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41396 Publications

A forward look into the US rare-earth industry; How potential mines can connect to the global REE market

Barakos, G.; Mischo, H.; Gutzmer, J.

It has been nearly eight years since rare-earth elements (REE) became the subject of front-page headlines. It was when the controversial Chinese export policy for these critical commodities was epitomized in a maritime border dispute with Japan in September 2010 that resulted in the big REE crisis and price spike of 2011 (Barakos et al., 2016c; Mancheri, 2015). The world was dismayed, especially in REE-importing countries such as the United States that was, and still is, totally dependent on Chinese production and exports (Barakos et al, 2016c; Kennedy, 2015). The short-lived alarm initiated a treasure hunt by way of exploration for REE deposits all over the world. The continuously growing demand on the one hand, and the Chinese sovereignty of the REE-market on the other, led the rest of the world to explore their own REE resources. In just a few years, more than 400 projects were initiated to explore REE deposits outside of China

Keywords: REE; USA; Mining; Resource Policy

  • Mining Engineering 70(2018)8, 30-37
    ISSN: 00265187

Permalink: https://www.hzdr.de/publications/Publ-27874
Publ.-Id: 27874


Development of Ga binding Peptides using Phage Display Technology

Schönberger, N.; Matys, S.; Lederer, F.; Pollmann, K.

Gallium is a strategically important metal for the German high-tech industry. It is used essentially in the semiconductor compounds GaAs, GaN or GaP for high-potential future technologies. This is offset by low recycling rates and declining availability on the world market. Therefore, the development of processes for the selective recovery of gallium from secondary raw material sources is a desirable starting point for dealing with the increasing scarcity of this resource on the world market. Particularly interesting is the development of a biotechnological method for selective biosorption by using the Phage Surface Display Technology.
This is a well-established method for the selection of highly specific peptide ligands in medicine and biotechnology. Random, short peptide sequences are presented on the surface according to genetically modified bacteriophages. In a biopanning called process, a pool of different bacteriophage is selected against a particular target, thereby enriching specific binding clone variants. A very effective method has been established for the selection of different phage display libraries. Gallium ions immobilized on a monolithic ion exchanger are made accessible for biopanning in an FPLC system. This chromatopanning allows the selective enrichment of gallium-binding clone variants under strictly controlled process conditions.
In the present study, we report about the enrichment, identification and characterization of several gallium-binding peptide motifs. Some promising gallium binding bacteriophage clones are chosen for further binding studies, including bacteriophage immobilization for real waste water treatment experiments.
The corresponding peptide sequences can be synthesized and used in subsequent experiments to characterize metal-peptide interactions and develop biosorptive materials for selective gallium recovery from industrial waste waters.

Keywords: Phage Display; Gallium; Peptides; Biosorption

  • Poster
    4th EURO bio-inspired materials 2018, 19.-22.03.2018, Potsdam, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-27873
Publ.-Id: 27873


The Implementation of an Activated Temperature Dependent Wall Boiling Model in an Eulerian-Eulerian Computational Fluid Dynamic Approach for Predicting the Wall Boiling Process

Ding, W.; Krepper, E.; Hampel, U.

In this work, we report on a development of time averaged Eulerian multiphase approach applied in the wall boiling process especially in the forced convective boiling process. Recently in order to get accurate bubble dynamics and reduce the case dependency, a single bubble model for nucleate boiling based on the known published models was developed. The model considers geometry change and dynamic contact and inclination angles during the bubble growth. The model has a good agreement with experiments. However the predicted bubble dynamics is wall superheat (cavity activation temperature) dependent. This single bubble model requires an update of the current nucleation site activation and heat partitioning models in time averaged Eulerian multiphase approaches. In this work, we will introduce this implementation in detail. Further with help of the multiple size group (MUSIG) model and a breakup and coalescence model, the time averaged Eulerian approach could simulate the bubble size distribution in a heated pipe. With the necessary calibration of the nucleation site density the comparisons between the calculation results and the Bartolomej’s experiments demonstrate the success of the implementation and the accuracy of this approach.

Keywords: Wall boiling; Eulerian multi-phase approach; microlayer; cavity group activation; updated heat partitioning

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Permalink: https://www.hzdr.de/publications/Publ-27872
Publ.-Id: 27872


Diagnostics for plasma-based electron accelerators

Downer, M. C.; Zgadzaj, R.; Debus, A.; Schramm, U.; Kaluza, M. C.

Plasma-based accelerators that impart energy gain as high as several GeV to electrons or positrons within a few centimeters have engendered a new class of diagnostic techniques very different from those used in connection with conventional radio-frequency (rf) accelerators. The need for new diagnostics stems from the micrometer scale and transient, dynamic structure of plasma accelerators, which contrasts with the meter scale and static structure of conventional accelerators. Because of this micrometer source size, plasma-accelerated electron bunches can emerge with smaller normalized transverse emittance (εn<0.1  mm mrad) and shorter duration (τb∼1  fs) than bunches from rf linacs. Single-shot diagnostics are reviewed that determine such small εn and τb noninvasively and with high resolution from wide-bandwidth spectral measurement of electromagnetic radiation the electrons emit: εn from x rays emitted as electrons interact with transverse internal fields of the plasma accelerator or with external optical fields or undulators; τb from THz to optical coherent transition radiation emitted upon traversing interfaces. The duration of ∼1  fs bunches can also be measured by sampling individual cycles of a copropagating optical pulse or by measuring the associated magnetic field using a transverse probe pulse. Because of their luminal velocity and micrometer size, the evolving structure of plasma accelerators, the key determinant of accelerator performance, is exceptionally challenging to visualize in the laboratory. Here a new generation of laboratory diagnostics is reviewed that yield snapshots, or even movies, of laser- and particle-beam-generated plasma accelerator structures based on their phase modulation or deflection of femtosecond electromagnetic or electron probe pulses. Spatiotemporal resolution limits of these imaging techniques are discussed, along with insight into plasma-based acceleration physics that has emerged from analyzing the images and comparing them to simulated plasma structures.

Keywords: Beam diagnostics; Electrostatic waves & oscillations; Laser driven electron acceleration; Laser wakefield acceleration; Particle acceleration in plasmas; Radiation & particle generation in plasmas

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Permalink: https://www.hzdr.de/publications/Publ-27870
Publ.-Id: 27870


Localization of magnon modes in a curved magnetic nanowire

Gaididei, Y.; Kravchuk, V. P.; Mertens, F. G.; Pylypovskyi, O. V.; Saxena, A.; Sheka, D. D.; Volkov, O. M.

Spin waves in magnetic nanowires can be bound by a local bending of the wire. The eigenfrequency of a truly local magnon mode is determined by the curvature: a general analytical expression is established for any infinitesimally weak localized curvature of the wire. The interaction of the local mode with spin waves, propagating through the bend, results in scattering features, which is well confirmed by spin-lattice simulations.

Keywords: magnetic wire; curvature; local mode; spin wave

Permalink: https://www.hzdr.de/publications/Publ-27869
Publ.-Id: 27869


Trivalent Actinide Incorporation into Zirconium(IV) oxide – Spectroscopic Investigations of Defect Fluorite Structures

Eibl, M.; Shaw, S.; Morris, K.; Stumpf, T.; Huittinen, N.

The structural incorporation of trivalent ions, i.e. Y(III), Eu(III) and Cm(III) was studied with powder X-ray diffraction (PXRD) and various spectroscopic methods including site-selective time-resolved laser fluorescence-spectroscopy (TRLFS) and extended X-ray absorption fine structure spectroscopy (EXAFS). A clear mismatch of the bulk behavior in the stabilized tetragonal and cubic phases with its local structure was observed. Furthermore, it could be seen, that no quantitative structural incorporation into the monoclinic phase is achieved. A very strong shift of the laser fluorescence emission maximum of Cm(III) doped cubic phases compared to the Cm(III) aquo ion could be measured. It was shown that TRLFS is a powerful method to study defect structures, especially in combination with PXRD as a bulk characterization method.

  • Poster
    Plutonium Futures 2018, 09.-14.09.2018, San Diego, USA

Permalink: https://www.hzdr.de/publications/Publ-27868
Publ.-Id: 27868


Analysis of Flow Pattern Transition from Segregated to Slug flow in Upward Inclined Pipes

Fan, Y.; Pereyra, E.; Sarica, C.; Schleicher, E.; Hampel, U.

Segregated and slug flows are two of the most common flow patterns encountered in two-phase upward inclined pipe flow. However, the transition between them is ambiguous. Coherent and distinctive structures have been observed within the transition. These structures have been classified as pseudo-slug flow. The nature of pseudo-slug flow is not well understood due to the complexity of the structure. At low liquid loading conditions, this flow pattern can occupy a large operating region and cannot be neglected. This paper presents a detailed experimental work conducted in a facility with a valley configuration, focusing on the transition region between segregated and slug flows. Wire-mesh sensors were employed to investigate the liquid phase distribution within the flow structure.
The current paper investigates the flow patterns and their transition in upward inclined pipe from different perspectives. The investigation includes analysis of images from high-speed videos, evaluation of 2-D liquid holdup axial evolution, 2-D liquid holdup distribution at pipe cross-section, 3-D interfacial structure evolution, and analysis of pressure gradient and liquid holdup measurement, flow characteristics, etc. Differences between slug and pseudo-slug flows are also presented.
Three superficial liquid velocities (0.001, 0.005 and 0.01 m/s) and five inclination angles (2°, 5°, 10°, 15°, and 20°) are studied. Simplified correlations are proposed for pseudo-slug structural velocity, showing fair agreement.

Keywords: Pseudo-slug Flow; Flow Pattern Transition; Two-phase Flow in Inclined Pipe; Wire-mesh Sensor; Low Liquid Loading

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Permalink: https://www.hzdr.de/publications/Publ-27867
Publ.-Id: 27867


Synthesis and Characterization of Tetravalent Actinide Complexes with Nitrogen Donor Ligands

Schöne, S.; Kloditz, R.; März, J.; Kaden, P.; Patzschke, M.; Roesky, P. W.; Stumpf, T.; Ikeda-Ohno, A.

In contrast to the dominant trivalent state for the lanthanide series (Ln(III)), a wide variety of oxidation states (from II to VII) of actinides (An) makes their chemistry intricate but attractive. Especially the early An thorium (Th), uranium (U), neptunium (Np) and plutonium (Pu) form highly charged cations with the oxidation state of four (An4+), which are of particularly interest for the coordination chemistry due to their strong interaction with ligands. Furthermore, the tetravalent oxidation state of these An is also preferred under reductive conditions that could potentially occur in the environment. Hence, the understanding of the interaction mechanisms between tetravalent An (An(IV)) and naturally occurring ligands is of crucial importance particularly for the safety assessment of nuclear waste repository.
The overall aim of our investigations lies in the comprehensive characterization of An(IV) complexes with ligands bearing soft donor atoms, such as nitrogen (N), both in the solid state and in solution. The present study focuses particularly on the interaction of An(IV) with N-donor ligands of amidinate and guanidinate type, which could be considered as a simplified model of naturally occurring N-donor organic compounds.

Recently, the Ln(III) complexes with the chiral benzamidine, (S,S)-N,N-Bis-(1-phenylethyl)-benzamidine ((S)-HPEBA, Fig.1), have been successfully synthesized by the group of Prof. Roesky1,2. Our study is inspired by these precedent studies and has succeeded to obtain the first chiral benzamidinate complexes of An(IV) [An((S)-PEBA)3Cl] (An= Th, U and Np) as well as that of Ce(IV), a chemical analog of An(IV).

The structure of the synthesized complexes was determined by single-crystal X-ray diffraction (SC-XRD), revealing that the An(IV) center is coordinated by three chiral benzamidinates and one chloride in a monocapped distorted octahedral coordination geometry.

The isostructurality of the obtained An(IV) complexes enables a direct comparison of the binding situation across the series. Quantum chemical calculations indicate that the bonding between An(IV) and the N atoms in the ligand strengthens by comparing Th(IV) to U(IV) due to the contribution of 5f-electrons to the chemical bonding.
The complexes were also characterized in solution with NMR spectroscopy. Due to the electronic interactions between the paramagnetic metal center and the ligand, significant NMR chemical shifts are observed, which can be further correlated with the distance between the metal center and the measured nuclei as well as the angle towards the principal axis of the molecule. The Th(IV) complex serves as a diamagnetic reference to subtract non-paramagnetic contributions from the observed chemical shift and to calculate the hyperfine shifts. Hence, the structure information on the paramagnetic complexes in solution can be acquired by the paramagnetic NMR spectroscopy.

ACKNOWLEDGEMENTS

This study was supported by the German Federal Ministry of Education and Research (BMBF) funding under the project No. 02NUK046B (FENABIUM).

REFERENCES

1. P. BENNDORF, C. PREUẞ, P W. ROESKY: “Synthesis of Enantiomeric Pure Lithium and Potassium Benzamidinate Complexes” J. Organomet. Chem., 696, 1150 (2011).
2. P. BENNDORF, J. KRATSCH, L. HARTENSTEIN, C. PREUẞ, P W. ROESKY: “Chiral Benzamidinate Ligands in Rare-Earth-Metal Coordination Chemistry” Chem. Eur. J., 18, 14454 (2012).

  • Poster
    Plutonium Futures 2018, 09.-14.09.2018, San Diego, USA

Permalink: https://www.hzdr.de/publications/Publ-27866
Publ.-Id: 27866


Second Reply to “Comment on Methodological accuracy of image-based electron density assessment using dual-energy computed tomography” [Med. Phys. 44, 2429-2437 (2017)]

Möhler, C.; Wohlfahrt, P.; Richter, C.; Greilich, S.

To the Editor,
The recent letter by Dr. Saito refers to the theoretical framework of electron-density determination by dual-energy computed tomography (DECT), as presented in the appendix of our article.1 After performing some calculations in this framework, the author of the Comment concludes that “the form of Eq. (A1) […] is not appropriate to rigorously derive Eq. (3)”. This conclusion is clearly illogical and contradictory to other statements by the author.

Keywords: dual-energy computed tomography; proton therapy; range prediction

Permalink: https://www.hzdr.de/publications/Publ-27865
Publ.-Id: 27865


Surficial and deep earth material prediction from geochemical compositions - a spatial predictive model

Talebi, H.; Mueller, U.; Tolosana-Delgado, R.; Grunsky, E. C.; Mckinley, J. M.; de Caritat, P.

Prediction of true classes of surficial and deep earth materials using multivariate geospatial data is a common challenge for geoscience modellers. Most geological processes leave a footprint that can be explored by geochemical data analysis. These footprints are normally complex statistical and spatial patterns buried deep in the high-dimensional compositional space. This paper proposes a spatial predictive model for classification of surficial and deep earth materials derived from the geochemical composition of surface regolith. The model is based on a combination of geostatistical simulation and machine learning approaches. A random forest predictive model is trained and features are ranked based on their contribution to the predictive model. To generate potential and uncertainty maps, compositional data are simulated at unsampled locations via a chain of transformations (isometric log-ratio transformation followed by the flow anamorphosis) and geostatistical simulation. The simulated results are subsequently back-transformed to the original compositional space. The trained predictive model is used to estimate the probability of classes for simulated compositions. The proposed approach is illustrated through two case studies. In the first case study the major crustal blocks of the Australian continent are predicted from the surface regolith geochemistry of the National Geochemical Survey of Australia project. The aim of the second case study is to discover the superficial deposits (peat) from the regional-scale soil geochemical data of the Tellus project. The accuracy of the results in these two case studies confirms the usefulness of the proposed method for geological class prediction and geological process discovery.

Keywords: Compositional data; Log-ratio; flow anamorphosis; geostatistical simulation; machine learning

Permalink: https://www.hzdr.de/publications/Publ-27864
Publ.-Id: 27864


Geostatistical Simulation of Geochemical Compositions in the Presence of Multiple Geological Units: Application to Mineral Resource Evaluation

Talebi, H.; Mueller, U.; Tolosana Delgado, R.; van den Boogaart, K. G.

An accurate prediction of benefit in ore deposits with heterogeneous spatial variations requires the definition of geological domains that differentiate the types of mineralogy, alteration, and lithology, as well as the prediction of full mineral and geochemical compositions within each modeled domain and across boundaries between different domains. This paper proposes and compares various approaches (different combinations of log-ratio transformation, Gaussian and flow anamorphosis, and deterministic or probabilistic geological models) for geostatistical simulation of geochemical compositions in the presence of several geological domains. Different approaches are illustrated through an application to a nickel–cobalt laterite deposit located in Western Australia. Four rock types (ferruginous, smectite, saprolite, and ultramafic) are considered to define compositionally homogeneous domains. Geochemical compositions are comprised of six different components of interest (Fe, Al, Mg, Ni, Co, and Filler). The results suggest that the flow anamorphosis is a vital element for geostatistical modeling of geochemical composition due to its invariance properties and capability for reproducing complex patterns in input data, including: presence of outliers, presence of several populations (due to the presence of several geological domains), nonlinearity, and heteroscedasticity.

Keywords: Compositional data; Log-ratio; Flow anamorphosis; Geostatistical simulation; Geological domaining

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Permalink: https://www.hzdr.de/publications/Publ-27863
Publ.-Id: 27863


Experimental modelling of continuous casting of steel in slab moulds using low melting liquid metals

Timmel, K.; Wondrak, T.; Eckert, S.

Electromagnetic actuators are widely used in industry for contactless control of the steel flow in the continuous casting process. However, a real control of the flow structure by those actuators is a challenging task due to the lack of flow monitoring devices. Even a satisfying non real-time characterisation of the melt flow from plant measurements is missing. Beside numerical simulations, only a very few spatially and temporally limited measurements in liquid steel are available to investigate the actual action of the magnetic fields on the fluid.
Therefore, model experiments with low melting point liquid metals are an important tool to investigate the flow structure and related transport processes in the mould of a continuous caster. Their advantage is the availability of a variety of measurement techniques for quantitative flow measurements. The application of the Ultrasonic-Doppler-Velocimetry (UDV) and the Contactless-Inductive-Flow-Tomography (CIFT) allows for a detailed characterization of the mould flow with a reasonable spatial and temporal resolution.
In recent experiments at HZDR, the systematic study on the influence of an electromagnetic brake on the mould flow in a slab caster was continued. The measurements were carried out using a 1:2 scaled model operated with SnBi and a 1:8 scaled model operated with GaInSn, respectively. The melt surface was partly measured by a laser scanner system. In particular, the immersion depth of the submergence entry nozzle (SEN) was varied during the experiments. It became obvious that changes in the mould flow had a strong influence on the free surface of the melt, where strong perturbations can significantly impair the surface quality of the final steel strands. Moreover, effects from the “artificial” clogging of one SEN-port or the injection of Argon gas at the stopper rod were investigated.

Keywords: Continuous Casting; Liquid metal models; ultrasonic wave guides

  • Lecture (Conference)
    The 9th International Symposium on Electromagnetic Processing of Materials, 14.-18.10.2018, Hyogo, Japan
  • Open Access Logo IOP Conference Series: Materials Science and Engineering 424(2018), 012032
    DOI: 10.1088/1757-899X/424/1/012032
    ISSN: 1757-899X
    Cited 1 times in Scopus

Permalink: https://www.hzdr.de/publications/Publ-27862
Publ.-Id: 27862


LSC-Anwendungen beim Rückbau von Kernkraftwerken

Barkleit, A.

Vorstellung FORKA-Projektskizzen

  • Lecture (Conference)
    LSC-Anwendertreffen, 11.-12.09.2018, Hannover, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-27861
Publ.-Id: 27861


Do rotating magnetic fields unconditionally lead to grain refinement? – A case study for directionally solidified Al-10wt%Cu alloys

Zimmermann, G.; Pickmann, C.; Schaberger-Zimmermann, E.; Galindo, V.; Eckert, K.; Eckert, S.

The effect of solidification velocity and electromagnetic stirring on grain refining was investigated experimentally during the directional solidification of rod-like Al-10wt%Cu alloy samples. Applying low solidification velocities leads to a dendritic microstructure consisting of elongated equiaxed crystals, which result from fragmented dendrite arms forming new grains. This grain-refining effect vanishes for higher solidification velocities, leading to a microstructure dominated by a lower number of larger columnar grains. Moderate electromagnetic stirring under laminar flow conditions does not promote grain refinement. By contrast, a sufficiently strong forced melt flow induced by a rotating magnetic field significantly increases the number of grains in the range of solidification velocities investigated within this study. It is assumed that a turbulent melt flow supports the fragmentation of dendrite arms and thus the formation of new grains, which finally leads to grain refinement.

Keywords: Aluminium-copper alloy; solidification; grain refinement, melt flow

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Permalink: https://www.hzdr.de/publications/Publ-27860
Publ.-Id: 27860


One-pot Cascade Synthesis of Pyrazole-based Isosteres of Valdecoxib by a [3+2] Cycloaddition/[1,5] Sigmatropic Rearrangement Sequence and Evaluation of their COX Inhibitory Activity

Roscales, S.; Bechmann, N.; Pietzsch, J.; Kniess, T.

A series of 5-methyl-3,4-diaryl-substituted 1H-pyrazoles, N-isosteres of valdecoxib, was synthesized by a [3+2] cycloaddition/[1,5] sigmatropic rearrangement sequence starting from tosylhydrazine, aryl methyl ketones and terminal aryl alkynes bearing various substituents (H, Me, OMe, F, SO2Me, SO2NH2). New pyrazoles were prepared regioselectively in a one-pot process with moderate-good yields. All compounds were used in in vitro cyclooxygenase (COX) assays to determine inhibitory potency and selectivity to COX-1 and COX-2. In general, these new pyrazoles are characterized by selective COX-2 inhibition activity in a micromolar range. Structure-activity relationship studies showed that compounds possessing an electron-withdrawing group (F) in one of the aryl rings displayed higher COX-2 inhibition selectivity and activity than was determined for compounds containing electron-donating groups (Me, OMe).

