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41356 Publications

Compton-like scattering of a scalar particle with N photons and one graviton

Ahmadiniaz, N.; Balli, F. M.; Corradini, O.; Dávila, J. M.; Schubert, C.

Tree-level scattering amplitudes for a scalar particle coupled to an arbitrary number N of photons and a single graviton are computed. We employ the worldline formalism as the main tool to compute the irreducible part of the amplitude, where all the photons and the graviton are directly attached to the scalar line, then derive a tree replacement rule to construct the reducible parts of the amplitude which involve irreducible pure N-photon two-scalar amplitudes where one photon line emits the graviton. We test our construction by verifying the on-shell gauge and diffeomorphism Ward identities, at arbitrary N.

Keywords: Scattering amplitudes; gravitons; Ward identities

Publ.-Id: 29738

Compliant magnetic field sensors for flexible electronics

Makarov, D.

I will review our recent activities on compliant magnetic field sensors.

Keywords: flexible electronics; shapeable magnetoelectronis

Related publications

  • Invited lecture (Conferences)
    FFlexCom Meeting 2019; DFG Priority Programme “High Frequency Flexible Bendable Electronics for Wireless Communication Systems”, SPP 1796, 07.10.2019, Dresden, Germany

Publ.-Id: 29737

Helium interactions with (Y, Ti, O) nanoclusters in bcc Fe

Vallinayagam, M.; Posselt, M.; Faßbender, J.

Nanometer size (Y, Ti, O) clusters in nanostructured ferritic/martensitic Fe-Cr alloys can act as sinks for the transmutation product helium. In this manner irradiation swelling can be retarded significantly. Many details of He storage in or near the clusters are still not understood. In this work interactions of He with (Y, Ti, O) clusters in bcc Fe are investigated by density functional theory (DFT) calculations. Four different cluster structures studied in our previous work [1] are considered: Cage-type clusters with (i) 6 O atoms, 9 vacancies (v) and 6 Y atoms, and (ii) with 7 O, 9 v, 3 Y, and 3 Ti, as well as clusters with O in the center containing (iii) 6 O, 9 v, 6 Y, and (iv) 7 O, 9 v, 3 Y, 3 Ti. It is found that the most stable position of He is in the center of the cluster, followed by the interfacial substitutional site and other interstitial positions between metal or oxygen atoms, and sites away from the cluster. This shows the He trapping may be nearly irrespective of cluster morphology and mainly depend on cluster composition. Adding a second He atom to the cluster structure is investigated for selected cases. Furthermore, barriers for possible jumps between different sites at the rim of the cluster and the center are determined. First results show that these barriers are higher if the cluster contains Ti and that there is a strong dependence on the particular position at the rim. For the discussion of the results also the DFT data obtained from studies on the interaction of He with single O, Y, and Ti atoms as well as with a single vacancy are used.

[1] Vallinayagam Investigation of structural models for O-Y and O-Y-Ti clusters in bcc Fe: A DFT study J. Phys.: Condens. Matter (2018)

Keywords: DFT; ODS; He storage

  • Lecture (Conference)
    EUROMAT-2019 Conference, 01.-05.09.2019, Stockholm, Sweden

Publ.-Id: 29736

Validating the Predictive Power of Statistical Models in Retrieving Leaf Dry Matter Content of a Coastal Wetland from a Sentinel-2 Image

Ali, A. M.; Darvishzadeh, R.; Rafiezadeh Shahi, K.; Skidmore, A.

Leaf dry matter content (LDMC), the ratio of leaf dry mass to its fresh mass, is a key plant trait, which is an indicator for many critical aspects of plant growth and survival. Accurate and fast detection of the spatiotemporal dynamics of LDMC would help understanding plants' carbon assimilation and relative growth rate, and may then be used as an input for vegetation process models to monitor ecosystems. Satellite remote sensing is an effective tool for predicting such plant traits non-destructively. However, studies on the applicability of remote sensing for LDMC retrieval are scarce. Only a few studies have looked into the practicality of using remotely sensed data for the prediction of LDMC in a forest ecosystem. In this study, we assessed the performance of partial least squares regression (PLSR) plus 11 widely used vegetation indices (VIs), calculated based on different combinations of Sentinel-2 bands, in predicting LDMC in a coastal wetland. The accuracy of the selected methods was validated using LDMC, destructively measured in 50 randomly distributed sample plots at the study site in Schiermonnikoog, the Netherlands. The PLSR applied to canopy reflectance of Sentinel-2 bands resulted in accurate prediction of LDMC (coefficient of determination (R-2) = 0.71, RMSE = 0.033). PLSR applied to the studied VIs provided an R-2 of 0.70 and RMSE of 0.033. Four vegetation indices (enhanced vegetation index(EVI), specific leaf area vegetation index (SLAVI), simple ratio vegetation index (SRVI), and visible atmospherically resistant index (VARI)) computed using band 3 (green) and band 11 of the Sentinel-2 performed equally well and achieved a good measure of accuracy (R-2 = 0.67, RMSE = 0.034). Our findings demonstrate the feasibility of using Sentinel-2 surface reflectance data to map LDMC in a coastal wetland.

Keywords: LDMC; PLSR; vegetation indices; Sentinel-2; wetland

Publ.-Id: 29735

First principles calculations of the thermodynamic stability of Ba, Zr, and O vacancies in BaZrO3

Nadarajan, R.; Devaraj, M.; Satyanarayana, S. V. M.; Posselt, M.

The temperature dependence of the stability of bulk BaZrO3 (BZO) and of the vacancies in this material is investigated by considering phonon contributions to the free energy. The stability diagram of BZO is determined for different chemical environments. With increasing temperature the stability region becomes smaller which is particularly caused by the strong temperature dependence of the chemical potential of gaseous oxygen. The free formation energy of Ba, Zr, and O vacancies in BZO is calculated for all possible charge states and for different atomic reservoirs. While the free formation energy of Zr vacancies is strongly influenced by temperature a weaker dependence is found for Ba and O vacancies. This has also an effect on the charge transition levels at different temperatures. Present results demonstrate that O poor reservoir conditions and a Fermi level close to the valence band maximum favour a high concentration of doubly positively charged O vacancies which is a prerequisite to get a large number of protonic defects and a good proton conductivity. In such a chemical environment the amount of Ba and Zr vacancies is low so that Ba and Zr deficiencies are not an important issue and BZO stays sufficiently stable.

Keywords: DFT; Barium Zirconate; thermodynamic stability; vacancies

Publ.-Id: 29734

Comparison of Eulerian QBMM and classical Eulerian – Eulerian method for the simulation of polydisperse bubbly flows

Li, D.; Marchisio, D.; Hasse, C.; Lucas, D.

The spatial gas distribution of poly-disperse bubbly flows depends greatly on the bubble size. To reflect the resulting polycelerity, more than two momentum balance equations (typically for the gas and liquid phases) have to be considered, as done in the multifluid approach. The inhomogeneous multiple-size group model follows this approach, also combined with a population balance model. As an alternative, in a previous work, an Eulerian quadrature-based moments method (E-QBMM) was implemented in OpenFOAM; however, only the drag force was included. In this work, different nondrag forces (lift, wall lubrication, and turbulent dispersion) are added to enable more complex test cases to be simulated. Simulation results obtained using E-QBMM are compared with the classical E – E method and validated against experimental data for different test cases. The results show that there is good agreement between E-QBMM and E – E methods for mono-disperse cases, but E-QBMM can better simulate the separation and segregation of small and large bubbles.

Keywords: bubbly flow; E – E method; E-QBMM; non-drag forces; wall peak

Publ.-Id: 29733

Radio- and photosensitization of plasmid DNA by DNA binding ligand propidium iodide: Investigation of Auger electron induction and detection of Cherenkov-emission

Kotzerke, J.; Runge, R.; Gotze, P.; Wunderlich, G.; Enghardt, W.; Freudenberg, R.

Purpose We investigated whether propidium iodide (PI) enhances DNA damaging effects of ionizing and non-ionizing radiation species (X-rays, alpha-, beta-, auger electron emission and light of various wavelengths, respectively). This biophysical experimental setting allowed us, furthermore, to investigate whether Cherenkov emission can be detected by photodynamic effects and increased DNA damage.
Material and methods Conformation changes of plasmid DNA were detected and quantified by gelelectrophoresis and fluorescence imaging. Hydrogen peroxide, stannous dichloride, and dimethylsulfoxide were used as chemical modulators, Tc-99m, Re-188, Ra-223, and x-ray (32 kV and 200 kV) reflected radiotoxicity and light (lambda = 254 nm, 366 nm and 530-575 nm) induced phototoxicity.
Results Radiotracers and x-rays induced dose dependent DNA damage. PI did not serve as radiosensitizer in radioisotopes, while a low effect was detected in X-rays. The phototoxicity was dependent on the wavelengths of light. Light with a wavelength range of 530-575 nm in combination with PI resulted in direct DNA damage. The yield of Cherenkov emission was far below the photon emission of light irradiation and not distinguishable from general radiotoxicity.
Conclusions PI binds to plasmid DNA, is not chemotoxic, and increases radiotoxicity only to minor extent. Phototoxicity and its stimulation by PI is dependent on the wavelength of the light. No kind of energy deposition was capable of inducing an Auger electron cascade.
Furthermore, no increase in DNA damage induced by photodynamic effects from Cherenkov emission was detectable.

Keywords: Probidium Iodide; Plasmid DNA; Auger Electrons; Cherenkov Emission

Publ.-Id: 29732

Radioresistance of KRAS/TP53-mutated lung cancer can be overcome by radiation dose escalation or EGFR tyrosine kinase inhibition in vivo

Gurtner, K.; Kryzmien, Z.; Koi, L.; Wang, M.; Benes, C.; Hering, S.; Willers, H.; Baumann, M.; Krause, M.

Recent clinical data have linked KRAS/TP53 comutation (mut) to resistance to radiotherapy (RT), but supporting laboratory in vivo evidence is lacking. In addition, the ability of different radiation doses, with/without epidermal growth factor receptor (EGFR)-directed treatment, to achieve local tumor control as a function of KRAS status is unknown. Here, we assessed clonogenic radiation survival of a panel of annotated lung cancer cell lines. KRASmut/TP53mut was associated with the highest radioresistance in nonisogenic and isogenic comparisons. To validate these findings, isogenic TP53mut NCI-H1703 models, KRASmut or wild-type (wt), were grown as heterotopic xenografts in nude mice. A clinical RT schedule of 30 fractions over 6 weeks was employed. The dose that controlled 50% of tumors (TCD50) was calculated. The TCD50 for KRASwt/TP53mut xenografts was 43.1 Gy whereas KRASmut/TP53mut tumors required a 1.9-fold higher TCD50 of 81.4 Gy. The EGFR inhibitor erlotinib radiosensitized KRASmut but not KRASwt cells and xenografts.
The TCD50 associated with adding erlotinib to RT was 58.8 Gy for KRASmut, that is, a 1.4-fold dose enhancement. However, the EGFR antibody cetuximab did not have a radiosensitizing effect. In conclusion, we demonstrate for the first time that KRASmut in a TP53mut background confers radioresistance when studying a clinical RT schedule and local control rather than tumor growth delay. Despite the known unresponsiveness of KRASmut tumors to EGFR inhibitors, erlotinib radiosensitized KRASmut tumors. Our data highlight KRAS/TP53 comutation as a candidate biomarker of radioresistance that can be at least partially reversed by dose escalation or the addition of a targeted agent.

Publ.-Id: 29731

Comparable radiation response of ex vivo and in vivo irradiated tumor samples determined by residual γH2AX

Rassamegevanon, T.; Löck, S.; Baumann, M.; Krause, M.; von Neubeck, C.

Purpose: a) To investigate if an ex vivo cultured and irradiated tumor biopsy reflects and predicts the radiation response of the corresponding in vivo irradiated tumor measured with the DNA double strand break marker γH2AX foci. Materials and methods: Five human head and neck squamous cell carcinoma (hHNSCC) xenograft models were used. Fine needle biopsies were taken from anesthetized tumor-bearing NMRI nude mice prior to in vivo single dose irradiation (0, 2, 4, or 8 Gy) under ambient blood flow. Biopsies were ex vivo reoxygenated and irradiated with equivalent doses. Tumors and biopsies were fixed 24 h post irradiation, and γH2AX foci were assessed in oxygenated tumor regions. Results: Linear regression analysis showed comparable slopes of the residual γH2AX foci dose–response curves in four out of five hHNSCC models when in vivo and ex vivo cohorts were compared. The slopes from ex vivo biopsies and in vivo tumors could classify the respective tumor model as sensitive or resistant according to the intrinsic radiation sensitivity (TCD50). Conclusion: The ability of ex vivo irradiated tumor biopsies to reflect and predict the intrinsic radiation response of in vivo tumors increases the translational potential of the ex vivo γH2AX foci assay as a diagnostic tool for clinical practice. © 2019 Elsevier B.V.

Keywords: Intrinsic radiation sensitivity; Predictive biomarker; Radiation therapy; γH2AX foci


Publ.-Id: 29730

Lift Forces on Solid Spherical Particles in Wall-bounded Flows

Shi, P.; Rzehak, R.

The present work is concerned with the lift forces acting on particles immersed in a wall-bounded fluid. Conditions where the particle translates in a fluid at rest and in a linear shear flow are considered. Likewise, non-rotating particles and particles in free rotation driven solely by the flow are considered. Furthermore, situations where the wall lies in the inner region and in the outer region of the flow disturbance produced by the particle are distinguished. The focus is on solid spherical particles at Reynolds numbers up to O(〖10〗^2 ) which are relevant for particulate flows in chemical and minerals engineering. A comprehensive review of existing results from analytical, experimental, and direct numerical simulation studies is given. The available correlations are critically assessed by comparison to data from these studies. Based on the comparison recommendations are given which correlations to use, including some new proposals, and gaps in the data are identified.

Keywords: lift force; particles; wall-bounded flow; particle rotation; inner / outer region; correlation

Publ.-Id: 29729

Au incorporation into various ZnO crystallographic cuts realised by ion implantation – ZnO damage characterization

Mackova, A.; Malinsky, P.; Jagerova, A.; Miksova, R.; Nekvindova, P.; Cajzl, J.; Böttger, R.; Akhmadaliev, S.

Non-polar surfaces, such as a-plane (11–20) and m-plane (10-10), for ZnO have become more attractive as numerous efforts have recently been made to grow non-polar ZnO facets for applications in nanoscale photonic devices. Noble-metal incorporation into transparent semiconductors such as ZnO has been investigated because of the non-linear optical response of such structures. This paper presents a study of defect evolution in various ZnO crystallographic cuts caused by Au implantation. The investigation has focused on ZnO structure characterisation, Au distribution and the interior morphology of the a-, m- and c-planes ZnO single crystals implanted with 400 keV Au+ ions at the ion fluences of 5 × 1014 and 1 × 1015 cm−2 and subsequently annealed at 600 °C in O2. The structure modification was studied using Rutherford backscattering spectrometry (RBS) in the channelling mode (RBS/C) and Raman spectroscopy. After the ion-implantation process, low surface damage was observed in all ZnO orientations unlike deep structural damage. Deep structural damage grew with increased Au-ion fluence and Au did not exhibit strong out-diffusion from the depth to the surface during the post-implantation annealing. Small but noticeable differences were observed between different ZnO orientations. RBS measurements during ion implantation revealed more progressive deep-damage formation in the c- and m-planes than in the a-plane ZnO. Simultaneously, the smallest Zn sub-lattice disorder deduced from RBS/C measurements was observed in the a-plane ZnO. During post-implantation annealing, a slight structure recovery (about 4%) was observed in all orientations. Raman spectroscopy confirmed the increasing structure disorder with the enhanced ion fluence for all as-implanted ZnO orientations and a partial reconstruction of the ZnO structure during annealing, when the intensity of E2 phonons was increased and that of longitudinal optical (LO) phonons was suppressed because of the disorder recovery. E2 (high) and E1(LO) Raman phonon modes connected with oxygen sub-lattice ordering/disordering have been investigated in detail – they show a significant modification mainly in the m-plane. The cause of the different behaviour of ZnO planes as well as the differences in the incorporation and movement of Au and Er atoms in the ZnO structure are discussed in the work.

