Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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33397 Publications

Kooperationspartnerschaft: Die Helmholtz-Gesellschaft und die TU Bergakademie

Meyer, B.; Sauerbrey, R.; Gutzmer, J.
Die Technische Universität Bergakademie trägt den Namenszusatz "Die Ressourcenuniversität. Seit 1765."
Keywords: Keine Keywords
  • Acamonta 21(2014), 20-23

Permalink: https://www.hzdr.de/publications/Publ-21372
Publ.-Id: 21372


Direct Condensation and Entrainment Steam Experiments at the TOPFLOW-DENISE facility

Seidel, T.; Beyer, M.; Lucas, D.
In a hypothetical Small Break Loss of Coolant Accident (SB-LOCA) in a Pressurized Water Reactor (PWR), the Reactor Pressure Vessel wall (RPV) may be exposed to thermal stress, since Emergency Core Cooling Systems (ECCS) injects cold water. The loads on the primary loop and RPV walls are determined by mixing processes with the surrounding hot water and by the condensation of steam on the surface.

For the development and validation of CFD-models, experiments have to meet a high standard of reproducibility, measurement certainty and temporal and local resolution. The pressure tank technology of the TOPFLOW facility allows conducting such experiments at reasonable effort.
The Direct Condensation and Entrainment Installation for Steam Experiments (DENISE) is made for CFD-grade condensation experiments at up to 50 bars pressure. Subcooled water is injected into the DENISE-basin in three different configurations to generate stratified flow, jet and plunging jet (steam entrainment with a jet) experiments with condensation.
The experimental facility is presented along with the high degree of instrumentation. High speed camera, a particular LED illumination, infrared observation, micro thermocouples, coriolis flow meters and movable thermal lances were used.

The available set of experiments is shown together with a comparison of surface waviness and fragmentation to temperature distributions and to the resulting condensation rates.
The results will be compared to the available literature.
Keywords: direct condensation, steam, water, pressure, experiment, CFD, computational fluid dynamics, SB-LOCA, thermal shock, PTS, stratified, jet, plunging, entrainment
  • Contribution to proceedings
    The 16th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-16), 30.08.-04.09.2015, Chicago, IL, USA
  • Lecture (Conference)
    The 16th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-16), 30.08.-04.09.2015, Chicago, IL, USA
  • atw - International Journal for Nuclear Power 60(2015)10, 599-602

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Permalink: https://www.hzdr.de/publications/Publ-21371
Publ.-Id: 21371


Production of three-dimensional quantum dot lattice of Ge/Si core-shell quantum dots and Si/Ge layers in an alumina glass matrix

Buljan, M.; Radic, N.; Sancho-Paramon, J.; Janicki, V.; Grenzer, J.; Bogdanovic-Radovic, I.; Siketic, Z.; Ivanda, M.; Utrobicic, A.; Huebner, R.; Weidauer, R.; Vales, V.; Endres, J.; Car, T.; Jercinovic, M.; Rosko, J.; Bernstorff, S.; Holy, V.
We report on the formation of Ge/Si quantum dots with core/shell structure that are arranged in a three-dimensional body centered tetragonal quantum dot lattice in an amorphous alumina matrix. The material is prepared by magnetron sputtering deposition of Al2 O3 /Ge/Si multilayer. The inversion of Ge and Si in the deposition sequence results in the formation of thin Si/Ge layers instead of the dots. Both materials show an atomically sharp interface between the Ge and Si parts of the dots and layers. They have an amorphous internal structure that can be crystallized by an annealing treatment. The light absorption properties of these complex materials are significantly different compared to films that form quantum dot lattices of the pure Ge, Si or a solid solution of GeSi. They show a strong narrow absorption peak that characterizes a type II confinement in accordance with theoretical predictions. The prepared materials are promising for application in quantum dot solar cells.
Keywords: Ge/Si core shell, 3D QD lattices, Type II confinement, Absorption Submitted

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Permalink: https://www.hzdr.de/publications/Publ-21370
Publ.-Id: 21370


Experimente und Simulation von Wasser- und Stofftransport an einem für Sachsen typischen Grundwassersystem

Peuker, L. C.
Es ist kein Abstract vorhanden.
  • Study thesis
    HZDR, Rossendorf, 2014
    Mentor: Dr. J. Lippmann-Pipke
    25 Seiten

Permalink: https://www.hzdr.de/publications/Publ-21369
Publ.-Id: 21369


Power of the sun is all we need for a power plant

Liedke, B.
Abstract was not needed
Keywords: sponge-like absorber, nanostructure, PV, science slam
  • Lecture (others)
    Science slam in Köln, 07.11.2014, Rathaus Köln, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-21368
Publ.-Id: 21368


Laser-wakefield acceleration and brilliant radiation sources -- A brief virtual tour of our work the Helmholtz-Center Dresden-Rossendorf

Debus, A.; Irman, A.; Couperus, J. P.; Jochmann, A.; Zarini, O.; Köhler, A.; Bussmann, M.; Kluge, T.; Pausch, R.; Steiniger, K.; Hübl, A.; Zeil, K.; Metzkes, J.; Krafft, S.; Richter, C.; Siebold, M.; Bock, S.; Helbig, U.; Röser, F.; Loeser, M.; Schramm, U.; Cowan, T.; Sauerbrey, R.
We show a broad overview on our experimental facilities at the HZDR (ELBE, Draco, Penelope) with the experimental and theoretical activities with respect to RF and laser-accelerated electrons and derived secondary radiation sources. On the experimental part we feature the Thomson source PHOENIX at ELBE and our spectrometer diagnostics for measuring electron bunch durations at sub-fs resolution at single shots. On the theoretical part we feature synthetic diagnostics in radiative particle-in-cell simulations for linking experimental observations and theory and our project of an optical free-electron laser based on traveling-wave Thomson scattering. (This is a summary, as there was no official abstract.)
Keywords: PHOENIX, OFEL, TWTS, Traveling-wave Thomson scattering, electron bunch duration measurements, radiative PIC, synthetic diagnostics, Laser wakefield accelerator, LWFA
  • Lecture (others)
    Invitation to give a seminar talk, 21.-28.7.2014, Austin, TX, United States

Permalink: https://www.hzdr.de/publications/Publ-21367
Publ.-Id: 21367


Diffraction and Small Angle Scattering in 2D and 3D

Grenzer, J.; Kharchenko, A.; Gateshki, M.; Holz, T.
The development of new materials is today closely related to the “creation” of new functional nanostructures. Structural investigations are the key to establish a connection between the functional and structural properties that generate this function. This knowledge makes it possible to design new materials with precisely predetermined properties. The function of nanostructures is not only determined by their internal structure, but in large part by their morphology and surface properties.
The development of advanced optical components and 2D detectors enable today measurements that were some years ago only possible using synchrotron radiation. The most important factor is the enhancement of the signal-to-noise ratio using a well optimized setup depending on the concrete measurement problem.
For example, the development of micro-focus sources in the combination of high-performance optics and especially the new semiconductor area detectors (here we used: 2x2 á 256x256 pixels with 55μm pixel size) has established the possibility of GISAXS investigations increasingly in the laboratory. The measurements were performed on a system equipped with a two-dimensional side-by-side optics using a Q-Q diffractometer. It was ensured that the primary beam width remains almost constant over the entire dynamic range and that no secondary maxima occur. The advantage of such an optimized approach is that using the same device both small-angle scattering and as well as additional necessary diffraction experiments without any change in the setup of the diffractometer are possible.
A great advantage of GISAXS is the investigation of buried nanostructures that can be investigated without any additional preparation. Based on thin films prepared by an energetic ion assisted by PVD process, we illustrate the potential of laboratory GISAXS studies.
2D detectors are very efficient for the measurement of large reciprocal space maps at medium resolution in reciprocal space. As an example we will show the investigation of Sn-Ge-Si layers on a Si(001) substrate that are used in modern detectors for telecom applications.
In this contribution we will demonstrate the advantages as well as the special care that is needed during use of modern semiconductor pixel detectors.
  • Poster
    Workshop on X-ray Scattering Methods for Thin Film Characterization, 25.-26.09.2014, Prague, Czech Republic

Permalink: https://www.hzdr.de/publications/Publ-21366
Publ.-Id: 21366


From electron beams to full-scale laser-plasmas -- Obtaining radiation ``sky-maps'' of LWFA within particle-in-cell codes.

Debus, A.; Pausch, R.; Burau, H.; Couperus, J. P.; Cowan, T.; Hübl, A.; Irman, A.; Köhler, A.; Schramm, U.; Widera, R.; Bussmann, M.
Spectra from laser-wakefield acceleration are readily available in experiment, but are challenging to model ab-initio. Yet, beyond the basic properties of synchrotron light sources, the emitted spectra from laser-plasmas include the complete phase-space dynamics and thus are applicable as a powerful tool to quantitatively resolve plasma structures on micrometer and femtosecond scales.

Classical, Liénard-Wiechert-type radiation models that include coherence and polarization properties are based on electron trajectory data, which in full-scale laser-plasmas are on the order of hundreds of TBs to several PBs and require about 10^18 kernel calculations for spectral computation in a single LWFA simulation. Since, such radiation calculations clearly cannot be performed in a post-processing step after a PIC simulation, we include the calculation of these radiation spectra into our multi-GPU particle-in-cell code PIConGPU as a synthetic diagnostic (code is available as open source).

We present current LWFA and laser plasma results, for which we calculated angularly resolved spectra ranging from infrared to X-ray wavelengths. Such an extensive treatment of plasma radiation across billions of macro particles makes it possible to explore temporally resolved plasma radiation spectra on linear and logarithmic photon energy scales over large solid angles ("sky-maps"). These 3D, radiative laser-plasma simulations run on current high-performance GPU clusters and scale up to petaflop performance.
Keywords: radiative PIC, plasma radiation, Laser wakefield accelerator, LWFA, Liénard Wiechert potentials, synthetic diagnostics, particle-in-cell code
  • Lecture (Conference)
    16th Advanced Accelerator Concepts Workshop (AAC 2014), 13.-18.7.2014, San Jose, United States

Permalink: https://www.hzdr.de/publications/Publ-21365
Publ.-Id: 21365


X-ray Diffraction and Scattering from Nanostructures

Grenzer, J.
Nowadays, the development of new materials is often associated with specific properties of functionalized nano structures. X-ray investigations are a very important tool to find the link between the functional (magnetism, luminescence) and the corresponding structural properties (size, orientation etc.) that are generating this function. This knowledge makes it possible to design new materials with specific properties.
This tutorial will show how modern X-ray scattering methods are used in material science. Beside standard X-ray diffraction techniques we will show that with up-to-date laboratory setups X-ray methods can be applied that were some years ago only possible using synchrotron radiation. The advantage and peculiarities of different geometries, 1- and 2-dimensional detectors will be discussed, e.g. they are very efficient for the measurement of large reciprocal space maps at medium resolution.
Different examples will be shown like the investigation of semiconductor nanostructures, of fluorescence up-converting nano particles potentially used in medical applications or grazing incidence diffraction measurements of thin magnetic metallic films.
  • Invited lecture (Conferences)
    Workshop on X-ray Scattering Methods for Thin Film Characterization, 25.-26.09.2014, Prague, Czech Republic

Permalink: https://www.hzdr.de/publications/Publ-21364
Publ.-Id: 21364


How to bring optical free-electrons lasers to table-top with Traveling-wave Thomson scattering

Debus, A.; Steiniger, K.; Bussmann, M.; Pausch, R.; Cowan, T.; Irman, A.; Jochmann, A.; Sauerbrey, R.; Schramm, U.
Optical FELs (OFELs) based on Traveling-wave Thomson scattering (TWTS) optimally exploit the high spectral photon density in high-power laser pulses by spatially stretching the laser pulse and overlapping it with the electrons in a side scattering setup. The introduction of a laser pulse-front tilt provides for interaction lengths appropriate for FEL operation. With careful dispersion control, electrons witness an undulator field of almost constant strength and wavelength over hundreds to thousands of undulator periods, thus giving enough time for self-amplified spontaneous emission (SASE) to seed the FEL instability and the realization of large laser gains.

The TWTS OFEL provides undulator wavelengths on the order of the laser wavelength, sub-meter gain lengths and optimum conditions for optical synchronization. The TWTS OFEL has several advantages over other compact FEL concepts, as it neither requires electron beam focusing nor material for producing or containing the undulator field in the interaction region.

Here, we emphasize similarities and differences of TWTS-OFELs to conventional SASE-FELs and discuss possible experimental scenarios with respect to challenges for high-power lasers and LWFA or RF-driven electron beam sources. Since TWTS-OFELs are highly scalable and tunable from EUV to hard X-rays in very different interaction configurations, we compare these different regimes including their experimental trade-offs.
Keywords: Optical free-electron laser, OFEL, Traveling-wave Thomson scattering, TWTS
  • Lecture (Conference)
    16th Advanced Accelerator Concepts Workshop (AAC 2014), 13.-18.7.2014, San Jose, United States

Permalink: https://www.hzdr.de/publications/Publ-21363
Publ.-Id: 21363


GISAXS Investigation using a Standard Laboratory Diffractometer

Grenzer, J.; Kharchenko, A.; Gateshki, M.; Holz, T.
The development of new materials is today closely related to the "creation" of new functional nanostructures. Structural investigations are the key to establish a connection between the functional and structural properties that generate this function. This knowledge makes it possible to design new materials with precisely predetermined properties. The function of nanostructures is not only determined by their internal structure, but in large part by their morphology and surface properties.
Small angle X-ray scattering in grazing incidence (GISAXS) has the advantage over imaging microscopy (TEM), that usually no complex sample preparation is necessary and larger sample volumes can be analyzed. GISAXS allows the morphology of near-surface structures as well as their (inner) electron density distribution to be determined. GISAXS studies have long been almost exclusively performed at specialized synchrotron beamlines, as the requirements on e.g. on the beam quality were only hard to met with conventional laboratory equipment. The development of microfocus sources in the combination of high-performance optics and especially the new semiconductor area detectors established GISAXS investigations increasingly in the laboratory.
  • Poster
    "XTOP" 2014, 15.-19.09.2014, Grenoble & Villard de Lans, France

Permalink: https://www.hzdr.de/publications/Publ-21362
Publ.-Id: 21362


The evolution and dynamics of damage accumulation due to ion beam implantation studied by X-ray diffraction

Grenzer, J.; Baehtz, C.; Roshchupkina, O. D.; Posselt, M.
In the last years, the development of XFEL facilities have stimulated the discussions on the application of highly intense, ultrafast and/or coherent X-ray pulses for nonconventional in-situ studies in order to improve the understanding of fundamental and atomic-level ultrafast, processes like athermal materials modification by intense fs- or ps-laser or ion pulses generating collision cascades. A predictive understanding of such processes on the performance of advanced (nano) materials on their fabrication and live time would have a strong influence on the development of new materials and technologies. We will discuss the layout of a potential experiment at the European XFEL that could it make possible to probe the cascade dynamics of individual cascades in the (sub-)picosecond temporal regime.

Today, with the present x-ray sources it is almost impossible to monitor a collision cascade in-situ. However, the accumulation of damage and the diffusion of defects in implanted species are much slower processes and can be studied in-situ already today.

Ion beam modification of materials consists usually of two steps (i) the ion implantation and (ii) a subsequent thermal treatment. The first step is characterized by the continuous formation and relaxation of collision cascades over the irradiation time leading to a super-saturation of different types of defects (vacancies, self-interstitials, clusters, etc.) and the resulting kinetic processes like defect diffusion, the build-up of strain etc., on the time scales ranging from ns up to minutes and even hours. The second step is directed towards a reduction of radiation damage formed by ion implantation. It is determined by kinetic processes whose duration is mainly given by the length of the thermal treatment, such as damage recovery, recrystallization of amorphous regions, migration and/or clustering or segregation of point defects and dopant atoms. As a result the material undergoes a strong modification that determines the way how its properties of are changed.
An in-situ ion beam implantation experiment was set up at ROBL/MRH at ESRF. For this purpose an ion gas source with a maximum acceleration voltage of 5keV was mounted on a sputtering chamber. To guarantee a sufficient volume damage the ion energy was further raised to 20keV. Si (001) samples were irradiated at room temperature using He+ at an ion flux of about 1013ions/cm2s. In-situ/in-operando subsequent reciprocal space maps (RSM) were measured to study the evolution of the implanted layer. The time resolution for one RSM as shown in figure 1 was 100ms resulting an acquisition time for one map of below 1min. The crystal truncation rod vanished within the first seconds of He-ion bombardment. In the following the Si (004) reflection broadens, forming a layer peak that gives clearly a hint of increasing strain in the material. After 50 minutes (>1016ions/cm2) a steady-state that corresponds to a heavily damaged or amorphized Si layer was reached.
  • Lecture (Conference)
    "XTOP" 2014, 15.-19.09.2014, Grenoble & Villard de Lans, France

Permalink: https://www.hzdr.de/publications/Publ-21361
Publ.-Id: 21361


LWFA at HZDR - Stability by understanding more data

Debus, A.; Pausch, R.; Steiniger, K.; Hübl, A.; Burau, H.; Widera, R.; Bussmann, M.; Cowan, T.; Couperus, J. P.; Zarini, O.; Jochmann, A.; Irman, A.; Schramm, U.
After a brief update on the current experimental facilities (DRACO & ELBE) we show how measuring plasma radiation can help understand the dynamics of Laser wakefield accelerators. As an example results of a LWFA simulation including plasma radiation using PIConGPU is shown. The radiation was calculated in many direction, in order to reconstruct a spatial image of the radiation sources within the LWFA structure -- corresponding to an experimental imaging diagnostic of plasma self-emission. This reconstruction enables to pinpoint position and time of LWFA electron injection. As an outlook of what to do with high quality LWFA electrons the project of an optical free electron laser is presented. (This is a summary, as there was no official abstract.)
Keywords: Laser wakefield acceleration, LWFA, plasma radiation, radiative PIC, optical free electron laser, Traveling-wave Thomson scattering, TWTS
  • Lecture (Conference)
    LAOLA Workshop, 06.-7.10.2014, Wismar, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-21360
Publ.-Id: 21360


He+ Ion Beam Implantation studied by In-situ X-ray Diffraction

Roshchupkina, O. D.; Baehtz, C.; Bischoff, L.; Posselt, M.; Grenzer, J.
Ion beam techniques are widely used in semiconductor industry for introducing dopant atoms into materials. Ion implantation is characterized by fast dynamic processes associated with the evolution of collision cascades resulting in formation of different types of defects such as vacancies, interstitials, etc. At large fluencies a strained layer that expands in the direction normal to the substrate surface is formed. This is due to the point that the bulk material prevents any lateral macroscopic expansion and as a result a thin irradiated layer is subjected to an in-plane biaxial compressive stress.

