron and the hole remain spatially separated in the two layers due to ultrafast charge transfer, is an intriguing feature of these heterostructures. The optoelectronic functionality of 2D heterostructure devices is critically dependent on the relative rotation angle of the layers. However, the role of the relative rotation angle of the constituent layers on intralayer absorption is not clear yet. Here, we investigate MoS2/WSe2 vdW heterostructures using monochromated low-loss electron energy loss (EEL) spectroscopy combined with aberration-corrected scanning transmission electron microscopy and report that momentum conservation is a critical factor in the intralayer absorption of TMDC vdW heterostructures. The evolution of the intralayer excitonic low-loss EEL spectroscopy peak broadenings as a function of the rotation angle reveals that the interlayer charge transfer rate can be about an order of magnitude faster in the aligned (or anti-aligned) case than in the misaligned cases. These results provide a deeper insight into the role of momentum conservation, one of the fundamental principles governing charge transfer dynamics in 2D vdW heterostructures.
Keywords: 2D materials, EELS, TEM, electronic structure calculations

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  • Secondary publication expected from 25.07.2020

Publ.-Id: 29678 - Permalink


Enhanced sensitivity of MoSe2 monolayer for gas adsorption induced by electric field
Ai, W.; Kou, L.; Hu, X.; Wang, Y.; Krasheninnikov, A.; Sun, L.; Shen, X.;
According to recent studies, gas sensors based on MoSe2 have better detection performance than graphene-based sensors, especially for N-based gas molecules, but the reason for that is not fully understood at the microscopic level. Here, we investigate the adsorption of CO, CO2, NH3, NO and NO2 gas molecules on MoSe2 monolayer by the density functional theory calculations. Our results reveal that indeed MoSe2 monolayer is more sensitive to adsorption of N-containing gas molecules than C-containing, which can be attributed to the distinct charge transfer between the gas molecules and MoSe2. The conductance was further calculated using the nonequilibrium Green's function (NEGF) formalism. The reduced conductance was found for NH3 and NO2 adsorbed MoSe2, consistent with the high sensitivity of MoSe2 for NH3 and NO2 molecules in the recent experiments. In addition, the adsorption sensitivity can significantly be improved by an external electric field, which implies the controllable gas detection by MoSe2. The magnetic moments of adsorbed NO and NO2 molecules can also be effectively modulated by the field-sensitive charge transfer. Our results not only give microscopic explanations to the recent experiments, but also suggest using MoSe2 as a promising material for controlled gas sensing.
Keywords: 2D materials , first-principles calculations

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  • Secondary publication expected from 02.08.2020

Publ.-Id: 29677 - Permalink


Fluctuation electron microscopy on silicon amorphized at varying self ion-implantation conditions
Radic, D.; Hilke, S.; Peterlechner, M.; Posselt, M.ORC; Bracht, H.
The medium range order of self-ion-implanted amorphous silicon was studied by variable resolution fluctuation electron microscopy and characterized by the normalized variance V(k, R). The ion-implantation was conducted at sequentially increasing ion energies ranging from 50 keV to 300 keV. Two silicon-on-insulator wafers were amorphized at different implantation conditions. From each material, one as-prepared and one ex situ annealed specimen were chosen for analysis. Fluctuation electron microscopy on cross-sectional prepared samples confirms the presence of medium range order due to the amorphization process. We propose three explanations on how the observed medium range order is created by silicon ion-implantation. Two of these suggestions involve paracrystals formed by thermal spikes while a third explanation assumes a medium range order due to nanoscale regions unaffected by the amorphization. Although the two amorphized silicon samples reveal different local structures due to the ion-implantation process, no difference in the self-diffusion behavior is evident, which demonstrates that self-diffusion mainly proceeds within the amorphous phase.
Keywords: fluctuation electron microscopy; amorphous silicon, ion implantation

Publ.-Id: 29676 - Permalink


Roadmap on photonic, electronic and atomic collision physics: III. Heavy particles: with zero to relativistic speeds
Aumayr, F.; Ueda, K.; Sokell, E.; Schippers, S.; Sadeghpour, H.; Merkt, F.; Gallagher, T. F.; Dunning, F. B.; Scheier, P.; Echt, O.; Kirchner, T.; Fritzsche, S.; Surzhykov, A.; Ma, X.; Rivarola, R.; Fojon, O.; Tribedi, L.; Lamour, E.; Crespo López-Urrutia, J. R.; Litvinov, Y. A.; Shabaev, V.; Cederquist, H.; Zettergren, H.; Schleberger, M.; Wilhelm, R. A.ORC; Azuma, T.; Boduch, P.; Schmidt, H. T.; Stöhlker, T.
We publish three Roadmaps on photonic, electronic and atomic collision physics in order to celebrate the 60th anniversary of the ICPEAC conference. Roadmap III focusses on heavy particles: with zero to relativistic speeds. Modern theoretical and experimental approaches provide detailed insight into the wide range of many-body interactions involving projectiles and targets of varying complexity ranging from simple atoms, through molecules and clusters, complex biomolecules and nanoparticles to surfaces and crystals. These developments have been driven by technological progress and future developments will expand the horizon of the systems that can be studied. This Roadmap aims at looking back along the road, explaining the evolution of the field, and looking forward, collecting nineteen contributions from leading scientists in the field.
Keywords: heavy particles, many-body interactions, clusters, complex biomolecules

Publ.-Id: 29667 - Permalink


Charge-Exchange-Driven Low-Energy Electron Splash Induced by Heavy Ion Impact on Condensed Matter
Schwestka, J.ORC; Niggas, A.; Creutzburg, S.; Kozubek, R.ORC; Heller, R.; Schleberger, M.ORC; Wilhelm, R. A.ORC; Aumayr, F.
Low-energy electrons (LEEs) are of great relevance for ion-induced radiation damage in cells and genes. We show that charge exchange of ions leads to LEE emission upon impact on condensed matter. By using a graphene monolayer as a simple model system for condensed organic matter and utilizing slow highly charged ions (HCIs) as projectiles, we highlight the importance of charge exchange alone for LEE emission. We find a large number of ejected electrons resulting from individual ion impacts (up to 80 electrons/ion for Xe40+). More than 90% of emitted electrons have energies well below 15 eV. This “splash” of low-energy electrons is interpreted as the consequence of ion deexcitation via an interatomic Coulombic decay (ICD) process.

Publ.-Id: 29666 - Permalink


Ultrasonic Determination of the Jahn–Teller Effect Parameters in Impurity-Containing Crystals
Averkiev, N. S.; Bersuker, I. B.; Gudkov, V. V.; Zhevstovskikh, I. V.; Sarychev, M. N.; Zherlitsyn, S.; Yasin, S.; Korostellin, Y. V.; Surikov, V. T.;
A method is developed to determine the symmetry properties of strains and the type of Jahn–Teller effect in crystals with impurity ions in a triply degenerate electronic T state. This method is based on a calculation of the isothermal contribution of the impurity subsystem to the elastic moduli of a crystal and the absorption and velocity of normal modes for all three possible problems, namely, T ⊗ e, T ⊗ t2, and T ⊗ (e + t2). The calculation results are compared with experimental data. The efficiency of the method is demonstrated for a CdSe:Cr2+ crystal. The CrSe4 center is found to be described in terms of the problem T ⊗ e. The parameters of the ground-state adiabatic potential are determined.

Publ.-Id: 29665 - Permalink


Pronounced 2/3 magnetization plateau in a frustrated S = 1 isolated spin-triangle compound: Interplay between Heisenberg and biquadratic exchange interactions
Chattopadhyay, S.; Lenz, B.; Kanungo, S.; Sushila, S.; Panda, S. K.; Biermann, S.; Schnelle, W.; Manna, K.; Kataria, R.; Uhlarz, M.; Skourski, Y.; Zvyagin, S. A.; Ponomaryov, A.; Herrmannsdörfer, T.; Patra, R.; Wosnitza, J.;
We report the synthesis and characterization of a new quantum magnet [2-[Bis(2-hydroxybenzyl) aminomethyl]pyridine]Ni(II)-trimer (BHAP-Ni3) in single-crystalline form. Our combined experimental and theoretical investigations reveal an exotic spin state that stabilizes a robust 2/3 magnetization plateau between 7 and 20 T in an external magnetic field. AC-susceptibility measurements show the absence of any magnetic order/glassy state down to 60 mK. The magnetic ground state is disordered and specific-heat measurements reveal the gapped nature of the spin excitations. Most interestingly, our theoretical modeling suggests that the 2/3 magnetization plateau emerges due to the interplay between antiferromagnetic Heisenberg and biquadratic exchange interactions within nearly isolated spin S = 1 triangles.

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Publ.-Id: 29664 - Permalink


Characterization of suprathermal electrons inside a laser accelerated plasma via highly-resolved K⍺-emission
Smid, M.ORC; Renner, O.ORC; Colaitis, A.ORC; Tikhonchuk, V. T.ORC; Schlegel, T.; Rosmej, F. B.
Suprathermal electrons are routinely generated in high-intensity laser produced plasmas via instabilities driven by non-linear laser-plasma interaction. Their accurate characterization is crucial for the performance of inertial confinement fusion as well as for performing experiments in laboratory astrophysics and in general high-energy-density physics. Here, we present studies of non-thermal atomic states excited by suprathermal electrons in kJ-ns-laser produced plasmas. Highly spatially and spectrally resolved X-ray emission from the laser-deflected part of the warm dense Cu foil visualized the hot electrons. A multi-scale two-dimensional hydrodynamic simulation including non-linear laser-plasma interactions and hot electron propagation has provided an input for ab initio non-thermal atomic simulations. The analysis revealed a significant delay between the maximum of laser pulse and presence of suprathermal electrons. Agreement between spectroscopic signatures and simulations demonstrates that combination of advanced high-resolution X-ray spectroscopy and non-thermal atomic physics offers a promising method to characterize suprathermal electrons inside the solid density matter.

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Publ.-Id: 29661 - Permalink


Experimental study on the air-side thermal-flow performance of additively manufactured heat exchangers with novel fin designs
Unger, S.; Beyer, M.; Gruber, S.; Willner, R.; Hampel, U.;
We introduce novel fin designs for finned tube heat exchangers which enhance the conduction heat transfer within the fin and the convective heat transfer along the fin surface simultaneously. Oval tubes with circular plain fins (CPF), circular integrated pin fins (CIPF) and a serrated integrated pin fins (SIPF) were additively manufactured via Selective Laser Melting (SLM) and their heat transfer and flow characteristics studied in a flow channel for different Reynolds number between 1800 and 7800 as well as fin spacing values between 6 mm and 16 mm. From the experiments an improvement of Nusselt number and a reduction of friction factor was found for all fin designs when fin spacing increases. CIPF showed a higher Nusselt number compared to CPF at all Reynolds numbers and fin spacing values. The highest Nusselt number as well as moderate friction factor values were found for the SIPF design. However, for SIPF the fin efficiency of 30:3 % is lowest due to the high heat dissipation along the fin surface. In order to evaluate the thermal and flow performance three parameters were studied: the performance evaluation criterion, the volumetric heat flux density and the global performance. CIPF gives a higher performance evaluation criterion compared to CPF and SIPF performs best compared to the other fin designs. Highest volumetric heat flux density of 2:72 mkW3K was achieved with CIPF at lowest fin spacing. Small differences in the global performance criterion between the fin designs and for various fin spacing were observed.
The SIPF design is of advantage, if the required surface area, the material cost and the weight of the finned tube heat exchanger are relevant. From the experimental results a heat transfer correlation that includes Nusselt number, Reynolds number, Prandtl number, fin spacing and fin design has been derived.
Keywords: Finned tube heat exchanger, Novel fin designs, Heat transfer, Friction factor, Thermal-flow performance, Additive manufacturing, Selective laser melting

Publ.-Id: 29658 - Permalink


Two types of magnetic shape-memory effects from twinned microstructure and magneto-structural coupling in Fe1+yTe
Rößler, S.; Koz, C.; Wang, Z.; Skourski, Y.; Doerr, M.; Kasinathan, D.; Rosner, H.; Schmidt, M.; Schwarz, U.; Rößler, U. K.; Wirth, S.;
A detailed experimental investigation of Fe1+yTe (y = 0.11, 0.12) using pulsed magnetic fields up to 60 T confirms remarkable magnetic shape-memory (MSM) effects. These effects result from magnetoelastic transformation processes in the low-temperature antiferromagnetic state of these materials. The observation of modulated and finely twinned microstructure at the nanoscale through scanning tunneling microscopy establishes a behavior similar to that of thermoelastic martensite. We identified the observed, elegant hierarchical twinning pattern of monoclinic crystallographic domains as an ideal realization of crossing twin bands. The antiferromagnetism of the monoclinic ground state allows for a magnetic-field–induced reorientation of these twin variants by the motion of one type of twin boundaries. At sufficiently high magnetic fields, we observed a second isothermal transformation process with large hysteresis for different directions of applied field. This gives rise to a second MSM effect caused by a phase transition back to the field-polarized tetragonal
lattice state.
  • Proceedings of the National Academy of Sciences of the United States of America 116(2019)34, 16697-16702
    DOI: 10.1073/pnas.1905271116

Publ.-Id: 29657 - Permalink


Cross section of the reaction 18O(p,γ)19F at astrophysical energies: The 90 keV resonance and the direct capture component
Best, A.; Pantaleo, F. R.; Boeltzig, A.; Imbriani, G.; Aliotta, M.; Balibrea-Correa, J.; Bemmerer, D.; Broggini, C.; Bruno, C. G.; Buompane, R.; Caciolli, A.; Cavanna, F.; Chillery, T.; Ciani, G. F.; Corvisiero, P.; Csedreki, L.; Davinson, T.; Deboer, R. J.; Depalo, R.; Di Leva, A.; Elekes, Z.; Ferraro, F.; Fiore, E. M.; Formicola, A.; Fülöp, Z.; Gervino, G.; Guglielmetti, A.; Gustavino, C.; Gyürky, G.; Junker, M.; Kochanek, I.; Lugaro, M.; Marigo, P.; Menegazzo, R.; Mossa, V.; Paticchio, V.; Perrino, R.; Piatti, D.; Prati, P.; Schiavulli, L.; Stöckel, K.; Straniero, O.; Strieder, F.; Szücs, T.; Takács, M. P.; Trezzi, D.; Wiescher, M.; Zavatarelli, S.;
The observation of oxygen isotopes in giant stars sheds light on mixing processes operating in their interiors. Due to the very strong correlation between nuclear burning and mixing processes it is very important to reduce the uncertainty on the cross sections of the nuclear reactions that are involved. In this paper we focus our attention on the reaction . While the channel is thought to be dominant, the (p,γ) channel can still be an important component in stellar burning in giants, depending on the low energy cross section. So far only extrapolations from higher-energy measurements exist and recent estimates vary by orders of magnitude. These large uncertainties call for an experimental reinvestigation of this reaction. We present a direct measurement of the cross section using a high-efficiency 4π BGO summing detector at the Laboratory for Underground Nuclear Astrophysics (LUNA). The reaction cross section has been directly determined for the first time from 140 keV down to 85 keV and the different cross section components have been obtained individually. The previously highly uncertain strength of the 90 keV resonance was found to be 0.53 ± 0.07 neV, three orders of magnitude lower than an indirect estimate based on nuclear properties of the resonant state and a factor of 20 lower than a recently established upper limit, excluding the possibility that the 90 keV resonance can contribute significantly to the stellar reaction rate.
Keywords: Experimental nuclear astrophysics Underground nuclear physics Hydrogen burning Stellar evolution

Publ.-Id: 29655 - Permalink


Dataset on Relationships between primary radiation damage, irradiation-induced microstructure and hardening of ion-irradiated Fe-Cr and ODS Fe-Cr alloys
Vogel, K.; Heintze, C.; Chekhonin, P.; Akhmadaliev, S.; Altstadt, E.ORC; Bergner, F.ORC

Dataset on Relationships between primary radiation damage, irradiation-induced microstructure and hardening of ion-irradiated Fe-Cr and ODS Fe-Cr alloys including SRIM calculations, nanoindentation, TEM and modelling.

  • Reseach data in the HZDR data repository RODARE
    Publication date: 2019-09-11
    DOI: 10.14278/rodare.183

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Publ.-Id: 29653 - Permalink


Research and Implementation of Efficient Parallel Processing of Big Data at TELBE User Facility
Bawatna, M.ORC; Green, B.ORC; Kovalev, S.ORC; Deinert, J.-C.ORC; Knodel, O.ORC; Spallek, R. G.
In recent years, improvements in high-speed Analog-to-Digital Converters (ADC) and sensor technology has encouraged researchers to improve the performance of Data Acquisition (DAQ) systems for scientific experiments which require high speed and continuous data measurements — in particular, measuring the electronic and magnetic properties of materials using pump-probe experiments at high repetition rates. Experiments at TELBE are capable of acquiring almost 100 Gigabytes of raw data every ten minutes. The DAQ system used at TELBE partitions the raw data into various subdirectories for further parallel processing utilizing the multicore structure of modern CPUs.
Furthermore, several other types of processors that accelerate data processing like the GPU and FPGA have emerged to solve the challenges of processing the massive amount of raw data. However, the memory and network bottlenecks become a significant challenge in big data processing, and new scalable programming techniques are needed to solve these challenges. In this contribution, we will outline the design and implementation of our practical software approach for efficient parallel processing of our large data sets at the TELBE user facility.
Keywords: Big Data, Data Processing Pipeline, Data Acquisition Systems, Signal Processing, Data analytics
  • Contribution to proceedings
    2019 International Symposium on Performance Evaluation of Computer and Telecommunication Systems (SPECTS), 22.07.2019, Berlin, Deutschland
    2019 International Symposium on Performance Evaluation of Computer and Telecommunication Systems (SPECTS): IEEE, 978-1-5108-8479-3
    DOI: 10.23919/SPECTS.2019.8823486

Publ.-Id: 29650 - Permalink


Dendritic structure formation of magnesium alloys for the manipulation of corrosion properties: Part 2-corrosion
Lakoma, P.; Ditze, A.; Scharf, C.;
In pure magnesium and aluminum-containing magnesium alloys, the microstructure also plays a role in the corrosion properties. In Part 1, the grain sizes, secondary dendrite arm spacings (SDAS) and precipitates of b phase were determined by casting samples with 0, 3, 6, 9 and 12% aluminum (all compositions in mass percentage) at different cooling rates. These samples were tested for corrosion properties by immersion and salt spray tests. The modeling of the corrosion process enables establishing a mathematical link between the microstructure and corrosion properties of an alloy. The results show an increase in the corrosion rate with increasing aluminum contents and the cooling rate.

