Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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31735 Publications
Two-phase Flow Pattern Measurements with a Wire Mesh Sensor in a Direct Steam Generating Solar Thermal Collector
Berger, M.; Mokhtar, M.; Zahler, C.; Willert, D.; Neuhäuser, A.; Schleicher, E.;
At Industrial Solar’s test facility in Freiburg (Germany), two phase flow patterns have been measured by using a wire mesh sensor from Helmholtz-Zentrum Dresden-Rossendorf (HZDR). Main purpose of the measurements was to compare observed two-phase flow patterns with expected flow patterns from models. The two-phase flow pattern is important for the design of direct steam generating solar collectors. Vibrations should be avoided in the peripheral piping, and local dry-outs or large circumferential temperature gradients should be avoided in the absorber tubes. Therefore, the choice of design for operation conditions like mass flow and steam quality are an important step in the engineering process of such a project. Results of a measurement with the wire mesh sensor are the flow pattern and the plug or slug frequency at the given operating conditions. Under the assumption of the collector power, which can be assumed from previous measurements at the same collector and adaption with sun position and incidence angle modifier, also the slip can be evaluated for a wire mesh sensor measurement. Measurements have been performed at different mass flows and pressure levels. Transient behavior has been tested for flashing, change of mass flow, and sudden changes of irradiation (cloud simuation). This paper describes the measurements and the method of evaluation. Results are shown as extruded profiles in top view and in side view. Measurement and model are compared. The tests have been performed at low steam quality, because of the limits of the test facility. Conclusions and implications for possible future measurements at larger collectors are also presented in this paper.
  • Contribution to proceedings
    SolarPACES 2016, 11.-14.10.2016, Abu Dhabi, United Arab Emirates
    AIP Conference Proceedings 1850(2017) 070003
    DOI: 10.1063/1.4984417

Publ.-Id: 23983 - Permalink


How Theory Can Probe The Chemical Bond: The Case Of Caged U2
Patzschke, M.;
"Nothing is simple in actinide chemistry" B. Roos
We present results on the intricate changes in An-An bonding in differently sized cages.
Methods used model the compounds are introduced and analysis tools are presented.
Keywords: computational chemistry, ELI, AIM, actinides, endohedral complexes
  • Invited lecture (Conferences)
    15. Koordinierungsgespräch PSI/LES - HZDR/IRE, 28.08.2015, Dresden, Deutschland

Publ.-Id: 23982 - Permalink


Computational chemistry for actinide compounds: examine the U-U bond inside fullerenes
Patzschke, M.;
Computational chemistry methods to further the understanding of chemical bonds in heavy-metal systems are presented. Results obtained in this manner are presented for U_2 inside various fullerenes and the usefulness of the presented methods demonstrated.
Keywords: computational chemistry, actinides, fullerenes
  • Lecture (others)
    Eingeladener Vortrag Universität Hannover, 13.04.2016, Hannover, Deutschland

Publ.-Id: 23981 - Permalink


How can Theoretical Chemistry contribute to coordination chemistry?
Patzschke, M.;
We present computational chemistry methods and tools useful in the understanding of coordination compounds, especially for complexes of actinides and technetium.
Keywords: computational chemistry, actinides, technetium
  • Invited lecture (Conferences)
    8th International Workshop on “Coordination Chemistry of Metals with Medical Relevance and Supramolecular Building Blocks“, 26.05.2016, Berlin, Deutschland

Publ.-Id: 23980 - Permalink


Probing the chemical bond: The case of caged U_2
Patzschke, M.;
We present computational results on the "unwilling" bonding of U2 in fullerenes. We explain the nature of the strong bond to cage and the weak U-U bond.
We show how this An-An bond changes whith cage size. We will show how understanding of this special bonding might help in development of An-An forcefields.
Keywords: computational chemistry, DFT, CASPT2, ELF, AIM, actinides, fullerenes
  • Invited lecture (Conferences)
    GöCH Vortrag Linz, 29.02.2016, Linz, Österreich

Publ.-Id: 23979 - Permalink


Uranyl Spectroscopy - Do We Know Everything?
Patzschke, M.;
Highly accurate thermodynamic data is necessary to model the behaviour of toxic/radiotoxic species in the environment. We show for the uranyl system, that TRLFS/CW spectroscopy in combination with theory is a powerful tool for such predictions.
Keywords: computational chemistry, TRLFS, PARAFAC
  • Invited lecture (Conferences)
    IX MMQC Mariapfarr Workshop on Theoretical Chemistry, 26.02.2016, Mariapfarr, Österreich

Publ.-Id: 23978 - Permalink


Using ADF in computational actinide chemistry
Patzschke, M.;
ADF (Amsterdam Density Functional code) is a quantum chemical code that allows computations for molecules containing all elements in the periodic table. We will present its capabilities, demonstrate its usage and instruct the participants to set up their own calculations.
Keywords: computational chemsitry, DFT, actinides
  • Invited lecture (Conferences)
    ThUL school 2105, 28.09.2015, Karlsruhe, Deutschland

Publ.-Id: 23977 - Permalink


Visualising Your Results - An Introduction to VMD
Patzschke, M.;
Visualising the results of quantum chemical computations is an important part of research. Producing high quality graphics becomes more and more a required skill. We will present the use of the program VMD, show applications and teach students to use it on their own.
Keywords: computational chemistry, visualisation, VMD
  • Invited lecture (Conferences)
    CSC Spring School 2015, 12.03.2015, Helsinki, Finnland
  • Invited lecture (Conferences)
    CSC Spring School 2016, 10.03.2016, Helsinki, Finnland
  • Invited lecture (Conferences)
    CSC Spring School in Theoretical Chemistry, 17.03.2017, Helsinki, Finnland

Publ.-Id: 23976 - Permalink


Quantum Chemistry Workshop - using Orca & Gabedit
Patzschke, M.;
The capabilities of the qc-code Orca and the versatile GUI gabedit are presented. Calculations with Orca are demonstrated and the students are taught to set up their own calculations.
Keywords: computational chemistry, Orca
  • Invited lecture (Conferences)
    CSC Spring School 2015, 11.03.2015, Helsinki, Finnland
  • Invited lecture (Conferences)
    CSC Spring School 2016, 09.03.2016, Helsinki, Finnland
  • Invited lecture (Conferences)
    CSC Spring School in Theoretical Chemistry, 13.-17.03.2017, Helsinki, Finland

Publ.-Id: 23975 - Permalink


Planned Projects of the New Theory- Group in Rossendorf
Patzschke, M.;
We present research projects of the newly established computational chemistry group at the FWO.
Keywords: computational chemistry, actinides
  • Lecture (others)
    Helmholtz-Koordinierungstreffen 2015, 04.03.2015, Jülich, Deutschland

Publ.-Id: 23974 - Permalink


Computational Methods for f-Elements
Patzschke, M.;
Theoretical chemistry is a comparatively new research area in chemistry. In the last 100 years enormous progress has been made in understanding the electronic structures of molecules. Almost every publication nowadays has a theory section. This means, that all chemists have to understand the basics of quantum chemistry.

The f-elements, and especially the actinides are very challenging to work with in the laboratory, to make matters worse, they are even very challenging to treat computationally. The reason for this is threefold:

1) Each actinide atom adds a lot of electrons to the system and as computational methods get much more time consuming when the amount of electrons in the system is increased, special care has to be taken to make the computations as efficient as possible.
2) Actinides, especially the later ones in low oxidation states contain many unpaired electrons, making many of the actinide-containing species multi-reference cases, where simple computational methods do not work.
3) For heavy elements, the expectation value of the speed of the innermost electrons approaches the speed of light. This means, normal quantum-chemical methods as used for light elements will not work.

In the light of the above mentioned points we will have a look at the methods available in the quantum chemical treatment of f-elements. We will spend some time looking at density-functional theory, the work-horse of computational chemistry. Special care will be taken to explain were this theory excels and what its shortcomings are.

We will then move to so called multi-reference methods, useful for treating actinide systems. Here the difference between static and dynamic correlation will be explained and methods to treat both will be introduced. The concept of an active space will be presented in some detail and guidelines for a successful choice of this active space will be given.

Finally, we will spend some time looking at the fundamental ideas of relativistic quantum chemistry and the effect of relativity on chemical properties. In this part we will also discuss the special requirements relativistic calculations impose.
Keywords: computational chemistry, actinides
  • Invited lecture (Conferences)
    Second Joint Student Workshop on f-Element Chemistry, 09.06.2015, Karlsruhe, Deutschland

Publ.-Id: 23973 - Permalink


Investigating Catalytic Activity with DFT
Patzschke, M.;
We present computational results for the regioselectivity of the Pauson-Khand reaction and the computationally validated catalytic cycle of the gold(III) catalyzed enynamine – cyclopentadiene cycloisomerisation.
Keywords: computational chemistry, DFT, CASPT2, catalysis
  • Invited lecture (Conferences)
    IXth Workshop on Modern Methods in Quantum Chemistry, 26.02.2015, Mariapfarr, Österreich

Publ.-Id: 23972 - Permalink


DFT in the f-block
Patzschke, M.;
Computational chemistry has become an important tool. The most popular approaches are based on the electronic density, methods known as DFT calculations. We review the basic principles as well as the applicability to f-element systems.
Keywords: Computational chemistry, DFT, f-elements
  • Invited lecture (Conferences)
    EUFEN 4, 09.04.2015, Lissabon, Portugal

Publ.-Id: 23971 - Permalink


Magnetically induced ring currents in actinide extraction ligand systems
Patzschke, M.;
Aromaticity is an old concept in chemistry. With newly developed metods, like GIMIC, it is possible to quantify this concept. With this method the ring current induced by an external magnetic field is evaluated (in nA/T), paramagnetic and diamagnetic contributions can be seen and the stabilisation due to aromaticity predicted. We present latest results for some typical actinide extraction ligands like BTP and look on the influence of complexation on these currents.
Keywords: Computational chemistry, actinides, aromaticity
  • Lecture (others)
    Eingeladener Vortrag TU München, 05.02.2015, München, Deutschland

Publ.-Id: 23970 - Permalink


Nanoparticle dispersion in liquid metals by electromagnetically induced acoustic cavitation
Kaldre, I.; Bojarevics, A.; Grants, I.; Beinerts, T.; Kalvans, M.; Milgravis, M.;
Ceramic nanoparticle dispersion in metallic matrix is a technical challenge to produce class of composite materials-Metal matrix nano-composites (MMNC). Current powder metallurgy has limitations producing these materials. Process is time consuming and dimensions of ingots are limited. Aim of this study is to investigate experimentally the effect of magnetically induced cavitation applied for the purpose of nanoparticle dispersion in liquid metals. We present a contactless electromagnetic method to induce ultrasound and disperse particles in liquid metals by simultaneously applied steady and alternating magnetic fields. The oscillating magnetic force due to the azimuthal induction currents and the axial magnetic field excites power ultrasound in the sample. If the fields are sufficiently high then it is possible to achieve the acoustic cavitation threshold in liquid metals. Cavitation bubble collapses create intense microscale jets, which can break nanoparticle agglomerates and disperse them. Cavitation bubble collapses are known to create microscale jets with a potential to break nanoparticle agglomerates and disperse them. The samples are solidified under the contactless ultrasonic treatment and later analyzed by electron microscopy and energy-dispersive X-ray spectroscopy (EDX). It is observed that SiC nanoparticles are dispersed in an aluminum magnesium alloy, whereas in tin the same particles remain agglomerated in micron-sizedclusters despite a more intense cavitation.
Keywords: Nanaoparticles, Metal matrix composites (MMCs), Cavitation, High magnetic field, Power ultrasound

Publ.-Id: 23969 - Permalink


Scalable critical-path analysis and optimization guidance for hybrid MPI-CUDA applications
Schmitt, F.; Dietrich, R.; Juckeland, G.;
The use of accelerators in heterogeneous systems is an established approach in designing petascale applications. Today, Compute Unified Device Architecture (CUDA) offers a rich programming interface for GPU accelerators but requires developers to incorporate several layers of parallelism on both the CPU and the GPU. From this increasing program complexity emerges the need for sophisticated performance tools. This work contributes by analyzing hybrid MPI-CUDA programs for properties based on wait states, such as the critical path, a metric proven to identify application bottlenecks effectively. We developed a tool to construct a dependency graph based on an execution trace and the inherent dependencies of the programming models CUDA and Message Passing Interface (MPI). Thereafter, it detects wait states and attributes blame to responsible activities. Together with the property of being on the critical path, we can identify activities that are most viable for optimization. To evaluate the global impact of optimizations to critical activities, we predict the program execution using a graph-based performance projection. The developed approach has been demonstrated with suitable examples to be both scalable and correct. Furthermore, we establish a new categorization of CUDA inefficiency patterns ensuing from the dependencies between CUDA activities.
Keywords: GPGPU, CUDA, MPI, wait states, critical-path analysis, performance analysis, performance optimization

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Publ.-Id: 23968 - Permalink


Advanced characterisation and optical simulation for the design of solar selective coatings based on carbon:transition metal carbide nanocomposites
Heras, I.; Krause, M.; Abrasonis, G.; Pardo, A.; Endrino, J. L.; Guillén, E.; Escobar-Galindo, R.;
Solar selective coatings based on carbon transition metal carbide nanocomposite absorber layers were designed. Pulsed filtered cathodic arc was used for depositing amorphous carbon: metal carbide (a-C:MeC, Me = V, Mo) thin films. Composition and structure of the samples were characterized by ion beam analysis, X-ray diffraction, Raman spectroscopy, and transmission electron microscopy. The optical properties were determined by ellipsometry and spectrophotometry. Three effective medium approximations (EMA), namely Maxwell-Garnett, Bruggeman, and Bergman, were applied to simulate the optical behaviour of the nanocomposite thin films. Excellent agreement was achieved between simulated and measured reflectance spectra in the entire wavelength range by using the Bergman approach, where in-depth knowledge of the nanocomposite thin film microstructure is included. The reflectance is shown to be a function of the metal carbide volume fraction and its degree of percolation, but not dependent on whether the nanocomposite microstructure is homogeneous or a self-organized multilayer. Solar selective coatings based on an optimized a-C:MeC absorber layer were designed exhibiting a maximum solar absorptance of 96% and a low thermal emittance of ~5 and 15% at 25 and 600ºC, respectively. The results of this study can be considered as predictive design tool for nanomaterial-based optical coatings in general.
Keywords: Solar selective coatings, Amorphous carbon:transition metal carbides, Effective Medium approximation, Pulsed filtered cathodic vacuum arc, Bergman representation

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Publ.-Id: 23967 - Permalink


Thermally induced formation of metastable nanocomposites in amorphous Cr-Zr-O thin films deposited using reactive ion beam sputtering
Rafaja, D.; Wüstefeld, C.; Abrasonis, G.; Braeunig, S.; Baehtz, C.; Hanzig, F.; Dopita, M.; Krause, M.; Gemming, S.;
Successive crystallization ofamorphous Cr-Zr-O thin films, formation of the (Cr,Zr)2O3/(Zr,Cr)O2 nanocomposites and the thermally induced changes in the hexagonal crystal structure of metastable (Cr,Zr)2O3 were investigated by means of in situ high-temperature synchrotron diffraction experiments up to 1100 °C. The thin films were deposited at room temperature by using reactive ion beam sputtering, and contained 3–15 at.% Zr. At low Zr concentrations, chromium-rich (Cr,Zr)2O3 crystallized first, while the crystallization of zirconium-rich (Zr,Cr)O2 was retarded. Increasing amount of zirconium shifted the onset of crystallization in both phases to higher temperatures. For 3 at.% of zirconium in amorphous Cr-Zr-O, (Cr,Zr)2O3 crystallized at 600 °C. At 8 at.% Zr in the films, the crystallization of (Cr,Zr)2O3 started at 700 °C. At 15 at.% Zr, the Cr-Zr-O films remained amorphous up to the annealing temperature of 1000 °C.Metastable hexagonal (Cr,Zr)2O3 accommodated up to ~3 at.% Zr. Excess of zirconium formed tetragonal zirconia, which was stabilized by chromium.
Keywords: Metastable oxides In situ synchrotron diffraction Crystallization Reactive ion beam sputtering Rutherford backscattering spectrometry

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Publ.-Id: 23966 - Permalink


Evaluation of the enantiomer specific biokinetics and radiation doses of [18-F]-fluspidine – a new tracer in clinical translation for imaging of σ1 receptors
Kranz, M.; Sattler, B.; Wüst, N.; Deuther-Conrad, W.; Patt, M.; Meyer, P. M.; Fischer, S.; Donat, C. K.; Wünsch, B.; Hesse, S.; Steinbach, J.; Brust, P.; Sabri, O.;
The enantiomers of [18F]-fluspidine, recently developed for imaging of σ1 receptors, exhibit promising and distinct pharmacokinetics which makes them attractive for different clinical questions. To support their clinical translation, human radiation dosimetry of (S)-(-)-[18F]-fluspidine and (R)-(+)-[18F]-fluspidine was estimated from ex vivo biodistribution and PET/MR imaging in mice after extrapolation to human scale. The results were validated by a first-in-human study where time-dependent activity data of (S)-(-)-[18F]-fluspidine was obtained by PET/CT. The time-activity curves were exponentially fitted and the integral used in OLINDA to calculate organ doses (ODs) and the effective dose (ED). According to different biokinetics of (S)-(-)-[18F]-fluspidine and (R)-(+)-[18F]-fluspidine, the EDs differ significantly with values of 12.9 µSv/MBq and 14.0 µSv/MBq (p<0.025, image-derived data of mice), respectively, as observed by ex vivo biodistribution too. In the human study, the ED was calculated to be 21.0 µSv/MBq. The preclinical dosimetry reveals the ED for [18F]-fluspidine comparable with other 18F-labeled PET imaging agents, despite differences of the EDs due to enantiomer specific kinetics. The first-in-human study confirmed that the radiation risk of (S)-(-)-[18F]-fluspidine imaging is within accepted limits. However, the ED in humans is underestimated when using preclinical imaging for dosimetry which needs to be considered when applying for first-in-human studies.