The penetration of an Ion into a solid is a very fast process of picoseconds and it is almost impossible to monitor it in-situ with present x-ray sources. However, the accumulation of damage and the diffusion of defects or the implanted species are much slower processes and can be studied in-situ already today.
An in-situ ion beam implantation experiment was set up at ROBL/MRH at ESRF using an ion gas source resulting in a maximal ion energy of 20keV. Si(001) samples were irradiated at room temperature using He+ with an ion flux of max. 1013ions/cm2s. In-situ/in-operando reciprocal space maps were measured to study the strain evolution. The time resolution for one high resolution reciprocal space maps as shown in figure 1 was 100ms resulting an acquisition time for one map of below 1min.
  • Poster
    The 13th conference on Surface X-ray and Neutron Diffraction, 07.-11.07.2014, Hamburg, Germany

Permalink: https://www.hzdr.de/publications/Publ-21359
Publ.-Id: 21359


In-situ X-ray experiments for material science

Grenzer, J.
Kein Abstract vorhanden.
  • Invited lecture (Conferences)
    Workshop „Advanced X-ray Diffraction for Semiconductor Materials and Technology“, 03.-04.04.2014, Frankfurt/Oder, Germany

Permalink: https://www.hzdr.de/publications/Publ-21358
Publ.-Id: 21358


Structural evolution upon thermal annealing for Fe ion irradiated Si(100)

Khanbabaee, B.; Grenzer, J.; Facsko, S.; Pietsch, U.
Off-normal irradiation of Si(100) by Fe ions leads to the surface patterning. In order to understand the mechanism of pattern formation, chemical reactions between Fe and Si atoms have to be considered to influence the surface instability required for pattern formation. Since the as-irradiated surface area is amorphous, we examined the recrystallization process of the Fe-Si layer formed by off-normal 20 keV irradiation using a Si(100) substrate comparing the effect of low (1X10^16 ions cm^-2) and high (5x10^17 ions cm-2) fluencies, where only the higher fluence leads to patterned surface. The samples were annealed up to a temperature of 800°C and characterized by in-situ grazing incidence X-ray diffraction (GI-XRD). Depth profiling by GI-XRD confirmed that ε-FeSi was formed close to the surface changing to a ß-FeSi2 phase with lower Fe content at larger depths. While the polycrystalline ß-FeSi2 phase dominates for higher ion fluencies, a nearly equal ratio between ε-FeSi and ß-FeSi2 is found for lower ones. Our results suggest that phase distribution is related to the Fe concentration profile and can be considered as the relevant factor in the process of pattern formation.
  • Lecture (Conference)
    DPG-Frühjahrstagung der Sektion Kondensierte Materie (SKM), 30.03.-04.04.2014, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-21357
Publ.-Id: 21357


Radiative Particle in Cell simulations on laser-plasma interactions

Debus, A.; Pausch, R.; Hübl, A.; Steiniger, K.; Schmitt, F.; Burau, H.; Widera, R.; Pugmire, D.; Juckeland, G.; Nagel, W. E.; Bussmann, M.; Schramm, U.; Cowan, T.; Sauerbrey, R.
We show how to simulate electromagnetic radiation from plasmas using the particle-in-cell code PIConGPU. After an introduction of the methods we present results from Laser-Wakefield simulations and a large scale Kelvin-Helmholtz-simulation (7.2 PFLOP/s) performed on the TITAN cluster in Oakridge. Towards the conclusion we show that these methods also translate to modeling optical free-electron lasers based on Traveling-wave Thomson scattering. (This is a summary, as there was no official abstract.)
Keywords: plasma radiation, laser wakefield acceleration, LWFA, Kelvin-Helmholtz instability, KHI, Traveling-wave Thomson scattering, TWTS, optical free-electron laser
  • Lecture (Conference)
    LA3NET TW3: Novel Acceleration Techniques,, 28.-30.4.2014, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-21356
Publ.-Id: 21356


Ion irradiation combined with nanoindentation as a screening test procedure for irradiation hardening

Heintze, C.; Bergner, F.; Akhmadaliev, S.; Altstadt, E.
Ion irradiation has long been recognized as a means to efficiently approximate neutron damage in structural materials. Likewise, nanoindentation has long been recognized as a tool to probe the mechanical behaviour of thin layers. The combination of both techniques in order to establish a screening test procedure for irradiation hardening requires consideration of a number of details. The objective is to specify one among several possible variants of such a screening test.
Important constituents of an approach based on ion irradiation and nanoindentation as a screening test procedure for the irradiation response of structural materials exposed to heavy neutron irradiation are: (1) the design of the ion irradiation experiments, e.g. using the MD code SRIM, (2) nanoindentation testing over a large range of indentation depths, (3) elimination of the indentation size effect, elimination of the substrate effect and pile-up correction, (4) careful documentation of the selected options and parameters.
A version of the approach sketched above was applied to unirradiated, ion-irradiated and neutron-irradiated 9%Cr ferritic/martensitic steel T91 (MATTER reference material). The findings indicate that the approach based on ion irradiation and nanoindentation is suitable as a screening test for F/M steels exposed to neutron irradiation.
Keywords: Ion irradiation; neutron irradiation; nanoindentation; T91; screening

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Permalink: https://www.hzdr.de/publications/Publ-21355
Publ.-Id: 21355


Mean-field model of the von Kármán sodium dynamo experiment using soft iron impellers

Nore, C.; Leorat, J.; Guermond, J.-L.; Giesecke, A.
It has been observed that dynamo action occurs in the von-Karman-Sodium (VKS) experiment only when the rotating disks and the blades are made of soft iron. The purpose of this paper is to numerically investigate the role of soft iron in the VKS dynamo scenario. This is done by using a mean field model based on an axisymmetric mean flow, a localized permeability distribution, and a localized α-effect modeling the action of the small velocity scales between the blades. The action of the rotating blades is modeled by an axisymmetric effective permeability field. Key properties of the flow giving to the numerical magnetic field a geometric structure similar to that observed experimentally are identified. Depending on the permeability of the disks and the effective permeability of the blades, the dynamo that is obtained is either oscillatory or stationary. Our numerical results confirm the leading role played by the ferromagnetic impellers. A scenario for the VKS dynamo is proposed.
Keywords: dynamo

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Permalink: https://www.hzdr.de/publications/Publ-21354
Publ.-Id: 21354


Recent LIMMCAST Results on the Modeling of Steel Casting

Gerbeth, G.; Eckert, S.; Timmel, K.; Wondrak, T.
Model experiments with low melting point liquid metals are an important tool to investigate the flow structure and related transport processes in melt flows relevant for metallurgical applications. We present recent results from the three LIMMCAST facilities working either with room-temperature GaInSn or with the alloy SnBi at temperatures of 200-400°C. The main value of cold metal laboratory experiments consists in the capabilities to obtain quantitative flow measurements with a reasonable spatial and temporal resolution, which is essential for code validation. Experimental results are presented covering the following phenomena: contactless electromagnetic tomography of the flow in the mold, flow monitoring by a multitude of ultrasonic sensors, mold flow under the influence of an electromagnetic brake, injection of argon bubbles through the stopper rod, X-ray visualization of gas bubble two-phase flow in the nozzle and in the mold.
Keywords: Continuous casting, physical modeling, flow measurements, magnetic field, flow control, electromagnetic brake
  • Journal for Manufacturing Science and Production 15(2015)1, 131-139
    DOI: 10.1515/jmsp-2014-0036
  • Lecture (Conference)
    2015 TMS Annual Meeting & Exhibition, 15.-19.03.2015, Orlando, USA

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Permalink: https://www.hzdr.de/publications/Publ-21353
Publ.-Id: 21353


Observation and manipulation of dipole-forbidden exciton transitions in semiconductors

Schneebeli, L.; Boettge, C. N.; Breddermann, B.; Kira, M.; Koch, S. W.; Rice, W. D.; Kono, J.; Zybell, S.; Winnerl, S.; Bhattacharyya, J.; Esser, F.; Schneider, H.; Helm, M.; Ewers, B.; Chernikov, A.; Koch, M.; Chatterjee, S.; Khitrova, G.; Gibbs, H.; M. Andrews, A.; Strasser, G.
We discuss recent experimental and theoretical results that report on the observation of dipole-forbidden intra-exciton transitions in semiconductors via terahertz excitation. Additional manipulation capabilities are gained through the application of a magnetic field.
  • Lecture (Conference)
    CLEO-QELS, 08.-13.06.2014, San José, USA

Permalink: https://www.hzdr.de/publications/Publ-21351
Publ.-Id: 21351


YMnO3-based photocapacitive detectors in the visible light regime

Bogusz, A.; Choudhary, O. S.; Selvaraj, L.; John, V.; Bürger, D.; Skorupa, I.; Lawerenz, A.; Schmidt, O. G.; Schmidt, H.
YMnO3 is one of the few materials that exhibit ferroelectricity and antiferromagnetism. Ferroelectricity and antiferromagnetism in case of YMnO3 can be observed up to 900 K and 80 K, respectively. The remanent polarization of YMnO3 amounts to 2 uC/cm2 and metal-YMnO3-metal thin film structures can be switched between a high resistance state (HRS) and a low resistance state (LRS). In case of YMnO3 thin film, the transition from HRS to LRS (set process) occurs at the voltages 10 V and higher, while the transition from LRS to HRS (reset process) is triggered at the smaller voltages. This unipolar resistive switching is nonvolatile and has a resistance ratio of 5 orders of magnitude [1]. In pure YMnO3, absorption occurs throughout the entire visible light region, resulting in its black color [2]. This work investigates the effect of light-irradiation on the capacitance of YMnO3-based metal-ferroelectric-insulator-semiconductor (MFIS) structures. The thickness and optical constants of all layers of the MFIS diodes have been investigated using spectral ellipsometry measurements with a VASE ellipsometer assuming the refraction index of SiN to be 1.95 [3]. The DC bias for the capacitance measurements was swept from +10 to -20 V and back under different light-irradiation at a sweep rate of 230 mV/s. It has been found that under dark conditions two nonvolatile capacitance minima exists at -11 and at -3.55 V, possibly when the YMnO3 is in the LRS and HRS state, respectively. If we rewrite the +10 and -20 V branch in shorter period of time then, low capacitance state (LCS) is non-volatile and pseudo volatile, respectively. Under illumination the capacitance at the two minima increases in the visible spectral range, depending on the wavelength illumination, YMnO3 thickness and capacitance state.
[1] A. Bogusz et al., IEEE Xplore (2013), DOI:10.1109/ISCDG.2013.656319
[2] A. E. Smith et al., J. Am. Chem. Soc. 131, 17084 (2009)
[3] A. Laades et al., Phys. Stat. Sol. C 9, 2124 (2012)
  • Poster
    8th Workshop on Ellipsometry, 10.-12.03.2014, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-21350
Publ.-Id: 21350


Near-surface density profiling of Fe ion irradiated Si (100) using extremely asymmetric x-ray diffraction by variation of the wavelength

Khanbabaee, B.; Facsko, S.; Doyle, S.; Pietsch, U.
In this work, we report on correlations between surface density variations and ion parameters during ion beam-induced surface patterning process. The near-surface density variations of irradi- ated Si(100) surfaces were investigated after off-normal irradiation with 5 keV Fe ions at different fluences. In order to reduce the x-ray probing depth to a thickness below 5 nm, the extremely asym- metrical x-ray diffraction by variation of wavelength was applied, exploiting x-ray refraction at the air-sample interface. Depth profiling was achieved by measuring x-ray rocking curves as function of varying wavelengths providing incidence angles down to 0°. The density variation was extracted from the deviations from kinematical Bragg angle at grazing incidence angles due to refraction of the x-ray beam at the air-sample interface. The simulations based on the dynamical theory of x-ray diffraction revealed that while a net near-surface density decreases with increasing ion fluence which is accompanied by surface patterning, there is a certain threshold of ion fluence to surface density modulation. Our finding suggests that the surface density variation can be relevant with the mechanism of pattern formation.
Keywords: ion irradiation, surface patterning, x-ray diffraction

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Publ.-Id: 21349


Photocapacitance change in YMnO3 based MFIS in the visible light regime

Choudhary, O. S.; Bogusz, A.; Selvaraj, L.; John, V.; Bürger, D.; Skorupa, I.; Lawerenz, A.; Schmidt, O. G.; Schmidt, H.
YMnO3 is one of the few materials that exhibit ferroelectricity and antiferromagnetism. Metal-YMnO3-metal thin film structures can be switched between a high resistance state (HRS) and a low resistance state (LRS), when a positive and negative writing bias is applied, respectively. This work investigates the effect of light-irradiation on the capacitance of YMnO3-based metal-ferroelectric-insulatorsemiconductor (MFIS) structures. The DC bias for the capacitance measurements was swept from +10 to -20 V and back under different light-irradiation at a sweep rate of ca. 103 mV/s. It has been found that under dark conditions two nonvolatile capacitance minima exists at -11 and at -3.55 V, possibly when the YMnO3 is in the LRS and HRS state, respectively. If we rewrite the +10 and -20 V branch in shorter period of time then, low capacitance state (LCS) is non-volatile and pseudo volatile, respectively. Under illumination the capacitance at the two minima increases in the visible spectral range, depending on the wavelength illumination, YMnO3 thickness and YMnO3 capacitance state.
  • Poster
    DPG Spring Meeting, 30.03.-04.04.2014, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-21348
Publ.-Id: 21348


Sequence dependence of electron-induced DNA strand breakage revealed by DNA nanoarrays

Keller, A.; Rackwitz, J.; Cauet, E.; Liévin, J.; Körzdörfer, T.; Rotaru, A.; Gothelf, K. V.; Besenbacher, F.; Bald, I.
The electronic structure of DNA is determined by its nucleotide sequence, which is for instance exploited in molecular electronics. Here we demonstrate that also the DNA strand breakage induced by low-energy electrons (18 eV) depends on the nucleotide sequence. To determine the absolute cross sections for electron induced single strand breaks in specific 13 mer oligonucleotides we used atomic force microscopy analysis of DNA origami based DNA nanoarrays. We investigated the DNA sequences 59-TT(XYX)3TT with X 5 A, G, C and Y 5 T, BrU 5-bromouracil and found absolute strand break cross sections between 2.66 ? 10214 cm2 and 7.06 ? 10214 cm2. The highest cross section was found for 59-TT(ATA)3TT and 59-TT(ABrUA)3TT, respectively. BrU is a radiosensitizer, which was discussed to be used in cancer radiation therapy. The replacement of T by BrU into the investigated DNA sequences leads to a slight increase of the absolute strand break cross sections resulting in sequence-dependent enhancement factors between 1.14 and 1.66. Nevertheless, the variation of strand break cross sections due to the specific nucleotide sequence is considerably higher. Thus, the present results suggest the development of targeted radiosensitizers for cancer radiation therapy.
Keywords: DNA, NANOSTRUCTURES, BIOPHYSICAL CHEMISTRY, CHEMICAL PHYSICS

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Publ.-Id: 21347


Resistive switching of flash lamp crystallized YMnO3 thin films prepared on Pt/Ti/SiO2/Si substrates by low temperature pulsed laser deposition

Bogusz, A.; Prucnal, S.; Skorupa, W.; Blaschke, D.; Abendroth, B.; Stöcker, H.; Skorupa, I.; Bürger, D.; Schmidt, O. G.; Schmidt, H.
Use of multiferroic oxides as a switching medium presents an opportunity to add the additional or novel functionalities into the switching device. Typically, the growth temperatures of such oxides are above 600°C and so far CMOS compatibility has not been achieved. YMnO3 exhibits unipolar resistive switching [1] however its high crystallization temperature (above 750°C) imposes difficulties in preparation of thin films on metal-coated substrates. This work presents the results of electrical and structural characterization of YMnO3 thin films grown on Pt/Ti/SiO2/Si substrates by pulsed laser deposition at 400°C and crystallized by flash lamp annealing (FLA). It is shown that the FLA process with optimized parameters allows the preparation of polycrystalline YMnO3 films without deformation of the Pt/Ti electrode and interdiffusion processes in the YMnO3/Pt/Ti/SiO2/Si stack.
[1] A. Bogusz et al., IEEE Xplore (2013), DOI:10.1109/ISCDG.2013.656319
  • Lecture (Conference)
    DPG Spring Meeting, 30.03.-04.04.2014, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-21346
Publ.-Id: 21346


Atomistic modeling of ion-beam and thermally induced processes in Si and Ge

Liedke, B.; Heinig, K.-H.; Schmidt, B.; Bulutay, C.; Böttger, R.; Posselt, M.; Bracht, H.
The abstract was not needed
Keywords: Kinetic Monte-Carlo, atomistic simulation, silicon, germanium, molecular dynamics, phase separation, self organization
  • Lecture (others)
    Seminar at the KTH Royal Institute of Technology - Reactor Physics, 12.11.2014, Stockholm, Sweden