The precipitations at the grain boundaries have a relevant impact on corrosion properties of the magnesium-aluminum alloys. A random comparison using the salt spray test tends to confirm the results.

Publ.-Id: 29641 - Permalink


Terahertz excitations in α-RuCl3: Majorana fermions and rigid-plane shear and compression modes
Reschke, S.; Tsurkan, V.; Do, S.-H.; Choi, K.-Y.; Lunkenheimer, P.; Wang, Z.; Loidl, A.;
Spin liquids may host emergent quasiparticles, collective excitations of the spin degrees of freedom with characteristic features of Majorana fermions, which experimentally are detectable by broad excitation continua due to spin fractionalization. The latter is predicted for the Kitaev spin liquid, an exactly solvable model with bond-dependent interactions on a two-dimensional honeycomb lattice. Here we report on detailed terahertz experiments in α-RuCl3, identifying these characteristic fingerprints of Majorana fermions. The continuum intensity decreases and finally vanishes on increasing temperature. It partly overlaps with phonon modes, representing characteristic sliding and compression modes of the van der Waals bonded molecular layers.
  • Physical Review B 100(2019), 100403

Publ.-Id: 29639 - Permalink


Electroforming-free resistive switching in yttrium manganite thin films by cationic substitution
Rayapati, V. R.; Bürger, D.; Du, N.; Patra, R.; Skorupa, I.; Blaschke, D.; Stöcker, H.; Matthes, P.; Schulz, S. E.; Schmidt, H.;
We report unipolar resistive switching in polycrystalline, hexagonal yttrium manganite thin films grown on unpatterned Pt metal coated SiO2/Si substrates with circular Al top electrodes. Electroforming-free or electroforming-based resistive switching is observed, depending on the chemical composition (Y1Mn1O3, Y0.95Mn1.05O3, Y1Mn0.99Ti0.01O3, and Y0.94Mn1.05Ti0.01O3). The number of loading cycles measured at room temperature for samples with Y1Mn1O3 and Y0.95Mn1.05O3 composition is larger than 103. The dominant conduction mechanism of the metal-insulator-metal structures between 295 K and 373 K in the high resistance state is space charge limited conduction and in the low resistance state is ohmic conduction. Activation energies in Ohm's law region in the high resistance state are calculated from the Arrhenius equation and are evaluated to be 0.39 ± 0.01 eV (Y1Mn1O3), 0.43 ± 0.01 eV (Y0.95Mn1.05O3), 0.34 ± 0.01 eV (Y1Mn0.99Ti0.01O3), and 0.38 ± 0.02 eV (Y0.94Mn1.05Ti0.01O3).

Publ.-Id: 29637 - Permalink


Alkyne-based cysteine cathepsin inhibitors as basis for PET tracer development
Behring, L.; Trapp, C.; Morales, M.; Wodtke, R.; Kuhne, K.; Belter, B.; Pietzsch, J.; Löser, R.;
Among the intertwined processes leading to cancer progression, protease activity plays an important role. Various attempts to develop molecular imaging probes have been made, as such probes can allow functional imaging and thus improve the understanding of tumour progression mechanisms and enable personalised cancer treatment. PET and SPECT tracers are particularly suitable for such applications. However, novel tracers have to overcome challenges such as stability, target efficiency and off-target effects.
Multiple members of the cathepsin family have been demonstrated to be involved in tumour invasion, metastasis, and angiogenesis. Especially high expression levels of the cysteine cathepsins B, K, L, S, and X are correlated with an increased metastatic potential and poor prognosis [1]. Due to their high expression in a multitude of tumours, those enzymes represent promising targets for the therapy and imaging of tumours.
Despite being virtually chemically inert, alkynes were shown to be able to irreversibly inhibit cysteine proteases: Both EKKEBUS et al. and SOMMER et al. independently described the unexpected inactivation of de-ubiquitinating enzymes by ubiquitin or ubiquitin-like modifiers bearing propargylamine in place of C-terminal glycine [2, 3]. We aimed to take advantage of those findings for designing alkyne-based cysteine cathepsin inhibitors suitable for radiolabelling with PET nuclides. The probes thus obtained would irreversibly bind to the target molecule without showing indiscriminate thiol reactivity.
Based on a potent, highly selective dipeptidyl nitrile-based cathepsin B inhibitor reported by GREENSPAN et al. (left structure) [4], we designed dipeptide alkynes by isoelectronic replacement of the nitrile nitrogen atom by a methine group. To avoid partial enantiomerisation during the formation of the C-C triple bond as observed for the open-chain serine-derived alkyne, the synthesis was performed via Garner’s aldehyde. This ensured high stereochemical purity of the final compounds. The inhibitory potential was investigated against cathepsin B, S, L and K. To optimise the inhibitory potential and selectivity, we consecutively varied all moieties attached to the dipeptidic scaffold.
We identified potent alkyne-based inhibitors for all tested cathepsins, with inactivation constants (kinact/KI) up to 10133 M-1s-1 and distinct selectivity profiles. We demonstrated irreversibility in a “jump-dilution” experiment and inhibitor reactivity in cell lysates and on living cells was exemplarily verified for cathepsin B. During our research, MONS et al. successfully demonstrated irreversible cathepsin K inhibition by alkyne-based small molecule inhibitors with no indiscriminate thiol reactivity [5], which indicates the viability of our concept.
Among the tested inhibitors we identified two promising radiotracer candidates which are selective for cathepsin S and L. We successfully radiolabelled the cathepsin S-selective inhibitor with N-succinimidyl 4-[18F]fluorobenzoate ([18F]SFB). Radiopharmacological characterisation of the activity-based probe obtained by that approach is in progress.

[1] Löser, R; Pietzsch, J.: Front. Chem., 2015, 3: 37.
[2] Ekkebus et al.: J. Am. Chem. Soc., 2013, 135(8): 2867-2870.
[3] Sommer et al.: Bioorg. Med. Chem., 2013, 21(9): 2511-2517.
[4] Greenspan et al.: J. Med. Chem., 2001, 44(26): 4524-4534.
[5] Mons et al.: J. Am. Soc. 2019, 141(8): 3507-3514.
  • Poster
    Annual Meeting of the German Pharmaceutical Society - DPhG, 01.-04.09.2019, Heidelberg, Deutschland

Publ.-Id: 29632 - Permalink


Radiotherapy Beamline Design for Laser-driven Proton Beams
Masood, U.;
Motivation: Radiotherapy is an important modality in cancer treatment commonly using photon beams from compact electron linear accelerators. However, due to the inverse depth dose profile (Bragg peak) with maximum dose deposition at the end of their path, proton beams allow a dose escalation within the target volume and reduction in surrounding normal tissue. Up to 20% of all radiotherapy patients could benefit from proton therapy (PT). Conventional accelerators are utilized to obtain proton beams with therapeutic energies of 70 – 250 MeV. These beams are then transported to the patient via magnetic transferlines and a rotatable beamline, called gantry, which are large and bulky. PT requires huge capex, limiting it to only a few big centres worldwide treating much less than 1% of radiotherapy patients. The new particle acceleration by ultra-intense laser pulses occurs on micrometer scales, potentially enabling more compact PT facilities and increasing their widespread. These laser-accelerated proton (LAP) bunches have been observed recently with energies of up to 90 MeV and scaling models predict LAP with therapeutic energies with the next generation petawatt laser systems.
  • Open Access LogoWissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-104 2019

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Publ.-Id: 29631 - Permalink


Implantable highly compliant devices for heating of internal organs: towards cancer treatment
Cañón Bermudez, G. S.; Kruv, A.; Voitsekhivska, T.; Hochnadel, I.; Lebanov, A.; Potthoff, A.; Fassbender, J.; Yevsa, T.; Makarov, D.;
Flexible electronics have a strong potential to revolutionize the health care sector. Numerous flexible diagnostic or therapeutic devices have been successfully demonstrated. However, tumor treatment remains rather unexplored in the field of flexible electronics. Here, we demonstrate that the electrical and mechanical properties of highly compliant electronics are advantageous for targeting tumor sites at internal organs. This kind of electronics could be implanted to heat and thereby render the treated tissue susceptible to chemotherapy, radiation or other available treatments. Our method relies on the implantation directly at the tumor site of an ultra-thin flexible device comprising a resistive heater and temperature sensor. The device consists of a 6 µm thick polymeric foil hosting the heater and sensor, capped with a 5 µm thick encapsulation layer. Due to its ultrathin nature, it seamlessly conforms to the very soft liver tissue and allows for precisely controlled thermal treatment. Its high mechanical compliance provides stable readings even upon severe mechanical deformations, enabling a temperature accuracy of 0.1°C at bending radii of 2.5 mm, characteristic for mouse liver tissues. We demonstrate a proof-of-concept prototype and evaluate its electrical and mechanical performance when applied to murine cancer models. The presented highly compliant device paves the way for handling of exophytic (located at the organ surface) tumor nodules via thermal destruction of tissue, targeted drug release, or enhancement of anti-tumor immune responses. In addition, it raises the possibility to further study the effects of thermal treatment in enhancing the development of the new cancer therapies, especially for severe malignancies as liver cancer.
Keywords: flexible electronics, cancer

Publ.-Id: 29629 - Permalink


Interplay Between Relaxation and Resonance in Ultrasound Attenuation by the Cubic Crystal ZnSe:Cr
Baryshnikov, K.; Averkiev, N.; Bersuker, I.; Gudkov, V.; Zhevstovskikh, I.; Sarychev, M.; Zherlitsyn, S.; Yasin, S.; Korostelin, Y.;
Resonance ultrasound attenuation, albeit broadened, is observed in doped cubic crystal ZnSe with a part of the Zn ions substituted by magnetic anisotropic Cr2+ ions. In the tetrahedral selenium environment the latter form a T term Jahn–Teller (JT) center with a T⊗e JT problem and three equivalent distortions along the three tetragonal axes. In sufficiently strong magnetic fields (B > 4 T) applied along the [001] direction the degeneracy of the ground state is removed, and the ultrasound wave propagating along [110] and polarized along [110] (at T = 1.3 K) does not interact with the center, its impurity attenuation being reduced to zero. By comparison, this allows to estimate the contribution of the Cr centers to the attenuation of ultrasound in the ZnSe:Cr crystal in zero magnetic field. The experimental data revealed a strong dependence of the attenuation on the ultrasound frequency, evidencing for the resonance nature of the attenuation: there is no frequency dependence in relaxational attenuation with the relaxation time much larger than the period of the ultrasonic wave. The resonance attenuation is attributed to transitions between the ground state energy levels, split by spin-orbital interaction. The high sensitivity of the resonance absorption on the ultrasound power is also discussed.

Publ.-Id: 29627 - Permalink


Diffusion of Phosphorus and Boron from Atomic Layer Deposition Oxides into Silicon
Beljakowa, S.; Pichler, P.; Kalkofen, B.; Hübner, R.;
Oxides containing group III or group V elements (B2O3/Sb2O5 and P2O5/Sb2O5) are grown by plasma-assisted atomic layer deposition (ALD) on single-crystalline silicon and serve as dopant sources for conformal and shallow doping. Transport phenomena in ALD-oxide–Si structures during rapid thermal annealing (RTA) are investigated subsequently by X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and secondary ion mass spectrometry (SIMS). The XPS and TEM analyses of the annealed ALD oxide–Si structures demonstrate that the ALD oxide converts to a silicon oxide and partially evaporates during annealing. In addition, dopant-containing, spherical, and partially crystalline particles form in the oxide, and Si-P precipitates at the oxide–Si interface. After diffusion annealing at 1000 °C, the SIMS analyses reveal phosphorus and boron concentration profiles in the silicon substrate with maximum concentrations exceeding their solid solubility limits by roughly one order of magnitude. Experimental doping profiles of phosphorus and boron in silicon are compared with simulation results, considering a slight injection of self-interstitials and dynamical defect clustering.

Publ.-Id: 29626 - Permalink


PIConGPU simulation settings for TWEAC
Debus, A.ORC; Steiniger, K.ORC; Pausch, R.ORC; Huebl, A.ORC; Widera, R.ORC

The input sets of the simulations as used in the publication "Circumventing the Dephasing and Depletion Limits of Laser-Wakefield Acceleration" by A. Debus et al. .

The input sets include TWEAC scenarios, the LWFA scenario and the laser-propagation scenario of Appendix D. The src-directories include custom additions to the PIConGPU source code.

The simulations were run using the beta-rc6, 0.3.1, and 0.4.0 releases of PIConGPU (see DOI: 10.5281/zenodo.591746). The input sets are shown according to the respective PIConGPU version used in the original simulation. However, for running the simulations we recommend adapting the input sets to the 0.4.0 release.

Keywords: Optics; Photonics; Plasma Physics
Related publications
Circumventing the dephasing and depletion limits of … (Id 25244) is documented by this publication
  • Reseach data in the HZDR data repository RODARE
    Publication date: 2019-09-04
    DOI: 10.14278/rodare.150
    License: CC-BY-4.0

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Publ.-Id: 29625 - Permalink


Efficiency estimation of tray columns based on flow profiles and vapor-liquid equilibrium characteristics of binary mixtures
Vishwakarma, V.ORC; Rigos, N.; Schubert, M.ORC; Hampel, U.

A systematic approach for estimating the column efficiency based on tray flow profiles and vapor-liquid equilibrium (VLE) characteristics of binary mixtures exclusively for each tray is proposed. A novel iterative technique for approximating the slope of the VLE curve and the tray efficiency is also developed. For demonstrating the predictive capabilities of the new approach, two case studies are formulated in this work - one with a theoretical column processing selected binary mixtures at total reflux, and the other involving an industrial column whose performance data is acquired from the literature. An in-depth analysis of these studies reveals the superiority of the new approach over the most applied method. Such an approach would allow a priori calculation of the column efficiency in the tray’s design phase.

Keywords: Column efficiency; Murphree tray efficiency; flow maldistribution; vapor-liquid equilibrium; residence time distribution.
  • Reseach data in the HZDR data repository RODARE
    Publication date: 2019-09-02
    DOI: 10.14278/rodare.148
    License: CC-BY-4.0

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Publ.-Id: 29624 - Permalink


Modulated Rotating Waves in the Magnetised Spherical Couette System
Garcia, F.; Seilmayer, M.; Giesecke, A.; Stefani, F.;
We present a study devoted to a detailed description of modulated rotating waves (MRW) in the magnetised spherical Couette system. The set-up consists of a liquid metal confined between two differentially rotating spheres and subjected to an axially applied magnetic field. When the magnetic field strength is varied, several branches of MRW are obtained by means of three-dimensional direct numerical simulations. The MRW originate from parent branches of rotating waves and are classified according to Rand’s (Arch Ration Mech Anal 79:1–37, 1982) and Coughling and Marcus (J Fluid Mech 234:1–18, 1992) theoretical description. We have found relatively large intervals of multistability of MRW at low magnetic field, corresponding to the radial jet instability known from previous studies. However, at larger magnetic field, corresponding to the return flow regime, the stability intervals of MRW are very narrow and thus they are unlikely to be found without detailed knowledge of their bifurcation point. A careful analysis of the spatio-temporal symmetries of the most energetic modes involved in the different classes of MRW will allow in the future a comparison with the HEDGEHOG experiment, a magnetised spherical Couette device hosted at the Helmholtz-Zentrum Dresden-Rossendorf.
Keywords: Magnetohydrodynamics, Nonlinear waves, Bifurcation theory, Symmetry breaking, Experiments, Astrophysics