Publ.-Id: 23965 - Permalink


[18F]FDG-PET/CT based response assessment of stage IV non-small cell lung cancer treated with paclitaxel-carboplatin-bevacizumab with or without nitroglycerin patches
de Jong, E.; van Elmpt, W.; Leijenaar, R.; Hoekstra, O.; Groen, H.; Smit, E.; Boellaard, R.; van der Noort, V.; Troost, E.; Lambin, P.; Dingemans, A.;
Purpose
Nitroglycerin (NTG) is a vasodilatating drug, which increases tumor blood flow and consequently decreases hypoxia. Therefore, changes in [18F]fluorodeoxyglucose-positron emission tomography ([18F]FDG-PET) uptake pattern may occur. In this analysis, we investigated the feasibility of [18F]FDG-PET for response assessment to paclitaxel-carboplatin-bevacizumab (PCB) treatment with and without NTG patches. And we compared the [18F]FDG-PET response assessment to RECIST response assessment and survival.
Methods
A total of 223 stage IV non-small cell lung cancer (NSCLC) patients were included in a phase II study (NCT01171170) randomizing between PCB treatment with or without NTG patches. For 60 participating patients a baseline and a second [18F]FDG-PET/CT scan, performed between day 22-24 after the start of treatment, were available. Tumor response was defined as a 30% decrease in CT- and PET-parameters, and was compared to RECIST response at week 6. The predictive value of these assessments for progression free survival (PFS) and overall survival (OS) was assessed with and without NTG.
Results
A 30% decrease in SUVpeak assessment identified more patients as responders compared to a 30% decrease in CTdiameter assessment (73% vs. 18%), however, this was not correlated to OS (SUVpeak30 p=0.833; CTdiameter30 p=0.557). Changes in PET parameters between the baseline and the second scan were not significant different for the NTG group compared to the control group (p-value range 0.159 - 0.634). The CT (part of the [18F]FDG-PET/CT) based parameters showed a significant difference between the baseline and the second scan for the NTG group compared to the control group (CT diameter decrease of 7 ± 23% vs. 19 ± 14%, p=0.016, respectively).
Conclusions
The decrease in tumoral FDG uptake in advanced NSCLC patients treated with chemotherapy with and without NTG did not differ between both treatment arms. Early PET-based response assessment showed more tumor responders than CT-based response assessment (part of the [18F]FDG-PET/CT), this was not correlated to survival. This might be due to timing of the [18F]FDG-PET shortly after the bevacizumab infusion.
Keywords: NSCLC, FDG-PET, bevacizumab

Publ.-Id: 23964 - Permalink


Precise tuning of the Curie temperature of (Ga,Mn)As-based magnetic semiconductors by hole compensation: Support for valence-band ferromagnetism
Zhou, S.; Li, L.; Yuan, Y.; Rushforth, A. W.; Chen, L.; Wang, Y.; Boettger, R.; Heller, R.; Zhao, J.; Edmonds, K. W.; Campion, R. P.; Gallagher, B. L.; Timm, C.; Helm, M.;
For the prototype diluted ferromagnetic semiconductor (Ga,Mn)As, there is a fundamental concern about the electronic states near the Fermi level, i.e., whether the Fermi level resides in a well-separated impurity band derived from Mn doping (impurity-band model) or in the valence band that is already merged with the Mn-derived impurity band (valence-band model). We investigate this question by carefully shifting the Fermi level by means of carrier compensation. We use helium-ion implantation, a standard industry technology, to precisely compensate the hole doping of GaAs-based diluted ferromagnetic semiconductors while keeping the Mn concentration constant. We monitor the change of Curie temperature (TC) and conductivity. For a broad range of samples including (Ga,Mn)As and (Ga,Mn)(As,P) with various Mn and P concentrations, we observe a smooth decrease of TC with carrier compensation over a wide temperature range while the conduction is changed from metallic to insulating. The existence of TC below 10K is also confirmed in heavily compensated samples. Our experimental results are naturally explained within the valence-band picture.
Keywords: Magnetic semiconductors; Ion irradiation; Fermi level

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Publ.-Id: 23963 - Permalink


Magnetocapacitance in CdCr1.8In0.2S4 Single Crystal Annealed in Cadmium Vapor
Xie, Y.; Chen, X.; Zhang, Z.; Song, W.; Zhou, S.; Yang, Z.;
CdCr2S4 single crystal was reported by Hemberger et al. to be multiferroic with the evidences of relaxor ferroelectricity and colossal magnetocapacitance (CMC), but whether these effects are intrinsic is under debate. Recently, we reported a one-to-one correlation between CMC and colossal magnetoresistance (CMR) in CdCr2S4 polycrystalline samples, and argued that CMC could be explained by the superposition of the CMR and the Maxwell-Wagner effects. In this paper, we further examined the magnetic, dielectric, and electric transport properties of CdCr2S4 and CdCr1.8In0.2S4 single crystals before and after annealing in cadmium vapor. The CdCr2S4 single crystal sample has no relaxor ferroelectricity and CMC, and in contrast to the CdCr2S4 single crystal reported by Hemberger et al., only the annealed CdCr1.8In0.2S4 displays CMC, but still does not exhibit the relaxor behavior. At the same time, it also shows CMR. All these results are in accordance with the results of our polycrystalline samples, and further confirm the resistive origin of the CMC in the CdCr2S4 system.
Keywords: Magnetocapacitance; Maxwell-Wagner effect; mangetoresistance; spinel

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Publ.-Id: 23962 - Permalink


Unraveling carrier’s kinetics in tuning the ferromagnetism of transparent Zn0.95Co0.05O epitaxial films
Satyarthi, P.; Ghosh, S.; Sekhar, B. R.; Wang, Y.; Zhou, S.; Skorupa, I.; Bürger, D.; Schmidt, H.; Srivastava, P.;
The search of transparent conducting and ferromagnetic properties in Zn1−xCoxO based diluted magnetic semiconductor is explored either by chemically alloying the different concentration (x) of Co or by n-type co-doping. The present work aims to explore the electrical conduction process at variable temperatures, in order to probe the room and low temperature ferromagnetism triggered in transparent Zn0.95Co0.05O films using inert xenon ion irradiation. The origin of the paramagnetism and the tunable ferromagnetism in transparent Zn0.95Co0.05O films is explained from different degree of concentric bound magnetic polarons (BMPs) stabilization inside variable range hopping spheres through implication of strongly and weakly bound carriers to O/Zn related lattice defects and tetrahedrally substituted Co2+ ions. The paramagnetic behavior in as deposited Zn0.95Co0.05O film arises from the smallest density of isolated concentric BMPs resulted mainly from marginal concentration of strongly localized carrier due to its highly insulating nature. The progressive enhancement in strongly localized carriers in post irradiated Zn0.95Co0.05O films as a function of fluence results in overlapping of static concentric BMPs to trigger onset of ferromagnetism. The strength of ferromagnetism is found to be maximal at a particular density of concentric BMPs optimized from the highest concentration of strongly localized carriers in insulating regime and substantial substituted Co2+ ions. Further enhancement in carrier concentration and reduction in substituted Co2+ ions is detrimental to ferromagnetism owing to non-static concentric BMPs percolation from the presence of weakly localized nature of carriers in intermediate regime.
Keywords: Transparent conducting oxides; Dilute magnetic semiconductors; Opto-spintronics

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Publ.-Id: 23961 - Permalink


Leadership-Scale, Open-Source, Full-Scale In-Situ Simulations Beyond GPUs and PFlop/s with PIConGPU
Huebl, A.; Widera, R.; Zenker, E.; Worpitz, B.; Burau, H.; Pausch, R.; Grund, A.; Matthes, A.; Garten, M.; Eckert, C.; Debus, A.; Kluge, T.; Cowan, T.; Schramm, U.; Bussmann, M.;
We present the scientific workflow and applications in plasma physics of the performance portable, open source, 3D3V electro-magnetic, many-core particle-in-cell (PIC) code PIConGPU. With an open and modern software environment, PIConGPU is already suited for the largest available supercomputers today and has now evolved to a single-source hardware independent PIC code running on conventional x86 architectures, upcoming OpenPOWER CPUs, many-core accelerators and as before, GPUs.
Keywords: PIC, GPGPU, PIConGPU, Simulation, LPA, OpenSource, Exascale
  • Poster
    17th Advanced Accelerator Concepts Workshop (AAC 2016), 31.07.-05.08.2016, National Harbor, Maryland, United States of America

Publ.-Id: 23960 - Permalink


Quasi Mono-Energetic Ion Acceleration from Mass-Limited Targets with Realistic Laser Contrast
Huebl, A.; Kluge, T.; Widera, R.; Hilz, P.; Schreiber, J.; Cowan, T.; Schramm, U.; Bussmann, M.;
We present first-principle, leadership-scale particle-in-cell simulations drawing a complete and consistent picture of the complex ion acceleration from truly isolated, spherical, mass-limited targets driven by a 500fs high-power laser with realistic contrast. Performing large-scale 3D3V simulations with PIConGPU on the Titan supercomputer allowed to correctly predict experimental observables such as charge, diction and divergence of generated mono-energetic, pencil-like proton beams that were otherwise unreproducible in simulations with reduced geometry or resolution.
Keywords: LPA, Ion Acceleration, Mass Limited, Paul Trap, PHELIX, PIC, Simulation, CUDA, PIConGPU, laser contrast
  • Invited lecture (Conferences)
    17th Advanced Accelerator Concepts Workshop (AAC 2016), 31.07.-05.08.2016, National Harbor, Maryland, United States of America

Publ.-Id: 23959 - Permalink


Beam transport and monitoring of laser-driven particle beams
Pawelke, J.;
no abstract available
  • Invited lecture (Conferences)
    ELI-ALPS Seminar, 08.07.2016, Szeged, Hungary

Publ.-Id: 23958 - Permalink


Radiotherapy with laser-driven beams
Pawelke, J.;
no abstract available
  • Invited lecture (Conferences)
    Lasers in Medicine and Life Sciences (LAMELIS), Advanced Summer School for Students in Medicine and Physics, 12.-21.07.2017, Szeged, Hungary
  • Invited lecture (Conferences)
    Lasers in Medicine and Life Sciences (LAMELIS), Advanced Summer School for Students in Medicine and Physics, 30.06.-09.07.2016, Szeged, Hungary

Publ.-Id: 23957 - Permalink


Second harmonic generation of diamond-blade diced KTiOPO4 ridge waveguides
Chen, C.; Rüter, C.; Volk, M.; Chen, C.; Shang, Z.; Lu, Q.; Akhmadaliev, S.; Zhou, S.; Chen, F.; Kip, D.;
We report on the fabrication of ridge waveguides in KTiOPO4 nonlinear optical crystals through carbon ion irradiation followed by precise diamond blade dicing. The diced side-walls have low roughness, which allows for low propagation loss of ~1dB/cm in fabricated of ridges. The waveguide property investigation has been performed at 1064 nm as well as 532 nm, showing good guidance at both TE and TM polarizations. Based on type II phase matching configuration, efficient second harmonic generation of green light at room temperature has been realized. High conversion efficiencies of ~1.12%W^−1 and ~12.4% have been obtained for frequency doubling under the pump of continuous-wave (CW) and pulsed fundamental waves at 1064 nm, respectively.
Keywords: Waveguides; Nonlinear optical materials; Nonlinear optics; Integrated optics

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Publ.-Id: 23956 - Permalink


A highly-parallel Monte-Carlo-Simulation of X-Ray-Scattering using a Particle-Mesh-Code on GPUs (Zwischenpräsentation Diplomarbeit)
Grund, A.;
Die Wechselwirkung extrem intensiver kurzer Laserpulse mit Festkörpern verspricht einige interessante Anwendungen und Einsichten in grundlegende Plasmaphysik. Eine Anwendung besteht darin, schnelle, durch die Laser-Plasmawechselwirkung erzeugte Ionen z.B. zur schonenderen und zielgerichteteren Behandlung von Krebspatienten zu nutzen als das mit klassischer Photonen-Strahlentherapie möglich wäre. Während die Ergebnisse der Wechselwirkung, nämlich die Ionenstrahlen, experimentell leicht untersuchbar sind, bleibt die Wechselwirkung selbst auf Grund der sehr kurzen Zeit- und Raumskalen und der Undurchdringlichkeit von Festkörpern für sichtbares Licht nur für Computersimulationen zugängig. Röntgenstreuexperimente werden als mögliche Lösung gesehen. Allerdings wird die Streuung der zur Beobachtung eingesetzten Röntgenstrahlen bislang hauptsächlich durch Fouriertransformationen angenähert, was insbesondere bei Mehrfachstreuung und zeitveränderlichen Dichten und Laserprofilen nicht mehr hinreichend ist. Im Rahmen dieser Arbeit wird eine Softwarelösung entwickelt, in der Propagation und Streuung der Röntgenstrahlung in einer Probe mit Monte-Carlo-Methoden simuliert werden und dadurch prinzipiell die vollen physikalischen Elementarprozesse berücksichtigt werden können. Durch die Nutzung von GPUs und einen skalierbaren Ansatz auf Basis der Bibliothek libPMacc können auch große Volumina verarbeitet werden. Da die numerische Genauigkeit eine große Rolle bei der Auswahl der Datentypen spielt, die wiederum die Geschwindigkeit beeinflusst, wird diese näher betrachtet. Anhand dieser Analyse werden die jeweils geeignetsten Lösungen vorgestellt und implementiert.
  • Other
    TU Dresden, 2016
    Mentor: Prof. Dr. W. Nagel, Dr. T. Kluge
    19 Seiten

Publ.-Id: 23955 - Permalink


Photo-neutron reaction cross-sections for natMo in the bremsstrahlung end-point energies of 12 - 16 and 45 - 70 MeV
Naik, H.; Kim, G. N.; Kapote Noy, R.; Schwengner, R.; Kim, K.; Zaman, M.; Shin, S. G.; Gey, Y.; Massarczyk, R.; John, R.; Junghans, A.; Wagner, A.; Cho, M.-H.;
The nat Mo(γ, x n)90,91,99 Mo reaction cross-sections were experimentally determined for the bremsstrahlung end-point energies of 12, 14, 16, 45, 50, 55, 60 and 70 MeV by activation and off-line gamma-ray spectrometric technique and using the 20 MeV electron linac (ELBE) at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR), Dresden, Germany, and the 100 MeV electron linac at the Pohang Accelerator Laboratory (PAL), Pohang, Korea. The nat Mo(gamma, x n)88,89,90,91,99 Mo reaction cross-sections as a function of photon energy were also calculated using the computer code TALYS 1.6. The flux-weighted average cross-sections were obtained from the literature data and the calculated values of TALYS based on mono-energetic photons and are found to be in general agreement with the present results. The flux-weighted average experimental and theoretical cross-sections for the nat Mo(γ, x n)88,89,90,91,99 Mo reactions increase with the bremsstrahlung end-point energy, which indicates the role of excitation energy. After a certain energy, the individual nat Mo(gamma, x n) reaction cross-sections decrease with the increase of bremsstrahlung energy due to opening of other reactions, which indicates sharing of energy in different reaction channels. The 100 Mo(gamma, n) reaction cross-section is important for the production of 99 Mo, which is a probable alternative to the 98 Mo(n, gamma) and 235 U(n, f) reactions.
Keywords: Photonuclear reactions, photodissociation, cross sections.

Publ.-Id: 23954 - Permalink


Covellite CuS as a matrix for “invisible” gold: X-ray spectroscopic study of the chemical state of Cu and Au in synthetic minerals
Tagirov, B. R.; Trigub, A. L.; Kvashnina, K. O.; Shiryaev, A. A.; Chareev, D. A.; Nickolsky, M. S.; Abramova, V. D.; Kovalchuk, E. V.;
Geological processes leading to formation of sulfide ores often result in precipitation of gold-bearing sulfides which can contain high concentrations of this metal in “invisible” (or ”refractory”) state. Covellite (CuS) is ubiquitous mineral in many types of the ore deposits, and numerous studies of the natural ores show that covellite can contain high concentrations of Au. At the same time, Au-bearing covellite withstands cooling in contrast to other minerals of the Cu-Fe-S system (chalcocite, bornite, chalcopyrite), where Au exsolves at low temperatures. This makes covellite a convenient model system for investigation of the chemical state (local environment and valence) of the “invisible” Au in copper-sulfide ores (copper-porphyry, epithermal, volcanogenic massive sulfide, SEDEX deposits). Therefore, it is necessary to determine the location of Au in the covellite matrix as it will have important implications for the methods employed by mineral processing industry to extract Au from sulfide ores. Here we investigate the chemical state of Cu and Au in synthetic covellite containing up to 0.3 wt.% of Au in the “invisible” state. The covellite crystals were synthesized by hydrothermal and salt flux methods. Formation of the chemically bound Au is indicated by strong dependence of the concentration of Au in covellite on the sulfur fugacity in the experimental system (d(log C(Au))/d(log f(S2)) ∼ 0.65). The Au concentration of covellite grows with increasing temperature from 400 to 450 °C, whereas further temperature increase to 500 °C has only minor effect. The synthesized minerals were studied using X-ray absorption fine structure spectroscopy (XAFS) in high energy resolution fluorescence detection (HERFD) mode. Ab initio simulations of Cu K edge XANES spectra show that the Cu oxidation state in two structural positions in covellite (tetrahedral and triangular coordination with S atoms) is identical: the total loss of electronic charge for the 3d shell is ∼ 0.3 for both positions of Cu. This result is confirmed by theoretical analysis of electron density performed using quantum theory of atoms in molecules (QTAIM). Modeling of the Au L3 edge EXAFS/XANES spectra showed that Au in covellite exists in the form of the isomorphous solid solution formed by substitution for Cu atoms in triangular coordination with the Me-S distance in the first coordination shell increased by 0.18 Å relative to the pure CuS structure. The “formal” oxidation state of Au in covellite is +1. The Bader partial atomic charge for Au in covellite is lower than the charge of Cu (+0.2 e vs. +0.5 e) indicating that the degree of covalency for the Au-bearing covellite is higher than that of pure CuS. The analysis of electronic density of states shows that this structural position of Au results in strong interactions between hybridized Au s,p,d, S p, and Cu p,d orbitals. Such chemical bonding of Au to S and Cu can result in the formation of Au-bearing solid solution with other minerals in the Cu-Fe-S system.

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Publ.-Id: 23953 - Permalink


Curvilinear magnetism
Makarov, D.;
Extending planar two-dimensional structures into the three-dimensional space has become a general trend in electronics, photonics, plasmonics and magnetics. In magnetism, a consequence of the curvilinear geometry is the appearance of novel curvature-driven effects including magnetochiral effects and topologically induced magnetization patterning, resulting in theoretically predicted unlimited domain wall velocities, chirality symmetry breaking and Cherenkov-like effects for magnons. These theoretical predictions and the application potential of 3D-shaped magnetic objects will be presented in this talk.
Keywords: curved magnetic thin films, magnetic caps
  • Invited lecture (Conferences)
    META2016: The 7th International Conference on Metamaterials, Photonic Crystals and Plasmonics, 25.-28.07.2016, Malaga, Spain

Publ.-Id: 23952 - Permalink


Eine Methode zur schnellen und genauen Berechnung und Kompensation der magnetischen Ablenkung des Protonenstrahls in der MRT-integrierten Protonentherapie
Schellhammer, S. M.; Hoffmann, A. L.;
Deutsch:
Die Integration von Protonentherapie und Magnetresonanztomografie (MRT) mit dem Ziel der Echtzeit-Bildgebung während der Bestrahlung steht vor dem Problem, dass der Protonenstrahl vom Magnetfeld des MRT-Scanners abgelenkt wird. Wir stellen eine Methode zur schnellen und genauen Vorhersage und Kompensation dieses Effektes vor. Die so berechnete Ablenkung sowie die Kompensationsparameter werden in Abhängigkeit der Protonenenergie und der magnetischen Flussdichte für den einfachen Fall eines Wasserphantoms in einem homogenen transversalen Magnetfeld betrachtet.