Related publications

Publ.-Id: 29728

Entwicklung des Gesamtsystems - Stand der Modellierungs- und Simulationsarbeiten

Fogel, S.

Entwicklung eines tubularen Dampf-Elektrolyseurs mit integrierter Kohlenwasserstoffsynthese (DELTA)

  • Lecture (others)
    5. Projekttreffen DELTA, 25.04.2019, Dresden, Deutschland

Publ.-Id: 29727

3. Zwischenbericht DELTA

Fogel, S.

Entwicklung eines tubularen Dampf-Elektrolyseurs mit integrierter Kohlenwasserstoffsynthese (DELTA)

  • Other report
    Dresden: HZDR, 2019
    27 Seiten

Publ.-Id: 29726

Single Cell and System Modeling of Tubular Proton Conducting Solid Oxide Steam Electrolyzers for Intermittent Operation

Fogel, S.; Kryk, H.; Hampel, U.

Due to the constantly growing utilization of wind and solar energy, the demand for technologies for temporal and spatial decoupling of energy provision and consumption is steadily increasing. The application of proton-conducting solid oxide electrolysis cells (H-SOEC) has been a main concern in recent research activities since they offer an environmentally friendly and efficient technique for the conversion of excess energy into hydrogen. As renewables occur intermittently, SOEC designs and all employed materials have to be capable of withstanding large electrical transients and therefore harsh operating conditions. Tubular cell designs of SOEC received increased attention in recent years due to their inherent advantages. They offer rapid startup capabilities as well as high resistance to heat, thermal cycling, thermal stresses and high-pressure application capabilities. Since the knowledge of the dynamic behavior of SOECs is key to their future application, this work aims to study the transient behavior of a single, proton conducting SOEC during rapid load variations and of multi-tubular stacks on a system scale under high-pressure operation. The use of different load variation speeds is discussed with respect to cell control.

Keywords: SOEC; load variation; transient operation; tubular cell; proton conduction

  • Lecture (Conference)
    12th European Congress of Chemical Engineering ECCE, 15.-19.09.2019, Florence, Italy

Publ.-Id: 29725

Transient Operation of Tubular H-SOECs for Hydrogen Production in CCU Processes

Fogel, S.; Kryk, H.; Hampel, U.

Since the utilization of wind and solar energy is constantly growing, the demand for technologies for temporal and spatial decoupling of energy provision and consumption is steadily increasing. The application of proton-conducting solid oxide electrolysis cells (H-SOECs) has been a main concern of recent research activities since they offer an environmentally friendly and efficient technique for the conversion of excess energy and steam into hydrogen. An appropriate coupling of stationary carbon dioxide (CO2) emitters and consumers offers a promising option for chemical energy storage and the production of valuable chemicals (e.g. methanol). Using electrolytic hydrogen production together with suitable downstream syntheses units as combined power-to-liquid technologies, a promising method for the recycling of carbon dioxide (CCU) can be provided. Since renewables occur intermittently, SOECs have to be capable of withstanding harsh operating conditions and the knowledge of their dynamic behavior is crucial for their future system application. This work studies the transient behavior of a single tubular, proton conducting SOEC during rapid load variations through 2D-FEM single cell and quasi-2D system scale simulations and evaluates the usability of the cell in combination with fluctuating loads.

Keywords: SOEC; dynamic operation; CCU; hydrogen; proton conduction; renewable energy

  • Poster
    17th International Conference on Carbon Dioxide Utilization ICCDU 2019, 23.-27.06.2019, Aachen, Deutschland

Publ.-Id: 29724

Transient behavior of tubular solid oxide electrolyzer cells under fast load variations

Fogel, S.; Kryk, H.; Hampel, U.

Solid oxide electrolyzer cells (SOEC) pose a promising technology for the production of hydrogen gained from renewables, such as wind and PV. Due to the fluctuating nature of these sources, the transient behavior of SOEC under various load cases plays a crucial role in terms of their long-time stability, degradation behavior, conver-sion efficiency and application. As a consequence of the intermittent occurrence of renewables, SOEC designs and all employed materials have to be capable of with-standing harsh operating conditions, leading to strict demands regarding process control and the overall cell design. Tubular cell designs of SOECs received in-creased attention in recent years due to their inherent advantages. They offer rapid startup capabilities as well as high resistance to heat and thermal stresses. Further-more, tubular cells are characterized by significantly smaller sealing lengths in com-parison to planar cells, enabling a high-pressure application. Operating SOECs at elevated pressures poses beneficial opportunities for their future system application, since the produced hydrogen does not need to be compressed using a separate compressor stage or the electrolyzer can be combined with promising downstream synthesis units (e.g. methanol synthesis). Dynamic simulations can be used to de-termine the transient behavior of SOECs during operation with harsh load-transients. This simulation work aimed to study the transient behavior of a single, proton conducting SOEC during rapid load variations under high-pressure opera-tion. For this purpose, a two-dimensional model of a tubular SOEC was developed and different load steps and their influence on crucial operational parameters, such as temperature profiles, cell potential and species concentrations were investigated. The feasibility of the cell design regarding harsh transient load variations was stud-ied. Various load-pulse shapes and durations, different flow configurations and steam mass flow rates have been investigated and their influence on the short-term transient behavior of the cell were examined. With the aid of the aforementioned simulations, limiting operational states of the cell (e.g. steam starvation and tempera-ture hot-spots) as well as beneficial process parameter combinations for an im-proved cell operational behavior were ought to be identified with respect to advanc-es in cell control strategies.

Keywords: SOEC; dynamic operation; proton conduction

  • Poster
    Jahrestreffen der ProcessNet-Fachgruppe Energieverfahrenstechnik, 06.-07.03.2019, Frankfurt am Main, Deutschland

Publ.-Id: 29723

Analog of cosmological particle creation in electromagnetic waveguides

Lang, S.; Schützhold, R.

We consider an electromagnetic waveguide with a time-dependent propagation speed v(t) as an analog for cosmological particle creation. In contrast to most previous studies which focus on the number of particles produced, we calculate the corresponding two-point correlation function. For a small steplike variation delta v(t), this correlator displays characteristic signatures of particle pair creation. As another potential advantage, this observable is of first order in the perturbation delta v(t), whereas the particle number is second order in delta v(t) and thus more strongly suppressed for small delta v(t).


Publ.-Id: 29722

Update the MUSIG model in ANSYS CFX for reliable modelling of bubble coalescence and breakup

Liao, Y.

The MUSIG (Multiple Size Group) model in the commercial CFD code ANSYS CFX is a population balance approach for describing binary bubble coalescence and breakup events. It is widely used in the simulation of poly-dispersed bubble flows. The purpose of this work is to identify some inconsistencies in the discrete method that applied for the solution of the population balance equation in MUSIG, and propose an improved one for discretising the source and sink terms that result from bubble coalescence and breakup. The new formulation is superior to the existing ones in preserving both mass and number density of bubbles, allowing arbitrary discretisation schemes and free of costly numerical integrations. The numerical results on the evolution of bubble size distributions in bubble flows reveal that the inconsistency in the original MUSIG regarding bubble breakup is non-negligible in both academic and practical cases. The updates presented in this work are necessary and important for calibration of bubble coalescence and breakup models using the MUSIG approach.

Keywords: MUSIG; ANSYS CFX; Coalescence and breakup; Method of classes; Discrete formulation; Population balance equation


Publ.-Id: 29721

Synthesis, Structural Characterisation, and Cytotoxicity Studies of Bi, W, and Mo containing Homo- and Hetero-bimetallic Polyoxometalates

Senevirathna, D.; Werrett, M.; Kubeil, M.; Stephan, H.; Andrews, P.

Three new and different homo- and hetero-bimetallic polyoxometalate (POM) species have been synthesised by simple one-pot synthetic methods utilising naturally occurring bismite (Bi2O3) (or Bi(NO3)3·5H2O) and aryl sulfonic acids. The POM species isolated are {(NH4)14[Bi2W22O76]·14H2O} (1·14H2O), {NH4[Bi(DMSO)7][Mo8O26]·H2O} (2·H2O) and {[(NH4)4(Mo36O108(OH)4·16H2O)]·45H2O} (3·45H2O). The compounds have been characterised by X-ray crystallography, energy dispersive X-ray spectroscopy (EDX), powdered X-ray diffraction (PXRD), mass spectrometry (ESI-MS), Raman spectroscopy, thermogravimetric (TGA) and ICP analyis. In vitro cytoxicity and proliferation studies conducted on 1 and 3, highlight the low toxicity of these species.


Publ.-Id: 29719

Effect of nozzle geometry on pressure drop in submerged gas injection

Xiao, J.; Yan, H.-J.; Schubert, M.; Unger, S.; Liu, L.; Schleicher, E.; Hampel, U.

Submerged gas injection into liquid leads to complex multiphase flow, in which nozzle geometries are crucial important for the operational expenditure in terms of pressure drop. The influence of the nozzle geometry on pressure drop between nozzle inlet and outlet has been experimentally studied for different gas flow rates and bath depths.
Nozzles with circular, gear-like and four-leaf cross-sectional shape have been studied. The results indicate that, besides the hydraulic diameter of the outlet, the orifice area and the perimeter of the nozzle tip also play significant roles. For the same superficial gas velocity, the average pressure drop from the four-leaf-shaped geometry is the least. The influence of bath depth was found negligible. A correlation for the modified Euler number considering the pressure drop is proposed depending on nozzle geometric parameter AoL o −2 and on the modified Froude number gd o 5 Q−2 with the hydraulic diameter of the nozzle do as characteristic length.

Keywords: submerged gas injection; nozzle geometry; hydraulic diameter; pressure drop; modified Euler number

Publ.-Id: 29718

Effect of Bath Depth and Nozzle Geometry on Spout Height in Submerged Gas Injection at Bottom

Xiao, J.; Yan, H.; Liu, L.; Möller, F.; Hu, Z.; Unger, S.

Spout height is a widely used parameter to quantitatively analyze the performance of the submerged gas injection in industrial applications. However, the effect of bath depth and nozzle geometry on spout height in submerged gas injection is still unclear. In this work, the effect of bath depth and nozzle geometry on spout height in submerged gas injection at bottom was experimentally investigated. Circular-shaped, three-leaf-shaped, four-leaf-shaped, and four-flower-shaped nozzles were used for this study. Spout height was extracted from the images captured by high-speed camera and analyzed by digital image processing. The results indicate that the effect of nozzle geometry on spout height is as important as gas flow rate and bath depth. Through dimensional analysis, predictive correlations of spout height from circular shape and four-leaf shape were developed with dimensionless bath depth and a modified Froude number using orifice perimeter and opening area as characteristic parameters. Experimental data were compared with the correlations from literature and good agreement was found.

Publ.-Id: 29717

Control and stimulation of three-magnon scattering in a magnetic vortex

Körber, L.; Schultheiß, K.; Hula, T.; Verba, R.; Hache, T.; Schultheiß, H.

When applying a large enough RF field amplitude, spin waves in a magnetic vortex disk can decay into two other spin waves via three-magnon scattering. In order to reach the threshold of this process, the energy flux from the decay of the directly excited mode must overcome the internal losses of the secondary modes. The resulting scattering processes obey certain selection rules which result in the two output frequencies to be distinct from one another. Moreover, three-magnon scattering of the directly excited mode into multiple pairs of secondary modes is possible. However, typically one of these scattering channels has a lower threshold than the others which leads to this channel being activated first and limiting the energy flux in the other possible “silent” channels. Here, we show that three-magnon scattering in such a system can be stimulated below the usual instability threshold by additionaly pumping one of the secondary modes. This is achieved by coupling the magnetic vortex to an adjacent magnonic wave guide. The response to the stimulation is instantaneous and can be used to activate the silent three-magnon channels, as well.

Keywords: nonlinear; magnon; vortex; magnetism; magnonics

  • Lecture (Conference)
    Magnonics 2019, 28.07.-01.08.2019, Carovigno, Italien

Publ.-Id: 29716

Liquid metal battery research activities at HZDR

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

Liquid metal batteries are promising candidates for low-cost, large-scale stationary electricity storage. Different systems investigated at HZDR are discussed with a focus on fluid dynamic phenomena like interfacial wave interactions, mass transfer, and electro-vortex flows.

Keywords: liquid metal batteries; mass transfer; electro-vortex flows

  • Invited lecture (Conferences)
    Institutskolloquium Institut für Thermo- und Fluiddynamik TU Ilmenau, 12.09.2019, Ilmenau, Deutschland

Publ.-Id: 29715

Multi-modality bedding platform for combined imaging and irradiation of mice

Müller, J.; Schürer, M.; Neubert, C.; Tillner, F.; Beyreuther, E.; Suckert, T.; Peters, N.; von Neubeck, C.; Lühr, A.; Krause, M.; Bütof, R.; Dietrich, A.

Preclinical imaging and irradiation yields valuable insights into clinically relevant research topics. While complementary imaging methods such as computed tomography (CT), magnetic resonance imaging (MRI), and positron emission tomography (PET) can be combined within single devices, this is technically demanding and cost-intensive. Similarly, bedding and setup solutions are often specific to certain devices and research questions. We present a bedding platform for mice that is compatible with various preclinical imaging modalities (combined PET/MRI, cone beam CT) and irradiation with photons and protons.
It consists of a 3D-printed bedding unit (acrylonitrile butadiene styrene, ABS) holding the animal and features an inhalation anesthesia mask, jaw fixation, ear pins, and immobilization for the hind leg. It can be embedded on mounting adaptors for multi-modal imaging and into a transport box (polymethyl methacrylate, PMMA) for experiments outside dedicated animal facilities while maintaining the animal’s hygiene status. A vital support unit provides heating, inhalation anesthesia, and a respiration monitor. We dosimetrically evaluated used materials in order to assess their interaction with incident irradiation. Proof-of-concept multi-modal imaging protocols were used on phantoms and mice.
The measured attenuation of the bedding unit for 40/60/80/200 kV x-rays was less than 3 %. The measured stopping-power-ratio of ABS was 0.951, the combined water-equivalent thickness of bedding unit and transport box was 4.2 mm for proton energies of 150 MeV and 200 MeV. Proof-of-concept imaging showed no loss of image quality. Imaging data of individual mice from different imaging modalities could be aligned rigidly.
The presented bed aims to provide a platform for experiments related to both multi-modal imaging and irradiation, thus offering the possibility for image-guided irradiation which relies on precise imaging and positioning. The usage as a self-contained, stand-alone unit outside dedicated animal facilities represents an advantage over setups designed for specific devices.