Publ.-Id: 29619 - Permalink


Direct measurements of low-energy resonance strengths of the 23Na(p,γ)24Mg reaction for astrophysics
Boeltzig, A.; Best, A.; Pantaleo, F. R.; Imbriani, G.; Junker, M.; Aliotta, M.; Balibrea-Correa, J.; Bemmerer, D.; Broggini, C.; Bruno, C. G.; Buompane, R.; Caciolli, A.; Cavanna, F.; Chillery, T.; Ciani, G. F.; Corvisiero, P.; Csedreki, L.; Davinson, T.; Deboer, R. J.; Depalo, R.; Di Leva, A.; Elekes, Z.; Ferraro, F.; Fiore, E. M.; Formicola, A.; Fülöp, Z.; Gervino, G.; Guglielmetti, A.; Gustavino, C.; Gyürky, G.; Kochanek, I.; Lugaro, M.; Marigo, P.; Menegazzo, R.; Mossa, V.; Munnik, F.; Paticchio, V.; Perrino, R.; Piatti, D.; Prati, P.; Schiavulli, L.; Stöckel, K.; Straniero, O.; Strieder, F.; Szücs, T.; Takács, M. P.; Trezzi, D.; Wiescher, M.; Zavatarelli, S.;
The NeNa and the MgAl cycles play a fundamental role in the nucleosynthesis of asymptotic giant branch stars undergoing hot bottom burning. The 23Na (p , γ)24Mg reaction links these two cycles and a precise determination of its rate is required to correctly estimate the contribution of these stars to the chemical evolution of various isotopes of Na, Mg and Al. At temperatures of 50 ≲ T ≲ 110MK, narrow resonances at Ep = 140 and 251keV are the main contributors to the reaction rate, in addition to the direct capture that dominates in the lower part of the temperature range. We present new measurements of the strengths of these resonances at the Laboratory for Underground Nuclear Astrophysics (LUNA). We have used two complementary detection approaches: high efficiency with a 4π BGO detector for the 140 keV resonance, and high resolution with a HPGe detector for the 251 keV resonance. Thanks to the reduced cosmic ray background of LUNA, we were able to determine the resonance strength of the 251 keV resonance as ωγ = 482 (82) μeV and observed new gamma ray transitions for the decay of the corresponding state in 24Mg at Ex = 11931keV. With the highly efficient BGO detector, we observed a signal for the 140 keV resonance for the first time in a direct measurement, resulting in a strength of ωγ140 = 1.46-0.53+0.58 neV (68% CL). Our measurement reduces the uncertainty of the 23Na (p , γ)24Mg reaction rate in the temperature range from 0.05 to 0.1 GK to at most -35%+50% at 0.07 GK. Accordingly, our results imply a significant reduction of the uncertainties in the nucleosynthesis calculations.
Keywords: LUNA; Nuclear Astrophysiscs; Underground nuclear physics; Hydrogen burning; Stellar evolution

Publ.-Id: 29612 - Permalink


Untersuchung disperser Zweiphasenströmungen in komplexen Geometrien – Methodenentwicklung und Experimente
Neumann, M.ORC; Hampel, U.ORC
Das Gesamtziel des Vorhabens war die Verbesserung der methodischen experimentellen Basis für die Weiterentwicklung von CFD-Codes zur Berechnung dreidimensionaler zweiphasiger Strömungsvorgänge, wie sie im Kühlkreislauf von Kernkraftwerken auftreten. Es ordnet sich damit in das strategische Ziel der Reaktorsicherheitsforschung ein, wobei die nachhaltige Verbesserung der experimentellen Basis zur Validierung von CFD-Modellen für die Berechnung sicherheitsrelevanter Strömungsvorgänge in Kernkraftwerken im Fokus stand. Die erzielten Ergebnisse der experimentellen Studien liefern zudem wertvolle Grundlagenkenntnisse zu Zweiphasenströmungen sowie Validierungsdaten für zukünftige Weiterentwicklungen von CFD-Codes.
Wesentliche Bestandteile aktueller CFD-Code-Weiterentwicklung, speziell für den Reaktorkreislauf, sind die Turbulenzmodellierung und Zweiphasenströmungen. Hierfür werden räumlich und zeitlich hochaufgelöste experimentelle Validierungsdaten benötigt. In diesem Vorhaben wurden dafür zwei moderne Messverfahren für die Charakterisierung von zweiphasigen Strömungen eingesetzt. Mit diesen wurden die Phasenverteilung und Gasphasendynamik, sowie Flüssigphasengeschwindigkeit und Turbulenz in ausgewählten generischen Experimenten untersucht.
Weiterhin wurden in diesem Vorhaben ausgewählte experimentelle Ergebnisse mit CFD-Vorausrechnungen verglichen. Die zweiphasige Strömungssimulation wurde mit dem verfügbaren Simulationswerkzeug ANSYS-CFX durchgeführt, um für diesen Anwendungsfall bereits verfügbare Standardmodelle auf ihre Anwendbarkeit zu prüfen.
Keywords: ultrafast x-ray CT, hot-wire anemometry, two-phase flow, bubbly pipe flow, three-dimensional flow, obstacle, CFD
  • Other report
    Dresden: Eigenverlag, 2019
    147 Seiten

Publ.-Id: 29604 - Permalink


Investigation of three-dimensional two-phase flow using combined ultrafast X-ray tomography and hot-film anemometry
Neumann, M.ORC; Hampel, U.ORC
Gas-liquid two-phase flow modelling is of highest relevance in nuclear safety analyses. This concerns e.g. the modelling of steam-water two-phase flow and heat transfer in the reactor core, the steam generators, the containment and the spent fuel pool under accident conditions. Prediction of flow conditions by Computational Fluid Dynamics (CFD) tools is of particular interest for supporting safety assessments. However, achieving physically correct simulations is quite challenging due to the complexity of the flow, which includes turbulence, highly deformable gas-liquid interfaces and heat, mass and momentum transfer across the interfaces. Today, two-phase flow models contain a large number of empirical correlations and closure models, which are derived from experimental data. The role of thermal hydraulics experiments nowadays still lies in the creation of such data but moreover they are also needed for model validation.
This contribution describes an experimental study of a generic three-dimensional two phase flow, which should serve as a future benchmark experiment for CFD code validation. The experiments were conducted at the Transient Two-Phase Flow (TOPFLOW) facility at Helmholtz-Zentrum Dresden – Rossendorf (HZDR) and are a continuation of earlier studies, which were performed using a moveable flow obstacle and the wire-mesh sensor technique. Although these investigations already provided very good data for a generic two-phase flow, the intrusiveness of both sensor and obstacle motion unit lead to some non-idealities with respect to the fully undisturbed flow. With a new imaging technique, ultrafast electron beam X-ray tomography, we are now able to perform investigations fully non-intrusively and to study the gas phase dynamics with high temporal and spatial resolution in two planes simultaneously. Furthermore, the previous studies did not provide measurement data of liquid velocities, which are required for CFD code validation. Thus, for this study ultrafast X-ray tomography and hot-film anemometry was used in combination to extend the available experimental database. This paper presents selected results of this experimental study.
Keywords: ultrafast x-ray CT, hot-wire anemometry, two-phase flow, bubbly pipe flow, three-dimensional flow, obstacle, CFD
  • Lecture (Conference)
    50th Annual Meeting on Nuclear Technology, 07.-08.05.2019, Berlin, Deutschland
  • Contribution to proceedings
    50th Annual Meeting on Nuclear Technology, 07.-08.05.2019, Berlin, Dresden
    Proceedings of the 50th Annual Meeting on Nuclear Technology

Publ.-Id: 29603 - Permalink


Investigation of three-dimensional two-phase flow using combined ultrafast X-ray tomography and hot-film anemometry
Neumann, M.ORC; Hampel, U.ORC
In vielen industriellen Prozessen und Apparaten treten Mehrphasenströmungen auf. Dies sind häufig Flüssigkeits-Gas-Strömungen, beispielsweise in der Kraftwerkstechnik, in Wärmetauschern, chemischen Reaktoren und Trennapparaten oder in Ölfördersystemen. Ein großes Ziel ist die Berechnung solcher Strömungen mittels computergestützter Simulationswerkzeuge (CFD Codes) zur Unterstützung der Auslegung, zur Optimierung, aber auch zur Sicherheitsbewertung. Die komplexe Physik von Zweiphasenströmungen erschwert dieses Vorhaben im Vergleich zu einphasigen Strömungen erheblich. Grund dafür ist die Komplexität der Transportprozesse über stark verformbare und sich verändernde Phasengrenzflächen in mehreren Zeit- und Längenskalen. Zudem werden durch anlagentechnische Komponenten, wie beispielsweise Krümmer, Ventile, T-Stücke oder querschnittsverändernde Einbauten, ausgeprägte dreidimensionale Strömungsfelder erzeugt, welche von aktuellen CFD-Codes nur sehr stark eingeschränkt berechnet werden können.
Der Beitrag beschäftigt sich mit der experimentellen Untersuchung von generischen dreidimensionalen Zweiphasenströmungen. Mit Hilfe neuartiger experimenteller Methoden wurde eine Datenbasis für die nachhaltige Validierung und Weiterentwicklung von CFD-Codes, speziell für dreidimensionale Strömungseffekte, generiert.
Keywords: ultrafast x-ray CT, hot-wire anemometry, two-phase flow, bubbly pipe flow, three-dimensional flow, obstacle, CFD
  • Lecture (Conference)
    Jahrestreffen Reaktionstechnik 2019 gemeinsam mit der Fachgruppe Mehrphasenströmungen, 27.-29.05.2019, Würzburg, Deutschland

Publ.-Id: 29602 - Permalink


Experimental investigation of three-dimensional bubbly two-phase pipe flows
Neumann, M.ORC; Hampel, U.ORC
Modelling gas-liquid two-phase flow is a topic of constant relevance in nuclear thermal hydraulics. Gas-disperse two-phase flows occur in e.g. fuel elements in the reactor core, in pipes and components during pressure loss, sudden reflooding or other events. Due to the deformable gas-liquid interface and the complexity of heat, mass and momentum transfer across the interface, gas-liquid two-phase flow is very difficult to model and simulate. On the device scale it is common to use Euler/Euler multi-fluid approaches for CFD simulations, which require a good number of empirical correlations as closure models. Such models are commonly derived from experiments. Validation of the correctness of predictive simulations then also requires experiments, which must be simplified to a degree to allow provision of CFD-grade experimental data but complex enough to resemble real flow situations. The latter calls especially for investigations on flow fields in more complex three-dimensional domains, which are prototypical for e.g. bends, valves, T-junctions and rod bundles.
Keywords: ultrafast x-ray CT, two-phas flow, three-dimensional flow, obstacle
  • Lecture (Conference)
    East German Centre of Competence in Nuclear Technology Workshop of Doctoral Candidates, 13.12.2018, Zittau, Deutschland

Publ.-Id: 29601 - Permalink


Mitigating Meniscus Instabilities in Solution-Sheared Polymer Films for Organic Field-Effect Transistors
Da Rocha, C. T.; Qu, G.; Yang, X.; Shivhare, R.; Hambsch, M.; Diao, Y.; Mannsfeld, S. C. B.;
Semiconducting donor−acceptor copolymers are considered to be a promising material class for solution-coated, large-scale organic electronic applications. A large number of works have shown that the best-performing organic field-effect transistors (OFETs) are obtained on low-surface-energy substrates. The meniscus instabilities that occur when coating on such surfaces considerably limit the effective deposition speeds. This represents a limiting factor for the upscaling of device fabrication for mass production, an issue that needs to be addressed if organic electronic devices are ever to become commercially relevant. In this work, we present a method to increase the accessible window of coating speeds for the solution shearing of donor−acceptor semiconductor polymers for the fabrication of OFETs. By incorporating a piezo crystal that is capable of producing high-frequency vibrations into the coating head, we are able to mitigate contact line instabilities due to the depinning of the contact line, thereby suppressing the commonly encountered “stick-and-slip” phenomenon.
Keywords: organic field-effect transistors, solution shearing, meniscus instabilities, vibration, large-area fabrication

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  • Secondary publication expected from 12.08.2020

Publ.-Id: 29600 - Permalink


p-type codoping effect in (Ga,Mn)As: Mn lattice location versus magnetic properties
Xu, C.ORC; Zhang, C.; Wang, M.; Xie, Y.; Hübner, R.; Heller, R.; Yuan, Y.; Helm, M.; Zhang, X.; Zhou, S.
In the present work, we perform a systematic investigation on p-type codoping in (Ga,Mn)As. Through gradually increasing Zn doping concentration, the hole concentration increases, which should theoretically lead to an increase of the Curie temperature (TC) according to the p-d Zener model. Unexpectedly, although the film keeps its epitaxial structure, both TC and the magnetization decrease. The samples present a phase transition from ferromagnetism to paramagnetism upon increasing hole concentration. In the intermediate regime, we observe a signature of antiferromagnetism. By using channeling Rutherford backscattering spectrometry and particle-induced x-ray emission, the substitutional Mn atoms are observed to shift to interstitial sites, while more Zn atoms occupy Ga sites, which explains the observed behavior. This is also consistent with first-principles calculations, showing that the complex of substitutional Zn and interstitial Mn has the lowest formation energy.

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Publ.-Id: 29599 - Permalink


Background in γ-ray detectors and carbon beam tests in the Felsenkeller shallow-underground accelerator laboratory
Szücs, T.ORC; Bemmerer, D.ORC; Degering, D.; Domula, A.; Grieger, M.; Ludwig, F.; Schmidt, K.; Steckling, J.; Turkat, S.; Zuber, K.
The relevant interaction energies for astrophysical radiative capture reactions are very low, much below the repulsive Coulomb barrier. This leads to low cross sections, low counting rates in γ-ray detectors, and therefore the need to perform such experiments at ion accelerators placed in underground settings, shielded from cosmic rays. Here, the feasibility of such experiments in the new shallow-underground accelerator laboratory in tunnels VIII and IX of the Felsenkeller site in Dresden, Germany, is evaluated. To this end, the no-beam background in three diff erent types of germanium detectors, i.e. a Euroball/Miniball triple cluster and two large monolithic detectors, is measured over periods of 26-66 days. The cosmic-ray induced background is found to be reduced by a factor of 500-2400, by the combined eff ects of, first, the 140 meters water equivalent overburden attenuating the cosmic muon flux by a factor of 40, and second, scintillation veto detectors gating out most of the remaining muon-induced eff ects. The new background data are compared to spectra taken with the same detectors at the Earth’s surface and at other underground sites. Subsequently, the beam intensity from the cesium sputter ion source installed in Felsenkeller has been studied over periods of several hours. Based on the background and beam intensity data reported here, for the example of the 12 C(α,γ) 16 O reaction it is shown that highly sensitive experiments will be possible.
Keywords: Nuclear Astrophysiscs; Underground experiment, sputter source, Felsenkeller

Publ.-Id: 29598 - Permalink


Photodecarbonylation and in vitro studies of dicarbonyl ruthenium complexes
Kubeil, M.ORC; Geri, S.; Stephan, H.
Carbon monoxide has been demonstrated to exhibit several beneficial effects on biological targets (anti-inflammatory, anti-proliferative, anti-apoptotic effects, causes vasodilation, etc.).[1] Consequently, the development of CO releasing molecules (CORMs) that allows a controlled release of CO under physiological conditions has therefore become a major field of scientific and medical interest.[2] Considerable research interest has been drawn on light-activated CORMs (photoCORMs) which only release CO upon radiation with certain wavelengths. However, despite a large number of photoCORMs reported, relatively little information is available on the precise mechanism of CO release from most photoCORMs and even less compounds have been tested as anti-cancer agents in cells so far. Herein, we report the synthesis of ruthenium(II) carbonyl complexes functionalized with (fluorescent) bidentate pyridyl (1) and tridentate diquinolyl ligands (2) and investigate the mechanism of CO release in aqueous media (before and after light-activation). The photo-induced CO release kinetics of the Ru(II) photoCORMs, as well as in vitro studies in cancerous and healthy cell lines will be presented [3].