English:
The integration of proton therapy and magnetic resonance (MR) imaging for real-time image-guidance faces the challenge that the proton beam is deflected by the magnetic field of the MR scanner. We propose a method for a fast and accurate quantification and correction of this effect. Deflection and correction parameters are studied as functions of the beam energy and magnetic flux density for the simple geometry of a water phantom in a uniform transverse magnetic field.
Keywords: proton therapy, image-guided radiotherapy, IGPT, magnetic resonance imaging, MR guidance, beam trajectory prediction
  • Lecture (Conference)
    47. Jahrestagung der Deutschen Gesellschaft für Medizinische Physik (DGMP) e. V., 07.-10.09.2016, Würzburg, Deutschland

Publ.-Id: 23951 - Permalink


Introducing a novel method for fast and accurate estimation and compensation of beam deflection in MR-integrated proton therapy
Schellhammer, S. M.; Hoffmann, A. L.;
Proton therapy is highly sensitive to anatomical variations due to steep dose gradients in proximity of the Bragg peak (BP). Magnetic resonance imaging (MRI) is a promising candidate to enable real-time tracking of such variations during treatment delivery with high spatial, temporal and contrast resolution and without ionizing radiation exposure. However, an MRI magnetic field applied during irradiation deflects the proton beam from its intended trajectory.
We present a numerical method for fast and accurate quantification and compensation of this effect. As compared to existing approaches, it features fewer approximations than analytical models and a strongly reduced computation time compared to Monte Carlo simulations. We use it to reconstruct the trajectory of a monoenergetic proton beam of energy E0 traversing a water phantom behind a 25 cm air gap inside a virtual MRI bore with a uniform transverse magnetic flux density B. We study the dislocation of the BP as function of E0 and B and introduce an optimization method to compensate for it.
The magnitude of BP dislocation ranges from 2 cm for E0=60 MeV and B=0.5 T up to 26 cm for E0=250 MeV and B=3.0 T. A unique solution exists for repositioning the BP by beam incidence angle and energy adjustment.
The predicted magnetic-field induced BP dislocation complies with results obtained by Monte Carlo methods and the model is more versatile than analytical methods. The proposed optimization of beam incidence angle and energy effectively repositions the BP to its intended location.
Keywords: proton therapy, image-guided radiotherapy, IGPT, magnetic resonance imaging, MR guidance, beam trajectory prediction
  • Poster
    55th Annual Conference of the Particle Therapy Co-operative Group (PTCOG 55), 22.-28.05.2016, Praha, Ceska republika
  • Poster
    10th HZDR PhD seminar, 02.-04.11.2015, Altenberg, Deutschland
  • Poster
    National Center for Radiation Oncology, 2nd Scientific Retreat, 14.-16.04.2016, Dresden, Deutschland

Publ.-Id: 23950 - Permalink


Characterisation of nano-particulate powder pellets
Garbe-Schönberg, D.; Renno, A. D.; Leißner, T.; Müller, S.; Nordstad, S.;
Matrix-matched reference materials are urgently needed for calibration and validation of (micro-)analytical data. It is desirable that these materials can be analyzed by different analytical techniques like LA-ICP-MS, LIBS, μ-XRF, EPMA, PIXE, SIMS etc. accomplishing a better definition of elemental and isotopic composition of materials and also allowing for systematic studies on elemental fractionation. Nano-particulate powder pellets have now been produced from a large variety of materials and shown to be of excellent homogeneity and cohesiveness enabling accurate and high precision determination of elemental composition by LA-ICP-MS with RSD <1-5% even at high spatial resolution with <32μm spot size (Garbe-Schönberg and Müller 2014). Here we present new data on particle size and surface roughness being quality criteria for micro-analytical techniques using electron (EPMA) or ion beams (PIXE, SIMS). We demonstrate homogeneity within and between pellets, and significantly improved accuracy after matrix-matched calibration with nano-pellets is shown for granite AC-E as an example. Meanwhile, nano-pellets are succesfully used also for LA-based Rb-Sr age determination (Karlsson et al., EWLA 2016) and Li-B isotopic studies (LeRoex et al., 2015) and were analysed by EPMA and LIBS.
Keywords: Reference Material, Nano-particulate powder pellets, homogeneity
  • Poster
    European Workshop on Laser Ablation, 12.-15.07.2016, Ljubljana, Slovenien

Publ.-Id: 23949 - Permalink


Investigation of surfactant effect on the bubble shape and mass transfer in a milli-channel using high-resolution microfocus X-ray imaging
Haghnegahdar, M.; Boden, S.; Hampel, U.;
In this paper we present an experimental study on the influence of surface active agents (surfactants) on Taylor bubble flow in a vertical millimeter-size channel. Moreover we give a short review on the subject and previous investigations. We investigated the shape and dissolution rate of individual elongated carbon dioxide Taylor bubbles, which were hydraulically fixed in a downward flow of water. Bubble shape and dissolution rate was determined from microfocus X-ray radiographs. From the shrinking rate we calculated the liquid side mass transfer coefficient.
The results show that the presence of surfactants causes a change of the bubble shape and leads to a slight increase of the liquid film thickness around the bubble and as a result the elongation of contaminated bubbles. In addition, the comparison of clean and contaminated bubbles indicate that presence of surfactant has a more significant impact on the dissolution rate of small bubbles. Furthermore, applying different concentrations of surfactant reveals that in our case, where surface coverage ratio of surfactant on the bubbles is high, increase of contamination does not have a noticeable influence on the mass transfer coefficient of bubbles.
Keywords: Surfactant; Film thickness; Mass transfer; Taylor bubble; Carbon dioxide; Milli-channels

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Publ.-Id: 23948 - Permalink


Investigation of influence of channel vibration on the dissolution rate of single bubbles in milli-channels
Haghnegahdar, M.; Boden, S.; Hampel, U.;
In the past decades, milli- and microreaction technology had intensive development with the numerous advantages such as intensification of heat and mass transfer, easy scale-up, reducing energy and resource consumption. Optimization of the chemical processes is one of main requirements put forward by modern industry with the aim to achieve technological efficiency and environmental safety. A new design and method for measurement of mass transfer rate of single bubbles in vibrating milli-channels is being developed with the claimed goal of process intensification [1],[2].
In this work, the dissolution rate of a single Taylor bubble of carbon dioxide in water is investigated using high resolution X-ray radiography technique in a vibrating vertical channel. The liquid-side mass transfer coefficient is calculated by measuring the changes in the size of the bubble at constant pressure. The experiments cover a large range of initial Taylor bubble length varying from 8 to 24 mm. The channel is a glass pipe with 6 mm inside diameter and circular cross section. The bubble is unceasingly monitored by holding the bubble stationary using the technique of Schulze and Schluender [3]. The glass channel is vibrated using a calibrated vibrator in horizontal direction. The amplitude and frequency of vibration is controlled by a wave generator accurately. The method which is used to measure the variation of the bubble size is X-ray radiography. This technique was qualified to disclose the three-dimensional shape of Taylor bubbles in capillary and enabled the acquisition of a series of high-resolution radiographic images of nearly stationary Taylor bubbles. The processed images which give volume (and also the interfacial area) of the bubble with high accuracy as a function of time, are used to evaluate the liquid side mass transfer coefficient between bubble and liquid using the mass conservation equation. The liquid phase is filtered-deionized water and the gas phase is CO2.
The results for the short term dissolution of single CO2 bubbles show that the channel vibration with high frequency (50, 100, 1000 and 10000 Hz) does not have a detectable influence on the rate of mass transfer for stationary single bubbles however, for channel vibrations lower than 50 Hz, the liquid-side mass transfer coefficient increases by more than 32%. In addition, it is shown that the measured mass transfer coefficients do not have intensive dependency on the bubble length and also equivalent diameter (diameter of the sphere having the same volume).
Keywords: Taylor bubble, Mass transfer, CO2, Vibration, X-ray
  • Contribution to proceedings
    22nd International Congress of Chemical and Process Engineering, CHISA 2016, 28.-31.08.2016, Prague, Czech Republic
    Proceedings of CHISA 2016
  • Lecture (Conference)
    22nd International Congress of Chemical and Process Engineering, CHISA 2016, 28.-31.08.2016, Prague, Czech Republic

Publ.-Id: 23947 - Permalink


Experimental investigation of Taylor bubble dissolution in milli-channels
Haghnegahdar, M.; Boden, S.; Hampel, U.;
In the work presented in this paper, the dissolution rate of a single Taylor bubble of carbon dioxide into water was compared within a square and circular channel of 6 mm hydraulic diameter. The bubbles were held stationary in the down-flowing liquid and observed with high resolution X-ray radiography and tomography. The acquired X-ray images of the bubbles were analyzed with respect to volume, surface area and length of the bubble and were utilized to obtain the liquid side mass transfer coefficient by measuring the changes in the size of the bubble at constant pressure. The X-ray method was chosen since it is not dependent on the refractive index; therefore it is the most accurate method in comparison with other conventional optical techniques. The results for the long term dissolution of single CO2 bubbles show that the dissolution curves for bubbles with different initial size follow the same trend and have relatively constant slope. In addition, the comparison of the results for the square and circular channels showed that, there are some distinguishable differences between the trend of the liquid side mass transfer coefficient, kL in two curves. For square channel, kL increases with decrease of bubble sizes, while no obvious trend could be detected for the circular channel.
Keywords: Taylor bubble, Mass transfer, milli-channel, CO2
  • Contribution to proceedings
    International Conference on Multiphase Flow, ICMF 2016, 22.-27.05.2016, Firenze, Italy
    Proceedings of ICMF 2016
  • Lecture (Conference)
    International Conference on Multiphase Flow, ICMF 2016, 22.-27.05.2016, Firenze, Italy

Publ.-Id: 23946 - Permalink


Resonant Four-Wave Mixing in Landau-Quantized Graphene
König-Otto, J.; Pashkin, A.; Schneider, H.; Helm, M.; Winnerl, S.;
Graphene in magnetic fields is a unique material because of its anomalous Landau level spectrum. Due to the linear density of states in graphene the energy of the Landau-levels scales with the square root of the index number and a zeroth level exists [1] (cf. Fig. 2a). Consequently individual Landau-level transitions can be addressed by varying the photon energy, in contrast to a classical Landau-quantized two-dimensional electron gas where the transition energies are degenerate. Pump-probe spectroscopy on Landau-quantized graphene (LQG) reveals fascinating effects such as an Auger-driven depopulation of an optically pumped level, recently demonstrated by some of us [2]. Theoretical calculations predict a giant non-linear χ(3) response for LQG [3]. We present for the first time results of a degenerated time-integrated transient four-wave mixing (FWM) experiment on LQG (cf. Fig. 1), where the photon energy of the linear polarized free-electron laser FELBE is resonant to the transitions from LL-1 (LL0) → LL0 (LL1) in a magnetic field of around 4.55T (cf. Fig. 2a). Comparing FWM (cf. Fig. 2c) and pump-probe (cf. Fig. 2b) signals at the same experimental conditions we observe a rapid dephasing (faster than pulse duration of ~4ps). Furthermore, we have confirmed the expected linear and quadratic dependencies of the FWM signal on the excitation intensities in directions k1 and k2, respectively. By sweeping the magnetic field and consequently shifting the energy difference between the Landau levels, the resonance behaviour of pump-probe and FWM signals was measured. In summary, we have experimentally verified that Landau-quantized graphene exhibits a significant nonlinear optical response despite the fact that it features a short dephasing time. It is an attractive nonlinear material, which allows one to tune the spectral position of the resonance by the magnetic field.

References
[1]. A. H. Castro Neto et al., Rev. Mod. Phys. 81, 109 (2009).
[2]. M. Mittendorff et al., Nat. Phys. 11, 75 (2015).
[3]. X. Yao and A. Belyanin, J. Phys. Condens. Matter 25, 054203 (2013).
Keywords: Graphene, Landau-quantized graphene, THz, Spectroscopy, Dynamics, nonlinear Dynamics
  • Lecture (Conference)
    ICSNN 2016 - 19th International Conference on Superlattices, Nanostructures and Nanodevices, 25.-30.07.2016, Hong Kong, China

Publ.-Id: 23945 - Permalink


A Strong Diffusive Ion Mode in Dense Ionised Matter Predicted by Langevin Dynamics
Mabey, P.; Richardson, S.; White, T. G.; Appel, K.; Barbel, B.; Chapman, D. A.; Döppner, T.; Falcone, R. W.; Fletcher, L. B.; Fortmann, C.; Galtier, E.; Glenzer, S. H.; Hastings, J. B.; Heimann, P.; Lee, H. J.; Lepape, S.; Ma, T.; Monaco, G.; Nagler, B.; Pak, A.; Turnbull, D.; Vorberger, J.; Wei, M.; Welch, J.; Zastrau, U.; Gericke, D. O.; Gregori, G.;
The state and the evolution of planetary cores, drown dwarfs and neutron star crusts is determined by microscopic properties, such as viscosity and thermal conductivity, of the dense and compressed matter of which such system are made of. Due to the inherent diffculties in modelling strongly coupled plasmas, where classical long-range Coulomb forces dominate interactions between ions while electrons are partially to fully degenerate, current predictions of transport coeffcients differ by many orders of magnitude. This not only affects our ability to understand the evolution of planets and evolved stars, but also impacts our ability to accurately predict the implosion material characteristics in inertial confinement fusion experiments. The response of the compressed matter to density perturbations gives rise to collective modes, either electrostatic or acoustic waves, that serve as an important tool to validate theoretical predictions. Until recently, only electron modes could be measured experimentally. With the recent advances in free electron laser technology, x-rays with small enough bandwidth have become available, allowing the investigation of the low-frequency ion modes in dense matter as well. Here, we present numerical predictions for these ion modes and demonstrate signifcant changes to their strength and dispersion if dissipative processes are included by Langevin dynamics. In particular, a strong diffusive mode around zero frequency arises which is not present, or much weaker, in standard simulations. Our results have profound consequences in the interpretation of transport coefficients in dense plasmas.
Keywords: warm dense matter, transport, ion acoustic modes, langevin dynamics

Publ.-Id: 23944 - Permalink


Multistage bioassociation of uranium onto an extremely halophilic archaeon revealed by a unique combination of spectroscopic and microscopic techniques
Bader, M.; Müller, K.; Foerstendorf, H.; Drobot, B.; Schmidt, M.; Musat, N.; Swanson, J. S.; Reed, T. D.; Stumpf, T.; Cherkouk, A.;
The interactions of two extremely halophilic archaea with uranium were investigated at high ionic strength as a function of time, pH and uranium concentration. Halobacterium noricense DSM-15987 and Halobacterium sp. putatively noricense isolated from the Waste Isolation Pilot Plant (WIPP) repository were used for these investigations. The kinetics of U(VI) bioassociation of both strains showed an atypical multistage behavior, meaning that after an initial phase of U(VI) sorption, an unexpected interim period of U(VI) release was observed, followed by a slow reassociation of uranium with the cells. By applying in situ attenuated total reflection Fourier-transform infrared (ATR FT-IR) spectroscopy, the involvement of phosphoryl and carboxylate groups in U(VI) complexation during the first biosorption phase was shown. Differences in cell morphology and uranium localization become visible at different stages of the bioassociation process, by using scanning electron microscopy (SEM) in combination with energy dispersive X-ray (EDX) spectroscopy. Our results demonstrate for the first time that association of uranium on the extremely halophilic archaeon is a multistage process, beginning with a sorption which is followed by another process, probably biomineralization.
Keywords: Uranium Biosorption Halophilic Archaea TRLFS in situ ATR FT-IR

Publ.-Id: 23943 - Permalink


Pushing the Limits of Lattice Monte-Carlo Simulations using GPUs
Kelling, J.; Ódor, G.; Heinig, K. H.; Weigel, M.; Gemming, S.;
Lattice Monte-Carlo methods are used to study out-of- and towards-equilibrium systems, like surface growth, spin systems and even phase separation in solid mixtures using kinetic Metropolis lattice Monte-Carlo (KLMC). Applications range from the study of universal scaling or aging behaviors to concrete systems, where coarsening of nanocomposites or self-organization of functional nanostructures is relevant, for example spinodal decomposition in solar cell absorber layers. In these systems, scaling needs to be followed for long times to allow structures to grow over orders of magnitude, which requires large-scale simulations. For the evolution of nanostructures, atomistic simulations at experimental spatiotemporal scales are often desired.

This talk will give an overview over a variety of lattice Monte-Carlo algorithms, which have been found or made suitable for implementation on GPUs: Stochastic cellular automata can be implemented very efficiently [1-3] and are suitable for many systems. The efficient implementation of random sequential dynamics is more challenging. Solutions will be presented for a dimer lattice gas mapped to surface growth [4,5] and KLMC [6]. The latter was also extended to implement dynamics driven by ion-beam mixing triggering long-range interactions. However, these implementations hinge on the fact, that only a very small number of states need to be encoded at each lattice site. A more flexible implementation, employing a variation of multisurface-coding to enable vectorization, will be presented for simulations of restricted solid-on-solid and Potts models with random sequential dynamics. [7]

[1] Block, B., Virnau, P., Preis, T.: Comp. Phys. Comm. 181(9), 1549 (2010)
[2] Lulli, M., Bernaschi, M., Parisi, G.: Comp. Phys. Comm. 196, 290 (2015)
[3] Kelling, J., Ódor, G., Gemming, S.: 2016 IEEE Int. Conf. Intell. Eng. Syst., arXiv:1606.00310 (2016)
[4] Kelling, J., Ódor, G.: Phys. Rev. E 84, 061150 (2011)
[5] Ódor, G., Kelling, J., Gemming, S.: Phys. Rev. E 89, 032146 (2014)
[6] Kelling, J., Ódor, G., Nagy, M. F., Schulz, H., Heinig, K.: EPJST 210, 175 (2012)
[7] Kelling, J., Ódor, G., Gemming, S.: arXiv:1605.02620 (2016)
  • Invited lecture (Conferences)
    Perspectives of GPU computing in Science, 26.-28.09.2016, Roma, Italia

Publ.-Id: 23942 - Permalink


Experimental-Scale Kinetic Lattice Monte-Carlo Studies on GPU
Kelling, J.; Heinig, K.-H.; Gemming, S.;
Resume : Micro- and nano-structured materials are crucial for future energy technologies. Key processes during production and life-time are governed by self-organization in phase separation processes at the micro and nano scale. Examples include nano-structured Silicon absorber layers in solar cells providing tailored band-gaps [Apl. Phys. Lett. 103, 133106 (2013)] as well as cheap production and micro-patterned electrolyte-matrices] enhancing life-time and efficiency in a range of fuel cell technologies. Simulations of these out-of-equilibrium, inhomogeneous real world systems provide important insights, finding potential for optimization of structures and process parameters. To this end, kinetic lattice Monte Carlo simulations can be used to model physical systems at experimental scales in an atomistic way, thereby side-stepping many caveats connected with the alternative phase-field simulations. In this contribution, we present two massively parallel implementations for large-scale simulations on GPUs: One is optimized to offer fast time-to-solution on experimental-scale simulations [Eur. J. Phys.: Spec. Top. 210, 175 (2012)], the other provides highly efficient parameter studies or large sample sizes for large-scale simulations [Phys. Rev. E (2016) submitted]. Harnessing the compute power of modern (multi-)GPU installations leads to increased energy efficiency as well as reduced time-to-solution.
  • Lecture (Conference)
    E-MRS Fall Meeting, 19.-22.09.2016, Warschau, Polen

Publ.-Id: 23941 - Permalink


Aging In The (2+1)-Dimensional Kardar-Parisi-Zhang Model Under Various Dimer Lattice-Gas Dynamics
Kelling, J.; Ódor, G.; Gemming, S.;
Extensive dynamical simulations of a 2 dimensional driven dimer lattice gas are presented, which can be mapped to (2+1) dimensional surface growth in the Kardar-Parisi-Zhang (KPZ) or Edwards-Wilkinson universality classes [1,2]. From this, autocorrelation and autoresponse functions have been determined for the KPZ universality class and the underlying lattice gas [3]. Studying the effects of different dimer lattice gas dynamics revealed strong differences in the aging behavior of the stochastic cellular automaton (SCA) and the random sequential update models. We show numerical evidence for nontrivial corrections and tests against log-local scale invariance [4] as well as different universal scaling behaviors. [1] G. Ódor, B. Liedke and K.-H. Heinig, Phys. Rev. E 79, 021125 (2009) [2] J. Kelling and G. Ódor, Phys. Rev. E 84, 061150 (2011) [3] J. Kelling, G. Ódor, S. Gemming, Phys. Rev. E 89, 032146 (2014) [4] M. Henkel, Nucl. Phy. B 869(2), 282 (2013)
  • Lecture (Conference)
    Stat'Phys 26 - Statistical Physics Conference Satellite Non-equilibrium dynamics in classical and quantum systems: From quenches to slow relaxations, 13.-22.07.2016, Pont-à-Mousson, France

Publ.-Id: 23940 - Permalink


Experimental x-ray ghost imaging
Pelliccia, D.; Rack, A.; Scheel, M.; Cantelli, V.; Paganin, D. M.;
We report an experimental proof of principle for ghost imaging in the hard x-ray energy range. We used a synchrotron x-ray beam that was split using a thin crystal in Laue diffraction geometry. With an ultra-fast imaging camera, we were able to image x-rays generated by isolated electron bunches. At this time scale, the shot noise of the synchrotron emission process is measurable as speckles, leading to speckle correlation between the two beams. The integrated transmitted intensity from a sample located in the first beam was correlated with the spatially resolved intensity measured on the second, empty, beam to retrieve the shadow of the sample. The demonstration of ghost imaging with hard x-rays may open the way to protocols to reduce radiation damage in medical imaging and in non-destructive structural characterization using Free Electron Lasers.
Keywords: Ghost imaging, optics, X-ray