Keywords: Small animal; Imaging; Irradiation; Protons; preclinical; transport; hyiene status

Publ.-Id: 29714

Anisotropic temperature-field phase diagram of single crystalline β-Li2IrO3: Magnetization, specific heat, and 7Li NMR study

Majumder, M.; Freund, F.; Dey, T.; Prinz-Zwick, M.; Büttgen, N.; Scurschii, I.; Jesche, A.; Tsirlin, A. A.; Gegenwart, P.

Detailed magnetization, specific heat, and 7Li nuclear magnetic resonance (NMR) measurements on single crystals of the hyperhoneycomb Kitaev magnet β-Li2IrO3 are reported. At high temperatures, anisotropy of the magnetization is reflected by the different Curie-Weiss temperatures for different field directions, in agreement with the combination of a ferromagnetic Kitaev interaction (K) and a negative off-diagonal anisotropy (Γ) as two leading terms in the spin Hamiltonian. At low temperatures, magnetic fields applied along a or c have only a weak effect on the system and reduce the Néel temperature from 38 K at 0 T to about 35.5 K at 14 T, with no field-induced transitions observed up to 58 T on a powder sample. In contrast, the field applied along b causes a drastic reduction in the TN that vanishes around Hc = 2.8 T, giving way to a crossover toward a quantum paramagnetic state. Li NMR measurements in this field-induced state reveal a gradual line broadening and a continuous evolution of the line shift with temperature, suggesting the development of local magnetic fields. The spin-lattice relaxation rate shows a peak around the crossover temperature 40 K and follows power-law behavior below this temperature.

Publ.-Id: 29713

A SERPENT2-SUBCHANFLOW-TRANSURANUS coupling for pin-by-pin depletion calculations in Light Water Reactors

Garcia, M.; Tuominen, R.; Gommlich, A.; Ferraro, D.; Valtavirta, V.; Imke, U.; van Uffelen, P.; Mercatali, L.; Sanchez, V.; Leppänen, J.; Kliem, S.

This work presents the development of a coupling scheme for Serpent2, a continuous-energy Monte Carlo particle transport code, SUBCHANFLOW,
a subchannel thermalhydraulics code, and TRANSURANUS, a fuel-performance code, suitable for large-scale high-fidelity depletion calculations for Light Water Reactors. The calculation method is based on the standard neutronic/thermalhydraulic approach, replacing the simple fuel-rod solver in SUBCHANFLOW with the more complex thermomechanic model of TRANSURANUS. The depletion method is fully coupled and semi-implicit, and the implementation relies on an object-oriented design with mesh-based feedback exchange. The results of the three-code system for a 360-day depletion calculation of a VVER-1000 fuel assembly with a pin-by-pin modelling approach are presented and analyzed. The performance of this tool, as well as the bottlenecks for its application to full-core problems, are discussed.



Publ.-Id: 29712

Microstructural Characterization of a VVER-440 type Reactor Pressure Vessel Steel by Electron Microscopy

Chekhonin, P.; Röder, F.; Müller, G.; Roßner, M.; Heintze, C.; Bergner, F.

A microstructural investigation of a VVER400-type reactor pressure vessel (RPV) steel in the initial state (unirradiated) is presented. Key points include a detailed characterization by electron backscatter diffraction and an analysis of precipitates and inclusions performed by transmission as well as scanning electron microscopy.

Keywords: Microstructure; Reactor Pressure Vessel Steels; Electron Microscopy

  • Lecture (Conference)
    IGRDM-21 - 21st meeting of International Group on Radiation Damage Mechanism, 19.-24.05.2019, Gifu, Japan
  • Lecture (Conference)
    Kompetenzverbund Ost für Kerntechnik, 05.12.2019, Dresden, Germany

Publ.-Id: 29711

Bainitic and Martensitic Microstructures Revealed by EBSD

Chekhonin, P.; Bergner, F.

To understand and to tailor the properties of nuclear materials, it is essential to investigate their microstructure. EBSD systems in SEMs facilitate local crystal orientation measurements providing surface mappings in which each point is characterized by three Euler angles [1]. This data is used to reveal microstructural features such as grains, their size and -shape, grain boundaries and other details.
In the present work, a dedicated EBSD evaluation software was developed and applied to study the type of grain boundaries. Former austenite grain boundaries are revealed and within certain limitations, it is possible to differentiate between packets and blocks. Additionally, details about the variant selection during the martensitic transformation are provided and differences between bainitic steels and ferritic/martensitic steels are identified. This information may be of use to understand grain boundary related differences regarding cluster formation and sink strength.

Keywords: EBSD; Microstructure; Steels; Bainite; Martensite

  • Poster
    M4F PhD and post-doc event, 23.-25.06.2019, Miraflores de la Sierra, Spain

Publ.-Id: 29710

Electronic properties of GaAs/InₓGa₁₋ₓAs and GaAs/InₓAl₁₋ₓAs core/shell nanowires studied by pump – probe THz spectroscopy

Fotev, I.; Balaghi, L.; Shan, S.; Hübner, R.; Schmidt, J.; Schneider, H.; Helm, M.; Dimakis, E.; Pashkin, A.

We report terahertz response of photoexcited core/shell nanowires. The obtained parameters of the localized surface plasmon mode allow us to estimate electron mobilities, concentrations and recombination lifetimes. The extracted mobilities reach 4000 cm²/V·s at room temperature, while the carrier lifetimes range from 80 to 300 ps, depending on the shell composition and the photoexcitation level.

  • Lecture (Conference)
    French-German THz Conference 2019, 02.-05.04.2019, Kaiserslautern, Germany

Publ.-Id: 29709

Thz User Operation With 200 pC CW Beam Generated by the ELBE SRF Gun II

Arnold, A.; Awari, N.; Chen, M.; Deinert, J.-C.; Evtushenko, P.; Green, B. W.; Klopf, J. M.; Kovalev, S.; Lehnert, U.; Ma, S.; Murcek, P.; Michel, P.; Schaber, J.; Teichert, J.; Xiang, R.; Zwartek, P.

As a new electron source with higher brilliance, the second superconducting RF photoinjector (SRF Gun II) has been built at the ELBE radiation center for high power radiation sources. One of the main goals of SRF gun II is to achieve a higher bunch charge (>200 pC) and lower emittance (3 mm mrad) than the present ELBE thermionic DC gun. SRF Gun II features a 3.5-cell niobium cavity as well as a superconducting solenoid in the same cryomodule. With Mg photocathodes the gun is able to provide medium current beam with bunch charge of more than 200 pC and sub-ps bunch length at 100 kHz repetition rate. With this contribution we present convincing results from long-term user operation of SRF gun II in combination with the bunching concept of the ELBE accelerator in order to produce THz radiation with much higher stability and power than available using the existing thermionic gun.

Keywords: SRF Gun; THz; ELBE; electron source; photoinjector

Related publications

  • Open Access Logo Poster
    63rd ICFA Advanced Beam Dynamics Workshop on Energy Recovery Linacs, 15.-20.09.2019, Berlin, Deutschland

Publ.-Id: 29708

Developing multi-sensor drones for geological mapping and mineral exploration: setup and first results from the MULSEDRO project

Heincke, B.; Jackisch, R.; Saartenoja, A.; Salmirinne, H.; Rapp, S.; Zimmermann, R.; Pirttijärvi, M.; Vest Sörensen, E.; Gloaguen, R.; Ek, L.; Bergström, J.; Karinen, A.; Salehi, S.; Madriz Diaz, Y. C.; Middleton, M.

The use of Unmanned Aerial Systems (UAS), also known as drones, is becoming increasingly important for geological applications. Thanks to lower operational costs and ease of use, UAS offer an alternative approach to aircraft-based and ground-based geoscientific measurements (Colomina & Molina 2014). Magnetic and hyperspectral UAS surveys hold particular promise for mineral exploration, and several groups have recently published studies of magnetic data collected by UAS for such applications (Malehmir et al. 2017; Cunningham et al. 2018), although equivalent studies using hyperspectral data are still rare (Kirsch et al. 2018). Combining both techniques is particularly useful. Magnetic measurements play an important role in mineral exploration, since magnetisation in rocks is mainly associated with magnetite and other iron minerals, which can be used in mapping and targeting of mineral deposits (Dentith & Mudge 2014). Hyperspectral imaging (HSI) is a powerful exploration and mapping technique in areas where the rock surface is well-exposed, and where geological units and mineral compositions can be estimated from spectral features of the electromagnetic spectrum in the visual and infrared range.

Keywords: Drones; Geological Mapping; Unmanned Aerial System; Hyperspectral imaging; Magnetic survey

Publ.-Id: 29707

Pump – Probe THz Spectroscopy Study of Electronic Properties of Semiconductor Nanowires

Fotev, I.; Balaghi, L.; Shan, S.; Hübner, R.; Schmidt, J.; Schneider, H.; Helm, M.; Dimakis, E.; Pashkin, O.

THz radiation is a perfect tool for probing electrical properties of semiconductor nanostructures in a contactless way. When applied to semiconductor nanowires, THz probe pulses can drive the oscillations of photoexcited electrons and holes in the form of localized surface plasmon. We used optical pump – THz probe spectroscopy to study plasmonic response of charge carriers in GaAs/InₓGa₁₋ₓAs core/shell nanowires. The carrier lifetimes are about 80-100 ps, depending on the shell composition and the photoexcitation level, while the extracted mobilities reach 3700 cm²/V·s at room temperature.

Keywords: GaAs nanowires; terahertz spectroscopy; ultrafast dynamics; electron mobility; plasmon; carrier lifetime

  • Lecture (Conference)
    44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), 01.-06.09.2019, Paris, France
  • Contribution to proceedings
    44th International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz, 01.-06.09.2019, Paris, France
    44th International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz, 153046
    DOI: 10.1109/IRMMW-THz.2019.8874068
    Cited 1 times in Scopus

Publ.-Id: 29706

Current management of pheochromocytoma/paraganglioma: A guide for the practicing clinician in the era of precision medicine

Nölting, S.; Ullrich, M.; Pietzsch, J.; Ziegler, C. G.; Eisenhofer, G.; Grossman, A.; Pacak, K.

Pheochromocytomas and paragangliomas (PCC/PGLs) are rare, mostly catecholamine-producing neuroendocrine tumors of the adrenal gland (PCCs) or the extra-adrenal paraganglia (PGL). They can be separated into three different molecular clusters depending on their underlying gene mutations in any of the at least 20 known susceptibility genes: the pseudohypoxia-associated cluster 1, the kinase signaling-associated cluster 2, and the Wnt signaling-associated cluster 3. Besides tumor size, location (adrenal vs. extra-adrenal), age of first diagnosis, and presence of metastatic disease (including tumor burden), other decisive factors for best clinical management of PCC/PGL include the underlying germline mutation. The above factors can impact the choice of different biomarkers and imaging modalities for diagnosis, as well as screening for other neoplasms, staging, follow-up, and therapy options. This review provides a guide for practicing clinicians summarizing current management of PCC/PGL according to tumor size, location, age of first diagnosis, presence of metastases and especially underlying mutations in the era of precision medicine.

Keywords: pheochromocytoma; paraganglioma; guideline; genetics; diagnosis; imaging; follow-up; therapy; precision medicine

Publ.-Id: 29705

Probing the Local Structure of Nanoscaled Actinide Oxides: A Comparison between PuO2 and ThO2 Nanoparticles Rules out PuO2+x Hypothesis

Bonato, L.; Virot, M.; Dumas, T.; Mesbah, A.; Dalodière, E.; Dieste Blanco, O.; Wiss, T.; Le Goff, X.; Odorico, M.; Prieur, D.; Roßberg, A.; Venault, L.; Dacheux, N.; Moisy, P.; Nikitenko, S. I.

Actinide research at the nanoscale is gaining fundamental interest due to environmental and industrial issues. The knowledge of the local structure and speciation of actinide nanoparticles, which possibly exhibit specific physico-chemical properties in comparison to bulk materials, would help in a better and reliable description of their behavior and reactivity. Herein, the synthesis and relevant characterization of PuO2 and ThO2 nanoparticles displayed as dispersed colloids, nanopowders or nanostructured oxide powders, allow to establish a clear relationship between the size of the nanocrystals composing these oxides and their corresponding An(IV) local structure investigated by EXAFS spectroscopy. Particularly, the probed An(IV) first oxygen shell evidences an analogous behavior for both Pu and Th oxides. This observation suggests that the often observed and controversial splitting of the Pu-O shell on the Fourier transformed EXAFS signal of PuO2 samples is attributed to a local structural disorder driven by a nanoparticle surface effect rather than to the presence of PuO2+x species.

Related publications

Publ.-Id: 29704

Investigating the fate of manufactured nanoparticles in waste water treatment by the use of radiolabeled nanoparticles

Schymura, S.; Hildebrand, H.; Neugebauer, M.; Lange, T.; Franke, K.

Waste water treatment plants (WWTP) are considered one of the largest sinks for manufactured nanoparticles (NPs), as well as a potential source for the reintroduction of NPs into the environment via the WWTP effluents. Consequently, the fate of NPs in WWT is an important factor for the risk assessment of the impact of manufactured NPs on Nature and human health. However the investigation of NP fate in WWT is hindered by large elemental and particulate backgrounds. To overcome these problems we used the radiolabeling of NPs as a means of sensitive selective detection of NPs in the complex media of activated sludge and cleared waste water in a model WWTP study. TiO2, CeO2, MWCNTs and quantum dots (QDs) were radiolabeled either by activation ([48V]TiO2), in-diffusion ([139Ce]CeO2), recoil labeling ([7Be]MWCNT) or radiosynthesis ([75Se]CdSe/[65Zn]ZnS QDs). The radiolabeling allowed us to quantify NP distribution between sludge and water phase in the WWTP and in the WWTP effluents. A distribution of about 10000 : 1 between sludge-associated NPs and free NPs in water is reached in the WWTP already shortly after injection of the NPs. Thus the elimination of the NPs from the WWTP is mainly controlled by the removal of surplus sludge taking place every day of operation. The NPs are eliminated from the WWTP with a half-life of about 6 days reflecting the pre-set sludge age. After about 22 days of operation 10 % of the initial NPs remain in the WWTP. Approximately 1 % of the NPs leave the WWTP via the cleared waste water, mainly associated with non-sedimented sludge particles, such that only about 1 ‰ of the NPs leave the WWTP as free particles via the cleared water. An impact of the NPs on the clearing process, as monitored by chemical oxygen demand of the inflow vs. the outflow, was not observed.

Keywords: Nanopartikel; nanoparticles; Radiomarkierung; radiolabeling; Abwasserbehandlung; waste water treatment; Kläranlage; waste water treatment plant

  • Lecture (Conference)
    Cycleur Workshop, 08.-09.05.2019, Dresden, Deutschland

Publ.-Id: 29702

Radiolabeling of Nanoparticles - A versatile Tool in Nanosafety Research

Schymura, S.; Hildebrand, H.; Rybkin, I.; Ma, M.; Fricke, T.; Mansel, A.; Neugebauer, M.; Freyer, A.; Rijavec, T.; Lapanje, A.; Jacimovic, R.; Strok, M.; Lange, T.; Holzwarth, U.; Gibson, N.; Franke, K.