References
[1] R. Motterlini, L. E. Otterbein, Nat. Rev. Drug Discov. 9 (2010) 728-743.
[2] U. Schatzschneider, Br. J. Pharmacol. 172 (2015) 1638-1650.
[3] M. Kubeil, R. R. Vernooij, C. Kubeil, B. R. Wood, B. Graham, H. Stephan, L. Spiccia, Inorg. Chem.
56 (2017) 5941-5952.
[4] M. Kubeil, T. Joshi, B. R. Wood, H. Stephan, ChemistryOpen (2019) accepted.
  • Lecture (Conference)
    19th International Conference on Biological Inorganic Chemistry, 11.-16.08.2019, Interlaken, Schweiz

Publ.-Id: 29597 - Permalink


Interlayer excitons in van-der-Waals heterostructures: MoS2 on GaSe
Wagner, C.; Rahaman, M.; Zahn, D. R. T.; Gemming, S.;
Hybrid van-der-Waals heterostructures of two-dimensional nanomaterials are a vibrant field of study: The (weak) electronic interaction between two layers is often reasonably described by a perturbation of the physical effects of the isolated layers, such as electrostatic doping and increased screening of intralayer excitons. However, it turns out that this picture of the weak interaction is not exhaustive in terms of all optical properties: the formation of bound excitons from electrons of one layer and holes from the other layer yields the formation of interlayer excitons. These mixed states are measured experimentally by photoluminescence and photocurrents and predicted by theory. Examples are of MoS2 or MoSe2 on WSe2, MoS2 or GaSe due to type-II band alignment [1-3].
The conditions for the formation of interlayer excitons are elucidated from a first-principles point of view. For this, first-principles studies of a minimal test system of MoS2 on GaSe is conducted [1].
This work envisions to predict the interlayer states as a function of the heterostack in order to specifically tailor efficient photon absorption.
Keywords: 2D materials, DFT, Bethe-Salpeter, Density-functional perturbation theory, MoS2, GaSe, bilayer, van-der-Waals heterostructure, interlayer exciton
  • Lecture (Conference)
    Chem2DMat, 03.-06.09.2019, Dresden, Deutschland

Publ.-Id: 29594 - Permalink


Order/disorder processes and electromechanical properties of monoclinic GdCa4O(BO3)3
Münchhalfen, M.; Schreuer, J.; Reuther, C.; Möckel, R.; Götze, J.; Mehner, E.; Stöcker, H.; Meyer, D.;
Large single crystals of GdCa₄O(BO₃)₃ (space group Cm) were grown by the Czochralski method. Dielectric, piezoelectric and elastic coefficients at room temperature as well as specific heat capacity, thermal expansion and cation disorder were studied employing a variety of methods including resonant ultrasound spectroscopy, differential scanning calorimetry, dilatometry and X-ray diffraction techniques. The electromechanical parameters (4 dielectric, 10 piezoelectric and 13 elastic stiffness coefficients) obtained on different samples are in excellent agreement indicating high internal consistency of our approach, whereas the values reported in literature differ significantly. The elastic behaviour of GdCa₄O(BO₃)₃ resembles the one of structurally related fluorapatite, i.e. the elastic anisotropy is relatively small and the longitudinal effect of the deviations from Cauchy-relations exhibit a pronounced minimum along the direction of the dominating chains of cation polyhedra. GdCa₄O(BO₃)₃ exhibits a maximum longitudinal piezoelectric effect of 7.67 × 10−12 CN−10, a value in the order of that of langasite-type materials. Significant changes of the calcium/gadolinium distribution on the 3 independent cation sites accompanied by characteristic anomalies of heat capacity and thermal expansion suggest processes of nonconvergent cation ordering above about 900 K in GdCa₄O(BO₃)₃.
Keywords: elasticity; GdCa₄O(BO₃)₃; heat capacity; nonconvergent cation ordering; piezoelectricity; thermal expansion

Publ.-Id: 29591 - Permalink


Sample preparation for AMS astrophysics projects – Size does (not) matter
Merchel, S.ORC; Child, D.; Faestermann, T.; Fröhlich, M.; Golser, R.; Hotchkis, M.; Koll, D.; Korschinek, G.; Pavetich, S.; Wallner, A.; a lot of more AMS colleagues
The determination of long-lived radionuclides by means of accelerator mass spectrometry (AMS) is usually outstandingly successful when an interdisciplinary team comes together. The “heart” of AMS research is of course an accelerator equipped with sophisticated ion sources, analytical tools and detectors run by experienced and ambitious physicists [e.g. 1-3]. Setting-up and further developing AMS systems is one of the most interesting and challenging topics. The reputation to be reached here is the greatest uniqueness of analysis possible, lowest detection levels, and/or most reliable data world-wide.
For sure, another primary pillar of AMS research is based on the questions addressed within fundamental and applied research. “How have supernovae explosions influenced Earth, our solar system and beyond?” [e.g. 4] or “How does the Earth’s surface and environment respond to earthquakes, climate change and anthropogenic influences?” [e.g. 5] are just two examples of high-quality studies.
However, somehow in-between there are groups of hidden figures like people developing software for data analysis or performing the required chemical sample preparation for AMS. These often unacknowledged individuals do crucial work for the overall outcome of the studies.
Chemists can spend weeks and months trying (and failing) on sample preparation before they find a “safe way” and start the actual work on the most valuable sample material, repeat all over again the same “recipe” for hundreds of samples, or train non-chemists the secrets of their successful recipes. Nevertheless, interdisciplinary AMS work can also be very exciting for a chemist: touching (and destroying) samples from outer space, the deep ocean or (currently) frozen places like Antarctica is quite thrilling. But at the end of the day, the whole AMS chemist’s work can be described as “reducing the sample matrix, other impurities and especially isobars to a level the AMS machine can handle while enriching the radionuclide of interest”.
Starting materials for applications such as astrophysical research can be “orders of magnitude” different: a neutron-irradiated sample of 1 g tungsten powder [6], over 40 g of clay-rich material from the Cretaceous–Tertiary (K-T) boundary, 100 g of ultra-pure sodium iodide, or 500 kg of snow from Antarctica [4] can cause totally different and sometimes unexpected problems in the chemistry lab. In general, smaller samples are not always easier to handle for example if they are chemically rather resistant or reactive. The cream of the crop of failure and success in a few AMS chemistry labs will be presented.

[1] P. Steier et al., Int. J. Mass Spectr. 444, 116175 (2019).
[2] G. Rugel et al., Nucl. Instr. Meth. B 370, 94 (2016).
[3] D. Koll et al., Nucl. Instr. Meth. B 438, 180 (2019).
[4] D. Koll et al., Phys. Rev. Lett. 123, 072701 (2019) and this meeting.
[5] W. Schwanghart et al., Science 351, 147 (2016).
[6] M. Martschini et al., this meeting.
Keywords: AMS, long-lived radionuclides
  • Lecture (Conference)
    Heavy Ion Accelerator Symposium on Fundamental and Applied Science (HIAS), 09.-13.09.2019, Canberra, Australia

Publ.-Id: 29588 - Permalink


Lanthanide–induced conformational change of methanol dehydrogenase involving coordination change of cofactor pyrroloquinoline quinone
Tsushima, S.;
There is emerging interests to the role of lanthanides as cofactor in XoxF-type methanol dehydrogenase (MHD). Here,
classical molecular dynamics simulations combined with fragment molecular orbital calculations were employed to
rationalize enzymatic activities of MHD (both XoxF- and MxaF- types) carrying different lanthanides. In XoxF–type MDH,
lanthanide binding to cofactor pyrroloquinoline quinone was found to switch from tridentate to unidentate fashion as it
switches from lighter to heavier lanthanide. This fact possibly plays crucial role to the enzymatic activity exclusive to XoxF–
type MDH incorporating lighter lanthanides.

Publ.-Id: 29587 - Permalink


A theranostic PSMA ligand for PET imaging and retargeting of T cells expressing the universal chimeric antigen receptor UniCAR
Arndt, C.; Feldmann, A.ORC; Koristka, S.; Schäfer, M.; Bergmann, R.ORC; Metwasi, N.; Berndt, N.; Bachmann, D.; Kegler, A.; Schmitz, M.; Puentes-Cala, E.; Soto, J. A.; Ehninger, G.; Pietzsch, J.; Liolios, C.; Wunderlich, G.; Kotzerke, J.; Kopka, K.ORC; Bachmann, M.ORC
Chimeric antigen receptor (CAR) T cells have shown impressive therapeutic potential. Due to the lack of direct control mechanisms, therapy-related adverse reactions including cytokine release- and tumor lysis syndrome can even become life-threatening. In case of target antigen expression on non-malignant cells, CAR T cells can also attack healthy tissues. To overcome such side effects, we have established a modular CAR platform termed UniCAR: UniCAR T cells per se are inert as they recognize a peptide epitope (UniCAR epitope) that is not accessible on the surface of living cells. Bifunctional adapter molecules termed target modules (TM) can cross-link UniCAR T cells with target cells. In the absence of TMs, UniCAR T cells automatically turn off. Until now, all UniCAR TMs were constructed by fusion of the UniCAR epitope to an antibody domain. To open up the wide field of low-molecular weight compounds for retargeting of UniCAR T cells to tumor cells, and to follow in parallel the progress of UniCAR T cell therapy by PET imaging we challenged the idea to convert a PET tracer into a UniCAR-TM. For proof of concept, we selected the clinically used PET tracer PSMA-11, which binds to the prostate-specific membrane antigen overexpressed in prostate carcinoma. Here we show that fusion of the UniCAR epitope to PSMA-11 results in a low-molecular weight theranostic compound that can be used for both retargeting of UniCAR T cells to tumor cells, and for non-invasive PET imaging and thus represents a member of a novel class of theranostics.
Keywords: PSMA ligand, UniCAR, prostate cancer, immunotherapy, PET imaging

Publ.-Id: 29586 - Permalink


1,4,7-Triazacyclononane ligands as bifunctional radiocoppper chelating agents
Stephan, H.; Joshi, T.;
design of tailor-made bifunctional chelating agents (BFCAs) for radioactive transition metals in view of nuclear medical applications as well as acquisition of reliable information about the biodistribution of different materials represents an intensive and rapidly developing field of research [1]. In this context, the tridentate macrocycle 1,4,7-triazacyclononane (TACN) is of special interest since it forms stable complexes with transition metal ions particularly with Cu(II) [2]. Further, the introduction of donor groups, such as pyridyl units, on the TACN scaffold, significantly enhances the thermodynamic stability as well as the kinetic inertness of the Cu(II) complexes formed. Furthermore, the ligand structure offers various possibilities to introduce biological vectors and suitable linkers for tuning the lipophilicity, overall charge and aqueous solubility of the final bioconjugates. For example, TACN ligands with two pyridylmethyl side-arms (DMPTACN derivatives) rapidly chelate copper(II) radionuclides under ambient conditions and the resulting complexes show high in vivo stability. One such derivative, 2-[4,7-bis(2-pyridylmethyl)-1,4,7-triazacyclononan-1-yl]acetic acid (DMPTACN-COOH), containing two coordinating picoline groups, not only exhibits excellent in vivo stability after 64Cu radiolabeling, but also allows for direct attachment of vector molecules as well as easy introduction of bioconjugatable functionalities (e.g., maleimide, isothiocyanate) via the carboxylate pendant. This makes DMPTACN-COOH and its derivatives promising BFCAs for radiocopper (DMPTACN-based BFCAs), facilitating the preparation of radiolabeled targeting molecules and bio(nano)materials.
Examples of target-specific peptides and bio(nano)materials equipped with DMPTACN ligands for labeling with 64Cu as an ideal positron emitter are discussed. This enables tumor imaging and the biodistribution of the materials to be studied over a period of days via positron emission tomography (PET).

[1] E. Boros, A. B. Packard, Chem. Rev. 119 (2019) 870-901.
[2] T. Joshi, M. Kubeil, A. Nsubuga, G. Singh, G. Gasser, H. Stephan, ChemPlusChem 83 (2018) 554-564.
  • Lecture (Conference)
    19th International Conference on Biological Inorganic Chemistry, 11.-16.08.2019, Interlaken, Schweiz

Publ.-Id: 29584 - Permalink


PIConGPU simulation setup for L|PWFA simulation
Pausch, R.ORC; Steiniger, K.ORC; Debus, A.ORC

The input set of the L|PWFA simulation as used in the publication "Demonstration of a compact plasma wakefield accelerator powered by laser-accelerated electron beams" by T.Kurz et al. .
To run the simulation use PIConGPU 0.4.2 (see DOI: 10.5281/zenodo.1491926).           

  • Software in the HZDR data repository RODARE
    Publication date: 2019-08-19
    DOI: 10.14278/rodare.146
    License: CC-BY-4.0

Downloads:

Publ.-Id: 29581 - Permalink


Coherent control of qudit modes in SiC at room temperature
Astakhov, G. V.ORC
We present room-temperature coherent control of high-dimensional quantum bits, the so-called qudits, associated with vacancy-related spins in silicon carbide enriched with nuclear spin-free isotopes. In addition to the excitation of a spectrally narrow qudit mode at the pump frequency, several other modes are excited in the electron spin resonance spectra whose relative positions depend on the external magnetic field.
  • Invited lecture (Conferences)
    4th International Conference on Metamaterials and Nanophotonics METANANO 2019, Special Symposium QuantuMetanano, 14.-19.07.2019, Saint Petersburg, Russia

Publ.-Id: 29579 - Permalink


Coherent control of qudit modes in SiC
Astakhov, G. V.ORC
We demonstrated coherent manipulation of spin qudit modes in isotopically purified SiC at room temperature. We also developed a theory describing the excitation and detection of these modes in inhomgeneously broadened systems and showed that qudits are characterized by multiple relaxation times. These findings can lead to dipole-coupled networks, unconditional electron-nuclear spin registers and spectral selection of highly coherent individual spins, particularly in nanocrystals. Our results hence open new possibilities to improve the sensitivity of quantum sensors and execute nontrivial quantum protocols in dense spin ensembles.
  • Invited lecture (Conferences)
    Invited colloquium at TU Dortmund, 13.06.2019, Dortmund, Germany

Publ.-Id: 29578 - Permalink


Effect of irradiation on defect coherence properties in silicon carbide
Astakhov, G. V.ORC
We have thoroughly investigated the irradiation impact on the room-temperature spin coherence properties of silicon vacancies in SiC. We have measured the spin-lattice relaxation time and the spin coherence time depending on the irradiation particle (electron, neutron and proton), irradiation fluence and irradiation energy.
  • Invited lecture (Conferences)
    Ion Beam for future Technologies 2019, 01.-03.04.2019, Dubrovnik, Croatia

Publ.-Id: 29577 - Permalink


UFXCT data of silo discharge of hydrogel spheres
Bieberle, M.ORC; Barthel, F.; Sancho Martinez, D.; Stannarius, R.

The outflow of hydrogel spheres from a cylindrical storage container with narrow outlet of two different sizes is imaged by means of ultrafast X-ray computed tomography (UFXCT) at different heights above the outlet. Sequences of cross-sectional images were recorded over 30 s with a frame rate of 1000 fps in dual plane mode.

Keywords: ultrafast measurement; X-ray CT; silo discharge
Related publications
UFXCT data of silo discharge of airsoft balls (Id 29573) is a supplement to this publication
High-speed X-ray tomography of silo discharge (Id 29464) is supplemented by this publication
  • Reseach data in the HZDR data repository RODARE
    Publication date: 2019-08-16
    DOI: 10.14278/rodare.144

Downloads:

Publ.-Id: 29575 - Permalink


UFXCT data of silo discharge of airsoft balls
Bieberle, M.ORC; Barthel, F.; Sancho Martinez, D.; Stannarius, R.

The outflow of airsoft bullets from a cylindrical storage container with narrow outlet is imaged by means of ultrafast X-ray computed tomography (UFXCT) at different heights above the outlet. Sequences of cross-sectional images were recorded over 30 s with a frame rate of 1000 fps in dual plane mode.

Keywords: ultrafast measurement; X-ray CT; silo discharge
Related publications
UFXCT data of silo discharge of hydrogel spheres (Id 29575) is supplemented by this publication
High-speed X-ray tomography of silo discharge (Id 29464) is supplemented by this publication
  • Reseach data in the HZDR data repository RODARE
    Publication date: 2019-08-16
    DOI: 10.14278/rodare.142

Downloads:

Publ.-Id: 29573 - Permalink


Single bubble dynamics during nucleate flow boiling on a vertical heater: Experimental and theoretical analysis of the effect of surface wettability,roughness and bulk liquid velocity
Sarker, D.; Ding, W.; Schneider, C.; Hampel, U.;
The present study reports the mutual effect of heater surface wettability, roughness and bulk liquid velocity on the bubble dynamics and departure in nucleate boiling. Boiling experiments were conducted at atmospheric pressure with degassed-deionized water at low subcooling (1.9 ± 0.25 K) for vertically oriented stainless steel heaters. Self-assembled monolayer (SAM) coating and wet-etching technique were used to alter the heater surface wettability and roughness. Liquid contact angle hysteresis ("θ" _"hys" ) and root mean square roughness (Sq) of the heater surfaces were adjusted between "42.32° "≤ "θ" _"hys" ≤ "68.56°" and roughness "0.01" µm≤"Sq"≤"0.549" µm. High resolution optical shadowgraphy has been used to record the bubble life cycle. Experimental results show that higher bulk liquid velocity yields smaller bubble departure diameters for all heater surface characteristics. Bubble departure diameters are greater for low wetting surfaces. The bubble growth rate and departure diameter were found maximum for an intermediate surface roughness Sq between 0.108 and 0.218 m. The corresponding roughness height is referred to as the ‘optimal roughness height’ in this study. Eventually, a bubble departure criterion was derived from the expressions of forces which act on a nucleating bubble throughout its growth cycle. 90% of the departing bubbles satisfy the bubble departure criterion with ± 25% deviation.
Keywords: Bubble growth, bubble departure, surface wettability, roughness, flow boiling

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  • Secondary publication expected from 24.07.2020

Publ.-Id: 29570 - Permalink


Transient Characteristics of Interdigitated GaAs Photoconductive Semiconductor Switch at 1-kHz Excitation
Xu, M.; Liu, X.; Li, M.; Liu, K.; Qu, G.; Wang, V.; Hu, L.; Schneider, H.;
To explore the stability of gallium arsenide (GaAs) photoconductive semiconductor switches (PCSSs) with avalanche multiplication mechanism, an interdigitated electrodestructure is presented at 1-kHz excitation by a femtosecond laser. The influences of optical excitation and bias electric field on switching characteristics are investigated. The transient current density and the distribution of electric field are demonstrated by the Monte Carlo simulation. The repetitive switching indicates that the avalanche multiplication mechanism could persist stably at 1-kHz repetition rate operation with this specific electrode structure.
Keywords: Gallium arsenide, GaAs, high gain, photoconductive semiconductor switch, avalanche multiplication, repetition rate

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Publ.-Id: 29564 - Permalink


Computer Modeling of Single-layer Nanocluster Formation in a Thin SiO2 Layer Buried in Si by Ion Mixing and Thermal Phase Decomposition
Prüfer, T.; Möller, W.; Heinig, K.-H.; Wolf, D.; Engelmann, H.-J.; Xu, X.; von Borany, J.;
A single sheet of Si nanoclusters with an average diameter of about 2 nm has been formed in a 30 nm Si / 7 nm SiO2 / Si layer stack by 50 and 60 keV Si+ ion-beam mixing at room temperature and fluences between 8.51015 and 2.61016 ions/cm2, and subsequent thermal annealing at a temperature above 1000°C. Computer modelling of the process is accomplished by TRIDYN dynamic ballistic simulation of ion mixing and subsequent lattice kinetic Monte Carlo simulation of the phase decomposition of sub-stoichiometric silicon oxide into Si nanoclusters in a SiO2 matrix. The simulation algorithms are briefly described with special emphasis on the choice of governing parameters for the present system. In comparison to the experimental results it is concluded that the predicted ion mixing profiles overestimate the interface broadening. This discrepancy is attributed to the neglect of chemical driving forces in connection with thermal-spike induced diffusion, which tends to re-constitute the Si/SiO2 interfaces. With a corresponding correction and a suitable number of Monte Carlo steps, the experimentally obtained areal densities and average diameters of the nanoclusters are successfully reproduced.
Keywords: Ion Beam Mixing; SiO2; Silicon; Thermal Spikes