Permalink: https://www.hzdr.de/publications/Publ-21345
Publ.-Id: 21345


Nonvolatile unipolar resistive switching in YMnO3 thin films

Bogusz, A.; Prucnal, S.; Skorupa, W.; Blaschke, D.; Abendroth, B.; Stöcker, H.; Skorupa, I.; Bürger, D.; Schmidt, O. G.; Schmidt, H.
Due to its promising applications, resistive switching in oxides known also as a memristive effect, has gained a lot of attention both from scientists and industry. The multiferroic oxides as a switching medium offer a novel functionalities of the switching devices. Typically, the growth temperatures of such oxides are above 600°C and so far CMOS compatibility has not been achieved. As an example, the multiferroic YMnO3 exhibits unipolar resistive switching [1]. However, its high crystallization temperature (above 750°C) imposes difficulties in preparation of thin films on metal-coated substrates. This work compares the results of electrical and structural characterization of YMnO3 thin films grown on Pt/Ti/SiO2/Si substrates by pulsed laser deposition with two different approaches. In the first one, the polycrystalline YMnO3 films are deposited at 800°C. In the second approach, amorphous films deposited at 400°C are crystallized by millisecond range flash lamp annealing. It is shown that the ultra short annealing allows the preparation of polycrystalline YMnO3 films without deformation of the Pt/Ti electrode which exhibits improved endurance of resistive switching.
  • Lecture (Conference)
    Workshop AK Materialien für nichtflüchtige Speicher, 28.-29.04.2014, Chemnitz, Germany

Permalink: https://www.hzdr.de/publications/Publ-21344
Publ.-Id: 21344


Evaluation of the new radioligand [18F]AQ-28A by small animal PET/MR demonstrates increase of PDE10A expression in striatum and brown adipose tissue (BAT) of obese mice

Wagner, S.; Kranz, M.; Hankir, M.; Deuther-Conrad, W.; Scheunemann, M.; Teodoro, R.; Wenzel, B.; Fischer, S.; Egerland, U.; Fenske, W. K.; Hesse, S.; Höfgen, N.; Steinbach, J.; Brust, P.
Objectives: Phosphodiesterase 10A (PDE10A) hydrolyses cAMP and cGMP. It is abundantly expressed in striatum, where it modulates intracellular dopamine signaling. There is evidence that PDE10A is involved in the regulation of whole body energy balance [1], but changes in its expression associated with obesity have not been described so far. To investigate this issue, we developed the new PDE10A radioligand [18F]AQ-28A and performed preliminary PET/MR studies in various animal models of obesity.
Methods: [18F]AQ-28A was synthesized by nucleophilic aromatic substitution from a nitro precursor. Ex vivo and in vitro autoradiography of [18F]AQ-28A was performed on mice and pig brain, respectively. Mice brain and plasma samples (30 min p.i) were investigated by radio-HPLC. Uptake of [18F]AQ-28A in striatum and brown adipose tissue (BAT) of adult female CD-1 mice (n=5) was studied by dynamic animal PET/MR before (control) and after a high fat diet for 12 weeks as well as in genetically obese leptin deficient (ob/ob) mice (n=5).
Results: [18F]AQ-28A was synthesized fully automated with a radiochemical yield of 31.0±7.0% (n=3), a specific activity of 65.9±19.9 GBq/μmol (n=3) and a radiochemical purity of >98%. Ex vivo and in vitro, distribution patterns of [18F]AQ-28A in mouse and pig brain corresponded to the expression of PDE10A. In vivo, 89% and 64% of intact tracer accounted for total radioactivity in brain and plasma of mice at 30 min p.i. Dynamic PET/MR studies revealed a target specific accumulation in striatum (max. SUVmean=2.04). Follow-up studies after high fat diet showed a 130% higher SUV in BAT and a 30% higher SUV in striatum of obese mice in comparison to controls. Similar radioligand accumulation was observed in genetically obese mice with 86% parent fraction in BAT at 30 min p.i.
Conclusions: We have successfully used the new radioligand [18F]AQ-28A for PET imaging of PDE10A in various animal models of obesity. Small animal PET/MR studies demonstrated for the first time that an increase of the PDE10A expression in the striatum of obese mice is accompanied by an even stronger increase in BAT suggesting that PDE10A is a potential therapeutic target.
References: [1] Nawrocki AR, et al. (2014) Diabetes, 63: 300.
  • Lecture (Conference)
    21st International Symposium on Radiopharmaceutical Sciences - ISRS2015, 26.-31.05.2015, Columbia, Missouri, USA
  • Open Access Logo Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 58(2015)1, 52
    DOI: 10.1002/jlcr.3302_1

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Publ.-Id: 21343


Radiation effects in structural steels for nuclear applications: an atomistic study

Bakaev, A.; van Neck, D.; van Oost, G.; Terentyev, D. Keywords: radiation effects, ferritic steels, austenitic steels, ab initio, molecular dynamics
  • Lecture (Conference)
    KTH seminar, 18.11.2014, Stockholm, Sweden

Permalink: https://www.hzdr.de/publications/Publ-21342
Publ.-Id: 21342


Segregation-induced embrittlement in RPV steels: assessment by atomistic simulations

Bakaev, A.; Terentyev, D.; Bonny, G.; Zhurkin, E. E.; van Neck, D.
Segregation-induced embrittlement in RPV steels: assessment by atomistic simulations
Keywords: ferrtitic steels, embrittlement, hardening
  • Lecture (Conference)
    FWI seminar, 14.08.2014, HZDR, Germany

Permalink: https://www.hzdr.de/publications/Publ-21341
Publ.-Id: 21341


Dislocation mechanism of deuterium retention in tungsten under plasma implantation

Dubinko, V. I.; Terentyev, D.; Grigorev, P.; Bakaev, A.; van Oost, G.; Gao, F.; van Neck, D.; Zhurkin, E. E.
We have developed a new theoretical model for deuterium (D) retention in tungsten-based alloys on the basis of its being trapped at dislocations and transported to the surface via the dislocation network with parameters determined by ab initio calculations. The model is used to explain experimentally observed trends of D retention under sub-threshold implantation, which does not produce stable lattice defects to act as traps for D in conventional models. Saturation of D retention with implantation dose and effects due to alloying of tungsten with, e.g. tantalum, are evaluated, and comparison of the model predictions with experimental observations under high-flux plasma implantation conditions is presented.
Keywords: dislocations, retention, plasma, hydrogen isotopes, rate theory

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Publ.-Id: 21340


Deuterium accumulation in tungsten under low-energy high-flux plasma exposure

Grigorev, P. Y.; Dubinko, V. I.; Terentyev, D. A.; Bakaev, A.; Zhurkin, E. E.
The accumulation of deuterium implanted in tungsten is simulated within the framework of kinetic diffusion theory. The influence of the tungsten microstructure (dislocation density and impurity concentration) on the process of deuterium capture and accumulation is considered. It is established that, under the chosen irradiation conditions, deuterium accumulation in the near-surface region is determined by capture at defects formed during implantation. The deuterium concentration gradient, together with the material microstructure, determines its accumulation in tungsten. Variation in the dislocation density and impurity concentration does not affect the simulation results, which is, first, related to the fact that the model used does not contain alternative mechanisms for the formation and growth of vacancy clusters under the subthreshold irradiation mode. The simulation results are compared with experimental data, and ways of improving the model are discussed in order to explain the deuterium-saturation effect for high fluences (more than 1023 m−2).
Keywords: tungsten, retention, hydrogen isotopes, plasma, rate theory
  • Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques 8(2014)2, 234-238
    DOI: 10.1134/S102745101402013X

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Publ.-Id: 21339


Many-body central force potentials for tungsten

Bonny, G.; Terentyev, D.; Bakaev, A.; Grigoriev, P.; van Neck, D.
Tungsten and tungsten-based alloys are the primary candidate materials for plasma facing components in fusion reactors. The exposure to high-energy radiation, however, severely degrades the performance and lifetime limits of the in-vessel components. In an effort to better understand the mechanisms driving the materials' degradation at the atomic level, large-scale atomistic simulations are performed to complement experimental investigations. At the core of such simulations lies the interatomic potential, on which all subsequent results hinge. In this work we review 19 central force many-body potentials and benchmark their performance against experiments and density functional theory (DFT) calculations. As basic features we consider the relative lattice stability, elastic constants and point-defect properties. In addition, we also investigate extended lattice defects, namely: free surfaces, symmetric tilt grain boundaries, the 1/2〈1 1 1〉{1 1 0} and 1/2〈1 1 1〉 {1 1 2} stacking fault energy profiles and the 1/2〈1 1 1〉 screw dislocation core. We also provide the Peierls stress for the 1/2〈1 1 1〉 edge and screw dislocations as well as the glide path of the latter at zero Kelvin. The presented results serve as an initial guide and reference list for both the modelling of atomically-driven phenomena in bcc tungsten, and the further development of its potentials.
Keywords: tungsten, interatomic potentials, classical molecular dynamics, ab initio

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Publ.-Id: 21338


Carbon-vacancy interaction controls lattice damage recovery in Iron

Terentyev, D.; Heinola, K.; Bakaev, A.; Zhurkin, E. E.
Ab initio techniques are applied to assess the positron lifetime of carbon–vacancy (C–V) complexes in iron for the first time. Positron lifetime is extremely sensitive to C–V arrangement and multiplicity. Following the ab initio lifetime data, a C–V complex can be detected as a single or clustered vacancy, or remain indistinguishable from bulk. Combining ab initio data with kinetic rate theory, we modelled annealing of irradiated Fe–C alloys and performed one-to-one comparison with experiment, which revealed a good agreement.
Keywords: Iron, Interstitial carbon, Lattice damage, Recovery, Annealing

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Permalink: https://www.hzdr.de/publications/Publ-21337
Publ.-Id: 21337


Dislocations mediate hydrogen retention in tungsten

Terentyev, D.; Dubinko, V.; Bakaev, A.; Zayachuk, Y.; van Renterghem, W.; Grigorev, P.
In this letter, a comprehensive mechanism for the nucleation and growth of bubbles on dislocations under plasma exposure of tungsten is proposed. The mechanism reconciles long-standing experimental observations of hydrogen isotopes retention, essentially defined by material microstructure, and so far not fully explained. Hence, this work provides an important link to unify material's modelling with experimental assessment of W and W-based alloys as candidates for plasma facing components.
Keywords: hydrogen isotopes, retention, tungsten, ab initio, DFT, rate theory

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Permalink: https://www.hzdr.de/publications/Publ-21336
Publ.-Id: 21336


Effect of carbon decoration on the absorption of 〈 100 〉 dislocation loops by dislocations in iron

Terentyev, D.; Bakaev, A.; Zhurkin, E. E.
This work closes a series of molecular dynamics studies addressing how solute/interstitial segregation at dislocation loops affects their interaction with moving dislocations in bodycentred cubic Fe-based alloys. We consider the interaction of 〈1 0 0〉 interstitial dislocation loops decorated by different numbers of carbon atoms in a wide temperature range. The results reveal clearly that the decoration affects the reaction mechanism and increases the unpinning stress, in general. The most pronounced and reproducible increase of the unpinning stress is found in the intermediate temperature range from 300 up to 600 K. The carbon-decoration effect is related to the modification of the loop–dislocation reaction and its importance at the technologically relevant neutron irradiation conditions is discussed.
Keywords: dislocation, carbon, iron, segregation

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Permalink: https://www.hzdr.de/publications/Publ-21335
Publ.-Id: 21335


Atomistic simulation of the interaction between mobile edge dislocations and radiation-induced defects in Fe-Ni-Cr austenitic alloys

Bakaev, A.; Terent’Ev, D. A.; Grigor’Ev, P. Y.; Zhurkin, E. E.
The classical molecular dynamics method is employed to simulate the interaction of edge dislocations with interstitial Frank loops (2 and 5 nm in diameter) in the Fe-Ni10-Cr20 model alloy at the temperatures T = 300–900 K. The examined Frank loops are typical extended radiation-induced defects in austenitic steels adapted to nuclear reactors, while the chosen triple alloy (Fe-Ni10-Cr20) has the alloying element concentration maximally resembling these steels. The dislocation-defect interaction mechanisms are ascertained and classified, and their comparison with the previously published data concerning screw dislocations is carried out. The detachment stress needed for a dislocation to overcome the defect acting as an obstacle is calculated depending on the material temperature, defect size, and interaction geometry. It is revealed that edge dislocations more efficiently absorb small loops than screw ones. It is demonstrated that, in the case of small loops, the number of reactions accompanied by loop absorption increases with temperature upon interaction with both edge and screw dislocations. It is established that Frank loops are stronger obstacles to the movement of screw dislocations than to the movement of edge ones.
Keywords: classical molecular dynamics, plastic behaviour, austenitic steels, dislocations
  • Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques 8(2014)2, 220-228
    DOI: 10.1134/S1027451014020062

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Publ.-Id: 21334


Basic Properties of Minor Alloying Elements in High-Cr Ferritic Steels: An Ab Initio Study

Bakaev, A.; Terentyev, D.; Bonny, G.; Klaver, T. P. C.; Olsson, P.; van Neck, D.
Basic properties of minor alloying elements, namely Mo, W, Nb, Ta, V, Mn, Si entering the conventional and reduced-activation structural Fe–(9–12)Cr steels have been analyzed using ab initio calculations. The electronic structure calculations were applied to study the interaction of minor alloying elements with a number of important and well defined lattice structures, such as point defects, the 1/2<111> screw dislocation core, high angle symmetric grain boundaries and free surfaces. The studied elements were classified according to their similarities and discrepancies regarding the interaction with the above mentioned defects. The refractory alloying elements are found to follow the same trend whereas Mn and Si exhibit peculiar behavior with respect to the interaction with both point and extended lattice defects. The obtained results are discussed and compared with previously published ab initio and available experimental data.
Keywords: minor alloying elements, ferritic steels, ab initio, DFT, lattice defects

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Publ.-Id: 21333


Interaction of carbon-vacancy complex with minor alloying elements of ferritic steels

Bakaev, A.; Terentyev, D.; He, X.; Zhurkin, E. E.; van Neck, D.
Interstitial carbon, dissolved in bcc matrix of ferritic steels, plays an important role in the evolution of radiation-induced microstructure since it exhibits strong interaction with vacancies. Frequent formation and break-up of carbon–vacancy pairs, occurring in the course of irradiation, affect both kinetics of the accumulation of point defect clusters and carbon spatial distribution. The interaction of typical alloying elements (Mn, Ni, Cu, Si, Cr and P) in ferritic steels used as structural materials in nuclear reactors with a carbon–vacancy complex is analyzed using ab initio techniques. It is found that all the considered solutes form stable triple clusters resulting in the increase of the total binding energy by 0.2–0.3 eV. As a result of the formation of energetically favourable solute–carbon–vacancy triplets, the dissociation energy for vacancy/carbon emission is also increased by ~0.2–0.3 eV, suggesting that the solutes enhance thermal stability of carbon–vacancy complex. Association of carbon–vacancy pairs with multiple solute clusters is found to be favorable for Ni, Cu and P. The energetic stability of solute(s)–carbon–vacancy complexes was rationalized on the basis of pairwise interaction data and by analyzing the variation of local magnetic moments on atoms constituting the clusters.
Keywords: ferritic steels, carbon, solute-rich clusters, ab initio, DFT

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Permalink: https://www.hzdr.de/publications/Publ-21332
Publ.-Id: 21332


Synergetic Effects of Mn and Si in the Interaction with Point Defects in bcc Fe

Bakaev, A.; Terentyev, D.; He, X.; Van Neck, D.
The interaction of Mn, Si and Cr with a vacancy and self-interstitial defects in BCC Fe has been analyzed using ab initio calculations. While the interaction of the considered solute clusters with a single vacancy is linearly additive, there is a considerable synergetic effect in the case of self-interstitial atoms, found to bind strongly with Mn–Si pairs. The latter therefore act as deep trapping configurations for self-interstitials. At the same time, the presence of the point defects nearby weakly attractive Mn–Si pairs significantly enhances the solute–solute binding. The revealed effects are rationalized on the basis of charge density and local magnetic moment distributions.
Keywords: solute clusters, bcc Fe, ab initio, DFT

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Publ.-Id: 21331


Three-feature dispersed barrier hardening model applied to Cu-bearing low-Ni RPV steels

Bergner, F.; Gillemot, F.; Hernandez-Mayoral, M.; Serrano, M.; Ulbricht, A.
The three-feature dispersed-barrier hardening model was successfully applied to neutron-irradiated RPV steels. Estimated values of the obstacle strength of loops, nanovoids and Cu-rich precipitates are largely consistent with reported estimates. For fluences representative of less than 60 years of operation (VVER440 base metal) nanovoids can be ignored, that means a two-feature version is sufficient.
Keywords: RPV steels, neutron irradiation, hardening
  • Lecture (Conference)
    18th Meeting of the International Group on Radiation Damage Mechanisms in Pressure Vessel Steels (IGRDM-18), 23.-28.11.2014, Miyazaki, Japan

Permalink: https://www.hzdr.de/publications/Publ-21330
Publ.-Id: 21330


Effect of neutron flux on the solute cluster characteristics and hardening in RPV steels

Bergner, F.; Chaouadi, R.; Dohi, K.; Hein, H.; Serrano, M.; Soneda, N.; Wagner, A.
Flux is an important variable of RPV steel embrittlement because of several reasons including the consideration of surveillance samples vs. RPV wall material, MTR vs. PWR/BWR irradiations and ions as a neutron substitute in the lab. The approach relies on the reasonable assumption that the flux effect on the mechanical properties is mediated by the flux-dependent evolutiooon of the irradiation-induced nanofeatures. In order to separate flux effects from the effect of the neutron fluence, pairs of samples of one and the same material irradiated at as different as possible flux up to about the same fluence are selected. These pairs of samples were fully characterized with respect to both mechanical property changes and the characteristics of irradiation-induced solute clusters. The results indicate that there is a pronounced effect of flux on cluster size, that there are minor flux effects on number density, volume fraction and composition of clusters and that SANS and APT provide consistent results on size and number density of clusters. The classical dispersed-barrier hardening model combined with deterministic growth and irradiation-enhanced diffusion describes the flux effect on the mechanical properties well.
Keywords: RPV steel, neutron irradiation, flux effect, SANS, APT
  • Lecture (Conference)
    18th Meeting of the International Group on Radiation Damage Mechanisms in Pressure Vessel Steels (IGRDM-18), 23.-28.11.2014, Miyazaki, Japan

Permalink: https://www.hzdr.de/publications/Publ-21329
Publ.-Id: 21329


Reverse epitaxy on Ge surfaces

Ou, X.; Keller, A.; Helm, M.; Fassbender, J.ORC; Facsko, S.
Arrays of semiconductor nanostructures have the potential for nanoelectronic and optoelectronic applications. Besides the conventional low efficiency lithographic techniques broad ion beam irradiation is a simple and mass productive technique to fabricate nanostructure patterns on semiconductor surfaces.[1] Based on a “self-organized” erosion process, periodic ripple, hole, or dot arrays can be produced on various semiconductor surfaces.
However, the main drawback of this method is that the irradiated semiconductor surfaces are amorphized. [1, 2] For device fabrication, a crystalline surface of high quality is indispensable. In this work we report the recent discovery of single crystal Ge nanopattern formation based on a “reverse epitaxy” process.[3] The low energy ion irradiation is performed in a defined temperature window. Vacancies created during ion beam irradiation distribute according to the crystallographic anisotropy, which results in an orientation-dependent pattern formation on single crystal Ge surface. This process shows nicely the equivalence of epitaxy with deposited adatoms and “reverse epitaxy” with ion induced surface vacancies on semiconductors. The formation of these patterns is interpreted as the result of a surface instability due to an Ehrlich-Schwoebel barrier for ion induced surface vacancies. The simulation of the pattern formation is performed by a continuum equation accounting for the effective surface currents.
The formation mechanism of these patterns is quite general and can be extended to other semiconductors, e.g. Si and compound semiconductors. Thus our work establishes an entirely new and complementary epitaxial method for the fabrication of high-quality faceted semiconductor nanostructures. A physical model for nanopatterning of crystalline semiconductor surfaces with ion beam irradiation will be demonstrated based on comparison between experimental results and computer simulations.