The employment of radiotracers is a versatile tool for the detection of nano-particulate materials in complex systems such as environmental samples or organisms. With the increasing usage of nanoparticles in applications outside of research laboratories a careful risk assessment of their release into the environment becomes mandatory. However, the monitoring of nanoparticles in such complex natural systems as soil, natural waters, plants, sewage sludge, etc. is very challenging using conventional methods, especially at environmentally relevant concentrations. This obstacle can be overcome by radiolabeling, which may be of crucial value in enabling such research. We have developed various methods of introducing radiotracers into some of the most common nanoparticles, such as Ag, carbon, SiO2, CeO2 and TiO2 nanoparticles. The labeling techniques are the synthesis of the nanoparticles using radioactive starting materials, the binding of the radiotracer to the nanoparticles, the activation of the nanoparticles using proton irradiation, the recoil labeling utilizing the recoil of a nuclear reaction to implant a radiotracer into the nanoparticle, and the in-diffusion of radiotracers into the nanoparticles at elevated temperatures. Using these methods we have produced [105/110mAg]Ag, [124/125/131I]CNTs, [48V]TiO2, [139Ce]CeO2, [7Be]MWCNT, [64Cu]SiO2, [44/45Ti]TiO2, etc.. The methods are adaptable for a wide range of other nanoparticles. The so-labelled nanoparticles can be detected at minimal concentrations well in the ng/L range even with a background of the same element and without complicated sample preparations necessary.
Using our methods one can radiolabel commercial nanoparticle samples for sensitive detection in environmentally relevant trace concentrations. The labeled particles have been successfully used in release studies, environmental mobility studies, fate studies in waste water treatment and plant uptake studies.

Keywords: Radiomarkierung; radiolabeling; Nanopartikel; nanoparticles; Zyklotron; cyclotron

  • Poster
    GDCh Fachgruppentagung Nuklearchemie, 25.-27.09.2019, Dresden, Deutschland

Publ.-Id: 29701

Migration of Actinide-Analogues visualized by Positron Emission Tomography GeoPET

Schymura, S.; Karimzadeh, L.; Mansel, A.; Franke, K.; Eichelbaum, S.; Frühwirt, T.; Zakhnini, A.; Jankovsky, F.; Zuna, M.; Molodtsov, K.; Kulenkampff, J.; Schmidt, M.; Lippmann-Pipke, J.; Fischer, C.

The search of a final repository for nuclear wastes from energy and weapon production calls for knowledge of actinide migration from molecular to kilometer scales. The migration behaviour on the mm to centimetre scale bridges a crucial step for the up- scaling of molecular knowledge and the validation of models based thereupon. Using the positron-emitting analogue for trivalent actinides 86Y we visualized its migration behaviour in a fractured granite core using positron emission tomography.
A granite drill core was obtained from the Bukov underground research facility in the Czech Republic. An artificial fracture was induced into the core by a geomechanical shear test and the core was subsequently encased in a plexiglas column. Radiotracers 18F and 86Y were produced at the in-house cyclotron at the HZDR Research Site Leipzig. 18F was produced by proton irradiation of 18O enriched water via 18O(p,n)18F. 86Y was obtained by proton irradiation of 86Sr enriched SrCO3 via 86Sr(p,n)86Y. Positon emission tomography was performed using the GeoPET setup at the HZDR Research Site Leipzig.
A transport experiment consisting of two steps was performed. First, aqueous [18F]KF solution was injected into the core to establish the conservative flow path through the fracture. Second, an aqueous 10-5 M [86Y]Y(NO3)3 solution in 0.1 M NaCl at pH 7.5 was flown through the fracture, followed by the eluent. The transport behaviour of the actinide analogue was monitored for a throughput of several pore volumes. After the conclusion of the experiment the core was opened and the sorption pattern on the fracture surface was additionally imaged by autoradiography.
Under the chosen conditions most of the 86Y got sorbed in the area close to the inlet and only 1% got eluted. The sorption pattern follows the conservative flow path. More detailed investigations of the sorbed species by μTRLFS (using Eu as a luminescent probe) and a modelling of the experiment based on the extracted flow path from the GeoPET data are planned.

Keywords: Positronenemissionstomographie; Positron Emission Tomography; Aktinide; Actinides

  • Poster
    GDCh Fachgruppentagung Nuklearchemie, 25.-27.09.2019, Dresden, Deutschland

Publ.-Id: 29700

Production of metal oxide nanoparticles through solvent extraction and crystallization stripping

Loredo, M. G. S.; Scharf, C.

In this work, the extraction of vanadium from alkaline solution, and the production of metal oxides through precipitation stripping, were carried out. The crystallization of calcium, copper, and iron vanadates from the extracts was performed using a solution containing a metal source as a stripping agent. In some experiments, a stabilizing polymer for controlling growth and avoiding agglomeration was added to the stripping solution. The structural characteristics of the crystallized products were studied. From the results, the synthesis of nanostructured vanadates is a simple and versatile method for the fabrication of valuable vanadium compounds.

  • Other report
    DAAD: DAAD-Bericht, 2019
    15 Seiten

Publ.-Id: 29698

Effect of DTPA on europium sorption onto quartz – Batch sorption experiments and surface complexation modeling

Karimzadeh, L.; Lippold, H.; Stockmann, M.; Fischer, C.

Sorption of radionuclides on mineral surfaces retards their migration in the environment of a repository. Presence of organic ligands, however, affects sorption and consequently influences their transport behavior. In this study, we quantify the sorption of Eu(III) onto quartz surfaces as a function of pH in the absence and presence of diethylenetriaminepentaacetic acid (DTPA). Batch sorption experiments show a pH-dependent sorption of Eu(III) on quartz. The presence of DTPA results in slightly higher sorption of Eu(III) at neutral to slightly acidic pH and considerably lower sorption at alkaline conditions. Sorption experiments were simulated using the Diffuse Double Layer Model (DDLM) with single sorption sites (≡QOH) and monodentate surface complexation. The reactions were established based on the aqueous speciation calculation under the experimental conditions, and the thermodynamic constants of surface reactions were obtained and refined by numerical optimization. Results of surface complexation modeling show the formation of a surface species ≡QOHEuDTPA2-, explaining the elevated sorption of Eu(III) at neutral to slightly acidic pH. In contrast, dissolved EuDTPA2- complex species are present at alkaline pH, resulting in an enhanced mobility of Eu(III).

Keywords: Sorption; Europium; Radionuclides; Diethylenetriaminepentaacetic acid; Surface complexation modeling


Publ.-Id: 29697

Influence of microturbulence on the bubble-particle interaction investigated with Positron Emission Particle Tracking (PEPT)

Sommer, A.-E.; Ortmann, K.; van Heerden, M.; Richter, T.; Leadbeater, T.; Cole, K.; Heitkam, S.; Brito-Parada, P.; Eckert, K.

In a flotation cell, turbulence significantly affects the recovery rate. Microturbulence influences the motion of solid particles and thus, the probability of bubble-particle aggregation. We investigated the effect of microturbulence on bubble-particle interactions with positron emission particle tracking (PEPT). Single air bubbles (db=2.5mm) were captured generated on a needle in a water flow channel. Upstream, a mesh produced an isotropic turbulent flow with 5-15% turbulence intensity. Depending on the distance to the grid, the incident flow near the captive bubble (Re=600) was characterized by eddies of different length scales and magnitude. The liquid contained up to 0.3% PMMA particles (dp=200-400µm) and up to six radiolabelled particles coated with PMMA (dp=300-400µm). The trajectories of the labelled particles were recorded, allowing us to determine the average particle distribution in the turbulent field and describe the bubble-particle interactions. These results provide valuable information to enhance our understanding of key flotation phenomena.

Keywords: PEPT; Bubble-Particle interaction; grid turbulence

  • Lecture (Conference)
    Flotation'19, 10.-14.11.2019, Kapstadt, Südafrika
  • Contribution to proceedings
    Flotation 19, 11.-14.11.2019, Kapstadt, Südafrika

Publ.-Id: 29696

Enhanced ion acceleration from a non-ideal laser pulse contrast

Garten, M.; Huebl, A.; Widera, R.; Göthel, I.; Obst-Huebl, L.; Ziegler, T.; Zeil, K.; Cowan, T.; Schramm, U.; Bussmann, M.; Kluge, T.

The major challenges of compact proton sources driven by an ultrashort high-intensity laser are currently to establish precise control over proton beam parameters and shot-to-shot stability. Shooting ultrathin targets has shown to yield higher proton energies, which became recently accessible due to temporal laser pulse shape control using plasma-mirror techniques. We find that the intensity ramp, transmitted to the target by the plasma mirror during the last picosecond before the pulse peak, becomes significantly decisive for the subsequent acceleration performance. Reliable characterization of this ramp with modern laser diagnostics remains challenging and immense computational needs required to fully resolve the plasma kinetics leave it mostly unexplored in today's simulations of laser-solid interaction. We present the results of 3D large-scale simulations with PIConGPU, taking into account realistic contrast conditions, bridging the scales from picosecond pre-plasma formation over transient, non-equilibrium dynamics of the tens of femtosecond laser duration down to attosecond plasma oscillations. Adding to beneficial acceleration conditions presented by hybrid acceleration mechanisms and the onset of relativistic transparency, we show that the maximum proton energy can be optimized by a specific leading pulse edge via a combination of pre-thermal and thermal TNSA, surpassing the performance of the ideal diffraction-limited Gaussian pulse.

Keywords: laser-ion acceleration; TNSA; simulation; PIConGPU; CSCS; Piz Daint; PRACE; HPC

  • Lecture (Conference)
    4th European Advanced Accelerator Concepts Workshop, 15.-21.09.2019, Isola d'Elba, Italia
  • Lecture (Conference)
    2nd WHELMI Annual Meeting, 18.-19.11.2019, Helmholtz-Zentrum Dresden - Rossendorf, Deutschland

Publ.-Id: 29695

Uranium(VI) reduction by anaerobic microorganisms within the mine water of a former uranium mine at pilot scale

Gerber, U.; Schäfer, S.; Paul, M.; Krawczyk-Bärsch, E.

Environmental pollution by metals and radionuclides is one of the biggest challenges which have to be solved globally. In the uranium mine of the Wismut GmbH near Königstein (Germany) uranium production was achieved by leaching the sandstone with sulfuric acid. As a consequence the geochemical nature of the mine water has been substantially changed leading to an increase in sulfate, metals and uranium concentrations. For remediation purposes the mine is currently in the process of being flooded. Mine water is pumped to the surface, where it is treated by a conventional water treatment plant which is cost-intensive and long-lasting. For that reason, biological concepts for remediation could be appropriate alternatives.
In our studies, we designed a pilot plant for a bioremediation approach using the mine water with the naturally occurring microorganisms. We added 10 mM glycerol to 100 L of the mine water and incubated the solution over six weeks at ambient temperature. During this time, we performed online-measurements of pH, redox potential (Eh) and temperature. The uranium concentration as well as the iron(II) and sulfate concentrations were measured periodically. Within the six weeks of incubation, we monitored a drastic decrease of Eh, from 650 mV to 80 mV. Theoretical predictions showed that this decrease could be associated with a uranium(VI) reduction. Thus, the prediction was confirmed using UV-vis and EXAFS/ XANES measurements. After 17 days of incubation uranium(IV) was detectable. In addition to the uranium(VI) reduction, we detected an iron(III) to iron(II) reduction during the first three weeks as well as a slight sulfate reduction after 30 days of incubation.
In summary, our results demonstrate a biological influence within the mine water of the former uranium mine only by adding 10 mM glycerol. As a result, uranium(VI) is reduced to uranium(IV). The investigation in pilot-plant scale confirmed our previous lab scale experiments. We were able to prove the microbial induced reduction of uranium(VI) which could by a possible bioremediation approach in combination with or instead of conventional water treatment.

Keywords: uranium; reduction; mine water; microorganisms

  • Poster
    WISSYM 2019 International Mining Symposium, 09.-11.10.2019, Chemnitz, Germany

Publ.-Id: 29694

Biofilms as a sink for radionuclides in future granitic nuclear waste repositories

Krawczyk-Bärsch, E.; Lehtinen, A.; Pedersen, K.

Usually, bacteria do not occur as individual cells in nature but as multicellular communities called biofilms. Biofilms are characterized by building up their own microenvironment, which can differ significantly from that of the bulk solution. They are known to provide a sink for dissolved heavy metals and actinides since EPS, cell walls, cell membranes, and cell cytoplasm can serve as sorption sites. In safety assessment studies for future nuclear waste repositories research on biofilms are becoming more important due to the potential retention for actinides in these microbial communities. For example, in the future underground rock characterization facility tunnel for high-level radioactive waste ONKALO in Finland, massive biofilms are growing next to fracture zones in a granitic rock environment, where groundwater is seeping from bedrock fractures. The biofilms are described as a pink and solid slime, consisting of Pseudomonas anguilliseptica, Arthrobacter bergeri, Hydrogenophaga sp., Methylobacter tundripaludum, Rhodoferrax ferrireducens, and Haliscomenobacter hydrossis. In laboratory experiments uranium was added to the circulating groundwater obtained from the fracture. EF-TEM investigations indicated that uranium in the biofilm was immobilized intracellularly in cells by the formation of metabolically mediated calcium uranyl phosphate, similar to needle-shaped autunite (Ca[UO2]2[PO4]2 ● 2–6H2O) or meta-autunite (Ca[UO2]2[PO4]2 .● 10–12H2O) [1].
Biofilms are also present in open fracture zones and on granitic tunnel walls at the Äspö Hard Rock Laboratory (HRL) in Sweden. The biofilms are predominantly formed by the indigenous iron-oxidizing bacterium Gallionella ferruginea with up to 90 wt% precipitated ferric oxyhydroxide. The combination of the biological material and iron oxides resulted in a large reactive surface area leading to a remarkably high bioaccumulation and adsorption of radionuclides.

Keywords: uranium; nuclear waste repository; biofilms; gallionella ferruginea

  • Invited lecture (Conferences)
    18. Sanierungskolloquium, Jena, 01.-02.10.2019, Jena, Germany

Publ.-Id: 29693

Conventional CARs versus modular CARs

Feldmann, A.; Arndt, C.; Koristka, S.; Berndt, N.; Bergmann, R.; Bachmann, M.

The clinical application of immune effector cells genetically modified to express chimeric antigen receptors (CARs) has shown impressive results including complete remissions of certain malignant hematological diseases. However, their application can also cause severe side effects such as cytokine release syndrome (CRS) or tumor lysis syndrome (TLS). One limitation of currently applied CAR T cells is their lack of regulation. Especially, an emergency shutdown of CAR T cells in case of life-threatening side effects is missing. Moreover, targeting of tumor-associated antigens (TAAs) that are not only expressed on tumor cells but also on vital tissues requires the possibility of a switch allowing to repeatedly turn the activity of CAR T cells on and off. Here we summarize the development of a modular CAR variant termed universal CAR (UniCAR) system that promises to overcome these limitations of conventional CARs.

Keywords: Immunotherapy; Chimeric antigen receptor; T cells; UniCAR; BiTE; TIMO XIV

Publ.-Id: 29692

Nanoscale Ferromagnetism in Alloy Thin Film via Lattice Disordering

Bali, R.; Schmeink, A. H.; Eggert, B.; Ehrler, J.; Liersch, V.; Semisalova, A.; Hlawacek, G.; Potzger, K.; Faßbender, J.; Thomson, T.; Wende, H.; Lindner, J.