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Publ.-Id: 29563 - Permalink


Cancer Stem Cells and Radioresistance: DNA Repair and Beyond
Schulz, A.; Meyer, F.; Dubrovska, A.; Borgmann, K.;
The current preclinical and clinical findings demonstrate that, in addition to the conventional clinical and pathological indicators that have a prognostic value in radiation oncology, the number of cancer stem cells (CSCs) and their inherent radioresistance are important Parameters for local control after radiotherapy. In this review, we discuss the molecular mechanisms of CSC radioresistance attributable to DNA repair mechanisms and the development of CSC-targeted therapies for Tumor radiosensitization. We also discuss the current challenges in preclinical and translational CSC research including the high inter- and intratumoral heterogeneity, plasticity of CSCs, and microenvironment-stimulated tumor cell reprogramming.
Keywords: cancer stem cells; DNA repair; radioresistance; 5Rs of radiation biology

Publ.-Id: 29561 - Permalink


Interference of tumour mutational burden with outcome of patients with head and neck cancer treated with definitive chemoradiation: a multicentre retrospective study of the German Cancer Consortium Radiation Oncology Group
Eder, T.; Hess, A.; Konschak, R.; Stromberger, C.; Johrens, K.; Fleischer, V.; Hummel, M.; Balermpas, P.; von der Grun, J.; Linge, A.; Lohaus, F.; Krause, M.; Baumann, M.; Stuschke, M.; Zips, D.; Grosu, A.; Abdollahi, A.; Debus, J.; Belka, C.; Pigorsch, S.; Combs, E.; Budach, V.; Tinhofer, I.;
Background: Tumour mutational burden (TMB) estimated from whole exome sequencing or comprehensive gene panels has previously been established as predictive factor of response to immune checkpoint inhibitors (ICIs).
Its predictive value for the efficacy of concurrent chemoradiation (cCRTX), a potential combination partner of ICI, remains unknown.
Methods: The accuracy of TMB estimation by an in-house 327-gene panel was established in the Cancer Genome Atlas (TCGA) head and neck squamous cell carcinoma (HNSCC) data set. Interference of TMB with outcome after cCRTX was determined in a multicentre cohort of patients with locally advanced HNSCC uniformly treated with cCRTX. Targeted next-generation sequencing was successfully applied in 101 formalin-fixed, paraffin-embedded pretreatment tumour samples. In a subset of cases (n = 40), tumour RNA was used for immune-related gene expression profiling by the nanoString platform. TMB was correlated with TP53 genotype, human papilloma virus (HPV) status, immune expression signatures and survival parameters. Results were validated in the TCGA HNSCC cohort.
Results: A high accuracy of TMB estimation by the 327-gene panel was established. High TMB was significantly associated with an increased prevalence of TP53 mutations and immune gene expression patterns unrelated to T cell-inflamed gene expression profiles. Kaplan-Meier analysis revealed significantly reduced overall survival in the patient group with high TMB (hazard ratio for death: 1.79, 95% confidence interval: 1.02-3.14; P = 0.042) which remained significant after correcting for confounding factors in the multivariate model. The prognostic value of TMB was confirmed in the TCGA HNSCC cohort.
Conclusion: High TMB identifies HNSCC patients with poor outcome after cCRTX who might preferentially benefit from CRTX-ICI combinations.

Publ.-Id: 29560 - Permalink


Mineral Precipitation in Fractures and Nanopores within Shale Imaged Using Time-Lapse X-ray Tomography
Godinho, Jose R. A.; Ma, L.; Chai, Y.; Storm, M.; Burnett, T. L.;
Barite precipitation in fractures and nanopores within a shale sample is analysed in situ, in 3D, and over time. Diffusion of barium and sulphate from opposite sides of the sample creates a supersaturated zone where barium sulphate crystals precipitate. Time-lapse synchrotron-based computed tomography was used to track the growth of precipitates over time, even within the shale’s matrix where the nanopores are much smaller than the resolution of the technique. We observed that the kinetics of precipitation is limited by the type and size of the confinement where crystals are growing, i.e., nanopores and fractures. This has a major impact on the ion transport at the growth front, which determines the extent of precipitation within wider fractures (fast and localised precipitation), thinner fractures (non-localised and slowing precipitation) and nanopores (precipitation spread as a front moving at an approximately constant velocity of 10 ± 3 µm/h). A general sequence of events during precipitation in rocks containing pores and fractures of different sizes is proposed and its possible implications to earth sciences and subsurface engineering, e.g., fracking and mineral sequestration, are discussed.
Keywords: time-lapse imaging; 3D imaging; shale; barite; mineral precipitation; scale; formation damage; porous media; fracking

Publ.-Id: 29557 - Permalink


Spin Hall magnetoresistance in heterostructures consisting of noncrystalline paramagnetic YIG and Pt
Lammel, M.; Schlitz, R.; Geishendorf, K.; Makarov, D.; Kosub, T.; Fabretti, S.; Reichlova, H.; Huebner, R.; Nielsch, K.; Thomas, A.; Goennenwein, S. T. B.;
The spin Hall magnetoresistance (SMR) effect arises from spin-transfer processes across the interface between a spin Hall active metal and an insulating magnet. While the SMR response of ferrimagnetic and antiferromagnetic insulators has been studied extensively, the SMR of a paramagnetic spin ensemble is not well established. Thus, we investigate herein the magnetoresistive response of the as-deposited yttrium iron garnet/platinum thin film bilayers as a function of the orientation and the amplitude of an externally applied magnetic field. Structural and magnetic characterization shows no evidence for the crystalline order or spontaneous magnetization in the yttrium iron garnet layer. Nevertheless, we observe a clear magnetoresistance response with a dependence on the magnetic field orientation characteristic for the SMR. We propose two models for the origin of the SMR response in paramagnetic insulator/platinum heterostructures. The first model describes the SMR of an ensemble of noninteracting paramagnetic moments, while the second model describes the magnetoresistance arising by considering the total net moment. Interestingly, our experimental data are consistently described by the net moment picture, in contrast to the situation in compensated ferrimagnets or antiferromagnets.
Keywords: spin Hall magnetoresistance, antiferromagnetic insulators

Publ.-Id: 29554 - Permalink


Tuning the interactions in the spin-ice materials Dy2Ge2−xSixO7 by silicon substitution
Stöter, T.; Antlauf, M.; Opherden, L.; Gottschall, T.; Hornung, J.; Gronemann, J.; Herrmannsdörfer, T.; Granovsky, S.; Schwarz, M.; Doerr, M.;
We report that the lattice constant of Dy2Ge2−xSixO7 (x = 0, 0.02, 0.08, 0.125) can be systematically reduced by substituting the nonmagnetic germanium ion in the cubic pyrochlore oxide with silicon. A multianvil high-pressure synthesis was performed up to 16 GPa and 1100 °C to obtain polycrystalline samples in a solid-state reaction. Measurements of magnetization, ac susceptibility, and heat capacity reveal the typical signatures of a spin-ice phase. From the temperature shift of the peaks, observed in the temperature-dependent heat capacity, we deduce an increase in the strength of the exchange interaction. In conclusion, the reduced lattice constant leads to a changed ratio of the competing exchange and dipolar interaction. This puts the new spin-ice compounds closer towards the phase boundary of a short-range spin-ice arrangement and antiferromagnetic long-range order consistent with an observed reduction in the energy scale of monopole excitations.

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Publ.-Id: 29552 - Permalink


Controlling Chiral Spin States of a Triangular-Lattice Magnet by Cooling in a Magnetic Field
Deng, S.; Fischer, G.; Uhlarz, M.; Wosnitza, J.; Bohnen, K.-P.; Heid, R.; Wang, C.; Sürgers, C.;
Magnetic materials with a non-collinear and non-coplanar arrangement of magnetic moments hosting a nonzero scalar spin-chirality exhibit unique magnetic and spin-dependent electronic transport properties. The spin chirality often occurs in materials where competing exchange interactions lead to geometrical frustrations between magnetic moments and to a strong coupling between the crystal lattice and the magnetic structure. These characteristics are particularly strong in Mn-based antiperovskites where the interactions and chirality can be tuned by substitutional modifications of the crystalline lattice. This study presents evidence for the formation of two unequal chiral spin states in magnetically ordered Mn3.338Ni0.651N antiperovskite based on density functional theory calculations and supported by magnetization measurements after cooling in a magnetic field. The existence of two scalar spin-chiralities of opposite sign and different magnitude is demonstrated by a vertical shift of the magnetic-field dependent magnetization and Hall effect at low fields and from an asymmetrical magnetoresistivity when the applied magnetic field is oriented parallel or antiparallel to the direction of the cooling field. This opens up the possibility of manipulating the spin chirality for potential use in the emerging field of chiral spintronics.

Publ.-Id: 29551 - Permalink


Evidence for the Single-Site Quadrupolar Kondo Effect in the Dilute Non-Kramers System Y1−xPrxIr2Zn20
Yanagisawa, T.; Hidaka, H.; Amitsuka, H.; Zherlitsyn, S.; Wosnitza, J.; Yamane, Y.; Onimaru, T.;
Acoustic signatures of the single-site quadrupolar Kondo effect in Y0.966Pr0.034Ir2Zn20 are presented. The elastic constant (C11 − C12)/2, corresponding to the Γ3(E)-symmetry electric-quadrupolar response, reveals a logarithmic temperature dependence of the quadrupolar susceptibility in the low-magnetic-field region below ∼0.3 K. Furthermore, the Curie-type divergence of the elastic constant down to ∼1 K indicates that the Pr ions in this diluted system have a non-Kramers ground-state doublet. These observations evidence the single-site quadrupolar Kondo effect, as previously suggested based on specific-heat and electrical-resistivity data.

Publ.-Id: 29550 - Permalink


High magnetic field phase diagram and failure of the magnetic Grüneisen scaling in LiFePO4
Werner, J.; Sauerland, S.; Koo, C.; Neef, C.; Pollithy, A.; Skourski, Y.; Klingeler, R.;
We report the magnetic phase diagram of single-crystalline LiFePO4 in magnetic fields up to 58 T and present a detailed study of magnetoelastic coupling by means of high-resolution capacitance dilatometry. Large anomalies at TN in the thermal-expansion coefficient α imply pronounced magnetoelastic coupling. Quantitative analysis yields the magnetic Grüneisen parameter γmag = 6.7(5) × 10−7 mol/J. The positive hydrostatic pressure dependence dTN/dp = 1.46(11) K/GPa is dominated by uniaxial effects along the a axis. Failure of Grüneisen scaling below ≈40K, i.e., below the peak temperature in the magnetoelectric coupling coefficient [7], implies several competing degrees of freedom. A broad and strongly magnetic field dependent anomaly in α in this temperature regime highlights the relevance of structure changes. Upon application of the magnetic field B||b axis, a pronounced jump in the magnetization implies spin reorientation at BSF = 32 T as well as a precursing phase at 29 T and T = 1.5K. In a two-sublattice mean-field model, the saturation field Bsat,b = 64(2) T enables assessing the effective antiferromagnetic exchange interaction Jaf = 2.68(5)meV as well as anisotropies Db = −0.53(4)meV and Dc = 0.44(8)meV.

Publ.-Id: 29549 - Permalink


High Temperature and Ion Implantation-Induced Phase Transformations in Novel Reduced Activation Si-Fe-V-Cr (-Mo) High Entropy Alloys
Gandy, A. S.; Jim, B.; Coe, G.; Patel, D.; Hardwick, L.; Akhmadaliev, S.; Reeves-Mclaren, N.; Goodall, R.;
For fusion to be realized as a safe, sustainable source of power, new structural materials need to be developed which can withstand high temperatures and the unique fusion radiation environment. An attractive aspect of fusion is that no long-lived radioactive wastes will be produced, but to achieve this structural materials must comprise reduced activation elements. Compositionally complex alloys (CCAs) (also called high entropy alloys, HEAs) are promising candidates for use in extreme environments, including fusion, but few reported to date have low activation. To address these material challenges, we have produced novel, reduced activation, HEAs by arc-melting, and investigated their thermal stability, and radiation damage resistance using 5 MeV Au2+ ion implantation. Whilst the alloys were designed to form single phase BCC, using room temperature and non-ambient in situ X-ray diffraction we have revealed the thermodynamically stable structure of these alloys is in fact a sigma phase. We propose that a BCC phase is formed in these alloys, but at high temperatures (>1000°C). A BCC phase was also formed during heavy ion implantation, which we propose to be due to the rapid heating and cooling that occurs during the thermal spike, effectively freezing in the BCC phase produced by an implantation induced phase transformation. The BCC phase was found to have high hardness and a degree of ductility, making these new alloys attractive in the development of reduced activation HEAs for nuclear applications.
Keywords: high entropy alloy (HEA), reduced activation, phase transformation, ion implantation, thermal stability, nuclear, radiation damage

Publ.-Id: 29548 - Permalink


Not all Neoproterozoic iron formations are glaciogenic: Sturtian-aged non-Rapitan exhalative iron formations from the Arabian–Nubian Shield
Abd El-Rahman, Y.; Gutzmer, J.; Li, X.-H.; Seifert, T.; Li, C.-F.; Ling, X.-X.; Li, J.;
Neoproterozoic iron formations are exposed in the Wadi Hamama area (Egypt) in the northwestern part of the Arabian–Nubian Shield. Mafic and felsic volcanic and volcaniclastic rocks of an intra-oceanic island-arc setting host multiple, thin iron-formation units. Major element compositions of the iron formation confirm a low detrital input, whereas the rare-earth elements and Y data suggest deposition related to an influx of low-temperature hydrothermal fluids. Unlike most Neoproterozoic banded iron formations, but similar to other iron-formation occurrences from the Arabian–Nubian Shield, the Nd isotopic compositions of the Wadi Hamama iron formations are predominantly mantle-like. SIMS U–Pb zircon ages of the host volcaniclastic units indicate that the age of iron-formation deposition is ca. 695 Ma, which is within the Sturtian epoch that is presumed to be a glacial event of global extent. Nevertheless, there is no robust evidence of any influence of Sturtian glaciation in the Arabian–Nubian Shield. Our results rather suggest that the iron formations in the area may have formed as low-temperature exhalites on the floor of an island-arc basin. The iron formations were deposited during periods of volcanic quiescence, with metals having been derived during low-temperature pervasive hydrothermal alteration of volcanic and volcaniclastic rocks exposed at the seafloor–seawater interface. Precipitation took place due to mixing of metal-bearing hydrothermal fluids and cold, oxygenated seawater. There is no need to invoke possible effects of global glaciation to explain the origin of the Sturtian-aged iron formations in the shield. Our study thus suggests that not all Neoproterozoic iron formations are necessarily linked to glacial events as the Hamama deposit represents a non-Rapitan exhalative iron formation.
Keywords: Cryogenian, Exhalite, Hydrothermal, Iron formations, Island arc, Sturtian glaciation

Publ.-Id: 29547 - Permalink


High temperature plasma immersion ion implantation using hollow cathode discharges in small diameter metal tubes
Ueda, M.; Silva, C.; de Souza, G. B.; Pichon, L.; Reuther, H.;
High temperature nitrogen plasma immersion ion implantation (HT-NPIII) method was used to treat the internal walls of small diameter metal tubes made of SS304 and of Ti6-Al4-V (TAV). Using a lid in one side of the tubes was essential to reach high temperatures of 700-900 °C, necessary for high thermal diffusion of nitrogen in Ti alloy samples placed inside the metal tubes for monitoring the HT-NPIII process. The used metal tubes also reached such high temperatures. New phases of TiN and Ti2N were successfully attained in the TAV samples with the treated layer thickness of more than 1.3 μm for all the tested cases. For tubes made of SS304, HT-NPIII treatments resulted in redeposition of FeN thick layers with high hardness on the surfaces of the internal walls of the tubes and on the monitoring samples. Obtaining such HT-NPIII conditions in these small metallic tubes was possible by achieving high plasma density through hollow cathode discharges inside those tubes. These results were compared to the ones obtained on the nitrogen implantation treatments of TAV samples in moderate to high temperatures carried out previously in the laboratory which indicated the superior performance of the presently reported method of surface modification.