[1] Stefan Facsko et al., Science 285, 1551 (1999).
[2] Xin Ou et al., AIP Advances, 1, 042174 (2011).
[3] Xin Ou et al., Physical Review Letters 111, 016101 (2013).
Keywords: Ge and ion irradiation
  • Invited lecture (Conferences)
    23rd Conference on Application of Accelerators in Research and Industry, 25.-30.05.2014, San Antonio, USA

Permalink: https://www.hzdr.de/publications/Publ-21328
Publ.-Id: 21328


Reverse Epitaxy on Semiconductor Surfaces

Ou, X.; Hübner, R.; Helm, M.; Fassbender, J.ORC; Facsko, S.
Arrays of semiconductor nanostructures are emerging as building blocks for next generation of electronic and optoelectronic nanodevices. In molecular beam epitaxy (MBE) the continuous deposition of atoms can lead to growth of self-organized 3D nanostructures. One of the possible surface instabilities, which is responsible for this kind of growth, is caused by the Ehrlich-Schwoebel (ES) barrier, i.e. an additional diffusion barrier for ad-atoms to cross terrace steps [1]. The arriving atoms are trapped on terraces and can again nucleate to form new terraces. This mechanism leads to the growth of pyramidal mounds on the surface with facets corresponding to energetically favored crystal planes. An analogous mechanism is also observed on ion irradiated surfaces. However, ion sputtering leads to the erosion of the surfaces and at room temperature semiconductor surfaces become amorphous. At these conditions various periodic patterns are observed. [2] For device fabrication, a crystalline surface of high quality is indispensable.
In this talk, we demonstrate single crystal elemental (Si and Ge) and compound semiconductor (III-V) nanostructure pattern formation (Figure 1) based on a “reverse epitaxy” process. [3] Vacancies created during ion beam irradiation at elevated temperature distribute according to the crystallographic anisotropy, which results in an orientation-dependent pattern formation on single crystal semiconductor surfaces. This process shows nicely the equivalence of epitaxy with deposited adatoms and “reverse epitaxy” with ion induced surface vacancies on semiconductors. The formation of these patterns is interpreted as the result of a surface instability due to an Ehrlich-Schwoebel barrier for ion induced surface vacancies. The simulation of the pattern formation is performed by a continuum equation accounting for the effective surface currents. Our work establishes an entirely new and complementary epitaxial method for the fabrication of high-quality faceted semiconductor nanostructures. The potential application of reverse epitaxy on fabrication of quantum devices and optical components will be discussed.
*email address: X.Ou@hzdr.de
Keywords: ion sputtering
  • Invited lecture (Conferences)
    The 10th international ESPS-NIS workshop, 20.-23.07.2014, Traunkirchen, Austria

Permalink: https://www.hzdr.de/publications/Publ-21327
Publ.-Id: 21327


Loaded and Unlocked - Accelerating OpenSource Plasma Physics

Bussmann, M.; Burau, H.; Cowan, T. E.; Debus, A.; Garten, M.; Helm, A.; Huebl, A.; Juckeland, G.; Kluge, T.; Pausch, R.; Schmitt, F.; Schneider, B.; Schramm, U.; Steiniger, K.; Widera, R.
PIConGPU is a fully relativistic 3D3V particle-in-cell (PIC) code for studying laser-plasma interactions. Todays graphics processing units (GPUs) are massively-parallel accelerators for scientific computing, pushing the limits for a new era of in situ plasma simulations.

During the last decades PIC codes became the workhorses for theoretical studies in laser-particle acceleration. Besides the ongoing demand for faster and more realistic simulations, interaction with the simulation and handling of peta-bytes of generated data per simulation are two of the challenging topics in high performance computing.

Moreover, we present a general explicit scheme to load charged relativistic particle beams in the PIC cycle. Taking care of the particle shape in combination with a discretization-dependent potential solver for one-time initialization allows for ab-initio conservation of Gauss' law.

PIConGPU is among the 2013 ACM Gordon Bell finalists, reaching the highest performance of a PIC simulation ever reported with 8 PFlop/s mixed precision. Utilizing the world's #2 supercomputer Titan (Oak Ridge National Lab), we present performance benchmarks up to 18,000 GPUs, scaling to a total of 50 million multi-processors.

PIConGPU is developed as open source by the Junior Group for Computational Radiation Physics at the Institute for Radiation Physics at Helmholtz-Zentrum Dresden - Rossendorf (HZDR) in close collaboration with the Center for Information Services and High Performance Computing (ZIH) of the Technical University Dresden (TUD).
Keywords: PIConGPU, LPA, OpenSource, GPU, HPC, Laser-Plasma
  • Invited lecture (Conferences)
    Séminaire LOA, 30.01.2014, Paris, France

Permalink: https://www.hzdr.de/publications/Publ-21326
Publ.-Id: 21326


Bigger, Better, Uncut - On New Accelerator Concepts And Next-Generation HPC Simulations at HZDR

Huebl, A.; Widera, R.; Burau, H.; Schmitt, F.; Eckert, C.; Zenker, E.; Knespel, M.; Garten, M.; Schneider, B.; Pausch, R.; Steiniger, K.; Huang, L.; Debus, A.; Kluge, T.; Couperus, J. P.; Koehler, A.; Jochmann, A.; Irman, A.; Metzkes, J.; Obst, L.; Schlenvoigt, H.-P.; Zeil, K.; Kraft, S.; Juckeland, G.; Cowan, T.; Schramm, U.; Bussmann, M.
The German national labs in the Helmholtz Association push the development of alternative acceleration schemes in large scale programs to overcome the limits set by conventional accelerators. Helmholtz-Zentrum Dresden - Rossendorf (HZDR) hosts high-power (PW), ultra-short (fs), high-repetition rate (Hz) lasers that are capable to pave the way to provide reliable, controlled laser-plasma sources.

Besides improving ion plasma-accelerators with techniques such as enhanced TNSA, cone targets and mass reduced targets, experiments successfully conducted at HZDR include new light sources from heads-on Thomson scattering with the synchronized linear accelerator ELBE and laser-wakefield electron acceleration. Upcoming large-scale international experiments such as solid-target, pump-probe science in strong-fields at the European XFEL (HIBEF) are coordinated by HZDR, uniting more than 350 scientists and 300 PhD students from 16 countries.

In the highly non-linear domain of plasma-based accelerators, many challenges today occur due to the missing control over arising instabilities, neglected effects in theoretical plasma models or strongly varying experimental parameters such as the driving laser pulses. In the same way as experiments evolve from best-shot practices, simulations have to evolve to full-scale, multi-physics parameter studies including extensive in-situ diagnostics. As shown in
this talk, even interactive live simulations on the biggest clusters of the US and Europe are possible today to drive exploration.

PIConGPU is a fully relativistic 3D3V particle-in-cell (PIC) code for studying laser-plasma interactions. Today's graphics processing units (GPUs) are massively-parallel accelerators for scientific computing, pushing the limits for a new era of in-situ plasma simulations. HZDR drives its development in an open source community effort, providing the horsepower that is required to approach the foremost mentioned challenges.
Keywords: LPA, PW Laser, HPC, GPUs, HIBEF, TNSA, LWFA, PIConGPU, PIC
  • Invited lecture (Conferences)
    Special CBP-Bella Center Seminar, 05.12.2014, Berkeley, USA

Permalink: https://www.hzdr.de/publications/Publ-21325
Publ.-Id: 21325


Ferromagnetic GaMnP Prepared by Ion Implantation and Pulsed Laser Annealing

Yuan, Y.; Wang, Y.; Khalid, M.; Gao, K.; Prucnal, S.; Gordan, O. D.; Salvan, G.; Zahn, D. T.; Skorupa, W.; Helm, M.; Zhou, S.
We present the magnetic, transport, and structural properties of GaMnP with different Mn concentrations prepared by ion implantation and pulsed laser annealing. The Curie temperature increases with Mn concentration and the samples show in-plane magnetic anisotropy due to the in-plane compressive strain in the GaMnP layer. Anomalous Hall effect and negative magnetoresistance are observed, indicating the carrier mediated nature of the ferromagnetism in GaMnP. According to the micro-Raman spectroscopy data after pulsed laser annealing, the implanted layer has been fully recrystallized and the carrier concentration (hole) increases with Mn concentration.
Keywords: Dilute magnetic semiconductors (DMS), GaMnP, ion implantation, pulsed laser annealing

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Permalink: https://www.hzdr.de/publications/Publ-21324
Publ.-Id: 21324


Electrochemical deposition of magnetic ions at electrodes which are exposed to small-scale gradients of the magnetic field

Mutschke, G.; Fröhlich, J.
The mechanism responsible for the spatially inhomogeneous thickness of metal layers obtained by electrochemical deposition in magnetic gradient fields at small scale is controversially discussed in the literature. The paper presents the results of numerical simulations which support the concept that local convection at the electrode, driven by the curl of the magnetic gradient force, is responsible for the effects observed. The deposition of paramagnetic and of diamagnetic ions is discussed, and the influence of electrically inert magnetic ions present in the electrolyte is highlighted.
Keywords: Electrochemistry, electrolysis, metal deposition, magnetic field, magnetic gradient force, numerical simulation, spatially-structured deposition
  • Poster
    Strömungstechnische Tagung 2014 anlässlich des 100. Geburtstages von Werner Albring, 10.10.2014, Dresden, Deutschland
  • Book chapter
    J. Fröhlich, S. Odenbach, K. Vogeler: Strömungstechnische Tagung 2014 - Tagung anlässlich des 100. Geburtstages von Werner Albring; Schriftenreihe aus dem Institut für Strömungsmechanik, Band 10, TU Dresden., Dresden: TUDpress Verlag der Wissenschaften GmbH, 2014, 978-3-944331-78-2, 373-376

Permalink: https://www.hzdr.de/publications/Publ-21323
Publ.-Id: 21323


New data on the quasi-free np -> npπ+π- and np ->ppπ-π0 reactions at 1.25 GeV with HADES

Kurilkin, A. K.; Admaczewski-Musch, J.; Arnold, O.; Atomssa, E. T.; Behnke, C.; Belyaev, A.; Berger-Chen, J. C.; Biernat, J.; Blanco, A.; Blume, C.; Böhmer, M.; Bordalo, P.; Chernenko, S.; Deveaux, C.; Dybczak, A.; Epple, E.; Fabbietti, L.; Fateev, O.; Fonte, P.; Franco, C.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzón, J. A.; Gill, K.; Golubeva, M.; González-Díaz, D.; Guber, F.; Gumberidze, M.; Harabasz, S.; Hennino, T.; Höhne, C.; Holzmann, R.; Ierusalimov, A.; Ivashkin, A.; Jurkovic, M.; Kämpfer, B.; Karavicheva, T.; Kardan, K.; Koenig, I.; Koenig, W.; Kolb, B. W.; Korcyl, G.; Kornakov, G.; Kotte, R.; Krása, A.; Krebs, E.; Krizek, F.; Kuc, H.; Kugler, A.; Kunz, T.; Kurepin, A.; Kurilkin, P.; Ladygin, V.; Lalik, R.; Lang, S.; Lapidus, K.; Lebedev, A.; Lopes, L.; Lorenz, M.; Maier, L.; Mangiarotti, A.; Markert, J.; Metag, V.; Michel, J.; Müntz, C.; Münzer, R.; Naumann, L.; Palka, M.; Pechenov, V.; Pechenova, O.; Petousis, V.; Pietraszko, J.; Przygoda, W.; Ramstein, B.; Rehnisch, L.; Reshetin, A.; Rost, A.; Rustamov, A.; Sadovsky, A.; Salabura, P.; Scheib, T.; Schmidt-Sommerfeld, K.; Schuldes, H.; Sellheim, P.; Siebenson, J.; Silva, L.; Sobolev, Y. G.; Spataro, S.; Ströbele, H.; Stroth, J.; Strzempek, P.; Sturm, C.; Svoboda, O.; Tarantola, A.; Teilab, K.; Tlusty, P.; Traxler, M.; Tsertos, H.; Vasiliev, T.; Wagner, V.; Wendisch, C.; Wirth, J.; Wüstenfeld, J.; Yurevich, S.; Zanevsky, Y.; Zumbruch, P.
The results on double-pion production in tagged quasi-free np collisions at a deutron incident beam energy of 1.25 GeV/c measured with the High-Acceptance Di-Electron Spectrometer (HADES) installed at GSI are presented. The specific acceptance of HADES allowed for the first time to obtain high-precision data on p+p􀀀 and p􀀀p0 production in np collisions in a region corresponding to large transverse momenta of the secondary particles. The obtained differential cross section data provide strong constraints on the production mechanisms and on the various baryon resonance contributions (DD, N(1440), N(1520), D(1600)). The invariant mass and angular distributions from the np!npp+p􀀀 and np! ppp􀀀p0 reactions are compared with different theoretical model predictions.
  • Open Access Logo Proceedings of Science (2015), PoS(Baldin ISHEPP XXII)120

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Permalink: https://www.hzdr.de/publications/Publ-21322
Publ.-Id: 21322


Säulenversuche zur Adsorption von MCPA an künstlichen Bodenmineralmischungen

Stuhlfauth, C.
Diese Diplomarbeit beschäftigt sich mit dem Transportverhalten von 2-Methyl-4-chlorphenoxyessigsäure (MCPA) in Wechselwirkung mit Goethit. Zur Untersuchung des Prozesses wurden eigens Säulenversuche im sauren Bereich unter definierten Bedingungen (pH-Wert, Konzentration der Lösungen) durchgeführt. Die Ergebnisse wurden mit einem zur Verfügung gestellten PHREEQC Modell (CD-MUSIC) model-liert. Die experimentell ermittelten MCPA-Durchbruchskurven konnten mit dem Mo-dell nachgezeichnet werden, in dem das PHREEQC-Modell wurde hinsichtlich der Oberflächenkomplexe an Goethit mittels Verwendung aktueller Werte ergänzt wurde (KERSTEN et al. 2014). Damit bestätigten die Ergebnisse der Säulenversuche die im Batchversuch beobachteten Sorptionsreaktionen aus KERSTEN et al. (2014) zwischen Goethit und dem transportierten MCPA auch für das Fließsystem.
  • Diploma thesis
    Johannes-Gutenberg-Universität Mainz, 2014
    Mentor: Dr. H. Lippold
    132 Seiten

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Permalink: https://www.hzdr.de/publications/Publ-21321
Publ.-Id: 21321


“High resolution Positron Emission Tomography for quantitative, spatio-temporal process visualization in geological material (GeoPET)”

Kulenkampff, J.; Lippmann-Pipke, J.
Es ist kein Abstract vorhanden.
  • Lecture (others)
    GeoCT Kick off Workhop Hannover, Nationaler Workshop von Forschungseinrichtungen mit tomographischen Methoden in den Geowissenschaften, 19.02.2014, Hannover, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-21320
Publ.-Id: 21320


Quantification of permeability and porosity changes of cement/clay materials by means of GeoPET.

Lippmann-Pipke, J.; Kulenkampff, J.
Es ist kein Abstract vorhanden.
  • Lecture (others)
    Cebama Proposal Consortium Meeting, 11.03.2014, Karlsruhe, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-21319
Publ.-Id: 21319


Quantifying bioleaching kinetics and efficiency: (3D+t)-visualization of Cu transport through dump material by means of PET - First results from HZDR-IRE (11/2014).

Barthen, R.; Lippmann-Pipke, J.
Es ist kein Abstract vorhanden.
  • Lecture (others)
    Ecometals Meeting 2014, 18.-19.11.2014, Orléans, France

Permalink: https://www.hzdr.de/publications/Publ-21318
Publ.-Id: 21318


Abschlussbericht des DFG-Vorhabens "Imaging and image simulation of organic target compound migration between different biogeochemical interfaces of a soil horizon using positron emission tomography and the lattice Boltzmann equation approach" im Schwerpunktprogramm 1315

Kersten, M.; Lippmann-Pipke, J.
Es ist kein Abstract vorhanden.
  • Other report
    Rossendorf: HZDR, 2014
    7 Seiten

Permalink: https://www.hzdr.de/publications/Publ-21317
Publ.-Id: 21317


HPV16 DNA status is a strong prognosticator of loco-regional control after postoperative radiochemotherapy of locally advanced oropharyngeal carcinoma: Results from a multicentre explorative study of the German Cancer Consortium Radiation Oncology Group (DKTK-ROG).