Keywords: pyrazole; COX inhibition; cycloaddition; sigmatropic rearrangement; tosylhydrazone

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Permalink: https://www.hzdr.de/publications/Publ-27859
Publ.-Id: 27859


Arming human regulatory T cells from healthy donors or multiple sclerosis patients with switchable chimeric antigen receptors for the treatment of inflammatory diseases

Kegler, A.; Koristka, S.; Bergmann, R.; Arndt, C.; Feldmann, A.; Albert, S.; Ehninger, G.; Bornhäuser, M.; Schmitz, M.; Akgün, K.; Ziemssen, T.; Bachmann, M.

Regulatory T cells (Tregs) possess a central role in impeding harmful immune reactions and represent important immunomodulatory players in the pathogenesis of inflammatory diseases. For that reason, Tregs are intensively studied as an innovative cell product for the treatment of autoimmunity e.g. multiple sclerosis (MS) or Graft-versus-Host disease. In recent years, several preclinical mouse model clearly demonstrate a superior suppressive capacity of antigen-specific Tregs compared to polyclonal cells. On the downside, isolation of Tregs with a distinct antigen-specificity is a highly time-consuming and laborious process.
To overcome these challenges, we armed polyclonal Tregs isolated from healthy donors or MS patients with a universal chimeric antigen receptor (UniCAR) construct. As T cells and target cells are indirectly cross-linked by a separate, antigen-binding targeting module (TM), this innovative technology enables side-specific redirection of Tregs to any desired surface structure. Moreover, UniCAR armed Tregs are silenced in the absence of the TM allowing for a finely tuned regulation of Treg activity between an “on” and “off” status.
Here, we demonstrate that highly pure CD4+CD25highCD127dimCD45RA+ Tregs isolated from both healthy donors or MS patients stably express a UniCAR construct with an intracellular 4-1BB/ζ signaling domain. UniCAR-engrafted Tregs vigorously expand and maintain their phenotype even under pro-inflammatory conditions. Most importantly, upon TM-activation UniCAR-endowed Tregs significantly hamper autologous T effector cells both in vitro and in vivo.
Taken together, our results underline the enormous therapeutic potential of the UniCAR system for treatment of inflammatory diseases including MS, as it facilitates an antigen-specific and precisely controlled Treg activation at the side of inflammation. Moreover, this innovative technology allows redirection of Tregs against a wide range of surface structures simply by exchanging the TM and might thereby broaden current treatment modalities.

  • Lecture (Conference)
    First International Conference on Lymphocyte Engineering (ICLE), 13.-15.09.2018, Madrid, Spain
  • Open Access Logo Abstract in refereed journal
    Human Gene Therapy (2018), ICLE8-0038
    DOI: 10.1089/hum.2018.29071.abstracts

Permalink: https://www.hzdr.de/publications/Publ-27858
Publ.-Id: 27858


Efficient suppression of effector T cells isolated from multiple sclerosis patients by autologous, UniCAR-engrafted Tregs

Kegler, A.; Koristka, S.; Arndt, C.; Feldmann, A.; Seifert, A.; Ehninger, G.; Bornhäuser, M.; Schmit, M.; Akgün, K.; Ziemssen, T.; Bachmann, M.

In multiple sclerosis (MS) patients pathogenic, autoreactive effector T cells (Teffs) provoke demyelination and central nerve system damage. To impede those harmful immune reactions, the adoptive transfer of regulatory T cells (Tregs) emerged as a promising therapeutic strategy. Several preclinical mouse models confirm an inferior functionality of polyclonal compared to antigen-specific Treg cells. However, isolation and expansion of Tregs with a desired antigen-specificity proves to be highly time-consuming and labor-intensive.
To overcome these hurdles, we armed polyclonal Tregs isolated from MS patients with a universal chimeric antigen receptor (UniCAR) construct. This innovative technology allows a site-specific redirection of cells against any desired surface structure, as cross-linkage to target cells is mediated by a separate, antigen-binding targeting module (TM).
Highly pure CD4+CD25highCD127dimCD45RA+ MS-Tregs could be genetically modified to stably express the UniCAR 4-1BB/ζ construct. UniCAR-endowed Tregs strongly expand and show phenotypic stability also upon pro-inflammatory challenge. By adding a TM in the presence of target cells, UniCAR-engrafted Tregs are antigen-specifically activated demonstrated by CD69 and LAP upregulation. Most importantly, upon TM-stimulation UniCAR-armed Tregs efficiently suppress pre-activated, patient-derived Teffs.
Taken together, the UniCAR system holds an enormous therapeutic potential for MS, as it not only allows a site-specific and precisely regulated Treg activation but also confers strong suppressive capacity to Tregs from MS patients. Thereby, this innovate technology might broaden current treatment strategies to overcome impaired functionality of Tregs as well as resistance of pathogenic Teffs to Treg suppression reported for MS patients.

Keywords: Multiple sclerosis; regulatory T cells; chimeric antigen receptor

  • Lecture (Conference)
    5th European Congress of Immunology, 03.-05.09.2018, Amsterdam, The Netherlands

Permalink: https://www.hzdr.de/publications/Publ-27857
Publ.-Id: 27857


Collision probability of particles within the bubble wake and the influence on the flotation recovery measured by 4D particle tracking velocimetry

Sommer, A.-E.; Heitkam, S.; Rudolph, M.; Eckert, K.

Froth flotation is a fundamental technique to separate minerals. Hydrophobized target particles attach to the fluidic interface of gas bubbles rising in a suspension. The success of the process depends on both the surface chemistry for the hydrophobization of particles and the hydrodynamics for an encounter between bubble and particle. To quantify this performance in terms of recovery, the number of target particles at various times in a reference volume is measured. One of the remaining challenges in this field is the flotation of fine particles with a size below 10µm. Caused by their small inertia, the particles follow the streamlines around the bubble and no collision occurs.

This work focuses on the measurement of the collision probability of particles with a small inertia at the bubble surface to advance our understanding of relevant microprocesses and its influence on the flotation recovery. With a 4D particle tracking velocimetry device the particle and bubble trajectories were measured simultaneously with a high temporal (1000 fps) and spatial resolution (0.03 mm/pixels). We developed an algorithm to evaluate the flotation recovery based on the collision and attachment probability. The three-phase flow within a rectangular bubble column consisted of fluorescent polystyrene particles (33 µm, 1.05 g/cm^3), a bubble chain(1 - 7mm) and deionized water with methanol. The variation of the bubble diameter and methanol concentration led to a change of the fluid flow around the bubble (Re=100 - 1200) and the particle hydrophobization. The results show the preferred collision of the particles at the rear of the bubble due to a higher acceleration within the vortices.

  • Lecture (Conference)
    12th European Fluid Mechanics Conference, 09.-13.09.2018, Wien, Österreich

Permalink: https://www.hzdr.de/publications/Publ-27856
Publ.-Id: 27856


Elimination of CAR-engineered lymphocytes by autologous anti-CAR T cells

Koristka, S.; Ziller-Walter, P.; Bergmann, R.; Arndt, C.; Feldmann, A.; Kegler, A.; Seifert, A.; Bornhäuser, M.; Bachmann, M.

The adoptive transfer of chimeric antigen receptor (CAR) T cells represents one of the fastest growing areas in cancer immunotherapy. Although gene-modified cells have shown unparalleled antitumor efficiency in patients suffering from hematological malignancies, highly potent CAR T cells can cause severe and partly life-threatening on-target and off-target effects including of cytokine release syndrome and neurological toxicity. Consequently, there is an increasing demand for developing effective strategies to selectively eliminate gene-modified cells in vivo.
One possible approach represents the insertion of a targetable moiety into CAR T cells. In that regard, we previously characterized a small peptide epitope (E-tag) derived from the human nuclear La protein which we incorporated into the extracellular spacer region of CARs. Based on a monoclonal anti-La antibody recognizing this epitope, we generated a CAR construct for specific binding and depletion of E-tag-labelled CAR T cells.
In flow cytometry-based cytotoxicity assays, T cells redirected via the novel CAR construct selectively eliminated E-tag-expressing CAR T cells whilst cells lacking this epitope on their surface were not attacked. Interestingly, T cell killing was reciprocal and dependent on an intracellular signaling domain as well as the effector to target cell ratio. Our studies further indicate that T cells expressing high CAR levels were more efficiently depleted than T cells with low CAR expression. In addition, CD4+ and CD8+ target cells were equally well eliminated by both CD4+ and CD8+ effector T cells.
Altogether, we here provide an approach for specific and efficient depletion of overactive CAR T cells in case patients experience severe side effects. The E-tag can easily be included into all CARs irrespective of the targeted tumor antigen and represents a promising tool to improve safety of cell-based immunotherapies.

Keywords: Chimeric antigen receptor; T lymphocytes; immunotherapy; toxicity management; epitope tag

  • Poster
    First International Conference on Lymphocyte Engineering (ICLE), 13.-15.09.2018, Madrid, Spain
  • Open Access Logo Abstract in refereed journal
    Human Gene Therapy 29(2018)11, ICLE8-0037
    DOI: 10.1089/hum.2018.29071.abstracts

Permalink: https://www.hzdr.de/publications/Publ-27855
Publ.-Id: 27855


Depletion of CAR-expressing lymphocytes using autologous anti-CAR-engrafted T cells

Koristka, S.; Ziller-Walter, P.; Bergmann, R.; Feldmann, A.; Arndt, C.; Kegler, A.; Seifert, A.; Ehninger, G.; Bornhäuser, M.; Bachmann, M.

Adoptive transfer of chimeric antigen receptor (CAR) T cells represents one of the fastest growing areas in cancer immunotherapy. Albeit gene-modified cells have demonstrated unparalleled antitumor efficiency in B cell malignancies, highly potent CAR T cells can cause severe and partly life-threatening side effects including cytokine release syndrome, neurological toxicity and off-target effects. Hence, there is an increasing demand for developing effective approaches to selectively ablate gene-modified cells in vivo.
Previously, we described an epitope tag (E-tag) derived from the human nuclear protein La that is incorporated into the extracellular domain of CARs and accessible by an anti-La monoclonal antibody (mAb). Based on this mAb, we generated a novel CAR construct for specific binding and depletion of E-tag-expressing CAR T cells.
We demonstrate that anti-E-tag-redirected T cells selectively eliminate CAR T cells that extracellularly express the E-tag whilst CAR T cells lacking this tag are not attacked. Interestingly, T cell killing is reciprocal and occurs in dependence of an intracellular signaling domain. Our studies further indicate that T cells expressing high CAR levels are more efficiently depleted than T cells with low CAR expression. Besides, CD4+ and CD8+ target cells are equally well eliminated by both CD4+ and CD8+ effector T cells.
Overall, we provide an approach for specific and efficient depletion of overactive CAR T cells in case patients experience severe side effects. The E-tag can be incorporated into all CARs irrespective of the targeted tumor antigen and represents a promising tool to improve safety of cell-based immunotherapies.

Keywords: Chimeric antigen receptor; T lymphocytes; immunotherapy; toxicity management; epitope tag

  • Poster
    5th European Congress of Immunology, 03.-05.09.2018, Amsterdam, The Netherlands

Permalink: https://www.hzdr.de/publications/Publ-27854
Publ.-Id: 27854


Integration of Terrestrial and Drone-Borne Hyperspectral and Photogrammetric Sensing Methods for Exploration Mapping and Mining Monitoring

Kirsch, M.; Lorenz, S.; Zimmermann, R.; Tusa, L.; Möckel, R.; Hödl, P.; Booysen, R.; Khodadadzadeh, M.; Gloaguen, R.

Mapping lithology and geological structures accurately remains a challenge in difficult terrain or in active mining areas. We demonstrate that the integration of terrestrial and drone-borne multi-sensor remote sensing techniques significantly improves the reliability, safety, and efficiency of geological activities during exploration and mining monitoring. We describe an integrated workflow to produce a geometrically and spectrally accurate combination of a Structure-from-Motion Multi-View Stereo point cloud and hyperspectral data cubes in the visible to near-infrared (VNIR) and short-wave infrared (SWIR), as well as long-wave infrared (LWIR) ranges acquired by terrestrial and drone-borne imaging sensors. Vertical outcrops in a quarry in the Freiberg mining district, Saxony (Germany), featuring sulfide-rich hydrothermal zones in a granitoid host, are used to showcase the versatility of our approach. The image data are processed using spectroscopic and machine learning algorithms to generate meaningful 2.5D (i.e., surface) maps that are available to geologists on the ground just shortly after data acquisition. We validate the remote sensing data with thin section analysis and laboratory X-ray diffraction, as well as point spectroscopic data. The combination of ground- and drone-based photogrammetric and hyperspectral VNIR, SWIR, and LWIR imaging allows for safer and more efficient ground surveys, as well as a better, statistically sound sampling strategy for further structural, geochemical, and petrological investigations.

Keywords: hyperspectral imaging; Structure-from-Motion (SfM); mineral mapping; virtual outcrops; geology; hydrothermal; UAV; long-wave infrared

Permalink: https://www.hzdr.de/publications/Publ-27853
Publ.-Id: 27853


Metal oxide double layer capacitors by electrophoretic deposition of metal oxides. Fabrication, electrical characterization and defect analysis using positron annihilation spectroscopy

Hoffmann, R. C.; Koslowski, N.; Sanctis, S.; Liedke, M. O.; Wagner, A.; Butterling, M.; Schneider, J. J.

Films consisting of nanocrystalline ZnO were deposited on ITO/glass electrodes using an electrophoretic process. The microwave-assisted thermolysis of zinc alkyl-acetoacetates resulted in the formation of stable dispersions for the electrophoretic deposition procedure. Uniform and smooth coatings could be achieved by starting the electrophoresis at lower voltages first and increasing to higher voltages at later stages of the deposition. The ZnO/ITO double layers were integrated in metal oxide semiconductor (MOS) capacitors by completing the set-up with a spin-coated PMMA dielectric layer and gold contacts. The MOS capacitors showed IV curves with a region of negative differential resistance, indicating charge trapping, both in the ZnO grains and at the ZnO/PMMA interface. Doppler broadening positron annihilation (DB-PAS) and positron annihilation life time spectroscopy (PALS) were employed to characterize the point defects and void space within the deposited ZnO layer which allowed to give insight into the bulk composition of the film composition. PALS revealed the presence of micropores in the range of 0.5 to 1.5 nm.

Keywords: positron annihilation spectroscopy; electrophoretic deposition; defect analysis

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Permalink: https://www.hzdr.de/publications/Publ-27852
Publ.-Id: 27852


Post-Younger Dryas fault instability and deformations on ice lineations in Finnish Lapland

Sutinen, R.; Andreani, L.; Middleton, M.

The Younger Dryas phase, which occurred between 12.8 and 11.5 ka as a part of the cyclic pattern of global climatic changes, was concurrent with maximum fault instability (13–10 ka) in the Fennoscandian shield. Ice lineations, indicative of glacial streaming toward the Younger Dryas end moraines (YDEMs), may have faced earthquake impacts within the glacial isostatic adjustment (GIA). Morphometric analyses for airborne laser scanning (ALS) revealed that ice lineations were deformed subglacially and subaerially in Finnish Lapland. The subglacial water outburst flows diagonally eroded the drumlins, 50 km from the YDEMs in Utsjoki, northern Finnish Lapland. Similarly north, in the Sevetti area, 40 km from the YDEMs a large portion of the ice lineations were entirely distorted by the subglacial squeeze-up Pulju moraine and liquefaction bowl formations. In the interior part of the Fennoscandian Ice sheet (FIS) in Kemijärvi, representing onset of an ice-stream fan 200 km from the YDEMs, mass flows had reworked the ice lineations. Based on the electrical-sedimentry anisotropy, mass flow sediments deviated from the ice flow pattern. Postglacial liquefaction craters were created on the drumlins in Utsjoki and also in Kuusamo, eastern Finnish Lapland, 70 km from the YDEMs in Russian Karelia. We interpret these features as indications of paleoseismic events associated with GIA.

Keywords: Lidar DEM; Pulju moraine; Liquefaction; Mass flow

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Permalink: https://www.hzdr.de/publications/Publ-27851
Publ.-Id: 27851


The role of sulfate-reducing microorganisms in the barrier-material bentonite

Matschiavelli, N.; Kluge, S.; Standhaft, D.; Podlech, C.; Grathoff, G.; Cherkouk, A.

The “Helmholtz-Zentrum Dresden-Rossendorf” (HZDR) is a registered, non-profit institution supported by the authorities of the Federal Go¬vernment and the Free State of Saxony (Germany). The HZDR conducts research in the sectors energy, health and matter. Besides the headquarters in Dresden, we have four other research sites in Grenoble/France, Freiberg, Leipzig, and Schenefeld near Hamburg.
We are working in the department of Biogeochemistry, which is part of the Institute of Resource Ecology. Here, research focusses on the assessment and reduction of risks related to the nuclear fuel cycle, particularly on the disposal of nuclear waste. Of special interest is the understanding of fundamental processes defining transport and accumulation of radiotoxic elements in the geo- and biosphere including the food chain. Chemists, biologists and physicists at our institute use a multitude of methods and tools to identify dominating processes in the ecosphere to understand the (biogeo-) chemistry of the processes on a molecular level with the objective of estimating their relevance for radionuclide migration and identification of potential risks during long-term storage of nuclear waste. In order to identify and characterize chemical species, varieties of spectroscopic tools are used. For the identification and characterization of microorganisms that could potentially influence migration processes of radionuclides or the geochemical properties of materials that are used in a nuclear waste repository, bio-geochemical and molecular biological methods are applied.

  • Lecture (others)
    Advanced training course in geomicrobiology in radioactive waste disposal, 08.-11.10.2018, Mol, Belgium

Permalink: https://www.hzdr.de/publications/Publ-27850
Publ.-Id: 27850


Development and characterization of novel anti GD2 target modules for retargeting of Universal CAR T cells toward GD2 expressing tumors

Mitwasi, N.; Feldmann, A.; Bergmann, R.; Berndt, N.; Rössig, C.; Bachmann, M.

Although chimeric antigen receptor (CAR) engineered T cells demonstrated promising therapeutic effect against cancer, they are still associated with adverse side effects which could be life threatening in some cases. Therefore, in our group we have developed a switchable universal CAR T cell platform “UniCAR”, which can be repeatedly switched on and off. This system consists of CAR T cells that cannot bind tumor antigens directly but instead they are redirected with a target module (TM). Such TMs are mainly composed of an epitope on one side, which is recognized by the UniCAR T cells, and on the other side a tumor antigen-binding domain. Once the TM is eliminated, the UniCAR T cells are no more activated. Disialoganglioside GD2 was shown previously to be a very promising target for several tumors such as neuroblastoma and Ewing’s sarcomas. Therefore, anti-GD2 TMs were developed and evaluated regarding their functionality. They were shown to be functional in activating the UniCARs to secrete important pro-inflammatory cytokines and to kill GD2+ tumor cells both in vivo and in vitro. To further characterize the anti-GD2 TM with PET imaging, it was labeled with radioactive Cu64 . The TM showed a specific enrichment at the site of the GD2+ growing tumor, and it was mainly eliminated through the kidneys within half an hour due to its small size. Such short half-life, provides the UniCAR system with the fast safety switch in case any complications occurred in patients treated with the UniCAR T cells.

  • Lecture (Conference)
    5th European Congress of Immunology, 02.09.2018, Amsterdam, the Netherlands

Permalink: https://www.hzdr.de/publications/Publ-27849
Publ.-Id: 27849


Direct Capture Cross Section and the Ep=71 and 105 keV Resonances in the 22Ne(p,γ)23Na Reaction

Ferraro, F.; Takács, M. P.; Piatti, D.; Cavanna, F.; Depalo, R.; Aliotta, M.; Bemmerer, D.; Best, A.; Boeltzig, A.; Broggini, C.; Bruno, C. G.; Caciolli, A.; Chillery, T.; Ciani, G. F.; Corvisiero, P.; Davinson, T.; D’Erasmo, G.; Dileva, A.; Elekes, Z.; Fiore, E. M.; Formicola, A.; Fülöp, Z.; Gervino, G.; Guglielmetti, A.; Gustavino, C.; Gyürky, G.; Imbriani, G.; Junker, M.; Kochanek, I.; Lugaro, M.; Marigo, P.; Menegazzo, R.; Mossa, V.; Pantaleo, F. R.; Paticchio, V.; Perrino, R.; Prati, P.; Schiavulli, L.; Stöckel, K.; Straniero, O.; Szücs, T.; Trezzi, D.; Zavatarelli, S.

The 22Ne(p,γ)23Na reaction, part of the neon-sodium cycle of hydrogen burning, may explain the observed anticorrelation between sodium and oxygen abundances in globular cluster stars. Its rate is controlled by a number of low-energy resonances and a slowly varying nonresonant component. Three new resonances at Ep=156.2, 189.5, and 259.7 keV have recently been observed and confirmed. However, significant uncertainty on the reaction rate remains due to the nonresonant process and to two suggested resonances at Ep=71 and 105 keV. Here, new 22Ne(p,γ)23Na data with high statistics and low background are reported. Stringent upper limits of 6×10−11 and 7×10−11  eV (90% confidence level), respectively, are placed on the two suggested resonances. In addition, the off-resonant S factor has been measured at unprecedented low energy, constraining the contributions from a subthreshold resonance and the direct capture process. As a result, at a temperature of 0.1 GK the error bar of the 22Ne(p,γ)23Na rate is now reduced by 3 orders of magnitude.