Structural disorder in certain alloys leads to the onset of strong ferromagnetism. Disorder can be induced in desired locations, at the nanoscale, making such materials useful for magnetic nano-patterning. Examples of these alloys include Fe60Al40,[1] Fe50Rh50,[2] and Fe60V40. Disorder can be generated locally using focussed ion- as well as laser- beams,[1 - 3] inducing nanoscale ferromagnetism. Furthermore, the effect can be reversed via thermal re-ordering of the alloy, achieving re-writeable magnetic structures.
Insights into the mechanisms of the ferromagnetic onset in prototype systems, helps achieve a broader understanding of magneto-structural correlations in general. For instance, in paramagnetic B2-ordered Fe60Al40 as well as D8b-type Fe60V40, the ferromagnetic onset is caused by antisite defects i.e. site swapping of the Fe and Al (V) atoms, resulting in a transition to the bcc (A2) structure. An increase of antisite defects can cause the Ms of Fe60Al40 as well as Fe60V40 to increase from nearly-zero in the ordered structures to 780 and 660 kAm-1, in their respective disordered structures. In contrast, in B2 Fe50Rh50 the well-ordered film is antiferromagnetic, and static disordering may be sufficient to fully transform the alloy to the ferromagnetic phase, possessing an Ms of ~ 1250 kAm-1 at 300 K. Thus, whereas the Ms in the above alloys increases drastically with lattice disorder, the microscopic nature of the disordering varies.
Here we deploy ion-irradiation to sensitively induce lattice disorder in the above binary alloy systems, while tracing the manifested ferromagnetic onsets, thereby obtaining insights into the correlation between magnetic behaviour and the structure. Properties of magnetic arrays and magneto-transport devices produced using lattice disorder will be discussed.
[1] “Printing Nearly-Discrete Magnetic Patterns Using Chemical Disorder Induced Ferromagnetism”, R. Bali et al., Nano Letters 14, 435 (2014).
[2] “Tuning the antiferromagnetic to ferromagnetic phase transition in FeRh thin films by means of low-energy/low fluence ion irradiation”, A. Heidarian et al., Nucl. Instrum. Methods Phys. Res. B 358, 251 (2015).
[3] “Laser-Rewriteable Ferromagnetism at Thin-Film Surfaces”, J. Ehrler et al., ACS Appl. Mater. Interfaces 10, 15232 (2018).

Related publications

  • Invited lecture (Conferences)
    6th International Conference from Nanoparticles and Nanomaterials to Nanodevices and Nanosystems (6th IC4N), 30.06.-03.07.2019, Corfu, Greece
  • Invited lecture (Conferences)
    Symposium „Spins, Waves and Interactions“, 03.-05.09.2019, Greifswald, Deutschland

Publ.-Id: 29691

Strain Anisotropy and Magnetic Domains in Embedded Nanomagnets

Nord, M.; Semisalova, A.; Kákay, A.; Hlawacek, G.; Maclaren, I.; Liersch, V.; Volkov, O.; Makarov, D.; Paterson, G. W.; Potzger, K.; Lindner, J.; Faßbender, J.; Mcgrouther, D.; Bali, R.

Nanoscale modifications of strain and magnetic anisotropy can open pathways to engineering magnetic domains for device applications. A periodic magnetic domain structure can be stabilized in sub-200 nm wide linear as well as curved magnets, embedded within a flat non-ferromagnetic thin film. The nanomagnets are produced within a non-ferromagnetic B2-ordered Fe60Al40 thin film, where local irradiation by a focused ion beam causes the formation of disordered and strongly ferromagnetic regions of A2 Fe60Al40. An anisotropic lattice relaxation is observed, such that the in-plane lattice parameter is larger when measured parallel to the magnet short-axis as compared to its length. This in-plane structural anisotropy manifests a magnetic anisotropy contribution, generating an easy-axis parallel to the short axis. The competing effect of the strain and shape anisotropies stabilizes a periodic domain pattern, in linear as well as spiral nanomagnets, providing a versatile and geometrically controllable path to engineering the strain and thereby the magnetic anisotropy at the nanoscale.

Keywords: embedded nanomagnets; curved magnets; strain anisotropy; ion-induced patterning; magnetic domains

Related publications

Publ.-Id: 29690

Multi-analytical characterization of slags to determine the chromium concentration for a possible re-extraction

Horckmans, L.; Möckel, R.; Nielsen, P.; Kukurugya, F.; Vanhoof, C.; Morillon, A.; Algermissen, D.

The CHROMIC project aims to recover chromium from steelmaking and ferrochrome slags to regain valuable resources and simultaneously reduce potential environmental impacts. To develop the recovery flowsheets, and reliably calculate metal recovery, an accurate assessment of chromium concentration and distribution is essential. Therefore, model streams were thoroughly characterized using a combination of analytical techniques . In all materials, chromium is present in distinct but often small spinel phases, intertwined with other minerals and showing a considerable zonation in Cr-content with higher amounts in the cores. The small size of the Cr-rich particles makes recovery by mineral processing challenging. Measured chromium content was found to differ largely based on the chemical dissolution method applied. Analysis of insoluble residues and comparison with a standard reference material evidenced that standard acid dissolution procedures based on HCl/HNO₃/HBF₄ and HNO₃/HF/H₂O₂ are insufficient to fully dissolve spinel structures, leading to severe underestimations of chromium content. A sodium peroxide treatment is required for a full dissolution of spinel. This is noteworthy since most legislation for reuse of slags are currently based on acid dissolution methods.

Keywords: steel slag; ferrochromium slag; chromium extraction; multi-analytical characterization; method comparison

Publ.-Id: 29689

Filling the 5-10 THz gap using Ge-based photoconductive emitter

Singh, A.; Pashkin, O.; 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

Related publications

  • 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

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

Related publications

  • Lecture (Conference)
    The 44th International Conference on Infrared, Millimeter and Terahertz Waves (IRMMW-THz'2019), 01.-06.09.2019, Paris, France
  • Contribution to proceedings
    44th International Conference on Infrared, Millimeter and Terahertz Waves (IRMMW-THz'2019), 01.-06.09.2019, Paris, France
    44th International Conference on Infrared, Millimeter and Terahertz Waves (IRMMW-THz'2019)
    DOI: 10.1109/IRMMW-THz.2019.8874010

Publ.-Id: 29687

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

Related publications

  • Lecture (others)
    Seminarvortrag, Harbin Institute of Technology, 22.07.2019, Harbin, China

Publ.-Id: 29686

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

Related publications

  • Lecture (Conference)
    VII International Conference “Frontiers of Nonlinear Physics”, 28.06.-04.07.2019, Nizhny Novgorod, Russian Federation

Publ.-Id: 29685

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

Related publications

  • Invited lecture (Conferences)
    Light Conference 2019, 16.-18.07.2019, Changchun, China

Publ.-Id: 29684

Gamma, neutron and muon background in the new Felsenkeller underground accelerator laboratory

Szücs, T.; Bemmerer, D.; Grieger, M.; Hensel, T.; Ludwig, F.; Zuber, K.

Astrophysically relevant nuclear reactions between charged particles usually occurring in stars at deep sub-Coulomb energies. A direct experimental study of such reactions in the laboratory requires high luminosity coupled with low background in the detectors to compensate for the tiny reaction yield to be measured. The new Felsenkeller underground accelerator laboratory is equipped with a high current particle accelerator and has very low background.
This contribution will report about the experimental study of the muon flux and angular distribution of the muons in the new laboratory, which is required to optimize the veto detector arrangements. In addition, the measured neutron flux and energy spectrum at Felsenkeller will be reported. Finally, the actual γ background in muon vetoed HPGe detectors will be presented. The measured background and known ion beam current will allow the study many astrophysically relevant reactions direct in their stellar energy range.

Keywords: Nuclear astrophysiscs; Underground; Felsenkeller; Laboratory background

  • Poster
    Nuclear Physics in Astrophysics IX, 15.-20.09.2019, Castle Waldthausen; Frankfurt, Germany

Publ.-Id: 29683

Background studies with actively vetoed germanium gamma-ray detector in Felsenkeller tunnels VIII and IX

Szücs, T.; Bemmerer, D.; Zuber, K.

A new underground accelerator facility is being built in tunnels VIII and IX of the Dresden Felsenkeller. Previous gamma-ray background measurements in another part of the tunnelsystem showed suitable conditions for in-beam nuclear astrophysics experiments [1, 2] using germanium detectors with active veto against the cosmic-ray muons. These stableion beam experiments are of high importance to understand the reactions of the stellar burning phases, and in particular the solar fusion reactions.
The new laboratory is now ready to host measurements mapping the background conditions. This work reports on the measured background in actively vetoed gamma-ray detectorat the place of the target station in the laboratory used for the upcoming experiments.
[1] T.Szücs et al., Eur. Phys. Jour. A 48 (2012) 8. [2] T.Szücs et al., Eur. Phys. Jour. A 51 (2015) 33.

Keywords: Nuclear astrophysics; underground; Felsenkeller; Gamma-background

  • Poster
    XV International Symposium on Nuclei in the Cosmos (NIC XV), 24.-29.06.2018, Assergi, Italy
  • Poster
    5th International Solar Neutrino Conference, 11.-14.06.2018, TU Dresden, Germany

Publ.-Id: 29682

Resonance strengths in the 14N(p,γ)15O astrophysical key reaction measured with activation

Gyürky, G.; Halász, Z.; Kiss, G. G.; Szücs, T.; Csík, A.; Török, Z.; Huszánk, R.; Kohan, M. G.; Wagner, L.; Fülöp, Z.

Background: The 14N(p ,γ )15O reaction plays a vital role in various astrophysical scenarios. Its reaction rate must be accurately known in the present era of high precision astrophysics. The cross section of the reaction is often measured relative to a low energy resonance, the strength of which must therefore be determined precisely. Purpose: The activation method, based on the measurement of 15O decay, has not been used in modern measurements of the 14N(p ,γ )15O reaction. The aim of the present work is to provide strength data for two resonances in the 14N(p ,γ )15O reaction using the activation method. The obtained values are largely independent from previous data measured by in-beam γ spectroscopy and are free from some of their systematic uncertainties. Method: Solid state TiN targets were irradiated with a proton beam provided by the Tandetron accelerator of Atomki using a cyclic activation. The decay of the produced 15O isotopes was measured by detecting the 511 keV positron annihilation γ rays. Results: The strength of the Ep=278 keV resonance was measured to be ω γ278=(13.4 ±0.8 ) meV while for the Ep=1058 keV resonance ω γ1058=(442 ±27 ) meV . Conclusions: The obtained Ep=278 keV resonance strength is in fair agreement with the values recommended by two recent works. However, the Ep=1058 keV resonance strength is about 20% higher than the previous value. The discrepancy may be caused in part by a previously neglected finite target thickness correction. As only the low energy resonance is used as a normalization point for cross section measurements, the calculated astrophysical reaction rate of the 14N(p ,γ )15O reaction and therefore the astrophysical consequences are not changed by the present results.

Keywords: Nuclear Astrophysics


Publ.-Id: 29681

Magnetic Nanoparticle Chains in Gelatin Ferrogels: Bioinspiration from Magnetotactic Bacteria

Sturm, S.; Siglreitmeier, M.; Wolf, D.; Vogel, K.; Gratz, M.; Faivre, D.; Lubk, A.; Büchner, B.; Sturm, E.; Cölfen, H.

Inspired by chains of ferrimagnetic nanocrystals (NCs) in magnetotactic bacteria (MTB), the synthesis and detailed characterization of ferrimagnetic magnetite NC chain-like assemblies is reported. An easy green synthesis route in a thermoreversible gelatin hydrogel matrix is used. The structure of these magnetite chains prepared with and without gelatin is characterized by means of transmission electron microscopy, including electron tomography (ET). These structures indeed bear resemblance to the magnetite assemblies found in MTB, known for their mechanical flexibility and outstanding magnetic properties and known to crystallographically align their magnetite NCs along the strongest <111> magnetization easy axis. Using electron holography (EH) and angular dependent magnetic measurements, the magnetic interaction between the NCs and the generation of a magnetically anisotropic material can be shown. The electro- and magnetostatic modeling demonstrates that in order to precisely determine the magnetization (by means of EH) inside chain-like NCs assemblies, their exact shape, arrangement and stray-fields have to be considered (ideally obtained using ET).

Keywords: bioinspiration; electron holography; electron tomography; gelatin; magnetite

Publ.-Id: 29680

Nanoscale Structure and Compositional Analysis of Surface Oxides on Hot–Dip Galvanized Press–Hardened Steel

Gaderbauer, W.; Arndt, M.; Steck, T.; Truglas, T.; Klingner, N.; Faderl, J.; Groiss, H.

Insights into the structure of surface oxides on Zn–coated press–hardened steel (PHS) are indispensable for further processing like welding or adhesive bonding. The main oxide on top of galvanized steel is Al2O3 from the primary galvanizing process. This oxide is strongly altered during final austenitization annealing before hot–forming resp. press–hardening, depending on the annealing time. Four different steel grades are investigated, whereupon two are standard galvanized and the other two are galvannealed. For both coatings, we can show that the main oxides after austenitization heat treatment are native ZnO and the initial Al2O3. Our results indicate that the main alloying component Mn forms (Mn,Zn)Mn2O4 spinel, which also contains traces of Fe and is embedded in the upper ZnO layer. Also noticeable was a varying, nanometer thick Cr enrichment at the initial Al2O3 layer depending on the availability of Cr in the steel alloy. Small precipitates of further alloy elements can be found at this (Cr,Al)2O3 layer. Further experiments with time–of–flight secondary ion mass spectrometry attached to a helium ion microscope allowed to reliably distinguish between ZnO and Zn(OH)2, which are both present in the oxide layers. All specimen show high local differences related to skin–passing prior to final heat treatment. This is especially the case for shorter annealed specimen, where thermodynamic equilibrium is not yet reached.

Keywords: ZnFe coating; PHS; SEM; HIM; TEM; AES; EBSD; EDX; SIMS; TOF

Related publications

  • Lecture (Conference)
    International Conference on Zinc and Zinc Alloy Coated Steel Sheet (Galvatech) 2020, 20.-24.06.2021, Wien, Österreich

Publ.-Id: 29679

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.; 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

Related publications


Publ.-Id: 29678

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

Related publications


Publ.-Id: 29677

Fluctuation electron microscopy on silicon amorphized at varying self ion-implantation conditions

Radic, D.; Hilke, S.; Peterlechner, M.; Posselt, M.; 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

Related publications

Publ.-Id: 29676

Spatial Coefficient of Variation of Arterial Spin Labeling MRI as a Cerebrovascular Correlate of Carotid Occlusive Disease

Mutsaerts, H. J. M. M.; Petr, J.; Bokkers, R. P. H.; Lazar, R. M.; Marshall, R. S.; Asllani, I.

Clinical interpretation of arterial spin labeling (ASL) perfusion MRI in cerebrovascular disease remains challenging mainly because of the method’s sensitivity to concomitant contributions from both intravascular and tissue compartments. While acquisition of multi-delay ASL images can differentiate between the two contributions, the prolonged acquisition is prone to artifacts and not practical for clinical research. Here, we evaluated the utility of the spatial coefficient of variation (sCoV) of a single-delay ASL image as a marker of the intravascular contribution. We tested the hypothesis that sCoV is more sensitive than CBF to the intravascular signal, and therefore will be a better predictor of the side of occlusion. To this end, we compared the hemispheric lateralization of sCoV and CBF ASL images obtained from 28 patients (age 73.9 ± 10.2 years, 8 women) with asymptomatic unilateral carotid occlusion. The results showed that sCoV lateralization predicted the occluded side with 96.4% sensitivity, missing only 1 patient out of the 28. In contrast, the sensitivity of the CBF lateralization was 71.4% with 8 patients showing no difference in CBF between the ipsi- and contra-lateral hemispheres. The findings demonstrate the potential clinical utility of sCoV as a cerebrovascular correlate of large vessel disease. Using sCoV in tandem with CBF, vascular information can be obtained in image processing without the need for additional scanning time.