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Publ.-Id: 23939 - Permalink


Low-energy M1 strength from shell-model calculations
Schwengner, R.;
Large-scale shell-model calculations were performed for 56Fe, 60Fe, 64Fe, 68Fe. The collective properties of yrast states are reproduced in the used model space.
The low-energy enhancement of M1 strength decreases with increasing neutron number while a bump around E = 3 MeV develops, which can be related with the scissors mode. The strength around E = 3 MeV includes transitions from 1+ states to the ground state as well as to excited 0+ states and contributions from other spins. This may explain the higher strength found in ion-induced reactions compared with the one observed in photon scattering.
Keywords: Gamma-ray strength functions, low-energy M1 strength, scissors resonance, shell-model calculations.
  • Invited lecture (Conferences)
    ECT* Workshop on "Statistical properties of nuclei", 11.-15.07.2016, Trento, Italien

Publ.-Id: 23938 - Permalink


Gamma-ray strength functions at low energy
Schwengner, R.;
Photon-scattering experiments were carried out with bremsstrahlung at gELBE and with quasi-monoenergetic gamma rays at HIGS. Strength in the quasicontinuum was included in the analysis. The observed strength was corrected for branching and feeding by means of statistical methods. Experimental information about E1 strength in the pygmy region and M1 strength in the spin-flip region is presented for nuclides around masses 80, 130 and 180.
Large-scale shell-model calculations of M1 and E2 strength were performed. The experimental low-energy upbend can be explained by enhanced M1 strength. Information about E2 strength at low energy is given. The described findings require modifications of phenomenological strength functions.
Keywords: Gamma-ray strength functions, photon scattering, bremsstrahlung, monoenergetic and polarized gamma rays, shell-model calculations.
  • Invited lecture (Conferences)
    1st Research Coordination Meeting of the IAEA Coordinated Research Project "Updating the Photonuclear Data Library and Generating a Reference Data Base for Photon Strength Functions"., 04.-08.04.2016, Wien, Österreich

Publ.-Id: 23937 - Permalink


Low-energy M1 strength in deformed nuclei
Schwengner, R.;
Large-scale shell-model calculations were performed for 56Fe, 60Fe, 64Fe and 68Fe. The collective properties of yrast states are reproduced in the used model space.
The low-energy enhancement of M1 strength decreases with increasing deformation, while a bump around E = 3 MeV develops, which can be related with the scissors mode. The strength around E = 3 MeV includes transitions from 1+ states to the ground state as well as to excited 0+ states and contributions from other spins.
The average M1 strength is rather independent of the excitation energy for Ei > 5 MeV. This validates the Brink-Axel hypothesis in this energy region.
Keywords: Gamma-ray strength functions, M1 transitions, shell-model calculations.
  • Lecture (Conference)
    Frühjahrstagung der DPG, 14.-18.03.2016, Darmstadt, Deutschland

Publ.-Id: 23936 - Permalink


Euler-Euler Simulation und Modellvalidierung einer Blasensäule
Krauß, M.;
Die Anwendung von Methoden der CFD („Computational fluid dynamics“) für Scale-up und Intensivierung verfahrenstechnischer Prozesse bietet die Möglichkeit, energie- und ressourceneffiziente Lösungen zu identifizieren, deren Untersuchung mit konventionellen halb-empirischen Methoden kostspielig und langwierig wäre.
Eine solche Simulation im großtechnischen Maßstab ist im Rahmen der Euler-Euler Beschreibung möglich, in der Prozesse auf der Skala einzelner Blasen modelliert werden.
Ein solches Schließungsmodell für Hydrodynamik und Stofftransport in Blasenströmungen wird am HZDR entwickelt. Ziel dieser Entwicklung ist, ein vorhersagetaugliches Modell zu etablieren, das für einen breiten Bereich von Anwendungsbedingungen validiert ist.
Zu diesem Zweck werden Simulationsrechnungen mit experimentellen Daten verglichen, die zunehmend komplexere Geometrien und Effekte einbeziehen. Auf Basis der jeweils erzielten Übereinstimmung werden Modellerweiterungen und -verbesserungen vorgenommen. Im Rahmen der Belegarbeit soll eine mit Wasser befüllte, von Luft bzw. Kohlenstoffdioxid durchströmte, zylinderförmige Blasensäule mit einem Innendurchmesser von 142 mm untersucht werden.
Keywords: Blasensäule, Euler-Euler Modell, CFD-Simulation, Modellvalidierung
  • Study thesis
    TU Dresden, 2016
    Mentor: Dr. Roland Rzehak (HZDR), Prof. Rüdiger Lange (TU-Dresden)
    94 Seiten

Publ.-Id: 23935 - Permalink


Effect of compression on the electronic, optical and transport properties of MoS2/graphene-based junctions
Ghorbani-Asl, M.; Bristowe, P. D.; Koziol, K.; Heine, T.; Kuc, A.;
Electronic, optical and transport properties of the MoS2/graphene heterostructure have been investigated as function of applied uniaxial compression normal to the interface plane using first principles calculations and a non-equilibrium Green’s function approach. The results show that a small compressive load (∼1 GPa) can open up the band gap (∼12 meV), reduce the optical absorption coefficient (∼7%), redshift the absorption spectrum, and create non-Ohmic I–V characteristics that depend on the magnitude of applied bias. This suggests that graphene/MoS2 heterostructure can be suitable for electromechanical and photomechanical devices where the electronic, optical and transport properties can be tuned by an appropriate application of bias and mechanical deformations.
Keywords: MoS2/graphene heterojunction, interlayer compression, transport properties, NEGF, DFT

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Publ.-Id: 23934 - Permalink


Benefit of particle therapy in re-irradiation of head and neck patients. Results of a multicentric in silico ROCOCO trial
Eekers, D. B. P.; Roelofs, E.; Jelen, U.; Kirk, M.; Granzier, M.; Ammazzalorso, F.; Ahn, P. H.; Janssens, G. O. R. J.; Hoebers, F. J. P.; Friedmann, T.; Solberg, T.; Walsh, S.; Troost, E. G. C.; Kaanders, J. H. A. M.; Lambin, P.;
Background and Purpose
In this multicentric in silico trial we compared photon, proton, and carbon-ion radiotherapy plans for re-irradiation of patients with squamous cell carcinoma of the head and neck (HNSCC) regarding dose to tumour and doses to surrounding organs at risk (OARs).

Material and Methods
Twenty-five HNSCC patients with a second new or recurrent cancer after previous irradiation (70 Gy) were included. Intensity-modulated proton therapy (IMPT) and ion therapy (IMIT) re-irradiation plans to a second subsequent dose of 70 Gy were compared to photon therapy delivered with volumetric modulated arc therapy (VMAT).

Results
When comparing IMIT and IMPT to VMAT, the mean dose to all investigated 22 OARs was statistically significantly reduced for IMIT and to 15 out of 22 OARs (68%) using IMPT. The maximum dose to 2% volume (D2) of the brainstem and spinal cord were statistically significantly reduced using IMPT and IMIT compared to VMAT. The data are available on www.cancerdata.org.

Conclusions
In this ROCOCO in silico trial, a reduction in mean dose to OARs was achieved using particle therapy compared to photons in the re-irradiation of HNSCC. There was a dosimetric benefit favouring carbon-ions above proton therapy. These dose reductions may potentially translate into lower severe complication rates related to the re-irradiation.
Keywords: In silico planning study, Head and Neck, re-irradiation, Multicentric trial, Radiotherapy, Particle therapy

Publ.-Id: 23933 - Permalink


Electron-beam induced transformations of layered tin dichalcogenides
Sutter, E.; Huang, Y.; Komsa, H.-P.; Ghorbani-Asl, M.; Krasheninnikov, A. V.; Sutter, P.;
By combining high-resolution transmission electron microscopy and associated analytical methods with first-principles calculations, we study the behavior of layered tin dichalcogenides under electron beam irradiation. We demonstrate that the controllable removal of chalcogen atoms due to electron irradiation, at both room and elevated temperatures, gives rise to transformations in the atomic structure of Sn−S and Sn−Se systems so that new phases with different properties can be induced. In particular, rhombohedral layered SnS2 and SnSe2 can be transformed via electron beam induced loss of chalcogen atoms into highly anisotropic orthorhombic layered SnS and SnSe. A striking dependence of the layer orientation of the resulting SnS parallel to the layers of ultrathin SnS2 starting material, but slanted for transformations of thicker few-layer SnS2is rationalized by a transformation pathway in which vacancies group into ordered S-vacancy lines, which convert via a Sn2S3 intermediate to SnS. Absence of a stable Sn2Se3 intermediate precludes this pathway for the selenides, hence SnSe2 always transforms into basal plane oriented SnSe. Our results provide microscopic insights into the transformation mechanism and show how irradiation can be used to tune the properties of layered tin chalcogenides for applications in electronics, catalysis, or energy storage.
Keywords: two-dimensional materials, defects, electron irradiation, structural transformation, sulfide, selenide

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Publ.-Id: 23932 - Permalink


Influence of phonon and electron excitations on the free energy of defect clusters in solids: A first-principles study
Posselt, M.; Devaraj, M.; Schiwarth, M.;
Although many processes of nanostructure evolution in solids occur at elevated temperatures, basic data obtained from ground state energetics are used in the modeling of these phenomena. In order to illustrate the effect of phonon and electron excitations on the free binding energy of defect clusters, first-principles calculations are performed for vacancy-solute pairs as well as vacancy and Cu dimers, trimers, and quadromers in bcc Fe. Based on the equilibrium atomic positions determined by the relaxation of the supercell with the defect in the ground state under constant volume (CV) as well as zero pressure (ZP) conditions, the contribution of phonon excitations to the free binding energy is calculated within the framework of the harmonic approximation. The contribution of electron excitations is obtained using the corresponding ground state data for the electronic density of states. Quasi-harmonic corrections to the ZP-based results do not yield significant changes in the temperature range relevant for applications. At 1000 K the maximum decrease/increase of the ZP-based data for the absolute value of the free binding energy with respect to the corresponding ground state value is found for the vacancy-W (43%) / vacancy-Mn (35%) pair. These results clearly demonstrate that contributions of phonon and electron excitation to the free binding energy of the defect clusters are generally not negligible. The general behavior of the free binding energy of vacancy and Cu dimers, trimers and quadromers is similar to that of the vacancy-solute pairs. The results obtained in this work are of general importance for studies on the thermodynamics and kinetics of defect clusters in solids.
Keywords: defect clusters, free energy, DFT, bcc Fe

Publ.-Id: 23930 - Permalink


A new model for volume recombination in plane-parallel chambers in pulsed fields of high dose-per-pulse
Gotz, M.; Karsch, L.; Pawelke, J.;
In order to describe the volume recombination in a pulsed radiation field of high dose-per-pulse this study presents a numerical solution of a 1D transport model of the liberated charges in a plane-parallel ionization chamber. In addition, measurements were performed on an Advanced Markus ionization chamber in a pulsed electron beam to obtain suitable data to test the calculation. The experiment used radiation pulses of 4 mu s duration and variable dose-per-pulse values up to about 1 Gy, as well as pulses of variable duration up to 308 mu s at constant dose-per-pulse values between 85 mGy and 400 mGy. Those experimental data were compared to the developed numerical model and existing descriptions of volume recombination.
At low collection voltages the observed dose-per-pulse dependence of volume recombination can be approximated by the existing theory using effective parameters. However, at high collection voltages large discrepancies are observed. The developed numerical model shows much better agreement with the observations and is able to replicate the observed behavior over the entire range of dose-per-pulse values and collection voltages. Using the developed numerical model, the differences between observation and existing theory are shown to be the result of a large fraction of the charge being collected as free electrons and the resultant distortion of the electric field inside the chamber. Furthermore, the numerical solution is able to calculate recombination losses for arbitrary pulse durations in good agreement with the experimental data, an aspect not covered by current theory.
Overall, the presented numerical solution of the charge transport model should provide a more flexible tool to describe volume recombination for high dose-per-pulse values as well as for arbitrary pulse durations and repetition rates.
Keywords: ionization chamber, volume recombination, pulsed radiation

Publ.-Id: 23929 - Permalink


Sites of recurrent disease in SCLC patients treated with radiochemotherapy – is selective nodal irradiation safe?
Gumina, C.; Valentini, C.; Bütof, R.; Appold, S.; Baumann, M.; Troost, E. G. C.;
Background: Concurrent radiochemotherapy (CCRT) is the standard treatment in locally advanced small cell lung cancer (SCLC) patients. Even though elective nodal irradiation (ENI) had been advocated, its use in routine clinical practice is still limited [van Loon, 2010]. Therefore, the purpose of this study is to assess the sites of recurrent disease in SCLC patients and to evaluate the feasibility of selective nodal irradiation (SNI) versus ENI.

Methods: A retrospective single-institution study was performed in stage I-III SCLC patients treated with radical CCRT. After state-of-the-art staging, all patients underwent three-dimensional conformal radiotherapy to a total dose of 45 Gy in twice-daily fractions of 1.5 Gy starting concurrently with the first or second cycle of chemotherapy (etoposide, cisplatinum) cycle. The gross tumor volume (GTV) consisted of the primary tumor and SNI visualized on CT and/or FDG-PET, or confirmed by cytology. The clinical target volume (CTV) was obtained by expanding the GTV, adjusting it for anatomical boundaries, and electively adding the supraclavicular lymph node stations. Thereafter, the CTV was expanded to a planning target volume based on institutional guidelines. After CCRT, prophylactic whole-brain irradiation (WBI; 30 Gy in 15 fractions) was administered to patients with a (near-complete) response. Follow-up consisted of a CT-thorax 6-8 week after completing treatment, followed by a 3-monthly chest x-ray or CT-scan. For this retrospective analysis, we reviewed all imaging data used for radiation treatment planning and during follow-up. The site of loco-regional relapse was correlated to the initial site and dose delivered.

Results: between April 2004 and December 2013, 54 patients underwent CCRT (followed by WBI in 63%). After a median time of 11.5 months, 17 patients (31.5%) had relapsed locally or regionally: six within the initial primary tumor volume, five within the initially affected lymph nodes, three metachronously within the primary tumor and initially affected lymph nodes, and three inside and outside of the initial nodal disease. Only one patient developed isolated supraclavicular lymph node metastases in the electively treated volume. All sites of loco-regional recurrence had received 92%-106% of the prescribed dose. Thirty-seven patients (69%) developed distant metastases (37.8% liver, 35% brain).

Conclusion: In this retrospective analysis, most patients recurred in the initially affected primary tumor or lymph nodes, or distantly. So, in order to reduce toxicity, one may consider omitting irradiation of the supraclavicular lymph node stations in those patients with affected lymph nodes in the lower hilar and mediastinal lymph node stations.

References:
Loon J, De Ruysscher D, Wander S, et al. Selective Nodal Irradiation on Basis of 18FDG-PET Scans in Limited-Disease Small-Cell Lung Cancer: A Prospective Study. Int J Radiat Oncol Biol Phys 2010,77(2):329-336.
Keywords: SCLC, selective nodal irradiation
  • Contribution to proceedings
    IASLC 17th World Conference on Lung Cancer, 04.-07.12.2016, Wien, Österreich
  • Abstract in refereed journal
    Journal of Thoracic Oncology 12(2016)1, S1038-S1039

Publ.-Id: 23928 - Permalink


Surprising effects of electron-electron scattering in graphene revealed by THz pump-probe spectroscopy
Helm, M.; König-Otto, J. C.; Mittendorff, M.; Pashkin, A.; Schneider, H.; Winnerl, S.; Wendler, F.; Winzer, T.; Malic, E.; Knorr, A.;
Electron-electron scattering in graphene gives rise to some unexpected behavior in the electron dynamics, as observed by THz pump-probe measurements.
When excited with a near-infrared femtosecond laser pulse, the pump-probe signal depends on the angle between the linear polarization of the pump and the probe pulse, which is due to preferential excitation of electrons perpendicular to the laser electric field. This indicates an anisotropic distribution function in momentum space that is preserved by electron-electron scattering, since it mainly occurs collinearly along the Dirac cone. Only after 150 fs the distribution function is rendered isotropic through optical-phonon scattering. The effect is even more pronounced when exciting at small photon energies (88 meV), below the optical-phonon energy: In this case the anisotropic distribution function survives for as long as 5 ps, when it is finally thermalized by non-collinear Coulomb scattering. These results challenge the common view of ultrafast thermalization by electron-electron scattering.
When a magnetic field is applied to graphene, Landau levels are formed that can be selectively excited by circular-polarized radiation. In a pump-probe experiment, exciting and probing all possible transitions between the n=-1, n=0 and n=+1 Landau levels in slightly n-type graphene, we observe an unexpected sign reversal of the n=0 →1 probe signal when pumping the -1→0 transition. This directly reflects the fact that the n=0 Landau level is depleted by electron-electron Auger-type scattering, even though it is optically pumped at the same time.
Both effects can be quantitatively reproduced by a microscopic calculation based on the graphene Bloch equations, and shed new light on the possibility of infrared and THz devices based on hot carriers in graphene.
Keywords: THz, graphene, free electron laser, pump-probe spectroscopy
  • Invited lecture (Conferences)
    International Workshop on Terahertz Science, Nanotechnologies and Applications, 16.-22.07.2016, Erice, Italy
  • Invited lecture (Conferences)
    Teranano VII, 02.-07.10.2016, Porquerolles, France

Publ.-Id: 23927 - Permalink


Annual Report 2015 - Institute of Ion Beam Physics and Materials Research
Faßbender, J.ORC; Heera, V.; Helm, M.; Zahn, P.
After the successful evaluation in 2015 we started research and further development of our largescale facilities, in particular the Ion Beam Center (IBC), in the framework of Helmholtz’s Programmeoriented Funding scheme (POF) which coordinates scientific cooperation on a national and international scale. Most of our activities are assigned to the Helmholtz program “From Matter to Materials and Life” within the research area “Matter”, in cooperation with several other German Helmholtz Centers. Our in-house research is performed in three so-called research themes, as depicted in the schematic below. What is missing there for simplicity is a minor part of our activities in the program “Nuclear Waste Management and Safety” within the research area “Energy”.
A few highlights which have been published in 2015 are reprinted in this annual report in order to show the variety of the research being performed at the Institute, ranging from self-organized pattern formation during ion erosion or DNA origami patterning, over ferromagnetism in SiC and TiO2 to plasmonics and THz-spectroscopy of III-V semiconductors. A technological highlight published recently is the demonstration of nanometer scale elemental analysis in a Helium ion microscope, making use of a time-of-flight detector that has been developed at the IBC. In addition to these inhouse research highlights, also users of the IBC, in particular of the accelerator mass spectrometry (AMS), succeeded in publishing their research on geomorphology in Nepal in the high-impact journal Science (W. Schwanghart et al., Science 351, 147 (2015)), which demonstrates impressively the added value of transdisciplinary research at the IBC.
In order to further develop the IBC, we have started in 2015 the design and construction of our new low energy ion nanoengineering platform which was highly recommended by the POF evaluators. It will consist of two-dimensional materials synthesis and modification, high-resolution ion beam analysis and high-resolution electron beam analysis and will come into full operation in 2019.
  • Open Access LogoWissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-069 2016