Keywords: asymptotic giant branch stars; nuclear astrophysics; LUNA Laboratory Underground for Nuclear Astrophysics; Hot Bottom Burning; Radiative Capture

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Permalink: https://www.hzdr.de/publications/Publ-27848
Publ.-Id: 27848


Extremely efficient terahertz high harmonic generation in graphene by hot Dirac fermions

Hafez, H. A.; Kovalev, S.; Deinert, J.-C.; Mics, Z.; Green, B.; Awari, N.; Chen, M.; Germanskiy, S.; Lehnert, U.; Teichert, J.; Wang, Z.; Tielrooij, K.-J.; Liu, Z.; Chen, Z.; Narita, A.; Müllen, K.; Bonn, M.; Gensch, M.; Turchinovich, D.

Multiple optical harmonics generation—the multiplication of photon energy as a result of nonlinear interaction between light and matter—has become one of the key technologies in modern electronics and optoelectronics. Owing to its unique electronic band structure featuring massless Dirac fermions, graphene has been repeatedly predicted to have high efficiency of optical harmonics generation in the technologically important terahertz frequency range. So far, experiments have failed to confirm these predictions under technologically relevant operation conditions. Here we report the generation of terahertz harmonics up to the seventh order in single-layer graphene at room temperature and under ambient conditions, driven by terahertz fields of only tens of kilovolts per centimetre, and with field conversion efficiencies in excess of 10⁻³, 10⁻⁴ and 10⁻⁵ for the third, fifth and seventh terahertz harmonics, respectively. The key to such highly efficient harmonics generation in graphene is the collective thermal response of its background Dirac electrons to the driving terahertz fields. The generated terahertz harmonics were observed directly in the time domain as electromagnetic field oscillations at these newly synthesized frequencies. The effective nonlinear optical coefficients of graphene for the third, fifth and seventh harmonics exceed the respective nonlinear coefficients of typical solids by 7–18 orders of magnitude. Our results provide a direct pathway to highly efficient terahertz frequency synthesis that is within the capabilities of the present generation of graphene electronics operating at fundamental frequencies of only a few hundreds of gigahertz.

Keywords: Graphene; Terahertz; High Harmonics; Nonlinear Optics; Ultrafast Electronics; Superradiant Terahertz

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Permalink: https://www.hzdr.de/publications/Publ-27847
Publ.-Id: 27847


Irradiation effects on the structural and optical properties of single crystal β-Ga2O3

Liu, C.; Berencén, Y.; Yang, J.; Wei, Y.; Wang, M.; Yuan, Y.; Xu, C.; Xie, Y.; Li, X.; Zhou, S.

In the present work, we report the 25 MeV oxygen irradiation effects in n-type single crystal β-Ga2O3 at different fluences. We demonstrate that the symmetric stretching modes and bending vibrations of GaO4 and GaO6 units are impaired upon increasing O irradiation fluence. Blue and green photoluminescence emission bands are found to be mainly associated with gallium-oxygen divacancies, gallium vacancies and oxygen interstitials. The increase of optically active centers at low fluence and the photoluminescence quenching at high fluence are ascribed to the reduction of carrier density and the production of non-radiative recombination centers, respectively. The results envisage the possibility of obtaining pre-designed spectral behaviours by varying the oxygen irradiation fluence.

Keywords: β-Ga2O3; ion irradiation; photoluminescence; radiation defect

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Permalink: https://www.hzdr.de/publications/Publ-27845
Publ.-Id: 27845


UDV flow measurements in a model of the Czochralski crystal growth process

Franke, S.; Pal, J.; Eckert, S.

This contribution describes a model experiment for the Czochralski crystal growth process. Low melting point liquid metals as GaInSn are an important tool to investigate the flow structure for such industrial processes. UDV flow measurements were conducted in a cylindrical Rayleigh-Bénard (RB) setup with modified thermal boundary conditions with and without the influence of an external rotating magnetic field. The topology of the prevailing thermally-driven convection might be very complex and is mainly determined by the aspect ratio of the liquid volume and the strength of the convection described by the characteristic dimensionless Grashof number. Two kinds of techniques were used to investigate the flow. Firstly, by means of single UDV transducers measurements of the radial velocity component were carried out shortly below the melt surface across the entire diameter of the cylindrical liquid column at various azimuthal angles. Secondly, a vertically arranged UDV array was applied at the side of the cylinder to obtain detailed information about the radial velocities in the covered meridional plane. The results reveal the complex flow structure of natural convection in a Czochralski crucible which gains in complexity with applied rotating magnetic field (RMF).

Keywords: Czochralski crystal growth; Rayleigh-Bénard convection; Ultrasound Doppler velocimetry; Flow measurements; Electromagnetic stirring

  • Lecture (Conference)
    11th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering, 05.-07.09.2018, Berlin, Germany
  • Contribution to external collection
    in: Proceedings of the 11th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering, Berlin: Eigenverlag, 2018

Permalink: https://www.hzdr.de/publications/Publ-27844
Publ.-Id: 27844


Coordination polymers of tetravalent neptunium with aromatic polycarboxylate ligands

Volkringer, C.; Martin, N. P.; März, J.; Hennig, C.; Ikeda-Ohno, A.; Loiseau, T.

Coordination polymers are organic-inorganic complexes built up from the association of metallic centers with O- or N-donor ligands. In the particular case of actinides (An), previous literature mainly has reported the synthesis of solid networks bearing U(VI) or Th(IV). Trans-uranium elements have been much less studied due to their high radiotoxicity and limited amount of the material source.
In this work, we studied the crystallization of Np(IV) with various aromatic polycarboxylate ligands in different solvents and analyzed their crystal structures. In water, an infinite chain of Np2O2(H2O)2(1,2-bdc)2 were isolated in the presence of phthalate, whereas mellitic acid leads to the oxidation of Np(IV) to Np(V) and the formation of inorganic layers of {NpO7H2O0-2}.1 The use of other solvents allowed the crystallization of large polynuclear discrete Np(IV) clusters. For example, using DMF, the hexanuclear unit of [Np6O4(OH)4] has been obtained with different dicarboxylic ligands and is the basic building unit to form an open-framework structure (Figure 1, left). This framework revealed the isolation of the hexanuclear cluster An6O8 with Np(IV).2 The formation of the giant neptunium-based polyoxo cluster called Np38 will be also presented.

Keywords: Actinides; neptunium; tetravalent; coordination polymers; metal-organic frameworks

  • Lecture (Conference)
    International Conference on Coordination Chemistry 2018, 03.08.2018, Sendai, Japan

Permalink: https://www.hzdr.de/publications/Publ-27843
Publ.-Id: 27843


Short-Range Order in Amorphous and Crystalline Ferroelectric Hf0.5Zr0.5O2

Erenburg, S. B.; Trubina, S. V.; Kvashnina, K. O.; Kruchinin, V. N.; Gritsenko, V. V.; Chernikova, A. G.; Markeev, A. M.

The microstructures of amorphous and polycrystalline ferroelectric Hf0.5Zr0.5O2 films are studied by X-ray spectroscopy and ellipsometry. EXAFS spectra demonstrate that the amorphous film consists of an “incompletely mixed” solid solution of metallic oxides HfO2 and ZrO2. After rapid thermal annealing, the mixed Hf0.5Zr0.5O2 oxide films have a more ordered polycrystalline structure, and individual Hf and Zr monoxide islands form in the films. These islands are several nanometers in size and have a structure that is similar to the monoclinic structure of HfO2 and ZrO2. The presence of the HfO2 and ZrO2 phases in the Hf0.5Zr0.5O2
films is also detected by ellipsometry

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Permalink: https://www.hzdr.de/publications/Publ-27841
Publ.-Id: 27841


When defects are not defects

Krasheninnikov, A. V.

Line defects in two-dimensional borophene can self-assemble into new crystalline phases, blurring the distinctions between perfect and defective crystal.

Keywords: 2D materials; STM; defects; first-principles calculations

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Permalink: https://www.hzdr.de/publications/Publ-27840
Publ.-Id: 27840


Ag nanoparticles embedded in Nd:YAG crystals irradiated with tilted beam of 200 MeV Xe ions: optical dichroism correlated to particle reshaping

Li, R.; Pang, C.; Amekura, H.; Ren, F.; Hübner, R.; Zhou, S.; Ishikawa, N.; Okubo, N.; Chen, F.

We report on the fabrication of reshaped Ag nanoparticles (NPs) embedded in a Nd:YAG crystal by combining Ag ion implantation and swift heavy Xe ion irradiation. The localized surface plasmon resonance (LSPR) effect is proved to be efficiently modulated according to the phenomenon of polarization-dependent absorption. The LSPR peak located at 448 nm shows red shift and blue shift at 0° and 90° polarization, respectively, which is in good agreement with calculation by discrete dipole approximation. Based on the near-field intensity distribution, the interaction between reshaped NPs shows a non-ignorable effect on the optical absorption. Furthermore, the polarization-dependence of the photoluminescence (PL) intensity is analyzed, which is positively related to the modulated LSPR absorption. It demonstrates the potential of the enhancement of PL intensity by embedded plasmonic Ag NPs. This work breaks the conventional view of the quenching effect of NPs by ion irradiation and opens a new way to realize the modulation of optical dichroism.

Keywords: nanoparticles; localized surface plasmon resonance; swift heavy ion irradiation; ND:YAG crystal

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Permalink: https://www.hzdr.de/publications/Publ-27839
Publ.-Id: 27839


Development and validation of NTCP models for acute side-effects resulting from proton beam therapy of brain tumours

Dutz, A.; Lühr, A.; Agolli, L.; Troost, E. G. C.; Krause, M.; Baumann, M.; Vermeren, X.; Geismar, D.; Schapira, E. F.; Bussière, M.; Daly, J. E.; Bussière, M. R.; Timmermann, B.; Shih, H. A.; Löck, S.

Background: The limited availability of proton beam therapy (PBT) requires individual treatment selection strategies, such as based on normal tissue complication probability (NTCP). We developed and externally validated NTCP models for common acute side-effects following PBT in brain tumour patients in effort to provide guidance on optimising patient quality of life.
Methods: An exploration cohort including 113 adult brain tumour patients who underwent PBT was investigated for the following endpoints: alopecia, scalp erythema, headache, fatigue and nausea. Dose–volume parameters of associated normal tissues were used for logistic regression modelling.
Statistically significant parameters showing high area under the receiver operating characteristic curve (AUC) values in internal cross-validation were externally validated on two cohorts of 71 and 96 patients, respectively.
Results: Statistically significant correlations of dose–volume parameters of the skin for erythema and alopecia were found. In internal cross-validation, the following prognostic parameters were selected: V35Gy (absolute volume receiving 35 Gy) for erythema grade ≥1, D2% (dose to 2% of the volume) for alopecia grade ≥1 and D5% for alopecia grade ≥2. Validation was successful for both cohorts with AUC >0.75. A bivariable model for fatigue grade 1 could not be validated externally. No correlations of dose–volume parameters of the brain were seen for headache or nausea.
Conclusion: We developed and successfully validated NTCP models for scalp erythema and alopecia in primary brain tumour patients treated with PBT.

Keywords: NTCP models; Brain tumours; Acute side-effects; Proton beam therapy

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Permalink: https://www.hzdr.de/publications/Publ-27838
Publ.-Id: 27838


Keine Überlegenheit der Protonentherapie gegenüber der IMRT beim lokal fortgeschrittenen NSCLC

Dutz, A.; Troost, E. G. C.; Löck, S.

Hintergrund: Inoperable und lokal fortgeschrittene nicht-kleinzellige Bronchialkarzinome (NSCLC) werden standardgemäß mit einer simultanen Radiochemotherapie behandelt. In dieser Arbeit untersuchten die Autoren die Hypothese, dass die Lungentoxizität (Strahlenpneumonitis, RP) nach PSPT geringer ist, ohne die Tumorkontrolle zu gefährden.
Methodik: Gemäß Protokoll wurden 149 Patienten behandelt (IMRT: 92, PSPT: 57). Als primärer kombinierter Endpunkt der randomisierten Studie wurde das erste Auftreten einer RP vom Grad ≥3 oder das Auftreten eines Lokalrezidivs innerhalb eines Jahres betrachtet.
Resultate: Die PSPT reduzierte die mittlere Herzdosis signifikant (p = 0,002), während in der mittleren Lungen- und Ösophagusdosis keine Unterschiede zur IMRT auftraten. Eine RP vom Grad ≥3 entwickelten 12 Patienten, je 6 pro Studienarm. Lokalrezidive traten ähnlich häufig in beiden Armen auf. Damit ergab sich kein signifikanter Unterschied im primären kombinierten Endpunkt (IMRT: 17,4 %, PSPT: 21,1 %; p = 0,175). Das mediane Gesamtüberleben betrug 29,5 Monate im IMRT-Arm und 26,1 Monate im PSPT-Arm.
Schlussfolgerung der Autoren: Bei Patienten mit lokal fortgeschrittenem NSCLC konnte kein Unterschied in der Häufigkeit von RP Grad ≥3 oder dem Auftreten von Lokalrezidiven zwischen IMRT und PSPT nachgewiesen werden.
Kommentar: Die vorliegende Arbeit präsentiert die erste abgeschlossene randomisierte klinische Studie, die bei Patienten mit lokal fortgeschrittenem NSCLC prospektiv Ergebnisse von IMRT mit PSPT vergleicht. Das gewählte adaptive Bayes-Studiendesign zur Randomisierung der Patienten erhöht die ethische Vertretbarkeit randomisierter Studien. Allerdings ist der Dosisvergleich in benachbarten Risikoorganen zwischen beiden Strahlungsmodalitäten kritisch zu sehen. Im PSPT-Arm wurden mehr Patienten mit der höheren Dosis von 74 Gy bestrahlt als im IMRT-Arm. Die hohe Rate an RP im PSPT-Arm wird mit einer Lernkurve des Personals erklärt, obwohl eine andere plausible Erklärung die signifikant höheren Tumorvolumina sein können. Eine Analyse der mittleren biologischen Lungendosis könnte vorteilhafter sein als die Analyse der physikalischen Dosis.

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Permalink: https://www.hzdr.de/publications/Publ-27837
Publ.-Id: 27837


Long term investigation of the degradation of coaxial cables in an ionizing radiation environment

Kuntzsch, M.; Schurig, R.; Burger, S.; Weber, T.

For the transport of RF signals coaxial cables with PTFE ("Teflon") as dielectric medium are widely used because they offer a wide bandwidth and low insertion loss. Coaxial cables that are routed in immediate vicinity to the beamline are exposed to ionizing radiation that is mainly generated by beam-loss. In this radiative environment cables change their electrical properties which directly affects the signal on the receiver side and in turn the measured beam parameters. This contribution describes a measurement setup at the superconducting CW accelerator ELBE that was used to investigate the degradation of coaxial cables under well-controlled conditions up to an accumulated dose of 94 kGy. Furthermore the acquired data up to 40 GHz of two coaxial cable samples are presented and the results are discussed.

Keywords: RF; cable; radiation; 40 GHz; ELBE

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  • Open Access Logo Contribution to proceedings
    International Beam Instrumentation Conference 2018 (IBIC18), 09.-13.09.2018, Shanghai, China
    Proceedings of IBIC18
  • Lecture (Conference)
    International Beam Instrumentation Conference 2018 (IBIC18), 09.-13.09.2018, Shanghai, China

Permalink: https://www.hzdr.de/publications/Publ-27836
Publ.-Id: 27836


Defect-induced exchange bias in a single SrRuO3 layer

Wang, C.; Chen, C.; Chang, C.-H.; Tsai, H.-S.; Pandey, P.; Xu, C.; Böttger, R.; Chen, D.; Zeng, Y.-J.; Gao, X.; Helm, M.; Zhou, S.

Exchange bias stems from the interaction between different magnetic phases and therefore it generally occurs in magnetic multilayers. Here we present a large exchange bias in a single SrRuO3 layer induced by helium ion irradiation. When the fluence increases, the induced defects not only suppress the magnetization and the Curie temperature, but also drive a metal-insulator transition at a low temperature. In particular, a large exchange bias field up to ~ 0.36 T can be created by the irradiation. This large exchange bias is related to the coexistence of different magnetic and structural phases that are introduced by embedded defects. Our work demonstrates that spintronic properties in complex oxides can be created and enhanced by applying ion irradiation.

Keywords: Exchange bias; Magnetization; Oxide thin film; Lattice distortion; Defect engineering

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Permalink: https://www.hzdr.de/publications/Publ-27835
Publ.-Id: 27835


Anti-CAR engineered T cells for epitope-based elimination of autologous CAR T cells

Koristka, S.; Ziller-Walter, P.; Bergmann, R.; Arndt, C.; Feldmann, A.; Kegler, A.; Cartellieri, M.; Ehninger, A.; Ehninger, G.; Bornhäuser, M.; Bachmann, M.

Although CAR T cell therapy has demonstrated tremendous clinical efficacy especially in hematological malignancies, severe treatment-associated toxicities still compromise the widespread application of this innovative technology. Therefore, developing novel approaches to abrogate CAR T cell-mediated side effects is of great relevance. Several promising strategies pursue the selective antibody-based depletion of adoptively transferred T cells via elimination markers. However, given the limited half-life and tissue penetration, dependence on the patients’ immune system and on-target/off-side effects of proposed monoclonal antibodies, we sought to exploit αCAR-engineered T cells to efficiently eliminate CAR T cells. For comprehensive and specific recognition, a small peptide epitope (E-tag) was incorporated into the extracellular spacer region of CAR constructs. We provide first proof-of-concept for targeting this epitope by αE-tag CAR T cells, allowing an effective killing of autologous E-tagged CAR T cells both in vitro and in vivo whilst sparing cells lacking the E-tag. In addition to CAR T cell cytotoxicity, the αE-tag-specific T cells can be empowered with cancer fighting ability in case of relapse, hence, have versatile utility. Our proposed methodology can most probably be implemented in CAR T cell therapies regardless of the targeted tumor antigen aiding in improving overall safety and survival control of highly potent gene-modified cells.

Keywords: Chimeric antigen receptor; immunotherapy; toxicity management; elimination tag

Permalink: https://www.hzdr.de/publications/Publ-27834
Publ.-Id: 27834


Engineering and coherent control of defects in silicon carbide

Astakhov, G.

Building quantum devices based on silicon carbide (SiC) is highly desirable, facilitated by established SiC CMOS technology. Optoelectronic SiC devices have already been demonstrated, however, the signal- mediating quantum defects are usually introduced in a semi-random manner, by bulk electron or neutron irradiation. We present the controlled generation of quantum centers in silicon carbide (SiC) by focused proton beam in a noncomplex manner without need for pre- or postirradiation treatment [1]. The generation depth and resolution can be predicted by matching the proton energy to the material’s stopping power, and the amount of quantum centers at one specific sample volume is tunable from ensembles of millions to discernible single photon emitters [2]. We identify the generated centers as silicon vacancies through their characteristic magnetic resonance signatures and demonstrate that they possess highy coherent spin properties even at room temperature [3].
[1] H. Kraus et al., Nano Lett. 17, 2865 (2017).
[2] F. Fuchs et al., Nat. Commun. 6, 7578 (2015).
[3] D. Simin et al., Phys. Rev. B 95, 161201(R) (2017).

Keywords: Spin defects; quantum applications; silicon carbide

  • Invited lecture (Conferences)
    25th Conference on Application of Accelerators in Research and Industry (CAARI-2018), 13.08.2018, Grapevine, USA

Permalink: https://www.hzdr.de/publications/Publ-27833
Publ.-Id: 27833


Feasibility Study for Detection of Fuel Assemblies State inside Sealed Dry Storage Casks using External Gamma Flux Measurements

Rachamin, R.; Hampel, U.

The license for the storage of spent nuclear fuel assemblies in dry casks is limited to 40 years. In Germany, a site for a final repository of spent fuel is not yet available. Therefore, this license has to be renewed for prolonged storage period. Currently, there is no experience with dry cask storage worldwide that goes beyond a period of 40 years. Beside regulatory and security aspects, there are questions concerning the long-term integrity of the spent fuel assemblies as this is of relevance for final transportation and reloading to final waste repository casks. Once the cask is filled and sealed, the knowledge about the state of the fuel assemblies is limited. This study investigates the feasibility of using external gamma flux measurements to detect the state of the spent fuel assemblies inside the cask. Monte-Carlo simulations were performed to evaluate the gamma flux distribution outside the sidewall of a cask with all intact fuel assemblies and a cask with one damaged fuel assembly, mimicking a fuel assembly with expanded rods and fuel relocation. The evaluation was performed for different location of the damaged fuel assembly and different storage times. The results of the investigation showed that the intensity and the shape of the gamma flux outside the sidewall of the cask are sufficient to identify the damaged fuel assembly, in case it is located near the inner wall of the cask. The detection of the inner damaged fuel assemblies, however, is less feasible. Due to the self-shielding of the fuel assemblies, the gamma photons which come from the inner fuel assemblies stopped within the fuel basket and assemblies materials. The gamma photons which do survive the fuel assemblies self-shielding reach the inner cask wall with not enough energy to escape the shielding of the thick cast iron wall. In general, it can be concluded that the more the damaged fuel assembly is close to the cask inner walls and that the damage is in a large scale (i.e., significant fuel relocation), the more it can be detected by external gamma flux measurements.