Lohaus, F.; Linge, A.; Tinhofer, I.; Budach, V.; Gkika, E.; Stuschke, M.; Balermpas, P.; Rödel, C.; Avlar, M.; Grosu, A.; Abdollahi, A.; Debus, J.; Bayer, C.; Belka, C.; Pigorsch, S.; Combs, S.; Mönnich, D.; Zips, D.; von Neubeck, C.; Baretton, C.; Löck, S.; Thames, H.; Krause, M.; Baumann, M.
OBJECTIVE:

To investigate the impact of HPV status in patients with locally advanced head and neck squamous cell carcinoma (HNSCC), who received surgery and cisplatin-based postoperative radiochemotherapy.
MATERIALS AND METHODS:

For 221 patients with locally advanced squamous cell carcinoma of the hypopharynx, oropharynx or oral cavity treated at the 8 partner sites of the German Cancer Consortium, the impact of HPV DNA, p16 overexpression and p53 expression on outcome were retrospectively analysed. The primary endpoint was loco-regional tumour control; secondary endpoints were distant metastases and overall survival.
RESULTS:

In the total patient population, univariate analyses revealed a significant impact of HPV16 DNA positivity, p16 overexpression, p53 positivity and tumour site on loco-regional tumour control. Multivariate analysis stratified for tumour site showed that positive HPV 16 DNA status correlated with loco-regional tumour control in patients with oropharyngeal carcinoma (p=0.02) but not in the oral cavity carcinoma group. Multivariate evaluation of the secondary endpoints in the total population revealed a significant association of HPV16 DNA positivity with overall survival (p<0.01) but not with distant metastases.
CONCLUSIONS:

HPV16 DNA status appears to be a strong prognosticator of loco-regional tumour control after postoperative cisplatin-based radiochemotherapy of locally advanced oropharyngeal carcinoma and is now being explored in a prospective validation trial.
Keywords: DKTK-ROG; HNSCC; HPV; Postoperative radiochemotherapy; p16; p53

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Permalink: https://www.hzdr.de/publications/Publ-21314
Publ.-Id: 21314


Effect of combined irradiation and EGFR/Erb-B inhibition with BIBW 2992 on proliferation and tumour cure in cell lines and xenografts.

Gurtner, K.; Ebert, N.; Pfitzmann, D.; Eicheler, W.; Zips, D.; Baumann, M.; Krause, M.
Background and purposeIn previous experiments an enhanced anti-proliterative effect of the EGFR/ErbB tyrosine kinase inhibitor (TKI) BIBW 2992 with single dose irradiation was observed in FaDu tumour xenografts. Aim of the present experiment was to determine if this effect can also be seen in combination with a fractionated radiotherapy. Secondly we investigate the efficacy of BIBW 2992 on local tumour control for UT-SCC-15.Material and methodsTumour pieces of FaDu, UT-SCC-14, A431, UT-SCC-15 (squamous cell carcinomas) and A7 (glioma) tumour models were transplanted onto the right hind leg of NMRI (nu/nu) nude mice. For evaluation of tumour growth mice were either treated daily orally with BIBW 2992 (30 mg/kg body weight), or carrier up to a final tumour size of 15 mm or with a fractionated radiotherapy (15f/15d, 30 Gy) with simultaneous application of BIBW 2992 or carrier. For local tumour control UT-SCC-15 tumours were treated with a fractionated radiotherapy (30f/6weeks) or received 30f/6 weeks in combination with daily orally BIBW 2992 (22.5 mg/kg b.w.) during RT.ResultsA significant effect on tumour growth time was observed in all tumour models for BIBW 2992 application alone. However, substantial intertumoural heterogeneity could be seen. In the UT-SCC-14, UT-SCC-15 and A431 tumour models a total regression of the tumours and no recurrence during treatment time (73 days) were determined where as for the A7 tumour only a slight effect was noticeable. For the combined treatment of fractionated radiotherapy (15f/15d) and BIBW 2992 administration a significant effect on tumour growth time was seen compared to irradiation alone for A7, UT-SCC-15 and A431 (ER 1.2 ¿ 3.7), this advantage could not be demonstrated for FaDu and UT-SCC-14. However, the local tumour control was not altered for the UT-SCC-15 tumour model when adding BIBW 2992 to fractionated irradiation (30f/6weeks).ConclusionA heterogeneous effect on tumour growth time of BIBW 2992 alone as well as in combination with fractionated irradiation could be demonstrated for all tumour models. However, the significant effect on tumour growth time did not translate into an improvement of local tumour control for the UT-SCC-15 tumour model.

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Permalink: https://www.hzdr.de/publications/Publ-21313
Publ.-Id: 21313


Creating a data exchange strategy for radiotherapy research: Towards federated databases and anonymised public datasets.

Skripcak, T.; Belka, C.; Bosch, W.; Brink, C.; Brunner, T.; Budach, V.; Büttner, D.; Debus, J.; Dekker, A.; Grau, C.; Gulliford, S.; Hurkmans, C.; Just, U.; Krause, M.; Lambin, P.; Langendijk, J.; Lewensohn, R.; Lühr, A.; Maingon, P.; Masucci, M.; Niyazi, M.; Poortmans, P.; Simon, M.; Schmidberger, H.; Spezi, E.; Stuschke, M.; Valentini, V.; Verheij, M.; Whitfield, G.; Zackrisson, B.; Zips, D.; Baumann, M.
Disconnected cancer research data management and lack of information exchange about planned and ongoing research are complicating the utilisation of internationally collected medical information for improving cancer patient care. Rapidly collecting/pooling data can accelerate translational research in radiation therapy and oncology. The exchange of study data is one of the fundamental principles behind data aggregation and data mining. The possibilities of reproducing the original study results, performing further analyses on existing research data to generate new hypotheses or developing computational models to support medical decisions (e.g. risk/benefit analysis of treatment options) represent just a fraction of the potential benefits of medical data-pooling. Distributed machine learning and knowledge exchange from federated databases can be considered as one beyond other attractive approaches for knowledge generation within "Big Data". Data interoperability between research institutions should be the major concern behind a wider collaboration. Information captured in electronic patient records (EPRs) and study case report forms (eCRFs), linked together with medical imaging and treatment planning data, are deemed to be fundamental elements for large multi-centre studies in the field of radiation therapy and oncology. To fully utilise the captured medical information, the study data have to be more than just an electronic version of a traditional (un-modifiable) paper CRF. Challenges that have to be addressed are data interoperability, utilisation of standards, data quality and privacy concerns, data ownership, rights to publish, data pooling architecture and storage. This paper discusses a framework for conceptual packages of ideas focused on a strategic development for international research data exchange in the field of radiation therapy and oncology.
Keywords: Data exchange; Data pooling; Interoperability; Large scale studies; Public data; Radiotherapy

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Permalink: https://www.hzdr.de/publications/Publ-21312
Publ.-Id: 21312


Pre-clinical research in small animals using radiotherapy technology - a bidirectional translational approach.

Tillner, F.; Thute, P.; Bütof, R.; Krause, M.; Enghardt, W.
For translational cancer research, pre-clinical in-vivo studies using small animals have become indispensable in bridging the gap between in-vitro cell experiments and clinical implementation. When setting up such small animal experiments, various biological, technical and methodical aspects have to be considered. In this work we present a comprehensive topical review based on relevant publications on irradiation techniques used for pre-clinical cancer research in mice and rats. Clinical radiotherapy treatment devices for the application of external beam radiotherapy and brachytherapy as well as dedicated research irradiation devices are feasible for small animal irradiation depending on the animal model and the experimental goals. In this work, appropriate solutions for the technological transfer of human radiation oncology to small animal radiation research are summarised. Additionally, important information concerning the experimental design is provided such that reliable and clinically relevant results can be attained.
Keywords: Kleintiere; Krebsforschung; Pre-clinical research; Präklinische Forschung; bildgeführte Strahlentherapie (IGRT); cancer research; image-guided radiation therapy (IGRT); small animals; translational research; translationale Forschung

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Permalink: https://www.hzdr.de/publications/Publ-21311
Publ.-Id: 21311


Be smart against cancer! A school-based program covering cancer-related risk behavior.

Stölzel, F.; Seidel, N.; Uhmann, S.; Baumann, M.; Berth, H.; Hoyer, J.; Ehninger, G.
BACKGROUND:
Several studies suggest that most school-age children are poorly informed about cancer risk factors. This study examines the effectiveness of the 'Be smart against cancer' (BSAC) program in promoting cancer awareness and intentions to engage in health-promoting behavior.

METHODS:
235 seventh-grade students were randomized to either the intervention (N = 152) or the wait-control group (N = 83). The intervention included the modules: "What is cancer?," "Sun protection," "Non smoking," and "Physical activity, Healthy nutrition, and Limited alcohol consumption." Outcomes measured at baseline and at the end of the one week BSAC program included knowledge of cancer and its behavioral risk factors, health-promoting intentions, and reported risk behavior.

RESULTS:
BSAC was effective in increasing knowledge about cancer and risk factors for cancer (p < .001), as well as in increasing intentions to engage in health-promoting behavior (p < .001), independent of a student's risk profile. Knowledge did not serve as a mediator for intention building.

CONCLUSIONS:
The BSAC is an effective school-based program for raising awareness of cancer, associated risk factors and intentions to engage in cancer-preventive behavior. The results indicate that the effectiveness of BSAC is independent of a student's risk profile. Therefore, it holds considerable promise as a broadly applicable program to raise cancer awareness and promote healthy behavior intentions.

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Permalink: https://www.hzdr.de/publications/Publ-21307
Publ.-Id: 21307


Application of organ tolerance dose-constraints in clinical studies in radiation oncology.

Dörr, W.; Herrmann, T.; Baumann, M.
In modern radiation oncology, tolerance dose-constraints for organs at risk (OAR) must be considered for treatment planning, but particularly in order to design clinical studies. Tolerance dose tables, however, only address one aspect of the therapeutic ratio of any clinical study, i.e., the limitation of adverse events, but not the desired potential improvement in the tumor effect of a novel treatment strategy. A sensible application of "tolerance doses" in a clinical situation requires consideration of various critical aspects addressed here: definition of tolerance dose, specification of an endpoint/symptom, consideration of radiation quality and irradiation protocol, exposed volume and dose distribution, and patient-related factors of radiosensitivity. The currently most comprehensive estimates of OAR radiation tolerance are in the QUANTEC compilations (2010). However, these tolerance dose values must only be regarded as a rough orientation and cannot answer the relevant question for the patients, i.e., if the study can achieve a therapeutic advantage; this can obviously be answered only by the final scientific analysis of the study results. Despite all limitations, the design of clinical studies should currently refer to the QUANTEC values for appreciation of the risk of complications, if needed supplemented by one's own data or further information from the literature. The implementation of a consensus on the safety interests of the patients and on an application and approval process committed to progress in medicine, with transparent quality-assuring requirements with regard to the structural safeguarding of the study activities, plays a central role in clinical research in radiation oncology.

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Permalink: https://www.hzdr.de/publications/Publ-21305
Publ.-Id: 21305


Radiosynthesis, in vitro and in vivo evaluation of 8-[4-(2-[18F]fluoroethoxy)benzyl]-1,4-dioxa-8-azaspiro[4.5]decane, a spirocyclic σ1 receptor ligand for tumor targeting

Kniess, T.; Bergmann, R.; Xie, F.; Jia, H.; Deuther-Conrad, W.; Steinbach, J.; Pietzsch, J.
Aim: Sigma (σ) receptors have a characteristic distribution in the brain and are implicated in many diseases of the central nervous system. In the past years a number of PET and SPECT radiotracers for visualization of σ‐receptors in the brain have been developed. In addition, σ‐receptors are up‐regulated in various tumor cells motivating us to develop a series of novel spirocyclic receptor ligands showing high affinity and good selectivity for σ1. One candidate was radiolabeled with fluorine‐18 as potential radiotracer for tumor targeting.
Methods: Six novel spirocyclic σ1 receptor ligands were designed, synthesized, and characterized. The affinity to σ1 and σ2 receptors was tested, one derivative, 8‐[4‐(2‐[18F]fluoroethoxy)benzyl]‐1,4‐dioxa‐8‐azaspiro[4.5]decane, was chosen for radiolabeling with fluorine‐18. The stability of the radiotracer in vitro and in vivo was evaluated, the logP value was determined. Biodistribution studies in rats and mice as well as dynamic small animal PET studies in nude mice xenografted with DU145 human prostate tumors were performed.
Results: The Ki values of the spirocyclic ligands were determined to be in the range 3.26‐11.2 nM for σ1 and 164.4‐312.2 nM for σ2. The radiotracer was prepared by 18F‐fluoroethylation of the corresponding hydroxyl precursor via a two‐step automated procedure in 20% yield and 99% radiochemical purity with a specific activity about 45 GBq/μmol. The logP value was determined 0.81 ± 0.13, and it was found to be stable in vitro in saline, ethanol, and human plasma. Biodistribution in normal mice and Wistar rats showed radiotracer uptake in σ1‐rich regions like brain and pancreas that could be blocked by pre‐administration of haloperidol. In mice fast degradation of the radiotracer
resulting in four metabolites was observed. However, PET studies in mouse tumor models showed tumor uptake of about 0.77+/‐0.45 (SUV, 1 h p.i.), which likewise could be substantially blocked by haloperidol.
Conclusion: We have developed an 18F‐labeled spirocyclic receptor ligand with high selectivity for σ1 and excellent hydrophilicity. We demonstrated by successful PET imaging in mice bearing σ1‐expressing DU‐145 tumors the principle of targeting tumors with radiolabeled σ‐ligands. However, the unfavorable in vivo stability of this spirocyclic derivative limits a broader application as an imaging agent.
  • Poster
    Annual Congress of the European Association of Nuclear Medicine (EANM), 18.-22.10.2014, Gothenburg, Sweden
  • Abstract in refereed journal
    European Journal of Nuclear Medicine and Molecular Imaging 41(2014), S416
    DOI: 10.1007/s00259-014-2901-9

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Permalink: https://www.hzdr.de/publications/Publ-21303
Publ.-Id: 21303


Focal adhesion signaling and therapy resistance in cancer.

Eke, I.; Cordes, N.
Interlocking gene mutations, epigenetic alterations and microenvironmental features perpetuate tumor development, growth, infiltration and spread. Consequently, intrinsic and acquired therapy resistance arises and presents one of the major goals to solve in oncologic research today. Among the myriad of microenvironmental factors impacting on cancer cell resistance, cell adhesion to the extracellular matrix (ECM) has recently been identified as key determinant. Despite the differentiation between cell adhesion-mediated drug resistance (CAMDR) and cell adhesion-mediated radioresistance (CAMRR), the underlying mechanisms share great overlap in integrin and focal adhesion hub signaling and differ further downstream in the complexity of signaling networks between tumor entities. Intriguingly, cell adhesion to ECM is per se also essential for cancer cells similar to their normal counterparts. However, based on the overexpression of focal adhesion hub signaling receptors and proteins and a distinct addiction to particular integrin receptors, targeting of focal adhesion proteins has been shown to potently sensitize cancer cells to different treatment regimes including radiotherapy, chemotherapy and novel molecular therapeutics. In this review, we will give insight into the role of integrins in carcinogenesis, tumor progression and metastasis. Additionally, literature and data about the function of focal adhesion molecules including integrins, integrin-associated proteins and growth factor receptors in tumor cell resistance to radio- and chemotherapy will be elucidated and discussed.
Keywords: Extracellular matrix; Focal adhesion; Integrins; Small molecules; Targeted therapy

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Permalink: https://www.hzdr.de/publications/Publ-21302
Publ.-Id: 21302


Detection of Radiation-Induced Changes in Healthy Mouse Brain Using Diffusion-weighted MRI and 18F-FDG-PET

Máthé, D.; Kovács, N.; Szigeti, K.; Bergmann, R.
Aim: To evaluate in vivo longitudinal PET and MRI parameter changes in images can be sensitively read out with radiation‐induced tissue changes in healthy mouse brain.
Materials and Methods: We irradiated a group of c57bl6 mice (n=6) with 5 Gy and another (n=6) with 20 Gy in the left hemisphere using an X‐ray tube (Yxlon Maxishot). Animals were imaged before, and 3‐7‐30 and 60 days post irradiation. For 18F‐Fluoro‐Deoxy‐Glucose (FDG) PET we injected 10 to 15 MBq FDG iv. PET and MR imaging was performed subsequently with a Mediso nanoScan PET/CT and a Bruker Biospec 7T MRI system. Arterial spin labeling (ASL) was probed using a FAIR‐EPI sequence. For DWI, a SE EPI‐based sequence was used. Standardized brain FDG‐PET uptake (SUV) values were determined for righ/left hemispheres and cerebellum using Rover software. ASL data and water apparent diffusion coefficients (ADC) were read out using a Matlab code after atlas coregistration. We determined statistical differences between readout results in both groups and between the time points in the same groups in these regions.
Results: There was no significant difference in ASL values neither in ADC values in the 5 Gy group compared to baseline or between time points. If both hemisphere’s respective VOI data were taken into account we could observe significant ADC differences between early (3 days) and late (30 to 60 days) changes in almost all VOIs of the brains. Using hemisphere VOI PET data we see a change at 7 days and 60 days both compared to baseline and all other time points in both groups by a decrease in SUVs of both hemispheres at Day 7 and and an increase at Day 60.
Conclusion: In our study ASL had no readout value on radiation‐induced changes. Using ADC maps, as early as 3 days and after one month post irradiation the late changes are visible throughout the brain. FDG‐PET provided us with a readable change at day 7. The direction of increased metabolism in the hemisphere 60 days read out with PET coregisters with the increase in ADC values at Day 60. These late changes are possibly due to second‐phase neuro‐inflammation and cell content increase in accordance with PET imaging results. Combined DWI MR/FDG PET is a promising means for radiation therapy side effect follow‐up.
This research reading to these results has received funding from the European Union Seventh Framework Programme FP7/2007‐2013 under grant agreement n° 305311/INSERT.
  • Poster
    Annual Congress of the European Association of Nuclear Medicine (EANM), 18.-22.10.2014, Gothenburg, Sweden
  • Abstract in refereed journal
    European Journal of Nuclear Medicine and Molecular Imaging 41(2014), S415
    DOI: 10.1007/s00259-014-2901-9