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Publ.-Id: 23926 - Permalink


Synthesis and evaluation of a 18F-labeled 4-phenylpiperidine-4-carbonitrile radioligand for σ1 receptor imaging
Ye, J.; Wang, X.; Deuther-Conrad, W.; Zhang, J.; Li, J.; Zhang, X.; Wang, L.; Steinbach, J.; Brust, P.; Jia, H.;
We report the design and synthesis of several 4-phenylpiperidine-4-carbonitrile derivatives as σ1 receptor ligands. In vitro radioligand competition binding assays showed that all the ligands exhibited low nanomolar affinity for σ1 receptors (Ki(σ1) = 1.22–2.14 nM) and extremely high subtype selectivity (Ki(σ2) = 830–1710 nM; Ki(σ2)/Ki(σ1) = 680–887). [18F]9 was prepared in 42–46% isolated radiochemical yield, with a radiochemical purity of >99% by HPLC analysis after purification, via nucleophilic 18F- substitution of the corresponding tosylate precursor. Biodistribution studies in mice demonstrated high initial brain uptakes and high brain-to-blood ratios. Administration of SA4503 or haloperidol 5 min prior to injection of [18F]9 significantly reduced the accumulation of radiotracers in organs known to contain σ1 receptors. Two radioactive metabolites were observed in the brain at 30 min after radiotracer injection. [18F]9 may serve as a lead compound to develop suitable radiotracers for σ1 receptor imaging with positron emission tomography.
Keywords: fluorine-18; σ1 receptor; positron emission tomography; 4-phenylpiperidine-4-carbonitrile derivatives; molecular probe
  • Open Access LogoJournal of Labelled Compounds and Radiopharmaceuticals (2016), 332-339
    DOI: 10.1002/jlcr.3408

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Publ.-Id: 23925 - Permalink


Structural information from total scattering on thorium/silica nanoparticles
Hennig, C.; Weiss, S.; Ikeda, A.; Scheinost, A.; Zänker, H.;
Nanoparticles may play a role in environmental migration of heavy metals. In case of absent Bragg reflections in diffraction pattern of nanoparticles with strong structural disorder the data can be treated by Fourier-transforming to real space which yield the atomic pair distribution (PDF). Real-space analysis of X-ray scattering data is sensitive to local structure even in case of structural disorder. This technique was used to gain information of the structure of thorium(IV)/silica nanoparticles [1]. Thorium(IV) is able to form meta-stable colloids with silica in aqueous solution at pH  7. The colloid structure can be regarded as amorphous because it shows no long-range order, indicated by the absence of distinct structural periodicity > 4 Å. The internal structure of the colloid particles consists of [Th(O(H))n] polyhedra, n = 8-9, coordinated partly by [SiO4] polyhedra with Th-Si distances of 3.250.02Å, and partly by [Th(O(H))n] polyhedra with Th-Th distances of 3.980.02Å. The near-order coordination shows similarity with that of the orthosilicates thorite, -ThSiO4, and huttonite, -ThSiO4. Supporting XPS analysis of the oxygen bonds revealed the presence of O2, OH and H2O. The colloids can be classified as oxyhydroxo colloids [(Th,Si)On(OH)4-nxH2O]4-2n-(4-n). Silica occurs in the colloid structure either in mononuclear or oligomeric subunits, depending on the Si/Th ratio and the silica precursor formed in the initial solution. Silica is enriched at the colloid surface if the concentration of the initial solutions is increased. The solution behaviour of the particles was analysed by in-situ methods. With rising silica content, the particles change gradually from metal oxide type colloids to silica type colloids, which strongly increase their colloidal stability.
Keywords: nanoparticles, total scattering, atomic pair distribution function
  • Poster
    EPDIC 2016 - 14th European Powder Diffraction Conference, 12.-15.06.2016, Bari, Italy

Publ.-Id: 23923 - Permalink


Solution species and crystal structure of Zr(IV) acetate
Hennig, C.; Weiss, S.; Kraus, W.; Kretzschmar, J.; Scheinost, A.;
The complex formation and the coordination of zirconium with acetic acid were investigated with Zr K-edge EXAFS spectroscopy and single crystal diffraction. Zr K edge EXAFS spectra show that a stepwise increase of acetic acid in aqueous solution with 0.1 M Zr(IV) leads to a structural rearrangement from initial tetranuclear hydrolysis species [Zr4(OH)8(OH2)16]8+ to a hexanuclear acetate species Zr6(O)4(OH)4(CH3COO)12. The solution species Zr6(O)4(OH)4(CH3COO)12 was preserved in crystals by slow evaporation of the aqueous solution. Single crystal diffraction reveals an uncharged hexanuclear cluster in solid Zr6(µ3-O)4(µ3-OH)4(CH3COO)12·8.5H2O. EXAFS measurements show that the structure of the hexanuclear zirconium acetate cluster in solution and solid state are identical.
Keywords: zirconium acetate, EXAFS, SC-XRD, NMR

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Publ.-Id: 23922 - Permalink


Controllable growth of vertically aligned graphene on C-face SiC
Liu, Y.; Chen, L.; Hilliard, D.; Huang, Q.-S.; Liu, F.; Wang, M.; Böttger, R.; Hübner, R.; N'Diaye, A. T.; Arenholz, E.; Heera, V.; Skorupa, W.; Zhou, S.;
We investigated how to control the growth of vertically aligned graphene on C-face SiC by varying the processing conditions. It is found that, the growth rate scales with the annealing temperature and the graphene height is proportional to the annealing time. Temperature gradient and crystalline quality of the SiC substrates influence their vaporization. The partial vapor pressure is crucial as it can interfere with further vaporization. A growth mechanism is proposed in terms of physical vapor transport. The monolayer character of vertically aligned graphene is verified by Raman and X-ray absorption spectroscopy. With the processed samples, d0 magnetism is realized and negative magnetoresistance is observed after Cu implantation. We also prove that multiple carriers exist in vertically aligned graphene.
Keywords: vertical graphene, graphene growth, physical vapor transport, magnetic properties, magnetoresistance, mobility, ion implantation, graphene doping

Publ.-Id: 23921 - Permalink


Electrode width dependent performance of THz photoconductive emitters
Singh, A.; Winnerl, S.; König-Otto, J. C.; Stephan, D. R.; Helm, M.; Schneider, H.;
Strip line geometries are important for modern large area photoconductive terahertz (THz) emitters with interdigitated electrode designs. Strip line structures with varying electrode widths have been studied for photoconductive terahertz emission. The amplitude of the emitted THz pulse depends linearly on the electrode width if the width is much smaller than the THz wavelength, whereas for wider electrodes, the THz emission shows saturation-like behavior with respect to the electrode width. Strip line width acts as antenna length in such emitters. Narrower strip line structures (less than 20 µm) acts as a short dipole antenna and hence gives a linear dependence of the radiated THz field on the strip line width.
Keywords: Terahertz emitter, strip line antenna
  • Poster
    IRMMW-THZ 2016 - 41st International Conference on Infrared, Millimeter and Terahertz Waves, 25.-30.09.2016, Copenhagen, Denmark

Publ.-Id: 23920 - Permalink


Enzymatic activity of the CaM-PDE1 system upon addition of actinyl ions
Brulfert, F.; Safi, S.; Jeanson, A.; Foerstendorf, H.; Weiss, S.; Berthomieu, C.; Sauge-Merle, S.; Simoni, E.;
The threat of a dirty bomb which could cause internal contamination has been of major concern for the past decades. Because of their high chemical toxicity and their presence in the nuclear fuel cycle, uranium and neptunium are two actinides of high interest. Calmodulin (CaM) which is a ubiquitous protein present in all eukaryotic cells and is involved in calcium-dependent signaling pathways has a known affinity for uranyl and neptunyl ions. The impact of the complexation of these actinides on the physiological response of the protein remains however largely unknown. An isothermal titration calorimetry (ITC) was developed to monitor in vitro the enzymatic activity of the phosphodiesterase enzyme which is known to be activated by CaM and calcium. This approach showed that addition of actinyl ions (AnO2n+), uranyl (UO22+) and neptunyl (NpO2+), resulted in a decrease of the enzymatic activity, due to the formation of CaM-actinide complexes, which inhibit the enzyme and alter its interaction with the substrate by direct interaction. Results from dynamic light scattering rationalized this result by showing that the CaM-actinyl complexes adopted a specific conformation different from that of the CaM-Ca2+ complex. The effect of actinides could be reversed using the decorporation ligand 5-LIO(Me-3,2-HOPO) in the experimental medium demonstrating its capacity to efficiently bind the actinides and restore the calcium-dependant enzyme activation
Keywords: nuclear toxicology, calmodulin, calcium signaling, enzyme, actinides, neptunium, ITC, UV-visible, decorporation

Publ.-Id: 23919 - Permalink


Corrosion of hot-dip galvanized containment installations – A potential cause for thermal-hydraulic effects after LOCA in PWR?
Kryk, H.; Harm, U.; Hampel, U.;
During the sump recirculation phase after loss-of-coolant accidents (LOCA) in pressurized water reactors (PWR), coolant spilling out of the leak in the primary cooling circuit is collected in the reactor sump and recirculated to the reactor core by residual-heat removal pumps as part of the emergency core cooling system (ECCS). The contact of the coolant with several forms of debris may influence the sump strainer clogging behavior as well as the cooling water chemistry. Damage to fibrous insulation materials located near to the leak may compromise the operation of the ECCS, if insulation fibers are transported to the strainers. Furthermore, the long-term contact of the boric acid containing coolant with hot-dip galvanized containment internals (e.g. grating treads, supporting grids of sump strainers) may cause corrosion of the corresponding materials.
Generic investigations regarding the influence of such corrosion processes on strainer clogging as well as on the coolant chemistry and possible resulting in-core effects are subject of joint research projects of the Helmholtz-Zentrum Dresden-Rossendorf (HZDR), TU Dresden (TUD) and Zittau-Görlitz University of Applied Sciences (HSZG). Lab-scale experiments at HZDR and TUD are focused on elucidation of physico-chemical corrosion and precipitation processes as well as resulting clogging effects.
Results of generic experiments in a lab-scale corrosion test facility, representing the ECCS operation in a simplified manner, suggest that there is a multi-stage corrosion process. The first stage comprises dissolution of the zinc layer in the coolant forming zinc ions and in turn affecting the coolant chemistry. During the second stage, the base material (steel) corrodes forming insoluble corrosion particles, which can subsequently lead to accelerated clogging of fiber-laden strainers within a few hours. The main influences on corrosion were identified as impact of the coolant jet onto the corroding surface, water chemistry and zinc surface / coolant volume ratio.
Furthermore, retrograde solubility of zinc corrosion products in boric acid containing coolants with increasing temperature was observed. Thus, formation and deposition of solid corrosion products cannot be ruled out if zinc containing coolant is heated up during its recirculation into hot downstream components (e.g. hot-spots in core). Corrosion experiments, which included formation of corrosion products at a heated cladding tube, proved that zinc, dissolved in the coolant at low sump temperatures, turns into solid deposits of zinc borates when contacting heated zircaloy surfaces. Due to alternating heating and cooling of the coolant during sump recirculation operation, a cycle of zinc corrosion and zinc borate precipitation may be initiated, which may eventually influence the thermal hydraulics in downstream components during the post-LOCA stage. The results obtained at lab-scale were confirmed by corresponding experiments in semi-technical test facilities of the project partner HSZG.
Based on the experimental results, water chemical measures were tested to reduce corrosion and/or zinc borate precipitation effects. Additionally, joint research projects have been established by the TUD and the HSZG dealing with local effects of corrosion, corrosion product precipitation and the interplay thereof at LOCA-specific conditions.
The investigations have been supported by the German Federal Ministry for Economic Affairs and Energy under contract nos. 1501363, 1501430, 1501467 and 1501496.
Keywords: loss-of-coolant accident, LOCA, pressurized water reactor, PWR, sump strainer clogging, chemical effects, corrosion, zinc borate
  • Lecture (Conference)
    ICONE 24 – International Conference on Nuclear Engineering, 26.-30.06.2016, Charlotte, USA
  • Contribution to proceedings
    ICONE 24 – International Conference on Nuclear Engineering, 26.-30.06.2016, Charlotte, USA
    ICONE 24 – Conference proceedings; Volume 3: Thermal-Hydraulics: ASME - Digital Collection, 978-0-7918-5003-9
    DOI: 10.1115/ICONE24-60273

Publ.-Id: 23918 - Permalink


Leaching of Rare Earth Elements from fluorescent powder using the tea fungus Kombucha
Hopfe, S.; Flemming, K.; Lehmann, F.; Möckel, R.; Kutschke, S.; Pollmann, K.;
In almost all modern technologies like flat screens, highly effective magnets and lasers, as well as luminescence phosphors, Rare Earth Elements (REE) are used. Unfortunately no environmentally friendly recycling-process is available so far (European 2014). Furthermore, only poor information is available regarding interactions of microorganisms with REE and there are almost no studies describing the bioleaching of REE. However, it can be assumed that microorganisms play an important role in the biogeochemistry of REE (Brisson et al. 2015; Chen et al. 2001; Goyne et al. 2010). This study investigates the potential of organic acid producing microbes to extract REE from technical waste.
In Germany, 175 tons of fluorescent phosphor (FP) are collected as a distinct fraction during the recycling of compact fluorescent lamps anually (Gallenkemper and Breer 2012; Riemann 2014). As the FP contains about 10% of REE-oxides bound in the so-called triband dyes it is a readily accessible secondary resource of REE (Haucke et al. 2011). Using the symbiotic mixed culture Kombucha, consisting of yeasts and acetic bacteria, significant leaching-rates were obtained. The highest leaching-rates were observed for the shaken cultivation using the entire Kombucha-consortium or its supernatant as leaching agent in comparison to experiments using the isolates Zygosaccharomyces lentus and Komagataeibacter hansenii as leaching organisms. During the cultivation the pH-value decreases due to the production of organic acids (mainly acetic and gluconic acid). Thus, the underlying mechanism of the triband dye solubilisation is probably connected with the carboxyl-functionality. According to the higher solubility of REE-Oxides in comparison to REE-phosphates and –aluminates, a preference in the solubilisation of the red dye Y2O3:Eu2+ containing relatively expensive REE was ascertained.
These results show that it is possible to dissolve the REE-compounds of FP by the help of microbial processes. Moreover, they provide the basis for the development of an eco-friendly alternative to the currently applied methods.
Keywords: bioleaching, Kombucha, fluorescent phosphor, rare earth elements, organic acids

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Publ.-Id: 23917 - Permalink


Optimisation of the bioleaching of REE from FP with chemoorgano-heterotrophic microorganisms.
Hopfe, S.; Kutschke, S.; Pollmann, K.;
Rare earth elements (REE) are used in mostly all new technologies and until now, there is nearly no recycling of REE containing end-of-life products [1]. Furthermore, only poor information is available regarding interactions of microorganisms with REE and there are almost no studies describing the bioleaching of REE. However, it can be assumed that microorganisms play an important role in the biogeochemistry of REE. This study investigates the potential of organic acid and metal binding molecules producing microbes to extract REE from technical waste.
During recycling of energy-saving bulbs fluorescent phosphor (FP) is collected as a distinct fraction. It contains about 10% REE-oxides bound in the hardly water-soluble triband dyes as oxides, phosphates, aluminates and silicates [2]. Previous experiments showed, that the chemoorgano-heterotrophic, organic acid producing micrrooganisms Yarrowia lipolytica, Komatogateiibacter xylinus and Lactobacillus casei as well as the mixed culture Kombucha are in principle suitable for the bioleaching of REE from FP. In this presentation the solubilisation process is investigated regarding the leaching metabolites and optimised with respect to maximal REE release. Thereto, the results are transferred from shake flasks to bioreactor and the media were adjusted. Furthermore, the influence of metal binding molecules like siderophores was tested.
It could be shown, that bioleaching is a potential alternative to technical leaching approaches, even though, the leaching efficiency is still low. This provides the basis for the development of an eco-friendly alternative to the currently applied methods.

[1] European Commission (2014) On the review of the list of critical raw materials for the EU and the implementation of the Raw Materials Initiative, Brüssel. [2] Haucke et al. (2011) Verfahren zur Rückgewinnung seltener Erden aus Leuchtstofflampen, Osram AG.
  • Poster
    Annual Conference 2016 of the Association for General and Applied Microbiology (VAAM), 13.-16.03.2016, Jena, Deutschland

Publ.-Id: 23916 - Permalink


Magnetic Excitations in Spin-1/2 Triangular-lattice Antiferromagnets: High-field ESR studies
Zvyagin, S.;
es hat kein Abstract vorgelegen
  • Invited lecture (Conferences)
    Lehrstuhl-Seminar (Seminar zur Statistischen Physik) an der Bergischen Universität Wuppertal, 23.06.2016, Wuppertal, Deutschland
  • Invited lecture (Conferences)
    International Conference for Young Scientists "Low Temperature Physics", 06.-10.06.2016, Kharkiv, Ukraine

Publ.-Id: 23915 - Permalink


Operational Experience of SRF Gun II
Arnold, A.; Teichert, J.; Xiang, R.;
In May 2014 the 1st superconducting photo injector (SRF gun) at HZDR was replaced by a new gun, featuring a new resonator and a new cryostat. The intention for this upgrade was to reach higher beam energy, higher bunch charge and lower emittance at the same time. With the improved parameters first user experiments of the superconducting CW accelerator ELBE are to be served, that benefit from an increased average beam current at a given repetition rate of some hundred kHz. Although the cavity performance stays behind its specifications (Ecath~12 MV/m), beam commissioning is underway. In this contribution we will report on our operational experiences of the first two years of SRF gun II.
Keywords: SRF gun, photo electron source, injector, ELBE, superconducting RF
  • Lecture (others)
    HOPE / SINEMP Projekttreffen im Rahmen BMBF Verbundforschungsinitiative, 21.-22.06.2016, Darmstadt, Deutschland

Publ.-Id: 23914 - Permalink


Probing Ionization and Buried Layer Plasma Physics Driven by Optical High Power Lasers using XFELs
Huang, L. G.; Prencipe, I.; Kluge, T.; Cowan, T.;
In the presentation, the fundamental plasma physics driven by high power lasers on bulk electron heating,solid target and ion heating is discussed. Probing the relative dynamics using XFELs is also presented.
Keywords: Heating,Ionization,XFEL,high power lasers
  • Lecture (Conference)
    The 1st Asia-Pacific User Meeting for HIBEF at European XFEL, 23.-24.06.2016, Shanghai, China

Publ.-Id: 23913 - Permalink


Identification of lanthanum-specific peptides for future recycling of rare earth elements from compact fluorescent lamps
Lederer, F. L.; Curtis, S. B.; Bachmann, S.; Dunbar, S. W.; Macgillivray, R. T.;
As components of electronic scrap, rare earth minerals are an interesting but little used source of raw materials that are highly important for the recycling industry. Currently, there exists no cost-efficient technology to separate rare earth minerals from an electronic scrap mixture. In this study, phage surface display has been used as a key method to develop peptides with high specificity for particular inorganic targets in electronic scrap. Lanthanum phosphate doped with cerium and terbium as part of the fluorescent phosphors of spent compact fluorescent lamps (CFL) was used as a target material of economic interest to test the suitability of the phage display method to the separation of rare earth minerals. One random pVIII phage library was screened for peptide sequences that bind specifically to the fluorescent phosphor LaPO4:Ce3+,Tb3+ (LAP). The library contained at least 100 binding pVIII peptides per phage particle with a diversity of 1x10^9 different phage per library. After three rounds of enrichment, a phage clone containing the surface peptide loop RCQYPLCS was found to bind specifically to LAP. Specificity and affinity of the identified phage bound peptide was confirmed by using binding and competition assays, immunofluorescence assays and zeta potential measurements. Binding and immunofluorescence assays identified the peptide’s affinity for the fluorescent phosphor components CAT (CeMgAl11O19:Tb3+) and BAM (BaMgAl10O17:Eu2+). No affinity was found for other fluorescent phosphor components such as YOX (Y2O3:Eu3+). The binding specificity of the RCQYPLCS peptide loop was improved 3-51-fold by using alanine scanning mutagenesis. The identification of peptides with high specificity and affinity for special components in the fluorescent phosphor in CFLs provides a potentially new strategic approach to rare earth recycling.
Keywords: Phage surface display, rare earths, fluorescent phosphors, specificity, LaPO4:Ce,Tb

Publ.-Id: 23912 - Permalink


Numerical adiabatic potentials of orthorhombic Jahn-Teller effects retrieved from ultrasound attenuation experiments. Application to the SrF2:Cr crystal
Zhevstovskikh, I. V.; Bersuker, I. B.; Gudkov, V. V.; Averkiev, N. S.; Sarychev, M. N.; Zherlitsyn, S.; Yasin, S.; Shakurov, G. S.; Ulanov, V. A.; Surikov, V. T.;
A methodology is worked out to retrieve the numerical values of all the main parameters of the sixdimensional adiabatic potential energy surface (APES) of a polyatomic system with a quadratic T-term Jahn-Teller effect (JTE) from the ultrasound experiments. The method is based on a verified assumption that ultrasound attenuation and speed encounter anomalies when the direction of propagation and polarization of its wave of strain coincides with the characteristic directions of symmetry breaking in the JTE. For the SrF2:Cr crystal, employed as a basic example, we observed anomaly peaks in the temperature dependence of attenuation of ultrasound at frequencies of 50-160 MHz in the temperature interval of 40-60 K for the wave propagating along the [110] direction, for both the longitudinal and the shear modes, the latter with two polarizations along the [001] and [11-0] axes, respectively. We show that these anomalies are due to the ultrasound Relaxation by the system of non-interacting Cr2+ JT centers with orthorhombic local distortions. The interpretation of the experimental findings is based on the T2g - (eg+t2g) JTE problem including the linear and the quadratic terms of vibronic interactions in the Hamiltonian and the same-symmetry modes reduced to one interaction mode. Combining the experimental results with a theoretical analysis, we show that on the complicated six-dimensional APES of this system with three tetragonal, four trigonal, and six orthorhombic extrema points, the latter are global minima, while the former are saddle points, and we estimate numerically all the main parameters of this surface, including the linear and quadratic vibronic coupling constants, the primary force constants, the coordinates of all the extrema points and their energies, the energy barrier between the orthorhombic minima, and the tunneling splitting of the ground vibrational states. To our knowledge, such a based-on-experimental-data numerical reconstruction of the APES of a JTE problem in the five-dimensional space of all active tetragonal and trigonal displacements has not been reported before.