  • Contribution to proceedings
    ANS RPSD 2018 - 20th Topical Meeting of the Radiation Protection & Shielding Division of ANS, 26.-31.08.2018, Santa Fe, NM, USA
  • Lecture (Conference)
    ANS RPSD 2018 - 20th Topical Meeting of the Radiation Protection & Shielding Division of ANS, 26.-31.08.2018, Santa Fe, NM, USA

Permalink: https://www.hzdr.de/publications/Publ-27832
Publ.-Id: 27832


Multidentate extracting agents based on calix[4]arene scaffold – UVI/EuIII separation studies

Bauer, A.; Jäschke, A.; Shams Aldin Azzam, S.; Glasneck, F.; Ullmann, S.; Kersting, B.; Brendler, V.; Schmeide, K.; Stumpf, T.

The development of new ligand systems for solvent extraction demands knowledge of the fundamental chemistry behind these processes. Thus, herein, we report the synthesis and structural characterization of a 6-hydroxymethylpyridine functionalized calix[4]arene (L2). Its complexation behavior towards the divalent uranyl cation as well as the trivalent europium cation was spectroscopically studied. In solution the formation of two uranyl complex species with L2 was proven by spectrophotometric titration experiments, with stability constants of log ß1:1 = 5.82±0.04 and log ß2:1 = 5.57±0.05, and of one europium complex species (log ß1:1 = 6.85±0.03). In addition, the concept of the desired proper planar binding pocket for the linear uranyl cation has been verified in solution. Moreover, comparative UVI and EuIII extraction studies with L2 and a structure related 8-hydroxyquinoline modified calix[4]arene (L1) were performed in which the effects of various conditions such as pH of the aqueous phase, presence of relevant anions (sulfate, phosphate, carbonate) and competitive extraction with ethylenediaminetetraacetic acid (EDTA) were investigated. It has been shown that both macrocyclic ligands offer a strong chelate effect, which enables them to extract even stable uranyl hydrolysis species. With these ligands, the selective separation of UVI from EuIII-containing solutions is possible under a variety of conditions.

Keywords: calix[4]arene; uranium(VI); europium(III); liquid-liquid extraction; spectroscopic properties

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Permalink: https://www.hzdr.de/publications/Publ-27831
Publ.-Id: 27831


Complexation of arsenite, arsenate, and monothioarsenate with oxygen-containing functional groups of natural organic matter: An XAS study

Biswas, A.; Besold, J.; Sjöstedt, C.; Gustafsson, J. P.; Scheinost, A. C.; Planer-Friedrich, B.

Arsenic (As) is reported to be effectively sorbed onto natural organic matter (NOM) via thiol coordination and polyvalent metal cation bridged ternary complexation. However, the extent of sorption via complexation to oxygen containing functional groups of NOM is poorly understood. By equilibrating arsenite, arsenate, and monothioarsenate with peat, followed by As K-edge X-ray absorption spectroscopic analysis, this study shows that complexation to the alcoholic groups can be an additional or alternative mode of As sorption to NOM. The extent of complexation was highest for arsenite, followed by monothioarsenate and arsenate. Complexation was higher at pH 7.0 compared to 4.5 for arsenite and arsenate, and vice versa for monothioarsenate due to partial transformation to arsenite at pH 4.5. EXAFS modelling of the As K-edge spectra revealed monodentate and bidentate complexation for arsenite and tridentate complexation for arsenate and monothioarsenate to the alcoholic group. Similarly, the As…C interatomic distance was relatively longer in arsenate- (2.83 ± 0.01 Å) and monothioarsenate-treated peat (2.80 ± 0.02 Å) compared to arsenite-treatment (2.73 ± 0.01 Å). This study implies that depending on acidity of the NOM, arsenate and monothioarsenate can have a higher mobility than arsenite in NOM-rich environments.

Keywords: Arsenic; biogeochemistry; sorption; peat; EXAFS

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Permalink: https://www.hzdr.de/publications/Publ-27830
Publ.-Id: 27830


Review of the electrical characterization of metallic nanowires on DNA templates

Bayrak, T.; Jagtap, N.; Erbe, A.

The use of self-assembly techniques may open new possibilities in scaling down electronic circuits to their ultimate limits. Deoxyribonucleic acid (DNA) nanotechnology has already demonstrated that it can provide valuable tools for the creation of nanostructures of arbitrary shape, therefore presenting an ideal platform for the development of nanoelectronic circuits. So far, however, the electronic properties of DNA nanostructures are mostly insulating, thus limiting the use of the nanostructures in electronic circuits. Therefore methods have been investigated, which use the DNA nanostructures as templates for the deposition of electrically conducting materials along the DNA strands. The most simple such structure is given by metallic nanowires formed by deposition of metals along the DNA nanostructures. Here we review the fabrication and the characterization of the electronic properties of nanowires, which were created using these methods.

Keywords: nanoelectronics; DNA origami; self-assembly; electrical characterization; DNA-origami metalization; DNA metalization

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Permalink: https://www.hzdr.de/publications/Publ-27829
Publ.-Id: 27829


Molecular interactions of fungi with U(VI) studied by microscopic and spectroscopic methods

Wollenberg, A.; Merroun, M.; Guenther, A.; Raff, J.; Stumpf, T.

Fungi play an important role in the microbial community of soil and their metabolic processes can influence the migration of radionuclides in the environment by different interaction processes like mainly sorption, accumulation or mineralization. The immobilization of radionuclides reduces their mobility, which thus prevents also the entry of radionuclide into the water pathway and into the food chain.
For this reasons the aim of this study is to determine the potential of fungi for precautionary radiation protection methods and bioremediation procedures for contaminated soils. In the assessment of the suitability of fungi, the first step is to investigate the molecular interactions with radionuclides in more detail to identify dominant interaction processes. Therefore, binding experiments with different initial conditions were performed and the molecular binding form was investigated with time-resolved laser-induced fluorescence spectroscopy. Furthermore, TEM-EDX analyses were used to determine whether immobilization takes place within the cell or on the cell surface.

Keywords: Fungi; Uranium; TRLFS; TEM-EDX

  • Lecture (Conference)
    Goldschmidt, 12.-17.08.2018, Boston, USA

Permalink: https://www.hzdr.de/publications/Publ-27828
Publ.-Id: 27828


Nachrechnung von Kondensationsversuchen in der COSMEA-Versuchsanlage mit dem Programm ATHLET

Zhang, Y.; Leyer, S.; Geißler, T.; Hampel, U.

Sicherheit ist ein wesentliches Thema im Entwicklungsprozess von Kernkraftwerken. Mehrere Reaktortypen der Generation III und III+ enthalten ein passives Sicherheitssystem zur Unfallkontrolle ohne externe Stromversorgung. Ein Beispiel ist der Notkondensator (EC) des KERENA-Reaktorkonzeptes. Der EC entzieht dem Reaktordruckbehälter bei Störfällen Wärme. Die Versuchsanlage COSMEA am Helmholtz Zentrum Dresden Rossendorf (HZDR) wurde eingerichtet, um die Strömungsmorphologie und die Wärmeübertragungsstruktur der Kondensation in einem leicht geneigten Rohr zu untersuchen. In diesem Beitrag werden Nachrechnung des Kondensationsprozesses in der Versuchsanlage COSMEA mit den thermohydraulischen Systemcode ATHLET vorgestellt. Die Leistungsfähigkeit der ATHLET Wärmeübertragungsmodelle wurde bestimmt. Die Simulationsergebnisse wurden mit den Experimenten verglichen. Der Wärmefluss, die Kondensationsrate und die Temperatur des Kühlwassers während der Kondensation wurden analysiert.

Permalink: https://www.hzdr.de/publications/Publ-27827
Publ.-Id: 27827


Analysis of flow patterns in a rotating packed bed using gamma-ray computed tomography

Bieberle, A.; Gross, K.; Gladyszewski, K.
Researcher: Schubert, Markus

In this study, gamma-ray computed tomography is employed to quantify the liquid hold-up and its distribution in a rotating packed bed using:

  • different insets
  • different rotational speeds
  • different fluid rate flows

Keywords: gas-liquid flow pattern; local liquid hold-up; rotating packed bed; fast imaging; computed tomography

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Permalink: https://www.hzdr.de/publications/Publ-27826
Publ.-Id: 27826


Nanostructuring few-layer graphene films with swift heavy ions for electronic application: tuning of electronic and transport properties

Nebogatikova, N. A.; Antonova, I. V.; Erohin, S. V.; Kvashnin, D. G.; Olejniczak, A.; Volodin, V. A.; Skuratov, A. V.; Krasheninnikov, A. V.; Sorokin, P. B.; Chernozatonskii, L. A.

he morphology and electronic properties of single and few-layer graphene films nanostructured by the impact of heavy high-energy ions have been studied. It is found that ion irradiation leads to the formation of nano-sized pores, or antidots, with sizes ranging from 20 to 60 nm, in the upper one or two layers. The sizes of the pores proved to be roughly independent of the energy of the ions, whereas the areal density of the pores increased with the ion dose. With increasing ion energy (>70 MeV), a profound reduction in the concentration of structural defects (by a factor of 2–5), relatively high mobility values of charge car- riers (700–1200 cm2 V−1 s−1) and a transport band gap of about 50 meV were observed in the nano- structured films. The experimental data were rationalized through atomistic simulations of ion impact onto few-layer graphene structures with a thickness matching the experimental samples. We showed that even a single Xe atom with energy in the experimental range produces a considerable amount of damage in the graphene lattice, whereas high dose ion irradiation allows one to propose a high probability of con- secutive impacts of several ions onto an area already amorphized by the previous ions, which increases the average radius of the pore to match the experimental results. We also found that the formation of “welded” sheets due to interlayer covalent bonds at the edges and, hence, defect-free antidot arrays is likely at high ion energies (above 70 MeV).

Keywords: graphene; ion irradiation

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Permalink: https://www.hzdr.de/publications/Publ-27825
Publ.-Id: 27825


Erratum: Charged Point Defects in the Flatland: Accurate Formation Energy Calculations in Two-Dimensional Materials [Phys. Rev. X 4, 031044 (2014)]

Komsa, H.-P.; Berseneva, N.; Krasheninnikov, A. V.; Nieminen, R. M.

No "expressive" abstract available.

Keywords: 2D materials; first-principles calculaitons

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Permalink: https://www.hzdr.de/publications/Publ-27824
Publ.-Id: 27824


1T phase as an efficient hole injection layer to TMDs transistors: a universal approach to achieve p-type contacts

Hu, X.; Wang, Y.; Shen, X.; Krasheninnikov, A. V.; Sun, L.; Chen, Z.

Recently, the fabricated MoS2 field effect transistors (FETs) with 1T-MoS2 electrodes exhibit excellent performance with rather low contact resistance, as compared with those with metals deposited directly on 2H-MoS2 (Kappera et al 2014 Nat. Mater. 13 1128), but the reason for that remains elusive. By means of density functional theory calculations, we investigated the carrier injection at the 1T/2H MoS2 interface and found that although the Schottky barrier height (SBH) values of 1T/2H MoS2 interfaces can be tuned by controlling the stacking patterns, the p-type SBH values of 1T/2H MoS2 interfaces with different stackings are lower than their corresponding n-type SBH values, which demonstrated that the metallic 1T phase can be used as an efficient hole injection layer for 2H-MoS2. In addition, as compared to the n-type Au/MoS2 and Pd/MoS2 contacts, the p-type SBH values of 1T/2H MoS2 interfaces are much lower, which stem from the efficient hole injection between 1T-MoS2 and 2H-MoS2. This can explain the low contact resistance in the MoS2 FETs with 1T-MoS2 electrodes. Notably, the SBH values can be effectively modulated by an external electric field, and a significantly low p-type SBH value can be achieved under an appropriate electric field. We also demonstrated that this approach is also valid for WS2, WSe2 and MoSe2 systems, which indicates that the method can most likely be extended to other TMDs, and thus may open new promising avenues of contact engineering in these materials.

Keywords: 2D materials; first-principles simulations

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Permalink: https://www.hzdr.de/publications/Publ-27823
Publ.-Id: 27823


Fermi surface reconstruction and dimensional topology change in Nd-doped CeCoIn5

Klotz, J.; Götze, K.; Sheikin, I.; Förster, T.; Graf, D.; Park, J.-H.; Choi, E. S.; Hu, R.; Petrovic, C.; Wosnitza, J.; Green, E. L.

We performed low-temperature de Haas–van Alphen effect measurements on a Ce1−xNdxCoIn5 series, for x = 0.02, 0.05, 0.1, and 1, down to T = 40 mK using torque magnetometry in magnetic fields up to 35 T. Our results indicate that a Fermi surface (FS) reconstruction occurs from a quasi-two-dimensional topology for Nd-2% to a rather three-dimensional one for Nd-5%, thus reducing the possibility of perfect FS nesting. The FS evolves further with increasing Nd content with no observed divergence of the effective mass between Nd-2% and 10%, consistent with the crossing of a spin density wave type of quantum critical point. Our results elucidate the origin of the Q phase observed at the 5% Nd-doping level [Raymond et al., J. Phys. Soc. Jpn. 83, 013707 (2014)].

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Permalink: https://www.hzdr.de/publications/Publ-27822
Publ.-Id: 27822


Spontaneous and field-induced magnetic phase transitions in Dy2Co3Al9: Effects of exchange frustration

Gorbunov, D. I.; Henriques, M. S.; Qureshi, N.; Ouladdiaf, B.; Salazar Mejia, C.; Gronemann, J.; Andreev, A. V.; Petricek, V.; Green, E. L.; Wosnitza, J.

Due to the long-range oscillatory character of RKKY exchange interactions, for Dy2Co3Al9 there exist positive and negative couplings between theDymagnetic moments that lead to magnetic frustration. As a result, the ground state can be easily perturbed, and the system displays a number of spontaneous and field-induced phase transitions. We performed magnetization, magnetic-susceptibility, specific-heat, and electrical-resistivity measurements as well as neutron-diffraction experiments on a single crystal. We find two transitions to distinct incommensurate antiferromagnetic phases at 6.2 and 5.2 K that evolve to a commensurate phase at 3.7 K. In applied magnetic field, new phases emerge. Field-dependent magnetization exhibits a multistep metamagnetic process with sharp transitions accompanied by pronounced magnetoresistance changes. The large number of phases and their complex magnetic structures suggest that the physical properties of Dy2Co3Al9 are ruled by exchange frustration in the presence of a large magnetocrystalline anisotropy.

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  • Secondary publication expected

Permalink: https://www.hzdr.de/publications/Publ-27821
Publ.-Id: 27821


New software protocols for enabling laboratory based temporal CT

Gajjar, P.; Jorgensen, J. S.; Da Assuncao Godinho, J. R.; Johnson, C. G.; Ramsey, A.; Withers, P. J.

Temporal micro computed tomography (CT) allows the non-destructive quantification of processes that are evolving over time in 3D. Despite the increasing popularity of temporal CT the practical implementation and optimisation can be dificult. Here, we present new software protocols that enable temporal CT using commercial laboratory CT systems. The first protocol drastically reduces the need for periodic intervention when making time-lapse experiments, allowing a large number of tomograms to be collected automatically.
The automated scanning at regular intervals needed for uninterrupted time-lapse CT is demonstrated by analysing the germination of a mung bean (vigna radiata), whilst the synchronisation with an in-situ rig required for interrupted time-lapse CT is highlighted using a shear cell to observe granular segregation. The second protocol uses golden-ratio angular sampling with an iterative reconstruction scheme and allows the number of projections in a reconstruction to be changed as sample evolution occurs. This overcomes the limitation of the need to know a priori what the best time window for each scan is. The protocol is evaluated by studying barite precipitation within a porous column, allowing a comparison of spatial and temporal resolution of reconstructions with different numbers of projections. Both of the protocols presented here have great potential for wider application, including, but not limited to, in-situ mechanical testing, following battery degradation and chemical reactions.

Keywords: tomography; time-lapse; minerallization; porous media

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Permalink: https://www.hzdr.de/publications/Publ-27820
Publ.-Id: 27820


Applying the Serpent-DYN3D Code Sequence for the Decay Heat Analysis of Metallic Fuel Sodium Fast Reactor

Pereira, G.; Johnson, A. E.; Bilodid, Y.; Fridman, E.; Kotlyar, D.

Recent developments of the reactor dynamics code DYN3D have introduced the micro-depletion model which allows for explicit calculation of radioactive decay heat. Such a unique combination of nodal diffusion, thermal hydraulic (T/H) and depletion solvers allows DYN3D to perform fuel cycle depletion and obtain detailed core isotopic concentration and decay heat distributions. The new sequence utilizes considerably less computational resources than coupled Monte Carlo-T/H-depletion systems, but with comparable accuracy. This capability was recently tested on a limited number of simple unit cell models. The main objective of this work is to further verify the decay heat calculation capabilities of DYN3D by applying it to a considerably more realistic and detailed full core model. For the purpose of the current analysis a 3D full core model of Advanced Burner Reactor (ABR) was adopted from the OECD/NEA Benchmark for Neutronic Analysis of Sodium-Cooled Fast Reactor Cores with Various Fuel Types and Core Sizes. In this work, the Monte Carlo code Serpent was used to generate macro- and microscopic parameters, and the neutron diffusion code, DYN3D, was used to perform neutronic and depletion analyses. Detailed spatial isotopic and decay heat distributions obtained with DYN3D were verified against the equivalent Serpent reference 3D full core solution. Results indicate very good agreement between the Serpent-DYN3D code sequence and the reference Serpent solutions, with a discrepancy in total decay heat on the order of 0.5%.

Keywords: Decay heat; cross section generation; microscopic depletion; DYN3D

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Permalink: https://www.hzdr.de/publications/Publ-27819
Publ.-Id: 27819


Experimental investigation of the froth height in columns with sandwich packings

Sohr, J.; Schubert, M.; Flechsig, S.; Kenig, E. Y.; Hampel, U.

Sandwich packings, consisting of alternatingly stacked conventional structured packings with different geometric surface areas, are promising to increase capacity and efficiency of separation columns. Film and froth flow evolve along a stack, which requires comprehensive fluid dynamic analysis. In particular, the froth height is an essential parameter to determine the spatial extent of the flow regimes. Ultrafast X-ray tomography and a 3D-printed pressure drop profile measurement module were applied to independently estimate this parameter. The results are compared with existing correlations.

Keywords: fluid dynamics; froth height; pressure drop; sandwich packing; ultrafast X-ray tomography

Permalink: https://www.hzdr.de/publications/Publ-27818
Publ.-Id: 27818


Rate-based-Modellierung von CO₂-Absorptionskolonnen mit Anstaupackungen

Flechsig, S.; Borgolte, T.; Utchenko, Y.; Sohr, J.; Schubert, M.; Hampel, U.; Kenig, E. Y.

Die Effizienz von Trennkolonnen für Fluidgemische kann durch die Anwendung von Anstaupackungen gesteigert werden. Dabei entstehen im Betrieb belastungsabhängige, in ihrer Trennwirkung unterschiedliche Regime. Um die Auswirkungen der einzelnen Strömungsregime in einem Modell erfassen zu können, werden sowohl Trennleis-tungsmessungen als auch tomographische Methoden verwendet. Ein rate-based-Modell wird vorgestellt, in dem die heterogenen Strömungsformen in Anstaupackungen mittels geeigneter Korrelationen berücksichtigt werden. Das Modell wird anhand gemessener Daten zur CO₂-Absorption getestet.

Permalink: https://www.hzdr.de/publications/Publ-27817
Publ.-Id: 27817


Access to 18F-labelled isoxazoles by Ruthenium-promoted 1,3-dipolar cycloaddition of 4-[18F]fluoro-N-hydroxybenzimidoyl chloride with alkynes.

Roscales, S.; Kniess, T.

4-[18F]Fluoro-N-hydroxybenzimidoyl chloride (18FHBIC) was developed as an 18F-labelled aromatic nitrile oxide precursor. The building block is obtained in a one-pot synthesis in up to 79% radiochemical yield starting from [18F]fluoride in 50 min with 4-[18F]fluorobenzaldehyde (18FBA) and 4-[18F]fluorobenzaldehyde oxime (18FBAO) as intermediates, including the reaction of 18FBAO with N-chlorosuccinimide (NCS) as a key step. 18FHBIC was found to be a suitable and stable synthon to give access to 18F-labelled 3,4-diarylsubstituted isoxazoles by [Cp*RuCl(cod)]-catalyzed 1,3-dipolar cycloaddition with various alkynes. By way of example, the radiosynthesis of a fluorine-18 labelled COX-2 inhibitor [18F]1b, a close derivative of valdecoxib, was performed by 1,3-dipolar cycloaddition of 18FHBIC with 1-ethynyl-4-(methylsulfonyl)benzene, providing purified [18F]1b in RCY up to 40% starting from [18F]fluoride in 85 min. The application of 18FHBIC as a building block in the synthesis of 18F-labelled heterocycles will generally extend the portfolio of available PET radiotracers.

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Permalink: https://www.hzdr.de/publications/Publ-27816
Publ.-Id: 27816


Experimental investigations and rate-based modeling of CO₂ absorption with sandwich packings

Flechsig, S.; Sohr, J.; Schubert, M.; Hampel, U.; Kenig, E. Y.