Publ.-Id: 29675

Ultrafast metallization in NbO2 studied by pump-probe THz spectroscopy

Rana, R.; Klopf, J. M.; Grenzer, J.; Schneider, H.; Helm, M.; Pashkin, A.

Niobium dioxide (NbO2) is an isovalent counterpart of VO2 with considerably higher transition temperature (Tc = 1080 K). We have performed time-resolved optical pump – THz probe measurements on NbO2 epitaxial thin film at room temperature. Notably, the pump energy required for the switching into a metastable metallic state is smaller than the energy necessary for heating NbO2 up to TC providing strong evidence for the non-thermal character of the photoinduced insulator-to-metal transition.

  • Lecture (Conference)
    44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz 2019), 02.-06.09.2019, Paris, France
  • Contribution to proceedings
    44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz 2019), 01.-06.09.2019, Parin, France
    44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz 2019), 8873838
    DOI: 10.1109/IRMMW-THz.2019.8873838

Publ.-Id: 29674

Ultrafast neutralization dynamics of highly charged ions upon impact on 2D materials

Wilhelm, R. A.

Heavy ions in high charge states carry a large amount of potential energy in addition to their kinetic energy. The potential energy can amount to several 10keV and is released upon neutralization [1]. We recently showed that neu- tralization of slow highly charged Ar and Xe ions proceeds on a sub-10fs time scale, i.e. during transmission through the very first monolayers of a solid [2]. This feat makes highly charged ions an intriguing tool for efficient modification of 2D materials preventing significant damage to a substrate at the same time. Here we present data on the neutralization dynamics of slow highly charged ions in freestanding single layer graphene and freestanding single layer MoS2. Special emphasise is put on charge exchange of the ions, their kinetic energy loss, and the emission of secondary electrons/photons from the interaction pro- cess.

Related publications

  • Invited lecture (Conferences)
    Towards Reality in Nanoscale Materials X, 12.-14.02.2019, Levi, Finnland

Publ.-Id: 29672

Interaction of highly charged ions with 2D materials

Wilhelm, R. A.

Slow highly charged ions (HCI) provide an efficient toolkit for surface modifications at the nanoscale [1]. Due to the potential energy of HCIs, nanoscale surface melting or atom sputtering can be ob- served in susceptible materials with an efficiency of about 100% (one surface feature per ion). The neutralization of the HCIs driving the potential energy deposition is typically considered to be finished in ’a shallow region’ in the surface, i.e. ’on the first nanometers’. To further quantify the HCI neutral- ization dynamics we recently took a new approach and used freestanding 2D materials as the target. Due to the atomic thickness of the materials, ions are not stopped in the materials and are available for spectroscopic analysis. At the same time the 2D materials are available for post-irradiation microscopic analysis, which finally al- lows us to determine (1) the kinetic and potential energy lost by the ion, (2) the energy dissipated by emission of secondary particles (electrons and photons), and (3) the en- ergy spend in the nanostructure formation process.
By applying our ion beam spectroscopy, we performed charge state and kinetic energy analysis of ions transmit- ted through freestanding single layer graphene (SLG) [2], amorphous 1nm thick Carbon Nanomembranes (CNM) [3], freestanding single layer MoS2, SLG/MoS2 het- erostructures and others. As a first result we found an ultrafast (sub-10 fs ∼ 1 monolayer) neutralization taking place, much faster than established models would have an- ticipated [4]. Furthermore, kinetic energy loss is signifi- cantly enhanced compared to the value of singly charged ions under the same conditions.
To facilitate a comprehensive understanding of the plethora of observed phenomena and their interplay, we use an en- ergy, angle, and charge state resolved spectroscopy in co- incidence with yield and energy resolved measurement of emitted secondary particles [5]. We further developed an exchange and electronic decay taking the time-dependent atomistic model for ion stopping, charge ion charge state explicitly into account [6].
In this contribution I will give an overview about our recent progress in the field of ion scattering from 2D materials and put the results in perspective to nanostructure formation.

Related publications

  • Invited lecture (Conferences)
    Nanopatterning Workshop, 07.-10.07.2019, Guildford, United Kingdom

Publ.-Id: 29671

Ion Beam Spectroscopy with 2D Materials

Wilhelm, R. A.

The spectroscopic analysis of ions transmitted or backscat- tered through/from a solid is a standard procedure in ion beam analysis and reveals material composition, crystallog- raphy, surface roughness and other properties. The infor- mation on material properties is typically gained through the determination of the ion energy (or energy of emitted secondary particles) and thus from the ion stopping. Addi- tionally, the ion charge state may change upon interaction with the solid material, which is typically considered as a ’complication’ in experiment, e.g. in the context of charge fractionization when using charge state selective detectors (magnetic spectrometers or electrostatic analyzers). How- ever, charge exchange is also determined by material prop- erties and can yield additional information in conjunction with kinetic energy loss analysis. In this contribution I will show that charge exchange and stopping of highly charged ions (and ions in general) are closely coupled, which implies that nuclear and electronic energy loss are coupled as well. Our results in combina- tion with a quantitative model for impact parameter depen- dent charge exchange and stopping can serve as an addi- tional tool for material structure determination on the sub- nm scale for 2D materials, especially in cases where elec- tron microscopy may not yield atomically resolved data. In our experiments we use slow (v < v0) highly charged Ar and Xe ions with charge states of 1 − 18 and 1 − 40, respec- tively. We transmit the ions through freestanding layers of 2D materials, i.e. single-, bi-, and tri-layer graphene, single- layer hBN, carbon nanomembranes, single-layer MoS2, and other transition metal dichalcogenides [1]. Secondary elec- trons emitted from the interaction process are recorded in a high voltage biased surface barrier detector serving as a start signal for time-of-flight measurements and also allow- ing us to determine the absolute amount of emitted elec- trons. Ions are detected by a position sensitive MCP detec- tor using a delay line anode. Utilizing a set of slits and parallel deflection plates we relate the impact position at the MCP to the scattering angle and charge state of the ions. The timing signal from the impact serves as the stop trigger for the ion’s time-of-flight. Thus, we obtain angle- resolved, energy-resolved charge exchange spectra in coin- cidence with the number of emitted electrons for each individual ion.
Comparing our highly differential data with an atomistic model for time-dependent charge redistribution between the ion and the target atoms allows us to link structural proper- ties and defects to the observed charge state pattern. Our model is based on the statistical description of atoms and an interatomic distance dependent ion de-excitation rate adapted from the Interatomic Coulombic Decay process [2, 3].
Fig. 1 shows a sketch of the ion transmission process in- volving the emission of secondary particles on the time scale of only femtoseconds. Thus, ion transmission studies with atomically thin materials not only are useful for materials science, but also to study inelastic ion-surface interaction on the femtosecond time scale simply by varying the ion velocity or tilting the sample.

Related publications

  • Invited lecture (Conferences)
    International Workshop on Inelastic Ion Surface Collisions, 17.-22.11.2019, Matsue, Japan

Publ.-Id: 29670

Collisions of highly charged ions with 2D materials
- What we learn from ion transmission spectroscopy -

Wilhelm, R. A.

Slow ions in high charge states impacting a solid surface represent a far-from-equilibrium system. Upon impact, the ions capture dozens of electrons and these electrons decay into the atomic ground state already during the collision driven by non-radiative de-excitation processes such as Interatomic Coulombic Decay [1]. The neutralization and electronic decay of the ion leads to the release of its potential energy, which amounts up to several 10 keV facilitating nanostructure formation in suscep- tible materials (mainly insulators with strong electron-phonon coupling).
When a freestanding 2D material is used as a solid target, the ions are still available for spectroscopic measurements after the ion-surface interaction. We performed charge state and kinetic energy analy- sis of ions transmitted through freestanding single layer graphene (SLG) [2], amorphous 1 nm thick Carbon Nanomembranes (CNM) [3], freestanding single layer MoS2, SLG/MoS2 heterostructures and others. As a first result we found an ultrafast (sub-10 fs) neutralization taking place, much faster than established models would have anticipated. Further, kinetic energy loss is significantly en- hanced over the expected value from singly charged ions under the same conditions. We are able to find charge exchange patterns, utilizing angle-resolved charge exchange spectroscopy [4]. To facilitate a comprehensive understanding of the plethora of observed phenomena and their interplay, we developed an atomistic model for ion stopping, charge exchange and electronic decay taking the time-dependent ion charge state explicitly into account [5].
In this contribution I will show that charge exchange pattern together with an atomistic and local model for charge exchange can be used to determine the structure of 2D materials on a sub-nm level, especially important for amorphous materials where atomically-resolved microscopy is hard to perform.

Related publications

  • Invited lecture (Conferences)
    XXXI International Conference on Photonic, Electronic and Atomic Collisions (ICPEAC), 23.-30.07.2019, Deauville, Frankreich

Publ.-Id: 29669

Development of a framework for generalized modelling of multiphase flow in OpenFOAM

Liao, Y.; Hänsch, S.; Meller, R.; Lehnigk, R.; Schlegel, F.; Lucas, D.

The multi-fluid CFD methodology is widely used in the simulation of multiphase flows. The numerical results are able to provide insight and knowledge on local phenomena, and frequently used to assist the design, optimization and safety analysis of industrial processes. However, current multi-fluid CFD simulations often suffer from two limitations. One is that the predictability for multiphase systems is not fully guaranteed. The transferability of a setup from its calibration case to other cases, where experimental data are not available, is not always reliable, and result-oriented tuning is often necessary. The deficiency is believed to be caused majorly by the imperfectness in the closure models that are required to reconstruct the processes occuring at the interface between phases. The other is that the state of the art multi-fluid model is usually limited to certain flow regimes. It fails to capture the transition between different flow regimes, e.g. bubbly flow to churn-turbulent flow, which are frequently encountered in the practice. This work aims to present a framework for generalized modelling of multiphase flow and the efforts made in the CFD department at HZDR towards closure model development. A new solver for the realization and validation of the framework is developed on the basis of the open source CFD code OpenFOAM. It is capable of capturing both dispersed and resolved gaseous structures in the liquid as well as the transfer between them.

Keywords: Multi-fluid model; baseline closure strategy; GENTOP model; OpenFOAM

  • Invited lecture (Conferences)
    SG-FANS-3 Workshop, 25.-27.09.2019, Xi'an, China

Publ.-Id: 29668

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.; 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

Related publications

Publ.-Id: 29667

Charge-Exchange-Driven Low-Energy Electron Splash Induced by Heavy Ion Impact on Condensed Matter

Schwestka, J.; Niggas, A.; Creutzburg, S.; Kozubek, R.; Heller, R.; Schleberger, M.; Wilhelm, R. A.; 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.

Related publications

Publ.-Id: 29666

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

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.


Publ.-Id: 29664

Chemical Shift and Exchange Interaction Energy of the 1s States of Magnesium Donors in Silicon. The Possibility of Stimulated Emission

Shastin, V. N.; Zhukavin, R. K.; Kovalevsky, K. A.; Tsyplenkov, V. V.; Rumyantsev, V. V.; Shengurov, D. V.; Pavlov, S. G.; Shuman, V. B.; Portsel, L. M.; Lodygin, A. N.; Astrov, Y. A.; Abrosimov, N. V.; Klopf, J. M.; Hübers, H.-W.

The results of experiments aimed at the observation of split 1s states in Mg-doped Si are reported. From the results, it is possible to determine the chemical shift and exchange interaction energy of a neutral Mg donor in Si. The position of the 1s(E), 1s(T2), and 2s(A1) parastates determines the possibility for attaining population inversion and the specific mechanism of stimulated Raman scattering. The energy of the 1s(T2) parastate is determined from the position of the Fano resonances in the photoconductivity spectrum of Si:Mg at T = 4 K, and the energies of the 1s(T2) and 1s(E) orthostates from the transmittance spectra at elevated temperatures. On the basis of the experimental data, the relaxation rates are estimated, and the possible mechanisms of stimulated emission are analyzed.

Keywords: neutral double donor; magnesium; spectroscopy; Fano resonance; photoconductivity; population inversion; stimulated Raman scattering

Publ.-Id: 29662

Characterization of suprathermal electrons inside a laser accelerated plasma via highly-resolved K⍺-emission

Smid, M.; Renner, O.; Colaitis, A.; Tikhonchuk, V. T.; 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.


Publ.-Id: 29661

Development of a plasma Faraday rotation calculator for an XFEL pulse

Ordyna, P.

This thesis presents a computational tool for obtaining the Faraday rotation of an X-Ray pulse propagating through a plasma. The fields, needed for the calculation, can be obtained from either a three or a two-dimensional simulation. In the 2D case, a half turn rotational symmetry is assumed and a numerical implementation of the underlying Abel integral is implemented so the Faraday effect can be obtained from the radial distribution. A time-resolved calculation is introduced by integrating the effect over an X-ray pulse, with a specified temporal shape, and using multiple outputs from various iterations. The prototype is developed using Python/Cython and tested in a few simple, analytically solvable scenarios. The main motivation for this tool are planned experiments to study relativistic laser-matter-interactions with help of the ultra-bright XFEL pulses. Hence, examples of such interaction are simulated with the PIConGPU framework, and the developed prototype is used to examine the influence of Rayleigh-Taylor and Weibel-like instabilities on the Faraday rotation effect.

  • Bachelor thesis
    TU Dresden, 2019
    47 Seiten

Publ.-Id: 29660

Synthetic characterization of ultrashort electron bunches using transition radiation

Carstens, F.-O.

This work describes the in-situ CTR plugin for the particle-in-cell code PIConGPU.
The C++ -plugin calculates coherent transition radiation (CTR) from millions to billions of macro-particles in a PIConGPU plasma simulation. In order to avoid excessive disk output of many GB to TB of data, as well as and extensive post-processing runtimes on only few CPUs, the plugin was parallelized on GPUs and implemented in-situ as part of PIConGPU.
The physics of this plugins was successfully implemented, tested and verified to agree with an initial python implementation, which again was verified using analytical CTR theory, with an average error of less than 1%. Additionally the plugin was benchmarked, resulting in typical time to solutions for complete transition radiation spectra on the scale of several minutes.
The CTR plugin was then used in several Laser-wakefield accelerator (LWFA) simulations, with self-injected and down-ramp injected electrons respectively. Mimicking the hypothetical placement of successive transition radiaton foils along the LWFA interaction length, the CTR plugin was used multiple times for observing how the electron bunch evolution leads to the characteristic features of transition radiation spectra. This new tool is a synthetic diagnostic, which enables direct comparison of experimentally measured transition radiation data to simulations. In future experiments this can provide insight into LWFA longitudinal electron pulse profiles on the fs-scale, required for future compact LWFA-driven free-electron laser applications.

Keywords: Transition Radiation; Coherent Transition Radiation; PIConGPU; Synthetic Analysis; Ultrashort electron bunches; Laser plasma accelerators; Laser wakefield accelerators; CTR

  • Bachelor thesis
    TU Dresden, 2019
    Mentor: Prof. Dr. U. Schramm, Prof. Dr. T. Cowan
    47 Seiten
    DOI: 10.5281/zenodo.3469663

Publ.-Id: 29659

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

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.