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Publ.-Id: 23911 - Permalink


Verbesserung der Reichweitevorhersage in der Ionentherapie durch dichteunabhängige Messung von Röntgen-/Ionenschwächung tierischer Gewebe
Möhler, C.; Russ, T.; Elter, A.; Latz, B.; Wohlfahrt, P.; Richter, C.; Greilich, S.;
Abstract
The conversion of CT numbers to ion stopping-power ratios for therapy planning necessarily includes an empirical component due to the different nature of interaction of photons and ions in tissue. Therefore, measurements are needed for calibration and evaluation. With a new combined measurement setup based on dual-energy CT such measurements can be significantly simplified.

Zusammenfassung
Die Umrechnung von CT-Zahlen in Ionenbremsvermögen im Rahmen einer Therapieplanung beinhaltet notwendigerweise eine empirische Komponente auf Grund der unterschiedlichen Wechselwirkungen von Photonen und Ionen im Gewebe. Zur Kalibrierung und Evaluierung werden daher Messdaten benötigt. Mit einem neuen, kombinierten Versuchsaufbau auf Grundlage der Dual-Energy Computertomographie (DECT) können solche Messungen erheblich einfacher durchgeführt werden.


Fragestellungen
Zur besseren Ausschöpfung des Potentials der Protonen- und Ionentherapie wird eine genaue Vorhersage von Ionenreichweiten benötigt. Bei der Umrechnung von CT-Zahlen in Ionenbremsvermögen treten jedoch Unsicherheiten auf, deren Ursache in den verschiedenen Mechanismen des Energieverlustes der beteiligten Teilchenarten liegt: kV-Photonen im CT, MeV-Ionen bei der Bestrahlung. Das für die Ionen wichtige mittlere Anregungspotential (der „I-value“) hat keine Entsprechung in den Wechselwirkungen der Photonen. Zur genauen Kalibrierung sowie Verifizierung praktisch sämtlicher Ansätze zur Reichweitevorhersage ist daher die kombinierte Messung von Röntgen- und Ionenschwächung unerlässlich.
Während der aktuelle klinische Goldstandard für die Vorhersage ein rein heuristischer Ansatz mittels einer sogenannten Hounsfield-Lookup-Tabelle (HLUT) [1, 2] ist, basieren neuere, experimentelle Arbeiten [3, 4] auf der DECT. Da bei letzterer die Elektronendichte eines Materials robust und universell bestimmt werden kann [5], muss lediglich die Bremszahl, also der vom I-value abhängige, verbleibende Teil der Bethe-Formel, empirisch bestimmt werden.

Material und Methoden
Verschiedene tierische Gewebe (Knochenmehl und Knochenmark vom Rind; Fett, Blut, Leber vom Schwein) wurden – ohne ihren ursprünglichen Zustand zu erhalten – in einem 3D-gedruckten Probenbehälter präpariert. Beim Design des Hybrid-Probenbehälters wurden dabei die verschiedenen Rahmenbedingungen für die DECT- und Ionenmessung berücksichtigt (vgl. Abb 1). Zunächst wurde die Schwächung zweier Photonenspektren (100/140Sn kVp) in den Proben mit einem Dual-Source CT-Scanner (Siemens Somatom Definition Flash) gemessen. Aus den DECT-Bildern der Gewebeproben wurde mit dem in [3] beschriebenen Algorithmus die Elektronendichte der Proben relativ zu Wasser berechnet. Durch Division erhält man als dichteunabhängige Größe den relativen Photonenwirkungsquerschnitt. Im zweiten Schritt wurde die Wasseräquivalente Pfadlänge (WEPL) der Proben für einen 200 MeV/u Kohlenstoff-Strahl mit dem PTW PeakFinder bestimmt und durch Division der bereits bekannten Elektronendichte die Bremszahl ermittelt.

Ergebnisse
Mit den ausgewählten Materialien konnte ein großer Bereich an relativen Wirkungsquerschnitten von 0.95 (Fett, Knochenmark) bis 1.88 (Knochentransplantat) und an relativer Bremszahl im Bereich von 1.03 (Knochenmark) bis 0.90 (Knochentransplantat) abgedeckt werden. Dies entspricht einem I-value-Bereich von 60 eV (Knochenmark) bis 182 eV (Knochentransplantat). Der optimierte Versuchsaufbau ermöglicht hierbei eine Bestimmung von WEPL, relativem Wirkungsquerschnitt und relativer Bremszahl mit einer mittleren Unsicherheit von 0.2%, 0.3% bzw. 0.5%.

Schlussfolgerung
Mit dem vorgestellten Hybrid-Versuchsaufbau konnten kombinierte Messungen von Röntgen- und Ionenschwächung in verschiedenen Geweben durchgeführt werden. Die Dichteunabhängigkeit der Zielgrößen erlaubt eine hohe Flexibilität in der Auswahl und Handhabung der Proben. In zukünftigen Studien soll in einem statistischen Ensemble die Variabilität der beteiligten Messgrößen analysiert werden.
Keywords: dual-energy CT, proton therapy, ion-beam therapy
  • Lecture (Conference)
    47. Jahrestagung der Deutschen Gesellschaft für Medizinische Physik (DGMP) e. V., 07.-10.09.2016, Würzburg, Germany

Publ.-Id: 23910 - Permalink


Robust range prediction for arbitrary tissue mixtures based on dual-energy CT
Möhler, C.; Wohlfahrt, P.; Richter, C.; Greilich, S.;
The treatment planning of proton or ion radiation therapy is affected by uncertainties arising from the heuristic conversion of computed tomography (CT) images to stopping-power ratio (SPR) maps. In this work, we present how these uncertainties can potentially be reduced by the use of dual-energy CT (DECT), via a physics-based SPR prediction. According to the Bethe formula, the SPR is the product of the electron density and the stopping number relative to water. The latter ranges between 0.96 and 1.02 for human tissue at a therapeutic beam energy of 200 MeV/u and depends on the mean excitation energy (I-value).
As a first step, the relative electron density can be directly determined from DECT images in a universal and robust procedure, based on a simple assumption for the cross section parameterization. Secondly, we propose to infer the relative stopping number from the relative photon absorption cross section obtained from DECT scans - instead of using an effective atomic number as a proxy for the I-value, which has previously been suggested in literature. Our choice of variables makes a proper treatment of tissue mixtures possible, which inevitably occur in patient CT images, and allows for a convenient definition of the uncertainties.
A calculation-based analysis of tabulated body tissues and tissue base components - such as water, lipid, carbohydrates and protein - suggests a maximum uncertainty below one percent for arbitrary mixtures of human tissue. We performed first experiments, combining particle range measurements with DECT scans, to validate our method of stopping-number prediction.
Keywords: dual-energy CT, proton therapy, ion-beam therapy
  • Poster
    55th Annual Conference of the Particle Therapy Co-operative Group (PTCOG), 22.-28.05.2016, Prag, Czech Republic

Publ.-Id: 23909 - Permalink


Numerical simulations for the precession dynamo experiment in the framework of the DRESDYN project
Giesecke, A.; Stefani, F.;
In a next generation dynamo experiment currently under development at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) a fluid flow of liquid sodium, solely driven by precession, will be considered as a possible source for magnetic field generation.

I will present results from hydrodynamic simulations of a precession driven flow in cylindrical geometry. In a second step, the velocity fields obtained from the hydrodynamic simulations have been applied to a kinematic solver for the magnetic induction equation in order to determine whether a precession driven flow will be capable to drive a dynamo at experimental conditions.

It turns out that excitation of dynamo action in a precessing cylinder at moderate precession rates is difficult, and future dynamo simulations are required in more extreme parameter regimes where a more complex fluid flow is observed in water experiments which is supposed to be beneficial for dynamo action.
Keywords: Dynamo Precession Magnetohydrodynamics Geodynamo DRESDYN
  • Lecture (Conference)
    European GDR Meeting 20016, 27.06.-01.07.2016, Barcelona, Spain

Publ.-Id: 23908 - Permalink


Innovative Technologien für Ressourceneffizienz - Strategische Metalle und Mineralien Ergebnisse der r³ Fördermaßnahme
Dürkoop, A.; Brandstetter, C.; Gräbe, G.; Rentsch, L.; (Editors)
Zum Abschluss der r³ Fördermaßnahme werden die Ergebnisse der r³ Verbundprojekte in einem gesammelten Buch veröffentlicht.
Keywords: Ressourceneffizienz, Sekundärrohstoffe, Recycling, Substitution, Urban Mining
  • Book (Editorship)
    Stuttgart: Fraunhofer Verlag, 2016
    ISBN: 978-3-8396-1102-9

Publ.-Id: 23906 - Permalink


Frustrated magnets in high magnetic fields—selected examples
Wosnitza, J.; Zvyagin, S. A.; Zherlitsyn, S.;
An indispensable parameter to study strongly correlated electron systems is the magnetic field. Application of high magnetic fields allows the investigation, modification and control of different states of matter. Specifically for magnetic materials experimental tools applied in such fields are essential for understanding their fundamental properties. Here, we focus on selected high-field studies of frustrated magnetic materials that have been shown to host a broad range of fascinating new and exotic phases. We will give brief insights into the influence of geometrical frustration on the critical behavior of triangular-lattice antiferromagnets, the accurate determination of exchange constants in the high-field saturated state by use of electron spin resonance measurements, and the coupling of magnetic degrees of freedom to the lattice evidenced by ultrasound experiments. The latter technique as well allowed new, partially metastable phases in strong magnetic fields to be revealed.

Publ.-Id: 23905 - Permalink


Magnetic properties of HoFe6Al6H hydride: A single-crystal study
Andreev, A. V.; Pelevin, I. A.; Sebek, J.; Tereshina, E. A.; Gorbunov, D. I.; Drulis, H.; Tereshina, I. S.;
Crystal structure and magnetic properties were studied on a single crystal of HoFe6Al6H and compared with those of the parent HoFe6Al compound with a tetragonal crystal structure of the ThMn126Al6 is a ferrimagnet with exact compensation of the Ho and Fe sublattices magnetizations at low temperatures. Both the hydride and the parent compound display a high magnetic anisotropy of the easy-plane type, a noticeable anisotropy exists also within the easy plane with the [110] axis as the easy magnetization direction. The hydrogenation increases slightly (from 10 to 10.45 µB) the magnetic moment of the Fe sublattice as a result of volume expansion. It leads to a decompensation of the Fe and Ho sublattices and HoFe6Al6H has a spontaneous moment 0.45 µB/f.u. The enhancement of the Fe-Fe intra-sublattice exchange interaction results in a higher Curie temperature (TC) value, 350 K in the hydride as compared to 315 K of HoFe6Al6. The Ho-Fe inter-sublattice interaction is also enhanced in the hydride. The molecular field Hmol created on Ho Ions by Fe sublattice is 38 T in HoFe6Al6 and 48 T in HoFe6Al6H. The inter-sublattice exchange constant nHoFe is 3.8 T/µB and 4.6 T/µB, respectively. High-field measurements confirm the enhancement of the Ho-Fe exchange interaction in the hydride found from the temperature dependence of magnetization.

Publ.-Id: 23904 - Permalink


Treatment of once rejected material - Investigating the recovery of cassiterite from tailings disposals using different flotation methods
Leistner, T.; Leissner, T.; Möckel, R.; Osbahr, I.; Rudolph, M.; Peuker, U. A.;
Tin-mining activities have taken place in the region of the German Erzgebirge (Ore Mountains) for over hundreds of years up until the late 1980s. For long times, gravity separation processes used to be the main beneficiation approach in those mining districts to recover cassiterite, the main tin-bearing mineral. Since for fine and very fine particles these approaches might not represent effective techniques, much valuable material could not be recovered and reported to tailings, where it was subsequently disposed. Thus, there are substantial amounts of cassiterite still present in these disposals, most of it as very fine particles with already high degrees of liberation. That fact brings these disposals into focus for potential reprocessing using beneficiation approaches, which are more sensitive to fine and very fine particles.

In this paper we present results concerning the laboratory-scale treatment of material from an exemplary heap of the former Ehrenfriedersdorf mining site using various flotation methods. The material used is previously classified into different size ranges. Conventional froth flotation is applied to the fine particles (20µm – 100µm). For the very fine particle (< 20µm), special emphasis is put on oil-assisted flotation methods, including oil agglomeration flotation and two-liquid flotation. Therefore, an aliphatic oil phase of alkane basis is used to either selectively aggregate or collect the cassiterite particles. Recovery and flotation performance results are presented with respect to different process parameters: various collectors (e.g. sulphosuccinamates, phosphonic acids) and depressants (e.g. sodium fluorosilicate, oxalic acid) regime, oil dosage, oil/pulp agitation time and pulp density. Furthermore, the oil/particle aggregation behavior is analyzed via particle image analysis and, additionally, collector adsorption characteristics are investigated by contact angle measurements, zeta potential analysis and infrared spectroscopy. The data obtained is correlated with the testwork results achieved in order to interpret the flotation response of very fine cassiterite particles.
  • Contribution to proceedings
    IMPC 2016 - XXVIII International Mineral Processing Congress, 11.-15.09.2016, Quebec, Kanada

Publ.-Id: 23903 - Permalink


Investigations on the selective particle/oil-aggregation as a processing strategy for ultrafine particle systems
Leistner, T.; Rudolph, M.; Peuker, U. A.;
Difficulties in the selective separation and recovery of ultrafine or even colloidal particles (ranging from 0.1 to 10µm in size) represent a common problem in various industrial fields, e.g. in the mineral processing industry. The difficulties arise due to the dominance of surface effects over bulk properties that strongly determine the behavior of such systems. In order to overcome these problems various physico-chemical process approaches, based on differences in particle wettability and the use of a non-polar, water-immiscible oil phase, are reported in different investigations. For these oil-assisted separation techniques, differing only in oil amount, addition and function, particle/oil aggregates could be achieved theoretically with a high degree of selectivity either by (selective) particle accumulation at the oil/water interface or even by (selective) particle transfer from the aqueous pulp into the oil phase.

In this paper we present investigations on the selective particle/oil aggregation behavior for various ultrafine model particle systems (e.g. quartz, magnetite, apatite) and aliphatic oil phases of alkane basis. Analytical investigations performed include the analysis of zeta potentials of oil droplets and solid particles in modifying reagent solution and reagent-free solution, the particle/oil aggregate structure by particle image analysis as well as wettability characterization by contact angle measurements. Experimental investigations include separation experiments using a modified laboratory-scale flotation column for different artificial solid mixtures. In order to selectively control the particle surface properties, different modifying reagents, including sodium oleate, CTAB, sodium silicate, citric acid, etc. were chosen to promote particle/oil aggregation for various target particles and more importantly the hindrance of particle/oil aggregation for the others. The degree of selectivity achieved as well as recovery and type of oil/particle aggregates formed are presented with regard to operational parameters like pH, electrolyte content, oil/water volume ratio and oil droplet size.
Keywords: ultrafine particle processing, particle/oil aggregation, oil-assisted flotation
  • Poster
    IMPC 2016 - XXVIII International Mineral Processing Congress, 11.-15.09.2016, Quebec, Kanada

Publ.-Id: 23902 - Permalink


Selective Separation of ultrafine particle systems - Chances and drawbacks when using non-polar oil as process aid
Leistner, T.; Rudolph, M.; Peuker, U. A.;
Selective fine particle separation based on differences in particle surface properties represents a key unit operation in various industrial fields, e.g. in the mineral processing industry in the form of flotation processes. One of the main challenges today for separation processes is the efficient processing of ultrafine or even colloidal particles ranging from 0.1 to 10 µm in size, because these particles are usually poorly recovered by conventional froth flotation. A promising approach for ultrafines recovery is the use of a non-polar, water-immiscible oil phase, as reported in various investigations. In a particle mixture in which only selected particles are wetted by the oil phase, particle/oil aggregates could be achieved theoretically with a high degree of selectivity either by particle accumulation at the oil/water interface or even by particle transfer from the aqueous pulp into the oil phase. Hence, different techniques of oil-assisted separations can be distinguished, differing only in oil amount, addition and function. The principle of these approaches is directly related to the stabilization of emulsions by very fine solid particles (so called Pickering emulsions).