In the process industry, packed columns are used in a variety of fluid separation operations, e.g. in distillation and absorption, in order to create a desirable flow pattern of two-phase systems. Due to the high energy requirements of separation processes, the interest on their optimization is vital. In particular, column internals have permanently been the focus of investigations.
An improvement of the separation efficiency can be achieved by the application of sandwich packings. The latter consist of two alternating layers of industrially available standard packings with different specific surface areas, one with lower (the so-called holdup layer) and another with higher (the so-called de-entrainment layer) capacity. Sandwich packings are typically used at operating conditions between the flooding points of holdup layer and de-entrainment layer. Above the holdup layer, a froth sublayer is formed, which reveals high separation efficiency due to intensified phase mixing. In the upper section of the de-entrainment layer, film-like flow patterns can be observed [1]. Under certain conditions, this intensive heterogeneous flow pattern can be used in a beneficial way for fluid separation processes. However, the application of this integrated packing type is hindered by lacking validated design methods [2].
An accurate prediction of the performance characteristics is essential for the design of sandwich packings. In our project, the effects of the individual flow regimes on fluid dynamics and mass transfer are investigated complementarily with both experimental and theoretical studies. In order to determine the impact of each individual flow regime, experiments on an absorption/desorption plant are supplemented by flow imaging measurements of sandwich packings. At the Paderborn University, CO2 absorption is examined in a pilot plant for various design and operating parameters. This plant allows measuring temperature profiles of the gas phase as well as concentration profiles of both phases. At the Helmholtz-Zentrum Dresden-Rosendorf, a detailed view on the phase distribution within the sandwich packings is realized bymeans of an ultrafast X-ray tomography. The measured data from both experimental methods are used to establish correlations for mass transfer coefficients, interfacial area, holdup and pressure drop, which are applied in a rate-based stage model for CO2 absorption processes with aqueous amine solutions.
The absorption experiments were performed under ambient conditions in a column with an inner diameter of 0,1 m and 3,2 m packing height. The influence of different operating and design parameters on the separation characteristics in sandwich packings was studied in order to identify appropriate operating conditions and to provide a sufficient basis for the experimental validation of a model, which is able to describe the heterogeneous flow patterns. In particular, we investigated the impact of the holdup-layer height and its corresponding specific surface area. In addition, the inclination angle of the flow channels in the de-entrainment layer was varied.
The rate-based approach, which accounts for the specifics of different column internals via correlations, was applied. We expected that different fluid dynamic regimes would have different impacts on the mass transfer. Therefore, each fluid dynamic regime was considered individually. The column was represented as a sequence of alternating segments, and each segment was described by a corresponding set of correlations. Experimental data of the CO2 absorption with sandwich packings were then compared with simulation results.
Acknowledgments
The authors are grateful to the Deutsche Forschungsgemeinschaft (DFG) for financial support (KE 837/26-1, HA 3088/10-1).
References
[1] U. Brinkmann, B. Kaibel, M. Jödecke, J. Mackowiak, E.Y. Kenig: Beschreibung der Fluiddynamik von Anstaupackungen, Chemie Ingenieur Technik 84, 36-45 (2012).
[2] Ö. Yildirim, E.Y. Kenig: Rate-based modelling and simulation of distillation columns with sandwich packings, Chemical Engineering and Processing: Process Intensification 98, 147-154 (2015).

  • Lecture (Conference)
    ACHEMA Congress 2018, 11.-15.06.2018, Frankfurt am Main, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-27815
Publ.-Id: 27815


Messung des 478 keV Gammaproduktionsquerschnitts nach inelastischer Streuung an ⁷ Li

Frotscher, A.

The inelastic neutron cross section of 7Li has no sharp resonances and a fairly low threshold of 546 keV. Below the breakup threshold at 5291 keV only one gamma-ray is emitted at E = 477,6 keV. It is therefore suited as a reference cross section. Lithium has technical usage as a 3H-producer in future fusion reactors as well as in molten salt reactors. But there are recent measurements disagreeing with already evaluated data. To resolve this dissonance, an 170 h Experiment was carried out at the nELBE facility of the HZDR. A 4 mm thick LiF-disk was used as a target, the neutron flux was determined with a 235U parallel plate fission chamber. The flight path for the 7Li(n,n’ )7Li reaction was 8,3 m. As detectors four two-inch LaBr3-detectors as well as three three-inch LaBr3-detectors and two miniball-type HPGe detectors with three 60 % crystals each were used. The measurement of the cross section is solely a measurement of the de-excitation of the first exited 7Li-State at 477,6 keV. The second exited state at 4,63 MeV already decays via particle emission and thus does not contribute any gamma-radiation. The experiment benefits from the high neutron flux at nELBE (80 n/s/keV @ 1 MeV) as well as from the precise fission chamber of the PTB (H19) for the neutron flux calibration. A Geant4-Simulation is used to determine correction factors as the transmission from the H19 to the target as well as the multiple scattering correction and the self absorption of the 477,6 keV Gamma-Rays. The deduced cross section from both detector types are consistent, but they can’t reproduce the data from Nyman et al. The deviations are up to 20 %. The half life of the by means of bremsstrahlung in air produced positroniums in the experiment is 116(7) ns.

Keywords: nELBE; inelastic neutron scattering; fast neutrons; Li-7

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  • Master thesis
    TU Dresden, 2017
    Mentor: Dr. Arnd Junghans

Permalink: https://www.hzdr.de/publications/Publ-27814
Publ.-Id: 27814


[MnO|SiO2,Al2O3,FeO,MgO] balanced log-ratio in chlorites-a tool for chemo-stratigraphic mapping and proxy for the depositional environment

Süssenberger, A.; Pospiech, S.; Schmidt, S.

The [MnO|SiO2,Al2O3,FeO,MgO] balanced ratio, i.e. the isometric log-ratio of the MnO concentration relative to the concentration of SiO2, Al2O3, FeO, and MgO of chlorite and of whole rock composition is an effective discriminant between Mesozoic stratigraphic formations in the Magallanes Basin (Chile). The MnO content in chlorite is only controlled by the host rock chemistry and is dependent on the geological environment. The MnO content in chlorite remains unchanged at low-grade metamorphic conditions. Single grain chlorite analysis (n > 1000, electron microprobe) and whole rock analysis (n = 40, X-ray fluorescence) was used to discriminate stratigraphic formations and to decipher differences in the depositional environment in the Magallanes Basin. The samples are from one Upper Jurassic and three Cretaceous sedimentary units which were affected either by low-grade regional metamorphism or by Miocene contact metamorphism. The highest [MnO|SiO2,Al2O3,FeO,MgO] values are recorded in the upper Zapata Formation. The Punta Barrosa, Cerro Toro and Tobífera Formations show slightly lower [MnO|SiO2,Al2O3,FeO,MgO] values. Elevated [MnO|SiO2,Al2O3,FeO,MgO] values at the transition between Zapata and Punta Barrosa Formation record an oxygenated shallow marine environment that can be linked to the closure of the Rocas Verdes Basin and the onset of fold- and -thrust belt formation. Decreasing [MnO|SiO2,Al2O3,FeO,MgO] values from the Punta Barrosa towards the Cerro Toro Formation indicate gradually increasing water depths during the Upper Cretaceous which correlate well with the global sea level.

Keywords: chlorite; compositional data; low-grade metamorphism; depositional environment; Magallanes Basin

Permalink: https://www.hzdr.de/publications/Publ-27812
Publ.-Id: 27812


Fano signatures between intersubband and ponderomotive responses in MQW structures

Pedroso, D. D. M.; Schmidt, J.; Passaro, A.; Helm, M.; Schneider, H.

We present an in-depth theoretical and numerical discussion on the Fano signatures observed in differential transmission spectra obtained from multiquantum well structures. These signatures stem from ponderomotive and intersubband polarization currents modified by the coupling between the optical responses of different layers. A detailed discussion of this process is provided, evaluating quantitatively the amplitude and shape of the Fano signatures and their dependence on structural parameters, such as carrier concentration and layer width. The theoretical model described here aims to predict quantitatively the weight of the contributions of the ponderomotive currents in relation to the intersubband ones. In order to include the effect of the entire structure in the theoretical spectra, the optical response of each layer is addressed within the density matrix formalism and encompassed in an optical transfer matrix. This method also ensures the correct inclusion of the phase sensitive superposition of optical responses of different layers on which the Fano signatures are based. Numerical simulations obtained from the presented theoretical approach are in excellent agreement with the behaviour observed in previous experiments.

Keywords: Fano interference; intersubband transition; free-carrier absorption; GaAs; multiple quantum well; MQW

Permalink: https://www.hzdr.de/publications/Publ-27811
Publ.-Id: 27811


Uranium(VI) complexation with aqueous silicates in the acidic to alkaline pH-range

Lösch, H.; Tits, J.; Marques, M.; Baeyens, B.; Stumpf, T.; Huittinen, N.

INTRODUCTION
An important parameter for safety assessments of radioactive waste respositories is the prediction and modelling of aqueous complex formation reactions between actinides and common dissolved inorganic and organic ligands. For this assessment, the knowledge of dissolved ligands in the groundwater produced by dissolution of waste canisters, backfill material, and host rock is required. Due to the ubiquitous existence of silicon in these materials, aqueous silicate species are important ligands to consider in the metal-ligand speciation, especially in contact zones of cement pore water with clay or granite where high silicate concentrations are expected as a result of alteration processes [1]. Depending on the used host rock and backfill material, the pH of the groundwater will vary between the neutral to alkaline range. However, in this pH-range, reported An-Si species are scarce or non-existent, and there is a lack of reliable thermodynamic data. In the acidic pH-range, only the 1:1 An(VI)-Si complex, i.e. An(VI)O ₂OSiOH₃+, is known for U(VI), Np(VI), and Pu(VI), and the complex formation constants differ by one order of magnitude.
In the alkaline pH-range (pH ~8), Yusof et al. [3] postulated the formation of either a ternary Pu-OH-Si PuO₂(H₂O)₃(OH)OSi(OH)₃ complex with the H₃SiO₄- ligand or a binary Pu-Si PuO₂(H₂O)₃O₂Si(OH)₂ complex with H₂SiO₄ ²-. For other hexavalent actinides, no complexes in the alkaline pH-range have been reported, however, following the analogy of the hexavalent cations comparable complexes should also exist for U(VI) and Np(VI).

Experimental
In this study the in-situ speciation of U(VI) in solution in the presence of silicates was monitored with laser-induced luminescence spectroscopy (TRLFS) and , the Schubert method. For the TRLFS measurements, a U(VI) concentration of 5×10-⁶ M was used, while the silicon concentration was varied between 3×10-⁴ and 2×10-³ M depending on the pH. Temperature-dependent measurements were performed in the T-range from 1°C to 40°C to improve the signal to noise ratio and to enable the extraction of thermodynamic parameters, such as the enthalpy ΔRH° and entropy ΔRS° of reaction. The TRLFS measurements were performed at two excitation wavelengths of 266 nm and 394 nm.
In the Schubert method, the desorption of U(VI) from an inert solid phase as a result of silicate complex formation in solution, is monitored. Here, monoclinic ZrO₂ was used as a solid phase and investigations were performed for a U(VI) concentration of 1×10-⁷ M and silicate concentrations between 5×10-⁵ and 5×10-³ M, at pH values ranging from 7.0 to 11.5. LSC measurements of the 233U activity were used to determine the U(VI) concentration in solution.

RESULTS
Based on the TRLFS investigations in the acidic pH-range, the formation of the 1:1 U-Si complex UO₂OSi(OH)₃+ could be confirmed in addition to a hitherto unidentified silicate species. The normalized emission spectra clearly show a change in the peak shape with increasing silicate concentration. Next to the change in the spectral shape, a significant increase in the luminescence intensity could be observed. Such an increase of the luminescence intensity speaks for the formation of a polynuclear U(VI)-silicate complex. However, investigations to confirm this hypothesis are still ongoing.

In the alkaline pH-range it was possible to identify a ternary U-OH-Si complex, most likely either a monodentate UO₂(OH)₂OSi(OH)₃- or a bidentate UO ₂(OH)OSi(OH)₂- complex with a complex formation constant of logβ0 = -15.6. Preliminary speciation calculations in clay and cement pore water show, that this ternary U-OH-Si will dominate the U(VI) speciation in the pH-range between 9.0 and 11.5. To resolve the stoichiometry of this complex, TRLFS investigations are planned together with complementary DFT calculations.

REFERENCES

1. D. SAVAGE, Mineralogical Magazine, 75, 2401-2418 (2011).
2. R. GUILLAUMONT, Update on the chemical thermodynamics of Uranium, Neptunium, Plutonium, Americium and Technetium 5, p. 252, Nuclear Energy Agency, Elsevier Science Publisher (2003).
3. A.B. YUSOF, A.M. FEDOSEEV, Russ. J. Coord. Chem., 29, 582-590, (2003).

  • Poster
    Plutonium Futures 2018, 09.-14.09.2018, San Diego, USA

Permalink: https://www.hzdr.de/publications/Publ-27810
Publ.-Id: 27810


Quantitative predictions of LWFA simulation with PIConGPU - from improved modeling to new measurement methods via synthetic radiation diagnostics

Pausch, R.; Debus, A.; Schramm, U.; Bussmann, M.; Steiniger, K.; Widera, R.; Huebl, A.; Garten, M.; Irman, A.; Couperus, J.; Zarini, O.; Köhler, A.

In a close interplay between particle-in-cell simulations and experimental measurements, we present new insights into the modeling of laser wakefield accelerators and discuss the arising challenges for laboratory diagnostics. These challenges were tackled by developing new methods for determining key parameters of the experiment by studying synthetic radiation diagnostics predicted by simulations.

The combination of an unprecedented experimental campaign studying the parameter dependence of beam loading during LWFA and an accompanying, extensive simulation campaign using the 3D3V particle-in-cell code PIConGPU made it possible to provide unique feedback between experiment and theory. This poster shows the step-by-step improvements through this interplay from the simulation perspective. Quantitatively more accurate methods such as the use of Gauss-Laguerre modes or a variety of ionization models are presented as well as more performant computationally procedures. Only through these improvements could the dynamics occurring in the experiment be reproduced and a deeper insight into the self-truncated ionization injection method be gained.

Moreover, this interplay also revealed the limits of current laboratory diagnostics. Synthetic in-situ radiation diagnostics in PIConGPU instigated the development of new diagnostic methods for experiments. For example, the shift of the laser focus position, compared to the vacuum, due to self-focusing in the plasma can now be quantified by spectral radiation signatures. Applying these new methods will enable an even more accurate understanding of laser plasma dynamics in experiments in the near future.

Keywords: Radiation; LWFA; aprticle-in-cell; PIConGPU

  • Poster
    The fourth annual meeting of the programme "Matter and Technologies", 12.-14.06.2018, Berlin, Deutschland
  • Lecture (Conference)
    The fourth annual meeting of the programme "Matter and Technologies", 12.-14.06.2018, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-27809
Publ.-Id: 27809


The cosmic-ray exposure history of the big iron Twannberg (IIG) meteorite

Smith, T.; Hofmann, B. A.; Leya, I.; Merchel, S.; Rugel, G.; Pavetich, S.; Scharf, A.

Introduction: The Twannberg iron meteorite is one out of only six members of the group IIG. This group of iron meteorites is characterized by large amount of schreibersite (Fe,Ni) ₃P, and usually low Ni contents (Hofmann et al., 2009#). With the recent new finds (n = 1119 samples, total recovered mass: ~118 kg, up to June 30th, 2018, communication B. A. Hofmann) we have the opportunity to reinvestigate the cosmic-ray exposure history of Twannberg, with a special focus on its terrestrial age, in order to better understand the distribution of the different masses in the context of the last glaciation occurrences in Europe.
Experimental methods: The isotopic concentrations for He, Ne, and Ar have been measured by noble gas mass spectrometry at the University of Bern, following the procedures described earlier (Ammon et al., 2008#, 2009#). Analyses of the cosmogenic radionuclides (i.e., 10Be, 26Al, 36Cl, and 41Ca) have been performed at the DREsden Accelerator Mass Spectrometry facility (DREAMS, Akhmadaliev et al., 2013#) using chemical procedures previously described in Merchel et al. (1999#). In this work, we measured the cosmogenic noble gas and radionuclide concentrations in 14 and 7 Twannberg samples, respectively, from different find locations (Gruebmatt, Twannbach, and Mont Sujet, cf. Figure 1, Smith et al., 2017#).
Fig. 1. Find locations of Twannberg specimens until June 1st, 2016 (n = 570). The larger (red) squares indicate the find locations of the fragments analyzed in this work. The find location of the first mass (TW1, 15.915 kg) is indicated. Red arrow on Mont Sujet is the linear correlation of all Sujet finds and an approximation of the fall direction. LGM = last glacial maximum based on Bini et al. (2009#); OGM = Older glacial maximum (probably corresponding to Beringen/Riss) corresponding to the upper limit of the occurrence of alpine drift (see the Geological Setting section). The area south of the LGM/OGM lines was covered by alpine ice and the general direction of ice flow was from southwest to northeast. The blue arrow indicates the probable transport vector of Gruebmatt meteorites during the Beringen/Riss glaciation. Contour interval is 100 m.
Results and Discussion: First, we observe a wide range of both cosmogenic noble and radionuclide concentrations, e.g. after corrections (i.e. for trapped components, sulfur and/or phosphorus contributions, cf. Smith et al., 2017#), the cosmogenic 21Necos and 38Arcos concentrations vary by factors of 190 and 110, respectively. Based on model calculation (Ammon et al., 2008#), the observed variation of more than two orders of magnitude within all measured samples is only possible when considering a meteoroid with a minimum preatmospheric radius of ~165 cm.
Another approach is to use the cosmogenic (4He/21Ne)cos ratio as a shielding indicator; doing so, we estimate the preatmospheric radius to be ~250 cm.
To conclude, based on both the spread in cosmogenic noble gases and the (4He/21Ne)cos ratio, we infer Twannberg to have a minimum preatmospheric radius in the range of ~2 m, which, when assuming a density of ~7.8 g cm-3, would correspond to a minimal mass of ~250 tons.
Second, we calculated the cosmic-ray exposure (CRE) age of Twannberg using the well-adopted 36Cl-36Ar method (e.g. Lavielle et al., 1999#). We determined an average CRE age of 182±41 Ma. Note that this value is slightly different from the one that has been recently published in Smith et al. (2017#), due to the fact we are now using a new 41Ca half-life of 0.995×10⁵ years (Jörg et al., 2012#) instead of the previous value of 1.04×10⁵ years (Kutschera and Ahmad, 1992#). This modifies the terrestrial age (cf. below), and in return decreases the CRE age by ~5%. However, the new CRE age is still in agreement with the CRE age of 230±50 calculated previously by Hofmann et al. (2009#), as well determined using the 36Cl-36Ar method.
Third, based on new Monte-Carlo calculations, we used the 36Cl-41Ca radionuclide pair to calculate the terrestrial age of Twannberg; we found an age of 190±48 ka. Again, this age is slightly different from the one we reported in Smith et al. (2017#) since we are using here the new 41Ca half-life (cf. above). This terrestrial age, although quite surprising when considering the humid conditions in Switzerland, is 1) consistent with geological evidences (Hofmann et al., 2009; Smith et al., 2017#); and 2) indicates that the Twannberg meteorite fell most likely during or before the second last glaciation in Europe, 185-130 ka ago. This reveals that some of the masses have been glacially transported from an initial position west of Mont Sujet, in the direction of east-northeast (cf. Figure 1).
Acknowledgments: This study heavily relies on samples collected in a great effort by a joint group of meteorite enthusiasts and scientists. We particularly thank for the collaboration and samples: Marc Jost, Manuel Eggimann, Hannes Weiss, Sergey Vasiliev, Andreas Koppelt, Ernst Wyler, Gino Bernasconi, Marcel Häuselmann, and Edwin Gnos. Parts of this research were carried out at the Ion Beam Centre (IBC) at the Helmholtz-Zentrum Dresden-Rossendorf e. V., a member of the Helmholtz Association. This work was supported by the Swiss National Science Foundation (SNF).
References:
Akhmadaliev S. et al. 2013. Nuclear Instruments and Methods in Physic B 294:5-10
Ammon K. et al. 2008. Meteoritics and Planetary Science 43:685-699
Ammon K. et al. 2011. Meteoritics and Planetary Science 46:785-792
Bini A. et al. 2009. Die Schweiz während des letzteiszeitlichen Maximums (LGM), Map 1:500000. Bern: Swiss Federal Office of Topography
Hofmann B. et al. 2009. Meteoritics and Planetary Science 44:187-199
Jörg G. et al. 2012. Geochimica et Cosmochimica Acta 88:51-65
Kutschera W. et al. 1992. Radiocarbon 34(3):436-446
Lavielle B. et al. 1999. Earth and Planetary Science Letters 170:93-104
Merchel S. and Herpers U. 1999. Radiochimica Acta 84:215-219
Smith T. et al. 2017. Meteoritics and Planetary Science 52:2241-2257

Keywords: AMS; cosmogenic nuclide; meteorite

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  • Lecture (Conference)
    Annual Meeting of the Chinese Geoscience Union (CGU), 21.-24.10.2018, Beijing, China

Permalink: https://www.hzdr.de/publications/Publ-27808
Publ.-Id: 27808


Three-Dimensional Composition and Electric Potential Mapping of III−V Core−Multishell Nanowires by Correlative STEM and Holographic Tomography

Wolf, D.; Hübner, R.; Niermann, T.; Sturm, S.; Prete, P.; Lovergine, N.; Büchner, B.; Lubk, A.

The nondestructive characterization of nanoscale devices, such as those based on semiconductor nanowires, in terms of functional potentials is crucial for correlating device properties with their morphological/materials features, as well as for precisely tuning and optimizing their growth process. Electron holographic tomography (EHT) has been used in the past to reconstruct the total potential distribution in three dimension but hitherto lacked a quantitative approach to separate potential variations due to chemical composition changes (mean inner potential, MIP) and space charges. In this letter, we combine and correlate EHT and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) tomography on an individual ⟨111⟩ oriented GaAs-AlGaAs core-multishell nanowire (NW). We obtain excellent agreement between both methods in terms of the determined Al concentration within the AlGaAs shell, as well as thickness variations of the few nanometer thin GaAs shell acting as quantum well tube. Subtracting the MIP determined from the STEM tomogram enables us to observe functional potentials at the NW surfaces and at the Au-NW interface, both ascribed to surface/interface pinning of the semiconductor Fermi level.