Publ.-Id: 29657

Ion-irradiation induced hardening and defect evolution in CoCrFeMnNi

Heintze, C.; Eißmann, N.; Kieback, B.; Akhmadaliev, S.

The operating conditions of future nuclear reactors, both fission and fusion, still pose a number of materials challenges. In this context, the novel class of high-entropy alloys (HEA) attracts attention due to good mechanical properties and corrosion resistance as well as an - mostly hypothesized -improved irradiation resistance. In the present work the single-phase fcc HEA CoCrFeMnNi, produced by means of powder metallurgy, was ion-irradiated with Fe ions at RT, 300°C and 410°C up to 0.6 and 1 dpa, respectively, along with the austenitic stainless steel 316 serving as a benchmark. Transmission electron microscopy and nanoindentation were applied to study the irradiation-induced hardening and the evolution of the microstructure. While similar hardening is observed for the HEA compared to the benchmark material 316 at RT and 410°C, substantially higher hardening was observed at 300°C. The origin of the hardening will be discussed based on the microstructural evidence.

Keywords: High entropy alloys; Irradiation tolerance; TEM; Nanoindentation

Related publications

  • Poster
    EUROMAT 2019, 01.-05.09.2019, Stockholm, Schweden

Publ.-Id: 29656

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

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.; Bergner, F.

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.

Related publications


Publ.-Id: 29653

Binding, uptake and transport of radionuclides and their analogues by the fungus Schizophyllum commune under natural conditions

Wollenberg, A.; Hübner, R.; Günther, A.; Freitag, L.; Raff, J.; Stumpf, T.

Radionuclides occur naturally and can be released into nature through anthropogenic effects. Through leaching and migration, also the anthropogenically released radionuclides can enter the groundwater and endanger the environment, animals and humans. However, the microbial community living in the soil may influence the mobility and thus the migration behaviour of radionuclides.
Since the Chernobyl accident at the latest, it became clear that various fungi are able to accumulate considerable amounts of heavy metals and radionuclides in their fruiting bodies [1-3]. However, it has not yet been determined, which processes lead to this significant accumulation in the fungal fruiting body.
For this reason, the interaction of a model fungus, namely Schizophyllum commune, with various radionuclides was studied in detail in the steps of binding and uptake by the fungal cells and transport within the mycelium.
For the visualization of the radionuclide and heavy metal transport through the hyphae, TEM and STEM imaging in combination with Energy-dispersive X-ray spectroscopy analysis were used to locate accumulation sites within the cells and to identify the formed species. The first results with uranium show that it is accumulated in form of phosphate minerals mainly on the cell membrane. Furthermore, microcosm experiments were conducted in which the bidirectional growth of the fungus was exploited: parts of the mycelium were growing upwards, while the other parts were growing into the contaminated soil. In order to check the transport of soil contaminants through the hyphae, the part of the mycelium that has no direct contact with the soil was sampled and analysed by ICP-MS. First results show that uranium could be detected in the samples, suggesting transport through the hyphae.
In addition to the transport of uranium, the experiments also investigate the transport of europium as an analogue for trivalent actinides, as well as the transport of inactive caesium and strontium within the mycelium.

Keywords: Fungi; Uranium; Transport; Uptake

  • Poster
    17th International Conference on the Chemistry and Migration Behavior of Actinides and Fission Products in the Geosphere, 15.-20.09.2019, Kyoto, Japan

Publ.-Id: 29652

Investigation of the potential of fungi for precautionary radiation protection in soil

Wollenberg, A.; Freitag, L.; Hübner, R.; Günther, A.; Raff, J.; Stumpf, T.

Due to the multifaceted use of radionuclides in research, medicine and industry, there is an increased risk of a release into the environment during the extraction and use of radioactive materials, but also during the storage of the resulting radioactive waste. If radionuclides are released into the soil, they can migrate through soil layers to the groundwater or can be absorbed by crops. In any case, it endangers the environment, animals and humans. For this reason, an effective precautionary radiation protection method must be found which can limit the mobility of possible released radionuclides in the environment.
Since the Chernobyl accident at the latest, it became clear, that fungi influence the migration behavior of radionuclides in the soil by accumulating them in large quantities. Due to other positive properties of fungi, such as the spread of one organism over several square kilometers and their high life expectancy, they provide a good basis for a bio-based precautionary radiation protection. Nevertheless, previous studies have also shown, that the effectiveness of radionuclide accumulation depends on the respective fungal strain [1-3].
For this reason, the molecular interactions of four different fungi with uranium were investigated and compared.
First TEM and STEM images of the fungus Schizophyllum commune, which is widely used as a model organism, show mineralization of uranium in form of needles at the cell membrane. Energy-dispersive X-ray spectroscopy analysis and time-resolved laser-induced fluorescence spectroscopy (TRLFS) have shown, that uranium is mineralized with phosphate. A second fungus, called Leucoagaricus naucinus, shows a different form of mineralization and localization of uranium in the cell. However, first TRLFS experiments suggest that it is a phosphate mineral as well. Together with two other fungi, Pleurotus ostreatus and Macrolepiota procera, a better understanding of the interactions of different fungi with radionuclides will be generated in order to evaluate the potential of fungi for the precautionary radiation protection of soils and to lay the basis for the development of a practicable process.

Keywords: Fungi; Radionuclide; TRLFS; precautionary radiation protection

  • Lecture (Conference)
    Jahrestagung der Fachgruppe Nuklearchemie 2019, 25.-27.09.2019, Dresden, Deutschland

Publ.-Id: 29651

Research and Implementation of Efficient Parallel Processing of Big Data at TELBE User Facility

Bawatna, M.; Green, B.; Kovalev, S.; Deinert, J.-C.; Knodel, O.; 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

Related publications

  • 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
    Cited 3 times in Scopus

Publ.-Id: 29650

Novel High Affinity Histone Deacetylase Inhibitors as Potential Radiotracers for PET

Clauß, O.; Schäker-Hübner, L.; Scheunemann, M.; Hansen, F. K.; Brust, P.

Epigenetics investigates heritable phenotype changes that do not involve alterations in the DNA sequence. The related phenomena play a key role in gene expression by enzyme-mediated post-translational modifications (PTMs) of proteins. One of the most relevant modifications is the process of deacetylation of the lysine side chains on histones, which are regulated by histone deacetylases (HDACs). The catalyzed deacetylation of lysine residues on histones modulates the chromatin and thus influences the gene expression and transcription. The class I histone deacetylases 1, 2 and 3 are overexpressed in several types of cancer, neurodegenerative diseases and inflammation. Inhibition of those zinc-dependent HDACs relaxes the chromatin structure and can result in transcriptional activation and anticancer effects, e.g. cell cycle arrest and induced differentiation. Consequently, radiolabeled HDAC inhibitors have emerged as a potential tool for the diagnostic imaging of tumors by positron emission tomography (PET). [1]
The aim of this work is the development of novel highly affine and selective fluorine-containing derivatives of a class I selective HDAC inhibitor to obtain the corresponding 18F-labeled PET radiotracers with an ortho-aminoanilide as zinc-binding motif for targeting class I HDACs in tumors. Recently, we discovered a new highly affine HDAC 1 ligand LSH-A30 with an IC50 for HDAC 1 inhibition of 4.4 ± 0.1 nM. In this connection, the structure of LSH-A30 serves as lead for the development of a series of fluorinated reference compounds, which are currently synthesized. The binding affinities and selectivities towards the class I HDAC isoforms will be determined. Our strategy is mainly focused on the medicinal chemistry of fluorine-containing derivatives, which are suitable for direct and indirect nucleophilic radiofluorination. For the most promising compounds, precursors for radiolabeling will be synthesized, the evaluation of physicochemical properties, e.g. stability and lipophilicity of the radiolabeled compounds will be assessed and further in vitro and in vivo investigations will be performed.

Keywords: HDAC inhibitors; PET tracer development; ortho-aminoanilides

  • Open Access Logo Poster
    GDCh Wissenschaftsforum Chemie 2019, 15.-18.09.2019, Aachen, Deutschland


Publ.-Id: 29649

Terahertz Nonlinear Optics of Graphene: From Saturable Absorption to High-Harmonics Generation

Hafez, H. A.; Kovalev, S.; Tielrooij, K.-J.; Bonn, M.; Gensch, M.; Turchinovich, D.

Graphene has long been predicted to show exceptional nonlinear optical properties, especially in the technologically important terahertz (THz) frequency range. Recent experiments demonstrated that this atomically-thin material indeed exhibits possibly the largest nonlinear coefficients of any material known to date. These findings in particular pave ways for practical graphene-based applications in ultrafast electronics and optoelectronics operating at THz rates. Here we report on the advances in the booming field of nonlinear THz optics of graphene, and describe the state-of-the-art understanding of the nature of the nonlinear interaction of electrons in graphene with intense THz fields based on the thermodynamic model of electron transport in graphene. We also provide a comparison between different mechanisms of nonlinear interaction of graphene with light fields in THz, infrared and visible frequency ranges.
We conclude the report with the perspectives for the expected technological applications of graphene based on its extraordinary THz nonlinear properties. This report covers the evolution of the field of THz nonlinear optics of graphene from the very pioneering to the state-of-the-art works. It also serves as a concise overview of the current understanding of THz nonlinear optics of graphene, and as a compact reference for researchers entering the field, as well as for the technology developers.

Keywords: Graphene; High Harmonics Generation; Terahertz; ultrafast

Related publications

Publ.-Id: 29648

Phase-resolved Higgs response in superconducting cuprates

Chu, H.; Kim, M.-J.; Katsumi, K.; Kovalev, S.; Dawson, R. D.; Schwarz, L.; Yoshikawa, N.; Kim, G.; Putzky, D.; Li, Z. Z.; Raffy, H.; Germanskiy, S.; Deinert, J.-C.; Awari, N.; Ilyakov, I.; Green, B. W.; Chen, M.; Bawatna, M.; Christiani, G.; Logvenov, G.; Gallais, Y.; Boris, A. V.; Keimer, B.; Schnyder, A.; Manske, D.; Gensch, M.; Wang, Z.; Shimano, R.; Kaiser, S.

In high energy physics, the Higgs field couples to gauge bosons and fermions and gives mass to their elementary excitations. Experimentally, such couplings can be verified from the decay product of the Higgs boson, the scalar (amplitude) excitation of the Higgs field. In superconductors, Cooper pairs bear a certain analogy to the Higgs field. Coulomb interactions between the Cooper pairs give mass to the electromagnetic field, which leads to the Meissner effect. Additional coupling with other types of interactions or collective modes is foreseeable, and even highly probable for high-Tc superconductors, where multiple degrees of freedom are intertwined4. The superconducting Higgs mode may reveal such couplings spectroscopically and uncover interactions directly relevant to Cooper pairing. To this end, we investigate the Higgs mode of several cuprate thin films using phase-resolved terahertz third harmonic generation (THG) to. In addition to the heavily damped Higgs mode itself, we observe a universal jump in the phase of the driven Higgs oscillation as well as a non-vanishing THG above Tc. These findings indicate coupling of the Higgs mode to other collective modes and a nonzero pairing amplitude above Tc. Our study demonstrates a new approach for investigating unconventional superconductivity. We foresee a fruitful future for phase-resolved spectroscopy in various superconducting systems.

Keywords: Superconductors; terahertz; Higgs; Nonlinear dynamics; ultrafast

Related publications

Publ.-Id: 29647

Non-perturbative high-harmonic generation in the three-dimensional Dirac semimetal Cd₃As₂

Kovalev, S.; Dantas, R. M. A.; Germanskiy, S.; Deinert, J.-C.; Green, B. W.; Ilyakov, I.; Awari, N.; Chen, M.; Bawatna, M.; Ling, J.; Xiu, F.; van Loosdrecht, P.; Surówka, P.; Oka, T.; Wang, Z.

Harmonic generation is a general characteristic of driven nonlinear systems, and serves as an efficient tool for investigating the fundamental principles that govern the ultrafast nonlinear dynamics. In atomic gases, high-harmonic radiation is produced via a three-step process of ionization, acceleration, and recollision by strong-field infrared laser. This mechanism has been intensively investigated in the extreme ultraviolet and soft X-ray regions, forming the basis of attosecond research, e.g. real-time observation of electron dynamics and sub-atomic tomography of molecular orbitals. In solid-state materials, which are characterized by crystalline symmetry and strong interactions, yielding of harmonics has just recently been reported. The observed high-harmonic generation was interpreted with fundamentally different mechanisms, such as interband tunneling combined with dynamical Bloch oscillations, intraband thermodynamics and nonlinear dynamics, and many-body electronic interactions. Here, in a distinctly different context of three-dimensional Dirac semimetal, we report on experimental observation of high-harmonic generation up to the seventh order driven by a strong-field terahertz pulse. The observed non-perturbative high-harmonic generation is interpreted as a generic feature of terahertz-field driven nonlinear intraband kinetics of Dirac fermions. We anticipate that our results will trigger great interest in detection, manipulation, and coherent control of the nonlinear response in the vast family of three-dimensional Dirac and Weyl materials.

Keywords: Dirac semimetals; High Harmonic Generation; Tehahertz; Nonlinear dynamics

Related publications

Publ.-Id: 29646

Pulse- and Field-resolved THz-diagnostics at 4th Generation Lightsources

Chen, M.; Deinert, J.-C.; Green, B. W.; Wang, Z.; Ilyakov, I.; Awari, N.; Bawatna, M.; Germanskiy, S.; de Oliveira, T.; Geloni, G.; Tanikawa, T.; Gensch, M.; Kovalev, S.

Multi-color pump-probe techniques utilizing modern accelerator-based 4th generation light sources such as X-ray free electron lasers or superradiant THz facilities have become important science drivers over the past 10 years. In this type of experiments the precise knowledge of the properties of the involved accelerator-based light pulses crucially determines the achievable sensitivity and temporal resolution. In this work we demonstrate and discuss the powerful role pulse- and field-resolved- detection of superradiant THz pulses can play for improving the precision of THz pump - femtosecond laser probe experiments at superradiant THz facilities in particular and at 4th generation light sources in general. The developed diagnostic scheme provides real-time information on the properties of individual pulses from multiple accelerator based THz sources and opens a robust way for sub femtosecond timing. Correlations between amplitude and phase of the pulses emitted from different superradiant THz sources furthermore provide insides into the properties of the driving electron bunches and is of general interest for the ultra-fast diagnostics at 4th generation light sources.

Keywords: Terahertz; Synchronization; ultrafast; diagnostics; accelerator

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Publ.-Id: 29645

Modelling heat and mass transport in Liquid Metal Batteries

Personnettaz, P.; Weber, N.; Weier, T.

Liquid metal batteries (LMBs) are a promising electrical energy storage (EES) technology. An LMB is an electrochemical cell made of three stably stratified liquid layers. Two liquid metal electrodes are separated by a molten salt electrolyte. The high operating temperatures limit experimental studies to few measurable quantities. Numerical studies based on continuum mechanics are required to understand the relevant physical mechanisms. Simultaneous charge, heat, mass and momentum transfer together with chemical and electrochemical reactions takes place in the bulk fluids and at the liquid interfaces. These processes affect the electrochemical behavior of LMBs and the cell efficiency. In the initial presentation we have presented the study of heat and mass transport in a three layer liquid metal battery developed with a segregated multi-region approach. In the final presentation we have presented the study of thermal convection in a three layer liquid metal battery developed with a coupled single-region approach.