Publ.-Id: 29546 - Permalink


Structure–Affinity Relationships of Fluorinated Spirocyclic Sigma2 Receptor Ligands with an Exocyclic Benzylamino Moiety
Bergkemper, M.; Kronenberg, E.; Schepmann, D.; Ludwig, F.-A.; Brust, P.; Wünsch, B.;
To identify a potent and selective σ2 receptor ligand appropriate for development as a positron emission tomography (PET) tracer, several fluorinated analogues of the spirocyclic lead compounds trans- and cis-6 (N-(2,4-dimethylbenzyl)-3-methoxy-3,4-dihydrospiro[[2]benzopyran-1,1′-cyclohexan]-4′-amine) were designed. In multistep syntheses, a fluorine atom was introduced directly or as a 2-fluoroethoxy moiety on the 2-benzopyran scaffold, on the dimethylbenzylamino moiety, or on the central amino moiety. The σ1 and σ2 receptor affinity was determined in receptor binding studies with radioligands. With respect to σ2 affinity and σ2/σ1 selectivity, cis-N-(2,4-dimethylbenzyl)-5-fluoro-3-methoxy-3,4-dihydrospiro[[2]benzopyran-1,1′-cyclohexan]-4′-amine (cis-15 c, Ki(σ2)=51 nm) and cis-N-[4-(fluoromethyl)-2-methylbenzyl]-3-methoxy-3,4-dihydrospiro[[2]benzopyran-1,1′-cyclohexan]-4′-amine (cis-28 e, Ki(σ2)=57 nm) are the most promising ligands. The combination of both structural elements in one molecule, cis-N-[4-(fluoromethyl)-2-methylbenzyl]-5-fluoro-3-methoxy-3,4-dihydrospiro[[2]benzopyran-1,1′-cyclohexan]-4′-amine (cis-28 c: Ki(σ2)=874 nm), resulted in decreased σ2 and σ1 affinity. Methylation of secondary amines led to three tertiary methylamines with moderate affinity for both σ receptor subtypes.
Keywords: cis–trans configuration, fluorinated PET tracers, receptor selectivity, spirocyclic ligands, structure–affinity relationships, σ receptors

Publ.-Id: 29545 - Permalink


Opportunities for measurements of astrophysical‐relevant alpha‐capture reaction rates at CRYRING@ESR
Forstner, O.; Bemmerer, D.; Cowan, T.; Dressler, R.; Junghans, A.ORC; Schumann, D.; Stöhlker, T.; Szücs, T.; Wagner, A.ORC; Zuber, K.
The heavy‐ion storage ring CRYRING@ESR has recently been installed and commissioned at GSI as one of the first installations of the upcoming Facility for Antiproton and Ion Research (FAIR). It is designed to store highly charged ions in the energy range between 300 keV/u and about 10 MeV/u. It will incorporate a gas‐jet target providing high‐density jets of, among other gases, hydrogen and helium. This will allow to study alpha‐capture reaction rates of astrophysical interest in the energy range of the Gamow window for core‐collapse supernovae. Special interest comes from the long‐lived radio‐isotope 44Ti (t1/2 = 58.9 years), which is supposed to be produced in the alpha‐rich freeze‐out during such an event. The nucleosynthesis of this isotope is of great interest, as the amount of material produced can be estimated by direct observation in remnants of recent supernovae. The disagreements between the observations and the estimations from astrophysical models show the need of more experimental data for the production and consumption reactions in the energy range of a core‐collapse supernova. In this article, we will describe the proposed method of injecting beams of 44Ti into CRYRING@ESR and performing the actual reaction rate measurements.
Keywords: 44Ti core-collapse supernova alpha-capture

Publ.-Id: 29543 - Permalink


Crystal structure and dehydration behaviour of Ag+-exchanged levyne
Cametti, G.; Churakov, S. V.; Scheinost, A.;
Levyne is a natural zeolite Ca2.53Na0.72K0.23(Al6.26Si11.8O36)·17.58H2O with LEV framework type. The structure can be described by a sequence of single six-membered rings (S6R) and double six-membered rings (D6R) stacked along the c axis with AABCCABBCAA sequence [1,2]. This sequence originates columns along [001] of [496583] polyhedra (levyne cages) alternating with [4662] polyhedra (double six-rings). Two-dimensionally interconnected channels (free diameters 3.6 × 4.8 Å) confined by eight-membered rings run perpendicular to [001]. In this study we investigated the crystal structure and thermal stability of a Ag-exchanged levyne by using a multimethodological approach.
Keywords: zeolite levyne Ag-doping XAFS
  • Poster
    32nd European Crystallographic Meeting (ECM 32), 18.-23.08.2019, Wien, Austria

Publ.-Id: 29541 - Permalink


Study of mixing enhanced by a magnetic field in a microfluidic channel
Yang, X.; Wojnicki, M.; Zabinski, P.; Mutschke, G.;
Mixing in a microfluidic environment is challenging due to the laminarity of flow. The idea of the present study is to apply a magnetic force to a stratified channel flow. Due to the different magnetic susceptibilities of the liquid layers, mixing might be triggered. The magnetic gradient force is generated simply by the application of permanent magnets. Fig. 1 shows the channel setup with two entries and two outflows. The upper entry is fed with water, whereas the lower entry is fed with 0.1 M HoCl3 solution. On top of the front part, the magnets are applied. Different flow rates and magnet configurations were studied. The degree of mixing is measured by determining the concentration of HoCl3 in the upper outlet by a spectrophotometer measuring the absorbance at a specific wavelength. Additional Micro-PIV measurements are performed to resolve the related flow pattern in detail. Numerical simulations are performed to complement the investigation.
Keywords: microfluidics, mixing, paramagnetic solution, magnetic field, Kelvin force
  • Poster
    11th International PAMIR International Conference - Fundamental and Applied MHD, 01.-05.07.2019, Reims, Frankreich

Publ.-Id: 29535 - Permalink


Study of the Marangoni effect during electrolytic gas evolution
Mutschke, G.; Massing, J.; Hossain, S. S.; Yang, X.; Baczyzmalski, D.; Cierpka, C.; Eckert, K.;
lectrolytic gas evolution is a fundamental phenomenon occurring in a large number of industrial applications. Near the electrode, bubble growth is understood to appear due to mass flux of dissolved gas across the bubble interface from a supersaturated electrolyte. Because of related thermal, electrical or solutal effects, a gradient of the surface tension along the interface may exist. The resulting shear stress would cause convection at the interface (Marangoni effect), which may affect the mass transfer across the interface during growth and also the departure of the gas bubble. This Marangoni effect was unveilled only recently in an experimental study [1]. The present work aims to investigate the origin of the effect in more detail. Numerical simulations are performed including only the thermal Marangoni effect near a hydrogen gas bubble growing electrochemically at a microelectrode in an acidic electrolyte. The simulation results are compared with experimental data of the near-bubble convection obtained by Particle Tracking Velocimetry (PTV) and by temperature measurements. The comparison allows to conclude on a strong thermocapillary effect at the microelectrode [2]. The related force on the bubble is found to retard the release of the bubble.

[1] X. Yang et al, Phys. Chem. Chem. Phys., 20: 11542-11548. 2018.
[2] J. Massing et al., Electrochim. Acta. 2019. IN PRESS
Keywords: Electrolysis, gas evolution, hydrogen evolution, Marangoni, thermocapillary effect
  • Invited lecture (Conferences)
    11th International PAMIR International Conference - Fundamental and Applied MHD, 01.-05.07.2019, Reims, Frankreich
  • Lecture (others)
    Institutskolloquium, 22.08.2019, Ilmenau, Deutschland

Publ.-Id: 29534 - Permalink


Feasibility assessment of using external neutron and gamma radiation measurements for monitoring the state of fuel assemblies in dry storage casks
Rachamin, R.; Hampel, U.;
This study assesses the feasibility of using external neutron and gamma flux measurements to detect the state of spent fuel assemblies inside a sealed cask. Several Monte-Carlo simulations were performed to evaluate the neutron and gamma flux distribution outside the sidewall of a cask with all intact fuel assemblies and a cask with one damaged fuel assembly, mimicking a fuel assembly with expanded rods and fuel relocation. The evaluation was performed for different positions of the damaged fuel assembly and different storage times. The results show that in case the damaged fuel assembly is located near the inner wall of the cask, it can be detected by both of the radiation modes. The detection of the inner damaged fuel assemblies, however, can be feasible only by the external neutron flux.
Keywords: Monte-Carlo, dry storage cask, monitoring, neutron and gamma radiation

Publ.-Id: 29532 - Permalink


FLUKA simulations with and without magnetic field
Müller, S.ORC
Presentation at Mu2e Simulation WG meting August 1, 2019
Keywords: Mu2e, FLUKA
  • Lecture (others)
    Mu2e Simulation WG meeting, 01.08.2019, Batavia, USA

Publ.-Id: 29531 - Permalink


Improved magnetostructural and magnetocaloric reversibility in magnetic Ni-Mn-In shape-memory Heusler alloy by optimizing the geometric compatibility condition
Devi, P.; Salazar Mejia, C.; Ghorbani Zavareh, M.; Dubey, K. K.; Kushwaha, P.; Skourski, Y.; Felser, C.; Nicklas, M.; Singh, S.;
We report an improved reversibility of magnetostriction and inverse magnetocaloric effect (MCE) for the magnetic shape-memory Heusler alloy Ni1.8Mn1.8In0.4. We show that the magnetostriction and MCE crucially depends on the geometrical compatibility of the austenite and martensite phases. Detailed information on the compatibility of both phases has been obtained from the transformation matrix calculated from x-ray diffraction data. The uniqueness of the lattice parameters results in an improved reversibility of the magnetostriction and the MCE. In the thermal hysteresis region of the martensitic transformation, the maximum relative length change is 0.3% and the adiabatic temperature change Δad ≈ −10 K in pulsed magnetic fields. Our results reveal that the approach of geometric compatibility will allow one to design materials with reversible magnetostriction and reversible inverse MCE at a first-order magnetostructural phase transition in shape-memory Heusler alloys.

Publ.-Id: 29530 - Permalink


Magnetic phase transitions, metastable states, and magnetic hysteresis in the antiferromagnetic compounds Fe0.5TiS2−ySey
Baranov, N. V.; Selezneva, N. V.; Sherokalova, E. M.; Baglaeva, Y. A.; Ovchinnikov, A. S.; Tereshchenko, A. A.; Gorbunov, D. I.;
The phase transitions and magnetization processes in the antiferromagnetic compounds Fe0.5TiS2−ySey [FeTi2(S,Se)4] with an ordered layered crystal structure of the CrS4 type have been studied by using x-ray diffraction, measurements of the specific heat, electrical resistivity, magnetoresistance, and the magnetization in steady and pulsed magnetic fields together with calculations within the Ising model accounting the magnetoelastic interactions. The change from the spin-flip to spin-flop type phase transition and a monotonic growth of the critical transition field from ∼50 kOe at y = 0 up to 470 kOe at y = 2 has been observed with the Se for S substitution in antiferromagnetic (AFM) compounds Fe0.5TiS2−ySey. In the selenium-poor compounds (y < 0.5), the field-induced AFM-FM phase transition at low temperatures is accompanied by ultrasharp changes in the magnetization and magnetoresistance and by huge magnetic hysteresis. The presence of remnant magnetoresistance in these compounds after the application of a magnetic field indicates the formation of a metastable field-induced FM state. Despite an AFM ground state, the Fe0.5TiS2−ySey compounds with y < 0.5 after application of a magnetic field behave at low temperatures as high-anisotropic Ising-type ferromagnets with the coercive field Hc up to ∼60 kOe. It has been shown, that magnetoelastic interactions may be responsible for the formation of the metastable field-induced high-coercive FM state in the Ising-type antiferromagnets.

Publ.-Id: 29529 - Permalink


Tailoring the ferrimagnetic-to-ferromagnetic transition field by Interstitial and substitutional atoms in the R–Fe compounds
Tereshina, I. S.; Ivanov, L. A.; Tereshina-Chitrova, E. A.; Gorbunov, D. I.; Paukov, M. A.; Havela, L.; Drulis, H.; Granovsky, S. A.; Doerr, M.; Gaviko, V. S.; Andreev, A. V.;
Fundamental characteristics of rare-earth (R) – iron intermetallics R2Fe14B are highly sensitive to the atomic substitutions and interstitial absorption of light elements. We studied a combined influence of the substitutions in the rare-earth sublattice and hydrogen absorption on the magnetization behavior in magnetic fields up to 60 T Er2Fe14B and Tm2Fe14B ferrimagnets chosen for the study showed that the substitution of Nd for Er or Tm increases the saturation magnetization as a result of ferromagnetic ordering of Nd and Fe moments. Under sufficiently high magnetic fields the magnetic moments rotate and the field-induced ferromagnetic state may be observed. The field at which a transition occurs is related to the strength of the inter-sublattice exchange interaction. The role of hydrogen is primarily to weaken the inter-sublattice ferrimagnetic coupling so that the reorientation becomes achievable at the available magnetic field strength (in hydrides Tm2Fe14BH5.5 and (Tm0.5Nd0.5)2Fe14BH5.5). We analyze the volume dependence of the R–Fe magnetic interaction in R2Fe14B and compare it with other R–Fe compounds.

Publ.-Id: 29527 - Permalink


Shifts in bentonite bacterial community and mineralogy in response to uranium and glycerol-2-phosphate exposure
Povedano-Priego, C.; Jroundi, F.; Lopez Fernandez, M.; Sánchez-Castro, I.; Martin-Sánchez, I.; Huertas, F. J.; Merroun, M. L.;
The multi-barrier deep geological repository system is currently considered as one of the safest option for the disposal of high-level radioactive wastes. Indigenous microorganisms of bentonites, may affect the structure and stability of these clays through Fe-containing minerals biotransformation and radionuclides mobilization.
The present work aimed to investigate the behavior of bentonite and its bacterial community in the case of a uranium leakage from the waste containers. Hence, bentonite microcosms were amended with uranyl nitrate (U) and glycerol-2-phosphate (G2P) and incubated aerobically for 6 months. Next generation 16S rRNA gene sequencing revealed that the bacterial populations of all treated microcosms were dominated by Actinobacteria and Proteobacteria, accounting for >50% of the community. Additionally, G2P and nitrate had a remarkable effect on the bacterial diversity of bentonites by the enrichment of bacteria involved in the nitrogen and carbon biogeochemical cycles (e.g. Azotobacter). A significant presence of sulfate-reducing bacteria such as Desulfonauticus and Desulfomicrobium were detected in the U-treated microcosms. The actinobacteria Amycolatopsis was enriched in G2P‑uranium amended bentonites. High Annular Angle Dark-Field Scanning Transmission Electron Microscopy analyses showed the capacity of Amycolatopsis and a bentonite consortium formed by Bradyrhizobium-Rhizobium and Pseudomonas to precipitate U as U phosphate mineral phases, probably due to the phosphatase activity. The different amendments did not affect the mineralogy of the bentonite pointing to a high structural stability. These results would help to predict the impact of microbial processes on the biogeochemical cycles of elements (N and U) within the bentonite barrier under repository relevant conditions and to determine the changes in the microbial community induced by a uranium release.
Keywords: Deep geological repository Bentonite Bacterial diversity Uranium Glycerol-2-phosphate Microscopy

Publ.-Id: 29526 - Permalink


Statistical Analysis of Community RNA Transcripts between Organic Carbon and Geogas-Fed Continental Deep Biosphere Groundwaters
Lopez Fernandez, M.; Broman, E.; Simone, D.; Bertilsson, S.; Dopson, M.;
Life in water-filled bedrock fissures in the continental deep biosphere is broadly constrained by energy and nutrient availability. Although these communities are alive, robust studies comparing active populations and metabolic processes across deep aquifers are lacking. This study analyzed three oligotrophic Fennoscandian Shield groundwaters, two “modern marine” waters that are replenished with organic carbon from the Baltic Sea and are likely less than 20 years old (171.3 and 415.4m below sea level) and an extremely oligotrophic “thoroughly mixed” water (448.8m below sea level) of unknown age that is composed of very old saline and marine waters. Cells were captured either using a sampling device that rapidly fixed RNA under in situ conditions or by filtering flowing groundwater over an extended period before fixation. Comparison of metatranscriptomes between the methods showed statistically similar transcript profiles for the respective water types, and they were analyzed as biological replicates. Study of the small subunit (SSU) rRNA confirmed active populations from all three domains of life, with many potentially novel unclassified populations present. Statistically supported differences between communities included heterotrophic sulfate-reducing bacteria in the modern marine water at 171.3m below sea level that has a higher organic carbon content than do largely autotrophic populations in the H2- and CO2-fed thoroughly mixed water. While this modern marine water had signatures of methanogenesis, syntrophic populations were predominantly in the thoroughly mixed water. The study provides a first statistical evaluation of differences in the active microbial communities in groundwaters differentially fed by organic carbon or “geogases.”
IMPORTANCE
Despite being separated from the photosynthesis-driven surface by both distance and time, the deep biosphere is an important driver for the earth’s carbon and energy cycles. However, due to the difficulties in gaining access and low cell numbers, robust statistical omics studies have not been carried out, and this limits the conclusions that can be drawn. This study benchmarks the use of two separate sampling systems and demonstrates that they provide statistically similar RNA transcript profiles, importantly validating several previously published studies. The generated data are analyzed to identify statistically valid differences in active microbial community members and metabolic processes. The results highlight contrasting taxa and growth strategies in the modern marine waters that are influenced by recent infiltration of Baltic Sea water versus the hydrogen- and carbon dioxide-fed, extremely oligotrophic, thoroughly mixed water.
Keywords: deep biosphere, groundwaters, metatranscriptomes, protein-coding RNA, rRNA

Publ.-Id: 29525 - Permalink


¹⁸F-Labeled benzylpiperazine derivatives as highly selective ligands for imaging σ1 receptor with positron emission tomography
Ye, J.; Wang, L.; Deuther-Conrad, W.; Chen, Y.; Zhang, X.; Zhang, J.; Huang, Y.; Brust, P.; Jia, H.;
We report the design, synthesis, and evaluation of a new series of benzylpiperazine derivatives as selective σ1 receptor ligands. All seven ligands possessed low nanomolar affinity for σ1 receptors (Ki(σ1) = 0.31-4.19 nM) and high subtype selectivity (Ki(σ2)/Ki(σ1) = 50-2448). The fluoroethoxy analogues also exhibited high selectivity toward the vesicular acetylcholine transporter (Ki(VAChT)/Ki(σ1) = 99-18252). The corresponding radiotracers [18F]13, [18F]14, and [18F]16 with high selectivity (Ki(σ2)/Ki(σ1) > 100, Ki(VAChT)/Ki(σ1) > 1000) were prepared in 42% to 55% radiochemical yields (corrected for decay), greater than 99% radiochemical purity (RCP), and molar activity of about 120 GBq/μmol at the end of synthesis (EOS). All three radiotracers showed high initial brain uptake in mouse (8.37-11.48% ID/g at 2 min), which was not affected by pretreatment with cyclosporine A, suggesting that they are not substrates for permeability-glycoprotein (P-gp). Pretreatment with SA4503 or haloperidol resulted in significantly reduced brain uptake (35%-62% decrease at 30 min). In particular, [18F]16 displayed high brain-to-blood ratios and high in vivo metabolic stability. Although it may not be an optimal neuroimaging agent because of its slow kinetics in the mouse brain, [18F]16 can serve as a lead compound for further structural modifications to explore new potential radiotracers for σ1 receptors.
  • Journal of Labelled Compounds and Radiopharmaceuticals 62(2019)8, 425-437
    DOI: 10.1002/jlcr.3738

Downloads:

Publ.-Id: 29524 - Permalink


Haemodynamic impairments in asymptomatic unilateral carotid artery stenosis are most pronounced within individual watershed areas
Kaczmar, S.; Goettler, J.; Petr, J.; Hansen, M.; Kufer, J.; Hock, A.; Kufer, J.; Mouridsen, K.; Hyder, F.; Christine, P.;
Objectives
Severe internal carotid-artery stenosis (ICAS) is a major public health issue, as it accounts for approximately 10% of all strokes.1 Despite several studies,2–5 mechanisms of related haemodynamic impairments are still not well understood, which limits the currently insufficient treatment guidelines6. To improve diagnostic significance, we propose a multimodal-MRI protocol to better characterise haemodynamic impairments in asymptomatic ICAS. Since perfusion impairments arise first in the highly variableborder zones7 between perfusion territories,8 we hypothesize to be most sensitive to ICAS-impairments within subject’s individual watershed areas (iWSAs)7.