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Publ.-Id: 21301


The Role of Phospholipid Headgroup Composition and Trehalose in the Desiccation Tolerance of Caenorhabditis elegans

Abusharkh, S. E.; Erkut, C.; Oertel, J.; Kurzchalia, T. V.; Fahmy, K.
Anhydrobiotic organisms have the remarkable ability to lose extensive amounts of body water and survive in an ametabolic state. Distributed to various taxa of life, these organisms have developed strategies to efficiently protect their cell membranes and proteins against extreme water loss. Recently, we showed that the dauer larva of the nematode Caenorhabditis elegans is anhydrobiotic and accumulates high amounts of trehalose during preparation to harsh desiccation
(preconditioning). Here, we have used this genetic model to study the biophysical manifestations of anhydrobiosis and show that, in addition to trehalose accumulation, dauer larvae dramatically reduce their phosphatidylcholine (PC) content. The chemical composition of the phospholipids (PLs) has key consequences not only for their interaction with trehalose, as we demonstrate with Langmuir−Blodgett monolayers, but also, the kinetic response of PLs to hydration transients is strongly influenced as evidenced by time-resolved FTIR spectroscopy. PLs from preconditioned larvae with reduced PC content exhibit a higher trehalose affinity, a stronger hydration-induced gain in acyl chain free volume, and a wider spread of structural relaxation rates of their lyotropic transitions and sub-headgroup H-bond interactions. The different hydration properties of PC and phosphatidylethanolamine (PE) headgroups are crucial for the hydration-dependent rearrangement of the trehalose-mediated H-bond network. As a consequence, the compressibility modulus of PLs from preconditioned larvae is about 2.6-fold smaller than that from non-preconditioned ones. Thus, the biological relevance of reducing the PC:PE ratio by PL headgroup adaptation should be the preservation of plasma membrane integrity by relieving mechanical strain from desiccated trehalose-containing cells during fast rehydration.
Keywords: Fourier transform infrared spectroscopy biomembrane preservation hydration

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Publ.-Id: 21300


In-situ investigations of ion implantation at ROBL-MRH

Baehtz, C.; Grenzer, J.; von Borany, J.; Posselt, M.
The Helmholtz-Zentrum Dresden-Rossendorf (HZDR) operates since 1998 a bending magnet beamline with two end stations at the ESRF, Grenoble. In 2011 the complete beamline optics was renewed with new focusing mirrors and a double crystal monochromator equipped with3 pairs of differently oriented Si-crystals and two sets of multilayers. The Materials Research Station is focusing on in-situ measurements using different scattering techniques like XRR, GISAXS, HRXRD or GIXRD that can be combined with spectroscopy measurements. In the center of interest are the CVD growth of graphite materials, phase change materials under operation and hydrogen storage materials. Additionally the syntheses of various nano-structured materials by magnetron sputtering were explored. A similar sample environment is used to investigate in-operando the He and Ar-ion implantation processes on single crystalline Si and Al2O3. Ions were provided by an ion gun operated at 5 keV, an additional potential of up to 20keV on the sample was applied to accelerate the ions further. Using a Mythen detector, a series of reciprocal space maps were recorded with duration of less than 1 minute per map. The crystal truncation rod vanished within the first seconds of He-ion bombardment. In the following the Si (004) reflection broadens, forming a layer peak that give clearly a hint of increasing strain in the material. After 50 minutes a steadystate that correspond to a heavily damaged or amorphized Si layer is reached
Keywords: Synchrotron radiation, in-Situ investigation, magnetron sputtering, ion implantation
  • Poster
    Deutsche Tagung für Forschung mit Synchrotronstrahlung, Neutronen und Ionenstrahlen an Großgeräten 2014, 21.-23.09.2014, Bonn, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-21299
Publ.-Id: 21299


Synthese neuartiger Vesamicolanaloga als potentielle Liganden für den vesikulären Acetylcholintransporter

Lindemann, M.
Es ist kein Abstract vorhanden.
  • Master thesis
    Universität Leipzig, Fakultät für Chemie und Mineralogie, 2014
    Mentor: Dr. Barbara Wenzel
    94 Seiten

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Permalink: https://www.hzdr.de/publications/Publ-21298
Publ.-Id: 21298


Pretherapeutic scan time-normalized tumor to blood standard uptake ratio (SUR) is superior to SUV as a prognostic factor in patients with esophageal carcinoma

Hofheinz, F.; Bütof, R.; Zöphel, K.; Schütze, C.; Löck, S.; Steffen, I. G.; Stadelmann, T.; Kotzerke, J.; Baumann, M.; van den Hoff, J.
Aim: Determination of tumor SUV is widely used for quantitative assessment of tumor metabolism in FDG PET and its potential for therapy outcome prediction in various cancer diseases is under scrutiny. However, the SUV approach has several well known limitations compromising its ability to act as a surrogate parameter of glucose consumption. Recently, we have shown that SUR overcomes most of these limitations as long as FDG kinetics in the target structure can be considered irreversible [1,2]. The aim of this work was to evaluate the prognostic value of SUR in comparison to SUV in patients with esophageal carcinoma.
Methods: FDG-PET/CT was performed in 97 consecutive patients ((64+/-10)y, 83 males) with newly diagnosed esophageal cancer prior to definitive radiochemotherapy. In the PET images the metabolic active volume (MTV) of the primary tumor was delineated with an adaptive threshold method. For determination of the blood SUV the aorta was delineated manually in the attenuation CT. The aorta ROI was transferred to the PET image. Blood SUV was computed as the mean value of the aorta ROI. SUR values were computed as ratio of tumor SUV and blood SUV. SUR values were scan-time-normalized to 60 min p.i. as described in [2]. Univariate Cox regression with respect to overall survival (OS), locoregional control (LRC), and distant-metastases-free survival (DM) was performed for SUVmax, SURmax and clinically relevant parameters. Additionally, a multivariate Cox regression including N stage and smoking status (univariate significant) as confounding parameters was performed.
Results: Both, SUVmax and SURmax, were prognostic factors for OS and DM, but not for LRC. With respect to OS a univariate Cox regression showed a slightly increased hazard ratio (HR) for SURmax (HR=2.3, p=0.001) compared to SUVmax (HR=2.1, p=0.001). With respect to DM HR of SURmax was notably larger than HR of SUVmax (HR=5.7, p=0.005 compared to 3.1, p=0.006). Moreover, in a multivariate Cox regression the prognostic value of SUR was slightly higher for OS and notably higher for DM.
Conclusion: Our results indicate an increased prognostic value if lesion uptake is characterized by time-normalized SUR instead of SUV in pretherapeutic FDG PET of patients with esophageal carcinoma. More comprehensive investigations are necessary to confirm these results.
Literature: [1] van den Hoff et al, EJNMMI Res 2013, 3:77 [2] van den Hoff et al, EJNMMI Res 2014, 4:18
  • Lecture (Conference)
    Annual Congress of the European Association of Nuclear Medicine (EANM), 18.-22.10.2014, Gothenburg, Sweden
  • Abstract in refereed journal
    European Journal of Nuclear Medicine and Molecular Imaging 41(2014), S232-S233
    DOI: 10.1007/s00259-014-2901-9

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Publ.-Id: 21297


Capability of X-ray diffraction for the study of microstructure of metastable thin films

Rafaja, D.; Wüstefeld, C.; Dopita, M.; Motylenko, M.; Baehtz, C.
Metastable phases are often used to design materials with outstanding properties, which cannot be achieved with thermodynamically stable compounds. In many cases, the metastable phases are employed as precursors for controlled formation of nanocomposites. This contribution shows how the microstructure of crystalline metastable phases and the formation of nanocomposites can be concluded from X-ray diffraction experiments by taking advantage of the high sensitivity of X-ray diffraction to macroscopic and microscopic lattice deformations and to the dependence of the lattice deformations on the crystallographic direction. The lattice deformations were determined from the positions and from the widths of the diffraction lines, the dependence of the lattice deformations on the crystallographic direction from the anisotropy of the line shift and the line broadening. As an example of the metastable system, the supersaturated solid solution of titanium nitride and aluminium nitride was investigated, which was prepared in the form of thin films by using cathodic arc evaporation of titanium and aluminium in a nitrogen atmosphere. The microstructure of the (Ti,Al)N samples under study was tailored by modifying the [Al]/[Ti] ratio in the thin films and the surface mobility of the deposited species.
Keywords: metastable thin films; microstructure; X-ray diffraction

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Permalink: https://www.hzdr.de/publications/Publ-21296
Publ.-Id: 21296


Crystallography of phase transitions in metastable titanium aluminium nitride nanocomposites

Rafaja, D.; Wüstefeld, C.; Dopita, M.; Motylenkoa, M.; Baehtz, C.; Michotte, C.; Kathrein, M.
The isostructural decomposition of the titanium aluminium nitride supersaturated solid solution crystallising in the face centred cubic (fcc) crystal structure into the titanium-rich fcc-(Ti,Al)N and almost titanium-free fcc-(Al, Ti)N and the transformation of metastable fcc-(Ti,Al)N into the wurtzitic aluminium nitride are discussed from the crystallographic point of view by taking the observed orientation relationships between the adjacent phases into account. It is shown that the isostructural decomposition of fcc-(Ti,Al)N into Ti-rich fcc-(Ti,Al)N and fcc-(Al, Ti)N and the transformation of themetastable fcc-(Ti,Al)N into the thermodynamically stablewurtzitic phase are concurrent processes, which are controlled not only by the thermodynamic stability of the respective compound and by the diffusivity of Al and Ti, but also by the local lattice strains. A part of the local lattice strains is regarded to result from the lattice misfit at the interfaces between the titanium aluminium nitrides having different [Al]/ [Ti] concentration ratios and, in the case of the fcc/wurtzite-type interface, also having different crystal structures. The phase transition of the fcc-(Ti,Al)N to thewurtzitic onewas predicted to be facilitated by stacking faults. The results of crystallographic considerations were verified experimentally by using in situ high-temperature synchrotron diffraction experiments that were performed on cathodic arc evaporated (Ti,Al)N thin films containing titanium and aluminium in different amounts.
Keywords: Ti–Al–N Cathodic arc evaporation X-ray diffraction Phase transformation Stacking faults High-resolution transmission electron microscopy

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Permalink: https://www.hzdr.de/publications/Publ-21295
Publ.-Id: 21295


Density change upon crystallization of Ga-Sb films

Putero, M.; Coulet, M.-V.; Muller, C.; Cohen, G.; Hopstaken, M.; Baehtz, C.; Raoux, S.
Besides crystallization time and temperature, the mass density change upon crystallization is a key parameter governing the reliability of phase change random access memory. Indeed, few percentages density change induces considerable mechanical stress in memory cells, leading to film delamination with subsequent electrical failures. This letter presents an extensive study of density change upon crystallization in a series of Ga-Sb thin films with various antimony contents. The mass density of the films is precisely determined by x-ray reflectivity in both their amorphous and crystalline states. The variations of the density in crystalline and amorphous films according to the Sb content found to cross with a zero-density change for 70 at. % Sb. The peculiar behavior of Ga-Sb thin films upon crystallization may be linked to their stress state and mechanical properties.
Keywords: phase change material, x-ray, diffraction, reflectivity

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Publ.-Id: 21294


Nitrogen controlled iron catalyst phase during carbon nanotube growth

Bayer, B. C.; Baehtz, C.; Kidambi, P. R.; Weatherup, R. S.; Mangler, C.; Kotakoski, J.; Goddard, C. J. L.; Caneva, S.; Cabrero-Vilatela, A.; Meyer, J. C.; Hofmann, S.
Close control over the active catalyst phase and hence carbon nanotube structure remains challenging in catalytic chemical vapor deposition since multiple competing active catalyst phases typically co-exist under realistic synthesis conditions. Here, using in-situ X-ray diffractometry, we show that the phase of supported iron catalyst particles can be reliably controlled via the addition of NH3 during nanotube synthesis. Unlike polydisperse catalyst phase mixtures during H2 diluted nanotube growth, nitrogen addition controllably leads to phase-pure c-Fe during pre-treatment and to phase-pure Fe3C during growth. We rationalize these findings in the context of ternary Fe-C-N phase diagram calculations and, thus, highlight the use of pre-treatment- and add-gases as a key parameter towards controlled carbon nanotube growth.
Keywords: Carbon nano tubes, x-ray diffraction, xps

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Publ.-Id: 21293


In Situ Phase Evolution of Ni/Ti Reactive Multilayers

Cavaleiro, A. J.; Ramos, A. S.; Martins, R. M. S.; Baehtz, C.; Vieira, M. T.; Braz Fernandes, F. M.
Joining shape-memory alloys (SMA) to other materials is strongly required in order to enlarge their fields of application. Fusion welding induces strong compositional and microstructural changes that significantly affect the shape-memory effect and the superelastic behavior of these alloys. The exothermic and in some cases self-propagating character of some nano-multilayer reactions is explored in this study as an alternative for joining SMA. To follow these very fast reactions, high brilliance sources, such as synchrotron radiation, are required. In situ high-resolution x-ray diffraction data, giving the phase evolution sequence with temperature of the Ni/Ti multilayer thin films under study, are presented. A correlation between the multilayer design and the tendency for the sequence of phase formation is established.
Keywords: advanced characterization, intermetallic, x-ray

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Publ.-Id: 21292


Influence of a passivation layer on strain relaxation and lattice disorder in thin nano-crystalline Pt films during in-situ annealing

Gruber, W.; Rahn, J.; Baehtz, C.; Horisberger, M.; Geckle, U.; Schmidt, H.
In this work we compared the relaxation of strain and lattice disorder in thin nano-crystalline Pt films for samples covered with a Si3N4 layer and samples without a cover layer, respectively.We measured thickness and interplanar distance of the Pt film by X-ray reflectometry and X-ray diffractometry during insitu annealing using synchrotron radiation. The results show that strain and lattice disorder relaxation are impeded if the Pt film is sealed with a cover layer to suppress the creation of vacancies at the Pt surface. This emphasizes the postulated important role of the generation of vacancies at the free surface of thin metal films for strain relaxation during isothermal annealing.
Keywords: Nano-crystalline platinum Thin films Strain relaxation Vacancy creation

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Publ.-Id: 21291


An inverted cylindrical sputter magnetron as metal vapour supply for electron cyclotron resonance ion sources

Weichsel, T.; Hartung, U.; Kopte, T.; Zschornack, G.; Kreller, M.; Silze, A.
An inverted cylindrical sputter magnetron device has been developed. The magnetron is acting as a metal vapor supply for an electron cyclotron resonance (ECR) ion source. FEM simulation of magnetic flux density was used to ensure that there is no critical interaction between both magnetic fields of magnetron and ECR ion source. Spatially resolved double Langmuir probe and optical emission spectroscopy measurements show an increase in electron density by one order of magnitude from 1 × 1010 cm−3 to 1 × 1011 cm−3, when the magnetron plasma is exposed to the magnetic mirror field of the ECR ion source. Electron density enhancement is also indicated by magnetron plasma emission photography with a CCD camera. Furthermore, photographs visualize the formation of a localized loss-cone - area, when the magnetron is operated at magnetic mirror field conditions. The inverted cylindrical magnetron supplies a metal atom load rate of R > 1 × 1018 atoms/s for aluminum, which meets the demand for the production of a milliampere Al+ ion beam.