Keywords: GaAs-AlGaAs; III−V nanowire; 3D elemental mapping; functional potential; quantum well tube; tomography; holography

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Permalink: https://www.hzdr.de/publications/Publ-27807
Publ.-Id: 27807


Terahertz pump-induced anisotropy and nonlinear susceptibility in graphene

Schneider, H.; König-Otto, J. C.; Mittendorff, M.; Winzer, T.; Kadi, F.; Malic, E.; Knorr, A.; Wang, Y.; Belyanin, A.; Pashkin, A.; Helm, M.; Winnerl, S.

We report on investigations of the carrier dynamics in graphene close to the Dirac point by nonlinear terahertz spectroscopy. At terahertz frequencies and low temperatures, optical-phonon scattering is suppressed. In this case, the decay of the pump-induced anisotropy in the carrier distribution is observed to be very slow, long as several ps, which is theoretically explained by non-collinear Coulomb scattering. In Landau-quantized graphene, degenerate four-wave mixing experiments in resonance to the lowest Landau level transition allow us to investigate the induced coherent polarization and to compare its dependence on THz field strength and B-field detuning with theoretical expectations.

Keywords: graphene; nonlinear terahertz spectroscopy; nonlinear susceptibility; pump-probe

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  • Poster
    34-th International Conference on the Physics of Semiconductors (ICPS 2018), 29.07.-03.08.2018, Montpellier, Frankreich

Permalink: https://www.hzdr.de/publications/Publ-27805
Publ.-Id: 27805


High-performance and room-temperature QWIPs & terahertz spectroscopy

Schneider, H.

The topic of this seminar talk is high-performance and room-temperature quantum well photodetectors and terahertz spectroscopy.

Keywords: quantum well infrared photodetector; terahertz spectroscopy

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  • Lecture (others)
    Seminarvortrag, Yunnan University, 03.05.2018, Kunming, China

Permalink: https://www.hzdr.de/publications/Publ-27804
Publ.-Id: 27804


Nonlinear THz spectroscopy of graphene and GaAs quantum wells using a free-electron laser

Schneider, H.

This talk reviews some recent experiments using FEL-based intense narrow-band terahertz fields, in particular pump-induced optical anisotropy and nonlinear four-wave mixing in graphene, and dressing of excitons, exciton-polaritons, and intersubband transitions in GaAs quantum wells.

Keywords: nonlinear terahertz spectroscopy; graphene; interaubband; exciton

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  • Invited lecture (Conferences)
    The 9th International Symposium on Ultrafast Phenomena and Terahertz Waves (ISUPTW 2018), 23.-26.04.2018, Changsha, China
  • Invited lecture (Conferences)
    International Conference on "Synchrotron and Free electron laser Radiation: generation and application" (SFR-2018), Budker Institute of Nuclear Physics, 25.-28.06.2018, Novosibirsk, Russische Föderation

Permalink: https://www.hzdr.de/publications/Publ-27803
Publ.-Id: 27803


Nonlinear THz free-electron laser spectroscopy of graphene and GaAs quantum wells

Schneider, H.

This talk reviews some recent experiments on graphene and on GaAs quantum wells using FEL-based strong THz fields.
In graphene, we have investigated the pump-induced anisotropy of the carrier distribution upon excitation with linearly polarized light. Since optical-phonon scattering is suppressed at THz frequencies and low temperatures, we observe the decay of this anisotropy to be very slow, as long as several ps, which is theoretically explained by non-collinear Coulomb scattering. We also report on degenerate four-wave mixing experiments in Landau-quantized graphene to investigate the induced coherent polarization. In GaAs quantum wells, intense narrow-band THz fields are exploited for dressing elementary electronic excitations. We will address THz-induced dressing of excitons, exciton-polaritons, and intersubband transitions.

Keywords: Graphene; intersubband; nonlinear terahertz spectroscopy

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  • Lecture (others)
    Seminarvortrag, University of California at Santa Barbara (UCSB), 05.02.2018, Santa Barbara, USA
  • Lecture (others)
    Physikalisches Kolloquium der TU Chemnitz, 13.06.2018, Chemnitz, Deutschland
  • Lecture (others)
    Seminar, Chengdu Campus of CAEP, 23.07.2018, Chengdu, China

Permalink: https://www.hzdr.de/publications/Publ-27802
Publ.-Id: 27802


Terahertz orientational relaxation and phase relaxation in graphene

Schneider, H.; König-Otto, J. C.; Mittendorff, M.; Winzer, T.; Kadi, F.; Malic, E.; Knorr, A.; Wang, Y.; Belyanin, A.; Pashkin, A.; Helm, M.; Winnerl, S.

We report on investigations of the carrier dynamics in graphene close to the Dirac point by nonlinear terahertz spectroscopy. At terahertz frequencies and low temperatures, optical-phonon scattering is suppressed. In this case, the decay of the pump-induced anisotropy in the carrier distribution is observed to be very slow, long as several ps, which is theoretically explained by non-collinear Coulomb scattering. In Landau-quantized graphene, degenerate four-wave mixing experiments in resonance to the lowest Landau level transition allow us to investigate the induced coherent polarization and to compare its dependence on THz field strength and B-field detuning with theoretical expectations.

Keywords: graphene; nonlinear terahertz spectroscopy; nonlinear susceptibility; four-wave mixing; pump-probe

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  • Lecture (Conference)
    SPIE Photonics West, Symposium on "Ultrafast Phenomena and Nanophotonics XXII", 27.01.-01.02.2018, San Francisco, USA

Permalink: https://www.hzdr.de/publications/Publ-27801
Publ.-Id: 27801


Halbleitertechnik im Osten der Republik

Skorupa, W.

Eingeladener Vortrag anlässlich des Workshops zum 60. Gründungsjubiläum des Institutes für Halbleitertechnik an der Universität Stuttgart mit Bezug zur Ionenstrahlphysik und -technologie am Forschungsstandort Dresden-Rossendorf, jetzt Helmholtzzentrum Dresden-Rossendorf

Keywords: Halbleitertechnik; Chiptechnologie; DDR; Geschichte; Ionenstrahlphysik; Ionenstrahltechnologie

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  • Invited lecture (Conferences)
    Workshop anlässlich des 60. Jahrestages des Institutes für Halbleitertechnik an der Universität Stuttgart, 01.08.2018, Stuttgart, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-27800
Publ.-Id: 27800


Incorporating analytical errors in log-ratio based compositional discriminant analysis

Pospiech, S.; Tolosana-Delgado, R.

Uncertainties in the measurement of the geochemical composition of various sample materials are rarely included for statistical analyses of the data.
In case of log-ratio methods, incorporating errors in the analysis has even not yet been done, up to the authors' knowledge.
Many calibration procedures provide relative cell-wise errors, which can be conveniently combined to deliver error assessments for any set of log-ratios.
In this contribution we incorporate all these errors in estimates of the mean vector and covariance matrix of the data on a particular log-ratio.
Thanks to the linear/bilinear relation between mean/covariance estimates among different log-ratio representations, such error-integrating estimates are affine equivariant.
These means and covariances are the building blocks of many statistical analysis.
Here we focus on developing an error-integrating Fisher rule, but the methodology can be readily applied to other linear models with compositional variables, like regression or ANOVA.
In general, results show that the incorporation of errors produce a more conservative (and honest) assessment of the discrimination direction and separability of the subpopulations considered.
The application of using cell-wise errors and its impact on interpretation of results will be shown by case studies of geochemical composition of tea plants in relation to geological source rock.

  • Open Access Logo Contribution to proceedings
    IAMG2018 19th Annual Conference, 02.-08.09.2018, Olomouc, Czech Republic
    Prodeedings of IAMG2018

Permalink: https://www.hzdr.de/publications/Publ-27799
Publ.-Id: 27799


All-optical quantum thermometry based on spin-level cross-relaxation and multicenter entanglement under ambient conditions in SiC

Anisimov, A. N.; Soltamov, V. A.; Breev, I. D.; Babunts, R. A.; Mokhov, E. N.; Astakhov, G.; Dyakonov, V.; Yakovlev, D. R.; Suter, D.; Baranov, P. G.

All-optical thermometry technique based on the energy level cross-relaxation in atomic-scale spin centers in SiC is demonstrated. This technique exploits a giant thermal shift of the zero-field splitting for centers in the triplet ground state, S=1, undetected by photoluminescence (so called “dark” centers) coupling to neighbour- ing spin-3/2 centers which can be optically polarized and read out (“bright” centers), and does not require radiofrequency fields. EPR was used to identify defects. The width of the cross-relaxation line is almost an order of magnitude smaller than the width of the excited state level-anticrossing line, which was used in all-optical ther- mometry and which can not be significantly reduced since determined by the lifetime of the excited state. With approximately the same temperature shift and the same sig- nal intensities as for excited state level-anticrossing, cross-relaxation signal makes it possible to increase the sensitivity of the temperature measurement by more than an order of magnitude. Temperature sensitivity is estimated to be approximately 10 mK/Hz1/2 within a volume about 1 μ3, allocated by focused laser excitation in a scanning confocal microscope. Using cross-relaxation in the ground states of “bright” spin-3/2 centers and “dark” S=1 centers for temperature sensing and ground state level anti-crossing of “bright” spin-3/2 centers an integrated magnetic field and tempera- ture sensor with submicron space resolution can be implemented using the same spin system. The coupling of individually addressable “bright” spin-3/2 centers connected by a chain of “dark” S=1 spins, could be considered in quantum information pro- cessing and multicenter entanglement under ambient conditions.

Keywords: Defects; Quantum Technology; Thermometry; Silicon Carbide

Permalink: https://www.hzdr.de/publications/Publ-27798
Publ.-Id: 27798


On-Chip THz spectrometer for bunch compression fingerprinting at fourth-generation light sources

Laabs, M.; Neumann, N.; Green, B.; Awari, N.; Deinert, J.; Kovalev, S.; Plettemeier, D.; Gensch, M.

In this letter we present the layout and demonstrate the performance for an integrated millimeter-scale on-chip THz spectrometer. The device is based on eight Schottky-Diode detectors which are combined with narrow-band THz antennas, thereby enabling the simultaneous detection of eight frequencies in the THz range on one chip. The size of the active detector area matches the focal spot size of superradiant THz radiation utilized in bunch compression monitors of modern linear electron accelerators. The 3 dB bandwidth of the on-chip Schottky-Diode detectors is less than 10% of the center frequency and allows pulse-resolved detection at up to 5 GHz repetition rates. The performance of a first prototype device is demonstrated at a repetition rate of 100 kHz at the quasi-cw SRF linear accelerator ELBE operated with electron bunch charges between few pC and 100 pC.

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Permalink: https://www.hzdr.de/publications/Publ-27797
Publ.-Id: 27797


Expression of Glypican-3 is an Independent Prognostic Biomarker in Primary Gastro-Esophageal Adenocarcinoma and Corresponding Serum Exosomes

Rahbari, M.; Pecqueux, M.; Aust, D.; Stephan, H.; Tiebel, O.; Chatzigeorgiou, A.; Tonn, T.; Rao, V.; Ziegler, N.; Greif, H.; Lin, K.; Weitz, J.; Rahbari, N. N.; Kahlert, C.

Exosomes are nano-sized membranous vesicles of endosomal origin that carry nucleic acids, lipids and proteins. The cargo of exosomes is cell origin specific and the release of these exosomes and uptake by an acceptor cell is seen as a vital element of cell-cell communication. Here, we sought to investigate the diagnostic and prognostic value of the expression of glypican 3 (GPC3) on primary gastro-esophageal adenocarcinoma (GEA) tissue (tGPC3) and corresponding serum exosomes (eGPC3). Circulating exosomes were extracted from serum samples of 49 patients with GEA and 56 controls. Extracted exosomes were subjected to flow cytometry for the expression of eGPC3 and GPC3 expression on primary GEA tissue samples was determined by immunohistochemistry and correlated to clinicopathological parameters. We found decreased eGPC3 levels in GEA patients compared to healthy controls (p < 0.0001) and high tGPC3 expression.
This was significantly associated with poor overall survival (high vs. low eGPC3: 87.40 vs. 60.93 months, p = 0.041, high vs. low tGPC3: 58.03 vs. 84.70 months, p = 0.044). Cox regressional analysis confirmed tGPC3 as an independent prognostic biomarker for GEA (p = 0.02) and tGPC3 expression was validated in two independent cohorts. Our findings demonstrate that eGPC3 and tGPC3 can be used as potential diagnostic and prognostic biomarkers for GEA.

Keywords: Exosomes; Gastro-esophageal adenocarcinoma; Glypican-3; Prognostic biomarker; diagnostic biomarker

Permalink: https://www.hzdr.de/publications/Publ-27796
Publ.-Id: 27796


Detailed study of the Fermi surfaces of the type-II Dirac semimetallic candidates XTe2 (X = Pd, Pt)

Zheng, W.; Schönemann, R.; Aryal, N.; Zhou, Q.; Rhodes, D.; Chiu, Y.-C.; Chen, K.-W.; Kampert, E.; Förster, T.; Martin, T. M.; Mccandless, G. T.; Chan, J. Y.; Manousaki, E.; Balicas, L.

We present a detailed quantum oscillatory study on the Dirac type-II semimetallic candidates PdTe2 and PtTe2 via the temperature and the angular dependence of the de Haas–van Alphen and Shubnikov–de Haas effects. In high-quality single crystals of both compounds, i.e., displaying carrier mobilities between 103 and 104 cm2/ Vs, we observed a large nonsaturating magnetoresistivity which in PtTe2 at a temperature T = 1.3 K leads to an increase in the resistivity up to (5×104)% under a magnetic field μ0H = 62 T. These high mobilities correlate with their light effective masses in the range of 0.04 to 1 bare electron mass according to our measurements. For PdTe2 the experimentally determined Fermi surface cross-sectional areas show excellent agreement with those resulting from band structure calculations. Surprisingly, this is not the case for PtTe2, whose agreement between calculations and experiments is relatively poor even when electronic correlations are included in the calculations. Therefore, our study provides strong support for the existence of a Dirac type-II node in PdTe2 and probably also for PtTe2. Band structure calculations indicate that the topologically nontrivial bands of PtTe2 do not cross the Fermi level ɛF. In contrast, for PdTe2 the Dirac type-II cone does intersect ɛF, although our calculations also indicate that the associated cyclotron orbit on the Fermi surface is located in a distinct kz plane with respect to that of the Dirac type-II node. Therefore, it should yield a trivial Berry phase.

Permalink: https://www.hzdr.de/publications/Publ-27795
Publ.-Id: 27795


Experimental evidence for the microscopic mechanism of the unusual spin-induced electric polarization in GdMn2O5

Yahia, G.; Damay, F.; Chattopadhyay, S.; Baledent, V.; Peng, W.; Kim, S. W.; Greenblatt, M.; Lepetit, M.-B.; Foury-Leylekian, P.

We report in this paper the temperature evolution of the magnetic structure of GdMn2O5, in the range 2–40 K, studied by neutron diffraction on an isotope-enriched powder. We detail a thorough analysis of the microscopic mechanisms needed to release the different magnetic frustrations that are at the origin of the polarization. In addition to the usual exchange-striction term, known to be at the origin of the polarization in this family, an additional exchange-striction effect between the Gd3+ and Mn3+ spins is found to be responsible for the very large polarization in the Gd compound.

Permalink: https://www.hzdr.de/publications/Publ-27794
Publ.-Id: 27794


Pressure-induced commensurate order in TbMn2O5 and DyMn2O5: Influence of rare-earth anisotropy and 3d-4 f exchange

Deutsch, M.; Peng, W.; Foury-Leylekian, P.; Baledent, V.; Chattopadhyay, S.; Fernandez-Diaz, M. T.; Hansen, T. C.; Forget, A.; Colson, D.; Greenblatt, M.; Lepetit, M.-B.; Petit, S.; Mirebeau, I.

The magnetic structure of TbMn2O5 and DyMn2O5 multiferroics has been studied by high-pressure neutron diffraction in a large pressure range up to 6.6 GPa. In both cases, we observe a pressure-induced commensurate magnetic phase with propagation vector ( 1/2 0 1/2 ), growing with pressure at the expense of the ambient pressure phases. Being previously observed in YMn2O5 and PrMn2O5, this phase is most likely a generic feature of the RMn2O5 multiferroic family. A simple model is proposed to explain qualitatively the emergence of this pressure-induced phase. Differences between TbMn2O5 and DyMn2O5 behaviors at ambient and low pressures provide clues on the interaction scheme.

Permalink: https://www.hzdr.de/publications/Publ-27793
Publ.-Id: 27793


Probing the Jeff = 0 ground state and the Van Vleck paramagnetism of the Ir5+ ions in layered Sr2Co0.5Ir0.5O4

Agrestini, S.; Kuo, C.-Y.; Chen, K.; Utsumi, Y.; Mikhailova, D.; Rogalev, A.; Wilhelm, F.; Förster, T.; Matsumoto, A.; Takayama, T.; Takagi, H.; Haverkort, M. W.; Hu, Z.; Tjeng, L. H.

We report a combined experimental and theoretical x-ray magnetic circular dichroism (XMCD) spectroscopy study at the Ir-L2,3 edges on the Ir5+ ions of the layered hybrid solid state oxide Sr2Co0.5Ir0.5O4 with the K2NiF4 structure. From theoretical simulation of the experimental Ir-L2,3 XMCD spectrum, we found a deviation from a pure Jeff = 0 ground state with an anisotropic orbital-to-spin moment ratio (Lx/2Sx = 0.43 and Lz/2S = 0.78). This deviation is mainly due to multiplet interactions being not small compared to the cubic crystal field and due to the presence of a large tetragonal crystal field associated with the crystal structure. Nevertheless, our calculations show that the energy gap between the singlet ground state and the triplet excited state is still large and that the magnetic properties of the Ir5+ ions can be well described in terms of singlet Van Vleck paramagnetism.

Permalink: https://www.hzdr.de/publications/Publ-27792
Publ.-Id: 27792


Sorption, redox reactions and (nano-)particle formation of uranium and other early actinides at mineral-water interfaces: Lessons (to be) learned from synchrotron methods

Scheinost, A. C.; Kvashnina, K. O.; Hennig, C.; Schmidt, M.; Marques Fernandes, M.

The early actinides U, Np and Pu exhibit two to four different oxidation states within the oxic to anoxic regime of typical environmental systems, responsible for their rich and complex biogeochemistry. Due to their high surface area and catalytic activity, clay and iron oxide minerals play a crucial role in controlling the mobility of these radiotoxic elements in the environment. Understanding the underlying (geo-)chemical processes and reactions is of paramount importance for many applications from the design of nuclear waste repositories to the development of efficient remediation strategies for contaminated sites. The electronic and molecular structures of actinides, and their temporal evolution, can be studied in situ by a range of synchrotron methods, including high resolution absorption and emission spectroscopies (XES, RIXS, XANES, EXAFS), high resolution powder and single crystal X-ray diffraction and scattering (PDF) analysis, and surface sensitive techniques (CTR, RAXR). We recently upgraded The Rossendorf Beamline at ESRF to be able to apply all of these techniques to actinide samples. In this talk, I will present the different techniques and what we recently have learned about the geochemistry of uranium, neptunium and plutonium at the strongly dynamic surface of clay and Fe oxide minerals, including sorption, redox reactions, and formation of actinide Eigencolloids and of solid solutions.

Keywords: Uranium; EXAFS; XANES; RIXS; RAXR; CTR; Redox

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  • Invited lecture (Conferences)
    URANIUM Biogeochemistry: Transformations, isotopes, and applications, 21.-26.10.2018, Ascona, Switzerland

Permalink: https://www.hzdr.de/publications/Publ-27791
Publ.-Id: 27791


Short-range quasistatic order and critical spin correlations in α-Ru1−xIrxCl3

Do, S.-H.; Lee, W.-J.; Lee, S.; Choi, Y. S.; Lee, K.-J.; Gorbunov, D. I.; Wosnitza, J.; Suh, B. J.; Choi, K.-Y.

The magnetic ground states of the diluted α-Ru1−x IrxCl3 are systematically investigated by magnetization, specific heat, and muon spin rotation measurements. Introduction of moderate spin vacancies leads to a destabilization of the zigzag antiferromagnetic order towards a short-range ordered state. It is remarkable that the x = 0.2 sample located near a quantum critical point shows an extremely short correlation length of the magnitude of magnetic moments ζmag ∼ 1.2a (a = lattice spacing) and a power-law behavior of the magnetic susceptibility χ(T ) ∼ T−p below 14 K for μ0HIIab and below 30 K for μ0HIIc. Our work demonstrates that the α-Ru1−x IrxCl3 system hosts a short-range, quasistatic order characterized by critical spin correlations.

Permalink: https://www.hzdr.de/publications/Publ-27790
Publ.-Id: 27790


Perturbation theory for metal pad roll instability in cylindrical reduction cells

Herreman, W.; Nore, C.; Guermond, J.-L.; Cappanera, L.; Weber, N.; Horstmann, G. M.

We propose a new theoretical model for metal pad roll instability in idealized cylindrical reduction cells. In addition to the usual destabilizing effects, we model viscous and Joule dissipation and some capillary effects. The resulting explicit formulas are used as theoretical benchmarks for two multiphase magnetohydrodynamic solvers, OpenFOAM and SFEMaNS. Our explicit formula for the viscous damping rate of gravity waves in cylinders with two fluid layers compares excellently to experimental measurements. We use our model to locate the viscously controlled instability threshold in cylindrical shallow reduction cells but also in Mg–Sb liquid metal batteries with decoupled interfaces.