Methods
Fifty-nine participants (29 asymptomatic, unilateral ICAS-patients, age = 70.1 ± 4.8y and 30 age-matched HC, age = 70.3 ± 7.3y) underwent MRI on a Philips 3T Ingenia with written informed consent. Imaging yielded maps of cerebrovascular reactivity (CVR)9 by breathhold-fMRI;10 cerebral blood flow (CBF) by pCASL;11 relative oxygen extraction fraction (rOEF) by multiparametric-quantitative BOLD (mq-BOLD);12 relative cerebral blood volume (rCBV), capillary transit-time heterogeneity (CTH), and oxygen extraction capacity (OEC) by parametric modeling13 of dynamic susceptibility contrast (DSC) data14 (Fig.1C-H). Based on DSC-derived time-to-peak (TTP) maps, iWSAs were defined for each participant (Fig.1A).7 Mean haemodynamic parameter values within each hemisphere were compared between ICAS-patients vs. HC and inside vs. outside iWSAs (Fig.1B) within GM and WM.

Results
We found statistically significant lateralisation of CBF, CVR, rCBV, CTH and OEC for ICAS-patients, whereas no significant rOEF lateralisation was found (Fig.1I). Inside iWSAs, lateralisation was significantly enhanced for CBF and CVR (t-test, p < 0.05), with a strong trend for rCBV. Overall, lateralisation was stronger within WM than GM (Fig.1I). Contrary, OEC and CTH were indeed lateralised, but comparable inside vs. outside iWSAs (Fig.1I). For HC, all parameters were symmetrical between hemispheres (data not shown).



Discussion
The multimodal MRI-protocol is sensitive to haemodynamic impairments in unilateral-ICAS. Specificity was affirmed by symmetrical HC results. As hypothesized, impairments of CBF, CVR and rCBV were stronger within iWSAs (Fig.1I). Pronounced effects in WM-iWSA fit with the different blood supply in GM/WM. Ipsilaterally decreased CBF agrees with recent studies.2 Decreased CVR, along with increased rCBV, indicates chronic vasodilation.15 Consistent with current literature,2 no rOEF lateralisation was found on group level. Observed ΔCBF vs. ΔrOEF mismatch could imply variable oxygen diffusivity16– potentially moderated by CTH17,18. Increased CTH in ICAS agrees with previous studies.18 Interestingly, we found CTH and OEC lateralisation independent of iWSA-locations, which coincides with previous CTH and Tmax comparisons.19,20 This indicates different CTH and TTP sensitivities to macrovascular effects and microcapillary flow heterogeneity.18

Conclusion
We successfully analyzed haemodynamic impairments in unilateral-ICAS and found lateralisation in accordance with current literature. Application of iWSA confirmed increased sensitivity to CBF, CVR and rCBV changes. Interestingly, CTH and OEC increases are independent of iWSA-locations.
  • Contribution to proceedings
    The 29th International Symposium on Cerebral Blood Flow, Metabolism and Function, 04.07.2019, Yokohama, Japan
  • Lecture (Conference)
    The 29th International Symposium on Cerebral Blood Flow, Metabolism and Function, 04.07.2019, Yokohama, Japan

Publ.-Id: 29522 - Permalink


Recovery of cerebrovascular reactivity after treatment of asymptomatic carotid artery stenosis is assessable by non-invasive breath-hold fMRI within global watershed areas
Kaczmar, S.; Goettler, J.; Sollmann, N.; Hock, A.; Sorg, C.; Zimmer, C.; Mouridsen, K.; Hyder, F.; Preibisch, C.; Petr, J.;
Objectives
Accounting for approximately 10% of all strokes,1 severe internal carotid-artery stenosis (ICAS) is a major public health issue. The average 2-year mortality after the invasive treatment is very high with 32%,2 which creates the need for non-invasive methods to support treatment decisions and evaluate treatment efficacy.3,4 A highly promising biomarker of vascular health is cerebrovascular reactivity (CVR),3,4 however, commonly employed methods are either invasive acetazolamide injections or complicated gas applications.3-8 We therefore used an easily-applicable breath-hold fMRI (BH-fMRI) scheme for CVR measurements. To maximize sensitivity and ensure specificity, we evaluated CVR within global watershed areas (gWSAs) in ICAS-patients before and after treatment and in healthy controls (HC).9

Methods
Thirty-three participants (16 asymptomatic, unilateral ICAS-patients, age = 71.4 ± 5.8 y and 17 HC, age = 70.8 ± 5.3 y) underwent MRI on a 3 T Philips Ingenia with written informed consent. All participants were scanned twice, patients before and at least three months after treatment (by stenting or endarterectomy), HC with a similar follow-up delay. The BOLD-based BH-fMRI scheme comprised five breath-holds of 15 s, each. CVR-maps were calculated by data-driven analysis10 (Fig.1B,C). Artefact-affected CVR-maps were excluded based on visual ratings (CP,SK,JG). To investigate the role of chronic vasolidation,5 dynamic susceptibility contrast (DSC) MRI was additionally acquired in both scans to calculate relative cerebral blood volume (rCBV) maps11. Lateralization between hemispheres was calculated in MNI-space by mean parameter-values within GM of gWSAs for each participant (Fig.1A). ICAS-patients were evaluated within hemispheres ipsilateral and contralateral to the stenosis.

Results
Exemplary data of an ICAS-patient shows impaired CVR before treatment, which improves after treatment (see arrows in Fig.1B,C). On group level, CVR is significantly decreased in the ipsilateral hemisphere before treatment (Fig.1D, p = 0.0038). After treatment, CVR lateralization was significantly reduced (p = 0.0495) towards more symmetrical values between hemispheres (p = 0.25). Similarly, rCBV was ipsilaterally increased in ICAS before treatment and more symmetrical after treatment (data not shown). HC data was symmetrical between hemispheres at all scans (Fig.1E, p > 0.60).

Discussion
As hypothesized, BH-fMRI based evaluation of CVR lateralization within gWSAs was sensitive to subtle impairments in asymptomatic ICAS without compromising its specificity, as affirmed by symmetrical HC results (Fig.1E). Decreased CVR along with increased rCBV before treatment is associated with chronic vasodilation.5 Consistent with current literature, CVR recovery was detected after ICAS-treatment,4-8 demonstrating improved haemodynamic status. Compared to more accurate CVR-measurements with CO2 application and end-tidal gas analysis,3,12 breath-holds remain a viable alternative being much more tolerable and easily applicable at low costs within clinically feasible scan times.
  • Contribution to proceedings
    The 29th International Symposium on Cerebral Blood Flow, Metabolism and Function, 04.07.2019, Yokohama, Japan
  • Poster
    The 29th International Symposium on Cerebral Blood Flow, Metabolism and Function, 04.07.2019, Yokohama, Japan

Publ.-Id: 29521 - Permalink


Human exposure to uranium in South African gold mining areas using barber-based hair sampling
Winde, F.; Geipel, G.; Espina, C.; Schüz, J.;
Uranium (U) measurements in water, soil, and food related to gold mining activities in populated areas in Gauteng Province, South Africa, suggest the possibility of exposure levels that may lead to adverse health consequences, including cancer. Theoretical considerations on pathways of human uptake of significant exposures are plausible, but few data on directly measured human exposure are available. A cross-sectional study was conducted using human measurements to compare U levels with other settings around the globe (based on literature review), to explore potential exposure variability within the province, and to test the feasibility of recruiting subjects partially coming from vulnerable and difficult-to-reach populations. Wards of potentially high (HE) and low exposure (LE) were identified. Composite hair samples representing the respective local populations were collected from regular customers of selected barber shops over a period of 1–2 months. A total of 70 U concentrations were determined in 27 composite samples from 1332 individuals. U concentrations ranged from 31 μg/kg to 2524 μg/kg, with an arithmetic mean of 192 μg/kg (standard deviation, 310 μg/kg) and a median of 122 μg/kg. Although HE wards collectively showed higher U levels than LE wards (184 vs 134 μg/kg), differences were smaller than expected. In conclusion, detected U levels were higher than those from most other surveys of the general public. The barber-based approach was an efficient hair collection approach. Composite hair samples are not recommended, due to technical challenges in measuring U, and individual hair samples are needed in follow-up studies to determine predictors of exposure.

Publ.-Id: 29520 - Permalink


Phase Selectivity in Cr and N Co-Doped TiO2 Films by Modulated Sputter Growth and Post-Deposition Flash-Lamp-Annealing
Gago, R.; Prucnal, S.; Hübner, R.; Munnik, F.; Esteban-Mendoza, D.; Jiménez, I.; Palomares, J.;
In this paper, we report on the phase selectivity in Cr and N co-doped TiO2 (TiO2:Cr,N) sputtered films by means of interface engineering. In particular, monolithic TiO2:Cr,N films produced by continuous growth conditions result in the formation of a mixed-phase oxide with dominant rutile character. On the contrary, modulated growth by starting with a single-phase anatase TiO2:N buffer layer, can be used to imprint the anatase structure to a subsequent TiO2:Cr,N layer. The robustness of the process with respect to the growth conditions has also been investigated, especially regarding the maximum Cr content (<5 at.%) for single-phase anatase formation. Furthermore, post-deposition flash-lamp-annealing (FLA) in modulated coatings was used to improve the as-grown anatase TiO2:Cr,N phase, as well as to induce dopant activation (N substitutional sites) and diffusion. In this way, Cr can be distributed through the whole film thickness from an initial modulated architecture while preserving the structural phase. Hence, the combination of interface engineering and millisecond-range-FLA opens new opportunities for tailoring the structure of TiO2-based functional materials.
Keywords: TiO2, flash lamp annealing, doping,

Publ.-Id: 29519 - Permalink


Update on the FLUKA geometry modeling
Müller, S.ORC
Update on FLUKA geometry modeling
Keywords: FLUKA, Mu2e
  • Lecture (others)
    Mu2e Simulation Workinggroup Meeting, 18.07.2019, Batavia, USA

Publ.-Id: 29516 - Permalink


Update on FLUKA simulation activities for the Mu2e experiment
Müller, S.ORC
Update on the FLUKA simulation for the Mu2e experiment
Keywords: FLUKA, Mu2e
  • Lecture (others)
    Mu2e collaboration meeting, 26.06.2019, Minneapolis, USA

Publ.-Id: 29515 - Permalink


Electrovortex liquid metal flows in cells with localized current supply
Kolesnichenko, I.; Frick, P.; Stefani, F.; Eltischev, V.; Weber, N.; Mandrykin, S.; Ozernykh, V.; Khalilov, R.;
The paper studies the flow of a liquid metal in a cylindrical cell caused by the action of electromagnetic force. An electric current passes through the metal. The current is locally supplied to the area at the bottom of the cell and discharged at the top. Force generates from the joint action of an electric current and its own magnetic field. The vorticity of the force is nonzero and an electro-vortex flow (EVF) arises. The characteristics of the intensity and oscillations of EVF are studied numerically and experimentally. Methods for contactless determination of the position of the liquid metal boundary have been developed. The possibility of manipulation of the intensity and shape of EVF was studied.
  • Lecture (Conference)
    11th PAMIR International Conference - Fundamental and Applied MHD, 01.07.2019, Reims, Frankreich
  • Contribution to proceedings
    11th PAMIR International Conference - Fundamental and Applied MHD, 01.07.2019, Reims, Frankreich

Publ.-Id: 29514 - Permalink


Electro-vortex flow in a cylindrical container
Liu, K.; Li, B. W.; Stefani, F.; Weber, N.; Weier, T.;
In a cylindrical container filled with the eutectic alloy GaInSn, an electro-vortex flow (EVF) is caused by the interaction of a non-uniform current with the magnetic field that it generates. In this paper, we investigate the EVF numerically and experimentally. First, based on a solver by Weber, we develop a more advanced one, in which the effect of Joule heating is considered. The magnetic field, which is the combination of the current induced magnetic field and the external geomagnetic field, is also taken into account. For getting a higher computational efficiency, the so-called parent-child mesh technique is applied in OpenFOAM. Second, we conduct an experiment corresponding to the numerical simulation, in which Ultrasound Doppler Velocimetry (UDV) is applied for flow measurements. The results of the experiment are in good agreement with those of the simulation.
Keywords: electro-vortex flow, Joule heating, parent-child mesh, OpenFOAM
  • Contribution to proceedings
    11th PAMIR International Conference - Fundamental and Applied MHD, 01.-05.07.2019, Reims, Frankreich
  • Poster
    11th PAMIR International Conference - Fundamental and Applied MHD, 01.-05.07.2019, Reims, Frankreich

Publ.-Id: 29513 - Permalink


Novel Thyristor-Based Pulsed Current Converter for a Medical Application - a Conceptual Introduction
Wettengel, S.; Lindenmueller, L.; Bernet, S.; Schramm, U.ORC; Kroll, F.ORC; Brack, F.-E.ORC; Pawelke, J.
A novel ion beam radiation therapy apparatus employing pulsed high magnetic field coils for transporting the ion beam has been proposed. In this paper a new pulsed current converter topology is introduced, which can be used as a pulsed power supply for the therapy apparatus. Thyristors are selected as the semiconductors used in the pulsed current converter. Since the planned operating point is outside of the typical range of the semiconductors, research has been done to predict their behavior during turn-off (the most critical phase of the pulse). A behavioral model has been derived and experimentally parametrized to predict the turn-off behavior and to optimize snubber design.
  • Contribution to proceedings
    PCIM Europe 2018; International Exhibition and Conference for Power Electronics, Intelligent Motion, Renewable Energy and Energy Management, 05.-07.06.2018, Nuremberg, Germany
    PCIM Europe 2018; International Exhibition and Conference for Power Electronics, Intelligent Motion, Renewable Energy and Energy Management, 978-3-8007-4646-0

Publ.-Id: 29512 - Permalink


A Statistical Approach for Analysis of Dissolution Rates Including Surface Morphology
Pedrosa, E. P.; Kurganskaya, I.; Fischer, C.; Luttge, A.;
Understanding mineral dissolution is relevant for natural and industrial processes that involve the interaction of crystalline solids and fluids. The dissolution of slow dissolving minerals is typically surface controlled as opposed to diffusion/transport controlled. At these conditions, the dissolution rate is no longer constant in time or space, an outcome observed in rate maps and correspondent rate spectra. The contribution and statistical prevalence of different dissolution mechanisms is not known. Aiming to contribute to close this gap, we present a statistical analysis of the variability of calcite dissolution rates at the nano- to micrometer scale. A calcite-cemented sandstone was used to perform flow experiments. Dissolution of the calcite-filled rock pores was measured using vertical scanning interferometry. The resultant types of surface morphologies influenced the outcome of dissolution. We provide a statistical description of these morphologies and show their temporal evolution as an alternative to the lack of rate spatial variability in rate constants. Crystal size impacts dissolution rates most probably due to the contribution of the crystal edges. We propose a new methodology to analyze the highest rates (tales of rate spectra) that represent the formation of deeper etch pits. These results have application to the parametrization and upscaling of geochemical kinetic models, the characterization of industrial solid materials and the fundamental understanding of crystal dissolution.
Keywords: dissolution kinetics; calcite; surface morphology;