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Publ.-Id: 21290


IMALION – Creation and low energy transportation of a milliampere metal ion beam

Weichsel, T.; Hartung, U.; Kopte, T.; Zschornack, G.; Kreller, M.; Silze, A.
IMALION - which stands for IMplantation of ALuminum IONs - is a facility designed for high-current metal ion beam implantation and surface modification such as in semiconductor, medical or optical industry. IMALION is a newly developed 30 kV metal ion wide area implantation platform, which is suitable for the irradiation of a target width of 200 mm to produce homogeneous implantation profiles over the entire surface. Electrostatic and magnetic beamline elements such as a deflector as well as analyzing and parallelizationmagnetswere designed for precision guiding of a milliampere metal ion beam. The implanter is fed by a novel ECR metal ion source, which is equipped with an integrated cylindrical sputter magnetron as metal vapor supply. Stable operation of the sputter magnetron under ECR magnetic mirror conditions was proven by optical emission spectroscopy and Langmuir probe measurements.
  • Open Access Logo Contribution to proceedings
    5th International Particle Accelerator Conference, 15.06.2014, Dresden, Deutschland

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Permalink: https://www.hzdr.de/publications/Publ-21288
Publ.-Id: 21288


Ridge waveguides in Nd:ABC3O7 disordered crystals produced by swift C5+ ion irradiation and precise diamond dicing: Broad band guidance and spectroscopic properties

Chen, C.; Luan, Q.; He, R.; Cheng, C.; Akhmadaliev, S.; Zhou, S.; Yu, H.; Zhang, H.; Chen, F.
Optical ridge waveguides have been manufactured in the crystals of Nd:SrLaGa3O7 and Nd:SrGdGa3O7 by combining techniques of swift carbon ion irradiation with precise diamond blade dicing. The guiding properties of the waveguides are investigated at broadband (at wavelength of 633 nm, 1064 nm, and 4 µm). After annealing treatment at 200 °C for 1 h, the propagation losses of ridge waveguides could be reduced to as low as 1 dB/cm. The confocal microfluorescence emission spectra confirm that the fluorescence properties of Nd3+ ions are almost unchanged after the ion irradiation processing, showing promising potentials as application of miniature light sources in integrated optics.
Keywords: Optical ridge waveguides; Swift heavy ion irradiation; Diamond saw dicing

Permalink: https://www.hzdr.de/publications/Publ-21287
Publ.-Id: 21287


Beiträge zur Methodik und Anwendung der kontaktlosen induktiven Strömungstomographie

Wondrak, T.
Den Strömungszustand von Metall- oder Halbleiterschmelzen auch nur ungefähr zu kennen, wäre bei vielen technischen Anwendungen, wie z. B. beim kontinuierlichen Stranggießen von Stahl oder bei verschiedenen Kristallzüchtungsverfahren in der Halbleiterindustrie, von großem Wert. Die Messung der Strömung stellt aufgrund der hohen Temperaturen von oft mehr als 1000 ◦ C und aufgrund der Intransparenz der Schmelzen besonders hohe Anforderungen an die Messtechnik. Am Helmholtz-Zentrum Dresden-Rossendorf (HZDR) wurde ein auf der Induktion in bewegten Leitern basierendes kontaktloses Messverfahren, die kontaktlose induktive Strömungstomographie (contactless inductive flow tomography (CIFT)), entwickelt, die aus der Messung der durch die Strömung verzerrten angelegten Magnetfelder ein dreidimensionales Geschwindigkeitsfeld in der Schmelze rekonstruiert.
In der vorliegenden Arbeit wird untersucht, ob sich CIFT auch bei industriell relevanten Anwendungen wie beim kontinuierlichen Stranggießen oder beim Ziehen von monokristallinen Siliziumkristallen einsetzen lässt. Dazu wurde CIFT für ein Modell einer Stranggießanlage adaptiert und ein Messsystem mit 14 Magnetfeldsensoren entwickelt, das es ermöglicht die dominierende zweidimensionale Strömung in der Kokille für das Brammengießen mit einer zeitlichen Auflösung von 1 Hz zu rekonstruieren. In einer Versuchsreihe mit einer Zweiphasenströmung konnten bei hohen Gasdurchflüssen Übergänge zwischen unterschiedlichen Strömungsregimen visualisiert werden. Begleitende Ultraschall-Doppler Geschwindigkeitsmessungen wurden für die Validierung der von CIFT rekonstruierten Geschwindigkeitsverteilung herangezogen. Für die Anwendung von CIFT in einer industriell relevanten Umgebung wurde CIFT dahingehend erweitert, dass Gradientensonden, ein Wechselfeld als Messfeld und Tiegel mit leitfähigen Wänden eingesetzt werden können. Ein weiterer Schwerpunkt dieser Arbeit waren erste Magnetfeldmessungen für CIFT an einer in der Industrie eingesetzten Czochralski-Ziehanlage. Dabei konnte gezeigt werden, dass trotz des großen Abstands zwischen Tiegel und Magnetfeldsensor das durch die Strömung induzierte Magnetfeld außerhalb der Anlage detektierbar ist. Diese Arbeit belegt, dass trotz der typischerweise sehr kleinen zu messenden induzierten Magnetfelder CIFT ein großes Potential für den Einsatz in industriell relevanten Anwendungen hat, insbesondere für die permanente Überwachung der Strömungsverhältnisse im Stahlguss.
Keywords: contactless inductive flow tomography
  • Doctoral thesis
    Reihe Maxwell, Hans Georg Krauthäuser und Ralf Theo Jacobs, 2014
    Mentor: Professor Hans Georg Krauthäuser und Dr. Frank Stefani
    172 Seiten

Permalink: https://www.hzdr.de/publications/Publ-21286
Publ.-Id: 21286


Electron spin resonance study in the chiral ferromagnet Cu2OSeO3 using pulsed magnetic fields up to 64 T and terahertz free electron laser

Ozerov, M.
The recent discovery of skyrmions in Cu2OSeO3 has established a new platform to create and manipulate skyrmionic spin textures. We use high-field electorn spin resonance (ESR) spectroscopy combining a terahertz free electron laser and pulsed magnetic fields up to 64 T to probe and quantify ist microscopic spin-spin interactions. Besides providing direct access to the long-wavelength Goldstone mode, this technique probes also the high-energy part of the excitation spectrum which is inaccessible by Standard low-frequency ESR. Fitting the behavior of the observed modes in magnetic field to a theroretical Framework establishes experimentally that the fundamental magnetic building blocks of this skyrmionic magnet are rigid, highly entangled and weakly coupled tetrahedra.
  • Lecture (Conference)
    Science at FEL, 15.08.2014, Villligen, Switzerland

Permalink: https://www.hzdr.de/publications/Publ-21285
Publ.-Id: 21285


Quantum spin chains with frustration due to Dzyaloshinskii-Moriya interactions

Hälg, M.; Lorenz, W. E. A.; Povarov, K. Y.; Mansson, M.; Skourski, Y.; Zheludev, A.
The properties of two quantum spin chain materials, K2CuSO4Cl2 and K2CuSO42, are studied by a variety of experimental techniques, including bulk measurements, neutron spectroscopy, and electron spin resonance. The hierarchy of relevant terms in the magnetic Hamiltonian is established. It is shown that these two compounds feature substantial Dzyaloshinskii-Moriya interactions that are uniform within each chain, but antiparallel in adjacent chains. The result is a peculiar type of frustration of interchain interactions, which leads to an unusual fielderature phase diagram.

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Permalink: https://www.hzdr.de/publications/Publ-21284
Publ.-Id: 21284


Materials Research at the Dresden High Magnetic Field Laboratory

Wosnitza, J.
es hat kein Abstract vorgelegen
  • Invited lecture (Conferences)
    Functionalized Molecule-Based Magnetic Materials, 24.-27.11.2014, Bielefeld, Deutschland
  • Invited lecture (Conferences)
    Institutskolloquium des Instituts für Technische Physik am KIT, 02.07.2015, Karlsruhe, Deutschland
  • Invited lecture (Conferences)
    Seminar at the Tokyo Institute of Technology, 19.01.2016, Tokyo, Japan
  • Invited lecture (Conferences)
    Seminar at the International Laboratory of High Magnetic Fields and Low Temperatures, 14.04.2016, Wroclaw, Poland

Permalink: https://www.hzdr.de/publications/Publ-21283
Publ.-Id: 21283


The Tesla Race - Materials Research in Very High Magnetic Fields

Wosnitza, J.
es hat kein Abstract vorgelegen
  • Invited lecture (Conferences)
    International Conference "Materials Science and Engineering", 23.-25.09.2014, Darmstadt, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-21282
Publ.-Id: 21282


Performance study of high bandwidth pickups installed at FLASH and ELBE for femtosecond-precision arrival time monitors

Czwalinna, M. K.; Gerth, C.; Schlarb, H.; Sydlo, C.; Angelovski, A.; Jakoby, R.; Penirschke, A.; Kuntzsch, M.; Gensch, M.
At today’s free-electron lasers, high-resolution electron bunch arrival time measurements become increasingly more important in fast feedback systems for a timing jitter reduction down to the femtosecond level as well as for time-resolved pump-probe experiments. This is fulfilled by arrival time monitors which employ an electro-optical detection scheme by means of synchronised ultrashort laser pulses. Even more, at FLASH and the European XFEL the measurement has to cover a wide range of bunch charges from 1 nC down to 20 pC with equally sub-10fs resolution. To meet these requirements, recently a high bandwidth pickup electrode with a cut-off frequency above 40 GHz has been developed. These pickups are installed at the free-electron laser FLASH and at the continuous wave electron accelerator ELBE. In this paper we present an evaluation of the pickup performance by direct signal measurements with high bandwidth oscilloscopes. The integration of these pickups into the arrival time monitor system is described.
Keywords: FLASH ELBE BAM Diagnostic CW
  • Open Access Logo Contribution to proceedings
    Free Electron Laser Conference 2014 - FEL 2014, 25.-29.08.2014, Basel, Schweiz
  • Poster
    Free Electron Laser Conference 2014 - FEL 2014, 25.-29.08.2014, Basel, Schweiz

Permalink: https://www.hzdr.de/publications/Publ-21281
Publ.-Id: 21281


Spin dynamics in triangular-lattice antiferromagnets Cs2CuBr4 and Cs2CuCl4: high-field ESR studies

Zvyagin, S.
A spin-1/2 Heisenberg antiferromagnet (AF) on a triangular lattice is the paradigmatic model in quantum magnetism, which was intensively studied. In spite of numerous theoretical studies (which predict a rich variety of grounds states, ranging from a gapless spin liquid to Néel order), many important details of the phase diagram of triangular-lattice AFs remain controversial or even missing. In order to test the theory experimentally, a precise information on the spin-Hamiltonian parameters for the materials of interest is highly demanded. Here, we present results of high-field electron spin resonance (ESR) studies of spin-1/2 Heisenberg AFs Cs2CuCl4 and Cs2CuBr4 with distorted triangular-lattice structures in magnetic fields up to 50 T. In the magnetically saturated phase (H > Hsat), quantum fluctuations are fully suppressed, and the spin dynamics is defined by ordinary magnons. This allows us to accurately describe the magnetic excitation spectra in both materials and, using the harmonic spin-wave theory, to determine their exchange parameters. The viability of the proposed method was first proven by applying it to Cs2CuCl4, revealing good agreement with inelastic neutron-scattering results. For the isostructural Cs2CuBr4 we obtain J/kB = 14.9(7) K, J'/kB = 6.1(3) K, [J'/J ~ 0.41], providing exact and conclusive information on the exchange coupling parameters in this frustrated spin system. The approach has a broader impact and can be potentially used for any quantum magnet with reduced (e.g., by the staggered Dzyaloshinskii-Moriya interaction) translational symmetry, resulting, as predicted, in emergence of a new exchange mode above Hsat
  • Lecture (Conference)
    From Exotic Excitations to Novel Transport and Non-Equilibrium Phenomena, 01.-05.09.2014, Dresden, Deutschland
  • Invited lecture (Conferences)
    NHMFL Users Committee Meeting, 15.10.2015, Tallahassee, USA

Permalink: https://www.hzdr.de/publications/Publ-21280
Publ.-Id: 21280


Effect of Single-Ruler Electromagnetic Braking (EMBr) Location on Transient Flow in Continuous Casting

Thomas, B. G.; Singh, R.; Vanka, S. P.; Timmel, K.; Eckert, S.; Gerbeth, G.
Ultrasonic Doppler Velocimetry measurements and Large Eddy Simulations were conducted on a laboratory-scale physical model of a steel continuous slab caster with a low-melting alloy, both with and without an applied single-ruler magnetic field in one of two different vertical orientations. The computational model agreed very closely with the measurements in all respects, including time-average flow, velocity profiles, and transient velocity histories at specific locations. The magnetic field altered both the classic double-roll flow pattern and the flow stability. Lowering the magnetic field below the nozzle caused: steeper downward jet angles, lower surface velocities, lower turbulent kinetic energy at the surface, and better flow stability, especially towards the surface, and at higher frequencies. The experimental and computational results both show that the electromagnetic field should not be placed with its maximum directly across the nozzle ports, where it may aggravate unstable flow.
Keywords: liquid metal model, contactless inductive flow tomography, ultrasonic doppler velocimetry, large eddy simulations, two-phase flow, electromagnetic flow control
  • Lecture (Conference)
    2015 TMS Annual Meeting & Exhibition, 15.-19.03.2015, Orlando, USA
  • Journal for Manufacturing Science and Production 15(2015)1, 93-104
    DOI: 10.1515/jmsp-2014-0047

Permalink: https://www.hzdr.de/publications/Publ-21279
Publ.-Id: 21279


Steel casting characterisation: contactless inductive flow tomography and mutual inductance tomography

Wondrak, T.; Peyton, A. J.
Monitoring the steel flow through the submerged entry nozzle (SEN) and in the mould during continuous casting presents a challenge for the instrumentation system because of the high temperature environment and the opaqueness of the liquid steel. In this article we describe the development of two complimentary electromagnetic instrumentation systems which are able to visualise the steel flow profile in the SEN by means of Mutual Inductance Tomography (MIT) and the mean 2D/3D flow structure in the mould by means of Contactless Inductive Flow Tomography (CIFT). The flow structure in both sites is crucial for the quality of steel in respect of cleanliness and surface quality. The article will cover the development of both techniques from first principles and initial tests on a scaled (approx. 1:10) laboratory model of the continuous casting process. The experiments were performed with argon gas and GaInSn as an analogue for liquid steel, which has similar conductive properties as molten steel and allows the measurements at room temperature. The article will close with describing hot tests and subsequent plant tests.
Keywords: contactless inductive flow tomography, mutual inductance tomography, flow measurement, continuous casting, steel flow, tomography
  • Book chapter
    Rafael Colás, George E. Totten: Encyclopedia of Iron, Steel, and Their Alloys, New York: Taylor & Francis Group,, 2016, 978-1-4665-1104-0, 3320-3332

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Permalink: https://www.hzdr.de/publications/Publ-21278
Publ.-Id: 21278


Flow visualization by means of contactless inductive flow tomography in the presence of a magnetic brake

Ratajczak, M.; Wondrak, T.; Timmel, K.; Stefani, F.; Eckert, S.
In continuous casting DC magnetic fields perpendicular to the wide faces of the mold are used to control the flow in the mold. Especially in this case, even a rough knowledge of the flow structure in the mold would be highly desirable. The contactless inductive flow tomography (CIFT) allows to reconstruct the dominating two-dimensional flow structure in a slab casting mold by applying one external magnetic field and by measuring the flow induced magnetic fields outside the mold. For a physical model of a mold with a cross section of 140 mm × 35 mm we present preliminary measurements of the flow field in the mold in the presence of a magnetic brake. In addition, we show first reconstructions of the flow field in a mold with the cross section of 400 mm × 100 mm demonstrating the upward scalability of CIFT.
Keywords: continuous casting, contactless inductive flow tomography, flow measurement
  • Journal for Manufacturing Science and Production 15(2015)1, 41-48
    DOI: 10.1515/jmsp-2014-0037
  • Invited lecture (Conferences)
    TMS 2015 144th annual meeting & exhibition, 15.-19.03.2015, Orlando, United States of America

Permalink: https://www.hzdr.de/publications/Publ-21277
Publ.-Id: 21277


Europium(III)-Calcite study with site-selective TRLFS

Peschel, S.; Schmidt, M.; Stumpf, T.
Calcite is an important mineral that plays a significant role in nuclear waste disposal concerning the safety and performance in geological formations. At these sites it can be found in the near field as a secondary phase (weathering of the geochemical barrier) and as a rock-forming mineral in the surrounding rocks. Geochemically, calcite has the potential to adsorb as well as incorporate guest ions with a similar ionic radius, such as europium and curium, for calcium in the host lattice. Because of the long half-lives of actinides like curium and americium, they and their lanthanide homologues (i.e., europium) are the subject of recent research.
Calcite samples were doped with Eu(III) in batch experiments. Calcium carbonate powder was contacted with a Eu(III) solution (5 x 10-7 M) in a calcium carbonate saturated solution with a NaCl (10 mM) background electrolyte solution. Batch samples were analyzed at varying contact times to understand the step-by-step kinetic and mechanistic behavior of incorporation of Eu(III) into the solid phase. After the contact period, the supernatant was investigated with ICP-MS. The Eu(III) concentration in solution varies from 0.1 to 3.2 % of the initial concentration, which indicates that almost all Eu(III) is adsorbed.
The calcite powder was examined with site-selective TRLFS at temperatures below 20 K. The direct excitation of the 7F0 →5D0 transition in the range of 576-581 nm and the integration of the respective emission spectra yields a characteristic excitation spectrum. These excitation spectra show only one broad peak with a maximum at ~579.2 nm, independent of the sorption time (up to 31 days). This behavior is dissimilar to that determined by Stumpf and Fanghänel [1] who investigated Cm(III) sorption on calcite with NaClO4 as background electrolyte and found 2 peaks, which change over time. Lifetime measurements of our samples exhibit biexponential decay indicative of two species. The first specie has a lifetime of 460 to 985 µs and the second 2155 to 4577 µs. Using Horrock´s equation[2] the number of coordinating water molecules in the first sphere surrounding the Eu(III) can be determined. This value corresponds to its location (surface sorbed vs incorporated) on or within the calcite lattice. Therefore, calculated values of 0.5 to 1.7 indicate the formation of an inner sphere sorption species whereas a value of 0 is indicative of incorporation of the Eu(III) within the calcite. The emission spectrum shows a threefold splitting of the 7F1 band.This indicates a ligand field with low symmetry. To better understand these surface species, future measurements with CTR and RAXR will be performed.

[1] Stumpf, T. and T. Fanghanel (2002). J. of Colloid and Interface Science 249(1), 119-122.
[2] Horrocks (1979) J. Am. Chem. Soc. 101, 334.
Keywords: site-selective TRLFS Europium Calcite
  • Poster
    Advanced Techniques in Actinide Spectroscopy 2014 (ATAS 2014), 03.-07.11.2014, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-21276
Publ.-Id: 21276


Sorption of (trivalent) actinides and lanthanides

Hellebrandt, S.; Schmidt, M.; Stumpf, T.
Introduction
The study of trivalent actinides is of particular importance for the safety assessment of nuclear waste disposal sites due to the predominance of this valence in deep geological formations. In particular, studying the solution-solid interface chemistry of these trivalent radioelements in the aqueous phase with a mineral is fundamental for better understanding their interactions at or within the surface of a host phase in a repository. As a relevant near field material (geotechnical barrier) for nuclear waste disposal sites, clay minerals are very important due to their retardation properties. Muscovite, a phyllosilicate material of aluminum and potassium, is very similar to clay minerals but less complex, so we are able to assign results from muscovite to clay minerals. Additionally, investigations concerning trace concentration of actinides appearing in the far field of a nuclear waste disposal are also of interest. Site-Selective Time-Resolved Laser Fluorescence Spectroscopy (TRLFS) is a characterizational technique that can probe the behavior of low concentrated actinides on a molecular level. As a complementary technique resonant anomalous x-ray reflectivity (RAXR) will be used to get a deeper insight and a verification of the TRLFS results.