In this paper we present investigations on the potentially application of oil-assisted separation methods for ultrafines processing. The investigations performed involve the determination of the degree of particle/oil aggregation for ultrafine model particle systems in simple laboratory-scale batch trials as well as separation experiments using a modified separation column. Aliphatic oil phase of alkane basis and modifying reagents (to selectively control the particle surface properties and thus particle/oil aggregation) are used for the experiments. The response of the process, including recovery and selectivity is presented with regard to operational parameters like pH, oil droplet size, etc. Furthermore, analysis of zeta potentials of non-polar oil droplets and solid particles in modifying reagent solution and reagent-free solution are taken into account in order to interpret and physically model the particle/oil aggregation mechanism as well as the applicability of the processes.
  • Contribution to proceedings
    PARTEC 2016 - International Congress on Particle Technology, 19.-21.04.2016, Nürnberg, Deutschland

Publ.-Id: 23901 - Permalink


A study of the reprocessing of fine and ultrafine cassiterite from gravity tailing residues by using various flotation techniques
Leistner, T.; Embrechts, M.; Leissner, T.; Chehreh Chelgani, S.; Osbahr, I.; Möckel, R.; Peuker, U. A.; Rudolph, M.;
This study investigates the reprocessing of once disposed tin tailings from a historic German tin operation through different surface properties based processing techniques. Froth flotation and agglomeration flotation, by using commercially available cassiterite collectors from Clariant, were chosen as processing techniques. Isooctane as a nonpolar oil was used to promote the collection of ultrafine (-10 µm) cassiterite by selective agglomeration, and thus, size enlargement. Results indicate that by using sulfosuccinamates as a collector, around 80% of the fine (-50 µm) to very fine (-20 µm) cassiterite can be recovered (representing ~50% of the total cassiterite in the tailings sample). Agglomeration flotation experiments showed inferior results for recovering the ultrafine cassiterite (for feed fractions in the -25 µm size range). Oil/froth interaction and increased pulp ion content are considered as the main contributing causes.
Keywords: Tailings, Reprocessing, Cassiterite, Flotation, Ultrafine, Oil-assisted flotation

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Publ.-Id: 23900 - Permalink


Experimental discrimination of ion stopping models near the Bragg peak in highly ionized matter
Cayzac, W.; Frank, A.; Ortner, A.; Bagnoud, V.; Basko, M. M.; Bedacht, S.; Bläser, C.; Blazevic, A.; Busold, S.; Deppert, O.; Ding, J.; Ehret, M.; Fiala, P.; Frydrych, S.; Gericke, D. O.; Hallo, L.; Helfrich, J.; Jahn, D.; Kjartansson, E.; Knetsch, A.; Kraus, D.; Malka, G.; Neumann, N.; Pepitone, K.; Pepler, D.; Sander, S.; Schaumann, G.; Schlegel, T.; Schroeter, N.; Schumacher, D.; Seibert, M.; Tauschwitz, A.; Vorberger, J.; Wagner, F.; Weih, S.; Zobus, Y.; Roth, M.;
The energy deposition of ions in dense plasmas is a key process in inertial confinement fusion that determines the alpha-particle heating expected to trigger a burn wave in the hydrogen pellet and the resulting thermonuclear gain. However, measurements of ion stopping in plasmas are scarce and mostly restricted to high ion velocities where the theory agrees with data. Here, we report experimental data at low projectile velocities where the stopping force reaches its maximum (Bragg peak). This parameter range features the largest theoretical uncertainties and conclusive data are missing until today. The precision of our measurements, combined with a reliable knowledge of the plasma parameters, allows to clearly rule out several standard models for the stopping power for beam velocities typically encountered in inertial fusion. On the other hand, our data support theories that include a detailed treatment of strong ion-electron collisions.
Keywords: plasma, warm dense matter, stopping power, fusion, strong collisions

Publ.-Id: 23899 - Permalink


Solid state spectroscopy with THz free electron lasers
Helm, M.;
Some applications of infrared and THz free electron lasers in solid state spectroscopy are discussed. In particular, nonlinear experiments on semiconductor quantum well excitons and pump-probe studies on carrier relaxation in graphene are presented.
Keywords: free electron laser, infrared, terahertz, quantum well, graphene
  • Invited lecture (Conferences)
    Laser Optics 2016, 27.06.-01.07.2016, St. Petersburg, Russland

Publ.-Id: 23898 - Permalink


Interplay of the Open Circuit Potential-Relaxation and the Dissolution Behavior of a Single H2 Bubble generated at a Pt Microelectrode
Karnbach, F.; Yang, X.; Mutschke, G.; Fröhlich, J.; Eckert, J.; Gebert, A.; Tschulik, K.; Eckert, K.; Uhlemann, M.;
The dissolution behavior of a single H2 bubble electrochemically generated at a Pt microelectrode in 1 M H2SO4, was studied. The open circuit potential (OCP) relaxation after the polarization end was recorded and correlated with the dissolved H2 concentration at the interface electrode/electrolyte/gas. Simultaneously, the shrinking of the bubble was followed optically by means of a high speed camera. In addition, analytical modelling and numerical simulations for the bubble dissolution were performed. Three characteristic regions are identified in the OCP and the bubble radius transients: (i) slow relaxation and shrinking, (ii) transition region and (iii) a long-term slowed down dissolution process. The high supersaturation after polarisation remains longer than theoretically predicted and feeds the bubble in region (i). This reduces the dissolution rate of the bubble which differs significantly from that of non-electrochemically produced bubbles. Numerical multi-species simulations prove that oxygen and nitrogen dissolved in the electrolyte additionally influence the bubble dissolution and slow down its shrinkage compared to pure hydrogen diffusion. In region (iii), a complete exchange of hydrogen gas with nitrogen and oxygen has occurred in the gas bubble.
Keywords: electrochemistry, electrolysis, hydrogen evolution, gas dissolution, open circuit potential, numerical simulation

Publ.-Id: 23897 - Permalink


Crystallization of multi-crystalline silicon in a cone-shaped, inductively heated crucible: MHD melt flow and seeded growth
Poklad, A.; Galindo, V.; Schmid, E.; Heinze, V.; Pätzold, O.; Stelter, M.; Gerbeth, G.;
A novel, vertical Bridgman-type technique for growing multi-crystalline silicon ingots in an induction furnace is described. In contrast to conventional growth, a modified setup with a cone-shaped crucible and susceptor is used. A detailed numerical simulation of the setup is presented. It includes a global thermal simulation of the furnace and local simulation of the melt, which aims at the influence of the melt flow on the temperature and concentration fields. Furthermore, seeded growth of cone-shaped Si ingots using either a monocrystalline seed or a seed layer formed by pieces of poly-Si is demonstrated and compared to growth without seeds. The influences of the seed material on the grain structure and the dislocation density of the ingots are discussed.
Keywords: Bridgman growth, Dislocation density, Melt flow, Multi-crystalline silicon, Seeded growth
  • Contribution to proceedings
    10th PAMIR International Conference ‐ Fundamental and Applied MHD, 20.-24.06.2016, Cagliari, Italy
    Proceedings of the 10th PAMIR International Conference Fundamental and Applied MHD, Cagliari, 978-88-90551-93-2, 336-340
  • Poster
    10th PAMIR International Conference ‐ Fundamental and Applied MHD, 20.-24.06.2016, Cagliari, Italy

Publ.-Id: 23896 - Permalink


Transitions in a Magnetized Quasi-laminar Spherical Couette Flow
Kasprzyk, C.; Kaplan, E.; Seilmayer, M.; Stefani, F.;
First results from a new magnetized spherical Couette experiment are presented.
For a line in the Re-Ha instability diagram with constant Reynolds Number Re = 1000 and increasing Hartmann number Ha we study the liquid metal movement in a spherical gap under the influence of a vertical magnetic field.
The resulting flow structures are inspected with comprehensive ultrasound technique.
Increasing the magnetic field strength until Ha = 60, we observe the equatorially anti-symmetric jet instability with azimuthal wave number m = 3 at low Ha.
At intermediate Ha, no dominant m is identifiable.
At high Ha, an unstable, equatorially symmetric state with various transitions between different azimuthal modes becomes visible.
Our observations are in agreement with numerical linear instability analysis.
Keywords: Magnetized spherical Couette flow, Instabilities
  • Contribution to proceedings
    10th PAMIR International Conference Fundamental and Applied MHD, 20.-24.06.2016, Cagliari, Italy
    Proceedings of the 10th PAMIR International Conference Fundamental and Applied MHD, 9788890551932, 547-551
  • Lecture (Conference)
    10th PAMIR International Conference Fundamental and Applied MHD, 20.-24.06.2016, Cagliari, Italy

Publ.-Id: 23894 - Permalink


Rotating magnetic field driven spin-up flow in a rectangular cavity
Galindo, V.; Nauber, R.; Franke, S.; Räbiger, D.; Czarske, J.; Eckert, S.;
Numerical simulations of the rotating magnetic field (RMF) driven liquid metal flow and corresponding velocity measurements using a dual plane, two-component ultrasound array Doppler velocimeter were carried out in a rectangular cavity with an aspect ratio of unity. The liquid metal (GaInSn) was suddenly exposed to an azimuthal body force generated by a RMF. The measurements show a similar flow structure compared to the case of the RMF-driven flow in a cylindrical container, in particular the so-called initial adjustment phase followed by an inertial phase which is dominated by inertial oscillations of the secondary flow. The transition from the double vortex structure of the secondary flow to an oscillating regime was detected at a magnetic Taylor number of Ta_cr > 1.3×10^5. A proper orthogonal decomposition (POD) of the velocity field allows a detailed study of the structure and time development of the most important flow modes.
Keywords: Rotating magnetic field, Ultrasound velocity measurement, Spin-up, OpenFOAM, Proper orthogonal decomposition
  • Contribution to proceedings
    10th PAMIR International Conference - Fundamental and Applied Magnetohydrodynamics, 20.-24.06.2016, Cagliari, Italien
    Proceedings of the 10th PAMIR International Conference Fundamental and Applied MHD, Cagliari, 978-88-90551-93-2, 82-86
  • Lecture (Conference)
    10th PAMIR International Conference - Fundamental and Applied MHD, 20.-24.06.2016, Cagliari, Italien

Publ.-Id: 23893 - Permalink


Influence of magnetic fields on the behavior of single hydrogen bubbles generated via water electrolysis
Karnbach, F.; Uhlemann, M.; Yang, X.; Eckert, K.; Baczyzmalski, D.; Cierpka, C.; Mutschke, G.; Gebert, A.;
Hydrogen production via water electrolysis is an established method for energy storage the efficiency of which is limited by the gas bubbles blocking the electrode surface during the process. The application of a magnetic field can be a promising solution for an increased bubble detachment due to the Lorentz force induced electrolyte convection. Therefore single hydrogen bubbles offer a nice possibility for a detailed analysis of the underlying mechanisms. To analyze the impact of the magnetic field single hydrogen bubbles were produced potentiostatically at different potentials via electrolysis of sulfuric acid at a Pt microelectrode (Ø 100 μm) with a magnetic field superimposed in two different field configurations to the electrode surface for varying magnetic field strengths. The bubble behavior was visualized by a CCD camera and the electrolyte flow analyzed via Particle Image Velocimetry and Astigmatism Particle Tracking Velocimetry. Significant changes in the current signal were obtained (Fig. 1), depending on field orientation and strength, and are discussed due to the impact of the Lorentz force induced flow around the bubble, which possibly also influences the mass transfer in the vicinity of the bubble surface. If the magnetic field is applied parallel, a different bubble behavior is observed in comparison to a perpendicular applied magnetic field what may result in a higher efficiency.
Keywords: electrochemistry, electrolysis, renewable energy, hydrogen production, water splitting, magnetic field, Lorentz force, particle tracking velocimetry
  • Poster
    10th PAMIR International Conference on Fundamental and Applied MHD, 20.-24.06.2016, Cagliari (Sardinia), Italia

Publ.-Id: 23892 - Permalink


Functional DNA origami nanotubes for nanoelectronics
Teschome, B.; Facsko, S.; Kerbusch, J.; Schönherr, T.; Hübner, R.; Gothelf, K.; Keller, A.;
DNA origami [1] has become a key technique for designing well-defined nanostructures with any desired shape [2] and for the controlled arrangement of nanostructures with few nanometer scales [3]. These unique features of DNA origami make it a promising candidate for use as a scaffold for nanoelectronics [4] and nanophotonics [5] device fabrication.
In this work, we first demonstrate a compelling alternative approach to generate ordered arrays of DNA nanotubes on topographically patterned surfaces [6]. To this end, we combine two bottom-up techniques for nanostructure fabrication, i.e., DNA origami self-assembly and self-organized nanopattern formation on silicon surfaces during ion sputtering, thus avoiding the necessity of lithographic processing or chemical modifications. Then, we present the high-yield synthesis of high-density gold nanoparticle (AuNP) arrangements on DNA origami nanotubes with few unbound background nanoparticles and fabricate large arrays of aligned DNA origami nanotubes decorated with a high density of AuNPs [7]. The high yield of AuNP assembly was achieved by careful control of the buffer and the AuNPs concentrations and the hybridization time on Si surface. In addition, we optimize the metallization of DNA origami nanotubes to create DNA origami-templated nanowires and develop a platform for electrical contacting of those nanowires. We also demonstrate the assembly of heterogeneous nanostructures on a single DNA origami nanotube.

[1] P. W. K. Rothemund, Nature, 440, 297(2006).
[2] H. Dietz, S. M. Douglas and W. M. Shih, Science, 325, 725 (2009).
[3] B. Ding, Z. Deng, H. Yan, S. Cabrini, R. N. Zuckermann and J. Bokor, J. Am. Chem. Soc., 132, 3248 (2010).
[4] A. C. Pearson, J. Liu, E. Pound, B. Uprety, A. T. Woolley, R. C. Davis and J. N. Harb, J. Phys. Chem. B, 116, 10551(2012).
[5] J. Prinz, B. Schreiber, L. Olejko, J. Oertel, J. Rackwitz, A. Keller and I. Bald, J. Phys. Chem. Lett., 4, 4140 (2013).
[6] B. Teshome, S. Facsko and A. Keller, Nanoscale, 6, 1790 (2014).
[7] B. Teschome, S. Facsko, K. V. Gothelf and A. Keller, Langmuir, 31,12823 (2015).
  • Lecture (Conference)
    DNA-Based Nanotechnology, 19.-21.05.2016, Jena, Germany
  • Poster
    2nd Functional DNA Nanotechnology Workshop, 22.-24.06.2016, Rom, Italy

Publ.-Id: 23891 - Permalink


Comparative evaluation of SUV, tumor-to-blood standard uptake ratio (SUR), and dual time point measurements for assessment of the metabolic uptake rate in FDG PET
Hofheinz, F.; van den Hoff, J.; Steffen, I. G.; Lougovski, A.; Ego, K.; Amthauer, H.; Apostolova, I.;
Background

We have demonstrated recently that the tumor-to-blood standard uptake ratio (SUR) is superior to tumor standardized uptake value (SUV) as a surrogate of the metabolic uptake rate K m of fluorodeoxyglucose (FDG), overcoming several of the known shortcomings of the SUV approach: excellent linear correlation of SUR and K m from Patlak analysis was found using dynamic imaging of liver metastases. However, due to the perfectly standardized uptake period used for SUR determination and the comparatively short uptake period, these results are not automatically valid and applicable for clinical whole-body examinations in which the uptake periods (T) are distinctly longer and can vary considerably. Therefore, the aim of this work was to investigate the correlation between SUR derived from clinical static whole-body scans and K m-surrogate derived from dual time point (DTP) measurements.

Methods

DTP 18F-FDG PET/CT was performed in 90 consecutive patients with histologically proven non-small cell lung cancer (NSCLC). In the PET images, the primary tumor was delineated with an adaptive threshold method. For determination of the blood SUV, an aorta region of interest (ROI) was delineated manually in the attenuation CT and 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 from the early time point of each DTP measurement were scan time corrected to 75 min postinjection (SURtc). As surrogate of K m, we used the SUR(T) slope, K slope, derived from DTP measurements since it is proportional to the latter under the given circumstances. The correlation of SUV and SURtc with K slope was investigated. The prognostic value of SUV, SURtc, and K slope for overall survival (OS) and progression-free survival (PFS) was investigated with univariate Cox regression in a homogeneous subgroup (N=31) treated with primary chemoradiation.


Results

Correlation analysis revealed for both, SUV and SURtc, a clear linear correlation with K slope (P<0.001). Correlation SUR vs. K slope was considerably stronger than correlation SUV vs. K slope (R 2=0.92 and R 2=0.69, respectively, P<0.001). Univariate Cox regression revealed SURtc and K slope as significant prognostic factors for PFS (hazard ratio (HR) =3.4/ P=0.017 and HR =4.3/ P=0.020, respectively). For SUV, no significant effect was found. None of the investigated parameters was prognostic for OS.

Conclusions

Scan-time-corrected SUR is a significantly better surrogate of tumor FDG metabolism in clinical whole-body PET compared to SUV. The very high linear correlation of SUR and DTP-derived K slope (which is proportional to actual K m) implies that for histologically proven malignant lesions, FDG-DTP does not provide added value in comparison to the SUR approach in NSCLC.
Keywords: PET FDG Tumor-to-blood ratio SUR

Publ.-Id: 23888 - Permalink


Remarks on 3 years SSPA Operation at the Superconducting Linac ELBE
Büttig, H.; Arnold, A.; Kuntzsch, M.; Schurig, R.;
Since January 2012 the superconducting Linac ELBE is in operation with 1.3 GHz Solid State Power Amplifiers (SSPA). One system can deliver up to 20 kW per cavity.
The presentation revues the experiences gained within 3 years of operation and problems that have been solved.
Keywords: ELBE RF, Superconducting Linac RF-SSPA, SSA 1.3GHz, Solid state power amplifiers 1.3GHz
  • Poster
    CWRF2016 - The Continuous Wave and High Average RF Power Workshop, 20.-24.06.2016, Grenoble, France

Publ.-Id: 23887 - Permalink


Upgrade of the 1.3 GHz Resonant Ring for High Power RF Test of Accelerator Components
Arnold, A.; Büttig, H.; Staats, G.;
Since 2009 the ELBE center for high power radiation sources is using a 1.3 GHz resonant ring for RF conditioning of power couplers and to test different waveguide components. The poster describes the ring and two new features that are improving the ring significantly. First, a PLL system is used to stabilize the RF-power in the ring which normally drops with increasing temperature because the frequency of the structure shifts. And second, an adjustable test waveguide was designed that allows perfect matching of a pair of RF-couplers with different antenna tip lengths. All measurements are in good agreement with simulations and the ring is now routinely in use for travelling wave measurements of RF components up to 50 kW CW.
Keywords: Resonant Ring, RF-component tests, High power RF, Waveguide window test, RF Coupler tests
  • Poster
    CWRF2016 - The Continuous Wave and High Average RF Power Workshop, 20.-24.06.2016, Grenoble, France

Publ.-Id: 23886 - Permalink


Subsecond thermal processing for the advancement of thin layers and functional coatings
Skorupa, W.;
This talk reviews the advances that subsecond thermal processing in the millisecond range using xenon-filled flash lamps (FLA) brings to the processing of the most advanced thin layer and coating materials, thus enabling the fabrication of novel electronic structures and materials. It will be demonstrated how such developments can translate into important practical applications leading to a wide range of technological benefits. An important issue of our work was the formation and characterization of semiconductor materials and coatings for the green energy advancement. Regarding photovoltaic applications, we dealt with the ion beam doping and thermal processing of PV silicon demonstrating using FLA a distinct improvement of the minority carrier diffusion length compared to rapid thermal processing and furnace treatments. Moreover, we engineered the hydrogen content in photovoltaic silicon in correlation to the phosphorus doping using plasma immersion ion implantation and FLA. Recently, we demonstrated also FLA driven boron and phosphorus in-diffusion from surface coatings. Further, we prepared coarse grained dendritic crystal structures in thin silicon films on silicon dioxide to show that the addition of carbon prevents the agglomeration of the molten silicon films and largely influences the crystallisation process. Finally the strongly developing field of large area electronics is represented by reporting on our activities in regard to transparent conductive oxide (TCO) and copper paste coatings.
Keywords: subsecond thermal processing, flash lamp annealing, ion implantation, photovoltaics, transparent conductive oxide, copper paste
  • Invited lecture (Conferences)
    SVC (Society of Vacuum Coaters) 59th Annual Technical Conference (TechCon), 09.-13.05.2016, Indianapolis, IN, USA

Publ.-Id: 23885 - Permalink


Fragment molecular orbital (FMO) method for studying actinide interaction with DNAs and proteins
Tsushima, S.ORC; Ishikawa, T.; Tanaka, S.; Mori, H.; Saeki, M.; Nakano, T.; Komeiji, Y.; Mochizuki, Y.
Due to its potential health and environmental impacts, actinide binding to biomolecules has been a subject of intensive investigations. A large number of experimental works have been carried out but our understanding remains mostly in a macroscopic scale. Modeling actinide interaction with large biomolecules using ab initio quantum chemical calculations may drastically expand our molecular level knowledge but is challenged by a demand for huge computational resources.
Our strategy to overcome this difficulty is to apply fragment molecular orbital (FMO) method. In FMO, the molecular system of interest is partitioned into small fragments. Each fragment and fragment pair is subject to self-consistent field calculations under environmental electrostatic potentials and the electronic structure of the whole system is reconstituted [1]. This procedure drastically reduces computational cost of Hartree Fock calculations from N3 to N2 (or less) and is readily parallelizable. FMO has been extended to MP2 and to DFT to include electron correlation and was successfully applied to the systems such as hydrated DNA (~ 7500 atoms) [2].
Currently we are upgrading the FMO program Abinit-MP [3] to implement 5f elements into the program. We first choose uranyl-bound DNA for a case study. Calcu-lations are performed as follows. UO22+-bound d(CGCGAATTCGCG)2 (Dickerson-Drew dodecamer) with 20 Na+ ions and SPC/E water shell with 10 Å thickness (a to-tal of 15559 atoms in the system) is first thermally equilibrated and subsequently submitted to molecular dynamics (MD) simulation at 300 K for 100 ns interval using AMBER 14 program. Force field parameters for UO22+ and coordinating water are those developed by Pomogaev et al. [4]. At each 1 ns time step of MD simulation, the structure is extracted and submitted to FMO single point energy calculation at the MP2 level. In FMO, nucleic unit is appropriately divided into sugar, base, and phosphate fragments. Inter-fragment interaction energy analysis is performed to explore the binding affinity of uranyl to DNA and its influence on base pairing.
Binding of Eu3+ to Calmodulin and its comparison with Ca2+ binding is under in-vestigation.