Publ.-Id: 29511 - Permalink


Exploring new materials for optical thermometric sensing
Sharma, S.ORC; Beyer, J.; Fuchs, M.; Gloaguen, R.; Heitmann, J.
The luminescence intensity ratio (LIR) of emission from two thermally coupled excited states is one of the most popular temperature sensing schemes, which has proven to be reliable due to its non-invasive nature, minimal dependence on the measurement conditions, and high temperature-spatial resolution. However, it requires a special design effort to obtain stable luminescence emission, which can be used for any practical application, for example, optical thermometric sensing. In this work, we present our results on the influence of excitation-emission processes on the dynamical behaviour of charges, and their temperature dependence in a wide temperature range (300-870 K), on a single crystal of EuPO4. The EuPO4 host which previously did not appear suitable for temperature sensing, was successfully converted to a highly sensitive optical temperature sensor, by following appropriate experimental strategy. The coupling of two excited states of Eu3+ showed a relative sensitivity of 2.00 %K-1, while, the coupling between two ground states of Eu3+ showed a relative sensitivity of 0.34 %K-1. The results suggest that by optimizing experimental parameters, highly sensitive optical thermometric sensors can be prepared, with ease.
  • Lecture (Conference)
    2019 Spring Meeting of the European Materials Research Society (E-MRS), 27.-31.05.2019, Nice, France

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Publ.-Id: 29509 - Permalink


A Machine Learning Framework for Drill-Core Mineral Mapping Using Hyperspectral and High-Resolution Mineralogical Data Fusion
Contreras Acosta, I. C.ORC; Khodadadzadeh, M.; Tusa, L.; Ghamisi, P.; Gloaguen, R.
Mining companies heavily rely on drill-core samples during exploration campaigns as they provide valuable geological information to target important ore accumulations. Traditional core logging techniques are time-consuming and subjective. Hyperspectral (HS) imaging, an emerging technique in the mining industry, is used to complement the analysis by rapidly characterizing large amounts of drill-cores in a nondestructive and noninvasive manner. As the accurate analysis of drill-core HS data is becoming more and more important, we explore the use of machine learning techniques to improve speed and accuracy, and help to discover underlying relations within large datasets. The use of supervised techniques for drill-core HS data represents a challenge since quantitative reference data is frequently not available. Hence, we propose an innovative procedure to fuse high-resolution mineralogical analysis and HS data. We use an automatic high-resolution mineralogical imaging system (i.e., scanning electron microscopy-mineral liberation analysis) for generating training labels. We then resample the MLA image to the resolution of the HS data and adopt a soft labeling strategy for mineral mapping. We define the labels for the classes as mixtures of geological interest and use the classifiers (random forest and support vector machines) to map the entire drill-core. We validate our framework qualitatively and quantitatively. Thus, we demonstrate the ability of the proposed technique to fuse and up-scale high-resolution mineralogical analysis with drill-core HS data.
Keywords: Data fusion, drill-cores, hyperspectral (HS) data, machine learning, mineral liberation analysis (MLA), random forest (RF), support vector machine (SVM)
  • IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing (2020)
    Online First (2019) DOI: 10.1109/JSTARS.2019.2924292

Publ.-Id: 29508 - Permalink


Magnetoelastic coupling across the field-induced transition of uranium mononitride
Gorbunov, D.; Nomura, T.; Zvyagin, A. A.; Henriques, M. S.; Andreev, A. V.; Skourski, Y.; Zvyagina, G. A.; Troc, R.; Zherlitsyn, S.; Wosnitza, J.;
Uranium mononitride (UN) displays a spin-flop-like transition for magnetic field applied along all principal crystallographic directions just below 60 T. Here, we report on ultrasound and magnetocaloric-effect results for UN in pulsed magnetic fields up to 65 T. The field-induced phase transition causes a discontinuous temperature decrease, indicating a larger magnetic entropy above the transition. Furthermore, we find pronounced anomalies in the acoustic properties, which signals strong spin-lattice interactions. A further anomaly observed at fields slightly above the transition is likely related to the formation of magnetic domains. A model based on the exchange-striction coupling mechanism well reproduces the strong renormalization of the acoustic properties.

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Publ.-Id: 29502 - Permalink


Successive Trimming of a Permalloy Stripe to enhance the localized Edge Mode Spectrum probed by Ferromagnetic Resonance
Lenz, K.ORC; Schneider, T.; Hlawacek, G.; Narkowicz, R.; Stienen, S.; Lenz, M.; Lindner, J.
Finite-size effects in ultrathin magnetic films are a well-known feature. They usually play a role, when the surface and interface layers dominate over the volume contribution of the sample and have different properties, due to roughness, texture, hybridization, modified magnetic moment, or dipolar fields. For micro- and especially nanostructures these effects might be there as well—but at the side walls. Regarding the magnetization dynamics these effects lead to additional spin wave modes, e.g. localized spin wave modes (edge modes). It has been shown that these edge modes are influenced by the quality of the side walls, namely by angled side walls, edge roughness, beveled edges, or even magnetic dilution [1]. As these structures have to be prepared by means of lithography involving masks a certain edge roughness or even side wall slope are inevitable. Nevertheless, when it comes to micromagnetic simulations to corroborate or explain measurements these contributions are usually excluded from the model. Here we show, how successive trimming the sides of a 5 µm x 1 µm Permalloy stripe by a focused Ne ion beam improves the spin wave spectrum and enhances the edge mode spectrum as probed by ferromagnetic resonance (FMR). To achieve the sensitivity to detect the FMR of the weak edge modes of a single Permalloy stripe we use planar microresonator FMR [2,3]. The experimental results are corroborated by micromagnetic simulations. Including just edge roughness of ~4 nm (rms) in the simulations is enough to perfectly match the FMR experimental data. The residual edge roughness is in the order of the grain size of the polycrystalline permalloy. Although the focused ion beam and its motion are able to cut the side walls perfectly straight and vertical with sub-nm precision, the Ne ions penetrate the side wall up to 15 nm (called straggling). This is due to the collision cascade with the Ni and Fe atoms of the Permalloy causing possible lateral damage of the Permalloy lattice. Hence, we attribute the residual roughness to the ion induced damage by the lateral penetration during trimming of the side walls, and a small remaining edge roughness due to changes in sputter yield for differently oriented Permalloy grains.

[1] R.D. McMichael, B.B. Maranville, Phys. Rev. B 74,024424 (2006).
[2] A. Banholzer et al., Nanotechnology 22, 295713 (2011).
[3] R. Narkowicz et al., Rev. Sci. Instrum. 79, 084702 (2008).
Keywords: Magnetic nanostructures, ferromagnetic resonance, spin waves, edge modes, HIM
  • Poster
    International Conference on Magnetism ICM 2018, 15.-20.07.2018, San Francisco, United States of America
  • Poster
    9th Joint European Magnetic Symposia, JEMS 2018, 03.-07.09.2018, Mainz, Deutschland

Publ.-Id: 29500 - Permalink


Turbulent Multiphase CFD Modelling: State-of-the-art applications in Nuclear Engineering
Höhne, T.;
Two-phase flows occur in many industrial-relevant processes in power plants, chemical engineering, oil and gas industries and others.
Reliable predictions of the flow characteristics are important for the design of the facilities, the optimization of processes and safety analyses.
Experimental results are often hardly transferable to modified geometries, flow condition or scales.
Keywords: CFD, AIAD, GENTOP, Multiphase
  • Lecture (Conference)
    18th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-18), 18.-23.08.2019, Portland, USA

Publ.-Id: 29499 - Permalink


Colloidal Mercury-Doped CdSe Nanoplatelets with Dual Fluorescence
Galle, T.; Kazes, M.; Hübner, R.; Lox, J.; Khoshkhoo, M. S.; Sonntag, L.; Tietze, R.; Sayevich, V.; Oron, D.; Koitzsch, A.; Lesnyak, V.; Eychmüller, A.;
Quasi-two-dimensional (2D) CdSe nanoplatelets (NPLs) are distinguished by their unique optical properties in comparison to classical semiconductor nanocrystals, such as extremely narrow emission line widths, reduced Auger recombination, and relatively high absorption cross sections. Inherent to their anisotropic 2D structure, however, is the loss of continuous tunability of their photoluminescence (PL) properties due to stepwise growth. On top of that, limited experimental availability of NPLs of different thicknesses and ultimately the bulk band gap of CdSe constrain the achievable PL wavelengths. Here, we report on the doping of CdSe NPLs with mercury, which gives rise to additional PL in the red region of the visible spectrum and in the near-infrared region. We employ a seeded-growth method with injection solutions containing cadmium, selenium, and mercury. The resulting NPLs retain their anisotropic structure, are uniform in size and shape, and present significantly altered spectroscopic characteristics due to the existence of additional energetic states. We conclude that doping takes place by employing elemental analysis in combination with PL excitation spectroscopy, X-ray photoelectron spectroscopy, and single-particle fluorescence spectroscopy, confirming single emitters being responsible for multiple distinct emission signals.

Publ.-Id: 29498 - Permalink


Trimming of permalloy stripes to enhance the localized edge mode spectrum probed by ferromagnetic resonance
Lenz, K.ORC; Schneider, T.; Hlawacek, G.; Narkowicz, R.; Stienen, S.; Kákay, A.; Lenz, M.; Fassbender, J.; Lindner, J.
Finite-size effects in ultrathin magnetic films are a well-known feature, i.e., when the surface or interfaces dominate the volume of the sample due to different roughness, texture, hybridization, modified magnetic moment, or dipolar fields. For nanostructures these effects could arise at the side walls as well. This leads to localized spin wave modes (edge modes).
It has been shown that the quality of the side walls (angled side walls or roughness) influence these modes [1]. During preparation of samples by lithography a certain edge roughness and side wall slope are sometimes inevitable. Nevertheless, in micromagnetic simulations these contributions are usually excluded from the model. We show, how successive trimming the sides of a 5 μm x 1 μm Permalloy stripe by a focused Ne ion beam improves the spin wave spectrum and enhances the edge mode spectrum as probed by planar microresonator ferromagnetic resonance (FMR) [2,3] as depicted in Figure 1. Including an rms edge roughness of ~2 nm (within the order of the permalloy grain size) in the simulations is enough to match the FMR data. Hence, we attribute the residual roughness to the ion induced damage by the lateral penetration during trimming of the side walls, and a small remaining edge roughness due to changes in the sputter yield for differently oriented Permalloy grains.
Keywords: ferromagnetic resonance, nanostructures, trimming, HIM, FMR, edge modes, spin waves
  • Poster
    Magnonics 2019, 28.07.-01.08.2019, Carovigno, Italy

Publ.-Id: 29497 - Permalink


Direct measurements of the magneto-caloric effect of MnFe4Si3 in pulsed magnetic fields
Maraytta, N.; Skourski, Y.; Voigt, J.; Friese, K.; Herrmann, M. G.; Perßon, J.; Wosnitza, J.; Salman, S. M.; Brückel, T.;
We have studied the magnetic and magnetocaloric response of MnFe4Si3 to pulsed and static magnetic fields up to 50 T. We determine the adiabatic temperature change ΔTad directly in pulsed fields and compare to the results of magnetization and specific heat measurements in static magnetic fields. The high ability of cycling even in fields μ0H = 50 T confirms the high structural stability of MnFe4Si3 against field changes, an important property for applications. The magnetic response to magnetic fields up to μ0H = 35 T shows that the anisotropy can be overcome by fields of approx. 4 T.

Publ.-Id: 29496 - Permalink


Magnetic structure and spin waves in the frustrated ferro-antiferromagnet Pb2VO(PO4)2
Bettler, S.; Landolt, F.; Aksoy, Ö. M.; Yan, Z.; Gvasaliya, S.; Qiu, Y.; Ressouche, E.; Beauvois, K.; Raymond, S.; Ponomaryov, A. N.; Zvyagin, S. A.; Zheludev, A.;
Single crystal neutron diffraction, inelastic neutron scattering, and electron spin resonance experiments are used to study the magnetic structure and spin waves in Pb2VO(PO4)2, a prototypical layered S = 1/2 ferromagnet with frustrating next-nearest neighbor antiferromagnetic interactions. The observed excitation spectrum is found to be inconsistent with a simple square lattice model previously proposed for this material. At least four distinct exchange coupling constants are required to reproduce the measured spin wave dispersion. The degree of magnetic frustration is correspondingly revised and found to be substantially smaller than in all previous estimates.

Publ.-Id: 29495 - Permalink


Numerical study of simultaneous heat and mass transfer in Liquid Metal Batteries
Personnettaz, P.; Weber, N.; Weier, T.;
Liquid metal batteries (LMBs) are promising candidates for electrical energy storage. An LMB is a concentration cell made of three liquid layers, stably stratified by density. A molten salt acts as an electrolyte between two liquid metal electrodes. The simple chemistry and geometry, the liquid nature of the active layers and the presence of multi-physics phenomena have made the LMB an intriguing candidate for continuum mechanics investigations. Simultaneous transport of charge, heat, mass and momentum takes place in each liquid layer together with chemical reactions. The interfaces between layers are the places in which electrochemical reactions occur along with interfacial transport phenomena.
In our work we investigate heat and mass transport in LMBs with openFOAM libraries using a multi-region approach. We assign to each layer a numerical region and we design a procedure able to ensure the physical coupling between the different transport mechanisms through an iterative procedure. The heat and mass transfer equations are solved on a global mesh and in the positive electrode region respectively. Then we solve the Navier-Stokes equations in each fluid region. Appropriate boundary conditions were designed to ensure a consistent transport at the interfaces between different regions. Thanks to this procedure we can compute temperature and concentration distributions and the corresponding thermal and compositional convection. Therefore, we can investigate the interaction of different mechanisms and can give a prediction of the fluid flow in the interior of an LMB. The numerical procedure is introduced as well as the first results. Furthermore, the modeling limitations and the future developments are discussed.
Keywords: Liquid metal battery, openFOAM, mass transport, heat transfer, transport phenomena
  • Poster
    OpenFOAM Workshop 2019, 23.-26.07.2019, Duisburg, Deutschland

Publ.-Id: 29494 - Permalink


A semiconducting layered metal-organic framework magnet
Yang, C.; Dong, R.ORC; Wang, M.ORC; Petkov, P. S.ORC; Zhang, Z.ORC; Wang, M.; Han, P.ORC; Ballabio, M.; Bräuninger, S. A.; Liao, Z.; Zhang, J.ORC; Schwotzer, F.; Zschech, E.; Klauss, H.-H.; Cánovas, E.; Kaskel, S.ORC; Bonn, M.; Zhou, S.ORC; Heine, T.ORC; Feng, X.
The realization of ferromagnetism in semiconductors is an attractive avenue for the development of spintronic applications. Here, we report a semiconducting layered metal-organic framework (MOF), namely K3Fe2[(2,3,9,10,16,17,23,24-octahydroxy phthalocyaninato)Fe] (K3Fe2[PcFe-O8]) with spontaneous magnetization. This layered MOF features in-plane full π-d conjugation and exhibits semiconducting behavior with a room temperature carrier mobility of 15 ± 2 cm2 V−1 s−1 as determined by time-resolved Terahertz spectroscopy. Magnetization experiments and 57Fe Mössbauer spectroscopy demonstrate the presence of long-range magnetic correlations in K3Fe2[PcFe-O8] arising from the magnetic coupling between iron centers via delocalized π electrons. The sample exhibits superparamagnetic features due to a distribution of crystal size and possesses magnetic hysteresis up to 350 K. Our work sets the stage for the development of spintronic materials exploiting magnetic MOF semiconductors.

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Publ.-Id: 29493 - Permalink


Strain-induced perpendicular magnetic anisotropy and Gilbert damping of Tm3Fe5O12 thin films
Ciubotariu, O.; Semisalova, A.; Lenz, K.ORC; Albrecht, M.
In the attempt of implementing iron garnets with perpendicular magnetic anisotropy (PMA) in spintronics, the attention turned towards strain-grown iron garnets. One candidate is Tm3Fe5O12 (TmIG) which possesses an out-of-plane magnetic easy axis when grown under tensile strain. In this study, the effect of film thickness on the structural and magnetic properties of TmIG films including magnetic anisotropy, saturation magnetization, and Gilbert damping is investigated. TmIG films with thicknesses between 20 and 300 nm are epitaxially grown by pulsed laser deposition on substituted-Gd3Ga5O12(111) substrates. Structural characterization shows that films thinner than 200 nm show in-plane tensile strain, thus exhibiting PMA due to strain-induced magnetoelastic anisotropy. However, with increasing film thickness a relaxation of the unit cell is observed resulting in the rotation of the magnetic easy axis towards the sample plane due to the dominant shape anisotropy. Furthermore, the Gilbert damping parameter is found to be in the range of 0.02 ± 0.005.
Keywords: Thulium iron garnet, magnetic anisotropy, Gilbert damping
  • Poster
    Magnonics 2019, 28.07.-01.08.2019, Carovigno, Italy

Publ.-Id: 29492 - Permalink


Theranostic CAR T cell targeting: A brief review
Arndt, C.; Bachmann, M.; Bergmann, R.; Berndt, N.; Feldmann, A.; Koristka, S.;
More than 100 years ago Paul Ehrlich postulated that our immun system should be able to eliminate tumor cells. Just recently, the development of check point inhibitors, bispecific antibodies, and T cells genetically modified to express chimeric antigen receptors (CARs) underlines the true power of our immune system. T cells genetically modified with CARs can lead to complete remission of malignant hematologic diseases. However, they can also cause life-threatening side effects. In case of cytokine release syndrome, tumor lysis syndrome, or deadly side effects on the central nervous system, an emergency shut down of CAR T cells is needed. Targeting of tumor-associated antigens that are also expressed on vital tissues require a possibility to repeatedly switch the activity of CAR T cells on and off on demand and to follow the treatment by imaging. Theranostic, modular CARs such as the UniCAR system may help to overcome these problems.
Keywords: bispecific antibody, BiTE, chimeric antigen receptor, immunotherapy, T cells, UniCAR
  • Journal of Labelled Compounds and Radiopharmaceuticals 62(2019)8, 533-540
    DOI: 10.1002/jlcr.3727

Publ.-Id: 29490 - Permalink


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