TRLFS, the main tool
The aim of this study focuses on understanding the surface interactions of muscovite with aqueous trivalent actinides and lanthanides using Eu(III) and Cm(III), and characterization of the solid and aqueous phase species using TRLFS. Europium (III) is used as a non-radioactive homologue for trivalent actinides due to its similar chemical behavior and its spectroscopic properties as a probe for TRLFS. Direct excitation of the 7F05D0 electron transition and consecutive integration of the respective emission generates information pertaining to the chemical coordination and environment of the Eu(III). First investigations in the muscovite-europium system show that there appears one poorly defined species (broad excitation peak) present at one site. Lifetime measurements of the luminescence are used in accordance with the Horrocks equation (europium) [1] and the number of coordinated waters can be determined. The lifetimes between 208 and 230 µs indicates 4 to 5 coordinated water ligands in the inner sphere. As a consequence of this the europium species is interpreted as inner-sphere sorption on the surface of muscovite.

[1] Horrocks, W.D. and Sudnick, D.R. (1979) J. Am. Chem. Soc. 101, 334-340.
  • Poster
    2nd International Workshop on Advanced Techniques in Actinide Spectroscopy (ATAS 2014), 03.-07.11.2014, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-21275
Publ.-Id: 21275


AER Working Group D on VVER safety analysis – report of the 2014 meeting

Kliem, S.
The AER Working Group D on VVER reactor safety analysis held its 23th meeting in Garching, Germany, during the period 12-13 May, 2014. The meeting was hosted by the GRS Garching and was held in conjunction with the eighth workshop on the OECD Benchmark for Uncertainty Analysis in Best-Estimate Modelling (UAM) for Design, Operation and Safety Analysis of LWRs. Altogether 21 participants attended the meeting of the working group D, 19 from AER member organizations and 2 guests from non-member organization. The co-ordinator of the working group, Mr. S. Kliem, served as chairman of the meeting.
The meeting started with a general information exchange about the recent activities in the participating organizations.
The given presentations and the discussions can be attributed to the following topics:
• Safety analyses methods and results
• Code development and benchmarking including the calculation of the OECD/NEA Benchmark for the Kalinin-3 VVER-1000 NPP and 7th AER Dynamic Benchmark
• Future activities
A list of the participants and a list of the handouts distributed at the meeting are attached to the report. The corresponding PDF-files of the handouts can be obtained from the chairman.
  • Lecture (Conference)
    24th Symposium of AER on VVER Reactor Physics and Reactor Safety, 14.-18.10.2014, Sochi, Russian Federation
  • Contribution to proceedings
    24th Symposium of AER on VVER Reactor Physics and Reactor Safety, 14.-18.10.2014, Sochi, Russian Federation
    Proceedings of the 24th Symposium of AER on VVER Reactor Physics and Reactor Safety, Budapest: MTA Energoatom, 415-420

Permalink: https://www.hzdr.de/publications/Publ-21274
Publ.-Id: 21274


Recent developments in (H)LM measurement techniques

Wondrak, T.; Eckert, S.; Franke, S.; Shevchenko, N.; Buchenau, D.; Stefani, F.; Gerbeth, G.
In the field of advanced heavy-liquid-metal (HLM) cooled systems the knowledge of flow properties of the liquid metal is important for the design, the operation and the safety of such systems. The measurement of the flow properties is usually hampered by the high temperature and the opaqueness of liquid melts. We will give an overview of the recent developments of measurement techniques which can be used for model experiments as wells as for instrumenting a HLM cooled system. This includes ultrasound Doppler velocimetry, x-ray radioscopy and several inductive techniques like inductive flow meters and the contacless inductive flow tomography.
Keywords: liquid metal, flow measurement
  • Invited lecture (Conferences)
    SEARCH/MAXSIMA 2014 International Workshop, 07.-10.10.2014, Karlsruhe, Germany

Permalink: https://www.hzdr.de/publications/Publ-21272
Publ.-Id: 21272


Measurement techniques for the flow in a model of a continuous caster

Wondrak, T.; Timmel, K.; Stefani, F.; Eckert, S.; Shevchenko, N.; Röder, M.
In order to examine the flow structure in a continuous casting mold which is important for the quality of the produced steel, at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) three different models of a continuous caster are available to study the flow in a continuous casting mold. Those cold liquid metal models which use metallic alloys with low melting point e.g. up to 200 °C offer the application of different measurement techniques like ultrasound doppler velocimetry, x-ray and potential probes for flow investigation. Second, these models can be used to study the influence of magnetic actuators to the flow due to their high conductivity, contrary to water models. Third, these models can be used to develop new measurement techniques which can be applied in a real caster.
We will give a short overview of the measurement techniques available for those models. Additionally we will present the newly developed Contactless Inductive Flow Tomography which can reconstruct the flow in the mold by measuring the flow induced perturbation of an applied magnetic field. This technique has the ability to be deployed in a real caster.
Keywords: liquid metal model, measurement techniques, contactless inductive flow tomography
  • Contribution to proceedings
    8th European Continuous Casting Conference, 23.-26.06.2014, Graz, Österreich
    Proceedings of the 8th eccc
  • Lecture (Conference)
    8th European Continuous Casting Conference, 23.-26.06.2014, Graz, Österreich

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Permalink: https://www.hzdr.de/publications/Publ-21270
Publ.-Id: 21270


Source Terms, Shielding Calculations and Soil Activation for a Medical Cyclotron

Konheiser, J.; Naumann, B.; Ferrari, A.; Brachem, C.; Müller, S.
Calculations of the shielding and estimates of soil activation for a medical cyclotron are presented in this work. Based on the neutron source term from the 18O(p,n)18F reaction produced by a 28 MeV proton beam, neutron and gamma dose rates outside the building were estimated with the Monte Carlo code MCNP6(1). The neutron source term was calculated with the MCNP6 code and FLUKA(2) code as well as with supplied data by the manufacturer. Soil activation was performed using the FLUKA code.
The estimated dose rate in the public area is about 0.035 μSv/h and thus significantly below the reference value of 0.5 μSv/h(3). After 5 years of continuous beam operation and a subsequent decay time of 30 days, the activity concentration of the soil is about 0.34 Bq/g. Significant discrepancies between the manufacturer supplied data for the neutron source term and the calculations done using the MCNP6 and FLUKA codes were found.
Keywords: radiation shielding, cyclotron, soil activation, Monte Carlo, 18F production, dose rate

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Permalink: https://www.hzdr.de/publications/Publ-21269
Publ.-Id: 21269


Quantitative assessment of the asphericity of pretherapeutic FDG uptake as an independent predictor of outcome in NSCLC.

Apostolova, I.; Rogasch, J.; Buchert, R.; Wertzel, H.; Achenbach, H. J.; Schreiber, J.; Riedel, S.; Furth, C.; Lougovski, A.; Schramm, G.; Hofheinz, F.; Amthauer, H.; Steffen, I. G.
Background:
The aim of the present study was to evaluate the predictive value of a novel quantitative measure for the spatial heterogeneity of FDG uptake, the asphericity (ASP) in patients with non-small cell lung cancer (NSCLC).

Methods:
FDG-PET/CT had been performed in 60 patients (15 women, 45 men; median age, 65.5 years) with newly diagnosed NSCLC prior to therapy. The FDG-PET image of the primary tumor was segmented using the ROVER 3D segmentation tool based on thresholding at the volume-reproducing intensity threshold after subtraction of local background. ASP was defined as the relative deviation of the tumor's shape from a sphere. Univariate and multivariate Cox regression as well as Kaplan-Meier (KM) analysis and log-rank test with respect to overall
(OAS) and progression-free survival (PFS) were performed for clinical variables, SUVmax/mean, metabolically active tumor volume (MTV), total lesion glycolysis (TLG), ASP and "solidity", another measure of shape irregularity.

Results:
ASP, solidity and "primary surgical treatment" were significant independent predictors of PFS in multivariate Cox regression with binarized parameters (HR, 3.66; p < 0.001, HR, 2.11; p = 0.05 and HR, 2.09; p = 0.05), ASP and "primary surgical treatment" of OAS (HR, 3.19; p = 0.02 and HR, 3.78; p = 0.01, respectively). None of the other semi-quantitative PET parameters showed significant predictive value with respect to OAS or PFS. Kaplan-Meier analysis revealed a probability of 2-year PFS of 52% in patients with low ASP compared to 12% in patients with high ASP (p < 0.001). Furthermore, it showed a higher OAS rate in the case of low versus high ASP (1-year-OAS, 91% vs. 67%: p = 0.02).

Conclusions:
The novel parameter asphericity of pretherapeutic FDG uptake seems to provide better prognostic value for PFS and OAS in NCSLC compared to SUV, metabolic tumor volume, total lesion glycolysis and solidity.

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Publ.-Id: 21268


Abschlussbericht zum BMBF-Verbundprojekt Partitioning II: Multifunktionelle Komplexbildner mit N, O, S-Donorliganden für d- und f-Elemente - Synthese, Komplexbildung, Struktur und Transportverhalten

Günther, A.; Mansel, A.; Schulz, K.; Paulik, S.; Poetsch, M.; Bernhard, G.
Hauptziel des Verbundprojektes war es, die Wechselwirkung von neu synthetisierten supramolekularen Komplexbildnern mit N,O,S-Donorfunktionen gegenüber d- und f-Elementen zu untersuchen. Dabei standen für das HZDR im Teilprojekt 1 die Komplexierung von N,O-Donorliganden insbesondere mit den Aktiniden U(VI) und Cm(III) und den Lanthaniden Eu(III), Ce(III) und Yb(III) in wässriger und erstmalig in organischer Lösung in Abhängigkeit vom pH-Wert bzw. Redoxspannung im Mittelpunkt. Es wurden die entsprechenden Komplexstöchiometrien und die spektroskopischen Eigenschaften der gebildeten Komplexe mittels UV-Vis-Spektroskopie, verschiedener laserinduzierter Methoden als auch IR-Spektroskopie bestimmt. Durch Anwendung der NMR-und EXAFS-Spektroskopie konnten strukturelle Aussagen zu den Metallkomplexen in Lösung gemacht werden. Mit Hilfe von UV-Vis Daten war es möglich, reproduzierbare Komplexbildungskonstanten von Aktinid- bzw.- Lanthanidkomplexen mit verschiedenen ß-Diketonen sowie Schiffschen Basen in Lösung zu bestimmen. Ergebnisse der Arbeiten des HZDR im Teilprojekt 2 zeigten, dass die Wechselwirkung von wasserlöslichen Calixarenen mit Radionuklidmetallionen sowie das Adsorptionsverhalten von Calixarenen an Geomatrizes unter naturnahen Bedingungen (pH 4 - 9) vernachlässigbar sind. Für die Flüssig-Flüssig-Extraktion von divalenten Metallionen mittels Radiotracertechnik wurden wasserunlösliche Calixarene ermittelt, die elementselektiv die Radionuklide 85Sr, 56Co, 64Cu und 65Zn aus der wässrigen Phase separieren können. Für Strontium eignet sich Bis-Salicyliden-diamino-calixaren, welches sich unter milden Bedingungen rückextrahieren lässt. Dicarboxy-calixaren extrahiert die d-Elemente quantitativ. Diese Extraktion ist nicht vollständig reversibel. Für die gebildeten Calixaren-Komplexe wurden spektroskopische Daten ermittelt. Die Extraktionsverfahren wurden für vier natürliche Wässer erfolgreich angewendet. Festphasenfixierte Calixarene sorbieren die Radionuklide quantitativ, jedoch ist eine vollständige Desorption nicht realisierbar.
Keywords: radionuclide, actinide, lanthanide, Schiff base, ß-diketone, calixarene, complexation, spectroscopy, extraction, radiotracer technique
  • Other report
    Dresden-Rossendorf: HZDR, 2014
    128 Seiten

Permalink: https://www.hzdr.de/publications/Publ-21265
Publ.-Id: 21265


Feasibility and limitations of laser-driven proton therapy: A treatment planning study.

Hofmann, K.; Masood, U.; Pawelke, J.; Wilkens, J.
Purpose:
Laser-acceleration of particles may offer a cost- and spaceefficient alternative for future radiation therapy with particles. Laser-driven particle beams are pulsed with very short bunch times, and a high number of particles is delivered within one laser shot which cannot be portioned or modulated during irradiation. The goal of this study was to examine whether good treatment plans can be produced for laser-driven proton beams and to investigate the feasibility of a laser-driven treatment unit.

Methods:
An exponentially decaying proton spectrum was tracked through a gantry and energy selection beam line design to produce multiple proton spectra with different energy widths centered on various nominal energies. These spectra were fed into a treatment planning system to calculate spot scanning proton plans using different lateral widths of the beam and different numbers of protons contained in the initial spectrum. The clinical feasibility of the resulting plans was analyzed in terms of dosimetric quality and the required number of laser shots as an estimation of the overall treatment time.

Results:
We were able to produce treatment plans with plan qualities of clinical relevance for a maximum initial proton number per laser shot of 6*108. However, the associated minimum number of laser shots was in the order of 104, indicating a long delivery time in the order of at least 15 minutes, when assuming an optimistic repetition rate of the laser system of 10 Hz.

Conclusion:
With the simulated beam line and the assumed shape of the proton spectrum it was impossible to produce clinically acceptable treatment plans that can be delivered in a reasonable time. The situation can be improved by a method or a device in the beam line which can modulate the number of protons from shot to shot.
  • Abstract in refereed journal
    Medical Physics 41(2014), 112-112
    DOI: 10.1118/1.4887876
  • Lecture (Conference)
    American Association of Physicists in Medicine (AAPM) 56th Annual Meeting, 20.-24.07.2014, Austin, Texas, USA

Permalink: https://www.hzdr.de/publications/Publ-21264
Publ.-Id: 21264


Realizing a laser-driven electron source applicable for radiobiological tumor irradiation

Nicolai, M.; Sävert, A.; Reuter, M.; Schnell, M.; Polz, J.; Jäckel, O.; Karsch, L.; Schürer, M.; Oppelt, M.; Pawelke, J.; Kaluza, M.
  • Lecture (Conference)
    41st IOP Plasma Physics Conference, 14.-17.04.2014, London, UK
  • Contribution to proceedings
    41st IOP Plasma Physics Conference, 14.-17.04.2014, London, UK
    Book of Abstracts (2014) 18
  • Lecture (Conference)
    Frühjahrstagung des Fachverbandes Plasmaphysik der Deutschen Physikalischen Gesellschaft, 17.-21.03.2014, Berlin, Deutschland
  • Contribution to proceedings
    Frühjahrstagung des Fachverbandes Plasmaphysik der Deutschen Physikalischen Gesellschaft, 17.-21.03.2014, Berlin, Deutschland
    Verhandl. DPG 49,2 (VI) (2014) P26.3

Permalink: https://www.hzdr.de/publications/Publ-21262
Publ.-Id: 21262


Source and shielding calculations at a PET cyclotron and possible activation in the soil

Konheiser, J.; Ferrari, A.; Naumann, B.; Müller, S.; Brachem, C.
This presentation summarizes the results of the Monte Carlo simulation of the shielding calculations and estimates of the soil activation for the new cyclotron of the HZDR (Helmholtz-Zentrum Dresden-Rossendorf). The dose values were determined on base of the resulting neutron flux at the 18F production. The calculations were carried out with the Monte Carlo code MCNP5. The neutron source was used both calculated with ALICE-91 code (manufacturer) and calculated with MCNP6. The comparison of the sources shows that ALICE-91 produced significantly fewer neutrons. The calculation of the soil activations was performed with FLUKA. In addition the effects of the energy increasing of the protons from 24 to 28 MeV were evaluated.
It could be shown that the expected total dose rate in the public area is about 0.1 mSv/h and thus significantly below the permissible value of 0.5 microSv/h. The activities generated in the soil are mainly determined by radionuclides with short half-life. After 5 years of continuous beam operation and a subsequent decay time of 30 days, the allowable value is used up only to 0.2%.
Keywords: Monte Carlo simulation, cyclotron, 18F production, dose rate, neutron soure
  • Lecture (others)
    14. AAA Workshop, 01.12.2014, Garching, Germany

Permalink: https://www.hzdr.de/publications/Publ-21261
Publ.-Id: 21261


New systematically modified vesamicol analogs and their affinity and selectivity for the vesicular acetylcholine transporter – A critical examination of the lead structure.

Barthel, C.; Sorger, D.; Deuther-Conrad, W.; Scheunemann, M.; Schweiger, S.; Jäckel, P.; Roghani, A.; Steinbach, J.; Schüürmann, G.; Sabri, O.; Brust, P.; Wenzel, B.
To verify vesamicol as lead structure in the development of radioligands for imaging of VAChT in the brain by PET, we systematically modified this molecule and investigated five different groups of derivatives. Structural changes were conducted in all three ring systems A, B, and C resulting in a library of 67 different vesamicol analogs. Based on their in vitro binding affinity toward VAChT as well as σ1 and σ2 receptors, we performed an extensive structure-affinity relationship (SAR) study regarding both affinity and selectivity. The compounds possessed VAChT affinities in the range of 1.32 nM (benzovesamicol) to > 10 µM and selectivity factors from 0.1 to 73 regarding σ1 and σ2 receptors, respectively. We could confirm the exceptional position of benzovesamicols as most affine VAChT ligands. However, we also observed that most of the compounds with high VAChT affinity demonstrated considerable affinity in particular to the σ1 receptor. Finally, none of the various vesamicol analogs in all five groups showed an in vitro binding profile suitable for specific VAChT imaging in the brain.
Keywords: VAChT Vesamicol PET Sigma receptors

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Permalink: https://www.hzdr.de/publications/Publ-21260
Publ.-Id: 21260


Development of laser-driven proton radiotherapy

Pawelke, J.
  • Invited lecture (Conferences)
    4th University Cancer Center Discussion Platform on Radiation Research in Oncology, 30.04.2014, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-21259
Publ.-Id: 21259


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