FMO program Abinit-MP and its graphical user interface BioStationViewer are freely distributed online [5]. This project is funded by the Ministry of Education, Culture, Sports, Science, and Technology of Japan (MEXT).
  • Lecture (Conference)
    3rd International Workshop on Advanced Techniques in Actinide Spectroscopy (ATAS 2016), 07.-10.11.2016, Richland, USA

Publ.-Id: 23884 - Permalink


Ultrasonic flow measurement in liquid metal models of continuous steel casting
Timmel, K.; Wondrak, T.; Franke, S.; Eckert, S.;
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. One very important industrial process is the continuous casting of steel. But there exist almost no measurement data of the inner mold flow from real casting plants and there are no satisfying measurement techniques available for those harsh conditions. By this, e.g. a detailed understanding of the action of electromagnetic brakes on the complex flow is missing. Therefore we built model experiments for the continuous casting process of steel by using low melting liquid metals and investigated the mold flow under different conditions. The main value of cold metal laboratory experiments consists in the capabilities to obtain quantitative flow measurements by ultrasonic flow measurements with a reasonable spatial and temporal resolution. Standard transducers were used at the model operating at room temperature with the eutectic alloy of GaInSn. Ultrasonic transducers for high temperatures and ultrasonic waveguide sensors were used at the big model, which uses the alloy Sn60Bi40 as model liquid and is operated at temperatures of 200-350 °C. Results from the mold flow measurement will be presented, showing the effect of a static magnetic field on the flow structure. It turned out, that the magnetic field can locally accelerate the flow, contrary to the expected action as a brake. The ultrasonic velocity measurement data were further used for validation and for comparison with other measurement techniques at the model experiment.
Keywords: Continuous casting of steel, electro-magnetic flow control, liquid metal models, applied Ultrasonic Doppler Velocimetry, ultrasonic wave-guides, high temperature transducers
  • Lecture (Conference)
    10th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering (ISUD 10), 28.-30.09.2016, Tokyo, Japan
  • Contribution to proceedings
    10th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering (ISUD10), 28.-30.09.2016, Tokyo, Japan
    Proceedings of the 10th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering, Tokyo: Tokyo Institute of Technology, 17-20

Publ.-Id: 23883 - Permalink


Evaluierung iterativer Rekonstruktionsverfahren zur Optimierung der Bildqualität und Reduktion von Metallartefakten in der Computertomographie
Negwer, F.; Wohlfahrt, P.; Richter, C.;
Zusammenfassung
In dieser Studie wurde der Einfluss des iterativen Rekonstruktionsverfahrens SAFIRE und des iterativen Verfahrens zur Metallartefaktreduktion iMAR auf die Bildqualität untersucht. SAFIRE konnte das Bildrauschen um bis zu 50% oder die Dosis um bis zu 70% reduzieren. Der optische Bildeindruck verbessert sich durch die Metallartefaktreduktion iMAR signifikant, die quantitativen Parameter zur Beschreibung der Metallartefakte zeigen jedoch keine klare Verbesserung. Die erzielten Verbesserungen durch iMAR sind daher nicht ausreichend, um eine hochpräzise Protonentherapie gewährleisten zu können.

Abstract
In this study the influence of the iterative reconstruction method SAFIRE and the iterative method for metal artifact reduction iMAR on the image quality was investigated. SAFIRE was able to reduce the noise by 50% or the dose by 70%. The visual impression could be significantly improved by iMAR, although the quantitative parameters for the description of metal artifacts depend strongly on the investigated scan region. The achieved improvements by iMAR are not sufficient to ensure high precision proton therapy.

Einleitung
CT-Aufnahmen, die zur Bestrahlungsplanung verwendet werden, müssen hohe Qualitätsanforderungen erfüllen. Dies gilt insbesondere bei der Anwendung in der Protonentherapie. Es ist dabei entscheidend, dass sich CT-Zahlen für spezifische Gewebe trotz unterschiedlicher Patientenanatomie, das heißt unterschiedliche Strahlaufhärtungsverhältnisse, nicht unterscheiden, da auf deren Grundlage die Protonreichweite im Patienten berechnet wird.
Zunehmend werden von den CT-Herstellern iterative Rekonstruktionsverfahren angeboten, deren Auswirkung auf die strahlentherapeutische Anwendung evaluiert werden sollte. Ein Ziel dieser Untersuchung war den Einfluss des iterativen Rekonstruktionsverfahrens SAFIRE (Siemens Healthcare, Forchheim, Deutschland) auf Strahlaufhärtung und Bildrauschen in Abhängigkeit von der applizierten CT-Dosis für Single-energy (SECT) und Dual-energy (DECT) CT-Scans zu quantifizieren. Weiterhin wurde das iterative Verfahren zur Metallartefaktreduktion iMAR (Siemens Healthcare, Forchheim, Deutschland) auf CT-Aufnahmen mit Metallimplantaten angewendet, um dessen Effekt auf die Ausprägung von Metallartefakten zu analysieren.

Material und Methoden
Für die klinische Charakterisierung von SAFIRE hinsichtlich Bildrauschen und Strahlaufhärtung wurden 11 gewebeäquivalente Materialien, 5 Kunststoffe und Aluminium in einem Siemens SOMATOM Definition AS CT-Scanner in drei verschiedenen Messaufbauten, die unterschiedliche Körperregionen simulieren, aufgenommen. Hierbei wurde zum Einen bei konstanter Dosis (CTDIvol32cm = 28.5 mGy) die Hochspannung (80, 100, 120, 140 kV) und zum Anderen bei konstanter Hochspannung (SECT: 120kV, DECT: 80/140kV) die Dosis variiert (CTDIvol32cm = 28.3, 18.3, 8.1 mGy")" . Außerdem wurde der Einfluss von SAFIRE auf aus DECT-Scans berechneten pseudo-monoenergetischen CT-Datensätzen unterschiedlicher Energie (gewichtete Summe beider DECT-Aufnahmen) quantifiziert.
Die Evaluierung von iMAR erfolgte mit Hilfe eines Kopfphantoms der Firma CIRS (Norfolk, Virginia, USA), welches aufgrund eines Metallimplantates im Wirbelkörper und eines austauschbaren Zahnes (mit und ohne Metallfüllung) unterschiedlich stark ausgeprägte Artefakte aufweist. Für die Analyse wurden in ausgewählten Bereichen des Phantomes Konturen festgelegt, die von Metallartefakten beeinflusst werden. Für jede Kontur wurde anhand der mittleren CT-Zahl sowie deren Standardabweichung die Artefaktausprägung quantitativ evaluiert. Des Weiteren wurde der optische Bildeindruck von CT-Datensätzen, die mit iMAR rekonstruiert wurden, durch drei Ärzte und sechs Medizinphysikexperten (MPEs) bewertet. Mit dem Mann-Whitney-U-Test wurden die unterschiedlichen Bildeindrücke auf Signifikanz überprüft.

Ergebnisse
Die Abweichungen materialspezifischer CT-Zahlen zwischen gefilterter Rückprojektion (FBP) und iterativer Rekonstruktion mit SAFIRE sind für alle Messaufbauten stets kleiner als 3 HU. Da SAFIRE somit keinen relevanten Einfluss auf die im Rekonstruktionskern integrierte Strahlaufhärtungskorrektur hat, enthält ein mit SAFIRE rekonstruierter CT-Scan dieselben Materialeigenschaften wie ein FBP-Datensatz. Durch die Anwendung von SAFIRE kann jedoch das Bildrauchen um bis zu 50% für SECT-Scans und pseudo-monoenergetische CT-Datensätze im Vergleich zur FBP reduziert werden (Abb. 1). Um ein vergleichbares Bildrauschen zwischen FBP und SAFIRE zu erreichen, kann die applizierte CT-Dosis für SAFIRE-Rekonstruktionen um bis zu 70% reduziert werden (Abb. 1a).
Das iterative Verfahren iMAR kann zur Reduktion von Metallartefakten beitragen, wobei der Effekt stark vom betrachteten Bildbereich und der nach Anwendungsgebiet optimierten Korrektur (z.B. für Zahn-, Hüft oder Wirbelimplantate) abhängen. In artefaktreichen Gebieten kann iMAR zu einer Verringerung von Metallartefakten von bis zu 75% führen, wobei in artefaktarmen Gebieten teilweise künstliche Bildfehler erzeugt werden, die sich in einer bis zu 4-fach erhöhten Standardabweichung widerspiegeln. Der optische Bildeindruck kann durch iMAR für Ärzte und MPEs signifikant (p < 0,01) verbessert werden.

Diskussion und Zusammenfassung
Das iterative Rekonstruktionsverfahren SAFIRE kann basierend auf den Ergebnissen dieser Studie für die Bestrahlungsplanung in der Protonentherapie eingesetzt werden. Die durch den CT-Scan in den Patienten eingetragene Dosis kann durch SAFIRE ohne Bildqualitätsverlust deutlich reduziert werden. -Dies ist insbesondere für notwendige engmaschige Kontroll-CT-Aufnahmen während der Protonentherapie von Bedeutung. Diese sind in vielen Fällen notwendig, um den hohen Präzisionsanspruch der Protonentherapie und gegebenenfalls die rechtzeitige Planadaptation zu gewährleisten.
Mit Hilfe des iterativen Verfahrens iMAR können Metallartefakte in Abhängigkeit vom Anwendungsgebiet reduziert werden. Aufgrund des signifikant verbesserten optischen Bildeindruckes kann iMAR zu einer besseren Abgrenzung von Tumor bzw. Risikoorganen beitragen, die anderweitig durch Metallartefakte überlagert werden. Jedoch sind die Verbesserungen nicht ausreichend, um eine präzise Protonenreichweite und Dosisberechnung gewährleisten zu können, wodurch Metallartefakte weiterhin ein Ausschlusskriterium für die Protonentherapie sind. Darüber hinaus ist eine ausschließliche Verwendung von iMAR aufgrund von Bildveränderungen in nicht betroffenen Gebieten nicht zu empfehlen. Es sollten stets die CT-Bilder mit der Standardrekonstruktion verglichen werden.
Keywords: CT imaging, iterative reconstruction, metal artifact reduction
  • Lecture (Conference)
    47. Jahrestagung der Deutschen Gesellschaft für Medizinische Physik (DGMP) e.V., 07.-10.09.2016, Würzburg, Deutschland

Publ.-Id: 23882 - Permalink


Clinical implementation of dual-energy CT for proton treatment planning on pseudo-monoenergetic CT scans
Wohlfahrt, P.; Möhler, C.; Hietschold, V.; Menkel, S.; Greilich, S.; Krause, M.; Baumann, M.; Enghardt, W.; Richter, C.;
Purpose: To determine whether a standardized clinical application of dual-energy CT (DECT) for proton treatment planning based on pseudo-monoenergetic CT scans (MonoCT) is feasible and leads to more reliable proton range predictions as compared to single-energy CT (SECT).

Methods and Materials: To define an optimized DECT protocol, CT scan settings were analyzed experimentally concerning beam hardening, image quality and influence on the heuristic conversion of CT numbers into stopping-power ratios (SPRs) using phantoms consisting of tissue surrogates and compared to SECT scans with identical CT dose. Differences in range prediction and dose distribution between SECT and MonoCT were quantified for phantoms and patients.

Results: Dose distributions planned on SECT and MonoCT datasets revealed mean range deviations of 0.3 mm, gamma passing rates (1%, 1 mm) greater than 99.9% and no clinically relevant changes in dose-volume histograms. However, image noise and CT-related uncertainties could be reduced by MonoCT compared to SECT with identical CT dose, which might result in a more reliable proton range prediction. Consequently, DECT was clinically implemented at the University Proton Therapy Dresden. 120 planning and 499 control DECT scans of overall 144 patients were acquired from April 2015 until May 2016.

Conclusions: A standardized clinical use of MonoCT for proton treatment planning is feasible, leads to improved image quality, extends diagnostic variety and enables a stepwise clinical implementation of DECT towards a physics-based, patient-specific, non-heuristic SPR determination. Further reductions of CT-related uncertainties, as expected from such SPR approaches, can be evaluated on the resulting DECT patient database.
Keywords: dual-energy CT, proton therapy, clinical implementation, pseudo-monoenergetic CT scans

Publ.-Id: 23881 - Permalink


Range prediction for tissue mixtures based on dual-energy CT
Möhler, C.; Wohlfahrt, P.; Richter, C.; Greilich, S.;
The use of dual-energy CT (DECT) potentially decreases range uncertainties in proton and ion therapy treatment planning via determination of the involved physical target quantities. For eventual clinical application, the correct treatment of tissue mixtures and heterogeneities is an essential feature, as they naturally occur within a patient’s CT. Here, we present how existing methods for DECT-based ion-range prediction can be modified in order to incorporate proper mixing behavior on several structural levels. Our approach is based on the factorization of the stopping-power ratio into the relative electron density and the relative stopping number. The latter is confined for tissue between about 0.95 and 1.02 at a therapeutic beam energy of 200 MeV/u and depends on the I-value. We show that convenient mixing and averaging properties arise by relating the relative stopping number to the relative cross section obtained by DECT. From this, a maximum uncertainty of the stopping-power ratio prediction below 1% is suggested for arbitrary mixtures of human body tissues.
Keywords: proton and ion radiation therapy, treatment planning, computed tomography, volume averaging

Publ.-Id: 23880 - Permalink


Clinical implementation of dual-energy CT for proton treatment planning to reduce CT-based range uncertainties
Wohlfahrt, P.; Möhler, C.; Baumann, M.; Enghardt, W.; Krause, M.; Greilich, S.; Richter, C.;
Purpose/Objective:
Particle treatment planning is particularly afflicted by CT-based range uncertainties. A clinical application of dual-energy CT (DECT) provides additional tissue information to potentially achieve more precise range predictions compared to single-energy CT (SECT). Therefore, the clinical implementation of DECT was aimed to be reached in this study.

Materials/Methods:
To define an optimal DECT protocol (Siemens Somatom Definition AS: 80/140kVp, kernel D34), CT scan settings were experimentally analyzed concerning beam hardening, image quality and influence on the heuristic conversion of CT numbers into stopping-power ratios (SPRs) per look-up table (HLUT) using phantoms consisting of tissues and tissue surrogates. Differences in range prediction and dose distribution between SECT and pseudo-monoenergetic CT datasets (MonoCT), derived by a weighted sum of both DECT scans, were quantified for phantoms and patients.

Results:
For treatment planning a DECT-based MonoCT of 79 keV is optimal, since CT-based HLUT uncertainties can be reduced (Figure 1). Dose distributions planned on SECT and MonoCT datasets reveal mean range deviations of 0.3mm, gamma passing rates (1%,1mm) greater than 99.9% and no clinically relevant changes in dose-volume histograms. Therefore, DECT was clinically implemented for patients treated with protons. 70 planning and 400 control DECT scans of overall 90 patients were acquired until January 2016.

Conclusions:
More precise range predictions and a wider diagnostic variety are feasible with DECT-based MonoCTs. Further improvements are expected from a direct, patient-specific, non-heuristic SPR determination. To quantify their possible benefits, first investigations of intra- and interpatient variations were performed on the still growing patient database.
Keywords: dual-energy CT, proton therapy
  • Poster
    PTCOG - annual conference, 23.-28.05.2016, Prag, Czech Republic

Publ.-Id: 23879 - Permalink


Dual-energy CT for range prediction in proton and ion therapy
Möhler, C.; Wohlfahrt, P.; Richter, C.; Jäkel, O.; Greilich, S.;
Purpose/Objective:
Proton and ion therapy require accurate prediction of particle ranges in tissue. In current clinical practice, computed tomography (CT) images are voxel-wise converted to ion-stopping power ratio maps using direct heuristic relations. The general validity of these approaches is, however, limited due to the different physical regimes of photon and ion interaction. Using a more sophisticated method based on dual-energy CT (DECT), which provides access to the physical quantities influencing photon attenuation, Hünemohr et al. (2014) reported an improved ion-range prediction for homogeneous tissue surrogates. Here, we present a major modification of the latter method, enabling a proper treatment of heterogeneities and mixtures on several structural levels, which represent a crucial feature of the realistic clinical situation.

Material and Methods:
We treat the stopping-power ratio as the product of the electron density relative to water and a correction factor that implicitly involves the logarithmic dependence on the mean excitation energy (I-value). The relative electron density, being an important parameter in both photon and ion energy loss, can be derived directly from DECT scans using a universal and robust method. The correction factor, however, has to be determined with an empirical method. For this purpose, we propose to use the information from CT images that is complementary to the relative electron density, i.e. the electronic photon absorption cross section relative to water. Using the attenuation sum rule and Bragg’s additivity rule, the relative cross sections and correction factors were calculated for single elements, tissue base materials like water, lipid, etc. and tabulated real tissues.

Results:
For a therapeutic beam energy of 200 MeV/u, the correction factor varies between 1.15 and 0.70 for single elements with atomic numbers between 1 and 100. Building up compounds from a certain number of elements, a maximum spread of possible values for the correction factor can be quoted for a given relative cross section, due to the mathematical structure of the variable space. In practice, this could be used as an uncertainty estimate for a given calibration. The accessible variable space is drastically reduced by admitting only tissue base materials such as water, lipids and hydroxylapatite. The space is further reduced by admitting only mixtures of real tissue materials. For human tissue, the correction factor is thus limited overall to a small range around one (0.96 - 1.02).

Conclusions:
With the definition of the correction factor in the stopping-power ratio prediction and its relation to the relative cross section, a mathematically rigorous treatment of tissue mixtures was made possible. Such mixtures influence CT imaging of patients e.g. in the form of volume averaging in a CT voxel. This thorough treatment of mixtures, like the one presented here, is thus essential for the clinical applicability of DECT-based ion-range prediction.
Keywords: dual-energy CT, proton therapy
  • Poster
    ESTRO 35 - annual meeting, 29.04.-03.05.2016, Turin, Italy
  • Abstract in refereed journal
    Radiotherapy and Oncology 119(2016)Suppl.1, S869-S870

Publ.-Id: 23878 - Permalink


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