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Permalink: https://www.hzdr.de/publications/Publ-27789
Publ.-Id: 27789


Synthesis and Pharmacological Evaluation of Identified and Putative Metabolites of the A₁ Adenosine Receptor Antagonist 8-Cyclopentyl-3-(3-fluoropropyl)-1-propylxanthine (CPFPX)

Holschbach, M. H.; Bier, D.; Sihver, W.; Schulze, A.; Neumaier, B.

The A₁ adenosine receptor (A₁AR) antagonist [¹⁸F]cyclopentyl-3-(3-fluoropropyl)-1-propylxanthine ([¹⁸F]CPFPX), used in imaging human brain A₁ARs by PET, is stable in the brain but rapidly undergoes transformation into one major (M1) and several minor metabolites in blood. This report describes the synthesis of putative metabolites of CPFPX as standards for the identification of those metabolites.
Analysis by (radio)HPLC revealed that extracts of human liver microsomes incubated with n.c.a.[¹⁸F]CPFPX contained the major metabolite, M1, as well as radioactive metabolites corresponding to derivatives functionalized at the cyclopentyl moiety, but no N¹-despropyl species or metabolites resulting from functionalizations of the N³-fluoropropyl chain.
The putative metabolites displaced the binding of [³H]CPFPX to the A₁AR in pig brain cortex at Kᵢs between 1.9 and 380 nM and the binding of [³H]ZM 241385 to the A₂ᴀAR in pig striatum at Kᵢs greater than 180 nM. One metabolite, a derivative functionalized at the ω-position of the N¹-propyl chain, showed high affinity (Kᵢ 2 nM) to and very good selectivity (> 9000) for the A₁AR.

Permalink: https://www.hzdr.de/publications/Publ-27787
Publ.-Id: 27787


Code-to-code Comparison between ATHLET-CD and MELCOR for SBLOCA Severe Accident Scenario in Generic German PWR

Jobst, M.; Kretzschmar, F.; Sánchez-Espinoza, V. H.; Wilhelm, P.

The evolution of a hypothetic SBLOCA severe accident scenario for a generic German PWR of type Konvoi is investigated by means of the two severe accident computer codes ATHLET-CD and MELCOR. The simulation results derived from the both codes are compared and possible reasons for deviations between the results are analyzed.
For the assessment of scenarios with core degradation, correct prediction of physical phenomena and timings, such as beginning of core degradation, time of relocation of molten core material to lower head or time of vessel failure, is of particular interest. Validation of the obtained simulation results against experimental data is very limited simply due to the fact of unavailability of full integral experiments, especially for the late in-vessel phase of severe accident scenarios. Therefore two equivalent plant models with similar geometry, initial and boundary conditions were build, one for ATHLET-CD 3.0A and one for the MELCOR 1.8.6 code. A 50 cm² cold leg SBLOCA scenario was selected for the code-to-code comparison. Due to the assumed multiple failures of safety systems, the scenario develops into a severe accident scenario with beginning of core melting approximately 3 h after beginning of the transient.
The general comparison of the main parameters between both codes shows that qualitatively good agreement is reached. Similar time spans until the start of core heat-up are predicted by both codes. Initiation of zircaloy oxidation and the total amount of produced hydrogen agree. During the late in-vessel phase more significant deviations are identified, e.g. in the process of relocation to lower head.
In a second calculation, the effectiveness of mobile pump injection to the primary circuit as additional accident management measure is investigated. The results obtained by both codes show concordantly that a commercial high power fire pump system can be applied to stop the progression of the accident, with only slight degradation of the absorber rods.

Keywords: PWR; Severe Accident; Accident Management Measures; ATHLET-CD; MELCOR

  • Contribution to proceedings
    12th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics, Operation and Safety (NUTHOS-12), 14.-18.10.2018, Qingdao, China
  • Lecture (Conference)
    12th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics, Operation and Safety (NUTHOS-12), 14.-18.10.2018, Qingdao, China

Permalink: https://www.hzdr.de/publications/Publ-27786
Publ.-Id: 27786


Synthesis, characterization and initial biological evaluation of [⁹⁹ᵐTc]Tc-tricarbonyl labeled DPA-α-MSH peptide derivatives for potential melanoma imaging

Gao, F.; Sihver, W.; Bergmann, R.; Belter, B.; Bolzati, C.; Salvarese, N.; Steinbach, J.; Pietzsch, J.; Pietzsch, H.-J.

α-Melanocyte stimulating hormone (α-MSH) derivatives target the melanocortin-1 receptor (MC1R) specifically and selectively. In this study, the α-MSH derived peptide NAP-NS1 (Nle-Asp-His-D-Phe-Arg-Trp-Gly-NH₂) with and without linkers was conjugated with 5-(bis(pyridin-2-yl)methyl)amino)pentanoic acid (DPA-COOH) and labeled with [⁹⁹ᵐTc]Tc-tricarbonyl by two methods. With the one-pot method the labeling was faster than with the two-pots method, however obtaining similarly high yields. Negligible transchelation and high stability in physiological solutions was determined for the [⁹⁹ᵐTc]Tc-tricarbonyl-peptide conjugates. Coupling an ethylenglycol (EG)-based linker increased the hydrophilicity. The peptide derivatives displayed high binding affinity in murine B16F10 melanoma cells as well as in human MeWo and TXM13 melanoma cell homogenate. Preliminary in vivo studies with one of the [⁹⁹ᵐTc]Tc-tricarbonyl-peptide conjugates showed good stability in blood and both a renal and hepatobiliary excretion. Biodistribution was performed on healthy rats to gain initial insights into the potential relevance of the ⁹⁹ᵐTc-labeled peptides for in vivo imaging.

Keywords: melanocortin-1 receptor; α-MSH analogs; peptides; [⁹⁹ᵐTc]Tc-tricarbonyl labeling; radiopharmaceuticals

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Permalink: https://www.hzdr.de/publications/Publ-27785
Publ.-Id: 27785


The Potential of Reflectance and Laser Induced Luminescence Spectroscopy for Near-Field Rare Earth Element Detection in Mineral Exploration

Lorenz, S.; Beyer, J.; Fuchs, M.; Seidel, P.; Turner, D.; Heitmann, J.; Gloaguen, R.

New energy, transport, computer and telecommunication technologies require an increasing supply of rare earth elements (REEs). As a consequence, adequate and robust detection methods become essential for the exploration and discovery of new deposits, the improved characterization of existing deposits and the future recycling of today’s high-tech products. Within this paper, we investigate the potential of combining passive reflectance (imaging and point sampling) with laser stimulated luminescence (point sampling) spectroscopic measurements across the visible, near and shortwave infrared for REE detection in non-invasive near-field mineral exploration. We analyse natural REE-bearing mineral samples from main REE-deposits around the world and focus on challenges such as the discrimination of overlapping spectroscopic features and the influence of the mineral type on detectability, feature position and mineral matrix luminescence. We demonstrate that the cross-validation of results from both methods increases the robustness and sensitivity, provides the potential for semi-quantification and enables the time- and cost-efficient detection of economically important REE, including Ce, Pr, Nd, Sm, Eu, Dy, Er, Yb and potentially also Ho and Tm.

Keywords: laser induced luminescence spectroscopy; reflectance spectroscopy; hyperspectral imaging; laser-induced fluorescence; photoluminescence; rare earth elements

Permalink: https://www.hzdr.de/publications/Publ-27784
Publ.-Id: 27784


Exploring pitfalls of 64Cu‑labeled EGFR‑targeting peptide GE11 as a potential PET tracer

Striese, F.; Sihver, W.; Gao, F.; Bergmann, R.; Walther, M.; Pietzsch, J.; Steinbach, J.; Pietzsch, H.-J.

The epidermal growth factor receptor (EGFR) represents an important molecular target for both radiotracer-based diagnostic imaging and radionuclide therapy of various cancer entities. For the delivery of radionuclides to the tumor, peptides hold great potential as a transport vehicle. With respect to EGFR, the peptide YHWYGYTPQNVI (GE11) has been reported to bind the receptor with high specificity and affinity. In the present study, GE11 with β-alanine (β-Ala-GE11) was conjugated to the chelating agent p-SCN-Bn-NOTA and radiolabeled with ⁶⁴Cu for the first radio pharmacological evaluation as a potential probe for positron emission tomography (PET)-based cancer imaging. For better water solubility, an ethylene glycol-based linker was introduced between the peptide’s N terminus and the radionuclide chelator. The stability of the ⁶⁴Cu-labeled peptide conjugate and its binding to EGFR-expressing tumor cells was investigated in vitro and in vivo, and then compared with the ⁶⁴Cu-labeled EGFR-targeting antibody conjugate NOTA-cetuximab. The GE11 peptide conjugate [⁶⁴Cu]Cu-NOTA-linker-β-Ala-GE11 ([⁶⁴Cu]Cu-1) was stable in a buffer solution for at least 24 h but only 50% of the original compound was detected after 24 h of incubation in human serum. Stability could be improved by amidation of the peptide’s C terminus (β-Ala-GE11-NH₂ (2)). Binding assays with both conjugates, [⁶⁴Cu]Cu-1 and [⁶⁴Cu]Cu-2, using the EGFR-expressing tumor cell lines A431 and FaDu showed no specific binding. A pilot small animal PET investigation in FaDu tumor-bearing mice revealed only low tumor uptake (standard uptake value (SUV) < 0.2) for both conjugates. The best tumor-to-muscle ratio determined was 3.75 for [⁶⁴Cu]Cu-1, at 1 h post injection. In conclusion, the GE11 conjugates in its present form are not suitable for further biological investigations, since they presumably form aggregates.

Keywords: Epidermal growth factor receptor; ⁶⁴Cu-labeled peptide conjugates; Molecular imaging; Receptor tyrosine kinases; Positron emission tomography

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Permalink: https://www.hzdr.de/publications/Publ-27783
Publ.-Id: 27783


The electronic structure and band interface of cesium bismuth iodide on a titania heterostructure using hard X-ray spectroscopy

Phuyal, D.; Jain, S. M.; Philippe, B.; Johansson, M. B.; Pazoki, M.; Kullgren, J.; Kvashnina, K. O.; Klintenberg, M.; Johansson, E. M. J.; Butorin, S. M.; Karis, O.; Rensmo, H.

Bismuth halide compounds as a non-toxic alternative are increasingly investigated because of their potential in optoelectronic devices and their rich structural chemistry. Hard X-ray spectroscopy was applied to the ternary bismuth halide Cs3Bi2I9 and its related precursors BiI3 and CsI to understand its electronic structure at an atomic level. We specifically investigated the core levels and valence band using X-ray photoemission spectroscopy (PES), high-resolution X-ray absorption (HERFD-XAS), and resonant inelastic X-ray scattering (RIXS) to get insight into the chemistry and the band edge properties of the two bismuth compounds. Using these element specific X-ray techniques, our experimental electronic structures show that the primary differences between the two bismuth samples are the position of the iodine states in the valence and conduction bands and the degree of hybridization with bismuth lone pair (6s2) states. The crystal structure of the two layered quasiperovskite compounds plays a minor role in modifying the overall electronic structure, with variations in bismuth lone pair states and iodine band edge states. Density Functional Theory (DFT) calculations are used to compare with experimental data. The results demonstrate the effectiveness of hard X-ray spectroscopies to identify element specific bulk electronic structures and their use in optoelectronic devices

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Permalink: https://www.hzdr.de/publications/Publ-27782
Publ.-Id: 27782


Sensitivity control of carbon nanotube based piezoresistive sensors by drain-induced barrier lowering

Böttger, S.; Wagner, C.; Lorkowski, F.; Hartmann, M.; Schuster, J.; Hermann, S.

The superior performance of membrane-based carbon nanotube (CNT) sensors showing maximum gauge factors of up to 800 is analyzed by a device study combining technological and theoretical approaches. Drain-induced barrier lowering (DIBL) is found to contribute significantly to this high sensitivity. A high subthreshold voltage roll-off of (750±200) mV⋅V−1 and degradation of subthreshold swing is observed even for channel length of 200 nm. The piezoresistive behavior of the CNT sensor running in the DIBL regime is shown as a complex and input-voltage dependent interplay of strain-dependent Fowler-Nordheim tunneling and the intrinsic thermionic resistance change. We show, that this interplay can be controlled by the applied bias voltages 𝑉GS and 𝑉DS in such a way, that the overall sensitivity is enhanced up to 150 % with respect to the intrinsic effect. The control of the sensitivity via 𝑉DS is enabled by the DIBL effect, which appears for our CNT device at remarkably long CNT-channels.
The experimental findings are retraced by a simplified transport model, which combines a numerical device solver with an electronic model for strained carbon nanotube based field-effect transistors (CNT-FETs) covering thermionic as well as tunneling contributions. Strain dependent tunneling through the Schottky barriers (SBs) appears to be the key contribution to the strain sensitivity in our model. From the model device characteristics have been derived which reproduce the experimental findings emphasizing the significance of tunneling processes in combination with DIBL effects for the superior strain sensitivity of our device.

Keywords: carbon nanotube; CNT-FET; piezoresistive sensor; piezoresistive effect; DIBL; transport modeling

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Permalink: https://www.hzdr.de/publications/Publ-27781
Publ.-Id: 27781


Investigation of upstream and downstream flow conditions in a swirling inline fluid separator – experiments with a wire-mesh sensor and CFD studies

Sahovic, B.; Atmani, H.; Wiedemann, P.; Schleicher, E.; Legendre, D.; Climent, E.; Zamanski, R.; Pedrono, A.; Hampel, U.

Wire-mesh sensors have been developed to measure gas-liquid distributions in two-phase flows at high speed. In a wire-mesh sensor, a wire electrode grid is formed in the flow cross-section by wires running in two planes of a small axial distance. Its functional principle is based on the measurement of either electrical conductivity (conductivity wire-mesh sensor) or relative permittivity (capacitance wire-mesh sensor) in the electrode crossings. Repeated scanning gives high speed sequences of cross-sectional phase indicator distributions. The sampling frequency can be very high. Thus, for a wire- mesh sensor with 2 × 16 wire electrodes (16 × 16 crossings or image pixel in a square cross-section) 10,000 frames per second can be scanned. The high acquisition speed together with the small wire spacing of typically 3 to 4 mm allows to image gas bubbles in many slices, such that the size and shape of the bubbles and the interfacial area can be resolved, but only in case of very large bubbles. The technical challenge of wire-mesh sensor imaging is the high amount of data, which need to be analyzed by automated computer algorithms.
We used the wire-mesh sensor to study the flow conditions upstream a swirling device, which is used in the oil and gas industry as a separator. Our particular objective was the analysis of the correlation of upstream flow patterns with the shape of the swirling gas cores downstream the swirl. The upstream flow regimes depend on the gas and liquid superficial velocities and can range from bubble flow, via churn flow towards annular flow in vertical pipe orientation. The flow pattern and especially its transition have an impact on the shape and interface stability of the swirling gas core downstream. Hence the wire-mesh data can be used as a predictor for expected hollow vortex variations and can be used for automatic control of the swirling device. To assess the relationship between wire-mesh data and vortex shape we used a high-speed camera to record the downstream interface development at 200 Hz frame rate. As automatic control requires a good process model we intend to use an original computational fluid dynamics (CFD) coupling a Volume-of-Fluid (VoF) method for interface resolution and an Immersed Boundary Method (IBM) for the separator description. For that we performed first CFD studies which give key indications of required model improvements and future numerical research work.

Keywords: Computational fluid dynamics; gas-liquid flow; inline flow splitter; swirling element; wire-mesh sensor

  • Open Access Logo Contribution to proceedings
    9th World Congress on INDUSTRIAL PROCESS TOMOGRAPHY, 02.-06.09.2018, Bath, England
  • Lecture (Conference)
    9th World Congress on INDUSTRIAL PROCESS TOMOGRAPHY, 02.-06.09.2018, Bath, England

Permalink: https://www.hzdr.de/publications/Publ-27780
Publ.-Id: 27780


Comparative study of the effects of seven lanthanides onto two mammalian kidney cell lines

Heller, A.; Barkleit, A.; Bok, F.; Wober, J.

Exposure to lanthanides (Ln) poses a serious health risk to animals and humans. Since these elements are mainly excreted with urine, we investigated the effect of Ln in concentrations of 10⁻⁹ – 10⁻³ M on normal rat kidney cells (NRK-52E) and human embryonal kidney cells (HEK-293) after 24 and 48 h, respectively. Cell viability was measured using the XTT test and cell morphology was studied with light microscopy as well as fluorescence microscopy after immuno-chemical staining. Solubility of the Ln in the cell culture medium was determined with ICP-MS and Ln speciation was investigated using TRLFS as well as thermodynamic modelling.
The results from cell culture experiments demonstrate that the effect of Ln onto the cell viability are concentration- and time-dependent as well as cell line- and element-specific. Dose-response curves of all Ln reveal no cytotoxicity up to 10⁻⁴ M, whereas higher concentrations cause gradual loss of cell viability in both cell lines. Effective concentrations, for which cell viability was reduced to 50 % (EC50), were calculated. In general, first and last elements of the Ln family affect the cell viability more than Ln in the middle of the series. However, Ce exhibits the significantly strongest effect of all Ln. Besides the loss of cell viability, exposed cells undergo morphological changes like rounding and shrinking prior to cell death. Comparing both cell lines reveals NRK-52E being significantly more sensitive to Ln exposure than HEK-293.
ICP-MS measurements of Ln supplemented cell culture medium after filtration through 0.45 μm filters demonstrate that the Ln are 100 % soluble. Furthermore, TRLFS results reveal that Ln speciation in the cell culture medium is most probably dominated by a complex species formed with a protein from FBS. Due to a huge lack of complex formation and solubility constants of Ln with constituents from cell culture media as well as the unknown and variable composition of FBS, thermodynamic modelling failed to reproduce the experimental results and predicts a speciation dominated by several carbonate and phosphate species instead.
The results of this study underline the importance of combining biological, chemical, and spectroscopic methods in studying the effect of Ln on cells in-vitro and can contribute to the improvement of current risk assessment for Ln in the human body.

Keywords: lanthanides; mammalian kidney cell

  • Poster
    10th International Conference on f-Elements (ICFE-10), 03.-06.09.2018, Lausanne, Schweiz

Permalink: https://www.hzdr.de/publications/Publ-27779
Publ.-Id: 27779


Investigation of structural models for O-Y and O-Y-Ti clusters in bcc Fe: A DFT study

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

Six different structural models for atomic clusters in bcc Fe are investigated by density functional theory (DFT) calculations. Results for clusters with identical numbers of constituents (O, Y, Ti, and vacancies) are compared. It is found that the data on the stability or energetics of the relaxed clusters are comparable although their atomic configurations are often different. This contradicts the prevailing opinion in the related theoretical literature that favors the so-called structure matching model. In all studied cases, the absolute value of the total binding energy per cluster constituent becomes lower if Y is partially replaced by Ti. Therefore the driving force for the growth of O–Y clusters should be higher than that of O–Y–Ti clusters. This may be correlated with the experimental observation that the presence of Ti leads to a reduction of the size of the oxide clusters in nanostructured ferritic alloys and to a higher dispersion. Not only cage-like clusters but also clusters with oxygen in the center (cage) are investigated. In the absence of Ti, clusters with oxygen in the center attain more stability that cage-like clusters and the opposite holds for clusters with Ti. It is also shown that adding O atoms to cage-like clusters leads to structures with O in the center. In the present comprehensive DFT study only clusters with dimensions below 1 nm could be treated. This is still below or close to the limit of the experimental resolution of methods allowing for a simultaneous determination of atomic structure and composition of the clusters. These small clusters may be considered as nuclei for further structural evolution and growth during which a selection of the most favored cluster structures could occur.

Keywords: First-principle calculations; Atomic clusters in bcc Fe; Nanostructures ferritic

Permalink: https://www.hzdr.de/publications/Publ-27778
Publ.-Id: 27778


Microreactor Studies for Efficient Organic Oxidation Processes

Willms, T.; Kryk, H.; Hampel, U.

The industrially important partial oxidation of hydrocarbons is frequently characterized by low conversions and yields, which are mostly related to mass and heat transfer problems. Due to the reaction conditions, such processes include also important safety risks and are still not sufficiently investigated. To study the influence of the process parameters on the product selectivity, a lab facility including a silicon-coated micro reactor of stainless steel has been developed and constructed. Due to its modular construction (e.g. replaceable capillary), it permits for the first time to perform catalyzed and non-catalyzed oxidations of hydrocarbons with oxygen as a two-phase process in a capillary reactor in a wide range of residence times (some mins to 24 h), temperatures and pressures.
As an example the oxidation of isobutane to tertiary butyl hydroperoxide (TBHP) is studied. TBHP, as an intermediate for the production of propylene oxide according to the Oxirane process, is currently produced at industrial scale by the partial oxidation of liquid isobutane at temperatures of 120 to 140 °C and pressures of 25 to 37 bars at high residence times of up to 12 hours using bubble columns or bubble tray reactors. The conversion is limited to 35 to 50 % in order to obtain a TBHP selectivity of 50 to 60 % minimizing the formation of by-products, which are caused by the decomposition of the TBHP due to the complex reaction mechanism. Besides safety aspects, the high reaction enthalpy of the oxidation as well as heat and mass transport problems are further issues of this process. In the frame of the Helmholtz-Energy-Alliance project “Energy efficient chemical multiphase processes“, this reaction has been investigated for the first time as a Taylor-Flow process in a micro reactor with the aim to enhance the space-time yield of the process. The advantages of micro reactors are the high surface – volume ratio for an efficient heat transfer and the improved, nearly inherent, safety. This permits to investigate yet unexplored process windows, for instance within the explosive region of a reaction mixture.
The reaction has been studied varying flow rates, temperature, pressure, the molar ratio of the starting products using two different initiators, namely TBHP and di-t-butyl peroxide (DTBP). For all experiments the selectivity of the reaction products and the conversion of the reaction have been studied by sampling and analyzing the reaction by GC/MS. The use of TBHP as initiator increased the selectivity of the reaction for the target product TBHP. TBHP as initiator seems to give a better selectivity since at high temperatures as they are necessary for DTBP, the formation of propanone already becomes important which favours the decomposition of TBHP. The replacement of the initiator diluent water by decane resulted in a very fast reaction and the highest non-catalyzed isobutane conversion (~18 %) obtained ever in a microreactor but the selectivity of TBHP dropped to zero. In this experiment the coating of the capillary was damaged, so a more stable material will be necessary.