Keywords: Liquid metal batteries; transport phenomena; mass trasnport; heat transfer; openFOAM

  • Lecture (Conference)
    NUMAP-FOAM Summer School 2019, 19.-30.08.2019, Zagreb, Hrvatska

Publ.-Id: 29644

Temperature‒dependent luminescence spectroscopic and mass spectrometric investigations of U(VI) complexation with aqueous silicates in the acidic pH‒range

Lösch, H.; Raiwa, M.; Jordan, N.; Steppert, M.; Steudtner, R.; Stumpf, T.; Huittinen, N. M.

In this study the complexation of U(VI) with orthosilicic acid (H4SiO4) between pH 3.5 and 5 with electrospray ionization mass spectrometry (ESI‒MS) and laser‒induced luminescence spectroscopy was comprehensively characterized. The ESI‒MS experiments performed at a total silicon concentration of 5∙10‒5 M (exceeding the solubility of amorphous silica at both pH‒values) revealed the formation of oligomeric sodium‒silicates in addition to the UO2OSi(OH)3+ species. For the luminescence spectroscopic experiments (25 °C), the U(VI) concentration was fixed at 5∙10‒6 M, the silicon concentration was varied between 1.3∙10‒4 ‒ 1.3∙10‒3 M (reducing the formation of silicon oligomers) and the ionic strength was kept constant at 0.2 M NaClO4. The results confirmed the formation of the aqueous UO2OSi(OH)3+ complex. The conditional complexation constant at 25 °C, log *β = ‒0.31± 0.24, was extrapolated to infinite dilution using the Davies equation, which led to log *β0 = ‒0.06 ± 0.24. Further experiments at different temperatures (1 – 25 °C) allowed the calculation of the molal enthalpy of reaction ΔrHm0 = 45.8 ± 22.5 kJ∙mol‒1 and molal entropy of reaction ΔrSm0 = 152.5 ± 78.8 J∙K‒1∙mol‒1 using the van’t Hoff equation, corroborating an endothermic and entropy driven complexation process.

Keywords: luminescence; silicates; Uranium(VI); complexation; thermodynamic constants; temperature dependent

Publ.-Id: 29643

Defect-Driven Magnetization Configuration of Isolated Linear Assemblies of Iron Oxide Nanoparticles

Rastei, M. V.; Pierron-Bohnes, V.; Toulemon, D.; Bouillet, C.; Kákay, A.; Hertel, R.; Tetsi, E.; Begin-Colin, S.; Pichon, B. P.

The magnetization state of 1D magnetic nanoparticle (NP) chains plays a key role in a wide range of applications ranging from diagnosis and therapy in medicine to actuators, sensors, and quantum recording media. The interplay between the exact particle orientation and the magnetic anisotropy is in turn crucial for controlling the overall magnetization state with high precision. Here, a 3D description of the magnetic structure of one-NP-wide chains is reported. Here, two complementary experimental techniques are combined, magnetic force microscopy (MFM) and electronic holography (EH) which are sensitive to out-of-plane and in-plane magnetization components, respectively. The approach to micromagnetic simulations is extended, which provides results in good agreement with MFM and EH. The findings are at variance with the known results on unidirectional NP assemblies, and show that magnetization is rarely strictly collinear to the chain axis. The magnetic structure of one-NP-wide chains can be interpreted as head-to-head magnetic domain structures with off-axis magnetization components, which is very sensitive to morphological defects in the chain structure such as minute size variation of NPs, tiny misalignment of NPs, and/or crystal orientation with respect to easy magnetization axis.

Keywords: AFM/MFM; e-holography; HR-TEM; magnetization states; micromagnetic simulations; one-NP-wide chains


Publ.-Id: 29642

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

Development of an in-situ cryo high resolution instrument for multimodal analysis in nano-toxicology

de Castro, O.; Lovric, J.; Barrahma, R.; Bouton, O.; Serralta, E.; Klingner, N.; Hlawacek, G.; Gnauck, P.; Duarte Pinto, S.; Lucas, F.; Wirtz, T.

Nowadays many consumer products contain nanoparticles in order for them to have certain desired properties. However, with the addition of nanoparticles these products can have potentially unknown health risks to humans, animal and plant species, and to the environment in general. The nanomaterial risk identification involves their physico-chemical characterization currently employing a variety of techniques and separate instruments. This makes the characterization an expensive and time-consuming process.
In the framework of the Horizon2020 project npSCOPE, we are developing a new integrated instrument for the characterization of nanoparticles. The aim is to improve the efficiency of the nanomaterial characterization workflow by integrating several techniques in one single instrument. The npSCOPE instrument is equipped with the ultra-high resolution Gas Field Ion Source (GFIS) technology [1] allowing the sample to be irradiated with very finely focused He+ and Ne+ ion beams at the nano-scale. Furthermore, the instrument incorporates detectors for secondary electron imaging, a secondary ion mass spectrometer (SIMS) for chemical analysis [2-4] and a detector allowing the detection of transmitted ions/atoms to obtain in-situ structural/3D visualisation data. The instrument will allow the characterization of nanoparticles in their native state as well as embedded in complex matrices (e.g. biological tissue, liquid, etc.). A further key feature of the instrument is cryo-capability, including a 5 axis cryo-stage, in order to perform analyses of biological samples in a frozen-hydrated state and thus avoid artefacts caused by classical sample preparation (e.g. chemical fixation) used for HV or UHV imaging of biological specimens at room temperature.
Here, we will present the instrument, report on the instrument’s performance and discuss the correlative microscopy capabilities. We will present first results obtained with the npSCOPE instrument on different kinds of nano-particle samples relevant in the field of nano-toxicology.
Beside analyses of nano-toxicological samples we are planning to use this instrument in different material science fields as well as other life science domains that require high resolution imaging in cryo-conditions (e.g. lipid research) [5].

Keywords: Helium Ion Microscopy; Scanning transmission helium ion microscopy; secondary ion mass spectrometry; cryo microscopy

Related publications

  • Lecture (Conference)
    MRS Fall Meeting 2019, 01.-06.12.2019, Boston, United States of America

Publ.-Id: 29640

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.

Publ.-Id: 29639

A comparative evaluation of calix[4]arene-1,3-crown-6 as a ligand for selected divalent cations of radiopharmaceutical interest

Bauer, D.; Blumberg, M.; Köckerling, M.; Mamat, C.

Radionuclides of divalent metals like lead-203, lead-212 and the radionuclides of alkaline earth metals barium-131 and strontium 89 are promising candidates for a radiopharmaceutical application. In addition, the heavy homologues radium-223 and radium-224 – with similar properties to barium - are suitable alpha-emitters for the targeted alpha-particle therapy. However, there is a lack of suitable chelation agents, especially for heavy group 2 metals. The macrocycle calix[4]arene-1,3-crown-6 seems to strongly interact with these metals. Therefore, this ligand and its coordination to the divalent cations of barium, strontium, and lead have been investigated. The complex formation was analyzed by NMR and UV/Vis titration experiments in acetonitrile, and stability constants were determine with both methods. It was found that the stability of these complexes increase in the order of strontium, barium, and lead. Additional to these investigations, X-ray crystallography, solvent-dependent 1H-NMR, and 207Pb NMR measurements were performed to deliver a deeper insight into the coordination chemistry of this ligand.

Keywords: Calix[4]arene; Radium; Barium; X-ray


Publ.-Id: 29638

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

Liquid flow visualization in packed-bed multiphase reactors: Wire-mesh sensor design and data analysis for rotating fixed beds

Timaeus, R.; Berger, R.; Schleicher, E.; Hampel, U.; Schubert, M.

Wire-mesh sensors are increasingly used for flow imaging in packed-beds. In this study, a capacitance wire-mesh sensor is applied to measure the cross-sectional liquid phase distribution in a rotating fixed bed reactor. The liquid filling level is derived as a crucial parameter defining the operational window of the reactor concept. Contrary to the standard sensor configuration, wireless data transfer and autonomous power supply is integrated. Furthermore, appropriate data processing is required to visualize the liquid flow of the three-phase system (nitrogen, cumene and γ-Al2O3 particles).

Keywords: Gas-liquid flow; Process intensification; Rotating fixed bed; Sensor design; Wire-mesh sensor

Publ.-Id: 29636

Droplet retention time and pressure drop in SiSiC open-cell foams used as droplet separation devices – A numerical approach

Hernandez, J. N. C.; Lecrivain, G.; Schubert, M.; Hampel, U.

Open-cell foams are a promising alternative for the separation of liquid droplets suspended in gas flows at comparably low pressure drop. The separation in such ceramic foams is investigated using the residence time distribution of droplets derived from pore-scale CFD-simulations. 20 and 45 pores per inch (ppi) silicon-infiltrated silicon carbide (SiSiC) open-cell foams samples are considered. The foam structure was reconstructed from micro-computed tomography (µCT) images. To track the droplets, a Lagrangian discrete-phase model was used. The effect of pore size and pore density on the droplet retention time was studied. The flow pressure drop showed a remarkable agreement with the in-house experimental measurements. The droplet separation efficiency within the foam structure was found to generally increase with the inlet gas velocity and the droplet inertia.

Keywords: Ceramic foams; liquid droplet entrainment; gas-droplet flow; resolved pore-scale CFD simulations; droplet residence time; droplet separator device


Publ.-Id: 29635

An expanding view on actinide oxide nanoparticles

Kvashnina, K.

Understanding the mechanisms of different chemical reactions with actinides at the atomic level is a key step towards safe disposal of nuclear wastes and towards the identification of physical-chemical processes of radionuclides in the environment. This contribution will provide an overview of the recently performed studies on Uranium, Thorium, Plutonium and Cerium oxide nanoparticles at the Rossendorf Beamline (ROBL) of the European Synchrotron in Grenoble (France). This innovative, recently upgraded, world-wide unique experimental station, funded and operated by HZDR in Dresden (Germany) was used to study actinide systems by by X-ray absorption spectroscopy in high energy resolution fluorescence detection (HERFD) mode and resonant inelastic X-ray scattering (RIXS) at the An/Ln L3 and An M4 edge. The experimental results have been analysed using a number of theoretical methods based on density functional theory and atomic multiplet theory. This research has received funding from European Research Council (ERC) under grant agreement 759696.

Related publications

  • Lecture (Conference)
    the 43d Symposium on Scientific Basis for Nuclear Waste Management, 21.-24.10.2019, Vienna, Austria

Publ.-Id: 29634

A Kinetic Study On Grinding And Flotation Of Untreated And Microwave-Treated Copper Sulfide Ore

Gholami, H.; Rezai, B.; Hassanzadeh, H.; Mehdilo, A.; Yarahmadi, M. R.; Rudolph, M.

The present work aims to study the impact of microwave irradiation on grinding and flotation kinetics of a porphyry copper ore. For this purpose, the kinetic trails were carried out on the samples (d80=1.5mm) pretreated in the absence and presence of microwave irradiation varying the exposure time from 15 to 150s. Semi-quantitative X-ray diffraction technique (SQ-XRD), energy-dispersive X-ray spectroscopy (EDX) and scanning electron microscopy (SEM) techniques were used for elemental, surface and mineralogical analyses. Breakage and selection functions were determined using the top-size-fraction method. Commonly used first-order flotation kinetic model and Berube model were utilized for estimating the related parameters. The results disclosed that the ore’s breakage rate constant monotonically increased by increasing the exposure time particularly for the coarsest fraction size (400µm) owing to the creation of thermal stress fractures alongside grain boundaries. Chalcopyrite’s flotation rate constant and infinitive recovery of pyrite improved while samples irradiated to the shorter exposure time (<60s) in comparison with the untreated ones. We finally concluded that the MW-treated copper ore was ground faster and floated similarly compared to the untreated one. Further fundamental studies are required for profound understanding of these phenomena from analytical points of view.

Keywords: Kinetic; microwave; grinding; flotation; copper sulfide ore

  • Contribution to proceedings
    IMPC - EURASIA 2019, 30.10.-02.11.2019, Antalya, Turkey

Publ.-Id: 29633

Pages: [1.] [2.] [3.] [4.] [5.] [6.] [7.] [8.] [9.] [10.] [11.] [12.] [13.] [14.] [15.] [16.] [17.] [18.] [19.] [20.] [21.] [22.] [23.] [24.] [25.] [26.] [27.] [28.] [29.] [30.] [31.] [32.] [33.] [34.] [35.] [36.] [37.] [38.] [39.] [40.] [41.] [42.] [43.] [44.] [45.] [46.] [47.] [48.] [49.] [50.] [51.] [52.] [53.] [54.] [55.] [56.] [57.] [58.] [59.] [60.] [61.] [62.] [63.] [64.] [65.] [66.] [67.] [68.] [69.] [70.] [71.] [72.] [73.] [74.] [75.] [76.] [77.] [78.] [79.] [80.] [81.] [82.] [83.] [84.] [85.] [86.] [87.] [88.] [89.] [90.] [91.] [92.] [93.] [94.] [95.] [96.] [97.] [98.] [99.] [100.] [101.] [102.] [103.] [104.] [105.] [106.] [107.] [108.] [109.] [110.] [111.] [112.] [113.] [114.] [115.] [116.] [117.] [118.] [119.] [120.] [121.] [122.] [123.] [124.] [125.] [126.] [127.] [128.] [129.] [130.] [131.] [132.] [133.] [134.] [135.] [136.] [137.] [138.] [139.] [140.] [141.] [142.] [143.] [144.] [145.] [146.] [147.] [148.] [149.] [150.] [151.] [152.] [153.] [154.] [155.] [156.] [157.] [158.] [159.] [160.] [161.] [162.] [163.] [164.] [165.] [166.] [167.] [168.] [169.] [170.] [171.] [172.] [173.] [174.] [175.] [176.] [177.] [178.] [179.] [180.] [181.] [182.] [183.] [184.] [185.] [186.] [187.] [188.] [189.] [190.] [191.] [192.] [193.] [194.] [195.] [196.] [197.] [198.] [199.] [200.] [201.] [202.] [203.] [204.] [205.] [206.] [207.] [208.] [209.] [210.] [211.] [212.] [213.] [214.] [215.] [216.] [217.] [218.] [219.] [220.] [221.] [222.] [223.] [224.] [225.] [226.] [227.] [228.] [229.] [230.] [231.] [232.] [233.] [234.] [235.] [236.] [237.] [238.] [239.] [240.] [241.] [242.] [243.] [244.] [245.] [246.] [247.] [248.] [249.] [250.] [251.] [252.] [253.] [254.] [255.] [256.] [257.] [258.] [259.] [260.] [261.] [262.] [263.] [264.] [265.] [266.] [267.] [268.] [269.] [270.] [271.] [272.] [273.] [274.] [275.] [276.] [277.] [278.] [279.] [280.] [281.] [282.] [283.] [284.] [285.] [286.] [287.] [288.] [289.] [290.] [291.] [292.] [293.] [294.] [295.] [296.] [297.] [298.] [299.] [300.] [301.] [302.] [303.] [304.] [305.] [306.] [307.] [308.] [309.] [310.] [311.] [312.] [313.] [314.] [315.] [316.] [317.] [318.] [319.] [320.] [321.] [322.] [323.] [324.] [325.] [326.] [327.] [328.] [329.] [330.] [331.] [332.] [333.] [334.] [335.] [336.] [337.] [338.] [339.] [340.] [341.] [342.] [343.] [344.] [345.] [346.] [347.] [348.] [349.]