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Entwicklung und Synthese neuartiger fluorhaltiger Liganden zur molekularen Bildgebung des Adenosin A2B-Rezeptors im Gehirn mittels Positronen-Emissions-Tomographie

Lindemann, M.

Der G-Protein-gekoppelte A2B-Rezeptor unterscheidet sich von den anderen Adenosinrezeptorsubtypen (A1, A2A, A3) durch die niedrige Affinität zu seinem endogenen Liganden Adenosin. Es wird beschrieben, dass der Rezeptor in verschiedenen pathologischen Prozessen, die durch eine erhöhte Adenosinkonzentration ausgezeichnet sind, wie beispielsweise bei Entzündungen (Inflammation), Hypoxie oder auch Krebs, eine wichtige Rolle spielt. Ziel dieser Arbeit ist die Entwicklung eines Fluor-18 markierten Radioliganden für die molekulare Bildgebung des A2B-Rezeptors im Organismus bzw. im speziellen des Gehirns mittels PET. Es soll damit der Einfluss des Rezeptors bei neurodegenerativen, neuroinflammatorischen und neuroonkologischen Erkrankungen untersucht werden. Die hier erstellte Arbeit basiert auf drei verschiedenen Leitstrukturen: den Pyrazinen (PA), Pyrimidinen (PYM) und Xanthinen (PXS). Für die ersten beiden Strukturklassen wurden zunächst die Leitverbindung und verschiedene fluorierte Derivate dargestellt. Für die Xanthine wurden zwei verschiedene Derivate synthetisiert. Alle Verbindungen wurden hinsichtlich ihrer Affinität und Selektivität gegenüber den Adenosinrezeptorsubtypen untersucht. Für die Klasse der Pyrazine wurde die bis dahin beste Verbindung PA51 ausgewählt. Trotz geringer Defizite gegenüber der Selektivität zu den anderen Adenosinrezeptorsubtypen, sollte PA51 zur Untersuchung der Hirngängigkeit der Verbindungsklasse genutzt werden. Nach erfolgreicher manueller Radiomarkierung und Transfer in eine automatisierte Radiosynthese, wurde die In-vivo-Gehirnaufnahme (Autoradiographie, PET) und der In-vivo-Metabolismus von [18F]PA51 in Mäusen untersucht. Bei In-vivo- Verteilungsstudien in Mäusen wurde eine homogene Verteilung des Radiotracers im Gehirn bestimmt. Des Weiteren wurden Gehirn- und Plasmaproben zu unterschiedlichen Zeitpunkten mit verschiedenen Methoden (RP-HPLC und MLC) auf enthaltene Radiometabolite untersucht. Nach 30 min p.i. konnten 70% an intaktem Radiotracer und ein Hauptradiometabolit mit einem Anteil von 30% im Gehirn nachgewiesen werden. Dessen Struktur konnte durch Synthese einer nichtradioaktiven Vergleichssubstanz aufgeklärt werden. Auf Grund dieser Ergebnisse ist die Substanzklasse der Pyrazine nicht geeignet als PET Radiotracer. Im Vergleich zu den Pyrazinen sind die Pyrimidinderivate in der Literatur als metabolisch stabiler beschrieben. Aus diesem Grund wurde zunächst die Leitverbindung PYM80, unter leichter Modifizierung der beschriebenen siebenstufigen Syntheseroute, dargestellt. Die fluorierte Verbindung PYM81 wurde über eine neu entwickelte sechsstufige Syntheseroute dargestellt. Diese weist eine hohe Affinität und Selektivität zum A2B-Rezeptor auf, weshalb PYM81 großes Potential für die Anwendung als neuartiger fluorierter Radioligand für die molekulare Darstellung des A2B-Rezeptors mittels PET besitzt. Als dritte Strukturklasse wurden zwei Xanthinderivate PXS7-1 und PXS7-2 dargestellt. Diese Strukturen basieren auf dem literaturbekannten, hochaffinen und selektiven Liganden PSB-603. Durch Reduzierung des sterisch anspruchsvollen Sulfonamidrestes sollten die molare Masse und die stark polaren Eigenschaften dieser Verbindungsklasse gesenkt werden. An Stelle der sterisch anspruchsvollen Sulfonamidreste sollten kleine Substituenten wie 4-Fluorpiperidin oder 4-Amino-2-fluorpyridin eingeführt werden. Diese beiden Verbindungen zeigten moderate Affinitäten und Selektivitäten gegenüber dem A2B-Rezeptor, weshalb weitere strukturelle Modifizierungen, zur Steigerung der Affinität und Selektivität zum A2B-Rezeptor, folgen sollen.

The G protein-coupled A2B receptor differs from other adenosine receptor subtypes (A1, A2A, A3) by its low affinity towards the endogenous ligand adenosine. It is suggested to be involved in various pathological processes accompanied by increased levels of adenosine, e.g. inflammation, hypoxia, and cancer. In this work, the development and synthesis of a fluorine-18 labelled radioligand with the particular aim for the imaging of the A2B receptor is described, to enable the investigation of the function and expression of A2B receptor in the organism and the influence of neurodegenerative, neuroinflammatory and neurooncological processes with PET. This work is based on three different lead structures: pyrazines (PA), pyrimidines (PYM), and xanthines (PXS). For the first two structure classes, the syntheses of the lead and different fluorinated compounds were performed. For the xanthines two different molecules were synthesized. The binding affinities for the different adenosine receptor subtypes were determined for each compound. To check the brain penetration of the pyrazine class, the best candidate so far, PA51 (although lacking selectivity), was labeled with 18-fluorine. After transfer of the manual radiolabeling procedure to the automated synthesis module, the in vivo brain uptake and the in vivo metabolism studies of [18F]PA51 in mice were performed. The in vivo brain uptake studies (brain sampling, autoradiography and PET) showed a homogeneous distribution of [18F]PA51. After different time intervals, brain and plasma samples were investigated by using different methods for metabolite analytics, showing only 70% of intact radiotracer in the brain 30 min p.i. A main brain radiometabolite with an amount of 30% after 30 min p.i. was structurally identified by use of a synthesized nonradioactive reference compound. In summary, this compound class is not suitable for the use as PET radiotracer, because of the fast metabolism of the compound and the formation of a brain-penetrable radiometabolite. The pyrimidine derivatives are described in literature as more metabolically stable as the pyrazines. For this compound class, the lead compound PYM80 was synthesized in a slightly modified seven-step synthesic route. A fluorinated derivative, PYM81, was synthesized over a newly developed six-step synthesic route. The compound showed good affinity and selectivity towards the A2B receptor. Therefor PYM81 has a high potential as a novel fluorinated radioligand for the molecular imaging of the A2B receptor with PET. As third class, xanthine derivatives were synthesized because of the highly affine and selective lead compound PSB-603. Due to the high molar mass and high polarity of these compounds the sulfonamide group was modified. Instead of this group, a small 4-amino-2-fluoropyridine or 4-fluoropiperidine groups was introduced to form derivatives PXS7-1 and PXS7-2. The compounds showed moderate affinities and selectivities for the A2B receptor. In conclusion, various fluorinated compounds were synthesized and showed different affinities and selectivities for the A2B receptor and its subtypes. Furthermore, the synthesis of additional fluorinated structures with the pyrimidine lead structure is required to enhance affinity and selectivity. For a first checkup of the brain uptake of this compound class, PYM81 needs to be radiolabeled with fluorine-18 because of the literature described higher metabolic stability in comparison to the pyrazine derivatives. PYM81 and the class of pyrimidines had a high potential as novel ligands for imaging the A2B receptor with PET in the brain.

Keywords: A2B-Rezeptor; 18-Fluor; Pyrazine; Pyrimidine; Xanthine; Pyrido[2; 3-d]pyrimidin-2; 4(1H; 3H)dione; Positronen-Emissions-Tomographie

  • Doctoral thesis
    Universität Leipzig, 2018
    Mentor: Prof. Dr. P. Brust, Dr. B. Wenzel
    274 Seiten

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Publ.-Id: 27776


Structural Properties of Al–O Monolayers in SiO₂ on Silicon and the Maximization of their Negative Fixed Charge Density

Hiller, D.; Göttlicher, J.; Steininger, R.; Huthwelker, T.; Julin, J.; Munnik, F.; Wahl, M.; Bock, W.; Schoenaers, B.; Stesmans, A.; König, D.

Al₂O₃ on Si is known to form an ultra-thin interfacial SiO₂ during deposition and subsequent annealing, which creates a negative fixed charge (Qfᵢₓ) that enables field-effect passivation and low surface recombination velocities in Si solar cells. Various concepts were suggested to explain the origin of this negative Qfᵢₓ. In this study we investigate Al–O monolayers (MLs) from atomic layer deposition (ALD) sandwiched between deliberately grown/deposited SiO₂ films. We show that the Al-atoms have an ultra-low diffusion coefficient (~4×10⁻¹⁸ cm²/s at 1000°C), are deposited at a constant rate of ~5×10¹⁴ Al-atoms/cm²/cycle from the first ALD-cycle on, and are tetrahedral O-coordinated, since the adjacent SiO₂ imprints its tetrahedral near-order and bond length into the Al–O MLs. By variation of the tunnel-SiO₂ thickness and the number of Al–O MLs, we demonstrate that the tetrahedral coordination alone is not sufficient for the formation of Qfᵢₓ but that a SiO₂ /Al₂O₃ interface within a tunneling distance from the substrate must be present. The Al-induced acceptor states at these interfaces have energy levels slightly below the Si valence band edge and require charging by electrons from either the Si substrate or from Si/SiO₂ dangling bonds to create the negative Qfᵢₓ. Hence, tunneling imposes limitations for the SiO₂ and Al₂O₃ layer thicknesses. In addition, Coulomb repulsion between the charged acceptor states results in an optimum number of Al–O MLs, i.e., separation of both interfaces. We achieve maximum negative Qfᵢₓ of ~5×10¹² cm⁻² (comparable to thick ALD-Al₂O₃ on Si) with ~1.7 nm tunnel-SiO₂ and just 7 ALD-Al₂O₃ cycles (~8 Å) after optimized annealing at 850°C for 30 s. The findings are discussed in the context of a passivating, hole-selective tunnel contact for high-efficiency Si solar cells.

Keywords: atomic layer deposition; aluminum oxide; silicon oxide; negative fixed charge; silicon surface passivation; hole-selective contact

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Publ.-Id: 27775


Modification of magnetic properties of Pt/Co/Pt Films by Ga+ Ion irradiation: Focused versus uniform irradiation

Sveklo, I.; Mazalski, P.; Jaworowicz, J.; Jamet, J.-P.; Vernier, N.; Mougin, A.; Ferre, J.; Kisielewski, M.; Zablotskii, V.; Bourhis, E.; Gierak, J.; Postava, K.; Fassbender, J.; Kanak, J.; Maziewski, A.

30 keV Ga+ irradiation-induced changes of magnetic and magneto-optical properties of sputtered Pt/Co/Pt ultrathin trilayers films have been studied as a function of the ion fluence. Out-of-plane magnetic anisotropy states with enhanced magneto-optical e ects were evidenced for specific values of cobalt thickness and irradiation fluence. Results obtained after uniform or quasi-uniform focused ion beam irradiation on either out-of-plane or in-plane magnetized sputtered pristine trilayers are compared. Similar irradiation-induced magnetic changes are evidenced in quasi-uniformly focused ion beam or uniformly irradiated films, grown either by sputtering or molecular beam epitaxy. We discuss on plausible common mechanisms underlying the observed effects.

Keywords: ion irradiation; magnetism; perpendicular anisotropy

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Permalink: https://www.hzdr.de/publications/Publ-27774
Publ.-Id: 27774


Processing of prompt gamma-ray timing data for proton range measurements at a clinical beam delivery

Werner, T.; Berthold, J.; Hueso-Gonzalez, F.; Koegler, T.; Petzoldt, J.; Roemer, K.; Richter, C.; Rinscheid, A.; Straessner, A.; Enghardt, W.; Pausch, G.

In proton therapy, patients benefit from the precise deposition of the dose in the tumor volume due to the interaction of charged particles with matter. Currently, the determination of the proton stopping point in the patient’s body during the treatment is not a clinical standard. The resulting range uncertainties cause broad safety margins around the tumor, which limit the actual potential of proton therapy.To overcome this obstacle, different methods are under investigation aiming at the verification of the proton range in real time during the irradiation.One approach is the Prompt Gamma-ray Timing (PGT) method, where the range of the primary protons is derived from the time-resolved emission profiles (PGT spectra)of promptly emitted gamma rays, which are produced along the particle track in the tissue. After verifying this novel technique in an experimental environment but far away from treatment conditions, the translation of PGT into clinical practice is intended. Therefore, new hardware was extensively tested and characterized in a close-to-clinical scenario using short irradiation times of 20 ms and clinical beam currents of 2 nA. Experiments were carried out in the treatment room of the University Proton Therapy Dresden. A pencil beam scanning plan was delivered to a target without and with embedded cylindrical air cavities of down to 5 mm thickness. The induced range shifts of the proton beam due to the material variation could be identified from the corresponding PGT spectra, comprising events collected during the delivery of a whole layer. Additionally, an assignment of the PGT data to the individual pencil beam spots allowed a spot-wise analysis of the variation of the PGT distribution mean and width indicating range shifts induced by the different air cavities. Furthermore, the paper presents a comprehensive software framework which standardizes future PGT analysis methods and calibration algorithms for technical limitations that have been encountered in the presented clinical-like experiments

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

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Permalink: https://www.hzdr.de/publications/Publ-27773
Publ.-Id: 27773


Measurement of interfacial wave dynamics in orbitally shaken cylindrical containers using ultrasound pulse-echo techniques

Horstmann, G. M.; Wylega, M.; Weier, T.

We present a novel experiment on interfacial wave dynamics in orbitally shaken cylindrical vessels containing two- and three fluid layers. The experiment was designed as a hydrodynamical model for both aluminum reduction cells and liquid metal batteries to gain new insights into the rotational wave motion driven by the metal pad roll instability. Different options are presented to realize stable and measurable multi-layer stratifications. We introduce a new acoustic measurement procedure allowing to reconstruct wave amplitudes also in opaque liquids by tracking ultrasonic pulse echoes reflected on the interfaces. Measurements of resonance curves and phase shifts were conducted for varying interface positions. A strong influence of the top and bottom walls were observed, considerably reducing wave amplitudes and eigenfrequencies, when the interface is getting close. Finally, measured resonance curves were successfully compared with an existing forced wave theory that we extended to two-layer interfacial waves.
The comparison stresses the importance to carefully control the boundary condition at the contact line.

Keywords: Interfacial Waves; Liquid Metal Batteries; Aluminum Reduction Cells

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Quaternary evolution of the Ploučnice River system (Bohemian Massif) based on fluvial deposits dated with optically stimulated luminescence and in situ-produced cosmogenic nuclides

Stor, T.; Schaller, M.; Merchel, S.; Martínek, K.; Rittenour, T.; Rugel, G.; Scharf, A.

The Ploučnice River system, located in the central Bohemian Massif, is draining an area not covered by continental ice sheets, but instead archiving the fluvial deposits. The fluvial style changes from a high-energy braided to a long-bend meandering river in the upper terrace levels (36 to 31 m above present floodplain). The middle terrace levels (22 to 16 m above present floodplain) indicate a fluvial style changing from a high- to medium-energy braided river. In the lower terrace levels (13 to 7 m above present floodplain), the terrace deposits indicate high-energy braided to long-bend meandering river environments. To provide greater details on the timing of fluvial terrace formation, this study applied ²⁶Al and ¹⁰Be isochron burial and optically stimulated luminescence (OSL) dating methods to terraces of the Ploučnice River system. Terraces found at 36 m, 31 m and 16 m above present floodplain are dated with isochron burial dating whereas terraces 22 m, 13 m and 7 m above present floodplain are dated with OSL. Due to differences in age results between the two dating methods, we establish two different evolution models: The first is based on isochron burial and OSL dating and the second model is on the OSL dating results only. The time span represented by the river terraces remains unclear and varies from Eburonian to Eemian (1680 to 56 ka) or from Elsterian to Eemian (138 to 56 ka), respectively. The former river evolution model is based on tectonic activity at least since 1000 ka. Morphotectonic analysis recognized new lineaments of which the general direction corresponds with the main direction of the Ohře fault zone (NE to ENE-striking) and Lužice fault zone (NW-striking). Based on dated terrace ages of 1153 ka at 14 m above present floodplain and 138 ka at 19 m above present floodplain, we suppose a normal fault being active from at least 1153 ka. The second river evolution model assumes possible remobilization of clasts analyzed by isochron burial dating before their final deposition. From three OSL ages we calculated a mean incision rate and estimated an age of upper terrace levels at 34 m above present floodplain to be 248 ka (Saalian age). As remobilization of clasts in high-energy fluvial and glaciofluvial environments is very likely, age determination is challenging. Nevertheless, we interpret the terrace record in the Ploučnice River system as a product of Quaternary climatic changes influenced by tectonic processes.

Keywords: cosmogenic nuclides; optically stimulated luminescence; fluvial terraces; Bohemian Massif; Pleistocene; neotectonics

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Publ.-Id: 27771


Evolution of structure and residual stress of a fcc/hex-AlCrN multi-layered system upon thermal loading revealed by cross-sectional X-ray nano-diffraction

Jäger, N.; Klima, S.; Hruby, H.; Julin, J.; Keckes, J. F.; Mitterer, C.; Daniel, R.

Understanding the influence of process conditions and coating architecture on the microstructure and residual stress state of multi-layered coatings is essential for the development of novel thermally and mechanically stable coatings and requires advanced depth resolving characterization techniques. In this work, an arc-evaporated multi-layered coating, consisting of alternating Al₇₀Cr₃₀N and Al₉₀Cr₁₀N sublayers with an individual layer thickness between 120 nm and 380 nm, was investigated. The as-deposited state of the multi-layered coating and the state after vacuum annealing at 1000 ◦C for 30 min was studied along its cross-section by synchrotron X-ray nano-diraction using a beam with a diameter of 50 nm. The results revealed sublayers with alternating cubic and hexagonal phase, causing repeated interruption of the grain growth at the interfaces. The in-plane residual stress depth distribution across the coating thickness could be tuned in a wide range between pronounced compressive and slight tensile stress by combining the effects of the coating architecture and the modulated incident particle energy controlled by the substrate bias voltage ranging from −30 V to −250 V . This resulted in an oscillatory stress profile fluctuating between −2 GPa and −4.5 GPa or pronounced stress gradients with values between −4 GPa and 0.5 GPa. Finally, the decomposition routes of the metastable cubic Al₇₀Cr₃₀N phase could be controlled by the Al₉₀Cr₁₀N sublayers which acted as nucleation sites and governed the texture of the decomposition products as Cr₂N. The results demonstrate that the cross sectional combinatorial approach, relying on a sophisticated multi-layer architecture combining various materials synthesized under tailored conditions, allowed for resolving structural variations and stress proles in the individual layers within the complex architecture and pioneers the path for knowledge-based development of multi-layered coatings with predefined microstructure and a dedicated stress design.

Keywords: Coating; Multilayers; Microstructure design; Residual stress; X-ray nano-diffraction

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Permalink: https://www.hzdr.de/publications/Publ-27770
Publ.-Id: 27770


64Cu-labeled bioconjugates based on triazacyclononane bifunctional chelators for radiopharmaceutical applications

Stephan, H.; Pant, K.; Joshi, T.; Zarschler, K.

The development of multi-functional complexing agents for radiometal nuclides for nuclear medical application represents an intensively studied and rapidly evolving field of research. In this context, multifunctionalisable ligands that can form highly stable metal complexes are of particular interest. Their use enables the simultaneous introduction of radiolabels for nuclear imaging and vector molecules for pharmaceutical targeting.1-2
The tridentate azamacrocycle 1,4,7-triazacyclononane (TACN) is one such ligand that is of special interest for the development of bifunctional chelating agents (BFCAs), TACN forms stable Cu(II)complexes and the azamacrocyclic ligand structure can be easily modified. The introduction of further donor groups on the ligand scaffold, such as pyridine units, significantly enhances the thermodynamic stability as well as the kinetic inertness of the Cu(II) complexes formed. These ligands mostly form Cu(II) complexes with square-pyramidal and distorted octahedral coordination geometry.
Examples of target-specific conjugates (peptides, antibody fragments) and bio(nano)materials equipped with appropriate BFCAs based on TACN (Figure 1), suitable for labeling with 64Cu, will be presented. This enables tumor imaging and biodistribution studies of the materials over a period of days via positron emission tomography (PET).

1. E.W. Price, C. Orvig, Chem. Soc. Rev. 2014, 43, 260. 2. G. Singh, M.D. Gott, H.-J. Pietzsch, H. Stephan, Nuclearmedicine, 2016, 55, 41.

  • Lecture (Conference)
    43rd International Conference on Coordination Chemistry, 30.07.-04.08.2018, Sendai, Japan

Permalink: https://www.hzdr.de/publications/Publ-27769
Publ.-Id: 27769


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.]